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HomeMy WebLinkAboutEnergy Projects 1984 Appendix D-2Bethel Area Power Plan Feasibility Assessment APPENDIX D-2 GEOLOGY OF HYDROELECTRIC SITES DRAFT Prepared for the Alaska Power Authority by Harza Engineering Company and Harding Lawson Associates Draft April 1984 TABLE OF CONTENTS Chapter I.CHIKUMINUK LAKE SITE GEOLOGY Introduction Regional Geologic Setting Site Geology General Site Conditions Bedrock/Structure Soils Seismicity Chikuminuk Lake Site Comparison Dam Axes Spillways Reservoirs Diversion Tunnel and Cofferdam Power Tunnels/Underground Powerhouse Conclusions Engineering Geology Rock Tunneling and Underground Excavation Dam Foundation Reservoir Upstream Cofferdam Airstrip If.GEOLOGY OF ALTERNATIVE HYDROELECTRIC SITES Kisaralik River -Lower Falls Kisaralik River -Golden Gate Falls Kisaralik River -Upper Falls Kipchuk River Upnuk Lake Milk Creek IAnuUnS&(eonieBoeleI LIST OF EXHIBITS Exhibit No.Title 1 Conceptual Project Plan,Chikuminuk Lake Downstream Site 2 Conceptual Project Plan,Chikuminuk Lake Upstream Site 3 Chikuminuk Lake Site Geology 4 Regional Seismicity 5 Kisaralik River Lower Falls Site Geology 6 Kisaralik River Golden Gate Falls Site Geology 7 Kisaralik River Upper Falls Site Geology 8 Kipchuk River Site Geology 9 Upnuk Lake Site Geology 10 Milk Creek Site Geology -ii- Chapter I CHIKUMINUK LAKE SITE GEOLOGY Introduction Two site visits were conducted in August 1982.During the first visit,attention was focused on a potential dam axis and left-bank spillway approximately 2,800 feet south of the Chikuminuk outlet (See Exhibit 1).During the second site visit,the above-mentioned site (downstream)was reviewed more critically and an upstream site (See Exhibit 2)was also inves- tigated. Geologic investigations included photogeologic interpreta- tion of 1:60,000 scale infra-red photography,three days in the field reviewing and evaluating the site geology,and performing a refraction geophysical survey (240 lineal feet)in the spill- way area of the downstream site.The evaluations contained in this appendix are therefore preliminary,limited to surface expressions of the site geology.Subsurface exploration will be required during the feasibility studies. Regional Geologic Setting The hydroelectric sites for the Bethel Project lie on the flanks of the Kuskokwim/Kilbuck/Wood River Mountain Range of the west-central interior,550 miles west-southwest of Anchorage. Average maximum elevation of the rugged,east-northeast trending Range is 5000 feet,and relief across the range is 4000 to 4500 feet.The lowlands to the east are part of the Nushagak River system and the western lowlands,extending to Bethel and beyond, are part of the extensive Yukon/Kuskokwim River Delta. Bedrock units in the region are primarily folded and fault- ed clastic sedimentary rocks of Cretaceous age.Minor occur- rence of Tertiary age igneous and volcanic rock units,and pre- cambrian to Devonian age metamorphic rock units also comprise the bedrock.The dominant structural trends of N10°-20°E are parallel to the linear mountain trends.The most recent major faulting,accounting for the uplift of the mountain system,is ascribed to the Late Cretaceous and Tertiary.Primary bounding faults for the uplift appear to be the Togiak Fault,a steeply dipping upthrust,marking the western front of the range.Mid- dle Paleozoic rocks are raised to the surface along this western fault system coincident with the Golden Gate site. Late Tertiary and Cenozoic periods have largely involved erosion of the high-standing mountain trends and filling of the I-1 adjacent lowlands.Limited volcanic extrusive and intrusive activity also is ascribed to the Tertiary.The current land- scape in the region is dominated by glacial landforms including, pitted ground moraines,recessional moraines,outwash plains and steepwalled bedrock valleys. Site Geology General Site Conditions Lake Chikuminuk occupies a glacially-enlarged valley system bound on the southeast margin by a series of recessional mo- raines.The moraines have been breached to a bedrock spillpoint at the very southern outlet of the lake.From this point,the Allen River has carved an "S"-shaped,steep-walled canyon 60 to 80 feet deep through hard,metasedimentary rocks of the Cretaceous Gemuk Group.The river flows out of the 1/2 mile long canyon to gently sloping outwash terraces lying downstream of the recessional moraines.Exhibit 3 illustrates the surface geology of the Chikuminuk Lake project area. Bedrock /Structure Outcrops at the Chikuminuk site are limited primarily to the lower 60 to 70-foot sidewalls of the inner canyon.Heavy alder growth,brush,and tundra further reduce the outcrop area to approximately 10 percent or less.The exposed rock units are very hard,siliceous carhonates,sandstones,shales and conglo- meratic sandstones.Bed thickness ranges up to 15 feet,and the outcropping rock has a massive appearence.Thin-hedded (one to two inch thick)units,primarily in shales,are exposed local- ly. No dominant joint sets were observed in the site area, rather,the massive,brittle rock appears to have heen fractured randomly.The network of closely spaced,hairline fractures at 1 to 2 inches spacing,is healed tightly with silica to provide the massive outcrops. Discordant dips and strikes in the rock outcrops downstream of the lake outlet suggest local tight folding and/or faulting. Two shear zones in the promontory downstream site are suggested by a deeply-cut swale and a 5 to 8 foot-wide zone of closely fractured rock,respectively.There is no indication of dis- placement of the overlying glacial deposits in the damsite area. Soils The surface soils at the Chiktuminuk site are glacial in origin and include ground moraines,lateral and recessional end moraines,and outwash (alluvial)deposits.Exposures are quite limited,however,a recent land slump in the moraine at the lake outlet (designated as the Lake Moraine)has exposed 40 to 50 feet of unsorted to poorly sorted gravelly sands,and sandy gravel with minor cobble to boulder sizes.Boulders range to 2 feet in maximum diameter;most of the exposed sand is coarse and angular;and there are only minor interbeds of low-plasticity silty clay,about 4 to 6 inches thick. The Lake Moraine appears to be approximately 100 feet thick and extends approximately one mile across the southeast arm of Chikuminuk Lake.The two recessional moraines downstream of the Lake Moraine are estimated to he 50 feet or less in thickness near the site.In the immediate upstream site area,morainal cover on the west (right)bank of the Allen River is thin,per- haps 20 feet or less within a horizontal distance of 400 feet from the river. Broad,alluvial,sand and gravel terraces extend below the rapids downstream of the downstream site.The deposits are dominantly gravels and sands although,minor,one to two foot thick lenses of clay have been reported in the river banks near the mid-channel island about 0.75 mile downstream of the rapids. Significant clay deposits are not apparent in the area. Thin clay beds do occur however,and future exploration,espe- cially in the intermorainal swales,may confirm glacio-lacus- trine clay deposits that could he used in construction. The moraine deposits should provide an adequate source of sand,gravel and random fill for embankments and possibly aggre- gate.Processing will be necessary.Testing will be required to identify the occurrence of alkali-reactive aggregate.The downstream alluvium will be available for construction mater- ials.No large boulder deposits have been identified to date. Large riprap could he developed from required spillway excava- tion. Seismicity The initial evaluation of regional seismicity involved a review of data maintained on computer file by NOAA (National Oceanographic and Atmospheric Administration),Boulder Colorado. A search was conducted for all reported and/or instrument- recorded events with assigned epicenters within 200 miles of the I-3 site.Approximately 1,300 events are on file for this area, dating back to the year 1786.The vast majority of the events are concentrated 160 miles to the southeast along the Aleutian Range (See Exhibit 4). The largest nearby event was rated at 5.1 Magnitude and occurred within of 15 to 20 miles from the site.This instru- ment recorded event occurred September 7,1976.These data suggest that a value of 0.lg be used for preliminary design purposes. Chikuminuk Lake Site Comparison Two alternative dam sites were investigated for the Chikuminuk Lake project.The sites are shown on Exhibits 1 (downstream site)and 2 (upstream site). Dam Axes At the current level of evaluation,bedrock conditions at both sites are considered to be nearly identical.Both loca- tions are in tight,steep-walled gorge sections and details of stratigraphy,faulting and fracture condition are unknown. From the standpoint of distance to fill materials,the upstream site has an advantage as the Lake Moraine is only 1,000 feet away. Spillways Foundation conditions beneath the spillway at the down- stream site are questionable.The major questions relate to the nature of materials in the ridge beneath the spillway and parti- cularly,the depth to solid bedrock.The initial reconnaissance indicated slump deposits on both the upstream and downstream sides of the ridge.Present mapping was unable to locate evi- dence of bedrock in the northern half of the proposed spillway, while bedrock outcrops were noted in adjacent slopes.It is considered possible that former streamflow from the "Dry"Valley (See Exhibit 3),or the upper reaches of the Allen River,may have cut a valley through the ridge which was later filled with morainal or alluvial deposits.An alternative hypothesis is that weaker,relatively erodible rock underlies the area at shallow depth beneath a cover of glacial moraine deposits. A preliminary refraction seismic profile,240 feet long, was obtained beneath the spillway ridge.Seismic velocities obtained from this survey are inconclusive,in that such veloci- ties could represent compact,saturated glacial fill or some of the weaker sedimentary rocks. The spillway at the upstream site would be in an area of thin (10 to 20 feet)morainal cover overlying massive bedrock. Discharge would be to the "Dry"Valley,which,as an underlift stream,appears to have sufficient capacity to receive large spills and dampen the effect of surging into the Allen River. Little erosion of the spillway proper would be expected. However,alluvium in the valley would be subject to erosion. Reservoirs The general water-retaining capabilities of the reservoir would be similar for each site.However,the indicated unfavor- able foundation conditions of the spillway ridge at the down- stream site would prohably require special grouting and/or cut- off facilities.Concentrated short-path seepage could occur through the zone of weak rock or glacial-alluvial fill. Diversion Tunnel and Cofferdam Access for the upstream site diversion tunnel would be simple from the intermorainal area,while the downstream site diversion scheme would involve the construction of spur roadways to the portal area. From a diversion standpoint,the upstream site has the advantage of good access to the river and abundant fill material close at hand from the morainal deposits to construct an emhank- ment.The downstream diversion would involved building a diver- sion dam from the southwest side of the "Dry"Valley to the northwesterly trending bedrock spur currently between the plann- ed dam and spillway.The "Dry"Valley contains a stream flowing about 100-200 cfs (August 1982 estimate)which will require diversion,hence the location 500+feet downstream from the diversion tunnel itself.Access for machinery to the lower reaches of the "Dry"Valley would require an extensive cut or fill ramp from the northwest head of the Valley,and turning space would he very limited. Power Tunnels/Underground Powerhouse Both schemes involve excavations for the power tunnel and powerhouse in the left abutment.The power tunnel for the down- stream site would he shorter,yet the longer tunnel at the up- stream site could be worked from two headings,which could have an effect on the work schedule. Tunneling conditions at both sites would be favorable. Rock cover conditions for an underground powerhouse at hoth sites appears to be marginal. Conclusions From the standpoint of access,proximity to embankment construction materials,competancy of the spillway foundation and reservoir water-retaining capability,the upstream Chikuminuk site is recommended for further investigation. Engineering Geology Rock Tunneling and Underground Excavation In general terms,the hard,siliceous,sedimentary rock sequence should provide favorable tunneling conditions.Stan- dard steel set support for 30 to 40 feet at tunnel portals,and moderate rock bolting and/or local gunite work should be suffic- ient for temporary support prior to lining.It appears that there is insufficient rock cover for an underground powerhouse. Subject to an exploration program designed to evaluate an under- ground powerhouse,it is recommended that a surface powerhouse be used for preliminary conceptual design. Dam Foundation The dam site is in a steep-walled (4V:1H),flat-bottomed canyon.Locally scoured and cobble-filled bedrock pockets may be encountered in the river channel but,in general,little alluvium is expected. Abutment rock may contain open joints due to stress relief and near-surface ice-wedging.Approximately 10-15 feet of rock may have to be removed to reach acceptable foundation rock. Detailed planning estimates of grouting requirements will require drillhole permeability testing. Based on present information,it is expected that the foundation rock will be adequate to support the loads of either a gravity or rockfill dam. Reservoir The proposed reservoir will require further investigation. It is necessary to assess the water-retaining capability of the morainal ridges which form natural embankments across the south- east arm of the lake.The moraines are essentially soil embank- ments laid down on the pre-existing valley floor. For the purpose of conceptual design it is recommended that a slurry wall be constructed to reduce seepage in the left abut- ment moraine for reservoirs above El.620. Upstream Cofferdam Construction will require that diversion cofferdams be placed in moving water with bedrock at,or very near,the bottom surface.Successful diversion probably will require larye rock and large volumes of readily accessible,randomly sized fill, all to be placed during the minimum flow season. Airstrip The airstrip could be located on the outwash plain down- stream from the site.The plain apparently consists of well- drained alluvium,with a surface slope of 1 to 2°to the south- east.Accurate elevation control may indicate the need for large fill volumes to achieve an acceptable 1 to 2%runway grade. As an alternative for further investigation,the scoured bedrock surface in section 15,about 2 miles north west of the Lake outlet should be considered.A constructed fill at this site,to essentially fill bedrock lows.may be a iess costly than the airstrip location mentioned above. Chapter II GEOLOGY OF ALTERNATIVE HYDROELECTRIC SITES Numerous hydroelectric sites were considered during the screening studies,described in Chapter II of Appendix D.This chapter describes the geology of the following alternative sites: fe)Kisaralik River -Lower Falls fe)Kisaralik River -Golden Gate Falls fe)Kisaralik River -Upper Falls fe)Kipchuk River fe)Upnuk Lake fe)Milk Creek Kisaralik River -Lower Falls The Lower Falls site is located (SW 1/4,S17,T4N,R62W)on the Kisarlik River in a narrow gorge about 64 miles east south- east of the City of Bethel and 30 river miles downstream from the outlet of Kisaralik Lake.The Lower Falls site geology is shown on Exhibit 5. The river has carved a deep,steep-walled valley which has a thin veneer of colluvium and glacial till.Hard,cherty meta- sediments and meta-volcanics of the Cretaceous Gemuk Formation are partially exposed at the site. Bedrock units at the site consist of Cretaceous age meta- sedimentary and meta-volcanic rocks of the Gemuk Formation. Strike and dip values of bed attitudes were difficult to obtain because of the massive nature of the units and limited rock exposures.Several readings were taken,but no well defined pattern was evident.The rocks in outcrop are hard,very dura- ble,dense and siliceous,and all appear to be inclined at 45° or more to the horizontal. Three prominent joint sets (striking N45°W,N-S and E-W) cross the site at spacings of 1 to 2 feet.The joints appear to be tight in outcrop,and there is no evidence of crushing or weathered zones associated with the joint sets.The deeply incised "S"-shaped stream pattern in the site area gives no indication of either joint or plan fault control. II-1 The site area does not appear to have soils in sufficent volume for use as construction material.The steep sidewalls of the canyon are veneered with colluvium.Local gqravel/sand bars that occur in the stream channel,and crude,point bar deposits developed locally,lack sufficient volume for use as construc- tion material. A survey of the area 1 to 2 miles downstream from the site revealed a general scarcity of alluvial material.Terraces on the Kisaralik and tributary streams are generally cut on rock with little to no appreciable thickness of alluvial cover.The tundra and vegetation cover may be concealing useable deposits, but none are obvious. The Lower Falls site is in a region of west central Alaska which is subject to relatively minor earthquake hazard.A com- puter file search for epicenters within approximaely 200 miles of the site is summarized on Exhibit 4.The epicenter indicated 15 to 20 miles southeast of the Lower Falls site is believed to be a duplicate report (NOAA,1982)of the 5.1 M event for September 7,1976 shown southeast of the Chikuminuk Lake site. Present information indicates that the rock encountered in tunnel excavations will be blocky,competent material which can be excavated with only moderate support requirements.The long axis of an underground powerhouse could be oriented approximate- ly N20°E.Pattern rockbolts and shotcrete would be required in the powerhouse excavation. Ten to 15 feet of weathered surface rock and overburden may have to be removed to reach an acceptable rock foundation. Normal dental treatment/slush grout procedures and a convention- al grout curtain should he expected. Drainage of the abutments may also be required to assure stability under high reservoir head,but no unusally expensive facilties are envisioned at this time. The surface spillway would involve a large rock cut.The principal adverse effects of rock structure on the stability of the curving leftside spillway cut will he created by hedding and,in the downstream portion,the N-S striking east dipping joint set.The other two joint sets dip steeply (70°-80°)and should not adversely affect the stability of properly designed rock cuts.Detailed design would call for benching,appropriate rock support systems,and careful study of the slope ahove any major cut will also be required to determine the potential for creep of soils and talus. II INO Road access to the site can best be gained along the right bank from the downstream.This would involve one or two large culvert-and fill-sections,minor rock trimming,and heavy stone shoulders extending the roadway into the edge of the stream flow.Left bank access is not recommended since it would in- volve extensive undercutting of the steep valley walls.Access to the left abutment for construction of the left bank diversion tunnel most probably would involve building a temporary bridge crossing about 2,000 feet downstreamn from the axis. A construction camp can be located conveniently in the downstream terrace area. No unusual foundation problems are envisioned in developing a landing strip on the right bank to integrate with the access road system. Kisaralik River -Golden Gate Falls The Golden Gate Falls dam site is located (NW 1/4,S28, T5N,R62W)on the Kisaralik River about 58 miles east-southeast of the City of Bethel and 35 river miles downstream from the outlet of Kisaralik Lake.The Golden Gate Falls site geology is shown on Exhibit 6. The dam site is characterized by low-grade metamorphism consisting of interbedded green graywacke and siltstone,with lesser amounts of pebble grit and conglomerate.The graywacke is typically very hard and strong,and is closely to moderately fractured.Dominant bedding orientation range from N40-50°and dips 51°-67°NW.A minor bedding orientation at the location of the proposed foundation has a strike of NI1O°W and a vertical dip.Major feature orientations are N40°E,55°NW along bedding planes and N84°E,62°NW.Most fractures are either closed or quartz-filled and can usually be traced across the Kisaralik River. Greenstone Ridge trends directly southwest of the left abutment and is a massively bedded green amphibole and chlorite schist sequence interbedded with metachert.The ridge is bound- ed on the west by the Golden Gate Fault,a large reverse fault that dips steeply to the southeast and upthrown on the southeast side. Overlying the bedrock on the lower reaches of each abutment is 10 to 15 feet of colluvial soils.Colluvium thins upslope where,in many places,it is on the order of six feet or less. On the right abutment a notch in the bedrock at the approximate crest elevation for a 200-foot high concrete dam could encounter II-3 20 to 40 feet of weathered rock and soils.This appears to be an old relict channel. The construction of a rockfill dam at the site would require impervious fill material which is not available in the area.A concrete gravity dam could be located here and keyed into the strong,competent bedrock.Moderate foundation treat- ment would be required.Alluvial sand and gravels suitable for fill could be mined from the active floodplain upstream.The terraces of the Kisaralik River are cut on bedrock and probably would not yield the required aggregate quantities.Potential riprap sources are available downstream in the Kuskokwim group, which could yield blocks 4 to 5 tons each. Construction of a spillway could be done on the left abut- ment and would require cutting back the slope uphill.Maximum allowable cut slopes in the graywacke and siltstone would be on the order of 1H:4vV. The graywacke and siltstone in the abutments are suitable for the construction of underground openings,and the gently sloping surface area north of the right abutment appears to be Suitable for location of a surface powerstation.The stand-up time for underground openings should be excellent. Construction camp and facilities could be located behind the hill on the right abutment.Permafrost is probably present in the glacial outwash soils mantling the area.Therefore, structures will have to be constructed above grade to avoid thawing of the permafrost. Kisaralik River -Upper Falls The Upper Falls dam site is located (SW 1/4,S7,T3N,R61W) on the Kisaralik River about 70 miles east-southeast of the City of Bethel and 20 river miles downstream from the outlet of Kisaralik Lake.The Upper Falls site geology is shown on Exhi- bit 7. Upper Falls consists of two separate vertical drops. Graywackes and siltstones of Late Cretaceous Age (Hoare et al., 1959)outcrop in both abutments at the site.The graywacke weathers to a dark brown color,is hard,strong,and occurs in massive outcrops up to 70 feet thick.Individual beds from 1 to 6 feet thick were observed in the massive outcrops.The graywacke strikes N 30°E and dips 52°SE (upstream).The graywacke beds outcropping in the abutments can be traced con- tinuously across the creek and form the upstream and downstream falls where they cross the river channel. II-4 The graywacke outcrops at the dam site are separated by a siltstone bed approximately 100 feet thick.The siltstones are dark gray to black,moderately hard,moderately strong and part readily along bedding planes 1/4 to 1/2 inch in thickness. Graywacke interbeds up to 8 inches thick were observed in the siltstones on the right abutment.The siltstones are less resistant to weathering than the graywackes and form the rapids between the upstream and downstream falls. No predominant joint set was observed in either the gray- wackes or the siltstones.The graywackes parted along bedding planes to form large irregularly shaped blocks up to 2 feet across.The siltstones tended to part along their bedding planes to form thin flat plates up to 1 inch across. The site appears to be suitable for construction of either a rock fill or concrete gravity dan.Excavation 5 to 10 feet deep would be required to expose unweathered rock in both abut- ments.The upstream and downstream toes of the dam should be founded on the massive graywacke outcrops that form the falls. Foundation treatment to prevent seepage through both the abut- ments and beneath the toe of the dam should be minimal at this site. Based on the rock exposed in the left abutment,it is concluded that bedrock is probably continuous beneath the flat broad bench topping the left abutment and occurs within 10 to 15 feet of the surface.Due to erosion by the Kisaralik River,the bedrock surface beneath the bench will be irregular and the depressions in the bedrock surface will be filled with alluvial gravels. Alluvial gravels are exposed in the active flood plain of the Kisaralik River immediately upstream of the proposed dam site.However,boulder and cobble size material observed in this area could pose problems for cellular cofferdam construc- tion. With the exception of impervious fill,construction materi- als for a rockfill dam are available in the project area.The graywackes (Map symbol Kg)are hard,strong and would be suita- ble for use as rock fill and rip rap.It may be possible to develop a quarry uphill from the dam site on the right abutment in the vicinity of the graywacke outcrops.It should be possi- ble to produce rip rap stone up to four to five tons in weight through controlled quarry blasting.The siltstones will proba- bly not produce material acceptable for use as either rip rap or armour stone. II-5 Alluvial gravels could be mined from either the active flood plain or terraces of the Kisaralik River.Based on the terrace length of 3000 feet and a width of 800 feet,it is esti- mated 1 million cubic yards of gravel would be available within 15 feet of the surface.Sporadic permafrost may be present in the terrace gravels. The siltstones and graywackes exposed in the right abutment appear to be suitable for the construction of underground cham- bers.Chambers with a length to span ratio greater than 2 should be oriented with the long axis northwest-southeast.This will result in placing the bedding planes in the slates and graywackes parallel to the span of the opening.Permafrost may be present in the right abutment and seepage along bedding planes in the siltstones could be a problem.Rock bolting and other support measures will probably be required in the silt- stones. The bench topping the left abutment is 900 feet wide at the dam site and lies at an elevation of 1020 feet.Local differ- ences in topography across the bench are on the order of 5 to 10 feet.This area could be utilized for construction facilities. Kipchuk River The dam site is located (NW 1/4,S19,T8N,R56W)on the Kipchuk River 90 miles east of the City of Bethel.The Kipchuk River site geology is shown on Exhibit 8. Two potential dam site locations were visited on the Kipchuk River.At both locations,Tertiary volcanic tuffs are overlain by basalts of Tertiary age (Hoare,et al.,1959).The tuffs and basalts outcrop and are well exposed in the right abutment.The left abutment is composed mainly of colluvial and slump deposits derived from the weathering of the basalts and tuffs.The slump deposits are composed primarily of wet to saturated plastic silts containing basaltic rubble.Occasional highly fractured basalt outcrops in the left abutment generally at elevations greater than 1,100 feet.An isolated outcrop of volcanic tuff was found in the left abutment at the waterline at elevation 910 feet.No tuff outcrops were found in the left abutment above elevation 910 feet.This suggests the left abut- ment is downfaulted relative to the right abutment. The construction of a rockfill dam at either location would require extensive excavations in the left abutment.Estimated minimum excavation depth in the left abutment at Location 1 would be on the order of 20 to 30 feet.Sporadic permafrost is probably present in the colluvium along the left abutment.If II-6 encountered,ripping and/or light blasting may be required to excavate the permafrost. At both locations the right abutment would be founded in the volcanic tuff.Although it was not possible to visit the tuff outcrops on the right abutment,at Location 1 they were standing vertically and appeared well indurated.The contact between the tuffs and the overlying basalts occur at an eleva- tion of 1200 feet in this area -well above potential reservoir elevations.The contact between the tuffs and basalts strikes approximately N 30°E and dips 16°to the NW.Poorly developed columnar jointing was observed in the basalts.No evidence of major jointing was observed in the underlying tuffs. The tuffs in the right abutments at Location 2 appear to be more heavily weathered than those at location 1.However,a fairly continuous cover of basaltic talus obscures the tuff in this area.It is estimated that a minimum of 10 to 15 feet of the weathered tuff would have to be excavated to expose sound rock in the right abutment at Location 2. The tuffs underlying the river bottom at both locations will probably support the loads imposed by a rockfill dam. However,extensive foundation treatment will probably be required to prevent seepage beneath the toe of the dam.The tuffs in the river bottom appear to be overlain by a relatively thin veneer of cobble and boulder size material that would pre- clude construction of a cellular cofferdam. Construction materials for a rockfill dam appear to be available within the project area.The plastic silts (Map Symbol Oc and Os)may be suitable for use as impervious core material.Processing to remove the hasaltic rubble would be required.The basalts (Map Symbol Tvb)are hard,strong and would be suitable for use as rockfill and rip rap.Based on the degree of fracturing and weathering observed in the basalt out- crops in the left abutment,it should be possible to produce rip rap stone up to 2 to 3 tons through controlled quarry blasting. Quarry spalls could be used as rock fill.The tuffs probably will not produce material acceptable for use as rip rap. Alluvial gravels could be mined from either the active flood plain or terraces of the Kipchuk River upstream from the line shown on Exhibit 8.Based on a floodplain width of 300 feet and a length of 5000 feet,an estimated 500,000 cubic years of gravel could be available within 19 feet of the surface. Permafrost probahly does not exist within the active flood plain but may be encountered in the terraces. TI-7 Construction of a spillway on rock in the left abutment at Location 1 would require removing a minimum of 20 to 30 feet of colluvial material.A large rotational slump was observed in the spillway area at the location shown on Exhibit 8.This slump is approximately 400 feet wide and extends 300 feet into the left abutment.The crest of the slump scarp lies at eleva- tion 1030 feet.The slumps are probably caused by the thawing of permfrost (ice)in the thaw unstable colluvial soils.A spillway could be founded on the tuff exposed in the right abut- ment at Location l. Construction of a spillway on rock in the left abutment at Location 2 would require excavating a minimum of 10 to 20 feet of colluvial material.A spillway founded on the tuff exposed in the right abutment at Location 2 would require cutting back the slopes uphill of the spillway.Maximum allowable angles for cut slopes in the basalts and tuffs will be on the order of 1H:4V.Allowable slope angles for the colluvial material will vary depending on the moisture content and the presence of permafrost.Natural slopes in the right abutment soils were observed to vary from a maximum of 40°in the colluvial material to near horizontal in the slump areas. The tuff exposed in the right abutment is a preferred loca-- tion for the construction of underground openings.Underground openings constructed in the tuff will probably require extensive rock bolting and/or grouting.Creep would be a problem espe- cially in large openings such as for the powerhouse.Diversion, tailrace,and penstock tunnels will probably have to be lined. Construction camp and plant facilities could be located on the bench uphill from the left abutment at an elevation of 1150 feet.The bench is approximately 400 feet wide at this point and runs sub-parallel to the Kipchuk River for approximately 2000 feet. Permafrost is probably present in the colluvial soils mMantling the bench.Therefore,structures such as construction camp and shop buildings would be constructed above grade. Upnuk Lake The Upnuk Lake dam site is located (SW 1/4,S36,T3N,R55W) on the outlet creek of Upnuk Lake about two miles downstream from the outlet.The site is about 110 miles east-southeast of the City of Bethel.The outlet creek is an unnamed tributary to the Tikchik River.The Upnuk Lake site geology is shown on Exhibit 9. II-8 No bedrock was observed at either the dam site or along the penstock alignment.The entire project area appears to be overlain by glacial drift (Map Symbol Qd).The glacial drift is composed of poorly sorted sand and gravel and contains cobble and boulder size material.Based on the thickness of drift exposed in the outlet creek and its tributaries,and the distance to the mountains west of the project area,estimated depth to bedrock could be in excess of 100 feet at the dam site. Sporadic permafrost is probably present within the glacial drift in the divide between Upnuk and Chikiminuk Lakes,as well as in the colluvium (Map Symbol Qc)mantling of the upland areas.Many small slumps were observed along the banks of the outlet creek and its tributaries.These slumps could be the result of thawing of the permafrost within the glacial drift and solifluction.Permafrost is probably not present along the shores of Upnuk and Chikuminuk Lakes due to their warming effect. Milk Creek The Milk Creek dam site is located (MW 1/4 S21,TIN,R58W) on Milk Creek,a tributary to Chikuminuk Lake,about nine miles upstream from its mouth.The site is about 95 miles east-south- east of the City of Bethel.The Milk Creek site geology is shown on Exhibit 10. An area suitable for airstrip construction lies 4 miles northeast of the project area.Variations in local topography in this area could require large fill volumes along the runwayalignment.Aircraft approaches from the southwest to this alignment would be poor. Access road construction from the airstrip to the camp site would be difficult due to the number of side hill cuts,high fills,and bridges required.Construction of the access roads would require steep side hill cuts which would probably have to be supported with retaining structures. The rock exposed on the left abutment belongs to the Gemuk Group (Map Symbol Kcg)-an interbedded sequence of thin bedded shales and massively bedded graywackes standing at natural slopes of 1H:4V and steeper.The shales appear to be very weak and soft.The graywacke tends to be resistant to weathering and is hard and strong.The shales and graywackes strike N60-85°W, and dip 75°to 90°SW.The left abutment is composed primarily of shale;seepage zones are evident at the shale/graywacke con- tacts.Large scale rock slope failures are present above the left abutment immediately upstream of the proposed dam site at elevations greater than 1200 feet. II-9 No rock outcrops were observed on the right abutment.The right abutment is composed of unconsolidated glacial outwash Material estimated to be 50 to 200 feet thick which appears to thin downstream.The outwash is composed of sands and gravels with numerous cobbles and boulders.Slump deposits or landslide scars in the glacial outwash deposits are evident near the pro- posed dam alignment and along the downstream area.The crest of the right abutment is flat and has poorly developed drainage indicating that permafrost may be present. The Milk Creek Dam site is located along the strike of the Milk Creek Fault,which can be traced for approximately 25 miles in this area.The right abutment appears to be downthrown rela- tive to the left abutment.Some evidence of strike slip move- ment was observed in the lateral offset in a graywacke bed in the left abutment.Most of the streams draining into the pro- posed reservoir area appear to be fault controlled.As a result of poor access conditions,extensive faulting in the dam and reservoir area,and weak abutments,the Milk Creek site was eliminated from further study. II-10 % CHIKUMINIK LAKE SCALE 0 400 800 FEET La a 1”=800' NOTE: Base map topography enlarged from USGS Quadrangle sheets 1:63,360 series. irstrip Tee ROCKFILL DAM ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CONCEPTUAL PROJECT PLAN CHIKUMINUK LAKE DOWNSTREAM SITE HARZA ENGINEERING COMPANY December 1982 EXHIBIT 2 VICINITY MAP POWER ree | Ss \ ACCESS ROAD ACCESS TUNNEL UNDERGROUND FOwERSTATION{ 1 URGE CHAMBER[nade : -TAILRACE TUNNEL \) 650 q SPILLWAY ROCKFILL DAM BRIDGE SCALE 0 800 FEET400 ALASKA POWER AUTHORITY Ly |4 _] 1”=800°BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT NOTE: Basemap topography enlarged from USGS Quadrangle sheets 1:63,360 series. CONCEPTUAL PROJECT PLAN CHIKUMINUK LAKE UPSTREAM SITE HARZA ENGINEERING COMPANY December 1982 OTNeTee,«CHIKUMINUK LAKE Me 'DRY”VALLEY 100-200 cfs Aug.982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation)LegitBoREMAStonesiat or <5Sft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Preliminaryrefractionlineshown between X-X SCALE 0 200 400 FEET l 1 ] 1"=400' ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) ator <5ft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Preliminary refraction tine shown between X-XCHIKUMINUKLAKE Island El. 200 400 FEET i } 1"=400° ALASKA POWER AUTHORITY 'DRY”VALLEY 100-200 cfs Aug.,1982 BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT SITE No.7 CHIKUMINUK LAKE SITE GEOLOGY po _- HARZA ENGINEERING COMPANY December 1982 CHIKUMINUK LAKE 'DRY”VALLEY 100-200 cfs Aug.1982 SITE No.1 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) at or <5ft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Preliminary/”refraction line shown between X-X SCALE 0 200 400 FEET ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) ator <5ft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Preliminary refraction line shown between X-XCHIKUMINUKLAKE SCALE 0 200 400 FEET ALASKA POWER AUTHORITY 'DRY”VALLEY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT100-200 cfs Aug.,1982 SITE No.1 CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 es vara [ +r wr,meresPieneanen o60 a=» ©4 eo aed €oy E . 2s e [ee] ° =8= c = €e 4-x Be) 5° € E§ x e¢-£we * a x36 = s fo} bad £ See u 2 e >Ye ° s von } c = _ z=§2fe¢ = sE2% Oo} 3g$5*83gEF $5Ex i4 _ S2aE%xVy, 9x SES§ ro)8€ S 8.8 2 . wes ul§88&€gee =F§ Fee 4 a Os O a2 w« N5eaLAKECHIKUMINUK .+605IslandEl 2SITENo.600 400 FEET200SCALE0 1”=400' ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT LAKE SITE GEOLOGY CHIKUMINUK HARZA ENGINEERING COMPANY December 1982 SRA Lag labresccaaie VALLEY 200 cfs 982 'DRY 100 Aug 1SITENo CHIKUMINUK 600 'SITE No.2 Q 'ORY VALLEY 100-200 cfs Aug.1982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) ator <5ft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Preliminary refraction line shown between X-X SCALE 0 200 400 FEET La 1"=400' ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY see eee ee a December 1982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Aliluvium Bedrock (Gemuk Formation) ator <5ft.from ground surtace Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Preliminary CHIKUMINUK \REESE oe 3s 4 Baha:abr eee fe Es wee isan',oe 43 PES OS refraction fine shown between X-X Island El.+605 NAS SITE No.2 YQN 600 SCALE 0 200 400 FEET La ALASKA POWER AUTHORITY 'DRY VALLEY ::Tt 0 500 vy Sa eenenneane 100-200 cfs \ -ph BETHEL AREA POWER PLAN Aug.1982 FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY a eee eee December 1982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) ator <5Sft.from ground surface Strike and dip of strata Shear zone Recent land stump ao£Ecx=gisLawx=exore|os2G-% £5eSSEeof&zeereo1.sYNowLAKECHIKUMINUK *605IslandEl. g00 SITE No.2 400 FEET200SCALE0 1°=400° "VALLEY 200 cfs 'DRY 100 982Aug. z<b » rjaw} wy < « x a o/@y {>2 zioo ae o!lS 2/24 wSo|® < - eijaW” >Ozro wig Zw (fg yw> =0 [wit o, Wwe = rig 0 CT, >w iolyg </4S3;, Yk Zia BigP, FA 718! «WOH = i« tila O le"owsaPd ot: , { ©2uwEe” EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) ator <5ft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Preliminary refraction line shown between X-XCHIKUMINUK Island El.+605 »a x ee :pny Ne/a nies)fee nee®wyee eoxSCALE 0 200 400 FEET Y L i J ALASKA POWER AUTHORITY 'DRY”VALLEY 100-200 cfs Aug.,1982 BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT < CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY -_-,December 1982 CHIKUMINUK LAKE 'DRY”VALLEY 100-200 cfs Aug.1982 SITE No.1 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) at or <5ft.from ground surface Strike and dip of strata Shear zone Recent land siumop Zone of weak rock or channel fill Preliminary refraction tine shown between X-X 200 l 1 400 FEET ALASKA POWER AUTHORITY 'BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moratne and /or stope wash Outwash Aliluvium Bedrock (Gemuk Formation) ator <5Sft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock \era Bo "14 au $:.Bs;ee 'SERS ¥fe rattan or channel fill Preliminary * ' 4 <"a Q et oo *ba .is et ee Bas 2.%"i '4 v $e:aad n -3 =ere :e:,ft af Y .NS refraction line shownLAKEEeeLrLERANEneae'et eis Kae refraction lineCHIKUMINUK SCALE 0 200 400 FEET La 1°=400° ALASKA POWER AUTHORITY eee a'DRY'VALLEY 100-200 cfs » Aug.,_1982 . BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE GEOLOGY Pe _oe ee ee ee HARZA ENGINEERING COMPANY ee December 1982 ” - | b 8 > > i. -2 a i £ £ e&2 £ - z | x c E ae = Es uw Soe: 1>| x rc Ee w<¢€E . ariI ue rit w (Zz. Ww 3 ° E Sere Er} ao & » 2xr ° 5 Caw oO ci2¥> |¢ <& 3 Eo 2 = xrmex & 9,mM<q 12 © =&g& ® S20 7] ivy) a8'Bigo%ss 9° 22¢ za.% >Ww ,° Lal® za ¢ i] c € fo] z= eSec <ow Swwoi; Pile Wug33% Vy © N - SCe$ o ¢ eian DO|z. (as) a c 8.8 cy . c So oS4nu w <2wW : rf33 cS 8 x % o wig3 4 i sid 2 iw,'8a5 BSS =f 23 5°55 - Fiur| sO'wiea)ie Os'o)ana"wvcx Nolo Cciaok Sw (zig<|"2"ie1Zz16 Y o=- xi4a = Wn ,we . |W x= <. *y w < ”Oo rr ° 0 2 z,i« ia 3 er ; soy a } :1 4'©9 (ot! 2x | SITE No.1 982 'DRY”VALLEY -200 cfs100 Aug SITE No.2 *605IslandEl. LAKE 600 CHIKUMINUK CHIKUMINUK Island El.+605 'DRY VALLEY 100-200 cfs Aug.,1982 a riresoeOKeras..Ta ONa D SITE No.1. EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) at or <_5ft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill Pretiminary refraction line shown between X-X SCALE 0 200 400 FEET l nl } ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE.GEOLOGY HARZA ENGINEERING COMPANY December 1982 CHIKUMINUK island El. EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Aliuvium Bedrock (Gemuk Formation) ator <Sft.from ground surface Strike and dip of strata Shear zone Recent land slump Zone of weak rock or channel fill,Preliminary refraction line shown between X-X SCALE 0 200 400 FEET La 1°=400' ALASKA POWER AUTHORITY 'DRY'VALLEY 100-200 cfs > Aug.1982 : BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 EXHIBIT 3 LEGEND Recesstonal Moraine Ground Moraine and /or slope wash Outwash Alluviem Bedrock (Gemuk Formation) ator <5ft.from ground surface Strike and dip of strata Shear zone Recent land stump Zone of weak rock or channel fill)Preliminary refraction line shown between X-XCHIKUMINUKLAKE Island El.+605 SCALE 0 200 400 FEET La ALASKA POWER AUTHORITY 'DRY”VALLEY 100-200 cfs Aug.,1982 BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT .ta _SITE No.1 CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY eee December 1982 EXHIBIT 3 LEGEND Recessional Moraine Ground Moraine and /or slope wash Outwash Alluvium Bedrock (Gemuk Formation) sulle at or <5ft.from ground ran surface Strike and dip of strata Shear zone Recent land stump Zone of weak rock or channel fill Preliminaryrefractionlineshown between X-XCHIKUMINUK Island El.+605 SCALE 0 200 400 FEET esrenee| 1”=400° ALASKA POWER AUTHORITY 'DRY VALLEY 100-200 cfs Aug.,1982 BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT SITE No.1 CHIKUMINUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY .December 1982 extwie 164°W 183fw 1620 (161"W 160"159°H 158"157" EXHIBIT 4 156"15S"WIS4'HIS3'W 624 x 6yNag| ie] o 0 x o °x °62°N x o x fe]0 0 le] o 61°NBethelLOWERFALLS0x-= +LAKE CHIKUMINUK =? (s)fe)ie)o @ o {(Xp '0 *"ON 6O'N {°60N 5.1M x x ""Sept.7,1976 °@ Dillingham 59°N 4 so'n aRsanBRISTOLBAYA cen ie] 57°..+:.-+.:,57° 105°W 164'W 163 1G2"wtSI*W 80H 159°H)158°WS7"W ISTH LSS'SA"ISO" MAGNITUDENGSDC/EDIS/NORA =BOULDER,COLORADO --a 1276 EARTHOURKES PLOTTED x 3.9945.99 82/08/25.14.28.38.&5.99 8.00 ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT REGIONAL SEISMICITY HARZA ENGINEERING COMPANY December 1982 DAM SITE f>Ly xx a Sa SoeFESO,eeecesereens Mm me -_--__LEGEND: , ALASKA POWER AUTHORITY , SCALE 0 200 400 FEET BETHEL AREA POWER PLAN l l _}FEASIBILITY ASSESSMENTSlopewashandtalus,vegetated 4 Strike and dip of bedding 7"=400° Bedrock,Gemuk Formation,Zz ...KISARALIK RIVERveryhard,fine grained meta ce Strike and dip of joint zone LOWER FALLSvolcanics/meta sedimentary rock, exposed at surface SITE GEOLOGYHardingLawsonAssociates 10'-15'Sand/Gravel Bench r==Engineers,Geologists &Geophysicists {lhHARZA ENGINEERING COMPANY December 1982 AINZ{<,GOLDEN GATE FAULT ---- a,_EXHIBIT 6RRR,Tere (Location off Map)TO N LOCATION OF POTENTIAL RELIEF - CHANNEL LEGEND: ul Outwash deposits ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT XN4.4/ )DOS Schist and Metachert KKS Kuskokwim Group interbedded graywauke,siltstone,pebble grit and conglomerate KISARALIK RIVER GOLDEN GATE FALLS Harding Lawson Associates SITE GEOLOGY Engineers,GeologistsSCALEO400800FEET=8 GeophysicistsLH.tO 4 HARZA ENGINEERING COMPANY 1”=800 December 1982 Le POTENTIAL BORROW AREA UPSTREAM OF THIS LINE a a "t:]Qa Alluvial sands and gravels Coliluvium:chiefly frost derived rubble intermixed with windblown silts Kkg Graywackes of the Kuskokwim Group Mh A 50 Kks Siltstones of the Kuskokwim Group a Contacto” Strike and dip measured in field EXHIBIT 7 SCALE 0 400 800 FEET La 1”=800' NOTE: Base map topgraphy enlarged from USGS Quadrangle sheets 1:63,360 series. ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT Harding Lawson Associates Engineers,Geologists &Geophysicists -KISARALIK RIVER UPPER FALLS SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 ©| NAL RACTURED BAS OUTCROPS:ABOVE ELEVATION 1100' We SCALE 0 400 800 FEET --" L,f ,Jf K1=800° nw,DNOTE, Base map topography enlarged from Slump Deposits -Colluvial deposits reworked by downslope movement Volcanic Tuffs-Heavily weathered tuffs containing basalt inclusions Vesicular Basalt-Black basalt that weathers dark brown Colluvium plastic silts containing frost derived basaltic rubble Contact Strike and dip estimated in field FAULT U,Upthrown side D,Downthrown side USGS Quadrangle sheets 1:63,360 series. ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT Harding Lawson Associates Engineers,Geologists KIPCHUK RIVER SITE GEOLOGY &Geophysicists HARZA ENGINEERING COMPANY December 1982 UPNUK LAKE atmred>.ryyaefLEGEND: 7 Inferred Contract Qd_Glacial Drift -Poorly sorted sand, gravel and boulders Qc Colluvium -Frost derived rubble locally includes reworked Od Keg Gemuk Group -undifferentiated fine grained siliciceous rocks SCALE 0 1/2 1 Mi Lf,J "=1 Mi ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT Harding Lawson Associates Engineers,Geologists &Geuphysicists UPNUK LAKE SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 MARSHY TS A tT ee, SCALEQO 400 800 FEET L.|4 J 1"=800° NOTE: Base map topography enlarged from USGS Quadrangle sheets 1:63,360 series. EXHIBIT 10 Slump Deposits-Colluvial and glacial outwash deposits reworked by downslope movement Glacial Drift-Unsorted and poorly sorted sand,gravel, and boulders:Small areas of outwash,colluvium and alluvium included with unit Gemuk Group-Undifferented chiefly massive to thin- bedded,fine-grained,silliceous rocks,some volcanics, siltstone,and limestone and varicolored argillitic shale Fault (U,Upthrown side:D,Downthrown side) Solid where clearly interpreted: Queried where inferred,dashed where approximately located Strike and dip estimated in the field Slump ALASKA POWER AUTHORITY BETHEL AREA POWER PLAN FEASIBILITY ASSESSMENT MILK CREEK &Geophysicists Harding Lawson Associates Engineers,Geologists SITE GEOLOGY HARZA ENGINEERING COMPANY December 1982 -