On January 25, 2018, the US EPA issued a memorandum rescinding the Clean Air Act’s Once in Always in (OIAI) policy for major sources of hazardous air pollutants. EPA intends to publish regulatory text for this new policy direction in the Federal Register in the near future.
The once in always in policy was first established in a 1995 memorandum commonly referred to as the Seitz Memorandum. The once in always in policy requires any major source of hazardous air pollutants (HAP) subject to a Maximum Achievable Control Technology (MACT) standard (such as a NESHAP) applicable to major sources of HAP to always be categorized as a major source for purposes of the MACT standard. This has meant that even if a source that was initially designated as a major source of HAP decreases its emissions or potential to emit (PTE) to those of an area source (below 10 tons per year for any single HAP or 25 tons per year for any combination of HAPs), it will always have to follow the MACT standard subject to it as a major source and any other applicable major source requirements.
As a result of EPA’s decision to rescind this policy, any major source that takes an enforceable limit on its potential to emit HAP below the major source threshold and takes measures to do so becomes an area source and will be subject to any standards applicable to area sources rather than those applicable to major sources. EPA’s decision, according to the memorandum, was based on a plain reading of Section 112 of the Clean Air Act, finding that nothing in the act’s language permitted the creation of this policy.
The policy is effective as of January 25, 2018, however, the memorandum states that EPA intends to publish regulatory text to codify the policy.