Michelle R. Plampin Eric A. Morrissey Stefan Finsterle Steven T. Anderson Ashton M. Wiens 20250916 groundwater model Reston, VA, USA U.S. Geological Survey https://doi.org/10.5066/P14PBU3J Michelle R. Plampin Steven T. Anderson Stefan Finsterle Ashton M. Wiens 2025 Journal article Lausanne, Switzerland Frontiers https://doi.org/10.3389/feart.2025.1639952 We developed a methodology to estimate maximum CO2 injection rates in subsurface layers across wide geographic areas using inverse modeling-based optimization techniques. We first defined geographic areas where groundwater was too saline to meet the standard for drinking water and where sufficient confining units existed above and below the injection layers. We then assumed concurrent CO2 injection into a system of wells on a consistent 25 km x 25 km spacing across the entire modeled area. Taking advantage of symmetry, we modeled each 25 km x 25 km injection area using a mesh shaped as a right-angle prism measuring 12.5 km by 12.5 km on the two orthogonal sides of the triangle. The domain therefore represents one eighth of the injection volume. This domain was divided into 10 rows of grid blocks of equal thickness. In the lateral directions, grid blocks measured 125 m by 125 m. The mesh contained 10 rows of grid blocks, each of which was set to a thickness equal to one-tenth of the layer thickness at the hypothetical injection area being modeled. Fifty years of CO2 injection were simulated into one of the bottom corners that formed a 45-degree angle in the plan view, and in some simulations water extraction was simulated from the other triangular corner. Pressure buildup was monitored at the CO2 injection location as well as the grid block at the corner of the domain that takes the shape of a right angle in the plan view (i.e., the corner grid block that takes the shape of a square prism). The injection rate was automatically adjusted to meet a maximum pressure buildup to 80% of the fracturing pressure, estimated as the least principal stress, at the injection location. A secondary constraint of 1 bar maximum pressure increase at the far-field boundary grid block after 50 years of injection was applied. We demonstrated this method on four stratigraphic layers in the Illinois Basin, which is a well-known CO2 injection target with a large estimated CO2 storage capacity. CO2 storage could be optimized by extracting brine from the injection layer and injecting it into a different one, which was the reason for implementing pressure increase mitigation via brine extraction in some cases. We also tested the effects of different brine extraction locations, either from the bottom grid cell only or from the entire thickness of the layer. Finally, we investigated the effects of geologic heterogeneity and anisotropy by running optimization simulations in which the porous media porosity and permeability were calculated as functions of depth. This groundwater model was designed to estimate the maximum rate at which CO2 could be injected into geologic formations. The modeling methodology was demonstrated on four subsurface layers in the Illinois Basin, including the Mt. Simon sandstone, where CO2 injection is ongoing. The models, along with pre- and post-processing tools, will run successfully only if the original directory structure is correctly restored. Instructions for reconstructing the original directory structure and running the models included in this data release and described in the journal article can be found in the readme.txt ASCII file which can be downloaded as part of this data release. This zip file contains model input and output files from simulations conducted using the TOUGH family of numerical modeling tools from Lawrence Berkeley National Laboratory. The user must obtain the iTOUGH2 modeling software from https://tough.lbl.gov/software/itough2-software/. More details on software acquisition, installation, and use are given in the file readme.txt. The zip file also contains data available in ESRI shapefile format. The user must have software capable of uncompressing the WinZip file and displaying the shapefile. In lieu of ArcView or ArcGIS, the user may utilize another GIS application package capable of importing the data. One or more files contain data available in comma separated value (.csv) file format. The user must have software capable of opening and viewing a .csv file. 2025 publication date Complete None planned -90.8020 -84.4347 41.3639 37.3283 ISO 19115 Topic Category geoscientificInformation USGS Thesaurus Groundwater None - Free Keywords Groundwater Model CO2 Sequestration iTOUGH2 PEST USGS Metadata Identifier USGS:67f010a9d4be02766d636812 Geographic Information Names System Illinois Indiana Kentucky Missouri Illinois Basin None None USGS Thesaurus Phanerozoic Cenozoic Quaternary Holocene Devonian Silurian Ordovician Cambrian None None Eric A. Morrissey U.S. Geological Survey Information Technology Specialist (Internet) mailing and physical

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Reston VA 20192 USA 703-648-6409 emorriss@usgs.gov The simulations estimated maximum injection rates into various subsurface layers throughout the Illinois Basin. These estimates were based on many assumptions and simplifications, such as homogeneous rock properties (i.e., porosity, permeability, etc.) within each of the 4 potential injection layers, a hydrostatic initial pressure gradient, and a constant linear temperature gradient. Estimate accuracy could potentially be improved by defining any of these elements in more detail. No formal logical accuracy tests were conducted. Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record and the associated journal article (https://doi.org/10.3389/feart.2025.1639952) for additional details. No formal positional accuracy tests were conducted. No formal positional accuracy tests were conducted. The processes used to develop and apply the modeling-based optimization algorithm are fully described in the journal article (https://doi.org/10.3389/feart.2025.1639952). 2021 1.0E-8 1.0E-8 Decimal degrees North American Datum 1983 GRS_1980 6378137.0 298.257222101 plampin2025_FES.zip Model archive, containing simulation input and output files, georeferencing information, and instructions for use. Producer defined georef Folder for georeferencing information Producer defined GIS shape files and a readme file describing them input Folder containing model input files Producer defined Within the model folder are subdirectories for each simulation described in the journal article, each of which contains ASCII text files for running the simulations, and a usgs.model.reference file describing the model output Folder containing model output files Producer defined Within the output folder are subdirectories for each simulation described in the journal article, each of which contains ASCII text files produced from running the simulations source Folder for the numerical modeling source code Producer defined A readme text file containing information about the numerical modeling source code modelgeoref.txt Text file containing geographical coordinates that define a bounding rectangle surrounding the area that was considered in the study Producer defined North American Datum 1983 NAD83(CORS96), NAD_1983_Albers Equal Area Conic readme.txt Text file describing the model archive Producer defined Text The data are described in the accompanying journal article. Plampin, M.R., Anderson, S.T., Finsterle, S. and Wiens, A.M., 2025, Estimation of dynamic geologic CO2 storage capacity in the Illinois Basin, including effects of brine extraction, anisotropy, and hydrogeologic heterogeneity, Frontiers in Earth Sciences https://doi.org/10.3389/feart.2025.1639952 U.S. Geological Survey ScienceBase mailing and physical

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Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. readme.txt Version 1.0 ASCII text file ASCII text file describing the model data release, including descriptions of the model input and output files and instructions on how to run the models contained in the data release. 0.018 https://doi.org/10.5066/P14PBU3J None This zip file contains model input and output files from simulations conducted using the TOUGH family of numerical modeling tools from Lawrence Berkeley National Laboratory. The user must obtain the iTOUGH2 modeling software from http://esd1.lbl.gov/research/projects/tough/. More details on software acquisition, installation, and use are given in the file readme.txt. The zip file also contains data available in ESRI shapefile format. The user must have software capable of uncompressing the WinZip file and displaying the shapefile. In lieu of ArcView or ArcGIS, the user may utilize another GIS application package capable of importing the data. A free data viewer, ArcExplorer, capable of displaying the data is available from ESRI at www.esri.com 20250924 Eric A. Morrissey U.S. Geological Survey Info Tech Spec (Internet) mailing and physical

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Reston VA 20192 USA 703-648-6409 emorriss@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998