The project is provided in response to both the Water Quality and Delivery Reliability LOS goals. The purpose of the San Antonio Backup Pipeline (SABPL) is to provide a means of discharging up to 315 mgd of Hetch Hetchy flow that does not meet water quality requirements due to a treatment failure or raw water quality event. This discharge can also be used in the event of an emergency shutdown of the transmission system downstream of the Alameda East Portal. The pipeline allows discharge of the Hetch Hetchy flow while simultaneously pumping water from San Antonio Reservoir to the SVWTP through the existing San Antonio Pipeline (SAPL). This new pipeline will enable the SVWTP to serve 160 mgd of treated local reservoir water while the Hetch Hetchy water is being discharged, since the Calaveras Reservoir supply to the SVWTP is limited to only 90 mgd (San Antonio needs to supply the additional 70 mgd). This function meets the LOS goal for providing average day demand to the system during an unplanned outage of the Hetch Hetchy supply. The SABPL will also serve as a redundant facility to the existing SAPL, which is aging and is constructed of PCCP.
Description
The SABPL consists of 11,300 feet of 66-inch-diameter, mortar-lined steel pipe and extends from the Alameda Siphons at the San Antonio Pump Station (SAPS) to a point on San Antonio Creek just downstream of the San Antonio Dam. There are three tie-in facilities with air gap provisions from the SABPL: one connecting to Alameda Siphon No. 3, a second to the SAPL near the SAPS, and a third to the SAPL near the San Antonio Reservoir. The alignment of the SABPL parallels that of the existing SAPL, terminating with an energy-dissipating valve in a new discharge stilling basin, just downstream of the existing stilling basin. The project includes new chemical storage, feed and water quality monitoring facilities for dechlorination and pH adjustment of any discharges through the SABPL or the Alameda East Portal overflow pipe. The project also includes security-related site improvements at the existing Alameda East Portal.
Scope Refinements
The project originally included a 60-inch pipeline extending from the San Antonio Reservoir to SAPS; planning studies have determined that a 66-inch diameter pipe is required. Also, the pipeline currently is planned to extend to a point just below the San Antonio Reservoir and a discharge location just downstream of the existing reservoir discharge site. In addition, the project includes security-related site improvements at the existing Alameda East Portal.
Need more information?
Contact Michele Liapes at (415) 554-3211 or via email at mliapes@sfwater.org or Betsy Lauppe Rhodes at (415) 554-3240 or via email at blauppe@sfwater.org.
