Investigations of soil as a source of indoor radon

The predominant source of indoor radon in US housing containing higher than average concentrations is the soil adjacent to the house substructure. In most cases, the observed indoor concentrations are not due to the presence of uraniferous soils, either naturally occurring or due to industrial contamination. Factors influencing the product and transport of radon in soil and into buildings have been reviewed. A number of important parameters have been identified that have a significant effect on the movement of radon-bearing soil gas, including the air permeability, moisture content and grain-size distribution of soils. These effectively determine the relative importance of diffusive and convective transport of soil gas. Coupling between the building shell and the surrounding soil has been investigated using pressure-field mapping and tracer gas techniques. Observed soil-gas flows are compared with flows calculated from basic transport equations and with flows estimated from general soil characteristics