The Clean Air Act (CAA) directs the Environmental Protection Agency (EPA) to define “hazardous air pollutants (HAPs)” that may pose acute health hazards, and to impose regulations to reduce those hazards. Controls include permits for “major sources” of HAPs based on “Maximum Achievable Control Technologies (MACT),” and lesser controls for non-major “area sources.” Effective September 10, 2024 EPA has reinstated a policy that an emission source that met major source criteria at the time an applicable MACT became effective is “once in, always in” – even if a source makes binding changes reducing its “potential to emit” below the applicable major source threshold, it still cannot formally requalify as a less-regulated area source. This policy was in force from 1995 until EPA reversed it in January 2018 to allow full reclassification. EPA subsequently codified this approach in a rule issued in 2020. However, EPA has now revised that rule to reinstate “once in, always in.” The rest of this note summarizes CAA requirements for HAP sources, and the latest change.
How are Major and Area Sources Defined and Regulated?
The CAA statute directs EPA to list emissions of particular HAPs by “source categories,” and provides for National Emission Standards for Hazardous Air Pollutants (NESHAPs) to define applicable requirements. Since the 1990 CAA Amendments, most NESHAPs are based on MACT standards defined by EPA. Major sources require extensive permits, while area sources typically do not.
CAA defines a major source of HAPs as follows
“‘major source’ means any stationary source or group of stationary sources located within a contiguous area and under common control that emits or has the potential to emit considering controls, in the aggregate, 10 tons per year [tpy] or more of any hazardous air pollutant or 25 [tpy] or more of any combination of hazardous air pollutants. “
In contrast, an “area source” means a stationary source of one or more HAPs with actual or potential emissions too low to qualify as a major source. Readers should note that this determination may not be as obvious as it seems. For example, EPA may:
- Aggregate sources within a single facility to reach the “major source” threshold.
- Establish a lesser quantity (or for radionuclides different criteria), for a major source than that specified in the quoted text above, based on the potency, persistence, potential for bioaccumulation, or other characteristics of the pollutant, or other relevant factors.
- Consider a source’s “potential to emit,” not just its present emissions. Therefore, if a source operates for limited hours per year, but would exceed the major source threshold if it operated full time, EPA (or state regulators) may consider it a “major” source and require a permit. Conversely, a source that accepts a binding limit on its potential to emit – limiting hours of operation, for example – might be treated as less than major.
This last possibility plays into the change EPA has just announced.
How is EPA changing major sources’ flexibility?
Beginning in 1995 (with a policy memo from then-Director Seitz of EPA’s Office of Air Quality Planning and Standards), EPA allowed sources to negotiate binding limits on their potential to emit while MACT rules were pending, so that on the date a MACT rule took effect the source was not major. However, EPA did not allow these changes after a MACT rule takes effect, continuing to regulate the source as major regardless of such operational changes or limits. This “once in, always in” policy meant there was no way for a source to negotiate its way out of major source status.
However, in January 2018 EPA ended the “once in, always in” policy, allowing a major source to negotiate binding limits on its potential to emit at any time, in order to cease to be regulated as a major source and reclassified as an area source. EPA explained that this flexibility was appropriate for sources, and not restricted by the agency’s reading of CAA requirements. (I wrote about this change HERE). EPA subsequently codified this flexible approach in a regulation issued in November 2020 (effective January 19, 2021) (40 CFR 63.1(c)(6)).
EPA has now restored the “once in, always in” provision, subject to a clarifying limitation that it applies to those sources necessary for EPA to reach its CAA statutory requirement that sources emitting 90% of a HAP’s total emissions are regulated. Note that federally-enforceable emissions restrictions can become permit conditions, which may provide alternatives to other more onerous conditions, so it may still be advantageous to restrict emissions.
What happens now?
Effective September 10, 2024, a HAP source that qualifies as “major” on the day a new MACT requirement becomes effective will continue to be subject to major source permit requirements even if it agrees to binding restrictions on emissions. If a new MACT is pending, however, a source can take steps to restrict its emissions in order to qualify as a non-major “area source” when the new regulation takes effect.
Self-Assessment Checklist
Do any of the organization’s activities emit regulated HAPs in quantities that may exceed CAA thresholds for a “major source?”
Do any activities qualify as a major source subject to an adopted MACT?
Would any activities qualify as a major source subject to a proposed or anticipated MACT?
- If so, has the organization evaluated whether it is eligible to negotiate binding limitations on the activity’s “potential to emit” to qualify as an “area source” subject to reduced regulation?
Where Do I Go For More Information?
- EPA –
- webpage “Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act”
- latest regulatory change (9/10/24 Federal Register)
About the Author
Jon Elliott is President of Touchstone Environmental and has been a major contributor to STP’s product range for over 30 years.
Mr. Elliott has a diverse educational background. In addition to his Juris Doctor (University of California, Boalt Hall School of Law, 1981), he holds a Master of Public Policy (Goldman School of Public Policy [GSPP], UC Berkeley, 1980), and a Bachelor of Science in Mechanical Engineering (Princeton University, 1977).
Mr. Elliott is active in professional and community organizations. In addition, he is a past chairman of the Board of Directors of the GSPP Alumni Association, and past member of the Executive Committee of the State Bar of California's Environmental Law Section (including past chair of its Legislative Committee).
You may contact Mr. Elliott directly at: tei@ix.netcom.com