As part of the San Francisco Public Utilities Commission’s “New Irvington Tunnel Project,” the Board of Supervisors voted 10-0 Tuesday to add another $3.9 million for such things as geotechnical investigation and engineering design service with the URS Corporation.
The existing $9.9 million was increased by 39.1 percent for a total of $13.8 million.
The project is part of the agency’s seismic upgrade of its water distribution pipelines.
The Irvington Tunnel connects the water collected from the Sierra Nevada mountains and the Alameda Creek Watershed to the Bay Area water distribution pipelines, according to Budget Analyst Harvey Rose’s report.
The tunnel was completed in 1930 “and has served a steadily increasing number of water customers to the point where the tunnel cannot be taken out of service for repairs or maintenance without impacting water supply to existing customers,” the report said.
Also, the eastern end of the tunnel is within 2,000 feet of the Calaveras Fault, making it seriously prone to earthquakes.
The “New Irvington Tunnel Project” includes construction of a second tunnel that is 8.5 feet to 10.5 feet in diameter, 30 to 700 feet below ground and 3.5 miles long.
The new tunnel “would be parallel to the existing horseshoe-shaped Irvington tunnel” and would allow for the shutdown and repair of the existing tunnel.
This project would “greatly improve the seismic reliability of this section of the Hetch Hetchy Water System,” the report said.
Project completion date is December 2013.