Radon levels in Washington: Low
The model predicts a population-weighted basement average of 1.6 pCi/L across Washington's 39 counties - close to the US average of 1.8 pCi/L. Above-ground floors average 0.8 pCi/L.
Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.
7 / 39
EPA Zone 1 counties (18%)
14 / 18
Zone 2 / Zone 3 counties
0
counties predicted ≥ 4 pCi/L
0%
of ZIP codes predicted ≥ 4 pCi/L
Washington counties by predicted radon
Sorted highest to lowest predicted basement average. 39 counties.
| County | Predicted basement | Upstairs | Grade | EPA zone | ZIPs |
|---|---|---|---|---|---|
| Pend Oreille County | 3.1 pCi/L | 2.1 | Moderate | EPA Zone 1 | 5 |
| Ferry County | 2.9 pCi/L | 1.8 | Moderate | EPA Zone 1 | 8 |
| Stevens County | 2.8 pCi/L | 1.9 | Moderate | EPA Zone 1 | 16 |
| Garfield County | 2.4 pCi/L | 1.2 | Moderate | EPA Zone 2 | 1 |
| Columbia County | 2.4 pCi/L | 1.4 | Moderate | EPA Zone 2 | 1 |
| Lincoln County | 2.3 pCi/L | 1.2 | Moderate | EPA Zone 2 | 12 |
| Okanogan County | 2.3 pCi/L | 1.4 | Moderate | EPA Zone 1 | 15 |
| Spokane County | 2.3 pCi/L | 1.4 | Moderate | EPA Zone 1 | 35 |
| Whitman County | 2.2 pCi/L | 1.2 | Moderate | EPA Zone 2 | 16 |
| Asotin County | 2.2 pCi/L | 1.4 | Moderate | EPA Zone 2 | 3 |
| Kittitas County | 2.1 pCi/L | 1.1 | Moderate | EPA Zone 2 | 5 |
| Walla Walla County | 2.1 pCi/L | 1.2 | Moderate | EPA Zone 2 | 6 |
| Adams County | 2.0 pCi/L | 1.1 | Moderate | EPA Zone 2 | 5 |
| Yakima County | 2.0 pCi/L | 1.1 | Moderate | EPA Zone 2 | 18 |
| Grant County | 2.0 pCi/L | 1.0 | Low | EPA Zone 2 | 11 |
| Douglas County | 2.0 pCi/L | 1.1 | Low | EPA Zone 2 | 9 |
| Klickitat County | 1.9 pCi/L | 1.0 | Low | EPA Zone 2 | 12 |
| Chelan County | 1.8 pCi/L | 1.0 | Low | EPA Zone 3 | 9 |
| Benton County | 1.8 pCi/L | 1.1 | Low | EPA Zone 2 | 9 |
| Clark County | 1.8 pCi/L | 1.0 | Low | EPA Zone 1 | 18 |
| Franklin County | 1.7 pCi/L | 0.9 | Low | EPA Zone 2 | 4 |
| Lewis County | 1.6 pCi/L | 0.8 | Low | EPA Zone 3 | 18 |
| San Juan County | 1.6 pCi/L | 0.8 | Low | EPA Zone 3 | 4 |
| Cowlitz County | 1.5 pCi/L | 0.9 | Low | EPA Zone 3 | 9 |
| Clallam County | 1.5 pCi/L | 0.8 | Low | EPA Zone 3 | 6 |
| Pacific County | 1.5 pCi/L | 0.8 | Low | EPA Zone 3 | 10 |
| Whatcom County | 1.5 pCi/L | 0.8 | Low | EPA Zone 3 | 16 |
| Skagit County | 1.5 pCi/L | 0.8 | Low | EPA Zone 3 | 9 |
| Grays Harbor County | 1.5 pCi/L | 0.8 | Low | EPA Zone 3 | 16 |
| Island County | 1.5 pCi/L | 0.7 | Low | EPA Zone 3 | 7 |
| Pierce County | 1.5 pCi/L | 0.7 | Low | EPA Zone 3 | 49 |
| Thurston County | 1.5 pCi/L | 0.7 | Low | EPA Zone 3 | 11 |
| Wahkiakum County | 1.5 pCi/L | 1.0 | Low | EPA Zone 3 | 3 |
| Jefferson County | 1.5 pCi/L | 0.8 | Low | EPA Zone 3 | 8 |
| Mason County | 1.5 pCi/L | 0.7 | Low | EPA Zone 3 | 9 |
| Kitsap County | 1.4 pCi/L | 0.7 | Low | EPA Zone 3 | 17 |
| Skamania County | 1.4 pCi/L | 0.9 | Low | EPA Zone 1 | 6 |
| Snohomish County | 1.4 pCi/L | 0.6 | Low | EPA Zone 3 | 25 |
| King County | 1.4 pCi/L | 0.6 | Low | EPA Zone 3 | 79 |
Washington radon questions
- Is radon high in Washington?
- Washington's population-weighted predicted basement average is 1.6 pCi/L, close to the US average of 1.8. 0 of its 39 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 14 are in the 2-4 "consider fixing" range and 25 are below 2. 0% of Washington ZIP codes are predicted at 4 or higher.
- Which Washington county has the highest radon?
- Pend Oreille County has the highest predicted basement average in Washington at 3.1 pCi/L (EPA Zone 1). The lowest is King County at 1.4 pCi/L. These are modeled area averages; individual homes in any county can test far higher.
- How many EPA Zone 1 counties are in Washington?
- 7 of Washington's 39 counties (18%) are EPA Zone 1 (highest potential), 14 are Zone 2 and 18 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.
- Should I test for radon in Washington?
- Yes. Even though Washington's predicted average is below 2 pCi/L, the EPA recommends every home be tested - radon varies house to house, and 28.1% of Washington ZIP codes are still predicted at 2 pCi/L or higher.
Washington radon program
Many states offer free or discounted test kits and keep lists of certified mitigators. Find the Washington radon office through the EPA state radon contacts page. Then read how to test and what mitigation costs.