On August 21, the U.S. Environmental Protection Agency (EPA) announced its proposal to replace the Obama administration’s Clean Power Plan. The new plan, titled the Affordable Clean Energy Rule (ACE Rule), proposes to establish emissions guidelines for states to develop their own plans to reduce greenhouse gas emissions from approximately 600 existing coal-fired power plants at 300 facilities across the country. The ACE Rule prioritizes efficiency upgrades at existing plants and will include a definition of “best system of emission reduction” as “on-site, heat-rate efficiency improvements.” The plan also gives states a list of “candidate technologies” to assist with determining the appropriate plant performance standards and revises EPA’s New Source Review permitting program to further incentivize efficiency improvements. EPA projects that the ACE Rule will provide $6.4 billion in avoided compliance costs as compared with the Clean Power Plan. Once the ACE Rule is published in the Federal Register, EPA will accept comments for 60 days. The EPA is also still in the administrative process of repealing the Clean Power Plan.