U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5115

Valley and Ridge

siliciclastic-rock aquifers

Valley and Ridge

carbonate-rock aquifers

S h a l e Limestone and dolomite

S h a l e

S a n d s t o n e

National Water-Quality Assessment Program

Factors Affecting Groundwater Quality in the Valley and 

Ridge Aquifers, Eastern United States, 1993–2002

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

National Water-Quality Assessment Program

Scientific Investigations Report 2011–5115

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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reproduce any copyrighted materials contained within this report.

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.

ISBN 978 1 4113 3216 4
iii

Foreword

The U.S. Geological Survey (USGS) is committed to providing the Nation with reliable scientific information that helps to 

enhance and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral 

resources (http://www.usgs.gov/). Information on the Nation’s water resources is critical to ensuring long-term availability of 

water that is safe for drinking and recreation and is suitable for industry, irrigation, and fish and wildlife. Population growth 

and increasing demands for water make the availability of that water, measured in terms of quantity and quality, even more 

essential to the long-term sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support national, regional, 

State, and local information needs and decisions related to water-quality management and policy (http://water.usgs.gov/

nawqa). The NAWQA Program is designed to answer: What is the quality of our Nation’s streams and groundwater? How are 

conditions changing over time? How do natural features and human activities affect the quality of streams and groundwater, 

and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, 

stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water 

issues and priorities. From 1991 to 2001, the NAWQA Program completed interdisciplinary assessments and established a 

baseline understanding of water-quality conditions in 51 of the Nation’s river basins and aquifers, referred to as Study Units 

(http://water.usgs.gov/nawqa/studies/study_units.html).

In the second decade of the Program (2001–2012), a major focus is on regional assessments of water-quality conditions and 

trends. These regional assessments are based on major river basins and principal aquifers, which encompass larger regions 

of the country than the Study Units. Regional assessments extend the findings in the Study Units by filling critical gaps in 

characterizing the quality of surface water and groundwater, and by determining water-quality status and trends at sites 

that have been consistently monitored for more than a decade. In addition, the regional assessments continue to build an 

understanding of how natural features and human activities affect water quality. Many of the regional assessments employ 

modeling and other scientific tools, developed on the basis of data collected at individual sites, to help extend knowledge of 

water quality to unmonitored, yet comparable areas within the regions. The models thereby enhance the value of our existing 

data and our understanding of the hydrologic system. In addition, the models are useful in evaluating various resourcemanagement scenarios and in predicting how our actions, such as reducing or managing nonpoint and point sources of 

contamination, land conversion, and altering flow and (or) pumping regimes, are likely to affect water conditions within a region.

Other activities planned during the second decade include continuing national syntheses of information on pesticides, volatile 

organic compounds (VOCs), nutrients, trace elements, and aquatic ecology; and continuing national topical studies on the fate of 

agricultural chemicals, effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, effects 

of nutrient enrichment on stream ecosystems, and transport of contaminants to public-supply wells.

The USGS aims to disseminate credible, timely, and relevant science information to address practical and effective waterresource management and strategies that protect and restore water quality. We hope this NAWQA publication will provide you 

with insights and information to meet your needs, and will foster increased citizen awareness and involvement in the protection 

and restoration of our Nation’s waters. 

The USGS recognizes that a national assessment by a single program cannot address all water-resource issues of interest. 

External coordination at all levels is critical for cost-effective management, regulation, and conservation of our Nation’s water 

resources. The NAWQA Program, therefore, depends on advice and information from other agencies—Federal, State, regional, 

interstate, Tribal, and local—as well as nongovernmental organizations, industry, academia, and other stakeholder groups. Your 

assistance and suggestions are greatly appreciated.

William H. Werkheiser

USGS Associate Director for Water
iv

Contents

Foreword ........................................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Previous Studies ...................................................................................................................................3

Study Area.......................................................................................................................................................4

Physiography.........................................................................................................................................4

Climate....................................................................................................................................................5

Land Use and Population.....................................................................................................................5

Hydrogeology.........................................................................................................................................6

Water Availability and Use..................................................................................................................7

Data Sources and Methods .........................................................................................................................8

Well and Spring Networks ..................................................................................................................9

Water-Quality Sampling and Analysis.............................................................................................12

Quality-Assurance Methods.............................................................................................................13

Human-Health Benchmarks..............................................................................................................13

Statistical Methods.............................................................................................................................13

Geographic Information System Methods and Topographic Variables ....................................13

Groundwater Quality in the Valley and Ridge Aquifers .........................................................................16

Basic Groundwater Properties and Chemical Composition........................................................16

Residence Time, Oxygen, and Chemical Equilibria .......................................................................20

Water Quality in Relation to Land Use and Topography...............................................................22

Selected Contaminants in Groundwater from the Valley and Ridge Aquifers and 

the Factors that Affect Their Occurrence.........................................................................26

Nitrate..........................................................................................................................................26

Occurrence and Distribution of Nitrate ........................................................................26

Factors Affecting Nitrate Concentrations ....................................................................29

Pesticides....................................................................................................................................32

Occurrence and Distribution of Pesticides ..................................................................35

Assessment of Potential Effects of Pesticides on Human Health ............................35

Factors Affecting Occurrence of Frequently Detected Pesticides ..........................40

Other Pesticides Analyzed ..............................................................................................44

Volatile Organic Compounds ...................................................................................................44

Occurrence and Distribution of VOCs ...........................................................................45

Assessment of Potential Effects of VOCs on Human Health ....................................48

Factors Affecting Occurrence of VOCs.........................................................................48

Fecal-Indicator Bacteria ..........................................................................................................51

Occurrence and Distribution of Fecal-Indicator Bacteria.........................................51

Factors Affecting Occurrence of Fecal-Indicator Bacteria ......................................52
v

Radon...........................................................................................................................................53

Occurrence and Distribution of Radon .........................................................................54

Factors Affecting Concentrations of Radon.................................................................54

Distribution of Sites with Background Concentration and Sites with Evidence of 

Anthropogenic Contamination ............................................................................................55

Summary and Conclusions.........................................................................................................................55

Acknowledgments.......................................................................................................................................58

References Cited..........................................................................................................................................58

Figures

1. Map showing Valley and Ridge aquifers and the major river basins from which 

water-quality samples were collected......................................................................................2

2. Map showing land-use categories overlying the Valley and Ridge aquifers in 1992........4

3. Box plots showing well depths, casing lengths, and water levels for well networks 

in the Valley and Ridge aquifers, 1993–2002...........................................................................10

4. Cross section indicating locations of topographic variables, normalized lateral 

position variables, and topographic sections........................................................................14

5. Map showing examples of calculating distance to nearest topographic divide 

and distance to nearest major stream in central Pennsylvania.........................................15

6. Box plots showing specific conductance, pH, dissolved oxygen, total dissolved 

solids, and alkalinity for water samples from networks in the Valley and Ridge 

aquifers, 1993–2002 ....................................................................................................................17

7. Box plots showing concentrations of constituents and calcite saturation index 

values for groundwater samples from networks in the Valley and Ridge 

aquifers, 1993–2002 ....................................................................................................................18

8. Box plots showing concentrations of constituents by lithologic group for 

groundwater samples from the Valley and Ridge aquifers, 1993–2002 .............................19

9. Graph showing groundwater residence time distribution in the Valley and Ridge 

carbonate- and siliciclastic-rock aquifers .............................................................................20

10. Pie charts showing dominant redox processes by aquifer type and 

groundwater age ........................................................................................................................21

11. Block diagram illustrating distribution of land use with respect to topography 

and aquifer type in the Valley and Ridge ................................................................................22

12. Box plots showing distribution of specific conductance, dissolved oxygen 

concentrations, and pH by topographic section and aquifer type, for the Valley 

and Ridge aquifers, 1993–2002 .................................................................................................23

13. Cross section of Shenandoah Valley illustrating distribution of groundwater 

residence time.............................................................................................................................23

14. Diagram showing distribution of wells, land use surrounding wells, and dominant 

redox states by topographic sections within Valley and Ridge carbonate-rock 

aquifers, 1993–2002 ....................................................................................................................24
vi

15. Diagram showing distribution of wells, land use surrounding wells, and dominant 

redox states by topographic sections within Valley and Ridge siliciclastic-rock 

aquifers, 1993–2002 ....................................................................................................................24

16. Map showing nitrate distribution in the Valley and Ridge aquifers, 1993–2002...............27

17. Box plots showing nitrate concentrations by network for samples from the Valley 

and Ridge aquifers, 1993–2002 .................................................................................................28

18. Box plots showing nitrate concentrations in groundwater samples from the Valley 

and Ridge aquifers grouped by land use and aquifer type, 1993–2002. ............................28

19. Box plots showing distribution of nitrate concentrations by topographic section 

and aquifer type in the Valley and Ridge aquifers, 1993–2002 ............................................29

20. Map showing sample locations and pesticide detection frequency at any 

concentration in groundwater samples from wells and springs in the Valley and 

Ridge aquifers, 1993–2002 .........................................................................................................36

21. Graphs showing groundwater samples with zero, one to two, three to four, and five 

or more pesticide compounds at any concentration in relation to, A, groundwater 

network, B, redox state, C, land-use classification, and, D, aquifer type .........................37

22. Box plots showing distribution of, A, atrazine and, B, metolachlor concentrations 

in groundwater samples from well and spring networks in the Valley and Ridge 

aquifers, 1993–2002 ....................................................................................................................37

23. Graphs showing concentrations and benchmark quotient values of the most 

common pesticides in areas underlain by carbonate- and siliciclastic-rock 

aquifers stratified by various land-use categories in the Valley and Ridge 

aquifers, 1993–2002 ....................................................................................................................39

24. Box plots showing distribution of atrazine, deethylatrazine, simazine, prometon, 

and metolachlor concentrations by combined land use/aquifer setting 

in the Valley and Ridge aquifers, 1993–2002...........................................................................43

25. Map showing volatile organic compounds detected at a concentration greater 

than 0.2 micrograms per liter in the Valley and Ridge aquifers, 1993–2002......................46

26. Graphs showing detection frequency for samples with volatile organic compounds 

detected at the 0.2-microgram per liter assessment level by, A, groundwater network 

and, B, land-use classification and by, C, redox state and, D, aquifer type for samples 

in the Valley and Ridge aquifers, 1993–2002...........................................................................48

27. Graphs showing concentrations and benchmark quotients of the most common 

volatile organic compounds in various land-use categories in the Valley and Ridge 

siliciclastic-rock and carbonate-rock aquifers, 1993–2002.................................................49

28. Graph showing percentage of detections by redox state for selected volatile 

organic compounds in the Valley and Ridge aquifers, 1993–2002......................................50

29. Graph showing ratio of detection frequencies in oxic and anoxic samples 

for selected volatile organic compounds in the Valley and Ridge aquifers, 

1993–2002. ...................................................................................................................................50

30. Box plots showing detection frequency and distribution of concentrations 

of Escherichia coli bacteria in groundwater samples from well and spring 

networks in the Valley and Ridge aquifers, 1993–2002.........................................................52

31. Box plots showing detection frequency and distribution of concentrations 

of Escherichia coli bacteria in groundwater samples by aquifer type in the 

Valley and Ridge aquifers, 1993–2002......................................................................................52

32. Box plots showing detection frequency of Escherichia coli bacteria 

in groundwater samples from wells by land-use group in the Valley and Ridge 

aquifers, 1993–2002 ....................................................................................................................53
vii

33. Graph showing detection frequency of Escherichia coli bacteria in groundwater 

samples from wells by land-use group and aquifer type in the Valley and Ridge 

aquifers, 1993–2002 ....................................................................................................................53

34. Box plots showing distribution of radon levels in groundwater samples among 

carbonate- and siliciclastic-rock aquifers in the Valley and Ridge aquifers, 

1993–2002 .....................................................................................................................................54

35. Box plots showing distribution of radon levels in groundwater samples by 

lithologic group and aquifer type in the Valley and Ridge aquifers, 1993–2002 ...............54

36. Graph showing normalized lateral position and dissolved oxygen concentration 

in groundwater samples from the Valley and Ridge aquifers, 1993–2002, for sites 

with background concentrations consisting of no detects for volatile organic 

compounds or pesticides and nitrate less than 2 milligrams per liter, and sites of 

concern which had pesticide or volatile organic compound concentrations greater 

or equal to 0.1 times health benchmark values or nitrate greater than or equal to 

10 milligrams per liter...................................................................................................................56

Tables

1. Land use categories for major geologic subdivisions of the Valley and Ridge 

aquifers, 1992.................................................................................................................................5

2. Lithologic groups and hydrogeologic terranes in the Valley and Ridge aquifers..............6

3. Description of groundwater networks sampled in the Valley and Ridge aquifers, 

1993–2002 .......................................................................................................................................8

4. Summary of sampled constituent groups in groundwater networks in the Valley 

and Ridge aquifers, 1993–2002 ...................................................................................................9

5. Summary of soil characteristics within a 1,640-foot radius of wells and springs 

in groundwater networks in the Valley and Ridge aquifers.................................................11

6. Summary of generalized land-use categories in the groundwater networks 

in the Valley and Ridge aquifers, 1993–2002...........................................................................12

7. General land-use designation guidelines for wells and springs in the Valley 

and Ridge aquifers......................................................................................................................12

8. Description of topographic variables derived using geographic information 

system methods ..........................................................................................................................14

9. Threshold concentrations for identifying oxidation-reduction designation.....................21

10. Spearman’s rho correlations between groundwater age and well construction 

or water chemistry .....................................................................................................................21

11. Spearman’s rho correlations between normalized lateral position and water 

chemistry for Valley and Ridge carbonate-rock aquifers (without springs) and for 

selected topographic sections, 1993–2002.............................................................................25

12. Spearman’s rho correlations between normalized lateral position and water 

chemistry for Valley and Ridge siliciclastic-rock aquifers and for selected 

topographic sections, 1993–2002 .............................................................................................25

13. Summary of Spearman’s rho correlations between nitrate concentrations and 

explanatory variables for normalized lateral position and general water-quality 

values in groundwater in the Valley and Ridge aquifers, 1993–2002 .................................30
viii

14. Summary of Spearman’s rho correlations between nitrate concentrations and 

explanatory variables for land use and nitrogen sources in groundwater 

in the Valley and Ridge aquifers, 1993–2002...........................................................................30

15. Sources of nitrogen in groundwater networks in the Valley and Ridge aquifers, 

1990–2002 .....................................................................................................................................31

16. Summary of Spearman’s rho correlations between nitrate concentrations 

in groundwater and explanatory variables for hydrogeology and soils for 

the Valley and Ridge aquifers, 1993–2002...............................................................................32

17. Detection frequency of 47 pesticides in wells and springs in the Valley 

and Ridge aquifers, 1993–2002. ................................................................................................33

18. Summary of pesticide detections at any concentration for selected pesticides 

in individual well networks and springs in the Valley and Ridge aquifers, 

1993–2002 .....................................................................................................................................38

19. Physical properties of selected pesticides detected in the Valley and Ridge 

aquifers, 1993–2002 ....................................................................................................................40

20. Summary of pesticide compounds most frequently applied in basins in 

the Valley and Ridge aquifers...................................................................................................41

21. Summary of Spearman’s rho correlations between frequently detected pesticide 

concentrations and selected site-specific and source variables in groundwater 

in the Valley and Ridge aquifers, 1993–2002...........................................................................42

22. Summary of Spearman’s rho correlations between frequently detected pesticide 

concentrations in groundwater and normalized lateral position by aquifer type 

in the Valley and Ridge aquifers, 1993–2002...........................................................................44

23. Detection frequency of 63 pesticides, pesticide degradates, and organic 

compounds using High Performance Liquid Chromatography and High 

Performance Liquid Chromatography/Mass Spectrometry for groundwater 

samples from wells and springs in the Valley and Ridge aquifers, 1993–2002.................66

24. Detection frequency of 87 volatile organic compounds in groundwater samples 

from the Valley and Ridge aquifers, 1993–2003......................................................................68

25. Number of volatile organic compounds detected, percentage of sites with 

detections by volatile organic compound group, and number of compounds 

detected in each volitile organic compound group for groundwater samples 

from networks in the Valley and Ridge aquifers, 1993–2002................................................47

26. Percentage of samples with detections by redox state, and the oxic/anoxic 

ratio of detection frequencies for selected volatile organic compounds 

in groundwater samples from the Valley and Ridge aquifers, 1993–2002.........................51
ix

Conversion Factors and Datums

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

inch per hour (in/h) 0 .0254 meter per hour (m/h)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Radioactivity

picocurie per liter (pCi/L) 0.037 becquerel per liter (Bq/L) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Soil organic carbon-water partition coefficient is given in milliliters per gram (mL/g).

Concentrations of bacteria in water are reported in colonies per 100 milliliters (col/100 mL).
x

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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

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.

Introduction

The Valley and Ridge Physiographic Province of the 

eastern United States stretches from Alabama to Pennsylvania, 

spans nine states, and covers approximately 46,000 square 

miles (mi2) (fig. 1). Groundwater in this province (hereafter 

simply termed the “Valley and Ridge”) is an important source 

of water for public and domestic supply. Although most public 

water supplies in the Valley and Ridge rely heavily on surfacewater sources (Hutson and others, 2004), about 4 million 

people, roughly half of the region’s population, live in rural 

areas (U.S. Bureau of the Census, 1999, 2001a, 2001b) where 

many people rely on unregulated domestic wells for water. 

Generally, data from domestic water-supply wells regarding 

groundwater quality and related human-health concerns are 

limited—especially for pesticides and volatile organic compounds (VOCs).

Groundwater quality can be affected by a number of 

physical characteristics of wells or springs and by the land 

surrounding them. These characteristics may include land use 

and soil conditions at the surface as well as the deeper bedrock 

geology (lithology, mineralogy, chemical composition, and 

structure) of the principal aquifers from which water is drawn. 

About half of the Valley and Ridge is underlain by carbonaterock aquifers, which are particularly susceptible to contamination from the land surface through relatively rapid recharge 

and groundwater flow through karst conduits (Quinlan and 

others, 1991; Field, 1993; Leibundgut, 1998; Stueber and 

Criss, 2005; Lindsey and others, 2009). How this contamination influences the quality of water in local wells and springs 

also may be related to soil thickness and topographic position 

of wells in relation to contaminant sources. 

The U.S. Geological Survey (USGS) National WaterQuality Assessment Program (NAWQA) conducted a series 

of investigations from 1993 to 2002 to evaluate the quality of the groundwater in major river basins throughout the 
2 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

85° 80° 75°

40°

35°

Base from U.S. Bureau of the Census digital data, 1990a, 1:500,000 to 1:5,000,000

Universal Transverse Mercator projection, Zone 18N

Horizontal datum: North American Datum of 1983 (NAD 83)

0 50 100 25 KILOMETERS

0 50 100 25 MILES

Principal aquifers from U.S. Geological Survey, 2003

NAWQA study units from Hitt and Nakagaki, 2006

Virginia

North Carolina

South Carolina

West Virginia

Maryland

New

Jersey

Pennsylvania

New York

Ohio

Tennessee

Alabama

Georgia

Kentucky

Illinois

Delaware

Indiana

SUSQUEHANNA DELAWARE

POTOMAC

TENNESSEE

EXPLANATION

Aquifer type in the Valley and Ridge aquifers

Siliciclastic-rock aquifers

Carbonate-rock aquifers

State boundary

Study unit/River basin boundaries

Figure 1. Valley and Ridge aquifers and the major river basins from which water-quality samples were collected.

eastern United States, including parts of aquifers in the Valley 

and Ridge. Individual NAWQA groundwater investigations 

included areas of four major river basins in the Valley and 

Ridge (Delaware, Susquehanna, Potomac, and Tennessee 

River basins) and identified several natural and man-made 

contaminants in groundwater at concentrations that can affect 

human health (Ator and others, 1998; Lindsey and others, 

1998; Hampson and others, 2000; Fischer and others, 2004). 

The compilation of results of multiple NAWQA investigations 

focused on the Valley and Ridge aquifers produced a comprehensive and quality-assured dataset. This dataset has been 

used in this study to address important questions concerning 

factors that can degrade or improve groundwater quality and 

concerning the possible consequences for human health for 

those using groundwater as a source of domestic supply from 

these aquifers.

Purpose and Scope

This report is a compilation and analysis of groundwater 

quality and factors affecting the occurrence and distribution 

of selected constituents in aquifers of the Valley and Ridge. 

The analysis will (1) provide a geographic and topographic 

framework to examine groundwater quality, (2) identify constituents of concern related to human health, and (3) describe 

controls, such as land use and aquifer type, on groundwater 

quality across the region. The data presented in this report 

were collected in parts of Georgia, Tennessee, Virginia, Maryland, Pennsylvania, and New Jersey. Data included analyses of 

samples from 230 wells and 35 springs collected from 1993 to 

2002. The analyses included pH, temperature, specific conductance, alkalinity, dissolved oxygen, dissolved organic carbon 

(DOC), and major ions. Analytes of potential human health 
Introduction 3

concern included nutrients, pesticides, pesticide degradation 

products, VOCs, and radon. Fecal-indicator bacteria also were 

enumerated for selected samples. 

Previous Studies

Regional groundwater quality of the Valley and Ridge 

was described by Briel (1997) as part of the USGS Regional 

Aquifer-System Analysis study, which resulted in the analysis 

of major ions and nutrients in 3,012 wells and 428 springs. 

Water quality also was evaluated in regional studies presented 

in a series of hydrologic atlases of the United States (Miller, 

1990; Lloyd and Lyke, 1995; Trapp and Horn, 1997) and was 

summarized by state in the USGS National Water Summaries (U.S. Geological Survey, 1985, 1988). Numerous other 

watershed, statewide, and small-scale investigations have also 

been done. 

A national study of water quality in carbonate-rock 

aquifers indicated that water from wells in carbonate-rock 

aquifers in the Valley and Ridge had some of the highest concentrations of nitrate and the highest frequencies of detection 

for pesticides when compared to 11 other carbonate aquifers 

(Lindsey and others, 2009). High concentrations of nitrate in 

groundwater were attributed to the intensity of agricultural 

activity in the Valley and Ridge, the lack of confining layers, 

and the presence of organic carbon. Open karst conduits at 

the land surface, abundant contamination sources, and short 

residence times make carbonate aquifers of the Valley and 

Ridge highly vulnerable to contaminant migration (Lindsey 

and others, 2009).

Studies of groundwater in the major river basins in the 

Valley and Ridge have been described in a series of reports. 

Lindsey and others (1997) reported that nitrate levels in 

groundwater for agricultural areas in the Susquehanna River 

basin were significantly higher where underlain by carbonate 

rock as compared to sandstone and shale for similar nitrogen 

inputs. Nitrate concentrations in water from siliciclastic-rock 

aquifers in the Susquehanna River basin appear to reflect a 

two-layer system described by Schnabel and others (1993), 

Gburek and Folmar (1999), and Lindsey and others (2003). 

In such a system, nitrate concentrations tend to be high in an 

upper shallow layer of highly fractured bedrock where transmissivities are high and water is relatively young, and tend to 

be lower in deeper, less fractured rock where transmissivities 

are lower, water is older, and conditions favor denitrification 

(Lindsey and others, 1997). 

Ator and Denis (1997) reported that in the Potomac River 

basin, concentrations of nitrate in groundwater were higher in 

agricultural and urban areas than in forested areas and were 

highest overall where agriculture was underlain by carbonate 

rock. The authors observed that elevated nitrate concentrations in water from the carbonate-rock aquifers may indicate 

enhanced transport through karst but also may reflect a higher 

density of agricultural land use in areas underlain by carbonate rocks in the Potomac River basin and associated higher 

rates of fertilizer use in such areas. Further, Ferrari and Ator 

(1995) found that nitrate concentrations in groundwater in the 

Potomac River basin were higher in areas dominated by crop 

production as compared to livestock grazing, and Donnelly 

and Ferrari (1997) reported that pesticide detections also were 

more frequent in water samples from sites in agricultural areas 

over carbonate-rock aquifers.

Johnson (2002) examined water quality in 35 springs 

flowing from carbonate-rock aquifers in the Valley and Ridge 

area of the Tennessee River basin. Fecal-indicator bacteria 

were in water samples from all 35 springs, VOCs were present in samples from 30 springs, and pesticides were detected 

in samples from 24 springs. In subsequent sampling of eight 

community water-supply sources in the area (four wells and 

four springs), culturable viruses were present in three of the 

six samples from “low-risk” sites (three wells and one spring) 

identified by prior analysis of fecal indicators and susceptibility factors such as the thickness of overburden, and in six of 

the eight samples from “high-risk” sites (Johnson and others, 

2010). In Pennsylvania, Lindsey and others (2002) reported 

culturable viruses in water from 2 of the 25 wells in carbonaterock aquifers, in 1 of 25 wells in crystalline-rock aquifers, 

and in 1 of the 5 wells completed in siliciclastic-rock aquifers 

in the Valley and Ridge, Piedmont, and Blue Ridge Physiographic Provinces.

Bickford and others (1996) reported that fecal-indicator 

bacteria were more prevalent in water from household supply 

wells completed in carbonate-rock aquifers in the Great Valley 

and Appalachian Mountain regions of the Susquehanna River 

basin than in water from wells completed in either siliciclastic-rock or crystalline-rock aquifers in those regions or 

from carbonate-rock aquifers in the Piedmont Physiographic 

Province. Total coliform, fecal coliform, and fecal streptococcus bacteria concentrations were higher in groundwater from 

agricultural areas as compared to non-agricultural areas and 

were most strongly related to land use and physiographic 

province. Escherichia coli (E. coli) concentrations also were 

significantly higher in water from wells in areas underlain by 

carbonate bedrock. A subsequent study reported detections 

of E. coli bacteria only in water from wells in carbonaterock aquifers, with highest detection frequency in wells that 

were not grouted along the entire casing (Zimmerman and 

others, 2001). 

A recent study of the effect of sinkholes on water quality 

(Lindsey and others, 2010) reported that groundwater in areas 

with a high density of sinkholes was more likely to contain 

detectable concentrations of some contaminants. Detection 

frequencies of the pesticides prometon and metolachlor in 

groundwater were highest in areas with the highest sinkhole 

density, although detection frequency of other pesticides and 

concentrations of nitrate in groundwater were not significantly different among areas of differing sinkhole density in 

the Valley and Ridge carbonate-rock aquifers (Lindsey and 

others, 2010). As an indication of overall karst development, 

high sinkhole density was related to greater spring discharge, 

a higher density of caves, and more developed conduit 

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

Study Area

The Valley and Ridge Physiographic Province 

(Fenneman, 1938) extends about 1,200 miles (mi) from 

near Scranton, Pennsylvania, to Birmingham, Alabama, and 

encompasses approximately 46,000 mi2 of the eastern United 

States (figs. 1 and 2; Swain and others, 1991). The width of 

this mountainous region averages about 50 mi but varies from 

80 mi in central Pennsylvania to 65 mi in Maryland, to 40 mi 

in Tennessee (Davies, 1968). The province takes its name 

from the characteristic topographic sequence of alternating 

ridges and stream valleys, which are roughly oriented parallel to the long northeast-to-southwest axis of the province 

(Fenneman, 1938). 

Physiography

 The Valley and Ridge is part of the mountainous area of 

the eastern United States called the Appalachian Highlands 

Physiographic Division (Fenneman and Johnson, 1946). The 

province is bordered on the east by the Blue Ridge Physiographic Province and on the northeast by the Piedmont 

Physiographic Provinces. It is bounded to the west by the 

Appalachian Plateaus Physiographic Province and directly 

north by the St. Lawrence Valley Physiographic Province 

(Fenneman and Johnson, 1946). The western boundary of the 

Valley and Ridge is easily distinguished topographically and is 

known as the Allegheny Front in Pennsylvania, Maryland, and 

West Virginia and as the Cumberland Escarpment in Virginia 

Birmingham

Chattanooga

Knoxville

Kingsport

Johnson City

Bristol

Roanoke

Washington, D.C.

Philadelphia

Allentown

Bethlehem

Easton

Lebanon

Harrisburg Carlisle

Bethlehem

Allentown

85° 80° 75°

40°

35°

Base from U.S. Bureau of the Census, 1990a, 1:500,000 to 1:5,000,000

Universal Transverse Mercator projection, Zone 18N

Horizontal datum: North American Datum of 1983 (NAD 83)

Tennessee

Alabama

Georgia

South Carolina

North Carolina

Virginia

West Virginia

Maryland

New

Jersey

Pennsylvania

New York

Kentucky

Ohio

0 25 50 100 KILOMETERS

0 25 50 100 MILES

Populated places from U.S. Bureau of the Census, 1990b

Land cover digital data from Nakagaki and others, 2007

NAWQA Study units from Hitt and Nakagaki, 2006

POTOMAC

SUSQUEHANNA

DELAWARE

TENNESSEE

Delaware

EXPLANATION

Land cover

Agriculture

Urban Other

Forest

State boundary

Study unit/River basin boundaries

Scranton

Figure 2. Land-use categories overlying the Valley and Ridge aquifers in 1992.
Study Area 5

and Tennessee (U.S. Army Corps of Engineers, 2001). The 

boundary is not visually distinct everywhere the Valley and 

Ridge meets the Blue Ridge Physiographic Province in the 

east. The mountains of the Blue Ridge Physiographic Province 

are underlain mainly by complex metamorphic and igneous 

rocks, which produce a thick apron of colluvium and alluvium 

at the boundary. This layer of colluvium and alluvium, which 

overlies and is unevenly eroded into the fine-grained residuum 

and dolomite of the Valley and Ridge, forms the Elkton aquifer (Hollyday and Hileman, 1996). 

The Valley and Ridge is underlain mainly by deformed 

sedimentary rocks of Cambrian to Pennsylvanian age that 

intersect the surface to form long, narrow northeast-trending 

ridges and valleys overlying metamorphic and igneous rock 

of Precambrian age (Meyer, 1965). These sedimentary rocks 

were originally deposited as horizontal layers, but over time 

were folded, faulted, fractured, and weathered into a highly 

deformed bedrock foundation overlain by unconsolidated 

regolith ranging in texture from clay to gravel and varying 

in thickness from 0 to 450 feet (ft) (Hollyday and Hileman, 

1996). Sedimentary formations in this area are composed 

predominantly of two rock types: carbonate rock including 

limestone and dolomite in places variously interbedded with 

each other or with shale, and siliciclastic rock, which is mostly 

sandstone and shale but also includes siltstone, conglomerate, and mixed sandstone and shale (Hollyday and Hileman, 

1996; Harlow and others, 2004). The order of abundance of 

these rocks is shale (37.4 percent), dolomite (21.0 percent), 

sandstone (16.3 percent), limestone (13.8 percent), siltstone 

(4.6 percent), mudstone (1.0 percent), and graywacke (1.0 percent). Other non-carbonate rocks can be found in lesser 

abundance, including quartzite, granitic gneiss, chert, basalt, 

granulite, slate, and minor occurrences of metamorphic and 

crystalline rock. These others, however, represent only about 

4.9 percent of bedrock geology in the province (Dicken and 

others, 2005a, 2005b; Nicholson and others, 2005, 2007) and 

are not discussed in this report. 

Climate

Reflecting the region’s geographic extent, average annual 

temperatures in the Valley and Ridge vary widely from north 

to south. From 1971 to 2000, the lowest average annual 

temperature in northeastern extreme (Pennsylvania) was about 

5.7 degrees Celsius (°C); the highest average annual temperature at the southern extreme (northeastern Alabama and 

northwestern Georgia) was about 17.3 °C (PRISM Group at 

Oregon State University, 2006a). The average minimum temperature in January was -7.6 °C in the north and 6.8 °C in the 

south. In July average temperatures reach about 17.0 °C in the 

north and 26.9 °C in the south (PRISM Group at Oregon State 

University, 2006b).

Average annual precipitation also varies across the 

province but not in a consistent way from north to south. Over 

the 30-year period 1971–2000, precipitation varied across 

the entire province from less than 40 inches per year (in/yr) 

to greater than 70 in/yr. Precipitation was greatest in the 

southern part of the province and lowest in the mid-latitudes. 

Locally, precipitation is influenced by orographic effects and 

prevailing weather patterns. Annual precipitation was greatest in the western part of the Valley and Ridge in Tennessee, 

averaging about 70 in/yr and least in eastern West Virginia, 

averaging only about 32 in/yr (PRISM Group at Oregon State 

University, 2006c).

Land Use and Population

The predominant land use in 1992 in the Valley and 

Ridge was forest, which covered about 65 percent of the area 

(fig. 2, table 1). Agriculture covered about 26 percent of the 

area, and urban development covered about 6 percent of the 

area (Vogelmann and others, 2001; Nakagaki and Wolock, 

2005; Price and others, 2007). The relative proportion of land 

uses in the province varied somewhat from north to south, 

Table 1. Land use categories for major geologic subdivisions of the Valley and Ridge aquifers, 1992.

[mi2, square miles]

Geology Area

Land-cover classifications1

Water Developed Bare rock/

quarries Forest Row crop/hay pasture Wetlands

Carbonate Area (mi2) 258 1,520 115 7,950 5,910 96

Percent 1.6 9.6 0.7 50.1 37.4 0.6

Siliciclastic Area (mi2) 368 1,140 253 21,300 5,750 139

Percent 1.3 4.0 0.9 73.6 19.9 0.5

Total Area (mi2) 626 2,660 368 29,200 11,700 235

Percent 1.4 5.9 0.8 65.3 26 0.5

1

 Land-cover classification from Nakagaki and others (2007).
6 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

tending toward greater agricultural use in the north. Twentynine percent of land north of the Tennessee-Virginia line, for 

example, was agricultural compared to 20 percent south of 

that line. Areas overlying carbonate-rock aquifers tended to 

have less forested land use and somewhat higher agricultural 

and urban land use (50 percent forest, 37 percent agriculture, 

and 10 percent urban) than areas overlying siliciclastic-rock 

aquifers (74 percent forest, 20 percent agriculture, and 4 percent urban). 

In 2000, the population of the Valley and Ridge was 

approximately 8 million people, and about half of this population lived in rural areas (U.S. Bureau of the Census, 2001a, 

2001b). The remainder were concentrated in several metropolitan statistical areas (MSAs), including Birmingham, Alabama 

(777,640 people); Chattanooga, Tennessee (445,205); Knoxville, Tennessee (687,531); Johnson City–Kingsport–Bristol, 

Tennessee–Virginia (479,398); Roanoke, Virginia (177,425); 

Harrisburg–Lebanon–Carlisle, Pennsylvania (588,984); and 

Allentown–Bethlehem–Easton, Pennsylvania (513,120) (U.S. 

Bureau of the Census, 1999, 2001a, 2001b). MSA populations were calculated by multiplying the census block group 

population densities by the fraction of area within the Valley 

and Ridge. Of these, Allentown–Bethlehem–Easton, Pennsylvania, was reported as having the densest population (586 persons per square mile). Overall, the population of the Valley 

and Ridge is about evenly split between those living in areas 

of predominately carbonate rock (50.2 percent) and areas of 

predominately siliciclastic rock (49.8 percent) (U.S. Bureau of 

the Census, 2001a, 2001b; Dicken and others, 2005a, 2005b; 

Nicholson and others, 2005, 2007). 

Hydrogeology

Hydrogeologic terranes are regionally contiguous 

areas characterized by similar rock type and water-yielding 

properties. Hollyday and Hileman (1996) developed a classification of hydrogeologic terranes to group aquifers of the 

Valley and Ridge on the basis of these properties. Based on 

12 rock types, they classified hydrologic terranes into 5 types: 

alluvium, dolomite, limestone, argillaceous carbonate rock, 

and siliciclastic rock (table 2). In the context of this report, 

these terranes can be grouped into two major aquifer types. 

Table 2. Lithologic groups and hydrogeologic terranes in the Valley and Ridge aquifers.

[N/A, no data in that category; principal aquifer from U.S. Geological Survey, 2003]

Hydrogeologic terranes

(Hollyday and Hileman, 1996)

Lithologic descriptor group

(Hollyday and Hileman, 1996)

Lithologic groups

(this report) Principal aquifer 

Alluvium

Sand N/A N/A

Sand and gravel N/A N/A

Dolomite

Dolomite Dolomite

Carbonate

Limestone and dolomite Limestone and dolomite

Limestone Limestone Limestone

Argillaceous carbonate rock

Limestone and shale

N/A

Dolomite and shale

Siliciclastic rock

Conglomerate N/A

Siliciclastic

Sandstone and shale

Sandstone Mixed siliciclastic

Siltstone

Shale Shale
Study Area 7

Carbonate-rock aquifers in the Valley and Ridge consist 

mainly of fractured limestone and dolomite with localized 

solution-enlarged conduits. Siliciclastic-rock aquifers consist 

primarily of fractured sandstone but may include fractured 

shale and have been described by Trapp and Horn (1997) 

as “undifferentiated sedimentary rock aquifers.” The term 

“siliciclastic-rock aquifers” is used in this report to emphasize 

the contrast with carbonate-rock aquifers in terms of mineralogy, hydraulic characteristics, and structural properties.

Carbonate-rock aquifers in the Valley and Ridge are 

characterized by karst features such as sinkholes and solution 

openings. The term “karst” describes a landscape underlain by 

rocks in which chemical dissolution has enlarged joints, fractures, bedding planes, or other openings through which water 

flows (Quinlan and others, 1991). Groundwater levels in karst 

conduit systems can fluctuate up to tens of feet during periods 

as short as a few hours or days (Milanovic, 1981; Quinlan 

and Ewers, 1985; Wolfe, 1996), and groundwater velocities 

in such systems can be relatively high even in areas with low 

hydraulic gradients (Nelms and others, 2003). These systems 

may have several layers of networked conduits and discharge 

points whose relative importance varies with groundwater 

level (White, 1988). 

In the Valley and Ridge, solution openings in carbonate-rock aquifers may extend to a depth of up to 500 ft in 

places, reflecting the steep vertical dip of interbedded rock 

strata (Wolfe and others, 1997). Most solution openings, 

however, are confined to a depth of 300 ft or less (Brahana 

and others, 1986). Groundwater storage also can be substantial in the regolith and along bedrock fractures, joints, and 

bedding planes. 

Springs in karst settings are generally of three types: (1) 

depression springs, where the water table intersects a low spot 

in the land surface; (2) contact springs, where an impervious layer directs water to an outcrop; and (3) tubular springs, 

where solution openings are under positive hydrostatic pressure at the surface (Sun and others, 1963). Tubular springs 

tend to be more common in the southern three-fourths of the 

Valley and Ridge where groundwater may discharge from 

single large openings at rates as high as 67.3 million gallons 

per day (Mgal/d) (Hollyday and Smith, 1990). Spring flow 

tends to concentrate into a few large openings, rather than 

many small openings. The geologic transition at the eastern 

boundary with the Blue Ridge also creates a unique hydrologic 

setting, which results in highly productive wells and springs 

in solution openings in the dolomite bedrock overlain by thick 

mantles of coarse alluvium and colluvium and fine-grained 

residuum (Hollyday and Hileman, 1996).

The movement of water in siliciclastic-rock aquifers 

in the Valley and Ridge is fundamentally different from that 

in carbonate-rock aquifers. In the absence of large solution 

openings, water in siliciclastic-rock aquifers moves primarily 

through permeable regolith and along fractures, joints, and 

bedding planes. Groundwater storage is concentrated in the 

same features (Nelms and others, 2003).

Water Availability and Use

The geologic complexity of the Valley and Ridge results 

in a large variation of water-yielding properties among and 

between the carbonate-rock and siliciclastic-rock aquifers, and 

the yield of a single aquifer unit may vary by four orders of 

magnitude over its geographic extent (Hollyday and Hileman, 

1996). McGuinness (1963) found that yields from carbonaterock aquifers in the Valley and Ridge are highly variable. 

Clastic shale and siltstone formations generally have the lowest 

yields, sandstone formations have intermediate yields, and carbonate rocks have the highest yields. Locally, however, even 

shales may produce water adequate for use when sufficiently 

fractured (Seaber and others, 1988). 

Taken in aggregate, the repeating sequences of interbedded rock types (carbonate and siliciclastic rocks) and other 

lithologic variation within types, in combination with the 

strike-oriented drainage networks that define the Valley and 

Ridge, have the effect of isolating groundwater into many local 

and relatively shallow flow systems. Hydraulic gradients naturally follow topographic relief and run from ridge to valley. In 

a folded terrain, this often means that flow paths along major 

hydraulic gradients are directed across strike where they may 

be intercepted and redirected at exposed joints. Because of this, 

flow paths are commonly indirect and follow alternative directions, first along and then perpendicular to prevailing gradients. 

Coarse-grained carbonate rock with well-developed secondary 

porosity and fracture zones tend to be more permeable and 

may act to collect or channel water (Seaber and others, 1988). 

Estimated groundwater recharge to the Valley and Ridge 

aquifers was calculated based on an analysis of base flow of 

streams and mean annual runoff during the period 1951–1980 

(Wolock, 2003). Comparisons of the rainfall and recharge illustrate the complex relation between the two factors. The lowest 

average annual recharge rate occurred in northwestern Maryland in the siliciclastic-rock aquifers and was about 4 in/yr 

(compared to precipitation of 37.5 in/yr). The highest average 

annual recharge rate occurred in southeastern Tennessee (also 

in the siliciclastic-rock aquifers) and was about 21 in/yr (rainfall is 55 in/yr). 

Although population in the province was evenly split 

between those living in areas underlain by the two rock types 

(carbonate and siliciclastic), groundwater use from carbonaterock aquifers tends to be much greater, which perhaps reflects 

greater availability. Total groundwater withdrawals from carbonate-rock aquifers in 2000 were about 267 million gallons 

per day (Mgal/d), which was composed of irrigation, publicsupply, and self-supplied industrial water withdrawals of 5.65, 

177, and 83.9 Mgal/d, respectively (Maupin and Barber, 2005). 

In contrast, withdrawals from siliciclastic-rock aquifers were 

considerably less at a total of about 95 Mgal/d, or 0.61, 48.9, 

and 45.5 Mgal/d for irrigation, public-supply, and self-supplied 

industrial uses, respectively (Maupin and Barber, 2005). Selfsupplied domestic withdrawals from the Valley and Ridge 

aquifers was 110 Mgal/d in 2005 (Maupin and Arnold, 2010).
8 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Data Sources and Methods

The analysis presented in this report is based on a compilation of results derived from 11 USGS NAWQA investigations completed in 4 major river basins over a period of 

9 years beginning in June 1993 (table 3). Overall, these data 

come from one of two general kinds of sampling networks. 

Seven networks were designed to document the characteristics of groundwater quality within a single land use (forest, 

agriculture, urban, or “reference”), and four “major aquifer 

networks” were designed to document groundwater quality 

within a single aquifer type (carbonate or siliciclastic) without 

regard to land use. In general, sampling protocols, analytical 

techniques, and quality-assurance standards were consistent 

among these studies though the purposes of these studies 

and the objectives of site selection have varied. The combined datasets were tested for significant differences across 

the Valley and Ridge and were compared to human-health 

benchmark standards to identify issues of concern. Finally, the 

influences of geologic and topographic factors on groundwater quality were evaluated using a combination of spatial and 

statistical analysis. 

Table 3. Description of groundwater networks sampled in the Valley and Ridge aquifers, 1993–2002.

Groundwater 

network

 abbreviation 

used in 

report

River basin

Aquifer 

bedrock 

type

Type of network

(aquifer or land 

use targeted)

Lithologic group

 (number of wells) Dates sampled

DSM Delaware Siliciclastic Major aquifer

Shale (28)

4/25/2000–7/19/2000

Mixed silicliclastic (2)

SCA2 Susquehanna Carbonate Agricultural

Limestone (10)

Dolomite (4) 7/25/1994–8/16/1994

Limestone and dolomite (16)

SCA3 Susquehanna Carbonate Agricultural

Limestone (1)

06/26/1995–8/9/1995

Dolomite (12) limestone and dolomite (17)

SCU Susquehanna Carbonate Urban

Limestone (6)

7/5/1995–8/7/1995

Limestone and dolomite (14)

SSM Susquehanna Siliciclastic Major aquifer

Mixed siliciclastic (26)

7/26/1993–8/11/1993

Shale (3)

PCR Potomac Carbonate Reference sites Dolomite (2) 6/4/2002–6/11/2002

PCA Potomac Carbonate Agricultural

Limestone (30) 6/1/1993–9/20/1993

Dolomite (2) 6/6/2002–6/11/2002

PSA Potomac Siliciclastic Agricultural

Dolomite (1)

6/13/1995–7/12/1995 Shale(17)

Mixed siliciclastic (5)

Limestone (1)

PSF Potomac Siliciclastic Forested

Shale (1)

6/16/1995–7/12/1995

Mixed siliciclastic (2)

TCS Tennessee Carbonate Major aquifer (Springs)

Limestone (22)

8/19/1997–11/20/1997

Dolomite (13)

TCM Tennessee Carbonate Major aquifer

Limestone (7)

9/24/1998–2/11/1999

Dolomite (23)
Data Sources and Methods 9

Well and Spring Networks

Data from each of the networks included in this analysis 

are identified for clarity using an abbreviated, three- or fourcharacter naming convention for the wells and networks from 

which they were derived (table 3). The first character of each 

well name (denoted as D, S, P, or T) indicates the major river 

basin (Delaware, Susquehanna, Potomac, or Tennessee River 

basin) in which the study was conducted. The second character in each name (C or S) indicates the aquifer bedrock type 

(carbonate or siliciclastic, respectively); the third character 

indicates the purpose of the network (major-aquifer wells, M; 

major-aquifer springs, S; agriculture, A; urban, U; forest, F; 

or reference, R). A fourth character, present in two instances, 

indicates a sequence of networks for similar investigations 

at different times. For example, SCA2 and SCA3 were both 

designed as an agricultural land-use study on carbonate-rock 

aquifers in the Susquehanna River basin. 

The number of wells included in these networks varied 

between a minimum of 2 for the Potomac River basin reference network (PCR) and a maximum of 35 for the Tennessee River basin spring network (TCS) but typically ranged 

between 20 and 30 wells (table 4). Groundwater samples 

from nearly all of the 265 wells or springs were analyzed for 

concentrations of nutrients, major ions, and a suite of pesticides. A different set of groundwater samples (190 samples) 

was analyzed for concentrations of selected VOCs, and yet 

another set of 190 samples was analyzed for bacteria. Where 

more than one sample set was available for a given well, the 

set encompassing the most complete analytical schedule was 

favored. 

Though the depths of sampled wells ranged from less 

than 50 ft to more than 600 ft, the median depths of all wells 

within the networks were less than 250 ft; median well casing 

depths were less than 100 ft, and median depths to water were 

less than about 65 ft (fig. 3). Wells were deepest in the Tennessee carbonate-rock aquifer (TCM) network, which included 

three public supply wells and three commercial wells. However, the deepest wells in this network were domestic supply 

wells that were drilled into rock of poor primary porosity 

where greater depths are sometimes required to produce adequate yield or borehole storage. Wells were shallowest in the 

Susquehanna carbonate-rock aquifer urban (SCU) network. 

Soil characteristics were summarized for a 1,640-ft radius 

surrounding each well for comparison to patterns in groundwater quality and anthropogenic contamination (table 5). Soil 

permeability, thickness, organic-matter content, and particlesize class were area-averaged from the State Soil Geographic 

Database (STATSGO; U.S. Department of Agriculture, Natural 

Resources Conservation Service, 1994; Wolock, 1997), and 

hydraulic runoff potential (in hydrologic groups) was derived 

from an enhanced version of STATSGO (Barbara C. Ruddy 

and William A. Battaglin, U.S. Geological Survey, written 

commun., 1998) using an interpolation technique described 

by Foth and Schafer (1980). Runoff potential was categorized 

into four hydraulic groups from lowest potential (A) to highest 

(D) (U.S. Department of Agriculture, 1986). Nitrogen inputs 

from specific anthropogenic sources were estimated for the 

 Table 4. Summary of sampled constituent groups in groundwater networks in the Valley and Ridge aquifers, 

1993–2002.

Groundwater 

network1

Number of 

wells or 

springs

Constituent group and number of samples

Nutrients Major ions Pesticides Volatile organic 

compounds Bacteria

DSM 30 30 30 29 30 30

SCA2 30 30 30 30 9 30

SCA3 30 30 30 30 20 28

SCU 20 20 20 20 20 8

SSM 29 29 29 29 29 29

PCR 2 2 2 2 0 0

PCA 32 31 32 32 17 0

PSA 24 23 22 24 0 0

PSF 3 3 3 3 0 0

TCS 35 35 35 35 35 35

TCM 30 30 30 30 30 30

Total 265 263 263 264 190 190

1

 Groundwater network abbreviations are defined in table 3.
10 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

N/A

AB ABC BC C BC BC BC A

30 30 30 20 29 2 32 24 3 30

AB AB A AB AB AB B AB

28 30 30 19 28 2 12 6 0 30

ABC AB AB C BC AB C A

30 30 30 18 29 2 32 14 1 30

DSM SCA2 SCA3 SCU SSM PCR PCA PSA PSF TCM

200

400

600

50

100

150

200

250

-10

40

90

140

190

240

0

0

A Statistical group from 

nonparametric Tukey’s test

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

Groundwater network

Individual data points

DSM Groundwater network code,

see table 3 for network

abbreviation codes

Water level, in feet below land surface Casing depth, in feet below land surface Well depth, in feet below land surface

30 Number of samples

Figure 3. Well depths, casing lengths, and water levels for well 

networks in the Valley and Ridge aquifers, 1993–2002.
Data Sources and Methods 11

Table 5. Summary of soil characteristics within a 1,640-foot radius of wells and springs in groundwater networks in the Valley and Ridge aquifers.[OM, organic matter; STATSGO, State Soil Geographic Database]

Groundwater 

network2

STATSGO Soil characteristics1

Median percentage of area by runoff potential 

(hydrologic groups) Median soil thickness

(inches)

Median 

permeability

(inches per hour)

Median soil content, percentage

Low

(A)

Medium low

(B)

Medium high

(C)

High

(D) OM Clay Silt Sand

DSM 0 13 52 4 45.6 3.03 0.92 19.5 52.7 27.8SCA2 0 83.7 14.3 0 69.6 1.38 0.59 36.1 54.4 9.5SCA3 0 83.7 14.3 0 69.6 1.38 0.59 36.1 54.4 9.5SCU 0 83.7 14.3 0 69.6 1.38 0.59 36.1 54.4 9.5SSM 0 19.5 52 3.2 36.4 3.04 0.86 19.5 52.7 27.8PCR 0 53.7 43.8 1.5 56.1 1.81 0.66 35.6 42.3 19.11PCA 0 82 18 0 55.3 1.38 0.56 39.4 42.3 13.8PSA 1.4 11 52.2 0 34.4 3.84 0.88 18.3 49 32.8PSF 3 0 76.1 0 29.2 7.27 0.88 14 47.8 38.3TCS 0 92.7 5.6 0 58 1.39 0.35 40.9 44 19.8TCM 0 76.9 18.5 0 57.7 1.51 0.38 40.9 44 19.8

1 U.S. Department of Agriculture (1994). 2 Groundwater network abbreviations are defined in table 3.
12 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

following categories: septic systems, atmospheric deposition, agricultural fertilizer use, non-agricultural fertilizer use, 

manure from confined animal operations, and manure from 

unconfined animals (Ruddy and others, 2006). 

Land-use characteristics were determined for a 1,640-

ft radius around each well (table 6), based on a 30-meter 

resolution digital land-use map from Price and others (2007). 

Agricultural land use included any combination of row crops, 

pasture, and hay. Urban land use included residential, commercial, and industrial areas. Forest included deciduous, 

coniferous, and mixed forests. For some analytical comparisons, individual wells were further assigned to predominant 

land-use categories under one of four general designations 

(agricultural, urban, undeveloped, and mixed; table 7) following Gilliom and others (2006). 

Water-Quality Sampling and Analysis

Groundwater and spring-flow samples were collected 

using consistent protocols and were analyzed at the USGS 

National Water Quality Laboratory in Denver, Colorado. 

Well selection and installation guidelines are described in 

Lapham and others (1997). Water-quality samples initially 

were collected using field protocols described in Koterba 

and others (1995) and described in the USGS National Field 

Manual (U.S. Geological Survey, variously dated). Springs 

were sampled using groundwater protocols with the sampling pump placed as close to the spring orifice as possible 

(Johnson, 2002). 

Nutrient analyses included nitrogen concentrations 

in several forms (nitrite plus nitrate, nitrite, ammonia, and 

ammonia plus organic nitrogen) and phosphorus concentrations in two forms (orthophosphate and total). As a rule, 

nitrate concentrations are determined by subtraction of nitrite 

from nitrate plus nitrite concentrations. Because nitrite concentrations were very low [less than (<) 0.1 milligram per 

liter (mg/L)] in 86 percent of samples, nitrate plus nitrite and 

nitrate concentrations were assumed to be equivalent for all 

samples. Hereafter, the laboratory reported value for nitrite 

plus nitrate as nitrogen concentration is simply referred to as 

nitrate concentration. 

Forty-seven pesticides and degradation products were 

analyzed using gas chromatography/mass spectrometry 

(GC/MS) with selected ion monitoring (Zaugg and others, 

1995). A second set of 38 pesticides and pesticide degradation products (Werner and others, 1996) was analyzed using 

high performance liquid chromatography (HPLC) at 242 of 

the 265 sites, and a third set of 25 pesticides and other organic 

compounds (Furlong and others, 2001) was analyzed using 

high performance liquid chromatography/mass spectrometry 

(HPLC/MS) at 46 sites.

Samples from 190 wells and springs were analyzed for 

various fecal-indicator bacteria (including total coliform, 

E. coli, fecal streptococcus, and fecal coliform). Media used 

for E. coli analyses included NA-MUG (U.S. Environmental 

Protection Agency, 1991) for the Lower Susquehanna, and 

modified mTEC (U.S. Environmental Protection Agency, 

2002) for the Delaware and the Tennessee River basins. E. coli

concentrations from all three river basins were analyzed 

Table 6. Summary of generalized land-use categories in the 

groundwater networks in the Valley and Ridge aquifers, 

1993–2002.

Groundwater 

network2

Land use within a 1,640-foot radius 

of wells and springs1

( median value in percent)

Agricultural Urban Forested

DSM

SCA2

SCA3

SCU

SSM

PCR

PCA

PSA

PSF

TCS

TCM

32.8

97.1

98.1

11.7

77.4

10.3

88.6

60.6

0.7

30.1

33.2

0

0

0

74

0

7.6

0

0

0

0.8

0.3

63.3

2.5

1.8

1.7

19.1

80.3

8.6

36.4

99.7

58.3

56.9

1

 Price and others, 2007. 

2

 Groundwater network abbreviations are defined in table 3.

Table 7. General land-use designation guidelines for wells and 

springs in the Valley and Ridge aquifers.

[>, greater than; <, less than]

General Land use in 1,640-foot radius 

land-use around well or spring

designation Agricultural land-use Urban land-use

Agricultural >50 percent <10 percent

Urban <25 percent >25 percent

Undeveloped <25 percent <5 percent

Mixed All not meeting above definitions
Data Sources and Methods 13

together. Analytical methods varied in the use of maximum 

reporting levels. The data from the Lower Susquehanna River 

basin were analyzed using a 100-milliliter (mL) sample and 

a plate count that resulted in “too numerous to count” designations for counts greater than 80 colonies per 100 mL. The 

Tennessee River basin samples were analyzed using a method 

of multiple dilutions so that bacteria counts greater than 80 

were possible. For consistent comparison purposes, statistical 

analysis was conducted using a consistent maximum concentration of 80 colonies per 100 mL. A minimum reporting limit 

of 1 colony per 100 mL was common to all of the analyses.

Samples collected prior to 1996 (95 samples) were 

analyzed for 60 VOCs using a laboratory reporting level of 

0.2 microgram per liter (μg/L). After 1996, the number of 

VOC analytes for the remaining 95 samples was increased to 

87, and low-level analytical methods were adopted, generally 

reducing detection levels depending upon the compound, with 

laboratory reporting levels ranging from 0.018 to 3.4 μg/L.

Quality-Assurance Methods

Three types of quality-assurance samples (blanks, spikes, 

and replicates) were collected as routine elements of NAWQA 

groundwater-quality studies in the Valley and Ridge aquifers. 

These included 26 nutrient field blanks, 28 pesticide field 

blanks, 30 major ion field blanks, 18 VOC field blanks, 9 

pesticide replicates, 21 nutrient replicates, 8 VOC replicates, 

15 VOC spikes, 9 VOC spiked replicates, 20 pesticide spikes, 

and 3 pesticide spiked replicates. Detection rates and spike 

recoveries were similar to those reported by Lindsey and 

others (2009) and Martin (1999, 2001), and confirmed that 

process contamination of environmental samples was minimal 

and acceptable for the purposes of this study (Martin and others, 1998). 

Human-Health Benchmarks

Human-health benchmarks were used to assess the 

potential safety of drinking water and are defined in this study 

as either the U.S. Environmental Protection Agency (USEPA) 

drinking-water maximum contaminant level (MCL) or the 

health-based screening level (HBSL) for compounds without 

MCLs. MCLs are enforceable standards that refer to the highest level of a contaminant that is allowed in public drinkingwater systems (U.S. Environmental Protection Agency, 2006). 

HBSLs are non-enforceable levels that were developed by the 

USGS in collaboration with the USEPA and other organizations (Toccalino and others, 2008). The HBSL for a noncarcinogenic compound is the maximum concentration in drinking 

water that is not expected to cause any adverse effects from 

chronic exposure over a lifetime (Toccalino and others, 2008). 

HBSLs for carcinogenic compounds are established as higherand lower-level HBSLs, which correspond to concentrations 

of a compound in drinking water that increase estimated 

lifetime cancer risk by one chance in 10,000 (the higher 

HBSL) and one chance in 1 million (lower HBSL).

Statistical Methods

Four nonparametric statistical tests were used to evaluate 

the significance of relations and differences among waterquality sample data and descriptive characteristics. Two of 

these, the Spearman’s rank correlation coefficient (rho) (Helsel 

and Hirsch, 2002) and a censored Kendall’s tau (Helsel, 2005) 

were used to test for significance in relations among variables. 

The other two statistical tests, the Kruskal-Wallis (Helsel and 

Hirsch, 2002) and Tukey’s multiple-comparison test (MCT), 

were used to test for the significance of differences among 

multiple groups. Spearman’s rho is a monotonic correlation test in which a positive value of rho indicates that the 

response variable (Y) increases as the explanatory variable (X) 

increases. Higher values of Spearman’s rho indicate a stronger 

monotonic correlation. Kendall’s tau is a test of concordance 

(changing in the same direction) among pairs of observations. 

The censored Kendall’s tau is a modified approach to better 

handle multiple detection limits. The Kruskal-Wallis test was 

used to identify the presence of significant differences in medians among three or more groups. When the Kruskal-Wallis test 

indicated the presence of statistically significant differences 

among groups (alpha = 0.05), a Tukey’s multiple-comparison 

test (MCT) was used to identify groupings within significance 

categories. All of these nonparametric tests were performed 

on rank-transformed datasets. In assigning ranks, non-detects 

were ranked lower than the lowest value detected or estimated, 

following the methodology of Gilliom and others (2006). All 

other measured concentrations and estimates were ranked 

according to their nominal values. 

Geographic Information System Methods and 

Topographic Variables

A series of geographic variables was computed for each 

well or spring to establish its position in relation to principal 

topographic features (table 8). These included (a) the distance 

to the nearest topographic divide (ridgeline), (b) the distance 

to the nearest major downgradient stream, and (c) the distance 

to the nearest mapped stream of any magnitude. In addition, 

“a” and “b” were summed to produce a measure of (d) the 

distance from the topographic divide to the nearest major 

downgradient stream, which was then divided into “a” to 

produce an estimate of (e) the relative distance of each well or 

spring along the slope of an inferred hydraulic gradient from 

ridge to valley (fig. 4). This computed geographic term (e) has 

been described elsewhere as the normalized lateral position 

(Landon and others, 2010), and that term is used in this report. 

The normalized lateral position (NLP) is interpreted such that 

a value near 0.0 places a point near a local high (ridge) and a 

value near 1.0 places a point near a local low (stream).
14 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Table 8. Description of topographic variables derived using geographic information system methods.

Variable name Description Source or method

Distance to nearest 

topographic divide

Distance from sampling point to nearest upgradient 

topographic divide (ridge), in meters

U.S. Department of Agriculture, Natural Resources 

Conservation Service, 1999

U.S. Geological Survey, 2002

Distance to nearest major 

stream

Distance from sampling point to nearest downgradient 

major stream, in meters Falcone, 2003

Distance to nearest mapped 

stream

Distance from sampling point to nearest mapped stream 

of any magnitude, in meters Falcone, 2003

Distance from topographic 

divide to major stream

Distance from topographic divide to nearest 

downgradient major stream measured through 

sampling point, in meters

Distance to nearest topographic divide divided by 

distance to nearest major stream

Normalized lateral position

Relative location of sampling point between 

topographic divide and nearest major stream, as a 

decimal fraction

Distance to topographic divide divided by the 

distance from topographic divide to major stream

Stream density Density of stream network in meters of stream per 

square meter of land surface Falcone, 2003

0 .40 .70 1.00 .70 .40 0

Topographic 

section

Major stream Sampling point

Distance to nearest 

major stream

Distance to nearest 

topographic divide

Distance from topographic divide to major stream

Topographic

divide Topographic

divide

Upper Middle Lower Middle Upper

Normalized 

lateral 

position

Older or

Mixed Younger Younger

Inferred 

groundwater 

residence time

Figure 4. Locations of topographic variables, normalized lateral position variables, and topographic sections.
Data Sources and Methods 15

Principal topographic features (ridges and streams) were 

determined from available digital geospatial datasets. Topographic divides were defined where possible using 12-digit 

hydrologic unit code (HUC12) drainage basin boundaries 

(U.S. Department of Agriculture, Natural Resources Conservation Service, 1999). Where HUC12 topographic divides did 

not represent basin boundaries of sub-watersheds, ridgelines 

were manually digitized from hill shades using digital elevation models (DEMs) from the Shuttle Radar Topography 

Mission Elevation Dataset (U.S. Geological Survey, 2002). 

Streams were mapped using the USGS National Hydrography 

Dataset (NHD) at the 1:100,000 scale (Falcone, 2003). 

Distances to topographic features were computed using 

automated geographic information system (GIS) tools. A 

proximity analysis identified the shortest separation between 

each well and spring and a corresponding topographic divide 

or stream (fig. 5). All distances were checked to verify that 

selected topographic features reflected realistic local flow 

paths (for example, ensuring that the “nearest stream” was not 

separated from a given well by a topographic divide), and corrections were made manually where necessary. Distances from 

springs to streams were assumed to be 0 ft.

77°0' 76°53' 76°48' 76°41' 76°36' 76°30'

40°41'

40°36'

40°30'

Base from U.S. Geological Survey raster digital data, 2002

Universal Transverse Mercator projection, Zone 18N

Horizontal datum: North American Datum of 1983 (NAD 83)

Basin boundary digital data from U.S. Department of Agriculture, 1999

Stream digital data from Falcone, 2003

0 2.5 5 MILES

0 52.5 KILOMETERS

}

}

{

{ }

Pennsylvania

EXPLANATION

ELEVATION

Ridge

Sampling point

Major stream

Stream

1,481 METERS

36 METERS

Total distance from topographic divide to major stream Distance to nearest topographic divide

Distance to nearest major stream

Nearest major stream does not represent major drainage in same

valley where sampling point is located, so distance must be corrected.

Corrected distance to nearest major stream.

Figure 5. Examples of calculating distance to nearest topographic divide and distance to nearest major stream in central Pennsylvania.
16 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Groundwater Quality in the Valley and 

Ridge Aquifers

Groundwater quality in the Valley and Ridge aquifers is 

influenced by natural and anthropogenic factors. Natural factors, such as topographic position and 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 factors, 

such as land use and surface contamination, can contribute 

nutrients, pesticides, pesticide degradation products, dissolved 

organic carbon (DOC), VOCs, and fecal-indicator bacteria 

to groundwater. Although natural and anthropogenic factors 

may affect water use and availability independently, they also 

interact. Chemical properties, for example, can influence the 

fate and transport of contaminants. Land use can influence 

recharge and soil properties, and recharge can influence residence time, dissolved oxygen, and pH. 

Basic Groundwater Properties and Chemical 

Composition

With a few exceptions, specific conductance, dissolved 

oxygen, alkalinity, and total dissolved solids were greater in 

water from sites in networks in carbonate-rock aquifers than 

in siliciclastic-rock aquifers (fig. 6). Samples from sites in 

the Tennessee basin networks (TCS and TCM) had distinctly 

lower specific conductance, alkalinity, and dissolved solids 

concentrations than samples from other networks in carbonaterock aquifers and appeared to more closely resemble the 

Potomac basin siliciclastic-rock agricultural network (PSA), 

which had somewhat higher concentrations for the same 

properties and constituents than other networks in siliciclasticrock aquifers. Median pH concentrations were about the same 

(between 7.0 and 7.3) for all networks without regard to geology, but the range of pH was greater in water from networks in 

the less-buffered siliciclastic-rock aquifers.

The major ion chemistry of groundwater in the Valley 

and Ridge aquifers reflected geologic controls similar to those 

influencing physical properties. Values for specific conductance, alkalinity, and total dissolved solids and concentrations of calcium and magnesium are higher in samples from 

carbonate-rock aquifers than in samples from siliciclastic-rock 

aquifers (fig. 7). The dissolution of limestone and dolomite 

in the carbonate-rock aquifers probably is the cause of these 

higher values and concentrations. Calcite saturation tended to 

be least where (1) pH variability was greatest, (2) iron, sulfate, 

and manganese concentrations were greatest, and (3) dissolved 

oxygen was least (PSA network). As a rule, iron, manganese, 

and sulfate are largely insoluble in the presence of oxygen, 

and are likely to be in solution only when dissolved oxygen 

concentrations are less than 1 mg/L. Water from carbonaterock aquifers generally is well oxygenated (McMahon and 

Chapelle, 2008).

Non-enforceable guidelines for secondary maximum 

contaminant levels (SMCLs) have been established for some 

constituents for aesthetic considerations (taste, color, cosmetic effects, corrosivity, or staining) for public water-supply 

systems (U.S. Environmental Protection Agency, 1992). Six 

percent of samples from carbonate-rock aquifers and 46 percent of samples from siliciclastic-rock aquifers exceeded 

the SMCL for manganese (50 μg/L). Iron concentrations 

exceeded the SMCL (300 mg/L) in 1.7 percent of samples 

from carbonate-rock aquifers and in 27 percent of samples 

from siliciclastic-rock aquifers (fig. 7). Two SMCLs represent 

a desirable range for pH; pH values were lower than desired in 

24 percent of samples from siliciclastic-rock aquifers (fig. 6). 

Total dissolved solids exceeded the SMCL of 500 mg/L in 

one sample from siliciclastic-rock aquifers and in 10 samples 

from carbonate-rock aquifers (fig. 6). No samples exceeded 

the SMCL of 250 mg/L for sulfate or chloride, nor did any 

samples exceed the SMCL of 2 mg/L for fluoride.

In general, major ion concentrations in samples from 

carbonate-rock aquifers showed significant differences when 

grouped by lithology (dolomite, limestone, or dolomite and 

limestone; fig. 8), notably including higher concentrations of 

sodium, calcium, sulfate, and chloride in the limestone-anddolomite rock type than in other carbonate lithologies. Sodium 

and chloride occur naturally through mineral weathering, and 

their concentrations can increase with groundwater age. Both, 

however, can also be related to anthropogenic sources (road 

salts and disinfectants). Chloride concentrations were well 

correlated to sodium (p = <0.0001, Spearman’s rho = 0.62), 

and both were highest in samples from the northern urban 

network (SCU) and least in the southern networks (TCM and 

TCS) where road salt is used less often. No significant patterns 

were apparent for magnesium when summarized by lithology. Given differential rates of dissolution of dolomite and 

calcite, higher concentrations of magnesium might have been 

expected where groundwater is older. If the ages of water are 

similar, then the sources of sodium and chloride are likely 

to be anthropogenic. The fact that rock type was generally 

unimportant in describing major ions in water samples from 

siliciclastic-rock aquifers may relate to the lower solubility of 

minerals in sandstones (mostly silicates) but may also reflect 

the age of the water and its relative topographic position.
Groundwater Quality in the Valley and Ridge Aquifers 17

0

200

400

600

800

Total dissolved solids, in milligrams per liter

SCA2

SCA3

SCU

PCA

TCS

TCM

SSM

PSA

DSM

30 322030 35 30 29 22 30

5

6

7

8

pH, standard units

0

400

800

1,200

Specific conductance,

in microsiemens per centimeter 

0

4

8

12

Dissolved oxygen, in

milligrams per liter

SCA2SCA3

SCU

PCA

TCS

TCM

SSM

PSA

DSM

0

100

200

300

400

Alkalinity, in milligrams per liter

30 322030 35 30 29 22 30

A Statistical group from 

nonparametric Tukey’s test

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

30 Number of samples

Secondary maximum contaminant level 

for pH, above 8.5 and below 6.5;

for total dissolved solids, above 500 milligrams per liter

A A A A B B C CB

AA A B AB ABB ABAB

AB A DEF ABC AB CDE EF F BCD

A ABAB A BCC CD D AA A A C BC D B D

Groundwater network Groundwater network

Groundwater network code,

see table 3 for network

abbreviation codes

DSM

Carbonate-rock

aquifers

Siliciclastic-rock

aquifers

Figure 6. Specific conductance, pH, dissolved oxygen, total dissolved solids, and alkalinity for water samples from 

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

A Statistical group from 

nonparametric Tukey’s test

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

Secondary maximum contaminant level 

for iron, equals 300 micrograms per liter;

for manganese, equals 50 micrograms per liter

0

40

80

120

160

Calcium, in milligrams per liter

0

50

150

100

200

Sulfate, in milligrams per liter Iron, in micrograms per liter

0

2,000

4,000

6,000

8,000

10,000

0

400

800

1,200

Manganese,

in micrograms per liter

SCA2 

SCA3

SCU

PCA

TCS

TCM

SSM

PSA

DSM

SCA2 

SCA3

SCU

PCA

TCS

TCM

SSM

PSA

DSM

0

50

100

150

Chloride, in milligrams per liter

0

20

40

60

Magnesium,

in milligrams per liter Sodium, in milligrams per liter

-6

-4

-2

0

Calcite saturation index

0

50

100

150

AA A A B B CC B

CCC CC AB B AB A

ABAB ABCA BCD

BC C ABCC AB A

AABB B CC C C

ABCC C D D BC C AB

A B B B AB AB B C

B AA A B BC BC C B C

D C

C

AB BCDBCD

Groundwater network Groundwater network

Groundwater network code,

see table 3 for network

abbreviation codes

Carbonate-rock DSM

aquifers

Siliciclastic-rock

aquifers

Figure 7. Concentrations of constituents and calcite saturation index values for groundwater samples from 

networks in the Valley and Ridge aquifers, 1993–2002.
Groundwater Quality in the Valley and Ridge Aquifers 19

A C C

1

10

100

BC B A C C

Chloride, in milligrams per liter

1

10

100

B BC

1

10

100

Calcium, in milligrams per liter

BC C D B 10,000

1,000

100

10

Iron, in micrograms per liter

1

10

100

Sodium, in milligrams per liter

1

10

100

Sulfate, in milligrams per liter

C BC A AB BC

A Statistical group from 

nonparametric Tukey’s test

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

55 Number of samples

55 79 47 49 35 55 79 47 49 35

B A A C C

AB

A A A B B

1

0.1

10

100

1,000

Manganese,

in micrograms per liter

DOLOMITE

LIMESTONE

LIMESTONE 

AND DOLOMITE

SHALE

MIXED SILICICLASTIC

A AB C BC BC

Magnesium,

in milligrams per liter

1

10

A A A B B

B B A C C

0

-2

-4

-6

Calcite, saturation index

DOLOMITE

LIMESTONE

LIMESTONE 

AND DOLOMITE

SHALE

MIXED SILICICLASTIC

Secondary maximum 

contaminant level 

for iron, equals 300 

micrograms per liter;

for manganese, equals 

50 micrograms per liter

Siliciclastic-rock

aquifers

Carbonate-rock

aquifers

Figure 8. Concentrations of constituents by lithologic group for groundwater samples from the Valley and Ridge aquifers, 1993–2002.
20 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Residence Time, Oxygen, and Chemical 

Equilibria

The age of water in the various aquifers of the Valley and 

Ridge is an important determinant of groundwater quality. 

In combination with factors such as reaction rates, groundwater residence time determines oxidation state, which in 

turn influences concentrations of dissolved metals, controls 

denitrification, and moderates processes of biodegradation and 

natural attenuation of organic contaminants. Concentrations of 

oxygen in groundwater are generally the result of two timedependent processes: the introduction of oxygen from aerated 

surface waters and the removal of free oxygen by oxidation of 

minerals and organic compounds. The introduction of oxygen 

is largely controlled by climatic and environmental factors 

that determine recharge rates. The removal of free dissolved 

oxygen may be controlled by geochemical reaction rates, but 

in most cases is moderated by bacterial alteration of minerals 

and organic compounds. Bacteria harvest energy in groundwater by transforming chemical compounds through successive 

states of oxidation, reducing one compound to oxidize another, 

each reaction yielding energy for metabolic use. Those chemical reactions that yield the most energy at any point in time 

are generally favored such that specific oxidation states follow 

somewhat predictable orders of transformation. In general, 

the order of metabolic efficiency among successive oxidizing 

agents is as follows: oxygen, nitrate, manganese, ferric iron, 

sulfate, and carbon dioxide. This order is referred to as the 

ecological succession of terminal electron-accepting processes 

(McMahon and Chapelle, 2008). As a result, the relative concentrations of constituents in varying states of oxidation may 

be an indication of the sources and age of groundwater. 

Although most of the sample analyses presented in this 

report did not include measurements of groundwater age, 

recent studies by the USGS and others have addressed groundwater age and the relation of age to oxygen in carbonate- and 

siliciclastic-rock aquifers of the Valley and Ridge (Lindsey 

and others, 2003; Nelms and others, 2003; McCoy and Kozar, 

2007; Hinkle and others, 2010). Although the overall ranges 

of measured residence times (0–48 years) and median residence times (about 15 years) were similar for the two aquifer 

types, the distributions were clearly different at the older ages, 

with samples from about 8 percent of wells in carbonate-rock 

aquifers exceeding a 25-year residence time, but with samples 

from about 28 percent of wells in siliciclastic-rock aquifers 

exceeding the same residence time (fig. 9). These studies also 

found that groundwater residence time was positively correlated with silica concentration, magnesium-to-calcium ratios 

(for the carbonate-rock aquifers), and sodium concentrations 

(for siliciclastic-rock aquifers), and was negatively correlated 

with dissolved oxygen.

Overall, total dissolved solids, specific conductance, 

and alkalinity tend to increase with time and may provide a 

relative measure of residence time. Recharge water initially is 

dilute. As water resides in the ground, concentrations of dissolved solutes tend to increase at rates that vary with mineral 

concentration and environmental conditions. In carbonate-rock 

aquifers, water can reach saturation with respect to calcite in 

a matter of days (White, 1988), so it is not surprising that the 

calcite saturation indices (SI) for the carbonate-rock aquifers 

in the Valley and Ridge were generally near zero. The rate of 

dissolution of dolomite is slower than that of calcite, so the 

dolomite SI or magnesium-calcium molar ratios can provide 

an indication of residence time in the carbonate-rock aquifers 

(Musgrove and Banner, 2004). Similarly, strontium/calcium 

ratios have been used as indicators of groundwater residence 

time, with greater strontium indicating older water (Musgrove 

and Banner, 2004). Within siliciclastic-rock aquifers, where 

calcite is less abundant, the SI for calcium also may provide 

some indication of residence time. Lindsey and others (2003) 

demonstrated a positive relation of sodium to age in siliciclastic-rock aquifers. 

Several possible indicators of residence time in the Valley 

and Ridge aquifers were tested for correlation to groundwater age using the dataset summarized in figure 9. Sites were 

classified into one of three reduction-oxidation (redox) states 

(oxic, anoxic, or mixed) based on concentrations of dissolved 

oxygen, manganese, and iron (McMahon and Chapelle, 2008) 

using criteria detailed in table 9. Manganese and iron were 

preferred among other constituents because their presence in 

water is sensitive to anoxic conditions in otherwise oxic systems. In general, these tests indicated a prevalence of mixed 

oxic-anoxic conditions, as supported by the finding of elevated 

dissolved iron and dissolved oxygen in the same samples. 

Mixed oxic-anoxic samples indicate complex flow systems in 

which multiple sources of water mix during sample extraction. 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Probability of exceeding value

0

10

20

30

40

50

60

Groundwater residence time, in years

Valley and Ridge 

carbonate-rock aquifers

Valley and Ridge 

siliciclastic-rock aquifers

EXPLANATION

Data from Lindsey and others (2003), 

Nelms and others (2003), McCoy and 

Kozar (2007). Data for 13 additional 

NAWQA groundwater samples from

Hinkle and others, (2010)

Figure 9. Groundwater residence time distribution in the Valley 

and Ridge carbonate- and siliciclastic-rock aquifers.
Groundwater Quality in the Valley and Ridge Aquifers 21

Table 9. Threshold concentrations for identifying oxidationreduction designation.

[≥, greater than or equal to; <, less than; N/A, no threshold identified]

Oxidationreduction 

designation

Water-quality criteria1

(milligrams per liter)

Dissolved 

oxygen Manganese Iron

Oxic ≥ 0.5 < 0.05 < 0.1

Mixed ≥ 0.5 ≥ 0.05 ≥ 0.1

Anoxic < 0.5 N/A N/A

1

McMahon and Chapelle (2008).

Overall, groundwater residence time was negatively 

correlated to dissolved oxygen concentrations in both aquifer 

types (table 10), and the progression with age from oxic to 

anoxic or to mixed conditions appears faster in the siliciclastic-rock aquifers than in the carbonate-rock aquifers based on 

differences in the proportions of anoxic and mixed conditions 

in relatively young water (residence time of less than 20 years) 

in the two aquifer types. Anoxic or mixed conditions were 

more prevalent in both aquifer types in groundwater that was 

generally older (fig. 10). However, relatively few samples 

from carbonate-rock aquifers had residence times greater than 

20 years. A substantially greater number of sites in siliciclastic-rock aquifers produced water with residence times greater 

than 20 years.

Oxic

Mixed source

Anoxic

n = 67

n = 43 n = 24 n = 39 n = 10

n = 49

Valley and Ridge 

siliciclasticrock aquifers

Valley and Ridge 

carbonaterock aquifers

Young = Groundwater residence time less than 20 years

Redox state

Old = Groundwater residence time 20 years or more

n = Number of samples

EXPLANATION

Young Old Young Old

Data from Lindsey and others (2003), Nelms and others (2003), 

McCoy and Kozar (2007). Data for 13 additional NAWQA 

groundwater samples from Hinkle and others (2010)

Figure 10. Dominant redox processes by aquifer type and 

groundwater age.

Table 10. Spearman’s rho correlations between groundwater age and well 

construction or water chemistry.

[rho shown for variables statistically correlated at the 95-percent confidence level; NS, not statistically 

significant; n, number of observations].

Variable Groundwater age1

All Carbonate Siliciclastic

Well depth NS 0.44

(n=31) NS

Dissolved oxygen concentration -0.52

(n=117)

-0.44

(n=31)

-0.54

(n=67)

Sodium 0.27

(n=64)

0.45

(n=34) NS

Magnesium/ calcium ratio 0.34

(n=34)

0.48

(n=34) NS

Silica 0.47

(n=40) NS 0.47(n=21)

1

Data from Lindsey and others, 2003, Nelms and others, 2003, McCoy and Kozar, 2007. Data for 

13 additional NAWQA groundwater samples from Hinkle and others, 2010.
22 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Water Quality in Relation to Land Use and 

Topography

In the Valley and Ridge aquifers, topography and land 

use commonly are related. Steep slopes near the tops of ridges 

are typically forested, whereas valleys are generally more 

agricultural or urban, and discharge areas and streams attract 

development (fig. 11). Thus, location may determine both the 

quality of source water and residence times for groundwater.

Water-quality characteristics associated with groundwater 

residence time (dissolved oxygen, specific conductance, pH, 

and redox state) were compared to measures of relative topographic position (NLP) and aquifer type for the 230 network 

wells (springs excluded). When NLP is grouped into three 

topographic sections (upper = 0.0–0.39, middle = 0.4–0.7, and 

lower = 0.71–1.0), specific conductance values are slightly 

lower in samples from sites in the upper topographic sections 

when compared with samples from the lower topographic 

sections in both carbonate- and siliciclastic-rock aquifers; pH 

also appears to be slightly lower in samples from the upper 

topographic sections when compared with the samples from 

lower topographic sections in the siliciclastic-rock aquifers 

(fig. 12). These observations are consistent with the notion of 

water aging as it moves downgradient and with the results of 

Yager and others (2009), which related differences in the age 

of water to topographic section (fig. 13). None of these patterns, however, were statistically significant, perhaps reflecting 

localized variations in land use and lithology or limitations of 

the NLP as an explanatory tool when applied to the hydrology 

of the Valley and Ridge aquifers. 

Redox states, when viewed by topographic section, fail 

to show obvious patterns in carbonate-rock aquifers (fig. 14) 

though there may be some trend in the presence of anoxic 

conditions with increasing NLP in siliciclastic-rock aquifers 

(fig. 15). These results may be confounded by the distribution 

of land use among topographic sections and the distribution of 

wells within sections. In general, the distribution of sampled 

wells among the three topographic sections was remarkably 

similar in the two aquifer types. In the carbonate- and siliciclastic-rock aquifers, about 50 percent of wells were located 

in the lower 30 percent of slopes, and only 18 percent of wells 

were located in the upper 40 percent of slopes.

Valley and Ridge

siliciclastic-rock aquifers

Valley and Ridge

carbonate-rock aquifers

S h a l e Limestone and dolomite

Well in urban 

area

Well in agricultural 

area

Spring

Wells completed in

major aquifer

Hypothetical groundwater flow path in cross-section view

Hypothetical groundwater flow path in map view

EXPLANATION

S h a l e

S a n d s t o n e

Figure 11. Distribution of land use with respect to topography and aquifer type in the Valley and Ridge.
Groundwater Quality in the Valley and Ridge Aquifers 23

Specific conductance,

in microsiemens

per centimeter

500

1,000

1,500

Upper

Middle

Lower

Dissolved oxygen, 

in milligrams per liter

5

10

0

0

Topographic section

Upper

Middle

Lower

34 64 83 25 4215

34 64 82 24 4315

34 64 83 25 4215

7

8

6

5

9

pH, standard units

Maximum value

75th percentile

Median

25th percentile

Minimum value

Siliciclastic-rock

aquifers

Carbonate-rock

aquifers

EXPLANATION

34 Number of samples

Figure 12. Distribution of specific conductance, dissolved oxygen 

concentrations, and pH by topographic section and aquifer type, for 

the Valley and Ridge aquifers, 1993–2002. 

Overall, few statistically significant correlations were 

apparent between NLP and geochemical indicators of residence time in samples from sites in carbonate-rock aquifers. 

No significant correlations were apparent in comparisons of 

the dataset as a whole. Analyses of the correlation of NLP 

to various geochemical measures within subsets of the data 

showed several significant positive correlations in samples 

within specific topographic sections of carbonate-rock aquifers—particularly involving calcium and strontium in the 

upper topographic section (table 11). A negative correlation 

between NLP and dissolved oxygen in the middle and lower 

topographic sections was consistent with the expectation of 

decreasing oxygen with residence time, but the absence of 

anoxic conditions in the middle section may suggest a deeper, 

indirect flow path (fig. 14). The absence of calcium correlations within lower topographic sections may reflect groundwater already being near saturation with respect to calcite as it 

moves downgradient. Although these results are hardly definitive, they support a basic conceptual model in which topography provides one of several controls on the age and chemistry 

of groundwater. 

Geochemical changes along the NLP also were evident in 

the samples from sites in siliciclastic-rock aquifers where correlation analysis showed significant, though relatively weak, 

positive correlations between NLP and calcite SI, dolomite 

SI, sodium concentration, magnesium concentration, and 

specific conductance in samples for the set of wells spanning all topographic sections (table 12). Comparisons within 

specific topographic sections produced results that were no 

better than those for carbonate-rock aquifers but which were 

notably different in that the majority of significant correlations 

in samples were confined to the lower topographic section. 

Only sodium had a significant increase in concentration with 

NLP in samples in the upper topographic section. One point of 

0

10

20

30

40

> 50

Altitude, in kilometers

1

0

Upper Upper

Topographic section 

Middle Lower Middle 

North Fork

Shenandoah

River

Shenandoah Valley

Massanuten

Mountain

Groundwater age,

in years

Virginia

Cross section in Maryland

Shenahdoah 

Valley

Pennsylvania

New

Jersey

West

Virginia

0 50 100 25 KILOMETERS

0 50 100 25 MILES

Figure 13. Cross section of Shenandoah Valley illustrating distribution of groundwater residence time (from Yager and others, 2009). 
24 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Deep flow path*

Carbonate-rock aquifers

Stream

Deep flow path*

Carbonate-rock aquifers

Stream

Lower

Topographic

section

n=(83)

Upper 

Topographic

section

n= (34)

Middle

Topographic

section

n= (64)

Lower

Topographic

section

n=(82)

Upper 

Topographic

section

n= (34)

Middle

Topographic

section

n= (64)

*Largely unsampled, 95 percent of wells were less than 360 feet deep *Largely unsampled, 95 percent of wells were less than 360 feet deep

EXPLANATION

Oxic

Mixed

Anoxic

Dominant redox 

state by section

Section boundary

Conceptual flow path

Siliciclastic

Carbonate

Bedrock type

Undeveloped

Mixed

Agriculture

Urban

Land use overlying

aquifer

n Number of wells 

sampled in section

Figure 14. Distribution of wells, land use surrounding wells, and dominant redox states by topographic sections within Valley 

and Ridge carbonate-rock aquifers, 1993–2002.

Siliciclastic-rock aquifers

Deep flow path*

Stream

Siliciclastic-rock aquifers

Lower

Topographic

section

n=(43)

Lower

Topographic

section

n=(43)

Upper 

Topographic

section

n= (16)

Upper 

Topographic

section

n= (14)

Middle

Topographic

section

n= (25)

Middle

Topographic

section

n= (24)

Deep flow path *

Stream

*Largely unsampled, 95 percent of wells were less than 360 feet deep *Largely unsampled, 95 percent of wells were less than 360 feet deep

EXPLANATION

Oxic

Mixed

Anoxic

Dominant redox 

state by section

Section boundary

Conceptual flow path

Siliciclastic

Bedrock type

Undeveloped

Mixed

Agriculture

Urban

Land use overlying

aquifer

n Number of wells 

sampled in section

Figure 15. Distribution of wells, land use surrounding wells, and dominant redox states by topographic sections within Valley 

and Ridge siliciclastic-rock aquifers, 1993–2002.
Groundwater Quality in the Valley and Ridge Aquifers 25

Table 11. Spearman’s rho correlations between normalized lateral position and water chemistry for Valley and Ridge 

carbonate-rock aquifers (without springs) and for selected topographic sections, 1993–2002.

[rho shown for variables statistically correlated at the 95-percent confidence level; NS, not statistically significant; n, number of observations; 

NLP, normalized lateral position].

Variable All 

Upper

topographic

section

NLP less than 0.40

Middle

topographic

section

NLP 0.40 to 0.70

Lower

topographic

section

NLP greater than 0.70

Dissolved oxygen concentration NS NS -0.30

(n=50)

-0.25

(n=72)

Calcium concentration NS 0.45

(n=23) NS NS

Strontium/ calcium ratio NS 0.64

(n=12) NS NS

Strontium concentration NS 0.76

(n=12) NS NS

Table 12. Spearman’s rho correlations between normalized lateral position and water chemistry for Valley and Ridge 

siliciclastic-rock aquifers and for selected topographic sections, 1993–2002.

[SI, saturation index; n, number of observations; NLP, normalized lateral position; NS, not statistically significant]

Variable All 

Upper

topographic

section

NLP less than 0.40

Middle

topographic

section

NLP 0.40 to 0.70

Lower

topographic

section

NLP greater than 0.70

Dissolved oxygen concentration -0.32

(n=82) NS NS -0.45(n=43)

Magnesium concentration 0.34

(n=82) NS NS NS

Specific conductance 0.32

(n=82) NS 0.41(n=25)

0.35

(n=42)

Calcite SI 0.24

(n=82) NS NS 0.32(n=42)

Dolomite SI 0.27

(n=82) NS NS 0.32(n=42)

Sodium concentration 0.24

(n=82)

0.52

(n=15) NS NS

similarity between the aquifer types was a negative correlation 

between dissolved oxygen and NLP in samples in the lower 

topographic section. This pattern can be seen in increased 

anoxic conditions as water moves downgradient (fig. 15). 

The results of the analysis of natural water chemistry and 

NLP are consistent with the concepts of groundwater aging 

along a flow path and the mixing of younger and older water 

near the end of a flow path. Samples with somewhat stronger 

correlations between natural water chemistry and NLP within 

siliciclastic-rock aquifers may reflect distinct topographic, 

lithologic, and land-use differences between siliciclastic- and 

carbonate-rock aquifers. The middle and lower topographic 

sections of siliciclastic landscapes are generally not as flat 

as those of carbonate-rock aquifers, and local groundwater 

recharge may be lower for siliciclastic-rock aquifers (Yager 

and others, 2009). Steeper gradients and limited local recharge 

in siliciclastic-rock aquifers would tend to preserve the effects 

of broader regional gradients and flow patterns. Also, the 

upper topographic section over siliciclastic-rock aquifers was 

substantially less developed than that overlying carbonate-rock 

aquifers, and the lower section overlying carbonate-rock aquifers was distinctly more urban than that overlying siliciclasticrock aquifers (figs. 14, 15). Few samples were collected from 

wells completed in areas along the forested ridges, and no 

samples were collected from wells in predominantly urban 

areas overlying siliciclastic-rock aquifers. 
26 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Selected Contaminants in Groundwater from the 

Valley and Ridge Aquifers and the Factors that 

Affect Their Occurrence

The following sections discuss the occurrence and 

distribution of selected contaminants and analysis of the factors affecting contaminants in the Valley and Ridge aquifers. 

The analysis includes contaminants associated with human 

sources, such as nitrate, pesticides, VOCs, and fecal-indicator 

bacteria, as well as the naturally occurring contaminant, radon. 

Constituent concentrations were compared to explanatory variables, such as land use, source factors, geologic setting, and 

NLP. Comparisons also were made between networks because 

of different land-use practices and because of climatic differences for the TCM and TCS networks in the south and the 

other networks in the northern part of the Valley and Ridge, as 

well as other localized geological differences.

Nitrate

Nitrogen can take the form of organic nitrogen, ammonia (NH4

), nitrite (NO2), or nitrate (NO3). Of these, nitrate is 

of the greatest concern in groundwater. Nitrate is soluble in 

water, can easily leach through soil, and can persist in shallow groundwater for decades (Nolan, 1999). Human activities, 

including agricultural and urban uses of fertilizer, agricultural 

use of manure, and combustion of fossil fuel, have increased 

nitrate concentrations in shallow groundwater in many parts 

of the United States (U.S. Geological Survey, 1999). Elevated 

nitrate concentrations in drinking water can cause human 

health problems, notably methemoglobinemia, which is a 

potentially fatal condition in infants (Spalding and Exner, 

1993). The USEPA established the MCL for nitrate at 10 mg/L 

as nitrogen (U.S. Environmental Protection Agency, 2006). 

Recent studies indicate possible adverse effects at nitrate concentrations below the MCL (Ward and others, 2005). 

Occurrence and Distribution of Nitrate 

 Background concentrations of nitrate in shallow groundwater are typically about 2 mg/L; concentrations exceeding 

this level probably reflect human activities (U.S. Geological 

Survey, 1999). Of 263 analyses for nitrate in groundwater 

from the Valley and Ridge aquifers, 16 percent had concentrations of nitrate below the detection limit of 0.05 mg/L, 

46 percent had concentrations above background levels of 

2 mg/L, and 12 percent (33 samples) had concentrations that 

exceeded the nitrate MCL of 10 mg/L. All of the samples containing concentrations above the nitrate MCL were taken from 

domestic water-supply wells situated in agricultural areas in 

the northern part of the Valley and Ridge aquifers; all but three 

of these wells were completed in carbonate-rock aquifers. 

In general, median nitrate concentrations and the proportion 

of samples exceeding the MCL were greater for carbonate 

aquifers in the Valley and Ridge than for other carbonaterock aquifers studied by NAWQA, except for the Piedmont 

carbonate-rock aquifer where 63 percent of samples exceeded 

the nitrate MCL (Lindsey and others, 2009). 

Nitrate concentrations in water from sites in the Valley 

and Ridge aquifers (fig. 16) may be influenced by a number of factors, including nitrogen inputs, land use, and well 

characteristics, such as rock type, NLP, and redox state. A 

categorical comparison of nitrate concentrations in samples 

from the 11 groundwater networks in the Valley and Ridge 

aquifers using Tukey’s multiple-comparison test (MCT) 

showed lower median concentrations in samples from sites 

in siliciclastic-rock aquifers (median = 0.09 mg/L) compared to carbonate-rock aquifers (median = 3.4 mg/L) with 

the exception of the two southern networks (TCS and TCM) 

(fig. 17). Median nitrate concentrations exceeded 2 mg/L 

(background level) in water from wells in the four networks 

in northern carbonate-rock aquifers (excluding the reference 

network) but were below 2 mg/L for the Tennessee River 

basin carbonate-rock aquifer networks and for networks in 

siliciclastic-rock aquifers.

Land use can affect sources of nitrogen and interact with 

lithology to influence the distribution of nitrate on the landscape. Groundwater from sites in agricultural land-use areas 

and mixed land-use areas had higher median nitrate concentrations in carbonate-rock aquifers compared to samples from 

siliciclastic-rock aquifers (figure 18). Samples from the SCU 

network had a median nitrate concentration of 3.45 mg/L 

(fig. 17). Nearly all of the SCU wells were likely to have been 

influenced by agricultural activity upgradient as indicated by 

the coincident detection of low concentrations of agricultural 

pesticides. Concentrations of nitrate in water samples tended 

to decrease as the percentage of land use surrounding the site 

became less agricultural and more undeveloped, but differences were only statistically significant within the carbonaterock aquifer type (fig. 18).

The effects of topographic position are less clear and may 

be confounded by a relation to land use. Although not statistically significant, concentrations of nitrate appear to decrease 

in samples from sites in the upper to the lower topographic 

sections in the carbonate-rock aquifers (fig. 19). Although 

agricultural land use is high across all topographic sections 

over carbonate-rock aquifers, the decrease in nitrate concentrations observed may be explained by slight increases in anoxic 

conditions and mixing with older water near the end of the 

flow path (fig. 14). Similarly in the siliciclastic-rock aquifers, 

concentrations of nitrate are not significantly different among 

topographic sections, but tend to be highest in samples in the 

middle topographic section (fig. 19). Although the proportion 

of agricultural land is high in both the middle and lower topographic sections overlying siliciclastic-rock aquifers (fig. 15), 

the greater proportion of anoxic conditions in the lower topographic section may explain this pattern. 
Groundwater Quality in the Valley and Ridge Aquifers 27

85° 80° 75°

40°

35°

SUSQUEHANNA DELAWARE

POTOMAC

TENNESSEE

Base from U.S. Bureau of the Census, 1990a, 1:500,000 to 1:5,000,000

Universal Transverse Mercator projection, Zone 18N

Horizontal datum: North American Datum of 1983 (NAD 83)

Populated places from U.S. Bureau of the Census, 1990b

Agricultural and urban network boundaries from Siwiec and others, 1997

Principal aquifers from U.S. Geological Survey, 2003

NAWQA study units from Hitt and Nakagaki, 2006

EXPLANATION

Aquifer type in the Valley and Ridge aquifers

Siliciclastic-rock aquifers

Carbonate-rock aquifers

Study unit/River basin boundaries

Less than 0.5

Nitrate concentrations, in milligrams per liter

0.5 to 3.9

4.0 to 9.9

10.0 and Greater

Not Analyzed

0 105 MILES

0 105 KILOMETERS

Harrisburg

0 50 100 25 MILES

0 50 100 25 KILOMETERS

ONLY CARBONATE AQUIFERS ARE SHOWN

EXPLANATION

Lower Susquehanna 

Carbonate Network

boundaries

Agricultural Network

Urban Network

Nitrate concentrations, in milligrams per liter

Urban

Network

Agricultural

Network

Less than 0.5

0.5 to 3.9

4.0 to 9.9

10.0 and Greater

Figure 16. Nitrate distribution in the Valley and Ridge aquifers, 1993–2002.
28 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Maximum value

Number of samples

75th percentile

Median

25th percentile

Minimum value

Siliciclastic-rock 

aquifers

Carbonate-rock 

aquifers

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

Maximum contaminant 

level for nitrate is

10 milligrams per liter

SCA2

SCA3

SCU

PCR

PCA

TCS

TCM

SSM

PSA

PSF

DSM

0

5

10

15

20

25

Nitrate, in milligrams per liter

A A B AB CC C CD

30 30 20 2 31 35 30 29 3023 3

Groundwater network

Groundwater network 

code, see table 3 for 

network abbreviation 

codes

DSM

Individual data points

30

Figure 17. Nitrate concentrations by network for samples from the 

Valley and Ridge aquifers, 1993–2002. 

Land-use categories

Urban

Agricultural

Mixed

Undeveloped

0

5

10

15

20

25

CARBONATE

SILICICLASTIC

CARBONATE

SILICICLASTIC

CARBONATE

 SILICICLASTIC

CARBONATE

Nitrate, in milligrams per liter

Maximum contaminant level for nitrate

A CD BC D D D AB

107 46 36 17 22 21 16

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

46 Number of samples

Figure 18. Nitrate concentrations in groundwater samples from the Valley and Ridge aquifers grouped by land use and aquifer type, 

1993–2002. 
Groundwater Quality in the Valley and Ridge Aquifers 29

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

73 Number of samples

Nitrate concentration, 

in milligrams per liter as nitrogen

Upper Middle Lower

Topographic section

Siliciclastic-rock aquifer

16 24 43

Carbonate-rock

aquifer

23 49 73

Maximum contaminant 

level for nitrate is

10 milligrams per liter

0

5

10

15

20

25

0

4

8

12

14

Figure 19. Distribution of nitrate concentrations by topographic 

section and aquifer type in the Valley and Ridge aquifers, 1993–2002.

Factors Affecting Nitrate Concentrations

Nitrate concentrations were positively correlated to 

dissolved oxygen for all samples and for both aquifer types 

(table 13). The NLP was not correlated with nitrate concentrations for all topographic sections combined, except within 

carbonate-rock aquifers when the springs were removed from 

the dataset (table 13). When NLP is grouped by topographic 

sections (upper, middle, and lower topographic sections) 

a number of correlations become apparent. The combined 

carbonate- and siliciclastic-rock aquifers dataset may be a 

good representation of actual field conditions, with siliciclastic bedrock units forming ridges and carbonate bedrock units 

typically in the valleys. For the combined dataset, the upper 

topographic section had increasing nitrate concentrations as 

the NLP increased (rho = 0.37). In the lower topographic 

section, the nitrate and dissolved oxygen concentrations 

decreased with increasing NLP, indicating anoxic conditions 

and the possibility of denitrification. When the carbonaterock aquifer networks were evaluated separately, the nitrate 

concentrations in samples in the upper topographic section 

were positively correlated with the NLP (rho = 0.41) and were 

negatively correlated with the NLP in the lower topographic 

section (table 13). In the lower topographic section, dissolved 

oxygen concentrations were negatively correlated with NLP 

for the carbonate-rock aquifers (excluding springs) (table 11) 

and the siliciclastic-rock aquifers (table 12). The distance 

to the nearest stream was positively correlated with nitrate 

concentrations for both aquifer types and for carbonate-rock 

aquifers without springs. Specific conductance concentrations 

were positively correlated to nitrate concentrations for samples 

from carbonate-rock aquifers (table 13). 

The results of correlation analyses comparing nitrate 

concentrations to land-use characteristics and nitrogen sources 

are shown in table 14 and figure 18. World-wide, fertilizer is 

the largest anthropogenic source of nitrogen to watersheds, but 

other sources include animal and human waste and exhaust 

from automobiles and utilities (Fields, 2004). Agricultural 

fertilizer and manure from confined animal operations each 

contributed about 30 percent of total inputs of nitrogen to the 

lands immediately surrounding network wells in the Valley 

and Ridge. Manure from unconfined animals contributed 

19 percent of the total, atmospheric deposition contributed 

12 percent, non-agricultural fertilizer contributed 0 percent, 

and septic systems contributed about 1.3 percent (table 15). 

Atmospheric deposition was the predominant source of nitrogen in undeveloped areas (PSF and PCR networks). In areas of 

low-intensity agriculture (parts of TCM and TCS) unconfined 

animal manure contributed the most nitrogen, and in urban 

areas (SCU), non-agricultural fertilizer for lawn care was a 

dominant source of nitrogen (table 15). 

Nitrate concentrations were most strongly correlated to 

land use (rho = 0.67 for agricultural land use) and nitrogen 

inputs (rho = 0.54 for total nitrogen inputs) for samples from 

the relatively oxic carbonate-rock aquifers (table 14). Samples 

from siliciclastic-rock aquifers, where conditions are more 

likely to be anoxic, tend to show weaker correlations. Combining carbonate- and siliciclastic-rock aquifer data into a single 

analysis (all data) shows some residual correlation but less 

than for carbonate-rock aquifers alone. Urban land use was 
30 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Table 13. Summary of Spearman’s rho correlations between nitrate concentrations and explanatory variables for normalized lateral 

position and general water-quality values in groundwater in the Valley and Ridge aquifers, 1993–2002.

[rho shown for variables statistically correlated at the 95-percent confidence level; n, number of samples; NS, not statistically significant]

Explanatory variable

All data

(n=263, except 

where noted)

Carbonate aquifers

(n=180, except 

where noted)

Carbonate aquifers 

without springs

(n=145, except 

where noted)

Siliciclastic aquifers

(n=83, except 

where noted)

Normalized lateral position

Distance to nearest stream 0.34 0.43 0.23 0.32

Distance to major stream 0.36 0.23 0.27 0.22

Distance to nearest ridge 0.30 NS NS NS

Normalized lateral position (all) NS NS -0.20 NS

Upper 0.37 0.41 0.50 NS

Middle NS NS NS NS

Lower -0.31 -0.30 -0.28 -0.42

General water quality

Alkalinity 0.44

(n=261) 0.32 NS -0.28(n=81)

Dissolved Oxygen 0.59

(n=260)

0.40

(n=179)

0.50

(n=144)

0.60

(n=81)

Specific Conductance 0.55

(n=261) 0.56 0.44 NS

Table 14. Summary of Spearman’s rho correlations between nitrate concentrations and explanatory variables for land use 

and nitrogen sources in groundwater in the Valley and Ridge aquifers, 1993–2002.

[rho shown for variables statistically correlated at the 95-percent confidence level; n, number of samples; NS, not statistically significant]

Explanatory variable

All data

(n=263, except 

where noted)

Carbonate aquifers

(n=180, except 

where noted)

Carbonate aquifers 

without springs

(n=145, except 

where noted)

Siliciclastic aquifers

(n=83)

Land use1

Agricultural 0.59 0.67 0.67 0.34

Pasture 0.39 0.46 0.41 NS

Row crop 0.56 0.62 0.62 0.37

Urban NS -0.25 -0.28 NS

Forested -0.66 -0.65 -0.56 -0.35

Population density 2000 0.25 NS NS 0.32

Nitrogen sources

Nitrogen from septic systems2 0.19 NS NS 0.36

Agricultural fertilizer3 0.55

(n=260)

0.53

(n=177)

0.58

(n=142) 0.47

Confined—agricultural manure3 0.42

(n=260)

0.64

(n=177)

0.60

(n=142) NS

Unconfined—agricultural manure3 0.21

(n=260) NS NS NS

Atmospheric deposition3 -0.19

(n=260)

-0.30

(n=177)

-0.19

(n=142) -0.33

Total nitrogen input 0.49

(n=260)

0.54

(n=177)

0.55

(n=144) NS

1

 Vogelmann and others, 2001; Price and others, 2007.

2

 U.S. Bureau of the Census, 1990a, 1992a, 1992b.

3

 Ruddy and others, 2006.
Groundwater Quality in the Valley and Ridge Aquifers 31

Table 15. Sources of nitrogen in groundwater networks in the Valley and Ridge aquifers, 1990–2002.[mg/L, milligrams per liter; <, less than]

Groundwater 

network1

Median nitrate 

concentration 

in groundwater 

samples

(mg/L)

Median nitrogen input in 1,640-ft radius around wells and springs in each network 

(kilograms per square mile per year)

Agricultural 

land use within 

1,640-foot radius 

of sample site

(percent)

Atmospheric 

deposition2

Agricultural 

fertilizer2

Non-agricultural 

fertilizer2

Confined—

animal manure2

Unconfined—

animal manure2 Septic systems3 Total nitrogen from all sources4

DSM 0.62 369 939 0 326 73 68 2,189 32.8SCA2 9.05 412 2,149 0 1,835 1,084 34 5,081 97.1SCA3 8.55 373 2,207 0 2,089 798 100 5,662 98.1SCU 3.45 369 231 1,011 289 92 76 2,294 11.7SSM 0.13 387 1,286 0 2,124 441 59 4,481 77.4PCR 5.16 391 168 11 320 191 63 1,145 10.3PCA 5.1 369 2,171 0 3,005 1,259 63 6,890 88.6PSA <0.05 405 612 0 1,385 1,154 15 3,861 60.6PSF <0.05 407 10 0 6 11 12 449 0.7TCS 1.16 458 958 2 250 1,168 60 3,378 30.1TCM 0.59 459 1,160 2 240 1,303 71 3,580 33.2All Sites 1.71 490 1,298 0 1,140 791 58 4,240 67.51 Groundwater network abbreviations are defined in table 3.2 Calculated for the year 1997 from Ruddy and others, 2006.3 Calculated for the year 1990 from U.S. Bureau of Census 1990b, 1992a, 1992b.4 Totals are median values for each network and may not equal the sum of inputs across table. 
32 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

negatively correlated to nitrate concentrations (table 14), and 

row crops were more strongly and positively correlated to 

nitrate concentrations than pasture, reflecting higher fertilizer 

application for row crops. Forested area was negatively correlated to nitrate concentration. The inclusion of springs in this 

analysis had little to no effect on correlations between nitrate 

concentrations and environmental factors in carbonate-rock 

aquifers (table 14). 

Nitrate was variably correlated to several input sources 

of nitrogen. Agricultural fertilizer as a source of nitrogen 

was correlated to nitrate concentration in samples from both 

carbonate- and siliciclastic-rock aquifer types (rho = 0.53 and 

0.47, respectively); however, nitrogen inputs from unconfined 

agricultural manure were not well correlated with nitrate 

concentrations in samples from either aquifer type. Nitrogen 

from septic systems was significantly correlated with nitrate 

concentration only in the siliciclastic-rock aquifers (rho=0.36), 

and nitrogen from confined-animal manure showed reasonably 

strong correlation to nitrate only in carbonate-rock aquifers 

(rho = 0.64). Atmospheric deposition from 1997 was negatively correlated to nitrate in carbonate-rock aquifers (rho = 

-0.30) and in siliciclastic-rock aquifers (rho = -0.33). The reason for this is not entirely clear. To the extent that atmospheric 

(wet) deposition rates vary across the Valley and Ridge, they 

may reflect annual rainfall and orographic patterns that favor 

greater inputs on higher and undeveloped slopes where other 

inputs are less. 

Nitrate concentrations can be correlated to a number of 

soil characteristics and soil groups (table 16). The correlation 

between nitrate concentration and percentage of clay was 

negative for carbonate-rock aquifers and positive for siliciclastic-rock aquifers. Silt was positively correlated and sand 

negatively correlated to the nitrate concentrations for carbonate- and siliciclastic-rock aquifers. Correlations of nitrate to 

hydrologic soils groups tended to be stronger when aquifer 

types were combined. The strongest positive correlation was 

with the presence of group B (medium-low runoff potential); 

the strongest negative correlation was with the presence of 

group C (slow infiltration rates) and D (high runoff potential). 

Generally, the lower the runoff potential, the more infiltration 

and the greater potential for transport into aquifers. 

Pesticides

Groundwater samples from the Valley and Ridge aquifers were analyzed for 47 common pesticides and degradation products; more than half of the samples contained no 

pesticides or degradation products above detection levels 

(table 17). During the periods of these analyses, reporting 

levels varied for many of the 47 compounds; therefore, some 

constituent data are censored at multiple detection levels. 

Some values were qualified as “estimated” when uncertainties in analytical methods were large. Three evaluation criteria 

(laboratory reporting level, any concentration, and common 

assessment level) were applied to detection frequency data. A 

laboratory reporting level is the concentration below which a 

compound cannot be identified with certainty. Because a given 

Table 16. Summary of Spearman’s rho correlations between nitrate concentrations in groundwater and 

explanatory variables for hydrogeology and soils for the Valley and Ridge aquifers, 1993–2002.

[rho shown for variables statistically correlated at the 95-percent confidence level; n, number of samples; NS, not statistically 

significant]

Hydrogeology and soils1

All data

(n=263, except 

where noted)

Carbonate 

aquifers

(n=180)

Carbonate 

aquifers without 

springs

(n=145)

Siliciclastic 

aquifers

(n=83, except

where noted)

Water level 0.24

n=214

NS NS 0.30

n=73

Percent organic matter -0.12 0.39 0.32 -0.22

Percent clay 0.34 -0.25 NS 0.29

Percent silt 0.49 0.56 0.48 0.45

Percent sand -0.66 -0.59 -0.52 -0.37

Percentage soil in hydrologic group A -0.34 NS NS -0.36

Percentage soil in hydrologic group B 0.45 NS 0.19 0.24

Percentage soil in hydrologic group C -0.38 NS -0.20 NS

Percentage soil in hydrologic group D -0.37 -0.30 -0.26 NS

1

 Foth and Schafer, 1980; U.S. Department of Agriculture, Natural Resources Conservation Service, 1994; Wolock, 1997; 

Barbara C. Ruddy and William A. Battaglin, U.S. Geological Survey, written commun., 1998; U.S. Department of Agriculture, 

2003.
Groundwater Quality in the Valley and Ridge Aquifers 33

Table 17. Detection frequency of 47 pesticides in wells and springs in the Valley and Ridge aquifers, 1993–2002.—Continued[Pesticide types: D, degradate; H, herbicide; I, insecticide.; N/A, Not applicable; MCL, Maximum Contaminant Level (U.S. Environmental Protection Agency, 2006); >, greater than; HBSL, Health-Based Screening Level (Toccalino and others, 2008); μg/L, micrograms per liter; CAS, Chemical Abstracts Service]

Pesticide name

CAS 

registry 

number

Pesticide 

type

Number of 

analyses

Number of 

detections at 

any concentration1

Percent 

detections at 

any concentration1

Number of 

detections 

greater 

than 

0.01 μg/L

Percent 

detections 

greater 

than 

0.01 μg/L

Maximum 

concentration 

(μg/L)

Benchmark 

level (μg/L) 

[upper HBSL]2

Benchmark 

type

Percent 

detections 

greater 

than 

benchmark 

level

Percent 

detections 

>0.1 of the 

benchmark 

level

Atrazine 1912-24-9 H 264 147 55.7 111 42.0 2.21 3 MCL 0 9.8Deethyl-atrazine (CIAT) 3 6190-65-4 D 264 145 54.9 116 43.9 1.40 NONE N/A N/A N/ASimazine 122-34-9 H 264 95 36.0 62 23.5 1.30 4 MCL 0 0.4Metolachlor 51218-45-2 H 264 83 31.4 39 14.8 0.862 700 HBSL 0 0Prometon 1610-18-0 H 264 77 29.2 52 19.7 1.38 400 HBSL 0 0Tebuthiuron 34014-18-1 H 264 28 10.6 21 8.0 17.3 1000 HBSL 0 0p,p ́-DDE 72-55-9 D, I 264 11 4.2 0 0.0 0.002 .1 [10] HBSL 0 0Alachlor 15972-60-8 H 264 9 3.4 3 1.1 0.178 2 MCL 0 0Cyanazine 21725-46-2 H 264 8 3.0 6 2.3 0.160 1 HBSL 0 0.8Dieldrin 60-57-1 I 264 7 2.7 1 0 0.019 .002 [.2] HBSL 2.3[0] 2.6[0]Carbaryl 63-25-2 I 264 6 2.3 5 2 0.032 40 [4,000] HBSL 0 0Metribuzin 21087-64-9 H 264 5 1.9 1 0 0.012 90 HBSL 0 0Diazinon 333-41-5 I 264 3 1.1 0 0 0.003 1 HBSL 0 0Pronamide 23950-58-5 H 264 2 0.8 1 0 0.013 1 [100] HBSL 0 0Benfluralin 1861-40-1 H 264 1 0.4 0 0 0.006 4 HBSL 0 0EPTC 759-94-4 H 264 1 0.4 1 0 0.013 200 HBSL 0 0Napropamide 15299-99-7 H 264 1 0.4 1 0 0.034 800 HBSL 0 0Pebulate 1114-71-2 H 264 1 0.4 0 0 0.002 50 HBSL 0 0Propanil 709-98-8 H 264 1 0.4 0 0 0.001 6 HBSL 0 0Terbacil 5902-51-2 H 264 1 0.4 1 0.4 0.033 90 HBSL 0 0Triallate 2303-17-5 H 264 1 0.4 0 0 0.001 20 HBSL 0 0Trifluralin 1582-09-8 H 264 1 0.4 0 0.0 0.005 20 HBSL 0 02,6-Diethyl-aniline 579-66-8 D 264 0 0 0 0 N/A NONE N/A N/A N/AAcetochlor 34256-82-1 H 230 0 0 0 0 N/A 1 [100] HBSL 0 0alpha-HCH 319-84-6 I 264 0 0 0 0 N/A .006 [.6] HBSL 0 0Azinphos-methyl 86-50-0 I 264 0 0 0 0 N/A 10 HBSL 0 0
34 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002 Table 17. Detection frequency of 47 pesticides in wells and springs in the Valley and Ridge aquifers, 1993–2002.—Continued [Pesticide types: D, degradate; H, herbicide; I, insecticide.; N/A, Not applicable; MCL, Maximum Contaminant Level (U.S. Environmental Protection Agency, 2006); >, greater than; HBSL, Health-Based Screening Level (Toccalino and others, 2008); μg/L, micrograms per liter; CAS, Chemical Abstracts Service] Pesticide name CAS registry number Pesticide type Number of analyses Number of detections at any concen- tration1 Percent detections at any concen- tration1 Number of detections greater than 0.01 μg/L Percent detections greater than 0.01 μg/L Maximum concentration (μg/L) Benchmark level (μg/L) [upper HBSL]2 Benchmark type Percent detections greater than benchmark level Percent detections >0.1 of the benchmark level Butylate 2008-41-5

H 264 0 0 0 0 N/A 400 HBSL 0 0

Carbofuran 1563-66-2 I 264 0 0 0 0 N/A 40 MCL 0 0Chlorpyrifos 2921-88-2 I 264 0 0 0 0 N/A 2 HBSL 0 0cis-Permethrin 54774-45-7 I 264 0 0 0 0 N/A 4 [400]4 HBSL4 0 0Dacthal (DCPA) 1861-32-1

H 264 0 0 0 0 N/A 70 HBSL 0 0

Disulfoton 298-04-4 I 264 0 0 0 0 N/A 0.9 HBSL 0 0Ethalfluralin 55283-68-6

H 264 0 0 0 0 N/A 30 HBSL 0 0

Ethoprop 13194-48-4 I 264 0 0 0 0 N/A 1 [100] HBSL 0 0Fonofos 944-22-9 I 264 0 0 0 0 N/A 10 HBSL 0 0Lindane 58-89-9 I 264 0 0 0 0 N/A 0.2 MCL 0 0Linuron 330-55-2

H 264 0 0 0 0 N/A 5 HBSL 0 0

Malathion 121-75-5 I 264 0 0 0 0 N/A 50 HBSL 0 0Molinate 2212-67-1

H 264 0 0 0 0 N/A 0.7 HBSL 0 0

Parathion 56-38-2 I 264 0 0 0 0 N/A 0.02 HBSL 0 0Parathion-methyl 298-00-0 I 264 0 0 0 0 N/A 1 HBSL 0 0Pendi-methalin 40487-42-1

H 264 0 0 0 0 N/A 70 HBSL 0 0

Phorate 298-02-2 I 264 0 0 0 0 N/A 4 HBSL 0 0Propachlor 1918-16-7

H 264 0 0 0 0 N/A 1 [100] HBSL 0 0

Propargite 2312-35-8 I 264 0 0 0 0 N/A 1 [100] HBSL 0 0Terbufos 13071-79-9 I 264 0 0 0 0 N/A 0.4 HBSL 0 0Thiobencarb 28249-77-6

H 264 0 0 0 0 N/A 70 HBSL 0 0

1 Total detection frequency information at any concentration used for this analysis (no common assessment threshold used).2 Some compounds have a high and a low value for HBSLs. For those compounds that have both a high and a low value, the high value is given in brackets.3 The compound 2-Chloro-4-isopropylamino-6-amino-s-triazine (CIAT) can be derived from either degradation of atrazine (deethylatrazine, desethylatrazine, or DEA) or propazine (deisopropylpropazine). 

The term deethylatrazine is used for the compound CIAT in this report because atrazine is much more widely used and is more likely to be the parent compound.

4 HBSLs not developed for cis-Permethrin; concentrations of cis-Permethrin can be compared to the HBSL range of 4–400 mg/L for Permethrin (Toccalino and others, 2008).
Groundwater Quality in the Valley and Ridge Aquifers 35

compound may be present in a sample at very low concentrations, non-detects are reported as “less than” the minimum 

reporting levels for the analytical method. The qualifier “at 

any concentration” in table 17 refers to the number of estimated values and quantified detections (above any of the 

multiple reporting levels). This approach was used to calculate 

overall detection frequency for each pesticide as described by 

Gilliom and others (2006). Additional censoring of results to a 

common assessment level facilitates a comparison of detection 

frequencies and median concentrations among compounds 

with different reporting levels. A common assessment level 

of 0.01 μg/L was useful for this purpose. As such, any values (reported or estimated) below 0.01 μg/L were classified 

as non-detects.

Occurrence and Distribution of Pesticides

In general, pesticides and their degradation products 

were fairly common in groundwater samples from the Valley 

and Ridge aquifers. Almost half of the pesticide compounds 

analyzed (22 of 47) were detected in at least one sample 

(table 17), and detections of more than one pesticide compound in the same sample were common (fig. 20). At least 

one pesticide or degradate was detected in about 65 percent 

of the samples from wells and springs in the aquifers. Overall, detection frequency was greatest in samples from the 

Susquehanna carbonate-rock aquifers in agricultural and urban 

networks (SCA2, SCA3, and SCU) where 3 or more pesticides were detected in 88 percent of the samples (70 of 80) 

and 5 or more pesticides were detected in 56 percent of the 

samples (45 of 80) (fig. 21A). Multiple pesticide compounds 

were more frequently detected in samples with an oxic redox 

state (fig. 21B). Multiple pesticide compounds were more 

frequently detected in samples from wells completed in agricultural, urban, or mixed land-use settings (fig. 21C) and in 

samples from carbonate-rock aquifers (fig. 21D). 

The pesticides most frequently detected in samples of 

groundwater from the Valley and Ridge aquifers were herbicides, an herbicide degradation product, and an insecticide 

degradation product. The herbicide atrazine and its degradation product, deethylatrazine (also known as CIAT), were the 

pesticides most frequently detected. Atrazine and deethylatrazine were detected in 56 percent and 55 percent of samples, 

respectively (table 17). Four other herbicides—simazine, 

metolachlor, prometon, and tebuthiuron—and p,p’-DDE, a 

degradation product of the insecticide DDT, were detected in 

at least 10 samples (table 18). Not surprisingly, samples from 

wells in agricultural land-use networks (SCA2, SCA3, and 

PCA) had frequent detections of the agricultural herbicides 

atrazine and metolachlor (fig. 22) and the general-use herbicides simazine, prometon, and tebuthiuron (table 18). Less 

expected was the frequent presence of all of these pesticides in 

samples from the urban land-use network (SCU). 

Generally, samples from the major aquifer networks had 

the fewest detections of herbicides, reflecting the various land 

uses in these networks. Although, the highest concentration of 

any single pesticide in any network (tebuthiuron at 17.3 μg/L; 

table 17) was in a sample from a well in the TCM network, 

the frequency of pesticide detections in the TCM network 

otherwise was quite low (table 18). The number of detections of herbicides was somewhat higher in the TCS network 

compared to the other major aquifer networks and the PSA 

network but was lower than in samples from sites in agricultural and urban networks in carbonate-rock aquifers (table 18). 

Samples from networks in siliciclastic-rock aquifers had 

fewer detections of herbicides than samples from networks in 

carbonate-rock aquifers, without respect to land use. Median 

agricultural land use for wells in the Potomac carbonate- and 

siliciclastic-rock aquifer agricultural networks (PCA and 

PSA) were 89 and 61 percent, respectively (table 6). Although 

agricultural land use is somewhat less in the PSA network 

compared to the PCA network, the difference in the number of 

pesticide detections was appreciable (5 for the PSA compared 

to 111 for the PCA). 

Assessment of Potential Effects of Pesticides on Human 

Health

No samples of water from the Valley and Ridge aquifers 

had pesticide concentrations that exceeded any USEPA MCLs. 

The only pesticide analyzed in the Valley and Ridge aquifers 

to exceed an HBSL (non-enforceable) was the insecticide 

dieldrin. Six groundwater samples had dieldrin concentrations 

greater than the HBSL of 0.002 μg/L; the highest concentration measured was 0.019 μg/L. Three of these six samples 

were from wells used as sources of drinking water, two were 

used for private domestic supplies, and one was used for public supply. All three of these wells were in the SCU network 

(fig. 23). Dieldrin was discontinued for most agricultural uses 

in 1974 and for all uses in 1987 (U.S. Environmental Protection Agency, 2003), but remains in the environment as a 

persistent, bioaccumulative, and toxic pollutant.

Because most of the wells and springs sampled in the 

Valley and Ridge aquifers were used as sources of drinking 

water, a concentration greater than one-tenth of a humanhealth benchmark (either enforceable MCLs or non-enforceable HBSLs) was used in this study to provide an indication 

of contaminants that may approach concentrations of potential 

human-health concern and to identify those that may warrant 

additional monitoring and study (Toccalino and others, 2008; 

DeSimone and others, 2009). The ratio of a pesticide concentration to its human-health benchmark is referred to as a 

benchmark quotient. Benchmark quotients greater than 0.1 but 

less than or equal to 1.0 indicate concentrations approaching 

levels of a potential human-health concern; benchmark quotients greater than 1.0 indicate levels above the threshold of a 

potential human-health concern (Toccalino and others, 2008). 

Benchmark quotients were calculated for unregulated carcinogenic compounds using the lower of two HBSL exposure 

thresholds. 

Within the Valley and Ridge aquifers, four pesticides 

were at or were approaching levels of potential human-health 
36 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

85° 80° 75°

40°

35°

SUSQUEHANNA DELAWARE

POTOMAC

TENNESSEE

Base from U.S. Bureau of the Census, 1990a, 1:500,000 to 1:5,000,000

Universal Transverse Mercator projection, Zone 18N

Horizontal datum: North American Datum of 1983 (NAD 83)

Populated places from U.S. Bureau of the Census, 1990b

Agricultural and urban network boundaries from Siwiec and others, 1997

Principal aquifers from U.S. Geological Survey, 2003

NAWQA study units from Hitt and Nakagaki, 2006

EXPLANATION

Aquifer type in the Valley and Ridge aquifers

Siliciclastic-rock aquifers

Carbonate-rock aquifers

Study unit/River basin boundaries

0

Pesticide detection frequency, in number detected

1 to 2

3 to 4

5 and greater

0 5 10 MILES

0 5 10 KILOMETERS

Harrisburg

0 25 50 100 MILES

0 25 50 100 KILOMETERS

ONLY CARBONATE AQUIFERS ARE SHOWN

EXPLANATION

Lower Susquehanna 

Carbonate Network

boundaries

Agricultural Network

Pesticide detection frequency,

in number detected

Urban Network Urban

Network

Agricultural

Network

0

1 to 2

3 to 4

5 and Greater

Figure 20. Sample locations and pesticide detection frequency at any concentration in groundwater samples from wells and springs in the 

Valley and Ridge aquifers, 1993–2002.
Groundwater Quality in the Valley and Ridge Aquifers 37

3029 30 20 29 32 24 35 30

A

DSM

SCA2

SCA3

SCU

SSM

PCAPSA

TCS

TCM

Groundwater network

20

40

0

60

80

100

Frequency, in percent

20

40

0

60

80

100

20

40

0

60

80

100

Frequency, in percent

20

40

0

60

80

100

Frequency, in percent

20

40

0

60

80

100

Frequency, in percent

35 21 204

152 53 43 16

Agricultural

Mixed

Undeveloped

Urban

Carbonate-rock Siliciclastic-rock

Land use

C

Anoxic Mixed Oxic

Redox state

1 to 2 detected

3 to 4 detected

5 or more detected

None

EXPLANATION

Number of pesticides 

detected per sample

30 Number of samples

B

D

181 83

Aquifer type

Groundwater network 

code, see table 3 for 

network abbreviation 

codes

DSM

Figure 21. Groundwater samples with zero, one to two, three to four, and five or more pesticide compounds at any concentration in 

relation to, A, groundwater network, B, redox state, C, land-use classification, and, D, aquifer type. Results are based on analysis 

of 47 pesticide compounds in groundwater samples from the Valley and Ridge aquifers, 1993–2002.

Maximum value

75th percentile

Median

25th percentile

Minimum value

Siliciclastic-rock 

aquifers

Carbonate-rock 

aquifers

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

30 Number of samples

Groundwater network 

code, see table 3 for 

network abbreviation 

codes

DSM

A

B

AB A AB AB CD D D D D

30 30 20 32 35 30 29 24 29

Groundwater network

SCA2SCA3

SCUPCA

TCS

TCM

SSMPSA

DSM

Groundwater network

SCA2SCA3

SCUPCA

TCS

TCM

SSMPSA

DSM

Atrazine concentration, 

in micrograms per liter

0.001

0.010

0.100

1.000

ABC A A ABC BC BC C C BC

30 30 20 32 35 30 29 24 29

0.001

0.010

0.100

1.000

Metolachlor concentration,

in micrograms per liter

Figure 22. Distribution of, A, atrazine and, B, metolachlor 

concentrations in groundwater samples from well and spring 

networks in the Valley and Ridge aquifers, 1993–2002.
38 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002 Table 18. Summary of pesticide detections at any concentration for selected pesticides (compounds detected in 10 or more wells) in individual well networks and springs in the Valley and Ridge aquifers, 1993–2002. Type of network Urban land use Agricultural land use Major aquifer Bedrock aquifer Carbonate Carbonate Siliciclastic Total for agricultural land-use networks Siliciclastic Carbonate Carbonate (Springs) Total for major aquifer networks Groundwater network1 SCU SCA2 SCA3 PCA PSA SSM DSM TCM TCS (Number of samples) 20 30 30 32 24 116 29 30 30 35 124 Atrazine 18 30 30 28 1 89 1 9 8 20 38 Deethylatrazine 18 30 30 27 1 88 2 7 9 19 37 Simazine 16 20 29 22 1 72 0 2 1 3 6 Metolachlor 18 11 25 14 0 50 0 8 2 4 14 Prometon 18 6 25 14 1 46 0 0 5 6 11 Tebuthiuron 7 1 3 2 0 6 0 0 4 11 15 p,p-DDE 0 0 0 4 1 5 0 3 1 1 5 Total number of detections2 95 98 142 111 5 356 3 29 30 64 126 Total number of compounds2 6 6 6 7 5 7 2 5 7 7 7

1 Groundwater network abbreviations defined in table 32 For the seven compounds listed in this table. 
Groundwater Quality in the Valley and Ridge Aquifers 39

0.001 0.01 0.1

Siliciclastic

Pesticide concentration, in micrograms per liter

0.001 0.01 0.1 1.0 10.0

10-5 10-4 10-3 10-2 0.1 1.0 10 10 10 10 0.1 1.0 10 -5 -4 10-6 -3 -2

Agricultural

Mixed

Undeveloped

Urban

Land Use

Siliciclastic Carbonate

Benchmark quotient

Benchmark quotient value (BQ) = Atrazine concentration

Atrazine MCL = 3 μg/L 

MCL is Maximum Contaminant Level for regulated compounds 

(U.S. Environmental Protection Agency, 2006). 

HBSL is Health-Based Screening Level concentrations for 

unregulated compounds (Toccalino and others, 2008).

Benchmark Quotient value of 0.1 -- Values 

greater than this line are within one order 

of magnitude of an MCL or HBSL

Benchmark quotient value of 1.0 -- Values 

greater than this line would indicate concentrations 

of potential health concerns

EXPLANATION

Carbonate

Atrazine

Deethylatrazine

Simazine

Metolachlor

Prometon

Tebuthiuron

p,p’-DDE

Alachlor

Cyanazine

Dieldrin

Atrazine

Simazine

Metolachlor

Prometon

Tebuthiuron

p.p’-DDE

Alachlor

Cyanazine

Dieldrin

Figure 23. Concentrations and benchmark quotient values of the most common pesticides in areas underlain 

by carbonate- and siliciclastic-rock aquifers stratified by various land-use categories in the Valley and Ridge 

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

concerns—atrazine, simazine, cyanazine, and dieldrin 

(table 17 and fig. 23). Although deethylatrazine is frequently 

detected in network samples, human-health benchmarks 

for this constituent have not been established; therefore, 

no benchmark quotient could be computed. Detections of 

atrazine and simazine in samples from sites in carbonate-rock 

aquifers had benchmark quotients between 0.1 and 1.0, and 

the samples were primarily from agricultural settings. Of the 

27 benchmark quotients above 0.1 for atrazine, 18 were for 

samples from well networks SCA2, SCA3, and SCU (16 of 

the 18 samples were from domestic supply wells); 8 were for 

samples from PCA wells, all of which were used for domestic 

supply; and 1 was for a sample from the TCS spring network, 

which was not used for drinking-water supply. Cyanazine was 

detected in water samples from two domestic supply wells in 

agricultural areas (SCA2) at a benchmark quotient greater than 

0.1, but neither detection exceeded the HBSL of 1 μg/L. 

Factors Affecting Occurrence of Frequently Detected 

Pesticides

In the Valley and Ridge aquifers, the most frequently 

detected pesticides (atrazine, deethylatrazine, simazine, 

metolachlor, prometon, and tebuthiuron) were detected in at 

least 10 percent of all samples analyzed regardless of reporting level (table 17). The prevalence of these pesticides in the 

environment reflects a combination of influences that determine the rate and spatial extent of application, the exposure of 

groundwater systems to entry, and the persistence of compounds once they are in the system. 

The persistence of pesticides in the environment in their 

original form is affected by decay rates and solubility. Kerle 

and others (1996) separated pesticides into three categories 

based on rates of decay—persistent pesticides with typical 

soil half-lives of more than 100 days, moderately persistent 

pesticides with typical soil half-lives of 30 to 100 days, and 

non-persistent pesticides with typical soil half-lives of less 

than 30 days. Pesticides with low solubility (hydrophobic 

pesticides) as indicated by high soil-water partitioning coefficients (Koc) are likely to bind to soil particles and accumulate 

in soils, and highly soluble (hydrophilic) pesticides with low 

Koc are more likely to be transported to aquifers or streams 

as solutes. Fuhrer and others (2004) placed the hydrophobic/

hydrophilic Koc threshold at 300 milliliters per gram (mL/g). 

Any pesticide released in the environment will remain for a 

period of time and undergo transport or degradation to some 

degree. The pesticides with the greatest potential for transport 

are those that are both highly soluble in water and relatively 

persistent (Kerle and others, 1996). The potential for pesticide 

transport through soil to groundwater was approximated by 

Vogue and others (1994) in a pesticide movement rating based 

on pesticide half-life and Koc in soil (table 19). 

In general, detection frequencies for common pesticides 

in water samples from sites in the Valley and Ridge aquifers 

are consistent with the hypothesis that high-use pesticides 

with high movement ratings will be detected more frequently 

than low-use and low movement rating pesticides. Chlorpyrifos was among the 15 pesticides most frequently applied 

within the Valley and Ridge (table 20) (Naomi Nakagaki, U.S. 

Geological Survey, written commun., 2009), but it was not 

detected in a single groundwater sample (table 17). As might 

be expected, chlorpyrifos is only a moderately persistent to 

non-persistent compound (short half-life) of low solubility 

and very low movement rating (table 19). Commensurately, 

atrazine, simazine, and metolachlor, which also are widely 

used in the Valley and Ridge (table 20), have high movement 

Table 19. Physical properties of selected pesticides detected in the Valley and Ridge aquifers, 1993–2002.

[Koc, soil-water partition coefficient; mL/g, milliliters per gram; mg/L, milligrams per liter]

Pesticide compound

Physical properties1

Pesticide movement 

rating

Soil half-life

(days)

log Koc

(Koc in mL/g)

Solubility

(mg/L)

Atrazine High 60 2 33

Deethylatrazine2 High3 170 1.9 3,200

Simazine High 60 2.11 6.2

Metolachlor High 90 2.3 530

Prometon Very high 500 2.18 720

Tebuthiuron Very high 360 1.9 2500

Chlorpyrifos Very low 30 3.78 0.4

1

 Soil half-life, log Koc, and solubility for all pesticides except deethylatrazine were obtained from Vogue and others (1994).

2

 Soil half-life and log Koc for deethylatrazine were obtained from Mackay (2001); solubility for deethylatrazine was obtained 

from the U.S. National Library of Medicine (2008).

3

 A pesticide movement rating was not determined for deethylatrazine (Kerle and others, 1996). Deethylatrazine is a breakdown product of atrazine, so the pesticide movement rating for atrazine was used for comparison.
Groundwater Quality in the Valley and Ridge Aquifers 41

Table 20. Summary of pesticide compounds most frequently applied in basins in the Valley and Ridge aquifers.

 [Compound names in bold were included in the 47 pesticides analyzed in the current study]

Rank2

Pesticide compounds most frequently applied in the Valley and Ridge aquifer system1

Delaware 

River Basin

Susquehanna 

River Basin

Potomac 

River Basin

Tennessee 

River Basin

1 Sulfur Metolachlor Oil Methyl Bromide

2 Metolachlor Atrazine Sulfur 1,3-D

3 Atrazine Oil Metolachlor Oil

4 Oil Pendimethalin Atrazine Maleic Hydrazide

5 Alachlor Alachlor Captan Atrazine

6 Captan Captan Alachlor 2,4-D

7 Pendimethalin Cyanazine 2,4-D Captan

8 Glyphosate Sulfur Ziram Acephate

9 Cyanazine Chlorpyrifos Mancozeb Chlorpyrifos

10 Mancozeb Methyl Bromide Simazine Ziram

11 Chlorothalonil Glyphosate Chlorpyrifos Sulfur

12 Maneb Simazine Azinphos-Methyl Alachlor

13 2,4-D Mancozeb Metiram Metolachlor

14 Cryolite Dimethoate Pendimethalin Chloropicrin

15 Chlorpyrifos 2,4-D Glyphosate Carbaryl

1

 Naomi Nakagaki, U.S. Geological Survey, written commun., 2009.

2

 Pesticide compounds are sorted in descending order of amount of active ingredient applied in the river basin.

ratings and are among the most frequently detected pesticides (table 17). In contrast, tebuthiuron, though not among 

the 15 most frequently applied pesticides, was frequently 

detected, perhaps because of its high persistence and solubility 

(table 19). 

Dissolved oxygen concentrations were positively correlated to all of the most frequently detected pesticides except 

tebuthiuron (table 21). The apparent persistence of compounds 

such as atrazine, deethylatrazine, simazine, and metolachlor 

in the presence of oxygen suggests relatively young water in 

which microbial oxidation is unable to degrade these compounds faster than they are replaced in recharge (Kaufman 

and Kearney, 1970; Barbash and Resek, 1996; Seybold and 

Mersie, 1999; Lindsey and others, 2009). Although atrazine 

and deethylatrazine were detected frequently in samples that 

were oxic, the degradation characteristics can be seen by comparing the deethylatrazine fraction among redox groups. The 

fraction, calculated by dividing the deethylatrazine concentration in moles by the molar sum of atrazine and deethylatrazine, 

is an indicator of how much of the total product has degraded 

to a given daughter product. Deethylatrazine fractions were 

higher in oxic samples (50 percent) than in mixed and anoxic 

samples (40 percent). The higher deethylatrazine fraction in 

the oxic samples is an indication that more degradation is 

likely taking place in the oxic parts of the aquifer; however, 

detection frequency is still high in those areas because oxic 

water was also likely to be receiving a regular influx of atrazine in recharge from overlying agricultural lands.

Strong positive correlations were observed between 

nitrate and all of the most frequently detected pesticides 

except tebuthiuron (table 21). Not surprisingly, agricultural 

land use (row crop, hay, and pasture) also was positively correlated to concentrations of the agricultural pesticides atrazine 

(including its degradate deethylatrazine) and metolachlor. 

Nitrate and agricultural pesticides generally co-occur because 

both are applied to crops. Concentrations of the general-use 

pesticides simazine, prometon, and tebuthiuron were not correlated as strongly to agricultural land use, and concentrations 

of all the frequently detected pesticides except tebuthiuron 

were negatively correlated with forested land use. Prometon 

and tebuthiuron concentrations were weakly correlated with 

urban land use. 

Overall, soil type and land use appear to have a dominant influence on the presence of pesticides in groundwater in 

the Valley and Ridge. Pesticide concentrations were strongly 

and negatively correlated to percent sand and percent forest. 

Based on soil properties alone, pesticide transport should be 

enhanced in sandy soils due to high inherent permeability 
42 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Table 21. Summary of Spearman’s rho correlations between frequently detected pesticide concentrations and selected site-specific 

and source variables in groundwater in the Valley and Ridge aquifers, 1993–2002.

[Spearman’s rho only shown for variables statistically correlated to pesticide concentrations at the 95-percent confidence level (probabilities less than 0.05); 

NS, correlation not significant at the 95-percent confidence level (probabilities greater than 0.05); No significant correlations were found between pesticide 

concentration and normalized lateral position. See table 22 for correlations that were observed between pesticide concentrations and normalized lateral position 

in selected topographic sections.]

Variable Atrazine Deethylatrazine Simazine Metolachlor Prometon Tebuthiuron

Site-specific variables

Dissolved oxygen 0.49 0.52 0.35 0.3 0.19 NS

Nitrate 0.81 0.81 0.68 0.57 0.49 NS

Percent sand -0.72 -0.71 -0.64 -0.52 -0.52 -0.2

Percent silt 0.5 0.5 0.55 0.44 0.35 NS

Percent clay 0.35 0.33 0.21 0.19 0.24 0.22

Well depth below land surface -0.14 NS -0.21 -0.17 NS NS

Water level 0.18 0.17 NS NS NS NS

Source variables

Row crop, hay, pasture 0.52 0.54 0.41 0.24 0.15 -0.18

Forest -0.63 -0.64 -0.58 -0.48 -0.46 NS

Urban NS -0.12 NS NS 0.21 0.26

1990 population density 0.24 0.21 0.28 0.35 0.43 0.19

and low organic carbon. This effect would be reversed in clay 

soils (Barbash and Resek, 1996), so one might expect a positive correlation of pesticide concentration to sand content. A 

similar negative correlation to sand content has been observed 

in other studies (Lindsey and others, 2006; Lindsey and others, 

2009), where it was attributed to the possible effects of macropore flow and karst features that allow contaminated water to 

bypass clay soils. However, the strong correlation of pesticides 

to nitrate when taken in context of the relatively strong correlations of nitrate to agricultural and sandy soils (tables 15 and 

16) suggests a conceptual model in which agricultural pesticides are preferentially applied to agricultural lands which in 

turn are preferentially located on non-sandy soils (silt-clay). 

Still, differences between agricultural networks (PCA 

and PSA) maintain the possibility that soils and the inherent 

susceptibility of bedrock to contamination play some role in 

pesticide occurrence in groundwater of the Valley and Ridge. 

Atrazine, deethylatrazine, and simazine were all detected in a 

higher percentage of the samples and at higher concentrations 

from agricultural and urban land-use areas overlying carbonate-rock aquifers than in samples from any other combination 

of land use and aquifer type (fig. 24). In contrast, metolachlor 

and prometon detection frequencies and concentrations were 

higher in samples from urban areas than in samples from 

agricultural areas in carbonate-rock aquifers. Concentrations of atrazine were significantly lower in water samples 

from sites in siliciclastic-rock aquifers, regardless of land use 

(fig. 24). Tebuthiuron detections were too few in number to 

evaluate the effects of the combined land use/aquifer setting 

on concentrations.

Across the spectrum from ridge to stream, landscape 

position (NLP) does not appear to play a defining role in 

occurrence of frequently detected pesticides (table 22). Concentrations of the six most frequently detected pesticides were 

not correlated with NLP when viewed over the whole range of 

NLP. However, concentrations of atrazine and deethylatrazine 

may be somewhat correlated to NLP when considered only 

within the upper or lower topographic sections for carbonaterock aquifers or lower topographic section for siliciclasticrock aquifers; generally positive correlations are in the upper 

section, and negative correlations are in the lower section. 

Significant negative correlations were observed for simazine 

concentrations in only the lower section in the carbonate-rock 

aquifers and for metolachlor concentrations in only the lower 

section in the siliciclastic-rock aquifers. These correlations 

suggest the effect of relatively recent recharge in the lower 

topographic section as indicated by correlations with dissolved 

oxygen noted earlier (tables 12 and 21). 
Groundwater Quality in the Valley and Ridge Aquifers 43

0.001

0.01

0.1

1

Prometon concentrations,

 in micrograms per liter

107 45 36 17 22 21 16

B C B C C C A

0.001

0.01

0.1

1

Simazine concentrations,

 in micrograms per liter

Agricultural carbonate

Agricultural siliciclastic

Mixed carbonate

Undeveloped carbonate

Mixed siliciclastic

Urban carbonate

Undeveloped siliciclastic

107 45 36 17 22 21 16

A B B B B B A

0.001

0.01

0.1

1

Metolachlor concentrations,

 in micrograms per liter

Agricultural carbonate

Agricultural siliciclastic

Mixed carbonate

Undeveloped carbonate

Mixed siliciclastic

Urban carbonate

Undeveloped siliciclastic

B C BC C C C A

0.001

0.01

0.1

1

Deethylatrazine concentrations,

 in micrograms per liter

A BC B C BC C A

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

45 Number of samples

Most common 

laboratory reporting

level for individual 

pesticide

Atrazine concentrations,

 in micrograms per liter

0.001

0.01

0.1

1

107 45 36 17 22 21 16

A C B C BC C A

Predominant land use and aquifer type

107 45 36 17 22 21 16 107 45 36 17 22 21 16

Predominant land use and aquifer type

Figure 24. Distribution of atrazine, deethylatrazine, simazine, prometon, and metolachlor concentrations by combined 

land use/aquifer setting in the Valley and Ridge aquifers, 1993–2002.
44 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Table 22. Summary of Spearman’s rho correlations between frequently detected pesticide concentrations 

in groundwater and normalized lateral position by aquifer type in the Valley and Ridge aquifers, 1993–2002.

[Spearman’s correlation test results only shown for variables statistically correlated to pesticide concentrations at the 95-percent confidence level (probabilities less than 0.05); NS, correlation not significant at the 95-percent confidence level (probabilities greater than 0.05); ND, no detections of this compound; n, number of observations; NLP, normalized lateral position]

Pesticide All 

Upper

topographic

section

NLP less than 0.40

Middle

topographic

section

NLP 0.40 to 0.70

Lower

topographic

section

NLP greater than 0.70

Carbonate aquifers (springs included)

Atrazine NS 0.38

(n=34) NS -0.22(n=83)

Deethylatrazine NS 0.39

(n=34) NS -0.25(n=83)

Simazine NS NS NS -0.3

(n=83)

Metolachlor NS NS NS NS

Prometon NS NS NS NS

Tebuthiuron NS NS NS NS

Siliciclastic aquifers

Atrazine NS NS NS -0.33

(n=42)

Deethylatrazine NS NS NS NS

Simazine NS ND ND NS

Metolachlor NS ND NS -0.38

(n=42)

Other Pesticides Analyzed

High performance liquid chromatography (HPLC) was 

used to analyze a subset of samples from 242 sites for additional pesticides; relatively few pesticides were detected 

during this analysis (table 23, at end of report). The herbicides 

diuron, bentazon, and dichlobenil, for example, were detected 

at only 8, 4, and 2 sites, respectively. Diuron was detected only 

in samples from carbonate-rock aquifers and mostly in urban 

settings. Bentazon was detected in samples from three out 

of four siliciclastic-rock aquifer networks. Other pesticides, 

including 2,4-D, acifluorfen, bromacil, dicamba, fenuron, 

linuron, norflurazon, and oryzalin were each detected once. All 

of the pesticides analyzed using HPLC tend to be less mobile 

in groundwater, which partly accounts for their relatively low 

detection rates.

Analyses for 25 other pesticides, pesticide degradation products, and organic compounds using HPLC/MS for 

samples from 30 wells in the DSM network and samples from 

16 wells in the PCA network indicate more frequent occurrence of pesticide degradation products in carbonate- than in 

siliciclastic-rock aquifers. Atrazine and simazine degradation 

products didealkyl atrazine (CAAT), deisopropylatrazine/DIA 

(CEAT), and hydroxyatrazine (OIET) were detected in 38, 

56, and 63 percent of samples, respectively, in carbonate-rock 

aquifers and in 13, 7, and 3 percent of samples, respectively, 

in siliciclastic-rock aquifers. This pattern of greater detection 

frequency in the carbonate-rock aquifers is similar to the pattern seen in detections of other pesticides.

Volatile Organic Compounds 

Volatile organic compounds (VOCs) include a wide range 

of natural and synthetic carbon-based compounds that have 

high vapor pressure and relatively low solubility in water. 

VOCs are used in industrial, commercial, and domestic applications and can enter the groundwater as liquid through spills 

and leaks or by atmospheric deposition. VOCs typically found 

in groundwater include industrial solvents, fuel hydrocarbons 

and oxidizers, fumigants, organic synthesis compounds, refrigerants, and disinfection byproducts (trihalomethanes) (Carter 

and others, 2007). 
Groundwater Quality in the Valley and Ridge Aquifers 45

Occurrence and Distribution of VOCs

VOCs are the most commonly found contaminant class 

associated with industrial and commercial sites, dumps, 

landfills, hazardous waste facilities, and military bases 

(Zogorski and others, 2006) and are widespread wherever 

human activities occur. Historically, many waste chemicals 

were disposed of indiscriminately, and the widespread use of 

VOCs has resulted in considerable mass of material released 

to the environment. Localized releases of VOCs occur from 

many sources, including leakage from storage tanks, direct 

application of pesticides containing VOCs (Barbash and 

Resek, 1996), septic systems, and leaking sewer systems. 

VOCs also are released to the atmosphere through engine 

exhausts, aerosol sprays, leakage of refrigerants, and application of fumigants and pesticides. Trihalomethanes (THMs) are 

frequently associated with chlorinated water and chlorinated 

cleaning products. 

The VOCs detected in water samples from sites in the 

Valley and Ridge aquifers were a mixture of THMs, solvents, 

fuel-related products, and organic synthesis compounds 

(table 24, at end of report). At a detection level of 0.2 μg/L, 

the 10 most frequently detected VOCs were chloroform, tetrachloroethene (PCE), 1,1,1-trichloroethane (TCA), chloromethane, styrene, carbon disulfide, methyl tert-butyl ether (MTBE), 

trichloroethene (TCE), toluene, and bromodichloromethane. 

Analyses for carbon disulfide were only added after April 

1996. At this detection level (0.2 μg/L), VOCs were unevenly 

distributed (fig. 25) and were mostly in samples from the 

urban network (SCU) where THMs were most commonly 

detected (at 55 percent of sites) (table 25). VOCs were not 

detected in samples from sites in two Susquehanna networks 

(SSM and SCA2) and were detected at less than 17 percent 

of sites in each of the remaining networks. The presence of 

VOCs by group varied from a single group of compounds 

(solvents) in one agricultural network (SCA3) to the presence 

of four groups (THMs, gasoline compounds, solvents, and 

organic synthesis compounds) in the SCU and TCM networks. 

The presence of the THM chloroform in groundwater 

may reflect its use as a solvent or its use in various industrial 

processes but also may be attributed to chlorinated water 

entering aquifers from multiple sources (Zogorski and others, 

2006). The relatively frequent detection of THMs in samples 

from sites in the Valley and Ridge aquifers is consistent 

with a nationwide study by Zogorski and others (2006) that 

reported THMs in 5.3 percent of domestic well samples and 

in 15 percent of public water-supply samples. In the Valley 

and Ridge, 9.5 percent of samples had detects above 0.2 μg/L 

(table 25). Chloroform was the most frequently detected THM 

in the group and the most frequently detected VOC overall (at 

9.5 percent of sites) (table 24), which is also consistent with 

national results (5.2 percent of domestic wells and 11.4 percent of public wells; Zogorski and others, 2006). THMs are 

often byproducts of the chlorination of drinking water and 

wastewater and the disinfection of wells (Zogorski and others, 

2006) and may be formed in wastewater treatment and septic 

systems where chlorine is present. The high numbers of THMs 

present in samples from sites in the urban network (SCU) may 

reflect a combination of aging infrastructure, leaking sewer 

systems, and local industrial processes. 

Solvents, mostly chlorinated compounds, were the 

second most commonly detected group of VOCs in the Valley and Ridge aquifers. Overall, nine solvents were detected 

in 9 percent of the groundwater samples (table 25). This is 

generally consistent with national results where solvents were 

detected in 4.9 percent of domestic well samples and 9.9 percent of public water-supply samples (Zogorski and others, 

2006). Three of 9 solvents detected were among the 10 VOCs 

most frequently detected in samples from the Valley and Ridge 

aquifers. After chloroform, the chlorinated solvent TCA was 

the second most frequently detected VOC followed by PCE. 

TCE was eighth in order of detection frequency. 

Gasoline-related compounds were the third most commonly detected group of VOCs, with detections above 

0.2 μg/L in 6.8 percent of samples (table 25). A total of 23 gasoline compounds were analyzed (only 14 prior to 1996), 10 of 

which were detected at levels above 0.2 μg/L in the urban 

network (SCU) where 35 percent of the samples contained 

from 1 to 9 gasoline-related compounds (table 25). Among 

the compounds associated with gasoline, collectively known 

as BTEX compounds, are benzene, toluene, ethylbenzene, 

and various xylene isomers (o-, m- and p-xylene, which are 

summed together as total xylene). Benzene, toluene, and total 

xylene were detected in 1.1 percent of samples, and ethylbenzene was detected in 0.5 percent of samples (table 24). 

MTBE, a common fuel oxygenate, was the second most 

commonly detected VOC (above 0.2 μg/L) in the Valley and 

Ridge aquifers (5.9 percent of samples; table 24) and nationally (3 percent in private well samples and 5 percent in public 

well samples; Zogorski and others, 2006). MTBE was detected 

in 35 percent of samples from urban network wells (SCU). 

MTBE also was detected in 10 percent of samples from DSM 

wells, which were located in a high MTBE-use area as defined 

by the Federal Reformulated Gasoline Program (U.S. Environmental Protection Agency, 1990, 2007). MTBE was detected 

in one sample from the southern part of the Valley and Ridge 

(TCS network) at a site downgradient from fuel storage tanks 

and close to railroad tracks where MTBE was transported.

Organic synthesis compounds are used as precursors in 

the manufacturing of other organic compounds. This was the 

least commonly detected group of VOCs in the Valley and 

Ridge aquifers, with only 0.5 percent of samples exceeding 

0.2 μg/L (table 25). Carbon disulfide and 1,3,5-trimethylbenzene were each detected once above 0.2 μg/L; however, 

carbon disulfide was detected seven times at concentrations 

below 0.2 μg/L (table 24). 

Overall, the detection of one VOC at a site increased 

the likelihood of finding others. About 18 percent of samples 

from the Valley and Ridge aquifers contained one or more 

VOCs (detected above 0.2 μg/L), about 8 percent of samples 

contained two or more VOCs, about 5 percent of samples 

contained three or more VOCs, and about 3 percent of samples 
46 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

85° 80° 75°

40°

35°

SUSQUEHANNA DELAWARE

POTOMAC

TENNESSEE

Base from U.S. Bureau of the Census, 1990a, 1:500,000 to 1:5,000,000

Universal Transverse Mercator projection, Zone 18N

Horizontal datum: North American Datum of 1983 (NAD 83)

Populated places from U.S. Bureau of the Census, 1990b

Agricultural and urban network boundaries from Siwiec and others, 1997

Principal aquifers from U.S. Geological Survey, 2003

NAWQA study units from Hitt and Nakagaki, 2006

EXPLANATION

Aquifer type in the Valley and Ridge aquifers

Siliciclastic-rock aquifers

Carbonate-rock aquifers

Study unit/River basin boundaries

Not Detected

Volatile organic compound (VOC) 

detection occurrence

Detected

0 105 MILES

0 105 KILOMETERS

Harrisburg

0 50 100 25 MILES

0 50 100 25 KILOMETERS

Not Analyzed

ONLY CARBONATE AQUIFERS ARE SHOWN

EXPLANATION

Lower Susquehanna 

Carbonate Network

boundaries

Agricultural Network

Volatile organic compound (VOC) 

detection occurrence

Urban Network

Not Detected

Not Analyzed

Detected Urban

Network

Agricultural

Network

Figure 25. Volatile organic compounds detected at a concentration greater than 0.2 micrograms per liter in the Valley and Ridge aquifers, 

1993–2002.
Groundwater Quality in the Valley and Ridge Aquifers 47

Table 25. Number of volatile organic compounds detected, percentage of sites with detections by volatile organic compound group, and number of compounds detected in each volitile organic compound group for groundwater samples from networks in the Valley and Ridge aquifers, 1993–2002.[VOC, volatile organic compound; THMs, trihalomethanes, μg/L, micrograms per liter; ≥, greater than or equal to]

Groundwater 

network1

Summary of VOC detections Percentage of sites with detections ≥ 0.2 μg/L, by compound group Number of compounds in each group detected at the ≥ 0.2 μg/L screening level

Number of 

sites with 

VOC data

Total 

number of 

detections 

≥ 0.2 μg/L

Percent of 

sites with 

detections 

≥ 0.2 μg/L 

THMs Gasoline compounds Solvent Organic synthesis compound THMs Gasoline compounds Solvent Organic synthesis compound 

DSM2 30 6 16.6 0 10 6.7 0 0 1 3 0SCA2 9 0 0 0 0 0 0 0 0 0 0SCA3 20 4 10 0 0 10 0 0 0 3 0SCU 20 56 75 55 35 45 5 3 10 8 1SSM 29 0 0 0 0 0 0 0 0 0 0PCA 17 2 5.9 5.9 5.9 0 0 1 1 0 0TCS2 35 10 17.1 11.4 2.9 8.6 0 1 1 4 0TCM2 30 5 16.7 6.7 3.3 3.3 3.3 1 1 1 1Total 190 83 21.1 9.5 6.8 9 0.5 3 10 9 2Total number of compounds analyzed by group 4 23 30 17Number of compounds analyzed prior to April 1996 4 14 21 6

1 Groundwater network abbreviations are defined in table 3.2 Beginning April 1996, analyses for samples in these networks had more constituents and lower detection limits (less than 0.2 μg/L).
48 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

contained four or more VOCs (fig. 26). One sample from 

a well in the urban network (SCU) contained 14 detectable 

VOCs. The percentage of samples in the Valley and Ridge 

aquifers containing one or more VOCs was similar to national 

findings. In all NAWQA studies, 19 percent of samples 

contained one or more VOCs (Zogorski and others, 2006), 

and 20 percent of the samples from carbonate-rock aquifers 

contained one or more VOCs (Lindsey and others, 2009). 

Assessment of Potential Effects of VOCs on Human Health 

Benchmark quotients for VOCs in samples from the Valley and Ridge aquifers indicate some developing issues but no 

immediate concerns related to human health. Currently (2010), 

MCLs have been established for 20 of the 87 VOCs analyzed as part of this study, and HBSL benchmarks have been 

established for 25 of the 87. MCLs or HSBLs have not been 

established for VOCs where data are insufficient to evaluate 

human-health effects. None of the VOCs detected exceeded 

USEPA MCLs (U.S. Environmental Protection Agency, 2006) 

or HBSLs (Toccalino and others, 2008). HBSL benchmark 

quotients for five VOCs were within the range of 0.1 to 1.0, 

indicating that concentrations approached levels of potential 

concern for human health (table 24, fig. 27). In particular, 

benchmark quotients for chloroform, PCE, TCE, benzene, 

and carbon tetrachloride, exceeded 0.1 in 0.5 to 2.1 percent 

of samples. The MTBE concentration at one site in the urban 

network (SCU) exceeded a taste and odor advisory guideline 

of 20 to 40 μg/L established by the USEPA (U.S. Environmental Protection Agency, 1997). 

Factors Affecting Occurrence of VOCs

The occurrence of VOCs in groundwater of the Valley 

and Ridge aquifers is generally affected by the same basic 

processes and conditions associated earlier in this report with 

Agricultural

Mixed

Undeveloped

Urban

Detection frequency, in percent

93 44 38 15

0

20

40

60

80

100 B

Land use

Detection frequency, in percent

26 10 153

Anoxic Mixed Oxic

0

20

40

60

80

100

C

Redox state

DSM

SCA2

SCA3

SSM

PCR

All data

TCS

TCM

Detection frequency, in percent

30 9 20 20 29 17 35 30 190

0

20

40

60

80

100

SCU

A

Detection frequency, in percent

D

1 detected

2 detected

3 detected

4 or more detected

None

EXPLANATION

Number of VOCs detected 

per sample

30 Number of samples

131 59

0

20

40

60

80

Groundwater network

Carbonate-rock Siliciclastic-rock

Aquifer type

Groundwater network 

code, see table 3 for 

network abbreviation 

codes

DSM

Figure 26. Detection frequency for samples with volatile organic compounds (VOCs) detected at the 0.2-microgram per liter assessment 

level by, A, groundwater network and, B, land-use classification and by, C, redox state and, D, aquifer type for samples in the Valley and 

Ridge aquifers, 1993–2002.
Groundwater Quality in the Valley and Ridge Aquifers 49

0.01 0.1 1.0 10

Styrene

Benzene

Chloromethane

Bromodichloromethane

Toluene

Trichloroethene (TCE)

Methyl tert-butyl ether 

 (MTBE)

Tetrachloroethene (PCE)

1,1,1-Trichloroethane

Chloroform

Siliciclastic

VOC concentration, in micrograms per liter

Carbon disulfide*

Carbon Tetrachloride

Benzene

Carbon Tetrachloride

Carbon disulfide*

Styrene

Chloromethane

Bromodichloromethane

Toluene

Trichloroethene (TCE)

Methyl tert-butyl ether 

 (MTBE)

Tetrachloroethene (PCE)

1,1,1-Trichloroethane

Chloroform

0.01 0.1 1.0 10

10-5 10-4 10-3 10-2 0.1 1.0 10 10 10 10 0.1 1.0 -5 -4 -3 -2

Agricultural

Mixed

Undeveloped

Urban

Land Use

Siliciclastic Carbonate

Benchmark quotient

Benchmark quotient value (BQ) = Chloroform concentration

Chloroform MCL = 80 μg/L 

MCL is Maximum Contaminant Level for regulated compounds 

(U.S. Environmental Protection Agency, 2006). 

HBSL is Health-Based Screening Level concentrations for 

unregulated compounds (Toccalino and others, 2008).

Benchmark quotient value of 0.1 -- Values 

greater than this line are within one order 

of magnitude of an MCL or HBSL

Benchmark quotient value of 1.0 -- Values 

greater than this line would indicate concentrations 

of potential health concerns

USEPA guidelines for drinking-water advisory range for taste 

and odor (U.S. Environmental Protection Agency, 1997)

* Carbon disulfide was only measured in half of the samples

 

Shaded area represents concentrations reported that were 

less than 0.2 μg/L. Samples collected prior to 1996 used

0.2 μg/L as a laboratory reporting limit (LRL); later samples 

had lower LRLs. Comparisons cannot be made among 

samples in the shaded area. 

EXPLANATION

Carbonate

Figure 27. Concentrations and benchmark quotients of the most common volatile organic compounds in various land-use 

categories in the Valley and Ridge siliciclastic-rock and carbonate-rock aquifers, 1993–2002.
50 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

pesticides: the availability of sources, the chemical persistence 

of compounds, and the efficiency of transport mechanisms. In 

a national summary of groundwater quality, the most common 

factors associated with VOC concentrations in aquifers were 

the presence of septic systems, urban land, hazardous waste 

facilities, and gasoline storage sites (Zogorski and others, 

2006). The presence of VOCs also was related to well characteristics, soil conditions, and most significantly, dissolved 

oxygen in groundwater. In a study evaluating groundwater 

samples from carbonate-rock aquifers in the United States, 

differences in the detection frequencies for the eight most 

commonly detected VOCs—chloroform, tetrahydrofuran, toluene, PCE, acetone, methyl ethyl ketone (MEK), MTBE, and 

TCE—were associated with different land uses and also were 

affected differently by degree of confinement of the aquifers 

and redox state of the groundwater (Lindsey and others, 2009). 

Of the several factors affecting the occurrence of VOCs in 

groundwater from the Valley and Ridge aquifers, land use may 

predominate as an indicator of source availability. The highest 

percentages of VOC detections above 0.2 μg/L were associated 

with areas of urban land use in carbonate-rock aquifers. The 

majority of these detections (56 of 83) were identified in 20 

wells in the urban network (SCU) (table 25); 50 percent of the 

wells had samples with multiple detections (fig. 26). Chloroform concentrations were significantly and positively correlated to urban land use (tau b = 0.30) and population density 

(tau b = 0.26) using a censored Kendall tau test, and chloroform concentrations were positively correlated to the presence 

of storage tanks (tau b=0.36) and public sewer density (tau b = 

0.26) in carbonate-rock aquifers. 

A negative correlation of chloroform to dissolved oxygen 

concentrations in samples from sites in carbonate-rock aquifers 

using the censored Kendall tau test (alpha = 0.05) suggests that 

chemical processes (redox conditions) and chemical degradation may play a mixed or muted role in VOC occurrence in 

the Valley and Ridge aquifers (fig. 28, table 26). The ratio of 

VOC detections in oxic versus anoxic conditions is consistent 

with national results indicating the persistence of chloroform 

in oxic conditions and of carbon disulfide in anoxic conditions 

(fig. 29). However, oxic/anoxic detection ratios for toluene and 

bromodichloromethane were only about 1:1—lower than that 

reported in national results (Zogorski and others, 2006). Further, a ratio of 1:1 was higher than expected for toluene, which 

is known to degrade in oxic conditions. These departures from 

expectations may in part be caused by the low overall detection frequency of VOCs but may also be related to the fact that 

the majority of wells sampled for toluene were oxic. 

Despite somewhat unbalanced representation with respect 

to redox conditions, the results from the Valley and Ridge 

aquifers analyses appear overall to be consistent with results 

from the national studies of VOCs. Multiple VOC detections greater than 0.2 μg/L also were typically associated 

with mixed or oxic conditions (fig. 26C). This is consistent 

with national results where TCA, TCE, PCE, bromodichloromethane, and chloroform concentrations were strongly 

associated with oxic conditions and methylene chloride and 

Toluene

Chloroform 

Tetrachloroethene (PCE)

Trichloroethene (TCE)

Methyl tert-butyl ether (MTBE) 

1,1,1-Trichloroethane (TCA)

Bromodichloromethane 

Carbon disulfide 

0

10

20

30

40

50

60

Detection frequency, in percent

EXPLANATION

Anoxic

Mixed source

Oxic

Chloroform 

Bromodichloromethane 

Carbon disulfide 

Toluene

0

.2

.4

.6

.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Ratio of detection frequency in

oxic samples to detection 

frequency in anoxic samples 

Detection frequency greater in oxic groundwater

Detection frequency greater in anoxic groundwater

Figure 28. Percentage of detections by redox state for selected 

volatile organic compounds in the Valley and Ridge aquifers, 

1993–2002.

Figure 29. Ratio of detection frequencies in oxic and anoxic 

samples for selected volatile organic compounds in the Valley and 

Ridge aquifers, 1993–2002. 
Groundwater Quality in the Valley and Ridge Aquifers 51

Table 26. Percentage of samples with detections by redox state, and the oxic/

anoxic ratio of detection frequencies for selected volatile organic compounds in 

groundwater samples from the Valley and Ridge aquifers, 1993–2002.

[--, insufficient number of samples with anoxic conditions to calculate ratio; PCE, tetrachloroethene; TCE, trichloroethene; TCA, 1,1,1-trichloroethane; MTBE, methyl tert-butyl ether]

Volatile organic 

compound

Detection frequency

(percent)

Ratio of detection 

frequency in oxic water 

to detection frequency 

in anoxic water Anoxic Mixed Oxic

Toluene 11.5 0.0 11.8 1.02

Chloroform 15.4 20.0 32.0 2.08

PCE 0.0 20.0 14.0 --

TCE 0.0 10.0 6.5 --

TCA 0.0 10.0 15.0 --

MTBE 0.0 10.0 7.9 --

Bromodichloromethane 3.8 0.0 3.9 1.02

Carbon disulfide 30.0 0.0 4.9 0.16

chloromethane concentrations were associated with anoxic 

conditions (Zogorski and others, 2006). Generally, oxic conditions prevailed (81 percent of wells) across the Valley and 

Ridge aquifers, and anoxic conditions were concentrated in 

siliciclastic-rock aquifers (70 percent of the total anoxic samples). Where VOCs were detected in samples from siliciclastic-rock aquifers, the samples were always oxic. Conversely, 

where VOCs were detected in anoxic samples, those samples 

were always from wells in carbonate-rock aquifers.

The relatively high detection frequency of chlorinated 

solvents may be partly explained by the persistence and 

transport properties of these compounds. Chlorinated solvents 

have relatively long half-lives in groundwater compared to 

other VOCs and may be relatively persistent. With specific 

densities greater than 1.0, chlorinated solvents are denser than 

water, move downward through aquifers, and are resisted only 

by capillary pore pressure. In karst aquifers with enlarged 

conduits, chlorinated solvents can migrate to great depths 

as dense non-aqueous phase liquids (DNAPLs) (Wolfe and 

others, 1997; Loop and White, 2001) where they may provide 

a continuous source of dissolved-phase chlorinated solvents 

in groundwater. For some highly chlorinated molecules, such 

as PCE, degradation may produce other chlorinated solvents, 

such as TCE. The degradation of PCE to TCE occurs preferentially under anoxic conditions where bacteria exploit redox 

potential in a chain of reactions (Wiedemeier and others, 

1998; Chapelle and others, 2007), resulting in biodegradation 

through reductive dechlorination (Lawrence, 2006).

Gasoline hydrocarbons are among the most intensively 

and extensively used VOCs (Zogorski and others, 2006) but as 

a group are relatively insoluble (Mackay and others, 1992) and 

often evaporate to the atmosphere before entering groundwater 

systems. MTBE, which was the most commonly used gasoline oxygenate in 2004, was completely or partially banned 

in some states after the oxygen requirement for gasoline was 

eliminated in 2005 (Zogorski and others, 2006). MTBE has 

low sorption to organic material, is slow to biodegrade, and 

is more soluble than other gasoline compounds, which allow 

MTBE to move faster and further in aquifers than BTEX and 

other gasoline components.

Fecal-Indicator Bacteria

Microbiological analyses are important in determining 

the associated human-health risk of potentially pathogenic 

(disease-causing) waterborne organisms. The most common 

of these analyses include tests for total coliform and E. coli. 

Coliform bacteria are ubiquitous in the environment and 

are not always pathogenic. Some strains of E. coli, such as 

O157:H7, can cause severe illness, and the presence of E. coli

may indicate general fecal contamination because of the strong 

association of E. coli with the intestines of warm-blooded 

animals. Any detection of E. coli in public drinking-water supplies is considered cause for concern and a violation of health 

standards (U.S. Environmental Protection Agency, 2001). 

Although current drinking-water standards for E. coli were 

developed for public water supplies, USEPA criteria can be 

used to provide a reference point for domestic wells.

Occurrence and Distribution of Fecal-Indicator Bacteria

The overall detection frequency for E. coli in water samples from sites in five networks in the Valley and Ridge aquifers (SCA2, SCA3, TCS, DSM, and TCM) was 43 percent; 
52 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

this included detections in water from 28 percent of wells and 

91 percent of springs. E. coli detections were less frequent 

in water samples from sites in siliciclastic-rock aquifers and 

more frequent in carbonate-rock aquifers (figure 30). Where 

detected, counts were generally higher in carbonate- than in 

siliciclastic-rock aquifers and were higher in springs than 

in wells. Counts rarely exceeded 80 colonies per 100 mL in 

samples from most well networks but did so in about 11 percent of samples from springs in the Tennessee River basin 

(TCS) where counts were reported as high as 660 colonies per 

100 mL. 

Factors Affecting Occurrence of Fecal-Indicator Bacteria

Overall, the presence of E. coli in samples of groundwater from the Valley and Ridge aquifers appears to be most 

strongly influenced by the aquifer type and the presence of 

potential fecal sources. Among samples from wells in agricultural and mixed use areas, E. coli detection frequencies 

and colony counts were higher in samples from carbonaterock aquifers than in samples from siliciclastic-rock aquifers (fig. 31). This is consistent with earlier observations 

concerning the relatively high rates of transport through 

Maximum value

75th percentile

Median

25th percentile

Minimum value

Siliciclastic-rock 

aquifers

Carbonate-rock 

aquifers

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

87 Number of samples

Upper detection limit

Lower detection limit

Detection of a single

E. coli colony exceeds

the USEPA MCL

Note: Analyses with no colonies 

are reported as less than one 

colony per 100 milliliters. Plates 

with more than 80 colonies were 

considered too numerous to 

count and are reported as 

greater than 80 colonies per 

100 milliliters, which is the 

upper detection limit. Samples 

analyzed using multiple 

dilution techniques with 

concentrations greater than 

the upper detection limit are 

also reported as greater 

than 80 colonies per

100 milliliters.

0

20

40

60

80

100

40

60

80

20

0

E. coli concentration,

in colonies per 100 milliliters

Detection frequency, 

in percent

A B

35 87 30

C

Springs Wells Wells

Site type

E. coli

MCL is U.S. Environmental 

Protection Agency Maximum 

Contaminant Level for regulated 

compounds (U.S. Environmental 

Protection Agency, 2006). 

Maximum value

75th percentile

Median

25th percentile

Minimum value

Siliciclastic-rock 

aquifers

Carbonate-rock 

aquifers

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

78 Number of samples

Detection frequency,

 in percent

0

20

40

60

80

100

E. coli

20

0

40

60

80

E. coli concentration,

in colonies per 100 milliliters

Aquifer type

(Agricultural and mixed

land-use wells only)

Upper detection limit

Note: Analyses with no colonies 

are reported as less than one 

colony per 100 milliliters. Plates 

with more than 80 colonies were 

considered too numerous to 

count and are reported as 

greater than 80 colonies per 

100 milliliters, which is the 

upper detection limit. Samples

analyzed using multiple

dilution techniques with

concentrations greater than

the upper detection limit are

also reported as greater

than 80 colonies per

100 milliliters.

A B

78 30

Lower detection limit

Detection of a single

E. coli colony exceeds

the USEPA MCL

MCL is U.S. Environmental 

Protection Agency Maximum 

Contaminant Level for regulated 

compounds (U.S. Environmental 

Protection Agency, 2006). 

Figure 30. Detection frequency and distribution of 

concentrations of Escherichia coli bacteria in groundwater 

samples from well and spring networks in the Valley and Ridge 

aquifers, 1993–2002.

Figure 31. Detection frequency and distribution of 

concentrations of Escherichia coli bacteria in groundwater 

samples by aquifer type in the Valley and Ridge aquifers, 

1993–2002 (wells only, agricultural and mixed land-use only). 
Groundwater Quality in the Valley and Ridge Aquifers 53

carbonate-rock aquifers and their susceptibility to surface 

contamination. E. coli concentrations were not significantly 

different among samples from wells surrounded by different land-use types, but their detections were more common 

in samples from wells in agricultural areas (fig. 32). Further 

grouping of detection frequencies for wells by aquifer type 

and land use indicates that land use and aquifer type play an 

important role in explaining the presence of bacteria (fig. 33). 

In carbonate-rock aquifers, detections were most frequent in 

samples from wells in agricultural areas but were not entirely 

absent even in the samples from wells in undeveloped areas. 

In siliciclastic-rock aquifers, E. coli were detected only in 

samples from wells in agricultural areas. The highest colony 

counts tended to be in samples from wells in agricultural 

E. coli

Detection frequency,

 in percent

0

20

40

60

80

100

Agricultural Undeveloped

LAND-USE GROUP

Mixed

20

0

40

60

80

E.coli concentration,

in colonies per 100 milliliters

Maximum value

75th percentile

Median

25th percentile

Minimum value

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

88 Number of samples

Upper detection limit

88 30 34

A A A

Note: Analyses with no colonies 

are reported as less than one 

colony per 100 milliliters. Plates 

with more than 80 colonies were 

considered too numerous to 

count and are reported as 

greater than 80 colonies per 

100 milliliters, which is the 

upper detection limit. Samples

analyzed using multiple

dilution techniques with

concentrations greater than

the upper detection limit are

also reported as greater

than 80 colonies per

100 milliliters.

Lower detection limit

Detection of a single

E. coli colony exceeds

the USEPA MCL

MCL is U.S. Environmental 

Protection Agency Maximum 

Contaminant Level for regulated 

compounds (U.S. Environmental 

Protection Agency, 2006). 

Figure 32. Detection frequency and distribution of 

concentrations of Escherichia coli bacteria in groundwater 

samples from wells by land-use group in the Valley and Ridge 

aquifers, 1993–2002.

Detection frequency, in percent

0

20

40

60

80

100

E. coli

Aquifer type and land-use group

Carbonate-rock agricultural

Siliciclastic-rock mixed

Carbonate-rock undeveloped

Siliciclastic-rock agricultural

Siliciclastic-rock undeveloped

Carbonate-rock mixed

no detectionsno detections

Figure 33. Detection frequency of Escherichia coli bacteria in 

groundwater samples from wells by land-use group and aquifer 

type in the Valley and Ridge aquifers, 1993–2002.

areas overlying carbonate-rock aquifers, reflecting the role of 

agricultural practices and animals as sources of fecal contamination. Higher detections and counts in samples from springs 

were likewise consistent with the greater susceptibility of 

springs to surface influences. 

Radon

Radon is a colorless, odorless gas that is produced by the 

radioactive decay of uranium. It has a relatively short half-life 

of 3.8 days (Hem, 1985) and is typically detected at higher 

levels in water from aquifers composed of rocks containing relatively more uranium (Faure, 1986). The health risk 

from radon in water supplies comes from either ingesting it 

directly in tap water or breathing radon vapor as it degasses 

from tap water. Radon is the second leading cause of lung 

cancer in the United States (U.S. Environmental Protection 

Agency, 2009). Some of the radon in indoor air comes from 

radon that escapes from tap water. The USEPA has proposed 

regulations for radon at two levels for public water supplies 

(U.S. Environmental Protection Agency, 2009). A proposed 

MCL of 300 picocuries per liter (pCi/L) addresses radon in 

groundwater or a mixture of groundwater and surface water 

for public supply; an alternative MCL (AMCL) of 4,000 pCi/L 

has been proposed for radon if the public water supplier enacts 

community plans to address all sources of radon (known as a 

multimedia mitigation program). 
54 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Occurrence and Distribution of Radon

Radon levels were significantly higher in samples from 

sites in siliciclastic-rock aquifers than in samples from sites 

in carbonate-rock aquifers (fig. 34). A large number of wells 

(74 percent) in carbonate- and siliciclastic-rock aquifers 

produced water with radon levels that exceeded the proposed 

MCL. However, samples from only five wells (2 percent of 

wells) exceeded the higher AMCL for radon, and all of these 

wells were in siliciclastic-rock aquifers. In contrast, siliciclastic-rock aquifers (PSA) also produced some of the lowest 

radon concentrations in the Valley and Ridge aquifers. 

Factors Affecting Concentrations of Radon

The presence of radon in groundwater can be explained 

to a large degree by the mineral composition of rocks through 

which water moves and by other factors, such as exposure 

to surface influences. Carbonate rocks, for instance, typically contain less uranium than siliciclastic rocks, reflecting 

differences in parent mineralogy and weathering processes. 

Not surprisingly, radon levels were significantly lower in 

carbonate-rock aquifers. Differences in radon levels were 

not significant among carbonate lithologic groups (limestone, dolomite, limestone and dolomite; fig. 35). Among the 

carbonate-rock aquifers, springs (TCS) produced the lowest 

radon concentrations. This may reflect degassing from groundwater as hydrostatic pressures decline when the groundwater 

approaches the spring mouth. Median radon levels were 

somewhat, but not significantly, higher in water samples from 

sites in the mixed siliciclastic lithologic group, but sample 

variance was greatest in samples from wells completed in 

shale. Relatively larger variance in radon levels in shale and 

mixed siliciclastic-rock aquifers than in the carbonate-rock 

aquifers (fig. 35) may result from local differences in mineralogy (Lindsey and Ator, 1996). The variation in the amount of 

felsic or other uranium-bearing minerals in the parent rocks 

for a given sedimentary rock formation could explain this high 

amount of variability.

Maximum value

75th percentile

Median

25th percentile

Minimum value

Siliciclastic-rock 

aquifers

Carbonate-rock 

aquifers

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

81 Number of samples

Aquifer type

Carbonate rock

Siliciclastic rock

100

1,000

10,000

Radon level,

in picocuries per liter

161 81

B A

Proposed Alternate

Maximum Contaminant 

Level

Proposed Maximum

Contaminant Level

Figure 34. Distribution of radon levels in groundwater samples 

among carbonate- and siliciclastic-rock aquifers in the Valley and 

Ridge aquifers, 1993–2002.

Maximum value

75th percentile

Median

25th percentile

Minimum value

Siliciclastic-rock 

aquifers

Carbonate-rock 

aquifers

EXPLANATION

A Statistical group from 

nonparametric Tukey’s 

test

35 Number of samples

Dolomite

Lithologic group and

aquifer type

Limestone

Limestone

and Dolomite

Shale

Mixed 

Siliciclastic

100

1,000

10,000

Radon level,

in picocuries per liter

62 46 53 46 35

AABABBB

Proposed Alternate

Maximum Contaminant 

Level

Proposed Maximum

Contaminant Level

Figure 35. Distribution of radon levels in groundwater samples 

by lithologic group and aquifer type in the Valley and Ridge 

aquifers, 1993–2002.
Summary and Conclusions 55

Distribution of Sites with Background 

Concentration and Sites with Evidence of 

Anthropogenic Contamination

Of the 265 sites sampled in the Valley and Ridge aquifers, 55 showed no clear indication of marked anthropogenic 

effects as indicated by the absence of pesticide or VOC detections and low nitrate concentrations (less than 2 mg/L). The 

abundance and distribution of these 55 sites provide a point of 

reference for background conditions and illustrate the spatial 

extents of human alteration of groundwater quality in the Valley and Ridge aquifers. Most of these sites with background 

concentrations (84 percent) were located in siliciclastic-rock 

aquifers, even though the sites in siliciclastic-rock aquifers 

compose only 31 percent of the total sites. Although only 

16 percent of the sites overall had surrounding land use classified as undeveloped, 27 percent of the sites with background 

concentrations were in undeveloped areas. Only 4 percent 

of wells in carbonate-rock aquifers classified as having 

agricultural land use surrounding the wells had background 

concentrations, although this category composed more than 

40 percent of the wells overall. Given that a high percentage 

of background sites are in siliciclastic-rock aquifers and the 

tendency toward lower dissolved oxygen levels as water ages 

(fig. 10), it is not surprising that a majority of background sites 

were anoxic—40 percent anoxic compared to 33 percent oxic. 

Further, it may be reasonable to conclude that background 

conditions are most often observed in older (anoxic) water 

that has not been influenced by recent landscape change. Of 

the sites in the siliciclastic-rock aquifers, more than half of the 

sites (58 percent) had limited or no influence of anthropogenic 

alteration. This was true of only small fraction of sites (2 percent) in carbonate-rock aquifers.

In contrast, a similar number of sites in the total set 

(57 out of 265) showed clear indications of anthropogenic 

influence as indicated by one or more pesticides or VOCs 

exceeding health-related benchmark quotients of 0.1 or nitratenitrogen concentrations exceeding 10 mg/L. These sites were 

nearly all (54 out of 57) located in carbonate-rock aquifers 

and were associated with agricultural (79 percent) or urban 

(16 percent) land uses. As might be expected, the majority of 

sites with anthropogenic influence (96 percent) were oxic, suggesting a system in which relatively young water in carbonaterock aquifers respond more quickly and clearly to surface 

processes. Overall, 54 sites (or 30 percent) in carbonate-rock 

aquifers had groundwater quality at or approaching levels of 

potential concern for human health. Only 3 sites (4 percent) 

in siliciclastic-rock aquifers had groundwater quality at or 

approaching levels of potential concern for human health. 

Disparities in the spatial distributions of contaminated 

and background sites in the Valley and Ridge aquifers suggest 

opposing associations of groundwater quality with groundwater age and the susceptibility of aquifers to the entry and 

movement of contaminants. In the presence of such association, and providing that substantial sources exist (coming from 

land uses), observed groundwater-quality conditions at any 

location might be expected to correlate with some combination of landscape position and dissolved oxygen. Generally, 

relative distance downgradient from ridges (as indicated by 

NLP) was somewhat greater for background sites than for 

sites of concern (fig. 36). Among carbonate-rock sites, the 

median NLP of background sites was 0.83 compared to 0.63 

for sites of concern. Among siliciclastic-rock sites, the median 

NLP of background sites was 0.77 compared to 0.70 for sites 

of concern. 

Beyond the well-established associations of oxic conditions with carbonate-rock aquifers and anoxic conditions with 

siliciclastic-rock aquifers, comparisons of background sites 

and sites of concern across ranges of NLP and dissolved oxygen suggest three possible inferences. 

• First, anthropogenic effects and background conditions 

can be observed at any position in the landscape.

• Second, oxic conditions in both aquifer types tend to 

be variable in the middle topographic section and tend 

toward more anoxic conditions in the lower topographic sections. 

• Third, evidence of the importance of physical properties may only become clear where conditions depart 

from the usual within a given aquifer type. For 

example, sites of concern in siliciclastic-rock aquifers 

were all high in dissolved oxygen, and background 

sites in carbonate-rock aquifers were all low in dissolved oxygen and very low in the topographic section 

(high NLP). 

Summary and Conclusions

Groundwater samples were collected from 230 wells and 

35 springs in 11 networks within the Valley and Ridge aquifers 

during 1993-2002 as part of the U.S. Geological Survey 

(USGS) National Water-Quality Assessment (NAWQA) Program. The results of sample analyses from these studies were 

combined to evaluate the role of rock type, land use, redox 

conditions, and relative landscape position in the occurrence 

and distribution of nitrate, pesticides, volatile organic compounds (VOCs), fecal bacteria, and radon.

Patterns of groundwater quality mainly reflect the two 

principal aquifer types: carbonate-rock and siliciclastic-rock 

aquifers. Specific conductance, alkalinity, calcium concentrations, and calcite saturation index were typically higher in 

water samples from sites in carbonate-rock aquifer networks, 

and iron and manganese concentrations were higher in water 

from samples in siliciclastic-rock aquifers, except in areas of 

the Tennessee River basin. Indicators of human effects, such as 

elevated nitrate concentrations and detections of pesticides and 

VOCs, were greatest and most frequent in samples from the 

carbonate-rock aquifers. Results for carbonate-rock aquifers 
56 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

0.1 0.3 0.5 0.7 0.9

Normalized lateral position

0

2

4

6

8

10

12

Dissolved oxygen, in milligrams per liter

Siliciclastic-rock aquifer - Background concentration

Carbonate-rock aquifer - Background concentrations

EXPLANATION

Siliciclastic-rock aquifer - Concentrations of concern 

Carbonate-rock aquifer - Concentrations of concern

Figure 36. Normalized lateral position and dissolved oxygen concentration in groundwater samples from the Valley 

and Ridge aquifers, 1993–2002, for sites with background concentrations consisting of no detects for volatile organic 

compounds or pesticides and nitrate less than 2 milligrams per liter, and sites of concern which had pesticide or volatile 

organic compound concentrations greater or equal to 0.1 times health benchmark values or nitrate greater than or equal to 

10 milligrams per liter.
Summary and Conclusions 57

may be somewhat skewed by the inclusion of one urban network, which accounted for 65 percent of all VOC detections in 

the Valley and Ridge aquifers. E. coli counts were significantly 

higher in water samples from sites in carbonate-rock aquifers, 

but radon levels were significantly higher in water from sites 

in siliciclastic-rock aquifers. 

The strong relation between aquifer type and water 

quality is reflected in comparisons between groundwater 

samples and safe drinking-water standards and humanhealth benchmarks established by the U.S. Environmental 

Protection Agency (USEPA) and other agencies. The maximum contaminant level (MCL) for nitrate was exceeded in 

samples from about 12 percent of sites; 90 percent of these 

exceedances were in samples from carbonate-rock aquifers. 

The insecticide dieldrin was the only pesticide to exceed a 

human-health benchmark, and these exceedances were only 

in samples from urban wells in carbonate-rock aquifers. 

Three other pesticides (atrazine, simazine, and cyanazine) 

were within an order of magnitude of benchmarks, generally in agricultural wells in carbonate-rock aquifers. Five 

VOCs [chloroform, tetrachloroethene (PCE), trichloroethene 

(TCE), benzene, and carbon tetrachloride] were within an 

order of magnitude of human-health benchmarks for multiple 

samples from sites in carbonate-rock aquifers. E. coli were 

present and exceeded the MCL in about 10 percent of wells 

in siliciclastic-rock aquifers, 30 percent of wells in carbonaterock aquifers, and 90 percent of springs (all carbonate). Radon 

levels exceeded a proposed MCL of 300 picocuries per liter 

(pCi/L) at 74 percent of sites tested without regard to aquifer 

type, but five samples from sites in siliciclastic-rock aquifers 

had radon amounts that exceeded the alternative maximum 

contaminant level of 4,000 pCi/L. Human-health concerns 

from elevated contaminant concentrations are an important 

finding, especially because most of the sites in this study are 

domestic supply wells, which are infrequently studied and 

commonly unregulated.

Overall, samples from 57 sites had sufficient contamination to be at or approaching levels of potential human health 

concern for pesticides, VOCs, or nitrate. Samples from 55 

sites had no detectable pesticides or VOCs and nitrate-nitrogen 

concentrations below 2 milligrams per liter (mg/L). Almost 

all of the sites with concentrations at or approaching levels of 

concern (95 percent) were in carbonate-rock aquifers; a majority of background sites (84 percent) were in siliciclastic-rock 

aquifers. Oxic conditions were prevalent in carbonate-rock 

aquifers and may reflect the relatively young age of water 

associated with contamination. Background sites in siliciclastic-rock aquifers were more frequently anoxic (40 percent) or 

mixed, which may suggest a prevalence of older water. 

The land-use activities around wells and springs were 

found to be significant in explaining variations in concentration of a number of constituents including nitrate, pesticides, 

and E. coli. Generally, agricultural activities were associated 

with the highest concentrations and the greatest number of 

detections of these constituents. Samples from wells in urban 

areas had the greatest number of VOC detections. Overall, 

concentrations and detection frequencies were lowest in 

undeveloped areas. A measure of the relative topographic 

position between ridge and stream (NLP) correlated with 

several water-quality characteristics, but relations were not 

monotonic. Mineral constituents tend to increase with the 

residence time of groundwater. Specific conductance, calcite 

and dolomite saturation indices, and sodium concentrations, 

all generally increased with relative distance from ridge to 

valley [normalized lateral position (NLP)]. Dissolved oxygen 

concentrations decreased as NLP increased but only in the 

lowest topographic section and particularly in siliciclasticrock aquifers. Dissolved oxygen and redox state positively 

correlated with detection frequencies for the most commonly 

detected pesticides except tebuthiuron, suggesting that in the 

highly oxygenated aquifers, transport may have greater effect 

than microbial transformation on the presence of pesticides. 

Deethylatrazine/atrazine ratios were highest in oxic water, as 

would be expected because atrazine is transformed to deethylatrazine in oxic environments, and atrazine is more stable in 

anoxic environments. 

Wells and springs in carbonate-rock aquifers in the 

Valley and Ridge are much more likely to have anthropogenic contaminants than wells in siliciclastic-rock aquifers 

because of a combination of aquifer susceptibility and the 

land-use practices preferentially located on the land overlying these aquifers. Thus, the most powerful single predictor 

of elevated groundwater contaminant levels in the Valley and 

Ridge aquifers is rock type, as shown by higher likelihoods of 

elevated nutrients, pesticides, VOCs, and bacteria counts in 

carbonate-rock aquifers and of elevated radon and dissolved 

mineral concentrations in siliciclastic-rock aquifers. This pattern is largely explained by correlations between rock type and 

several spatial and temporal factors that determine sources, 

transport, and accumulation of contaminants in groundwater. 

Urban centers and agriculture, which are sources of nutrients, 

pesticides, VOCs, and bacteria, are most prevalent in areas 

overlying carbonate rocks. Likewise, physical properties of 

carbonate-rock aquifers, notably high secondary porosity from 

the dissolution of carbonate minerals, encourage relatively 

rapid groundwater recharge and transport, increasing the 

vulnerability of these aquifers to contamination from surface 

sources and reducing opportunities for attenuation. Longer 

groundwater residence times and generally anoxic conditions 

enhance the accumulation of dissolved metals and enhance 

degradation of contaminants such as nitrate in siliciclasticrock aquifers. Conversely, though generally oxic conditions 

might tend to accelerate attenuation rates for some contaminants (such as atrazine or toluene), such acceleration is evidently insufficient to have much ameliorative effect given the 

relatively young groundwater age in carbonate-rock aquifers. 

Taken together, this complex of mutually reinforcing or offsetting interactions determine the safety, adequacy, and treatment 

costs of groundwater as a source of water supply in the Valley 

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

Acknowledgments

The authors thank the landowners that allowed access 

to their private wells and springs. Without their cooperation, 

this study would not have been possible. The authors also 

gratefully acknowledge the many well drillers and employees of many state agencies who provided well-construction 

information for domestic wells. The authors would also like 

to acknowledge the following reviewers for their input into 

the development of this report: James A. Kingsbury, George 

E. Harlow, William J. Wolfe, W. Scott Gain, and Michael W. 

Bradley, all of the U.S. Geological Survey. 

References Cited

Ator, S.W., Blomquist, J.D., Brakebill, J.W., Denis, J.M., Ferrari, M.J., Miller, C.V., and Zappia, H., 1998, Water quality 

of the Potomac River Basin, Maryland, Pennsylvania, Virginia, West Virginia, and the District of Columbia, 1992–96: 

U.S. Geological Survey Circular 1166, 38 p.

Ator, S.W., and Denis, J.M., 1997, Relation of the nitrogen 

and phosphorus in ground water to land use in four subunits 

of the Potomac River Basin: U.S. Geological Survey WaterResources Investigations Report 96–4268, 26 p.

Barbash, J.E., and Resek, E.A., 1996, Pesticides in ground 

water—Distribution, trends, and governing factors: Chelsea, 

Mich., Ann Arbor Press, 598 p.

Bickford, T.M., Lindsey, B.D., and Beaver, M.R., 1996, 

Bacteriological quality of ground water used for household 

supply, Lower Susquehanna River Basin, Pennsylvania and 

Maryland: U.S. Geological Survey Water-Resources Investigations Report 96–4212, 31 p. 

Brahana, J.V., Mulderink, D., Macy, J.A., and Bradley, 

M.W., 1986, Preliminary delineation and description of the 

regional aquifers of Tennessee—The East Tennessee aquifer 

system: U.S. Geological Survey Water-Resources Investigations Report 82–4091, 30 p.

Briel, L.I., 1997, Water quality in the Appalachian Valley and 

Ridge, the Blue Ridge, and the Piedmont Physiographic 

Provinces, eastern United States: U.S. Geological Survey 

Professional Paper 1422-D, 115 p.

Carter, J.M., Delzer, G.C., Kingsbury, J.K., and Hopple, J.A., 

2007, Concentration data for anthropogenic organic compounds in ground water, surface water, and finished water 

of selected community water systems in the United States, 

2002–05: U.S. Geological Survey Data Series 268, 30 p.

Chapelle, F.H., Novak, John, Parker, John, Campbell, B.G., and 

Widdowson, M.A., 2007, A framework for assessing the sustainability of monitored natural attenuation: U.S. Geological 

Survey Circular 1303, 35 p.

Davies, W.E., 1968, Physiography in mineral resources of the 

Appalachian Region—A compilation of information on 

the mineral resources, mineral industry, and geology of the 

Appalachian Region: Geological Survey Professional Paper 

580, U.S. Geological Survey and the U.S. Bureau of Mines, 

United States Government Printing Office, Washington, D.C.

DeSimone, L.A., Hamilton, P.A., Gilliom, R.J., 2009, Quality of water from domestic wells in principal aquifers of the 

United States, 1991–2004—Overview of major findings: 

U.S. Geological Survey Circular 1332, 48 p.

Dicken, C.L., Nicholson, S.W., Horton, J.D., Foose, M.P., and 

Mueller, J.A.L., 2005a, Integrated geologic map databases 

for the United States—Alabama, Florida, Georgia, Mississippi, North Carolina, and South Carolina: U.S. Geological 

Survey Open-File Report 2005–1323, accessed October 31, 

2008, at http://pubs.usgs.gov/of/2005/1323/.

Dicken, C.L., Nicholson, S.W., Horton, J.D., Kinney, S.A., 

Gunther, G., Foose, M.P., and Mueller, J.A.L., 2005b, Integrated geologic map databases for the United States—Delaware, Maryland, New York, Pennsylvania, and Virginia: U.S. 

Geological Survey Open-File Report 2005–1325, accessed 

October 31, 2008, at http://pubs.usgs.gov/of/2005/1325/.

Donnelly, C.A., and Ferrari, M.J., 1997, Summary of pesticide data from streams and wells in the Potomac River 

Basin: U.S. Geological Survey Open-File Report 97-666, 

accessed December 28, 2009, at http://md.water.usgs.gov/

publications/ofr-97-666/ofr-97-666.html.

Falcone, J., 2003, Coverages for 1:100k stream tiles, assembled 

from NHD 1:100k streams: U.S. Geological Survey digital 

data, accessed February 19, 2008, at ftp://disftp.er.usgs.gov/

pub/NAWQA/ecology/GIS_DATA/streams.

Faure, G., 1986, Principles of isotope geology: New York, John 

Wiley and Sons, Inc., 589 p.

Fenneman, N.M., 1938, Physiography of Eastern United States: 

New York, McGraw-Hill, 714 p.

Fenneman, N.M., and Johnson, D.W., 1946, Physical divisions 

of the United States: U.S. Geological Survey Physiography 

Committee Special Map, scale 1:7,000,000.

Ferrari, M.J., and Ator, S.W., 1995, Nitrate in ground water in 

the Great Valley Carbonate subunit of the Potomac River 

Basin: U.S. Geological Survey Water-Resources Investigations Report 95–4099, 6 p.
References Cited 59

Field, M.S., 1993, Karst hydrology and chemical contamination: Journal of Environmental Systems, v. 22, no. 1, 

p.1–26.

Fields, Scott, 2004, Global nitrogen—Cycling out of control: Environmental Health Perspectives, v. 112, no. 10, 

p. A556–A563.

Fischer, J.M., Riva-Murray, Karen, Hickman, R.E., Chichester, 

D.C., Brightbill, R.A., Romanok, R.M., and Bilger, M.D., 

2004, Water quality in the Delaware River Basin, Pennsylvania, New Jersey, New York, and Delaware, 1998–2001: 

U.S. Geological Survey Circular 1227, 38 p.

Foth, H.D., and Schafer J.W., 1980, Soil geography and land 

use: New York, John Wiley and Sons, Inc., 484 p.

Fuhrer, G.J., Morace, J.L., Johnson, H.M., Rinella, J.F., 

Ebbert, J.C., Embrey, S.S., Waite, I.R., Carpenter, K.D., 

Wise, D.R., and Hughes, C.A., 2004, Water quality in the 

Yakima River Basin, Washington, 1999–2000: U.S. Geological Survey Circular 1237, 44 p.

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of pesticides in water 

by graphitized carbon-based solid-phase extraction and 

high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations 

Report 01–4134, 73 p.

Gburek, W.J., and Folmar, G.J., 1999, Patterns of contaminant 

transport in a layered fractured aquifer: Journal of Contaminant Hydrology, v. 37, no. 1–2, p. 87–109.

Gilliom, R.J., Barbash, J.E., Crawford, C.G., Hamilton, P.A., 

Martin, J.D., Nakagaki, Naomi, Nowell, L.H., Scott, J.C., 

Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 2006, 

The quality of our Nation’s waters—Pesticides in the 

Nation’s streams and ground water, 1992–2001: U.S. Geological Survey Circular 1291, 172 p.

Hampson, P.S., Treece, M.W., Jr., Johnson, G.C., Ahlstedt, 

S.A., and Connell, J.F., 2000, Water quality in the upper 

Tennessee River Basin, Tennessee, North Carolina, Virginia, 

and Georgia, 1994–98: U.S. Geological Survey Circular 

1205, 32 p.

Harlow, G.E., Orndorff, R.C., Nelms, D.L., Weary, D.J., and 

Moberg, R.M., 2004, Hydrogeology and ground-water 

availability in the carbonate aquifer system of Frederick 

County, Virginia: U.S. Geological Survey Scientific Investigations Report 2005–5161, 30 p.

Helsel, D.R., 2005, Nondetects and data analysis—Statistics 

for censored environmental data: New Jersey, John Wiley 

and Sons, Inc., 250 p.

Helsel, D.R., and Hirsch, R.W., 2002, Statistical methods in 

water resources: Techniques of Water-Resources Investigations of the U.S. Geological Survey, book 4, 510 p.

Hem, J.D., 1985, Study and interpretation of the chemical 

characteristics of natural water: U.S. Geological Survey 

Water-Supply Paper 2254, 263 p.

Hinkle, S.R., Shapiro, S.D., Plummer, L.N., Busenberg, 

Eurybiades, Widman, P.K., Casile, G.C., and Wayland, J.E., 

2010, Estimates of apparent tracer-based piston-flow ages 

of groundwater from selected sites—National Water-Quality 

Assessment Program, 1992–2005: U.S. Geological Survey 

Scientific Investigations Report 2010–5229, 90 p., accessed 

June 28, 2011, at http://pubs.usgs.gov/sir/2010/5229/.

Hitt, K.J., and Nakagaki, N., 2006, National Water-Quality 

Assessment (NAWQA) study-unit investigations in the conterminous United States, 1991–2001 [digital data], accessed 

July 30, 2008, at http://water.usgs.gov/GIS/metadata/

usgswrd/XML/nawqacyc1.xml.

Hollyday, E.F., and Hileman, G.E., 1996, Hydrogeologic terranes and potential yield of water to wells in the Valley and 

Ridge Physiographic Province in the Eastern and Southeastern United States: U.S. Geological Survey Professional 

Paper 1422-C, 30 p.

Hollyday, E.F., and Smith, M.A., 1990, Large springs in the 

Valley and Ridge Province in Tennessee: U.S. Geological 

Survey Water-Resources Investigations Report 89–4205, 

9 p.

Hutson, S.S., Barber, N.L., Kenny, J.F., Linsey, K.S., Lumia, 

D.S., and Maupin, M.A., 2004, Estimated use of water in 

the United States in 2000: U.S. Geological Survey Circular 

1268, 52 p.

Johnson, G.C., 2002, Water quality of springs in the Valley 

and Ridge Physiographic Province in the Upper Tennessee River Basin, 1997: U.S. Geological Survey WaterResources Investigations Report 02–4180, 24 p.

Johnson, T.B., McKay, L.D., Layton, A.C., Jones, S.W., Johnson, G.C., Cashdollar, J.L., Dahling, D.R., Villegas, L.F., 

Fout, G.S., Williams, D.E., and Sayler, G., 2010, Viruses 

and bacteria in karst and fractured rock aquifers in East Tennessee, USA: Journal of Groundwater, v. 48, accessed May 

13, 2010, at http://www3.interscience.wiley.com/cgi-bin/

fulltext/123325116/PDFSTART.
60 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

Kaufman, D.D., and Kearney, P.C., 1970, Microbial degradation of s-triazine herbicides: Residue Reviews, v. 32, 

p. 235–265. 

Kerle, E.A., Jenkins, J.J., and Vogue, P.A., 1996, Understanding pesticide persistence and mobility for groundwater and 

surface water protection: Oregon State University Extension 

Service, EM 8561, 7 p.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, 

Ground-water data-collection protocols and procedures for 

the National Water-Quality Assessment Program—Collection and documentation of water-quality samples and related 

data: U.S. Geological Survey Water-Resources Investigations Report 95–399, 114 p.

Landon, M.K., Belitz, Kenneth, Jurgens, B.C., Kulongoski, 

J.T., and Johnson, T.D., 2010, Status and understanding of 

groundwater quality in the Central–Eastside San Joaquin 

Basin, 2006—California GAMA Priority Basin Project: 

U.S. Geological Survey Scientific Investigations Report 

2009–5266, 97 p.

 Lapham, W.W., Wilde, F.D., and Koterba, M.T., 1997, Guidelines and standard procedures for studies of ground-water 

quality—Selection and installation of wells, and supporting 

documentation: U.S. Geological Survey Water-Resources 

Investigations Report 96–4233, 110 p.

Lawrence, S.J., 2006, Description, properties, and degradation 

of selected volatile organic compounds detected in ground 

water—A review of selected literature: U.S. Geological Survey Open-File Report 2006–1338, 62 p., available at http://

pubs.usgs.gov/ofr/2006/1338/.

Leibundgut, C., 1998, Vulnerability of karst aquifers, Karst 

Hydrology, Proceedings of Workshop W2 held at Rabat, 

Morocco, April–May 1997, IAHS Publ. no. 247, 16 p.

Lindsey, B.D., and Ator, S.W., 1996, Radon in ground water 

of the Lower Susquehanna and Potomac River Basins: U.S. 

Geological Survey Water-Resources Investigations Report 

96–4156, 6 p.

Lindsey, B.D., Berndt, M.P., Katz, B.G., Ardis, A.F., and 

Skach, K.A., 2009, Factors affecting water quality in 

selected carbonate aquifers in the United States, 1993–2005: 

U.S. Geological Survey Scientific Investigations Report 

2008–5240, 117 p.

Lindsey, B.D., Breen, K.J., Bilger, M.D., and Brightbill, R.A., 

1998, Water quality in the Lower Susquehanna River Basin, 

Pennsylvania and Maryland, 1992–95: U.S. Geological 

Survey Circular 1168, 38 p. 

Lindsey, B.D., Falls, W.F., Ferrari, M.J., Zimmerman, T.M., 

Harned, D.A., Sadorf, E.M., and Chapman, M.J., 2006, 

Factors affecting occurrence and distribution of selected 

contaminants in ground water from selected areas in the 

Piedmont Aquifer System, eastern United States, 1993–

2003: U.S. Geological Survey Scientific Investigations 

Report 2006–5104, 72 p.

Lindsey, B.D., Katz, B.G., Berndt, M.P., Ardis, A.F., and 

Skach, K.A., 2010, Relations between sinkhole density and 

anthropogenic contaminants in selected carbonate aquifers 

in the eastern United States: Environmental Earth Sciences, 

v. 60, no. 5, p. 1073–1090.

Lindsey, B.D., Loper, C.A., and Hainly, R.A., 1997, Nitrate in 

ground water and stream base flow in the Lower Susquehanna River Basin, Pennsylvania and Maryland: U.S. 

Geological Survey Water-Resources Investigations Report 

97–4146, 66 p.

Lindsey, B.D., Phillips, S.W., Donnelly, C.A., Speiran, G.K., 

Plummer, L.N., Bohlke, J.F., Focazio, M.J., Burton, W.C., 

and Busenberg, Eurybiades, 2003, Residence times and 

nitrate transport in ground water discharging to streams in 

the Chesapeake Bay Watershed: U.S. Geological Survey 

Water-Resources Investigations Report 03–4035, 201 p. 

Lindsey, B.D., Rasberry, J.S., and Zimmerman, T.M., 2002, 

Microbiological quality of noncommunity supply wells in 

carbonate and crystalline aquifers of Pennsylvania: U.S. 

Geological Survey Water-Resources Investigations Report 

01–4076, 30 p.

Lloyd, O.B., Jr., and Lyke, W.I., 1995, Ground water atlas of 

the United States—Segment 10, Illinois, Indiana, Kentucky, 

Ohio, and Tennessee: U.S. Geological Survey Hydrologic 

Investigations Atlas 730–K, 30 p.

Loop, C., and White, W.B., 2001, A conceptual model for 

DNAPL transport in karst ground water basins: Ground 

Water, v. 39, no. 1, p. 119–127.

Mackay, Donald, Shiu, W.Y., and Ma, K.C., 1992, Illustrated 

handbook of physical-chemical properties of environmental fate for organic chemicals, Volume 1, Monochromatic 

hydrocarbons, chlorobenzenes and PCBs: Chelsea, Mich., 

Lewis Publishers, 697 p. 

Martin, J.D., 1999, Quality of pesticide data from environmental water samples collected for the National Water-Quality 

Assessment Program, 1992–96, and examples of the use of 

quality-control information in water-quality assessments, 

accessed June 23, 2009, at http://water.usgs.gov/nawqa/

pnsp/pubs/qcsummary.html.
References Cited 61

Martin, J.D., 2001, Variability of pesticide detections and 

concentrations in field replicate water samples collected for 

the National Water-Quality Assessment Program, 1992–97: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4178, 84 p.

Martin, J.D., Gilliom, R.J., and Schertz, T., 1998, Summary 

and evaluation of pesticides in field blanks collected for the 

National Water-Quality Assessment Program, 1992–1995: 

U.S. Geological Survey Open-File Report 98–4112, 102 p.

Maupin, M.A., and Barber, N.L., 2005, Estimated withdrawals from principal aquifers in the United States, 2000: U.S. 

Geological Survey Circular 1279, 47 p.

Maupin, M.A., and Arnold, T.L., 2010, Estimates for selfsupplied domestic withdrawals and population served for 

selected principal aquifers, calendar year 2005: U.S. Geological Survey Open-File Report 2010–1223, 10 p.

McCoy, K.J., and Kozar, M.D., 2007, Relation of chlorofluorocarbon ground-water age dates to water quality in the 

aquifers of West Virginia: USGS Scientific Investigations 

Report 2006–5221, 37 p. 

McGuinness, C.L., 1963, The role of ground water in the 

national water situation: U.S. Geological Survey WaterSupply Paper 1800, 1121 p.

McMahon, P.B., and Chapelle, F.H., 2008, Redox processes 

and water quality of selected principal aquifer systems: Ground Water, v. 46, no. 2, p. 259–271.

Meyer, Gerald, 1965, Geology and mineral resources of the 

region, in Schneider, W.J., and others, Water resources of 

the Appalachian region, Pennsylvania to Alabama: U.S. 

Geological Survey Hydrologic Atlas 198, Sheet 3.

Milanovic, P.T., 1981, Karst hydrogeology: Denver, Water 

Resources Publications, 434 p.

Miller, J.A., 1990, Ground water atlas of the United States—

Segment 6, Alabama, Florida, Georgia, South Carolina: 

U.S. Geological Survey Hydrologic Investigations Atlas 

730-G, 28 p.

Musgrove, M., and Banner, J.L., 2004, Controls on the spatial 

and temporal variability of vadose dripwater geochemistry—Edwards Aquifer, Central Texas: Geochimica et 

Cosmochimica Acta, v. 68, p. 1007–1020.

Nakagaki, Naomi, and Wolock, D.M., 2005, Estimation of 

agricultural pesticide use in drainage basins using land 

cover maps and county pesticide data: U.S. Geological 

Survey Open-File Report 2005–1188, 46 p. 

Nakagaki, Naomi, Price, C.V., Falcone, J.A., Hitt, K.J., and 

Ruddy, B.C., 2007, Enhanced national land cover data 1992 

(NLCDe 92) [digital data], accessed March 31, 2008, at 

http://water.usgs.gov/GIS/metadata/usgswrd/XML/

nlcde92.xml.

Nelms, D.L., Harlow, G.E., Plummer, L.N., and Busenberg, 

E., 2003, Aquifer susceptibility in Virginia, 1998–2000: 

U.S. Geological Survey Water-Resources Investigations 

Report 03–4278, 58 p.

Nicholson, S.W., Dicken, C.L., Horton, J.D., Foose, M.P., 

Mueller, J.A.L., and Hon, R., 2007, Preliminary integrated 

geologic map databases for the United States—Connecticut, 

Maine, Massachusetts, New Hampshire, New Jersey, Rhode 

Island, and Vermont, Version 1.1: U.S. Geological Survey 

Open-File Report 2005-1272, accessed October 31, 2008, at 

http://pubs.usgs.gov/of/2006/1272/.

Nicholson, S.W., Dicken, C.L., Horton, J.D., Labay, K.A., 

Foose, M.P., and Mueller, J.A.L., 2005, Preliminary 

integrated geologic map databases for the United States—

Kentucky, Ohio, Tennessee, and West Virginia, Version 

1.1: U.S. Geological Survey Open-File Report 2005–1324, 

accessed October 31, 2008, at http://pubs.usgs.gov/

of/2005/1324/.

Nolan, B.T., 1999, Nitrate behavior in ground waters of the 

southeastern USA: Journal of Environmental Quality, v. 28, 

p. 1518–1527.

Otton, J.K., 1992, The geology of radon: U.S. Geological 

Survey, General Interest Publications of the U.S. Geological 

Survey, 28 p.

Price, C.V., Nakagaki, N., Hitt, K.J., and Clawges, R.M., 

2007, Enhanced historical land-use and land-cover data 

sets of the U.S. Geological Survey: U.S. Geological Survey 

Data Series 240 [digital data], accessed June 25, 2010, 

at http://pubs.usgs.gov/ds/2006/240.

PRISM Group at Oregon State University, 2006a, United 

States average monthly or annual maximum temperature, 1971–2000: PRISM Group at Oregon State 

University digital data, accessed May 19, 2009, at 

http://www.prism.oregonstate.edu/products/matrix.

phtml?vartype=tmax&view=data.

PRISM Group at Oregon State University, 2006b, United 

States average monthly or annual minimum temperature, 1971–2000: PRISM Group at Oregon State 

University digital data, accessed May 19, 2009, at 

http://www.prism.oregonstate.edu/products/matrix.

phtml?vartype=tmin&view=data.
62 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

PRISM Group at Oregon State University, 2006c, United 

States average monthly or annual precipitation, 1971–2000: 

PRISM Group at Oregon State University digital data, 

accessed May 19, 2009, at http://www.prism.oregonstate.

edu/products/matrix.phtml?vartype=ppt&view=data.

Quinlan, J.F., and Ewers, R.O., 1985, Ground-water flow 

in limestone terranes—Strategy rationale and procedure 

for reliable, efficient monitoring of ground-water quality 

in karst areas, in National Symposium and Exposition on 

Aquifer Restoration and Ground-Water Monitoring, 5th, 

Columbus, Ohio, Proceedings: Dublin, Ohio, National 

Water Well Association, p. 197–234.

Quinlan, J.F., Smart, P.L., Schindel, G.M., Alexander, E.C., 

Edwards, A.J., and Smith, A.R., 1991, Recommended 

administrative/regulatory definition of karst aquifers, 

principles for classification of carbonate aquifers, practical 

evaluation of vulnerability of karst aquifers, and determination of optimum sampling frequency at springs, in Conference on Hydrogeology, Ecology, Monitoring, and Management of Ground Water in Karst terrains, 3rd, Proceedings: 

Ground Water Management (Publisher: Dublin, Ohio, Water 

Well Journal Publishing Co.), v. 10, p. 573–635.

Ruddy, B.C., Lorenz, D.L., and Mueller, D.K., 2006, Countylevel estimates of nutrient inputs to the land surface of the 

conterminous United States, 1982–2001: U.S. Geological 

Survey Scientific Investigations Report 2006–5012, 17 p.

Schnabel, R.R., Urban, J.B., and Gburek, W.J., 1993, Hydrologic controls in nitrate, sulfate, and chloride concentrations: Journal of Environmental Quality, v. 22, p. 589–596.

Seaber, P.R., Brahana, J.V., and Hollyday, E.F., 1988, Region 

20, Appalachian Plateaus and Valley and Ridge, in Back, 

W., Rosenshein, J.S., and Seaber, P.R., eds., Hydrogeology: 

Boulder, Colo., Geological Society of America, The Geology of North America, v. O-2, 524 p.

Seybold, C.A., and Mersie, W., 1999, Metolachlor fate and 

mobility in a tidal wetland soil: Wetlands, v. 19, no. 1, 

p. 228–235.

Siwiec, S.F., Hainly, R.A., Lindsey, B.D., Bilger, M.D., 

and Brightbill, R.A., 1997, Water-quality assessment of 

the Lower Susquehanna River Basin, Pennsylvania and 

Maryland—Design and implementation of water-quality 

studies, 1992–95: U.S. Geological Survey Open-File Report 

97–583, 121 p.

Spalding, R.F., and Exner, M.E., 1993, Occurrence of nitrate 

in groundwater—A review: Journal of Environmental Quality, v. 22, p. 392–402.

Stueber, A.M., and Criss, R.E., 2005, Origin and transport of 

dissolved chemicals in a karst watershed, southwestern Illinois: Journal of the American Water Resources Association, 

v. 41, no. 2, p. 267–290. 

Sun, P-C.P., Criner, J.H., and Poole, J.L., 1963, Large springs 

of East Tennessee: U.S. Geological Survey Water-Supply 

Paper 1755, 52 p.

Swain, L.A., Hollyday, E.F., Daniel, C.C., III, and Zapecza, 

O.S., 1991, Plan of study for the regional aquifer-system 

analysis of the Appalachian Valley and Ridge, Piedmont, 

and Blue Ridge Physiographic Provinces of the eastern and 

southeastern United States, with a description of study area 

geology and hydrogeology: U.S. Geological Survey WaterResources Investigations Report 91–4066, 44 p.

Toccalino, P.L., Norman, J.E., Booth, N.L., and Zogorski, J.S., 

2008, Health-based screening levels—A tool for evaluating 

what water-quality data may mean to human health: U.S. 

Geological Survey, National Water-Quality Assessment 

Program, accessed April 1, 2009, at http://water.usgs.gov/

nawqa/HBSL/.

Trapp, H., Jr., and Horn, M.A., 1997, Ground water atlas 

of the United States—Segment 11, Delaware, Maryland, 

New Jersey, North Carolina, Pennsylvania, Virginia, West 

Virginia: U.S. Geological Survey Hydrologic Investigations 

Atlas 730-L, 24 p.

U.S. Army Corps of Engineers, 2001, Automated IFSAR Terrain Analysis System, Defense Advanced Research Projects 

Agency (DOD) Information Sciences Office, accessed 

February 20, 2008, at http://www.tec.army.mil/publications/

ifsar/lafinal08_01/cover/cover_frame.htm.

U.S. Bureau of the Census, 1990a, 1990 state & state equivalent areas [digital data], accessed June 11, 2008, 

at http://www.census.gov/geo/www/cob/st1990.html.

U.S. Bureau of the Census, 1990b, 1990 generalized block 

groups for the conterminous United States: Washington, 

D.C., U.S. Bureau of the Census, accessed September 09, 

2006, at http://www.census.gov/geo/www/cob/bg1990.html.

U.S. Bureau of the Census, 1992a, 1990 Census of Population 

and Housing: Summary Tape File 1A: Washington, D.C., 

U.S. Bureau of the Census, accessed September 09, 2006, 

at ftp://ftp.census.gov/census_1990/.

U.S. Bureau of the Census, 1992b, Census of population and 

housing—Summary tape file 3A: Washington, D.C., U.S. 

Bureau of the Census, accessed September 09, 2006, 

at ftp://ftp.census.gov/census_1990/.

U.S. Bureau of the Census, 1999, 1999 Metropolitan Statistical Areas: U.S. Bureau of the Census, Geography Division, 

accessed April 24, 2008, at http://www.census.gov/geo/

www/cob/ma1999.html.

U.S. Bureau of the Census, 2001a, Cartographic Boundary 

Files for Census 2000 Block Groups: U.S. Bureau of the 

Census, Geography Division, accessed April 24, 2008, 

at http://www.census.gov/geo/www/cob/bg2000.html.
References Cited 63

U.S. Bureau of the Census, 2001b, CensusCD 2000 Short 

Form Blocks: U.S. Bureau of the Census, Geography Division, accessed April 24, 2008, at http://www.geolytics.com/

census2000.htm.

U.S. Department of Agriculture, 1986, Urban hydrology for 

small watersheds, Technical Release 55 (2d ed.): NTIS 

PB87-101580, Washington, D.C., Soil Conservation Service.

U.S. Department of Agriculture, 2003, National soil survey handbook, Title 430-VI: U.S. Department of Agriculture, Natural Resources Conservation handbook, 

National Resources Conservation Service, National Soil 

Survey Center.

U.S. Department of Agriculture, Natural Resources Conservation Service, 1994, State Soil Geographic (STATSGO) data 

base for the United States and Puerto Rico [digital data on 

CDROM]: Ft. Worth, Tex., U.S. Department of Agriculture. 

U.S. Department of Agriculture, Natural Resources Conservation Service, 1999, 12-digit watershed boundary data 

1:24,000: National Cartography and Geospatial Center digital data, accessed February 19, 2008, at http://datagateway.

nrcs.usda.gov/.

U.S. Environmental Protection Agency, 1990, The Clean Air 

Act amendments: Washington, D.C., U.S. Congress 101st, 

Sec. 219, p. S.1630-1938, accessed March 30, 2009, at 

http://www.epa.gov/oar/caa/caaa.txt.

U.S. Environmental Protection Agency, 1991, Test methods 

for Escherichia coli in drinking water—Test Method 1105: 

EPA/600/4-91/016, 2 p.

U.S. Environmental Protection Agency, 1992, Secondary 

Drinking Water Regulations—Guidance for nuisance chemicals: EPA 810/K-92-001, accessed May 18, 2009, at http://

www.epa.gov/OGWDW/consumer/2ndstandards.html.

U.S. Environmental Protection Agency, 1997, Drinking water 

advisory—Consumer acceptability advice and health effects 

analysis on methyl-tertiary-butyl ether: Washington, D.C., 

U.S. Environmental Protection Agency, Office of Water, 

EPA-822-F-97-009.

U.S. Environmental Protection Agency, 2001, Total coliform 

rule—A quick reference guide: Washington, D.C., U.S. 

Environmental Protection Agency, Office of Water, EPA 

816-F-010035, 2 p.

U.S. Environmental Protection Agency, 2002, Method 

1603—Escherichia coli (E. coli) in water by membrane 

filtration using modified membrane-thermotolerant Escherichia coli agar (modified mTEC): Washington, D.C., U.S. 

Environmental Protection Agency, Office of Water, EPA821-R-02-023, 9 p. 

U.S. Environmental Protection Agency, 2003, Contaminant 

candidate list regulatory determination support document 

for Aldrin and Dieldrin: Washington, D.C., U.S. Environmental Protection Agency, Office of Water, Standards and 

Risk Management Division, EPA 815-R-03-010, 48 p.

U.S. Environmental Protection Agency, 2006, 2006 Edition of 

the drinking water standards and health advisories: Washington, D.C., U.S. Environmental Protection Agency, Office 

of Water, EPA 822-R-06-013, 18 p.

U.S. Environmental Protection Agency, 2007, List of reformulated gasoline program areas: Office of Transportation 

and Air Quality, accessed March 30, 2009, at http://epa.gov/

otaq/rfg/whereyoulive.htm. 

U.S. Environmental Protection Agency, 2009, Technical Fact 

Sheet—Proposed radon in drinking water rule, accessed 

May 15, 2009, at http://www.epa.gov/safewater/radon/

remove/fact.html.

U.S. Geological Survey, 1985, National Water Summary, 

1984—Hydrologic events, selected water-quality trends, 

and ground-water resources: U.S. Geological Survey WaterSupply Paper 2275, 467 p.

U.S. Geological Survey, 1988, National Water Summary, 

1986—Hydrologic events and ground-water quality: U.S. 

Geological Survey Water-Supply Paper 2325, 560 p.

U.S. Geological Survey, 1999, The quality of our Nation’s 

waters—Nutrients and pesticides: U.S. Geological Survey 

Circular 1225, 82 p.

U.S. Geological Survey, 2002, Shuttle Radar Topography 

Mission (SRTM) Elevation Dataset: SDE raster digital 

data, accessed July 27, 2010, at http://edcsns17.cr.usgs.gov/

EarthExplorer/.

U.S. Geological Survey, 2003, Principal aquifers of the 48 

conterminous United States, Hawaii, Puerto Rico, and the 

U.S. Virgin Islands, accessed April 22, 2008, at http://www.

nationalatlas.gov/mld/aquifrp.html.
64 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002

U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data : U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chaps. A1-A9, available online at http://pubs.water.usgs.

gov/twri9A. 

U.S. National Library of Medicine, 2008, U.S. National 

Library of Medicine ChemID plus Lite database of the U.S. 

National Institute of Health, accessed May 5, 2009, 

at http://chem.sis.nlm.nih.gov/chemidplus/chemidlite.jsp. 

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and VanDriel, N., 2001, Completion of the 

1990’s national land cover dataset for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.

Vogue, P.A., Kerle, E.A., and Jenkins J.J., 1994, Oregon 

State University Extension Pesticide Properties Database, 

in National Pesticide Information Center, accessed May 4, 

2009, at http://npic.orst.edu/ppdmove.htm.

Ward, M.H., deKok, T.M., Levallois, P., Brender, J., Gulis, G., 

Nolan, B.T., and VanDerslice, J., 2005, Workgroup report—

Drinking-water nitrate and health—Recent findings and 

research needs: Environmental Health Perspectives, v. 113, 

no. 11, p. 1607–1614.

Werner, S.L., Burkhardt, M.R., and DeRusseau, S.N., 1996, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—Determination of pesticides in 

water by Carbopak-B solid-phase extraction and high-performance liquid chromatography: U.S. Geological Survey 

Open-File Report 96–216, 42 p.

White, W.B., 1988, Geomorphology and hydrology of karst 

terrains: New York, Oxford University Press, 464 p. 

Wiedemeier, T.H., Swanson, M.A., Moutoux, D.E., Gordon, 

E.K., Wilson, J.T., Wilson, B.H., Kampbell, D.H., Haas, 

P.E., Miller, R.N., Hansen, J.E., and Chapelle, F.H., 1998, 

Technical protocol for evaluating natural attenuation of 

chlorinated solvents in ground water: Cincinnati, Ohio, U.S. 

Environmental Protection Agency, National Risk Management Research Laboratory, Office of Research and Development, EPA/600/R-98/128, 244 p.

Wolfe, W.J., 1996, Hydrology and tree-distribution patterns of 

karst wetlands at Arnold Engineering Development Center, 

Tennessee: U.S. Geological Survey Water-Resources Investigations Report 96–4277, 46 p.

Wolfe, W.J., Haugh, C.J., Webbers, A., and Diehl, T.H., 1997, 

Preliminary conceptual models of the occurrence, fate, and 

transport of chlorinated solvents in karst regions of Tennessee: U.S. Geological Survey Water-Resources Investigations 

Report 97–4097, 80 p.

Wolock, D.M., 1997, STATSGO soil characteristics for the 

conterminous United States: U.S. Geological Survey OpenFile Report 97–656 [digital data], accessed February 17, 

2004, at http://water.usgs.gov/lookup/getspatial?muid.

Wolock, D.M., 2003, Estimated mean annual natural groundwater recharge in the conterminous United States: U.S. 

Geological Survey Open-File Report 03–311 [digital data], 

accessed April 21, 2008, at http://water.usgs.gov/GIS/

metadata/usgswrd/XML/rech48grd.xml.

Yager, R.M., Voss, C.I., and Southworth, S., 2009, Comparison of alternative representations of hydraulic-conductivity 

anisotropy in folded fractured-sedimentary rock—Modeling 

groundwater flow in the Shenandoah Valley (USA): Hydrogeology Journal, v. 17, no. 5, p. 1111–1131.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—Determination of pesticides in water by C-18 solid-phase extraction 

and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring: U.S. Geological Survey 

Open-File Report 95–181, 49 p., available online at http://

wwwnwql.cr.usgs.gov/Public/pubs/OFR95-181/OFR95-181.

html.

Zimmerman, T.M., Zimmerman, M.L., and Lindsey, B.D., 

2001, Relation between selected well-construction characteristics and occurrence of bacteria in private householdsupply wells, south-central and southeastern Pennsylvania, 

2001: U.S. Geological Survey Water-Resources Investigations Report 01–4206, 22 p.

Zogorski, J.S., Carter, J.M., Ivahnenko, I., Lapham, W.W., 

Moran, M.J., Rowe, B.L., Squillace, P.J., and Toccalino, 

P.L., 2006, The quality of our Nation’s waters—Volatile 

organic compounds in the Nation’s ground water and 

drinking-water supply wells: U.S. Geological Survey Circular 1292, 101 p.
Tables 23 and 24
66 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002 Table 23. Detection frequency of 63 pesticides, pesticide degradates, and organic compounds using High Performance Liquid Chromatography and High Performance Liquid Chromatography/Mass Spectrometry for groundwater samples from wells and springs in the Valley and Ridge aquifers, 1993–2002.—Continued [Pesticide types: D, degradate; H, herbicide; I, insecticide; F, fungicide.; W, waste-water indicator; N/A, not applicable; ≥, greater than or equal to; HBSL, health-based screening level (Toccalino and others, 2008); CAS, Chemical Abstract Service; μg/L, micrograms per liter] Compound name CAS number Pesticide type Number of analyses Number of detections at any concentration1 Percent detections at any concentration1 Number of detections greater than 0.01μg/L Percent detections greater than 0.01μg/L Maximum concentration Benchmark level (μg/L) Benchmark type Percent detections greater than benchmark level Percent detections 

≥ 0.1 of the 

benchmark 

level

Compounds analyzed by High Performance Liquid Chromatography

2,4-DB 94-82-6

H 242 0 0 0 0 N/A 200 HBSL 0 0

2,4-D 94-75-7

H 242 1 0.4 1 0.4 0.11 None N/A N/A N/A

2,4,5-T 93-76-5

H 196 0 0 0 0 N/A 70 HBSL 0 0

3-Hydroxy carbofuran 16655-82-6

D 242 0 0 0 0 N/A None N/A N/A N/A

Acifluorfen 50594-66-6

H 242 1 0.4 1 0.4 0.19 90 HBSL 0 0

Aldicarb sulfone 1646-88-4

D 242 0 0 0 0 N/A 7 HBSL 0 0

Aldicarb sulfoxide 1646-87-3

D 242 0 0 0 0 N/A 7 HBSL 0 0

Aldicarb 116-06-3 I 242 0 0 0 0 N/A 9 HBSL 0 0Bentazon 25057-89-0

H 242 4 1.7 4 1.7 0.88 200 HBSL 0 0

Bromacil 314-40-9

H 242 1 0.4 1 0.4 2.24 70 HBSL 0 0

Bromoxynil 1689-84-5

H 242 0 0 0 0 N/A 10 HBSL 0 0

Carbaryl 63-25-2 I 242 0 0 0 0 N/A 40 HBSL 0 0Carbofuran 1563-66-2 I 242 0 0 0 0 N/A None N/A N/A N/AChloro-thalonil 1897-45-6 F 242 0 0 0 0 N/A 5 HBSL 0 0Clopyralid 1702-17-6

H 242 0 0 0 0 N/A None HBSL N/A N/A

DNOC 534-52-1

H 196 0 0 0 0 N/A None N/A N/A N/A

Dacthal-monoacid 887-54-7

D 242 0 0 0 0 N/A None N/A N/A N/A

Dicamba 1918-00-9

D 242 1 0.4 1 0.4 0.21 3,000 HBSL 0 0

Dichlobenil 1194-65-6

H 196 2 1.0 2 1.0 0.21 9 HBSL 0 0

Dichlorprop 120-36-5

H 242 0 0 0 0 N/A 300 HBSL 0 0

Dinoseb 88-85-7

H 196 0 0 0 0 N/A None N/A N/A N/A

Diuron 330-54-1

H 242 8 3.3 6 2.5 0.46 None N/A N/A N/A

Fenuron 101-42-8

H 242 1 0.4 1 0.4 0.021 None N/A N/A N/A

Fluomet-uron 2164-17-2

H 242 0 0 0 0 N/A 4 HBSL 0 0

Linuron 330-55-2

H 242 1 0.4 0 0 0.001 5 HBSL 0 0

MCPA 94-74-6

H 242 0 0 0 0 N/A 30 HBSL 0 0

MCPB 94-81-5

H 242 0 0 0 0 N/A 100 HBSL 0 0

Methomyl 16752-77-5 I 242 0 0 0 0 N/A 200 HBSL 0 0Methiocarb 2032-65-7 I 242 0 0 0 0 N/A 40 HBSL 0 0Neburon 555-37-3

H 242 0 0 0 0 N/A None N/A N/A N/A

Norflurazon 27314-13-2

H 242 1 0.4 1 0.4 0.0142 10 HBSL 0 0

Oryzalin 19044-88-3

H 242 1 0.4 1 0.4 0.05 4 HBSL 0 0

Oxamyl 23135-22-0 I 242 0 0 0 0 N/A None N/A N/A N/APicloram 1918-02-1

H 242 0 0 0 0 N/A None N/A N/A N/A

Propham 122-42-9

H 242 0 0 0 0 N/A 100 HBSL 0 0

Propoxur 114-26-1 I 242 0 0 0 0 N/A 9 HBSL 0 0Silvex 93-72-1

H 196 0 0 0 0 N/A None N/A N/A N/A

Triclopyr 55335-06-3

H 242 0 0 0 0 N/A 400 HBSL 0 0
Table 23 67

Table 23. Detection frequency of 63 pesticides, pesticide degradates, and organic compounds using High Performance Liquid Chromatography and High Performance Liquid Chromatography/Mass Spectrometry for groundwater samples from wells and springs in the Valley and Ridge aquifers, 1993–2002.—Continued[Pesticide types: D, degradate; H, herbicide; I, insecticide; F, fungicide.; W, waste-water indicator; N/A, not applicable; ≥, greater than or equal to; HBSL, health-based screening level (Toccalino and others, 2008); CAS, Chemical Abstract Service; μg/L, micrograms per liter]

Compound name CAS number Pesticide type Number of analyses

Number of 

detections 

at any 

concentration1

Percent 

detections 

at any 

concentration1

Number of 

detections 

greater than 

0.01μg/L

Percent 

detections 

greater than 

0.01μg/L

Maximum 

concentration

Benchmark 

level 

(μg/L) 

Benchmark 

type

Percent 

detections 

greater than 

benchmark 

level

Percent 

detections 

≥ 0.1 of the 

benchmark 

level

Compounds analyzed by High Performance Liquid Chromatography/Mass Spectrometry

2,4-D methyl ester 1928-38-7 D 46 0 0.0 0 0 N/A None N/A N/A N/A3-Keto-carbofuran 16709-30-1 D 46 0 0.0 0 0 N/A None N/A N/A N/ABendiocarb 22781-23-3 I 46 0 0.0 0 0 N/A 9 HBSL 0 0Benomyl 17804-35-2 F 46 1 2.2 1 2.2 0.072 40 HBSL 0 0Bensulfuron-methyl 83055-99-6 H 46 0 0.0 0 0 N/A 1,000 HBSL 0 0CAAT2 3397-62-4 D 46 10 22 7 15 0.0718 None N/A N/A N/ACEAT3 1007-28-9 D 46 11 24 11 24 0.0882 None N/A N/A N/ACaffeine 58-08-2 W 46 5 11 1 2.2 0.0238 None N/A N/A N/AChlorimuron-ethyl 90982-32-4 H 46 0 0 0 0 N/A 600 HBSL 0 0Cycloate 1134-23-2 H 46 0 0 0 0 N/A 40 HBSL 0 0Diphenamid 957-51-7 H 46 0 0 0 0 N/A 200 HBSL 0 0Flumet-sulam 98967-40-9 H 46 0 0 0 0 N/A 7,000 HBSL 0 0Imazaquin 81335-37-7 H 46 3 6.5 2 4.3 0.0452 2,000 HBSL 0 0Imazethapyr 81335-77-5 H 46 0 0 0 0 N/A 2,000 HBSL 0 0Imidacloprid 105827-78-9 I 46 0 0 0 0 N/A 400 HBSL 0 0Metalaxyl 57837-19-1 F 46 1 2.2 1 2.2 0.0548 600 HBSL 0 0Metsulfuron-methyl 74223-64-6 H 46 0 0 0 0 N/A 2,000 HBSL 0 03(4-Chloro-phenyl)-1-methyl urea 5352-88-5 D 46 1 2.2 0 0 0.005 None N/A N/A N/ANico-sulfuron 111991-09-4 H 46 0 0 0 0 N/A 9,000 HBSL 0 0OIET4 2163-68-0 D 46 11 24 6 13 0.0744 70 HBSL 0 0Propi-conazole 60207-90-1 F 46 0 0 0 0 N/A 70 HBSL 0 0Siduron 1982-49-6 H 46 1 2.2 0 0 0.0033 1,000 HBSL 0 0Sulfo-meturon-methyl 74222-97-2 H 46 0 0 0 0 N/A 2,000 HBSL 0 0Terbacil 5902-51-2 H 46 1 2.2 1 2.2 0.0213 90 HBSL 0 0Tribenuron-methyl 101200-48-0 H 30 0 0 0 0 N/A 6 HBSL 0 0

1 Total detection frequency information at any concentration used for this analysis (no common assesment threshold used).2 The compound chlordiamino-s-triazine (CAAT) is derived from the degradation of deethylatrazine, and is also referred to as deethyldeisopropylatrazine (DDA) or didealkyl atrazine. The term CAAT is 

used in this report.

3 The compound 2-chloro-6-ethylamino-4-amino-s-triazine (CEAT) can be derived from either degradation of atrazine (deiospropylatrazine/DIA) or simazine (deethylsimazine). The term CEAT is used in 

this report.

4 The compound 2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine (OIET) is derived from the degradation of atrazine and is also referred to as hydroxyatrazine or HA. The term OIET is used in this 

report.
68 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002 Table 24. Detection frequency of 87 volatile organic compounds in groundwater samples from the Valley and Ridge aquifers, 1993–2003.—Continued [THMs, trihalomethanes; FUM, fumigant related compound; PC, personal care and domestic use product; REF, refrigerants or propellant; SOL, solvent; SYN, organic synthesis compound; μg/L, micrograms per liter; CAS, Chemical Abstract Service; MCL, maximum contaminant level; HBSL, health-based screening level; N/A, not applicable] Volatile organic compound CAS number Type of compound1 Number of detections greater than or equal to 0.2 μg/L Percent detections greater than or equal to 0.2 μg/L Number of detections at any concentration Percent detections at any concentration Number of analyses Maximum concentration (μg/L) Benchmark level (μg/L) Benchmark type2 Percent detections greater than benchmark level Percent detections within a factor of 0.1 of benchmark level Chloroform (trichloromethane) (TCM) 67-66-3 THM 18 9.5 56 29.6 189 61 380 MCL 0 1.59 Methyl tert-butyl ether (MTBE) 1634-04-4 GAS 11 5.9 13 7.0 187 51 NONE N/A N/A 1,1,1-Trichloroethane (TCA) 71-55-6 SOL 10 5.3 24 12.6 190 3 200 MCL 0 0 Tetrachloroethene (PCE) 127-18-4 SOL 9 4.8 24 12.8 188 4.3 5 MCL 0 2.11 Trichloroethene (TCE) 79-01-6 SOL 6 3.2 11 5.8 190 2.7 5 MCL 0 2.11 Bromodichloro-methane (CHBrCl2

) 75-27-4 THM 3 1.6 7 3.7 190 3.5 380 MCL 0 0

cis-1,2-Dichloroethene 156-59-2 SOL 3 1.6 5 2.6 190 4.4 NONE N/A N/AMethyl ethyl ketone (MEK) 78-93-3 SOL 1 1.1 1 1.1 93 2.7 4,000 HSBL 0 0Carbon disulfide 75-15-0 SYN 1 1.1 7 7.4 94 0.25 700 HBSL 0 01,1-Dichloroethane 75-34-3 SOL 2 1.1 5 2.7 188 0.58 NONE N/A N/ABenzene 71-43-2 GAS 2 1.1 4 2.1 188 4.4 5 MCL 0 1.06total Xylene 1330-20-7 GAS 2 1.1 4

4 2.1 188 41 510,000 MCL 0 0

Dichloromethane (Methylene chloride) 75-09-2 SOL 2 1.1 3 1.6 188 0.40 5 MCL 0 0Naphthalene 91-20-3 GAS 2 1.1 2 1.1 188 2.0 100 HBSL 0 0Toluene 108-88-3 GAS 2 1.1 611 5.8 190 12 1,000 MCL 0 01,2,4-Trimethylbenzene 95-63-6 GAS 1 0.6 7

1 0.6 179 12 NONE N/A N/A

p-Isopropyltoluene 99-87-6 GAS 1 0.5 1 0.5 186 0.30 NONE N/A N/ADibromochloro-methane 124-48-1 THM 1 0.5 2 1.1 188 0.40 380 MCL 0 0Carbon tetrachloride (tetrachloromethane) 56-23-5 SOL 1 0.5 1 0.5 188 0.60 5 MCL 0 0.531,3,5-Trimethylbenzene 108-67-8 GAS 1 0.5 1 0.5 189 4.0 NONE N/A N/A1,1-Dichloroethene 75-35-4 SOL 1 0.5 2 1.1 190 0.50 7 MCL 0 0Ethylbenzene 100-41-4 GAS 1 0.5 1 0.5 190 5.4 700 MCL 0 0Isopropylbenzene [(1-Methylethyl) benzene] 98-82-8 GAS 1 0.5 1 0.5 190 0.80 700 HBSL 0 N/An-Propylbenzene 103-65-1 SOL 1 0.5 1 0.5 190 0.60 NONE N/A N/AChloromethane (Methyl Chloride) 74-87-3 SYN 0 0 19 11.9 160 0.09 30 HSBL 0 0Styrene 100-42-5 GAS 0 0 15 7.9 190 0.04 100 MCL 0 0m- & p-Xylene 179601-23-1 GAS 0 0 4

2 2.2 93 0.02 510,000 MCL 0 0

Dichlorodifluoromethane (CFC-12) 75-71-8 REF 0 0 3 1.6 188 0.16 1,000 HBSL 0 01,1,2-Trichlorotrifluoroethane (CFC-113) 76-13-1 REF 0 0 3 1.6 190 0.04 200,000 HBSL 0 0.01,4-Dichlorobenzene (p-dichlorobenzene) 106-46-7 FUM 0 0 3 1.6 190 0.06 NONE N/A N/ADiethyl ether (Ethyl ether, 1,1’-oxybisethane) 60-29-7 SOL 0 0 1 1.1 93 0.06 1000 HBSL 0 0Diisopropyl ether (DIPE) 108-20-3 GAS 0 0 1 1.1 93 0.05 NONE N/A N/Atert-Pentyl methyl ether 994-05-8 GAS 0 0 1 1.1 93 0.17 NONE N/A N/A1,2-Dichloropropane 78-87-5 FUM 0 0 2 1.1 188 0.07 5 MCL 0 0Chloroethane 75-00-3 SOL 0 0 1 0.5 188 0.07 NONE N/A N/ATrichlorofluoro-methane (CFC-11) 75-69-4 REF 0 0 1 0.5 188 0.01 2,000 HBSL 0 0
Table 24 69

Table 24. Detection frequency of 87 volatile organic compounds in groundwater samples from the Valley and Ridge aquifers, 1993–2003.—Continued[THMs, trihalomethanes; FUM, fumigant related compound; PC, personal care and domestic use product; REF, refrigerants or propellant; SOL, solvent; SYN, organic synthesis compound; μg/L, micrograms per liter; CAS, Chemical Abstract Service; MCL, maximum contaminant level; HBSL, health-based screening level; N/A, not applicable]

Volatile organic compound CAS number Type of compound1

Number of 

detections 

greater than 

or equal to 

0.2 μg/L

Percent 

detections 

greater than 

or equal to 

0.2 μg/L

Number of 

detections 

at any 

concentration

Percent 

detections 

at any 

concentration 

Number of 

analyses

Maximum 

concentration

(μg/L)

Benchmark 

level 

(μg/L)

Benchmark 

type2

Percent 

detections 

greater than 

benchmark 

level

Percent 

detections 

within a factor 

of 0.1 of 

benchmark 

level

1,1,1,2-Tetrachloroethane 630-20-6 SOL 0 0 0 0.0 188 N/A 70 HBSL 0 01,1,2,2-Tetrachloroethane 79-34-5 SOL 0 0 0 0.0 188 N/A 0.3 HBSL 0 01,1,2-Trichloroethane 79-00-5 SOL 0 0 0 0.0 188 N/A NONE N/A N/A1,1-Dichloropropene 563-58-6 SYN 0 0 0 0.0 188 N/A NONE N/A N/A1,2,3-Trichlorobenzene 87-61-6 SYN 0 0 0 0.0 188 N/A NONE N/A N/A1,2,3-Trichloropropane 96-18-4 SYN 0 0 0 0.0 188 N/A 40 HSBL 0 01,2,3-Trimethylbenzene 526–73–8 GAS 0 0 0 0.0 93 N/A NONE N/A N/A1,2,4-Trichlorobenzene 120-82-1 SOL 0 0 0 0.0 188 N/A NONE N/A N/A1,2-Dibromo-3-chloropropane (DBCP) 96-12-8 FUM 0 0 0 0.0 188 N/A NONE N/A N/A1,2-Dibromoethane (EDB) 106-93-4 FUM 0 0 0 0.0 190 N/A NONE N/A N/A1,2-Dichlorobenzene 95-50-1 SOL 0 0 0 0.0 188 N/A NONE N/A N/A1,2-Dichloroethane (ethylene dichloride) 107-06-2 SOL 0 0 0 0.0 188 N/A 5 MCL 0 01,3-Dichlorobenzene (m-dichlorobenzene) 541-73-1 SOL 0 0 0 0.0 186 N/A 600 HBSL 0 01,3-Dichloropropane 142-28-9 FUM 0 0 0 0.0 188 N/A NONE N/A N/A2,2-Dichloropropane 594-20-7 FUM 0 0 0 0.0 188 N/A NONE N/A N/A2-Chlorotoluene 95-49-8 SOL 0 0 0 0.0 190 N/A NONE N/A N/A2-Ethyltoluene (1-Ethyl-2-methylbenzene) 611-14-3 GAS 0 0 0 0.0 93 N/A NONE N/A N/A2-Hexanone (Butyl methyl ketone) 591-78-6 SOL 0 0 0 0.0 93 N/A NONE N/A N/A2-Methyl-2-propenitrile (Methyl acrylonitrile) 126-98-7 SYN 0 0 0 0.0 93 N/A 0.7 HSBL 0 03-Chloro-1-propene 107-05-1 SYN 0 0 0 0.0 93 N/A NONE N/A N/A4-Chlorotoluene 106-43-4 SOL 0 0 0 0.0 188 N/A 100 HSBL 0 0Acetone (2-propanone) 67-64-1 SOL 0 0 0 0.0 93 N/A 6,000 HBSL 0 0Acrolein (2-Propenal) 107-02-8 SYN 0 0 0 0.0 19 N/A 4 HSBL 0 0Acrylonitrile (2-Propenenitrile) 107-13-1 SYN 0 0 0 0.0 93 N/A 80.06/6 HSBL 0 0Bromobenzene 108-86-1 SOL 0 0 0 0.0 190 N/A NONE N/A N/ABromochloromethane 74-97-5 PC 0 0 0 0.0 189 N/A 90 HBSL 0 0Bromomethane (methyl bromide) 74-83-9 FUM 0 0 0 0.0 188 N/A 100 HSBL 0 0Chlorobenzene 108-90-7 SOL 0 0 0 0.0 190 N/A 100 MCL 0 0cis-1,3-Dichloropropene 10061-01-5 FUM 0 0 0 0.0 188 N/A 8,90.3/30 HSBL 0 0Dibromomethane 74-95-3 SOL 0 0 0 0.0 190 N/A NONE N/A N/AEthyl methacrylate 97-63-2 SYN 0 0 0 0.0 93 N/A NONE N/A N/AEthyl tert-butyl ether (ETBE) 637-92-3 GAS 0 0 0 0.0 93 N/A NONE N/A N/AHexachlorobutadiene 87-68-3 SYN 0 0 0 0.0 188 N/A 80.9/90 HSBL 0 0Hexachloroethane 67-72-1 SOL 0 0 0 0.0 93 N/A 0.7 HSBL 0 0Iodomethane 74-88-4 SYN 0 0 0 0.0 93 N/A NONE N/A N/AIsodurene (1,2,3,5-Tetramethylbenzene) 527-53-7 GAS 0 0 0 0.0 93 N/A NONE N/A N/A
70 Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002 Table 24. Detection frequency of 87 volatile organic compounds in groundwater samples from the Valley and Ridge aquifers, 1993–2003.—Continued [THMs, trihalomethanes; FUM, fumigant related compound; PC, personal care and domestic use product; REF, refrigerants or propellant; SOL, solvent; SYN, organic synthesis compound; μg/L, micrograms per liter; CAS, Chemical Abstract Service; MCL, maximum contaminant level; HBSL, health-based screening level; N/A, not applicable] Volatile organic compound CAS number Type of compound1 Number of detections greater than or equal to 0.2 μg/L Percent detections greater than or equal to 0.2 μg/L Number of detections at any concentration Percent detections at any concentration Number of analyses Maximum concentration (μg/L) Benchmark level (μg/L) Benchmark type2 Percent detections greater than benchmark level Percent detections within a factor of 0.1 of benchmark level Methyl acrylate (methyl-2-propenoate) 96-33-3 SYN 0 0 0 0.0 93 N/A NONE N/A N/A Methyl isobutyl ketone (MIBK) 108-10-1 SOL 0 0 0 0.0 93 N/A NONE N/A N/A Methyl methacrylate 80-62-6 SYN 0 0 0 0.0 93 N/A 10,000 HSBL 0 0

n-Butylbenzene 104-51-8 GAS 0 0 0 0.0 188 N/A NONE N/A N/Ao-Xylene (1,2-Dimethylbenzene) 95-47-6 GAS 0 0 4

0 0.0 93 N/A 510,000 MCL 0 0

Prehnitene 488-23-3 GAS 0 0 0 0.0 93 N/A NONE N/A N/Asec-Butylbenzene 135–98–8 GAS 0 0 0 0.0 190 N/A NONE N/A N/Atert-Butylbenzene 98-06-6 GAS 0 0 0 0.0 188 N/A NONE N/A N/ATetrahydrofuran (1,4-epoxybutane) 109-99-9 SOL 0 0 0 0.0 93 N/A NONE N/A N/Atrans-1,2-Dichloroethene 156-60-5 SOL 0 0 0 0.0 190 N/A 100 MCL 0 0trans-1,3-Dichloropropene 10061-02-6 FUM 0 0 0 0.0 188 N/A 8,90.3/30 HSBL 0 0trans-1,4-Dichloro-2-butene 110-57-6 SYN 0 0 0 0.0 93 N/A NONE N/A N/ATribromomethane (Bromoform) 75-25-2 THM 0 0 0 0.0 188 N/A 380 MCL N/A N/AVinyl bromide (Bromoethene) 593-60-2 SYN 0 0 0 0.0 93 N/A NONE N/A N/AVinyl chloride (Chloroethene) 75-01-4 SYN 0 0 0 0.0 188 N/A 2 MCL N/A N/A

1 Carter and others, 2007.2 U.S. Environmental Protection Agency, 2006; Toccalino and others, 2008.3 Part of total trihalomethane maximum contaminant level of 80 μg/L.4 Pre-1996 samples were analyzed for total Xylene; later samples were analyzed for o-xylene and 

m- & 

p-xylene, which are summed together to get total xylene.

5 Part of total xylene maximum contaminant level of 10,000 μg/L.6 Included concentrations greater than or equal to 0.03 μg/L for toluene.7 Included concentrations greater than or equal to 0.05 μg/L for 1,2,4-trimethylbenzene.8 HSBL-low/HBSL-high values, Toccalino and others, 2008.9 Sum concentrations from cis-1-3 and trans-1.3-dichloropropene may be compared to the HBSL range (0.3–30 μg/L) for the mixed isomer dichloropropene.
For additional information about NAWQA studies in the Piedmont and Valley and Ridge aquifers contact:

Bruce D. Lindsey

U.S. Geological Survey

215 Limekiln Road

New Cumberland, PA 17070

http://water.usgs.gov/nawqa/

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Johnson and others—Factors Affecting Groundwater Quality in the Valley and Ridge Aquifers, Eastern United States, 1993–2002—Scientific Investigations Report 2010–5176

Early Mesozoic basin aquifers

Piedmont and Blue Ridge carbonate-rock aquifers

Piedmont and Blue Ridge crystalline-rock aquifers

Valley and Ridge siliciclastic-rock aquifers

Valley and Ridge carbonate-rock aquifers