2002-07-03_PERMIT FILE - M2002004

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Exhibit D locations for the leach field were determined to have no effect on the surface water management plan or • the evaporative pond for process water discharge (see above). Mining Activities Mining activities include the initial box-cut, temporary stockpiles, blasting, removal of resource material, backfill, and reclamation of the land surface. Management of surface runoff from these activities will include detention, sediment ponds, and diversion ditches with the following goals and objectives: Control storm water within active mining area. Control storm water discharges from active mining area. Control Storm Water Within Active Mining Area During the initial box-cut operation, there will be limited space available to stockpile materials within the mining area. Therefore, temporary stockpiles will be placed near the northeast side of panel 1 for a period likely less than 1-year. Storm runoff from these temporary piles will be trapped by earth or hay bale dikes constructed along the down slope perimeter of the stockpiles. Sediment in the runoff will be deposited by gravity in ponding that occurs adjacent to the dikes and/or filtered by the hay bales before discharging to Diversion Ditch #1 and Arroyo "E." After the initial box cut expands to the full panel size, management of surface runoff and sediment will adjust to the larger area. Storm water generated in the pit (and including tributary area outside the pit • boundary) will be conveyed by ditches to an "in-pit detention/sediment pond." The in-pit ponds are sized to store storm runoff from the 10-year, 24-hour event and for sediment. Runoff from larger floods will still be contained within the pit area, because the low-wall is anticipated to be at least 15-feet above the pit floor. This arrangement provides even greater flood protection to areas outside of the mining limits. For mining block years 1 through 5, the drainage area is 85 acres, requiring a pond with storage for 9 acre feet. The pond will be constructed below the pit floor to avoid interference with mining operations. During mining block years 6 through 10, the existing Arroyo E Stock Pond and Diversion Ditch #3 will limit the drainage area tributary to the active mine area to 210 acres. These facilities minimize the volume of runoff draining into the active mine area. During this mining period, an intermediate size, in-pit detention/sediment pond can be constructed with a volume of 22 acre feet As the mining progresses above the Arroyo "B" Stock Pond, the in-pit detention/sediment pond will be increased to accommodate the larger drainage area of 470 acres during block years 11 through 25. This tributary area requires a pond with a volume of approximately 49 acre feet. The Arroyo "E" Stock Pond will be replaced during reclamation (see below). When mining progresses to block years 26 through 50, a new, in-pit detention/sediment pond will be constructed (see Exhibit D-3). The pond sizes during this mining block can also be staged, according to tributary drainage area. For instance, up to block year 40, the eastern branch of Arroyo "I" can continue to bypass the mining operation, reducing the tributary area for the pond from 740 acres to 500 acres. Control Storm Water Discharges from Active Mine Area • Storm water will be temporarily stored (for example, for 3 to 5 days) within the in-pit detention/sediment 1180-Mine Permit Exhibits (Jul.03.02)FINAL.doc D-11 July 3, 2002