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submitted a design for the gully repair as part of TR-36, which was subsequently approved by Colorado Division of Mining and Geology (now known as Colorado Division of Reclamation, Mining and Safety). ~' Recent observations indicate that the meandering channel design and construction (TR-36 design) has not totally stabilized the Bullied area. Consequently, SCC has prepared a new design for the upper PM-8 area (the TR-41 design). The two meandering flow paths have been removed and replaced with V-ditches constructed across contour. The spacing of the V- ditches limits down-slope flow distances, which should reduce ivelocities and erosive forces. The V-ditches will then convey the collected run-off to Channel SI1PM-8. The locations of the V-ditches are shown on Exhibit 7-19, Postutining Drainage Control, as well as Exhibit 13-2A, Postmining Topography and Permanent. Features. The SEDCAD4 demonstration is presented in Appendix A on pages 7-12-73 Through 7-12-84B. The V-ditch design is summarized in the following sections. Hydrology The upper PM-8 area has been divided into five subwatersheds (see Exhibit 7-22). Drainage areas range from 8.7 acres to 31.4 acres. Recent vegetation monitoring in the general vicinity shows that average vegetative cover varies biaween 30% and 70%, which the SCS (1986) indicates is a fair cover condition. The SC:i suggests that a herbaceous type cover rated "fair", with a "B" soil hydrologic condition corresponds to a curve number of 71 (CN=71) and, consequently, what SCC used in the V-ditch design. This curve number reflects a more conservative design, which SCC: believes is warranted in this area due to the recent erosional forces (circa 2004 - 2006) thai plague this area. Reclaimed Soil Type: B Ground Cover Type: Herbaceous Ground Cover: Fair CN: 71 V-ditch #1 collects run-off from upper part of the watershed area. This ditch will be constructed across contour at a gradient of approximately 5%.. The contributing drainage area is approximately 31.4 acres. The SEDCAD4 demonstration (see Appendix A, pages 7-12-73 through 7-12-84B) estimates the 10-year, 24-hour storm event will generate a peak run-off of 2.2 cubic feet per second (cfs). V-ditch #2 is a new ditch that traverses across contour at a gradient of approximately 5%. The contributing drainage area is 16.7 acres. The SEDCAD4'demonstratian estimates the 10-year, 24-hour storm event will generate a peak run-off of 1:2 cfs. C J TR-41 7-12-10 ~ ' Revised 04/07