Washington County, ID radon potential

EPA places Washington 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. Nationally, Washington County ranks higher in radon potential than 8% of rated counties (the 8th percentile).

Washington County by the numbers

Washington County, Idaho is home to about 11,539 people across 1,452.855 square miles. That works out to roughly 8 people per square mile. Within its own EPA zone, Washington County is bigger by population than 24% of the counties that share it. EPA's geology-based Region 10 groups Washington County with 141 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

A Zone 3 county like Washington County is predicted closer to the 0.4 pCi/L typical outdoors than to EPA's 4 pCi/L action level. A Zone 3 label describes Washington County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

If Washington County tests above the action level

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 Idaho's state radon program

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

Where Washington County's figures come from

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