sump pit radon seal

https://getyorkparadonprosradoncorner.greyhavendaily.com/posts/why-radon-mitigation-in-york-pa-matters-for-your-home-s-safety

A sump pit radon seal is a critical barrier installed around the opening of a basement sump pit to prevent radon gas from seeping into your home. Radon, a radioactive soil gas, can enter through these exposed pits, so a tight seal using rubber gaskets, concrete, or specialized membranes effectively blocks that pathway. I've seen homes where a simple retrofit seal drastically lowered radon levels.