Ill. Admin. Code tit. 35, § 734.610
a) At a minimum, the Agency must review each application for payment submitted pursuant to this Part to determine the following:
d) Following a review, the Agency has the authority to approve, deny or require modification of applications for payment or portions thereof. The Agency must notify the owner or operator in writing of its final action on any such application for payment. Except as provided in subsection (e) of this Section, if the Agency fails to notify the owner or operator of its final action on an application for payment within 120 days after the receipt of a complete application for payment, the owner or operator may deem the application for payment approved by operation of law. If the Agency denies payment for an application for payment or for a portion thereof or requires modification, the written notification must contain the following information, as applicable: