SUPPLEMENTARY INFORMATION:

Table of Contents

I. Introduction

A. Federal UIC Program and Primary Enforcement Authority (Primacy)

B. Class VI Wells Under the UIC Program

II. Legal Authorities

III. Colorado's Application for UIC Class VI Primacy

A. Background

B. Public Participation Activities Conducted by Colorado

C. Summary of the EPA's Comprehensive Evaluation

D. Public Participation Activities Conducted by the EPA

IV. Public Comments and the EPA's Response

A. Public Comments

B. The EPA's Response to Comments

V. The EPA's Action

A. Incorporation by Reference

B. The EPA's Oversight

VI. Statutory and Executive Orders Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 14094: Modernizing Regulatory Review

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

C. Paperwork Reduction Act (PRA)

D. Regulatory Flexibility Act (RFA)

E. Unfunded Mandates Reform Act (UMRA)

F. Executive Order 13132: Federalism

G. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

H. Executive Order 13045: Protection of Children From Environmental Health and Safety Risks

I. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use

J. National Technology Transfer and Advancement Act (NTTAA)

K. Congressional Review Act

VII. References

I. Introduction

A. Federal UIC Program and Primary Enforcement Authority (Primacy)

The SDWA protects public health by regulating the nation's public drinking water supply, including both surface and groundwater sources. Among other things, the SDWA requires the EPA to develop minimum requirements for effective State and Tribal UIC programs to prevent underground injection of fluids (such as water, wastewater, brines from oil and gas production, and carbon dioxide) from endangering underground sources of drinking water (USDWs). In general, USDWs are aquifers or parts of aquifers that supply a public water system or contain enough groundwater of sufficient quality to supply a public water system. See 40 Code of Federal Regulations (CFR) 144.3 (defining USDW).

The EPA's UIC program regulates various aspects of injection throughout the lifetime of the project. These regulated aspects include technical elements such as site characterization, construction, operation, and testing and monitoring through site closure, as well as permitting, site inspections, and reporting to ensure that well owners and operators comply with UIC permits and regulations.

SDWA section 1421 directs the EPA to establish requirements that States, territories, and authorized Tribes must meet to be granted primary enforcement responsibility or “primacy” for a UIC program. 42 U.S.C. 300h. SDWA section 1422 provides that an applicant seeking primacy for a UIC program must demonstrate to the EPA that the applicant's proposed UIC program meets the applicable requirements promulgated by the EPA pursuant to section 1421 for protecting USDWs. 42 U.S.C. 300h-300h-1. An applicant must demonstrate, among other things, that it has jurisdiction over underground injection and that it possesses the administrative, civil, and criminal enforcement authorities required by the EPA's implementing regulations. See 40 CFR part 145, subpart B. After the EPA approves an applicant for a UIC primacy program, that UIC program may later be revised with EPA approval. See 40 CFR 145.32.

The EPA evaluates each primacy application in accordance with SDWA section 1422 and the EPA's implementing regulations to determine whether the applicant (in this instance, the State of Colorado) has satisfactorily demonstrated that, after reasonable notice and public hearings, it has adopted and will implement a UIC program that meets the requirements of the SDWA regulations at 40 CFR parts 144, 145, and 146.

In this final rule, the EPA approves Colorado's primacy program application to administer the UIC Class VI program for Class VI wells located in the State. The EPA determined that the application meets all applicable requirements for approval under SDWA section 1422 and the EPA's implementing regulations and that the State is capable of administering a UIC program consistent with the SDWA and applicable UIC regulations. The EPA will remain the permitting authority for all Class VI wells located on Indian land within Colorado and will oversee Colorado's administration of the State's UIC Class VI program as authorized under the SDWA.

B. Class VI Wells Under the UIC Program

Class VI wells are used to inject carbon dioxide into deep rock formations for long-term underground storage, also known as geologic sequestration. The geologic sequestration of carbon dioxide in UIC Class VI wells is used as part of carbon capture and storage for carbon dioxide emissions from industrial sources. Class VI injection wells are regulated under a SDWA permitting framework that provides multiple safeguards that work together to protect USDWs.

Owners or operators that wish to inject carbon dioxide underground for geologic sequestration must demonstrate to the permitting authority that their proposed injection well and injection activities will meet all regulatory requirements and receive a Class VI permit for each well. The UIC Class VI program requires applicants to meet technical, financial, and managerial requirements to obtain a Class VI permit, including:

• Site characterization to ensure the geology in the project area will contain ( printed page 64782) the carbon dioxide within the zone where it is authorized to be injected.
• Modeling to delineate the predicted area influenced by injection activities through the lifetime of the project.
• Evaluation of the delineated area to ensure all potential pathways for fluid movement have been identified and addressed through corrective action.
• Well construction requirements that ensure the Class VI injection well will not leak carbon dioxide.
• Testing and monitoring throughout the life of the project, including after carbon dioxide injection has ended. Requirements include, for example, testing to ensure physical integrity of the well, monitoring for seismic activity near the injection site, monitoring of injection pressure and flow, chemical analysis of the carbon dioxide stream that is being injected, and monitoring the extent of the injected carbon dioxide plume and the surrounding area (e.g., ground water) to ensure the carbon dioxide is contained as predicted.
• Operating requirements (for example, injection pressure limitations) to ensure the injection activity will not endanger USDWs.
• Financial assurance mechanisms sufficient to cover the costs for all phases of the geologic sequestration project including the post-injection site care period and until site closure has been approved by the permitting authority.
• Emergency and remedial response plans.
• Reporting of all testing and monitoring results to the permitting authority to ensure the well is operating in compliance with all permit requirements.

The permitting authority ensures that these protective requirements are included in each Class VI permit. A draft of each Class VI permit is made available for public comment before the permitting authority decides whether to issue a final permit.

II. Legal Authorities

SDWA section 1421 requires the EPA to promulgate minimum requirements for effective State UIC programs to prevent underground injection activities that endanger USDWs. 42 U.S.C. 30h0(b)(1). SDWA section 1422 requires that States seeking primacy demonstrate that they have adopted (after notice and public hearings) and will implement a UIC program which meets the requirements that the EPA promulgated under SDWA section 1421. 42 U.S.C. 300h-1(b)(1)(A)(i). The statutory authority for this final rule approving Colorado's UIC Class VI primacy program is SDWA sections 1422 and 1450, 42 U.S.C. 300h-1 and 300j-9.

As directed by the SDWA, the EPA has promulgated regulations setting forth the applicable procedures and substantive requirements for applicants seeking primacy for UIC programs under SDWA section 1422. The regulations in 40 CFR part 144 outline general program requirements that States must meet to obtain primacy. The regulations in 40 CFR part 145 specify the procedures the EPA will follow in approving, revising, and withdrawing UIC programs and outlines the elements and provisions that an applicant must include in its application for primacy. Also, 40 CFR part 145 includes requirements for State UIC permitting programs (by reference to certain provisions of 40 CFR parts 124 and 144), compliance evaluation programs, and enforcement authority, as well as requirements for sharing information between the EPA and the State. The regulations in 40 CFR part 146 contain the technical criteria and standards applicable to each well class, including Class VI wells.

III. Colorado's Application for UIC Class VI Primacy

A. Background

On October 7, 2025, Colorado submitted a Class VI primacy program application to the EPA under SDWA section 1422. Colorado's UIC Class VI primacy program application includes a description of the State's proposed UIC Class VI program, copies of all applicable State legal authorities and forms, a statement of legal authority from Colorado's Attorney General, a summary of Colorado's public participation activities, a letter from the Governor of Colorado requesting primacy program approval and a Memorandum of Agreement (MOA) between Colorado and the EPA's Region 8 office. The EPA reviewed the application for completeness and performed a technical and legal evaluation of the application materials to assess and confirm that Colorado's proposed UIC Class VI program meets Federal requirements.

B. Public Participation Activities Conducted by Colorado

Prior to submitting a Class VI primacy application for the EPA's approval, Colorado needed to expand ECMC's regulatory authority to include direct air capture facilities and geologic storage operations and on July 1, 2021, State law SB23-016 became effective expanding ECMC's regulatory authority. Once the State expanded ECMC's authority, ECMC conducted a comprehensive UIC Class VI rulemaking process that included extensive stakeholder outreach and engagement. The goal of the outreach efforts was to inform stakeholders about ECMC's rule development process and to explain and present drafts of the State Class VI rules. Transparency and engagement were central in the outreach process. ECMC hosted a series of hybrid, virtual, and in-person outreach engagements across the State, for the general public, the regulated community, and the Tribes located in Colorado. ECMC also conducted a presentation on Class VI primacy at a public hearing, led a carbon management tour for communities near a potential development, and held seven general stakeholder meetings and several targeted stakeholder meetings.

In particular, ECMC held a series of virtual stakeholder engagements and rulemaking hearings from June to December 2024, to develop regulations for Class VI injection wells. The engagements provided opportunities for public input and informed the development of Colorado's Class VI rules. Following ten Class VI rulemaking and primacy hearings, ECMC finalized the rules for a UIC Class VI program on December 16, 2024.

In February 2025, ECMC published notices for public hearings in seven Colorado newspapers, on its website, and via email distribution to stakeholders. The public notice provided the hearing schedule and identified specific issues for public input, including the State's intent to request UIC Class VI primacy from the EPA. During the 30-day comment period, ECMC received one oral comment that expressed general concerns regarding carbon capture and storage. ECMC summarized and addressed the input in the responsiveness summary; the comment did not necessitate any changes to the State's proposed primacy application.

Documentation of Colorado's public participation activities, including the comments received and ECMC's responses, can be found in the EPA's Docket ID No. EPA-HQ-OW-2025-2829.

C. Summary of the EPA's Comprehensive Evaluation

The EPA evaluates primacy applications in accordance with SDWA section 1422 and the Agency's implementing regulations to determine whether an applicant has satisfactorily demonstrated that it has adopted, after reasonable notice and public hearings, and will implement, a UIC program that meets applicable regulatory ( printed page 64783) requirements. 42 U.S.C. 300h-1(b)(1)(A)(i). The EPA conducted a comprehensive technical and legal evaluation of Colorado's primacy application to determine whether the State's UIC Class VI program—including State statutes and regulations, program description, State Attorney General statement, MOA, and documentation of public participation—demonstrates that Colorado has met the requirements of SDWA section 1422. Upon review, the EPA determined that Colorado has adopted and will implement a UIC Class VI program that meets the requirements of 40 CFR parts 144, 145, and 146.

The EPA evaluated Colorado's UIC program description for consistency with 40 CFR 145.23, which lists all the information that must be submitted as part of the program description. The EPA's evaluation of the UIC program description included reviewing the scope, structure, coverage, and processes of the State's program. The EPA assessed Colorado's permitting, administrative, and judicial review procedures, as well as the State's permit application, reporting, and manifest forms. The EPA also reviewed the State's compliance evaluation program and enforcement authorities and the State's demonstration that its UIC Class VI program will have adequate in-house staff or access to contractor support for technical areas including site characterization, modeling, well construction and testing, financial responsibility, and regulatory and risk analysis.

The EPA evaluated Colorado's Attorney General's statement for consistency with 40 CFR 145.24. In an Attorney General's statement, the State's top legal officer affirms that applicable statutes, regulations, and judicial decisions demonstrate adequate authority to administer the UIC program as described in the program description and consistent with the EPA's regulatory requirements for UIC programs. The EPA confirms that the Colorado Attorney General's statement certifies that Colorado's environmental audit privilege, which protects certain self-reported information, will not affect the ability of the State to meet the enforcement and information gathering requirements under the SDWA, nor will it prevent the public from obtaining information about noncompliance or prevent the public from bringing citizen suits under the SDWA.

The EPA determined that the Class VI MOA meets the Federal requirements at 40 CFR 145.25 for primacy MOAs. The MOA is the central agreement setting the provisions and arrangements between the State and the EPA concerning the administration, implementation, and enforcement of the State UIC program. The EPA's evaluation includes ensuring that the MOA contains the necessary provisions pertaining to coordination, permitting, compliance monitoring, enforcement, and EPA oversight.

Colorado has demonstrated that it has the legal authority to implement all UIC Class VI permit requirements found in 40 CFR 145.11. Colorado's UIC Class VI permitting provisions and technical criteria and standards meet the Federal requirements in 40 CFR parts 124 and 144 through 146. The State has incorporated necessary procedures pursuant to 40 CFR 145.12 to support a robust UIC Class VI compliance evaluation program. Additionally, Colorado has the necessary administrative, civil, and criminal enforcement authorities pursuant to 40 CFR 145.13. Colorado's UIC Class VI regulations regarding permitting, inspection, operation, and monitoring meet requirements in 40 CFR parts 145 and 146. Colorado's reporting and recordkeeping requirements meet the requirements in 40 CFR 144.54 and 40 CFR part 146.

As a result of this comprehensive review, the EPA approves Colorado's UIC Class VI primacy program application. The EPA has determined that the application meets all applicable requirements for Class VI primacy under SDWA section 1422 and that the State has demonstrated it is prepared to implement a UIC Class VI program in a manner consistent with the SDWA and all applicable UIC regulations.

D. Public Participation Activities Conducted by the EPA

On March 18, 2026, the EPA Region 8 Water Division Director sent a letter via email to leaders of four Tribes (Navajo Nation, Southern Ute Indian Tribe, Ute Indian Tribe, and Ute Mountain Ute Tribe) in Colorado offering an opportunity for Government-to-Government consultation on Colorado's primacy application for the UIC Class VI program. The EPA received no requests for Tribal consultation during the period beginning March 18 and ending with the close of public comment on May 4, 2026.

On March 19, 2026, the EPA published a proposed rulemaking in the Federal Register (91 FR 13266) proposing to approve Colorado's application to implement a UIC Class VI program within the State. The proposal initiated a 45-day public comment period that closed on May 4, 2026. The EPA held a public hearing on April 23, 2026, that participants could attend virtually or by phone. In addition to the Federal Register publication, the EPA published notice of the hearing on the EPA's website and in the Denver Post, the Durango Herald, the Grand Junction Daily Sentinel, the Greeley Tribune, the Loveland Reporter Herald, and the Trinidad Chronicle News.

IV. Public Comments and the EPA's Response

A. Public Comments

During the public comment period, the EPA received eleven written comments from several individuals, as well as from interest groups, including the Southern Ute Indian Tribe, the Ground Water Protection Council, the Colorado Energy Council, the Consumer Energy Alliance, and Reliant Carbon Capture and Storage, LLC.

The EPA considered these comments in the development of this final rule. All comments are available as part of the public record and can be accessed through the EPA's docket (ID No. EPA-HQ-OW-2025-2829). Documentation of the EPA's public participation activities, including comments received and the EPA's comment response document, can also be found in the docket (ID. No. EPA-HQ-OW-2025-2829).

B. The EPA's Response to Comments

The EPA received comments supporting and opposing the proposed approval of Colorado's UIC Class VI primacy program, with a majority supporting. EPA also received a comment from the Southern Ute Indian Tribe recommending modified regulatory language, as well as some comments outside the scope of this primacy approval action.

Commenters supporting Colorado UIC Class VI program primacy approval state that Colorado's UIC Class VI rules meet or exceed the EPA's UIC requirements. They also agree that ECMC is well positioned to successfully implement Colorado's Class VI UIC program as it has in-house resources and permitting experience from administering Colorado's UIC Class II program. Commentors supporting Colorado's Class VI primacy application note that Colorado primacy approval will distribute workload between the EPA and ECMC and, that State UIC primacy, generally, will help address a national backlog of Class VI permit application. Another commenter urges that approving Colorado's Class VI program aligns with the EPA's “Powering the Great American Comeback” by promoting permitting efficiency, cooperative federalism, and the ( printed page 64784) protection of health and the environment.

One commenter opposing Colorado UIC Class VI program primacy approval expressed concerns with the Tribal consultation process, alleging a lack of thoroughness by both the EPA and ECMC and requesting more Tribal input on the primacy decision. The commenter also asserted that the SDWA requires that the EPA consider Colorado's “historical conditions” when assessing the State's primacy request, such as the State's historical conditions of Tribal consultation related to water rights. Additionally, another commenter raised concerns about carbon dioxide plume migration and the risk to groundwater.

The Southern Ute Indian Tribe (SUIT) submitted a comment supporting EPA's proposed approval of Colorado's primacy program but requested a modification to regulatory language regarding the definition of “Indian lands.” SUIT noted that the EPA's proposed amendment to 40 CFR 147.301 applies Colorado's UIC Program for Class VI wells to all “Class VI wells in the State of Colorado, except those located on Indian lands,” but “Indian lands” used by EPA in the text of its proposed rule is not defined within the rule or within the Federal Register document. SUIT noted that the EPA's use of the term “Indian lands” as referenced in the consultation letter dated March 18, 2026, differs from ECMC's definition of “Indian Lands” found at ECMC's regulations. SUIT further noted that those subtle differences are of no material consequence so long as EPA, ECMC, and the public understand that ECMC's rules, “will not apply to . . . Class VI UIC Wells located on surface lands within the exterior boundaries of the Southern Ute Indian Reservation or the Ute Mountain Ute Indian Reservation.”

Comments received outside the scope of this primacy approval action recommended the EPA focus on phasing out fossil fuels, consuming less and recycling more, and transitioning to cleaner energy alternatives.

The EPA has noted and addressed all topics, including out of scope topics, in the Agency's response to comments document included in the docket (ID. No. EPA-HW-OW-2025-2829). In brief, the EPA assures commenters that the EPA performed an extensive review of Colorado's proposed program and it meets all applicable requirements for primacy approval.

V. The EPA's Action

A. Incorporation by Reference

The EPA is approving the State of Colorado's UIC program primacy application for Class VI injection wells in the State, except for those located on Indian lands. This action amends 40 CFR 147.300 through 40 CFR 147.305 and incorporates by reference Colorado's EPA-approved statutes and implementing regulations that contain standards, requirements, and procedures applicable to UIC well owners and operators within the State. Any provisions incorporated by reference, as well as all permit conditions issued pursuant to such provisions, are enforceable by the EPA pursuant to SDWA section 1423 and 40 CFR 147.1(e).

The EPA compiled the applicable Colorado statutes and regulations to be incorporated by reference into 40 CFR 147.301 in a document titled “Colorado SDWA § 1422 Underground Injection Control Program Class VI Statutes and Regulations to be Incorporated by Reference,” dated January 8, 2026. This compilation is publicly available at www.regulations.gov in the EPA's Docket No. EPA-HQ-OW-2025-2829 for this rulemaking. The EPA also codifies a table in 40 CFR 147.300 listing the EPA-approved Colorado Statutes and Regulations for Class VI wells that the EPA is incorporating by reference.

The “Oil and Gas Conservation Commission Revised Rules and Regulations in the 800, 900, and 1200 series,” as of January 15, 2021, includes the revised Oil and Gas Conservation Commission (OGCC) rules in the 800, 900, and 1200 series, of which the 800 series rules include the State's Class II UIC regulations. The compilation is publicly available at www.regulations.gov in the EPA's Docket No. EPA-HQ-OW-2025-2829.

In order to better serve the public, the EPA is reformatting and updating the codification of 40 CFR 147.300 State-administered program-Class II wells to incorporate non-substantial changes to Colorado's UIC program for Class II injection wells, previously approved by letter under 40 CFR 145.32(b)(4). Colorado submitted a Class II program revision to EPA Region 8 because of the State's Mission Change Rulemaking to align OGCC rules with the statutory amendments adopted in the Colorado Senate Bill 19-181. This State rulemaking revised the OGCC rules in the 800, 900, and 1200 series, of which the 800 series rules include the State's Class II UIC regulations. EPA Region 8 reviewed the regulations in the 800 series to ensure they retain all necessary authority for the OGCC to enforce the new statutory requirements applicable to Class II injection wells. The EPA is not undergoing notice and public comment on these non-substantial revisions because the Agency had previously approved them by letter in 2021 and is now simply updating the CFR to reflect these previously approved, non-substantial revisions. Because these revisions have already been approved, the codification of these revisions is ministerial. As a result, EPA finds there is “good cause” pursuant to 5 U.S.C. 553(b) to incorporate these codifications without prior notice and opportunity for comment. The letters from EPA approving the non-substantial revisions to Colorado's statutes and regulations (OGCC rules in the 800, 900, 1200 series) are included in the docket for reference, along with the updated Memoranda of Agreement and State Attorney General's statements. The revised documents are publicly available at www.regulations.gov in the EPA's Docket No. EPA-HQ-OW-2025-2829.

B. The EPA's Oversight

The EPA will oversee Colorado's administration of its UIC program. The EPA will require quarterly reports on instances of permittee non-compliance and annual UIC performance reports pursuant to 40 CFR 144.8. The MOA between the EPA Region 8 and ECMC specifies that the EPA will oversee the State's administration of the UIC program on a continuing basis to assure that such administration is consistent with the program MOA, the SDWA and implementing regulations, UIC grant agreements, and other applicable requirements.

VI. Statutory and Executive Orders Reviews

Additional information about these statutes and Executive orders can be found at: www.epa.gov/​laws-regulations/​laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 14094: Modernizing Regulatory Review

This action is exempt from review under Executive Order 12866 because the Office of Management and Budget (OMB) has exempted, as a category, the approval of State UIC programs. This exemption also applies to EPA approvals of revisions to existing State UIC programs. ( printed page 64785)

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

Executive Order 14192 does not apply because actions that approve State UIC programs are exempted from review under Executive Order 12866.

C. Paperwork Reduction Act (PRA)

This action will not impose an information collection burden under the PRA. OMB has previously approved the information collection activities contained in the existing regulations and has assigned OMB control number 2040-0042.

D. Regulatory Flexibility Act (RFA)

I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. This action will not impose any requirements on small entities. This action transfers regulatory authority from the EPA to a State program with substantially the same requirements.

E. Unfunded Mandates Reform Act (UMRA)

This action does not contain an unfunded mandate as described in UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect small governments. The action imposes no enforceable duty on any State, local, or Tribal governments or the private sector. The EPA's approval of Colorado's Class VI program will not constitute a Federal mandate because there is no requirement that a state establish UIC regulatory programs and because the program is a State, rather than a Federal program.

F. Executive Order 13132: Federalism

This action does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the National Government and the states, or on the distribution of power and responsibilities among the various levels of government.

G. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

This action does not have Tribal implications as specified in Executive Order 13175. This action contains no Federal mandates for Tribal governments and does not impose any enforceable duties on Tribal governments. Thus, Executive Order 13175 does not apply to this action.

H. Executive Order 13045: Protection of Children From Environmental Health and Safety Risks

The EPA interprets Executive Order 13045 as applying only to those regulatory actions that concern environmental health or safety risks that the EPA has reason to believe may disproportionately affect children, per the definition of “covered regulatory action” in section 2-202 of the Executive Order. This action is not subject to Executive Order 13045 because it approves a State program.

I. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use

This action is not subject to Executive Order 13211, because it is not a significant regulatory action under Executive Order 12866.

J. National Technology Transfer and Advancement Act (NTTAA)

This final rule does not involve technical standards.

K. Congressional Review Act (CRA)

This final rule is subject to the CRA, and the EPA will submit a rule report to each House of the Congress and to the Comptroller General of the United States. This action is not a “major rule” as defined by 5 U.S.C. 804(2).

VII. References

Attorney General's Statement “Attorney General's Statement to Accompany Colorado's Underground Injection Control Program Class VI Primacy Application”, signed by the Attorney General of Colorado on May 27, 2025.

Class VI Underground Injection Control Program Description “State of Colorado Class VI Underground Injection Control 1422 Program Description”, Colorado Energy and Carbon Management Commission, September 23, 2025.

Letter from the Governor of Colorado to the Regional Administrator, EPA Region 8, signed on April 2, 2025.

The Memorandum of Agreement between the Colorado Energy and Carbon Management Commission and the EPA Region VIII, signed by the EPA Regional Administrator on October 8, 2025.

State of Colorado Energy and Carbon Management Commission of Colorado Department of Natural Resources Class VI UIC Primacy Application, “Relevant State Statutes and Regulations”, September 23, 2025.

State of Colorado Energy and Carbon Management Commission of the Colorado Department of Natural Resources Class VI UIC Primacy Application, “Public Participation Documentation”, September 23, 2025.

U.S. Environmental Protection Agency. “Colorado SDWA § 1422 Underground Injection Control Program Statutes and Regulations to be Incorporated by Reference.” January 8, 2026. Office of Water.

State of Colorado Oil and Gas Conservation Commission Revised Rules and Regulations in the 800, 900, and 1200 series, as of January 15, 2021.

The Memorandum of Agreement between EPA Region VIII and the Colorado Oil and Gas Conservation Commission, signed by the EPA Regional Administrator on March 3, 1984, amended on August 30, 1989, and amended July 29, 2021.

The amended Memorandum of Agreement between EPA Region VIII and the Colorado Energy and Carbon Management Commission, signed by the EPA Regional Administrator on July 15, 2026.

Letter from Colorado Attorney General to the Acting Regional Administrator, U.S. EPA Region VIII, “RE: Colorado Attorney General Statement Regarding Class II UIC Well Rules”, December 9, 2020.

Letter from Colorado Attorney General to the Regional Administrator, U.S. EPA Region VIII, “RE: Colorado Attorney General Statement Regarding Class II UIC Well Rules”, May 20, 2026.

For the reasons set forth in the preamble, the EPA hereby amends 40 CFR part 147 as follows:

91 FR 64780