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The "per acre" erosion of each sub-area, which are referred to here as <br />"Reclamation Units", were then extended to simple tons/year for the entire area <br />. by multiplying the per/acre erosion losses by the respective Reclamation Unit <br />areas in acres. The pre-mining and post-mining erosion values can then be <br />compared on a common basis. <br />For this analysis no adjustment was made for "sediment delivery ratio". Rather, it <br />has been conservatively assumed that all soil eroded off the natural surface or <br />the reclaimed mine areas would eventually report to receiving streams, even <br />though it is likely that some sediment will become trapped on site before reaching <br />a stream. <br />The 28 Reclamation Units are identified in the attached Table 4, including their <br />respective surface areas. The same areas were used in the pre-mining and the <br />reclaimed post-mining conditions. Pre-mining and reclaimed post-mining <br />RUSLE factors are also presented in the table. It can be observed in the table <br />that the reclaimed lands will produce less erosion than would be expected in the <br />natural pre-mining condition. <br />The following discussion provides the basis for selection of each factor in the pre- <br />mining and reclaimed post-mining cases. Where appropriate, reference is made <br />to commonly accepted texts and government publications. <br />Erosivity Index, R <br />is This factor is mapped by USDA NRCS. It represents a combination of the rainfall <br />intensity and energy, which are recognized as a major factor in dislodging soil <br />particles. The value for the Colowyo Mine area is 19. <br />Soil Erodibility Factor, K <br />This is an empirical factor, with values published by USDA NRCS for mapped <br />soils throughout the United States. The data are typically presented in county <br />soil surveys. <br />Phase I and 11 Bond Release Application 14