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32.05 APPLICATION FOR PERMIT FOR SURFACE OR UNDERGROUND MINING ACTIVITIES -- MiN%MUM REQUIREMENTS FOR OPERATION AND RECLAMATION PLANS. 2.05.6 Mitigation of Surface Coal Mining Operation ',mpacts, (Cont'd.) (3) (b) (i) Drainage Plan-Colorado Westmoreland ;nc. - Orchard Valley Mine. See Maps 8-1, 8-2, and 8-3 . The Orchard Valley Mine Site Drainage Plan consists of five major components: (1) the upper diversion ditch and auxiliary diversion ditch; (2) the mine site drainage; (3) Sedi- mentation Pond Nos. 1 through 4; (4) the waste disposal area sedimentation pond; and, (5) the timber storage area sedimentation pond. The train loadout area and transportation facili- ties have a separate drainage plan. Mine Site Drainage Control Plan The Mine Site Drainage Control Plan diverts away from the mine site as murh upstream drainage as possible, and then controls the run-off on the site by means of sedimentation ponds. The drainage plan utilizes a contour channel • to divert storm runoff from the upper basin. The channel is described in Section 2.05.3(3)- (b), Operations Plan. The channel discharges water into adjacent watersheds to the east and west of the mine site. The channel is a crit- ical component of the overall Drainage Plan. Since under extreme circumstances failure could re suit in extensive damage and even loss of life, the channel is designed to carry run- off From the Probable Maximum Thunderstorm. Discharge of both ends in such an event would be 550 cfs. in order to further assure diversion of up- stream drainage, an auxiliary diversion chan- nel was constructed. This channel is designed to contain a 100-year, 24-hour storm. See the Diversions Appendix in Volume 8A for detailed auxiliary channel designs and construction. The second element of the drainage plan is to handle flows generated from the lower basin, Revised 03/01/84 Revised 10/01/87 100