California

United States EPA State Map of Radon Gas Concentration

California is considered to have a low to moderate potential for radon gas. However, it is still recommended that residents of California test their homes for radon gas, as high levels of radon have been found in some areas of the state. The California Radon Program provides information and resources for testing and mitigating radon gas. The Program is under the California Department of Public Health and it also provides information on how to obtain a radon test kit and interpret the results.

The U.S. EPA and the U.S. Geological Survey have evaluated the radon potential in the U.S. and have developed this map is to assist National, State, and local organizations to target their resources and to assist building code officials in deciding whether radon-resistant features are applicable in new construction. This map is not intended to be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested regardless of geographic location. The map assigns each of the 3,141 counties in the U.S. to one of three zones based on radon potential. Each zone designation reflects the average short-term radon measurement that can be expected to be measured in a building without the implementation of radon control methods. The radon zone designation of the highest priority is Zone 1.

	Zone 1	Highest Potential (greater than 4 pCi/L)
	Zone 2	Moderate Potential (from 2 to 4 pCi/L)
	Zone 3	Low Potential (less than 2 pCi/L)