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Kathy Welt and Christine Johnston <br />March 7, 1997 (DRAFT) <br />Page 14 <br />2. MCC is in the process of separating "clean" flows in the mine from those flows which would fail <br />to comply with the NPDES limits. As of late January 1997, the mine flows that exceed the <br />NPDES limits are directed into the sumps, while the "clean" flows aze pumped to the surface, <br />treated if necessary and dischazged to the North Fork in compliance with the NPDES permit. <br />As previously discussed, there is substantial volume in the sumps to accommodate large new <br />fracture/fault inflows, should they be experienced. <br />Water Quality Impacts After Treatment Plant Operational <br />Afer mid to late 1997, the risk to North Fork water quality posed by the mine will be low because: <br />1. The treatment facility will be functioning. The discharge capacity of this facility is planned to be <br />up to 2,000 gpm. <br />2. Flow segregation within the mine will have been completed. <br />3. MCC will have the capability to convey as much as 800 acre-feet into the sumps before the seals <br />are reached (when outflows from the sumps to the mine will commence). This fact, in <br />conjunction with a treatment facility with capacity of up to 2,000 gpm, makes the risk of direct <br />discharge to the North Fork small enough to be insignificant. <br />North Fork Impacts from Sumped Groundwater Flows <br />As presented in the Sump Operations Section, if the sumps are ultimately used by MCC to their full <br />capacity, a maximum groundwater inflow to the North Fork of approximately 25 gpm is projected to <br />occur. Filtration, adsorption, absorption, and other factors will act on constituents in the water as it <br />moves downgradient. At a dischazge rate of only 25 gpm, North Fork water quality will not be <br />measurably affected by groundwater outflows from the sumps. <br />Fault Water Quality and Temperature <br />Because the water quality of the B East Mains fault and 1 SE Headgate fault meets the NPDES <br />discharge standazds, MCC will directly dischazge these waters to the North Fork and/or reuse the <br />water in the mine. Based on current (January 1997) inflow rates, the canbined direct dischazge of <br />both fault inflows would be approximately 2,600 gpm (5.8 cfs). Although the fault water is warm <br />(typically 80°F to 84°F), calculations and field measurements demonstrate that the water can be <br />discharged to the North Fork without exceeding relevant temperature criteria because: (1) the <br />dilution ratios are large, even under low, wintertime flow conditions, and (2) mine inflows are <br />substantially cooled by the time they are actually discharged. <br />1996 NPDES Exceedances in Association with Fault Inflows <br />On three occasions during 1996, MCC experienced NPDES permit exceedances. Specitically, on <br />April 11 - 17, 1996, July 31 - Augus[ 2, 1996 and August 15 - 16, 1996, MCC had exceedances for <br />TSS. On these occasions, there were not WET test failures using Daphnia magna <br />On the occasions when MCC had NPDES exceedances in 1996, water quality monitoring in the <br />North Fork was conducted both upstream and downstream from the mine outfall. The maximum <br />