Class VI - Wells used for Geologic Sequestration of Carbon Dioxide
On this page:
- What is a Class VI well?
- Protecting drinking water resources
- Public participation and Community Engagement
- Lifecycle of a Class VI project
- Class VI permitting process
- Current Class VI projects at EPA
- Permit application and permitting tools for Class VI
- Geologic Sequestration Data Tool
- Class VI guidance documents and reports to Congress
- Regulatory and statutory authorities relevant to carbon capture and storage projects
- Contact us
- Other resources for Class VI
What is a Class VI well?
Class VI wells are used to inject carbon dioxide (CO2) into deep rock formations. This long-term underground storage is called geologic sequestration (GS). Geologic sequestration, as part of carbon capture and storage (CCS), is a technology that can be used to reduce CO2 emissions to the atmosphere.
Possible sources of CO2 for GS include CO2 captured from point source emissions, such as from an industrial facility (e.g., steel and cement production) or energy production (e.g., ethanol, hydrogen production, or power plants), as well as CO2 captured directly from the atmosphere.
Protecting drinking water resources
EPA is authorized by the Safe Drinking Water Act (SDWA) to develop requirements and provisions for the Underground Injection Control (UIC) Program. This program regulates the injection of fluids (such as water, wastewater, brines from oil and gas production, and CO2) into the subsurface for the purposes of storage or disposal. The main goal of the UIC Program is the protection of Underground Sources of Drinking Water (or USDWs). USDWs are aquifers or parts of aquifers that supply a public water system or contain a sufficient quantity of groundwater to supply a public water system now or in the future. Class VI wells are one of six classes of injection wells regulated under the UIC Program.
The Class VI well requirements are designed to protect public health and USDWs from the unique nature of CO2 injection for GS, including the:
- Relative buoyancy of CO2
- Subsurface mobility
- Corrosivity in the presence of water
- Large injection volumes
Requirements include:
- Site characterization requirements to ensure the geology in the project area can receive and contain the CO2 within the zone where it will be injected, including that the area is free of faults and fractures and that induced seismicity is not a concern.
- Requirements to predict the extent of the injected CO2 plume and associated pressure front for the project using computational modeling, and to identify and address any deficiencies of existing wells within the Area of Review through corrective action. The Area of Review includes the area where the injected plume and its associated pressure front may impact pore fluids.
- Well construction requirements to ensure the Class VI injection well and in-zone monitoring wells are constructed in a manner that will prevent any CO2 or formation fluids from leaking outside of the injection zone. Class VI injection wells and in-zone monitoring wells are designed for the life of the project.
- Owners or operators must demonstrate that the well materials are corrosion resistant and compatible with the conditions and fluids to which they may be exposed.
- Appropriate construction materials depend upon site specific conditions including the CO2 stream, the formation fluids, and formation temperatures and pressures.
- Laboratory testing and modeling based upon site specific conditions may be used to determine appropriate well construction plans.
- Testing and monitoring requirements to monitor the integrity of the injection well, the integrity of other wells such as monitoring wells, groundwater quality, and the movement of the CO2 plume and pressure front. These requirements are in place throughout the life of the project, including after CO2 injection has ended, until the permitting authority determines no additional monitoring is needed to ensure that the GS project does not pose and endangerment to USDWs.
- Corrosion monitoring is required from the commencement of CO2 injection through site closure
- Operating requirements to ensure the injection activity is appropriate to the well’s construction and geologic characteristics so that it will not endanger USDWs or human health.
- Requirements to plug the injection well in a manner that will not allow fluid movement that endangers USDWs.
- Requirements for the operator to establish and maintain financial instruments sufficient to cover the cost of corrective action, plugging the injection well, post-injection site care, and emergency and remedial response for the GS project (i.e., financial responsibility).
- Requirements to develop and maintain a site-specific emergency and remedial response plan.
- Requirements for the Class VI well owner or operator to report all testing and monitoring results to the permitting authority to ensure the project is operating in compliance with all permit and regulatory requirements.
EPA developed a brochure that offers more information on how UIC Class VI regulations protect USDWs throughout project planning, construction, injection, and site closure. Please click the link below to download the brochure.
Class VI Risk Mitigation Brochure (pdf)
The brochure includes a diagram showing several aspects of risk mitigation that can also be downloaded separately at the link below.
Class VI Risk Mitigation Graphic (pdf)
The UIC Program may be directly implemented by the U.S. Environmental Protection Agency (EPA) regional offices or by states, territories, or tribes with EPA-approved primary enforcement authority. Activities performed by the UIC Program include maintaining a well inventory, reviewing permit applications and issuing permits for injection wells, performing inspections, and ensuring compliance with permit requirements. If operators manage wells in a way that does not meet the applicable UIC requirements, the approved agency alerts operators to issues and may assist operators in returning the wells to compliance or take enforcement action.
Review EPA's Final Rule for Class VI Wells.
Public participation and Community Engagement
Public participation and transparency are important components of EPA’s UIC regulatory framework. EPA follows the requirements to provide opportunities for participation to communities that may be affected by permitting decisions and encourages Class VI permit applicants to enhance this via community engagement.
When EPA prepares a draft permit for a new Class VI GS project, it is published for public review with a minimum of 30 days for public comment. Communities are notified through newspaper and other media announcements and mailing lists. There are several opportunities for public participation, including submitting comments on the draft permits, requesting and attending public hearings, and filing appeals of final permitting decisions to the Environmental Appeals Board.
In addition to EPA's public participation process around draft permits, EPA recommends applicants engage the local community surrounding their proposed project before applying. Effective community engagement can help establish lines of communication between project developers and local stakeholders, foster inclusion, and (re)build the trust that is essential to the long-term success of a Class VI GS project. Prospective Class VI permit applicants are encouraged to consider the potential disproportionate and cumulative impacts posed to communities near the project area and local stakeholders. Applicants should engage stakeholders early in the permitting process to learn about each community’s specific concerns, especially before making any requests of that community. Effective community engagement approaches are tailored to the needs of the community and may include developing outreach materials in multiple languages and/or flexible meeting times to accommodate work schedules. Community engagement is informed via research to understand community needs, such as participating at community events to learn about local stakeholders’ concerns.
For UIC regional information, please see UIC Where You Live.
Lifecycle of a Class VI project
Each Class VI well requires a permit to construct and operate the well through site closure. In states, territories, or tribes with EPA-approved Primary Enforcement Authority (primacy), the state, territory, or tribal agency issues the permit. Otherwise, EPA has direct implementation authority for Class VI, and EPA regional offices evaluate permit applications and issue permitting decisions.
The Class VI permitting process includes the following phases:
- Pre-permitting phase: The prospective owner or operator notifies the permitting authority of their intent to prepare a Class VI permit application and is encouraged to meet with the permitting authority to discuss the permitting process. EPA recommends applicants engage the local community surrounding their proposed project before applying. Effective community engagement can help establish lines of communication between project developers and local stakeholders, foster inclusion, and (re)build the trust that is essential to the long-term success of a Class VI GS project. Prospective Class VI permit applicants are encouraged to consider the potential disproportionate and cumulative impacts posed to communities near the project area and local stakeholders. Applicants should engage stakeholders early in the permitting process to learn about each community’s specific concerns, especially before making any requests of that community.
See resources for applicants developing Class VI permit applications.
- Pre-construction phase: After the prospective owner or operator submits a Class VI permit application, the permitting authority will perform a thorough review of every component of the detailed permit application. If appropriate, the permitting authority will issue a draft Class VI permit to construct or convert the injection well for the public to review. The review process includes a minimum 30-day public comment period, and public comments are evaluated before a final permit decision is made.
- Pre-operation phase: If a permit is issued, the Class VI well operator constructs the well, performs pre-operational testing, and submits additional information before they are authorized to inject CO2. This additional information includes the results of required pre-operational testing, updated information about site geology; the final area of review; any needed amendments to the Project Plans; and information about the construction and testing of the well. If the additional information collected necessitates changes to the permitting conditions, this phase leads to a major modification of the permit with an additional public comment period before authorization to inject. If not, this phase ends when the permitting authority issues the Class VI permit holder authorization to inject CO2 into the well.
- Injection phase: Class VI well owners or operators begin operation of the injection well. Owners or operators are responsible for performing testing and monitoring, reevaluating the Area of Review described in the Class VI permit and Project Plans, and submitting the results to the permitting authority. The permitting authority reviews testing and monitoring results, and these results are made available to the public.
- Post-injection phase: The Class VI well owner or operator plugs the injection well, monitors the CO2 plume and pressure front, and, after demonstrating USDW non-endangerment, closes the site. The permitting authority confirms that all post-injection phase milestones are met, including proper plugging of the injection and monitoring wells, a demonstration of non-endangerment to USDWs, and restoring the site to pre-operation conditions. Site closure may be only authorized after the operator can demonstrate that the project no longer poses an endangerment to USDWs.
For more details, please see the Class VI Implementation Manual.
Class VI permitting process
The Class VI permitting process includes the following :
- Completeness Review: The first step of the review is determining that the permit application is complete and contains all of the required information. Completeness reviews typically take 30 days for applications where Notice of Deficiencies (NODs) are not needed. EPA has developed a series of templates to help applicants develop a complete permit application.
- Review the Class VI permit application completeness checklist.
- Notice of Deficiency: A NOD identifies any required information that is missing from an application. NODs are sent to the applicant, who must provide the missing information before the application can be deemed complete.
- Technical Review: After an application is determined to be complete, the Technical Review will begin. This involves a thorough review of all application materials and an ongoing dialogue with the applicant to understand the proposed project and ensure that it will be constructed and operated in a manner that will not endanger USDWs. This is accomplished through an ongoing dialogue between the applicant and the permitting authority.
- Request for Additional Information (RAI): An RAI is a formal request from the permitting authority that additional information be provided to address questions that arise during the Technical Review of the application. RAIs are sent to applicants, who must provide the requested information for the agency to evaluate the suitability of the proposed project. Applicants should respond with 30 days or provide an alternative timeline if necessary to prepare the response.
- Prepare Draft Permit: If the technical review determines that the permit application meets the requirements of the Class VI Rule and the proposed project is suitable for CO2 injection for GS, a draft permit will be prepared, specifying the conditions that the well would be able to operate under. The permit includes the Class VI Project Plans as enforceable conditions.
- Public Comment Period: Public comment periods allow the public an opportunity to review and provide comment on the draft permit. The public comment period is also when the public can request the Agency to conduct a hearing on the draft permitting decision.
- Prepare Final Permit: The final permit is prepared with modifications based on feedback received during the Public Comment Period, where appropriate. Additionally, the agency prepares a document with responses to comments received. A final permit authorizes the applicant to construct or convert the injection well and monitoring wells and perform required preoperational testing.
EPA aims to review complete Class VI applications and issue permits when appropriate within approximately 24 months. This timeframe is dependent on several factors, including the complexity of the project and the quality of the submitted application. It is important for the applicant to submit a complete application and provide any information requested by the permitting agency in a timely manner so as not to extend the overall time for the review.
Current Class VI projects at EPA
See Class VI projects currently under review at EPA.
Review the Class VI Data Repository. This data repository contains Class VI permitting materials, such as permit applications (applicant narratives and attachments), final draft permits (i.e., those that go out for public comment), final permits, final community engagement documents, testing and monitoring reports, and permit violation notifications. This repository contains information on Class VI projects submitted to EPA as of May 2025 and will be updated regularly.
View a video tutorial on how to use the Class VI Data Repository.
Permit application and permitting tools for Class VI
EPA developed a suite of tools for Class VI permit applicants and regulatory authorities to facilitate the permit application and review process. The Class VI permit application and permitting tools page will be updated as new tools become available.
Review the Class VI permit application and permitting tools.
Geologic Sequestration Data Tool (GSDT)
Owners or operators of Class VI wells must submit permit applications and GS project information directly to EPA in an electronic format approved by EPA. This requirement applies regardless of whether the project is located in a state with primary enforcement authority (primacy) for Class VI wells.
EPA’s Geologic Sequestration Data Tool (GSDT) is a centralized, web-based system that receives, stores, and manages Class VI data and satisfies the Class VI electronic reporting requirement. Operators applying for Class VI permits in states where EPA has direct implementation authority must submit application materials to EPA via the GSDT. Permit applicants can request access to the GSDT by following the instructions in the document linked below.
GSDT Registration Process (pdf)
See the resources below for additional information on the GSDT, Class VI data management, and reporting.
Resources
Class VI Permit Application Templates
Guidelines for UIC Class VI Applicants Submitting Proprietary Business Information (pdf)
GSDT Troubleshooting Guide (pdf)
Class VI guidance documents and reports to Congress
EPA developed guidance documents to help permit applicants and operators meet the Class VI requirements. The guidance documents, which cover the range of required technical activities, were prepared to provide program implementation assistance for UIC Program Directors and compliance assistance for owners or operators of Class VI wells. The guidance documents clarify the requirements of the Class VI regulations and provide additional recommendations for implementation and compliance.
Review the Class VI guidance documents.
EPA submitted a report to Congress on "Recommendations to Improve Class VI Permitting Procedures for Commercial and Research Carbon Sequestration Projects" as required by Division G in the Consolidated Appropriations Act, 2021. The report provides background on Class VI wells, describes the Class VI permitting regulations, explains EPA’s permit application and review process, summarizes stakeholder feedback on the Class VI permitting process, and presents EPA’s recommendations for improving Class VI permitting. The Class VI permitting report can be viewed below.
UIC Class VI Permitting Report to Congress (pdf) (1.79 MB)
EPA submitted a report to Congress on “EPA Class VI Underground Injection Control Program Relevance to Outer Continental Shelf Carbon Sequestration Projects Under Department of Interior Authority,” as directed by the Committee on Appropriations in House Report 117-83. The report discusses aspects of the Class VI program that may be instructive to geologic sequestration (GS) projects on the Outer Continental Shelf (OCS) and was prepared in consultation with the Bureau of Ocean Energy Management (BOEM). This report can be viewed below.
Class VI Relevance to OCS Carbon Sequestration Projects Report to Congress
EPA submitted a Report to Congress, "Geologic Sequestration of Carbon Dioxide in Deep Saline Formations." The EPA prepared the report as directed by Congress as part of the Consolidated Appropriations Act, 2021. As requested by Congress, the report discusses risks and benefits associated with large-scale carbon dioxide storage in deep saline formations. The report describes how the EPA’s Underground Injection Control Class VI Program and other Federal initiatives contribute to large-scale implementation of Carbon Capture and Storage.
Geologic Sequestration of Carbon Dioxide in Deep Saline Formations Report to Congress (pdf)
Regulatory and statutory authorities relevant to carbon capture and storage projects
Carbon capture and storage (CCS) involves a variety of activities that can potentially affect various environmental media. The Class VI requirements apply only to the injection of CO2 into the subsurface and focuses on the protection of underground sources of drinking water. However, CCS project operators are subject to a variety of other federal, state, and local requirements to ensure the protection of natural resources, infrastructure, people, and wildlife.
The document linked below lists the regulatory and statutory authorities that may be relevant to the development of a CCS project in the United States. It provides an overview of the types of permits and permissions that may be needed for CCS; however, the applicable permits and reviews will depend on the characteristics of the particular project and the state and locality where it is sited. These authorities are divided into those that may apply to project site selection, CO2 point source capture, CO2 transportation, and CO2 sequestration.
Regulatory and statutory authorities relevant to carbon capture and storage (CCS) projects (pdf)
Contact Us
View the UIC Program's Class VI contact list.