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I• <br />u <br />portion of the upland area (7.4 acres) has been diverted to flow beneath the existing <br />haul road, through CMP-3, and joins a natural drainage channel. Drainage from the <br />western portion of the upland area (0.8 acres) is diverted away from the sediment pond <br />by berms. <br />The 10-year 24-hour storm event for the site is 1.5 inches and will generate <br />approximately 0.32 acre feet of runoff. The pond has been designed to contain <br />approximately 0.56 acre feet of water which is about the run-off generated by the 25- <br />year event. The sediment pond will be dewatered if it contains water above the <br />maximum sediment level. This dewatering event should occur within 48 hours after the <br />storm event which caused the water accumulation. <br />The mine waste pile and associated sedimentation structures are designed for <br />compliance with the effluent limitations of Rule 4.05.2. The sedimentation pond is also <br />designed to collect sediment loss from the disposal area. Erosion potential will be <br />limited to direct precipitation over the site. The estimated annual erosion rate, based on <br />the Universal Soil Loss Equation, is on the order of 0.03 acre feet per year. The pond <br />is designed to contain 0.19 acre feet which is over six years of sediment accumulation. <br />When sediment accumulation reaches 60% of the maximum storage, the sediment will <br />be removed and placed in the waste pile. Drainage calculations are presented in <br />Appendix M(vii). <br />An NPDES permit will be obtained for this sediment pond prior to commencing <br />construction. <br />The following design specification for the sediment pond is adapted from DMG <br />Rule 4.05.9(7): <br />The sediment pond is basically a dugout pond. Therefore, very little if any <br />embankment will be constructed. Material will be excavated from original ground to <br />form the sediment pond. However, if topsoil and organic material are deep, some <br />embankment may be required. <br />If an embankment is required, the embankment foundation area shall be cleared <br />• <br />of all organic matter, all surfaces sloped no steeper than 1 h:i v, and the entire <br />foundation surface scarified. <br />Permit Renewal <br />2-13 <br />09/03 <br />