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EXHIBIT 15 - Subpart H (40 CFR Part 434.82) Sedimentation Control Plan: <br />Discharge permit CO0048988 requires a demonstration "designed to prevent an <br />increase in the average annual sediment yield from pre -mine, undisturbed <br />conditions. The sediment control plan must identify the best management <br />practices (BMPs) and also must describe design specifications, construction <br />specifications, maintenance schedules, criteria for inspection as well as expected <br />performance and longevity of the best management practices. <br />Using watershed models, the operator must demonstrate that implementation of <br />the Sediment Control Plan will result in average annual sediment yields that will <br />not be greater than the sediment yield levels from pre -mined, undisturbed <br />conditions. The operator must use the same watershed model that was, or will <br />be used, to acquire the SMCRA permit' <br />Sediment Ponds 005, 006, 007, 008, 030 and 031 are in place and function as <br />the Sediment Control Plan required for the demonstration. Design criteria for the <br />sediment ponds can be found in Exhibits 15-9 through 11 a. Maintenance and <br />inspection criteria can be found in Section 2.05.3(4). <br />Pre -mining, undisturbed runoff will be calculated using SedCad. SedCad uses <br />the Revised Universal Soil Loss Equation (RUSLE) to demonstrate sediment <br />loss. Where applicable, specific factors derived in Exhibit 15 have been used. <br />SedCad Input Derivation: <br />A description of the derivation of curve numbers can be found in Exhibit 15, Pond <br />Drainage Design, beginning on page 2. <br />Curve Numbers for flows draining into Lorencito Canyon, and side Canyons are <br />as follows; <br />#- Ponderosa Pine Communities, CN = 66 or 69 <br />�_ Mountain Shrub Communities, CN = 51 <br />Curve Numbers for flows draining into Cow Canyon are as follows; <br />4- Grassland Communities, CN = 56 <br />4- Mountain Shrub Communities, CN = 61 <br />Soil Series description, see Exhibit 15, Table 7. In general, for the undisturbed <br />analysis, there is an upland area, and a grassland area. For the most <br />conservative analysis, the higher curve number will be used for the entire area. <br />For the sedimentology portion, only one soil type will be used and it will be the <br />most conservative Soil Series in order to demonstrate the biggest sediment loss <br />potential for each area. <br />Soil Erodibility factors "K" are shown on Exhibit 15, Table 9. <br />Subpart H Demonstration Page 1 03/15 <br />