The storm water runoff mixed with domestic and industrial wastewater from the City’s west drainage area is collected in the Westside Wet Weather Facilities. The Westside system includes three large storage/transports: Westside Transport, Richmond Transport, and Lake Merced Transport. The Westside Transport is a 2.5-mile long box-like structure located beneath the Great Highway and has a storage capacity of 49.3 million gallons (MG). The Richmond Transport, located to the north, has a storage capacity of 12 MG; and the Lake Merced Transport located to the south, has a storage capacity of 10 MG. The combined storage capacity in all three transports (including 2.2 MG of sewers) is 73.5 million gallons.
 

Wastewater from the Westside Transport System flows in the Oceanside Treatment Plant, a secondary wastewater treatment plant with a peak secondary treatment capacity of 43 million gallons per day (MGD). During wet weather, the Oceanside wet weather facilities provide primary treatment up to an additional 22 MGD of mixed storm water and sewage. All dry weather and wet weather flow from the Oceanside Plant is discharged into the Pacific Ocean via a 80-feet deep and 3.75 miles long pipe (Southwest Ocean Outfall- SWOO) to ensure adequate dilution.

Flows above 65 MGD and up to 175 MGD receive flow-through treatment within the combined sewer overflow (CSO) structures and are discharged to the SWOO. Flows above 175 MGD also receive flow-through treatment within the CSO structures but are discharged at the shoreline. Flow-through treatment in the CSO storage structures is equivalent to primary treatment in that solids are allowed to settle and a baffle system acts to retain floatable materials prior to discharge.

VIEW a schematic of the way the transport boxes and overflows work...