40 CFR § 179.93 - Testimony.
(a) The presiding officer will conduct such proceedings as are necessary for the taking of oral direct testimony and for the conduct of oral examination of witnesses by the parties. The presiding officer shall limit oral examination to prevent irrelevant, immaterial or unduly repetitious examination.
(b) Direct testimony shall be submitted in writing, except that the presiding officer may order direct testimony to be presented orally in those unusual cases where the memory or demeanor of the witness is of importance. Written direct testimony shall be in the form of a verified statement of fact or opinion prepared by the witness, in narrative form or in question-and-answer form. Written direct testimony may incorporate exhibits. Such a verified statement or exhibit may not be admitted into evidence sooner than 14 days (or such other reasonable period as the presiding officer may order) after the witness has delivered to the presiding officer and each party a copy of the statement or exhibit. The admissibility of the evidence contained in such a statement is subject to the same rules as if such testimony had been given orally.
(c) Oral cross-examination of witnesses will be permitted. Each exhibit that a party intends to rely upon in cross-examining a witness shall be furnished to the other parties not later than 3 days (or such other reasonable period as the presiding officer may order) before such exhibit is used in the cross-examination.
(d) Witnesses shall give testimony under oath or affirmation.