2009-10-13_REVISION - C1982056 (2)

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TWENTYMILE COAL COMPANY - FOIDEL CREEK MINE TECHNICAL REVISION TR09-67 COAL REFUSE DISPOSAL AREA EXPANSION TECHNICAL ADEQUACY RESPONSES (10/09) 1. Cover for the RDA needs to be non-toxic and non-combustible (Rule 4.10.4(5) & Act 129(2)(k). TCC is proposing to use the backfilled spoil from the reclaimed slope for the cover material TCC needs to provide evidence that the spoil material is non-toxic and non-combustible. Response: The area proposed for the CRDA expansion is an area of reclaimed mine spoils, generated by surface coal mining operations under Permit C-81-071. As a required component of that permit application, a comprehensive program of overburden sampling and analysis was conducted, and the resulting data was evaluated and presented in the overburden suitability discussion of the permit (Section 779.14 of Permit C-81-071), demonstrating that the overburden materials were not potentially acid- or toxic-forming. The CMLRD reviewed and approved Permit C-81-071, including the overburden suitability analysis presented therein. The facts that this area, which was reclaimed approximately 20 years ago, has showed no evidence of toxic spoil conditions or combustion potential, was successfully reclaimed to an effective vegetative cover, and that the CMLRD approved final bond release, provide additional documentation that the soil/spoil materials in this area are non-toxic and non combustible. 2. TCC provided Exhibit 26C. NWCC report. On page 10 of this Exhibit, the surface area of the disturbance footprint is greater than the final surface area of the pile. The table on the bottom of this page indicates that the surface area of the completed pile will be less than the footprint of the pile. The west side of the pile abuts the existing RDA. Only a portion of the RDA has received cover material and topsoil It is not clear, based on the provided cross-sections, how the surface of a 20 million cubic yard refuse pile, extending approximately 200-250 feet above the current topography will have a smaller surface area than its footprint. Please provide an explanation or additional cross-sections to demonstrate this Response: The previously provided surface area calculations were based on a three-dimensional model of the existing ground surface (reflecting the topographic configuration of the existing RDA, the topography of the existing reclaimed spoil basin which will be covered by the proposed CRDA Expansion, and the proposed final CRDA Expansion configuration). The reason for the differential in surface area between the base and the final surface is that the calculated base area (in 3-D) included the large sloping eastern-facing surface of the existing RDA. At the CDRMS's request, revised two- dimensional calculations (assumes a median reference elevation between the concave reclaimed spoil basin and the convex final CRDA surface) have been developed, and are provided for the new CRDA Expansion footprint, the portion of existing RDA on which cover and soil materials have already been placed, and areas of the existing RDA where cover and soil materials have not been replaced. Design volumetrics for the pile have been reviewed and corrected, where appropriate, and additional descriptive text developed, with appropriate revisions to the descriptive text and supporting materials. It should be noted that TCC plans to directly place the cover and soil materials stripped from the east- facing surface of Area 1 of the existing RDA on the western side of the same area. In addition, materials previously removed and stockpiled from the east-facing surface of Areas 2.0, 2.5, and 3.0 of the existing RDA, will be replaced on the completed CRDA surface, and will supplement the materials