Consideration of Geologic Conditions in Optimizing a Tunnel and Ocean Outfall Alignment within the Los Angeles Basin, California

Sackett, David M.¹, Thomas W. McNeilan¹, Calvin G. Jin² (1) Fugro West, Inc, Ventura, CA (2) County Sanitation Districts of Los Angeles County, Whittier, CA

The Sanitation Districts of Los Angeles County are evaluating the feasibility of a new tunnel and ocean outfall in the context of a comprehensive master facilities plan to cover its Joint Outfall System which serves a large portion of metropolitan Los Angeles County. The new tunnel and ocean outfall would extend from their Joint Water Pollution Control Plant in Carson to the offshore continental shelf, a distance of up to twenty kilometers. The six-meter tunnel is planned to be installed at up to one hundred meters below ground surface under a densely populated urban area, and may trend beneath the Port of Los Angeles (POLA), one of the world's busiest ports. The feasibility/design phases of the project started in 2006 and are planned through 2012, with construction set to begin in 2013.

This paper discusses feasibility phase studies designed to evaluate how geologic conditions will affect the selection and comparison of several tunnel/outfall corridors. Both urban development and geologic conditions will impact final design and construction of the outfall. Other factors include access shaft locations and optimal diffuser effluent dilution and dispersion. Modeling will be based upon available satellite and aerial imagery, water well logs, and geologic data from the USGS, CGS, scientific institutes, and proprietary oil & gas studies.

The final choice of a preferred alignment will result from a careful balance between the most favorable geologic conditions for tunneling, locating shafts in areas that minimize disruption to urban activities, and avoidance of environmental impact in areas of high sensitivity.