2008-09-29_PERMIT FILE - C1981019A (9)

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RULE 4 PERFORMANCE STANDARDS ......................... 4.05.5 Sediment Control Measures Sediment control measures to be implemented are shown on the Hydrology - South Map (Map 12) and the Hydrology - North Map (Map 11). These facilities, consisting primarily of diversion ditches and sedimentation ponds, will be located, constructed and maintained to avoid erosion and increased contribution of sediment load to runoff. Discussion on the sediment and drainage control is presented under Section. 2.05.6. The design parameters of the various sedimentation control measures are found in Exhibit 7, Hydrology Information. As necessary, facilities to control sediment will be installed in areas above or below the planned sites of disturbance. "Upstream" facilities, such as temporary diversion ditches and- check dams up slope from the mining activities, will divert runoff away from the disturbed areas. Temporary diversion ditches below the disturbed area will divert runoff into sediment ponds. The actual mining areas will aid in retaining sediment within the disturbed areas by catching water in pits, small depressions and dozer basins, etc. in active, unreclaimed mine workings. Water leaving the reclaimed areas will drain into contour furrows or other sediment traps, as necessary, before entering the sedimentation pond. Small Area Exemptions From time to time, it may be necessary to have small areas that do not drain to a sediment pond. Alternative sediment control measures will be used for these areas. These will be designed to meet the requirements of Rule 4.05.2.3 and Rule 4.05.5. Exhibit 7, Item 14-P (Volume 2C) provides a specific design for a small borrow pit needed to construct the embankment for the Section 28 Sediment pond. 4.05.6 Sedimentation Ponds The location of all existing and planned sedimentation ponds are presented on the Hydrology - South Map (Map 12) and the Hydrology - North Map (Map 11). The design plans and specifications for the sedimentation ponds are described in this section. The design parameters and detailed sedimentation calculations for the sedimentation ponds are shown in Exhibit 7, Hydrology Information. The sedimentation pond embankment and emergency spillway design are also shown in Exhibit 7, Hydrology Information. All sedimentation ponds will be located as close as practical to the areas to be disturbed. Other methods of sediment control will be located on the reclaimed areas; these methods include the use of contour furrowing, contour drainage ditches, chisel plowing and revegetation etc. This application contains calculations used to determine runoff volumes and flow rates for a theoretical 10-year, 24-hour precipitation event and subsequent sediment volumes. The precipitation data were obtained from the NOA Atlas 2, Volume 3 for Colorado; soil types were obtained from the Soil Conservation Service, and are shown on the Soils - South Map (Map 6) and the Soils - North Map (Map 5). The ongoing mining activities within each watershed of the permit area will create constantly changing hydrologic conditions. The design models are generally based on a static, theoretical scenario, utilizing SEDCAD+ Version III which considers a final reclamation and pit closure scenario in each watershed. Refer to Drawing 41 - Watershed Boundaries for Hydrologic Modeling for a delineation of the areas used for these modeling purposes as well as the individual maps associated with each SEDCAD run. The dates indicated on Drawing 41 are for development of the worst case scenario for hydrologic modeling and are not a definitive schedule for mining and reclamation activities. It is Colowyo's contention that the proposed models represent nothing more than our best hydrologic estimates for a described range. of conditions. According to Applied -Hydrology and Sedimentology for Disturbed Areas, Barfield, Warner and Haan, 1981, "Hydrologic calculations are estimates, with the error Rule 4 Performance Standards 4.05-4 Revision Date: 6/23/08 Revision No.: MR-91