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Postmining Topography, and designs are discussed in further detail in Tab 20, Backfilling and Grading and Tab 17, <br />Probable Hydrologic Consequences. Seeding the soil stockpiles with an annual grain cover crop or native grasses <br />and forbs, including vigorous rooting and nitrogen fixing plants such as alfalfa, will be done to prevent erosion and <br />also improve the fertility and physical tilth of the soil. The seed mixture, seeding method, and seeding rate for <br />topsoil stockpiles is described in the Revegetation Plan, Tab 22, Table 22 -6, the Seed Mixes and Plant Material Lists <br />section of Tab 22, and the Soil Storage section of this tab. The soil removal area at any one time shall be <br />minimized to prevent both wind and water erosion. <br />SCC does not propose to use any selected overburden materials as soil substitutes or plant seedbed media. This is <br />based on results of the soil survey and soil inventory for Yoast. Sufficient quantities of suitable quality soil are <br />available to restore the disturbed areas to the desired postmine land use. Following mining, an average of 1.8 feet of <br />suitable soil will be replaced over the final graded spoil medium in the mine area and 1.1 feet of soil will be replaced <br />along Haul Roads A and B and the facilities in Section 8. The minimum thickness of soil replaced in the mine area <br />will be 1.0 feet excluding shrub island areas where 0.5 feet of soil will be applied (see Tab 22, Seed Mixes and <br />Planting Lists section). The minimum replaced along Roads A and B and the facilities in Section 8 will be 0.5 feet. <br />Per TR -37, no soil will be replaced on those facilities which are to be retained to compliment the final postmine land <br />use. A 20- foot -wide section of Haul Road A and Haul Road B and various light use roads (approximately 12 feet <br />wide) will be left as permanent and not topsoiled. Numerous postmine channels will be left with no topsoil within <br />the channel. In addition, four sediment ponds and one stock pond will be left as permanent features and will not be <br />topsoiled. At the end of 2007, when the majority of topsoiling was completed, the average replacement depth was <br />21.4 inches. The original projected replacement thickness was 21.6 inches. <br />Upon completing the final reclamation in the Yoast disturbed area, it was determined that there would be excess <br />topsoil remaining in Topsoil Stockpiles A, B and C. Therefore these stockpile areas will remain as permanent post - <br />mine features. <br />Research over the last ten years (pre -1995) has demonstrated that soil depths required for optimum production are <br />related to the quality of the underlying spoil, with greater depths of good quality soil needed to restore production <br />on poor quality spoil (U.S. Congress, 1986). Poor quality spoil material may require more than three feet of soil <br />replacement whereas good quality spoil may need less than one foot. In North Dakota, the replacement of one foot <br />of subsoil plus one foot of soil over good quality spoil materials is recommended (Doll et al, 1984). Power et al., <br />(1976) and Barth and Martin (1982) demonstrated that three feet of soil was necessary for optimum production on <br />sodic spoil. Barth and Martin, 1981, showed fine sandy loam soil depths for optimum production in southeastern <br />Montana to be less than one foot for optimum perennial grass production on nonsaline, nonsodic silt loam spoil. <br />Schuman and others (1980) found that native grass production on reclaimed spoil in Wyoming equaled forage <br />production on an undisturbed native area when the soil thickness was 1.3 feet. In northwestern Colorado, <br />MR -40 23 Revised 10/12 <br />