Spokane County, WA radon potential

EPA places Spokane County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Spokane County sits at the 99th percentile nationally for radon potential — above 99 of every 100 rated counties.

Spokane County by the numbers

Spokane County, Washington is home to about 555,947 people across 1,764.224 square miles. Averaged across its land area, Spokane County runs about 315 people per square mile. Within its own EPA zone, Spokane County is bigger by population than 97% of the counties that share it. Spokane County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Spokane County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. Some Spokane County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Next steps for a home in Spokane County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Washington's state radon program

For Spokane County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Spokane County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where Spokane County's figures come from

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