The Pine Mountain Tanks Project is a two-phase effort, which will span multiple years, and adds a pair of seismically resilient 2-million-gallon concrete water storage tanks near Concrete Pipe and Sky Oaks roads. Known as the Pine Mountain Tanks Project, because these tanks will eventually replace the Pine Mountain Tunnel for water storage, this generational project will ultimately bolster the District’s water supply resiliency by improving seismic stability and water quality, boosting firefighting capabilities on the watershed and increasing water system capacity for Ross Valley.
In the first phase of construction, a large retaining wall was built to help make room for the tanks. Phase Two involves the on-site construction of the tanks, which will be known as the Gibson Tanks, named in honor of former Marin Water Board member Jack Gibson. The second phase will occur over the next several years, with construction planned to conclude in the winter of 2029.
Construction Update (August 2026)
Following a seasonal pause, work on Phase Two of the Pine Mountain Tanks Project has re-started. This year marks the third consecutive year of construction — but the second year of Phase Two. From August to December 2026, crews will be pouring the concrete foundation, core walls and columns for the pair of large tanks.
For Mt. Tam Watershed visitors: During construction, Concrete Pipe Road between Bolinas Road and Taylor Trail will be closed during normal working hours. Additionally, there will be intermittent closures of Bon Tempe and Bullfrog roads during hauling operations. Please heed project signage on the Mt. Tam Watershed.
Schedule and Status
Planning: Winter 2020/21 – Spring 2021
Design: Spring 2021 – Summer 2025
Construction: Summer 2024 – Winter 2029
*Construction window will typically range from Aug. 1 – Jan. 31 to protect Northern Spotted Owl
Contact Information
- Marin Water Construction Management team: 415-945-1560
- Azul Works, Inc. (project contractor): 415-558-1507
Investing in your water system
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%. This is a major, multi-year construction project that is expected to be ongoing through January 2029.
Funding Sources
| Capital Maintenance Fund | Other Funding Sources | Total |
| $23,188,370 | – | $23,188,370 |