The surcharge shall be determined as follows. The excess pounds of BOD (or COD) and of suspended solids will each be computed by first multiplying the customer’s billing sewage volume measured in units of 100 cubic feet for the current billing period by the factor 0.0062321 and then multiplying this product by the difference between: the concentrations measured in milligrams per liter of the BOD (or COD) and of the suspended solids respectively in the customer’s sewage; and the allowed concentrations set out in § 51.155. The surcharge for each constituent will then be determined by multiplying the excess pounds of each constituent by the appropriate rate of surcharge set out in § 51.157.
(2008 Code, § 2.3.11)