Beneath a wide swath of central Illinois lies one of the Midwest's most vital sources of drinking water. The Mahomet Aquifer stretches across 13 counties and supplies water to hundreds of thousands of people. Now, a proposal to inject compressed carbon dioxide deep underground, just miles from that aquifer, has sparked a serious debate about what happens when climate technology and drinking water security collide.

What Is Being Proposed — and Where

The EPA has published a public notice outlining its intent to issue permits to One Earth Sequestration for three Class VI injection wells in McLean County, Illinois. Class VI wells are a federally regulated category specifically designed for geologic carbon sequestration — the process of capturing carbon dioxide and pumping it underground for long-term storage. The EPA's own permitting authority under the Underground Injection Control program explicitly includes protecting underground sources of drinking water.

According to WGLT, environmental advocates have raised pointed concerns about how close the proposed injection sites are to freshwater resources. McLean County sits within the Mahomet Aquifer's footprint, and critics argue the proximity creates meaningful risk.

The Mahomet Aquifer: What's at Stake

This isn't an abstract concern. As The Daily Illini has reported, the Mahomet Aquifer is a primary drinking water source for communities across central Illinois. A CO₂ leak underground can dissolve into groundwater, making it acidic and potentially mobilizing heavy metals and other contaminants that would otherwise stay locked in surrounding rock.

The concern is widespread enough that it has moved legislators to act. Illinois passed a law in 2025 specifically banning carbon sequestration at the Mahomet Aquifer, a development covered by IPM Newsroom. Champaign County went further in early 2026, approving a temporary ban on carbon sequestration projects within its borders, citing water contamination fears, as IPM Newsroom reported. And as IPM Newsroom noted, protecting the aquifer from sequestration projects has remained a key priority for central Illinois lawmakers and advocates.

How the Federal Permitting Process Works

The Congressional Research Service explains that Class VI well permits are intended to include strict requirements — among them groundwater monitoring, mechanical integrity testing, financial assurance to cover long-term site care, and emergency response plans. These safeguards exist precisely because injected CO₂ plumes can migrate unpredictably and persist underground for centuries. The adequacy of those protections in any given permit depends entirely on how rigorously the EPA applies them.

The public comment period on the One Earth Sequestration permits closed September 23. The decision now rests with EPA Region 5.

A Decision with Long-Term Consequences

Carbon sequestration is one tool among many being deployed to address climate change. But the communities who depend on the Mahomet Aquifer will live with the consequences of this permitting decision for generations. The question isn't whether carbon storage has a role to play — it's whether the protections put in place before drilling begins are strong enough to safeguard the water people drink every day.

Residents, scientists, and local officials have already made their concerns known. The EPA Region 5 Regional Administrator now holds the authority — and the responsibility — to require that every available safeguard is in place before these wells are approved.

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