Radon in Washington

About 3 in 10 homes tested in Washington were at or above the EPA action level of 4 pCi/L.

57%18%25%

5,879 homes tested, 2008–2017

The line marks the EPA action level, 4 pCi/L.

The EPA puts 7 of Washington's 39 counties in Zone 1, its highest radon category, 14 in Zone 2 and 18 in Zone 3.

Every county in Washington

Sorted by the share of homes tested at or above 4 pCi/L. Select a county for local details and costs.

County	Homes tested	At or above 4	Median	EPA zone
Columbia County	2 tests	–	–	2
Pend Oreille County		63%	4.8 pCi/L	1
Garfield County	1 tests	–	–	2
Klickitat County		41%	2.2 pCi/L	2
Spokane County		41%	2.9 pCi/L	1
Lincoln County	14 tests	–	–	2
Skamania County		40%	2.9 pCi/L	1
Grays Harbor County	9 tests	–	–	3
Stevens County		36%	2.3 pCi/L	1
Douglas County	10 tests	–	–	2
Okanogan County		35%	2.3 pCi/L	1
Clark County		25%	1.8 pCi/L	1
Ferry County	16 tests	–	–	1
Kittitas County	8 tests	–	–	2
Grant County	16 tests	–	–	2
Whitman County		22%	1.5 pCi/L	2
Benton County		20%	2.0 pCi/L	2
Walla Walla County		16%	1.4 pCi/L	2
Chelan County		15%	1.8 pCi/L	3
Adams County	5 tests	–	–	2
Clallam County	12 tests	–	–	3
Cowlitz County		11%	1.1 pCi/L	3
Franklin County	12 tests	–	–	2
Island County	17 tests	–	–	3
Thurston County		10%	0.7 pCi/L	3
Jefferson County	16 tests	–	–	3
Lewis County	7 tests	–	–	3
Yakima County		8%	0.7 pCi/L	2
Whatcom County		5%	0.9 pCi/L	3
Kitsap County		5%	0.7 pCi/L	3
Pierce County		5%	0.7 pCi/L	3
Skagit County		3%	0.8 pCi/L	3
King County		3%	0.7 pCi/L	3
Snohomish County		2%	0.5 pCi/L	3
Asotin County	6 tests	–	–	2
Mason County	13 tests	–	–	3
Pacific County	2 tests	–	–	3
San Juan County	8 tests	–	–	3
Wahkiakum County	1 tests	–	–	3

"–" means fewer than 20 tests or no lab data, too few for a reliable figure.

EPA Map of Radon Zones (public domain).
CDC Environmental Public Health Tracking Network, radon tests from labs, 2008–2017. Pre-mitigation tests only.