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Outfall Tunnel

Sanitation Districts of Los Angeles County

The County Sanitation Districts of Los Angeles County are planning to add a third treated-effluent outfall tunnel to the two existing outfall tunnels transporting secondary effluent from the Joint Water Pollution Control Plant (JWPCP) in Carson, California to the existing ocean outfall. The new tunnel, referred to as the JWPCP Effluent Outfall Tunnel will be about 6.9 miles long with 18-foot finished internal diameter tunnel constructed with a TBM. The TBM will be launched from a shaft. To create more space for the TBM assembly, the Contractor selected to construct a SEM Starter and Tail Tunnel at the bottom of the launch shaft.

Management of Implementation of SEM Excavations:

Gall Zeidler Consultants (GZ) provided onsite service with SEM Engineer and SEM Superintendents to manage implementation of the SEM excavation and installation of the shotcrete initial lining in the Starter and Tail Tunnels. Moreover, GZ was responsible for interpretation of monitoring data and geotechnical consulting.


Los Angeles, California


2020 - 2021


TBM Starter/Tail Tunnel


TBM Starter/Tail Tunnel


23’ x 23’ ovoid


Lakewood Formation sands


$630 Million


Dragados USA


Sanitation Districts of Los Angeles County