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Pine Mountain Tanks Project

A black and white image of Pine Mountain Tunnel from 1917.

Year 1 of Phase 1 construction underway

The Pine Mountain Tanks Project is a two-phase effort, which will span multiple years, and adds a pair of 2-million-gallon concrete water storage tanks near Concrete Pipe and Sky Oaks roads, bolstering water supply resiliency for firefighters, as well as for the town of Ross and other area residents. 

Construction Update as of Oct. 9, 2023

Watershed closures reduced

After several weeks of work to off-haul material as part of the effort to prepare the construction site for the installation of the concrete storage tanks, hauling-related closures along much of Concrete Pipe Road and Shaver Grade have been lifted. Some closures and controlled access points remain in place while Phase 1 construction continues through January 2024. 

Watershed Visitor Access Interruptions

The following measures are in place through Jan. 31, 2024:

  • Traffic controls in place along Sky Oaks/Bon Tempe/Bullfrog roads. 
  • Concrete Pipe Road is closed Mon – Fri, 8 a.m. to 5 p.m. at Bolinas-Fairfax Road and at Shaver Grade 
  • Motorist parking along Bolinas-Fairfax Road at Concrete Pipe Road is prohibited.
  • During the project's active construction months, Watershed reservations will continue to be permitted for use of the Lake Lagunitas picnic grounds, though visitors should expect traffic delays. The issuance of Land Use Permits for other locations on the Watershed will be limited to areas that do not interfere with construction activity and will be considered on a case by case basis. Active construction months include Aug 2023-Jan 2024 and Aug 2024-Jan 2025.

Watershed road/trail impacts map (PDF) 


Contact Information

  • Marin Water Construction Management team:  415-945-1560
  • Maggiora & Ghilotti, Inc., (project contractor):  415-459-8640

Maintaining Infrastructure is Top Priority

The Pine Mountain Tunnel was constructed in 1919 to convey water from Alpine Reservoir to Fairfax and San Rafael and was converted to a water storage facility in 1971 and remains in that use today. The storage replacement project will enhance water system resiliency and replaces aging infrastructure on the District’s watershed. A pair of 2-million gallon pre-stressed concrete storage tanks will replace the existing Pine Mountain Tunnel with a modernized design that provides seismic stability, water quality improvements, and low maintenance.  This project also increases water system capacity in Ross Valley by approximately 30%.


Project Pine Mountain Tunnel Tanks Replacement 
Program A1A11 Replacements - Storage Tanks 
Project Number D21043
Contact Alex Anaya | 
Map of two purple circles between Concrete Pipe Rd and Sky Oaks Rd
Trees shading a hillside

Project Description 

This project will cease use and replace the Pine Mountain Tunnel with two 2-million gallon pre-stressed concrete tanks located on Concrete Pipe Road at culvert marker CP-5. 


The benefit of this project is to cease use of Pine Mountain Tunnel for storage, improving water quality, and increase the reliability of storage within Ross Valley, providing emergency storage on the watershed to aid in firefighting capabilities and allow for the future replacement of Ross Reservoir. 

Schedule and Status

Planning: Winter 2020/21 - Spring 2021

Design: Spring 2021 - Summer 2025

Construction: Summer 2024 - Spring 2029

*Construction window from August 1 - January 31 to protect Northern Spotted Owl

Expenditure Schedule

Actuals Through
FY 22 (Rounded)
FY 23
FY 24
FY 25
FY 26
FY 27
FY 28
FY 29

*Pending funding

Funding Sources 

Capital Maintenance Fund
State Appropriation
Other Funding Sources*

*Other funding sources to be determined