A surcharge covering the cost of treatment of excessive industrial wastes shall be determined in the following manner:
(A) The approving authority shall fix the rate to be charged during the new fiscal year, at the beginning of the fiscal year, for the excess BOD or suspended solids, from actual costs per 1,000 pounds removed from the combined domestic and industrial wastes as experienced at the sewage treatment plant(s) during the preceding fiscal year.
(`95 Code, § 4-2-64)