that flue-gas temperatures around 300°C are associated with peak secondary dioxin formation, and research by Environment Canada and others showed that lower emissions of mercury, dioxins, and acid gases occurred when flue-gas temperatures were around 150°C, EPA did not propose any specific flue-gas temperature requirement for either new or existing plants.

The technology on which MACT standards are based might have resulted in greater emissions reductions, but at higher costs if more-advanced technologies—such as activated-carbon filters or static beds for control of dioxin and mercury and selective catalytic reduction for NO_x control—were considered.

The database on which MACT standards were calculated contained important omissions. For example, EPA chose not to include data from any incinerators in Europe in its database for determining the MACT floor.

Finally, environmental activists have called for siting criteria that take into account proximity to sensitive populations (e.g., the old, and the very young), sensitive land uses (e.g., schools and hospitals), facilities with long-term residents (e.g., prisons), and areas with multiple sources of pollution that impose a cumulative burden on residents. The MACT-based regulations do not reflect those concerns.

Incinerators and other combustors (e.g., light-weight aggregate kilns and cement kilns) that use hazardous wastes as fuels are regulated principally under RCRA and CAA. A hazardous waste is one that either exhibits specific characteristics of ignitability, corrosivity, reactivity, and toxicity or is specifically listed in 40 CFR §§ 261.31 through 261.33. Facilities that treat, store, and dispose of hazardous wastes are comprehensively regulated under RCRA. Operators of hazardous-waste incinerators must obtain an operating permit from either federal or state regulators under standards promulgated by EPA. The permitting process for a new hazardous-waste incinerator generally takes at least 3 years and entails the investment of $5-10 million (Steverson 1994).

Incinerators burning waste contaminated with PCBs, which fall under the Toxic Substances Control Act, must obtain a federal permit. Under Section 112 (d) of the CAA, EPA is required to develop national emission standards for hazardous air pollutants (NESHAP) for major source categories. EPA has determined that industrial/commercial/institutional boilers may be a major source of emissions of one or more HAPs. To the extent that an incinerator discharges pollutants into navigable waters,³ the operator must also obtain a permit under the Clean Water Act.