This action adds standards of performance for new municipal waste combustor (MWC) units and emission guidelines for existing MWC's. The standards and guidelines implement sections 111 and 129 of the Clean Air Act and are based on the Administrator's determination that MWC's cause, or contribute significantly to, air pollution that may reasonably be anticipated to endanger public health or welfare. The standards and guidelines apply to MWC units at plants with aggregate capacities to combust greater than 35 megagrams per day (Mg/day) (approximately 40 tons per day) of municipal solid waste (MSW) and require sources to achieve emission levels reflecting the maximum degree of reduction in emissions of air pollutants that the Administrator determined is achievable, taking into consideration the cost of achieving such emission reduction, and any non-air-quality health and environmental impacts and energy requirements. The promulgated standards and guidelines establish emission levels for MWC organics (dioxins/furans), MWC metals (cadmium (Cd), lead (Pb), mercury (Hg), particulate matter (PM), and opacity), MWC acid gases (hydrogen chloride (HCl) and sulfur dioxide (SO<INF>2)), nitrogen oxides (NO<INF>X), and MWC fugitive ash emissions. Some of the pollutants being regulated are considered to be carcinogens and at sufficient concentrations can cause toxic effects following exposure. The standards and guidelines also establish requirements for MWC operating practices (carbon monoxide (CO), load, flue gas temperature at the PM control device inlet, and operator training/certification). Additionally, the standards for new MWC plants also require a siting analysis and materials separation plan.