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drainage on the refuse pile stability and the potential for blockage of the primary <br />subdrain if significant subsidence were to occur, the CMLRD specified and Dorchester <br />designed and constructed a secondary subdrain as the existing stockpile advanced to <br />the west. <br />As the refuse pile advanced west to its current footprint, EFCI extended both existing <br />primary and secondary subdrains in sequence with topsoil removal operations. Rock <br />subdrain specifications and construction were consistent with design recommendations <br />presented in Exhibit 18, Geotechnical Information. The rock subdrain extensions were <br />established with a minimum gradient of 2%. subdrain material consists of durable rock <br />fills wrapped with Typar 3401 filter cloth or equivalent to prevent clogging. Both <br />subdrains are completed to their respective designed lengths. <br />Following extension of drainage collection ditches and preparation of stockpile <br />foundation areas, EFCI will continue to advance existing refuse fill benches to the west. <br />Coarse and fine refuse materials will be hauled from the preparation plant to the coal <br />refuse pile and dumped using rear-dump haulage trucks. Refuse materials will be <br />spread by tracked dozers, motor graders, and wheel loaders in horizontal lifts no greater <br />than 2 feet. Typically, a lift of fine refuse will be placed first, followed by one or more lifts <br />of coarse refuse. Each lift of refuse will be compacted to minimum dry density of 52 pcf. <br />All lifts will be compacted in such a manner to minimize the flow of air through the pile, <br />ensure stability of the structure, and maintain the required 1.5 factor of safety. <br />Compaction of each lift will be completed prior to placement of the next successive lift. <br />Final compaction of fine refuse lifts will occur during compaction of the overlying lift(s) <br />of coarse refuse. Coal refuse will be dewatered prior to placement. If material moisture <br />levels are too low to facilitate effective compaction, a water truck will be utilized during <br />construction to maintain optimal moisture levels. <br />During refuse pile construction, active working area will be sloped and oriented to <br />provide effective drainage from the surface of each completed lift. If necessary, <br />temporary ditches will be established in working areas to collect and route runoff from <br />the refuse pile and immediately adjacent areas to perimeter collection ditches. <br />2.05.3 - 35 Revised 522/97 <br />Technical Revision No. 27 <br />