Thurston County, WA Radon Zone Data

Thurston County, WA: EPA's radon zone, explained

EPA places Thurston 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. Thurston County sits at the 30th percentile nationally for radon potential — above 30 of every 100 rated counties.

Where Thurston County sits nationally

Thurston County, Washington is home to about 302,912 people across 722.513 square miles. That works out to roughly 419 people per square mile. By population, Thurston County is the 87th largest of every county sharing its EPA zone — the 92nd percentile by population within that zone. EPA's geology-based Region 10 groups Thurston County with 141 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Thurston County

At Zone 3, Thurston County's predicted county average is under the national indoor average (~1.3 pCi/L) and well below EPA's 4 pCi/L action level — outdoor air nationally runs about 0.4 pCi/L for comparison. Don't read Zone 3 as a pass for Thurston County — EPA's guidance to test every home makes no exception for counties predicted low.

Next steps for a home in Thurston County

For a Thurston County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Washington's state radon program

For Thurston County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Thurston County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

Where Thurston County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.