Geologic controls on indoor radon in the Pacific Northwest

This paper reports on comparisons of average indoor radon levels, soil radium content (derived from aerial gamma-ray data), and soil characteristics for selected townships in Washington, Oregon, and Idaho which show that: soil radium content provides a first-order estimate of the relative amounts of indoor radon where soils are either of low to moderate intrinsic permeability or of permeability reduced by high moisture; in drier parts of the study area (east of the Cascade Mountains), unusually high average indoor radon levels are almost all characterized by soils that have high effective permeabilities (greater than 20 inches per hour), based on available country soil descriptions; and in the wetter parts of the study area (west of the Cascade Mountains), townships with unusually high indoor radon levels are characterized by steeply sloped soils