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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 the <br />pile will be sloped back to the south to ensure run-off from the fill surface flows to the <br />collection ditches and is not allowed to flow over the outslope of the 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 densities <br />to ensure mass stability, prevent mass movement and prevent formation of voids. The <br />coal mine waste will be compacted to attain 90 percent of the maximum dry density to <br />prevent spontaneous combustion and to provide the strength required for stability of the <br />refuse pile. Dry densities will be 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 results <br />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 drive <br />the mass of soil downhill and the anticipated internal strength of the soil along the <br />expected plane of failure that will resist downhill movements. If the driving forces are <br />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 />Permit Renewal 2-19 09/03 <br />