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designed to safely pass peak discharges resulting from the 10-year, 24- <br />hour storm event. All temporary diversions have been designed and <br />constructed to remain stable under design flow conditions. In addition, <br />calculated flow velocities have been utilized as the basis for design of <br />either vegetative channel linings or specification of riprap and bedding <br />materials to ensure channel stability. Locations of all temporary <br />diversions are shown on the Mine Area Surface and Groundwater Hydrology <br />Map, (Map 12), Loadout Area Surface and Groundwater Hydrology Map, (Map <br />13) and Drainage and Sediment Control Map, (Map 20). Design calculations <br />are included and design methodologies are discussed in Exhibit 19, <br />Drainage and Sediment Control Plan. <br />EfCI has also designed several permanent post-mining diversions including <br />the coal refuse pile diversion and the north, south and west refuse pile <br />collection ditches, to effectively control drainage during ongoing <br />operations and provide for effective post-mining drainage from disturbed <br />areas following site reclamation. All permanent diversions have been <br />designed to safely pass the peak flows resulting from the 100-year, 24- <br />hour storm event. <br />The permanent coal refuse pile diversion will continue to intercept and <br />route runoff from undisturbed areas around the refuse pile disturbance <br />area, with any resulting flows discharging to an adjacent natural drainage <br />channel. The north, south and west refuse pile collection ditches will <br />continue to provide drainage control for all runoff from the permanent <br />coal refuse pile with resulting disturbed area runoff flowing to <br />Sedimentation Pond No. 4 during both active operations and the extended <br />reclamation liability period. Upon effective restoration of the refuse <br />L <br />4.05-8R Revised -November, 1990 <br />