2008-11-10_PERMIT FILE - C1996083A (2)

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Sedimentation Pond The sediment pond and the general drainage plan for the waste disposal site were prepared under the direction of J. E. Stover, Colorado Professional Engineer, No. 19230. See Figure 3. The total drainage area associated with the proposed site is approximately 388 acres. The area was divided into separate watersheds draining into run-off and collection ditches designed to handle the run-off from the 100-year, 24-hour precipitation event. The drainage areas are shown on Map 20 in Volume II. The sediment pond was sized to contain the run-off from the 10-year 24-hour precipitation event (1.8 inches). This storm event will generate approximately 3.5 acre feet of runoff. Sediment accumulation was estimated with the use of the Universal Soil Loss Equation. The pond has been designed to contain approximately 3.5 acre feet of water and 0.3 acre feet of sediment. The sediment pond will be dewatered if it contains water above the maximum sediment level. This dewatering event should occur within 48 hours after the . storm event which caused the water accumulation. When sediment accumulation reaches 75% of the maximum storage, the sediment will be removed and placed in the waste pile. The mine waste pile and associated sedimentation structures are designed for compliance with the effluent limitations of Rule 4.05.2. Drainage calculations are presented in Appendix B. The following design specification for the sediment pond is adapted from DMG Rule 4.05.9(7): The sediment pond is basically a dugout pond. Therefore, very little if any embankment will be constructed. Material will be excavated from original ground to form the sediment pond. However, if topsoil and organic material are deep, some embankment may be required. If an embankment is required, the embankment foundation area shall be cleared of all organic matter, all surfaces sloped no steeper than 1 h:1v, and the entire foundation surface scarified. TR-44 - 7 - 02/07 AOP2ouEo 3/~O/D7