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Radon zones in Washington

The EPA assigns every county in Washington to one of three radon potential zones. 7 are in Zone 1, the highest category, home to about 15% of the state's residents.

39
Counties
7
Zone 1 counties
Predicted average above 4 pCi/L
14
Zone 2 counties
Predicted average 2-4 pCi/L
18
Zone 3 counties
Predicted average below 2 pCi/L

The map

Radon potential across Washington

Every county in Washington, filled by the zone the EPA assigns it. Zones follow geology rather than county lines, so the colour usually changes where the bedrock does, not where the border is.

Zone 1 · 7Zone 2 · 14Zone 3 · 18

Hover a county · click to open it

County by county

All 39 Washington counties

Zone 1 · > 4 pCi/LZone 2 · 2 - 4 pCi/LZone 3 · < 2 pCi/L
CountyZonePopulationCOPDSmokingLung ca. deaths
Clark County1521k5.5%11.0%31.5
Ferry County17,4979.8%16.0%39.3
Okanogan County144k8.7%15.5%43.2
Pend Oreille County114k8.7%13.6%35.8
Skamania County113k7.0%12.0%31.9
Spokane County1551k6.0%11.7%31.2
Stevens County149k8.6%14.0%29.7
Adams County221k6.9%14.0%19.4
Asotin County223k8.1%13.3%24.6
Benton County2215k5.6%10.4%27.8
Columbia County24,0537.6%11.9%35.4
Douglas County245k6.3%11.7%30.4
Franklin County299k5.4%12.1%30.4
Garfield County22,3637.0%11.4% -
Grant County2103k6.4%12.6%31.2
Kittitas County246k6.1%11.1%29.7
Klickitat County224k7.2%12.1%29.6
Lincoln County212k7.3%11.7%24.2
Walla Walla County262k6.0%11.1%30.3
Whitman County248k4.9%10.1%33.3
Yakima County2257k6.5%12.9%31.1
Chelan County380k6.3%11.4%28.6
Clallam County378k7.8%11.8%33.4
Cowlitz County3113k7.5%13.4%47.8
Grays Harbor County377k8.2%15.0%37.3
Island County386k5.9%9.5%26.3
Jefferson County334k7.2%9.5%21.6
King County32.3M3.4%7.2%22.6
Kitsap County3278k5.4%10.4%27.7
Lewis County386k7.5%14.4%34.1
Mason County368k7.5%13.0%42.7
Pacific County324k8.5%13.1%36.5
Pierce County3929k5.2%11.6%32.6
San Juan County319k6.4%8.9%21.3
Skagit County3131k6.5%11.4%33.8
Snohomish County3845k4.8%10.1%30.8
Thurston County3299k5.3%10.2%32.2
Wahkiakum County34,7659.2%13.3%38.9
Whatcom County3232k5.4%10.8%25.4

Zones from the EPA Map of Radon Zones. COPD and smoking are CDC PLACES model-based estimates of adult prevalence. Lung cancer death rates are age-adjusted deaths per 100,000 per year, 2019-2023, from NCI State Cancer Profiles. A dash means the source does not report a value for that county.

Highest potential

Zone 1 counties in Washington

These 7 counties have a predicted average indoor radon screening level above the EPA action level. The EPA recommends every home in them be tested.

Other states

Radon zones elsewhere