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Mr. Jim Stover <br />August 9, 1996 -New App./Bowie 2 <br />Page 13 <br />partially upon J. E. Stover & Associates observations conducted at the site throughout the <br />previous year. With WPSTEC's proposal to constnrct.an underdrain beneath the pile, the <br />Division will accept this observation concerning the hydrology of the proposed coal <br />processing waste pile site. <br />4.1.4 Runoff Control Ditches - <br />Please add a commitment to the Volume IV text which specifies that subgrade density <br />testing will be conducted and reported if the grout option is used. <br />4.1.5 Material Stockpiles - <br />It appears that the June 20, 1996 BRL response did not address this concern. Please <br />address. <br />4.3.2 Slope Stability -Material Properties <br />The Division expressed a concern because NESTEC assumed material properties for three <br />of the four involved earthen materials in completing its slope stability analysis for the <br />proposed waste pile. Only strength parameters for the coal waste material "1" were <br />determined by performing a direct shear test in the laboratory. Strength parameters for <br />existing sandstone-derived colluvial material underlying the proposed waste pile, material <br />"2", were theoretically developed from interpretation of the Standard Penetration Test <br />(SPT) blow counts recorded in the field. Strength parameters for the Marcos Shale <br />bedrock, material "3", were similarly deduced from SPT blow counts. Strength parameters <br />for the historic coal mine waste fill material located beneath the toe of the waste pile, <br />material "4", were also deduced from SPT blow count conversions. <br />WESTEC's stability analysis of the proposed Bowie No. 2 mine's coal waste pile <br />determined the overall static slope stability safety factor of the structure to be 1.54. This <br />calculated static safety factor (SSF) narrowly exceeds the required value of 1.5. If the <br />ultimate waste pile volume, in excess of 225,000 cubic yards of combined waste, coverfill <br />and topsoil were to fail, it could compromise the function and integrity of the sediment pond <br />adjacent to the waste pile toe, and it might compromise the drainage facilities adjoining <br />State Highway 133 and subject the public to a health and safety risk. For this reason the <br />Division requested that BRL obtain samples of each of the three earthen materials for which <br />WESTEC assumed strength parameters and verify those properties by appropriate laboratory <br />testing. Based upon its "experience with similar materials in this region, its belief that it <br />considered "conservative saturation condition of all of its foundation materials" in <br />performing the 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 perform sensitivity- <br />