Is Clarke County, IA a radon risk area?

EPA's own radon map rates Clarke County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts Clarke County in the 75th percentile nationally for radon potential — higher than 75% of the counties EPA has rated.

How Clarke County compares

About 9,524 people live in Clarke County, Iowa, spread over 431.111 square miles. That works out to roughly 22 people per square mile. Rank 779 by population within its EPA zone puts Clarke County at the 27th percentile among zone peers. Clarke County falls in EPA Radon Region 7, one of 412 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Clarke County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Clarke 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 Clarke County tests above the action level

Nothing about Clarke County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find Iowa's state radon program

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

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.