Joint Water Pollution Control Plant Sewer Tunnel Outfall — Los Angeles, CA

We are the lead designer for the Joint Water Pollution Control Plant (JWPCP) Sewer Tunnel Outfall Tunnel project. The Sanitation Districts of Los Angeles County are 24 independent special districts serving the wastewater and solid waste management needs of approximately 5.6 million residents in Los Angeles County. Seventeen of the Sanitation Districts are signatories to a Joint Outfall Agreement providing a regional, interconnected system of wastewater management facilities known as the Joint Outfall System (JOS).

Purpose Of The Joint Outfall System (JOS)

The JOS provides wastewater collection, treatment, reuse, and disposal for residential, commercial, and industrial users, and it includes seven treatment plants, the largest of which is the JWPCP, located in the City of Carson. Currently, secondary treated effluent from the JWPCP is conveyed through two 6-mile-long tunnels to a manifold structure located near White Point on the Palos Verdes Peninsula. Four sea-floor outfalls extend offshore from the manifold structure. The two main outfalls are 90 and 120 inches in diameter and extend approximately 1.5 miles offshore, discharging approximately 200 feet below sea level.

Key Features Of The Joint Water Pollution Control Plant Sewer Tunnel Outfall

The new effluent outfall tunnel will be approximately 7 miles long, have an 18-foot internal diameter, and include 1,350 feet of 16-foot diameter steel liner at the Palos Verdes Fault crossings. The new tunnel will allow for inspection of the existing tunnels, provide redundancy for the effluent management system, ensure capacity for future growth, and convey peak storm flows. The upstream end of the project will include constructing a junction structure to connect the tunnel to an active 14-foot-diameter force main. The existing manifold structure at the downstream end of the project will be demolished, and a new manifold structure will be constructed. Since the existing tunnels and main outfalls are always required to be in service, a temporary bypass system will be constructed and operated during this project phase.

Construction of the tunnel and associated structures was packaged under a single contract and was awarded to Dragados USA (DUSA) in January 2019. Notice to Proceed (NTP) was received in April 2019, and construction is expected to be completed in seven and a half years.

TBM advance started in October of 2021. In April 2022, the TBM and launch shaft were reconfigured for continuous production tunneling, which began in May 2022. Currently, tunneling is approximately 59 percent complete (21,560 linear feet of 36,806 linear feet). Preconstruction activities have started for the junction (upstream) and manifold (downstream) structures. These activities include potholing, surveying the existing facilities, and constructing and testing a 168-inch diameter pipeline to connect the existing effluent flows to the new tunnel.  A 168-inch diameter butterfly valve has been fabricated to divert existing flows.  Weighing about 70 tons with an approximate size of 21ft x 17ft x 4ft, the 168-inch diameter butterfly valve is one of the largest ever built in the United States. 

Project Completion

The overall project is estimated to be completed in 2026. Once built, the 18-foot tunnel and associated structures will ensure that the wastewater needs of the JOS are fulfilled for the foreseeable future.