Soil-gas entry into houses driven by atmospheric pressure fluctuations—The influence of soil properties

Atmospheric pressure fluctuations can draw soil gas into houses without the indoor-outdoor pressure differences commonly associated with the advective entry of radon and other soil-gas contaminants. To study this phenomenon, we employ a transient finite-element model based on Darcyʹs law to simulate the soil-gas flow around a prototypical basement caused by changes in atmospheric pressure. The characteristic response time and the capacitance of the soil are used to characterize how changes in permeability, air-filled porosity, and water-table depth affect this soil-gas flow. The shorter the characteristic response time and the larger the capacitance of the soil, the larger the soil-gas flow rate into a basement caused by a given fluctuation in atmospheric pressure. Such a soil must have a high permeability and a large air-filled porosity. The addition of a high permeability subslab gravel layer increases the soil-gas flow rate into the basement by a factor of 3. Relative to entry driven by steady indoor-outdoor pressure differences, contaminant entry induced by atmospheric pressure fluctuations will likely be most important in houses situated in a soil of low permeability (< 10−12 m2) and large air-filled porosity.