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proposed projects near the site in May 2006 and the winter of 2007 were used in the analysis and <br /> design of the Southwest Reservoir Slurry Wall. The borings extended 40 to 50 feet below the <br /> existing ground surface. The locations of the exploratory borings are shown on Figure 2. The <br /> borings were logged by and engineering geologist as the drilling progressed and samples were <br /> obtained of the various soils and bedrock encountered. One of the borings was cored a minimum of <br /> 10 feet into the bedrock to obtain undisturbed samples of the Pierre Shale. A Packer permeability <br /> test was performed in the bedrock in this test hole to provide information on the bedrock <br /> permeability. <br /> Summary logs of the exploratory borings used in the design are provided on Figure 3 with the <br /> locations as surveyed by handheld GPS coordinates for northing, easting, and elevation at each <br /> boring. <br /> Laboratory Testing <br /> Samples of the soil and bedrock were tested in the laboratory for various physical and engineering <br /> properties, including: grain size analysis, Atterberg Limits,percent passing the No.200 sieve, <br /> moisture content and dry density. The sands and gravels ranged from 4.6 to 20.3 percent passing <br /> the No. 200 sieve, and classified as well graded sands with gravels to well graded sands. The fill <br /> and overburden soil samples encountered ranged from 29.6 to 76.6 percent passing the No. 200 <br /> sieve. The liquid limit and plasticity index ranged from 24 to 54 and 6 to 33, respectively. The fill <br /> and overburden soils classified as clayey sands-silty sands and low to high plasticity clayey soils. <br /> Samples of available supplemental fines for the slurry backfill were laboratory tested for percent <br /> passing the No. 200 sieve and Atterberg Limits. The supplemental fine samples ranged from 91.4 <br /> to 99.6 percent passing the No. 200 sieve. The liquid limit and plasticity index ranged from 42 to <br /> 84 and 12 to 56, respectively. The supplemental fines classified as high plasticity clay to silt. The <br /> results of the laboratory tests are summarized on Table 1. Laboratory data sheets are included in <br /> Appendix A. <br /> Subsurface Soil and Bedrock Conditions <br /> The site stratigraphy identified in the exploratory borings includes five geologic units. These units <br /> include: 1)Pierre Shale Bedrock, 2) alluvial sands and gravels, 3)thin mud lenses were <br /> occasionally encountered on-site, 4) clayey overburden soils were located near the surface, and 5) <br /> clayey and silty soils native to the site and used as fill were encountered in the test holes. In <br /> general,the subsurface geology consists of approximately 1 to 12 feet of overburden soils and/or fill <br /> and approximately 15 to 30 feet of loose to very dense sand and gravel soils. Areas of sandy clay to <br /> clay unit, typically referred to as "mud lenses",were encountered in the sand and gravel units of a <br /> couple of test holes during the geotechnical investigation at the Southwest Reservoir site. The mud <br /> lenses encountered were approximately 1 foot thick within the sand and gravel unit. Other areas of <br /> mud lenses may be encountered during excavation of the slurry wall. <br /> The bedrock generally consisted of stratified, locally platey, clayey to silty shale and is very thinly <br /> bedded,hard to very hard, dry and dark grey with some fossils along with minor interbedded <br /> limestone beds and lenses. At the soil-bedrock interface,there is locally a weathered zone of shale <br /> two to three inches thick, characterized by thin zones of oxidation between the shale beds. <br /> Excavation into suitable shale bedrock should provide an effective seepage cutoff. Areas of <br /> SW RESERVOIR SLURRY WALL DESIGN REPORT PAGE 2 <br />