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RULE 4 PERFORMANCE STANDARDS <br />Rule 4 Performance Standards 4-10 Revision Date: 6/4/25 <br />Revision No.: MR-264 <br />4.05.5 Sediment Control Measures <br />Sediment control measures to be implemented are shown Map 12. These facilities, consisting <br />primarily of diversion ditches and sedimentation ponds, will be located, constructed and <br />maintained to avoid erosion and increased contribution of sediment load to runoff. Discussion on <br />the sediment and drainage control is presented under Section. 2.05.6. The design parameters of the <br />various sedimentation control measures are found in Exhibit 7, Hydrology Information. <br />As necessary, facilities to control sediment will be installed in areas above or below the planned <br />sites of disturbance. “Upstream” facilities, such as temporary diversion ditches and- check dams <br />up slope from the mining activities, will divert runoff away from the disturbed areas. Temporary <br />diversion ditches below the disturbed area will divert runoff into sediment ponds. The actual <br />mining areas will aid in retaining sediment within the disturbed areas by catching water in pits, <br />small depressions and dozer basins, etc. in active, unreclaimed mine workings. Water leaving the <br />reclaimed areas will drain into contour furrows or other sediment traps, as necessary, before <br />entering the sedimentation pond. <br />Small Area Exemptions from time to time, it may be necessary to have small areas that do not <br />drain to a sediment pond. Alternative sediment control measures will be used for these areas. <br />These will be designed to meet the requirements of Rule 4.05.2.3 and Rule 4.05.5. Exhibit 7, Item <br />14-P (Volume 2C) provides a specific design for a small borrow pit needed to construct the <br />embankment for the Section 28 Sediment pond. <br />4.05.6 Sedimentation Ponds <br />The location of all existing and planned sedimentation ponds are presented Map 12 and 12A. The <br />design plans and specifications for the sedimentation ponds are described in this section. The <br />design parameters and detailed sedimentation calculations for the sedimentation ponds are shown <br />in Exhibit 7, Hydrology Information. The sedimentation pond embankment and emergency <br />spillway design are also shown in Exhibit 7, Hydrology Information. All sedimentation ponds will <br />be located as close as practical to the areas to be disturbed. Other methods of sediment control will <br />be located on the reclaimed areas; these methods include the use of contour furrowing, contour <br />drainage ditches, chisel plowing and revegetation etc. <br />This application contains calculations used to determine runoff volumes and flow rates for a <br />theoretical 10-year, 24-hour precipitation event and subsequent sediment volumes. The <br />precipitation data were obtained from the NOA Atlas 2, Volume 3 for Colorado; soil types were <br />obtained from the Soil Conservation Service, and are shown Maps 5A through 5D. <br />The ongoing mining activities within each watershed of the permit area will create constantly <br />changing hydrologic conditions. The design models are generally based on a static, theoretical <br />scenario, utilizing SEDCADTM which considers a final reclamation and pit closure scenario in each <br />watershed. Please see Map 12 for watershed boundaries used for hydrologic modeling.