"Commence," as applied to construction of a major stationary source or major modification, means that the owner or operator has all necessary preconstruction approvals or permits and either has:

a) Begun, or caused to begin, a continuous program of actual on-site construction of the source, to be completed within a reasonable time; or

b) Entered into binding agreements or contractual obligations, which cannot be cancelled or modified without substantial loss to the owner or operator, to undertake a program of actual construction of the source to be completed within a reasonable time.

(Source: Added at 49 Ill. Reg. 6237, effective April 23, 2025)