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~-~a <br />~~•~ ~fr~ <br />69. Upon additional review of literature, and in light of the site specific <br />topsoil, subsoils and climate, proposed re vegetation species and expected <br />rocky nature of the waste rock piles, heap leach pad and mine benches, the <br />Division is amending its recommended soil replacement depth from 2 to 3 feet <br />of subsoil below the proposed 8 to 12 inches of topsoil to an 18 inch depth of <br />topsoil/subsoil replacement on waste rock piles heap pad and solid rock mine <br />benches. <br />In Norman E. Hargis and Edward F. Redente's Soil Handling for Surface Mine <br />Reclamation, printed in Volume 39, Number 5, September-October, 1984 of the <br />Journal of Soil and Water Conservation, the following discussions .and findings <br />from other researchers was presented: <br />Water, light, carbon dioxide, and soil nutrients are most critical to <br />terrestrial production. Of these factors, soil nutrients are related directly <br />and water is related indirectly to the soil. To optimize plant production in <br />a given environment, the factors associated with soil - nutrients .and water <br />retention and availability - must be in balance with all other factors. Thus, <br />soil must be replaced to a thickness that allows the vegetation to derive <br />maximum benefit from the other factors not related to soil. Likewise, f~ r <br />economic reasons soil should not be replaced to an excessive thicknness so <br />~/ that, for example, precipitation or length of growing season are n~nt <br />sufficient to allow the vegetation to derive maximum benefit from the soil.... <br />The thickness of soil replaced depends upon three important ecological factors <br />(in order of importance: quality of the overburden to be covered, annual <br />average effective precipitation and soil quality... <br />Singleton and Barker, in southern Wyoming, found that so~~,f rmation on orphan <br />.~ mine overburden was very slow and that satisfactory over was not <br />established unless the overburden was covered with 12 to 18 inches of soil.... <br />P1cGinnies and Nicholas, in greenhouse and field tests conducted using 0 to 18 <br />inches of northwestern Colorado topsoil and overburden, found that herbage and <br />root yields of wheat and intermediate wheatgrass grown in the greenhouse <br />increased as topsoil thickness on overburden increased from 0 to 18 inches. <br />Rangeland vegetation improved in field studies with similar growth media as <br />topsoil thickness increased from 0 to 18 inches.... <br />The soil layer must be thick enough to store precipitation and spring runoff <br />at field capacity for plant use during the dry summer months. Cook and <br />associates recommended a general guideline of a 18-inch thick soil layer - 6 <br />to 8 inches of topsoil and 10 inches of subsoil in separate layers - for most <br />locations in the semiarid west. Their specific guidelines, according to <br />geographic location and vegetation type, included: northern great plains, 12 <br />to 18 inches of topsoil or subsoil; sagebrush foothills, 10 to 12 inches of <br />topsoil over 6 to 8 inches of subsoil; pinyon-juniper, 18 to 24 inches of <br />suitable of topsoil or subsoil; and ponderosa pine and mountain bnush, 10 <br />inches of topsoil over 8 inches of subsoil.... <br />