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,~ Poor quality spoil material may require more than 60 inches of topsoil <br />and/or subsoil replacement whereas good quality spoil may not need any. <br />Ooll et al. (1984) and Barth and Martin (1982) demonstrated that from 36 <br />to 60 inches of topsoil and/or subsoil was necessary for optimum <br />production on sodic or acidic spoil. Barth (1984) found that production <br />of perennial grasses on bare spoil with no adverse properties was as <br />great as when spoil was covered with soil of any thickness. <br />In the northern Great Plains, maximum production is generally achieved <br />on suitable spoil when topsoil replacement depths range from 10 to 18 <br />inches. Schuman et al. (1980) showed that 15 inches of topsoil provided <br />the maximum native forage production, highest infiltration, and greatest <br />water holding capacity on reclaimed spoil in Wyoming. Pinchak et al. <br />(1985) also found 15 inches of topsoil to be optimum in Wyoming in terms <br />of seeded species production and limited infestation of non-seeded <br />species. Barth and Martin (1981) showed fine sandy loam topsoil depths <br />• to be 10 inches for optimum perennial grass production on nonsaline, <br />nonsodic silt loam spoil in southeastern Montana. In northwestern <br />Colorado, McGinnies and Nicholas (1982) demonstrated with field and <br />greenhouse studies that vegetation stands, herbage yield, and root <br />production all increased linearly as topsoil depths increased from 0 to <br />18 inches. <br />DePuit (1984) points out that optimum plant community composition and <br />diversity is often reached at shallower topsoil depths than what is <br />required for maximum production. This phenomenon apparently exists at <br />the Seneca and Trapper Mines. Pfannenstiel and Wendt (1985) <br />demonstrated that six to eight inches of topsoil applied to Wadge spoil <br />at Seneca Mine in 1976 has produced a native looking sagebrush grassland <br />community with a shrub density of 1,450 stems per acre. Redente and <br />Hargis (1985) demonstrated at Trapper Mine that with the compromise of <br />same above ground production, performance of more life forms was <br />maximized by replacing only six inches of topsoil. <br />• Topsoil replacement depths at Nucla Mine will be adjusted by both mine <br />area and the proposed post-mine land use. Mean topsoil replacement <br />9-3-12 Revised 07/18/88 <br />