Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Clark County, Washington
EPA puts Clark County in Zone 1, its highest radon zone, and 17.6% of its 490 reported radon tests (2020) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
17.6%
1.4 pts below WA
- Clark
- 17.6%
- Washington
- 19.0%
490 tests, 2020
Median result
1.2pCi/L
Below action level
- Clark
- 1.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2020
Tests reported
490
3rd of 10 by tests
- Clark
- 490
- Spokane
- 721
Reported to CDC before any fix, 2020
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Washington
4 of 10
Middle half
- Clark
- 17.6%
- Spokane
- 40.6%
By share, of 10 with 30+ tests
Read a result for Clark County
Starts at Clark County's median, 1.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.2 pCi/L
Below 2 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Clark County's median reported result, 2020.
The data
Clark County, At a glance
Clark County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Clark County in
USGS geologic potential: Moderate across 71% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Clark County, 2020
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 18.6% |
| 2015 | 21.4% |
| 2016 | 20.0% |
| 2017 | 16.8% |
| 2018 | 21.9% |
| 2019 | 19.3% |
| 2020 | 17.6% |
2020: 17.6%. Across these years the share ran from 16.8% to 21.9%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 490 tests reported to CDC for Clark County over 2020, many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.
Measured: CDC tracking data. Figure above: 2020. Measured data period: 2005 to 2020 (every CDC figure on file).
Clark County, Compared
Clark County radon figures, compared
Calculated by Radon411Clark County's 490 reported tests in 2020 had a middle value of 1.2 pCi/L and a maximum of 39.1 pCi/L, and 17.6% reached 4 pCi/L. Washington as a whole (37 Washington counties, pooled) comes to 19.0%: 1.4 points higher than here.
Among its state's counties it ranks 4th of 10 Washington counties with 30 or more tests for the same period. Statewide for the same period, Spokane County reported the highest share (40.6%) and Kitsap County the lowest (0.0%).
Below the action level, 317 tests (64.7%) came in under 2 pCi/L, against 67.6% statewide, and 87 tests (17.8%) fell between 2 and 4, against 13.3% statewide. The busiest year on file was 2015, with 1,680 tests reported; the quietest, 2020, had 490.
EPA's 1993 zone map puts Clark County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 71% of the county's land moderate radon potential.
Next door, the shares run from 19.9% in Multnomah County, OR to 28.4% in Columbia County, OR. Over 7 years of annual figures the share held within 2 points, from 18.6% in 2014 to 17.6% in 2020; its peak was 21.9% in 2018.
Clark CountyWashington, pooled
| Year | Tests | Clark County, at or above 4 pCi/L | Washington, pooled |
|---|---|---|---|
| 2014 | 571 | 18.6% | 15.0% |
| 2015 | 1,680 | 21.4% | 17.4% |
| 2016 | 1,506 | 20.0% | 16.6% |
| 2017 | 1,229 | 16.8% | 19.1% |
| 2018 | 493 | 21.9% | 16.1% |
| 2019 | 627 | 19.3% | 20.9% |
| 2020 | 490 | 17.6% | 19.0% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Clark County, Geology
The ground under Clark County
PredictedUSGS's geologic map splits Clark County: 70.9% of its land is moderate radon potential and 26.0% low. The map puts 70.9% of Clark County in the area it calls Columbia River Gorge and 26.0% in Cascade Mountains. USGS gives the first a radon index of 9, in the moderate band (9 to 11), and the second 6, in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Columbia River Gorge | River and lacustrine delta deposits and volcanic debris flows. | Moderate | 9 | 70.9% |
| Cascade Mountains | Northern Cascade Mountains are Mesozoic metamorphic rocks intruded by Mesozoic and Tertiary granitic rocks. Southern Cascade Mountains are composed primarily of Tertiary and Holocene volcanic rocks. | Low | 6 | 26.0% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Clark County beside the ground around it
Across Washington 13.7% of the land is rated high; none of Clark County's is. Of the 4 counties that border it, 2 have more moderate-potential ground, Columbia County, OR the most at 91.6%.
The map rates the ground, not the air in any home.
Local help
Clark County, Local resources
Radon testing and mitigation in Clark County
- Radon ProgramRadon Program, run by Washington State Department of Health, offers free or discounted test kits, and answers questions about testing and mitigation in Washington.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
We have a limited supply of free radon test kits.
- Compare kits
- See the Washington directoryNo professionals are listed in Washington yet. The state program can point you to registered testers and mitigators.
What Washington's program says
- Phone
- 360-236-3200
- doh.radon@doh.wa.gov
What it means
Clark County, Questions
Questions about radon in Clark County
Are radon levels high in Clark County?
In 2020, 17.6% of the radon tests reported to CDC for Clark County, Washington were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.2 pCi/L. Of 10 Washington counties with 30 or more tests for the same period, 3 reported a higher share; pooled, the state comes to 19.0%.
Which counties border Clark County?
Clark County borders 4 counties: Multnomah County, OR, Cowlitz County, WA, Columbia County, OR and Skamania County, WA.
Products
Clark County, Products
Testing a home in Clark County
In Clark County, 17.6% of 490 tests reported to CDC in 2020 reached 4 pCi/L, against 19.0% pooled across Washington. In Zone 1 the year-round level in Clark County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
Monitor
RM-63Pro rechargeable radon monitor with a touchscreen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Clark County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Clark County
Explore
Clark County, Bordering counties
Counties bordering Clark County
Calculated by Radon411- Radon levels in Skamania County, WAEPA zone 1
52.9%at or above 4 pCi/L
Median 4.9 pCi/L · 17 tests · 35.3 points above Clark County
- Radon levels in Columbia County, OREPA zone 2
28.4%at or above 4 pCi/L
Median 1.7 pCi/L · 116 tests · 10.8 points above Clark County
- Radon levels in Multnomah County, OREPA zone 2
19.9%at or above 4 pCi/L
Median 1.7 pCi/L · 1,753 tests · 2.3 points above Clark County
- Radon levels in Cowlitz County, WAEPA zone 3
4.2%at or above 4 pCi/L
Median 1.1 pCi/L · 24 tests · 13.4 points below Clark County
Clark County, Cities and towns
Cities and towns in Clark County
Clark County is growing: the Census Bureau puts it at 532,119 residents on July 1, 2025, up 5.3% from 505,325 in 2020. That works out to 847 people per square mile of land. Its largest town, Vancouver, has 199,698 residents, 37.5% of the total. Testing is reported here more often than across the state: CDC's 490 reported tests for 2020 come to 0.9 for every 1,000 residents (2025 estimate), against 0.3 for Washington.
From Vancouver to Yacolt, CDC publishes no figure by town: each reads Clark County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Vancouver | 199,698 | +4.4% | 37.5% |
| Camas | 27,749 | +4.4% | 5.2% |
| Battle Ground | 23,513 | +12.7% | 4.4% |
| Washougal | 18,028 | +5.8% | 3.4% |
| Ridgefield | 16,132 | +48.3% | 3.0% |
| Woodlandextends beyond Clark County | 6,611 | +1.0% | Counted whole |
| La Center | 4,433 | +27.6% | 0.8% |
| Yacolt | 1,730 | +3.2% | 0.3% |
Places in Clark County with a city page: 1 of 1
8 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Clark County is counted whole, so it has no share.
Clark County, Homes
Homes in Clark County
Of Clark County's 201,114 homes, 67% are detached houses, against 62% across Washington; 17% are in buildings of five or more homes. Much of Clark County is recent building: 34% of its homes have gone up since 2000 and the middle year built is 1993, against 1984 for Washington. 66% of occupied homes are lived in by their owner (Washington: 64%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Clark County | Washington |
|---|---|---|
| Housing units | 201,114 | 3,262,667 |
| Detached houses | 67% | 62% |
| In buildings of 5 or more | 17% | 22% |
| Mobile homes | 4% | 6% |
| Built before 1960 | 11% | 21% |
| Built since 2000 | 34% | 28% |
| Middle year built | 1993 | 1984 |
| Owner-occupied | 66% | 64% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.