The Influence of Geology on Radon Levels in S.W. England

S.W. England contains 53% of UK homes estimated to contain a concentration of 222Rn above the Action Level of 200 Bq.m-3. Although the indoor concentration of 222Rn in many of these homes has now been measured, the majority of homes with high levels remain unidentified. The link between the local geology, soil gas radon concentration and indoor level has been investigated. The results presented are from the most exhaustive study yet undertaken in this region. Nearly two thousand soil gas measurements were made using alpha scintillation, and the indoor concentration was determined in over 250 homes using etched track detectors. Although there are many other factors that influence an indoor concentration, clearly the geology is the most important in defining the source potential. The expected correlation between granitic areas and high indoor levels was accompanied by some interesting results in areas of sedimentary rocks. It was found that the metamorphic aureole has a significant impact on indoor concentrations. (author)