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thalweg underdrain. The specific dimensions of lateral drains will be determined based on estimated <br />seepage rates. <br />4.4 Refuse Pile Drainage <br />To enhance drainage of water that may infiltrate through the refuse pile, buried rock drains will be <br />constructed prior to placing refuse. The buried drains will initially be constructed as temporary <br />clearwater and sediment ditches to divert water away from the working pad, or to divert water on the <br />pad away from the underdrain to sediment ditches. Drawing C -13A shows the locations of these <br />ditches. As shown on this drawing, filter rock will be placed in the bottom of the ditches to stabilize <br />the ditches as they are used for surface water diversion. The filter rock will be left in place as the <br />ditches are covered with refuse to intercept and divert water that infiltrates through the refuse to the <br />sediment ditches on the east and west sides of the refuse pile. Filter rock will be placed to a depth of <br />approximately one to two feet in the bottom of the ditches. <br />4.5 Compaction <br />Refuse will be compacted to 90 percent (or greater) of the maximum standard Proctor dry density and <br />lifts will be no greater than 24 inches in thickness, as required by Rule 4.10.4 (3). <br />4.6 Cover <br />The refuse pile will be contemporaneously reclaimed with an average of 18 to 24 inches of soil <br />cover obtained from the uppermost soil horizon(s) of colluvial soils stripped from the refuse pile <br />foundation area and revegetated with MCC's permanent seed mixture found in Table 37 of the <br />Permit document. As the coal refuse material and soils characteristics are similar to (but <br />expected to be more coarse - grained than) that of the existing LRP and RPE refuse piles, the <br />variance from four -feet of soil cover that was approved by the CDRMS for both the LRP and <br />RPE construction has been applied to the RPE East construction. Contemporaneous reclamation <br />will begin once the lowest part of the refuse pile has reached design grades after construction of <br />Phase 3 of the rock buttress. <br />Revised March 19, 2010 <br />P \Mpls \06 CO \26 \06261003 RPE E Permit Mod Support\WorkFiles \Permit Application \Text \Exhibit 82 RPEE design 2011 -07 -21 TR 127.doc 20 <br />