35 Ill. Adm. Code 204.830
Permit Expiration
Section 204.830 Permit Expiration
Approval to construct shall become invalid if construction
is not commenced within 18 months after receipt of approval, if construction is
discontinued for a period of 18 months or more, or if construction is not
completed within a reasonable time. The Agency may extend the 18-month period
upon a satisfactory showing that an extension is justified. This provision
does not apply to the time period between construction of the approved phases
of a phased construction project; each phase must commence construction within
18 months after the projected and approved commencement date.