40 CFR §179.75

1. (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.
2. (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.
3. (c)A deciding official who is aware of grounds for disqualification shall withdraw from the proceeding.