What EPA's radon map says about Washington County

EPA places Washington 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 Washington County lands in the 83rd percentile for radon potential.

Where Washington County sits nationally

About 22,631 people live in Washington County, Iowa, spread over 568.828 square miles. Population density there runs about 40 people per square mile. Among counties sharing Washington County's EPA zone, it outranks 50% of them by population. Washington County falls in EPA Radon Region 7, one of 412 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Washington County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. Some Washington County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Next steps for a home in Washington County

Mitigation cost doesn't depend on Washington 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 Iowa's state radon program

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