In a September 2, 2025, letter to an Arizona air permitting authority, USEPA signaled that it intends to amend its New Source Review (NSR) regulations to authorize a broader set of construction activities before (or without) receiving an NSR permit. In the letter, USEPA advises that it agreed with the Maricopa County Air Quality Department's interpretation that the semiconductor project proposed by TSMC Arizona Corporation could proceed with construction of the core and shell elements of the facility as long as it does not involve emission units, its foundations, or related piping and ductwork.
Proceeding with construction would be at TSMC's own risk. Any pre-permitting construction would not influence the permitting decision; the permitting authority would still be entitled to deny the permit. If changes are needed to meet air quality standards or other permit requirements, TSMC may need to modify or rebuild parts of the structures that were already constructed. Subject to those conditions, though, TSMC could proceed with beginning construction on non-emission source elements of the proposed facility. Under previous interpretations of the construction permit requirements, only a much narrower set of activities, such as site clearing and grading and storage of materials, were allowed prior to receipt of an NSR permit.
This case-by-case determination by USEPA is in accordance with draft guidance issued under the first Trump Administration in March 2020. The agency indicated that it did not currently intend to finalize the existing guidance, but would be proceeding with formal rulemaking in 2026 to provide greater clarity on the construction activities that are permissible under the CAA prior to obtaining an NSR permit.
For further information on air permitting requirements for construction, please contact Greg Johnson, Clare Bienvenu, Emily von Qualen, or Colin North.
If a structure contains no emissions unit(s) it is not a 'source' subject to Clean Air Act permitting authorities because it does not emit or have the potential to emit pollutants.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
