Is Ferry County, WA a radon risk area?

EPA places Ferry 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 Ferry County lands in the 73rd percentile for radon potential.

Where Ferry County sits nationally

About 7,543 people live in Ferry County, Washington, spread over 2,203.23 square miles. Population density there runs about 3 people per square mile. Rank 831 by population within its EPA zone puts Ferry County at the 22nd percentile among zone peers. Ferry County falls in EPA Radon Region 10, one of 142 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 — Ferry 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 Ferry County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Ferry County tests above the action level

Nothing about Ferry 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 Washington's state radon program

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

Ferry County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Ferry County carries, the zone explainer covers what it does and doesn't tell you about any one house.