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Scientific Investigations Report 2011–5115

National Water-Quality Assessment Program

Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

By Gregory C. Johnson, Tammy M. Zimmerman, Bruce D. Lindsey, and Eliza L. Gross

Thumbnail of and link to report PDF (8.9 MB)Abstract

Chemical and microbiological analyses of water from 230 wells and 35 springs in the Valley and Ridge Physiographic Province, sampled between 1993 and 2002, indicated that bedrock type (carbonate or siliciclastic rock) and land use were dominant factors influencing groundwater quality across a region extending from northwestern Georgia to New Jersey. The analyses included naturally occurring compounds (major mineral ions and radon) and anthropogenic contaminants [pesticides and volatile organic compounds (VOCs)], and contaminants, such as nitrate and bacteria, which commonly increase as a result of human activities. Natural factors, such as topographic position and the mineral composition of underlying geology, act to produce basic physical and geochemical conditions in groundwater that are reflected in physical properties, such as pH, temperature, specific conductance, and alkalinity, and in chemical concentrations of dissolved oxygen, radon, and major mineral ions. Anthropogenic contaminants were most commonly found in water from wells and springs in carbonate-rock aquifers. Nitrate concentrations exceeded U.S. Environmental Protection Agency maximum contaminant levels in 12 percent of samples, most of which were from carbonate-rock aquifers. Escherichia coli (E. coli), pesticide, and VOC detection frequencies were significantly higher in samples from sites in carbonate-rock aquifers. Naturally occurring elements, such as radon, iron, and manganese, were found in higher concentrations in siliciclastic-rock aquifers. Radon levels exceeded the proposed maximum contaminant level of 300 picocuries per liter in 74 percent of the samples, which were evenly distributed between carbonate- and siliciclastic-rock aquifers. The land use in areas surrounding wells and springs was another significant explanatory variable for the occurrence of anthropogenic compounds. Nitrate and pesticide concentrations were highest in samples collected from sites in agricultural areas and lowest in samples collected from sites in undeveloped areas. Volatile organic compounds were detected most frequently and in highest concentrations in samples from sites in urban areas, and least frequently in agricultural and undeveloped areas. No volatile organic compound concentrations and concentrations from only one pesticide, dieldrin, exceeded human-health benchmarks.

Revised October 3, 2011

First posted August 11, 2011

For additional information about NAWQA studies in the Piedmont and Valley and Ridge aquifers contact:
Bruce D. Lindsey
Pennsylvania Water Science Center
U.S. Geological Survey
215 Limekiln Road
New Cumberland, PA 17070
http://water.usgs.gov/nawqa/

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Suggested citation:

Johnson, G.C., Zimmerman, T.M., Lindsey, B.D., and Gross, E.L., 2011, Factors affecting groundwater quality in the Valley and Ridge aquifers, eastern United States, 1993-2002: U.S. Geological Survey Scientific Investigations Report 2011-5115, 70 p.



Contents

Foreword

Abstract

Introduction

Purpose and Scope

Previous Studies

Study Area

Physiography

Climate

Land Use and Population

Hydrogeology

Water Availability and Use

Data Sources and Methods

Well and Spring Networks

Water-Quality Sampling and Analysis

Quality-Assurance Methods

Human-Health Benchmarks

Statistical Methods

Geographic Information System Methods and Topographic Variables

Groundwater Quality in the Valley and Ridge Aquifers

Basic Groundwater Properties and Chemical Composition

Residence Time, Oxygen, and Chemical Equilibria

Water Quality in Relation to Land Use and Topography

Selected Contaminants in Groundwater from the Valley and Ridge Aquifers and the Factors that Affect Their Occurrence

Nitrate

Occurrence and Distribution of Nitrate

Factors Affecting Nitrate Concentrations

Pesticides

Occurrence and Distribution of Pesticides

Assessment of Potential Effects of Pesticides on Human Health

Factors Affecting Occurrence of Frequently Detected Pesticides

Other Pesticides Analyzed

Volatile Organic Compounds

Occurrence and Distribution of VOCs

Assessment of Potential Effects of VOCs on Human Health

Factors Affecting Occurrence of VOCs

Fecal-Indicator Bacteria

Occurrence and Distribution of Fecal-Indicator Bacteria

Factors Affecting Occurrence of Fecal-Indicator Bacteria

Radon

Occurrence and Distribution of Radon

Factors Affecting Concentrations of Radon

Distribution of Sites with Background Concentration and Sites with Evidence of Anthropogenic Contamination

Summary and Conclusions

Acknowledgments

References Cited


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