Washington Radon Levels
7Zone 1 (High)
14Zone 2 (Moderate)
18Zone 3 (Low)
18% of counties in Washington are classified as EPA Zone 1 (highest radon potential), meaning predicted average indoor radon levels exceed 4 pCi/L — the EPA action level. The EPA recommends that all homes be tested for radon, regardless of zone classification.
| County | EPA Zone | Risk Level |
|---|---|---|
| Adams County | Zone 2 | Moderate Potential |
| Asotin County | Zone 2 | Moderate Potential |
| Benton County | Zone 2 | Moderate Potential |
| Chelan County | Zone 3 | Lowest Potential |
| Clallam County | Zone 3 | Lowest Potential |
| Clark County | Zone 1 | Highest Potential |
| Columbia County | Zone 2 | Moderate Potential |
| Cowlitz County | Zone 3 | Lowest Potential |
| Douglas County | Zone 2 | Moderate Potential |
| Ferry County | Zone 1 | Highest Potential |
| Franklin County | Zone 2 | Moderate Potential |
| Garfield County | Zone 2 | Moderate Potential |
| Grant County | Zone 2 | Moderate Potential |
| Grays Harbor County | Zone 3 | Lowest Potential |
| Island County | Zone 3 | Lowest Potential |
| Jefferson County | Zone 3 | Lowest Potential |
| King County | Zone 3 | Lowest Potential |
| Kitsap County | Zone 3 | Lowest Potential |
| Kittitas County | Zone 2 | Moderate Potential |
| Klickitat County | Zone 2 | Moderate Potential |
| Lewis County | Zone 3 | Lowest Potential |
| Lincoln County | Zone 2 | Moderate Potential |
| Mason County | Zone 3 | Lowest Potential |
| Okanogan County | Zone 1 | Highest Potential |
| Pacific County | Zone 3 | Lowest Potential |
| Pend Oreille County | Zone 1 | Highest Potential |
| Pierce County | Zone 3 | Lowest Potential |
| San Juan County | Zone 3 | Lowest Potential |
| Skagit County | Zone 3 | Lowest Potential |
| Skamania County | Zone 1 | Highest Potential |
| Snohomish County | Zone 3 | Lowest Potential |
| Spokane County | Zone 1 | Highest Potential |
| Stevens County | Zone 1 | Highest Potential |
| Thurston County | Zone 3 | Lowest Potential |
| Wahkiakum County | Zone 3 | Lowest Potential |
| Walla Walla County | Zone 2 | Moderate Potential |
| Whatcom County | Zone 3 | Lowest Potential |
| Whitman County | Zone 2 | Moderate Potential |
| Yakima County | Zone 2 | Moderate Potential |