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Susitna-Watana Hydroelectric Project Document
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Title:
Geology and soils characterization study, Study plan Section 4.5 : Initial
study report
SuWa 207
Author(s) – Personal:
Author(s) – Corporate:
MWH
AEA-identified category, if specified:
Draft initial study report
AEA-identified series, if specified:
Series (ARLIS-assigned report number):
Susitna-Watana Hydroelectric Project document number 207
Existing numbers on document:
Published by:
[Anchorage : Alaska Energy Authority, 2014]
Date published:
February 2014
Published for:
Alaska Energy Authority
Date or date range of report:
Volume and/or Part numbers:
Study plan Section 4.5
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Draft
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Pagination:
v, 20 p.
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Notes:
All reports in the Susitna-Watana Hydroelectric Project Document series include an ARLIS-
produced cover page and an ARLIS-assigned number for uniformity and citability. All reports
are posted online at http://www.arlis.org/resources/susitna-watana/
Susitna-Watana Hydroelectric Project
(FERC No. 14241)
Geology and Soils Characterization Study
Study Plan Section 4.5
Initial Study Report
Prepared for
Alaska Energy Authority
Prepared by
MWH
February 2014 Draft
INITIAL STUDY REPORT GEOLOGY AND SOILS CHARACTERIZATION STUDY (4.5)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page i February 2014 Draft
TABLE OF CONTENTS
Executive Summary ..................................................................................................................... iv
1. Introduction............................................................................................................................ 1
2. Study Objectives .................................................................................................................... 1
3. Study Area .............................................................................................................................. 2
4. Methods and variances in 2013 ............................................................................................ 2
4.1.1. Review of Project Documentation .......................................................................... 3
4.1.2. Regional Geologic Analysis and Mineral Resources Assessment .......................... 3
4.1.3. Geologic and Geotechnical Investigation and Testing Program Development ...... 4
4.1.4. Field Geologic and Geotechnical Investigations .................................................... 5
4.1.5. Reservoir-Triggered Seismicity .............................................................................. 5
4.1.6. Reservoir Slope Stability Study .............................................................................. 5
4.1.7. Long-Term Earthquake Monitoring System ........................................................... 6
4.1.8. Geologic and Engineering Analyses ....................................................................... 6
5. Results ..................................................................................................................................... 7
5.1.1. Review of Project Documentation .......................................................................... 7
5.1.2. Regional Geologic Studies ...................................................................................... 7
5.1.3. Geologic and Geotechnical Field Investigation and Testing Program Development
9
5.1.4. Field Geologic and Geotechnical Investigations .................................................... 9
5.1.5. Geologic and Engineering Analyses ..................................................................... 10
5.1.6. Seismic Hazard Study ........................................................................................... 10
6. Discussion ............................................................................................................................. 11
7. Completing the Study .......................................................................................................... 11
8. Literature Cited ................................................................................................................... 12
9. Figures .................................................................................................................................. 12
INITIAL STUDY REPORT GEOLOGY AND SOILS CHARACTERIZATION STUDY (4.5)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page ii February 2014 Draft
LIST OF FIGURES
Figure 3.1-1. Susitna Watana Project Area .................................................................................. 13
Figure 5.1-1. Terrain Unit Analysis, Watana Site to Upstream of Deadman Creek .................... 14
Figure 5.1-2. Preliminary Assessment of Reservoir Rim Stability – Watana Site to Deadman
Creek ............................................................................................................................................. 15
Figure 5.1-3. Locations of State Mining Claims in Project Area ................................................ 16
Figure 5.1-4. Locations of Mineral Licks in the Project Area ..................................................... 17
Figure 5.1-5. Regional Geologic Map for the Project Area ......................................................... 18
Figure 5.1-6. Regional Geologic Map for the Project Area – Legend ......................................... 19
Figure 5.1-7. Ground Temperature Data Plots – Examples ......................................................... 20
INITIAL STUDY REPORT GEOLOGY AND SOILS CHARACTERIZATION STUDY (4.5)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page iii February 2014 Draft
LIST OF ACRONYMS, ABBREVIATIONS, AND DEFINITIONS
Abbreviation Definition
AEA Alaska Energy Authority
AEIC Alaska Earthquake Information Center
ANCSA Alaska Native Claims Settlement Act
BLM Bureau of Land Management
BOC Board of Consultants
DSHA Deterministic Seismic Hazard Assessment
FERC Federal Energy Regulatory Commission
INSAR Interferometric Synthetic Aperture Radar
ISR Initial Study Report
LiDAR Light Detection and Ranging
PSHA Probabilistic Seismic Hazard Assessment
RSP Revised Study Plan
RTS Reservoir Triggered Seismicity
SPD Study Plan Determination
USGS United States Geologic Survey
INITIAL STUDY REPORT GEOLOGY AND SOILS CHARACTERIZATION STUDY (4.5)
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FERC Project No. 14241 Page iv February 2014 Draft
EXECUTIVE SUMMARY
Geology and Soils Characterization Study 4.5
Purpose Identify and document the geology and soils resources at the dam site and
reservoir areas, evaluate the potential impacts of Project construction and
operation, develop mitigation measures, and acquire data to support design
of the Project.
Status Field data collection and studies have begun; however, certain elements of
the field investigation and testing program were deferred to a later date.
Field activities included reconnaissance geologic mapping for development
of regional geology, evaluation of reservoir slope stability, assessment of
mineral resources, etc.
Study Components The key study methods include field site investigations, drilling and
sampling, downhole testing and instrumentation, geophysical surveys, and
instrumentation monitoring; geologic mapping of the dam site and reservoir
areas; geologic characterization and identification of construction material
sources; assessment of seismic hazards, mineral resources, and reservoir
slope stability; monitoring of earthquake events in the Project area; and
geologic and engineering analysis.
2013 Variances Land access restrictions in 2013 limited ground studies on CIRWG lands
that were scheduled to be undertaken. This restriction largely impacted
geologic mapping, geotechnical exploration and testing (e.g., drilling,
geophysical surveys, geo-instrumentation monitoring), and the seismic
hazard study. Consequently, the field exploration and testing program will
be deferred to a later date.
Steps to Complete
the Study
As explained in the cover letter to this draft ISR, AEA’s plan for
completing this study will be included in the final ISR filed with FERC on
June 3, 2014.
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Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page v February 2014 Draft
Geology and Soils Characterization Study 4.5
Highlighted
Results and
Achievements
The regional geologic studies, terrain unit analysis update, and the
preliminary reservoir slope stability studies were completed. The mineral
resources assessment study was largely completed. A partial program of
core drilling, sampling, and testing has been conducted at the dam site
(2011–2012). A long-term earthquake monitoring network has been
established and data on events are being collected. Seismic hazard studies
are in progress with a preliminary probabilistic seismic hazard assessment
(PSHA) and reservoir triggered seismicity studies completed and the
crustal seismic source characterization study is underway.
INITIAL STUDY REPORT GEOLOGY AND SOILS CHARACTERIZATION STUDY (4.5)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 1 February 2014 Draft
1. INTRODUCTION
On December 14, 2012, Alaska Energy Authority (AEA) filed with the Federal Energy
Regulatory Commission (FERC or Commission) its Revised Study Plan (RSP) for the Susitna-
Watana Hydroelectric Project (FERC Project No. 14241), which included 58 individual study
plans (AEA 2012). Included within the RSP was the Geology and Soils Characterization Study,
Section 4.5. RSP Section 4.5 focuses on the methods for evaluating the geology and soils and
defining the existing geological conditions at the dam site, reservoir, and access road and
transmission line corridors. This is necessary for developing design criteria to ensure that the
proposed Project facilities and structures will be safe and adequate to fulfill their stated
functions. RSP 4.5 provided goals, objectives, and proposed methods for data collection
regarding this study.
On February 1, 2013, FERC staff issued its study determination (February 1 SPD) for 44 of the
58 studies, approving 31 studies as filed and 13 with modifications. RSP Section 4.5 was one of
the 31 study plans approved with no modifications.
Following the first study season, FERC’s regulations for the Integrated Licensing Process (ILP)
require AEA to “prepare and file with the Commission an initial study report describing its
overall progress in implementing the study plan and schedule and the data collected, including an
explanation of any variance from the study plan and schedule” (18 CFR 5.15(c)(1)). This
Geology and Soils Characterization Study Initial Study Report (ISR) has been prepared in
accordance with FERC’s ILP regulations and details AEA’s status in implementing the study, as
set forth in the FERC-approved RSP as approved by FERC’s February 1 SPD (referred to herein
as the “Study Plan”).
Following the first study season, FERC’s regulations for the Integrated Licensing Process (ILP)
require AEA to “prepare and file with the Commission an initial study report describing its
overall progress in implementing the study plan and schedule and the data collected, including an
explanation of any variance from the study plan and schedule.” (18 CFR 5.15(c)(1)) This Initial
Study Report (ISR) on the Geology and Soils Study has been prepared in accordance with
FERC’s ILP regulations and details AEA’s status in implementing the study, as set forth in the
FERC-approved RSP (referred to herein as the “Study Plan”).
2. STUDY OBJECTIVES
The overall goals of this study are to conduct a geology and soils evaluation to define the
existing geological conditions at the dam site, reservoir, and access and transmission line
corridors, and to develop design criteria to ensure that the proposed Project facilities and
structures will be safe and adequate to fulfill their stated functions. The study objectives are
established in RSP Section 4.5.1 as follows:
• Identify the existing soil and geology at the proposed construction site, reservoir area,
and access road and transmission line corridors.
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• Determine the potential effects of Project construction, operation, and maintenance
activities on the geology and soil resources (including mineral resources) in the Project
area including identification and potential applicability of protection, mitigation, and
enhancement (PM&E) measures.
• Identify known mineral resources and mineral potential of the Project area.
• Acquire soils and geologic information for the Project area for use in the preparation of a
supporting design report that demonstrates that the proposed structures are safe and
adequate to fulfill their stated functions.
The field investigation activities for each season will be coordinated with resource agencies and
ANCSA Corporation landowners. A Geotechnical Exploration Program Work Plan (Work Plan)
will be developed that outlines the field programs and information needed for submitting
applications and obtaining land access permits from applicable agencies and ANCSA
Corporation landowners. The Work Plan will identify field investigations and studies to be
carried out to assess potential impacts to geology and soil resources in the Project area, including
the dam, reservoir, and access road and transmission line corridors, and the general arrangement
and foundation conditions for the dam and appurtenance structures. FERC regulations require
“evaluation of unconsolidated deposits, and mineral resources at the project site” (18 CFR
5.6(d)(3)(ii)(A)). For the Exhibit E, AEA must provide a report on the geological and soil
resources in the proposed Project area and other lands that would be directly or indirectly
affected by the proposed action and the impacts of the proposed Project on those resources. This
study report provides the basis of the information needed for the Exhibit E.
3. STUDY AREA
As established by RSP Section 4.5.3, the study area includes the dam site area, reservoir area,
construction material sources, tailwater downstream of the dam, access road and transmission
line corridors, airport facilities, and construction camp and permanent village sites (Figure 3.1-
1).
4. METHODS AND VARIANCES IN 2013
AEA implemented the methods as described in the Study Plan with the exception of variances
explained in Section 4.2. Study methods implemented in 2013 are described in the following
sections organized by the following study components as found in RSP Section 4.5.4:
• Review of Project Documentation
• Regional Geologic Analysis and Minerals Resources Assessment
• Geologic and Geotechnical Investigation and Testing Program Development
• Field Geologic and Geotechnical Investigations
• Reservoir-Triggered Seismicity
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FERC Project No. 14241 Page 3 February 2014 Draft
• Reservoir Slope Stability Study
• Geology and Engineering Analysis
4.1.1. Review of Project Documentation
The existing documentation from the 1970s and 1980s was brought into geo-referenced,
geotechnical databases to bring the information from the earlier studies into modern digital
formats.
4.1.2. Regional Geologic Analysis and Mineral Resources Assessment
Existing published information, air photo interpretation and reconnaissance mapping, and new
LiDAR survey data were used to (1) update information about the geology at the proposed dam
site and in the surrounding Project area, including surficial and bedrock geology, geologic
structure, seismicity and tectonics, mass wasting, and mineral resources; (2) determine siting of
Project components or structures; (3) identify geologic features of significance; and (4) assess
potential impacts (e.g., erosion) and potential mitigation measures to address impacts on geology
and soil resources and Project design and construction.
The recently acquired LiDAR imagery was used to compile geologic information for a large
area. The approach that had been used for this Project, which was developed during the Trans-
Alaska Pipeline geotechnical investigations (Kreig and Reger 1972), was to undertake a terrain
unit analysis, i.e., the identification of landforms resulting from geomorphic origin or mode of
deposition. This effort included an update to the original terrain unit mapping developed from
aerial photographs completed in the 1980s (Acres American 1982a).
A survey of the mineral resources was performed to assess proven and probable mineral resource
potential and mining activity in the impoundment area using existing data. The impoundment
area is the area where access to mineral resources may be affected by the Project. In addition to
the impoundment area, the road and transmission corridors were evaluated for potential quarry
and aggregate sites and known mineral deposits to identify whether access to mineral resources
may be adversely or beneficially affected by the Project. The survey included mapping of
known mineral deposits and identification of likely areas of mineral resources, plus field
reconnaissance of selected areas of high mineral potential, review of area mining claims, and
analysis of mineral potential from borings and other sampling work done for the dam and other
facilities through ongoing geotechnical investigations.
Recently-acquired LiDAR and INSAR data in the region were used to identify lineament
features and to examine the regional landscape for potential faults for evaluation of activity and
Project significance. Field reconnaissance, geologic mapping, and subsurface investigations, if
necessary, were performed and the data were used to update the seismic source characterization
model, site-specific ground motion evaluations, and probabilistic seismic hazard assessment
(PSHA).
INITIAL STUDY REPORT GEOLOGY AND SOILS CHARACTERIZATION STUDY (4.5)
Susitna-Watana Hydroelectric Project Alaska Energy Authority
FERC Project No. 14241 Page 4 February 2014 Draft
4.1.3. Geologic and Geotechnical Investigation and Testing Program
Development
The development of a 2014–2015 geologic and geotechnical exploration and testing program
Work Plan for completion of geologic and geotechnical field studies for engineering feasibility,
final design and construction was completed. The Work Plan is centered on continuation of data
collection efforts and studies to supplement previous field site investigations and testing
performed in the 1970s–1980s and more recently in 2011–2013. Based on review of the existing
data including previous geologic mapping, subsurface investigations, and laboratory testing,
additional site investigations and testing will be conducted as described below:
• Delineate and characterize geology and soil resources including geologic features, rock
structure, and weathering/alteration zones.
• Undertake physical and chemical testing, as well as petrographic analysis, to characterize
the geology and soils materials, as appropriate.
• Evaluate lineaments’ and faults’ relative level of activity and significance to site-specific
ground motion evaluations for the Project.
• Delineate and characterize construction material sources for the dam and appurtenant
structures, access road, and construction camp.
• Determine the effects of discontinuous permafrost on the dam foundation and abutments
relative to foundation treatment, grouting, and drainage, as well as reservoir slope
stability and access road and transmission line construction.
• Evaluate the effect of Project features on permafrost and periglacial features (thawing of
permafrost), as well as the impact of these features on permanent structures, work camps,
temporary construction areas, road corridors, transmission lines, etc.
• Evaluate the need for, and potential sources of borrow materials for ancillary facilities
including upland structures, access roads, and transmission lines.
• Evaluate potential waste stockpiles and storage sites including plans to help reduce the
impact of these facilities on adjacent areas.
• Evaluate plans and methods for the reclamation of borrow area and quarry sites.
• Evaluate the Project’s impact on access to geologic resources (mineral resources) by
reviewing existing state and federal databases, as well as readily available geologic maps
and surveys.
• Conduct a preliminary evaluation of the effect of soils composition in the Project area on
construction, operation, and maintenance of the proposed Project.
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FERC Project No. 14241 Page 5 February 2014 Draft
• Evaluate potential reservoir leakage on the right abutment just upstream of the dam site
(e.g., relict channel).
• Establish seismic monitoring stations in the Project area to augment the stations in the
Alaska Earthquake Information Center network to monitor and detect any local
earthquakes.
4.1.4. Field Geologic and Geotechnical Investigations
Geologic and geotechnical field investigations are being carried out in phases each study year
with portions of that work contributing to the report on geology and soils in 2013 and with
updates in subsequent year(s). The geotechnical investigations and testing undertaken as part of
the Project feasibility, licensing, and design effort are to include geologic mapping, drilling,
sampling and in situ testing, test trenches, pump tests, exploratory adits, laboratory testing,
instrumentation monitoring, etc. Initial and limited geologic exploration and testing programs
were undertaken in the 2011–2012 seasons to investigate the dam foundation and a new quarry
site for concrete aggregate material. This included installation and monitoring of geotechnical
instrumentation and reconnaissance geologic mapping in the Project area for understanding the
regional geology, and was also associated with terrain unit analysis, the mineral resources study,
seismic hazard study, and reservoir area geology. Multiple field investigation programs are
planned for continuation in subsequent year(s).
4.1.5. Reservoir-Triggered Seismicity
Seismic hazard study and evaluations are being undertaken for the Project under a separate study
(see RSP Section16.6) and include conducting a crustal seismic source characterization study;
identifying and evaluating lineaments and if tectonic in nature; completing a fault evaluation
process; developing a new subduction seismic source model; preparing a deterministic and
probabilistic seismic hazard assessment, including ground motion estimates; and developing
seismic design criteria for the Project. In addition, a long-term earthquake monitoring system
was installed and the seismicity data are being collected to better understand the seismological
characteristics of local terrain or regional area and seismic hazards in the Project area, and to
provide a baseline of seismic activity prior to impoundment of the reservoir for assessing
potential reservoir triggered seismicity. The Geology and Soils and Seismic Hazard
characterization will contribute information to the overall study.
4.1.6. Reservoir Slope Stability Study
A preliminary assessment was made of reservoir rim stability based on the geologic conditions in
the reservoir area, particularly in the reservoir drawdown zone. Geologic information from the
previous study on reservoir slope stability (Acres American 1982a) as well as LiDAR imagery,
geologic and terrain unit mapping, field investigations, and instrumentation monitoring were
used to assess the stability and erosion concerns of the reservoir rim area. Key factors in this
study are the planned reservoir level and anticipated range of drawdown, rock and soil type and
conditions, presence of permafrost, topography, and slope aspect and conditions.
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FERC Project No. 14241 Page 6 February 2014 Draft
4.1.7. Long-Term Earthquake Monitoring System
A long-term seismic monitoring system is to be established in the Project area to monitor and
document earthquake events (see RSP Section 16.6). The system was expanded in 2013 and
currently consists of seven instrumented locations within about 30 miles of the dam site, four
6-component strong motion and broadband seismograph station, and three 3-component
broadband seismograph stations. Previously (2012) four seismograph stations had been
installed. The monitoring system is linked and integrated into the Alaska Seismographic
Network operated by the Alaska Earthquake Center for real-time data acquisition, processing,
and analysis.
4.1.8. Geologic and Engineering Analyses
Geologic and engineering analyses are being undertaken to identify and evaluate construction
material sources to provide adequate quantities of suitable materials for construction; to evaluate
horizontal alignments and foundation design for the access road, construction and permanent
camps, and transmission line corridor; and to identify potential re-use of excavated materials
and/or disposal areas. The geology and engineering study includes an assessment of soil erosion
potential along the transmission and access road corridors, along with other effects of design and
construction on geology and soils, and identification of the suitability of measures to reduce and
mitigate impacts.
Additionally, a number of geologic, seismic, and engineering analyses are being undertaken to
develop the geologic model for the dam site area and to assess foundation design, abutment
stability, seepage and piping potential, slope stability, ground motion, and site-specific
probabilistic seismic hazards for the dam site area. These activities will also help identify
impacts and measures to mitigate impacts to geology and soil resources.
4.2. Variances from Study Plan
Due to land access restrictions in the study area, which were unanticipated for the 2013 field
season, the planned field exploration and testing program, specifically geologic mapping,
geophysical surveys, drilling and testing, and excavation of an exploratory adit at the dam site,
was deferred. In areas where land access restrictions were imposed, no on-the-ground activities
could be performed. In these areas, field investigation and data collection were limited to aerial
reconnaissance, a high-level review in connection with reconnaissance geologic mapping
activities associated with development of the regional geology, mineral resources assessment,
and continuation of seismic hazard studies.
As a consequence, the methods of data collection for the dam site, consisting of geologic
mapping, drilling and in situ testing, surface geophysical surveys, excavation of exploratory
adits, and geotechnical instrumentation installation and monitoring as well as the methods of data
collection for the proposed Project infrastructure (e.g., proposed access roads and transmission
corridors and camp/village) are being re-scheduled for future field seasons. Several broader
study area field investigation efforts were restricted, specifically related to geology and soils
methods of investigation and data collection, including regional geologic mapping, mineral
resources survey, drilling at Watana Creek, and field reconnaissance to ground-truth
interpretations for the terrain unit mapping and preliminary slope stability evaluation. The
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seismic hazard studies, lineament, and fault evaluation in connection with the crustal seismic
source evaluation were curtailed due to access restrictions, in particular in the dam site, lower
reservoir, and Fog Lakes areas.
5. RESULTS
5.1.1. Review of Project Documentation
The existing geologic, geotechnical, and seismic documentation from the 1970s and 1980s was
brought into geo-referenced, geotechnical databases to build new information databases in digital
formats, which will be developed and expanded upon through additional data collection from
future phases of field investigations. The data currently in digital format includes boring and test
pit logs, laboratory testing data, and geotechnical instrumentation monitoring data for
groundwater and ground temperature.
Additionally, several 1980s drawings (e.g., exploration plans), which were in the Alaska State
Plane, Zone 4, NAD27 coordinate system, were updated to the present coordinate system,
NAD83, and included on base topographic maps and GIS-databases created from the recently
acquired LiDAR imagery (Acres American 1982b; Harza-Ebasco 1983).
Some of the rock cores from the earlier field investigations are being stored by the ADNR DGGS
in Eagle River and were reviewed to ascertain what samples remained from the 1980s studies
and to become familiar with the bedrock conditions at the dam site prior to beginning the recent
field investigations.
5.1.2. Regional Geologic Studies
Existing published information, air photo interpretation, reconnaissance mapping, and new
LiDAR survey data are being used to (1) update information about the geology and soils
resources in the Project area with a focus in the dam site area, including the surficial and bedrock
geology, geologic structure, seismicity and tectonics, mass wasting, and mineral resources;
(2) determine the siting of some Project components and/or structures; (3) identify geologic
features of significance that may impact the general arrangement and design of Project
components or need to be mitigated through excavation, support, treatment, etc.; and (4) assess
potential impacts to the geology and soil resources and develop appropriate mitigation measures
relative to design, construction, and operation of the Project. The various methods being
employed for this study include both desktop studies and field investigations and are described
below.
5.1.2.1. Terrain Unit Analysis
Terrain unit analysis was undertaken using a desktop approach for generating and compiling
geologic information for the large area beyond the dam site area that has had limited
investigation. Terrain unit mapping was a product of the interpretations of aerial photographs
and “bare earth” 3D digital imagery, terrain unit analysis, and limited field reconnaissance.
Utilizing these techniques, landforms resulting from geomorphic origin or mode of deposition
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were identified and cataloged as terrain units. Terrain unit is a special purpose term comprising
landforms expected to occur from the ground surface to a depth of about 25 feet.
The general objective of this effort was to review and update the 1982 terrain unit mapping
interpretation using more advanced aerial imagery (e.g., LIDAR, INSAR models) (Acres
American 1982a). The analysis included the area from about 7 miles west of the dam site to just
east of Vee Canyon (about 38 miles east of the dam site) and about 7 miles north–south centered
on the Susitna River. Fifteen landforms were identified that document the geologic features and
general geotechnical conditions, noting such geologic and terrain factors as soil types,
permafrost, potentially unstable slopes, etc. An example of the work product created to
document the terrain units is presented on Figure 5.1-1.
5.1.2.2. Reservoir Slope Stability Study
A preliminary assessment was made of the potential for a major landslide or slope failure that
could threaten or negatively impact the safety or safe operation of the dam and/or associated
critical facilities. Additionally, the study also includes an assessment of the potential slope
conditions as a result of mass wasting and erosion processes along the reservoir rim that may
develop following reservoir impoundment, based on the anticipated reservoir operation
conditions. This preliminary assessment performed as a desktop study was based on the current
Project physical parameters, reservoir operational levels, and geologic, topographic, and
vegetation conditions.
Geologic information from the previous study on reservoir slope stability (Acres American
1982a) as well as LiDAR imagery-3D “bare earth” model, the terrain unit analysis (see Section
4.1.2.1), and published geologic maps were used to identify and assess areas of concern. Key
factors that were considered in this study were the anticipated range of reservoir drawdown, rock
and soil type and conditions, delineation of areas of frozen ground (e.g., permafrost),
topography, slope aspect and conditions, and current location and types of mass wasting. A GIS
map book was created to compile the data and preliminary interpretation including terrain unit
maps, current slope mass wasting, and anticipated future slope conditions post-impoundment
(Figure 5.1-2).
5.1.2.3. Mineral Resources Assessment
A desktop study and field reconnaissance was undertaken to document and assess the mineral
resources in the dam and reservoir area, including the corridors. This assessment was conducted
to determine if and where mineral resources, metallic and non-metallic resources, may be
affected by the Project in either a beneficial or detrimental way. The study included identifying
mining claims and prospects in the Project area from data sources (e.g., State of Alaska mining
claim website); field reconnaissance of selected areas of high mineral potential, mineral licks,
and mining claims; and consultations with active miners and geologists familiar with the area
(USGS, BLM, Alaska Earth Sciences, CIRI, and claimholders). Additionally, several rock
samples were collected and chemically analyzed for a wide range of potentially economic
minerals.
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FERC Project No. 14241 Page 9 February 2014 Draft
Preliminary maps of active mining claims, known mineral deposits, and mineral prospects have
been produced based on a review of the State of Alaska database. An example map of active
mining claims for the Project area and adjacent lands is presented on Figure 5.1-3. Based on the
data compiled on the claims and regional geology, a 5-day field reconnaissance was conducted in
late August 2013 to evaluate and/or confirm the information on the claims, to review areas of
high mineral potential, and to obtain rock samples.
The survey also included identification of non-metallic resources, potential construction material
sources, rock quarry, and aggregate sites that might be considered and utilized along the
transportation and transmission corridors (e.g., Gold Creek, Denali, and Chulitna corridors)
during construction or might be adversely or beneficially affected as a result of the Project. The
approximate extent of the feasible non-metallic resource was classified by deposit type and
mapped.
The mineral resources assessment also included the identification and review of potential sources
of acid rock drainage (ARD) and mineral licks (Figure 5.1-4) that provide nutrients to wildlife.
As part of this study, rock outcrops were reviewed for characteristics that were highly oxidized,
which could result in acidic runoff.
Ground access was limited due to land access restrictions in 2013 and only locations on state and
federal lands were visited on the ground.
5.1.2.4. Regional Geologic Mapping
A regional geologic map is currently being compiled based on available geologic map data,
aerial imagery, and recently-acquired LiDAR and INSAR data. Data from these available
sources were compiled, and areas of interest were investigated to verify the geologic unit and
structure mapped previously during a 10-day field mapping program. The reconnaissance
geologic mapping effort collected data related to soil or rock type, grain size, composition,
degree of weathering, hardness/strength, rock structure and characteristics, geomorphic landform
type, groundwater springs or seepage, unfrozen or frozen condition, etc.
A regional geologic map is currently being compiled; a draft work in progress document is
provided herein (Figure 5.1-5). The geologic data is being compiled in a GIS database.
5.1.3. Geologic and Geotechnical Field Investigation and Testing Program
Development
The development of a geologic and geotechnical exploration and testing program Work Plan for
completion of geologic and geotechnical field studies for engineering feasibility, licensing, and
ultimately for final design and construction was completed.
5.1.4. Field Geologic and Geotechnical Investigations
In 2011 and 2012, eleven borings were completed at the dam site and two potential construction
material sources (Quarry A and M) on the south side of the river. Diorite bedrock was
encountered in the dam site and Quarry M while andesite and diorite were encountered in
Quarry A. Water pressure testing was conducted and geotechnical instruments, vibrating wire
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piezometers, and temperature acquisition cables were installed in many of the borings. In a few
borings, downhole optical and acoustical surveys were performed. Rock core samples were
selected from the subsurface investigations and laboratory testing performed to determine the
engineering properties of the rock material (e.g., unconfined compressive strength, LA abrasion,
freeze-thaw).
In 2013, the planned field investigation and testing program—which included geologic mapping,
surface geophysical surveys, drilling and in situ testing, geotechnical instrumentation
monitoring, excavation of an exploratory adit as well as laboratory testing of samples collected at
the dam site and/or infrastructure areas—was deferred to due to land access restrictions. The
program included a winter geologic mapping program to access rock outcrops to collect
information on the bedrock conditions and to evaluate lineaments in the dam foundation area and
a spring/summer program of mapping, geophysical surveys, drilling, instrumentation monitoring,
and excavation of the exploratory adit.
An assessment was made of the 1970s and 1980s geotechnical instrumentation to determine what
if any of the boreholes or instruments in the area of interest (e.g., dam site) could be recovered
and automated. Dataloggers were installed in five borings from the 1970s and 1980s for
recording ground temperature (4) and groundwater (1) measurements. In addition, seven borings
from 2012 were instrumented and dataloggers installed for continuous recording of ground
temperature and/or groundwater measurements. Some data have been obtained from the
dataloggers; however, due to the restricted access matter, the data record is not complete. In
addition to those borings with dataloggers, there are several borings (3) where manual
measurements were made. Based on the data collected during the 1980s on ground temperature,
it appears that frozen ground conditions exist in the south abutment (DH-24) and may be present
in the lower north abutment (Figure 5.1.6).
Some geologic mapping was performed in 2011–2012 to obtain additional geologic data in the
vicinity of the proposed dam foundation, in particular on the right or north abutment. The data
obtained during the mapping are being used along with the LiDAR to update the bedrock
geology map for the dam site previously developed by Acres American (1982b).
5.1.5. Geologic and Engineering Analyses
Geologic and engineering analyses were undertaken utilizing the geologic and geotechnical data
that had been obtained during the earlier (1970s–1980s) and more recent field investigations and
laboratory testing. These data formed the framework of the geologic characterization and
development of a geologic model for optimization of the general arrangement, development of
foundation and underground structures designs, and preliminary geotechnical assessments of
abutment stability and the dam foundation for development of finite element models for analysis.
5.1.6. Seismic Hazard Study
The crustal seismic source field evaluation of identified lineaments and potential faults is
underway. In 2013, about 50% of the lineament features were evaluated. Field evaluations were
undertaken to assess the geomorphologic landforms and characteristics around the lineaments
and to identify positive evidence for (or against) tectonic deformation associated with the
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lineament. On-the-ground field mapping and evaluation are required in the dam site and
reservoir areas on CIRWG lands
A preliminary assessment of the potential for reservoir triggered seismicity (RTS) to occur
during and after filling of the reservoir was completed. Empirical data suggest that most RTS
events will have relatively small magnitudes and would most likely occur within 10 years of
initial reservoir filling. From these types of observations, ICOLD (2011) and Allen (1982)
suggest that maximum RTS magnitudes may be on the order of 6.3 and 6.5, respectively. The
results of the crustal seismic source assessment and additional seismic event data are needed to
improve the understanding of the local geologic and seismotectonic characteristics that are
significant to RTS. In 2015, the RTS study will be revisited and updated.
The long-term seismic monitoring network for the Project was expanded in 2013. Three
additional seismograph stations were added and one GPS station. This brings the total project
network to seven seismograph stations, four 6-component broadband and strong motion stations,
and three 3-component broadband stations, and one GPS monitoring station. The stations are all
located within 31 miles of the proposed dam site. Data on seismic events in the area are
provided to the Alaska Earthquake Information Center (AEIC) in real-time. For additional
information on the seismic hazard studies, see ISR 16.6.
6. DISCUSSION
Limited progress was made with respect to field investigations and testing in 2013 due to land
access restrictions, with ground access only on state and federal lands. The tasks undertaken
were mostly desktop studies with some field reconnaissance, primarily in the broader regional
area and not the dam site and lower reservoir area, which was to be the focus for the field work.
Therefore, limited field reconnaissance was undertaken to verify the interpretations made from
the desktop studies, i.e., regional geologic data collection, mineral resources and slope stability
assessments, and seismic hazard studies.
Additional efforts have been made in the planning of future phases of field investigations and
testing to be under taken as a result of the delay in the data collection efforts (see Section 5.1.3).
Geologic and engineering analysis undertaken in 2013 has been based on the data primarily
obtained during the 1970s and 1980s field investigation and testing programs as augmented by
the recent limited field work in 2011–2012. The engineering work tasks have included selection
of appropriate engineering properties of soils and rock, characterization of rock mass,
development of design criteria, evaluation of abutment stability and feasibility design, and
development of general arrangement, foundation excavation, and treatment for the dam and
powerhouse, underground structure support, and lining, etc.
7. COMPLETING THE STUDY
[As explained in the cover letter to this draft ISR, AEA’s plan for completing this study will be
included in the final ISR filed with FERC on June 3, 2014.]
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8. LITERATURE CITED
Acres American. 1982a. Susitna Hydroelectric Project 1980–81 Geotechnical Report, Volumes 1
through 3. Prepared for Alaska Power Authority.
Acres American.1982b. Susitna Hydroelectric Project, 1982 Supplement to the 1980–81
Geotechnical Report. Prepared for Alaska Power Authority, Anchorage, Alaska.
AEA (Alaska Energy Authority). 2012. Revised Study Plan: Susitna-Watana Hydroelectric
Project FERC Project No. 14241. December 2012. Prepared for the Federal Energy
Regulatory Commission by the Alaska Energy Authority, Anchorage, Alaska.
http://www.susitna-watanahydro.org/study-plan.
Allen, C. 1982. Reservoir-induced seismicity and public policy, California Geology, November,
248-250.
Harza Ebasco, 1983. Susitna Hydroelectric Project, Watana Development, 1983 Geotechnical
Exploration Program. Volumes 1 and 2.
ICOLD, 2011. Committe on Seismic Aspects of Dam Design, Reservoirs and Seismicity - State
of Knowledge- Bulletin 137.
Kreig, R. A., and Reger, R. D. 1982. Air-Photo Analysis and Summary Landform Soil Properties
Along the Route of the Trans-Alaska Pipeline System. Alaska Division of Geological
and Geophysical Surveys. Geologic Report 66.
9. FIGURES
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Figure 3.1-1. Susitna Watana Project Area
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Figure 5.1-1. Terrain Unit Analysis, Watana Site to Upstream of Deadman Creek
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Figure 5.1-2. Preliminary Assessment of Reservoir Rim Stability – Watana Site to Deadman Creek
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Figure 5.1-3. Locations of State Mining Claims in Project Area
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Figure 5.1-4. Locations of Mineral Licks in the Project Area
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Figure 5.1-5. Regional Geologic Map for the Project Area
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Figure 5.1-6. Regional Geologic Map for the Project Area – Legend
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Figure 5.1-7. Ground Temperature Data Plots – Examples