Best Available Control Technology

Best available control technology (BACT) is a standard established under the U.S. Clean Air Act (CAA) that requires regulated activities to incorporate the use of currently available technology to reduce their emissions of criteria pollutants (i.e., particulate matter, carbon monoxide, nitrogen oxides, sulfur oxides, and volatile organic compounds) to the maximum degree possible while taking into consideration economic, energy, environmental and other related costs. Under the U.S. federal New Source Review (NSR) program, BACT applies to construction of major new sources and major modifications (including relocation) of existing facilities within areas that meet U.S. Environmental Protection Agency (EPA) ambient air quality standards.

For the purposes of the NSR program, a major project is defined as one that has the potential to significantly increase emissions of pollutants, ammonia, or any factor that contributes to depletion of the ozone layer. This potential is considered relative to the prevention of significant deterioration (PSD) increment in any given area. The PSD increment is the difference between the baseline level of ambient air pollutants (carbon monoxide, lead, nitrogen dioxide, PM10 and PM 2.5 [particulate matter smaller than 10 micrometers or 2.5 micrometers], ozone, and sulfur dioxide) and the maximum concentration for those pollutants allowed under the U.S. National Ambient Air Quality Standards (NAAQS) established by the CAA. BACT only applies to projects in areas that comply with the NAAQS (attainment areas) and criteria subject to PSD. Major new or modified facilities in areas that do not meet NAAQS (nonattainment areas) must meet the stricter standard of lowest achievable emissions rate (LAER), and control for criteria for which the region is out of attainment. Existing facilities located in nonattainment areas are required to use reasonably available control technology (RACT).

Permits to construct (PTCs) and permits to operate (PTOs) are issued either by state, regional, or local air quality regulatory agencies. Due to regional differences in air quality, the thresholds for project review under NSR vary. Furthermore, because the extenuating [Page 12]circumstances of environment, energy, and economics vary from place to place, the technology that constitutes BACT for any given application may vary on a case-by-case basis. BACT is a time dependent determination; for example, given two similar facilities, the BACT required when the second one seeks a permit may be substantially different from the technology approved for the first if a more effective or efficient technology becomes available after the first facility was permitted.

A project proponent initiates the process of identifying BACT for a particular project with an application for a PTC or a PTO. Any activity that will result in increased emissions of pollutants is considered a project. The first step is to identify all available control options, including those designated LAER. Applicants are expected to consider technologies in use both in the United States and abroad. They are directed to investigate the possibility of transferring technology from other similar facilities, and encouraged to consider adopting innovative control technology. BACT determinations in recently awarded permits for similar facilities are often helpful in expediting the search process. The EPA maintains the RACT/BACT/LAER Clearinghouse, an online, searchable database that proposers can use to identify control technologies for potential use in their own facilities. Many state, regional, and local agencies maintain similar databases.

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