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OPEN-FILE REPORT

Sources of High-Chloride Water to Wells, Eastern San Joaquin Ground-Water Subbasin, California

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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Abstract

    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.

CONTENTS

Introduction

Hydrogeology

Purpose and Scope

Test Drilling and Well Installation

Borehole Geophysical Data

Electromagnetic logs

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

Methods

Summary

Acknowledgements

References Cited

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