Where does Radon Come from?

Radon is constantly being generated by the radium in rocks, soil, water and materials derived from rocks and soils. The radon generated in rocks or water usually stays trapped in that material unless the rocks are fractured or the water is mixed with the air. Radon-222 is the decay product of radium-226. Radon-222 and its parent, radium-226, are part of the long decay chain for uranium-238. Since uranium is essentially everywhere in the earth's crust, radium-226 and radon-222 are present in almost all rock and all soil types.

The amount of radon soil can produce depends on local geology and can vary from house to house. Radon levels in the soil range from a few hundred to several thousand pCi/L (picoCuries per Liter). The amount of radon that escapes from the soil to enter the house depends on the suction created within the house, soil porosity, soil moisture, and the weather.

What is the average levels of Radon found in homes in the US?

Based on a national residential radon survey completed in 1991, the average indoor radon level in the United States is about 1.3 picoCuries per liter (pCi/L). The average outdoor level is about 0.4 pCi/L.