Is Lewis County, WA a radon risk area?

EPA places Lewis County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Lewis County sits at the 25th percentile nationally for radon potential — above 25 of every 100 rated counties.

How Lewis County compares

About 87,049 people live in Lewis County, Washington, spread over 2,402.782 square miles. Averaged across its land area, Lewis County runs about 36 people per square mile. Rank 235 by population within its EPA zone puts Lewis County at the 77th percentile among zone peers. Lewis County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Lewis County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. Don't read Zone 3 as a pass for Lewis County — EPA's guidance to test every home makes no exception for counties predicted low.

Next steps for a home in Lewis County

Nothing about Lewis 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

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

Lewis County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.