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"We urge local governments who rely on the Mahomet Aquifer for their water supply and the General Assembly to adopt a ban on injecting and storing CO2 under the Mahomet Aquifer. This is the only way we can be certain that the Mahomet will remain a viable source of fresh water for future generations."

-Coalition to Stop CO2 Pipelines

Why a ban?
The Mahomet Aquifer is one of Illinois' most important groundwater resources. It provides hundreds of millions of gallons of water every day to nearly 1 million people in East Central Illinois for residential, industrial, and agricultural uses.  In 2015 it was designated by the U.S. EPA as a sole-source aquifer. The Safe Drinking Water Act gives EPA authority to designate all or part of an aquifer as a "sole source" if contamination of the aquifer would create a significant hazard to public health and there are no physically available or economically feasible alternative sources of drinking water to serve the population that relies on the aquifer.

Why is CO2 a threat to the Aquifer?
The Illinois Basin has been determined by scientists to be one of the best locations for geologic sequestration. Fueled by the IRS tax credit known as 45Q, private companies are planning to capture, transport, and store their CO2 waste in Illinois. But there are NO guarantees that highly pressurized carbon stored underground won't leak into aquifers, threatening water supplies. This includes the Mahomet Aquifer. If it does leak, CO2 will form carbonic acid that can leach heavy metals from surrounding sand and rock that include:  that include: arsenic, antimony, cadmium, chromium, copper, lead, selenium and many more. People that consume high levels of heavy metals risk acute and chronic toxicity, liver, kidney, and intestinal damage, anemia, and cancer.

In a study published in Environmental Science & Technology, authors Mark Little and Robert B. Jackson studied samples of sand and rock taken from four freshwater aquifers located around the country that overlie potential carbon capture and sequestration (CCS) sites. One of these was the Mahomet Aquifer.

"The CO2 caused concentrations of manganese, cobalt, nickel, and iron to increase by more than 100 times the original levels (or 2 orders of magnitude), and potentially dangerous uranium and barium increased throughout the entire experiment in some samples. In general, they found that iron and manganese concentrations increased within 100 days. The response of other potentially harmful metals was more varied."

-Catherine M. Cooney. Study Charts How Underground CO2 Can Leach Metals into Water. Reuters. 2011.


Image Source: Figure 1. Mechanisms and impacts of CO2 leakage from geological sequestration sites. Creative Commons license.

Potential Pathways for Leakage
CO2 can leak along injection or monitoring wells, and through existing faults and fractures of the cap rock or those that could be created by natural or induced seismic activity. Abandoned wells are also recognized as providing conduits for stored CO2 to move into underground drinking water sources. Leaky wells could cause serious environmental harm and cancel out purported climate benefits of CCS.

People's Gas Leak. In 2016, People's Gas reported the corrosion and leak of  an injection well in the Manlove Gas Field under the Mahomet Aquifer near Fisher, Illinois. This leak contaminated residents’ water with methane gas and required the Illinois Attorney General to file a complaint that ultimately led to a consent order. While this order requires People's Gas to supply bottled water to affected residents, it did not include funding for connecting to a new water supply.  In 2021, Senator Chapin Rose secured $3.8 million in state funding for the first phase of a project to extend Sangamon Valley Water Authority lines to provide the clean water source for families with contaminated water. In 2022, the Champaign County Board allocated $500,000 to complete the design work. Eight years later, those same residents are still waiting to be connected to a new supply of water.

Natural Seismicity.  Illinois is no stranger to earthquakes. Three active seismic zones, the Ste. Genevieve, New Madrid and the Wabash Valley, traverse the central and southern part of the state. According to the USGS, 15 earthquakes occurred throughout the state from January 2023 through June 2024. These ranged from 1.7 M to 3.6 M.

Induced Seismicity. Injection of CO2 also can induce earthquakes large enough to damage the wellbore or break the caprock. We know injecting produced water from oil and gas production far below groundwater or aquifers causes earthquakes:

Scientists have expressed concern that injecting larger volumes of CO2, at higher pressures and for longer duration associated with CCS has an even higher probability of inducing earthquakes. But, U.S. EPA Class VI permitting does not address induced earthquakes.

Abandoned Wells. The Illinois Department of Natural Resources says they believe there are more than 32,000 oil & gas wells in Illinois, but acknowledges they don’t know where all of them are. According to the IDNR, “orphaned" or unplugged wells total over 4,000.

  • According to the 2018 Mahomet Aquifer Task Force Report commissioned by the General Assembly, "Prospecting for oil and gas with deep wells has occurred across the Mahomet Aquifer region, although the only economically significant pools of oil occur just off the aquifer in Piatt, Macon, and DeWitt Counties". Unfortunately, the abandonment status is unknown for many of the deep wells drilled prior to 1939 and for many wells drilled afterward that have incomplete records.
  • Illinois has had oil and gas well regulations since 1939 that include proper cementing and abandonment procedures. But research has shown that CO2 can leak from wells that are properly plugged. This occurs when carbonic acid forms due to dissolution of CO2 into brines and then corrodes the cement.

Isn't the Mahomet Aquifer protected by new legislation?
The recent adoption of SB 1289, the Safety and Aid for the Environment in Carbon Capture and Sequestration Act, helps address regulatory gaps that affect the health and safety of Illinois residents. But this bill does not include hoped-for bans of geological sequestration that could contaminate the Mahomet Aquifer. Although this bill is expected to be signed by Governor Pritzker in July, it will need to undergo rule-making by a variety of agencies. This process can take between 12 and 18 months.

But companies like Archer Daniels Midland and Heartland Greenway Carbon Storage have been pursing geological sequestration, and the U.S. EPA is about ready to begin issuing draft permits for four proposals that would inject carbon dioxide through or store it under the Mahomet Aquifer and its recharge areas.

Three of the four projects under review by the U.S. EPA would inject CO2 through and store it under the Mahomet Aquifer or a recharge. The fourth would inject CO2 near and store it under the aquifer. Graphic provided by Eco-Justice Collaborative, 2024..

Join our campaign!
We need local governments who rely on the Mahomet Aquifer to work for a legislative ban. In the meantime, they can use moratoriums or a local ban to prevent CO2 injection and storage in the Mahomet Aquifer and its recharge areas.  Here is how you can help. Local governments listen to their constituents. Will you meet with your government officials and ask them to support a legislative ban, and to adopt a moratorium until such time as a Mahomet Aquifer ban is in place?  Contact us here, and we will work with you.

Speak out at upcoming EPA hearings!
We need you to tell the U.S. EPA that allowing CO2 to be injected and stored under this aquifer is risky, and NOT consistent with its sole-source designation.  We will assist by providing all you need to testify.  If you are not yet on our mailing list, you can contact us here for more information and updates.

One Earth Sequestration, LLC (Ford and McLean Counties)
Draft permit 9-4-24; Public comment 10-19-24; Final permit 1-17-25

  • 90 MMT CO2 would be stored through life of this project
  • Three wells (One Earth says they will reduce the project to two wells “for now”, but their application shows three, which is consistent with their intent to add third party users)
  • Would inject CO2 through and store it under recharge areas of the Mahomet Aquifer
  • Must return to McLean County Board for approval

ADM Marora (Macon County)
Draft permit 1-14-25; Public comment 2-23-25; Final permit 5-24-25

  • 39.60 MMT CO2 would be stored over the life of this project
  • Three wells
  • Would inject adjacent to the Mahomet Aquifer, and store CO2 under it

Heartland Greenway Carbon Storage, Vervain (McLean and Logan Counties)
Draft permit 2-14-25; Public comment 3-21-25; Final permit 6-29-25

  • 62.50 MMT CO2 would be stored over the life of this project
  • Three wells
  • Would inject CO2 through and store it under the Mahomet Aquifer

Heartland Greenway Carbon Storage, Compass (DeWitt County)
Draft permit 2-15-25; Public comment 3-17-25; Final permit 6-15-25

  • Application is not posted on Region V's website
  • Proposed storage is not yet known
  • Two wells
  • Would inject CO2 through and store it under the Mahomet Aquifer

Banner Photo: Figure 5: Composite potentiometric surface map of the Mahomet aquifer based on measurements from 1990 to 2009. An Introductory Guide to the Mahomet Aquifer and Natural Gas Storage in East-Central Illinois. Published 2018