EPA Upholds 2009 New Source Review Aggregation Interpretation

In the November 15, 2018 Federal Register EPA retained its 2009 “Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NSR): Aggregation and Project Netting and set an effective date of November 15, 2018 for the action. The 2009 Aggregation Action has been under reconsideration since 2010, and the effective date was stayed for the duration of the reconsideration. With the lifting of the stay, the action became effective upon publication in the Federal Register.

The 2009 Aggregation Action detailed EPA’s interpretation of when changes should be combined into a single “project” when determining major NSR applicability. Project aggregation is important to prevent facilities from breaking larger projects that would trigger major NSR applicability into several smaller projects that individually would not trigger major NSR applicability. EPA’s interpretation is that physical or operational changes should be considered a single project when they are “substantially related.” To further explain this, EPA noted that: a source need not group changes based on timing alone; changes are not required to be aggregated simply because they support the plant’s overall basic purpose; and EPA would have a rebuttal presumption that changes at least three or more years are not substantially related. Often, activities that occur in unrelated portions of a major stationary source will not be considered substantially related.

Because the 2009 Aggregation Action is not a rule change that amended regulatory text, but is instead an interpretation, state and local air pollution agencies with approved state implementation plans are not required to adopt this interpretation. EPA does encourage state and local agencies to adopt this interpretation to ensure national consistency. If an agency wishes to adopt this interpretation, EPA believes most agencies can adopt this interpretation without formal adoption into their rules.


EPA, Final Action, Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NNSR): Aggregation; Reconsideration, 83 FR 57324, November 15, 2018