2016-01-07_PERMIT FILE - C2010089A (16)

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Table 2.05.4(2)(d)-1 Criteria for Evaluating Bench 1 Suitability PARAMETER SUITABLITY pH Between 6.1 and 8.5 Neutralization Potential Ratio (NPR) >2 Course Fragment Content (%) < 20 Sodium Absorption Ratio (SAR) < 15 Electrical Conductivity (mmhos/cm) < 6 Carbonate (%) < 20 Selenium (ppm)1 < 1 Texture All soil textures except: s, Is, sc, sic, c 'This value for selenium was chosen based on guidance from Dave Dearstyne of NRCS and recent data that other states are using. Mr. Dearstyne is currently working extensively (2008) with the Selenium Task Force on the western slope and is very knowledgeable about this issue. Mr. Dearstyne noted that there is no concern for selenium unless Mancos shale strata are being placed near the surface. At the NHN Mine, no Mancos shale has been encountered in the overburden. Also, all tests of water soluble selenium in the pre -mine soil survey of NHN Mine show all values less than 0.1 ppm. Mr. Dearstyne believes a threshold suitability level of 0.2 ppm in the topsoil material and 1.0 ppm in the subsoil material is adequate. These are the levels proposed. Unsuitable Bench 1 Backfill Mitigation Plan If the results of the sampling indicate that one or more of the unsuitable levels are reached, the Division will be contacted. Also at that juncture, WFC will resample the area to determine the extent of the unsuitable Bench 1. If the problem area is greater than one acre in size it will be necessary to remove or cap the area. If only the lower sample Bench 1 failed, then only two feet of Bench 1 will be added to the area and resampled. If both samples (0-2' & 2'-4') failed where the post -mine land use is Dryland Pasture, any area over one acre will be capped with four feet of suitable material. For areas that have a post -mine land use of irrigated pasture the problem area will be excavated to a depth of four feet, and four feet of suitable Bench 1 will be placed within the excavated area. Topsoil Management Plan The NHN Mine topsoil management plan is based upon the detailed topsoil survey contained in Section 2.04.9, and it has been developed to insure that the most suitable topsoil materials within the disturbance area are salvaged. The topsoil management plan evaluates the topsoil resources and describes salvage depths and techniques, storage, redistribution, and maintenance or testing procedures necessary to restore the disturbed areas to the desired post -mine land use. Evaluation of Topsoil Resources The topsoil resources found in the NHN Mine permit area are shown on Map 2.04.9-3 — Topsoil Salvage Map, and are typical of topsoil found in the semi -arid Colorado Plateau Physiographic Province, Canyon Land Section. A total of eleven different topsoil mapping units were delineated in the survey performed on the NHN Mine Area. Five of these topsoil mapping units lack salvageable topsoil and include livestock ponds, roads, drainage channel, soils mapping unit 78UT (5 to 30 percent slopes), and soils mapping unit RO (40 to 90 percent slopes). These areas Section 2.05.4(2)(d) Page 3 Sept. 2015 (TR -11)