Five ways CO₂ and brine could reach our drinking water — and why EPA hasn’t looked
By Pam Richart, Eco-Justice Collaborative

The written comment period on One Earth Sequestration’s three draft Class VI permits closed on October 4, 2026. Before EPA Region 5 can make a final decision, it has to answer the comments it received. This is the time to understand what is at stake and what EPA still has to explain.

One Earth wants to inject 90 million metric tons of carbon dioxide over twenty years. The CO₂ would go about a mile and a quarter underground, into rock near Gibson City that is already full of salt water. The site sits in a recharge area EPA designated in 2015 along with the Mahomet Aquifer, which supplies drinking water to nearly 1 million people in east-central Illinois. I am one of them.

This slide presentation walks through what we found in the permit record. This post explains how to read it.

What we are — and are not — saying
We are not predicting that this project will contaminate anyone’s water. We are saying something narrower, and harder to dismiss. The company’s own documents and EPA’s own findings identify at least five routes by which CO₂, or the brine it pushes ahead of it, could move upward toward our water. The record never follows any of them from the injection zone to a tap.

The pieces are all in the record. But the record never puts them together.

Why pressure matters more than the plume
Most discussion focuses on how far the CO₂ will spread. The model says about 3.2 miles. But injecting into rock that is already full doesn’t make room. It raises pressure, and that pressure reaches much farther than the CO₂ does.

The permit’s own “area of review” is drawn where the added pressure falls to 77.5 psi. That is the smallest increase One Earth says could push fluid toward drinking water through an open path. That circle covers nearly 200 square miles, about eight miles in every direction. Inside it, the pressure is above that threshold. Gibson City’s wells are inside it. So is about half of the area that EPA designated as the Mahomet Aquifer or this recharge zone.

So the real question is not whether the CO₂ will travel eight miles. It is whether there is a path.

The five pathways.

1. 1. An abandoned 1946 oil well. The Erp #1 well reaches into the rock meant to seal in the CO₂. It was filled with drilling mud, not cement. EPA itself found that “corrective action is necessary to prevent endangerment” to drinking water. Then it declined to require the well be plugged. On One Earth’s own model, pressure at that well passes the 77.5 psi threshold in about year 3 and stays above it for decades.
   2. A fault next to the injection wells. The company’s 2022 seismic survey mapped a fault about 4,000 feet long inside the planned CO₂ plume. It is not mentioned once in any of EPA’s five permit documents.
   3. The Osman Monocline. This fold has faults in its core, including three mapped inside the seal itself. Thirty miles south, where the same structure crosses the Mahomet, State scientists have documented salty bedrock water entering the aquifer.
   4. Old wells above the seal. There are 573 wells and borings in the review area. Only one was checked. About 21 others pass through the shale layers EPA counts on as backup protection, and none was examined.
   5. Pressure alone. Raised pressure can push brine up any opening, with no CO₂ involved at all.

What is missing
Two gaps stand out.
First, the model used to draw these boundaries includes only three rock layers. It sets the top of the seal as a wall nothing can cross. It cannot show fluid leaving, so it cannot be used to rule out the ways fluid might leave.

Second, almost nothing has been measured in the water people actually drink. The word “Mahomet” does not appear once in the three permits — only in EPA’s explanatory fact sheet, which binds no one. There is no baseline water chemistry for the Mahomet or Gibson City’s wells. EPA asked One Earth for that baseline during its review and did not get it. If a well changes ten years from now, there will be nothing to compare it to.

What EPA should do
Under federal rules, the company — not the public — carries the burden of showing that drinking water is protected. Before any final decision, EPA should:

1. Require Erp #1 to be properly plugged, with verification, before injection begins.
2. Analyze the faults it has mapped, including whether injection pressure could make them slip.
3. Sample the Mahomet and Gibson City’s wells before injection, and write the Mahomet into the permits by name.
4. Either lock in the smaller injection volume it relied on to skip plugging Erp #1, or evaluate the full 90 million tons.
5. Treat these as substantial changes: issue a revised draft permit and reopen public comment.

The Illinois General Assembly has already directed the Prairie Research Institute to study the risks of carbon storage in the Mahomet and its project review areas. That report is due in 2030. These permits would issue years before it is finished.

We are asking EPA to finish the analysis before it permits the project, not after. Please look through the presentation, share it, and stay with us as EPA responds.