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. Washington County sits at the 71st percentile nationally for radon potential — above 71 of every 100 rated counties.

How Washington County compares

About 5,572 people live in Washington County, Kansas, spread over 894.759 square miles. Population density there runs about 6 people per square mile. Among counties sharing Washington County's EPA zone, it outranks 15% of them by population. Washington County falls in EPA Radon Region 7, one of 412 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, Washington County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Washington County will test well under the action level, and EPA's guidance is to test regardless of zone.

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 Kansas'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

The methodology guide shows exactly which EPA and Census sources feed Washington County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.