EPA Finalizes Changes to “Once In, Always In” Rule

On November 19, 2020, the United States Environmental Protection Agency (EPA) published a final rule to revise its “once in, always in” policy under the 40 CFR Part 63 of the Maximum Achievable Control Technology (MACT), or National Emission Standards for Hazardous Air Pollutants (NESHAP), rules. The revisions clarify “major source” and “minor source” definitions and allow sources that were previously MACT-major to reclassify to an “area source” if their hazardous air pollutants (HAP) potential to emit (PTE) falls below 10 tons per year (tpy) for an individual HAP or 25 tpy combined for HAPs. EPA has also included specific notification requirements whenever reclassification occurs. Further, the revisions specify that if a source goes from major to minor and back to major, the applicable MACT requirements become immediately effective.

Some background

Until 2018, the EPA had maintained a “once in, always in” policy for 25 years regarding major HAP sources. In 2018, EPA issued a memorandum rescinding the “once in, always in” policy. The latest rulemaking, which becomes effective January 19, 2021, codifies the tenets of the 2018 memorandum, meaning a major source can become an area source at any time by limiting its PTE. Without a “once in, always in” policy, facilities could "backslide" from MACT control levels by obtaining PTE limits that remove MACT standard applicability and then can increase emissions to the major-source threshold.

Questions? Contact us

Jay Christopher
Senior Scientist
[email protected]

Jeremy Sell, P.E.
Vice President, Air & Process Services
[email protected] 

Jay Christopher
Senior Scientist Specialist, Englewood, Colorado

Jay has over 40 years of environmental experience. Since 1990, he has specialized in air quality issues and permitting programs affecting a broad range of facility operations, with hands-on experience in both corporate headquarters and facility regulatory settings, as well as in the environmental consulting world. Jay has managed the environmental compliance program and environmental professional staff for a major refinery’s downstream businesses and is involved in regional air quality issues and national trade groups.

Did you find this information useful? Click the icons below to share on your social channels.

facebook twitter linkedin
Other News


Receive the latest technical and regulatory updates in your inbox.