Keeping thirst at bay

July 2012 » Features » ENGINEERED SOLUTIONS
San Francisco Public Utilities Commission undertakes major water system upgrades in the Sunol Valley.
The 45-year-old San Antonio Pump Station in the Sunol Valley is located close to the Calaveras Fault and required structural retrofitting of the building to improve its reliability following an earthquake.
Photo: © San Francisco Public Utilities Commission /R. Scheswohl

What would you do if your 70-year-old water infrastructure crossed three of the nation—€™s most active fault lines? This is reality for the San Francisco Public Utilities Commission (SFPUC), the third largest municipal utility agency in California, responsible for supplying drinking water to 2.6 million customers in the greater San Francisco Bay Area. The agency also collects and treats wastewater and provides municipal power services within San Francisco.

The majority of the system—€™s high-quality water supply comes from the historic Hetch Hetchy Regional Water System, managed by the SFPUC. The system is fed by collecting snowmelt accumulated in the California Sierra Mountains and storing it in Hetch Hetchy Reservoir in Yosemite National Park. From there, this pristine water travels west 167 miles via gravity through a complex system of pipelines, tunnels, and reservoirs to provide approximately 260 million gallons per day (mgd) of drinking water to customers. The Hetch Hetchy Regional water delivery system traverses three major active fault lines —€” the San Andreas Fault, the Calaveras Fault, and the Hayward Fault. And according to experts, a major earthquake along any of these lines is long overdue.

The Hetch Hetchy Water System, built in the 1920s and 1930s, not only needs repair, but also needs seismic engineering upgrades to its pipes, some of which are the original riveted steel and are nearing the end of their useful life. The SFPUC is addressing this challenge by implementing the Water System Improvement Project (WSIP) to repair, replace, and seismically upgrade portions of the Hetch Hetchy system. This major capital infrastructure program includes more than 80 separate projects to improve aging pipelines, tunnels, dams, reservoirs, pump stations, treatment facilities, and storage tanks spread across six counties to help ensure SFPUC customers have water within 24 hours after a major earthquake. Approved by the voters in 2002 and targeted for completion in 2016, the WSIP is currently one of the largest water capital improvement programs in the nation.

New water lifeline in the Sunol Valley
The Sunol Valley region is home to a number of important WSIP projects and has housed many of the SFPUC facilities and pipelines for decades. Located 45 minutes outside of San Francisco, the Sunol Valley is surrounded by Fremont, Livermore, and other developed East Bay communities, yet retains its rural nature, making it a particularly unique setting for large construction projects. These projects are to seismically upgrade and improve reliability of the crucial facilities located in the Sunol Valley that ensure water delivery to customers in the Bay Area, accounting for approximately $1.2 billion of the total $4.6 billion WSIP cost.

One of the most critical seismic reliability projects within the WSIP was recently completed in the Sunol Valley. Three aging, large existing pipelines (siphons) carry water from Hetch Hetchy Reservoir and the local watershed across the Sunol Valley floor to connect to Bay Area customers. However, these pipelines cross the Calaveras Fault and are vulnerable to damage during a major earthquake. As a result, the SFPUC needed to create some redundancy with the water infrastructure in the system that currently is lacking.

In December 2011, substantial construction was completed for the Alameda Siphon No. 4 project (AS4), which helped address that challenge. This project included building a new seismically resistant water lifeline across the Calaveras Fault. This lifeline included installation of a new 3,000-foot-long, 66-inch-diameter pipeline built to withstand a 6.8 magnitude earthquake on the Calaveras fault. A critical feature of the new pipeline is the special seismically designed fault crossing, which includes a 310-foot-long section of thicker-walled pipe (1-inch-thick steel) and loose, cohesion less gravel backfill built at an oblique angle to the fault crossing. The fault crossing is designed to enable the pipeline to move as much as 4 feet horizontally and 1 foot vertically to ensure water delivery to customers after an earthquake if the other water pipelines were severed.

The Alameda Siphon No. 4 project (AS4) creates redundancy in the water infrastructure that carries water from the Hetch Hetchy Reservoir. The project included installation of a new 3,000-foot-long, 66-inch-diameter pipeline built to withstand a 6.8 magnitude earthquake on the Calaveras fault.
Photo: © San Francisco Public Utilities Commission

This project also included a new 96-inch-diameter water quality —€œblending structure—€ consisting of a pipe and valve manifold structure to maintain a consistent blend of local waters processed at the nearby Sunol Valley Water Treatment Plant with waters from Hetch Hetchy Reservoir. Other ancillary project components include new seismically activated valves on the existing seismically vulnerable siphons that automatically close in the event of fault rupture, ventilation improvements, chemical injection facilities, overflow pipe, road improvements at the Calaveras Road intersection, and improvements to the bridge crossing Alameda Creek.

Seismic upgrades to the core of the system
Another key Sunol Valley project completed in September 2011 included upgrades to the San Antonio Pump Station (SAPS). The SAPS is the literal and figurative center of the SFPUC—€™s regional water system in the Sunol Valley. Normal operating mode for SAPS is to pump 70 mgd of water from the nearby San Antonio Reservoir to the Sunol Valley Water Treatment Plant for treatment. For emergency operations or in the unusual event that Hetch Hetchy water temporarily does not meet water quality standards, SAPS also can be used to pump Hetch Hetchy water to either San Antonio Reservoir for temporary storage or directly to the Sunol Valley Water Treatment Plant.

Similar to the nearby Alameda siphons, this pump station is positioned within several feet of the Calaveras Fault, making it vulnerable to damage during an earthquake. This project—€™s purpose was to upgrade the pump station equipment and structurally retrofit the buildings to increase the reliability of the 45-year-old pump station. It will ensure the SAPS can remain operational after a major earthquake. It also meets the SFPUC—€™s delivery reliability level of service goals, which requires it to have a 160-mgd sustainable capacity even during power outages. The SAPS Upgrade Project included the following components:

  • replacing three, 1,000-horsepower electrical pumps;
  • adding two, 1.5-megawatt emergency generators (sized to power the three electric pumps) installed in a sound-attenuated enclosure;
  • seismically retrofitting the pump station to reinforce the walls, complete foundation improvements, and connect the roof to the walls;
  • adding a new, 10,000-gallon above-ground fuel storage tank system to provide fuel to the two new generators;
  • upgrading the pump station electrical system; and
  • upgrading security hardware and programming.
San Francisco Public Utilities Commission projects in the Sunol Valley will account for $1.2 billion of the total $4.6 billion WSIP cost. Replacement of Calaveras Dam (lower right) with a new, seismically robust structure is the largest WSIP project.
Photo: © San Francisco Public Utilities Commission/R. Scheswohl

The SAPS facility was built in 1966 and no major renovations had been made to the facility since then. This meant that the 45-year-old pump station had some unknowns about the location and condition of the equipment in the facility. It also was discovered that the as-built drawings for the buildings were not entirely accurate, which meant the construction team encountered many surprises as construction work unfolded. These included crucial electrical conduits obstructing the new construction work or facilities not being located where they were expected to be. The entire project team, including the construction manager, project designers, contractor, and operations staff, overcame this challenge by working together to develop and implement creative solutions to the unexpected conditions encountered during construction —€” without impacting the project schedule. Despite these challenges, construction for the SAPS Upgrade Project was completed on time and on budget.

WSIP shutdowns
One of the unique aspects of the WSIP is that construction of these projects must be completed without any interruption of water service to customers. The water system normally undergoes four or five shutdowns each year, but to accommodate construction on the WSIP, the program requires more than 150 shutdowns on various components of the system during a five-year period. Whenever sections of the system are taken out of service, there is a loss of operational flexibility. Therefore, the challenge has been keeping the system operational during all of the scheduled shutdowns of various components of the system. A system shutdown for WSIP construction is like fixing an airplane while it is in flight, without crashing the plane. The shutdowns are absolutely critical, and any delays could potentially throw off the entire WSIP schedule.

During construction for both the AS4 and SAPS projects, several key system shutdowns were required. The SFPUC schedules the most complex shutdowns during low water use months, typically between December and February. For example, in early 2010, during a peak time for construction on the AS4, a risky 41-day shutdown was required of the nearby Coast Range Tunnel, where the system was isolated from its main Hetch Hetchy supply. This shutdown required emptying the 25-mile-long Coast Range Tunnel, which is the main conduit that brings water across the Sierra Nevada Mountains into much of the Bay Area. Ensuring this shutdown was successful and on-time required extensive planning and coordination between the AS4 construction management team, contractors, and the SFPUC—€™s Water Supply and Treatment Division.

The San Antonio Pump Station (SAPS) normally pumps 70 million gallons per day (mgd) of water from the nearby San Antonio Reservoir to the Sunol Valley Water Treatment plant. Upgrades included replacing three, 1,000-horsepower electrical pumps and adding emergency generators to provide 160-mgd sustainable pumping capacity even during power outages.
Photo: © San Francisco Public Utilities Commission /R. Scheswohl

One of the biggest challenges for the SAPS Upgrade project was to overcome the fact that the SAPS would not be operational for extended periods of time because of three critical water system shutdowns that occurred during construction. These shutdowns ended up defining this project—€™s construction schedule and required construction work often to be executed in a short window of time. Additionally, the shutdowns required significant coordination and extensive planning and cooperation among the entire project team to ensure success. With a combination of excellent planning and standardized procedures, the WSIP shutdowns to date have been executed without major problems or delay.

Other key WSIP projects in Sunol Valley
Several of the largest WSIP projects are now underway in the Sunol Valley. These include seismic upgrades to the existing Sunol Valley Water Treatment Plant that will enable it to treat and deliver water more reliably to customers after an earthquake. A new 17.5 million-gallon circular balancing reservoir will store treated water leaving the plant and along with other improvements will enhance the overall efficiency of the treatment process at the facility.

Construction also is progressing on the largest WSIP project to rebuild Calaveras Dam, which is located near an active fault and stores drinking water in the system—€™s largest Bay Area reservoir. Once this new, seismically robust dam is complete, the SFPUC will be able to restore Calaveras Reservoir to its original storage capacity. Construction also is underway to build the New Irvington Tunnel, a major water transmission tunnel between the Sunol Valley and Fremont that will remain operable after a major seismic event and allow the SFPUC to perform much needed inspection and repair of the existing Irvington Tunnel.

View progress of all Sunol Valley WSIP construction projects at www.sfwater.org/sunolvalley

Daniel L. Wade, P.E., G.E., is the regional manager for the Sunol Valley Projects within the WSIP. In his current role at the SFPUC, he is responsible for the delivery of 10 capital improvement projects in the Sunol Valley totaling more than $1 billion. Emily Powell, with Katz & Associates in San Francisco, is an onsite community outreach consultant for the WSIP at the SFPUC.

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