Short-term kit
RA400 short-term liquid scintillation radon test kit, lab fee included
- Lab fee included
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in San Juan County, Colorado
EPA puts San Juan County in Zone 2, its middle radon zone, and only 13 radon tests from it are on file with CDC (2023). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
85.5%
46.9 pts above CO
- San Juan
- 85.5%
- Colorado
- 38.6%
55 tests, 2022
Median result
6.9pCi/L
Action level reached
- San Juan
- 6.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2022
Tests reported
55
31st of 36 by tests
- San Juan
- 55
- Jefferson
- 3,793
Reported to CDC before any fix, 2022
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Rank in Colorado
1 of 36
Top quarter
- San Juan
- 85.5%
- San Juan
- 85.5%
By share, of 36 with 30+ tests
Read a result for San Juan County
Starts at San Juan County's median, 6.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 6.9 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. San Juan County's median reported result, 2022.
The data
San Juan County, At a glance
San Juan County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
San Juan County is a
USGS geologic potential: Moderate across 97% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for San Juan County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 100.0% |
| 2015 | 100.0% |
| 2016 | 100.0% |
| 2017 | 33.3% |
| 2018 | 60.0% |
| 2019 | 25.0% |
| 2020 | 0.0% |
| 2021 | 100.0% |
| 2022 | 85.5% |
| 2023 | 46.2% |
2023: 46.2%. Across these years the share ran from 0.0% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 13 tests were reported to CDC for San Juan County over 2023, and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2023. Measured data period: 2014 to 2023 (every CDC figure on file).
San Juan County, Compared
San Juan County radon figures, compared
Calculated by Radon411More than half: 85.5% of the 55 radon tests reported to CDC for San Juan County in 2022 read at least 4 pCi/L. That places it 1st of 36 Colorado counties with 30 or more tests for the same period. That is 46.9 points above the 38.6% pooled from 60 Colorado counties.
The newest figure, in 2023, counts only 13 tests (46.2% at or above 4 pCi/L), too few to compare, so this reading uses the 55-test figure.
The median result, 6.9 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 28.9 pCi/L. The rest split 7.3% under 2 pCi/L and 7.3% from 2 to 4 (Colorado: 39.4% and 22.0%). The reported tests do not follow EPA's Zone 2 label for San Juan County (predicted average between 2 and 4 pCi/L): 85.5% of them reached 4 pCi/L, fewer than that label suggests.
No bordering county with a figure for the same period reported a higher share; the closest is La Plata County at 26.4%, the lowest Montezuma County at 14.3%. Statewide for the same period, Morgan County reported the highest share (82.1%) and Montezuma County the lowest (14.3%).
The busiest year on file was 2022, with 55 tests reported; the quietest, 2014, had 1.
Nationally, every county with a figure for the same period pools to 23.9%; San Juan County sits 61.6 points above it.
Pooled shares: Radon411's sum of CDC's county counts for one period.
San Juan County, State data
Colorado's own radon test data
MeasuredWhat Colorado's own agencies publish about radon tests in San Juan 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 San Juan 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
63.9%
69 of 108 tests
Median result
5.3 pCi/L
Highest result
61.0 pCi/L
Tests behind these figures
108 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.
San Juan County, Geology
The ground under San Juan County
PredictedMost of the ground under San Juan County is one class on USGS's geologic map: 96.7% of its land is moderate radon potential, with 3.3% high. The map puts 78.0% of San Juan County in the area it calls San Juan Volcanic field and 18.7% in San Juan Basin, with one smaller area beside them. USGS gives both a radon index of 11, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| San Juan Volcanic field | Volcanic rocks, rhyolite, tuff, basalt | Moderate | 11 | 78.0% |
| San Juan Basin | Mesozoic marine and non-marine sedimentary rocks including sandstone, siltstone, shale, minor limestone. | Moderate | 11 | 18.7% |
| Uravan Belt | Uranium-bearing Cretaceous and Jurassic sedimentary rocks of the Uravan mineral belt. | High | 13 | 3.3% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
San Juan County beside the ground around it
Colorado as a whole has more high-potential ground than San Juan County: 74.8% of its land, against 3.3% here. Of the 6 counties that border it, 4 have more high-potential ground, San Miguel County the most at 96.5%.
The map rates the ground, not the air in any home.
Local help
San Juan County, Local resources
Radon testing and mitigation in San Juan 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.
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
San Juan County, Questions
Questions about radon in San Juan County
Are radon levels high in San Juan County?
In 2023, 46.2% of the radon tests reported to CDC for San Juan County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.6 pCi/L. Of 36 Colorado counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 38.6%.
Which counties border San Juan County?
San Juan County borders 6 counties: Hinsdale County, Ouray County, La Plata County, San Miguel County, Dolores County and Montezuma County.
Products
San Juan County, Products
Testing a home in San Juan County
In San Juan County, 85.5% of 55 tests reported to CDC in 2022 reached 4 pCi/L, against 38.6% pooled across Colorado. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in San Juan County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
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
Monitor
Hello Radon C battery radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Screen
Method: Alpha spectrometry
First reading: Within 24 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
San Juan County, Bordering counties
Counties bordering San Juan County
Calculated by Radon411- Radon levels in Hinsdale CountyEPA zone 2
75.0%at or above 4 pCi/L
Median 33.1 pCi/L · 8 tests · 10.5 points below San Juan County
- Radon levels in Ouray CountyEPA zone 1
40.0%at or above 4 pCi/L
Median 1.9 pCi/L · 10 tests · 45.5 points below San Juan County
- Radon levels in San Miguel CountyEPA zone 1
36.8%at or above 4 pCi/L
Median 2.2 pCi/L · 19 tests · 48.7 points below San Juan County
- Radon levels in Dolores CountyEPA zone 1
33.3%at or above 4 pCi/L
Median 0.3 pCi/L · 3 tests · 52.2 points below San Juan County
- Radon levels in La Plata CountyEPA zone 1
26.4%at or above 4 pCi/L
Median 2.3 pCi/L · 1,132 tests · 59.1 points below San Juan County
- Radon levels in Montezuma CountyEPA zone 1
14.3%at or above 4 pCi/L
Median 1.1 pCi/L · 84 tests · 71.2 points below San Juan County
San Juan County, Cities and towns
Cities and towns in San Juan County
San Juan County is growing: the Census Bureau puts it at 813 residents on July 1, 2025, up 14.5% from 710 in 2020. Spread over its land, that is 2.1 people to the square mile. Silverton, its one incorporated place, has 721 residents, 88.7% of the total. Testing is reported here more often than across the state: CDC's 55 reported tests for 2022 come to 67.7 for every 1,000 residents (2025 estimate), against 4.7 for Colorado.
Silverton is the one incorporated place here; CDC publishes no figure by town, so it reads San Juan County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Silverton | 721 | +14.6% | 88.7% |
One incorporated place, 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).
San Juan County, Homes
Homes in San Juan County
Of San Juan County's 720 homes, 61% are detached houses, against 62% across Colorado; 20% are in buildings of five or more homes. The homes are older than Colorado's as a whole: half were built before 1976 (1987 for Colorado), and 37% date from before 1960. 56% 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 | San Juan County | Colorado |
|---|---|---|
| Housing units | 720 | 2,545,124 |
| Detached houses | 61% | 62% |
| In buildings of 5 or more | 20% | 22% |
| Mobile homes | 7% | 4% |
| Built before 1960 | 37% | 16% |
| Built since 2000 | 13% | 31% |
| Middle year built | 1976 | 1987 |
| Owner-occupied | 56% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.