Perchlorate in Lake Water from an Operating Diamond Mine

Smith LJ, Ptacek CJ, Blowes DW, Groza LG, Moncur MC. Perchlorate in lake water from an operating diamond mine. Environmental Science and Technology. 2015 Jun 3.

Mining-related perchlorate [ClO4-] in the receiving environment was investigated at the operating open pit and underground Diavik diamond mine, Northwest Territories, Canada. Samples were collected over four years and ClO4- was measured in various mine waters, the 560 km2 ultra-oligotrophic receiving lake, background lake water and snow distal from the mine. Groundwaters from the underground mine had variable ClO4- concentrations, up to 157 µg L-1, and were typically an order of magnitude higher than concentrations in combined mine waters prior to treatment and discharge to the lake. Snow core samples had a mean ClO4- concentration of 0.021 µg L-1 (n=16). Snow and lake water Cl-/ClO4- ratios suggest evapoconcentration was not an important process affecting lake ClO4- concentrations. The multi-year mean ClO4- concentrations in the lake were 0.30 µg L-1 (n=114) in open water and 0.24 µg L-1 (n=107) under ice, much below the Canadian drinking water guideline of 6 µg L-1. Receiving lake concentrations of ClO4- generally decreased year-over-year and ClO4- was not likely [biogeo]chemically attenuated within the receiving lake. The discharge of treated mine water was shown to contribute mining-related ClO4- to the lake and the low concentrations after 12 years of mining were attributed to the large volume of the receiving lake.

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