RCW 90.48.165 empowers the department of ecology, as successor to the water pollution control commission to grant to any city, town, or municipal corporation operating a sewerage system including treatment facilities the authority to issue permits for the discharge of wastes into such system, provided that the department finds to its satisfaction that the sewerage system and 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 water as provided in the Water Pollution Control Act, chapter 90.48 RCW. Permits for the discharge of wastes into publicly operated sewerage systems are required for commercial or industrial operations by virtue of RCW 90.48.160.