Cameco Corporation flooded the Rabbit Lake mine pit in 1991. The resulting 5 million cubic meter lake contained elevated levels of arsenic and nickel. In 1992, Boojum Research Limited began an exhaustive study of the impounded lake to determine the rate and means by which naturally occurring biological polishing agents would clean the water (see BIOLOGICAL POLISHING).
As expected, the new water body was contaminated by elevated levels of nickel, arsenic, and suspended solids. Boojum Research was hired to prepare the pit-lake for eventual inclusion in the adjacent Lake Wollaston, after breaking down the massive dyke. A detailed mass balance was calculated that defined the source and sinks of all contaminants in the pit. By analyzing and measuring the solids suspended in the pit-lake water, and the rate at which they were settling to the bottom, it was possible to estimate the total volume of contaminants that had accumulated on the pit-lake bottom.
From 1996 to 2001, arsenic concentrations accumulated in the sediments and declined in the water column to below regulatory limits. Nickel concentration in the sediments increased, a corresponding decline was not observed for the water column. Eventually, an external source of nickel in a nearby roadbed was identified and removed in October 2001. Since then, all of the contaminants in the water, including nickel, have declined in the water at a predictable rate. The mass balance, constructed by Boojum, confirms that no new contaminants are reaching the pit lake.
For a PDF of the Report please send an email to: margarete.kalin@utoronto.ca
Kalin, M., C. Cao, M.P. Smith and M.M. Olaveson, Development of the Phytoplankton Community in a Pit-Lake in relation to Water Quality Changes, Water Research (35:13), 2001, pp. 3215-3225.
Kalin, M., M.P. Smith and Y. Cao, Sedimentation in a pit lake in relation to water quality changes, Proceedings of the International Symposium on the Process Metallurgy of Uranium, Uranium 2000, Saskatoon, Saskatchewan, September 9-15, 2000, pp. 613-630.