First tunnel underneath San Francisco Bay closer to carrying water for area

A dull hum in the 9-foot-wide pipeline Thursday was the result of a fan blowing in fresh air for workers 5 miles across San Francisco Bay, who were busy pumping concrete into a void around the metal to make it strong enough to withstand a major earthquake.

The tunnel through which the water pipeline runs is the first to be bored underneath the floor of the Bay. Other pipes and tunnels, including BART’s Transbay Tube, run in trenches along the top of the Bay floor.

The $286 million San Francisco Public Utilities Commission water pipeline project is part of the larger $4.6 billion Water System Improvement Project. The single pipeline, which runs about 125 feet underground, emerging in Menlo Park on the west and Newark on the east, will replace two aging pipelines.

Workers are currently working from the eastern side of the tunnel and pumping concrete into the gap between the outer and inner layers, enabling the pipeline to withstand a major temblor on either the San Andreas or Hayward faults, SFPUC officials said, The project is expected to be completed in late 2014.

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