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III IIIIIIIIIIIIIIII~ 999 KERR COAL COMPANY RESPONSES TO DMG 8/11/93 720 PIT WATER DISCHARGE CONCERNS 1) What is the estimated volume of wtixter that may b° discharged and at what maximum rate will the water be discharged? A rough ralculation that /(Randy Price) performed shows that the pit is being backfilled at a rate ojapproximately 25 ft' per second (givrn the capacity of the scrapers and a turnaround time of S minutes). If the pit is filled until the water tops over, the pond would receive inflows at the rate of 25 ft' per second. Given the highly bentonitic nature of the overburden and the past problems that the mine has had with suspended solids, does Pond A have the capacity to treat these inflows and still meet effluent standards? Are the diuhes to Pond A sized to handle the overflow from the 710 Pit? Response: Based on existing available information, the current volume of accumulated water in the 720 Pic is estimated at 208 acre-feet (ac-ft). Taking into consideration the current pit water volume, runoff to the pit during backfilling operations, evaporative losses, water loss due to resaturation of spoils, and probable range of accuracy for the calculations, the discharge volume is expected to range from approximately 20 ac-ft to 120 ac-ft, with probable discharge in the median range of 60 - 80 ac-ft. Supposing calculations are attached. Kerr will control both discharge rate and water quality using an integrated systems approach in order to prevent or minimize potential adverse hydrologic impacts. Rerr's overall objective will be maintenance of required stormwater storage capacity in any of the existing sediment ponds used for temporary storage and discharge of pit water and compliance with applicable effluent limitations. At the present time the water surface elevation is so far below the ground surface as to effectively preclude reasonable discharge and treatment options. As ongoing backfilling results in displacement of accumulated water and a gradual increase in elevation of the water surface, however, Kerr will implement one or more of the following water discharge and treatment activities: • Controlled discharge using floating or portable pumps to decant clarified water from the pond surface with dischazge to Ponds A, B, and/or C or to a land application system • Gravity discharge from the pit to Pond A using a series of temporary in- pit dikes and catch basins to provide surge capacity and control flows • Removal of frozen water using eanhmoving equipment once the water dep[h is sufficiently shallow to eliminate operational and safety concerns • Treatment of dischazge (excludes land application) to meet appliable effluent limitations using temporary holding ponds, flocculents, sediment fences, straw bales or other methods individually or in combination Pumping and/or gravity discharge will be initiated, scheduled and controlled so as not to exceed design discharge capacities for either receiving ditches or ponds. As an example, Ditch Al has a design capacity of 4 cubic feet per second (cfs) which would be the maximum discharge apacity if this ditch is used to route pit water discharge to Pond C:L..VJOTR1oDOC 09/OL9] 4pm ACZ Inc. • P.O. Box 774018 ` Srmmtnar Springs, Colorado 80477 • (303J 879-6260