Laserfiche WebLink
representative samples of waste rock. Of analyses conducted at <br /> three labs, the leachate exceeded drinking water standards in <br /> four parameters. One lab reported dissolved iron concentrations <br /> of 6.62 mg/1 (secondary drinking water standards = .3 mg/I); <br /> the other labs reported iron at .05 mg/I and .06 mg/I. Two labs <br /> reported pH's of 8.9 and 9.1 (secondary drinking water <br /> standards = 6.5 - 8.5 pH). Selenium exceeded standards at two <br /> labs which were .04 mg/I and .025 mg/l (primary drinking <br /> water standards = .01 mg/1). One lab analysis exceeded nitrate <br /> levels with 30 mg/l (primary drinking water standards = <br /> 10 mg/1). TDS levels were 782 mg/I and 720 mg/l at two labs. <br /> The amount of leachate flow in the underdrains is expected to <br /> be low and will be diluted in the sediment ponds with surface <br /> runoff. <br /> The lower refuse pile is expected to have no significant effects <br /> to the surface water system even under worst-case low flow <br /> conditions. The amount of leachate expected to be generated <br /> from the pile is small in relation to the adjacent drainage areas. <br /> The quality of the leachate is predicted to be comparable to <br /> similar waste piles in the North Fork valley with moderately <br /> high TDS, elevated sodium and sulfates, and low concentrations <br /> of metals. <br /> A worst-case discharge projection from the lower refuse pile <br /> has been estimated. Based on an estimated annual infiltration <br /> of 5.7 inches, an annual leachate production of about 19 <br /> acre-feet is predicted from the 40-acre upper refuse site. A <br /> seasonal maximum leaching rate was estimated at twice the <br /> average annual leaching discharging rate of 11.8 gpm. When <br /> added to the leaching rates estimated for the lower refuse pile, <br /> a worst case total seasonal discharge of nearly 50 gpm could <br /> result. <br /> No adverse impact would be anticipated with respect to arsenic, <br /> boron, cadmium, chloride, manganese, nitrate, lead, selenium <br /> and zinc since concentrations of these parameters in the <br /> leaching tests were well below the stream standards on the <br /> North Fork Gunnison River. Furthermore, no adverse impact <br /> would be anticipated with respect to total and dissolved iron, <br /> sulfate, TDS and SAR. <br /> Concerns were raised by the Division regarding surface water <br /> effects of the lower waste pile leachate reaching the North Fork <br /> Gunnison River after the waste pile sediment pond is removed <br /> and the mine site has been permanently reclaimed. In response, <br /> MCC provided an analysis of the worst case effects to the <br /> North Fork of the Gunnison from leachate generated by the <br /> 42 <br />