What EPA's radon map says about Grant County

Grant 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. Nationally that's the 60th percentile for radon potential — Grant County outranks 60% of every county EPA has rated.

Where Grant County sits nationally

About 104,717 people live in Grant County, Washington, spread over 2,679.554 square miles. Averaged across its land area, Grant County runs about 39 people per square mile. Among counties sharing Grant County's EPA zone, it outranks 81% of them by population. Geologically, Grant County is grouped into EPA Region 10 alongside 141 other counties that share its rock and soil setting.

What this actually means for a house in Grant County

EPA's Zone 2 rating for Grant County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. A Zone 2 rating is a moderate county-wide average, not a guarantee about any one house in Grant County — testing is the only way to know an individual home's actual level.

Testing and mitigation in Grant County

Mitigation cost doesn't depend on Grant 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

Grant County's test kit answers today; a Airthings radon monitor keeps answering for Grant 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 Grant County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.