Thank you all. I am not opposed to installing a radon mitigation system, if conservative measures do not work, that's exactly what I will do. But I feel given the relatively low radon exposure and the fact sealing the penetration will take an hour tops of my time, why not try it. Jim, you mentioned heavy rains have an even stronger effect on radon levels. Thank you for sharing this, I did not realize this. Up until this summer, the back yard was pitched toward the house and rainwater from the downspouts would flow right up against the house. I have solved this by regrading and installing d