GEOLOGICAL AND GEOCHEMICAL FACTORS AFFECTING THE RADON CONCENTRATION IN HOMES IN CORNWALL AND DEVON, UK

Recently collected data for radon levels in houses in Devon and Cornwa ll are compared with geological and geochemical information. The regio n is underlain by granites intruded into folded sedimentary rocks. The highest incidence of affected houses is on granites. The granites are characterised by moderate uranium concentrations, a deep weathering p rofile and uranium in mineral phase which is easily weathered. However , while the uranium may be removed, radium, the immediate precursor of radon, can remain in situ. Radon is emanated easily from the host roc k, and high values of radon in ground and surface waters and soil gase s have been detected. The granite areas are also characterised by high values of uranium in stream sediments and waters. In contrast, other zones of high uranium in stream sediment samples do not necessarily ex hibit high house radon concentrations, especially when underlain by re latively impermeable rocks. Permeable ground can give rise to high inc idences of affected houses despite having uranium levels close to the crustal abundance. It is concluded that the most efficient method of i dentifying zones of high radon potential is the soil gas radon survey.