The Denison Mine closed in 1992. The decommissioned Denison mine site contains two flooded tailings management areas (TMAs) (Denison TMA 1 and Denison TMA 2) and two effluent treatment plants (ETP).
During rehabilitation, nearly 2.8 million cubic yards of tailings were hydraulically relocated mostly into deeper areas of TMA-1 while some tailings were placed into the underground workings.
Water cover is used to inhibit oxidation and acidification of the tailings and reduce gamma and radon exposure. Pond water, which passively flows to the ETP when levels are high enough, is treated to remove radium-226 at the ETPs prior to being discharged into the watershed. Effluent quality at all ETPs met provincial and federal limits included in the site licenses and guidelines prior to release.
The pictures below show the former Denison Mill location and the related Tailings Management Areas (TMA-1 in the top right and TMA-2 in the middle right) in 1997 and 2007.