Design and Construction of a Relief Sewer Siphon under the Santa Clara River by Microtunneling

The Sanitation Districts of Los Angeles County (Districts) own, operate and maintain a wastewater treatment and collection system that includes approximately 1,300 miles of sanitary sewers ranging in diameter from 8-inch to 144-inch. This project is the last of a series of projects that provides relief for the District 32 Main Trunk Sewer system, which serves the Santa Clarita Valley. This relief sewer siphon project was successfully constructed by microtunneling a 60-inch steel casing with a 48-inch fiberglass carrier pipe at a depth of 40 feet below the unimproved Santa Clara River at a construction cost of $7.7 million. The 28-foot diameter, 80-foot deep microtunneling shafts were constructed by sinking a concrete caisson without dewatering due to the inability to discharge groundwater into the river because of environmental and permitting restrictions. The project was successfully completed in August 2010.