Laserfiche WebLink
for stability considerations. The proposed RDA can have a consistent series of 2.2:1 <br />slopes with benches at 50 foot vertical interval to the top. <br />The benches should be a minimum of 20 feet wide and be constructed with <br />a slope back into the pile at about 5 percent (1 foot fora 20 foot width). The <br />benches should be crowned from the center to both sides. Recommended center <br />and end elevations are shown on Sheet 2, a conceptual detail of the crowned <br />benches is shown on Sheet 3. These elevations will result in slopes of 2 to 3 percent <br />from the center of the bench to the sides. This includes an allowance for long term <br />settlement of the RDA of 2 percent of the fill height. If this occurs then positive <br />drainage to the sides should still be present. The bench elevations are based upon <br />a 50 foot vertical distance from the existing third bench and may vary, provided the <br />maximum distance is not exceed. As each bench is completed, the center and end <br />• elevations should be checked and the next bench planned 50 feet above. The <br />surface of the completed RDA should be sloped as illustrated on Sheet 2. The <br />perimeter and top surface of the RDA may be modified to accommodate required <br />slopes for surface drainage and ditches. <br />The estimated volume versus elevation for the proposed RDA is shown on <br />Sheet 2. The existing RDA was completed to about elevation 7600 at the time of this <br />report and is estimated to contain 1.1 million cubic yards (mcy) of coal refuse. The <br />completed RDA is estimated to contain 12.7 mcy. <br />Uncomaacted Zone. <br />A review of the stability analysis indicates that the critical failure surfaces are <br />located within the first several hundred feet of the RDA face. We believe an <br />• <br />23 <br />