The project is part of the Bay Area agency's $4.8 billion Water System Improvement Program
The San Francisco Public Utilities Commission (SFPUC) announced that after more than four years of construction, a new 3.5 mile long seismically improved tunnel is now delivering water to 2.6 million people in the San Francisco Bay Area. The New Irvington Tunnel Project completes the last of three new tunnels creating a water lifeline able to withstand earthquakes on the Hayward, Calaveras and San Andreas faults. Located between the Sunol Valley and Fremont, the project is part of the agency's $4.8 billion Water System Improvement Program.
"The seismically-resilient New Irvington Tunnel is a project that strengthens the backbone of the Hetch Hetchy Regional Water System," said SFPUC General Manager Harlan L. Kelly, Jr. "Our successful work investing in the water system will help ensure that we can reasonably protect the health and safety of our Bay Area customers and the economy."
The 8.5-ft diameter New Irvington Tunnel was constructed parallel to the existing Irvington Tunnel, which was completed in 1932. A secondary tunnel allows the SFPUC to take either tunnel out of service for maintenance and inspections.
"Our goal is to restore water deliveries within 24 hours after a major earthquake in the Bay Area," said WSIP Director Daniel L. Wade. "The completion of this tunnel takes us a huge step closer to that critical goal."
The project has not been without its challenges. With the anticipation of complex geology, the new tunnel was constructed using conventional mining techniques rather than a tunnel boring machine. The crews mined from four separate headings using road headers and controlled detonation. The miners experienced frequent ground class changes and extreme ranges of rock hardness during construction. In addition, heavy groundwater inflows and "squeezing" ground needed to be addressed along the way. In 2011, CalOSHA reclassified the tunnel as "gassy" requiring more rigorous measures to monitor for explosive or toxic gas, and enhanced protective measures for worker safety.
Construction began in August 2010, and crews achieved their first "hole through," where the two tunneling teams met underground, on June 12, 2012. The second hole through on Oct. 8, 2013 marked the completion of tunnel excavation. In the coming weeks, crews will take the existing tunnel out of service for inspection. Meanwhile, the project team will work to restore aboveground facilities around the new tunnel. This aboveground work will last through fall of 2015.
Nicole Sandkulla, CEO of the state-authorized Bay Area Water Supply and Conservation Agency, said that her organization supported construction of the new tunnel in 2002 as part of the SFPUC's capital improvement program. "The New Irvington Tunnel will provide redundancy and secure access to the water from the Hetch Hetchy, San Antonio and Calaveras Reservoirs, which flows through this tunnel, for the 1.6 million residents and 30,000 businesses in Alameda, San Mateo and Santa Clara counties who depend on this water, whose interests we represent, and who pay two-thirds of the cost," she said.
Currently, the Water System Improvement Program, which is comprised of 83 projects, is more than 85% complete.