What EPA's radon map says about Ravalli County

EPA's own radon map rates Ravalli County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rank it against the rest of the country and Ravalli County lands in the 90th percentile for radon potential.

How Ravalli County compares

About 48,187 people live in Ravalli County, Montana, spread over 2,390.967 square miles. Population density there runs about 20 people per square mile. Among counties sharing Ravalli County's EPA zone, it outranks 70% of them by population. Ravalli County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Where the national indoor average runs about 1.3 pCi/L, Ravalli County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. That doesn't mean every Ravalli 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.

If Ravalli County tests above the action level

Mitigation cost doesn't depend on Ravalli 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

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

Ravalli County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.