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For post-mining blocks, the USLE is calculated as: <br />A(") = (R)(K)(LS)(C)(P) <br />= (30)(.25)(6.2)(.010)(1.0) . <br />= 0.47 tons per acre per year <br />R 30 SCS Map of R factors for Colorado <br />K 0.25 Trapper Permit C-81-010 Appendix Q <br />LS 6.2 SCS LS table; 510 feet, 15.7% <br />C 0.010 SCS C factor for Permanent Pasture, Rangeland, Idle Land, <br />and Grazed Woodland - no canopy, 85% herbaceous cover, <br />grass type (Table 1.2-1 of Bond Release submittal) <br />P 1.0 SCS P factor <br />The USLE demonstrates that the existing condition of the reclaimed blocks results in equal or lesser <br />sediment contributions to surface runoff as compared to pre-mining conditions on an annual basis. <br />1.4.2 SEDCAD 4 <br />Trapper has developed a site drainage.and sedimentology model to estimate the total quantity of <br />sediment produced from a storm event for the runoff from each block under pre-mining and post-mining <br />conditions. The block drainage and sedimentology models were developed utilizing SEDCAD 4 for <br />Windows, a computer software program developed to assist in the evaluation of stormwater runoff, <br />erosion, and sediment control management techniques. <br />To develop representative models of the pre-mining conditions in each block, baseline information from <br />the permit was utilized as input data in the SEDCAD 4 program. To develop comparative models <br />representing existing conditions for each block, the vegetation survey information outlined in Section 1.2 <br />was utilized as input into the SEDCAD 4 program with input parameters modified as appropriate in <br />accordance with this information. Given the irregular shapes of the blocks in relation to the topography <br />and recognizing that portions of individual blocks may fall within adjacent sub-watersheds, it is difficult to <br />develop specific pre and post-mining runoff models for each entire block. In order to develop <br />representative and comparable runoff models, typical twenty acre sections of each block were modeled <br />using the average slope and slope length for the entire block. A summary of the SEDCAD 4 program <br />inputs and results for both the pre-mining and post-mining land conditions are shown on Tables 1.4-1 and <br />1.4-2 respectively. The SEDCAD 4 computer printouts and input calculation sheets can be found in <br />Appendix 3. Input parameter references are also provided in Appendix 3. <br />12