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• The slope stability analysis was performed using SB-Slope by Geosystem software. <br />The slope stability analysis considered numerous possible failure surface iterations <br />to help identify the potential theoretical slope stability. The stability analysis <br />indicates a minimum factor of safety of 3,04 and 3.58 for the alluvial and colluvial <br />strength parameters respectively. A copy of the computer analysis with the <br />assumptions made is included in Appendix N. <br />The stability analysis was performed with the strength parameters utilized by SGC. <br />Results were similar to those listed above with a minimum factor of safety of 2.68. <br />Relatively high factors of safety are a result of the relatively flat slope, 3H:1 V, of the <br />waste pile. <br />At the worst case, the only point of instability which could occur would be at the toe <br />of the slope due to a high buildup of the phreatic surface. The stability analysis was <br />run with a phreatic surface at the base of the gob pile. The factors of safety ranged <br />from 2.5 to 3.1. Rather than building expensive underdrain systems, monitoring <br />well GW-6 will be used to monitor the phreatic surface. Ground water monitoring <br />well GW-6 is twenty (20) feet deep. The bottom of the well is at approximate <br />elevation of 5420. The base of the refuse pile will be about elevation 5434 near <br />GW-6. If afree-standing water surface elevation of 5434 feet or higher develops in <br />Monitoring well GW-6, a toe drain will be constructed as follows prior to additional <br />placement of coal mine waste material or (should the critical groundwater elevation <br />develop following completion of waste placement) prior to Phase III bond release. <br />The toe drain will consist of 4 inch diameter perforated pipe surrounded by about 4 <br />to 6 cubic feet per linear foot of pipe of free draining concrete sand. <br />The proposed coat 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 supports <br />the Operator's position that an underdrain system should not be required for this <br />refuse pile. <br />In the event that seeps or springs are encountered during topsoil or cover material <br />stripping for the Munger Canyon Mine Waste Pile, subdrain(s) will be incorporated <br />into the permit. Coal Mine waste placement will be suspended if seeps or springs <br />are encountered, until sub-drain designs have been approved by the Division, and <br />constructed by the operator. <br />M" 2.2-12viii 10/02 <br />