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The comt~ined capacities of these two disposal areas represent the refuse generated by <br />the production of 60 million tons of coal. At the maximum projected annual production <br />rate of 4.(1 million tons, this represents a 15-year disposal capacity. <br />The pile h.as been designed with maximum facial outslopes of 4:1 (horizontal to vertictd) <br />and a tnav:imum height of 55 feet. A stability analysis performed by CTIJThompson, <br />Inc. ascertained a minimum static slope safety factor of 3.6, assunung an angle of <br />internal friction of 42° and cohesion of 0 pounds per square foot. Confirming laboratory <br />testing performed by the applicant determined an angle of intemal friction of 42° and a <br />cohesion of 1,500 pounds per square foot. Therefore, the safety factor determination <br />presented within the preliminary stability analysis has proven to be conservative in <br />nature and exceeds the required 1.5 minimum acceptable static slope safety factor <br />required by the regulations. <br />The foundation area of the coal processing waste pile has been prepared by removal of <br />topsoil an<I unacceptable subsoils and the installation of a gravel and file subdrain and <br />peripheral toe drain. These drains will prevent ground water from flowing into the <br />waste maU:rial. Waste material will be placed in 24-inch horizontal lifts, compacted to <br />90 percent of the waste material's maximum dry density, as determined utilizing <br />AASHTO testing specification T-99. Compliance with the certified inspection <br />requirements of Rule 4.10.2 will assure compliance with the approved plans and <br />construction standards. <br />The operator has requested a variance from the 4-toot-thick, non-toxic cover <br />requirements of Rule 4.10.4(4). The resolution of this aspect to the coal processing <br />waste pile's design is stipulated within the vegetation portion of this findings document, <br />Section B.V1II. <br />A. The Division is proposing to approve plans for use, construction, and maintenance <br />of a coal mine waste disposal area (4.10.1(1)). <br />B. The disposal area will be inspected on a regular basis by a qualified professional <br />specialist under the direction of the professional engineer, experienced in <br />construction of similar earth and waste structures. Inspection by this person has <br />been approved by the Division as appropriate (4.10.2(1)). <br />VII. Backfilling and Grading <br />Rule 2.05.` requires aplan/schedule for backfilling and grading in sufficient detail to <br />allow the Division to evaluate the feasibility of the proposed post-mining topography <br />and the required bond estimate. Volumes of material to be moved were presented on <br />Table 63 of the permit application, and the final backfilled topography is depicted on <br />Map 29. <br />The applicant received approval of technical revisions in May of 1986 to extend <br />development work from [he No. 5 Mine to the F seam of the No. 6 Mine. The waste <br />28 <br />