What EPA's radon map says about Columbia County

EPA's own radon map rates Columbia County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. Nationally that's the 35th percentile for radon potential — Columbia County outranks 35% of every county EPA has rated.

Where Columbia County sits nationally

About 4,025 people live in Columbia County, Washington, spread over 868.585 square miles. Population density there runs about 5 people per square mile. Among counties sharing Columbia County's EPA zone, it outranks 7% of them by population. EPA's geology-based Region 10 groups Columbia County with 141 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Columbia County's predicted average falls between EPA's 4 pCi/L action level and the national indoor average of about 1.3 pCi/L (outdoor air runs roughly 0.4 pCi/L). A county-wide moderate average, like Columbia County's, can still hide a specific house well above or below it — testing is what actually answers the question.

If Columbia County tests above the action level

Mitigation cost doesn't depend on Columbia 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 Washington's state radon program

Columbia County's test kit answers today; a Airthings radon monitor keeps answering for Columbia 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 Columbia County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.