40 C.F.R. § 24.19
If the Regional Administrator does not adopt portions of the initial order, or finds that modification of the order is necessary, the signatory official on the initial administrative order shall modify the order in accordance with the terms of the final decision and file and serve a copy of the final administrative order. If the Regional Administrator finds the initial order appropriate as originally issued, the final decision shall declare the initial administrative order to be a final order, effective upon service of the final decision. If the Regional Administrator declares that the initial order must be withdrawn, the signatory official on the initial administrative order will file and serve a withdrawal of the initial administrative order. This may be done without prejudice.
40 C.F.R. § 24.19