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• Sedimentation Pond <br />The sediment pond and the general drainage plan for the waste disposal site <br />were prepared under the direction of J. E. Stover, Colorado Professional <br />Engineer, No. 19230. <br />The total drainage area associated with the proposed site is approximately 24.6 <br />acres. The area was divided into separate watersheds draining into diversion <br />channels designed to carry peak flows generated from the 10-year and 100-year <br />precipitation events. These drainage areas are indicated on Figure 2.2-6. <br />Drainage of the eastern portion of the upland area (7.4 acres) has been diverted <br />to flow beneath the existing haul road, through CMP-3, and joins a natural <br />drainage channel. Drainage from the western portion of the upland area (0.8 <br />acres) is diverted away from the sediment pond 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 <br />• 25-year event. The sediment pond will be dewatered if it contains water above <br />the maximum sediment level. This dewatering event should occur within 48 <br />hours after the 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 <br />also designed to collect sediment loss from the disposal area. Erosion potential <br />will be limited to direct precipitation over the site. The estimated annual erosion <br />rate, based on the Universal Soil Loss Equation, is on the order of 0.03 acre feet <br />per year. The pond is designed to contain 0.19 acre feet which is over six years <br />of sediment accumulation. When sediment accumulation reaches 60% of the <br />maximum storage, the sediment will be removed and placed in the waste pile. <br />Drainage calculations are presented in Appendix M(vii). <br />An NPDES permit will be obtained for this sediment pond prior to commencing <br />construction. <br /> <br />M" 2.2-12 10/02 <br />