What EPA's radon map says about Carbon County

EPA places Carbon County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Rank it against the rest of the country and Carbon County lands in the 77th percentile for radon potential.

Where Carbon County sits nationally

About 11,498 people live in Carbon County, Montana, spread over 2,047.889 square miles. That works out to roughly 6 people per square mile. Among counties sharing Carbon County's EPA zone, it outranks 31% of them by population. Geologically, Carbon County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

Zone vs. an actual test

Carbon County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. That doesn't mean every Carbon County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

Testing and mitigation in Carbon County

Mitigation cost doesn't depend on Carbon 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

Carbon County's test kit answers today; a Airthings radon monitor keeps answering for Carbon 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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.