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Kathy Welt and Christine Johnston <br />March 7, 1997 (DRAFT) <br />Page 7 <br />In short; MCC concluded that there was no alternative but to utilize the NW Panel sealed sump in <br />1996 in order to: (I) to avoid hydraulic overloading of the treatment facility, (2) maintain the <br />required capacity to store runoff from the ] 0-year, 24-hour storm event in the ponds, and (3) provide <br />the necessary sedimentation pond residence time to remove the colloids and other constituents to <br />levels that would enable NPDES permit compliance. After the NE Panels have been mined, MCC <br />also plans to utilize this mined-out azea as an emergency sutnp. <br />Storing water underground is a proven and effective water management approach that is often <br />advocated because it saves land, eliminates evaporation, reduces dam safety hazards, reduces certain <br />liability issues and optimizes water management. There is precedent for utilizing sumps in Colorado <br />coal mines. In addition, many municipalities, water districts and industries actively use underground <br />storage in the same way that they would surface storage. <br />Sump Operations <br />There aze two considerations of overriding importance regarding operation of the NW and NE Panel <br />sealed sumps: <br />1. The sumps should be viewed as an interim measure that will be regularly utilized by MCC. By <br />mid to late 1997, MCC projects that a new mine water treatment facility will be operational, <br />capable of treating up to 2,000 gpm. <br />2. After the new, large capacity treatment facility is functioning, the sumps will be used only for <br />emergency purposes to store large, unexpected inflows to the mine, which cause the total mine <br />inflow rate to exceed 2,000 gpm. Given the historic growndwater inflow rate to the mine of 12 <br />gpm over its fifteen-yeaz history and relative to the average 1996 groundwater inflow rate after <br />intercepting that fault of approximately 235 gpm, a treatment facility with capacity of up to <br />2,000 gpm is a substantial and conservative commitment by MCC. <br />The current mine water management practices are shown schematically in Figure 3. In general, the <br />schematic represents three key components: 1) mine inflows, 2) mine outflows, and 3) in-mine <br />water transfers. In order to keep track of the quantities of water coming into, leaving and being stored <br />in the mine, MCC has installed numerous totalizing flow meters. <br />Mine inflows consist of imported water from the North Fork, miscellaneous groundwater inflows and <br />significant groundwater inflows, such as the B East Mains fault. Estimates for vazious mine inflows <br />for 1996 aze as follows: <br />1. Imported water from the North Fork = 260 acre-feet (160 gpm). <br />2. Miscellaneous groundwater inflows = 19 acre-feet (12 gpm). <br />3. B East Mains fault inflows = 300 acre-feet (185 gpm). <br />There are presently many ways for water [o leave the mine, including: water pumped to the <br />sedimentation ponds; groundwater outflow from the sealed panel sumps; direct discl~azge of B East <br />Mains fault water; direct discharge of F-Seam water; proposed direct discharge of 1 SE Headgate <br />fault water; proposed discharge to Lone Pine Gulch; water retained in the product and gob; and <br />miscellaneous losses. If the fault inflows persist at significant rates, or if new fault inflows are <br />,,: <br />