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Plan). By dividing the number of acre-feet available topsoil (102.8) by the number of <br /> acres to be or that are disturbed (73.4), it is estimated that approximately 1.4 feet (17 <br /> inches) of suitable topsoil is available to be replaced. <br /> Approximately 9.9 acre-feet of suitable topsoil/subsoil is available for replacement in <br /> Mine Areas 2 and 3 over the life-of-mine (1988-1989) operation at Nucla Mine (Table <br /> 21-3 and Exhibit 19-1, Reclamation Plan). The disturbance area requiring topsoil <br /> replacement totals about 29.9 acres (Table 21-3 and Exhibit 21-1, Topsoil Balance Plan). <br /> By dividing the number of acre-feet available topsoil/subsoil (9.9) by the number of acres <br /> to be or that are disturbed (29.9), it is estimated that approximately 0.3 feet (4 inches) <br /> of suitable topsoil/subsoil is available to be replaced. <br /> Topsoil Depth Requirements. Topsoil is generally beneficial for increasing infiltration, <br /> improving seedbed and rooting mediums for germination and plant establishment, enhancing <br /> nutrient cycling, and serving as a source of seed, rhizomes, and root cuttings that can <br /> promote species diversity. Topsoil depth requirements on mined lands are site specific. <br /> The quality of topsoil and spoil materials, climatic factors, seeded plant specie <br /> • requirements, and concurrent reclamation practices all influence the optimal topsoil <br /> replacement depth for a specific mine site (Pinchak et al ., 1985). Often, the quality of <br /> spoil material to be covered by topsoil is the major controlling factor (Schuman and <br /> Power, 1980; Barth and Martin, 1982). Together, the ultimate topsoil replacement depth <br /> and resultant spoil quality can greatly influence productivity and longevity of the <br /> vegetation established on reclaimed lands (Schuman et al., 1985).. <br /> Poor quality spoil material may require more than 60 inches of topsoil and/or subsoil <br /> replacement whereas good quality spoil may not need any. Doll et al . (1984) and Barth and <br /> Martin (1982) demonstrated that from 36 to 60 inches of topsoil and/or subsoil was -- <br /> necessary for optimum production on sodic or acidic spoil. Barth (1984) found that <br /> production of perennial grasses on bare spoil with no adverse properties was as great as <br /> when spoil was covered with soil of any thickness. <br /> In the northern Great Plains, maximum production is generally achieved on suitable spoil <br /> when topsoil replacement depths range from 10 to 18 inches. Schuman et al . (1980) showed <br /> that 15 inches of topsoil provided the maximum native forage production, highest <br /> 21-15 Revised 08/19/88 <br />