What EPA's radon map says about Washington County

EPA's own radon map rates Washington County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Washington County ranks higher in radon potential than 95% of rated counties (the 95th percentile).

Where Washington County sits nationally

About 139,642 people live in Washington County, Tennessee, spread over 326.548 square miles. Population density there runs about 428 people per square mile. Among counties sharing Washington County's EPA zone, it outranks 87% of them by population. Washington County falls in EPA Radon Region 4, one of 736 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Washington County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. 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.

If Washington County tests above the action level

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 Tennessee'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. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

Washington County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.