Tunneling to Bring New Water Line to Bay Area
A video posted on YouTube captures the moment when a roadheader, an enormous tracked tunneling machine, breaks through a wall of rock and earth and workers step through to greet their fellow miners on the other side. Titled "NIT's Road Header Rendezvous," the clip shows one grinning crew member shouting congratulations over the drilling noise as he reaches out to shake hands with a teammate.
The clip shows the moment on June 12 when the two mining crews working on the 3.5-mile New Irvington Tunnel project—the NIT—met below ground to complete the first of four tunnel headings. Two teams of miners had been steadily excavating an 8.5-ft-dia corridor, with one group moving eastward from the tunnel's Irvington Portal in Fremont and the other heading westward from the Vargas Shaft 4,500 ft away.
Upgrade Program
The $318-million New Irvington Tunnel, begun in May 2011, is one of 80 projects that comprise the San Francisco Public Utilities Commission's (SFPUC) Water System Improvement Program (WSIP). The $4.6-billion program will renovate and seismically upgrade the Hetch Hetchy Water System.
That network of waterworks channels Sierra Nevada runoff in the Hetch Hetchy Valley in Yosemite National Park 160 miles to the San Francisco Bay Area, providing water to about 2.6 million people in San Francisco, Alameda, Santa Clara and San Mateo counties. The program began in 2003 and is expected to be completed in 2016.
When finished, the New Irvington Tunnel project will parallel the existing water tunnel from the Sunol Valley south of Interstate 680 to Fremont.
With the Irvington-Vargas Shaft hole-through achieved, workers now will turn the roadheader eastward and plow toward another rendezvous, with a crew heading west from the line's Alameda section—a tunneling distance of 14,400 ft.
To keep the workers safe and the tunnel work flowing, overhead water fissures are blocked and a network of 23 dewatering wells has been installed. After the digging is done, crews will install a 103-in.-dia steel pipe composed of 50-ft-long segments. It can convey up to 300 million gallons of water per day to the Bay Area.
Southland Tutor Perini, a joint venture of Sylmar-based Tudor Perini Corp. and Southland Contracting Inc., Fort Worth, Texas, is the project's contractor team. Hatch Mott MacDonald, headquartered in Milburn, N.J., is the construction manager.
SFPUC project manager David Tsztoo says that building an alternative pipeline across the region's Sheridan Valley gives the agency the freedom to take the existing 80-year-old tunnel out of service for much-needed maintenance and repair.
"The New Irvington Tunnel provides a seismically designed connection between water supplies from the Sierra Nevada Mountains and the Alameda Watershed to Bay Area water distribution systems," Tsztoo says. He notes that the New Irvington course crosses seven minor fault lines that could "react sympathetically" if an earthquake occurs along the major Hayward Fault, west of the tunnel, or the Calaveras Fault to the east.
Dan McMaster, Hatch Mott MacDonald project construction manager, says the presence of those faults is a big reason why the New Irvington Tunnel line should be completed without delay.
"With the original cast-in-place line, there could be severe damage and potential collapse in the event of a major quake," McMaster says. "That's why it's critical to get this in place as soon as possible."
WSIP is funded by a bond measure that San Francisco voters approved in 2002.
Other key WSIP projects include: construction of the $224-million Bay Division Pipeline No. 5—a 46,350-ft line running through Redwood City, North Fair Oaks, San Mateo County and Menlo Park—and replacement and repair of the $59-million, 19-mile Crystal Springs Pipeline No. 2, through parts of San Francisco and San Mateo counties. Mountain Cascade Inc., Livermore, is the contractor for Bay Division Pipeline No. 5 and San Francisco-based Ranger Pipelines Inc. has the Crystal Springs construction contract.
WISP's largest project is the $434-million replacement of the Calaveras Dam in Alameda County, which is the system's main backup to the Hetch Hetchy Reservoir. Built in 1925, the earth-fill dam, located about a mile from the active Calaveras Fault, is considered seismically vulnerable. In fact, the state Dept. of Water Resources scaled back to 30% capacity there in 2001 because of safety concerns. The dam's normal capacity is 96,850 acre-ft of water, or 31 billion gallons, representing nearly half of the water storage capacity in the Bay Area.
Construction of its earth-and-rock-fill replacement began in August 2011.
The new 210-ft-high dam will have a crest length of 1,210 feet, a base thickness of 1,180 feet and a crest thickness of 80 feet. The new spillway will be 1,550 ft long. When finished, it will have a storage capacity of about 31 billion gallons—about the same as its original capacity. It also will be able to withstand a magnitude 7.25 earthquake. A joint venture of Dragados USA, Flatiron Construction and Sukut Construction is the replacement dam's construction contractor team. Completion is scheduled for late 2015.
