NOTE: The Once In Always In Policy was withdrawn on January 25, 2018. Please click here to read the official Memorandum from U.S. EPA dated January 25, 2018. This guidance supersedes the May 1995 Seitz Memorandum.

On February 8, 2018, the withdrawal notice of the Once In Always In Policy was published in the Federal Register and can be found here.

You may also access Ohio EPA’s February 2018 Fact Sheet for the Withdrawal of the Once In Always In Policy here.

On November 19, 2020, US EPA published a Final Rule entitled "Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act". You may find the Final Rule Federal Register notice here.

Background:

Section 112 (c) of the Clean Air Act (CAA) requires U.S. EPA to publish a list of industry group (major source and area source) categories and subcategories that employ, manufacture or emit hazardous air pollutants (HAP). The 1990 CAA Amendments require U.S. EPA to promulgate technology-based emission standards and allow for the possible supplementation of health-based standards. The regulatory standard for the HAP sources is the Maximum Achievable Control Technology (MACT) standard. Prior to the 1990 CAA Amendments, the regulatory standards for the HAP sources were health-based standards. The 1970 CAA Amendments had established the National Emission Standards for Hazardous Air Pollutants (NESHAP) program, establishing standards and providing national conformity. A NESHAP based on Maximum Achievable Control Technology is called a MACT standard or simply a MACT.

What is a MACT standard?

The Maximum Achievable Control Technology (MACT) standard is a level of control that was introduced by Title III of the 1990 Clean Air Act Amendments. The purpose of these Amendments was to expedite the development of standards that would reduce hazardous air pollutant (HAP) emissions.

When developing a MACT standard for a particular source category, U.S. EPA looks at the level of emission control currently being achieved by the best-performing similar sources through various control methods, such as clean processes, control devices and work practices. These emission levels set a baseline, often referred to as the "MACT floor," for the MACT standard.

The "MACT floor" is the initial determination of the MACT standard for each industry source category. It provides the minimum level of HAP emission control requirement for new and existing sources. The MACT floor for new sources is equivalent to the level of HAP emission control achieved by the best-controlled similar source, and the "MACT floor" for existing sources is the average level of HAP emission control achieved by the top 12 percent of that industry group's currently operating sources. At a minimum, a MACT standard must achieve, throughout the industry, a level of emissions control that is at least equivalent to the MACT floor. Under 1990 CAA Amendments, U.S. EPA can establish a more stringent standard when this makes economic, environmental and public health sense.

Who is regulated by the MACT standards?

All source categories that include major sources and area sources of hazardous air pollutants (HAPs) are listed within Section 112(c) of the Clean Air Act. This list has been divided into three groups, or "bins," of Maximum Achievable Control Technology (MACT) standards. 112(e) of the Clean Air Act cites the initial promulgation schedule for the MACT standards. The two- and four-year standards were required to be promulgated within four years of the passage of the Clean Air Act Amendment of 1990, which was in 1994. The seven-year standards were required to be promulgated in 1997, and the 10-year standards are required to be promulgated in the year 2000. The determination of whether area sources in any given source category should be regulated is based upon the health risk those sources present to the public.

Section 112(d)(6) of the Clean Air Act requires U.S. EPA to review and revise each promulgated MACT standard as necessary (taking into account developments in practices, processes, and control technologies), no less often than every 8 years to protect public health. This process is called the Risk and Technology review of NESHAPs.

What MACT standard applies to my company?

All source categories and subcategories that include major sources and area sources of hazardous air pollutants (HAPs) are listed within Section 112(c) of the Clean Air Act. To find which Maximum Achievable Control Technology (MACT) standards apply to your company, first select the best-matched source category from the MACT promulgated standard list source description. Then, from this list, an industry can obtain further information about what processes are regulated by the MACT standard and what are the compliance deadlines in the standard.

• The list of promulgated MACT standards

Permitting and Compliance Assessment of Major and Area Source MACT/GACT Standards

Permitting and Compliance Assessment of Major and Area Source Maximum Achievable Control Technology (MACT)/Generally Available Control Technology (GACT) Standards

The Division of Air Pollution Control (DAPC) created an Engineering Guide to provide permitting staff DAPC’s position concerning the permitting and compliance assessment of major and area source Maximum Achievable Control Technology (MACT)/Generally Available Control Technology (GACT) standards. Engineering Guide #88 – MACT and GACT Guidance can be found by clicking here.

MACT requirements apply to major sources of HAPs or area sources of HAPs, and these standards are congressionally mandated. GACT standards apply to some area sources, and they are considered to be an optional alternative approach to MACT. For area sources within each source category, the Clean Air Act allows U.S. EPA to develop standards or requirements which provide for the use of generally available control technologies (GACT) or management practices rather than the maximum achievable control technology (MACT) required for major sources.

The Division of Air Pollution Control has also created a spreadsheet called the MACT Tracker. The MACT Tracker is an Excel Spreadsheet that is a “go-to” document for MACT/GACT standards. It outlines all promulgated MACT/GACT standards to date. The MACT Tracker should be used as a guide. Due to the frequent changes in the standards, the Tracker will be updated periodically.

Within the MACT Tracker, it has the Subpart Name, associated Subpart letter, if the Subpart is major or area source, the promulgation date, amendments, the CFR reference, the current action of the standard and date of the current action.

You may access the MACT Tracker by clicking [here] and instructions on how to use the MACT Tracker by clicking [here].

You may access the Memorandum of Agreement for Clean Air Act Section 112 by clicking [here]. 

The compliance deadlines according to 112(e)(1)(A) of the CAA for MACT standard promulgation for an industry source are to be within 10 years of the enactment of the CAA Amendments, or within two years from the date the categories or subcategories were listed for an industry source, whichever is later. The completion schedule for this list includes 40 categories to be completed within two years of the 1990 Amendments, with 25 percent of the remaining entries on the list to be completed within four years of the 1990 Amendments, another 25 percent within seven years and the remainder before the 10-year deadline.

Other Related Sites

• U.S. EPA TTN Air Toxics Website
• Code of Federal Regulations (eCFR) – 40 CFR Part 63
• Federal Register

For more information, please contact Briana Hammond by email at briana.hammond@epa.ohio.gov or by phone at (614) 644-3698.