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<br />VII. Coal Mine Waste Banks <br />1. The Division has approved plans for use, construction and <br />maintenance of a coal mine waste disposal area. <br />(4.10.1(1)) <br />Details on the coal mine waste bank, referred to the mine <br />refuse area, can be found in Sections 2.05.3 "Operation <br />Plan", 2.05.4 "Reclamation Plan", 4.10 "Coal Processing <br />Waste Banks", and Exhibits 15 and 18 of the permit <br />application. Maps of the refuse pile are shown on Map <br />18, "Mine Area Surface Facilities Map" as well as the <br />Annual Reclamation Report Map for 1993. Contents of the <br />refuse pile include sandstones, shales and rock partings <br />or inclusions that are separated from the coal in the <br />processing plant. <br />The refuse pile was initially designed for Dorchester in <br />1980-81 by Geo Testing Laboratories, Inc. and re- <br />evaluated by Rocky Mountain Geotechnical (RMG) in 1982 to <br />adjust for increased refuse volume. The RMG report is <br />the design basis for the ongoing refuse pile construction <br />at the Southfield Mine. In brief, the report recommended <br />the construction of another underdrain (a total of two) <br />and advocated the maximum height of the refuse pile to be <br />75 feet, while using compaction techniques of two foot <br />lifts to provide a safety factor of 1,5. The RMG report <br />can be found in Exhibit 18 of the permit application. <br />Technical Revision No.7, approved 3/5/90, allowed for <br />the expansion of the refuse pile. In 1992 the Division <br />expressed concerns on the stability of the pile under the <br />practices of varying fine material lifts with coarse <br />lifts. Technical Revision No.14, approved 6/12/92, <br />concluded that layered placement and variable coarse to <br />fine ratios would have no adverse impact on the pile's <br />stability while maintaining the 1.5 factor of safety. <br />2. With the construction of the two underdrains, an <br />alternative subdrainage system for the coal mine waste <br />area has been approved. The Division finds that such an <br />alternative will ensure the applicable static safety <br />factor, stability of the fill, and protection of the <br />surface and ground water. (4.10.3(5)) <br />VIII.Backfilling and Grading <br />After removal of all mine structures and facilities and <br />sealing of mine openings, mine disturbed areas will be <br />backfilled and regraded. EFCI will establish a post-mining <br />configuration which complies with regulatory requirements for <br />long-term stability that blends with the surrounding terrain. <br />40 <br />