Radon in Colorado: County Levels, Laws, and Mitigation

Overview of Radon and Its Risks

Radon is a colorless, odorless, radioactive gas that comes from the natural decay of uranium in soil and rock. It can seep into homes through foundations and accumulate indoors. Colorado’s geology leads to widespread radon: all 64 Colorado counties are classified as having high radon potential. Health authorities consider radon the second-leading cause of lung cancer (after smoking) and the #1 cause in non-smokers. Long-term radon exposure is estimated to cause about 21,000 lung cancer deaths per year in the U.S., including around 500 deaths annually in Colorado. There are usually no immediate symptoms of radon exposure; the risk is long-term lung damage. Because radon is invisible and odorless, the only way to know your radon level is to test your home.

Radon levels are measured in picocuries per liter (pCi/L), a unit of radioactivity. The U.S. Environmental Protection Agency (EPA) recommends taking action (mitigation) if indoor radon is 4.0 pCi/L or higher. However, no amount of radon is completely risk-free – even lower concentrations carry some risk over time. Reducing radon as much as reasonably possible is advised to protect health.

Average Radon Level In Colorado: 6.8 pCi/L

The EPA advises that any home or building in Colorado with radon levels at or exceeding 4.0 pCi/L should undergo mitigation. Additionally, the World Health Organization (WHO) sets a lower threshold, recommending action for radon concentrations of 2.7 pCi/L or above.

EPA's Action Level: 4.0 pCi/L
WHO's Action Level: 2.7 pCi/L
Average Level In Colorado: 6.8 pCi/L

Living or working in areas with elevated radon levels can pose significant health risks. The only reliable method to ascertain the radon concentration in your specific home or building is through radon testing. This is a crucial step in ensuring your environment is safe and adheres to recommended health standards.

Radon Levels Across Colorado Counties

Radon is a statewide concern in Colorado. Surveys show that homes in every Colorado county have the potential for radon levels above the EPA’s 4.0 pCi/L action level. In fact, the average indoor radon level in Colorado is about 6 pCi/L, significantly higher than the U.S. national average of ~1.3 pCi/L. According to the Colorado Department of Public Health & Environment (CDPHE), about 50% of radon tests in Colorado homes come out above 4.0 pCi/L – meaning roughly one in two homes has elevated radon.

There is some variation across counties, but risk is widespread. For example, an analysis of test data found average radon concentrations ranging from about 2.7 pCi/L in Conejos County up to 53.8 pCi/L in Hinsdale County (among counties with sufficient test data). Many highly populated areas also show elevated levels; Jefferson County, for instance, logged over 11,700 radon tests with a mean level around 5.4 pCi/L. All but a few Colorado counties were classified as Zone 1 (highest risk) in EPA’s radon zone maps, and Colorado’s state radon map treats the entire state as high-risk. In practical terms, every homeowner or renter in Colorado should assume their home may have high radon and consider testing, regardless of which county they live in. (Even neighboring houses can have very different radon levels due to differences in construction and soil pockets.) Radon data maps are available through CDPHE and the EPA that show county-by-county radon test results and risk zones, reinforcing that elevated radon is a statewide issue.

Health Risks of Radon Exposure

Breathing high levels of radon over time can damage lung tissue and increase the risk of lung cancer. Radon decays into radioactive particles that, when inhaled, bombard lung cells with alpha radiation. Over years of exposure, this can lead to cellular damage and eventually cancer. Radon’s status as a carcinogen is well documented: it is the leading cause of lung cancer among non-smokers, and overall second only to cigarette smoking. The EPA estimates about 21,000 lung cancer deaths each year are attributed to radon in the U.S., including roughly 500 per year in Colorado. Smokers exposed to radon have an especially high risk, as the two risk factors multiply each other’s effects.

It’s important to note that radon-induced lung cancer develops over long periods – there are no immediate symptoms of radon exposure. You can’t see or smell radon, and it doesn’t cause headaches or irritation. This is why testing and mitigating high levels is critical before health problems occur. Health experts emphasize that there is no truly “safe” level of radon. The EPA’s action guideline of 4.0 pCi/L is not a threshold of zero risk, but rather a level at which the risk (~7 out of 1,000 lifetime lung cancer risk for a non-smoker) is considered significant enough to strongly recommend mitigation. Even at 2.0 pCi/L, there is some risk (about half the risk of 4.0 pCi/L). For perspective, a long-term radon level of 4 pCi/L gives a lifetime lung cancer risk roughly comparable to the risk of dying in a car accident, according to EPA comparisons. The bottom line: reducing radon reduces risk. Families in Colorado – where high radon is so common – should treat radon as an important environmental health concern, similar to testing smoke detectors or drinking water quality.

Colorado Radon Regulations and Local Laws

Colorado has recently strengthened its laws and regulations to address radon testing, disclosure, and mitigation. These measures impact home sellers, landlords, radon professionals, builders, and others. Below are key legislative updates and policies related to radon in Colorado:

Real Estate Radon Disclosure Law (SB 23-206, effective August 2023): This law now requires that during any home sale or new rental lease, the parties are informed about radon. Home sellers must include a written warning about radon, disclose any known radon tests or mitigation on the property, and provide the buyer with the latest CDPHE radon information brochure. Similarly, landlords must give prospective tenants a radon disclosure before signing a lease, including a warning about radon’s dangers, any knowledge of the property’s radon levels or mitigation, and a CDPHE brochure. While the law does not force testing, it ensures buyers and renters are aware of radon and any existing test results.
Licensing of Radon Professionals (HB 21-1195, effective 2022): Anyone performing radon measurement or mitigation for a fee in Colorado must be licensed by the state. This ensures that radon contractors follow strict ANSI/AARST standards for radon work.
Radon Testing in Schools and Child Care Facilities: State law requires all K-12 schools and licensed child care centers to test for radon and keep records of results. However, there is no law requiring them to mitigate high radon levels.
Local Building Codes for Radon-Resistant Construction: Many Colorado cities and counties require new homes to be built with radon mitigation systems. Boulder County, for example, mandates radon-resistant features in all new homes.
Radon Awareness and Mitigation Programs: Colorado offers free or low-cost radon test kits and financial aid for mitigation through a Low-Income Radon Mitigation Assistance Program.

Radon Testing and Mitigation

Test your home using a short-term or long-term radon test kit, available online or at county health departments.
If results are 4.0 pCi/L or higher, consider mitigation. Even 2-4 pCi/L carries some risk.
Radon mitigation systems (sub-slab depressurization) use a vent pipe and fan to reduce radon. Costs typically range from $800 to $2,500.
Retest after mitigation to ensure levels remain low. New homes with passive radon systems should still be tested.

Conclusion

Radon is a serious health risk in Colorado, but it is manageable. Testing and mitigation can prevent long-term lung cancer risk. Colorado’s new laws are increasing awareness, and homeowners, renters, and real estate professionals all play a role in addressing radon. If you live in Colorado, assume you have radon until proven otherwise – testing is simple, and solutions exist to keep your home safe.

Additional Resources About Radon Levels In Colorado

Here are some resources for reading about radon levels in Colorado:

Additional menu