Radon levels in Washington: Low
The model predicts a population-weighted basement average of 1.6 pCi/L (model estimate) 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
Test Washington once anyway - radon varies house to house
The predicted basement average here is 1.6 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.
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What the data says about radon in Washington
7 of Washington's 39 counties are EPA Zone 1 (18%), 14 are Zone 2 and 18 are Zone 3 on the EPA's county-level map. Most counties fall in Zone 3, the EPA's lowest-potential class (predicted screening average under 2 pCi/L), but 7 counties are still Zone 1. The zones were drawn once, from geology and the tests available in 1993, and the EPA itself notes that homes with elevated radon exist in all three zones.
Weighted by where people live, Washington's predicted basement average is 1.6 pCi/L - close to the US average of 1.8 - which puts the state in the low range. Of the 39 counties with predictions, 0 are predicted at or above 4 pCi/L, 14 in the 2-4 band and 25 below 2. The highest predicted county is Pend Oreille County at 3.1 pCi/L; the lowest is King County at 1.4 - a 1.7 pCi/L spread that means a statewide average tells you little about any one county.
Nationally 4.2% of ZIPs are predicted at 4+ pCi/L and 48.7% at 2+; in Washington it is 0% and 28.1% - below the national figures on both counts. No ZIP in the state is predicted above 4 on average - but averages hide individual homes, which is why the EPA still asks everyone to test.
Washington counties by predicted radon
Sorted highest to lowest predicted basement average (model estimate). 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 |
Radon levels in Washington cities
The 29 most-populous Washington places among the 1,000 largest US cities (Census incorporated places and CDPs), by population. City figures are ZIP-land-weighted means of the model's ZIP predictions (model estimate).
| City | Population | Predicted basement | Upstairs | Grade | ZIPs ≥ 4 |
|---|---|---|---|---|---|
| Seattle | 755,078 | 1.3 pCi/L | 0.6 | Low | 0% |
| Spokane | 229,447 | 2.1 pCi/L | 1.4 | Moderate | 0% |
| Tacoma | 222,906 | 1.4 pCi/L | 0.6 | Low | 0% |
| Vancouver | 196,442 | 2.0 pCi/L | 1.1 | Low | 0% |
| Bellevue | 151,574 | 1.4 pCi/L | 0.6 | Low | 0% |
| Kent | 133,378 | 1.4 pCi/L | 0.6 | Low | 0% |
| Everett | 111,180 | 1.3 pCi/L | 0.6 | Low | 0% |
| Spokane Valley | 108,235 | 2.5 pCi/L | 1.4 | Moderate | 0% |
| Renton | 104,491 | 1.3 pCi/L | 0.6 | Low | 0% |
| Federal Way | 97,701 | 1.4 pCi/L | 0.5 | Low | 0% |
| Yakima | 96,750 | 2.0 pCi/L | 1.1 | Moderate | 0% |
| Bellingham | 94,720 | 1.5 pCi/L | 0.8 | Low | 0% |
| Kirkland | 91,194 | 1.3 pCi/L | 0.6 | Low | 0% |
| Kennewick | 85,158 | 1.7 pCi/L | 1.0 | Low | 0% |
| Auburn | 83,870 | 1.5 pCi/L | 0.6 | Low | 0% |
| Redmond | 80,280 | 1.2 pCi/L | 0.5 | Low | 0% |
| Pasco | 80,038 | 1.7 pCi/L | 0.9 | Low | 0% |
| Marysville | 72,916 | 1.5 pCi/L | 0.6 | Low | 0% |
| Sammamish | 65,116 | 1.3 pCi/L | 0.6 | Low | 0% |
| Richland | 63,757 | 1.7 pCi/L | 1.0 | Low | 0% |
| Lakewood | 62,303 | 1.6 pCi/L | 0.7 | Low | 0% |
| Shoreline | 61,353 | 1.3 pCi/L | 0.6 | Low | 0% |
| Lacey | 58,326 | 1.5 pCi/L | 0.7 | Low | 0% |
| Olympia | 55,733 | 1.4 pCi/L | 0.6 | Low | 0% |
| South Hill | 52,431 | 1.5 pCi/L | 0.7 | Low | 0% |
| Burien | 50,730 | 1.4 pCi/L | 0.7 | Low | 0% |
| Bothell | 50,213 | 1.4 pCi/L | 0.6 | Low | 0% |
| Bremerton | 45,450 | 1.4 pCi/L | 0.7 | Low | 0% |
| Lynnwood | 43,867 | 1.4 pCi/L | 0.5 | Low | 0% |
Highest-radon ZIP codes in Washington
The 10 Washington ZIP codes with the highest predicted basement average (model estimate), out of 520 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.
| ZIP | County | Predicted basement | Upstairs | Grade |
|---|---|---|---|---|
| 99180 | Pend Oreille County | 3.1 pCi/L | 2.1 | Moderate |
| 99139 | Pend Oreille County | 3.1 pCi/L | 2.0 | Moderate |
| 99156 | Pend Oreille County | 3.1 pCi/L | 2.2 | Moderate |
| 99131 | Stevens County | 3.1 pCi/L | 1.9 | Moderate |
| 99167 | Stevens County | 3.1 pCi/L | 1.8 | Moderate |
| 99121 | Ferry County | 3.0 pCi/L | 1.9 | Moderate |
| 99101 | Stevens County | 3.0 pCi/L | 1.8 | Moderate |
| 98859 | Okanogan County | 3.0 pCi/L | 1.9 | Moderate |
| 99123 | Grant County | 3.0 pCi/L | 1.8 | Moderate |
| 99141 | Ferry County | 3.0 pCi/L | 1.7 | Moderate |
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 area figures; 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
Washington's radon program page is at doh.wa.gov and, when we checked it, offered a limited supply of free radon test kits. The EPA also keeps a directory of every state radon contact: EPA state radon contacts page. Then read how to test and what mitigation costs.