What EPA's radon map says about Powell County

Powell County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Powell County sits at the 73rd percentile nationally for radon potential — above 73 of every 100 rated counties.

Powell County by the numbers

About 7,120 people live in Powell County, Montana, spread over 2,326.043 square miles. That works out to roughly 3 people per square mile. Among counties sharing Powell County's EPA zone, it outranks 21% of them by population. EPA's geology-based Region 8 groups Powell County with 290 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Powell County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. Being in Zone 1 raises the odds Powell County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

Next steps for a home in Powell County

Mitigation cost doesn't depend on Powell County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Montana's state radon program

Powell County's test kit answers today; a Airthings radon monitor keeps answering for Powell County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Powell County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.