1986-12-11_PERMIT FILE - C1981017

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-15- Mines 1 and 2 Sediment Control Mines 1 and 2 have a common sediment control system with the exception of the Mine No. 2 bin pati. The Mine 1 and 2 areas are formed on excavated rock surfaces which are inclined toward the highwall at 2 to 10 percent slopes. The pad areas are composed of loose, fractured sandstone and shale, and coal spoil . Each pad area has been notched into very steep mountainous terrain with average natural undisturbed slopes that commonly range from 10 to 100 percent and greater in some areas. Other disturbed areas in the vicinity of Mines 1 and 2 include a coal storage silo pad (0.44 acres) and a storage pad for lumber and supplies (1 .14 acres) . Sediment and runoff from the Mine 1 and 2 pads is collected and conveyed to a series of two sediment ponds via a 12-inch corrugated metal pipe (CMP) . All undisturbed drainage is routed around the disturbed area. Runoff from the storage pad for lumber and supplies and the coal storage pad is routed to the sediment pond by culverts. The first sediment pond in series functions to settle the majority of the sediment from the disturbed area. This pond has only one discharge structure, an 18-inch CMP which discharges into the second pond. This pipe is capable of handling the peak runoff from a 25-year, 24-hour precipitation event. The second pond is equipped with an 18-inch CMP principal spillway and an incised emergency spillway capable of handling the peak flow from a 25-year, 24-hour precipitation event. The second pond is capable of containing the runoff from a 10-year, 24-hour precipitation event. The function of the first pond is to allow additional detention time for the settling of clays. The primary spillway on the second pond is located at the top of the 10-year, 24-hour storage volume. However, this pond is designed to accommodate the runoff from a 25-year, 24-hour storm without discharge from the incised emergency spillway. In addition, the applicant has committed to pumping any excess water to maintain adequate storage for the 10-year, 24-hour event. Sediment and runoff from the Mine No. 2 bin pad is routed through a series of two sediment ponds below the bin pad bench. The sediment ponds drain a pad area of 1.42 acres. In addition, the ponds are sited for an estimated 0.1 cfs of runoff from the conveyor line above the bin pad. The sediment ponds are equipped with 24 inch cmp principle spillways and incised emergency spillways. The principal spillway contains gated orifice holes which can be either left open or closed if additional detention time is required. Mine No. 3 Sediment Control The Mine No. 3 pad area includes 4.86 acres of excavated surface with a 5-1 percent grade towards the highwall . The steep inclined rock highwall extends 50 to 100 feet above the mine portal . Above the highwall is an abandoned exploration road that traverses the entire length of the highwall. This road is used to divert undisturbed drainage around the mine pad.