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i To provide a comparison, Powderhom (Snowcap) Coal Company (SCC) used the <br />following strength parameters in its analysis of its two Cameo Refuse Disposal Areas: <br />Material Density pcf Cohesion psf Angle of Friction <br />Coal Waste 84 200 32 <br />Colluvial/Alluvial 112 0 32 <br />Ref: SCC permit Volume 4, Appendices 13-4 and 13-5.The stability analysis assumes <br />the fill will be well drained and that no pore pressures will develop in the fill. The soil <br />strength values were varied from those listed above to assess the sensitivity of the <br />analysis to varying soil strength parameters. The variations in the analysis produced <br />relatively small and predictable changes to the calculated factor of safety indicating that <br />.the stability analysis was not sensitive to slight variances in the soil strength values. <br />The slope stability analysis was performed using SB-Slope by Geosystem <br />software. The slope stability analysis considered numerous possible failure surface <br />iterations 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 <br />SCC. Results were similar to those listed above with a minimum factor of safety of <br />2.68. Relatively high factors of safety are a result of the relatively flat slope, 3H:1 V, of <br />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. 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 well <br />GW-6 will be used to monitor the phreatic surface. Ground water monitoring well GW-6 <br />RN-05 2-20 09/07 <br />