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Phase II RUSLE Soil Loss Data <br />General Comments and Observations, Sediment Demonstration <br />Rule 3.03.1(3)(b) states that "No more than sixty (60) percent of the bond shall be <br />released so long as the lands to which the release would be applicable are contributing <br />suspended solids to streamflow or runoff outside the permit area in excess of premining <br />levels as determined by baseline data or in excess of levels determined on adjacent <br />nonmined areas..." <br />Rule 4.15.1(2)(b) states that "(t)he vegetation cover shall be capable of stabilizing the soil <br />surface to achieve erosion control equal to premining levels." <br />Colowyo has previously submitted at least one Phase II Bond Release application that <br />used the Revised Universal Soil Loss Equation (RUSLE) to estimate pre-mining and <br />post-mining sediment production. The RUSLE 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 material at a <br />particular site under standard experimental conditions. The value of "K" is a function of <br />the particle-size distribution, organic-matter content, structure, and permeability of the <br />soil or surface material. For undisturbed soils, values of "K" are often available from soil <br />surveys conducted by the NRCS. For disturbed soils, nomograph equations are <br />sometimes used to compute appropriate erodibility values. <br />The LS factor is an expression of the effect of topography, specifically hillslope length <br />and steepness, on rates of soil loss at a particular site. The value of "LS" increases as <br />hillslope length and steepness increase, under the assumption that runoff accumulates and <br />accelerates in the downslope direction. This assumption is usually valid for lands <br />experiencing overland flow but may not be valid for forest and other densely-vegetated <br />areas. <br />The C factor is an expression of the effects of surface covers and roughness, soil biomass, <br />and soil-disturbing activities on rates of soil loss at a particular site. The value of "C"