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CTL /Thompson also performed a stability analysis of the Lorencito Canyon Mine waste to be processed at the <br />New Elk Mine and stored in the RDA. Results of this study are also presented in Exhibit 30, Geotechnical <br />Study — Coal Processing Waste Bank. <br />The Development Waste Pile west of the mine entrance been successfully reclaimed. A new development <br />waste disposal area (DWDA) is necessary to accommodate the waste rock excavated during development and <br />preparation of areas incident to underground mining. The refuse material is expected to be identical to the <br />material in the reclaimed waste disposal area. Experience on site dictates that the makeup of these materials is <br />not indicative of the components of that would potentially lead to acidic runoff or adversely affect groundwater <br />quality. The mine has a long history of stockpiling coal without encountering spontaneous combustion. <br />The development waste, ditch, and pond cleanings will be permanently stored in the new DWDA located south <br />of Highway 12 (DWDA #2). This area was previously permitted as the clean coal stockpile area as shown on <br />Map 11 Surface Facilities and Roads East Portal. As part of TR -66, the design configuration for DWDA <br />#2 will change. The storage capacity of the revised pile will be about 125,000 BCY. Refer to Figure 13 for the <br />plan and section view of the proposed DWDA. The overall pile height will be 50 ft tall. Each l Oft bench will <br />be placed in up to 1 ft lifts and compacted with a track dozer. Setbacks of 20 ft for each bench will result in an <br />overall slope of 2.0(H):1(V) during construction. A stability analysis for the TR -66 revised configuration can <br />be found in Exhibit 37(1). <br />Compaction testing was conducted by CTL/Thompson, Inc. of the New Elk Coal Waste Development pile at <br />approximately 3 month intervals in June, September, November of 1995 and March of 1996. The results are <br />included in Exhibit 31 as documentation supporting a permit revision. "Compaction Test Results New Elk <br />Mine Development Waste Pile CTUThompson job No. 22905 ". CTUThompson observed pile conditions and <br />excavated four test pits. The results indicated that the waste dump was stable if compacted to at least 90% of <br />standard Proctor maximum dry density (ASTM D 698). A CTUThompson evaluation at that same time of <br />alternatives for the disposal of pond dippings and ditch cleaning material indicated that the materials could be <br />disposed of on the development waste pile provided they are adequately drained and compacted. <br />DWDA #2 is at full capacity. NECC needs a temporary pile as a transition to DWDA #3. A temporary pile <br />will be located north and east of the stockpiles shown on Map -11, Sheet 3. Development waste will be <br />stockpiled for at least 30 days, and until such time that final approval is received for Technical Revision No. 65 <br />(DWDA #3). Material will be placed in two foot lifts and compacted as stated above in reference to DWDA <br />#2. <br />A new DWDA (DWDA 0) is planned for the area west of the west mine fan. The storage capacity of the west <br />pile is about 155,000 CY. Refer to Map 12 for the plan and profile sections of the proposed West DWDA. <br />The overall pile height will be a maximum of 90 feet. Material will be placed in up to 2 ft lifts and compacted <br />to achieve at least 90% of standard Proctor maximum dry density (ASTM D 698). The pile will have 3H:1 V <br />side slopes, and one 15' bench. The bench will slope back toward the pile at 2% and to the runoff collection <br />ditches at 2 -5 %. Design recommendations for the West DWDA are included as Exhibit 43. The West <br />DWDA will be constructed in accordance with the design recommendations. <br />DWDA#3 is located over a historical mine structure referred to as a rail/rope slope. Prior to placement of <br />waste at DWDA #3, the rail slope should be demolished in accordance with the recommendations included in <br />Exhibit 43. <br />(9) Return of Coal Processing Waste to Abandoned Workings <br />The New Elk Mine Preparation Plant receives mined coal from the Lorencito Canyon Mine. As the coal is <br />washed, refuse is deposited in the thickener, dewatered by the belt press, and sent by conveyor to the Refuse <br />Disposal Area. Handling of these fines has caused problems for the operating efficiency of the Prep Plant. <br />Basin is proposing to dispose of these fines by pumping a refuse /water slurry into the abandoned New Elk <br />Mine and recovering clear water from gravity dewatering for returned use in the Prep Plant. <br />TR -66 2.05 -44 Revised 8/24/12 <br />