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• equal to or greater than the resisting forces then failure is imminent. A theoretical <br />calculated factor of safety of 1.5 is considered by the geotechnical engineering industry <br />as a minimum factor of safety for a slope to be considered stable which is consistent <br />with DMG Rule 4.10.4(2). <br />As described in Section 4.4.2.1, there are no observed springs or seeps in the <br />area; and no potential aquifer is present in the alluvial fill of Munger Creek. Because of <br />these conditions and the fact that surface water will be diverted from the site, no <br />seepage conditions were considered. Rock underdrains are considered unnecessary <br />for this refuse pile. Monitoring well GW-6 is located in alluvial material near the base of <br />the site has been dry during all monitoring events, see Figure 2.3-5 for sampling <br />locations. <br />The cross-section shown in Figure 2.2-7 is typical of the design fill. The slope of <br />the finished slope will be a relatively flat 3H:1 V. A rotational equilibrium analysis was <br />performed on this fill to determine its factor of safety. <br />The coal mine waste will be similar to the coaly material from the Loma loadout <br />placed at the Munger Portals. Lambert and Associates analyzed to coaly material from <br />the Munger Portal for triaxial shear strength tests. The coal material has a cohesion of <br />3psi or 432 psf, a angle of friction of 33° and a density of 82 pounds per cubic foot. Two <br />strength values were used for the alluvial colluvial material. Page 3-25 lists the <br />following strength parameters that were used for the alluvial colluvial material in the <br />stability analysis. <br />Material Density Cohesion Angle of Friction <br />Alluvial 125 200 25 <br />colluvial 130 1300 15 <br />Coal Mine Waste 82 432 32 <br />r~ <br />.~ <br />RN-05 2-19 09/07 <br />