2016-04-29_REVISION - C1982056 - Laserfiche WebLink

Home Browse Search

been designed based on the 10 -year, 24-hour precipitation event. The toe drains primary purpose is to prevent any significant build-up of hydrostatic pressure within the pile, which could affect pile stability. Based on design calculations, the required toe drain would consist of durable 9 -inch rock with a cross-sectional area of approximately 50 square feet, enclosed by graded cover material to minimize the potential for fines infiltration and Plugging. A minor drainage design modification, incorporated during the initial construction phase, will shift the northern end of the toe drain approximately 120 feet to the east, allowing the toe drain to discharge to the Area 1 Pit rather than Sedimentation Pond D. This minor design modification will allow for use of any drainage in the mine water system, and provide for better control of the water relative to mixing and water quality, while not affecting the stability of the pile. Drainage from the intermediate pile benches and the surface of the pile (both during construction and on completion) will be controlled by sloping benches and the pile surface away from the outslope, with the benches connecting into the perimeter drains along the margins of the pile. All drainage structures will route drainage to existing Pond D, which will continue to operate in compliance with applicable effluent standards. Designs for drainage structures associated with the CRDA are presented in Exhibit 8EE — Coal Refuse Disposal Area Expansion — Drainage Designs. Similar to the existing CRDA, the CRDA Expansion is designed to accommodate both temporary (winter) placement and permanent disposal of coal refuse materials generated by ongoing underground development and mining operations, and operation of the TCC coal preparation facilities. The coal refuse materials to be placed in the expansion area are essentially the same as the materials that have been placed in the existing CRDA, and have similar physical and chemical characteristics (ie: non-toxic and non-acid, refer to Table 20A, Waste Material Analyses). For the CRDA Expansion, coal refuse materials would continue to be hauled from the Foidel Creek Mine Facilities Area or the potential future Sage Creek Project Area, and placed in a controlled manner on the refuse pile using either TCC's existing mobile equipment fleet or contractor equipment. Any refuse materials hauled from the future Sage Creek operations and placed in the CRDA Expansion area, will be transported on existing designed haulroads and the County Road (RCR27). These materials will come from the same geologic units that are mined or affected at the Foidel Creek Mine, and therefore, will have similar characteristics, with little or no potential to adversely affect water quality, flows or vegetation; create public health hazards; or cause instability in the CRDA Expansion area. Permanent placement will involve dumping the material in piles or windrows, and then spreading and compacting the materials in uniform lifts of 12 -inches or less, to 90 percent of maximum dry density (AASHTO). If field testing indicates that compaction requirements can be consistently met with thicker lifts, lift thickness may be increased up to a maxinuun of 24 -inches. Proper moisture control will be important in assuring adequate compaction. Compaction will be verified through regular compaction testing and documentation of compaction results and proper construction in both the Construction Certification (30CFR77.214-215) and the Quarterly Refuse Pile Inspection Report. In addition to regular compaction testing and monitoring of water levels, the design engineer (NWCC) will inspect (and test, as appropriate) key construction activities, including: 1) Foundation conditions following soil and cover material stripping; 2) Underdrain materials and construction (to be photo - documented consistent with the applicable requirements of Rule 4.09.1(11)(c)); 3) Coal refuse materials; 4) Initial and ongoing coal refuse placement (quarterly); and 5) Cover ands soil material placement and revegetation. A report will be prepared and submitted to the CDRMS within two weeks following each regularly scheduled quarterly inspection, and a copy will be retained at the mine site. If an inspection identifies potential hazards, TCC will notify the CDRMS promptly, and develop appropriate emergency protection and remediation plans. Temporary refuse placement (primarily during the winter months) will involve placement of refuse materials in temporary stockpile areas to avoid placement when these materials may be frozen. When prevailing weather conditions warm to the point where any frozen materials are thawed, the material which has been temporarily stockpiled will be re -handled, placed, and compacted, consistent with permanent placement practices. initial CRDA construction will involve placement of up to approximately 3.0 MM cubic yards of refuse material to a height of approximately 100 feet. Subsequent progressive CRDA construction will result in refuse placement up to the maximum design height and capacity, with progressive soil and cover material stripping and stockpiling, and extension of designed drainage structures. As CRDA construction progresses, fill areas and benches will be completed and graded, and cover and soil materials will be replaced to stabilize and reclaim these areas. Both cover and soil materials may either be direct handled and placed or recovered and placed from stockpile, dependent on construction scheduling and equipment availability. A minimum of 4.0 feet of suitable cover (2.5 feet) and soil PR 14-10 2.05-97.5 04/28/16