EPA radon action level 2

https://myhomeradontestworks.greyhavendaily.com/posts/why-every-homeowner-needs-a-reliable-home-radon-test

The EPA's radon action level is set at 4 picocuries per liter, indicating the point where homeowners should take steps to reduce radon gas in their homes. This guideline helps prevent long-term exposure, as radon is a leading cause of lung cancer. Testing for radon is recommended every few years, especially if you've made structural changes to your home.