_GENERAL DOCUMENTS - C1981017 (283)

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Surface runoff from disturbed areas will be routed through sediment ponds. Nineteen sediment ponds have b�e,�n :onstructed at the Coal Basin mines. Two sediment ponds at the rock tunnel are to be constructed as the disposal pile progresses in size, four ponds are planned for Mirn� Nlo. 4, two ponds are planned to be constructed on the two-year :null processing waste disposal area and one pond will be co,istr'icted on the five-year waste disposal area. Mines 1 and 2 Sediment Control n Mines 1 and 2 have a common sediment control system. The Mine 1 and 2 areas are formed on excavated rock surfaces which are inclined toward th(I highwall at 2 to. 10 percent slopes. The pad areas are composed of loose, fractured sandstone and shale, anu coal spoil . Each pad area has been notched into very steep mountainous terrain with average natural undisturbed slopes that commonly range from 70 to 100 percent and greater in spine areas. Other disturbed areas in the vicinity of (lines 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 f rin the ,dine 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 culvert. 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 accoirnnodate the runoff from a 25-year, 24-hour store :without discharge from the incised emergency spillwway. In addition, the applicant has committed t0 pumping any exc.'SS 'V3i:.'.r Go 'LainC-ji l the 10-year, 24-�rrjr Mine No. 3 Sediment Control . The Mine iNo. 3 pad area includes -.36 acres of excavated surface with a 5-7 percent grade towards the nighwall . The steep inclined rock niohwail extends 50 to 100 feet above the mine por.al .' Above the highwall is in abandonea exploration road that traverses the entire length of the highwall . This road is us•�•I :f) •iiverc indist'irbed .;rainage around the mine pad.