Carbon Storage

Carbon capture and storage (CCS) is a proven, science‑based technology that safely stores carbon dioxide (CO₂) deep underground in stable geologic formations. Illinois is one of the best‑studied and most suitable regions in the United States for long‑term CO₂ storage, thanks to decades of research by the Prairie Research Institute (PRI), the Illinois State Geological Survey (ISGS), and the Midwest Regional Carbon Initiative (MRCI).

This page explains why Illinois geology is ideal, how CO₂ is stored, and what scientific institutions have learned from more than 20 years of research.

The Midwest Regional Carbon Initiative (MRCI)

The Midwest Regional Carbon Initiative is a multi‑state collaboration working to accelerate the deployment of carbon capture, utilization, and storage (CCUS) across 20 states in the Midwest, Northeast, and Mid‑Atlantic. MRCI brings together:

  • The Midwest Regional Carbon Sequestration Partnership (MRCSP) led by Battelle

  • The Midwest Geological Sequestration Consortium (MGSC) led by ISGS

Together, these groups represent more than 20 years of CCUS research, field testing, and monitoring experience.

MRCI provides:

  • Technical resources

  • Public education materials

  • Infographics and fact sheets

  • Frequently asked questions

  • Regional geologic assessments

This work helps communities, policymakers, and industry understand how CCS works and why it is safe.

Why Illinois Geology Is Ideal for CO₂ Storage

Deep beneath the surface of Illinois lies the Illinois Basin, a deep geologic structure with enormous capacity for permanent CO₂ storage — estimated at 12–17 billion metric tons.

Two formations make this possible:

Mt. Simon Sandstone — The Storage Reservoir

A thick, porous sandstone layer more than a mile underground. Its pore spaces act like a natural sponge, allowing injected CO₂ to move into the formation and remain trapped under pressure. The Mt. Simon is one of the most studied and well‑characterized storage reservoirs in the United States.

Eau Claire Formation — The Confining Layer

A dense, impermeable sequence of shale and siltstone that sits directly above the Mt. Simon. This formation acts as a geologic seal, preventing upward movement of CO₂ and ensuring long‑term containment. Its integrity has been confirmed through decades of drilling, core analysis, and seismic imaging.

Groundwater Protection and the Mahomet Aquifer

Protecting groundwater is a core requirement of all carbon storage projects. The Mahomet Aquifer — the primary drinking water source for much of central Illinois — lies thousands of feet above the deep geologic formations used for CO₂ storage.

At the OES site:

  • The deepest Underground Source of Drinking Water (USDW) is the St. Peter Sandstone at ~2,217 feet, with TDS of 1,779 mg/L.

  • The proposed CO₂ injection zone — the Arkose interval of the Mt. Simon Sandstone — is located at approximately 6,262 feet.

  • This provides more than 4,000 feet of low‑permeability confining units between the injection zone and the deepest USDW, including the Mahomet Aquifer system.

These layers — including the Eau Claire Formation — have prevented fluid movement for millions of years. This natural geologic separation is the foundation of EPA’s Class VI safety framework and is verified through drilling, core analysis, seismic imaging, and long‑term monitoring.

Two Decades of Scientific Research in Illinois

For nearly 20 years, PRI and ISGS scientists have conducted:

  • Test well drilling

  • Core sampling

  • Seismic imaging

  • Injection tests

  • Long‑term monitoring

  • Pressure and plume modeling

These studies have repeatedly demonstrated that:

  • CO₂ can be stored safely

  • The Mt. Simon reservoir behaves predictably

  • The Eau Claire seal prevents migration

  • Monitoring technologies can track CO₂ with precision

PRI’s mission is to provide objective, science‑based information to support public understanding and policy decisions. Their 2021 CCUS report, published under Public Act 102‑0341, remains one of the most comprehensive assessments of carbon storage in the state.

How CO₂ Storage Works

  1. Capture CO₂ is captured at the source — in this case, from ethanol fermentation at One Earth Energy.

  2. Compression The CO₂ is compressed into a dense, supercritical fluid.

  3. Transport The CO₂ is transported through a pipeline to the injection site.

  4. Injection CO₂ is injected more than a mile underground into the Mt. Simon Sandstone.

  5. Storage & Monitoring The CO₂ remains trapped by:

    • Physical trapping in pore spaces

    • Residual trapping

    • Solubility trapping

    • Mineralization over time

    Monitoring wells, seismic surveys, and pressure sensors ensure long‑term safety.

Safety and Long‑Term Monitoring

Carbon storage projects in Illinois use multiple layers of protection:

  • Deep geologic confinement

  • Continuous pressure monitoring

  • Groundwater protection protocols

  • Seismic monitoring

  • Regulatory oversight by state and federal agencies

These systems work together to ensure CO₂ remains securely stored.

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