Understanding Your Radon Test Results: What Metro East Illinois Homeowners Need to Know

When you buy a home in Metro East Illinois, radon testing is one of those things that gets added to the to-do list. You might order a radon test kit, set it up in the basement, and wait the required number of days. Then the envelope arrives or the email lands in your inbox, and you are staring at a number. That number is your radon test results. It can feel abstract at first, but it tells you something very specific about the air you breathe every day.

I have spent years working with homeowners across Belleville, Edwardsville, O'Fallon IL, and Collinsville. Over that time I have seen a lot of confusion around what those numbers really mean. A result of 2.7 pCi/L might seem low, but it is still above the action level that the EPA recommends. Another house might show 1.8 pCi/L and the owners think they are fine, yet the levels vary by season and by room. The short-term test you did in August might look completely different from a long-term radon test run through the winter. So let us walk through what those radon test results actually tell you and what you should do next.

How Radon Gets Into Your Home

Radon is a radioactive gas that comes from the natural decay of uranium in soil and rock. It moves up through the ground and enters buildings through cracks in the foundation, gaps around pipes, and sump openings. In Metro East Illinois, the geology varies quite a bit. Some neighborhoods sit on soil that allows soil gas to move freely, while others have clay that slows it down. That is why the radon map for this area shows pockets of elevated potential rather than a uniform risk. You cannot predict your home's radon level by looking at your neighbor's test results. Every house is different.

The EPA has set an action level of 4.0 pCi/L. If your radon test results come back at or above that number, the EPA recommends that you take steps to reduce the level. That does not mean you have to panic. It means you should contact a professional who does radon mitigation and get a plan in place. Even levels between 2.0 and 4.0 pCi/L still carry some risk, and many homeowners choose to address them.

Short-Term vs Long-Term Testing

Most initial tests are short-term radon tests. They use an activated carbon detector or an alpha track detector that sits in the lowest livable area of your home for two to seven days. The device is then sent to a lab for analysis. These tests give you a snapshot. They are useful for real estate transactions because they are fast, but they can be influenced by weather, open windows, and recent renovations.

A long-term radon test runs for more than 90 days, usually with an alpha track detector. That longer period smooths out daily and seasonal fluctuations. The results from a long-term test are more reliable for deciding whether you need radon mitigation. In my experience, the short-term number can be off by a factor of two or more when compared to a year-long average. If you have the time, do the long-term test first. It saves you from making a decision based on a single windy week in October.

Reading Your Results Correctly

When you open your radon test results, you will see a number expressed as picocuries per liter of air (pCi/L). That is the standard unit in the United States. Anything below 2.0 is generally considered low, but low does not mean zero. The EPA estimates that about 21,000 lung cancer deaths per year in the U.S. are linked to radon exposure. So even low levels carry some risk over a lifetime.

One thing that surprises people is that the test report often includes a margin of error. A result of 3.8 pCi/L might have an uncertainty of plus or minus 0.5 pCi/L. That means the true value could be 4.3 pCi/L, which puts it above the action level. Do not ignore the uncertainty. If you are close to the line, it is worth running a second test or switching to a continuous radon monitor for a few weeks. Those devices give you hourly readings and can show you if the radon level spikes at certain times of day.

What to Do With Elevated Results

If your radon test results come back above 4.0 pCi/L, the next step is radon mitigation. The most common system for homes in this area is sub-slab depressurization. It involves drilling a small hole through the basement floor, creating a radon sump under the slab, and installing a radon fan that pulls the soil gas from beneath the house and vents it safely above the roofline. That fan runs continuously and is usually quiet enough that you forget it is there.

Air Sense Environmental has installed many of these systems across Belleville, Edwardsville, O'Fallon IL, and Collinsville. The key is that the system must be designed for your specific house. A house with a crawlspace needs a different approach than one with a finished basement. A house on a slab needs yet another method. The radon fan size, the placement of the sump, and the sealing of cracks all matter. A good mitigation contractor will test the system after installation to confirm that the levels have dropped, usually to below 2.0 pCi/L.

Cost and Practical Considerations

Radon mitigation is not cheap, but it is far less expensive than the health consequences of long-term exposure. A typical sub-slab depressurization system in Metro East Illinois runs between $800 and $1,500, depending on the complexity. Some homeowners also choose to seal cracks and gaps themselves, which can help but rarely solves the problem on its own. The radon fan and the sump are what actually move the gas out.

If you are building a new home, you have an opportunity to install passive radon-resistant features during construction. A layer of gravel under the slab, a vapor barrier, and a vent pipe that runs up through the roof can all be added for a few hundred dollars. If the post-construction radon test results are low, you never need to activate the system. If they are high, you just add a fan and you are done. It is cheap insurance.

Seasonal Variation and Retesting

Radon levels change with the seasons. In winter, homes are sealed tight and the stack effect pulls more soil gas inside. In summer, open windows and running fans can dilute the concentration. That is why the EPA recommends testing during the heating season if possible. But do not assume that a summer test is worthless. It just gives you a different baseline.

After mitigation, you should retest within 30 days to verify that the system works. After that, retesting every two years is a good habit. Radon fans have a lifespan of about five to ten years, and if the fan fails, your levels can creep back up without you noticing. A simple alpha track detector placed in the same spot you tested before will tell you if everything is still working.

Local Context in Metro East Illinois

I have seen radon test results from every corner of this region. Some areas near the Mississippi River show consistently higher readings because of the alluvial soils. Inland areas like O'Fallon IL and Collinsville tend to be more variable. There is no single radon map that can tell you your exact risk. The only way to know is to test your own home.

If you live in Belleville or Edwardsville and your test came back at 2.8 pCi/L, you might decide to live with it. That is a personal choice. But if you have young children or someone in the house who smokes, the combined risk of radon and tobacco smoke is much higher than either alone. In that case, even moderate levels become worth addressing.

Final Thoughts on Taking Action

Your radon test results are not a judgment. They are a piece of data. The question is what you choose to do with it. If the number is low, you can breathe easier. If it is high, you have a clear path forward. The technology for radon mitigation is mature and reliable. Sub-slab depressurization with a good radon fan will protect your home for decades with very little maintenance.

I have been in crawlspaces and basements all over Metro East Illinois, and I can tell you that the difference between a house with mitigation and one without is night and day. The peace of mind alone is worth the investment. So take that test result seriously, and if you need help, find someone who knows the local soil and the local building styles. That expertise makes all the difference.