Radon is an odorless, tasteless, and invisible radioactive gas that is released during the radioactive decay of radium. While some radon is present everywhere in soil, rocks and water, high levels occur in regions rich in uranium, granite, shale and phosphate. The gases seep through openings/cracks in a basement floor or the slab foundation.
It measured in pico Curies per liter or pCi/L – the higher the number, the more concentrated and dangerous the gas. Corrections are recommended if your house has an average level of 4pCi/L or higher. Some areas of the country are more radon rich than others. The EPA has a map of radon zones at www.epa.gov/radon/zonemap.html and links to certified testing companies at www.epa.gov/iaq/whereyoulive.html.