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Sorting out source reclassification for HAPs.
One portion of the regulations that has been changing over the past few years is reclassification of major sources to area sources (MM2A) for hazardous air pollutants (HAPs). In the mid-1990s, when EPA was first implementing the Part 63 air toxics standards (aka NESHAPs), the agency issued the “once in, always in” policy, which said any source that was a major source on the compliance date for an air toxics standard would always be a major source for that standard. Thus, even if the source lowered its HAP emissions below major source thresholds, it would remain a major source for that standard forever.
This policy was withdrawn in 2018, allowing major sources to reclassify as area sources at any time. EPA then issued its MM2A rule that codified this into the regulations on November 19, 2020. [85 FR 73854]
On September 10, 2024, in a reversal to control sources of bioaccumulative HAPs, EPA listed 33 source categories that are once again—subject to once in, always in, and this is the current status. [89 FR 73293] Because this is a delegated program, these changes are generally effective in all states at the same time. For more compliance morsels, visit our website.
UPDATE: Congress repealed the September 2024 rule under the Congressional Review Act (CRA), and the resolution was signed into law on June 20, 2025. We expect legal challenges to ensue.
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