Under a new EPA proposal, a major source of hazardous air pollutants (HAPs) could be reclassified as an area source at any time by limiting its potential to emit (PTE) HAPs to below the major source thresholds of 10 tons per year (tpy) of any single HAP or 25 tpy of any combination of HAPs. The proposal would provide regulatory language for a policy the EPA is already implementing following the Agency’s issuance of a memo in January 2018, which withdrew what had been known as the Once-in-always-in (OIAI) policy.  

In addition, in place of the existing requirement that sources meet federally enforceable PTE limits, the Agency is proposing that HAP PTE limits that meet legally and practicably enforceable criteria are effective.

OIAI policy

Clean Air Act (CAA) Section 112 distinguishes between major stationary sources and area sources—that is, any stationary source of HAPs that is not a major source. Major sources are subject to emissions limits based on the maximum achievable control technology (MACT), while area sources are generally required to meet less stringent emissions limits based on the generally achievable control technology (GACT).

In 1995, John Seitz, then the director of the EPA’s Office of Air and Radiation (OAR), issued what became known as the Seitz Memo, which articulated the OIAI policy. Seitz stated that once a source of HAPs was listed as a major source, it could only be reclassified as an area source before the first compliance date of the standard to which it was subject. The reason, according to Seitz, is that compliance with the MACT often results in a major source reducing its emissions to levels substantially below the major source limits. Absent the OIAI policy, these facilities could “backslide” from MACT control levels by obtaining PTE limits, thereby escaping applicability of the MACT and legally increasing emissions right up to the major source threshold. In other words, the intent of the OIAI policy was to block backsliding on emissions control.

No temporal limitations

But in the 2018 policy statement, William Wehrum, the assistant administrator for the OAR, stated that in the CAA, Congress placed no temporal limitations on the determination of whether a source emits or has the PTE HAPs in sufficient quantity to qualify as a major source.

“To the extent the OIAI policy imposed such a temporal limitation (i.e., before the ‘first compliance date’), EPA had no authority to do so under the plain language of the statute,” wrote Wehrum.

The memo therefore stated that any major source that takes an enforceable limit on its PTE and takes measures to bring its HAP emissions below the applicable threshold becomes an area source, “no matter when the source majy choose to take measures to limit its PTE. That source, now having area-source status, will not be subject thereafter to those requirements applicable to the source as a major source under CAA section 112, including, in particular, major source MACT standards—so long as the source’s PTE remains below the applicable HAP emission thresholds.”

The proposal would give regulatory status to the policy articulated in the 2018 memo. Regarding backsliding, the Agency said it analyzed the reclassification of 34 sources and found that 31 of those would have no change in emissions as a result of reclassification, while the remaining 3 sources would have reduced emissions.

PTE effectiveness criteria

The EPA is proposing that a major source that reduces its PTE HAP emissions to below the major source thresholds by taking HAP PTE limits that meet the proposed criteria for effective PTE limits may request and, upon approval, be reclassified to area-source status. To be effective, the Agency is proposing that HAP PTE limits must be legally and practicably enforceable. Legally enforceable means either federally enforceable or legally enforceable by a state, local, or tribal authority. The EPA proposes that to be practicably enforceable, HAP PTE limits must be written so that it is possible to readily verify compliance and to document violations when enforcement action is necessary.

This part of the proposal goes hand-in-hand with a new definition of PTE, which the Agency is also proposing.