If you've searched "average radon levels in Colorado" or wondered why your neighbor in Arvada just had a mitigation system installed, you're asking the right question at the right time. Colorado's geology puts nearly every home in the state at elevated risk, and the only way to know your actual number is to test.
What is the average radon level in Colorado?
There isn't a single verified "average" number that applies to every house, because radon concentrations vary block-to-block and even room-to-room depending on soil, foundation type, and ventilation. What is verifiable: the U.S. EPA classifies every county in Colorado, including Jefferson County, Boulder County, and Denver County, as Zone 1 — the agency's highest radon potential category, meaning predicted indoor levels are expected to average above the EPA's 4 pCi/L action level. That's why public health guidance is consistent statewide: every home should be tested, regardless of age, style, or whether the basement is finished.
Why Colorado's Front Range sees so much radon
Radon gas forms from the natural decay of uranium in soil and bedrock. The Front Range corridor — including Arvada, Boulder, Lakewood, and the foothills west of Denver — sits on granite and uranium-bearing geology that produces more radon than average soil profiles elsewhere in the country. The gas moves up through foundation cracks, sump pits, and utility penetrations, then gets trapped inside a sealed home, especially during Colorado's cold season when windows commonly stay closed for six months or more.
What an Arvada or Boulder radon test actually involves
A short-term radon test uses either a charcoal canister or a continuous radon monitor placed on the lowest livable level of the home. For an accurate result:
- Close all windows and exterior doors for at least 12 hours before the test starts, and maintain those "closed-house conditions" for the entire test period.
- Run the test for a minimum of 48 hours; continuous monitors log hourly readings so a technician can flag a single windy or stormy day that might skew the result.
- Avoid running exhaust fans, whole-house fans, or a wood stove during the test window — they can pull outdoor air, and radon, in or out unnaturally.
- Place the device at least 20 inches off the floor, away from drafts, exterior walls, and windows.
Winter testing tends to capture a home's worst-case radon levels since closed-house conditions happen naturally, which is one reason many Boulder and Lakewood homeowners test in late fall through early spring. That said, the EPA notes radon can be measured any time of year as long as closed-house protocol is followed correctly.
What a radon mitigation system involves
If a test comes back at or above 4 pCi/L, the standard fix is active soil depressurization (ASD), sometimes called sub-slab depressurization. A qualified mitigation contractor typically:
- Seals a suction point through the foundation slab or into a crawlspace vapor barrier.
- Runs PVC pipe from beneath the foundation up through the structure — often through a garage, closet, or exterior wall chase — to a discharge point above the roofline.
- Installs an inline radon fan that continuously pulls soil gas from under the slab and vents it outside, away from windows and eaves.
- Adds a U-tube manometer near the fan so the homeowner can visually confirm the system is still operating under vacuum.
A properly installed system commonly reduces indoor radon levels by 80-99%, and a confirmation test after activation verifies the new number rather than assuming it worked.
Choosing a radon professional in Colorado
Look for a contractor certified through a recognized national program such as the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB) — Colorado does not require a separate state radon license, so certification and local references matter more than a state credential. If you're buying or selling a home, a radon test is frequently part of the inspection period on Front Range transactions, and mitigation costs are often a negotiation point between buyer and seller. Always get the scope of work in writing, including pipe routing, fan placement, and whether a post-installation test is included.
Frequently Asked Questions
How much does a radon test cost in Arvada or Boulder?
Pricing varies by contractor and by whether you choose a short-term charcoal kit or a continuous monitor with a technician visit — get quotes from a couple of local, certified providers rather than assuming a flat statewide price.
Is Boulder radon mitigation different from mitigation elsewhere in Colorado?
The core technology, active soil depressurization, is the same statewide. System design depends on your home's specific foundation — slab-on-grade, basement, or crawlspace — not on which city you're in, so a contractor should evaluate your foundation type before recommending a layout.
Do I need to retest after installing a mitigation system?
Yes. A post-mitigation test, usually run within 30 days of system activation, confirms the fan and pipe network actually brought levels below the EPA action threshold. Many contractors include this retest in their installation package — ask before you sign.
This article is general educational information, not a substitute for a site-specific inspection or legal/regulatory advice. Radon testing protocols, contractor certification expectations, and disposal or building-code rules vary by municipality and county in Colorado — check with your local building department or a certified radon professional before making testing or mitigation decisions.