The role of diffusion in radon entry into houses

This paper reports on pressure-driven flow of radon-bearing soil gas that is commonly accepted as the usual mechanism whereby radon moves from the exterior of a house foundation to cause an elevated indoor radon concentration. It is less clear how radon moves to the backfill-and subslab zone just outside the foundation. Twenty-three houses having elevated indoor radon concentrations were investigated by the U.S. Environmental protection Agency and its contractors. The permeability of the ground to gas flow was measured next to and several meters away from each house foundation. For 6 of the 23 houses none of the permeability values exceeded 8 x 10-12 m2, below which diffusion is likely to be the dominant mechanism of radon movement. Because it can be significant in unsaturated soils of moderate-to-low permeability, diffusion should not be ignored in considering radon movement to house foundations