The city, or its city engineer, shall determine the total annual costs of operation and maintenance of the wastewater system which are necessary to maintain the capacity and performance, during the service life of the treatment works, for which such works were designed and constructed. The total annual cost of operation and maintenance shall include, but need not be limited to, labor, repairs, equipment replacement, maintenance, necessary modifications, power, sampling, laboratory tests, and a reasonable contingency fund. (Ord. 414 § 2, 1982)