1996-01-26_GENERAL DOCUMENTS - C1980007

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percent changes in North Fork flow volumes due to withdrawals for projected mine requirements. The NPDES permit allows for a discharge of 10,000 gpd, based on a 30-day average, from the sanitary waste water treatment plant. The potential impact of discharge of waste water effluent would be greatest when the dilution ratio for effluent is smallest. Total mine water inflow in the F Seam is estimated to not have exceeded 15 acre-feet in any one year. The quality of mine water is considered good and offers no problem for treatment and discharge. Mine water discharge is treated in sedimentation pond MB-1. B Seam inflow amounts are expected to be similar to the mine water inflow amounts of the F Seam. Overland runoff passes over disturbed areas within the permit area to one of the five sedimentation ponds, mentioned previously in this section. This water may be discharged to the North Fork or stored when water rights are in priority. From previous Annual Hydrology Reports, it appears that these discharges have had no adverse effect on the North Fork. In fact, the quality of the discharge usually exceeds the quality of the North Fork. i. Refuse Material Disposal Impacts on Surface Water - Lower Refuse Disposal Area - Runoff from the Lower Permanent Waste Disposal site will be routed through the sediment control system and must meet effluent limitations. Final designs for the waste rock pile, which include surface and subsurface drainage systems, allow for the collection of water leachate from the pile. Analysis of sample rock provided by MCC indicates that potential toxicity levels are below the Environmental Protection Agency (EPA) standards. Consequently, it appears that if runoff were to develop from the waste piles, minimal impact will occur on the North Fork of the Gunnison River. MCC will be monitoring for both ground water quality and levels under the piles, leachate quality and levels from the subdrains, and spring quality from the base of the pile site. MCC has had leach tests performed on representative samples of waste rock. Of analyses conducted at three labs, the leachate exceeded drinking water standards in four parameters. One lab reported dissolved iron concentrations of 6.62 mg/I (secondary drinking water standards = .3 mg/1); the other labs reported iron at .05 mg/1 and .06 mg/l. Two labs reported pH's of 8.9 and 9.1 (secondary drinking water standards = 6.5 - 8.5 pH). Selenium exceeded standards at two labs which were .04 mg/1 and .025 mg/1 (primary drinking water standards = .01 mg/1). 37