(a) When a proceeding involving common questions of fact affecting a particular location or area of pollution is pending before the hearing officer, the hearing officer, upon his own initiative or upon motion of a party, may order a joint hearing of any or all the matters in issue, may order the actions consolidated, and may make such other orders concerning proceedings therein as may tend to avoid unnecessary delay.

(b) In furtherance of convenience or to avoid prejudice, the hearing officer may order a severance of the hearing and may order separate hearings in respect to all the issues or of any separate issue.

(c) Non-joinder of a party who should be joined in the proceeding may be a ground for dismissal of a hearing without prejudice unless the hearing officer allows the hearing to proceed without such party.

(d) Mis-joinder of parties is not a ground for dismissal of the charges. Parties may be added or dropped by the hearing officer, on motion of any party or on his own initiative at any stage of the hearing and upon such terms as may be just.

(e) The hearing officer may order any hearing against a party severed and proceed with it separately.