California Air Resources Board

Best available control technology (BACT) requirements are defined in federal and state statute, and the implementation of each air district’s program varies across California.  Individual air districts further define BACT requirements in their individual BACT policies and rules, which include important considerations such as BACT definitions, trigger levels, and cost-effectiveness thresholds.  

Federal LAER

Federal Lowest Achievable Emissions Rate (LAER) is the most stringent level of BACT required under both state and federal law.  In federal law, LAER applies to major new and modified stationary sources in nonattainment areas under the New Source Review (NSR) (NSR) program.  The California LAER is the same as the federal LAER definition.

42 U.S.C. § 7501(a)(3):“The term “[LAER]” means for any source, that rate of emissions which reflects-- (A) the most stringent emission limitation which is contained in the implementation plan of any State for such class or category of source, unless the owner or operator of the proposed source demonstrates that such limitations are not achievable, or (B) the most stringent emission limitation which is achieved in practice by such class or category of source, whichever is more stringent.  In no event shall the application of this term permit a proposed new or modified source to emit any pollutant in excess of the amount allowable under applicable new source standards of performance.”

Federal BACT

Federal BACT is the least stringent level of BACT required under both state and federal law.  Federal BACT applies to major new and modified stationary sources, under state law in nonattainment areas under state NSR programs, and under federal law in clean Prevention of Significant Deterioration (PSD) areas. BACT is defined in federal law, but not in state law, except for South Coast Air Quality Management District (SCAQMD).

42 U.S.C.7479(3):BACT “means an emission limitation based on the maximum degree of reduction of each pollutant subject to regulation under this chapter emitted from or which results from any major emitting facility, which the permitting authority, on a case-by-case basis, taking into account energy, environmental, and economic impacts and other costs, determines is achievable for such facility through application of production processes and available methods, systems, and techniques, including fuel cleaning, clean fuels, or treatment or innovative fuel combustion techniques for control of each such pollutant.”

California BACT

California BACT is the most stringent level of BACT but is only defined under state law for South Coast Air Quality Management District (SCAQMD).  California BACT allows air districts to require controls beyond LAER if they are found to be both technologically feasible and cost-effective.

HSC § 40405: BACT for SCAQMD is defined in the same manner as federal LAER.  

HSC § 40440.11: SCAQMD, may establish a more stringent BACT than LAER as defined by federal law, as specified, by considering control options or emission limits to be applied to the basic production or process equipment existing in that source category or a similar source category. Further sets forth requirements for SCAQMD when establishing BACT or making a BACT determination for a source, including the requirements for the cost-effectiveness calculation and a determination that the proposed emission limitation has been met by production equipment, control equipment, or a process that is commercially available for sale, and has achieved the BACT in practice on a comparable commercial operation for a least one year, or a period longer if a longer period is reasonably necessary, as specified.

BACT Limit Categories

Each BACT stringency level includes different approaches for identifying the appropriate emissions limit, referred to in the figure below as the limit category.   

While each district has their own internal policies that define these limit categories, in general the following definitions and guidance applies to equipment and technology identified in the Clearinghouse:

• Achieved in Practice: Commercially available equipment that has been demonstrated as effective and reliable on a full-scale unit for a specific class and category of source.  U.S. EPA Region 9 has concluded that this includes technologies employed outside of the United States (see 1990 NSR Workshop Manual). 
  • For federal LAER, technology that has been achieved in practice is required for all new or modified equipment within the class/category without requiring a cost-effectiveness analysis.  
• Federal Rule Limits: The minimum level of control required for BACT must be no less than the limits defined in federal New Source Performance Standards (NSPS) and National Emissions Standards for Hazardous Air Pollutant (NESHAP) rules.
• SIP Limit: Most stringent emissions limit found in an approved state implementation plan (SIP) in any state as a rule, regulation, or permit.
• Technologically Feasible & Cost-Effective:
  • Conventional Equipment (New and Existing Sources): Cost-effective technology determined to be commercially available, reliable, and effective at achieving an emissions limit (also referred to as proactive BACT).  This technology may not yet be installed, or installed long enough to be considered achieved in practice.  Often technologies identified in this category include new technologies, technology transfers (from a class/category of source with similar characteristics), or technology adopted by a Hearing Board. 
  • Alternative Equipment (New Sources Only): Equivalent equipment or process that emits less air pollutants than the equipment proposed by the applicant.  This category generally excludes add-on technologies, and would require a change in the process or technology utilized, therefore it is often only considered for new sources (e.g. fuel cell replacing a Tier 4 diesel generator).
  • For federal BACT, technology is evaluated for each permit on a case-by-case basis, and considering economic, energy, and environmental factors.