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RUSLE was used to calculate predicted annual sediment erosion in tons/acre/year based on the <br /> equation: <br /> A(soil loss in tons/acre/year) = R•K•L•S•C•P <br /> Where: A = predicted erosion in tons/acre/year <br /> R = erosivity index of local rainfall <br /> K = soil erodibility factor <br /> LS = length/slope factor <br /> C = vegetative cover factor <br /> P = management practice factor <br /> Representative slopes for the Phase II bond release block and associated reference areas were <br /> selected to calculate predicted soil loss in in tons/acre/year. For this analysis, no adjustment was made <br /> for sediment delivery ratio, rather it has been conservatively assumed that all soil eroded off the natural <br /> surface or the reclaimed mine areas would eventually report to receiving streams even though it is likely <br /> that the majority of the sediment will become trapped on site before reaching a stream. The following <br /> discussion provides the basis for selection of each factor. <br /> Erosivity Index R <br /> The R factor is mapped by USDA NRCS, and represents a combination of the rainfall intensity and <br /> duration, which are recognized as major factors in dislodging soil particles. The value of the R factor for <br /> the Colowyo Mine area is 19. <br /> Soil Erodibility Factor K <br /> The K factor is an empirical factor with values published by USDA NRCS for mapped soils throughout <br /> the United States. The Soil Survey of Moffat County, Colorado shows the following mapped soils in the <br /> Phase II bond release block, along with corresponding K factors. The post-mining K Factor was calculated <br /> in RUSLE 1.06c, and accounted for the lower bulk density and increased permeability of recently disturbed <br /> soil. Site collected soil samples were used to determine the inputs for calculating the post-mining K Factor. <br /> 14 <br />