Radon is an odorless, colorless, radioactive gas that comes from the natural decay of uranium that is found in nearly all soils and areas. The average indoor radon level is estimated to be about 1.3pCi/L and about 0.4pCi/L for outdoors. An estimated 40% of homes are believed to contain elevated levels of radon.
Radon gets in through cracks in solid floors, construction joints, cracks in walls, gaps in suspended floors, gaps around service pipes, cavities inside walls, and the water supply. Radon is estimated to cause about 21,000 lung cancer deaths per year; these risks can be reduced by lowering the radon level if found in your home.
The EPA recommends having all homes tested for radon; fix the problem if your radon level exceeds 4.0pCi/L; and consider reducing levels if found to be above 2.0pCi/L.