The Environmental Protection Agency (EPA) intends to revise the New Source Review preconstruction permitting program’s definition of “begin actual construction.” EPA’s proposed definition will address which physical on-site construction activities a source owner or operator may, prior to obtaining an NSR permit, lawfully undertake that would not constitute construction activities on an emissions unit that are of a permanent nature. This action is intended to provide additional flexibility for source owners or operators and permitting authorities to determine, on a case-by-case basis, what constitutes beginning actual construction of a new stationary source or major modification prior to which an NSR permit must be obtained.