Radon Map
Sections 307 and 309 of the Indoor Radon Abatement Act of 1988 (IRAA)
directed EPA to list and identify areas of the U.S. with the potential for
elevated indoor radon levels. EPA’s Map of Radon Zones assigns each of
the 3,141 counties in the U.S. to one of three zones based on radon potential:
Zone 1 counties have a predicted average indoor radon screening level
greater than 4 pCi/L (picocuries per liter) (red zones)Zone 2 counties have a predicted average indoor radon screening level
between 2 and 4 pCi/L (orange zones)Zone 3 counties have a predicted average indoor radon screening level
less than 2 pCi/L (yellow zones)
MAP DEVELOPMENT: The Map was developed using five factors to
determine radon potential: indoor radon measurements; geology; aerial
radioactivity; soil permeability; and, foundation type. Radon potential
assessment is based on geologic provinces. Radon Index Matrix is the
quantitative assessment of radon potential. Confidence Index Matrix shows
the quantity and quality of the data used to assess radon potential. Geologic
Provinces were adapted to county boundaries for the Map of Radon Zones.