All contested enforcement proceedings, all contested licensing proceedings, and all adjudicatory proceedings under chapter 17.6 of Title 42 shall be heard by the division of administrative adjudication pursuant to the regulations promulgated by the director of environmental management; provided, however, that no adjudicatory proceeding in hearing prior to the establishment of the division by this chapter shall be subject to the provisions of this chapter. Notwithstanding the foregoing, the director shall be authorized in his or her discretion to resolve contested licensing and enforcement proceedings through informal disposition pursuant to regulations promulgated by the director.