Dominguez Gap Seawater Barrier

The Dominguez Gap Seawater Barrier Project was part of a Los Angeles County Department of Public Works (LACDPW) project designed to limit intrusion of seawater into the West Coast Groundwater Basin. Jacobs Associates provided preliminary and final design, contract documents, and cost-estimating services to the LACDPW on the three-year project, which was completed in 2004. It involved design and construction of parallel utility pipelines, including steel water pipelines 18 to 30 inches (46 to 76 cm) in diameter, steel air pipelines 4 to 6 inches (10 to 15 cm) in diameter, electrical and telemetry conduits 2.5 inches (6.35 cm) in diameter, and a 10 inch (25 cm) gravity disposal pipeline. The pipelines connect to groundwater injection wells and provide water for injection, air for lifting of wastewater during well redevelopment, and a gravity drain line for removing wastewater from well redevelopment.

Approximately 2,900 feet (884 m) of pipeline was installed as a bundle inside a 54 inch (137 cm) casing using microtunneling and pipe jacking to avoid impact to traffic and an existing container facility. Approximately 1,500 feet (475 m) of the disposal line was installed separately using pilot tube microtunneling in drive lengths of over 270 feet (82 m). Geology generally consisted of interbedded silts, silty sands, and poorly graded sands.

At each injection well, pipelines were routed up the walls of an access manhole and connected to existing well vaults. Challenges included installation of the pipeline bundle inside the casing, maintaining drain pipeline grade within the casing, corrosion protection of steel pipelines, and vertical and lateral support of pipeline in manholes.