This action addresses the Standards of Performance for New Stationary Sources and Emission Guidelines for Existing Sources for Large Municipal Waste Combustors promulgated under section 129 of the Clean Air Act (CAA). The New Source Performance Standards (NSPS), subpart Eb, and the Emission Guidelines, subpart Cb, were first established on December 19, 1995, and amended on May 10, 2006, pursuant to CAA section 129(a)(5) which requires review of these standards every 5 years. The NSPS and emission guidelines established emission limitations based on maximum achievable control technology for controlling emissions of hazardous air pollutants and criteria pollutants from large municipal waste combustors. The EPA received a petition for reconsideration of the 2006 rulemaking and, in 2007, EPA announced its reconsideration of several aspects of the rule. Additionally, following a challenge to the 2006 rulemaking, the D.C. Circuit granted EPA a voluntary remand in 2008 for the Agency to re-evaluate the MACT floors established in 1995 based on the D.C. Circuit’s decisions in Northeast Maryland Waste Disposal Facility v. EPA, 358 F.3d 936 (D.C. Cir. 2004) and related cases. The EPA proposed updated NSPS and emission guidelines for large municipal waste combustors on January 23, 2024 (89 FR 4243). This final rule will respond to the voluntary remand and review of the NSPS and emission guidelines pursuant to CAA section 129.