On September 14, 2026, U.S. Environmental Protection Agency (U.S. EPA) Administrator Lee Zeldin signed two concurrent actions that together would dismantle the federal greenhouse gas (GHG) program for fossil fuel-fired power plants under Clean Air Act (CAA) Section 111.
The first action is a final rule, effective on November 16, 2026, that repeals most provisions of the 2024 Carbon Pollution Standards (CPS), including:
- GHG emissions guidelines for existing fossil fuel-fired steam generating units in 40 CFR Part 60, Subpart UUUUb,
- The carbon capture and sequestration/storage (CCS)-based standards for coal-fired steam generating units undertaking a large modification in 40 CFR Part 60, Subpart TTTTa, and
- The CCS-based standards for new base-load stationary combustion turbines in 40 CFR Part 60, Subpart TTTTa.
The second action is a supplemental proposal that would repeal all remaining GHG standards for the source category (e.g., 40 CFR Part 60, Subpart TTTT and the remainder of Subpart TTTTa). Comments on the proposal are due on or before November 2, 2026, with a virtual public hearing on October 1, 2026.
Background on Power Plant GHG Regulation
These two September 2026 actions are the latest rulemakings in the long saga of U.S. EPA regulation of GHG emissions through past administrations. To recap, here is a brief summary of key GHG regulations that have led us here:
- In 2009, U.S. EPA issued a formal determination that GHG emissions from new motor vehicles and engines endanger public health and welfare. This “Endangerment Finding” provided the legal foundation for subsequent federal regulation of GHG emissions under the CAA, including regulation of GHG emissions from fossil fuel-fired electric generating units (EGUs) under Section 111.
- In 2015, U.S. EPA determined under CAA Section 111(b) that GHG emissions from the fossil fuel-fired EGU source category contribute significantly to dangerous air pollution. U.S. EPA subsequently established the first New Source Performance Standards (NSPS) for carbon dioxide (CO₂) emissions from new, modified, and reconstructed fossil fuel-fired EGUs in 40 CFR Part 60, Subpart TTTT.
- On May 9, 2024, U.S. EPA finalized the Carbon Pollution Standards (2024 CPS) (89 FR 39798), establishing GHG emission standards for fossil fuel-fired power plants under CAA Section 111. The rule established emission limits based on what U.S EPA determined to be the best system of emission reduction (BSER) for different types of fossil fuel-fired EGUs. The 2024 CPS included requirements for new, modified, and reconstructed sources, as well as emission guidelines for existing sources in 40 CFR Part 60, Subpart TTTTa and 40 CFR Part 60, Subpart UUUUb.
Past Repeal Actions from Current Administration
On June 11, 2025, responding to President Trump’s energy-related Executive Orders, U.S. EPA signed a Notice of Proposed Rulemaking (June 2025 NPRM) that included a primary proposal and alternative proposal.
The June 2025 NPRM’s primary proposal was to repeal all GHG emissions standards for fossil fuel-fired power plants, including:
- 40 CFR Part 60, Subpart TTTT — Standards of Performance for GHG Emissions for Electric Generating Units;
- 40 CFR Part 60, Subpart TTTTa — Standards of Performance for GHG Emissions for Modified Coal-Fired Steam EGUs and New/Reconstructed Stationary Combustion Turbine EGUs; and
- 40 CFR Part 60, Subpart UUUUb — Emission Guidelines for GHG Emissions for existing Electric Utility Generating Units. (See ALL4’s blog on that proposal here.)
The key basis of the June 2025 NPRM’s primary “repeal everything” strategy was two-fold. U.S. EPA proposed that in order to regulate GHG emissions under CAA Section 111, GHG emissions from fossil fuel-fired power plants would have to “contribute significantly” to “air pollution which may reasonably be anticipated to endanger public health or welfare.” U.S. EPA then proposed to find that power plant GHG emissions fall short of that threshold.
The alternative proposal was a reevaluation of the BSER determinations that were made in the 2024 CPS under the previous Administration (90% carbon capture and 40% natural gas co-firing) were not adequately demonstrated or otherwise justified. This supported a narrower proposal to repeal Subpart UUUUb and the carbon capture-based standards in Subpart TTTTa, while leaving Subpart TTTT in place.
September 2026 Rulemakings: What’s Changed
The final September 2026 rulemaking is U.S. EPA finalizing the alternative proposal from the June 2025 NPRM: finding the BSER determinations from the 2024 CPS are not adequately demonstrated, cost effective, or other achievable. This rule was published in the Federal Register on September 17th, opening the door to legal action, which is already underway.
The accompanying supplemental proposal is a direct follow-up to the June 2025 NPRM; U.S. EPA is continuing to “test the waters” with a full repeal of all GHG regulations for power plants. Now, in addition to the question of whether power plant GHG emissions “contribute significantly” to harmful air pollution, U.S. EPA is further considering the full repeal in light of the Endangerment Finding repeal. U.S. EPA is seeking additional public comment on its statutory authority to regulate GHG emissions from power plants from both angles: “contribution” and “endangerment.”
The table below provides an at-a-glance summary of each affected 40 CFR Part 60 regulation and the impacts of the final rule and supplemental proposal.
| 40 CFR Part 60 Regulation | Requirement | September 2026 Final Rule | September 2026 Supplemental Proposal | Current Status |
| Subpart TTTT — New/reconstructed/modified turbines & steam units prior to May 2023 | CO2 emissions performance standards | Not repealed, left in effect | Proposed to repeal | In effect |
| Subpart TTTTa — Efficiency-based standards for new base, intermediate, and low load turbines | Efficiency-based CO2 limits for new combustion turbines | Not repealed, left in effect | Proposed to repeal | In effect |
| Subpart TTTTa — New base load turbines: CCS-based standards (effective Jan 1, 2032) | ~90% capture via CCS for new base load combustion turbines | Repealed, CCS is not achievable as BSER | N/A, already repealed | Repealed, effective November 16, 2026 |
| Subpart TTTTa — Coal steam units undertaking a large modification | ~90% capture via CCS on large modification | Repealed, CCS is not achievable as BSER | — | Repealed, effective November 16, 2026 |
| Subpart UUUUb — §111(d) guidelines: existing long-term coal | ~90% capture via CCS; state plans; Jan 1, 2032 | Repealed, CCS is not achievable as BSER | — | Repealed, effective November 16, 2026 |
| Subpart UUUUb — §111(d) guidelines: existing medium-term coal | 40% gas co-firing; state plans; Jan 1, 2030 | Repealed, generation-shifting not allowed per West Virginia v. U.S. EPA | — | Repealed, effective November 16, 2026 |
| Subpart UUUUb — §111(d) guidelines: existing gas and oil-fired steam | State plans setting standards | Repealed, inefficient once coal standards are removed | — | Repealed, effective November 16, 2026 |
What This Means for Power-Generating Facilities
The complete repeal of Subpart UUUUb removes requirements for existing coal units that would otherwise have forced 90% CCS retrofits (long-term units) or 40% gas co-firing (medium-term units) by 2032 and 2030, respectively. Along with the repeal of CCS requirements triggered by large modifications under Subpart TTTTa, U.S. EPA notes that this rulemaking is aimed at preventing “mass closures of coal-fired power plants,” keeping in step with Executive Order 14261: Reinvigorating America’s Beautiful Clean Coal Industry and Amending Executive Order 14241.
For combustion turbines, the repeal of the January 1, 2032 CCS-based standards for base load turbines in Subpart TTTTa removes one of the main compliance risks facing new combined-cycle projects, since it was unclear whether the necessary CCS infrastructure would exist by that date. That said, the efficiency-based standards for base, intermediate, and low load units are still in effect, so the supplemental proposal would be more noteworthy for affected combustion turbines. Given the significance of these rulemakings, substantial public comment and legal challenges are expected, so it will be important to closely track further developments.
The regulatory landscape in the power sector continues to evolve, and ALL4 is helping clients evaluate what these actions mean for existing units and new combined-cycle and simple-cycle projects, and develop strategies across permitting, commissioning, and ongoing compliance. To discuss how these changes may affect your facilities or assistance preparing comments on the supplemental proposal, please reach out to me or ALL4’s Power Sector Lead Rich Hamel to learn more.
