The Environmental Protection Agency (EPA) is approving the Clean Air Act (CAA) State Plan for Municipal Waste Combustor (MWC) units submitted by the Maine Department of Environmental Protection (Maine DEP). This submission includes revisions to Maine's previously approved State Plan for existing Large MWCs in response to amended emission guidelines (EGs) for Large MWCs. This submission also includes a State Plan for existing Small MWCs. Maine DEP's State Plans for Large and Small MWCs implement and enforce provisions at least as protective as the EGs applicable to these subcategories of solid waste incinerators. This action is being taken in accordance with the CAA.