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• protect toe buttress excavations and drain sections which have been constructed <br />but not covered with coal waste. This should control contamination of drain rock or <br />silting in the excavations due to surface water flows during storms. <br />Drain Construction <br />Drain locations, sections and material requirements are shown on Figs. 3 and <br />4. The drain and filter materials will not require compaction. The material should be <br />loose dumped to provide a continuous section with the minimum dimensions shown. <br />The drain and filter material should be protected from excessive contamination. <br />~ Cover Material <br />The cover layer will consist of 2.5 feet of soil and approximately 1.5 feet of <br />• topsoil, for a total cover thickness of 4.0 feet. Cover soil can be obtained by <br />excavating native soils, bedrock or spoil materials in the area. Our calculations <br />indicate that the overall surface area of the proposed RDA is about 2 percent greater <br />~ than the surface area beneath the RDA. The ratio will vary for different areas of the <br />pile as construction proceeds from north to south. During excavation and <br />stockpiling, soil volumes will increase (swell), and with nominal compaction will then <br />~ decrease. Volume change due to shrinkage during excavation and placement is <br />estimated to be 5 percent. <br />The increase in the area of the RDA, compared to the area which the RDA <br />~ covers, may require an increase in the depth of cut for cover soils. If cover soil is <br />to be obtained from below the pile, our best estimate is to increase the planned <br /> <br />depth of cut for cover soil by 7 percent. For example, if a 2.5-foot depth of cut is <br />. planned, then increasing the depth of cut 7 percent would result in a cut of 2.8 <br />20 <br /> <br />