Over and above the rates and charges established by Sections 915.04 and 915.12, there may be established in special instances and upon special agreement between the City and the owner of any premises served by the system, such additional charges for industrial wastes of unusual strength or composition which are accepted by the City for treatment as may be determined to be fair and equitable. Similarly, rates supplemental to those established by Sections 915.04 and 915.12 may also be established by special agreement in any case not clearly defined in such section or where satisfactory provision has been made for direct measurement of the quantity of sewage discharged into the system. Payment shall be proportionate to actual additional costs incurred in treating or handling extra-strength wastes or unusual discharges and in further conformity with this chapter. Each such special agreement and the charges established thereby shall not become effective until ratified by a resolution duly passed by Council. (Ord. 84-91. Passed 10-16-84.)