The uranium mine at Rabbit Lake (northern Saskatchewan) has an open pit.  Effluents from the waste rock pile and mine slimes from the excavation of this pit contain elevated levels of radium and uranium. These effluents eventually entered Lake Wollaston, a natural, clean recreational and fishing lake. The radium and uranium had to be removed before the effluents could enter the lake. Boojum proposed using an indigenous alga, Nitella, to remove the radium and uranium (see BIOLOGICAL POLISHING), relegate these elements to the sediments, and transform them into stable precipitate (see ARUM).

Before a pit mine could be developed, Rabbit Lake was emptied and dredged to expose the bedrock below it.  The removed sediments were dumped into Upper Link Lake, creating turbidity which killed the in situ algae and aquatic plants. On average, 1.63 M-Bq.d^-1 of 226Ra was leaving the lake and flowing into Lower Link Lake, the next small lake in the chain. By the time the effluents had passed through Lower Link Lake, the level had dropped to .0.5 M-Bq.d^-1. Cameco and provincial regulators this posed three questions; why was the radium disappearing from Lower Link Lake? Where was it going? And why was it not disappearing in Upper Link Lake?

In 1988, Michael Babcock, vice president of operations for Eldorado (a precursor of Cameco), put the questions to Boojum Research and Margarete Kalin. Martin Smith, Boojum’s vice president of field operations had recently completed a master’s thesis on the nutrient requirements of a species of Characeae, an algal group that thrives in alkaline waters and that often grows spontaneously in wastewaters emanating from uranium tailings. Commonly known as stonewort, these algae have a strong affinity for 226Ra.

During the conversation with Babcock, Kalin predicted that some form of these Characean algae must be growing in Lower Link Lake. A few days later at the ice-bound lake, Kalin dredged up samples of Nitella flexilis through a hole in the ice. Analysis subsequently confirmed that the algae contained high concentrations of 226Ra and uranium.  Captured in the mineralized sheaths of the aquatic alga, Nitella, the radium was settling into the sediments when the plants died. It was then transformed into a more stable form by an active microbial community, nurtured by the decaying, organic algae. In effect, Lower Link Lake was a natural settling and polishing pond.

The same effect was not occurring in Upper Link Lake because of the absence of algae and aquatic plants in the lake. That shortcoming could be corrected, Kalin reported to Cameco, if Nitella was re-established in the lake. She submitted a plan, subsequently approved by regulators to transplant 12 tonnes of the algae from Lower Link Lake. The work was carried out by hand, in the summer of 1989. This was the beginning of an exhaustive 12 year study of the fate of contaminants in the two Link lakes.

For a PDF of the report please send an email to: margarete.kalin@utoronto.ca

C96 Kalin, M., M.P. Smith and M.B. Wittrup, Ecosystem restoration incorporating minerotrophic ecology and Stoneworts that accumulate 226Ra.  Proceedings of the Uranium Mining and Hydrogeology III conference, Freiberg, Germany, September 15-21, 2002, pp. 499-508.