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• Placement and Compaction <br />The coal mine waste material will be hauled by truck to the refuse disposal area <br />where it will be spread in maximum lifts of 24 inches and compacted. The top of <br />the pile will be sloped back to the south to ensure run-off from the fill surface <br />flows to the collection ditches and is not allowed to flow over the outslope of the <br />fill. <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 />Compaction tests will be taken at a frequency and location of not less than one <br />per every other layer, at random locations across the pile. Test locations and <br />• results will be reported to the Division in the appropriate construction reports. <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 all monitoring <br />events, see Figure 2.3-5 for sampling locations. <br />M" 2.2-12vi 10/02 <br />