The East Bay Municipal Utility District has completed construction of an 11-mile emergency pipeline that would let water flow between Castro Valley and San Ramon.
Prior to completion of the pipeline, if the existing Claremont Tunnel line had been damaged, as in the case of an earthquake on the Hayward Fault, customers in Oakland and Berkeley could have been without water for up to six months.
The $45 million southern loop project was a key element in EBMUD's $189 million, 10-year plan to seismically strengthen the district's water treatment, distribution and storage facilities.
More than 90 percent of the district's water supplies are delivered from the Mokelumne River, flowing 90 miles away in the Sierra Nevada foothills, to treatment plants in Walnut Creek and Orinda.
The treated water serves roughly two-thirds of the district's 1.3 million customers and is delivered through the Claremont Tunnel, an underground pipe running parallel to the Caldecott Tunnel.
The new pipeline will allow the district to move water from both east to west and west to east during emergencies.
EBMUD spokesman Charles Hardy said the district is currently working on an environmental impact report exploring options for upgrading the seismically vulnerable Claremont Tunnel. The alternatives, ranging from retrofit to replacement, would cost between $30 million and $50 million.