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Page 2 <br />Section 3.03.1 <br />(b) No more than sixty (60) percent of the bond shall be released so long as the lands to <br />which the release would be applicable are contributing suspended solids to streamf/ow or runoff <br />outside the permit area in excess of premining levels as determined by baseline data or in <br />excess of levels determined on adjacent nonmined areas, until soil productivity for prime <br />farmlands has returned to equivalent levels of yield as nonmined land of the same soil type on <br />the surrounding area under equivalent management practices as determined from the soil <br />survey performed under 2.04.12 and 2.06.6 and the success determination methodology of <br />4.25.5(3)(a); or, on alluvial valley floors, until the essential hydrologic functions and agricultural <br />productivity have been reestablished. <br />Rule 4.15.1(2)(b) also requires that the vegetation cover control erosion equal to pre- <br />mining levels. <br />At least one previous bond release application has been submitted and approved at this <br />site where the applicant has chosen to use the Revised Universal Soil Loss Equation <br />(RUSLE) to estimate pre-mining and post-mining sediment production. The RUSLE <br />equation is; <br />A=RK(LS)CP <br />A = Average annual soil loss in tons per acre per year <br />R = Rainfall/runoff erosivity <br />K = Soil erodibility <br />LS = Hillslope length and steepness <br />C = Cover-management <br />P = Support practice <br />The R factor is an expression of the erosivity of rainfall and runoff at a particular <br />location. The value of "R" increases as the amount and intensity of rainfall increase. <br />The K factor is an expression of the inherent erodibility of the soil or surface <br />material at a particular site under standard experimental conditions. The value of "K" is <br />a <br />function of the particle-size distribution, organic-matter content, structure, and <br />permeability <br />of the soil or surface material. For undisturbed soils, values of "K" are often available <br />from <br />soil surveys conducted by the NRCS. For disturbed soils, nomograph equations <br />are sometimes used to compute appropriate erodibility values. <br />The LS factor is an expression of the effect of topography, specifically hillslope <br />length and steepness, on rates of soil loss at a particular site. The value of "LS" <br />increases as