How to choose a St. Louis radon mitigation contractor: what to check before you sign, from NRPP/NRSB certification and system warranties to post-mitigation testing and transparent pricing.EDWARDSVILLE, Ill., June 23, 2026 (GLOBE NEWSWIRE) -- Air Sense Environmental is urging homeowners across the St. Louis metro to test for radon this summer after the Missouri Department of Health and Senior Services reported that one in three homes in its residential testing program tested above the EPA action level of 4.0 pCi/L. In St. Louis County, average indoor radon measures 3.4 pCi/L, more than double the national average, according to Air Chek data.