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Slurry Wall Design Report <br /> Loloff Pit <br /> 5/24/2016 <br /> Page 5 of 16 <br /> 3 SUBSURFACE CONDITIONS <br /> 3.1 Regional Geology <br /> The project location consists of gravels and alluvium including Piney Creek, Broadway and <br /> Louviers (Tweto 1979). According to the geologic map of the Boulder, Fort Collins, Greeley <br /> area, the site contains Post-Piney Creek Alluvium and eolian deposits. The Post-Piney Creek <br /> alluvium is from the upper Holocene and is comprised of sandy to gravelly alluvium with <br /> scattered plant remains. The eolian deposit is from the upper Holocene to Bull Lake Glaciation <br /> and is comprised of deposits of windblown clay, silt, sand, and loess. <br /> Bedrock in the Greeley area consists predominantly of the Pierre Shale Formation, particularly <br /> the upper shale unit and the upper transition member. The upper transition member contains <br /> beds intermediate in character between the Pierre Shale and the Fox Hills Sandstone, and its <br /> assignment has therefore always been controversial. This member is composed of friable <br /> sandstone and soft shaley sandstone containing thin-bedded sandy shale and large calcareous <br /> sandstone concretions. <br /> The upper shale unit of the Pierre Shale is chiefly silty shale that contains beds of gray- or <br /> brown-weathering silty calcareous concretions, iron-stained limestone concretions, and brown to <br /> dusky-red ironstone concretions. <br /> 3.2 Summary of Subsurface Materials <br /> Test borings revealed alluvial soils overlying sedimentary bedrock. The alluvial soils consist of a <br /> fine to coarse alluvium (overburden) extending from the ground surface to the top of bedrock. <br /> Overburden was encountered in all of the borings, as indicated on Table I. The depth to the top <br /> of bedrock ranged from 39.1 to 105.0 ft bgs, with an average depth of 62.1 ft bgs from the <br /> existing ground surface. Bedrock elevations ranged from 4556.5 ft to 4595 ft. All borings were <br /> surveyed by Morning Star Survey, LLC. of Johnstown, CO. At the time of this report writing, the <br /> alignment has not been surveyed. The alignment will be surveyed prior to start of construction of <br /> the slurry wall. <br /> Fine alluvium consists primarily of clayey sand, sandy lean clay, silty sand and silt, while coarse <br /> alluvium consists of well graded sand, well graded sand with gravel, poorly graded sand and <br /> poorly graded sand with gravel that contain an average of 12% fines. The sedimentary bedrock <br /> consisted of completely weathered, tan-orange/light-brown to fresh, blue-gray/dark-gray shale of <br /> the Pierre Shale Formation. The extent of weathering in the bedrock appears to occur within the <br /> upper 0 to 6 ft of the bedrock. The bedrock rock quality designation (RQD) ranged from 0 to 72 <br /> percent. Low RQD is an indicator of fractured or completely weathered rock. The fractures <br /> within the cored bedrock are typically described as primarily horizontal, smooth to slightly rough, <br /> planar to stepped, with no infill. <br /> Bedrock typically consists of a laminated siltstone with small interbeds of claystone and clayey <br /> siltstone. Weathered sections appear tan-orange/tan/light-brown in color and grades with depth <br /> to blue-gray/dark-gray/gray/light-gray slightly mottled bedrock. In the southwestern corner of the <br /> pit, silty, clayey very fine-grained sandstone was encountered. Other occurrences of sandstone <br /> beds are anticipated to be present along the proposed alignment. In addition, the subsurface <br /> BRIERLEY <br /> ASSOCIATES <br /> Creating Space Underground <br />