How to Interpret Your Radon Test Results for a Safer Home

When you buy a home in Metro East Illinois, you expect that the inspection covers the big items: roof, foundation, wiring. But there is one hazard that does not show up in a standard home inspection, and it is the second leading cause of lung cancer in the United States. I am talking about radon. Unlike a leaky pipe or a cracked window, radon is invisible and odorless. The only way to know if you have a problem is to run a test and then understand what the numbers mean.

Over the years, I have tested hundreds of homes in Belleville, Edwardsville, O'Fallon IL, and Collinsville. I have seen people open their radon test results with the same mix of hope and dread that you might feel waiting for a medical report. The good news is that radon is a solvable problem. The bad news is that many homeowners either ignore the results or panic. Neither response is helpful. What you need is a clear reading of the numbers and a practical plan for what to do next.

What the Numbers Mean

Radon is measured in picocuries per liter of air, written as pCi/L. The EPA has set an action level at 4.0 pCi/L. If your radon test results show a level at or above that number, the EPA recommends that you fix your home. But that does not mean a result of 3.9 is safe and 4.1 is dangerous. Radon risk exists on a continuum. The higher the number, the greater the exposure, and the greater the long-term health risk. I have tested homes in Metro East Illinois that came back at 20 pCi/L and higher. Those are not rare outliers. They happen in neighborhoods that look perfectly normal from the street.

One mistake I see often is treating the radon test results as a pass/fail exam. A result below 4.0 is not a guarantee that your home is safe. It means that the level is below the threshold where the EPA says you should take action. Some people choose to install radon mitigation when their home tests at 2.5 pCi/L, especially if they have young children or spend a lot of time in the basement. That is a personal decision, and it is a reasonable one. Radon is a radioactive gas, and any exposure carries some risk.

Short-Term Tests vs. Long-Term Tests

The most common way to get radon test results is with a short-term radon test. You leave a radon test kit in your home for two to seven days, then mail it to a lab. These tests use activated carbon or an alpha track detector to capture radon decay products. They are cheap and quick, but they are also influenced by weather, ventilation, and how you use your home. A short-term test is a snapshot, not a full picture.

A long-term radon test runs for three months or more. The EPA recommends long-term testing because radon levels fluctuate with the seasons, with barometric pressure, and with how often you open windows. A long-term test gives you an average that is much closer to your actual year-round exposure. In my work with Air Sense Environmental, I have seen short-term radon test results that were twice as high as the long-term average, and I have seen the opposite happen. If you are serious about knowing your risk, run a long-term test with an alpha track detector. It is the most reliable method for residential radon testing.

The Role of the Radon Map

Before you even run a test, you might look at the EPA radon map for your county. St. Clair County and Madison County, where we have Belleville, Edwardsville, O'Fallon IL, and Collinsville, are both in Zone 1. That is the highest risk zone, meaning the average indoor radon level is predicted to be above 4 pCi/L. But a map is not destiny. I have tested homes in Zone 1 that came back below 1 pCi/L, and I have tested homes right next door that hit 15 pCi/L. The radon map is a starting point, not a final answer. The only way to know your home is to test it.

What Affects Your Results

Radon comes from soil gas. It seeps up through the ground and enters your home through cracks in the foundation, gaps around pipes, and sump pumps. The amount of radon that gets into your home depends on the soil composition, the construction of your house, and how the house is ventilated. In Metro East Illinois, we have a lot of clay and limestone, which can trap radon underground and then release it as the ground shifts. Older homes with slab foundations are particularly vulnerable because they often lack a gravel layer underneath that can help vent the gas.

Weather also plays a big role. A short-term radon test taken during a rainstorm or a period of low barometric pressure will often show higher numbers because the gas is being pushed out of the ground. I recommend that homeowners run their test during normal living conditions and avoid opening windows or running exhaust fans more than usual. If you cheat the test by airing out the basement, you are only cheating yourself.

What to Do If Your Results Are High

If your radon test results come back above 4.0 pCi/L, do not panic. Radon mitigation is a proven, effective technology. The most common system is sub-slab depressurization. A contractor drills a hole through the basement floor, creates a radon sump under the slab, and installs a radon fan that draws the soil gas out from under the house and vents it safely above the roofline. The fan runs continuously, and it is quiet and unobtrusive. I have seen these systems bring a home from 25 pCi/L down to below 2 pCi/L. It is not cheap, but it is far cheaper than the medical costs of lung cancer treatment down the road.

Some homeowners try to fix the problem on their own by sealing cracks and caulking gaps. That helps, but it is rarely enough. Radon is a gas, and it will find the smallest opening. A professional radon mitigation system is the only reliable way to bring high levels down to safe ones. In Metro East Illinois, I recommend working with a contractor who uses a continuous radon monitor to verify that the system is working after installation. That monitor gives you a real-time readout, so you can see the drop in radon levels within hours.

The Bottom Line

Your radon test results are not the end of a process. They are the beginning. Whether the number is 2.0 or 20.0, you now have information that lets you make a smart decision. If you live in Belleville, Edwardsville, O'Fallon IL, or Collinsville, you are in a high-risk area. Test your home. If the level is elevated, install radon mitigation. It is one of the best investments you can make in your family's health. I have worked with Air Sense Environmental on dozens of mitigation projects, and I have seen the difference it makes. The peace of mind alone is worth it.