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Memo to Dave Berry <br />Bowie No. 2 Geotechnical Adequacy Responses <br />page 4 <br />the toe of the waste pile, material "4", were also deduced from SPT blow <br />count conversions. <br />WESTEC's stability analysis of the proposed Bowie No. 2 mine's coal waste <br />pile determined the overall static slope stability safety factor of the <br />structure to be 1.54. This calculated static safety factor (SSF) narrowly <br />exceeds the required value of 1.5. If the ultimate waste pile volume, in <br />excess of 225,000 cubic yards of combined waste, coverfill and topsoil <br />were to fail, it could compromise the function and integrity of the <br />sediment pond adjacent to the waste pile toe, and it might compromise <br />the drainage facilities adjoining State Highway 133 and subject the public <br />to an health and safety risk. For this reason the Division requested that <br />BRL obtain samples of each of the three earthen material for which <br />WESTEC assumed strength parameters and determine those properties by <br />appropriate laboratory testing. Based upon its "experience with similar <br />materials in this region, its belief that it considered "conservative <br />saturation condition of all of its foundation materials" in performing the <br />stability analyses, and its opinion that the required SSF value of 1.5 is <br />"relatively high", BRL declined to conduct any additional testing or to <br />perform sensitivity-style stability analyses. <br />Subsequent to the Division's issuance of its adequacy comments for the <br />Bowie No. 2 Mine application, BRL submitted a "Preliminary Geotechnical <br />Study" of the surface facilities area performed by Maxim Technologies, <br />Inc., as a subcontractor to Morrison Knudsen, Inc. Having identified the <br />proliferation of mass wasting problems throughout the proposed surface <br />facilities area, Maxim performed extensive boring, sample collection and <br />laboratory testing of materials at the site. Maxim characterized the <br />general colluvial materials encountered throughout the site as a "Lean <br />Clay with Gravel (CL-GC)", observing that "the majority of the overburden <br />materials at this site can be described as a matrix of silty lean clay <br />supporting scattered to numerous fragments of sandstone." WESTEC <br />referred to the corresponding colluvial cover on the processing refuse pile <br />site as "the colluvial sandstone above the Mancos Shale". <br />WESTEC chose to convert from blow count observation conducted during <br />penetration sampling, using procedures outlined by Peck, et. al. (1974) and <br />