40 CFR 179.75: Disqualification of deciding officials.

(a) A deciding official in a hearing under this part (including, e.g., the Administrator, judicial officer, or presiding officer) shall not decide any matter in connection with which he or she has a financial interest in any of the parties, or a relationship that would make it otherwise inappropriate for him or her to act.

(b) A party may request that a deciding official disqualify himself/herself and withdraw from the proceeding. The party may obtain interlocutory review by the Administrator of a denial of such a request made to any deciding official other than the Administrator.

(c) A deciding official who is aware of grounds for disqualification shall withdraw from the proceeding.