Dynegy Claims the Mysterious Middle Fork Discharge

—This post is a follow-up to A Mysterious Discharge on the Middle Fork. See Part 1 and Part 2

An image of the tributary taken a month after it carried millions of gallons of opaque white water into the Middle Fork. No evidence of this mysterious flow is immediately apparent. This tributary was flowing full from bank to bank with milky white water on April 25th.

Dynegy now states that they released an estimated 12 million gallons of water over the spillway of the cooling lake dam of their closed Vermilion Power Station on April 25th.

That day, hikers noticed a small stream flowing full from bank to bank with cloudy white water. Canoers saw this small stream flow into the Middle Fork River and mix until it turned the entire river white. Both the hikers and the canoers noted that the color and flow rate of the stream was unusual and striking; not your typical brown sediment runoff but cloudy, white, and flowing fast. There hadn’t been any rain to cause a flow like that.

Here’s a description from one of the canoers, who describes the cloudy flow mixing with the Middle Fork:

“The water from the tributary was light gray in color. Whatever was suspended in the water was very light in color – not typical soil color which is brown to dark olive gray. This was light gray to white. The water from the tributary was so laden with suspended material you could not see even an inch into the water (it was opaque). It was a striking display of mixing of the stream and tributary. We could follow the two water ‘streams’ through at least the first bend after the tributary. After a stretch, the tributary water was completely mixed with the main stream and the entire Middle Fork was opaque from the light gray suspended load from the tributary.”

The white and cloudy tributary enters the Middle Fork in the bottom of the image. Following the tributary’s valley northward, hikers identified it as the stream that comes from Dynegy’s dam.

Illinois EPA spoke with residents near the site the next day, April 26th, but found nothing that could have created the mysterious flow. They did not investigate Dynegy’s property, but Dynegy indicated via phone call that they did not see anything unusual.

Two weeks later, Illinois EPA met with Dynegy for a follow-up inspection. During that inspection, Dynegy confirmed that they were responsible for the water but could not explain its cloudy white color. Illinois EPA concluded that the white material could not have come from Dynegy’s dam. They explored portions of the site downstream of the dam but were not able to locate a source for the discoloration.

What caused the mysterious flow on the Middle Fork?

In Illinois EPA’s inspection report, Dynegy indicated that contractors on a weekly inspection of the Vermilion Power Station noticed a beaver dam blocking the spillway on April 24th, the day before the mysterious flow. The next day, another contractor removed the beaver dam, causing a flow over the spillway approximately 8 inches deep which lasted for hours.

The story seems to make sense. The math certainly checks out – the lake level was lowered by 8 inches, and the lake is approximately 100 acres, so the volume that went over the spillway (area x depth = volume) matches PRN’s estimated 20 million gallons of flow from the stream gage record.

The flow in the Middle Fork river is measured downstream at Oakwood. This image shows an increase of 40 cubic feet per second around noon on April 25th which seems to last until the early morning of April 26th. Eighteen hours of 40 cubic feet per second flow is about 20 million gallons.

However, a closer inspection of the story reveals some inconsistencies or a complete lack of communication.

Dynegy should have known about the discharge on April 25th and reported it. Dynegy had two different contractors at the power station on the 24th and 25th, one to inspect the site and then a second to remove the beaver dam from the spillway. Surely, one or both of those contractors would have reported their activities to Dynegy. Why then would Dynegy report to Illinois EPA on April 26th that nothing unusual had occurred that might cause the mysterious flow?

It also seems improbable that a lake could fill up by 20 million gallons during a week that had no rain. Dynegy’s contractors inspect the site weekly. If the spillway was not blocked on the 17th, then all 20 million gallons would have had to accumulate between the 17th and the 24th. Without rain, that is impossible, unless for some reason Dynegy was pumping water into the lake from the Middle Fork, where they have a pumping station.

The last problem with this story is the obvious one: what caused the white color? No explanation is given. There is only Dynegy property between the tributary where hikers identified the mysterious discharge and Dynegy’s dam. Whatever caused the stream to turn white is, or was, on Dynegy’s property.

What could have made the water white and cloudy?

There are a few things that could explain the white color. The most likely possibilities include bentonite clay or aluminum. Coal ash has turned rivers a white color depending on the ash’s composition. It could even be white paint! We don’t really know without evidence.

Let’s take a moment to explore a theory that could have explained the mysterious flow – a mine blowout.

Multiple abandoned mines sit below the infrastructure that supports Dynegy’s Vermilion Power Station. There are mines close to both the cooling lake dam and the New East Ash Pond, a coal ash impoundment. Mines leave behind mine voids: empty space that once contained coal. At this site, the extent of the mine voids is unknown because the mines were dug over 100 years ago and weren’t properly mapped.

A mine void can collapse if the supports of the mine roof fail. Collapse can result in the instability of structures built on the land surface above the mine, such as Dynegy’s cooling lake dam and the nearby impoundments which store coal ash. The known extent of the mines relative to the coal ash impoundments and the dam are shown below.

This map shows the relative location of the underground mines and some of Dynegy’s structures at the site – the New East Ash Pond and the cooling lake’s dam, which is the structure forming the southeast border of the lake. The light yellow areas represent the range of potential surface influence from underground mines. This map also depicts the land surface elevation, which reveals the river valleys and land surface through the trees. Mine data is from the Illinois State Geological Survey’s ILMINES mine map.

It is possible Dynegy’s coal ash is seeping through the mines and collecting on the surface. Mine voids have been known to create pathways for contamination. Coal waste has entered the environment through old mines before. In 2000, Massey Energy leaked coal slurry into an abandoned mine in Kentucky which then spilled 300 million gallons of coal waste into multiple nearby rivers.

Perhaps the white material is a result of a mine blowout, and the material was then picked up by the larger-than-usual flow in the tributary. We really don’t know and don’t have a way of knowing without a thorough investigation of the site.


The amount of material it would take to turn millions of gallons of water opaque would surely leave behind a record. That much material doesn’t just appear in a tributary in the middle of a river valley. However, Dynegy owns all the land between the tributary and the dam so investigation is impossible without trespassing.

Illinois EPA has closed the investigation – see the report.

The mysterious flow was over a month ago, and May was particularly stormy this year, so it may be too late to turn up any clues. Please reach out to us if you have any ideas.

Click here to read about Dynegy’s coal ash on the Middle Fork.

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