(a) Within 90 days after receipt of the transcript of the hearing, the administrative law judge shall issue a decision.

(b) The decision of the administrative law judge shall include a statement of findings and conclusions, with reasons and basis therefore, upon each material issue presented on the record. The decision shall also include an appropriate order which may affirm, deny, reverse, or modify, in whole or in part, the determination of the Administrator; the reason or reasons for such order shall be stated in the decision. The administrative law judge shall not render determinations as to the legality of a regulatory provision or the constitutionality of a statutory provision.

(c) The decision shall be served on all parties in person or by certified or regular mail.