Any person discharging 80 Ccf (60,000 gallons) or more of water to the sewer within one month may be subject to surcharge for treatment of wastes exceeding the strength of “normal wastewater”. Normal wastewater is defined by MSD Ordinance 12561 as wastewater which has a five-day biochemical oxygen demand (BOD) less than or equal to 300 milligrams per liter, total suspended solids (TSS) less than or equal to 300 milligrams per liter, and chemical oxygen demand less than or equal to 600 milligrams per liter.

The wastewater collected at each sampling point receiving industrial process wastewater is analyzed for BOD, COD and TSS. The analytical data generated is used to calculate a high strength surcharge for wastewater discharged from facilities, as applicable. Analytical data is considered current for each subsequent billing period until it is replaced by updated data which is certified to represent normal operational conditions.