Fugro is conducting the geological and geotechnical feasibility evaluation for design and construction of a proposed new ocean tunnel/ outfall that would extend from the Joint Water Pollution Control Plant (JWPCP) onto the San Pedro Shelf. This alignment alternative is anticipated to extend southward from the JWPCP, extend beneath the Port of Los Angeles and the San Pedro Breakwater, and continue about 8 to 12 kilometers offshore, to a water depth of between about 60 and 90 meters. The anticipated alignment will cross the active Palos Verdes fault zone beneath the Los Angeles Harbor and also will cross the potentially active Cabrillo fault offshore from the San Pedro Breakwater.

A variety of offshore and onshore exploration borings were accomplished using Fugro’s drillship, the M/V Fugro Explorer, dedicated seismic vessel, and ocean-going derrick barges. Multibeam bathymetry and high resolution seismic reflection data were collected and correlated with the geotechnical data, along with existing public domain and private studies by others.

Any new ocean tunnel/outfall alignment and profile beneath the San Pedro Shelf will penetrate through difficult, variable, and complex subsurface conditions. A key goal during design will be to identify optional routes and construction techniques that minimize the difficulties posed by these geologic conditions.

Results/Benefits of the Project

• Provide insight into how the ocean bottom and subsurface conditions will affect the planning, permitting, design, construction, and operation of a new tunnel/outfall.
  
  
• Improve definition of regional geology and structure, including the variability of subsurface conditions in the offshore project area.
  
  
• Determine that complex geologic conditions in the area include materials that have been extensively faulted, folded, and compressed by tectonic forces, and lithified to various degrees by diagenetic changes.
  
  
• Provides initial characterization of complex geologic conditions representative of the San Pedro Shelf for preliminary planning and design of the new LACSD Tunnel/Outfall.
  
  
• Contract is implemented to take advantage of timely availability of a variety of vessels, including the M/V Fugro Explorer, one of the most technologically advanced offshore drilling vessels in the world.
  
  
• Develop a preliminary regional geologic model and allowed for planning future geotechnical drilling techniques and procedures.
  
  

Project Challenges:

• Value engineering approach taken to optimize the numbers and depths of borings within specified charter period.
  
  
• Preliminary geophysical data acquisition performed in optimized survey grids to minimize degradation of acoustic source due to unfavorable sea conditions and to allow uninterrupted acquisition effort.
  
  
• Boring and CPT locations selected to provide representative samples of various geologic strata underlying the study area.
  
  
• Micropaleontological studies and downhole suspension logging were performed to improve stratigraphic correlation across fault zones.
  
  
• Carefully scripted drilling program was adjusted while in the field to take provide additional boring for stratigraphic control in area underlain by dipping strata.