Ill. Admin. Code tit. 35, § 325.520 – Agency Response

a) The Agency shall respond in writing to any request for reconsideration pursuant to Section 325.510 within 45 days after receipt of the request. The written response shall constitute final Agency action. Failure by the Agency to respond within 45 days after receipt of the request shall be considered a denial of the request and shall also constitute final Agency action.
b) Upon written notification to the permit holder, the Agency may extend the response period under subsection (a) by up to an additional 45 days.