Colorado Radon Testing: CDPHE Program and Zone 1 Reality
Colorado has the most extensive radon program of any US mountain-state. The state’s geology — Pikes Peak granite, Front Range decomposed-granite outwash, and Colorado Plateau sedimentary rock with uranium-bearing strata — produces some of the highest indoor radon levels in the country. EPA designates the entire state as Zone 1, the highest risk category in the national radon map. CDPHE responds with a comprehensive program: subsidized $15 test kits for qualifying households, certification of Measurement and Mitigation specialists, public registry verification, and county-by-county risk data. This guide walks through how Colorado radon testing actually works, what the Zone 1 designation means practically, and how Front Range homeowners should approach testing decisions. Guidance summarizes EPA, CDPHE, American Lung Association, and NIEHS guidance current as of 2026; consult a CDPHE-certified Radon Measurement Specialist for transactional or post-mitigation testing.
Part of our Radon Levels guide — start there for the full picture →
Why Colorado warrants comprehensive radon testing
Colorado’s geology is the primary driver of its elevated indoor radon profile. Uranium-bearing rock and soil release radium-226, which decays to radon-222 over geologic time. The radon gas migrates through soil pores, fractures, and faults until it reaches the surface or enters basement spaces through foundation cracks, slab joints, sump pits, and pipe penetrations. The Front Range’s combination of granite bedrock, decomposed-granite alluvium, and sedimentary cover creates abundant pathways for radon migration.
EPA designates Colorado entirely within Zone 1, the highest-risk band in the national radon map. CDPHE estimates that approximately half of all Colorado homes have indoor radon levels at or above the EPA 4 pCi/L action level. The actual concentration varies substantially by county, by neighborhood, and even between adjacent properties. The statewide Zone 1 designation means every Colorado home warrants testing regardless of local lore about which neighborhoods are “safe.”
The CDPHE radon program structure
CDPHE administers the Colorado Radon Program through the Air Pollution Control Division. The program covers four primary functions: public education and outreach on radon health risks, subsidized test kit distribution to qualifying households, certification and oversight of radon Measurement and Mitigation specialists, and coordination with EPA on national radon policy and standards. Program funding comes from a combination of state appropriations and federal EPA grants.
The program publishes county-by-county radon data based on accumulated test results from homes across Colorado. The data shows substantial variation. Some Front Range counties show median indoor radon levels above the EPA action level. Mountain counties with extensive granite bedrock can show even higher medians. Counties with thicker sedimentary cover sometimes show lower averages but still substantial variation property-to-property within the county.
Subsidized test kits at $15 per household
The CDPHE-subsidized radon test kit program provides short-term charcoal canister kits at $15 to qualifying Colorado households. The subsidy targets households that have not previously tested or who have moved into housing that warrants initial baseline testing. Eligibility criteria vary by program year and funding availability but typically include income-qualifying households, first-time testers, and households in higher-priority counties.
Households outside the subsidy criteria can still purchase commercial kits at retail pricing — typically $20 to $35 for short-term kits from major brands like AccuStar, AirChek, RadonAway PRO-Lab, and FirstAlert. The home radon kit buying guide covers commercial options in more depth. Both subsidized and commercial kits use EPA-recognized methods and produce comparable accuracy when handled properly.
CDPHE-certified Radon Measurement Specialists
Colorado certifies radon Measurement Specialists through a state-administered credentialing program. Measurement Specialists are authorized to perform professional radon testing using Continuous Radon Monitor (CRM) equipment, document chain-of-custody, produce reports satisfying real-estate transaction requirements, and conduct post-mitigation verification testing. Certification requires completing accredited training, passing a state exam, and renewing annually with refresher training.
The CDPHE registry of currently certified Measurement Specialists is public-searchable through the agency website. Front Range homeowners hiring a professional for transactional or post-mitigation testing should verify the specialist’s certification status before booking. Real-estate inspection contingencies typically specify CDPHE-certified Measurement Specialist testing rather than DIY kit results, which makes the registry check a routine step in the inspection workflow.
CDPHE-certified Radon Mitigation Specialists
The CDPHE Mitigation Specialist certification covers professionals who design, install, and service active sub-slab depressurization (SSD) and related mitigation systems. Certification requires Measurement Specialist prerequisite work plus additional Mitigation-specific training, examination, and annual renewal. Mitigation Specialists are the appropriate professionals for installing residential radon mitigation systems in Colorado.
The registry of certified Mitigation Specialists is also public-searchable. Front Range homeowners scoping mitigation work should verify the contractor’s CDPHE certification before signing an installation contract. Mitigation systems typically run $1,200 to $2,800 installed on residential properties depending on the design complexity, the home’s foundation type, and any structural features that complicate the pipe network routing.
Colorado-specific geology and county risk
The Pikes Peak granite formation underlies much of El Paso County and parts of Teller and Douglas counties. The granite contains naturally elevated uranium concentrations that drive elevated radon production in soil and basements. The Front Range decomposed-granite alluvium extends across Jefferson, Boulder, Larimer, and parts of Denver and Adams counties. The decomposed granite creates abundant soil pore space for radon migration.
The Colorado Plateau in western Colorado includes sedimentary rock formations with uranium-bearing strata. Counties like Mesa, Garfield, Rio Blanco, and Montrose show elevated radon in many properties because of this geology. The northeastern plains counties — Logan, Sedgwick, Phillips, Yuma — have generally lower radon profiles because the surface geology contains less uranium-bearing rock. Even in lower-risk counties, individual properties can show elevated readings depending on specific foundation type and soil conditions.
How Front Range homeowners should approach testing
The practical approach for Front Range homeowners is straightforward. Every home should be tested at least once to establish a baseline. Initial testing typically uses a short-term home test kit, either CDPHE-subsidized at $15 if eligible or commercial at $20 to $35. The test follows the EPA closed-house protocol with the kit placed on the lowest livable level for two to seven days exposure.
Results below 2 pCi/L generally do not warrant further action, with retesting every two to three years for ongoing baseline confirmation. Results between 2 and 4 pCi/L warrant consideration of mitigation depending on occupant profile and time spent in the tested area. Results at or above 4 pCi/L warrant either a confirming test or direct mitigation planning. Radon testing in Colorado walks through the broader decision framework.
Real-estate transaction testing in Colorado
Real-estate transactions in Colorado typically include radon testing as part of the inspection contingency. The standard inspection objection form lists radon among the items the buyer can object to and request remediation. Sellers commonly receive a buyer inspection objection that includes a 48-hour CRM radon test result above 4 pCi/L plus a request for either pre-closing mitigation system installation or a closing credit toward post-closing mitigation.
The negotiation outcome depends on local market conditions. In a seller’s market, buyers sometimes accept a credit toward post-closing mitigation rather than waiting for installation before closing. In a buyer’s market, sellers more often agree to pre-closing mitigation. Either way, the certified Measurement Specialist’s test result drives the negotiation. Radon testing during home inspection covers the transactional workflow in more detail.
Health risk context
Radon is the second-leading cause of lung cancer in the United States after smoking. The risk is greatest for smokers and former smokers due to multiplicative interaction between radon and smoking-related lung damage. EPA estimates 21,000 US lung cancer deaths per year are attributable to radon exposure. The risk scales roughly linearly with cumulative exposure: longer exposure at lower concentrations produces similar cumulative risk to shorter exposure at higher concentrations.
For non-smoking occupants of homes with indoor radon at 4 pCi/L, the lifetime lung cancer risk is approximately 7 in 1,000. For smoking occupants in the same conditions, the risk rises to approximately 62 in 1,000. Both rates substantially exceed the cancer-risk thresholds that EPA uses for most environmental contaminants. NIEHS and American Lung Association publish detailed health risk data for ongoing reference.
What testing does not cover
A radon test measures airborne radon concentration in the tested location during the test period. It does not measure water-borne radon (a separate concern in some Colorado wells), radon in adjacent rooms or floors of the home, or radon during weather or seasonal conditions outside the test window. Comprehensive radon understanding sometimes requires multiple tests in different locations or different seasons to fully characterize a property.
For homes with private well water supplies in counties with uranium-bearing aquifer rock, water-borne radon testing is a separate analysis from the indoor air test. Water test kits use specific sample collection methods and target the dissolved radon in the water supply rather than the airborne concentration. Front Range homeowners on municipal water generally do not need water-borne radon testing; well-water homeowners in higher-uranium regions should consider it.
Putting Colorado radon testing into practical action
The combination of Zone 1 designation, CDPHE-subsidized test kits, accessible certified professionals, and substantial state outreach makes Colorado one of the best-supported markets for radon testing in the US. Front Range homeowners can move from initial baseline test through professional CRM testing and mitigation installation if needed within a few weeks at reasonable cost. The lung cancer risk reduction over an ownership period is substantial when elevated levels are identified and mitigated.
Front Range homeowners with radon testing questions can connect with our team for a referral to a CDPHE-certified Measurement or Mitigation Specialist. The state’s program structure makes professional verification quick and the testing decision pathway straightforward.
CDPHE radon outreach beyond test kits
CDPHE’s radon outreach extends well beyond test kit distribution. The program publishes county-by-county radon data, hosts public education events in higher-priority counties, partners with local health departments and county sustainability offices, and produces educational materials for distribution at home shows and community events. The outreach aims to raise testing rates from the current statewide average toward universal baseline coverage of Colorado homes.
The program also coordinates with EPA on national radon policy and contributes data to the federal radon database used in Map of Radon Zones updates. Colorado’s leading position on indoor radon makes the state a significant contributor to national radon research and policy. NIEHS and EPA-funded studies of radon health effects sometimes include Colorado cohorts because of the elevated exposure profile.
Multi-unit and rental property testing
Colorado multi-unit and rental properties present specific testing considerations. Rental property owners are not legally required by Colorado state law to test for radon in occupied units, though several local jurisdictions have implemented testing or disclosure requirements. The state recommendation is that rental property owners test units in higher-risk counties as a routine maintenance practice and address elevated readings through mitigation.
Tenants in Colorado rentals concerned about radon can request testing from the landlord or, where the landlord declines, can purchase their own subsidized or commercial kit and run the test independently. Test results that document elevated levels in occupied rental units can prompt local code enforcement intervention in some jurisdictions, though enforcement varies. The CDPHE program publishes tenant-facing resources covering the request and documentation process.
References
- EPA radon program and Zone 1 designation — US Environmental Protection Agency
- CDPHE Radon Program and certified professional registry — Colorado Department of Public Health and Environment
- American Lung Association radon resources — American Lung Association
- NIEHS radon health research — National Institute of Environmental Health Sciences
Frequently asked questions
Why is Colorado the highest-risk radon state?
Colorado's geology — Pikes Peak granite, decomposed granite outwash, and Colorado Plateau uranium-bearing sedimentary rock — produces elevated radon migration into homes. EPA designates the entire state as Zone 1, the highest-risk category nationally. CDPHE estimates that about half of Colorado homes have indoor radon at or above the 4 pCi/L action level.
What is the CDPHE subsidized radon test kit program?
CDPHE provides short-term charcoal canister radon test kits at $15 to qualifying Colorado households. The program targets first-time testers and households in higher-priority counties. Eligibility and ordering information is available through the CDPHE radon program website.
How do I verify a Colorado radon professional?
CDPHE maintains a public registry of currently certified Radon Measurement Specialists and Radon Mitigation Specialists searchable through the agency website. Verify certification before hiring any radon professional for transactional, mitigation, or post-mitigation testing work.
Do all Colorado counties have the same radon risk?
No. Risk varies substantially by geology. Mountain counties with extensive granite bedrock and Colorado Plateau counties with uranium-bearing sedimentary rock show higher medians. Northeastern plains counties show generally lower averages. Every county has Zone 1 designation, so individual property testing is warranted regardless of county average.
Front Range homeowners scoping radon testing or mitigation work can contact our team for a referral to a CDPHE-certified Measurement or Mitigation Specialist before committing to testing scope or mitigation installation.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
| Product | Why | Buy |
|---|---|---|
 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $17.95 |
 Airthings Corentium Home | Digital monitor with a long-term average. | Amazon — $142.49 |