Ill. Admin. Code tit. 35, § 170.104
b) For the purposes of this procedure only, a significant project for the various Agency Divisions and media will be as defined below.
1) For purposes of the Division of Air Pollution Control, a significant project is: a new facility; a modification, replacement or reconstruction of an existing facility; or the addition of controls to an existing facility for which the uncontrolled emissions:
2) For purposes of the Division of Water Pollution Control, a significant project is: a new wastewater facility; a modification or expansion of an existing facility; or the addition of treatment to an existing facility for which:
4) For purposes of the Division of Public Water Supplies, a significant project is one which comes under the jurisdiction of the Division of Public Water Supplies and may be