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Kathy Welt and Christine Johnston Mazch 7, 1997 (DRAFT) Page 17 years for the NW Panel sealed sump to drain, if it were filled to capacity (i.e., sump volume below the seals). At maximum storage capacity, the maximum groundwater outflow into the Beaz Mine would be 25 gpm. Operators of the Beaz Mine commented in their 199.1 Annual Hydrology Report to the effect that storage of water within the NW Panel sealed sump was causing inflows of up to 30 gpm in their Third West area. The probability of this seems low, however, given the following facts: 1. Based on discussions with Bear Mine personnel, their inflows were first observed in the latter part of 1994, increasing to maximum observed flows in Mazch 1995. MCC did not have an operational sump updip of their inflow locations and in fact, did not begin active storage of water within the NW Panel sealed sump until November 1996, over / % years later. 2. As of late January 1997, only 150 acre-fee[ of water has been pumped into the N W Panel sealed sump. Thus, based on the stage/storage relationship developed by WWE, the maximum potential groundwater outflow into the Bear Mine is between 10 and 15 gpm at this time. X. GROUNDWATER QUALITY PHCs Water quality data available for the B East Mains fault inflows show this water to be similar in chemistry to that of other groundwater which has been intercepted by the mine.tTlte only tangible difference is water temperature, with typical mine inflows at about 68°F to 72°F and the fault inflow at about 83°F. Data presented herein demonstrate that the fault water can meet MCC's NPDES discharge requirements without treatment, including the applicable temperature requirements. Direct dischazge of the B East Mains fault inflow water was approved by the CWQCD in April 1996. Most of the fault water inflows are now conveyed in the mine via pipelines, so solids concentrations do not increase from conveyance. For those inflows which do accumulate solids and which are conveyed into the sumps, the solids consist primarily of clay tmd coal particles/dust. Neither clay nor coal will degrade the ambient water quality of the groundwater resources of the host geologic formations. MCC anticipates a net benefit to the quality of water migrating downgradient from the large capacity sumps as a result of filtration. The Colorado Water Quality Control Commission (CWQCC) groundwater quality regulations Basic Standards For Groundwater 3.1].0 (SCCR 1002-8, 1996) essentially operate on the principle that activities should not significantly impact ambient groundwater quality. Whether in terms of direct discharge to the North Fork, treatment and discharge to the North Fork or storage in the sumps with slow-rate return flow into or beneath the North Fork as the sumps drain, MCC's management of the fault inflow water is consistent with these regulations. Namely, ambient groundwater quality will not be adversely impacted as a consequence of the B East Mains fault inflow or of MCC's utilization of the underground sumps. The intent of the CWQCC groundwater quality regulations is satisfied. For this reason, MCC has not applied for a groundwater discharge permit. In fact, in December 1996, MCC was encouraged by CWQCD staff to maximize sump storage to relieve the hydraulic load on the treatment facilities at ponds MB-l and MB-2R. If the CWQCD requires a groundwater discharge permit, MCC should be able to obtain this petmit.