The EPA estimates that the average indoor concentration of radon in the US is what?

The average indoor concentration of radon in the U.S. is estimated by the EPA to be 1.3 pCi/L (picocuries per liter). This figure is significant as it serves as a benchmark for homeowners and radon measurement professionals when assessing indoor radon levels. Understanding this average helps in interpreting radon test results, guiding the need for mitigation strategies in homes and buildings that may show elevated radon levels. The 1.3 pCi/L estimate is particularly important since it is below the action level recommended by the EPA, which is 4.0 pCi/L. Levels above this action level are associated with an increased risk of lung cancer, which underscores the importance of awareness and testing for radon in residential and commercial properties.