EPA radon action level 3

https://getlongtermradontestfacts.oakridgedigest.com/posts/why-a-long-term-radon-test-gives-you-the-most-accurate-picture-for-your-home

The EPA radon action level is the threshold at which the agency recommends taking steps to reduce radon levels in your home. Set at 4 picocuries per liter, this guideline helps homeowners know when to act, since radon exposure is a leading cause of lung cancer. Tests above this level often prompt sealing cracks and improving ventilation to lower the gas.