Results
A Play-Based Exploration of CCS in the Illinois Basin
View this StoryMap to learn more about the results.
Developing Suitability Maps
It can be difficult to conceptualize suitability based on maps showing raw data. To address this, we use measures such as distance (e.g., miles from a fault) and density (e.g., population per square mile) to define suitability criteria for each play element based on research, regulations, or best practices. These criteria are used for screening purposes and do not represent hard siting thresholds.
The suitability maps display a continuum of suitability for carbon storage development based on available information. Dark blue areas are classified as most suitable and represent locations with well-supported, highly favorable conditions for near-term study. Less suitable areas are shown in yellow and present conditions that may hinder development or increase technical, environmental, or social challenges, reducing the likelihood of successful projects. Areas shown in white lack sufficient data for evaluation. In all cases, suitability classifications may change as new data become available.
Suitability Map Results
Below is one example of a suitability map with community water supply wells as the play element. For this project, many suitability maps were made for each associated play element.
Societal Suitability: Community Water Supply Wells
Illinois has abundant groundwater resources that provide water for public, agricultural, and commercial use. These groundwater resources are accessed by community water supply wells. A community water supply well serves at least 15 service connections used by residents or regularly serves at least 25 residents for at least 60 days per year.
Areas located farther from community water supply wells are considered more suitable for carbon storage projects, as greater separation helps minimize potential conflicts with drinking water resources and supports public confidence in project siting decisions. Areas closer to community water supply wells are classified as less suitable because additional regulatory review, monitoring, and stakeholder engagement may be required. As with other societal elements, these rankings reflect screening-level considerations and may evolve as additional hydrogeologic and community information becomes available.
Composite Suitability Map Results
Below is an example of a composite map for the Mt. Simon Sandstone storage complex. For this project, the St. Peter Sandstone was also evaluated as a storage complex and mapped.
Mt. Simon Sandstone
The Mt. Simon Sandstone Composite Play Map integrates subsurface, surface, and societal suitability maps to delineate a broad suitable to most suitable fairway across much of Illinois, particularly in the southern two-thirds of the state. Subsurface suitability decreases northward, primarily due to declining formation-water salinity and, secondarily, reduced depth. Additional reductions occur in southwestern Illinois where the Mt. Simon thins or is absent due to non-deposition or erosion, and in southeastern and southernmost Illinois adjacent to known faults. Within the otherwise favorable fairway, localized areas of lower suitability are associated with a high density of legacy wellbores penetrating the confining unit or the presence of saline springs.
Surface constraints reduce suitability in wetlands, karst terrains, and mined areas, while societal considerations indicate generally favorable conditions statewide, with reduced suitability over the Mahomet Aquifer Sole Source Aquifer (where carbon capture and storage siting is restricted under Illinois Public Act 104-0119) and areas of uncertainty within city limits where additional public-acceptance information is needed.
Conclusion
This project demonstrates that a PBE framework provides a robust, transparent, and scalable approach for evaluating and communicating geologic carbon storage potential in Illinois while explicitly accounting for basin-scale stratigraphic variability, legacy subsurface use, and surface and societal constraints. By synthesizing subsurface reservoir and seal characteristics with surface and policy-related screening criteria, the composite play maps move beyond single-formation or project-specific evaluations and instead highlight regional fairways where multiple lines of evidence converge to support suitable locations for carbon storage.
The composite play maps should be viewed not as final siting determinations, but as a screening-level decision-support tool that narrows the search space, clarifies dominant risk drivers, and helps prioritize areas for more detailed site-specific characterization, regulatory engagement, and stakeholder outreach.