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takes into account land use, vegetative canopy cover, effective cover and grass type. The Curve <br /> Number represents vegetation. The pre-mining calculation utilized baseline vegetation cover values <br /> from the permit application (Table 2.3-13 and 4.4-2). The post-mining calculation uses vegetation <br /> cover data for the disturbed area collected in 2020. <br /> The variables used in the calculations are reasonable for making the comparison. The comparison <br /> therefore is technically valid. A chief cause of soil loss is transport of solids in suspension. The <br /> comparison indicates the total drainage area does not yield more suspended solids than pre-mining <br /> conditions. <br /> Photo 3(right): Well vegetated reconstructed <br /> drainage AB16 with check dam in foreground. <br /> The USLE is an empirical formula approximating <br /> expected sediment yield from a parcel of land. It is <br /> reasonable to hypothesize that the USLE is useful <br /> for discriminating between two significantly <br /> different yield rates. However, it is not useful for <br /> discriminating between two yield rates of similar <br /> magnitude. For the bond release parcels in SL22, 1► �` '�� ox , <br /> Trapper calculated a premining sediment yield rate of <br /> 3.02 tons per acre per year and a postmining rate of <br /> 2.21 tons per acre per year. The difference between <br /> these two calculated rates illustrates that the X <br /> postmining rate is less than the premining rate. This <br /> conclusion is only valid if Trapper used reasonable <br /> variables in the USLE calculations. The variables <br /> employed in the USLE equation and their <br /> definitions are presented in the table below: <br /> Table 3. USLE Variables and their Definitions <br /> Variable Definition <br /> R Climatic erosivity factor due to precipitation <br /> K Soil erodibility under a standard condition <br /> LS Slope length and steepness factor <br /> C Cover management/land use <br /> P Support practices factor <br /> The Division finds Trapper's selected USLE variables reasonable. The variables are similar to those <br /> found acceptable by the Division for Trapper's previous bond releases. The lands in SL22 are similar <br /> to lands in previous bond releases. Trapper's basis for selecting each variable and the Divisions review <br /> of each variable is presented in the table below: <br /> Permit Number C1981010 <br /> SL22 Page 12 of 18 <br />