After years of delay dating back to 2016, Marin Municipal Water District’s board has finally greenlit a major fix to one of the county’s oldest water lifelines. This month the board approved a plan to replace two aging pipeline crossings over San Geronimo Creek, clearing the way to shore up the North Marin Line that carries raw water from Kent Lake and Nicasio Reservoir to the valley’s treatment plant.
Under the updated design, one creek crossing will be hoisted onto a new steel truss and roughly 1,700 feet of new pipe will be routed beneath Sir Francis Drake Boulevard. Crews will also cut out the old pipe and concrete pilings in the creek. District officials say they are aiming for late summer construction so any in-stream work avoids sensitive nesting seasons.
What the project will do
According to Marin Water, the North Marin Line went in back in 1957 and the existing creek crossings are now near the end of their useful life. The current spans sit on concrete trestles in the creek, have a history of leaks, and no longer match modern standards for reliability.
The revised plan calls for one of the crossings to be replaced with a 36-inch pipe mounted on a single-span steel truss supported by drilled piers. A second segment of the line will be installed under Sir Francis Drake Boulevard for about 1,700 feet. The new truss will elevate the pipe roughly 2 to 3 feet above the adjacent ground at the creek bank, which is intended to cut down on in-channel work and bump up seismic resilience, according to Marin Water.
Board sign-off and price tag
Earlier this month, the Marin Municipal Water District board voted to approve the revised plan and authorized staff to move ahead with final permitting and procurement. District staff estimate the construction will cost somewhere between $3 million and $5 million. Board President Matt Samson noted that the project has been on hold since 2016.
The board’s approval came after the release of a supplemental environmental assessment this fall, the Marin Independent Journal reported.
Environmental review and safeguards
The district prepared a supplemental Initial Study/Mitigated Negative Declaration and filed it with the state CEQA clearinghouse. The state record lists the North Marin Line Stabilization Project as a mitigated negative declaration.
The CEQAnet entry and supporting documents describe how work areas would be dewatered to create dry conditions, the planned removal of existing piles and pipe, and technical appendices that respond to agency comments. The public review period ran through late November and the state file includes the full supplemental IS-MND along with review letters from state agencies.
Timing, staging and construction details
Marin Water says construction and material staging will stay largely within the district’s 20-foot pipeline easement, at Kent Lake near Peters Dam, and potentially at the Leo T. Cronin parking lot to help limit impacts on traffic. The environmental review sets a work window that avoids the February 1 through July 31 nesting season and anticipates primary construction between August and November to reduce wildlife disturbances.
Planned work includes temporary dewatering of the creek work areas, cutting and removing the existing pipe and concrete piles, and installing the elevated steel truss span to improve seismic performance, according to Marin Water.
What it means for local supplies
District engineering manager Elysha Irish told the Marin Independent Journal that the North Marin Line is a critical link in the system because Kent Lake and Nicasio Reservoir are two of the district’s largest water sources. Soulajule Reservoir could also be fed through the line under certain operating scenarios.
Irish added that while the San Geronimo Creek crossings are being addressed first, the entire pipeline will ultimately need to be replaced as part of a broader program to modernize the district’s transmission system, the Marin Independent Journal reported.
Permits, oversight and next steps
The supplemental IS-MND went through a public comment period that closed in late November. The CEQAnet file shows that state agencies submitted review letters and technical comments, which the district has addressed in the final documents.
Now that the board has signed off, district staff will pursue final permits, secure funding, and begin the process of hiring a contractor while coordinating traffic control and staging with county and state partners. Residents along Sir Francis Drake Boulevard should expect periodic traffic control and staging notices as the construction schedule firms up.
The upgrades are framed as a long-sought safety and reliability fix for one of Marin’s oldest transmission lines. District staff say they will post construction updates and contact information on the project page as the timeline and contracts are finalized.
