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steepness. This value represents how erodible the particular slope length and steepness is <br /> relative to a 72.6 foot long and 9% steep slope unit plot. These values were unique to each parcel and <br /> were determined using the RUSLE 1.06c application with the inputs of the BR parcel lengths and slope <br /> gradient values. <br /> C Factor, Cover Management <br /> The C Factor represents the effects of plants, soil cover, soil biomass, and soil distributing activities of <br /> erosion. The C factor accounts for all surface cover including non-plant material. Data from the <br /> vegetation report in attachment D were used as inputs to the RUSLE 1.06c application to determine the C <br /> Factor of 0.003. <br /> P Factor, Support Practice <br /> The P factor reflects the impact of support practices on the annual average erosion rate. A conservative <br /> value of 1 indicates that there is no consideration for deposition where as a value of 0 indicates that no <br /> sediment left the slope. In this scenario a value of 0.9 is appropriate. <br /> The Division finds SPL's selected RUSLE variables reasonable. SPL's basis for selecting each variable <br /> and the results of the analysis can be referenced in the Phase II Sediment Demonstration section and <br /> Tables 6 and 7 of the Application. The Divisions review of each variable found SPLs methodology <br /> appropriate. Table 7 illustrated below demonstrates the reference area calculations. <br /> Table 7:SL6 Seneca II West Bond Release RUSLE Variables and Calculations for Reference Area Comparison <br /> Length of Slope <br /> Reference Area R K Segment 6 Elev Gradient L5 C P A <br /> Aspen RA 16 0.24 1000 260 26 8.51 0.012 0.9 0.3529 <br /> Mountain Brush RA 16 0.32 860 160 19 5.32 0.012 0.9 0.2942 <br /> Sage/Snowberry RA 16 0.32 1000 120 12 2.79 0.004 0.9 0.0514 <br /> Steep Mountain Brush RA 16 0.2 430 225 52 13.2 0.02 0.9 0.7603 <br /> Western Wheat/Sage RA 16 0.37 630 120 19 4.97 0.011 0.9 0.2913 <br /> The results of the RUSLE analysis (Table 6), submitted with the application, show that the average <br /> ton/acre/year of sediment yield on the requested parcels amounts to 0.052. When compared with the <br /> weighted results of the reverence areas(Table 7),the 0.052 ton/acre/year is less than any of the <br /> contributing reference areas and meets the requirements of rule 3.03.1(3)(b). <br /> Suspended Solids Analysis <br /> A comparison of dissolved iron in post mine samples from 2015 through 2019 to initial samples collected <br /> (1989),indicated that no statistical significant change had occurred over time. Five stream monitoring <br /> points exist at the site encompassing the Dry Creek Watershed including Hubberson Gulch and the Sage <br /> Creek watershed. Monitoring of these locations took place from 2013 through 2019. Between 2015 and <br /> 2019 monitoring and Dry Creek(WSD5), Sage Creek(WSSF3),and Hubberson Gulch(WSHFI),indicate <br /> TSS is less than or comparable to pre mine results. At stream point WSH7,located downstream of ponds <br /> 016 and 017 in Hubberson Gulch and upstream of pond 6,shows an increasing TSS trend. Once the <br /> drainage status is"reclamation"NPDES outfalls are no longer monitored for TSS. Between 2015 and 2019 <br /> TSS was sampled from the Dry Creek Watershed(outfalls 005, 006,016,and 017). Monitoring results were <br /> less than the average and maximum pre mine concentrations,indicating stability in the reclaimed areas <br /> reporting to the outfalls. Regarding the trend at stream point WSH7,measurements between 2015 through <br /> Permit Number C1982057 Prepared by: R.Reilley MS,GISP <br /> SL6 Phase II and III Page 10 of 16 <br />