Use of D-C Resistivity to Map Saline Ground Water

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by Christina L. Stamos, U.S. Geological Survey, San Diego, United States,
Steven K. Predmore, U.S. Geological Survey, San Diego, United States,
Adel A. R. Zohdy, U.S. Geological Survey, San Diego, United States,

Document Type: Proceeding Paper

Part of: Irrigation and Drainage: Saving a Threatened Resource—In Search of Solutions

Abstract: It has been estimated in previous studies that 23 square miles of the Oxnard aquifer, a member of a multi-layered aquifer system beneath the Oxnard plain in Ventura County, California, has been contaminated as a result of seawater intrusion. To investigate this and other potential sources of saline water, a direct-current resistivity survey was made as an alternative to the costly and time-consuming method of well drilling in the part of the Oxnard plain where ground water is believed to be most affected by seawater. Findings from this survey and water-quality data collected from wells as part of this study suggest that the extent of seawater intrusion is much less than reported. A field inventory of the current monitoring-well network utilized by managing agencies suggests that the integrity of most of the well casings is questionable. Leakage of saline water from an unconfined `perched zone' through these and other failed or corroded well casings is a possible source of increasing chloride concentration in the underlying Oxnard aquifer. Saline water also may be present in fine-grained deposits along the eastern limit of the Oxnard aquifer. Pumping near this area could induce the lateral migration of saline water from these deposits.

Subject Headings: Salt water intrusion | Aquifers | Mapping | Salt water | Groundwater | Wells (water) | Hydrographic surveys | Groundwater quality | North America | California | United States

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