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Reclassification of Major Source as Area under CAA Section 112

Updated: Jun 29, 2021

The “Once in, Always In” policy established in 1995 required facilities that meet major source criteria based on Hazard Air Pollutant (HAPs) thresholds comply permanently with Maximum achievable Control Technology (MACT) standards regardless of their ability to obtain area source status. Specifically, this meant that major sources that were able to reduce their potential to emit (PTE) below major source thresholds, 10 tpy for any one HAP or 25 tpy total for any HAPs in total, were subject to MACT. This was viewed as a regulatory burden inconsistent with the Clean Air Act (CAA) because the “One in, Always In” rule only allowed facilities to switch to area source status up to the compliance date and not after. This meant that sources could be subject to the same regulations based on their temporary HAP emissions and was seen as a lack of incentive for operators to seek ways of reducing their emission levels.

However, in January of 2018, the EPA issued a memo similar to their 2007 proposal, effectively withdrawing their “Once In, Always In” policy allowing for major sources able to reduce its potential to emit to below MACT threshold to no longer be subject to MACT, or to “reclassify” the facility as an area source. The now proposed rule, allows sources to reclassify to an area source after the compliance date. The EPA is also proposing to remove the requirement for federally PTE limits and requiring instead a limitation based on physical or operational capacity of the source.


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