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3.3 Sedimentoloav Evaluation <br />The purpose of the sedimentology evaluation is to demonstrate that the completed revegetation and <br />grading in the Phase II Bond Release Blocks has achieved erosion control at least equal to pre -mining <br />levels as required in Rule 4.15.1 (2) (b), and suspended solids delivered to streamflow outside the permit <br />area will not exceed pre -mining levels as required under Rule 3.03.1 (3) (b). The methodology used is <br />the Revised Universal Soil Loss Equation RUSLE using site-specific soil and vegetation data along with <br />slope measurements comparing the Bond Release Block and associated reference areas. <br />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) = RoKeLoSeCoP <br />Where: A = predicted erosion in tons/acre/year <br />R = erosivity index of local rainfall <br />K = soil erodibility actor <br />LS = length/slope factor <br />C = vegetative cover factor <br />P = management practice factor <br />Representative slopes for Phase II Bond Release Blocks 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 />This factor is mapped by USDA NRCS, it represents a combination of the rainfall intensity and <br />duration which are recognized as major factors in dislodging soil particles The value for the Colowyo Mine <br />area is 19. <br />Soil Erodibility Factor K <br />This is an empirical factor with values published by USDA NRCS for mapped soils throughout the <br />United States. The Soil Survey of Moffat County, Colorado shows the following mapped soils in the Phase <br />II Bond Release Blocks. The K Factor for pre -mining condition was determined using the soil survey. <br />Corresponding K Factors from the referenced soil survey are also provided. The post -mining K Factor <br />was calculated in RUSLE 1.06c. This was done to account for the lower bulk density and increased <br />16 <br />