Reassessment of Treated Overflows

Client: San Francisco Public Utilities Commission

The West Side Transport conveys dry- and wet-weather flows from the Richmond, Sunset, and Lake Merced watersheds in the City of San Francisco to the Oceanside Water Pollution Control Plant and the Southwest Ocean Outfall. The transport system consists of two adjacent rectangular concrete channels, each 25 feet wide and over 35 feet high. The transport structures run north to south directly underneath San Francisco’s Great Highway. The east channel carries dry- and wet-weather flows; the west channel carries flows only in wet weather.

WRE participated in the evaluation of several conceptual schemes to increase the volume of water that could be pumped from the West Side transport system to the Southwest Ocean Outfall.  Work included hydraulic analyses and evaluation of implementation costs for three alternatives that would increase system capacity and reduce the number of overflow events (i.e., instances when the influent exceeded treatment plant capacity and had to be released untreated).  Alternatives ranged in cost from $2M to over $16M for capacity increases of between 40 and 150 million gallons per day.