2016-04-29_REVISION - C1982056 - Laserfiche WebLink

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downgradient of each disturbance area. Auger drilling is a dry drilling operation, so no mud pits were required, and no discharge of drilling fluids occurred. Because the auger -holes and test pits were in reclaimed mine spoils on a hillslope. the potential for intercepting any significant quantities of ground water was negligible. Air was not used a circulation medium, so dust generation was not a concern. Immediately following completion of sampling, each auger -hole and test pit was backfilled with excavated material and leveled, with seeding of all sample sites following, either prior to snowfall, or in early spring when ground conditions permitted. It should be noted that all minor surface disturbance associated with the site geotechnical investigations falls within both previously disturbed areas, and the footprint of the proposed Refuse Pile Expansion, and will be re -disturbed by Refuse Pile Expansion foundation preparation activities. Design of the CRDA Expansion is based on design of, and operating experience gained from, the existing CRDA; historic designs for a similarly -sized refuse disposal facility in the same location (CTL/Thompson, Inc., 08/14/92); and site-specific topographic and foundation testing information. Design work for the CRDA Expansion has included design of required foundation, perimeter, and surface drains by Hydro -Environmental Solutions, Inc.: design of the required Coal Refuse Haulroad and refuse fills by Civil Design Consultants, Inc. and completion of design stability analyses, and overall project management and coordination by NWCC. The designed CRDA Expansion will contain a maximum of approximately 20.0 MM cy of refuse material, will be approximately 200- 250 feet high (relative to the existing terrain), and will be constructed with 3H: IV slopes with 20 foot intermediate benches at 50 foot vertical intervals, resulting in overall slope angles of approximately 3.5H:1V. The CRDA Expansion and associated facilities will re -disturb a total of approximately 140 acres of the existing refuse pile and areas of reclaimed spoils. The upper surface of the CRDA Expansion will slope back to the southeast to prevent drainage over the outslope, and a toe drain and designed perimeter drains will provide for drainage off of and under the refuse fills. Stability analyses of the proposed CRDA Expansion resulted in an overall Factor of Safety of 2.0, given consideration of reasonable input design parameters. One of the key input parameters was the assumption that the pile will be self -draining (based on experience with the existing RDA). In order to validate this assumption, TCC will install three piezometers at the locations shown on the design drawings. Piezometers will be installed on completed fill benches by drilling through the coal refuse materials and 5 feet into the foundation materials, casing the holes with slotted 2.0 -inch Schedule 40 PVC pipe, with a sand pack and grout seal. The piezometer casing will be protected by a PVC riser and a steel casing with lockable cap. Piezometers will be monitored monthly, and the results will be included in the quarterly refuse pile reports. While stability analyses indicated that the overall CRDA expansion would be stable, as designed, there is some potential for localized shallow surficial slope failures. If shallow failures occur, they would be expected to be associated with moist fine materials, and would be addressed by removing these materials and replacing them with compacted coarse materials. If such failures occur with any frequency, the slope configuration may be modified or other measures implemented to minimize the potential for future failures. Design documentation for the road and refuse pile design and stability analyses is presented in Exhibit 26C, Coal Refuse Disposal Area Expansion. Designs for drainage structures associated with the CRDA are presented in Exhibit 8EE — Coal Refuse Disposal Area Expansion — Drainage Designs. Construction of the CRDA Expansion will be progressive, both from north to south, and with the pile increasing in elevation, as dictated by refuse placement requirements. Construction will begin with implementation of temporary erosion and sediment control measures, including placement of silt -fence and/or straw wattles downslope from initial construction areas. Available soil materials will then be removed from the initial road corridor, drainage channels, and refuse toe bench area (includes east -facing slope of existing RDA Area 1). It is anticipated that soil material recovery will be extended, both to provide for approximately two years of scheduled refuse placement, and to provide a reasonable buffer between the active construction and refuse placement activities and undisturbed (reclaimed and revegetated) areas. Soil materials from the initial CRDA construction areas will be placed in designated temporary stockpiles for future use in reclaiming completed CRDA benches or areas. Stockpile areas will be accessed by either temporary scraper tracks or temporary haulroads within the CRDA footprint. As CRDA construction progresses, the option will exist to live -handle the soil materials, with recovery from new placement areas and direct placement on completed CRDA areas, or placement in/recovery from stockpile. To the extent operationally practical, TCC will attempt to use live -handling practices in order to obtain the best reclamation PR14-10 2.05-97.3 04/28/16