2016-03-25_REVISION - C1981012 (2)

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