EPA’s long-awaited proposal would set aggressive emission reduction targets with many different approaches and timelines to achieve them.
By Stacey L. VanBelleghem and Jennifer Garlock

On May 11, 2023, the US Environmental Protection Agency (EPA) released its proposed rule[1] to regulate carbon dioxide (CO2) emissions from electric generating units (EGUs) at power plants under Section 111 of the Clean Air Act (CAA) (the Power Plant GHG Rule or the Proposed Rule).
The Power Plant GHG Rule consists of five proposed actions:
- determinations and updates to current CO2 standards of performance (promulgated in 2015) for new and reconstructed stationary combustion turbines (generally natural gas-fired) pursuant to Section 111(b) of the CAA;
- determinations and updates to current CO2 standards of performance (promulgated in 2015) for modified fossil fuel-fired steam-generating EGUs (generally coal-fired) pursuant to Section 111(b) of the CAA;
- determinations and CO2 emission guidelines for existing fossil fuel-fired steam-generating EGUs (generally coal-fired) pursuant to Section 111(d) of the CAA;
- determinations and CO2 emission guidelines for large, frequently used existing fossil fuel-fired stationary combustion turbines (generally natural gas-fired) pursuant to Section 111(d) of the CAA; and
- a repeal of the Trump-era Affordable Clean Energy (ACE) Rule.
EPA is also soliciting comment on a number of topics, including potential options and emission guidelines for existing fossil fuel-fired stationary combustion turbines not otherwise covered by the Proposed Rule (generally natural gas-fired units that are either smaller or less frequently used).
On June 30, 2022, the US Supreme Court issued its long-awaited ruling in West Virginia v. EPA — the consolidated petitions addressing EPA’s authority to regulate existing power plant greenhouse gas (GHG) emissions under Section 111(d) of the Clean Air Act (CAA). In a 6-3 opinion drafted by Chief Justice Roberts, the Court ruled against EPA, holding that EPA’s attempt to force an overall shift in power generation from higher-emitting to lower-emitting sources exceeded EPA’s statutory authority. Indeed, the Court noted that such a sweeping transformation of the nation’s power sector implicated a “major question” requiring explicit congressional authorization, that the Court argued the CAA did not provide.
On January 19, 2021, on the eve of President Biden’s inauguration, in American Lung Association, et al. v. EPA, the US Court of Appeals for the District of Columbia Circuit overturned the Environmental Protection Agency’s (EPA’s) Affordable Clean Energy (ACE) Rule, which sought to replace the Obama Administration’s Clean Power Plan (CPP). Both rules would regulate carbon dioxide (CO2) emissions from existing electric generating units (EGUs) under Section 111(d) of the Clean Air Act (CAA).