--> Consideration of Geologic Conditions in Optimizing a Tunnel and Ocean Outfall Alignment within the Los Angeles Basin, California, by David M. Sackett, Thomas W. McNeilan, and Calvin G. Jin, #80008 (2007).

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

By

David M. Sackett¹, Thomas W. McNeilan¹, and Calvin G. Jin²

Search and Discovery Article #80008 (2007)

Posted September1, 2007

*Adapted from poster presentation at AAPG Annual Convention, Long Beach, California, April 1-4, 2007

¹Fugro West, Inc, Ventura, CA ([email protected])

²County 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 (Figure 1-2) 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) (Figure 1-3), 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 (Figure 1-5). 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 and 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.

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Background and Setting

Proposed Tunnel/Ocean Outfall Quick Facts

Vertical shaft at the JWPCP
Length of tunnel onshore: 30,000 ft (~9150 m)
Elevation of tunnel onshore: EL= -200 ft (~-60 m)
Vertical shaft near onshore/ offshore transition
Length of tunnel offshore: 25,000 ft (~7600 m)
Elevation of tunnel offshore: EL= -250 ft (~-75 m)
Vertical riser located at tunnel/seafloor pipe transition
Length of seafloor pipeline: 35,000 ft (~10,700 m)
Length of diffuser on seafloor: 10,000 ft (~3,000 m)

Figure 1-1 – 1-6

	Figure 1-1. Project area.
	Figure 1-2. Aerial view of JWPCP in Carson. The JWPCP is located adjacent to I-110, south of Sepulveda Blvd. in Carson.
	Figure 1-3. Aerial view of Port of Los Angeles. The Port of Los Angeles has significantly altered the geomorphology of the original San Pedro Bay.
	Figure 1-4. Aerial view of Palos Verde Peninsula. The Palos Verdes Peninsula results from compressional forces and thrusting of the Palos Verdes fault zone.
	Figure 1-5. Project drivers.
	Figure 1-6. Three-dimensional topographic/bathymetric view of project area. The project area is within the ancestral Los Angeles and San Gabriel alluvial plain and adjacent San Pedro continental shelf. Elevations range from about EL +15 meters at the JWPCP to EL -100 meters at the continental shelfbreak.

Regional Geomorphology and Seismicity

Geomorphic Provinces

Inner Continental Borderland
- 250 km wide zone of irregular topography that separates the California coastline from the Pacific Ocean Basin.
Peninsula Ranges
- Series of sub-parallel, NW-SE trending mountain ranges and valleys structurally controlled by the San Andres Fault. This province includes most of the greater Los Angeles Basin.
Transverse Ranges
- East-West trending steep mountain ranges and valleys oblique to normal structural trend of coastal California. Province formed due to intense North-South compression causing significant uplift.

Figure 2-1 – 2-6

	Figure 2-1. Geomorphic provinces in vicinity of project area.
	Figure 2-2. Cenozoic plate tectonic evolution of western North America. California coastline has formed due to complex tectonic interaction of North American, Pacific, and Farallon plates throughout the post-Eocene Epoch.
	Figure 2-3. Bathymetric relief map. Offshore portion of project area includes complex submarine geomorphic features along and below the continental shelfbreak.
	Figure 2-4. Faulting and seismicity within 100 km. The project area is situated within an active seismic zone. Major historical earthquakes within 100 km include the 1933 Long Beach earthquake and the 1994 Northridge earthquake.
	Figure 2-5. Net regional slip rates per fault. The estimated net slip rate of 50 mm/yr includes 50-60% along the San Andres Fault Zone. The cumulative offshore slip in the project area is estimated at about 5 mm/yr including about 3 mm/yr for the Palos Verdes fault zone.
	Figure 2-6. Fault slip rate and estimated magnitude.

Regional geology / faults

Figures 3-1 - 3-7

	Figure 3-1. Geologic map with key and earthquake epicenters.
	Figure 3-2. Seismic line, Palos Verdes fault zone within L.A. Harbor.
	Figure 3-3. Seismic line across Palos Verdes anticlinorium.
	Figure 3-4. Seismic line south of San Pedro breakwater.
	Figure 3-5. Section A: Stylized geologic section under Palos Verdes Peninsula. This section modified from Dibblee, 1999 and based upon original 1937 Tunnel Outfall from JWPCP to offshore Whites Point.
	Figure 3-6. Section B: Stylized geologic section through central project area. This section is stylized from survey data collected across San Pedro Shelf in 2004. Note the steeply dipping and irregular Miocene stratigraphy approaching the Continental shelfbreak.
	Figure 3-7. Section C: Stylized geologic section east of Palos Verdes fault. This section shows the generally flat-lying stratigraphy east of the Palos Verdes fault zone. However, the relationship between the onshore and nearshore dominantly granular materials and the cohesive materials at the Beta oil field are poorly understood.

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