Why Every St. Louis Homeowner Should Consider a Radon Gas Test

If you have lived in the St. Louis area for any length of time, you know our region sits on some interesting geology. Limestone, shale, and glacial deposits shape our hills and valleys. What you might not realize is that the same ground that gives us our scenic bluffs can also release a radioactive gas into your basement. Radon gas is a natural byproduct of uranium decay in soil and rock. It is odorless, colorless, and tasteless. And it is the second leading cause of lung cancer in the United States, according to the EPA.

The good news is that radon is completely manageable once you know it is there. The first step is getting a reliable radon gas test. I have been involved in indoor air quality work for years, and I cannot count how many times I have walked into a finished basement that looked perfect but had a radon level well above the EPA action guideline of 4 pCi/L. The homeowners usually had no idea. They had never tested, because the house did not smell funny or make anyone feel sick right away. That is the thing about radon. It does not announce itself.

Testing for radon is straightforward, but the method matters. A lot of people grab a do-it-yourself kit from a hardware store, set it up in the basement for two days, and mail it off. That is a short-term radon test, and it can give you a ballpark number. But radon levels fluctuate with weather, barometric pressure, and even how often you run your HVAC system. A single two-day reading can miss a spike that happens the following week. For a more reliable picture, many experts now recommend a continuous radon monitor. These devices sit in your home for a minimum of 48 hours and take readings every hour or so. They average the results and can even detect tampering or unusual conditions. If you are in the middle of a real estate transaction, a continuous monitor is often the standard because it gives both buyer and seller confidence in the result.

I remember a deal in a West County subdivision that nearly fell apart over radon. The buyer had done a short-term radon test with an activated charcoal test kit and got a reading of 6.2 pCi/L. The seller was convinced the test was wrong, because they had lived in that house for fifteen years without issues. We ended up placing a continuous radon monitor in the same spot for three days. The final average came back at 4.8 pCi/L. Still above the EPA guideline, but much closer to reality. That number gave everyone a starting point for negotiations, and the seller agreed to install a radon mitigation system before closing. Nobody got sick, and the deal closed. That is why I tell home buyers and sellers in St. Louis to invest in a proper radon gas test early in the process. It saves arguments and protects your health.

How Radon Gets Into Your Home

Radon gas enters buildings primarily through the ground. As the gas rises through soil, it can seep into your home through foundation cracks, gaps around utility pipes, sump pump openings, and even the porous concrete slab itself. Once inside, it gets trapped and can build up to unhealthy concentrations. The lower levels of a house are almost always the worst. Basements, crawl spaces, and slab-on-grade rooms are the most vulnerable.

St. Louis homes built before the 1990s are especially likely to have higher radon levels, because radon resistant construction was not common until later. Modern building codes in many St. Louis counties now require passive radon-resistant features, like a layer of gravel under the slab and a vent pipe through the roof. But even those houses can still have elevated levels if the passive system is not activated with a fan. That is why testing is recommended for every home, regardless of age.

Short-Term vs. Long-Term Testing

The EPA recommends starting with a short-term radon test. If the result is 4 pCi/L or higher, they advise taking a follow-up test or moving straight to mitigation. Short-term tests typically use an activated charcoal test device that absorbs radon over two to seven days. They are inexpensive and widely available. But they are not the final word. Radon levels can vary dramatically with the seasons. Winter tends to be worse because homes are closed up and the stack effect pulls more soil gas inside. Summer can be lower, especially if you open windows.

For a truer annual average, many homeowners choose a long-term radon test. These usually use an alpha track detector that stays in place for three to twelve months. The alpha track detector is a small plastic chip that records damage from alpha particles over time. It is more accurate for determining your actual year-round exposure. If you are planning to live in your home for years, a long-term test gives you the most useful data. On the other hand, if you are buying or selling a home, you rarely have three months to wait. In that case, a continuous radon monitor is the best compromise between speed and accuracy.

What the Numbers Mean

The EPA action level is 4 pCi/L. That does not mean levels below that are perfectly safe. There is no safe level of radon. The risk of lung cancer increases linearly with exposure. The EPA simply chose 4 pCi/L as a threshold where mitigation is strongly recommended because it is a practical point for action. If your radon level is between 2 and 4 pCi/L, you might still want to consider radon reduction, especially if you have children or spend a lot of time in the basement.

Radon levels are measured in picocuries per liter of air. One pCi/L is a very small amount of radioactivity, but remember that you breathe that air every day for years. The EPA estimates that about 21,000 lung cancer deaths per year in the U.S. are radon-related. That is a staggering number for a problem that can be fixed with a vent pipe and a fan.

Mitigation: What Happens After the Test

If your radon gas test comes back high, do not panic. Radon mitigation is a well-established field. The most common method is sub-slab depressurization. A contractor drills a hole through the basement floor, pulls soil gas from underneath the slab with a fan, and vents it above the roofline. This system can often reduce radon levels by 90 percent or more. In some cases, sealing foundation cracks and improving ventilation can help, but sub-slab depressurization is the gold standard.

Air Sense Environmental, a St. Louis company I have worked with, uses continuous radon monitors for all their testing. They do not rely on the old charcoal kits for critical decisions. They place a monitor in the lowest livable area, run it for at least 48 hours, and give you a detailed report. If the result is high, they can recommend a qualified mitigator. They do not do the mitigation themselves, which I appreciate. It keeps the testing honest.

I once saw a home where the sump pump pit was acting like a chimney for radon. The pit was not sealed, and the pump cycle was drawing soil gas right into the basement. A simple sump pump cover with a gasketed lid and a vent to the outside solved the problem for under two hundred dollars. Sometimes the fix is that simple. Other times you need the full sub-slab system. But you will never know until you test.

Testing for Real Estate Transactions

If you are buying or selling a home in St. Louis, a radon gas test is almost always part of the inspection contingency. Most home inspectors can perform a radon test, but not all of them use continuous monitors. Some still use the old two-day activated charcoal test. If you are the buyer, you have every right to specify that the test be done with a continuous radon monitor. It is harder to cheat, and it gives a more reliable average. Sellers should also consider testing before listing. If you already know your radon level is low, you can put that in the disclosure and avoid last-minute surprises. If it is high, you can fix it on your own timeline rather than under the pressure of a closing date.

I have seen transactions where the radon test came back at 3.9 pCi/L, just under the action level, and the buyer still wanted a mitigation system. That is a negotiation. But having a continuous monitor result gives both sides a defensible number. It is hard to argue with a device that recorded readings every hour for three days.

Final Thoughts on Testing

Testing for radon is one of the cheapest and easiest things you can do to protect your family's health. A radon gas test costs anywhere from fifteen dollars for a do-it-yourself kit to a few hundred for a professional continuous monitor test. Compare that to the cost of a lung cancer treatment or the stress of a failed real estate deal. It is a no-brainer.

If you live in St. Louis, the geology here means we are in a Zone 1 area, the highest risk category according to the EPA. That does not mean every home has a problem, but it does mean every home should be tested. Whether you use a short-term test to screen or a long-term test for precision, do not skip it. And if you are in the middle of a real estate transaction, insist on a professional test with a continuous radon monitor. Your lungs and your wallet will thank you.