"Begin actual construction" means in general, initiation of physical on-site construction activities on an emissions unit that are of a permanent nature. Such activities include, but not limited to, installation of building supports and foundations, laying of underground pipework, and construction of permanent storage structures. With respect to a change in method of operations, this term refers to those on-site activities other than preparatory activities which mark the initiation of the change.

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