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concentration at Outfalls 012 and 013 are below the pre -mine average measured at downstream <br />point YSS2 (23.6 mg/L) and the average TSS concentration at Outfall 014 only exceeds the pre - <br />mine average at downstream point YSS2 by a few milligrams per liter. The average at Outfall <br />014 is strongly influenced by a single sample with elevated TSS (170 mg/L) and its important to <br />note that TSS concentrations in the 13 other samples collected during this time period did not <br />exceeded 42 mg/L. A statistical comparison of pre -mine stream points and post mine NPDES <br />TSS concentrations is provided in Attachment 1. The analysis indicates there is no statistically <br />significant difference (95% Confidence Level) between the TSS concentrations measured at the <br />Yoast NPDES outfalls and the pre -mine stream concentrations. This further indicates that the <br />reclaimed parcels reporting to these ponds are adequately stable. <br />RUSLE <br />In order to meet CDRMS Regulation 3.03.1(3)(b), SPL has demonstrated the sediment <br />contributions to the surface post -mining and reclamation activities by the use of RUSLE, <br />Revised Universal Soil Loss Equation. The major bond release parcels within this bond release <br />request have been processed using RUSLE and the average sediment contribution to the surface <br />in tons per acre per year have been calculated and compared to that of the reference areas <br />designated for the vegetation success. <br />The Revised Universal Soil Loss Equation is used to predict and compare the gross annual <br />erosion per acre on the reclaimed and vegetated parcels and compare them to the undisturbed <br />reference areas. <br />The RUSLE equation and variables are as follows: <br />A=RKLSCP <br />Where A = Gross erosion per acre per year <br />R = Erosivity of rainfall and runoff <br />K = Soil Erodibility <br />LS = Hill slope -length and gradient <br />C = Cover management <br />P = Support Practice <br />R Factor, Erosivity of Rainfall and Runoff <br />The R Factor quantifies the effect of raindrop impacts and reflects the amount and rate of runoff <br />associated with annual precipitation. The value used for this factor was obtained from the EPA <br />Rainfall Erosivity Factor Calculator. The calculator accounts for the mine location and <br />disturbance dates to relate back to historic rainfall data. For this demonstration a R Factor of 16 <br />was used. <br />SL-8 - 11 <br />