In this section, “individual sewerage system” means a privately owned system of sewers, piping and treatment tanks or other facilities that: Serves only a single lot for the disposal of sewage; and Discharges to the surface waters of the State. Except as provided in subsection (c) of this section, a person may not install an individual sewerage system in the State. Subject to the Department’s approval, a person may install an individual sewerage system in the State for residential use if an existing on–site sewage disposal system fails and cannot be repaired or replaced by any means.