Radon in Alberta Groundwater

Abstract

Radon exposure in indoor air is the leading cause of lung cancer among non-smokers. Many efforts have focused on mapping radon exposure potential based on geology. However, few have integrated the potential of exposure from groundwater use and water wells. Therefore, this study sought to evaluate groundwater’s role by assessing differences in indoor air radon between homes on different water supplies, understand the distribution of radon concentrations in Alberta groundwater and evaluate geological and geochemical controls on radon’s distribution. When radon concentrations in indoor air from the EvictRadon.ca database were separated into homes assumed to rely on domestic wells for water supply versus surface water, the former had significantly higher indoor radon concentrations (mean=137.0 Bq/m3, n=783) than those relying on surface water (mean=104.1 Bq/m3, n=16,362). Radon concentrations and geochemical parameters were measured in groundwater from 40 monitoring wells in various geologic formations (0.20 to 75.1 Bq/L, mean=8.1 Bq/L). Radon concentrations were substantially less than the Canadian recommended action level for radon in household water supplies, suggesting water well pumping is not a significant pathway for radon in indoor air. Overall, elevated radon was not correlated with a specific groundwater type or to the geochemical evolution of groundwater. Moderate negative Pearson’s correlations (0.4 to 0.65) were observed with radon and methane, 13C-CO2, and total dissolved gas pressure (PTDG), and moderate positive correlations with sulphate and uranium. Overall, no significant radon concentrations differences were found between aquifer formations except for when comparing between two bedrock classifications and surficial deposits, where the non-Paskapoo bedrock formations had significantly lower radon. The lack of strong (R > 0.65) correlation between radon and geochemical parameters and the absence of a relationship with groundwater type or evolution suggests that radon in groundwater is not derived from rock-water interaction in the screened formation. However, the moderate correlations between radon and methane, sulphate, and PTDG supports the hypothesis that i) free phase methane gas migration out of gas charged, methane-rich aquifers is stripping radon from groundwater, and ii) the low redox of methane-rich groundwater is consistent with low dissolved sulphate and uranium concentrations.