Vertical distribution of uranium mill tailings contaminants in Langley bay, Lake Athabasca sediments

Abstract

The Gunnar Mill, located on the north shore of Lake Athabasca in the Uranium City area, generated nearly five million tonnes of tailings which were initially discharged into a nearby small lake. Significant quantities of these tailings subsequently moved into another small water body in the area and then into Langley Bay, a shallow bay opening onto Lake Athabasca. Analyses of several sediment cores for both radioactive and non-radioactive constituents reveal that the contamination, covering the entire bottom of the bay, has reached Lake Athabasca. It is estimated that about 11% of the total 226Ra activity discharged from the mill resides in the Langley Bay sediments with about 76% still remaining at the original disposal areas. The 137Cs measurements suggest that natural cover on the submerged tailings will develop at a very slow rate. A very small fraction of 222Rn generated in the Langley Bay delta deposit escapes to the atmosphere.