Thursday, February 12
Class VI UIC Session
8:30 AM – 10:00 AM
Injecting supercritical carbon dioxide increases pressure within the injection zone. If an improperly plugged borehole that penetrates the confining zone is near the injection site, an increase in pressure could induce formation fluid to flow upward through that borehole from the injection zone. Upward flow of fluid in the borehole could carry dissolved constituents, potentially endangering underground drinking water sources. The pressure at which this would occur is called the threshold pressure, a key factor in delineating the Area of Review for a Class VI Permit Application.
The EPA Class VI Guidance approach to calculate threshold pressure is conceptually flawed and has proven difficult to implement. The approach in the guidance does not consider typical project time scales and ignores important physical processes. EPA is currently reviewing the details of this approach and considering revisions to the guidance.
In this work, SCS can identify the geologic conditions under which the equilibrium approach grossly underestimates the critical pressure, as well as the operational details that affect pressure buildup in the injection zone over time. SCS can identify conditions under which the equilibrium approach is not appropriate for evaluating the critical pressure, and we establish a kinetic framework for its evaluation.
This kinetic approach, using time-based single-phase computational modeling, is less complicated than the multiphase flow modeling already required by the Class VI regulations and is equally capable of calibration, monitoring, testing, and reevaluation during the operational phase of a Class VI project.
Tara Gross, Project Advisor, SCS Engineers
Ms. Gross is a Project Advisor on the Deep Well Initiative team. She is a geologist with over 20 years of experience in oil and gas (O&G), land-use permitting, subsurface mapping, and compliance. Project experience includes support developing Class I, II, and VI Underground Injection Control (UIC) applications, oil production plans, midstream O&G pipeline permitting, surface and groundwater compliance, subsidence evaluation, critical minerals, carbon capture, utilization, and storage (CCUS), produced water, seismicity, lithium extraction, environmental studies, Department of Energy grant programs such as CarbonSAFE and CarbonBASE, and CEQA analysis.
Join Tara at the Class VI UIC Session
February 12, 2026
8:30 am – 10:00 am
Tara will present Advancing Class VI Permitting: A Lessons Learned Approach to Critical Pressure Modeling and Impact Analysis at 9:30 am.
Class VI permitting requires robust computational models to demonstrate containment and integrity. A recent development of a Class VI permit application by SCS Engineers revealed restrictions on the ability of the EPA-recommended Method 2 for Critical Pressure (CP) calculations, underscoring the need for a practical, structured approach to Critical Pressure (CP) modeling.
CP modeling is important to the viability of proposed carbon sequestration projects because it determines the size of the Area of Review and the scope and cost of Corrective Action. This blog presents a lessons-learned framework that balances rigor with simplicity and introduces an innovative concept for analyzing the impacts of emerging risks.
The proposed methodology is built on five key elements:
Applying this framework has shown measurable benefits: improved clarity in model documentation, reduced regulatory review time, and greater confidence in outputs. By emphasizing simplicity, defensibility, and sensitivity, the approach mitigates common pitfalls in current review processes and fosters stronger communication between operators and regulators. Ultimately, this methodology provides a template for consistent, efficient Class VI permitting and lays the foundation for future advancements in risk assessment and regulatory alignment.
To learn more, please reach out to our co-authors at SCS Engineers.
Meet the Co-Authors:
Kacey Garber has professional experience as a geologist and hydrogeologist. Her expertise includes Class VI Underground Injection Control (UIC) permitting for CO2 storage projects, Class I UIC permitting for liquid waste disposal, and environmental permitting and groundwater studies for landfills and coal combustion residual disposal sites.
Tara Gross is a project advisor providing strategic insight and technical oversight for key initiatives, including critical minerals, oil and gas, carbon capture, utilization, storage, underground injection control Class I, II, and VI well permitting, lithium extraction, and Department of Energy grant programs.
Dr. Charles Hostetler is an experienced project manager and subject matter expert in geochemistry, hydrogeology, risk assessment, environmental regulations and permitting, and natural resources assessment. He serves clients in the coal combustion residue, solid waste, real estate, manufacturing, mining, nuclear waste, and governmental sectors.
Additional Resources for Critical Pressure Modeling and a New Standard for Class VI Permits:
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