Distance to faults as a proxy for radon gas concentration in dwellings

• Structural geology characteristics were used to identify the radon-prone areas.
• Relationships between radon concentrations and distance to fault were established.
• Two approaches were investigated based on the U content of the bedrock units.
• Statistically similar classes of distance were merged based on the ANOVA results.
• A distance to fault where the radon potential is high was determined.

This research was done to demonstrate the usefulness of the local structural geology characteristics to predict indoor radon concentrations. The presence of geologic faults near dwellings increases the vulnerability of the dwellings to elevated indoor radon by providing favorable pathways from the source uranium-rich bedrock units to the surface. Kruskal–Wallis one-way analyses of variance by ranks were used to determine the distance where faults have statistically significant influence on indoor radon concentrations. The great-circle distance between the 640 spatially referenced basement radon concentration measurements and the nearest fault was calculated using the Haversine formula and the spherical law of cosines. It was shown that dwellings located less than 150 m from a major fault had a higher radon potential. The 150 m threshold was determined using Kruskal–Wallis ANOVA on: (1) all the basement radon measurements dataset and; (2) the basement radon measurements located on uranium-rich bedrock units only. The results indicated that 22.8% of the dwellings located less than 150 m from a fault exceeded the Canadian radon guideline of 200 Bq/m3 when using all the basement radon measurements dataset. This percentage fell to 15.2% for the dwellings located between 150 m and 700 m from a fault. When using only the basement radon measurements located on uranium-rich bedrock units, these percentages were 30.7% (0–150 m) and 17.5% (150 m–700 m). The assessment and management of risk can be improved where structural geology characteristics base maps are available by using this proxy indicator.