1987-12-01_PERMIT FILE - C1981017 (93)

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November 12, 1979 04,37-101 The three sedim -station ponds A, 3, and C have a total storage capacity of 11.1 ac. ft. All sit accumulated over a 3-year period can be stored within upper ponds B and C. The total runoff volume developed by a 10-year 24-hour Type II Storm can be stored within ponds B and A if Pond C is full of sediment. Excess volume for water storage has been designed for these three ponds. Dine effluent of 0.5 ac. ft./day can be stored temporarily. The collector ditch is designed to convey flows of 25 to 30 cfs. This riprap lined ditch will have an average 87. gradient and be 4 feet wide across the invert with 2 to 1 side slopes. Where possible, vegetation will be Em- ployed to protect the earth.-lined ditch channel from erosion. Mine effluent of 1 cfs will be conveyed daily through the collector ' ditch to the sedimentation ponds. The control of flood runoff larger than 25 year storm is made possible by including a ditch concrete spillway. This spillway operates when water levels exceed 0.5 ft. , such as would be expected for larger storms in excess of 25- year frequency. Several diversion ditches located upstream from all disturbed areas will be constructed to divert all overland flows (25-year max.) and sediment from undisturbed areas. The sediment and runoff developed on natural wooded slopes (Figure II-B-App . 7-2 and Exhibit II-B-App . 5-1) uphill from the Yard Area { Figure 2 and Plate 1) will be conveyed to the sed- iment ponds. ''" sediment and runoff developed on natural wooded slopes uphill (Exhibit II-B-App . 5-21) from the Waste Fill area will be diverted to the cross-over culvert, (Plate 2) uphill from the sedimentation Pond C or downhill, past sedimentation Pond A. These diversion ditches and cross-over culvert have been designed to carry 25- year storms. Channel protection where channel grades are in excess of 4 ,411 be required i.e. riprap and/or grass lined. -2- 5