Laguna Beach Tunnel

The over 60-year-old tunnel currently houses a gravity sewer that provides wastewater service for the northern portion of Dana Point and homes along the west side of coast highway at Three Arch Bay and in South Laguna. It is buried approximately 50 feet beneath the bluff from Three Arch Bay to Aliso Beach. The tunnel, located 20–30 feet from the edge of the cliffs, and underneath multi-million dollar homes, could have a pipeline break that could take 36 hours or longer to control and allow over 800,000 gallons of sewage to flow into a federally protected marine life habitat.

When built in 1964, the tunnel became an innovative engineering model because it relies solely on gravity flow, which eliminates costly and unsightly infrastructure, including unnecessary lift stations and several thousand feet of sewer mains. The system has maintained a minimal carbon footprint since its first day of operation, and it remains a vital piece of regional infrastructure.

Part of this project called for a section of pipe that had been removed to be backfilled with flowable fill. The challenge was that even though there was access doors from the beach to the tunnel, it was inaccessible due to the private neighborhoods in the area. So the solution was to grout the area from the access shaft located 6,300’ away from point of injection, the size of the void was unknown so a series of tremie pipes were bored to access the void space and then placement of the material began. This solution helped ensure homeowners above this tunnel there would be no risk for damage to property due to this void in the ground.