What EPA's radon map says about Mason County

EPA places Mason 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. Rank it against the rest of the country and Mason County lands in the 24th percentile for radon potential.

How Mason County compares

About 69,632 people live in Mason County, Washington, spread over 959.565 square miles. That works out to roughly 73 people per square mile. Among counties sharing Mason County's EPA zone, it outranks 74% of them by population. EPA's geology-based Region 10 groups Mason County with 141 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Mason County

A Zone 3 county like Mason County is predicted closer to the 0.4 pCi/L typical outdoors than to EPA's 4 pCi/L action level. Low doesn't mean zero: EPA's own data shows homes in Zone 3 counties like Mason County testing above the action level often enough that skipping a test isn't the safe assumption.

If Mason County tests above the action level

Mitigation cost doesn't depend on Mason 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

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

The methodology guide shows exactly which EPA and Census sources feed Mason County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.