Any city, town or municipal corporation operating a sewerage system including treatment facilities may be granted authority by the department to issue permits for the discharge of wastes to such system provided the department ascertains to its satisfaction that the sewerage system and the inspection and control program operated and conducted by the city, town or municipal corporation will protect the public interest in the quality of the state's waters as provided for in this chapter. Such authority may be granted by the department upon application by the city, town or municipal corporation and may be revoked by the department if it determines that such city, town, or municipal corporation is not, thereafter, operated and conducted in a manner to protect the public interest. Persons holding municipal permits to discharge into sewerage systems operated by a municipal corporation authorized by this section to issue such permits shall not be required to secure a waste discharge permit provided for in RCW 90.48.160
as to the wastes discharged into such sewerage systems. Authority granted by the department to cities, towns, or municipal corporations to issue permits under this section shall be in addition to any authority or power now or hereafter granted by law to cities, towns and municipal corporations for the regulation of discharges into sewerage systems operated by such cities, towns, or municipal corporations. Permits issued under this section shall automatically terminate if the authority to issue the same is revoked by the department.