Long-term trend of uranium concentrations in Beaverlodge Lake, Saskatchewan, Canada, under mine decommissioning

The annual mass balance of uranium for Beaverlodge Lake (which is impacted by uranium mining) was analysed using limited observation data. Annual water discharges of the basin, or discharges at the lake outlet are estimated using the discharge ratios of a sub-basin from 1985 to 2006. Uranium loadings are determined using observed concentrations and discharges from two creeks flowing into Beaverlodge Lake. The relationships between inflow loadings, outflow volumes and lake concentration changes are established. Then, given the trends of loading, the long-term trends of outflows from the lake and concentrations in the lake are predicted. Along with a continuous reduction in loadings from 3473 kg/year in 1985 to 0 kg/year in 2092, uranium concentration of the lake decreases from 125 μg/L in 1985 to 10 μg/L in 2118. The natural restoration of the lake water would need 112 years to reach the 10 μg/L Canadian drinking water standard.