40 C.F.R. § 67.15
If the Administrator determines that a State with a program approved under § 67.13 is not administering the program in conformity with the requirements of the Act or § 67.11 , or the delegation of authority, he shall provide the State written notice of that determination, setting forth his reasons. Copies of all supporting materials shall accompany the notice if requested, or shall be placed on file in the appropriate Regional Office and made available for inspection during normal business hours. The State shall have 90 days in which to respond in writing to this determination. If the Administrator finds after reviewing the State response that (a) the State is in fact administering the program in conformity with § 67.11 , or (b) there are reasonable grounds to believe the State program will immediately be brought into conformity with that section, he shall withdraw his determination. If he finds that neither of these conditions has been met, he shall withdraw the delegation of authority to the State.
40 C.F.R. § 67.15