EPA Hints At NSR Changes With Interpretation Of "Begin Actual Construction"

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.