Environmental Permitting

Shutdown of the SSM exemption

What is a SIP and why is it important in this case?
A state implementation plan (SIP) is a plan prepared by each state detailing how the state will attain and maintain compliance with each NAAQS.  SIPs contain enforceable emissions limits needed to comply with the CAA and prohibit emissions that would cause or contribute to violations of a NAAQS

Many states have provisions for SSM exemptions in their SIPs, and the Sierra Club’s position is that “these SSM exemptions undermine the emission limits in SIPs and threaten states’ abilities to achieve and maintain compliance with NAAQS, thereby threatening public health and public welfare.”  If a SIP does not meet the requirements of the CAA it must be deemed inadequate.  Under such circumstances EPA can issue a SIP Call requiring states to revise and resubmit the plan, which is what is being proposed in this case. 

Why do SSM exemptions exist?
In 1982 EPA took the position that excess emissions may prevent attainment or interfere with the maintenance of attainment, and therefore, all excess emissions are violations.  However, at the time many SIPs contained provisions that were not consistent with EPA’s policy, which the agency attributes to inadvertent approval or preexisting provisions that were never removed.

In a 1999 memorandum, EPA confirmed its position on excess emissions always being a violation, but stated that there are circumstances under which such exceedances are unavoidable and for which enforcement discretion may be appropriate.  In addition, EPA opened the door for states to include SIP provisions that would “excuse a source from penalties if the source can demonstrate that it meets certain objective criteria,” otherwise known as an affirmative defense.

What exactly is EPA proposing to do?
EPA policy is that all exceedances of emissions limits are violations, and SIP provisions that are not consistent with that policy, such as SSM exemptions, are not allowed.  Recent court decisions have confirmed this, and the Sierra Club has submitted a petition for EPA to act.  Therefore, EPA is responding by:

  • Proposing that the SIPs of 36 states are inadequate and proposing a SIP Call compelling each state to update their SIP with respect to SSM exemptions; and
  • Revising the policy for affirmative defenses in SIPs by continuing to allow affirmative defenses for excess emissions due to malfunction, but not for excess emissions during startups or shutdowns. 

Once the findings of SIP inadequacy are final, states will have 18 months to update their SIPs and submit them to EPA for approval.

What is the impact of EPA’s proposal?
Sources that operate intermittently or on an as-needed basis are obviously the most likely to be impacted due to the frequency of startups and shutdowns. The elimination of SSM exemptions would mean that exceeding emissions limits during those periods would constitute violations, subject to enforcement.  However, EPA maintained that SIPs can contain provisions for enforcement discretion of state agencies, provide it does not preclude federal enforcement or third party lawsuits.

Additional Resources:


Timothy P. Fagan is a Legal Editor for BLR’s environmental publications, focusing primarily on air quality related topics. Mr. Fagan has covered environmental developments with BLR since 2000. Before joining BLR, he spent 5 years in environmental consulting and was responsible for air quality permitting and compliance for a broad range of industries in both the private and public sector. He received a Bachelor of Science degree in chemical engineering from Villanova University and a Master’s degree in environmental engineering from the Pennsylvania State University.

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