Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
Locations and reports
Radon Levels in Costilla County, Colorado
EPA puts Costilla County in Zone 2, its middle radon zone, and only 2 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
Highest bordering
77.1%
Taos County
- Taos
- 77.1%
- Alamosa
- 26.6%
4 of 6 neighbours have 30+ tests, 2008 to 2017
Nearest county
26.6%
Alamosa County, 28 miles
- Alamosa
- 26.6%
- Colorado
- 47.0%
Share at 4+ pCi/L, 79 tests, 2008 to 2017
Ground above low
100.0%
Level with Colorado
- Costilla
- 100.0%
- Colorado
- 100.0%
Share of land USGS rates moderate or high potential
Tests reported
11
Too few for a share
- Costilla
- 11
- Needed
- 30
2008 to 2017, laboratory
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Read a result for Costilla County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 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.
The data
Costilla County, At a glance
Costilla County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Costilla County is a
USGS geologic potential: Moderate across 61% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Costilla County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2015 | 0.0% |
| 2016 | 0.0% |
| 2017 | 0.0% |
| 2018 | 0.0% |
| 2020 | 50.0% |
| 2022 | 33.3% |
| 2023 | 0.0% |
2023: 0.0%. Across these years the share ran from 0.0% to 50.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 2 tests were reported to CDC for Costilla 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: 2005 to 2023 (every CDC figure on file).
Costilla County, Compared
Costilla County radon figures, compared
Calculated by Radon411CDC's largest figure for Costilla County rests on 11 tests over the 2008 to 2017 laboratory totals, 4 of them at or above 4 pCi/L, so each test moves its share by 9.1 points and no rank or comparison is drawn from it. Results reached as high as 21.2 pCi/L, with a middle value of 3.0 pCi/L.
Of the counties bordering it, 4 have a figure over the 2008 to 2017 laboratory totals: Taos County, NM reported the largest share at or above 4 pCi/L, 77.1%, and Alamosa County the smallest, 26.6%, with Las Animas County at 61.9% and Huerfano County at 53.7% between. Farther out, Rio Grande County (57 miles away) at 37.5%, Custer County (57 miles away) at 54.8% and Pueblo County (80 miles away) at 70.1% have figures too. Pooled across 63 Colorado counties, 47.0% of reported tests reached that level; across every county in the country with a figure, 35.7%.
Statewide for the same period, Kit Carson County reported the highest share (71.4%) and Alamosa County the lowest (26.6%). EPA's 1993 map puts Costilla County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 61% of the county's land moderate radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Costilla County, State data
Colorado's own radon test data
MeasuredWhat Colorado's own agencies publish about radon tests in Costilla 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 Costilla 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
53.8%
14 of 26 tests
Median result
4.4 pCi/L
Highest result
21.0 pCi/L
Tests behind these figures
26 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.
Costilla County, Geology
The ground under Costilla County
PredictedUSGS's geologic map splits Costilla County: 61.4% of its land is moderate radon potential and 38.6% high. The map puts 61.4% of Costilla County in the area it calls San Juan Volcanic field and 38.5% in Rocky Mountains. USGS gives the first a radon index of 11, in the moderate band (9 to 11), and the second 15, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| San Juan Volcanic field | Volcanic rocks, rhyolite, tuff, basalt | Moderate | 11 | 61.4% |
| Rocky Mountains | Precambrian granites, gneiss, amphibolite, variable uranium content, abundant shear zones.Sedimentary rocks shed from the granitic highlands. | High | 15 | 38.5% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Costilla County beside the ground around it
Colorado as a whole has more high-potential ground than Costilla County: 74.8% of its land, against 38.6% here. Of the 6 counties that border it, 3 have more high-potential ground, Taos County, NM the most at 91.9%.
The map rates the ground, not the air in any home.
Local help
Costilla County, Local resources
Radon testing and mitigation in Costilla 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
Costilla County, Questions
Questions about radon in Costilla County
Are radon levels high in Costilla County?
In 2023, 0.0% of the radon tests reported to CDC for Costilla County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.5 pCi/L. Of the counties bordering it, 4 have a figure over the 2008 to 2017 laboratory totals: Taos County, NM reported the largest share at or above 4 pCi/L, 77.1%, and Alamosa County the smallest, 26.6%, with Las Animas County at 61.9% and Huerfano County at 53.7% between.
Which counties border Costilla County?
Costilla County borders 6 counties: Alamosa County, CO, Huerfano County, CO, Conejos County, CO, Taos County, NM, Colfax County, NM and Las Animas County, CO.
Products
Costilla County, Products
Testing a home in Costilla County
No CDC figure names Costilla County; the nearest county with one, Alamosa County (28 miles away), reported 26.6% of its tests at or above 4 pCi/L over the 2008 to 2017 laboratory totals, the only reading nearby until a test of this home. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Costilla County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
View Plus radon and air quality monitor
- C-NRPP 2024/25: Approved
- Battery
- Wi-Fi, Bluetooth
- Screen, app
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Costilla County, Bordering counties
Counties bordering Costilla County
Calculated by Radon411- Radon levels in Taos County, NMEPA zone 1
77.1%at or above 4 pCi/L
Median 8.5 pCi/L · 83 tests
- Radon levels in Las Animas County, COEPA zone 1
61.9%at or above 4 pCi/L
Median 5.4 pCi/L · 181 tests
- Radon levels in Huerfano County, COEPA zone 1
53.7%at or above 4 pCi/L
Median 4.2 pCi/L · 67 tests
- Radon levels in Colfax County, NMEPA zone 1
40.0%at or above 4 pCi/L
Median 2.6 pCi/L · 15 tests
- Radon levels in Alamosa County, COEPA zone 2
26.6%at or above 4 pCi/L
Median 2.1 pCi/L · 79 tests
- Radon levels in Conejos County, COEPA zone 2
15.4%at or above 4 pCi/L
Median 2.4 pCi/L · 13 tests
Costilla County, Cities and towns
Cities and towns in Costilla County
Costilla County is growing: the Census Bureau puts it at 3,679 residents on July 1, 2025, up 5.1% from 3,499 in 2020. Spread over its land, that is 3.0 people to the square mile. No town dominates: San Luis, the largest, has 597 residents, 16.2% of the total. Together its 2 incorporated places hold 24.9% of those residents; the other 75.1% live outside any of them. Reported testing is thin here: 11 tests over 2008 to 2017, or 3.0 for every 1,000 residents (2025 estimate), where Colorado as a whole comes to 16.0.
From San Luis to Blanca, CDC publishes no figure by town: each reads Costilla County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| San Luis | 597 | −0.5% | 16.2% |
| Blanca | 320 | −0.3% | 8.7% |
2 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).
Costilla County, Homes
Homes in Costilla County
Costilla County is a place of houses on their own lots: 78% of its 2,418 homes are detached single-family houses, against 62% across Colorado. Half of its homes were built before 1986, close to Colorado's 1987: 24% date from before 1960 and 27% from 2000 or later. Owners live in 79% of the occupied homes (Colorado: 66%), so for most households a test and a fix are their own to order.
| Homes | Costilla County | Colorado |
|---|---|---|
| Housing units | 2,418 | 2,545,124 |
| Detached houses | 78% | 62% |
| In buildings of 5 or more | 2% | 22% |
| Mobile homes | 18% | 4% |
| Built before 1960 | 24% | 16% |
| Built since 2000 | 27% | 31% |
| Middle year built | 1986 | 1987 |
| Owner-occupied | 79% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.