Resources

Area of Review (AoR)

• The Area of Review refers to the region surrounding a CO₂ injection site where underground sources of drinking water may be at risk and must be evaluated for potential impacts. 

Carbon Dioxide (CO₂)

• CO₂ is a colorless, odorless gas that occurs naturally and plays a vital role in Earth’s climate and ecosystems. However, when released in excessive amounts from industrial activities, it becomes a major contributor to climate change. 

Brine

• Also known as saline water, brine is found in deep geologic formations and is commonly associated with sites where carbon dioxide (CO₂) is stored through the Carbon Capture and Sequestration (CCS) process. 

Carbon Capture and Sequestration (CCS)

• CCS is a process that captures carbon dioxide (CO₂) emissions from human-made sources—such as power plants or industrial facilities—and permanently stores the CO₂ deep underground to prevent its release into the atmosphere. 

Carbonic Acid

• Carbonic acid forms when carbon dioxide (CO₂) dissolves in water. In the context of Carbon Capture and Sequestration (CCS), carbonic acid can weaken cement well casings, making them more prone to cracking or degradation. This can increase the risk of fluid leakage through the well structure, potentially allowing CO₂ or other substances to migrate into underground sources of drinking water or other unintended areas, both horizontally and vertically. 

Class VI Well

• Class VI well is a type of injection well permitted by the U.S. Environmental Protection Agency (EPA) specifically for the long-term storage of carbon dioxide (CO₂) as part of Carbon Capture and Sequestration (CCS). These wells are designed to protect underground sources of drinking water. 

CO₂ Toxicity

• Carbon dioxide (CO₂) is a normal part of Earth’s atmosphere, but in high concentrations, it can be dangerous to humans and animals. CO₂ is heavier than oxygen and can displace it near the ground, reducing available oxygen for breathing. According to the National Institutes of Health (NIH), low levels of CO₂ are generally harmless. However, exposure to concentrations above 5% can lead to health issues by increasing blood acidity and causing respiratory problems. At higher levels (above 10%), CO₂ can impair the nervous system, slowing breathing and heart rate, and may lead to seizures, unconsciousness, or death. Concentrations above 30% can cause loss of consciousness within seconds. 

Department of Energy (DOE)

• Since 1997, the DOE has funded research and development of Carbon Capture and Sequestration (CCS) technology to reduce greenhouse gas emissions and support cleaner energy production.

Enhanced Oil Recovery (EOR)

• EOR refers to the process of injecting carbon dioxide (CO₂) into existing oil reservoirs to increase oil production by reducing the viscosity of the oil and improving its flow.

Eau Claire Formation

• The Eau Claire Formation is a geologic formation within the Illinois Basin. It serves as a caprock, sealing carbon dioxide (CO₂) within the underlying Mt. Simon Sandstone formation, which is used for CO₂ sequestration.

Injection Well (Class VI)

• A Class VI injection well is a specialized well used to inject carbon dioxide (CO₂) deep underground for long-term storage. It is a critical component of the Carbon Capture and Sequestration (CCS) process, designed to prevent CO₂ from entering the atmosphere and contributing to climate change. 

Monitoring Well

• Monitoring wells play a crucial role in ensuring the safety and effectiveness of Carbon Capture and Sequestration (CCS) projects. They are designed to detect early signs of potential issues, such as CO₂ leaks or unexpected underground movement, before problems become serious. Unlike injection wells, monitoring wells are strategically placed to observe subsurface pressure, track the behavior of injected CO₂, and detect any migration into surrounding areas.

Mt. Simon Formation

• Mt. Simon Formation is a deep sandstone geologic formation found across several Midwestern states. It is commonly used for carbon dioxide (CO₂) sequestration due to its high porosity and permeability, making it well-suited to hold large volumes of injected CO₂. 

PHMSA (Pipeline and Hazardous Materials Safety Administration)

• PHMSA is an agency within the U.S. Department of Transportation responsible for overseeing the safe transportation of energy and hazardous materials, including the regulation of pipelines used in carbon dioxide (CO₂) transport for Carbon Capture and Sequestration (CCS) projects. 

Pickling Well (or Pickling Liquor Well)

• In steel production, pickling is a process used to clean the surface of steel by removing rust, scale, and other impurities. This is done using a strong acid solution known as pickling liquor. After use, the pickling liquor becomes a hazardous waste containing residual acid and dissolved metals. Due to its high corrosivity, one method of safe disposal is deep well injection—where the waste liquid is pumped deep underground into designated rock formations for long-term containment. 

Plugged Well 

• In the context of deep well injection, a plugged well is one that has been permanently sealed and closed to prevent any further fluid injection. 

Plume 

• In Carbon Capture and Sequestration (CCS), a plume refers to the underground zone where injected carbon dioxide (CO₂) migrates and spreads within the storage formation, such as a deep saline aquifer or sandstone layer. Monitoring the plume helps ensure that the CO₂ remains safely contained over time. 

Pore Space and Pore Space Ownership

• Pore space refers to the tiny voids or gaps between particles of soil, sand, or rock, which can store fluids such as water, oil, or injected carbon dioxide (CO₂). In the context of Carbon Capture and Sequestration (CCS), these spaces are critical for holding CO₂ deep underground. In Illinois, the legal ownership of pore space belongs to the surface landowner, meaning that anyone wishing to use it for CO₂ sequestration must obtain the landowner’s permission. 

Supercritical State

• Supercritical state refers to a condition in which carbon dioxide (CO₂) is subjected to temperatures and pressures above its critical point, causing it to exhibit properties of both a gas and a liquid. In this state, CO₂ is dense like a liquid but flows like a gas, making it ideal for injection and storage in Carbon Capture and Sequestration (CCS) projects. However, this state also allows CO₂ to migrate both vertically and horizontally through subsurface formations, which can lead to unanticipated movement and potential leakage risks. 

Safe Setbacks

• Safe setbacks refer to the minimum required distance between carbon dioxide (CO₂) pipelines and nearby structures—such as homes, schools, or churches—to protect public safety in case of a pipeline leak or rupture. These distances are intended to reduce the risk of harm to people by keeping populated areas far enough from potential hazards. Ongoing research is helping to determine appropriate setback standards. 

Test Well

• In Carbon Capture and Sequestration (CCS) projects, a test well is drilled to collect detailed geologic data from deep underground formations. This data—such as rock type, porosity, permeability, pressure, and fluid composition—is essential for assessing whether a site is suitable and safe for long-term CO₂ sequestration.

Underground Injection Control (UIC)

• UIC stands for Underground Injection Control, a program managed by the U.S. Environmental Protection Agency (EPA) to protect underground sources of drinking water. In the context of Carbon Capture and Sequestration (CCS), the UIC program regulates the injection of carbon dioxide (CO₂) to ensure that it does not endanger groundwater. Class VI wells, specifically designed for CO₂ sequestration, fall under this program. 

45Q Tax Credit

• The 45Q tax credit, named after Section 45Q of the U.S. Tax Code, is a federal incentive designed to encourage the deployment of Carbon Capture and Sequestration (CCS) technologies. It provides a per-ton credit for carbon dioxide (CO₂) that is either permanently sequestered underground or used in qualified applications, such as enhanced oil recovery. The credit aims to reduce CO₂ emissions by increasing the profitability of the CCS process.