2007-10-31_REVISION - M2006080 (2)

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II. SUBSURFACE CONDTTIONS 2.01 Lyman Henn Investigations Lyman Henn completed 28 test borings along or neaz the proposed slurry wall alignment to characterize subsurface conditions. Lyman Henn retained Dakota Drilling of Denver, Colorado as the drilling subcontractor. These borings were advanced to investigate general subsurface conditions and to obtain soil samples to aid in the detemunation of engineering properties along the proposed slurry wall alignment. Prior to drilling, the alignment was staked at 100 ft centers by CDS Engineering. The boring locations were selected and staked by Lyman Henn using the CDS stakes as a reference. The test boring locations aze shown in plan view on Sheet 102. A summary of test boring results is presented in Table I. Test boring reports are included in Appendix A. The test boring program included 4-1/4 inch diameter hollow-stem auger drilling in the soils and bedrock, NQ- core drilling in bedrock in 16 of the boreholes, drive sampling of the soil and bedrock, and bedrock in-situ permeability (packer) testing in 16 boreholes, Test borings revealed alluvial soils overlying sedimentary bedrock. The alluvial soils consist of a fine alluvium (overburden) extending from the ground surface to depths ranging from 4 ft to 19 ft below ground surface (bgs) and coazse alluvium (sand and gavel) extending below the overburden to the top of bedrock. Overburden was encountered in all but three of the borings (LHP-3, LHP-5, and LHP-6), as indicated on Table I. The depth to the top of bedrock ranged from 19 to 25 ft bgs, with an average depth of 21 ft bgs. Bedrock elevations ranged from 4787.1 ft to 4802.6 ft. The overburden consisted primarily of sandy lean clay and clayey sand, as well as limited amounts of silty sand and poorly graded sand with clay. The sand and gravel consisted of wel]- to poorly-graded sand and gravel, sometimes with clay and silt. The sedimentary bedrock consisted of highly weathered to slightly weathered, blue and gray shale, clay shale, claystone, siltstone, and fine grained sandstone of the Pierre Shale Transition Zone. The general bedrock conditions encountered during the coring of borings LHP-1 through LHP- 16 generally consisted of highly to moderately weathered, fractured, sandy, clay shale and shale underlain by nearly massive to massive, moderately weathered to fresh clayey sandstone and sandy claystone. The fractured clay shale and shale were highly jointed and packer test permeability results indicated this lithologic unit is relatively permeable with results of 10"3 and 10~ cm/sec. The fractured clay shale and shale range from approximately 7 ft to approximately 18 ft, averaging 13 ft in thickness. The fractured clay shale and shale appear to become sandier with depth, eventually becoming a massive clayey sandstone /sandy claystone. The massive clayey sandstone encountered generally had higher RQD and lower permeability (10.5 to 10.6 cm/sec) than the overlying fractured clay shale and shale. A total of four samples of the bedrock were tested for unconfined compressive strength with results ranging from 125,655 pounds per squaze foot (psf) to 303,319 psf The hydraulic conductivity of the bedrock was variable across the site and ranged from G:\PROIECTS\10'!0'.1-000 Lovelavd Ready Mu Shury WaII~R. Rttvrds ~ Cortapondevice~R.l l Repvns~Fi~W Shirty Wall Desiyv Repvn.do<