On September 1, 2026, the U.S. Environmental Protection Agency (U.S. EPA) published a memorandum (September 2026 Memo) intended to clarify how they evaluate Startup, Shutdown, and Malfunction (SSM) provisions in State Implementation Plan (SIP) submittals. The guidance follows years of uncertainty due to ongoing litigation around whether exemptions from emissions limitations during periods of SSM are permissible under the Clean Air Act (CAA).
As background, a SIP is a state’s means for implementing, maintaining, and enforcing the National Ambient Air Quality Standards (NAAQS). The following primary types of SIP provisions have come under scrutiny by various stakeholders (as summarized in this article by Amy Marshall):
- Automatic exemptions (e.g., provisions stating that a SIP emissions or opacity limit does not apply during periods of startup or shutdown or during a malfunction).
- Director’s discretion provisions (e.g., provisions that allow a facility to ask the state agency Director to determine that excess emissions during SSM events were not a violation).
- Overbroad enforcement discretion provisions (e.g., the provisions could be read to allow officials to foreclose U.S. EPA enforcement actions and citizen suits).
- Affirmative defense provisions (where a state could prevent U.S. EPA and citizens from holding facilities liable for excess emissions during SSM).
U.S. EPA issued SIP Calls to nearly every state regarding these types of provisions in 2015, requiring those states to update their SIPs to remove the provisions and/or require emissions limits to apply at all times. As explained in Amy’s article, many of those SIP Calls were vacated in 2024 as U.S. EPA’s authority to issue the SIP Calls was challenged.
More recently, two decisions by the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit Court) informed U.S. EPA’s September 2026 Memo:
- Environmental Committee of the Florida Electric Power Coordinating Group, Inc. v. EPA, 94 F.4th 77 (D.C. Cir. 2024) (Florida Electric) pertained to all four of the provision types above, and was the basis for a December 19, 2024 memo that is now superseded by the September 2026 Memo.
- SSM Litigation Group v. EPA, 150 F.4th 593 (D.C. Cir. 2025) (SSM Litigation Group) pertained to affirmative defense provisions.
At issue with the SSM SIP provisions is that “emissions limitations” must apply at all times and determining whether it is “necessary and appropriate” for provisions of a SIP to be “emissions limitations.”
In the September 2026 Memo, U.S. EPA said they will review state SIP submittals in the context of SSM by considering the following two categories of provisions:
- The provision is required to be an emission limitation or emissions standard under a provision of the CAA other than section 110(a)(2)(A).
- The State is using the provision explicitly to achieve attainment or maintenance of a NAAQS or to meet another comparable requirement in the CAA.
To clarify the meaning of each category, U.S. EPA provides examples. The first category pertains to provisions that are already required to be emissions limitations, such as a Best Available Control Technology (BACT) or New Source Performance Standard (NSPS) limits. The second category pertains to provisions that are necessary to achieve compliance with the NAAQS, but where an SSM exemption would undermine the compliance demonstration.
U.S. EPA indicates they will rely on a state’s determination of whether it is “necessary and appropriate” for a provision to be an emissions limitation, while recognizing that U.S. EPA has final say. U.S. EPA also clarifies that SIP provisions do not always need to be numerical emissions limitations and, therefore, may not need to apply at all times, but that “at least some” limits that apply at all times are needed to ensure compliance with the NAAQS.
While the September 2026 Memo is directed at state agencies, the regulations in a state’s SIP ultimately impact the regulated entities. Clarity is welcomed, but SIPs are likely to be more restrictive when it comes to SSM provisions going forward. Contact lkroos@all4inc.com or your ALL4 Project Manager for questions about what SSM provisions in SIPs (or the lack thereof) may mean for your facility’s compliance.
