Radon levels in Colorado: Moderate
The model predicts a population-weighted basement average of 2.6 pCi/L (model estimate) across Colorado's 64 counties - about 1.4× the US average of 1.8 pCi/L. Above-ground floors average 2.0 pCi/L.
Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.
53 / 64
EPA Zone 1 counties (83%)
11 / 0
Zone 2 / Zone 3 counties
3
counties predicted ≥ 4 pCi/L
1.8%
of ZIP codes predicted ≥ 4 pCi/L
Test Colorado - the EPA says "consider fixing" in this range
The predicted basement average here is 2.6 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.
Monitor link goes to the Airthings store - use code RADONGRADE-10OFF at checkout for 10% off any Airthings monitor.
Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.
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What the data says about radon in Colorado
53 of Colorado's 64 counties are EPA Zone 1 (83%), 11 are Zone 2 and 0 are Zone 3 on the EPA's county-level map. Zone 1 - the highest-potential class, predicted screening average above 4 pCi/L - is the most common designation in Colorado. The zones were drawn once, from geology and the tests available in 1993, and the EPA itself notes that homes with elevated radon exist in all three zones.
Weighted by where people live, Colorado's predicted basement average is 2.6 pCi/L - 1.4× the US population-weighted average of 1.8 - which puts the state in the moderate range. Of the 64 counties with predictions, 3 are predicted at or above 4 pCi/L, 60 in the 2-4 band and 1 below 2. The highest predicted county is Pueblo County at 4.2 pCi/L; the lowest is Douglas County at 1.8 - a 2.4 pCi/L spread that means a statewide average tells you little about any one county.
Nationally 4.2% of ZIPs are predicted at 4+ pCi/L and 48.7% at 2+; in Colorado it is 1.8% and 94.9% - below the US share at the action level but above it at 2 pCi/L. With more than half of ZIPs above 2, a test is worth doing before any purchase or renovation here.
Colorado counties by predicted radon
Sorted highest to lowest predicted basement average (model estimate). 64 counties.
| County | Predicted basement | Upstairs | Grade | EPA zone | ZIPs |
|---|---|---|---|---|---|
| Pueblo County | 4.2 pCi/L | 2.5 | High | EPA Zone 1 | 12 |
| Chaffee County | 4.1 pCi/L | 3.3 | High | EPA Zone 1 | 3 |
| Teller County | 4.0 pCi/L | 2.9 | High | EPA Zone 1 | 4 |
| Gunnison County | 3.9 pCi/L | 2.9 | Moderate | EPA Zone 1 | 10 |
| Jackson County | 3.7 pCi/L | 2.4 | Moderate | EPA Zone 1 | 1 |
| Montrose County | 3.7 pCi/L | 2.8 | Moderate | EPA Zone 1 | 7 |
| Phillips County | 3.7 pCi/L | 2.4 | Moderate | EPA Zone 1 | 3 |
| Fremont County | 3.6 pCi/L | 2.4 | Moderate | EPA Zone 1 | 5 |
| Summit County | 3.5 pCi/L | 2.6 | Moderate | EPA Zone 1 | 4 |
| Washington County | 3.5 pCi/L | 2.2 | Moderate | EPA Zone 1 | 6 |
| Delta County | 3.5 pCi/L | 2.5 | Moderate | EPA Zone 1 | 6 |
| Las Animas County | 3.5 pCi/L | 2.4 | Moderate | EPA Zone 1 | 7 |
| Morgan County | 3.5 pCi/L | 2.1 | Moderate | EPA Zone 1 | 7 |
| Bent County | 3.4 pCi/L | 2.1 | Moderate | EPA Zone 1 | 4 |
| Park County | 3.4 pCi/L | 2.7 | Moderate | EPA Zone 1 | 6 |
| Otero County | 3.4 pCi/L | 2.0 | Moderate | EPA Zone 1 | 3 |
| Yuma County | 3.4 pCi/L | 2.0 | Moderate | EPA Zone 1 | 7 |
| Kiowa County | 3.3 pCi/L | 2.0 | Moderate | EPA Zone 1 | 4 |
| Ouray County | 3.3 pCi/L | 2.7 | Moderate | EPA Zone 1 | 2 |
| Crowley County | 3.3 pCi/L | 1.9 | Moderate | EPA Zone 1 | 3 |
| Lake County | 3.3 pCi/L | 2.7 | Moderate | EPA Zone 1 | 2 |
| Kit Carson County | 3.3 pCi/L | 2.0 | Moderate | EPA Zone 1 | 6 |
| Gilpin County | 3.3 pCi/L | 2.3 | Moderate | EPA Zone 1 | 2 |
| Logan County | 3.3 pCi/L | 2.1 | Moderate | EPA Zone 1 | 8 |
| Huerfano County | 3.3 pCi/L | 2.1 | Moderate | EPA Zone 1 | 4 |
| Hinsdale County | 3.2 pCi/L | 2.7 | Moderate | EPA Zone 2 | 1 |
| Baca County | 3.2 pCi/L | 2.0 | Moderate | EPA Zone 1 | 6 |
| Cheyenne County | 3.2 pCi/L | 1.9 | Moderate | EPA Zone 1 | 3 |
| Mineral County | 3.1 pCi/L | 2.4 | Moderate | EPA Zone 2 | 1 |
| Custer County | 3.1 pCi/L | 2.6 | Moderate | EPA Zone 1 | 2 |
| Dolores County | 3.1 pCi/L | 2.2 | Moderate | EPA Zone 1 | 4 |
| Larimer County | 3.1 pCi/L | 2.2 | Moderate | EPA Zone 1 | 17 |
| San Juan County | 3.1 pCi/L | 2.6 | Moderate | EPA Zone 2 | 1 |
| Grand County | 3.1 pCi/L | 2.4 | Moderate | EPA Zone 1 | 8 |
| Montezuma County | 3.1 pCi/L | 2.1 | Moderate | EPA Zone 1 | 6 |
| Lincoln County | 3.1 pCi/L | 1.9 | Moderate | EPA Zone 1 | 6 |
| Garfield County | 3.0 pCi/L | 2.3 | Moderate | EPA Zone 1 | 6 |
| La Plata County | 3.0 pCi/L | 2.4 | Moderate | EPA Zone 1 | 5 |
| Pitkin County | 3.0 pCi/L | 2.5 | Moderate | EPA Zone 1 | 4 |
| Rio Blanco County | 3.0 pCi/L | 2.2 | Moderate | EPA Zone 1 | 3 |
| Clear Creek County | 3.0 pCi/L | 2.6 | Moderate | EPA Zone 1 | 6 |
| Moffat County | 2.9 pCi/L | 2.5 | Moderate | EPA Zone 1 | 4 |
| San Miguel County | 2.9 pCi/L | 2.3 | Moderate | EPA Zone 1 | 5 |
| Routt County | 2.9 pCi/L | 2.5 | Moderate | EPA Zone 2 | 7 |
| Prowers County | 2.9 pCi/L | 1.9 | Moderate | EPA Zone 1 | 4 |
| Sedgwick County | 2.8 pCi/L | 1.7 | Moderate | EPA Zone 1 | 3 |
| Weld County | 2.7 pCi/L | 1.9 | Moderate | EPA Zone 1 | 29 |
| Mesa County | 2.7 pCi/L | 2.2 | Moderate | EPA Zone 1 | 16 |
| Archuleta County | 2.7 pCi/L | 2.3 | Moderate | EPA Zone 2 | 1 |
| Eagle County | 2.5 pCi/L | 2.2 | Moderate | EPA Zone 2 | 6 |
| Jefferson County | 2.5 pCi/L | 2.1 | Moderate | EPA Zone 1 | 22 |
| Elbert County | 2.5 pCi/L | 2.1 | Moderate | EPA Zone 1 | 7 |
| Denver County | 2.5 pCi/L | 1.9 | Moderate | EPA Zone 1 | 26 |
| Rio Grande County | 2.5 pCi/L | 2.2 | Moderate | EPA Zone 2 | 3 |
| Arapahoe County | 2.5 pCi/L | 1.9 | Moderate | EPA Zone 1 | 17 |
| Boulder County | 2.4 pCi/L | 1.9 | Moderate | EPA Zone 1 | 14 |
| Saguache County | 2.4 pCi/L | 1.9 | Moderate | EPA Zone 2 | 4 |
| Costilla County | 2.4 pCi/L | 1.7 | Moderate | EPA Zone 2 | 4 |
| Conejos County | 2.3 pCi/L | 1.7 | Moderate | EPA Zone 2 | 2 |
| El Paso County | 2.3 pCi/L | 1.9 | Moderate | EPA Zone 1 | 37 |
| Broomfield County | 2.3 pCi/L | 2.0 | Moderate | EPA Zone 1 | 2 |
| Alamosa County | 2.3 pCi/L | 1.8 | Moderate | EPA Zone 2 | 3 |
| Adams County | 2.2 pCi/L | 1.9 | Moderate | EPA Zone 1 | 19 |
| Douglas County | 1.8 pCi/L | 1.7 | Low | EPA Zone 1 | 13 |
Radon levels in Colorado cities
The 21 most-populous Colorado places among the 1,000 largest US cities (Census incorporated places and CDPs), by population. City figures are ZIP-land-weighted means of the model's ZIP predictions (model estimate).
| City | Population | Predicted basement | Upstairs | Grade | ZIPs ≥ 4 |
|---|---|---|---|---|---|
| Denver | 716,577 | 2.1 pCi/L | 1.8 | Moderate | 0% |
| Colorado Springs | 488,664 | 2.4 pCi/L | 2.0 | Moderate | 0% |
| Aurora | 395,052 | 2.3 pCi/L | 1.8 | Moderate | 0% |
| Fort Collins | 170,376 | 3.0 pCi/L | 2.1 | Moderate | 0% |
| Lakewood | 155,961 | 2.6 pCi/L | 2.1 | Moderate | 0% |
| Thornton | 144,922 | 2.1 pCi/L | 1.8 | Moderate | 0% |
| Arvada | 121,414 | 2.3 pCi/L | 2.0 | Moderate | 0% |
| Westminster | 114,875 | 2.2 pCi/L | 1.9 | Moderate | 0% |
| Greeley | 112,609 | 3.0 pCi/L | 1.9 | Moderate | 0% |
| Pueblo | 111,077 | 3.8 pCi/L | 2.3 | Moderate | 33% |
| Centennial | 106,883 | 2.5 pCi/L | 2.1 | Moderate | 0% |
| Boulder | 105,898 | 2.3 pCi/L | 2.0 | Moderate | 0% |
| Longmont | 98,630 | 2.6 pCi/L | 2.0 | Moderate | 0% |
| Highlands Ranch | 96,713 | 1.6 pCi/L | 1.6 | Low | 0% |
| Castle Rock | 81,415 | 1.6 pCi/L | 1.7 | Low | 0% |
| Loveland | 79,352 | 3.2 pCi/L | 2.1 | Moderate | 0% |
| Broomfield | 76,860 | 2.3 pCi/L | 1.9 | Moderate | 0% |
| Grand Junction | 69,412 | 2.7 pCi/L | 2.2 | Moderate | 0% |
| Commerce City | 68,245 | 1.7 pCi/L | 1.8 | Low | 0% |
| Parker | 62,743 | 1.9 pCi/L | 1.8 | Low | 0% |
| Littleton | 44,451 | 2.9 pCi/L | 2.2 | Moderate | 0% |
Highest-radon ZIP codes in Colorado
The 10 Colorado ZIP codes with the highest predicted basement average (model estimate), out of 453 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.
| ZIP | County | Predicted basement | Upstairs | Grade |
|---|---|---|---|---|
| 81007 | Pueblo County | 5.5 pCi/L | 3.2 | High |
| 80814 | Teller County | 5.5 pCi/L | 3.3 | High |
| 80816 | Teller County | 5.0 pCi/L | 3.6 | High |
| 81224 | Gunnison County | 4.7 pCi/L | 3.1 | High |
| 81211 | Chaffee County | 4.6 pCi/L | 3.4 | High |
| 81019 | Pueblo County | 4.4 pCi/L | 2.1 | High |
| 81005 | Pueblo County | 4.1 pCi/L | 2.4 | High |
| 81006 | Pueblo County | 4.1 pCi/L | 2.3 | High |
| 81023 | Pueblo County | 4.0 pCi/L | 2.2 | Moderate |
| 81004 | Pueblo County | 3.9 pCi/L | 2.3 | Moderate |
Colorado radon questions
- Is radon high in Colorado?
- Colorado's population-weighted predicted basement average is 2.6 pCi/L, about 1.4× the US average of 1.8. 3 of its 64 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 60 are in the 2-4 "consider fixing" range and 1 are below 2. 1.8% of Colorado ZIP codes are predicted at 4 or higher.
- Which Colorado county has the highest radon?
- Pueblo County has the highest predicted basement average in Colorado at 4.2 pCi/L (EPA Zone 1). The lowest is Douglas County at 1.8 pCi/L. These are area figures; individual homes in any county can test far higher.
- How many EPA Zone 1 counties are in Colorado?
- 53 of Colorado's 64 counties (83%) are EPA Zone 1 (highest potential), 11 are Zone 2 and 0 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.
- Should I test for radon in Colorado?
- Yes - with some urgency. Colorado's predicted average is in the moderate range, and 94.9% of its ZIP codes are predicted at 2 pCi/L or higher. A short-term charcoal kit or a continuous digital monitor will tell you your actual level within days.
Colorado radon program
Colorado's radon program page is at cdphe.colorado.gov; it lists testing and certified-mitigator guidance for the state. The EPA also keeps a directory of every state radon contact: EPA state radon contacts page. Then read how to test and what mitigation costs.