Radium and uranium in the Missouri River valley: Defiance, Weldon Spring and Augusta

This is the question I get asked out here more than any other, usually by somebody who just bought a place on the bluff or down in the bottoms and heard something about the old uranium plant. It deserves a straight answer, including the part most people skip, which is exactly how much our records actually prove and where they stop. Austin and I would rather lose a sale than hand somebody a scary number we can't back up.

How this was built: Everything here comes from Jones Air & Water's own 57-town water dataset, built from utility consumer confidence reports, DNR and EPA well data, and our own in-home testing, pulled in 2026. Where our file records a measured number I've given it. Where it doesn't, I've said so plainly rather than estimate.

What is actually documented at Weldon Spring

Weldon Spring is the site of the old Mallinckrodt uranium plant. Our record on the town describes a $1 billion, 16-year federal cleanup, with documented uranium, radium and nitrate that leaked more than 100 feet into groundwater, and notes that Burgermeister Spring still tests above background today. Our O'Fallon notes add that state regulators described the groundwater situation there as not improving.

That is a real industrial legacy, not a rumor, and it is the reason this corridor gets talked about. Our Augusta well notes put a boundary on it: the Defiance and Weldon Spring corridor, described as roughly 10 to 15 miles out, has documented sulfate, nitrate, fluoride, uranium and radium above background.

Now the part that matters for your house: the three town taps

All three of these public supplies test compliant. None of them is in violation for anything radiological in our file.

I want to be blunt about that last column, because it's the most important sentence in this post. Our dataset does not contain a measured radium or uranium figure in picocuries per liter for Augusta, Defiance or Weldon Spring. The records mention radium, and in Weldon Spring's case a trace of gross alpha radioactivity, but they do not attach a number to it the way our records do for other towns. Anybody quoting you a specific radium level for these three taps is not getting it from data like ours.

The town of Weldon Spring's tap is also worth separating out. Our record is explicit that the city supply is Missouri River water and tests compliant. The uranium site story there is a groundwater story, which makes it a private well story, not a city tap story.

What the same aquifer does where it is measured

Here's how I'd calibrate the risk honestly. Look at nearby St. Charles County towns where our file does carry a number. The federal limit for combined radium 226 and 228 is 5 pCi/L, and for gross alpha it is 15 pCi/L.

Every one of those is legal. None is a violation. But Wentzville at 4.0 is sitting at four fifths of the ceiling, and that is ordinary regional geology rather than anything to do with Mallinckrodt. Radium in this part of Missouri is mostly natural, and it comes out of deep limestone and dolomite bedrock. Our Defiance notes say it directly: deep bedrock wells can carry radium.

So there are two separate stories in this valley and people constantly blend them into one. Natural radium from bedrock is widespread and measurable across the county. The uranium site legacy is specific, documented, and concentrated around that corridor. They call for the same test, which is convenient, but they are not the same thing.

Why nobody has tested your well

This is the part that surprises new owners. Our Weldon Spring notes state that rural Weldon Spring, Defiance, Femme Osage and the Missouri River bottoms run on private wells the county does not routinely test, and that the state lab only checks nitrate and fluoride. Radium and uranium are not on that list. Neither is bacteria.

Our Augusta notes close with the honest version: specific per-home values are unknown until tested. That is not a sales line, it's the actual situation. There is no agency quietly watching your well.

What I would test for out here, in order

If you're on a private well in this corridor, I would not start with radium. I'd start with the things that are both more common and more likely to hurt somebody this year.

First, coliform and E. coli. Our Defiance notes cite the statewide Missouri survey finding 56% of sampled private wells positive for total coliform and 22% for E. coli. That is the highest-probability problem out here by a wide margin, especially for shallow flood-prone wells after high water.

Second, nitrate, particularly near ag fields and septic, and particularly if there's an infant in the house.

Third, iron and manganese, which our Augusta notes say exceed the standard in nearly all monitored river-bottom wells. That's your orange staining, black spotting and metallic taste.

Fourth, hardness, because these wells commonly run 15 to 30 plus grains, far harder than any of the treated town numbers above.

Then radium, gross alpha and uranium, which I'd add specifically because of where you live. Reverse osmosis is the standard fix once a test actually confirms radium or uranium, and not one minute before. I am not going to sell somebody an R/O system for a contaminant we haven't demonstrated is there.

What a real problem looks like, for scale

For perspective on what an actual radiological violation looks like in our territory, our file has one, and it isn't in this valley. Silex, up in Lincoln County, shows combined radium at 7.7 pCi/L against the 5 pCi/L limit, an EPA violation standing since 2012, with gross alpha at 13 pCi/L near the 15 limit. I wrote about that situation in radium in Lincoln County wells. Nothing in the Defiance, Weldon Spring or Augusta records comes anywhere near that.

For the county-wide view of how these towns compare on hardness and what else is in their records, see St. Charles County town by town, and for the broader well versus city picture, well water vs. city water: what 30 years of testing taught me.

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