1994-10-21_GENERAL DOCUMENTS - C1980007

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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/l (secondary drinking water standards = .3 mg/1) ; the other labs reported iron at .05 mg/l 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/l (primary drinking water standards = .01 mg/1) . One lab analysis exceeded nitrate levels with 30 mg/1 (primary drinking water standards = 10 mg/1) , TDS levels were 782 mg/l and 720 mg/l at two labs. The amount of leachate flow in the underdrains is expected to be low and will be diluted in the sediment ponds with surface runoff. The lower refuse pile is expected to have no significant effects to the surface water system even under worst-case low flow conditions. The amount of leachate expected to be generated from the pile is small in relation to the adjacent drainage areas. The quality of the leachate is predicted to be comparable to similar waste piles in the North Fork valley with moderately high TDS, elevated sodium and sulfates, and low concentrations of metals. A worst-case discharge projection from the lower refuse pile has been estimated. Based on an estimated annual infiltration of 5.7 inches, an annual leachate production of about 19 acre-feet is predicted from the 40-acre upper refuse site. A seasonal maximum leaching rate was estimated at twice the average annual leaching discharging rate of 11.8 gpm. When added to the leaching rates estimated for the lower refuse pile, a worst case total seasonal discharge of nearly 50 gpm could result. No adverse impact would be anticipated with respect to arsenic, boron, cadmium, chloride, manganese, nitrate, lead, selenium and zinc since concentrations of these parameters in the leaching tests were well below the stream standards on the North Fork Gunnison River. Furthermore, no adverse impact would be anticipated with respect to total and dissolved iron, sulfate, TDS and SAR. Concerns were raised by the Division regarding surface water effects of the lower waste pile leachate reaching the North Fork Gunnison River after the waste pile sediment pond is removed and the mine site has been permanently reclaimed. In response, MCC provided an analysis of the worst case effects to the North Fork of the Gunnison from leachate generated by the lower waste pile. For the analysis, MCC assumed a 10-year 7-day low flow in the river, maximum leachate production, and that all of the leachate would reach the river undispersed and undiluted. The results of the analysis showed that 39