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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.
Construction Update (June 2025)Phase 2 of Pine Mountain Tanks project underway After two construction seasons, the future site of a pair of 2-million-gallon water storage tanks is prepared for tank installation on the Mount Tamalpais Watershed. The construction site now boasts an impressive, 560-foot-long retaining wall that rises 75 feet at its highest point. The wall has been stained a natural brown to blend in with the surrounding environment. Phase 2 work to construct the tanks, which will each stand 45 feet high and 90 feet in diameter, began in June 2025. Reminder: Road and trail access are limited near the construction site on weekdays during construction hours, and Mt. Tam visitors are encouraged to review watershed visitor notices before visiting and heed all construction-related signage as work commences. |
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 |