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Oklahoma Water Science Center

Prepared in cooperation with the Oklahoma Department of Environmental Quality

Comparison of Ground-Water Quality in Samples From Selected Shallow and Deep Wells in the Central Oklahoma Aquifer, 20032005

By Carol J. Becker

U.S. Geological Survey Scientific Investigations Report 20065084

This report is available as a pdf.


Abstract

The aquifer units of the Central Oklahoma aquifer underlie about 2,890 square miles of central Oklahoma and are used extensively to supply water for municipal, domestic, industrial, and agricultural needs. The Central Oklahoma aquifer also is commonly referred to as the Garber-Wellington aquifer because the Garber Sandstone and Wellington Formation yield the greatest quantities of usable water for domestic and high-capacity wells.

The major water-quality concerns for the Central Oklahoma aquifer described by the U.S. Geological Survey National Water Quality Assessment Program (1987 to 1992) were elevated concentrations of nitrate nitrogen in shallow water and the occurrence of arsenic, chromium, and selenium in parts of the aquifer. The quality of water from deep public-water supply wells in the Central Oklahoma aquifer is monitored by the State of Oklahoma. The chemical quality of water from shallow domestic wells is not monitored, and, therefore, there is a concern that well owners may be unknowingly ingesting water with nitrate nitrogen, arsenic, chromium, selenium, and other chemical constituents at concentrations that are considered harmful. As a result of this concern, the Oklahoma Department of Environmental Quality and the U.S. Geological Survey collaborated on a study to sample water during June 2003 through August 2005 from 23 shallow wells (less than 200 feet in depth) and 28 deep wells (200 feet or greater in depth) completed in the bedrock aquifer units of the Central Oklahoma aquifer. The objectives of the study were to describe the chemical quality of water from shallow and deep wells and to determine if the differences in constituent concentrations are statistically significant.

Water from shallow wells had significantly higher concentrations of calcium, magnesium, bicarbonate, sulfate, chloride, and nitrate nitrogen than water from deep wells. There were no significant differences between concentrations of dissolved solids, sodium, and fluoride in water from shallow and deep wells. Water from 9 shallow wells had nitrate nitrogen concentrations greater than 2 milligrams per liter, suggesting nitrogen sources at land surface have had an effect on water from these wells. Water from three shallow wells (13 percent) exceeded the nitrate nitrogen maximum contaminant level of 10 milligrams per liter in drinking water.

Water from shallow wells had significantly lower concentrations of arsenic, chromium, iron, and selenium than water from deep wells, whereas, concentrations of barium, copper, manganese, and zinc were similar. Water-quality data indicate that arsenic frequently occurs in shallow ground water from the Central Oklahoma aquifer, but at low concentrations (<10 micrograms per liter). The occurrence of chromium and selenium in water from shallow wells was infrequent and at low concentrations in this study.

It does not appear that the quality of water from a shallow well can be predicted based on the quality of water from a nearby deep well. The results show that in general terms, shallow ground water has significantly higher concentrations of most major ions and significantly lower concentrations of arsenic, chromium, and selenium than water from deep wells.

Contents

Abstract

Introduction

Purpose and scope

Description of the Central Oklahoma Aquifer

Location and Physiography

Land Use, Population, and Water Use

Aquifer Units

Previous Study — National Water Quality Assessment Program

Acknowledgments

Methods

Description of Wells

Site Selection

Sample Collection and Analytical Methods.

Quality Control

Data Analysis

Comparison of Ground-Water Quality from Shallow and Deep Wells

Water Properties

Major Ions and Nitrate Nitrogen

Trace Elements

Implications of the Ground-Water Quality Comparison.

Summary

References cited

Appendix

 

   Appendix 1. Median values, measured water properties, and concentrations of chemical constituents in water from shallow wells in the Central Oklahoma aquifer, 2003–2005.
   Appendix 2. Median values and measured water properties and concentrations of chemical constituents measured in water from deep wells in the Central Oklahoma aquifer, 2003-2005.
   Appendix 3. Concentrations for equipment blank samples for water-quality samples from wells sampled in the Central Oklahoma aquifer, 2003–2005.
   Appendix 4. Analytical relative percent difference for chemical constituents analyzed in water-quality samples from wells sampled in the Central Oklahoma aquifer, 2003–2005.

 

Suggested citation:
Becker, C.J., 2006, Comparison of Ground-Water Quality in Samples From Selected Shallow and Deep Wells in the Central Oklahoma Aquifer, 20032005: U.S. Geological Survey Scientific Investigations Report 20065084, 55 p.

This report is available as a pdf. (5.1 MB)

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For information about water-resource studies in the State of Oklahoma, please visit our Web site at http://ok.water.usgs.gov/.



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