Capital Improvement - Water Storage Project
Capital Improvement - Water Storage Improvement Project
MMWD is beginning the process of planning, designing and constructing two treated water storage facilities on the Mt. Tamalpais Watershed. The proposed facilities are replacements for two existing facilities: the Pine Mountain Tunnel, built in 1918, and the Ross Reservoir, built in 1929.
The water storage currently provided by these two aging facilities is insufficient for operational peak demand and emergency use. In addition, both facilities create potential water quality challenges due to their structural deterioration.
The Water Storage Improvement Project will provide eight million gallons of potable water storage, enough to meet customers’ peak daily demand, to provide operational flexibility and for sufficient storage for fire flow within this section of the district’s distribution system.
The project includes the following components:
Construction of one or two concrete water tanks to provide four million gallons of storage capacity above Phoenix Lake at or adjacent to the existing Ross Reservoir.
Construction of one four-million-gallon concrete tank on the district’s watershed near Five Corners.
Decommissioning the Pine Mountain Tunnel.
Project Schedule (all dates are estimates)
Complete design report - May 2013
Complete CEQA review and permits - Summer 2015
Complete Road and Trail Improvements - Fall 2015
Complete Design - Early 2016
Start Construction - Spring 2016
Complete Construction of Five Corners Tank and Ross Valley Tank #1, Remove Ross Reservoir and Pine Mountain Tunnel from service - Fall 2017
Complete Construction of Ross Valley Tank #2 - October- Fall 2018
Complete Decommissioning of Pine Mountain Tunnel - Early 2019
The Pine Mountain Tunnel is an 8,700-foot long tunnel completed in 1919 to convey water from Alpine Lake on the Mt. Tamalpais Watershed to San Rafael and the Ross Valley. The district abandoned the use of the tunnel as a conveyance facility in 1971, after which it was used to store three million gallons of treated water for distribution and surge protection.
Due to its deteriorating condition, the California Department of Public Health has directed MMWD to either remove the tunnel from service or completely repair the tunnel to ensure the reliability of the tunnel to store water, prevent bacterial growth and ensure that the tunnel meets all drinking water standards.
In 2009 MMWD established an advisory committee to assist in evaluating the status of the Pine Mountain Tunnel as a storage facility. The advisory committee consisted of representatives from the San Geronimo Valley, Fairfax, Marin County Open Space District, as well as MMWD staff and board members. MWH Americas, Inc., an engineering firm specializing in the planning, design and construction of water transmission and storage facilities, assisted the district and the advisory committee in evaluating the tunnel and developing a recommended course of action.
Built in 1929, Ross Reservoir is an in-ground, concrete-lined trapezoidal shaped facility that stores one million gallons of treated water for distribution to the lower Ross Valley. Because of its age, continued deterioration of the wooden roof, the possibility of a significant landslide threatening the northeast corner of the reservoir, and its limited storage volume for operational and emergency use, the district has determined that a replacement storage facility is needed in that location.
If you have any questions regarding this project, please e-mail firstname.lastname@example.org.
MWH Americas, Inc. Technical Memoranda:
1. Storage Recommendations (Sept. 3, 2010) (2 MB)
2. Potential SCADA Enhancements (Sept. 10, 2010) (<1 MB)
3. Ross Reservoir Sizing (May 23, 2011) (<1 MB)
4. Pine Mountain Tunnel Rehabilitation (July 20, 2011) (3.5 MB)
5. New Storage Reservoir Siting Study (Nov. 28, 2011) (10.5 MB)
6. Sensitivity to Supply and Demand Assumptions (Nov. 30, 2011) (<1 MB)
HDR Work Plan: Preliminary Design and Design Report (Aug. 29, 2012) (43.2 MB)