See the latest EHS federal and state regulatory updates due to COVID-19

What is “Once In, Always In”?

“Once In Always In” (OIAI) is a phrase used in a May 16, 1995 memo signed by John Seitz, then Director of the U.S. Environmental Protection Agency (EPA) Office of Air Quality Planning and Standards (OAQPS). At that time, EPA had just begun promulgating the first 40 CFR Part 63 National Emission Standards for Hazardous Air Pollutants (NESHAPs) as directed by the 1990 Amendments to the Clean Air Act. The Hazardous Organic NESHAP, also known as the HON, had been promulgated the year before (for the Synthetic Organic Chemical Manufacturing Industry); other standards had also been recently promulgated or were in the works. EPA issued several policy memos during this time period in response to questions from the regulated community about implementation of the rules and programs mandated by the 1990 Amendments.

OIAI EPA photoFor purposes of Section 112 of the Clean Air Act (CAA) and the Part 63 NESHAPs, major sources are those that have the potential to emit 10 tons per year or more of any single hazardous air pollutant, or 25 tons per year or more of any combination of hazardous air pollutants. Area sources have potential emissions below those thresholds and are subject to less stringent requirements than major sources; certain types of area sources are not subject to any requirements. (See our online NESHAPs Source Categories Table for a list of industry categories subject to major and area source requirements, at In the memo that put the OIAI policy in place, titled “Potential to Emit for MACT Standards - Guidance on Timing Issues,” Mr. Seitz asserted the following:

  • Existing major sources must either:
    • Comply with applicable major source MACT (Maximum Achievable Control Technology)standards, or
    • Obtain and comply with federally enforceable limits to bring them below major source thresholds for hazardous air pollutants (HAPs) prior to the first compliance date associated with a substantive regulatory requirement in the major source MACT standard.
  • New major sources must either:
    • Comply with applicable major source MACT standards, or
    • Obtain and comply with federally enforceable limits to bring them below major source thresholds for HAPs prior to the promulgation date of the major source MACT standard or startup, whichever is later.
  • Sources that are required to comply with major source MACT standards due to the choice made in the aforementioned situations are required to permanently comply with that MACT standard (Once In, Always In). The stated rationale in the 1995 memo was to prevent facilities from “backsliding” from MACT control levels through obtaining potential to emit limits and increasing emissions up to just below the major source threshold.
  • Sources that are required to comply with major source MACT standards will be required to obtain a Title V Part 70 operating permit.
  • Facilities that have sources subject to a major source MACT standard because of OIAI but that have a potential to emit (PTE) below major source thresholds for HAPs will be considered area sources for purposes of subsequently installed equipment, and subsequently promulgated MACT standards.

OIAI_green boxWhat has happened since the 1995 OIAI policy was released?

The OIAI policy presented companies with a number of challenges. Facilities with multiple affected sources constructed at different points in time may have some that are subject to major source MACT, while other identical units are subject to area source MACT. Consider the following example at a compressor station.

In 2010, a compressor station was a major source of HAPs and subject to the NESHAP for Stationary Reciprocating Internal Combustion Engines (Subpart ZZZZ). In 2011, three of the eight engines at the site were removed from the facility and the PTE was reduced to area source levels. In 2017, an engine was added but the facility PTE remained at area source levels. In this scenario, the five engines that were at the facility from 2011 onward are subject to major source requirements in Subpart ZZZZ and the engine added in 2017 will be subject to area source requirements in Subpart ZZZZ. The facility will have to ensure it is complying with the appropriate, but different, requirements for each engine.

Some facilities, unaware of the existence of this policy, have been subject to enforcement action due to following only the requirements as written in the NESHAPs and associated General Provisions (40 CFR 63 Subpart A). Additionally, some facilities not only have continued to be subject to major source MACT when their potential emissions are below major source thresholds, but also have become subject to more stringent standards when the NESHAP is revised.

In 2002, a gas plant was a major source of HAPs and subject to the NESHAP for Oil and Natural Gas Production Facilities (Subpart HH). In 2010, that facility removed two engines and became an area source of HAPs, but remained subject to major source MACT for Subpart HH. In 2012, EPA revised the leak definition in Subpart HH for valves from 10,000 ppm to 500 ppm. Thus the facility was subject not only to major source MACT, but also to a more stringent leak definition even though it was an area source at the time the standard was revised.

EPA proposed regulatory amendments in 2003 and 2007 that would have altered the OIAI policy, but none were finalized (with the exception of limited provisions associated with EPA's National Environmental Performance Track Program).

Opponents of the policy have asserted that it resulted in a disincentive for pollution prevention. The Environmental Council of the States (ECOS), in its response to Executive Order 13777 “Enforcing the Regulatory Reform Agenda,” recommended that EPA provide an exception to the OIAI policy for cases where emissions reductions were made through the use of pollution prevention measures. The Association of Air Pollution Control Agencies (AAPCA), in its response to the Order, stated that the policy limited the incentive for industry to reduce emissions or find alternative materials. The State of Maine noted that, as a result of the policy, small facilities were required to obtain a “complex, costly, and stringent Title V permit” creating a “competitive disadvantage” and unfairly limiting “the abilities of subject sources to make modifications or operate in a competitive market.”

The New Memo

On January 25 of this year, William Wehrum, EPA Assistant Administrator for Air, issued a memorandum superseding the 1995 Seitz guidance and withdrawing the OIAI policy in the preceding memo, effective immediately. The new memo states “EPA has determined that the OIAI policy articulated in the May 1995 Seitz Memorandum is contrary to the plain language of the CAA, and, therefore, must be withdrawn.” EPA's current view is that the definitions of major source and area source in Section 112 of the Clean Air Act “compel the conclusion that a major source becomes an area source at such time that the source takes an enforceable limit” on its PTE to below major source thresholds. EPA now asserts that the Act places no temporal limitations on the ability of a source to become an area source and that EPA did not have authority to impose such limitations “under the plain language of the statute.”

EPA also states in the memo that it anticipates publishing draft regulatory text reflecting its current interpretation in the Federal Register “soon.” (The 1995 Seitz memo had also stated an intention to proceed with a rulemaking, which was never completed.)

OIAI_Webinar boxWhat's Next?

So… where does that leave us now?

Not surprisingly, there has already been a broad range of responses by state and local regulators. For example, one state re-noticed a Title V permit renewal within two weeks of the release of the Wehrum memo, changing the applicability of a MACT standard from major (as had been described in the original notice) to area, due to the removal of the OIAI policy. Facilities that are not major sources for criteria pollutants and are only Title V permittees becauseof the OIAI policy may be able to get out of Title V entirely.

Some proponents of EPA's current interpretation conclude that, as the original policy was implemented via memorandum, a subsequent memo issued by EPA is similarly valid and can be implemented immediately. Others are taking a more conservative approach and are waiting for EPA to proceed with a rulemaking. It is reasonable to expect that EPA's new memo will be challenged, and any rulemaking effort will generate negative comments from some stakeholders. Facilities that want to apply the new interpretation should be prepared for challenges from citizen groups that perceive this as reducing the stringency of environmental requirements. If a facility has a permit (Title V or construction) that states major source MACT applies, a permit revision may be needed. Facilities currently in enforcement proceedings due to a lack of awareness or understanding of the OIAI policy may be able to negotiate a settlement with a reduced or withdrawn penalty.

Sources planning to make use of the new policy to opt out of a major source MACT standard should be sure to consider other possible implications of the change, including whether removing emission control requirements would create compliance challenges for other non-HAP pollutants (for example, VOC and particulates), or trigger New Source Review (NSR) permitting due to increases in emissions. Depending on the permit programs in place for a particularfacility, there may also be Compliance Assurance Monitoring (CAM) implications. It will be critical for any entity wishing to pursue action as a result of EPA's new memo to work closely with their permitting authority.

EPA's press release, as well as the 2018 withdrawal memorandum and the original 1995 OIAI policy, can be found at .

Trinity has extensive experience in evaluating MACT applicability and working with state, local, and federal agencies. For assistance in developing the best approach for your particular situation, call (800) 229-6655.