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Susitna-Watana Hydro Project Engineering Feasibility Report AEA11-022 December 2014
SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. Report 14-21-REP v0.0 Susitna-Watana Hydroelectric Project Engineering Feasibility Report AEA11-022 Prepared for:Prepared by: Alaska Energy Authority MWH Americas,Inc. 813 West Northern Lights Blvd.1835 South Bragaw St.,Suite 350 Anchorage,AK 99503 Anchorage,AK 99508 December 2014 Significant parts of this report are subject to FERC CEll regulations and should not be disclosed. /=ALASKA 13-1421-REP-073114> QM)ENERGY AUTHORITY --Z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. Susitna-Watana Hydroelectric Project Engineering Feasibility Report December 2014 Significant parts of this report are subject to FERC CEIl regulations and should not be disclosed.MWHAmericas,Inc.14-21-REPv0.0 __ SEE ee O acres ©| -Ae ee iP , In ; 4 Significant parts of this report are vasubjecttoFERCCEIlregulationsand|& 2 should not be disclosed.<! 3 j a .7 susitn,A-W,be eamanaryono (Tyng.Feas,Rep."Deo.2014 * -yw SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. Report 14-21-REP v0.0 Susitna-Watana Hydroelectric Project Engineering Feasibility Report AEA11-022 Prepared for:Prepared by: Alaska Energy Authority MWH Americas,Inc. 813 West Northern Lights Blvd.1835 South Bragaw St.,Suite 350 Anchorage,AK 99503 Anchorage,AK 99508 December 2014 Significant parts of this report are subject to FERC CEIl regulations and should not be disclosed. /=ALASKA 13-1421-REP-073114 (MBE)ENERGY AUTHORITY PREFACE This report has been prepared in accordance with the terms set out in Contract No.AEA-1 1-022 between the Alaska Energy Authority (AEA)and MWH Americas Inc.(MWH),under task order authorization designated as NTP 13 -Engineering Feasibility Studies.Neither MWH,nor AEA, nor any person acting on any of their behalf,make any warranty,express or implied,or assume any liability with respect to the use of any information,method,or statement contained in this report. Any recipient of this report,including AEA,any prospective lenders,contractors,or any other stakeholder,by their receipt and use of this report,hereby releases MWH and AEA from any liability for direct,indirect,or consequential loss or damage,whether arising in contract,tort (including negligence),strict liability,or otherwise. MWH was neither requested to perform,nor has performed,environmental site assessments in connection with the proposed facilities described in this report.Also,MWH was neither requested to,nor has performed,any economic analyses or detailed evaluation of any permits or license requirements other than what is required by the Federal Energy Regulatory Commission (FERC)for a license application. This report has been prepared for the exclusive use of AEA.Any third party use of the report,or any reliance on or decisions made on the basis of this report will be the responsibility of such third party.This report must be read in its entirety,MWH will not be liable for reliance on excerpts or portions of this report in the abstract. The content of this report is governed by confidentiality clauses in the contract between MWH and AEA.The contents of this document may not be disclosed to other parties in a manner not consistent with the terms of the confidentiality clauses of that contract. Some information contained herein is subject to FERC Critical Energy Infrastructure Information (CEII)Regulations and required non-disclosure documentation. Transmittal Letter @)mwH January 26,2015 File No.14-21-REP Wayne Dyok Project Manager Susitna-Watana Hydro Project 813 W.Northern Lights Blvd. Anchorage,AK 99503 Re:-Engineering Feasibility Report -December 2014 Dear Wayne: We herewith submit our Engineering Feasibility Report describing investigations,and assessments of the Susitna-Watana Hydro Project carried out through December 2014, together with a suggested layout. The report incorporates results of feasibility work on the Project conducted by MWH and sub- consultant firms during the period from 2011 through 2014,and updates the information contained in the previous Interim Report Summary dated December 2012. As highlighted within the text of the report in-various sections,although key findings such as dam type etc.are final,additional important work is needed to support ongoing project development and design.Among the required supplemental tasks are the completion of detailed site investigations (including drill holes and adits within and around the dam footprint), the completion of the Site Specific Seismic Hazard Analysis,and a thermal analysis of the dam construction sequence.Analyses and verifications that would further clarify costs and details of the proposed project are dependent on the completion of these tasks. We have enjoyed our collaboration with you,your staff and other key stakeholders in completing this phase of the work.We look forward to discussing our findings with you at any time. We are available of course to present the results of the studies to AEA,or to key stakeholders. Respectfully submitted, MWH Americas,Inc. Brian E.Sadden,P.E. Project Manager Enclosure 1835 S.Bragaw Street TEL 907 248 8883 Suite 350 FAX 907 248 8884 .Anchorage,AK 99508 www.mwhglobal.com CERTIFICATE OF ENGINEER ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDROELECTRIC PROJECT ENGINEERING FEASIBILITY REPORT The technical material and data contained in this report were prepared under the supervision and direction of the undersigned,whose seals,as professional engineers licensed to practice as such are affixed below. aor 'a &ny OF ACA ¢ o Benen esseereenmrnsenersyg#e Breas esas aes agozBrianE.Sodden *&cre hy ?ys No.CE9083 ,Ss@"€o*oa&top see Fr a”NepFEss\otyer Brian E.Sadden Project Manager and Supervising Engineer asdBta,MWH Americas,Inc. Xa OF A at Yanhok@5La 4,ait.'.S 4 e #4°see eepmeanulcnrmlUhhmhlUM HhUchhlUhFRhlhU "8eaJulieR.Stonaszek *&#O*No.CE14055 .*Se?Do°.*a..yal S57n01 atiseaeity&wayKLWy,POFESSIN ©Julie R.Stanaszek (Beaatd ..Senior Engineer MWH Americas,Inc. Michael P.Bruen Licensed Geologist MWH Americas,Inc. License Number 134 LIST OF PREPARERS MWH Americas,Inc. Brian Sadden -Project Manager Michael Bruen -Geology and Geotechnical Exploration Don Crone -Cost Estimating Specialist Andrew Frisk -CAD Kirby Gilbert -FERC Licensing Specialist John Haapala -Hydrology and Power Operations Engineer Aled Hughes -Lead Dam Engineer Dina Hunt -Seismicity Specialist Farrokh Javanmardi -Finite Element Analysis Joseph Kovacich -Geotechnical Julie Stanaszek -Civil Engineer Lead Sub Consultants Applied Weather Associates -Edward Tomlinson Electric Power Systems Inc.-David Burlingame Fugro Consultants,Inc.-Justin Pearce Golder Associates,Inc.-Robert Dugan Hanson Alaska,LLC -Michael Pochop Norm Abrahamson -Independent Consultant,Seismicity Slater Consulting -Kenneth Slater Tom Lovas -Energy &Resource Economics Senior Technical Reviewers MWH -Peter Dickson -Geotechnical MWH-Peter Donalek -Transmission MWH --Howard Lee -Hydropower MWH -Jose Mayen -Electrical MWH -Glenn Tarbox -Dams Nuss Engineering,LLC -Larry Nuss -Finite Element Modelling Table of Contents -2Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT TABLE OF CONTENTS EXECUTIVE SUMMARY ......ccceecccceseecesseeseesscessneesneceaceeseecseeceecenseseneeseatensesesdassaaeeseeesaesaeaeaees ES-1 1.INTRODUCTION ......ccccessecsccensctccesceseeesteseeseesscenceseeaeesessecseeesesseesaconaecseseasesseseeeaseneees 1-1 1.1.Background...eee eseeseeseeeeeseecseseeceseseeeseeeeseeseasesnseseesseuseesseessessesssaseesneeseegees 1-1 1.2.Summary of Previous Studies...cecessecssecesecesesssseesecssescssesersessesesecsanesseees 1-6 1.3.Scope of Current Engineering Work...eee eee centre eeeseeecesseeneeecneneeeeees 1-7 1.4.Overview of FERC Licensing Process ..0......ceesceeessceceseeeeseeesseceeesnecesseeeseeerseeeees 1-9 1.5.Status of Environmental Study Program...eeccessceceeceeseeeeeeeeeesseeeeeceeseeeees 1-11 1.6.-Project Description...eee eceeseessceeececeesessessssosssesseecasessnsessesssensesseeseensenaeee 1-15 1.6.1.Gerneral 00...ceeececceessceceessceesesaaeeeseseeecessaceesesseeesessaesessssnaesessaeescosseees 1-15 1.6.2.Watana Dam and ReServolr ou...eeeceseesseesseeseeesseseeeeseeeesecesaeensesaes 1-16 1.6.3.POWETNOUSE ........sceecceesceeseeeseeencecseeeesecececseeeeeeencesaeseseesseeneeesaeeseesaes 1-19 1.6.4.Ancillary Facilities ..........:ccccscessseecsseesseeeeeeeccesseeeeeeevsaneesseeeeaeeesseeenes 1-20 1.6.5.Transportation ACCOSS.........ceeeseeeeseeesseesesseseeanecssseenseeeseseesseeeseeaaensaes 1-20 1.6.6.Electric Transmission and Interconnection Facilities...eee 1-22 1.6.7.Project Operations...........ceeeeseeceeseeeeseeeceeeeeesecessseesesseecsueesscerssaneesaees 1-23 1.6.8.Construction Schedule .0......eee eeeeeseceesseceeneceesseeesseeeeseeeeseeessaeeeaees 1-24 1.7.Visualization oo...cccceeeeecneeseceseceseesseeeseeesasesseseesessassasessessassesesessasssecsssosseseeeeeaes 1-25 1.8.Principal Project Parameters...lice ees ecee cece eeeeesesseeseessesseeecenteseeeensaenaees 1-25 1.9.Board of Consultants Review .0.......eceescesssesseeseseeesecesseseaasesesessessseensaessssesaenaes 1-30 2.SCOPE OF WORK1...ccecccescseeeeecetsceeeeeeeneceeceaeesscensersaeeeeeseeaenseceaaeesaseaesesassensesaeeaneneg 2-1 2.1.Evolution of Plan of Study...cee ceeeessesseseseesceeseeeseeeessesseseasessessseessereseseneensneees 2-1 2.2.Hydrology occ ecesecscececeeeessereasessesescesseesseceaseesscssesescssesessesseseescsseeseseaseeseenseened 2-1 2.3.--Power Studies.......cccccssccsssecssecseseececeresneesncecsseecsssecssnesesesaseceeceaeeeesseessateenegeessesenes 2-2 2.4.Geotechnical Exploration and Characterization ........cccccccsssessessesesssseeeeseaeenes 2-2 2.5.SEISMIC Studies ........ceccseceseeseesecenceeseeeseeeesessesseessesssesessecseeessessssesseseaeensesseeseesesees 2-3 2.6.Development of Layout and Design oo...ccscssssscescseescesessessessessesecnetaeeeseaseneenes 2-3 2.7.ACCESS ..ceseessecsecsecesecseecessecetecssaueeeaceesseseessceeaesesasessaccessesessassesusecseeesseestsacersnesseneees 2-4 2.8. TraMSMISSION ......se eeeescesseeeneeseeeeseeeseesseceeeessecsescsssessecseseneessasessesedeenaesaeeeseeseneessees 2-4 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page i December 2014 -Z- .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 2.9.-SUIVEYS.....eeecccceseesseeeeseeesseceessnecesaeessesesseesaecssuscesseceessseseaeeceauecesneeecesueesseeeseaesesas 2-4 2.10.Site Facilities...ee eesseecssceceeeeeeesceseceseeesesecsacecsssseesseeessseecssneeessneeeeeessreseseneas 2-5 2.11.Construction Cost Estimates and Schedules...ceccessesseeeereseeeceeeeeaeeeseeeesees 2-5 3.PREVIOUS STUDIES1.ececsseeseesscesscesssecacesessessnesseceseeseeseseaeseaeceesenecnsensenevneeeees 3-1 3.1.Early Studies of Hydroelectric Potential...ccccseserssnceescesseeseeseeceeeeeeeeeeenes 3-1 3.2.U.S.Bureau of Reclamation -1953 Study...eessessseccestecessseeeeseeesseeesseeeees 3-2 3.3.U.S.Bureau of Reclamation -1961 Study...cececsssecsseeenseeeeesetessseeeseeese 3-2 3.4.Alaska Power Administration -1974 oo...cescesessesseeeseeeseeseeeceeneeseessresenerseeeeees 3-3 3.5.Kaiser Proposal for Development -1974.0...ei cceccscssscssscessecsseecssceesseesasesseesees 3-3 3.6.U.S.Army Corps of Engineers 1975 and 1979 Studies...ceecsseseeeeseeeeeees 3-4 3.7.Alaska Power Authority -Acres /Harza/Ebasco 19808 .......cccccsscssseesseeeeseeee 3-4 3.8.Alaska Energy Authority -2009-2010 oo...eee eeseecseceeseceeseneeesneeeeseeeessnevensnees 3-6 4.RAILBELT LOAD FORECASTS.....cee eeseeseesseeseesecesaeeeacenseesseeceaeeeeeseaeeeanenenesnaeeazes 4-] 4.1.Regional Generation Facilities...eee seesecceeeeecesseeeenecesnecesseecsseeseaeeeeenees 4-1 4.2.Regional Transmission Facilities 0.0...eeecesecsseesecssccesseeeeeesseesseeeseseseeeeeeesseees 4-2 4.3.Regional Electrical Load Requirement ...........ccceeeeeeeeceeeeceeeeeteceacensesseeeseeeeenees 4-3 5.INTEGRATION INTO THE RAILBELT SYSTEM...eeceeeeeeeseceseeeestseesneessseeseeees 5-1 5.1.-Ellectric System Studies...sce eesseceeeeesseeeseceenneecnseeeseneseeueeesenesenaeacseseesaeeeees 5-1 5.2.Transmission Study Improvements Pre-Watana...........ccccsccsceeseeceseeeseeeseeeneeenes 5-1 5.3.Study Criteria...eee scssesssecssessseesssssceeseseesseessessaessseseaasssaseeeseseeeceesneeesaeeseneaes 5-2 5.4.System Study Methodology...ee sesesscesseesecsseceseeseeceseeseeceseesseessaceneneeeeeeenes 5-2 5.5.RESUIES.eee ee eeeeeneeceeseneceseceescsnseseeecssssesseessesessesscascesescsseesescsssesseceeeeseseesceseaeeesees 5-4 5.6.Future Studies 20...cee eeeesescseessecsseceeceseceeenceseessesesaeeseseseeeaeesseesscesenseessessseesseeeuees 5-5 5.7.Project Operation and Resource Integration...eee eeseccsseecsssseeesseeessseessaneeeenees 5-6 5.7.1.Basis Of Studies...ee ceescsessrsseesseessesseecsseeseesseseneessaesnseeenaeeoneeeees 5-6 5.7.2.Plant and System Operation Requirement...........c:ccscsseesesssseseseseees 5-8 5.7.3.General Power Plant and Railbelt System Criteria...eee 5-9 5.7.4.Operating Security Criteria...ccc csesecsseessesseceseecseeessecsetesseeesees 5-9 5.7.5.Plant Operation and Maintenance...eeccsesssseeeseceseesseseeesseeees 5-10 5.7.6.Economic Operation ........cs cscessscesseesecseeceseesseesssesecsseessseesseeesseeenes 5-11 5.7.7.Modeling Exercise and Results...cc ceescsseceseceseesesseeeseessesseesats 5-11 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ii December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 5.7.8.2013 Modeling and Analysis ...........cccesscessececsesseecneecsaeeeseeenseceseeenees 5-15 5.7.9.Forecast Data and Results for 2013 Amalyses..........seeeeeeeeseeeseeees 5-17 5.7.10.Updated Analysis 2014 ee eeeceeeseseeeeeeeceeeeeeteseecneseseeesareneeees 5-21 6.SUSITNA BASIN AND DAM SITE CHARACTERISTICS...ce ceeseeseeeseesseeneeeeaee 6-1 6.1.Climatology....c.eceeccscseceeceeceeaeceaceeseceanersneceseceseeesaeessaseaeessaeeseeessacesssseasesaeeoaaeenes 6-1 6.2.Hydrology oo.eeeeeceeseseeeseceecesceseesssseeesesssesssesseussessessessessescessseesesssrenssseeseesenenes 6-4 6.2.1.Hydrologic Record.......eeeescescesseresesescarseesseesseessasesaeseaeseseensesseeeeaee 6-4 6.2.2.Monthly Flow Frequency and Flow Duration ......ccc ceeeeeeeeeees 6-8 6.2.3.Watana Dam Site Historical Inflows .00......eee eeeeeeseeeeeeeeeeeeeeeseetees 6-14 6.2.4.Flood Frequency .......:ceeccesecceseseecssceeeseeeeeneeeeseceeseasecssesesauneeesecsueesaes 6-18 6.2.5.Probable Maximum Precipitation /Probable Maximum Flood.......6-23 6.2.6.Susitna Watershed Flow Distribution ...........cee ceesseeeseeeeeeeeeneeeeneees 6-23 6.2.7.Hydrologic Change 0...ce scecesecssesssseesesessesessessesescseeseseesnsseeeseasees 6-25 6.3.GOOLY....eeeceessseeeeereeceteeeeseeecenceeeeseeresessessessssscasseessassesssssseesssessessesseeseseseenessesees 6-28 6.3.1.Sources Of Information 0.0...eeseeeeeeeetereseesesseseaeeeaecesssenseseseenaneegs 6-28 6.3.2.Regional Geologic Setting 0...ce esssssecsscesesereeseetseeeseetseeseeeeeeee 6-42 6.3.3.Seismic Hazard .........ccececsceeeeeecseceesseceeeseeeeceesseceesseeseeresersneeeneeseaeeees 6-61 6.3.4.Site GeOlOQy......se eeeeeceseeeseresssssesessessssesesssceseessseaeseeeesesesessesestesesreess 6-71 6.3.5.Dam Site Area Fault Rupture Evaluation ..........eee eeeseeesseeeeeeeeees 6-104 6.3.6.Reservoir Geology .......csccccsseccsseesseeceseseessneesseecsacecesacenseeecesaeessseesees 6-115 7.SELECTION OF WATANA GENERAL ARRANGEMENT...ccccesseseesesreseeeeeeeneees 7-1 T.1.Site Topography...eee eseesscsseesssesserscerecceeeceseeeessasesssaneessesseesseecnseeessenenseneae 7-1 7.2.Environmental Considerations...............:cceeececeseccesseeesneeessseesseseseeesseeeseseseeseeseeeeees 7-2 7.3.Selection of Reservoir Levels ..........ecceesccesseeceseeeeseceessecesesenesesauaveseeseeaeeessaeeaes 7-4 7.4.Selection of the Inflow Design Fl00d ....cece eeesscceseetesesseessecssesereeeseesessasenes 7-6 7.5.Selection of Installed Capacity .......ccc ccc cccccssseseessecssecserseesseesecseneeecseesseeeeneeeeseas 7-6 7.5.1.IntrOductiOn .......c.cccsccesceeseeeeeseceseceeeseeeesacecsacesnecssceesesseessseeteseeesseseaees 7-6 7.5.2.Future Railbelt Electrical System Reliability /Redundancy Requirements .........ccceecesceeeeesseeeeeseesseeessesssesseseseeesesessesesessessesseeeeaeaes 7-8 7.5.3.Selection of Powerhouse Total Installed Capacity «0.0...eeeeseeees 7-9 7.5.4.Generating Unit Selection and Capacity...ec cccceeeseeseereeeeteees 7-15 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page iii December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 7.5.5.Discussion and Selected Configuration ..........:ccccssssseceesnecessesseeees 7-23 7.6.Project Configuration Evaluation 0...ccc escscsssesecseessectseeeceseseeesseesaseneeseeenees 7-25 7.6.1.Daim...eeeesccessceesteeseeeneecenseseessecssonaeeaceeesesaesseesaeseaeesseeeneeeeeaeeaeeesseesaes 7-25 7.6.2.DIVETSION uc.eesceseeescesseeesoessceeesseeneeesncesessseceatesseeeaeseaeesseeesaeesees 7-28 7.6.3.SpillWay .0....eeeeceesceesseeseeseeseteaceeaeeeeevseesseeseeeceseseaesesaeeseeeseaseeaseeaeres 7-29 7.6.4.Power Facilities...cceccceecesseeceecseeceeceneennesseesseeeeseeeesseneeseeeesensessaes 7-29 7.6.5.Summary of Comparison and Selection of RCC...eeeeseeseees 7-30 8.SITE ACCESS PLANQo...ceeceeesceseecenerescesseecseancescesseeseecnseaeeeseeaeeeseseaesseeeeeaeeseeseceeeaseeseees 8-1 8.1.Background...eee eeceseeseecseeseeeeeseecesecessecseessessesssesssceseseaesseeseeeeseeeseeeseeeeeseeeseees 8-1 8.2.ODJOCTIVES oo.e ccc cceecescescsecsessesesseersaeessesesscssssansusssessseseseenseesseneecaseneeneee 8-2 8.3.Approach eee..ecceeeesccsssecseeeseeessevescecseecenecessesseeseeeseeeaeesseeseseaceneesaeseaseecaeeneseeeseasees 8-2 8.4.Corridor Selection and Evaluation...eeceseecsecesseseeneceeeeesseeceseeeetaesenereesenseses 8-2 8.4.1.Description of Basic Plans...eeeesesssceeeeesetsneesseeeeeesaeeseesenseenees 8-4 8.5.Evaluation oo...cceccessssesseeeseeecssceesssseeessceseseeeseeessesesaeesasecsnessacersucenseneeesaeeeseneeses 8-7 8.6.Evolution of Access Plans .........cceceessccsscceessreseeeneeseeeseeeeeaeesaeseeeeeaeeeseseasessees 8-11 8.7.Access Plan for Estimate 0...eee ccssssessessecesesseecaeenaesatenetesseceseesneeneeseaeeeeees 8-13 8.8.Bridge at Site...eesscsseeeseeeseeseeceeeseesseecesaceeseceseeseesaseseeneeeaersasesseesnseseness 8-13 8.9,Ratlhead oo...ec eecceseessesseeseesecenececesccessceceessesascasesevseesssnseneeeeaseeseeeseseenseaeeseseeses 8-14 8.9.1.Previous Studies and Site Selection...eeceseeeeseseeeseesseeesseesnes 8-14 8.9.2.Transportation Methods 0...eesesssescesecseccesceaeeneeeeeeeaeceeesnseseeeee®8-14 8.9.3.RailWay Cats ......ccccsssccssscssessseeseesessessceeseeeseeceeceecesaeeeesueeesseessaeesses 8-15 8.9.4.Transloading Facility -Cantwell Site...ee eeeseeseseneseeeeeeenees 8-16 8.9.5.Railway Comstruction........cccccessessscseceseseessesecsseeseeeeseseseesseeseeees 8-16 8.9.6.Gold Creek Site Alternative...ccccscecsessecsessseescsssessssesssesseenseees 8-17 8.9.7.Chulitna Site Alternative...ccc seecsecsseeseesesssssscesteesssessseessesensees 8-17 8.9.8.Necessary Modifications to the Railroad oo...ceesesseesseeeeteeeees 8-17 8.9.9.Other Potential Facilities...ce eeccseseesseseesssssssssscssecesseesasesseeeeees 8-18 8.10.AIrstrip ....eeeeeeeeceeceeeesceeeserssseeseeeseesecenssscesscessensesseesescsesseessaseeeesseseaeseaesenereneseeee®8-19 8.10.1.PreviOUS Siting ......cecesscesssessssessseseeescecessessscssssseessscssteseecseseseeeeneees 8-19 8.10.2.Airstrip Criteria...ccccseseccssesssssscsescceeseeseessseseesseesaseesssceseusesneees 8-19 8.10.3.Selected Airport .....eee cseessseeseessseesseesseeseneesssseesssseeseeeeeseesesateesaes 8-20 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page iv December 2014 zm ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for-the next 100 years. 8.10.4.Runway Length and Width...ee eceeseeseeenecesseeesseeeseeeseeesasensees 8-21 8.10.5.APPTOaches ....ceeceescesceseesecesneesseesssessssucseeeseusseecssuerseeessesensesesseaea®8-21 8.10.6.Runway Ends and Aproms...........secssseesseceeesseseseesacessaseceeesseseasensees 8-22 8.10.7.Aircraft Operational Aids oo...cece cesecereecneeesseeeseeeeseenensaseesees 8-23 8.10.8.Facilities...ccc cecssessseecessceeeecsecereeseecreesecsecsnceacecaeensecseseasenneseeenes 8-23 8.10.9.SUIMIMALY 00...esceeesceceeeeeesscceseecessecesanaereseesessseceaesesnsceseseeecersseenneessreses 8-24 8.11.Unconventional AcCeSS.........ccecceesscescccesseereneeecesssersssaseeesscaseeenssesssasessseesesseesen 8-24 B.LL.1. -Hoverbarge.....e eee eeeecerececneeseseseseecereeeseesseeceeseessesessseaseessseseneetaees 8-25 B.11.2.CAT Trains oo...eee eecceesccecceeseceseeeseteesesessecsaeessassansesascensessessseseneseues 8-25 8.11.3.Air Transport of Heavy Equipment .......0.ceseesseseeessesseeeseeeseeees 8-25 9.PROBABLE MAXIMUM PRECIPITATION AND PROBABLE MAXIMUM FLOOD woeeeecccccccesecseessccecsssscessceeeecenecscecscesseesenecsesesseesneseaaseanseasesescsaaseseecsseseneaenterseeeseees 9-1 9.1 IntrOGuctiOn.......cccceesscccsssecesseceseeesececeeeseseeeeeseesecaeeeessesenseeeesesesseasessaseneeseesasesaeees 9-1] 9.2.Watershed Description...ceccesccsccnsceseceescssssessssssssssesessecssecsseesenecsessseseseesseeees 9-1 9.3.--Historic FIOOdS.......c cc cccscecesseeeeeceecceeeneeeneceneeeesseeeesseeeesseeessseesssasesesseseesessasesseesoes 9-2 9.4.Hydrologic Model oes cccscsscssesescssssesscesesecenesessecssesessessessseceesseesaseneaseseees 9-3 9.5.Probable Maximum Precipitation ......eee eesscesesecssssessseeesseeeseseeceresserssseseeeesees 9-4 9.6.-SMOWPaCk ....eeeeeecesecesseeseenssesessssessesecsesssesecneecsesssesssecseesesegsessecaeesseenesesesaneseeeaneneees 9-6 9.7.Coincident and Antecedent Conditions 00...eeeccsessecesseeesseseeseesesseceseseesees 9-9 9.8.Probable Maximum Flood Hydrograph .......eee ees ecsseeseeseeseseseeseessecessseesesooeees 9-9 10...WATANA DEVELOPMENT DESCRIPTION......eee cess eesseeeeeeseesesseeeseesseeeneeee 10-1 LO.1.Introduction...ceeceescceseeseecsesesceeeeseeeeseecssecseesseassnassesesessseeaessssseseseesreeeeesens 10-1 10.1.1.Site Survey and Mapping......ccccccccccecessceecesssesseeeseeseeesseeseeereneens 10-1 10.1.2.-Project General Arrangement ............cccccceceessceeeeeeeneeeeeeeeeseeeaeesessaes 10-2 10.2.Site Facilities.........cccccsccsssesecseceseceseesseseseeseeeeseeesaeseeessesesneceeescnsesssecnesenseseanys 10-3 10.2.1.Location of Facilities 0...cele lesssseessessesssecsscesseesesessecsscsseeneesees 10-4 10.2.2.Temporary Construction Camp......cccccccccsesecsreesseeseessessesseessesaeeeneees 10-5 10.2.3.Contractor Facilities ...........:ccscccsssceeseceeseceeseeeeeneeeeaeeetsecessacessneeseaeess 10-7 10.2.4.Permanent Village.........csssesccssssssssecsseecesreseressscasccsssessseaseseseeeeees 10-7 10.2.5.Owner OFFICES «0....ecccceccececcessececeseeeceesceecessaeeesesneeseeseaeeressseeseeneeeseneees 10-8 10.2.6.Operators ACCOMMOAATION oo...eee sesesseeesecseseseseseseenceseeeseeeenensese 10-8 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page v December 2014 -zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.2.7.Water Supply .0.....cc ccccssssesssscsneeessseesescessscecesaeeessneeseesseeesssesensesens 10-9 10.2.8.Wastewater Collection and Treatment............cccessseesssessrseeseeseeeees 10-15 10.2.9.Solid Waste Disposal ......ccc csscsecescsscesesseeseeeeeeaceeseeesscecseeeseeenes 10-18 10.2.10.Fire Protection System...cceeseescssecssscsneceseeesecestecesseessseessessseeees 10-20 10.3.Geotechnical Design Considerations ...........ccescccsssccsesteceeseeeeseeeeseneceseesssseenees 10-21 10.3.1.Engineering Geology ......cc cescssccsssssesesseeseecsscessreesseesseeeseeesseeeeeeees 10-21 10.3.2.Construction Materials SOurCES 0.0....eceeseesceeeteeeseeesneesseeesseseneeeees 10-42 10.3.3.|Design and Construction Considerations..........ccecccseseccesseeseseeeeenes 10-45 10.3.4.Underground Excavations...........cessesesesceseeteeereeeecsseeseesseeeaeneens 10-59 10.3.5.Cofferdams..........cecceesccssessssceecceeceeesseeceeeseeeeseeseseeseseesaeesssesenseeeees 10-61 10.3.6.Watana Relict Channel ..0....ee eeeseecesceeseeeseeseecesseeesseesseeesseeseres 10-62 10.4.River Diversion.........cee csesseceeseeeseeeceeeeseeseceecceesneeeeseessceeesneesesseeeeneseeaeeseneeees 10-63 10.4.1.Goerneral 0...eeeeeseesceseeeseesesscecececcesceseeseeceeaeesaeeeaeeseeeeseeseneseeesereees 10-63 10.4.2.CYIteria voce eccscesceeesessesseseessseseseseessensnensseseseeeeseseseeseneenseeneneteeees 10-63 10.4.3.-Amalytical Results 2...ee esesesseeseceeeesccsesseeseessecsaesaceraeeaneeeees 10-65 10.4.4.Operation of Diversion 00...cece eeeesceseecneceseeeeeeecneceneeeeeaceeeeeaes 10-67 10.5.Dam -Layout Development...eessesseesseeseeeseeeeeeeseeeseeesscessetesseeesnessneass 10-69 10.5.1.General Methodology ......cicecccsscsstecsseeesseecssnecenaceesseeeesesessseeesneees 10-69 10.5.2.Pre-application Document (PAD)Dam (Layout 1).........eeseeseees 10-72 10.5.3.Optimization of Dam Configuration...eeeseeeseenecenecneeeeeeees 10-72 10.5.4.Curved Alignment AmalySsis...........:cscccsscecsececestecsensecesceeeseseseseeees 10-77 10.5.5.Analytical Development ..0.....eee eseececsscesecseeeseeseseeeseeeseessnseeseeeaes 10-79 10.5.6.Preliminary Design Criteria -Structural Analyses............ceeeee 10-80 10.5.7.Two-Dimensional Gravity Analysis .........:cccccessesscsssceseeereeeeeeneee 10-81 10.5.8.Finite Element Modeling of Dam ........cee ceeeesseesseesseesseessscsseeneees 10-82 10.6.Dam -Preliminary Analysis ...........cccesecsssscsscesessseesseceseecseeesesesssescessaessseenees 10-83 10.6.1.Initial Dam Configuration (Layout 2)00...ccceseessecsssceseeeeseeseees 10-83 10.6.2.Revised Dam Configuration (Layout 3)oo...cc ecscccssesseesseeeeesnees 10-99 10.6.3.2nd Revised Dam Configuration (Layout 4)....ccc cccceeseeeees 10-114 10.6.4.Sensitivity to Foundation Conditions...........ccccssccscsesssssessesseeeees 10-129 10.6.5.Discussion on Analysis without Foundation Mass ...........cccecce 10-130 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page vi December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 160 years. 10.6.6.Modeling of Fluid Structure Interaction ..........ee eeseeeceeneeteeeeees 10-133 10.7.Dam -Final Modeling including FSI,Foundation Mass and Damping........10-134 10.7.1.Final Dam Layout (Layout 4 -Modified).......eee eeeeeseeseeeneeees 10-134 10.7.2.LS-DYNA Analysis Software.........cesccesesceeseceeeseeeeeeeeeeaeeeteeenens 10-134 10.7.3.Selection of Time Histories for Final Modeling ............ce eeeeeee 10-137 10.7.4.Methodology of Structural Analysis...ceecseseeeeseeeeesseeeeeeeeees 10-154 10.7.5. -»COmCIUSIONS .....eee eee eeeeeceeseeeeeceeeeeneeesseeeceaeeeseaeeesseeessaeeeseeteneneenses 10-175 10.8.RCC Placement...cee eescsscesseeeresesseessesessecsseceseeessecsseessesssuessaeseseseasseseoenes 10-177 10.8.1.RCC and Aggregate Quantities /Production...eeeceeeees 10-177 10.8.2.RCC Placement Sequencing ..0....eee eeecsseseeseeseeeseeseesseeeseesseeees 10-178 10.9.Dam -Thermal Considerations 0.0.0...cecceseessecececeeecesseeseassaeeesseseeessseesaneoeaee 10-186 10.9.1.Gere ral ee eee eeeeeseeessseeeceneeesceresseeseseesssesesssseesssessesaesesaeeeseaes 10-186 10.9.2.Transverse JOInts.......ee seceeseeecseeeeseceesseeseeeecenaeeeeneeeesscessseeesseeeees 10-186 10.9.3.Abutment Temperature «00.0...cceccesseeesescceeeecceeseeeseceeesneesnaeeeeaceesees 10-187 10.9.4.Insulation Requirements «0.0.0.0...:eesseesceesreeeneceseeeseeesetceneeenenseeeanee 10-187 10.9.5.Control of Mixing and Placing Temperatures 00.0...ceseeseesereneee 10-188 10.9.6.Preliminary Simplified Thermal Analysis ..........ee eeeeeeeeeeeeeeeee 10-188 10.10.Instrumentation 0...ee eeeeceeseeeeseeeeesseessseeessseceseeessseasesesesesecesaasonsaseseeeseues 10-196 LOVO1.General...eee eeeesseceeceseeeneessseeesseeseseesesseasseeaceseeseneeseseaaeeaes 10-196 LO.10.2.Daim.eeseeeseeecneeeeesseeseceaeessesececeseseeseessesseassesseaeeseseeseaeeges 10-197 10.10.3.Rock Slopes and Abutment 0000...eee ceeesseceeesseeeseeseeseneeenee 10-200 10.10.4. Relict Chante]...eee eeeeseeesceeseeeseeceneeeseeeeeseesessassseeeseeeseteneeenes 10-201 LO.LL.Freeboard 0...ccsecssecsecessecesacecsaceesseeeeseeeesseesenceessaaeesseeersseresseeossesonnerees 10-201 LO.LL.1.Analysis...cceeseeceseeseessccsecseessesseessessesessesesenessescsersaseeesneosenase 10-201 10.11.2.Wind Speed...ceccesssssecsessessscsesacsecsesssssecsessessessesssesensesssees 10-202 10.11.3.Wave Run Up and Set Up...ccc ceeneeeereeeneenseseeneeseeeeee 10-203 10.12.SpillWay ......cccccccssessesesseccceessersesecsccseesscsecseceesssssessessaseassassaseassaneassseeseeses 10-210 10.12.1.Radial Gates and Operators .0....ce cecsceeeseceeeeseeseeeesseseaseseeesaeeees 10-214 10.12.2.Spillway Bulkheads ......cee eescssscssscssecesessesseeeseesssesseessaseneeeaes 10-215 10.12.3. Spillway Gantry Crane.....ccccecsecessesesssscessseessssesseeseseessseerssneesegs 10-216 10.13.Emergency Release Facilities 0.0...cescescssesesscsseessssessecssesssecnseseseesssensessaeeses 10-216 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page vii December 2014 -Z SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 10.14.Outlet Facilities 0.eeeesteeeseeeeeseeeeeees 10.14.12. Intakeo i eeeeceeeeeeeeeeeees 10.14.2.Intake Gate.eeeeeeeeeeee 10.14.3.Intake Bulkheads........eee 10.14.4.Intake Trashracks .....eee 10.14.5.Gantry Crane...eceeeeeee 10.14.6.Pipes and Manifold... 10.14.7.Discharge Structure... 10.14.8.|Fixed-Cone Discharge Valves 10.14.9.Butterfly Valves oo...eee 10.14.10.Monorail Hoist...eee 10.14.11.Bridge Crane...eseeeeeeee 10.14.12.Discharge Area...ceeeeeseeeeees 10.15.Fish Passage Considerations.............:::eee 10.16.Power Intake oo...eee eeseeeceseeseseeeetesseeenes 10.16.1.Intake Gates and Operators........ 10.16.2.Intake Bulkheads......ee 10.16.3.Intake Shutters 2.0... 10.16.4.Intake Trashracks 0...eee 10.16.5.Intake Gantry Crane............. 10.17.Penstocks.....eee cecesseeeceeeseceeeesecensersseesrenes 10.18.Powerhouse ........ceeeeesceceeseeeseetseeeteneneeetenees 10.18.1.General Arrangement.............0... 10.18.2.Turbine Inlet Valve... 10.19.Turbines...eeceseeeeeseecneeeeseseeeeessesseeees 10.19.1.Turbine Components..............0.4 10.19.2.Governing System.......cece 10.20.Generators 0...ee eeeeeeceeeeeeeeseeeeeeereeesereeeesee 10.20.1. Gemreral eee eeeeeeeeeesreeereneeene 10.20.2..Configuration and Ratings......... 10.20.3.Generator Structure... Susitna-Watana Hydroelectric Project FERC Project No.14241 Page viii Alaska Energy Authority December 2014 a SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 10.21.Exciter...ccccccccsseesceesseesseeeceeacecssceeeseeeesceeesecesssaeeecsseeesseeesseeeseaeessaeeenaeeeseees 10-238 10.22.Generator Step-up Transformenrs........cccescesescssecesscesescneseseesssesereseseecseseeseeeaes 10-238 10.22.10. Gemeral eee eeecceseceessccessceesececesaeeesaceesaceeeseesesceessaeesesaeeeneeeensees 10-238 10.22.2.Ratings and Characteristics...........c:ccccsscesecceeesceeesceeseneeeneeeeseaeeeaes 10-238 10.22.3.Tank ...eeeeeesscsesescesseesecssesseesecssecseeesesseeesessaceseessesseseaseeseeseneesees 10-239 10.22.4.Base.eeceeeseeeesseeeseresseceseeeseeseseeeceseasenseeesstersneeesseecesdenesseaneeees 10-239 10.22.5.Core ASSEMDLY.....ce ceeeeseceeceseecesccsescessesensesseseaesesesesesennoesseseeees 10-239 10.22.6.Winding...eee eee cesceceseeeeeeeeeeeesesneecssaeseuasesssecessersadasesseeerenees 10-240 10.22.7.BUSHINGS...eee eee eseeeceesseeeseeseeessesessecsesesseseeesesasesssessesenaseasenseees 10-240 10.22.8.Surge Arresters........cececesseceeeeeeseseececeneeceeeeeneeeeaeessaeeeseaeeseseeeeeeees 10-240 10.22.9. ACCESSOTIES 00...ceeeeeeesseecsseceeceeseeeeessceceseeceseecsseeeenseeesseesesseseeneeees 10-240 10.22.10.Oil Preservation System...ee eeecesescreessesssceseecsseesseseseseanesenes 10-241 10.22.11.Cooling System oo...eseeeseseceeeessecesecseneeseesaceeessaeeeserseneeeseaeees 10-241 10.23.Unit Protection and Control System w......cece eeececeneeesecesceeneceseeeneesenessaeeeseees 10-241 LO.23.1. Gereral ui...eeeceeescceseeseseeesseceseeeeeeacesesaeecsaeecseeeesacesssaeeesaeeseaeesaes 10-241 10.23.2.System Configuration 2.0.0...ceccecsscceesseccececeececeeeeeeseeeeeseetenseeeees 10-242 10.23.3.Unit Control Panel .0....eee eeeeeceseeeneceseecnseeeecenceeneceseeeneeeseeenaee 10-243 10.23.4.Control Room Operations ..........ceesccessseeeeceeceeeeceeeeseneeseaneesseeeeass 10-244 10.23.5.Unit Protection oo...eee eeeseecennceesseeeesceeessceseeeecssneeesceeeseeteeeesaes 10-245 10.23.6.Station MOMItoring ......ee eee eeseceesseeeeneeeeecceseeceeeseesseneeeeeeseneeeees 10-246 10.23.7.Instrumentation Cabinet...eee eeeseesseceesceesseeeeeeeseeeeetseeeeeaeees 10-246 10.23.8.Distributed Input /Output...ec eseceeeesecereseeeseeeeesseseeeenees 10-247 10.23.9.HMI Terminals............ceceecceeseceeeceeecessceeneeeeeeeacesseesaceeeeeseaeeeseeeeees 10-247 10.24.Miscellaneous Mechanical Equipment ..........ec ceeceeessseseseesseeeeeneeteesteseaceenees 10-249 10.24.1.Powerhouse Bridge Crane...cee eeeeescseseeseceesesesercneeeeneseeeeenees 10-249 10.24.2.Draft Tube Bulkheads 0.0.0...ceecesscceeeeeeecseesacceeeeenecereeenetensensees 10-249 10.24.3.Draft Tube Gantry Crane oo...eee ec eecesereceeseeeenecnserseeaesnseneees 10-250 10.24.4.Station Drainage System .........ceeeesecsseeseesseeseseesssessceerneeseneeene 10-250 10.24.5.Unit Dewatering System.......cece eee eeeeseseeeeeeseeesseesssoseneees 10-250 10.24.6.Station Raw Water System .......cee eeseeseseeeeseeeeeceeteseeeetseesaeeseeees 10-250 10.24.7.Compressed Air System...ceescsesssscesscessecesseesesreeesasersseeseeeeees 10-251 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page ix Alaska Energy Authority December 2014 -yzw- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.24.8.HVAC Systems...cccccceccccssssccssseecessseeeessnseeseesseaeecceseeesesseeanees 10-251 10.24.9.Standby Generator...eee eesessecceneeeeseeeseneeeeseeeeseeseeneeerssseveneeees 10-251 10.25.Accessory Electrical Equipment...ccc esesesssesscecseecenereceeseeessaseeeesseseaees 10-251 10.25.1.Powerhouse Alternating Current System...cee ceseeeeeeeeereeee 10-251 10.25.2.Powerhouse DC System .........cecesceeesssesesseeeeseeeeeeeeeeseeeeseaeeesaeeesnes 10-251 10.25.3.Powerhouse Lighting ..00......eee eeseescceeeeeceeeeeeeeseeereseneceseeeessaeesues 10-252 10.25.4.Powerhouse Grounding System...eeceeceesseeeseeseeeeeeeeeeteeeeeaee 10-252 10.26.Switchyard Structures and Equipment...ieee eseeseeeseceeeseeeeeeeeeeeaseseesaes 10-252 10.26.1.Switchyard Arrangement .........eee sesceeeeeeseeceacesseeesseeeaceeseeeees 10-252 10.26.2.Circuit Breakers oe.ee eeeecescceeeseseeseeesseseaceeseeeseesseaeesesesseesseeenees 10-253 10.26.3.Instrument Transformers...eesceeseeeeeeeeseceeeseeeetseesesaeeesneees 10-253 10.26.4.Bus,Overhead Lines and Structures...ccecceeceecceeseeeseseeeees 10-253 10.26.5.Grounding oo...eee eee eeeee renee seeneeeeesesaeesseasesseeseseesereasesreresseeaenes 10-254 10.26.6.Control House .0......eee eeesecessceeseeeseeeesseerenneseeaseseeaeteeseesesseeeaeenes 10-254 10.27.ReSCLrVOID .......cceececseeeceseesececeeesceececeessneccaaceseceaseaeecsuecseeseaseesesessecsadeesesenseeseses 10-255 10.27.1.Reservoir Clearing 0.0...cc ceesccceeeseenecesneeseceeecessesesceesaeenseseaeoesaees 10-255 10.28.Relict Channel Treatment 20.0...eee eee ceseeseeeessscessesecseasssecessseseeseeeeeseeseees 10-255 10.28.1.Surface FIOWS.........:cecccessssseeeseeceeeceeeeeseceessceeseesensessesseessneeeeseeesaes 10-255 10.28.2.Subsurface FIOWS ........eeecseesessseeeceeeseeeeereseseesaeessessaaneseseasecneseans 10-256 10.28.3.Permafrost ........cececeeseesecssnseseeseesecsccenceceseseseeseesaeeaeesseeseeneeeaseesens 10-256 10.28.4.Liquefaction ......ccieesesseesscesseseeeersserecessessessassesconeaevseesateaeensvansens 10-256 10.28.5.Remedial Work Influence on Construction Schedules ...........0....10-257 10.28.6. Relict Channel Treatment 00.0...ececeecseeeeeeeseeeeseesneeeeeateneaes 10-257 11.TRANSMISSION AND INTERCONNECTION FACILITIES uo...eee eeeeseeeeeeeeeee 11-1 11.1.Electric System Studies...eee sseesssesssesseeeeeseseesesssscsessesssseessaessesenesaseaeeatenes 11-1 11.1.1.Goereral ........ccccccccsscesseesseescseeeeesseesesesesesecsaacsaeesaeecseeseeceeeseseenseesaeesees 11-1 11.1.2.Transmission Study ASSUMPUIONS..........cece esccesseeneeeeeeeseeeeeeeseenes 11-1 11.1.3.Study Criteria...cccccceccscssesseseeessssecsssssesscesesseeeaseseesneseeeaeeeeeeeeesers 11-2 11.1.4.System Study Methodology........cescsscssescssececsseesessrenesteeseeseseeeees 11-4 L1.1.5.Results....cceeceeecsceessecseesneesrseesseesesearsaeeeacenscecseesenessesessessaeesseeseeteneens 11-6 11.1.6.Future Studies 2.0...eeceesseseeescceseeeneeecseeesseeceaneeesesescesessneeesseeeeeeeeaes 11-9 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page x December 2014 -w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 11.2.Corridor Selection...cece eecessessescseceseeceneceeeecseeesecesseeesaeseaeeeeeenseseaeeeeeesaes 11-10 LD.2.1.Gemeral neice ceesceesesscessessaeeseeeeseessneessecsecessaeeeseeeseeseeerensessneeens 11-10 11.2.2.-Evaluation Criteria...ce eecessecesecssreesseceeesseeesseeeseeseaeeseeeseeeaes 11-11 11.2.3.Route Alternatives occ cceecceseceeeeeseeeeacesssecssecseceesaeeeeesaeeenteess 11-12 11.3.Towers,Foundations and Conductors...........ccccccccssscccccecsesessnsccececeeesssstecescsecees 11-13 11.4.Interconnections...eee eeecseeessecseceeseecseeseecscersnecsaeeescessneeeseceeeecasenseseaeeeseres 11-13 11.4.1.Substation Costs.......cescccssseceseeeeseeecseneecseeeeeeecsenecseaneceseeeesneeesnseees 11-14 11.4.2.BESS Costs oo.eeccescecesceeseceseeeseecsneseeesseceseecsnecsneeeesseseeseeecseeeaes 11-14 L1.5.Comparative Costs 0...eecssccsscessessscessesssecsscessesessacsecsenersseceseeenatensesseeeeneeees 11-17 12.PROJECT OPERATION AND RESOURCE UTILIZATION1.00...eeeeeeeseeeteeteeeeees 12-1 12.1.Proposed Project Operation 0.0...cece ssesssceseeseesseeeeseaecesesecteaeeseeeseeseteaeesesentenes 12-2 12.1.1.Background .......ee seeccescesereesesessecesceeseecscesenceseecanessasenseeenaeeeeesaeesaes 12-2 12.1.2.-Environmental FIOWS 20...eee escsscceseeceaceseeeseeceeceseeseeeseneeseeseneeues 12-3 12.1.3.Reservoir Operation oo...eee sssesesseeseseceseeceeeeeteeeseeeaeesseeasenseeseeeas 12-4 12.1.4.Operating SCOMari0.......ee eeseeseceesseececeeeeseeeeseeceeseeceneeeenseceeesseneeees 12-10 12.2.Project Generation oes esesseeseesesesecseesseeseceessseesaeceseaeeseseaeesaseseseneeneesnens 12-18 12.3.Downstream River Flows and Depths ............cccccscccssseeceseecesseeenaceesseeeseeeeeseees 12-22 13.CONSTRUCTION METHODOLOGY AND ESTIMATES OF COST........cesses 13-1 T3.1.0 Gemeral oe.ceeeeceeseeeecceesecceseceeseceesececescessaeesesaeseaeessaaeeeeaeeeseeersceeeseaneseneeeneneeeeees 13-1 13.2.Estimating Methodology -Construction...ccc ceesesseesseseseeeseecneeceeseeaeesaeenseeees 13-5 13.2.1.Basis Of Pricing .........ceseeeessceseceseecsecesesenseeeseeeneeerasesaeesseseneeeaeeneeees 13-5 13.2.2.-_Estimate Classification...ee ceeessesssceeseceseeceseeseeeseeeseeeseeeeeeeeees 13-5 13.2.3.Estimating /Scheduling Methodology or System ...........eeeeeeeeeeeees 13-7 13.2.4.Estimating Accuracy and Contingency.........cescescessceeeeeeeeeeteeeseenees 13-8 13.2.5.QUANTITIES 0.0...eee eeeeceesereecesseceseneeeccesneeseeseeeoessaaeecesaceseesaeerenteneneeseee 13-8 13.2.6.Significant ASSUMPTIONS «0.0...ce eeeeecceeeeeeeetseeseeeeeeeeseeeaerseeeeseesseeees 13-9 13.2.7.Direct Cost Development...cc cecceesseseeceteeecesceeesseeseessesesesseeneess 13-9 13.2.8.Indirect Costs .......cccccsccssccssececeseeceseeceaetceceacesseeececseeesseenstenseeseeensees 13-10 13.2.9.-Estimate Add-On .........ceeeecessescsceeseeeeceseeeesecsacesseeeaeenseeseeeeeesnetens 13-10 13.2.10.Labor Rate...ceeeescesseecseteseeeseeesseessacssessaneeseseaeseaecnetennenseteaees 13-10 13.2.1].Equipment Rate...eee eeeseesesscesecseseeeeeeesaeenesnetsaeeseesessseneseaeonses 13-10 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xi December 2014 -w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.2.12.Escalation...ce iesscssessssseeseceseeceeesnnersceceseeceeecnaeesseeeseeseeeseeessaes 13-11 13.2.13.Allowances and Contingency .0........cccccescsssseseeeseeesseesseresneeseeesaes 13-11 13.2.14.Market Conditions 00...ee eeeseesccescesseecsseceseesseeeseeeeseseneeeneeseeeennes 13-11 13.2.15.Construction and Contracting Aspects.........ccscccssceesseecenscesreeeeees 13-11 13.3.Assumed Construction Methodology .........ccccscssecestecsesesseseecesecseseeesesesesseees 13-13 13.3.1.Gerneral 00...eee seeeeeeeeseceessenneceseeceecesseeecsaaeceaceeeaesessaeesseaeeeseeesenseeeees 13-13 13.3.2.Main Access Road .........cssssssssesecsseesesceeeecseessnseenecessessseesseeennessaes 13-14 13.3.3.Railroad Offloading Facility 0.0.0...ccescccssscsessesseseccssecesseeecsseeeensees 13-18 13.3.4.Camp and Airstrip Civil Works ......cele eeeeeeseeeeeeesceseeeeeeeenteeeensess 13-20 13.3.5.Supply and Erect Camp oo...cecsecsesssessccseecsesesseeeseseeaessneeeseeeeeees 13-23 13.3.6.Main Civil Works Construction...ceeceescesseeeeeeeeseeeeeeeeeeaeeeneees 13-25 13.3.7.Turbine and Generator Supply Contract...ee eeeeseecereeeeeeeeeees 13-32 13.3.8.Transmission Line and Interconnection............ceceeeceeseeeeeeeeeeeeeees 13-35 13.3.9.Site and Reservoir Clearing ..........cceececseeceeeeceeseeeensneeesneeesteeeeteeeees 13-37 13.3.10.Air Transport Services ......ceeceacecseseceseecscceeseeseeceeeeecesseeeeseeseetenes 13-39 13.3.1].Railroad Operations 2.0.0...eseeeesceeeeeeesececeeeecencessseeeenacesseeessaeesees 13-41 13.3.12.Camp Operation...eeescesececsesseesseeecseecseeaseseeeesaeeeesateseeaes 13-44 13.3.13.Medical Services...eeecesscesesscerceseecnserseenacesseeseeseneesseseaeensees 13-46 13.3.14.Service Contracts -Manpower .......csescssssesesesseseceeceseeesersneeeeeeesnes 13-46 13.3.15.Construction Manpower -All Contracts .........cccecccccssecesecssneeeeee 13-47 13.3.16. LoOQistics ........ceecscccessseeesnceeeseteceeeeseecseecnscesseceesaeeesasesseeseenseenaeeess 13-48 13.4.Construction Cost Estimate Derivation .......eee ee eceeeeeeeeseeeceneeeseeceseeeseneees 13-50 13.4.1.First Read of Estimate...cece ceseseessscsseeeseeeeeeseeeseecsssenseesseesnees 13-52 13.4.2.Second Read of Estimate .0....eee eesceesseeeseceesseeseeeceseeesseeeesenees 13-53 13.4.3.Final Draft Construction Cost Estimate...ceececccesesseeeseeeeees 13-55 13.5.Non Construction Costs ........c:ccccccssccsssseesseesseseeesscseecsssessceeaseseeesseeseneesaeesseenseees 13-56 13.5.1.Gerneral ......ccccccesseeesseceseceeseeeeeseceseecsuescscerssenecsneeceseeensesessseeensaeeeees 13-56 13.5.2.Cost Items 0...ceeeeesccesscessrecseeeseeseessecssessecenaeesseesseceseeesescseeeereeeeeess 13-57 13.5.3.Derivation of Non-Construction Costs .........ccccsccsceseeseesssesseeeesens 13-57 13.6.Total Project Cost Estimate 0...ieeceeseessssesssercecseesscecseessseessessesessnesseeeeseees 13-60 13.7.Cashflow oo...eeeesessssesceseecssceseesssossscsessscsesssessessssessseeseseaeeseesaeeeeeseaseeaeeeatenes 13-60 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xii December 2014 -w-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 13.8.Cost Variability Analysis...cceccccscceccsseeesseeecssnseesseeceesnecnseececeseceesessneeeeanees 13-61 13.9.Risk AmallySis 0.0.0...seccessceessneccsececssceesseecesseeecesneessceeeesaeeeeeaeesnacersanesereneesneessaes 13-65 13.10.Operation and Maintenance Plan and Budget...eee eee eee ne eeeeeeees 13-65 13.10.1.Operation and Maintenance Plan...ceeeeceeseeeeteceneeeseeeeneeeeeenaees 13-66 13.10.2.Site Staffing 0...ee secsseceesseeeseeeeeeeceeeseeeseaaeesaeeeesaeeeseaeseseeeessaees 13-67 13.10.3.Power Dispatch Arrangements and Staffing...eeeseeeeeeees 13-67 13.10.4.Annual Operation and Maintenance Budget...eee eeceseeceeeees 13-68 13.10.5.Annual General and Administrative Budget...cee ceeeeeneeeeeees 13-68 13.10.6.Environmental Monitoring and Compliance .......eee eeeeeeeeeeeeeees 13-69 13.10.7.Special Considerations in the Early Years...ce ceseeseeeeeeeseenes 13-69 14.|.ENGINEERING AND CONSTRUCTION SCHEDULES...eeeeeceeeseeeteceseeeees 14-1 14.1.Preparation of Schedules...eee eecsssseeseesssesssseessesesesesssessasssesssseesesosssorsaeeaee 14-1 14.1.1.Calendar 00...ceeeeescceesscecescesesseeceneeessceceeseecenseesseseeseessessesesueeneetees 14-2 14.1.2.COmStraints ........eeeeesscecesccesecceeseecesececssaceceseeeesaeecsaeeceaaeessneresseeesseeesses 14-3 14.1.3.Individual Contract Schedules «0.0.0...:eceseseseseteseseseeeeeeeseeneneteeeeneaeeees 14-3 14.2.Construction Schedule Derivation oe.eee seeeneeecesneecnceeeeereeesaesensaseensesesss 14-13 14.2.1.Goerneral .....eceeeceesseeeeseceseceeeseeeeeanecesneceseeecesueeeseaeecanesesseessseesssaeeseneeens 14-13 14.2.2.-Potential Early Works...cece ceseceessenceseeesseessecesessasenseseseseseoes 14-14 14.2.3.Schedule Notes.........ccccecesseecesssseeesssseeeeessseeecssseeeeesseeessesseeeeseeaeees 14-15 15..CONCLUSIONS AND RECOMMENDATIONS.....cece ccesssesesseeseeeeeeeaceseesseenepseseaeens 15-1 15.1.Comclusions......cccceescessceeseceseceneeseeecneeesnecsaaseseeeseessceseseseseessesesessssaeesseeasesaeenaeens 15-1 15.1.1.Technical Feasibility...ce cccesceessesceeeeeeeecseeessarseeesseseeeenaes 15-1 15.1.2.Economic Feasibility .........:..c:ceeeescesecceeeneeeeenseeseeseeeeeeeneeeseeesenereeaee 15-5 15.1.3.Environmental Considerations ...........cesceeccessseseeeceesseeeeneeseeeseeenaeens 15-6 15.2.Recommendations ...........c:ccssccesceeessceceeeceseeeencesesaeeesseeecsaeeeseneeesaeeseeseessaeeneeossees 15-7 15.2.1.FUMING ee eee eeeeeceeeeseeeseseeceeenesesesseessenssuseeceesseeseesseeeneseeesensees 15-7 15.2.2.Geotechnical .......eeeeecsecssecssecesescesecsseecesseecssesssereceeessssasessaceesesees 15-7 15.2.3.-EMgineering......e eee eeceeeessesscsscesesesseeseesseessesesseesseesseseeeneeeeeseeasensenss 15-7 15.2.4.Procurement Plan.........ccccccsscssscesseceesseeeeeceeseseeseeeersneeseeeessaeeseaseeensees 15-7 15.2.5.Integrated System Studies...ccc ceesseessessesseeseesseeseeseceeeseesessenens 15-7 15.2.6.|Centralized Dispatch Planning...........cccececsecesesseseeeseeeeeseneseseessenns 15-8 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xiii December 2014 -zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 16.PRELIMINARY DESIGN CRITERIA1...cece cssceececceeseeeeeneesseceneveaceseaeeesseeseesessenseeeaees l 17.REFERENCES .o..eccccccccccccsccesesesescesssesceessscsssessssssocsseresseecseseseeesessaseseseessasesaeaeeseeeaees 17-1 Table of Figures Figure 1.1-1.General Location...eeccscceseceseeetsetesenecsseceneesesesaeeseeeesaecesssaceesseesesueceseesnseensees 1-2 Figure 1.1-2.Watana Dam Site on Susitna River,Looking Upstream ..........escescsssssesseceeeeeeeens 1-3 Figure 1.1-3.Site Plan oo.eee eeeeeesesecescesseesceseesecsesseesaeseecsecaessaesseesseseaeeseseeesssesseessseaeeneeeasenes 1-4 Figure 1.6-1.Proposed Watana Dam Site,Looking Upstream...ceeessessecesseeeseesreeeseeseeee 1-16 Figure 1.6-2.Dam Arrangement...cece ec csccssccscecssssecsecsseseesseesacesaeesaeasseesaceseessneaeesaeensens 1-17 Figure 4.3-1.Scenario 1A:Capacity Requirements Including Committed Units with DSM/EE1...ee eeseceseeeseeseeessoeecscessconscssessecsassaeesessnecneessssessceascaeesevsceseesseseeeaeeseeadeeseseaeersesseeeaeeneeana®4-5 Figure 4.3-2.Scenario 1A:Capacity Requirements Including Committed Units without DSM/EE........escessceseesstesececsecsencesceessescecessceuaessceseeeaeesacssenscesseescesaeseeeseesueesesnesecscesanecsseseeaeseeserens 4-5 Figure 5.7-1.Overall Impact of Susitna-Watana Project on Railbelt Annual Generation COSUS.....ceseecsescesneeceessseeeeesseeeessssaeeeessaeeceesaceesssaeeeeessaeeaeseessseesssaecessaeescssuaeeceenanesensneeeseseesesenensaeeese 5-15 Figure 6.1-1.Monthly Average Precipitation ......0.ceescssecssceseceseceeeseeeeseeeecestesnseesseeensessneeseees 6-2 Figure 6.1-2.Average Temperatures .......cc ccescscscescsssssesesssesesessececseesseeseseseeceeseceseceseeeeenssennees 6-3 Figure 6.2-1.Susitna Watershed Boundary and USGS Gage Locations.............ccccsesessseeteeeeeees 6-5 Figure 6.2-2.Susitna Watershed USGS Flow Data -Chronological Availability...6-6 Figure 6.2-3.Average Monthly Flows in the Susitna Watershed ...........ceeescseeeseeeeeeeseeseeeeeees 6-8 Figure 6.2-4.Susitna River Flow Frequency at Cantwell...eeeseseeeseeereenecseeeeeeeneeeeeeees 6-10 Figure 6.2-5.Susitna River Flow Duration at Cantwell .........c.eeeessscssseessseeseseecsseeesesseeeseeesees 6-11 Figure 6.2-6.Susitna River Flow Frequency at Gold Creek...ceeessessesseseceeeeeeeeeeeceseenees 6-13 Figure 6.2-7.Flow Duration Curve for the Susitna River at Gold Creek 0.0.0...eceesceesseeseeeees 6-14 Figure 6.2-8.Modeled Susitna River Flow Frequency at Watana Dam...eeseeseeseeeeeeees 6-17 Figure 6.2-9.Modeled Susitna River Flow Duration at Watana Dam...eee eeeeeeeeeeeeeeees 6-18 Figure 6.2-10.Log Pearson Type III Flood Frequency Plot for the Susitna River at Cantwell oo...cccccccccescessceseececesseceecseeeesnesscessneesnecsaeessnaeessessesnssseessesscssaeseeseessaeeseessaesesaseatesseses 6-20 Figure 6.2-11.Log Pearson Type III Flood Frequency Plot for the Susitna River at Gold Creek oo...ceecececccssccssscessecsseesnecessenscecessscecsuessecessenscesscessensceasessesseeseassaecssesssseaseeeeceeceseseeasesusennsenes 6-22 Figure 6.2-12.Average Annual Flow Distribution for the Susitna River........c.ceesseseeenseeeee 6-24 Figure 6.2-13.Watana Reservoir Annual Inflows and Trendline.........ccceesccssesssessseereesseeeees 6-25 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xiv December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 6.2-14.Example Month with Trend toward Increasing Flows -April...eee 6-26 Figure 6.2-15.Example Month with Trend toward Decreasing Inflows -June..........sees 6-27 Figure 6.3-1.Major Physiographic Provinces ..........:csssesscessesscesecsseeseesssessssseseeesseeseeeeseseasenees 6-43 Figure 6.3-2.Regional Tectonic Terranes and Basins -Part 1 Of 2...eeeeeeeereeeeeeneeneee 6-45 Figure 6.3-3.Regional Tectonic Terranes and Basins -Part 2 of2 sevevetsssssssssnsevessessssnutessessten 6-46 Figure 6.3-4.Schematic Evolution of South-Central Alaska oo...ce ssseseeseseeceeeeseeseseaeeeetens 6-48 Figure 6.3-5.Correlations of Cenozoic Tectonic,Magmatic,and Sedimentary Events in South-Central Alaska...cseececssceeeseeeseeeseseescesseessesesasessesesssessoesseseseascasessaesseseaasssasesseseaeeenesen 6-49 Figure 6.3-6.Acres Geologic Map Updated With Observations from 2014.0...eee 6-51 Figure 6.3-7.Acres Geologic Map Updated With Observations from 2014.0...eeeeeeeee 6-52 Figure 6.3-8.Tectonic Setting of South-Central Alaska During the 1964 Earthquake............6-53 Figure 6.3-9.Map View of Slab Planes..........ccccsessesssssesessessesceseceessssesssessessesscescnesseeseesenses 6-55 Figure 6.3-10.Schematic Showing Subducting Slab Geometry..........ccccesceseeetseescesecsecseees 6-56 Figure 6.3-11.South-Central Alaska Regional Faults...ccc cece ces sesesessssseesessensseeeeesseneees 6-57 Figure 6.3-12.Denali Fault Characterization ........ccccsccccsccssecesscseessecnesseessesseesseesssseeesssesssees 6-58 Figure 6.3-13.Castle Mountain Fault Characterization .......ccccsscsesccesesesserssesescesesessssesseeaes 6-59 Figure 6.3-14.Late Wisconsin Glacial Limits and Age Control .........cccccececeeeeeseenneene 6-61 Figure 6.3-15.Seismicity within the Susitna-Watana Seismic Network Project Area, November 16,2012 to December 31,2013 .......ccescccccccsccscccscscceccccececeeecesessnssnnsnneseeeuseeeeaeeeeeeeses 6-67 Figure 6.3-16.'Seismicity Section A-A',November 16,2012 to December 31,2013.00...6-68 Figure 6.3-17.USGS Shake Map for 2002 Denali Earthquake...cscseeseseseesesseseseseenes 6-71 Figure 6.3-18.Shear Zone in Outcrop at GF1.......ceceesscceseeseeseeseesseneeseeneeneetsesessssseeseeeseeeees 6-78 Figure 6.3-19.Close-up of 3 to 4 ft.Wide Shear Zone at GF]......ec eceeeteeseeeteseeeseeeseeeeeneenes 6-79 Figure 6.3-20.Northwest Trending Gully of GF4B ........ceeecceseseseeseseeseeeseeesesesseeseseeeeeeees 6-83 Figure 6.3-21.North-northwest Trending Gully Of GF4B ......cece ecceeceesenesesseseeeneeeceeeenees 6-84 Figure 6.3-22.Rock Core from DH12-3 with Closely Fractured Rock and Shear Zone at Depth of about 179 ft.oe secceecssessecseesseenecssessnesseesecseecsseseesseesesensessecssssseseseeasaneneeesesensceeteas 6-85 Figure 6.3-23.75 ft.High Cliff on Right Abutment Forming the Downstream (Southwest)Boundary of GFS oo...cc cseesccsecseesssssessesecaeeacsscssenseesessecsesseseenecsecsesseeseeseessessenseets 6-86 Figure 6.3-24.Rock Core from DH14-11 with Closely Fractured Rock and Shear Zone at Depth of about 102 ft...ccc cesscseeesecrssssnsessscsecsessessessessssssssessecsacsesensenscsecseessensenseneeneeses 6-89 Figure 6.3-25.GF1 Located 2,200 ft.Upstream of the Dam AXIS 00...cc cescsesseseetsenseseeeeees 6-90 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xv December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 6.3-26.Narrow Gully in Area Of GF1 ou...eseseeseceessceeeeseeesenceaeeeeeseeseeseeseeeseeessneeeees 6-91 Figure 6.3-27.Subhorizontal Slickensides along Outcrop Surface near GF7Q .........eseesseesees 6-95 Figure 6.3-28.Narrow Shear Zone with Slickensides,Calcite Filling in DH14-10 at a Depth of 507 ft.cece cee ccccseccessesssenessseecssssescrecssesseesscsesssssasssssesussscasoseseaeacssesssesessaeseaesaseraseneees 6-97 Figure 6.3-29.Close-up of Shear Zone with Slickensides in DH14-10 at Depth of 507 ft......6-97 Figure 6.3-30.Gully Downstream (west)Boundary of GFS5 on the North Bank ............ee 6-98 Figure 6.3-31.Shear Zone near BS 36,Main Shear Zone on Right with Inclined Shear ZONE Splay .....ce eeecessceseecesecesseseesessesescessseesseeesseseseessneeeesaeesnanseeeeeeseeeseessseeseeseseeeereeseeeeseeeeeeseees 6-100 Figure 6.3-32.Shear/Alteration Zone at BS27 Cross-cut by Felsic Dike...eee eeeeeeeees 6-101 Figure 6.3-33.Continuous,Thin,Joint extending through a Healed Shear/Alteration ZONE ...eeeeceseceeeseeeeecccesseeecesdeeesneeesseasesseseesueesesseesssscessaaessssssesseesseeessnsesseeeseseeeesaseeseeeeeenerseneeeeneees 6-102 Figure 6.3-34.Crustal Stress Orientations and Strain Ellipses........c.eeeesseeseeneeeseeeeeeeseeseens 6-109 Figure 7.5-1.Susitna-Watana Hourly Generation from PROMOD........cee eeeeeeeeeeeneeneeentennees 7-13 Figure 7.5-2.Susitna-Watana Hourly Generation Duration Based on PROMOD Results ......7-13 Figure 7.5-3.Powerhouse for 6 X 100 MW Units...eee eeesccceneesseesseeeeeeeteeceseseeseeseeesenesseee 7-19 Figure 7.5-4.Powerhouse for 4 x 150 MW Units...ccc ccceececssceseceseeeeeereeeesaeesaeesseeteeeeeseees 7-20 Figure 8.10-1.Wind Rose Full Yeatee...cece eesessecseseecsessnceacecsececeeseeeceeseaeeeseecsseessseesnseneen 8-21 Figure 8.10-2.Safe Aircraft Approach Surfaces .0.....cccesssssseeeccesecseceesecsesseeeeessessceeeasenssseenes 8-22 Figure 9.3-1.Susitna Watershed Boundary and USGS Gage Locations .........cceseesseesteeeseeesees 9-2 Figure 9.4-1.Susitna Watershed Sub-Basins.......ces eesessesecessesseesseesseecsceeseeseeeeeseesteseneeesseeeseees 9-3 Figure 9.5-1.Incremental and Accumulated All-Season PMP -August 1967 Temporal Distribution ..........cecceeeesecceeecessceccceessccessaeeessesessceesssasaeesseceseeseaceceseeseseeseaseeseaseesaeeeeneeeeseeeeseeesees 9-6 Figure 9.8-1.PMF Inflow,Outflow,and Reservoir Elevation 0.0.0...cescecseceseeeeseeseeeeseeeaseees 9-11 Figure 10.3-1.Lower Hemisphere,Equal Angle Stereograph Plots of Principal Joint Sets from Surface Mapping .......:cccsecccsseessceeeseseccceeeceaesensecaeseseeesseecacsaacseesaeeesceneeesesessseenseseseseeanenss 10-33 Figure 10.3-2.Lower Hemisphere,Equal Angle Stereograph Plots of Principal Joint Sets from Downhole Logging..........:ccesscecsscecstseeeteeesneeessesesesseesecesecesseeseseceusnecsaesseaeseesseceeneessanerena 10-33 Figure 10.3-3.Evaluation of Shallow Joints from Downhole Logo...eceecessesseeesesseeseeens 10-36 Figure 10.3-4.Schematic Rock Block within the Abutment of an Arch Dam........eeeeeeeeees 10-47 Figure 10.3-5.Plan,Left Abutment Wedges 1a and 1D...eeeeseeeeeseeeneeesesseesseesneaes 10-48 Figure 10.3-6.Plan,Left Abutment Wedges 2a and 2D...eeececeeteeeeeeeeeaeessesseeeseesseeaes 10-49 Figure 10.3-7.Schematic Profile along Dam Axis Left Abutment showing Wedges 1a, 1b 2a and 2b;Scale of Wedge Boundaries is Approximate...sceececssesssessscesscesseessteesseenees 10-50 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xvi December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 10.3-8.ANSYS Foundation Models Showing Principal Bedrock Zones ............00++10-55 Figure 10.4-1.Tailwater Rating Curve at Dam Site 20...eeeeseeeneeceeeeeneeeaeeeteeeeeeenereneeees 10-65 Figure 10.4-2.Derived Diversion Scheme Rating Curve wo...ee cescesseessecesecsseeseeeeesseesaseeneees 10-67 Figure 10.5-1.RCC Dam Configuration Evolution...cece ceeeeeeeeeeseeseeseeeseeeseeeeseseneas 10-71 Figure 10.5-2.RCC Volume,Dam Layouts 2 and 3 showing Layout 4 before Optimization .....ce ceeeeeeeneeeeeeeereteceeesecseeeneceeceseceeseeeseeeessseesesesessseesssseeeeeeaseesseseeessesseaseeseeeneeseeae 10-75 Figure 10.5-3.Typical Elements Used in the Trial Load Method...eee eeeceseeseeeereeeeees 10-78 Figure 10.6-1.Layout 2 (Dam J)-Crown Cantilever Stresses wo...cc cceseesseseeseseeseeneeseneaes 10-85 Figure 10.6-2.Finite Element Model Upstream Side (Layout 2)...cee eecesecssesseeseessecneee 10-87 Figure 10.6-3.Finite Element Model Downstream Side (Layout 2)0.0...cee eeeeeeeeeeeee 10-87 Figure 10.6-4.Response Spectra for Watana Dam Site...eee cece ceeecee cee ree eeeeneneseees 10-89 Figure 10.6-5.Mode Shapes -First Six Vibration Modes (Dam Layout 2).........eceeeeeeeees 10-96 Figure 10.6-6.Layout 3 -Static Loads -Cantilever Stresses at the Crown Cantilever.......10-101 Figure 10.6-7.Layout 3 Static Loads -Horizontal Stresses at the Crown Cantilever......10-102 Figure 10.6-8.Finite Element Model of the Dam (Layout 3)...cccceeceseseseeeeeeesenseenens 10-104 Figure 10.6-9.Vertical Cantilever Stress Upstream Face (Layout 3)......0..ccesseseeeeeeees 10-105 Figure 10.6-10.Vertical Cantilever Stress -Downstream Face (Layout 3).......0.0 cece 10-105 Figure 10.6-11.Horizontal Stress -Upstream Face (Layout 3).........ccccecsesscssersesteeseseeeeeee 10-106 Figure 10.6-12.Horizontal Stress -Downstream Face (Layout 3).......ccccscesseeseeseeresseeseens 10-106 Figure 10.6-13.Envelope of Maximum Tensile Cantilever Stress due to IWT010 Earthquake -U/S View (Layout 3)oc ccccccccceccsscsscsssseesnsssssssssecsseseeseessecseuseesseeseessesseanees 10-108 Figure 10.6-14 Envelope of Maximum Tensile Cantilever Stress due to IWT010 Earthquake -D/S View (Layout 3)......ccccccssccssssssseesssssssscssessesseseeseeseeseesecaeceeseesseseeseesessueas 10-109 Figure 10.6-15.Envelope of Maximum Compressive Cantilever Stresses due to IWT010 Earthquake -U/S View (Layout 3)...ccccsscssssssccssesesscssessecsssnecsecseresesenrsssesessceasessseeseesanees 10-109 Figure 10.6-16.Envelope of Maximum Compressive Cantilever Stresses due to IWT010 Earthquake -D/S View (Layout 3)0...cc ceesssssscsessesssessssseesecsscesecsesssessreseesssessessassesseasessnee 10-110 Figure 10.6-17.Residual Sliding Displacement at the end of IWT010 Earthquake looking d/s (Layout 3)...ecessssssssessseeeceseeceneeseseseaessssseseseeesseesseesseseseassesnesessssessesseeseeseseens 10-111 Figure 10.6-18.Envelope of Max.and Min.Cantilever Stresses in Crown Cantilever for Layout 3 for Selected Events ..0....ccceccsseescesssesesseseesssasessessessesecseecsesscsesessesessasessessssecsseeseaas 10-112 Figure 10.6-19.Cantilever Stresses at the Crown Cantilever (Layout 4)..........cceseeeeees 10-116 Figure 10.6-20.Horizontal Stresses at the Crown Cantilever (Layout 4)oc.10-117 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xvii December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 10.6-21.Finite Element Model of Layout 4 oo.eeeeeeeeeeeeeateseeeseeseaeseareneeees 10-118 Figure 10.6-22.First Four Vibration Mode Shapes (Dam Layout 4)..........ceseessessteeeeeeseees 10-121 Figure 10.6-23.Envelope of Maximum Tensile Cantilever Stresses due to IWTO10 Event -U/S view (Layout 4)...ce cccssccneessecnsecseseeesesssscssessssssesseessssessececansesaeesseeeeaeseesessneeeaees 10-122 Figure 10.6-24.Envelope of Maximum Tensile Cantilever Stresses due to IWT010 Event -DIS view (Layout 4)...ceeceeceecsssccesseeeesceseceeessneeseesseeeeasessacesnsecsaeeesauaeessneessaueeeseesesseeeseaes 10-123 Figure 10.6-25.Residual Sliding Displacement of the Dam at the End of IWT010 Event looking D/S (Layout 4)oo.eeeecssecsecesecsssesessecesssseessssesesaseneeeseeesseessneesaeeeseeeceseeaeenseensens 10-124 Figure 10.6-26.Envelope of Maximum and Minimum Stresses in Crown Cantilever for Layout 4 oo.eeseecesceesnceesceeesseesssaeecsneeessetesssevesseescassaeeessersneeeseeeesceeeesasesesauecenaseesseeesenesesese 10-125 Figure 10.6-27.RCC Volume vs Elevation (Layout 4)oo...ccc ececsscesscssecesseeeeeceeeeesteessnees 10-129 Figure 10.6-28.Effect of Foundation Deformation Modulus on Maximum/Minimum Stresses (Layout 4)...eee eesseeesseeeeseecesneceseeessaceessseneeseseecseeesseesseeessaeeseseeeassaeessseeeseaeesnaeeeses 10-130 Figure 10.6-29.FE Model of Dam Layout 4 with Fluid 80 Acoustical Elements to represent ReSCIVOIL 0...eeessesseeeseesseesecseeeaceseeseessessscscsaersecsseaseaeeseesscesssesseesccseeesareneesseeeteeees 10-134 Figure 10.7-1.Plan and Elevation of Dam Layout 4 -Modified 0.0.0...eeesseeseeseneeseeeees 10-136 Figure 10.7-2.Sections of Layout 4 -Modified...ee eeeeseeseeseesseseaessaceseesseesererseaeeees 10-137 Figure 10.7-3.Design Response Spectra .......ccescessesesesscssceessseeessesssasesecesseeeseeeeseesaceneeseaes 10-139 Figure 10.7-4.Intraslab M8.0 -69"Percentile Design Response Spectra and IntraslabM7.5 -84"Percentile Design Response Spectra ....c.ssscssssssssssesesssscsesssessssseesessecsseesesstessesses 10-141 Figure 10.7-5.Interface M9.3 -88"Percentile Design Response Spectra ........cssseseeseeeeees 10-142 Figure 10.7-6.Crustal M7.0 -84""Percentile Design Response Spectra .....cccecsssseseeseeceee:10-143 Figure 10.7-7.OBE Response Spectra and Scaled Crustal Event...cee escseseecerseeeeeeeees 10-154 Figure 10.7-8.AutoCAD Inventor Model -simplified for use in Finite Element Analysis 10-159 Figure 10.7-9.3-D View of Model Developed in LS-DYNA1.0...cece ceneeeseceeeteesteesnneees 10-160 Figure 10.7-10.Enlarged 3-D View of LS-DYNA Model 0...ecce eee eeeeseeseeeeeeseeeseeeereneens 10-160 Figure 10.7-11.Maximum Vertical Stresses in U/S Face of Crown Cantilever Monolith During MCE...cccccccessesssccsseessecescesscecscensceescessesessecsceseeseseaeesesetecsseessessseesseesaceseaeesseesaeeensenees 10-164 Figure 10.7-12.Maximum Vertical Stresses in D/S Face of Crown Cantilever Monolith During MCE...eseecessseseesseesecenseeenseeseseeeseseaeseeseeseessseesesesseesseessecsaseuseessesenesaesaseaeseaseasenes 10-165 Figure 10.7-13.Maximum Principal Stresses in D/S Face of Crown Cantilever Monolith During MCE...eecseesecsesececssesscesesesessceseceeeseessessusnssesescasessssessseeessssusesesesaesseeseesaneeaeensenees 10-165 Figure 10.7-14.Time History of Normal Stress at the Peak Stress Point in U/S Face During MYG EVEeM1.....cece cscscescesseessscsseessasseseesseresseceeseuceesessssssensesseseseeesesseseasesnasenaees 10-166 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xviii December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 10.7-15.Maximum Vertical Tensile Stress on Upstream Face of the Dam during MYG EVEN...ee eee ceeessceseceecncesscsssceenecsesesessasessesscesssesesseesasesaseasesascssesaesseeeaecaeesessaeesnecsesenees 10-167 Figure 10.7-16.Time History of Principal Stress at the Peak Stress Point in D/S Face During Four MCE Events .0....eee eececsescessecssecsecsesensesecseecsesenevsscessesseesesseseasonseseeeneteeeenaeens 10-168 Figure 10.7-17.Maximum Principal Tensile Stress on Downstream Face and Crown Cantilever Monolith of the During MYG Evenit.........ccecscecesseeesnecesseeceeneeesneeesaneseaeeeeeaeeessnees 10-169 Figure 10.7-18.Monoliths Numbering .......cece eeesscsseeseeseceseseeesseseneeeeeeeeacestecaeeneceneceeeneeees 10-170 Figure 10.7-19.Dam Base Sliding Displacement During MYG Earthquake..............ccce 10-171 Figure 10.7-20.Dam Base Sliding Displacement During STTEC Earthquake...................10-172 Figure 10.7-21.Dam Base Sliding Displacement During CURI Earthquake...10-172 Figure 10.7-22.Dam Base Sliding Displacement During GIL Earthquake .....0..eee 10-173 Figure 10.8-1.Seasonal Sequence of RCC Placement .......cece cccseeeeeeseeseesecsceseeseeeeeneeees 10-179 Figure 10.8-2.Season 1 RCC Placement :Right Abutment...eeeeeeeeeeneeeeeenereeees 10-180 Figure 10.8-3.Season 1 RCC Placement :Left Abutment...cece eeeeceeeseeeeeeeeeeeeseesenees 10-180 Figure 10.8-4.Season 2 RCC Placement :Middle Dam Section 0...ee eeeseeseeeeeeeeeeeeees 10-181 Figure 10.8-5.RCC Layer Volume vs Elevation...cee eeeessesseeceseeeecsseeseseeesaeseeeeeeenneens 10-182 Figure 10.8-6.Season 3 RCC Placement :Middle Dam Section ...........ccceseeeseessesseeseeeees 10-183 Figure 10.8-7.Season 4 RCC Placement :Middle Dam Section ..........eeeeseceeeeseeeeeeseeneeees 10-183 Figure 10.8-8.Season 5 RCC Placement :Middle Dam Section...ees eaeseeseeeeeeeeeeeees 10-184 Figure 10.8-9.Season 5 RCC Placement :Right Abutment...eee eseeseeeeeneeeeeeane 10-185 Figure 10.8-10.Season 5 RCC Placement :Left Abutment...cc ccceccsseesssssesseeseseeeeees 10-185 Figure 10.9-1.Susitna River Estimated Mean Monthly Water Temperature near Gold Figure 10.9-2.3-D Finite Element Model of the Dam for Simplified Thermal Analysis ....10-192 Figure 10.9-3.2-D Finite Element Model of the Dam for Simplified Thermal Analysis ....10-193 Figure 10.9-4.Location of LIFT 55 Used for Surface Cracking Calculations ..............c0 10-194 Figure 10.9-5.LIFT 55 Temperature Profile ...........cece ecescesssssessesseseessesseccsseseceeeseeeseeaeees 10-195 Figure 10.11-1.Wind Speed Frequency .......ccccccccsscsscsssessesessssssessssssecssceesacesesseesseeenenegens 10-202 Figure 10.11-2.Return Period Wind Speeds ........ccccscssssssssessesseeesseseceeesstsesseseseeseeeteeenees 10-203 Figure 10.11-3.Effective Fetch Calculation ........cccccsssssssessesccesssssscsssssssssesnessesseeecseeses 10-204 Figure 10.11-4.Effect ofa Clapotis Adjacent to a Vertical Face...eeeseeeeetereeteeeeees 10-207 Figure 10.11-5.Wave Run-up and Set-up and Wind Speed Frequency...........ce eeeseeseeeeeee 10-208 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xix December 2014 -w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 10.11-6.Wave Run-up and Set-up and Wind Speed Relationship............ee 10-209 Figure 10.12-1.Routed PMF Flow through Four Fully Open Gates -Plunge Pool Location |oo...ccesssscccssseccecessececsesseeessscseesessaaeesecsssaceeeseseascsaaeesesssaeasesssaeeesoeseaeeeensaeeessseeeaees 10-212 Figure 10.12-2.Routed PMF Flow through Four Fully Open Gates -Plunge Pool LOCAtION 2 .o....eecceccesccsseecessceesseeeceeceeseeeesseeceaeeesnsessseeensesucecsasesseeeceseeceaueeseseeeceseeseeaeerenaceseneeonea 10-212 Figure 10.12-3.Two Gates Open -Discharging 60,000 cfs -Center Wall Height Determination .........ceccceecccesccecescecesceeeseeeceeseesseesesseasesssaccsseesssscseeseesteeessseesesasecessaucseesorsasensags 10-213 Figure 10.12-4.Two Gates Open -Discharging 60,000 cfs -Unbalanced Flow................10-213 Figure 10.13-1.CFD Model of 30,000 cfs Flow in Emergency Outlet...10-217 Figure 11.4-1.Typical Intertie Connection...cccccsccseessecseeesnseseessceeeeeesseeseneetenaes 11-15 Figure 11.4-2.Typical Layout of the Substation Interconnection .......ccc esscseereteeeeenee 11-16 Figure 12.1-1.Minimum Environmental Flows and Average Natural Monthly Flows at Gold Creek ........cccccccesscssssesseccssceceseecencecensecseoneeseseecesscseecaseeseessaeceesaeeeseaeecseneeeeaesesseeseeseeenseeseanees 12-4 Figure 12.1-2.Watana Reservoir Elevation-Area-Capacity Table ...........scecscesesesereeeeseeeeees 12-7 Figure 12.1-3.Daily Reservoir Elevations 00.0.0...ecccccccse ese ceeeceecesseeecsessesssssseseessseeeeseneonees 12-8 Figure 12.1-4.Tailwater Rating Curve .......ccccccccccssecseseesscseesesssesssesseseseessesecsesseseesseaseeneese 12-9 Figure 12.1-5.Intermediate Hourly Load Following Operation for an Average Water VOCAL...eceeeesseccceccessssneceeceessesneeesereesssecseseessseaseeseceesssseaeeseassesseeesosssseeeeeesseseessenseeseseseseaeateseeeesaaes 12-13 Figure 12.2-1.Annual Average Generation Potential ...0..ccceeeseeeeeceeeeecesaeeseeeeseeeaeeees 12-20 Figure 12.2-2.Comparison of Susitna-Watana and Total Railbelt Monthly Generation Pattern ......ccesccceseeesscceeceeesseeesssceessesessaeeusceseesecsecessesesssnsnsessceneesenesesseesesneeseseesesesoessscenseaesesansnss 12-20 Figure 12.2-3.Modeled Susitna-Watana Powerhouse Hourly Generation Duration Curve...12-21 Figure 12.2-4.Modeled Hourly Susitna-Watana Generation for an Average Water Year.....12-21 Figure 12.3-1.Monthly Average Natural and Modeled Post-Project Flows in the Susitna River at Gold Creek 00...cceccecssssessesscecscecescesseceneeesesecssseesassaacaessseceseccesccsancesaesaeseseecaecenessaseneees 12-22 Figure 12.3-2.USGS Surveyed Cross-Section at Gold Creek...ecscsssesseseeseeseeeeeeseees 12-23 Figure 12.3-3.Recorded and Simulated Susitna River at Gold Creek Stage Comparison.....12-24 Figure 13.2-1.Variability in Accuracy Ranges for a Hydropower Estimate -from AACE GORA L2...ececcccssesccssceecsteseesseeeceeseceeseneneseaceeecneeeeeseceaeeecerssssseesssecssasussescsesseessceseeseeceneeaseneseesnees 13-7 Figure 13.3-1.Permanent Access Road Manpowe'l.......cccccsscescessesseessesscsessscsssssecesesseeeeneeens 13-17 Figure 13.3-2.Rail Siding Construction Manpowe?l........ccccccsessesesccesssssesscesesssesenseaeeaeeeseees 13-19 Figure 13.3-3.Camp and Airstrip Civil Works Manpower ..........cccccscscsscesseseceeeeseeeeeeneeneeees 13-22 Figure 13.3-4.Camp and Airstrip Building Manpowe?........cccccccceeseeeseeseceaeeeeeeeeenerseesneees 13-24 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xx December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Figure 13.3-S. Figure 13.3-6. Figure 13.3-7. Figure 13.3-8. Figure 13.3-9, Figure 13.3-10. Figure 13.3-11. Figure 13.3-12. Figure 13.3-13. Figure 13.3-14. Seasonal Sequence of RCC Placement .0.....cece cessesseceeceseceseessnsesensssseeseoees 13-28 Construction of Powerhouse Substructure within a Protected Environment ..13-30 Main Civil Works Manpower .........::csccssccssessecereeseceesseeesaeeeeeseneeatenesteaseesaseea 13-31 Transformer Transport by Rall...ces eeecceseeeeseeeeeseceeeseeeesneceseesenaeesseeeeeeeeeeese 13-33 Transformer Transport by R0ad........ee eeeeeeseseeereeceeeeessecseeeseeeaeeseaeoneeseasenseones 13-34 Turbine and Generator Manpowe P......ccccesecessscesseessssecssesesssesesseseneeessees 13-35 Transmission Line and Interconnection Manpowe.........ccessescesseesseessceseees 13-37 Clearing Manpowe?.........cscessesseessecsecsesesesesscessoesseseseeeseessasessessseseessessesseeees 13-39 Talkeetna River Bridge .........cceescseecesseeeeeseceresseneecessaaeeessceeeseseesesesaeeseseeeeeees 13-43 Total Construction Manpower All Projects ..........seeeessseseceseeseeeeeseeeseneeeeees 13-45 Figure 13.3-15.All Services Contracts Manpower .........sccsscessssseesseseeeseeeeneceseeaeesseeasensenseenees 13-47 Figure 13.3-16.Total Construction Manpower All Contracts .........cccccsssssssscsessscseseseeeesees 13-48 Figure 13.7-1.Cash flow of Construction and Service Contract .........ccscesessessserseeeseetereee 13-61 Figure 13.8-1.Construction Cost S Curve ....s.ccccccsssssssssssssssesseseesesseeseessessesecsscessessecensens 13-63 Figure 13.8-2.Non-Construction Cost S Curve......cccccsscssscsssscsssesssessneesssereseaceeseseeeenere 13-64 Figure 13.8-3.Total Project Cost S Curve...ccccccccccssessssssssssssessecsssseeseesssssensesseessessenseeeees 13-65 Figure 14.1-1.Clearing Construction Schedule...cece cscseessesseseessessessesesseneessenseneeneensenees 14-5 Figure 14.1-2.Permanent Access Road Construction Schedule...........cccsssssesessersersseeeseeees 14-6 Figure 14.1-3.Rail Siding Construction Schedule ..........cccccscescesssscesseeceseseeeeeeessesseseaseeseesees 14-7 Figure 14.1-4.Camp and Airstrip Civil Works Construction Schedule .........ccccscsssssseeeens 14-8 Figure 14.1-5.Camp and Airstrip Building Construction Schedule..........cecccssesseesseetecseneeees 14-9 Figure 14.1-6.Main Civil Construction Schedule....ccccscsscssesseseessesecsessessenseseenecssenseneenes 14-12 Figure 14.2-1.Rolligon -Low Ground Pressure Vehicle ...........cscesessessessseseetsereeneeseseenenes 14-15 Figure 14.2-2.Susitna-Watana Engineering and Construction Schedule:Critical Path.........14-17 Table of Tables Table 1.8-1.Principal Project ParameterS...........ccescescssesecssseesecessessesssessecessersssesssensesseesseseaee 1-25 Table 4.1-1.Railbelt Installed Capacity 2009 oo...ce cecessecssecssecsseessessecessesessnsseseseseeseasensaegs 4-2 Table 4.3-1.Potential Economic Development Projects oe.eeecessceseesseceeseseeseaseeesesseesateeneees 4-6 Table 5.4-1.Existing Generating Units on the Railbelt System,2014 oo.ceeeeeeeeeees 5-3 Table 5.7-1.Railbelt Demand and Energy Forecasts .......c.ceesccseeseeseeteseeseeceeeesseceseseeseeseesaees 5-13 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxi December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 5.7-2.Railbelt Electrical Energy Sources in 2024.0...ec eesscsseeseeeseeenecesreeeseeeeaseeseeees 5-14 Table 5.7-3.Variable Cost Savings Due to Susitna-Watana Project ..........ccscccssscsssescseteesseeees 5-14 Table 5.7-4.Railbelt Demand and Energy Forecasts -2013 2.0....ccessecessesseeeeesseeceseesnesensesaes 5-17 Table 5.7-5.Future Generating Plant Reserves with and without Susitna-Watana Project -2013 Forecast .......ceecceceessseecesseeseessseeccceseeeessaeeesesssensuaesesseesesaceesecaeeseessaneeeersaaeeesersaeeeeetaeeesees 5-18 Table 5.7-6.Future Generating Plant with and without Susitna-Watana Project -2013 FOTECASE .....ccesssecccecssnceccssneerecsanessesneeesersuaeesssseeeceesaeeeseseessaesessneeeeaeeecensessecessesneesseeuaseseseseecenananes 5-19 Table 5.7-7.Comparison of Natural Gas Supplies for Scenarios Studied in 2012.................5-20 Table 5.7-8.Total Annual System Production Cost Impact of Susitna-Watana Project..........5-21 Table 5.7-9.AEA Financing Plan 3.0...ccc ceesssessescseeceneceneesanecesseeeesuecseaescessecesaeesseesesenseseetees 5-21 Table 5.7-10 Total System Production Cost Impact of Susitna-Watana Project...5-23 Table 6.1-1.Monthly Precipitation...eee eseseeceeecseeseesecsecssesaesseeesersaersneseseeessaeerseaseaeeneeses 6-1 Table 6.1-2.Maximum,Minimum,and Average Monthly Temperatures ............cecsesseseseseeeees 6-2 Table 6.2-1.USGS Streamflow Gages in the Susitna Watershed ...........ccccccccsssseesteeesseessseeesees 6-4 Table 6.2-2.Average Monthly Flows at Selected USGS Gages in the Susitna Watershed .......6-7 Table 6.2-3.Flow Frequency at USGS Gage 15291500 -Susitna River near Cantwell ...........6-9 Table 6.2-4.Flow Frequency at USGS Gage 15292000 -Susitna River at Gold Creek .........6-12 Table 6.2-5.Modeled Monthly Average Flow at the Watana Dam Site 0.0.0...cesesesteeeteeeaees 6-15 Table 6.2-6.Modeled Flow Frequency at the Watana Dam Site...cceesccssssecesecsseecesneeesees 6-16 Table 6.2-7.Peak Annual Flows in the Susitna River at Cantwell...ecessceseessreeeesesessees 6-19 Table 6.2-8.Calculated Flood Frequency for the Susitna River at Cantwell .............csceeseeees 6-20 Table 6.2-9.Peak Annual Flows in the Susitna River at Gold Creek........cccccsscssseecsreesenteees 6-21 Table 6.2-10.Calculated Flood Frequency for the Susitna River at Gold Creek .............c.00 6-22 Table 6.2-11.Estimated Peak Annual Flows in the Susitna River at Watana Dam................6-23 Table 6.2-12.Percent Contribution of Flow at Susitna River Watershed USGS Gage Stations to Flow at the Susitna Station USGS Gage...eecsscsesseeeeeeeseseeceeeesseecesseessesesenees 6-24 Table 6.3-1.Summary of Previous Site Investigations.0.0.0...ceecceeesseseeesreseeeeeeeeeaeeaesteesnees 6-29 Table 6.3-2.Summary of 2011 to 2014 Site Investigations .........eee ceeeeseessecssseeseeessesseeeeees 6-34 Table 6.3-3.Ground Motions -Deterministic Results...ccc cesseseceessreesesecesecsesersseecsseeenes 6-65 Table 6.3-4.Deterministic Input Parameter ..0.....cc ccescscsseessesscssseseessecssresssesseeeseseseeseneeees 6-70 Table 6.3-5.Discontinuity Types...........:cccscssscesecssssessescsseecsecenssaaeseeeeseeccsecsassessenseesaeeseeesssseesens 6-74 Table 6.3-6.Summary ofJoint Set Orientations...lee eeeeeeeesececsseeeeseecnseeesseeeesaeenseesseeees 6-75 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxii December 2014 -Za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 7.2-1.Railbelt Electrical Power Generation Carbon Dioxide Emissions.............scesee 7-3 Table 7.5-1.Typical Generating Unit Ramping Rates .0...lees eeceeeeeeeseeseseeseeecneseeseneeeseneas 7-9 Table 7.5-2.Annual Generation for Alternative Installed Capacities,without Inflow FOLeCAStING ........eseceeeeeeeceeseesceesceescesesconseeoaseseessacceaecesseceesesesesesnaseeseesssesesessessensessesenisseesseessenase 7-11 Table 7.5-3.Annual Generation for Alternative Installed Capacities,with Inflow FOreCAStING «0...ceeeeeccesceseeeseeseseneecsencessseessecsasessesesesceseseseeeseseeesesseseessesssaeseaesesseeensedseesaesssneesseeeeed 7-11 Table 7.5-4.Reliability of Plant Capability for Maximum Hourly Generation........00.ee 7-14 Table 7.5-5.Comparative Costs of Various Generating Equipment Combinations................7-18 Table 7.5-6.Comparative Civil Costs of Various Powerhouse SizeS...........eesescseessecseeeseeees 7-20 Table 7.5-7.Comparative Costs of Various Powerhouse and Unit Size Combinations...........7-21 Table 7.5-8.Selected Unit Ratings ........cc ceesccesseeceseceesseeecseeeeseeeesseecssneeseneeesseessseessacersseeeenseaes 7-24 Table 7.6-1.Summary of Comparative Costs.......ccccccsscssssesscesssesssssesessesesssessssessseessseeeseeease 7-27 Table 7.6-2.Summary of WRAM Comparison ..........eceeeeeeseeseeeseeeeeseeeesseensesseseeeesessessesaeseeanee 7-28 Table 8.10-1.Airstrip Criteria 00...ceseseecssesessecssesssecssessseccseesseessaesssseesessssesseesssseseesessseees 8-24 Table 9.5-1.All-Season PMP by Sub-Basin for Various Durations...........ccccsessesseeeeseseneseeeeee 9-5 Table 9.6-1.100-Year Snowpack at Snow Course Stations 0.0...eecesseesseeeseneeeenaeeeeeseereeeeee 9-7 Table 9.6-2.100-Year All-Season Snowpack Snow Water Equivalent ............ceeseeseeseeseeeeeeees 9-8 Table 9.8-1.PMF Routing Sensitivity Analysis Results ........ccc cescsssesescsecssesesesesessssoesesenness 9-11 Table 10.2-1. Table 10.2-2. Table 10.2-3. Table 10.2-4. Table 10.3-1. Table 10.3-2. Table 10.3-3. Table 10.3-4. Table 10.3-5. Table 10.3-6. Typical Operations Staffing ....0.elec ceeeeeeeseesessseessesneassscseaseaseeseessseeens 10-8 Preliminary Water System Design Criteria...cece ceeeeeseseesssoeseseeseceesees 10-10 Preliminary Wastewater System Design Criteria...ccc eeeeseeeseeseeeeneetesenes 10-15 Total Combined Solid Waste Volume...cesceecesscseessecesesenssesesssosssseseseess 10-19 Summary of Unit Weight Tests...cescesessecssscssescscesseceseessesesessseeseesrasenes 10-23 Summary of Unconfined Compression Strength Tests 0...eeesseeeeeseeceeeee 10-24 Summary of Point Load Index Strengths 0.0...ce ceseescesesecsseeeseessseesnesssseerensaes 10-24 Summary of Brazilian Tensile Strength Tests ......ccc cesecsssessssessesesseeeeeeeaes 10-25 Summary of Intact Rock Modulus Parameters...ceessssessecsceeseeeseeeseenees 10-25 Summary of Compressional and Shear Wave Velocities and Dynamic PLOPerties 2.0...ceeececessssseseesesesseescneesseesscesscessesensesseseseesseeeseesseeeseenseeeseeeseeseneenseeseeeeeeseeeneeeeaeees 10-26 Table 10.3-7. Table 10.3-8. Table 10.3-9. Ranges and Average GSI for Engineering Units........eee escssseeeesessseteeeneee 10-29 Recommended Intact Rock Properties ........ccccesesseessessscsscseessessneneesesesereeees 10-30 Recommended Rock Mass Strength and Deformation Parameters.............04.10-30 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxiii December 2014 -yzZO- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.3-10.Summary of Joint Set Orientations..........ccccessccesscssceessecsseeecssessseeseceneeeseeeans 10-31 Table 10.3-11.Summary of Joint Set Characteristics from Geologic Mapping..............000 10-34 Table 10.3-12.Foundation Parameters for Preliminary 3-D FEA............ccccccsccsscessreesseeneeeses 10-56 Table 10.4-1.Flood Frequency at Watana Dam Site...cee ccecessessceseeceeneesaeessesesseeseeeass 10-63 Table 10.4-2.Criteria for the Diversion Tunnel Intake...ce cesesessssseeesesesennersseeeessesenens 10-64 Table 10.4-3.Diversion Tunnel and Sluice Features......ccccsssssessssesseecsssessesssesseeesseeeseens 10-66 Table 10.5-1.RCC Volume (Layout 4 -modified)0.0...cc cessccsscesseeceseeeeeseesseeseseesesee 10-77 Table 10.5-2.Preliminary Dam Design Parameters for Layout Development..................0065 10-80 Table 10.6-1.Analyzed Dam Plan Configurations for Layout 2 (high dam)............:csceeeee 10-83 Table 10.6-2.Periods of Vibration and Modal Participation Mass Ratio of Dam (Layout QD)csccescceccsscescesescsceesscscccueesnsenecseeeasessesseeseessesssesseeasesecsssscassenecssasesaeeseessesesssseaeeeaeesesseceeeseesseaaes 10-90 Table 10.6-3.Comparison of Seismic Analysis Results -Maximum Tensile Stresses (Layout 2)..cceciccceccssscsssecsssesssnsecsnsescsrsensecssssessssesecssssacssssesarssseessseesesescesseeseseesseseeeseegeersereeas 10-97 Table 10.6-4.Comparison of Seismic Analysis Results -Maximum Compressive Stresses (Layout 2)...eeseeeseeeesscecesceceseceeeseeeseeeeseeesensneeeseeesseeecaeeseseeseeaeeeseseseseesseaneseaneeeseees 10-97 Table 10.6-5.Susitna-Watana High Dam:ADSAS Estimated Dam Volumes................0006 10-98 Table 10.6-6.Watana Dam (Layout 2):ADSAS Estimated Dam Volumes..............cccccceeeee 10-99 Table 10.6-7.Dam Frequency and Periods of Vibration (Layout 3)..........cccccssscssseesreeseeenes 10-107 Table 10.6-8.Summary of Dam Layout 3 Response to 8 Earthquake Loadings..................10-113 Table 10.6-9.RCC Quantities (Layout 3)...ce cesscsscsseecsecssceceeecsseecesaeesessecesseeesseessneesees 10-114 Table 10.6-10.Frequencies and Modal Mass Participation Ratio for Layout 4................4.10-119 Table 10.6-11.Summary of Dam Response to 8 Earthquake Loadings (Layout 4).............10-126 Table 10.6-12.Comparison of Dam Responses for Dam Layouts 3 and 4 0...eeeeeeee 10-127 Table 10.6-13.RCC Volume (Layout 4)wo...ceeccecsssseeseeceeeessceeseeeesseceessnesesasescseecesatensaees 10-128 Table 10.7-1.Deterministic Seismic Input Parameters 000.0...lees eeeeeeeeeestecesseeesseeeestecentes 10-138 Table 10.7-2.Median Vertical /Horizontal Rattos...........ccesseesceeeseeesseesscesesecessseesseeessesees 10-140 Table 10.7-3.Horizontal and Vertical Design Response Spectra for Intraslab Events ........10-141 Table 10.7-4.Horizontal and Vertical Design response Spectra for Interface Events..........10-142 Table 10.7-5.Horizontal and Vertical Design Response Spectra for Crustal Events...........10-143 Table 10.7-6.Record Parameters for Selected Slab Time Histories -M8.0 -69th Percentile (PGA=0.8 1)....ccccccsscccssseceeesecessssecssseneceesescesesaeceseaeeesssesesessseesecsesssessesuscenauees 10-146 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxiv December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-7.Record Parameters for Selected Slab Time Histories -M7.5 -84th Percentile (PGA=0.69)......csescesccesesseesstsssesssncessecseseesscsenscseesseseasisssesseseassaseesseseeeaesenesesseses 10-147 Table 10.7-8.Record Parameters for Selected Interface Time Histories -M9.2 -88th Percentile (PGA=0.58)......cccecceceetseteseceseeseeeeeseeceseeseeeseseeseesnessesasesesesseusesensesseaseeessaseseasonenees 10-148 Table 10.7-9.Record Parameters for Selected Crustal Time Histories --M7.0 -84th Percentile (PGA=0.49).......ceescsecsseceeesseceeeseececescesseeseeseeseseceusersssassassesssesesssersseseseeseeseesenees 10-149 Table 10.7-10.Estimate of Significant Duration using the Brookhaven Model .................10-151 Table 10.7-11.Selected Time Histories for Feasibility Analysis-Intraslab and Crustal.....10-152 Table 10.7-12.Selected Time Histories for Feasibility Analysis -Interface...ees 10-153 Table 10.7-13.PGAs for Selected Return Periods...eee seeesseecseeeeeneeessnecesseseeseeeeneeeeenees 10-153 Table 10.7-14.Foundation and Dam Material Properties used in LS-DYNA........eee 10-161 Table 10.7-15.Foundation Rock Material Properties and the Corresponding Wave Velocities and Lysmer Damper Coefficients...ccccesescssecssesssesseesseesseeesereesereneeesesesnesens 10-162 Table 10.7-16.Scaled Damper Coefficients used in Three Directions as a Result of DeCONnVOLUtION.........cccesccessscesessecessescaceecessanecesnaeeesssseeeesesaeeseessaeeeesaeeecessaeesessaeeseessneeeossseeesonses 10-163 Table 10.7-17.Maximum Tensile Stresses for MCE Evemt.......ccccecsessseessssesssesessenensosees 10-166 Table 10.7-18.Maximum Sliding on Selected Momoliths ..0....ce ceeeeeeseeseeeeseeseeesneasenaeenees 10-171 Table 10.7-19.Maximum Tensile Stress in the Dam during OBE Events...ec eeeeeeeees 10-174 Table 10.7-20.Maximum Sliding during OBE Event........ccccccscsssesessesceseseesescessesssseesenees 10-174 Table 10.7-21.Maximum Tensile Stress Sensitivity to Foundation Properties ..................10-175 Table 10.7-22.Maximum Sliding Displacement Sensitivity to Foundation Properties .......10-175 Table 10.7-23.Comparison of Results of Massed Foundation Model with Massless Foundation Model ..........:ccccscsssccssesecessnecssceseseeceeeececeesaceceseeeceaeeessesensneesseeceeessseesentaeersuaeraaae 10-176 Table 10.8-1.RCC Production Schedule...eee eeeesesceceseeeseeesneesesneceeecssneeenseeeesereesaees 10-178 Table 10.8-2.RCC Placement Locations...........cescceessseessesseeceessseesesseeeesesnsecesseeeesesseaseesagen 10-178 Table 10.8-3.End of Season Elevations:Middle Section 0.0...ce ceeceseeseeeseeescecseeeeneceeeeess 10-182 Table 10.9-1.Susitna Project Site Monthly Temperature Data...eeesseeceseeeeeneeeneesen 10-189 Table 10.9-2.Susitna River Mean Monthly Water Temperature near Gold Creek.......0000...10-190 Table 10.9-3.Foundation and RCC Thermal Properties 2.0.0...esse eesceeseceeseceesceeereeeeseeeeses 10-191 Table 10.9-4.Surface Tensile Stress Gradient Calculations....0..ccc cece esses eee sence 10-196 Table 10.11-1.Wind Speed Frequency..........eececesccsssessesseecsesesseeseeesseeeneecsessseeneesesseenesenseceaes 10-202 Table 10.11-2.Return Period Wind Speeds..........ccceecessssesscesessesssessesesseesseeesseeseesseeseeeaes 10-203 Table 10.11-3.Wave Run-up and Set-up Values .......eccccescsseeseseseeseesseseseeessesersereeseeees 10-207 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxv December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.11-4.Adopted Wind Set up and Wave Run-up Values ..........cc cceceesseeeeeeeneeeee 10-209 Table 10.17-1.Economic Penstock Diameter...eee seeceseceeceeeeesnseeeeeesessecesssenessecensaes 10-227 Table 10.19-1.Preliminary Turbine Specifications...esccscesesscessecsseseseeceeesssseeseesteeees 10-231 Table 11.2-1.Summary of Transmission Alternatives .........cccseeeecseesseeeeseeeseeesesseeeeseeeeeens 11-13 Table 11.4-1.Substation Cost...ccecescsseessccesseeessccsseseesssessscssessseeesseessasesseseassesssesseesasenseseaes 11-14 Table 11.5-1.Estimated Comparative Transmission Line Costs...ce eeeessceseseseseeseeeseeeees 11-17 Table 12.1-1.Monthly Average Reservoir Elevations ........cccccecscceseeseeecsesseseeneeseseseeeneee 12-14 Table 12.1-2.Monthly Susitna-Watana Powerhouse FlOW ........0cceecsseeesesseeseeseseseesueeesneeees 12-15 Table 12.1-3.Monthly Total Release to River at Watana Dam...........ccceeeeesessesesesssteeeeenees 12-16 Table 12.1-4.Monthly Flows at Gold Creek .....cc ce cecccceseeeescessesseeenseeceseeseesessensesseeeneaaees 12-17 Table 12.2-1.Susitna-Watana Powerhouse Generation Potential ........eee eeeeeeeeeeeeeeenereees 12-19 Table 12.3-1.Ice-Free Season Monthly Average Flows and Depths at Gold Creek..............12-24 Table 13.2-1.AACE Estimate Classes ..0.........ccescescesseseesseeesesseseasessesessecseecereecseevsasessoseneseneses 13-6 Table 13.2-2.Typical Estimating Methodology Relative to AACE Cost Estimate Classification........ccccccssccsscessecesscesscsseececescesseeeeessneesseseceseseseenstessecsseseaeeeseeesscesasenseseresoeeesseasanaenes 13-8 Table 13.2-3.Estimating Contingency Level Recommendation...ee ee eeseesseseeeeeeereneeee 13-8 Table 13.3-1.Large Loads and Approximate Dimensions ...........ececececeeeseeeeneeeneneees 13-31 Table 13.3-2.Large Turbine Loads and Approximate Dimensions ..............s:cscessessessessereeeees 13-33 Table 13.3-3.Typical Large Construction Items to be moved to and from Site...13-49 Table 13.3-4.Key Materials to be Shipped through Supply Chain...ceesseseeeeeeeee 13-50 Table 13.4-1.First Read of Two Comparative Estimates...cceceseseecesessseseesneseeesseeeeaes 13-53 Table 13.4-2.Second Read of Two Comparative Estimates .........cccccsssscssseesesereseseesseseees 13-54 Table 13.4-3.Opinion of Probable Construction Cot .......cccssesssessessssessesseseessesseseeseesessneees 13-56 Table 13.5-1.Non-Construction Costs .......ccccsccessecrsneessecsseseeessesssssssesessscseesesesssesonesessooseeengs 13-58 Table 13.6-1.Program Base Cost Estimate -2Q 2014 wo ceccccseeseseeesesssssessesseseesecseeeees 13-60 Table 13.10-1.Budget Allowances for Environmental ..........ccccsscssessseseesssesseeeeesessseseneteee 13-69 Table 14.2-1.Key Activity Durations...cece csessseseeeeeseeenseseneesssesessesssessessseeseessseensneasa 14-20 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxvi December 2014 -zZ SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Appendices Appendix A 00-00G000 00-00G001 01-00G000 01-00G001 Geotechnical 01-01GTO001 01-01GT002 01-01GT003 01-01GT004 01-01GT005 01-01GT006 01-01GT007 01-01GT008 Site Roads 02-01C001 02-01C002 02-01C003 02-01C004 02-01C005 02-01C006 02-15C001 Drawings Drawing List -I Drawing List -II Overall Area Plan Site Area Plan Exploration Plan Relict Channel Borrow Site D Exploration Plan Dam Site Surficial Geology Dam Site top of Rock Isopach Relict Channel Borrow Site D top of Rock Isopach Dam Site Bedrock Geology Dam Site River Channel Isopach Location of Microseismic Stations Site Road Plan Site Road -Profiles N-1,N-2,N-3,and N-4 Site Road -Profiles N-5,N-6,and N-7 Site Road -Profiles S-1 AND S-2 Site Road -Profiles S-3,S-4,S-5,S-6,AND S-7 Typical Road Sections Permanent Bridge at Dam Site Gold Creek Access Road 02-15C002 02-17C001 02-17C002 02-17C003 Typical Access Road Bridge Plan and Profile MP 00 to MP 05.6 Plan and Profile MP 05.6 to MP 11.4 Plan and Profile MP 11.4 to MP 17.0 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page xxvii Alaska Energy Authority December 2014 -z SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 02-17C004 02-17C005 02-17C006 02-17C007 02-17C008 02-17C009 Plan and Profile MP 17.0 to MP 22.6 Plan and Profile MP 22.6 to MP 28.0 Plan and Profile MP 28.0 to MP 33.8 Plan and Profile MP 33.8 to MP 39.6 Plan and Profile MP 39.6 to MP 45.2 Plan and Profile MP 45.2 to End Denali West Access Road 02-18C001 02-18C002 02-18C003 02-18C004 02-18C005 02-18C006 02-18C007 02-18C008 Plan and Profile MP 00 to MP 05.9 Plan and Profile MP 05.9 to MP 11.9 Plan and Profile MP 11.9 to MP 17.8 Plan and Profile MP 17.8 to MP 23.8 Plan and Profile MP 23.8 to MP 29.7 Plan and Profile MP 29.7 to MP 35.7 Plan and Profile MP 35.7 to MP 41.6 Plan and Profile MP 41.6 to End Denali East Access Road 02-18CO01A 02-18C002A 02-18C003A 02-18C004A 02-18CO0SA 02-18C006A Plan and Profile Sta.MP 00.0 to MP 05.2 Plan and Profile MP 05.2 to MP 11.0 Plan and Profile MP 11.0 to MP 16.8 Plan and Profile MP 16.8 to MP 22.5 Plan and Profile MP 22.5 to MP 28.5 Plan and Profile MP 28.5 to MP 32.0 Chulitna Access Road 02-19C001 02-19C002 02-19C003 02-19C004 02-19C005 02-19C006 Plan and Profile MP 00 to MP 05.9 Plan and Profile MP 05.9 to MP 11.8 Plan and Profile MP 11.8 to MP 17.7 Plan and Profile MP 17.7 to MP 23.6 Plan and Profile MP 23.6 to MP 29.5 Plan and Profile MP 29.5 to MP 35.4 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page xxviii Alaska Energy Authority December 2014 -Zw-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 02-19C007 Plan and Profile MP 35.4 to MP 40.25 Site Infrastructure 03-10C001 03-10C002 03-10C003 03-10C004 03-12C001 03-12C002 03-13C001 03-13C002 Construction Camp -Permanent Village Plan Airstrip and Contractors Area Plan Permanent Village Living Arrangement Typical Details Construction Camp Living Arrangement Typical Details Quarry Batching and Stockpile Area Plan Quarry Sections Water and Wastewater Process Flow Diagram Water and Wastewater Details ARRC Facilities 03-16C001 03-16C002 03-16C003 03-16C004 03-16C005 03-16C006 03-16C007 Site Layout Gold Creek Alternative Site Layout Chulitna Alternative Site Layout Cantwell Alternative Railway Typical Sections Railway Transloading Facility -Cantwell Alternative -Plan and Profile Sta.99+00 to 114+00 Railway Transloading Facility -Cantwell Alternative -Plan and Profile Sta.114+00 to 129+00 Railway Transloading Facility -Cantwell Alternative -Plan and Profile Sta.299+50 to 312+50 Power Facilities 04-01C002 Dam Plan 04-01C003 Dam Typical Sections 04-01C004 Dam Profile A 04-01C005 Dam Gallery Typical Details 04-01C006 Dam Joint Detail 04-03C007 Spillway Low Level Outlet Plan and Profile 04-03S001 Spillway Control Structure Plan 04-03S004 Spillway Sections and Drainage Details Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxix December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 04-04S001 04-04S002 04-05C001 04-05C002 04-05C003 04-05G001 04-05G002 04-06S001 04-07S001 05-06S001 05-06S002 05-06S003 05-08C001 05-08S001 05-08S002 05-08S003 05-08S004 05-08S005 05-08S006 05-08S007 05-08S008 05-08S009 05-08S010 05-08EM001 06-09C001 06-09C002 Low Level Outlet Intake Plan and Sections Low Level Outlet Outlet Section River Diversion Cofferdam Plan and Sections River Diversion Tunnel Inlet Elevation and Sections River Diversion Tunnel Outlet Plan and Sections River Diversion General Arrangement Plan and Profile Emergency Release System General Arrangement Plan and Profile Emergency Release Facilities Sections Diversion Sluice Plan and Section Penstock Section Power Intake Structure Plan Power Intake Structure Elevation and Section Powerhouse Site Plan Powerhouse Main Floor Powerhouse Generator Floor Powerhouse Turbine Floor Powerhouse Scroll Case Floor Powerhouse Draft Tube Floor Powerhouse Drainage Pumps Floor Powerhouse Sections Powerhouse Sections Powerhouse Elevation Powerhouse Isometric Single Line Diagram Switchyard Plan Switchyard/Transmission Line Sections Gold Creek Transmission 06-17T001 06-17T002 Plan and Profile MP 00 to MP 03.1 Plan and Profile MP 03.1 to MP 08.9 Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page xxx December 2014 -ywNO .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 06-17T003 Plan and Profile MP 08.9 to MP 14.8 06-17T004 Plan and Profile MP 14.8 to MP 20.6 06-17T005 Plan and Profile MP 20.6 to MP 26.4 06-17T006 Plan and Profile MP 26.4 to MP 32.1 06-17T007 Plan and Profile MP 32.1 to MP 37.9 06-17T008 Plan and Profile MP 37.9 to End Denali West Transmission 06-18T001 06-18T002 06-18T003 06-18T004 06-18TO05 06-18T006 06-18T007 06-18T008 06-18T009 06-18T010 06-18T011 Plan and Profile MP 00 to MP 05.9 Plan and Profile MP 05.9 to MP 11.9 Plan and Profile MP 11.9 to MP 17.8 Plan and Profile MP 17.8 to MP 23.8 Plan and Profile MP 23.8 to MP 29.7 Plan and Profile MP 29.7 to MP 35.7 Plan and Profile MP 35.7 to MP 41.6 Plan and Profile MP 41.6 to MP 47.6 Plan and Profile MP 47.6 to MP 53.5 Plan and Profile MP 53.5 to MP 59.5 Plan and Profile MP 59.5 to End Denali East Transmission 06-18TOOIA 06-18T002A 06-18T003A 06-18T004A 06-18TO05A 06-18TO06A Plan and Profile MP 21.7 to MP 26.8 Plan and Profile MP 26.8 to MP 32.2 Plan and Profile MP 32.2 to MP 37.8 Plan and Profile MP 37.8 to MP 43.6 Plan and Profile MP 43.6 to MP 49.4 Plan and Profile MP 49.4 to MP 53.8 Chulitna Transmission 06-19T001 06-19T002 06-19T003 Plan and Profile MP 00 to MP 06 Plan and Profile MP 06 to MP 12 Plan and Profile MP 12 to MP 18 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page xxxi Alaska Energy Authority December 2014 -zw SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 06-19T004 06-19T005 06-19T006 06-19T007 Appendix B Bl B2 B3 B4 BS B6 B7 B8 B9 B10 Bll B12 Visualization Plan and Profile MP 18 to MP 24 Plan and Profile MP 24 to MP 30 Plan and Profile MP 30 to MP 36 Plan and Profile MP 36 to End Technical Memoranda and Reports Geotechnical Data Report Site Specific Seismic Hazard Analyses Interim Crustal Seismic Source Evaluation Probable Maximum Flood Study Rock Wedge Analysis Development of Time Histories Deterministic Ground Motion for Slab Events Finite Element Analysis Electric Power Systems Transmission Reports Opinion of Probable Construction Cost Engineering and Construction Schedule Preliminary Design Criteria Susitna-Watana Animation Draft Susitna-Watana Hydroelectric Project FERC Project No.14241 Page xxxii Alaska Energy Authority December 2014 -zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Acronyms and Abbreviations $U.S.dollars 2-D two dimensional 3-D three dimensional AACE Association for the Advancement of Cost Engineering AAR alkali-aggregate reactivity ac-ft.acre-feet ADOT&PF Alaska Department of Transportation and Public Facilities ADSAS Arch Dam Stress Analysis System (Software) AEA Alaska Energy Authority AEC Alaska Earthquake Center ANSI American National Standards Institute ANSYS Finite Element Analysis Software APA Alaska Power Authority (State) APD analytical probabalistic dispatch ARRC Alaska Railroad Corporation ASTM American Society for Testing and Materials ATK023 Japanese Interface Earthquake Record -March 2011 ATV all terrain vehicle AUL Italian Crustal Earthquake Record -November 1980 BESS battery energy storage system BH borehole BIL basic impulse level BOD biochemical oxygen demand BTU British thermal units C Carbon 14 CADAM Computer Analysis of Dams (software) CD compact disk CFD computational fluid dynamics CFRD concrete faced rockfill dam cfs cubic feet per second CHBO12 Japanese Interface Earthquake Record -March 2011 Chile Chile Interface Earthquake Record -February 2010 Chugach Chugach Electric Association c/mmBTU cents per million British thermal units CO2 carbon dioxide Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxxiii December 2014 -yzZ SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT CSV CURI CVC cy Dips DSM DSM/EE ECRD EFR EIS comma-separated value format Chile Interface Earthquake Record -February 2010 conventional concrete cubic yard software for interactive analysis of orientation base geological data demand side management demand side management /energy efficiency earth core rockfill dam Engineering Feasibility Report environmental impact statement elevation Electric Power System Inc. energy storage system fahrenheit Federal Aviation Administration finite element (analysis) Federal Energy Regulatory Commission factor of safety Federal Power Commission fluid structure interaction feet full time equivalents fiscal year gravitational acceleration -32.2 ft./sec” geologic feature Loma Prieta,CA Crustal Earthquake Record -October 1989 grouting intensity number geographic information system ground motion prediction equations gallons per capita per day gallons per day gallons per minute global positioning system geologic strength index generator step up (transformer) Golden Valley Electric Association gigawatt hours Susitna-Watana Hydroelectric Project FERC Project No.14241 Page xxxiv Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT HB House Bill HB 306 House Bill 306 HDPE high density polyethylene (also high-density polyethylene) HEA Homer Electric Association HEC Hydraulic Engineering Center HMC-TAM hourly Monte Carlo-transmission analysis mode HMR Hydrometeorological Report hr.hour(s) HVAC heating,ventilating and air conditioning Hz hertz IDF inflow design flood IEEE Institute of Electrical and Electronics Engineers IFSAR Interferometric Synthetic Aperture Radar ILP Integrated Licensing Process VO inputs and outputs IPCC International Panel on Climate Change ISO International Standards Organization ISR Initial Study Report IWT010 Japanese Intraslab earthquake record-April 2011 JRC joint roughness coefficient kemil one thousand circular mils -area ofa circle with a diameter of one mil (one thousandth of an inch) kips 1,000 Ibs km kilometer(s) kV kilovolt kW kilowatt Ibs/ft°pounds per cubic foot Ibs/in”pounds per square inch LiDAR Light Detection and Ranging Ma megaannum /one million years MCE maximum credible earthquake MCF one-thousand cubic feet MEA Matanuska Electric Association MG million gallons mgd million gallons per day mi mile(s) mi square mile Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxxv December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT ML&P Anchorage Municipal Light &Power mm millimeter(s) MOL minimum operating level MONT El Salvador Intraslab earthquake record -Jan 2001 MP milepost(s) MPMR modal participation mass ratio msl mean sea level MVA megavolt-ampere MW megawatt(s) MWh megawatt hour(s) MWH MWH Americas,Inc. MYG 009 Japanese Intraslab earthquake record-April 2011 NAD North American Datum NAD83 Horizontal North American Datum of 1983 NAVD88 North American Vertical Datum of 1988 NERC North American Electricity Reliability Council NFFTB Northern Foothills Fold and Thrust Belt NMOL normal maximum operating level NOI notification of intent NPS National Parks Service O&M operation and maintenance OBE operating basis earthquake OFAF oil forced air forced OMB Office of Management and Budget ONAN oil natural air natural OPCC opinion of probable construction cost PAD Pre-Application Document pef pounds per cubic foot PGA peak ground acceleration PLC Programmable Logic Controller PMF probable maximum flood PMP probable maximum precipitation PRM project river miles PROMOD Production Modeling Software psi pounds per square inch PSS/e Power System Simulation for Engineering pu per-unit Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxxvi December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. RCA Regulatory Commission of Alaska RCC roller-compacted concrete RIRP Alaska Railbelt Regional Integrated Resource Plan RM river mile(s) ROW right-of-way (also right of way) rpm revolutions per minute RPZ runway protection zone RQD rock quality designation RSP Revised Study Plan RTS reservoir triggered seismicity RUS Rural Utilities Service SAB Southern Alaska Block SCADA Supervisory Control and Data Acquisition SCR silicon controlled rectifier SDM El Salvador Intraslab Earthquake record -Jan 2001 SES City of Seward Electric System sf;fi?square foot (feet) SF°sulphur hexafluoride SI site investigation SPM Shoreline Protection Manual SPP South Anchorage Power Project sq.mi.square mile SSSHA site specific seismic hazard analysis STTEC El Salvador Intraslab Earthquake record -Jan 2001 SVC Static VAR Compensator(s) SWE snow water equivalency ™technical memorandum TOC total organic carbon TSS total suspended solids UCS uniaxial compression strength UFLS under frequency load shed USACE U.S.Army Corps of Engineers USBR U.S.Bureau of Reclamation USGS U.S.Geological Service USR Updated Study Report UV ultra violet VALPM Chile Interface Earthquake Record -Feb 2010 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxxvii December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Vs30 Seismic Shear-Wave Velocity (from the surface to a depth of 30 m) WBS work breakdown structure wl water level WRAM Water Resources Assessment Methodology WTP Water Treatment Plant yr.year Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page xxxviii December 2014 Executive Summary -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT EXECUTIVE SUMMARY E.1.Introduction The Alaska Energy Authority (AEA)is conducting engineering and environmental studies for the Susitna-Watana Project in preparation for a License Application that will be submitted to the Federal Energy Regulatory Commission (FERC).This Engineering Feasibility Report (EFR) was prepared to support the licensing process.The report will provide the basis for required License Application exhibits -most notably the Supporting Design Report,Exhibit F -which must be filed concurrently with the FERC License Application. The EFR incorporates the results of studies conducted between February 2011 and December 2014.During the summer of 2014,AEA conducted geotechnical studies at the dam site to verify various assumptions presented in this report.As a starting point for the EFR,the November 23, 2010 AEA Railbelt Large Hydro Evaluation Preliminary Decision Document was used.That document concluded that the Susitna-Watana Project was favored over other potential large hydro projects to serve future Railbelt power needs.Also used in the preparation of the EFR were reports and designs prepared as part of the 1980s FERC License Application (and subsequent revision)for the larger Susitna Hydro project proposed at that time.Ongoing environmental studies may influence the engineering design and proposed project operations, such as the choice of access and transmission routes,operational criteria and downstream flow regime.Accordingly,this EFR is a snapshot in time. The study results described in this EFR reflect a progression from the proposal presented in the Pre-Application Document (PAD),which was submitted to FERC in December 2011. Engineering feasibility updates based on additional geotechnical investigations and environmental studies can be expected to result in further design refinements and modifications to the proposed project features,as well as to the operational criteria proposed in the FERC License Application. The Railbelt utilities have been engaged with AEA during the past three years in the development process for the EFR.This engagement has focused on the operational modeling of the Project,sizing of the generating units,and system integration work,all of which are key to the benefits this long-term resource will bring to the Railbelt region. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-1 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT E.2.Previous Studies The Project site has been studied for decades,principally in the early 1980s by the State of Alaska,through the Alaska Power Authority (APA),although both the United States Bureau of Reclamation (USBR)and the United States Army Corps of Engineers (USACE)had also previously studied the site.APA conducted extensive engineering,environmental and economic studies and,in 1983,filed a License Application to FERC.The License Application was revised in 1985 to propose a three-phase development including the initial development of a 700-foot high dam at Watana.In March 1986 the License Application was withdrawn. E.3.Project Description The Project will be a major development on the Susitna River 184 river miles upstream from the mouth of the Susitna River,approximately 125 miles north and east of Anchorage and about 140 miles south of Fairbanks.The general location of the proposed project is shown on Figure E.3-1. The Project is being developed to provide long-term dependable power supply to the Railbelt.It will be capable of generating about 50 percent of the Railbelt's electricity,or approximately 2,800 Gigawatt hours (GWh)per annum (depending on the agreed operating rules). The Watana Dam will be a curved gravity dam constructed using Roller Compacted Concrete (RCC)methodology,together with a straight gravity (thrust)section on each abutment.It will have a nominal crest elevation (El.)2065 ft.North American Vertical Datum of 1988 (NAVD88) corresponding to a maximum height of approximately 705 ft.above the prepared rock foundation (assumed to be at El.1360 ft.)and a crest length of approximately 2,810 ft.The maximum height of the structure will depend on the results of the further site investigations (which will indicate the extent of rock excavation required below the river bed).The current site plan is shown in Figure E.3-2. The Watana Reservoir normal maximum operating water level (NMOL)is proposed as El.2050 ft.At NMOL,the reservoir will be approximately 42 miles long (along the reservoir centerline)and average 1.25 miles wide.The maximum reservoir width is three miles at Watana Creek.The reservoir will have a total storage capacity of approximately 5.2 million acre-ft.,of which approximately 3.4 million acre-ft.will be active storage. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-2 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT BSiMROAORRI a)CoNCHULITNAROADTScorripor) ibe ere Y,t-FEROLOSED WATANAMeeeieEhe:Sores 2 -cr 'CHULITINASTIY SSIQN 2 ."|RESERVOIR EL 2,050"attye:-LORRIDOR 7 WATANA :Et RIDOR F-fra.,<i3Cates.ij|We 4 DAN ff :| Soak:ana3GOUDICREEKROADIS34elRANSMISSION.CORRIDOR.}_¢SP JHEbiltd Ale \CHORAGE -|FAIRBANKSsv].|TRANSMISSION INTERTIE Lf)mSPareNOTE:FORLEGENDSEEhabaz=DRAWING 01-00G000 ees |fof VK 3 vm Figure E.3-1.Proposed Project -General Location Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-3 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Figure E.3-2.Dam Site Plan Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page ES-4 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Emergency release facilities installed within the plugged diversion tunnel will be capable of operation,if necessary for reservoir drawdown,when the water level is at the minimum operating level (MOL)of El.1850 ft.(or lower). The low-level outlet facilities will provide a discharge of up to 32,000 cubic ft.per second (cfs). Together with the maximum powerhouse flow,the outlet facilities will be capable of passing the 50-year flood without opening the spillway gates.During the 50-year flood event the reservoir will be temporarily surcharged.The low level outlet facilities will be located so that they may be used even when the reservoir elevation is at its minimum operating level. The bulk of the rock excavated to provide aggregate for concrete and road base will be obtained from a quarry located on the left abutment upstream of the Watana Dam.The lowest level of the quarry will be below the projected minimum operating level of the reservoir to minimize visual impact.A spoil area upstream of the Watana Dam has also been identified,and configured so that it will also be permanently submerged within the reservoir. The powerhouse will be located immediately downstream of the Watana Dam,and will house three generating units,each with a rated turbine capacity of approximately 153 MW at a reservoir elevation of El.1950 ft.,but a maximum turbine capacity of 206 MW at the normal maximum operating level (i.e.,full pool),for a total rated plant installed turbine capacity of 459 MW (and maximum turbine capacity of 618 MW at normal maximum operating level).The powerhouse will be designed and constructed with an extra unused unit bay to facilitate the potential installation of a fourth unit in the future. The Project will incorporate a spillway with a gated ogee crest at El.2010 ft.Four hydraulically operated radial gates will allow controlled release of floods above the 50-year flood.The spillway will be able to safely pass the routed Probable Maximum Flood (PMF).To further enhance project safety,the 10,000-year flood can be passed with one spillway gate inoperable. Permanent housing will be constructed at the site,sufficient for operating and security staff. Permanent works will include community facilities for operation and maintenance (O&M)staff members and guests.Other permanent works will include maintenance buildings for use during local operation of the power facilities. E.4.Site Access A site access road will be constructed to facilitate project construction and for long-term operational access.Three possible alternatives for access roads were identified based on a corridor route study by the Alaska Department of Transportation and Public Facilities Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-5 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT (DOT&PF)which incorporated 1980s study results.The corridor routes have been refined during these feasibility studies.The three potential corridor routes are: »East from a railway offloading area at Gold Creek,along the south side of the Susitna to the project site,unconnected to the State highway system. =East from a railway offloading area at Chulitna,along the north side of the Susitna to the project site,unconnected to the State highway system. «South from the Denali Highway to the project site.There are two variations of this route, which allows direct connection of the project site to the State highway system without necessitating use of the Alaska Railroad Corporation (ARRC)rail facilities.If the Denali Corridor is selected,the sections of the Denali Highway that will be used by construction traffic will be upgraded in order to facilitate safe construction of the Project. During the execution of the feasibility studies,AEA has proposed to FERC to eliminate the Chulitna corridor from further consideration.All three competing routes have been examined in the EFR and no access corridor recommendation has been made in the report.The final proposal for access will be based upon the results of environmental studies,together with stakeholder input.FERC and the USACE will ultimately approve the selection of the access corridor during the Environmental Impact Statement (EIS)process. A permanent road bridge is planned downstream of the Watana Dam irrespective of the selected access route. To conservatively estimate construction costs of the access,the Gold Creek access route was used because it has the most bridge crossings and will likely exhibit a higher construction cost compared to the other access corridors. At the chosen location for connection to the existing ARRC rail facilities,a railhead and storage facility occupying up to 40 acres will be constructed alongside the existing railroad.For the Gold Creek corridor this would be at Gold Creek,for the Chulitna corridor,at Chulitna,and for the Denali corridor this would be at Cantwell.New sidings would be constructed so that off- loading and transfer of goods and materials could take place both during construction and operation without interrupting the daily operations of the ARRC. In addition to the access road,an airstrip will be constructed at the project site to facilitate construction access and operational access. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-6 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT E.5.Transmission and Interconnection Power will be transmitted from the Project to the existing power grid through the Watana switchyard.Transmission arrangements will consist of three 230-kilovolt (kV)lines,in either single-or double-circuit configuration.The same corridors under consideration for the access road are also under consideration to connect the project primary transmission lines to the Alaska Intertie.Essentially the transmission line corridor would be co-located with the access road corridors,but because transmission lines can be routed over steep terrain more easily,there may be occasional alignment separation within the corridors between the access road and transmission line.One or two transmission corridors may be chosen in order to allow lines to be separated,to provide redundancy in case of line failure. In parallel with the choice of the Gold Creek access route for construction cost estimating,a configuration incorporating two circuits within the Gold Creek transmission corridor and one circuit within the Denali corridor was used to estimate construction costs for transmission.No recommendation of the preferred transmission configuration or routing has been made in the EFR,and the final choice of transmission corridor (or corridors)will depend on the environmental assessment and stakeholder input. Each chosen route will include an interconnection at the point of tie in to the Alaska Intertie (Chulitna,Gold Creek and/or Cantwell). The right-of-way for the transmission lines within the corridors will consist of a linear strip of land;the width will depend on the number of lines.The transmission rights-of-way will be 200, 300,or 400 ft.wide,depending on whether one,two,or three lines run in parallel. The Railbelt Utilities and the State of Alaska are evaluating transmission additions to provide for firm energy transfers and improved reliability of the Railbelt electrical system.These "pre- Watana”Railbelt system improvements are independent of the Susitna-Watana Project and would eliminate the single contingency conditions between the Railbelt load areas.The construction costs associated with the upgrading of the Alaska Intertie have not been included in the project cost,as most of the upgrades are needed irrespective of the Susitna-Watana Project. The results of the system studies performed as part of the planning of the Railbelt transmission improvements have been available for the benefit of the Susitna-Watana feasibility studies. E.6.Temporary Infrastructure Construction of the Project will require various facilities to support activities throughout the entire construction period.The most significant item among the temporary site facilities will be a construction camp.The construction camp will be a largely self-sufficient community Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-7 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT normally housing approximately 800 persons,but with a peak capacity of up to 1,200 people. After construction,AEA plans to remove most of the infrastructure of the camp facility,leaving only those buildings and facilities that are to be used to support the smaller permanent residential and O&M facilities. Other site facilities include contractor work areas,site power,services,and communications. Site power and fiber optic cabling for construction will be brought either on the transmission line,or along the side of the access road.Items such as power and communications will be required for construction operations,independent of camp operations. E.7.Project Operation Project operating flexibility is important to Railbelt utilities that will utilize the project's capacity and energy output.To maximize the benefit of the Watana generation for the entire Alaska Railbelt interconnected system and provide operational flexibility,project operation simulations included load-following when and if needed and maximizing energy during the critical winter months of November through April each year.Minimum downstream flow requirements during the summer months may dictate the amount of available reservoir storage for provision of winter energy production.Energy simulations were conducted using the minimum instream flow releases proposed in the APA 1980s FERC License Application.No operational scenario has been recommended in the EFR. Production cost modeling has encompassed the whole Railbelt system and has highlighted the benefits that will accrue to the whole system if a centralized dispatch method of operation is selected. To facilitate efficient dispatch,the reservoir would be drafted annually by an average of about 140 ft.to 150 ft.,and subject to a rare maximum drawdown of 200 ft.during dry years,as shown in Figure E.7-1.Minimum instream flow releases would be made through the powerhouse -or through low level outlet works during the rare occasions when the power plant is offline.Flow discharges through the powerhouse under the operating plan would range from the minimum required instream flow release (yet to be determined)to a high of about 14,000 cfs (based on all generating units operating)during times of maximum power generation.Daily power generation during a peak winter month (January)would average about 8,250 MWh and powerhouse discharges would average approximately 8,360 cfs during that time. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-8 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 2070 3060 . 2030 2010 -LU 1990 |ReservoirElevation(feet)onQo1890 -- |-Reservoir Elevation 1870 '-Normal Maximum Operating Level :- Minimum Operating Level i 1850 + |Incorporates existing hydro load following at !Bradley,Eklutna,and Cooper and forecasting. i 2024 Railbelt generation toads.VRBO ba ert cent ot a oe .:po ed So -©©RK Be mW MH &BW re OP YH he BW He mM YD Ke B®=m2 YH F&F B®re Oo HY &@aaaeSss©OS ©©=SO 3 DO SS ===SS SS SS >SS ©=©SS 2 ©DS >DS ©=)§6¢8eo¢6¢9¢99899¢9999¢9998990988989889889998aai Figure E.7-1.Daily Reservoir Elevations (feet) For efficient operation of the whole Railbelt system,powerhouse discharges are expected to vary over a 24-hour period during the peak winter months,typically ranging from a low of about 7,000 cfs to a high of 9,050 cfs.The daily flow variation may be constrained by environmental protection,mitigation and enhancement measures.However,flow variations immediately downstream of the powerhouse will be partially attenuated by the time the flow reaches Gold Creek,Talkeetna,and the other downstream locations. Average annual energy generation is estimated to be 2,800 Gigawatt hours (GWh)with approximately half that energy provided in the November to April period.Figure E.7-2 displays hourly generation during an average water year under PROMOD assumed operational scheme. A proposed operating plan will be prepared and submitted in the FERC License Application. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-9 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 600 T I !|Average water conditions. |2024 Railbett generation ioads.|| 500 |--Watana Generation | __400=iz|| c )oe3:! 5 300 -t§ =pl iT3hn*hy i | 200 q + h ]i||100 i 1 |:emcee | 0 '} }\j 1-Jan 31-Jan 1-Mar 31-Mar 30-Apr 30-May 23-Jun 29-Jul 28-Aug 27-Sep 27-Oct 26-Nov 26-Dec Figure E.7-2.Watana Hourly Generation as Developed by PROMOD for Average Water Conditions E.8.Design and Construction Schedule A schedule for the design and construction of the project has been derived,based on the times for completion of site investigations (including exploratory adit excavation)and the required time for design,preparation of contract documents,the bidding process,and construction.No construction on site (including the construction of the access road)will be permitted until the FERC license has been issued,Clean Water Act Section 404 and 401 permits have been granted, and FERC has performed any required reviews of the design and drawings. The schedule and cost estimate are based on the assumption that the project would be implemented using eight separate supply or construction contracts,and four service contracts. The contracts are assumed to be traditional design-bid-build contracts and separate design contracts are assumed as appropriate.Because no project construction can begin until the FERC License is issued (and associated design review and permitting are completed),it will be difficult to shorten the schedule by using different contracting strategies. The schedule spans 12 years from the time that final design phase site investigations (SI)are initiated to commercial operation of the first turbine-generator unit.Several assumptions have been made regarding the times required for the various activities. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-10 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The following are approximate time periods for major components of project construction, including concurrent activities: «Total Project development from SI initiation 12 years «Site Investigation and design engineering 3 years *Access road construction 2 years «Dam and power facilities construction 7.5 years "Reservoir filling 1 to 2 years »Site restoration throughout construction Design work would be initiated during the licensing process to maintain the project schedule. Construction activities critical to the schedule (such as access roads and construction support facilities)will be ready to commence shortly after issuance of the FERC license and the other required regulatory approvals. E.9.Project Cost The project cost estimate is classified as Class 4 according to recommended practice of the Association for the Advancement of Cost Engineering (AACE).However,some facilities have been defined in greater detail,and their construction cost estimates approach Class 3.The current construction cost estimate was developed employing a "joint venture”type of methodology,using an independent estimator as a "cross-check”. The anticipated project cost is estimated to be approximately US$5.655 billion (July 2014 dollars),including licensing,design,and construction,but excluding escalation and interest during construction.AEA has included these costs in its financing plans developed independently from the EFR. Probabilistic analysis has been performed on the quantities and unit costs used in the current estimate to develop a range of probable total costs shown in Figure E.9-1.Contingencies were applied in accordance with AACE guidelines. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-11 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 100% nn 80%- 95th percentile$6.247 Billion 60%- e Bose Estimote=$5.655 Bilton :70th percentile &$5.872 Billion40%- SOth percentile $$.654 Billion a 20%- o%...r 7 .r 48 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 Cost in Billions ($) Figure E.9-1.Project Cost Range (S-Curve) E.10.Key Design Considerations E.10.1.Seismic Hazard Evaluation One of the 58 environmental study plans required by FERC is a Site Specific Seismic Hazard Analysis (SSSHA,Study Plan 16.6).Work on the SSSHA began in 2011 and is complete except for the final crustal lineament studies,which are expected to be finished in 2015.The work to date has been used to determine ground motions applicable to the feasibility studies. A microseismic network has been set up for the project (first installed in September 2012) including seven seismographic stations linked to the seismic network operated by Alaska Earthquake Center (AEC).The seismic analyses completed to date indicate that the governing seismic event -from which the seismic criteria for the project will be derived -will be a subduction intraslab zone event,not a crustal event.The results from the microseismic network Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-12 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT have helped to achieve excellent definition of the subducting plate,which has contributed to the definition of potential sources of interface and intraslab events. In determining the ground motions for the seismic design of the project features (for the Maximum Credible Earthquake [MCE]),the analysis followed guidance furnished by FERC in "Engineering Guidelines for the Evaluation of Hydropower Projects,Draft Chapter 13 - Evaluation of Earthquake Ground Motions”.For the initial (preliminary)analyses of the dam structure -when different geometries were being compared uniform hazard spectra from the initial results of the site specific seismic hazard analysis were used.Later in the preliminary dam analysis,time histories were developed using spectral matching techniques for four deterministically calculated response spectra:intraslab M8.0;intraslab M7.5;interface M9.2;and crustal M7.0.The largest of the peak ground accelerations from these four selected scenario events was determined to be the intraslab M8.0 at 0.81g.For the final finite element analysis for the feasibility studies (including mass in the foundation)the response spectra and time histories were refined to suit required model input. The key structures must safely withstand a MCE,but the whole project must continue to operate satisfactorily under the Operating Basis Earthquake (OBE).Although published guidelines (including Alaska Dam Safety guidelines)for determining the OBE call for an earthquake with a 50 percent probability of occurring in the life of the project,such an event would translate to a peak ground acceleration of 0.16 g,which is deemed too low,and not sufficiently conservative for such a large dam.It was therefore decided to adopt a conservative approach and instead use the 500 yr.event for the OBE -reflecting a peak ground acceleration of 0.27g. The criteria adopted will be revisited when the crustal lineament studies are complete,but they are not expected to change because the subduction events produce such large ground motions relative to crustal events. Equally important to the deterministic analysis of the seismic hazard is the verification that there are no features within the foundation of the project dam that could suffer coseismic movement. In particular,in the past,the existence of a "Watana lineament”along the Susitna River channel has been postulated -but previous angled intersecting drill holes had not identified the existence of such a feature,and it was discounted during the 1980s investigations.Angled holes drilled during 2014 have again confirmed that such a feature does not exist.Structural mapping of the site area and crustal lineament inspection (both performed in 2014),together with the reinterpretation of the postulated geologic features,demonstrate that any local lineaments will not exhibit coseismic behavior. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-13 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT E.10.2.Probable Maximum Precipitation and Probable Maximum Flood Studies The Probable Maximum Flood (PMF)is the flood that may be expected from the most severe combination of critical meteorological and hydrologic conditions that are reasonably possible in the drainage basin under study,generated by the Probable Maximum Precipitation (PMP).PMP is defined as theoretically the greatest amount of precipitation for a given duration that is physically possible for a given size storm area at a particular geographic location at a certain time of year. FERC also required,as one of the 58 study plans,a PMP/PMF study (Study 16.5).The Inflow Design Flood (IDF)used in the sizing and design of spillways can range from a 100-year flood to the Probable Maximum Flood (PMF).Because of its size,downstream hazard potential,and economic importance to the Railbelt,the selected IDF for Watana Dam was determined to be the PMF. PMPs are often derived using publications such as Hydrometeorological Report (HMR)57 (for the Pacific Northwest).The existing standard U.S.Weather Bureau (now National Weather Service)PMP guidance document for Alaska is however only applicable to drainage areas up to 400 square miles and for storm durations up to only 24 hours.Because the Susitna River basin above the dam site is,at 5,180 square miles,an order of magnitude larger,a site specific PMP was developed.The site-specific all-season (maximum)PMP was found to occur in July or August and was derived on an hourly basis for a 216 hour (nine day)time sequence for each of the 29 sub-basins tributary to the Watana Dam site. Associated concurrent meteorological data (temperature,wind speed,dew point)were also derived for the 216 hour PMP period plus 24 hours prior to and 72 hours subsequent to the PMP for a total of 312 hours.Because snowpack and snowmelt are significant hydrologic conditions in the Susitna River watershed that affect the estimated PMF,seasonal PMP and meteorological data were derived for the period from April through October based on different factors applied to the all-season data. The critical PMF case used for spillway sizing was found to be formed by a spring PMP combined with the 100-year snowpack and with conservative low infiltration loss rates.For the critical PMF case including a conservative assumption that the reservoir is already at full pool, the maximum reservoir level was modeled to be El.2064.5 ft.with a peak inflow of 310,000 cfs, a peak outflow of 282,000 cfs,and a 13-day total inflow volume to the reservoir of 3,980,000 acre-ft.The flood routing is shown on Figure E.10-1. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-14 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 400,000 2066 350,000 [iN 2064 -Inflow L 2062300,000 -Outflow --Reservoir Elevation X 2060250,000 -[|. a /_f-ns 2050Flow(cfs)/ReservoirElevation(feet)1-Jun 3Jun §-Jun 7-Jun 9-Jun 1ivun 13Jun Figure E.10-1.PMF Inflow,Outflow,and Reservoir Elevation E.10.3.Type of Dam The 1980s proposed project configuration at Watana was based on an Earth Core Rockfill Dam (ECRD),but in the years since,dam construction technologies and experience have developed such that a Concrete Faced Rockfill Dam (CFRD)and a Roller Compacted Concrete (RCC)Dam are viable alternatives for a safe dam of a height considered for Watana.All three dam types have performed satisfactorily during large seismic events,most notably the Sechuan,China,M8 event in 2008 which epicenter was 10 miles from a CFRD,and 22 miles from a large RCC dam. Project configurations were developed based on each of the three types of dams and included either a surface power plant or underground power facilities as appropriate for the project layout. Two variants of the CFRD configuration were created,one with an underground powerhouse and one with a surface facility.Comparative costs were derived -with no common items being included.The lowest cost alternative was determined to be that based on an RCC dam with a surface powerhouse.To ensure that non-cost items were also considered in the choice of the type of dam at Watana,a further analysis was performed,based on the Water Resources Assessment Methodology (WRAM).The analysis considered:seismic resistance;ease of raising;risk of price increase;visual intrusion;possibilities for construction schedule acceleration;cold weather construction;potential for optimization;accommodation of Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-15 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT environmental mandates;and long term cold weather performance.The results of the WRAM analysis confirmed and supported the choice of a project configuration based on a RCC dam.In addition,an RCC dam could be constructed quicker than a CFRD or ECRD. E.10.4.Turbine-Generator Unit Size and Rating The individual power plant generating unit size and total plant installed capacity were investigated from two perspectives.Unit size and plant capacity were first considered with respect to reservoir operation and power studies,and then to optimize production costs with respect to the whole Railbelt integrated electrical system. The installed capacity,unit size and normal maximum operating level of the reservoir have all been reviewed during the course of the current feasibility studies,taking into account the maximum annual generation that can be achieved,the possible operating scenario,minimizing reservoir spills,and requirements for redundancy to account for unit maintenance and downtime. Reservoir operation and hydroelectric power studies modeling of the plant operation using 61 years of hydrological flow records,on an hourly basis,was performed for two different installations.The first installation considered was three turbine units rated at 153 MW at reservoir level of El.1950 ft.This unit is equivalent to 206 MW at NMOL of EI.2050 ft.The second installation considered was three 206 MW units (turbine capacity)rated at an elevation of El.1950 ft.The larger units would not increase the annual generation substantially,and the difference in production of the smaller units can be minimized by forecasting of basin runoff and implementing a consequent adjustment of the operation.Larger units would,however,allow for a little more flexibility for mitigating unit outage and for operation as spinning reserve. Following these studies,and in the absence of any stated system requirement for greater redundancy,it was determined that an installed total turbine capacity of 459 MW at reservoir level of El.1950 ft.(618 MW NMOL and 315 MW MOL)is most appropriate and would provide an annual energy generation similar to larger units. The system studies performed during this feasibility study indicate that the required system energy storage (that is being considered under the separate studies of system improvements) would need to be larger if Susitna-Watana were to be constructed.A small amount of extra energy storage would be necessary to restrict load shedding -in the event of a Watana unit trip - to the current regime of allowable load shedding.However,the incremental cost of the energy storage specifically required for the various Watana unit sizes considered is relatively small. Production cost modeling was performed for the year of 2024 and beyond to assess the project operation within the whole Railbelt system using an average water year.Production cost modeling showed that the turbines are adequate for meeting the required generation with high Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-16 December 2014 ---z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT reliability,although additional thermal generation would be required during the very rare times when the Watana reservoir was abnormally low due to a dry water cycle. E.10.5.Hydraulic Analysis Hydraulic analysis was focused on two key aspects of the project layout;the spillway and the emergency outlet works.The PMF peak inflow of 310,000 cfs (and corresponding peak outflow of 282,000 cfs),was used to size the spillway taking advantage of the 32,000 cfs low level outlet capacity,the curved dam,and the abutment topography.A four bay spillway was selected;with a bay width of 42 ft.and an ogee crest elevation of El.2010 ft.Computational Fluid Dynamics (CFD)software was used to model the spillway,to verify hydraulic performance,wall heights, location of aeration,and the angle of the flip bucket to determine the plunge pool location and geometry.A central wall was introduced into the spillway so that one side can be operated up to 60,000 cfs while any required maintenance is underway in the other chute. The emergency outlet was also subject to extensive hydraulic analysis.The diversion tunnel will be converted to an emergency outlet and allow for a maximum flow of 30,000 cfs at MOL. E.10.6.Dam Structural Analysis The analysis of the dam centered on dam stability -using FERC criteria -and stress analysis under the MCE event.After the choice of an RCC dam had been made,an iterative series of analyses was performed incorporating a progressive adjustment of the dam geometry,using the foundation rock characterization derived from the 1980s site investigations and interpretation (and re-interpretations).Industry standard software was used,including ADSAS (a computer version of Trial Load Analysis),CADAM (2D stability software),and ANSYS (finite element software).Dam alternatives with three centers,simple circular curves and a single curve with straight abutments were analyzed progressively using ANSYS and without modeling mass in the foundation.Post-earthquake stability was checked each time.As the geometry was progressively modified,the concrete tensile stresses at the crown cantilever predicted by the software reduced.The most favorable geometry was determined to be a dam curved in plan with a radius of 2,600 ft.,and two straight abutment sections,acting as gravity dams and thrust blocks. Academic studies have compared analyses of existing dams without -and secondly including - the mass of the foundation rock,and have concluded that the inclusion of the mass of the foundation rock into the finite element model represents a more realistic representation of the structural behavior of the structure,compared to a numerical model that ignores the foundation mass.Therefore,the selected dam configuration for Susitna-Watana was reanalyzed including foundation mass,and for that final analysis the downstream face geometry was adjusted slightly. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-17 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The analysis was carried out using time histories for four different seismic events representing two intraslab events,an interface event and a crustal event.The results showed that the configuration and geometry proposed in the EFR is appropriate,and the expected overstressing during the MCE is acceptably restricted to one or two cycles.Under these conditions,minimal damage can be expected,although there could be some displacement between RCC "blocks” formed by the induced joints.Vertical drains at the induced joints will be sized accordingly during detailed design so that they will continue to function properly after the MCE.Post- earthquake stability was checked and is satisfactory,so the geometry chosen is considered acceptable for a feasibility level design.The structure was also modeled for an OBE greater than that suggested under Alaska dam safety guidelines,and was found to perform adequately. Although the foundation characterization remains under study,sensitivity analyses were performed (using conservative assumptions)to assess the structural behavior if foundation conditions are determined to be less favorable than assumed from the previous investigations for the 1980s feasibility studies.Under these assumed (sensitivity)ranges of foundation conditions, the structure still performed satisfactorily as modeled.The reinterpretation of the foundation performed during the 2014 field season -and after completion of the finite element modeling and sensitivity studies -indicates that previous interpretation of width and continuity of the various geological features has been very conservative,and confirms that the sensitivity modeling has also been conservative. Once dam structural foundation mapping is available,proposed exploratory adits have been excavated,and various geological features have been drilled and the cores tested,the proposed foundation excavation and characterization will be able to be better defined -and the design assumptions and feasibility analyses will be verified,or adjustments in geometry will be included during detailed design. E.11.Board of Consultants Review As endorsed by FERC,AEA convened an (independent)Board of Consultants for the purposes of review of the feasibility studies as they relate to dam safety.The key elements and decisions recorded in this report -relating to the type of dam,the PMP and PMF studies,the Site Specific Seismic Hazard Analysis,the Finite Element studies of the dam structure,and the projected site investigations required to verify the designs adopted -have been subject to review by the Board of Consultants through the feasibility study period and their observations have been incorporated in the EFR. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-18 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT E.12.Conclusions The project as presented in the EFR -incorporating a RCC dam with a crest El.2065 ft.;a downstream powerhouse with an installed turbine capacity of 459 MW (at reservoir El.1950 ft.); a four bay gated ogee spillway;and a low level outlet -is technically feasible,safe,and sufficient to withstand the Maximum Credible Earthquake and safely pass the Probable Maximum Flood. Feasibility plans and layouts incorporate technically viable alternatives for both site access and transmission -including transmission/Alaska Intertie interconnection.In each case a preferred route has not been suggested. The base project cost -excluding escalation,interest during construction,etc.is estimated to be approximately US$5.655 billion in Q2 2014 dollars.After probability analysis of estimating variabilities,it was determined that this estimate represents approximately the 50"percentile cost -1.e.,there is a 50 percent probability that the cost will not be greater than US$5.655 billion. Considering only the construction tasks -which cannot commence until a FERC license is approved,and subsequent approvals and permits are issued -the total time from commencement of construction (access road)to provision of power from the first unit is approximately eight years. Projected improvements to the Alaska Intertie are sufficient to allow power from Susitna-Watana to be transmitted both north to Fairbanks and south to Anchorage.The sole extra modification to the system that might be required to accommodate Susitna-Watana power is a small increase in the projected energy storage on the system. The results of production modeling simulations with -and without the project show that the inclusion of the project in the integrated Railbelt system will result in a significant reduction in the use of gas and oil by the utilities,and a large decline in the use of what is now (thermal) peaking plant over time.Because it has the lowest operating cost and the highest reliability among generation options,the implementation of substantial hydro capacity at Susitna-Watana will inevitably reduce the need for gas fired generation in future years.Maximum benefits will accrue if the integrated Railbelt system is centrally dispatched. E.13.Further Engineering Work Necessary Although there has been extensive engineering performed for the preparation of the feasibility design,additional dam site subsurface investigations are necessary to better define the foundation character,design criteria and other parameters required for verification of the Susitna-Watana Hydroelectric Project Alaska Energy.Authority FERC Project No.14241 Page ES-19 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT assumptions made during this study,and to improve the accuracy of the construction cost estimate.The geotechnical information used in the project feasibility design was largely derived from the site investigation program performed in the 1980s (which was oriented towards the footprint of an ECRD,with the focus on a core)and the drilling conducted in 2012.Geological mapping and drilling during the 2014 season has assisted in the definition.When information is available from further foundation drilling specific to the chosen dam type,together with the excavation of adits,rock testing and enhanced geological mapping,the assumptions made in the formulation of the feasibility design should be re-examined,and the layout,design,features and the project cost estimate verified or adjusted if necessary. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page ES-20 December 2014 Section 1 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 1.INTRODUCTION On January 25,2011,Alaska Energy Authority (AEA)engaged MWH Americas,Inc.(MWH) and its subcontractors,under AEA Contract No.AEA-11-022,to conduct engineering feasibility studies and support them with Federal Energy Regulatory Commission (FERC)licensing of the Susitna-Watana Hydroelectric Project (Susitna-Watana Project or the Project).The starting point for this work was the November 23,2010 Railbelt Large Hydro Evaluation Preliminary Decision Document prepared by AEA,determining that the Susitna-Watana Project be favored over other potential large scale hydro projects to serve future Railbelt power needs.The engineering feasibility studies conducted between February 2011 and July 2014 are documented in this draft report.Future geotechnical investigations beyond those completed to date may alter the conclusions reached thus far,as documented herein.The result of any future geotechnical exploration will be reflected in the license application. 1.1.Background The Project will be a major development on the Susitna River some 125 miles north and east of Anchorage and about 140 miles south of Fairbanks.The general location of the proposed project is shown in Figure 1.1-1 and in Figure 1.1-2. This Project is being developed to provide long-term power supply to the Railbelt.It will be capable of generating up to 50 percent of the Railbelt's electricity,or approximately 2,800,000 megawatt hours (MWh)of annual energy (depending on the agreed operating rules),once all units come on line,which is dependent on the timely award of a FERC license.The Project's installed rated turbine power capacity will be 459 megawatts (MW),equivalent to 446 MW generator output. As proposed,the Susitna-Watana Project would include construction of a dam,reservoir,and related facilities in a remote part of the Susitna River as shown on Figure 1.1-3 (also included as Drawing 01-00GO001I in Appendix A,where all drawings for this report are located).The project is located 187 project river miles (PRM)from Cook Inlet,and more than 80 PRM upstream of Talkeetna and 32 PRM above Devils Canyon.Transmission lines connecting to the existing Railbelt transmission system and an access road and railhead improvements would also be constructed. AEA is engaged in a complex licensing and permitting process overseen by FERC,the federal agency,which oversees all hydropower development in the United States,and is currently scheduled to file an application for license on December 1,2016. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-1 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT -) Z g Alaska . i i Canada Vs,'e Location Map A'LQHUKITNA BOA D =f Se"PBROBOSED WATANA|ieKRESERVOIR-EL 2,050 £.paic :. °r ON be.|:holy ehEZ ROADr&y \|7 BANSMISSION.CORRIOOR. eA AneANCHORAGE -|FAIRBANKSSNAan'oo amet ON : qirsmn'NOTE:FOR LEGEND SEE Ee ae DRAWING 01-00G000IeeBogIinesOv5aoefoKetNZa1.1-1.General Location Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-2 December 2014 ---Z-.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. eal ianaseerstees Neng Figure 1.1-2.Watana Dam Site on Susitna River,Looking Upstream Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-3 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. SYepEsfASe oy iJ (QUARRY {SEE SHEET63120009) f rc _i A \7 \casmanun DENALI EASTAVEBT Levene ail ;naw warenCONALS i oe woe Figure 1.1-3.Site Plan Susitna-Watana Hydroelectric Project ,Alaska Energy Authority FERC Project No.14241 Page 1-4 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The anticipated project cost at the date of this report is currently estimated to be approximately US$5.655 billion (July 2014 dollars),including licensing,design,and construction,but excluding escalation,and interest during construction.Probabilistic simulation has been performed on the current estimate to derive a range of probable costs. While the evaluation of alternative financing plans for the project is beyond the scope of this report,initial economic model runs indicate that future power rates from the project will be competitive with other energy sources at the time it is expected to commence operation,and will contribute significantly to a reduction in projected power prices in the long term. This Feasibility Report reflects the proposed project development as of July 2014,at the end of the engineering study program.The various study results described in this Report reflect a progression from the results presented by AEA in its Pre-Application Document (PAD),which was submitted to FERC in December 2011,and MWH's Interim Feasibility Report Summary dated December 2012.Planned geotechnical investigation programs were not implemented in 2013 due in part to funding limitations and lack of site access;an abbreviated investigation program was carried out during 2014 and more investigation is vital to enable detailed design to proceed.Results of those investigations may modify the information contained in this draft report,so the feasibility design remains preliminary until such time that the geotechnical work is completed.This is discussed further in Section 10.Engineering feasibility updates based on more in-depth geotechnical investigations (including adits to verify rock properties,the extent and character of "permafrost”and shear zone characteristics),and results of environmental studies completed during 2014 and proposed in 2015,are expected to result in further design refinements and modifications to the proposed project features as well as to the operational criteria ultimately proposed for the Project in the FERC License Application. The Railbelt utilities have been actively engaged with AEA during the past three years in the development process as key partners and stakeholders.To date this engagement has focused on the operational modeling of the project,sizing of the generating units,and system integration work,all of which are key to the benefits this long-term resource will bring to the utilities. The status of the preliminary design work conducted to date with respect to the key foci noted below is: «With careful construction planning,particularly the planning of the logistics,it appears that the Project can be completed within 12 years of commencing the final design phase geotechnical investigations; #The projected construction cost of the Project is as stated above,with the probabilities described in Section 13; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-5 December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. #Depending on the financing plan,and the expected increases in natural gas prices,the Project is financially viable,and will contribute to a general lowering of the expected Regional wholesale price of power in the long term;and, «The Project appears to be technically feasible using a roller-compacted concrete (RCC) dam (if shears capable of co-seismic behavior are not present in the foundation)and the currently proposed layout as described in Section 10. 1.2.Summary of Previous Studies The Project has been studied for many years,principally in the early 1980s by the State of Alaska,through the vehicle of the Alaska Power Authority (APA).Engaged by APA (which was renamed AEA in 1989),Acres American Incorporated,and subsequently Harza-Ebasco, evaluated a large number of alternatives for hydroelectric power development on the Susitna River and conducted extensive engineering,environmental and economic studies.Following those studies,in 1983 a draft Application for a license to construct a major power project was submitted to FERC.After further studies,it was concluded that a phased development of the Susitna basin would be the most attractive approach to the Project and a three-phase development was selected as appropriate.StageI of the Project was to have been a 700-foot high dam at Watana with a 440 MW powerhouse.Subsequent stages outlined in the amended License Application in 1985 included the downstream Devils Canyon dam/powerhouse complex forming Stage II,followed by raising of Watana Dam as Stage III,increasing the total installed power capacity of the complex to about 1,790 MW.Those subsequent Stages II and III were intended to be brought on line as power demands in the region grew over the decades. After submission of the License Application,and the preparation of a draft Environmental Impact Statement,in March 1986 the Project was put on hold by APA primarily because of the low cost and ample supply of oil and natural gas.In response,APA withdrew the License Application. In 2008,the Alaska State Legislature,in the fiscal year (FY)2009 capital budget,authorized AEA to reevaluate the Project as previously conceived in 1985.Future demand predictions were evaluated together with options to meet the demand,such as from renewables,demand-side management,and energy efficiency. In 2010,the Alaska Legislature enacted House Bill 306 (HB 306),creating a goal that the State should obtain 50 percent of its electric generation from renewable and alternative energy sources by 2025.Hydropower is considered a renewable resource in Alaska.Following HB 306,a Preliminary Decision Document was prepared by AEA,documenting a comparison between the two major projects competing to satisfy the requirements of HB 306,Chakachamna and Susitna- Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-6 December 2014 zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Watana.The result of the comparison was a recommendation by AEA to develop the Susitna- Watana site,the upper of the two sites that were the subject of the 1983 License Application. In early 2011,after competitive proposals,AEA engaged MWH and its subcontractors to assist in the completion of engineering feasibility studies and FERC licensing of a revised concept for the Susitna-Watana Project.The engineering feasibility studies have been documented in this report,but the conclusions and recommendations are tentative until the results of ongoing site geotechnical investigations are completed. Although the previous studies were used at the outset of these feasibility studies to advance the preliminary engineering designs for the major features as much as possible,for much of the early project analysis documented in this report,an up-to-date topographic survey was not available. Significant dam analysis and hydrological analysis had to be performed with 1980s data.For example,the only topography available for the first reconnaissance study of the roads had contour intervals of 100 ft.Similarly,the initial review of the dam types,and the first drafting of the layouts for the dam and power facilities was performed using hand digitized topography from the printed copy of the 1980s site plan drawings (using Horizontal North American Datum of 1927 and National Geodetic Vertical Datum of 1929).During 2012,the first topographic data became available using the Interferometric Synthetic Aperture Radar (IFSAR)elevation data and the MatSu-North Susitna Bare Earth Data using Horizontal North American Datum of 1983 and North American Vertical Datum of 1988).The IFSAR data had a vertical accuracy of +/-3 meters.As a result,a secondary exercise was initiated to transfer all data to the newer more accurate topography. All elevations referenced throughout this document and appendices are North American Vertical Datum 1988,unless otherwise described. 1.3.Scope of Current Engineering Work The objectives of the current engineering feasibility studies were to finalize the feasibility designoftheProject,derive the size capacity and type of the major features,develop the design to sufficient detail for verification of project development cost estimates and construction schedule, and define the project components and operation so that related environmental studies can be completed in support of preliminary designs and the FERC License Application. Essentially,the work has focused on: «Defining the proposed project and its operational parameters; «Development of a schedule for design and construction of the project; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-7 December 2014 -7w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «Estimating the project construction cost; «Establishing the project's technical feasibility;and =Identifying uncertainties and defining the path forward. At the completion of this stage of the feasibility studies in mid-2014,the project definition (with an understanding that revisions may be necessary because of the subsequent inclusion of future geotechnical investigation and environmental study results)has been deemed by AEA to be sufficient for the subsequent drafting of required License Application exhibits. The Project engineering studies have been completed in stages,loosely aligned to calendar years, and the scope of the work documented in this Feasibility Report includes: «Hydrological investigations to support project sizing; "Geological and geotechnical investigations necessary to characterize the site and foundation conditions and facilitate the preliminary design work on the proposed facilities; *Analysis of alternative dam types and selection of the preferred alternative; *Preliminary optimization and verification of the project layout associated with the type of dam selected; "Verification of the proposed normal maximum operating level (NMOL)for the reservoir; "Verification of the proposed maximum reservoir drawdown; #Verification of the size and number of installed generating units for the powerhouse,and the total installed capacity; «Definition of preliminary project operating parameters and determining generation output; «Derivation of the probable maximum precipitation (PMP)and probable maximum flood (PMF); *"Derivation of the routed PMF outflow,to determine freeboard on the dam and to size the spillway and emergency outlet works; =Partial preparation of a site-specific seismic hazard analysis (SSSHA)(to be completed); «Selection of the seismic design criteria; «Establishing a long term seismic monitoring network; =Preparation of the project site layout; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-8 December 2014 -yzZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «Preparation of a layout for temporary works and associated site infrastructure; «Preparation of the layout of the airstrip and operators permanent village and associated infrastructure; «Development of alternative site access routes; =Development of transmission corridors to connect the project with the existing grid; «Outline design of a railhead transfer facility for construction access; *Identification and assessment of construction material sources; «Preliminary structural and thermal analysis of the dam; =Construction planning of all major features of the project; «Development of an Opinion of Probable Construction Cost (OPCC)at July 2014 together with an analysis of major risk factors that could impact the cost determination;and, *Operational modeling of the project,integrated within the Railbelt system. 1.4.Overview of FERC Licensing Process An initial licensing process was carried out by the Alaska Power Authority,predecessor of AEA, in the 1980s for a much more extensive project,involving a two-dam complex.An application for license for what was then referred to as the Susitna Project was submitted to the Federal Power Commission (FPC)(predecessor of FERC)in 1983 under FPC number P-7114,and the application was subsequently amended under that same number in 1985.That application was withdrawn in March 1986. After re-commencing the Project in 2009,as noted above,on December 29,2011,AEA filed with FERC a Notification of Intent (NOI)and PAD to start the formal licensing process for the proposed Susitna-Watana Project,FERC No.14241.The default FERC licensing process that is being used is the Integrated Licensing Process (ILP).The PAD provides licensing participants summaries of existing relevant,and reasonably available information related to the project and identified issues and preliminary study concepts AEA believes are important to address the identified issues.This document can be found on AEA's public website at:http://www.susitna- watanahydro.org/type/documents. On February 24,2012,FERC issued a public notice acknowledging the filing of AEA's NOI and PAD,officially commencing the licensing process,and soliciting public comment on the PAD and study requests from licensing participants.In addition,FERC issued a Scoping Document to outline the subject areas to be addressed in its environmental analysis of the project pursuant to the National Environmental Policy Act.FERC held six Scoping Meetings for the project in Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-9 December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. March 2012 in major communities around the project site area.These were focused on obtaining comments and input on resource issues related to project operations from resource agencies, Alaska Natives,local governments,non-governmental organizations,and members of the public. The purpose of the meetings was for FERC to initiate scoping of the issues,review and discuss existing project information,identify information and study needs,and discuss the process plan and schedule for licensing activities required under the Integrated Licensing Process (ILP) requirements (18 Code of Federal Regulations §5.11).As discussed below,initial environmental review was carried out during 2012 to catalogue the relevant 1980s data that were collected and inform the future study planning process. In parallel with the above activities,a number of Environmental Consulting firms were retained by AEA and detailed study plans were prepared covering the 2013-2015 timeframe.An initial Study Plan was prepared containing detailed scopes for 58 specific resource study areas,most of which have been carried out under various environmental services contracts. Under the licensing protocol,FERC specifically requested three engineering studies -that would,in any case,have been performed as part of the engineering feasibility work -be covered in the Revised Study Plan (RSP)as follows (FERC numbering): 4.5 Geology and Soils Characterization 16.5 PMF Study 16.6 Site-Specific Seismic Hazard Analysis (SSSHA) AEA filed the Proposed Study Plan for the 58 studies (including the three engineering oriented studies)with FERC on July 16,2012.After extensive review and collaboration with licensing participants and FERC staff,AEA prepared a RSP and filed updates to the 58 study plans on December 14,2012.The RSP provides a complete overview of the remainder of the licensing process and timeline and an update to the project description.FERC approved the study plans on February 1 and April 1,2013.The first year of studies was carried out in 2013 and initial results reported in a draft Initial Study Report (ISR)filed on February 3,2014.A complete Initial Study Report with plans for the second study season was filed June 3,2014.All studies are anticipated to be complete by end of 2015 and an Updated Study Report (USR)will be filed with FERC in February 2016.Final results will be presented in the USR and the ensuing documentation included in AEA's License Application that is currently planned to be filed with FERC in late 2016.Interim updates for all studies being conducted by AEA have been provided through periodic Technical Workgroup meetings -which will continue until submittal of the License Application.The intent of the meetings is to update interested parties with information on study progress,initial results,and changes to anticipated conditions or study methodologies. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-10 December 2014 -w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Engineering subjects under study,and documented in this report,will contribute to the following sections of the License Application: Exhibit A Project Description Exhibit B Project Operation and Resource Utilization Exhibit C Proposed Construction Schedule Exhibit D Project Costs and Financing Exhibit E,Chapter 6 Geological and Soil Resources Exhibit F Supporting Design Report and Project Drawings Exhibit G Project Maps 1.5.Status of Environmental Study Program A thorough discussion of the environmental study program and schedule is included in the Revised Study Plan and Final Study Plans posted on AEA's Website (http://www.susitna- watanahydro.org).This work has been conducted by other consultants under separate contracts to AEA,and was not part of MWH's services.The work is summarized below for reference purposes only. AEA completed 18 initial environmental studies during 2012.These initial studies helped inform the study planning process for the remaining work and provided updated information that supplements existing information gathered during the previous studies in the 1980s.Much of the information that was gathered in 2012 was used to help AEA and its consultants plan logistical aspects necessary to carry out complex field investigations,as well as provide vital input to the early concept design efforts for the project features and operational modeling studies.In some cases,updating information consisted of taking information developed in the 1980s and converting it into modern digital datasets for use in comparative analysis with the new information being obtained in the FERC formal licensing studies. Key target milestone dates for the formal ILP study program are listed below: »Study Season No.|-calendar year 2013 «Initial Study Report (ISR)(results of 2013 Study Season)draft,February 3,2014 and final June 3,2014 #Initial Study Report Meeting,October 15,2014 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-11 December 2014 -zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. =Initial Study Report Meeting Summary (and any AEA proposed changes to Study Plans) due October 31,2014 =Study Season No.2 -Currently planned for calendar year 2015 "Updated Study Report (USR)to be submitted to FERC by February 1,2016 =Updated Study Report Meeting,February 16,2016 "Updated Study Report Meeting Summary,March 2,2016 *Preliminary Licensing Proposal,July 5,2016 «Final License Application filed with FERC,December 1,2016 A complete discussion of the ongoing environmental study program can be found on AEA's public licensing web site as noted above.The 58 studies are categorized below: Geology and Soils studies to conduct a study to define the geologic,geotechnical,seismic,and foundation conditions at the sites of project works. *Geology and Soils Characterization Study (by MWH) Water Resources studies to characterize and evaluate any potential effects to the water quality of the Susitna River. «Baseline Water Quality Study «Water Quality Modeling Study »Mercury Assessment and Potential for Bioaccumulation Study *Geomorphology Study *Fluvial Geomorphology Modeling below Watana Dam Study »Groundwater-related Aquatic Habitat Study "Ice Processes in the Susitna River Dam Study #Glacial and Runoff Changes Study Fish Aquatics and Riparian studies to assess hydrology characteristics and its relations with fish and aquatic biota and their habitats. «Fish and Aquatics Instream Flow Study *Riparian Instream Flow Study Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-12 December 2014 -O O -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Fish and Aquatic Resources studies to better understand the Susitna River fish populations. Fish Distribution and Abundance in the Upper Susitna Fish Distribution and Abundance in the Middle and Lower Susitna River Salmon Escapement Study River Productivity Study Characterization of Aquatic Habitats in the Susitna River with Potential to be Affected by the Susitna-Watana Project The Future Watana Reservoir Fish Community and Risk of Entrainment Study Study of Fish Passage at Watana Dam Study of Fish Passage Barriers in the Middle and Upper Susitna River and Susitna Tributaries Aquatic Resources Study within the Access Alignment,Transmission Alignment,and Construction Area Genetic Baseline Study for Selected Fish Species Analysis of Fish Harvest in and Downstream of the Susitna-Watana Hydroelectric Project Area Eulachon Distribution and Abundance in the Susitna River Cook Inlet Beluga Whale Study Wildlife Resources studies of distribution,movements,population size,productivity,and habitat of wildlife in the Susitna River and surrounding area. Study of Distribution,Abundance,Productivity and Survival of Moose Study of Distribution,Abundance,Movements,and Productivity of Caribou Study of Distribution,Abundance,and Habitat Use of Dall's Sheep Study of Distribution,Abundance,and Habitat Use by Large Carnivores Study of Distribution and Abundance of Wolverines Study of Terrestrial Furbearer Abundance and Habitat Use Study of Aquatic Furbearer Abundance and Habitat Use Study of Species Composition and Habitat Use of Small Mammals Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-13 December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. *Study of Distribution and Habitat Use of Little Brown Bat »Survey Study of Eagles and Other Raptors =Waterbird Migration,Breeding and Habitat Study «Breeding Survey Study of Landbirds and Shorebirds «Study of Population Ecology of Willow Ptarmigan in Game Management Unit 13,South- central Alaska »Study of Distribution and Habitat Use of Wood Frogs «Evaluation of Wildlife Habitat Use Study #Wildlife Harvest Analysis Study Botanical Resources studies to collect necessary baseline data to evaluate the potential impacts to vegetation,wildlife habitat,wetland,and vascular-plant resources in the project area. =Vegetation and Wildlife Habitat Mapping Study «Riparian Study »"Wetland Mapping Study »Rare Plant Study »Invasive Plant Study Recreation and Aesthetic Resources studies to document baseline conditions and help assess potential impacts on recreation and aesthetic resources from construction and operation of the proposed Susitna-Watana Project. «Recreation Resources Study «Aesthetics Resources Study "Recreation Boating/River Access Study Cultural and Paleontological Resources studies that will be used to assist in identifying appropriate protection,mitigation,and enhancement measures of cultural resources. #Cultural Resources Study «Paleontological Resources Study Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-14 December 2014 C -zw .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Subsistence Resources studies to document traditional and contemporary subsistence harvest and use and to collect baseline data to facilitate the assessment of potential impacts. «Subsistence Baseline Documentation Study Socioeconomic and Transportation Resource studies that will evaluate regional economic effects as well as effects on social conditions and public goods and services. *Regional Economic Evaluation Study *Social Conditions and Public Goods and Services Study «Transportation Resources Study =Health Impact Assessment Study «Air Quality Study Project Safety studies to assess the stability of project facilities during flood loading conditions, to estimate earthquake ground motion parameters,and verify the lack of potential hazard of fault or shear zone movements. #Probable Maximum Flood Study (by MWH) «Site Specific Seismic Hazard Study (by MWH) 1.6.Project Description 1.6.1.General This brief overview of the project location,facilities,and proposed operational characteristics reflects the project development at the time of writing of this report.| Locations along the Susitna River referenced in this report are designated by two sets of river miles.River Miles (RM)refer to the distance along the river channel measured upstream from its mouth in Cook Inlet and reported in various studies originating in the 1980s.Project River Miles (PRM)refer to the recalibrated distance (for these current studies)along the channel measured upstream from its mouth.There is no single conversion between the older RM and the recent PRM;however,the maximum difference is about three miles.Precise conversion between RM and PRM ata particular location can be determined using GIS. The proposed Project is located in the South-central region of Alaska,approximately 125 miles north-northeast of Anchorage and 140 miles south-southwest of Fairbanks.As proposed,the Project would include construction of a dam,reservoir,and power plant on the Susitna River starting at 187 PRM,approximately 32 PRM upstream of Devils Canyon,as shown on Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-15 December 2014 -Z- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 1.6-1.Transmission lines connecting into the existing Railbelt transmission system and an access road and railhead improvements would also be constructed.Because engineering and environmental studies are helping define the locations and configurations of the project components,the current study area for the Project is larger than that which will be proposed as the FERC Project Boundary for the licensed project works.The study area includes alternative transmission and road corridors that may eventually be narrowed down to one or two proposed corridors for the license application.wetaad"w."eo se is yonied S ws'wh Beesaodpawnee Figure 1.6-1.Proposed Watana Dam Site,Looking Upstream 1.6.2.Watana Dam and Reservoir As currently envisioned,the Project would include a significant dam with a 23,500-acre reservoir (at normal maximum operating level).The Watana Dam arrangement is shown on Figure 1.6-2 and on Drawings 04-01C002 and 04-01C004 in Appendix A.The Watana Dam has a nominal crest elevation (El.)2065 ft.corresponding with a maximum height of approximately 705 ft. above the prepared rock foundation and a crest length of approximately 2,810 ft.The maximum height of the structure will depend both on the results of the ongoing site investigations (which will indicate the extent of rock excavation required below the river bed)and any requirements for downstream flow release negotiated with agencies as part of the licensing process. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-16 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. enSNe ES Figure 1.6-2.Dam Arrangement Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-17 December 2014 --Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The Watana Reservoir normal maximum operating level has been reassessed since that initially proposed in the PAD,and is now proposed as El.2050 ft.The impounded reservoir will be approximately 42 miles long (along reservoir centerline)with a maximum width of approximately three miles (at Watana Creek;the typical width of the reservoir is approximately 1.25 miles).The minimum reservoir level will be 1,850 ft.in the extreme year,resulting in a maximum drawdown of 200 ft.In normal years,the reservoir would be drawn down only about 120 to 150 ft.The reservoir will have a total storage capacity of approximately 5.2 million acre- ft.,of which approximately 3.4 million acre-ft.will be active storage. Certain provisions have been incorporated in the proposed project configuration to facilitate any future decision to raise the dam.Among them are positioning the powerhouse sufficiently downstream,with extra RCC between the dam and the powerhouse.The total cost of these provisions for dam raising is US$27.2 million. The Watana Dam will incorporate the following facilities for making reservoir releases before using the spillway: *Penstocks which direct water through the turbines in the powerhouse;and, «Low level outlet facilities discharging below the spillway. In addition,there will be emergency release facilities installed within the diversion tunnels capable of operation only with a water level at or below the minimum power pool level of El.1850 ft. The low level outlet facilities enable the discharge of up to 32,000 cubic ft.per second (cfs) (which together with the maximum powerhouse flow represents the reservoir attenuated outflow of up to a 50-year flood or a flushing flow)without opening the spillway gates.Reservoir storage between El.2050 ft.and El.2057.6 ft.has been allocated for attenuation of up to a 50- year flood so that opening of the spillway gates would be a rare event.The facilities will be located at an elevation that they may be used even when the reservoir level is at its minimum operating level. Construction materials for the Watana Dam and appurtenant structures will utilize,as far as possible,rock from the structure excavations to minimize the quarry development.Stable excavations and rock cuts will be designed with suitable rock reinforcement and berms. It is proposed that the bulk of the aggregate for construction be excavated from a quarry to be located on the left abutment upstream of the Watana Dam.A criterion for the quarry planning will be to ensure,as far as possible,that the final flat floor of the quarry is below the projected minimum operating water level of the reservoir to minimize visual impact.In a similar manner, Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-18 December 2014 -wa ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. the area upstream of the quarry is being investigated to try to define a spoil area upstream of the Watana Dam that will be permanently submerged. Clearing of shrubs and trees is not contemplated through the whole reservoir area.It is proposed that clearing of all substantive vegetation only be initiated for a distance of some two to three miles upstream of the Watana Dam,although consideration will be given during final design to clearing of trees in the area between the top and bottom water level throughout the length of the reservoir. AEA may research and review the potential use of biomass (from the reservoir clearing)as an energy source. The quarry will incorporate sloping roads to facilitate access from bench to bench,and during operation,it is expected that any floating debris will be captured by boat and brought to the ramps in the flooded quarry for removal and disposal.The intakes themselves will incorporate trash racks and rakes for removal of any debris not collected by boat operations. Thick alluvial deposits will be removed from the river bed at the Watana Dam site,and there will be excavation of weathered or loose rock to found the Watana Dam and appurtenant structures on sound bedrock. 1.6.3.Powerhouse The powerhouse will be located immediately downstream of the Watana Dam,and will house three generating units,each with a turbine rated capability of 153 MW unit output at reservoir water level of El.1950 ft.for a total plant rated installed turbine capacity at maximum head of 618 MW.An overall plan,elevation view,and profile of the powerhouse complex are shown on Drawings 04-01C002,05-08S001,05-08S007,05-08S008,and 05-08S009.Studies have addressed Railbelt electrical system stability,and the arrangement chosen has been determined to be satisfactory. The average annual generation capability of the Project is currently estimated to be approximately 2,800 gigawatt hours (GWh)at the generator bus.The powerhouse will be designed and constructed with an extra empty generating unit bay for the potential installation of a fourth unit at a future time.There will be two low level outlet works facility structures and four power intake structures (one corresponding to the extra unused powerhouse bay). Certain measures have been included in the proposed power facilities that will allow expansion by the addition of a fourth unit.Such measures include the fourth intake structure,a penstock Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-19 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. stub,and concrete works below deck level.The total cost of these provisions for powerhouse expansion is US$41.5 million. 1.6.4.Ancillary Facilities Construction of the Susitna-Watana site development will require various facilities to support activities throughout the entire construction period.Following construction,the operation of the Project will require a small permanent staff and facilities to support the permanent operation and maintenance (O&M)program.A plan view of the site infrastructure is shown on Drawing 01- 00G001 in Appendix A. The most significant item among the temporary site facilities will be a construction camp.The construction camp will be a largely self-sufficient community normally housing approximately 800 persons,but with a peak capacity of up to 1,200 people.After construction,AEA plans to remove most of the infrastructure of the camp facility,leaving only those aspects that are to be used to support the smaller permanent residential and O&M facilities. Other site facilities include contractor work areas,site power,services,and communications. Site power and fiber optic cabling for construction will be brought either on the transmission line route,or along the side of the access road.Items such as power and communications will also be required for construction operations,independent of camp operations. Permanent facilities will include community facilities for O&M staff members and any families. Other permanent facilities will include maintenance buildings for use during operation of the power plant. Both the gravel airstrip and helicopter/airplane hard standing that will be constructed to facilitate construction will be left in place after construction is completed. 1.6.5.Transportation Access There will be both temporary,and permanent,site access facilities to provide a transportation system to support construction activities -and to facilitate orderly development and ongoing operation and maintenance of the Project.The current planning assumes restricted public access during construction for safety considerations.Another goal is to co-locate access roads and transmission facilities,to the extent possible,in the same corridor to minimize environmental impacts. Three possible alternatives for access roads and transmission lines have been identified for the Project (Drawing 01-00G000)and this report makes no recommendation of a favored route. Two of the alternatives would accommodate east-west transmission lines in combination with a Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-20 December 2014 -zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. new site access road connecting to the Alaska Intertie Transmission Line (Alaska Intertie)and a transloading facility at the Alaska Railroad.One of these corridors,designated as the Chulitna Corridor,would run north of the Susitna River,and extend to the Chulitna siding area.The other alternative,designated as the Gold Creek Corridor,would run south of the Susitna River,and extend to the Gold Creek area.Neither of these two access roads would connect to public roads, instead terminating at the railway tracks. A third corridor,designated as the Denali Corridor,would run due north,connecting the project site to the Denali Highway by road over a distance of about 43.5 miles.If a transmission line is constructed along this corridor,it would be extended westward along the existing Denali Highway and connect to the Alaska Intertie near Cantwell. If the Denali Corridor is selected,the affected sections of the Denali Highway will be upgraded to facilitate safe construction of the project.The Denali Highway upgrades would not be within the FERC project boundary,although costs are included. Regardless of which road is chosen,the majority of the new road will follow terrain and soil types that allow construction using side borrow techniques,resulting in minimum disturbance to areas away from the alignment.At the chosen location for connection,a railhead and storage facility occupying up to 40 acres will be constructed alongside the existing railroad.New sidings will be constructed so that off-loading and transfer of goods and materials can take place without interrupting the daily operations of the Alaska Railroad Corporation (ARRC).This facility will act as the transfer point from rail to road transport,as a backup or interim storage area for materials and equipment,and as an inspection and maintenance facility for trucks and their loads. Within the 40 acres would be a small residential camp for early use before the main camp at the site is complete.It is intended that elements of this camp will be moved to the main site camp, leaving only sufficient facilities for drivers trucking equipment to the construction site,for laborers and staff operating the transfer,for emergency use,and for support staff such as cooks and maintenance workers. If the Denali Corridor is chosen for road access,the pavement on the first section of the Denali Highway in the community of Cantwell will be extended for a distance of approximately 4 miles to eliminate any problem with dust and debris from construction vehicles.In addition,the following measures will be taken: *Speed restrictions will be imposed along appropriate segments. «Improvements will be made to the intersections including pavement markings and traffic signals. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-21 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Some consideration has been given to the use of expected airship development,particularly as a means of commencing early site construction while the permanent access is developed.The date of commencement of commercial and economic use of heavy lift airships is not yet clear,so it has been discounted at the time of writing.During further project design and construction contract development,it will be reconsidered if commercial certification and application appears more certain. 1.6.6.Electric Transmission and Interconnection Facilities Transmission lines to deliver full Susitna-Watana power to the existing grid will begin at Watana Powerhouse Switchyard and consist of three 230-kilovolt (kV)lines,in either single-or double- circuit configuration.The same three corridors under consideration for the access road are also those under consideration to connect the project primary transmission lines to the Alaska Intertie (see Drawing 01-00G000)and this report makes no recommendation for a route.One or two transmission corridors may be chosen to allow the lines to be separated somewhat,in case of line interruption.Depending on which corridor is (or corridors are)chosen,the transmission system will include a switching station at the point of tie-in (at Chulitna,Gold Creek,or Cantwell). From the Watana substation,the transmission corridors are essentially co-located with the access road corridors except for three specific areas: 1.For the northern westward route (Chulitna Corridor),the first five miles (westward from the power facilities)of the double circuit 230-kV transmission lines will not follow the coincident road corridor.The two lines will cross the river from the switchyard (together with any line destined for the northern route)in a northerly direction for two miles,after which the two lines will turn northwesterly to cross Tsusena Creek and three miles later will intersect the Chulitna road corridor.The westerly end of the corridor will be wider to facilitate the divergence of the road and the transmission line,which will continue to a switching station on the Alaska Intertie. 2.For the southern westward route (Gold Creek Corridor),the transmission lines would occasionally not follow the planned road corridor,because the transmission lines can span some of the rough topography that the road must avoid.Near the westerly end of the corridor,both the transmission lines and road can be co-located into one single corridor.Some five miles northeast of Gold Creek will be a switching station on the existing Alaska Intertie,beyond which,to the west,the road will be the sole occupant of the corridor. 3.For the northern route (Denali Corridor),there are two options for transmission line routes.The transmission will generally follow the road corridors with the transmission Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-22 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years.+ corridor following the Denali Highway.The transmission corridor will then continue west along the Denali Highway to the Cantwell interconnection with the Alaska intertie. The right-of-way for the transmission lines within the corridors will consist of a linear strip of land;the width will depend on the number of lines.The transmission rights-of-way will be 200, 300,or 400 ft.,depending on whether one,two,or three lines run in parallel. The switching and substations will each occupy a total of approximately 16 acres. Rights-of-way for permanent access to switchyard and substations will be required,connecting to the permanent site access road.These rights-of-way will be 100 ft.wide. Access to the transmission line corridors will be: =via unpaved vehicle access track from the permanent access roads at intermittent points along the corridor (the exact location of these tracks will be established in the final design phase);or "by helicopter,where there is no access road projected. Within the transmission corridor itself,an unpaved vehicle access track up to 25-ft.-wide will run along the entire length of the corridor,except at areas such as major river crossings and deep ravines where an access track would not be utilized for the movement of equipment and materials. 1.6.7.Project Operations Project operating flexibility is understood to be important to Railbelt utilities that will utilize the project's capacity and energy output.The "production modeling”simulation encompassed the entire Alaska Railbelt interconnected system to maximize the benefit of the Susitna-Watana generation.The simulation resulted in a decision by AEA to select an operating regime such that the power plant has flexibility to operate in a load-following mode when and if needed,such that energy is maximized during the critical winter months of November through April each year to meet Railbelt utility load requirements. Reservoir storage capability is vital to the project's intended function -to provide critical winter generation capacity -by regulating the flows of the Susitna River,and to serve as a major long- term power generating resource for the region.The requirement for substantial storage clearly identified in all the previous studies of the Susitna River,documented in Section 3,provides for capture and storage of spring snowmelt for later release through the powerhouse during the winter months.This capability also serves to ensure that seasonal flow releases needed to both protect environmental habitat and enhance river recreational opportunities downstream of the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-23 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. project can be provided.In contrast,a run-of-river hydro project on the Susitna (or any river) without storage cannot provide these important system,environmental and/or recreational benefits. Production cost modeling has encompassed the whole Railbelt system and has highlighted the benefits that will accrue to the whole system if a centralized dispatch method of operation is selected. To facilitate efficient dispatch,the reservoir would be drafted annually by an average of about 120 ft.to 150 ft.,and subject to an occasional maximum drawdown of 200 ft.Minimum in-stream flow releases would be made through the powerhouse -or through low level outlet works during the rare occasions when the power plant is offline.Flow discharges through the powerhouse under the operating plan would range from the minimum required in-stream flow release (yet to be determined)to a maximum of about 14,000 cfs (based on the 618 MW turbine capacity at normal maximum operating level),with all generating units operating)during times of maximum power generation.Daily power generation during a winter month of peak demand (January)would average about 8,300 MWh and powerhouse discharges would average approximately 8,390 cfs during that time. For efficient operation of the whole system,powerhouse discharges are expected to vary over a 24-hour period during the winter months of peak demand,typically ranging from a low of about 5,400 cfs to a high of 10,800 cfs.The daily flow variation may be constrained because of environmental concerns yet to be defined.It is expected that any flow variations immediately downstream of the powerhouse will be partially attenuated by the time the variation in flow reaches Gold Creek,Talkeetna,and the other downstream locations. A final operating plan will be prepared and submitted by AEA in Exhibit B of the FERC License Application. 1.6.8.Construction Schedule The current schedule allows 7.5 years for dam and power facilities construction.Additional time has been allotted for final design phase site investigations and access road construction. The following are the approximate time periods for major components of project construction: »Site investigation and design engineering 3 years *Access road construction 2 years =Dam and power facilities construction 7.5 years Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-24 December 2014 -Z- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «Reservoir filling 1 to 2 years (in parallel with final construction activities) »Site restoration throughout construction Design work would be initiated as necessary for project completion,and could be initiated during the license application review period so that construction critical to the schedule (such as access roads and construction support facilities)will be ready to commence shortly after issuance of the FERC license and obtaining other required subsequent regulatory approvals. 1.7.Visualization During the performance of the feasibility study,many 3-D models have been constructed using various software.In late 2013,all models were combined into a visualization that is enclosed on a flash drive with this report.Although there have been some changes since the visualization was completed (for example,number of spillway gates,length of airstrip),it represents a reasonable depiction of the project works as proposed. 1.8.Principal Project Parameters After all the various optimizations and analysis,the principal project parameters of the feasibility design -which forms the basis of the cost estimate -are shown in Table 1.8-1. Table 1.8-1.Principal Project Parameters Dam Dam Type Curved Gravity Construction Material Roller Compacted Concrete Axis Radius (along upstream edge of crest)2,600 ft.(with straight flanks)-Aeré 'wakl curve Crest Road Elevation El.2065 ft. Crest Length 2,810 ft. Lowest Foundation Elevation El.1360 ft. Height Above Foundation (approx.)705 ft. Crest Width 4S ft. Downstream Face Slope Verhcal curve ofCurvedSection(H:V)1,650 ft.(csant radius) Straight Section 0.85:1 Upstream Face Slope Below El.1770 ft.(H:V)0.1:1 Above El.1770 ft.Vertical Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-25 December 2014 Zz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Top of Parapet Wall Elevation Volume of Dam Concrete (not including powerhouse) (gross -including spillway and intakes) Volume of Roller Compacted Concrete Volume of Conventional Vibrated Concrete (dam) Volume of CVC Intakes and Spillway E].2068 ft. 5,671,000 cy 5,215,000 cy 20,000 cy 436,000 cy Seismic Parameters -Peak Ground Acceleration (PGA) MCE Deterministic Interface (88""percentile)PGA 0.58 g (scaled to 5000 yr.@ 0.55 sec) Intraslab (84"percentile)PGA 0.81 g Intraslab (69 percentile)PGA 0.69 g Fog Lake Graben (84""percentile)PGA 0.49 g OBE 500 yr.return period 0.27 g Reservoir Normal Maximum Operating Level (NMOL)El.2050 ft. Maximum Level (@ PMF)El.2064.5 ft. Minimum Operating Level (MOL)El.1850 ft. Area at NMOL 23,500 acres Length at NMOL 42 miles (approx.) Total Reservoir Storage Live (Active)Storage 5,170,000 acre-ft. 3,380,000 acre-ft. Average Tail Water Elevation El.1456 ft. Diversion Diversion Tunnel Length 2,060 ft. Number One,modified horseshoe Width/diameter 36 ft.internal Lining Concrete Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 1-26 Alaska Energy Authority December 2014 -Zz- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Div.Tunnel Capacity Sluice Structure capacity Sluice dimensions Cofferdams Type Upstream Crest Elevation Downstream Crest Elevation Maximum upstream Water Level (wl) Emergency Outlet Facilities 52,000 cfs @ El.1530 ft.wl 82,000 cfs @ El.1553 ft.wl"fn 44 ft.high x 50 ft.and 525,length Rockfill with earth core 1,560 ft. 1,479 ft. 1,553 ft. Location Type Capacity Low Level Outlet Facilities In diversion tunnel Gated sluices 30,000 cfs @ El.1850 ft.wl Intake Structure (Two) Control Gates Number Dimensions Water Passage Diameter Outlet Control Structures Single-level,gated 2 23 ft.H x 23 ft.W2-23 ft.diameter (s fee /-/ined) 8-Fixed Cone Valves Diameter 79 inches Capacity 4,000 cfs each @ El.2057.5 ft. (Total 32,000 cfs) Spillway (preliminary) Capacity at 50-yr.flood surcharge (El.2057.5 ft.)205,000 cfs Capacity at PMF surcharge (El.2064.5 ft.)Control 250,000 cfs Structure Type Gated Ogee Crest Elevation 2010 ft. Gates Type Radial Number 4 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 1-27 Alaska Energy Authority December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Dimensions Top of Gate Level Chute width Energy Dissipation Power Intakes 50.5 ft.H x 42 ft.W El.2058.5 ft. 82 ft.(Total 164 ft.) Flip bucket Intake structures Number of Levels Number of shutters per level Dimensions of Shutters Control Gates 4,Multi-level,gated 5 8 25 ft.H x 22 ft.W Number 8 Dimensions 19 ft Hx 10 ft.W Invert Elevation El.1800 ft. Penstocks Number 3 The horizontal section of the fourth penstock will be installed and capped,so that it is available for future addition of a unit. Type Inclined,horizontal Diameter 19.0 ft.I.D. Material Steel Powerhouse Type Surface Size 300 ft.L x 88 ft.W x 100 ft.H Turbine (No.and Type)3 Vertical Francis Speed 180 rpm Max.Turbine Capacity at Max.Operating Level Net Head (est.) Flow @ Operating Head (est.) 206.2 MW (Gen.202.1 MW) 577 ft. 4,618 cfs Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 1-28 Alaska Energy Authority December 2014 --za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Rated Turbine Capacity @ Res.Level 1950 ft. Net Heat (est.) Flow @ Capacity at Operating Head (est.) Min.Turbine Capacity @ Min Operating Level Net Head (est.) Flow @ Min.Head (est.) Generator Continuous Rated Capacity 153 MW (Gen.148.5 MW) 480 ft. 4,083 cfs 105.9 MW (Gen.100.9 MW) 383 ft. 3,592 cfs Vertical Synchronous 225 megavolt-Ampere Power Factor 0.9 Voltage 13.8kV Frequency 60 Hz Speed 180 rpm Transformers Location Draft Tube Deck Number 3 +1 spare Voltage 230 kV Project Output Nominal Turbine Capacity (maximum head)618 MW Nominal Generator output (maximum head)606 MW Average Annual Generation (rounded)2,800 GWh Switchyard Location Plan Dimensions Transmission (Depends on chosen route) Left abutment 350 ft.by 300 ft. Length Voltage Access Road (Depends on chosen route) 141 circuit miles 230 kV Length Number of Bridges Up to 50 miles Up to 7 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 1-29 Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Permanent Facilities Airstrip Length 5,500 ft. Housing Accommodation Capacity 30 families 1.9.Board of Consultants Review AEA has convened a Board of Consultants for the purposes of review of the feasibility studies as they relate to dam safety.The key elements and decisions recorded in this report -relating to the type of dam,the PMP and PMF studies,the Site Specific Seismic Hazard Analysis,the Finite Element studies of the dam structure,and the projected site investigations required to verify the designs adopted -have been subject to review by the Board of Consultants. FERC approved the board members by letter dated October 23,2012.This Board of Consultants has been,and will continue to be,supplemented from time to time by particular specialists for specific parts of the analysis and design.Initially,for example,the Board has been expanded by the addition of a meteorologist and hydrologist to review the site-specific PMP studies being performed as part of RSP Section 16.5 as noted above,and by a seismologist for opinions on the seismic hazard assessment being performed as part of RSP Section 16.6.Meetings of the Board have been held on four separate occasions during the preparation of this Feasibility Report.An initial meeting of some (but not all)of the board members was held in November 2012 to consider the study plans for the PMP determination and for the seismic hazard assessment. Subsequent board meetings were held on the following dates: #March 7-8,2013 in Bellevue,Washington #May 28-30,2013 in Anchorage,Alaska (including a site visit) »April 4-6,2014 in Bellevue,Washington The Board has reviewed the text of applicable sections of this report and where appropriate their comments have been addressed. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 1-30 December 2014 Section 2 -yzw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 2.SCOPE OF WORK 2.1.Evolution of Plan of Study The purpose of this feasibility study is to define all aspects of the Project in sufficient detail to support the State's decision process regarding project development,and further to support eventual submission of a FERC license application.This Engineering Feasibility Report documents the status of all engineering work undertaken through December 2014.The Engineering Feasibility Report may be supplemented or modified at the completion of required future geotechnical investigations,which will include excavation of adits,additional foundation boreholes,in-situ testing,etc. All engineering work undertaken for the feasibility report has utilized,to the extent possible,the results of the engineering studies carried out during feasibility study and licensing work that were performed in the 1970s through the mid-1980s.Some items,such as the dam type selection,probable maximum flood (PMF)studies,and the previous sizing of the generating units are now not applicable,and thus have been updated. In addition,in order to properly focus the environmental studies needed to support the license application,some project definition work was accelerated to reduce the number of alternatives for detailed analyses.Other studies have also been completed to address specific issues that have arisen.An overview of the scope of work for the current phase of study is given below. 2.2.Hydrology Hydrological studies include: «Development of a 61-year Watana Dam inflow data set to use in reservoir operation simulation modeling studies; «Establish a meteorological network in the upper Susitna Basin,from Gold Creek to the Alaska Range (by others),to develop an understanding of the weather parameters; =Perform maximization and transposition analysis of selected historic storms to provide data toward development of a site-specific PMP study to update the work performed during the 1980s feasibility studies; *Perform flood frequency analysis,and sub-basin segmentation,and develop a rainfall- runoff model of the Susitna River upstream of Gold Creek.Apply the model to recreate previous PMF studies,initiate calibration of the model to historic floods,and determine Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 2-1 December 2014 -zw.ALASKA ENERGY AUTHORITY. AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. the 100-year and probable maximum snowpack depths and areal distribution all to support derivation of the PMF inflow to the reservoir; *Confirmation of the diversion flood magnitude to be used to size temporary diversion facilities for project construction;and, «Derivation of the pre-project and post-project flow variations in the Susitna River downstream of the dam and powerhouse. 2.3.Power Studies Power studies include: «Determination of the available average and firm energy from the project for different reservoir sizes and power plant capacities; Modeling the effect of projected reservoir operation and power plant discharges on downstream river stage and flow; «Preliminary assessment of climate change effects on energy generation; «Determination of the available,average,and firm energy for various operating scenarios including load-following,base load,intermediate load-following,and run-of-river operation;and, Modeling of the operation of the project in conjunction with the rest of the integrated Railbelt utilities'electrical system based on Susitna-Watana generation data provided by Slater Consulting. 2.4.Geotechnical Exploration and Characterization Geotechnical tasks include: =Preparation and inception of site investigation programs to supplement the 1980s work; *Supervision of the field exploration program; *Data compilation and analysis; *Establish geotechnical instrumentation network in the dam site area; »Interpretation of the geological and geotechnical investigations of the foundations for the dam and powerhouse and surrounding areas; «Preparation of a Geotechnical Data Report;and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 2-2 December 2014 -y .ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. «Update terrain unit mapping (regional geology)and preparation of a preliminary reservoir slope stability assessment. A significant site investigation program was planned for 2013 and 2014,including at least one adit in the right abutment at the dam site.Due to circumstances beyond the control of the engineering team,this site investigation program at the dam site had to be postponed,so this draft report has been compiled based on information gathered prior to December 2014. 2.5.Seismic Studies Seismic studies include: «Establishment of a seismic monitoring network at the project site; «Paleoseismic investigation and seismic source characterization; «Site Specific Seismic Hazard Assessment;and, #Reservoir Triggered Seismicity Assessment. 2.6.Development of Layout and Design Layout studies include: «Analysis of the type of dam and project layout to assess which is most economic;Earth Core Rockfill Dam,Concrete Faced Rockfill Dam,or Roller Compacted Concrete Dam; #Verification of location,plan and cross-section of the selected dam; =Verification of the number and size of generating units; *Verification of the number,size and optimization of diversion tunnel(s); #Verification of the normal maximum operating level,range of annual reservoir drawdown and dam height; «Preliminary structural and thermal analyses of the dam; "Verification of spillway size and configuration; «Verification of size and optimization of environmental release facilities;and, »Development of preliminary design criteria and assumptions. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 2-3 December 2014 -zZ ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 2.7.Access Access studies include: =»Reconnaissance studies of various alternative access road (and railway)alignments to the project site that were identified for the Alaska Energy Authority (AEA)by Alaska Department of Transportation and Public Facilities (ADOT&PF); =Further definition of the potential access routes,and selection of the associated environmental study corridors; *Preliminary design of a railroad off-loading facility from the Alaska Railroad Corporation (ARRC)to the potential road access route;and, *Selection of the location and the design of an airstrip and associated facilities at the project site. 2.8.Transmission Studies associated with the power delivery from the Project to the interconnected system include: «Evaluation of future system improvements necessary on the Railbelt intertie,whether Susitna-Watana is built or not (performed under a separate contract to AEA). »System studies to: -verify load flow in the system; -verify the maximum size of units that can be installed at Susitna-Watana without significant destabilizing of the system during load variances;and, -verify system improvements necessary to accept Susitna-Watana power. «Determination of three alternative transmission corridors,each close to the potential access road alignments (to lower total costs). *Interconnection substation layouts. The work carried out under this evaluation relating to system improvements on the Railbelt intertie was preliminary in nature.In 2013,a second more detailed study was initiated separately. 2.9.Surveys The early stages of the project analysis relied upon data that was developed as part of the 1980s study.The dam analysis and hydrological assessments were limited to the quality of the data. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 2-4 December 2014 -y .ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. The topographic data used was hand digitized from paper copies of the 1980s topographic survey.For the first reconnaissance study of the roads,the survey used Horizontal North American Datum of 1927 and National Geodetic Vertical Datum of 1929).Contour intervals were 100 ft. After this initial work was completed,the first topographic data became available using the Interferometric Synthetic Aperture Radar Elevation Data (IFSAR)elevation data and the MatSu- North Susitna Bare Earth Data using Horizontal North American Datum of 1983 and North American Vertical Datum of 1988.The IFSAR data had a vertical accuracy of +/-10 ft.(+/-3 meters).A secondary scope of work was initiated to transfer all applicable data to the new,more accurate,topography and to recalibrate the survey coordinate system. 2.10.Site Facilities Studies of the facilities required to support construction and subsequent operation and maintenance include: =Preliminary layouts of the temporary field investigation and construction camps; «Layout of permanent operators'village;and, «Layout of water supply,fire water,wastewater collection and treatment,roads,solid waste disposal etc.together with associated infrastructure. 2.11.Construction Cost Estimates and Schedules Tasks associated with estimating include: =Construction planning,including matters such as quarry development,excavation planning,sequencing/staging and materials supply chain,etc.; =Identification of risk elements; *Derivation of a cost estimate for the whole project construction at the time of submission of the Pre-Application Document (December 2011 /January 2011); «Preparation of a schedule for development and construction of the selected project configuration; «Probabilistic analysis of the schedule to determine likely finish dates and to highlight areas of project development and design upon which to focus as priorities; =Development of cost estimate assumptions; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 2-5 December 2014 yz ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. =Further cost estimation after 12 months of preliminary design development (December 2012); =Further cost estimation,using a "joint venture”approach in December 2013; «Probabilistic analysis of the cost estimates in 2012,2013 and 2014 to assess range of probable costs;and, »Final Opinion of Probable Construction Cost of the chosen feasibility level design,at 2014 prices. There has been engineering judgment (and conservatism)used in the selection of geotechnical parameters relating to the design,and ranges have been used in the cost estimate reflecting uncertainties,for example,bedrock surfaces.It is therefore important that this report is updated when the results of drilling,seismic profiling,structural geologic mapping,and the adit construction,mapping and testing becomes available. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 2-6 December 2014 Section 3 Zz.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 3.PREVIOUS STUDIES 3.1.Early Studies of Hydroelectric Potential Shortly after the end of World War II,the U.S.Bureau of Reclamation (USBR)conducted an initial investigation of hydroelectric potential in Alaska,issuing a report in 1948.Responding to a recommendation made in 1949 by the nineteenth Alaska territorial legislature that Alaska be included in the USBR program,the Secretary of Interior provided funds to update the 1948 work.The resulting report,issued in 1952,recognized the vast hydroelectric potential within the territory and placed particular emphasis on the strategic location of the Susitna River between Anchorage and Fairbanks. After the report of 1952,the USBR performed a study of a number of sites,and compiled a report in 1953. At various times,studies were commissioned to identify potential dam sites and to conduct geotechnical investigations.By 1961,the Department of the Interior proposed authorization of a two-dam power system encompassing the Devil Canyon and the Denali sites.The definitive 1961 report was subsequently updated by the Alaska Power Administration (APA)(an agency of the USBR)in 1974,at which time the desirability of proceeding with hydroelectric development was reaffirmed. The U.S.Army Corps of Engineers (USACE)was also active in hydropower investigations in Alaska during the 1950s and 1960s,but focused its attention on a more ambitious development, Rampart,on the Yukon River.This project would have been capable of annually generating five times as much electric energy as the Susitna development.The size and technological challenges associated with Rampart diverted attention from the Susitna Basin for more than a decade.The Rampart initiative was finally abandoned in the early 1970s because of environmental concerns and the uncertainty of demand for electrical energy,in doubt because of natural gas that had been discovered in the Cook Inlet. The world energy crisis precipitated by the Organization of the Petroleum Exporting Countries oil boycott in 1973 provided further impetus for seeking development of an Alaskan renewable energy resource.Federal funding was made available both to complete the Alaska Power Administration's updated report on Susitna in 1974,as well as to launch a prefeasibility investigation by the USACE.The State of Alaska itself commissioned a reassessment of the Susitna Project by the Henry J.Kaiser Company in 1974. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 3-1 December 2014 -yz .ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Although the gestation period for a viable hydroelectric project in the Susitna Basin has been lengthy,federal,state,and private organizations have been almost unanimous,over the years in recommending that a hydro project proceed. Salient features of the various reports to date are outlined in the following sections. 3.2.U.S.Bureau of Reclamation -1953 Study The USBR 1952 report to Congress on Alaska's overall hydroelectric potential was followed shortly by the first major study of the Susitna Basin in 1953.Ten dam sites were identified above the Gold Creek railroad bridge: 1.Gold Creek 2.Olson 3.Devil Canyon 4.Devil Creek 5.Watana 6.Vee 7.Maclaren 8.Denali 9.Butte Creek 10.Tyone (on the Tyone tributary) Fifteen more sites were considered below Gold Creek.However,more attention was focused over the years on the Upper Susitna Basin where the topography is better suited to economic dam construction and where less impact on anadromous fisheries is to be expected.Field reconnaissance eliminated half the original Upper Basin list,and further USBR consideration centered on Olson,Devil Canyon,Watana,Vee,and Denali.All of the USBR studies since 1953 have regarded these sites as the most appropriate for further investigation. 3.3.U.S.Bureau of Reclamation -1961 Study In 1961,the USBR prepared a more detailed feasibility study that recommended a five-stage development specifically planned to match the projected load growth curve at that time. Devil Canyon was to be the first development,incorporating a 635-foot-high arch dam together with an installed capacity of about 220 megawatts.The reservoir formed by the Devil Canyon Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 3-2 December 2014 -yz .ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Dam alone would not have stored enough water to permit economic installation of higher capacities,because of the long periods of low flow in the winter months.The second stage would have increased storage capacity by adding an earthfill dam at Denali in the upper reaches of the basin.Subsequent stages proposed adding generating capacity to the Devil Canyon Dam. Geotechnical investigations conducted at the Devil Canyon site were more thorough than at Denali.At Denali,test pits were dug,but no drilling was initiated. 3.4.Alaska Power Administration -1974 The report on studies by the federal Alaska Power Administration suggested little change from the USBR proposal of a five-stage development in 1961.This later effort,however,offered a more sophisticated design,provided updated cost estimates and construction schedules,and addressed load growth and marketing,economics,and environmental considerations. 3.5.Kaiser Proposal for Development -1974 The Kaiser study,commissioned by the Office of the Governor in 1974,proposed that the initial Susitna development consist of a single dam known as High Devil Canyon.No field investigations were made to confirm the technical feasibility of the High Devil Canyon location because the funding level was insufficient for such efforts.Visual observations by engineers suggested the site was probably favorable.The proposal for a high dam at Devil Canyon addressed the concerns USBR had expressed with respect to foundation conditions at the Denali site,the project necessary to establish storage during long periods of low flow.Kaiser instead proposed to build a rockfill dam at High Devil Canyon that,at a height of 810 ft.,would create a large enough reservoir to overcome the storage problem.Although the selected sites were different,the USACE reached a similar conclusion (a preference to avoid the Denali option) when it later chose the high dam at Watana as the prime candidate for initial development. Subsequent developments suggested by Kaiser included a downstream dam at the Olson site and an upstream dam at a site known as Susitna III.The information developed for these additional dams was confined to estimating energy potential.As in the USACE study,future development of Denali remained a possibility if foundation conditions were found to be adequate and if the value of additional firm energy provided economic justification in the future. Although Kaiser had substantial commercial interests in aluminum smelting,their conclusion did not suggest that the development of an energy consumptive aluminum plant was necessary to justify the proposed project economically. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 3-3 December 2014 -zZ .ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 3.6.U.S.Army Corps of Engineers -1975 and 1979 Studies Prior to the efforts by the APA in the 1980s,the most comprehensive study of the Upper Susitna Basin was completed in 1975 by the USACE.Twenty-three alternative developments were analyzed,including those proposed by the USBR.The study also considered the use of coal as the primary energy source for Railbelt electrical needs.The USACE study concluded that an arch dam at Devil Canyon was appropriate,but found that a high dam at the Watana site would provide sufficient seasonal storage and would permit continued generation during low flow periods. The USACE recommended the construction of an earthfill dam at Watana with a height of 810 ft.In the longer term,development of the Denali site remained a possibility that,if it were to be constructed,would have increased the amount of firm energy available in dry years. An ad hoc task force was created by Governor Jay Hammond upon completion of the 1975 USACE Study.The task force recommended endorsement of the USACE request for Congressional authorization,but pointed out that extensive further studies,particularly those dealing with environmental and socioeconomic attributes,were necessary before any development decision could be made. At the federal level,concern was expressed at the Office of Management and Budget (OMB) regarding the sufficiency of geotechnical data available from the Watana site as well as the economic analysis.Other parts of the USACE report dealing with the construction schedule and the thin arch dam proposed for Devil Canyon were also questioned by the OMB.In response, further investigations were funded and the USACE produced an updated report in 1979.Devil Canyon and Watana were both reaffirmed as appropriate sites,but alternative dam types were investigated.A concrete gravity dam was analyzed as a potential alternative for the thin arch dam at Devil Canyon and the Watana Dam proposal was changed from earthfill to rockfill. Subsequent cost and schedule estimates still indicated economic justification for the project. 3.7.Alaska Power Authority -Acres /Harza /Ebasco 1980s In 1979,under Governor Jay Hammond,the State of Alaska articulated its first energy policy that included a number of principles: 1.Equitable distribution of Alaska's energy wealth 2.Improved efficiency of production and delivery 3.State planned and funded facility construction 4 .Technical assistance in conservation and management Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 3-4 December 2014 -yZN ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 5.Support for development of locally oriented energy technologies 6.Public participation and local input in energy planning decisions In 1977,the State created a public corporation,the APA,as a vehicle for development of state energy resources under the principles above.Several conditions at the start of the 1980s heavily influenced development plans including the concept that developing cheap power,primarily through investment in hydropower projects such as Susitna and Bradley Lake (as well as various projects in Southeast Alaska),would stimulate economic development.It was also assumed that state revenues from the newly producing oil fields at Prudhoe Bay could provide the money needed to support the required investments.The high price of oil and the expectation that it would continue to rise also led to the assumption that there would be no financial stress during development (the 1981 price of crude oil was close to US$40 per barrel -equivalent to US$89 in 2014 dollars). In 1980,the APA commissioned a comprehensive analysis to determine whether hydroelectric development on the Susitna River was viable. Initially those studies were performed by Acres,under an assignment to prepare a feasibility study and a license application to the Federal Energy Regulatory Commission (FERC).Twelve major areas of study were initiated,including:power studies;surveys and site facilities; hydrology;seismic studies;geotechnical exploration;design development;environmental studies;transmission;cost estimating and scheduling;licensing;marketing and financing;and public participation.Based on those studies,the APA submitted a license application to FERC in 1983 for the Watana/Devil Canyon Project on the Susitna River (commonly known as the Susitna-Watana Hydroelectric Project). Subsequent to the submission of the first license application to FERC,an assignment for continuing the studies was given to a joint venture of Harza and Ebasco.An updated license application was prepared and submitted to FERC in 1985. From 1978 to 1986,the State of Alaska through APA,expended $145 million (of the $227 million appropriated)on extensive field work,biological studies,and activities to support the FERC license application.Financing difficulties,along with the falling cost of gas-fired electricity in the Railbelt region,the declining price of oil throughout the 1980s,and the financial burden on the State budget,resulted in the termination of work on project development.Though the APA concluded that project impacts were manageable,the license application was withdrawn in March 1986. The final configuration,documented in the feasibility studies (including a substantial subsurface geotechnical drilling program),included a staged development of the two dams.The initial Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 3-5 December 2014 -yw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. phase would have been a "low”dam at Watana together with a powerhouse,followed by the full development at Devil Canyon.The final stage would have been based on the raising of the Watana Dam to the full height contemplated.The Watana Project was proposed as an earth core, rockfill dam,with a separate gated,chute spillway,and an underground powerhouse.The Devil Canyon development would have been a high concrete arch dam,and an underground powerhouse. More than 3,500 reports and documents are available from the studies in the 1980s. 3.8.Alaska Energy Authority -2009-2010 The APA was reconstituted as the Alaska Energy Authority (AEA)in 1989,and in 2008,the Alaska State Legislature authorized AEA (as successor organization to APA)-in the fiscal year 2009 capital budget -to reevaluate the project as it was conceived in 1985.Future demand predictions,and options to meet the demand,such as from renewables,demand-side management,and energy efficiency,were evaluated. During 2009,two reports were commissioned by AEA;Susitna Project -Watana and High Devil(s)Canyon -RCC Dam Cost Evaluation,prepared by R&M Consultants/Hatch Acres;and Susitna Hydroelectric Project -Conceptual Alternatives Design report prepared by HDR. In 2010,the Alaska Legislature enacted House Bill 306 (HB 306),creating a goal that the State should obtain 50 percent of its electric generation from renewable and alternative energy sources by 2025.Hydropower is defined as a renewable resource in Alaska.Following HB 306,a Preliminary Decision document was prepared,documenting a comparison between the two major projects competing to satisfy the requirements of HB 306,Chakachamna and Susitna-Watana. The result of the comparison was a recommendation by AEA to develop the Susitna-Watana site, the upper of the two sites that were the subject of the 1983 License Application. Also in 2010,after evaluation of competitive proposals,AEA engaged MWH and its subcontractors to assist in the completion of engineering feasibility studies and FERC licensing of a revised concept for the Susitna-Watana Project.These feasibility studies have been used to complete this report. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 3-6 December 2014 Section 4 zw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 4.RAILBELT LOAD FORECASTS Much of the generation and transmission infrastructure of the Railbelt region of Alaska is aging and is at or near its time for replacement.The Railbelt is generally defined as the service areas of six regulated public utilities:Anchorage Municipal Light &Power (ML&P),Chugach Electric Association (Chugach),Golden Valley Electric Association (GVEA),Homer Electric Association (HEA),Matanuska Electric Association (MEA),and the City of Seward Electric System (SES).This region covers a significant area of the state and contains the majority of the state's population and economic activity;it extends from Homer to Fairbanks and includes major metropolitan areas such as Anchorage,Fairbanks,and the Matanuska-Susitna Valley. Concern over both the future cost and supply of fuel for electricity generation in South-central and Interior Alaska,and the projected high capital costs of new energy projects,caused the State Legislature in 2008 to task AEA with developing an Alaska Railbelt Draft Regional Integrated Resource Plan (RIRP).At the same time,the State re-evaluated the hydroelectric power potential of the Susitna River.The draft RIRP was completed in 2010,and represents a long- range conceptual generation and transmission plan for the Railbelt to minimize future power costs,and maintain or improve on current levels of power supply reliability.The intent of the RIRP was to compile system load data and use it to evaluate options for development of a diverse portfolio of power supply,and reliable,stable priced electrical energy over a 50-year planning horizon. 4.1.Regional Generation Facilities It was determined that even if very low future electricity demand increases are assumed for the Railbelt region,retirement of older generating units will require substantial new generation capacity to be constructed over the next two decades to meet demands and provide system reserves. Section 4 of the draft RIRP provides a detailed description of existing Railbelt utility generation resources.As indicated in Table 4.1-1,total combined installed capacity in 2009 was about 1,275 megawatts (MW),an amount which is just sufficient to meet current demands plus contingency reserve requirements (see Figure 4.3-1 and Figure 4.3-2). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 4-1 December 2014 ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. Table 4.1-1.Railbelt Installed Capacity 2009 (MW) Thermal Bradley Eklutna Cooper Utility Existing Lake Lake Lake Total Capacity |Capacity!Capacity Capacity MEA 0 16.1 6.7 0 22.8 HEA 42 14.0 0 0 56.0 CEA 500.5 35.6 12 20 568.1 GVEA 278.1 19.8 0 0 297.9 ML&P 278.3 30.3 21.3 0 329.9 SES 0 1.2 0 0 1.2 Total 1,098.9 117 40 20 1275.9 Notes: 1 The nameplate rating for Bradley Lake is 120 MW with 90 MW dispatchable and 27 MW available for spinning reserve under normal conditions. 4.2.Regional Transmission Facilities For purposes of the RIRP study,the Railbelt transmission system was defined as having four main load centers: =»GVEA,or the interior; =»MEA; «Anchorage,comprised of Chugach's and ML&P's service areas;and, =the Kenai Peninsula,comprised of HEA and SES. Within each load center,energy is assumed to flow freely without transmission constraints.The existing transmission system of the Railbelt is characterized as weak and in need of improvement.Power transfer between areas of the system is currently constrained by weak transmission links and stability constraints.Generating reserves cannot be readily shared between areas and project development activities are seriously affected. GVEA -GVEA's service area is connected with 138-kilovolt (kV)lines that supply Delta Junction,Fairbanks,and Healy. The interior and MEA load centers are interconnected via the Alaska Intertie and the Healy- Fairbanks and Teeland-Douglas transmission lines.The Alaska Intertie is a 345-kV (operated at 138-kV),170-mile transmission line that is owned by AEA connecting the Douglas and Healy substations.The Healy-Fairbanks transmission line is a 230-kV,90-mile transmission line, Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 4-2 December 2014 7 ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. operated at 138-kV,and runs from the Healy to the Wilson substations,which deliver power from the Alaska Intertie directly into the city of Fairbanks.Another 138-kV transmission line also runs from Healy to Nenana to Goldhill and delivers power to Fairbanks.The 138-kV, 20-mile Douglas-Teeland transmission line stretches between the Douglas and Teeland substations and connects the southern portion of the Alaska Intertie to the MEA load center.The current transfer capability of the Alaska Intertie and Healy-Fairbanks transmission lines are assumed to be 75 MW and 140 MW,respectively. MEA --MEA serves customers along the southern half of the intertie and beyond through the cities of Wasilla and Palmer. Anchorage -The Anchorage load center consists of ML&P's and Chugach's service territories. ML&P serves the load of the residents and businesses in the central core of Anchorage. Chugach also serves residents and businesses in Anchorage along with the area south of Anchorage,the City of Seward,and into the southern portion of the Kenai Peninsula.For modeling purposes,the City of Seward's load and generation were placed in the Kenai Peninsula to allow economic commitment and dispatch in accordance with regional requirements. The MEA and Anchorage load centers are connected via two transmission lines.A 230-kV transmission line connects the Teeland substation to Chugach's Beluga plant in the western portion of the Anchorage load center.A 115-kV transmission line connects the Eklutna Hydro Project and runs through ML&P's area,continuing into Chugach's service territory.The current total transfer capability of these lines is assumed to be 250 MW when power is flowing north into MEA and 50 MW when power is flowing south into Anchorage. The Anchorage and Kenai load centers are connected via a 135-mile,115-kV transmission line, referred to as the "Southern Intertie,”which connects the Chugach system to that of the Kenai Peninsula.The current transfer capability of the Southern Intertie is assumed to be 75 MW when power is flowing north to Anchorage,and 60 MW when the flow is south into the Kenai. Kenai Peninsula -The Kenai Peninsula load center consists of HEA's and the SES service territories.The HEA service area includes the cities of Homer,Kenai and Soldotna. 4.3.Regional Electrical Load Requirements For development of the draft RIRP,current load data and forecasts of future loads were provided by the utilities in response to a data request.Since the draft RIRP Study has a 50-year planning horizon,load forecast data was extrapolated through 2060.The load forecast does not include incremental Demand Side Management/Energy Efficiency (DSM/EE)programs not inherently included in the utilities'forecasts. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 4-3 December 2014 yz ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Each utility provided load forecasts spanning different lengths of time that required extrapolation to develop annual peak and energy requirements for the regional electrical system over the 50- year study period.Typically,simple extrapolation of load forecasts is based on exponential growth by using the average annual percentage growth rate for the last 5 or 10 years.This potentially can lead to over-forecasting when these percentage growth rates are applied over long periods.To compensate for this potential over-forecasting,the load forecasts were extrapolated in two different ways and took the average of the two extrapolations as the forecast used in the draft RIRP. The first method of extrapolation was the typical approach of extrapolating at the average annual percentage load growth over the last 10 years. The second method extrapolated the average annual increase in load over the last 10 years.In addition to peak load forecasts,annual minimum load,or valley,forecasts were also developed for the regional system.The peak and valley demand and net energy for load requirements forecasts were developed at the time;it should be noted that demand and energy forecasts do not include estimates of transmission losses between utilities. The following load curves,Figure 4.3-1 and Figure 4.3-2 (Figure 9-6 from the draft RIRP) illustrates the base case scenario used to model the various future supply options and compare total system power costs under a wide variety of underlying assumptions.As indicated,even with DSM/EE reductions,existing resources are only sufficient to meet overall demands, including reserve requirements,until about the year 2029.Without these reductions new resources will be needed much sooner.As indicated,with DSM/EE reductions total capacity requirements,including a 30 percent reserve margin allowance,are estimated to be approximately 1,400 MW by the year 2060.This assumes that DSM measures are implemented to reduce demand over that time period.Without this level of DSM/EE load reductions,total capacity requirements would be about 130 MW higher. Again,this information is excerpted directly from the 2010 RIRP.Since the development of the RIRP,AEA has been working closely with the Railbelt utilities on further evaluation of future electrical load requirements and evaluating options for future generation system improvements. Since project sizing to match future load requirements is a critical factor for the Susitna-Watana Project feasibility study,utility system planning has been undertaken as a parallel effort to the feasibility study and the Federal Energy Regulatory Commission (FERC)licensing studies.As part of that effort,updated load and resource data was compiled for use in more specific system model studies to provide the most current and accurate information for use in future financial analyses and project sizing efforts.This work was carried out by Slater Consulting,under subcontract to MWH,and is described in Section 5. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 4-4 December 2014 wz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 18004 (MW)800 --e-tr-tr al alldTN |==DSM Adjusted Load -B-30%Reserves tr Existing and CommittedGeneration Capacity Source:RIRP,Figure 9-6 Figure 4.3-1.Scenario 1A:Capacity Requirements Including Committed Units with DSM/EE 1600+ 1200+ 10004 " ,}600 4004 2004 Ce a eeeeeeeeeeeeee|2011 2018 2025 2032 2039 2046 2053 2060 Year |-Load -@ 20%Reserves t=Existing and CommittedGeneration Capacity Source:RIRP,Figure 9-5 Figure 4.3-2.Scenario 1A:Capacity Requirements Including Committed Units without DSM/EE Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 4-5 December 2014 -z ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. The Susitna-Watana Project is a key resource that is factored into individual Railbelt utilities' expansion plans as a resource available to meet projected electrical loads starting about 2025.In conjunction with ongoing feasibility study work for the proposed project,additional regional transmission system stability and reliability modeling has also been conducted -by Electrical Power Systems Inc.(EPS)under subcontract to MWH.Results from all of these concurrent activities has provided input to project sizing studies,finalization of design concepts for major features,operational parameters for the project,and determination of how it will best integrate into the Railbelt electrical system. There are possibilities of increased loads in the Railbelt from large new industrial loads.A list of potential economic development projects compiled by the Alaska Industrial Development and Export Authority and included in the last RIRP is presented in Table 4.3-1 below. Table 4.3-1.Potential Economic Development Projects Potential Project Area Location Load (MW) Ore Processing Facility Anchorage 300 Internet Server Facility Anchorage 300 Coal Mine Anchorage 50 Subtotal -Anchorage Area 650 Gold Mine Interior 150 Mine Interior 200 Subtotal -Interior 350 Nitrogen/Urea Facility Kenai 50 TOTAL 1050 Other potential large loads could be from electric compressors for the proposed natural gas pipelines from the North Slope.Many of these compressors,however,would likely be remotely located.It appears conceivable that 1,000 MW of new load could potentially be developed in the Railbelt within the horizon of the previous RIRP study.Such new load would likely require specific policies to be implemented whether from fuel switching or large industrial loads. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 4-6 December 2014 Section 5 -yzw.ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 5.INTEGRATION INTO THE RAILBELT SYSTEM Electric system studies -and the PROMOD studies described herein -were performed utilizing regular consultation with the Railbelt utilities,to ensure that their input,guidance and comment was available to the team throughout the work.This consultation has been maintained by AEA throughout the course of the feasibility studies.Results of both the system modeling work and project interconnection studies are summarized below. 5.1.Electric System Studies Transmission studies were performed by Electric Power System Inc.(EPS)under subcontract to MWH during 2012 to identify possible transmission interconnections from the project site to the electrical transmission system of the Railbelt (after improvements expected to be implemented before the projected completion of the Susitna-Watana Project).The studies also assessed the system improvements to the Railbelt electrical system that may be required for effective operation of the Project,and any further system improvements necessary to accommodate the (then)largest proposed generating unit size of 200 MW. 5.2.Transmission Study Improvements Pre-Watana The Railbelt electrical system,to which the Project will connect to the Alaska Intertie - approximately midway between Anchorage and Fairbanks,currently consists of a single transmission line between Anchorage and Healy (with two lines between Healy and Fairbanks) as well as a single line between the Kenai Peninsula and Anchorage.The Railbelt utilities and the State of Alaska are in the process of evaluating transmission additions to provide for firm energy transfers and improved reliability of the Railbelt electrical system.These "pre-Watana” Railbelt system improvements are independent of the Susitna-Watana Project and would eliminate the single contingency conditions between the Railbelt load areas.The additional transmission facilities would provide for total coordination among all currently available electrical resources and those now in development. The Railbelt transmission system is expected to undergo substantial configuration changes from the present to 2024,and the system studies for the Susitna-Watana Project interconnection assume that those improvements necessary for the reliability of the Railbelt power supply will have been completed by 2024,and are therefore in service at the commencement of Susitna- Watana interconnection and operation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-1 December 2014 --yw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. The exact electrical and mechanical characteristics of the project generators were not known at the time of the model runs.Representative unit parameters were assumed from similar sized units selected by MWH. 5.3.Study Criteria The studies for the interconnection of the Project were completed using Railbelt electric system planning and reliability criteria that have been established among the utilities,and the loads and resources expected to be in place in the year 2024.The criteria included: «No instability following any transmission system fault; «No loss of load-following any single contingency; =No abnormal voltages during steady-state or following N-1 contingency;and, =No overloads of transmission lines or equipment during steady-state conditions. At the time the system studies were performed,the two sizes of unit that were being considered were 150 MW rated at average head,and 200 MW units rated at average head.These would have provided an output of approximately 200 MW and 272 MW,respectively,at maximum head.At the completion of the feasibility studies a recommended turbine unit size of 153 MW at a reservoir level of El.1950 ft.was selected -approximately equivalent to 206 MW turbine output at normal maximum operating level of 2050 ft.The conclusions of the system studies are not affected by the slight mismatch between the assumed ratings for the system studies and the ratings of the selected equipment. 5.4.System Study Methodology The "pre-Watana”transmission system expected to be in service by 2024 was the starting point for the Susitna-Watana Project electrical system studies. The Susitna-Watana studies can be divided into two distinct categories:(1)transmission system analysis required for the incorporation of the Project into the Railbelt electrical system;and (2)unit sizing studies designed to evaluate the system impacts resulting from two different unit sizes being evaluated for the Project. The transmission system studies evaluated the electrical transmission interconnections between the project site and the Railbelt system and the requirement of any transmission improvements outside the immediate project area. The unit sizing studies focused on the differences in transmission system improvement requirements between a 150 MW unit and a 200 MW unit. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-2 December 2014 -yZ ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The studies were completed utilizing the Railbelt utilities'PSS/e database for 2020 as the starting point.This database includes the utility improvements and changes the utilities are planning to their transmission and generation systems through 2020.The PSS/e 2020 database was modified to include all the pre-Watana improvements. The studies consisted of applying faults to transmission lines in the project area and suspected key transmission points in the Railbelt transmission system.The faults were applied and subsequently cleared by opening the faulted line section.The stability of the transmission system was then evaluated by plotting various generator rotor angles relative to each other and system frequency. To put the studies in context,the units on the Railbelt system are shown in Table 5.4-1. Table 5.4-1.Existing Generating Units on the Railbelt System,2014 (MW) Plant Unit #capatity Type Plant Unit #Capacity Type AURORA 1 24 Coal EKLUTNA 10 17 Gas-Oil BELUGA 1 18 Gas-Oil EKLUTLK 1 23 Hydro BELUGA 2 18 Gas-Oil EKLUTLK 2 23 Hydro BELUGA 3 67 Gas-Oil EVA CREEK (total)25 Wind BELUGA 5 65 Gas-Oil HEALY 1 27 Coal BELUGA 6 82 Gas-Oil HEALY 2 53 Coal BELUGA 7 82 Gas-Oil HEALY D 1 3 Gas-Oil BERNICE 2 19 Gas-Oil MLP1 3 29 Gas-Oil BERNICE 3 26 Gas-Oil MLP2 5 37 Gas-Oil BERNICE 4 26 Gas-Oil MLP2 7 82 Gas-Oil BRADLEY 1 63 §Hydro MLP2 8 88 Gas-Oil BRADLEY 2 63 §Hydro MLP2A 2x1 125 *Gas-Oil CHUGACH WIND (total)15 Wind NIKISKI 2 59 Gas-Oil COOPER 1 10 Hydro NP 1 63 Gas-Oil COOPER 2 10 Hydro NP 2 61 Gas-Oil DPP 6 26 Gas-Oil NPCC 3 63 Gas-Oil EKLUTNA 1 17 Gas-Oil SEWARD D 1 3 Gas-Oil EKLUTNA 2 17 Gas-Oil SEWARD D 2 3 Gas-Oil EKLUTNA 3 17 Gas-Oil SOLDOTNA 1 46 Gas-Oil EKLUTNA 4 17 Gas-Oil SOUTHAPP 3x1 188 #Gas-Oil EKLUTNA 5 17 Gas-Oil ZEHN IC 5 3 Gas-Oil Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-3 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Plant Unit #Capacity Type Plant Unit #Capacity Type EKLUTNA 6 17 Gas-Oil |ZEHNIC 6 3 Gas-Oil EKLUTNA 7 17 Gas-Oil |ZEHNDER 1 19 Gas-Oil EKLUTNA 8 17 Gas-Oil |ZEHNDER 2 20 Gas-Oil EKLUTNA 9 17 Total MW 1830 Notes: MLP2A unit 1 is a 2x1 combined cycle unit utilizing GE LM6000 CTs.The owners consider that this configuration exhibits equivalent risk to three 62.5 MW units. # SOUTHAPP unit 1 is a 3x1 combined cycle unit utilizing GE LM6000 CTs.The owners consider that this configuration exhibits equivalent risk to three 62.5 MW units. §The total output of the Bradley plant is limited to 117 MW. The unit sizing studies were dominated by simulating the loss of a Susitna-Watana unit on the Railbelt transmission system under various loading conditions.As can be seen from Table 5.4-1, both of the evaluated generator sizes are considerably larger than units that will exist in the Railbelt in the 2020 timeframe.Larger units will put strain on the Railbelt system if tripped under full load and mitigating measures will be required.These studies were intended to evaluate the incremental costs of the mitigating measures of the potential unit sizes for Susitna- Watana. The studies attempted to determine the mitigating measures that would be required to limit the loss of load in the Railbelt system to its first stage of load shedding following the loss of a Susitna-Watana unit,similar to the conditions that exist prior to construction of the project. 5.5.Results The system studies indicate that the Project can be integrated into the planned infrastructure with few improvements required to the Alaska Intertie (1.e.,outside the immediate project area).For transmittal of the power from the Project to the Alaska Intertie,the Project will need to include either: 1.Three 230-kV transmission lines from the Project to the Alaska Intertie and a modest Static VAR Compensator (SVC)located at the point of interconnection;or possibly, 2.Two transmission lines and a much larger SVC at the interconnection location. The sizes of the proposed Susitna-Watana units (whether 150 or 200 MW)are larger capacity than any generator in the Railbelt system.The modeling indicates that these unit sizes will need to be mitigated by some storage technology.The location of the battery energy storage system (BESS)could be the same as that already planned for the system. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-4 December 2014 -yZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO E AEA11-022 NGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. These devices will prevent any excessive load shedding in the Railbelt system following the loss of one of the Susitna-Watana units at peak load,and allow complete coordination of the Project with the existing and planned generation resources in the Railbelt. The size of the BESS is determined by the loss of the largest Susitna-Watana unit during the minimum load period of the Railbelt.In simulations,the boundary condition of the system model was determined by forcing unequal loading of the Susitna-Watana units.The total Railbelt load during minimum load periods does not require the full use of the plant capacity. Therefore,for modeling of the worst possible operating conditions,the units must be operated with unequal loading to produce the worst-case condition of the loss of a Susitna-Watana unit at full capacity. Operational agreements could reduce the requirement for energy storage,particularly because hydro units are much more responsive than thermal units.Multiple hydro units in a plant are usually run,in parallel,at part load so that in the event of a trip of one unit,the other unit ramps up quickly to "take over”generation.This is more readily achieved if the units are slightly oversized,and such operation would reduce the required contingency,and the corresponding size of the BESS required for the system. The initial comparison indicated: *For 3 x 200 MW units at Susitna-Watana -The system would require approximately 180 MW of stored energy devices to limit load shedding to Stage 1 in the Railbelt system during the extreme case of a unit operating at its maximum capability at high reservoir levels during the lightest load condition of the Railbelt.The system requires 150 MW of storage for the loss of a 200 MW unit operating during the summer peak load periods. This is a small increase in compensation requirements over the 150 MW units and does not appear to present any significant challenges or system issues. =For 4 x 150 MW units at Susitna-Watana -The system would require 120 MW of storage devices during the summer minimum load periods to mitigate the loss of a unit that is operating at 150 MW maximum capability,but only a 20 MW storage device would be required during the typical summer loading periods. 5.6.Future Studies Study results indicated that the 150 MW generating units would require less extra infrastructure (SVCs,storage,etc.)-than the larger 200 MW units -to maintain stability throughout the Railbelt system.However,it was concluded that the incremental increase in cost for the infrastructure associated with the larger 200 MW units is less than two percent of total project Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-5 December 2014 -yz ALASKA ENERGY AUTHORITY .AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. cost and the differences between the two unit sizes do not present any large cost increases with respect to the system costs or system implementation issues.The cost comparisons for the construction of the power facilities for each of the two sizes of unit are recorded in Section 7. The studies reported herein used a wide range of possible energy transfers for the Northern and Southern utilities to evaluate the electrical transmission system.Future studies will need to factor in the actual proposed energy split between the Northern and Southern systems based on the maximum expected capacity of each respective system and the transmission requirements of the final configured energy flow.Those studies would help confirm whether any transient aids are required for either transmission line faults or unit trips and provide acceptable reliability and service characteristics for the utilities. Future studies will also identify the proposed sizing and location of the storage devices to be implemented on the Railbelt as well as refine the system studies once more information is known regarding the actual Susitna-Watana generating unit characteristics.Future studies should also provide a more detailed analysis of the system response to an expanded list of transmission contingencies,including breaker-fail and N-1-1 contingency analysis. The future studies will also need to analyze the response of the Railbelt system units,such as Bradley Lake,to the proposed Susitna-Watana Project in addition to the response of the project to the interconnected system. 5.7.Project Operation and Resource Integration 5.7.1.Basis of Studies Although previous production modeling of generation available to the interconnected system had been undertaken during the preparation of the draft Integrated Resource Plan ,the modeling had not considered the detailed performance capabilities of Susitna-Watana,or the various flow constraints that might be in effect.Therefore it was determined that further detailed production modeling needed to be performed in support of project feasibility studies,using current forecasts of Railbelt loads,fuel costs and including Watana hydrology.This update of production modeling reflects the proposed configuration for the Susitna-Watana Project and other Railbelt system facilities to assist in the conceptual design of the Project and its integration into the Railbelt system at its expected on-line date,which for the purposes of the calculations was assumed to be 2024.The updated system production modeling has been performed by Slater Consulting under subcontract to MWH,using PROMOD IV modeling software.The software simulates electric system and markets incorporating extensive details of generating unit operating characteristics,transmission grid topology and constraints,and market system operations to support economic transmission system dispatch and project planning. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-6 December 2014 -zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO E AEA11-022 NGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. The production modeling assumes centralized dispatch of generation on the Railbelt system, which will require -if enacted -mechanisms for payment between utilities,and agreed provisions among utilities for recognition of the financial burden for retired and unused thermal units. An indication of the economic optimized use of the Susitna-Watana Project was needed to determine parameters including,but not limited to: «Size of the generating units; «Extent of generation change;and, =Power ramping rates and resulting flow releases. Meetings were held with the various Railbelt utilities to verify and update the various input data needed for PROMOD runs,including: "Load forecasts; «Existing generating plants and units; »Planned unit additions and retirements; #Fuel prices; «Operations and Maintenance (O&M)costs; =Unit availability and maintenance requirements;and, «Relevant aspects of the present and projected transmission system. Data were obtained from the utilities using questionnaires,group meetings,telephone calls,and individual face-to-face meetings.Where appropriate,aggregate data for all utilities were collected.AEA provided the fuel cost forecasts used in the model.Publicly available data,(as found in regulatory filings,reports,websites,etc.)were used as a secondary source and for cross- checking.To maintain the required schedule for analysis,it was often necessary to commence model runs using assumed data that was improved after the utilities viewed interim results and provided their comments. Modeling runs were conducted in 2012,2013,and early 2014,increasing in sophistication as more and better data emerged.After the initial financial modeling of the project by AEA financial consultants,a final PROMOD run was performed in December 2014 using a key financial scenario. Elements that have been considered in the model input data are recorded in the following sections. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-7 December 2014 -z ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 5.7.2.|Plant and System Operation Requirements Discussions with utilities in 2012 indicated that in recent years the Railbelt utilities overall have experienced negative load growth and were forecasting very low growth over the period through 2024.The utilities indicated that they suspect the drop in load has resulted from electricity conservation efforts that could well have been price induced,and predicted that by 2024,the Railbelt peak load would be less than two percent above 2012 levels. Compared to systems throughout the Lower 48,the Railbelt system is relatively small,and therefore,the present thermal generating units lack the necessary size to achieve the economies of scale available to most of the industry in the rest of the continental United States.As discussed elsewhere,system security and reliability requirements favor the use of relatively small generating units,compared to the Lower 48. The age of much of the existing thermal generation is such that modern similarly sized units would provide greater efficiency and reliability.Therefore,it is not surprising that various utilities have committed to acquiring more modern plant with better heat rates and higher availability.The units displaced from the daily dispatch by new generation will be relegated to "standby”status.Some will be retired,but a comprehensive planned "retirement schedule”was not available from any utility,and -it is understood -is not currently in place for the region. The utilities'near-term plans for additions and retirements of generating capacity include a significant addition of combined cycle capacity and large modern gas-fired diesel units,coupled with the retirement of older inefficient combustion turbine units. The three existing hydro plants (Bradley Lake,Cooper Lake,and Eklutna)clearly perform a valuable role in reducing the peak demands needed to be served by the thermal units.This role in the reduction in peak demand by the hydro projects also allows some of the older combustion turbine units to avoid costly startups for small amounts of energy production at the peak.This improves overall generation efficiency by permitting the use of more combined cycle capacity with vastly superior heat rates.Because of these drivers,simple cycle combustion turbines will, in the future,populate the ranks of "standby”units. Because it will have the lowest operating cost and the highest reliability among the generation sources,the addition of further substantial hydro capacity to the system by the construction of the Susitna-Watana Project will reduce the need for gas and oil fired generation,even from combined cycle units. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-8 December 2014 Za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 5.7.3.|General Power Plant and Railbelt System Criteria The utilities'stated objectives are to provide a high reliability electricity supply to their customers at the lowest reasonable cost,in keeping with existing and future environmental concerns.At all times,the Railbelt utilities must have sufficient generating capacity available to service their customer loads and to provide their individual share of the system's required operating reserves.Of course,each generating unit needs to undergo regular maintenance if it is to remain useful.Currently,to provide for these requirements,the utilities have a target reserve margin of 30 percent.That is,installed generating capacity equal to 130 percent of annual peak load.This does not include units that have been placed in a preservation or "mothballed”state. In examining the potential impact of 200 MW generating units at Susitna-Watana,attention will need to be given to the suitability of the current agreed reliability criteria.It should be noted that,although they would be the largest units on the system,modern hydro experience shows that the Susitna-Watana Project units will have significantly more reliable generation than all others on the Railbelt system (national statistics indicate that hydro exhibits half the number of forced outages compared to thermal units). The 2012 PROMOD dispatch analysis did not provide any insights into the continued suitability of the 30 percent reserve margin criterion as the actual reserve margins included in model runs, both with and without the Susitna-Watana Project,greatly exceeded the 30 percent target,and no reliability issues appeared.Because construction of the Susitna-Watana Project may hasten the retirement of older generating plant and because of the larger size of combined cycle units and the project units,it is suggested that specific reliability studies be included in the future PROMOD analyses,to check the advisability of retaining or modifying this 30 percent planned reserve margin within the Railbelt system. 5.7.4.Operating Security Criteria It is generally accepted that,in an isolated system,unforeseen events such as the sudden loss of a generator,or transmission line,can result in significant customer supply interruptions if provisions are not made.It is important that restoration of supply be carried out swiftly.To facilitate this restoration,the current operating criteria for the Railbelt system require that the system carry spinning reserve equal to 100 percent of the capacity of the largest unit on line,and additional operating reserve capacity (such as quick-start reserve or further spinning reserve) equal to 50 percent of that largest unit capacity.Addition of the project's large hydro units raises challenges concerning the application of these operating security criteria,and/or system adjustments to maintain reliability.These questions are addressed in Section 11. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-9 December 2014 -yz ALASKA ENERGY AUTHORITY . AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. At the time the data for the 2012 model runs were assembled,plans to improve the Railbelt transmission system,irrespective of the building of the project,had not been fully investigated. Furthermore,options being studied for connection of the Susitna-Watana Project to the existing system using either one transmission corridor or two (i.e,two different points of interconnection). In developing the Railbelt databases,provision was made to represent a variety of operating reserve and system security arrangements,as well as model transmission flow restrictions.In the series of model runs examining the economic impact of the Project,the spinning reserve requirement of 100 percent of the largest unit on line and the additional operating reserve requirement of 50 percent of that largest unit were used.In the model,the representation of transmission flow restrictions was set to describe a transmission system in which flow restrictions did not constrain the economic operation.These same conditions were preserved in the runs that were made to develop a full 8,760-hour representation of the operation of the Susitna-Watana Project for the 2024 calendar year. As discussed later,impacts of recommended transmission changes and system configurations on the economic operation of the system were included in the PROMOD input data for the 2013- 2014 model runs.When firm transmission proposals for the pre-Watana upgrades and the incorporation of the Susitna-Watana Project are available or accepted,any attendant power flow restrictions or additional operating criteria could be examined in future system modeling. 5.7.5.Plant Operation and Maintenance As noted,each generating plant and unit that is available to serve system load has to be regularly maintained and worn parts replaced.Generating plant has to be protected from the elements with appropriate housing,which has to be maintained.When needed in service,most units require some operating personnel,and in-service units need to be supervised.The costs involved in these activities are known as non-fuel O&M costs. O&M costs are important items in the planning of new generating capacity.For operating purposes,the total O&M costs are divided into Fixed O&M and Variable O&M costs.Fixed O&M costs are used to keep a generating unit ready to operate and serve load.Variable O&M costs result from the use of that unit to serve load,and are important to the commitment and dispatch of the unit.Utilities often divide the Variable O&M into up to three separate cost items, $per start,$/hour on line and $/MWh.Historical O&M information was compiled from available data by the modelers for use in the Railbelt model,and then checked and/or modified by the utilities before the final runs.The data were specific to each unit and varied significantly according to the technology,size and age of the particular unit concerned.In 2012 dollars,Fixed O&M costs varied from about $7,000 to $8,000/month for small diesels to over $400,000/month Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-10 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. for combined cycle and coal-fired units.Start-up O&M ranged from around $1,000/start for smaller combustion turbines to around $5,000/start for combined cycle units.Must-run units did not have any start-up O&M,as it would have no bearing on their commitment.$/MWh Variable O&M costs ranged from about $1.30/MWh for older combustion turbines to around $12/MWh for diesels.The Railbelt utilities do not appear to separate $/hr.O&M costs from $/MWh costs. 5.7.6.|Economic Operation The economic operation of a utility is generally carried out in three sequential processes: «First,there is a process of production planning whereby the utility schedules maintenance,makes contract purchases and arranges fuel supplies,with the objective of having sufficient operating capacity at all times to satisfy its customer loads and provide its share of appropriate reserve capacity. =The second process is unit commitment whereby the utility arranges to have in-service sufficient capacity to serve its current load and provide its share of spinning reserve,and to have readily available any additional capacity needed to fulfill operating reserve and regulation requirements. «The final process is the dispatch or loading of the in-service capacity to provide,at all times,the exact amount of electricity being consumed by the customers.This process makes use of Automatic Generation Control apparatus,supervised by 24/7 system operating staff. These three sequential processes are organized and programmed to minimize the variable production costs of the utility (that is fuel,Variable O&M,and purchases from other utilities, less sales to other utilities). The addition of resources at the Susitna-Watana project capable of generating up to (approximately)600 MW to serve the total Railbelt system -together with sufficient transmission to incorporate it into that system -will almost certainly result in a re-evaluation of commitment and dispatch practices throughout the Railbelt system.As the maximum benefit from the Project would be realized through a centralized commitment and dispatch process,the modeling work carried out thus far has included the simulation of a centralized dispatch of the Railbelt system,using the average water availability under the postulated river flow rules -with the objective of minimizing total variable production costs. 5.7.7.Modeling Exercise and Results The PROMOD software was initially used to model production of power on the Railbelt system in 2024 with,and without,the construction of the Susitna-Watana Project,based on the system Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-11 December 2014 -yw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. characteristics represented in the model data,which had been gathered from the utilities and a variety of other sources. In the "Without Susitna-Watana”case,the Railbelt system was modeled as an isolated multi- area,multi-company system,centrally dispatched,with sufficient transmission so that flow restrictions would not constrain the economic operation.The "With Susitna-Watana”case modeled that same system with the addition of the Susitna-Watana Project and any associated transmission for its interconnection to the Railbelt system.Initial calibration model runs showed that under average water conditions,the project's operation could save nearly $220 million per year in overall Railbelt variable production costs.This figure does not include savings accruable to the overall transmission improvements discussed elsewhere. After the first runs were made and the model was calibrated,the model was refined to simulate system operation with and without the Project in future years 2024 (1.¢.,the then expected first year of Susitna-Watana operation),2034,and 2044.Economic evaluations were then performed against the required debt service and fixed costs for the Project,so that the contributions to system economics could be validated through an extended study period. To prepare for this modeling,the data that had been included in the model for each utility were provided to that utility for checking of its accuracy.At subsequent face-to-face meetings,utility representatives verified/corrected the data including load forecasts,existing generating plants and units,planned additions and retirements,historic fuel prices,O&M costs,availability,and maintenance requirements.As corrected,the overall Railbelt Utility System was still modeled as an isolated multi-area,multi-company system,centrally dispatched.Because of the significance of future gas prices to the economic value of the Project,AEA provided a set of scenarios of future gas prices to be used in this analysis.MWH/Slater Consulting contributed a further gas price scenario and coal and oil price forecasts were provided by Slater Consulting. Railbelt production cost savings due to addition of the Susitna-Watana Project were determined for years 2024,2034,and 2044 for each gas price scenario. The 2012 model studies were intended to establish a basic measure of Railbelt production cost savings due to the project's hydro generation,and to compare different proposed generating unit configurations.The 2012 model was used to examine the impacts of:(i)four units of about 150 MW each;and,(ii)three units of about 200 MW each. In addition,the utilities'planned generating resources were examined to determine what possibilities existed for savings in capital costs and fixed costs associated with these resources. The 2012 modeling studies are summarized below. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-12 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO FE AEA11-022 NGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Load Projections -The Railbelt load has very little projected growth through 2024,and projected low growth from 2024 onward.Table 5.7-1 below shows the regional capacity and energy load growth projections through the year 2044 -provided by the utilities during discussions with them in 2012. Table 5.7-1.Railbelt Demand and Energy Forecasts Year Peak Demand Annual Energy MW GWh 2014 805 5149.2 2024 830 5287.2 2034 858 5432.7 2044 888 5620.1 Unit Retirements -The utilities'current commitment to new plant is essentially the acquisition of more efficient plant to operate in base load -to displace older less efficient thermal generating equipment -rather than expanding generation to serve new load.The more useful pieces of the older plant,not required for active generation or reserves,are to be retained as "standby” capacity.Plant clearly at the end of its useful life would be candidates for retirement.If the project is constructed,utilities will have the opportunity to retire older,less efficient "standby” plant without compromising the reliability of the Railbelt system. Susitna-Watana Power Output and Unit Sizing -The projected generation of the project was used without system generation downtime to predict the hourly generation through a full year (8,760 hours).By this means,the required unit output and the corresponding reservoir elevation have been determined to more fully define the required unit rating and rated head.The comparison between 3 x 200 MW and 4 x 150 MW units at the Susitna-Watana Project did not indicate any conclusive system production cost advantage for either arrangement.(Note, although not modeled,the current proposed arrangement includes 3 x 150 MW.) System Cost Savings -Modeling results show that there are potential retirements of "standby” plant if the project is built.The accompanying savings in fixed operating costs would be $16,500,000 in 2024,$18,300,000 in 2034,and $23,100,000 in 2044.The PROMOD runs with and without the project show that the inclusion of the Susitna-Watana Project in the system will result in a significant reduction in the use of gas and oil by the Railbelt utilities,and a large decline in the use of what is now (thermal)peaking plant.Table 5.7-2 below indicates the future make-up of Railbelt energy sources in the year 2024,both with and without the Susitna-Watana Project.The reduction in gas and oil consumption is largely responsible for the reduction of variable operating costs on the Railbelt system.Even in the initial years of Susitna-Watana Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-13 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT operation,those reductions are comparable with the annual fixed costs of having and operating the Project.Annual fixed costs consist of debt service and fixed O&M. Table 5.7-2.Railbelt Electrical Energy Sources in 2024 Annual Energy Contribution (GWh) Energy Source Without Project With Project Coal 811.3 811.3 Gas and Oil 3768.8 1080.4 Wind 126.3 126.3 Hydro 580.8 3269.2 Total 5287.2 5287.2 As this computation of variable cost savings was carried out for each of the three years for each of five gas price scenarios,the results are best viewed in tabular form,as presented below in Table 5.7-3 below. Table 5.7-3.Variable Cost Savings Due to Susitna-Watana Project (2012 prices escalated) Natural Gas Price Scenario ($million) Year $62 $83 /$10'/$125)|$6.505/MCF"MCF MCF MCF MCF 2024 236.8 299.2 366.2 436.4 283.7 2034 323.8 439.0 §25.2 596.7 480.3 2044 436.1 567.7 687.4 817.2 626.5 Notes: 1.MCF -one-thousand cubic feet 2.$6 -2012 gas price in Anchorage area is $6/MCF,escalation is 2.75 percent 3.$8 -2012 gas price in Anchorage area is $8/MCF,escalation is 2.75 percent 4,$10 -2012 gas price in Anchorage area is $10/MCF,escalation is 2.75 percent 5.$12-2012 gas price in Anchorage area is $12/MCF,escalation is 2.75 percent 6.$6.50 -2012 gas price in Anchorage area is $6.5/MCF,escalation is 4 percent Total annual net savings to the system will depend on the ultimate cost to develop the Susitna- Watana Project,as well as the future price of natural gas.When the Susitna-Watana Project production cost savings,together with fixed cost savings -because of standby plant retirements -are combined with the annual project fixed costs (including project debt service),the result is the impact on system operating costs of building the project.Figure 5.7-1 shows this overall impact (in nominal $)for each year for each gas price scenario. Alaska Energy Authority December 2014 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 5-14 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 400,000 300,000 LO 200,000 oS -$6S100,000 a °:ee a/) b ---$10a0 = Refer to notes<A =: me $6.50 100,000 a a for Table 5.7-3.ao 200,000 - 300,000 2024 2034 2044 Figure 5.7-1.Overall Impact of Susitna-Watana Project on Railbelt Annual Generation Costs The overall Railbelt PROMOD model is structured so that it can be used for a variety of future studies by AEA and the utilities involving the economic,operational and reliability impacts of the Susitna-Watana Project in whatever configuration is considered.Each analysis would be carried out by comparing the PROMOD simulations of the Railbelt system both with and without the item or feature of interest,over the years of concern. 5.7.8.2013 Modeling and Analysis During late 2012 and through the middle of 2013,Slater Consulting performed further modeling and analysis encompassing the proposed Railbelt transmission improvements -under contractual arrangements separate from those for assistance in the Susitna-Watana project feasibility. Results were,however,provided (as appropriate)to MWH for inclusion in this report,in the context that the system improvements will be required to fully utilize the power potential of the Susitna-Watana Project within the improved,interconnected system. These proposed system improvements were developed and analyzed by EPS.Slater Consulting used PROMOD on this assignment and worked with EPS and Chugach Electric Association (Chugach)and the other utilities.The purpose of the studies was to investigate the savings in Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-15 December 2014 -yw ALASKA ENERGY AUTHORITY| AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. power production costs that could be achieved for the Railbelt utilities through the implementation of transmission improvements,both individually and collectively. The transmission studies began with the database developed in the 2012 Susitna-Watana studies, and through the course of the analysis,anomalies and further data was identified to enable some corrections and improvements to be made to the modeling of the utilities'physical plant,and to their modeled operating procedures. The transmission improvements were more appropriately analyzed using the PROMOD IV solution algorithm -best suited for line-by-line transmission studies.Thus the 2012 study data was reconfigured to run in HMC-TAM (hourly Monte Carlo-transmission analysis mode),and paired with appropriate transmission load flow data. As mentioned above,the work on the transmission studies provided enhanced insights into Railbelt data and operations,and this information was captured for insertion into the Susitna- Watana PROMOD data to ensure that the transmission studies and the ongoing Susitna-Watana studies were compatible. Overall Railbelt system transmission improvements are divorced from the development of Susitna-Watana,and therefore,the transmission studies were conducted for the pre-Watana period.For use in the ongoing Susitna-Watana studies,the data with all of its improvements was extended through 2044 to match the timeframe of the data used in the 2012 Susitna-Watana analyses. The final database including all recommended transmission improvements derived from the transmission studies became the "without Watana”database for the 2013 Susitna-Watana analyses.At this point the modelers had updated compatible data for running PROMOD studies in both the Analytical Probabilistic Dispatch (APD)mode and the HMC-TAM mode for the years 2024,2034 and 2044.The APD was used for optimizing the month-by-month water releases and the HMC-TAM for hour-by-hour dispatch within the month and presentation of the hour-by-hour water releases.For improved accuracy,the modelers also developed a procedure to use the monthly water releases from an initial run to obtain monthly average Watana reservoir elevations to utilize in a second final run. In early August 2013,there was another set of "face-to-face”meetings with the individual utilities -this time in connection with the transmission studies.During these meetings,some information was gathered allowing further corrections to model data,together with greater insight into how the utilities wished to operate their generation.This information was added to the data sets for Susitna-Watana analyses. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-16 December 2014 -yzZ ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. To explore the long-term continuing benefits available from the Susitna-Watana Project,one of the tasks performed in 2013 was the extension of the PROMOD analysis through 2054.This extension of the task captured the development of all Railbelt generation that would have been implemented under a planning scenario that assumed that Susitna-Watana generation was a possibility.Likely unit retirements and -in the "without Watana”case -appropriate generation additions were developed through 2054.It is very important to note again that,it was assumed that beyond 2020,the Railbelt pool would be dispatched as a single system and that over time each utilities'generation planning would reflect this manner of operation. While the 2013 work was being performed,questions arose concerning the hour-to-hour variations in Susitna-Watana discharge and the consequences of seeking to control these variations.For this reason,the 2013 analyses included a change from hour-by-hour typical week per month dispatch to hour-by-hour weekly dispatch for 53 weeks per year,necessary so that all hours of the year were separately modeled. 5.7.9.Forecast Data and Results for 2013 Analyses 5.7.9.1 Loads During the transmission studies performed in 2013,the utilities provided further (and updates) details of their own near term load forecasts and long term prospects.To reflect their updated projections,changes were made to the overall utility-by-utility load forecast (previously shown in Table 5.7-1).As demonstrated in Table 5.7-4,forecasts are now for near term increases in total Railbelt load but with a low overall long-term growth trend. Table 5.7-4.Railbelt Demand and Energy Forecasts -2013 Year Peak emend Annu energy 2014 805 5149.2 2024 874 5673.7 2034 899 5780.3 2044 916 5904.8 2054 930 5975.5 5.7.9.2 Capacity Additions and Retirements Given the lack of retirement schedules for plant in the Railbelt system,the development of the updated forecast of future generating capacity retirements and additions can be viewed within three timeframes.The near term,through 2024,was provided entirely by the utilities and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-17 December 2014 -zZ .ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. consisted of selected retirements of older plant and the completion of planned,more efficient new combined cycle plant and modern larger diesel generation. The mid-term,2025 through about 2038,was a combination of utility scheduled retirements and a nominal retirement at age 65 for units without retirement dates.No additions were scheduled or necessary to maintain planning reserves either with or without the completion of Susitna- Watana. The long term 2038 through 2054 was beyond the planning horizon of any of the utilities.All of the remaining pre-1990 combustion turbine equipment was retired at age 65.In the "without Watana”case,about 366 MW of new generation was added in the form of Combined Cycle equipment and large gas-fired diesels,similar equipment to that being added to the system at this time.This new capacity was added to follow utility plans,to provide sufficient base load capacity to produce the required energy at a reasonable cost,and to provide reasonable generating capacity reliability.In the "with Watana”case,capacity reserve margin,reliability and base load energy supply appeared satisfactory without the addition of additional capacity. Table 5.7-5.Future Generating Plant Reserves with and without Susitna-Watana Project -2013 Forecast Peak Load Railbelt Capacity ReservesYearMWMW% Without Susitna-Watana Project 2024 874 1822 108 2034 899 1526 70 2044 916 1335 46 2054 930 1310 41 With Susitna-Watana Project 2024 874 2462 182 2034 899 2166 141 2044 916 1610 76 2054 930 1584 70 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-18 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Table 5.7-6.Future Generating Plant with and without Susitna-Watana Project -2013 Forecast Coal and Diesel and Year Combined Combustion Hydro Total Cycle Turbine MW MW MW MW Without Susitna-Watana Project 2024 590.5 1049.2 182.2 1822 2034 539.5 804.6 182.2 1526 2044 822.7 330.0 182.2 1335 2054 822.7 304.5 182.2 1310 With Susitna-Watana Project 2024 590.5 1049.2 782.2 2422 2034 539.5 804.6 182.2 2126 2044 539.5 247.8 782.2 1570 2054 539.5 222.3 782.2 1544 5.7.9.3 Fuel Prices The fuel price estimates used in the 2013 analyses were developed from present prices,known changes (for example gas pricing recently approved by the Alaska Regulatory Commission for 2018+),and escalation forecasts taken from the preliminary projections prepared for the Federal DOE's Energy Information Administration's 2014 Annual Energy Outlook. Because natural gas is the major fuel displaced by the Susitna-Watana generation,the natural gas future price is the major determinant of the extent of the production cost savings resulting from the inclusion of the Susitna-Watana Project in the system.The updating of the natural gas price scenario developed for the later evaluations results in prices considerably different from those used in the 2012 evaluations,and plays a significant role in the scale of the Susitna-Watana benefits identified in the 2013 evaluations. Table 5.7-7 below compares the 2013 natural gas price scenario with the five scenarios used in the 2012 evaluations. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-19 December 2014 -qN- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO E AEA11-022 NGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Table 5.7-7.Comparison of Natural Gas Supplies (USS -nominal)for Scenarios Studied in 2012 2013 Forecast 2012 Scenarios Year Scenario 0 Scenario 12 |Scenario 23 |Scenario 34 |Scenario 45 Scenario 5° 9c/mmBTU!in clmm BTU |cimmBTU |clmmBTU |cimmBTU cimm BTU 2024 1171.5 831 1108 1385 1662 1041 2034 1741.7 4.05 1090 1453 1816 2180 1540 2044 3002.9 5.60 1429 1906 2382 2859 2280 2054 4887.3 4.99 1875 2500 3125 3750 3375 Notes: 1.c/mmBTU -cents per million British Thermal Units 2.2012 Anchorage NG price $6/mmBTU escalating at 2.75%/yr. 3.2012 Anchorage NG price $8/mmBTU escalating at 2.75%/yr. 4.2012 Anchorage NG price $10/mmBTU escalating at 2.75%/yr. 5.2012 Anchorage NG price $12/mmBTU escalating at 2.75%/yr. 6.2012 Anchorage NG price $6.50/mmBTU escalating at 4%/yr. 5.7.9.4 Fixed Costs In the financial analysis performed in 2012,AEA used an escalation rate of 2.75 percent/yr.for capital costs and O&M costs.This escalation rate was applied to the existing estimates of O&M costs provided by the utilities to produce the long-term projections included in the PROMOD data.For the purposes of this analysis,and in the absence of a final finance plan,the assumptions of the MWH model -which also used this same escalation rate -were included in the fixed costs.That model assumed a fixed annual debt service based on an interest rate of 5.5 percent (which is conservative),and a bond term of 30 years,as well as the accumulation of a debt reserve fund.No Alaska state equity investment was assumed. 5.7.9.5 Results of 2013 Analyses Because the 2013 analyses did not include the estimation of the capital costs for new thermal generation required for the "without Watana”case beginning in about 2042,the results presented below in Table 5.7-8 show conservative estimates of overall savings in the 2044 and 2054 study years based on the 2013 natural gas price scenario (Scenario 0 above). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-20 December 2014 SUSITNA-WATANA HYDRO -yzZ Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 5.7-8.Total Annual System Production Cost Impact of Susitna-Watana Project (USS million-nominal) Year increase in Fixed Costs Decrease in Variable Costs Net Saving in Total CostsDuetoSusitna-Watana Due to Susitna-Watana Due to Susitna-Watana 2024 461.1 295.5 -165.6 2034 468.0 484.0 16.0 2044 <457.8 636.8 >179.0 2054 <24.8 1,031.5 >1,006.7 Despite the absence of the capital cost savings,the prospect of production cost savings in excess of $1 billion per year beyond 2050 is compelling. 5.7.10.Updated Analysis 2014 Additional PROMOD runs were performed to update the production modeling analysis with the revised construction cost compiled in July 2014,financing terms,unit sizes and the outlook on future gas prices. The key details of the financing plan used in the updated analysis (AEA Financing Plan 3)are shown in Table 5.7-9, Table 5.7-9.AEA Financing Plan 3 2010-2018 Licensing and Engineering Costs Initially Paid by State,converted to a loan in 2023 AEA Revenue Bond financing backed by Power SalesDescriptionContractswithStateMoralObligation Issuance Dates 2019-023 2019-2023 Assumed Rating High A,Low AAConstructionCosts :Interest Cost Assumption 5% Financing Term 2047 for debt,2085 for State loan for L&D costs Interest Cost During Construction Capitalized Description Rural Utilities Service (RUS)loans Issuance Dates 2024-2027 Assumed Rating Not-Rated eee Construction Interest Cost Assumption 4% Financing Term 2059 RUS Yes Interest Cost During Construction Capitalized Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 5-21 Alaska Energy Authority December 2014 | wz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 2010-2018 Licensing and Engineering Costs Initially Paid by State,converted to a loan in 2023 Description Long-term construction financing refinanced Refinancing Issuance Dates 2047 Assumed Rating High A,Low AA Interest Cost Assumption 5% Financing Term 2077 Term in Which Debt is Paid 2028-2085 Overall TIC 4.015% Total Unreimbursed State Contribution $0 State Cash Outlay Amounts Pre-Construction:$550 million State Cash Repayment Amounts Pre-Construction:$550 million Unreimbursed State Contribution Zero The analysis was run with the following inputs -reflecting the design presented in the feasibility report: «The forecast of future electricity demands was unchanged. «The projected plant retirements and additions (in the "without Watana”case)were unchanged. *The Susitna-Watana plant would be operating in 2028,but capital repayment would not *JATURAL commence until 2029.Therefore the years to be modeled were 2029,2039,2049 and GAS -2059. BASE «The Susitna-Watana plant would operate over a headwater range of El.1850 ft.minimum AK LNG to El.2050 ft.maximum,and would include three generating units with nominal ratings PRICES -_>of 106 MW at reservoir El.1850 ft.,153 MW at El.1950 ft.and 206 MW at El.2050 ft. FORECAST 1-M 14 The future price of Anchorage area natural gas would be 1,459 c/mmBTU in 2029 (nominal cents),rising to 2,379 c/mmBTU in 2039 (nominal cents),3,278 c/nmmBTU in 2049 (nominal cents)and 4,361 c/mmBTU in 2059 (nominal cents). Between the 2013 and 2014 analyses,and independent of the feasibility study for Susitna- Watana,Slater Consulting had continued work on Railbelt transmission additions and pooling of operations.During this assignment,several refinements were made to the PROMOD databases being used,which were transferred to the "with”and "without Watana”databases used in this analysis.The data refinements were minor in scope,and included the following: *Actual operating characteristics (minimum capacity,heat rate,maintenance requirements and variable O&M costs)for the Eklutna Generation Station units. Alaska Energy Authority December 2014 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 5-22 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. «A heat rate adjustment for SPP,from actual performance,which was also carried over to the MLP2A CC unit. «=MLP2A maintenance requirements were reduced. =MLP2 unit 5 retirement date was confirmed. With these changes,the December 2014 production analyses were performed in the same way as the 2013 analyses for the years 2029,2039,2049 and 2059.Table 5.7-10 shows the results of this work.As in Table 5.7-8 above,the saving in fixed costs associated with capital cost recovery for the additional generating plant needed by the system in the "without Watana”case have not been evaluated.This results in the inequalities in the Table 5.7-10. In addition,because the financial plan for Susitna-Watana used in this analysis (AEA Financing Plan 3)took longer to pay down the capital cost of Susitna-Watana than the financing plan incorporated in the 2013 analysis (results shown in Table 5.7-8),the net savings does not increase as quickly as in the 2013 analysis.Therefore,the modeled results for the years 2029- 2059 have been extrapolated,(conservatively)to the years 2069 and 2079,to reach a point where the construction cost has been repaid as shown in Table 5.7-10,and net savings accrues faster. Table 5.7-10 Total System Production Cost Impact of Susitna-Watana Project (USS million-nominal) Increase in Fixed Costs Decrease in Variable Net Saving in Total CostsYearosts Due to Susitna-Watana Due to Susitna-Watana Due to Susitna-Watana 2029 629.1 394.0 -235.14 2039 638.6 687.8 49.2 2049 <515.4 781.9 >266.5 2059 <523.8 1042.3 >518.5 2069*<292 1400 >1108 2079"<91 1870 >1779 Note:The results for 2069 &2079 are not the result of production modeling analysis,but instead have been conservatively extrapolated from the 2029 -2059 modeling analysis results. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 5-23 December 2014 Section 6 -yzw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 6.SUSITNA BASIN AND DAM SITE CHARACTERISTICS 6.1.Climatology The proposed Susitna-Watana Project is located in the south-central region of Alaska, approximately 125 miles north-northeast of Anchorage and 140 miles south-southwest of Fairbanks.The Susitna River basin,which has a drainage area of almost 20,000 square miles at its mouth and 5,180 square miles at the proposed Watana Dam site,has a wide range in climate due to elevation differences and proximity to the Gulf of Alaska.The climate of the upper Susitna basin is characterized by cold dry winters and warm but moderately moist summers.The yearly precipitation distribution shows that about two-thirds of the annual precipitation occurs from June through October.The climate is classified into three categories:(1)a coastal zone dominated almost entirely by maritime influences;(2)a zone of transition from maritime to continental influences;and (3)a zone dominated by continental climatic conditions.The upper Susitna basin,where the Susitna-Watana Project is located,falls within the transitional zone. The contrast between coastal maritime-influenced areas and continental conditions at Fairbanks are marked.Within the confines of the upper Susitna basin,the lack of moderating influence of maritime air results in greater temperature extremes than on the coast of the Gulf of Alaska. Relatively severe winter temperatures contrasted by warm summers will occur within the basin. Mean annual precipitation at lower elevations of the basin would be expected to range between 18 and 22 inches,while precipitation in higher elevations,because of orographic effects,would be expected to reach 80 inches per year.Mean annual snowfall would range from 60 inches in the lowlands to as much as 400 inches in the high mountains.Monthly average precipitation values for long-term stations (60 years of data at Fairbanks;56 years at Talkeetna;55 years at Anchorage)are presented in Table 6.1-1 and plotted on Figure 6.1-1.Talkeetna is representative of the lower Susitna River basin. Table 6.1-1.Monthly Precipitation (inches) Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov'Dec Fairbanks 0.59 043 0.34 0.29 060 1.37 2.03 1.83 1.07 0.78 066 0.69 Talkeetna 1.49 1.51 1.28 1.27 144 218 3.34 463 423 284 1.64 1.73 Anchorage 0.75 0.82 0.64 0.56 066 1.04 1.89 263 2.78 1.89 1.11 1.12 Project Site No data Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-1 December 2014 -yz- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 5.0 =a==Fairbanks we Aa°mg Talkeetna @ Anchorage ada||NOoy4rrAveragePrecipitation(inches)Nan||=|||||||or od HHH HE :|| { 0.0 T T TT T T T 7 TT TJanFebMarAprMayJunJulAugSepOctNov Dec Figure 6.1-1.Monthly Average Precipitation Table 6.1-2 and Figure 6.1-2 shows the significant annual variation in maximum,minimum,and average monthly temperatures among Fairbanks,Talkeetna,and Anchorage,from National Weather Service data.Data for the project site was derived from 1980s records.The continental climatic zone winter temperatures exhibited at Fairbanks are far lower,while summer temperatures are slightly higher at Fairbanks than at Talkeetna and Anchorage. Table 6.1-2.Maximum,Minimum,and Average Monthly Temperatures Maximum Temperature (°F) Location Jan |Feb |Mar |Apr |May |Jun j Jul Aug |Sep |Oct |Nov |Dec Fairbanks "1.1 |82 23.9 |424 |59.9 [707 |727 |663 |545 |321 (115 |16 Talkeetna 19.7 |261 |336 |446 1569 |65.7 679 |648 1554 |399 [263 |20.5 Anchorage 21.7 |26.0 |329 |436 (551 |623 |653 |634 |551 |40.5 |27.8 |228 Project Site 32.2 |31.2 |344 |363 |719 |855 |81.1 |765 |605 |443 |27.4 |35.1 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-2 December 2014 -yzw SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Minimum Temperature (°F) Location Jan |Feb |Mar |Apr |May |Jun |Jul Aug |Sep |Oct {Nov |Dec Fairbanks -18.7 |-14.2 |-3.0 |20.1 |37.7 (49.1 |519 |467 |356 {172 |-49 |-152 Talkeetna 2.1 5.5 10.0 |23.3 |348 (45.2 |496 |463 |37.2 |240 |10.2 |37 Anchorage 8.7 120 |176 |286 /|390 |473 |51.7 1496 |415 |286 |160 |10.3 Project Site -26.4 |-7.4 |-134 |-55 |13.7 |36.9 |420 |318 |209 (48 8.1 |-18.8 Average Temperature (°F) Location Jan |Feb |Mar |Apr |May |Jun |Jul Aug |Sep |Oct |Nov |Dec Fairbanks 9.9 |-3.0 1105 [312 |488 |599 |6241 |565 /|451 |246 |33 -6.8 Talkeetna 10.9 |15.8 |218 |340 (458 |555 |587 |555 |463 |319 [183 |12.1 Anchorage 15.2 119.0 |252 |36.1 |47.0 {548 |585 |/565 |483 |345 |219 |165 Project Site 12.5 [159 /129 |17.5 |379 {585 (57.1 |521 |412 |19.3 |7.7 3.4 70 60 m Fairbanks 1wTalkeetna ra 50 m Anchorage oe LL Y Ly rl 2 40 EE EPR Be a ®; z=:- ©30 Leo Pt EE RH Ty2:: [se];ion : o E on cal i 7 --]-Ee :jl8,10 Ft T+FA Fh -oe a yn 6 :: S a : <oo -_--|__|-||a -10 HH He 4 HR He HEH FF H 7 k -20 ia ---+= Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 6.1-2.Average Temperatures (°F) Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 6-3 Alaska Energy Authority December 2014 -2N- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.2.Hydrology This section summarizes available existing U.S.Geological Service (USGS)hydrologic data in the Susitna River watershed,and presents statistics for estimated flow at the Watana Dam site. Included in this section are (1)a summary of the hydrologic record;(2)monthly flow frequency and flow duration;(3)Watana Dam site historical flows;(4)flood frequency;and (5)Susitna watershed flow distribution. 6.2.1.Hydrologic Record A summary of recorded flow data in the Susitna River watershed is useful for many purposes associated with the Susitna-Watana Project.Recorded flow data is also needed to develop a long-term estimate of flow and flood frequency at the Watana Dam site for use in project design, reservoir operation and power generation studies.Fourteen gaging stations have been intermittently operated by the USGS within the Susitna River watershed between 1949 and 2013 as shown in Table 6.2-1.At the time of preparation of this report,water year 2014 was not included because the water year was still in-progress and the USGS had not yet made data available for the 2013-2014 river ice season.An additional station on the Little Susitna River, which is not a tributary of the Susitna River,was included in Table 6.2-1 due to its proximity to the Susitna River and the exceptionally long period of record for this gage. Table 6.2-1.USGS Streamflow Gages in the Susitna Watershed USGS Drainage Gage Gage Gage Name Area Latitude Longitude |Datum Available Period of Record Number (sq.mi)(feet) 15290000 Little Susitna River near Palmer 62 61°42'37"149°13'47"917 1948 -2013 15291000 Susitna River near Denali 950 63°06'14"147°30'57"2,440 1957 -1976;1978 -1986;2012 15291200 Maclaren River near Paxson 280 63°07'10"146°31'45"2,866 1958 -1986 15291500 Susitna River near Cantwell 4,140 62°41'55"147°32'42"1,900 1961 -1972;1980 -1986 15291700 |Susitna River above Tsusena Creek 5,160 62°49'24"|147°36'17"1,500 2013 15292000 Susitna River at Gold Creek 6,160 62°46'04"|149°41'28"677 1949 -1996;2001 -2013 15292400 Chulitna River near Talkeetna 2,570 62°33'31"150°14'02"520 1958 -1972;1980 -1986 15292700 Talkeetna River near Talkeetna 1,996 62°20'49"150°01'01"400 1964 -1972;1980 -2013 15292780 Susitna River at Sunshine 11,100 62°10'42"150°10'30"270 1981 -1986;2012 -2013 15292800 Montana Creek near Montana 164 62°06'19"150°03'27"250 2005 -2006;2008 -2012 15294005 Willow Creek Near Willow 166 61°46'51"|149°53'04"350 1978 -1993;2001 -2013 15294010 Deception Creek near Willow 48 61°44'52"149°56'14"250 1978 -1985 15294100 Deshka River near Willow 591 61°46'05"150°20'13"80 1978 -1986;1988 -2001 15294300 Skwentna River near Skwentna 2,250 61°52'23"151°22'01"200 1959 -1982 15294345 |Yentna River near Susitna Station 6,180 61°41'55"150°39'02 80 1980 -1986 15294350 |Susitna River at Susitna Station 19,400 61°32'41"150°30'45 40 1974 -1993 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-4 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The location of the five USGS gaging stations located in the area tributary to or just downstream of Watana Dam,along with the watershed boundaries,are shown on Figure 6.2-1. s1-W 150%w ew ww Figure 6.2-1.Susitna Watershed Boundary and USGS Gage Locations 7 agiab BSPO a ActiaesaP Cink colo z :v8"18?aepeepafeefi,'"Le yi #4 aa FEL [Fite ere Per §f hisat WE Zea:<p F404 5 fo ALEVE EFvdSeeGIGL2eety"9 ALoe |ey aof.einenae neseoni BeteDenaliagesatfifygotOF,nd.42h,we ht yO bs 9:Ft ry rope oe velStlAGCs5ALDSEBS,2 Ai BENSéct:43 »Apathy.;at a ota :ey,z oa .f ait a Aah,£yD "as Clam?ee Bk x ee :YE"wo gt ww,os i)7 8 pe a Cee:se,+aNT ="f..*zoezensoe f iran aE 5 at =aE,be 's woe J -MAS 4 7 4 .ea eh ie og pp een sie aN PF :: |ho mid.ae nb fe él g O ' .dAbtreo44apne.Soey @ Leza'Paspea md Pa O }5 Pe,(f>man i }a¥re (as i}-oT c Kn Ale [aod ];rapper ©!ree p .ao ":TT)' *:if be A ee..4 .fo :addies o a:ais at' Figure 6.2-2 shows the chronological availability of USGS flow data in the Susitna watershed. A modeled daily flow data set for the Watana Dam site was developed from the daily data at the downstream gage at Gold Creek and the upstream gage near Cantwell.The drainage area at the Watana Dam site,5,180 square miles,is approximately halfway between the drainage area at Cantwell (4,140 square miles)and Gold Creek (6,160 square miles).The drainage areas for these sites were confirmed with geographic information system measurements.The 17 years of concurrent data at the Cantwell and Gold Creek gaging stations were used to calculate monthly scaling factors for use in estimating flows at Watana,as described below. Figure 6.2-2 also shows an active period of flow gaging in the early 1980s,with at least four years of concurrent data at almost all sites. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-5 December 2014 -yz .ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Station Name ODAIDM™NOTIN OR DADE NOTIN DH DOAIOKN OM TIM OR DAHIGCK NOM TIM OM DAIODOT AM TIN OR OBAIDSKE NOM TID OR DBRBIOMK NMYTTIMNOMYHOOHHYMIOOOOCHOO©OO Ol[KF ROKR RRIN BERK EID ODO DO DIDD OO HOIRDAADWI*RAAAGMiooaceoeoeoccgqoolrrxre .AAAMA|AMDAAONO HH DAADAAAaDGHAD ANANDA AA AHWRADA AA AA AAVGDMWAAAAAAWAVWA HAMA AGHMooeoccocnoo»ococodsd{USGS Station Number)erle eee ele ee er ele eee ele ee ee fe er ree fe Cee ele eRe ele Oe ele RPO fe KK EK HINN NAN NINNANN NINN AN Little Susitna River near Palmer fee : (15290000)pe Susitna River near Denali (15291000) Maclaren River near Paxson (15291200) Susitna River near Cantwell (15291500) Susitna River at Gold Creek (15292000) Chulitna River near Talkeetna (15292400) Talkeetna River near Talkeetna (15292700) Susitna River at Sunshine (15292780) Montana Creek near Montana (15292800) Willow Creek Near Willow (15294005) Deception Creek near Willow (15294010) Deshka River near Willow (15294100) Skwentna River (15294300) Yentna River near Susitna Station (15294345) Susitna River at Susitna Station (15294350) Note:Data are on a calendar year basis. Legend Complete years of record Partial years of record Figure 6.2-2,Susitna Watershed USGS Flow Data -Chronological Availability Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Paae 6-6 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Within the period of record for gages in the Susitna watershed,there have been several periods of no gage-height record,some lasting for several consecutive months.The USGS has developed estimated flows for the period of no gage-height records,as is their customary practice,to provide a continuous period of record during operational years.All of the data used in hydrologic analyses for the Susitna watershed are accepted measured or estimated values published by the USGS. Average monthly flows over the period of record for the main stem Susitna River plus the Paxson River,which is tributary to the Watana Dam site,are presented on Table 6.2-2.As shown in Table 6.2-2 and in Figure 6.2-3,flow in the Susitna River and its tributaries is highly seasonal,with peak flows in July corresponding with summer snow melt conditions,and low winter flows occurring when much precipitation is stored in the watershed as snow. Table 6.2-2.Average Monthly Flows (cfs)at Selected USGS Gages in the Susitna Watershed Susitna Susitna Maclaren Susitna Susitna Susitna River at Rivernear Rivernear Rivernear River at River at Susitna Denali Paxson Cantwell Gold Creek Sunshine Station (950mi2)(280mi2)(4,140mi*)(6,160mi?)(11,100mi*)(19,400mi?) January 262 105 961 1,590 4,375 8,487 February 220 90 828 1,414 3,939 7,739 March 199 82 779 1,297 3,496 7,136 April 233 89 915 1,753 3,948 10,021 May 2,135 850 7,908 14,138 27,970 64,825 June 7,279 2,894 18,230 26,417 56,472 118,479 July 9,831 3,240 17,542 23,871 66,238 130,317 August 8,159 2,548 14,918 21,365 60,972 113,051 September 3,296 1,136 7,936 13,741 35,202 74,446 October 1,181 421 3,365 6,345 16,600 39,578 November 525 192 1,575 2,679 6,787 15,966 December 339 130 1,117 1,892 4,877 9,983 Annual 2,793 981 6,340 9,805 23,864 50,417 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-7 August 2014 -27Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 140,000 - -e Susitna River near Denali :a :Based on Hestonc Recorded Datly Flows .i :in the Susitna River Watershed i o-Maclaren River near Paxson fo '| 120,000 : }i ::|-«-Susitna River near Cantwell !| ! -e-Susitna River at Gold Creek | 100,000 ;-Susitna River at Sunshine ! £-a Susitna River at Susitna Station z2 80,000 ry o a£$<>60,000 =g = 40,000 | 20.000 | Figure 6.2-3.Average Monthly Flows in the Susitna Watershed 6.2.2.|Monthly Flow Frequency and Flow Duration The nearest long-term gaging stations upstream and downstream from Watana Dam were used to create flow frequency and flow duration plots.USGS gaging station 15291700 Susitna River above Tsusena Creek is located about two miles downstream from the Watana Dam site,but flow records began in water year 2012 so the period of record is inadequate for determining average flows or flow frequency data.Daily flow data at Cantwell and Gold Creek on the Susitna River was used;these stations are 41 river miles upstream and 47 river miles downstream respectively.Table 6.2-3 and Table 6.2-4 present monthly flow frequencies for flows in the Susitna River at Cantwell and Gold Creek,respectively.The flow frequency was calculated at five percent exceedance intervals except at the high and low flow ends where l percent exceedance intervals were used to provide additional definition where the flow duration values change rapidly. Figure 6.2-4 through Figure 6.2-7 show the flow frequency and flow duration curves for these sites.The flow frequency curves demonstrate the same seasonal flow as Figure 6.2-3,with peak flows occurring in June at the middle watershed sites of Cantwell and Gold Creek. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-8 December 2014 -yz.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 6.2-3.Flow (cfs)Frequency at USGS Gage 15291500 -Susitna River near Cantwell %of Time Flowis Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual (all months)Exceeded )1800 1,500 1,500 3,000 32,500 49,100 34,000 55,000 21,000 9,400 3,600 1,900 55,000 1 1,800 1,500 1,500 1,800 23,740 43,310 29,400 35886 18,427 7,353 3,200 1,774 28,775 2 1,700 1,500 1,500 1,682 22,000 37,848 28000 28800 17,088 7,000 2,982 1,600 26,000 3 1,700 1,500 1,500 1,500 20,200 35,251 27,036 28,258 16,183 6,536 2,600 1,600 24,000 4 1,696 1,500 1,500 1,400 20,000 33,396 26,248 26,000 16,000 6,070 2,500 1,600 22,100 5 1,600 1,500 1,400 1,400 19,100 32455 25,860 24600 15,010 6,000 2,400 1,600 21,000 10 1,500 1,200 4,200 1,400 16,000 27,000 23,100 20,830 13,010 5,200 2,200 1,600 18,000 15 1,300 1,200 1,100 1,226 14,000 25,360 21,800 18,445 12,000 5,000 2,200 1,400 16,000 20 1,300 1,200 940 1,200 12,700 23,240 20,700 17,960 10,520 4,500 2,000 1,400 14,500 25 1,300 1,000 940 1,200 11,300 21,150 19,900 17,100 9,500 4,175 1,900 1,400 12,000 30 1,200 965 900 1,100 10,000 20,000 19.000 16490 8624 3918 1,800 1,400 9,865 35 1,094 904 850 1,070 10,000 19,000 18,600 16,000 8,000 3,600 1,800 1,400 7,100 40 1,000 850 825 1,000 9,380 18,000 18,000 15,800 7,900 3,600 1,700 1,300 4,970 45 1,000 850 760 940 8660 17,000 17,600 15,200 7,570 3,406 1,600 1,200 3,200 50 970 690 690 900 7,500 16,000 17,000 14,700 7,100 3,200 1,530 1,200 2,100 55 760 680 660 850 6,500 15,805 16,700 14,000 6,786 3,000 1,500 1,080 1,600 60 760 670 650 750 §,200 15,200 16,000 13,100 6,600 2,844 1,486 994 1,400 65 730 650 600 720 3,700 15,000 15,580 12,400 6,230 2,600 1,400 932 1,200 70 700 647 560 660 3,000 14,970 15,000 12,000 §,975 2,400 1,364 860 1,100 75 680 640 550 650 2,500 14,200 14800 11,400 5515 2,200 1,100 800 950 80 680 560 550 550 2,200 13,600 14,000 10,700 5,132 2,026 1,100 750 850 85 610 500 480 500 1,700 12,635 13,300 9,856 4,430 1,900 918 720 720 90 500 480 460 500 1,500 11,000 12,200 9,267 3,818 1,800 800 650 650 95 460 440 460 485 800 8,823 11,340 7,637 3,396 1,586 780 565 500 96 440 423 440 467 750 8,381 11,000 7,121 3,200 1,423 780 550 500 97 436 420 431 460 750 7,951 11,000 5,684 3,034 1,239 758 550 480 98 420 420 400 440 710 7,232 10,904 4,728 2,800 1,100 709 500 460 99 420 420 400 440 580 6,980 10,000 4,371 2,515 1,026 655 500 440 100 420 420 400 440 580 6,130 8,550 3,600 2,080 840 600 480 400 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-9 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 :ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 35,000 ||| #-5%Exceedance Based on Historic Recorded Daily Flows 30,000 -+10%Exceedance in the Susitna River near Cantwell -USGS Gage 15291500-*-25%Exceedance 25,000 -e-50%Exceedance [N -* -90%Exeedance NS Z 20,000 f - EK-} L mio= &15,000 \ 10,000 x \\\ 5,000 SK 7 SS Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 6.2-4.Susitna River Flow Frequency at Cantwell Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-10 December 2014 -z .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 30,000 Based on Historic 25,000 Recorded Daily Flows in the Susitna River near Cantwell -USGS Gage 15291500 20,000 \a 2 3 15,000L,oN > 3 Q 10,000 5,000 e-__| 0 0%10%20%30%40%50%60%70%80%90%100% Percent of Time Flow is Equaled or Exceeded Figure 6.2-5.Susitna River Flow Duration at Cantwell Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 6-11 December 2014 -zO ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 6.2-4.Flow (cfs)Frequency at USGS Gage 15292000 -Susitna River at Gold Creek %of Time Flow is Jan Feb Mar Aor May Jun Jul Aug Sep Oct Nov Dec Annual(all months)Exceeded 0 2,900 3,700 2,400 24000 55,500 85900 60,800 77,700 47,700 36,200 8,940 4,400 85,900 1 2,500 2,400 2,100 7,242 37,958 62,003 42,934 51,206 32,305 16,860 5,184 3,500 39,857 2 2,400 2,150 1,900 5,384 35,116 51,782 39,000 43,006 30,300 14,630 4,800 3,200 35,300 3 2,400 2,000 1,900 4,169 33,074 46473 37,008 39,045 27,900 13,100 4,500 2,900 32,700 4 2,300 2,000 1,900 3,684 31,532 43428 35,436 34824 26,088 12,460 4,400 2,800 31,000 5 2,200 2,000 1,900 3,400 31,000 41,710 34,500 32,900 25,000 12,000 4,202 2,713 30,000 10 2,025 1,900 1,800 2,500 27,800 37,110 31,300 29,000 21,710 10,300 3,700 2,500 25,470 15 2,000 1,800 1,700 2,200 24270 34,265 29,500 26445 19,500 9,268 3,400 2,400 22,600 20 2,000 1,790 1,600 2,000 22,000 32420 28,000 25200 18,000 8,480 3,200 2,300 20,200 25 1,900 1,700 1,600 1,900 20350 30,600 26,800 24,000 16,900 7,800 3,100 2,200 18,000 30 1,850 1,600 1,500 1,800 18800 29,300 25,800 23,000 15,600 7,210 3,000 2,200 15,300 35 1,800 1,500 1,500 4,700 17,700 28,000 25,000 22,400 14,700 6,740 2,900 2,100 12,000 40 1,700 1,500 1,400 1,650 16400 27,000 24,200 21,700 14,000 6,300 2,800 2,000 8,400 45 1,600 1,500 1,350 1,600 15,000 26,000 23,500 21,000 13,200 5,900 2,700 2,000 5,200 50 1,600 4,400 1,300 1540 13,600 25,350 22,800 20,200 12,500 5,500 2,600 1,900 3,500 55 1,600 1,400 1,300 1,500 12,000 24,300 22,200 19600 11,900 5,200 2,600 1,900 2,650 60 1,500 41,300 1,200 1500 10360 23,300 21,700 18800 11,300 4,950 2,400 1,700 2,200 65 1,500 4,300 1,100 1,400 9,000 22,200 21,200 18,000 10,665 4,600 2,400 1,700 1,950 70 1,400 1,200 1,000 1,200 7,160 21,200 20,600 17,500 10,100 4,500 2,300 1,600 1,800 75 1,300 1,200 995 1,200 5,050 20,000 19,900 17,000 9,520 4,215 2,100 1,500 1,600 80 1,200 1,000 940 1,100 4400 18900 19,200 16,200 8,936 4,000 1,900 1,500 1,500 85 1,100 970 880 1,000 3,400 17,800 18,500 15,400 8,249 3,700 1,700 1,300 1,400 90 960 860 800 920 2,800 16400 17,560 14,500 7,199 3,400 1,600 1,110 1,200 95 900 800 750 830 2,055 15,000 16,300 12,985 6,000 2,898 1,400 1,000 950 96 850 750 740 830 1,900 14,700 16,000 12,288 5,791 2,784 1,300 1,000 900 97 850 750 740 780 1,700 13,827 15,600 11,800 5,500 2,500 1,300 900 850 98 800 720 700 756 1,500 13,218 15,032 10,988 5,316 2,200 1,200 850 800 99 718 700 660 710 1,400 12,200 14,600 8,088 4,900 1,900 1,100 850 750 100 700 600 660 700 900 10,000 11,800 5,280 3,710 1,500 950 800 600 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-12 December 2014 -za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 45,000 ||||| -#-5%Exceedance LN Based on Historic 40,000 Recorded Daily Flows ->-10%Exceedance in the Susitna River at Gold Creek -USGS Gage 1529200035,000 -*-25%Exceedance < -e-50%Exceedance l QT.230,000 -*-90%Exeedance I NS N\A$25,000 oS uw =20,000 PN a [/aa \.|/\\\\10,000 )5,000 Bii N So 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 6.2-6.Susitna River Flow Frequency at Gold Creek Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-13 December 2014 -yZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Based on Historic Recorded Daily Flows in 40,000 |the Susitna River at Gold Creek -USGS Gage 15292000 DailyFlow(cfs)NaQofo)oO20,000 NN15,000 \10,000 N 5,000 \ oNee rmnemmeacl 0%10%20%30%40%50%60%70%80%90%100% Percent of Time Flow is Equaled or Exceeded Figure 6.2-7.Flow Duration Curve for the Susitna River at Gold Creek 6.2.3.Watana Dam Site Historical Inflows The Watana Dam site is located between USGS gage locations at Cantwell and Gold Creek. Because long-term flow data are not available for the dam site,daily flow data from Cantwell and Gold Creek were used to create a modeled historical flow data set for Watana. For Watana Dam,the reservoir inflows are a continuous 61-year record of daily flows for Water Years 1950 through 2010.The USGS provided the basis for the continuous long-term daily flows with a Susitna River watershed record extension study (Curran 2012)that includes both recorded and correlated flows.Two of the USGS gages included in the record extension study were Susitna River at Gold Creek (USGS gage 15292000)that has a drainage area of 6,160 square miles,and Susitna River near Cantwell (USGS gage 15291500)that has a drainage area of 4,140 square miles.Watana Dam has a drainage area of 5,180 square miles,about halfway between these two USGS gages.USGS gage 15291700 Susitna River above Tsusena Creek, located two miles below the Watana Dam site,was not included in the USGS record extension study and was therefore not used in developing inflows at Watana Dam.Inflows to Watana Reservoir are based on proportioning the USGS flows based on drainage area.As shown on Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-14 December 2014 Clean,reliable energy for the next 100 years. za SUSITNA-WATANA HYDRO ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 6.2-5,the long-term average inflow at the Watana Dam (cfs).The flow frequency at the Watana Dam site is presented on Table 6.2-6. Table 6.2-5.Modeled Monthly Average Flow (cfs)at the Watana Dam Site Water Year 1950 1951 1952 4953 1954 1958 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Average Maximum Minimum Oct 5,164 3,113 4,529 6,697 4,554 4,359 4,017 4,720 6,702 3,900 5,342 6,362 4,638 5,560 5,187 4,759 5,224 3,270 4,019 3,135 2,403 3,768 4,979 3,913 3,019 3,025 6,314 3,132 6,174 3,980 5,959 6,632 5,700 5,154 6,882 4,257 5,073 10,415 4,814 6,262 6,552 5,622 4,730 3,546 8,116 3,670 5,278 2,815 3,171 6,285 5,588 6,592 3,925 8,973 6,627 2,663 Nov Jan 817 763 1,280 876 1,037 1,436 779 1,360 1,575 1,157 1,477 1,971 1,609 1,309 852 863 1,060 1,102 1,618 619 636 1,097 1,671 956 694 4,212 775 1,464 1,627 1,116 1,399 1,858 1,380 1,797 1,782 1,479 1,207 1,292 1,248 1,602 1,413 1,519 1,574 1,493 1,650 1,485 995 1,277 1,084 1,344 1,321 1,411 1,238 1,324 1,176 1,149 1,118 1,622 1,476 1,106 1.173 1,275 1,971 619 Feb 625 651 Apr May Jun 691 9,449 16,180 1,295 11,586 17,169 731 4,435 26,820 1,295 15,900 22,627 986 14,253 20,892 956 7,637 24,756 755 14,578 27,534 956 11,328 24,990 1,226 10,601 21,269 997 13,194 19,282 1,038 12,995 12,773 2,133 13,638 22,784 1,457 11,333 36,020 777 =15,297 20,663 609 3,579 42,839 1,232 10,964 21,214 1,338 7,094 25,941 850 12,556 24,715 1,577 12,825 25,704 1,262 9,311 13,962 986 9,537 14,401 814 2,857 27,613 1,305 15,972 27,428 817 6,741 22,974 789 13,361 14,726 1,274 12,661 26,784 1,098 10,361 20,170 1,344 10,439 31,366 1,362 9,803 15,712 1,158 11,429 20,429 1,337 9,846 23,400 1,641 14,415 16,737 1,196 10,878 21,441 1,565 11,671 20,603 1,613 10,831 22,911 1,517 8.440 21,226 1,162 9,736 17,817 1,644 10,671 19,016 1,269 14,335 24,637 1,715 11,292 22,163 3,446 21,223 28,001 1,290 4,934 21,210 1,685 4,985 19,122 2,042 17,252 19,421 2,603 12,014 25,724 2,293 14,604 20,451 1,078 5,403 12,922 1,282 7,885 15,738 1,370 7,856 20,300 1,087 7,662 19,026 1,354 9.415 25,738 1,271 7,376 25,715 1,061 9,473 13,624 1,750 6,553 20,125 2,203 19,489 20,957 2,112 22,327 28,455 1,227 12,996 19,261 1,827 14,166 16,260 1,336 9,736 17,438 3,701 18,949 19,105 1.481 16.183 16,524 4,398 11,284 21,718 3,701 22,327 42,839 609 2,857 12,773 site is 8,015 cubic feet per second Aug 16,401 16,234 17,270 17,014 21,560 21,212 20,308 16,950 18,589 25,674 19,511 19,479 19,890 21,012 14,044 17,392 17,387 26,106 14,144 7,772 Sep 6,777 17,550 11,907 12,566 10,602 11,746 15,123 16,339 6,155 13,943 16,930 10,148 12,746 10,799 7,524 16,226 9,216 13,670 7,164 4,260 7,224 12,190 10,957 7,418 10,050 13,424 5,603 10,367 7,030 8,823 10,995 11,666 13,979 11,194 7,347 11,700 10,558 10,962 11,326 12,695 21,863 10,130 8,331 17,589 7,654 15,779 8,524 11,132 13,257 9,273 12,724 8,479 13,376 11,110 5,252 18,893 10,093 11,095 11,934 10,242 13,031 11,257 21,863 4,260 Annual 6,599 7,495 7,865 8,306 7,966 8,442 9,465 8,551 7,787 8,691 7,989 8,701 9,834 9,277 8,262 8,451 7,374 9,096 8,032 4,912 6,115 8,588 8,963 6,641 6,268 8,468 6,728 8,311 6,720 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 6-15 Alaska Energy Authority December 2014 oe SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 6.2-6.Modeled Flow (cfs)Frequency at the Watana Dam Site %of Time Flow is Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Exceeded 0 2,301 2,973 1,919 19,537 40,500 72,758 49,445 66,835 39,343 29,745 7,260 3,551 1 2,031 1,935 1,697 5,838 30,947 49,630 35,464 42,415 26,363 13,075 4,265 2,825 2 2,004 1,769 1,681 4,203 28,249 41,923 32,449 35,082 24,867 11,624 3,877 2,572 3 1,929 1,694 1,604 3,228 26,424 38,456 30,822 32,017 23,030 10,706 3,643 2,334 4 1,827 1,680 1,560 2,897 25,654 35,293 29,498 28,328 21,491 10,167 3,547 2,252 5 1,791 1,602 1,522 2,659 25,005 34,128 28,709 27,058 20,623 9,749 3,400 2,170 10 1,642 1,451 1,441 2,013 22,262 30,396 26,123 23,623 17,945 8398 2,949 1,975 45 1,602 1,441 1,360 1,692 19,510 28,170 24,690 22,279 16112 7,479 2,744 1,916 20 1,601 1,361 1,280 1,604 17,716 26,690 23,584 20,924 14,841 6821 2621 1,835 25 1,521 1,320 1,201 1,819 16,419 25,202 22,646 19897 13,811 6,301 2,509 1,768 30 1,441 1,257 1,199 1,445 14,943 24,066 21,746 19,421 12,799 5,853 2,415 1,762 35 1,396 1,199 1,153 1,374 13,975 23,138 21,031 18813 11,999 5392 2,346 1,709 40 1,361 1,198 1,115 1,319 12,982 22,181 20,299 18153 11,407 5,079 2,263 1,609 45 1,309 1,185 1,042 1,280 11,846 21,359 19,783 17,626 10,698 4,734 2,177 1,589 50 1,280 1,119 1,037 1,221 10,683 20,663 19,226 16,999 10,131 4463 2,096 1,523 55 1,257 1,118 984 1,199 9,630 19,948 18,704 16,350 9,685 4,243 2,067 1,496 60 1,199 1,040 956 1,151 7,936 19,104 18,231 15,668 9,188 3,964 1,943 1,403 65 1,165 1,037 884 1,105 6,866 18,421 17,883 14,993 8,727 3,734 1,930 1,369 70 4,118 1,021 876 1,006 5,409 17,743 17,344 14,595 8,288 3,606 1,774 1,280 75 1,060 957 807 957 4,086 16,686 16,728 14,035 7,856 3,406 1,682 1,211 80 1,037 809 773 878 «3,541 15,783 16,111 13.440 7,316 «63,148 1,521 1,186 85 876 773 715 798 «2,783 14,859 15,661 12,801 6840 2916 1,393 1,118 90 795 750 644 755 2,256 13,599 14,790 12,058 5906 2609 1,344 981 95 756 630 595 694 1,693 12,134 13,740 10,720 4,952 2,179 1,119 875 96 684 627 587 689 1,579 11,825 13,446 10,340 4,859 2,018 1,081 796 97 656 505 587 638 1,460 «11,382 «13,082 «9,728 «4,567 «1,847 -1,040 769 98 644 588 555 604 1,228 «10,887 12,670 9,071 4,356 1,695 1,037 737 99 618 571 533 581 1,146 10,087 12,285 6,792 3,964 1,537 924 696 100 599 476 523 557 748 «8,385 «10,531 «4,622,3,103 1,214 798 684 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-16 December 2014 oO O -z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The monthly flow frequency based on modeled daily flow at the Watana Dam site is presented graphically in Figure 6.2-8.Figure 6.2-9 shows the annual flow duration curve for modeled flow at the Watana Dam site. 40,000 | -e-5%Exceedance 35,000 --10%Exceedance w-25%Exceedance /\30,000 -e50%Exceedance /,7 \ -x--90%Exceedance aN25,000 poomr \ 2 3 20,000 /po-\-\ uw , "a /\'3 a 45,000 /\|//oN \10,000 //\\\\ 1 /NX SYWN7SSS -Sa y x * Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 6.2-8.Modeled Susitna River Flow Frequency at Watana Dam Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-17 December 2014 -zw-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 cI liab! ENGINEERING FEASIBILITY REPORTean,reliable energy for the next 100 years. 35,000 30,000 25,000 20,000 N 15,000 \ 10,000 xX 5,000 NXNNeeDailyFlow(cfs)0 10 20 30 40 50 60 70 80 90 100 Percent of Time Flow Is Exceeded Figure 6.2-9.Modeled Susitna River Flow Duration at Watana Dam 6.2.4.Flood Frequency Peak annual flows have been recorded by the USGS at Cantwell and at Gold Creek,as summarized in Table 6.2-7 and Table 6.2-9.Peak flow rates provided by the USGS include both average daily values and instantaneous peaks. Peak flows for return periods up to 10,000 years were estimated for the Susitna River at Cantwell and Gold Creek.Peak flows were estimated for various return periods by fitting recorded peak flow data with a Log Pearson Type III distribution according to methods in Bulletin 17B (I[ACWD 1982).Estimated peak flows for the Susitna River at Cantwell and Gold Creek are presented in Table 6.2-8 and Table 6.2-10. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-18 December 2014 -yZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 6.2-7.Peak Annual Flows in the Susitna River at Cantwell Peak FlowDate(cfs) June 23,1961 30,400 June 15,1962 46,800 July 18,1963 32,000 June 08,1964 51,200 July 13,1965 26,000 June 06,1966 27,000 August 14,1967 38,800 May 22,1968 25,000 July 15,1969 19,300 August 01,1970 20,500 August 10,1971 55,000 June 17,1972 44,700 July 29,1980 28,500 August 14,1981 30,900 June 21,1982 24,100 June 04,1983 25,800 June 16,1984 33,400 July 03,1985 28,200 The quality of the fit of the parameterized Log Pearson Type III distribution to the observed data is evaluated by plotting the data and the parameterized distribution together.A good fit is indicated by data points for observed annual peaks,which are close to,and randomly distributed above and below,the computed Log Pearson Type III curve.The probability values assigned to each data point,called plotting positions,and the scale of the x-axis,are selected so that the Log Pearson Type III distribution appears as a straight line when the skew value is zero. The fitted distribution and resulting estimated peak flows at specified return periods are approximations.The ability to fit a distribution depends on the size and the variability within the sample.Confidence limits around the computed distribution curve provide a measure of the uncertainty for the predicted discharge at a specified exceedance probability. Figure 6.2-10 and Figure 6.2-11 below show the fit Log Pearson Type III distribution as a solid line,5 percent and 95 percent upper and lower confidence limits on the distribution as dashed lines,the observed annual peak flow data,and return periods for which peak flows were estimated in Table 6.2-9 and Table 6.2-11. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-19 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Retum Period (Years) 2 5 10 20 50 100 §00 1,000 10,000 = ¢ ¢ Log Pearson Type II!,”A)Flood Frequency for ° the Susitna River at ma 100.000 Cantwell i , ;I ,7 L_.7 ¢?”- Computed Curve 7 os =|" a ©Observed Annual Peaks a AO Pian o &e q a o ”g F3 ---5%and 95%Confidence xt LA >ra Limit Curves _o °JlGbe@°a.- 10,000 +++++++++++4++14-441, -2.6 -16 -0.6 0.4 14 2.4 3.4 Standard Normal Variable Figure 6.2-10.Log Pearson Type III Flood Frequency Plot for the Susitna River at Cantwell Table 6.2-8.Calculated Flood Frequency for the Susitna River at Cantwell Return Period Flow (Years)(cfs) 2 30,300 5 39,700 10 46,600 25 56,000 50 63,600 100 71,700 200 80,200 500 91,900 1,000 101,000 10,000 133,000 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-20 December 2014 -Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Table 6.2-9.Peak Annual Flows in the Susitna River at Gold Creek Peak Flow Peak Flow Peak FlowDate(cfs)Date (cfs)Date (cfs) June 21,1950 34,000 June 30,1970 33,400 September 15,1990 50,300 June 8,1951 37,400 August 10,1971 87,400 June 23,1991 35,300 June 17,1952 44,700 June 17,1972 82,600 July 19,1992 33,300 June 7,1953 38,400 June 16,1973 54,100 September 3,1993 36,300 August4,1954 42,400 May 29,1974 37,200 June 22,1994 46,600 August 26,1955 58,100 June 3,1975 47,300 June 25,1995 37,800 June 9,1956 51,700 June 12,1976 35,700 August 26,1996 26,100 June 8,1957 42,200 June 15,1977 54,300 August 1,2001 40,200 August 3,1958 49,600 June 23,1978 25,000 August 23,2002 36,200 August 25,1959 62,300 July 16,1979 41,300 July 28,2003 51,700 September 13,1960 41,900 July 29,1980 51,900 May 8,2004 43,400 June 23,1961 54,000 July 12,1981 64,900 June 19,2005 50,200 June 15,1962 80,600 June 21,1982 37,900 August 20,2006 59,800 July 18,1963 49,000 June 3,1983 37,300 May 28,2007 30,800 June 7,1964 90,700 June 17,1984 59,100 July 30,2008 34,400 June 28,1965 43,600 May 28,1985 40,400 May 5,2009 40,400 June 6,1966 63,600 June 18,1986 29,100 July 22,2010 37,400 August 15,1967 80,200 July 31,1987 47,300 May 29,2011 46,300 May 22,1968 41,800 June 16,1988 43,600 September 21,2012 72,000 May 25,1969 28,400 June 15,1989 46,800 June 1,2013 90,500 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-21 December 2014 -yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Return Period (Years) 2 5 10 20 50 100 500 1,000 10,000 a ?" Log Pearson Type III _a LH Flood Frequency for ot the Susitna River at a r _t ° Gold Creek a ye _?-Pa Ak -[--1950 -2013 Computed Curve "i 7 100,000 +-naan Sell ca ||©Observed Annual Peaks -y-o-To-r = ||---5%and 95%Confidence Limit Curves po _'ge <a }- 2 _ =2 z __ x oO o -._-a 10,000 -2.6 -1.6 -0.6 0.4 1.4 2.4 3.4 Standard Normal Variable Figure 6.2-11.Log Pearson Type III Flood Frequency Plot for the Susitna River at Gold Creek Table 6.2-10.Calculated Flood Frequency for the Susitna River at Gold Creek Return Period Flow (Years)cfs 2 44,700 5 58,600 10 68,700 25 82,700 50 93,800 100 106,000 200 118,000 500 135,000 1,000 149,000 10,000 195,000 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-22 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Peak flows were estimated for return periods up to 1,000 years at the Watana Dam site by transposing peak flow analysis results at Gold Creek to Watana according to the following equation: Awatana ) Qwatana =QGotd creek X (;Gold Creek where A is the drainage area for each site.Peak flows are frequently adjusted from a gaged to an ungaged location by the ratio of the square root of the drainage areas.A USGS publication on the Flood Characteristics of Alaskan Streams (Water Resources Investigations 78-129,indicates that the exponent of the drainage area ratio should be at about the selected 0.86 value.The flood frequency values for Watana Dam presented in Table 6.2-11 can also be used to develop the construction diversion floods. Table 6.2-11.Estimated Peak Annual Flows in the Susitna River at Watana Dam Return Period Flow (Years)(cfs) 2 38,500 5 50,500 10 59,200 20 68,300 25 71,300 50 80,800 100 91,300 500 116,300 1,000 128,400 6.2.5.Probable Maximum Precipitation /Probable Maximum Flood Estimates of Probable Maximum Precipitation (PMP)and Probable Maximum Flood (PMF)for the project are discussed in Section 9. 6.2.6.Susitna Watershed Flow Distribution Future reservoir development and alteration of the current flow regime,including lower summer flows,higher winter flows,and dampening of peak flows,resulting from reservoir regulation may affect downstream habitat,and therefore,is of interest.The potential magnitude of this impact can be preliminarily evaluated by comparing flow in the river at the Watana Dam site to flow at downstream locations.Gages in the lower Susitna River watershed were used to determine the average monthly and annual flow distribution for the river.Figure 6.2-12 presents the annual average flow distribution,and Table 6.2-12 presents the average monthly flow at gaging stations,as a percent of the flow at Susitna Station,the furthest downstream gaging Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-23 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. station.Flows at the Watana Dam site account for between 15 to 20 percent of the total flow in the river as measured at the Susitna Station USGS gage. 17%Susitna River at Watana local inflow between Watana and Gold Creek 4% Watana Dam site 21%Susitna River at Gold Creek 4%local inflow between Gold Creek and Sunshine Chulitna River 18% 9%Talkeetna River 52%Susitna River at Sunshine YentnaRiver 41% 7%local inflow between Sunshine and Susitna Station 100%Susitna River at Susitna Station /,Cook Inlet Figure 6.2-12.Average Annual Flow Distribution for the Susitna River Table 6.2-12.Percent Contribution of Flow at Susitna River Watershed USGS Gage Stations to Flow at the Susitna Station USGS Gage Drainage Area(sq.mi.)Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Susitna River at Watana 5,180 20 19 21 18 20 20 18 £16 15 14 15 18 17 localinflow*980 5 5 5 4 5 4 3 3 4 4 3 4 4 Susitna River at Gold Creek 6,160 24 24 +2 22 25 24 =-21 19 19 18 18 22 21 Chulitna River near Talkeetna 2,570 20 16 17 14 13 17 21 20 17 16 16 19 18 Talkeetna River near Talkeetna 1,996 9 8 8 7 8 10 9 9 9 8 7 9 9 localinfow?374 2 7 7 6 6 5 3 4 3 1 1 0 4 Susitna River at Sunshine 11,100 55 56 57 50 =51 56 53 52 48 43 42 450 52 Yentna River near Susitna Station 6,180 38 38 40 45 42 44 44 44 37 34 32 35 41 localinflow?2,120 6 6 3 6 6 1 3 4 15 23 26 15 7 Susitna River at Susitna Station 19,400 100 100 100 100 100 100 100 100 100 100 100 100 100 3 Percent of flow attributed to local inflow is equal to the increase in flow between gaged locations on the Susitna River. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-24 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The percent contribution values presented in Table 6.2-12 were calculated from monthly averages for the four years of concurrent data,from 1982 to 1985,available for the Susitna River at Gold Creek,Sunshine,and Susitna Station,and for the Chulitna,Talkeetna,and Yentna Rivers.Local inflow between gaging locations in Figure 6.2-12 and Table 6.2-12 was calculated as the difference in flow between gaging stations.The drainage area contributing to local inflow was similarly assumed to be the difference in drainage area for gaged sites. 6.2.7.Hydrologic Change Climate change can modify the expected energy from hydroelectric projects like the Susitna- Watana Project due to altered seasonal and annual reservoir inflow regimes.In comparison with projected future temperature changes,future changes in runoff patterns are considered to be significantly less certain. Preliminary hydrology studies conducted to date indicates that there has been no historic trend in annual flows.Figure 6.2-13 plots the annual Susitna Reservoir inflows presented on Table 6.2-5. The lack of historic trend is indicated by the trendline,which is essentially horizontal.There has been an observed seasonal trend toward earlier snow and glacier melt runoff in the Susitna River basin.Analysis of the long-term record of annual average flows at Gold Creek indicates that there is no statistically significant trend. 12,000 Linear Trendline =Watana Reservoir Inflows 40,000 Bw 8.000 - 2 =[oJ ms o 2 6,000 -:}4 ELE $< 3 J c i=] <4,000 - 2,000 9)4 ZESSSSSSSSSSSSSSSSSSSSSSESSSSSSSSSSSSSSIIISSIS338888888385882AESASASSSASSASSSSASSSSSSSSASSIABASSASSSSSSSASASSSSSASASASSRRERRRRRRARAWaterYears Figure 6.2-13.Watana Reservoir Annual Inflows and Trendline Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-25 December 2014 -yw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Statistically significant streamflow trends are most prevalent and consistently upward during the cool season months.This is likely due to more precipitation falling as rain rather than snow,and more frequent periods of snowmelt during the cool months.The month of April,as shown on Figure 6.2-14,has the most pronounced upward trend that is also due to an earlier onset of significant snowmelt in recent years.There is a consistent trend toward decreasing runoff in the months of June,as shown in Figure 6.2-15,through August.The net effect is that the increasing flows in some months and decreasing flow in other months balance out such that total annual flows remain approximately the same.Projecting the continued historic monthly trends to the year 2050 will result in a changed monthly flow distribution.The shape and relative magnitude of projected changes in monthly flows at Watana Dam are very similar to those that are expected to occur for the snowmelt runoff dominated Columbia River (Climate Impacts Group 2009).If the seasonal shift of flow continues to occur without any change in average annual flow,it would result in a small increase of a few percent in the available winter energy from the project. 4,000 3,500 3,000 _| ;.Linear Trendline a ms Watana Reservoir April Inflows |o 2,500 2 Lk = 2.0005 -i =oe i;>Le | §1,500 ee TToagndZaaLaeaneeeendera=oman af 1,000 eas i--" 500 | O- Years Figure 6.2-14.Example Month with Trend toward Increasing Flows -April Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-26 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 45,000 40,000 oa Watana Reservoir June Inflows 35,000 Linear Trendline 00101 ena (eae||25,000 -eects geeee aw Bo gp -__9 e-__-Fe- 20,000 ----gh -_| 15,000-F PETTUS L ET ae 10,000 5,000 oA EEE .: a8 Figure 6.2-15.Example Month with Trend toward Decreasing Inflows -JuneAverageMonthlyFlow(cfs)------___;Two potentially significant additional hydrologic changes should also be noted.Over the past decades,many glaciers have been in retreat worldwide and in Alaska.Glacier volume loss has been a component of Susitna River flow that cannot be sustained indefinitely.Using downstream Susitna River data published in a recent study (Neal et al.2010),approximately 5.8 percent of the flow near the mouth of the Susitna River could be estimated as glacier volume loss.The second potentially significant additional hydrologic change is an anticipated general trend toward increasing precipitation and runoff in the region of the Susitna watershed.Using information developed by the Intergovernmental Panel on Climate Change (IPCC 2007),average runoff in the region of the Susitna watershed is projected to increase by about 10 percent by 2050 in comparison to 1990.Because clear evidence of the opposing effects of glacier volume loss and increasing average annual runoff are not apparent in the historic runoff record,neither was included in the hydrology and power studies performed thus far. The hydrologic change studies performed to date have been directed at determining whether the available historic hydrologic record provides a hydrologic change signal of sufficient magnitude that would warrant inclusion in the current reservoir sizing and project operation studies.Only a seasonal shift in flow timing that could result in a small increase in winter energy was found. Among the proposed studies submitted by AEA to the Federal Energy Regulatory Commission (FERC)in the Revised Study Plan is a Glacier and Runoff Changes Study.This study Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-27 December 2014 -zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. (performed by others)will quantitatively evaluate the effects of projected changes in precipitation and temperature on watershed hydrology over the next 100 years in the Upper Susitna River Segment basin.The Glacier and Runoff Changes Study (scheduled for completion in 2015)will be performed in greater detail than the preliminary hydrologic change studies that have been performed to date.Depending on the timing and extent to which results of the Glacier and Runoff Changes Study become available,they could be incorporated as a sensitivity analysis in the reservoir operation and power feasibility studies. Due to substantial uncertainty in determining any potential climate change effects on extreme flood runoff,the lack of guidelines for incorporating potential climate change into the PMF studies,and due to the already conservative nature of assumptions and procedures used in determining the PMF,climate change was not explicitly included as a parameter in the PMF study. 6.3.Geology Geologic studies and investigations have been performed to develop an understanding of the regional and site geology,hydrogeology,tectonics,and seismic conditions associated with the project.The summarized results,interpretations,and conclusions from studies are described in this section. An understanding of the project geology forms the basis for developing the geotechnical design of the project.The geotechnical design includes characterizing the rock mass conditions and rock structure;evaluating construction materials;identifying geotechnical design and construction considerations;identifying areas of risk and uncertainty;and recommending additional investigations and studies to collect additional information.The geotechnical design is discussed further in Section 10.3 of this Feasibility Report. 6.3.1.Sources of Information Geologic and geotechnical field investigation programs have been performed during a number of phases over the last nearly 60 years.Field work in the area was initiated by the U.S.Bureau of Reclamation (USBR)in the late 1950s,but were not followed until field programs were conducted in the 1970s and 1980s (USACE 1975,1979;Acres 1982a,1982b;Woodward Clyde Consultants 1980,1982;and Harza-Ebasco 1983,1984)and more recently (2011-2014)in support of the engineering feasibility study.Site investigations are ongoing and additional investigations are still planned for the future.These will acquire additional data to improve characterization of dam site geologic and geotechnical conditions,reduce uncertainties in interpretations,and support the feasibility study and associated FERC study plans. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-28 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.3.1.1.Previous Studies and Investigations To date,site investigations have focused on characterizing the dam site,quarry and borrow areas, and relict channel areas using aerial photointerpretation,geologic mapping,drilling and in situ testing,geotechnical instrumentation monitoring,test pits,and geophysical surveys.Packer testing for determining rock mass permeability was performed,and instrumentation,piezometers and thermistors were installed in most boreholes to assess hydrogeological and ground temperature conditions in the soil and bedrock.Soil and rock samples were collected for laboratory testing to assess material properties.As the studies advanced,investigations were increasingly targeted at geologic conditions in certain locations (e.g.,relict channels)or assessment of the conditions associated with specific project features (e.g.,thickness of alluvium in river channel along dam centerline)or proposed project structures. The site investigations were originally developed and implemented based on a proposed 885-ft. high embankment dam with an underground powerhouse complex on the right abutment.Thus, the type of dam,areal extent of the dam footprint,and general arrangement differed from that which is proposed in the current engineering feasibility study. 6.3.1.1.1.Scope of Work of Previous Studies Table 6.3-1 summarizes the studies that have been performed at the Watana dam site prior to the commencement of the present engineering feasibility study.For locations of the investigations at the dam site,refer to Drawings 01-01GT001,01-01GT002,and 01-01GTO005,as well as the original reports of the investigations. Table 6.3-1.Summary of Previous Site Investigations Dates Lead Investigator |Studies Performed 1957 to 1958 USBR *-Limited geologic reconnaissance mapping. 1975 USACE «22,500 ft.of seismic refraction survey lines. 1978 USACE *Geologic mapping. *47,665 ft.of seismic refraction survey lines. *Rock core drilling:28 vertical and inclined boreholes,left and right abutments,and river bottom,relict channel area. *27 test pits and 24 auger borings for materials investigations. =Laboratory testing of borrow materials. *-Instrumentation:10 open-well piezometers,13 temperature logging casingsinstalledinboreholes. 1980-1981 Acres «Geologic mapping including aerial reconnaissance. (Alaska Power »-Reservoir area aerial photo interpretation;terrain unit mapping.Authority)«Preliminary assessment of reservoir slope stability. =-100,000 ft.of seismic refraction survey (includes Watana and Devil's Canyon). *Soil borings and sampling,Borrow D (14),Borrow E. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-29 December 2014 SUSITNA-WATANA HYDRO zw ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Dates Lead Investigator |Studies Performed #-Rock core drilling -8,000 ft.and geologic logging for holes in left and right abutments,and relict channel area. =Packer or water pressure testing. =-Test pits,and bulk sampling for materials investigations. =Downhole geophysical logging in two boreholes for temperature,caliper,resistivity, and sonic velocity. =-Laboratory testing of soils and rock material characterization and shear strength (discontinuities). *-Instrumentation installation and monitoring:pneumatic piezometers with thermistor strings. 1982 Acres *Reconnaissance geologic mapping along Susitna River,Fog Creek,Deadman Supplement to |(Alaska Power Creek,and Tsusena Creek,and Watana Creek. 1980-1981 Authority)*Geologic mapping at dam site including focus on potential fracture,shear,and Study alteration zones.Detailed mapping of abutments including "geologic features” GF1 and GF7. *-Soil borings (16)-2,300 ft.in Borrow Site D and Watana relict channel with split- spoon sampling and undisturbed sampling.Permeability testing and instrumentation installation. =Reservoir mapping by aerial photo interpretation. =Seismic refraction surveys: -21,400 ft.,Watana dam site abutments; -26,000 ft.,Watana relict channel/Borrow Site D; -45,000 ft.,Fog Lakes relict channel. «-Laboratory testing,soils -on site lab. « Freeze-thaw and aggregate testing. «-Instrumentation installation pneumatic and stand-pipe piezometers and thermistors,and monitoring. 1983 Harza-Ebasco «Winter program. (Alaska Power «Geophysical surveys,river channel: Authority)-Ground penetrating radar,8,490 ft.,14 profiles; -Seismic refraction,8,785 ft.,10 profiles. »Downhole geophysical surveys:gamma logging,22 river borings and 8 relict channel borings. «Becker drilling: -14 boreholes and 1,927 ft.of drilling in Watana relict channel plus water well; -43 boreholes and 3,710 ft.of drilling in the river channel. «-Constant head hydraulic conductivity tests in river overburden. «Water pressure tests in rock. =-Laboratory testing of soils.=-Instrumentation installation,pneumatic piezometers and thermal probes,and monitoring. 1984 Harza-Ebasco =-Geologic mapping at dam site include with focus on fracture,shear,and alteration (Alaska Power Authority) zones;in area of geologic features GF1 and GF7. Rock core drilling,11 boreholes and 4,370 ft.of drilling in area of GF1, downstream portal,and underground powerhouse.Evaluation of the persistence of shearing/faulting and seepage potential associated with "geologic feature”GF 1, and the degree of fracturing/shearing in the downstream portal underground powerhouse areas. Constant and falling head tests in soil. Water pressure tests in rock. Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 6-30 December 2014 -za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Dates Lead Investigator |Studies Performed =Downhole geophysical logging using gamma gamma,neutron,and natural gamma. =Borehole alignment surveys. *Laboratory testing of soils. «-Instrumentation installation,pneumatic and open standpipe piezometers;and monitoring. *Groundwater sampling. 6.3.1.1.2.Results and Conclusions of Previous Studies The significant findings from the geologic investigations performed during the 1970s and 1980s, pertinent to the general arrangement and dam type in this engineering feasibility report,are summarized below.In some cases,the results and conclusions below have been modified slightly or simplified from what was included in the original reports,to reflect knowledge gained from the subsequent studies.Reference should be made to the original reports for results and conclusions from the individual investigations and for additional details from each study. 1.Bedrock at the dam site is generally fresh to slightly weathered,hard to very hard, diorite to quartz diorite,with local widely spaced felsic and andesite dikes and veins.Andesite porphyry is found downstream of the dam and on the upper left abutment (the location of proposed Quarry A). a.The contact between the andesite and diorite is generally highly fractured, weathered,and poor rock quality.It is less than 10 ft.wide. The rock is fractured,sheared and hydrothermally altered. Cc.Beneath the river channel,bedrock ranges from altered to fresh,hard, diorite.Areas of moderately to closely fractured rock were encountered as were a few shear zones containing fine-grained gouge. d.Water takes from pressure testing within these zones were low. Subsurface investigations indicate that rock quality is suitable for large underground facilities (right abutment). Overburden on the dam abutments is generally 10 to 20 ft.thick consisting of talus,till and alluvium but locally may reach depths of 50 ft.(upstream of the dam axis on the left abutment). Alluvium in the river channel consists of well-graded coarse-grained gravels, sandy gravels,and gravelly sands with cobbles and boulders ranging in thickness from 40 to 80 ft.,but may be locally 140 ft.thick. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-31 December 2014 -yzw- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. a.The bedrock channel shape is generally symmetric about the river centerline.The channel bottom is nearly flat with the exception of two pronounced depressions upstream of the dam axis. b.The bedrock in the river channel ranges from altered to fresh,hard,diorite. Areas of moderately to closely fractured rock were encountered as were a few shear zones containing fine-grained gouge.Water takes from pressure testing within these zones were low. 5.Localized fracture,shear,and altered zones have been mapped within the dam site and are generally less than 10 ft.wide. a.Two major and two minor joint sets were identified:a)strike 320 (azimuth),dip near vertical;b)strike 045 to 080,dip near vertical; c)strike 340 to 030,dip 40°to 60°west;d)strike 080,low dip angle. b.Fractures are closely spaced on the surface and more widely spaced at depth.Healed fractures are common. c.Some fractures have clay gouge seams and slickensides. 6.No evidence of major faulting was found. 7.The groundwater table at the dam site tends to follow the topography.The groundwater in the right abutment is 40 to 280 ft.deep.Groundwater on the left abutment is complicated by permafrost,and artesian conditions were encountered below the permafrost. 8.Permafrost on the left abutment appears continuous and ranges from about 200 to 300 ft.thick.At lower elevations of the right abutment,local permafrost was encountered to depths of 50 to 60 ft.Ice was found in cores DH84-3 and DH84-8, and ice blocked hole DH84-6 after it was completed. 9.Two prominent "fracture /shear zones”were mapped in exposures upstream (GF1)and downstream of the dam site (GF7).The GF!and GF7 features are considered unsuitable rock for construction of surface or underground works and should be avoided (they are remote from the current proposed dam location. 10.Drilling investigations of the GF1 feature above the rock outcrop encountered no evidence of major shearing or faulting that would lead to significant seepage or erosion under filled reservoir conditions.Groundwater levels in the area of GF are high indicating low transmissibility. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-32 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 11.A relict channel was identified above the right abutment between the Susitna River and Tsusena Creek.Glacial,fluvial,and lacustrine deposits fill the channel and are as much as 450 ft.thick (El.1800 ft.).The average hydraulic gradient from maximum pool (El.2185 ft.)to Tsusena Creek is about nine percent. 12.Potentially suitable borrow materials were identified near the dam site for aggregates (Quarry A,B),rockfill (Borrow E,I,J),filters,and impervious (Borrow D,H)materials. 6.3.1.2.Investigations and Studies for this Feasibility Report Site investigations and studies were performed from 2011 to 2014 to support the development of the engineering feasibility and licensing studies.They supplemented the earlier geologic investigations and interpretations conducted in the 1970s and 1980s and included evaluation of previous results and interpretations.The latest site investigations and studies are incomplete and this report therefore reflects only the information acquired prior to the release of this report. Additional investigations and studies are planned -in particular (but not limited to)the excavation of adits,together with associated in situ testing. The most significant difference between the previous engineering arrangements and that documented in this report is that the current proposed arrangement includes a curved RCC dam instead of a zoned embankment dam as previously proposed.The engineering feasibility study of the new arrangement required that all available geologic information and interpretations be re- examined with emphasis given to foundation characterization and the associated structural properties of the bedrock. Investigations included re-examination and improved characterization of previously identified geologic structures in the dam site area that could conceivably influence dam type selection and design of rigid concrete structures.They also included characterizing a new potential construction material source,Quarry M,and performing a site-specific seismic hazard analysis for the project to update previous studies performed by Woodward Clyde Consultants in the 1980s.Site investigation methods included analysis of LiDAR data,geologic mapping,drilling and in situ testing,instrumentation installation and monitoring,and laboratory testing.In addition,analysis of LiDAR data and geologic mapping were performed on a regional basis, including the reservoir area,to support both the site-specific seismic hazard analysis and the soils and geological studies required for FERC licensing.For locations of the drilling and mapping investigations at the dam site area,reference should be made to Drawing 01-01GTOO1 and Drawing 01-01GT002. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-33 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. As part of the latest site investigations program,new methods not available in the 1980s were used to collect additional types of information and improve interpretations.Newly acquired LiDAR data (Drawing 01-01GT002)were used to create detailed ground surface maps that enabled geomorphic evaluations and facilitated more focused geologic mapping.For the drilling programs,downhole televiewer logging was used to supplement available information on discontinuity orientations.Additionally,geotechnical instrumentation,which included data loggers,was installed to measure and record piezometric levels and ground temperatures to assess hydrogeological and ground temperature (permafrost)conditions.Laboratory testing was also conducted focusing on the engineering properties of the rock and aggregate sources. Table 6.3-2 summarizes the studies performed between 2011 and 2014 at the Watana dam site in support of this feasibility study.The Geotechnical Data Report is attached as Appendix B1 and contains details of the geotechnical investigations performed in support of this engineering feasibility study. Table 6.3-2.Summary of 2011 to 2014 Site Investigations Dates Studies Performed 2011 «-Rock core drilling,3 boreholes,600 ft.at Quarry A.«-Water pressure testing in rock.«-Instrumentation installation,open standpipe piezometers. =Laboratory testing and petrographic analysis of rock core and bulk samples. =-Microseismic monitoring stations established (4). 2012 =Geologic mapping of the dam site,Quarry M and surrounding areas using LIDAR base map. =-Rock core drilling,8 boreholes,2,355 ft.at the dam site. =Water pressure testing in rock. «Downhole optical and acoustic televiewer logging in 4 boreholes. *Instrumentation installation for groundwater levels and ground temperature.Instrumentation monitoring. «Laboratory testing and petrographic analysis of rock core samples;engineering properties of rock and construction aggregates. «-LIDAR digital imagery evaluation for updating terrain unit maps,lineament analysis,and preliminary assessment of reservoir area slope conditions. «-Microseismic monitoring stations expanded (total 8). 2014 «-Geologic mapping of the dam site and surrounding areas.«-Rock core drilling,4 boreholes,1,750 ft.of drilling at the dam site. =Water pressure testing in rock. «-Continuous downhole optical and acoustic televiewer logging in all boreholes. =Laboratory testing of rock core samples. «-Instrumentation installation for groundwater levels and ground temperature.Instrumentation monitoring.«-Crustal seismic source evaluation. *Microseismic station network monitoring. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-34 December 2014 -wZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.3.1.2.1.2012 Drilling and Testing The 2012 drilling and testing program focused on the evaluation of conditions in the dam footprint and Quarry M.Eight boreholes were cored using HQ3-wireline methods.Three boreholes were advanced in the left abutment,two boreholes were advanced in the right abutment and three boreholes were advanced in Quarry M.Water pressure testing was conducted at regular intervals in each of the boreholes.Selected boreholes were surveyed using either downhole optical or acoustic televiewer logging.Geotechnical instrumentation including piezometers and thermistors were installed in selected boreholes.Laboratory testing was conducted on selected rock core samples and bulk surface samples collected from the talus slopes on the left abutment. Because prior to 2012,few explorations had been conducted in the left abutment of the dam footprint,cored drill holes were made at DH12-1,DH12-2 and DH12-8 to improve the understanding of the left side.DH12-1 and DH12-2 were drilled in the upper portion of the left abutment to depths of about 300 and 200 ft.,respectively.Both of these drill holes were inclined at approximately 20 degrees from vertical to the northeast.Rock conditions encountered in DH12-1 and DH12-2 were observed to consist primarily of fresh,strong to very strong diorite with occasional zones of weathering.Weathered zones were generally five feet thick or less, with highly weathered portions limited to less than one to two feet thick.DH12-8,oriented to the south and 30 degrees from vertical,was advanced to approximately 350 ft.in the lower left abutment near river level.DH12-8 also encountered mostly fresh,strong to very strong,diorite with weathered zones approximately five feet wide or less. Previous interpretations of the earlier site investigations postulated the presence of multiple geologic features (GFs)that transect the dam footprint.Therefore,new drill holes DH12-3 and DH12-4 targeted geologic features GF4A and GF4B (per Acres nomenclature)and GF5, respectively.Drill hole DH12-3 was drilled to a depth of about 400 ft.in the area of feature GF4B.DH12-3 trends southwest and is inclined 30 degrees from vertical.To investigate GFS, DH12-4 was advanced 350 ft.trending west-southwest and 20 degrees from vertical.Both DH12-3 and DH12-4 encountered closely spaced discontinuities over large portions of these holes.Discontinuities were commonly stained with iron oxide nearer to the surface and tended to be healed at depth.While zones of highly weathered rock and shear zones were encountered in these boreholes,they were generally three to five feet thick or less.Prominent,wide shear zones or thick zones of heavily altered rock were absent in the holes. Boreholes DH12-5,DH12-6 and DH12-7 were drilled within the proposed Quarry M,located upstream of the left abutment,specifically to verify the suitability of the area as a source for the production of concrete aggregate.DH12-5 was drilled to a depth of about 250 ft.and inclined Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-35 _December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 20 degrees from vertical toward the northwest.In general,DH12-5 encountered fresh,strong to very strong diorite over the length of the hole.Localized zones of moderately weathered rock were observed to be typically three to four feet wide or less.DH12-6 was drilled near the mapped location of GF4 (Acres 1982a;1982b),on the upper south bank.This hole was advanced approximately 350 ft.and inclined 10 degrees from vertical toward the east.DH12-6 encountered closely fractured rock over significant portions of the hole.A large percentage of this core is moderately to slightly weathered;however,several zones of highly to completely weathered rock up to 14 ft.thick (apparent thickness)were encountered.DH12-7 was drilled near the mapped locations of GF2 and GF3.This borehole was drilled to a depth of 150 ft.and was inclined 10 degrees from vertical toward the east-northeast.DH12-7 encountered significant zones of completely or highly weathered rock up to approximately 18 ft.wide (apparent width). A 5-foot wide (apparent width)shear zone was noted at a depth of 118.5 ft. Lugeon values were determined over regular intervals in the 2012 drilling program using a five- step water pressure test procedure in accordance with the recommendations presented by Houlsby (1976).Test results varied widely from zero to greater than 100 Lugeons (1 Lugeon = 1.3x10°cm/sec for N-and H-sized holes).Hydraulic conductivity was typically highest near the ground surface where open discontinuities were encountered with greater frequency and decreased with depth. Downhole televiewer surveys were conducted in drill holes DH12-3,DH12-4,DH12-6,and DH12-8.Optical televiewers were used to survey DH12-3 and DH12-4 since groundwater levels were relatively deep.An acoustic televiewer was used to survey DH12-6 and DH12-8 due to cloudy water in the hole,which made conditions for optical methods less suitable.The televiewer surveys were also limited in some places by unstable hole conditions,particularly in DH12-6 where caving conditions were encountered,limiting the survey between the depths of 289.5 ft.and 347 ft.Unstable hole conditions also precluded televiewer surveys above a depth of 62 ft.in DH12-3. New geotechnical instrumentation was installed in each new borehole.Vibrating wire piezometers were installed in DH12-1 through DH12-6 and DH12-8.Thermistor strings and temperature acquisition cables were installed in all holes with the exception of DH12-5 and DH12-7.Piezometers and thermistor strings are equipped with data loggers programed to record measurements at regular intervals.A 1'4-inch diameter PVC standpipe piezometer was installed in DH12-7. The 2012 laboratory testing program consisted of tests to measure rock strength,seismic modulus,and properties of aggregates.Rock strength tests included 11 uniaxial compression strength (UCS)tests,nine point load index tests,five Brazilian tensile strength tests,and five Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-36 December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. direct shear tests of discontinuities.The testing indicated that fresh to slightly weathered rock has an average UCS of over 26,500 psi.One test conducted on moderately weathered rock resulted in a UCS of about 7,600 psi.Brazilian tensile strength tests were conducted on slightly weathered to fresh samples,yielding an average value of approximately 2,200 psi.Direct shear strength tests were conducted on various discontinuities including iron-stained joints,calcite- coated joints,and saw-cut surfaces. 6.3.1.2.2.2014 Drilling and Testing The 2014 exploration and testing program included investigation of conditions beneath the bed of the Susitna River and previously mapped geologic features on the right abutment.Drill holes DH14-9b and DH14-10 were drilled beneath the Susitna River in opposing directions to explore the presence/absence of any significant geologic structure in the river bed parallel to the Susitna River at the dam site.Drill holes DH14-1land DH14-12 targeted postulated geologic features GF4 and GF5 (per Acres 1982 terminology)on the lower to middle sections of the right abutment.All holes were drilled using HQ3-wireline drilling methods.Water pressure testing and downhole logging were performed in all holes,and a laboratory testing program was completed. It had been postulated that a significant geologic feature could potentially be present below the Susitna River at the location of the dam.If present,such a feature would present a significant engineering challenge to the project,and could conceivably require re-examination of the choice of dam type.Combined,holes DH14-9b and DH14-10 were drilled across the width of the river in opposing directions with the intent intersecting any significant geologic structure,if present. DH14-9b was drilled to a depth of 683 ft.from the right abutment inclined 30 degrees from vertical toward the south.DH14-10,located approximately 300 downstream of the dam axis on the southern bank of the river,was drilled to a depth of 692 ft.and inclined 30 degrees from vertical toward the north.In general,DH14-9b and DH14-10 encountered slightly weathered, strong to very strong diorite with occasional zones of alteration.Alteration zones were typically comprised of moderately weathered,medium strong diorite and were about five feet thick or less;however,some altered diorite zones were up to about 14 ft.thick.While small shears with one to two inches of clay gouge were encountered,no significant geologic structures were observed in either hole.This provides subsurface evidence in support of interpretations made from geologic mapping that the existence of a through-going fault in the thalweg of the river at the dam site is improbable. Drill hole DH14-11,located about 230 ft.downstream of DH12-4,was drilled in a northeast direction to further improve the understanding of conditions within the dam footprint along the postulated geologic feature GF5.DH14-11 was drilled to a depth of approximately 197 ft.and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-37 December 2014 yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. was inclined 30 degrees from vertical toward the northeast.Rock encountered in DH14-11 primarily consisted of fresh to slightly weathered,strong to very strong diorite.Zones of closely fractured rock were common throughout much of the borehole.These fractured zones were more common in the upper portions of the hole.Altered diorite zones two to five feet thick were encountered in the upper 105 ft.of the exploration.Three zones of completely to highly weathered rock where encountered that ranged from about an inch to two feet thick. Drill hole DH14-12 targeted a fracture and shear zone previously mapped by Acres (1982).This feature was mapped parallel to GF5 and approximately 300 ft.downstream of the dam axis on the right abutment.DH14-12 was drilled to a depth of 175 ft.and was inclined 30 degrees from vertical toward the northeast.Bedrock encountered in DH14-12 typically consisted of slightly weathered,strong diorite with occasional zones of altered diorite.Approximately six zones of altered diorite were encountered ranging in thickness from 0.5 to 11 ft.(apparent thickness).A shear zone having I-inch of gouge was encountered at a depth of about 76 ft.A second shear zone containing about 20 inches of gouge was encountered at a depth of 110.0 ft.within an approximately 5-foot wide zone of altered rock. Lugeon values were determined over regular intervals in the 2014 boreholes using a five-step water pressure test procedure in accordance with the recommendations presented by Houlsby (1976).Test results varied widely from zero to about 70 Lugeons.Tests typically indicated very low to very high permeability,with few intermediate test results.High test values commonly coincided with open jointing or fracture zones near the ground surface,or discrete fractures or fracture zones at depth.Test values indicated that permeability generally decreases with depth. Each of the four 2014 boreholes were surveyed using both optical and acoustic downhole televiewers.Because the groundwater surface was encountered above the bedrock elevation in explorations DH14-9b and DH14-10,both were surveyed over their entire length using both optical and acoustic televiewers.Optical televiewer surveys were conducted over the entire length of DH14-11 and DH14-12;however,acoustic televiewer surveys were limited in these two holes by relatively deep groundwater levels.Accordingly,acoustic surveys were conducted below a depth of approximately 34 ft.in DH14-11 and about 95 ft.in DH14-12. The 2014 laboratory testing consisted of UCS,Brazilian tensile strength,and direct shear testing. In contrast to the 2012 program,the 2014 program focused on testing samples of poor, weathered,or altered character.Eight UCS tests were conducted.Tests conducted on moderately weathered rock had an average UCS of about 9,500 psi.Two tests conducted on slightly weathered to fresh rock had an average UCS of about 19,000 psi.One test conducted on moderately to highly weathered rock had UCS of about 1,600 psi.Brazilian tensile strength tests were conducted on two moderately weathered samples,which had strengths of about 420 and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-38 December 2014 ww ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 860 psi.Eight direct shear strength tests were conducted on various discontinuities including calcite coated joints or joints with slickensides. 6.3.1.2.3.|Regional Mapping Regional mapping was done to develop a better understanding of the geologic and structural relationships in the area at the dam site and surrounding areas and to evaluate the potential impacts of local faulting on the dam and other critical structures. Existing regional geologic mapping depicting both the dam site and the general vicinity within 5 to 10 miles has been developed by Csejtey et al.(1978),Acres (1982b),and Wilson et al.(2009). The existing maps were developed at a variety of scales,using various methods and level of detail,and for multiple purposes;therefore,there is inconsistency in the local completeness and accuracy of geologic mapping which has led to several areas of general disagreement across the maps.The emphasis of most prior mapping in the region was directed to reconnaissance level bedrock framework and mineral resource evaluations.Along the Susitna River,much of Wilson's (2009)map is a compilation of Csejtey's (1978)work,and several prominent outcrops in the area were not recognized.Previous dam site-specific geologic mapping was,by definition, highly focused and of limited aerial extent. Geologic observations made during this recent study included examination of prominent outcrops that seem to have been un-recognized in previous mapping.The regional mapping is intended to indicate confirmation or disagreement with existing mapping,and to provide a level of transparency as to where outcrops are present or absent,and from which locations outcrop- based interpretations are possible. Field investigations identified and inspected a number of exposures to collect structural (strike and dip)information,and to understand the distribution and deformation of rocks in the site area and vicinity.The data was collected along an east-west transect along the Susitna River,and a north-south transect along Watana Creek.Bedding attitudes were collected using a Brunton compass set to 19 degrees declination and GPS-enabled ruggedized laptop for location. Additional bedding attitude data were compiled from existing data sources including Army Corps of Engineers (USACE)(1979),Acres (1982b)and Woodward Clyde Consultants (1982). Strike and dip data were collected from outcrop locations and a small number of observation points were made from the air.Long extents of the south side of the Susitna River had no outcrop or exposures because of vegetation and soil cover.Good exposures on the south side of the Susitna River generally were located at the confluence of tributary creeks,and seemingly erosion-resistant Cretaceous rocks.However,the field traverses along the Susitna River and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-39 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Watana Creek provides somewhat limited structural insight because they capture only a one- dimensional traverse characterization of a three-dimensional volume. 6.3.1.2.4.|Recent Dam Site Geologic Mapping Mapping was performed at the dam site to evaluate and update the interpretations from earlier studies,to fill information gaps,and to improve characterization of bedrock conditions at the dam site -to a level that could support the assumptions made during the structural analysis of the proposed dam. The original geologic mapping was performed at the dam site beginning in the late 1970s and continued during the 1980s,during which time the distribution of geologic materials was defined and the orientations and character of rock discontinuities were measured at outcrops.In addition, the mapping efforts in the dam site area,combined with information from the contemporaneous drilling and geophysical explorations,identified eight geologic features (GF1 to GF8). The objective of the mapping at the dam site has been to evaluate the previous work and to update specifically the characterization of the geologic features identified by Acres (1982a, 1982b)and the geologic interpretation of the site that was developed during the earlier studies. In addition,the recent mapping efforts attempted to fill information gaps identified during previous studies,or further define structural features that affect the design of a concrete gravity structure.Specifically,the objectives of the dam site mapping included: 1.Interpret the site geology and structure using the newly acquired LIDAR digital imagery. 2.Field locate geologic features previously identified as well as new features,most particularly those that may be encountered in the dam foundation.Update the locations of these features using new topographic (LIDAR)mapping and sections as well as the geologic descriptions. 3.Identify rock outcrops throughout the dam site area and provide the following at each outcrop: a.Rock type,weathering/alteration,strength Orientations of rock discontinuities. c.Descriptions of discontinuities in accordance with criteria established by the International Society of Rock Mechanics (Barton and Choubey 1977). Assessments of discontinuities include persistence,aperture,fillings and stains,surface shape and roughness,larger scale roughness (Joint Roughness Coefficient [JRC]),and spacing. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-40 December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. d.Estimate the Geologic Strength Index (GSI)of the rock mass in outcrop considering rock structure and joint surface conditions. e.Estimate the typical size of blocks bound by the joint sets. 4.Evaluate discrepancies between orientations of discontinuities in outcrop and downhole logs.Downhole televiewer logging performed in 2012 and 2014 indicated an overabundance of shallow dipping joints compared with observations made during geologic mapping of rock outcrops.Mapping indicated the dominant geologic structure is steeply inclined joints trending in the northwest- southeast and northeast-southwest directions,which is consistent with the interpretations from the 1980s. 5.Identify rock types in outcrops and update locations of geologic contacts as appropriate. Geologic mapping of rock outcrops was performed on the north and south banks (right and left abutments)of the river beginning about 2,000 ft.upstream of the dam axis near geologic feature GF1 and extended to about 1,500 ft.downstream of the dam near GF7.Measurements and observations of structure and geologic features were made at outcrops distributed on both banks of the river;however,greater effort was focused on geologic structure anticipated to appear within the dam foundation. Navigating was managed using GPS (Trimble GEO7X)equipped with ArcGIS preloaded with maps that included topography,slopes angles,geologic maps,etc.,to facilitate navigation and interpretations.The locations of outcrops (designated as OC 1 to OC 118),observation points (designated as BS 1 to BS 37),and geologic structures were recorded by GPS and numbered sequentially are shown on Drawing 01-01GT002. To obtain representative measurements,outcrops distributed throughout the site and on both abutments up to the proposed reservoir rim were mapped.At each outcrop,the orientations of the prominent joint sets were measured and characterized following ISRM criteria.In addition, the rock type,weathering or alteration condition,color,strength,block dimensions,and an estimate of the GSI were recorded.This information is used to estimate the engineering properties of the joints and rock mass needed for design analyses. Observations (BS |to BS 37)were recorded at locations of geologic interest (e.g.,gullies,shear zones)that did not necessitate or allow for measurement of all joints or a full assessment of the rock outcrop. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-41 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Field measurements were recorded on data sheets and field notebooks,which were compiled into spreadsheets.Rock discontinuity data were input into DIPS (Rocscience,Inc.)software to identify orientations of the prominent joint sets.After identifying which set each joint belonged to,the joints were grouped so that the ISRM criteria could be developed for each joint set. The geologic features and structure that had been mapped during previous studies were re mapped and characterized.Many of the geologic features and prominent structures are associated with topographic features such as gullies instead of being observed directly in outcrop.In the absence of direct observation,the surface and geologic conditions were described and measurements of discontinuities were made at the nearest outcrops to constrain the possible location and orientation of the structure.The mapping information,combined with information from the recent drilling investigations and downhole logging,has been combined to constrain the locations of prominent geologic structures and to update the descriptions of geologic features. 6.3.2.Regional Geologic Setting 6.3.2.1.Physiographic Provinces The Project is located in the south-central region of Alaska where three principal physiographic provinces exist:the Copper River Basin,the Susitna Basin,and the Talkeetna Mountains as shown in Figure 6.3-1.The Copper River Basin is an intermontane basin surrounded by the Alaska,Talkeetna,Chugach,and Wrangell mountains.It is characterized by flat-lying to hummocky topography and is overlain by extensive glacial,glacio-fluvial,and glacial-lacustrine deposits.The Susitna Basin is a north-south trending feature and is the principal deposition center for alluvium transported by numerous major river systems originating in the surrounding mountains.The Susitna River source is in the ranges north of the Copper River Basin and it flows from there westward through the northwestern Copper River Basin and through the Talkeetna Mountains in a deeply incised canyon.Downstream,sediments from the Susitna River contribute to alluvial deposition in the Lower Susitna Basin.The dam site is located within the Talkeetna Mountains province.The Talkeetna Mountains are an elevated area that lies between the Copper River and Susitna Basins,with glaciated peaks between 6,500 ft.and 9,800 ft.in elevation as shown in Figure 6.3-1. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-42 December 2014 --z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT ".152°0'0"W po taebow * OF yeSaga i Psa':Copper River Basini.Susitna Pp fh OOOTordilio=Se PPLE EE I od27Mins.Se Chugach Mins.7,-7 a roPortFa, wf "Lo z cationMap Ws7y Figure 6.3-1.Major Physiographic Provinces 6.3.2.2.Regional Tectonic Setting and History The tectonic evolution of south-central Alaska is defined by plate convergence,with Mesozoic (i.e.,Jurassic-Cretaceous)collisions of the Wrangellia composite terrane followed by later Cenozoic collision of the Yakutat terrane.The Wrangellia terrane generally consists of late Triassic flood basalts;the Peninsular terrane consists of Jurassic arc volcanics,metasediments, and plutons.The two terranes originated well south ( 30°latitude)of their current position. Together,the Wrangellia and Peninsular terranes are referred to as the Wrangellia composite terrane (Figure 6.3-2 and Figure 6.3-3),and likely were sutured together in the Late Jurassic (Csejtey et al.1978).The composite terrane,in turn,was accreted onto North America in the Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 6-43 December 2014 -yw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. mid-to late-Cretaceous when the southern plate margin of North America was roughly along the position of the Denali fault.Between the converging terrane and North America was a marine basin (Kahiltna basin)that accumulated Jurassic-Cretaceous sedimentation shed from the southeast direction (Kalbas et al.2007).The northeast striking Talkeetna fault is the principal eastern terrane-bounding structure in the region,separating the Jurassic-Cretaceous sediments (i.e.,Kahiltna assemblage deposits)on the northwest from the Wrangellia terrane metavolcanics to the southeast (Figure 6.3-2 and Figure 6.3-3).Thus,in terms of terrane accretion,the region of crust south of the Denali fault and northeast of the Talkeetna fault is a large suture zone that narrows to the east,reflecting oblique plate convergence and the long-term closing of the Kahiltna basin.The rocks that formed in the Kahiltna Basin have been uplifted through the Cenozoic,making up much of the Alaska Range and northwestern Talkeetna Mountains and forming a structural inversion.Essentially,formerly low-lying areas (i.e.,basins)have now become high topography (i.e.mountains)as a result of plate convergence and mountain-building uplift along generally northeast trending folds and thrust faults. Jurassic plutonism from melting of the oceanic subducting slab formed the batholitic complex of the southeastern Talkeetna Mountains (Nelson 2009)by intruding into the Peninsular terrane (Figure 6.3-3,map unit TKg).Subsequent uplift initiated northeast-directed sedimentation within proto-Kahiltna Basin in what is now the northeastern Talkeetna Mountains (Kalbas et al. 2007).Kahiltna Basin sediments continued to accumulate during the Cretaceous as westward sediment transport on fluvial,shallow marine and submarine fan depositional environments.The Kahiltna assemblage is about 3 to 5 km thick,and consists of turbidite sequences,chert, mudstone,sandstone,and greywackes that comprise eight distinct lithofacies (Kalbas et al. 2007).Progression in the understanding of the relationships between the terrane units and tectonics has allowed a deeper understanding about the Kahiltna Basin rocks and their significance as a recorder of long-term tectonic deformation,in contrast to previous interpretations that generalized the complex stratigraphic unit as "argillite”or "flysch”. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-44 December 2014 -z- SUSITNA-WATANA HYDRO ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Ca at .TOF te Re')EST ee ee ae,*pdf wen 1%)<i Chae .7 Fa!AL Sow ptm 'A we es:Mesozoic conpnental [> oe eee :':,ca I yee be ukan-lananawoa7wesa (tor *NE Kahilina assemblage 4 icentrat Alaska Range set gre otYoooh73 a =. Q Kahiltna assombiage Tatkee§na Ming } ee ayNGS ee> -N ALS i Sgt PE -iF ;ons ;7 nee -:meee t ¥Sw amen atte ai ::=annBepeehote(Watlace et al.1999 JAE ar Figure 6.3-2.Regional Tectonic Terranes and Basins -Part 1 of2 (Fugro 2014) Kalbas et al.,2007 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 6-45 Alaska Energy Authority December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. B)64a'N NEY S"oyDoear=fa <a Range vseat-a Nokelberg and Richter,2007 Late Jurassic -early Cretaceous Kahiltna assemblage Tertiary plutonic intrusions TKg }Cretaceous-Tertiary plutonic intrusions Tv_|Tertiary volcanics Figure 6.3-3.Regional Tectonic Terranes and Basins Part 2 of2 (Fugro 2014) Oblique subduction of an oceanic spreading center during Paleocene to early Eocene initiated magmatism and formation of short-lived northwest trending extensional (normal)faults shown in Figure 6.3-4 (from Ridgeway and Trop 2007).Included in these volcanics are the Cantwell and Jack River volcanic fields dated at 55 to 60 Ma,and 50 to 56 Ma,respectively shown in Figure 6.3-5 (from Cole et el,2007).To the southeast,volcanic flows that overlie and cap the Talkeetna fault are dated at 50 Ma (Csejtey et al.1978).Thus,Tertiary magmatic intrusions punctuate both the Kahiltna Basin assemblage,the Wrangellia composite terrane,and the Talkeetna fault (Figure 6.3-3). Regional crustal rotation of southern Alaska took place sometime in the early to mid-Tertiary, with rotation of 30 to 50 degrees in the counterclockwise direction accommodated by the dextral _Denali and Castle Mountain faults to the north and south,respectively.Consequently,regional Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-46 December 2014 --2Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. transpressive deformation occurred during middle Eocene to Oligocene time,generating narrow fault-bounded basins along major strike slip faults as well as northeast trending folds (Trop and Ridgeway 2007).The Watana Creek basin probably was formed during this time as the Talkeetna fault re-activated as a strike slip structure from the changing crustal stress orientations (Figure 6.3-4 and Figure 6.3-5). Post-Eocene tectonic growth of southern Alaska is controlled by the oblique collision of the Yakutat terrane,probably 15 to 10 Ma,with construction of continental magmatic arcs (i.e.,the Wrangell volcanic field)from subduction of the Yakutat microplate,and development of large coastal mountain ranges (e.g.,St.Elias Mountains).The collision of the Yakutat microplate is considered to have substantial influence on the deformation and counterclockwise rotation in the interior of south-central Alaska (Haeussler 2008).Subduction of the Pacific plate continued beneath North America from Eocene onwards,with growth of the Aleutian Islands from three main pulses of arc-wide magmatism occurring at 38 to 29 Ma,16 to 11 Ma,and 6 to 0 Ma (Jicha et al.2006). Since the latest Cenozoic through today,south-central Alaska has experienced rapid rates of tectonic deformation driven by the obliquely convergent northwestward motion of the Pacific Plate relative to the North American Plate.In this region,the Pacific Plate is converging with North American Plate at a rate of 54 mm/yr.(2.1 in/yr.)at a slightly oblique angle (DeMets and Dixon 1999;Carver and Plafker 2008).Consequently,rates and magnitudes of seismicity are also accordingly high.In southern and southeastern Alaska,the oblique convergent plate motion is accommodated by subduction of the Pacific Plate along the Alaska-Aleutian megathrust trench,and dextral (right-lateral)transform faulting along the Queen Charlotte and Fairweather fault zones.Transpressional deformation primarily is accommodated by dextral slip along the Denali and Castle Mountain faults,as well as by horizontal crustal shortening to the north of the Denali fault. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-47 December 2014 -yw SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Mo tne SET"ear er ra fusamiat aptalhadraRnesoebaseuence EYoo)> ss Souhwed Urucdang etd loiter)Od oni cokunny hea denen CIM UD UBT ae Tsar a tues uray fatty drang vrokimere Lo)ed cysidesac,nated by VCS a potas"as Peretd Of OcalcatmuptngrtheseAy, Thies wf}sulle Ie buns hn cemeany manevatiyséWoeaterart(faut a 0-8 "cctyba.oFexedthrewederm Peary 'N én,asinan iThywtiicaonMa {Yokefarangtomers=[(Seiomme be D 112-83 Ma F 61-33 Ma mae et H 26-0 Ma Lap pineemne gnc qunmsmens Early Late Cretaceous Late Paleocene-Eocene oe t ao.aa Latest Oagocene-F recur stteme Cete.s de ead rem Albian-Santonian OP 7 Tt Fy ¢'ey NeogeneSTybenTymeereWInenreeyyiidoOa*-"utaeraameesSeaeorZ::i "4 ne 2 x ee aM A es meaeTabwargierear]f OA ™Ps,:;hasty ovine Ped Jc aps =_us |akeadtuad-auiaiee orcotane |th,faa vantexsthe tt are yet ON ce ft ntact freatoted hasan TATENayeanata y.}QOs amond tera tet ce)ard :ore 2 4 f i |sacka Sar Gt it ine |+-- Sin Vt ay a "ruaracns)ty an eos,Feeti.+i 3 . MEi turned fy aiurut! 3 " trtts Southwant i Abhayais egusie at jedernrd thenagat |aeuraRe er heanied5PNTeMiteShePREUIST.|[GIRSDarts oa .a Cretacaras ors upediondt ||Yd "cnnte teredabingTeteDareihiroreeUreabocakdebye Schiren.s,ree -enee,Stora sath stuart 3 Sevier agg Crt alone a tf 4 cn Alida dither pedacuitinie Uncool |aever Lae bear E 83-68 Ma nedainn yt tiraarg ome3fFm)otha tte tear lB)Cerna dened tom Latest Cretaceous CREME IM Mes FF PE A om ™--"SATE CONTENTS Fete ad ub ed eete :*aR iene te ets Campanan-Maastrichtian Lontrmorsg ac reagan scross boththethere.mar conarerctsé manger (tubs G 33-26 Ma Otigocene Catia PaneraanedexterergsorgCom toutIFSarampesareofWesco +- "coasan bears (LICR L&E UNL Ares of "oh gerarentyzedllagecatlquares .Cra Oe IT OTeWyAanlgtstaat"OepRos eRaeatl Saas LOCred wiretgh aid a]Ghagsiidain 9)bailLEreeehao| Jtatatitan<< Codaece!ated ardorTishh)OF Vabutsttarone apnesued.atn conden BigSowmemertelegyerchpiees:{i Datesocenet of icaora!com i ea)foreieg cerry wath gn tea Vjere fb cere vercbber races[be ete docu deamon Hea Se Fan 5nmtanansCretecdpagsih)ooardot DecattetCelrdultcotacnalbeansWCELe3nw,TONAGE CES atid Sociend Saneho "i _ommern ere [Raimasriomrence”; .«ee ven Gen i.Lh ae Teids1aiefaauratieweintynnceattinsCath ieGrandfewer,(00 OeHERTenensctmrerage5innova 3éLenaytCoe6pasting<4.sruatioa bub seitiad Letat ate ' Wee Le Te]3ME TONS ed womans tan .'=Ss .es wa,aana oe Coat gated Mia:I sect *ee hieHs{me Bi fecard ear 2 frenomam ouecaeiern x 17 Coober Baar bar "KR ® ited Latest Crvsseuurs m-DAUTIOT Rag Teton,Sa ralace Outon Cade Min fads:MEH .=faanMogoh_ab uinurnetn trade RaGay,geater Gaus,omhuge aj =e -*Onesic Fite a qublutit ClChests *§ Trop and Ridgeway,2007. SregachTarranecapesMARIScoir-Bre, Me wre TareeeenReinertAoWeNGeetheppzaterjrhemicakConchirrerater,Ne \YaaTrccet.Fin jin Cock trier ore er Oe v cs Tetris Explanation Geographic references Terranes Outboard Margin Basins Volcanic Fields,Plutonic Beks Inboard Margin Basins Faults,Shear Zones +A Andh AT -Alexander CIB -Gack Inlet AA-Aleutan-Alaska are CB -Cantwell BHF -Border Ranges-Hanagita fautFAAnchorageCTChugachCRB-Copper River CV -Caribou Creek volcanics CCB -Colorado Creek BLF -Bruin Bay-Litthe Oshetna fault ¥F -Fasrbanks PT -Peninsular CV6 -Chitina Valley CTV -Central Talkeetna Mins voicanics 08 -Dezadeash CMF -Castte Mountain faust FM -McCarthy PWT -Prince Wikam M8 -Matanuska -S.Talkeetna Mins.JV -Jack River volcanics/piutons KB -Kahiltna CTS -Chitna thrust belt N-Nabesna WT -Vewangelira 58 -Susitna MI -Matanuska Valley inwusives MCB -MacCathum Creek DE -Denali tauit¥YT -Yakutat WB -Wrangell Mountaens Pl -Prince William Sound intrusives NOB -Northway HCF -Hines Creek Fault YTT -Yukon-Tanana {(Prefixed wth U=Uphfied)TK -Takeoina Mountains-Kluane arc NB -Nutzotsn LO -Lost Creek decollement {Prefixed wth F=Future position)VAN -Wrangell volcanic feld TB -Tanana TF -Tatschunda fault WCB -Watana Creek TAF -Tarat fault (Prefixed with U=Uplifted)TKF -Talkeetna faut (Prefxed 'eith F=Future postion)VCS -Valdez Creek shear zone Figure 6.3-4.Schematic Evolution of South-Central Alaska (Fugro 2014) Magmatism i,Locus of active volcanismsa2Paleocene-Eocene intrusives TD”Mid-Cretaceous Chisana arc rocks STICM Upper Jurassic Talkeetna-Chaina arc rocks <2"Middle Jurassic Talkeetna arc rocks==IeEEre Lower Jurassic Talkeetna arc rocks Deformational Features "y Active subduction zone (barb on downgoing plate) "n Active crustal shortening (barb on thrust sheets) af.Regional topographic uplifts wa folang/fauiting .Active crustal extension Via nommai fauks <=Regional dextral stnke-slip fault Os Strke-cip movement away §2)or toward (3) Depositional Features wn Aitumai -..™Sy Submanne FansC=Fal '>tacusmne ".Manne environments feRS FareD -Active daposstional basinaean-Detta/3&>Prodeita Slope-Marine Shelf ComeneSsee, Uptifted basinal strata Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 6-48 Alaska Energy Authority December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT A)Epoch'Cook Intet Matanuska Reginant Romangell Mins.|Tanane Foreland |Subduction-RelatedStage(Ma)|Forearc Basin a7Forearc Basin'|(MB)Basi Basin'(TB)Events WH 18 .. Pliocene . -"53 |Alfuvial,fluvial, ,Abuvial,fuvial,andLateMiocene!ang a7 Is lacustrine H-11.2 -j conglomerate,conglomerate,Subduction --14.8 -4 sandstone,siltstone,sandstone,mudstone.]|of ThickEarlycoal,and tuff 2 and coal Oceanic CrustMiocene(7,500 m)(2000 m)-_=823 AlluvialLi Z):Oligocene |Alhuvial,fluvial and [ rolcanic (minor H 339 tidally-influenced [7ty V7intrusive)rock :=a sandstone intercalated ce). conglomerate,Gy,alluvial,fluval,anoandtuff(2,100 m)-A . Eocene Alluvial,fluvial,Spreadin282andiacustrine|N Fridge =ocNonmannegrconglomerate,Subduction »is|54g -]sandstone.siltstone,|62¢Sandstone,$30"castandcoat(419 m)mudstone,.fecoal(>2800 m)&AcePaleoceneLLINpebrogressignp-65 Wes:'of near-trenchineSanCOEte" t plutonsLateROSee+reetaandiresxiato Normal SubductionCretaceousYA:Wetigee Gy Arc Magmatism EXPLANATION ("7 Unconformity/depositional hiatus [77]Range of isotopic age determinations from volcanic rocks of Wrangell Lavas [(<"=*]Isotopic age determinations on near-trench plutons From Ridgeway et al.,2011 Other Igneous Rocks in the Southern ...GaribouGreek Alaska Orocine Hinga Area Regional Magmatic and Tectonic Events B)C This ;Other Wrangeilia Composite Terrane |SouthemaE.Miocene study studies c Margin=*mi 2 43 OMPpPasi205(of 2 2)Terrane E L.Oligocene . Alaska- 7 CTM :Matanuska Valley |NCM :PWS!Aleutian Norpwestward=4 :an30aE.Ofgocanes : Pacific plate s -i 3:>L.Eocene a f Demise of g3 r =Kula plate ag__40 f=$=2 _/oesstr&|M.Eocene ay ac=-ha =}:Ss H .5S i3§f ges +i gas<o£:Gas SzFE2382e,Joessofna i 2 80 [S30 |e.2q&.Eocene 56 ef3e5 833 288a82eastaestfezZ=7 Gb 3 a L.Paleocene *%a z :BS sot-{=:gS ="83-:aS s .5FE.Paleocene ' 16 .e a S £'3 Northward Accretion -Stab window formation in area of southem 2 oO subduction of the 7or-8 aa Alaska orodiine ©£8 Jot Kuta andor WrangelliaEFIMaastrichtian%gs 5,[Resurrection [compositeLéZee[plates terrane ©Volcanics in the Arkose Ridge Fm)-Aintrusions near Border Ranges F."®=7 ca.44-41 Maintrusions®19.12 W Mafic lavas"4@TuffintheChickatoonFm4 ©Matanuska Valley intrusions *1.8.6 X Reset metaplutonics and schist7:9 16 Gg ca.38-32 Ma intrusions of' ca.57-47 Ma intrusions5-8.10-12 10,13 Prince William Sound %&Felsic domes'® ©Mafic lavas andfelsicdome17 From Cole et al.,2007 Age-event diagram showing radiometric ages of volcanic rocks in the Caribou Creek volcanic field. Figure 6.3-5.Correlations of Cenozoic Tectonic,Magmatic,and Sedimentary Events in South-Central Alaska (Fugro 2014) Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 6-49 Alaska Energy Authority December 2014 -2 ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The regional magmatism described above directly forms the rocks that make up the dam site though plutonic intrusions and volcanism.Multiple ages of early Cenozoic (i.e.,Tertiary) volcanics intruded the Kahiltna formation,as well as the Wrangellia Terrain rocks and the Talkeetna suture zone (i.e.,Wilson 2009).The rocks present at the dam site range in mineralogical composition and texture,including diorite intrusions,andesite,and felsic dikes and,to a lesser extent,mafic volcanic extrusive rocks (Acres 1982b).Previous geologic mapping reveals that the volcanic rocks have a complex field relationship at the dam site with intrusive and extrusive rocks often occurring proximal to each other with gradational contacts.A range of mineralogical variability within intrusional bodies is relatively common (USACE 1979). Review of rock core drilled for the project (Golder 2013,MWH 2014)as well as inspection of field outcrops confirms the complexity of the igneous history.Both andesite and diorite rocks include a wide range of textures on compositions.In some instances,diorite bodies locally are cut by felsic dikes.In both outcrop and core samples,inclusions of diorite have been observed within the andesite.No dikes were found cutting the andesite,suggesting it is the youngest volcanic unit at the site based on these cross cutting relationships (Acres 1982a;p.6-7).The intrusions likely occurred sometime between 50 to 60 Ma,the field observations and relationships confirm multiple ages (or,episodes)of volcanism,intrusion,or flows of which the specific chronology has yet to be defined.Mapping by Csejtey et al.(1978)suggests that the dam site rocks could be of the order of 58 Ma;however,these dates were not collected on rock at the dam site.Rock samples were collected during 2014 field investigations to submit for absolute dating purposes to establish site geochronology. 6.3.2.3.Regional Structure The geologic mapping transect along the Susitna River,extending through the Watana dam site area,suggests that the site area lies within a relatively coherent crustal block of Kahiltna assemblage sedimentary rocks which are overall gently tilted to the northwest,moderately folded,and intruded by multiple early to mid-Tertiary plutonic and volcanic rocks (Figure 6.3-6 and Figure 6.3-7).Field observations and mapping along the Susitna River,several kilometers upstream and downstream of the Watana dam site -discussed in the Interim Crustal Source Evaluation which forms Appendix B -have not disclosed any major faults,either parallel to or crossing the Susitna River downstream of the structures,associated with the Talkeetna fault and Watana Creek basin.The Watana dam site area lies within an area of Tertiary intrusive rocks. Kahiltna assemblage rocks and additional intrusive rocks downstream of the Watana dam site near the confluence of the Tsusena Creek and Susitna River appear structurally congruent,with an apparent absence of major cross-cutting structure or extensive penetrative deformation.There are likewise no significant expressions of vertical uplift or tectonics along the Susitna River transect,downstream of the Talkeetna fault and Watana Creek basin. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-50 December 2014 -yw SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 95000 So00ne $05000 1 Nae oe ne See OylapsereesaoeawhiNTatCoOByExposuresnotTap No visual evidencetoconfirm ;.Heavily vegetated end steep;a ;og and Qid is transcribed TadKag 3 meter thick.Contaci?andesite dike No exposures <<}Trend and plunge of anuickne hinge <f Trend and plunge of syncine hinge -Arrows pomnt to outcrop observabons. Lt Brackets are an approximation of tateralSxtonlOFBaposureoUICIOD @ Observation trom ground or aena hover Strike and Dp Strikeicep from USACE 1979,map 0-3Fs]t a j 'Stnhevckp from Acres,1932 2 f Faun iocenens.ts study 2 t Stnkefcsp tag.thes study an }Stnkesap Tsu,thes study Fs)k Stnheidp Tsu WCC,1962 v .oe cymntaline Keg t ad*ee wreck '",ti accessible dueLeeehTapy,°?Yun te atertineob”Matic intrusion oo - Oe (7)exposed .@.(an along wateriine ra i Te ExplanationAnnotationsfromthisStudy Symbols ames Shear wav Trust Geologe Units (Actes,1982) Aluvium,aluvial terraces and fans Ice disintegration deposits [or]m Oulwasn Surfiaal deposits,undfferenbatad,gener aly thin [7 ]Terbary voleandastic sandsine,silstone and shale Tetbary andesde porphyty,minor basalt Torbary donte to quetz Gonte,manor ganoucte Crotacious osotite ofan odiority Trassk atpiste and giaywacke (Kahiltna) Palaozas basa metavolcanie rocks Metdbasal and date[ew |Cretaceous basalts to andesite metavalcams rocks Notes 1 See text tor desorption of compiled data sources2RegistrationartifactsfromongnalAcres(1952)map ale nod corrected 3 This Jayout ts 1 color at 11417 swe ad ." poe "Le A a ho. Z. fokc anc lastic? Figure 6.3-6.Acres Geologic Map Updated With Observations from 2014 (Fugro 2014)69650066960000Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 6-51 Alaska Energy Authority December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT SOSA S 10000 515000 520000 v ¥¥7 ¥ Explanation Annotations from this Study Acres Mapping ”"-e Symbois i 4«f Trend and plunge of antickne tinge Sheer vw Thrust oe<f-Trand and plunge of syncline hinge Geoiogee Unts 9 : |Acres (1982)Wilsonefef (2009)ry \e tn,o ,= O a SET BON «a :Arto Foxnt to catcrop obsene .Alluvwmn,alluvial terraces and tans Quaenary sediment junadvided)c 4 ° Lo Brachers ate ft approwmation of wera Poeaxtentofexposureoutcropleedisntegabondeposits Ca]. Tertary congomerate,sandstone and claystone Cretaceous argiita and oF aywacke (Kahiltna) Thasac basaite @ =Observation from yound or aerial hover Sie and Dp Strikevap trom USACE 1979.map D-3 |.StrikenaptromAcres,1982 Fauit locabons,this stuay Stnkefap Kag,ts study Forks,Metab asalt Tarhary sediment (undnsded) Trassic Nikole greenstone Jurassi/Paleozoic metabasatt Notes 1 See text for descnpbon of compeed data sources 2 Regs atifacts trom oniyinal Actes |1982}map 'é on Limit of Acres ($882)mapping ;,po i(| \ a f Strivetap Tsu,this study and slate are not corrected n 3 This layout ts in coloratWt?aze}Strkevap Tou WCC,1382 F Wilson et af.(2008)mapping en mee %,: . \mn ioe ae . "1 "-} ; as ?| j '4am}Jpe:can éva § ane aoe vd a ; -..4|,Babueure s 2 ' "occ”(outa von Sao OTR on ht ; e hep po TRaeExposedbutnoQa?2 'Feboe'4 .'pe oi {tin meVoleanictestic?GuMensy geStan, a VerbraltautNE}8exposedinTRvs ae(inacoessableSue emer (Cane i"torwor)'as i -i 7 ee intWataneCreek 6975006974000Figure 6.3-7.Acres Geologic Map Updated With Observations from 2014 (Fugro 2014) Susitna-Watana Hydroelectric Project Fr ™Project No.14241 Pav 7.52 Alaska Energy Authority Decembe "4 -zZ- ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORTClean,feliable energy for the next 100 years. 6.3.2.4.Seismotectonics South-central Alaska experiences significant tectonic deformation and seismicity driven by the oblique convergent northwest motion of the Pacific Plate relative to the North American Plate. The Talkeetna Mountains formed as a direct result of the convergence of these plates as the Pacific Plate was subducted below the North American Plate as shown in Figure 6.3-8. EXPLANATION Fault sarctons ruptured m testoncal record FarnveatterFault19581AleubenMeqathirustFautandPattonBay Fault Zone (PBFZ.1Se4),Danah and Tots:trade Faults {2002)Bart on upper plain Faults vath prehestoneal ruptures Bard on upper plata Movernent of plates Voi ane 1964 epicenter and surface projection af rupture patch in subduction zone Figure 6.3-8.Tectonic Setting of South-Central Alaska During the 1964 Earthquake (modified from Brocher et al.2014) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-53 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The Alaska-Aleutian subduction zone is one of the longest and most tectonically active plate boundaries in the world.It extends for nearly 2,500 miles (4,000 km)from south-central Alaska to the Kamchatka peninsula,and has produced some of the world's strongest earthquakes -such as the 1964 magnitude (M)9.2 Great Alaskan (or Good Friday)earthquake.The subduction zone has three tectonic regimes:continental subduction in the east,an island arc along the central Aleutian volcanic chain,and oblique subduction and transform tectonics in the west (Nishenko and Jacob 1990).The eastern continental subduction zone,in the vicinity of Prince William Sound,is significant in the evaluation of the seismic hazards at the Watana Dam site.In this region,the Pacific Plate is converging with the North American Plate at a rate of 54 millimeters (mm)/year (2.1 inches/year)at a slightly oblique angle (DeMets and Dixon 1999;Carver and Plafker 2008). It has been recognized that the Alaska-Aleutian subduction zone is segmented in central Alaska, and may be broken into independent fragments (e.g.,Ratchkovski and Hansen 2002).In addition,it has been recognized that the Alaskan-Aleutian subduction zone's eastern termination lies within 100 km northeast of the Susitna-Watana site (Fuis et al.2008).The precise location and geometric character of the slab edge are not well determined.Ruppert and Hansen (2002), define three major sections of the slab,which they termed the McKinley,Kenai,and Kodiak Blocks.The dam site is located within the McKinley Block as shown in Figure 6.3-9.A schematic of the subducting slab,which has a shallow dip (Carver and Plafker 2008)and a typical forearc basin is shown on Figure 6.3-8.The slab thickness of 12.3 km,as shown in Figure 6.3-10,is based on observed seismicity.In this area,the slab is considerably thinner than the in central Alaska,where the slab is approximately 50 km thick. Further south,transform motion along the eastern edge of the subducting slab is accommodated by the Fairweather and Queen Charlotte (not shown)fault zones on Figure 6.3-8. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-54 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. qT u q u t qT T q T 64h 4-McKinley:3-McKinley:=NE 115-150km NE 90-115km 63.5 2 -McKinley:7 SW 90-150km 63+ { 4 OJECT SITE 625+4 1-McKinley: 50-90km6-Kenai North: 62-below 100km 5 6tS-4 61-4 60.5 4 60+4 7 -Kenai South 595,4 S59 1 1 1 it 1 1 1 1 J "155 -154 -153 -152 -151 -150 -149 -148 -147 -146 Figure 6.3-9.Map View of Slab Planes (Fugro 2013) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-55 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Surface Hypocentral Depth Interface Intraslab Possible Slab Ruptures Figure 6.3-10.Schematic Showing Subducting Slab Geometry (Fugro 2013). The dam site is located within a distinct geologic domain referred to as the Talkeetna block.The Talkeetna block is bounded by the Denali fault system to the north,the Castle Mountain fault to the south,the Wrangell Mountains to the east and the northern Aleutians and Tordrillo Mountains volcanic ranges to the west (Figure 6.3-1).Major stress is released along the Denali and Castle Mountains bounding faults during earthquakes resulting in movement (i.e.,strain). However,it is less clear how stress and strain are accommodated to the east and west.There is a relative absence of large historical earthquakes within the Talkeetna block as well as a lack of mapped faults with documented Quaternary displacement (Koehler 2013;Koehler et al.2012, 2013).The absence of earthquakes and mapped Quaternary faults within the block implies that the block is behaving rigidly with little to no internal deformation. The Talkeetna suture zone is the proposed term by Glen et al.(2007)which refers to the Talkeetna thrust fault labeled in Figure 6.3-11.They describe the Talkeetna suture zone as a deep crustal structure bonding the northwestern edge of the Wrangellia Terrane. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-56 December 2014 -yz .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. q ;iz J152°0'0";W :Jt rf 148°0'0°W wed -McCallum.”:°State Creek fault. ot Sonona Creek fault Explanation Fault Activity {tum Historic jo==- Quatemary wees Suspicious a -*|Talkeetna Thrust |.”* _,hydropolys oy reTo Figure 6.3-11.South-Central Alaska Regional Faults (Fugro 2012) The Denali fault predominantly shows right-lateral,strike-slip fault motion;in plan view has an arcuate shape and defines the northern margin of the Talkeetna block as shown in Figure 6.3-1. The Denali fault has been a major structural component of Alaska since it formed during the Late Jurassic to early Cretaceous Period (Ridgway et al.2002).Offsets of 56 Ma metamorphic and intrusive rocks suggests at least 249 mi (400 km)of total right lateral displacement (Nokleberg etal.1985).Offset is also constrained in the Denali region where the 38 million year old Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-57 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Mt.Foraker pluton is displaced 24 mi (38 km)from the McGonagal Pluton (Reed and Lamphere 1974). In 2002,movement on the Denali fault produced an M 7.9 earthquake,the largest strike-slip earthquake to occur in North America in almost 150 years (Eberhart-Phillips et al.2003). Detailed studies of offset glacial features along the fault following the earthquake have demonstrated a westward decrease in the Quaternary slip rate along the fault (Matmon et al. 2006;Meriaux et al.2009),as shown in Figure 6.3-12. 148°"COW fom at .radiiSoeNorthernFoothills-Fold.Ti tthe and Thrust:Belt?="aay HLSrikfond om.ahcanT 59008 e4ae"2WWatana _Slip rate (sources discussed 2002 Denali fault rupture, f Rescee _aan SSop |foe ao KE'Dam Site 2:7 ”8442.2 rey Oh ..oe Fe at : :Na "Lr:a e)-yLetaug 7 Muy Lo cone hs Pe &:Or 2_PET Se itriesetaraeo"Jee ater]rE Cad ,td 1h7}j,Ect eee"Aye. Legend Symbols Faults Abbreviations @®Earthquake epicenter Denali fault BR -Bull River fault BP -Broad Pass fault in text)Haeussler (2008).BG -Broxson Gulch fault if FF -Foraker fault3%Watana Dam Site Southem Denali faults gc -McCallum-Slate Creek fault ---Other fault SG -Susitna Glacier fault Figure 6.3-12.Denali Fault Characterization Along the north and south sides of the Denali fault lie two zones of deformation.To the north is the Northern Foothills Fold and Thrust Belt (NFFTB),a zone of variably dipping,but generally Quaternary thrust faults and folds that accommodates transpressional deformation along the north side of the Alaska Range (Figure 6.3-12).The westward reduction in Denali fault slip rate is considered to be predominantly the result of strain partitioning onto the NFFTB (Haeussler 2008;Meriaux et al.2009). The other zone of deformation adjacent to the Denali fault lies south of the fault where several thrust faults splay from the Denali fault's central section as shown on Figure 6.3-12.Most of these faults are recognized as Tertiary terrane-bounding features in which Mesozoic or Paleozoic Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-58 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. rocks are thrust over Tertiary sediments and volcanics (Haeussler 2008).Rupture along the previously unmapped Susitna Glacier thrust fault during the 2002 Denali fault earthquake highlighted the potential for seismogenic activity in this area,in contrast to the relatively sparse mapping of Quaternary faults south of the Denali fault.This concept is well expressed in the Neotectonic Map of Alaska fault explanatory note (Plafker et al.1994). The Castle Mountain fault defines the southern margin of the Talkeetna block.This fault is described by some as a dextral oblique strike-slip fault whose western segment is defined by a 39 mi (62 km)long Holocene fault scarp.Recent field and LiDAR-based geomorphic observations by Koehler et al.2014,support the inference that the Castle Mountain fault is a high angle oblique reverse fault.The eastern section is primarily evident in bedrock,and there is no indication of Holocene surface rupture as shown in Figure 6.3-13.Paleoseismic studies,by Haeussler et al.(2002),on the western section demonstrate four earthquakes on the fault in the past 2,800 years,with a recurrence interval of approximately 700 years.More recent work by Koehler et al.(2014),suggest only two earthquakes in the Holocene indicating that the recurrence interval could be longer than previously thought.Despite the apparent lack of Holocene surface rupture on the eastern section,this section of the fault is spatially associated with historic seismicity as high as M 5.7 (Lahr et al.1986). z 3 uedow”z LS eH ie 4 ee este at J -4 |ve . -OF - zSs 3 Legend Symbols Faults @ Earthquake epicenter Castle Mtn.fault,western Paleoseismic Investigations segment =Hausler et al..2002 Castle Mtn.fault,eastern oO -7 segment and Caribou faultWillisetal.,2007 Other fault Note:Site is 100 km to the north Figure 6.3-13.Castle Mountain Fault Characterization Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-59 December 2014 -z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.3.2.5.Quaternary Geology A period of cyclic climatic cooling during the Quaternary Period resulted in repeated glaciation of southern Alaska.Unlike the north side of the Alaska Range,which is characterized by alpine type glaciations,the Susitna Basin experienced coalescing piedmont glaciers that originated from both the Alaska Range and the Talkeetna Mountains,which merged and filled the upper basin area shown on Figure 6.3-14 (Wahrhaftig 1965;Hamilton 1994;Kaufman etal.2011).The repeated glaciations have carved the Talkeetna Mountains into the ridges,peaks,and broad glacial plateaus that are observed today.Post-glacial uplift has induced down cutting of streams and rivers,resulting in the 500 to 700 foot deep V-shaped canyons such as Devil Canyon and Vee Canyon on the middle and upper Susitna River. At least three periods of glaciation have been delineated for the region based on the glacial stratigraphy.During the most recent period (i.e.,Late Wisconsinan),glaciers filled the adjoining lowland basins and spread onto the continental shelf.Waning ice masses formed ice barriers that blocked the drainage of glacial meltwater and produced proglacial lakes as shown in Figure 6.3-14.As a consequence of the repeated glaciation and ice-damming,the Susitna and Copper River basins are covered by varying thicknesses of till and lacustrine deposits.Many of the distinct landforms found within the project area are a direct result of this glaciation and/or the presence of ice-dammed lakes. The Project area is located within the zone of discontinuous permafrost.Within this region, numerous isolated pockets of permafrost are found in fine-grained deposits (e.g.glacio-lacustrine sediments)and bedrock while coarse-grained deposits are generally permafrost free -or at least free of appreciable ice.It is believed that permafrost in this region is a relatively "warm” permafrost (near 0°C)and is evidenced by the presence of frozen ground in the scarps of recent shallow landslide deposits in the area and borehole ground temperature readings that are one or two degrees below freezing in some locations at the proposed dam site. The rock temperatures below freezing are particularly found in boreholes in the north-facing slopes of the left abutment,in which it is reasonable to assume that discontinuities,joints and fractures,could be ice-filled. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-60 December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. "Sh5 Legend Alaska Paleo-Glacier Atlas v.2 Data (Kaufman et al.,2011) *3)Limit of Late Wisconsin glaciers ----- -==Quaternary fault,solid where well Cosmogenic Exposure Sample Locations constrained,long dashed line where ©Dortch et al..2010a moderately constrained,short dashed line where inferred (Alaska Division of*Dortch et al.,2010b Geological and Geophysical Surveys, «Matmon et al.,2006 2012) Glacial Lake Elevation Extents (meters) -800m -975m Figure 6.3-14.Late Wisconsin Glacial Limits and Age Control (Kaufman et al.2011) 6.3.3.Seismic Hazard A Site-Specific Seismic Hazard Analysis (SSSHA)has been performed for the Project,but is,at time of writing,incomplete.The seismic sources associated with the subduction zone (interface and intraslab)are expected to drive the Project seismic design criteria,and additional analyses on the intraslab are included in Deterministic Ground Motions for Slab events,which forms Appendix B7.However,finalization of the crustal seismic source studies -including additional Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-61 December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Vs30 measurements,focal mechanism assessments based on additional seismic monitoring and update of the SSSHA,as required by the FERC Study Plan 16.6 -remains to be completed. The derivation of seismic design criteria from the results of the preliminary SSSHA is described in Section 10 of this report. 6.3.3.1.Seismic Sources During the 1980s studies,a site-specific seismic hazard investigation of the regional tectonics, and an evaluation of the seismic hazards,using both deterministic and probabilistic approaches, was performed.Between 2012 and 2014,the seismic studies were updated under FERC Study Plan 16.6 to characterize the seismic sources and to define and estimate the ground motion hazard.New geologic and seismic hazard information has been collected from field investigations,and long-term seismic monitoring.This information has been used together with the current research regarding large earthquake events,and the new ground motion prediction equation developed since the 1980s studies -most recently for subduction zone earthquakes. The updated seismic source model for the region includes structural elements that are relatively consistent with previous studies,such as the Denali Fault,Castle Mountain Fault,subduction- related sources,and "background”sources.New data and observations from tectonic,geologic, paleoseismic,and seismologic studies,as well as data from recent large earthquakes,are being incorporated into the new source model.The new seismic source model also considers the potential implications of newly recognized zones of distributed tectonic deformation within the region;potentially active structures within the Talkeetna block;time-dependent scenarios for the subduction interface to consider the effects of the Great Alaskan 1964 earthquake;and time- dependent scenarios for the Denali Fault based on the 2002 earthquake.Stress accumulation and release in the form of strain,appears to be occurring primarily along the margins of the Talkeetna block,as there is an absence of major historical earthquakes within the block,as well as an absence of faults with recent displacement.Studies of selected faults and lineaments in the 1980s did not indicate that there would be potential seismic sources that could cause surface rupture through the dam site (Woodward Clyde 1982). The original seismic source characterization and ground motion studies have been updated to account for interface and intraslab earthquakes,the recent M 7.9 Denali earthquake originating on the Susitna Glacier fault in November 2002 (Eberhart-Phillips et al.2003)about 59 miles from the dam site;potential faults defining a postulated Fog Lakes graben (Glen et al.2007a, 2007b);and a 10,000-year return period earthquake for the background source.The Fog Lake graben is a poorly documented structure,but it is included because of its proximity to the dam site.The Fog Lake graben structure was also included in the preliminary seismic hazard analysis Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-62 December 2014 -yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. as a sensitivity test for the potential reactivation of existing structures within the vicinity of the Talkeetna thrust lineament region near the dam site. 6.3.3.2.Surface Faulting Identification Recent earthquakes in the region have demonstrated the potential for fault rupture on poorly or uncharacterized fault strands close to the Denali system.For this reason,it is important to understand the occurrence of identified fault strands and the potential for coseismic movement along features near the dam site,and particularly in the foundation.A comprehensive understanding of the stress regime in the vicinity of the dam site will endorse the interpretation that there is low potential for coseismic movement. Active or potentially active faults near the dam site include the Talkeetna Thrust fault.Other local postulated features include the "Watana lineament”,a northwest trending geologic feature GF1,and several other identified geologic features.Study of these geologic features started in the 1980s and continued through 2014.It has been concluded that these local features are not tectonic faults or major shear zones,nor show evidence of recent movement.It has also been concluded that there is a lack of geologic evidence supporting fault activity. The Talkeetna thrust/suture zone is a terrane bounding structure associated with continental accretion in the late Cretaceous and early Tertiary periods.The Talkeetna thrust fault (i.e. Csejtey et al.1982;Nokelberg et al.1994)has been questioned by Glen (2007a,2007b)who have interpreted that the structure is a deep crustal suture that branches upward into a 12 mile zone of Tertiary or younger faults. The feature known as the "Watana lineament”has been postulated,manifesting itself as a series of east-west trending linear segments of the Susitna River.It was identified from high-altitude land satellite and Side-Looking Airborne Radar imagery by Gedney and Shapiro (1975).The feature has been the focus of study because of its potential manifestation at the dam site. Locations along the postulated feature have been examined,and angled boreholes have been drilled at the Watana dam site,beginning with investigations by the USACE (1979)and Acres (1982a)and most recently in 2014 to investigate further the geologic conditions beneath the Susitna River.No evidence has been found in any of these studies to corroborate existence of a continuous lineament or pattern of lineaments suggestive of faulting.All the short surface lineaments examined that might form part of a more extensive lineament have been interpreted to be of glacial origin,or related to surface processes such as slumping. As described earlier,upstream of the proposed dam site,on the north bank,a prominent cliff exposure of northwest trending rock ridges and gullies is present.This geologic feature (GF 1) approximately coincides and subparallels the western margin of a buried valley that follows a Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-63 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. morphological depression in the topography that extends between the Susitna River and Tsusena Creek.GF1 was initially interpreted as a two-mile-long fault without "recent”displacement (Woodward-Clyde 1982).However,the subsequent field investigations,geologic mapping and drilling have led to a reinterpretation and the conclusion that GF1 is a zone of closely spaced fractures,some with slickensides and clay infilling suggestive of minor shearing and alteration separated by ribs of sound bedrock but with no evidence of "major faulting”(Harza-Ebasco 1984). 6.3.3.3.|Ground Motion Estimates The seismic source evaluation and preliminary probabilistic seismic hazard analysis provide a basis for selecting the critical seismic sources for a deterministic evaluation.The critical sources include the subduction interface and intraslab,Fog Lake graben,and background seismicity. Other faults capable of large magnitude events were included in the deterministic assessment, including the Denali and the Pass Creek -Dutch Creek faults.These two faults have a small contribution to the overall hazard,due to the distance from each of these faults to the project site. Appendix B3 contains the Interim Crustal Seismic Source Evaluation with details of the seismic source evaluation. The median peak ground acceleration (PGA)values computed for the sources are shown in Table 6.3-3.The deterministic results assumed an input shear wave velocity in the upper 30 km of the crust (defined as Vs39)equal to 3,610 ft./s (1,100m/s),except where noted.Initial probabilistic analyses were performed prior to field testing for shear wave velocity.In 2013,the Vs39 was assumed to be 3,610 ft./s (1,100m/s),and the deterministic results reflect this revision. The results indicate that the ground motions for the intraslab sources are the more significant, and the crustal sources are less significant. For the probabilistic evaluation,ground motion prediction equations (GMPE)are used to transform magnitude,distance and other ground motion-related parameters into ground motion amplitude distributions for a wide range of vibration frequencies.Three types of GMPEs were used for this study:crustal,interface,and intraslab sources.Based on the results of this probabilistic study,the PGA hazard is dominated by intraslab sources for all return periods. Complete details are contained in Appendix B2. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-64 December 2014 -yZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 6.3-3.Ground Motions -Deterministic Results MCE Rupture Ground Motion MedianSource(Mw)Distance?Prediction Equations'PGA (miles)(weight)(g) ZHO6 [0.25] Interface (interplate)'9.2 49 AM09 [0.25]0.26 BCH11 [0.50] 75 ZHO06 [0.25]0.33 Intraslab (intraplate)2 31 AB03 [0.25] 8.0 BCH11 [0.50]0.56 Denali fault -entire fault 79 44 0.095enalifault-entire fau BAOS [0.25]Castle Mtn.fault -entire fault 76 62 CY08 [0.25]- Fog Lake north 7.0 4 CBO08 [0.25]0.29 AS08 [0.25Crustalseismicity(10,000 yr.return period)4 6.5 9 (0.25)0.275 Notes: Source Appendix B2 and Fugro (2013)for deterministic analysis results. 1.Interface events also called interplate or megathrust events.Interface events normally occur at depths up to 40 km,which is the depth at which some of the largest magnitude events have been recorded. 2._Intraslab events are deeper events,often referred to as intraplate events can be attributed to the subduction at depths greater than about 40 to 60 km. 3.Rupture Distance is defined as the closest distance to the fault plane. 4.Based on weighted magnitude-distance-epsilon deaggregation for SAB Central source and 10,000-yr.return period. 5.Vs30=800m/s,from initial probabilistic analyses in Appendix B2.A Vs3o equal to 1100 m/s would slightly decrease the PGA for the crustal seismicity and the Denali fault. 6.3.3.4.|Microseismic Network To monitor seismicity in the region of the dam,the Susitna-Watana Seismic Network was established in August-September 2012 so that seismic activity in the vicinity of the Project - over an area of some 5,700 square miles could be captured.The first group of stations installed consisted of four seismograph stations (WAT1 to WAT4)within 20 mi of the dam site,with station spacing of 10 mi to 20 mi.In August 2013,three additional seismograph stations were installed (WATS to WAT7),which expanded coverage and reduced station spacing within 32 mi of the proposed dam site as shown on as shown on Drawing 01-01GT008. In the current network configuration,all seven seismograph stations have three-component broadband seismic sensors,and four of the stations have co-located,three-component,strong motion sensors.In addition,a GPS station has been co-located with the seismograph at the proposed dam site (WAT1). Data recorded by the seismic network is processed by the Alaska Earthquake Center (AEC), which monitors seismic activity from more than 400 seismograph stations throughout Alaska and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-65 December 2014 -yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. neighboring regions.Data is recorded continuously in real-time,at a sample rate of 50 Hz.AEC picks arrival times,and calculates locations and magnitudes for all events recorded on four or more stations.The addition of the Susitna-Watana Seismic Network has increased the event detection capabilities in the Project area;has increased the completeness of the data;has improved precision of hypocentral location precision;and overall has provided a clearer picture of seismicity within the Project area. During the period from November 16,2012,through December 31,2013,1,136 earthquakes were recorded with an epicenter located within the Susitna-Watana Seismic Network project area (Fugro 2014).The Susitna-Watana Seismic Network has recorded only low magnitude events since its initiation on November 16,2012:an average of 2.8 events per day (1.1 crustal events per day and 1.7 intraslab events per day).As shown on Figure 6.3-15,459 events were located in the crust at depths of less than 18.6 mi (30 km),and 677 events were located deeper,within the subducting North American Plate (intraslab seismicity).The crustal events were less than M 3.8;the intraslab events were less than M 4.0. Plotting the source locations attained by the microseismic network as a function of depth and taking a cross-section in the north-northwest to south-southeast direction,allows the boundaries of the crustal events and the boundary of the subducting plate to be defined as shown in Figure 6.3-16.The information collected by the network has increased confidence in the determination of Project design events and seismic design criteria,which are described in detail in Section 10.7. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-66 December 2014 ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT -Z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. -ee _ad Set ExplanationeABaareh@sunenDHfleweFSfonaea”er ere Ht .AEA Macrosetsmic Staton LocationsiratePabwdamines©86 nsurent r A Ay?GO he ri @ ah,2a nenrensghtreg)aan é alaw"7 :rye AVS?wel SesmctyBEDSTAPE|pec.ee tee sry ONy,ly |2 ||!o 230-049 @ a-29 -|45 ©050-098 @ v-x8 oO.O 100-199 .A I ©200-298 '177 He ©)300-398 we |{¢.@ «0{- ; e|}1e\|:rem Locaban of cross secban%'fn L oat Oe .y --_Proposed reservar exert|ee '|(2,000 feet above sea eves) a ce |- ';%{"e pee |fi a |4 han N hd |¢i 0 Om . s de ft)10 hm e I,F] | ae a RTS zone | 7;a e é :fepeeditoefee ey otetesoee Figure 6.3-15.Seismicity within the Susitna-Watana Seismic Network Project Area,November 16,2012 to December 31,2013 (Fugro 2014) Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 6-67 Alaska Energy Authority December 2014 -zZ ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. A Dam Site A 0+! 20-7 _40-= E c- =4 L g 60-- 80-4 - 100 I J 1 I |I U ! 0 20 40 60 &0 100 120 140 Distance (km) Explanation ®Crustal events (depths <30 km) ®Intraslab events (depths 230 km) Notes:1.Vertical and horizontal standard location errors are shown. 2.Location of section is shown on Figure 4. Figure 6.3-16.Seismicity Section A-A',November 16,2012 to December 31,2013 (Fugro 2014) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-68 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.3.3.5.Reservoir Triggered Seismicity Reservoir-triggered seismicity has been described as earthquake events that are triggered by the filling of a reservoir,or by water-level changes or fluctuations during operation of the reservoir. It is believed that reservoir triggered seismicity (RTS)primarily represents the release of pre- existing tectonic strain,with the reservoir being a perturbing influence (Yeats etal.1997; USCOLD 1997;ICOLD 2008).Thus,the reservoir does not cause or induce the seismicity,it merely triggers the release of the accumulated,naturally occurring tectonic strain that already existed. At reservoirs where RTS has been suspected,the maximum reported earthquake magnitudes for RTS events are primarily less than M 6.0,and typically less than M 4.0,and often below the range felt by the public. The most significant aspect of the RTS record is that of the verified RTS cases large enough to be potentially damaging.Of recorded instances of RTS,just four events have exceeded M 6.0 and only 13 events were in the range M 5.0 to M 5.9 (USCOLD 1997;Yeats et al.1997).The largest reported RTS earthquake was the 1967,magnitude M 6.5,Koyna,India event.The other three events were Hsinfengkiang (China 1962)M 6.1,Kariba (Zambia 1963)M 6.0,and Kremasta (Greece 1966)M 6.3. For this Project,the reservoir depth,reservoir volume,existing tectonic stress state,rock type underlying the reservoir,and the rate of filling were considered when evaluating the probability of RTS.The Project reservoir will have characteristics that might make it somewhat susceptible to RTS,in that the maximum reservoir depth is greater than 575 ft.(175 meters),and it is within an active tectonic region. As described above,the Talkeetna Block is bordered by the Denali Fault to the north,and the Castle Mountain Fault to the south,and the Wadati-Benioff Zone (Intraslab)lies at a depth of approximately 50 km below the site based upon the focal depth of recent earthquakes,Figure 6.3-16.These distant sources do not lie within the zone potentially influenced by reservoir filling,and thus RTS is unlikely to occur on them. Studies performed in the 1980s estimated the probability of RTS for the Project to be between 30 percent and 95 percent,with an event up to M 6.0 (WCC 1982).Recalculations performed during the present studies indicate that the reservoir has a potential for producing an RTS event up to M 6.5,but the probability of an RTS event is between 16 to 46 percent.Any event would most likely occur within 10 years of initial filling. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-69 December 2014 -zZ-.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. RTS has been considered in the derivation of the seismic design parameters for the Project,and will be further updated during detailed design.However,triggered seismicity requires the presence of a causative fault.A seismic hazard assessment requires that all faults be identified; hence,any fault identified during the seismic hazard assessment would likely cover those with the potential for RTS. For completeness the present studies have also considered the potential effects of RTS on the nearest populated area,the town of Talkeetna,which is about 62 miles (100 km)from the site. Using the RTS event of M 6.5 and GMPE,deterministic methods were used to estimate the peak ground accelerations (PGA).The calculation estimates a PGA in Talkeetna of 0.02g for the median and 0.04g for the 84"percentile (+1 standard deviation).The inputs to calculate this hypothetical event are shown in Table 6.3-4. Table 6.3-4.Deterministic Input Parameters CASE Crustal Magnitude 6.5 Reup (km)100 (Rus=100) Vs3a (m/s)760 Type of faulting Strike-slip Dip (degrees)90 Seismogenic Depth (km)20 Width (km)20 PGA(g)[percentile]0.02[50%] 0.04 [84th Ground Motion Prediction Equation [weight]BA08 [0.25] CY08 [0.25] CBO08 [0.25] AS08 [0.25] Notes: Acronyms:BA08=Boore and Atkinson 2008;CY08=Chiou and Youngs 2008; CBO8=Campbell and Bozorgnia 2008;ASO8=Abrahamson and Silva 2008 For comparison,the Shake Map for the 2002 Denali earthquake (Figure 6.3-17;USGS)was reviewed and indicates the peak ground acceleration in Talkeetna were light and ranged between about 0.09g to 0.18g.Based on the above analysis it is considered that the maximum RTS event would expose the nearest town of Talkeetna to ground shaking substantially less than that experienced during the 2002 Denali event. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-70 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. USGS Rapid Instrumental Intensity Map for event:22614036 Sun Nov 3.2002 10:12.41PMGST M7.9 N63.52W147.53 Depth:5.0km 1D:22614036 65 64 63 ..fz q Le ; 61 60 oe Harney eae 156 -154 +152 -150 -148 -146 -144 -t42 8 -140 PROCESSED:Fri Jan 31,2008 06:30:04 PM GST, Perec [Not fett]Weak |Light |Moderate|Strong |Very strong]Severe Violent |Extreme POAMAGE.none |none |none |Very light]Light |Moderate |ModeratatHeavy|]Heavy |Vary Heavy PEAK ACC(%g)|<97 [97-94]7.4-3.9]2.99.2 |9.2-98 18-34 34-65 65-124 a124 PEAK VEL{enva)}<O.1 /0.1-1.1 |1.1-3.4]3.48.1 |8.1-16 16-31 31-60 60-116 >716 No eNaee |Itt IV Vv Vi Vil VII Z-|.Xe-- Figure 6.3-17.USGS Shake Map for 2002 Denali Earthquake (USGS) 6.3.4.Site Geology The Project site has been the subject of study primarily since the 1970s having undergone numerous site investigations and studies as described above.The following describes the overburden and bedrock,geologic structure,and hydrogeological conditions at the site. Discussions of geotechnical design criteria and engineering design considerations are included in Section 10.3 of this feasibility report. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-71 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.3.4.7.|Overburden Materials The overburden on the upper areas of the abutments,near the top of the slopes,consists primarily of glacial deposits (e.g.till)and colluvium,and talus (Drawing 01-01GT003).Overburden thickness in the dam site area is generally less than 50 ft.but may reach 70 ft.or more locally as indicated on bedrock contour map (Drawing 01-01GT004).Above El.1900 ft.,overburden thickness averages 20 ft.but is locally up to 50 ft.(upstream of the dam)on the left abutment. On the right abutment,the overburden thickness typically ranges from about 20 to 40 ft.Below El.1900 ft.,where overburden consists primarily of colluvium and talus,overburden has an apparent thickness typically between 15 and 20 ft.Subsurface investigations indicate that the contact between the overburden and bedrock is relatively unweathered and distinct. In the river channel,alluvium beneath the proposed dam site area is typically between 70 to 80 ft.thick,but it is up to 140 ft.thick within the two bedrock depressions located upstream of the dam (Drawing 01-01GT004 and Drawing 01-01GT007).Within the dam footprint,the river channel alluvium typically ranges from about 60 to 105 ft.thick.The alluvium is comprised primarily of well-graded coarse-grained gravels,sandy gravels,and gravelly sands with cobbles and boulders (Harza-Ebasco 1983).Boulders are visible on the gravel bars and banks of the river and generally range from one to three feet in diameter but some are as large as five feet in diameter.Near the south abutment,the alluvium transitions to a thick talus deposit of diorite boulders. For discussion of the overburden materials in the Watana Relict Channel refer to Section 6.3.6.4.1. 6.3.4.2.Bedrock Geology The dam site is primarily underlain by Tertiary volcanic intrusions that range in composition from diorite to granodiorite to quartz diorite (Drawing 01-01GT003 and Drawing 01-01GT006). The bedrock is medium to dark green gray,fine to medium grained,generally hard to very hard, strong to very strong,competent,and generally fresh.However,bedrock is typically slightly to moderately weathered at the top of rock and along discontinuities to depths of 50 to 80 ft.Below the surficial zone of weathering,the rock mass is typically closely to moderately closely fractured.In outcrop,joints are typically tight to open,although they are mostly tight at greater depths,rough to smooth in profile,planar,and some contain iron stains,carbonate deposits,or are slickensided.At depth,local weathering can occur in areas of highly fractured rock,and the fractured rock may also contain breccia and clay gouge (shear zones)and/or be hydrothermally altered. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-72 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Bedrock directly downstream of and at higher elevations above the left abutment the dam site consists of extrusive volcanics,mostly andesite porphyry,which varies locally to dacite or latite. The andesite is similar in chemical composition to the diorite,and is generally dark gray to black,slightly weathered,strong to very strong,competent and in places contains diorite xenoliths.The nature of the contact of the andesite with the diorite is poorly understood. However,where mapped along the left abutment downstream of the dam,or drilled through,the contact zone is generally weathered and fractured in a zone up to 15 ft.wide and can exhibit signs of fracturing and shearing as evidenced by slickensides.Such shear fracturing suggests a manifestation of igneous and volcanic emplacement.The rock within this contact zone may have low RQD and can locally have core loss.Despite the fracturing,the hydraulic conductivity along the contact is relatively low.Downstream of the dam site on the south bank,the andesite exhibits slight to moderate alteration.There is strong hematite staining and the phenocrysts show signs of alteration to chlorite and clay minerals.Detailed discussion of the andesite porphyry/diorite contact is presented in an Acres (1982a)report. The diorite body has been intruded by mafic and felsic dikes that are generally a few feet wide, and exhibit contacts that are tight and competent.Felsic dikes are observed in outcrop as well as boreholes.The dikes are light gray,aphanitic to medium grained,fresh,hard,and strong to very strong. Mafic dikes are less common than felsic dikes but were encountered in outcrop and in several boreholes.The mafic dikes typically consist of andesite and are less than 5 ft.wide.They are dark gray to green-gray,fine-grained,fresh,hard,and strong.Mafic dikes may be porphyritic, include xenoliths of the parent rock (diorite),and generally have tight contacts with the parent rock. Upstream of the dam site,a 300 to 400 ft.wide northwest-southeast trending dike consisting of diorite-andesite porphyry is mapped on the north and south sides of the river.The dike is dark gray to green-gray,fine-grained with medium-grained feldspar phenocrysts.The rock is generally fresh,hard,and locally exhibits weak flow banding.Toward the west,the contact of the dike with the diorite pluton coincides with an approximately 10 ft.wide shear and alteration zone that is mapped as part of previously identified "geologic feature”GF1.The east contact appears to coincide with a gully,but the contact is mostly obscured by talus and the contact could not be traced over a significant distance. In a number of boreholes,hydrothermally altered bedrock was penetrated.Hydrothermal solutions have caused the chemical breakdown of the feldspars and mafic minerals in the host rock leaving a lighter greenish-gray to tan to white appearance.These altered zones are rarely seen in outcrop because the bedrock has been eroded into gullies where alteration is moderate to Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-73 December 2014 Zz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT severe.Where encountered in rock cores,the width of the altered zones in boreholes ranges up to 20 ft.but are typically less than five feet,which altered rock is often associated with close fracturing,fracture zones,or shear zones.The transition between fresh and altered rock is gradational over a few inches to a few feet.The degree of alteration encountered is highly variable,but in the areas of severe alteration,the rock can be weak to extremely weak and contain zones of rock completely altered to clay minerals over several inches. 6.3.4.3.|Geologic Structure Geologic mapping and core drilling at the dam site have identified three major classes of rock mass discontinuities as summarized in the Table 6.3-5.The most common and pervasive class are joints.Fracture zones,which are less common than joints,consist primarily of very closely to closely spaced joints over short zones of depth intervals.Least common are shear zones, which exhibit some evidence of relative displacement such as the presence of gouge,breccia, and/or slickensides.Shear zones are often relatively narrow can be identified within fracture zones and altered zones. Fracture zones and shear zones are typically oriented parallel to the major joint sets.The most prominent and persistent of the fracture and shear zones have been termed "Geologic Features” (e.g.GF1,etc.)beginning with reports by Acres (1982a).Joints,fracture zones,and shear zones exhibit a wide range of weathering,alteration,and healing,as they may have been conduits for fluid migration.Detailed characteristics of each type of discontinuity are described in the following subsections. Table 6.3-5.Discontinuity Types Discontinuity ae wo:Width/: Type Distinguishing Characteristics Aperture Persistence Example Generally planar breaks and Less than |Individual joints are typicallyyPAreet0.01 inch to |continuous from several ft.to more , .fractures;some with minor infilling f Joint Sets 4Jointandmineralization.Healed joints are |MO"than 1 |than 50 ft.Joints generally occur and 2°J inch in as coplanar joint sets with variedalsopresent.'outcrop |spacing. Areas of very closely to closely spaced (less than 1 inch to 8 inches)Fracture Zone jointed rock where no apparent Up to 20 ft.|Tens to thousands of feet relative movement has occurred. Zone of rock along which there has GF-1,GF-4BbeenvisibleevidenceoforCF-5measurabledisplacement.These Few inches Shear Zone |zones are characterized by breccia,butless |Tens to thousands of feet gouge,and/or slickensides and than 5 ft. frequently associated within fracture zones or altered zones. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-74 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.3.4.3.1.Joints Two major and two minor joint sets have been identified at the dam site,and the orientations are summarized in Table 6.3-6.Joint set1 (JS1),which is the most prominent set,trends the northwest-southeast (300°)and dips between 70°northeast to 80°southwest (Acres 1982a;Acres 1982b;MWH 2014).JS1 is found throughout the dam site and parallels the dominant geomorphic trend in the lower valley (i.e.,gullies).JS2 trends northeast-southwest (040°)and dips between 70°northwest to 80°southeast,but downstream of the dam dips more prominently to the northwest.JS3 and JS4 are considered minor sets but can be locally well developed.JS3 is better developed in the northwest quadrant of the dam site area,and trends between north- northwest to north-south,with an average trend to 350°,with steep dips to the east and west.JS3 is generally considered to form numerous open joints on the cliff faces downstream of the dam and is associated with fracture and shear zones that parallel this orientation (Acres 1982b).JS4 includes shallow dipping discontinuities of variable orientations.Results from the site investigations show that dominant discontinuities and structural features at the dam site are oriented mostly transverse to the Susitna River. Table 6.3-6.Summary of Joint Set Orientations Strike Joint Set i Strike (Azimuth)wv Acimuth)Dip JS1 270°to 330°300°70°NE to 80°SW JS2 025°to 060°040°70°NW to 80°SE JS3 340°to 020°350°70°E to 80°W JS4 Variable Variable Less than 35° In outcrop,discontinuities of the JS1 and JS2 are typically close to moderately spaced (2 inches to 2 ft.),planar,and rough and persistence between 10 and 30 ft.although can be more than 30 ft. Minor joint sets and random joints have similar spacing although the spacing may be greater in some areas due to decreased frequency.The minor joints and random joints have persistence generally less than 10 ft.It was also observed that the persistence is indirectly related to spacing, with wider spacing associated with more persistent joints,and vice versa. In outcrop joint surfaces are typically fresh to slightly weathered and clean,but can be discolored or have iron staining or carbonate filling.Steeper joints can be tight,but many are open and have been widened due to stress relief,freeze-thaw,and other erosive forces.Shallow to moderate dipping joints tend be have narrower aperture.The joint patterns create a blocky rock mass structure and in areas with a greater numbers of joint sets and oblique joints,blocks can have a tetrahedral or,less frequently,a rhombohedral shape.The combination of the joint Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-75 December 2014 ---yZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. patterns and slope faces produce blocks and wedges capable of sliding or toppling,and ultimately form talus at the base of the outcrops and within gullies. At depth,joint orientations and character are similar to those in outcrop,but joints tend to be tight to very tight,planar,smooth to rough,and have less staining or infilling than observed in outcrop.However,iron and carbonate infilling are observed more frequently near surface where the bedrock is more fractured and susceptible to weathering and effects of groundwater movement.Some joints,particularly those located near fracture,shear,and/or altered zones exhibit slickensides. For additional details of joint orientations,characteristics,and properties used in engineering design and stability analyses refer to Section 10.3. 6.3.4.3.2.Fracture Zones Fracture zones consist of very closely to closely spaced (less than 1 inch to 8 inches)jointed rock where no apparent relative movement has occurred.Fracture zones are common to all rock types and are generally encountered in boreholes and less frequently observed in outcrop.In general, fracture zones consist of rock that is more fractured rock,represents a structural weakness compared to surrounding rock and are preferentially eroded.Over time,fracture zones are widened by stress relief and freeze-thaw action and other processes,which form gullies and topographic lows along the fracture zone.The geomorphic landscape of the dam site appears to be developed,particularly lower in the river valley,from the prominent geologic structure or fabric that are oriented in the northwest-southeast direction (paralleling JS1)and to lesser extent to north-south features (paralleling JS3).Because fracture zones are generally not observed in outcrop and it is difficult to assess the orientation of fracture zones from downhole logs since fracture zones contain a large number of fractures over a wide range of orientations.Thus,the best indicator of orientation of fracture zones is trend of topographic features and the presence of discrete narrow shear zones within the wider fracture zone,from which orientations can be more easily identified. 6.3.4.3.3.Shear Zones A shear zone is a zone of rock along which there has been visible evidence of movement or measurable displacement and are characterized by the presence of clay gouge,breccia,and/or slickensides. Two types of shears are found at the site.The first type,which is found only in the diorite,is a healed shear zone and healed breccia.This type of shear zone consists of a well indurated diorite breccia healed within a matrix of aphanitic to fine grained and andesite/diorite.The diorite Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-76 December 2014 -yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. fragments range from less than 5 percent to 90 percent of the zone and are generally subrounded. The matrix and rock fragments,which are observed in both outcrop and boreholes,are fresh and very hard to hard.The contacts,although irregular,are tight and unfractured.Based on the characterization of these shear zones,they are interpreted to be features that formed during emplacement. In outcrops,healed shear zones and breccia range from less than one inch to about 18 inches wide.One-foot offsets along these features have been observed where they cross felsic dikes. Two general orientations were found for this type of shear:305°and dipping 45°to 70°to the northeast,and 300°(120°if using strike azimuth)and dipping 65°to the southwest.Healed shear zones and breccias were found in many recent boreholes.In all cases,the zone was found to be competent with high rock quality designations (RQDs)and high core recoveries.The largest healed shear zone was up to 140 ft.wide (apparent width)in borehole DH-11 (Acres 1982a).Lacking borehole orientation data,no correlations could be made between the healed shears and breccias noted in the drill holes from the 1980s and surface exposures. The second type of shear zone is common to all rock types and consists of brecciated rock with clay gouge.This type of shear zone is most frequently associated with fracture zones and altered rock that typically trend northwest-southeast (paralleling JS1),particularly within the dam footprint and areas immediately upstream and downstream.These shear zones typically consist of coarse to fine-grained rock fragments (breccia)weathered to tan-yellow,orange,brown and sometimes includes a narrow zone (few inches)of silt or clay gouge within the central portion. Both the breccia and gouge can be soft to medium stiff,and friable.These shear zones vary from less than 0.1 inch up to 10 ft.wide (apparent width;Acres 1982a),but are generally less than 1 to 2 ft.wide.An example of a typical shear zone in outcrop is shown on Figure 6.3-18 and Figure 6.3-19.Carbonate and chlorite mineralization are commonly associated with this type of shear zones,and some are partially to completely filled and cemented with carbonate.Slickensides are often found in most shear zones,but not all,and can occur on both the carbonate and chlorite surfaces.When found in association with these fracture or alteration zones,shear zones have been referred to as shear/fracture and shear/alteration zones. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-77 December 2014 -2-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years.eTyngFnCom'XYohheWare AL Se eSllRee!on alr ee I, Figure 6.3-18.Shear Zone in Outcrop at GFI. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-78 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. wt a 'it ed.yoSee,SoC arn |ata ile tts A NENA Ss Figure 6.3-19.Close-up of 3 to 4 ft.Wide Shear Zone at GF1 Given the relatively narrow width of most shear zones with respect to the dimensions of the dam foundation,these features are not anticipated to be sources of major structural weaknesses in a foundation consisting of otherwise relatively fresh and sound bedrock.However,shear zones are expected to require local treatment,to remove soft or deteriorated materials to limited depth below the foundation level,and be replaced with dental concrete. 6.3.4.3.4.Structural Features During the 1980s site investigations,geologic interpretations were developed that included characterization of the geologic conditions and the preparation of a geologic map of the dam site area (Acres 1982a,1982b).Therein,a geologic framework was presented that identified several structural features that largely coincided with geomorphic expressions (e.g.,gullies)in the abutment landscape,which were further defined by geologic mapping observations,drilling and in situ testing evidence of fracture,shear,and alteration zones,and lower bedrock velocities from seismic refraction data.The so-called "geologic features”identified by Acres (1982a,1982b), were interpreted,and the postulated persistence of these features were depicted in the geologic maps produced at that time.Eight geologic features (designated GF1 through GF8)were delineated,which included fracture or shear zones with widths greater than 10 ft.and wide zones of alteration with associated fracture and shear zones (Acres 1982b;Figure 5.2). Geologic features GF4A/GF4B and GFS are projected to be encountered in the foundation of the proposed dam.It is these structural features in particular that were the focus of the 2012 and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-79 December 2014 --yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 2014 site investigation programs to reduce geologic uncertainties.These geologic features are expected to have significant influence on the design of the project,in particular the detailed siting and foundation design of the dam. As part of the feasibility study,a new data set and tools were employed to investigate,define and evaluate the previously identified structural features.Light Detection and Ranging (LiDAR) surveying was performed in 2012 to develop bare-earth imagery and a detailed topographic map of the project area.The LiDAR imagery was also used to examine the dam site area landscape and to assess surficial geology and geomorphic features,and to identify potential lineaments or faults.Additionally downhole optical and acoustical televiewer logging was performed in the boreholes to obtain rock discontinuity orientations. Based on a review of the earlier studies and the current geologic site investigations,the interpretation of the dam site geology has evolved,and updates and revisions of the interpretation are described herein.Evidence from seismic refraction surveys to support the extension or persistence of several "geologic features”over several thousands of feet,as depicted on the dam site geologic map (Acres 1982b)and extending from one abutment to the other is speculative or absent.Geomorphic evaluation using LIDAR elevation data;geologic mapping; drilling and in situ testing;and a careful review of the original geophysical testing supports the updated geologic interpretations as shown on Drawing 01-01GT006. Other structural features,located upstream or downstream of the dam site that are not expected to directly impact the general arrangement or dam and other project structures,were also reviewed at a reconnaissance level for completeness and are discussed separately. 6.3.4.3.4.1.Structural Features in Dam Site Area As alluded to earlier,a review of the existing data on the dam site geology was made and site investigations were performed that included lineament analysis of the dam site area using the newly acquired digital elevation data and abutment geologic mapping of and the drilling across the largely northwest-southeast trending structural features previously identified.The following is a discussion of the observations and reinterpretations made based on the efforts under this study. Geologic Feature GF4 The 1980s studies interpreted GF4 to consist of two fracture/shear zones that are continuous across the current dam foundation and therefore,might also appear in the diversion tunnel and spillway excavations proposed at that time.The descriptions and interpretations from the 1980s indicate that on the south bank GF4 consists of two fracture zones with some minor shear zones Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-80 December 2014 -z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. -each inferred to be less than 10 ft.wide -that extend upslope from the shoreline through a northwest-southeast trending gully to about El.1950 ft.,where it appears to terminate at a relict crescent-shaped rounded scarp-like feature between El.1950 ft.to El.2250 ft.Overall these two fracture zones with evidence of shearing (e.g.gouge)were postulated to extend across the dam site over a distance of up to 3,500 ft.According to Acres (1982b),the fracture zones contain moderately weathered rock that may be altered and is characterized by very closely to closely spaced joints from JS1,JS2,and JS3 and are heavily coated with carbonate and iron oxide staining. In contrast,the mapping performed in 2014 indicates that the continuity and persistence of GF4A and GF4B (named by Acres 1982)cannot be reliably traced from the south bank to the north bank.To do so,would require the two fracture zones to transect a prominent 30-ft-high outcrop along the south river bank,which consists of sound,massive to blocky diorite.Thus,GF4A and GF4B are not persistent over the length previously shown and are reinterpreted as two features on either side of the river as shown on Drawing 01-01GT006. Geologic mapping and drilling performed to intersect these structural features at depth in 2012 to 2014 have helped revise the previous interpretations of GF4 on the north bank.GF4B is described as multiple discrete fracture zones,splays or branches,orientated in the northwest- southeast direction,that intersect a north-south trending fracture zone.The fracture zones,which may contain narrow shear zones typically less than eight inches wide consisting of breccia and clay gouge,are correlated to several prominent gullies immediately upstream of the dam right abutment between the shoreline to about El.1850 ft.that are as much as 40 to 50 ft.wide. Although the gullies appear wide at the surface,mapping and drilling suggest that the fracture zones are much narrower. During 2012,drill hole DH12-3,was drilled inclined to the southwest to intersect the geologic structure below this group of gullies.Information from this drill hole indicates the rock alternates between zones of slightly to moderately fractured rock to very closely to closely fractured rock in the upper 300 ft.Some of the fracture zones contain some minor shear zones (less than 1 ft.wide)consisting of breccia and clay gouge.For example,there are three fracture zones some with gouge in the upper 300 ft.for the borehole.Between a depth of 76 and 80 ft.,a 6-inch wide zone of completely weathered rock oriented east-west (278°to 288°)with vertical dip is associated with extremely close to closely spaced joints.At 130 ft.depth,another fracture zone included a 6-inch wide zone of plastic silt was encountered,but the orientation is not known.At a depth of 179 ft.,an 8-inch wide zone of plastic clay was encountered within a fracture zone and oriented to the northwest-southeast (313°)and dipping 70°to the southwest. Below 300 ft.,fracture zones in this borehole are generally less than about five to seven feet wide and occur less frequently in what is generally moderately fractured rock.Discontinuities Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-81 December 2014 -zO .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. within fracture zones are typically tight,surfaces are rough to smooth with iron oxide staining, white carbonate deposits,or chlorite,and some surfaces contain clay infilling with slickensides. The fracture zones appear to contain some minor shear zones,which are typically less than a few ft.wide. In the 1980s studies the continuity or persistence of GF4B (formally GF4A and GF4B)had been tentatively correlated to lower seismic velocity zones and a change in bedrock slope on seismic profiles.However,re-examination of the geophysical profiles does not provide evidence sufficient to warrant this interpretation nor the extension of these fracture zones to the northwest as had been represented.The previous interpretation of geophysical survey line SL82-9 was that GF4A and GF4B were associated with a change in seismic velocity from 20,000 fps (ft.per second)to 16,500 fps.Both velocity values are high,and according to the criteria used at that time,are indicative of fresh to extremely fresh bedrock (Acres;1982b).Therefore,it is not appropriate to consider such a minor contrast in the bedrock seismic velocity related to fracture zones to be of any major significance.If anything,such a contrast is more likely due to the presence of multiple narrower features of lesser prominence,slight changes in the rock material properties,or other variations. Although fracture zones were not directly observed in outcrop,the drilling information and particularly observations from mapping support the interpretation that GF4B consists of multiple narrower fracture zones trending in the northwest-southeast to north-south directions.Mapping within the gullies suggests that the gullies formed by preferential erosion of narrower fracture zones (with or without minor shear zones)that were enhanced and widened by weathering processes.Continued removal of rock blocks and wedges by erosional processes such as stress relief along steep joints and freeze-thaw,has created the present geomorphic surface and filled the gully floors with boulder talus.For example,Figure 6.3-20 shows an approximately 5 to 7 ft. wide gully between outcrops of competent diorite.This width constrains the maximum width of the fracture zone to these dimensions. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-82 December 2014 -2 ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. ye o ye s . Figure 6.3-20.Northwest Trending Gully of GF4B (width of fracture zone is constrained by the gully width) Another example of gully formation on the right abutment is shown in Figure 6.3-21.The gully appears to have formed along a narrower zone of weaker geologic materials (e.g.,fracture zone), but has been widened by erosion.On the left side of the photo (west)is an outcrop of competent rock with prominent joint set dipping 35°to 55°to the east (toward the gully),and on the right side of the photo (east)the outcrop has joints that dip steeply to the southwest (into the gully). The line of intersection of these joint sets trends to about 345°(nearly north-northwest to south- southeast),which parallels the trend of this gully.This observation supports the notion that the gullies were likely initiated by erosion of a relatively narrow fracture zones consisting of weaker rock.Projecting the major joints from each outcrop to the gully floor,constrains the maximum width of this fracture zone to about 10 ft.The gully has likely been widened by erosion of blocks from both outcrops and talus blocks are deposited in the gully floor. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-83 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Soe chin PREY Rieriis ea daeste 3toNtBe,iis y ae,io oeSea,heb PS ahaa ee te Figure 6.3-21.North-northwest Trending Gully of GF4B Although fracture zones are not readily observed at the ground surface,the conditions are better represented in the rock cores.Several fracture zones with breccia and gouge can be observed in the rock core from DH12-3,which is believed to cross several fractures zones comprising GF4B on the north abutment.For example,at a depth of 179 ft.a northwest-southeast trending fracture zone consisting of close to very closely fractured rock and eight-inch thick zone of clay gouge shown in Figure 6.3-22 was encountered.Although these fracture and shear zones are considered relatively minor features with respect to the dimensions of the dam,the project structures have been moved slightly downstream,to reduce the potential that this or similar structural features will impact the dam or require foundation treatment. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-84 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 6.3-22.Rock Core from DH12-3 with Closely Fractured Rock and Shear Zone at Depth of about 179 ft.(red box) Geologic Feature GF5 GF5 is located downstream of GF4A and GF4B and consists of multiple fracture zones with some minor shear zones that cross the dam footprint on the lower right abutment.The geologic structures comprising GFS are similar to those of GF4B and trend northwest-southeast (310°to 320°).The structures are steeply dipping,and were anticipated to be encountered in the dam foundation,diversion tunnel,and spillway excavations.On the north bank of the river,GF5 is interpreted to fall within a 100-foot wide gully that extends from the shoreline to about El.1700 ft.,bound by the 75-ft-high rock face (Figure 6.3-23)immediately downstream.On the south abutment,GF5 was interpreted to extend to the SW to about El.2100 ft.Overall,the fracture zones with evidence of shearing (e.g.,breccia and gouge)are shown to extend across the dam site over a distance of up to 1,500 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-85 December 2014 -z- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. ma) i.reNT>ret Figure 6.3-23.75 ft.High Cliff on Right Abutment Forming the Downstream (Southwest)Boundary of GF5 Although there is no topographic expression of the fracture and shear zones at the surface on the north abutment above about El.1700 ft.,GF5 was correlated with several shear and fracture zones intersected in borehole DH-9 (Acres 1982).The joints and fractures in DH-9 are generally iron stained and carbonate-coated,and faint slickensides occur on some surfaces.The RQDs in DH-9 are lower,with an average of 57 percent.Hydraulic conductivities are generally between 10°!cm/sec and 10°cm/sec,and decrease with depth.However,the orientation of the fracture zone in DH-9 is not known and therefore cannot be positively correlated with fracture zones of GF5. Northwest of the spillway and dam proposed at the time,it was speculated (Acres 1982b)that GF5 is correlated to lower-bedrock velocity zones along several geophysical survey lines (SL82-1 and SL82-9).No low-velocity zones were encountered along SL80-2 that could imply continuation of this feature further.It is also worth noting that the low velocity zones observed in some profiles could also be due to north-south trending fracture zones that are more prevalent downstream of the dam in the northwest quadrant,localized weathered rock,changes in the rock material properties,undulating bedrock profile difference in overburden materials,or the presence of localized ice layers.In the absence of more reliable evidence,such as more inclined boreholes it is now considered speculative to assume GF5 extends more than 2,000 ft.to the northwest beyond the gully it has formed. On the south bank,GF5 is correlated to a 10 ft.wide fracture zone at river level and a series of minor northwest trending shears between El.1650 ft.and El.1850 ft.upstream of the dam Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-86 December 2014 --zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. footprint (Acres 1982).In addition,further upslope,GF5 was correlated with a 15,000 fps bedrock velocity zone along SL80-3 and a bedrock depression found in borehole DH-25 and SL82-12.In this area,overburden thickens from 10 or 15 ft.to nearly 80 ft.However,upon recent re-examination of the topography and the geophysical data,the seismic velocities along SL80-3,which follow a relatively steep ridge,may instead be representative of a rock mass with open stress relief joints that are very common in steeper rock outcrops.In addition,the bedrock depression in DH-25 and SL82-12 may be associated with the fracture zones of GF4A and the landslide scarp located immediately upslope. In 2012 and 2014,inclined drill holes DH12-4 and DH14-11 were drilled across this gully on the right abutment approximately normal to GF5.Based on a review of the geologic logs,downhole logging,and core photographs for DH12-4,several fracture and shear zones were observed in the upper 150 ft.At a depth of 74 to 79 ft.,a shear zone consisting of closely fractured rock that is moderately to highly weathered that includes approximately 8 to 14 inches of light gray silty clay was observed.The downhole logging indicates this shear zone trends to the northwest-southeast (303°)and dips 86°to the southwest.Between depths of about 106 to 116 ft.,the RQD ranges from 8 to 40 percent and contains a 6 to 12 inch wide shear zone at depth of about 113 ft.Within this zone,several prominent discontinuities in the rock core trend northwest and dip steeply to the northeast.Between depths of about 120 and 150 ft.the rock contains zones of closely fractured rock that is moderately to highly weathered,and some individual discontinuities are slickensided.Within this zone at a depth of about 137 ft.and again at about 148 ft.,the joints are closely to extremely closely spaced over lengths of 8 inches to 2 ft.with some discontinuities exhibiting planar and slickensided surfaces with calcite,chlorite,and some clay infilling and coatings.In general,these discontinuities appear to trend in the northwest-southeast direction and have steep dips.Below 150 ft.,the RQD is typically greater than 90 percent although a few runs had RQDs between 60 and 70 percent. Data collected from drill hole DH14-11 indicate that the upper 65 ft.of the hole contains rock with moderate to closely spaced fracturing and localized zones of moderately to highly weathered rock.The discontinuities have heavy iron oxide staining,likely due to their proximity to the ground surface and the adjacent rock face.At a depth of 78 ft.,a one-inch wide shear zone trending 303°and dipping 83°to the southwest was encountered and contains two-inches of altered rock on each side of the shearing plane and a fracture zone that extends to a depth of about 81 ft.Between depths of 87 to 103 ft.,the rock is very closely to moderately closely fractured rock and includes an 8 to 12 inch zone of very closely fractured rock at about 90 ft.that is oriented nearly east-west (84°or 264°)that is nearly vertical.In addition,moderately to highly weathered rock at a depth of 101.5 to about 103 ft.includes a shear zone oriented west- northwest (about 284°)that is nearly vertical.Below a depth of 103 ft.,the rock is slightly to moderately fractured with only localized fracture zones.A zone of close to very closely Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-87 December 2014 --yw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. fractured rock was encountered between depths of 165 to 170 ft.,which included a 1 to 2 inch shear zone at a depth of 165.6 ft.oriented north-south and dipping 77°to the west.Finally,a fracture zone consisting of closely to very closely fractured rock was encountered between depths of about 190 and 192 ft. While subsurface and surface data relative to GF5 lack compelling demonstration for the presence of a significant,through-going,fault or shear zones,it has been depicted as the widest and most continuous feature in the dam foundation.However,based on the site investigations and a review of the previous studies,it appears that GFS consists of several fracture zones ranging from about 5 to 10 ft.in width and some contain shear zones or gouge up to 14 inches wide.In addition,the persistence of GF5 to the northwest and southeast is only based on perceived "low”bedrock velocity zones and is therefore speculative at best.Therefore,in the current interpretation,the width of and presumed length of GF5 has been narrowed and reduced compared to representations from the 1980s studies.As with GF4A and GF4B,the fracture zones were not directly observed in outcrop,the drilling information and particularly observations from mapping support the interpretation that GF5 consists of multiple narrower fracture zones trending in the northwest-southeast directions with steep dips to the southwest and northeast.Mapping within the gullies suggests that the gullies formed by preferential erosion of narrower fracture zones that were enhanced and widened by weathering processes.Continued removal of rock blocks and wedges by erosional processes such as stress relief along steep joints and freeze-thaw,has created the present geomorphic surface and filled the gully floors with boulder-sized talus. Because fracture zones in GF5 are readily observed at the ground surface,the conditions are best observed in the rock cores.In DH14-11 at a depth of 102 ft.a northwest-southeast trending fracture zone consisting of close to very closely fractured rock and approximately 20 inch wideshearzone(apparent width)of moderately to completely weathered and friable and brecciated rock as shown Figure 6.3-24.Although considered relatively minor features with respect to the dimensions of the dam,due to the location and trend of this and similar fracture zones and shear zones in GF4B,the project structures were moved slightly downstream,to reduce the potential impacts that this or similar structural features could have on the dam foundation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-88 December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. oe -Suwa HER”Zor!. Met 1-14.TN Box&of Tet.WA do loFS Ft*aFigure 6.3-24,Rock Core from DH14-11 with Closely Fractured Rock and Shear Zone at Depth of about 102 ft.(red box) 6.3.4.3.4.2..Additional Geologic Features In addition to geologic features encountered within the dam footprint,six additional geologic features are located both upstream and downstream of the dam. Geologic Feature GF1 Geologic Feature GF1 is located approximately 2,200 ft.upstream of the dam axis,and is visible on the north bank at the sharp bend in the river.The area is characterized predominantly by sound,jointed bedrock that includes steeply inclined northwest trending zones of closely fractured rock up to 15 to 20 ft.wide,5 to 10 ft.wide zones of weak,friable altered rock,and shears that measure |inch to approximately 3 ft.in width (Figure 6.3-25).The 3 to 4 ft.wide shear zone exposed at river level is oriented 334°and dips 64°to the northeast.This particular structure is known as GF1E as mapped by Acres (1982b)is presumed to extend about 400 to 500 ft.to the northwest and intersect with another fracture/shear zone located within a steep sided gully. The weaker zones have contributed to the erosion of steep gullies (Figure 6.3-26),which are separated by intact rock ridges.The gully (near OC 10 and OC 11 on Drawing 01-01GT002)is formed along the fracture and shear zone comprising the contact between the diorite to the left side of the photo (southwest)and andesite porphyry on the right side (northeast).The narrowest portion of the gully is between 5 and 10 ft.wide,which constrains the maximum width of the fracture and/or shear zone that forms this gully.The upstream part of GF1 also coincides with a steep,narrow gulley that is an approximately 10 ft.wide shear/alteration zone that forms the contact between the diorite and a large mafic dike.Above GF1,along its possible projection to the northwest,GF1 is blanketed by a thick layer of glacial drift,about 15 to 95 ft.thick.Beneath the glacial drift,unique to this location,a zone of highly weathered to decomposed diorite exists locally at the bedrock surface that is as much as 70 to 80 ft.thick.At depth,individual zones of closely fractured rock and alteration are as much as 15 ft.wide.These weaker and fractured Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-89 December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. zones have occasional slickensides and clay infilling,which may be related to local shearing, was observed.Healed breccia and microfractures are also common in the rock mass (Harza- Ebasco 1984). In assessing the hydraulic characteristics of the highly weathered bedrock at elevations above GF1,the rock mass permeability was found to be very low and the groundwater levels in the rock were determined to be 10 to 20 ft.below the ground surface.The individual zones comprising GF1 are difficult to trace due to the steepness of the terrain and talus cover,and the thick glacial overburden deposits above El.2000 ft. In 1984,drilling was performed a short distance from the outcrops to the northwest along the projection of the GF in order to determine the persistence or continuity and the erosion potential of the northwest trending fracture and shear zones (Harza-Ebasco 1984).Based on the lack of any structural discontinuities other than fracture zones and relatively narrow shear zones,the low rock mass permeability,and high groundwater levels,it is concluded that there is no evidence of a major structural zone of weakness,that would be indicative of a distinct and continuous "fault” to the northwest.Neither is there a structure that would permit excessive seepage or internal erosion within the rock mass toward Tsusena Creek. be PnP eee 4in”ed aden ante"nbd <4 a if mae '.7 ok ba of 'ae *a t wet mae ot «peg.:*4 :I eget yyyeMHty:one -s ;a am 4 "a "3 ':0 Fel : oe BPA 'ain ae co"rey .raRSee(eae ees eet are{*s ¥are t-bags .*.a .)ed.ren1wiresPeSereCaeoTate')iD tg *be in re Ay if::aos heioloeADRESCOOCTOeMOa:i os in xt wah.is et ye le we 'gso af{WN;aod t vot.STA,aA }me nee ae rah yteSe bse 8 ]irs ee ans eee tet ge atyeaOEYfigttyc©@he >it oS a ee pre Me"wy Mince SO tb Nag noes Figure 6.3-25.GF1 Located 2,200 ft.Upstream of the Dam Axis (view looking northwest) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-90 December 2014 -Z.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years.oaf=eetMee oe Saget nn a>tegh rs ait oe7straca Figure 6.3-26.Narrow Gully in Area of GF1 Geologic Feature GF2 GF2 is a northwest-southeast trending fracture zone with minor internal shear zones that is presumed to extend through prominent gullies on the north and south banks of the river.On the north bank,the fracture zone is located between outcrops that are oriented parallel to JS1 and about 70 to 100 ft.apart (Acres 1982a,1982b).However,the fracture zone is not observed in outcrop on the north bank due to presence of blocky talus on the gully floor.The topography of the gully within which the geologic feature is located can be used to constrain the width of the geologic feature.On the south bank,GF2 is presumed to coincide with an incised gully that has side walls formed by close to very close spaced and open joints belonging to JS1.The Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-91 December 2014 -2wz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. topography indicates that the width of the narrowest part of the gully on the north and south river banks is about 20 to 30 ft.Presuming that the fracture zone has a similar character to the north, the narrower GF2 formed within a wider gully there suggests the width of the north gully has been enhanced due to erosion processes,similar to what was observed in other geologic features described above. At higher elevations along the north bank,several geophysical survey lines correlated slower bedrock velocities with the extension of poorer quality and fractured rock of GF2.However,the survey lines do not clearly explicit anomalous velocities at these locations.Acres (1981) indicated apparent anomalies in SL81-15 might be due to topographic effects or slight changes in thickness of surficial materials.In addition,the geophysical surveys performed furthest to the northwest did not record any low velocity bedrock zones,a finding that suggests that GF2 is discontinuous to the northwest (Acres 1982b).Therefore,the extension of the fracture zone to the northwest beyond the surface expression of the gully is now considered speculative. Geologic Feature GF3 GF3 is an area approximately 1,200 to 1,500 ft.wide on the north and south banks bound by GF2 and GF4A (south bank)and GF4B (north bank).Outcrops are well exposed on the south bank and are limited on the north side due to a wide blanket of talus covering the slopes below about El.1650 ft.The fracture and shear zones in this area are predominantly parallel to Joint Set I, although geologic structure parallel to JS2 and JS3 have been measured (Acres 1982). GF3 area is characterized by fracture and minor shear zones on the south bank that are generally less than 6 ft.wide.The most significant feature that was identified is a 20 ft.wide fracture zone within a deep gully,which is suggested to correlate with narrow gully on the north bank and is believed to parallel GF2 to the northwest (Acres 1982a).The gully is located more than 1,000 ft. upstream of the dam axis.Review of the topography and LiDAR data indicates that the outcrops on both walls of the gully constrain the fracture zone width to about 10 ft.The weaker fracture zone has likely been eroded,leaving a wider gully,a similar process that was observed in GF4B and GF1 described above. Although the evidence of distinct fracture and minor shear zones is based on the gullies observed on the south abutment,there is no surface evidence for the continuation of these suspected features to the northwest and beneath the talus on the north bank.The talus has formed because of erosion of rock outcrops. Based on the descriptions presented above,the fracture and shear zones that have been encountered in this area of the south bank are considered relatively minor and local features.As minor features in an otherwise competent rock mass,they would only locally influence the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-92 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. engineering design of the Project and if encountered during construction,they would likely receive localized ground treatment as needed.Therefore,it was misleading to characterize a 1,200 to 1,500 ft.wide zone of relatively minor features as a single geologic feature.Thus,it is now considered that GF3 is a non-existent feature and no longer applies.Instead,this area is now described as a zone of minor fracture zone and shears. Geologic Feature GF6 Geologic feature GF6 is characterized by a north-south trending shear zones,fracture zones,and open joints;east-west trending open joints;and northwest trending shears.These features are exposed in deep gullies in the northeast-facing high,massive rock cliff on the south side of the river.As described by Acres (1982)in north-south gully features up to 2.5 ft.of gouge was observed in slope debris,and open joints dip to the east and may be several feet wide.East-west trending joints dip 70 to 80 degrees to the north (towards the river).The intersection of these joint sets has resulted in purported localized block slumping.These features were not inspected during the 2012 and 2014 investigations due to difficult access and because they are located 1,000 ft.or more downstream of the dam site. Geologic Feature GF7 GF7 is characterized by numerous north to northwest trending,nearly vertical shear,fracture, and alteration zones that parallel JS1.North-south trending features,parallel to JS3 are also present.Initial mapping was performed in this area by the USACE (1978)and Acres (1980)and detailed mapping was performed by Acres in 1982 after this area was recognized as a zone where more prominent geologic structures were evident.These structural features are best exposed on the north bank of the Susitna River,as rock outcrops are limited on the south bank. The northwest trending features typically trend 295°to 305°and have high angle dips ranging from southwest and northeast.These northwest trending features subparallel the trend of the Susitna River at this location.Within the diorite,alteration zones consisting of gouge and breccia up to 2 ft.wide is yellow-orange,soft,and friable.The rock surrounding these areas is generally fresh to slightly weathered,but the surrounding rock may have very closely spaced jointing.The extent of these features could not be traced accurately further downstream.In most areas,the shear zones were projected across outcrops,and where not exposed in the slope as they tend to form topographic lows or gullies.Slightly further upstream,the features are covered with talus,and their presence is inferred by lower seismic velocities. The most prominent northwest trending features GF7J (Acres 1982)extends from the north bank to the shoreline along the south bank.On the north bank,GF7J lies in a deep,vegetated gully trending at 290°.Exposures in the gully show very closely spaced vertical fractures trending Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-93 December 2014 --yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. approximately 290°with thin zones of breccia and gouge.The andesite porphyry of the gully walls is slightly to moderately weathered.GF7J is projected south of the river to correlate with features exposed along the base of the high,massive rock cliff (associated with GF6)located about 1,000 ft.downstream of the toe of the dam.Based on the slope of the cliff,GF7J appears to dip about 75°to the northeast.GF7J has also been correlated with a shear zone between depths of 97.8 to 104.0 ft.in DH-1 in which the rock is slightly to moderately altered and includes shear zones less than 6 inches wide.The rock is moderately hard,but soft in shear zones.RQDs are generally less than 40 percent in DH-1 with permeabilities about 10°cm/sec. Drilling investigations of the northwest trending features by Harza-Ebasco (1984)indicated variable jointing,local shearing,alteration,and healed breccia,but did not encounter major structural features. On the south bank,GF7J projects from the river bank and is correlated to an exposure in a steep- walled,10 to 15 ft.wide gully at the andesite porphyry/diorite contact near El.1750 ft.,which cross-cuts both rock types.The rock within GF7J has a granular,nearly schistose,character typical of cataclastic rocks,although it has been healed and re-sheared.No exposures of GF7J have been found above the contact,but a projection of the exposure indicates that it may found in the dam foundation high on the left abutment. Over more than a 600 ft.section of the south abutment downstream of the dam,the slope area is sparsely populated with rock outcrops,a break in the nearly continuous rock cliff and outcrop exposure that is seen from the dam left abutment upstream and in the bend downstream in the area of GF6.The slope is covered by talus and colluvium material.This area coincides with the projection of suspected northwest trending discontinuities that likely is subparallel to GF7,and may explain the lack of rock outcrops lower in the abutment on the south bank.No drilling investigations have been performed on the slope in this area and future investigations will be required to evaluate the conditions and any possible significance to the design.At this time,the general arrangement for the project has avoided placing any structures in this area. Geologic Feature GF7Q (Acres 1982)is a north-south trending feature located about 2,800 ft. downstream from the dam and is most prominently exposed in a 40 ft.wide,deep talus-filled gully that coincides with the andesite porphyry/diorite contact.The rock is moderately close to closely fractured with local shears and alteration zones which trend parallel to JS1 (330°)and JS3 (0°).Slickensides on the gully wall indicate vertical displacement.The degree of rock fracturing varies widely in this area,and is influenced by structural control and near surface stress relief fracturing.Because of the lack of surface exposure,and the variability of the features,no major structural features could be identified in outcrop. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-94 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. GF7Q is correlated to a prominent gully on the south bank.However,no surface exposures of the fracture and shear zones were observed in this gully,instead only talus filled gullies were encountered.However,the east face of the gully,oriented 294°and dipping 70°to the southwest,exhibited slickensides (Figure 6.3-27)plunging about 3°to 294°. The presence of slickensides with different relative movements from one side of the river to the other suggests there may be multiple features with a relatively limited area or complex relative motions. For a more detailed discussion of the geologic features and sub-features associated with GF7, refer to the Acres (1982b)and Harza-Ebasco (1984)reports. Figure 6.3-27.Subhorizontal Slickensides along Outcrop Surface near GF7Q Geologic Feature GF8 An approximately 400-ft wide northwest trending zone of altered rock had been previously interpreted on the south abutment downstream of the dam.The extent and trend of this alteration zone was largely inferred based on limited borehole data,and geophysical surveying performed by Acres in 1981 and 1982 due to the lack of bedrock outcrops,the area is overlain by glacial till. From a single geophysical survey line,a lower velocity zone (12,000 fps)was noted that extends for about 1,100 ft.toward the east-southeast.Nearby,borehole BH-12 purportedly encountered Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-95 December 2014 -ywZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. nearly 200 ft.of altered rock.The core recovery was good,but the quality of rock was relatively poor.The altered rock included localized areas of moderate to severe alteration and shear zones less than 6 inches wide.Joints were generally closely spaced,healed,with some carbonate,and chlorite.However,in reviewing the alteration zone it is believed that there is insufficient evidence to support the delineation of a 400-ft.wide zone of altered rock.In reviewing the log for BH-12,the overlying 80-ft.thick andesite was largely unaltered except for an approximately 10 ft.wide band at depth associated with shear.Other features included %-inch thick clay gouge and fracturing and discrete alternation or shear alteration zones ranging in width from about one to four feet to a depth of about 290 ft.in diorite.Below this depth there are several zones of alteration or shear/alteration,in particular the slightly to moderately altered zones between depths of about 290 to 305 ft.and 345 to 386 ft.below the ground surface. In most instances,the rock mass is only slightly altered,which has limited impact on the overall physical properties of the rock.Moreover,lacking evidence of shearing and alteration in the nearby boreholes BH-8,DH-12,DH-23,and DH-24 or in outcrops,the extension of the alteration zones of unknown orientation that was encountered at depth in BH-12 would be speculative.Thus,the wide band that had been part of earlier geologic interpretations has been omitted from the current interpretation of the site geology.Instead,only the limits of altered rock encountered in outcrop are shown on Drawing 01-01GT006. Geology beneath the Susitna River Because of east-west trending linear sections in the Susitna River valley near to and at the dam site,in earlier studies it had been conjectured that perhaps erosion of the river valley was structurally or fault-controlled.Gedney and Shapiro (1975)had identified an east-west trending lineament that roughly coincided with the Susitna River valley,but at the dam site,the lineament appeared to cross through the right abutment.Although drilling had been performed within the river for other objectives,sufficient data had not been obtained to understand the geologic conditions beneath the river. During the 2014 site investigations,two inclined drill holes,DH14-9b and DH14-10,each just under 700 ft.long were drilled beneath the river,approximately 200 ft.apart from opposite banks.These boreholes provide about 90 percent overlay over the width of the river channel.In general,bedrock beneath the river channel is fresh to slightly weathered,strong to very strong diorite with occasional discrete zones of alteration and minor fracture and shear zones.The alteration zones were typically comprised of moderately altered,medium strong to strong diorite and were about five feet thick or less;however,some altered diorite zones were up to 14 ft. thick.Zones of closely to very closely fractured rock,generally less than five feet in width and sometimes less than two feet wide were encountered sporadically at depth.Minor shear zones Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-96 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. with one to two inches of brecciated rock and clay gouge were encountered in DH14-9b at about 146 ft.,633 ft.,and 660 ft.depth and in DH14-10 at depths of about 142 ft.,225 ft.,and 507 ft. (Figure 6.3-28 and Figure 6.3-29),and included slickensides.These shear or shear/altered zones are not anticipated to be sources of major structural weaknesses in the otherwise sound bedrock foundation.The drilling encountered no large-scale shears zones or faulting beneath the river. "Seth a oO ANCA NCE SOCEM AM leper meee eeeto8SSeelite --ee eee wee Q - eh ee owe =-heae I I Cd rnsia"on :W HE?,.-Pay a P2oyl4 y Figure 6.3-28.Narrow Shear Zone with Slickensides,Calcite Filling in DH14-10 at a Depth of 507 ft. zc We - :---_iia 7 £2 -\- t_]an oe ae Figure 6.3-29.Close-up of Shear Zone with Slickensides in DH14-10 at Depth of 507 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-97 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Fracture Zone Downstream of GF5 on North Bank A narrow gully appears on the north bank approximately 220 ft.downstream of GF5 (Drawing 01-01GT006).This gully appears similar in character and orientation to those of GF4B and GFS,but is only 10 to 20 ft.wide on the gully floor (Figure 6.3-30).In 2014,borehole DH14-12 was drilled perpendicular to this gully to intersect the discontinuities and to characterize the geologic structure that may have contributed to this geomorphic feature. Qn PT ee re yee '- |eeeebaPliesed:.geae PROS ,Soars $a ¥sae nsAextaareustepasted: Figure 6.3-30.Gully Downstream (west)Boundary of GF5 on the North Bank (view to southeast) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-98 December 2014 -yzZO ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Data collected for borehole DH14-12 indicate that the upper 70 ft.of the hole contains rock with moderate to closely spacing and zones less than 3 ft.wide consisting of closely fractured and weathered rock.The discontinuities have heavy iron oxide staining due to their proximity to the ground surface and adjacent rock face.At a depth of 74.5 ft.,a three-foot wide zone of closely fractured rock was encountered with a shear zone with |inch of gouge.This minor feature is oriented approximately east-west (100°to 280°)and dips near vertical.At a depth of about 107.5 ft.,a five feet wide zone of moderately to highly weathered and altered rock was encountered,and between depths of about 110 ft.and 112 ft.,the rock is brecciated and contains gouge.This interval is oriented approximately northwest-southeast (325°)and dips steeply to the northeast.Below a depth of 112 ft.,the rock is lightly to moderately fractured with RQD greater than about 75 percent. During mapping within this gully a shear zone was identified on the southwest wall of the gully and oriented approximately 290°and dipping about 70°to the southwest (Figure 6.3-31).The shear zone is approximately nine-inches wide and contains brecciated diorite and a two-inch wide central zone of clay gouge-breccia with angular sand size rock fragments.The brecciated rock is orange-brown and gouge is orange-yellow-tan.Eight inches on either side of the shear zone is moderately weathered and stained with iron oxide. A second shear zone (or possibly a splay)inclined to the main shear zone is about 2 to 5 inches wide and is oriented 289°and dips 79°to the northeast.A third shear zone is 3 to 4 ft.west of the main shear zone and is oriented 315°and dips 78°to the southwest and is only about 1/2-inch wide and is rehealed with carbonate.It is suspected that that the gully is associated with the minor shear zones encountered in the borehole between 110 and 112 ft.depth,and to a lesser degree the nearly east-west trending shear zones. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-99 December 2014 wz.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Ma aoe oeilav he e ay E=."8 Meee f :AteFa ¥xd inaat .a |Pv baa E2SeePeaplyyy Ceeseo.tga.Figure 6.3-31.Shear Zone near BS 36,Main Shear Zone on Right with Inclined Shear Zone Splay South Bank Shear Zones between GF4A and GF5 Several narrow shear and alteration zones were observed along the south bank of the river upstream of the dam between GF4A and GF5 near observation points BS25 to BS29 (Drawing 01-01GT002 and Drawing 01-01GT006).These narrow features were identified at four locations over approximately a 75 ft.wide stretch of the river bank that predominantly consists of sound rock,an outcrop that is about 30 ft.high.Each zone is about 1 to 6 inches wide and consists of highly to intensely fractured,weathered and altered diorite.The central portion of each zone has yellow-orange-brown plastic clay gouge-breccia up to %inch wide.Although slickensides were not observed due to the weak and friable nature of the material,slickensides Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-100 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. were observed on joints immediately adjacent to the shear zones.Some of the narrower zones are rehealed by carbonates.In addition,at two of the four locations the shear zones appear to have been cross-cut by felsic dikes at the shoreline (the dike was not observed at the other two locations).Although the dikes exhibit joints parallel to the shear/alteration zones,which trend northwest-southeast),the shear zones or carbonate did not extend through the dike as shown on Figure 6.3-32.This suggests that the dike intruded after the shear zone formed,and that no appreciable movement has occurred subsequent to dike emplacement. cory ne ee Shear/alteration zones in diorite on 'Diorite '&.a ee eat ,a eee ae,3LtAa2aeEMPIeaseeeeee=FaePO gtOT gi aes;See Cee ondaosaoontet=nr en : Figure 6.3-32.Shear/Alteration Zone at BS27 Cross-cut by Felsic Dike Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-101 December 2014 -zw- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Furthermore,one of the shear zones exhibits very thin healed joints that extend through the shear zone (Figure 6.3-33).This suggests that little to no movement has occurred since the joints were healed;otherwise the fragile joint structure within the shear/alteration zone would likely have been disturbed by subsequent shearing. ON ehme Dee entiesa age Ne ie. we Healed shear,alteration zone pees "al :ae oer, 'i 5B:Pa Ye (4 Figure 6.3-33.Continuous,Thin,Joint extending through a Healed Shear/Alteration Zone 6.3.4.4.Hydrogeology 6.3.4.4.1..|Groundwater Units The groundwater regime at the dam site is largely dominated by groundwater movement along fractures and joints in the rock mass (i.e.secondary porosity),the continuity of open fractures, and the gradients within the dam site proper.In general,the water table follows the shape of the surface topography.The groundwater conditions at the dam site are complicated by the presence of permafrost,on the left abutment and lower right abutment.Ice can be seen in numerous locations on both abutments in the winter,particularly on the steep slopes and gullies of the left (south)abutment. Several piezometers were rehabilitated and re-established during the recent site studies,and instrumentation was installed in new boreholes to enable future monitoring of groundwater levels at the dam site.The groundwater table on the right abutment is generally from 30 to 150 ft. below the ground surface except in areas with steep terrain,where it is 5 to 80 ft.deep.Below Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-102 December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. El.1750 ft.near the dam axis,the groundwater table appears to be about 140 to 150 ft.below the ground surface on the right abutment. On the left abutment,the groundwater conditions are influenced by the presence of permafrost. A relatively shallow aquifer within 10 ft.of the ground surface during the summer months appears to represent a "thawed”perched groundwater layer.In deeper piezometers,the groundwater level is 170 to 180 ft.below the ground surface.One exception is borehole BH-12, where artesian conditions were encountered at a depth of about 200 ft.,and the hole produced about 2 to 3 gallons per minute. 6.3.4.4.2.Hydraulic Conductivity The hydraulic conductivity of the rock mass does not vary significantly within the dam site area. Fresh,sound bedrock is generally characterized as low to very low permeability,less than 15 lugeons (2x10*cm/s).Areas of high hydraulic conductivity (e.g.,30 to 50 lugeons)are generally associated with fracture and shear zones.The hydraulic conductivity was also found to decrease with depth as fewer and tighter joints conduct less flow. Due to the presence of frozen ground and ice-filled discontinuities,the low to very low rock mass permeability on the left abutment may be misleading,as the hydraulic conductivity may be influenced by ice restricting flow through joints.Therefore,tests in areas where ice filled joints were encountered are considered to represent a lower bound of hydraulic conductivity and would likely be greater if ice were not present.It should be assumed that the left abutment and other areas where ice and permafrost are encountered will need to be thawed prior to constructing the grout curtain. 6.3.4.4.3.Permafrost Conditions Permafrost,frozen soil,and potentially ice-filled rock discontinuities are believed to be present at the dam site and in the project area.Permafrost is evident by periglacial or geomorphic features,observations of frozen soil exposed in landslide scarps,ice fillings observed in discontinuities in recovered rock cores,and ground temperature readings in boreholes.Frozen ground is believed to exist sporadically in the right abutment,based on ground temperature readings in two boreholes lower on the slope.In BH-6 (ground surface at El.1607 ft.),just downstream from the dam axis,frozen conditions were encountered from about 60 ft.to as much as 160 ft.below the ground surface.In DH12-6 (ground surface at El.1530 ft.),downstream of the dam axis and downstream diversion portal,frozen ground was detected from about 5 ft.to more than 40 ft.below the ground surface.In addition,in a few boreholes downstream of the powerhouse access tunnel portal,small,ice-rich samples were encountered in boreholes DH84-3 (ground surface at El.1503 ft.),DH84-6 (ground surface at El.1521 ft.)and DH84-8 (ground Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-103 December 2014 -w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. surface at El.1677 ft.).Elsewhere on the right abutment,higher on the valley slope,no ice or permafrost were encountered. On the left abutment,on the north-facing slopes and in general below approximately El.2100 ft. (or possibly higher),ground temperature measurements indicate that permafrost exists to depths of 200 to 230 ft.below the ground surface (e.g.,DH12-1 and DH12-6).The permafrost is believed to extend nearly continuously down to at least El.1640 ft.(or lower)based on ground temperature monitoring data in the boreholes.The active permafrost layer,the layer subject to seasonal thawing,appears to be generally in the range of 10 ft.thick,but may extend deeper locally.The characteristics of the permafrost indicate that the site is underlain by a "warm” permafrost (within 2°F of freezing),and for the purposes of the feasibility design analysis,a temperature of 30°F is a reasonable assumption. 6.3.5.Dam Site Area Fault Rupture Evaluation 6.3.5.1.General Permanent ground deformation from surface fault rupture can occur as primary,secondary,or sympathetic (triggered)rupture.Primary rupture is ground displacement associated with the main trace of a seismogenic fault.Secondary rupture is ground displacement from a fault that is structurally connected to the seismogenic fault,but is not the main seismogenic source. Sympathetic rupture is ground displacement from neither the main seismogenic source nor a secondary fault,but occurs principally from the effects of co-seismic strong ground shaking. Potential sources of surface fault rupture hazard that were considered and characterized to the extent possible at the proposed Watana dam site consist of:1)crustal seismic source faults with surface expression which transect the dam foundation directly or extend nearby,2)buried or "blind”crustal seismic source faults with no direct surface expression,or 3)features,proximal to the dam site,not active in the contemporary stress regime that could be potentially reactivated through mechanisms of reservoir triggered seismicity.Each of these potential sources of surface fault rupture hazard was evaluated based on differing aspects and combinations of the existing geological,geophysical,and seismological data.Evaluation of crustal scale seismic source faults,either those with surface expression or "blind”structures,which are the source of primary or secondary fault rupture hazards underscores the importance of regional data because the source dimensions of these structures requires features with scales on the order of tens of kilometers.Evaluation of potential fault reactivation emphasizes knowledge of the existence, extent,and orientation of potential faults in the immediate site vicinity because of the potential significance to the dam.One common element for evaluation of each source of potential fault rupture hazard is the existence and characteristics of faults within the dam foundation.In an Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-104 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. absence of known seismogenic faults at the dam site,the evaluation of fault rupture hazard focuses on the possibility of displacement along existing planes of weakness in the bedrock. 6.3.5.2.|Methodology The approach for evaluating surface rupture hazard at the dam site relies on four principal lines of independent data and analyses: 1.Assessment of the contemporary tectonic framework (stress field)of the site region as an indication of the potential for reactivation of site geologic features; 2.Geomorphic evaluation of Quaternary and post-glacial faulting (i.e.,lineament mapping and analyses)to assess whether potential seismogenic faults are present near the site vicinity; 3.Field geologic transects to assess styles and patterns of structural deformation near the site;and, 4.Assessment of results of site-specific investigations of geologic structure in the dam foundation. Collectively,these four lines of independent and relatively indirect evidence are integrated to develop the evaluation of (or supporting argument for no)fault rupture hazard at the dam site. This approach is in accordance with accepted methods and practices currently used for similar evaluations on projects involving major dam projects or critical facilities that pose potential hazard to the public and environment. The evaluation collectively considers regional tectonic history,sub-regional deformation patterns observed in Mesozoic and Cenozoic rocks around the site,emplacement of intrusions and volcanics at the dam site,crustal stress orientations from earthquake focal mechanisms,known active faulting,plate motions,and GPS data,geomorphic landform evaluations,and current understanding of geologic features at the dam site.The surface fault rupture evaluation assesses the weight of evidence in relation to three topical areas: =The regional and subregional evidence of Quaternary faulting; «The presence or absence of faults and large-scale shear features at the dam site proper; and, «The qualitative potential for reactivation of geologic structures at the dam site within the current tectonic framework. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-105 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Regional and sub-regional evidence of Quaternary faulting through geomorphic evaluation of post-glacial faulting is the strongest argument to address late Quaternary faulting at the dam site. The evaluation of post-glacial faulting consisted of carefully inspecting and analyzing the detailed LIDAR elevation data in the dam site area (and vicinity)to identify evidence of tectonic geomorphology suggestive of faulting.In addition,field investigations were conducted to verify the results of desktop based LiDAR lineament mapping (refer to the Crustal Seismic Source Evaluation which will be completed in 2015). Certain methods used elsewhere to evaluate the paleoseismic characteristics of potentially active faults (such as trenching and dating of materials overlying fault traces)and help establish slip rates were not applicable in this terrain.This is largely due to the recent glacial history of the region and absence of materials that would be able to provide meaningful data to constrain activity and slip rates. Data on the potential existence and characteristics of faults and shear features in the dam foundation are discussed in earlier sections of this report,and are further evaluated in the framework of the regional seismic source evaluations and sub-regional mapping near the dam Site. To evaluate the contemporary tectonic framework of the dam site,the updated information from the Susitna-Watana Seismic Network and the AEC regional network,as well as published literature,have been reviewed (AEC 2014).This includes data on crustal stress orientations from earthquake focal mechanisms,known active faulting,plate motions and GPS data, geomorphic landform evaluations,and current understanding of geologic features at the dam site. 6.3.5.3.Regional Evidence The evaluation of potential crustal seismic sources has not identified any specific features with evidence of late Quaternary faulting within at least 25 mi of the Watana dam site.Within this region,faults depicted on existing geologic maps were evaluated through field and imagery analyses for evidence of late Quaternary faulting,and multiple types of imagery were reviewed to define lineaments,which were then evaluated through field investigation for evidence of potential Quaternary faulting (Fugro 2013,2014).The area along the Susitna River,and extending at least 3 mi north and south in proximity to the dam site and deeper portions of the proposed reservoir,was also imaged with high-resolution LiDAR and aerial photography.This data improved resolution and potential detection capability to reveal the geomorphic expression and thus,the existence of potential late Quaternary faults.These efforts indicate that at least over the past 12,000 to 15,000 years -the time since deglaciation of much of the area there is no evidence for major surface-rupturing earthquakes from crustal scale seismic sources within the dam site region (25 mi radius). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-106 December 2014 -qN.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Over longer periods,the crustal seismic source evaluation also indicates an absence of significant zones of uplift or vertical deformation localized along specific surface or blind fault structures. Recurrent large earthquakes on blind faults,e.g.M 6.5 or larger,with repeated dip slip motion over many events,eventually result in recognizable geomorphic features and topographic uplift which persists in the landscape proximal to these features.Thus,even for features with uplift rates as low as 0.1 mm/yr.,a fault slip rate associated with large earthquake recurrence approaching 10,000 years,would result in relative uplift of about 3,300 ft.(1 km)over a period of 10 million years.For comparison,the topographic relief along the northwestern side of Mount Watana to the Fog Lakes area,taken as a proxy for maximum uplift in that area,is about 1,650 ft.( 500 m).Maximum topographic relief along even short,relatively linear sections of hills surrounding the Fog Lakes basin near the Watana dam site is primarily less than about 1,000 ft.( 300 m).For example,the Susitna Glacier fault,which was a "blind”initiating fault plane of the 2002 Denali M7.9 earthquake,ruptured the ground surface near the base of south- facing mountains that have about 1,500 ft.of relief.This illustrated the premise that blind or previously undetected Quaternary faults produce noticeable long-term topographic uplift near the "buried”fault tip even if the ground expression of surface rupture is not recognized.No such high-relief topography is present either at the dam site or in the site vicinity that would be a basis on which to postulate the presence of a nearby blind fault that might transect the site footprint. The contemporary stress regime,as defined by current plate tectonic models,GPS observations, earthquake focal mechanisms,and Quaternary faulting indicates that the Watana dam site area is subject to northwest-southeast oriented sub-horizontal compressive stress associated with the long-term ongoing subduction of the Pacific Plate in south central Alaska.Crustal deformation associated with the plate interactions has been accommodated primarily along the Denali fault,as right-lateral motion,at a relatively constant rate over the past 10 million years (Freymuller et al. 2008).Between the Denali fault and the Castle Mountain fault,geologic evidence suggests that the intervening Talkeetna Block -a region including the Watana dam site between the Copper River Basin to the east and the Susitna Basin to the west -has been relatively stable.This is consistent with the sub-regional mapping described above that indicates only gentle structural deformation (folding)and a relative paucity of penetrative faulting.Paleomagnetic data from volcanic rocks with ages of 30 to 50 million years indicates an absence of significant internal rotation or deformation within the Talkeetna Block (Figure 6.3-1).Likewise,the extent and distribution of these Tertiary volcanic rocks across the landscape of the Talkeetna Block argues against the existence of large-scale vertical or lateral fault displacements within the area. Within the contemporary stress regime of the Talkeetna Block,the primary modes of tectonic deformation appear to involve right-lateral strike slip structures with east-northeast strikes (sub- parallel to the closest portion of the Denali and Castle Mountain faults),and with dip slip or compressional shortening along structures with northeast strikes or elongations (roughly Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-107 December 2014 -2- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. perpendicular to the regional direction of crustal shortening),Figure 6.3-34.Structures with these orientations would be oriented roughly parallel to the overall structural grain of the pre- existing tectonic terrains and rock units within the Talkeetna Block.Secondary modes of tectonic deformation might involve left-lateral strike-slip motions along north to north-northwest striking faults,or potentially lessor amounts of extensional deformation along structures with northwest strikes.Because evidence suggests the dam site region is dominated by compression (Figure 6.3-34),extensional features are expected to be relatively less common and would primarily be expected as second or third order local structures,found locally in association with structural complexities of the primary east-northeast or northeast striking structures,instead of northwest-southeast trending structures that dominate the dam site (Drawing 01-01GT006). 6.3.5.4.Sub-Regional Geologic Transects For evaluation of primary bedrock crustal structure,two sub-regional transects,one oriented roughly east-west along the Susitna River,and a second oriented roughly northeast-southwest along Watana Creek,provide the most complete bedrock exposures near the Watana dam site. These transects demonstrate that the Watana dam site lies within a relatively coherent structural block of folded Kahiltna Basin rocks which have been extensively intruded by mid to early Cenozoic igneous units.Data from these transects,and evaluation of existing geologic mapping, does not define any apparent crustal scale faults within at least 3 mi of the Watana dam site. The most significant crustal fault structure in the area is the northeast-striking fault-bounded basin along Watana Creek that accommodated Tertiary sedimentation.Structural and stratigraphic data suggests that this basin most likely formed tectonically as an extensional graben in a right step-over between two strands of the Talkeetna fault,which was active at the time as a right lateral strike slip fault (essentially,a syntectonic depocenter).The dips,apparent section thickness,and extent of the Watana Creek basin sediments suggest vertical displacements of at least a few hundred meters,which would imply possible lateral offsets of at least a few kilometers.The Watana Creek basin contains non-marine sediments and undated volcanic flows that are tentatively correlated by Csejtey et al.(1978)to the Paleocene Chickaloon Formation of the Matanuska Valley.There appears to be a lack of sedimentary detritus from the surrounding more than 50 million year old dioritic and granitic sediments exposed in the surrounding the area,which in aggregate suggest a relatively older age for this period of strike slip faulting associated with the Talkeetna fault.The mid to early Cenozoic age of faulting implied by this data are consistent with existing mapping,which shows that the Talkeetna fault does not appear to offset or significantly displace plutonic rocks distally to the southwest of the Watana dam site (e.g.,WCC 1982;Wilson et al.2009).It is also consistent with new mapping in the Talkeetna Mountains Quadrangle that shows an absence of continuity for the Talkeetna fault south and east of the Susitna River (Twelker et al.2014). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-108 December 2014 -Zz.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Explanation Ca Earthquake focal mechanism seeeses Lineaments from WCC.1982 Denali fault regional shortening ellipse Average crustal focal NUVEL-1 Average nechanism strain ellipse plate motion 6 =a Ea Explanation me .« <<--GPS vector ot WAT 1 <<Gutf of Alaska relative a SN Hy'of Ala ii w plate motion <P.a008 azimuths from focal Mechanem solubone 0 1 210 180 wa P-axis (compression)azimuths determined from Crustal focal mechanisms (11/2012 -9/2014) Figure 6.3-34.Crustal Stress Orientations and Strain Ellipses (Fugro 2014) Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 6-109 December 2014 -yzw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Published regional mapping does not depict any other faults that would intersect the sub-regional transects or within at least 3 mi of the Watana dam site (Csejty et al.1978;Wilson et al.2009). Some earlier studies suggested the possibility of structural control of the east -west trending sections of the Susitna River near the Watana dam site (e.g.Gedney and Shapiro 1975;and Watana lineament of WCC 1982)based on regional-scale lineament evaluations.However,the recent field mapping evaluations have not revealed evidence for such structures and dam site drilling investigations in 2014,which included two inclined boreholes drilled from opposite banks of the river (DH14-9b and DH14-10)beneath the river channel,through bedrock, encountered no large-scale shears or fault beneath the river nor east-west oriented features. Previous mapping conducted for Watana dam site has depicted or inferred several nearby potential faults of crustal scale (WCC 1982;Acres 1982b)as shown on Figure 6.3-6 and Figure 6.3-7.These faults are depicted with maximum map lengths of about 0.5 to 3 mi and are primarily inferred extensions of shear features found in river valley wall exposures upstream and downstream of the Watana dam site,and extended kilometers northwest to apparently similar features in the nearest bedrock exposures along Susitna River tributaries and Tsusena Creek. Bedrock exposures in the intervening areas are covered by Quaternary deposits,and geomorphic evaluations based on the detailed LiDAR data and ground reconnaissance do not disclose evidence of the fault continuity or offset of the Quaternary units.This fault is approximately 0.5 mi upstream of the Watana dam site and correlates to GF1. An additional north-northeast trending fault is shown by Acres (1982b)upstream of the dam site near the mouth of Deadman Creek (Figure 6.3-6 and Figure 6.3-7);however,no detailed description of the fault was provided.No exposure of this "fault”,or of structures with similar orientations in the Kahiltna Basin rocks near the dam site were observed during mapping for the sub regional transects along the Susitna River in 2014.Moreover,there is no expression in the LiDAR data set of this fault along possible extensions to the northeast,and no indications of this structure in the Susitna River canyon exposures to the southwest or at the dam site.As depicted by Acres (1982),much of the trace of this fault lies beneath the Susitna River channel or beneath Quaternary glacial deposits.Near the confluence of Deadman Creek and the Susitna River,the mapped location of this "fault”was inferred from widely spaced outcrops at river level observed during 2014 mapping.However,additional outcrops of Kahiltna Basin rocks observed from aerial traverses and evident in the LiDAR data set to the north and east of the confluence suggest the "fault”is more likely the intrusive contact zone between the Tertiary intrusive rocks and the Cretaceous Kahiltna Basin rocks,with an irregular,not planar geometry. Mapping in 2014 identified two additional minor faults in bank exposures of the Cretaceous rocks along the north bank of the Susitna River at approximately 3.5 mi upstream of Deadman Creek.Neither fault can be traced beyond the bank exposures,and no indication of these faults Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-110 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. is evident along strike in the detailed LiDAR data set.The two faults are located about 165 ft. apart from each other and have strike and dip of 303°,42°S and 300°,32°S;thus,the faults trend northwest-southeast similar to the structural fabric observed (e.g.,geologic features)at the dam site.Bed separation measured on the shallow dipping fault plane was 4 inches on both faults.Net slip estimated based on fault plane slickensides and a dipping bed offset by the fault indicates less than 3 ft.of net slip;hence these are considered minor faults.Based on the sub- regional transects,these faults appear to represent a distinctly different style and orientation of faulting compared to that expressed by the geologic features observed at the Watana dam site. Overall,the Cretaceous rocks appear to be a structurally coherent block,not disrupted by major faults and there is no expression of these faults in the overlying Quaternary deposits. . 6.3.5.5.|Dam Foundation Geologic Features Based on recent site mapping and re-interpretation of previous mapping,the principal geologic features that underlie the dam footprint are: *"Geologic Feature GF4 "Geologic Feature GF5 #Other similar but unnamed geologic features: -Anunnamed structure delineated as underlying part of the dam foot print on the north bank of the Susitna River,approximately 220 ft.downstream from GF5. -Another unnamed feature mapped 580 ft.downstream of GF5 on the north bank of the Susitna River. Each of these features,described in detail elsewhere in this report,was evaluated for their significance as potential fault rupture hazards. 6.3.5.6.|Summary of Dam Foundation Fault Rupture Evaluation In the evaluation of fault rupture hazards in the dam foundation,the approach used involved separate lines of enquiry that took into consideration various independent types of evidence.The evaluation assessed the weight of evidence in relation to:a)the regional and subregional evidence of Quaternary faulting,b)the presence of significant faulting or shear zones at the dam site,and c)the qualitative potential for reactivation of geologic structures at the site within the current tectonic framework. The evaluation found that one of the more compelling findings is the absence of crustal scale surface faults or apparent "blind”structures within several kilometers of the dam site.From Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-111 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. detailed evaluations of new imagery data,evaluations of local and regional scale mapping,and field investigations,no evidence has yet been revealed of potential Quaternary faulting within at least 15 mi of the Watana dam site.Thus,this information strongly suggests that potential sources of primary or secondary,surface fault rupture at the dam site are absent.Further, geomorphic evaluations based on the detailed LIDAR data within about 3 mi of the site has not identified any expression or continuity of potential faults or specific geologic features extending from the site area that would be indicative of deformation of Quaternary deposits.Given the absence of potentially active crustal scale seismic sources in the immediate site vicinity,the potential existence of small and minor structural features in the dam foundation bedrock does not indicate an elevated potential for a fault rupture hazard. From sub-regional transects and evaluation of the existing mapping within about 3 mi of the dam site suggest that the Watana dam site lies within a relatively coherent block of relatively gently folded Kahiltna Basin rocks that have been cross cut and locally disrupted by early Tertiary igneous and volcanic rocks.The intrusive process likely resulted in numerous alteration zones, fractures,and shears,but does not appear to be associated with nearby fault structures of significant crustal extent.The few short faults near the dam site depicted by Acres (1982b)are mostly likely similar features,and not post-intrusive,crustal scale faults.The closest major Tertiary structure appears to be the fault-bounded depositional basin along Watana Creek, approximately 8.5 mi upstream of the Watana dam site. The orientation of discontinuities and narrow shear features mapped at the site chiefly have northwest strikes and steep,vertical to near-vertical dips (USACE 1979;Acres 1982;Harza- Ebasco 1984;this study).Based on review of the 2012 and 2014 drill hole logs,the bedrock encountered is pervasively fractured,with jointing prevalent in each and every boring.The joints are high-angle,and are reported as 70°dip or greater.Thin shear zones,generally less than one-foot wide are occasionally present in the rocks encountered beneath the dam footprint but with a much lesser frequency than joints.Elsewhere in the site area,shear zones are generally less than 2 ft.wide.Based on geologic mapping and oriented discontinuities in rock core in recent drill holes it appears that thin shear zones present are high-angle features of about 80°dip.This is relatively consistent with the near vertical shears exposed in outcrop. Regarding specific features that may lie within the dam footprint,existing data show a dominant structural fabric of northwest strikes and high-angle dips.Site mapping and overlapping drill holes beneath the Susitna River appear to exclude structures with orientations parallel to the river channel at the site.Those joints and shear zones that do cross the dam footprint appear to be relatively discontinuous along strike and are challenging to map and correlate from outcrop to outcrop.The shear zones and fracture zones appear to be spatially associated with erosional gullies that have been enhanced in size at the ground surface due to weathering,stress relief, Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-112 December 2014 -wZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. freeze-thaw,and/or block movement.Thus,the subset of geologic features that are depicted to transect the dam footprint appear to be relatively minor structures,with potentially limited bedrock continuity or persistence,and appear to have dominant orientations that are least favorable to reactivation in the contemporary stress regime. The following is a summary of the principal findings and lines of evidence in relation to potential surface fault rupture: 1.The contemporary stress regime,as defined by current plate tectonic models,GPS observations,earthquake focal mechanisms and Quaternary faulting,indicates that the Watana dam site area is subject to northwest-southeast oriented sub-horizontal compressive stress associated with the long-term ongoing subduction of the Pacific Plate in south central Alaska.Crustal deformation associated with the plate interactions has been accommodated primarily along the Denali fault,as right-lateral motion,at a relatively constant rate over the past 10 million years. Between the Denali fault and the Castle Mountain fault,geologic evidence suggests that the intervening Talkeetna Block,a region including the Watana dam site,has been relatively stable. 2.Paleomagnetic data from volcanic rocks with ages of 30 to 50 million years indicates an absence of significant internal rotation or deformation within the Talkeetna Block.Similarly,the extent and distribution of Tertiary volcanic rocks across the Talkeetna Block argues against the existence of large-scale vertical or lateral fault displacements within the area. 3.Within the current stress regime of the Talkeetna Block,the primary modes of tectonic deformation appear to involve right-lateral strike slip structures with east- northeast strikes,and with dip slip or compressional shortening along structures with northeast strikes or elongations (roughly perpendicular to the regional direction of crustal shortening).Structures with these orientations would be oriented roughly parallel to the overall structural grain of the pre-existing tectonic terrains and rock units within the Talkeetna Block.Secondary modes of tectonic deformation might involve left-lateral strike-slip motions along north to north- northwest striking faults,or potentially smaller amounts of extensional deformation along structures with northwest strikes.Because regional evidence suggests the dam site region is dominated by compression,extensional features are expected to be relatively less common and would primarily be expected as second or third order local structures found locally in association with structural complexities of the primary east-northeast or northeast striking structures. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-113 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 4.Detailed evaluations of new imagery data,evaluations of local and regional scale mapping,and field investigations have not identified any evidence of potential Quaternary faulting within at least 15 mi of the Watana dam site.These data strongly suggest that potential sources of primary or secondary,surface fault rupture at the dam site are absent. 5.Evaluation of existing mapping within the dam site area,and data from sub- regional transects along the Susitna River do not support the existence of major crustal faults near the dam site.Mapped shear zones within this area appear to be primarily associated with the mid-early Tertiary intrusive rocks,similar to those at the site. 6.Geomorphic evaluations based on the detailed LIDAR data within the dam site area have not identified any expression or continuity of potential faults or specific geologic features extending from the site area that would be indicative of deformation of Quaternary deposits.This indicates that although shear features may be present in the foundation,there is evidence to support lack of surface displacement along these features in the last 12,000 to 15,000 years. 7.Recurrent large earthquakes on blind faults,e.g.M 6.5 or larger,with repeated dip-slip motion over many events,produce and eventually result in recognizable geomorphic features and topographic uplift which persists in the landscape.No such high-relief topography is present at the dam site,which would be a basis on which to postulate the presence of a nearby blind fault or seismic source in the site vicinity. 8.Bedrock beneath the proposed dam,powerhouse,spillway and appurtenance structures consists of fresh to slightly weathered,blocky,strong to very strong diorite that is locally altered and fractured and includes minor shears and shear zones.Fracture zones,shear zones,and alteration zones tend to trend in a northwest-southeast direction.On the south abutment just upstream of the proposed dam,several narrow northwest trending shear zones are cross-cut by a felsic dike and at least one healed fracture cuts across the shear zones.Together with the observations of healed shear and alteration zone,these observations suggest that many of the fracture and shear zones are likely associated with mid- early Tertiary intrusive processes and are not related to geologically recent seismotectonic processes. 9.Inclined drilling beneath the Susitna River,encountered generally fresh to slightly weathered,strong diorite.Although some widely spaced,narrow fracture zones Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-114 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. and minor shear zones were intersected in the drill holes,no significant geologic structure was revealed beneath the river.This supports the interpretation that the river at the dam site is not controlled by a major through-going fault or shear zone. 10.Investigations were made of previously identified "geologic features”,shear and/or fracture zones greater than 5 ft.in width,several of which cross beneath the dam site.It is now considered that the prominence of these features, particularly those that would be encountered in the dam and spillway foundations, has been over-represented in geologic characterization conducted in previous studies.Further,the subset of geologic features that are depicted to transect the dam footprint appear to be relatively minor structures,with potentially limited bedrock continuity or persistence,and appear to have dominant orientations that are least favorable to reactivation in the contemporary stress regime. In conclusion,therefore,it is considered that the potential for any reactivation of the geologic features that might transect the dam footprint must be considered extremely low given the following: «The apparent lack of continuity and small scale of structural geologic features at the site (shear zones)upon which surface fault rupture could conceivably take place; «The dominant northwest-southeast trend is unfavorably oriented with respect to the contemporary tectonic stress regime,as the primary mode of tectonic deformation appear to involve right-lateral strike slip structures with east-northeast strikes; «The absence of any nearby crustal scale fault structures and any neotectonic or paleoseismic evidence of Quaternary faulting;and, =The absence of Quaternary faults mapped with about 15 mi of the dam site. 6.3.6.Reservoir Geology 6.3.6.1.|Geomorphology The dam site and reservoir areas lie within the Upper Susitna River basin in the Talkeetna Mountains and the proposed reservoir extends approximately 42 mi to the east of the dam site. The river basin consists of a high,broad plan of low relief.Through this basin,the Susitna River has incised an approximately 800-ft-deep,east-west trending gorge at the dam site.The glacial upland and higher valley walls of the Susitna River and tributaries were likely widened and leveled by repeated cycles of glacial action while the deeper and rugged canyons at lower elevations were carved by down cutting from glacial melt water or subglacial rivers. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-115 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 6.3.6.2.Overburden Overburden deposits mask much of the bedrock in the area,especially in the lower and uppermost reaches of the reservoir.The soil stratigraphy is complex,generally consisting of variable thicknesses of late-Quaternary glacial till,lacustrine,colluvium,outwash and alluvium overlying igneous and metamorphic bedrock.Bedrock is exposed along much of the main channel confining deep deposits of coarse alluvium. Generally,the lower section of the Watana Reservoir and adjacent slopes are covered by a veneer of glacial till and lacustrine deposits.Two main types of till have been identified in this area:ablation and basal tills.The basal till is predominately overconsolidated,with a fine grain matrix (more silt and clay)and low permeability.The ablation till has fewer fines and a somewhat higher permeability.Lacustrine deposits consist primarily of poorly graded fine- grained sands and silts,with lesser amounts of gravel and clay,and exhibit a crude stratification. On the south side of the Susitna River,the Fog Lakes area is characteristic of a fluted ground moraine surface.Upstream in the Watana Creek area,glaciolacustrine material forms a broad, flat plain that mantles the underlying glacial till and the partially lithified Tertiary sediments. Significant glacial features such as kames and eskers have been observed on the upland slopes adjacent to the river valley. 6.3.6.3.|Geologic Units The oldest bedrock unit proximal to the dam site is comprised of Cretaceous shales,argillite,and greywacke of the Kahiltna assemblage (Csejtey et al.1978).The Cretaceous sediments are regionally intruded by small bodies of Paleocene granite units with interfingering migmatite and pelitic schists,and granodiorites with minor diorite (Csejtey et al.1978). The intrusive rocks in and around the dam site are part of a large suite of largely granitic and granodioritic rocks that intruded between 53 to 64 Ma.The youngest bedrock units in the site vicinity are Paleocene to Miocene volcanic rocks and related shallow intrusives that may be related to the Paleocene plutons (Woodward Clyde 1980).Basalt flows outcropping in Deadman Creek,to the east of the dam site,are approximately 48 Ma (Schmidt et al.2002). For additional information regarding geology of the reservoir,refer to Section 6.3.1.2.3. 6.3.6.4.Buried Valleys (Relict Channels) The existence of buried valleys or relict channels near the dam site beneath the glacial and interglacial unconsolidated sediments was first identified by the USACE (1979).The exploration programs undertaken during the 1980s were performed to improve definition of the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-116 December 2014 -yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. limits of the materials that have infilled the Watana and Fog Lakes relict channels to the north and south of the dam site,respectively. 6.3.6.4.7.Watana Relict Channel The Watana Relict Channel is located on the north bank of the Susitna River,just downstream of Deadman Creek,and meanders beneath the thick sequence of glacial and fluvial deposits blanketing the area to Tsusena Creek (Drawing 01-01GT003).The minimum distance between the proposed reservoir and Tsusena Creek is approximately 7,000 ft.,or about 8,000 ft.along the thalweg of the relict channel.The Watana relict channel extends about 9,000 ft.from the Susitna River near Deadman Creek to about 3,600 ft.upstream of the dam site and empties into Tsusena Creek (Drawing 01-01GT005).The maximum thickness of overburden in the thalweg is approximately 450 ft.or approximately 300 ft.below the normal maximum operating level,at approximately El.1750 ft.However,there is a depression that extends to depths below about El. 1700 ft.nearby,and the overburden is about 500 ft.thick.Overall,the course of the channel is irregular but trends from the southeast to the northwest.Several low depressions in the bedrock surface,downstream of Deadman Creek,coalesce and form the deep bedrock valley. The stratigraphy in the channel has been differentiated into a number of glacial and fluvial stratigraphic units designated Unit A through Unit K.Detailed discussions of the Watana Relict Channel stratigraphic units are presented in the Acres (1982a)report,Acres (1982b)report,and the Harza-Ebasco (1983)report. 6.3.6.4.2.|Fog Lakes Relict Channel Subsequent to the findings of a the Watana relict channel on the right abutment,investigations were undertaken to determine if there were any other relict channels in the reservoir area.This work was initially undertaken when the proposed maximum reservoir operating level was considerably higher,El.2185 ft. In 1981,seismic refraction surveys indicated a bedrock low on the south side of the river in the Fog Lakes area,between the dam site and the higher ground approximately five miles to the southeast.Seismic refraction surveys in this area indicated a series of ridges and valleys that trend roughly northeast-southwest,between River Mile 186 and 195.In this area,the bedrock surface is as much as 350 ft.below ground surface,El.1900 ft.,or 150 ft.below normal maximum operating level of the current reservoir.However,there is bedrock separating the relict channel and the reservoir,so this relict channel does not appear to present a problem with respect to seepage or stability.The channel is filled with unconsolidated glacial deposits to the present day surface. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-117 December 2014 -yz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Detailed discussions of the Fog Lakes Relict Channel stratigraphic units are presented by Acres (1982a,1982b). 6.3.6.5.|Landslides and Slope Stability Near the dam site,landslide scarps are noted on the north and south banks of the river.One circular shaped scarp was identified above El.2100 ft.and upstream of the left abutment in what appears to be confined within glacial deposits,although may extend into the upper part of bedrock.This feature appears to be ancient and inactive,but a smaller,secondary scarp may be considered active as the LIDAR shows some possible surface erosion (Drawing 01-01GT003). On the north bank and about 600 ft.upstream of the dam,an approximately 300 ft.long scarp parallels the slope between EL.1650 ft.and El.1700 ft.The scarp is characterized by open joints oriented parallel to the slope and exhibit downslope movement.Downstream of the dam in the area of GF7,several scarps on the north bank parallel the slope and define a 200 ft.wide slide block that is considered active. Although highly unlikely,breaching of the reservoir rim must be evaluated where the bedrock surface is below the proposed reservoir elevation.As mentioned earlier the Watana Relict Channel is identified just upstream of the dam site.Although previous studies have not completely eliminated the possibility for a slide to occur within the Watana Relict Channel,field investigations and studies indicate that the likelihood of such a catastrophic event is remote due to the low gradient,density of soil deposits,the low permeability of the upper stratigraphic units, and the discontinuous nature of the more permeable sorted sand and silt lenses that were encountered.Because of the bedrock elevation and other conditions at the Fog Lakes Relict Channel,it is considered even less critical than the Watana Relict Channel although geotechnical investigations before final design will be required.Relict Channel treatment is discussed in Section 10.28. Numerous active and inactive landslides have been identified on the slopes in the proposed Watana Reservoir area,especially in sediments comprising basal till!(MWH 2013).The Watana Creek area appears to be the most active area in terms of slope instability.In this area,instability of slopes occurs in lacustrine deposits that overlie basal till that are interpreted to be frozen. Slope movement appears to be the result of the thawing of ice-rich permafrost in the basal till. As the basal till thaws and fails,the overlying lacustrine deposits are undermined and the slide debris is comprised of both materials.The head scarps from these failures are typified by near- vertical slopes in the capping lacustrine deposits and significantly lower-angled slopes in the basal till.The most active slide areas typically have wet surface soils indicating the thawing of excess ice in the basal till. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-118 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Preliminary assessments of the slope conditions in the proposed reservoir area indicate that bi- modal and debris flows are present,particularly in the lower reservoir area.Slope instability is associated with progressive actions from thawing permafrost within slopes and the bi-modal and debris flows are the primary modes of slope erosion and failure of both active and historical slope development and movement.These movements are generally shallow as they occur within the active layer of the soil profile,and move with a slow to moderate rate of movement. Following impoundment of the reservoir,slope movement due to the reservoir or reservoir operation is expected to be confined to near shore areas.No geomorphic evidence was found within the reservoir area of a large scale,rapid movement landslide that would have the potential to create a large impulse wave within the reservoir.Additionally,no evidence was found that would indicate that large-scale landslides or slope failures,either alone or in aggregate,that will cause a significant environmental impact due to the reservoir or reservoir operation. 6.3.6.6.Permafrost Permafrost distribution in the greater Susitna-Watana region has been characterized as "discontinuous”(50 to 90 percent)except along the immediate river corridor itself,which is characterized as "sporadic”(0 to 10 percent)(Jorgenson et al.2008).Permafrost is evidenced by ground ice,patterned ground such as stone nets,and slumping.Based on the subsurface investigations,most of which are within two miles of the proposed dam site,permafrost is generally continuous beneath north-facing slopes.The frozen ground is typically encountered within 10 ft.of the surface and extends to depths up to approximately 230 ft.Ground temperatures typically range from 30°F to 38°F.Permafrost has typically been absent directly under the river channel and south-facing slopes under the right abutment,although sporadic permafrost was encountered in a few boreholes downstream of the dam.Gentle south-facing slopes in upland areas above the canyon on the right abutment have been investigated with numerous boreholes in the wider vicinity of the dam and typically encountered unfrozen ground, although sporadic permafrost was present in localized zones (Acres 1983).This evidence suggests that the presence of permafrost is sensitive to sun angle. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 6-119 December 2014 Section 7 zw ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 7.SELECTION OF WATANA GENERAL ARRANGEMENT The proposed Susitna-Watana Project incorporates a concrete dam structure and a surface powerhouse,at a slightly different location than was originally planned in the 1980s.At that time,the Watana Project consisted of an earth core dam,together with an underground power plant,requiring a significant volume of fill materials for the dam (32.1 million cubic yards for Stage|Watana)and crushed rock for concrete aggregate.Accordingly,the construction materials would have been excavated from upland areas adjacent to the dam and at downstream locations (which would have been flooded by the reservoir formed by the proposed Devils Canyon Dam).The current proposed project,including the change in the dam type,a more compact general arrangement and the need for a large volume of construction aggregates has required additional investigations and engineering to determine technical feasibility. 7.1.Site Topography The Susitna River Basin is bordered by the Alaska Range to the north,the Chulitna and Talkeetna Mountains to the west and south and the northern Talkeetna plateau and Gulkana uplands to the east.This area is largely within the Coastal Trough province of south-central Alaska,a belt of lowlands extending the length of the Pacific Mountain system and interrupted by the Talkeetna,Clearwater,and Wrangell mountains. The Susitna Basin has distinct and diverse combinations of landforms and waterforms.The deep V-shaped canyon of the middle Susitna River and tributary valleys,the Talkeetna Mountains, and the upland plateau to the east are the dominant topographic forms.Elevations in the basin range from approximately 700 ft.to more than 9,000 ft.Distinctive landforms include tundra highlands,active and post-glacial valleys,and numerous lakes. In the vicinity of the proposed Watana Dam site (project river mile 187),the Susitna River has incised a narrow,steep-walled,east-west valley up to 800-ft.deep into the broad Fog Lakes upland formed by repeated glaciations and surrounded by mountains of 3,000-6,300 ft.in elevation.The Susitna River at the dam site is relatively wide and turbulent.On the right bank (north)the valley rises at about a 2H:1V slope from river level at El.1450 ft.,for approximately 600 ft.,then flattens to a maximum elevation of 2,350 ft.Conversely,the left bank (south)rises more steeply from the river for about 450 ft.at a slope of 1.4H:1V,then flattens to 3H:1V or less to approximately El.2600 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-1 December 2014 ALASKA ENERGY AUTHORITY-z-AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 7.2.Environmental Considerations Project environmental studies are being conducted under 55 Federal Energy Regulatory Commission (FERC)approved study plans (plus three engineering studies)authorized and managed by AEA.The environmental studies are being performed by separate contractors administered by AEA.The results of those studies will be used to prepare a licensing proposal and license application that will form the foundation of discussions culminating in the formulation of project mitigation and enhancement measures and to prepare environmental monitoring plans and programs. While the costs associated with potential project environmental monitoring and mitigation cannot be estimated accurately until the environmental studies are complete and discussions with licensing participants have ensued,an initial overall estimate has been made by AEA in order to have some basic funding considered in the full cost estimates for the Project.This initial overall environmental mitigation cost estimate is included in the total project cost estimate as described in Section 13. With respect to feasibility analysis,the following environmental considerations have been taken into account in the proposed design,and/or in the Opinion of Probable Construction Cost (OPCC): *Environmental mitigation during construction operations including but not limited to: --Sedimentation and erosion control; -Revegetation and landscaping at the end of construction; -Stormwater pollution prevention; -Invasive species monitoring and control;and, -Avian protection plans including potential scheduling to avoid cutting and clearance during bird migratory periods.The Avian Protection Plan would also include transmission line designs that assist with raptor protection. «The inclusion of as much flexibility as possible in the design and configuration of the various hydraulic components so that the following options are viable: Releases during reservoir filling (impounding)to maintain river flow and water quality,as well as maintain downstream ice conditions and boating use initially through the emergency release system (which will have a varying capacity up to 30,000 cubic feet per second [cfs]at minimum reservoir elevation 1,850 ft.),and then through the low level outlets; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-2 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. -Discharges of flows during operation up to the 50 year flood through the low level outlets -to avoid using the spillway -benefiting the downstream fishery; -Facilities to vary the depth at which water is drawn into the turbines to enhance downstream water temperatures as desired;and, -Discharges during operation to maintain river flow,maintain desired downstream ice conditions or boating depths,or to provide flushing (pulse)flow through the low- level outlet. *Orientation of permanent lighting (on the dam and around the permanent village)to minimize disruption of migratory birds. No provisions have been made at this point for wildlife protection measures as those are not yet known until the studies and agency consultation process is complete.Similarly,the feasibility study does not address any potential anadromous fish passage past the completed dam.This aspect of the development is being investigated as one of the 58 ongoing studies that include technical workshops with resource agencies with expertise in fish passage considerations. Aspects being considered in that study includes "trap and haul”,a ladder,a fish lift,and fish movement via Tsusena Creek.No cost has been included in the OPCC to reflect any infrastructure for fish passage. A benefit of the operational modeling -that has been performed (and described in Section 12) using the PROMOD software package -has been a detailed assessment of the Railbelt carbon dioxide (CO,)emissions resulting from electrical power generation.The Railbelt system was modeled -using economic dispatch -in 2024 (around the time the project is expected to be operational),and 2034 (ten years after the start of operation),and indicates the following emission per megawatt hour (MWh)with and without the Susitna-Watana Project as shown below in Table 7.2-1: Table 7.2-1.Railbelt Electrical Power Generation Carbon Dioxide Emissions (tons x 1000) Railbelt Year 2024 Without Watana 2893.52 With Watana 1665.03 Reduction 1228.49 Year 2034 Without Watana 2777.65 With Watana 1395.69 Reduction 1381.96 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-3 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Reductions in CO2 emissions also result from the proposed transmission upgrades that are being considered separately from the Susitna-Watana Project. 7.3.Selection of Reservoir Levels A brief review of the history of proposed reservoir levels at the Watana Dam site is an appropriate starting point for the current selection of the Watana Dam maximum normal operating level (NMOL).The proposed StageI Watana Dam from the 1985 Susitna Hydroelectric Project FERC License Application (APA 1985)was a 700-foot-high dam with a reservoir NMOL at El.2000 ft.The Stage I Watana Dam was planned to exist by itself for six years.The 1985 Stage II plan included construction of a downstream Devils Canyon Dam.The 1985 Stage III plan,which represented the ultimate project development,would have raised Watana Dam by 185 ft.so that the NMOL was at El.2185 ft.The Stage III Watana Dam was scheduled to be completed seven years following completion of Stage II.This clearly indicates that the El.2000 ft.Watana Reservoir was not envisioned in 1985 as the appropriate long-term Watana NMOL. The Railbelt Large Hydro Evaluation Preliminary Decision Document (AEA 2010)identified a 700-foot-high dam at Watana as the preferred project.In this document,Susitna-Watana was selected as the preferred alternative from among two major projects (the Chakachamna Hydro Project was the other alternative)but the document did not attempt to evaluate alternative sizes of Watana Dam.In the Pre-Application Document (PAD),Watana Dam was described as having a nominal crest level at El.2025 ft.Watana Dam is currently planned to be a standalone project and there are no current plans to stage the height of the dam.This brief history of Watana Dam plans indicated that further evaluation of the maximum normal reservoir level for Watana Dam is appropriate. The primary benefit of Watana Dam is the generation of hydroelectric energy.In the Alaska Railbelt region,electricity demand is substantially greater during the cold season months of November through April than during the remainder of the year,which means that energy from the Susitna-Watana Project is most needed during the November through April season. However,the reservoir inflows at the Watana Dam site are out of phase with the energy demand. The reservoir inflows for the six months from May through October (5,300,000 acre-ft.average inflow)are on average about ten times greater than the reservoir inflows for the six months of November through April (510,000 acre-ft.average inflow). Providing substantial active reservoir storage is the means by which the natural reservoir inflows can be reshaped and released in a seasonal pattern that closely follows the electricity demand. Active storage is the volume of water that will normally be stored or withdrawn for power operations and minimum flow releases.Active storage is the reservoir storage in acre-feet Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-4 December 2014 an ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. between the NMOL and the minimum operating level (MOL).Water stored below the MOL is termed "dead storage.” For the previously conceived (AEA,PAD 2011 and Preliminary Decision Document 2010) Watana Dam with El.2000 ft.maximum normal pool,there would be 2,310,000 acre-ft.of active (live)storage between the MOL at El.1850 ft.and the NMOL at EI.2000 ft.The gross Watana Reservoir storage capacity is about 4,100,000 acre-ft.up to El.2000 ft.With an average annual inflow to the reservoir of about 5,800,000 acre-ft.(8,015 cfs),the active storage volume is about 40 percent of the average annual inflow volume.This amount of active storage provides the potential to shift at most 44 percent of the May through October inflows to the November through April cold season when Watana power generation is most needed. Subsequent feasibility study work conducted during the period from 2011 through 2013 led to consideration of incorporating more reservoir storage into project plans to optimize power production for the maximum benefit of the Railbelt utilities.Raising the NMOL to El.2050 ft.., while still maintaining the minimum operating level at El.1850 ft.,increases the active storage to 3,380,000 acre-ft.This active storage would represent 58 percent of the average annual inflow volume and 64 percent of the average May through October inflow volume.The El.2050 ft. NMOL would result in an increase of about 31 percent in the energy generation from November through April in comparison to the El.2000 ft.maximum normal pool studied previously.An El.2050 ft.Watana reservoir offers the potential to shape outflows so that they are much more similar to the seasonal pattern of Railbelt electricity demand.It is also noted for comparison purposes that the Watana Stage III reservoir (ultimate development)as proposed in 1985 had a similar reservoir active storage of 3,700,000 acre-ft.between El.2065 ft.(MOL)and El.2185 ft. (NMOL). Although increasing the reliable energy generation during the November through April high electricity demand season by increasing active storage is the primary reason for setting the - Watana Dam NMOL at EI.2050 ft.,there are several other supporting factors including the following: »Increased active storage also increases the reliability of releases for other purposes,such as minimum instream flow releases,flushing flows,or other environmental releases. «Increased active storage reduces non-power releases (spill)at the dam,and the attendant loss of energy benefits. «A raised Watana Dam slightly increases the average head on the turbines resulting in a slight increase in generation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-5 December 2014 ALASKA ENERGY AUTHORITYZzAEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. «There is a relict channel between the right reservoir bank and Tsusena Creek.Seepage that could occur through coarse-grained material in the relict channel is a function of hydraulic gradient and distance.For Watana Dam NMOL above about EI.2050 ft., remedial treatment of the relict channel could become a substantial cost factor. =The mouth of the Oshetna River would not be inundated with the NMOL at EI.2050 ft. #The El.2050 ft.NMOL would place the Watana Dam height within existing industry experience for constructed roller-compacted concrete (RCC)dams. «Greater active storage reduces downstream flooding. Considering the substantially increased benefits of setting the NMOL at El.2050 ft.,it was selected as the maximum normal operating level for the reservoir. 7.4.Selection of the Inflow Design Flood The Inflow Design Flood (IDF)is used in the design of the spillways and other structures that are affected by maximum flood water levels.The adequacy of a spillway is evaluated by considering the hazard potential as well as the economic and environmental consequences that would result from hypothetical failure of the project works during passage of very large flood flows.For dams of different sizes and hazard potentials,the IDF may range anywhere from the 100-year flood up to the Probable Maximum Flood (PMF).Because of its size,downstream hazard potential,and economic importance to the Railbelt,the selected IDF for Watana Dam will be the PMF. The PMF is the flood that may be expected from the most severe combination of critical meteorological and hydrologic conditions that are reasonably possible in the drainage basin under study.The PMF is generated by the probable maximum precipitation (PMP),which is defined as theoretically the greatest amount of precipitation for a given duration that is physically possible for a given size storm area at a particular geographic location at a certain time of year. PMPs are often derived using publications like HMR 57 for the Pacific Northwest.However, there is no applicable guidelines for the Alaska region due to the large basin area,and it was therefore decided to prepare a site specific PMP.The determination of the PMP and the PMF are described in detail in Section 9 of this report. 7.5.Selection of Installed Capacity 7.5.1.Introduction The selection of optimized installed capacity and generating unit size is a function of the expected performance in (and of)the Railbelt system,which will be most clearly defined as and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-6 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. when there are agreed upon operating rules,payment provisions and protocols established between the participating utilities in a centrally dispatched system.When these parameters are defined,the required peak capacities of the Susitna-Watana generating units can be finally determined,prior to the start of detailed design. Although it is possible to install a wide range of installed capacities at a hydroelectric powerhouse,installed capacities tend to fall within established ranges depending on the type of reservoir and operating mode associated with the project.In addition to the average annual energy,the generation attainable during winter months is of particular importance.It is established experience worldwide however that any hydro plant in a system tends to be relied upon over time more than the original expectations,because of its inherent flexibility.Many projects have added (and are adding)more generating capacity because the incremental cost of capacity at most hydroelectric power facilities is relatively low,dynamic benefits are recognized and becoming increasingly more valuable over time,and the flexibility of load following and peak shaving is of increasing value to the integrated system. The initial selection of an installed capacity of 600 megawatts (MW)was made in the "Susitna Hydroelectric Project,Conceptual Alternative Design Report,2009”by HDR and reaffirmed in the "Railbelt Large Hydro Evaluation -Preliminary Decision Document,November 2010”- also by HDR.The proposal,at that time,included four units each rated at 150 MW at a net head of 540 ft.A reduction in efficiency of 2 percent was assumed for every 100 ft.of head so the total capacity of the four units at MOL was suggested as 436 MW,and at normal maximum operating level as 608 MW.Normal maximum operation level of the pool was quoted as El. 2014 ft.,and MOL as El.1850 ft.The 98 percent firm winter capacity of the project was calculated to be 245 MW. Clearly,any capacity above that immediately usable in the system at the time of project commissioning might be regarded as "overinvestment”.However projected load growth through 2024 and beyond is currently estimated to be extremely low -at an average of between 0.15 percent and |percent per annum,depending on the projection and which ten year period is being considered (as reported in the 2010 RIRP and other estimates prepared for this study by the utilities).It is prudent to consider that if -because of some unrecognized economic or societal phenomenon -load growth has been underestimated by just one percent for about five years out of the next ten or twenty years,the system peak load at 2024,2034,and 2044 could well be higher by 100 MW or more.It is notable that even the difference in the various load growth projections examined from 2010 and 2012 was more than 100 MW.Therefore,it is prudent to allow for some flexibility in setting the project installed capacity at the feasibility stage. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-7 December 2014 ALASKA ENERGY AUTHORITY-Zz-AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 7.5.2.Future Railbelt Electrical System Reliability /Redundancy Requirements 7.5.2.1...Hydro Unit Reliability Hydro units are very reliable.According to performance statistics gathered by the North American Electricity Reliability Corporation (NERC),the average forced outage rate (percent time of unit downtime due to forced outage)for hydro units from 2007 to 2011 is 2.72 percent for units over 30 MW and of an average service life of more than 52 years.The average number of times each unit suffers a forced outage during this period is two per year.It should be noted that the statistics do not necessarily refer to unit trips alone.Importantly it should be remembered that the reliability of new units and larger units is better than older and smaller units -and NERC statistics include unit sizes down to 30 MW and an average age of more than 50 years. The corresponding NERC reliability average forced outage rates for coal units up to 100 MW and for gas units of the same size are 6.99 percent and 5.81 percent,respectively,more than double the outage rate for hydro units.In addition,no gas or coal unit can be expected to reach the average age of the hydro units sampled,and the maximum life is likely to be of the order of 25 to 30 years for coal and significantly less for gas turbines. Though a trip of a heavily loaded large unit at Watana Dam would be a significant event in the Railbelt system -and is discussed in Section 11 of this report -experience demonstrates that such a forced outage is significantly less probable for a hydro unit compared to thermal units on the system. 7.5.2.2.System Location of Spinning Reserve As discussed in Section 11 there is a concern by utilities at the spinning reserve requirements for what will be the largest units in the system at Watana Dam.The worst-case scenario would be for a fully loaded unit -operating at normal maximum operating level -to trip,and the restriction of load shedding to the current condition of StageI load shedding is discussed in Section 11. The time for various units on the system to ramp up and replace a Susitna-Watana unit is critical to the sizing of any mitigation of load shedding,and the following figures shown in Table 7.5-1 below are typical and achievable responses and ramp rates of units -drawn from industry experience and the specific units on the Railbelt System. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-8 December 2014 an ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Table 7.5-1.Typical Generating Unit Ramping Rates Unit type MWiminateor sec Gas Turbine-spinning 5 MW per minute Diesel -spinning 2 MW per minute Steam Turbine -spinning (Coal)3 MW per minute Large Hydro -spinning 7 to 12 MW per second Large Hydro -full load from standstill 180 seconds Large Hydro -spinning in air to full power 120 seconds The expected potential ramp rate of 7 to 12 MW per second (dependent on the water column acceleration)for the Susitna-Watana hydro units can be increased with some expense,and rates as high as 20 MW per second have been achieved in various plants.If the option to spin in air were included as a criterion for the project,then fast acting spherical valves would have to be incorporated into the powerhouse configuration. It is reasonable that extra capacity above the basic capacity required for servicing the system demands could usefully be incorporated at Susitna-Watana,particularly as units loaded at 60 percent of full capacity will be the fastest and (operationally)the cheapest spinning reserve on the system.Such an arrangement would minimize the size of any mitigation such as a battery energy storage system (BESS)that might be instituted around the system.Assuming that some frequency droop will be tolerated (without other system units tripping),and using a ramp rate of 10 MW per second,a fast discharge battery bank or ultracapacitor (if development progress is satisfactory in the next 10 years)of 180 MW capacity and a storage of 1.5 to 2 MWh would seem appropriate for the units proposed.Conceivably a flywheel bank of similar performance would be acceptable to limit load shedding in the rare event of a unit trip at full load. The BESS (or capacitors or flywheels)in the system would also be required if smaller units were installed at the Susitna-Watana Project,and is discussed in Section 11. 7.5.3.Selection of Powerhouse Total Installed Capacity 7.5.3.1.Selection Criteria The following items potentially have an influence on the selection of the powerhouse total installed capacity at Susitna-Watana: *Maximizing total generation and the use of the available water -with the corresponding minimizing of spill; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-9 December 2014 ALASKA ENERGY AUTHORITY-z-AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. »The extent to which the plant would be expected perform load following,peaking or peak shaving -governed by the rules of discharge agreed with other river stakeholders; *The capability to meet assigned generation loads with a high reliability; =A plant factor within a normal range for hydroelectric facilities; «The extent to which other Railbelt thermal generating resources can increase generation during portions of dry year sequences when Watana Reservoir is at unusually low levels; =The extent to which the project will "hold”spinning reserve for the system,whether by under loading units or by running a unit as a synchronous condenser (in air); *The extent of "redundancy”in generating capacity selected for the project; «The potential need for emergency operation of the project; *The importance of seasonal generation requirements compared to reservoir levels;and, *Any potential provision to be made for operating flexibility for future load growth whether by the capacity of the initial units installed,their capacity to be operated at a higher head if the reservoir were ever to be raised,and or the provision for installation of further units. 7.5.3.2.Project Energy 7.5.3.2.1..|Long-Term Average Generation Simulation Early in the project feasibility studies,it was established that increasing the installed capacity above 600 MW to as high as 1,000 MW would not provide appreciable average annual energy benefits or increases in the November through April firm generation.However,increases in installed capacity above 600 MW could potentially be justified based on some other criterion. More recent power studies have included revised operating scenarios (load following alternatives),a higher normal maximum operating level for the reservoir,and inclusion of a dry year rule curve and preliminary inflow forecasting which allows generation to be maximized.To determine if these factors had a significant effect on the relationship of installed capacity to average annual generation,the power study runs described below were performed. The average annual energy was calculated on an hourly basis for a 61-year period of reservoir historical inflow record for the Intermediate Load Following scenario.Intermediate Load Following assumes that the existing Bradley Lake,Eklutna Lake,and Cooper Lake hydroelectric plants would operate in a peaking mode to reduce the amount of load following that would be necessary at Susitna-Watana.No load following was assumed to occur at the gas-fired generation plants.Emergency load variations are excluded. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-10 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Two different installed capacities were used to verify the energy generation -three 200 MW units rated at normal maximum operating level for a total output of 600 MW,and three 200 MW units rated at average operating level (assumed to El.1950 ft.)that are capable of about 785 MW at the normal maximum operating level. The generation values presented herein represents generator output without deductions for outages and assumes that all potential generation is usable in the integrated system to meet load. Calculated average annual energy in GWh,without the added benefit of inflow forecasting is presented in Table 7.5-2. Table 7.5-2.Annual Generation for Alternative Installed Capacities,without Inflow Forecasting Intermediate Load Following (GWh) 3 x 200 MW @ operating level 1950 2,814 3 x 200 MW @ normal maximum operating level * Installed Capacity 2,745 Difference in annual generation 2.5% *Equivalent to approx.150 MW@ operating level 1950 ft. The calculated energy noted above assumes no inflow forecasting (based on,for example snowpack data).The use of forecasting would better shape the monthly generation to the monthly load pattern,while reducing spill if smaller units are used.Because forecasting potentially may affect the selection of the installed capacity,model runs similar to those presented above were also performed to include preliminary forecasting.Forecasting is discussed in more detail in Section 12.Calculated average annual energy (GWh)for the cases that include preliminary inflow forecasting is shown in the following Table 7.5-3: Table 7.5-3.Annual Generation for Alternative Installed Capacities,with Inflow Forecasting Intermediate Load Following (GWh) 3 x 200 MW @ operating level 1950 2,802 3 x 200 MW @ normal maximum operating level * installed Capacity 2,780 Difference in annual generation 0.8% *Equivalent to approx.150 MW@ operating level 1950 ft. These results confirm that the larger units would not provide appreciable incremental average annual energy benefits.It is noted that the results show inflow forecasting slightly increasing the average annual generation for the 3 x 200 MW @ normal maximum operating level installed capacity,but slightly decreasing the average annual generation for the 3 x 200 MW @ average Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-11 December 2014 ALASKA ENERGY AUTHORITY-z-AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. operating level installed capacity.The increased generation with the smaller units occurs because water that otherwise would have spilled is used for generation in earlier months through forecasting.The decreased generation with the larger units occurs because water that is used for potential generation as the reservoir reaches the full pool level at El.2050 ft.in the late summer becomes generation in the spring when the reservoir level is lower.At lower reservoir levels, each unit of water generates less energy than it would at higher reservoir levels.This transfer of generation from late summer to spring is justified because it better shapes generation to the electricity demand pattern of the Railbelt. 7.5.3.2.2..©PROMOD Average Water Condition Generation Simulation The Railbelt electric system,including all anticipated 2024 loads and individual generating resources,was simulated for one year of average water conditions using a production costing model called PROMOD.The year 2024 was assumed in the modeling to be the initial year of project operation.PROMOD model runs have been performed on the whole system assuming that the identified weak links in the Railbelt transmission system have been addressed,and centralized dispatch is undertaken so as to maximize system economic benefits.PROMOD, which is discussed in more detail in Section 5 and Section 12,performs economic dispatch of the generating resources on an hourly basis that results in integration of the Susitna-Watana generation into the Railbelt system.Susitna-Watana generation results for the Intermediate Load Following case are shown on Figure 7.5-1.The maximum hourly required generation in year 2024 was calculated to be 494.7 MW in November.A generation duration curve is shown on Figure 7.5-2,which corresponds to the year of hourly generation shown on Figure 7.5-1. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-12 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 600 Average water conditions. 2024 Railbelt generation loads. 500 ee te ieee tere . ||--Watana Generation , 400 .|HourlyGeneration(MWh)onQoOo200 | 100 Data provided by Stater Consulting,May 2014 0 1-Jan 31-Jan 1-Mar 31-Mar 30-Apr 30-May 29-Jun 29-Jul 28-Aug 27-Sep 27-Oct 26-Nov 26-Dec Figure 7.5-1.Susitna-Watana Hourly Generation from PROMOD 600 Average water conditions. 2024 Railbelt generation loads. 500 4 -*Watana Generation 400 = = = € 2 s5 300 c oe (0) 4)= ] o *200 100 Data provided by Slater Consulting,May 2014 (e) 0%10%20%30%40%50%60%70%80%90%100% Percent of Time Generation is Exceeded Figure 7.5-2.Susitna-Watana Hourly Generation Duration Based on PROMOD Results Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-13 December 2014 -a ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. A larger installed capacity has greater capacity at all reservoir operating levels compared to a smaller installed capacity that is rated at the same level.For the case of an installed capacity of 600 MW at the maximum normal operating level (equivalent to approximately 450 MW at reservoir level 1950 ft.),Table 7.5-4 shows the maximum monthly hour of generation from the PROMOD simulation,the Watana Reservoir elevation required to generate the maximum hour load,and the percent of time over 61 years that the reservoir level is high enough to generate the required maximum hourly load for the month.The results indicate that the installed capacity of 600 MW at the maximum normal operating level can generate to meet the required loads with very high reliability.Thermal generation would occasionally be increased when the Watana reservoir levels were unusually low and the generation requirements were high. Table 7.5-4.Reliability of Plant Capability for Maximum Hourly Generation Watana |Required |%of Time Required |Watana |Required Month Max.Hr Elev.Elev.Is (MW)(feet)Exceeded Jan 467.6 1967.4 88% Feb 311.8 1857.3 100% Mar 297.9 1850.0 100% Apr 284.9 1850.0 100% May 310.4 1856.2 97% Jun 351.2 1886.5 96% Jul 385.9 1911.4 100% Aug 436.8 1946.8 100% Sep 456.9 1960.3 100% Oct 490.7 1982.6 98% Nov 494.7 1985.2 94% Dec 381.2 1908.0 100% Average 389.2 1913.7 98% 7.5.3.2.3.|Energy Results Summary The above project energy information leads to the following conclusions regarding installed capacity: *The amount of assumed load following at Susitna-Watana has an insignificant effect on average annual generation for alternative installed capacities. *The inclusion of inflow forecasting reduces the increase of annual potential generation of the larger installed capacity over the smaller installed capacity from about 2.5 percent to 0.8 percent. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-14 December 2014 aan ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. *The powerhouse with an installed capacity of 600 MW at normal maximum operating level (equivalent to 450 MW at a reservoir elevation of 1950 ft.)is capable of meeting required generation loads with high reliability. «Based on modeled energy generation results,there does not appear to be any compelling reason to increase the installed capacity above 600 MW at the normal maximum operating level. As discussed in the following pages,a value of 600 MW was selected as the installed capacity for the Susitna-Watana powerhouse at maximum normal operating level (equivalent to 450 MW at a reservoir elevation of 1950 ft.). 7.5.3.3.Plant Factor A reference value for installed capacity is also the plant factor.Plant factor is the ratio (may be expressed as a percent)of the average plant generation compared to the generation that would result if the plant generated continuously at the aggregate rating of all of the units.Run-of-river plants,which have no active storage,frequently have plant factors in roughly the 30-40 percent range.A hydroelectric peaking plant that has no minimum release requirements can have a plant factor of 25 percent or less.Hydroelectric plants that operate in purely a base load mode can have plant factors of 60 percent or higher.Hydroelectric plants that have substantial minimum release and base load requirements,but also work in a load-following mode (a combined operating mode),tend to have plant factors in the 40-60 percent range.The Susitna-Watana Project would be placed in the latter category -with a plant factor of approximately 53 percent, which falls into the normal range for a storage reservoir with a combined operating mode. 7.5.4.Generating Unit Selection and Capacity 7.5.4.1.Governing Criteria The units described in the PAD were 3 x 200 MW at average net head.This feasibility study has modified that proposal based on power studies and optimization,but maintaining the average annual generation.Studies have examined 100 MW units,150 MW units and 200 MW rated at a reservoir El.1950 ft.,as well as 200 MW units rated at reservoir El.2050 ft. (which are similar to 150 MW units rated at El 1950 ft.),before making an optimum selection.The project installed turbine capacity has been selected as 459 MW at a reservoir El.1950 ft.,equivalent to 446 MW generator output.Electrical system studies were performed on the unit selection in the PAD,and 150 MW units. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-15 December 2014 yz ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. The following have an influence on the selection of unit size at Susitna-Watana: *The system response to a single unit trip at the project; «The chosen operating regime at the project; «The reliability of large hydro units compared to other thermal units within the system; «The cost comparison between various unit sizes (capital cost dominates as operating costs are incrementally different though in favor of fewer units); «The extent of "redundancy”in unit capacity selected for the project;and, «The provision to be made for future load growth whether by the capacity of the initial units installed,their capacity to be operated at a higher head if the reservoir were ever to be raised,and/or the provision for installation of a further unit. Additional factors to be considered include: «The location of the Susitna-Watana Project halfway between two of the two main loads, Anchorage and Fairbanks; =The possibility that the units can operate as synchronous condensers in air,which can also provide transmission stability benefits; =The marginal cost of hydro capacity once the dam and associated costs are amortized; «The convenience of having all units at a project the same size -even future units; «The speed at which hydro units can be loaded compared to thermal units -particularly those at the proposed project with very short water column lengths;and, «FERC License guidelines allow for an increase or decrease in the installed capacity of +15 percent before a "Capacity Amendment”is triggered,so a modicum of flexibility is available if the proposed installed capacity were to change before construction commences. 7.5.4.2.Unit Rating For the Susitna-Watana site,the selected turbine will be a vertical Francis reaction turbine,which is appropriate for the expected range of heads and flows and it can be expected to perform well over these conditions.However,for the purposes of project analysis and feasibility level design a rating must be chosen -which usually takes into account the operational regime of the plant. At this stage for the verification of feasibility,but without a full "Owners Requirements”based on agreement on the operation of the whole Railbelt system,assumptions have been made.As discussed below,the selected rating of the turbine units is 153 MW at reservoir level El.1950 ft., Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-16 December 2014 ,ALASKA ENERGY AUTHORITY-z-AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. for a total installed powerhouse turbine capacity of 459 MW -equivalent to 446 MW generator output.There is also provision for adding a future,fourth unit. Based on the revised tailwater rating curve and a single unit operating,the range of net head on the units during operation (assuming a conservative three percent losses)can vary between approximately 383 ft.(at minimum operating level)and 577 ft.(at maximum normal operating level).The project is also being designed so that it is technically feasible for a future generation to raise the dam to accommodate a normal maximum operating water level of up to El.2185 ft., which corresponds to a maximum net head on the units of 708 ft. Using the USBR rule of thumb for the power head range for acceptable performance of a Francis turbine (from 65 percent to 125 percent of the rated head),and based on this envelope of required performance without other agreed constraints,it is common to set the rating of the unit (i.e.,the head at which the turbine demonstrates peak efficiency)at the average net head of 480 ft.which facilitates satisfactory operation over the full anticipated range of reservoir operation (i.e., between minimum reservoir El.1850 ft.and maximum reservoir El.2050 ft.).Upon further modeling -during detailed design -based on the anticipated actual operation of the centrally dispatched system,it is possible that a turbine rating at a different head corresponding to the best overall efficiency (highest generation)might be considered.This elevation is liable to be somewhat higher than average reservoir elevation used for rating thus far. For sizing of the water passages,flows and head losses commensurate with both the initial conditions,and the potential future raised reservoir level scenario,must be satisfied.It is assumed that the turbine runners themselves would need to be replaced if the dam is raised,to maintain high overall unit efficiency.This methodology has been successfully used at other dam raises,such as that of Guri in Venezuela. In the Railbelt system,currently units range in size from 3 MW to 88 MW,although some units may be grouped on busses,and act as a larger unit.Clearly,the Susitna-Watana units will be the largest on the system for the foreseeable future., 7.5.4.3.Incremental Cost of Capacity The incremental cost of capacity can be viewed from two perspectives,and both options were investigated: «The incremental cost of installing larger units;and, «The incremental cost of adding extra units. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-17 December 2014 -zw ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 7.5.4.3.1.Unit Costs Water to wire costs have been derived from MWH's database,which is kept up-to-date and includes all significant awards of turbines,generators and transformers in the world market.The quoted prices in Table 7.5-5 below are total water-to-wire cost for each unit,based on three alternatives:six units of 100 MW,four units of 150 MW,and three units of 200 MW,all rated at an operating level of El.1950 ft.,and 3 x 200 MW at maximum head.In each case it is assumed that the first unit is more expensive than the other similar units,but they have been normalized for the comparison. Table 7.5-5.Comparative Costs of Various Generating Equipment Combinations 3x 200 MW @ operating level El.1950 ft.US$255,150,000 4x 150 MW @ operating level El.1950 ft.US$278,784,000 6 x 100 MW @ operating level El.1950 ft.US$348,300,000 3 x 150 MW @ operating level El.1950 ft.US$209,088,000 7.5.4.3.2.Associated Civil /Structural Costs Using MWH's proprietary parametric graphical drafting software,the dimensions of each type of unit have been derived and a "bay width”derived -as well as a penstock dimension.For each size of unit,power facilities have been drafted,and the typical output is shown in Figure 7.5-3 and Figure 7.5-4 for a 6 x 100 MW plant and for a 4 x 150 MW plant respectively. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-18 December 2014 ALASKA ENERGY AUTHORITY-z-AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years --115983 ZmL||_|[|| 3 3 CS TS OCS CS SN.SSRyeeeSQ0997PTDt0881=onealalyi 0 PS x PD 17 VieifWY NAW ay Le(o)(Oo);(o)(0)7,SS .ae Lie NAN 4 y We Py 3 anne NeetaeaeSsLeSu,ZSSLVa Figure 7.5-3.Powerhouse for 6 x 100 MW Units (dimensions in millimeters) Alaska Energy Authority December 2014 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 7-19 -ae ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. SOB hee ; a _Ai --i | :?oa a "a .4 ----7 ae]ki]ShRe?rem Ee ra Figure 7.5-4.Powerhouse for 4 x 150 MW Units (dimensions in millimeters) The software automatically generates quantities for comparison,and these have been used for comparison as recorded in Table 7.5-6 below.The total comparative civil cost has been derived for each option (assuming an erection bay of 1.5 times the bay width). Table 7.5-6.Comparative Civil Costs of Various Powerhouse Sizes Unit Size Pay Civil rors)Cost 200 MW @ average operating level El.1950 ft.72 329,466,647 150 MW @ average operating level El.1950 ft.62 380,086,494 100 MW @ average operating level El.1950 ft.52 488,326,131 150 MW @ operating level El.1950 ft.62 296,615,325 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-20 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 7.5.4.3.3.Comparison of Total Construction Costs for Each Unit Size The comparison of estimated cost for the three sizes of unit (without application of camp costs and other establishment costs)are shown in Table 7.5-7 below: Table 7.5-7.Comparative Costs of Various Powerhouse and Unit Size Combinations Unit Size Construction Cost ress)US)oe eest(US$)Difference 3 x 200 MW @ operating level El.1950 ft.329,466,647 255,150,000 584,616,647 1.16 4 x 150 MW @ operating level El.1950 ft.380,086,494 278,784,000 658,870,494 1.30 6 x 100 MW @ operating level El.1950 ft.488,326,131 348,300,000 836,626,131 1.65 3 x 150 MW @ operating level El.1950 ft.296,615,325 209,088,000 505,703,325 0 The current total estimated construction cost of the Project is of the order of US$5.655 billion in 2014 dollars,while the total cost of the generating units and powerhouse is about US$0.408 billion.The results of the analysis of the total costs of the different sized units shows that -if normal contractor "markups”are applied -the incremental cost differential associated with installing the larger units -compared to the smaller units -represents just under two percent of the total project construction cost.These costs do not include the cost of BESS -because the overall estimated project costs do not include for BESS costs,but if the additional cost of the slightly larger BESS units required for the larger units were included,the incremental difference in using the larger units would increase to very slightly over two percent of the total project cost. 7.5.4.3.4._Operational Aspects of Unit Size First,as discussed in Section 7.4.2.1,large hydro units are typically more reliable than thermal units,by a factor of about two.However,detailed industry reliability statistics are not readily available for hydro units to such an extent as to enable assessment of the long-term availability differential between generating units sized at 100 MW,150 MW,or 200 MW to allow determination of the optimum unit size for this study. However,there is a body of experience related to O&M costs associated with plants of this size, sufficient to indicate that these costs are generally in proportion to the number of generating units installed.Put in other words,generally speaking the more units the higher the long-term O&M expenditures will be for a hydro plant of given capacity.This is assumed to be due to the increased maintenance associated with the increased number of working parts subject to wear and tear,and the more complex controls associated with the increased volume of plant equipment. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-21 December 2014 ALASKA ENERGY AUTHORITYzaAEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Generally the most efficient range of operation of a Francis turbine is between approximately 70 percent gate opening and 90 percent gate opening,representing (ignoring the small variation in efficiency over the range)approximate outputs of 140 MW to 180 MW for a 200 MW unit, 105 MW and 135 MW for the 150 MW unit and 70 MW to 90 MW for a 100 MW unit. Second,given that there is a concern that a trip of a large hydro unit at the Susitna-Watana Project would destabilize the Railbelt system,operational rules might be established so that for the early years of the project use -before any load growth of the Railbelt system -the effects of a unit trip could be mitigated.Examples of rules that might be included in the power facilities operations are: «Whenever possible,operate the Susitna-Watana Project units in pairs splitting the required output so that if one unit trips,the other Susitna-Watana Project unit can pick up the majority of the load. =Maintain Susitna-Watana units or other Railbelt system generating units at varying stages of spinning reserve,again to pick up load quickly if one Susitna-Watana Project unit trips. «Based on system load studies,adjust the under frequency trip points of all the key generating units on the Railbelt system,so that cascading trips do not result from trips of a Susitna-Watana unit. Third,the project life is expected to be at least 100 years,with an expected refurbishment of the major electrical and mechanical components after 40 to 50 years of service (or approximately in 2065-2075).It is very difficult to predict the societal conditions and energy demand 60 years hence,but history shows -in general -a continuing long-term upward trend in energy consumption that often accompanies an increase in population and/or an increase in standard of living. This being the case,it should be recognized that the inclusion -in a major capital project such as the Susitna-Watana Project -of design features that will not preclude expansion,but that will facilitate expansion,may well provide long term significant benefits even though during the first years of operation such features will not be of significant value.Experience around the world demonstrates that additional capacity at hydro projects is an economically attractive option for a majority of utilities because of the flexibility of the resource and the balance of total project costs between civil costs and electrical and mechanical costs -which is sharply biased towards the initial high cost of the civil structures that retain the reservoir.With the civil /structural provisions for future expansion already in place,the incremental cost of additional hydropower generating equipment is relatively low,and so this often proves to be the most economically attractive option for system capacity expansion. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-22 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. The preliminary designs incorporate features that have small incremental civil/structural cost,but which will provide an opportunity for a future generation of Alaskans to gain significant added value from the project if they choose to do so when demand for additional generation occurs. Such features include: «A spare unit bay in the powerhouse and a fourth penstock "stub”so that an additional unit can be added easily; «Capacity in the installed units above what is predicted to be necessary at the projected in- service date as long as the restriction imposed on operation -to protect the system from disruption -are acceptable; «Allowing sufficient space at the downstream side of the dam to allow for raising of the dam by up to 135 ft.;and, «Sizing and design of the proposed generating units such that they could accommodate increased hydraulic head if necessary. Any increase in capacity or significant dam modifications would be the subject of debate during relicensing in 50 years'time,or would be the subject of a license amendment application to FERC at any time.Incorporating the potential for expansion of the project does not prejudice any decision that FERC would make at some future date. 7.5.5.|Discussion and Selected Configuration Although it is possible to install a wide range of generating capacities and unit sizes at a hydroelectric powerhouse,installed capacities tend to fall within established ranges depending on the type of reservoir and operating mode associated with the project.In an isolated electric system such as the Railbelt,specific power requirements dictate the peak capabilities of the generating units. For the Susitna-Watana Project,the installed capacity was verified primarily based on (1)annual average generation,and (2)on the maximum hourly power output for each month that would be required.As determined by an hourly system production costing model (PROMOD;see Section 12),the maximum hourly economic generation from Susitna-Watana would vary from about 285 MW to about 495 MW,depending on the time of year.With a powerhouse capacity of 600 MW at the maximum power pool level,the required Susitna-Watana generation can be met with high reliability.Therefore,459 MW at operating level of El.1950 ft.was selected as the installed turbine capacity for the Susitna-Watana Project powerhouse (equivalent to a generator output of 446 MW),acknowledging that the project may need some additional support from thermal generating units during unusually dry hydrologic sequences. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-23 December 2014 ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Zz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. In contrast -and assuming that appropriate mitigation for potential system disruptions from large unit trips can be incorporated -selection of a total plant capacity of approximately 600 MW at the average water level would provide for occasionally higher hourly generation at very little extra cost.Increasing the installed capacity would not provide any significant additional annual energy,but it could rearrange the generation into higher hourly peaks,with corresponding reduction in generation during other hours,if that capability is deemed desirable. After using sizing software,the selected hydraulic turbine units have been determined to have a rated capacity of 153 MW at operating level El.1950 ft.This selection results in the following overall unit performance: Table 7.5-8.Selected Unit Ratings Reservoir Level eM)Sen)Rating rane)Rating E2050)operating level 206.2 202.1 200 Cr te0h)level 153.1 148.5 147.0 E1880 ihe level 105.1 101.9 100.7 With proper predictive operation discussed above and in Section 12,such units could be used in a manner that would minimize spilling,and would achieve a minimum power contribution of about 300 MW at minimum operating level. Although the project has been configured in accordance with the above recommendation,the incremental costs of using slightly bigger units (200 MW @ average operating level)has been demonstrated,and AEA should consider installing such units in readiness for increased operating flexibility for Railbelt load increases during the 100 year project life.In addition,the spare bay will give flexibility for future generations to obtain more benefits from the resource. The analyses of installed capacity and unit size conducted to date can potentially be refined in a number of ways to: *Incorporate any shift of spinning reserve to Susitna-Watana from Bradley and other plants,freeing them to use more of their capacity for peak shaving; "Reflect any system rules for dispatch resulting from utilities agreements; "Reflect any intended system redundancy being located at Susitna -Watana; Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 7-24 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. «Incorporate firming of any significant future wind generation that may be built in the Railbelt system;and, «Lower carbon emissions by substitution of Susitna-Watana Power for fossil-fuel generation. Most of these adjustments would tend to drive an increase in the installed capacity,as could more detailed PROMOD runs over a longer period -closer to the hydrological modeling period of 61 years.Accommodation of the potential for load growth beyond the currently maximum projected one percent and the expected greater use of hydro in the future (similar to most other large hydro)would also drive for a larger installed capacity or the need to provide in the design and construction for a relatively (technically)straightforward capacity increase at some undefined time in the future. 7.6.Project Configuration Evaluation 7.6.1.Dam 7.6.1.1.Type In the 1980s,the height of dam proposed at Watana (approximately 705 ft.)limited the choice of dam type.The only types of dam that had been constructed to this height were concrete thin arch dams,concrete gravity dams,and earth core rockfill dams.The selected type of dam for the 1980s license application was an earth core rock fill dam (ECRD). Since 1980,numerous concrete-faced rockfill dams (CFRD)and RCC gravity dams have been constructed throughout the world in the size range contemplated for Susitna-Watana Hydro. Both dam types are suitable candidates for the new Watana Dam initiative.There has been more frequent use of CFRD,often in highly seismic regions,for increasing dam heights,culminating in the Shuibuya Dam in China,which is currently the highest of its type at 233 meters (765 ft.). During earlier periods of dam building,compared to embankment dams,concrete gravity dams built in the traditional manner with conventional concrete placement have usually been more expensive.However,since the 1980s the efficient placement of concrete using RCC methodology has been perfected,and is now a proven,mature and economic technology.More than 550 RCC dams have been constructed worldwide,with heights ranging to over 700 ft. Other such dams -higher than the Watana Dam are currently in the planning and construction stages as well.With the precedent established -for all three types of dams possible at the Susitna-Watana site -an initial engineering study task was performed to compare the costs of the project using,as a basis,the following three types of dam:ECRD,CFRD,and RCC. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-25 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 7.6.1.2.Seismic Performance All types of dam considered are safe for a project located in a seismic region unless there is movement along a geological structure within the dam foundation -and the adopted design criteria will be crafted according to the expected seismic loads.As discussed,the possibility of co-seismic movement along a feature in the foundation would render an ECRD as more favorable which is why site investigations have focused on clarifying that such movement will not occur.Recent performance of dams in China is relevant.On May 12,2008,an M8.0 earthquake occurred in Sichuan province,China.The focal depth of the earthquake was 2.8 miles and the maximum peak ground acceleration (PGA)experienced was 0.98g horizontally and 0.97g vertically.Four dams higher than 325 ft.have been completed (and are in operation) in the region near to the earthquake epicenter,and all experienced significant ground motions. The nearest two dams are Zippingpu,a 510 ft.high CFRD located 10 miles away,and Shapai,a 432 ft.RCC thin arch dam,22 miles distant. The Shapai dam experienced slight opening of the joints on the right side and the grouting and drainage galleries were flooded because of blockage of the river downstream of the dam.No other damage was sustained.A local landslide also affected the spillway tunnels outlets.All four dams in the vicinity remained structurally intact following the earthquake and there was no uncontrolled release of water from their respective reservoirs. The crest of the Zippingpu dam settled by 2.66 ft.,with an associated seven-inch downstream movement.Foundation seepage increased from 2.6 to 5.3 gallons per minute following the event and the concrete facing joints slipped 13.8 inches vertically and 6.7 inches horizontally. 7.6.1.3.|Comparative Cost Estimate The comparison of the three types considered for Watana dam was performed by estimating the construction costs of the dam and all facilities that are unique to each dam type.All items that are common,such as spillway gates,turbine and generators,switchyard,transmission line,and access road were excluded from the comparison.Thus,the costs quoted in this section do not constitute complete "project”cost estimates,but rather,comparative cost estimates for the dam component. Although the overall project layouts for an ECRD and CFRD,which are both based on an embankment,are very similar,the arrangement using an RCC concrete gravity structure is significantly different.A concrete gravity structure allows for a much more compact structure, with penstocks through the dam,a spillway over the dam,and a powerhouse at the toe of the dam;advantages that can mitigate the comparatively high cost of the RCC itself. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 _Page 7-26 December 2014 yz ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. At a later stage in the exercise -when the first comparative layouts had been estimated -the extent of the contribution (to reduction in cost)of a surface powerhouse was explored.This question was raised because the RCC configuration was the sole layout that included a surface powerhouse.It was therefore decided to draft a fourth configuration,based on a surface powerhouse and a CFRD.To accommodate this arrangement,the required power tunnels would have to be constructed on the opposite (south)side of the river to the diversion tunnels,and a substantial excavation would be required to allow the powerhouse construction to commence independent of the cofferdams and diversion tunnels and cofferdam construction. The cost of this alternative,which has been included in Table 7.6-1,is some $201,420,000 higher than the RCC alternative.Key Items driving the cost difference include a twin power tunnel and gate shafts and the excavation required to construct the powerhouse on the left side of the river. The intake structure for this alternative is also complex and further drives up the cost of the alternative.A similar concept was not prepared for the ECRD alternative since its total cost for the basic alternative (including an underground powerhouse)was substantially greater than the similar concept using a CFRD layout. A separate layout was drawn for each type of dam and detailed as necessary to determine the basic unit quantities associated with each development. Quantities were derived for the four developments and an estimate (of the non-common items) was made and compared.A summary of the comparative estimates is shown in Table 7.6-1. Table 7.6-1.Summary of Comparative Costs Alternative Amount %increase relative (US$)to lowest RCC 1,730,500,000 0 CFRD Surface powerhouse 1,931,920,000 11.6 CFRD U/G Powerhouse 1,959,300,000 13.2 ECRD 2,325,410,000 34.4 7.6.1.4.Water Resources Assessment Methodology Although the cost comparison shown in Table 7.6-1 is compelling,it is recognized that cost is not the sole determinant in the choice of project configuration,so other non-cost factors were also compared based using the Water Resources Assessment Methodology (WRAM)method. The WRAM method is based on two parallel judgments: 1.The creation of a list of attributes of importance.In the case of Watana Dam the following attributes were selected;ease of raising;seismic resistance;risk of price Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-27 December 2014 ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. increase;visual intrusion;possibilities of acceleration;cold weather construction; potential for design optimization;the accommodation of any environmental mandates; and the long-term cold weather performance.Weightings or "Relative Importance Coefficients”were assigned by the engineering team to each attribute as a decimal,the total of which must be unity.(For some applications,the weighting can be selected by using the pair comparison discussed below.) 2.Following the determination of the weightings or RIC,the three basic alternatives (this comparison was performed before the derivation of the CFRD with a surface powerhouse)were compared on a pair-by pair basis for each of the attributes.A "dummy”was introduced to ensure that each alternative scored at least one -necessary for the mathematical extensions.For each attribute,each of the alternatives was compared with every other alternative pair by pair to determine which was considered to be the "better”.The option considered to be better was assigned a value of one,and a value of zero was assigned to the other.Ifa decision could not be made regarding rank, or if both options were considered equal,a value of 0.5 was assigned to each. For each attribute,the scores were multiplied by the weightings,and then the results were totaled to determine a total score.The pair comparisons were made by the project engineering team,and they also provided one set of weightings.However,a completely independent set of weightings was provided by MWH staff familiar with,but not performing assignments for the feasibility study.The summary of the WRAM analysis -which supports the choice of the RCC based alternative -is given in Table 7.6-2 (using the two different weighting). Table 7.6-2.Summary of WRAM Comparison Alternative Weighted Score A Weighted Score B RCC 2.45 2.325 CFRD 19 1.98 ECRD 1.65 1.695 The alternative with the highest weighted score is the preferred alternative and Table 7.6-2 supports the conclusion that RCC is the preferred alternative for both weighted score assessments. 7.6.2.Diversion The diversion arrangements included in the comparisons differed slightly.For the ECRD,the river diversion works were sized to pass a flood with a return frequency of 1:50-years as determined in the 1980's,equivalent to peak inflow of 89,500 cfs,using twin diversion tunnels. Routing effects are small;thus,at peak flow the diversion works would discharge 77,000 cfs. Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 7-28 Alaska Energy Authority December 2014 2 ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. The estimated maximum water surface elevation upstream from the cofferdam for this discharge would be El.1532 ft. The diversion arrangements for the CFRD are essentially the same except that because of the steeper slopes of the rockfill embankment for a CFRD,the cofferdams can be closer together, allowing the diversion tunnels to be 120 ft.and 550 ft.shorter. For the RCC dam,although the cofferdam heights and type were (for the purposes of comparison)essentially the same,the distance between the upstream and downstream cofferdams was reduced considerably,from the 3,150 ft.for the ECRD,to 1,150 ft.Most importantly,the opportunity was taken to eliminate one of the diversion tunnels,and include a sluice through the dam to accommodate flood flows that would overwhelm a single tunnel. 7.6.3.Spillway For the comparison exercise,the spillway ogee and control structure were considered the same in all three alternatives.However,the spillway for the RCC dam was placed over the dam,which eliminated the considerable excavation of the approach channels and spillway chute required for the embankment dam alternatives.It is acknowledged that the joint between the conventional concrete of the spillway and the RCC body of the dam is a critical technical detail and care should be taken in the final design and detailing of this joint. 7.6.4.Power Facilities The ECRD and CFRD layouts considered the use of an underground powerhouse arrangement. The overall layout costed is generally similar to that proposed in the 1980s license application with the exception that three turbines are proposed with the potential to add another unit in the future.In contrast,a surface powerhouse would be an integral part of the layout of the RCC alternative.The powerhouse for the RCC variant would be located at the downstream toe of the dam,which has several advantages in terms of construction and cost.As noted above,a surface powerhouse arrangement would also be feasible for the embankment dam options,but would require more underground works arising from the penstock tunnels. Following the initial screening of the three dam types,an outline assessment was prepared for a surface powerhouse associated with the CFRD alternative. The surface powerhouse arrangement (at the toe of the dam)possible for the RCC layout allows for very short penstocks (through the dam)together with intake structures on the face of the dam. In contrast,the embankment dam options require long penstock tunnels and large and deep approach channels,as well as large freestanding intakes. Susitna-Watana Hydroelectric Project .Alaska Energy Authority FERC Project No.14241 Page 7-29 December 2014 a ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. As noted,an option of a surface powerhouse at the south bank of the river (rather than at the toe of the dam)was also drafted.However,such an arrangement needs even longer penstock tunnels and substantial rock cut at the back of the powerhouse,raising costs compared to the chosen option. 7.6.5.|Summary of Comparison and Selection of RCC The comparative cost exercise indicated that the CFRD with a surface powerhouse would have costs within 12 percent of the RCC dam.However,the CFRD layout includes more risk associated with underground works compared to the RCC variant.It also includes risks and costs associated with the unconventional intake,and the significant excavation costs associated with optimizing the location of a powerhouse. The construction schedules for the configurations examined at this stage indicate that the RCC alternative would require a seven and a half year construction program while the CFRD alternative would require an additional two years of construction schedule.The two-year saving in construction would enable AEA to commence generation earlier thereby start to receive revenue at an earlier stage. The application of the WRAM approach to the evaluation exercise confirmed the RCC alternative to be the most attractive option even after a sensitivity analysis was performed on the WRAM results by adjusting of the weighting factors. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 7-30 December 2014 Section 8 a ALASKA ENERGY AUTHORITY AEA11-022SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 8.SITE ACCESS PLAN This report does not favor any access route to the project site.Initial analysis of a number of potential access routes was carried out by Alaska Department of Transportation and Public Facilities (ADOT&PF)-the results of which are summarized in Sections 8.2 through 8.5. Sections 8.6 and 8.7 record further detailed analysis by MWH of three of the routes selected by ADOT&PF using aerial imagery and topographic surveys. 8.1.Background Although it is expected that most personnel,fresh food,and emergency equipment and supplies would be transported to the construction site by air as discussed in Section 8.9 below,most bulk materials (e.g.,cement,fuel,reinforcing steel)and manufactured materials (e.g.,transformers, power parts)for dam construction would be transported to the site by a road access from a railhead.Much of the required material is assumed to arrive at one of the ports of south-central Alaska.For the purposes of estimating the cost of the project,it has been assumed that all materials will arrive at Whittier. Although the port of Whittier is assumed in this study,currently under development is the Port Mackenzie Rail Extension which is a 32-mile rail line north from the port facility in Matanuska Susitna Borough connecting to the existing Alaska Railroad Corporation (ARRC)rail system near Houston.Although Port MacKenzie is the closest port to the Susitna-Watana Project,it is not clear that it would be the port of choice for the project.It is expected that materials would be transported either directly by rail to the offloading site at the railhead,or by road to an interim staging post and thence on the railway to the offloading site.As discussed below,this offloading site would require about 5,000 ft.of new railroad siding along existing rail lines.Also necessary would be a marshaling/laydown yard for the stockpile and storage of materials being transferred from rail to truck. The initial analysis of the potential road access corridors was performed by Alaska Department of Transportation and Public Facilities (ADOT&PF)with technical work contracted out to the. engineering firm,HDR.The feasibility of using the ARRC,and the preliminary design of a railhead facility was performed by Hanson Alaska LLC under subcontract to MWH.This section describes the work performed and the conclusions reached at the end of the two studies, together with the assessment of a potential airstrip location at the project site. The initial studies of road access routes were performed in the 1980s,but a fundamental difference in those studies was the requirement to service the Devils Canyon site. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-1 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. For the current analysis,although using some of the 1980s analysis,the road routes were first examined using topography at 100 ft.contours,and a ranking was derived.An examination was also made,at this preliminary level,of a railroad link paralleling the 1980s studies. Following the initial analysis,the routes were examined in greater detail;after 20 ft. topographical maps became available,to derive more accurate road alignments,panel maps,etc. 8.2.Objectives The objectives of the studies carried out in 2012 were to: ="Confirm the primary ground transportation mode (road or rail)to be used during construction and for the operational life of the project; «Identify,review and evaluate potential access corridors;and, «Confirm the reasonableness of the originally proposed airstrip locations. The requirement for separation of the public from the construction traffic and concern about extending the project boundaries led to a focus on terminating some of the road routes at a railhead,rather than planning to continue them to form an "all road”route. 8.3.Approach As previously mentioned,initial road and rail access analyses were conducted by others.MWH subsequently developed a methodical approach to the selection of an overall site access plan by utilizing information from their reports.The preliminary design criteria were confirmed and amended where necessary.The preliminary road alignments were then refined based on more detailed topographic maps.Finally,the cost was reevaluated based on these changes. Additionally,MWH paid close attention to aspects not addressed in the ADOT&PF Report and there may need to have further studies conducted. 8.4.Corridor Selection and Evaluation The basic alternatives considered by ADOT&PF were the three road and one rail alignment previously identified in the 1982 APA licensing studies.The three basic corridors are as follows: a corridor running west to east on the north side of the Susitna River from the Parks Highway to the dam site,which is often referred to as the North (Chulitna)corridor;a corridor running west to east on the south side of the Susitna River from the Parks Highway to the dam site,often referred to as the South (Gold Creek)corridor;and a corridor running north to south from the Denali Highway to the Watana Dam site,often referred to as the Denali (Seattle Creek)corridor. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-2 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The access corridors were digitized using geographic information system (GIS)software, adjusted to the preliminary design criteria,and mapped. In addition,a further route was added to the study in the Butte Creek area.In late 2011 a fatal crash of a U.S.Air Force F-22 Raptor occurred and environmental examination of the route was performed and permissions given quickly to allow the wreckage to be examined and cleared. This route initially appeared attractive because the existing permitted route represented about 50 percent of the road length necessary to reach the project site.The concept was to look at the possibility of upgrading the permitted route,leaving approximately 20 miles of new road to be sited and permitted.However,because the route was never developed beyond a cleared track, and because the route accesses the Denali Highway far to the east of the project area it was determined more direct routes might be more favorably advanced. After the presentation of the initial transportation access study,further,and more accurate topography was developed from Interferometric Synthetic Aperture Radar (IFSAR)Elevation Data and the MatSu-North Susitna Bare Earth Data (Horizontal NAD83 and Vertical NAVD88) together with 20 ft.contours.MWH transposed the previously selected three routes onto the new topography,and made alignment adjustments as necessary -most particularly on the South (Gold Creek)corridor.These adjustments are further discussed in "Section 8.6 -Evolution of Access Plans.” The three routes are presented herein and have been considered equally throughout this feasibility study.The three routes will continue to be considered equally,and also studied for environmental factors such as wetlands and wildlife habitats.Additional criteria will be part of the overall evaluation of the corridors.The following measures were important for the selection of possible routes:total estimated construction cost,land status,and constructability.Other criteria considered were:number of creek crossings,construction schedule,terrain slope,terrain classification,original ground profiles,operation efficiency during dam construction,shadow analysis and necessary permits for new construction.Some geologic and geotechnical criteria: field reconnaissance;rock borrow availability and quality;soil borrow availability and quality; subgrade support;permafrost conditions;drainage;rock slope stability;and soil slope stability were also considered.These aspects will however,need to be studied further as there is a lack of quantifiable data. Following the evaluation of the alternatives,the initial reconnaissance selected three alternative routes. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-3 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 8.4.1.Description of Basic Plans During the first (HDR)study,the following alternatives,and their variants,were analyzed and are described briefly below.(HDR,2012.Draft Watana Transportation Access Study.) South Road -Based on the Plan 16 corridor identified in the 1982 studies,this corridor would begin at the ARRC Gold Creek Station (ARRC MP 263),adjacent to the Susitna River,i.e.there is no interconnection with the Parks Highway.The corridor would be approximately 54.8 miles long and ranges in elevation from 750 ft.at its origin to 3,500 ft.at its midpoint.This corridor has some very favorable qualities:it contains the least amount of its length above 3,000 ft. enabling the transmission lines to be in close proximity;it would not require any use or need for upgrades to Denali Highway;it provides a lower total travel time to Anchorage than any other; and is anticipated to have fewer adverse impacts to caribou and sheep than the other alignments. The route does however require a number of bridges over creeks entering the Susitna River from the south. Three variants of the base alignment were also studied as part of the initial reconnaissance: »South Road Fog Creek Variant:This option shortens the corridor by approximately 4.4 miles by crossing Fog Creek closer to the Susitna River.The variant includes 1,300 total feet of stream crossing versus the 1,000 ft.for the original South Road alignment. By crossing Fog Creek closer to the Susitna,the alignment stretches across a wider (700 foot)gap,increasing the cost of this variant by approximately $27 million. =South Road B Variant:This option was developed in an effort to shorten the overall length of the South Road.The variant is roughly 4 miles shorter than the South Road base route by continuing along the north-facing slope of the Susitna River between mileposts (MP)15.5 and 36.While this option provides a shortened distance between Gold Creek and the Watana Dam site,it would require three additional bridges with clear spans between 200 and 300 ft.increasing cost and potentially increasing construction schedule. *South Road Corridor-Gold Creek Variant (South C):Topographical map review identified the potential to ascend the Gold Creek drainage and avoid deep ravines and side hilling while providing a level,gently rolling terrain for most of the corridor.While this variant provides favorable landscape,it contains several areas with deep gullies and exposed bedrock.The additional costs required by the extra bridges and major rock excavation would be substantial. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-4 December 2014 -z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. South Rail -The South Rail corridor would begin at the ARRC Gold Creek Station and include 60.9 miles of new rail line along the north-facing side of the Susitna River.The route's lowest elevation is 750 ft.at its starting point,and its maximum elevation is 3,550 ft.at MP 32.8. Hurricane (West)-Based on North-Access Plan 13 from the 1982 study,this alternative would require construction of 51.7 miles of new road from ARRC's Hurricane Station (near MP 171 of the Parks Highway)to the dam site.Its elevations would range between 1,750 ft.at its origin to 3,550 ft.near MP 32.8.While this alternative has many favorable conditions which include its overall cost,construction schedule,travel time to Cantwell,and a small effect on the moose and caribou habitat,the alternative will have the most stream crossings posing a threat to the salmon present in this corridor's path. Variants include: *Chulitna Variant -Road:This variant would use the ARRC Chulitna siding instead of Hurricane.The road component would remain the same as the Hurricane (West) alignment.Additional information would be needed to definitively identify the most suitable rail siding to use.As a result,this variant was retained in the Hurricane (West) corridor for future study. *Chulitna Variant -Rail Only:This variant would use the ARRC Chulitna siding instead of Hurricane.An approximately one mile access road would connect Chulitna to the Hurricane (West)alignment near MP 7.The first seven miles of the Hurricane (West) alignment would not be constructed resulting in this variant having no direct access to the Parks Highway. Seattle Creek (North)-This road alternative was based on the Denali-Access Plan 18 in the 1982 study,and would start nearly 20 miles east of Cantwell at MP 113.7 of the Denali Highway.Approximately 43.3 miles of new roadway and improvements to nearly 20 miles of the Denali Highway are necessary to support the additional volume and type of construction road traffic.Upgrades to Denali Highway would include:widening the highway by 8 ft.; approximately 56 culvert replacements;a new bridge structure to replace an existing multiple pipe culvert structure;additional signage;and an improvement of the Parks Highway/Denali Highway intersection to include a traffic signal and turning lanes.The alternative would begin at 2,700 ft.at its origin and peak at nearly 4,100 ft.near MP 20.9.It is the corridor with the highest elevation and containing the most length of new road above 3,000 ft.,and thus is not suitable for close proximity transmission lines.This alternative seems to disrupt the most wetland area of the routes,however because of its use of the existing Denali Highway it is the most economical option. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-5 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Variants include: «Kettle Lake Variant:The eastern portion of Seattle Creek (North)goes through a group of kettle lakes located in the center of the Brushkana Creek drainage.While the Kettle Lake variant is 1.8 miles shorter and is better exposed to the sun,it also appears to be wetter and would likely require additional stream crossings.Additional field work and research would be required to identify a more suitable location for the alignment.For the purposes of the reconnaissance study it was decided to have the alignment use the western segment. »Deadman East Variant:At MP 14.8,the corridor runs parallel to Brushkana Creek for a short distance before turning south to ascend up to a higher valley along the western edge of Deadman Mountain.Near MP 18.5,the corridor splits into western and eastern segments because the Deadman Mountain area has the highest elevation along the alignment.The east side of Deadman Mountain would be a viable location for the road if it made economic sense. Butte Creek -This road alternative was identified during the map review of alternatives,and would begin at MP 79 of the Denali Highway,approximately 53 miles east of Cantwell.It would utilize part of a winter trail developed from the Denali Highway in 2011 during recovery of a crashed U.S.Air Force F-22 Raptor as basis for a 47.1 mile roadway and more than 55 miles of upgrades to the Denali Highway.These upgrades would include:widening 53 miles of the highway by eight feet;replacement of approximately 116 culverts;replacing an existing bridge over Seattle Creek;replacing a multiple pipe culvert structure with a new bridge structure; additional signage;and improvement of the Parks Highway/Denali Highway intersection to include a traffic signal and turning lanes.While this alternative required the least amount of new road,the Butte Creek route is the longest of all the corridors at 92.8 miles from the Parks Highway and thus not as desirable of an option relative to the other alternatives. ="Butte Lake Variant A:This variant intersects the Denali Highway at MP 94.5 to head southwest extending toward Butte Lake.The alignment then threads through numerous small and large ponds,continuing to run southwest until it meets Deadman Creek at MP 29.Variant A then extends along the south side of Deadman Creek until it passes between Deadman Lake and Big Lake,at which point it crosses Deadman Creek twice to skirt around the east side of Deadman Lake,extending west to connect to the Seattle Creek alignment.This option is not favorable due to expected permafrost conditions, high water table,and prevalent wetlands.Also,Butte Lake Variant A would require two bridges where it crosses Deadman Creek adding to overall cost. ="Butte Lake Variant B:This variant departs the Butte Lake A variant SW of Butte Lake and runs to Butte Creek (East)alternative at approximately the midpoint.This option is Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-6 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. not favorable as it contains a five mile section that is possibly too steep for construction and is expected to have extensive rock excavation. If any of the Denali Corridors are chosen for road access,the pavement on the first section of the Denali Highway in the community of Cantwell will be extended for a distance of approximately four miles to eliminate any problem with dust and debris from construction vehicles.In addition, the following measures will be taken: «Speed restrictions will be imposed along appropriate segments;and, «Improvements will be made to the intersections including pavement markings and traffic signals. 8.5.Evaluation Prescreening was performed on the five ADOT&PF alternatives (and nine variants),and the remaining alternatives advanced for detailed screening during the HDR study (HDR 2012). The detailed screening used a two-tier approach to identify the most suitable access corridors. The first stage was an initial screening to identify any alternatives that were so unsuitable that they would not warrant further consideration.The second screening was more detailed,and was intended to identify the preferred access corridor using criteria that could be qualitatively or quantitatively assessed.The first screening was based on: «Land Status:This criterion evaluates the general land ownership and status along the corridors.All five corridors have a mixture of State,Federal,Native,and private properties which influence the potential impacts to right of way (ROW)acquisition. "Creek Crossings:All corridors include various creek crossings along their routes.The crossings were used as an evaluation metric with attention to how they would impact the overall cost and schedule of the alignments. "Mode Evaluation:This criterion screened the corridors and their relative efficiency of road vs.rail to support the construction at the project site and operation of the facilities. «"Range of Magnitude Cost:After a comprehensive cost estimate,it was determined that a mile ofrail would on average cost $2.5 million versus a mile of road at $1.5 million.The individual corridor's costs per mile will vary based on terrain. «Field Reconnaissance:Aerial reconnaissance was performed to validate each corridor's terrain,geologic conditions,and drainage characteristics.All of the corridors had similar terrain,excluding the South Road/Rail which contained incised drainages.The banks on these drainages were observed to have sloughing soils and consist generally of poor Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-7 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT foundation materials which would result in larger spans and abutments.The original evaluation noted the more robust structures on this alignment,a difficulty that has been addressed. "Ability to Support Dam Construction Schedule:The original evaluation noted that the more robust structures have an influence on the construction schedule.At a minimun,it was estimated by HDR that the South Road/Rail would take at least one additional year to construct than the other three alignments. Based on the first screening by ADOT&PF,due to cost the rail access option was removed from further consideration as the primary transportation to the project site.Four road corridors were recommended for further consideration:South (Gold Greek),North (Seattle Creek),West (Hurricane),and Butte Creek. The secondary screening considered: «Engineering: Terrain Types &Roadway Grades:Studies were conducted to assess the terrain and original ground profiles along the corridors.Alignments should be minimized,when possible to maximize the performance and operating efficiency of the access route. However,design grades can be increased in certain situations to decrease grading costs.Results of the studies show that Seattle Creek (North)and Butte Creek (East) have the most amount of level terrain,while the South Road and Hurricane (West) alignments have significantly more mountainous terrain. Operational Efficiency During Dam Construction:These criteria were evaluated to compare the movement efficiency of goods between the South-central Alaskan ports and the dam site.The South Road and Hurricane (West)alignments are the most favorable as they have the least travel time between two of the three ports.Seattle Creek (North)is somewhat favorable,as it is the closest to Cantwell of the four corridors,but relatively far from Hurricane. Shadow Analysis:For road design and maintenance it is preferable to have a roadway that is in direct sunlight as it minimizes icing during the winter months,delays road freeze-up until later in the fall,and thaws more quickly in the spring.These factors greatly reduce snow-clearing costs. Construction Season:It is estimated that,on average,20 miles of roadway could be built in one construction season.This is based on the assumption that a construction season is the summer months of the year as winter construction may not be preferred due to the need to achieve compaction with moisture and density controls.The South Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-8 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Road will take longer than the other three corridors as it contains more mountainous terrain. -Geological/Geotechnical Considerations:Due to lack of readily quantifiable data to evaluate the geological and geotechnical conditions,a set of specific development criteria has been developed and assigned to each criterion as a value between one and five.Pages 33-42 of the ADOT&PF Watana Transportation Access Study provide for more detailed information on the following criteria: e Rock Borrow Availability e Rock Borrow Quality e Soil Borrow Availability e Soil Borrow Quality e Subgrade Support e Permafrost Conditions e Drainage e Rock Slope Stability e Waste Area Availability e Foundation Support e Hydrology -Stream Crossings:All four corridors require a similar number of bridges,however the length of bridges on the South Road and Hurricane (West)alignments are substantially greater than the Seattle Creek (North)and Butte Creek alignments. Alternatively,the Seattle Creek (North)requires more fish and drainage culverts than the other corridors.The corridors which utilize Denali Highway will need to replace or upgrade culvert and bridge structures on their respective portions of the highway. #Environmental Considerations: -Fish Streams/Waterbodies:Maintenance of access by fish to water bodies and streams is important in Alaska for the health of this resource.A total of 14 fish species have been documented to occur throughout the streams and waterbodies within all the proposed access corridor study area.Hurricane (West)seems to have the greatest impact on the fish as it has the most crossings of salmon streams and other fish habitat.Seattle Creek (North)seems to have the least impact as it has no salmon crossings and the lowest amount of resident fish crossings. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-9 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. -Wildlife:\t is difficult to equate the effect of the four corridors because all four impact different habitats to some degree.The South Road appears to pose the least disruption to caribou and moose habitat,but the highest with respect to other winter animals and bear habitat.The Butte Creek (East)corridor intersects more trumpeter swan habitat than any of the other corridors while it has a similar level of intersection of the migratory duck habitat as the South Road.The Hurricane (West)corridor intersects the most migratory duck habitat of all of the alternatives.Overall,the Seattle Creek (North)appears to have the least effect on terrestrial resources as it intersects with the lowest amount of all terrestrial species habitats and migratory bird habitats. -Wetlands:Currently,the National Wetlands Inventory mapping does not include half of the Butte Creek (East)alternative and a portion of the South Road alternative making it difficult to evaluate the corridors against each other.For more information on wetlands,construction suitability categories,and vegetation refer to pages 61-65 in the ADOT&PF Watana Transportation Access Study. -Land Status:As stated above,the status of ownership of the land can substantially impact the ROW acquisition.After evaluation,it appears the South Road has no federal lands,but it has four times more Native lands than any other alternative. Butte Creek (East)appears to be the best alternative as it has a low percentage of federal lands and the highest percentage of state lands. -Socioeconomics:The development of a road to the dam site will affect the socioeconomic characteristics of the surrounding region,and these effects may be both positive and negative.It is probable that they will be greater during construction of the dam than during its operation.Construction and operation of the South Road alignment could have impacts on cabin owners in the area.Although access would still be limited to ARRC and all-terrain vehicle access from the Parks Highway,it would be easier for people to travel between Gold Creek and the dam site.Project impacts by Hurricane (West)to Talkeetna would likely be relatively large in terms of socioeconomic effects.Traffic increases would be negligible to the Talkeetna community,but would likely be substantial to the Parks Highway.The greatest impact the Hurricane (West)corridor would have is that to the property/cabin owners of the Chulitna areas who have purchased the land to be remote from others.The corridor would not give direct access to the Chulitna land;however it would provide an alternative point of access to trails leading to those locations.Seattle Creek (North)would likely shift the socioeconomic impacts further along Parks Highway and that may affect the highway with an increase in traffic during construction. Likely there would be an impact on Cantwell with fewer impacts on Talkeetna and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-10 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Trapper Creek,similar to the Butte Creek (East)alignment.Butte Creek (East)is near Cantwell and as part of this alignment's construction,Denali Highway east of Cantwell would be upgraded and become available for year-round use.Comparable to Seattle Creek (North),Cantwell would see a socioeconomic benefit as traffic and a larger demand for housing,community service,and utilities. «Cost and Permitting: -Cost:The overall examination of costs which include new road costs,upgrades to Denali Highway,rail sidings,intersection improvements,etc.,have indicated -at the reconnaissance level -that the South Road is the most costly of the corridors while Seattle Creek (North)is the least costly. -Permitting Requirements:All four corridors need the same permits with one exception;the Seattle Creek (North)and Butte Creek (East)corridors are not anticipated to need a Title 16 Habitat permit. After all the screening,the resulting favored routes were used in the initial cost estimating in 2011.Further analysis was delayed until more detailed topography was available. 8.6.Evolution of Access Plans During the second stage of the access analysis,which was performed by MWH,three of the routes initially analyzed in the ADOT&PF report were refined to better fit the more detailed 20-foot contour topographic maps subsequently obtained.The South (Gold Creek)route,North (Denali)route,and Chulitna road alignments defined in the initial studies were plotted on the 20-foot contour maps,and then selected sections of the road were realigned to minimize cut and fill quantities,to avoid lakes and other features not previously identified,to avoid obvious wetlands,and to shorten the route. Field reconnaissance of the Gold Creek route was performed by helicopter in September 2012. The seven bridge locations were identified from the air,and the road alignment in the vicinity of each bridge was further refined based on visual observation of the topography and ground conditions. In addition,several aspects of the road and transmission corridors were re-examined.Specific changes resulting from the reexamination of the routes included: «A 15-mile-long section of the Gold Creek road was rerouted to the north to avoid an 800-foot change in elevation shown along the initial alignment studied. =Several of the bridge locations on the Gold Creek route were changed to cross the canyons at more favorable locations defined by the 20-foot contours. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-11 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. *Areas along the Chulitna route previously identified as having avalanche potential were reviewed with the more detailed topography,which showed that the avalanche prone areas cannot be avoided along that route. «Partial rerouting of the Denali route to the east,with the consequent junction with the Denali highway being moved some 10.8 miles further east. The initial reconnaissance of all routes performed on behalf of ADOT&PF had been based on their standards -including their standards for permanent bridges.The bridges on the southern (Gold Creek)route were seen as a major challenge associated with an otherwise attractive option.In particular,because the linear construction of the access road is on the critical path of the whole Susitna-Watana Project,it is necessary to minimize bridge construction time to render the Gold Creek route viable.Therefore a specific investigation of the potential for use of prefabricated modular steel bridges was instigated for crossing the several deep canyons along the Gold Creek route,and manufacturers were canvassed to determine the viability of such prefabrication and the speed of construction.The use of such prefabricated "modular”bridges is commonplace for construction initiatives,for logging roads,and even within Alaska (and elsewhere)for extended use on public highways.In considering these types of bridge,it has been noted that the two west access routes will not be accessible by non-project traffic (and the Gold Creek route is almost entirely on private land),and it is a simple matter to institute one way (or restricted speed)traffic across such bridges without sacrificing supply chain economics or safety.In that light,a decision was taken to base the Gold Creek route on the use of prefabricated steel modular bridges that can be quickly assembled on site. Modular bridges are commonly "launched”from one abutment,so the most complex aspect of the bridging of the various creeks will be the installation of the required intermediate piers.The fabricators of the bridges considered usually propose the creation of vertical piers by the use of the standard truss panels bolted together (and the cost estimates include this method of implementation)but a faster method may well be to assemble space frames (pre-fabricated off site from standard steel pipes)at the site and lower them onto small concrete foundation blocks - rock bolted to the valley sides -to form pin ended connections at the base of angled piers.A rigid,yet light,structure can be created thus,and the bridge can be launched across each creek (depending on total superstructure weight and span)in a period of between 10 and 40 days, depending on the total bridge weight.The bridge deck width has been chosen as 24 ft.which allows for the passage of the widest projected vehicle using the road,a Caterpillar 777 dump (rock)truck (during mobilization and demobilization).The bridge itself would encompass a design load of HL-93 and comprise side trusses at least two deep with the deck mounted between them -so that any large load on a flatbed (and wider than the bridge deck width)could pass above the top of the upper side truss.As well as the Caterpillar 777,weighing (empty)82 tons the bridge will be capable of handling a 190 ton transformer load on a suitable multi axle trailer. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-12 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. It is envisaged that a road with such bridges would be sufficient for construction and for normal operation.In the future,if ADOT&PF were to take over the road or its maintenance,or if the private land owner wished to invest in upgrading the road for more extensive traffic -the bridges could be replaced with standard spans and the roads could be realigned at the bridge abutments to suit. 8.7.Access Plan for Estimate The engineering studies to date have not identified a preferred access route because that selection will be made after the appropriate environmental analysis has been undertaken.Of the three corridors and routes further refined after the initial reconnaissance study,the Chulitna route was subsequently under evaluation for potential elimination,and each of the other two have advantages and disadvantages.The South (Gold Creek)route has,however,been selected for use in preparing the cost estimate for the Project,and the cost of overcoming its main disadvantage (the bridges)has been included in the overall cost estimate. The Gold Creek route begins at the ARRC Gold Creek Station (ARRC MP 263),is 55 miles long,has seven deep canyon bridge crossings,and does not appear to cross avalanche prone terrain.The Gold Creek route contains the shortest total distance of corridor above an elevation of 3,000 ft.so that the transmission line can be located close by.As noted in the previous study, it would not require any use of or need for upgrades to Denali Highway;it provides a lower travel time to Anchorage;ensures that construction traffic is separated from residential areas,and it is anticipated to have fewer adverse impacts to caribou and sheep habitat than the Denali Corridor routes. 8.8.Bridge at Site Whichever access route is selected,a permanent bridge -immediately downstream of the dam - will be required for construction access and in the long term for providing access to both sides of the river upstream and downstream.A location for the bridge has been selected to minimize the span,provide for sound rock abutments,and to be far enough downstream to be unaffected by the plunging jet from the operating spillway.The same key design criteria as selected for the access road bridges would apply -HL-93 loading,traverse by an unloaded Caterpillar 777 dump truck and a 190 ton transformer on a multi wheel trailer. Although the tailrace downstream of the dam and powerhouse is expected to be relatively ice free,the river gravels are deep so it is advisable to avoid a configuration using a central pier.For the purposes of estimation therefore,a long span (330 ft.),through-truss steel bridge has been selected,and it is envisaged that it will be delivered in pre-engineered sections for assembly on site.If the project utilizes a "CAT train”across the snow for mobilizing some of the early Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-13 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. contractors,the bridge could usefully be constructed from the surface of the river ice -thus simplifying construction. A bridge design is included with the feasibility drawings and includes a 28 foot roadway,and 18 ft.clearance suitable for the Caterpillar 777 dump truck. 8.9.Railhead 8.9.1.Previous Studies and Site Selection The ADOT&PF study identified three possible locations for a railhead facility for transloading construction materials from the ARRC to highway vehicles.Those sites were along the ARRC's main line at Gold Creek,Chulitna,and Cantwell.Following evaluation of the three sites,the Cantwell site was selected for the preparation a preliminary design.Subsequently designs were prepared for the other two locations for transloading facilities. Project staff,in late 2013 travelled with ARRC staff in a Hi-rail pick-up truck from Talkeetna to Gold Creek (and back)on the track to examine the conditions and the Gold Creek site.The assessments made during that examination have been incorporated in the Susitna-Watana Project feasibility design,and cost estimate. 8.9.2.Transportation Methods The bulk of the construction materials (besides the primary generating equipment components) required to be transported from outside of Alaska to the project site are cement and pozzolans. There are two methods for transporting these materials over long distances utilizing railway, marine,and roads: *In covered hopper railway cars between the initial source and the transload site,with the cars carried directly on barges between Seattle and (currently)Whittier.The materials would be transloaded at the railhead to cement trailers for final roadway movement to the project site. =In bulk material tank containers between the initial source and the project site.The containers would be transferred as needed between modes (barge/rail/road)without directly handling the material. Capacity limitations with the Alaska Rail Marine service,the potential need to construct additional barges to carry railcars,and the cost to construct cement and pozzolan transfer facilities indicated that the most economical method for hauling would be in bulk material tank containers.Similarly,fuel and other materials would be containerized to the maximum extent feasible. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-14 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Although Port MacKenzie and the associated railroad spur are projected to be completed sufficient for project needs by 2017 -well before the initiation of substantial construction -the railroad is not projected to extend to the dockside at Port MacKenzie,so no "roll on roll off'of railcars will be possible from Alaska Rail Marine,and CN Aquatrain rail equipped barges.Any delivery of special rail cars -such as those normally used to transport large transformers -will necessarily be routed through Whittier.It has not yet be determined if a supply chain substantially based on containers would be more economic through Whittier or Port Mackenzie because container transit has to include -at Port Mackenzie -an intermediate truck haul,up the bluff from the dock. The required track capacity at the railhead was estimated to accommodate a delivery rate based on the maximum possible containerization.Additional track capacity was determined to allow equipment on flat cars to be unloaded by end or side ramp. 8.9.3.Railway Cars The weight limit for railcars on ARRC is 263,000 pounds,which yields a car load capacity of approximately 100 tons,depending on the tare weight of the car.ARRC currently transports containers of various lengths on flat cars with deck lengths ranging nominally from 50 to 89 ft. Liquid petroleum products such as fuel and oil can be transported in large quantities in two ways: a petroleum tank car or an International Standards Organization tank container in an intermodal well car.For track capacity purposes,tank cars and container flat cars are estimated at 55 ft.in length. Bulk transport of cement and pozzolans during each construction season are expected to average more than 8,200 tons per week.Covered hopper cars or dry bulk containers in intermodal well cars could be used for transport so that offloading of these high volumes can be done using pneumatic discharge.However,as noted above,for the purposes of estimating,it is being assumed that all bulk materials will be delivered in containerized tanks minimizing the potential for spills,etc. It is planned that steel reinforcement will be shipped as straight bar.Normal "rebar”length is 40ft.Reinforcing bars are typical for formed concrete structures shipped on various lengths of flat cars,bulkhead flat cars,or gondola cars. Large project components such as turbine parts and spillway gates will likely be transported on flat cars.Very heavy equipment such as transformers will likely be transported on specialized multi-axle flat cars configured to accommodate the weight. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-15 December 2014 Zz .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 8.9.4.Transloading Facility -Cantwell Site The Cantwell site is located at ARRC MP 319 and is accessible by highway. The layout of the transloading facility at Cantwell and the amount and arrangement of the tracks was determined from the types,quantities,and delivery rates of the railway cars expected to be used,and the means by which the various railway cars will be unloaded. ARRC initially indicated that they are willing to use their existing mainline and siding tracks to exchange a train of incoming loaded cars for a train of outgoing empty cars.The existing siding at Cantwell has approximately 6,200 ft.of capacity,with approximately 4,500 ft.of that capacity south of the existing turnout to the Section Track that also leads to Track 1.This is sufficient capacity,south of that turnout,to store the length of the assumed twice weekly shuttle train and its locomotives,without fouling the mainline. In addition to the track arrangements,the site layout would include the following new facilities: «Fuel storage for tractor trailers performing the delivery to site =Flat area for manipulating and storing up to 100 containers =Covered storage area «Offices for the logistics controllers «Lodging for 40 drivers and associated canteen and recreational *Parking for 43 tractor/chassis units #60,000 sq.ft.of concrete hard standing *Helicopter pad *Tractor maintenance workshop 8.9.5.Railway Construction Most of the transloading facility will be constructed by a contractor.However,due to existing labor contracts,and the requirements for track standards,ARRC will procure and install any new turnouts that need to be installed in existing ARRC track and any new track leading away from new turnouts out to the "clearance”point.ARRC stores preassembled track suitable for sidings, etc.,in their yards,so placement of sidings is not a problem.It is understood that each required siding,using pre-assembled track -could easily be laid by ARRC in three weeks.During detailed planning,it might be more appropriate and economic to negotiate with ARRC the construction of al]the rail facilities at the railhead. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-16 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 8.9.6.Gold Creek Site Alternative The Gold Creek site is located at ARRC MP 263 and is not accessible by highway.The site would be located on the east side of the tracks to be away from the Susitna River and so that construction traffic would not have to cross the ARRC tracks to access the road to the construction site.Tracks |and 2 have a combined capacity of 9,000 ft.for unloading and loading containers.Since space is available,these tracks would be double ended and two turnouts installed in the existing ARRC tracks.While a second turnout increases the cost of the site,it provides considerable switching flexibility for ARRC while serving the site. ARRC did not provide details of their right of way at Gold Creek.Adjacent private property owners are unknown. All the facilities described for the Cantwell site would also be incorporated in the Gold Creek railhead. 8.9.7.Chulitna Site Alternative A facility was designed for the Chulitna alternative located at ARRC MP 273.8,and like Gold Creek,not accessible by highway.The site would be located on the west side of the tracks to avoid impacting private structures and a private runway on the east side.Construction traffic would have to cross the ARRC tracks to access the road to the Susitna-Watana construction site. Tracks 1 and 2 have a combined capacity of 9,000 ft.for unloading and loading containers.The short length of the mainline tangent between Curves 273A and 274 suggest that these tracks would be stub ended similar to those in the Cantwell site concept.The existing Chulitna Siding is too short for locomotives to run around the typical 4,000-foot long train that would be delivered to the facility twice per week.To avoid long backing movements of this train length, the locomotives would run around the train at Hurricane Siding,eight miles north of Chulitna. Grades of up to 1.8 percent exist immediately north and south of Chulitna siding,which would add difficulty to switching cars into the facility. ARRC did not provide details of their right of way at Chulitna.Adjacent private property owners are unknown. 8.9.8.|Necessary Modifications to the Railroad During the investigation of the ARRC track from Talkeetna to Gold Creek,most of the track was observed to be suitable for moving materials without problem.There are occasional passing locations where trains of the size required could be held while more important traffic passed. Principal among these in current use are: Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-17 December 2014 --z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. ="Chase 6200 ft. ="Dead Horse 6700 ft. ="Gold Creek 5200 ft. In general each siding has 15 ft.centerline to centerline spacing from the main line. An unknown issue however is the extent to which a contractor would wish to move wide loads up and down the railroad.The following were noted as modifications that might be required if any wide loads were contemplated: *At ARRC MP 227.1 is the Talkeetna River Bridge,a through truss bridge which represents the most significant width limit between Talkeetna and Gold Creek -and the sole height limit.Approach to the bridge is straight,and the bridge includes two spans of 200 ft.Ifthe transport of wide loads is essential,then rebuilding of the bridge using plate girders might be required to allow for wide loads. «At ARRC MP 227.9 is the Billion Slough Bridge.Although this is a straight over bridge it has side structural plate girder members supported by angled webs.The width at about 4 ft.above rail is 19 ft.This bridge includes one span of 120 ft.with the side members and a 22 ft.span at grade.At a later stage of project planning,it must be determined if this bridge would need to be replaced to allow for wide loads. «At various points north from Talkeetna,on the east side of the track there are locations at which the rock cuts are close,and the rock wall can sometimes be as close as 9 ft. 6 inches from the track centerline (although 12 ft.is more normal in these particular locations).However,the total length of line with these limited clearances is less than 500 ft.The ARRC staff member conducting the visit indicated that a routine maintenance task for the railroad is to use their onboard backhoe (on work trains)to remove these materials.It 1s therefore considered that it would not be a difficult job to increase clearance by two feet or more -thus facilitating 13 ft.of clearance -at these locations.This type of modification could easily be accommodated within the normal scheduled track maintenance operations. 8.9.9.Other Potential Facilities It is conceivable that a contractor may wish to use road transport for many items for as much of the journey to site as possible,and it may be necessary to establish another facility for the assembly of equipment,or the transfer of equipment from road to rail.Just south of Talkeetna - at ARRC MP 223 mile is McKinley siding and yard.The principle siding is 2,300 ft.long,but of interest is an associated pit for which ARRC has built a spur.The spur is at significant grade -and moving a train out of the area could require extra assistance -but the pit could easily be Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-18 December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. used by a contractor as a storage area/transshipment area to load trains after bringing material by road from south.ARRC could easily include in the track a derailing link under their control so that a contractor could work within the area without ARRC interference until ready to move out. The land is all owned by ARRC but the area is used as a "bone yard”so is probably available. The area available is estimated to be 12 acres or more.There is considerable space for laying down and sorting of equipment and materials,as well as for transferring from trucks to railcars - if material has been brought from Anchorage by road.The location is sufficiently far from Talkeetna that its use would not affect the town. If the McKinley spur is not deemed suitable,at MP 215 is Sunshine siding -which is 5,800 ft. long and very close to the Parks Highway. 8.10.Airstrip 8.10.1.Previous Siting In the 1980s study,consideration was given to the construction of both a temporary and a permanent airstrip,and nine sites were examined in the report entitled "Construction Camp and Village Siting Study.”The site deemed most favorable did however have a potential interference with an eagle's nest.A temporary airstrip site,closer to the project was located on an area which was to form a borrow area. The Watana Transport Access Study prepared by ADOT&PF examined two airstrip sites one north of the river at the approximate location of Option 9 of the 1980s study,and one south of the river near Fog Lakes.Both sites were found suitable. For the current study,the previous study was reviewed,and further aerial and surface observations were made -particularly with regard to the fact that using a layout based on an RCC dam,there is no longer a requirement for a borrow area on the right abutment. 8.10.2.Airstrip Criteria Although much of the heavy equipment and consumables will be transported to the site using the ARRC and the access road,it is highly desirable to construct facilities for air transport of personnel and urgent items such as food,spare parts,medicine and rush goods. At this planning stage,it has been assumed that the criteria for an airstrip will be similar to that adopted in the 1980s study."At that time it was assumed that an airstrip would be constructed suitable for use by a Boeing 737 (now known as the B737 -100 and 200 series)and a C130 (now known in its civilian version as a Lockheed L-382).It is known that local cargo carriers Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-19 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. such as Northern Air Cargo,Lynden,Air North Canada,Everett,and others have used jet aircraft that would be suitable for landing at the Watana strip. A recent study by ADOT&PF (of Kotzebue airport relocation)indicated that through 2026, Northern Air Cargo would continue to operate B737-200s,while Alaska Airlines would continue to operate B737-400s.Lynden are expected to operate L-382s.The aircraft reference codes for these planes are respectively ADG C-III and ADG C-IV. It is assumed that the strip will be an unsurfaced gravel strip,which would require jets such as the B 737 to be equipped with a "gravel kit.”No parallel taxiways are envisaged,so the turning areas at either end of the single runway would need to be surfaced,as would the apron and the taxiway for access to the apron.Initially it was thought appropriate to provide a strip length suitable for a 737 with gravel kit,but further research has indicated that all 737-200s (the last model with engines mounted high enough to facilitate gravel kit modification)may well have reached their cycle limit for landings and takeoff by the time the Susitna-Watana Project proceeds.Therefore the airstrip length was reduced slightly to 5,500 ft.,which is safe for economic use by the L-382 and CASA CN 235 planes on which the estimate was based. Based on Federal Aviation Authority (FAA)requirements set out in the "Airport Design Advisory Circular AC 150/5300-13”and in "Boeing 737 Airplane Characteristics for Airport Planning”,the requirements/criteria assumed are described in the following sections. A location close to the original 1980s location 9 was reexamined based on topography,and an examination at the site.It appears that a suitable strip can be located on relatively flat topography,and on ablation till,somewhat closer to the dam site,but more detailed examination of the extent of wetlands vs.till must be carried out during the future site investigation. 8.10.3.Selected Airport The available meteorological data from the site weather station has been examined.A wind rose is shown in Figure 8.10-1. This wind rose indicates that the runway alignment should be at an orientation of 068/248. Using this orientation the location of the southern end of the runway has been chosen at N 3234102.6794,E 1890592.8668 as shown on Drawing 03-10C002.This is deemed to be suitable for safe landing in the prevailing wind.The strip would have a rolled gravel surface of at least six inches with no areas of deep loose gravel.Aircraft manufacturers recommend that the surface be smooth,with no bumps higher than three inches in 100 ft.The gravel surface must be checked frequently and rolled as soon as possible after damage. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-20 December 2014 zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Watana Stationynw +Monthly Data a \_fa Figure 8.10-1.Wind Rose Full Year 8.10.4.Runway Length and Width As noted runway length was originally determined from the performance curves in the Boeing handbook.The required runway length so derived with a contingency of 15 percent for a "contaminated”(i.e.,snow covered runway)was 6,300 ft.so for this stage of the study a length of 6,500 ft.was originally assumed.However as noted,because of the retirement of early 737 aircraft,a strip length of some 5,500 ft.was ultimately chosen which is sufficient for the turbo prop planes expected.Potential operators may prefer slightly longer lengths,and they should be consulted before finalizing design.A location has been chosen that would allow for a runway some 2,500 ft.longer,if expansion in the future is deemed worthwhile. FAA guidelines suggest a runway width of 150 ft.,but 737s are operating throughout the world from 100-foot runways,so this width has been adopted and will be suitable for all types of aircraft that would feasibly use the strip. 8.10.5.Approaches FAA Advisory Circular 150/5300-13 and FAR Part 77 indicate the required approaches,and the proposed airstrip has been reviewed with these criteria in mind. Figure 8.10-2 below describes the Imaginary Surfaces established by the FAR Part 77 which have been taken into account for the orientation of the airstrip.Imaginary Surfaces define the areas where,for the approach of an airstrip,there may be no physical obstructions penetrating for safety purposes. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-21 December 2014 -w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Conical Surface Precision instrument Approach Visual or Non Precision Approach 2c __'(Slope-E) Runway Centerlines (image url:http://airspaceusa.com/FAR_77.25_Civil_Airport_Imaginary_Surfaces.htm) Image in accordance with FAR Part 77.25(a)Horizontal Surfaces:Chart of Surface Dimensions Figure 8.10-2.Safe Aircraft Approach Surfaces The proposed airstrip is expected to have a Visual Aid Slope Indicator System which will provide descent guidance information during approach.The given imaginary surface above for this system shows a 50:1 slope directly behind the approach side of the runway for 10,000 ft. Following that a 40:1 slope for 50,000 ft.until the slope has reached an elevation of 1,200 ft. These areas have been checked for the selected site around the proposed airstrip and it has been verified there are no current physical objects or geographical features that will classify as obstructions. 8.10.6.Runway Ends and Aprons The airstrip will not be busy enough to warrant parallel taxiways,so arriving and departing aircraft must be able to turn 180°at each end of the runway.The Boeing manual indicates that a minimum pavement width for a 180°turn is 60 ft.,so it has been assumed that at each end of the runway the full width (100 ft.)will be surfaced,for a distance of 200 ft.,which should provide sufficient area for aligning the aircraft. In a similar manner,the apron must be sized so that a plane can turn 180°,and so that two planes can simultaneously be offloading.Thus the apron must be at least 100 ft.wide for each plane. As noted in the ADOT&PF Watana transportation report,it is suggested that a surfaced apron some 400 ft.by 200 ft.is appropriate. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-22 December 2014 -wa ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT There will also be a helicopter pad,approximately 45 ft.by 90 ft. The apron has been set back more than 500 ft.from the runway in accordance with FAA requirements. 8.10.7.Aircraft Operational Aids Certain basic aids will be required for the safe landings and take off in inclement weather.These include: A beacon An instrument landing system (Transponder Landing System) Radio Automated weather observational system Wind indicator Visual glide slope indicators Runway and apron lighting Also desirable and included in the project cost estimate are: Radar (Potentially)identifying lights on any peak or equipment 8.10.8.Facilities Permanent facilities associated with the airstrip will include: An office/control room for controlling the airstrip A small waiting room and toilet facilities Fuel storage -probably in tank containers A fuel truck A fire truck that also services the township Pneumatic truck Mobile air stair as necessary Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-23 December 2014 -yw SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 8.10.9.Summary The basic dimensions and criteria for the airstrip are summarized in Table 8.10-1 below: Table 8.10-1.Airstrip Criteria Minimum Runway Length:5,500 ft.,with a clear area available for extension Runway Width:100 ft.;possible 25 ft.shoulders Runway Safety Area:7,500 ft.by 500 ft Runway Protection Zone (RPZ):1,000 ft.at end closest to runway &1,510 ft.at remote end by 1,700 ft.long Clearance between Runway &RPZ:200 ft. Runway Object Free Zone 1,000 ft.by 7,500 ft. Clearway (Departure end of Runway):500 ft.by 1,000 ft.@ 1.25%slope Threshold Siting Approach:No penetrations (FAA AC 150/5300-13 CHG 12) Prevailing Wind:SW-NE Precision Instrument imaginary Surface:|FAR Part 77 Runway Blast Pad:N/A Stopway:N/A *Dimensions above were found in the USDOT FAA 150/5300-13 Airport Design,Tables 2-4 and 3-3. 8.11.Unconventional Access This section has dealt with the suggested arrangement that can be made for construction and ongoing access to the project site,based on road and railroad access,implemented in a sequential manner. At a later stage -to,and during development of,the individual project procurement packages - AEA must decide the extent to which they will dictate to the main contractor the methodology for -and contractual rules for access,given that the cost and reliability of the supply chain logistics will greatly influence the cost of the project and the schedule for construction. There are also drivers however which may necessitate the consideration of unconventional access.Two key aspects will have to be considered: =If required by an accelerated schedule,the extent to which material and equipment can be relocated to the site before the full construction access has been established;and «The size of the largest items and the economics of establishing particular transport of those pieces. Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 8-24 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. These drivers are important because the ability to move material,equipment and consumable stores to site before the road is built -or later in the construction process without requiring disassembly for movement along the railroad -may beneficially affect cost and schedule. 8.11.1.Hoverbarge The use of the ARRC will impose a constraint on the maximum size of any equipment that can be delivered to the site (whether for the permanent works or for the construction).Some items may have to be brought to site in pieces and assembled,either at the railhead or at the site. Typical are the Caterpillar 777 trucks expected to be used in the quarry,which are,fully assembled,more than 21 ft.wide.Such trucks are able,fully assembled to drive on normal highways as an escorted load,from (say)Port MacKenzie to Talkeetna,but would not be able to be shipped on the ARRC. However,there exist hoverbarges (both self-propelled,and towed)that could be used to move large loads,such as the 777s up the Susitna river from Port Mackenzie to Gold Creek during the winter,over the river ice.There are varying sizes of hoverbarge available,up to 300 tons cargo capacity.The speed of the barges is a maximum of five knots,but delivery to Gold Creek of particular oversize equipment unsuitable for the ARRC is practical.An offloading area would have to be developed at Gold Creek. 8.11.2.CAT Trains If it is deemed useful to move equipment to site before the access road is completed,CAT trains can be used.For delivery to the southern abutment,the train can be assembled at Gold Creek and follow a similar route to that used by others in the upgrading of Stephan Lodge.For delivery of equipment to the northern abutment the CAT train would be assembled at the Denali Highway.It may be advisable -for passage to the northern abutment -to use the winter trail developed from the Denali Highway in 2011 during recovery of a crashed U.S.Air Force F-22 Raptor,and then extend the CAT trail on snow through to the site. 8.11.3.Air Transport of Heavy Equipment During the feasibility study,the team was requested to examine the possibility of movement of equipment -and heavy equipment -to the site by air,even if this method was solely used for initial mobilization before the road is complete. At the date of writing,the only potential for lifting heavy equipment is by helicopter.The largest helicopter that is relatively easily available is the Chinook which are limited to 26,000 lbs.on the hook.The Russian manufacturer Mil Moscow Helicopter Plant has built a number of Mi-26 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-25 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. helicopters that can lift 20 metric tons (44,000 lbs.)but these are only in service with Aeroflot and the Russian military. There are no heavy lift airships -either rigid or hybrid designs -currently possessing FAA airworthiness certificates by air. Although no rigid airships are currently used for heavy lifting,hybrid airships are being researched for such purpose. The project team researched the "state of the art”of hybrid airships and the current situation is: Aero Vehicles,Inc.,based in Argentina,produces the AeroCat,a hybrid airship.The AeroCat has a 20 ton (44,000 Ibs.)capacity with a cruising speed of 70 knots.The company was non-responsive when asked about potential FAA certification.No operating costs were provided. ILC Dover,based in Frederica,Delaware has designed the lighter than air Cargolifter,a hybrid airship.The Cargolifter will have a 75 ton lift capacity.Cruising speed was not available.ILC Dover does not directly manufacture this product,but supplies design to other firms.No operating costs were provided. Hybrid Air Vehicles Ltd,based in the United Kingdom,produces the Sky CAt -a hybrid airship.The Sky CAt has a 20 ton capacity with a cruising speed of 78 knots.The company was non-responsive when asked about FAA certification.No operating costs were provided. Worldwide Aeros Corp.,based in Montebello,California,produces the Aeroscraft,a Rigid Variable Buoyancy Air Vehicle.The Aeroscraft has a 20 ton capacity with a cruising speed of 100 knots.Aeros currently has FAA Production approval and is working with FAA towards obtaining an airworthiness certificate.This certificate is anticipated in the 2015-2016 time frame.No operating costs were provided. Lockheed Martin is developing the Hybrid Air Vehicle (P-791).A 20 tons cargo airship would be available for service (FAA Certified)in the 2014-2015 timeframe.A larger projected airship will be about 70 tons capacity and is projected to be available for service in the 2015-2016 timeframe.Both aircraft will accomplish the 70 mile range and return without refueling at the site and would travel between 60-80 knots airspeed.No operating costs were provided. Northrup Grumman Aerospace Systems produces the ISR Hybrid,a hybrid airship. Currently building a 20 ton capacity model for the U.S.Army but are also looking at 50 ton,100 ton and 200 ton configurations.Northrup Grumman said they could meet the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-26 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. operational need for construction in 2016,but cannot guarantee an airworthiness certificate by that time.No operating costs were provided. No manufacturer can give a definite date for the FAA to provide an airworthiness certificate for a hybrid airship.Postulated dates are as early as 2015,but the developments are prototypes and that date must be regarded as tentative.Construction planning based on the use of hybrid airships therefore appears premature,but the situation can be re-examined periodically to see if potential manufacturers can provide more definite information about an airworthiness certificate and operating costs. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 8-27 December 2014 Section 9 3 ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 9.PROBABLE MAXIMUM PRECIPITATION AND PROBABLE MAXIMUM FLOOD 9.1.Introduction Due to the size of Watana Dam and the economic importance of the Project to the Railbelt,the Probable Maximum Flood (PMF)was selected as the inflow design flood for Watana Dam.The PMF is an industry standard design criterion that federal regulatory authorities apply to large dams like Watana Dam.The PMF is the highest flood design standard applied to any dam.The PMF is defined as the largest flood that may be expected from the most severe combination of critical meteorological and hydrologic conditions that are reasonably possible in the drainage basin tributary to Watana Dam.The PMF results from the Probable Maximum Precipitation (PMP)and other coincident conditions including snowmelt.The PMF inflow hydrograph was routed through the reservoir with the ultimate purpose of sizing the spillway and outlet works and providing information for selection,at a later date,of a dam crest level that ensures the passage of a flood without jeopardizing the safety of the dam.This section of the report briefly summarizes development of the PMP and PMF.A complete PMF study report,which also includes a complete site-specific PMP report,is included as Appendix B4 to this Engineering Feasibility Report. 9.2.Watershed Description The watershed is in a remote part of the Susitna River,with Watana Dam located 187 project river miles upstream from Cook Inlet.The drainage area tributary to the Watana Dam site is about 5,180 square miles (sq.mi.),which compares to about 20,000 sq.mi.for the entire Susitna River watershed.The topography upstream from the proposed Watana Dam is mostly rugged, ranging from hilly to mountainous with glaciers.Although watershed elevations reach over 13,000 ft.,almost 70 percent of the watershed tributary to the Watana Dam site is below 4,000 ft. in elevation and 88 percent is below 5,000 ft.The predominant types of watershed cover include shrub/scrub,45 percent;evergreen forest,17 percent;and barren land,15 percent.Glaciers and perennial snow cover about five percent of the area and open water and lakes account for about three percent of the area tributary to the Watana Dam site.Streamflow is highly seasonal with over 85 percent of the annual average flow occurring during the five-month period of May through September. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-1 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 9.3.Historic Floods In 60 years of historical record at the U.S.Geological Survey (USGS)gaging station downstream of the dam site at Gold Creek,which has a drainage area of 6,160 sq.mi.,the peak recorded flow has been 90,700 cfs.The estimated 100-year peak flow at the Watana Dam site is 91,300 cfs.In the 134 station-years of flow data for USGS gages at or upstream from Gold Creek,100 percent of the annual peak flows have occurred during the months of May through September.Susitna River floods were found to be of two types,those in May or June that primarily result from snowmelt,and those in July,August or September that primarily result from rainfall. Figure 9.3-1 shows the watershed boundary for the drainage area tributary to Watana Dam,and the boundary of the additional drainage area tributary to Gold Creek where a long-term USGS gaging station is located.The five USGS gaging stations shown on Figure 9.3-1 were the ones used in the current study for calibration of the flood runoff model. ow low aw "ew ae iw)-'<}t4Ae i:-,wr .Was yy 3 a J Lig:Ate Pv he y f -i :ig)fe °"i ee,ww .fe'7 a 30 t en 4 i PE -a ee a.$.fp !'yt aw kg J 4 a A ie i eee peer anBeeie,1,Bx Ly Al <tpz Vey axa 7 Aa po acePSGa'rd al S72 i :,¥-' de"fn:pce%wyiaeNenekaNoteefoe«aeftaeWe-2Ls,SsFyAA:wtih.Ass wrig "|?he”ae so ve oH i.Dye Aig le ae De rdSy-122 fa a,Fo ANY )Age PS SPSBZe,NBOf°fo pn OP:Sy OKABetg.ae saad EY Ty SAO TE Fag,x Ww fi:Aa :ct se 7 one -Pere el _ ; on 7 .é 2 rani we ..OepoyPs4Fileyaneax!a aA rays wo”-ir aes 2 :Os tyonFea =ace sees . s t ! Figure 9.3-1.Susitna Watershed Boundary and USGS Gage Locations Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-2 December 2014 wz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 9.4.Hydrologic Model The HEC-1 Flood Hydrograph Package was chosen as the rainfall-runoff model to develop the PMF because it is one of the models recommended by the Federal Energy Regulatory Commission (FERC)specifically for this purpose,it includes the preferred energy budget method for snowmelt,and a wealth of experience data is available for this model.This model was developed by the Hydrologic Engineering Center (HEC)of the U.S.Army Corps of Engineers and has been (and possibly still is)the most widely used model in PMF studies. As shown on Figure 9.4-1,the watershed was divided into 29 sub-basins tributary to the Watana Dam site plus five additional sub-basins tributary to the USGS gage at Gold Creek that were necessary for model calibration.The area of each sub-basin in 1,000-foot elevation bands and the sub-basin area for each watershed cover type were determined from geographic information system (GIS)data. sw Low'famin[eb Geate Raa:areh River 2 USGS gage af #anson USGS Gage 10 15291000,d 'SusanaRiverneatDerak q .oeUSGSGage©18201700SustnaRiveaboweTaysenaCreat RxfaxfotsfofessfBifccdecfcse|sfoffFeon.oewetae 1 --od x 4 USGS,Gage ©1201500 *a m2 ower near CantalSusana yay >. -an ne Latina wien Figure 9.4-1.Susitna Watershed Sub-Basins Streamflow data for model calibration and verification were available at four relatively long-term Susitna River USGS gages at Gold Creek,Cantwell,and Denali,and on the tributary Maclaren River at Paxson.The recently established USGS gaging station above Tsusena Creek,near the Watana Dam site,also contributed data for one flood.Because Susitna River floods of two different types have been noted (primarily from spring snowmelt and primarily from summer Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-3 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. rainfall),three spring floods and three summer floods were selected for runoff model calibration and verification.Preference was given to selecting floods of the greatest magnitude that had recorded data at the most USGS gaging stations that would also satisfy the spring/summer distribution.Although selecting a total of three floods for calibration and verification is more typical,the flood characteristics of the Susitna River and the magnitude of the Susitna-Watana Project provided justification for using six floods.Based on the near maximum sunny weather flood that occurred during May-June 2013,consideration was also given to a variation of the spring snowmelt flood herein called a sun-on-snow PMF.After calibrating the model to the May-June 2013 flood,maximum temperatures without rainfall were used to derive a sun-on- snow PME. Runoff model calibration challenges included a general lack of historical meteorological data (precipitation,temperature,wind)within the watershed tributary to the Watana Dam site and the lack of historical snowpack data concurrent with the spring floods.Given these limitations,the watershed model calibration was in all cases considered to be within the normal range of acceptable results. 9.5.Probable Maximum Precipitation Because the existing standard U.S.Weather Bureau (now National Weather Service)PMP guidance document for Alaska is applicable to drainage areas up to 400 sq.mi.and for durations up to 24 hours,development of a site-specific PMP was necessary.Derivation of the site specific PMP is fully detailed in a separate report prepared by MWH sub-consultant Applied Weather Associates,which is included in Appendix B4 to this report.The site-specific all- season (maximum)PMP was found to occur in July or August and was derived on an hourly basis for a 216 hour (nine day)time sequence for each of the 29 sub-basins tributary to the Watana Dam site. Alternative temporal distributions for the PMP were evaluated.The critical basin-wide all- season average PMP values are shown on Table 9.5-1.All-Season PMP by Sub-Basin for Various Durations values averaged over the watershed tributary to Watana Dam were 1.78 inches for six hours,4.40 inches for 24-hours,7.19 inches for 72 hours,and 10.00 inches for 216 hours.The temporal and accumulated precipitation for the critical distribution of the PMP, which was based on the August 1967 storm,is shown on Figure 9.5-1. Associated concurrent meteorological data (temperature,wind speed,dew point)were also derived for the 216 hour PMP period plus 24 hours prior to and 72 hours subsequent to the PMP for a total of 312 hours.Because snowpack and snowmelt are significant hydrologic conditions in the Susitna River watershed that affect the estimated PMF,seasonal PMP and meteorological Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-4 December 2014 za SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT data were derived for the period from April through October based on different factors applied to the all-season data.The data sets for various seasonal time periods and sensitivity runs form cases from which the PMF can be determined. Table 9.5-1.All-Season PMP by Sub-Basin for Various Durations Drainage |All Season |All Season |All Season |All Season |All Season Sub-basin|Area 1-hr PMP 6-hr PMP |24-hr PMP {|72-hr PMP |216-hr PMP (sq.mi.)(inches)(inches)(inches)(inches)(inches) 1 52.6 0.60 2.47 6.09 9.95 13.83 2 226.4 0.50 2.04 5.02 8.21 11.41 3 295.4 0.37 1.53 3.77 6.16 8.56 4 149.3 0.56 2.31 5.69 9.31 12.93 5 354.0 0.44 1.79 4.43 7.24 10.06 6 153.4 0.48 1.97 4.86 7.94 11.03 7 67.5 0.32 1.31 3.23 5.29 7.35 8 189.9 0.39 1.60 3.94 6.44 8.95 9 187.7 0.41 1.69 4.18 6.83 9.50 10 326.8 0.39 1.61 3.98 6.51 9.04 11 273.5 0.41 1.67 4.12 6.73 9.35 12 74.7 0.36 1.46 3.61 5.90 8.21 13 222.5 0.34 1.39 3.44 5.62 7.81 14 135.1 0.33 1.36 3.35 5.48 7.62 15 185.1 0.36 1.50 3.69 6.03 8.38 16 164.3 0.37 1.51 3.73 6.10 8.48 17 253.2 0.35 1.45 3.57 5.84 8.12 18 100.0 0.43 1.78 4.39 7.18 9.98 19 202.2 0.50 2.04 5.04 8.24 11.45 20 36.3 0.37 1.53 3.77 6.16 8.56 21 162.7 0.50 2.06 5.07 8.29 11.52 22 92.0 0.36 1.47 3.63 5.93 8.25 23 174.2 0.41 1.70 4.19 6.86 9.53 24 157.4 0.43 1.78 4.38 7.17 9.96 25 184.0 0.61 2.52 6.23 10.18 14.15 26 222.9 0.54 2.23 5.50 8.99 12.49 27 269.6 0.47 1.94 4.78 7.81 10.85 28 218.5 0.52 2.13 5.26 8.60 11.96 29 36.8 0.43 1.75 4.31 7.05 9.80 Total/Avg.|5168.2 0.43 1.78 4.40 7.19 10.00 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-5 December 2014 ---z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 0.50 0.45 + 0.40 +1 8 |va | 35 /an -7 ne mincremental !5 -Accumulated°°wfo)i]fo)aNyi |"incrementalPrecipitation(inches)°o°anNDaaonAccumulatedPrecipitation(inches)3 2sooell.Ha ithIinlthitilada-oe ame7020100120140160180200 Hour Figure 9.5-1.Incremental and Accumulated All-Season PMP -August 1967 Temporal Distribution 9.6.Snowpack Snowmelt is an important and potentially a controlling component of the PMF for Watana Dam. Snow course data (measured monthly during the winter)is available at several locations within the area tributary to Watana Dam,and SNOTEL data (measured daily)is available near the watershed boundaries and in nearby watersheds.This data was generally adequate for developing the necessary snow water equivalent values antecedent to the seasonal PMP sequences. Table 9.6-1 presents the calculated 100-year snow water equivalent (SWE)values on or about the first of the month from February through May.Also shown is the October through April average total precipitation at the snow course locations.The last column of Table 9.6-1 shows the ratio of the calculated May 1,100-year SWE values to the October through April total average precipitation.These are the key values used to distribute the 100-year snowpack over the watershed. The last column ratios in Table 9.6-1 for snow courses in areas tributary to Watana Dam (not highlighted in red)range from 1.51 to 1.94 and average 1.68.The data for the snow courses highlighted in red,which are all outside the area tributary to Watana Dam,are all outside the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-6 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years, 1.51 to 1.94 range and have therefore been eliminated from further consideration.Therefore,the tributary area average factor of 1.68 times the average October through April total precipitation was selected and was used to develop the 100-year May and June snowpacks.Due to the potential for cold weather to persist from April up to the start of June,the May and June snowpacks were considered to be equal.The precipitation that falls during May would essentially offset any snowmelt that occurs. Table 9.6-2 presents the 100-year snowpack SWE averaged by sub-basin.It is noted that the 100-year SWE tributary to Watana Dam that averages 15.7 inches substantially exceeds the 100-year all-season PMP average of 10.0 inches at Watana Dam.The runoff model separates the 100-year SWE values within each sub-basin by 1000-foot elevation bands.Based on a Weather Bureau study for the Yukon River,the probable maximum spring snowpack was estimated to yield a snow water equivalent equal to 3.0 times the average October through April total precipitation. Table 9.6-1.100-Year Snowpack at Snow Course Stations Is Station Area 100-Year Snow Water Equivalent Oct-Apr Avg.|Ratio May 1 Station Name Tributary to |Elevation]Feb.1 Mar.1 Apr.1 May 1 |Total Precip.}100-Year/ Watana Dam (1)}_(feet)(inches)|(inches)|(inches)|(inches)|(inches)|Oct-Apr (2) Blueberry Hill No 1,200 24.0 32.8 36.5 33.8 16.9 2 Clearwater Lake Yes 2,650 8.1 8.2 9.8 11.6 6.0 1.94 E.Fork Chulitna River No 1,800 23.6 28.8 31.5 34.3 11.8 2.90 Fog Lakes Yes 2,120 11.6 12.1 12.9 11.9 6.7 1.78 Horsepasture Pass Yes/Border 4,300 9.4 11.8 12.5 12.8 7.0 1.82 Independence Mine No 3,550 39.6 48.1 50.1 50.1 24.5 2.05 Lake Louise Yes 2,400 6.7 7.1 8.2 7.2 44 1.63 Monchan Flat Yes/Border 2,710 12.7 13.8 14.7 12.0 8.5 1.40 Monsoon Lake Yes/Border 3,100 8.3 9.6 10.8 -_6.0 1.79 Square Lake Yes 2,950 6.0 6.5 7.4 7.2 4.8 1.51 Susitna Valley High No 375 13.6 15.5 16.5 19.0 13.3 -143- Talkeetna No 350 11.3 15.9 18.4 16.7 12.0 1.39 Tyone River Yes 2,500 5.7 6.2 7.3 -4.8 1.53 Average of non-red values 1.68 Notes: (1)Border indicates that the stations are on or near the watershed boundary. (2)Where May 1 data is missing,April 1 data was used. Values in the red boxes were not used to determine the 100-year snowpack. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-7 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 9.6-2.100-Year All-Season Snowpack Snow Water Equivalent Basin Annual Oct-Apr |100-Year Sub-Basin Area Precip.Precip.SWE Number (sq.mi.)|(inches)|(inches)|(inches) 1 52.6 37.9 16.9 28.4 2 226.4 28.9 12.2 20.6 3 295.4 18.1 6.7 11.2 4 149.3 41.7 19.2 32.3 5 354.0 30.9 13.5 22.6 6 153.4 42.8 19.9 33.4 7 67.5 23.9 9.5 16.0 8 189.9 27.8 11.6 19.4 9 187.7 26.9 10.5 17.6 10 326.8 21.3 8.0 13.4 11 273.5 22.9 9.0 15.0 12 74.7 16.8 5.8 9.8 13 222.5 14.2 4.8 8.0 14 135.1 13.8 4.3 7.3 15 185.1 16.2 5.8 9.7 16 164.3 16.8 5.9 9.9 17 253.2 15.0 5.1 8.5 18 100.0 20.8 7.5 12.6 19 202.2 24.5 8.8 14.9 20 36.3 17.1 5.4 9.2 21 162.7 25.6 9.2 15.4 22 92.0 16.4 5.5 9.2 23 174.2 20.9 7.0 11.8 24 157.4 21.9 7.8 13.2 25 184.0 33.6 12.2 20.6 26 222.9 27.7 10.1 17.0 27 269.6 23.6 9.0 15.1 28 218.5 26.3 10.0 16.9 29 36.8 18.7 6.7 11.3 30 146.4 28.8 11.4 19.1 31 181.9 26.9 9.6 16.1 32 208.1 28.5 11.5 19.3 33 273.4 31.3 13.3 22.3 34 164.8 36.6 16.1 27.0 To Gold Creek Gage 6,143 25.0 9.8 16.5 To Watana Dam 5,168 24.0 9.3 15.7 To Denali Gage 914 33.5 14.8 24.9 To Maclaren Gage 279 30.6 13.1 22.0 To Cantwell Gage 4,079 23.4 9.2 15.5 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-8 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 9.7.Coincident and Antecedent Conditions The primary coincident conditions to be evaluated are several cases formed by seasonal combinations of the 100-year snowpack and the PMP.Coincident seasonally varying temperatures and wind speeds are also important factors.The combination of the probable maximum snowpack and the 100-year precipitation is another case that was evaluated.Based on the historic near maximum Susitna River flood of May-June 2013 that occurred with little to no contributing rainfall,the FERC Independent Board of Consultants suggested performing a sun- on-snow PMF case.The sun-on-snow PMF case is detailed in the Sensitivity Analysis section of the PMF report in Appendix B1,but it did not become the critical PMF case. For Watana Dam,initial reservoir level considerations include both the starting reservoir level at the beginning of the PMP sequence and the reservoir level at which the spillway gates begin to open.Low-level outlet works valves are assumed to be used to make reservoir releases until the peak 50-year flood reservoir level has been exceeded,to limit the frequency of spillway operation and the potential for downstream gas super-saturation in the Susitna River which might adversely affect fish.Potential variations in the initial reservoir level were evaluated with sensitivity runs. 9.8.Probable Maximum Flood Hydrograph After evaluating all of the candidate cases for the PMF including alternative temporal,seasonal, and sensitivity runs,including the sun-on-snow PMF case,it was apparent that there is significant sensitivity in the results to infiltration loss rates,wind speed and temperature input data.Several PMF routing.sensitivity runs are summarized on Table 9.8-1.Given the sensitivity in these parameters,the critical PMF case used for spillway sizing was found to be formed by a spring PMP combined with the 100-year snowpack and with conservative low loss rates (Case S3 in Table 9.8-1).The conservative low loss rates were confirmed with reanalysis of the spring historic calibration and verification floods.For the critical PMF case,the maximum reservoir level was at El.2064.5 ft.with a peak inflow of 310,000 cfs and a 13-day total inflow volume to the reservoir of 3,980,000 acre-ft. To safely pass the PMF with a maximum reservoir level below El.2065 ft.with a spillway crest at El.2010 ft.,a spillway with a total width of 168 ft.(four gates each at 42 ft.wide)was required.This spillway size is preliminary and subject to change pending further review. Including a total outflow of 32,000 cfs through eight fixed-cone valves and a peak outflow of 250,000 cfs through the spillway,the total peak PMF outflow was estimated to be 282,000 cfs based on HEC-1 model results.A total of 14.5 ft.above the maximum normal operating pool level at El.2050 ft.is used for flood control storage with 7.6 ft.allocated to the 50-year flood Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-9 December 2014 ---Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. and an additional 6.9 ft.allocated to safely pass the PMF.With the inclusion of a standard 3.5- foot high parapet wall on top of the dam crest,the required freeboard would be provided for both normal and flood conditions.Figure 9.8-1 is a plot of the PMF inflow,total outflow,and reservoir elevation. The 310,000 cfs PMF peak inflow is about 3.4 times the estimated 100-year flood at the Watana Dam site.The 3.4 ratio of the PMF to the 100-year flood is within a typically expected range. One additional safety check is the ability of the dam to pass the 10,000-year flood (estimated to be 168,000 cfs)with one gate stuck shut.Because the total outflow capability of Watana Dam spillway would be 190,000 cfs at El.2065 ft.with one gate shut,and the Project would have the capability to pass an additional 32,000 cfs through the low-level outlets,it was determined that the peak inflow of the 10,000-year flood could be passed with one spillway gate shut. The spillway gates will be capable of being controlled by a microprocessor based controller (or programmable logic controller)using inputs of upstream reservoir water level and spillway gate position.Preliminary flood operating guidelines can be summarized as follows: 1.Ifthe reservoir water level exceeds El.2050 ft.,all flows would be diverted through the turbines and low-level outlets until the reservoir reaches El.2057.6 ft.The low-level outlets operate at all levels above El.2050 ft.and the turbines would operate to the maximum extent possible.For the PMF study,the turbines were assumed to operate at 7,500 cfs to reservoir El.2057.6 ft.,with turbine shutdown necessary above reservoir El. 2057.6 ft. 2.If the reservoir water level rises above El.2057.6 ft.,the spillway gates would begin to open.The spillway gates should be fully open at reservoir El.2060 ft. 3.The sequence of gate opening would begin with two of the four spillway gates opening as needed until they reach 80 percent open,at which point the other two spillway gates would begin to open. 4.If all gates were to reach 80 percent open with the reservoir level still rising,two gates would be fully opened and the other two gates would close slightly.If the reservoir level continues to rise,all four gates would be fully open at reservoir El.2060 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-10 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 9.8-1.PMF Routing Sensitivity Analysis Results Maximum Modification (if any)Peak Peak Reservoir Case to June 1 or August 15 PMF Inflow Outflow W.S.Elev. Number (cfs)(cfs)(feet) Si No modification to June 1 PMF 196,000 195,000 2059.3 $2 June 1 PMF with summer loss rates 241,000 239,000 2059.8 $3 June 1 PMF with constant 0.02 in/hr loss rates 310,000 282,000 2064.5 $4 June 1 PMF with +10 mph winds 232,000 231,000 2059.7 $5 June 1 PMF with +3 degree F temperatures 235,000 |234,000 2059.8 S6 June 1 PMF with Harza-Ebasco temp and wind 312,000 |277,000 2063.7 S7 June 1 PME with initial reservoir level at El 2030 196,000 191,000 2059.3 $8 August 15 PMF with constant 0.02 in/hr loss rates 246,000 |}244,000 2059.9 ror Sun-on-snow PMF -No rainfall,maximum temperatures |255,000 254,000 2060.1 400,000 +2066|| 350,000 i !;2064 inflow i L \|; 300,000 -outflow : |+2062 -Reservoir Elevation _ 250,000 A X KK 2060 #:Hl i=] ° 2 :|3 200,000 :NX |-2058 & 2 ::rvy1 , :3|/if SN $150,000 -2056 & i 1 a |[va 100,000 2054 50,000 2052 | 0 2050 4-Jun 3-Jun §-Jun 7-Jun 9-Jun 11-Jun 43-Jun Figure 9.8-1.PMF Inflow,Outflow,and Reservoir Elevation Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 9-11 December 2014 Section 10 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.WATANA DEVELOPMENT DESCRIPTION This section provides a description of the main project works and the factors that were considered in selecting the preliminary designs for the major features.The site access and transmission facilities are described in other sections -Site Access Facilities are described in Section 8 and Transmission and Interconnection Facilities are described in Section 11. 10.1.Introduction 10.1.1.Site Survey and Mapping The site survey and base mapping was created during 2012.After initial layouts were crafted using topography obtained by digitizing the 1980s topographical maps,the first new topographic data became available for the current feasibility studies using the Interferometric Synthetic Aperture Radar elevation data and the MatSu-North Susitna Bare Earth Data (both datasets are using Horizontal North American Datum of 1983 [NAD83]and North American Vertical Datum of 1988 [NAVD88]). On the drawings prepared in the 1980s,the vertical datum has been described as "USC &GS MSL”or "Mean Sea Level”.In APA document No.14,"Horizontal and Vertical Control Surveys”,dated March 1981,by R&M Consultants,it is stated that "Elevations are based on a local NGS mean sea-level datum which approximates the U.S.sea-level datum of 1929”. Although no single document serves as the official defining document for NAVD 88 (www.ngs.noaa.gov/datums/vertical),detailed information is available in an NGS-NOAA Special Report,"Results of the General Adjustment of the North American Vertical Datum of 1988”.This document indicates that for the 48 adjacent states,the vertical difference in datums between NAVD 88 and NGVD 29 ranges from -40 cm (-1.31 ft.)to +150 cm (4.92 ft.),and that in Alaska,the differences range from +94 cm (3.08 ft.)to +240 cm (7.87 ft.).The NGS-NOAA Special Report also indicates that the NGVD 29 to NAVD 88 datum conversion in Fairbanks is +160 cm (5.25 ft.),and in Anchorage it is +190 cm (6.23 ft.). Given that no official datum conversion is available in the vicinity of Watana Dam,a reasonable approximation could potentially be determined from a current resurvey of benchmarks (brass cap monuments)near Watana Dam.Among the monuments in the project area,difference varies between a maximum value of 5.950 ft.and a minimum value of 5.821 ft.,for a range of 0.129 ft. (1.5 inches)among the 10 benchmarks.The average difference is 5.901 ft.and the benchmark closest to Watana Dam (22-C)has a difference between datums of 5.899 ft.The vertical datum differences at the benchmarks also fall between the given values for Fairbanks (5.25 ft.)and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-1 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Anchorage (6.23 ft.).From this,it appears that the vertical datum differential at Watana Dam between NAVD 88 and NGVD 29 can be given as about 5.9 ft. 10.1.2.Project General Arrangement The proposed Watana Dam will create a reservoir approximately 42 miles long,with a surface area of about 23,500 acres,and a gross storage capacity of 5,170,000 acre-feet (ac-ft.)at the normal maximum operating level (NMOL)of El.2050 ft.as shown in Figure 1.6-2. The maximum water surface elevation of the project shown in the accompanying figures during probable maximum flood (PMF)conditions will be El.2064.5 ft.The minimum operating level of the reservoir will be El.1850 ft.,providing 3,380,000 acre-ft.of active storage during normal operation. The dam will be a concrete gravity structure constructed using roller compacted concrete (RCC) methodology.The dam will have a central section with a curved axis radius equal to 2,600 ft.at the upstream edge of the crest.At each abutment there will be straight gravity sections (with downstream slopes of 0.85H to 1.0V)acting as "thrust blocks”and intersecting the curved section at tangent points.The downstream face of the dam will be curved (vertically)at a radius of 1,650 ft.from the crest which will be 45-ft.-wide.The upstream face will be vertical except for a batter with a slope of 0.1H to 1.0V below El.1770 ft.The nominal crest elevation of the dam will be El.2065 ft.,with a maximum dam height of approximately 705 ft.above the foundation.The crest length will be approximately 2,810 ft.The total volume of the RCC concrete structure will be approximately 5,215,000 cubic yards,with an additional 456,000 cubic yards of conventional concrete placed in the dam crest,spillway and outlet works.During +-W construction,the Susitna River will be diverted through a concrete-lined diversion tunnel on the north side of the river,36 ft.in diameter and approximately 2,060 ft.long.A 44 ft!by ay/hsquaresluicewillbeconstructedthroughthedamtoprovidesupplementalriverdivefsion capacity. Each installed generating unit will be served by a single power intake located on the upstream face of the dam.Each power intake will be a concrete structure with multi-level gates capable of operating over the full reservoir operating range.From each intake structure,a steel penstock with an internal diameter of 19 ft.will penetrate the concrete dam and will be anchored to the downstream face of the dam leading to the powerhouse complex.The steel penstock will be surrounded in a concrete encasement where it is positioned on the downstream face of the dam. The powerhouse will house three generating units with vertical shaft Francis-type hydraulic turbines driving direct connected synchronous generators.A fourth penstock will pass through Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-2 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT the concrete dam,and the downstream end will be semi permanently capped-to be removed if and when an additional generating unit is eventually installed in the future. Access to the powerhouse floor level will be by means of a shotcrete-lined access tunnel from the north (right)side of the valley,necessary because of the steep valley sides,and a road from the north bank of the downstream river valley.Turbine discharge will flow through three draft tubes (one per unit)and into the common tailrace. One three-phase generator step up transformer for each unit will be mounted on the powerhouse deck,downstream of the powerhouse building,together with a spare transformer.From the transformer bushings there will be 230 kilovolt (kV)high voltage lines that will connect to a switchyard on the left downstream abutment.The switchyard will provide switching to three transmission lines. The intakes for the low-level outlet facilities will be located on the upstream face of the dam to the north side of the spillway,with a total combined capacity of approximately 32,000 cubic feet per second (cfs)at a surcharge of 7.5 ft.In combination with the average powerhouse flow of 7,830 cfs,the arrangement provides for the storing and releasing of the 50-year flood without raising the pool level above El.2057.5 ft.and without spillway operation. The spillway located on the north side of the powerhouse will consist of an upstream ogee control structure with four radial gates and an inclined concrete chute and flip bucket designed to pass a maximum discharge of 250,000 cfs.This spillway,together with the outlet facilities,will be capable of discharging 282,000 cfs -the routed peak discharge from the estimated PMF inflow of 310,000 cfs,while maintaining a maximum water level of El.2064.5 ft.Additionally, emergency release facilities will be located in the diversion tunnel after closure to allow controlled filling and for lowering of the reservoir -after the low level outlets have drawn the water down to El.1850 ft.-over a period of time for emergency inspection or repair of impoundment structures. The general arrangement of the dam and powerhouse facilities is shown in Figure 1.6-2 and on Drawing 04-01C002. 10.2.Site Facilities The site facilities covered by this section include the construction facilities,temporary construction camp,permanent village,water supply,wastewater treatment,and solid waste disposal,shown in Figure 1.1-3.Refer to Drawing 01-00G001 for details. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-3 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The siting of these facilities was originally examined during the 1980s feasibility studies and documented in the Watana Support Facilities-Master Plan,dated July 1985.The methodology used in,and the results of,that report have been used in preparing the project arrangement shown on the drawings. The proposed facilities assume that workers performing summer (seasonal)tasks such as RCC placement,would remain at the project site throughout the whole construction season,while those performing year-round tasks (such as tunneling or conventional concrete placement)would be subject to a rotational method of working (such as two weeks on,one week off)similar to other major infrastructure developments in Alaska. Key infrastructure includes: =temporary construction camp; =contractor facilities; "permanent village for operators (used during construction for supervising staff); "temporary housing at the permanent village (removed at the end of construction); =»water treatment facilities; =wastewater treatment facilities;and, =solid waste facilities. Other temporary facilities,such as the quarry development,construction roads,concrete batching facilities,etc.,are described in construction planning in Section 13.The airstrip,the camp at the railroad offloading area,and the permanent site access roads,all of which are important to construction,are described in Section 8. 10.2.1.Location of Facilities The site facilities will be located to the north of the Project as shown on Drawing 01-00G001. The permanent village will be located around the panhandle lake as shown,although the exact position will be defined after wetland and other environmental surveys have been completed. The temporary construction camp will be located alongside the adjacent long lake,which (with the addition of a small dock)is long enough to be used for float plane access.In a similar manner to the permanent village,the exact position of the construction camp will be defined after wetland and environmental surveys.It is expected that the detailed layout of the accommodation facilities will be adjusted to minimize wetlands impacts. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-4 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The water treatment facilities and waste water facilities will be located between the construction camp and the permanent village so that they can be left in place to conveniently service the permanent village. An area available for a temporary camp for site investigations is also shown -although to date alternative arrangements have been made. 10.2.2.Temporary Construction Camp The temporary construction camp and contractors'facilities will provide housing for the contractors'workforce,and buildings and facilities for the management of the workforce and the maintenance of contractors'equipment.With the exception of particular buildings/workshops,it is proposed that all buildings are removed at the end of construction,and the area landscaped and revegetated. Manpower planning has been carried out concurrently with construction schedule preparation, and the cost estimation,and recognizes the difference between seasonal workers and those performing tasks year-round.Those working during the summer season are assumed to remain on the site all season,while those with year-round work will rotate.Accommodation planning assumes that every worker will need a single room to themselves,and those that are working on a rotational basis will not "vacate”their rooms.Therefore,more rooms will be needed than there are workers on site. The construction camp will provide temporary housing for up to 1,200 contractors'personnel, including laborers,foremen,section managers,etc.although normally there will be a lower number in residence.The senior management staff are assumed to be accommodated in the (enlarged)permanent village described in Section 10.2.4.Support facilities for the temporary accommodation will include: *kitchen =dining hall ="administration offices =store =laundry facilities =recreational facilities,such as a movie theatre,gym,and recreation hall »playing fields Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-5 December 2014 Za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «medical facility sized for the project site (located near the airstrip to facilitate evacuation in case of a serious medical condition) Fire fighting vehicles/pumps will be located at the airstrip,but will service the whole project site during construction and permanent operation. The construction camp will be fenced to minimize human/bear interactions. It is expected that the construction camp will be primarily single status. Based on the proposed schedule and the balance of all season and rotational workers,the residential accommodation will be sufficient for 1,200 individuals,and at any one time 800 are expected to be in residence and using the common facilities. To mobilize workers to commence construction,including the construction of a temporary construction camp at the site,the initial work will be performed based on a temporary camp at the railhead.It is estimated that this would need to accommodate between 60 and 300 persons. During the construction of the access road and the mobilization stage,this will be used as a base of operation,but production will suffer because of the long daily "commute”to the site. However,as soon as a temporary camp at the dam site is partially complete and available for occupancy,the base of operations will shift from the railhead to the site,leaving the facilities at the railhead for their ongoing intended use. The temporary facilities at the railhead will include: «kitchen «dining hall =administration offices *laundry facilities *recreational facilities,such as a gym,and recreation hall Power and fiber optic services will be required at the railhead.The power will be drawn from a tapping on the intertie -which will also be used to service the main construction -and a tapping will be made to the fiber optic cables that are within the ARRC right of way.There will be water and wastewater facilities constructed at the location. The railhead facilities will provide for those supporting the logistics chain there,as well as some "emergency”accommodation for drivers or those prevented from using the road or rail because of inclement weather. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-6 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.2.3.Contractor Facilities The contractor facilities will include: "offices =store *mechanical workshop ®tire workshop *electrical shop «lumber shop =covered storage «fenced outdoor storage *fuel storage »explosives storage (located remote from other facilities) «bar bending shop A transport hub,including waiting room will be located at the airstrip,to facilitate the rotation of a significant proportion of the contractors'workers each Monday and Friday. 10.2.4.Permanent Village The village will provide housing for management personnel,AEA staff and consultants,and guest accommodation for visitors during the construction of the Project.A portion of the village around the lake shore will be constructed as permanent housing suitable for long-term use by families after completion of the Project.The permanent housing in the village is expected to comprise two-bedroom homes,and one-bedroom apartments.In addition,extra two-bedroom housing units will be temporarily located in the village,and will be removed at the end of construction to leave the appropriate number of houses for permanent operators,as further described in Section 10.2.6. Included in the village will be a block with small units (one bedroom)for single staff -which at the end of construction will be removed -and a block of studio apartments for construction site visitors that will be refurbished and retained for large maintenance groups who might relocate to the site,during operation,for major maintenance.After construction this block will be maintained,and heated,but will only be opened for use during major maintenance. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-7 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. In addition to the accommodation,the village will include: «dining facilities ="gymnasium =recreation hall/club "sports fields The permanent village will be robustly fenced to minimize human/bear interactions. The temporary housing will be removed at the completion of construction,and the appropriate areas landscaped,and the medical facilities and fire station constructed for the construction phase will be refurbished for long term use. 10.2.5.Owner Offices Construction supervision offices will be constructed at the site for AEA staff,construction management staff retained by AEA and the design consultants.They will comprise offices, conference rooms,document storage,a drafting group office,and a small kitchen.There will also be a laboratory for ongoing testing of construction materials and concrete. At the present time,it is assumed that these offices will be removed at the end of construction, and the requisite offices for ongoing operation will be in the powerhouse.However,if preferred by AEA,a permanent owner/operator office building could be constructed on the right (north) abutment. 10.2.6.Operators Accommodation During the operation of the project,it is assumed that AEA or its contracted operator will require the staff listed in Table 10.2-1,who will reside at the project: Table 10.2-1.Typical Operations Staffing Staff Number Plant Manager (non-shift work)1 Operators (shift work)3 Electric lead technician (shift work)3 Electric labor (non-shift work)2 3 2 1 Mechanical lead technician (shift work) Mechanical labor (non-shift work) Civil lead technician (non-shift work) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-8 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Staff Number Civil labor (non-shift work)3 Administrative manager { Security 5-10 Total FTEs 24-29 Note:FTE -full time equivalents As noted,it is expected that a security staff of between 5-10 persons will be required. At this time it is assumed that all these staff members would be full time at the site,and would not work on a rotating basis,so 29 family houses will be necessary.For occasional guests it is suggested that other houses also be left in place (and kept heated).As mentioned above,these houses will be built as part of the temporary facilities and will be used by management personnel,AEA staff,consultants,and guests during the construction of the project,but will be built more robust to later serve as permanent housing. In addition,the apartment building to be included in the permanent village which will house single management personnel and guests during construction will be remodeled after construction of the Project is complete.That building will be reconfigured as approximately 50 studio apartments for the use of larger maintenance crews when they are sent to the project for extended periods for rebuilds,additions or expansions.The building will include a kitchen/dining facility and recreation rooms,but will not normally be open,and will be maintained with nominal heating until needed. 10.2.7.Water Supply 10.2.7.1.General A water supply system will be provided for the construction camp and will be left in place for the permanent village,powerhouse and any permanent office building.This water system will include adequate supply for drinking (potable)water,fire protection,laboratory operations and miscellaneous uses for the construction of the Project and on-going operations after completion. The following Table 10.2-2 presents the preliminary water system design criteria which were used to generally size the water and wastewater supply and treatment facilities for both the construction camp and permanent village.Water supply for construction activities including the concrete batch plant will be sized separately and will be the responsibility of the selected main contractor. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-9 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 10.2-2.Preliminary Water System Design Criteria Parameter Construction Permanent Population Served 1,200 80 Average Daily Per Capita Usage,gpcd 100 100 Daily Average Water Usage,mgd 0.12 0.03 Maximum Day Water Usage,mgd 0.22 0.05 Maximum Hour Water Usage,mgd 0.32 0.08 Fire Flow,gom 1,060 560 Fire Demand,gallons 318,000 134,400 Note: gpcd:gallons per capita per day mgd:million gallons per day gpm:gallons per minute The water supply system will include the following key components: «Raw water intake,and pump station in a prefabricated building; =Raw water pipeline and raw water storage tank; «Water treatment system including low-pressure microfiltration membrane treatment with primary disinfection by ultraviolet light irradiation; «Treated water storage tank; «Treated water pumping and distribution system;and, «Fire protection pumping and piping system (assuming that untreated water is used for fire protection supply). A process diagram for these facilities is shown on Drawing 03-13-C001.Each of the systems is described in greater detail in the subsections below. 10.2.7.2.Raw Water Intake and Pump Station The water supply system will include a raw water intake utilizing a sub-surface intake gallery. Preliminary assessment of the site indicates year round water will be available from Deadman Creek,northeast of the proposed construction camp site,making this a favored location for the intake.This type of intake has been demonstrated to be successful at providing year-round water supplies in cold,arctic regions.During the winter months,the intake gallery will be heated using conventional electric heat tracing to prevent freezing.A pump station located in a well-insulated prefabricated building above the intake will have a firm pumping capacity (i.e.,assuming one pump out of service)of approximately 200,000 gallons per day (gpd)to meet maximum day usage requirements. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-10 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. It is proposed that the pump station be designed for continuous operation,with continuous water recirculation (even when the treatment systems are offline)to avoid the plugging and freezing issues that are prevalent with start/stop operations in cold weather.Continuous operation,along with the raw water storage described below,will also reduce the need for operational changes during peak flows.The intake and pump station will be designed such that the installation can be easily "down-sized”after the construction camp is decommissioned to a lower pumping rate of approximately 50,000 gpd for the permanent facility needs.The pump station will convey water through the raw water pipeline to the raw water storage tank located in a building between the construction camp and the permanent village. Additional fire protection supply may also be available on a seasonal basis from the lakes adjacent to the construction camp and permanent village sites (designated,respectively,Lake A and Lake B).During detailed design,the feasibility of using the lakes as a supply for fire suppression should be investigated and if acceptable,raw water intakes and pump stations will be designed and constructed at one or both lakes to supply untreated water directly to the fire protection system.As noted elsewhere,the fire protection system for the power facilities will be based on extraction from the tailrace.Further discussion on the fire protection system is presented below. The power for the raw water pump station will come from the main construction camp power supply,with backup power provided by an additional 100-kW diesel generator located at the water/wastewater treatment building.At the end of construction,the normal power supply will be provided from the power facilities.Electrical conduits buried along the raw water pipeline alignment will supply power to the raw water pump station. Instrumentation and controls will be installed at the raw water pump station to allow for remote monitoring of pump status and provide alarms in the event of equipment failures.These signals will be relayed to a control panel in the water/wastewater treatment building for easy control and operation by the operator(s)during the construction phase with further relaying to the main power facilities control room after construction is complete. Deadman Creek is located a significant distance from both the construction camp and permanent village,which adds cost and operational difficulties.Further investigation with regard to the soils and groundwater levels surrounding the permanent village would be beneficial to determine if wells or galleries in locations closer to the point of use could be a reliable,cost-effective alternative.Another possible alternative raw water supply is the Susitna River,although this alternative would require the creation of settling basins.These options will be more thoroughly investigated during detailed design. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-11 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. There will be significant use of raw water during construction including the following activities: »"Aggregate production »RCC and CVC production "Aggregate heating «Abutment warming *Abutment cleaning *Drilling and Grouting *"RCC and CVC curing »Dust suppression The majority of the use is on the left (south)abutment,so the contractor can be expected to pump water out of the main river on the left bank,or possibly Fog Lake,creating a distribution system for raw water from the river around the site. 10.2.7.3.Raw Water Pipeline and Raw Water Storage Tank The raw water pipeline will convey water approximately 3.6 miles to an approximate 0.3 million gallons (MG)raw water storage tank located inside a building and adjacent to the water treatment plant also inside the same treatment building.The tank has been shown in the drawings at grade,but during detailed design it may be relocated lower for enhanced insulation. The raw water pipeline will comprise two separate three-inch diameter pipes.Using this configuration,adequate scouring velocities will be maintained for both the construction phase (using both pipelines simultaneously)and the permanent village (using a single pipeline)flow regimes,without having to install new piping in the future.To the extent possible continuous circulation through the two pipes will be practiced.The raw water pipelines will need to either be buried sufficiently deep,or be insulated,for its entire length to prevent freezing of the water in the pipes.A decision will be made after site investigations have been carried out,but (apart from insulation considerations)burying is preferable to prevent damage by wildlife.Given the proximity of bedrock in this area,buried raw water pipelines may not be feasible making insulated,heat-traced pipe the sole option.In either case,continuously delivering or recirculating the raw water through these pipelines,as discussed above,will help prevent freezing. To minimize disturbance to the land during construction and thereafter,the pipeline route will be selected to collocate with other facilities as far as possible.Therefore,as far as possible the pipeline will be located alongside permanent roads and the airstrip. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-12 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The raw water storage tank will be located inside a climate-controlled water/wastewater treatment building to avoid freezing and to maintain a higher water temperature to improve treatability,as discussed below. The proposed raw water storage tank provides several functions including: =Serves as a buffer/feed tank for the water treatment plant (WTP)to improve system reliability due to the long distance between the intake and the WTP; =Serves as a feed tank for the fire protection supply with a full tank meeting the estimated fire flow volume as discussed below;and, *Can provide supply for some construction water uses,if demands are relatively low. It is proposed that the raw water tank be co-located with the WTP and treated water storage tank and appurtenant systems which will be located inside a common building adjacent to the camp and village areas. If further investigation finds that raw water is not available during the winter months,additional raw water storage in a lined reservoir could be required.Such a lined raw water reservoirs, will-typical of cold region water systems -be designed with adequate depth to allow for freezing of the surface while maintaining a sufficient useable volume below the ice layer.If such winter storage was required,an estimated usable volume of up to 18 MG of storage might be required to serve the construction camp during the projected five-month freezing period - depending on the occupancy.This requirement will be further investigated during detailed design,when water source investigations have been performed in greater detail. Given the distance between the raw water intake and the treatment plant there may be difficulty maintaining the raw water pipeline during the winter.An alternative system of wells in closer proximity to the treatment plant building will be installed to provide nominal water supply to avoid complete breakdown during inclement weather.Availability of groundwater in this area will be examined in detail during detailed design. 10.2.7.4.Water Treatment System A pre-engineered package-type water treatment system is appropriate for the location. Determination of the specific characteristics of a water treatment system for the proposed source will depend on the raw water quality,treatment goals,regulatory requirements when commissioned,and operation and maintenance (O&M)requirements.Potable water will be required to meet all Federal Maximum Contaminant Levels as well as any state-specific regulations adopted prior to construction.Two types of pre-engineered (package-type)treatment systems can be considered including: Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-13 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. =Conventional flocculation/sedimentation/granular media filtration;and =Low-pressure membrane filtration. Both systems can be pressurized without a free water surface inside the tankage,or have a free water surface within the tankage.Further analysis of the options will be considered after more extensive analysis of raw water quality data from Deadman Creek or an alternate raw water source.Key water quality parameters which can affect treatment process selection include temperature,turbidity,color,pH,alkalinity,total organic carbon,and iron/manganese.However, a low pressure membrane filtration system is included in this conceptual design for cost estimating purposes.A membrane water treatment system has many advantages,including providing robust treatment in a compact footprint. Ultraviolet disinfection downstream of filtration is included for enhanced disinfection. Following ultra violet (UV)disinfection,chlorine will be added to maintain a free-chlorine residual in the distribution system.A process flow diagram for the water treatment system is shown on Drawing 03-13C002. An on-site hypochlorite generation system which uses salt as the primary delivered chemical is proposed for chlorine supply.Other chemicals will also be required to support operations of the WTP,such as coagulant and clean-in-place chemicals for membrane units (including caustic soda,acid,and sodium bisulfite).Some of these chemicals can be shared with the wastewater treatment system. Other features of the treated water supply will include: *«0.3 MG treated water storage tank; *Treated water pumps with a hydropneumatic (pressure)tank to deliver water to the distribution system;and, =Backup power generator to provide basic water supply needs during periods of prolonged outages of the primary camp power supply. During detailed design of the facilities,to the extent that State regulations allow it,consideration should be given to the supply of interior fire protection water,toilets and outside water for automobile washing etc.direct from the raw water tank through a separate distribution system. Such a dual system should reduce demand for treatment chemicals etc. 10.2.7.5.Water/Wastewater Treatment Building It is proposed that the raw water tank,water treatment plant,and treated water storage tank and appurtenant water supply systems be co-located inside a common building adjacent to the camp Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-14 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT and village areas (alternatively,a location suitable for the construction camp could be chosen and the equipment and tankage could be relocated near the permanent village after construction). This building will be climate-controlled to reduce the effects of freezing temperatures on the treatment processes and equipment.A conceptual layout for the building is shown on Drawing 03-13C002.For speed of construction a pre-engineered metal building is suggested to allow for ease of material delivery and construction in the remote construction camp location,however careful design and construction of the building foundation will be required to prevent failure from permafrost or to protect against frost jacking.The building will be heavily insulated and contain areas for electrical/HVAC equipment,chemical storage,and operations/office space. It is also proposed that the wastewater treatment system be co-located in the treatment building. Precautions will need to be taken to segregate the wastewater system from any drinking water system components including segregation of O&M tasks.At this level of feasibility,the building plan has been defined with no direct connection (doors)between the wastewater treatment and raw water treatment sections of the building. 10.2.8.Wastewater Collection and Treatment 10.2.8.1.General A wastewater collection,treatment,and disposal system will be provided for the construction camp,permanent village,airport facilities and construction yard area. Table 10.2-3 presents the preliminary wastewater system design criteria used to size the wastewater treatment and discharge facilities. Table 10.2-3.Preliminary Wastewater System Design Criteria Construction Camp Permanent Facilities Population Served 1,200 80 Avg.Daily Per Capita Flow,gpcd 100 100 Avg.Daily Wastewater Flow,mgd 0.12 0.03 Max.Daily Wastewater Flow,mgd 0.19 0.05 Note: gpcd:gallons per capita per day mgd:million gallons per day The average daily flows will be affected by the typical daily diurnal flow variations common to most municipal wastewater treatment systems.This will be mitigated,to some degree,by the 24-hour operation schedule that will be employed during the summer months.Reduction of operations -and thus camp staff -in the winter will help reduce the overall load on the wastewater treatment plant when cold water will make treatment less efficient.A batching Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-15 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. system,or equalization tank,at the head of the wastewater treatment plant will help to balance daily fluctuations in wastewater flow and will improve overall system capacity and performance. Wastewater will require secondary treatment to meet state and federal standards.This includes compliance with the "30/30 rule,”limiting the 30-day average wastewater discharge to no more than 30 mg/L of BODs (five day biochemical oxygen demand)and 30 mg/L of Total Suspended Solids.Additional treatment requirements for nutrients and/or toxics (regulated constituents with a reasonable potential for toxicity to human or aquatic life)such as metals may also be applicable depending on a biological opinion on the receiving waters.Careful analysis of the chosen raw water source will also be beneficial to the wastewater system planning,to determine if any constituents of concern are prevalent. The wastewater system,as provided in the current concept,consists of the following key components: =Wastewater collection system and raw wastewater pump stations located in a subsurface collection tanks; ®Influent equalization tank; »Influent screens; »Packaged submerged membrane wastewater treatment plant; =Inline UV disinfection; »Treated wastewater discharge pipeline and outfall (gravity flow);and, «Sludge handling system including mechanical dewatering and dewatered sludge storage. Other alternative treatment methods,such as the use of Sequencing Batch Reactor technology might also be an appropriate fit,depending ultimately on the long-term treatment goals of the facility.For space allocation and costing purposes at this planning level phase,submerged membrane technology as the primary treatment system adequately serves as a placeholder until further investigation during detailed design determines that other treatment methods are more beneficial. Special "fogs”treatment (fats,oils,and grease)would be applied at the source -the largest of which will be the contractor's yard. 10.2.8.2.Collection System and Influent Pump Station The wastewater collection system will consist of both gravity and pumped connections.Ideally, the construction camp wastewater will flow by gravity to a centrally-located collection tank and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-16 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT then will be pumped into the wastewater treatment facility.For the permanent village,a similar but separate gravity collection system to a central storage/transfer tank is recommended.The collection system piping will consist mostly of high-density polyethylene pipe,which has a key advantage over other types of pipe as it can be frozen full of water with reduced probability of damage. From the collection tank,wastewater will be pumped to the wastewater treatment system. Similar to the raw water pipeline,as discussed above,buried depth,heat tracing and insulation considerations will require careful evaluation for freeze protection of the collection system piping during detailed design. 10.2.8.3.Wastewater Treatment System Wastewater treatment will be accomplished in a packaged,pre-manufactured treatment plant. The most common types of package wastewater treatment plants are extended aeration plants, sequencing batch reactors,oxidation ditches,contact stabilization plants,rotating biological contactors,and membrane biological reactors.Of these,the most applicable systems for this site are extended aeration plants,sequencing batch reactors,and membrane biological reactors.The current conceptual design utilizes membrane biological reactors,with the membranes being located submerged within stainless steel extended aeration tanks.This system is advantageous as it provides: =Acompact footprint,advantageous for indoor installation; *"Modular systems that can support the construction camp,but also be easily pared down for the permanent village; «Ease of construction with factory assembled treatment modules delivered to the site with minimal field construction required; «Excellent effluent water quality,capable of meeting more stringent requirements for nutrients and metals if required as discussed above;and, =»Low maintenance. The packaged treatment plant will feature aerobic wastewater treatment to remove biochemical oxygen demand (BOD)as well as membrane filtration to remove solids,bacteria,and viruses. To facilitate a compact design,while maintaining systematic redundancy,it is recommended that the membranes be submerged within each of two tanks,which will operate as batch systems cycling through aeration and decant (membrane filtration)modes.A process flow diagram for the wastewater treatment system is shown on Drawing 03-13C001. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-17 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Treated wastewater will be discharged to the Susitna River upstream of the dam.Careful planning of the outfall will be required to make sure this remains free flowing throughout the year.This includes consideration of ice depth and water movement as needed to produce an adequate mixing zone,if allowed by the discharge permit,even during the cold winter months. An effluent storage tank may be necessary to store treated wastewater and discharge it in batches to prevent freezing in the pipeline and outfall. 10.2.8.4.Sludge Handling Both the water treatment and wastewater treatment plants will generate a significant amount of residual waste streams including sludge.These treatment by-products will need to be dewatered and disposed of appropriately.The most typical method of treatment sludge disposal in cold regions is the use of a sludge pit,but these are often messy and difficult to operate in the winter. Sludge thickening and/or dewatering is recommended to reduce the volume of sludge needed to be disposed.A belt press thickener is recommended for sludge dewatering for its simple mechanics and ease of operation.The dewatered sludge can then be trucked to the dewatered sludge disposal site.The disposal site should be a solid waste landfill or separate sludge drying basins,depending on the level of dewatering achieved.Co-processing of the water treatment plant sludge may be possible with careful isolation (air gaps)of the water treatment sludges from the wastewater treatment systems. 10.2.9.Solid Waste Disposal The temporary construction camp as well as the permanent operations village will require a solid waste collection system and disposal site.Steel dumpsters are often best suited for refuse collection as they are typically easily available,large enough to hold several days of accumulation,can be locked for prevention of bear ingress,and can easily be prevented from blowing over in strong winds. The solid waste landfill will also require careful siting and sizing to protect public and environmental health especially with relation to the water source.The location relative to the airstrip is also a consideration to avoid bird hazards.Acceptable land area and adequate soil cover material is likely available adjacent to both temporary and permanent communities. Fencing will be necessary to prevent animal use (such as bears). It is recommended that both the solid waste and the sludge (solid waste)generated by the water/wastewater treatment processes be combined into a single disposal site.A single,lined sanitary landfill will reduce the disposal site footprint,streamline the collection process,and minimize waste-wildlife interactions.The proposed disposal site is located to the North of the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-18 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT airstrip at a distance of 10,000 ft.,or,another area could be chosen that maximizes the distance from the airstrip and is not within the aircraft approach/departure path to minimize bird hazards. Preliminary design calculations were completed assuming occupants in the construction camp for an eight year construction period and a permanent village design life (before major refurbishment)of 50 years following construction (total design life of 58 years).Analogous to similarly-sized cold weather,remote,communities,the solid waste landfill can be expected to contain approximately 290,000 cubic yards of material at the completion of its design life.A lined disposal site footprint of 600 ft.by 450 ft.(approximately six acres)and a nominal solid waste depth of 30 ft.will provide necessary volume.Additional capacity could be achieved by introducing an effort to compact the refuse.At the end of construction,that part of the landfill site used for the construction period could be permanently sealed and landscaped,because annual demands on the site will dramatically reduce after the construction is completed. To reduce conflicts with wildlife,specifically bears,approximately 2,500 linear ft.of bear-proof fencing will be installed around the perimeter of the landfill facility.Typically,electrified fencing is the most effective in deterring bears.This would result in an approximate area of seven acres within the fence line -but when the sealing and landscaping is performed at the end of construction the fencing could be reduced to that needed for permanent occupation of the housing. The total combined solid waste volume of the construction camp with an eight year construction time and the permanent village with a 50 year design life is shown in Table 10.2-4. Table 10.2-4.Total Combined Solid Waste Volume Municipal Solid Waste Sludge Solid Waste (CY)(cy) Construction Camp 64,500 11,500 Permanent Village 191,000 21,500 Type Total 255,500 33,000 Total Volume:288,500 The volume of watered sludge cake (using belt presses)from the water and wastewater treatment systems is based on the assumption of 15 percent solids production. approximately three wet tons/day and 0.8 wet tons/day for the camp and village,respectively, with a bulk density of approximately 50 pounds per cubic foot. Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-19 This equates to Alaska Energy Authority December 2014 ---z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.2.10.Fire Protection System The construction camp facilities and permanent village will be equipped with a reliable method for fire protection,and alarm.Any occupied buildings will be equipped with interior fire sprinklers which will be connected to the water distribution system.The State of Alaska has adopted the International Fire Code as its standard on fire protection systems.The systems will comply with the applicable requirements of the International Fire Code and the National Fire Protection Association codes and standards. In addition to the interior system,a large capacity fire protection system,serving hydrants around the construction camp and permanent infrastructure facilities,will also be installed to provide greater flows during severe events.A raw water storage and piping system separate from the treated water distribution system will be required.The large diameter fire protection pipeline serving the various hydrants would remain dry under normal conditions (to prevent freezing)and would be pressurized when needed. As described above,it is proposed to provide fire protection water supply by using the raw water storage tank which serves as the feed tank for the water treatment plant.A fire booster pump station located adjacent to the tank will be required to deliver adequate flow/pressure from the tank into the large capacity fire pipeline system. Ideally,fire protection supply would be available "by gravity”and not require use of electro- mechanical systems (pumps and generator)during an emergency.However,use of an elevated tank to store untreated and/or treated water at the camp location is not feasible due to winter temperatures.As mentioned above,an additional fire protection supply may be available on a seasonal basis from the lakes (denoted A and B)adjacent to the construction camp and permanent village site. At the end of construction,the large capacity facilities for the construction camp will be removed,leaving the system serving the permanent housing and facilities,and the airport.A fire pump truck will be garaged at the airport available for use around the site during operation. Firefighting at the power facilities will be accomplished using water pumped from the tailrace. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-20 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.3.Geotechnical Design Considerations The foundation characterization necessary for engineering analyses and feasibility design decisions is usually performed with the benefit of a focused site investigation.In this case, until the full site investigation and laboratory testing has been completed,including completion of drilling in the river channel,geophysical surveys,exploratory adits and in situ testing,it has been necessary to characterize the foundation based on the geotechnical information available from studies performed in the 1970s and 80s and those performed through the 2014 investigation program.An exploration and testing work plan has been developed of which a portion of the recommended investigations for feasibility has been completed (MWH,2013).The site investigation and testing program are a "work in progress”. 10.3.1.Engineering Geology The general geological setting and site conditions are described in Section 6.3.The engineering geology characterization,design parameters and considerations related to the overburden; bedrock units;discontinuities (e.g.,joints;shears,and fracture zones),weathering and alteration; geological features and the relict channel are described below. 10.3.1.1. Overburden Overburden in the dam site area consists of till,colluvium,and talus the limits of which are shown on Drawing 01-01GT003.The overburden thickness in the dam abutments is typically less than 20 ft.thick but in areas may reach a thickness of 50 ft.or more (e.g.,left abutment upstream of the dam axis.Subsurface investigations indicate that the contact between the overburden and bedrock is relatively unweathered and distinct.For additional information refer to the top of bedrock contour map (Drawing 01-01GT004). In the river channel,alluvium beneath the proposed dam site area is typically between 70 to 80 ft.thick,but it is up to 140 ft.thick (Drawing 01-01GT007)within the two bedrock depressions located upstream of the dam.Within the dam footprint,alluvium ranges from about 60 to 105 ft.thick.The alluvium is comprised primarily of well-graded coarse-grained gravels, sandy gravels,and gravelly sands with cobbles and boulders (Harza-Ebasco 1983).The boulders are visible on the gravel bars and banks of the river and generally range from 1 to 3 ft.in diameter but some are as large as 5 ft.in diameter.Near the south abutment the alluvium transitions to a thick talus deposit of diorite boulders. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-21 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.3.1.2.Bedrock Units The dam site is primarily underlain by Tertiary volcanic intrusions that range in composition from diorite to quartz diorite to granodiorite (Drawing 01-01GT006).Therefore,the foundation for the dam,spillway,powerhouse and all other principal structures will involve diorite lithology.The bedrock is medium to dark green gray,fine to medium grained,generally hard to very hard,strong to very strong,competent,and generally fresh.However,bedrock is typically slightly to moderately weathered at the top of rock and along discontinuities to depths of 50 to 80 ft.Below the surficial zone of weathering,the rock mass is typically closely to moderately closely fractured.In outcrop,joints are typically tight to open,although they are mostly tight at greater depths,rough to smooth in profile,planar,and some contain iron stains,carbonate deposits or are slickensided.At depth,weathering locally can occur in areas of highly fractured rock,and the fractured rock may also contain shear zones with clay and breccia and/or be hydrothermally altered. Bedrock directly downstream of and at higher elevations above the left abutment of the dam site consists of extrusive volcanics,mostly andesite porphyry which varies locally to dacite or latite. Andesite is not known to occur in the foundation of the dam or appurtenant structures.The andesite is similar in chemical composition to the diorite and is generally dark gray to black, slightly weathered,strong to very strong,competent and in places contains diorite xenoliths. The diorite pluton has been intruded by mafic and felsic dikes that are generally a few feet wide, and exhibit contacts that are tight and competent.Felsic dikes are observed in outcrop as well as boreholes.The dikes are light gray,aphanitic to medium grained,fresh,hard,and strong to very strong.Mafic dikes are less common than felsic dikes but were observed in outcrop and in several boreholes.The mafic dikes typically consist of andesite and are less than 5 ft.wide. They are dark gray to green-gray,fine-grained,fresh,hard,and strong. In a number of boreholes,hydrothermally altered diorite was encountered.The degree of alteration encountered is highly variable,but in the areas of severe alteration,the rock can be weak to extremely weak and contain zones of rock completely altered to clay minerals over several inches.These altered zones are rarely seen in outcrop because the bedrock has been eroded into gullies where alteration is moderate to severe.Where encountered in rock cores,the (apparent)width of the altered zones in boreholes range up to 20 ft.but are typically less than 5 ft.,and altered rock is often associated with close fracturing,fracture zones,or shear zones. The transition between fresh and altered rock is gradational over a few inches to few feet. Representative NQ and HQ rock core samples were tested to determine the engineering properties of the diorite,andesite,and altered diorite.Since the properties of diorite,quartz diorite,and granodiorite were found to be similar,they were all recorded under the heading for Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-22 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT diorite.It should be noted that in general samples from the upper 250 to 300 ft.were selected as these are considered more representative of conditions affecting foundation design.However, where the number of samples was limited (e.g.sonic velocity),results from all depths were considered. Due to the quality and extent of moderately to highly altered rock,which occurs in some locations over intervals of a few feet of core,high quality samples could not be collected or tested reliably and are therefore not well represented in the testing and results below.Such samples are expected to be of lower density,strength,and deformability. The rock test results reported in the following sections include data from studies performed in the 1980s and the current studies,2011 to 2014 and the level of investigations and testing is considered adequate for feasibility level design purposes.Additional geotechnical work including drilling,down-hole testing,geophysics,exploratory adits,laboratory and in situ testing,will be required as part of the detailed design. 10.3.1.3.Engineering Properties of Rock Material 10.3.1.3.1.Unit Weight Tests for unit weights were performed in conjunction with unconfined compression and tensile strength tests.The results from testing are summarized in Table 10.3-1: Table 10.3-1.Summary of Unit Weight Tests Rock Type Number of Minimum Maximum Mean +Standard Deviation ests (pef)(pcf)(pcf) Diorite 22 164.8 172.0 168.0 +1.6 Andesite 10 162.6 166.9 164.8 +17 Altered Diorite 1 165.6 165.6 165.6 The results are consistent for these rock types,and the unit weight of altered diorite is slightly less than that of fresh diorite,which is expected since some of the minerals have been altered to clay. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-23 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years, 10.3.1.3.2.Unconfined Compressive Strength The results from unconfined compressive strength (UCS)tests are summarized in Table 10.3-2. Table 10.3-2.Summary of Unconfined Compression Strength Tests Rock Type Number of Minimum Maximum Mean +Standard Deviationests(psi)(psi)(psi) Diorite 33 7,610 31,130 21,590 +6,200 Andesite 10 6,100 26,210 17,000 +6,100 Altered Diorite 9 1,580 15,500 7,600 +4,100 The diorite and andesite are both classified as strong to very strong.Excluding the altered diorite,more than 90 percent of andesite and diorite samples have UCS greater than 12,000 psi. Although not represented,zones where the rock is highly weathered and altered may be classified as very weak to weak over short (few feet)intervals. 10.3.1.3.3.Point Load Index Testing Point load index testing was performed at regular intervals on core from two boreholes drilled in 1984 and at select locations during other campaigns.The ease of this test enables a large number of samples to be tested covering a wider range of sample quality than UCS testing.The point load index (PLI)strength tests were used to estimate the compressive strength of the rock by applying a UCS:PLI ratio equal to 24.9 (HQ-size core)and 21.9 (NQ-size core)for samples from 1984.A ratio of 19 was used for samples tested in 2012 (HQ -size core)based on an evaluation of the testing data.The results from point load index tests are summarized in Table 10.3-3. Table 10.3-3.Summary of Point Load Index Strengths Rock Type Number of Minimum Maximum Mean +Standard Deviationests(psi)(psi)(psi) Diorite 77 4,760 31,330 18,460 +5,830 Andesite 6 -19,620 +3,150 Altered Diorite 13 3,710 26,620 11,590 +6,600 In addition to the results presented above,more than 300 point load tests were performed during the 1980-1981 study,but detailed test data are not available for analysis.In general,the 1980- 1981 tests had correlated compressive strengths ranging from less than 10,000 psi to more than 40,000 psi.Although the strengths from testing in 1980-1981 are higher than those from 1984 and 2011 to 2012,both data sets indicate the rock is strong to very strong,but less so in areas of localized alteration. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-24 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT In general,the compressive strengths estimated from point load index testing are in the same range as unconfined compressive strength tests and indicate that fresh,sound andesite and diorite bedrock is strong to very strong,and zones of slightly altered rock can be moderately strong to strong. 10.3.1.3.4.Tensile Strength Brazilian tensile strength (Tpr)results summarized in Table 10.3-4 indicate a high tensile strength.The ratio of the mean tensile strength to the UCS (Tpr /UCS)ranges from about 8 percent and 10 percent for the three rock types.In general,the tensile strength is between 5 and 10 percent of the UCS;thus,the test results are consistent with expectations. Table 10.3-4.Summary of Brazilian Tensile Strength Tests Number of Minimum Maximum Mean +Standard Ter!UCSRockTypeTests(psi)(psi)Deviation (psi)(%) Diorite 9 1,820 2,360 2,160 +170 10% Andesite 3 1,620 1,720 1,680 +60 9.9% Altered Diorite 2 470 810 640 +240 8.4% 10.3.1.3.5.Intact Rock Deformation Properties Elastic properties were measured on intact samples under unconfined compression using electronic strain gages bonded to the sample in the horizontal and vertical directions.Stress, axial,diametric,and volumetric strain were measured and plotted against axial stress from which the intact modulus and Poisson's ratio were calculated at 50 percent failure load.The tangent modulus was calculated for the tests performed in the 1980s,and the secant modulus was calculated for the 2012 and 2014 tests.The results from all testing are combined in Table 10.3-5. Table 10.3-5.Summary of Intact Rock Modulus Parameters Rock Type |Numberof |Minimum |Maximum fe iation |Poison'psi)(x 108 psi)(x 108 psi)Ratio Diorite 21 6.7 12.8 10.0+1.4 0.23 +0.04 Andesite 4 5.6 10.5 8.6+2.2 0.25 +0.01 Altered Diorite 7 2.0 10.9 6.7+3.3 0.21 +0.06 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-25 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.3.1.3.6.Dynamic Elastic Properties Compressional (V,)and shear (V;)wave velocities were measured on five samples of intact diorite.The results of the tests are summarized in Table 10.3-6. Table 10.3-6.Summary of Compressional and Shear Wave Velocities and Dynamic Properties Rock Type Numjer of Vp (ft./s)Vs (m/s)ets)Poi eae io Diorite 5 17,050 +820 9,670 +320 9.0+1.0 0.28 +0.03 Andesite 0 ----- Altered Diorite 0 ----- Note:Mean values and standard deviations are reported. The sonic velocity testing of intact samples indicates that the static and dynamic deformation properties for intact diorite are similar. 10.3.1.4.Rock Mass Characterization and Properties The rock mass characterization and material properties used in the analyses of the proposed design configuration draws heavily on the studies performed in the 1980s but is supplemented by information collected in 2012 and 2014. 10.3.1.4.1.Rock Quality Designation Rock Quality Designation (RQD)was determined for all rock cores extracted during the 1980s and the current investigations (2011 to 2014).Some of the boreholes implemented during the USACE studies were rotary drilled without core recovery so RQDs values are not available from them and the data from the 2014 investigations has not yet been verified,but available results since 2011 are consistent with results from previous investigations. Rock quality encountered in the drilling was generally good to excellent with RQD values averaging between 75 and 90 percent.In general,rock quality improves with depth,with the upper 50 to 80 ft.of rock being weathered and more fractured and RQD averaging between 40 and 70 percent.Below this weathered zone,rock quality is good to excellent (85 percent to 100 percent)with localized zones of fractured,sheared,or altered rock,which are generally one to five feet thick,but can occasionally be up to 30 ft.thick.RQD correlates well with the hydraulic conductivity (sometimes referred to as "rock mass permeability”)testing data (see Section 0), which is normally a function of rock quality. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-26 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT In general,weathering appears to be primarily physical in nature,with weathered rock being restricted to the upper 40 ft.at the dam site.The weathering is light to moderate in joints,with penetration generally less than an inch from the joint wall.Rock within shear and fracture zones is more weathered,and many of these zones exhibit chemical weathering and hydrothermal alteration. 10.3.1.4.2.Rock Mass Characterization Geological field data and empirical methods were used to assess rock mass properties for the feasibility design.This consisted of the following: «Evaluate foundation geologic conditions by performing geologic mapping,core drilling, and in situ testing. «Identify different engineering geologic units having generally uniform properties with respect to rock strength,degree of fracturing,and weathering. =Characterize and develop rock mass classification for each engineering geologic unit and assign material properties. Using data from the studies through 2012 and 2014 geologic mapping in and adjacent to the dam site footprint area,rock mass classifications were carried out in order to identify and differentiate distinct engineering units using the 1989 Bieniawski rock mechanics rating system (RMRgo). RMRgg is computed using the following six parameters: =Uniaxial compressive strength; =RQD; »Spacing of discontinuities; =Condition of discontinuities; «Groundwater conditions;and «Adjustment for orientation of discontinuities. The borehole log for each hole was reviewed,and the character of the rock in each core run was evaluated to estimate the RMRgg for each run.The Geological Strength Index (GSI;Hoek and Marinos 2000)was then estimated using Bieniawski's (1989)joint condition (Jcond)and an evaluation of the Rock Quality Designation (RQD)using the relationship proposed by Hoek et al.(2013)as described below: GSI =1.5Jcondgg+RQD/2 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-27 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. In addition to empirical relationship between GSI and RMR from the drilling investigation,GSI is typically assessed during mapping.At the dam site,the outcrops generally have a blocky to massive appearance with two or three prominent joints sets plus minor sets.Typically JS1 and JS2 were encountered and one of the minor sets or random sets formed the other prominent set. Block sizes ranged from small (2.5 inches to 8 inches per side)to large (2 ft.to 6 ft.per side),but were typically medium sized (8 inches to 2 ft.per side).Medium-sized blocks typically form the boulder talus observed on steep slopes,below rock outcrops,and in gullies throughout the dam site. The jointing creates a blocky to very blocky rock mass structure with good to fair quality joint surfaces when evaluated with respect to GSI.The tight to open joints give the rock mass a tight to slightly loosened structure with a moderate to high degree of block interlocking.Based on these characterizations,the GSI for all measured outcrops ranged between 40 and 75.However, the GSI was typically between 55 and 65,and overall averaged about 60 in outcrop. Overall,the dam site is underlain by relatively lightly to moderately fractured diorite intersected by discrete geologic features and linear zones of moderately to highly fractured rock,narrow shear zones and zones of hydrothermal alteration.Considering the type of rock,distribution,and quality that has been encountered,the bedrock is divided into three engineering units,which are expected to have distinctly different engineering properties.It is important to distinguish between different materials because heterogeneous foundation materials can introduce stress concentrations into the foundation and structure,which need to be accounted during design.The following describes each of the units and Table 10.3-7 summarizes the GSI for each of the units. 1.Engineering Unit 1 -Sound Bedrock -Fresh,hard,strong to very strong,and lightly to moderately fractured and jointed diorite.The rock mass is characterized as blocky to very blocky.Joints are typically rough to smooth,slightly weathered to fresh,and tight. In the upper 20 ft.of the foundation,where the bedrock may be slightly more weathered, the GSI generally ranges from about 40 to 70,and averages about 55.Below 20 ft.depth, the GSI for Engineering Unit |generally ranges from about 50 to 80 and averages about 65. 2.Engineering Unit 2 -Moderately to Highly Fractured Bedrock -Fresh to slightly weathered,hard,strong,and moderately to highly fractured diorite (refer to Section 10.3.1.5.3).The rock mass is characterized as very block to sheared/disturbed/seamy with joints that are rough to smooth,slightly to moderately weathered to fresh,and tight. The character of the rock within the upper 20 ft.of the foundation is similar to that at depth.The GSI for Engineering Unit 2 generally ranges from about 30 to 50,and averages about 40. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-28 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 3.Engineering Unit 3 -Sheared and Altered Bedrock -Bedrock within discrete 5 to 30 ft. wide zones (apparent width)consisting of highly fractured rock with shear zones up to 2 ft.wide and zones of alteration (see Section 10.3.1.5.4 and Section 10.3.1.5.5).The rock mass is moderately to highly weathered/altered,weak to strong,and characterized as sheared/disturbed/seamy.Joints are smooth to slickensided,slightly to moderately weathered and altered,tight to partly open.The GSI for this engineering unit generally ranges from about 15 to 40,and averages about 25. Table 10.3-7.Ranges and Average GSI for Engineering Units Depth Below GSI Material Ground Surface ,;(feet)Min Maximum -_|Recommended oo ; 0 to 201 40 70 55EngineeringUnit1Greaterthan20608065 Engineering Unit 2 2 All 30 50 40 Engineering Unit 3 2 All 15 30 25 Note: 1.Recommended value based on geologic mapping of outcrops in 2014 and degree of weathering observed in rock cores in the upper 20 ft. 2.The minimum,maximum,and recommended GSI values for Engineering Unit 2 and Unit 3 are slightly higher at depths greater than 20 ft.,but the difference is considered minor (less than five);thus,these units are described as having a single set of values. 10.3.1.4.3.Rock Mass Strength and Deformability Rock mass strength and deformation properties are developed using empirical relationships that combined rock mass characterization with the results from laboratory testing. Strength and deformation parameters for each of the engineering units are computed using RocLab software (RocScience,Inc.)and empirically based formulations and the anticipated foundation loading conditions.The rock mass strength is based on the generalized non-linear Hoek-Brown criterion (Hoek et al.2002),from which equivalent Mohr-Coulomb strength parameters for the rock mass in terms of cohesion and friction angle are calculated.The rock mass deformation modulus is calculated using the formulation by Hoek and Diederichs (2006). For each of the three engineering units at the dam site foundation the parameters listed in Table 10.3-8 are recommended to be used to estimate the rock mass strength and deformation parameters -based on sample characteristics from all the site investigations to date. Recommended rock mass strength and deformation parameters are listed in Table 10.3-9. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-29 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.3-8.Recommended Intact Rock Properties Unit Hoek-Brown Intact Rock .' Material Dep feet)rval Weight tosh constant Modulus Porsson s(pcf)P (m)(1 x 10 psi) oo ; 0 to 20 168 21,590 25 10 0.23EngineeringUnit1Greaterthan2016821,590 25 10 0.23 Engineering Unit 2 All 168 15,300 20 8.6 0.23 Engineering Unit 3 All 165 7,600 20 2.0 0.21 Table 10.3-9.Recommended Rock Mass Strength and Deformation Parameters ."Rock Mass Material Perla GSI "a <rcn Deformation ModulusPg(x 106 psi) 0 to 20 55 340 53°4.1EngineeringUnit1Greaterthan206550057°6.3 Engineering Unit 2 All 40 240 48°14 Engineering Unit 3 All 25 130 38°0.12 Note: 1.Based on confining pressure of about 720 psi based on unit weight of rock and assuming a dam height of about 700 feet. 2.The Disturbance Factor,D varies from 0 to 1.The effects of the disturbance due to blasting are expected to be shallow with some minor stress relief occurring within 10 feet of the ground surface.This depth is relatively minor compared to the depth influence of the dam on the foundation or high slopes.Therefore,a D =0 is recommended for calculating the rock mass strength and deformation modulus. 10.3.1.4.4.Rock Mass Permeability Water pressure tests were performed in exploratory boreholes during all investigations phases. Rock mass permeability is controlled by the jointing,fracturing,weathering,and if present,ice within joints. The rock mass permeability is based on the secondary permeability formed by joints since the intact rock is considered impermeable.The rock mass permeability of the bedrock generally ranges between 1 x 10°cm/sec to 2 x 10%cm/sec.As would be expected in fractured rock near the surface or in localized areas of fracture zones,rock mass permeability can be as much as 4 x 10*cm/sec to 7 x 10%cm/sec.In a few instances,water takes exceeded the pump capacity and the desired injection pressures could not be achieved.In such cases the rock mass permeability may be on the order of 1 x 10°cm/s or greater.Overall,the rock mass permeability tends to decrease with depth as joint frequency is reduced and joints have narrower aperture. Artesian conditions were encountered in borehole BH-12 along the upper left abutment at a depth of about 325 ft.,which corresponded with the altered and sheared contact between diorite Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-30 December 2014 o Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT and andesite.Because of the structural relationship of these two rock units,greater hydraulic conductivity is likely to be expected at the contact. Frozen ground conditions are believed to be present locally within the rock mass and likely has an effect on rock mass permeability.Ice-filled joints restrict flow through the rock mass,thereby giving misleading values of low rock mass permeability values.Therefore,thawing of localized areas of the foundation and/or post-construction foundation treatment will be required to obtain more reliable estimates and for foundation treatments,such as grouting.Refer to Section 0 for additional discussion of approaches to grouting of frozen ground. 10.3.1.5.Rock Mass Structure From geologic mapping and core drilling at the dam site,three major classes of discontinuities have been identified in the rock mass.As described in Section 6.3,the most common and pervasive class through the site are joints.Fracture zones,which are less common than joints, consist primarily of closely spaced or concentrated areas of jointed rock.Least common are shear zones,which exhibit some evidence of relative displacement such as the presence of gouge,breccia,and/or slickensides.The most prominent of the fracture and shear zones have been termed "Geologic Features”beginning with reports by Acres (1982a).Joints,fracture, shear,and alteration zones exhibit a wide range of characteristics.More detailed characteristics of each type of discontinuity are described in the following subsections. 10.3.7.5.1.Joints Mapping performed during the 1980s and site investigations performed between 2012 and 2014 have identified four joint sets at the site.The orientations of these four sets,which includes two primary and two secondary sets are summarized in Table 10.3-10.Some minor subsets and other random joints are also encountered in outcrop and boreholes.The joint sets are common to all rock types at the dam site.For detailed discussion ofjoints refer to Section 6.3 of this report. Table 10.3-10.Summary of Joint Set Orientations Joint Strike Strike Average DipSet(Azimuth)(Azimuth) JS1 270°to 330°300°80°SW to 70°NE JS2 025°to 060°040°80°SE to 70°NW JS3 340°to 020°350°70°E to 80°W JS4 Variable Variable Less than 35° Note:Strikes are reported in the upper hemisphere regardless of the dip direction. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-31 December 2014 -w-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Orientations were also evaluated with respect to four quadrants (e.g.,NE,SE)around the dam axis and for the north and south banks to evaluate potential spatial variations.Figure 10.3-1 shows stereonets with contoured poles representing the orientation of discontinuities from 2014 surface geologic mapping,in which northwest-southeast trending set,northeast-southwest set, and shallow dipping sets were identified.Minor variations were observed when evaluating the data for the north and south banks.However,the northwest quadrant exhibited a greater abundance of north-south trending discontinuities (JS3)than in other quadrants,which was similarly reported by Acres (1982b).These joints sets and some minor subsets were used to evaluate three dimensional wedges in each abutment which were subjected to limit equilibrium sliding stability analyses described in Section 10.3.3.2. The discontinuity data from downhole logging performed in 2012 and 2014 are shown in Figure 10.3-2.The downhole survey encountered discontinuities that are mostly shallow dipping;the northwest-southeast trending set is less prominent;and the northeast-southwest trending joint set is nearly absent.This inconsistency,when compared to the surface mapping data set,is attributable to the bias introduced by the orientation of the boreholes drilled and the linear nature of downhole logging,as well as the selected borehole orientation with respect to JS1 and JS2. The 2012 and 2014 boreholes in the dam site footprint area are steeply inclined and trend to the northeast-southwest or north-south directions.Holes of this orientation and inclination will encounter shallow dipping features with greater frequency than steeply inclined joints or those that tend to parallel the borehole.Bias correction was applied during the stereographic analysis, but the bias cannot be eliminated.Furthermore,the data sets cannot be combined due to number of discontinuities within each data set.It is easy for the analyst to identify discontinuities on the borehole image such that a large number of discontinuities can be selected -in this case 3312 discontinuities -including many closely spaced joints of the same set.During geologic mapping of rock outcrops,the focus was on identifying the major and minor sets (plus prominent random joints)within each outcrop but limiting the number of measurements to only those sets present, and this approach yielded about 558 measurements.Therefore,the data sets from surface mapping and the downhole logging were evaluated separately and then compared to verify that the relevant joint sets have been identified. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-32 December 2014 =) Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Fisher Concentrations %of total per 1.0 %area 0.00 0.10 % 0.10 0.46% 0.46 082% 0.82 119% 119 155% 155 191% 1.91 2.27% 2.27 2.64% 2.64 3.00% >3.00 %poyentliNo Bias Correction Max.Conc.=3.7659% Equal Angle Lower Hemisphere 558 Poles 558 Entries S Figure 10.3-1.Lower Hemisphere,Equal Angle Stereograph Plots of Principal Joint Sets from Surface Mapping Fisher Concentrations %of total per 1.0 %area 0.00 0.10% 0.10 0.40% 0.40 070% 0.70 1.00% 1.00 1.30% 1.30 1.60% 1.60 1.90% 190 220% 2.20 250% |eaenanse |>2.50% Terzaghi Correction Min.Bias Angle =15 deg Max.Conc.=4.2368% Equal Angle Lower Hemisphere 3312 Poles 3312 Entries Figure 10.3-2.Lower Hemisphere,Equal Angle Stereograph Plots of Principal Joint Sets from Downhole Logging Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-33 December 2014 Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. After the joint sets were identified,the individual discontinuities recorded during mapping were assigned to respective joint sets and grouped so that the characteristics of each joint set could be evaluated.Joints were described in accordance with International Society for Rock Mechanics (ISRM)guidelines (1978)such that joint engineering properties could be developed.In addition, the joint spacing was evaluated to estimate the approximate block size formed by the intersecting joints.The characteristics of the joint sets are summarized in Table 10.3-11 and are described below. Table 10.3-11.Summary of Joint Set Characteristics from Geologic Mapping ..Typical AmplitudeJoint|Joint :Shape and a: ;Persistence Aperture and Filling RoughnessSet|Spacing (ft)Surface Roughness URC) 16”Tight to open,clean with local iron 9JS1(4°to 4)10 to 60 Planar,rough to locally smooth staining and carbonate infill (4 to 16) 15”Very tight to open,clean with local 9JS2(2°to 3!3 to 30 Planar,rough to locally smooth iron staining (2 to 16) JS3 10”Less than 3 Planar to locally irregular,rough to Tight to open,iron staining or 9 (4"to 12”)to 30 smooth carbonate infill (6 to 14) 16”Tight to very wide,clean with local 8JS4(1”to 5')3t0 30 Planar,rough to locally smooth iron staining and carbonate infill (2 to 16) Note:Parenthetic value is the range. Joint Set 1 (JS1)and JS2 are major sets that occur throughout the site area,although the orientation of JS2 varies slightly around the site.JS3 is generally more prominent downstream of the dam site,particularly in the northwest quadrant.JS4 is also widely distributed throughout the site but has shallow dips in all directions.Other minor subsets and random joints are also present,but the focus is on the four principal joint sets. Joint surfaces for JS1 are typically planar,smooth to rough,and exhibit minor iron staining and carbonate deposits.The joint spacing typically ranges from 4 inches and 4 ft.and average about 16 inches.The joints typically have medium to high persistence,10 to 60 ft.,but is often dependent on the height of the outcrop,which can be more than 60 ft.in some places.These joints are generally tight,but open joints of this set are found in outcrop.The larger amplitude roughness (JRC)ranges from 4 to 16 and averages about 9.Fracture zones,shear zones,and alteration zones are most frequently oriented parallel to JS1. Downstream of the dam JS2 joints typically dip to the northwest.The joints are generally planar, rough to smooth,and are clean or can have iron staining and carbonate deposits.Joint spacing typically ranges from 2 inches to 3 ft.and averages approximately 15 inches.JS2 joints have moderate persistence,typically between 10 and 30 ft.Joints are very tight to open,and in outcrop were generally open.The larger amplitude roughness (JRC)ranged from 2 to 16 and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-34 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT averages about 9.No fracture,shear,or alteration zones that have been identified are associated with JS2. JS3 is considered a minor set,although it is locally prominent downstream of the dam, particularly in the northern bank.The joint spacing typically ranges from 4 inches to 12 inches, and averages about 10 inches.Joints are generally planar to irregular,and rough to smooth. Joints are tight to open with minor carbonate and iron staining.The larger amplitude roughness (JRC)ranged from 6 to 14 and averages about 9.Fracture and shear zones parallel to JS3 were mapped at a number of locations,but these tend to be less critical features with respect to the dam footprint than structures of JS1. Shallow dipping joints comprise JS4 and are found throughout the dam site and dip less than 30 in nearly all directions,although there is slightly greater percentage dipping to the northeast. Joints in this set are planar,smooth to rough,tight to very wide open and in some locations show carbonate deposits and iron staining.The joint spacing ranges from about |inch to 5 ft.and averages about 16 inches.Joints from this set typically have low to moderate persistence,3 to 30 ft.The larger amplitude roughness (JRC)ranged from 2 to 16 and averages about 8.No significant mineralization,shearing,fracture,or alteration zones appear to be associated with this joint set. It has been postulated that gently inclined and flat lying joints (less than 30°dip)may be the result of stress relief after glacial unloading and/or erosion of the river valley.The data from the 2012 and 2014 downhole televiewer logs were evaluated to assess the ratio of shallow joints per linear foot of vertical depth below ground surface to total joints per linear foot of survey for depth in increments of 50 ft.(i.e.depth below ground surface 0 to 50 ft.,50 to 100 ft.,etc.).If related to stress relief,one would expect the ratio of shallow dipping joints to decrease with depth below ground surface (adjustments were made to account for hole inclination and depth of discontinuity). The analysis indicates that joints dipping less than 30°account for about 40 percent of joints down to depths of 600 ft.below ground surface (see Figure 10.3-3).The percentages of joints dipping less than 15°were also plotted against depth,and again the percentage of shallow dipping joints remains fairly uniform with depth,generally ranging from 12 to 20 percent.The relatively consistent percentage of shallow dipping joints to depths as much as 600 ft.below ground surface suggests the effect of stress relief extends to depths below 600 ft.or that shallow dipping joints are not related to stress relief or rebound but are instead formed by other geologic processes. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-35 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 2.50 100% -> Total jts/ft survey -r 90%2.25 -O shallow jts/ft survey --Percentage (Shallow<30/Total Jts.) 2.00 -+80% <Percentage (Shallow<15/Total Jts.) 70% NO 60%L 50% 40%LoabJointsPerFootofSurveyPerformedrayNwaBae Pva0XkPoO\LF).EE RL” 0.00 1 1 7 T T 1 T 1 T t T 0%PercentageShallowJointstoTotalJoints50-100150-200550-600100-150200-250300-350500-550Vertical Depth Below Ground (ft) Figure 10.3-3.Evaluation of Shallow Joints from Downhole Logs 10.3.1.5.2.Fracture,Shear,and Alteration Zones As described in Section 6.3 fracture,shear,and alteration zones and combinations thereof have been mapped at the site,although the majority of mapped features are less than 10 ft.wide and discontinuous.Where zones more than 10 ft.wide were identified,both boundaries have been delineated on the geologic maps and sections.In general,these features are aligned with JS1 and some with JS3.The characteristics of fracture,shear,and alteration zones are detailed in Section 6.3 and summarized below.The primary focus here is on those geologic features that are expected to be evident in the footprint of the dam foundation. 10.3.1.5.3.Fracture Zones Fracture zones consist of very closely to closely spaced (less than 1 inch to 8 inches)typically over widths less than 10 ft.of jointed rock where no apparent relative movement has occurred. Fracture zones are common to all rock types and are generally encountered in boreholes and less frequently observed in outcrop.In general,fracture zones consist of rock that is more fractured, Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-36 December 2014 =) O -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT very close to closely fractured zones comprised of poorer quality rock mass.In addition,the RQD and GSI within fracture zones may be quite low and such zones are generally associated with increased hydraulic conductivity. 10.3.1.5.4.Shear Zones A shear zone is defined as a zone of rock along which there has been measurable or discernable displacement characterized by breccia,gouge,and/or slickensides indicating relative movement and cataclasis.Such shear zones are common to all rock types at the site and are most frequently associated with fracture zones and moderately to severely altered rock.These shear zones typically trend northwest-southeast (paralleling JS1),and particularly trend this direction within the dam footprint.Infilling within shear zones typically consists of coarse to fine sand-size rock fragments weathered to tan-yellow,orange,brown and sometimes includes a narrow zone (few inches)of silt or clay gouge within the central portion.Both the breccia and gouge are soft to medium stiff,friable,and erodible.Thicknesses of these shear zones in the dam footprint based on the current geologic mapping are generally less than |to 2 ft.wide.In the broader dam site area,Acres (1982b)had reported that shear zones vary from less than 0.1 inch up to 10 ft. (apparent thickness).The reason for this discrepancy is unclear but it may be due to how a shear zone is defined. 10.3.1.5.5.Alteration Zones Alteration zones are areas where hydrothermal solutions have caused the chemical breakdown of the feldspars and mafic minerals.The products of alteration are kaolinitic clay from feldspar and chlorite from mafic minerals.These zones are found in both the diorite and in the andesite porphyry but appear to be less common in the andesite porphyry. Most of the information regarding alteration zones is from the boreholes since alteration zones are rarely seen in outcrop because they are relatively easily eroded.They are exposed on the surface on the north bank in one outcrop at river level near the dam axis.The degree of alteration is highly variable ranging from slight,where the feldspars show discoloration,to complete where the feldspars and mafics are completely altered to clay and chlorite.Widths of these zones most often range up to 20 ft.but are generally less than 5 ft.An exception is in the inclined borehole BH-12,on the south bank and downstream of the dam,which encountered very thick zones of alternation (slight or moderate)over a length of approximately 260 ft.with discrete shears and zones of shearing The orientation of the zones of alteration with respect to the borehole are not known,however if it assumed that each zone has a similar orientation and is near vertical the maximum apparent width may be on the order of 215 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-37 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. No increase in joint frequency is evident in association with these alteration zones.Thin (less than 2 inches wide)shear zones are associated with a number of the alteration zones.RQDs are generally low;however,core recovery is generally more than 90 percent within the alteration zones.The transition from fresh to altered rock is gradational,generally occurring over less than one foot. Given the character of the altered zones with respect to the dimensions of the dam foundation, these features are not anticipated to be sources of major structural weaknesses in the otherwise sound bedrock foundation.However,foundation preparation will require local dental treatment to remove soft materials at the foundation level and replacement with dental concrete.If associated with fracture zones and shear zones,localized grouting may also be necessary to control seepage,prevent piping,and to improve strength and deformability of the foundation. 10.3.1.5.6.Geologic Feature GF4B In general,fracture,shear and alteration zones will be encountered through the project area in all types of excavations.Analysis and review of the existing data on the dam site geology was made and site investigations were performed that included lineament analysis of the dam site using the newly acquired digital elevation data and abutment geologic mapping of and drilling across the largely northwest-trending structural features.The goal was to identify and characterize the geologic features that will intersect the dam foundation.Refer to Section 6.3 and Drawing 01- 01GT006 for additional detailed descriptions of the geologic features. GF4B consists of multiple discrete fracture zones,splays or branches,oriented in the northwest- southeast direction,that intersect a north-south trending fracture zone.The fracture zones,which may contain narrow shear zones typically less than 8 inches wide consisting of breccia and clay gouge,are correlated to several prominent gullies immediately upstream of the dam right abutment between the shoreline to about El.1850 ft.that are as much as 40 to 50 ft.wide. Although the gullies appear wide at the surface,information from mapping and drilling suggest that the fracture zones are much narrower and the geomorphic expressions are a manifestation of erosion processes. Based on a review of rock core from DH12-3,bedrock in this area of the foundation alternates between zones of very closely to closely fractured rock in the upper 300 ft.It is postulated that the more highly fractured zones correlate with gullies manifested at the ground surface and less fractured core correlates with more competent outcrops.Some of the fracture zones contain some minor shear zones (i.e.less than 1-ft.wide).Below 300 ft.,fracture zones in this borehole are generally less than about 5 to 7 ft.wide and occur less frequently in what is generally moderately close fractured rock.Discontinuities within fracture zones are typically tight, surfaces are rough to smooth with iron oxide staining,white carbonate deposits,or chlorite,and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-38 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT some surfaces contain clay infilling with slickensides.The fracture zones appear to contain some minor shear zones,which are typically less than a few feet wide. Although considered relatively minor features with respect to the dimensions of the dam,due to the location and trend of these fracture zones and similar fracture zones and minor shear zones, the project structures were moved slightly downstream,to reduce the potential impacts these or similar structural features could have on the dam foundation.However,where encountered in the foundation,highly fractured rock and shear zones might need to require mitigation by means of dental excavation and backfilling,consolidation grouting to improve strength and deformability,and stitch grouting to reduce seepage. Projecting GF4B to the north and northwest would intersect the alignments of the diversion tunnel and access tunnel excavations.Localized sections of highly fractured rock are anticipated to be encountered in the tunnels which may require increased rock support to achieve suitably stable openings.In addition,the more highly fractured rock may be a source of groundwater infiltration and may require water control grouting to reduce groundwater inflow and to facilitate placement of concrete and shotcrete linings. 10.3.1.5.7.Geologic Feature GF5 GFS consists of multiple fracture zones with some minor shear zones that cross the dam footprint on the lower right abutment.The geologic structures comprising GFS5 are similar to those of GF4B and trend northwest-southeast (310°to 320°).The structures are steeply dipping,and are anticipated to be encountered in the dam and spillway foundations and diversion tunnel excavations. Although there is no topographic expression of this fracture and shear zones at the surface on the north abutment above about El.1700 ft.,GFS was correlated with several shear and fracture zones intersected in borehole DH-9 (Acres 1982b).However,the orientation of the fracture zone is not known and therefore cannot be positively correlated with GF5.Regardless,the joints and fractures in DH-9 are generally iron stained and carbonate-coated,and faint slickensides occur on some surfaces.The RQDs in DH-9 are low,with an average of 57 percent.Hydraulic conductivities are generally between 10°'cm/sec and 10°cm/sec,and decrease with depth. In 2012 and 2014,inclined boreholes DH12-4 and DH14-11 were drilled across this gully on the right abutment approximately normal to GF5.Based on the site investigations and a review of the previous studies,it appears that GF5 consists of several fracture zones typically ranging from about 5 to 10 ft.in width and some contain shear zones up 20 inches wide.While data relative to GF5 lacks compelling demonstration for the presence of a significant,through-going fault or shear zone,it is depicted as the widest and most continuous feature in the dam foundation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-39 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. It is expected that GF5 may require special treatment in the dam foundation,including measures such as over-excavation or dental excavation and replacement with concrete.In addition, consolidation and stitch grouting area may be required to improve foundation characteristics. GF5 is also expected to intersect the proposed diversion tunnel and access tunnel and may require additional rock support to achieve suitable stable openings.In addition,it could be a source of groundwater infiltration,which may necessitate grouting and drainage to control seepage during construction and installation of tunnel linings. 10.3.1.5.8.|Strength of Discontinuities Direct shear tests have been performed on natural,saw-cut,and polished surfaces to estimate the peak and residual (or basic)shear strength.Direct shear tests were conducted on saw-cut surfaces;natural calcite coated surface inferred to be an in situ healed joint;a natural,iron oxide- stained joint surface;polished rock surfaces;polished rock surface against mortar;and some joints from altered rock and some with calcite or other fillings.The results of the direct shear tests are provided in the Geotechnical Data Report,included in Appendix B1. The natural joints show relatively high peak and residual friction angles.The peak friction angles of natural joints ranged from about 36°to 48°,neglecting cohesion.Analyses of vertical and horizontal displacements in samples from BH-8 indicate an approximately 10°incline, which appears to reflect the asperity angle of the natural joint. Polished rock,as expected,resulted in the lowest basic friction angle of 18°.This angle is not considered representative of joints since it does not include effects of asperities as found in situ. Typically the basic friction angle of the rock is estimated for saw cut joints,which for these tests ranged from 21°to 35°degrees.Literature indicates the basic friction angle for medium grained granitic-type rocks are typically in the range of 29°to 35°.This suggests that the tests that have lower strengths (DH12-8,DS1)may be anomalous or may be at least partly due to sample alteration (DH12-8,DS6)or the infillings. The bedrock is intersected by several types of discontinuities such as joints,formation contacts, and shear zones or alteration zones.The shear strength parameters of discontinuities are based on the Barton-Bandis non-linear strength criterion.The friction angle and apparent cohesion used in stability analyses are the "instantaneous”values taken as the tangent to the Barton- Bandis strength envelope for the applicable normal load associated with the particular loading condition being analyzed.The Barton-Bandis equation is given below: Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-40 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT T=0,ail +sec W¢4{25}O,, where: T:shear strength along the joint Or:residual friction angle JRC:joint roughness coefficient JCS:joint wall compressive strength For fresh,clean discontinuities (tight,no infilling material)in diorite,based on experience,the following values are recommended for use in feasibility level analysis: Residual Friction Angle,Qy.......:cccsscccssecessesessseecsnceceeaneessnseesnecesaeeesseeesesaeeseateceteseateseanees 30° Joint Roughness Coefficient,IRC oe.eeeesccsscsseeeecececsessaseecceseessesseeseeseeeseeseeneeseeenees 8-10 Joint Wall Compressive Strength,JCS .0....cee ceecssscesseeceensecssneessasecesseeeesseeseasensees 21,590 psi For joints and shear zones or alteration zones with clay infilling and no rock-wall contact,the strength of the discontinuity will be governed by the infilling material and will be lower. 10.3.1.6.In Situ Stresses No direct measurements of in situ rock stresses have been undertaken as part of the previous or present feasibility-level site investigation and testing programs.Although the magnitudes of in situ stresses are not known,the approximate orientations of the principal in situ stresses can be assessed based on observations and evaluation of the contemporary stress regime,as defined by current plate tectonic models,GPS observations,earthquake focal mechanisms and Quaternary faulting.A qualitative evaluation indicates that the project area is subject to northwest-southeast oriented sub-horizontal compressive stress associated with the subduction of the Pacific Plate in south-central Alaska.This is the maximum in situ principal stress direction,which is sub horizontal. It is common practice to assume that the three in situ principal stresses are orthogonal to each other.Because the project area has been undergoing uplift due to glacial rebound,it can be surmised that the vertical in situ principal stress is the minimum in situ principal stress,leaving the intermediate in situ principal stress oriented in the horizontal direction and oriented in the northeast-southwest direction. Due to the present tectonic stress regime,it is worth noting that ratio of vertical to horizontal could be much less than 1.0.This could present some conditions that need to be evaluated further in next phase of study -including evaluation of the potential for heave and excessive Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-41 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. loosening in foundation excavations,potential for grout-jacking in the vertical direction and other stress related effects. 10.3.2.Construction Materials Sources For the RCC dam,the bulk construction materials required for the project will largely be aggregate obtained from quarry sources.Additionally,some impervious and rip rap materials will be needed for cofferdam construction. The 1980s investigations and license application contemplated sequential development of Watana and Devils Canyon dam,which would have formed a reservoir extending to the tailrace of the Watana Dam.Under these conditions,it would have been feasible to contemplate the use of construction materials from gravel borrow areas downstream of the Susitna-Watana Project,as they would be inundated by the Devils Canyon reservoir. In contemplating sources of construction materials for the proposed project,site investigations and laboratory testing focused on evaluation of previously defined rock aggregate material source,Quarry A,and identification and delineation of new aggregate material sources adjacent to the proposed dam.The change in the dam type from the rockfill embankment of the 1980s to a RCC dam dictated a change in the construction material requirements for the project.Field investigations were conducted in 2011 and 2012 of potential quarry sites that could produce suitable aggregate for the project.These were Quarry A,identified in the 1970s and immediately south of the dam site,and a new quarry,designated Quarry M,just upstream of the dam site on the left abutment.Bedrock at these two proposed sites differs;andesite to dacite porphyry is found at Quarry A and diorite is found at Quarry M.Rock core and bulk samples have been tested for alkali reactivity,freeze thaw,soundness and abrasion,to determine the suitability of the material as an aggregate in the production of both RCC and conventional concrete.Any altered seams of diorite materials found in the quarry will be selectively wasted within quarry management protocols.A spoil area has been designated upstream of the Quarry M site. Based on preliminary testing,the results indicate these rock types are of overall good physical- mechanical quality.This was reflected by their generally low sulfate soundness losses (less than one percent),low LA abrasion losses (dacite around 14 percent,diorite about 20 percent), absorption of less than 1.2 percent,and reasonable density values.Alkali-Aggregate Reactivity (AAR)characteristics were evaluated on a very limited basis and indicate that these rock types are considered as "inconclusive”to "potentially reactive”,depending upon the criteria being used.With the use of an appropriate supplementary cementitious material (e.g.,fly ash)in the concrete and RCC mixes (which is planned to limit the heat of hydration anyway)potential expansion would be mitigated. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-42 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT At the feasibility stage,it was decided that some simple tests should be performed to verify that the aggregate available could have AAR potential mitigated with the mixes being considered. Petrographic examinations -in accordance with ASTM C 295 and CSA A 23.2-15A -were performed on the samples.As recorded in the laboratory results from samples in DH 12-2 the extent to which the quartz diorite could be alkali reactive depends on the nature of the quartz. Although examination of thin sections indicated that the samples lacked undulatory extinction (an indicator of strained quartz),it is universally acknowledged that some strained quartz may cause a deleterious alkali-silica reaction if present as a constituent of concrete aggregate in sufficient amounts.Some papers have suggested that the criterion for reactive strained quartz is to be more than 20 percent strained quartz with an average undulatory extinction angle greater than 15 degrees.Length changes of mortar bars containing such strained quartz will be 0.025 and 0.040 percent (or more)at 6 and 12 months. Crushed samples from "quarry”drill holes were used in accelerated mortar bar testing,based on ASTM C 1260 and C 1567.Because the testing was only performed to verify that the sorts of mixes considered were appropriate to mitigate reaction,they deviated from these standards in two respects:cementitious proportion and length of test. The tests were performed using two types of fly ash -Class C and Class F -both provided from the Centralia thermal plant in Washington State,which would be the probable source if the project is constructed before 2028 when the plant is due to close. The tests were performed on two mixes: »A "mass concrete”mix using a fly ash replacement of 35 percent and a total cementitious content of 71.2 percent of the mass specified in ASTM C 1260 and C 1567. »A RCC mix using a fly ash replacement of 45 percent and a total cementitious content of 17 percent of the mass specified in ASTM C 1260 and C 1567.This mix represents the lower envelope of fly ash content that might be considered for RCC,and it is expected that a greater proportion will in fact be specified. For each mix,in each case,the length in the mortar bars was measured through 28 days,and then at 60,90,120 days. For the "RCC”mix,the expansion in the mortar bar ranged from 0.026 percent to 0.034 percent at 28 days,and from 0.062 percent to 0.088 percent at 120 days.Although not performed strictly in accordance with the ASTM requirements,the results indicate that the amount of fly ash being considered for the RCC mix is sufficient to render the mix safe against AAR.For the feasibility Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-43 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. design-and the associated estimation of cost of cement and fly ash -this result is seen as acceptable. With respect to the conventional concrete mix tested,the expansion in the mortar bar ranged from 0.069 percent to 0.083 percent at 28 days and from 0.24 percent to 0.29 percent at 120 days.This level of expansion is seen to warrant further testing during detailed design in order to determine the required specification for the adopted conventional concrete mix. Freeze-thaw testing was also conducted and indicates both the dacite and diorite have low losses. Historical data from Acres (1982)reported slightly over two percent loss for 150 cycles on both rock types in Quarry A.A test on split NQ core of dacite from Quarry A in 2011 had a loss of 10 percent after 55 cycles.The later test may be attributable to pre-existing fractures and therefore does not appear to be representative of the loss for unfractured material.In addition,two freeze- thaw tests on rock from Quarry M were conducted on samples of diorite collected in talus below the outcrops.These tests resulted in 0.01 percent and 0.02 percent loss after 55 cycles.These loss percentages are very low.The results from the laboratory testing are summarized in the Geotechnical Data Report in Appendix B1. Additional field investigation and testing is required to better define the quality of the material, potential wastage,available reserves,etc.This should include a small quarry development to perform test blasts.During final design,the material should be crushed for trial mixes of RCC and conventional concrete and for RCC trial placement.It is not envisaged that the quarry will be sufficiently developed in time to provide material for the cofferdams.Required materials could be obtained from the dam foundation excavations on the abutments. The impervious core material for the cofferdams may be available from the removal and stripping of overburden (till)from the upper abutment slopes or could be obtained from a nearby borrow area,which consists of compact and dense glacial deposits,primarily consisting of till, outwash and lacustrine materials.Extensive field investigations and testing of the materials in Borrow AreaD near Deadman Creek were conducted in the 1980s to characterize this impervious construction material source.The soil type for the till (e.g.,Units M,G',and J')and much of the outwash (e.g.,Units E/F and I)soils is a silt-sand (SM)which both contain cobbles and boulders (which are not part of the soil classification).Clayey sand (SC)and cohesive clayey and silty (CL,ML)soils are also common to the glacial lacustrine and till deposits. Acres (1982a,1982b)reported that the engineering properties of the materials include a moisture content of 11 to 12 percent and Atterberg Limits for the more granular material contains relatively low plasticity (PL 15 percent,PI 5 percent)constituents except for the tills and lacustrine deposits that are cohesive and have a high plasticity.Compaction testing of a composite material using a Standard Proctor Test indicate that the material has a maximum dry Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-44 December 2014 oS -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT density of about 128 to 134 pcef at an optimum moisture content of 8 percent to 10.4 percent while Modified Proctor Test results (material <%inch sieve)indicate a maximum dry density of 135 pcf at 7.5 percent moisture content.Consolidation compressive indices (Cc)of 0.061 and 0.091,respectively at 2 percent above optimum moisture content. Processing and blending of outwash (Units E/F)with some other soils (Unit M)is required to achieve the proper gradation and moisture content while removing oversized material.Thus, construction material source includes suitable percentage of fine particles,e.g.,silty-sands (SM), which can be compacted to achieve relatively low hydraulic conductivity.The underlying lacustrine deposit (Unit G),characterized by high moisture content (23 percent)of the sandy silts (Unit G)material,is considered unsuitable. 10.3.3.Design and Construction Considerations 10.3.3.1.Slope Stability Cut slopes in soil for foundation excavation are anticipated to vary from 2H:1V to 1.5H:1V for permanent cuts in overburden with temporary cuts at 1H:1V to 1.5H:1V.The steepness of these cuts is necessitated by the topography of the site,and slope stabilization will be required in several areas to prevent sloughing. Rock discontinuities (e.g.,joints)will control the design of rock excavations and rock slopes and are used to evaluate foundation and abutment stability.The design of rock slopes and excavation openings consider the orientation of the joint sets with respect to the orientation of the excavation face,and the joint characteristics.Excavation cuts in rock will vary from 1H:2V to 1H:3V in weathered material but will generally be 1H:4V in fresh rock. The slopes of rock cuts will be designed as stable excavations without rock reinforcement,but where this is not feasible,slopes will be reinforced with pattern or spot bolts and shotcrete (or concrete)with proper drainage as needed.Flattening of slopes,rock bolting,wire mesh and shotcrete will also be necessary in areas of more fractured rock,and in areas exhibiting unfavorable dip,to stabilize rock blocks and wedges.It is anticipated that rock reinforcement and slope protection of permanent rock slopes will include rock dowels and bolts,wire mesh and possibly reinforced shotcrete,and drainage will be necessary in local areas,such as highly weathered rock. All rock cuts will have surface drainage ditches established at the top of the cut,on intermediate benches,and at the toe of the slope to collect and channel water away to reduce water infiltration and thereby improve slope stability.Drain holes will be drilled into the face of the rock cuts as necessary to relieve ground water pressure deeper within the rock mass and patterned weep holes Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-45 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. will be drilled to shallow depths to relieve pressure acting against shotcrete or concrete.Rock fencing and rock fall netting could also be provided on benches for protection of roads and other temporary and permanent facilities. Cut slopes will be reexamined during detailed design considering the orientations and continuity of the local structure,slope orientation,and consider local fracture and shear zones as well. 10.3.3.2.Dam Abutment Stability Analysis A key factor in the design of any dam is the abutment stability.For a concrete arch dam,in which the abutment is expected to carry thrust loads,abutment stability is of critical importance. Therefore,the stability of major (and minor)rock blocks and wedges subjected to the imposed dam loads,steady-state seepage,and during seismic events is paramount.The stereoplots from the 1980s studies were used in the analysis of rock wedges on the left and right abutments.The results from the 2014 mapping and investigations are generally consistent with the prior studies. A series of preliminary limit equilibrium analyses have been carried out to evaluate and confirm the stability of the left and right abutments of the dam.These analyses,which used simplified dam geometry,were carried out to determine the overall impact of critical structural geology features on abutment sliding stability,and not to design the project.It was intended to determine:(a)the possible impact of the identified discontinuity sets on abutment stability;and, (b)the influence of varying piezometric loads.These simplistic analyses were intended to explore the potential for any major design issues that would need to be addressed in later design phases.However,the analyses employed are not considered to be precise design tools and therefore the results are not to be used as a basis for detailed design. The following section summarizes the abutment stability analyses conducted in support of the current feasibility study. 10.3.3.2.1._Abutment and Rock Block Arrangement A series of preliminary limit equilibrium analyses were carried out to provide a general assessment of the stability of the left and right abutments considering the critical orientations of geologic features and discontinuities.In general,the joint orientations described in Table 10.3-10 were used in the analysis,although different nomenclature was used.In addition,the stability analysis was completed before the 2014 mapping was performed and the joint sets were updated.Thus,the stability analysis needs to be updated to more accurately reflect the orientations within each abutment. The general layout of the hypothetical abutment rock blocks (wedges)within the abutments of a curved concrete gravity dam is shown schematically on Figure 10.3-4.For the proposed dam,a Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-46 December 2014 oS Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT total of eight 3-D tetrahedral wedges were analyzed,four in each abutment.Typical plans and sections of the wedges in the left abutment are shown on Figure 10.3-5,Figure 10.3-6 and Figure 10.3-7.The basal planes of all wedges are made up by a series of gently dipping planes at different elevations in the abutments,intended to simulate with the shallow dipping joint set. The side planes are defined by a steeply inclined joint set in the left and right abutments.The grout curtain forms the upstream limit of each wedge.Each wedge daylights in the slope immediately downstream of the dam.Analyses for static loading conditions and normal reservoir levels were carried out for each of the eight wedges.In addition seismic stability analyses were conducted to assess the impact of pseudostatic earthquake loadings on rock stability. Plane 3 *.Plane 2 Plane 1,Plane 2,and Plane 3 are Discontinuity Planes;Uplift 1,Uplift 2,and Uplift 3 are Water Forces;W is the Block Weight;and Dam Force is the Thrust from the Dam (From Scott,G.A.1999,"Guidelines Foundation and Geotechnical Studies for Existing Concrete Dams”,USBR,adapted from Londe Figure 10.3-4.Schematic Rock Block within the Abutment of an Arch Dam Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-47 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 10.3-5.Plan,Left Abutment Wedges la and Ib Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-48 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. y toy Figure 10.3-6.Plan,Left Abutment Wedges 2a and 2b Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-49 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 1 €1 2000 1 T elu tte.=1 !{\ Bevervole £5 20 REL Vow |' Figure 10.3-7.Schematic Profile along Dam Axis Left Abutment showing Wedges 1a,1b 2a and 2b; Scale of Wedge Boundaries is Approximate 10.3.3.2.2.Limit Equilibrium Analysis Static limit equilibrium analyses were carried out on multiple wedges in the left and right abutments for normal to extreme piezometric loading conditions and approximated pseudostatic loads using kinematic analysis and DIPS software.The analyses incorporate the following: =Wedge weight. *Dam weight load applied to the top of the wedge.Thrust loads from the dam were not included. =Water pressure distribution on each block face.Hydrostatic loadings were applied on the J1 side plane and J5 basal plane of the wedge.It was assumed that the water pressure in these planes declines linearly from the grout curtain to the point where the discontinuity daylights in the slope downstream of the dam.Parametric studies were carried out to evaluate the effects of drainage by varying the uplift at the downstream side of the grout curtain from 100 percent (no effective drainage)to zero (100 percent effective drainage). It should be noted that,based on precedent experience in arch dam abutments,a 33 percent uplift case would be considered a reasonable design assumption.The other cases Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-50 December 2014 -yz- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT show the effects of varying uplift pressures from the design ideal.Drilled drain holes - including those drilled from any required extension of the adits that might be needed to address wedge drainage -will extend far enough to intersect the lowest critical plane that daylights. Pseudostatic loads (most critical blocks only).Given that the wedge would actually have a complex internal response to seismic shaking,it was considered that the simplistic application of a single horizontal seismic load was sufficient for a preliminary estimate of stability.More rigorous seismic analysis of critical wedges will be carried out during the final design of the project. Orientations of the discontinuities and block face. Friction cone contours at 5°increments plotted on stereoplot. The resultant force vector plotted on the stereoplot. Inspect the friction cone contours and resultant plots. Establish the friction angles (Mreq)needed for limit equilibrium (FOS =1.0)and compute the factor of safety (FOS)against sliding as per the procedures described by Londe,Goodman and other authorities assuming the sliding plane has no cohesion and a friction strength (Dgisc)of 45°. The results of the stability analyses are provided in Appendix B5,but are summarized below. The analyses of the left abutment indicate the following: The wedges have acceptable static (FOS >2.0)and seismic stability (FOS >1.0)for the 33 percent uplift case.This is a normal design uplift assumption that assumes that foundation drainage is two thirds effective.For this drainage case,the required friction resistance for FOS=1.0 varies from 24°to 27°for the static case and 32°to 43°for the earthquake case.The FOS for assumed @disc =45°,varies from about 2.0 to 2.2 for the static case and from about 1.07 to 1.6 for the earthquake case. In all drainage cases,the static FOS is greater than 1.0.The earthquake FOS values are less than 1.0 when the drainage efficiency is 33 percent or less (67 percent uplift)in Wedge la. Overall stability is very sensitive to the hydraulic uplift forces in the side (J1)and base (J5)planes.As piezometric load increases,the direction of the resultant vector rotates northwards,towards the valley.Thus,the sliding FOS is reduced by almost half when the hydraulic loadings in these planes are increased from 33 to 100 percent.This confirms the requirement for a well-constructed grout curtain and effective drainage of the foundation and abutments. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-51 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The stereoplots show that critical sliding and thrust loads are directed along the basal J5 plane and there are no significant loadings across the J1 plane.The orientations of the resultant vectors show that sliding stability is controlled by the shear strength of the J5 plane and indicate that the strength of the J1 plane has very little influence on stability. The analyses of the right abutment indicate the following: The right abutment wedges have acceptable static (FOS_>2.0)and pseudostatic seismic stability (FOS>1.0)for the 33 percent uplift case.This is a normal design assumption that assumes that foundation drainage is two thirds effective.For this drainage case,the required friction resistance for FOS=1.0 varies from 11°to 25°(Myeq).The FOS for assumed Wgjsc =45°,varies from about 2.1 to 5.1 for the static case and the FOS is greater than 1.0 for all drainage cases. Overall stability is very sensitive to the hydraulic uplift forces in the side (J1)and base (J5)planes.As piezometric load increases,the direction of the resultant vector rotates southwards,towards the valley.Thus,the sliding FOS is reduced by almost half when the hydraulic loadings in these planes are increased from 33 to 100 percent.This confirms the requirement for a well-constructed grout curtain and effective drainage of the foundation and abutments. The stereonets show that critical sliding and thrust loads are directed along the J4 basal planes on the left bank and there are no significant loadings across the J2 side plane.The orientations of the resultant vectors show that sliding stability is controlled by the shear strength of the J4 plane and indicate that the strength of the J2 plane has very little influence on stability. The results of this preliminary analysis are considered to be conservative because: Dam loading forces were represented by the dead weight of the dam plus the water load on the upstream face of the dam.Thrust loads resulting from the dam curvature,which direct some of the loadings into the abutment (with consequent increase of the sliding FOS)were conservatively excluded from this analysis. The theoretical hydraulic loadings used for the three discontinuity planes are usually reduced when flow net values,which consider head losses along the flow paths,are used. Cohesion resistance along the sliding planes was not considered.It is assumed that shear strength is controlled by friction resistance.Given that the basal sliding planes are made up of a series of en-echelon,discontinuous joints,it is probable that failure planes would have to shear through a number of intact and competent rock bridges along the failure path imparting a significant cohesion strength component. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-52 December 2014 O Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.3.3.2.3.Conclusions The results from preliminary analyses of theoretical abutment blocks indicate that the left and right abutments have acceptable sliding stability for reservoir loads under static and assumed pseudostatic seismic conditions.The analyses used conservative shear strength parameters and piezometric uplift assumptions in the rock mass.While considered preliminary,the analyses indicate that the abutments have robust stability for the "arch action”expected from the planned curved gravity dam design. It must be pointed out that the pseudostatic earthquake stability assessment is a rough approximation of earthquake loadings but is sufficient for feasibility level design.The analyses carried out herein demonstrate that the abutments are expected to have a robust resistance to uniform horizontal loadings,but the analyses do not accurately assess the effects of the final chosen design loading cases.More detailed dynamic stability assessments will be required during detailed design.In addition,since this analysis was performed -because of ongoing development of the dam configuration -the dam has been rotated (by less than 5°on the left abutment),and the robust stability should not be impacted greatly by the repositioning. It should be noted that this assessment is based on incomplete geological information with respect to the geotechnical properties of the critical discontinuity sets.Future foundation and joint characterization from the planned exploratory adit investigations needs to be incorporated into the geologic model to enable more representative analyses of the right and left abutments based on improved information on the subsurface geologic conditions including persistence of sub horizontal discontinuities and the presence and persistence of ice-filled discontinuities,final dam configuration,and completion of a seepage analysis to evaluate the hydraulic forces. 10.3.3.3..Dam Foundation Design The foundation area for the proposed curved RCC dam has a considerably reduced area compared to the 1980s proposal for an ECRD.However,the integrity of the foundation of an RCC dam is paramount to the stability and safety of the dam,and a more detailed characterization of the foundation will be necessary to perform detailed design of the dam.To that end,before future detailed design,a more extensive site investigation program is recommended to be implemented,which would include excavating adits and the associated drilling,in situ testing,and instrumentation monitoring within the adits in both abutments. For this report,the existing information derived from the 1980s and site investigations and geologic mapping from the 2012 and 2014 investigations was used to characterize the foundations.Rock elevations and quality were plotted using the new site contours derived from the LIDAR ground surface contours,together with the borehole data from the 1980s studies.The Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-53 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. data were adjusted from the NAD27 datum,Alaska State Planes coordinate system used in the 1980s studies to the NAD83 datum coordinate system currently in use together with NAVD88. Based on the revised bedrock contours and assessment of rock quality at the dam site including rock outcrops,a plot of the rock surface was made to estimate excavations necessary to achieve an acceptable dam foundation (Drawing 01-01GT004).In addition,the following assumptions and design and construction considerations pertinent to project include: #The bedrock foundation level has been chosen so that the foundation of the dam will be non-erodible under the projected and calculated seepage gradients. «The foundation level has been chosen so that the contact between the dam and the bedrock surface will be on fresh to slightly weathered or altered,strong and sound rock. Dental excavation will be performed to remove significant bedrock irregularities to provide a smoothly varying foundation surface. *Dental excavation and treatment will be performed in the bedrock foundation at locations of highly fractured,sheared,and moderately to highly altered zones (e.g.,where geologic features GF4B and GF5)are present in the foundation.Conventional concrete infill will be placed in these areas of extra excavation. «The potential for encountering bedrock on the left abutment and lower right abutments at temperatures slightly below freezing and the variations in the rock surface temperatures over the dam footprint are likely to require special procedures for placement of RCC and conventional concrete against the cold rock.Having a large foundation area against which concrete will be placed,will necessitate development of special procedures during detailed design.Construction methodology will need to be developed to facilitate thawing of the foundation prior to placement of concrete and foundation treatments. As part of the preliminary design,the dam foundation design includes characterization of the foundation,preliminary finite element analyses,and assessments of dam foundation treatments necessary to provide a foundation suitable for carrying intended loads. 10.3.3.3.1.Finite Element Analysis A key aspect of evaluating the feasibility of the RCC dam is to understand the behavior of the dam and how it interacts with the foundation.To understand the stresses and deformations that might be experienced by the dam and foundation in response to the anticipated loading, preliminary finite element analyses (FEA)were performed using ANSYS and LS-DYNA. The 3-D ANSYS foundation model included sensitivity of dam stability and performance of the structure relative to changes in discrete foundation elements with differing deformation parameters.The diagrams shown in Figure 10.3-8 show the basic zoning used for the analyses - Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-54 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT which was compiled before the geological mapping of 2014,and the subsequent reinterpretation of the geological features in the dam foundation.Generally the reinterpretation of the foundation has postulated narrower and less continuous geological features than previous interpretations,so the simplified model used in the analysis is conservative -with regard to size of feature and continuity -compared to that which will be used in the detailed design analysis.The preliminary analyses examined static and dynamic stability of the dam using a relatively coarse mesh for the foundation,which required simplification of the geologic interpretation of the foundation geology presented on Drawing 01-01GT006.In particular,in the Acres interpretation used,the lower right abutment of the dam foundation is shown to be comprised of several fracture zones (Engineering Unit 2)and narrow altered/shear zones (Engineering Unit 3)within the area of geologic features GF4B and GFS5S that are separated by more intact rock (Engineering Unit 1).Because the dimensions of the elements forming the FEA mesh are larger than the width of the fracture zones,the lower right abutment was oversimplified as a wider zone having rock mass properties that are a composite of the three engineering units. While not directly correlated with the Engineering Units defined in Table 10.3-9 since the preliminary modeling was completed before the foundation parameters were finalized,Zone A is approximately equivalent to Engineering Unit |below a depth of 20 ft.and the "Weak Layer” approximates the upper 20 ft.of the foundation.Zone B is modeled using a deformation modulus that covers the estimated range for Engineering Unit 1,Unit 2,and Unit3.The properties incorporated into the finite element analyses are summarized in Table 10.3-12.The model was run using linear elastic materials,thus the rock mass strength parameters are not pertinent. Left 'Weak Layer\ \ ,- (a)Bedrock foundation zoning (b)Weak layer of blast disturbed rock Figure 10.3-8.ANSYS Foundation Models Showing Principal Bedrock Zones Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-55 December 2014 ---za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 10.3-12.Foundation Parameters for Preliminary 3-D FEA ;|Deformation Modulus,E (x 108 psi)Analysis Case Description Weak Layer Zone A Zone B HomogeneousLayout3-ANSYS Foundation -3.5 3.5 Base Case -3.5 1.5 Layout 4 -ANSYS Sensitivity -High -7.0 3.0 Sensitivity -Low -1.75 0.75 'ences |2a |as 28 Layout 4 - (Modified)ANSYS Homogeneous and LS-DYNA Foundation 2.0 3.5 3.5 Base Case -3.5 1.5 10.3.3.3.2.Consolidation Grouting Although controlled blasting will be used for the final excavation of the dam foundation (and other structures such as the spillway and powerhouse)it is prudent to assume that rock within about 20 ft.of the excavated surface may have experienced stress release and loosening of joints. Therefore,in accordance with normal practice for large dams,consolidation grouting will be performed to improve the rock quality and modulus under the entire dam contact area and up to 30 ft.upstream and downstream of the footprint.In addition,consolidation grouting is assumed under the spillway structure,powerhouse,and other appurtenant structures. It has been assumed at this time that consolidation grout holes approximately 25 ft.deep will be drilled into the dam foundation on a 10 ft.by 10 ft.grid,except in the areas where ground temperatures are below freezing,which will require a tighter spacing,6 ft.by 6 ft.(e.g.,left abutment).In addition,localized consolidation grouting may be necessary in localized zones of fracturing associated with fracture,shear,or altered bedrock to improve the strength and deformability of the rock mass.The holes will be oriented such that they intersect as many of the discontinuity sets as is reasonable.Based on the information available at the present time, Joint Set 1 and Joint Set 2 are the dominant joint sets and are near vertical and there is a shallow dipping joint set.Thus,holes will be oriented a maximum of 15°from vertical. From data available from the existing borehole instrumentation,it is postulated that the bedrock may be at a stable residual temperature of about 30°F within much of the lower left abutment, and potentially in pockets on the right abutment.The low temperature zone appears to extend more than 200 ft.below the ground surface in the left abutment bedrock.A ground temperature of more than 40°F is normally required for grouting.Therefore,for consolidation grouting to Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-56 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT achieve its purpose,it is envisaged that the ambient bedrock temperature must be raised to at least 40°F. Grouting of bedrock that exhibits a temperature below freezing point of water (and may contain ice filled joints)will require some approaches that differ from conventional grouting.Planning for this aspect of the project is very important,and it is envisaged that,during future site investigations,a test grouting program will be initiated to assess the merits of various alternative methods and procedures for consolidation grouting and curtain grouting particularly with regard to frozen bedrock.In the meantime,the following methodologies for grouting frozen ground are postulated for raising the rock mass temperature some of which are discussed in Section 10.9 with respect to preparation of the foundation for placement of RCC.Allowances have been included in the cost estimates for the following measures,as appropriate: 1.Closer consolidation hole spacing. 2.Early stripping of overburden and rock materials to promote thawing.Insulate and heat the areas over winter. 3.Circulate hot water in consolidation holes. 4.Circulate steam in consolidation holes. 5.Install electric heaters in holes. Where structural features (sheared and altered zones and poor quality bedrock)pass through the dam foundation,additional stitch grouting will be performed as required if it has been determined that structural features are potential pathways for seepage.In general,where encountered,such zones will be capped with conventional concrete,and then a number of inclined holes will be drilled from each side to intersect with the feature at various depths,and from which grouting can be carried out.Structural features will be carefully mapped,and if considered necessary,extra or lengthened galleries will be introduced into the RCC so that higher pressure grouting of the feature is possible after the RCC has been placed,and to measure and remediate seepage through the feature after impoundment. 10.3.3.3.3.Curtain Grouting Curtain grouting will be performed to reduce seepage and reduce the potential for piping of weak foundation materials or joint infillings.The challenges relating to curtain grouting at the dam site,as with the consolidation grouting,primarily relate to encountering ice-filled discontinuities. Otherwise,curtain grouting is expected to follow standard industry practice. The grout curtain will be constructed beneath the dam foundation,along the dam axis extending up both abutments.The maximum depth of the curtain will be approximately 375 ft.below Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-57 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. foundation level (i.e.,50 percent of maximum total head).Foundation grouting will be performed from galleries within the dam that will collect water from foundation drain holes drilled downstream of the grout curtain.In accordance with modern practice,a single row grout curtain is assumed to have holes inclined holes 15°from vertical and oriented in the upstream direction.This arrangement is suitable to intersect the large number of discontinuities dominated by JS1,JS2,and JS3.Standard split-spacing techniques will be used beginning with primary holes drilled at 20-ft.spacing,followed by secondary holes and together with tertiaries and quaternary holes as required to achieve closure.In specific areas,as dictated by the final evaluation of the dam foundation and optimization of treating frozen ground,an additional row (or rows)of grout holes may be used. In accordance with modern practice for dam construction,grouting will be performed using balanced,stabilized grout mixes consisting of water and Portland cement having a water:cement (W:C)ratio generally between 0.5 and 2.0 (by weight)and super-plasticizer,additives,and admixtures to meet criteria with respect to viscosity,density,stability,set times,and bleed. Grouting pressures will be limited to prevent the possibility of foundation jacking or uplift of the dam.For feasibility level design,it is assumed that the target residual hydraulic conductivity for the grout curtain is about 3 Lugeons.Closure will be based on a preliminary established value of cubic feet of grout per foot injected.This value will be assessed during an initial test grout program prior to production grouting. The objective of curtain grouting will be to fill discontinuities within the dam foundation down to approximately 50 ft.,and for the rest of the curtain to reduce turbulent flow through discontinuities to a manageable level.Although,for the purposes of cost estimating a fixed grout curtain depth has been assumed,the work will take into account the actual rock conditions encountered during the program and will be modified on site. While multiple holes for consolidation grouting might be required to facilitate thawing in the near surface bedrock,it is less practical to thaw the bedrock at great depths to facilitate curtain grouting,although in areas of ice-filled joints extra rows or holes may be needed locally or over limited depth intervals.It is envisaged that thawing could take longer,if it is not achieved by delivery of appropriately warm grout.However,grouting will be performed from the adits in the abutments and the galleries within the dam and thus it can continue year round,and if required even after the dam is complete.Additional holes in the left abutment have been allowed for in the cost estimate where rock temperatures are known to be below 32°F. It is prudent to allow for further grouting during the initial years of project operation after foundation thawing has occurred due to the reservoir impoundment.Additional grouting would Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-58 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT also be done from the galleries and adits,and an allowance for this work is included in the O&M costs during the early years of operation. Where the diversion tunnel plug will be aligned with the grout curtain,extensive contact, consolidation grouting and radial grouting will be performed from the diversion tunnel to tie the tunnel plug grouting to the dam grout curtain and provide a continuous cutoff.Contact grouting will also be performed in the annular space around all other tunnel linings and the concrete plug placed in the sluice through the base of the dam. 10.3.3.3.4.Foundation Drainage A drainage curtain will be constructed downstream of the grout curtain to intercept seepage,and to relieve hydraulic pressure beneath the dam.Drain holes will be drilled from the drainage galleries and the adits that extend into the abutments. A single row of drains will be drilled downstream of the grout curtain,10 ft.apart,to a depth estimated between 60 and 80 percent of the grout curtain depth,although seepage analysis will be performed during detailed design to finalize the required level of the drainage curtain. Seepage will be collected by gutters in the invert of the gallery and directed to the lower points in the dam for measurement and for discharge.It is important that facilities are also included for measuring seepage flows at specific locations or for particular,discrete,areas of the foundation for purposes of monitoring drain performance. 10.3.4.Underground Excavations 10.3.4.1.Diversion Tunnel The orientation of the diversion tunnel on the right bank has been selected for the best hydraulic performance and to suit the project layout,while accommodating issues that might arise with respect to the stability of the portal.The joint set orientations will control the support requirements for the diversion tunnel together with any geological features encountered such as GF4B and GFS (see Section 6.3).It appears that an east-west tunnel orientation is favorable as it crosses the two major joint sets at about 45°.Controlled blasting methods will be employed to reduce the potential for damaging the rock during excavation of the 36 ft.diameter horseshoe tunnel (and the enlarged 45 ft.section).The most efficient method of excavating the diversion tunnel will be to use a top heading and bench.Primary support of the excavation will consist of rock bolts (where needed),wire mesh and shotcrete.However,it is anticipated that zones of fracturing,shearing,and alteration will be encountered and will require steel channels or ribs or lattice girders for support.After excavation is complete,the tunnel will be lined with 12 inches of reinforced concrete,and an 18-inch-thick lining will be placed in the emergency release Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-59 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. chamber.Fracture,shear,and alteration zones are anticipated to be sources of groundwater inflow,which will require grouting to reduce inflows,for contractor construction safety,and to facilitate placement of shotcrete and final concrete linings. The diversion tunnel will be converted to an emergency release tunnel,after the plug has been inserted and will require that the floor of the tunnel be excavated a further 46 ft.deep.This excavation could be performed during the original excavation of the diversion tunnel (and temporarily backfilled and a concrete floor placed).However,in order to facilitate diversion,it is likely that second-stage excavation would be performed after the temporary plug is inserted and while the final diversion plug is being placed.The appropriate method and sequence should be left to the contractor to suite its means and methods. The approach channels to the portals will be excavated through talus and bedrock.Due to the thickness of the loose talus upslope of these cuts,large excavations and significant rock stabilization methods of the adjacent slopes will be required. A challenge that has arisen at some projects -where there is limited cover over the diversion tunnel downstream of the closure gate -relates to the rapid external loading (as the reservoir fills)of the diversion tunnel lining during initial reservoir filling and before the completion of the plug.For Watana this difficulty has been mitigated because the sluice through the dam will remain open until the plug has been completed and the diversion tunnel gates have been removed.Thus the diversion tunnel lining upstream of the plug will never be subject to high external loading and there will be greater flexibility in the final on-site choice of the upstream portal of the diversion tunnel. 10.3.4.2.Access Tunnels The location of the powerhouse at the toe of the dam necessitates the use of a tunnel for access, because the walls of the canyon are too steep for an open cut road to be practical. Delivery of equipment for the powerhouse will be through the access tunnel.The largest pieces of equipment that will be transported through the tunnel include the generator step up transformers,the turbine runner,the powerhouse crane beam and possibly penstock pipe sections.The tunnel has been dimensioned to accommodate these items. The tunnel excavation will be reinforced with rock dowels and reinforced shotcrete lining. Careful analysis of support requirements will be necessary for the spur tunnel used to store the standby generator and for the vertical shaft that extends to the low level outlet valve gallery. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-60 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The configuration at the crossing of the diversion tunnel and the access tunnel will require careful analysis,design,and construction,as the intersection of the two will alter the effective rock stress.Care will need to be taken in design.The diversion tunnel will never be pressurized, and it is envisaged at this time that the limited vertical separation between the two tunnels can be mitigated by an over excavation of the diversion tunnel and the inclusion of a (reinforced) structural concrete "bridge”forming part of the diversion tunnel lining crown and the floor of the access tunnel.It is assumed that rock tendons will be required in each of the tunnels at that location to stabilize the intersection.During detailed design,the option of reconfiguring the access tunnel to increase the vertical separation of the tunnels will be investigated. Pattern drain holes will be required in the access tunnels to relieve pressure on the lining,and flows will be directed to a formed drainage channel in the concrete invert. 10.3.5.Cofferdams Zoned embankments will be constructed upstream and downstream of the proposed dam to close river flow and maintain diversion of the river through the diversion tunnel. When the powerhouse substructure has reached an elevation of El.1476 ft.and the upstream section of the RCC has reached an elevation of approximately El.1530 ft.,the cofferdams can be allowed to fall into disrepair.Until that time,they are necessary to divert the river flow through the diversion tunnel,although under certain circumstances the upstream cofferdam can be overtopped so that ice or water flows through the sluice. There is a considerable thickness of alluvial deposits beneath the river consisting of gravelly sand with cobbles and boulders,and the banks of the river the talus deposits consist of angular cobbles and boulders,all of which are highly pervious.Therefore,a slurry cut-off wall will be necessary,constructed from the cofferdam and extend through the alluvium.The cutoff is not expected to fully cutoff seepage,and continuous 'dewatering will be required to remove seepage ™ from the excavation until the structures have achieved the elevations noted above.) The cofferdams should be located to avoid deeper alluvium cover (greater than 100 ft.thick)and where possible,avoid significant geologic features (fracture and/or shear zones)beneath the impervious material. .The diversion is described in detail in Section 10.4,but the initial closure will be achieved using rockfill stockpiled on either bank and then dozed into the river from either side.It is most convenient to perform closure at the lowest possible flow,even when the river is frozen,when it may be possible to use the ice as a working surface.After closure has been achieved,and the river has been diverted through the diversion tunnel,the closure cofferdam will be enhanced as Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-61 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. necessary by the placement of a choker course of silt on the upstream side.The next step will be to complete the cutoff wall behind the closure dyke,and then complete the remainder of the upstream cofferdam.The final work on the upstream cofferdam will be the excavation of bypass channels to allow flow and ice to pass the cofferdam without damage and flow through the sluice when flows exceed the capacity of the diversion tunnel,or during ice "breakout”when and if the diversion tunnel became blocked with ice.Because of the speed of placement of RCC,this situation is considered to constitute a risk for only one "breakout”season. The design and construction of the downstream cofferdam is very similar to that of the upstream cofferdam.At completion,the downstream cofferdam must be removed to form a suitable tailrace.The upstream cofferdam can be left in place and will be inundated by the reservoir. 10.3.6.Watana Relict Channel Studies performed in the 1980s indicate the existence of a deep buried valley (relict channel)that crosses from the north bank of the Susitna River gorge,upstream from the proposed dam site, and extends to Tsusena Creek,a distance of about 1.5 miles.Along the buried valley thalweg, the highest bedrock surface is estimated to be located at approximate El.1750 ft.,which is about 300 ft.below the NMOL of the proposed reservoir (El.2050 ft.).The maximum hydraulic gradient along the buried channel (El.2050 ft.to Tsusena Creek)would be low,approximately 4.3 percent. Potential challenges posed by the relict channel are: «Subsurface leakage from the reservoir through potentially permeable material along the buried channel. « Thawing of permafrost,if present,in the relict channel over time resulting in increased ”seepage. The average hydraulic gradient along the channel is considered low,and there may be no need to make any provisions for remedial treatment.However remedial measures currently being considered for the deep buried valley are placement of a downstream toe drain at Tsusena Creek, a filtered exit,to control the potential problem of piping.In addition,long-term monitoring to determine the hydraulic gradient and rate of thaw of permafrost that may be realized following initial reservoir impoundment is also considered. The final proposal treatment will be determined during detailed design and after the completion of additional investigations (e.g.,pumping tests).Inthe meantime,for the project cost estimate an allowance has been included for remedial measures. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-62 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.4.River Diversion 10.4.1.General The 1985 Federal Energy Regulatory Commission (FERC)license application adopted a twin 36 ft.circular tunnel configuration for diversion based on a design flow of 77,000 cfs,equivalent to a 50-year return period flood.The criteria used were appropriate for a clay core embankment dam,and an upstream cofferdam elevation of El.1550 ft.During the comparison of alternative configurations performed for this report,the potential for alternative,more economic diversion arrangements was investigated for the RCC dam and for the CFRD variants. The available hydrological analysis has been updated for the project site to include about 30 more years of flood data than was available in the 1980s.The updated flood frequency is presented in Table 10.4-1. Table 10.4-1.Flood Frequency at Watana Dam Site Return Period Flow (years). (cfs) 2 38,500 5 50,500 10 59,200 20 68,300 25 71,300 50 80,800 100 91,300 500 116,300 1,000 128,400 As noted previously,the arrangements adopted for the chosen RCC dam project will comprise a single diversion tunnel through the north (right)bank and a sluice incorporated within the dam. The tunnel will be converted to serve as emergency release facilities upon completion of the Project and the sluice will be completely filled with concrete and grouted. 10.4.2.Criteria The diversion tunnel will be concrete-lined throughout. Because the annual peak flow frequently occurs in conjunction with the spring river ice cover breakup,the diversion facilities will conservatively account for the potential for complete plugging (with ice and tree trunks)of the diversion tunnel at the gated intake. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-63 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Flood routings have been carried out,and indicate that routing effects will be minimal for the diversion flood.Therefore,the diversion facilities will be designed for the peak flood flow. The criteria for the diversion tunnel intake are shown in Table 10.4-2. Table 10.4-2.Criteria for the Diversion Tunnel Intake Diversion tunnel alone (water level below cofferdam spillways)5-year return period flood Sluice alone (assumes complete plugging of the diversion tunnel)50-year return period flood Tailwater rating See Figure 10.4-1 Upstream cofferdam freeboard 30 ft.minimum above spill channels Diversion tunnel Manning's 'n'0.013 Hydraulic losses HARZA design guide -DG-112 The diversion tunnel will be sized to convey at least the five-year return period flood (50,500 cfs),considered reasonable protection for the cofferdam construction,the initial foundation excavation tasks (which will be carried out over a period of six months),and the initial RCC placement up to the top level of the cofferdam.: The dam sluice and has been sized to pass the 50-year flood,assuming the diversion tunnel has been completely plugged during spring breakup with ice and woody debris.A consideration in detailing of the tunnel and sluice was that the same gates would be used for closure on both at different times.To facilitate passage of flow to the sluice without associated failure of the cofferdam,an overflow channel will be excavated on both abutments either side of the cofferdam and the channels will be lined with concrete. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-64 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 1500 + 1495 1490 + 1485 :eieeeeeneneceeeeecemneeenecneeecaeeee a sete cee 1480 - 1475 WaterSurfaceElevation(feet)1470 + 1465 1460 +_sae :|/ 1455 hee 0 50,000 100,000 150,000 200,000 250,000 Flow (cfs) Figure 10.4-1.Tailwater Rating Curve at Dam Site 10.4.3.Analytical Results Analysis of the hydraulics of the diversion tunnel and sluice were performed for a variety of cross sections,elevations,grades and lengths.The final configuration of the emergency outlet is discussed in Section 10.13.During the development of the design,the sluice length was reduced (because the curvature of the dam allows a steeper downstream face and thus a shorter sluice length). The locations of the tunnel portals were selected so that rock cover at the crown equal to twice the projected tunnel excavated diameter.The portals will necessitate overburden excavation to facilitate tunneling. Hydraulic analysis indicated that the tunnel capacity was substantially limited by the size of the intake gates.Consideration was given to an enlarged 44 ft.wide inlet with no piers and then transitioning to the 36 ft.tunnel about 100 ft.downstream from the intake.This alternative was not selected because any jamming would be inaccessible inside the tunnel. An alternative to assuming plugging of the diversion tunnel would be to construct a larger tunnel that has demonstrated the capability to pass a major spring river ice breakup,such as the 48 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-65 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. diversion tunnel at Bennett Dam on the Peace River,Canada.However,a 48 ft.diversion tunnel was considered to be uneconomical,and to involve risk at the portals. The selected tunnel alternative includes an enlarged two gate intake.Compared to the 1985 design,the intake gates were increased from 14 ft.wide to 22 ft.wide to increase the tunnel capacity.During ice breakout heavy equipment could be pre-positioned above the intake to assist in clearing jams.The outlet structures used in the 1985 design was adopted for the analysis. The size of the total sluice opening through the RCC dam would be 44 ft.by 50 ft.,which includes a 6 ft.width allowance for a removable steel central pier.The central pier would not be installed when the sluice was operational -but would be installed when the sluice was to be closed.The same 22 ft.wide gates used on the tunnel could also be used on the sluice. After the analysis,a selection was made of the features shown in Table 10.4-3. Table 10.4-3.Diversion Tunnel and Sluice Features Diversion Tunnel! Size .36 ft.diameter vertical-sided horseshoe pares 2 each at 22-ft.wide by 36-f.high Inlet El.1463 ft. Outlet El.1450 ft. Length 2,060 ft. Slope 0.64% Sluice 44 ft.high x 50 ft.wide (includes 6 ft.of Size width allowance for a removable central pier) Inverts Inlet El.1460 ft. Outlet El.1450 ft. Length 525 ft. Slope 10% Upstream Cofferdam Crest elevation El.1560 ft. Top of impervious core El.1553 ft. Overflow spillway elevation El.1530 ft. Overflow spillway length (each)2 each at 120 ft.7 |7 qDownstreamCofferdam-- _ Crest Elevation |El.1475 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-66 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The downstream cofferdam will be designed to wash away if it is substantially overtopped by flow from the sluice. The resulting river diversion rating curve is shown in Figure 10.4-2.Due to the complexity of the river diversion hydraulics,the river diversion rating curve should be confirmed at a minimum with a 3-D computational fluid dynamics (CFD)model and potentially also with a physical hydraulic model. 1560 1550 7-Top of cofferdam ys a,nd atimperviouscoreEl1553|a ro £ €1530 "ioBo)Cofferdam .o spillway crest <<30 X00 cts54520|E1 1530 ” Oo s ec 2 1510cs 5-year flood250,500 cfs 'a 1500 S5 D 1490 -#Total Outflow 2 -eSluice Flow E-4 4480 -*-Tunnel Flow 1470 5 1460 + 0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 :Flow (cfs) "ryte Figure 10.4-2.Derived Diversion Scheme Rating Curve 10.4.4.Operation of Diversion After.diversion,the diversion tunnel capacity will allow the construction area (foundation) within the river to remain dry for all river flows up to 50,500 cfs.At this flow the headwater level at the upstream cofferdam will be at the bypass "weir”crest.The tailwater level will be about three feet below the crest of the downstream cofferdam.This provides protection from the five-year flood." Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-67 December 2014 Zz.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. For floods greater than the five-year return period event -or if the diversion tunnel was blocked by ice or debris -the upstream cofferdam would be bypassed by flow through the overflow bypass (constructed on each abutment of the upstream cofferdam)in a manner such that no damage will occur to the structure. During the first 13 months of construction operations in the river bed,work could be disrupted by a flood event (or ice breakout)that caused the cofferdam to be bypassed.However after this initial period,the RCC being placed during the summer season would have attained El.1520 ft. (quickly achieving El.1529 ft.during the first month of the subsequent season)and the sluice would have been completed allowing bypass through the sluice under all conditions,and thus 'allowing operations on the dam to continue without further danger of inundation. Powerhouse substructure concrete will commence at the same time as the RCC and has been scheduled to be completed in 22 months -encompassing two seasons of snowmelt.This would mean that the powerhouse construction could be at danger of inundation,from the downstream side,for 11 months more than the RCC dam construction.During detailed design,the powerhouse concrete design tasks will include a focus on methods for facilitating the construction of the downstream,and south (end)wall between the powerhouse and the spare bay to at least El.1475.6 ft.(the tailwater elevation for the 50-year flood)so that these walls could be constructed faster -allowing bulkheads to be placed in the stoplog slot and achieving full protection from flooding the powerhouse early. After the completion of RCC to approximately El.1540 ft.the upstream cofferdam will not be needed and can be abandoned,and not removed.The downstream cofferdam can be breached after the downstream powerhouse wall has reached El.1469.5 ft.and will be removed at a convenient time thereafter. The first closure will be of the diversion tunnel in year nine -which will result in the diversion of the river through the sluice.After completion of the plug,the plug grouting and all the electrical and mechanical works for the emergency outlet,the diversion tunnel gates will be removed from the diversion tunnel and relocated to the sluice to effect final closure -after which the sluice will be filled with concrete and grouted,and minimum flow during reservoir filling will be discharged through the emergency outlet until the reservoir level reaches El.1850 ft., after which minimum flow will be released through the low level outlets. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-68 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.5.Dam -Layout Development 10.5.1.General Methodology Sections 10.5,10.6,and 10.7 record the development of the dam layout and geometry,using multiple analytical tools.Having selected the type of dam,prior to submission of the Pre- Application Document (PAD),the engineering team recognized that development of the dam geometry to include curvature could benefit the project by reducing the footprint of the project, reducing the volume of concrete and reducing the construction period. It was decided to perform iterative analysis of different dam configurations,commencing with inexpensive analysis to guide in the selection of further optimizations.It was decided to delay a detailed and expensive FE analysis until configuration had been developed -using relatively inexpensive modeling -that appeared to satisfy the stability and structural criteria. The intent of the first "preliminary”analyses therefore -described in Section 10.6 -was to determine a dam configuration that will maintain the required stability and safety,while providing the opportunity for minimization of the RCC volume,and thus the shortest construction period.The key factors in the assessment of the viability of the various layouts examined,was the stability per FERC criteria,and the concrete stresses -principally on the upstream face. During the time that the structural and stability analyses were being performed,ongoing site inspections were in progress and geotechnical analysis were being performed (although these cannot be completed until all boreholes have been completed,all adits constructed,and all rock testing has been carried out).The principal geotechnical data available was drawn from the 1980s reports.In addition,the SSSHA was in progress (but not complete).The PMP/PMF and flood routing studies were in progress during the analyses,as well as the derivation of the proposed seismic design criteria,and the results of these two efforts were incorporated into the structural and stability analyses when available.Sensitivity studies were performed for varying foundation conditions,but these cannot be exhaustive until the results of site investigation studies are available. An overview of the evolution and logic of the dam configuration studies is shown in a flow chart in Figure 10.5-1 and can be used to aid in understanding the descriptions and sequence of the analyses documented in Sections 10.6 and 10.7 of the report.Availability of external information developed concurrently with the dam layouts and incorporated into the analyses is shown in the rust-colored circles in the figure. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-69 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The criteria for stability are clearly defined in FERC guidelines,but the criterion for concrete stress is less well documented.For the preliminary analysis -performed for layouts 2,3,and 4, a comparison with the allowable tensile stresses in RCC and horizontal joints in RCC was a key factor.For the "Final”modelling described in Section 10.7 -which included mass in the foundation -a comparison was made of the allowable RCC tensile stresses and the predicted stresses at the dam faces during the time history of the selected seismic events that formed the model input. During future detailed design of the project,after the results of the site investigation (including results from the adits and rock testing)are available to characterize the dam foundation;and the various geological features,the precise orientation of the dam,and a revised foundation excavation profile have been developed,it is expected that the feasibility layout and geometry (of Layout 4 [Modified])will be refined and adjusted to optimize the complete configuration, and further FE analysis will be performed including mass in the foundation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-70 December 2014 Zz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT LAYOUT 1 (PAD) RCC Gravity Dam Straight Axis Crest level El.2025 ft. NMOL El.2000 ft. Crest width 35 ft. D/S face 0.85H:1V RCC volume approx. 5,108,000 cy Refine layout to Include curved axis.Select location and suitable axis layouts for potential High Dam (El.2185 ft.NMOL} ¥ Analyze layouts using ADSAS (93 permutations] Select preferred layout (3)for Low Dam assessment LAYOUT 2 Curved -Three centered 1300 ft.central 40°arc, 4000 ft.radius abutments Crest level El.2075 ft NMOL El.2050 ft. Crest width 35 ft. D/S face 0.50H:1V RCC volume approx. 5,325,000 cy Perform ADSAS analysis on Low Dam layout (Layout 2-J) Calculate dam volume Analyze layout using ANSYS Examine predicted stresses -too high ¥ Perform 2D stress analysis using CADAM (30 configurations assessed) ¥ Select cross section that satisfies FERC criteria Refine plan layout of the dam LAYOUT 3 Curved -single center 3500 ft radius Crestlevel El.2075 ft. NMOL El.2050 ft Crest width 35 ft. D/S face 0.85H:1V RCC volume approx. 6,380,000 cy Perform ADSAS analysis Calculate dam volume Analyze layout using ANSYS, ¥ Examine predicted stresses -too high ¥ Refine plan layout of the dam Figure 10.5-1.RCC Dam Configuration Evolution LAYOUT 4 Curved -Single center and straight abutments 2600 ft.radius Crestlevel El.2065 ft. NMOL EI.2050 ft. Crest width 35 ft. DfS face 0.7H:1V Abutments 0.85H iV RCC volume approx. 5,468,000 cy Perform ADSAS analysis Calculate dam volume Modify foundation shape ¥ Analyze layout using ANSYS ¥ Examine predicted stresses -too high ¥ Sensitivity studies for foundation conditions ¥ Modify dam geometry (Crest width,downstream face) LAYOUT4 (MODIFIED) Curved -Single center and straight abutments 2600 ft.radius Crest level El.2065 ft NMOL El.2050 ft. Crest width 45 ft B/S face vertical curve Abutments 0.85H:1V RCC volume approx. 5,213,000 cy Analyze layout using ANSYS and LS-DYNA Sensitivity studies for foundation conditions Examine predicted stresses -ACCEPTABLE FEASIBILITY LAYOUT Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-71 Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.5.2.Pre-application Document (PAD)Dam (Layout 1) During the preparation of the PAD,three alternative dam types were considered:ECRD,CFRD and RCC.The project layout also considered the location of the powerhouse:surface vs underground.The findings of the assessment of the various layouts based on the various dam types,and described in Section 7,concluded that the most economic arrangement was found to be based on a RCC dam and a surface powerhouse at the toe of the dam.The dam detailed in the PAD had a straight axis with a vertical upstream face and a downstream face sloping at 0.85H:1V (Layout 1).The intakes to the power waterways and low level outlet were located on the upstream face of the dam and the spillway was integral to the dam on the north (right)side of the river channel. 10.5.3.Optimization of Dam Configuration 10.5.3.1.Gravity Dam -Layout Optimization Sequence Following submission of the PAD the design of the RCC dam was revisited with the aim of optimizing the layout to reap benefits in terms of reduced concrete volume,while maintaining stability and safety,thereby reducing cost and minimizing the construction schedule.The optimization focused on the reduction in concrete volume while ensuring a structurally sound and safe dam. The optimization of the dam initially focused on steepening the downstream face of the straight axis dam.The straight axis dam solely relied upon the weight of the structure to resist the forces applied by the impounded reservoir. The examination of possible configurations was performed both using the expected NMOL of the pool and also for a higher dam with a NMOL equivalent to the Stage 3 proposal in the 1980s. The analysis of the higher dam was performed so that any design decisions for the dam proposed in this report would not preclude future raising. The project site is remote and necessitates a significant investment in infrastructure to enable transportation of materials,plant,and construction workers to and from the site.Any reduction in imported materials could noticeably reduce the capital cost.In addition,the costs of maintaining the construction infrastructure,feeding and housing the workers,and maintaining the required supply chain will be extraordinarily high,so shortening the construction period is paramount.Any reduction in the time for construction would allow generation to commence earlier to commence revenue flows. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-72 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The most significant potential optimization of the project is founded on a reduction in the volume of concrete to be placed.Savings could accrue in the direct cost of the cement,fly ash, and the aggregate processing as well as the reduction in the time on site and thus the establishment costs. The derivation of the proposed configuration is described below and has been an attendant iterative process aimed at selecting a configuration that is safe and (following the applicable optimization and detailed design)will be proven to perform within FERC,and other,guidelines at reasonable cost.The intent in this report is not to finally design all aspects of the dam shape or completely resolve all aspects of the dam shape and performance,so the level of detail of the various analyses is somewhat less than would be undertaken in final,detailed design. The first challenge in the exercise was the lack of sufficient site investigation focused on the projected dam foundation.Detailed design of an RCC dam will require focused and specific site investigation,including the excavation of adits in the abutments to afford visual examination, mapping and in-situ testing of the rock mass. Subsequent to the straight axis RCC gravity dam (Layout 1)included in the PAD,three additional configurations have been examined for the dam (Layouts 2,3,and 4).Each configuration is classified as a curved gravity dam -i.e.,the dam relies on its weight for the largest contribution to its stability,but also utilizes some horizontal arch action to enhance the stability and structural performance.Each configuration had a different curvature and slope of the downstream face,and each was located most favorably to the topography and existing rock conditions (e.g.,avoiding certain geologic features)as understood at the time each was developed. 10.5.3.2.Three-centered Curved Dam (Layout 2) To investigate the possibility of further steepening of the downstream face,beyond that for a gravity structure,the introduction of a curve in the dam plan was investigated.The inclusion of a curve in the dam axis would enable transfer of limited loading to the abutments.The configuration of the curved axis was selected assuming (based on the previous investigations) competent bedrock. Unlike a gravity dam where the structure could be analyzed as a 2-D structure,the assessment of load transfer to the abutments required a 3-D structural analysis. The configuration was selected based on extensive modeling of 13 possible dam geometrics using the Trial Load Method as described in Section 10.5.3.The computerized version of the Trial Load Method,ADSAS (Arch Dam Stress Analysis System)provides a rapid means of Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-73 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT analyzingthe 3-D stress distribution within a dam based on static loads.The 13 possible geometrics comprised a range of radii using different downstream face slopes from 0.3 H:1V to 0.85H:1V.Ninety eight different combinations were examined,including the PAD layout (straight dam)which was designated 'N'.Each run of ADSAS provided upstream and downstream arch,cantilever and principal stresses and a volume of concrete.The most promising arrangement was chosen for a more detailed analysis,using FE analysis for both static and dynamic loading. The selected geometry comprised a three-centered dam utilizing a downstream slope of 0.5H:1V, a center arc of 40°,and a radius of 1,300 ft.,together with flank radii of 4,000 ft. (configuration J). The preliminary FE analysis procedure is described in Section 10.6 below and the results verified the static results of the ADSAS analysis while recording slightly higher than anticipated stresses during the dynamic loading condition.Following the presentation of the preliminary results to the Board of Consultants in March 2013 it was decided to review the configuration presented to increase the gravity contribution to the stability of the structure. 10.5.3.3.Single Curvature Gravity Dam (Layout 3) A single curvature gravity dam was developed (Layout 3)to increase the dam's reliance on gravity for stability. A radius of 3,500 ft.was adopted so that the single curvature structure was positioned symmetrically in the valley and performs predominantly as a gravity structure although with limited benefit realized by load transfer to the abutments.The maximum cross section of the dam was analyzed in 2-D using the Computer Analysis of Dams (CADAM)software to determine the section properties necessary to satisfy FERC stability criteria)CADAM demonstrated that a vertical upstream face and a downstream face sloping at 0.85H:1V was appropriate to satisfy the criteria and was then analyzed using ADSAS and FE analysis. As noted,the performance of the abutments under load,and the significance of any features in the foundations will be examined more fully following future site investigations. Layout 3 was considered to be conservative and represents the upper bound of the spectrum of possible configurations,but a reconfiguration from Layout 2 to Layout 3 resulted in approximately one million extra cubic yards of RCC being needed for the dam.Layout 2 is considered the lower bound option of the appropriate dam,so a plot of volume versus height was made for the two configurations (single centered and three centered curves)to indicate a final direction of study for this stage of optimization.These curves are included as Figure 10.5-2 and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-74 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT show the general range of dam height vs.volume towards which the optimization was then directed. Using input from the project hydrological studies with respect to the eventual desirable storage,a target volume of RCC of between 5.4 and 5.6 million was selected.With reference to Figure 10.5-2,the maximum crest elevation for the dam would be between El.2040 ft.for Layout 2 and El.2075 ft.for the Layout 3 configuration. 2075 > -e-Layout2-3centered.0.5 D/S slope ST i)ae e Be -@=Layout 3 -3500 ft radius,0.85 D/S slope .se Soe .--ss -7 -rs toe :|Layout 4 (Before |.Foe,2050 ::«|Optimization) i i : 1 ' 2025 -'Optimization i Envelope i a 2000 a oy Ft etmeeneemer een ae eae kate ..oe *mo cese hee a ete ee eee ae Se nene ee Se eS § rj8 2tad -%1975ce] 1950 +ae 1925 hee cere enter ee sb cas oe ore ae 4 se omnes cae mee os ae *ET Cee eT Oe ne |\ 1900 +: L 2,500,000 3,000,000 3,500,000 4,000,000 4,500,000 5,000,000 5,500,000 6,000,000 6,500,000 RCC Volume (cy) Figure 10.5-2.RCC Volume,Dam Layouts 2 and 3 showing Layout 4 before Optimization The final selected operational rules for use of the low level outlet -and the surcharge required to pass any selected discharge without opening the gates -are key elements in determining the dam height,as the normal freeboard will be the total of the required surcharge for the use of the low level outlet plus any PMF surcharge.For a NMOL of El.2050 ft.a total surcharge for both conditions would likely be a maximum of 15 ft.This assumption resulted in a dam crest of El. 2065 ft.being selected. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-75 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.5.3.4.Single Curvature Gravity Dam with Straight Axis Abutments (Layout 4) Although the construction cost estimate prepared at the end of 2013 included the single radius dam,it was recognized that if the total RCC volume could be reduced to approximately 5.5 million cubic yards or less,then a full season of construction could be eliminated and substantive reductions in project cost achieved.Using the original comparison of volumes for the high dam, a compromise among Dams A,D,and E appeared promising,so a layout was prepared for a single radius for the central part of the dam of 2,600 ft.,together with straight gravity sections on either end.By using this combination,the dam foundation footprint remains almost exactly the same as that of Layout 3,and the right abutment location does not change.The left abutment rotates slightly downstream,but is judged to be acceptable -at this level of geotechnical knowledge of the site. The updated configuration (Layout 4)for the Watana Dam thus comprised a central portion with an axis radius of 2,600 ft.The dam axis changes to a straight line at a tangent point and continues to the abutments. The crest of the dam is 35 ft.wide,and at El.2065 ft.is 10 ft.lower than previous iterations. This 10 ft.lowering of the crest level resulted from a reassessment of the flood and freeboard requirements for the dam at the completion of the PMP/PMF studies (which was completed part way through this analysis)and after selection of an acceptable reservoir rise of 15 ft.for the efficient use of the low level outlets and for passage of the PMF.The curved section has a downstream face slope of 0.7H:1V and the straight gravity section includes a 0.85H:1V slope on the downstream face.All portions have a sloping upstream face (0.1H:1V)below El.1770 ft. transitioning to a vertical face above.The change in downstream face slope reflects the reliance on gravity at the abutments. 10.5.3.5.Single Curvature Gravity Dam with Curved Downstream Face (Layout 4 - Modified) Following FE analysis of Layout 4 as described in Section 10.6.6.4,the dam configuration was further modified to increase the width of the dam crest to 45 ft.,and the downstream face of the curved section of the dam was modified from a straight sloping section to a single radius curve. The dam geometry selected for the modified Layout 4 is shown in Figures Figure 10.7-2 and Figure 10.7-3. The inclusion of a single radius curve to the downstream face of the curved portion of the dam results in a further reduction in the volume of RCC required to construct the structure.The Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-76 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. estimated RCC volume for the modified Layout 4 (final)configuration was calculated and the predicted volumes are shown in Table 10.5-1. Table 10.5-1.RCC Volume (Layout 4 -modified) Section RCC Volume (cy) Left Abutment 595,600 Center 3,706,340 Downstream fill 125,260 Right Abutment 786,750 Total 5,213,950 The Layout 4-modified configuration results in a reduction of more than 254,000 cy of RCC relative to Layout 4;this would result in a one month reduction in the placement schedule. 10.5.4.Curved Alignment Analysis 10.5.4.1.Trial Load Method Unlike a gravity dam,where the structure could be analyzed as a 2-D structure the assessment of load transfer to the abutments associated with a curved dam requires a 3-D structural analysis. The structural analysis of a curved gravity dam required the use of proprietary modeling software to analyze the distribution of stresses within the body of the dam. The examination of the benefits of introducing curvature into the dam design was accomplished by the use of the traditional Trial Load Method analysis which allowed a first pass at the optimization of the curvature and downstream slopes of the structure before embarking on a more detailed FE analysis of the structural performance of the selected dam configuration.A FE Model does not readily lend itself to alteration,thus any adjustment (trial and error)in geometry is a time consuming exercise. The Trial Load Method is a process developed by the Bureau of Reclamation from 1923 to 1935. The analysis was performed using the ADSAS a computerized version of the trial load method approach which utilizes a matrix solution in arriving at the proper division of load between vertical and horizontal elements. The trial load method assumes that the dam is divided into a system of vertical and horizontal elements with each system occupying the entire volume of the dam and independent of the other. The loads applied to the dam are then divided between these systems in such a way that geometrical continuity is attained throughout the structure.Representative horizontal elements Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-77 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT and vertical elements are selected to be used in the analysis (see Figure 10.5-3).The conditions of deformation for a 3-D structure may then be expressed in terms of three mutually perpendicular linear displacements and three angular displacements. )ELEVATION PROFILE Figure 10.5-3.Typical Elements Used in the Trial Load Method The requirements for a correct solution of this analysis may be inferred from the Kirchhoff uniqueness theorem in the theory of elasticity.These requirements are: «The elastic properties of the solid must be completely expressible in terms of two constants:Young's modulus and Poisson's ratio. *Ifthe volume of the solid in the unstressed state is divided into small elements by passing intersecting surfaces through it,each element must remain in equilibrium. =Each of these elements must deform as the solid passes into the stressed state so that it will continue to fit with its neighbors on all sides. «The stresses or displacements at the boundaries of the solid must conform to the stresses or displacements imposed. The basic assumptions necessary for the method are: «The concrete of the dam is homogeneous,isotropic,and uniformly elastic material. «Vertical displacements caused by dead load,shrinkage,and temperature changes prior to joint closure,take place in the cantilever elements before arch action commences,so that no lateral transfer of these effects occurs. »Stresses calculated from the final load distribution on the selected elements represent the stresses in the dam for the assumed loading. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-78 ;December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The 1980s studies had recommended a NMOL of El.2185 ft.as the ultimate development at the site.In order that any site development option chosen for the current licensing (and construction)would not preclude a future generation from raising the dam,the trial load analysis was initially performed for a NMOL of El.2185 ft.The results of the analysis were then used to identify a suitable configuration that was then analyzed again with a NMOL of El.2000 ft. Completion of the power operations modeling studies eventually concluded that the NMOL would be El.2050 ft. 10.5.4.2.Material Properties and Loads Material properties used in the ADSAS analysis were: Sustained modulus of elasticity of concrete:4,000,000 psi Poisson's ratio for concrete:0.25 Unit weight of concrete:150 pef Compressive strength of concrete:4,500 psi Deformation modulus of the foundation rock:4,000,000 psi Poisson's ratio for rock:0.33 At this conceptual stage of analysis,dead loads and static water loads were included.Thermal, sediment,ice and seismic loads were not considered,but the examination of the output of the analysis was made with the understanding that the stresses could be somewhat higher than generated (1.e.,decisions were taken conservatively). 10.5.5.Analytical Development The first conceptual layouts developed were based on a single curvature,of 1,800-ft.radius, chosen from experience and with regard to the projected rock contours (from the 1980s investigation)at the dam foundation.The radius was selected with respect to a final crest elevation of approximately El.2025 ft.from the previous HDR studies.Horizontal angles of intersection between the downstream face of the dam and the contour line of competent rock of 30°or less was used as the guideline for establishing the orientation and abutment conditions.A 1,800-ft.radius ensured angles of contact less than the critical value. Based on the first ADSAS analysis,unacceptable tensile stresses were evident in the horizontal (arch)elements at the downstream face.To address this unacceptable tensile stress,the radius of curvature was reduced to 1,300 ft.with a transition to a 4,000-ft.radius at each flank.The three- centered arrangement was used in all subsequent runs of ADSAS,with a NMOL of EI.2185 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-79 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT (and a dam crest elevation of El.2210 ft.)representing the largest development that could reasonably ever be constructed at the site. So that the most suitable dam configuration was eventually modeled in the FE analysis,various dam alternatives were assessed.In total 98 alternative configurations were considered (including different downstream slopes)to identify the optimum arrangement. 10.5.6.Preliminary Design Criteria -Structural Analyses The design parameters used in the analyses for all layouts were selected to be sufficiently conservative that the eventual criteria adopted after a full site investigation (which is yet to be performed),such as foundation conditions,material properties,etc.,would not cause substantial reworking of the layout or cross section at the detailed design stage.The material properties and parameters used in the analyses are presented in Table 10.5-2 below.Parameters were revised as the analyses progressed and the dam geometry was refined. Table 10.5-2.Preliminary Dam Design Parameters for Layout Development Design Data -Dam Crest of dam El.2075 ft.(initial) Crest width 35 ft. Crest length 3,094 ft. Upstream face Vertical Downstream face (sloping section)0.5H:1.0V (initial) Structural height at maximum section 705 ft. Design Data -Water Surface Elevations Normal maximum water level El.2050 ft. Flood surcharge level El.2067.1 ft. Tailwater-Normal at Foundation Level Material Properties Water Unit weight 62.4 pef Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-80 December 2014 -yzw- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Roller-Compacted Concrete Unit weight 150.0 pef Unconfined static compressive strength (ASTM C39,C172,C31)fc'=5500 psi Dynamic compressive strength 7150 psi Static direct tensile strength (ASTM C496)385 psi Dynamic tensile strength 580 psi Friction angle 45° Static elastic modulus (ASTM C469)3,000,000 psi Dynamic elastic modulus 3,900,000 psi Poisson's ratio 0.25 Coefficient of thermal expansion 0.0000055 /°F Diffusivity 0.045 sq.ft./hr. Foundation Rock Unit weight 150 pef Static deformation modulus 4,000,000 psi Dynamic deformation modulus 3,500,000 psi Friction angle at concrete-rock interface 45° Cohesion at concrete-rock interface 100 psi Poisson's ratio 0.25 Unconfined compressive strength (intact rock)17,750 psi Tensile strength (intact rock)1,845 psi Specific heat 0.20 btu/lb./°F Thermal conductivity 1.0 btu/lb./°F Note:ASTM -American Society for Testing and Materials 10.5.7.Two-Dimensional Gravity Analysis As the dam would predominantly act as a 2-D structure,various cross sections were analyzed using CADAM dam stability analysis software.The software was developed by the research group on dam safety at Ecole Polytechnique,University of Montreal,Canada,for static and seismic stability analysis of concrete gravity dams.The software is based on the gravity method using rigid body equilibrium and beam theory to perform a stress analysis,compute crack lengths,and sliding safety factors.Seismic analysis can be performed using either the pseudostatic or a simplified response spectra method.The analysis was performed to estimate the cross-sectional geometry that would satisfy stability criteria for the usual and unusual load cases required by the FERC Engineering Guidelines for the Evaluation of Hydropower Projects, Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-81 Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Chapter 3,Gravity Dams.The simplified analysis was also used to assess the potential for cracking at the base of the dam as the result of a seismic event. 10.5.8.Finite Element Modeling of Dam 10.5.8.1.Background and Approach The configurations of the dam determined from preliminary stress analysis were subsequently analyzed using FE methods. The FE structural and thermal analyses were performed generally in accordance with the FERC Engineering Guidelines for the Evaluation of Hydropower Projects,Chapter 11,Arch Dams. The FE studies performed in the preparation of this report were intended to: «extend the understanding of the dam performance from the results of the Trial Load Method analysis; *verify the layout and cross section of the dam throughout configuration development, including seismic loads; =study the thermal performance in sufficient detail that the construction planning can be completed in greater detail; «identify the necessity for and extent of the next stage of site investigations of the foundation;and, =confirm that the selected cross section and layout "does no harm”to any future generations consideration of raising of the dam. 10.5.8.2.Progression of Finite Element Analyses FE studies performed for Layouts 2,3 and 4 are described in Sections 10.6 and 10.7.Results from each analysis were used to refine the dam geometry and to further develop the layout for the subsequent analysis. Dam Layout 2 was analyzed using ANSYS and the linear response spectra method.Layouts 3, 4,and 4(Modified)were analyzed using ANSYS and the nonlinear time history method.Layout 4 (Modified)was then analyzed using the nonlinear time history method and LS-DYNA, including mass in the foundation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-82 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.6.Dam -Preliminary Analysis 10.6.1.Initial Dam Configuration (Layout 2) As noted above,multiple alternatives (14 including the straight-axis PAD layout)were first considered and each alternative was analyzed for the potential ultimate development of the dam to a crest level of El.2190 ft.using ADSAS.Downstream face slopes ranged from 0.3H:1V to 0.85H:1V.Ninety-eight permutations were considered in total.The dam configurations analyzed are described in Table 10.6-1. Table 10.6-1.Analyzed Dam Plan Configurations for Layout 2 (high dam) Dam ,Rov (Feet)male Crest LengthMiddleSection|Outer Sections |(Degrees)(Feet) A 1800 Straight 91.3 4543 B 2000 Straight 79.8 4335 C 2200 -4350 D 2400 -4251 E 4000 -3979 F 1300 4000 30 4241 G 1500 4000 30 4171 H 1700 4000 30 4150 |1800 4000 30 4133 J 1300 4000 40 4426 K 1500 4000 40 4391 L 1700 4000 40 4287 M 1800 4000 40 4252 N*Straight -3805 *Dam N was the straight-axis configuration in the PAD The ADSAS software cannot model straight axes,so an approximation was made using a radius of 999,999 ft.This technique was used to model the outer portions of the dam for the Dam A,B and N alternatives. > After the analysis of the "high”dams (a possible ultimate development corresponding to the Stage 3 Watana layout included in the 1980s License Application),configurations F and J were identified as preferred,with a downstream face at 0.5H:1V.A steeper downstream face resulting in a thinner vertical cross section would result in a significant transfer of stresses from the vertical to the horizontal plane which would result in the dam no longer performing completely as a gravity structure.These two alternatives,along with Dam N were then assessed for the low Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-83 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT dam configuration being studied at this time for downstream slopes ranging from 0.4H:1V to 0.6H:1V. The preliminary stress analysis did not take into account seismic or thermal loads which could affect the stress values negatively.As analyzed,both dams F and J were satisfactory alternatives as analyzed.However,the result of the addition of these extra loads would be less pronounced for Dam J,and it was therefore selected as the configuration for further analysis. Thus the selection of alternative J for "Layout 2”consists of a central portion with a curved axis of 1,300 ft.radius which changes to a 4,000 ft.radius at a tangent point on the abutments.The downstream face is a uniform slope of 0.5H:1V and the upstream face is vertical.The central portion is defined by a phi angle of 40°.The dam crest for Layout 2 remains at El.2075 ft. 10.6.1.1.Arch Dam Stress Analysis System (ADSAS) ADSAS was used in advance of FE analysis to limit the time spent performing multiple seismic analyses at this feasibility stage of design,and the results of the ADSAS analysis provided a level of confidence that the selected dam cross section would be capable of withstanding the expected seismic loads. The results of the analysis of alternative J (Layout 2)are shown in Figure 10.6-1 for the crown cantilever. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-84 December 2014 ---yzw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 2100 l J d|--e-Cantilever UpstreamiDamCrest:EL 2075 ft |2050 |Reservoir NMOL:EL 2050ft _-A ' vDamJ\Downstream Slope :0.5:1 '2000 -v . '-t-=Horizontal Upstream ;f |====Horizontal Downstream |-- |.4 V4 i'4.1900 Yo + s Lt q\:|Cantilever Upstream |.,/sy1800a a\"sso ba x \/"i." ¢1650 -|Horizontal Upstream f ef |@ |--e-Cantilever Downstream rRwe)NIOouwofo)Elevation(ft)» s s by ' ' x4 ' :'Ny Horizontal Downstream F -__s o a 'S/S.;|a//|Cantilever Downstream1400'77WA, 1350 ¢ -600 -550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 ie)50 100 #150 200 Compression Stress (psi)TensionraywOooO>aVaheenFigure 10.6-1.Layout 2 (Dam J)-Crown Cantilever Stresses 10.6.1.2.FE Structural Analysis The 3-D static and dynamic FE analyses of Dam Layout 2 were performed using the FE analysis program ANSYS,Version 14.ANSYS is a state-of-the-art commercially available general FE method program,which is widely used as an analytical tool for static and dynamic evaluations of dams. The ultimate development height of the dam was not dynamically analyzed because it is assumed that the results of the ADSAS calculations give sufficient indication that a safe dam raising is feasible in the future.The only major aspect of the current project that would depend on the requirements for future raising is the distance between the downstream toe of the dam and the powerhouse.It is considered that for the accuracy of the project estimates at this time,the ADSAS analysis was sufficient.During detailed design it is recommended that one analysis be performed of the postulated high dam to verify the required separation of the powerhouse and dam. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-85 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT A linear FE model was created consisting of 5160 elements and 6658 nodes.Mostly hexagonal ("brick”)elements were used,while prism ("wedge”)elements were utilized in portions of the model where the geometry was not regular.The dam and rock foundation elements used in the model consisted of 8-node elements,with one node at each corner.Three-dimensional mass elements (added mass)attached to the nodes of the elements on the upstream face of the dam were used to simulate hydrodynamic effects of the reservoir.The weights of the added masses on the dam face were computed as noted below. The FE method model of the dam comprises four elements in thickness and 20 vertical columns of elements at the crown cantilever.The rock foundation was modeled to a depth equal to the height of the dam,a width equal to three times the dam height and a length equal to the dam height in the upstream and downstream directions.The elements of the dam body are connected directly to the elements of the foundation neglecting any possible separation (opening)at the dam-foundation interface due to applied loadings.This model is shown in Figure 10.6-2 and Figure 10.6-3. The rock foundation of the FE method model was assigned stiffness in accordance with the review of existing boreholes and engineering properties of rock determined from laboratory testing and similar materials by the project geological engineers -but was assigned no mass.A massless foundation allows for transmission of the seismic ground motion time history from the boundary of the model to the dam foundation.Thus the inertial effects of the foundation mass were not included,leading to a conservative transmission of energy and an overestimate of the seismic force applied to the dam.This was rectified later in subsequent studies when mass was added to the dam foundation as discussed in Section 10.7. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-86 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT SEP 25 2012 |'12:06:08 |' Figure 10.6-2.Finite Element Model Upstream Side (Layout 2) SEP 25 2012 12:04:49 eeeIMMA:TAT Figure 10.6-3.Finite Element Model Downstream Side (Layout 2) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-87 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.6.1.2.1.Dead Loads The gravity load was applied as a gravitational acceleration of 32.2 ft./sec”.The weight of the dam was based on the average density of concrete of 150 Ibs./ft?.Loading due to silt was not considered in the analysis.No gravity loads from the foundation were included,as the foundation elements were assumed to be massless,and simply provided stiffness in the model. 10.6.1.2.2.Hydrostatic Load The hydrostatic reservoir load was applied in the model as a distributed force load on the dam face based on the maximum normal operating pool reservoir condition of El.2050 ft.No flood, overtopping,or any other reservoir level fluctuation and resulting load combination was considered in the dynamic analysis. 10.6.1.2.3.Internal Hydrostatic Loads (Uplift) Uplift pressure at the dam-foundation interface could affect overall stability of the dam but has limited effect on the dam body internal stress distribution being investigated by the FE modeling. In the model for Layout 2 dam elements were continuously attached to the foundation elements and no uplift pressure was considered -although this boundary condition was modified for later configuration modeling. 10.6.1.2.4.Ice Loads No ice loads were included in the analysis,but will be considered during detailed design. 10.6.1.2.5.Seismic Loads Concurrently with the development of the FE models,the site specific seismic hazard analysis was in progress,and so the ground motions used for the analysis have been adjusted slightly as the studies progressed.For the initial dynamic analysis of Layout 2 the linear response-spectrum analysis method was used.The horizontal response spectra shown in Figure 10.6-4 were used in the analyses. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-88 December 2014 ---za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 2.2 =-@=-2,500 yrs -B-5,000 yrs A °10,000yrs |Acceleration(Sa/g)Period (seconds) Figure 10.6-4.Response Spectra for Watana Dam Site An earthquake with 2,500 year return period was adopted as the MCE during the studies performed for Layout 2,with a peak ground acceleration (PGA)of 0.52g.The dam was also analyzed for earthquakes with 0.66g and 0.82g PGA corresponding to the 5,000 yr.and 10,000 yr.event respectively.The return period for the MCE was later modified as the layout development progressed. 10.6.1.2.6.Silt Load No silt loads were included but will be included in subsequent analysis. 10.6.1.2.7.Hydrodynamic Load Hydrodynamic reservoir loading on the upstream face of the dam was estimated based on a NMOL of El.2050 ft.and orientation of each element using the Westergaard method and applied to the model as added masses attached to the upstream nodes for the full reservoir condition. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-89 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.6.1.3.Static Analysis Analyses using normal static loading were performed and compared with the results of the ADSAS analysis.Some deviations in the stress distribution between the methodologies were observed and were attributed to the way dead load is considered.The trial load method assumes that the dam is built as separate vertical cantilever blocks resulting in the dead load being transferred vertically to the cantilevers with no "arch”action.Elastic FE analysis considers the dam weight as a single block and arch stresses are developed within dam body due to the dam weight.The two-step odd-even cantilever method (described in Section 11-5.2.2 of FERC Engineering Guidelines,Chapter 11 -Arch Dams)was used to analyze the dam for dead loading conditions.The dead load stresses determined using the odd-even cantilever method are in agreement with the ADSAS analysis. 10.6.1.4.Dynamic Analysis 10.6.1.4.1._Modal Analysis A modal analysis of the dam was performed to calculate the fundamental periods of vibration and mode shapes of the linear model.In response spectra analysis,modal mass is used as an indicator of the number of modes to consider in the analysis.The first twelve natural periods of the dam and respective modal participation mass ratios are shown in Table 10.6-2.The mode shapes for the first six vibration modes are shown in Figure 10.6-5. Table 10.6-2.Periods of Vibration and Modal Participation Mass Ratio (MPMR)of Dam (Layout 2) Mode Period MPMR Sum of MPMR Number Sec u/D Cross stream Vertical u/D Cross stream Vertical 1 0.657 0.470 0.002 0.018 0.470 0.002 0.018 2 0.495 0.002 0.074 0.000 0.470 0.076 0.018 3 0.385 0.040 0.000 0.000 0.510 0.076 0.018 4 0.313 0.080 0.005 0.001 0.590 0.081 0.019 5 0.308 0.210 0.010 0.006 0.800 0.090 0.025 6 0.262 0.012 0.003 0.007 0.810 0.094 0.032 7 0.258 0.001 0.700 0.059 0.820 0.790 0.091 8 0.254 0.002 0.061 0.730 0.820 0.850 0.820 9 0.232 0.000 0.001 0.000 0.820 0.850 0.820 10 0.224 0.000 0.001 0.000 0.820 0.850 0.820 11 0.198 0.012 0.000 0.001 0.830 0.850 0.820 12 0.189 0.000 0.000 0.000 0.830 0.860 0.820 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-90 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Review of the results indicates that the first 12 vibration modes represent more than 80 percent of the total mass of the structure in all directions.Adopting twelve modes in the analysis will adequately approximate the seismic response of the structure at this stage of the design process. More vibration modes would be necessary in final design if this response spectra methodology represented the full extent of simulation,but the use of full time integration (ANSYS and LS- DYNA)-described in section 10.7 -supersedes these calculations. The fundamental period of the analyzed dam is 0.657 seconds (1.52 cycles/sec.). NODAL SOLUTION STEP=1 SUB =1 FREQ=1 .53303 USUM (AVG) RSYS=0 DMX =.118E-03 SMN =.761E-06 SMX =.118E-03 ee BADIA!LR,Se amnnanneRNRETELe Ue Laeaa ta»gapgumananennemmmmacrenapamg SE Og ace TS.REE,ELSE SS Creve peoerenyl -761E-06 .268E-04 -528E-04 -788E-04 -105E-03 38E-04 -398E-04 -658E-04 -918E -04 -118E-03 Mode 1 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-91 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT NODAL SOLUTION STEP=1 SUB =2 FREQ=2 .09198 USUM (AVG) RSYS=0 DMX =.137E-03 SMN =.462E-06 SMX =.137E-03 |wee aman.|:" * E -s -462E-06 .309E-04 -613E-04 -916E-04 .122E-03 -157E-04 -461E-04 -765E-04 -107E-03 -137E-03 Mode 2 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-92 December 2014 yz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT .AN;: NODAL SOLUTION STEP=1 SUB =3 FREQ=2.73356USUM(AVG) RSYS=0 DMX =.158E-03 SMN =.518E-06 SMX =.158E-03 ¥me |i=pe | -518E-06 .355E-04 -705E-04 .105E-03 .140E-03 -180E-04 .880E-04 -123E-03 -158E-03 Mode 3 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-93 Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT NODAL SOLUTION STEP=1 SUB =4 FREQ=3.25123 USUM (AVG) RSYS DMX SMN SMX Oo-154E-03 -731E-06 -154E-03oe z a a :=| .731E-06 -348E-04 .689E-04 .103E-03 -137E-03 -178E-04 -518E-04 -859E-04 -120E-03 -154E-03 Mode 4 Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 10-94 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT NODAL SOLUTION STEP=1 SUB =5 FREQ=3.42258 USUM (AVG) RSYS DMX SMN SMX Oo.173E-03 -130E-05 -173E-03Holwu |<=|:1-4 we| -130E-05 -395E-04 -776E-04 -L16E-03 -154E-03 -204E-04 .985E-04 -967E-04 -135E-03 -173E-03 Mode 5 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-95 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. AN>: NODAL SOLUTION STEP=1 SUB =6 FREQ=3.73415 USUM (AVG) RSYS=0 DMX =.698E-04 SMN =.435E-05 SMX =.698E-04 oe |aa "i =eee oleaeI er hee pe a .435E-05 .189E-04 .335E-04 .480E-04 .626E-04 .116E-04 .262E-04 -407E-04 .553E-04 .698E-04 Mode 6 Figure 10.6-5.Mode Shapes -First Six Vibration Modes (Dam Layout 2) 10.6.1.5.Response Spectra Analysis Elastic dynamic analysis of the dam was performed using response spectra to compute the maximum response of the dam due to earthquake loading.Model input included the two horizontal and the vertical response spectra.The dam was analyzed for three earthquake load scenarios: =Earthquake with 2,500-year return period with a PGA of 0.522g «Earthquake with 5,000-year return period with a PGA of 0.664g «Earthquake with 10,000-year return period with a PGA of 0.827g Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-96 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT The maximum (tensile)and minimum (compressive)horizontal and vertical stresses on the upstream and downstream faces of dam are summarized in Table 10.6-3 and Table 10.6-4.In accordance with ANSYS convention -and for ease of comparison -tensile stresses are positive, and compressive stresses are negative. Table 10.6-3.Comparison of Seismic Analysis Results -Maximum Tensile Stresses (Layout 2) Upstream face Downstream face Earthquake Return Vertical Stress Horizontal Stress Vertical Stress Horizontal Stress Period (psi)(psi)(psi)(psi) 2,500 yrs.711 628 663 345 5,000 yrs.983 909 877 533 10,000 yrs.1300 1240 1130 752 Table 10.6-4.Comparison of Seismic Analysis Results -Maximum Compressive Stresses (Layout 2) Upstream face Downstream face Earthquake Return Vertical Stress Horizontal Stress Vertical Stress Horizontal Stress Period (psi)(psi)(psi)(psi) 2,500 yrs.-1132 -1256 -910 -917 5,000 yrs.-1403 -1538 -1122 -1105 10,000 yrs.-1721 -1868 -1379 -1324 Current FERC dam safety practice does not judge the seismic safety of the dams based on allowable stress criteria,and limited damage is allowed during the maximum credible earthquake.However,the computed maximum compressive and tensile stresses from a linear elastic analysis remain useful as an indicator of the expected level of damage in a concrete dam. The maximum compressive cantilever stress and compressive horizontal stress are 1,721 psi and 1,868 psi respectively.Therefore the compressive stresses are below the corresponding allowable compressive stress of 2,700 psi for all earthquakes and no compressive damage is to be expected. The maximum cantilever tensile stress for the 2,500 year return period earthquake is 711 psi, which is in excess of the apparent dynamic tensile strength of RCC.This overstressing is indicated only for a small area on the upstream and downstream face of the dam.The localized nature of the overstress is such that the proposed dam geometry will be acceptably safe against the developed stresses in the dam body during an earthquake with return period of 2,500 yrs. The overstressing will occur for just one or two cycles during the early part of the time history, as discussed in Section 10.7. Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-97 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The results for the 5,000-yr.and 10,000-yr.events indicate that,should these levels of ground motion be used as criteria there may well be overstress which could cause appreciable damage on the dam body.If more detailed analysis with less conservative criteria still shows overstressing,dam geometry would need to be revised to reduce developed stresses in the dam. It is also noted that the range of computed tensile stresses at the dam-foundation interface and tensile horizontal stresses between the dam monoliths exceed the tensile capacity of these interfaces.This reinforces the conclusion that linear elastic analyses do not present a realistic seismic response of the dam,and a more sophisticated analysis considering nonlinear contact elements at these locations is more appropriate. 10.6.1.6.RCC Volume The optimization of RCC volume -while robustly maintaining dam safety -was the crux of the early analyses.The ADSAS program calculates the volume of concrete in the analyzed structure.It should be noted that the concrete volume predicted by ADSAS for the PAD layout (Dam N)is larger than that estimated in December 2011.This difference is due to the spacing between the cantilever sections analyzed in ADSAS.The 2011 estimate was based on sections at every 100 ft.whereas the spacing of sections used in the ADSAS model varied from 95 ft.to 395 ft. The sections analyzed for the curved dams were all radial from the center of curvature.The base of each vertical element coincided with the end of a horizontal element.The entire base of each vertical element must be founded on rock,so the highest foundation elevation was located at the downstream toe of the dam in several instances.This would generate significant excavation at the foundation as the section would progressively get deeper into the rock abutment as it extended towards the dam's upstream face.This leads to conservative volume estimation.For the purposes of this analysis,however the volume estimations are primarily used for the comparison of the dam alternatives and serve as a measure of the relative scale of the dams.The volumes estimated for a Susitna-Watana high dam with a NMOL of El.2185 ft.(maximum possible development as determined in the 1980s studies)are listed in Table 10.6-5. Table 10.6-5.Susitna-Watana High Dam:ADSAS Estimated Dam Volumes (cubic yards) Dam -Slope of Downstream Face (xH:1V) 0.3 0.4 0.5 0.6 0.7 0.8 0.85 A 6,416,000 7,746,000 |9,041,000 10,300,000 11,525,000 12,714,000 13,295,000 B 6,416,000 7,767,000 |9,086,000 10,372,000 11,626,000 12,847,000 13,446,000 C 6,370,000 7,700,000 |9,002,000 10,277,000 11,523,000 12,742,000 13,340,000 D 6,271,000 7,589,000 |8,882,000 10,149,000 11,391,000 12,607,000 13,206,000 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-98 December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Dam Slope of Downstream Face (xH:1V) 0.3 0.4 0.5 0.6 0.7 0.8 0.85 E 5,911,000 7,178,000 |8,432,000 9,671,000 10,896,000 12,107,000 12,708,000 F 6,341,000 7,655,000 |8,932,000 10,174,000 11,380,000 12,550,000 13,121,000 G 6,305,000 7,615,000 |8,891,000 10,133,000 11,342,000 12,518,000 13,093,000 H 6,176,000 7,463,000 {8,719,000 9,945,000 11,139,000 12,303,000 12,873,000 |6,261,000 |7,574,000 |8,856,000 10,108,000 11,330,000 12,521,000 13,105,000 J 6,379,000 |7,686,000 |8,950,000 10,174,000 11,356,000 12,496,000 13,051,000 K 6,319,000 |7,620,000 |8,883,000 10,111,000 11,301,000 12,455,000 13,018,000 L 6,233,000 |7,523,000 |8,780,000 10,003,000 11,193,000 12,350,000 12,916,000 M 6,207,000 7,496,000 |8,754,000 9,979,000 11,172,000 12,332,000 12,900,000 N 5,801,000 7,079,000 |8,356,000 9,634,000 10,911,000 12,189,000 12,828,000 The volumes for the selected favorable configuration for the lower dam (Layout 2,Alternate J) postulated during these studies were also estimated by the ADSAS program and the results are shown in Table 10.6-6. Table 10.6-6.Watana Dam (Layout 2):ADSAS Estimated Dam Volumes (cubic yards) D Slope of Downstream Face (xH:1V) am 0.4 0.5 0.6 0.7 0.85 J 4,521,000 5,276,000 6,009,000 -- 10.6.2.Revised Dam Configuration (Layout 3) 10.6.2.1._Configuration Description After being presented with the results of the FE analysis of the initial configuration (Layout 2, Alternate J),the Board of Consultants suggested that a simple single radius configuration be analyzed,so the team reassessed the work performed to derive the initial configuration with the object to establish an upper envelope of conservatism in the layout.Upon examination of the original ADSAS volume calculations,the most economical of the traditional curved gravity sections was Alternative E with a single axis radius of 4,000 ft.,but on examination of the topography,it was found that a radius of 3,500 ft.resulted in a better angle of intersection with the abutment topographic ground contours.This radius was therefore selected for Layout 3,but is not represented in the original volume calculations. 10.6.2.2.Two-Dimensional Gravity Analysis Using the 3,500-ft single radius layout,2-D analysis was performed to estimate the cross- sectional geometry that would satisfy stability criteria for the usual and unusual load cases Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-99 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT required by the FERC Guidelines,Chapter 3,Gravity Dams.Multiple cross-sections were analyzed using CADAM,for downstream face slopes ranging from 0.7H:1.0V to 1.0H:1.0V and upstream face batters ranging from vertical to 0.2H:1.0V. The dam cross-section that satisfied 2-D stability criteria for all load cases -with no tension at the foundation interface (no crack forming at the foundation contact)-had a downstream face slope of 0.85H:1.0V and an upstream face batter of 0.1H:1.0V.The 2-D analysis assumed zero cohesion at the dam foundation interface and included uplift applied on the dam base according to the distribution prescribed by the FERC Guidelines.This cross-section was then further refined and analyzed using ADSAS and FE methods as described in the sections that follow. Post-earthquake stability was also analyzed for comparison to results of the FE analysis done for stability of the cracked dam in a post-seismic condition.As reported in discussion of the FE analysis below,permanent displacement was computed at the base of the crown monolith at the end of the earthquake event;however the dam remained stable for static reservoir loads in the post-seismic condition.Post-seismic uplift pressure distribution on the fully cracked base was assumed to vary linearly from normal headwater pressure at the upstream heel to a reduced level at the drain line and then linearly to full tailwater pressure at the dam toe. A simplified analysis was also performed at this stage of the dam layout development using PGA of 0.66g and 0.82g for the purpose of estimating the increase in dam volume required for the higher ground motions.For that condition the downstream face of the dam was estimated to require a slope of 1.0H:1V. 10.6.2.3..Arch Dam Stress Analysis System (ADSAS) In concert with the 2-D gravity analysis,the ADSAS program was again used to perform the analysis of the cross-section with a 0.85H:1.0V downstream face slope and an upstream face batter of 0.1H:1.0V.A dam cross section with a 1.0H:1.0V downstream face slope was also analyzed. 10.6.2.4.ADSAS Results The stresses calculated by ADSAS for Layout 3 for the cantilever and horizontal elements at the crown cantilever are shown graphically in Figure 10.6-6 and Figure 10.6-7 below. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-100 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Crest Elevation :EL 2075ft Downstream Face Slope :0.85H:1V Axis Radius :3500ft 10 |ae MA ||Upstream Face i'/.,\j ¢ ava Elevation(feet)..-?-Upstream Face =Downstream Face WA '-Downstream Face | -700 -600 -500 -400 -300 -200 -100 Compressive Stress (psi) Figure 10.6-6.Layout 3 Static Loads -Cantilever Stresses at the Crown Cantilever Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-101 Alaska Energy Authority December 2014 Zz.ALASKA ENERGY AUTHORITY Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 2110 2060 +2..a.TA :' 2010 : ::LN Crest Elevation :EL 2075 ft a [i WA oo i ooON Downstream Face Slope :0.85H:1Vi:i |R i /::Axis Radius :3500ft1960.:+m =x a |:Lf se E i :::H 1910 +:on }:i [WA :! :i'i |1860 + [ ::N C i :::NG _.1810 -\ %[}Upstream Face |:N o C ::; '=1760 x.| £t :\BG :;.SN ®1710 --_!2 [:|i ;i '1st\:,---__-"4660 :; \ :|Downstream Face -a c :i i t1610! F :\i ;' 1560 +:a 4510 E |\:;i ;r [\i 1460 i"-e-Upstream a 1410 +-m@ Downstream 1360 +Sa :1 ::: -250 -200 -150 -100 -50 0 50 100 150 Compression Stress (psi)Tension Figure 10.6-7.Layout 3 -Static Loads -Horizontal Stresses at the Crown Cantilever The ADSAS analysis shows that the vertical cantilever stresses are compressive at the upstream and downstream faces for the entire height of the dam.The maximum vertical compressive stress is less than 37 percent of the allowable compressive stress. The analysis also shows that there is transfer of some load horizontally to the abutments.This demonstrates that the curved axis reduces the loads carried by cantilevers,and the horizontal "wedge action”resulting from the curvature of the dam increases sliding stability of the dam. In summary,the Layout 3 configuration is stable under static loading conditions.The Layout 3 cross section was then used for 3-D analysis using FE method software to assess the effect of dynamic loading. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-102 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.6.2.5.FE Structural Analysis 10.6.2.5.1.ANSYS Model Initially ANSYS Version 14.5 was used for analyzing Layout 3 but subsequent to the first runs, MWH upgraded to Version 15 and also made some adjustments to the foundation of the dam for the analysis of subsequent configuration designated Layout 4.Therefore,to permit reasonable comparison between the various analyses,ANSYS,Version 15.0,was used to perform a re-analysis of Layout 3 which is recorded herein.The geometric model of the dam was created directly within the "Design Modeler”of ANSYS,and subsequently used as the basis for creating the FE method mesh.The FE model consisted of 14,133 elements and 13,236 nodes.The FE model of the dam included 2 elements (thickness)at the dam crest and 16 elements (thickness)at the dam base together with 19 elements along the height of crown cantilever.The maximum element size was thus 40 ft.and further analysis for design development should be undertaken with a significantly (smaller and)more detailed mesh.The rock foundation was modeled to a depth equal to the height of the dam,a width equal to three times the dam height,and a length (in the upstream and downstream directions)equal to the dam height.Three-dimensional mass elements (added mass)attached to the nodes of the elements on the upstream face of the dam were used to simulate hydrodynamic effects of the reservoir.Figure 10.6-8 shows a general 3-D view of the model and a cross section of the crown cantilever. Taking into account FERC and Board of Consultant observations the following features were included in the FE model: "Nonlinear frictional contact elements were used to model the contraction joints in the dam body.These contact elements cannot transfer tensile stresses across the interface but can transfer shearing forces based on the coulomb friction criteria.During detailed design the distance between contraction joints will be determined based on a thermal analysis of the dam but is expected to be between 50 to 100 ft.The distance of the contraction joints for this analysis is assumed at 200 ft.to reduce the nonlinear analysis time.A friction coefficient of 1.2 was assumed for these contacts. =To allow movement on the foundation,nonlinear frictional contact elements,similar to contact elements of dam monoliths,were used to connect the dam body to the foundation. The elements of the dam-foundation contact are connected at the surface of the foundation elements (no embedment,hence no resistance against sliding other than friction).Figure 10.6-8 also shows all the contact elements used in the model.Assuming that the drainage system is 66 percent effective,uplift pressure (with an equivalent triangular distribution)at the base of monoliths was calculated and applied on contact surfaces. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-103 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years.»eX)yeSnena'4,YAAsFE U/S view FE D/S View RNeYs 'ngtsMra[y i EEREECEE 'io 150.00 Maximum Cross section of dam model Contact elements in the model Figure 10.6-8.Finite Element Model of the Dam (Layout 3) 10.6.2.5.2.Static Analysis The initial analysis included the static loading condition of dead weight,reservoir water and uplift,but without temperature,ice or sediment.Figure 10.6-9 to Figure 10.6-12 graphically show the resulting horizontal and cantilever stress contours in the dam body. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-104 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. AEA11-022 ENGINEERING FEASIBILITY REPORT B:Transient Structural-mass tensile cantilever stress ASa”om: SidExpression:sz*.0001 45 , Time:2 : 193.84 Max 82.271 -29.297 -140.86 -252.43 -587.13 -698.7 -810.27 Min Se+003 SY,5 aadtede [o.0 1e+004 (in) ;Zz es aa Figure 10.6-9.Vertical Cantilever Stress (psi)-Upstream Face (Layout 3) B:Transient Structural-mass Expression:sz*.0001 45 Time:2 193.84 Max 82.271 -29.297 -140.86 -252.43 tensile cantilever stress A +iAT -364 -Seer os 7 are 2.054 FT -587.13 , -698.7 -810.27 Min cal04e+004 (in)Zz ; = 5e+003 Figure 10.6-10.Vertical Cantilever Stress (psi)-Downstream Face (Layout 3) Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-105 Alaska Energy Authority December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. B:Transient Structural-mass /\TrtensilearchstressfiSExpression:sy*.000145 A "*eeTime:2 1ate a 158.69 Max 99.475 ow Mawr amenrae;wr, -192.38 a |-0.45514 a '.[78.813 - 315.01 a {238.73 >j as -374.22 Min ek wnra Y [s.0 1e+004 (in):z _-- _ 5e+003 Figure 10.6-11.Horizontal Stress (psi)-Upstream Face (Layout 3) B:Transient Structural-mass -ie tensile arch stress A |'\boa"Expression:sy*.000145 OY nh BelTime:2 iam 158.69 Max §99.475 40.263 -18.949 -78.161 srd0.28755_> -255.8 -315.01 -374.22 Min Y al01e+004 (in)Zz ; = §e+003 Figure 10.6-12.Horizontal Stress (psi)-Downstream Face (Layout 3) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-106 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The FE analysis of Layout 3 indicates that the stresses in the dam body under static conditions are lower than the allowable values.The structure is in a state of compression except for two monoliths on the left and three on the right side with zero horizontal stresses.Because the model includes joints at 200 ft.centers,no tensile stresses developed in the FE model. The current construction planning anticipates that -to minimize the total project construction schedule -the dam will be constructed in three large monoliths,corresponding to the left abutment,right abutment and central portion of the dam.Therefore the expected response of the dam to dead load would be slightly different from these results.In the detailed design,the dam body will be modeled using three distinct monoliths and additional vertical formed joints -with shear keys -between those monoliths,although "induced”joints normally created during RCC placement will also be included.The model will be analyzed for the weight of the dam by simulating the proposed construction schedule. 10.6.2.5.3.Modal Analysis A modal analysis of the Layout 3 configuration was performed to calculate the fundamental periods of vibration and mode shapes of the linear model.The first 8 natural frequencies and periods of the dam are shown in Table 10.6-7. Table 10.6-7.Dam Frequency and Periods of Vibration (Layout 3) Mode No 1 2 3 4 5 6 7 8 Frequency (Hz)|1.88841 2.58056 3.21403 3.70938 3.83099 3.97313 4.21945 4.44512 Period (sec)0.52955 0.38751 0.31114 0.26959 0.26103 0.25169 0.23700 0.22497 The fundamental period of vibration is 0.529 second,smaller than the period of 0.657 seconds for dam Layout 2,thus confirming that Layout 3 is stiffer than Layout 2. Review of the modal analysis results indicates that the first 30 vibration modes represent more than 90 percent of the total mass of the structure in all directions.Rayleigh damping mass coefficient and stiffness coefficient were calculated using the first and 30"circular frequency for an equivalent seven percent damping ratio. 10.6.2.5.4.|Transient Analysis Three acceleration time histories were developed for each type of earthquake events.Two earthquake records from each type of events were used in the analyses.Transient dynamic analyses were performed for a total of eight earthquake records.Developed stresses in the dam body and sliding displacement of dam monoliths are the main parameters to assess the response of the dam against the earthquake.The results indicate that no tensile horizontal stresses develop Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-107 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT in the dam because of the "no tension”behavior of the contact elements.However compressive horizontal stresses develop on the upstream and downstream face of the dam depending on the direction of the earthquake loading. The envelope of maximum (tension and compression)cantilever stress on the upstream and downstream face of the dam for the (Japan 2011)ITWO10 earthquake are shown in Figure 10.6-13 to Figure 10.6-16 (because the figures were drawn directly from ANSYS output,positive values are exceptionally used for compressive stresses only in these figures and care must be taken in interpretation).No tensile cantilever stresses were developed along the dam-foundation interface because of the "no tension”contact elements.High tensile cantilever stresses were developed at the mid-height of the crown cantilever -around 1150 psi. B:Transient Structural-massmaxtensilecantileverstress hf |WS CSExpression:sz*.0001 45 fAL ay &.Maximum Over Time "hwd 1230.9 Max 1000 842.9 685.79 ao ee 277.24 ofa web,ie oot ae : .=I,pF .|67.372 '7 ;wo :tet -99.732 na -256.84 Min 'o ?ee aA Y 0 1e+004 (in)'Zz bn 5e+003 Figure 10.6-13.Envelope of Maximum Tensile Cantilever Stress (psi)due to IWT010 Earthquake -U/S View (Layout 3) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-108 December 2014 -Zz- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT B:Transient Structural-mass max tensile cantilever stress Expression:sz*.000145 Maximum Over Time 1230.9 Max 1000 842.9 685.79 528.69 371.58 2 - (AMENa2x4 57.372 -99.732 -256.84 Min 1e+004 (in) 5e+003 Figure 10.6-14 Envelope of Maximum Tensile Cantilever Stress (psi)due to IWT010 Earthquake -D/S View (Layout 3) B:Transient Structural-mass max compressive cantilever stress Expression:-sz*.000145 Maximum Over Time 2317.3 Max 1500 {i381 9.00 | on psyVENA abe a 4555.87 we :- .a ¥ L-.300.00 (m) }Zz 150.00 Figure 10.6-15.Envelope of Maximum Compressive Cantilever Stresses (psi)due to IWT010 Earthquake -U/S View (Layout 3) Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-109 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT B:Transient Structural-mass coo gtsig yomaxcompressivecantileverstressA\SY LoExpression:-sz*.000145 adh sala al Maximum Over Time thoes 2317.3 Max 1500 18.727 Min e 0.00 300.00 (m)|SS) 450.00 Figure 10.6-16.Envelope of Maximum Compressive Cantilever Stresses (psi)due to [WT010 Earthquake - D/S View (Layout 3) Figure 10.6-17 shows the residual sliding displacement of the dam monoliths at the end of the, IWI010 earthquake.The maximum sliding exhibited at the base of the crown cantilever is around 1.5 in.The magnitude of the sliding increased for the side monoliths to 2.9 inches and the maximum sliding of five inches occurred on the left side monolith.It is noted that the computed sliding displacement of each monolith is affected by dam-foundation interface geometry,friction coefficient and contact pressure,and state of the contact at the beginning of the earthquake event.Therefore the actual sliding displacements would be expected to be somewhat different from computed values at this stage. Subsequent,more complex modeling -including foundation mass -described in Section 10.7 provided a more representative estimation of potential displacements for the recommended dam configuration,and in detailed design the final characterization of the foundation,the proposed foundation excavation,any proposed grouting of joints (formed or induced)and the sequence of construction will be taken into account. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-110 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. B:Transient Structural-mass * Directional Deformation Type:Directional Deformation(X Axis) Unit:in Global Coordinate System Time:50 Figure 10.6-17.Residual Sliding Displacement (inches)at the end of IWT010 Earthquake looking d/s (Layout 3) The basic structural responses of the model to eight earthquake records were similar,but different in magnitude.The detailed stress contours of the dam due to other earthquakes are not shown but the maximum cantilever stress variations along the height of the crown monolith for eight earthquakes are plotted in Figure 10.6-18.The maximum computed stresses in the dam body and permanent displacement of dam monoliths due to the eight earthquakes applied are also summarized in Table 10.6-8. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-111 December 2014 za SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Slab events -M8.0 -69th Percentile (PGA=0.81) Cantilever stress at U/S Cantilever stress D/S2100'a 2100 i2000aeaad2000<=_.1900 amt ra _.1900z>z at al=1800 ry ri =1800 we '3 1700 oe emt &1700 b+3 "a g on%1600 ae r =1600 pa1500°F 1500 f 1400 «.,|--e--spm 1400 t a |--e--som2.a «--B--MYG --8--MYG1300t:1300 t ; -2000 -1500 -1000 -500 0 500 1000 1500 -2000 -1500 -1000 -500 0 S00 1000 1500 Stress (psi)Stress (psi) Slab events -M7.5 -84th Percentile (PGA=0.70g) Cantilever stress at U/S Cantilever stress D/S2100i2100a2000raw2000oare _ 1900 I BP |1900 on va=1300 'fi =1800 o5aa5'721700onae21700iBsa7a&1600 +a”B 1600 i [vt]lad .1500aa" -®--IWTOI0 400 --@--IWT0101400*-T [--a--sttec oe)Sl --w--sttec1300+r :1300 +, -2000 -1500 -1000 -500 0 S00 1000 1500 -2000 -1500 -1000 -500 0 500 1000 1500 Stress (psi)Stress (psi) Crustal events -M7.0 -84th Percentile (PGA=0.49g) Cantilever stress at U/S Cantilever stress at D/S21002100i|Ps she ia :2000 >a as 2000 re)3 _.1900 #4 PP |190 'rs f©1800 an £'d =1800 Bhs adcabs45=s&1700 er i.2 1700 5 usgom”$ip%1600 ri rag 3 1600 a9 HeaUd1500:"e all WT --e--aur +400 r g --®--AULwr--8 -Gil "'--8--Gil1300rr1300}}: -2000 -1500 -1000 -500 0 500 1000 1500 -2000 -1500 -1000 -500 0 500 1000 1500 Stress (psi)Stress (psi) Interface events -M9.2 -84th Percentile (PGA=0.52g) 2100 Cantilever stress at U/S 2100 Cantilever stress at D/S _T2000aa:2000 --od °__1900 t+a _1900 Poy rr<1800 :=1800 e . 2 1700 ex ¥-$1700iJ%1600 -ym §1600 Se 'susul15001500400asd--@=+Curi 1400 #<--@--Curi1biP--8--Valp on ba --B -Valp1300+}.1300 +, -2000 -1500 -1000 -500 0 500 1000 1500 -2000 -1500 -1000 -500 0 500 1000 1500 Stress (psi)Stress (psi) Figure 10.6-18.Envelope of Max.and Min.Cantilever Stresses in Crown Cantilever for Layout 3 for Selected Events Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-112 Alaska Energy Authority December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.6-8.Summary of Dam Layout 3 Response to 8 Earthquake Loadings Horizontal Vertical Stress Sliding DisplacementEventStressStress(psi)(psi)(in)Event Station |Location C .Tensil c ;Crown SideompressiveensileompressiveMonolith|Monoliths Slab events -M8.0 -69th Percentile (PGA=0.81) .UIS -1330 1388 -1680ElSalvador13SDM 44 6.4Jan-01 DIS -1043 788 -909 U/S -1175 1344 -1558Japan2011MYG009 3.8 447-Apr-11 D/S -903 848 -919 Slab events -M7.5 -84th Percentile (PGA=0.69g) UIs -794 913 -760ElSalvadorSTTEC 18 2213-Jan-01 DIS -596 695 -1330 U/S -732 1149 -839Japan2011IWT010 15 37-Apr-11 DIS -721 726 -1346 Crustal events M7.0 -84th Percentile (PGA=0.49q) Irpinia,Italy U/S -762 841 -1265 AUL 0.8 1.223-Nov-80 DIS -538 557 -682 Loma Prieta,U/S -697 1252 -916 California GIL 0.2 0.548-Oct-89 DIS -607 363 -858 Interface events -M9.2 84th Percentile (PGA=0.52g) u/s -969 726 -1552ChileCURI 21 25(M 8.8)DIS -619 797 -634 U/S -630 791 -1250ChileVALPM 15 2(M 8.8)DIS -639 563 -563 Note: AUL-Italian Crustal Earthquake Record -November 1980 CURI -Chile Interface Earthquake Record -February 2010 GIL -Lomo Prieta,CA Crustal Earthquake Record -October 1989 VALPM-Chile Interface Earthquake Record -Feb 2010 The maximum tensile cantilever stress of 1,388 psi occurred in the dam body during the El Salvador (SDM)earthquake.However the average of maximum tensile stresses from all selected earthquakes is around 945 psi.This stress is greater than the projected dynamic tensile strength of the RCC,hence cracking of the dam could be expected according to these results.The maximum displacement calculated at the base of the crown monolith is 4.1 in.which occurred during the SDM earthquake -and the average displacement is approximately 2.2 in.These represent permanent displacements at the end of the earthquake event.CADAM was used to analyze the dam with a fully cracked base and uplift distribution per FERC criteria,and the dam Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-113 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT was shown to remain stable for the post-seismic condition.Post-seismic uplift pressure distribution on the fully cracked base was assumed to vary linearly from normal headwater pressure at the upstream heel to a reduced level at the drain line and then linearly to full tailwater pressure at the dam toe.As discussed in other sections,dam and foundation drains will be sized to accommodate potential sliding displacements and to remain effective following movement of the dam during extreme loading. 10.6.2.5.5.RCC Volume To check the ADSAS volume calculations,the volume of the Layout 3 dam was calculated using an excel spreadsheet in two ways:(1)per one foot elevation;and (2)at five feet increments along the dam crest.The spreadsheet calculated the gross volume of the dam;adjustments were then made to the estimated volume to include the concrete between the powerhouse and the downstream face of the dam and to include volume reductions for inserts including penstocks, spillway and intakes. The volume estimates are listed in Table 10.6-9.A batter in the upstream direction (0.1H:1V) was included at the upstream face of the dam below El.1770 ft. Table 10.6-9.RCC Quantities (Layout 3) Downstream Face Slope 0.85H:1V Gross RCC volume 6,831,000 cy Quantity adjustment 416,000 cy Net RCC volume 6,415,000 cy 10.6.3.2nd Revised Dam Configuration (Layout 4) 10.6.3.1.Configuration Description As described in Section 10.5,the dam configuration for Layout 4 comprised a central portion with an axis radius of 2,600 ft.,and straight-axis abutment sections. The crest of the dam is 35 ft.wide,and at El.2065 ft.is 10 ft.lower than previous iterations. This 10 ft.lowering of the crest level resulted from a reassessment of the flood and freeboard requirements for the dam at the completion of the PMP/PMF studies (which was completed part way through this analysis)and after selection of an acceptable reservoir rise of 15 ft.for the efficient use of the low level outlets and for passage of the PMF.The curved section has a downstream face slope of 0.7H:1V and the straight gravity section includes a 0.85H:1V slope on the downstream face.All portions have a sloping upstream face (0.1H:1V)below El.1770 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-114 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. transitioning to a vertical face above.The change in downstream face slope reflects the reliance on gravity at the abutments. 10.6.3.2.Two-Dimensional Gravity Analysis A preliminary check of 2-D stability of the 2,600-ft radius dam was performed using CADAM, for the cross-section with a downstream face slope of 0.7H:1.0V and upstream face batter of 0.1H:1.0V.The 2,600-ft radius dam with this center cross-section was then further analyzed using ADSAS and the FE method as discussed below.As reported in the discussion of the FE analysis,permanent displacement was computed at the base of the crown monolith at the end of the earthquake events. Assuming zero cohesion at the dam base,the simplified analysis showed the dam satisfied stability criteria for the normal static,flood and post-seismic conditions with a cracked base. The resultant location for all forces under the cracked condition fell within the dam base,and sliding factor of safety was adequate using residual friction angle at the dam foundation contact surface.Post-seismic uplift pressure distribution on the fully cracked base was assumed to vary linearly from normal headwater pressure at the upstream heel to a reduced level at the drain line and then linearly to full tailwater pressure at the dam toe. 10.6.3.3.ADSAS As noted earlier,ADSAS has the capability of analyzing three centered dam configurations including those that include straight sections at both ends -as selected for Layout 4. Modeling of the curved portion of the Layout 4 dam has been carried out to assess the stresses both vertically and horizontally within the dam.The analysis omitted the straight portions at the abutments as they will perform as gravity sections.The outer sections have been defined with a cross section that is typical for a gravity dam and the stress analysis can be performed using a traditional 2-D analysis approach. Similar to the previous configuration (Layout 3)the ADSAS analysis shows that the cantilever stresses are compressive at the upstream and downstream faces for the entire height of the dam. The cantilever stresses within the dam are more evenly distributed than Layout 3;the resultant is nearer to the center of dam section and is lower in magnitude. Cantilever stresses and horizontal stresses are plotted in Figure 10.6-19 and Figure 10.6-20 respectively.The revised configuration results in slightly greater transfer of loading to the arches.The stresses within the arches at the extrados are compressive for the full height of the crown cantilever while the along the intrados the stresses transition from compressive to tensile about 160 ft.below the crest.The analysis shows that the upper section of the dam,where the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-115 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. arch effect is most noticeable,has a larger compressive component than Layout 3.The stresses are low,relative to the allowable stresses but demonstrate that the dam shape is more efficient in accommodating the applied loads. The analysis confirmed that the dam cross-section was stable under static loading conditions. This cross section was then used for analysis using FE method software to assess the effect of dynamic loading. :__]Crest Elevation :EL 2065ftiaDownstreamFaceSiope:0.70H:1¥ t Axis Radius :2600 ft Elevation(feet)tees]medi Upstream Face =Downstream Face -100 0 Compressive Stress (psi) Figure 10.6-19.Cantilever Stresses at the Crown Cantilever (Layout 4) Alaska Energy AuthoritySusitna-Watana Hydroelectric Project December 2014FERCProjectNo.14241 Page 10-116 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Elevation(feet}Crest Elevation :EL 2065 ft Downstream Face Slope :0.70H:1V Axis Radius :2600 ft 1460 +-ao -e-Upstream 1410 --TT |atten Downstream [ 1360 +--Sees on wee we ene cme ie ge ooo foes ne -280 -200 -150 -100 +50 (°)50 100 150 200 Compression Stress (psi)Tension Figure 10.6-20.Horizontal Stresses at the Crown Cantilever (Layout 4) 10.6.3.4.FE Structural Analysis Structural Analysis was performed using ANSYS v15.A new FE model was developed for this 2nd revised curved dam configuration (Layout 4).The developed FE model is basically similar to the previous model of Layout3 with the same modeling characteristics but with a new geometry and new FE mesh.Because the foundation surface had to be re-evaluated for the slightly revised geometry,an opportunity was taken to adjust the foundation,and also to use the revised foundation for the Layout 3 as recorded above.Nonlinear frictional contact elements were used between the dam and the foundation and also between dam monoliths in both Layout 3 and 4. Eight earthquake time histories were used for transient analysis of the dam foundation.For each analysis,dead weight of the dam was applied in first step and hydrostatic and dam base uplift forces were applied in second step,the seismic velocity time history was applied in subsequent steps.Results of Layout4 analyses indicated higher tensile cantilever stresses on the downstream face at the top of the dam.It has been observed,during the detailed design of other similar dams,that such stresses can be reduced by small geometric adjustments of the dam Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-117 Alaska Energy Authority December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. profile -which are easy to accommodate in RCC construction.Therefore,the dam cross section was slightly modified for this analysis by increasing the width of the dam cross section at the top. The width of the dam crest was increased by 10 ft.at crest level (to 45 ft.)with no changes at the base of dam.The FE model was revised accordingly and continued analyses were performed using the modified cross section.Figure 10.6-21 shows the FE model for the modified geometry of Layout 4. S\PRARESEEptAeapsyFaded,AsidewodabaesaefSeem!SoCrown cantilever meshing and frictional contacts in the model Figure 10.6-21.Finite Element Model of Layout 4 10.6.3.5.Modal Analysis A modal analysis of the dam was performed and the computed periods of vibration for first 30 free vibration modes of the dam and respective modal mass participation ratios are shown in Table 10.6-10.The mode shapes for the first 4 vibration modes are shown Figure 10.6-22.The fundamental vibration frequency of the Layout 4 dam is just 3 percent smaller than the frequency Susitna-Watana Hydroetectric Project Alaska Energy Authority FERC Project No.14241 Page 10-118 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. of the Layout 3 dam.The Layout 4 dam is thinner and was expected to be more flexible than the Layout 3 dam.However,its smaller radius increases its stiffness resulting in similar vibration frequencies for the two layouts. Table 10.6-10.Frequencies and Modal Mass Participation Ratio for Layout 4 .Mass Participation Ratio Mass Participation Ratio CumulativeModeFrequency|Period(Hz)(sec)Stream Cross Vertical Stream Cross VerticalDirectionStreamDirectionStream 1 1.82631 0.54755 |4.64E-01 2.06E-04 1.12E-02 0.464 0.000 0.011 2 2.49171 0.40133 1.96E-04 5.05E-03 1.53E-04 0.464 0.005 0.011 3 3.14058 0.31841 4,15E-02 5.75E-05 2.37E-04 0.505 0.005 0.012 4 3.71290 0.26933 2.49E-01 5.61E-03 3.64E-03 0.754 0.011 0.015 5 3.76679 0.26548 1.80E-02 3.34E-03 7.63E-04 0.772 0.014 0.016 6 4.22878 0.23647 1.94E-03 7.81E-01 6.49E-03 0.774 0.795 0.022 7 4.40551 0.22699 1.58E-02 2.13E-05 1.90E-02 0.790 0.795 0.041 8 4.49801 0.22232 2,39E-03 8.53E-03 7.27E-01 0.793 0.804 0.769 9 4.89662 0.20422 5.91E-05 1.21E-02 2.14E-03 0.793 0.816 0.771 10 5.05699 0.19775 3.92E-06 4.81E-05 6.01E-06 0.793 0.816 0.771 11 5.69345 0.17564 7,63E-03 5.94E-05 6.24E-04 0.800 0.816 0.772 12 5.96243 0.16772 2.29E-03 4.01E-04 1.94E-04 0.802 0.816 0.772 13 6.13543 0.16299 5.95E-03 2.34E-02 1.40E-07 0.808 0.840 0.772 14 6.17244 0.16201 8.23E-02 9.30E-04 3.88E-03 0.891 0.841 0.776 15 6.33437 0.15787 |4.95E-05 7.23E-05 8.94E-06 0.891 0.841 0.776 16 6.93305 0.14424 1.72E-03 5.19E-06 3.96E-03 0.893 0.841 0.780 17 7.00990 0.14266 2.53E-03 6.62E-04 2.72E-02 0.895 0.842 0.807 18 7.07257 0.14139 1.36E-03 5.52E-05 1.05E-02 0.896 0.842 0.817 19 7.59786 0.13162 |8.23E-07 1.40E-03 2.35E-04 0.896 0.843 0.818 20 7.69704 0.12992 1.67E-04 6.42E-05 6.19E-06 0.897 0.843 0.818 21 7.82501 0.12780 3.16E-03 8.64E-05 3.26E-02 0.900 0.843 0.850 22 8.08248 0.12372 5.63E-03 6.96E-09 8.22E-03 0.905 0.843 0.858 23 8.21690 0.12170 5.12E-06 2.71E-04 2.07E-03 0.905 0.843 0.860 24 8.26867 0.12094 8.72E-05 1.42E-02 3.17E-05 0.905 0.858 0.860 25 8.68587 0.11513 |2.19E-04 3.43E-05 1.07E-03 0.906 0.858 0.862 26 8.98427 0.11131 2.67E-03 1.84E-03 7.93E-05 0.908 0.859 0.862 27 9.06453 0.11032 1.74E-02 1.25E-04 3.49E-03 0.926 0.860 0.865 28 9.24927 0.10812 |4.56E-04 9.18E-04 5.02E-05 0.926 0.861 0.865 29 9.40572 0.10632 7.21E-04 6.17E-03 2.33E-03 0.927 0.867 0.867 30 9.50533 0.10520 2.84E-04 3.17E-02 2.26E-03 0.927 0.898 0.870 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-119 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT B Modal-no bake Osrectional Deformation ANSYSType:Directional Deformation(XAxis)ete Frequency:18263 Hz Unit:m 7 Global Coordinate System42/25/2014 2:51 PM7 2.3926e-5 Max ae 3.0164e-5 2.6402e-§ 2.2641e-5 18879¢-5 LS117e-5 Li355e-5 1.5935e-6 3.931Te-6 6.9917e-8 Min 0.00 190.00 200.00 (m)DN|50.00 150.00 @:Modano te geting . Osrectional Deformation 2 il :y {Type:Directional Deformation(x Axis)ee Frequency:2.4917 Hz . Unt m Giobal Coordinate System i 2/25/2014 2:5LPM i 3.9714e-5 Max <<”3.108e-5 a 2.2447 e-5 138-5 5.1788e-6 3.455 1e-6 -L2089e-5 +2.6723e-5 +2,9357e-5 -3.7991e-5 Min 0.00 100 00 200.90 (m)a,Vt }50,00 150.06 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-120 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT B:Modal-no bake Owectionai Deformation 3 AMY Type:Directional Deformation(X Axis)AN >|€ Frequency:3.1406 Hz Unit m Global Coordinate SystemFyassavia251M 47282e-5 Max 3.822e-5 2.9258e-5 2.0986e-5 L1034e-5 L972 1e-6 -7.0899e-6 -L6152e-5 "2.52 14e-5 -3.4276e-5 Min 0.00 100.90 200,00 (m)LeIEE50.00 150.00 &Modal-no lake Directional Deformation 4 Type:Directional Deformation(X Anas) Frequency:3.7129 He Unit im Global Coordinate System{2/25/2014 2:52 PM 7 5 47695e-5 Max 4,0903e-5 2.41 Re-5 2.7321e-5 2.0525e-5 £3738e-§ 6.9463e-6 L549 1e-7 6.6365e-6 -1.3428e-5 Min 0.00 109.00 200.00 (en) EE 56.00 150.00 Figure 10.6-22.First Four Vibration Mode Shapes (Dam Layout 4) Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-121 Alaska Energy Authority December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.6.3.6.Transient Analysis Results Transient dynamic analyses were performed for eight earthquake records (two earthquakes for each selected type of event -Slab M8.0,Slab M7.5,Crustal M7.0,and Interface M9.2). The envelope of maximum tensile cantilever stress on upstream and downstream face of the dam for IWTO1L0 earthquakes are shown in Figure 10.6-23 and Figure 10.6-24.Figure 10.6-25 shows the residual sliding displacement of the dam monoliths at the end of the (Japan 2011),IWT010 earthquake. A:Transient Structural-no lake ™ ;max_cantilever:Type:Normal Stress(Y Axis);Unit:psi 'Global Coordinate System Maximum Over Time 965.33 Maxfe _|696.25 |a 561.71 104.67 > |7 paul 328.78 > A -245.53 Min rs ee a oe a -Pantie eS oy nan ot Figure 10.6-23.Envelope of Maximum Tensile Cantilever Stresses (psi)due to IWT010 Event -U/S view (Layout 4) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-122 December 2014 --Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. f A:Transient Structural-no lake - i max_cantilever|Type:Normal Stress(Y Axis)'Unit:psi Global Coordinate System Maximum Over Time 965.33 Max ,bed .245.53 Min SE [-75.785 > 4 ooo i fi ll mt Nl a Ate es no ii a tie mes anche ns sl Figure 10.6-24.Envelope of Maximum Tensile Cantilever Stresses (psi)due to IWT010 Event -D/S view (Layout 4) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-123 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT X Axis -Directional Deformation oaType:Directional Deformation(X Axis)we Unit:in ° - Global Coordinate System Time:50 A:Transient Structural-no lake ee ! | 1.5143.2771 X&-Lo 0.94282 --.0.37088 --0.20105 -0.772991a-1.3449 Min L.:mn wy .j -_- \alin Figure 10.6-25.Residual Sliding Displacement of the Dam (inches)at the End of [WT010 Event looking D/S (Layout 4) The maximum cantilever stress variations along the height of crown monolith for eight earthquakes are plotted in Figure 10.6-26.The maximum computed stresses in the dam body and permanent displacement of dam monoliths due to eight earthquakes are also summarized in Table 10.6-11 for comparison. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-124 December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Slab events -M8.0 -69th Percentile (PGA=0.81) 2100 Cantilever stress at U/S 2100 Cantilever stress at D/S i .ay!ni geet ge ie va Mary190077 '1900 tH en v |le 4 ry=1800 ort >1800 »Pra&1700 "es hal 2 1700 b wiJ%1600 ao an 3 1600 re riadq|8 i "1500 |-Sy esas]|8 a oo1400--@--MYG --§--MYG1300:.1300 7 r -2000 -1500 -1000 -500 0 500 1000 1500 -2000 -1500 -1000 -500 0 500 1000 1500 Stress (psi)Stress (psi) Slab events -M7.5 -84th Percentile (PGA=0.70g) Cantilever stress at U/S Cantilever stress D/S2100T2100i.Sal2000soeg2000x"ms -1900 >_1900 o 'e "| =1800 /-#2 1800 7 c ae BA i=|»ry"w21700Lssledg170aomao¢ %1600 +Ag %1600 n al™'1500 o*al "1500 *an,#--@--!WT010 1400 a on --@--IWT0101400--M--STTEC i ----STTEC1300:,1300 f :: -2000 -1500 -1000 -500 0 500 1000 1500 -2000 -1500 -1000 -500 0 S00 1000 1500 Stress (psi)Stress (psi) Crustal events --M7.0 -84th Percentile (PGA=0.49g) Cantilever stress at U/S Cantilever stress at D/S2100ia|2100 r T2000aeitaasl2000aw*,a'Yo e ?_.1900 ots > ._.1900 ae " =1800 ane é rT ae 1800 vt5.feet §me as&1700 *o--2 1700 a'g éu”g hal %1600 *a 3 1600 +>;#-_-#©1500 Lt a *4500 np ape»--@--AUL 1400 i «--@="AUL1400|--8--GIL --8--GIL1300t,1300 +, -2000 -1500 -1000 -500 0 500 1000 1500 -2000 -1500 -1000 -500 0 500 1000 1500 Stress (psi}Stress (psi} Interface events -M9.2 -84th Percentile (PGA=0.52g) Cantilever stress at U/S Cantilever stress at D/S2100L|2100 5 |2000 otal 2000 ”we_.1900 _.1900 ¥a=a ==1300 é i =1300 os <A Fd c y21700"od £1700 ry aai]=1600 i a =1600 *#@ 4500 a3 s_|1500 *x1400aem|--@--CURI 1400 a a --@--CURI- §--VALPM [--t--VALPM1300':1300 +Y . -2000 -1500 -1000 -500 0 500 1000 1500 2000 -1500 -1000 -S00 0 500 1000 1500 Stress (psi)Stress (psi) Figure 10.6-26.Envelope of Maximum and Minimum Stresses in Crown Cantilever for Layout 4 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-125 Alaska Energy Authority December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 10.6-11.Summary of Dam Response to 8 Earthquake Loadings (Layout 4) Horizontal Vertical Stress Sliding Displacement .Event Stress Stress (psi)(in)Event Title ::.Station Location |Compressive Tensil .Crown Side(psi)ensile |Compressive |wonotith |Monoliths Slab events -M8.0 -69th Percentile (PGA=0.81) El Salvador UIS -1278 942 -1830SDM 4.7 6.513-Jan-01 DIS -995 1182 -772 Japan 2011 U/S -1277 1109 -1549MYGO009 4.1 7.77-Apr-11 DIS -947 841 -837 Slab events -M7.5 84th Percentile (PGA=0.69g) EI Salvador U/S -1008 945 -1692STTEC 2.4 .13-Jan-01 DIS -698 957 -855 38 Japan 2011 U/S -867 886 -1581IWT010 1.9 2.57-Apr-11 DIS -638 772 -821 Crustal events -M7.0 -84th Percentile (PGA=0.49g) Irpinia,Italy UIS -703 584 -1206AUL 1 1.23-Nov-80 DIS -573 587 -725.9 5 Loma Prieta,u/s -801 1091 -998 California GIL 1.4 1.6 18-Oct-89 DIS -634 409 -905 Interface events -M9.2 -84th Percentile (PGA=0.52g) Chile (M 8.8)CURI vis all al 1184 27 3.6ile...DIS -673 611 -744 ; US -730 852 -1245Chile(M 8.8)VALPM 1.6 2.2DIS-615 507 744 Note: AUL -Italian Crustal Earthquake Record -November 1980 CURI -Chile Interface Earthquake Record -February 2010 GIL -Lomo Prieta,CA Crustal Earthquake Record -October 1989 VALPM -Chile Interface Earthquake Record -Feb 2010 The average stresses and displacements for each of four earthquake events were calculated for dam Layout 4 and Layout 3 and shown in Table 10.6-12.The average of maximum cantilever stresses on the upstream face of dam Layout 4 is generally less than stresses in dam Layout 3 at similar locations.The maximum tensile cantilever stress of 1366 psi in Layout 3 (slab event, PGA=0.81)is reduced to 1021 psi in Layout 4.The contribution of the transfer of horizontal load is higher in Layout 4 -because of the shorter radius and enhanced thickness of the section at the upper part of the dam discussed earlier --compared to Layout 3,resulting in a reduced cantilever action and cantilever tensile stresses.The maximum tensile stress in the downstream Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-126 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT face increases from 818 psi in Layout3 to 1011 psi in Layout4 (slab event,PGA=0.81g). However it is still below the maximum tensile stresses on upstream face of the dam. Table 10.6-12.Comparison of Dam Responses for Dam Layouts 3 and 4 .Vertical Stress Sliding Displacement Stress Horizontal Stress (psi)(in)Event Title -Compressive -Location (psi)Tensile |Compressive Crown Side Monolith Monoliths Slab events -M8.0 -69th Percentile (PGA=0.81) UIS -1253 1366 -1619Layout3 4.0 5.4DIS-973 818 -914 UIS -1277.5 1025.5 -1689.5Layout4 44 71D/S -971 1011.5 -804.5 Slab events -M7.5 84th Percentile (PGA=0.69g) U/S -763 1031 -800Layout3 17 2.6DIS-659 711 -1338 US -937.5 915.5 -1636.5Layout4 2.15 2.9DIS-668 864.5 -838 Crustal events -M7.0 -84th Percentile (PGA=0.49g) UIS -730 1047 -1091Layout3 0.5 0.9DIS-573 460 -770 US -752 837.5 -1102Layout4 1.0 1.5DIS-603.5 498 815.45 Interface events -M9.2 -84th Percentile (PGA=0.52q) UIS -800 759 -1401Layout3 1.8 2.3DIS-629 680 -600 UIS -803.5 746.5 -1213Layout4 2.15 2.9DIS 644 559 -741 The average sliding displacement for Layout4 in all cases is greater than the sliding displacement of Layout 3.Sliding displacement increased up to 100 percent for crustal events, but remains at about 10 percent for slab (PGA=0.81g)events.Although the sliding displacement is greater for this Layout 4,the dam remains stable during the earthquake events and in the post seismic condition,as discussed in Section 10.6.5.5.4. 10.6.3.7.RCC Volume Estimation of the RCC volume in the Layout 4 dam was carried out using the same approach as that used for Layout 3.An Excel spreadsheet was used to calculate the dam volume using two Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-127 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. independent methods,by elevation and by station.Adjustments were made to the previous spreadsheet to allow the straight and curved portions to be calculated and for different downstream slopes.The spreadsheet analysis was also refined to include the sloping portion of the upstream face. The analysis accounts for the RCC fill between the dam and powerhouse and also the reduction in dam RCC volume arising from placement of the penstocks,power intakes,low level outlet intake and pipes,sluice and the spillway crest. The volume of RCC in Watana Dam for the updated Layout 4 configuration is shown in Table 10.6-13 follows: Table 10.6-13.RCC Volume (Layout 4) Section RCC Volume (cy) Left Abutment Straight portion 80,970 Curved portion 513,810 Center Curved portion 3,949,590 Downstream fill 125,260 Right Abutment Curved portion 697,010 Straight portion 101,360 Total 5,468,000 As part of the ongoing development,and in preparation for the thermal analysis of the dam,the locations of the vertical construction joints between the abutments and center section have been selected to make certain that the projected first season RCC placement volume could be completely placed while the river diversion was progressed,and also to ensure that the RCC beneath the spillway crest would be at the required finished elevation to facilitate commencement of construction of the spillway crest at the end of the first RCC placement season.The formed vertical joints will include large shear keys,and are also expected to be grouted at the end of dam construction. The volume-elevation relationship for the updated configuration is shown graphically in Figure 10.6-27 below: Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-128 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Elevation(Feet)| i ---Total eocee Left Abutment - -Center tb 2.0 2.5 3.0 3.5 4.0 45 5.0 5.5 RCC Volume (Million cy) Figure 10.6-27.RCC Volume vs Elevation (Layout 4) The estimated volume of RCC in the previous configuration was 6,420,000 cy.The updated configuration requires 952,000 cy less RCC to construct and thus can be completed one season earlier than that projected for Layout 3. 10.6.4.Sensitivity to Foundation Conditions Following the desk review of the foundation conditions -absent any on site verification -the foundation was divided into two zones,and assigned different characteristics.The dynamic analyses performed for Layout3 and Layout4 were subject to sensitivity studies based on different characteristics of the foundation.However,the results reported here are for only the sensitivity studies of Layout 4.Two transient analyses of Layout4 subjected to IWTO10 earthquake loading were performed and stress results are shown in Figure 10.6-28.(The results shown are for Layout4 before the cross section was modified.)In the first analysis the deformation modulus of both zones was doubled (E=2E;)and in the second analysis a value of E=0.5Er¢was used. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-129 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Arch stress at U/S Arch stress at D/S2100as:1 2100 |||1 . j (xe:i ixo|-Syy |g rw |LR,-_1900 '4 ¥1900 Wy > =1800 RY."=1800 |52§1700 xa9 i}\§1700 |:+&1600 a "4 ----+--|omenE 3 1600 --&)- |wate o£[vy1500as_a -0.5E 1500 Ko |ese x1400 --2E 1400 "|=e 261300+t r 1300 --4 +-t-- -1500 -1000 -S00 0 S00 1000 =1500 -1500 -1000 -500 7)500 1000 1500 Stress (psi)Stress (psi) 3100 Cantilever stressat U/S 2100 Cantilever stress at D/S1:T T T Tpl||quer wes...|2000 pag nnn Og 4 2000 2 -er?I {yes1900-4 of ox 1900 xe 3 ooE100|if -¥fp =1800 air wal5aysos|a x”|3g 1700 Rte 6 xn g 1700 nd oFet_.1 431600rhon'wweck &1600 ,ff en 3[vv]ry 11500pABt|-0--058 1500 Z $y Oe -0.5Eww=:-.o%®@|em14002|oe 22 1400 :we -261300--e 1300 { -2000 -1500 -1000 -S0O0 0 500 1000 1500 -2000 -1500 -1000 -500 0 S00 1000 1500 Stress (psi)Stress (psi) Figure 10.6-28.Effect of Foundation Deformation Modulus on Maximum/Minimum Stresses (Layout 4) The variability between foundation blocks was not subject to sensitivity analyses because the softer area of the foundation did not extend over more than one monolith or two for the size of elements detailed in the model.Future analyses in which a greater numbers of elements are modeled should consider the variability in foundation conditions. Results of the sensitivity studies show that lower deformation modulus of the foundation has negligible effect on the stress distribution in the dam.However,increasing the deformation modulus of the foundation by 100 percent will increase the maximum tensile stresses in the dam around 25 to 30 percent.The magnitude of the foundation deformation modulus has some effect on the developed stress and requires in situ testing from the proposed adits and laboratory testing of the dam foundation rock to verify rock properties. 10.6.5.Discussion on Analysis without Foundation Mass 10.6.5.1.Review of Preliminary Analysis The results of the analysis presented in Section 10.6 were for the purposes of defining -at feasibility level -the proposed configuration of the dam structure.It was an iterative process, and has been organized so that realistic feasibility design progress can be made in the absence of Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-130 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. robust site investigation data,but taking into account the input of external parties such as the Board of Consultants.At this feasibility level of design,the focus has been comparison of various dam geometries rather than an excessively detailing of structural elements of the dam. Thus the stability and dynamic analysis has been targeted at realizing the most promising arrangement rather than defining the final geometric solution.Together with the current appreciation of the geological features of the site,the selected dam configuration will define the site investigation and adit location -the results from which will allow more accurate and representative analysis to be carried out together with more complete sensitivity analysis. An RCC dam that includes curvature represents the optimum arrangement -utilizing a substantial component of gravity action,but that redistributes loads horizontally in a manner that enhances stability.RCC construction is a methodology that allows easy accommodation of somewhat complex shapes such as the three centered dam originally postulated as a possible layout.Layout2 was postulated as the most aggressive layout in terms of achieving a safe project while minimizing concrete -and was recognized as one bound of the envelope of possible solutions.Layout 3 -including a gravity section while maintaining a "traditional” gravity cross section with a 0.85 downstream slope -is considered to be the most conservative of the options studied,but carries a penalty of one million extra yards of RCC and one year extra construction period.Layout4 provides a compromise,well within the envelope of safe and reasonable solutions but with the benefit of the reduction of 920,000 yds'. Comparison of the 2-D analysis shows that -assuming zero cohesion at the base -Layout 3 performed in accordance with FERC stability criteria,but could suffer a cracked base at higher ground motions.For Layout 4 -also assuming zero cohesion at the dam base -the simplified analysis showed the dam satisfied FERC stability criteria for the normal static,flood and post- seismic conditions with a cracked base.The resultant location for Layout 4 for all forces under the post-seismic cracked condition fell within the dam base,and sliding factor of safety was adequate. With respect to the results of the nonlinear FE analysis using a massless foundation,the results for Layout3 and Layout4 were similar,with all compressive stresses within the limits of expected RCC design strengths.With regard to tensile cantilever stresses,Layout 4 exhibited a better response compared to Layout 3.The maximum tensile stresses on the upstream face of the dam is reduced from 1366 psi in Layout 3 to 1,025 psi in Layout 4 (slab event,PGA=0.81)and the average reduction in upstream vertical stresses is around 15 percent for all earthquake events. Although the computed tensile stresses on the downstream face of Layout 4 are slightly higher than the similar stresses in Layout 3,the maximum developed tensile stress on the downstream face is still smaller than the maximum tensile stress on the upstream face.Sliding displacements Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-131 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT predicted for each layout can be managed through design -generally being under two inches for the crown cantilever,but sometimes over four inches for the side monoliths.Dam and foundation drains will be sized to accommodate potential sliding displacements and to remain effective following movement of the dam during extreme loading. In reviewing the results -even though the ongoing site specific seismic hazard analysis and the PMP/PMEF studies have resulted in modifications to the required dam criteria -it is evident that the 2-D stability requirements can be achieved by Layouts 3 and 4 but the FE analysis (using simplistic assumptions)have shown calculated tensile stresses that are above those projected for well mixed and placed RCC -but which can be reduced to acceptable levels by shaping of the upper part of the dam,and by more refined FE analysis. RCC produced and placed by a competent contractor -even in the strenuous conditions in Alaska can be expected to exhibit compressive strength of 6,000 psi,and tensile strength of up to 400 psi,based on strength of parent material and lift joints measured at existing RCC dams. Under seismic loads a tensile strength of 580 psi on the lift joints can be assumed,based on experience at Olivenhain and San Vicente dams.Based on the static and dynamic analyses presented for Layout 4 it is clear that nonlinear analysis,with massless foundation,indicates stress values that exceed the expected tensile strength of the RCC. However,the main factors that influence the 3-D analysis of curved dams have been identified by several researchers (Chopra 2008,USBR 2006).The current state of the art in seismic analysis and evaluation of concrete dams is to carefully consider these factors in the numerical simulation,to avoid over-conservative or under-conservative design.More careful modeling of the fluid structure interaction considering the compressibility of the water;and foundation rock inertia and damping are major factors which have been identified as contributing to a more representative and accurate model of the stresses in the structure. According to a series of example analyses,it was demonstrated that (Chopra 2008): =By neglecting water compressibility,stresses may be significantly overestimated for some dams or underestimated for others. «By neglecting foundation-rock mass and damping,the stresses may be overestimated by a factor of two or three. In the analyses described above water compressibility has been neglected and the foundation has been assumed to be massless -in the interests of speed of analysis.To more accurately estimate the performance of the structure,further analytical development of the selected alternative was performed including Chopra's recommendations. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-132 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.6.6.Modeling of Fluid Structure Interaction Water compressibility effect can be considered by performing a Fluid Structure Interaction (FSI) analysis using acoustic elements to model the dam reservoir. ANSYS Acoustic elements,fluid 30,were used to add the reservoir to the FE model. However,transient analysis of the model using acoustic elements (Fluid30)and nonlinear elements did not converge.After discussion with ANSYS technical support team,Fluid 80 element was identified as an appropriate substitute for Fluid30 element.Satisfactory results were obtained by conducting an example benchmark. Subsequently,Fluid 80 elements were used for FSI analysis of Watana Dam Layout 4 and the model is shown in Figure 10.6-29.Absorbing boundary conditions were considered at the far end boundary of the reservoir to absorb the outgoing pressure waves in the reservoir. Using FSI analysis the computed dam sliding was reduced about 50-100 percent compared to the similar results from the previous added mass model.The maximum tensile stresses of the concrete derived from the two analyses appeared to be close and it is concluded that the compressibility of the water does not affect the maximum tensile stresses for the model although the stress distribution was changed. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-133 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. INVENASamestageohas) : i t sessssennen 3 4 _ i oye pt '-'re7aL---4LttLait s 7 L_A a ene Ltrt"4 o>omeel ap ae PL ne|Lot _Ln v4 -jst|nad aes eee " awenhens Zz e _4 Figure 10.6-29.FE Model of Dam Layout 4 with Fluid 80 Acoustical Elements to represent Reservoir 10.7.Dam -Final Modeling including FSI,Foundation Mass and Damping 10.7.1.Final Dam Layout (Layout 4 -Modified) For final feasibility analysis,the model of the Layout 4 configuration was modified to increase the width of the dam crest to 45 ft.,and instead of a straightdgwngtream face,the downstreamfaceofthecurvedsectionofthedamwasmodifiedtoasingletadiuscurve. The dam geometry selected for the modified Layout 4 is shown in Figure 10.7-1 and Figure 10.7-2. 10.7.2.LS-DYNA Analysis Software As discussed above,a more realistic FE analysis of dams can be performed by including Fluid Structure interaction,and adding mass (and damping)to the foundations.Incorporating these aspects,a significant reduction in the calculated tensile stresses can be expected,compared to the simple analysis without mass in the foundations.The proposed configuration -developed as a result of the analyses described in Section 10.6 was therefore analyzed using LS-DYNA to Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-134 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. include the mass of the foundation.LS-DYNA is a commercialized version (by Livermore Software Technology Corporation [LSTC])of computer program DYNA developed at Lawrence Livermore National Laboratory.It is a highly nonlinear transient dynamic FE code using explicit solutions.It can model mass in the foundation,model the reservoir with fluid elements, model contraction joints and foundation discontinuities,and has non-reflecting boundaries at the foundation and reservoir extents.LS-DYNA has been successfully used by the Bureau of Reclamation,US Army Corps of Engineers,the California Department of Water Resources,and many private consulting firms in several seismic dam-reservoir-foundation simulations. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-135 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT x 5 2200 ms 2200 :EXISTING GROUND :o2150:”2150 2400)wre Me 2100 2050|ed J 2050 2000]wv ee .2000 1900 EL 1900_1900 1850 18501800EL1800_-4800 1750 1750 47001 --EL 1700 4700 1650]1650 1600!--EL 1600 7 4600 1550)1550 1500 1500 1450 1450 1400 1400 1350)1350 1300 1300-1+00 0+00 1400 2+00 3+00 4+00 5+00 6+00 7+00 8+00 9+00 10400 11400 12400 13+00 14+00 15+00 16+00 17400 18+00 19400 20+00 21 +00 22400 23400 24+00 25+00 26+00 27+00 28+00 29+00 30+0D+65 PROFILE ALONG AXIS (LOOKING DOWNSTREAM) Figure 10.7-1,Plan and Elevation of Dam Layout 4 -Modified Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-136 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 1210045°-0" EL 2065 1750 1700 1650 1600 1550 1500 450 1400 TR:CONCRETE->--- ee 'TO ROCK SECTION B-B0100200CONTACT(CROWN CANTILEVER) 1350 Figure 10.7-2.Sections of Layout 4 -Modified 10.7.3.Selection of Time Histories for Final Modeling The selection of seismic criteria for the final modeling was reviewed as described in this section to include -in the modeling -the regional seismic data obtained during the feasibility studies to date. 10.7.3.1._Approach Response spectra were developed from a deterministic seismic hazard analysis for each design event.After the design response spectra were developed representative earthquake records were selected and spectrally matched.The following sections include additional discussion on the development of design response spectra,selection of time histories,spectral matching technique and earthquake record parameters before and after spectral matching.Plots of the acceleration, Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-137 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. velocity,displacement,Arias intensity and Fourier amplitude spectra are included in Appendix B6. 10.7.3.2.Development of Design Response Spectra Based on the Preliminary SSSHA Report (Fugro 2012),the seismic hazard at the dam site encompasses contributions from three different sources:the subduction zone events -interface and intraslab (also referred to as the slab),and crustal events.Time histories were developed for each type of event to evaluate the difference in frequency content. Guidance furnished by FERC,Evaluation of Earthquake Ground Motions,was followed and a deterministic spectra was used (Idriss &Archuleta 2007).Table 10.7-1 contains the deterministic parameters for each of the selected events,and Figure 10.7-3 illustrates the response spectrum.The 2,500,5,000,and 10,000 year return period uniform hazard spectra are also included on Figure 10.7-3;this data is from the SHA Report (Fugro 2012).It should be noted that the Vs3o used in the probabilistic seismic hazard assessment is 800 m/s. The 84th percentile or above was used for all of the events,except the magnitude 8.0 event for the slab,where the 69th percentile is used.Additional discussion regarding the selection of the 69""percentile forms Appendix B7.The interface event was scaled up at the fundamental period of the dam (0.55 seconds)to match the 5,000 year return period,resulting in the 88th percentile, see Figure 10.7-3.In contrast to the results of the probabilistic seismic hazard,current field data indicate a Vs39 of 1,100 m/s which was used,as provided in Draft Revised Intraslab Model and PSHA Sensitivity Results (Fugro 2014).The increase in Vs39 will decrease the ground motions; therefore,it should be noted that the uniform hazard spectra will be slightly higher compared to the deterministic spectra. Table 10.7-1.Deterministic Seismic Input Parameters Crustal Interface Intraslab CASE Fog Lake Alaskan Subduction Zone Magnitude 7.0 9.2 75 8.0 Hypocentral distance (km)--50 Rrup (km)7.0 (Rus=3.5)78 - Vs30 (m/s)1,100 m/s Type of faulting Normal Reverse Normal Dip (degrees)80 - Seismogenic Depth (km)20 -- Width (km)20.3 -- Z1.0 (km) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-138 December 2014 Zz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Crustal Interface |IntraslabCASE -Fog Lake Alaskan Subduction Zone Z25(km) Z tor (km)0.5 Hanging Wall YES -YES YES PGA(g)[percentile]0.49 [84th]0.58 [88]0.69 [84h]0.81 [69"] Ground Motion Prediction BA0S [0.25]BCH11 [0.5]BCH11 [0.5] Equation [weight]CY08 [0.25]ZHO06 [0.25]ZHO06 [0.25] CBO08 [0.25]AM09 [0.25]ABO03 [0.25] AS08 [0.25] Note: km -kilometer(s) Source:Deterministic Seismic Hazard Analysis;Fugro 2013 Acronyms:BA08=Boore and Atkinson 2008;CY08=Chiou and Youngs 2008;CBO8=Camphell and Bozorgnia 2008; AS08=Abrahamson and Silva 2008;BCH11=BC Hydro 2012;ZHO6=Zhao 2006;AM09=Atkinson and Macias 2009, AB03=Atkinson and Boore 2003 3 10,000 Year Return Period -Vs30=800m/s ooeceeees 5,000 Year Return Period -Vs30=800m/s -_--=2,500 Year Return Period -Vs30=800m/s mo (ntrasiab M8,D5SOkm Vs30=1100m/s -69th 25 ewes (ntrasiab M7.5,D50km Vs30=1100m/s -84th JoeInterfaceM9.2,D78km Vs30=1100m/s -88th oe Crustal M7.0,D7km Vs30=1100m/s -84th NSpectralAcceleration(g)wEN Fundamental Period Range 0.55-0.62 s ry0.1 Period (s) Figure 10.7-3.Design Response Spectra Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-139 December 2014 --yzw SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT A vertical response spectrum was developed by computing a vertical to horizontal ratio following the guidance of Giilerce and Abrahamson (2011).The applicability to subduction zone events was based on the work performed by Gregor et al.(2012).The magnitude and distance pair used for the deterministic analysis was used as the input parameters to develop the vertical to horizontal ratios.The ratios correspond to median values and are presented in Table 10.7-2.The vertical and horizontal response spectra are shown in Table 10.7-3 through Table 10.7-5 for each event type together with plots shown in Figure 10.7-4 through Figure 10.7-6. Table 10.7-2.Median Vertical /Horizontal Ratios Period (s)Slab M8.0 Slab M7.5 Interface Crustal 0.010 0.658 0.652 0.579 0.728 0.020 0.659 0.652 0.579 0.728 0.030 0.715 0.708 0.600 0.791 0.050 0.719 0.710 0.582 0.902 0.075 0.695 0.684 0.642 0.921 0.100 0.670 0.657 0.638 0.798 0.150 0.652 0.640 0.634 0.660 0.200 0.656 0.647 0.648 0.597 0.250 0.668 0.661 0.656 0.586 0.300 0.683 0.678 0.669 0.590 0.400 0.713 0.713 0.696 0.597 0.500 0.729 0.732 0.709 0.596 0.750 0.838 0.842 0.802 0.655 1.000 0.825 0.829 0.776 0.634 1.500 0.820 0.824 0.794 0.648 2.000 0.791 0.795 0.782 0.639 3.000 0.773 0.777 0.787 0.643 4.000 0.805 0.808 0.836 0.683 5.000 0.816 0.820 0.848 0.693 7.500 0.816 0.820 0.848 0.693 10.00 0.816 0.820 0.848 0.693 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-140 December 2014 -z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-3.Horizontal and Vertical Design Response Spectra for Intraslab Events Period M8.0 69*Percentile M7.5 84"Percentile T(s)Horizontal Vertical Horizontal VerticalAcceleration(g)Acceleration (g)Acceleration (g)Acceleration (q) 0.01 0.8075 0.531 0.6870 0.4479 0.02 0.8553 0.564 0.7337 0.4784 0.03 1.0121 0.724 0.8675 0.6142 0.05 1.2464 0.896 1.0668 0.7574 0.075 1.7055 1.185 1.4522 0.9933 0.1 2.0342 1.363 1.7286 1.1357 0.15 2.1449 1.398 1.8046 1.1549 0.2 1.9965 1.310 1.6686 1.0796 0.25 1.7432 1.164 1.4413 0.9527 0.3 1.5443 1.055 1.2646 0.8574 0.4 1.2174 0.868 1.0162 0.7246 0.5 0.9581 0.698 0.8078 0.5913 0.75 0.6262 0.525 0.5289 0.4453 1 0.4679 0.386 0.3960 0.3283 1.5 0.2835 0.232 0.2326 0.1917 2 0.1986 0.157 0.1603 0.1274 3 0.1226 0.095 0.0935 0.0726 Note:Deterministic Inputs shown in Table 10.7-1. 2.50 |Horizontal-Intraslab M8.0 'a Vertical -Intraslab M8.0 2.00 Horizontal -Intraslab M7.5\'--=Vertical -Intraslab M7.51.50 f |_\\|SpectralAcceleration(g)1.00 LO Lf .\- \0.50 -\ TS 0.01 0.1 1 10 Period (s) 0.00 Figure 10.7-4.Intraslab M8.0 -69"Percentile Design Response Spectra and Intraslab M7.5 -84"Percentile Design Response Spectra Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-141 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-4.Horizontal and Vertical Design response Spectra for Interface Events Period M9.2 88 Percentile Horizontal :;T (s)Acceleration (g)Vertical Acceleration (g) 0.01 0.5754 0.3332 0.02 0.60114 0.3481 0.03 0.6328 0.3797 0.05 0.6697 0.3898 0.08 0.8857 0.5686 0.10 1.0832 0.6911 0.15 1.2221 0.7748 0.20 1.1724 0.7597 0.25 1.0975 0.7199 0.30 1.0472 0.7005 0.40 0.9222 0.6419 0.50 0.8005 0.5675 0.75 0.6308 0.5059 1.00 0.5298 0.4111 1.50 0.3848 0.3056 2.00 0.2964 0.2318 3.00 0.1914 0.1506 Note:Deterministic Inputs shown in Table 10.7-1. 2.50 Horizontal -Interface M9.2 _..2.00 Vertical -Interface M9.2 oO ce Ss |®1.50 2 |<ro 1.00o q |7):||i |!a of |=a 0 TS. 0.00 4 -_ 0.01 0.1 1 Period (s) Figure 10.7-5.Interface M9.3 -88"Percentile Design Response Spectra Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-142 December 2014 -Zz- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 10.7-5.Horizontal and Vertical Design Response Spectra for Crustal Events Period M7.0 845 Percentile T(s)Horizontal Acceleration (g)Vertical Acceleration (g) 0.01 0.4910 0.3574 0.02 0.5022 0.3656 0.03 0.5487 0.4340 0.05 0.6859 0.6187 0.08 0.9005 0.8294 0.10 1.0523 0.8397 0.15 1.2028 0.7938 0.20 1.1882 0.7094 0.25 1.0686 0.6262 0.30 0.9567 0.5645 0.40 0.8077 0.4822 0.50 0.6615 0.3943 0.75 0.4455 0.2918 1.00 0.3476 0.2204 1.50 0.2289 0.1483 2.00 0.1611 0.1029 3.00 0.0965 0.0620 Note:Deterministic Inputs shown in Table 10.7-1.SpectralAcceleration(g)2.50 Horizontal-Crustal M7.0 2.00 ==Vertical -Crustal M7.0 1.50 1.00 Fi NX0.50 | 0.1 Period (s) 10 Figure 10.7-6.Crustal M7.0 -84"Percentile Design Response Spectra Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-143 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.7.3.3.Selection of Time Histories Pre-selection of time histories was completed by searching COSMOS,PEER,K-NET (Japanese Earthquake Database),and a database run by the University of Chile and the Chile Ministry of the Interior and Public Safety for ground motions that had magnitude,distance and record properties similar to the controlling events. Ideally,the selected time histories should have the same source,style-of-faulting,magnitude, distance,site conditions and directivity condition as the event for which the evaluation is being performed.However,in practice,it is not always possible to find a perfect match. The criteria used to select the events are discussed below. 10.7.3.3.1. Intraslab The catalog search for slab events included motions recorded during the El Salvador 2001 M7.6 event (14 recordings),Japan 2003 M7.1 event (412 of recorded motions),Chile 2005 M7.9 event (10 recordings)and available records for the Japan 2011 M7.0 event (504 recordings). The number of slab ground motions considered was then narrowed down to those events that had a recording distance from 50 to 115 kilometers (km)and included all three components.The design distance was 50 km and it was initially chosen to select those events that fell between +/-50 km,however this limited the database to a total of 28 events.By increasing the maximum distance to 115 km and additional 24 events were able to be included.The closest event distance was 72 km away,so the distance range was revised to 72-115 km.Chile M7.9 events were not able to be used because no records fell within 115 km;the closest distance was recorded to be 135 km.This narrowed down the database to 52 events,21 from the 2003 M7.1 Japan event,20 from the 2011 M7.0 Japan event and 11 from the El Salvador event.Those 52 events were then visually compared to the design response spectra and those with similar spectral shapes were spectrally matched.By putting together a catalog of those strong motion events that occurred on the slab,it is believed that the ground motion parameters (e.g.,duration and equivalent number of cycles)should be representative of the target slab scenario.Currently,there is a very limited amount of earthquake events,and strong motions,available that can be comparable to the large slab scenario (i.e.M8.0),which leads to high scaling factors.If the selection of time histories includes the record properties of the scaled ground motions,then the time histories could be scaled by large factors without affecting the average response (Watson-Lamprey &Abrahamson 2005).In addition,large scaling factors do not lead to a bias in median nonlinear structural response if,after scaling,the ground motions have similar target spectral acceleration,magnitude and the closest distance (Luco &Bazzurro 2007). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-144 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.7.3.3.2.Interface The catalog search for interface events included motions recorded during Japan 2011 M9.0 event (1400 of recorded motions)and available records for the Chile 2010 M8.8 event (55 recordings). The design distance is 92 km and it was chosen to select those events that fell between +/-50 km (42-142 km).This narrowed down the database to 148 events;138 from the 2011 M9.0 Japan event and 10 from the 2010 M8.8 Chile event.Those 148 events were then visually compared to the design response spectra and those with similar spectral shapes were spectrally matched.By putting together a catalog of those strong motion events greater than M8.8 that occurred on the interface,it is believed that the ground motion parameters (e.g.,duration and equivalent number of cycles)should be representative of the target slab scenario. 10.7.3.3.3.Crustal The search for the crustal time history was performed using the PEER NGA West |Database for those events having a magnitude ranging between 6.5 and 7.5 at distances of 0 to 15 km, contained all three components and a Vs39 greater than or equal to 400 m/s.After using the search criteria the time histories were then narrowed down to those motions that had similar spectral shape. 10.7.3.3.4.Selected Events Once the ground motions with similar spectral shape were complied,then selected recorded strong motions were synthetically modified to match the target spectra.The record parameters for the seed events are presented for the slab,interface and crustal events in Table 10.7-6 through Table 10.7-9. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-145 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-6.Record Parameters for Selected Slab Time Histories -M8.0 -69th Percentile (PGA=0.81) Arias |Predominate |Predominate Significant NEventTitleStationIntensityPeriodFreq.Duration (s)c cles(mis)(sec)(Hz)5-95%|5-75%|> Seed 0.19 1.53 0.65 33.8 12.8 83 MYGOOSEW |SpectrallyMatched 16.05 0.22 4.46 33.5 12.6 79 wrt)Seed 0.18 0.22 4.53 39.7 13.7 91 'MYGO09NS05/26/2003 Spectral |16.06 0.23 4.34 366 |146 |87Rrup=107km atched Seed 0.08 0.71 1.40 36.0 16.1 135 MYGO09UD |SpectrallyMatched 8.12 0.21 472 36.1 16.6 118 Seed 1.12 0.57 1.77 17.3 10.4 44 MONTEW |Spectrally Matched 9.10 0.57 1.77 20.6 11.2 39 urs)Seed 1.14 0.25 3.95 18.2 11.2 33 ,MONTNS01/13/2001 Spectra |9.41 0.25 3.95 20.0 |129 40 Rrup=142km Matched Seed 0.77 0.25 3.95 19.6 14.1 79 MONTUD |Spectrally Matched 5.67 0.25 3.95 24.6 16.0 55 Seed 771 0.29 3.43 10.8 5.5 36 Matched 6.98 0.29 3.43 11.7 6.7 27 urs)Seed 6.54 0.16 6.16 14.3 6.9 52 .STTEC18001/13/2001 spec |9.15 0.16 6.08 176 |89 49 Rrup=114km atched Seed 2.80 0.31 3.19 15.8 11.3 47 STTECUP |Spectrally Matched 3.64 0.10 9.87 15.9 11.6 47 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-146 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-7.Record Parameters for Selected Slab Time Histories -M7.5 -84th Percentile (PGA=0.69) Arias |Predominate |Predominate Significant NoEventTitleStationIntensityPeriodFreq.Duration (s)Cycles(m/s)(sec)(Hz)5-95%|5-75%y Seed 0.19 1.53 0.65 33.8 12.8 83 Matched |1150 0.37 271 34.1 12.8 72 rah Seed 0.18 0.22 4.53 39.7 13,7 91 MYGOO9NS05/26/2003 vpecrally 11.07 0.26 3.90 36.6 14.1 92 Rrup=107km atche Seed 0.08 0.71 1.40 36.0 16.1 135 Matched 5.89 0.13 7.79 36.0 16.5 120 Seed 1.12 0.57 177 17.3 10.4 44 MONTEW |Spectrally Matched 6.60 0.24 4.12 21.3 11.8 45 mre)Seed 1.14 0.25 3.95 18.2 11.2 33 MONTNS01/13/2001 opera 6.85 0.20 4.99 20.3 12.9 32 Rrup=112km atche Seed 0.77 0.25 3.95 19.6 14.1 79 MONTUD |Spectrally Matched 4.06 0.25 4.04 25.6 16.1 60 Seed 7.71 0.29 3.43 10.8 5.5 36 STTECO90 |Spectrally Matched 4.76 0.20 4.94 12.6 6.9 27 urs)Seed 6.54 0.16 6.16 14.3 6.9 52 STTEC18001/13/2001 pera 6.79 0.15 6.79 178 94 46 Rrup=114km Matche Seed 2.80 0.31 3.19 15.8 11.3 47 STTECUP |Spectrally Matched 2.54 0.10 9.87 16.8 11.8 44 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-147 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-8.Record Parameters for Selected Interface Time Histories -M9.2 -88th Percentile (PGA=0.58) Arias |Predominate |Predominate Significant NoEventTitleStationIntensityPeriodFreq.Duration (s)c cles(mis)(sec)(Hz)5-95%|5-75%| Seed 10.55 1.45 0.69 49.3 37.0 102 CURIEW Spectrally Matched 13.06 0.23 4.35 51.1 37.3 76 (M8)Seed 2.85 0.73 1.37 53.1 40.1 277 :CURINS02/27/2010 peer |az.at 0.55 1.83 573 |430 |175Rrup=85km atche Seed 10.88 0.42 2.40 50.7 38.2 134 CURIUD Spectrally Matched 6.06 0.42 2.40 51.8 38.9 128 Seed 0.39 1.09 0.92 93.8 57.0 87 Matched 15.2 1.09 0.92 100.3 59.8 83 M8)Seed 0.49 0.78 1.28 94.3 56.8 129 :ATKO23NS03/11/2011 Speer |19.09 0.54 1.84 1022 |618 |106Rrup=105km atche Seed 0.23 0.43 2.35 95.2 61.3 130 Matched 7.47 0.43 2.35 95.1 61.6 139 Seed 2.03 0.27 3.66 62.6 35.6 58 CHB012EW pera |10.27 1.35 0.74 728 |458 |46 Japan (M9.0)Seed 2.63 0.34 2.94 57.7 33.0 86 Rrup=130km Matched |12:00 0.30 3.38 73.1 |43.5 47 Seed 0.62 4.88 0.21 66.0 36.3 84 Matched 4.68 4.88 0.21 69.2 40.3 89 Note: ATK023 -Japanese Interface Earthquake Record -March 2011 CHBO012 -Japanese Interface Earthquake Record -March 2011 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-148 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-9.Record Parameters for Selected Crustal Time Histories -M7.0 -84th Percentile (PGA=0.49) Arias |Predominate |Predominate Significant NoEventTitleStationIntensityPeriodFreq.Duration (s)Cycles(m/s)(sec)(Hz)5-95%|5-75%y Seed 0.90 0.37 2.68 5.0 16 20 GILO67 epecray 1.36 0.22 4.56 58 2.0 30 California M6.93 GIL3371or13/89 spectral)4.34 0.45 2.23 55 18 23 Rrup=9.2km Seed 0.17 0.44 2.28 75 28 22 GILUP Spectrallyitched.|0-71 0.30 3.38 74 33 27 Seed 0.06 0.59 1.69 19.0 127 36 AULO00 spear 3.67 0.48 2.10 19.6 13.9 35 Iran Dayhooh Seed 0.07 0.36 2.80 19.2 13.1 34 M7.1 AUL270Na/i6r1978 pectraly |3.47 0.32 3.15 199 |136 |27 Rrup=13.9km Seed 0.02 0.44 2.28 193.|134 30 AUL-UP Spectral 1.65 0.45 2.22 19.0 13.6 30 Seed 142 0.39 2.56 123 67 35 DAYLN vetshad.2.56 0.95 1.05 13.6 75 32 Italrina Seed 1.36 0.43 231 12.4 6.9 15 (M6.9)DAYTR Spectrally11/23/1980 Matched 2.05 0.77 1.30 11.9 6.4 24 Rrup=9.5km Seed 0.65 0.18 5.54 14.8 83 68 DAYUP pera 1.93 0.18 5.55 15.2 8.9 56 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-149 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.7.3.3.5.Spectral Matching Approach Time histories were developed using spectral matching techniques.The spectral matching approach uses a time domain approach (RSPMatch,Abrahamson 2012)with the goal of modifying a given time history to be spectrum compatible with a given target spectrum but without any significant modification to the non-stationary characteristic of the original time history. Spectral matching adjusts the time series in the time domain by adding wavelets to the initial time series.A formal optimization procedure for this type of time domain spectral matching was first proposed by Kaul (1978)and was extended to simultaneously match spectra at multiple damping values by Lilhanand and Tseng (1987,1988).While this procedure is more complicated than the frequency domain approach,it has good convergence properties and in most cases preserves the non-stationary character of the reference time history. Several passes were performed using the RSPMatch program until the fit to both the spectral shape and displacement time history were acceptable. 10.7.3.4.Results -Selected Ground Motions The ground motions selected for the intraslab,crustal and interface events are presented in Table 10.7-6 through Table 10.7-9.The record properties for the seed and output time history are also summarized in the tables. The Arias intensity for the crustal events was calculated using empirical correlations developed from the NGA West |dataset (N.Abrahamson,personal communication 2014).Equally weighting the five ground motion prediction equations resulted in a median Arias intensity of 0.65 m/s and an 84th percentile Arias intensity of 1.48 m/s.The Arias Intensity for the horizontal components of the spectrally matched crustal time histories range from approximately 1.34 to 3.67 m/s. The Brookhaven Model (Silva et.al.1996)was used to estimate the significant duration between 5 and 75 percent for each of the four response spectra.The rupture distance was used as input to the Brookhaven Model for the crustal and interface events,and the hypocentral distance was used for the intraslab event (N.Gregor,personal communication,August 29,2014).The Brookhaven Model was originally developed for crustal events,but has been shown to work adequately for the interface and is the best model available for the intraslab (N.Abrahamson, personal communication 2014).The results are summarized in Table 10.7-10. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-150 December 2014 SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. -yz .ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 10.7-10.Estimate of Significant Duration using the Brookhaven Model Event Horizontal Duration (5-75%),seconds Vertical Duration (5-75%),seconds 16"percentile 84"percentile 16"percentile 84'h percentile Intraslab My 7.5 6.7 20.9 78 20.4 Intrastab Mw 8.0 9.6 29.8 9.7 25.3 Crustal Mw 7.0 3.4 10.6 3.7 9.6 Interface Mu 9.2 25.6 79.3 19.7 53.3 Overall,the durations of both the seed and spectrally matched time histories generally fall within the 16"to 84"percentile predicted by the Brookhaven Model.The exceptions are the vertical interface motion recorded at station AKT023 and both horizontal motions for the M8 intraslab event recorded at station STTEC.The spectrally matched vertical motion at station AKT023 had a higher significant duration of 61.6 seconds (5-75 percent)compared to the 84"percentile from the Brookhaven Model of 53.3 seconds.The spectrally matched horizontals from station STTEC intraslab motion were 6.7 seconds and 8.9 seconds which are slightly lower than the 16" percentile predicted value of 9.6 seconds. Appendix B6 contains the earthquake records plots.In Appendix B6,Figure |through Figure 5 show plots of acceleration,velocity,normalized displacement,response spectra,Husid plots,and Fourier amplitude spectra for each time history component before and after spectral matching. Each motion has two horizontal components and one vertical component. Acceleration,velocity,and normalized displacement are plotted in Appendix B6,Figure |in blue (labeled SEED)for the first horizontal component.The spectrally matched acceleration, velocity,and normalized displacement time histories are shown in Appendix B6,Figure 1 in red. The plots of acceleration,velocity,and normalized displacement are overlaid so that they can easily be compared.The purpose of these plots is to confirm that the spectrally matched time history remains similar to the original input motion and that extraneous wavelets are not being added to the motion.Appendix B6,Figure2 is a plot of the acceleration,velocity,and displacement for the SEED motion and Appendix B6,Figure 3 is the same for the spectrally matched motion. Appendix B6,Figure 4 illustrates the match to the horizontal design spectrum (black line labeled TARGET),with the recorded motion shown in blue and the spectrally matched motion shown in red.The overall goal of spectral matching is to achieve a fit as close as possible to the design response spectrum.It is important to note that the fit to the lower periods (0.01s to 0.02s)for some events has more variability about the target spectrum;this result is limited by the sampling rate of 100-200 samples per second and has little impact on the structure,as most dams are impacted by periods greater than 0.1 seconds. Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-151 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The Arias normalized intensity (also called a Husid plot)for the initial and spectrally matched acceleration time history is plotted at the top in Appendix B6,Figure 5;the bottom plot in Appendix B6,Figure 5 is the Fourier amplitude spectra.Again,the blue line is the seed or initial motion and the red line is the spectrally matched motion.These plots show that the Arias intensity is not significantly different from the original input motion.The Fourier amplitude spectra plot illustrates that the frequency content was not significantly modified in the frequency range of 0.1 to 10 Hz (period range of 0.1 to 10 seconds). The same presentation order is followed for each component and motion -acceleration,velocity, and normalized displacement;SEED acceleration,velocity,and displacement;spectrally Matched acceleration,velocity,and displacement;response spectra;and Husid plot (top),Fourier amplitude spectra (bottom). Twelve sets of three component spectrum compatible time histories were developed:three sets were developed for the intraslab event M8.0-69""percentile,three sets were developed for the intraslab event M7.5-84"percentile,three sets for the M9.2-Interface-84""percentile,and three sets for the crustal M7.0-84"percentile. 10.7.3.5.Time Histories Used in the Analysis For the feasibility analysis,one spectrally matched time history was selected from each of the design events (two intraslab,one interface and one crustal).Two events were selected from the intraslab to represent the different magnitude levels,7.5 or 8.0;as this part of the seismic hazard assessment is still in progress. In total,four sets of time histories containing three records each have been developed for the slab,interface and crustal events using spectral matching techniques.All of the ground motions are based on the deterministic analyses using a Vs39 of 1,100 m/s.The intraslab event utilized two different earthquake records,one was from the El Salvador M,,7.6 and the other was from the Japan M,,7.0. For the MCE,the following time histories shown in Table 10.7-11 have been used: Table 10.7-11.Selected Time Histories for Feasibility Analysis-Intraslab and Crustal El Salvador (M 7.6)STTEC Mw 7.5 -84"percentile Intraslab Japan 2011 (M 7.0)MYG 009 My 8.0 -69%percentile Intraslab Loma Prieta,California (M 6.93)GIL Mw 7.0 -84"percentile Crustal Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-152 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Based on comments received from the Board of Consultants to increase the response spectra,the following response spectra for the interface event in Table 10.7-12 was also used for the analysis: Table 10.7-12.Selected Time Histories for Feasibility Analysis -Interface Chile 2010 CURI Mw 9.2 -88"percentile Interface The ground motions selected for the slab,interface and crustal events are presented in Table 10.7-6 through Table 10.7-9.The record properties for the seed and output time history are also summarized in the tables.Plots are included in Appendix B6. According to the published guidelines (ICOLD,FEMA,Alaska Dam Safety,and USACE)the normal choice of operating basis earthquake (OBE)would be the earthquake that can reasonably be expected to occur within the service life of the project,that is,with a 50 percent probability of exceedance during the service life.(This corresponds to a return period of 144 years for a project with a service life of 100 years.)For Susitna-Watana,such an event would equate to a PGA of the order of 0.16g,which could be regarded as unacceptably low by the general public who are not conversant with civil and structural design guidelines.The following Table 10.7-13 shows the PGAs for selected return periods: Table 10.7-13.PGAs for Selected Return Periods Return Period,years PGA 100 0.139 150 0.169 500 0.279 1000 0.379 MWH recommends that the OBE be selected as the 500 year event,equating to a PGA of 0.27. The dam structure will be evaluated under this event and from a structural perspective all facilities will be able to continue to operate without interruption or significant repair. 10.7.3.5.1.OBE Time History For the purposes of the feasibility level design only one event was run for the OBE case.The crustal motion,GIL,was scaled by 0.61 to match the 500 year return period from the Probabilistic Seismic Hazard Analysis.The geometric mean of the horizontal components from the Crustal GIL motion was also computed.Figure 10.7-7 plots the 500 year return period (OBE),the geometric mean from the GIL horizontal components with a factor of 0.61 applied and the crustal response spectrum scaled to 500 year return period event for comparison. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-153 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 0.6 i 0.5 VA \S.J__\0.3 _\ 0-2 |-=500 Year Return Period SS --Crustal Response Scaled to 500 year Geometric Mean of Horizontals Crustal-GIL ™sySpectralAcceleration(g)0.01 0.1 1 Period (s) Figure 10.7-7.OBE Response Spectra and Scaled Crustal Event 10.7.4.Methodology of Structural Analysis Considering mass of the foundation and compressibility of the reservoir in nonlinear transient analysis of a dam-foundation-reservoir system is a complicated analysis.It includes a series of analyses performed in steps,the result of each step being used as input for the subsequent analysis. The complexity requires that each analysis be performed with caution and the results of each step verified by performing some simple bench mark tests. Thus the procedure adopted was to initially model the structure in 2-D to develop and verify the analysis method and steps.After the 2-D modeling had been completed satisfactorily,the 3-D model of the structure was developed and final analyses were performed. Both ANSYS and LS-DYNA software were used in parallel to develop and verify the procedure for transient analysis of the dam-foundation-reservoir system.It is noted that the LS-DYNA has several advantages over ANSYS Mechanical for performing analysis;however ANSYS is more powerful and user friendly for developing the model geometry and preparing the mesh.ANSYS Mechanical and ANSYS Design Modeler were used for developing the geometry and meshing the model,using the Inventor model of the dam provided by the design team. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-154 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT LS-DYNA has "built in”absorbing boundaries;however,defining these types of boundaries in ANSYS requires significant extra effort.Moreover LS-DYNA has available wide varieties of the required contact elements and its explicit solver with relatively short time steps is reliable for capturing the nonlinear response (opening/closing and sliding of contacts)of the dam during the earthquake. ANSYS Explicit export was used to export the LS-DYNA input data file (-k File).The LS- DYNA input data file was revised and additional commands added according to the type of analysis.After performing the analysis with LS-DYNA,output results were post processed with LS-PrePost. To accelerate the process,cloud computing services were engaged to allow the software to run on multiple computer cores. After performing all the basic analytical runs,various sensitivity runs were performed as described below. 10.7.4.1..Two-Dimensional Analysis Nonlinear transient seismic analysis of the dam-reservoir-foundation system with LS-DYNA includes several individual analysis steps.The analysis steps include static analysis, deconvolution analysis,and non-linear time history.Implementation of these steps in LS-DYNA was first verified by a 2-D model to ensure that procedure was being applied properly and considering mass of foundation can reduce the tensile stresses in the dam body.A 2-D model of the dam-foundation and reservoir (section through crown cantilever monolith)was developed and extruded 10 ft.in perpendicular direction to create a simple 3-D model.While this model represents a simplified 2-D behavior of the dam cross section it had the advantage of utilizing 3-D elements of the LS-DYNA which were used in the final 3-D modeling of the dam.It provided a simple and fast way for developing and verifying analytical steps.These steps are: 1.Re-convolution analysis:This analysis was performed to correctly apply the ground motions at depth in the foundation and to allow the seismic motions to propagate up through the foundation and around the canyon -essentially producing a spatially varying, and more realistic seismic loading.The following steps were followed to make sure the applied ground motions at depth produced the surface motions postulated by the seismologists: a.Compute the minimum FE size to properly transmit the seismic wave through the FE model.The element size is based on the P-wave of the foundation rock and the largest frequency expected to be captured in the model.The ground motion is Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-155 -December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. normally applied along a horizontal layer of element faces at least 10 (finite) elements beneath the ground surface.The nonreflecting boundaries are then three (finite)elements beneath this layer and at the sides of the box.The horizontal extent of the foundation box normally needs to extend at least three dam heights away from the dam,and have a length to depth ratio of at least 4:1. b.Build the box shaped foundation model with the same horizontal dimensions as the final model that will include the dam,canyon,and reservoir.The top of the box is located at the elevation of mid-height of the dam.The flat box model allows for application of the ground motion at depth,capture of the computed motion at the ground (top)surface,verification of how well it matches the free- field (target)motion provided by the seismologist,and determination of any scaling factors,if needed,to apply to the ground motions at depth.Comparisons by the Bureau of Reclamation have shown that scaling factors vary very little whether the top of the flat box is positioned at the elevation of base,mid-height, or top of the dam. c.Deconvolute the three components for the ground motion to the level the ground motion is to be applied at depth (accounting for damping in the model)in units of velocity.This step was overlooked in feasibility study because the rock material has high deformation modulus and low damping and hence minor filtering/amplification effect is expected.Hence the free field motions were implemented at the base of the model in the next step. d.Compute constant values to apply to the velocity records to convert the velocities into stress-based on the compressional wave speed,shear wave speed,modulus of elasticity,and shear modulus. e.Run a dynamic analysis with only the box model and capture acceleration or velocity time histories at the top surface of the box. f.Compare the acceleration response spectra of the computed surface motions to the target response spectra.Accelerations of various nodal points along the top surface of the flat box model were not compared.The sides of the foundation model were positioned considerable distance from the dam model to minimize the influence of the non-reflective boundaries near the dam.Acceleration from a node point at the center of the top surface (where the dam would be in the topographic dam-reservoir-foundation model)was used to compare with the target response spectra.Calculate applicable scaling factors for the three Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-156 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT components.Rerun the box model and check again the computed motions against the target motions. 2.Static run for static loadings: a.Build the dam-reservoir-foundation model and restrain the foundation and reservoir extents. b.Apply gravity loads to the dam and reservoir and uplift forces over five second solution time. c.Capture the reaction forces at all the nodal points of the restrained boundary. 3.Transient run for the rerun static and applied seismic loads: a.Replace the restraints on the nodal points along the foundation and reservoir extents with nonreflecting boundaries and the reaction forces captured in 2c. b.Repeat the static analysis over five seconds and add an additional five-second "quiet”time to let the model stabilize. c.Apply the ground motions at depth on the foundation as traction stresses along a horizontal layer of element faces,from 10 seconds to the end of the earthquake. Detailed discussion of the implementation of the analytical steps in LS-DYNA is presented in Appendix B8.The results of the analysis showed that considering mass of the foundation and compressibility of water could reduce the maximum normal stress in the dam up to 40 percent which is in line with other investigators (USBR 2006,Chopra 2008).It is noted that the degree of reduction varies with the geometry of structure or applied earthquake loading. Thus the 2-D analysis confirmed the assumption that running a full 3-D model of the Watana Dam considering the mass of foundation and compressibility of the water is beneficial and would likely predict lower dam stresses compared to the stresses calculated by a massless foundation model. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-157 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.7.4.2.Three-Dimensional Analysis A 3-D geometric model of the dam had been previously developed in AutoDesk Inventor and is shown in Figure 10.7-8.In a similar manner a 3-D model of the dam-foundation-reservoir was developed.The overall dimensions of the dam-foundation-reservoir model were chosen based on guidance from the U.S.Bureau of Reclamation's Design of Gravity Dams (USBR 1976),and were 1,500 ft.vertical,4,000 ft.upstream-downstream,and 5,000 ft.cross stream.3-D views of the developed model are shown in Figure 10.7-8,Figure 10.7-9,and Figure 10.7-10.The dam- foundation interfaces were simplified compared to the proposed foundation excavation to facilitate modeling and meshing of the dam and to limit computational time.This simplification is acceptable -particularly in view of the limited site investigation of the rock foundation of the dam.In the future,when more detailed site investigation results are available,and more informed analytical design can be implemented,the proposed foundation will be re-evaluated, and the final chosen surface can be included in updated FE analysis. According to the current proposed excavation plan the dam foundation (in the upstream/ downstream direction)is horizontal in most areas except two locations on the left and right abutments.It is sloping upstream in some parts of the right abutment and it is stepped in some parts of the left abutment to eliminate the assumed natural downstream slope of the rock surface. To create a regular and simple FE mesh the complex interface geometry was replaced with horizontal interfaces under all dam monoliths in the 3-D model.This assumption may well create conservative results for the sliding displacement along the right abutment. The developed Inventor 3-D model was imported into ANSYS Design Modeler.This software was used to modify the model as required so that ANSYS Mechanical was able to be used to develop the FE mesh.Standard eight node elements were used to mesh the dam,foundation and reservoir.Element sizes were chosen based on the limitation of the explicit solution method for capturing wave propagations in the model.A maximum element size of 60 was used for foundation and reservoir;however a smaller element size was used in the dam body for more accurate stress calculation in the dam body. The FE model consisted of 722,796 elements and 777,823 nodes. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-158 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 10.7-8.AutoCAD Inventor Model -simplified for use in Finite Element Analysis Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-159 December 2014 za .ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years.beyeee"fees:pensBsABPRborecess.."Eamesr=N,Figure 10.7-10.Enlarged 3-D View of LS-DYNA Model Alaska Energy AuthoritySusitna-Watana Hydroelectric Project Page 10-160 December 2014FERCProjectNo.14241 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 10.7.4.2.1.Material Properties Table 10.7-14 summarizes the material properties used in the LS-DYNA model. Table 10.7-14.Foundation and Dam Material Properties used in LS-DYNA Mass Deformation Poisson's Material Density Modulus Ratio (pcf)E (psi) Foundation 170 3.5E+6 0.25 Concrete 150 3.9E+6 0.25 Water 62.4 3.1E+05 (Bulk Modulus) The fluid elements in LS-DYNA are 3-D solid elements with water material properties.The formulation also incorporates an Equation of State that minimizes the shear in the fluid.In accordance with expected construction practice,the FE model included vertical (unformed) contraction joints between dam monoliths at every 50 ft.along the dam axis.Contraction joints were modeled as frictional contact surfaces with no tensile capacity.Frictional contact surfaces were also used to model the interface between the dam and foundation.A total of 161 contact surfaces were included in the model.Each contact surface consists of a master list of 3-D planar elements forming a surface and a slave list of 3-D planar elements forming a surface.The nodes of the master surface are independent from the nodes of the slave surface so the surfaces can slide and come apart,but not penetrate one another. 10.7.4.2.2.Static Analysis In LS-DYNA the static loading is applied like a dynamic ramped load over a time period (larger than the natural period of vibration of structure).An additional quiet time (while holding the static loading constant)is also required to stabilize the model at the end of the analysis. Weight of the dam and reservoir and uplift pressure at the contact between the dam and foundation contact were applied as static load in the analysis.These forces were ramped from zero to five seconds and kept constant for five seconds to achieve steady state conditions at the end.During the static analysis the sides and base of the foundation and the extent of the reservoir were constrained against movement perpendicular to their faces.The nodal traction forces along the constrained boundary conditions were recorded at the end of analysis for use in the next step of transient analysis. The results of the static analysis were verified by performing a separate static analysis of the model in ANSYS Mechanical.Distribution of the vertical stresses in the dam body and horizontal displacement at the dam crest from the two separate analyses were examined and Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-161 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT found to be identical.The existing hydrostatic pressure in the reservoir elements at the end of the "quiet time”was also verified through manual calculations. 10.7.4.2.3._Deconvolution Analysis Seismic records must be implemented in the analysis as traction loads along a horizontal layer of element faces in the foundation model.These tractions in each direction were calculated as the product of the corresponding earthquake velocity and a damping coefficient.Lysmer dampers were used as initial estimation.A deconvolution analysis was performed to update the Lysmer damper values for the foundation geometry and mesh that was used in the simulations. The tangential (c;)and normal (c,)Lysmer dampers (per unit area)were calculated based on shear wave and longitudinal wave velocities, Cr =p-S;=18.89 psi.sec/in Cn =P-Spn =32.71 psi.sec/in where S,and S,are the shear wave and longitudinal wave velocities calculated using the foundation material properties, G=E/2(1+v)=1400 ksi A=E.v/(1+v)(1 -2v)=1400 ksi S,=VG/p =6177.2 ft/sec Sn =V¥A+2G)/p =10698.8 ft/sec The following Table 10.7-15 summarizes the Lysmer damper values for the foundation. Table 10.7-15.Foundation Rock Material Properties and the Corresponding Wave Velocities and Lysmer Damper Coefficients .:'Shear Longitudinal Lysmer LysmerassenPorsonsWaveWaveDamper-Damper -y Velocity Velocity Tangential Normal P E y Vs Vi Ct Cn (pcf)(psi)(ft./sec.)(ft./sec.)(psi/in./sec.)(psi/in./sec.) 170 3.5E+06 0.25 6177.2 10698.8 18.89 32.71 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-162 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT A 3-D box model of the foundation was prepared with similar geometry,mesh size and damping as the complete model and absorbing boundary conditions were applied to the base and sides of the model.In addition,tractions were implemented in three directions at the base of the model. These tractions were calculated as the product of Lysmer damper (tangential for shear directions and normal for vertical direction)and the corresponding velocities. A simulation was performed and three components of acceleration at the top of foundation were captured.Acceleration response spectra were computed for the three components which were compared with the corresponding response spectra of the free-field motion.The damping factors were adjusted so that the responses were identical at the natural frequency of the dam. This numerical analysis was performed for the Gil and MYG earthquakes and resulted in comparable values for the damping factors.As a result,the adjusted damping coefficients, shown in Table 10.7-16,were used for the transient analysis of the complete model. Table 10.7-16.Scaled Damper Coefficients used in Three Directions as a Result of Deconvolution Stream Direction Cross Valley Direction Vertical Direction Cx Cz Cy (psiin/sec.)(psi/in./sec.)(psi/in./sec.) 17.10 17.88 36.14 10.7.4.2.4.Transient Analysis For the transient analysis,the constrained boundaries in the 3-D model of dam-foundation- reservoir were replaced with non-reflecting boundaries and static and seismic loadings were applied to the model.Ramped static loading was applied for the first 10 seconds to the model along with the computed reaction forces from static analysis as static initialization boundary forces.The computed earthquake traction loadings from the earthquake velocity records and the damper coefficients were applied to the foundation. Explicit analyses are conditionally stable based on the solution time step.LS-DYNA computes an initial stable time step based on the smallest element size,the wave speed of the material (which is based on modulus and mass density),and the damping.As sliding occurs,or contraction joints open and close,nonlinearities are introduced into the model that may require a smaller solution time step.The computed time step can be scaled down to attempt to reach convergence based on the response of the model.In addition to analysis with the calculated time step,two additional analyses were performed using time steps of 5 and 10 times smaller than the calculated time step.It was determined that using a five times smaller time step (At=2.4e° seconds)gave acceptable results for this case. Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-163 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Transient seismic analyses were performed for four MCE cases and one OBE case as described in Section 10.7.3.5 and the results are summarized below: MCE Loading Cases The maximum tensile vertical stresses on the upstream and downstream faces of the dam and the maximum principal stress on the downstream face of the dam are shown in Figure 10.7-11 to Figure 10.7-13.The maximum stresses were extracted from these figures and are presented in Table 10.7-17 for comparison.The maximum tensile vertical stress on the upstream face of the dam was determined to be 662 psi and occurred at El.1770 ft.(peak stress point)during the MYG earthquake.The maximum tensile vertical stress and maximum tensile principal stress on down face of the dam was determined to be 745 psi and 929 psi respectively,both occurring at elevation 1930 during the MYG earthquakes. Maximum Vertical Stress U/S +Max Stress (psi)-MYG Max Stress (psi)-STTEC -*-Max Stress (psi)CUR!Elevation(ft)3-+-Max Stress (psi)-GIL 1600 .Min Stress (psi)-MYG -#-Min Stress (psi)-STTEC 1500 - +-Min Stress (psi)-CURI 2 -*Min Stress (psi)-GIt 1400 -2000 -1500 -1000 -500 0 500 1000 Stress (psi) Figure 10.7-11.Maximum Vertical Stresses in U/S Face of Crown Cantilever Monolith During MCE Susitna-Watana Hydroelectric Project : Alaska Energy Authority FERC Project No.14241 Page 10-164 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Maximum Vertical Stress D/S 2100 y :2000 aeDeape 1900 ?os :Maa eT YO:+MaxStress(psi)-MYG =”as +MaxStress(psi)-STTEC,-ae eo .... §Toff pop io -+-Max Stress (psi)-CURI &1700 +8 fe :-+-Max Stress (psi)-GIL e Sind nn Pore]1600 'ye soo -+--Min Stress (psi)-MYG feos:Doe -*-Min Stress(psi)-STTEC 1500 '-=-Min Stress (psi)CURT '--#-Min Stress (psi)-GIL s 1400 1300 -2000 -1500 -1000 -500 [4]500 1000 Stress (psi) Figure 10.7-12.Maximum Vertical Stresses in D/S Face of Crown Cantilever Monolith During MCE Maximum Principal Stress D/S 2100 -, :aay :St +oo a.ak000ts2anbe4 "ivesLee::'poe ;r1900y eer tote Do ee ofoSeeeeLees:Max Stress(psi)-MYG=1800 7 bi r .a -+-Max Stress (psi)-STTEC .+a Boe .e =at ... 5 aot 7 it an ne - w Max Stress (psi)-CURI g :a Pott Dt zy vo Dg!-+-MaxStress(psi)-GILcoongSeseeee" MinStress(psi)-MYG .rs Doe Sot ia Do ae -e-Min Stress(psi)-STTEC 1500 on a ---Min Stress (psi)-CURI ee a re ee,OO .ae at a ee a Ye * Min Stress {psi)Git1400+ 1300 -2000 -1500 -1000 -500 0 500 1000 Stress (psi) Figure 10.7-13.Maximum Principal Stresses in D/S Face of Crown Cantilever Monolith During MCE Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-165 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.7-17.Maximum Tensile Stresses for MCE Events Vertical Tensile Stress Principal Tensile Stress Earthquake Type Event Name (Psi)(Psi) Upstream Downstream Downstream Intraslab M8 (PGA=0.81)MYG 662 745 929 Intraslab M7.5 (PGA=0.70)STTEC 576 621 743 Interface M9.2 (PGA=0.58)CURI 580 597 738 Crustal,M7.0 (PGA=0.48)Gil 597 240 293 Using RCC with approximately 600 psi of dynamic tensile strength between RCC lifts would be enough to prevent cracking along the RCC lift joints on the upstream face of the dam during the MYG event.The maximum tensile stress on the upstream face of the dam was determined to be smaller for all other cases except the MYG earthquake.Even with the MYG event the number of and duration of overstressing is very short,as shown in Figure 10.7-14,and the extent is limited to a small area on the upstream face of the dam as shown in Figure 10.7-15.These conditions are unlikely to create any significant damage to the dam structure. 800 600 Psi 400 F go vit iN i |Sh)PUNO FLL;mA MR RH iN ep5-400 ai to-800 | -1,200 °20 40 Time (5)80 100 120 Figure 10.7-14.Time History of Normal Stress at the Peak Stress Point in U/S Face During MYG Event Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-166 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. LS-DYNA user InputTimes4180 Fringe LoveisContoursofY-siress 8.2000+02mins-1364.95,at elems 64231 'max=803.083,at stem#99132 2wpe 5.990002 {wen 3.7900+02 _|reenitleenncay®1.5700+02Ce?arsanaeoneepie 64000401preietestiBae*ontategit 28500402 ''velt eat tall -5.0600+02_-ot xt raat fesoosassenttaretesfettaHetreHse 7.2700+02_| 'seesuilt if HEHE ena cared BAB0e+02 _. pogneretscsasenristeseel sansentsese i i ste :fap lie -1.469¢+03statetttsreeetsseateiret,Mi;Sie atte Ht :tect aoe 1.3900+03_| .t powtettonetaretty 'p'spicheaette chet daneteuaeerT ie asgie a rerrtit aayHot+ret a Re ni+pasate see tall 'aewaste*'is ath het!eratNTH3sfrotaoatHseaneey ae Figure 10.7-15.Maximum Vertical Tensile Stress on Upstream Face of the Dam during MYG Event (red area shows tensile stress >600 psi) On the downstream face of the dam,the vertical tensile stresses should be compared with the tensile strength of RCC lifts,while the principal stresses should be compared with the tensile strength of the parent concrete of RCC as the acceleration is horizontal.To prevent cracking on the downstream face of the dam,at least 750 psi of tensile strength on the RCC lift joints and 900 psi of tensile strength in the parent RCC is required.If the constructed RCC strength is lower than these values cracking may occur on the downstream face during the event.However, industry accepted design guidelines allow cracking as long as the structure remains stable during, and after,the event. Figure 10.7-16 shows the variations of the principal tensile stress at the peak stress point on the downstream face of the dam,if a tensile strength of 600 psi for parent RCC is achieved.There is a single overstressing during the MYG earthquake while there are two or three during the STTEC and CURI earthquakes.The extent of the overstressed area on the downstream face of the dam and on the crown cantilever monolith (as shown in Figure 10.7-17 for MYG earthquake) shows that estimated cracking will be very limited.For a crack to create instability in a large structure such as Watana Dam,it has to be substantially through the dam body and the duration of overstressing must be long.As shown,the computed overstressed area is very small and does not extend through the dam body,and the duration of overstress is restricted to a few hundredths of a second.These two factors show the dam is stable during and after a major seismic event with only minor damage and not enough time to cause any movement in the body of the dam. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-167 December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT During detailed design,more refinements to the dam configuration will be explored and more FE analysis undertaken to further reduce the magnitude of projected tensile stresses. MYG Earthquake1,000 800 600 Stress(Psi)nie 20 40 100 120 STTEC Eartquake Stress(Psi)10 20 60 70 Earthquake Stress(Psi)TeHi 10 20 40 50 60Time(S)Stress(Psi)od 10 30 40 SO Time (S) Figure 10.7-16.Time History of Principal Stress at the Peak Stress Point in D/S Face During Four MCE Events Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 10-168 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT LS-DYNA user Input Tes 41.81 Contours of Maximum Principal Stress. mins-471.88,at elem 95636 Max=1052.69,at lems 92518 wrenratt metternreesttas Figure 10.7-17.Maximum Principal Tensile Stress on Downstream Face and Crown Cantilever Monolith of the During MYG Event (red area shows tensile stress >600 psi) A 2-D model of the crown cantilever with a horizontal cracked section (at the level of peak stress points)was developed.This crack was modeled as a continuous sliding surface.Analysis results showed that a maximum of four inches downstream sliding could happen during the GIL earthquake.Much smaller sliding displacements are expected at this interim joint in the monoliths because of the 3-D behavior and tapering geometry of individual monoliths. Sliding Displacements Results of the analyses have shown that the dam monoliths will slide during the earthquake in the absence of consideration for cohesion at the dam/foundation contact.The modeled sliding displacements along five typical monoliths as shown in Figure 10.7-18 -are presented in Table 10.7-18 as the maximum sliding along the base of the monoliths at the end of four different MCE events,and as a function of time in Figure 10.7-19 through Figure 10.7-22. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-169 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT LS-DYNA user input Monolith 17 Monolith 26 te Figure 10.7-18.Monoliths Numbering The maximum sliding displacement of 3.9 inches projected by the analysis occurs at monolith 37 (right abutment)during the CURI event while the sliding at the center of dam is approximately 2.2 inches.As noted above,the proposed dam foundation interface will slope upstream at the right abutment,but is modeled as horizontal in the current analysis for simplicity.Hence,sliding of the right abutment would be expected to be less than the computed value of 3.9 inches. Moreover,the assumed 1.2 friction coefficient (friction angle of 55 degrees)used in the non- linear analysis is regarded as a conservative assumption.A greater friction coefficient (1.4 to 1.5)is expected,due to the character of the foundation rock,strength of the RCC,and the additional sliding resistance that would be realized from the powerhouse and mass concrete at the toe of the dam.For comparison,analysis using a friction coefficient of 1.48 (friction angle of 56 degrees)was performed for the CURI earthquake.The results,presented in Table 10.7-18 show 20 percent reduction in sliding displacement compared to the similar case with a friction coefficient of 1.2. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-170 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 10.7-18.Maximum Sliding on Selected Monoliths Monolith 7 Monolith 17 Monolith 26 Monolith 37 Monolith 47EarthquakeEvent(inches)(inches)(inches)(inches)(inches) MYG (friction coeff.=1.2)3.7 2.8 2.2 3.3 3.9 STTEC (friction coeff.=1.2)1.3 1.2 1.2 2.9 2.6 CURI (friction coeff.=1.2)3.0 2.6 2.2 3.9 3.0 GIL (friction coeff.=1.2)0.3 0.9 0.9 0.7 0.9 CURI (friction coeff=1.48)2.5 2.2 1.7 3.2 2.4 Sliding Displacements-MYG Earthquake 4.0 ;se 35}=ne - a -OEE. 3.0 =heel"aided ea =nr eee |eee |Gen ean oe2styp af .E mol i wih foc ober:--Monolith7E20+-acaienti =: -Monolith 17 r=} :[a aaaen Oe {|__.--Monolith 26 si noe pony 5 -Monolith 37 4 rie pe y -Monolith 47 1.0 -q - 0.5 ge : 0.0 f |a 0 10 20 30 40 50 60 70 80 90 100 110 Time (sec) Figure 10.7-19.Dam Base Sliding Displacement During MYG Earthquake Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-171 Alaska Energy Authority December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Sliding Displacements-STTEC Earthquake =”= bog5 L E '-Monolith 7 e +8 --Monolith 17ztrmaoh--Monolith 26i+ 3 :-- Monolith 37i)|be --Monolith 47 50 60 Time (sec) Figure 10.7-20.Dam Base Sliding Displacement During STTEC Earthquake Sliding Displacements-CURI Earthquake 4.0 IiagreeSeesUSSUSOONEGEDUDEDGINEMDUSUEEEEUHVTWS(oW'T CV COND yowr prenaan 35 :- 3.0 foce cept fp ceceenceriefmee ge cerefeey bog tape pegs ome arn bod 2 5 nes k A on as Neve .ear - 3 a are Det)ebrrp iis]-=Monolith7CT]r 4 2.0 aoe ian -en ne --Monolith 17 a NO aa sal Wop oo Poor |=Monolith 26 3*°EL eS eee eee :Monolith 374premyptc:--Monolith471.0 -- 0.5 - 7 0.0 : 0 10 20 30 40 50 60 70 80 90 100 Time (sec) Figure 10.7-21.Dam Base Sliding Displacement During CURI Earthquake Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-172 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Sliding Displacements-Gil Earthquake 40 ..... T 3.5 a ana a 3.0 po =PP ibid: 225 -{--__}- 5 £:cores :--Monolith 7id....-.=2.0 pnp --Monolith 17 a on rrr an --Monolith 26_Phdg15anaan --Monolith37 4":DoD :--Monolith 471.0 .re re BRAN -Te a et didi bi0.0 |} 0 5 10 15 20 25 30 35 40 Time (sec) Figure 10.7-22.Dam Base Sliding Displacement During GIL Earthquake The estimated sliding displacements of two to four inches can be accommodated by the appropriate design of the vertical drains to minimize the effects.Dam and foundation drains will be sized to remain effective following movement of the dam during extreme loading. OBE Loading Cases The developed OBE record as explained in section 10.7.2.5.1 was used to perform seismic analysis and assess the response of the dam for the operational basis earthquake.The summary of the results including developed tensile stresses and sliding displacements are shown in Table 10.7-19 and Table 10.7-20. The maximum tensile normal stress is 240 psi equating to about 80 percent of the static tensile strength of RCC.No cracking in the dam body,or between the RCC lifts is expected during OBE event.Maximum of 0.55 inches of sliding displacement along the base of dam model is very small.These small displacements are probably initial adjustments along the contact surfaces in the model and can be neglected. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-173 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 10.7-19.Maximum Tensile Stress in the Dam during OBE Events Vertical Tensile Stress Principal Tensile Stress Earthquake Type Event Name (Psi)(Psi) US DS DS Crustal,500 yrs.Gil 0 194 240 Table 10.7-20.Maximum Sliding during OBE Events Earthquake Event Monolith 7 Monolith 17 Monolith 26 Monolith 37 Monolith 47 GIL 0.05 0.45 0.55 0.35 0.2 10.7.4.3.Sensitivity Studies -Non-homogeneous Foundation The foundation conditions are not yet fully characterized by site investigation.It was therefore important to perform sensitivity analyses to account for potential variations from the assumed conditions. Three analyses were performed to investigate the sensitivity of the computed results to the foundation material properties,and in each case the STTEC event was used for these analyses. During excavation of any dam foundation,it is possible to "overblast”the foundation and - although careful blasting will be specified and consolidation grouting will be performed over the whole foundation to create an excellent foundation against which to place RCC -it is prudent to examine the effect,should there be a thin disturbed layer at the top of the foundation.Two analyses were performed for this condition -first including a layer exhibiting a deformation modulus of E=2.8e6 psi;and second a similar analysis assuming a deformation modulus of E=2.0e6.The stresses and sliding displacements computed from these analyses are shown in Table 10.7-21 and Table 10.7-22.Comparing these results with those of the previous analyses that included a homogeneous foundation shows that the presence of a thin layer under the dam base of lower deformation modulus does not significantly affect the results. The reinterpretation of the characterization of the foundation recorded in Section 6 has significantly reduced the postulated widths,number and continuity of the geological features first identified in the Acres reports of the 1980s.This recent reinterpretation -which became available in December 2014 late in the feasibility study -was unable to be incorporated into the completed FE analyses.For the determination of the zones of lower modulus used in the sensitivity studies,the rock mass assessments from the 1980s information were therefore used - as discussed in Section 10.3.3.3.1 -which indicated much larger areas of potentially lower quality foundation than are now indicated. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-174 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The sensitivity analysis results are shown in Table 10.7-21 and Table 10.7-22.The tensile stresses in the dam body (both upstream and downstream)decreased as a result of the assumed foundation properties;however,greater sliding displacements (25 percent increase)were computed for monoliths on the right abutment.It will be very important in the ongoing mapping and site investigation to fully characterize the geologic features so that FE analyses during detailed design can be undertaken using more informed foundation properties,and any required foundation treatment of geological features can therefore be correctly assessed.However,the 2014 reinterpretation of the foundation character shows that the assumptions made for the 2013 ANSYS sensitivity analyses were very conservative,and the width of the geologic features is such that they will likely be treated by normal over excavation -and filling with conventional concrete -and are likely to have minor influence on the overall behavior of the structure. Table 10.7-21.Maximum Tensile Stress Sensitivity to Foundation Properties Vertical Tensile Stress |Principal Tensile Stress Foundation Property (psi)(psi) US DS DS Homogeneous foundation 576 621 743 Weak Layer (E=2.8e6)605 644 776 Weak Layer (E=2.0e6)584 657 792 Weak Right Abutment 559 567 670 Table 10.7-22.Maximum Sliding Displacement Sensitivity to Foundation Properties FomvdaionPropery |Menalh?T MonoihT |Menoitae ]Monoihs7 [Merah Homogeneous foundation 1.3 1.2 1.2 2.9 2.6 Weak Layer (E=2.8e6)1.4 1.2 1.2 3.0 27 Weak Layer (E=2.0e6)1.4 1.3 1.3 3.1 3.0 Weak Right Abutment 1.3 13 1.3 3.7 2.6 10.7.5.Conclusions Results of FE analyses considering mass of the foundation and compressibility of the reservoir water shows that computed stresses and sliding displacements of the dam were reduced 30 to 40 percent on average compared to analysis without foundation mass.The comparison is shown in Table 10.7-23. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-175 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 10.7-23.Comparison of Results of Massed Foundation Model with Massless Foundation Model Normal Stress (psi) Fane Massed Foundation Massless Foundation Reduction (%) Upstream Downstream Upstream Downstream Upstream Downstream MYG 662 745 1109 841 40%11% STTEC 576 621 945 957 39%35% CURI 580 597 641 611 10%2% Gil 587 240 1097 409 46%41% Sliding Displacement (in) Earthquake Massed Foundation Massless Foundation Reduction (%)Event Crown Side Crown Side Crown Side Monolith Monoliths Monolith Monoliths Monolith Monoliths MYG 2.2 3.9 4.1 77 46%49% STTEC 1.2 2.6 2.4 3.3 50%21% CURI 2.2 3 27 3.5 19%14% Gil 0.9 0.9 1.1 1.6 18%44% For the OBE events the results of analyses showed that the computed tensile stresses on the upstream or downstream face of the dam were less than the allowable stresses.The computed sliding displacements were small along the base of the dam.The displacements are interpreted as the minimum required to engage the contact along the dam-foundation interface and can be neglected.No cracking or damage in the dam body or along the dam-foundation interface is expected during the OBE events and the dam would remain completely operational after an OBE event. For the MCE events,the developed tensile stresses on the downstream face of the dam are higher than the tensile strength of the RCC and limited cracking of the dam would likely occur at the top of the dam.However,the overstressed area and the total time of overstressing are limited. The probable damage in the dam body would be limited.The separate 2-D analysis investigated the response of the damaged (cracked)dam during the earthquake.Results show that no instability or uncontrolled release of water can be expected. Hence,Dam Layout 4 (Modified)would remain fully operational after the OBE event.During the MCE event the dynamic analysis shows that there may be some cracking at the upper elevations of the dam,and sliding displacement at the foundation but post earthquake analysis using FERC criteria and CADAM indicates no instability or uncontrolled release of water is expected.The dam is estimated to remain stable for static reservoir loads with a cracked base and uplift applied to the foundation.Dam and foundation drains will be sized to accommodate potential sliding displacements and to remain effective following movement of the dam during Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-176 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. extreme loading.During detailed design,more refinements to the dam configuration will be investigated and additional FE analysis will be performed to verify expected reductions in tensile stresses and estimated sliding displacement. 10.8.RCC Placement 10.8.1.RCC and Aggregate Quantities /Production The volume of the dam was calculated in vertical intervals for use in developing production rates for various zones of RCC placement. Placement of RCC will be carried out using the sloping layer method.The sloping layer method was first used in 1997 on the Jiangya Dam (China)and has been used successfully at numerous RCC dams including Murum Dam,Kinta Dam (both Malaysia)and Al Wehdah (Jordan)-and on nearly all Chinese constructed RCC dams. The technique has advantages of creating an upper surface that is of such size as to enable the subsequent layer to be placed while the previously placed surface is still "green”avoiding the need for special treatment of the surface.This creates homogeneous monolithic RCC across lift joints,an important feature for a dam of the height planned at Watana Dam.At Murum,for example core has been drilled through the placed RCC and continuous core of up to 70 ft.has been recovered.The technique reduces the number of horizontal construction lift joints by up to 90 percent.The technique also reduces the area of "fresh”RCC that could be exposed to rainfall or subject to freezing. The RCC placement analysis calculated the dam volume on one foot thick layers.Ten layers were combined to estimate the duration of placement for a sloping layer zone.The dam will be constructed with two defined construction joints,and additional transverse vertical induced contraction joints spaced at approximately 50 ft.intervals created as RCC placement progresses. The joints will extend the full thickness of the dam cross section,and as noted consideration will be given during detailed design to incorporating facilities within the joints -or some of the joints -to enable post contraction grouting to enable full arch action to be developed by the reservoir under reservoir loading.The proposed construction schedule attached in Appendix B10 sets out the planned duration and placement quantity of RCC in each season.These durations and volumes are summarized in Table 10.8-1 below. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-177 December 2014 SUSITNA-WATANA HYDRO -yzw Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 10.8-1.RCC Production Schedule Season Days Start RCC careheoretical)ute 1 150 May 08 1,000,000 335.6 2 150 April 23 1,000,000 335.6 3 150 April 27 1,000,000 335.6 4 150 May 02 1,214,000 407.4 5 150 May 07 1,000,000 335.6 "Based on a 20 hr.working day 10.8.2.RCC Placement Sequencing Sequencing of the seasonal RCC placement is described below.The placement locations and estimated volumes are shown in Table 10.8-2 and the placement sequence is shown in Figure 10.8-1. Table 10.8-2.RCC Placement Locations .Volume (cy)Season Location -Location Season 'Right Abutment 562,750 Left Abutment 435,500 998,250 Middle &Downstream Platform 1,006,850 1,006,850 Middle 1,000,300 1,000,300 Middle 1,231,850 1,231,850 Middle 610,600 Left Abutment 160,100 5 Right Abutment 224,000 994,700 Total §,213,950 Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-178 Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Season 1 Season 2 Season 4 §SeasonS =|=| Ee Season 3 |=»|| Figure 10.8-1.Seasonal Sequence of RCC Placement 10.8.2.1.Season 1 of RCC Season |of RCC placement will focus RCC placement at both abutments.Placement will begin at the right abutment and about 563,000 cy of material will be placed.This will enable the construction of the intake to the elevations of the low level outlet and the spillway crest to commence in the first construction year.Placement at the right abutment will be completed by about August,and will take about 84 days.The finished surface of the RCC will generally be completed to El.1985 ft.apart from beneath the footprint of the intake to the low level outlet pipes. Construction will then move to the left abutment where about 435,500 cy will be placed over an approximately 65 days.At the end of the placement season,the left abutment will be constructed to El.1968 ft. Placement rates are shown in Figure 10.8-2 and Figure 10.8-3. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-179 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 2000 '|Season 1.Right Abutment .: RCC Volume Placed:562,750cy :' 1950 -Duration :84 days _Elevation(Feet)81650 -- Duration (Days) Figure 10.8-2.Season 1 RCC Placement :Right Abutment 2000 Season4-Left AbutmentRCCVolumePlaced:435,500cy ::::1950 .|Ouration :65 days Pe ee eee he eee aElevation(Feet)-81750 1700 +-- 1650 |. 1600 +-- Ouration (Days) Figure 10.8-3.Season 1 RCC Placement :Left Abutment Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-180 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.8.2.2.Season 2 of RCC The second season will focus on placement of RCC in the riverbed at the bottom of the valley. The river diversion tunnel will have been completed,the diversion of the river implemented and foundation excavation completed -in advance of the start of the second season of RCC placement.The season will involve placement of RCC across the entire width of the valley floor. A key goal for the season is to place RCC such that the finished surface level -at least at the upstream part -is at least five feet above the elevation of the top of the sluice as soon as possible during the season,so that the upstream cofferdam can be allowed to be overtopped in the event that the diversion tunnel is blocked or overwhelmed.The early placement during the season will have a crest width of about 45 ft.and the downstream face formed at a slope of 0.85H:1V.At the end of the season,the fill between the dam and powerhouse will be completed;the finished surface of the dam will be at El.1520 ft.or more at the upstream portion.The relationship between elevation and volume for the season is shown in Figure 10.8-4. 1550 ='|Season2-Middte:]RCC Volume Placed:1,006,850cy'|Duration:150 days a ot V45O fe ene cece eee eet be mercencecene pee ep eae ene i Elevation(Feet)1400 I || 1350 |.)ee ceefeette e feneee cerewedfees : bene 0 10 2 430 40 SO 60 70 80 90 100 110 120 130 140 150 Duration (Days) Figure 10.8-4.Season 2 RCC Placement :Middle Dam Section 10.8.2.3.Seasons 3 and 4 of RCC Seasons 3 and 4 will focus on RCC placement within the middle section of the dam.Placement rates will be the highest during the fourth season.Figure 10.8-5 shows the relationship of Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-181 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT elevation and layer volume and indicates that the largest layer is at El.1604 ft.with a volume of approximately 9,330 cy. 2100. 2080+--+.+s 1950 be ee ce 1800 :Be 17SQ b -ee a a errr 1700 sm rt ee es Elevation(feet)1650 ee eee ee ee ene W580 fe 1450 ----ee ee ee ee ee 1400- PBSO ee ce ee t)1000 2000 3000 4000 so0o 6000 RCC Volume {cy) 8000 9000 10000 =110007000 Figure 10.8-5.RCC Layer Volume vs Elevation During Season 3,all RCC will be placed beneath the power intakes and penstock footprints,to allow construction of the power intakes to commence as soon as possible as shown in Figure 10.8-6.RCC layer elevations at the end of Seasons 3 and 4 are shown in Table 10.8-3. Table 10.8-3.End of Season Elevations:Middle Section Season |RCC Layer Elevation 3 El.1555 ft.with the portion beneath the penstocks and power intakes at El.1795 ft. 4 El.1816 ft.either side of the previously placed Power Intake footprint RCC. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-182 December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 1700 Elevation(Feet)raawn°o1550 +-- 1800 ||Season3-Middle .RCC Volume Placed:1,000,300cy iDuration:150 days re ::::4 1750 nn ne Se ee ee ee ee en Se a ee Se ee erees tees eee ee 60 70 80 Duration (Days) Figure 10.8-6.Season 3 RCC Placement :Middle Dam Section (Beneath Power Intakes Footprint) 1850 "])Season 4-Middle "|RCC Volume Placed:1,213,850cy "|Duration :150 days YBOQ be anne nnn ne eee re ne ee ee re ne eee ne ee pee bet neuen nee Rete re Cea en gee eaepeng naw eneee 1750 Elevation(Feet)VIOO iene nee eeee neeene Ee neem ee ep eee cto es isso + 70 80 90 100 110 120 130 140 #150)160 Duration (Days) Figure 10.8-7.Season 4 RCC Placement :Middle Dam Section Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-183 Alaska Energy Authority December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.8.2.4.Season 5 of RCC The fifth and final season will encompass the completion of the RCC -which will be done while the reservoir fills.The middle portion of the dam will be completed first,followed by the right abutment.The left abutment will be the final portion of the dam to be completed.Elevation- volume relationships are shown in Figure 10.8-8 through Figure 10.8-10. 2100 Season §-Middle RCC Volume Placed:610,600cy Duration :91 days 2050 Elevation(Feet)-bdr=)1850 |- 1800 -o-_ee ee ee ee )10 20 30 40 50 60 70 80 90 100 Duration (Days) Figure 10.8-8.Season 5 RCC Placement :Middle Dam Section Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-184 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 2100 ; -|Season $-Right Abutment _|RCC Volume Placed:224,100 cy Ouration :33 days 2050 |Elevation(Feet)8te)5 10 1900 ne 15 20 25 30 35 Duration (Days) Figure 10.8-9.Season 5 RCC Placement :Right Abutment 2100 Season5-Left Abutment"1 RCC Volume Placed:160,100cy Duration :24 days 2050 - 3£ 32 uw 2000 - 1950 - 0 5 10 Duration (Days) 15 20 2s Figure 10.8-10.Season 5 RCC Placement :Left Abutment Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 10-185 Alaska Energy Authority December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.9.Dam -Thermal Considerations 10.9.1.General Thermal behavior will be an important aspect to consider in the final design of the Watana Dam, for reasons that include,but are not limited to: *For RCC,external considerations -such as cooling on the large areas of RCC (or thermal gain from the sun)-are often more significant than the hydration of cement; «Because of the speed of construction,there can be significant thermal gradients between the mass of RCC and the open faces; «The seasonal nature of construction at the Watana site will require very careful attention to the "cold joints”between seasons; *The curved axis of the dam will result in some arch action which will be mobilized after the shrinkage of the structure; -"The abutments of the dam are cool -and possibly below 32°F on much of the left abutment -and provisions must be made to avoid thermal shock during initial covering of the foundation. A full thermal analysis to address all issues has not been carried out at this stage,but a detailed analysis -taking into account the placement sequence shown in Section 13.3.6;proposals for insulation;the selected mix design;projections of mixing and placement temperatures;and the proposed abutment preparation -will be performed,and planning of the whole sequence of placement made,prior to finalizing the contract specifications. This section describes the topics that will need to be addressed in the detailed design and construction planning related to thermal performance as well as a simplified analysis that has been made of the dam section. 10.9.2.Transverse Joints Temperature induced cracks are to be expected in a RCC gravity section,and current practice is to induce a transverse crack/joint at approximately every 50 ft.along the axis of the dam.It should be noted that the proposed design of Watana Dam includes two formed joints -with shear keys -which have been included to facilitate,during the seasons prior to river diversion,the construction of the upper sections of the dam on each abutment. The formed joints and the induced joints will all be constructed with double waterstops at the upstream face,and a large diameter vertical drain between them.If the dam stability relied Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-186 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. solely on gravity action,there would be no consideration of further treatment of the joints,but there is expected to be some mobilization of "arch action”during a seismic event.Detailed design may indicate that the formed joints incorporate facilities for grouting (and regrouting)at, or near,the end of construction -thus allowing "arch action”to be mobilized.In addition,the inclusion of grout pipes in some or all of the induced joints will be investigated if the detailed design analyses show benefit from such post construction grouting.It may be that few (or no) areas of the dam will need such post placement grouting -for example the RCC placed in season 2 will be heavily restrained by the bedrock foundation,while the central area (to facilitate early construction of the intakes),placed in season 3 is effectively unconstrained.It is envisaged that the RCC placed in season 4 -between the previously placed abutment sections and the central section placed in season 3 -will be the main candidate for grouting of induced joints.Grouting of induced joints has been practiced at Shapai in China,among other curved RCC dams. 10.9.3.Abutment Temperature The bedrock at the left abutment -in at least some areas -has a stable temperature at or below 32°F.No concrete is to be placed against frozen surfaces (formwork,rock etc.)and the rock surfaces will therefore need to be covered and heated to the RCC placing temperature or higher for a minimum period of 24 hours before placing.It is assumed that this can be achieved using heating pads,or by drilling short holes and circulating hot water or steam through them (as discussed in Section 10.3).Once the RCC is placed,the abutment will act as a heat sink,and the heat of hydration will establish a steady state condition such that the interface between the rock and concrete will be at an acceptable temperature.This will be checked by thermal modeling during detailed design and will be monitored post construction. 10.9.4.Insulation Requirements Mean ambient temperatures at the site fall below 32°F throughout the winter,so at the end of each placing season all exposed RCC will have to be covered with insulation materials.Heavy insulation will be needed on the top surface during the winter period to protect the RCC against "curling”. In addition,it is expected that it will be in the interest of the contractor to extend the RCC placement season as much as possible.The extension of the placing season in the fall will be more straightforward than starting earlier in the year,so a contractor intent on beating the overall schedule will wish to extend the end of each season as much as possible.It is expected that season extension by two or three weeks might be achieved by the establishment of insulation above each 10 ft.layer of RCC,so that as the sloped layers are placed,the insulation is removed and immediately replaced.The possibilities for such methodology and the insulation requirements will be investigated using sophisticated thermal modeling during detailed design. Susitna-W atana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-187 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.9.5.Control of Mixing and Placing Temperatures As noted,the monthly mean ambient temperature during the placing season is no higher than 52°F and at the shoulder seasons it is approximately 40°.It is therefore seen to be straightforward to limit the RCC placing temperature to 40°F by using river water (which is above 50°F only in June and July,when some ice can be added).The passing of river water through the stockpiles early and late in the season,together with use of ice during the middle of the season should maintain a constant and acceptable placing temperature without the need for cooling of the structure.However,it is foreseen that heating and insulation of the stockpiles will be needed throughout the winter,and it is prudent to cover and insulate the conveyor belts (both to move aggregate and to deliver RCC)-particularly at the shoulder seasons. 10.9.6.Preliminary Simplified Thermal Analysis Although a complex thermal!analysis,taking into account all the variables discussed above is beyond the scope of the feasibility study,a simplified study was performed to investigate the behavior of the suggested cross section of the dam.Preliminary thermal calculations showed that surface cracking of the RCC would likely occur during construction of the dam.Cracking can be prevented by providing insulation until the RCC has gained sufficient strength and the thermal stresses are relieved due to cooling of the dam interior body.The time required for insulation can be optimized by carrying out parametric studies on the initial placing temperature of RCC. The current analysis has been based on typical RCC thermal properties derived from similar projects.Final analysis will require properties determined from the actual RCC mix that will be used on the project. The developed model did not include the openings for the power or low level outlet intakes or spillway.The effect of the conventional concrete portions of these elements on the thermal response of the dam was not analyzed.These geometric anomalies are more susceptible to thermal cracking and will need to be investigated in the subsequent design phase.Final thermal analysis would consider the effect of all geometric features in the dam's thermal response. Parametric studies on the initial placing temperature and insulation time would be required to control the cracking and to optimize the construction cost. A detailed 3-D model of the dam can be developed to include stage construction,all openings and construction features of the dam.This model can be used for analysis and determining the overall thermal response of the dam.The stresses for inclusion in the final structural FE analysis of the operating dam can also be derived from this model. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-188 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.9.6.1.Design Criteria 10.9.6.1.1.|Climatological Properties 10.9.6.1.1.1.Ambient Temperature The monthly ambient temperature values used in the simplified analysis were taken from the Acres feasibility study dated 1982.The values are reproduced below in Table 10.9-1. Table 10.9-1.Susitna Project Site Monthly Temperature Data Max |Min |Mean Max |Min |Mean of °C January 8 48 1.6 -13.4 -20.4 -16.9 February 13.5 -0.4 6.6 -10.3 -18.0 -14.1 March 19.4 3 11.2 -7.0 -16.1 -11.6 April 32.9 14.2 23.5 0.5 -9.9 47 May 45.7 29.1 37.4 76 -1.6 3.0 June 58 39.9 49 14.4 44 9.4 July 60.2 43.8 52 15.7 6.6 11.1 August 56 41.4 48.6 13.3 5.1 9.2 September 47.1 32.6 39.9 8.4 0.3 44 October 30.4 17.5 24 -0.9 -8.1 4.4 November 15.7 3.7 9.7 9.1 -15.7 -12.4 December 9.2 -3.4 29 -12.7 -19.7 -16.2 10.9.6.1.1.2.Water Temperature The USGS publication titled "Sediment Discharge Data for Selected Sites in the Susitna River Basin,Alaska,October 1982 to February 1984”,records water temperature readings taken in the Susitna River at Gold Creek and near Talkeetna.An average of the readings has been collated and is listed in Figure 10.9-1 and Table 10.9-2 below. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-189 December 2014 ---zZ SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Susitna River AK Estimated Water Temperature $$.0 --$°MonthlyTemperature(deg)&o8°o35.0 - Jan Jul Figure 10.9-1.Susitna River Estimated Mean Monthly Water Temperature near Gold Creek Table 10.9-2.Susitna River Mean Monthly Water Temperature near Gold Creek Water TemperatureMonth (°F)(°C) January 32.0 0.0 February 32.0 0.0 March 32.0 0.0 April 33.8 1.0 May 40.6 48 June 52.9 11.6 July 56.3 13.5 August 49.4 9.7 September 42.8 6.0 October 32.9 0.5 November 32.0 0.0 December 32.0 0.0 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-190 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.9.6.1.2.Thermal Properties of RCC Thermal properties of RCC were selected from similar projects and references with sufficient conservatism required for the feasibility level analysis.The thermal properties of RCC and foundation rock used in the analysis are presented in Table 10.9-3 below. Table 10.9-3.Foundation and RCC Thermal Properties (used in analysis) RCC Unit weight 150 pcf Heat of Hydration of cement 150 to 175 Btu/lb.@ 28 days Adiabatic temperature rise of RCC 59°F @ five days and 68°F @ 28 days RCC mix contains (per cubic yard)125 pounds of cement;and 200 pounds of fly ash Coefficient of Thermal Expansion 4.8 E-6/°F Specific Heat 0.22 Btu/lb.°F Thermal Conductivity 1.25 Btu ft./(hr.ft2 °F) Placement Temperature (minimum)50°F Foundation Rock Unit weight 170 pcf Specific Heat 0.21 Btu /lb.°F Thermal Conductivity 1.15 Btu ft./(hr.ft?°F) Foundation Temperature Left abutment 30°F Right abutment 32°F The thermal convective (or heat transfer)coefficient of the RCC surface in contact with air was calculated based on the wind velocity of 6 mph.The thermal convective coefficient for RCC with no formwork was calculated to be 2.91 Btu/(hr.ft?°F)and for RCC with no formwork to be 0.80 Btu/(hr./ft?°F). 10.9.6.2.Finite Element Method ANSYS Version 15 was used for thermal analysis of the dam to evaluate the developed temperature field in the dam body during construction.A 3-D FE model was created representing dam Layout 4 (but not the modified Layout 4)as shown in Figure 10.9-2,and a 2-D FE model was created representing the dam cross section as shown in Figure 10.9-3.Eight node solid elements with thermal conductivity capacity and the material properties presented above were used to model the dam.The model included 10 ft.high elements to simulate the expected RCC lifts between "cold”joints.The "death and birth”of elements option,available in ANSYS, was used to simulate the construction of dam layers in a simple manner -not in the staged construction method that will ultimately be developed in accordance with Figure 10.8-1. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-191 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. oy Ay PEN StonyDiieneiANbees i sreeeetrissiies3ead sieean es KAARvtyfeeereeeait ae ena Fe;Sennen mutase i °3 Sascoueeenen mentees=Ze ve on i ft : save eieenes BSEATSMREARES y NYUSESRINIKINIET SESEKOOL ee tiaee Soper Eee ienternhrewnrnss . 0.00 350.00 700.00 (ft) a 175.00 525.00 Figure 10.9-2.3-D Finite Element Model of the Dam for Simplified Thermal Analysis Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-192 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. LEMENTS L >-«,see eee sore .peeestessiey oe et Pee ee.*w+treaaeeae at See cee bse eaten F4T4+14 5 .2OCroeene Showa me:nad kane +$74FOttbbeceetetttreeeseeaeet Figure 10.9-3.2-D Finite Element Model of the Dam for Simplified Thermal Analysis Analysis results show that the temperature in the dam body can reach 77°F during construction. Results from the thermal analyses were used to compute strains in the dam body in accordance with ACI 207.2R,where peak temperatures and temperature drop computed in the FE model were used to evaluate the potential for thermally induced cracking. 10.9.6.2.1.Surface Gradient Cracking Analysis A surface gradient strain evaluation was performed.The surface gradient evaluation considered the potential for development of surface cracks during the critical period in the days immediately after placement when the surface of the concrete cools and contracts more rapidly than the warmer interior mass concrete. Calculations were performed across the center of lift 55 as shown in Figure 10.9-4.Figure 10.9-5 shows the computed temperature across the center of lift 55 for different ages of the lift. The surface gradient strains were evaluated based on the difference between actual temperatures Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-193 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. throughout the cross section and the concrete placement temperature.The critical point in surface gradient strain evaluations required determining where stress in the concrete is zero,or where it switched from tension (at the surface)to compression (beneath the surface).By plotting balanced temperature differences through the cross section,the depth at which this transition occurred was determined. oo _wee ceeineeees erage wae anne -e 4anyae cence aoe aol"e,4 r ct Sn A ed A SNRLSaa ea a en a bern ee ae }"ae 4 %3 Dee re AAS en Anes OER A OREN ' -Ac A TTUT +a Sas a 2 o 1 =e RTA mere Se oo A RRR? ee ee atten negtate,.aaoatins sreweenaaemnnenenagy*(Rp CI =--:Be ne cee anea Aatenna RUE eC nh7,==fee eee =,an A eee .ae.::CBee ssserese mEeeeann9)Said=sree a ee a ot ---we,SidaWyameemee _- ay aon.OV a Ur it wae snttneneaminendfmo,mmemmpmnnaneneal _ewmyaaa-Saeinreis ame nee ne Pyem,°ae.wee Sadie doUErae08 tins IWEVAT7/442014 12:30 PM cia CJ unss upstream X=80 downstream X=0 Y ad03e+004 (mm)ee!J1.5e+004 Figure 10.9-4.Location of LIFT 55 Used for Surface Cracking Calculations Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-194 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 80.00 1 Ln 7 Concrete age 70.00 Ls (day)WLLL -os y ify -10 if -3060.00 aa,-_-5.0 |/-T7.0 --9.0 50.00 -; --110 is ?- 28.0 =ri -50.0 5 40.00£-90.0a 5 mm 75vur-128.5 30.00 -158.5 -189.5 :au -2205 20.00 -+ 'a 248.5 ee 309.5 --370.510.00 omer 523.5, a 735.5 0.00 + 0.0 25.0 50.0 75.0 100.0 125.0 150.0 175.0 200.0 225.0 250.0 275.0 Distance From Upstream Face (ft) Figure 10.9-5.LIFT 55 Temperature Profile This depth was subsequently used to calculate the strain modification factor,Kr.for input into strain computations as defined in ACI 207.2R.For the surface gradient evaluation,age of the concrete during the curing process was used to determine the time dependent material properties for input into the calculation of strain capacity. A summary of calculations and the possibility of surface cracking are shown in Table 10.9-4. Analysis results shows that surface cracking of the RCC may develop during the first 28 to 50 days of RCC placement.Therefore insulation is recommended. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-195 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 10.9-4.Surface Tensile Stress Gradient Calculations Concrete age Lift 55 Hours 24 72 120 168 216 264 672 |1200 |2160 |2339 |3083 |3803 Days 1 3 5 7 9 11 28 50 90 97 128 158 Depth of the Tension Block (ft.) =5.35 |7.81 8.96 |9.58 |9.81 |10.10 |15.88 |19.62 |20.05 |24.74 |26.80 |28.81 H(downstream)|5.35 |7.81 |896 |9.58 |9.81 |10.10 |15.88 |19.62 |20.05 |24.74 |26.80 |28.81 X=257.15 |256.69 |254.72 |253.84 |253.51 |253.15 |248.16 |244.98 |240.75 |234.00 |237.2 |235.53 H(upstream)5.18 }568 |7.64 |853 |883 |9.19 |14.17 |17.36 |21.62 |22.38 |25.16 |26.81 Effective Temperature Differences at Surface (°F) AT(downstream)|-4.47 |-14.19 |-18.19 |-20.38 |-25.89 |-29.43 |-31.69 |-32.07 |-31.81 |-31.73 |-31.41 |-31.09 AT(upstream)|-3.89 |-13.85 |-18.82 |-21.62 |-26.95 |-30.99 |-33.22 |-33.53 |-33.17 |-33.08 |-32.72 |-32.37 Restraint Factors Ke at Surfaces Ka(downstream)|0.74 |0.64 |060 {057 }056 |055 |0.35 |0.24 |0.11 0.11 0.09 |0.08 Kr(upstream)0.75 |0.73 |065 |061 |060 |059 |0.41 0.30 |0.148 |0.16 |0.10 |0.09 Surface Tensile Strain x10 corrected for internal restraint (Kr) (downstream)|27.0 |77.4 |946 |102.7 |127.6 |1427 |976 |664 |312 |298 |259 |225 e(upstream)25.1 87.0 |104.8 |113.8 |139.0 |156.1 |115.9 |87.5 |51.1 45.2 |294 |26.2 emax.27.0 87.0 |104.8 |113.8 |139.0 |156.1 |115.9 |87.5 51.1 45.2 29.4 26.2 Slow Load Tensile Strain Capacity x106 vs Concrete age Concrete age 1 3 5 7 9 11 28 50 90 97 128 158 SlowloadTSC |40.0 |56.0 |660 |74.0 |780 |81.0 |90.0 |96.0 |100.0 |100.0 |100.0 |100.0 Checking Cracking |NO!|ves!|ves!|ves!|ves!|ves!|ves!|no!|No!|No!|No!|No! 10.10.Instrumentation 10.10.1.General Chapter 9,Instrumentation and Monitoring of the Engineering Guidelines for the Evaluation of Hydropower Projects (FERC,undated)sets out minimum instrumentation recommendations for new dams.The recommendations vary depending upon the type of dam and the hazard classification of the structure.Watana Dam will be a High Hazard potential structure,and the recommended project parameters to be monitored are as follows: *Reservoir level; =Tailwater level; =Drain flow,seepage and leakage; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-196 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. =Pore/Uplift pressure,under dam foundation and downstream; =Surface alignment; =Internal movement; =Stress and strain; =Joint displacement; #Thermal profile in the RCC and in abutment rock; ="Foundation movement;and, #Seismic motion in the dam body and foundation. As well as the dam,there will need to be careful measurement of rock slopes in the vicinity of the dam,and the groundwater conditions in the Relict Channel. As far as possible,the instrumentation shall be set up for real time monitoring remotely,or for ease of downloading data.Also the instrumentation design shall as far as possible include redundancy and the possibility of checking the real time conditions in at least two ways. 10.10.2.Dam 10.10.2.1.Reservoir and Tailwater Level Water level measurement can be accomplished using simple devices that are also inexpensive. A staff gauge will be fixed to the upstream face of the dam which would be manually measured by reading the gage either at the dam,or remotely by CCTV cameras that could be trained onto the gage.This will be a secondary,failsafe method of monitoring the reservoir water surface elevation. The reservoir water level will fluctuate by up to 200 ft.each year.At lower water surface elevations the reading of the gage would be difficult.A gage located at the upstream face,near the spillway would provide a useful means of monitoring the reservoir surface elevation during periods of spillway operation. Automated water level measurement options comprise float type water level gage,ultrasonic sensor or a bubbler installation.A bubbler level sensor will be installed which determines water/ liquid level by measuring backpressure of a gas bubbler system.An advantage of this technique of level measurement is that the electronics are remote from the water,ensuring long term reliability and accuracy.Bubbler systems capable of operating to the full operational range of the reservoir are commercially available. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-197 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.10.2.2.Drain Flow,Seepage and Leakage The drainage system installed in the foundation downstream of the grout curtain will relieve uplift pressures beneath the dam that may arise from the seepage of water beneath or through the grout curtain.Any flow through the drains will discharge into the drainage gallery/adit and be conveyed along a capture channel to a sump that will be located at the lowest point in the gallery system. Measurement of the flow within the capture channel will be achieved by weirs or Parshall flumes.Ultrasonic sensors could be placed at the weir locations to allow automated real-time measurement of the seepage flows.The capture channel system will be divided into discreet sections,with weirs installed at the downstream end of each section.In the event of unusual or unexpected changes in the amount of seepage,the section of grout curtain in question can be quickly isolated for further investigation. Vertical drains will also be drilled from each of the upstream galleries both upwards and downwards,at appropriate regular intervals so that all potential leakage through the RCC is captured and measured by weirs at various levels within the access and drainage galleries. 10.10.2.3.Pore /Uplift Pressure Pore pressure and uplift pressure in the dam foundation will be monitored by vibrating wire piezometers.Vibrating wire piezometers are insensitive to freezing conditions,and automated results can be transmitted over long distances.This type of piezometer has a very short lag time, allowing real-time monitoring of the pore pressures. The location and number of piezometers will be selected to allow an understanding of the uplift pressure distribution beneath the dam.Five lines of piezometers,radially aligned will be installed,one along the highest section of the dam,one line near to the edge of the river bed,one beneath the spillway section,one within the right flank section,and one within the left flank section.The line at the highest dam position will comprise four boreholes,each with two piezometers at defined elevations;the other lines will comprise three boreholes as shown on the same figure.Four boreholes are planned at the highest dam location;the furthest downstream borehole will provide data on uplift pressures beneath the concrete fill between the dam and the powerhouse and also for future monitoring in the event the dam is raised. 10.10.2.4.Surface Alignment Survey measurement of the dam (crest and downstream face)is necessary to monitor the movement of the structure.To monitor the dam's movement,a triangulation network will be necessary.The network will consist of a series of monuments embedded into the crest of Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-198 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Watana Dam,targets located on the downstream face and at least six theodolite piers located on the sides of the valley downstream of the dam,three on each side of the river.The targets on the downstream face of the dam will be positioned to correspond with the location of the plumb lines. 10.10.2.5.Internal Movement Inclinometers or plumb lines are the most common types of instrumentation that are installed to measure internal movement.Plumb lines are considered to be the most accurate device (ICOLD 2005).Three plumb lines will be installed within the dam body,one at the maximum section of the dam (the crown cantilever)and one at the midpoint to each abutment.The cross sectional profile of the dam will enable a single plumb line to extend from the dam crest down to the drainage gallery.As necessary,inverted plumb lines will also be installed in the dam. 10.10.2.6.Strain Strain gages will be installed to monitor load distribution within the dam.Clusters of strain meters (12 per cluster)will be installed at strategic locations in the dam. 10.10.2.7.Joint Displacement The two construction joints formed during RCC placement will be monitored to observe their performance arising from reservoir level fluctuation and ambient temperature changes.The joint meters will be located to monitor vertical and horizontal joint performance.All induced contraction joints daylighting in galleries -and any observed cracks in galleries will have 3-D joint movement monitors mounted at them.Additional joint meters will be installed at the junction of the powerhouse and the adjacent upstream concrete pad.These will be used to monitor the relative position of the dam and powerhouse. 10.10.2.8.Foundation Movement To complement the plumb lines within the dam,inverted plumb lines will continue into the foundation.Inclinometers will also be installed within the foundation and will enable information to be obtained of areas of interest within the foundation during construction and operation of the project.Inverted plumb lines will also be included in the foundation of both abutment blocks. Extensometers,installed within boreholes in the foundation will also provide measurement information on the foundation.Early installation will enable the characteristics of the foundation to be monitored during construction of the dam and powerhouse.The location of the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-199 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT extensometers will coincide with the other instrument groups.The total length of each extensometer will be between 25 percent and 50 percent of the dam height. 10.10.2.9.Seismic Response The effects of an earthquake will be monitored using accelerometers.An accelerometer will be installed on the dam crest and another installed within the drainage gallery near the dam foundation.These will allow the damping effect of the structure to be measured. 10.10.2.10.Temperature In addition to ambient temperature,the water temperature and internal body temperature of the dam will be monitored.These parameters,in conjunction with water level and movement data can be used to verify the expected performance of the dam calculated during the design process. Internal dam temperature measurement will be carried out using thermometers embedded in the concrete during construction.Thermometers are the preferred instrument as they have been found to be more dependable are more precise and are simple in their operation. Four rows of thermometers are proposed.The number of thermometers in each row will vary depending on the thickness of the dam.Temperature sensors will also be installed on the upstream face of the dam,at the same elevations as the internal sensors.The external sensors will provide information on the temperature profile within the reservoir and allow the temperature profile within the dam body to be monitored. 10.10.3.Rock Slopes and Abutments In addition to the use of instrumentation to monitor the performance of the dam,the performance of various rock slopes -in particular the dam abutments -will need to be monitored. Rock slope monitoring requirements are normally determined by inspection during construction, and comprise survey targets fixed onto the face of the rock slope (monitored using the same survey monitoring monuments as installed for monitoring of the dam stability);extensometers often installed in subhorizontal boreholes in the slopes and particularly near the base of any identified rock wedges;and vibrating wire piezometers to assess groundwater conditions. Typically instrumentation is installed early -as soon as a potential rock instability is noticed -so that monitoring can be performed while construction occurs and thereafter during the operation of the project. The abutments of the dam will require more comprehensive instrumentation.Any significant rock wedges identified during the design of the dam will be monitored using an array of Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-200 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. instrumentation.Extensometers,monitors and vibrating wire piezometers will also be used,and if appropriate,the grouting galleries accessible from the dam galleries will be extended to enable extensometers and piezometers to be placed at the most appropriate locations and angles. Abutment temperature will be measured both during construction and operation to determine the condition of any frozen joint materials. As with all instrumentation,the instruments will be installed early in the construction period so that monitoring can be performed while construction occurs and thereafter during the operation of the project. To the extent that it is possible,all data recorded will be relayed in real time to a central monitoring station for analysis. 10.10.4.Relict Channel The groundwater conditions within the relict channel must be monitored during the project operation -together with ground temperature.It may be appropriate to also measure any leakage into Tsusena Creek using open drains and weirs. 10.11.Freeboard The freeboard required for a particular dam is influenced by the water level increase during the design flood event,wave run-up and wind set-up. The analysis followed procedures contained in the U.S.Department of the Interior Bureau of Reclamation (USBR)publication ACER Technical Memorandum No.2 (ACER TM No.2). 10.11.1.Analysis The magnitude of wave run-up and wave set-up is directly related to wind speed and fetch length. The fetch length is the maximum uninterrupted straight-line length over water for a particular wind direction.ACER TM No.2 sets out the approach to be followed in calculating the effective fetch,described later. Wave run-up refers to the maximum vertical height attained by a wave running up a dam face relative to the stillwater level.Run-up is a complex phenomenon that depends on the local water level,the incident wave properties and the nature of the face being run-up (slope,height, reflectivity,roughness and permeability). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-201 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Wave set-up is the result of wind stresses which results in water levels increasing at the downwind end,and subsequently decreasing at the upwind end of the reservoir.This is most noticeable for reservoirs that are straight and long. 10.11.2.Wind Speed 10.11.2.1.Wind Data The wave height and run-up at Watana Dam was estimated by Acres in the 1982 feasibility report.The report used wind data recorded at Summit Station which was considered representative of wind conditions at the dam site. Additional wind speed data was obtained for the Summit Station.Hourly wind speed data was obtained for the period 1948 through 1982 from the National Oceanic and Atmospheric Administration,National Climatic Data Center website.Summit station stopped recording climatological data in 1984. The data was used to calculate the hourly recorded wind speeds for the months of June,July and August of each year.These months were focused upon as they correspond to when the reservoir is predicted to be the fullest and therefore the least amount freeboard would be available. A statistical analysis was performed to determine the wind speed exceedance distribution.The results of the analysis are summarized in Table 10.1 1-1 and Figure 10.11-1. Table 10.11-1.Wind Speed Frequency Percentage |Wind Speed a Exceeded mph 20 - 1 20.21 a 2 18.65 v- 5 16.51 _s 10 14.62 zi: 20 12.21 z 2 30 10.59 Zo. 40 9.06 ze) 50 7.85 7 7- 60 6.47 - 70 5.13 :. 80 3.79 2 - 90 1.56 7 95 0.53 Exceedence (%) 98 0.15 Figure 10.11-1.Wind Speed Frequency Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-202 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.11.2.2.Wind Speed Frequency The available data was analyzed using the Pearson and Gumbel methods to arrive at return period wind speeds.The two methods are commonly adopted methods in determining flood frequency relationships and can be applied to perform similar statistical analyses of wind data. For return periods exceeding 1000 years the methodologies display a divergence in the estimated wind speeds due to uncertainties in the extrapolation methods.The estimated wind speeds are summarized in Table 10.11-2 and Figure 10.11-2 shows the divergence between the two methods. Table 10.11-2.Return Period Wind Speeds Wind speed (mph)Return 140 a ee ee eee _ Period Pearson GumbelTypeIll wo 1 19 16 2 25 26 = 5 31 27 2 10 35 32 i v0 20 39 35 E 50 45 39 fo 100 50 44 3 200 55 47 o 500 62 51 1000 68 56 ok oe 10000 89 59 oO:ne eee nee eta ne vete nn pees 100000 109 71 1 10 100 s000 soaoo sosoon 'sconoe 1000000 129 82 Serum Peston (veo) Figure 10.11-2.Return Period Wind Speeds 10.11.3.Wave Run Up and Set Up 10.11.3.1.Effective Fetch The ACER TM No.2 sets out a method to estimate fetch that involves constructing nine radials from the point of interest at 3°intervals.The length of each radial is measured and arithmetically averaged.Figure 10.11-3 shows the nine radials selected in determining the effective fetch for Watana Reservoir.The effective fetch length is 2.87 miles. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-203 December 2014 -z-ALASKA ENERGY AUTHOoRIIY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Legend om Wave Fetch Lengihs 3°Interval [_]Watana Reservoir 2.050 EL Angie Length (Fect) 72 15,956 75 14,182 78)15,260) 81 16,945 84 59,442) 87 4,432 90)4,207, 93 3,056)96 3,009] AVG=1S,186 ft =2,BT mi.£ Location Map Q 05 1 15te)Mites eed Komeiors q .|Fropecion NAD 1963 StatePlane Abeshe 4 FPS 5004 FastDateCreated8/27/2014.|Map Author MH «Bec ZimmermanFéSuWaWave,Prop Fetch Ugthd_ttx17_Land08272014 nso Figure 10.11-3.Effective Fetch Calculation Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 10-204 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.11.3.2.Wind Set Up For deep reservoirs,wind set up is commonly calculated using the Zeider Zee equation.The equation is expressed as: where: S =wind setup (feet)above the undisturbed water level U =average wind velocity (miles per hour)over the fetch F =fetch length (miles) d =average depth (feet)of water generally along the fetch line 10.11.3.3.Wave Run Up Two methods of calculating the wave run-up are presented.Both methodologies use the same techniques to estimate the wave properties (height,length,and period)but digress when estimating the actual wave run-up. Estimation of wave run up is calculated by following the steps described below: 1.Calculate the significant wave height:H,(feet) H,=0.0177(V)*23(F)°> 2.Calculate wave period:T (seconds) T =0.559(0.589(V)123(F)) 3.Determine deep water wavelength:L (feet) Lo =5.12T? 4.Check relative depth (depth of water/wavelength)if relative depth >2,no need to modify the results to reflect shallow water conditions. 10.11.3.3.1.Shoreline Protection Manual The methodology recognized and accepted in the U.S.is that defined in the U.S.Army Corps of Engineers EM-1110-2-1100 -Coastal Engineering Manual (USACE 2002)encompassing the methodology described in the Shoreline Protection Manual (SPM). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-205 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Once the wave properties have been calculated,the next step is to calculate Hj /(g *To?).H',is the equivalent deep-water wave height and 7%is the deep-water wave period.This value is used to estimate the wave run-up,A,at the dam.Figures 7-8 through 7-12 in SPM Vol.II show the relationships between R/H,and slope of upstream face of the dam (reservoir side)for a series of d;/Hg values.Figure 7-12 (SPM)is the most relevant to the situation at the Watana Dam.Fora vertical upstream face the slope is zero and depending upon the value of Hj /@ *7o2),the relationship R/Hg is estimated. Based on the value determined from Figure 7-12 (SPM),the wave run-up is determined. However the wave run-up values predicted by Figure 7-12 (SPM)are expected to be smaller than the wave run-up on the prototype structure because of the inability to scale roughness effects in small-scale laboratory tests (reference SPM Vol.II).The wave run-up values are therefore adjusted for scale effects by using Figure 7-13 (SPM).The upstream face of the dam will be vertical at the dam crest and therefore the scaling effects are not significant.Figure 7-13 (SPM) indicates that the scaling effect will be zero. 10.11.3.3.2.Clapotis (Standing Wave)Method For a deep reservoir impounded by a dam with a vertical upstream face,a standing wave or clapotis is established adjacent to the structure.The interaction between the clapotis and dam is shown in Figure 10.11-4.The actual wave run-up is the summation of the raised water surface level (hg)and the wave height. The raised water surface level of the standing wave (hg)is calculated using the following equation: mH?2ndho=>cotanh () where: L =deep water wave length (feet) d =depth from Stillwater level (feet) H =height of free wave (feet) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-206 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. H "hyywei. mee AN ----|R= vertical wall-__|\d:\\\:\\ "Le Prineed le Pmax > Figure 10.11-4.Effect ofaClapotis Adjacent to a Vertical Face (Novak) The wave run-up and set-up values have been estimated using both methodologies for the return period wind speeds as determined by the Pearson and Gumbel methods.The results are presented in Table 10.11-3 and Figure 10.11-5. Table 10.11-3.Wave Run-up and Set-up Values Wind Speed Wave run-up +Set-up (feet) eesih (miles per hour)SPM Standing Wave Pearson Gumbel Pearson Gumbel Pearson Gumbel 1 19 16 1.24 1.00 1.28 1.03 25 26 1.73 1.82 1.83 1.92 31 27 2.26 1.90 2.41 2.02 10 35 32 2.62 2.39 2.82 2.51 20 39 35 2.99 2.62 3.25 2.82 50 45 39 3.57 2.99 3.91 3.25 100 50 44 4.07 3.47 4.49 3.80 200 55 47 457 3.77 5.08 4.14 500 62 51 5.30 4.17 5.94 4.60 1000 68 56 5.94 467 6.71 5.20 10000 89 59 8.27 4.98 9.56 5.57 100000 109 71 10.62 6.26 12.51 7.10 1000000 129 82 13.07 7.48 15.65 8.58 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-207 December 2014 SUSITNA-WATANA HYDRO -yzZ Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Waverun-upandset-up(feet)10 ] Effective Fetch :2.87 miles NMOL:EL 2050 ft Vertical Face Faiaral A LZ.ae eral ---rl -- o7”Lae 'a pO LA yer --Standing Wave -Pearson Type III -@¢Standing Wave -Gumbel '-e-=SPM -Pearson Type IllL|-ae SPM-Gumbel 1 10 100 1000 10000 100000 1000000 Return Period (years) 10.11.3.4.Freeboard Assessment Figure 10.11-5.Wave Run-up and Set-up and Wind Speed Frequency ACER TM No.2 recommends that the adequacy of the proposed freeboard is assessed using a design wind speed of 100 miles per hour with the reservoir at the NMOL.This wind speed equates to a return period of approximately 33,000 years based on the Pearson Type III analysis; the Gumbel method equates to a return period wind in excess of 1,000,000 years. A second check is recommended in the USBR Design of Small Dams where the freeboard is assessed using a 50 miles per hour wind with the reservoir at the NMOL.The Pearson type III method estimates that this wind speed would be a 1 in 100 year event while the Gumbel analysis estimates the wind speed would equate to a 1 in 400 years return period event.Add saton onTradedegg_-_- Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority December 2014Page10-208 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years.ay(on)NenWw|ayNON\\PrRPoFNGaNLtWaverun-upandset-up(feet)i --@-Standing Wave -Pearson Il -™-SPM -Pearson Type Ill 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Windspeed (miles per hour)OoOrReNWwWffNDNCOW/OFigure 10.11-6.Wave Run-up and Set-up and Wind Speed Relationship The relationship between wind speed and wave run-up and set-up is shown in Figure 10.11-6 based on the Pearson Type III analysis.Inspection of the curves shows that the wind setup and wave run up for the two design wind speeds are as follows in Table 10.11-4: Table 10.11-4.Adopted Wind Set up and Wave Run-up Values Design Wind Speed SPM Standing(mph):Wave 50 4.07 4.49 100 9.55 11.16 Thus using the most conservative value the required freeboard for the NMOL is 11.16 ft.,which requires a dam crest of El.2061.16 ft.However the necessary crest elevation for the PMF is El. 2065 ft.which satisfies the freeboard criteria. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-209 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.12.Spillway At the commencement of this feasibility study,for the purposes of examining the various dam types and selection of the preferred configuration,the spillway configuration derived in the 1980s was used -which comprised an ogee weir with three radial gates,and a spillway approximately 164 ft.wide.However,while the comparison of layouts was in progress,during 2012 (and encouraged by FERC),a site specific PMP study was initiated,which has led to a revised calculation of the PMF inflow and routed outflow,and thus a reanalysis of an optimized spillway configuration and crest elevation of the dam.The final derived PMF -as documented in Section 9 together with the PMP study -is close to that originally conceived for the 1980s studies,although there is a slight reduction. To provide flushing flows,the Project will include the capacity to discharge a substantial release from low level outlets,without opening the spillway gates.Initially,the design called for six valves,but during design development,as noted above,this was increased to eight. The design criteria adopted was for the discharge of the 50-year-flood without opening of the gates,and it was discovered,by examining and estimating the cost of different configurations, that this could be achieved,reasonably,by including an ability to surcharge the reservoir by 7.5 ft.(to El.2057.5 ft.). The initial feasibility study spillway configuration (similar to the 1980s studies)included three spillway bays,and gates of a height of 64 ft.Radial gates of this height have been used relatively often around the world,but the Board of Consultants suggested that a reduction in pier height would be beneficial as a response to cross valley seismic waves.When the various flood routings were performed for the PMF -based on the first part of the flood being passed by the low level outlet without gate opening -one of the options checked was a spillway with four gates,and lower piers.Of the options examined,such an arrangement,incorporating four gates, was found attractive,and a final configuration was chosen including an ogee weir crest level of El.2010 ft.,with gates suitable to hold the surcharge at El.2057.5 ft.as discussed above. The chosen arrangement allows for the routed passage of the PMF with a top water level of El. 2064.5 ft.,and four gates 42 ft.wide and 50.5 ft.high.A further check was performed,and the 10,000-year-flood can be routed through the project -without overtopping the dam -with one gate inoperative.Divided by a center wall,each spillway chute is 82 ft.wide.Optimization is possible and depending upon bedrock level the chute floors can be at different elevations. The chute spillway is located on the right abutment and founded on bedrock and on the RCC of the dam.During detailed design,the joint between the convention concrete of the spillway and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-210 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. the RCC of the dam will be carefully considered and the stability of the spillway chute on the right abutment will be verified. Overtopping of an embankment dam due to wave run up can be a serious matter of dam safety, but criteria adopted by various authorities around the world (including USBR)allow for zero freeboard for concrete dams during the PMF event.Therefore,as described elsewhere,the crest elevation of the Watana Dam has been selected as El.2065 ft.A solid concrete parapet wall will be constructed,however,on the upstream side of the crest with a top level of El.2068 ft.,which will provide for some protection against oversplash.On the downstream side of the crest there will be guard rails and/or an "open”barrier so that water can drain downstream,and snow can be blown or plowed off the crest. As the number of gates has been increased to an even number (four)the opportunity was taken to include a concrete wall between the two identical halves of the spillway.This arrangement will allow the spillway to be used under low flood conditions,even if there are repairs being carried out on one side of the chute.For the purposes of feasibility design,it has been assumed that a flow of 60,000 cfs must be passed while repairs are carried out on one half of the spillway,and therefore under such flow conditions water must not spill over the center wall. CFD modeling has been performed for the various spillway configurations investigated -both three gates with an ogee crest level of El.2000 ft.,and four gates with an ogee crest elevation of El.2010 ft.-allowing spillway parameters to be confirmed.Typical output from the CFD modeling is shown in Figure 10.12-1 through Figure 10.12-4 for the critical spillway discharges, and has been used to derive the proposed location of aeration,to verify the general spillway configuration,verify the wall heights of the side walls and center wall and to verify the flip angle and impact for plunge pool stability. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-211 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT teva.veroty RAST py oe 40.667 27.111 -x -SREY assg ef)il ie 310 ft.=ars. a ety A z 9 1000 200.00 im)e |i)2000 43000 Figure 10.12-1.Routed PMF Flow through Four Fully Open Gates -Plunge Pool Location 1 27.111 13.556 a woe ome es oe [m 91) 100.00 (m) J 75.00 Figure 10.12-2,Routed PMF Flow through Four Fully Open Gates -Plunge Pool Location 2 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-212 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10006 (mm)3 37.09 24.73 12.36 C7)40.00 100 UO (m) )24.000 7300 Figure 10.12-4.Two Gates Open -Discharging 60,000 cfs --Unbalanced Flow Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-213 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The spillway shown in the drawings will perform satisfactorily,but the CFD results show that it will need slight optimization during detailed design to address the upper shape of the chute walls, which lead to the slight unbalanced flow shown in Figure 10.12-4. CFD modelling indicated the locations at which air should be introduced into the spillway flow. Aeration slots have been indicated at three locations and consist of a gallery through the base of the spillway and three air entry towers through the spillway walls.The design of the top of the towers will stop snow being introduced into the system. The soffit of the spillway bridge beams will be set to El.2062.3 ft.to allow the passage of floating debris under the bridge without damage during a PMF event.This will require that the spillway bridge deck and pier top surface level be above crest level requiring a ramp from the general crest level of El.2065 ft. During detailed design,consideration could usefully be given to an alternative form of spillway used on the 360 ft.high Theodore Roosevelt Dam in Arizona,amongst others.At Roosevelt Dam,two rectangular submerged orifice spillways were used -controlled by top sealing radial gates -sufficient to pass a flow of 150,000 cfs.Depending on the final orientation of the Watana Dam -chosen after the full site investigations are complete -an arrangement similar to the Roosevelt Dam might offer the following advantages: «Smaller,and less expensive spillway chute;and, »Better accommodation of horizontal stresses in the dam. However,the passage of any debris such as logs is more complicated in such an arrangement (possibly leading to a requirement to clear the whole reservoir),and the stoplogs necessary to be able to service and maintain the radial gates are more complex and bigger than required for a normal chute spillway. 10.12.1.Radial Gates and Operators Four radial type spillway gates will be provided to control the water flow through the spillway structure.Radial gates will also retain the reservoir between the spillway crest at El.2010 ft.and the top of the gates El.2058.5 ft.The gate system will include an independently operated, hydraulically operated,42 ft.wide by 50.5 ft.high radial gates,located at each of the spillway bays.In general,design of the radial gates and operators will be identical for all four spillway bays except that at least two radial gates will include a flap gate for ice and debris removal (passage). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-214 °December 2014 --z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The structural arrangement of each gate will include a skin plate supported by a system of vertical curved ribs carried on horizontal beams.The horizontal beams will be supported by vertical girders framed on to two sloped radial arms joining at the trunnion.Each trunnion assembly will consist of a hub which will connect to the radial arms and rotate approximately 43 degrees on a trunnion pin.Each side of the gate will be equipped with four guide rollers that will be mounted on the gate horizontal girders for convenient lifting and lowering of the gate in spillway bay.In addition,rubber seals will be provided on sides and bottom of the gate and will seal against the embedded stainless steel sealing surfaces,of which the side plates will be heated. Each gate will be operated by two hydraulic hoists,mounted on the sides of the piers downstream of the gate skins.Each cylinder operator will be of approximately 125 tons rated capacity and maximum of 42 fi.stroke length.The location of the mounting of the hydraulic cylinders on the spillway piers will need to be optimized during detailed design to minimize the stroke length of the cylinders,and the response of the cylinders to seismic loads.Excessive stroke is detrimental to the life of the cylinder rod end seal and bearings because of the side load caused by bending of the rod when it is inclined to the vertical.Each gate will be provided with an individual hydraulic power unit located on the spillway pier.The gates will be capable of being operated automatically and from a pushbutton control station located in the remote control room or from a control station located on the spillway pier. A diesel-powered standby generator will be located in an alcove in the powerhouse access tunnel,close to the spillway for operation of the gates during complete power failure.The power and control cables will be routed to minimize the potential for damage,through a vertical shaft drilled from the spillway structure down to the powerhouse access tunnel,and within the spillway concrete and in the shaft without any exposure to the elements. 10.12.2.Spillway Bulkheads One set of bulkheads will be provided to permit maintenance of the spillway radial gates. Bulkhead guides will be installed upstream of the each of the spillway gates.The bulkheads will be designed to withstand the full differential head. The spillway bulkhead will be deep enough to extend from the seal plate at the ogee crest up to El.2060 ft.The bulkhead will be sectionalized into sections for the ease of transportation to the site.Each section will be the full width of the spillway bay.The sections will seal on the downstream side and the transfer of the hydrostatic load from the two end posts of the leaf to the supporting structure will be through bearing pads mounted on the end posts.Bulkhead sections will be installed and removed with a semi-automatic lifting beam connected to a spillway gantry crane.They will be installed and removed under balanced head and a manual fill valve will be provided in the lowest bulkhead section to fill the space between the bulkhead and radial gate. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-215 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT There will be convenient storage within the coverage area of the spillway gantry crane. 10.12.3.Spillway Gantry Crane A 75-ton capacity electrical travelling gantry crane will be provided at El.2065 ft.to facilitate handling and maintenance of the bulkhead and gate equipment for both the spillway gates and the low level outlet facilities.The gantry crane will have sufficient travel,and extra outrigger booms (if necessary)to facilitate maintenance and handling of both water passage equipment. 10.13.Emergency Release Facilities The diversion tunnel will be converted to a permanent emergency release facility upon completion of dam construction.These facilities will be used initially to pass the required minimum discharge during the reservoir filling period (until the reservoir level reaches El.1850 ft.)and will also be used to assist in draining the reservoir in an emergency.The discharge criteria (based on the 1980s planning criteria)selected is the discharge of 30,000 cfs at a pool elevation of El.1850 ft.-which assumes that the reservoir can be drawn down from the operating level to the minimum operating level using the powerhouse flow in conjunction with the spillway,and then the low level outlet. The facilities first analyzed during this study were those presented at the end of the 1980s study, and included in the PAD,which it is understood were based on a physical model of the facilities proposed at that time for Mica Dam in BC.The facilities included the enlargement of the diversion tunnel to a 45-ft.diameter concrete lined tunnel for a length of about 820 ft.Two concrete plugs would have been installed,one near the upstream end of the enlarged tunnel and the second 340 ft.downstream of the first plug.Each plug was to contain three steel lined water passages controlled by bonneted high pressure slide gates. From published papers at the time (1980s)it was evidently intended that during operation, energy would be partially dissipated within the energy dissipating expansion chamber. Computational Fluid Dynamics (CFD)modeling was performed for this proposed arrangement, and stable flow was not able to be achieved without pressurization of the chamber between the two plugs,and without highly unstable pulse flows throughout the system.The PAD design was therefore abandoned.It was also discovered that the Mica project abandoned the original design before construction. A revised arrangement was investigated using CFD numerical modeling software.Nine iterations were performed to achieve a stable emergency discharge of 30,000 cfs at minimum operating level. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-216 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Stable discharge can be achieved by constructing a stilling chamber downstream of the plug,so that all energy can be dissipated and the flow in the rest of the diversion tunnel can be sub critical. Enlargement of a tunnel by excavation of the floor is the safest and easiest way of enlarging the cross section,so after the plug is installed in the diversion tunnel,a stilling basin will be excavated in the floor of the tunnel some 46 ft.deep and 520 ft.long. Within the plug will be two steel lined conduits,with flow controlled by bonneted gates, approximately 16 ft.high by 7 ft.wide.The gates will be protected by isolation valves allowing the main gates to be maintained.An air vent will be installed at the downstream side of the gates. The tunnel downstream of the stilling basin will be sized so that there is open channel flow with sufficient space above so that there will always be air above the flow. Figure 10.13-1 shows a section of the stilling basin and the result of the CFD analysis for the maximum flow that will pass through the system.The feasibility level analysis shows that the design should be able to be developed into a safe arrangement. .VelocityMaes ims THE |a a c S;%ee es "ey " Pearce nent etn ee _-scan rae ,Cees A."a =ag)ttV=Ho'h 13)Ze . -_----eee ;!4 Figure 10.13-1.CFD Model of 30,000 cfs Flow in Emergency Outlet Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-217 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Further analysis will need to be performed during detailed design,to confirm that the flow is stable and there is no contact on the tunnel crown by flow..This can be achieved by the refinement of the locations and sizes of energy dissipation blocks in the floor and wall,and by shaping of the steel conduits downstream of the gates before the jet enters the basin.The emergency outlet works is shown in Drawing 04-05G002. 10.14.Outlet Facilities During the 1980s studies the primary function of the outlet facilities was deemed to be to discharge floods with recurrence frequencies of up to once in 50 years after they have been routed through the Watana reservoir.Those outlet facilities have been included in the present design.At an early stage in the derivation of the configuration,it was decided that the discharge valves could economically be served by two steel pipes embedded in the foundation of the chute spillway,and depending on the iteration of the layout,they have been variously located in the left or right abutment. The final recommended location is on the north (right)side of the dam as shown on Drawings 04-01C002 and 04-03S001 and will consist of a gated intake structure,steel pipes,and an energy dissipation and control structure located beneath the spillway flip bucket.This structure will accommodate up to eight fixed-cone valves which will discharge into the river below,although after discussions with stakeholders the capacity may be reduced.The use of fixed-cone discharge valves will minimize downstream erosion and lower the dissolved nitrogen content in the discharges so as to avoid harmful effects on the downstream fish population.The facilities will also be used to provide additional outflow during any required reservoir evacuation down to El.1850 ft. 10.14.1.Intake The twin intake will have an invert elevation of El.1800 ft.,allowing operation down to normal minimum operating level.Each intake will contain three columns of steel trashracks on the face of the structure separated by concrete piers and spanning the openings to the water passage.The trashracks will be split into panels mounted one above the other in vertical steel guides installed at the upstream face.The trashrack panels can be raised and lowered for cleaning and maintenance by a mobile gantry crane located at deck level. Two fixed-wheel gates will be located downstream of the trashracks between the pier and each of the sidewalls.These gates will be operated by hydraulic hoists mounted in the gate shaft.The fixed-wheel gates will not be used for flow control but will function as closure gates to isolate the downstream steel pipe and allow dewatering for maintenance of the pipe or ring gates located in the discharge structure. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-218 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Bulkhead guides will be provided upstream from the two fixed-wheel gates to permit dewatering of the structure and access to the gate guides for maintenance. 10.14.2.Intake Gate The intake gate system for each intake tunnel will include an independently operated, hydraulically operated vertical wheel gate located downstream of the trashracks between pier and each of the sidewalls.The intake gates and hydraulic hoists will be identical for both intakes. Each gate will be a fix-wheeled type vertical lift gate,approximately 23 ft.wide by 23 ft.high. Each gate will be spliced into two sections for the ease of transportation of gate sections to the site.The connection of the two sections will be sealed by bolting together two machined steel surfaces.Rubber seals will be provided on all four sides of gates and will seal against embedded stainless steel sealing surfaces around the perimeter of the gate opening. Each gate will be provided with guide shoes which will engage side guide rails over the entire height of the intake for convenient lowering of the gate into the slot.A wheel track of uniform strength and construction will extend two gate heights above the sill elevation such that the gate wheels will always be engaged on the tracks over the entire opening range of the gate. Each intake gate will be operated with hydraulic hoist mounted in the gate shaft.The gates will be capable of being lowered either from a pushbutton control station located in the remote control room or from a control station near the intake area.Raising will only be allowed from the stations located near the intake area.Both gates will be operated from a common hydraulic power unit.A backup HPU will also be provided. 10.14.3.Intake Bulkheads Two sets of intake bulkheads will be provided for closing the two intakes upstream of the intake gates.The intake bulkheads will be used to permit inspection and maintenance of the intake gates and intake gate guides.The intake bulkheads will be designed to withstand the full differential head. Each intake bulkhead will be approximately 23 ft.wide by 23 ft.high.Each bulkhead will be spliced into two sections for the ease of transportation of bulkhead sections to the site.Rubber seals will be provided on all four sides of the bulkhead on upstream side of the bulkhead. Bulkheads will be installed and removed under near balanced head conditions.Fill valves, operated by the lifting beam,will be provided in the bulkheads to fill the void space in the downstream tunnel. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-219 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.14.4.Intake Trashracks Three sets of steel trashracks will be provided at the entrance of each intake to prevent debris from being drawn into the discharge valves.Each of the three trashrack sets will include the following general design features. Each trashrack set will be provided in four panels.All four panels will be stacked on top of each other and supported by each other.The trashrack frame load/support bars will be designed to span horizontally.The rack bar sub-panels will consist of vertical and horizontal bars forming a grill having clear opening of 6 inches by 6 inches.The rack bars will be designed to span vertically between the frame horizontal support plates.Trashrack structure will be designed for a maximum differential head of 40 ft.which corresponds to a fully clogged trashracks.For high- pressure,high-velocity intakes,the industry practice has been to design the trashrack structure to withstand a load equivalent to one-half the head on the racks,with a maximum of 40 ft. Trashrack structural components will be designed to prevent resonant vibration induced by the flow through the trashracks.The maximum net velocity through the racks will be approximately 5.0 ft.per second.Provisions will be made for monitoring the head loss across the trashracks. 10.14.5.Gantry Crane The 75 ton gantry crane for the spillway facility will also be used for the low level outlet facility. As aresult,a separate gantry crane for the low level outlet facility will not be required. 10.14.6.Pipes and Manifold Discharges from each intake will be conveyed from the upstream gate structures by 23-ft. diameter steel pipes that will be embedded within the dam,near its downstream face.Each pipe will continue beneath the spillway chute before dividing into four pipes which will pass through the main spillway flip bucket structure to the fixed-cone valves mounted in line with the downstream face. 10.14.7.Discharge Structure The concrete discharge structure will form a part of the flip bucket for the main spillway and will house the fixed-cone valves and individual upstream ring follower gates.Four valves will be set with a centerline elevation of El.1569 ft.and four will be set at El.1549 ft.and will discharge into the river below.Openings for the valves will be formed in the concrete and the valves will be recessed within these openings sufficiently to allow enclosure for ease of maintenance and heating of the movable valve sleeves.An access gallery upstream from the valves will run the length of the discharge structure,and will terminate in the access tunnel on the north side of the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-220 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. structure.A vertical shaft to the powerhouse access tunnel will allow for installation and removal of the valves when required. Housing for the butterfly valves will be located upstream from the fixed-cone valve chambers. The butterfly valves will serve to isolate the discharge valves.Provision will be made for relatively easy equipment maintenance and removal by means of a 25-ton service crane and a 25- ton monorail hoist. 10.14.8.Fixed-Cone Discharge Valves Eight 79-inch diameter fixed-cone valves will be installed at the downstream end of the outlet manifold to control the discharge through the low-level outlet facility.The valves will be operated by hydraulic cylinder operators either from locally or remotely from control room. The valve body will consist of a cylinder with a conical deflector head on the downstream end, internal radial ribs and an upstream mounting flange for attachment to the conduit liner.The valve gate will consist of a cylinder designed to slide over the valve body.The gate will slide upstream to open and downstream to close off the valve ports.Each valve will be operated with the two hydraulic cylinders,mounted diametrically opposite.Additionally,an embedded steel hood will be provided for each valve to reduce the spray and to reduce the risk of erosion from the water jet against the immediate environment.Each valve will be designed to withstand a total static head of approximately 530 ft. The current valve design shows the piping and valves discharging straight out in the horizontal plane.This provides symmetric flow to the discharge valve.Depending on the constraints of a project,discharge valves can be angled above the horizontal plane to further "arc”the discharge path to either provide more energy dissipation in the air or change the "throw”distance out from the valve.So far there have not been any constraints to the discharge location identified that would require reconfiguring the outlet valves in such a way.Angling of the valves right at the end of the pipeline introduces issues such as asymmetric flow distribution though the valve,and off-axis loading on the valve and pipeline structures and their anchorages.There is no benefit to configuring the outlet with angled valves absent significant downstream constraints that would require such a design. Plunger valves could also be used for controlling the discharge through the low-level outlet.The plunger valve is similar to needle,tube,or ring jet valves in that water flows around a central bulb within the valve body creating an annular flow path.The plunger valve has an axial cylinder that seals against the downstream edge of the flow path and retracts into the central bulb to increase the annular discharge area.This type of arrangement offers a much simpler design than the fixed cone valve.For the same size,the plunger valve is less expensive,but also has Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-221 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT smaller discharge capacity.In this case,a larger plunger to meet the same capacity would likely be comparable in cost to the fixed cone valves.The plunger valve would be relatively smaller in actual physical size,would require less surrounding structural support,and would likely provide comparable energy dissipation.The cylinder is also customizable to provide additional energy dissipation options. Further investigation of the design features and cost comparison between the two types of valves will be carried out in the design phase to make the final selection of the discharge valve type. 10.14.9.Butterfly Valves Butterfly valves will be installed upstream of each of the fixed-cone valve to permit inspection and maintenance of the fixed-cone valves;to relieve hydrostatic pressure on the fixed-cone valve when they are in closed position;and to close against flowing water in case of malfunction or failure of valves or the upstream gate.Each butterfly valve will be operated by hydraulic cylinders either from locally or remotely from a control room. Each valve will have a nominal diameter of 90 inches and will be designed to withstand a total static head of approximately 530 ft.Each valve will be located within a heated enclosure with suitable provision for servicing the equipment.The valve will primarily consist of a cylindrical body with two flanges,valve blade,bypass system,and a hydraulic operator.Valves will be designed to be closed under flowing water condition and opened under balanced head condition. Prior to opening of the valve,pressure will be balanced by means of a bypass pipe. The current valve sizing of a 90 inch butterfly guard valve and 79 inch fixed cone valve can work,but the velocities through those valves to achieve the required 4000 cfs flow rate are also very high and might usefully be lowered depending on the expected use of the valves.High velocity can lead to cavitation and vibration at various points along the butterfly valve disc or at the outlet surfaces of the fixed cone valve,as well increased turbulence and thus increased losses that can reduce discharge capacity.Early feedback from two valve manufactures is that either additional design considerations would need to be made,particularly for the butterfly valve disc design to minimize cavitation and vibration,or the valve sizing should be increased to 102 inch and 90 inch respectively.Also an increase to these sizes would allow the maximum required flow rate to be achievable throughout the entire head range,not just at full reservoir. Further review of the design goals of the project and a comparison of costs and benefits should be performed in further detail in the project's design phase to optimize the valve sizing. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-222 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.14.10.Monorail Hoist One 25-ton monorail hoist will be provided above the fixed-cone discharge valves for the maintenance and handling of the valves.Primary function of the monorail hoists will be to mobilize valves and equipment to and from the service room during the maintenance. 10.14.11.Bridge Crane One 25-ton overhead type,top running bridge crane will be provided for the maintenance and installation of butterfly valves in the discharge structure.Primary function of the crane will be to handle and mobilize valves and equipment to the service room during the maintenance. 10.14.12.Discharge Area Immediately downstream from the discharge structure,the rock will be excavated at a slope of 2H:3V to a lower elevation of El.1510 ft.The excavated face will be reinforced by rock bolts and protected by a concrete slab anchored to the face.The lower section of the rock slope extending to the river will be unlined. 10.15.Fish Passage Considerations No provision has been made in the feasibility design of the project for the passage of anadromous fish.AEA is conducting separate studies on the incidence of such fish at the dam site and on the viability and economy of transporting them past the proposed dam under Study Plan 9.11.Options being investigated under the study plan include: «Trap and haul; =Fish ladder; =Fish lift; «Use of Tsusena Creek together with enhancement of flow;and, *Other options developed from workshop sessions. 10.16.Power Intake Each penstock (including the spare)will have its own separate power intake.The power intakes will be conventional concrete structures extending upstream from the dam upstream face and will be supported,if necessary for construction sequencing,on concrete extending to the dam foundation.The intakes will be fully accessible from the dam crest. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-223 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT&)hres CS CBS 003?shows FG 050EachintakewillcontainpairsofopeningsCotovelsintheupstreamconcretewallofthe structure,to facilitate withdrawal of water from the reservoir at specific levels over an expected Go F wo Askdrawdownrangeof200ft.For each vertical series of intake openings,flow through each.pen nee?Ke ;.;or Bhuit eeopeningwillbecapableofbeingobstructed(but not completely sealed)by a series of Six Sliding steel shutters operated in two common guides.Upstream trashracks will protect all openings. To maintain an ice-free trashrack system,a heated boom will operate in guides upstream of the racks.Behind the intakes at the entry to the penstocks,a control gate will be provided with routine maintenance being possible by the installation of a bulkhead gate upstream of the control gate. Each intake will be 65 ft.wide with the upper level of the concrete structure set at El.2065 ft. The level of the lowest intake is governed by the vortex criterion for flow into the penstock from the minimum reservoir level elevation of El.1850 ft.The arrangement of the power intakes is shown on Drawings 05-06S002 and 05-06S003. 10.16.1.Intake Gates and Operators The intake gate system for the power intake facility will act as a dependable emergency closure device in the event of a penstock rupture or a turbine runaway condition at the plant.The intake©gates will also allow complete dewatering of the penstock for inspection and maintenance. There will be an independent intake gate system for each of the four power intakes.Each intake =) gate system will include an independently operated,hydraulically operated vertical fix-wheeled ae vegate,downstream of the bulkhead slots.Each gate will be approximately 21 ft.wide by 20. high,and could be upstream sealing or downstream sealing.The decision ich type of gate to use will be made during detailed design,but will probably be downstream sealing -although substantial air would be required for this type of arrangement. Each intake gate will be a welded fabricated construction with rubber seals.Rubber seals will be provided on all four sides of gates and will seal against embedded stainless steel sealing surfaces around the perimeter of the gate opening.Each gate will be provided with guide shoes which will engage side guide rails over the entire height of the intake for convenient lowering of the gate into the slot.A wheel track of uniform strength and construction will extend two gate heights above the sill elevation such that the gate wheels will always be engaged on the tracks over the entire opening range of the gate. Each intake gate will be operated with a hydraulic hoist.The gates will be capable of being lowered either from a pushbutton control station located in the remote control room or from a oO control station near the intake area.Each of the two intake gates for each intake unit will be Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-224 December 2014 Ls Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. operated using a common hydraulic power unit assigned to each intake unit.Furthermore,a backup hydraulic power unit will also be provided for each of the three power intake units. During detailed design,the bypass arrangements will be addressed so that the penstock can be refilled and the gate opened.Options include a valve in one of the gates,built in pipework in the concrete structure for filling,cracking of the gate,or pumping in water. 10.16.2.Intake Bulkheads Within each power intake,arrangements will be included for placing two sets of intake bulkheads to close the intake ports upstream of the intake gates.The intake bulkheads will be used to permit inspection and maintenance of the intake gates and intake gate guides.The intake bulkheads will be designed to withstand the full differential head. One set of intake bulkheads will be placed in the spare intake,and a second set will be stored for use in any of the operating power intakes.Each intake bulkhead will be approximately 21 ft. wide by 27 ft.high,probably spliced into two sections for the ease of transportation to the site. Each intake bulkhead section will be of downstream sealing type and the transfer of the hydrostatic load from the two end posts of the leaf to the supporting structure will be through bearing pads mounted on the end posts.Intake bulkheads will be installed and removed with a semi-automatic lifting beam connected to a gantry crane.Intake bulkheads will be installed and removed under near balanced head conditions.Fill valves,operated by the lifting beam,will be provided in the bulkheads to fill the void space in the downstream tunnel. 10.16.3.Intake Shutters a vet IThe operators will be able to select the intake openings to be used for draw off to the penstocks, but movement of the shutters will be accommodated by using the intake gantry crane so remote operation will not be possible.To draw from the reservoir surface over an expected drawdown range of 200 ft.,two adjacent openings at each of five levels will be provided in the upstream concrete wall of the structure for each of the intakes.Openings will be able to be closed off by steel shutters operated in two common guides.The downstream guide will accommodate the upper three shutters,and the upstream guide will accommodate the lower two shutters.Two guides are included to facilitate the accommodation of all the (individual)lifting cables (two for each shutter)in the protected environment of the guides.As the reservoir level varies,the shutters will be relocated as necessary using the powerJntake gantry crane.N2Eachshutterpanelwillbeapproximately24ft.wide by 25.5 ft.high and will be spliced into two sections for the ease of transportation to the site.Each shutter will be welded steel plate with upstream skin plate and downstream framing.No seals are envisaged,as some leakage around Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-225 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT the shutters is acceptable.Under normal conditions,shutter panels will always be under balanced head,and will be operated under balanced head.However,the shutter structure will be designed to withstand 15 ft.of differential head in case of blockage of intake openings.Flap gates or blow out sections will be provided in each shutter panel to prevent failure of the shutters in the event that the differential head exceeds 15 ft.due to unforeseen circumstances. When an intake opening is selected,the appropriate shutter will be moved up to be shielded by the concrete wall between openings,so that they will not be subject to the hydraulic instability associated with partial opening.Shutters will be installed and removed under balanced head condition,with a semi-automated lifting beam connected to the power intake gantry crane. 10.16.4.Intake Trashracks Each power intake will have a set of trashracks at the entrance to prevent debris from entering the penstocks.Each trashrack set will be provided in six panels.Each panel will be approximately 24 ft.wide by 29.5 ft.high,and delivered in two sections for the ease of transportation and handling. The trashracks will be removable,and guide tracks will be provided for installation and removal of panels.The trashrack frame load/support bars will be designed to span horizontally.The rack bar sub-panels will consist of vertical and horizontal bars forming clear openings of six inches by six inches.The rack bars will be designed to span vertically between the frame horizontal support plates. The trashrack structure will be designed for a maximum differential head of 40 ft.corresponding to a fully clogged condition,based on industry practice which has been (for high-pressure,high- velocity intakes)to design the trashrack structure to withstand a load equivalent to one-half the head on the racks,with a maximum of 40 ft.Structural components will be designed to mitigate resonant vibration induced by the flow through the trashracks.The maximum net velocity through the racks will be approximately five feet per second,and provisions will be made for monitoring the head loss across the trashracks.Trashracks will be installed and removed using a semi-automatic lifting beam connected to the power intake gantry crane. Trash rakes have not been included,but accommodation can be made during final detailed design.The decision to include them in the project will depend on the reservoir clearing policy chosen. 10.16.5.Intake Gantry Crane A 75 ton capacity electrical traveling gantry crane will be provided on power intake deck at El. 2065 ft.for handling and servicing the intake gates. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-226 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.17.Penstocks To convey water from each power intake to the powerhouse,one steel penstock will be provided for each generating unit.The penstock geometry encompasses a short horizontal reach through the dam structure,a 63°bend,a penstock down the (vertically curved)face of the dam,another 63°bend and a horizontal reach connecting to the spiral case.Drawing 05-06S001 shows the penstock alignment.The penstock will be supported by steel mountings in a "trench”in the downstream face of the RCC,and will be encased in conventional concrete. The penstock diameter of 19 ft.was selected after applying velocity criteria for turbine flow of 6000 cfs at NMOL of El.2050 ft.and industry recognized formulas to estimate economic diameters.Diameters estimated by four different methods are summarized in Table 10.17-1. Table 10.17-1.Economic Penstock Diameter Method Diameter (ft.) Sakaria (1979)17.2 Warnick (1984)19.6 Fahlbusch (1989)19.9 Gulliver (1991)18.0 The design static head on each penstock is 625 ft.,at turbine centerline distributor El.1425.5 ft. An allowance of up to 20 percent has been made for pressure rise in the penstock caused by hydraulic transients. Further analysis will be performed during detailed design to verify the economic diameter of the penstocks. The powerhouse design allows for the potential future addition of a fourth turbine-generating unit.The work would require converting the outlet bay of the sluice into the fourth turbine- generator bay.To enable future construction of the additional turbine bay while maintaining the normal operating level within the reservoir,the fourth power intake (including gates,bulkheads, and trashrack guides)for the future turbine and the penstock section through the dam will be constructed as part of this work,and the exposed downstream end of the penstock will be capped. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-227 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.18.Powerhouse 10.18.1.General Arrangement The powerhouse has been arranged based on similar surface powerhouse designs by MWH.It is of traditional design with standard bays and the following floors: «Main floor and transformer deck at El.1476 ft. *Generator floor at El.1457 ft. *Turbine floor at El.1439 ft. *Scroll case floor at El.1415 ft. =Pump floor at El.1382 ft. The elevation selected for the main floor is based on the revised tailwater curve derived from cross sections of the river immediately below the site that were surveyed in 2014. Access to the main floor will be via an access tunnel on the right bank sized for the generator step up (GSU)transformers,which are the largest single item to be delivered or removed from the powerhouse.From the access tunnel on the right abutment,entry to the powerhouse will be by a roller door in the north end of the powerhouse superstructure. The main floor will be serviced by the main powerhouse crane which facilitates the installation and subsequent maintenance of all equipment,and the unloading of the GSU transformers onto the embedded rails for movement to the tailrace deck. The substructure of the powerhouse below El].1476 ft.will be conventional concrete.Above El. 1476 ft.,the superstructure will be constructed using a steel frame,prefabricated cladding and roofing materials.The lower part of the downstream powerhouse wall,which will form the blast wall behind the transformers,will be of reinforced concrete.The steel superstructure has been chosen to allow the fastest possible construction of a weatherproof enclosure so that year-round work on the powerhouse can be initiated as soon as possible in the construction schedule. During detailed design,the extent to which the steel columns and crane rail supports can be founded and installed lower in the superstructure -together with precast concrete wall panels - will be investigated.As demonstrated in projects in northern Canada,by founding the crane and superstructure columns lower in the substructure,weatherproof cladding (even if temporary)can be installed earlier with the result that year-round powerhouse construction can begin earlier. This approach is illustrated in Figure 13.3-5. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-228 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The superstructure of the powerhouse will encompass three bays and an assembly area of approximately 1.5 bays,and the substructure will extend to the south to form the substructure for an extra bay -which will be available for future expansion if AEA needs warrant it.The design of the superstructure will be suitable for demolition of the south wall of the powerhouse and the extension of the superstructure over the fourth bay.During the construction of the project,the sluice through the dam will discharge through the spare bay,but will be finished to El.1476 ft. between the spare bay and the dam so that emergency evacuation of the area is possible on the south side of the river on roads S4P and S6P. Within the powerhouse,there will be two enclosed staircases through all floors at the northwest corner and at the southeast corner.In addition there will be a high capacity elevator at the northwest corner.A rotor pedestal will be built in on the main floor. Equipment on the generator floor at El.1457 ft.will include generator and excitation switchgear; station service transformer;motor control centers for the units;unit transformers and switchboard;neutral grounding cubicle;and station service switchgear. The turbine floor at El.1439 ft.will contain the governor control system;unit cooling water pumps,tanks and heat exchangers;air compression systems;and the station battery room. The scroll case floor at El.1415 ft.will house the inlet valve controls and the draft tube suppression system. The pump floor at El.1382 ft.will contain the main sump and dewatering pumps;drainage pumps;and the station oil-water separator. The powerhouse will be constructed on the cleaned rock surface below the river,and rock excavation will be performed for the three unit bays and the spare bay.The final configuration of the powerhouse below the assembly bay will depend on the rock surface profile which will be derived during future site investigations.The powerhouse lower levels will be constructed to a configuration that minimizes the rock excavation. The powerhouse will contain a control room,located either below the assembly bay or as a mezzanine room above the entrance door. 10.18.2.Turbine Inlet Valve Each turbine inlet will have a butterfly shut-off valve,of about 14-ft.diameter (the diameter remains to be optimized)between the spiral case and penstock.The final diameter will be determined by the supplier of the turbine and in accordance with the final diameter of the spiral case inlet. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-229 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The valve will be capable of: *Normal opening and closing times of less than 45 seconds. «Isolating an individual turbine from the penstock so its spiral case can be emptied (in conjunction with closing the draft tube gate and dewatering the draft tube)for maintenance work without draining the penstock. =Normal operational shut-off to eliminate leakage through the turbine wicket gates when the unit is shut down. «Secondary independent means of emergency shut-off of flow in the event the turbine wicket gates are unable to close.If this function is adopted as a criterion,a metal-seated butterfly valve will be used. The requirement for a shut-off valve will be reviewed during detailed design.A valve is considered good practice where the penstock or power tunnel is long or serves more than one turbine.In the case of the Susitna Watana Project,each penstock can be isolated at the power intake and each penstock is relatively short which will make emptying and refilling them a fairly straightforward operation.Many utilities elect to eliminate the valve as a matter of economy. The exclusion of the valve would reduce the overall width of the powerhouse,and that would have benefits in terms of reduced construction cost and construction duration. 10.19.Turbines The powerhouse will contain three turbine-generating units,with provision for adding a fourth as noted above. The rating of the units was determined in a two-step process.It is recognized that the units at Watana will be the largest capacity units on the Railbelt system and have the potential for transient disturbances to the entire Railbelt if a Watana unit trips while generating. As discussed in Section 7 configurations with 6 x 100 MW,4 x 150 MW and 3 x 200 MW units were considered and the capital costs estimated for comparison.From the perspective of machinery cost and construction cost,larger units were shown to be more economic. During the analysis of the project energy,200 MW units rated at minimum head were used to determine the initial annual output -leading to a rating at maximum head that would present a problem to system stability in the event of a unit trip.The maximum unit output under maximum head could be electrically limited to minimize that risk,but the units would then have a very narrow operating range at maximum head,reducing their operational flexibility. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-230 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. However,the PROMOD studies described in other sections indicated that the optimum use of the project does not require maximum capacity at the minimum reservoir elevation. As a result of the various modeling,the proposed turbine unit rating is 153 MW at a head of approximately 480 ft.(equivalent to an intermediate reservoir level of El.1950 ft.).Turbine rated capacity at maximum normal operating level (equivalent to a head of 577 ft.)would be 206 MW,and at minimum operating level (equivalent to a head of 383 ft.)would be 106 MW.Note these values are different than those used in the system studies comparing the use of 200 MW and 150 MW units and recorded in Section 11. The selected units will operate at a synchronous speed of 180 rpm,although this will be revisited during detailed design.Each turbine will be a vertical-shaft,single-runner,reaction type Francis turbine with movable wicket gates,fixed stay vanes,steel-plate spiral cases,and elbow type draft tubes. The movable wicket gates are used to regulate flow through the turbines for regulation of power output and speed (system frequency),and for control of speed during starting,synchronizing,and shutting down the turbine.Preliminary turbine specifications are listed in Table 10.19-1. Table 10.19-1.Preliminary Turbine Specifications Item Quantity Rated output (each)153 MW Synchronous speed 180 rpm* Runner throat diameter 13.3 ft. Spiral case intake diameter 14.3 ft. Total width of spiral case 47.9 ft. Depth of draft tube (from spiral case center line to lowest point)41.7 ft. *A synchronous speed of 225 rpm is also feasible. The dimensions given in the above table are estimated values based on parametric data obtained from other projects within MWH's experience.The final dimensions of the procured turbine will differ slightly from those provided above. 10.19.1.Turbine Components The embedded turbine components consist of the draft tube liner,discharge ring,stay ring,spiral case and pit liner.These components are a structural part of the foundation for the turbine and generator.Access to the water passages will be provided by watertight doors in the spiral case and the draft tube liner. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-231 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Turbine rotating parts consist of the runner and the turbine shaft.The runner is bolted directly to the lower end of the flanged shaft.The turbine rotating parts,together with the generator rotating parts),are supported by the thrust bearing immediately below the generator.Radial movement loads on the turbine rotating parts are constrained by a turbine guide bearing mounted on and close to the turbine head cover.A turbine shaft seal is provided between the turbine guide bearing and the turbine head cover. The distributor assembly includes the moveable wicket gates which are operated by levers and links attached to a wicket gate operating ring.The gate operating ring is moved by two or more servomotors,which are typically mounted on the pit liner wall,but may also be mounted on the turbine head cover.Also mounted on the head cover are the piping for the air,water,pressure equalizing,bearing oil and governor oil systems;and the pit maintenance platform and walkways.The turbine pit may also be provided with a monorail hoist to facilitate removal of the turbine wicket gates. 10.19.2.Governing System Each turbine will be provided with an electro-hydraulic governing system,which will be of the solid-state,digital microprocessor type using proportional-integral-derivative speed control.The governing system will include speed and acceleration sensing,speed regulation,stabilizing,and diagnostic functions.The digital processor provides a control signal to an electro-hydraulic servo valve that controls positioning of oil-distributing valves directing pressure oil to the individual wicket gate servomotors,to move and position the wicket gates. The governing system will have provisions for local and remote start/stop for automatic load control.Each governing system includes an electrical speed sensor,a digital microprocessor control,an actuator,restoring connection,an oil pump set,sump tank,pressure tank,oil piping to the wicket gate servomotors,and all controls,instruments and accessories necessary for a complete governing system.Additionally,the governor will have a digital interface to the overall unit and plant controls. 10.20.Generators 10.20.1.General Various generator sizes were examined resulting in a generator rating of just over 200 MW at maximum normal operating level.Analysis of turbine performance resulted in a suggested rotational speed of 180 rpm.Therefore a generator rating of 225 MVA at 0.90 power factor and 180 rpm was chosen. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-232 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. It is expected that under normal conditions,under-excited operation of the units will not be required;however,under abnormal system conditions,it may be necessary to energize part of the 230 kV system from the plant.Therefore,each generator will have a line charging capability of 140 MVA reactive which is adequate for energizing approximately 600 miles of 230 kV transmission line.This means that any one of the units will be capable of energizing the longest line connected (either present or planned)to the 230 kV switchyard. 10.20.2.Configuration and Ratings The generators will be of the vertical-shaft,hydraulic-turbine driven synchronous type complete with bearings,fire protection system,and a closed system of ventilation with surface air-to-water coolers.Each generator will be of the semi-umbrella type construction with a lower thrust/guide bearing and upper guide bearing.The generator will be compatible with the turbine,particularly in terms of capacity,vibration,normal speeds and over speeds up to and including runaway speed,loadings,and stresses.All parts of the generator,including bearings,will be designed to withstand all electrical,mechanical and structural stresses resulting from operation under rated conditions,including stresses caused by temporary conditions of overspeed and short circuits. The generator ratings will be as follows: =Continuous rated capacity at rated voltage and power factor:225 MVA =Rated power factor:0.90 «Rated frequency:60 Hz =Rated speed:180 RPM =Number of phases:3 ="Maximum stator winding temperature rise over 40°C ambient:75°C The generator system will be configured to operate in the condensing mode should transmission line voltage support be required.Each unit will have approximately 140 MVA reactive condensing capacity. 10.20.3.Generator Structure 10.20.3.1.Stator Frame The stator frame will be supported on soleplates embedded in the concrete foundation.Bolts and dowels will be provided for fastening the stator frame to the soleplates and for preserving the alignment between the frame and the soleplates.An adequate number of dowels will be Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-233 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT provided to prevent any undue movement of the stator frame on the soleplates when the generator is subjected to stresses resulting from short circuit conditions. The lower bracket supporting the thrust and guide bearing assemblies will support the weight of the entire rotating element of the generator together with the turbine runner and shaft and will have adequate rigidity and strength for safe operation under conditions of maximum unbalanced hydraulic thrust of the turbine runner or unbalanced conditions caused by short circuits, including short circuits of one-half of the field windings. The generator brakes will be mounted on the lower bracket.The foundations for the brackets or supports will be designed so as not to reduce the clear opening for removal of turbine parts through the stator bore. 10.20.3.2.Bearings The thrust bearing will have ample capacity to support the combined weight of the rotating parts of the generator and turbine,including the maximum unbalanced hydraulic thrust of the turbine. The thrust bearing will have a removable one-piece runner and be arranged to permit easy inspection,adjustment,dismantling and assembly of the thrust bearing shoes without disturbing the rotor,stator or bearing bracket other than jacking the rotor to remove the load from the bearing.The runner will be removable after lifting the rotor and the shaft from the pit. The guide bearing will meet all normal and unbalanced operating requirements of the generator, including the unbalanced loads caused by a short circuit of one-half of the field windings.The guide bearing will be combined with the thrust bearing in the same enclosure.The guide bearing will be of the segmental,screw-adjustable,oil immersed,babbitted type.The bearing will be designed and constructed so that it can be easily dismantled,assembled and adjusted without disturbing the thrust bearing,the rotor or collector ring. 10.20.3.3.Lubrication The generator will be provided with a complete,self-contained,lubricating system,which will include provisions to eliminate the throwing of oil and the escape of oil vapor from the bearings and lubricating system.Adequate provisions will be provided,if necessary,to prevent excessive churning or aeration of the oil. 10.20.3.4.Generator Housing A generator stator housing will be provided to enclose the stator core,frame and cooling radiators.The enclosure will be sealed and provided with cooling air baffles and duct work to provide an enclosed cooling air circulation system for cooling the rotor,and stator components. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-234 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Access will be provided for maintenance and inspection of the generator winding and cooling components.The top of the enclosure will be provided with removable plates for purposes of rotor removal,access to the stator and field windings,and removal of the coolers.Lighting will be provided within the enclosure. 10.20.3.5.Stator Core The stator core will be designed in such a way as to permit replacement of the core laminations without major disassembly of the stator frame.The stator design will permit partial or complete field replacement of the stator windings and/or core laminations without requiring major cutting, welding,heating or rework of the stator core,core retaining assembly or frame. 10.20.3.6.Stator Winding The stator winding will be wye-connected,suitable for grounded operation.The winding will consist of Roebel bars with copper conductors completely (360°)transposed in the slot.The bars will be insulated for 20 kV with full Class F insulation. Sufficient parallel circuits will be provided to keep the bar current less than 2,000 amps. 10.20.3.7.Circuit Rings Circuit rings complete with all necessary connections,taps,adapters,braces,supports,and materials for making the necessary line and neutral connections between the windings and the terminals of the phase and neutral buses will be provided.The individual bars in each of the parallel paths which are connected to the circuit rings,will be connected in locations to minimize circulating currents between the parallel paths caused by misalignment of the rotor with respect to the stator. 10.20.3.8.Stator Air Coolers The generators will be furnished with surface air coolers spaced symmetrically around the periphery of the stator frame for a closed,recirculating,cooling system.Water headers will be furnished with the coolers.The cooling system will be designed to fit within the generator housing while providing adequate space for inspection,maintenance,disassembly/reassembly, and air circulation. The surface air coolers will have sufficient cooling capacity to maintain the temperature of the air leaving the coolers at 40°C,or less,with the generator delivering continuously rated output, and with 20°C cooling water temperature and 25 percent of the tubes blocked. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-235 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The circulation of air will be by means of the generator rotor fans.The air will circulate through the stator core,frame and coolers and back into the rotor. 10.20.3.9.Fire Protection A high-pressure type water fire extinguishing system will be furnished for the generator and will conform to National Fire Protection Agency 851,"Recommended Practice for Fire Protection for Hydroelectric Generating Plants”.The system will consist of remote control stations, discharge nozzles,manual releases,automatic releases,thermostats,guards,and all appurtenances required for a complete operating system. The system will be so designed that it can be discharged by action of the generator differential relays,by fixed temperature type and rate-of-rise-heat detectors and smoke detectors located inside the generator housing,by manual operation of remote emergency pushbuttons,or by direct manual operation of directional valves and cylinder releases. 10.20.3.10.Rotor The rotor spider including a central hub will be a cast or weld fabricated steel structure, subdivided into a minimum number of sections to facilitate handling,transporting,and assembling.The spider will have adequate tangential and vertical rigidity to prevent undue deformation,center the rim and the poles,and to allow passage of the cooling air to the rim.The rotor rim will be shrunk fit and keyed to the rotor spider. The pole pieces will be built up of high-grade,cold-finished,thin steel laminations fastened to the rotor rim secured in place by tapered keys.The poles will be replaceable without lifting the rotor. 10.20.3.11.Brakes The generator will be provided with air-operated brakes of sufficient capacity to bring the rotating parts of the generator and turbine,under normal operating conditions,to a stop from 33 percent rated speed within sixty seconds after the brakes are applied,without injurious heating of the braking surface on the rotor,without field excitation on the generator,and with the leakage torque through the turbine wicket gate seals not exceeding an amount which will produce two percent of the full rated turbine torque.The brakes will also be designed to serve as hydraulic jacks to lift the generator rotor and the turbine runner for assembly,dismantling or adjustment of the thrust bearing.Provision will be made for blocking the rotor in the fully raised position. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-236 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.20.3.12.Generator Shaft The shaft will be made from forged,vacuum degassed,open hearth carbon or alloy steel properly heat treated.The shaft will be of ample size and strength to ensure safe operation at any speed up to the maximum runaway speed without harmful vibration or distortion. The diameter of the generator main shaft will be coordinated with the turbine shaft diameter and will have a coupling flange for connection to the turbine shaft flange. 10.20.3.13.Generator Neutral Grounding A generator neutral grounding cubicle will be provided for grounding the neutral point of the generator windings.A distribution transformer and secondary resistor will be furnished to provide a high resistance connection to ground for the generator neutral.Secondary side of the distribution transformer will be loaded by a resistor.This combination will be connected to a protection relay for stator earth fault protection. The distribution transformer will be a conventional-type,single-phase,dry-type,and epoxy encapsulated with the following ratings: =Capacity 75 kilovolt amperes «Rated Primary Voltage 18,000 V #Rated Secondary Voltage 240 V #Basic Impulse Insulation Level 125 kV =Time Rating 10 min The resistor will be of the edge-wound,stainless steel,non-breakable type.Ill resistor components will be completely insulated ground.The resistor will have the following ratings: =»Resistance TBD »Rated Voltage 240 V ="Rated 1-minute current TBD The generator neutral cubicle will be a metal enclosed cubicle.The enclosure will provide protection against dust,insects and dripping water.All equipment installed within the cubicles will be fully accessible for inspection and maintenance. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-237 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.21.Exciter A digital type excitation system will be used.The digital excitation system will be designed to work directly into the generator main field complete with controls,limiters,and protection to safeguard the generator.The digital excitation system will also incorporate a Power System Stabilizer function operating in conjunction with the Automatic Voltage Regulator/Exciter function to dampen local mode,inter-area and inter-unit power system oscillations. The exciter will consist of multiple thyristor power converters,each with its own digital firing control.Operator control will be provided through a local operator interface terminal,and the plant supervisory control and data acquisition (SCADA)system.Power to the exciter will be supplied via a power potential transformer powered from the generator bus.The exciter control channel will consist of microprocessor-based modules for digital sensing,regulation,silicon controlled rectifier firing control and sequence control algorithms.The cabinet lineup will include a logic cabinet and the required number of cabinets for the power converters and auxiliary devices. 10.22.Generator Step-up Transformers 10.22.1.General For optimum performance,the GSU transformer will be a dual rated transformer,and will have normal rating of 225 MVA,a base rating of 185 MVA and a rating of 230 MVA with increased cooling.The base rating will be with natural circulation of oil and air (ONAN)with an increased rating using forced oil and air (OFAF)circulation. Transformer design will be per the latest IEEE Standard C57 Series.The GSU transformer will be designed to withstand the sudden over excitation that can be produced when the transformer is separated from the line by the line breaker or other upstream device. 10.22.2.Ratings and Characteristics The transformer will have the following ratings: "Capacity 185/230 MVA at 60°C Rise »#Winding Temperature Rise by Resistance 65°C «Hottest Spot Winding Temperature Rise 80°C «Top Oil Temperature Rise by Thermometer 65°C "Type of Cooling ONAN/OFAF Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-238 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. =Impedance at 75°C,ONAN Rating TBD «Number of Phases 3 *Frequency 60 Hz =High Voltage Winding,Rated Voltage 230.00 kV «High Voltage Winding Connection Grounded Wye «High Voltage Winding BIL at Phase Terminal 900 kV «High Voltage Winding BIL at Neutral Terminal 550 kV =Low Voltage Winding,Rated Voltage 18kV =Low Voltage Winding Connection Delta «Low Voltage Winding BIL 150 kV «High Voltage Side Taps (2)+2.5%above 230.00 kV,(2)-2.5%below 230.00 kV 10.22.3.Tank The transformer tank and cover will be of welded construction,and such that the cover may be removed and rewelded without damage to the core and coil assembly.The transformer will be designed,where possible,so that components can be maintained without personnel entering the enclosed space of the tank.Access portals for essential maintenance and inspection will be provided as required.The transformer will have pulling eyes that are unobstructed by accessories to allow the transformer to be pulled in both directions. 10.22.4.Base The transformer tank base will be designed to permit skidding on rollers in both directions and anchoring to a concrete foundation by welding/bolting to embedded steel angles or channels. 10.22.5.Core Assembly The transformer will be designed and constructed either as a core-form or a shell-form type assembly.Exciting current for the core assembly will not exceed 0.5 percent of the rated current at rated voltage.The temperature rise limits will not be exceeded under the condition of maximum MVA with power factor of 0.80 and 105 percent voltage on the loaded winding. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-239 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.22.6.Winding Winding conductor will be copper.All windings will be a circular design.Individual conductors of the high and low-voltage windings will be rectangular with rounded edges.The high voltage winding will be furnished with full capacity taps. 10.22.7.Bushings Bushings will conform to American National Standards Institute/Institute of Electrical and Electronics Engineers Standards and will be capable of carrying daily transformer overloads. Provisions will be made for connecting the isolated phase bus to the transformer low voltage bushings.A metal housing with flanges for terminating the isolated phase bus enclosure will be provided.Flexible braided copper bus connections will be provided for bolting the phase bus bars to the transformer bushings. Each high voltage bushing will be furnished with one multi-ratio bushing current transformer with current ratios and accuracy class as required.Each current transformer will have a four- section winding with each winding section distributed along the full length of the secondary core to provide the tap ratios and accuracy classification required. 10.22.8.Surge Arresters The transformer will be protected against surges on the high voltage windings by means of surge arresters.Surge arresters will be gapless metal-oxide station class suitable for operation on a solidly grounded neutral system for protection of the windings at the specified nominal and maximum line-to-line voltages and the insulation BIL rating. 10.22.9.Accessories Temperature indicating and control equipment will be located not more than six ft.above the base of the transformer.Indicators (dials),thermometers,and relays will be constructed and located in such a manner that the temperature sensing portions can be removed from the transformer with the transformer energized. The transformer will be equipped with the following devices: =Magnetic Liquid Level Gauge «Rapid Pressure Rise Relay ="Mechanical Relief Device Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-240 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. *Liquid Temperature (top oil)Indicator =Electronic Temperature Monitor 10.22.10.0il Preservation System The transformer will include an oil preservation system of the atmospheric positive-pressure (sealed conservator)type with bladder,designed to prevent the oil from coming in direct contact with the air.The bladder membrane will prevent saturation of the oil with air.The oil connection to the main tank will be provided with a Buchholz-type (gas accumulation/excessive flow)relay. 10.22.11.Cooling System Heat-exchangers will be so designed that there will be no recesses or surfaces on which water can accumulate and so arranged that surfaces will be readily accessible for cleaning and repainting without removing the heat-exchangers from the tank.Construction will be galvanized steel flat-plate type arranged in groups or banks for attachment to the main tank. The heat-exchanger mounting flanges on the main transformer tank,both top and bottom,will be equipped with a butterfly valve to shut-off the oil flow from the main tank to the heat- exchangers.Drain valves and vent plugs will be furnished in the cooling system to permit draining oil from the heat-exchanger.Flexible connections will be furnished with pipe systems to minimize piping strains on coolers and to facilitate maintenance. Fan and pump motors will be furnished in a National Electrical Manufacturers Association frame size and equipped with sealed bearings.Fan and pump groups will have in-line starters.Each motor will be protected by internal overload elements in each ungrounded conductor.Each motor will be furnished with an electrical disconnecting means to allow removal from the circuit without affecting other motor(s)in the same cooling group.Cooling equipment controls will be mounted in the control cabinet. 10.23.Unit Protection and Control System 10.23.1.General The Protection and Control System (PCS)will be based on modern microprocessor based components networked together to provide a highly reliable system for monitoring and controlling the turbine-generator and associated plant equipment.Using software based technology for implementing the operating and monitoring functions allows for ease in Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-241 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. customizing the processes to fit specialized operating conditions,while also allowing for ease in making future changes. While the PCS components and software will be designed to provide options for individual local control or centralized (SCADA stations)remote control of each of the turbine-generator systems, optimum utilization of generation will be through centralized remote dispatch operation.The plant SCADA system will be designed to interface with the remotely located generation dispatch center. 10.23.2.System Configuration The PCS will be a programmable logic controller (PLC)based automation system with human machine interface (HMI)terminals for local monitoring and control.The PLC based system will be integrated with a plant SCADA system located in the Control Room.The PCS PLC based components will exchange information using a local area network (LAN).The LAN will transfer data over a fiber optic cable system using managed Ethernet switches for managing data traffic.The plant SCADA will be provided with a gateway connection into the LAN to monitor and initiate PCS automation functions.Access to the plant SCADA system from the remote dispatch center will be via a VPN connection to the plant LAN. To provide the high level of availability required by the various critical applications a Hot Standby system will be required for each of the PLC based automation systems.The "Primary” PLC will execute the application program and control the system Inputs and Outputs (I/O).The "Standby”PLC will stay in the background,ready to take over if necessary.The "Standby”PLC will be connected to the "Primary”PLC via a high-speed fiber optic link.This link will update user application data cyclically on the "Standby”PLC.The Hot Standby system software will provide a smooth changeover from primary to standby at the I/O system.The changeover process will be transparent,and will continue to be managed without any permanent ill-effects from the occurrence of inoperative hardware. A personal computer (PC)based SCADA system will be furnished to provide a centralized system (plant Control Room SCADA HMI stations)for monitoring and controlling the turbine- generator units and associated plant systems.SCADA servers will access the LAN through a secure gateway connection.PC HMI stations will be provided in the Control Room for accessing information from the servers and sending control initiating commands to the PCS PLCs.The SCADA software will generate HMI screens for use in monitoring the turbine- generator and plant systems and for initiating command signals for the PCS PLCs.When the plant SCADA system is in the "remote”mode of operation,generation control will be via the central dispatch center. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-242 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. A GPS satellite controlled clock with an IRIG-B unmodulated time code output will be provided. The IRIG-B time code will be used for providing accurate time stamping for all alarm and fault recording. All of the unit control systems will be designed for a "black-start”type situation.Critical systems required for unit starting will be supported by the station battery for a minimum of 8- hours upon loss of AC station service.Large AC station equipment and plant lighting will be supported by the standby diesel generator (32-hour local fuel supply).In the event that the transmission line system is down causing a loss of AC station service,it will be possible to start one of the units and operate locally in an islanded condition to provide local station service until the transmission line connection can be restored. 10.23.3.Unit Control Panel A Unit Control Panel (UCP)will be provided for each of the turbine-generator units.The UCPs will be located in the plant Control Room.The UCP will be provided with features for either manual or automatic control of the turbine-generator system.Each UCP will be provided with a HMI for control and monitoring of the turbine-generator system.The UCP will also be provided with features for remote control from the Control Room HMI Operator Stations.Each UCP will be provided with a Mode Selection switch (Manual-Auto-Remote)for selecting unit mode of operation.UCP operating modes will be as follows: 10.23.3.1.Manual Mode Control In Manual mode of operation the turbine-generator unit will be started,synchronized,connected to the system,and loaded using controls at the UCP.This control mode does not have automatic sequences;the operator will follow the standard manual operating procedures to start and connect the turbine-generator to the line.This mode of operation is typically used for maintenance and testing purposes. 10.23.3.2.Auto Mode Control In Auto mode of operation the turbine-generator unit will be started,synchronized,connected to the system,and loaded using the UCP automation systems.Single action start or stop commands will be made from the UCP Start-Stop switch or from the UCP HMI terminal.The UCP PLC system will be programmed and interconnected with the plant LAN system to implement the required process for automatically starting,synchronizing,connecting to the line,and loading the unit. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-243 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.23.3.3.Remote Mode Control This is the preferred method of operation and transfers turbine-generator system control from the UCP location to the SCADA HMI Operator Stations located in the Control Room.Control commands will be issued to the UCP from the PC based SCADA/Operator Station servers. 10.23.4.Control Room Operations The Control Room Operating Stations will permit centralized control of all units.The Control Room Operator Stations will be designed to initiate control functions on the units with their UCP in the "Remote”mode of operation.However,the Operator Stations will be able to monitor the systems under all UCP operating modes.The Operator Station HMIs will be provided with screens for displaying the required control and monitoring information.Standard SCADA software will be used to develop the required system screen displays.Interface with the HMI screens will be via standard PC keyboards and mouse.The Operating Stations will be configured to provide three automatic operating modes:Automatic Step-By-Step,Automatic Continuous,and Automatic Remote Dispatch.It is proposed that the normal mode of operation be Automatic Remote Dispatch. 10.23.4.1.Automatic Step-By-Step Sequence In this mode the unit starting and stopping sequences are executed step by step.All prerequisites and conditions will be displayed on the HMI screen and when all step prerequisites are met,the operator can then proceed to the next step.This mode is primarily used for trouble shooting and maintenance operations. 10.23.4.2.Automatic Continuous Sequence In this mode the unit start and stop sequences are initiated by the operator,but no additional operator intervention will be required.Once the process is initiated the unit will automatically sequence through all required steps.The operator will be able to monitor all conditions and actions on the Operator Station HMI screens.This will be the normal operating mode from the plant Control Room. 10.23.4.3.Automatic Remote Dispatch In this mode,a remote computer located at the generation dispatch center will be able to connect to the PCS and perform the same monitoring and control functions available at the plant SCADA Operator Station HMIs (based on security privileges).The remote connection will be encrypted using virtual private network (VPN)technology.When in this mode of operation the dispatch Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-244 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. operator will have full control of the unit generation,including starting,stopping and loading. This is the intended normal operating mode. 10.23.5.Unit Protection Unit protection panels will be provided for protection of the turbine-generator and GSU transformer systems.Multifunction microprocessor based generator and transformer protection relays will be provided.Each system will be fully redundant from the instrument transformers up through the protective relay.The relay trip signals will output to hand-reset type lockout relays (86-relay)for locking the systems out of operation.The relays will be provided with sequence of events recording retained in nonvolatile memory. 10.23.5.1.General Protection Features The generator protection relay will contain as a minimum the following protective features: *Loss-of-field detection «100 percent stator ground fault detection «DC field ground protection «Out-of-step protection =Over excitation detection based on volts/hertz measurement ="Negative-sequence overcurrent elements «Anti-motoring,over-power «"Two-zone mho phase distance,for backup protection »Phase over voltage =Phase under voltage «Supervision of voltage transformers *"Over-under frequency elements ="Phase current differential elements 10.23.5.2.GSU Transformer Protection Features The transformer protection relay will contain as a minimum the following protective features: «Percentage Differential Protection *Harmonic Restraint Elements Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-245 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT «Unrestrained Differential Protection for Severe Internal Faults =Overcurrent Fault Protection »Unit Breaker Failure Protection 10.23.5.3.Lockout Relays The unit protection system will be provided with manually reset unit lockout relays to facilitate proper shutdown and lockout of the unit upon sensing a fault condition.The lock out relays (86) will be electrically tripped,manually reset,high-speed multi-contact type with an operating time of approximately 1/2 cycle.Built-in coil monitoring will be provided. 10.23.6.Station Monitoring A Station Monitoring Panel will be provided for monitoring the station electrical and mechanical service equipment.The panel will use a hot backup PLC system connected to the LAN for gathering and processing the principle station service equipment.A HMI will be provided on the panel front for accessing status of the station equipment. The following station service equipment will be monitored: #Station 480V switchgear «Station battery system *Reservoir elevation =Tail water elevation «Fire alarm system «Intrusion »Station air system »Station sump 10.23.7.Instrumentation Cabinet A turbine-generator instrumentation cabinet will be provided at each unit for collection of the instrumentation signals associated with the turbine and generator assembly.The cabinet will use a PLC system for gathering the instrumentation signals and processing them for transfer to the LAN connected equipment.The temperature,pressure,position,and level signals monitoring the various systems will be collected at the PLC I/O.The signals will be sent to the UCP via the LAN for processing,alarming and monitoring. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-246 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.23.8.Distributed Input/Output Distributed I/O panels containing I/O and communication modules for collection of local /O instrumentation will be provided at major equipment locations.Collected I/O information will be transferred to the appropriate control and monitoring panels via the LAN.Distributed I/O panels will be provided at each of the GSU transformers and the 480V switchgear. 10.23.9.HMI Terminals 10.23.9.1.General In general,access to the system control and monitoring functions will be via HMI terminals located at the UCPs,Station Monitoring Panel,and the SCADA Operating Stations.The UCPs and Station Monitoring Panel HMIs will use color touch screens for accessing control and monitoring functions,while the Control Room SCADA Operating Stations will use LED widescreen monitors with keyboard and mouse interface. 10.23.9.2.UCP and Station Monitoring Panel HMIs The UCP and Station Monitoring Panel HMIs will be provided with a touchscreen interface for accessing system control and monitoring functions.Software configured graphic screens will be provided for displaying the monitoring and control information.The graphic symbols used for equipment that change operating state such as the generator,circuit breakers,valves,brakes, pumps,etc.will be color coordinated.The graphic symbols will show red when in their operating state (circuit breaker closed,pump running,valve open,etc.),and green when in non- operating state (circuit breaker open,pump stopped,valve closed,etc.). Each screen will be provided with a navigation bar with tabs for navigating to the various screens.Access to system control functions will be password protected to protect against unauthorized operations.The Overview Screen will have a location for entering the access password.The navigation bar will block access to secure screens until the proper password has been entered.All screens not password protected may be viewed by anyone,but all control functions will be blocked until the proper password has been entered and confirmed by the system.Access to the following screens and functions will be password protected: »Unit Control Screen ®Valve Control Screens #Alarm Acknowledge and Reset Functions Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-247 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT «Trending Screens «Alarm and Trip Set Point Screens An alarm banner will display on all of the screens at the initiation of an alarm condition.The alarm banner will remain until the alarm condition has been acknowledged via the Alarm Summary Screen. 10.23.9.3.Control Room SCADA Operating Station HMI Each of the Control Room SCADA Operating Stations will be provided with two LED widescreen monitors with keyboard and mouse interface for accessing system control and monitoring functions.Software configured graphic screens will be provided for displaying the monitoring and control information.The graphic symbols used for equipment that change operating state such as the generator,circuit breakers,valves,brakes,pumps,etc.will be color coordinated.The graphic symbols will show red when in their operating state (circuit breaker closed,pump running,valve open,etc.),and green when in non-operating state (circuit breaker open,pump stopped,valve closed,etc.). Each screen will be provided with a navigation bar with tabs for navigating to the various screens.Access to system control functions will be password protected to protect against unauthorized operations.The default,or Overview Screen,will have a location for entering the access password.The navigation bar will block access to secure screens until the proper password has been entered.All screens not password protected may be viewed by anyone,but all control functions will be blocked until the proper password has been entered and confirmed by the system.Access to the following screens and functions will be password protected: #Unit Control Screens »Alarm Acknowledge and Reset Functions »Trending Screens An alarm banner will display on all of the screens at the initiation of an alarm condition.The alarm banner will remain until the alarm condition has been acknowledged via the Alarm Summary Screen. As a minimum,each of the SCADA HMIs will be provided with the following screens for control and monitoring of the turbine-generator systems: #"Overview Screen «Unit Control Screens (one screen for each unit) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-248 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. »Unit Start/Stop Sequence Screens (one screen for each unit) *Governor Screen »Exciter Screen »Bearing Temperature Screens (one screen for each unit) =Generator Temperature Screen (one screen for each unit) »Alarm Summary Screen «Alarm History Screen «Trending Screens 10.24.Miscellaneous Mechanical Equipment The powerhouse will be provided with the following miscellaneous mechanical systems and equipment. 10.24.1.Powerhouse Bridge Crane One 300-ton capacity overhead traveling-bridge type crane will be installed in the powerhouse. The crane will be primarily used for installation of turbines,and other powerhouse equipment; and subsequent dismantling and reassembly of equipment during maintenance overhauls. The powerhouse crane will be electrically operated double girder,overhead travelling bridge type,equipped with a main hoist and trolley and auxiliary hoist.The auxiliary hoist will be trolley-mounted or under-hung from the bridge girder.Bridge,hoist,and trolley drives will be provided to facilitate equipment transport in vertical,lateral,and longitudinal directions.The capacity of the main hoist will be sufficient for the heaviest equipment lift,which will be generator rotor plus the lifting device.The crane will be provided with operator's can to permit operation of the crane. 10.24.2.Draft Tube Bulkheads Two sets of draft tube bulkheads will be provided to permit dewatering of the turbine water passages for inspection and maintenance of the turbines.Bulkhead guides will be installed at each draft tube openings.The bulkheads will be designed to withstand the full differential head. Each draft tube bulkhead will be sectionalized into two sections for the ease of transportation of bulkhead to the site.Each section will be approximately 26.5 ft.wide by 13 ft.high.Each bulkhead section will be of downstream sealing type and the transfer of the hydrostatic load from the two end posts of the leaf to the supporting structure will be through bearing pads mounted on Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-249 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT the end posts.Bulkhead sections will be installed and removed with a semi-automatic lifting beam connected to a draft tube gantry crane.Bulkhead sections will be installed and removed under near balanced head conditions.Fill valves,operated by the lifting beam,will be provided in the bulkhead to fill the void space in the draft tube. 10.24.3.Draft Tube Gantry Crane A 25 ton capacity electrical travelling gantry crane will be provided on powerhouse deck at EI. 1475 ft.for installation,removal,and handling of draft tube bulkheads. 10.24.4.Station Drainage System The powerhouse will be designed with a series of floor and trench drains to capture and route any water seepage or leakage.The drains will be routed to a central sump with an integral oil- water separator.The sump will be provided with two pumps to provide 100 percent redundancy for the design inflows.The pumps will pump the drainage water (after oil and other contaminants are separated out)to tailwater. 10.24.5.Unit Dewatering System Each unit will be dewatered to tailwater through the main turbine water passages.To completely dewater each unit (after the draft tube gates and intake gate or inlet butterfly valve are closed), water will be piped from the low point of each draft tube to a dewatering pump which will pump the remaining water to the tailrace.After dewatering is complete,any leakage into the turbine water passages will be routed to the station sump and handled by the station sump pumps. 10.24.6.Station Raw Water System The powerhouse will be provided with a raw water system.The system will either include a tap off each unit penstock,with a pressure reducer to reduce the penstock water pressure to 100 psi or less,or the water will be pumped from the tailrace to the required system pressure.Both systems would include redundant strainers at the system inlet to eliminate particulates and debris. Economic life-cycle cost analyses will determine which design concept is the lowest cost. Piping inside the powerhouse will distribute the water to suitable locations for general station use. The raw water system will also be the source of water supply to the generator coolers,unit bearing coolers,and turbine shaft seal water.All these will be open-loop systems discharging to the tailrace.A secondary fine filter will be added to the shaft seal water supply to meet the cleanliness requirements of that water supply. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-250 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.24.7.Compressed Air System The powerhouse will be provided with a compressed air system for general station use and for the generator brakes.The system will consist of redundant compressors,an air dryer,an air receiver tank,distribution piping,and quick disconnect couplings in locations where pneumatic tools may be used. 10.24.8.HVAC Systems The powerhouse will be provided with heating equipment to maintain suitable interior temperatures for worker comfort.Distributed electrical heaters will be the primary heating sources and using generator waste heat will be considered during detailed design.Forced air ventilation will be provided to all locations in the powerhouse,with the specific ventilation requirements determined for applicable ASHRAE codes.In addition air conditioning (cooling plus humidity control)will also be provided in the main control room,offices,and other spaces where workers will be routinely located. 10.24.9.Standby Generator A diesel-powered standby generator will be located in an alcove in the powerhouse access tunnel.The generator will be used for black starts and for operation of the spillway gates and other equipment during a power failure. 10.25.Accessory Electrical Equipment The powerhouse will be provided with the following accessory electrical systems and equipment. 10.25.1.Powerhouse Alternating Current System The powerhouse will be provided with a distributed alternating current system to provide electrical power for the electrical equipment and miscellaneous system use.The system will be fed though redundant 13.8 kV/480V dry-type station service transformers that can be fed either from a generating unit or backfed from the Railbelt system through one of the generator step-up transformers.The system will distribute 480V AC power to the station motor control centers and other individual electrical demand sources.The system will also include step-down transformers to 120 VAC and a 120V distribution system for lighting and general station uses. 10.25.2.Powerhouse DC System The powerhouse will be provided with a 125VDC system to power essential equipment when AC power is lost.The system will consist of a battery bank,redundant chargers,and a DC distribution system. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-251 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.25.3.Powerhouse Lighting The powerhouse will be provided with a lighting system to light all areas where workers may be located.Lighting types and lighting levels will be selected based on location,occupation levels, and specific lighting requirements. 10.25.4.Powerhouse Grounding System The powerhouse will be provided with a comprehensive grounding system consisting of a ground grid inside the powerhouse and a grounding field located and sized to provide an acceptably low ground potential to the grounding grid.All equipment and ferrous metal elements will be connected to the ground grid.Grounding terminals will be provided at locations where workers may use electrical equipment that should be grounded. 10.26.Switchyard Structures and Equipment 10.26.1.Switchyard Arrangement The switchyard will be a breaker-and-a-half arrangement with three bays and space for a future fourth bay.This configuration provides two normally energized main buses interconnected with three circuit breakers in each bay.Between each pair of bay breakers a circuit is provided (total of two circuits per bay).Each of the three bays provides two circuits,one circuit connects to one of the GSU transformers and the other provides a line connection to the transmission grid.The breaker-and-a-half configuration was chosen because of its high reliability and flexibility. Advantages include: =Isolation of either main bus for maintenance without disrupting service; «Isolation of any circuit breaker for maintenance without disrupting service; *Double feed to each circuit; *Bus fault does not interrupt service to any circuit;and, #All switching done with circuit breakers. Connection of each bay to the GSU transformers will be via a 230 kV overhead transmission line.A total of three transmission lines,with space for a fourth line,will be routed from the switchyard to the GSU transformers located on the powerhouse draft tube deck,and anchored to the downstream face of the dam or steel tower anchorages as appropriate.Three overhead 230 kV transmission lines will exit the switchyard with two connecting to the Gold Creek intertie and one to the Denali East intertie (arrangement selected for the cost estimate). Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-252 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.26.2.Circuit Breakers The circuit breakers will be sulfur hexafluoride (SF¢)type breakers with dead-tank construction. Because of the low ambient temperatures experienced at the switchyard,the breakers will be provided with tank heaters to maintain the required SF¢insulation levels.Bushing type current transformers will also be furnished to interface with the switchyard protection and control system. The circuit breaker will have the following ratings and characteristics: #Rated Nominal Voltage 230 kV »Rated Maximum Voltage 245 kV *Rated Frequency 60 Hz *Rated Continuous Current 1200 Arms *Rated BIL 900 kV «Rated Short-Circuit Current TBD =Max.Symmetrical Interrupting Capacity TBD «Interrupting Time 3 cycles Each circuit breaker will be provided with a three-pole,gang operated disconnect switch on the incoming and outgoing terminals of the circuit breaker. 10.26.3.Instrument Transformers Voltage transformers will be provided for monitoring the voltage at the two main buses and at each line circuit termination.Capacitive coupled type voltage transformers will be used. 10.26.4.Bus,Overhead Lines and Structures Aluminum tube bus will be used for overhead distribution with flexible type connector at equipment connections.Galvanized steel support structures with station post type insulators will be used for supporting the bus. Galvanized steel tower supports will be used for supporting the 230 kV lines entering and exiting the switchyard.Each of the 230 kV lines will be provided with gang operated isolating switches and surge protection.Grounding switches will also be provided for each of the 230 kV lines Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-253 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 10.26.5.Grounding The switchyard will be provided with a ground grid designed to limit step and touch potential to safe values.The ground grid will be designed using the latest IEEE 80 and IEEE 81 Standards. All steel structures and fencing will be bonded to the ground grid.It may be necessary to use chemically enhanced ground rods to reduce the grid-to-earth resistance to an acceptable value. 10.26.6.Control House A control house will be provided to house the switchyard protection and control equipment, along with their required support systems.It is proposed that a prefabricated modular control house be provide.The control house will house the following: *Switchyard Protection and Control Panels »Switchyard Battery and Battery Charger »Station Service Distribution Equipment 10.26.6.1.Protection and Control Panels The protection and control panels will be PLC based with microprocessor type multifunction protection relays and HMI type interface.Provisions will be made for either local manual control of the circuit breakers,remote control from the powerhouse,or remote control from the dispatch center.Standard line protection relaying will be provided for the 230 kV transmission lines.A dedicated fiber optic communication link will be provided between the switchyard and powerhouse to integrate the GSU transformer protection with the required switchyard circuit breaker tripping. A local SCADA system,similar to that used at the powerhouse will be provided at the switchyard.Desk-top operator terminals will be provided for monitoring the switchyard equipment status and for control of the circuit breakers.A server will be provided for storing alarm and operation information. 10.26.6.2.Station Service Two station service transformers will be installed to provide 480V AC station service for the contro!house.The transformers will be connected to the switchyard's two main buses. Automatic switching at the 480V service will be provided to maintain station service in the event one of the switchyard main buses needs to be de-energized.Small distribution transformers will also be provided for lighting and other small 120V loads. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-254 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. A lead acid,wet cell type battery with charger will be provided for operation of the switchyard circuit breakers and provide critical power for the control and protection systems. A small standby generator will be provided to furnish backup AC station service in the event of an extended line outage.The standby generator will be sized to support the battery system and critical heating loads to protect the control house equipment during cold weather. 10.27.Reservoir 10.27.1.Reservoir Clearing It has been assumed that complete reservoir clearing will not be undertaken.Complete clearing will only be performed for the first 3.5 miles upstream of the dam.Further upstream,the remaining reservoir perimeter will be cleared 200 ft.below the normal maximum water surface elevation. 10.28.Relict Channel Treatment During this stage of the feasibility investigation,no work has been performed with respect to the relict channel that exists on the north bank of the Watana reservoir approximately 2,600 ft. upstream from the dam.Future geotechnical studies will revisit the feature and further site investigation will be carried out.At this stage,the results of the investigations carried out during the 1980s are repeated for clarity. The relict channel runs from the Susitna River gorge to Tsusena Creek,a distance of about 1.5 miles.The surface elevation of the lowest saddle is approximately El.2210 ft.Glacial deposits of depths up to 454 ft.have been identified.The maximum average hydraulic gradient along any flow path in the buried channel from the edge of the reservoir NMOL (El.2050 ft.)to Tsusena Creek is approximately two percent.Tsusena Creek at the relict channel outlet area is at least 120 ft.above the natural river level.There are several surface lakes within the channel area,and some artesian water is present in places.Zones of permafrost have also been identified throughout the channel area. To confirm the integrity of the rim of the Watana reservoir and to control losses due to potential seepage,a number of conditions were evaluated in the 1980s.Studies covered settlement of the reservoir rim,subsurface flows,permafrost,and liquefaction during earthquakes. 10.28.1.Surface Flows Based on information gained from past exploration programs,the relict channel soils are either dense or cohesive and as such are not deemed to be subject to settlement resulting from seismic Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-255 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT shaking.Therefore,the low ground surface in the relict channel area will provide more than adequate freeboard as it is 135 ft.above the dam crest. 10.28.2.Subsurface Flows The potential for progressive piping and erosion in the area of discharge into the Tsusena Creek will be controlled by the placement of properly graded granular materials to form a filter blanket over any zones of emergence.Field investigations will be carried out to further define critical areas,and mitigation measures will be developed.Subsequent to construction of the dam,the relict channel will be continuously monitored at the outlet area after reservoir filling to verify that a state of equilibrium is established with respect to permafrost and seepage gradients in the buried channel area. 10.28.3.Permafrost Thawing of permafrost will occur in portions of the relict channel area.This thawing is expected to have minimum impact on subsurface flows and ground settlement.Although no specific remedial work is foreseen;flows,groundwater elevation,and ground surface elevation in the buried channel area will be carefully and continuously monitored by means of appropriate instrumentation systems and any necessary maintenance work carried out to maintain freeboard and control seepage discharge. 10.28.4.Liquefaction Underground information compiled in the 1980s indicates that the buried channel area is filled with outwash,glacial till and lacustrine deposits.Initial evaluations,outlined in the original license application indicated concern with regard to the upper outwash deposits because they did not appear dense enough to resist seismic shaking without experiencing considerable loss in stability. The most likely prospects for liquefaction are saturated foundations consisting of fine grained, poorly graded,cohesionless deposits (sands and silts),that are not laterally confined and are loose or moderately dense.Based on available data,an assessment of the liquefaction potential of the relict channel area indicates the deposits are either well graded,dense to very dense,or cohesive,and therefore,have low potential for liquefaction.Consequently,no remedial measures are currently considered necessary as a precaution against the effects of liquefaction. Further geotechnical studies will be carried out to fully define the extent and characteristics of the materials in the relict channel.Should these studies indicate that mitigation is required, provisions will be made for treatment to cover the conditions identified. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-256 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 10.28.5.Remedial Work Influence on Construction Schedules Relict channel remedial treatment construction work,if necessary,will have no impact on the Watana Dam construction schedule. 10.28.6.Relict Channel Treatment During future design investigations,additional boreholes and inspection trenches will be employed to further delineate the relict channel foundation.The area will also be thoroughly monitored by observation during reservoir filling to assess actual hydrological conditions in the relict channel.In response to the unlikely event that construction remedial measures are considered necessary following those observations and data assessment,a positive remedial treatment such as a downstream toe drain will be employed. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 10-257 December 2014 Section 11 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 11.TRANSMISSION AND INTERCONNECTION FACILITIES Three transmission line corridors have been investigated in this report,but no route (or routes)has been recommended.One of the five possible configurations has been used for the sole purpose of cost estimating. This section provides a description of the proposed transmission and interconnection facilities and the factors that were considered in selecting the preliminary designs for the major features. The main project dam and powerhouse features and site infrastructure are described in Section 10;site access roads important to transmission line construction and maintenance are described in Section 8. 11.1.Electric System Studies 11.1.1.General The transmission studies performed were to identify possible transmission interconnections from the Susitna-Watana Project site to the electrical transmission system of the Railbelt (which itself is expected to be improved before the projected completion of the project).The studies were also used to assess system improvements to the Railbelt electrical system that may be required - in excess of other required improvements -specifically to accept generation from the Project.In particular there was a focus on examining any further system improvements necessary to accommodate 200 megawatts (MW)units at Susitna-Watana Project,rather than 150 MW units. A more extensive discussion on the choice of unit size is included in Section 7. 11.1.2.Transmission Study Assumptions The Railbelt electrical system -to which the project will connect approximately midway between Anchorage and Fairbanks -currently consists of a single transmission line between Anchorage and Healy (with two lines between Healy and Fairbanks),as well as a single line between the Kenai Peninsula and Anchorage.These single lines are a constraint and limit the transfer between both areas to approximately 60-80 MW of non-firm power between any of the areas.The Railbelt Utilities and the State of Alaska are in the process of developing a transmission plan to promote energy transfer and improve the reliability of the electrical transmission system.The plan identifies needed upgrades to the transmission system,whether the Susitna-Watana Project is implemented or not.The projected improvements would eliminate the single contingency lines between the Railbelt areas and allow total hydro coordination among all resources in the Railbelt.The studies for the Susitna-Watana Project interconnection assume the improvements required in the Railbelt for energy and reliability have been completed by Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-1 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 2025,and are therefore in service and available for use in the transfer of Susitna-Watana Project energy throughout the Railbelt. The exact electrical and mechanical characteristics of the Susitna-Watana Project generators were not known at the time the initial system planning studies (described in this section)were performed.Representative unit parameters used in the studies were assumed from similar sized units at other projects.The system planning studies will be updated at the time of detailed design. 11.1.3.Study Criteria The planning criteria for the Railbelt system includes desired operating parameters for both steady-state conditions as well as transient conditions.The planning criteria are divided into four main areas;reliability,power flow,stability,and voltage,and are discussed in detail below. 11.1.3.1.Reliability The ultimate goal of any planning criteria is to provide the desired level of reliability at a cost the system can afford.For islanded systems this level of reliability is often less than large interconnected systems due to the evaluation of reliability against the costs required to obtain the same level of reliability standards in the Lower 48.For the Susitna-Watana Project,the interconnecting transmission system was planned to withstand the loss of any single contingency item without experiencing a loss of firm load on the Railbelt system for transmission system contingencies and to result in no more than the first stage of under frequency load shedding for Susitna-Watana generation contingencies. The planning criteria used to evaluate the impact of the Susitna-Watana Project are outlined below. 11.1.3.2.Power Flow The power flow criterion includes limits on voltage levels as well as branch flow levels for the Railbelt during steady state conditions.The power flow criterion is listed below and was used for normal (all equipment in service)and N-1 (single outage)contingency analysis: =underground works (tunneling); =Flows on transmission lines below their megavolt-Ampere (MVA)rating (winter or summer);and, =Flows on transformers below their maximum MVA rating. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-2 December 2014 Za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The Railbelt system experiences large temperature swings between the winter and summer seasons.These changes in temperature require the power flow analysis to use the appropriate conductor rating for the specific temperature (load)season. It is assumed that short term thermal overloads are acceptable if planned remedial action schemes (generation dispatch changes,non-firm energy contract reductions)are designed to minimize and or eliminate the overload. 11.1.3.3.Stability The transient stability criteria include limits on the system frequency,voltage levels,system response,and unit response.The transient criteria listed below will be used for N-1 contingency analysis. «Sustained voltages on the transmission system buses must not be below 0.8 per unit (pu); #Frequency must stay between 57 hertz (Hz)and 62 Hz (trip limits); «System response must not exhibit large or increasing amplitude oscillations in frequency or voltage; «Units must not exhibit out of step or loss of synchronism response;and, #Single contingency events cannot cause uncontrolled load shedding. It is not acceptable to operate the system in a configuration that would result in unstable system response for single contingencies.Therefore,infrastructure improvements or operational constraints must be completed/implemented to eliminate the possibility of an unstable condition occurring. 11.1.3.4.Voltage The criterion to be applied includes limits on the maximum and minimum voltages allowed on the Railbelt system as well as operation limits of the generators and the Static Var Compensators (SVCs).The criteria are listed below: «Voltages at 230 kilovolt (kV),138kV undersea cables must be below 1.02 pu; »Voltages at 230 kV,138 kV,and 115 kV substations serving load must be below 1.05 pu; *Voltages at 230 kV,138 kV,and 115 kV substations NOT serving load must be below 1.10 pu; =Voltages at 230 kV,138 kV,and 115 kV substations must be above 0.95 pu; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-3 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «High Voltage limits must be met with online generators operating at unity power factor; and, *Voltage limits must be met with SVC's operating with a minimum five MVA report of margin. As with the stability criteria,it is not acceptable to operate the system in a configuration that would result in the system violating the voltage criteria.Therefore,infrastructure improvements or operational constraints must be completed/implemented to eliminate the possibility of an unstable condition occurring. 11.1.4.System Study Methodology The studies for the interconnection of the Susitna-Watana Project were completed using the Utility supplied loads and generation schedule expected to be in place in the year 2024.As noted above the Railbelt transmission system is expected to undergo substantial changes from its existing configuration to the 2025 system configuration.These changes are required to alleviate the restrictions on Bradley Lake and Cooper Lake energy and increase reliability and transfer capacity between the load/generation areas of Kenai Peninsula,Anchorage/Mat-Su,and Fairbanks,as identified by the current State of Alaska and Utility transmission plan.This "pre- Watana”improved transmission system is expected to be in service by 2025,and was the starting point for the Susitna-Watana studies. The Susitna-Watana studies can be divided into two distinct categories: «Transmission system analysis required for the Susitna-Watana interconnection with the Railbelt electrical system;and, «Unit sizing studies designed to evaluate the system impacts resulting from two different unit sizes for the Susitna-Watana Project. 11.1.4.1.Transmission System Analysis The transmission system studies evaluated the transmission infrastructure requirements for interconnection of the Susitna-Watana Project and the Railbelt system based on the planning criteria listed above.The studies consisted of utilizing single contingencies (N-1)for both transient (stability)analysis and steady state (power flow)analysis. 11.1.4.1.1 Stability Analysis Stability analysis consists of applying faults to the transmission lines both in the project area and at key points in the Railbelt transmission system.The faults were applied and subsequently cleared by opening the faulted line section.The stability of the transmission system was then Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-4 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT evaluated by plotting various generator rotor angles relative to each other and the system frequency. The stability analysis was used to determine the sensitivity of the system response to clearing times of the Susitna-Watana interconnection,and to determine the required transmission infrastructure to ensure stable Railbelt system operation following the addition of Susitna- Watana.Analysis was completed to determine the impact of utilizing Power System Stabilizers for the Susitna-Watana units,and to determine the feasibility of utilizing SVC to reduce the required transmission infrastructure. 11.1.4.1.2 |Reactive Support Analysis Reactive analysis was completed to determine if the feasibility of line energization utilizing support from Susitna-Watana units as well as the ability of the Railbelt system to maintain voltages during low Susitna-Watana output conditions. 11.1.4.1.3.Power Flow Analysis Power flow analysis was completed for the different load season cases to determine if single contingencies during high Susitna-Watana output would result in thermal overloads of transmission lines or transformers. 11.1.4.2.Unit Size Analysis As input to the final choice of unit size,the unit sizing studies focused on the requirement for transmission system improvements for a nominal 150 MW generator and for a nominal 200 MW generating unit.These potential improvements relate to any necessity for stored energy devices at various places in the Railbelt to accommodate Susitna-Watana unit sizes and characteristics. The thrust of the unit sizing studies were centered on simulating the loss of a Susitna-Watana unit on the Railbelt transmission system under various total loading conditions and to determine if there were any differences between the unit sizes for various transmission line faults.The proposed generator sizes are considerably larger than units that will exist in the Railbelt in the 2025 time frame.These proposed larger units would put strain on the Railbelt system if tripped when operating under full load,requiring mitigating measures to be implemented.These studies were intended to evaluate the costs of the mitigating measures of the large unit sizes. In general,when electrical systems suffer load or generating conditions that result in a severe mis-match between load and generation,the response is to shed load to stabilize the system.The under frequency load shed (UFLS)scheme in the Railbelt is designed with multiple stages of decreasing frequency set points.The first stage of UFLS activates at 59.0 Hz,with the second, third,and final stages activating at 58.7 Hz,58.5 Hz,and 58.2 Hz,respectively.When the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-5 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years, system frequency drops below these set points,the load shed relays will activate (after a short timer delay)and shed load.The first stage of UFLS results in approximately 10 percent of the load in the Railbelt being shed or turned off to help stabilize the system.If all stages of UFLS were activated,approximately 75 percent of the Railbelt Consumers would be without power. The studies of Susitna-Watana attempted to determine the mitigating measures that would be required to limit the loss of load in the Railbelt system to its first stage of UFLS following the loss of a Susitna-Watana generating unit -similar to the conditions that exist prior to construction of Susitna-Watana. 11.1.5.Results The system studies indicate that the Susitna-Watana Project can be integrated into the planned upgraded Railbelt transmission infrastructure with few transmission improvements required specifically to accepting Susitna-Watana energy (i.e.,outside the immediate project area).In general,the difference in unit sizes has no appreciable impact on transmission line faults,but both units require additional energy storage within the Railbelt to prevent load shedding in excess of the "first stage”situation (currently existing)if a unit is lost at maximum output. 11.1.5.1.Transmission Infrastructure As discussed later,there are a number of possible configurations of transmission interconnection with the Alaska Intertie.At a minimum,however,for evacuation of energy from the project to the interconnection(s)with the Alaska Intertie,the Project will need to include the following: *New Susitna-Watana 230 kV substation »Gold Creek substation operated at 230 kV -New Gold Creek -/+150 MVA report SVC -4cycle Susitna-Watana -Gold Creek clearing times »Three 230 kV transmission lines,double bundled Rail conductor,from the Project to the Intertie =Power System Stabilizers on all Susitna-Watana units =Healy -Gold Creek -Douglas lines operated at 230 kV «Teeland -Douglas 138 kV line converted to 115 kV operation During summer loading seasons,where the transmission line ratings are reduced due to higher ambient air temperatures,single contingencies can result in thermal overloads of transmission Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-6 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT lines during transfers south of Douglas greater than 500 MW.Reducing Susitna-Watana transfers to the south to a total of 310 MW will eliminate the overload conditions. 11.1.5.2.Energy Storage The sizes of the proposed project units considered early in the feasibility study (nominal 150 MW or 200 MW (at average water level)-which represent a peak of 200 MW or 275 MW respectively at maximum normal operating level)are substantially larger capacity than any generator in the Railbelt system.Although later proposals -discussed in Section 7 -are for turbine units of 206 MW rated at normal maximum operating level,they are still the largest units of the system.The analysis indicates that a trip of one of these projected unit sizes (operating at full output)will need to be compensated (to control subsequent load shedding to that experienced prior to Susitna-Watana)by the addition of an Energy Storage System (ESS)at specific locations within the Railbelt.The ESS can be comprised of batteries,fly wheels or other storage technologies.Such systems -whether batteries or fly wheels -are modular and can be scaled to high power levels,whether centralized or distributed.The energy storage will be required to feed power into the system and thus maintain the system frequency while other units on the system -that are providing spinning reserve -are brought on line.Based on simulations,the ESS will be required to go to full output in as little as one second.Therefore,for a recommended ESS of 100 MW,the ramp rate required would be 100 MW per second.The ESS would stay at this high level until other units at Susitna-Watana or elsewhere in the Railbelt could ramp up to replace the energy of the ESS. The maximum requirement for the ESS was determined by a worst case study that assumed one Susitna-Watana unit was operated at full load,while the remaining Susitna-Watana units are at minimum load or off-line.This operating condition would likely never occur in the plant's operation,but does outline the boundary case for the amount of required ESS for the Susitna- Watana units.In actual practice the units would likely be more evenly loaded,reducing the unit's loading to a much lower level than in the study. Hydro units are often operated "part gate”allowing very fast response to low frequency conditions,with typical ramp rates of 10 MW per second.The fast response of the Susitna- Watana units would replace the power provided by the ESS very quickly,but requires reserving part of the unit rating as "spinning reserve.” 17.1.5.2.1 4x 150 MW Units For the worst possible case to limit load shedding to first stage conditions existing today and with Susitna-Watana comprised of approximately 150 MW units requires the following: Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-7 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «#Summer minimum load 120 MW ESS «=Summer peak load 100 MW ESS »Winter peak load 80 MW ESS A total of 100 MW of ESS is recommended to mitigate the UFLS action to a stage 1 event.The mitigation will limit the UFLS to a Stage 1 event for winter and summer peak load conditions. Summer valley conditions may reach stage 2 UFLS with the 100 MW ESS recommendation, however a dispatch scenario that would provide a potential for a 200 MW unit trip is most likely not practical.To stress the system (for the model),a dispatch of one unit at 200 MW with the remaining two units dispatched to 50 MW (300 MW total plant output)was used.In actual practice,it is unlikely the units would have such a large disparity between loading amounts -as good practice is to run units at approximately equivalent output.A 20 MW battery energy storage system (BESS)is required during the typical summer loading period. The amount of energy storage required for the 100 MW ESS depends upon the speed of the spinning reserves and the time it will take to displace the power provided by the ESS.Assuming there is enough capacity on the Susitna-Watana units to displace the ESS,and the units will respond seven seconds after an event with a ramp rate of 10 MW per second (requiring 10 seconds to increase output 100 MW),the total energy requirement of the ESS will be approximately 0.0079 MWh.This is a very small energy requirement,due to the Susitna- Watana plant requiring a maximum of 17 seconds to displace the ESS. 11.1.5.2.2 3x 200 MW Units For the worst possible case to limit load shedding to first stage conditions and with Susitna- Watana comprised of 200 MW units requires the following: »Summer minimum load 180 MW ESS »Summer peak load 150 MW ESS #Winter peak load 120 MW ESS This is a nominal increase in compensation requirements over the smaller 150 MW units.The ESS will require further review and study,however the technology and maturity of the technology provide a high degree of confidence in the proposed solution. The amount of energy storage required for the 180 MW ESS depends upon the speed of the spinning reserves and the time it will take to displace the power provided by the ESS.Assuming there is enough capacity on the Susitna-Watana units to displace the ESS,and the units will respond seven seconds after an event with a ramp rate of 10 MW per second (requiring 16 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-8 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT seconds to increase output 90 MW each),the total energy requirement of the ESS will be approximately 0.0153 MWh. 11.1.5.2.3 Railbelt Transmission Plan ESS The recently completed draft Railbelt Transmission Plan recommended a 25 MW ESS to mitigate issues on the Railbelt without the Susitna-Watana Project online.These studies assumed the 25 MW ESS is built and can be utilized for the Susitna-Watana Project,limiting the size of additional energy storage due to the Susitna-Watana Project to 75 MW if Susitna-Watana incorporates 150 MW units. 11.1.5.3.Energy Storage Locations The location of the ESS does not impact the ability of the chosen storage to provide support to the system for the loss of a large Susitna-Watana unit trip.Other benefits to the system that are beyond the scope of this study could be realized by splitting the total ESS system into different areas of the Railbelt,and may drive the location of and optimization of the ESS.Locating a portion of the ESS on the Kenai Peninsula would allow total hydro-hydro coordination between the hydro resources of the Kenai Peninsula and the Susitna-Watana Project.The ESS would eliminate generation restrictions on the Kenai Peninsula by providing an energy resource to stabilize the Kenai Peninsula system following loss of one of the Kenai Peninsula -Anchorage transmission lines.Stabilization would be provided by the ESS until Kenai Peninsula generation could be dispatched on the system.Studies indicate a minimum of 20 MW ESS would be required on the Kenai Peninsula to provide stabilizing support. Locating a portion of the ESS (approximately 30 MW)in the GVEA area near the North Pole Station would allow the system to support large motor cycling for existing and future mine or industrial loads without additional Fairbanks area generation or transmission improvements. Siting the remainder (approximately 25 MW)of the ESS adjacent to the 25 MW ESS in the Anchorage area would increase the transfer capability of the Kenai Peninsula -Anchorage system and eliminates import restrictions into the Anchorage area.Elimination of import restrictions would allow full Kenai Peninsula hydro-hydro and thermal generation coordination with the Susitna-Watana Project. 11.1.6.Future Studies The studies of the units rated at average head indicate that the smaller 150 MW project units require less extra infrastructure (SVCs,BESS,or Flywheels)than the larger (200 MW)units to maintain stability throughout the Railbelt system;however,the incremental increase in cost of the required infrastructure relative to the total cost of the project is relatively small between the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-9 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. two unit sizes and the differences between the two proposed unit sizes do not present any large cost increases or system implementation issues.Discussion of all the costs associated with unit sizing are contained in Section 7 of this report.The revised proposal -for 206 MW turbine rated at normal maximum operating level -approximates to the units studied in this evaluation (150 MW at average head). Future studies will further refine the impacts of unit size and plant configurations.The preliminary studies reported herein used a wide range of possible energy transfers for the Northern and Southern utilities to evaluate the electrical transmission system.Future studies will concentrate on the actual proposed energy split between the Northern and Southern systems based on the maximum expected capacity of each respective system and the transmission requirements of the final energy flow.The studies will confirm any additional infrastructure that is required for transmission line faults and or unit trips to provide acceptable reliability and service characteristics. Future studies will also identify the proposed sizing and location of the energy storage devices on the Railbelt as well as refine the system studies once more information is known regarding the actual Susitna-Watana generating unit characteristics.Future studies will also provide a more detailed analysis of the system response to an expanded list of transmission contingencies, including breaker-failure and N-1-1 contingency analysis. The future studies will also need to analyze the response of the Railbelt system units,such as Bradley Lake,to the proposed Susitna-Watana Project in addition to the response of the project to the interconnected system. 11.2.Corridor Selection 11.2.1.General Preliminary studies indicate that to transmit a peak generation of approximately 600 MW from the Project,three 230 kV transmission lines will be required to connect to the Railbelt interconnected system.The Project will provide power to the Fairbanks area to the north and to the Anchorage/Mat-Su/Kenai Peninsula areas south of the project.At the time of assessing transmission alternatives for the project,it was assumed that a maximum of 200 MW of capacity will be supplied north and 500 MW will be shipped south,although not simultaneously. The corridor selection studies have been described in detail in the Watana Hydro Transmission Corridor Report prepared by EPS and included as Appendix B9. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-10 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Three corridors have been identified in which the new transmission lines could be constructed to connect the project with the existing Railbelt transmission system.The corridors generally follow the same corridors selected for study for the access road,so that significant portions of the transmission facilities can be constructed using the project access.The transmission corridors are shown in Figure !.1-1. It may be beneficial to the reliability of the Railbelt system that power is evacuated from Susitna- Watana through two corridors (rather than in a single corridor),and if such an option is finally selected,one of the lines will have to be constructed by helicopter,which would increase the cost of that line (or lines). In particular areas,the selected transmission route diverges from suggested road alignments, either to take advantage of a straighter route (where road construction would be difficult or impossible)or to avoid high altitude.Such deviations may require some helicopter construction. Three circuits could be constructed in one corridor or -if a split evacuation is selected -in combination with a second corridor.The selected alternatives for consideration,therefore, included three routes with all circuits in the same corridor,and two alternatives with the circuit split between corridors. The examination of corridors has required consistent criteria as discussed below. 11.2.2.Evaluation Criteria The criteria below describe the differences between routes and the level of suitability to meet the purpose and needs.They are not being used to eliminate routes at this stage,but have been used in development of the routes,in parallel with the access road route derivation.The following describes the evaluation criteria: «Adjacent to an Access Road -This is significant to the construction cost ofthe line. "Avoid Land Use Conflicts -Used to exclude areas that could provoke major conflicts in land use (i.e.,airports,dedicated recreation areas,and densely populated areas). ="Avoid Major Terrain Obstacles -Used to exclude areas that could cause significant construction and/or major difficulty in construction or maintenance (i.e.,large rivers, mountains,high value wetlands,ponds,and lakes -landslide prone areas). «Avoid Particular Land Ownership -If the transmission were to utilize a corridor in Bureau of Land Management land,the whole project could be subject to additional permitting and regulation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-11 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. *Minimize Climatological Conditions --Alaskan climatological conditions are significantly influenced by elevation and the higher elevations produce more severe conditions,such as snow accretion,avalanche,icing,and wind.As a result,routes are selected that primarily avoid higher elevations.Maximum corridor elevations are approximately: Chulitna El.3400 ft. Gold Creek El.2400 ft. Denali El.3800 ft. As a comparison,the Anchorage/Fairbanks Intertie in this region reaches an elevation of about 3,000 ft.and has exhibited a good performance record. ="Minimize Route Distance -Used to minimize route distance and decrease the total cost of the project. *Minimize Environmental Impacts -This aspect of selection is complex with many attributes.For the current level of this study,the avoidance of wetlands that can be determined from aerial photographs was the only criterion used.The width of the proposed corridors is expected to be sufficient to adjust the detailed transmission line route in response to field studies that will be undertaken.The adjustments will be made within the corridor so that the final route of the line will minimize environmental impact. It is anticipated that some agency stipulations will require that at least portions of the construction will be required to be completed in the winter when ground conditions reduce construction impacts. Intangible criteria such as visual impacts,public safety,existing facilities,construction impacts, and land use primarily deal with impacts to the public.These criteria will be addressed during later stages of the design.The routing alternatives costing factors are noted in Section 12. 11.2.3.Route Alternatives Based on the three corridors,and a project configuration in which two corridors are used,Table 11.2-1 shows the Route Miles (length of the corridor)and Circuit Miles (total miles of circuits within the corridor)for the various possible routes. Plans and profiles of each route are shown in Drawings 06-17T001 through 008,06-18T001 through 011,and 06-18T001 through 012 for the Gold Creek,Denali,and Chulitna corridors, respectively. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-12 December 2014 Za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 11.2-1.Summary of Transmission Alternatives Corridor Description Route Miles {|Circuit Miles 1 |Chulitna 3 Circuits Susitna-Watana to Chulitna Substation 37 111 2 |Gold Creek 3 Circuits Susitna-Watana to Gold Creek Substation 35 105 Denali 3 Circuits Susitna-Watana to Cantwell Substation 62 186 2 Circuits Susitna-Watana to Chulitna Substation;4 |Chulitna and Denali 1 Circuit Susitna-Watana to Cantwell Substation 99 136 2 Circuits Susitna-Watana to Gold Creek Substation;5 |Gold Creek and Denali 1 Circuit Susitna-Watana to Cantwell Substation 97 132 For the Denali route,the interconnection would be close to Cantwell and therefore some 19 miles of the transmission line would be alongside of the Denali Highway. Although no recommendation is made in this report,and no decision has been taken by AEA on the appropriate transmission route(s),the estimate of project cost detailed in Section 13 has assumed Alternative 5,using two circuits in a southern corridor to Gold Creek and one circuit to Cantwell. 11.3.Towers,Foundations and Conductors Power flow studies have identified the need to use twin bundled 954 thousands of circular mil (kcmil)conductors on all transmission lines to achieve satisfactory electrical performance.A single optical ground wire and a single overhead ground wire are also assumed to be attached to each structure. Typical transmission line tangent structures used in Alaska that would be suitable to support three twin bundles of 954 kcmil conductor and two ground wires are the steel H-frame structure, the steel X tower,or the steel single-pole structure. Structures may be guyed or self-supporting.Foundations will vary with soil conditions and access and may include direct embedment,driven pile,grouted pile,rock anchor,or micro-piles. 11.4.Interconnections A substation location has been identified for interconnection with the Alaska Intertie for each selected corridor as follows: «For the Chulitna corridor,approximately eight miles northeast from the Parks Highway; «For the Gold Creek corridor,approximately five miles northwest of the Gold Creek railroad bridge;and, Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-13 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. *For the Denali corridor,to the north side of the Denali highway approximately one mile east of the junction with the Parks Highway. A drawing of a typical intertie connection is shown in Figure 11.4-1,and a typical layout of the substation interconnection is indicated in Figure 11.4-2. 11.4.1.Substation Costs The substation costs will vary dependent upon the line configuration and number of lines selected for the project's interconnection with the Railbelt system.Comparative costs of the options associated with the transmission line configurations identified are presented in Table 11.4-1. Table 11.4-1.Substation Cost Location Description ,Watana Lines Low Costs High Costs Chulitna Alternative 1 --8 mi NE of Watana Access Road 3 lines +4 Interties $35M $42M Chulitna Alternative 1 -8 mi NE of Watana Access Road 2 lines +4 Interties $40M 348M Gold Creek |Alternative 2-5 mi NW of Gold Creek Bridge 3 lines +4 Interties $35M $42M Gold Creek |Alternative 2-5 mi NW of Gold Creek Bridge 2 lines +4 Interties $40M $48M Denali Alternative 3 -Denali Highway location 3 lines +4 Interties $42M $50M Denali Alternative 3 -Denali Highway location (No SVC)1 lines +4 Interties $8.7M $11.5M 11.4.2.BESS Costs The two unit sizes for the Susitna-Watana Project require differing amounts of stored energy in the Railbelt system.This stored energy will likely be split between battery energy storage systems BESS and rotating inertia systems (Flywheel)systems.In general,for high capacity short-term energy requirements,Flywheel technology may offer some savings over BESS installations.Siting and sizing studies in the next phase of the project will determine the cost of recommended mix between the two technologies.For the purposes of this phase of the project, all storage systems are considered to be BESS technologies. The costs of the required storage systems are between US$75M and US$115M.These costs have not been included in the project estimate described in Section 13. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-14 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. HEAYUNE 1 HEALY LIME 2 DOUGLAS LINE $DOUGLAS LINE 2 WATAWA UME 1 VT-20 193K ' 18aeev 1a0/7000.11VTOne on » \m \o \m \1073 \un ci @ iY Vea sah 198 Vea ssotv 196 Mbderihiad veo 1398:ww:13 tapaao0n:1 3 't200/2008.1 3.12007200%13ws\"/m we"Jen we VT]ws \"dow re y |= \m \=\e \"\= fe =i |« VES 133 KV:198 V4 133 6:198 VT-#139 eV:118 V1-12 1338:VU-48 san:sev sav sav saev 18800¥20070081 3 'apoc0on1 3 '20020001 3 1200200%1 9 s200re00K13vrajmvrs/m vrs /m ve Jun vrs Jun Shoe Shoe shoon]a =«(«\S o \*%Jam \"wn «7 wn =«(\'" is &i]|je 'VU-21133RV:tTogsaoorzong1VT "ia )san -ianaae| nownLscTORREACTOR E mows WATANA WATANAue2UNE3230kvSWATANALINES4INTERTIELINES,2 REACTORS,1 SVC Figure 11.4-1.Typical Intertie Connection Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 11-15 December 2014 Zz -ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Cslaliallal z **wee "-+SalaRatalatelenele'r"aallalialiel 4bffrawomennenenenenneeceeneaneee<Niiums\\ ||=l t a Lat |\a Tr «re a |a q ted are.+H |LINE +--+UNE 1at'|L TK ht |!AREA FOR|\4=FF-----”* -----+F_----__-,{|i SVC t |eo aniH|(a ete a otp a \|ia}LfLINE$44 UNE ||PAP ee DS OE ax4|t +>aT?1 rR Sees at tk iLINE+14<{-ott pk pet poe aaMERanen!Ne ee|!:i{¢to --_--_4tte.ee ee eeiii”"aa a ie"EE APB BS DEEN fay |}"elt dt ee is CEtr=p o>(rt=EH base arti ||vat EET eet DS Ds Ds Gal\bd -.ba od bd a,HyVSS"/&ee =euuweunni TENETSEINEDEEN Pennunnuntheccanannt Figure 11.4-2.Typical Layout of the Substation Interconnection Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 11-16 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 11.5.Comparative Costs Comparative costs have been prepared for the conceptual arrangements,both for routes alongside an all-weather road (which can be used to access the transmission corridor for construction)and assuming a road is not constructed and construction access is via all terrain equipment and helicopters.Table 11.5-1 compares the costs of these two scenarios for the five alternatives described above.At this stage,without a final decision on which transmission arrangements are to be used,the maximum cost,shown for Alternative 3,has been used in the overall project cost estimate presented in Section 13. Table 11.5-1.Estimated Comparative Transmission Line Costs Road Nearby No Road Alternative Description Low High Low High ($1,000)($1,000)($1,000)($1,000) 1 3 Circuits Chulitna Corridor 37 +miles $147,174 $171,703 $178,518 $208,271 3 Circuits Gold Creek Corridor 35 +miles |$163,856 $190,114 $170,021 $198,357 3 Circuits Denali Corridor 62+miles $246,484 $287,565 $298,946 $348,771 2 Circuits Chulitna Corridor 37+miles and41circuitDenaliCorridor62+miles $196,692 $229,474 $238,569 $278,330 2 Circuits Gold Creek Corridor 35+miles5and1circuitDenaliCorridor62+miles $208,240 $242,220 $232,150 $270,842 There will also be some upgrades required to the Alaska Intertie transmission facilities,which are the subject of a separate study being undertaken for AEA. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 11-17 December 2014 Section 12 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 12.PROJECT OPERATION AND RESOURCE UTILIZATION Project operation and resource utilization was developed with two types of models that both model reservoir operation and hydroelectric generation.The models differ significantly in the generating resources included in each model and the time period of simulation. The first model is a production costing model called PROMOD,which determines the economic hourly dispatch of the various Railbelt resources as required to meet the Railbelt electricity load at various locations.The PROMOD data set as developed for this study includes all the Railbelt generating resources of all types and operates for one year on an hourly basis with long-term average inflows to Watana Reservoir.That modeling work is described in Section 5. The second model,discussed in this section,is a reservoir operation and hydroelectric power study model.The only generating resource included is Susitna-Watana Hydro,so it does not simulate complete power generation within the interconnected Railbelt electrical system.The model operates for 61 continuous years on an hourly basis.It models the generation of a fixed portion of the total Railbelt load,or a remaining portion of the Railbelt load after considering generation from individual resources developed in the PROMOD simulation.An example of Susitna-Watana Hydro hourly generation for a year as developed in a PROMOD simulation run is shown on Figure 12-1.PROMOD results differ from the hydroelectric power study model results presented below because PROMOD focuses on hourly generation that minimizes production costs whereas the hydroelectric power study model maximizes generation from Susitna-Watana Hydro to meet pre-assigned hourly loads. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-1 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Average water conditions. 2024 Railbelt generation loads. 500 -Watana Generation 400 300 HourlyGeneration(MWh)200 100 Data provided by Slater Consulting,May 2014 1-Jan 31-Jan 1-Mar 31-Mar 30-Apr 30-May 29-Jun 29-Jul 28-Aug 27-Sep 27-Oct 26-Nov 26-Dec Figure 12-1.Susitna-Watana Hourly Generation as Developed by PROMOD for Average Water Conditions 12.1.Proposed Project Operation 12.1.1.Background Project operating flexibility is important to the Railbelt utilities that will be utilizing the power output from the Project.As noted above,PROMOD simulations encompass the entire Alaska Railbelt connected electrical system,to determine how to maximize the benefits of the Susitna- Watana Project within the integrated system. It is expected that based on this modeling work,and with consideration of potential environmental needs,AEA will most likely propose to operate the project in some form of an intermediate load following mode such that total energy is maximized while shaping monthly generation to be proportional to Railbelt utility total load requirements.The following discussion of flows and power operation is based on this premise.It is an update to the discussion of planned project operations included in Section 3.5 of the December 2011 Pre- Application Document (PAD).The modeling performed since December 2011 reflects further refinements in project development plans that have been made since that time,including the decision to establish the normal maximum reservoir level at El.2050 ft.and to increase the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-2 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT maximum annual drawdown from 150 ft.to 200 ft.to maximize annual power generation while providing greater flexibility for environmental flow releases. Reservoir storage capability is vital to the project's intended function -to provide critical winter generation capacity by regulating the flows of the Susitna River -and to serve as a major long- term power generating resource for the region.The requirement for substantial storage clearly identified in all the previous studies of the Susitna River,documented in Section 3,provides for capture and storage of spring snowmelt for later release through the powerhouse during the winter months.This capability also serves to ensure that seasonal flow releases can be provided to both protect environmental habitat and enhance river recreational opportunities downstream of the Project.In contrast a run-of-river hydro project on the Susitna (or any river),without storage and release capability cannot provide these important system,environmental and/or recreational benefits.Therefore,the Susitna-Watana Project is proposed as a storage-type resource in order to maximize overall regional benefits. Further engineering and environmental studies,system modeling and collaboration with Railbelt utilities and other stakeholders will continue to be carried out up to submittal of the Federal Energy Regulatory Commission (FERC)License Application to more clearly define the expected integration into the Railbelt system. 12.1.2.Environmental Flows Minimum flow requirements in the Susitna River downstream of the proposed Watana Dam are potentially significant to project operation,but have not yet been established.An acceptable flow regime will be determined through the continuing FERC licensing studies and through collaboration with licensing participants. Initial model runs were made using the Case E-VI from the Susitna 1985 FERC License Application.Those criteria specified a minimum wintertime flow of 2,000 cubic feet per second (cfs)at Gold Creek,and a minimum summertime flow of varying amounts up to 9,000 cfs. At this time,for planning purposes,AEA is considering a minimum winter flow of not less than 3,000 cfs at Gold Creek.The modified minimum daily flows at Gold Creek are shown on Figure 12.1-1.For reference,the average monthly natural flows at Gold Creek are also shown on Figure 12.1-1.The reservoir operation and power study model runs also included a provision to potentially limit releases at Watana Dam to the natural inflow,although this would be an infrequently controlling condition with the minimum daily flows at Gold Creek as shown on Figure 12.1-1. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-3 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT After the Project is constructed,downstream flows at the project site are expected to vary on a seasonal,weekly,and daily basis.In addition to the flows discharged through the powerhouse for generation purposes,flow augmentation,when required,would also be undertaken by making releases through the low-level outlets (if the powerhouse is not operational). 30,000 :coy 25,000 -Monthly Average Natural Flow 20,000 +------------a -Minimum Environmental Flows - Modified Case E-VI 15,000 Flow(cfs)10,000 l 1 i f[-:rr|dépeff-_4-Oct 1-Nov 1-Dec 1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep Figure 12.1-1.Minimum Environmental Flows and Average Natural Monthly Flows at Gold Creek 12.1.3.Reservoir Operation 12.1.3.1.Reservoir Operation Model A reservoir operation model developed by MWH was used to develop the results presented in this report.The U.S.Army Corps of Engineers Reservoir System Simulation Model HEC- ResSim was also used for preliminary runs.The two reservoir operation models are functionally similar,but each has significant advantages.HEC-ResSim is a free,publicly available model. Execution times in the MWH reservoir operation model are several times faster than for HEC- ResSim,and the MWH model can be programmed to simulate unique or complex operation requirements including dry water year rule curves and inflow forecasting.Both models determine energy generation,reservoir levels,and outflows at the dam.The MWH model does not include riverine flow routing capabilities.The remaining description in this section applies to the MWH reservoir operation model. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-4 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT The model is a water balance type of reservoir operation model that accounts for flow through the project reservoir,penstocks,and powerhouse on an hourly basis for a continuous period of 61 years.The model is written in FORTRAN and uses a number of text input and output files. The operation model input includes (1)daily inflows to the reservoir;(2)daily local inflows between Watana Dam and the USGS gaging station at Gold Creek;(3)general model input parameters that describe the physical and operating rules and characteristics of the reservoir;(4) Susitna-Watana powerhouse characteristics,which contains the preliminary turbine efficiencies as a function of flow and head,preliminary generator efficiencies as a function of output,and limiting maximums of the units;(5)the Railbelt electricity load for each hour of the year from which the generation requirements at Susitna-Watana are developed;and (6)minimum flow requirements at Gold Creek for each day of the year. The operation model produces tabular text output along with files that are designed to facilitate graphical presentation in a spreadsheet.The tabular text output is separated into monthly,daily, and hourly summary files.In the monthly tables,the entire 61-year period of operation is summarized into one table for each parameter.In the daily tables,one year of operation is summarized in a table.For the hourly tables,one month of output is summarized in each table for each parameter.The tabular text output is extensive and includes the following parameters: "Inflows to the reservoir and natural local inflows between Watana Dam and the USGS gaging station at Gold Creek «Generation from each turbine and total for the project «Net head on the units «Turbine-generator efficiencies for each unit «Water surface elevation and water storage in the reservoir =Reservoir elevation frequency for each month of the year «Ranked monthly energy output for each month of the year (a measure of generation reliability) =November through April total generation for a specified reliability =Flow through each turbine and total powerhouse flow «Total release to the river at Watana Dam ="Non-powerhouse flow (low-level outlet plus spillway flow) =»Flow at Gold Creek,which is the instream flow location «Water balance at the reservoir as a means of checking model computations Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-5 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Separate monthly,daily,and hourly output files are also created in a linear,comma-separated value format (.CSV)that imports easily into a spreadsheet for the purpose of creating graphical presentations. 12.1.3.2.Dry Year Rule Curve Placing the same electricity generation requirements on the project in every year would mean that either the active storage in the reservoir would be empty at times (causing generation to be abruptly greatly reduced or stopped),or the electricity generation requirements would be relatively low,controlled by the driest sequence of years.It would be preferable to reduce generation in a controlled manner for part of the year in about 15 percent of the years.Railbelt thermal generation could be increased in the dry years to compensate.To facilitate the controlled reduction of generation in unusually dry years,a preliminary dry year rule curve was developed.The dry year rule curve reduces generation when the reservoir level falls below the rule curve for any given day of the year,and increases the reduction up to a specified maximum as the distance of the reservoir level below the rule curve becomes greater.Reduction in generation at Susitna-Watana was limited to a maximum of 32 percent in any hour of the year compared to the same hour of the year in full generation years. 12.1.3.3.Forecasting Because a substantial portion of the total inflow to Watana Reservoir results from snowmelt,the opportunity exists to forecast spring and early summer inflow based on snowpack data that could potentially be collected in the watershed tributary to Watana Dam.In average to high snowpack years,generation could be increased beginning in March once the snowpack level was established.In low snowpack years,there would be no generation increases.Because a snowpack measurement network does not currently exist in the Watana watershed,historic March through June total inflows were used as a proxy for a snowpack inflow forecast.Based on the preliminary inflow forecast method,generation was increased beginning in March in 70 percent of the years.Generation was increased by a variable monthly amount that tended to result in monthly generation that was in proportion to monthly Railbelt generation needs.It is expected that this preliminary forecasting methodology can be improved.One potential forecasting improvement would be a wet water year rule curve that increased generation when reservoir levels were relatively high at a given time of year. 12.1.3.4.Reservoir Levels As shown on Figure 12.1-2,the Watana Reservoir maximum normal operating level would be at El.2050 ft.and the minimum operating level would be at El.1850 ft.The active (live)storage Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-6 December 2014 -a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT between El.1850 ft.and El.2050 ft.is 3,380,000 acre-ft.The total reservoir storage to El.2050 ft.,including the dead storage below El.1850 ft.,is 5,170,000 acre-ft. Reservoir Surface Area (acres) 50,000 40,000 30,000 20,000 10,000 0 2200 ]|--220021002100 Maximum : .: Ls §=Normal .. Operating :eataara:2000 =1900 Wa on 1900 =mImMumMzzWaiOperating 2 LevelS1800 1800 6 :-_fy]w >:>a fo ||o WW 4700 1700 W '|: :if|| 4600 , e-Storage (acre-feet)41600[-m-Area (acres) 1500 1500 eo 1400 :::1400 0 2,000,000 4,000,000 6,000,000 8,000,000 10,000,000 Total Reservoir Storage Capacity (acre-feet) Figure 12.1-2.Watana Reservoir Elevation-Area-Capacity Table To accomplish efficient dispatch,the project reservoir would be drafted annually by an average of about 120 ft.to 150 ft.,if the Susitna-Watana Project was being operated to deliver maximum potential generation with high reliability.A maximum drawdown of 200 ft.(to El.1850 ft.) would be possible and could occur.A more refined future operating plan that incorporated coordination of Railbelt resources could prevent Watana Reservoir from ever reaching El. 1850 ft. Figure 12.1-3 presents the modeled daily reservoir elevations for the 61-year period of modeled reservoir operations.As indicated by this model,the reservoir would have been filled to El.2050 ft.in about 80 percent of the years,but at times the reservoir would have remained unfilled for two or more years.The more recent period of record,from 1978 to the present, would have had notably fewer extreme drawdowns -with none reaching El.1850 ft.This is,at Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-7 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT least in part,because there was a seasonal shift in flows that generally increased flows in the low flow season,reduced flows in the high flow season,and advanced the sharp rise in inflows in April.All of these events would effectively have moved the inflows more "in phase”with the generation required to satisfy electricity demands. 2070 2050 2030 4A EE EE EE LE TELE EEE GE Bh Bd Pps BE PB Bb eee feces 2010 + 1990 =obev]o-©@i|ReservoirElevation(feet)reao1910 -}H F--se sree poe -nn sone 1890 4 -Reservoir Elevation 1870 -Maximum Normal Operating Level -- -Minimum Operating Level 1850 Incorporates existing hydro load following at Bradley,Eklutna,and Cooper and forecasting, 2024 Railbeit generation loads.1830 41-Oct-49+-----=-9 0)Fe OD we ©YOY Fe DW fF 78 4)OW re 90 YD Fe OW Ff Om He hUmumlUCODmUmUCUCUOlCUDDLUCUMnLUCUCN CUD5696668©©9 6 &FF PF Fe 8 G9 8 F&F 8G FGFS FSF 8 BF B55es>eS a >SS DO >nS SS 2S >©©OS Ss 2 Ss ©SS Rs Ss cs ss es°¢9°99°9°9990989¢9989898998869668G88sSB222222222828232288228222822822222222898 Figure 12.1-3.Daily Reservoir Elevations (feet) 12.1.3.5.Tailwater Rating Curve A tailwater rating curve,as shown on Figure 12.1-4,is used to determine the static head on the units.For a reservoir level at the normal maximum operating level at El.2050 ft.,the available static head is about 589 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-8 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 1500 1495 1490 =hhooaiaN>aoO1475 |a 1465 -WaterSurfaceElevation(feet)=ayN°1460 - 1455 0 50,000 100,000 150,000 200,000 250,000 Flow (cfs) Figure 12.1-4.Tailwater Rating Curve 12.1.3.6.Operational Objectives The 1985 FERC License Application envisioned the Alaska Power Authority Susitna-Watana Hydroelectric Project as a load-following project.The degree to which the project will be designed to carry system load swings is still under study and a definite operating plan for the project will not be developed until prior to submittal of the FERC license application.In the meantime,alternative operating scenarios have been developed.One operating scenario, designated as maximum load following,assumed that the Susitna-Watana powerhouse would provide the entire load variability of the Railbelt.This is conservative,in that other hydro on the system -though much smaller capacity -could be used to assume some of the load-following. Under the currently assumed operating mode there would be diurnal variations in powerhouse discharge as the generating units are used to meet hourly and daily Railbelt electrical load fluctuations,satisfy assumed downstream environmental flow requirements,and prevent spill, therefore optimizing power generation within the constraints of the Railbelt system.As noted above,this mode of operation was used as one premise for the initial model runs for the current studies.These model runs reflected the anticipated maximum variations that could occur from load-following,but operations due to infrequent,sudden starts and stops of other Railbelt units could potentially result in greater variations. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-9 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. However,system modeling results demonstrate that the Susitna-Watana Project will not need to carry the full hourly load deviations. For the current model runs,the primary operating objectives of the project were assumed to be similar to those described in the PAD,except that other system hydro would provide the primary means of peak generation,and include the following: #Maximize power generation with high reliability during the months of November through April. =Generate power as necessary to meet modified Case E-VI. ="Maximize power generation during the months of May through October -i.e., minimizing spills -without reducing the power generation during the November through April period. =Shape generation according to Railbelt area power requirements,to the extent possible with environmental needs,and considering other generating unit availability on the interconnected grid. Continuing system modeling in conjunction with project operations model runs are examining variations from this Base Case scenario,and results will be presented to and discussed with stakeholders during the licensing study process with the goal of including the final selected operating plan in the FERC License Application. Ultimately,the Railbelt system modeling results from the ongoing work described previously will be used to confirm the anticipated system requirements over the economic life of the project to help AEA and the utilities jointly determine the most economical dispatch arrangements. Generally speaking this work involves critical analysis of the operating mode of the largest power plants expected to be on line in the system in future years,including Susitna-Watana,to determine how best to achieve long-term system reliability,and minimize investment and thus future regional electricity costs. 12.1.4.Operating Scenario Results are presented in this section for the intermediate load following scenario (ILF-1).The Bradley Lake,Eklutna Lake,and Cooper Lake hydroelectric plants (other hydro on the system) were assumed to operate in a peaking mode to reduce the amount of load following that would be necessary at Susitna-Watana.No load following was assumed to occur at the gas-fired generation plants.Emergency load variations are excluded. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-10 December 2014 -_a-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Flow releases would be made through the powerhouse or through low level outlet works during the rare occasions when the power plant is off line during emergency outages.Flow discharges through the powerhouse under this operating plan would range from the minimum required instream flow release (yet to be determined)to a high of about 14,000 cfs (based on the 618 MW nominal power plant turbine capacity at maximum water level)during times of maximum power generation.Based on preliminary studies,daily power generation during a peak winter month (January)would average about 8,250 megawatt hour (MWh)and powerhouse discharges would average approximately 8,360 cfs during that time. For efficient operation of the whole interconnected Railbelt system,powerhouse discharges are expected to vary over a 24-hour period during the peak winter months.It is difficult to characterize typical powerhouse operations before production modeling simulation of the Railbelt is complete.However,to provide a preliminary indication of powerhouse discharge variability under the relatively conservative assumption of the Susitna-Watana powerhouse providing the entire load variability of the Railbelt during a typical January,simulation model runs have been performed using those criteria.Under that scenario,typical 24-hour powerhouse discharges would range from a low of about 7,000 cfs to a high of about 9,050 cfs.Powerhouse discharges could be as high as about 13,000 cfs for short periods of time during the day to meet load spikes or emergency conditions.The daily flow variation may be constrained because of environmental requirements. Once the Susitna-Watana Project is in operation,reservoir storage and release patterns will seasonally shift some of the normal Susitna River flow from the high flow summer months to the cooler winter months,which will result in less variability in flow over the course of the year and changes to typical downstream river stages. Figure 12.1-5 illustrates the intermediate load following operation for the 15 month period from July 1,1984 through September 30,1985.This period was selected as an average water period for the concurrent Susitna-Watana environmental studies.Hourly outflows at Watana Dam (blue line)and hourly flows at Gold Creek (purple line)are plotted against the flow scale on the left side of the plot,as are daily average reservoir inflows (red line).The reservoir elevation (green line)is plotted against the right vertical axis.The results presented on the figure include use of the dry year rule curve and preliminary forecasting. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-11 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Monthly average results for the 61-year period of operation for the intermediate load following case are presented in the following tables,which incorporate the dry year rule curve and preliminary forecasting: «Table 12.1-1.Monthly Average Reservoir Elevations (feet) =Table 12.1-2.Monthly Susitna-Watana Powerhouse Flow (cfs) «Table 12.1-3.Monthly Total Release to River at Watana Dam (cfs) "Table 12.1-4.Monthly Flows at Gold Creek (cfs) Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-12 December 2014 -Zz-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 55,000 2070 Average -July 1,1984 -Sept.30,1985 50,000 =<+2050 Incorporates existing hydro load following at 45,000 Bradley,Eklutna,and Cooper and forecasting.2030 2024 Railbelt generation loads. 40,000 4/2010-Watana Outflow XY35,000 1990 roy ® a 2-Watana Inflow \= --2@30,000 Gold Creek Flow |_1970 oO .. =-Reservoir Elevation FA3i -25,000 1950 opam= ° 2 ®20,000 +1930 @\,o 15,000 '1910 10,000 1890 5,000 +1870 O+1 1 r 1 1 1 Y 'a 1 r Y 7 r r 1850 1-Jul-84 31-Jul-84 30-Aug-84 29-Sep-84 29-Oct-84 28-Nov-84 28-Dec-84 27-Jan-85 26-Feb-85 28-Mar-85 27-Apr-85 27-May-85 26-Jun-85 26-Jul-85 25-Aug-85 24-Sep-85 Figure 12.1-5.Intermediate Hourly Load Following Operation for an Average Water Year Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 12-13 December 2014 -z- SUSITNA-WATAN A HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 12.1-1.Monthly Average Reservoir Elevations (feet) Year Qct Nov Dec dan Feb Mar Apr May Jun Jul Aug Sep =Annual19502046.3 2036.7 2019.3 1995.8 19703 19444 19199 1909.5 19394 19815 20248 2039.4 1985.7 1951 2087.6 2023.7 2002.2 19746 1943.6 1911.7 18797 1876.1 19141 1956.6 1996.0 20347 19627 1952 2048.1 2038.8 20223 2000.9 19774 19514 1920.6 18845 19076 1968.2 2016.8 20396 1981.4 1953 2048.8 2043.1 2027.8 20065 1983.1 1958.0 19292 1927.2 19726 20104 20428 20506 2000.2 1954 2049.0 2039.0 2021.5 19990 19747 1947.9 1916.2 1903.3 1941.2 1982.9 2023.8 2049.2 1987.4 1955 2048.6 2039.9 2024.1 2003.5 1981.1 19568 19282 19030 19295 19933 20339 2050.4 1991.1 1956 2048.3 2037.7 2019.4 1995.9 19704 1942.7 19096 1890.8 1946.1 20096 2049.9 20508 1989.5 1957 2049.1 2040.9 2025.8 20053 1983.5 1959.9 19322 19120 19616 2006.0 2041.5 2051.1 1997.5 1958 2049.9 2045.0 2032.9 2015.2 1995.1 1973.4 1948.7 1934.7 1971.1 20102 2047.9 2049.9 2006.3 1959 2048.1 2038.0 2020.0 1997.8 1973.9 19475 19162 18956 1932.3 1977.3 2021.5 20505 1985.0 1960 2048.8 2040.1 2024.6 20044 1982.4 1961.1 1941.0 1939.14 1971.5 2001.7 20443 2051.1 2001.0 1961 2049.5 2041.8 2027.3 20088 1989.0 19676 19449 1939.8 1975.3 20243 2050.7 2049.8 2005.9 1962 2048.3 2039.1 2023.4 2003.2 1981.4 19580 1931.4 19167 19743 2042.4 2051.3 2050.3 2001.8 1963 2049.5 2042.3 2027.4 2007.2 1985.6 1962.4 19347 19185 1967.4 2024.2 2051.3 2050.3 20019 1964 2049.4 2040.5 2023.3 2000.8 1976.5 1949.9 19181 18798 19469 2020.2 2047.0 2049.9 1992.0 1965 2049.2 2040.6 2024.3 20017 1977.6 1951.8 1922.2 18987 19334 1988.1 2031.2 2049.6 1989.2 1966 2048.1 2037.0 20189 1996.0 1971.4 19449 19140 1883.8 19200 1961.9 1998.6 2020.7 1976.4 1967 2021.4 2005.3 1981.1 1949.2 19196 18934 1868.9 18613 19139 1966.6 2026.4 2050.5 1955.0 1968 2048.5 2038.4 2021.9 2001.3 1979.7 1957.2 1931.4 1913.0 1962.7 2019.4 2049.0 20498 1997.9 1969 2046.5 2034.6 2015.1 1989.9 1962.4 1935.1 1909.5 18992 1922.0 1949.5 1967.2 1967.4 19666 1970 1965.8 1957.3 1942.7 19248 1906.2 1889.2 1871.2 1867.1 1895.2 1938.5 1983.4 20016 1928.7 1971 1998.0 19823 1961.0 19434 19191 1893.2 18687 18516 1890.2 1959.6 20196 2050.0 19449 1972 2049.2 2041.4 2026.6 2007.3 19868 1965.2 1940.1 1931.7 1990.8 20406 2051.2 2049.8 2006.9 1973 2045.9 2036.3 2018.3 1995.0 1970.0 1945.3 19218 19058 19426 1993.1 2021.4 20433 19867 1974 2041.6 2028.3 2007.8 1981.2 1951.8 1921.9 1892.0 18786 1924.6 1957.0 1987.7 20066 1965.0 1975 2007.5 1989.4 1964.0 19437 19195 18936 18696 1864.0 19201 1980.7 2021.8 20419 19515 1976 2049.6 2041.3 2023.2 2000.0 1975.4 1948.8 1917.6 1900.0 19284 1962.2 1997.1 20082 1979.4 1977 2001.9 1985.1 1962.5 1943.9 1919.7 1893.8 1869.9 1860.2 19208 1983.2 2019.8 2037.8 1950.1 1978 2045.9 2040.1 2025.7 2006.4 1985.4 1965.4 1947.4 1946.0 1971.6 2009.9 20403 20495 2003.0 1979 2047.9 2038.5 2021.5 1999.3 19756 1950.0 1920.0 1896.9 19347 19823 2030.5 20465 1987.1 1980 2049.6 2043.9 2030.7 2011.4 1990.7 1968.8 1943.7 1929.7 1963.1 2020.6 2051.1 2050.1 20046 1981 2049.9 20445 20305 2011.7 1992.7 19719 19484 1946.8 1977.1 2020.3 2051.5 2050.4 2008.1 1982 2049.9 2044.0 2028.7 2008.7 1987.4 1964.4 1938.0 1922.1 19560 20005 20344 2048.0 19986 1983 2049.3 2040.5 2024.8 20055 19849 19634 1938.2 1926.0 19608 20027 2039.3 2050.1 1998.9 1984 2049.8 2043.6 2029.0 2010.2 1990.9 1971.0 19485 1935.3 1967.9 20183 2049.2 20499 2005.4 1985 2048.7 2039.9 2024.5 2004.2 1982.4 19594 19333 19087 19393 19935 2033.1 2049.7 19932 1986 2049.2.2040.2 2023.7 2002.3 1979.5 1957.6 1937.3 19297 19637 20035 2034.8 20493 1997.7 1987 2050.0 2044.0 2029.0 2008.8 1987.5 1965.2 1939.9 1927.8 19583 2003.8 2047.7 2050.2 2001.1 1988 2049.2 2041.2 20243 2002.8 1980.2 19565 1929.0 19190 19648 20182 20485 20503 1998.8 1989 2049.5 2042.2 2026.6 2006.6 1985.8 1964.0 19393 19297 19626 20082 2045.1 2050.5 2001.0 1990 2049.5 2042.7 2026.8 2006.4 1985.1 1963.1 1939.9 1951.0 2017.6 2050.7 2051.2 2051.3 2011.5 1991 2049.1 2039.6 20236 2003.3 19816 1961.3 1942.5 19284 1957.7 2009.1 2039.2 20498 1998.9 1992 2049.0 2039.3 2023.2 2002.9 1981.4 1961.2 19437 19304 19583 20090 2047.0 2050.0 19998 1993 2047.5 2037.5 2021.2 2000.1 1977.8 1954.1 1927.1 1923.2 1970.7 20029 2033.0 20506 1995.6 1994 2049.7 2043.8 20295 2010.8 19908 19695 1945.9 1941.8 19796 20294 20501 2049.9 2007.7 4995 2047.3 2037.5 2021.3 2000.3 1977.9 19543 1928.1 1927.4 1957.1 2007.9 20436 2050.9 1996.3 1996 2049.0 2040.6 20236 2001.3 19776 19547 19336 1917.7 19346 19592 1986.3 2005.4 1982.0 1997 2002.8 1984.2 1961.0 19435 19195 1894.7 1872.1 1864.4 1891.6 19394 19945 2029.0 1941.5 1998 2031.2 2016.6 1995.1 1967.0 1935.2 19025 1873.2 18633 19089 19643 2013.0 2040.8 1959.4 1999 2049.5 2042.3 2026.9 2006.7 19848 1963.7 1943.9 1935.0 1965.7 2010.6 2047.9 2050.0 2002.4 2000 2049.5 2042.1 2026.8 20064 19846 19616 1935.1 1917.1 19533 2016.1 20484 20502 1999.4 2001 2049.7 2042.3 2027.0 2006.9 1985.5 19628 19366 19123 1949.4 19964 2035.4 20499 19963 2002 2048.2 2038.5 2022.0 20004 1977.3 1955.0 1934.2 19233 19532 19826 2017.5 20476 1991.8 2003 2050.1 20476 2036.0 2017.7 1998.7 1981.8 1965.6 19598 19906 2037.7 2051.1 2050.3 2015.72004©2049.2 2040.5 2024.0 2002.6 19796 19548 19266 19345 19816 20199 20448 20494 2000820052044.6 2031.6 2012.7 1989.0 1963.0 1934.1 1899.4 1905.3 19735 2033.3 20512 2051.2 1991.0 2006 2049.7 2041.0 2023.6 2001.7 19785 1954.0 19258 1906.2 19309 19859 20288 20502 1990.5 2007 2049.2 2041.2 2026.0 2006.4 1985.8 1964.0 19392 19347 1965.6 1997.8 2031.5 20485 1999.3 2008 2048.4 2039.3 2025.1 20056 1983.7 19625 1943.6 1939.9 19708 2009.9 20467 2049.9 2002.3 2009 2049.0 2038.3 20196 19966 19724 19463 1917.5 19332 1972.4 20061 20322 20496 19946 2010 2049.7 2042.3 20265 20055 1983.2 19595 19326 19295 19640 20037 20443 20506 1999.4 Average 2043.3 2034.00 2017.2 1996.0 1973.0 19492 19236 19122 1950.7 1997.8 20321 2043.7 1989.5 Maximum 2050.1 2047.6 2036.0 2017.7 1998.7 1981.8 1965.6 19598 2017.6 2050.7 2051.5 2051.3 20157 Minimum 1965.8 1957.3 19427 19248 1906.2 1889.2 1868.7 1851.6 1890.2 1938.5 1967.2 1967.4 1928.7 Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 12-14 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Table 12.1-2.Monthly Susitna-Watana Powerhouse Flow (cfs) Year Oct Noy Dec Jan Feb Mar Aor May Jun dul Aug Sep =Annual19505,909 7,234 8,263 8682 8747 7,310 6,674 6,144 5820 5235 5559 5388 6,736 1951 6,093 7,564 8812 9440 9799 8357 7,873 6918 6211 5.462 5686 4,982 7,252 1952 5,868 7,180 8,170 8,522 8,500 8,393 9,296 10,436 9,888 7,591 6,011 5,408 7,934 1953 6,018 7,075 8,016 8,339 8,311 8,181 8,939 8,546 7,455 6,410 7,498 12,452 8,092 1954 6,103 7,174 8,195 8,576 8,588 8,518 9,488 9,537 8,423 7,145 5,525 8,442 7,967 1955 5,858 7,151 8,125 8,438 8.375 8,223 8,977 9,517 8,903 6,865 6,864 11,440 8,217 1956 5,954 7,210 8259 8679 8742 8711 9,788 10,151 8306 6,456 11,970 13,585 8,978 1957 5,892 7,128 «8,076 8,378 8,306 «68,128 «=8817 «9,133 7,780 «=«6,527 7,264 «13,800 _-«8,257 1958 7,375 7,034 7,868 8074 7,953 7,738 8215 8,238 7,495 6,421 10577 6,083 7,760 1959 5,869 7,201 8,242 8619 8620 8533 9489 9,900 8754 7,317 6,312 11,385 8,342 1960 6,713 7,146 8,113 8,408 8,331 6,802 6,069 5,379 6,142 5,410 8613 13,800 7,563 1961 7,394 «7,105 8,031 8,271 8,129 7,908 §=8,341 8,088 =7,375 «6,165 12.620 10,459 8,32619626,390 7,173 8,140 8,448 8,365 8,181 8,849 8,931 7,471 9,319 13,800 11,837 891419636,270 7,092 8,028 8,315 8,234 8,056 8,717 8,887 7,599 7,163 13,800 11,171 8,61419646,284 7,137 8,143 8,526 8,533 8,444 9,402 10,643 8,548 6,557 9,479 7,440 8,26119656,047 7,136 8,118 8,494 8,493 8,378 9,227 9,732 8,718 7,009 6,124 11,451 8,2321966©7867 «7,228 «=8,274 8,675 8,706 =8,631 «9,586.«10,472 9.315 7,704 «=«6.081 s«5,754_-sB,189 1967 6,469 «8,084.9,588 =10,042 7.947 6,903 5638 7,239 9570 7,586 6659 11,639 8,1081968=55,902,7,191 8,182 8,508 =8.423.8210 8,849 «9,103 7,738 «=«6.241 «10,889 7,362 -s8,050 1969 5,903 7,284 8,393 8,883 9,039 7,603 7,006 6,455 7,334 7,777 6,451 4,280 7,193 1970 3,676 4,442 5,102 5,300 5,259 4,398 4,782 5,856 6,544 5,961 5,748 5,650 5,225 1971 7,070 8,824 6675 6,800 7,479 6691 5596 3920 8693 7,826 6030 10,342 7,146 1972 6,164 7,117 8,050 8,314 8,196 7,974 8,517 8,373 6,949 8,166 13,800 11,580 8,604 1973 5,914 7,247 «8,293 8,708 «=8,756 «7,282,6.617 6,242 ««5,507 8,821 «5,623.«5,239,761 1974 6,007 7,445 8626 9,188 9456 8028 7,601 7,165 6,007 5820 6108 5526 7,237 1975 6,821 8,583 7,956 6,960 7,824 7,101 5,720 7,741 9,305 7,223 5,880 6,873 7,325 1976 7,123 7,118 8,146 8,550 8,566 8,485 9,427 9,668 8,916 7,738 6,245 6,116 8,005 1977 6,966 8,728 7,561 7,189 7,961 7,207 5,776 7,260 9,330 7,139 5,856 5,640 7,2101978«=«45,915 7,146 =8,078 9 8,343 8,243 «6,681 «=5,902 5,213 5,524 5,366 6,130 6,224 6,55419795,873 7,188 8,195 8,571 8,561 8,443 9,321 9,823 8,668 7,179 5,717 6,200 7,80519806,660 7,063 7,932 8,191 8,079 7,868 8,383 8,412 7,725 6,294 13,800 10,939 8448 1981 6,992 7,047 7,935 8,184 8,023 7,777 8,221 7,868 7,306 6,849 13,800 11,611 8,47119825,943 7,054 7,988 «=8,272 8,176 =8,001 8.593.8.714 «67,935 6,649 6978 9,544 7,813 1983 6,136 7,137 8,105 8,372 8,258 8,031 8,585 8,563 7,797 6,955 7,619 10,786 8,02119847,468 7,063 7,980 8,225 8,070 7,803 8,218 8,228 7,590 6468 11,833 7,623 8,052 1985 5,857 7,151 8,115 8,414 8,331 8,143 8,773 9,267 8,493 6,935 5,967 10,309 7,969 1986 6,359 7,143 8,130 8.477 8,431 6,905 6,169 5,598 6,689 7,592 5,978 9,188 7,211 1987 9,698 7,057 7,981 8,270 8,174 7,974 8,520 8,488 7,863 6,601 10,457 10,444 8463 1988 5,846 7,121 8,122 8,460 8,405 8,235 8,944 8,859 7,680 6,233 10,641 10,810 8,275 1989 7,133 7,095 8,053 8,337 «8,230 8,010 8545 «8416 7,743 «6,471 «9,123 13,0358,342 1990 7,363 7,082 8,045 «8,343.8,253.8,038 «=8,523.7,755 «6.267.12,779 13,800 13,800 9,181 1991 7,309 7,158 8,135 8,444 8,358 6,798 6,029 5,619 5,085 5,431 6,017 10,107 7,03049926,275 7,166 8,142 8,455 8,367 6,799 6,000 5,568 5,162 4,857 10,055 8,583 7,113 1993 5,881 7,215 8,205 8,550 8,490 8,307 9,023 8,711 7,496 6,599 5,874 12,774 8,079 1994 8,395 7,059 7,966 8212 8077 7,854 8308 8006 7,263 5,986 12,313 7,773 8,106 1995 5,886 7,215 8,201 8,543 8,483 8,298 8,985 8,533 7,892 6,485 7,420 13,800 8,29819966,742 7,138 8,136 8,509 8,495 6,991 6,273 5,899 6,201 6,191 6,056 5,544 6,840 1997 6,940 8759 6676 6825 7,836 6,738 5367 5,746 6552 5825 5248 5078 6,455 1998 6,238 7,756 9,060 9,744 10,175 8724 6128 5,168 6,298 5,462 5,157 6,103 7,150 1999 7,508 7,094 8,043 8,334 8,261 6,729 5,993 5,462 §,138 5,181 10,511 9,580 7,31620006,472 7,097 8,045 8,344 8,267 8,079 8,702 8,910 8,031 6,293 9,822 11,211 8,267 2001 «7,836 7,093 «8,039 8,327 8,239 «8,047 8.646 «9,103 8,170 «6,773.«5,683.«85907873 2002 «5,867 7,188 8179 8537 8505 6982 6254 5,762 6,031 5838 5427 8655 6,921 2003 9,255 7,024 7,782 8,003 7,862 6,252 5,467 4,908 4,847 7,379 13,800 10,251 7,74420047,829 7,136 8,125 8,465 8,426 8,285 9,045 8,312 7,187 6,185 8,600 5,997 7,79920055,942 7,362 8,463 8,910 9,016 9,051 10,288 9,523 7,451 6,673 13,800 13,800 9,1862006«=8,083 7,126 «8,134.8,497 8,462,8,305 «9,077 «9,403 8.466 =7,064 =7,137 10,269 -«8,330 2007 «9,472 7,122,8,068 =8,343.«8,231 8,010 8.547 8,259 7,642 «6,737 «=«5,773 «8652s 7,901 2008 5,945 7,167 8,098 8,367 8,299 6,762 6,001 5,351 5,253 5,325 9,662 12,107 7,351 2009 «5,882 7,194 «8,253 8,653.«8,671 «8,578 «=9,437 8345 7,453.«6.517 5,888 -s-B,780-s 7,793 2010 6512 7093 8054 8370 8310 8133 8803 8466 7.692 6594 8332 12,222 8206Average6,614 7,238 8,064 8,364 8,356 7,771 7,907 7,868 7,421 6,686 8,320 9,271 7,817 Maximum 9,698 8,824 9588 10,042 10,175 9,051 10,288 10643 9,888 12,779 13,800 13,800 9,186 Minimum 3,676 4,442 §,102 5,300 §,259 4,398 4,782 3,920 4,847 4,857 5,157 4,280 §,225 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-15 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT a Table 12.1-3.Monthly Total Release to River at Watana Dam (cfs) Year Oct Nov Dec Jan Feb Mar Apr May dun dul Aug Sep =Annual19505,909 7,234 8263 8682 8747 7,310 6674 6,144 5,820 5,235 5,559 5,388 6,736 1951 6,093 7,564 8812 9,440 9799 8357 7,873 6,918 6,211 5,462 5686 4,982 7,252 1952 5,868 =7,180 98,170 8,522,8,500 «8.393 9.296 «10,436 «9,888 «=7,591 6,011 5,408 -s 7,93419536,018 7,075 8,016 8,339 8311 8181 8939 8546 7,455 6410 8,026 13,038 8,18519546,103 7,174 8195 8,576 8,588 8,518 9,488 9,537 8,423 7,145 5,525 8,442 7,967 4nw19555,858 7,151 8,125 8,438 «8.375 8,223 8977 9,517 8,903.6,865 «8,708 12,266 8.442 SS |1956 5,954 7,210 8.259 8,679 8,742 8,711 9,788 «10,151 8306 6456 15,778 15649 9,471 &BS19575,892 7,128 =8,076)8,378 «=8,306)8,128 «8.817 «69,133.7,780 «6,527 7,706 =16,425 8,510 qa '-1958 7,375 7,034 7,868 8074 7,953 7,738 8215 8,238 7,495 6,421 11,330 6,083 7,824 @w19595,869 7,201 8.242 8619 8620 8533 9489 9,900 8,754 7,317 7,315 14664 8697 B »|1960 6,713 7,146 «8,113 8,408 «=8331 «6,802 «6.069 5,379 6,142 5,410 10,065 17,305 7.974 Ss 1961 7,394 «7,105 8,031 8,271 8,129 7,908 98,341 «=8,088)=-7,375 «6,165 17,152 10,459 8,710 so196263907,173 8140 8448 8365 8181 8849 8931 7,471 12,627 19,931 13,285 9,835 ?RN19636,270 7,092 8,028 8315 8234 8,056 8,717 8887 7,599 7,598 21,066 11,281 9,277 yy:1964 6,284 7,137 8143 8526 8533 8444 9,402 10643 8548 6557 9,479 7,440 8,261 ce RY vv19656,047 7,136 8,118 =8,494 8,493 8,378 9,227 9,732 «8,718 7,009 6,124 13,676 8.415 FY19667,867 7,228 «8.274 «8675 8,706.8.631 «9,586 «10,472 9,315 7,704 6,081 5,754 8,189 te196764698,084 9,588 10,042 7,947 6,903 5638 7,239 9,570 7,586 6,707 14143 8318 AR A19685,902 7,191 8182 8508 8423 8210 8849 9,103 7,738 6,241 10,890 7,362 8,050.1969 5,903 7,284 8393 8883 9,039 7,603 7,006 6,455 7,334 7,777 6,451 4,280 7,193 &+ 1970 3,676 4,442 5,102 5,300 5,259 4,398 4,782 5856 6,544 5,961 5,748 5,650 5,225 1971 7,070 8,824 6,675 6,800 7,479 «6,691 5,596 93,920 8,693 7,828 6,030 10,741 7,179197261647,117 8,050 8,314 8,196 67,974 8,517 8,373 «=6,949)8,812 17,780 11,801 9,01519735,914 7,247 8,293 8,708 §9=-8,756 «=7,282 6617 6,242,5,507 5,821 5,623 5,239 «76119746,007 7,445 8626 9,188 9,456 8,028 7,601 7,165 6,007 5,820 6,108 5,526 7,237 1975 «6,821 8,583.7,956 6,960 7,824 7,101 5,720 7,741 9,305 7,223 5880 6873 7,32519767,123 7,118 «=8.146 8,550 8,566 «=8,485 «9,427 9,668 8.916)7,738 «=6,245,116 8,00519776,966 |=8,728 7,561 7,189 «7,961 7,207 «5,776 =7,260 «9,330 7,139 «5,856 5,640 7,21019785,915 7,146 8078 8343 8243 6,681 5,902 5,213 5524 5,366 6,130 6,224 6,554 1979 5,873.7,188 «98,195 8,571 8561 8,443 «9,321 9.823 8.668 «=7,179 «5,717 =6,200 7,805198066607,063 7,932 8191 8079 7,868 8,383 8412 7,725 6,294 18,000 11,182 8,824 1981 6,992 7,047 7,935 8184 8023 7,777 8221 7,868 7,306 7,368 30,571 12,198 9,987 1982 5,943 7,054 7,988 +=8,272,8,176 98,001 8,593 «8,714 «7,935 «6,649 «6,978 =10,848 7,92019836,136 «7,137 8,105 8,372,8,258 «=8,031 8,585 868,563.7,797 «6,955.9,382)«11,619 8,239 1984 7,468 7,063 7,980 8,225 8070 7,803 8218 8,228 7,590 6,468 13,370 7,623 8,182 1985 5857 7,151 8115 8414 8331 8143 8773 9,267 8493 6,935 5,967 10,309 7,969 1986 6,359 7,143 8130 8477 8431 6,905 6,169 5598 6689 7,592 5,978 9,188 7,211 1987 10,635 7,057 7,981 8270 8,174 7,974 8,520 8488 7,863 6,601 11,393 10,972 8,665 »1988 5,846 7,121 8122 8460 8,405 8,235 8,944 8859 7,680 6,233 11,535 11,829 8,434 s 1989 7,133 7,095 8,053.8,337 «8.230 8.010 «8545 8,416 7,743 6,471 10,062 13,091 8,426 \"N19907,363 7,082 8,045 «8,343 8,253 8,088 «=8,523.«7,755 +6267.17,041 19,618 22,092 10,719 NY 1991 7,309 7,158 8135 8444 8358 6798 6029 5619 5085 5431 6,017 10,107 7,030 AA's 1992 6275 7,166 8142 8455 8367 6,799 6,000 5568 5,162 4,857 10867 8583 7,182 ne199358817,215 8,205 8550 8490 8307 9,023 8711 7,496 6,599 5,874 15,704 8,320 NN199483957,059 7,966 8212 8077 7,854 8308 8,006 7,263 5986 13,265 7,773 8,187 || 1995 5,886 7,215 8201 8543 8483 8298 8985 8533 7,892 6485 7,420 15,617 8,447 \S 1996 6742 7.138 8136 8509 8495 6991 6.273 5,899 6201 6191 6056 5544 6840 1997 6940 8759 6676 6825 7,836 6,738 5,367 5,746 6,552 5,825 5,248 5,078 6,455 \1998 6,238 7,756 9,060 9,744 10,175 8,724 6,128 5,168 6,298 5,462 5,157 6,178 7,156 BN \1999 7,508 7,004 8043 8334 8,261 6,729 5,993 5,462 5,138 5,181 14,268 9,580 7,635 2000 6,472 7,097 8,045 8344 8,267 8,079 8,702 8910 8,031 6293 9,822 12,260 8,354 2001 «7,836 «=7,093 8,039 «8,327 8,239 «8,047 8.646 «9,103.8,170 «6,773.«5,683.8,590 7,873 2002 5,867 7,188 8,179 8537 8505 6,982 6,254 5,762 6,031 5,838 5,427 8740 6,928 2003 49,431 «7,024 «7,782 8,003 7,862 «6,252.5,467 «4,908 =«4,847.10,938 17,584 11,591 8,4932004«=7,829 7,136 8,125 8,485 «8,426 «8,285 «09,045 8,312 7,187 6,185 =8,600 «5,997 _ -s 7,7092005«5,942 7,362 «8,463 «8,910 9,016 =9,051 10,288 «9,523 7,451 «6,805 18,170 18,885 9,9862006«=«8,115 7,126 «8,134.8,497 8,462,8,305 «9,077,«9,403 8,466 =7,084 =9,104 10,659 8,5322007«9,740 7,122,8,068 «§=-8,343.8,231 8,010 8,547 8,259 7,642 «6,737 «5,773 8,653 7,9242008«=5,945 7,167 8,098 «=8,367 8,209 «6,762 «6,001 «45,351 «5,253 5,325 «9,662 12,107 7,351 2009 «5,882 «7,194 8,253 8,653 «8,671 «8,578 «=«9,437 «8,345.7,453,517 5,888 =8,780 7,793201065127.093 8054 8370 8310 8133 8803 8466 7692 6594 8672 13,801 8,365Average6,637 7,238 8,064 8,364 8356 7,771 7,907 7,868 7,421 6,896 9641 10,041 8,013 Maximum 10,635 8,824 9,588 10,042 10,175 9,051 10,288 10,643 9,888 17,041 30,571 22,092 10,719 Minimum 3,676 4,442 5,102 5,300 5,259 4,398 4,782 3,920 4,847 4,857 5,187 4,280 5,225 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-16 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 12.1-4.Monthly Flows at Gold Creek (cfs) Year Oct Nov Dec dan Feb Mar Aor May Jun dul Aug Sep =Annual19507,080 7,739 8,552 8,893 8,909 7,461 6,854 8,206 9,240 9,156 9,033 6,913 8,169 1951 6,828 7,827 9,036 9,637 9,968 8,510 8,194 9,421 9,828 9,384 9,125 8,674 8,863 1952 6,910 7,713 8,548 8,842 8,705 8,574 9485 11,421 15,439 12,149 9,663 7,980 9,62119537,523 7,748 8,356 8,563 8,480 8,350 9,259 11,916 12,152 9,940 11,622 15,745 9,97019547,153 7,590 8,496 8,839 8,793 8,680 9,737 12,566 12,782 10,710 10,061 10,756 9,682 1955 6,869 7,689 8,529 8,796 8,657 8,447 9,221 11,199 14,007 11,602 13,248 14,809 10,25619566,888 7,588 8,522 8,880 8,941 8,904 9,983 13,237 14,114 11,743 20,000 18859 11,480 1957 6,978 7,720 8,499 8,718 8,607 8,372 9,061 11,559 12,953 10,564 11,294 19,884 10,343 1958 8,885 7,790 8,497 8,464 8,218 7,972 8523 10,533 11,924 10,389 15,283 7,478 9,51319596,779 7,626 8,545 8,910 8,885 8,734 9,742 12,694 12,795 11,628 12,822 17,645 10,56619607,929 7,701 8,545 8,776 8,623 7,045 6,332 8,164 8,902 9,389 14,148 20,884 9,69819618,827 7,688 8,556 8,752 8,479 8,269 8.858 11,812 14,044 10,897 19,777 13,685 10,82019627,669 7,610 8,480 8,739 8,608 8,404 9,092 10,187 14,724 15,036 23,599 16,429 11,56819637,433 7,383 8,319 8,606 8,549 8,172 8,770 12,616 12,939 13,231 23,729 12,800 11,07219647,546 7,598 8,442 8,722 8,718 8,582 9,538 11,371 16,286 9421 11,870 9,487 9,797 1965 7,579 7,567 8,258 8,591 8,580 8,471 9355 11,754 13,223 11,615 9,848 16,803 10,132 1966 9,851 7,761 8,702 9,015 9,021 8,946 10,023 13,023 16,327 11,414 10,521 8291 10,247 1967 7,362 8,482 9,966 10440 8316 7,213 5,955 10,164 14,369 12,397 13,223 17,340 10,441 1968 6,783 7,610 8,532 8,871 8,763 8,550 9,182 12,455 13,584 10,577 13,913 9,014 9,82819696,590 7,559 8,521 8,988 9,154 7,733 7,254 8,190 8,875 9,035 7,558 5,113 7,87819704,397 4,636 §,259 5,488 5,424 4,549 4,876 7,700 10,777 10,212 9,462 7,547 6,701 1971 8,590 9,734 7,278 7,145 =7,737 6,924 5,865 4808 14014 10,650 10,490 12,994 8,842 1972 7,032 7,624 8,603 8,882 8,734 8,431 8.921 14,290 13,952 11,761 19,559 13,248 10,93719736,827 7,691 8,587 8,952 9,000 7,487 6,827 7,736 10,336 9,026 9,158 6,894 8,207 1974 6,721 7,751 8,838 9,368 9,616 8,179 7,803 9,984 9,146 9,118 8,973 7,722 8,59919757,535 8,923 8,277 7,264 8,120 7,383 6,039 10,435 14,830 11,975 9,059 9,755 9,13319768,547 7,512 8,366 8,750 8,761 8,670 9,703 11,930 13,126 11,053 9,697 7,395 9,46519777,708 9,245 8,032 7,554 8,285 7,508 6,112 9,497 15,931 11,104 9,221 7,909 9,00619787,312 7,824 8,584 8,745 8,577 7,002 6,242 7,356 8,862 9,024 9,021 7,801 8,02919796,800 7,684 8,531 8,853 8,821 8,687 9612 12,262 12,929 12,123 9,286 8,152 9,482 1980 8,011 7,862 8,407 8,540 8374 8,150 8716 10,631 13,405 12,211 20,958 13,467 10,746 1981 8,084 7,572 8,060 8,339 8,406 8,101 8620 10003 9,869 13,706 37,901 14,319 11,964 1982 7,706 7,846 8,270 8573 8,558 8,376 9,180 11,220 12,595 10,329 9,050 14652 9,69119837,875 7,638 8,570 8840 8645 8,294 8,920 11,837 11,703 9,332 13,019 14011 9,89319848,887 7,560 8,300 8,491 8,299 8,006 8415 10,359 11,451 9,303 16,346 9,705 9,608 1985 7,270 7,860 8,710 8,874 8,701 8,571 9,234 11,998 13,600 10,149 9,454 14,245 9,884 1986 8,230 7,777 8,634 8,927 8,861 7,261 6,571 7,944 8,878 9,035 9,023 11,491 8,549 1987 12,895 7,721 8,369 8,593 8,478 8,275 8,924 10,806 11,843 11,726 15,180 13,348 10,531 1988 6,956 7,607 8,442 8,773 8,706 8,536 9,262 11,895 12,766 10,662 14,957 14,284 10,24219898,544 7,679 8,451 8,735 8,589 8,369 8.966 10,865 12,351 10,568 13,956 15,828 10,245 1990 8,836 7,662 8,413 8695 8593 8,407 9,327 12,164 12,069 21,115 23,723 26,736 13,004 1991 8,582 7,638 8,567 8,822 8,717 7,122 6,352 6,733 9,501 9,124 9,226 12,323 8,553 1992 7,362 7,644 8,574 8.846 8,726 7,171 6,415 6,687 9,180 9,263 14,552 10,426 8,74119936,714 7,748 8,610 8,921 8,840 8,634 9,518 12,339 11,558 9,987 9,160 19,403 10,109199410,193 7,701 8,460 8,620 8,433 8,159 8925 10603 12,625 9636 16524 9,477 9,962 1995 6,747 7,757 8,616 8.912 8,827 8,638 9,537 11,641 12,151 10,883 10649 18,975 10,270 1996 7,946 7,656 8,426 8,762 8,737 7,218 6,545 7,109 8,986 9,028 9,074 7,432 8,076 1997 7,631 9,152 7,035 7,174 =8,175 7,065 5,726 7,521 9,912 10,094 9,581 7,538 8,049 1998 7,006 8,119 9,401 10,073 10,498 9,037 6,505 6,928 10,594 9,972 9,142 9,070 8,852 1999 8,961 7,700 8,469 8,689 8,589 7,035 6,317 7,179 9,185 9,202 18,771 11,661 9,326 2000 7,776 7,715 8,452 8,696 8608 8,409 9,070 11,010 13,572 11,498 12,747 15,041 10,217 2001 9,354 7,704 8,463 8,687 =8,584 8,382 8,993 10,743 13.455 10604 9,472 10,465 9,57720026,783 7,701 8,556 8,847 8,791 7,246 6,522 7,795 8,953 9,026 9,529 11,613 8,441200311,410 8,037 8,288 8,334 =8,302 6,555 5,891 6,373 9,051 15,999 21,252 13,995 10,319 2004 9,311 7,626 8,486 8,761 8,685 8,505 9572 12,397 11559 9,708 11,724 7,198 9,47220056,578 7,708 8,785 9,200 9,268 9,264 10,787 14139 13,319 11,406 21,985 22,849 12,114 2006 9,621 7,549 8,434 8779 8,742 8,579 9,384 12,141 12,492 11,075 14490 12,869 10,357200711,610 7,730 8523 8745 8610 8,358 8,993 11,284 11,088 10493 9151 11,062 9,645 2008 6,891 7,790 8,646 8,733 8,570 7,036 6,334 7,479 8,935 9,154 13,108 14693 8,945 2009 6,918 7,505 8,516 8,933 8,934 8.849 10,282 12,327 11,461 9,907 9128 11,019 9,480 2010 7.830 7638 8420 8665 8582 8396 9169 114.889 11191 14311 12177 16595 10,157 Average 7,860 7,758 8,436 8,682 8647 8,036 8,252 10,369 11,995 10,850 13,267 12,521 9,727 Maximum 12,895 9,734 9,966 10440 10498 9,264 10,787 14,290 16,327 21,115 37,901 26,736 13,004 Minimum =4,397 4,636 5,259 5,488 5,424 4,549 4,876 4,808 8,862 9,024 7,558 5,113 6,701 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-17 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 12.2.Project Generation Monthly project generation potential is summarized on Table 12.2-1,which shows a long-term average annual energy generation capability of 2,760 GWh (or 2,800 GWh when rounded to two significant figures).The generation values represent generator output without deductions for outages and assume that all potential generation is usable.The generation results presented in this section are for a powerhouse with a total generating output of 606 MW at the normal maximum operating level (equivalent to a turbine capacity of 618 MW)and including a preliminary inflow forecasting operation.Various alternative conditions (the amount of load following,the installed capacity,the inclusion of forecasting)within reasonable ranges have relatively small effects on the estimated total amount of annual generation.It is expected that further refinements in project operation plans will be made by AEA in future phases of project development. Figure 12.2-1 is a plot of the annual generation for the 61-year period of simulated operation. For a hydroelectric project that is dependent on variable natural inflows,annual generation is relatively uniform.Multi-year dry periods result in the lowest annual generation values. An objective of project operation was to shape the monthly potential generation in a manner that is similar to the Railbelt monthly electricity load.Because the natural reservoir inflows have a very high seasonal variability,including having the lowest inflows in the winter when electricity demand is highest,utilization of reservoir storage is the primary method of shaping seasonal generation to correspond to the Railbelt's needs.Figure 12.2-2 shows that Susitna-Watana generation can be shaped to closely correspond to monthly Railbelt generation demand.Further improvement could be made with more detailed inflow forecasting methods. Figure 12.2-3 is an hourly generation duration curve for the 61-year period of simulated operation.In the simulated operation,generation reaches a maximum of about 600 MW (606 MW generator output;600 MW transformer output)during periods when the reservoir reaches or exceeds the maximum normal operating level at El.2050 ft.Additional operating refinements would be expected to reduce the percentage of time the powerhouse operates at its maximum capability. Figure 12.2-4 is a plot of hourly Susitna-Watana generation for the 15 month period of simulation from July 1,1984 through September 30,1985,which is the selected average water period for Susitna-Watana environmental studies that are in-progress.The intermediate load following operation is apparent by the repeated daily fluctuations in generation. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-18 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Table 12.2-1.Susitna-Watana Powerhouse Generation Potential (GWh) Year Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Annual 1950 196 228 262 266 231 200 168 #§4(156 154 154 177 169 2,360 1951 200 233 273)«#278 «6.2420 «©6213 «©6179 «61600 «61540 =1840 174 153 2,413 1952 195 227 261 263 «228 «©6235 S235 246 240)217-Ss«*191 170 2,708 1953 201 225 258 260 225 232 230 226 209 202 245 #394 2,907 1954 204 227 261 264 «229°«23700 «2370 -238)=-223,212176 270)2,776 1955 195 227 260 262 226 232 =231 237)229)209)222,363s 2,893 1956 198 227 262 266 231 239 240 244 =221 203 390 429 3,149 1957 196 226 259 260 225 231 229.233°«213.2040237)4435s 2,949 1958 245 225 255 254 219 225 221 222 209 202 35 19%2,817 1959 195 227 262 265 229 237 237 8 241 227.0 214 ==.201 361 2,897196022422662606261225194161146#175 166 279 435 2,751 1961 246 226 258 258 222 228 222 220 208 #39199 411 335 3,032 1962 213°227-0 «2600 262)226 232s 2290 231 210 305 450 376 3,220 1963 209 226 «8258 6259 224 230 228 8 231 211 230 450 355 3,109 1964 210 226 260 263 228 236 236 «4246 )«©6225 «©6210 312 240 2,892 1965 202 226 260 263 228 235 234 4239 «82270 6«6©6210 6198 362 2,884 1966 260 228 263 266 231 238 238 4246 «6234 «66218 188 178 2,786 1967 207.243°«285 «=.278)S'_187)168 «=124s 1600 237)217)213,369s 2,687 1968 197 227 261 263 «2270 «232-2299 233 213)200 356 236s 2,873 1969 196 229 265 269 234 203 171 159 184 «215 186 118 )=2,430 1970 104 119 139 139 119 103 105 131 155 162 172 169 1,617 1971 216 255 190 186 174 163 123 83 204 =221 191 329 2,336 1972 206 226 258 259 223 229 225 224 «+203 268 «#34450 366 3,137 1973 196 228 263 266 231 199 167 157 146 178 178 165 2,374 1974 198 231 269 274 «6239's 209)178 «=167)1540 166185 166 2,435 1975 213 251 229 190 184 172 127 173 234 213 188 217 2,391 1976 237 «226 «©2600 =264 229-236 236 239 229)219 192.186 =2,753 1977 215 254 217 197 187 175 128 159 234 212 187 178 2,342 1978 196 226 259 260 224 193 159 143 155 167 202 200 2,384 1979 195 227 261 264 «#229 «©2360 «62350 240)2260S 212,185)=199 2,710 1980 222.225 256 257 22t 227)2230 «6224 )«66213 «201 450 347 3,067 1981 234 #225 256 257)220 225 8 221 217,207)219 =450 368 =3,099 1982 199 225 257 258 223 229 226 228 216 206 227 302 2,795 1983 205 226 259 260 224 230 226 226 214 215 248 343 2,877 1984 248 «#225 4257 4257 «6221 989226221 222211 207)«+387 =6245)-_-2,926 1985 195 226 260 261 225 231 228 235 224 =211 194 328 2,818 1986 212 226 260 262 227 195 162 149 185 234 196 293 2,601 1987 319 225 257 258 223 229 225 225 215 205 340 332 3,053 1988 195 226 260 262 226 233 230 230 212 199 347 343 2,964 1989 237-0 «226-258 =260 224)229)225 2240213.203.296)=-s 412 -s 3,008 1990 245 225 258 260 224 230 225 215 193 417 450 435 3,377 1991 242 227 260 262 226 194 8 161 149°#138 4169 197 323 2,547 1992 209 «227)««260 262-ss226-'-s 194 Ss 160 149 140)148)=3326S 2732574 1993 196 228 261 264 228 234 232 228 «6.209 «205 =191 403 2,8781994279°2250-257)257)2210227)222 219 207)194 §=-402 248)2,957 1995 196 228 261 264 228 234 231 226 215 203 244 435 2,963 1996 224 +226 260 263 228 196 163 153 162 177 183 166 2,401 1997 214 254 «86199 186 184 164 119 128 154 159 158 155 2,067 1998 203.237)277 86281 246 218 1370 114 #154 156 160 191 2,374 1999 248 226 258 259 224 193 160 147 141 160 341 306 2,664 2000 216 226 258 260 224 230 227 231 217 200 322 357 2,969 2001 260 226 258 259 224 230 227 233 219 208 185 274 2,802 2002 195 227 261 263 228 196 163 151 165 175 170 273 2,468 2003 306 «62260 «253.253)218)=187)152.138 =138)237)450 325)2,8812004260226260262227233°232 223 «6205 §«€6©198 §282 191 2,799 2005 197 230 266 270 234 244 244 237 209 217 450 435 3,234 2006 267 226 2600 263)227)2340 232-236 223 211)=229)327)2,935 2007 312.226 259 260 224 229 225 222 211 207 187 275 2,839 2008 198 227 259 260 225 193 160 145 147 164 314 384 2,678 2009 196 227 262 265 230 238 236 224 209 204 +191 282 2,765 2010 218 226 258 260 225 231 229 225 212 205 272 386 2.947 Average 218 227 255 256 221 216 201 200 199 204 268 293 2,760 Maximum 319 255 285 281 246 244 244 246 240 417 450 435 3,377 Minimum 104 119 #139 1389 «#6119 103 105 83 138 148 158 118 1,617 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-19 December 2014 Za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 4,000,000 Long-term average :annual energy generation. 3,500,000 \ 3,000,000 -_.|-___- = = =:=2,500,000 FPP EET EE TE EEE ELLE LP i--THEE TEEPEEE 72: %7 < &2,000,000 « a7 ¢ Ww -q 1,500,000 - } 4 Cc Pd 1,000,000 - 500,000 - 0 $Ses eB 8 8 SS PSESSESRSSSSeERSRRSRBE882SrrfeFr=rr Se er =er fr fe fF fF fF FF -+-r er Fe =-NN NNN ON Figure 12.2-1.Annual Average Generation Potential (MWh) 12% @ Total Railbelt : mWatana r<i 210%| g |||!5 a=:..ce)|:Ln ftai58%+oad 7 --_-4 3 i au 7.-_: e 3 :=<|! 8 6%+.abo af wef oe sefee he seofeee Be oni ve é || «i : CY=4%+-_aa oa :-+_-oa 4 3 |i-4 | ©|[O]i |i >: s i : |i 5 2%:ot.+ao +a ++.a -_4 2 [|||!| | 0% Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 12.2-2.Comparison of Susitna-Watana and Total Railbelt Monthly Generation Pattern Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-20 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 700 7||| 600 ** =Watana Hourly Generation Duration CurvenQOo||Based on 61 Years of Hourly Operation ,t =|= 2400 ----3 ° 2> 8 i=300 «: < s i iJ= 200 100,mp eepe -|- 'Incorporates existing hydro load following at Bradley,Eklutna,and Cooper and forecasting 2024 Railbelt generation loads., 0 0 10 20 30 40 50 60 70 80 90 100 Percent of Time Watana Output is Equaled or Exceeded Figure 12.2-3.Modeled Susitna-Watana Powerhouse Hourly Generation Duration Curve 700 Average -July 1,1984 -Sept.30,1985 | ::; |j i i600|||mob || || : ||:;-Watana Generation (MWh) 500 + =||Es=|_jo |g 400 i -pose be _. 3 |2 ipo cot300prPyegPeHD pty ll tthe fe fe Pee 5fe]if = i vt YWyA i!"vMy Incorporates existing hydro load following at Bradley.Exlutna.and Cooper and forecasting. ;|pot!i |tL ent tng tee ec :i i :|i : !i i ':i :|i ::|i |::2024 Railbelt generation loads.\\i :\! 1-Jul-84 31-Jul-84 30-Aug-84 29-Sep-84 29-Oct-84 28-Nov-64 28-Dec-84 27-Jan-85 26-Feb-85 28-Mar-85 27-Apr-85 27-May-85 26-Jun-85 26-Jul-85 25-Aug-85 24-Sep-85 Figure 12.2-4.Modeled Hourly Susitna-Watana Generation for an Average Water Year Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-21 December 2014 -za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 12.3.Downstream River Flows and Depths Reservoir operations of the project will result in a seasonal shift of flows at Gold Creek as depicted on Figure 12.3-1 for long-term average monthly flows.Historical Susitna River average flows would be decreased under post-project conditions for the ice-free season from June through September.Based on the monthly average flows,a brief initial comparison of pre- project and post-project river depths at Gold Creek is provided in this section. 30,000 25,000 emus Monthly Average Natural Flow20,000 +---==Monthly Average Post-Project Flows 15,000 Flow(cfs)10,000 5,000 0 || 1-Oct 1-Nov 1-Dec 1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep Figure 12.3-1.Monthly Average Natural and Modeled Post-Project Flows in the Susitna River at Gold Creek The USGS regularly measures flows at cross-sections near Gold Creek to provide data for gaging station 15292000.The USGS provided cross-sectional data is shown on Figure 12.3-2 (with exaggerated vertical scale)for the flow measurement of 18,800 cfs that was made on August 15, 2013,along with the maximum and minimum water levels recorded on that day.For the purposes of this analysis,the river depth will be taken as the average of the deepest 50 ft.width. At the measured flow of 18,800 cfs,the indicated average depth in the deepest 50 ft.width of channel would be 12.4 ft. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-22 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Figure 12.3-3 provides a comparison of hourly average flow stages at Gold Creek for the August 15,2013 day of flow measurement and a day (May 26,1985)from the simulated intermediate load following case (ILF-1)that had a similar flow.The recorded average flow at Gold Creek on August 15,2013 was 18,900 cfs and the simulated average flow on May 26,1985 was 18,800 cfs. Gold Creek | Gold Creek River Bottom 6 ow Maximum water level on 8-15-2013 -®Minimum water level on 8-15-2013 |1 || e+:: 2 o a %!i a 2 For the deepest50feet.the averageriverbottomlevelis-2.82 feet ||0 een .: ;!Note:This plot uses the same vertical datum as used in dataprovidedbytheUSGS. 2 i | A entree eter meenentanerttatabermmmmrnenencerrcercnrerseercrnnpc:ID on SIF crveneseeeseshesnnenaranerersrscessensnseennmamnsebesssrsessanersnanannnenssersrarssstsesfenasearearsrorerssesteserenaesnasantedueroareastasternannannasinerseenserenispesnacerariesstiscasenarasnneraeensaetipassanenns tenananmameetnsncnts sec} 5.so | 0 50 100 150 200 250 300 350 400 450 Horizontal Distance (feet) Figure 12.3-2.USGS Surveyed Cross-Section at Gold Creek Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-23 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 40.00 9.80 Stage(feet)'/Recorded |Simulated : Stage 8/15/2013 |5/26/19859.60 +J (feet)(feet):|aX /Average 9.71 9.68 |NjMaximum9.92 9.90 :Minimum 9.47 9.38 9.50 \Range 0.44 0.52 SY/ eRecorded Stage on August 15,20139.40 Veo -#Simulated Stage for May 26,1985 9.30 |!- ie)6 12 18 24 Hours Figure 12.3-3.Recorded and Simulated Susitna River at Gold Creek Stage Comparison Data provided in the previous two figures are for example days with comparable flow rates at one location.Flow and water level conditions will vary from day to day and from location to location.Table 12.3-1 provides the depths for pre-project and post-project average monthly flows at Gold Creek.The maximum depth reduction shown in Table 12.3-1 would be from 13.32 ft.to 11.05 ft.in June,which is a difference of 2.27 ft. Table 12.3-1.Ice-Free Season Monthly Average Flows and Depths at Gold Creek Pre-Project Conditions Post-Project Conditions Month Flow Stage Depth Flow Stage Depth (cfs)(feet)(feet)(cfs)(feet)(feet) June 26,292 10.50 13.32 11,995 8.23 11.05 July 23,988 10.22 13.04 10,850 8.01 10.83 August 21,382 9.88 12.70 13,267 8.48 11.30 September |13,737 8.57 11.39 12,521 8.34 11.16 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 12-24 December 2014 Section 13 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.CONSTRUCTION METHODOLOGY AND ESTIMATES OF COST The project procurement strategy and contract strategy -based on the project risk profile - have not yet been formulated.For the purposes of completing the construction planning and estimating recorded in Sections 13 and 14,a procurement strategy has been assumed that is a "best estimate”of an appropriate strategy,based on worldwide experience of similar project development of similar size and complexity under a similar risk profile. 13.1.General During the early part of 2012 -the first year of this feasibility study -a cost estimate was prepared for the project.The estimate was performed based on the concept presented in the Federal Energy Regulatory Commission (FERC)Pre-Application Document (PAD)submitted to FERC in December 2011.The estimate was updated at the end of 2012. As with all Opinion of Probable Construction Cost (OPCC)prepared by MWH and others,the results are classified according to AACE International -formerly the Association for the Advancement of Cost Engineering (AACE),as discussed below.The PAD estimate is regarded as between Class 5 and Class 4;the current estimate,as discussed below,is considered to be at a Class 4 level,although certain discrete elements of the work have been detailed and estimated using methodology that is more like that used for a Class 3 estimate.The OPCC has been organized in accordance with the FERC Uniform System of Accounts. Upon completion of the proposed geotechnical site investigations -including adits -sufficient information will be available to the engineering team to clarify and further design and detail key aspects of the project preliminary design,reducing cost uncertainties,such that a Class 3 estimate might be implemented. The project estimate,submitted to AEA in January 2012,was the subject of an independent check,under a separate contract issued by AEA.Much of that estimate was prepared,under subcontract,by Paul Hewitt of International Project Estimating Ltd.To maintain an independent review of the estimating process,the estimate included in this report also utilized the input of Mr. Paul Hewitt using the joint venture methodology described in Section 13.4. During the performance of engineering feasibility studies there have been many improvements, refinements,and adjustments made to the project layout and ever more detailed assessment of the construction challenges and logistics.These changes -as well as the ongoing escalation of construction costs according to price inflation -primarily account for the differences between the various estimates. , Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-1 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The estimating tasks consisted of estimating the anticipated total cost of the project,focusing on the construction costs and the OPCC,but also including the estimation of pre-construction project development activities,design and environmental work,various AEA costs,and the cost of construction management and engineering during construction.Licensing,environmental mitigation,owner's management,and land costs were provided by AEA for inclusion in the overall project estimate. The AACE classification system indicates the expected ranges of costs associated with its classifications.However,for this feasibility study probabilistic estimating practices were used, and an "adjusted”cost estimate was established accounting for possible price,quantity,and work scope variability in estimating.For the current estimate a "management reserve”has been suggested as explained below,but this should be explored in more detail in the future.All costs for the feasibility estimate are expressed in second quarter (Q2)2014 USS. The OPCC and project cost estimate described do not include financing costs,interest during construction,or escalation.Those items will be included in separate financial planning documents being prepared by AEA. The standard term used in the industry for the estimate of construction cost -and used herein -is the OPCC.Normally the OPCC is the estimated construction and equipment procurement cost (i.e.,the expected successful bid price,including various allowances a bidder will always include following its pre-bid assessment of "known unknowns”). Separately allowances for events and occurrences affecting cost after the commencement of construction have not been made at this stage.It is prudent to perform a further probabilistic analysis after the results of the current dam site geotechnical investigations and environmental studies are available,to address the possibility of unforeseen events impacting the "as built” project cost. The term "opinion”is important,as the estimating product represents -in many respects -an opinion based on a broad understanding of the construction industry.OPCCs presented herein, including evaluations of project budgets,and/or funding,represent MWH's best judgment as a design professional familiar with the construction industry.Such opinions or evaluations are based upon current market rates for labor,materials,and equipment.Future costs of labor, materials,or equipment,construction contractor's methods of determining bid prices, competitive bidding environments,unidentified field conditions,market conditions,hyper- inflationary or deflationary price cycles,and other factors may affect the OPCC.It is important to recognize that the OPCC is a "snapshot”in time and that the reliability of a given OPCC will degrade over time.MWH cannot and does not make any warranty,promise,guarantee,or representation,either express or implied that proposals,bids,project construction costs,or cost Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-2 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. associated with future operation or maintenance will not vary substantially from MWH's good faith OPCC as presented herein. For the 2013 round of project estimation,instead of an independent estimate,the methodology of 'Joint venture”estimating was implemented,using an independent estimator Mr.Paul Hewitt. Each party prepared a construction cost estimate completely independently,before meeting to rationalize their independent estimates,line by line. Having rationalized their two estimates,a joint agreement was reached for the potential highs and lows for each line item,for the variability analysis. A key part of the estimating tasks early in the feasibility studies related to comparative cost estimation of the type of dam and the number and capacity of the power plant generating units. The comparison of three different configurations of the project (based on three possible types of dams considered for this site),was carried out during the first year of studies.A comparison of the three types (Earth Core Rockfill Dam,Concrete Faced Rockfill Dam,and roller-compacted concrete [RCC])was performed by estimating the construction costs of the facilities that are not common to the dam types.A separate layout was drawn for each type of dam and detailed as necessary to determine the basic unit quantities associated with each development.The most economic dam that performs with the appropriate level of safety was determined to be one constructed of RCC.This exercise is described in more detail in Section 7. A similar exercise was performed later in the development of the project configuration,based on the comparison of three different potential unit sizes (3 x 200 MW @ water level El.1950 ft.; and 4 x 150 MW and 6 x 100 MW at the same head,all resulting in a 600 MW nominal capacity plant -also compared was 3 x 200 MW @ normal maximum operating level).In that comparison,also described in Section 7,the common items were not estimated,but all civil and mechanical components associated with each alternative power facilities arrangement were estimated and compared using proprietary MWH software,that prepares designs based on parametric algorithms. The following discussion is presented as five parts: »Estimating methodology; «Adopted construction methodology (forming the foundation of the estimate); «The construction cost estimate; »Non-construction costs; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-3 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «The total program cost estimate;and, «The projected construction schedule (addressed in Section 14). All these aspects of project planning,particularly construction planning,are completely interwoven.The estimating methodology section contains general material with respect to the estimating process.The adopted construction methodology highlights the construction planning, logistics and methodology for the various parts of the work,broken down in the assumed contracts.The construction and project cost estimate sections present the project team's estimate and background on the respective construction costs and the estimated total project cost.Finally, the schedule section highlights the schedule assumptions and the key dependencies of the schedule. Due to the project scale,the limited amount of design work completed to date,and validation time constraints,the Pareto principle was used to focus the pricing verification effort to the areas of significance,and aspects to which the project costs are particularly sensitive.The Pareto principle simply states that,when analyzing events or populations,approximately 80 percent of the effects will typically arise from just 20 percent of the causes.The 80/20 rule implies that a few (20 percent)drivers are vital and the many (80 percent)are trivial.Hence,typically a small minority of events or results can significantly impact or drive a cost estimate's bottom-line. Consequently,the analysis of the construction methodology and costs has been concentrated on those areas having the greatest likelihood of cost significance and impact on the bottom line project cost. The principle was applied as a tool to decompose the significant amount of cost estimate detail, thereby expediting the definition and segregation of cost driver elements.Hence,for the purposes of this validation exercise,a project cost driver is defined as a component of the minimum number of elements,within a specific feature of work,that approximate 80 percent of the feature's total costs. This simplification has allowed the project team to focus on the major items of work or efforts (such as the logistics)that most affect the total cost of the project.These major items were optimized to the greatest extent possible at this stage,and have the greatest potential to reduce overall project cost.These large cost items also will need additional scrutiny in ongoing project development and future reviews of project cost for accuracy. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-4 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.2.Estimating Methodology -Construction 13.2.1.Basis of Pricing The OPCC reflects the estimator's opinion as to the probable costs that a "prudent”contractor would include in the tender to construct the defined facilities. Pre-construction activities and expenses related to the management and support of field construction activities are included elsewhere in the reporting of estimated project costs.The estimate of the required overall project investment cost consists of three discrete parts: 1.Construction and equipment procurement (generally these are considered construction costs). 2.Other activities required to implement the project (i.e.,land acquisition,engineering services,legal,and project and financial management). 3.An allowance for additional costs arising from uncertainties and unplanned risk events which could occur on the project. The following sections address the derivation of the "construction cost”together with highlights of allowances applied,followed by a discussion on the derivation of other project costs. 13.2.2.Estimate Classification As noted above,estimates are usually classified in accordance with the criteria established in AACE's Cost Estimate Classification System,referred to as Recommended Practice 69R-12 (AACE,2013).The AACE Cost Estimate Classification System maps the various stages of project cost estimating together with a generic maturity and quality matrix,which can be applied across a wide variety of industries and capital infrastructure developments. This estimate is considered consistent with Class 4 classification criteria described by AACE as: "generally prepared based on limited information,where the preliminary engineering is from |to 15 percent complete.A Class 4 estimate is generally usedfor detailed strategic planning,business development,project screening,alternative project analysis, confirmation of economic and or technical feasibility,and where preliminary budget approvals are needed to proceed.Examples of estimating methods used would be equipment and or system process factors,scale-up factors,and parametric and modelling techniques.” Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-5 December 2014 -yzZ SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT For comparison,a Class 3 estimate is described by AACE (particularly with reference to hydropower development)as: "typically form the initial control estimate against which all actual costs and resources will be monitored.Typically,engineering is from 10 percent to 40 percent complete,and would comprise at a minimum the following:preliminary general arrangement drawings,powerhouse,intake and spillway drawings and specifications,essentially complete geotechnical investigations and hydrotechnical studies,preliminary earthwork drawings for excavation defining unclassified and rock,rock support and foundation treatment and for embankment complete with definition for various zones,complete one line diagrams,equipment performance specifications complete for turbines,generators, governors,and exciters,preliminary auxiliary mechanical and electrical systems,and preliminary piping and instrument/protection and control/telecom systems.Also, procurement strategy identifying long lead items of equipment.” It should be noted that -to achieve Class 3 status -"essentially complete geotechnical investigations”are necessary,a condition not achieved until the proposed adits and additional drilling are complete. Although there are many factors -depending on the type and complexity of the project, generally MWH interprets the classes defined by AACE as stated in Table 13.2-1. Table 13.2-1.AACE Estimate Classes AACE Class Development Phase Design Completion 5 Conceptual Design 0%and 2% 4 Preliminary Design 1%and 15% 3 Design Development 10%and 40% 2 Construction Document 30%to 75% 1 Check Estimate 65%to 100% The above is illustrated in Figure 13.2-1. Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 13-6 Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years.GrowthfromEstimatedCostsIncludingContingency(%)|sms -10 4 -20 4 _ ----2o-30 4 . 3a -40 4 Maturity Level of Project Definition Deliverables (%)-50 . ,fi ,rn f 1. 20 30 40 50 60 70 80 90 100 Class 2 j Class 3 {Class 1 { Figure 13.2-1.Variability in accuracy ranges for a Hydropower Estimate -from AACE 69R-12 Class 5 Class 4 +95 -25 13.2.3.Estimating /Scheduling Methodology or System The estimate described relies heavily on a unit pricing methodology using unit prices derived from cost reports and estimates for other major dams in the United States,including Alaska,as well as data from projects of a similar complexity and size around the world. Some key prices have been derived by considering work cycles,crew analysis,and resources. Detailed construction schedules have been completed in Primavera P6 project management software as described in Section 14. Table 13.2-1 below,summarizes the typical estimating methodology employed relative to AACE cost estimate classification. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-7 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 13.2-2.Typical Estimating Methodology Relative to AACE Cost Estimate Classification AACE Class System Methodology 5 Spreadsheet Parametric/Stochastic 4 Spreadsheet Semi-detailed Unit Price 3 IPE™Detailed Crew Analysis 2 IPE Detailed Crew Analysis w/Budget Quotes 1*IPE Detailed Crew Analysis w/Firm Quotes *Class 1 estimates are reserved for actual contractor proposals that rely on finalized bidding documents and access to all pre- tender addendums. **International Project Estimating System 13.2.4.Estimating Accuracy and Contingency AACE provides guidance with respect to estimating accuracy and typical contingencies. Estimating accuracy has been addressed by the probabilistic analysis of the price,quantity and scope variability as described below.Table 13.2-2 provides some basic guidance from AACE regarding contingency level recommendation relative to estimate class and input design. Table 13.2-3.Estimating Contingency Level Recommendation AACE Class Design Typical Contingency 5 <2%20%to 40% 4 <15%10%to 30% 3 10%to 40%5%to 20% 2 30%to 75%0%to 10% 1"65%to 100%0%to 5% *Class 1 estimates are reserved for actual contractor proposals that rely on finalized bidding documents and access to all pre- tender addenda. Based on the level of detail of the design presented in this report,and the required geotechnical investigation,it would be appropriate to allow a contingency in excess of 20 percent -and probably approaching 30 percent -to the estimate for the purposes of financial analysis. The high and low range of quantities and prices used as input to the probabilistic analysis are presented in Appendix B10. 13.2.5.Quantities Detailed line item quantities were developed by quantity take-offs from the three dimensional models,from the feasibility drawings and engineering sketches. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-8 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.2.6.Significant Assumptions Many assumptions of the contracting experience and competency must be made in deriving an estimate such as this.In this case the following have been assumed: =Competitive bid conditions will prevail at tender. *Normal and appropriate industry commercial terms will attach to all procurements. «Stable market conditions will prevail without significant geo-political events or economic disruptions. =An optimized contracting strategy will be employed by AEA to efficiently sequence and coordinate the work scope. ="No trade discounts were considered. «Bidders will develop competitive proposals with regards to materials pricing and labor productivity,and will not include allowances for changes,extra work, unforeseen conditions,or any other unplanned costs. «Estimated costs are based on a minimum of three bidders for each major contract. Actual bid prices may increase if there are fewer bidders or decrease for a greater number of bidders. *Bonding and Insurance will be available to the contractors. =Contractors will structure their proposals to promote positive cash flow and to minimize the requirement for them to finance their operations. 13.2.7.Direct Cost Development Directs costs representing the project's fixed physical scope have been estimated against a work breakdown structure (WBS)to organize the estimate details.Direct cost detail is decomposed to multiple sub-levels,which are referred to as item activities.Class 5 and 4 estimates typically apply all-in unit prices against the line item quantities whereas Class 3 and 2 estimates derive pricing under a crew based productivity analysis per line item. For the 2013 estimate,crew based productivity analysis has been performed for selective line items based on the construction planning performed to date in the study process -taking the estimate "beyond”a Class 4 estimate towards a Class 3 level.The construction planning is further documented in Section 14. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-9 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.2.8.Indirect Costs In accordance with normal practice for Class 4 estimates,indirect costs representing the contractor's time related variable field management expenses,or General Conditions costs,have been factored in a top-down approach as a function of running direct costs.The following have generally been used -although variations have been included for some of the packages: =Contractor General Conditions (Prime)20%of running direct costs *Contractor Design/Detailing 4%of running direct costs #Site Demobilization and Clean Up 3%of running direct costs 13.2.9.Estimate Add-Ons Similarly,add-ons representing the contractor's allowances for home office overhead expenses, sales taxes,insurance costs,risk provision and fee have been added to the cost estimate as a function of running direct costs.These are often referred to as "Overheads and Profit (OH&P). The following have been used: »Subcontractor Mark-ups:included in unit and equipment prices =Prime Contractor OH&P on Subs:included in unit and equipment prices *Prime Contractor OH&P on Self-Perform:10%of running direct costs *Contractor Insurance Program:2.0%of running direct costs "Forex cover (percent of any imported goods):0.5%of running direct costs. 13.2.10.Labor Rate As a Class 4 cost estimate,this estimate relies on all-in historical database prices and does not involve development of hourly rates for labor and equipment resources. 13.2.11.Equipment Rate In a similar manner to the labor rate development,this estimate has generally relied on all-in historical database prices and has not typically required development of hourly rates for labor and equipment resources,although some key aspects of the work such as RCC prices have been developed in more detail. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-10 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.2.12.Escalation Estimated costs reflect current (Q2-2014)prices.Unit rates or prices derived from other sources have been escalated to the second quarter 2014.No future escalation has been included in the estimate. 13.2.13.Allowances and Contingency Allowances have been made in the estimate where there is not a developed conceptual design for a specific feature that is required for construction.These items have been identified as allowances in the estimate.The only specific allowance included in the estimate is an allowance for unlisted items which has been included to cover items that are known to be included in the works but have not been detailed or measured at this early stage of design. The estimate includes an allowance for an installed price for the major generating equipment, including electrical and mechanical elements of the project.Costs for these components have been determined from a parametric analysis of completed hydro projects (maintained and regularly updated by MWH),as opposed to obtaining pre-construction pricing estimates from prospective equipment suppliers. 13.2.14.Market Conditions Prior to the global economic downturn in 2008,unprecedented market volatility was a significant unknown in contractor pricing over many years.Current market conditions have shown an aggressive approach to pricing,with contractors assuming more risk to win work.Consequently, while a bid price may be significantly under the reported "fair valuation”of the estimate,there is increased potential for claims and other compensation demands that contractors may employ to offset aggressive bidding strategies.This could affect the final price of the work being performed. 13.2.15.Construction and Contracting Aspects The following aspects of the contract strategy and administration will affect the bid (and final) price and should be carefully considered: «Extraordinary phasing constraints or requirements; =#QOnerous or unusual contract terms and conditions; *»Any owner reputation for payment and for processing changed conditions claims; and, =Owner reputation for prompt payment. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-11 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The derivation of a procurement and contract strategy has not been a part of the current engineering feasibility studies.AEA is performing internal studies on procurement and contracting strategy,the results of which were not available to the engineering team preparing this estimate and report.For this estimate,the project team has derived a contracting strategy based on the domestic and worldwide experience of MWH,the criticality of the interfaces between contractors and suppliers,a reasonable apportioning of risk between parties,and an assessment of what contract scopes would be performed by Alaskan based local contractors.The OPCC has therefore been derived based on dividing the construction work and the associated support and supply chain into the following twelve separate contracts -each initially executed with AEA,though some would most likely subsequently be assigned to the main contractor as "Nominated Subcontractors”for prudent management and the placing of risk: =Main Access Road Construction =Railroad Offloading Facility Construction #Site Development (for infrastructure) =Supply and Erect Camp «Main Civil Works Construction «Turbine and Generator Supply «Transmission Line and Interconnection Construction «Site and Reservoir Clearing «Air Transport Services «Railroad Operations «=Camp Operation «"Medical Services It is assumed that to ensure a "level playing field”for bidding,and to make sure that the contractor retains control of the various supporting work -the four service contracts below are all let by AEA as "Nominated Subcontracts”at a reasonably early stage,so that all bidders for the Main Civil Contract are aware of the terms of contract,the bidders or even the winning bidder,before submitting their own contract bid: «Air Transport Services "Railroad Operations #Camp Operation Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-12 December 2014 -Z-.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. "Medical Services After the award of the main civil works contract,the service contracts would be assigned to the main contractor to enable appropriate control over scheduling and interacting with the service providers. Although the approach has not been integrated into the estimating,it is postulated that it would be in AEA's interest to consider a number of subcontracts or supply contracts that could also be let as "Nominated Subcontracts (Suppliers)”,in the same way as the service contracts,and assigned to the main contractor for administration and direction.Potential nominated subcontracts could be: #Supply of cement to the railhead =Supply of fly ash to the railhead *Any other particular equipment supply over which AEA would wish to exercise more control,or provide as "Owner Furnished Equipment”-such as gate fabrication;crane fabrication;and instrumentation and controls. Adopting this approach would ensure competitive bidding and a greater control over costs and logistics. 13.3.Assumed Construction Methodology 13.3.1.General Detailed construction planning has been executed for the key project tasks such as road construction;bridge construction;river diversion;quarry development;dam foundation excavation;RCC placement;and transmission construction.Key factors are interwoven through the whole construction planning as follows: 1.The short construction season (but with long hours of daylight)factors into many aspects of construction. 2.The remote nature of the site results in logistical planning being a key attribute of all tasks.Although three potential road routes are still under consideration,project estimates were based on a discrete project configuration.For the sole purposes of estimation, planning and scheduling it is assumed that the southern access route will be used,with the consequent reliance on the Alaska Railroad Corporation (ARRC),and the necessary rail offloading facility at Gold Creek.Because of the complexity of this route,the result is judged to be a conservative estimate of the cost of access.No suggestion has been made of which access route to adopt. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-13 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 3.Similarly,transfer of power can be achieved in three corridors closely aligned with the three access routes.No suggestion of which transmission corridors to adopt has yet been made,but for the purposes of the estimate it has been assumed that two circuits will be placed in the east-west Gold Creek corridor and one circuit will be placed in the north (Denali)corridor. Construction planning and methodology is addressed below for each projected contract package, and there is a discussion on logistics at the end of this section. 13.3.2.Main Access Road This report does not recommend an access route.This discussion is based on the route chosen solely for the purposes of estimation ofproject cost. 13.3.2.1.Contract Description Construction of the access road,because it is almost independent of other work on the project, could be setup as a design-build or other nontraditional contractual method.For the purposes of estimation,this work has been priced as a traditional Design-Bid-Build project.The costs for design and owner cost are carried in the overall program cost. Three access routes are under consideration,but as explained above the Gold Creek route has been assumed for estimation,including an access road approximately 48 miles long.This contract does not include the permanent bridge at the site immediately downstream of the dam - which is necessary,in the interest of security,to avoid any public traffic across the dam crest. 13.3.2.2.Contract Scope This contract would include construction of the main access road from a new rail siding located at Gold Creek to the project site.The contract would include clearing and grubbing,culvert construction and all excavation.It will also include stringing the temporary power line and fiber optics lines alongside the road to provide construction power and the establishment of an interconnection with the Alaska Intertie. The contract would include the supply and erection of seven permanent bridges -each bridge being 24 ft.wide (sufficient for crossing by a Caterpillar 777 dump truck during delivery)with a capacity for a 190 ton load (such as a generator step up transformer).The permanent bridge downstream of the powerhouse will be constructed under the camp and airstrip civil works contract. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-14 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.2.3.Design Assumptions in Pricing The contract includes the construction of a 30 ft.wide roadway that will have a six inch layer of gravel surfacing.The clearing and grubbing consists of clearing the right of way,150 ft.wide for 48 miles.Seven of the bridges along the access road will be 24 ft.wide and specified to carry a load of 190 tons. The drainage across the road was assumed to be at a 300 ft.intervals.This drainage is assumed to be culvert type drainage.Guard rail has been assumed for a distance of 20 percent of the road length. 13.3.2.4.Key Aspects of Construction Methodology Once the contractor has been given notice to proceed for the construction of the access road, mobilization of equipment,manpower and supplies will be performed in two stages. The first mobilization will probably be performed via a CAT train,which will deliver some equipment and supplies to the halfway point of the road route,and also to the project site.The second mobilization of equipment and materials will take place,by railroad,to the Gold Creek Siding Area shown on Drawing 03-16C001. The Gold Creek Railroad Offloading Facility Construction will be mobilized immediately after all approvals and permit issuance.The contracts will need to establish a staging area and temporary camp areas at Gold Creek in order to allow construction to begin. The main access road construction will proceed on four fronts;from Gold Creek eastwards;from the project site westwards,and from an intermediate location both east and westwards.Once the work fronts are established,clearing and erosion controls will be first on the schedule followed by pioneering along the right of way to allow all fronts to meet up. Grubbing and stripping and stockpiling of organics will be followed by excavation and embankment construction along the alignment.Rock and common excavation will be balanced to complete embankments.Drainage crews will install culvert drainage along the way.When embankments are completed,topsoil that has been saved and stockpiled will be placed on the slopes for seeding. Bridge construction will commence at each of the seven bridge locations on the access road as the pioneering of the road reaches it.For ease of construction and an accelerated schedule a pre- engineered bridge system has been assumed.Each of the bridges -projected to be ACROW (or similar)bridges -includes multiple spans,so the immediate task that can be performed from the pioneering road is the construction of the pier foundations,piers,and abutments.It is envisaged Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-15 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. that the piers will be space frames,fabricated using large diameter steel pipe,in sections,so that they can be man-handled into place (using winches or helicopter lifts)and bolted together.To facilitate this,concrete pads will be constructed (and anchored into rock)after which the (space frame)piers will be attached,and temporarily guyed or strutted in position.After substructure completion -and when the road construction from Gold Creek has reached a stage of completion such that trucks carrying pre-engineered bridge panels can deliver them -the bridge superstructure will be launched from the west abutment of each location,immediately followed by the decking,after which the launch crew will move eastwards to the next location. Although the camp at the Railroad offloading facilities will be used for the crews working eastwards from Gold Creek,the contractor will probably elect to create small temporary camps at the other work fronts. 13.3.2.5.Construction Schedule The schedule for completion is based on a two season construction time frame.This can be accomplished with proper planning and execution of the contract.The project would be scheduled for a seven day work week on a two 10 hour shift basis for five to six months per construction season.The schedule is shown in Figure 14.1-2. 13.3.2.6.Construction Manpower The peak manpower will be approximately 230,occurring in the first season as shown in Figure 13.3-1. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-16 December 2014 wz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 250 229 200 :r \ 5-4 c >) 3 43 100 50 it) Year Year 4 S Construction Year Figure 13.3-1.Permanent Access Road Manpower 13.3.2.7.Key Logistical Aspects All equipment material and supplies will be transported to the Gold Creek Rail Siding for construction of the permanent access road and much of it will be moved by CAT Train to the east.The construction equipment required is estimated to total approximately 2,400 tons. Other major materials required for the permanent access road contract is estimated to be: Fuel 18,000 tons Food 230 tons Explosives 700 tons Cement 900 tons Fly Ash 500 tons Reinforcement 500 tons Structural Steel 4,000 tons Forms and Misc.Supplies 200 tons Total 25,030 tons As noted,helicopter usage would likely be necessary to move (space frame)pier sections across the creeks and canyons and on to the concrete pier foundations. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-17 December 2014 -w ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Prior to the establishment of appropriate borrow sources (or instead of establishing a quarry), there exists material at Curry (created as a byproduct of ARRC ballast production)that might be suitable for use as road surfacing. 13.3.3.Railroad Offloading Facility 13.3.3.1.Contract Description This contract can be setup as a design build or using other contractual methods.As part of negotiations with ARRC,and because the construction activities are so closely connected with ARRC,the construction could be carried out by ARRC as part of the Railroad Service contract. For the purposes of cost estimation,however,this construction has been priced as a traditional Design-Bid-Build contract.The costs for design and owner cost are carried in the overall program cost. 13.3.3.2.Contract Scope The scope of this work is the construction of two railroad sidings at Gold Creek,each approximately 4,500 ft.long,together with another shorter spur.It would require clearing and grubbing of the entire area needed for the facilities.Included in the contract work is the creation of storage areas,parking areas,fuel storage areas,concrete hard standing,covered storage areas, offices and maintenance shops (for use during the whole project construction)lighting, temporary and emergency power generation,a permanent connection into the fiber optic cables alongside the ARRC (for the project construction and for permanent use of the finished project) and necessary water supply and sewerage,etc. The contractor will also prepare the site for the temporary accommodation that will be provided by the Camp Supply and Erect.Part of the initial camp at Gold Creek,used for the road construction and initial site works,will subsequently be relocated to the dam site.The final accommodation (for the duration of the project)at the site after completion of the facility will be enough accommodation for those operating the offloading facilities,for transitory workers and for emergency -for example when inclement weather shuts down the access road or the ARRC, leaving personnel stranded. The contract scope will not include the installation of any switch on to the ARRC siding at Gold Creek -as ARRC insist that they perform that type of work themselves at all locations on the system. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-18 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.3.3.Key Aspects of Construction Methodology All work under this contract will be supplied via the ARRC,and must be done in close cooperation with the ARRC. At the same time that the offloading facility is being created,the contractor for the road will be using the facility,and the Camp Supply and Erect contractor will be constructing facilities which will immediately be used for workers for all other concurrent contracts until the facilities are subsequently partially removed. 13.3.3.4.Construction Schedule The schedule for completion is based on a single season construction time frame.This can be accomplished with proper planning and execution of the contract. The project would be scheduled for a seven day work week on a two 10-hour shift basis for five months,as shown in the schedule shown in Figure 14.1-3. 13.3.3.5.Construction Manpower The peak manpower will be approximately 200 as seen in the Figure 13.3-2 below. 250 : 200 194 2 »150 2 :c '> 3 4 100 50 = 0 -j Year 4 Construction Year Figure 13.3-2.Rail Siding Construction Manpower Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-19 December 2014 -Za-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.3.6.Key Logistical Aspects Almost all significant materials and plant for project construction will be offloaded at the Railroad Offloading Facility.The facility will also provide for utilization of a railroad owned quarry at Curry and the setup of an initial 350 person camp for the construction of rail siding and the permanent access road.It is assumed that a "secondary”mobilizing area will be set up further south on the ARRC by the contractor for loading materials on for the construction of this facility. 13.3.4.Camp and Airstrip Civil Works 13.3.4.1.Contract Description This is essentially the basic site infrastructure contract.It cannot be set up as a design build or other alternative contractual methods because the work being performed is essentially the civil works for another contract and significant integration between the designs for each contract are required.Thus this has been estimated as a traditional Design-Bid-Build contract. The costs for design and owner cost are carried in the overall program cost. 13.3.4.2.Contract Scope The scope of this work is implementation of the civil works necessary for the site temporary and permanent infrastructure on the north side of the dam site.The contract scope includes: «Clearing and grubbing for the site infrastructure works as necessary; =Site access roads around the camp and permanent village,to the airstrip,and to the contractors area; «Earthworks associated with the permanent village,the camp,and recreational facilities (both permanent and temporary); *Construction of a temporary airstrip,followed by the construction of the permanent airstrip,apron,turning areas and foundations for the associated buildings; *»Raw water intake,pipeline and treatment facilities (including the permanent protective buildings)and distribution lines to the sites of the various accommodation and project buildings,also included is the fire water system; =Sewerage from the site of the various accommodation and project buildings; »Wastewater treatment plant,permanent protective buildings,and outfall; »Float plane dock; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-20 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «The electrical distribution system and fiber optic cabling around the site from the emergency power facilities; »All fencing around the camp,airstrip,permanent accommodation and facilities,and the various infrastructure buildings and facilities;and, =Permanent bridge at the site (28 ft.wide). Although the construction cost estimate has assumed that the first (temporary)airstrip will be constructed at the site of the permanent airstrip,at a later stage of project development,the use of the airstrip at Stephan Lake should be considered.Upgrading of that airstrip -and the construction of a pioneering access road of about three miles (from Stephan Lake to the access road corridor)might be a more appropriate way of initiating site work at the dam site.If that were to be the case -the work associated with Stephan Lake would replace some of the scope of this contract. 13.3.4.3.Key Aspects of Construction Methodology Once the contractor has been given a notice to proceed for the contract,mobilization of equipment,manpower and supplies will be performed so that movement to the site can be undertaken by CAT train. The CAT train will transport all equipment and supplies to the north bank of the site from Cantwell -and no other significant mobilization will be possible for this contract as all contract tasks must be completed before the completion of the access road. A first task of the contractor will be to doze a 3,500 ft.long pioneer strip so that L-100 planes can land and take off,servicing the site before the access road is complete.The subsequent extension to form the permanent airstrip,while not interrupting the use of the temporary strip, will be a logistical challenge which might indicate the preferential use of the Stephen Lake airstrip,discussed above. A temporary camp will be required while this contract is being executed,which would be serviced by air. If the Stephan Lake option is found to be more efficient and economic,then the logistics -and the CAT train,would all be based on transporting equipment from Gold Creek,and upgrading of the Stephan Lake strip instead of bulldozing a new strip at the site. The permanent long span bridge at the site will also be pre-engineered,but as presently designed, cannot be launched.It is assumed that the abutments and piling will be constructed using the materials and equipment moved to site by the CAT train,and the span will be assembled in the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-21 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. following winter,using the frozen river as construction access across the entire span.If the river ice needs thickening,or smoothing,to facilitate construction,it is expected that the contractor will do so using conventional "ice road”methods. 13.3.4.4.Construction Schedule The schedule for completion is based on a single season construction time frame.This can be accomplished with proper planning and execution of the contract. The project would be scheduled for a seven day work week on a two 10-hour shift basis for the six month season per the schedule which is shown in Figure 14.1-4. 13.3.4.5.Construction Manpower The peak manpower will be approximately 150 as seen in Figure 13.3-3 below. 180 160 .JN" .Z_\ ;[\ .[\ ./\ a a \ Year 4LaborUnits Construction Year Figure 13.3-3.Camp and Airstrip Civil Works Manpower 13.3.4.6.Key Logistical Aspects This contract must be completed using equipment and materials brought in by the initial CAT train,or as supplied by an L-100 plane (or similar)using the temporary airstrip (or extension upgrade of Stephan Lake strip)that will be constructed. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-22 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.5.Supply and Erect Camp 13.3.5.1.Contract Description This contract could be setup as a Design/Build or other alternative contractual method.For the purposes of cost,this work has been priced as a traditional Design-Bid-Build execution.The design and owner costs are carried in the overall program cost. 13.3.5.2.Contract Scope This contract would essentially be a building and building supply contract,albeit using prefabricated (factory preassembled)items.All site works ready for the building will have been performed by another contractor,and this contract will include the supply and construction of: «=Camp accommodation at Gold Creek,and the relocation of part of that camp to the main site. =»Camp and recreation buildings at the main site for both workers and management staff including the temporary accommodation for construction management,AEA and engineering staff. «Completion of sports fields,etc. *Construction of airport buildings. =»Permanent houses at the main site. =Connection of water supply,sewerage,power,fiber optic cables,etc.to all buildings constructed under this contract. »Removal of temporary accommodation at the end of the project and refurbishment of permanent buildings.This aspect of the contract scope can be the subject of debate when final contract packages are chosen -depending on discussions with potential contractors with respect to salvage value. 13.3.5.3.Key Aspects of Construction Methodology It is assumed that the temporary camp will largely be constructed using prefabricated modular components -approximately the same size as a container -so that the components can be transported in the proposed supply chain via the ARRC. The temporary buildings and permanent buildings (such as houses,airport buildings,permanent recreational buildings,etc.)are expected to be manufactured in sizeable components off site,and finally assembled on site. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-23 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.5.4.Construction Schedule The schedule for completion is based on a single on-site season for construction assembly.This can be accomplished with proper planning and execution of the contract.However,prior to shipping to the site,a full year has been allowed for construction of the modules within a factory setting. The project would be scheduled for a seven day work week on a two 10 hour shift basis for five to six month construction season.The schedule is shown in Figure 14.1-5. 13.3.5.5.Construction Manpower Much of the manpower associated with the assembly of the temporary camp would be employed off site at the factory of the contractor.However there will be craftsmen on site and several managing personnel. The peak manpower on site will be approximately 340 as seen in Figure 13.3-4 below. 400 345 :350 -[|\ 250 c :2 :»200 : 4 |150 /\100 /\50 /\: Year 4 Construction Year Figure 13.3-4.Camp and Airstrip Building Manpower Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-24 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliabie energy for the next 100 years. 13.3.5.6.Key Logistical Aspects The substantial amount of material that is required for all the temporary and permanent infrastructure is such that it is not feasible to move it all to site early by CAT train. However the short period on site allowed for assembly of all the prefabricated buildings will require very careful and organized logistics to ship by rail and deliver to the site.All will be in sizes that can be handled by container handling units,and at this stage of construction,the very large numbers of shipments of cement and flyash will not have commenced.Nevertheless coordinating the building process will be a challenge. 13.3.6.Main Civil Works Construction 13.3.6.1.Contract Description The scope of the main civil works contract is such that it will need to be completed by an experienced dam contractor,or a consortium of experienced contractors.This effectively rules out local Alaskan (headquartered)companies as the lead participant in the group - although significant Alaskan participation is expected.It is possible for this contract to be offered as a Design/Build execution,but the size of the project works,and the consequent expected interest by FERC in the detailed design -as well as procedural constraints of the FERC process -render this a less favorable option that exhibits more risk.For the purposes of cost estimation,this contract has reasonably been assumed to be a traditional Design-Bid-Build contract and has been estimated thus.Much of the scope will be performed by subcontractors,either selected by the contractor based on the specifications,or as nominated subcontractors and suppliers assigned to the contract.The costs for design and owner cost are carried in the overall program cost. 13.3.6.2.Contract Scope This contract will be the largest of all entered into by AEA for the Susitna-Watana Project and will include in its scope: «Temporary roads around the site; =Development of the quarry,and installation of the crushing and batching plant; ®Portals,diversion tunnel,cofferdams,etc.; =Foundation excavation,and construction of the RCC dam and spillway; =Construction of all power facilities,including access tunnel,powerhouse,and supply and installation of all electrical,mechanical and electrical equipment -except the main equipment supplied under the Turbine-Generator Supply contract; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-25 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. *Supply and installation of all gates,cranes,valves,penstocks,pipes,etc.; =Supply and installation of all switchgear including all equipment in the switchyard; *Obtaining all needed materials both for construction and for permanent installation; =Creation of all temporary works needed for completion of the project,on site,as well as off-site storage and loading areas as required; »Provision of security and general maintenance of site infrastructure,access road,etc.; ®Removal of all unused construction materials and the reinstatement of all disturbed site areas; =Removal of any infrastructure at site and at Gold Creek not removed under other contracts; =Commissioning of the project;and, «Administration of any (nominated sub contract)let by AEA and subsequently assigned to the Main Civil Works contract. 13.3.6.3.Key Aspects of Construction Methodology To enable the earliest possible construction start,the draft feasibility report schedule is based on certain assumptions.These include making use of CAT trains for prepositioning of some initial construction and site preparation materials and supplies during the winter prior to a construction road being completed to the site. One or more CAT trains would transport equipment and supplies to the north bank of the site from Cantwell so as to stockpile materials and supplies for the purposes of establishing the contractors'work area on the north bank.Early delivery of materials and supplies will make it easier to create access roads to the upstream and downstream portals of the diversion tunnel as soon as regulatory authorization is granted (and other permits obtained)to more efficiently be able to start establishing the portals and to commence the excavation of the diversion tunnel. One or more other CAT trains will be mobilized to move,to the south bank of the site from Gold Creek,all material and equipment necessary to commence the opening of the quarry and the establishment of the crushing and batch plants. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-26 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT Temporary camps will be set up and the contractor will perform the following tasks concurrently with the construction of the access road,site civil infrastructure,and Gold Creek Offloading tasks: Construction of a temporary bridge across the river sufficient for personnel and nominal vehicles such as quad bikes and trailers; Excavation and lining of the diversion tunnel; Creation of site construction roads; Excavation of the dam foundation on the left and right banks;and, Development of the quarry and the crushing and batch plants. Once the access road from Gold Creek has been completed by another contractor,and the supply chain has been established,further equipment can be mobilized for the full project construction. To facilitate the earliest possible connection of the first unit on line,high productivity will be required in all areas of construction,but most particularly in RCC mixing and placement.It has been assumed that RCC placement will occur over five seasons -including a season before the diversion has been achieved,and the last season while the reservoir is filling.Seasons have been assumed to be five or six months long,with at least 1,000,000 yds?being placed each season and -governed by the following requirements and constraints: Placement on the right bank to a level that allows for the subsequent construction of the spillway using conventional concrete (CVC)as soon as possible; Placement in the center (river bed)to a level both upstream and downstream to facilitate the use of a sluice through the left side of the dam for ice passage during breakup,and so that CVC placement for the powerhouse substructure can be commenced as soon as possible; Placement in the center (river bed)to a level at the upstream to allow for the commencement of the power intakes in CVC as soon as possible;and, Placement of the remainder of the RCC such that the height of the dam is raised as quickly as possible and so that -at the time of closing the diversions -the reservoir can be safely filled to allow for the turbine-generating units to be commissioned,with reservoir level control]undertaken by the low level outlets and the emergency release. Figure 13.3-5 shows the anticipated placement sequence. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-27 December 2014 wz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Season 1CI Cc)Season 2|om |Season 3ann|Season 4[Season 5 Figure 13.3-5.Seasonal Sequence of RCC Placement Susitna-Watana Hydroelectric Project Alaska Energy AuthorityFERCProjectNo.14241 Page 13-28 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. To perform this RCC placement during the summer and fall seasons,the contractor will need to install sufficient conveying equipment to reliably deliver at rates exceeding 380 yds*per hour, allow for breakdowns,provide insulation of completed RCC,provide insulation of joints as the layers are completed and extend the placement season as long as possible.It is anticipated that the contractor will place by sloping layers,and will establish insulation and heating for many,if not all-aspects of storage of materials,batching,mixing and transport. It is anticipated that fly ash and cement will be delivered to site in tank containers to facilitate speed in the supply chain,and that buffer storage will be established by storage of such tank containers at the top of the left abutment so that their content can be blown out direct to the batch plant. The contractor is expected to draft a detailed construction schedule that will facilitate,as soon as reasonable,the all-weather construction of as many parts of the project as possible.Under cover, permanent or temporary,placement of structural concrete can be continued throughout the year. The intake,for example,1s compact and easy to weatherproof temporarily for construction.The powerhouse can be designed to include a structural steel framework from the lowest level - together with infill concrete panels -so that a weatherproof enclosure is constructed very early in the powerhouse construction sequence,and substructure concrete can be placed year round. These techniques -of using steel frames and precast panels -have been pioneered in Quebec and is illustrated in Figure 13.3-6 which shows a framed weatherproof (with concrete precast panels)structure erected from the lowest levels of the powerhouse,and the substructure being completed within the protected environment. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-29 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 13.3-6.Construction of Powerhouse Substructure within a Protected Environment (acknowledgements Hydro Quebec) 13.3.6.4.Construction Schedule The schedule for completion is based on a seven season construction time frame.RCC placement will only be performed during the summer seasons,but as much construction as possible will be continued throughout the year as discussed above.This schedule can be accomplished with proper planning and execution of the contract. The project would be scheduled for a seven day work week on a two 10-hour shift basis. Construction workers would be rotated out as discussed below,and as much work as possible would be prefabricated off site and brought to site in pieces as large as feasible to maintain productivity.The schedule for the main civil works is shown in Figure 14.1-6. 13.3.6.5.Construction Manpower The peak manpower will be approximately 960 as seen in Figure 13.3-7 below. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-30 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 1000 :... 958 LaborUnitsYear 6 Year?Yea 8 Year 9 Year 10 Construction Year Figure 13.3-7.Main Civil Works Manpower 13.3.6.6.Key Logistical Aspects The most challenging aspect of the logistics for this contract is the volume and weight of materials and equipment that will be shipped along the ARRC to the Gold Creek siding,and hereafter along the road. It is assumed that as far as possible the contractor will containerize the deliveries and will move as much material directly from Anchorage and the selected port (expected to be Whittier)to the site without double handling. Typical large loads that cannot be containerized for transportation are shown in Table 13.3-1 below. Table 13.3-1.Large Loads and Approximate Dimensions .Length |Height Width WeightEquipment(ft)(ft)(ft)(ton)Notes A full length crane beam is preferred,but it can beMainCraneBeam8088splitdowntoshorterlengths. Power Intake )115 4 30 Fach gate wilt m two sections,numbers shown Lower Level Outlet 24 11.5 4 35 Spillway Gates 50.5 21 6 70 The 21 ft.dimension can be reduced if necessary. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-31 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Length Height Width WeightEquipment(ft)(ft)(ft)(ton)Notes Draft Tube Bulkheads 33 12 3 95 Each bulkhead will be in two sections.Dimensionsandweightareforonesection. 19 ft.Penstock Cans 30 diameter 54 18 ft.6 ft.Butterfly Valves diameter (thickness)70 13.3.7.Turbine and Generator Supply Contract 13.3.7.1.Contract Description The design and manufacture/fabrication of the turbines,governors,generators,exciters, generator step up transformers,etc.constitutes specialist manufacturing.The supply contract is expected to be a traditional design,manufacture and deliver contract.Usually the supplier delivers the equipment to the site,but does not install it.Installation is performed by the main contractor (or a subcontractor)under the direction of installation supervisors provided by the manufacturer.Such a contractual arrangement minimizes the possibility of claims because of competing use of space in the powerhouse.The main civil contractor often (but not always) subcontracts installation back to the turbine generator supplier. The costs for preparing the specifications for the supply contract,and the owners cost are carried in the overall program cost. 13.3.7.2.Contract Scope The contract scope will include the following: *Design,model testing and manufacture of the turbines; »Design and manufacture of the generators; «Supply of the governors; =Supply of the exciters; «Supply of generator step up transformers; "Delivery of all supplied equipment to site;and, *Provision of installation supervisors at site. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-32 December 2014 ---Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.7.3.Key Aspects of Construction Methodology The key logistical challenge for this supply contract is the size and weights of the individual items of equipment to be supplied -and in some cases the delicate nature of the equipment. Most of the supplied equipment can be shipped in pieces,but it is preferable to minimize the on- site welding of equipment so the maximum size parts should be shipped,even if it results in oversized loads on the ARRC.To accommodate oversized loads,some of them may have to be moved by road to the siding at McKinley before loading on the ARRC. At the time of writing this report,a list of the large items associated with this contract to be shipped is given in Table 13.3-2 below. Table 13.3-2.Large Turbine Loads and Approximate Dimensions Equipment 'a "t).'o.ton).Notes Turbine Runner 14 14 7 40 Stay Rings 24 24 5 72 Can be detailed to be lesser dimensions than runner. Spiral Case 44 45 13 140 Can be detailed to be lesser dimensions than runner. Draft Tube 18 18 28 24 Can be detailed to be lesser dimensions than runner. Step-up Transformer 30 12 15 140 Transformers will be the largest items to be transported from a manufacturing facility to the project site and will require special treatment.They will be shipped either on a Schnabel rail car or a multi-axle trailer as shown in Figure 13.3-8 and Figure 13.3-9 below: bol '<3 ,EEEa oy:nie 9 os 4 J -we.a -'S anor Figure 13.3-8.Transformer Transport by Rail Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-33 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 13.3-9.Transformer Transport by Road 13.3.7.4.Supply and Installation Schedule The schedule for fabrication,supply and installation of the turbines,generators and associated equipment is usually dependent on the turbine testing required by the owner.In-house models can be accepted,but particularly for larger units,owners often prefer to use an independent testing laboratory to perform runner design modeling which adds time.This aspect will be discussed with AEA at the appropriate time,and the decisions made will affect the commencement date for the preparation of the Turbine and Generator supply contract. Completion of on-site work is expected to take approximately 18 months -but the sequencing of the work is completely dependent on the Main Civil Works contractor because of the second stage concrete that is an integral part of installing the major equipment.At this stage a detailed installation schedule has not been prepared,but 36 months has been allowed for manufacture, delivery and installation of the turbines,generators,and other major equipment,although the turbine supplier will continue to be involved for a few more months for testing and commissioning. The project would be scheduled for a seven day work week on a two 10-hour shift basis full time throughout the year.This will be possible because the main contractor is expected to complete Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-34 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. the powerhouse superstructure as quickly as possible -even using temporary weather proofing - to allow work in the powerhouse to continue throughout the year unaffected by the weather. 13.3.7.5.Construction Manpower The peak manpower on site will just be the supervisors -approximately three as seen in Figure 13.3-10 below. 35 --- ---fone enon we ee ce 8 we tee ce 25 -ve teeee --:-LaborUnksYear 6 Year?Years Year9 Year 10 Year 11 Construction Year Figure 13.3-10.Turbine and Generator Manpower 13.3.8.Transmission Line and Interconnection This report does not recommenda transmission configuration.The discussion is based on the corridors chosen solely for the purposes of estimation ofproject cost. 13.3.8.1.Contract Description This Contract can be set up as a design build contract or use other contractual methods.For the purposes of cost estimating,this project has been priced as a traditional Design-Bid-Build project.The costs for design and owner cost are carried in the overall program cost. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-35 December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.8.2.Contract Scope The scope of the contract includes for the supply of all towers,insulators and conductors,the installation of towers and stringing of the line,the construction of the interconnections at the Alaska Intertie and the connection of the circuits to the switchyard on site.The work will involve the creation of some access road spurs to the towers from the access road,and some construction by helicopter. 13.3.8.3.Key Aspects of Construction Methodology As with all transmission line construction,a key element will be the setting up of interim storage areas on the transmission route from which work will be performed both ways.The line is typical of many such lines in Alaska so the contractor will be familiar with the moving and erection of the towers and of the helicopter construction methods required at various locations. 13.3.8.4.Construction Schedule The schedule for completion is based on a three and a half season construction time frame.This can be accomplished with proper planning and execution of the contract. The project would be scheduled for a seven day work week on a two 10-hour shift basis for five to six months per construction season.The schedule is not critical and the work can be commenced at any time during the whole project implementation,though it may be affected by the migratory bird nesting constraints. 13.3.8.5.Construction Manpower The peak manpower will be approximately 43 as seen in Figure 13.3-11 below.Workers will sometimes be housed at the Railroad camp and sometimes at the main site temporary camp. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-36 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 3 | ! "43 | a0; i} 35 | i | = 2 3 25 ej Year6 Year?Year 8 Year9 Year 10 Year 11 Construction Year Figure 13.3-11.Transmission Line and Interconnection Manpower 13.3.9.Site and Reservoir Clearing 13.3.9.1.Contract Description This Contract can be set up as a single (or multiple small)project(s)if desired.For the purposes of cost,this project has been priced as a traditional Design-Bid-Build project;however very little design is required and input is more related to contract terms. 13.3.9.2.Contract Scope This contract includes the clearing of certain elements of the project that have not been included in other contracts.This contract includes clearing all of the dam footprint,quarry area,camp, airstrip,and a portion of the reservoir area.The construction of the main access road has clearing included in that contract. For this estimate it is assumed that burning of trees and brush will be allowed with an appropriate burn permit.AEA may however consider performing a reconnaissance study which considers various types of biomass facilities that could use the cleared trees. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-37 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.9.3.Key Aspects of Construction Methodology Once the contractor has been give the notice to proceed for the Clearing Contract,mobilization of equipment,manpower and supplies will be by rail to the Gold Creek Siding Area or a CAT train from the north to the site. Once the site is established,clearing and erosion controls for the camp areas and airstrip will be first on the schedule followed by clearing of access roads and quarry area. The higher elevations on the project require very light clearing.This would be the camp area, airstrip and the top of the quarry area.The heavy tree cover is located in the valley along the river bank in the reservoir area.Clearing will be done with dozers,backhoes and chainsaw clearing methods.The trees and brush will be piled for burning. 13.3.9.4.Construction Schedule The schedule for completion is based on an aggressive schedule for the clearing of the sites at and around the dam site so that work can be started on construction.The only clearing that could affect the overall project schedule is the camp and dam footprint and any site access roads which make up approximately 15 percent of the clearing.The clearing of the reservoir area can be performed over the following years as there are no other tasks dependent on completion.No clearing can be done during the migratory bird season. The project would be scheduled for a six or seven day work week on a two 10-hour shift basis for the summer season.The schedule is illustrated on Figure 14.1-1. 13.3.9.5.Construction Manpower The peak manpower will be approximately 103 as seen in Figure 13.3-12 below. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-38 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. ,jf L |Jp \ Year5 Year6 Year7LaborUnits Construction Year Figure 13.3-12.Clearing Manpower 13.3.9.6.Key Logistical Aspects Equipment could be mobilized from the north and other supplies could be by rail to the Gold Creek Siding.The construction equipment list is approximately 450 tons. Other major materials would include: Fuel .oocccccccccccecccccccsecceesereeeeenenes 2,600 tons Food and MiSC..........ccc0csceeseeees 100 tons Total ...cccececccccecscecetsesersereeeeeeees 2,700 tons 13.3.10.Air Transport Services 13.3.10.1.Contract Description As noted,construction is expected to be performed based on rotation of workers on and off site. Workers retained for tasks that continue throughout the year are expected to rotate off site on a regular basis,while those tasks that are seasonal -such as the RCC placement -would probably necessitate worker movement on a semi regular basis.This service contract would be negotiated by AEA with agreed rates that would apply to any selected contractor for the Main Civil Works contract through the mechanism of assigning the contract. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-39 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. The costs for preparing the contract and owner costs are carried in the overall program cost. 13.3.10.2.Contract Scope The scope of the contract would be to supply the following (all navigation,safety and fueling equipment would be refurbished at the completion of the project construction and remain as part of the permanent installation): «Supply and install any and all landing and navigation aids at the airstrip,together with all necessary equipment for expected servicing of the proffered planes; «Supply and install all necessary fixed equipment for airport operation such as radar, lighting,radio,passenger and cargo tracking facilities tugs,steps,etc.; «Arrange for delivery of required aviation fuel,install and maintain necessary facilities; =Operate regular and irregular fixed wing passenger flights to and from Anchorage, Talkeetna and Fairbanks as well as helicopter services and emergency evacuation services;and, «Operate regular and irregular cargo flights to and from Anchorage and Fairbanks. The cost of extra services that each contractor might want would be fixed in the contract documents for this service -apart from provisions for fuel variations etc. 13.3.10.3.Key Aspects of Construction Methodology A key component of the air service methodology will be the choice between letting the service contract to a "Part 135”company that can transport passengers and cargo in the same aircraft, compared to a "Part 121”operating company with more extensive restrictions and higher weather minimums. A Part 135 company will probably be more economic and would have greater flexibility to change schedules and react to weather issues.The extent of airport infrastructure required at Anchorage,Fairbanks and Palmer will also be a factor to be investigated to accommodate connections (principally at Anchorage)and the loading of freight. 13.3.10.4.Construction Schedule The Air Transport services contract would last from when the airport at the project site is put into service until the end of construction. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-40 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.11.Railroad Operations 13.3.11.1.Contract Description As noted,for the purposes of planning and estimating,the construction and use of the Gold Creek (southern)access route has been assumed.Thus the ARRC would form a vital part of the supply chain.It is suggested that AEA negotiate a basic contract with ARRC for the transport of materials to Gold Creek,with agreed rates that would apply to any selected contractor for the Main Civil Works contract through the mechanism of assigning the contract.The cost of extra services that each contractor might want would be pre-agreed -apart from provisions for fuel variations,etc. 13.3.11.2.Contract Scope The exact service contract scope remains to be determined,but it is envisaged that it would include for operations of at least three dedicated (minimum)55 car trains (or similar)per week from Whittier to Gold Creek during the construction period;operation of a dedicated train from (say)McKinley siding semi-regularly to Gold Creek;and delivery of other freight within the standard loading gauge from Anchorage,Whittier,or Point Mackenzie to Gold Creek. The service contract might also include,leasing of land at McKinley siding or Port Mackenzie, and possibly the replacement of the Talkeetna Bridge,and excavation of some rock slopes on the east side of the track as necessary for wide loads.It is also possible that the most efficient way to construct the railroad offloading facilities at Gold Creek (or any selected location)could be by the ARRC under this contract. 13.3.11.3.Key Aspects of Construction Methodology Some aspects of the use of the railroad are yet to be determined as follows: «Southern port -There are offloading facilities at Whittier,and Anchorage.In addition,in Mat-Su Borough on the north side of the Knik arm,Port MacKenzie has been under development,and currently includes a deep draft dock as well as nearly 15 acres of barge dock.There are plans to create -by 2016 and thus in time for the project -a spur of the ARRC some 32 miles from the main railroad near Houston to Port Mackenzie,thus rendering it the closest port to the project.It is possible that transshipment will be through Port Mackenzie for non-containerized materials and equipment sourced from outside the State of Alaska that are not brought up in railcars. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-41 December 2014 -zZ- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «=Port Mackenzie has a significant disadvantage in that the railroad does not extend down to the dock,but ends in a loop at the top of the bluff.Thus unloaded goods must be trucked up the bluff and then loaded on the ARRC.Thus the barge service from Seattle operated by Alaska Rail Marine will not bring railcars directly to Port Mackenzie.It should be noted that the use of such a service in the lower 48 will demand that all loads be within loading gauges and so they would be expected to be able to be transported through the whole ARRC system from Whittier. "Barge vs.freighter shipment -In discussions with ARRC and significant suppliers (of fly ash),the overall supply chain was explored.Alaska Rail Marine operates a regular "rail-water-rail”service through Seattle to Whittier using barges on which rail cars can be transported.This remains a method by which certain items might suitably be moved (such as the four Generator Step-Up transformers on a Schnabel car or similar).Canadian National Aquatrain also operates a similar service to Whittier from Prince Rupert. «Although the rail-to-rail convenience is attractive,the necessity to offload material at Gold Creek for transfer onto road vehicles renders full containerization as a more attractive alternative.Bulk materials such as fly ash,cement,fuel oil,etc.can be containerized -in tank containers that allow more dense "packing”on barges and freighters than railcars,so it appears to be more attractive to move as much material as possible using standard containers.Estimates have been based on this choice of shipment,and allowances made for container transfer equipment at the Gold Creek offloading facility. "Provision for wide or high loads -The project team has visited the railroad between Talkeetna and Gold Creek.There are three potential restrictions on wide or high loads (apart from those that might be imposed by ARRC with respect to stability and or speed of transport). -The Talkeetna River Bridge is located at ARRC milepost 227.1 and is shown below in Figure 13.3-13.The bridge is a through truss structure which represents the most significant width restriction between Talkeetna and Gold Creek -and the sole height limit.The ARRC clearance diagram gives a limit of 15 ft.-5 inch width at walking speed,and a height of 10 ft.-O inch CDNX.Approaches to the bridge are straight,and the bridge includes two spans of 200 ft. -Eight tenths of a mile north,at milepost 227.9 is the Billion Slough Bridge. Although this is a straight over bridge it has side structural members supported by angled webs.The width at about 4 ft.above rail is 19 ft.This bridge includes one span of 120 ft.with the side members and a 22 ft.span at grade. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-42 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. -A third restriction -at various points on the line -are locations at which the rock cuts on the east of the track are close;the excavated rock wall can sometimes be as close as 9 ft.,6 inches from the track centerline (although 12 ft.is more normal in these particular locations).However,the total length of line between Talkeetna and Gold Creek subject to these limited clearances is less than 500 ft. During detailed design,and logistical planning,the extent to which the three potential restrictions need to be mitigated must be discussed with ARRC.Replacement of the Talkeetna Bridge is a possibility,and normal maintenance work on the railroad could be expanded to remove the rock in the cuts that is too close.It is understood that these cuts are regularly trimmed and cleaned by ARRC maintenance crews.While formal discussions have not taken place,ARRC may be able to remove additional material during the next few years to improve clearance.Modifications to Billion Slough Bridge will be dependent on the exact dimensions of any wide load.y/7a4.esWtetaSAEewePMN.AATATTNAanFFFOOOOOMNESFoie"4 :eae%,ae 5 cee4<.x=.?vee Lae4"e OeLenme:" Yor ”on B,,4 aS*a)Pe 2:©end 'e See 8 wre -s*y we ue "."ss ,ere =ve io a =Ve |4 "ae£J \a,4GigerSaneiASRaaon;5Sweoeoe .\. Figure 13.3-13.Talkeetna River Bridge Laydown and loading areas alongside the ARRC -During detailed construction planning,staging and storage areas will need to be established next to the ARRC in addition to the Gold Creek Offloading area discussed above.A staging area with security will need to be established at the main port (Whittier or Port Mackenzie)and Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-43 December 2014 -Zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. at a location for transfer of truck loads onto the ARRC.Such staging areas may be on ARRC property,and this contract will need to include leasing. A candidate for a staging area was found at McKinley siding,which is at milepost 223 - a few miles south of Talkeetna and away from the town.This siding is used during the summer as a loading point for coach trips from Anchorage (cruise boats,etc.)so that tourists can board the railway for a trip to Cantwell,etc.The siding is 2,300 ft.long,but of interest is an associated pit for which ARRC has built a spur.The spur is at significant grade -and moving a train out of the area could require extra assistance -but the pit could easily be used by a contractor as a storage area/transshipment area to load trains after bringing material by road from the south.ARRC could easily include in the track a derailing switch under their control]so that a contractor could work within the area without ARRC supervision until ready to move out.The land is all owned by ARRC but the area is used as a "bone yard”so is probably available.The area available is estimated to be 12 acres or more. 13.3.11.4.Construction Schedule The Railroad Operations services contract would begin when the railroad is put into service until the end of the project. 13.3.11.5.Construction Manpower The consolidated peak manpower of all service contracts will be approximately 155 as seen in Figure 13.3-15. 13.3.11.6.Key Logistical Aspects The key logistical aspects of the use of the ARRC must be discussed in great detail with ARRC. It seems from early discussion that the (minimum)55 car trains being considered (even if the number were increased somewhat during peak construction)would not put undue strain on the railroad system,and the modifications to cuts and or bridges could be successfully arranged with ARRC,with enough "lead time'. 13.3.12.Camp Operation 13.3.12.1.Contract Description The camp operation contract can be set up as a service contract.The costs for preparing and negotiating the contract and owner cost are carried in the overall program cost. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-44 December 2014 ---Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.12.2.Contract Scope The scope of the contract will be the operation of the camp,including meals,cleaning,recreation facilities,maintenance,etc.The occupancy of the camp will be in accordance with Figure 13.3-14,which shows the summation of all construction manpower onsite throughout the construction period.The construction camp will have a peak capacity of up to 1,200 people and will normally house approximately 800 persons. 1400 1000-LaborUnitsConstruction Year Figure 13.3-14.Total Construction Manpower All Projects 13.3.12.3.Key Aspects of Construction Methodology A key aspect to remember when planning construction in more detail is the extent that the camp operator will want to use air transport for perishable food items,etc. 13.3.12.4.Construction Schedule The Camp Operation services contract would begin when the camp building is complete until the end of the project,although once the RCC placement in the dam is complete;the main work still continuing would be the turbine and generator commissioning.This would allow a partial but significant demobilization to be carried out. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-45 December 2014 Zw ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.3.12.5.Construction Manpower The consolidated peak manpower of all service contracts will be approximately 155 as seen in Figure 13.3-15. 13.3.13.Medical Services 13.3.13.1.Contract Description This Contract can be tendered to a private organization or possibly to any State or regional health care body.The costs for drafting and agreeing on a contract,and owner cost are carried in the overall program cost. 13.3.13.2.Contract Scope The contract scope includes the operation of the medical facility on site including the supply of the continuous presence of a doctor and paramedical staff.It is envisaged that minor surgery would be included,stabilization before emergency evacuation,occasional dentistry (by a visiting dentist)and isolated or non-isolated care for patients requiring short bed rest.The scope also includes for the provision of medical equipment and supplies -and pharmaceutical services as necessary -throughout the implementation of the project,and the organization of emergency evacuation by air. 13.3.13.3.Schedule The Medical Services contract would begin when the camp building is complete until the end of the project construction and commissioning. 13.3.13.4.Construction Manpower The consolidated peak manpower of all service contracts will be approximately 155 as seen in Figure 13.3-15. 13.3.14.Service Contracts --Manpower Rather than examine the peak manpower of each service contract,a consolidated assessment has been made as shown in Figure 13.3-15.The total will peak at approximately 155 encompassing Air Transport,Railroad Operations,Camp Operations,and Medical Services Contracts. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-46 December 2014 Za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 Clean,reliable energy for the next 100 years.ENGINEERING FEASIBILITY REPORT 180 te -_ooo eee _158 140- 120- 100 ---LaborUnits20 Year6 Yeu?Year 8 Yeu 9 Year 10 Yea 11 Year 12 Construction Year Figure 13.3-15.All Services Contracts Manpower 13.3.15.Construction Manpower -All Contracts Total construction manpower onsite throughout the construction period is shown in Figure 13.3-14,and will peak at approximately 1,200 persons. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-47 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 1400 1200: Year?Year 8 Year9 Year 10 Year 11 Year 12 Construction Year Figure 13.3-16.Total Construction Manpower All Contracts 13.3.16.Logistics As discussed at various points in the above analysis of the projected contracts,the logistics of delivery of materials,equipment,consumables and workers to the site is a significant challenge in this construction,principally because everything will need to be shipped along the ARRC in an ordered manner,and shipped through the Gold Creek Offloading area with the minimum of double handling.Permanent equipment has been highlighted in the various contract discussions, but there is a greater tonnage of consumables and general materials. As far as construction equipment is concerned Table 13.3-3 indicates some typical (but not exhaustive)large loads representing some of the largest equipment that will be moved.Multiple units of some of this equipment (such as the Caterpillar 777 trucks)will need to be moved, depending on the construction planning of the selected contractors.Plant and machinery can be broken down,but the contractor (or supplier of the equipment)will undoubtedly wish to move the equipment in the largest convenient pieces due to time and cost considerations. There are many other items of equipment that will need to be moved along the same supply chain. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-48 December 2014 wz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 13.3-3.Typical Large Construction Items (and approximate dimensions)to be moved to and from Site Approx.|Length |Width |Height |WeightItemsNumber|(ft)|(ft)|(ft)|(tbs)Notes ,Blade and cab can be removed toCaterpillarD10/11 7 36 12.5 15.25 |248,600 reduce dimensions slightly .Blade and cab can be removed toCaterpillar992251.5 18 18.5 214,948 reduce dimensions slightly Caterpillar 385 2 44.2 11.2 15.7 185,474 |Shipping dimensions Semi-trailer (road)25 40 8 4 Flat-bed for normal ISO containers .Articulated dump truck -can driveCaterpillarD3501934.9 10.7 11.5 66,560 on/drive off Caterpillar 777 6 34.6 21.3 17 163,090 Caterpillar 825 2 277 12 12.3 72,166 Concrete agitator 23 30 10 12 Truck-mounted concrete ,39.4 8.2 12.10pump Linkbelt 228 crane 2 24 19 13.3 American 9260 crane 8 24 18.7 14.6 Container handler 3 44 16.5 13.5 230,000 5,000 gallon water tanker |2 40 8 10 |125,000 weit includes (9,000 gal)water Note:A more complete list is shown in Appendix B10 ISO -International Standards Organization Actual equipment will be selected by each contractor and it is expected that there will be some cross sales. It is expected that during the first mobilization season,some 5,000 tons of equipment will need to be mobilized. Total quantities of selected materials that will need to be transported -as far as possible in containers or container sized shipping structures -are shown in Table 13.3-4. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-49 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 13.3-4.Key Materials to be Shipped through Supply Chain Key Material 'tons Note Initial Mobilization Construction Plant 10,000 Containers Fuel/Oil 7,500 Tank Containers Equipment Parts 1,100 Containers Permanent Equipment 1,500 Individual Food 8,000 Containers ANFO 3,000 Containers Misc.Sr.. 15,000 Containers RCC 5,215,000 CY HO RCC Cement 342,248 Tank Containers RCC Pozzolan ot 547,575 Tank Containers Structural Concrete 7 834,823 Cement 89,375 Tank Containers Fly Ash 48,125 Tank Containers Reinforcement 41,250 Railcars Demobilization $7.|e.1.0 nA Containers TOTAL 1,124,673- Tota!Kamded fap)1,200,000 In general,it is assumed that transport by air will mainly be used for personnel,perishable food, key repair parts that are required for disabled or damaged plant,pharmaceuticals,documents and cash,ete. 13.4.Construction Cost Estimate Derivation As noted above,previously AEA had commissioned an independent construction cost estimate for the project.That estimate was substantially compiled by Mr.Hewitt of International Project Estimating Limited. In deriving the estimate for the feasibility report,the construction planning and estimating was performed throughout a period from December 2013 through July 2014,so the initial estimating was performed using quantities derived in January 2014 and corrected by adjusting the material quantities as necessary to incorporate the design development from January 2014 to July 2014. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-50 December 2014 Zz.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. For the initial basic January 2014 estimate which forms the basis of at least 85 percent of the current Q2 2014 estimate,it was decided that a joint venture type estimate would be performed, using Mr.Hewitt as the second party,to take advantage of the experience of another estimator and his familiarity with the project.Mr.Hewitt was engaged as a subcontractor to MWH,and was given the same drawings and quantity take offs as the internal MWH estimator. MWH created a WBS for the construction pricing,to be estimated by both parties.This breakdown is more normally used to itemize the bid items for the project;however (as in this case)it can be used in a slightly different format to reflect "costs”rather than "bid prices”. Direct costs are estimated for each line item and at the end of the sheet indirect costs are added to the breakdown of direct costs facilitating detailed estimate comparison. Direct costs are the actual items of work and/or the features of the project or specific items relating to the contract. Typical indirect costs are contractor costs that are add-ons to the work items such as: =Contractor's Project Management *Contractor's Project Engineering »Surveying »Safety =Quality Control «Equipment Management »Administration Cost »Office and Shop Setup #Contractor Consultant Cost «Plant Setup Costs *Camp setup and Operation =Power Distribution or Operation =Equipment Mobilization and Demobilization *Other (as specified for the particular project) Mr.Hewitt used the same estimating sheet (breakdown)as the MWH estimator,separated into "contracts”as discussed below. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-51 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Once the work breakdown was established for all the contracts,MWH populated each contract with material quantities based on the current stage of feasibility design.MWH also established the labor cost for the various labor classifications to include,base wages,fringes,and labor burdens for an overall hourly labor rate reflecting Alaskan conditions.Overtime rates were also established from these base rates.The following steps were then followed. «Inquiries were made of Alaskan equipment suppliers and hourly equipment rates were established and agreed upon for the estimate. «Allowances,job material,permanent materials,and subcontract unit rates were established for major items,subject to adjustment during the review comparison for any quotes or opinions. «=Once all these steps were completed each party completed an independent cost estimate,using the items provided above. «During the preparation of the estimates,identical clarifications were given to each party by the engineering team as requested. ="Upon completion of the estimates,comparisons were initiated in an organized manner to achieve an acceptable estimate. 13.4.1.First Read of Estimate After MWH and Mr.Hewitt completed their estimates,the two estimating sheets were combined to initiate a line-by-line comparison and to highlight key differences.For joint venture estimating,this is typically referred to as the "first read.”Table 13.2-1 shows the summary result for construction costs from the first read of the estimate: Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-52 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 13.4-1.First Read of Two Comparative Estimates Main Cost Items MWH Hewitt Total Price (US$)Total Price (US$) Main Civil Works Contract 2,861 ,321,989 2,777 892,732 Reservoir Clearing 48,670,308 30,409,202 Turbine,Generator and Transformer Supply 187,713,673 222,080,752 Permanent Access Road 228,388,128 186,220,854 Rail Facilities and Storage Construction 33,770,632 23,898,495 Camp and Airstrip Civil Works Contract 33,761,641 19,003,721 Transmission Contract 176,917,469 243,339,977 Camp and Airstrip Buildings Construction Contract 163,159,200 170,612,524 Airport Operation Contract 45,638,816 168,576,407 Railroad (ARRC)Operation Contract 206,976,056 73,198,689 Medical and Evacuation Contract 48,421,330 15,138,568 Camp Operation and Security Contract 242,216,035 175,106,498 TOTAL $4,276,955,275 $4,105,478,420 The first read comparison indicated a difference of just over 4.0 percent which is regarded as well within the bounds of estimating error,and -in a commercial construction bidding situation -would probably be acceptable for a joint venture bid. However for this project,at this stage of development,it was considered worthwhile to continue to compare based on some of the important differences between individual "contracts”such as the permanent access road,and airport operations etc. After a telephone discussion that included both estimators and the design team -during which each line item of each estimate was discussed -each estimator made adjustments to their estimates for a second read.One of the larger adjustments was the allowance for unlisted items, profit,bond,insurances and contingency.These percentage amounts were agreed upon. 13.4.2.Second Read of Estimate After making adjustments based on the first read comparison,and the agreements for the percentage add-ons the resulting adjusted estimates were as shown in Table 13.4-2. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-53 December 2014 -zw-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Table 13.4-2.Second Read of Two Comparative Estimates Main Cost Items MWH (US$)Hewitt (US$) TOTAL 4,188,755,166 4,482,072,850 This represents a seven percent difference -greater than the earlier difference,but still,at this level of design,an acceptable accuracy for an OPCC. It was however considered appropriate to abandon portions of Mr.Hewitt's estimate -in favor of the MWH estimate -for four specific contract packages: Turbine,Generator and Transformer Supply -MWHs estimate was used for the turbine/generator supply contract,which includes the Generator step up transformers etc.MWH maintains a database of all bids for such equipment around the world and regularly updates it with the latest bids and awards,adjusting it to market sentiment. In the absence of calling for direct estimates from turbine/generator manufacturers, this database is considered to be more accurate than Hewitt's estimate and was therefore applied to both estimates. Transmission -The transmission line costs were provided by Electric Power Systems,Inc.(EPS),subcontractor to MWH --an Alaskan consultant that is one of the leading transmission consultants in the State.The "all in”cost that they provided was de-aggregated to fall in line with the general format of the estimate,and with EPS agreement an item for unlisted items was included.The resulting contract estimate was used for both MWH and Hewitt's estimates. ARRC -MWH have had considerable interaction with ARRC exploring the pricing and logistics of freight operations to Gold Creek,whereas Mr.Hewitt was using a more generic number for this contract.It was decided that both parties should use the ARRC cost derived by MWH after the detailed discussions. Airport Operation -The original estimate for airport operation -including provision of flights -provided by each party was grossly different because of the completely different methodologies.The two estimators therefore discussed their assumptions for the rotational nature of the worker inputs,and agreed the number of workers to be transported each week.MWH then re estimated from first principles - using input from Alaskan air transport operators -the cost of aircraft operations to facilitate the agreed rotation.During this examination,it became apparent that the airstrip that had been proposed was in excess of requirements.The original estimate assumed 737 operations,but by the time the project is constructed,there will be no 737s flying that can operate from gravel strips.The aircraft operation has therefore Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-54 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. been estimated using different turbo prop planes (CASA CN 235)and the design of the airstrip has been adjusted to incorporate a required airstrip of 5,550 ft.length. It was evident that,after incorporation of these four items into both estimates,the remaining differences centered on the Main Civil Contract,Permanent Access Road,and Camp Operation. No agreement was made at this time on the cost of the item;each estimator just explained their reasoning behind their estimate,considered each other's position,and then adjusted their estimates accordingly. 13.4.3.Final Draft Construction Cost Estimate After re-examination of the 2013 estimate in the light of the second read,the MWH OPCC was within 3.3 percent of that of the corresponding OPCC by Mr.Hewitt -but higher.The higher figure from MWH was selected as the base OPCC for the estimate,and the foundation for the final OPCC for this feasibility study. During 2014 -since the completion of the OPCC -the final analyses of the feasibility study have been completed.As a result of the design development and finalization of the report recommendations,the following actions have been taken to modify the initial work on the construction cost estimate: =Re-measurement of the quantities for the spillway,which has been modified to include four gates after the selection of the PMP and the calculation of the PMF inflow. =Re-measurement of dam quantities to reflect the adjustment of the dam configuration. =Re-measurement of the diversion tunnel and emergency outlet quantities to reflect the revised design. =Separation of the left and right abutment consolidation grouting to accommodate the costs of preparatory work. =Reassessment of the costs of the service contracts dependent on the construction schedule (which has been modified to reflect the reduction in RCC volumes for Watana Dam. These changes to the estimated quantities were incorporated into the OPCC together with escalation to calculate the base OPCC for second quarter 2014. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-55 December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT The derived base OPCC is US$4.096 billion,is shown in Table 13.4-3.Details of the estimate are attached as Appendix B10. Table 13.4-3.Opinion of Probable Construction Cost Main Cost Items MWH Total Price (US$) Main Civil Works Contract 2,878,841,278 Reservoir Clearing 45,297,999 Turbine,Generator and Transformer Supply 201,792,198 Permanent Access Road 192,031,833 Rail Facilities and Storage Construction 34,068,783 Camp and Airstrip Civil Works Contract 30,049,914 Transmission Contract 165,743,940 Camp and Airstrip Buildings Construction Contract 178,400,154 Airport Operation Contract 130,361,141 Railroad (ARRC)Operation Contract 59,508,577 Medical and Evacuation Contract 20,721,785 Camp Operation and Security Contract 159,115,083 TOTAL $4,095,932,685 13.5.Non Construction Costs 13.5.1.General The following non-construction costs have been estimated in discussion with AEA: #FERC Licensing Costs post January 2012 »AEA Administration and Legal Costs «Engineering Design for License Application -includes amounts paid to other (non- AEA)companies,firms,or individuals engaged by the owner to plan,conduct pre- design studies,prepare estimates,or give general advice and assistance to the owner in connection with feasibility and FERC Licensing phase work. =Geotechnical Investigations during License Application preparation "Logistics for Geotechnical Investigations «Engineering Final Design *Engineering During Construction Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 13-56 Alaska Energy Authority December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Construction Management *Environmental Monitoring During Construction *Quality Control and Inspection *Environmental Mitigation «Land and Land Rights »Permit Fees =Owner Insurance 13.5.2.Cost Items The following constitute the cost items included: »Legal Costs -includes the general legal expenditures incurred in connection with project construction and the court and legal costs directly related thereto,other than legal expenses included as part of insurance costs to cover injuries and damages. =General Owner's Administration -includes the portion of the pay and expenses of general officers,project and administrative staff time and expenses applicable to the construction work. «=Engineering Design Services -for Detailed Design and for Engineering Services During Construction -includes amounts paid to other (non-owner)companies,firms, or individuals engaged by the owner to plan,design,prepare estimates,supervise, inspect,or give general advice and assistance in connection with project design (final design and contract documents). *Construction Supervision -includes labor and expenses of engineers,surveyors, draftsmen,inspectors,superintendents and their assistants applicable to project construction (construction monitoring). =Insurance Costs -refers to owner All-Risks Project insurance. «Taxes -includes taxes on physical property (including land)during the period of construction and other taxes properly includible in construction costs before the facilities become available for service. 13.5.3.Derivation of Non-Construction Costs Program costs used for the feasibility cost estimate update were derived in 2011 from a discussion with AEA management.Up to December 2012,no escalation was included for those estimated program cost,although the first line item,FERC Licensing,was increased by about 14 Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-57 December 2014 -a- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT percent prior to the December 2012 estimate.Because of the previous large increase,from 2012 to January 2014 (the commencement of the estimate in this report)the FERC licensing cost estimate was held steady,but all other non-construction program costs were escalated by 2.75 percent (the figure agreed for use in the earlier financial analysis).The originally estimated costs of site investigation were divided into two separate components -site investigation and logistics support for site investigation -as requested by AEA. During further examination of the non-construction program costs,the original decision to apply no escalation from December 2011 to December 2012,was judged unrealistic.However,for this estimate,a "catch-up”percentage of 1.5 percent was initially judged reasonable to attempt to realistically address previous escalation. Finally in applying the corrections for the design development from January 2014 to July 2014 a further escalation of 0.025 percent was included,and Land and Land Rights costs suggested by AEA were added to the Environmental Mitigation Measures budget estimate. With regard to the line items for FERC licensing budget and the engineering design for licensing, the recent projected budget adjustments (of plus 30 percent and minus 4 percent respectively) were included. Based on this analysis,the base estimated non construction costs are shown in Table 13.5-1. Table 13.5-1.Non-Construction Costs Non-Construction items ea.a 4) FERC Licensing 267,253,000 Owner Cost Administration and Legal 184,664,354 Initial Camp and Access Inc.in Licensing Cost Engineering Design for Licensing 20,573,000 Engineering Detailed Design 184,664,354 Engineering During Construction 92,385,641 Construction Management 153,869,141 Environmental Monitoring During Construction 57,420,242 Geotechnical Investigations 28,870,513 Logistics for Site Investigation 8,554,226 Quality Control And Inspection 92,385,641 Environmental Mitigation (Summary,inc.Land Costs)407,738,281 Owner Insurance 61,590,428 TOTAL Non-Construction Costs $1,559,968,821 Note:Non-Construction Costs as agreed with AEA based on typical similar projects. Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 13-58 Alaska Energy Authority December 2014 -Z- ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Not included in Table 13.5-1 are Permits and Fees;Interest during construction;future project escalation;and financing costs,all of which will be determined by AEA for use in the financial models. Of particular interest are the environmental mitigation measures.The project construction cost estimate includes assumed environmental restrictions on construction activities (together with mitigations),but the above non construction cost items are,essentially,placeholders related to possible environmental mitigation programs that might result from the consultation and reviews in the FERC licensing procedure and USACE Section 404 permitting processes.The amounts included are based on similar project mitigation.This is somewhat speculative since feasibility engineering tasks are ongoing and environmental studies and stakeholder consultations have not yet been completed.Those activities will assist in definition of the final environmental measures to be proposed in the future FERC License Application. It should be noted that the environmental mitigation budget above does not include for specific individual mitigation actions but at this time the feasibility level construction cost estimates include some structural measures that contribute to the overall Environmental Mitigation Program.These include the use of up to eight low level outlet valves for discharging water for instream flow.The OPCC does include for a multi-level intake to enable water to be drawn from varying reservoir levels as the operating level changes month by month (similar to what is done at other large reservoir projects such as Lake Oroville in California).They also include some limited clearing of the reservoir upstream of the dam site as needed from a project construction standpoint;this will provide environmental benefits as well. However,it should be noted that the basic construction cost does not include any costs for possible future fish passage provisions. Extra facilities to those shown on the drawings would be regarded as mitigation,and are deemed to be included in the budgeted amount for "Environmental Mitigation Measures Summary” above. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-59 December 2014 --a- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 13.6.Total Project Cost Estimate The total program base cost estimate is shown below in Table 13.6-1. Table 13.6-1.Program Base Cost Estimate -2Q 2014 Program Cost (Reservoir TWL 2,050)US$ (2Q 2014) Non-Construction Costs (exc.Env.Mitigation and Insurance)1,090,640,112 Main Civil Construction 2,878,841 ,278 Environmental Mitigation (Summary inc.Land Costs)407,738,281 Permanent Access Road 192,031,833 Railhead Improvements 34,068,783 Camp and Airstrip Buildings 178,400,154 Turbine,Generator and Transformer Supply 201,792,198 Transmission and Interconnection 165,743,940 Clearing 45,297,999 Airport Civil Construction 30,049,914 Airport Operation Inc.in Air Service cost Air Service 130,361,141 Railroad Operation 59,508,577 Camp Operation 159,115,083 Medical and Evacuation 20,721,785 Owners Insurance 61,590,428 TOTAL PROGRAM COST $5,655,901,506 The estimate has been subject to probabilistic analysis as described below. It should be noted that,depending on the choice of procurement/contract strategy the construction cost could be up to 25 percent higher. 13.7.Cashflow Cash flow has been derived for the construction and supply contracts. The cumulative value of all construction and service contracts has been derived from the base cost estimate and the base schedule shown in Appendix B11 and is shown in Figure 13.7-1 below. Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 13-60 Alaska Energy Authority December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. $4,500 Retention Paid . $4,000 Total(Millions)$500 YEAR 4 YEAR 5 YEAR 6 YEAR 7 YEAR 8 YEAR 9 YEAR 10 YEAR 11 YEAR 12 Figure 13.7-1.Cash flow of Construction and Service Contracts This cash flow does not include any items from the non-construction costs and therefore commences at year four when the first construction contract is let.Non-construction costs have not been included,because the exact time of expenditure is not known,and a substantial percentage of the non-construction costs have already been spent. The first somewhat slow rate of expenditure is explained by the very limited amount of work performed during the early winter season on the project. The cash flow includes payment delay of 60 days,retention of five percent,and final payment 12 months after contract completion.Non-construction costs such as construction supervision/. management are not included. 13.8.Cost Variability Analysis To derive a risk-adjusted estimate for a project,two different assessments must be completed,the first of which -an uncertainty evaluation -can be completed at this stage of feasibility. Susitna-Watana Hydroetectric Project Alaska Energy Authority FERC Project No.14241 Page 13-61 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Uncertainty refers to a range of unit costs and quantities that create a distribution of likely costs for each planned construction line item. The effects of uncertainty in planned cost line items were explored using a probabilistic approach and modeling processes.The model was created using the Palisade @RISK software,and involved generating tens of thousands of realizations giving a probability distribution of the overall adjusted cost,which reflects the uncertainty of the estimating process. For each uncertain variable in the model the possible values were defined using probability distributions.The type of distribution used in uncertainty analysis depends on the factors surrounding the variable and the methods used in determining the upper and lower limiting values of costs and quantities.Some of the commonly used distributions are triangular,trigen, uniform or program/project evaluation and review technique.A combination of trigen and triangular distributions were used to characterize the variability in the construction costs; consistent with the estimators approach to determining the minimum,best estimate and maximum costs and quantities (as extended). @RISK uses these probability distributions to define the range of uncertainties associated with the construction line items and calculates many thousands of predicted values (simulations)of the overall construction cost,each time sampling values from the input distributions. The estimated range of possible values for the unit prices and quantities of each item was based on the previous experience of MWH,the history of estimating of the Susitna-Watana project in the last three years,and in particular by a comparison with other projects designed,estimated and/or supervised by MWH.Attention was focused on cost drivers,and consideration was given to the various factors that might drive the possible spread of costs.The final input values were modelled in the @RISK tool and can be defined as: «Expected Probable Estimate [Most Probable]or Best Estimate.The unit price/ quantity cost of an item based on realistic effort assessment for the required work and any predicted expenses. «=Expected Probable Low Estimate [Most Probable Low],a five percentile lower estimate.The unit price/quantity cost of an item based on analysis of best-case scenario for the item. =»Expected Probable High Estimate [Most Probable High],a 95 percentile upper estimate.The unit price/quantity cost of an item based on analysis of the worst-case scenario for the item. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-62 December 2014 -wZ ALASKA ENERGY AUTHORITY AEA11-022 FEASIBILITY REPORT SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years.ENGINEERING The result of the uncertainty analysis of quantities and unit prices is sh 13.8-1 for the construction costs,Figure 13.8-2 for the non-construction co for the total costs. As can be seen in Figure 13.8-3,the 50"percentile for the total project cost is US$5.655 billion, while the 75""percentile is US$5.872 billion. own below in Figure sts,and Figure 13.8-3 100%+ BOG4-22 cere ee ee errr ee ne ete e eee cece cee fhe enter eter e eee eeeee 70th percentile $4.088 Billion 95th percentile $4.145 Billion 60%4 2 P=] ¢ 7 2 oua 40%OeeeeeeSeerSees en Base Estimate 50th percentile $4.096 Billion $4.060 Billion 4 20%i eee eee Qe ee ee ee -----------ee beeeeeeeeee 0%t T T T T T 3.90 3.95 4.00 4.05 4.10 4.15 4.20 Cost in Billions (S$) Figure 13.8-1.Construction Cost S Curve Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-63 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 80%OS 95th percentile $2.178 Billion 60%a 2Pm]Base Estimate <oe o $1.560 Billion 2 o% BO%beeenee a Ne, 50th p ercentile 70th percentile$1.594 Billion $1,812 Billion QO%tonncnc cc eyfhee see Pope WA re Seen serenePal 0%T T T T T T T T 0.6 0.8 1.0 1.2 1.4 1.6 18 2.0 2.2 2.4 2.6 Cost in Billions ($) Figure 13.8-2.Non-Construction Cost S Curve Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-64 December 2014 -zZ ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 100% nn 80%SS aA[ns 95th percentile S$6.247 Billion 60%a as Snan a Sees o Base Estimate =$5.655 Billion 7) i 70th percentile 2 $5.872 Billion 40%ACesCenCleecanes,Sanna 50th percentile $5.654 Billion 20%ESA,CS a See,Snes 0%T T T T T ¥T 48 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 Cost in Billions ($) Figure 13.8-3.Total Project Cost S Curve 13.9.Risk Analysis A formal risk analysis has not been performed for this feasibility study,but when there is more project definition -of foundations and environmental mitigation in particular -it would be prudent to perform a risk analysis of cost and schedule.At the present time the reader is referred to the AACE ranges for a Class 4 estimate shown in Table 13.2-2 which indicates recommended contingency (or management reserve)of between 10 percent and 30 percent (a Class 3 contingency would be five percent to 20 percent). 13.10.Operation and Maintenance Plan and Budget AEA has not yet developed a detailed organization plan for the operating phase of the project. As such,only a general description of the likely operation and maintenance program requirements can be provided for this report based on experience gained by AEA and the Railbelt Utilities at Bradley Lake,and by other large utility organizations at remote large-scale hydro projects in North America.Therefore,an estimated annual operation and maintenance Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-65 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. (O&M)budget for the project must be derived through parametric means,using data on similar projects to make a provisional estimate for economic and financial modeling to be performed by AEA. In developing this estimate,data from a variety of sources were analyzed and compared.These include data from:(1)a 2011 U.S.Energy Information Administration publication for power plants owned by major U.S.investor-owned utilities;(2)historical information gathered by Canadian investigators from plants in the Canada and the United States and published in 1987 by "Water Power and Dam Construction”-updated by MWH using appropriate indices;(3)a Federal Columbia River Power System Asset Management Study conducted by Harza Engineering Co.in 1998-9;(4)a detailed O&M program and budget estimate prepared by MWH for FERC License Application for the 762 MW Oroville Hydroelectric Project for which there is significant operating history and publicly-available cost information;and (5)a 2008 Summary of FERC Form |filings by major U.S Investor Owned Utilities,published in FERC's eLibrary. The cost information presented below includes some provision for periodic "Renewals and Replacements”,but not for major generating equipment overhauls,which would typically be funded out of a Capital Budget account.It also does not include the owner's "General and Administrative”costs,which typically add in the range of 35 percent to 40 percent to the base annual O&M costs.Annual costs for such things as insurance,environmental monitoring and other owner costs associated with managing this and other system generation and/or transmission assets are also not included. 13.10.1.Operation and Maintenance Plan The following assumptions have been made in developing a preliminary operating plan and annual budget estimate for the project for the feasibility phase: *AEA's O&M strategy will be developed jointly with the Railbelt Utilities as part of a future phase of project development,in concert with power sales contract formulation,dispatch agreements,and financing arrangements. *O&M plans will be formulated loosely along the same lines as those implemented for the successful Bradley Lake. «Tentative plans would envision a facility staffed by personnel located on-site,with operational capability by the on-site staff;but with primary dispatch and load settings coming from new remote control centers to be established in both Anchorage and Fairbanks. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-66 December 2014 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «Routine maintenance,condition and performance monitoring,inspection,adjustment and minor repairs will be performed by AEA or contracted staff working at the facilities,or -for larger tasks -flown in from the Railbelt. «Major maintenance and repair,specialized inspections,tests,and adjustments will be performed by specialty contractors or participating utilities through various contracting arrangements depending on the service to be provided. «Support services including technical,special inspection,environmental monitoring and reporting,accounting,budgeting,financial reporting,procurement,human resources,legal,etc.will be provided from AEA headquarters in Anchorage. 13.10.2.Site Staffing A site staff of between 24 to 28 is assumed.Potential positions include:Plant Manager; Plant Engineer/Asset Specialist;Technical Supervisor -Electrical;Technical Supervisor - Mechanical;Operators (between two and five);Maintenance Trade Workers (Electrical/ Mechanical/Civil;Planner;Environmental Coordinator;Administrative Assistants/Office Clerks; and Security personnel.Because of the remote nature of the site,and the significant infrastructure (roads,airstrip and accommodation)with requirements for snow clearance,etc. there will be some additional civil and general labor tradesmen required. 13.10.3.Power Dispatch Arrangements and Staffing The addition of a Susitna-Watana Project resource intended to serve the total Railbelt system, together with sufficient transmission to incorporate it into that system will almost certainly result in a re-evaluation of generating unit commitments and dispatch practices as part of future planning and design work on the project.The production modeling demonstrates that maximum benefits from the project would be realized through a centralized commitment and dispatch process.The system modeling work (PROMOD)carried out thus far has been set up to simulate a centralized dispatch of the Railbelt system resources according to assumed operating rules, with the objective of minimizing total variable production costs for the utility participants. Therefore,the current estimate of annual operating costs assumes centralized dispatch from a remote control center -costs of which have not been included in this estimate. It is expected that as FERC licensing and final design work on the facilities is completed,more details regarding specific O&M requirements will be developed by AEA,a project-specific staffing plan will be established in collaboration with the utilities,and a more detailed O&M Program developed.That will enable a more detailed project-specific O&M budget to be prepared to support financial planning. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-67 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.10.4.Annual Operation and Maintenance Budget A provisional O&M budget is presented below,suitable for use in AEA's current Plan of Finance for the project.Annual costs for O&M would include: #Operating costs *Maintenance costs =Contracted specialty services =Interim replacements Values for these items for the feasibility studies were developed in concert with AEA based on an assumed level of required operation and staffing,AEA's own experience with operating and maintaining the Bradley Lake Hydropower project,and considering that this a large,remote site with difficult access.As noted earlier,to develop budgetary pricing for this study,industry databases were examined to determine historical O&M cost values for comparable large-scale, remote hydro projects in North America as a guide. Current-year annual O&M costs are estimated to be on the order of $14,500,000.For economic and financial modeling purposes,this value will need to be increased to cover expected labor and material price escalation between now and the projected on-line date of the project.This early estimate will be refined and updated as FERC licensing and design work progress,and a project- specific operating plan developed in concert with the utilities. 13.10.5.Annual General and Administrative Budget As noted above,without a specific plan for operating the project,a general assessment of likely Owner costs for administering the project O&M activities can only be provided at this early stage of study.Based on parameters provided in several documents outlining general and administrative (G&A)costs for large hydro projects in North America it is recommended that AEA assume a value equal to 40 percent of the basic annual O&M expenditure for planning an annual G&A budget.This would be approximately $5,800,000 per year. A full-time staff of from 12 to 15 people is assumed,covering a wide variety of management, technical and financial specialists and support staff.Potential positions include:managers; engineers;financial/accounting specialists;environmental specialists;project controls specialists; administrative assistants/office clerks;and support personnel. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-68 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 13.10.6.Environmental Monitoring and Compliance Environmental studies,monitoring and FERC license compliance work can be expected to continue for the life of the project.For large hydro projects of the scale of Susitna-Watana this could be a significant program,and due to the size and large footprint of the project,combined with the remoteness the project site,annual costs for these ongoing elements of work are expected to be significant -more so than for other large-scale projects in North America which have more direct access. For the current studies it is recommended that a target budget allowance shown in Table 13.10-1 for these elements of work be established as follows: Table 13.10-1.Budget Allowances for Environmental Target Budget for Environmental and Annual AmountRegulatoryCompliance Year 1 $15 million Year 2 $15 million Year 3 $15 million Year 4 $10 million Year 5 . $10 million Year 6 and beyond $5 million 13.10.7.Special Considerations in the Early Years During the early years of operation there are additional maintenance tasks beyond routine project O&M that might need to be carried out.One principal example is a possible continuation of construction-period grouting of the left abutment (from the galleries)as the abutment bedrock warms up under the influence of the reservoir.It is considered prudent to make an allowance, during the first five years,for regrouting -from the galleries -of the left abutment in case any ice melts in postulated ice filled features.For this and other potential short-term initial operation period needs,it is suggested that for the first five years that the project budget include an annual allowance on the order of US$2 to 3 million. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 13-69 December 2014 Section 14 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 14.ENGINEERING AND CONSTRUCTION SCHEDULES The project procurement strategy and contract strategy -based on the project risk profile - have not yet been formulated.For the purposes of completing the construction planning and estimating recorded in Sections 13 and 14,a procurement strategy has been assumed that is a "best estimate”of an appropriate strategy,based on worldwide experience of similar project development of similar size and complexity under a similar risk profile. 14.1.Preparation of Schedules This Section presents the proposed project Engineering and Construction Schedules,based on the selected project arrangement and major features presented in Sections 8,10,and 11. Originally,the schedule was created to include the activities required for preparing the Federal Energy Regulatory Commission (FERC)license application.Because of legislative uncertainty, and uncertainty associated with the FERC hcensing schedule,for this report -to assist in understanding the governing technical challenges of the project -the Engineering and Construction schedule has been "decoupled”from the FERC licensing schedule,although a key "predecessor”for any,and all,construction is the issue of a FERC license and the completion of associated reviews and permitting.A comprehensive integrated schedule will be prepared separately by Alaska Energy Authority (AEA)during subsequent stages of project development. A significant driver for the schedule is the necessity for a comprehensive site geotechnical investigation program and excavation of adits in the dam abutments which are required to establish more definitive foundation characterization to support feasibility and detailed design. Some basic site investigation has been undertaken in 2014,but -because of the unpredictability of the annual budget cycle -no certainty is attached to future funding of site investigation vital to support feasibility and detailed design.To accommodate these uncertainties surrounding project implementation,it was decided to prepare a design and construction schedule "without links”to the process of FERC licensing,and simply organized by year following any decision to initiate continuous project development -evidenced by the start of a linked site investigation and detailed design. Please refer to Appendix B11 for the comprehensive Susitna-Watana Engineering and Construction Schedule. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-1 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 14.1.1.Calendar Although the pre-construction activities will be performed on the basis of an "office”(i.e.5-day work week)calendar,there are also two different calendars applying to construction work on the site (described below),together with some key constraints. The weather at the site is a major factor,particularly the arduous winter weather which will have a significant effect on the various contractors construction scheduling. Certain activities can be continued during the winter economically and productively,as demonstrated during the construction of the recent Karahnjukar hydro project in Iceland.These activities include: ="underground works (tunneling); *conventional concreting,which can be performed under temporary insulated weather protection; =quarry development,and rock excavation can also be continued under adverse conditions, but it is expected that the output will be compromised somewhat during inclement weather; =overburden removal and the associated foundation rock excavation; *curtain grouting from within the galleries in the dam; «road construction,which may be able be performed in winter,depending on the geotechnical conditions in the corridor and moisture and density controls;and, *all activities within the powerhouse,after weather proofing of the powerhouse structure. There are also activities that are most appropriately and efficiently conducted during the winter months,when the river level is low,such as: *cofferdam construction; =river diversion;and, =permanent road bridge construction. In contrast,there are significant activities that,at this stage of planning,must be assumed to be carried out only during summer months,which in a typical year is effectively only a five to six month window.Principal among these are the final shaping of the dam foundations,the consolidation grouting of the dam foundations,and the placement of roller compacted concrete (RCC).The current project schedule places RCC on the left and right abutments until such time Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-2 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. as the cofferdams are constructed,the river diverted and the center portion of the dam is available to place RCC. The challenge for a contractor will be to organize all RCC placement activities in such a way that the season "shoulders”are extended as much as possible,particularly the period of September and October,to maintain production before having to shut down for the winter. Because of the two parallel "controls”on work,two calendars have been used for construction activities in the Primavera P6 scheduling software,one based on normal working weeks (including public holidays),and a second including specific winter shutdowns. 14.1.2.Constraints In addition to the nuances of summer and winter construction,one key environmental constraint has been included at this time -that is,the effect of migratory birds -which means that no clearing can be performed during bird nesting season.To comply with this regulation,initial clearing will take place in the winter season. Although activities leading up to the issue of a FERC license have not been included in the schedule,it has been assumed that no construction work of any kind -including the access road -can be commenced before the award of a FERC license and the associated approvals by FERC, and the issuance of permits,most particularly the Corps of Engineers Section 404 permit. This constraint on construction is particularly important because access to the site is currently considered to be within the licensed works and the access road (which is some 50-60 miles long) is the sole method of mobilization and hence on the critical path of the whole project development. As discussed in Section 13,construction is assumed to be implemented in seven construction packages and one supply contract,with (essentially)all implementation being performed under a traditional sequence of an engineering design contract,followed by a construction contract.It has also been assumed that at least four contracts will be let for the provision of services such as railroad service,and aircraft operation. 14.1.3.Individual Contract Schedules In deriving the comprehensive Engineering and Construction Schedule,six "break out” schedules were created for the assumed construction contracts: =Clearing =Permanent Access Road Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-3 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. =Rail Siding «=Camp and Airstrip Civil Works =Camp and Airstrip Buildings ="Main Civil Contracts They are shown below in Figure 14.1-1 through Figure 14.1-6. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-4 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Susitna-Watana Hydroelectric Project -Clearing Construction Schedule Activity ID |Activity Name |Original Total Float Year 5 Year 6 Year?Year 8Duration6|56 |57 |58 |59 |60 |61 |62 |63 |64 |65 |66 |67 |68 |69 |70]71 |72[73 |74]75 |76 |77 |78 |79 |80 [81 |82 |83 |84 |85 |86]87 |88 |89 |907 Clearing .§26.1d 743.0d a ee f Clearing|__S01 |Clearing NTP TS 0.00 |13440 Clearing NTP S02 _{Mobilization 5.0d 134.1d Mobilization S03 _|Permanent Village Clearing (56 Acres)12.0d 134.1d Permanent Village Clearing (56 Acres) S04 Clearing Camp &Contractor Yard (80.7 Acres)16.0d 134.1d Clearing Camp &Contractor Yard (80.7 Acres) S05 |Camp RoadsClearing (31 Acres)- 16.0d 134.14 Camp Roads Clearing (31 Acres) S06 Airport Clearing {160 Acres)20.0d 134.1d Airport Clearing (160 Acres) $07 Dam Site Clearing (50 Acres)11.0d 134.1d Dam Site Clearing (50 Acres) 1 $10 Site Access Roads -North &South (141.9 Acres)26.0d 134.1d Site Access Roads -North &South (141.9 Acres) ($20 |End Dam Site Clearing 0.0d 134.1d nd Dam Site Clearing im 'S60|Reservoir Clearing (2,887 Acres)|584.0d 814.0d 1 Reservoir Clearing (2,887 Acres) Figure 14.1-1.Clearing Construction Schedule Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-5 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Susitna-Watana Hydroelectric Project -Permanent Access Road Construction Schedule Activity 1D |Activity Name Original Total Float Year 4 Year 5 Year 6 Duration B |37 |38 {39 |40 |41 |42 |43 |44 |45 |46 |47 |48 |49 |50 [51 |52 |53 |54 |55 |56 |57 |58 |59 |60 |61 |62]63 |64 |65 |66 fe7|SU EGERVELE LED Hyd roelectric Project 2}Engineerin==$E46OGF |E2486.0d ae ee Ty Susitna-VWatana Hydroelectric Project -Engineering &Cor Construction Activities 646.0d 2486.0d ee if Construction Activities Permanent Access Road 646.0d 2486.0d re ny Permanent Access Road i $1084 |Permanent Access Road NTP |00d |01d |@ Permanent Access Road NTP $1085 |Mobilize Crews for Site Access 24.0d 3.1d |Mobilize Crews for Site Access $1090 |Pioneer to Center of 40 Mile Road 15.0d 3.1d fC]Pioneer to Center of 40 Mile Road $1095 |Clearing &Grubbing 125.0d 0.1d Clearing &Grubbing $1100 |Erosion &Sediment Controls (1st Season)147.0d 561.1d it ]_Erosion &Sediment Controis (1st Season) $1105 |Permanent Access Road -Excavation Common (1st Season)146.0d 0.1d ]Permanent Access Road -Excavation Common (ist Season) $1115 |Permanent Access Road -Excavation Rock (1st Season)146.0d 0.1d }Permanent Access Road -Excavation Rock (ist Season) $1120 |Permanent Access Road -Embankment (1st Season)146.0d 0.1d -Permanent Access Road -Embankment (1st Season) $1121 Winter Shutdown _ 212.0d 0.1d Ht -]Winter Shutdown $1130 |Erosion &Sediment Controls (2nd Season)74.0d 186.1d {J Erosion &Sedimen?Controls (2nd Season)|$1135 |Permanent Access Road -Excavation Common (2nd Season)74.0d 186.1d -{---]Permanent Access Road -Excavation Common (2nd Season) $1140 |Permanent Access Road -Excavation Rock (2nd Season)74.0d 186.1d {Permanent Access Road -Excavation Rock (2nd Season) $1145 |Permanent Access Road Embankment (2nd Season)74.0d 186.1d -----)"Permanent Access Road Embankment (2nd Season) $1150 |S1 Road (Main Access Road to Bridge)18.0d 2975.0d {J $1 Road (Main Access Road to Bridge) $1155 |Place Organics on Slopes 70.0d 186.1d ;CFF *Flace Organics on Slopes $1160 |Gravel Surfacing 40.0d 234.1d ol}_Gravel Surfacing $1170 |Permanent Access Road Long Span Bridge (MP 5.8)30.0d 3.1d Permanent Accegs Road Long Span Bridge (MP 5.8) $1175 |Permanent Access Road Long Span Bridge (MP 14.9)40.0d 3.1d Permanght Access Road Long Span Bridge (MP 14.9)$1180 |Permanent Access Road Long Span Bridge (MP 15.1)30.0d 3.1d "Permanent Access Road Long Span Bridge (MPy 15.1) $1185 |Permanent Access Road Long Span Bridge (MP 17.3)30.0d 3.1d =Permanent Access Road Long Span Bridge (MP 17.3) $1190 |Permanent Access Road Long Span Bridge (MP 21.6)45.0d 0.1d -AH Permapent Access Road Long Span Bridge (MP 21.6)$1195 |Permanent Access Road Long Span Bridge (MP 26)40.0d 0.id Permanent Acce$s Road Long Span Bridge (MP 26) $1200 |Permanent Access Road Long Span Bridge (MP 43)40.0d 0.1d ----]_Permang nt Access Road Long Span Bridge (MP 43)$1205 |Permanent Access Road Drainage 53.0d 274.1d Cl }Pemanent Access Road Drainage $1210 |Guard Rail 200.0d 274.14 [}*puard Rai $1215 |Rip Rap 24.0d 274.1d a a$1225 |Seeding 88.0d 186.1d Feeding $1230 |24.9 kV System Inc Transmission (&Fiberoptics)from Intertie 72.0d 244.14 24.9 kV System Inc/Transmission (&Fiberoptics)from Intertie =. $1235 |Demobilization 30.0d 244.1d eos Demobilizatian $1240 |Permanent Access Road Construction Complete 0.0d 186.1d @*Permanent Access Road Construction Complete Figure 14.1-2.Permanent Access Road Construction Schedule Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-6 December 2014 Zz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Susitna-Watana Hydroelectric Project -Rail Siding Construction Schedule Activity ID |Activity Name |Original |Total Float Year4 Duration Bg |40 }44 |42 |43 |44 |45 |46 |47 |48 i Susitna-Watana Hydroelectric Project *]Engineerin™E29 p ods PRS EEE EEE ey SysitinaVWVatana Hydroelectric Project -Engineer Rail Siding Construction 201.0d 542.1d Da i Rail Siding Construction |§1001|NTPRailSidmg ©|O0d°|842.4d-NTP Rail Siding {$1002 |Mobilization 10.0d 542.1d Mobilization ;$1003 |Construct 350 Man Camp 20.0d §42.1d Construct 350 Man Camp i $1004 |Clearing &Grubbing (40 Acres)20.0d §42.1d Clearing &Grubbing (40 Acres) |$1005 |Common Excavation (300,000 CY)50.0d §42.1d }Common Excavation (300,000 CY}$1010 |Borrow Selected Material (210,000 CY)50.0d 542.1d ]Borrow Selected Material (210,000 CY) $1015 |Grading D-1 Subballast (40,000 CY)10.0d 542.1d }-{---]_Grading D-1 Subbailast (49,000 CY) $1020 |Seeding (7 Acres)2.0d 585.1d Seeding (7 Acres) $1025 [Geogrid (135,000SY)__; 50.0d 597.14 7]Ghogrid (136,000 SY)_$1030 |Ballasted Track In Place (115 LB Rail /Wood Ties/11,900 FT)45.0d 542.1d [|Ballasted Track In Place (115 LB Rail/Wood Ties /11,$1035 |Turnout,Non-PTC Ready,ARRC std.No.11 115#(2 EA)6.0d 581.4d Tumout,Non-PTC Ready,ARRC std.No.11 115#(2 EA) $1040 |Tumout AARC std.No.11 1154 PTC Ready (2 EA)6.0d 581.1d Tumout AARC std.Na 11 115#PTC Ready (2 EA)$1045 |Concrete Storage Area (45,000 SF)12.0d 585.1d H-{---)Concrete Storage Area (45,000 SF) $1050 |Covered Storage Area (20,000 SF)20.0d 577.1d -___-)_Covered Storage Area (20,000 SF)$1060 |Helipad (10,000 SF)15.0d 582.1d {_----]_Helipad (10,000 SF) \$1065 |Transfer Ramp Loading 15.0d §82.1d -(-_---]_Transfer Ramp Loading {$1070 |Maintenance Shop (13,200 SF)24.0d 573.1d --_---]_Maintenance Shgp (13,200 SF)$1075 |Demobilization 10.0d 542.1d Demobilization $1080 |Rail Siding Construction Complete 0.0d 542.1d pee Siding Construction Complete Figure 14.1-3.Rail Siding Construction Schedule Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 14-7 December 2014 -Z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 14.1.3.1..Camp and Airstrip Civil Works Schedule Susitna-Watana Hydroelectric Project -Camp &Airstrip Civil Works Construction Schedule Activity ID [Activity Name Original |Total Float Year 3 Year 4 Duration 6 37 38 |39 |40 |41 |42 |4a |44 |45 |46 [47 Susitna-Watana Hydroelectric Project Engineerin==[322209 |IRS3S ca -_-_-_-_-_-----Sy susitna-Watana Hydrocectic Project -Engineering &Con Construction Activities 220.04 935.1d Construction Activities __Building,Camp &Airstrip Civil Works 220.00 985.10 MEY Building,Camp &Airstrip Civil Works |$1439 |NTP Building,Camp &Airstrip 0.0d 494.1d NTP Building,Camp &Airstrip i $1440 |Snow Road from the North 10.0d 494.id Snow Road from the North $1495 |Temporary Camp 20.0d sai |=Temporary Camp $1550 |Mobilization /SWPPP $1660 |Clearing $1715 |N2 Road (N1 Road to Construction Camp) $1770 |Permanent Bridge at Site --_-_2 $1685;Grubbing (167 acre) §1690,Earthworks Building Areas Including Roads &Locations for Water &... Nobilization ASWPPP _]Clearing a N2 Road {N1 Road to Construction Camp)]Permanent Bridge at Site Building &Camp Areas FEF}sSGrbbing (167 acre) >)Earthworks Building Areas Including Roads &Locations for Water &Sewerage Treatment Plants (183,000 CY) $1695,Gravel Surfacing (12 in./46,000 CY)58.0d 1010.14 [}<Sravel Surfacing (12 in./46,000 CY) $1700;Site Drainage 20.0d 1005.10 -(_-----J_ Site Drainage $1705,Sports Fields 20.0d 1036.14 +]_Sports Fields $1710!Fencing Building All Areas (15,666 LF)15.0d 1010.1d }>{---],_Fencing Building All Areas (15,666 LF) D " :.: - :5 EEE Air Strip $1730.Grubbing (160 Acres)32.0d 961.1d EF]«Grubbing (160 Acres) $1735,Earthworks (450,000 CY)75.0d 935.1d mf ]_Eartnworks (450,000 CY) $1740.Gravel Surfacing (24,000 CY)40.0d 935.1d [=ra¥el Surfacing (24,000 CY) $1745:Concrete Paving 24.0d 935.1d onkrete Paving $1750 Ancillaries (Lights,Radar,etc.)15.0d 935.id ' {-]Ancillaries (Lights,Radar,etc.) $1755:Demobilization 15.0d 935.1d -Demobilization$1760,Building,Camp &Airstrip Construction Complete 0.0d 935.1d uilding,Camp &Airstrip Construction Complete Figure 14.1-4.Camp and Airstrip Civil Works Construction Schedule Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-8 December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT 14.1.3.2..Camp and Airstrip Buildings Schedule Susitna-Watana Hydroelectric Project -Camp &Airstrip Buildings Construction Schedule Activity ID [Activity Name |Original Total Float Year 4 Year5Duration44]45 |46 |47 TT 4 49 [|so |51 [|52 [53 54 |(55 a ee ee ee ee --EEEE ee -y Susitna-Wate Construction Activities 457.0d 0.04 Construction Camp Construction 457.0d 0.0d Camp Const! |$1804 |NTPCampConstuction =”"|0.0d 1.00 if NTP Camp Construction$1805 |Factory Assembly of Prefab Units |366.0d 1.0d -|Factory Assembly of Prefab Units $1806 |Move 250 Man Camp to Main Dam 15.0d 0.0d Move 250 Man Camp to Main Dam $1810 |Construct Permanent Village 45.0d 0.0d -s Construct Permanent Village|$1815 |Construct Contractor Camp 90.0d 0.0d log J Construct Co $1820 |Camp Construction Complete 0.0d 0.0d amp Const Figure 14.1-5.Camp and Airstrip Building Construction Schedule Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 14-9 December 2014 -zZ.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Susitna-Watana Hydroelectric Project -Main Civil Construction Schedule Tviy lO Acovity Name |Original |Total Float YEAR 6 YEAR 7 YEAR 6 YEAR 9 YEAR 10 YEAR 11 YEAR 12 YEAR 13 YEAR 14aDuration21|22 |23 |24 |25 |26 |27 |28 |29 [30 [31 |32 |33 |34 [35 |36 [37 |38 [39 |40]41 [42]43 |44 [45 |46 |47 |48 |49]50]51 |52 |53 |54 7 56 |56 'PG Ocho v ¥Susitna-Watana Hydroelectric Project -Engineering 4 Construction Activities 1601.9d 0.04 v ¥Construction Activities Main Civit Contract 1601.84 0.0d 7 RS W Main Civil Contract "$1244..NTPMancwl :00d 00d ©NTP Main Civ _S!245 Main Civil Mobilization |30.0d :0.00 Main Civil Mobilization ]me Site Access Roads .ORE RRER:-peo28.Ode far570.Kian VF Site Access Roads$1250 N1&N4 Rood (Sndge to D/S Diversion Tunnel Ponal)|70d |21.0d N1 &N4 Road (Bridge to D/S Diversion Tunnel Portal) $1255 N7 Road (N2 Road to Right Abutment Foundation)_|80d 87.14 N7 Road (N2 Read to Right Abutment Foundation) $1260 N3 Roed (N2 Road to Main Dam Foundations to the Upstream Coff..15.04 i 0.0d N3 Road (N2 Road to Main Dam Foundations to the Upstream Cofferdam U/S Portal) ”$1265NS Road (FromN-2 Road)|15.0d 119.1d N&Road (From N-2 Road) $1270 N6 Road (NS Road to Upper--Level of Dam Foundations)!7 §.0d i 119,10 NS Road (N5 Road to Upper-Level of Dam Foundations)"$1280 $2 &S7 Road (S1 Road to Upper-Level at Quarry)i 18.0¢|0.1d $Z&S7 Road ($1 Road to Upper-Level at Quarry)$1285 $3 Road (S1Road to Mid-Level Dam Foundations to Mid-Level at ..i 20.0d '§70.4d $4 Road ($1 Road to Mid-Level Darn Foundations to Mid-Level at Quarry)"$1290 $4 &S6 Road.(D¥S Cofferdam to Low-Level Dam Foundation to U/...|10.0d :109.1d "Sap S6 Road (D/S Cofferdam to Low-Level Dam Foundation to U/S Cofferdam)$1295 $5 Road (S3 Road to Dam Foundations to U/S corerdam |80d 1 §70.1d ne s Road ($3 Road to Dam Foundations to U/S Cofferdam)acme t 2348.Oc:|ar 213,00s ---y Diversion Tunnel &Access Tunnels$1300 Downstream Portal Excavation |400d :21.0d :fownstream Rortal Excavation $1305 _Diversion |Tunnel Excavation from Downstream |200.04 :21.00 Ha Diversion Tunnel Excavation from Downstream$1310 Upstream Portal Excavation |§3.0d :0.0 Upstredm Portal Excavation$1315.Diversion Tunnel Excavation from Upstream |200.0d :0.0d Biversion Tunnel Excavation from Upstream "$1320 Access Tunnd to Diversion Tunnel |(128.0d >1443.0d a!}Addess Tunnel to Diversion Tunnel_$1325 Access Tunnel to Powerhouse "436.0d 232.00 mf Accdss Tunnel to Powerhouse $1335 Access Tunnel to Grout Gallery ,,200d |1413.00 mf]AdcessiTunsel to Grout Gallery"$1340 SetUp Structural ConcreteBatchPlant ee 28.0d 924d Hef}et Up pfructutal Concrete Batch Plant$1345 Upstream Portal Concrete &Gates (4,600 CY)'60.00 |964.04 i H Upstream Portal Cancrete &Gates (4.600 CY)$1350 Downstream Portal Concrete (7.095 CY)oe Tazo 7 59.00 Downstream Portal Concrete (7.095 CY)1365 Concrete Line Diversion Tunnel from Downstream (15.960 CY)|850d |00d Concrete Line Diversion Tunnel from Downstreayt (15.960 CY) $1360 Diversion Tunnel Ready for Diversion 1 00d |0.04 ep Diversion Tunnel Ready for Diversionner|WIRY cotercens $1365 titial Diversion Cofferdam 20d :00d 4 fritial Diversion Cbfferdam$1370 Construct Upstream Cofferdam (400,000 CY)96.0d ;243.1d {-]Construct Upstream Cofferdam (400,000 CY)"$1375 Constuct Downstream Cofferdam(100,000CY)|15d |58._Construct Downstream Cofferdam (100.099 CY)$1380 Grout Curtain Coflerdams 250d)283.1 Grout Curfain Cotferdams i an auttiicedtttnini stinstitaintakamietih 6B Ads W Foundation Excavation : $1390 Foundationenion-Right Abutment (174.000 CY)|130d;853d_hi Fdundation Exc vation --Right Abutmant (174,000 CY)"$1395 Consolidation Grouting-Right Abutment Foundation (8.350LF)--|_-15.0d 1"96347 FP]Gonsolidation Grouting-Right Abutment Foundation (8,360 LF)$1400 Foundation Clean Up &Dental Concrete (11 500 SY/2,850 CY)50d |903d :4™4 oundation Clan Up &Dental Concfete (11,500 SY/2,850 CY)"$1405 Excavate Tunnel Gallery-Right Abutment 140.00 |853d 4 Excavate Tunnpl Gallery-Right Abutihent$1410 Foundation Excavation-Left Abutment (320.000CY)20.00 883d =toundation Efcavdtion -Left Abutm ént (320.000 CY)__$1418 Consolidation Grouting-Left Abutment Foundation (15.405 LF)250d |240.1¢Consaiidatidh Grbuting -Left Abutment Foundation (15,405 LF)$1420 Foundation Clean Up &Dental Concrete (21.300 SY/5,200 CY)_36.00 ,240.10 _Foundatioh Cidan Up &Dental Concrete (21}300 SY,200 CY)$1425 Excavate Tunnel Gallery-LeftAbument |10.00 '1443.00 _ExcavatefTundel Gallery-Left Abutment $1430 Dewater Foundation &Cleanup ,a ”7.0d ;0.0d Dewater Foundafon &Cleanup $1436 Foundation Exc-Center (1.038,100 CY)700d;Od ral Foundation @xc-Centeri(1,038,100 CY)$1445 Consolidation Grouting -Dam Center Foundation (50.100LF)ss;80.00 |154.10 Consolifation Grouting -Dam Center Fpundation (50.100 LF)$1450.FoundationClean Up &Dental Concrete-Dam Center (69.000SY/1...|100.00 |184.10 --reukdaton Ciedn up &Dental Contfete -Dam Center (69,000SY/17,000CY)=w ftcas.08parrseen -W uery Operations_$1456 mitial Strip Overburden Develop Query |Od tO eX]Initial Strip Ovdrburgen Develop Quarty i i Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-10 December 2014 ---zZ-.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Susitna-Watana Hydroelectric Project -Main Civil Construction Schedule AcuvityID |Acuvity Name Onginal|Total Floa YEAR 6 YEAR 7 YEAR 8 YEAR YEAR 10 YEAR 11 YEAR 12 YEAR 13 YEAR 14 Duration 1 |22 [23 |24 |25 |26 |27 |28 |29 |30 |31 |32 |33 |34 [35 |36 [37 |38 [39 |40 [41 |42]43 |44 [45 |46 |47 |48 [49]50]51 |52 |53 |54 |55 |56$1460 Setup Crushing Piant 24,00 0.14 Setup Crushing Plant ”$1465 Produce Aggregates2019 tt”"780d |03d _oo neds pokoates 2019$1470 Produce Aggregates 2020 149.0d |700d tf}_Producd Aggregates 2020$1475 Produce Aggregates 2021 ee 449.00 |70.00 ©lop -}Produce Aggregnies 2021$1480 Produce Aggregates 2022,--7 -449.00 70.0d ]Produce Aggregates 2022 $1485 Produce Aggregates 2023 149.00 |70.0d Produce Aggregates 2023 "$1490 Produce Aggregates2024 ti (ti'é'eé*™*;*;*;*;*;*s:«CAO:008 1 rats nares Produce Aggregates 2024EEeeeNYROCDamm Consticton$1605 Set Up RCC Piants &Conveyor System a 13,34 90.0d 'f]_Set Up RCC A lantd &Conveyor System H$110 RCC Dam Left&Right Abutment (1,000,000 CY)-2020_149.04 0.36 'efi RCC Dein Left &Rignt Abutment (4,0003000 CY)-2020 H "$4515 RCC Dam Center (1,000,000 CY)-2021 "449.00 |08d fF}RCC Dam Centear(1,000,000 CY)32021$1520 RCC Dam Center (1.000.000 CY)-2022 149.0d 0.3d mf 1 RCC Dam Center (1.000.000 CY)-2022 }$1525RCCDam Center(1.213.958 CY)-2023 449.0d 51.00 oc RCC Dam Center (1,243,958 CY)-2023 ”$1830:RCC Dam Center (1,000,000 CY)-2024 =--<"<i' ™S™ * *:”:C*SYCNA |RCC Dam Center (1,000,000CY)-2024 $1646 Grouting 264.0d 416.0d Lot Grouting ""$1555 Build Top of Dam 29.0d 51.00 _Build Top of Dam [>Sluice Bypasswansesnenmmeunena:i jeaettinnatnennnamia tthe W Siyipe Bypass $1330 Stuice Inlet Portal Concrete (2,800 CY)|120d ;263.0d hea Siuike Intet Portal Concrete (2,800 CY) ennai if 092.00 |we:298.Ocha ' '¥Spillway Construction $1560 Spillway Excavation (310,000 CY)35.0d 139.0d HL]_Spillwpy Exca¥ption (310,000 C%$1565 Spillway Concrete (50,000 CY)300.0d 299.0d i { __PF}Spillway Concrete (50,000 CY) 399.00 |299.00 _ae Concrete Upstrsam Dam Face (60,000 CY)90.0d |299.0d Spillway Gates"$1570Spillway Concrete Upstream Dam Face (60,000 cy)t- - -S1575,Spillway Gates brvta imnatabiainetasinimmdatanhineanaititntitedemammmniantstibtcthbal wt:28.Oca ¥¥Power Intake $1580 Concrete (93,965 CY)|$36.00 |280d a!J]Concrete (93,965 CY) $1585Intake Electrical Mechanical 1133.00 |280d -<-Intake Electrical MechanicalvarLowLevelOutletaRaeNNERNRRANDORINNR}308,Od}im 209.Odom v Low Level Outlet $1590 Excavation Below Spillway (24,600 cy)|80d 139.0d Excavation B:thw Spillway (24,eho cy)$1695 install 20ft &&ft Diameter Piping (20,650 CY)i 210.0d 299.0d fou 20ft &8ft Diaineter Piping (20.650 CY$1665 Concrete Surround LLO Piping(14.959 CY)90.0d 299.0d i Concrete sunbund LLO Piping (14.959/CY)__$1670 |intake Low Level Concrete (22,705 CY)150.0d 139.0d F]_intakd Low Level Concrete (22,705 CY) $1675 intake Electrical Mechanica sti(i'é'éséés;*C*S#«OOM |88 PJ _fitake Electrical Mechanical atocks . :,ponte =:639 Oct prim:200.Od:en EY Penstocks $1600 Install Stee!Penstocks-Dam Toe 114.00 209.0d ' -{--}install Steel Pehstocks-Dam Toe”$1610 Install Steel Penstocks-Dam Slope SSSs=<"-s* *é'"' * * *:*”:”:*Y:C«C RS |S OL 1]Instat Steel Penstocks-Dam Siope$1615 install Steel Penstocks-Dam to Intake 160.0d 209.0d Install Steel Penstocks-Dam to Intake$1680Concrete EncasementPenstocks-DemToe(15.300CY)|(114.00 |734.00 C--}Concrete Encabement Penstock -Dam 'Toe (151300 CY)$1765 Concrete EncasementPenstocks-Dam Slope (16,000 CY)365.0d 369.0d }#Concrete Encasement Pebstocks-Dam Slope (16,000 CY) $1775 Concrete Encasement Penstocks -Dam to Intake (8.000 CY);160.00 209.0d C---}*Concretp Encaspment Penstocks-Dam to Intake (8.000 CY) =---_=ed ,_¥Powerhouse $1620 Power House Concrete (55,100 CY)239.0d 0.0d ver House Concrate (55,100 CY) $1625 Power House Concrete (Second Stage)90.0d |00d i [a ower House Concrete (Second Stage)_$1630 Steel Superstructure_120.04 00d PY Stee!Superstjucture$1636 Turbine &Generator(3 Units)710.0d 0.0d caratcoeneran os ma S74 Turbine &Generator(3 Units)$1640 Unit Testing1-(Complete February-Year13)ss s|s«80.00 0.0d H -it Testing 1 -(Complete February -Year 13) $1645.Unit Testing 2 100.0d |0.0d ;Unit Testing 2 $1650 Unit Testing 3 400.6d 0.0d H Unit Testing 3 " ling R pb428:Ochertegee 268:Od ¥.WY River Diversion &Filling Reservoir ||$171 |Close Diversion Tunnel Gates ,10d 4;57.00 im}Close Diversion Tunnel Gates Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-11 December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Susitna-Watana Hydroelectric Project -Main Civil Construction Schedule Activity 1D [Activity Name Original |Total Float YEAR 6 YEAR 7 YEARS YEARS YEAR 10 YEAR 11 YEAR 12 YEAR 13 YEAR 14 _Duration 21 |22 {23 |24 |25 |26 |27 |28 |29 |30 |31 |32 [33 |34 |35 |36 |37 |38 |39 [40 |41 |42 [43 |44 |45 |46 {47 |48 |49 [|50 [51 |62 |53 |54 |56 |56 | $1&Remove Downstream Cofferdam 21.04 1 675.00 Ci Remove Dqwnstream Cofferdam =} |Plug &Valve Chamber 427.0d 268.0d v WY Plug &Vaive Chamber|"$415 Valve Chamber Excavation (7.585 CY)25.0d 57.0d Valve Charhber Excavation (7,585 C¥)|$1;Vaive Chamber Concrete (675 CY)10.0d 570d Valve Chamber Concrete (675 CY) |$1.Construct Plug Piping 600d -57.0d Constrbict Plug Piping$4 Construct Concrete Plug 66.0d |570d Cdhstruct Concrete Plug:§1;Valve Chamber Mechanical 200d ' 57.0d Vpive Chamber Mechanical$8 "Excavate Tunnel Floor 80.0d i 87.00 *]Excavate Tunnel Floot :S17 |Concrete Tunnel Floor _;{220d ;570d Concrete Tunnel Flopr |Stt ;Remove Gate from Diversion Tunnel &Move/instail Siuice at Sluice...i 15.0d :57.0d Remove Gate from Diversion Tunnel &Move/install Stuice at Sluice Portal §tt Plug Sluice (37,000 CY)'129.0d i 268.0d Plug Sluice 137,000 CY) ing ue.}0340.0dc4rpee 570d cy!Reservoir Filling $1655 Reservoir Fiiling :340.0d ;57.00 Reservoir Filling Figure 14.1-6.Main Civil Construction Schedule Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 14-12 Alaska Energy Authority December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 14.2.Construction Schedule Derivation 14.2.1.General Preliminary project schedules have been developed first for the complete project engineering and construction works -beginning with the site investigation and adit construction -and included in Appendix B11;and,second for the various construction packages (except transmission)shown above using the shortest reasonable time based on knowledgeable,experienced,and qualified U.S.-based contractors using high efficiency equipment and working methods. The schedules can be regarded as aggressive,particularly in the earliest stages of construction. The construction of access to the site is critical to the current schedule.Access to the dam has been scheduled by pioneering to the site as soon as possible -along the line of the access road - with the conversion to permanent access road following.If this access cannot be completed,the overall schedule will be delayed. The construction sequence was scheduled initially based on the expected date of FERC license issuance.The schedule for engineering required to facilitate construction was developed subsequently.The feasibility level construction schedule was developed based on the current concept design,and based on a logical work flow and interrelation among activities. The following assumptions have been used to develop the construction schedule: »The time required for execution of each activity was based on expected production rates. =Activities start and finish dates reflect the "early start and finish”dates as that is the standard for Primavera until an activity is given an "actual start and finish”date. =Seven-day work week. «Surface work is based on two 10-hour shifts per day. *"Underground construction based on 24-hour per day production. «Regional public holidays will be observed. *Scheduling of electrical/mechanical equipment supply and installation is based on supply and installation times observed for similar types of equipment installed at similar dam and power house projects. «The supply chain,via barges from the Lower 48,the Alaska Railroad,and the project access road,is not a constraint,and logistics will always be organized to support the required construction activities. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-13 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Traditional analysis was performed before calculating the durations based on planned and expected resources.The analysis compared the derivation of the logic associated with each task, and the establishment of links and precedence. The tasks and links have been entered into Primavera P6 scheduling software and a Gantt chart derived,together with a critical path. 14.2.2.Potential Early Works The road contemplated for access to the site has no use other than for construction (and operation)of the works.As noted,because of this sole use,the project to be licensed by FERC includes the access route,and (if Gold Creek or Chulitna road route is chosen)the associated railroad offloading yard.As noted,the inclusion of the access within the project subjects it to prohibition of construction before the FERC license is granted,and all associated permits and design reviews are complete.In other circumstances,the access would normally be constructed in advance of the main works so that the main project works could be implemented as soon as the license (and associated permits)was granted. Although the linkage between the project works and the licensing has been removed for the reasons stated earlier,it is recognized that the schedule cannot be shortened if no works on site are commenced until the access road is complete.It is thus beneficial for construction works at the main site to begin as soon as possible,and the project team has considered the logic for,early access by "Rolligon”It must be noted,however,that although this storing of materials and plant has been included in the schedule,as described in the following paragraph,the implementation of such prepositioning might still be classed as "construction”by regulatory authorities and prudent scheduling would require that such activity not be commenced until the license is issued and the associated permits obtained. It has been assumed that for the preparation of the camp civil works -and the preliminary grading of the airstrip -Rolligons (or snow CAT train)access will be used to transport plant and materials to the site before the road construction has reached the dam site."Rolligon”is a generic name for a very low ground pressure vehicle used to transport equipment and supplies over snow covered tundra,such as the North Slope,as shown in Figure 14.2-1. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-14 December 2014 za ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. Figure 14.2-1.Rolligon -Low Ground Pressure Vehicle It is also possible that,while the access road is under construction,such low ground pressure vehicles could convey tunneling equipment,excavation equipment,camp facilities,general plant, fuel and supplies,etc.,from the north over the route of the Denali access so that critical tasks associated with the Main Civil construction contract -such as the diversion tunnel and quarry development -could also commence as early as possible. This option has not been included in the schedule,but can be investigated further when a detailed procurement strategy has been finalized and the economic viability of this type of mobilization can thus be properly assessed. For the Main Civil Contract works,the scale of the operation required to mobilize equipment, material and personnel to the project site means that importing everything to the site before the access road is completed,using this technique,is effectively impractical -or at the least so expensive as to be uneconomic. 14.2.3.Schedule Notes 14.2.3.1.General The schedule indicates the anticipated dates for generating unit commissioning and project completion. Following the notice to proceed with detailed site investigation,and assuming that the license and various permits are received in a timely manner (with regard to the current schedule),the total time for completion has been estimated as ten years and four months to the provision of first power from Unit 1 (i.e.,completion of testing of Unit 1),followed by an additional seven months to bring the other two units on line.It should be noted that the extent to which full power is Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-15 December 2014 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. drawn from each unit will determine the remaining time for reservoir filling and thus the time that the final load rejection and heat tests can be performed on all the units at full load. Considering only the construction phase,the total time from the commencement of construction work (on the access)to the provision of first power from Unit 1 is about 7.5 years. The critical path of the Engineering and Construction Schedule can be seen on the following page in Figure 14.2-2. The critical path of the engineering activities is defined by the following tasks: «Site Investigation -Contract Documents -Bidding -Bid Adjudication -Award -Investigation -Summer Season and Initial Report -Investigation --Winter Season -Testing /Report Writing *Permanent Access Road Engineering -Engineering and Contract Documents -Bidding -Bid Adjudication -Award «=Camp and Airstrip Buildings Engineering -Bidding Bid Adjudication -Award Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-16 December 2014 -za- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Orginal|Total FloatDuration |Cott rdarwe-- $1365 inmai Diversion Cofferdam roundatio $1430 Oewater Foundation&Cieanup oe gO 0.0d$1435 FoundationExc-Center (1,038,100 CY)"700d + O0d Powerhou .;Ferre 0.00$1620 Power House Concrete (55,100 CY)23900,00d ”$1625 Power House Concrete (Second Stsge)s*s-*= -<CS s -<CS * <"S*«S |SC $1630 Steel Superstucture 120.04 i 0.00 $1635 Turbine&Generator (3 Units)aa 710.04 0.04InaCVV\h -FT $1640 Unit Testing 1 -(CompleteFebruary {Year 13)/;"$30.08 5 (0.00 ;S 0 a $1645 Unit Testing 2 100.08 |0.08teg16s0untTesing3-7 100.00 0.04 © Susitna-Watana Hydroelectric Project -Critical Path Construction Schedule _Engineering Activities oF A0000 =Engineering NTP (September-Year 1)000 |0.00 Site Investigation aoe eee "336.08 ood A1000 Contract Documents 780d»0.0d A1010 Bidding 7 ae 600d |Od 41020 "Bid Adjudication oe eee 300d 7 Od|A10G0 "Award "40d 5 00d 7 A1060 investigation -Su &Intial Report "409.0d 7 0.00 A1051 |Investigation-Winter Seeson s70d °0.00 "41060 Testing/Report Writing 90.0d 0.00 ”Permanent Access Road Engineering ©.271.0d 0.04 __A1130_Engineering &Contract Documents (PAR)180.08 0.00 | A1140 "Bidding 450d >0.00 A150 Bid Adjudication =ee 480d)OdA1160|Award 1 10d 5 06d oe .res ny r.*ae Y,”tte__Construction Activities esd$1605 Construction Complete 00d +00d "PermanentAccessRoad =”_-609.0d Od $1084 Permanent Access Road NTP 0.04 0.00 $1095 "Clearing &Grubbing tt”wees 125.00 0.00 |”$1108 "PermanentAccessRoad-Exc n(ist )146.08"O08 |$1118 PermanentAccessRoad-Excavation Rock (1st Season)"446.08 7”0.00 |$1420 «PermanentAccess Road-Embankment(istSeason)=SSSCS«*NKGO |SO"$4921 WinterShutdown ween 212.00 0.04 :$1190”PermanentAccessRoadLongSpan Bridge(MP 21.6) _450d)00d -$1195 ”Permanent Access Road Long Span Bridge (MP 26)"490d 7 ood 7 ”$1200 "Permanent Access Road Long Span Bridge (MP 43)(i("(t*'"'«é'i RC "camp Construction_ee 90.04"00d $1806 Move 250 Man Camp to Main Dem 15.04 0.0d "$1810 °Construct Permanent Vilage _450d |0.08 |”$1815 |Construct ContractorCamp |-"good 7 008 5”$1820 Camp Construction Complete ™o00 7 90g "Main Civil Contract eee "46019d (Od$1244 NTP Main Civil °:00d 00d | i”$1245 'MainCnMobiizaion==-ss-"'CS;*SOS”*!*”!”!”!”!”!!!”! !™ C:«(C OO lO! pees Road -=CC$1260 N3 Road (N2 Road to Main Dam Foundatons to the Upstream Coff...150d :0.00 Diversion Tunnet&AccessTu arisernmnineeeB38.00 -$ove @.Och arent $1310 Upstream Portal Excavaton §3.0d |0.00 "$1315 Diversion Tunnel ExcavationfromUpstream 200.0 -SC«O.d $1385.Concrete Line Diversion Tunnel from Downstream (15.960CY)860d |00d$1360 Orversion Tunnel Ready for Diversion oe T0087 0.0d 'Year 1 2 3 4 5 6 7 8 9 10 11 v ¥v Eng Engineering NTP (September-Year 1) Acti 2 [|13)[14CaennnnrennererrreeeeeeeeeSusine-Watana Hydroeiectic Prd AcoessRoadErpineering neering&Contract Documerts (PAR) Bidding Bid Adjudication Award WC fon Act @*Lonstruction Complete vP Access Road Permanent Access Road NIPCleanng&Grubbing PemmanentAccegsRoad-Excavation C:(st PermanentAccesRoad-Excavation Rock (1st S:) Permanent len,Embankment(1st Season)Water S| Permagent Access Road Long Span Bridge (MP 21.6} Permpnent Access Road Long Span Bndge (MP 26) panent Access Road Long Span Bridge (MP 43)amp Construction re 250 Man Camp to Main Oem struct Permanent Vitage ponsiruct Contractor Camp ¥_--NTP Main Cv Main Civil Mobitization W Site Access Roads N3 Road (N2 Road to Main Dam Foundationstothe Upstream Cofferdam U/S Portal) (QaEEY DiversionTunnel&Access Tunnels Upstream Portal Excavation Diversion Tunnel Ex from Up Concrete Line Diversion Tunnel from Downstream (15.960 CY) jon Tunnel ReedyforDiversion V Cofferdams inital Diversion Cofferdam FF Foundation Excavation Oewater Foundation&Cleanup Foundaton Exc -Center (1,038,100 CY) a fren Civil Contract Power House Concrete (56.100 CY) Turbine &Generator (3 Urits) 'cower Housel Concrete (Second Stage) 'ing 1-(Complete February-Y ea Figure 14.2-2,Susitna -Watana Engineering and Construction Schedule:Critical Path Susitna-Watana Hydroelectric Project FERC Project No.14241 Page 14-17 Alaska Energy Authority December 2014 -z- SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT The critical path of the construction activities is formed by the following tasks: »Permanent Road Access -Notice to Proceed -Clearing and Grubbing -Excavation Common -(1st Season) -Excavation Rock -(Ist Season) -Excavation Embankment -(1st Season) -Winter Shutdown -Long Span Bridge (mile post [MP]21.6) -Long Span Bridge (MP 26) -Long Span Bridge (MP 43) «Camp Construction -Move 250 Labor Camp -Construct Permanent Village -Construct Contractor Camp -Camp Construction Complete It should be noted that the critical path does not follow the off-site factory assembly of the units that are to be transported to the site,but follows the on-site construction. #Main Civil Contract -Notice to Proceed -Main Civil Mobilization -Site Access Roads e N3 Road (N2 Road to Main Dam Foundations to the upstream Cofferdam) -Diversion Tunnel and Access Tunnels -Upstream Portal Excavation -Diversion Tunnel Excavation from Upstream -Concrete Line Diversion Tunnel from Downstream Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 14-18 December 2014 -z-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. Diversion Tunnel Ready for Diversion -Cofferdams e Initial Diversion Cofferdam -Foundation Excavation e Dewater Foundation and Cleanup e Foundation Excavation -center portion of the dam -Powerhouse e Powerhouse Concrete e Steel Superstructure e Turbines and Generators e Units 1,2 and 3 Testing It is evident that the earliest possible commencement of the diversion tunnels construction is vital to achieving the fastest possible completion of the Project,and hence the proposal for pioneering of an access road,and the recommendation to consider the advantages of a CAT train/Rolligon associated with the Main Civil Contract works for limited movement of materials and equipment. This could allow critical work to begin on site as soon as possible such as site access roads and the Diversion Tunnel and Access Tunnels. The use of the airstrip at Stephan Lake (in conjunction with a temporary access road to the road and transmission corridor)during the first years of construction may allow some schedule reductions.However,the temporary road is outside of the road corridor and project boundary and would be subject to extra study and permitting. 14.2.3.2.RCC Production The RCC dam volume (5.215 million cubic yards)will be one of the largest volumes of RCC dam constructed to date.The rate of placement of RCC has been assumed (on average)as 200,000 cubic yards per month over five seasons (25 months)of placement. Placement rates for RCC are very much dependent on the following factors (among others): =A well planned and properly developed quarry; «The amount of sorting required in the quarry; Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-19 December 2014 -Z ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. «The efficiency and capacity of the plant in the quarry:drilling,loading of holes,loading on to trucks,quarry clean up; «The provision and maintenance of appropriate haul roads; »Efficient,reliable and high capacity trucks; «The efficiency of the mixing and RCC transport plant; «The efficiency and reliability of the cement and fly ash delivery; «The efficiency and capacity of the spreading and rolling plant; «The overall planning of the work to minimize constricted working areas;and, «The adequacy of the plant maintenance arrangements. Although high average placement rates can be achieved with large,high capacity,high efficiency,heavy dump trucks and loaders,the construction consistency required in achieving an average of 200,000 cubic yards per month (or more)demands a sophisticated RCC delivery methodology,including multiple RCC batch plants (allowing for peak capacities and for limiting the effect of any unplanned outages),a high capacity and reliable supply chain for cement and aggregates,enhanced and well maintained haul roads,a well planned and executed quarry operation,and high capacity (oversized and reliable)conveying systems. 14.2.3.3..Summary of Important Activities A summary of the most important activities (or set of activities)is presented in Table 14.2-1 below,together with notes on the production and/or logic.A fundamental driving factor in the schedule is the necessity to "smooth”production and placement of RCC over as long a time as possible to ensure that the average rate of RCC production is reasonable (although it will still be one of the highest average production rates for such a dam): Table 14.2-1.Key Activity Durations Duration Activity (working days,Production Notes except as noted) Clearing cannot be performed between 'st of April and the 15*of June Clearing:Railyard,(although construction activities can be carried out on areas previously cleared) Access Roads,Roads at 526 because of migratory bird activity.With the exception of the rail yard work,for Site,Airport,etc.which an exception will be requested,all clearing activities will take place outside of the migratory window. To establish access to site,the first thrust of activity,after establishing an offloading facility at the railway,will be the creation of a narrow access road, 646 sufficient for moving plant,fuel and materials to site for the initial construction. The standard of the road will be low,speed of construction being the most important aspect of the work. Pioneer Access road to site Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 14-20 December 2014 yz SUSITNA-WATANA HYDRO Clean,reliable energy for the next 100 years. ALASKA ENERGY AUTHORITY AEA11-022 ENGINEERING FEASIBILITY REPORT Activity Duration (working days, except as noted) Production Notes Diversion tunnel portal é 261 Both portals will commence immediately after access is available to site.excavations Diversion tunnel 348 The diversion tunnel will be excavated from both ends to minimize the construction time,followed by concrete lining from the downstream end. Overburden clearance and foundation excavation (including the lowest level Foundation preparation 7 grouting adits)on each abutment will commence at the same time as the on the abutments diversion tunnel construction,to facilitate the early placement of RCC on the abutment sections of the dam. Quarry preparation will be another early task,initiated as soon as possible and Quarry preparation 44 before the diversion tunnel is complete,so that sufficient aggregates can beryPrepproducedforthefirstRCCplacementontherightabutmentwhichwilloccur before diversion. RCC placement on the right and left abutment will occur during the first season Dam RCC placement on 149 of placement while the foundations are being cleaned and excavated in the river right and left abutments bed following diversion.RCC placement will also occur in the fifth season to topping off the two abutments. Dam Center RCC 596 RCC placement for the Dam center will occur during the second season through placement the fifth season of placement to full height. The base schedule gives all anticipated dates in years from commencement of site investigation. It records the overall project completion expectation -but should be considered to be a schedule based on aggressive production rates with limited recognition of unplanned events.It should be understood that unforeseen circumstances and events beyond the control of the engineer,AEA, or contractor could cause delays beyond the anticipated dates indicated in the attached schedule. As more comprehensive information is available from upcoming site investigations,probabilistic analysis of the schedule is recommended. Susitna-Watana Hydroelectric Project FERC Project No.14241 Alaska Energy Authority Page 14-21 December 2014 Section 15 Zz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 15.CONCLUSIONS AND RECOMMENDATIONS This section provides a summary of the primary findings from the Feasibility Studies conducted by MWH during the period from 2011 through 2014,and offers a recommended path forward. 15.1.Conclusions 15.1.1.Technical Feasibility The Project as configured is technically feasible,taking into account the following major considerations. 15.1.1.1.Need for Project Alaska has a long,successful history of harnessing power safely from its abundant natural resources.Susitna-Watana Hydro is part of the state's long-term energy policy that calls for generating 50 percent of Alaska's power from renewable energy by 2025.In the Railbelt area where the Project is to be constructed,electrical loads are predicted to grow fairly slowly over the next 10 to 20 years.However,many factors can affect those future predictions,such as significant use of electric vehicles,or unexpected economic growth that introduces large,new loads on the system.Also,when the Project is constructed,utilities will then have the opportunity to retire older,less efficient "standby”thermal plant,thus improving the long-term reliability of the Railbelt system,while at the same time reducing overall system electricity costs over the 50-year economic life of the project (in fact,hydro is usually expected to perform for 100 years).These and other factors drive the need for this project. 15.1.1.2.Project and Unit Sizing A "rated”turbine capacity of 459 megawatts (MW)at a reservoir El.1950 ft.-equivalent to a generator output of 446 MW,was selected for the project based on reservoir operation and power generation modeling,including PROMOD runs,to determine how the project will best be integrated into the future Railbelt integrated electrical system.The Project would have a combined rated turbine output of 618 MW from the three 206 MW turbines operating at maximum head -equivalent to a generator outputs of 606 MW and 202 MW respectively.At lower pool levels,the plant output would be proportionately lower.At minimum operating level of El.1850 ft.the total plant turbine output would be approximately 315 MW -equivalent to a generator output of 303 MW.The generating units will be comprised of Francis reaction type turbines coupled to synchronous generators,which will be capable of operating at high efficiencies over the broad range of expected power head and flow at the site. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-1 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. It is suggested that the Project include provisions for the installation of a fourth generating unit, to allow future generations the flexibility to be able to use the resource in the most productive manner for the load at that time.The provisions for the installation of another unit will be a penetration through the dam and an empty unit bay.Under present regulations such an addition would require submissions to the Federal Energy Regulatory Commission (FERC)when and if an expansion decision is taken in the future. 15.1.1.3.Dam Type Preliminary engineering studies were performed to compare three alternative types of dams that were deemed to be most suitable for the Susitna-Watana site:Earth Core Rockfill Dam, Concrete Faced Rockfill Dam,and Roller Compacted Concrete Dam.Lack of updated site investigation meant that these comparative studies had to be carried out using the geotechnical data available from the 1980s studies.Safe configurations based on all three types were drafted and construction costs estimated.In addition to cost factors,a Water Resources Assessment Methodology analysis was also performed to compare non-cost factors,and arrive at a recommended alternative.The comparison included judgments on ease of future raising;seismic resistance;risks of cost increase;visual intrusion;possibilities of development acceleration;cold weather construction;potential for design optimization;the accommodation of environmental mandates;and long-term cold weather performance.Taking all relevant factors into consideration,a configuration based on a RCC dam was selected as the preferred alternative. Final verification of the foundation characterization of the dam is vital to support the decision - which can be established by the completion of proposed site investigations (drilling in the valley and in the footprint of the dam;exploratory adits;structural geological mapping,etc.)prior to initiation of detailed design. 15.1.1.4.Reservoir/Storage Capacity Elevation 2050 ft.was selected as the optimum normal maximum operating level -together with a minimum operating level of El.1850 ft.-to provide maximum energy benefits to the Railbelt over time,using the 3.38 million acre-feet of active storage capacity created to store and release water to maximize project energy generation in the critical cold weather months from November through April.This storage capacity will also enable the Project to provide the required seasonal instream environmental and recreation flows in the Susitna River downstream of the dam,which are expected to be defined through the FERC licensing process over the next two years. 15.1.1.5.Powerhouse Type The site is conducive to construction of a surface powerhouse,as opposed to the more costly subsurface powerhouse configuration envisioned in the 1980s studies.This is due to the fact that Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-2 December 2014 2 ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. the RCC dam type (versus the previous embankment dam type)allows for a much more compact site development,allowing the powerhouse to be placed at the toe of the dam and thereby significantly shortening the power conduit length compared to earlier designs.The penstock can readily be constructed integral with the downstream face of the concrete dam and extended the short distance down to the surface powerhouse located at the toe of the dam.In addition, advances in technology since the 1980s have led to cost effective means of using temporary enclosures around (or even early prefabricated construction of the outside wall of)a surface powerhouses during construction to permit conventional concrete placement as needed without weather-related construction shutdowns as might have occurred in the past.The primary access to the powerhouse will be by a short tunnel,and emergency egress is possible at the opposite end of the powerhouse. 15.1.1.6.Site Access and Infrastructure The site is remote,and requires the construction of a new road for access and operation.Three routes were proposed after lengthy studies by Alaska Department of Transportation and Public Facilities (ADOT&PF)for Alaska Energy Authority (AEA);including two southern routes which are not connected to the public road system (i.e.no public road access is possible).This study does not favor a particular route,but has utilized the southern (Gold Creek)route solely for the purposes of estimating the project construction cost. Most personnel,fresh food,and emergency spares would be transported to the construction site by air,but most bulk materials (e.g.,cement,fuel,reinforcing steel)and manufactured items (e.g.,transformers,power parts)for dam construction would be transported to the site by the road access froma railhead. In addition to the road and the associated railhead facilities and bridges,the Project will require substantial site infrastructure such as temporary and permanent housing for a construction workforce that peaks at approximately 1,200 personnel,water and wastewater infrastructure and an airstrip.Preliminary designs for these various facilities and infrastructure have been completed to a level of detail sufficient for feasibility-level cost estimating. 15.1.1.7.Transmission and Interconnection The Project will provide power to the Fairbanks area to the north and to the Anchorage/Mat- Su/Kenai areas south of the project site.Extensive planning and Railbelt system modeling studies,including economic comparisons,were undertaken to determine the proposed transmission line and interconnection configuration for the Project.The transmission alignment studies were performed in parallel with site access road studies to minimize construction cost and keep the corridor as small as possible to minimize environmental impacts.Although the Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-3 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. transmission will include three new 230 kilovolt lines interconnecting with the existing Alaska Intertie,no final transmission corridor selection has been made as yet.The estimate of construction costs is based on the transmission of Susitna-Watana power through two circuits running east to Gold Creek,and one circuit running north to Cantwell. 15.1.1.8.Estimated Project Cost Detailed construction planning has been executed for the key project tasks such as road construction;bridge construction;river diversion;quarry development;dam foundation excavation;RCC placement;transmission construction.Although AEA has not yet published any procurement strategy,for the Opinion of Probable Construction Cost (OPCC)it was assumed that there would be 12 separate supply,service and construction contracts -each initially executed with AEA.For proper management it is envisaged that some service and supply contracts would be assigned from AEA to the main contractor.It was assumed that all contracts would be engineered,then bid and constructed using the traditional Design-Bid-Build approach. In addition,non-construction costs have been estimated based on significant input from AEA. The total project cost is estimated to be US$5.655 billion,in Q2 2014 dollars.No allowance has been made in the estimate for escalation,interest during construction etc.The estimated costs have been subject to probability analysis to account for estimating variations. 15.1.1.9.Design and Construction Schedule A comprehensive engineering and construction schedule has been prepared based on the feasibility design work completed to date,and using the contract packages noted above.The current schedule shows that the first generating unit can be placed into service 10-years and four months after a notice to proceed is given for the site investigation and assuming no lag between phases.The schedule assumes that Licensing tasks,submission of license application and issuance of a FERC license will not be delayed,and that the construction contracts can be awarded immediately following the license issuance (together with the subsequent permitting, etc.). The construction of the road is vital to enable any work to begin on site,but the road construction cannot begin until the license is issued.The overall schedule for construction is aggressive including a high assumed rate for placement of RCC in the dam.Nevertheless,the schedule is considered to be achievable bya first rate,experienced contractor. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-4 December 2014 wz ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years, 15.1.1.10.Power Production Operation simulation modeling indicates that the average annual energy generation capability of the Project is approximately 2,800 gigawatt-hours (rounded up).This assumes that all of the potential power and energy can be utilized to meet future integrated Railbelt system electrical loads.The amount of load following assumed at Susitna-Watana will not materially affect annual energy generation.However,the current generation estimate does reflect the inclusion of forecasting of basin runoff from snowmelt,enabling shaping of monthly generation to best match monthly load shapes and minimizing spill that would reduce energy generation. 15.1.1.11.Operating Plans AEA has not yet developed a detailed organization plan for the operating phase of the Project. As such,only a general description of the likely operation and maintenance program requirements has been provided for this Report based on experience gained by AEA and the Railbelt Utilities at Bradley Lake,and from experience of other large utilities at other large, remote hydro projects in North America.An estimated annual operation and maintenance (O&M)budget for the project was derived through parametric means,using data on other similar projects to make a provisional estimate for economic and financial modeling being performed by AEA.An operating organization plan will need to be developed for inclusion in the FERC License Application. 15.1.2.Economic Feasibility A final determination on economic feasibility of the Project has not been established,however, extensive production cost modeling has been undertaken as part of the current feasibility studies, with the following general conclusions made possible at this time. 15.1.2.1.PROMOD Results Results of the most recent PROMOD (production modeling)simulations both with and without -the Project,show that the inclusion of the Project in the integrated Railbelt system will result in a significant reduction in the use of gas and oil by the utilities,and a large decline in the use of what is now (thermal)peaking plant over time.Because it has the lowest operating cost and the highest reliability among the generation sources,the addition of substantial hydro capacity at the Susitna-Watana Project will inevitably reduce the need for oil and gas fired generation,even from combined cycle units in future years. The most significant production savings for the whole Railbelt system will be realized if and when the system is operated with centralized dispatch.Discussions with the Railbelt utilities Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-5 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. will be required to arrive at the optimum contractual and organizational arrangements for regional power dispatch. Total annual net savings to the system will depend on the ultimate cost to develop the Project, financing terms,dispatch efficiency,and most importantly,the future price of natural gas. The addition of a 459 MW (turbine rating)Susitna-Watana Hydro resource intended to serve the total Railbelt system,together with sufficient transmission to incorporate it into that system will almost certainly result in a re-evaluation of commitment and dispatch practices,which will further enhance the long-term value of the Project. 15.1.2.2.Future Economic /Financial Studies by AEA Ongoing economic and financial studies being conducted by AEA and other consultants will determine the ultimate economic viability and optimal timing of the Project,as well as establish the Plan of Finance.Such evaluations are being made outside the context of this report. 15.1.3.Environmental Considerations The Susitna-Watana Project will be located in a remote region of Alaska with abundant natural resources.As such,it can be expected that it will have some impacts (both beneficial and potentially adverse)on these resources both during its construction and over the long-term operation.AEA is pursuing a license under FERC's Integrated Licensing Process regulations.A Pre-Application Document that identified existing information regarding the existing environmental conditions and potential impacts of the Project was filed with FERC in December 2011. AEA is currently performing 58 individual studies (of which three are engineering studies)as a result of an extensive collaborative study plan preparation process agreed with interested stakeholders in 2012. Implementation of the studies is well underway with one full year of study complete.The initial results from the first year of study efforts were documented in the Initial Study Report filed with FERC on June 3,2014.Calendar year 2015 is projected to be the second and final year of these studies with a final report due to FERC in 2016. AEA is taking a collaborative approach to performing the environmental studies.AEA is working closely with licensing participants in the execution of studies that will support their License Application,inform protection,mitigation and enhancement measures,serve as a foundation to environmental review under the National Environmental Policy Act,and support Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-6 December 2014 -z-.ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. all needed state and federal permits including FERC's licensing determination under the Federal Power Act. 15.2.Recommendations The following recommendations are offered regarding the path forward for the Project. 15.2.1.Funding Funding should be secured in sufficient amount to enable completion of the geotechnical site investigation and remaining environmental studies needed to support the FERC License Application as soon as practical. 15.2.2.Geotechnical Further geotechnical investigation before commencing design -including exploratory adit(s)in the dam site abutment foundation rock -are vital for the verification of assumptions made so far in the studies.The investigations should be completed in sufficient detail to support initiation of detailed design work as scheduled,without a delay caused by the need to adjust the feasibility design and/or first collect additional site geotechnical data. 15.2.3.Engineering Pre-design engineering work should be completed to enable AEA to initiate detailed design as early as possible,to ensure the targeted project on-line date is met. 15.2.4.Procurement Plan Additional work on developing a procurement plan should progress to firm up AEA's plans for contracting for project design and construction,to maintain the current project development schedule. 15.2.5.Integrated System Studies Should the utilities negotiate the rules and agreements associated with centralized dispatch -and as stakeholder agreements are reached with respect to releases etc.-additional system production modeling studies should be undertaken.These proposed studies should analyze the response of the integrated Railbelt system units,such as Bradley Lake Hydro,to the proposed Susitna-Watana Project,in addition to determining the response and benefits of the project in the interconnected system. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-7 December 2014 a ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 15.2.6.Centralized Dispatch Planning Studies to date have shown that the maximum benefits from the Project would be realized through a centralized commitment and dispatch process.Plans should progress for establishing a centralized dispatch organization so that maximum long-term economic impacts can accrue to the Railbelt and the State. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 15-8 December 2014 Section 16 -zZ-ALASKA ENERGY AUTHORITY SUSITNA-WATANA HYDRO AEA11-022 ENGINEERING FEASIBILITY REPORTClean,reliable energy for the next 100 years. 16.PRELIMINARY DESIGN CRITERIA Basic criteria have been used for the feasibility design,but have been modified throughout the studies as more data has been gathered. In order to proceed into final,detailed design two key documents must be produced.The first is the "Owner's Requirements”prepared by AEA in conjunction with the Railbelt Utilities,the project operator,and any combined transmission company that may be formed.The second is the Detailed Design Criteria that will reflect the detailed engineering requirements derived from and responded to the Owner's Requirements,these studies,and the results of the final site investigation and Geotechnical Data Report. At this stage,Preliminary Detailed Design Criteria have not been completely documented, because much of the content is an extraction of the contents of this feasibility report,and because the site investigation has not been completed.However,elements of the Detailed Design Criteria are attached as Appendix B12 to provide a basis for future development. Susitna-Watana Hydroelectric Project Alaska Energy Authority FERC Project No.14241 Page 16-1 December 2014 Section 17 2 ALASKA ENERGY AUTHORITY AEA11-022 SUSITNA-WATANA HYDRO ENGINEERING FEASIBILITY REPORT Clean,reliable energy for the next 100 years. 17.REFERENCES Consult the following links for additional references for (1)the work performed during the 1980s:http://www.arlis.org/resources/susitna-watana/,and (2)for recent FERC licensing documents:http://www.susitna-watanahydro.org/type/documents/. AACE,2013.AACE International Recommended Practice No.69R-12,Cost Estimate Classification System -as Applied in Engineering,Procurement,and Construction for the Hydropower Industry,TCM Framework:7.3 -Cost Estimating and Budgeting. Abrahamson,N.A.,2012.RSPMatch. Acres,1982a.Susitna Hydroelectric Project,1980-81 Geotechnical Report.For the Alaska Power Authority. Acres,1982b.Susitna Hydroelectric Project,1982 Supplement to 1980-81 Geotechnical Report. For the Alaska Power Authority. Alaska Department of Transportation and Public Facilities,June 26,2012.Susitna-Watana Hydroelectric Project Access Route Draft Report. Alaska Energy Authority,November 23,2010.Railbelt Large Hydro Evaluation Preliminary Decision Document. Alaska Energy Authority,December 29,2011.Susitna-Watana Hydroelectric Project No.14241 Pre-Application Document. Alaska Power Authority,November 1985.Susitna Hydroelectric Project,Draft License Application,Volume 1,Exhibit A,Project Description. Bemis et al.,in press. Bieniawski,Z.T.,1989,Engineering Rock Mass Classifications. Boeing,2013.Boeing 737 Airplane Characteristics for Airport Planning. Brocher,T.M.,Filson,J.R.,Fuis,G.S.,Haeussler,P.J.,Holzer,T.L.,Plafker,G.,and Blair,J.L., 2014,The 1964 Great Alaska Earthquake and Tsunamis-A Modern Perspective and Enduring Legacies,U.S.Geological Survey Fact Sheet 2014-3018,March 2014,available from http://pubs.usgs.gow/fs/2014/3018/. 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