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I • Inspection <br />The waste rock disposal area will be inspected for stability on a quarterly basis <br />by a qualified engineer. In addition the area will be inspected during the following <br />critical periods: removal of all organic material, large boulders and topsoil as <br />previously described, installation of surface drainage systems, placement and <br />compaction of fill materials, and during revegetation. A report will be provided to <br />the Division by the inspecting engineer within two weeks of the completed <br />inspections. A copy of this report will be kept at the mine site. <br />Compaction <br />Compaction of the coal mine waste will be by the handling and spreading <br />operation. Special compaction equipment will be used if necessary to achieve <br />densities to ensure mass stability, prevent mass movement and prevent <br />formation of voids. The coal mine waste will be compacted to attain 90 percent <br />of the maximum dry density to prevent spontaneous combustion and to provide <br />the strength required for stability of the refuse pile. Dry densities will be <br />• determined in accordance with AASHTO T99-74. <br />Stability Analysis <br />The stability of any slope is dependent on many factors. Typically the stability of <br />a slope is analyzed by calculating the anticipated gravitational forces that tend to <br />drive the mass of soil downhill and the anticipated internal strength of the soil <br />along the expected plane of failure that will resist downhill movements. If the <br />driving forces are equal to or greater than the resisting forces then failure is <br />imminent. A theoretical calculated factor of safety of 1.5 is considered by the <br />geotechnical engineering industry as a minimum factor of safety for a slope to be <br />considered stable which is consistent 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. <br />Because of these conditions and the fact that surface water will be diverted from <br />the site, no seepage conditions were considered. Rock underdrains are <br />considered unnecessary for this refuse pile. Monitoring well GW-6 is located in <br />. alluvial material near the base of the site has been dry during ail monitoring <br />events, see Figure 2.3-5 for sampling locations. <br />M" 2.2-12iii 6/02 <br />