Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Boulder County, Colorado
EPA puts Boulder County in Zone 1, its highest radon zone, and 34.2% of its 1,963 reported radon tests (2023) 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
34.2%
4.7 pts below CO
- Boulder
- 34.2%
- Colorado
- 38.9%
1,963 tests, 2023
Median result
2.5pCi/L
Below action level
- Boulder
- 2.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
1,963
4th of 38 by tests
- Boulder
- 1,963
- Jefferson
- 3,068
Reported to CDC before any fix, 2023
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Colorado
32 of 38
Lowest quarter
- Boulder
- 34.2%
- Park
- 57.5%
By share, of 38 with 30+ tests
Read a result for Boulder County
Starts at Boulder County's median, 2.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.5 pCi/L
Between 2 and 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Boulder County's median reported result, 2023.
The data
Boulder County, At a glance
Boulder County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Boulder County in
USGS geologic potential: High across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Boulder County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 41.9% |
| 2015 | 37.9% |
| 2016 | 39.2% |
| 2017 | 41.8% |
| 2018 | 40.5% |
| 2019 | 44.2% |
| 2020 | 39.3% |
| 2021 | 44.4% |
| 2022 | 34.4% |
| 2023 | 34.2% |
2023: 34.2%. Across these years the share ran from 34.2% to 44.4%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 1,963 tests reported to CDC for Boulder County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).
Boulder County, Compared
Boulder County radon figures, compared
Calculated by Radon411In Boulder County, about 3 in 10 reported tests in 2023 (672 of 1,963) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 0.8 points higher. Across 61 Colorado counties pooled together, 38.9% of tests reached that level, so Boulder County runs 4.7 points below its state.
Of 6 neighbours with a figure, 5 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 26.4% (Gilpin County) to 49.4% (Larimer County). By share, Boulder County is 32nd of 38 Colorado counties with 30 or more tests for the same period.
Year by year, 2014 opened at 41.9% and 2023 closed at 34.2% (down 7.7 points), with 2021 the high at 44.4%. Half the tests came in under 2.5 pCi/L and half over it; the single highest reached 77.6 pCi/L. Below the action level, 860 tests (43.8%) came in under 2 pCi/L, against 39.2% statewide, and 431 tests (22.0%) fell between 2 and 4, against 22.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 34.2% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 427 tests taken after mitigation in Boulder County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2018, with 3,223 tests reported; the quietest, 2014, had 928.
Boulder CountyColorado, pooled
| Year | Tests | Boulder County, at or above 4 pCi/L | Colorado, pooled |
|---|---|---|---|
| 2014 | 928 | 41.9% | 46.5% |
| 2015 | 1,035 | 37.9% | 47.2% |
| 2016 | 1,390 | 39.2% | 38.5% |
| 2017 | 1,265 | 41.8% | 41.0% |
| 2018 | 3,223 | 40.5% | 44.2% |
| 2019 | 2,653 | 44.2% | 44.1% |
| 2020 | 1,999 | 39.3% | 41.9% |
| 2021 | 2,347 | 44.4% | 47.3% |
| 2022 | 2,509 | 34.4% | 38.6% |
| 2023 | 1,963 | 34.2% | 38.9% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Boulder County, State data
Colorado's own radon test data
MeasuredWhat Colorado's own agencies publish about radon tests in Boulder County, with their period. These are not CDC's figures and are never added to them.
MeasuredState figures, not CDC's
What Colorado CDPHE reports for Boulder County
Radon data (county results): radon test results received from radon testing labs, primarily short-term household tests taken by the homeowner. Period: 2005-2025.
Share over 4 pCi/L
43.5%
8,668 of 19,914 tests
Median result
3.3 pCi/L
Highest result
384.6 pCi/L
Tests behind these figures
19,914 tests
- CDPHE says these data do not give actual radon levels in homes that have not been tested.
- When possible, only tests conducted before a mitigation system was installed are used.
- Some counties have very small numbers of test results, and their summaries may be less representative.
- These figures describe tests reported to Colorado CDPHE in this area. They count a different set of tests than CDC's figures and are not a reading of any one home.
Measured: Colorado CDPHE data, 2005-2025.
Boulder County, Geology
The ground under Boulder County
PredictedUSGS's geologic map puts all of Boulder County's mapped land in one class: high radon potential. The map puts 71.9% of Boulder County in the area it calls Rocky Mountains and 28.1% in High Plains. USGS gives the first a radon index of 15 and the second 12, both in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Rocky Mountains | Precambrian granites, gneiss, amphibolite, variable uranium content, abundant shear zones.Sedimentary rocks shed from the granitic highlands. | High | 15 | 71.9% |
| High Plains | Quaternary deposits and Cretaceous marine shales that locally have a high radiometric signature. | High | 12 | 28.1% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Boulder County beside the ground around it
Boulder County has more high-potential ground than Colorado as a whole: 100% of its land against 74.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Broomfield County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Boulder County, Local resources
Radon testing and mitigation in Boulder County
Listed radon businesses with an address in Boulder County:
- Colorado's radon programColorado Department of Public Health and EnvironmentColorado's radon program licenses or certifies radon professionals, offers free or discounted test kits and states the rule for disclosing radon when a home is sold, and answers questions about testing and mitigation in Colorado.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Order a discounted radon test kit
- Compare kits
- Professionals in Colorado25 professionals are listed in Colorado.
Listed radon professionals by town: Boulder
What Colorado's program says
- Licensing of radon professionals
Listed contractors are certified by the National Radon Proficiency Program or the National Radon Safety Board, and must be licensed by the Colorado Department of Regulatory Agencies.
- Disclosure when a home is sold or rented
As of August 7, 2023, landlords in Colorado are required to disclose radon information when a tenant signs a lease agreement.
What it means
Boulder County, Questions
Questions about radon in Boulder County
Are radon levels high in Boulder County?
In 2023, 34.2% of the radon tests reported to CDC for Boulder County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.5 pCi/L. Of 38 Colorado counties with 30 or more tests for the same period, 31 reported a higher share; pooled, the state comes to 38.9%.
Which counties border Boulder County?
Boulder County borders 6 counties: Broomfield County, Gilpin County, Larimer County, Jefferson County, Grand County and Weld County.
Products
Boulder County, Products
Testing a home in Boulder County
In Boulder County, 34.2% of 1,963 tests reported to CDC in 2023 reached 4 pCi/L, against 38.9% pooled across Colorado. In Zone 1 the year-round level in Boulder 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-65 rechargeable radon detector with a color screen and alarm
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 6 hours
Short-term kit
RA100 short-term liquid scintillation radon test kit
- Lab fee extra
Method: Liquid scintillation
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Boulder County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Boulder County
Explore
Boulder County, Bordering counties
Counties bordering Boulder County
Calculated by Radon411- Radon levels in Larimer CountyEPA zone 1
49.4%at or above 4 pCi/L
Median 3.8 pCi/L · 1,902 tests · 15.2 points above Boulder County
- Radon levels in Weld CountyEPA zone 1
46.0%at or above 4 pCi/L
Median 3.5 pCi/L · 663 tests · 11.8 points above Boulder County
- Radon levels in Grand CountyEPA zone 1
44.1%at or above 4 pCi/L
Median 3.3 pCi/L · 136 tests · 9.9 points above Boulder County
- Radon levels in Jefferson CountyEPA zone 1
41.8%at or above 4 pCi/L
Median 3.2 pCi/L · 3,068 tests · 7.6 points above Boulder County
- Radon levels in Broomfield CountyEPA zone 1
36.9%at or above 4 pCi/L
Median 2.3 pCi/L · 758 tests · 2.7 points above Boulder County
- Radon levels in Gilpin CountyEPA zone 1
26.4%at or above 4 pCi/L
Median 1.1 pCi/L · 129 tests · 7.8 points below Boulder County
Boulder County, Cities and towns
Cities and towns in Boulder County
About 328,560 people live in Boulder County by the Census Bureau's estimate for July 1, 2025, 2,422 fewer than in 2020 (−0.7%). That works out to 452 people per square mile of land. Its largest town, Boulder, has 105,689 residents, 32.2% of the total. Testing is reported here more often than across the state: CDC's 1,963 reported tests for 2023 come to 6.0 for every 1,000 residents (2025 estimate), against 3.6 for Colorado.
From Boulder to Ward, CDC publishes no figure by town: each reads Boulder County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Boulder | 105,689 | −2.5% | 32.2% |
| Longmontextends beyond Boulder County | 100,109 | +0.9% | Counted whole |
| Erieextends beyond Boulder County | 40,904 | +34.5% | Counted whole |
| Lafayette | 30,116 | −0.9% | 9.2% |
| Louisville | 20,581 | −2.9% | 6.3% |
| Superiorextends beyond Boulder County | 13,637 | +4.1% | Counted whole |
| Lyons | 2,119 | −3.9% | 0.6% |
| Nederland | 1,463 | −0.3% | 0.4% |
| Jamestown | 245 | −5.4% | Under 0.1% |
| Ward | 124 | −6.1% | Under 0.1% |
Places in Boulder County with a city page: 1 of 2
10 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 Boulder County is counted whole, so it has no share.
Boulder County, Homes
Homes in Boulder County
Of Boulder County's 142,809 homes, 58% are detached houses, against 62% across Colorado; 25% are in buildings of five or more homes. Half of its homes were built before 1986, close to Colorado's 1987: 13% date from before 1960 and 25% from 2000 or later. 62% of occupied homes are lived in by their owner (Colorado: 66%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Boulder County | Colorado |
|---|---|---|
| Housing units | 142,809 | 2,545,124 |
| Detached houses | 58% | 62% |
| In buildings of 5 or more | 25% | 22% |
| Mobile homes | 2% | 4% |
| Built before 1960 | 13% | 16% |
| Built since 2000 | 25% | 31% |
| Middle year built | 1986 | 1987 |
| Owner-occupied | 62% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.