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An underdrain system should be started at the toe and constructed to discharge flow into the <br />• toe ditch and routed to the sediment pond. The underdrain system is discussed in detail in <br />Section 4.1.2. The proper placement of the first coal waste lift is critical to overall stability <br />of the waste bank. Compaction of the waste coal material should be a minimum of 90 <br />percent of the maximum dry density according to AASHTO Specification T99-74 or ASTM <br />Test D-698 in maximum 24-inch lifts. Attached in Appendix A are results of a Standard <br />Proctor compaction test (ASTM D•698) performed on a sample of coal mine waste similar to <br />the waste to be stored at the Bowie No. 2 Mine. Since coal waste may be variable in material <br />properties, it is suggested that coal placed in the waste bank be checked for assurance of <br />proper compaction in regular intervals. <br />A haul road beginning east of the site along the old railroad alignment will climb at a 10 <br />percent grade to the west as shown on Drawing 95266-02 to EI. 6,035 ft. Until the coal <br />waste bank reaches the first bench, coal will be brought to this elevation via the haul road, <br />then dumped onto the top surface of the existing waste bank where it shall be spread and <br />compacted in proper lifts. Material obtained from the cutting of the haul road will be <br />temporarily stockpiled for later use as reclamation cover fill. When the waste bank is <br />• constructed to the EI. 6,035 ft level, a 20-toot wide bench with haul road will traverse the <br />waste at a two percent grade to the west side. Central ridge removal will continue from EI. <br />6,035 to the EI. 6,085 ft bench, On the west side of the pile, the haul road will switchback, <br />and continue at a 10 percent grade to the east as the coal waste bank develops, then <br />switching back on natural ground to head west to the bench at EI. 6,085 ft. as shown in the <br />drawings. Construction will continue in this manner until the crest reaches EI. 6,190 ft. <br />When each bench is constructed, the slope below will be reclaimed, i.e., covered with four <br />feet of cover material obtained from central ridge removal directly above, covered with topsoil, <br />and vegetated. <br />4.1.2 Underdrain System <br />An underdrain system is a requirement pursuant to Rule 4.10.3(1). Although there has been <br />no recorded springs within the proposed waste bank area and diversion ditches will be <br />constructed to route water off or around the site, an underdrain system has been developed <br />to ensure the full drainage of the coal waste bank. Drain material must be permeable, yet <br />meet filter criteria to prevent piping and clogging. Data obtained through laboratory grain size <br />• analysis of the coal waste and surficial material was used for filter criteria of the drain <br />96266/1424.RPT Coal Mine Waste Benk Finel Design for [he Bowie No. 2 Mine <br />June 1996 W E S T E C 7 <br />AOCQUACY-UI <br />