The Environmental Protection Agency (EPA) is taking final action to approve a revision to the State of Maryland's Clean Air Act (CAA) sections 111(d) and 129 State Plan for municipal waste combustors (MWCs). The revision reflects amendments to Code of Maryland Regulations (COMAR) 26.11.08.08, which update the MWC opacity compliance provisions. The Maryland Department of the Environment (MDE)'s revised regulations provide that quality assurance (QA) and quality control (QC) requirements for continuous opacity monitors (COMs) are found in COMAR 26.11.31, rather than the now discontinued Technical Memorandum (TM 90-01). EPA is approving this revision to Maryland's CAA sections 111(d) and 129 State Plan in accordance with the requirements of the CAA.