Over and above the rates and charges established by Section 923.02, 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, or for other unduly burdensome discharges into the system which are accepted by the City for treatment as may be determined to be fair and equitable. Each such special agreement and the charges established thereby shall not become effective until ratified by ordinance duly passed by Council.
(1957 Code §16-21)