A Site Study of Soil Charactersistics and Soil Gas Radon in Rochester, Minnesota

Abstract

In regional surveys, indoor radon is usually the parameter of interest, but occasionally soil gas radon at depths of 1 meter or less is also measured. At statewide scales, even limited data sets can be used to infer relationships between geology and soil gas or indoor radon. However, predicting the radon potential of a single house or even an area the size of a neighborhood is more difficult As the size of a surveyed area decreases, site-specific variables become more significant. During 1990 we completed a study of two residential neighborhoods within 7 kilometers of each other near Rochester, Minnesota. Eight holes were augered into glacial sediments to maximum depths of 4.5 meters and samples collected for grain-size analysis, measurement of radon parent/daughter nuclides and radon emanation. A total of sixty-five homes in the areas were provided with two alpha-track registration detectors for indoor monitoring between September 1988 and September 1989. Positive correlations were observed between the average soil radon, the average indoor radon, and the precursor/daughter radionuclides. The study area with the most topographic relief also had the highest radionuclide contents, the most variability with depth, and some variation with time and soil moisture; these results were not observed at the low-relief site. The type of study described would best be applied to site-specific preconstruction screening, rather than to predicting radon in existing structures.