(1) Any party may be a witness and may present witnesses at the hearing. All oral testimony at the hearing shall be under oath or affirmation.

(2) Upon the hearing examiner's motion or, upon the motion of a party, the hearing examiner may order that the testimony to be given upon direct examination by experts or other witnesses shall be prepared in advance in either question and answer or narrative format. Such prefiled testimony shall be served upon the hearing examiner and all parties at least 7 days prior to the first hearing date. The prefiled testimony will be part of the record in each proceeding as if read, but all of the witnesses whose substantive testimony is prefiled must be available for cross-examination at the hearing. Evidentiary objections (such as motions to strike) to such direct testimony may be made by any party at any time during the hearings conducted pursuant to these rules. At the hearing, the party presenting the testimony may, if they deem it appropriate, briefly summarize the prefiled testimony prior to the start of cross-examination. Nothing contained herein shall be deemed to foreclose any party from presenting rebuttal testimony or from presenting testimony in response to reasonably unforeseen areas without the necessity of prefiling.

(3) All parties shall be advised of a staff expert witness' findings, if any, based on any prepared written testimony filed by the parties pursuant to ARM 36.12.220(2) , site observations taken pursuant to ARM 36.12.225, materials noticed pursuant to ARM 36.12.221(4) and ARM 36.12.228(1) (b) , or testimony or other documents introduced during the proceeding. A staff expert witness' deposition may be taken by any party and the expert may be called to testify by any party and/or by the hearing examiner. The expert witness shall be subject to cross-examination by all parties. Nothing in this rule shall prevent any of the parties from producing other expert evidence on the same fact or matter to which the testimony of the staff expert witness appointed by the hearing examiner relates.