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Sedimentation Pond <br />The sediment pond and the general drainage plan for the waste disposal site <br />were prepared by Tammerin K. Stover - Bishop, Colorado Professional Engineer, <br />No. 43402. See Figure 3. <br />The total drainage area associated with the proposed site is approximately 385 <br />acres. The area was divided into separate watersheds draining into run -off and <br />collection ditches designed to handle the run -off from the 100 -year, 24 -hour <br />precipitation event. The drainage areas are shown on Map 20 in Volume Il. <br />The sediment pond was sized to contain the run -off from the 10 -year 24 -hour <br />precipitation event (1.8 inches). This storm event will generate approximately 3.8 <br />acre feet of runoff. Sediment accumulation was estimated with the use of the <br />Universal Soil Loss Equation. The pond has been designed to contain <br />approximately 3.8 acre feet of water and 0.8 acre feet of sediment. The <br />sediment pond will be dewatered if it contains water above the maximum <br />sediment level. This dewatering event should occur within 48 hours after the <br />storm event which caused the water accumulation. Sediment will be removed <br />when it is at or below the maximum sediment storage level. <br />The mine waste pile and associated sedimentation structures are designed for <br />compliance with the effluent limitations of Rule 4.05.2. Drainage calculations are <br />presented in Appendix B. <br />The following design specification for the sediment pond is adapted from DRMS <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 <br />to form the sediment pond. However, if topsoil and organic material are deep, <br />some embankment may be required. <br />If an embankment is required, the embankment foundation area shall be cleared <br />of all organic matter, all surfaces sloped no steeper than 1 h:1 v, and the entire <br />foundation surface scarified. <br />TR -81 _10- 10/13 <br />