The Bay Tunnel links the existing segments of Bay Division Pipeline (BDPL) Nos. 1 and 2 and the future BDPL No. 5 in the East Bay with those on the Peninsula. The existing portions of BDPL Nos. 1 and 2, which were built in the 1920’s and 30’s, lay along the bay floor and on trestles that cross over environmentally sensitive marsh land. The pipe and the trestle are in a deteriorated condition. The Bay Tunnel bypasses these environmentally sensitive wetlands.

The tunnel extends 5 miles under San Francisco Bay at depths of up to 100 ft. and was constructed using an earth pressure balance tunnel boring machine (EPBTBM) and supported by a precast concrete segment primary liner. The final tunnel lining is a 9 ft. diameter mortar lined welded steel pipeline. At each end there is a vertical shaft which connects the BDPL Nos. 1, 2, and 5 piping manifolds. The portion of the existing BDPL Nos. 1 and 2 that are replaced by the tunnel are capped on each end and abandoned in place.

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