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Postmining topography and designs are discussed in further detail in Tab 20 and Tab 17. Seeding the <br />topsoil stockpiles with an annual grain cover crop or native grasses and fortis, including vigorous <br />rooting and nitrogen fixing plants such as alfalfa, will be done to prevent erosion and also improve the <br />fertility and physical tilth of the soil. The seed mixture, seeding method, and seeding rate for topsoil <br />stockpiles is described in the Revegetation Plan, Tab 22, Table 22-6. The topsoil removal area at any <br />one time shall be minimized to prevent both wind and water erosion. <br />SCC does not propose to use any selected overburden materials as topsoil substitutes or plant seedbed <br />media. This is based on results of the soil survey and topsoil inventory for Seneca II-W. Sufficient <br />quantities of suitable quality topsoil are available to restore the disturbed areas to the desired postmine <br />land use. Following mining, an average of 1.3 feet of suitable topsoil will be replaced over the final <br />graded spoil medium. <br />No topsoil will be replaced on those facilities which are to be retained to compliment the final postmine <br />land use. These facilities include the high water line area and spillway of Ponds 005 and 006 15.0 <br />acresl, and a 100•foot-wide section of the mine entrance road 119.5 acresl, Road A (20.2 acresl, Road <br />G 121.8 acres), and Road H 119.7 acresl. <br />Research over the last ten years has demonstrated that topsoil depths required for optimum production <br />are related to the quality of the underlying spoil, with greater depths of good quality soil needed to <br />restore production on poor quality spoil IU.S. Congress, 79861 Poor quality spoil material may require <br />more than three feet of topsoil replacement whereas good quality spoil may need less titan one foot. In <br />North Dakota, the replacement of one foot of subsoil plus one Toot of topsoil over good quality spoil <br />materials is recommended (Doll et al, 1984), Power et al., 119761 and Barth and Martin (1982) <br />demonstrated that three feet of topsoil was necessary for optimum production on sodic spoil. Barth <br />and Martin, 1981, showed fine sandy loam topsoil depths for optimum production in southeastern <br />Montana to be less than one foot for optimum perennial grass production on nonsaline, nonsodic silt <br />loam spoil. Schuman and others (19801 found that native grass production on reclaimed spoil in <br />Wyoming equaled forage production on an undisturbed native area when the topsoil thickness was 1.3 <br />feet. In northwestern <br />30 Revised 04/24/91 <br />