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U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 03-4028

Quality and Sources of Shallow Ground Water in Areas of Recent Residential Development in Salt Lake Valley, Salt Lake County, Utah

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

By Susan A. Thiros,

ABSTRACT

Residential and commercial development of about 80 square miles that primarily replaced undeveloped and agricultural areas occurred in Salt Lake Valley, Utah, from 1963 to 1994. This study evaluates the occurrence and distribution of natural and anthropogenic compounds in shallow ground water underlying recently developed (post 1963) residential and commercial areas. Monitoring wells from 23 to 153 feet deep were installed at 30 sites. Water-quality data for the monitoring wells consist of analyses of field parameters, major ions, trace elements, nutrients, dissolved organic carbon, pesticides, and volatile organic compounds.

Dissolved-solids concentration ranged from 134 to 2,910 milligrams per liter (mg/L) in water from the 30 monitoring wells. Dissolved arsenic concentration in water from 12 wells exceeded the drinking-water maximum contaminant level of 10 micrograms per liter. Water from monitoring wells in the northwestern part of the valley generally contained higher arsenic concentrations than did water from other areas. Nitrate concentration in water sampled from 26 of the 30 monitoring wells (86.7 percent) was higher than a background level of 2 mg/L, indicating a possible human influence. Nitrate concentrations ranged from less than 0.05 to 13.3 mg/L.

Fifteen of the 104 pesticides and pesticide degradation products analyzed for were detected in 1 or more water samples from the monitoring wells. No pesticides were detected at concentrations that exceeded U.S. Environmental Protection Agency drinking-water standards or guidelines for 2002. The high detection frequency of atrazine, a restricted-use pesticide, in residential areas on the west side of Salt Lake Valley may be the result of application in agricultural or industrial areas that have been converted to residential uses or application in areas upgradient from the residential areas that was then transported by ground water.

Fifteen of the 86 volatile organic compounds analyzed for were detected in 1 or more water samples from the monitoring wells. The most frequently detected volatile organic compounds were chloroform (90 percent), bromodichloromethane (56.7 percent), tetrachloroethylene (53.3 percent), and 1,1,1-trichloroethane (50 percent). The widespread occurrence of chloroform and bromodichloromethane in shallow ground water is likely a result of the recharge of chlorinated public-supply water used to irrigate lawns and gardens in residential areas of Salt Lake Valley. Tetrachloroethylene (PCE), primarily used as a dry cleaning agent and solvent, was detected in water from 16 wells.

CONTENTS

Foreword
Abstract
Introduction
Purpose and Scope
Description of Study Area
Ground-Water Hydrology
Land Use
Acknowledgments
Study Design and Methods
Site Selection
Sample Collection and Analysis
Quality Assurance
Ground-Water Quality
Field Parameters
Inorganic Constituents
Major Ions
Trace Elements
Radionuclides
Nutrients and Dissolved Organic Carbon
Pesticides
Volatile Organic Compounds
Sources of Ground-Water Recharge
Stable Isotopes
Tritium and Tritium/Helium-3
Chlorofluorocarbons
Effects of Shallow Ground-Water Quality on Deeper Ground-Water Quality
Relation Between Ground-Water Quality and Land Use
Summary
References Cited
Appendix

This report is contained in the following file:

WRI034028 (5.8 mb)

Send questions or comments about this report to the author, Susan A. Thiros (sthiros@usgs.gov) 801.908.5063.

For more information about USGS activities in Utah, visit the USGS Utah District home page.

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U.S. Department of the Interior, U.S. Geological Survey
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