Mountain Tunnel South Fork Siphon Extension Improvements
Overview
As of August 2, 2024, the RFI is available on our "Bids On Line" website -- responses are due by September 17, 2024.
Beginning in July 2024, the San Francisco Public Utilities Commission (SFPUC) will be soliciting interest and feedback from potential builders, designers, and construction managers on a project delivery method for the proposed Mountain Tunnel South Fork Siphon Extension Improvements project.
Multiple alternative approaches are under consideration for completion of this project. Interested parties are asked to review the details of a formal Request for Interest (RFI) and respond to a series of questions in order to enable the SFPUC to evaluate the optimal project scope and delivery approach prior to a formal procurement process
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Project Background
The Mountain Tunnel is an 18.9-mile-long in-service water tunnel that has been in operation since 1925 and is part of the Hetch Hetchy Water Conveyance System located in Tuolumne County. The tunnel is divided into two segments, separated by a siphon beneath the South Fork of the Tuolumne River.
Upstream of the siphon at South Fork, a large volume of groundwater has been flowing into the tunnel. This has occurred due to fractured ground above and to the side of the tunnel, low ground cover, and the close proximity of the river to the tunnel. Previous work to seal the tunnel has reduced the diameter to ten feet, in places.
Access to the South Fork Siphon is via a steep and narrow road bounded by upslopes with rocky outcrops and downslopes to the South Fork of Tuolumne River. At the end of the access road is a landing pad above the river. The tunnel entry is reached via a stairway off of this landing pad and only allows for personnel access via a 30-inch manhole in the bulkhead.
Access point for the South Fork Siphon
The South Fork project envisions an extension of the existing siphon to bypass the fractured rock zone, abandoning the section of tunnel of concern and improving access to the existing tunnel and siphon.
Conceptual diagram for developing a bypass
South Fork of the Tuolumne River
O'Shaughnessy Dam / Hetch Hetchy Reservoir
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Request for Interest (RFI)
The RFI is available online with responses due by September 17, 2024
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