Radon soil gas in the Halifax Regional Municipality, Nova Scotia, Canada

Naturally occurring radon(222) is found in measurable quantities in soil gas across Nova Scotia. Next to smoking, exposure to radon is the leading cause of lung cancer. This study identifies relationships between the permeability and composition of the soil, and the geology of the respective bedrock types within Halifax Regional Municipality (HRM). Over 280 radon soil gas samples from 60 sites were collected and analyzed using protocols developed for the North American Soil Geochemical Landscapes Project. This study focused on soil developed on glacial till over three major bedrock types: the Cambrian-Ordovician Goldenville and Halifax groups, and Devonian granite of South Mountain Batholith. All samples contained radon soil gas. Fine-grained leucomonzogranite samples returned the highest mean radon concentration of 51.0 kBq m(-3), followed by coarse-grained leucomonzogranite (50.2 kBq m(-3)), monzogranite (44.3 kBq m(-3)), slate (36.1 kBq m(-3)), and metasandstone and Lawrencetown till, respectively 22.5 kBq m(-3) and 19.4 kBq m(-3). Analysis of the permeability readings was done in four major till types in HRM: granite (3.27 x 10(-12) m(2)), metasandstone (5.84 x 10-12 m(2)), and slate facies (5.20 x 10-12 m(2)) of the Beaver River Till (BRT), and Lawrencetown Till (1.18 x 10(-12) m(2)). The soil radon potential index (SRP), which is used to correlate soil gas and permeability readings with indoor radon potential, was applied to data collected for the HRM study area, where over 40% of Nova Scotia's population resides. The SRP index results show the granite facies of BRT returning the highest mean value of 34.5, followed by the slate facies (27.2) and metasandstone facies (15.1) of the BRT, and Lawrencetown Till (9.1). 1D soil-gas modeling demonstrated that it is unlikely that bedrock radon transport from depth alone can contribute to the concentrations measured at 60 cm; the overlying tills must also be producing radon.