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• The total drainage area associated with the proposed site is approximately 16.7 <br />acres. The area was further divided into separate watersheds draining into <br />diversion channels designed to carry peak flows generated from the 10-year and <br />100-year precipitation events. These drainage areas are indicated on Figure 2.2- <br />6. Drainage of the eastern portion of the area (7.4 acres) has been diverted to <br />flow beneath the existing haul road, through CMP-3, and joins a natural drainage <br />channel. <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 sedimentation pond is also designed to collect sediment loss from the <br />disposal area. Erosion potential will be limited to direct precipitation over the site. <br />The estimated annual erosion rate, based on the Universal Soil Loss Equation, is <br />• on the order of 0.03 acre feet per year. The pond is designed to contain 0.19 <br />acre feet which is over six years of sediment accumulation. When sediment <br />accumulation reaches 60% of the maximum storage, the sediment will be <br />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 embankment foundation area shall be cleared of all organic matter, all <br />surfaces sloped no steeper than 1 h:1 v, and the entire foundation surface <br />scarified. <br />The fill material shall be free of sod, large roots, other large vegetation matter <br />and frozen soil, and in no case shall coal-processing waste be used in <br />embankment construction. <br />u <br />M" 2.2-12 6/02 <br />