The standard strengths for biochemical oxygen demand and suspended solids, as shown in Section 931.13, shall be subtracted from the average strengths, as determined in Section 931.11(b) and (r) to determine the extra strengths of each industrial class user for each strength surcharge billing period. The extra strengths and the volume of sewage charged for the billing period shall then be used to determine the weight in pounds of biochemical oxygen demand, and suspended solids, to be charged for strength surcharge. (Ord. 3995. Passed 11-28-95.)