North Marin Line Stabilization Project Final Supplemental IS/MND

The Marin Municipal Water District is implementing the North Marin Line Stabilization Project to replace two seismically unsound pipeline crossings of San Geronimo Creek in Lagunitas, California, with seismically resistant structures. The project involves replacing existing 34-inch American concrete cylinder pipe with new 36-inch welded steel pipe. One crossing will be replaced by approximately 1,700 feet of new pipeline within Sir Francis Drake Boulevard, while the other will utilize a 36-inch pipeline installed within a single span steel truss supported by drilled piers. The new trestle structures are designed to be at a higher elevation to clear the anticipated 100-year flood elevation. The scope also includes the removal of existing piles and pipelines in the creek and the restoration of any disturbed improvements. Construction is scheduled to occur over approximately 26 months, with primary work windows between August and November of each year. To protect the northern spotted owl nesting season, all work must be conducted between August 1 and January 31. The project has undergone extensive environmental review under CEQA, resulting in a Mitigated Negative Declaration to address potential impacts on biological resources, including Coho salmon and California freshwater shrimp. The contractor is responsible for site safety and OSHA-compliant shoring, while the project applicant must coordinate with the California Department of Fish and Wildlife for biological surveys. Technical specifications require strict adherence to ASTM and California test methods for soil compaction, density, and classification.