Public hearings shall be conducted by the Department prior to action by the Department in the classification of the waters or the adoption of standards of purity and quality thereof as provided by this chapter. The Department may conduct public hearings prior to action in the following cases, either of its own volition or upon the request of affected persons, (a) an order of determination of the Department requiring the discontinuance of discharge of sewage, industrial waste or other wastes into the waters of the State or air contaminant into the ambient air, (b) an order issuing, denying, revoking, suspending or modifying a permit, (c) a determination that a discharge constitutes pollution of waters of a marine district and (d) any other proceeding resulting in a finding of fact or determination that a discharge of air contaminants into the ambient air or sewage, industrial waste or other wastes into the waters of the State contravenes the standards established for such air and waters.