radon crawl space
https://radonmitigationcostsource.currentvale.com/posts/understanding-radon-mitigation-cost-what-homeowners-should-expect
We had the house tested for radon and the inspector found a hotspot right in the crawl space. It's basically a low, unfinished area under part of the house where moisture and soil gases can collect. We're looking into sealing the dirt floor and improving ventilation down there to keep the air safe.