2018-01-03_PERMIT FILE - C1981010A (16)

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If there are no approved suitability criteria listed in these sources, the CDRMS recommended using suitability criteria provided in the Wyoming Department of Environmental Quality (WDEQ) Guideline No.1 Topsoil and Overburden Tables 1-2 Criteria to Establish Suitability of Topsoil and 1-4 Criteria to Establish Overburden Suitability (WDEQ 1984) and Guideline No. 1A Topsoil and Subsoil Attachment B2 Criteria to Establish Suitability of Soil or Soil Substitutes (WDEQ 2015). Many of the geochemical parameters contained in the CMLRD 1982 Guidelines do not have suitability criteria in either the Trapper Mine Permit or the WDEQ Guidelines. For these constituents, suitability criteria provided in the Soil Conservation Society of America text Reclaiming Mine Soils and Overburden in the Western United States - Analytic Parameters and Procedures (Williams and Schuman 1987) were used for comparison. Minino Methods The overburden geochemistry should be evaluated in light of the mining methods used at the Trapper Mine as these techniques result in considerable mixing of the spoils which homogenizes the bulk soil chemistry. As described in Sections 3.1.5 and 3.5.1, TMI uses a "multiple equipment scenario" in their mining and reclamation processes that results in topsoil being removed and stockpiled by scrapers, followed by overburden being removed by trucks/loaders, dozers, and draglines. Unmined rider coal seams or seams which are either too thin or have parting materials rendering them unsuitable for mining are removed along with the overburden. The mineable coal seams are then removed by mining and hauled to the power plant. As a general rule, following topsoil removal all near -surface overburden above the H coal seam will be stripped using a truck/loader mining method. This H overburden extends to a depth of approximately 49 feet and consists of the weathered geologic zone. All depths are referenced to the overburden drill holes drilled to characterize the PR -7 Mine Expansion Area. As depicted in Permit Figure 3.5-2, this surface geological material will be placed on top of the dragline spoils, and following the restoration of approximate original surface contour, will be covered with topsoil. The second overburden removal method used by TMI consists of dozer stripping operations in a zone below the H coal seam down to the top of the L coal seam, from a depth of approximately 56 to 167 feet. As shown in Figure 3.5-2, this material is pushed by dozers over the highwall and onto the bottom of the previous mine pit. With this mining method, dozer spoils are mixed twice. Once as they are stripped during the removal operations from a cut often hundreds of feet long, and secondly as the dozer spoils fall over the previous mine highwall onto the pit floor. The third overburden stripping method consists of dragline stripping, which typically handles all of the materials from the bottom of the L coal seam to the top of the final coal seam to be mined. Thus, the dragline will remove overburden materials from a depth of approximately 170 feet to a depth of approximately 236 feet. Dragline spoil will be mixed initially during removal and secondly as it is dumped from the dragline bucket into the previous mine pit. The "multiple equipment scenarios" mining technique employed by TMI results in a significant amount of mixing and homogenization that reduces the likelihood of marginal or unsuitable overburden or spoil pockets occurring. These different mining methods result in significantly more mixing or dilution of potential suspect materials than is typically associated with mining that uses a more uniform mining method. 2-391 u