Grays Harbor County, WA: EPA's radon zone, explained

EPA's own radon map rates Grays Harbor County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. That puts Grays Harbor County in the 25th percentile nationally for radon potential — higher than 25% of the counties EPA has rated.

Where Grays Harbor County sits nationally

Grays Harbor County, Washington is home to about 77,893 people across 1,902.268 square miles. Population density there runs about 41 people per square mile. By population, Grays Harbor County is the 256th largest of every county sharing its EPA zone — the 75th percentile by population within that zone. EPA's geology-based Region 10 groups Grays Harbor County with 141 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Well clear of both the 1.3 pCi/L national indoor average and EPA's 4 pCi/L action level, Grays Harbor County's Zone 3 prediction is the low end of the scale. A Zone 3 label describes Grays Harbor County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Testing and mitigation in Grays Harbor County

For a Grays Harbor 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 Washington's state radon program

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

Where Grays Harbor County's figures come from

Grays Harbor County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.