Understanding Your Radon Test Results: What West St. Louis County Homeowners Need to Know

Why Radon Testing Matters for West St. Louis County Homes

If you live in Chesterfield, Ballwin, Wildwood, or Town and Country, you already know how beautiful the rolling hills and wooded lots can be. But those same geological features that give West St. Louis County its character also mean that radon gas can seep into basements and crawl spaces more easily than in many other parts of the region. I have spent years testing homes across this area, and I can tell you that radon levels vary widely, even between houses on the same street. That is why getting a reliable set of radon test results is not just a box to check during a real estate transaction. It is the only way to know what is actually happening in the air you breathe every day.

Radon is a radioactive gas that comes from the natural decay of uranium in soil and rock. It has no smell, no color, and no taste. The only way to detect it is through testing. The EPA recommends action at 4 picocuries per liter (pCi/L), but I have seen homes in Wildwood with levels above 20 pCi/L that the owners never suspected. The moment you open a radon test kit and place it in your lowest living area, you are taking the first real step toward protecting your family. But what do the numbers really mean?

The Basics of Interpreting Radon Test Results

When you receive your radon test results, you will see a number expressed in pCi/L. That number represents the average concentration of radon gas in the air over the testing period. Short-term tests typically run two to seven days, while long-term tests using an alpha track detector can last three months to a year. I usually recommend a long-term test for the most accurate picture, especially if you are planning a mitigation system. The reason is simple: radon levels fluctuate with weather, soil moisture, and even how often you run your furnace. A short-term test might catch a spike or a lull, but a long-term test smooths out those variations.

One thing I see often is confusion about what the EPA action level actually means. The EPA says you should fix your home if your radon test results show 4 pCi/L or higher. But that is not a safety line. It is a guideline. Even at 2 pCi/L, there is some risk, and many homeowners in Ballwin and Chesterfield choose to install a radon mitigation system at levels well below 4. The goal is to get the number as low as reasonably achievable. If you see a result of 3.9, you are not in the clear. You are close enough to the threshold that I would recommend a follow-up test or a continuous radon monitor to see the daily swings.

Common Mistakes Homeowners Make When Reading Their Radon Test Results

The first mistake is treating the number as a fixed value. Radon test results are an average, not a constant. I once had a client in Town and Country who tested in July and got a 2.1. They felt safe. Then they tested again in January after a cold snap and got a 6.8. The ground had frozen, and the radon had no easy path to escape except through the house. That is why I tell people to test during different seasons if they can, or to use a continuous radon monitor that logs readings every hour. The second mistake is ignoring the conditions during the test. If you ran a test during a week of heavy rain, the soil saturation might have temporarily blocked radon entry, giving you a falsely low reading. Or if you left windows open, the reading could be artificially low because fresh air diluted the radon.

Another common error is placing the test kit in the wrong spot. The kit should sit in the lowest lived-in level of the home, away from drafts, heat sources, and exterior walls. I have found test kits sitting on a shelf right next to a radon vent pipe, which of course skewed the results. And I have seen kits placed in unfinished basements that are never occupied, which does not tell you what the air is like in the rooms where you spend time. A radon test kit is only as good as its placement and the conditions around it.

The Role of Professional Testing and Mitigation

While you can buy a radon test kit at a hardware store and do it yourself, there are times when hiring a professional like Air Sense Environmental makes sense. For one thing, a professional can run a simultaneous test with a continuous radon monitor to check for short-term spikes that a passive device might miss. For another, if your radon test results come back high, a professional can help you decide between a passive mitigation approach, like sealing cracks and improving ventilation, or an active system like sub-slab depressurization.

Sub-slab depressurization, also called active soil depressurization, is the most common and effective method for homes in West St. Louis County. It involves drilling a small hole in the basement floor, pulling radon gas from beneath the slab, and venting it above the roofline with a radon fan. The system includes a manometer, usually a U-tube manometer, so you can see at a glance that the fan is running and creating negative pressure under the slab. Without that manometer, you would never know if the fan failed. I always tell homeowners to check the manometer monthly, especially after a power outage. A radon mitigation system is a mechanical system, and like any mechanical system, it needs occasional attention.

In new construction, radon-resistant construction techniques can be built in from the start, saving the trouble of retrofitting later. But for existing homes in Wildwood, Ballwin, Chesterfield, and Town and Country, a properly installed active soil depressurization system usually reduces radon levels below 2 pCi/L. I have seen systems bring levels from 15 down to 0.8. That is a huge difference in long-term exposure.

What to Do After You Get Your Radon Test Results

Let us say you just opened your radon test results and the number is 5.2. Do not panic. But do act. The first step is to confirm the result with a second test, preferably a long-term alpha track detector or a continuous radon monitor. If the second test also comes back above 4, it is time to call a professional. In the meantime, you can take some interim steps: increase ventilation in the basement, seal obvious cracks in the foundation, and make sure your radon vent pipe, if you have one, is not blocked. But these are temporary measures. The real fix is a radon mitigation system.

I have worked with many homeowners in Chesterfield who waited a year or two after getting high radon test results. They thought they would get around to it. And during that time, their family was breathing elevated radon levels every day. The EPA estimates that radon causes about 21,000 lung cancer deaths per year in the United States. That is a number that should grab anyone's attention. It is not something to put off.

For homeowners in West St. Louis County, the good news is that radon mitigation is straightforward and usually not as disruptive as people imagine. A typical installation takes one day. The radon fan is installed outside or in the attic, so there is no noise inside the house. The radon vent pipe runs up the exterior of the house and can be painted to match the siding. After installation, the contractor will perform a follow-up test to confirm the system is working. That final set of radon test results should show a level well below the EPA action point, often below 2 pCi/L.

Final Thoughts from the Field

I have tested hundreds of homes in Wildwood, Ballwin, Chesterfield, and Town and Country. I have seen the same pattern over and over: homeowners who test once and forget about it. Radon levels can change over time as the soil settles, as new construction goes up nearby, or as the home's foundation ages. I recommend testing every two years, even after you install a mitigation system. The U-tube manometer will tell you if the system is running, but it will not tell you if radon is finding a new pathway. Only a fresh test can do that.

Understanding your radon test results is not complicated once you know what to look for. The number matters, but so do the conditions under which it was collected. And the most important step is not just reading the result. It is acting on it. If you live in West St. Louis County and have questions about your test results, talk to someone who has seen the local geology and the local housing stock. That kind of context makes all the difference.