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a i <br />J.E. Stover & Associates -22- May 31, 1996 <br />Bowie No. 2 Mine <br />4.1.5 Material Balance/Material Stockpiles <br />WESTEC requests that the topsoil stockpile just east of the toe <br />of the waste pile, and the coverfill stockpile located 600 east <br />of the toe of the waste pile, be exempted from sediment control <br />and considered small area exemptions. BRL also proposes to <br />build the haul road to the waste pile without a sediment control <br />facility. Further, BRL requests a variance because a portion of <br />these facilities lie within 100 feet of the Right-of-Way for old <br />State Highway 133. Old Highway 133 appears to provide access for <br />several of the neighboring residents as well as the Bowie No. 2 <br />mine. If Highway 133 were compromised emergency access might be <br />eliminated to the mine and the neighbors. BRL will have to <br />provide detail concerning the existing drainage conveyances along <br />and under old Highway 133 to demonstrate that changes within the <br />mine permit area, which affect water retention and routing will <br />not overload the existing ditches and culverts and compromise the <br />old Highway. Further, BRL will have to specify which alternative <br />sediment control devices and techniques will be implemented and <br />at what specific locations. <br />4.3 Slope Stability <br />4.3.2 Material Properties <br />WESTEC considered four earthen materials in completing its slope <br />stability analysis for the proposed waste pile. Strength <br />parameters for the coal waste, material '1" were determined by <br />performing a direct shear test in the laboratory. Strength <br />parameters for existing sandstone-derived colluvial material <br />underlying the proposed waste pile, material "2", were <br />theoretically developed from interpretation of the Standard <br />Penetration Test (SPT) blowcounts recorded in the field. <br />Strength parameters for the Mancos Shale bedrock, material "3', <br />were similarly deduced from SPT blowcounts. Strength parameters <br />for the historic coal mine waste fill material located beneath <br />the toe of the waste pile, material "4", were also deduced from <br />SPT blowcount conversions. <br />WESTEC's stability analysis of the proposed Bowie No. 2 mine's <br />coal waste pile determined the overall static slope stability <br />safety factor of the structure to be 1.54. The corresponding <br />pseudostatic factor of safety, assuming a pseudostatic horizontal <br />acceleration factor of 0.1 g was calculated at 1.14. This <br />calculated static safety factor narrowly exceeds the required <br />value of 1.5. If the ultimate waste pile volume, in excess of <br />225,000 cubic yards of combined waste, coverfill and topsoil were <br />to fail, it could compromise the function and integrity of the <br />sediment pond adjacent to the waste pile toe. Further, since the <br />