Radon in Washington: radon map by county
EPA's Map of Radon Zones puts 7 of Washington's 39 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 14 in Zone 2 and 18 in Zone 3. Of 5,879 building tests that radon laboratories reported for 2008 to 2017, 25.3% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 25 of 42 states with 1,000+ tests). The highest county share is Pend Oreille County (63.2% of 24 tests).
Radon by county in Washington
| County | EPA zone | Lab tests | Median | 4+ pCi/L |
|---|---|---|---|---|
| Adams County | Zone 2 | 5 | 1.5 | 14.3% |
| Asotin County | Zone 2 | 6 | 1.3 | 0% |
| Benton County | Zone 2 | 61 | 2.0 | 19.5% |
| Chelan County | Zone 3 | 40 | 1.8 | 14.6% |
| Clallam County | Zone 3 | 12 | 0.1 | 11.8% |
| Clark County | Zone 1 | 1,265 | 1.8 | 25.1% |
| Columbia County | Zone 2 | 2 | 6.6 | 100% |
| Cowlitz County | Zone 3 | 50 | 1.1 | 11.3% |
| Douglas County | Zone 2 | 10 | 2.3 | 35.7% |
| Ferry County | Zone 1 | 16 | 2.5 | 25% |
| Franklin County | Zone 2 | 12 | 1.8 | 10.5% |
| Garfield County | Zone 2 | 1 | 3.8 | 50% |
| Grant County | Zone 2 | 16 | 2.7 | 23.5% |
| Grays Harbor County | Zone 3 | 9 | 1.4 | 36.4% |
| Island County | Zone 3 | 17 | 0.9 | 10.5% |
| Jefferson County | Zone 3 | 16 | 1.0 | 9.1% |
| King County | Zone 3 | 950 | 0.7 | 2.6% |
| Kitsap County | Zone 3 | 63 | 0.7 | 4.9% |
| Kittitas County | Zone 2 | 8 | 1.4 | 25% |
| Klickitat County | Zone 2 | 22 | 2.2 | 41.4% |
| Lewis County | Zone 3 | 7 | 0.1 | 9.1% |
| Lincoln County | Zone 2 | 14 | 3.1 | 40% |
| Mason County | Zone 3 | 13 | 0.7 | 0% |
| Okanogan County | Zone 1 | 26 | 2.3 | 35% |
| Pacific County | Zone 3 | 2 | 0.5 | 0% |
| Pend Oreille County | Zone 1 | 24 | 4.8 | 63.2% |
| Pierce County | Zone 3 | 153 | 0.7 | 4.9% |
| San Juan County | Zone 3 | 8 | 0.6 | 0% |
| Skagit County | Zone 3 | 27 | 0.8 | 2.8% |
| Skamania County | Zone 1 | 39 | 2.9 | 39.7% |
| Snohomish County | Zone 3 | 172 | 0.5 | 2.3% |
| Spokane County | Zone 1 | 2,249 | 2.9 | 41.4% |
| Stevens County | Zone 1 | 131 | 2.3 | 36.2% |
| Thurston County | Zone 3 | 174 | 0.7 | 10.1% |
| Wahkiakum County | Zone 3 | 1 | 2.9 | 0% |
| Walla Walla County | Zone 2 | 87 | 1.4 | 16.4% |
| Whatcom County | Zone 3 | 88 | 0.9 | 5.4% |
| Whitman County | Zone 2 | 41 | 1.5 | 22.4% |
| Yakima County | Zone 2 | 42 | 0.7 | 7.5% |
Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).
What the zones mean
Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.
Radon in Washington: questions
What radon zone is Washington?
EPA's 1993 map does not give states one zone; it zones each county. In Washington, 7 counties are Zone 1, 14 Zone 2 and 18 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".
Which Washington counties have the highest radon levels?
By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Pend Oreille County 63.2% (median 4.8 pCi/L, 24 tests); Klickitat County 41.4% (median 2.2 pCi/L, 22 tests); Spokane County 41.4% (median 2.9 pCi/L, 2,249 tests); Skamania County 39.7% (median 2.9 pCi/L, 39 tests); Stevens County 36.2% (median 2.3 pCi/L, 131 tests).
How common is high radon in Washington?
25.3% of the 5,879 tests in the laboratory data for Washington (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.
Should I test for radon in Washington?
Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.
States bordering Washington
Other free hazard lookups
- Radon by county and ZIP codeEPA radon zone and the radon test results on file for any county, ZIP code or address.
- Fault lines near an addressUSGS-mapped earthquake faults within 5 miles, their age and slip rate, and the USGS seismic hazard value.
- Power lines near an addressHigh-voltage transmission lines within 1 mile from federal maps, with voltage and distance.
- Flood zone lookupThe FEMA flood zone mapped at any US address. Not an official flood zone determination.
- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Superfund sites in Washington · Radon map of every state
Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.