Older homes in the St. Louis area often have stone or block foundations, settling cracks, and crawl spaces that let radon enter more easily. Mitigation in these homes may require extra sealing and a system tailored to the foundation, with the EPA action level of 4.0 pCi/L as the target.Active sub-slab depressurization is the most common system for St. Louis area homes: a sealed suctio... https://airsenseenvironmental.com/radon-mitigation-older-st-louis-homes/