What EPA's radon map says about Pierce County

Pierce County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Rank it against the rest of the country and Pierce County lands in the 32nd percentile for radon potential.

Pierce County by the numbers

About 941,170 people live in Pierce County, Washington, spread over 1,668.025 square miles. That works out to roughly 564 people per square mile. Among counties sharing Pierce County's EPA zone, it outranks 97% of them by population. EPA's geology-based Region 10 groups Pierce County with 141 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

At Zone 3, Pierce 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. Even at Zone 3, Pierce County homes are not guaranteed a low reading — zone is a county-wide average, and EPA recommends testing every home regardless of zone.

If Pierce County tests above the action level

Mitigation cost doesn't depend on Pierce 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

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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Pierce County carries, the zone explainer covers what it does and doesn't tell you about any one house.