The term 'design capacity' applies to domestic wastewater treatment plants, onsite wastewater treatment systems, lift stations, and interceptors as follows:
For a treatment plant, the design capacity is comprised of two components, the hydraulic capacity and the organic loading capacity. The hydraulic capacity shall be given in gallons per day (gpd) or million gallons per day (MGD). The organic loading capacity shall be given in pounds of 5-day biochemical oxygen demand (BOD) per day or carbonaceous biochemical oxygen demand (cBOD) per day. The design capacity for a treatment plant shall generally be expressed as a maximum monthly average. When equalization is present, the hydraulic component of design capacity shall be determined at a point prior to any flow equalization.
For domestic wastewater treatment works also considered in accordance with the Regulation 43 - On-site Wastewater Treatment Systems, the proposed design capacity shall generally be expressed as the maximum month average daily flow, at full occupancy.
For a lift station, the design capacity is expressed as the firm pump capacity (i.e., capacity with largest unit out of service).
For an interceptor, the design capacity is expressed as the peak instantaneous hydraulic flow the interceptor is capable of conveying based on the limiting design conditions at a flow depth over internal diameter ratio of 0.8.
For all domestic wastewater treatment works, the design capacity may be expressed using another capacity measure where deemed appropriate by the Division.
A sewer with a minor number of building or lateral connections may be considered an interceptor sewer if it performs one or more of the functions listed above. Interceptor sewers are appurtenances to domestic wastewater treatment works.
5 CCR 1002-22.2