The city of East Helena or its engineer will determine the average total suspended solids (SS) and five (5) day biochemical oxygen demand (BOD) daily loadings for the average residential customer or in lieu of such a determination will consider the average residential strength wastes to be two hundred fifty milligrams per liter (250 mg/l) BOD and three hundred milligrams per liter (300 mg/l) SS. The city of East Helena will assess a surcharge rate for all commercial customers discharging wastes with BOD and SS strengths greater than the average residential customer. The surcharge will be sufficient to cover the costs of treating such customer's above normal strength wastes. Such customers will pay an additional service charge equal to six percent (6%) of the monthly operation and maintenance cost for each fifty milligrams per liter (50 mg/l) over two hundred fifty milligrams per liter (250 mg/l) of BOD and three percent (3%) of the monthly operation and maintenance cost for each fifty milligrams per liter (50 mg/l) over three hundred milligrams per liter (300 mg/l) SS. (Ord. 219, 8-15-2000)