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• <br />The slope stability analysis was performed using SB-Slope by Geosystem <br />software. The slope stability analysis considered numerous possible failure <br />surface iterations to help identify the potential theoretical slope stability. The <br />stability analysis indicates a minimum factor of safety of 3.04 and 3.58 for the <br />alluvial and colluvial strength parameters respectively. A copy of the computer <br />analysis with the assumptions made is included in Appendix N. <br />The stability analysis was performed with the strength parameters utilized by <br />SCC. Results were similar to those listed above with a minimum factor of safety <br />of 2.68. Relatively high factors of safety are a result of the relatively flat slope, <br />3H:1 V, of the waste pile. <br />At the worst case, the only point of instability which could occur would be at the <br />toe of the slope due to a high buildup of the phreatic surface. Rather than <br />building expensive underdrain systems, monitoring well GW-6 will be used to <br />monitor the phreatic surface. If high groundwater conditions unexpectedly occur, <br />a toe drain will be constructed along the face of the refuse pile to lower the <br />phreatic surface. The toe drain will consist of 4 inch diameter perforated pipe <br />surrounded by about 4 to 6 cubic feet per linear foot of pipe of free draining <br />concrete sand. <br />The proposed coal mine waste disposal area is geologically similar to SCC's <br />Cameo Refuse Disposal Area No. 2 which was constructed without underdrains. <br />SCC's coal mine waste was from a preparation plant so it was quite wet when <br />placed in the pile, however the phreatic surface did not buildup. This fact <br />supports the Operator's position that an underdrain system should not be <br />required for this refuse pile. <br /> <br />M" 2.2-12v 6/02 <br />