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3.3 Bedrock <br /> Colton(1978) maps the bedrock at the project site as the Lower Member of the Pierre Shale, <br /> which is described as a dark to light gray shale with interbedded sandstone and siltstone, and <br /> some concretionary limestone. The Pierre Shale underlies the alluvial deposit along the entire <br /> project site. In the reservoir floors of Treiber A and Overland Ponds Pond 2,bedrock appears <br /> to underlie a thin layer of overburden consisting of sand, silt, and organics. Similar conditions <br /> were assumed to existing in Treiber B. The bedrock encountered during test pit excavation <br /> had a relatively thin weathered zone approximately one or two feet thick, which is typical of <br /> bedrock in the area. <br /> The thickness and occurrence of the overburden and alluvial units within Overland Ponds <br /> Pond 2, Treiber A, and Treiber B is variable. In addition, these individual units, including <br /> bedrock, will likely vary in composition and type across the project site. <br /> G E I Subsurface Conditions 1 9 <br />