Palos Verdes, CA

Joint Water Pollution Control Plant (JWPCP) Tunnel and Ocean Outfall

Los Angeles County Sanitation Districts (LACSD)


This 18-foot-diameter (5.4 m), 7‑mile-long (11.3 km) tunnel will supplement the LACSD’s existing Joint Outfall System by providing long-term redundancy and allowing inspection, maintenance, and repair of the existing facilities. The existing disposal facilities, originally built in 1937 and expanded in 1958 and 1967, operate near their peak capacity. The new tunnel and ocean outfall will increase the reliability and flexibility of the total LACSD system.

Fast Facts
  • 18-foot-diameter (5.4 m), 7-mile-long (11.3 km) tunnel
  • Single shaft tunnel construction
  • Precast concrete segmental final lining
  • Very weak ground conditions and fault crossings

Scope of Work

Delve Underground provided tunnel design services and is now providing engineering services during construction for this $630 million project. Our services include final design/​construction documentation, geotechnical characterization, planning/​feasibility, and preliminary tunnel design.

Challenges & Innovations

Tunnel construction will be serviced from a single shaft at the Carson treatment plant since there is no available real estate to construct intermediate shafts.

The tunnel final lining design includes a steel lining at fault crossings and where the alignment crosses under the SR 110 freeway. This is the first tunnel in the United States to employ post-tensioning where ground cover is insufficient to counteract the internal peak operating pressure of 41 psi (283 kPa).