(a) Generally. Hearings shall be conducted by one or more members of the Commission, by the Executive Director, or by such other Hearing Officer as the Chairman may designate, except as provided in paragraph (b) of this section.

(b) Wasteload allocation cases. In cases involving the allocation of the assimilative capacity of a stream:

(1) The Executive Director shall appoint a hearing board of at least two persons. One of them shall be nominated by the water pollution control agency of the state in which the discharge originates, and he shall be chairman. The board shall have and exercise the powers and duties of a Hearing Officer;

(2) A quorum of the board for purposes of the hearing shall consist of two members; and

(3) Questions of practice or procedure during the hearing shall be determined by the Chairman.