Mountain Tunnel Improvements

open for bidding

The San Francisco Public Utilities Commission is seeking bidders to carry out improvements to Mountain Tunnel. The 19-mile long water tunnel, located in Tuolumne County, which has been in service since 1925, is unlined upstream for over 7 miles and has an unreinforced concrete lining for 11 miles in its downstream section. Inspections have revealed deterioration of the tunnel lining and other deficiencies, resulting in reduced flow rate, increased groundwater intrusion and increased turbidity. The repairs and improvements include: repairing with wired mesh and shotcrete the defects in the 11 miles of existing tunnel lining; constructing a new 1,075-foot adit tunnel at Priest Reservoir to improve maintenance access; constructing a new flow control facility with large flow control valves at the downstream end of the tunnel near Priest Reservoir to better control pressure in the tunnel, help protect the tunnel lining and improve operational flexibility; placing concrete along 5,000 ft of the floor of the unlined portions of the tunnel to improve maintenance access and improve hydraulic flow; and constructing a 750-ft bypass tunnel (siphon extension) at South Fork Siphon. The work will take place over seven years, including five winter shutdowns (when water demand is lowest). The project is valued at $140 million.