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Kathy Welt and Christine Johnston March 7, 1997 (DRAFT) Page l2 1. Water stored in these sumps has occurred when there was no call on the river; consequently, no vested downstream water rights have been damaged by the practice. 2. During 1996, MCC increased the river flow on an annual basis (discharges exceeded diversions). 3. The water quality of waters directed into the sumps was not suitable (per NPDES total suspended solids limitations) for discharge. 4. The practice is interim in nature. 5. Minimum streamflows were not materially affected by storing water in the sumps. 6. Some groundwater return flows to the North Fork may occur as a consequence of sump storage. 7. As of late Januazy 1997, there is no way that MCC could have avoided storing waters from the 1 SE Headgate fault in the sumps. At an inflow rate of as much as 8,000 gpm (estimate), such flows would have quickly overwhelmed the hydraulic capacity of ponds MB-I and MB-2R and the associated treatment facilities. As of January 1997, MCC is meeting with its engineering and legal consultants to determine whether a permanent water augmentation/exchange plan for the North Fork is necessary and, if so, what the nature of this decree should be. Until a decision is made in this regazd, and until a permanent plan is finalized (if relevant), MCC will operate the mine to ensure that no senior water rights on the North Fork are harmed by its water management practices. Out-of-priority depletions will be replaced in fidl, in the manner described above. MCC will obtain substitute supply plans, if necessary, until the permanent plan is in place. Based on available evidence, WWE has concluded that there are no significant hydrologic impacts from a water rights perspective associated with either North Fork surface diversions, the B East Mains fault inflow or MCC's utilization of the underground sumps. VIII. SURFACE WATER QUALITY PHCs Overview The principal water quality implications associated with sump construction and inflows from the B East Mains fault include: 1. The total volume of discharges to the North Fork during 1996 was considerably larger than in previous years due to the fault water. Although constituent concentrations during 1996 were not significantly different from concentrations in past years, the total constituent loads to the North Fork were higher by virtue of the increased outflow volume. Although the constituent loads were higher, the impact to the North Fork was insignificant, primarily due to the relatively small contribution of the mine discharges. During 1997 and succeeding years, however, constituent loads to the North Fork will decrease for a variety of reasons, including: availability of underground sumps; the new wastewater treatment facility; the B East Mains fault inflows have leveled off at approximately 85 gpm; and MCC will be better equipped to deal with future inflows.