Radon Resources

Radon is a naturally occurring radioactive gas produced by uranium decaying in soil and rock. It seeps through foundation cracks, sump pits, and slab penetrations, then collects in the lowest occupied levels of a building. The U.S. EPA and the Illinois Emergency Management Agency both tell homeowners to fix a home at 4.0 pCi/L or higher, and to consider fixing between 2 and 4 pCi/L. The documents below define how a home should be tested, how a mitigation system should be built, and what Illinois law requires a seller to give a buyer.

Air Sense Environmental is NRPP certified and holds IEMA license #RNM20232346. We build to the ANSI/AARST standards linked on this page, and we publish those standards here so clients can check our work against an independent published rule instead of taking our word for it. If you are trying to make a decision today rather than read a standard, the radon FAQ and our guides are the faster route.

ANSI/AARST National Radon Standards

ANSI/AARST standards are the national consensus rules for radon measurement and mitigation. They are developed through an ANSI accredited process by the AARST Consortium on National Standards, with input from regulators, laboratories, contractors, manufacturers, and academics. The EPA recommends that states reference them, and federal agencies including HUD rely on them. These are the documents a licensed contractor works from when designing a system, and all of them are free to read online.

The two that matter most to a single family homeowner are SGM-SF-2023, which governs how a mitigation system is built, and MAH-2023, which governs how a home is tested. Larger properties fall under the multifamily and commercial standards further down the list, which are the references behind our commercial radon mitigation and commercial radon testing work.

Illinois Radon Documents and Disclosure Forms

Illinois regulates radon work more tightly than most states. The Radon Industry Licensing Act requires anyone who tests or mitigates radon for hire to be licensed by IEMA, and 32 Illinois Administrative Code 422 sets out how systems must be designed and installed. Separately, the Illinois Radon Awareness Act requires a seller of residential real property to give the buyer the IEMA pamphlet Radon Testing Guidelines for Real Estate Transactions along with the Illinois Disclosure of Information on Radon Hazards.

If you are buying or selling in Madison, St. Clair, Monroe, or any other Illinois county in our service area, these are the documents that will cross your closing table. Our Metro East radon mitigation page covers how the Illinois rules change the job compared with a Missouri address, and our radon mitigation cost guide carries current pricing, since the figures printed in the older state documents are long out of date.

Missouri Radon Resources

Missouri handles radon differently from Illinois. The Missouri Department of Health and Senior Services runs the state radon program and directs homeowners to nationally certified professionals through the National Radon Proficiency Program and the National Radon Safety Board rather than to a state license lookup. Missouri also offers residents a free radon test kit, limit one per household. If you are using one, read how long you should test for radon first, because a kit pulled too early is the most common way a DIY result comes back misleadingly low.

That difference matters if you own property on both sides of the river. A crew working an Illinois address answers to IEMA licensing and the Radon Awareness Act; the same crew at a St. Louis County address is held to national certification and the ANSI/AARST standards. We hold both, which is why we can work the whole metro.

Federal Radon Resources from the EPA

EPA sets the national action level and publishes the risk data that state programs cite. If you want the underlying numbers behind any claim on this website, these are the primary sources.

What the 4.0 pCi/L Action Level Actually Means

Radon is measured in picocuries per liter of air, written pCi/L. The EPA action level is 4.0 pCi/L: at or above that number, EPA and IEMA both tell you to fix the home. Below it, the guidance is softer but not silent, because there is no concentration of radon that is known to be risk-free.

EPA puts average indoor radon at about 1.3 pCi/L and average outdoor radon at about 0.4 pCi/L. Radon is responsible for roughly 21,000 lung cancer deaths a year in the United States, about 2,900 of them among people who never smoked, which makes it the leading cause of lung cancer among non-smokers and the second leading cause overall.

One number on its own is a snapshot, not a verdict. Radon swings with season, soil moisture, and how tightly a house is closed up, which is why results taken in winter versus summer can differ so much. For a fuller discussion of where the danger threshold sits, see our guide on what counts as a dangerous radon level.

How to Read a Radon Test Report

A professional radon report contains more than a single number, and the extra fields are what tell you whether the number can be trusted. Here is what to look for before you accept a result or act on it.

• Average concentration in pCi/L: the headline result, and the figure compared against the 4.0 action level.
• Test start and end timestamps: a short-term test normally runs a minimum of 48 hours. A test that ran less than that is not a valid result.
• Device location: the detector belongs in the lowest level suitable for occupancy, away from drafts, exterior walls, and moisture. A meter left on a kitchen counter tells you very little.
• Closed-building conditions: windows and exterior doors closed for at least 12 hours before the test and throughout it. If this was violated, the result reads artificially low.
• Hourly readings: a continuous monitor logs hour by hour. A sudden mid-test collapse usually means a door or window was opened, which is exactly what a tampering check is for.
• Device serial number and calibration date: an uncalibrated instrument produces an unusable number.
• Technician certification: the NRPP or NRSB certification number, plus the IEMA license number for an Illinois property.

If your report is missing several of these fields, treat it as a screening measurement rather than a decision-grade result. Our pages on DIY radon test kit accuracy and post-mitigation radon testing go deeper on when a retest is the right call.

How to Verify a Radon Contractor Before You Hire

Radon mitigation is a trade where the work disappears behind drywall and under slabs, so the paperwork matters more than usual. Four checks take about ten minutes and will screen out most bad actors.

• Check the certification directly. Search the contractor’s name in the NRPP directory or NRSB directory. Confirm the certification is current and covers the work being quoted, since measurement and mitigation are separate credentials.
• For Illinois work, check the state license. Look them up in the IEMA license database. Illinois mitigation work performed without a license is illegal, not merely inadvisable.
• Ask which standard the design follows. The answer for a house should be ANSI/AARST SGM-SF-2023. A contractor who cannot name the standard is not designing to one.
• Require a post-mitigation test. A system is not finished until a follow-up test proves the level came down. Get that commitment in writing before work starts.

Radon Guides from Air Sense Environmental

The documents above are the official record. These are our own plain-English guides, written from what we see in St. Louis and Metro East basements every week.

Affiliates and Certifications

Air Sense Environmental is NRPP certified, licensed by the Illinois Emergency Management Agency, and an affiliate member of the realtor associations on both sides of the metro. Those memberships are the reason so much of our work arrives through agents and inspectors working a closing deadline.

IEMA radon mitigation license #RNM20232346. Certification and membership marks are the property of their respective organizations.

Frequently Asked Questions About Radon Resources

Which radon standard applies to a single family home?

ANSI/AARST SGM-SF-2023, titled Soil Gas Mitigation Standards for Existing Homes, is the mitigation standard for an existing single family house. For testing that same house, the applicable standard is ANSI/AARST MAH-2023. Both are free to read online through the AARST Consortium on National Standards, and both are linked in the standards section of this page.

What documents does Illinois require a seller to give a buyer?

Under the Illinois Radon Awareness Act, a seller of residential real property must give the buyer the IEMA pamphlet titled Radon Testing Guidelines for Real Estate Transactions along with the Illinois Disclosure of Information on Radon Hazards. Both documents are published by IEMA and are linked in the Illinois section above. Confirm the correct current form version with your attorney or brokerage before signing.

Does Missouri require radon disclosure or contractor licensing?

Missouri does not run a state radon license lookup the way Illinois does. The Missouri Department of Health and Senior Services directs homeowners to nationally certified professionals through the National Radon Proficiency Program and the National Radon Safety Board instead. Illinois, by contrast, requires an IEMA license under the Radon Industry Licensing Act for anyone testing or mitigating radon for hire.

What radon level requires action?

The EPA action level is 4.0 pCi/L. At or above 4.0 pCi/L, both the EPA and IEMA advise fixing the home. Between 2 and 4 pCi/L, the EPA advises considering a fix. EPA puts the average indoor level at about 1.3 pCi/L and the average outdoor level at about 0.4 pCi/L, and no level of radon is considered risk-free.

How do I verify that a radon contractor is certified?

Search the contractor in the NRPP or NRSB certification directory and confirm the certification is current and covers the specific work quoted, since measurement and mitigation are separate credentials. For an Illinois property, also search the IEMA licensed professional database. All three lookups are linked on this page. Air Sense Environmental is NRPP certified and holds IEMA license #RNM20232346.

Where can I get a free radon test kit?

Missouri residents can request a free radon test kit from the Missouri Department of Health and Senior Services, limited to one per household. A do-it-yourself kit is a reasonable first screen for your own information. A real estate transaction needs a professional test run to the applicable protocol, because a DIY kit does not carry the tamper controls and chain of custody a transaction requires.

Talk to a Licensed Radon Professional

Documents answer general questions. They cannot tell you what is happening under your specific slab. If you have a test result you do not understand, a closing date approaching, or a system you suspect was installed badly, we will look at it with you. Estimates are free and in person, and we serve the St. Louis metro and the Illinois Metro East.

Call 314-664-9807 or request a free estimate. If you are still gathering background, our radon mitigation and radon testing pages explain the process end to end.