Soil gas measurements below foundation depth improve indoor radon prediction

A soil gas measurement method developed earlier, Nucl Tracks Radiat Meas, 22Ž1 4. Ž1993. 468 was applied to boreholes drilled to below foundation depth. Radon concentration and permeability were measured at 50-cm intervals. In radon prone areas, permeability showed an increase with depth over several orders of magnitude, indicating a low permeability top layer with a thickness of 0.5 m and more. A radon availability index ŽRAI. was empirically defined and the maximum RAI of each boring proved to be a reliable indicator for radon problems in nearby houses. The permeability of the top layer also proved to be an important factor for a better understanding of soil gas transport and the influence of rain. Implications for radon mitigation are derived.