Any person discharging sewage, industrial waste or other waste or air contaminant into any of the waters or ambient air of the State, without regard to the time that such discharge began or whether such continued discharge has been by virtue of a permit issued by the Department, shall discontinue the discharge of such sewage, industrial waste or other wastes into, or in such manner or quantity as to cause pollution of, the waters of the State upon receipt of a final order of the Department issued pursuant to the provisions of this chapter. But in the case of such discharges, except those discharges causing an actual or potential hazard to public health, no final order of discontinuance of discharge shall be entered until a reasonable time after service of an order of the Department determining that such discharge constitutes pollution in contravention of the standards adopted by the Department and directing the alleged polluter to take such steps as may be necessary to abate the polluting content of such discharge to conform to the standards of the Department.