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Kathy Welt and Christine Johnston <br />March 7, 1997 (DRAFT) <br />Page 13 <br />2. MCC experienced NPDES permit exceedances associated with fault inflows in 1996 due to: (1) <br />the heavy hydraulic load which started in Mazch 1996 and continued through the yeaz, and (2) a <br />different kind of colloid which was very difficult to treat. MCC has taken many steps to <br />minimize the probability of future exceedances such as: sepazating inflows within the mine; <br />large capacity sump utilization; optimizing surface water management strategies; and <br />constructing treatment facilities in 1997 to increase the treatment capacity up to 2,000 gpm. <br />These facilities will be specifically geared to remove the suspended solids in mine outflows. <br />3. MCC staff diligently monitored chemical and biological impacts to the North Fork during 1996 - <br />1997 in response [o increased outflow volumes and constituent loads. On multiple occasions, <br />MCC collected water samples for chemical analysis and WET testing in the North Fork upstream <br />acid downstream from the relevant outfall and on the outfall stream itself. Although there were <br />constituent increases attributable to the mine, these increases were not significant. Temperature <br />increases in the North Fork were small due to the small contributions of mine water compared to <br />instreanr flows, the extended residence time of the fault water within the mine and within ponds <br />MB-1 and MB-2R, and the exposure to winter temperatures during conveyance. In terms of the <br />WET tests, all samples collected by MCC demonstrated compliance-that is, the effluent itself, <br />along with the North Fork both upstream and downstream from the outfall. Mass balance <br />computations conducted by W WE confirm the results of the instream monitoring and <br />demonstrate that instream concentrations downstream from the mine were only slightly higher <br />than upstream from the mine for constituents such as total dissolved solids (TDS) and TSS. <br />4. As of late January 1997, MCC has conveyed approximately 150 acre-feet of water into the NW <br />Panel sealed sumps. Due to extensive efforts by MCC to segregate "clean" from "dirty" <br />underground flows, the vast majority of the water conveyed into the NW Panel sealed sump has <br />been "dirty," with elevated levels of TDS and TSS. In the absence of the sump, this is water that <br />would have been, by necessity, pumped out of the mine entrance and discharged into Ponds MB- <br />1 and/or MB-2R. Due to the heavy hydraulic loading in 1996, the water would not have been <br />adequately treated. Consequently, discharges to the North Fork would have failed to meet <br />NPDES limits. <br />North Fork Water Quality Data <br />To quantity the changes in water quality in the North Fork as a consequence of MCC's discharges <br />during 1996, Table 2 has been prepazed. The table summarizes upstream and downstream <br />concentrations for selected constituents. Table 2 demonstrates that for TSS, TDS, total iron and <br />temperature, instream concentration increases were insignificant. <br />Water Quality Impacts from January 1997 Through Startup of New Treatment Facility <br />Relative to water quality from January 1 through mid to late 1997, North Fork water will not be <br />tangibly affected by mine outflows, for these reasons: <br />1. MCC presently has the capability to reliably treat between 200 gpm and 300 gpm of outflow <br />from the sedimentation ponds. This translates to between 325 and 485 acre-feet per year, which <br />is more than equivalent to the annual diversions from the North Fork via the Mount Gunnison <br />Pipeline. <br />