Map showing radon potential of rocks and soils in Montgomery County, Maryland

This map subdivides the county into three radon potential categories based on geology, soil-gas radon samples (595 sites), indoor radon concentrations (319 sites), and surface radioactivity measurements (278 sites). Areas ranked low may have less than 40% of homes above 4 pCi/L indoor radon, whereas areas ranked high may have 60% or more homes above 4 pCi/L indoor radon.