Tunnel Revision : Water District Starts Repairs on Pipeline Damaged in Quake

Hundreds of feet underground, scores of workers are turning the inside of a large Metropolitan Water District tunnel into a construction site each day, laboring to replace a steel liner that the Northridge earthquake bent into rippling waves.

Days after the 1994 quake crumpled the connector ramp between the Golden State and Antelope Valley freeways, water district officials inspected the 20-foot diameter Newhall Tunnel--which carries water from Castaic Lake to the Joseph Jensen Filtration Plant in Granada Hills--and discovered that the pipeline had been damaged along with the freeway that runs above it.

The concrete shell of the 3 1/2-mile tunnel was sound, said MWD spokesman Rob Hallwachs. But 160 feet of the half-inch-thick steel liner that keeps out oil and other contaminants was yanked several feet from the sides of the tunnel and crinkled like corduroy.

“No matter how hard we work or we over-design, the forces of nature can always do-in the best engineering,” said engineer and project manager Leslie J. Barrett.

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Despite temporary repairs after the quake, the tunnel was leaking 20,000 gallons a day, he said.

The district waited until February, when demand for water is lowest, to begin the $8-million reconstruction project to replace the bent steel liner, add an additional 12-inch layer of concrete inside the steel liner and improve the tunnel’s drainage system, which prevents natural oil deposits from contaminating the water. The tunnel is 220 feet below the ground in some places.

Hallwachs said the project is expected to be completed by the end of March. The MWD will apply to federal authorities for quake damage aid that they hope will cover at least some of the expense.

When in service, the Newhall Tunnel brings water to the Las Virgenes and Calleguas municipal water districts as well as to much of Los Angeles, including most of the San Fernando Valley.

Built in 1971, it serves about 1.3 million families each year and annually carries about 200 billion gallons of water--or enough to fill 10 million swimming pools.