By John A. Izbicki, Loren F. Metzger, Kelly R. McPherson, Rhett R. Everett, and George L. Bennett V
U.S. GEOLOGICAL SURVEY
Open-File Report 2006–1309
For chloride concentrations animation, download (4.7 MB PDF)
For changes in water-level contours animation, download (7.5 MB PDF)
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As a result of pumping and subsequent declines in water levels, chloride concentrations have increased in water from wells in the Eastern San Joaquin Ground-Water Subbasin, about 80 miles east of San Francisco (Montgomery Watson, Inc., 2000). Water from a number of public-supply, agricultural, and domestic wells in the western part of the subbasin adjacent to the San Joaquin Delta exceeds the U.S. Environmental Protection Agency Secondary Maximum Contaminant Level (SMCL) for chloride of 250 milligrams per liter (mg/L) (fig. 1) (link to animation showing chloride concentrations in water from wells, 1984 to 2004). Some of these wells have been removed from service. High-chloride water from delta surface water, delta sediments, saline aquifers that underlie freshwater aquifers, and irrigation return are possible sources of high-chloride water to wells (fig. 2). It is possible that different sources contribute high-chloride water to wells in different parts of the subbasin or even to different depths within the same well.
Purpose and Scope
Test Drilling and Well Installation
Borehole Geophysical Data
Fluid-velocity logs and depth-dependent water-quality sample collection
Sources of High-Choride Water to Wells
Major-Ion Composition of Water from Wells
Oxygen-18 and Deuterium Composition of Water from Wells
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