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Water Control Measures <br />Rule 4.09.1(13) requires that an appropriate underdrain be installed if seeps, <br />springs or waterways, natural or manmade, are in the coal waste disposal footprint <br />area. A June 2013 inspection of the site found that seepage from the Fire <br />Mountain Canal had surfaced in the upper diversion ditch. Wet areas were also <br />noted below the upper diversion ditch. The seepage did not cause any perceptible <br />flow. The design of a rock subdrainage system is detailed below. <br />The run -off and collection ditches are shown on Map 15. Run -off from the <br />benches will be directed to the east and west to collection ditches. The east and <br />west collection ditches D -J8 and D -J9 are; 1) lined with riprap where necessary <br />to ensure they are stable; 2) constructed off the fill and; 3) designed to safely <br />pass the run -off from the 100 -year, 24 -hour precipitation event. <br />See Volume III, Exhibit 8 for detailed design information of the run -off and <br />collection ditches. <br />Sedimentation Pond <br />Sediment Pond J will be modified so it will contain the additional run -off from the <br />coal mine refuse disposal area. The sediment pond and the general drainage <br />plan for the waste disposal site were prepared under the direction of J. E. Stover, <br />Colorado Professional Engineer, No. 19230. See Map 22 -J. <br />The total drainage area associated with the new coal mine waste disposal area <br />is approximately 25 acres. The area was divided into separate watersheds <br />draining into run -off and collection ditches designed to handle the run -off from <br />the 100 -year, 24 -hour precipitation event. The drainage areas are shown on <br />Map 20 in Volume II. <br />The modified sediment pond was sized to contain the run -off from the 10 -year <br />24 -hour precipitation event (1.8 inches). This storm event will generate <br />approximately 2.6 acre feet of runoff. Sediment accumulation was estimated <br />with the use of the Universal Soil Loss Equation. The pond has been designed <br />to contain approximately 2.6 acre feet of water and 0.2 acre feet of sediment. <br />The 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 />TR -80 - 5 - 07/13 <br />