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In order to meet CDRMS Regulation 3.03.1(3)(b), SPL provided modeling information demonstrating <br /> sediment transport,comparing the reclaimed areas to the adjacent unmined areas using the RUSLE <br /> Revised Universal Soil Loss Equation). The RUSLE calculates expected average annual soil loss per <br /> acre of land(rate of erosion),based on slope,rainfall pattern, soil type and vegetation type from the <br /> equation ARKLSCP;where A (average annual soil loss)represents the product of the six variables <br /> defined below. <br /> The RUSLE is an empirical formula approximating expected sediment yield from a parcel of land. It is <br /> reasonable to hypothesize that the RUSLE is useful for discriminating between two significantly different <br /> yield rates. However, it is not useful for discriminating between two yield rates of similar magnitude. <br /> The variables used in the calculations are reasonable for making the comparison. The comparison therefore <br /> is technically valid. A chief cause of soil loss is transport of solids in suspension. The comparison indicates <br /> the total drainage area does not yield more suspended solids than pre-mining conditions. <br /> The definition for the RUSLE variables are presented below in Table 4: <br /> Table 4. R LISLE Variables and their Definitions. Only the "C" factor varies <br /> Variable Definitio between the pre-mining and the <br /> R Climatic erosivity factor due to precipitation post-mining calculations; all <br /> K Soil erodibility under a standard condition other variables are constant for <br /> LS Slope length and steepness factor pre-and post-mining. The C <br /> C Cover management/land use factor takes into account land <br /> P Support practices factor use,vegetative canopy cover, <br /> effective cover and grass type. <br /> The pre-mining calculation utilized baseline vegetation cover values from the permit application. <br /> Table 5,of the 24 November 2020 adequacy review response comprises a portion of SPLs' response to The <br /> Divisions 21 August 2020 adequacy questions by addressing the RUSLE variables and calculations for each <br /> bond release polygon. The average tons/acre/year of sediment yield 0.06 from the SL8 proposed bond <br /> release areas when compared to the Divisions RUSLE demonstration for the Yoast reference areas (as per <br /> SL7), 0.37 tons/acre/year show that the proposed SL8 bond release areas contribute less sediment then the <br /> surrounding reference areas meeting Rule 3.03.1(3)(b) requirements. As the reference areas remain the <br /> same for both the SL7 and SL8 bond release actions, The Division considers the variables and associated <br /> comparison valid. <br /> IV. PROPOSED DECISION <br /> The approved post-mining land use for the land applicable to SL8 is livestock grazing and wildlife <br /> habitat. The bond release block,the subject of this bond release application (SL8),has been reclaimed for <br /> livestock grazing and wildlife habitat. The revegetation plan was designed to achieve the approved post <br /> mining land use and appears to be on track to meet this objective based on the vegetation cover <br /> established within the bond release block. <br /> Based on the observations above, the Division proposes to approve SPL's request for a partial Phase II <br /> bond release for the Yoast Mine. This proposed decision will release the applicant from Phase II liability <br /> Permit Number C1994 082 Page 14 of 15 <br />