CGS Monthly Meeting

Tuesday, May 17, 2011

 

Hydrogeologic Exploitation of a Raw Water Resource from an Unconfined Aquifer at Coast Guard Beach, San Nicolas Island, Offshore California

J. M. Saenz¹, G. Gong¹, K. Zaiger¹, D. Vann¹, and T. J. O'Neil^2
1US Department of the Navy, Naval Facilities Engineering Service Center, EV 411, Port Hueneme, CA, joseph.saenz@navy.mil, gilbert.gong@navy.mil, kimo.zaiger1@navy.mil, david.vann1@navy.mil
²Oxnard College, Oxnard, CA, toneil@vcccd.edu

Abstract:  The US Navy established an integrated technical assessment process to site seven new saltwater intake wells adjacent to a jetty on the shoreline at Coast Guard Beach, San Nicolas Island, offshore California. The three technical approaches used for the well siting process included a hydrogeologic survey, a geographic information system (GIS) shoreline time-series analysis, and an oceanographic assessment of coastal currents and sediment transport. Results integrated from these three different technical approaches were synthesized to accurately site and install seven new wells at Coast Guard Beach.

The detailed hydrogeologic survey identified a dynamic and coastal unconfined aquifer. This aquifer is composed of fine-grained beach sand with a clay-silt layer encountered at depth. The aquifer has direct hydraulic connection with the Pacific Ocean, and responds rapidly to tidal fluctuations. Survey results were supplemented with mathematical computations used for specifying well spacing and depth. GIS analysis of satellite images provided isolines representing shoreline changes over time. The oceanographic assessment and sediment transport analysis showed potential impacts on the shoreline by long shore currents and predicted future shoreward migration of the shore isoline. Analysis of erosion and deposition in the vicinity of the jetty allowed for accurate saltwater intake well siting and installation on this dynamic shoreline.

In December 2008, the existing saltwater intake well field was upgraded by installing seven new wells in addition to the three existing wells that provides raw saltwater supply to a Reverse Osmosis Unit (ROU). This upgrade increased the total raw water supply rate to 250 gpm. Using a unique well design, the wells were installed near the shoreline to about 25 feet below ground surface. Hydrogeologic materials provide a native filter for the raw seawater supply prior to transport to the ROU, where the seawater is converted into potable water to support the Island population.

 

Biography: 

 

Mr. Joseph M. Saenz "Manny" is employed as a Project Manager in the U.S. Navy's Environmental Restoration Program, and as an adjunct professor at Oxnard College and University of La Verne.  He received degrees at California State University, Northridge, earning a B.S. in 1991 and a M.S. in 2002.  His focus has been on investigations at sites requiring hydrogeologic and hydrocarbon exploration, facility installation, pollution prevention, remedial action, and emergency response clean-ups.  Saenz's practical experience in water resources and seismotectonics has allowed him to work on projects in various nations in the Horn of Africa, the Arabian Peninsula, and Southeast Asia.  He has led numerous field hydrogeologic expeditions for the purpose of siting, designing, testing, and installing facility infrastructure and shoreline protection technologies.  Saenz was a recent recipient of the prestigious Certificate of Commendation from the Combined Joint Task Force - Horn of Africa.