Radon Testing in Mahomet, IL
Radon testing and mitigation in Mahomet, IL, for new subdivision builds, older homes near the Sangamon River, and rural well water outside the village.
Mahomet is really three housing markets sharing a zip code, and each one asks us a different question. The new subdivisions want to know whether the passive pipe the builder installed is enough. The older homes near the river and the original village grid want to know what to do about a crawlspace with a dirt floor. The acreage properties outside town want to know whether their well is part of the problem.
None of that is exotic. It just means the answer depends on which Mahomet you live in, and a company that quotes the same system on every address is not paying attention. We start by asking about the foundation and the water before we talk about anything else, because those two facts determine most of the job.
What is consistent across all three is the ground itself. This is flat glacial till over the buried valley that gives the Mahomet aquifer its name, and Illinois sits entirely within the EPA's Zone 1. Growth does not change the geology. A house finished last year and a house finished in 1955 sit on the same soil.
Serving all of Mahomet, IL and the surrounding Champaign area.
Mahomet sits along the Sangamon River west of Champaign, next to Lake of the Woods, and has grown steadily as families trade the twenty-minute I-74 commute for the school district and the space. The result is a village with brand new subdivisions on one side, older river-adjacent homes on the other, and a ring of acreage properties outside the village limits drawing water from private wells over the Mahomet aquifer.
New subdivision homes tested to see whether the passive system is doing its job
Dirt-floor crawlspaces sealed with membrane rather than left to vent on their own
Well water radon tested separately from air for properties outside the village
Straight talk about which of the three Mahomet housing types your address is
Growth on Both Sides of the Sangamon
The subdivisions that have filled in around Mahomet over the last two decades are exactly the kind of construction people assume is safe: modern foundations, sealed vapor barriers, tight envelopes. The tight envelope is the part worth thinking about. A well-sealed house exchanges less air with the outdoors, so whatever soil gas does get in has fewer ways out, which is why newer construction sometimes tests higher than the drafty ranch down the road.
The older side of the village is a different build. Homes near the original grid and out toward the river tend to have block foundations, additions poured at a different time than the original house, and sometimes a basement under one half and a crawlspace under the other. Mixed foundations are the single biggest reason we place more than one monitor in a Mahomet home, because the two halves can behave nothing alike.
- •A tighter house is not automatically a lower-radon house
- •Mixed basement and crawlspace foundations need more than one reading
- •Additions poured later often bring their own entry points
Wells, the Aquifer, and Water You Should Test Separately
Properties outside the village water service pull from private wells, and groundwater picks up radon from the rock and soil it moves through. That is a separate exposure pathway from soil gas coming through the foundation, and it is not solved by a mitigation fan. Radon in water enters the air of the house mostly through agitation, so showers, laundry, and the dishwasher are what release it, which is why an elevated well can push up the air reading in a home whose foundation is otherwise doing fine.
If you are on village water, this is not your issue. If you are on a well and your air test comes back higher than the foundation seems to justify, testing the water tells you whether you are chasing the wrong source. Treatment, when it is warranted, is aeration or carbon filtration at the point where water enters the house, and it is a different piece of equipment entirely from what goes under your slab.
Crawlspaces on the Older River-Side Lots
An open dirt crawlspace is the most direct path soil gas has into a house. There is no slab in the way at all, just exposed ground under your floor, and the stack effect of the heated space above pulls straight from it. On Mahomet's older properties this is common, and it is often paired with a damp crawl that the owner has already been fighting for other reasons.
The fix is submembrane depressurization. A sealed vapor barrier gets laid across the crawlspace floor and up the walls, seams and edges are sealed, and a suction point under that membrane connects to a fan that vents above the roofline. Done properly it addresses the radon and takes a meaningful amount of moisture out of the space at the same time, which is usually the part homeowners here notice first.
Frequently Asked Questions
We just built in a new Mahomet subdivision. Is testing really necessary?
Yes. New construction in Illinois includes passive radon features by law, which is a head start, not a result. Tight modern building envelopes exchange less air with the outside, so a newer home can hold soil gas more effectively than an older one. Test the finished house under normal living conditions and you will know instead of assuming.
My house has a basement on one side and a crawlspace on the other. How do you handle that?
As two problems that happen to share a roof. We test both areas, because they commonly read differently, and the mitigation design usually needs a suction point serving each. Treating a mixed-foundation Mahomet home as if it were a single basement is how you end up with a system that fixes half the house.
I am on a private well outside the village. Should I test the water too?
It is worth doing if your air test is elevated, and reasonable regardless. Groundwater carries radon that gets released into your air every time you shower or run the washer, and no amount of sub-slab work addresses it. Village water customers do not need to worry about this. Well owners are the ones for whom it is a real second question.
Will sealing my crawlspace help with the damp too?
Usually yes, and that is the side benefit people in the older parts of Mahomet appreciate most. A properly sealed and depressurized membrane cuts the moisture rising out of the soil along with the soil gas. It is not a substitute for fixing grading or a drainage problem outside, but a lot of crawlspaces feel and smell different afterward.
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