Washington County, AR: EPA's radon zone, explained

Washington County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Washington County sits at the 30th percentile nationally for radon potential — above 30 of every 100 rated counties.

Washington County by the numbers

Washington County, Arkansas is home to about 266,184 people across 941.465 square miles. Averaged across its land area, Washington County runs about 283 people per square mile. By population, Washington County is the 96th largest of every county sharing its EPA zone — the 91st percentile by population within that zone. EPA's geology-based Region 6 groups Washington County with 502 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. Even at Zone 3, Washington County homes are not guaranteed a low reading — zone is a county-wide average, and EPA recommends testing every home regardless of zone.

Testing and mitigation in Washington County

For a Washington County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Arkansas'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

Washington County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.