What EPA's radon map says about Whitman County

Whitman County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. That puts Whitman County in the 55th percentile nationally for radon potential — higher than 55% of the counties EPA has rated.

How Whitman County compares

About 48,399 people live in Whitman County, Washington, spread over 2,159.262 square miles. That works out to roughly 22 people per square mile. Among counties sharing Whitman County's EPA zone, it outranks 66% of them by population. Whitman County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Neither at the 4 pCi/L action level nor down at the roughly 1.3 pCi/L national indoor norm, Whitman County's Zone 2 prediction lands in the gap between the two. Middle-of-the-pack doesn't mean risk-free for any one Whitman County address — a moderate county average still leaves individual homes to test either side of it.

If Whitman County tests above the action level

Mitigation cost doesn't depend on Whitman 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

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

The methodology guide shows exactly which EPA and Census sources feed Whitman County's numbers. Whatever zone Whitman County carries, the zone explainer covers what it does and doesn't tell you about any one house.