2008-03-21_PERMIT FILE - C1980007A (46)

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West E[k Mine • 3. MCC staff diligently monitored chemical and biological impacts to the North Fork during 1996-1997 in response to increased outflow volumes and constituent loads. On multiple occasions, MCC collected water samples for chemical analysis and WET testing in the North Fork upstream and downstream from the relevant outfall and on the outfall stream itself. Although there were instream constituent increases attributable to the mine water, the resulting downstream constituent concentrations were not significant. Temperature increases in the North Fork were small, due to the small contributions of mine water compared to instream flows, the extended residence time of the fault water within the mine and within MB-1 and MB-2R, and the exposure to winter temperatures during conveyance. MCC fully complied with WET tests on the effluent and for the North Fork downstream of the discharge point. MCC also commissioned WWE to complete a bioassessment of the North Fork prior to and after discharge from the 14SE Headgate fault inflow. This study also showed that there was no toxicity or biological impact as a result of discharging mine water to the North Fork. 4. Due to extensive efforts by MCC during 1996 and 1997 to segregate "clean" water from "dirty" water flows in the mine, the vast majority of the water conveyed into the NW Panels sealed sump was "dirty", with elevated levels of TDS and TSS. In the absence of the NW Panels sealed sump, this water would have been, by necessity, pumped out of the mine and discharged into MB-1 and/or MB-2R. Due to the heavy hydraulic loading in 1996, the water could not have been adequately treated. Consequently, dischazges to the North Fork would have failed to meet NPDES limits. In order to analyze the effect that MCC's discharges during this period had on the water quality of the North Fork, Table 54 was prepared. Table 54 shows the rates and water quality of both the pond dischazge and the North Fork and the resulting downstream mixed conditions. The downstream water quality was calculated rather than using the lower North Fork station data for two reasons. First, the North Fork water quality sampling did not always occur concurrently with pond dischazges; second, there aze other sources of constituents between the two North Fork water quality stations (i.e. Coal Creek, Sylvester Gulch, other unnamed minor tributaries, and drainage from the highway). The following conclusions can be drawn from Table 54: • The downstream increases in concentrations of total suspended solids during all months were not significant. During the month of maximum increase in TSS, the ambient TSS level increased from 7 mg/L to 10 mg/L. There is no practical significance to either this increase or the resulting mixed concentration. Note that during April 1996, the North Fork TSS concentration upstream from the mine was 168 mg/L - faz greater than any contribution attributable to MCC. This is typical of TSS concentrations during spring runoff. • Although MCC's increases for total iron appeaz noteworthy, inspection of the data indicates that these increases are not significant. During the two months that there were stream standazd exceedances for iron (March and April) even the ambient water quality upstream from the mine exceeded the stream standazd of 1.0 mg/L. Table 54 shows that MCC's contributions to downstream total iron concentrations during March were negligible (1 percent). In April, MCC dischazges actually reduced the downstream total iron concentration . in the North Fork. 2.05-234 Revised June 1005 PRl0; Rev. Minch 2006; Rev. May 2006 PRIG