HR: 14:10h
AN: H13L-03    [Abstracts]
TI: Source of High-Chloride Water to Deep Wells in a Coastal California Aquifer
AU: * Izbicki, J A
EM: jaizbick@usgs.gov
AF: U.S. Geological Survey, 5735 Kearny Villa Road, Ste. O, San Diego, CA 92123 United States
AU: Christensen, A H
EM: ahchrist@usgs.gov
AF: U.S. Geological Survey, 5735 Kearny Villa Road, Ste. O, San Diego, CA 92123 United States
AU: Smith, G A
EM: gasmith@usgs.gov
AF: U.S. Geological Survey, 5735 Kearny Villa Road, Ste. O, San Diego, CA 92123 United States
AU: Aiken, G R
EM: graiken@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St., Ste E-127, Boulder, CO 80303 United States
AB: The combination of well-bore flow and depth-dependent water-quality data was used to evaluate the source of high-chloride water to pumping wells in a coastal southern California aquifer underlying Pleasant Valley about 100 km northwest of Los Angeles, Calif. Advantages of this approach included greater resolution of the inorganic, isotopic, and organic composition of the high-chloride water than could be provided by samples collected only from the surface discharge of production wells, and greater spatial coverage than would have been available from existing monitoring wells. Chloride concentrations in the surface discharge of water from the sampled wells were as high as 230 mg/L. In contrast, chloride concentrations were as high as 500 mg/L in water yielded from deeper, less productive zones more than 450 m below land surface. High-chloride water at depth originated from surrounding and underlying marine deposits and was associated with naturally occurring petroleum hydrocarbons. These hydrocarbons, composed largely of hydrophobic neutral compounds, would not have been detected using traditional sampling techniques because of dilution within the well during pumping. Chloride concentrations in water from the surface discharge of wells increased since the wells were first drilled in the early 1980's as chloride concentrations in the deeper parts of the wells increased. Chloride concentrations also increased during drought periods as a result of lowering of the water level and a decrease in the contribution of low-chloride water from shallower aquifers as a result of increased pumping by other wells. Changes in well design that eliminate small amounts of high-chloride water contributed to the deeper parts of some wells may improve the quality of water yielded by the surface discharge of wells without greatly reducing well yield.
DE: 1055 Organic and biogenic geochemistry
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005