Cover: Conceptual diagram depicting shallow agricultural land-use monitoring wells and a domestic well 

completed in the Mississippian carbonate aquifer. Photograph on left side of cover shows a submersible 

pump in a monitoring well adjacent to a field of winter wheat near Huntsville, Alabama. Photograph on right 

side of cover is a cotton field in northern Alabama.
Shallow Ground-Water Quality in Agricultural 

Areas of Northern Alabama and Middle Tennessee, 

2000-2001

By James A. Kingsbury 

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 03-4181

Nashville, Tennessee

2003
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm name in this report is for identification

purposes only and does not constitute endorsement by the

U.S. Geological Survey.

For additional information write to: Copies of this report may be purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

640 Grassmere Park, Suite 100 Box 25286

Nashville, Tennessee 37211 Denver, Colorado 80225-0286

Information about the National Water-Quality Assessment (NAWQA) Program is available on the 

Internet at: http://water.usgs.gov/nawqa/
FOREWORD

Foreword iii

The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely scientific information that helps enhance and protect the 

overall quality of life, and facilitates effective management of water, biological, energy, and mineral 

resources. (http://www.usgs.gov/). Information on the 

quality of the Nation’s water resources is of critical 

interest to the USGS because it is so integrally linked 

to the long-term availability of water that is clean and 

safe for drinking and recreation and that is suitable for 

industry, irrigation, and habitat for fish and wildlife. 

Escalating population growth and increasing demands 

for the multiple water uses make water availability, 

now measured in terms of quantity and quality, even 

more critical to the long-term sustainability of our 

communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. (http://water.usgs.gov/nawqa/). Shaped by and 

coordinated with ongoing efforts of other Federal, 

State, and local agencies, the NAWQA Program is 

designed to answer: What is the condition of our 

Nation’s streams and ground water? How are the conditions changing over time? How do natural features 

and human activities affect the quality of streams and 

ground water, 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. NAWQA results can contribute 

to informed decisions that result in practical and effective water-resource management and strategies that 

protect and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 50 

of the Nation’s most important river basins and aquifers, referred to as Study Units. (http://water.usgs.gov/

nawqa/nawqamap.html). Collectively, these Study 

Units account for more than 60 percent of the overall 

water use and population served by public water supply, and are representative of the Nation’s major 

hydrologic landscapes, priority ecological resources, 

and agricultural, urban, and natural sources of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling and 

analysis. The assessments thereby build local knowledge about water-quality issues and trends in a particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multi-scale 

approach helps to determine if certain types of waterquality issues are isolated or pervasive, and allows 

direct comparisons of how human activities and natural processes affect water quality and ecological health 

in the Nation’s diverse geographic and environmental 

settings. Comprehensive assessments on pesticides, 

nutrients, volatile organic compounds, trace metals, 

and aquatic ecology are developed at the national 

scale through comparative analysis of the Study-Unit 

findings. (http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the communication and dissemination of credible, timely, and relevant science so that the most recent and available 

knowledge about water resources can be applied in 

management and policy decisions. We hope this 

NAWQA publication will provide you the needed 

insights and information to meet your needs, and 

thereby foster increased awareness and involvement in 

the protection and restoration of our Nation’s waters. 

The NAWQA Program 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 a fully integrated understanding of watersheds and for costeffective management, regulation, and conservation of 

our Nation’s water resources. The Program, therefore, 

depends extensively on the advice, cooperation, and 

information from other Federal, State, interstate, 

Tribal, and local agencies, non-government organizations, industry, academia, and other stakeholder 

groups. The assistance and suggestions of all are 

greatly appreciated.

Robert M. Hirsch

Associate Director for Water
Contents v

CONTENTS

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

Introduction .......................................................................................................................................................................... 2

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

Acknowledgments ....................................................................................................................................................... 3

Approach ............................................................................................................................................................................... 4 

Analytical Methods...................................................................................................................................................... 5

Quality Assurance and Quality Control ...................................................................................................................... 6

Delineation of Land Use and Soil Properties Near Wells............................................................................................ 6 

Statistical Methods ..................................................................................................................................................... 7

Hydrogeology ........................................................................................................................................................................ 7 

Estimated Age of Ground Water.................................................................................................................................. 8 

Land Use and Soils ..................................................................................................................................................... 11

Shallow Ground-Water Quality in Agricultural Areas .......................................................................................................... 12

Nitrate ......................................................................................................................................................................... 16

Pesticides .................................................................................................................................................................... 17

Implications for Drinking-Water Quality of the Mississippian Carbonate Aquifer ................................................... 23

Summary and Conclusions ................................................................................................................................................... 29

References ............................................................................................................................................................................ 30

Appendixes

1. Pesticides and pesticide degradates analyzed, common name, and use .................................................................. 35

2. Chlorofluorocarbon concentrations, calculated atmospheric partial pressures, and model

recharge dates for sampled wells ............................................................................................................................ 38
vi Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

FIGURES

1-2. Maps showing:

1. Location of the lower Tennessee River Basin with its delineated subunits, including the 

Eastern Highland Rim study area ................................................................................................................... 3

2. Location of wells sampled and 1992 distribution of cropland in the Eastern Highland Rim.......................... 4

3. Sketch and hydrographs showing conceptual model of ground-water flow in the regolith 

and bedrock of the Mississippian carbonate aquifer and monthly water levels for 

two wells that show different responses to precipitation .......................................................................................... 9

4-8. Graphs showing:

4. Percentage of cotton, cropland, and well-drained soils in buffer areas around land-use monitoring

wells in the Mississippian carbonate aquifer................................................................................................... 11

5. Relation between dissolved-oxygen concentration and water level in agricultural monitoring 

wells in the Mississippian carbonate aquifer .................................................................................................. 13

6. Relation between dissolved-oxygen concentration and calcite saturation index and 

young model ground-water ages as indicated by CFC-12 concentrations coincided 

with low calcite saturation indices in samples from the Mississippian carbonate aquifer .............................. 13

7. Nitrate and dissolved-oxygen concentrations for samples and cropland in buffer areas around wells

in the Mississippian carbonate aquifer, 2000................................................................................................... 16

8. Relation between ratio of chloride to nitrate and nitrate concentrations in samples

collected from the Mississippian carbonate aquifer ........................................................................................ 17

9. Map showing distribution of selected National Water-Quality Assessment Program agricultural 

land-use study areas, median nitrate concentration, and estimated average annual nitrogen 

input across the Nation ............................................................................................................................................. 18

10. Graph showing nitrate concentrations in samples from the Mississippian carbonate aquifer and from 

National Water-Quality Assessment Program agricultural land-use wells across the Nation .................................. 19

11. Maps showing number of pesticides detected and total pesticide concentration in samples 

from the Mississippian carbonate aquifer ................................................................................................................. 20

12-16. Graphs showing:

12. Concentrations of atrazine, fluometuron, and dissolved oxygen and estimated use of atrazine 

and fluometuron in buffer areas around wells in the Mississippian carbonate aquifer ................................... 22

13. Ratios of degradate to parent pesticide concentration for fluometuron, norflurazon, and

atrazine in samples from the Mississippian carbonate aquifer ........................................................................ 23

14. Relation between deethylatrazine to atrazine ratios (less than 1) and concentrations of atrazine 

and metolachlor in water samples from the Mississippian carbonate aquifer................................................. 23

15. Relation between dissolved-oxygen concentration, calcite saturation index, and total pesticide

concentration for samples from the Mississippian carbonate aquifer ............................................................. 24

16. Detection frequencies and concentrations of selected pesticides at or above 0.01 microgram per 

liter in samples collected from the Mississippian carbonate aquifer and from selected 

National Water-Quality Assessment Program agricultural land-use wells across the Nation......................... 24

17. Map showing estimated atrazine use across the Nation and detection frequency of atrazine for 

selected National Water-Quality Assessment Program agricultural land-use studies............................................... 25

18-23. Graphs showing:

18. Specific conductance, pH, and dissolved-oxygen concentrations for samples from agricultural 

land-use monitoring wells and drinking-water wells in the Mississippian carbonate aquifer......................... 26

19. Nitrate concentrations in samples from agricultural land-use monitoring wells and drinking-water

wells in the Mississippian carbonate aquifer................................................................................................... 26

20. Amount of cropland in buffer areas around agricultural land-use monitoring wells and

drinking-water wells in the Mississippian carbonate aquifer .......................................................................... 26

21. Detection frequency and median concentrations of selected pesticides and degradates detected 

at concentrations equal to or greater than 0.01 microgram per liter................................................................ 27

22. Number of pesticides detected in samples from agricultural land-use monitoring wells and

drinking-water wells in the Mississippian carbonate aquifer .......................................................................... 27

23. Total pesticide concentration for samples from agricultural land-use monitoring wells and

drinking-water wells in the Mississippian carbonate aquifer .......................................................................... 28
Contents vii

TABLES

1. Water level, well depth, and specific capacity of wells installed in regolith in the Mississippian carbonate 

aquifer and model recharge dates of selected samples, 2000-2001 .......................................................................... 10

2. Summary of major land uses in buffer areas of wells in agricultural areas in the 

Eastern Highland Rim, 2000..................................................................................................................................... 11

3. Spearman’s correlation coefficient, rho, for soil characteristics in buffer areas around wells ................................. 12

4. Water-quality properties and major inorganic constituent concentrations in samples 

from 32 wells in the Mississippian carbonate aquifer, 2000-2001 ........................................................................... 14

5. Summary statistics for pesticides detected at concentrations equal to or greater than 0.01 microgram 

per liter in samples from the Mississippian carbonate aquifer and estimated use 

of selected pesticides in buffer areas around wells ................................................................................................... 21

CONVERSION FACTORS, DATUMS, AND WATER-QUALITY UNITS

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 × °C) + 32

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29); horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

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).

Water-quality units

mg/L milligrams per liter

μg/L micrograms per liter

μS/cm microsiemens per centimeter

pg/kg picogram per kilogram

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

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

pound, avoirdupois (lb) 0.4536 kilogram (kg)

gallon per minute per foot [(gal/min)/ft] 0.2070 liter per second per meter [(L/s)/m]
Abstract 1

Shallow Ground-Water Quality in Agricultural Areas of 

Northern Alabama and Middle Tennessee, 2000-2001

By James A. Kingsbury 

ABSTRACT

As part of the U.S. Geological Survey 

National Water-Quality Assessment Program, 

32 monitoring wells were installed near cropland 

in parts of northern Alabama and Middle Tennessee to characterize the effect of row-crop agriculture on shallow ground-water quality. The wells 

were completed in regolith overlying carbonate 

bedrock. These geologic units are part of the Mississippian carbonate aquifer, a source of drinking 

water for domestic and municipal supply in the 

area. The majority of these wells were sampled in 

the spring of 2000 for inorganic constituents, 

nutrients, pesticides, and selected pesticide degradates. Land use and soil characteristics were 

delineated for a 1,640-foot radius buffer area 

around each well to relate water quality to environmental factors. A strong association among 

soil characteristics, land use, and hydrogeology 

limited the analysis of the effect of these factors 

on nitrate and pesticide occurrence.

Nitrate and pesticide concentrations generally were low, and no samples exceeded established drinking-water maximum contaminant 

levels. The maximum concentration of nitrate was 

about 8 milligrams per liter as nitrogen, and the 

median concentration was 1 milligram per liter. 

Nitrate concentrations were strongly correlated to 

dissolved-oxygen concentrations, and ratios of 

chloride to nitrate indicate nitrate concentrations 

were affected by denitrification in about a third of 

the samples. A pesticide or pesticide degradate 

was detected at concentrations greater than 

0.01 microgram per liter in 91 percent of the samples. Pesticides with the highest use typically 

were detected most frequently and at the highest 

concentrations; however, glyphosate had the highest estimated use but was not detected in any samples. Fluometuron and atrazine, two high-use 

pesticides, were detected in 83 and 70 percent, 

respectively, of the samples from wells where the 

pesticide was applied in the buffer area. Maximum concentrations of fluometuron and atrazine 

were 2.13 and 1.83 micrograms per liter, respectively. Detection rates of pesticide degradates 

were similar to parent pesticides, and concentrations of degradates generally were comparable to 

or greater than the parent pesticide. Pesticide 

detections were correlated to dissolved-oxygen 

concentrations, suggesting that pesticides are 

most likely to be detected at high concentrations 

where ground-water residence time is short and 

the rate of recharge is fast.

Nitrate and pesticide data collected in this 

study were compared to data collected from similar agricultural land-use studies conducted by the 

National Water-Quality Assessment Program 

throughout the Nation. Nitrate concentrations 

generally were lower in this study than in samples 

from other agricultural areas; however, pesticides 

were detected more frequently in samples from 

wells in this study. For example, atrazine and its 

degradate, deethylatrazine, were detected in 62 

and 47 percent, respectively, of water samples in 

this study but were detected in about 25 percent of 

the 851 wells sampled for agricultural land-use 

studies nationwide. In national study areas where 

atrazine use is greater than in the lower Tennessee 

River Basin, atrazine was detected in 30 percent 

of the water samples. Pesticides used on cotton 

were detected much more frequently in this study, 
2 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

but many of the study areas nationwide have 

smaller amounts of cotton acreage than the lower 

Tennessee River Basin.

Similarities in nitrate concentrations and 

the pesticides detected frequently in this agricultural land-use study and a network of drinkingwater wells in the same area completed in bedrock in the Mississippian carbonate aquifer (sampled in a previous study) indicate the aquifer is 

susceptible to contamination from nonpoint 

sources. Nitrate concentrations were not statistically different for the two well networks and were 

correlated to total pesticide concentrations in both 

networks. Although detection frequencies and 

maximum concentrations were higher in the landuse monitoring wells than in the drinking-water 

wells, the same pesticides were detected frequently, and median concentrations of these pesticides were similar. The similarity in water quality 

between samples from the shallow land-use and 

the deeper drinking-water wells is probably the 

result of the karst hydrology of the aquifer, which 

allows substantial transport of nonpoint-source 

contaminants from agricultural areas once water 

has moved through the regolith to conduits in 

bedrock.

INTRODUCTION

Nitrate and pesticide contamination of ground 

water in agricultural areas is an important issue 

because ground water is often the principal source of 

drinking water in northern Alabama and Middle Tennessee. Although local, regional, and national reconnaissance studies of nitrate and pesticides in ground 

water have been conducted, these studies typically 

have evaluated the quality of water obtained from 

existing domestic or public-supply wells. These types 

of wells commonly withdraw water from deep parts of 

aquifers where the effects of land use on water quality 

are less evident.

As part of the U.S. Geological Survey National 

Water-Quality Assessment (NAWQA) Program in the 

lower Tennessee River Basin (LTEN), a network of 

shallow land-use monitoring wells was installed in 

parts of northern Alabama and Middle Tennessee to 

characterize the quality of recently recharged ground 

water near agricultural fields (figs. 1 and 2). The data 

from these shallow wells represent parts of the aquifer 

most affected by land-use activities at land surface and 

serve as a point of comparison for the effects of land 

use on the drinking-water resource. Wells were 

installed near agricultural fields in the Eastern Highland Rim, one of nine subunits (fig. 1) that generally 

correspond to Level III and IV ecoregion boundaries 

(Griffith and others, 1997; Kingsbury and others, 

1999) and into which the LTEN was subdivided. These 

monitoring wells are nested within a network of predominantly domestic wells in the same subunit that 

was sampled in the summer of 1999 (Kingsbury and 

Shelton, 2002).

The Eastern Highland Rim is underlain by carbonate rocks of Mississippian age that make up the 

Mississippian carbonate aquifer, the most areally 

extensive and productive aquifer in the LTEN. Estimated ground-water withdrawals from the Mississippian carbonate aquifer for public and domestic supply 

in the Eastern Highland Rim was about 40 Mgal/d in 

1995 (U.S. Geological Survey, 1997). The City of 

Huntsville, Alabama, is the largest ground-water user, 

withdrawing about 14 Mgal/d from wells that have a 

maximum depth of 125 ft. Ground water accounts for 

about 40 percent of water used in Huntsville. About 25 

public water-supply systems rely on ground water 

from the Mississippian carbonate aquifer in the Eastern Highland Rim. About 5 Mgal/d of the total 

ground-water withdrawals for 1995 were for domestic 

use. 

Purpose and Scope

This report describes the quality of shallow 

ground water collected in the spring of 2000 and 2001 

from monitoring wells installed near agricultural areas 

in the Eastern Highland Rim of the LTEN study area. 

Soil properties, hydrogeology, and land-use data in the 

area near the monitoring wells are evaluated to determine the principal factors that affect the occurrence of 

nitrate and pesticides. The occurrence and distribution 

of nitrate and pesticides in the Mississippian carbonate 

aquifer are put into a broader context by comparing 

the results from other NAWQA agricultural land-use 

studies across the Nation. The nitrate and pesticide 

data in this study also are compared to data from a network of predominantly domestic wells sampled in 

1999 to characterize the effect of agricultural land use 

on the quality of drinking water in the aquifer.
Introduction 3

Acknowledgments

The author thanks the many landowners who 

permitted access to their land for the installation and 

sampling of shallow monitoring wells. The following 

Natural Resources Conservation Service District Conservationists were particularly helpful in locating 

potential sites for wells: Joe Berry, Madison County, 

Alabama; Billy Frost, Lawrence County, Alabama; 

Kathy Gotcher, Colbert County, Alabama; and 

Kenneth Swafford, Limestone County, Alabama. The 

following water departments provided water during 

drilling: City of Winchester Water, Manchester Water 

Department, and Lincoln County Water Department in 

Tennessee; Madison County Water Department, City 

of Huntsville, Limestone County Water Authority, 

Tuscumbia Water, and West Morgan and East 

Lawrence County Water Authority in Alabama.
4 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

APPROACH

A network of 32 monitoring wells was established to characterize shallow ground-water quality in 

the Mississippian carbonate aquifer in agricultural 

areas in the Eastern Highland Rim (fig. 2). Cropland 

delineated from 1992 digital land-use data in the Eastern Highland Rim were combined into about 40 equal 

subareas from which random locations were generated 

using a geographic information system (GIS) based 

computer program (Scott, 1990). Suitable sites for 

monitoring wells within about a mile radius of random 

points generated by this program were then located. 

Wells were installed near agricultural fields, usually 

along buffer strips adjacent to fields. The direction of 

ground-water flow was not known, so wells were 

installed in locations presumed to be downgradient of 

the fields.

The wells installed for this study were intended 

for sampling water near the water table to characterize 

the effect of row-crop agriculture on the quality of 

recently recharged ground water. Thirty-two wells 

were drilled using hollow-stem augers and completed 

with 2-in.-diameter threaded polyvinyl chloride (PVC) 

casing. The wells were completed in regolith and were 

drilled in 1999 during October and November when 

ground-water levels typically are lowest. The top of 

the well screens generally were within 10 ft of the 
Approach 5

water table. Eight of the wells had more than 10 ft of 

water above the screens, and 12 wells had water levels 

below the top of the screen at the time of sampling. 

Well screens were 0.01-in.-diameter slotted 10-ft-long 

PVC, with the exception of three wells with 5-ft-long 

screens. Wells ranged from 14 to 79 ft deep, with a 

median depth of 37.5 ft. A sand pack was placed 

around the well screens, and a bentonite seal was 

placed on top of the sand pack at least 2 ft above the 

top of the screen. The remainder of the annulus was 

grouted to land surface with a cement-bentonite mixture. Wells were developed several weeks prior to 

sampling, by pumping or bailing if the well did not 

produce enough water, typically until the turbidity was 

less than 10 nephelometric turbidity units. 

Samples were collected and processed according to NAWQA ground-water sampling protocols 

(Koterba and others, 1995). Wells were purged a minimum of three casing volumes; specific conductance, 

dissolved oxygen, pH, and temperature were monitored until they stabilized prior to sampling. Wells that 

could not be pumped continuously were pumped dry, 

and the water level was allowed to recover to 90 percent of the pre-pumping level, at which time the wells 

were sampled. Samples for inorganic constituents 

were filtered through a disposable 0.45-μm capsule filter, and samples for cation analysis were preserved 

with nitric acid. Pesticide samples were filtered 

through a 0.7-μm disposable glass-fiber filter. Nutrient 

and pesticide samples were kept chilled and shipped 

overnight to the U.S. Geological Survey National 

Water-Quality Laboratory (NWQL) in Denver, Colorado. All sampling equipment was constructed of 

stainless steel or teflon and was cleaned with three 

volumes (pump line) of soapy wash, tap-water rinse, 

and a final rinse with de-ionized water. The aluminum 

pesticide filtration unit also was rinsed with pesticidegrade methanol.

Analytical Methods

Samples were analyzed using approved U.S. 

Geological Survey (USGS) methods at the NWQL in 

Denver, Colorado, and at the USGS Organic 

Geochemistry Research Laboratory (OGRL) in 

Lawrence, Kansas. Dissolved inorganic constituents 

were determined by atomic absorbtion, inductively 

coupled plasma, ion chromatography, ion specific 

electrode, and colorimetric methods, as described in 

Fishman and Friedman (1989) and Fishman (1993). 

Two analytical methods were used at the NWQL 

(Zaugg and others, 1995; Furlong and others, 2001), 

and one method was used at the ORGL (Kish and others, 2000) to analyze a total of 93 pesticides and 19 

pesticide degradates (appendix 1). Pesticides were 

extracted from samples by pumping filtered samples 

through solid-phase extraction columns. Extracts from 

these columns were subsequently analyzed by gas 

chromatography/mass spectrometry (GC/MS) and 

high-performance liquid chromatography/mass spectrometry (HPLC/MS). Minimum reporting levels 

(MRL) range from 0.001 to 0.193 μg/L and are based 

on method detection limits (MDL) for each pesticide. 

The MDL represents the lowest concentration at 

which a constituent can be identified and measured 

with 99 percent confidence that the concentration was 

greater than zero (Wershaw and others, 1987) and varies based on the performance of the method for each 

pesticide. Some concentrations are qualified with an 

“E” indicating an estimated concentration. These concentrations are estimated because they are either above 

or below the range in concentration of the calibration 

standards; the sample matrix interfered with the measurement of the analyte; surrogates added to samples 

indicated that the method was not performing adequately; or the analyte has systematically had low or 

inconsistent recoveries throughout the development 

and implementation of the method and concentrations 

always are reported as estimates (appendix 1). 

Samples were analyzed by the HPLC/MS 

method before final approval by the USGS Office of 

Water Quality in April 2001. Although the analytical 

method did not change following approval, data analyzed before method approval are considered provisional. During initial implementation of this analytical 

method in 1999, a backlog of samples resulted in a 

number of samples exceeding the recommended 4-day 

holding time prior to sample extraction (Furlong and 

others, 2001). Samples collected from the agricultural 

monitoring wells in 2000 and 2001 met the recommended holding times, but samples from some of the 

drinking-water wells presented in this report did not. 

Degradation of pesticides during extended sample 

storage is likely, and concentrations and detection frequencies for the pesticides analyzed by this method 

may be biased low in the samples from the drinkingwater wells. Pesticides analyzed by HPLC/MS are 

shown in italics in appendix 1. 

Analyses of fluometuron and norflurazon degradates were conducted by GC/MS at the OGRL. 
6 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

Analytical methods are described in Kish and others 

(2000). The MRL for these degradates is 0.05 μg/L 

(appendix 1). Glyphosate was analyzed by enzymelinked immunosorbant assay at the OGRL (Lee and 

others, 2002) and had a MRL of 0.1 μg/L. At the time 

these samples were analyzed, these analytical methods 

also were not yet approved, so the results are considered provisional.

Quality Assurance and Quality Control

The low-level concentrations at which pesticides were analyzed in this study necessitated qualitycontrol sampling to demonstrate that equipment cleaning, sample collection and processing, and analytical 

procedures were noncontaminating and to identify 

bias in the methods. Field quality-assurance samples 

made up about 30 percent of all samples analyzed and 

included blanks, replicates, and pesticide spikes. Data 

from inorganic constituent and pesticide blanks indicate that equipment cleaning procedures were adequate and that sample collection and processing 

procedures generally were noncontaminating. Only 

two pesticides were detected in a total of five blanks. 

Terbacil was detected in two blanks but was not 

present in any environmental samples. Diuron was 

detected at an estimated concentration of 0.01 μg/L in 

one blank; environmental samples associated with this 

blank did not contain diuron. Recoveries of spiked 

pesticides ranged from 5 to 245 percent for all of the 

pesticides analyzed, and the median recovery was 

86 percent. For pesticides detected in this study, the 

range in recoveries was 52 to 245 percent with a 

median recovery of 86 percent. Recoveries of several 

spiked pesticides have had considerable and systematic bias with these analytical methods; deethylatrazine, aldicarb (52 percent) and its degradates, and 

hydroxyatrazine were biased low. Carbaryl and carbofuran (245 percent), which historically have had poor 

recoveries with this analytical method (Zaugg and others, 1995), were biased high in spiked samples 

analyzed.

Delineation of Land Use and Soil Properties 

Near Wells

Because the rate and direction of ground-water 

flow generally is not known for monitoring wells 

installed for the NAWQA Program, a 1,640-ft (500-m) 

buffer area was used for characterizing land use near 

monitoring wells. Based on data from other studies, 

Koterba (1998) concluded that a buffer area of this 

size likely would represent at least part of the recharge 

area for a well in a shallow, unconfined aquifer and 

should be used in NAWQA ground-water studies. 

High-resolution black and white aerial photographs at 

a 1:20,000 scale were used to delineate land use within 

the buffer area around each well. All of the aerial photographs, with the exception of one which was taken in 

1992, were taken between 1997 and 1999 by the 

National Aerial Photography Program. A mylar overlay was used to delineate land-use areas. Land uses 

identified from aerial photographs and crops were verified by site visits. The area of each land-use type in 

buffer areas was determined using a planimeter. 

Planimeter measurements were made three times and 

averaged. The sum of the land-use areas was within 

2 percent or less of the total buffer area measured with 

the planimeter for most of the wells. Differences for a 

few wells were as much as 5 percent because of measurement error associated with the large number and 

small size of land-use areas delineated. Land-use data 

also were delineated using the same methodology for a 

network of existing, predominantly domestic wells, 

and the relative percentages of land uses in those 

buffer areas were calculated by using GIS.

These land-use data were used to estimate pesticide use for the 2000 growing season in each of the 

buffer areas. Information about application rates was 

provided by local agricultural officials and also were 

obtained from the national pesticide use database 

maintained by the National Center for Food and Agricultural Policy (2002). These application rates were 

multiplied by the percentage of acreage typically 

treated and by the acreage of a given crop in the buffer 

areas determined from the aerial photographs.

Soil properties were characterized for the buffer 

areas around each well. County soil survey maps 

(scale 1:20,000) were used to delineate soil map units 

within the buffer areas. Mylar overlays with soil map 

unit boundaries were scanned and converted into digital coverages. The area of each map unit within the 

buffer was determined by GIS. Digital soil maps at a 

scale of 1:24,000 from the National Soil Survey Geographic (SSURGO) database (U.S. Department of 

Agriculture, 2001a) were available for Limestone and 

Madison Counties in Alabama. Soil map units in buffers around wells in these counties were delineated 

from these digital data. Soil attributes for map units 

were obtained from the National Map Unit Interpretation Record (MUIR) database (U.S. Department of 
Hydrogeology 7

Agriculture, 2001b). Soil properties were derived for 

only the first soil layer because not all map units had 

data for deeper layers and because soil attributes for 

deeper layers generally were similar to the first soil 

layer for map units with multiple layers. Minimum, 

maximum, and mean values were used for soil properties that had ranges. Percentages of sand and silt are 

not in the MUIR database but were calculated (following Burkart and others, 1999) by subtracting the percentage of material passing through a 0.08-mm and a 

50-mm sieve (sand) and the clay percentage from the 

0.08-mm sieve (clay). Categorical properties, such as 

hydrologic group, were converted to continuous variables by using the percentage of the buffer area containing soils in a given group. Soil data were not 

available for one well, so that well is not included in 

any data analysis involving soil properties.

Statistical Methods

Several statistical tests were used in this study to 

evaluate relations between water-quality constituents 

and environmental factors that could affect constituent 

concentrations in ground water. The Spearman rank 

correlation test (Helsel and Hirsch, 1992) was used to 

evaluate whether nitrate and pesticide concentrations 

are correlated to other water-quality constituents, site 

characteristics, and land use. Wilcoxon rank sum tests 

were used to determine if constituent concentrations 

are significantly different for two groups of samples. 

For example, samples from wells with detections were 

compared to samples from wells without detections to 

determine whether environmental factors are significantly different for the two groups of wells. Partial 

correlation analysis (Blalock, 1972) was used to determine whether two colinear variables contribute to the 

variability in nitrate and pesticide concentrations, or 

whether one variable explains most of the variability 

in concentration. Partial correlation analysis determines the strength of the correlation between two variables if a third, correlated variable were to be held 

constant (Lowry, 2000). A significance level of 5 percent (p< 0.05) was used for statistical analysis of the 

data for this study. A common reporting level of 

0.01 μg/L was used for computing detection frequencies for pesticides in this report, with the exception of 

those pesticides analyzed by the OGRL that did not 

include estimated concentrations below the MDL.

HYDROGEOLOGY

Much of the study area is underlain by the 

Mississippian-age Tuscumbia Limestone and Fort 

Payne Chert, a cherty limestone (Osborne and others, 

1989). Most of the wells were completed in regolith 

overlying these formations. In Tennessee, the equivalent units to the Tuscumbia Limestone are the Warsaw 

and St. Louis Limestones. Two wells were installed in 

regolith overlying the Monteagle Limestone, which 

crops out in the southern part of the Eastern Highland 

Rim. The predominantly carbonate geology of these 

formations has resulted in the development of karst 

landforms such as sinkholes, caves, disappearing 

streams, and springs throughout much of the subunit. 

The regolith is a layer of residual material derived in 

place from the weathering of the carbonate bedrock. 

The regolith consists of a mixture of clay, silt, and 

clay-sized chert, with some chert gravel and chert 

interbeds. Gravel is scattered throughout the regolith 

but typically is more abundant and larger above the 

contact with bedrock where locally, bedrock cobbles 

or boulders may be present. Locally, these sediments 

are reworked and redeposited. The regolith can be as 

much as 100 ft thick but typically is between 30 and 

60 ft thick.

The regolith and underlying bedrock are hydrologically connected, and in this report, the saturated 

regolith and bedrock are referred to as the Mississippian carbonate aquifer. Ground water in the aquifer 

typically is under water-table conditions; however, 

clay layers in the regolith can provide varying degrees 

of confinement locally. Recharge to the aquifer is 

largely from precipitation infiltrating and moving 

through the regolith. Focused recharge also occurs 

from surface drainage into sinkholes or losing stream 

reaches that intersect the aquifer.

Most of the wells were screened in parts of the 

aquifer that remained saturated throughout the year, 

but nine wells that were completed at the top of bedrock were dry during part of the year. Of these nine 

wells, some are well connected to ground water in 

bedrock, and the dry periods represent times of the 

year when the water level in the aquifer was below the 

top of bedrock (below the bottom of the well). Other 

wells were dry for part of the year because they may 

not be well connected to ground water in bedrock. 

These wells are analogous to wells completed in 

perched water-bearing zones in that they are not well 

connected to the water table and go dry as recharge 

decreases in the summer as water drains into conduits 
8 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

in bedrock. Without a nearby water-level measurement 

in a well completed in bedrock, determining which 

scenario applies to a given well is difficult. Figure 3 

shows a conceptual diagram of the hydrogeology of 

the Mississippian carbonate aquifer and hydrographs 

of wells that represent different hydrologic conditions 

in the regolith. Monthly measurements indicate that 

water levels fluctuated as much as 20 ft throughout the 

year (fig. 3) in some wells. Hydrograph A (fig. 3) represents a shallow well (well 18) screened in finegrained material at the top of bedrock that was dry for 

parts of the year. Water levels rose in response to rainfall in the winter and spring and declined at about the 

same rate as they had risen as precipitation decreased 

and evapotranspiration rates increased. Hydrograph B 

(fig. 3) represents data from a deeper well (well 11) 

screened in a gravel zone that remained saturated all 

year. Water levels responded more slowly to rainfall in 

the winter and continued to decline through the beginning of February before they began to rise (fig. 3). The 

rate of water-level decline was slower in well 11 than 

in well 18, which may represent a contribution of 

recharge from areas with low permeability or diffuse 

recharge.

Specific capacities of wells installed for this 

study generally were low (table 1). Only four of the 

wells had specific capacities greater than 1 (gal/min)/ft 

of drawdown; more than half of the wells had specific 

capacities less than 0.1 (gal/min)/ft of drawdown. 

These low specific capacities are not surprising considering the predominance of fine-grained material in 

the regolith and the small diameter of the wells. Lateral movement of ground water in the regolith near 

these low capacity wells is probably limited, and the 

principal direction of ground-water flow is downward 

toward conduits in bedrock; therefore, recharge to 

these wells likely is localized. Wells intersecting 

gravel zones have higher specific capacities and likely 

have larger areas of contribution and a larger component of lateral ground-water flow than wells completed in predominantly fine-grained material in the 

regolith (fig. 3).

Estimated Age of Ground Water

Chlorofluorocarbons (CFCs) have been used in 

numerous studies to estimate the recharge age of 

ground water (Busenberg and Plummer, 1992). The 

basis of CFC age-dating is that atmospheric concentrations of three CFCs (CFC-11, CFC-12, and CFC-113) 

increased from about 1945 to the mid 1990s because 

of increases in production of these chemicals. As a 

result, CFC concentrations in rainfall and recharge 

water have had corresponding increases in concentrations until the early to mid-1990s. The model recharge 

date (assuming piston flow) estimated for groundwater recharge represents the time at which infiltrating 

precipitation (recharge) was isolated from the atmosphere and assumes no modification of CFC concentrations in ground water as a result of degradation or 

sorption. CFC concentrations greater than atmospheric 

air and water equilibrium concentrations indicate that 

ground water is contaminated by a local source of 

CFCs, and reliable recharge ages cannot be estimated. 

With no modification of CFC concentrations in the 

subsurface, all three CFCs should yield the same 

model recharge date.

A subset of nine wells was analyzed for CFCs to 

estimate the ground-water age. These nine wells were 

selected for CFC analysis because they could be 

pumped without drawing the water level down to the 

pump intake during sample collection, which would 

allow air to enter the pump. Introduction of air during 

sampling could contaminate the sample and affect the 

apparent age of ground water. Model recharge dates 

determined for each of the CFCs indicated contamination by CFCs locally as well as some degradation of 

CFCs (table 1 and appendix 2). In general, CFC-12 is 

the most stable of the three CFCs and usually provides 

the most reliable age if local contamination does not 

occur (Busenberg and Plummer, 1992). CFC-12 model 

recharge dates for the nine wells ranged from about 

1969 to modern (post-1997) with most of the wells 

having recharge dates between 1992 and 1997 

(table 1). Samples collected from wells that are 

hydraulically connected to the bedrock part of the 

aquifer likely are mixtures of water with varying residence times in the aquifer. The earlier the model 

recharge date in samples from these wells, the greater 

the proportion of “old” water. Samples with model 

recharge dates prior to 1997 (table 1) indicate that at 

least some proportion of the water in these wells has a 

residence time of 3 or more years. Model recharge 

dates for wells 25 (1969) and 33 (1978) may be overestimates because of degradation of CFCs, which can 

occur in ground water with low concentrations of dissolved oxygen (Plummer and Busenberg, 2000). 

Dissolved-oxygen concentrations were 0.4 and 

4.7 mg/L, respectively, in these wells. Water from well 

33 may represent a mixture of water with low 

dissolved-oxygen and CFC concentrations with water 

containing both dissolved oxygen and CFCs.
Hydrogeology 9
10 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

Table 1. Water level, well depth, and specific capacity of wells installed in regolith in the Mississippian carbonate 

aquifer and model recharge dates of selected samples, 2000-2001

[NGVD, National Geodetic Vertical Datum; <, less than; --, no data; Modern, model recharge dates that are post-1997]

Well 

number Station number Date

Water level, in 

feet below land 

surface

Well Depth, 

in feet 

below land 

surface

Elevation,

 in feet 

above 

NGVD 29

Specific 

capacity, in 

gallons per 

minute per 

foot of 

drawdown

Model 

recharge 

date (data in 

appendix 2)

1 353341086074501 05/30/00 12.4 43 1,097 <0.01 --

2 352627086002601 05/30/00 7.91 15 1,098 <0.01 --

3 354014086093401 05/30/00 16.8 43.5 1,250 <0.01 --

4 350709086120701 06/06/00 48.15 51 958 2.13 --

5 351646086040701 05/30/00 34.74 43.5 1,018 <0.01 --

6 351459085555901 06/05/00 13.46 23 1,030 <0.01 --

7 351118086051801 06/05/00 68.95 73.5 950 1.43 1997

8 350203086391701 05/31/00 8.85 29 950 0.01 --

9 344407086273401 06/01/00 35.2 37 760 0.03 --

10 345539086241301 05/31/00 22.4 53 790 0.01 --

11 345822086254001 06/06/00 23.4 50 858 0.13 1996

12 345222086303301 06/07/00 72.76 79 765 7.92 Modern

13 345112086313401 06/01/00 24.6 35 705 0.23 1994

14 345247086415001 05/31/00 26.25 39.5 822 0.02 1992

16 345912086243901 05/31/00 16.55 30 845 0.13 --

17 344553086591301 05/25/00 13.9 38 697 <0.01 --

18 344124086531401 05/24/00 16.9 24 612 0.03 --

19 344439086532001 04/16/01 9.23 23 662 0.02 --

20 343836086562901 05/25/00 22.01 33 580 0.19 1997

21 344042086504301 04/16/01 26.78 32 608 0.05 --

22 344127087212001 05/23/00 3.63 55 593 <0.01 --

23 343919087182201 05/24/00 20.65 43.5 574 <0.01 --

24 344154087171201 05/24/00 5.4 14 565 0.85 --

25 344343087220101 05/24/00 7.05 53 550 0.47 1969

26 344557087253201 04/17/01 28.3 31.5 543 0.08 --

27 344217087283601 04/17/00 43.15 46 585 0.21 --

28 344036087320901 05/22/00 24.2 28 567 <0.01 --

31 344615086272201 06/01/00 19.37 36 663 0.11 --

33 344131087335201 05/22/00 22.97 53 538 0.04 1978

34 343530086213801 06/01/00 10.9 23 595 <0.01 --

35 344348086493401 05/25/00 42.25 53 640 2.85 1997

36 343613086441701 05/25/00 8.2 24.5 560 0.04 --
Hydrogeology 11

Land Use and Soils

Cropland accounted for about 16 percent of the 

land cover in the Eastern Highland Rim in 1992 

(Kingsbury and others, 1999), with much of the cropland concentrated along the Tennessee River in northern Alabama (fig. 2). Cotton, corn, soybeans, and 

winter wheat are the principal crops grown in the Eastern Highland Rim. A total of about 441,000 acres of 

these crops were harvested in 2000 (U.S. Department 

of Agriculture, 2001c). Cotton accounted for 43 percent of this acreage. Various cropping systems are 

used throughout the area, with significant crop rotation 

occurring; as a result, this study did not target a specific crop with respect to its effect on shallow groundwater quality.

The amount of cropland in buffer areas around 

the monitoring wells ranged from 20 to 100 percent, 

with a median of 63 percent (table 2). The majority of 

monitoring wells had some cotton and corn in the 

buffer area; however, wells with greater than about 

50 percent cropland in the buffer area typically were 

dominated by cotton (fig. 4). Cotton acreage was more 

prevalent around wells located in northern Alabama. 

Winter wheat and soybeans were present in buffer 

areas surrounding 12 and 7 of the wells, respectively, 

and typically represented less than 10 percent of the 

buffer area (table 2). Buffer areas around many of the 

wells included both conventional till and no-till fields. 

Only 6 of the 32 wells had buffer areas that included 

irrigated fields.

Many of the soil characteristics delineated in 

buffer areas are correlated to one another (table 3). 

Soils in the study area are predominantly silt loams 

and cherty silt loams. The soils are moderately well to 

well-drained, with an average slope of about 3 percent 

and organic matter content of less than 3 percent. Soil 

hydrologic group and drainage class, two variables 

that describe the movement of water through soil, are 

correlated to clay content and soil pH and are 

inversely related to organic matter content (table 3). 

The percentage of soil hydrologic group B and the percentage of well-drained soil are strongly correlated 

(table 3), so the amount of well-drained soil in the 

buffer areas was the principal soil characteristic used 

for data analysis. Given that the soil characteristics are 

not independent, discerning the effect of specific soil 

characteristics on water quality is difficult.

Land use is related to the soil properties near the 

wells. Most notably, the percentage of cotton, as well 

as the percentage of cropland, in buffer areas tends to 

be greater where soils are predominantly well-drained 

(fig. 4). Although not statistically significant at the 95-

percent confidence level, the amount of corn near the 

wells is inversely related to the amount of welldrained soil in the buffer areas. Soils also are less well 

drained and have higher organic matter content in 

areas with larger amounts of forest land. The strong 

correlations between soil characteristics and land use 

including the types of crops (and, therefore, the types 

of pesticides used) confound analysis of the effects of 

soil properties on nitrate and pesticide occurrence in 

this area.

Table 2. Summary of major land uses in buffer areas of wells in agricultural areas in the Eastern Highland Rim, 

2000

[Values in percent; N, number of wells with a particular land use in the buffer area]

Cotton Corn Soybeans

Winter

wheat

Cropland

(total)

Hay and

pasture Urban Forest

Minimum 11 2 7 2 20 3 1 2

Median 50 15 10 8 63 38 8 12

Maximum 100 58 16 41 100 61 43 47

N 24 21 7 12 32 20 21 26
12 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

The specific capacity and depth to water in the 

monitoring wells also were correlated to soil properties in the buffer areas. In areas with higher percentages of well-drained soils in the buffer areas, the depth 

to water generally increased as did the specific capacity of water in a well.

SHALLOW GROUND-WATER QUALITY IN 

AGRICULTURAL AREAS

Wells were sampled for major inorganic constituents, nutrients (nitrogen and phosphorus species), 

pesticides, and selected pesticide degradates. Nitrate 

typically is the most important nutrient in groundwater systems because of its potential effects on 

human health, solubility, and stability in oxic ground 

water; therefore, discussion of nutrients in this report 

is limited to nitrate. A large number of pesticides were 

analyzed in the samples collected (appendix 1); however, not all of them have significant use in the study 

area. Pesticides that were analyzed and detected, or are 

used extensively in the study area, are discussed in this 

report. Most of the wells were sampled in the early 

summer of 2000 (table 4). Four wells that were dry 

during the summer of 2000 were sampled in April 

2001, and five wells were resampled to evaluate 

whether constituent concentrations differed significantly between sampling periods. Rainfall for the 12-

month period prior to both sampling periods was about 

9 inches below the 30-year average annual rainfall 

(AWIS Weather Services, Inc., written commun., 

2001).

Major inorganic constituents and field properties did not vary substantially for four of the five wells 

that were resampled in 2001 (table 4). Differences in 

constituent concentrations between years typically 

were not greater than the variability associated with 

sampling and analysis as indicated by replicate samples. Calcium and alkalinity varied by more than 

15 percent in the samples collected from well 35 

(table 4), but other constituents in these samples did 

not vary substantially. Given the small amount of variability in major inorganic constituent concentrations 

between the sample periods, nitrate and pesticide data 

for the four wells sampled in 2001 are included with 

the data for the 28 samples from 2000.

About two-thirds of the samples collected were 

calcium bicarbonate water. In a few samples, particularly in low ionic strength samples (specific conductance less than 100 μS/cm), nitrate and chloride 

replaced bicarbonate as the dominant anion, and there 

was not a dominant cation in most of these samples. 

Samples from wells installed in regolith overlying the 

Fort Payne Chert had lower specific conductance and 

lower concentrations of constituents that are contributed from carbonate mineral dissolution, such as calcium and alkalinity, than samples from wells installed 

in regolith overlying the Tuscumbia Limestone 

(table 4). These differences for samples from wells in 

the Fort Payne Chert likely are the result of a greater 

amount of siliceous material in this formation than in 

Table 3. Spearman’s correlation coefficient, rho, for soil characteristics in buffer areas around wells

[Spearman’s rho bolded indicates significance at p<0.05 and italics indicates p<0.10; <, less than]

Slope

Percent

hydrologic 

group B

Percent 

well 

drained

Percent 

sand 

Percent 

silt

Percent 

clay

Available 

water 

capacity

Bulk 

density

Organic 

matter

Permeability pH

Slope 1.00 0.30 0.28 0.27 -0.59 0.48 0.35 0.30 0.04 0.07 0.54

Percent hydrologic group B 1.00 0.99 0.20 -0.00 0.44 -0.19 -0.35 -0.50 -0.13 0.48

Percent well drained 1.00 0.22 -0.02 0.46 -0.17 -0.35 -0.50 -0.16 0.53

Percent sand 1.00 -0.58 0.07 -0.20 0.20 0.02 -0.33 0.15

Percent silt 1.00 -0.54 0.67 -0.22 -0.15 0.08 -0.36

Percent clay 1.00 -0.67 -0.28 -0.28 -0.13 0.43

Available water capacity 1.00 0.03 0.06 -0.06 -0.11

Bulk density 1.00 0.46 0.18 0.03

Organic matter 1.00 0.32 -0.10

Permeability 1.00 -0.12

pH 1.00
Shallow Ground-Water Quality in Agricultural Areas 13

the Tuscumbia and Monteagle Limestones. The two 

samples with the highest specific conductance were 

completed in regolith overlying the Monteagle Limestone (table 4).

Dissolved-oxygen (DO) concentrations for most 

of the samples were greater than 1 mg/L (table 4) and 

were correlated to several factors. DO concentrations 

were positively correlated to the amount of welldrained soil in the buffer areas (Spearman’s rho=0.31, 

p=0.04). DO concentrations also tended to increase 

with depth to water (fig. 5). This somewhat atypical 

relation between DO and water level likely is a result 

of the hydraulic connection of water in wells completed in deep regolith to oxic water in the bedrock 

part of the aquifer. These deep wells generally had the 

highest specific capacities (table 1). Although the 

median DO concentration was lower in samples from 

the Tuscumbia Limestone than from the Fort Payne 

Chert (table 4), the difference was not statistically significant. DO concentrations were inversely related to 

the amount of forest land and positively related to the 

amount of agricultural land (cropland plus pasture) in 

the buffer area around wells. The inverse relation of 

DO to the amount of forest land in the buffer area 

likely is a result of a lower percentage of well-drained 

soils in forested areas related to greater amounts of 

respiration by soil microbes in forested areas.

Chloride concentrations were positively correlated with DO (Spearman’s rho=0.44, p=0.01), indicating that much of the chloride in the aquifer is 

transported from the surface with recharge rather than 

originating from dissolution of the carbonate rock. 

Median chloride concentrations were not statistically 

different for wells overlying the Tuscumbia Limestone 

and Fort Payne Chert; however, concentrations were 

considerably higher in the two wells completed in 

regolith overlying the Monteagle Limestone (table 4). 

The high concentrations of chloride in these two samples may reflect differences in the composition of this 

formation. Chloride can be contributed to ground 

water from numerous sources at land surface. Agricultural sources of chloride that could affect these wells 

include soil amendments such as potash (KCl) and 

sodium chlorate, a defoliant used on cotton.

The calcite saturation index is inversely related 

to DO concentrations, which may indicate relative differences in average ground-water residence times for 

some samples, particularly from wells completed in 

the Tuscumbia Limestone (fig. 6). The calcite saturation index relates the concentrations of calcium and 
14 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

Table 4. Water-quality properties and major inorganic constituent concentrations in samples from 32 wells in the Mississippian carbon[μS/cm, microsiemens per centimeter; oC, degrees Celsius; mg/L, milligrams per liter; μg/L, micrograms per liter; <, less than; E, estimated; --, no data; median value

second sample for wells with two samples]

Well 

number

Date 

sampled

Field pH 

(standard units)

Field 

specific 

conductance 

(μS/cm at 

25 oC)

Dissolved 

oxygen 

(mg/L)

Field 

alkalinity 

(mg/L as 

CaCO3)

Solids 

residue 

at 180 oC 

dissolved 

(mg/L)

Hardness, total 

(mg/L as 

CaCO3)

Calcium, 

dissolved 

(mg/L 

as Ca)

Magnesium, 

dissolved 

(mg/L 

as Mg)

Sodium, 

dissolved 

(mg/L as 

Na)

Potassium, 

dissolved 

(mg/L 

as K)

Chloride, 

dissolved 

(mg/L as Cl)

Sulfate, 

dissolved 

(mg/L as 

SO4)

Silica, 

dissolved 

(mg/L 

as SiO2)

Ir

d

so

(μ

as 

Fort Payne Formation

1 05/30/00 6.4 137 2.8 69 79 8 2.3 0.44 14 18 0.7 3.7 5.9 3 05/30/00 5.5 38 2.3 17 22 12 3.5 0.67 0.7 0.6 0.6 E0.3 9.4 8 05/31/00 4.8 45 0.8 7 23 7 1.7 0.62 4.0 0.4 3.8 2.4 9.3 1

10 05/31/00 5.3 32 1.4 7 18 7 2.0 0.48 1.5 0.4 3.8 E0.2 9.3 

11 06/06/00 4.6 66 7.8 4 61 20 5.1 1.7 1.9 0.9 4.3 0.4 7.7 11 04/19/01 4.9 67 7.7 8 58 20 5.2 1.8 1.7 1.1 4.4 0.3 7.8 

12 06/07/00 5.6 93 6.9 26 69 36 10 2.7 1.2 2.2 2.8 E0.3 8.7 13 06/01/00 7.1 248 6.7 96 140 120 28 12 1.1 0.5 5.7 0.5 8 13 04/18/01 6.8 215 7.2 91 110 110 25 11 1.5 0.4 5.1 0.5 8.1 14 05/31/00 6.7 123 6.6 54 72 58 17 3.8 1.4 E0.2 2.9 1 7.6 16 05/31/00 5.5 104 7.8 23 74 41 14 1.7 1.4 0.5 5.0 4.8 8 31 06/01/00 4.9 60 7.4 4 42 14 2.9 1.7 4.4 0.8 5.6 1.7 8.1 31 04/18/01 5.1 60 6.9 9 52 16 3.3 1.8 3.4 1 5.5 1.1 8.3 35 05/25/00 6.7 295 6.4 136 170 140 47 5.6 1.7 1 2.9 1.2 8.2 35 04/17/01 6.9 220 7.9 92 131 110 35 4.5 1.6 0.7 2.7 0.9 8 

Median of 11 

samples

5.5 93 6.6 23 69 20 5.14 1.72 1.5 0.6 3.8 1 8.1 

Tuscumbia Limestone

2 05/30/00 6.1 131 5.7 50 82 64 19 4.1 1.6 1.1 3.0 4 6.8 4 06/06/00 6.6 245 5.2 106 140 110 34 7.0 1.5 0.5 4.2 4 7.6 5 05/30/00 7.0 264 -- 115 158 130 48 2.0 4.7 0.8 1.2 7.6 8.4 6 06/05/00 6.8 178 7.7 39 127 70 17 6.7 4.1 0.7 9.7 2 8.4 7 06/05/00 6.2 263 7 99 162 120 39 4.5 1.7 0.7 6.9 2.7 6.9 
Shallow Ground-Water Quality in Agricultural Areas 15

Well 

number

Date 

sampled

Field pH 

(standard units)

Field 

specific 

conductance 

(μS/cm at 

25 oC)

Dissolved 

oxygen 

(mg/L)

Field 

alkalinity 

(mg/L as 

CaCO3)

Solids 

residue 

at 180 oC 

dissolved 

(mg/L)

Hardness, total 

(mg/L as 

CaCO3)

Calcium, 

dissolved 

(mg/L 

as Ca)

Magnesium, 

dissolved 

(mg/L 

as Mg)

Sodium, 

dissolved 

(mg/L as 

Na)

Potassium, 

dissolved 

(mg/L 

as K)

Chloride, 

dissolved 

(mg/L as Cl)

Sulfate, 

dissolved 

(mg/L as 

SO4)

Silica, 

dissolved 

(mg/L 

as SiO2)

Ir

d

so

(μ

as 

Tuscumbia Limestone—Continued

9 06/01/00 6.3 156 -- 51 94 73 16 8.2 1.8 0.5 5.6 1.2 6.3 

17 05/25/00 7.2 122 2.8 50 72 53 15 4.0 2.4 0.6 1.2 9.8 5.3 18 05/24/00 6.6 258 6.4 115 150 120 43 3.7 1.4 0.8 2.0 3.4 6.5 19 04/16/01 5.1 22 6.9 6 28 5 1.1 0.55 1.7 0.3 4.0 0.2 9.7 20 05/25/00 5.0 39 3.9 8 36 12 3.3 1.0 1.4 0.7 1.3 2.8 8.6 21 04/16/01 6.1 147 6.7 35 99 64 20 3.3 2.1 0.7 2.8 1.7 8.2 22 05/23/00 7.2 455 1 207 265 240 85 6.4 4.8 0.5 0.8 5.6 8.1 23 05/24/00 7.0 312 3.6 153 201 170 60 4.0 5.1 0.4 1.4 11 8.4 24 05/24/00 6.5 273 2.7 135 158 140 51 3.0 1.6 2.5 2.8 3.1 4.1 25 05/24/00 7.0 351 0.4 165 206 190 68 3.7 2.1 0.5 3.7 2.9 8.1 26 04/17/01 5.9 76 6.9 38 63 37 11 2.2 0.9 0.4 1.5 0.2 9 27 04/17/01 7.0 423 7.2 172 257 200 76 2.7 5.0 0.9 19 0.9 9.5 33 05/22/00 7.6 259 4.7 118 162 120 46 1.7 1.7 0.5 3.0 1.9 8.7 33 04/18/01 7.4 263 4.9 113 179 130 50 1.7 1.7 0.5 3.3 0.9 9 36 05/25/00 6.5 478 1 276 281 260 95 5.2 2.1 0.5 1.5 1.1 7.6 

Median of 19 

samples

6.6 258 5.2 106 150 120 39 3.6 1.8 0.6 2.8 2.85 8.1 

Monteagle Limestone

28 05/22/00 6.6 714 5.2 340 402 340 123 8.5 19 0.4 20 6 8.2 34 06/01/00 7.1 816 1.1 366 490 340 122 8.5 40 0.7 26 41.4 13.5 

Table 4. Water-quality properties and major inorganic constituent concentrations in samples from 32 wells in the Mississippian carbonContinued
16 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

carbonate ions in solution to the solubility of calcite. 

The calcite saturation index is expressed as the logarithm of the ion activity product of bicarbonate and 

calcium divided by the solubility constant for calcite. 

Saturation indices were calculated using the geochemical modeling code PHREEQC (Parkhurst and Appelo, 

1999). Saturation indices close to zero indicate water 

is near to saturation with respect to calcite. The degree 

of calcite saturation is a qualitative indicator of the 

contact time between the ground water and carbonate 

aquifer material. A small saturation index may indicate a short amount of contact time between the water 

and carbonate rock. As DO concentrations decrease, 

the calcite saturation index tends to be higher (fig. 6). 

As previously noted, differences in saturation indices 

also can be attributed to differences in the composition 

of bedrock as well as to ground-water residence time. 

Chert in both the Fort Payne Chert and the Tuscumbia 

Limestone could affect this relation and may account 

for the low calcite saturation indices for several samples also having low DO concentrations (fig. 6). For 

the small number of samples with CFC-12 age dates, a 

relation seems to exist between ground-water age and 

the calcite saturation index (fig. 6). 

Nitrate

Nitrate concentrations generally were low with 

no samples exceeding the drinking-water maximum 

contaminant level (MCL) of 10 mg/L. The maximum 

concentration of nitrate (as N) was 8.4 mg/L, and the 

median concentration was about 1 mg/L. Nitrate and 

DO concentrations were strongly correlated (fig. 7); 

therefore, nitrate concentrations were correlated to 

many of the same variables to which DO was correlated. For example, nitrate concentrations increase 

with the depth to ground water in the wells as did DO 

concentrations. This relation contrasts with the typical 

relation of decreasing nitrate concentrations with 

increasing depth to the water table documented in 

other ground-water studies (Hallberg and Keeney, 

1993). In this setting, increased depth to water in these 

regolith wells may reflect a hydraulic connection to 

oxic ground water in bedrock. These parts of the aquifer represent the active part of the flow system, where 

nitrate likely is more stable. Partial correlation analysis of variables related to both nitrate and DO indicates 

that DO concentration accounts for most of the variation in nitrate concentrations in ground water. Nitrate 

concentrations in four of the five wells sampled twice 

varied less than 5 percent (table 4), similar to the 

amount of variability between replicate samples. 

Nitrate concentrations were about 10 percent different 

in the two samples from well 33 (table 4).

The correlation of nitrate to DO suggests that 

nitrate concentrations are affected by denitrification 

and are low where either the average ground-water 

residence time is long or where recharge is slow as 

indicated by low DO concentrations. Nitrate and chloride concentrations are correlated and appear to be 

contributed to the aquifer predominantly from activities at land surface. Given that chloride is conserved in 

ground-water systems, the ratio of chloride to nitrate 

(Cl:NO3) may indicate whether nitrate concentrations 

in samples are affected by denitrification. Samples 

with nitrate concentrations greater than 2 mg/L generally had DO concentrations greater than 6 mg/L and 

Cl:NO3 ratios less than 2 (fig. 8). In contrast, samples 

with nitrate concentrations less than 1 mg/L tended to 

have lower DO concentrations and higher Cl:NO3

ratios. Two samples with high Cl:NO3 ratios were 

from wells completed in the Monteagle Limestone, 

and the elevated chloride in these samples may be 

from natural sources. Samples with nitrate concentrations less than 1 mg/L and a Cl:NO3 greater than about 

5 (fig. 8) likely represent samples from areas where 

denitrification is occurring. About a third of the samples fit these criteria. In addition, nitrate concentrations were inversely related to manganese 

concentrations (Spearman’s rho=-0.5, p=0.002). Dissolved manganese concentrations are greatly affected 

by the oxidation-reduction (redox) state of ground 
Shallow Ground-Water Quality in Agricultural Areas 17

water. The reactions that reduce manganese oxides to 

the soluble ionic form (Mn+2) follow denitrification in 

the sequence of redox reactions (Stumm and Morgan, 

1996). The inverse relation between nitrate and manganese concentration indicates that where nitrate concentrations are low, the redox conditions were 

favorable to denitrification.

Nitrate concentrations in the Eastern Highland 

Rim were lower than in other agricultural areas across 

the Nation. The median nitrate concentration for samples collected from 848 monitoring wells installed in 

agricultural areas in 30 NAWQA study areas across 

the Nation (fig. 9) was 2.3 mg/L compared to a median 

of about 1 mg/L for wells in this study (fig. 10). The 

NAWQA wells nationwide were sampled between 

1991 and 2001 and ranged in depth from 7 to 200 ft 

with a median depth of 25 ft, compared to a median 

depth of 37.5 ft for the wells in this study. However, 

the interquartile range in nitrate concentration generally is comparable for the two data sets, and the nitrate 

concentration distributions are not statistically different (fig. 10). The maximum nitrate concentration measured in this study was equal to the 75th percentile in 

the NAWQA wells nationwide. About 21 percent of 

the samples from the wells nationwide equaled or 

exceeded the drinking-water MCL of 10 mg/L. No 

samples from the monitoring wells in the Mississippian carbonate aquifer exceeded the MCL.

Pesticides

Pesticides have increased the productivity of 

agricultural land in the Nation by controlling weeds, 

fungi, insects, and nematodes, all of which can lower 

crop yields. Despite the increases in agricultural productivity and the associated economic benefits, a general concern exists about the effects of dispersing large 

quantities of potentially harmful pesticides into the 

environment. The fate of pesticides in the environment 

is influenced by many factors such as the method of 

application, physical and chemical properties of each 

pesticide, and numerous environmental factors. Pesticides typically are designed to degrade in a few days 

or weeks after application under ideal conditions. Degradation occurs by several processes including photolysis, hydrolysis, and biologically mediated reactions. 

Most of these processes occur more rapidly in the 

near-surface soil environment than in ground water. 

Movement of pesticides into ground-water systems 

may reduce the rate at which pesticides degrade, and 

pesticide residues may persist in ground water longer 

than in the soil zone. During the 1990s, numerous 

studies documented the importance of pesticide degradates in ground water (for example, Kolpin and others, 

1998).

Of the 32 wells sampled, 29 (91 percent) contained one or more pesticides or pesticide degradates 

(fig. 11). Thirty-five different pesticides and pesticide 

degradates were detected (appendix 1), but 11 of them 

were detected in only one sample at concentrations 

below 0.01 μg/L, and are not included in the summary 

of detections (table 5). Atrazine, fluometuron, norflurazon, and their degradates were detected frequently 

and at the highest concentrations (table 5). No pesticide concentrations exceeded established MCLs for 

drinking water, but 32 of the 35 pesticides detected do 

not have MCLs. Degradates generally do not have 

MCLs. More than half of the samples contained 5 or 

more pesticides (fig. 11), and the maximum number of 

pesticides detected in a single sample was 13. The 

maximum concentration of a single pesticide was 

3.21 μg/L for demethylnorflurazon, a degradate of the 

cotton herbicide norflurazon (table 5). About half of 

the samples had a total pesticide concentration of 

1 μg/L or more (fig. 11), and the maximum total pesticide concentration measured in a sample was 7.2 μg/L.

The frequency of detection and magnitude of 

concentrations was related to the estimated use of pesticides (table 5). Atrazine, fluometuron, and norflurazon are among the most heavily used pesticides in the 

study area and were detected more frequently than 

pesticides with lower estimated use. Aldicarb, which 
18 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

had comparable estimated use to fluometuron and also 

is used on cotton, was not detected, and its degradates 

were detected less frequently and at lower concentrations than fluometuron (table 5). The physical and 

chemical properties of these two pesticides are similar; 

however, the field dissipation half-life of fluometuron 

is about twice as long as that of aldicarb (Wauchope 

and others, 1992). Glyphosate, the exception to the 

relation between use and detection frequency, had the 

highest estimated use and was applied within the 

buffer areas of all of the wells but was not detected 

(table 5). The analytical method for glyphosate had a 

higher MRL (0.1 μg/L) than many of the other pesticides (table 5), but that probably does not account for 

the lack of detections. Median concentrations of 

fluometuron and atrazine detections 

were 0.41 and 0.12 μg/L, respectively 

(greater than the MRL for glyphosate), 

even though fluometuron and atrazine 

applications were about a third of the 

estimated amount of glyphosate 

applied. Glyphosate has a soil sorption 

coefficient two orders of magnitude 

higher than atrazine and fluometuron, 

and the aerobic soil half-life of glyphosate is 47 days compared to 146 and 

189 days for atrazine and fluometuron, 

respectively (U.S. Department of Agriculture, 2002). Degradates of glyphosate were not analyzed in this study.

Fluometuron and atrazine generally were detected in samples from 

wells where these pesticides were 

applied in the buffer area (fig. 12). 

Fluometuron was detected in samples 

from 83 percent of wells with buffer 

areas that had estimated use during 

2000 (fig. 12). Three of the four samples in which fluometuron was not 

detected had low DO concentrations 

(less than 1.5 mg/L), indicating long 

average ground-water residence times 

at these wells, slow rates of recharge, 

or some degree of confinement in the 

regolith (the fourth well could not be 

pumped continuously and did not have 

a DO measurement). Atrazine was 

detected in about 70 percent of the 

wells where it was applied in the buffer 

area in 2000; and, like fluometuron, 

five of the six samples from wells with estimated use 

in which atrazine was not detected had DO concentrations less than 1.5 mg/L (the sixth sample did not have 

a DO measurement). Fluometuron was detected only 

in samples from wells where it was applied in the 

buffer area during the 2000 growing season; however, 

atrazine was detected at concentrations between 0.014 

and 0.21 μg/L in samples from six monitoring wells 

where no atrazine was applied in the buffer area during 

the 2000 growing season (fig. 12). These low-level 

detections of atrazine indicate either that residues persist in the subsurface for periods greater than a year, or 

that the contributing area for these wells includes areas 

not accounted for by the buffer areas.
Shallow Ground-Water Quality in Agricultural Areas 19

Pesticide degradates represented 38 percent of 

the pesticides detected at concentrations greater than 

0.01 μg/L; however, degradates accounted for only 

17 percent of the pesticides analyzed. Nine of the 12 

most frequently detected pesticides were degradates 

(table 5). The occurrence of degradates generally coincided with detection of the parent pesticide. Atrazine, 

fluometuron, and norflurazon degradates were commonly detected at concentrations comparable to or 

greater than the parent pesticide (table 5 and fig. 13). 

In some samples, the parent pesticide was not 

detected. Aldicarb sulfone and sulfoxide (degradates 

of the cotton insecticide aldicarb) were detected at 

concentrations less than 0.2 μg/L (table 5) in about 

22 percent of the samples, but aldicarb was detected 

only once at a concentration of 0.004 μg/L. Not all 

degradates analyzed were detected. Although carbofuran was detected in two samples at low concentrations 

(less than 0.03 μg/L), two degradates analyzed 

(3-ketocarbofuran and 3-hydroxycarbofuran) were not 

detected. The MRLs for these degradates are 0.072 

and 0.062 μg/L, respectively.

Concentrations of the degradates of fluometuron 

generally were less than the fluometuron concentration, in contrast to norflurazon and atrazine degradates, which typically were detected at higher 

concentrations than norflurazon and atrazine (fig. 13). 

The lower relative concentrations of fluometuron degradates compared with atrazine and norflurazon may 

be the result of additional applications of fluometuron 

later in the growing season or may reflect slower rates 

of degradation for fluometuron. The principal degradate of fluometuron detected was demethylfluometuron (41 percent of samples, table 5). The degradate 3-

(trifluromethyl) aniline (TFMA) forms from degradation of fluometuron or demethylfluometuron and was 

detected in 19 percent of the samples; 3-phenylurea, 

the degradate of demethylfluometuron was not 

detected. TFMA concentrations typically were low 

(median was 0.07 μg/L) and were less than demethylfluometuron concentrations; however, in the two 

samples from well 33, TFMA concentrations were 

considerably higher (0.24 and 0.42 μg/L), and demethylfluometuron concentrations were less than TFMA 

concentrations (< 0.05 and 0.18 μg/L). Samples from 

this well had a calcite saturation index near zero 

(table 4), indicating a longer average ground-water 

residence time than for other samples. Estimated 

recharge dates from CFC data for this well were in the 

mid- to late-1970s. The relatively high TFMA concentrations may be the result of the longer average residence time for ground water at this well, allowing 

more degradation to occur than at the other wells.

The deethylatrazine to atrazine ratio (DAR) has 

been used as a qualitative indicator of the pathways 

through which water and atrazine move into the subsurface (Adams and Thurman, 1991). Deethylatrazine 

forms from the breakdown of atrazine by microbes in 

the soil environment. A DAR less than 1 may indicate 

rapid transport to the subsurface with short residence 

times for water and atrazine in the soil zone. In the 

Eastern Highland Rim, sinkholes in addition to soil 

macropores could provide pathways for rapid movement of water and pesticides into the ground water. 

The majority of atrazine concentrations were less than 

0.25 μg/L. The five samples with atrazine concentrations greater than 0.75 μg/L had DARs less than 1 

(fig. 14), suggesting that these high atrazine concentrations are the result of rapid recharge to the aquifer 

with a short residence time in the soil zone. The few 

detections of metolachlor, which has a shorter aerobic 

soil half-life than atrazine (U.S. Department of 
20 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

 
Shallow Ground-Water Quality in Agricultural Areas 21

Table 5. Summary statistics for pesticides detected at concentrations equal to or greater than 0.01 microgram per liter 

in samples from the Mississippian carbonate aquifer and estimated use of selected pesticides in buffer areas around 

wells

[F, fungicide; H, herbicide; I, insecticide; Degr., pesticide degradate; E, estimated value; --, no data; NA, not applicable; MRL, minimum reporting 

level; μg/L, micrograms per liter; lbs, pounds]

Pesticide 

Detection 

frequency

(percent)

Number of 

detections

Maximum 

concentration 

(μg/L)

Median 

detection

(μg/L) MRL

Pesticide 

type

Median 

estimated 

use (lbs)

Number of 

buffer 

areas with 

use during 

2000

Atrazine 62 20 1.83 0.12 0.007 H 36 21

Fluometuron 59 19 2.13 0.41 0.062 H 27 24

Deethyldeisopropylatrazine 59 19 0.071 E .022 E 0.06 Degr. NA NA

Norflurazon 53 17 0.71 0.081 0.077 H 8 24

Hydroxyatrazine 50 16 0.168 E .035 E 0.193 Degr. NA NA

Demethylnorflurazon 47 15 3.21 0.41 0.05 Degr. NA NA

Deethylatrazine 47 15 0.71 E .19 E 0.002 Degr. NA NA

Deisopropylatrazine 47 15 0.1 E .034 E 0.074 Degr. NA NA

Demethylfluometuron 41 13 1.85 0.39 0.05 Degr. NA NA

Aldicarb sulfone 22 7 0.16 E .12 E 0.160 Degr. NA NA

3-(trifluromethyl) aniline 

(TFMA)

19 6 0.42 0.07 0.05 Degr. NA NA

Aldicarb sulfoxide 16 5 0.085 E .029 E 0.027 Degr. NA NA

Metolachlor 12 4 0.92 0.19 0.002 H 5 22

Prometon 9 3 0.17 0.02 0.018 H -- --

Diuron 9 3 0.14 .016 E 0.079 H 11 24

Imazethapyr1 7 2 0.056 E NA 0.088 H < 0.5 15

Metalaxyl 6 2 0.022 E NA 0.057 F 4.3 24

Carbofuran 6 2 0.028 NA 0.003 I 0.8 21

Simazine 6 2 0.021 NA 0.005 H 0.5 21

Acetochlor 3 1 0.057 NA 0.002 H 5 21

Metribuzin 3 1 0.015 NA 0.004 H 3 24

Pendimethalin 3 1 0.059 NA 0.004 H 3.5 21

2,4-D methyl ester 3 1 0.025 E NA 0.086 H -- --

Diphenamid 3 1 0.014 E NA 0.058 H -- --

Glyphosate2 0 0 -- NA 0.1 H 127 32

Aldicarb 0 0 -- NA 0.082 I 28 24

Carbaryl 0 0 -- NA 0.003 I 2.7 21

Prometryn 0 0 -- NA 0.05 H 4.7 24

1Analyzed in 28 samples

2Analyzed in 17 samples
22 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

Agriculture, 2002), at high concentrations predominantly in samples with DARs less than 1 (fig. 14), supports the interpretation that high concentrations of 

atrazine result from rapid infiltration of recharge.

Given that pesticides used in buffer areas of 

wells differed, the total pesticide concentration (sum 

of all pesticide and pesticide degradates in a sample), 

in addition to the amount of cropland near a well, was 

used to evaluate which factors were related to pesticide occurrence. Because soil properties are directly 

correlated to land use, discerning the influence of differences in soil properties on the occurrence of 

pesticides in this setting is not possible. The 

total pesticide concentration was correlated to 

DO concentration and, in turn, related to factors 

correlated to DO concentrations. Although DO 

is positively correlated to nitrate concentration, 

partial correlation analysis indicates that nitrate 

and DO account for some of the variation in 

total pesticide concentration. Given the predominance of cropland near these wells and the 

relation between total pesticide and nitrate concentrations, fertilizer application to cropland is 

the probable source of nitrate to these wells. 

The relation between DO and total pesticide 

concentration indicates that pesticides are more 

likely to be detected at high concentrations 

where ground-water residence time is short and 

the rate of recharge is fast. Although the relation between total pesticide concentration and 

the calcite saturation index was not statistically 

significant, samples with the highest total pesticide concentrations were associated with wells 

having ground water with a short residence 

time based on DO and the saturation index 

(fig. 15).

Pesticides were detected more frequently 

in samples from monitoring wells in this study 

than in samples from other agricultural areas 

across the Nation. Atrazine and its degradate, 

deethylatrazine, were detected in 62 and 

47 percent, respectively, of samples collected 

from the Mississippian carbonate aquifer 

(fig. 16). Atrazine and deethylatrazine were 

detected in about 25 percent of the monitoring 

wells sampled between 1991 and 2001 as part 

of agricultural land-use studies conducted by 

the NAWQA Program (U.S. Geological Survey, 

2002a) and were the most frequently detected 

pesticides nationwide. The greater frequency of 

detection in this study could reflect greater atrazine 

use in the LTEN than in the areas sampled in the 

national data set; however, about half of the wells in 

the national data set were in areas that had greater estimated use of atrazine than in the LTEN (Thelin and 

Gianessi, 2000) (fig. 17). The average detection frequency of atrazine in samples from areas nationwide 

with atrazine use greater than the LTEN was about 

30 percent, much lower than the 62 percent detection 

frequency in samples collected for this study. Metolachlor was the third most frequently detected pesticide 
Shallow Ground-Water Quality in Agricultural Areas 23

FLUOMETURON ATRAZINE 

 19 17 28

 RATIO OF DEGRADATE CONCENTRATIONS

 TO PARENT PESTICIDE CONCENTRATION

Figure 13. Ratios of degradate to parent pesticide concentration

for fluometuron, norflurazon, and atrazine in samples from the

Mississippian carbonate aquifer.

Degradate concentration

equal to parent

pesticide

NORFLURAZON

Note: Samples without a degradate detection were assigned

ratios of 0.1.

0.01

0.1

1

10

17 NUMBER OF DETECTIONS

 (28 includes some samples

 with atrazine degradate

 detections only)

EXPLANATION

75th 

Median

25th

10th

90th

Percentiles

Percentiles

nationwide and was the fourth most frequently 

detected pesticide in this study (not including degradates). Median concentrations of atrazine, deethylatrazine, and metolachlor were not statistically different 

between the data sets, but tended to be slightly higher 

in samples collected for this study than in samples collected nationwide (fig. 16).

The cotton herbicides fluometuron and norflurazon also were detected more frequently in this study 

than in samples from agricultural land-use studies 

across the Nation (fig. 16). Fluometuron and norflurazon were detected in 59 and 53 percent, respectively, 

of samples in this study compared to 2 and 1 percent, 

respectively, of samples from the other study areas. 

These herbicides had limited use in the areas of the 

country represented by the national data (fig. 17, Thelin and Gianessi, 2000), which may explain the lower 

detection frequency. Median concentrations of 

fluometuron and norflurazon were 0.41 and 0.08 μg/L, 

respectively, in this study, compared to median concentrations of 0.1 and 0.07 μg/L, respectively, for the 

national data (fig. 16).

Implications for Drinking-Water Quality of the 

Mississippian Carbonate Aquifer

Water-quality data collected for this land-use 

study and from a previous study of drinking-water 

wells located in the Eastern Highland Rim (Kingsbury 

and Shelton, 2002) indicate that the Mississippian carbonate aquifer is susceptible to contamination from 

nonpoint sources and that the water quality throughout 

much of the aquifer has been affected by activities 

associated with crop production. In the summer of 

1999, water samples from a network of drinking-water 

wells (predominantly domestic wells completed in 

bedrock) were analyzed for a broad range of constituents to characterize the quality of water in the aquifer 

(Kingsbury and Shelton, 2002). Domestic and publicsupply wells in the Eastern Highland Rim typically 

withdraw ground water from the bedrock in the Mississippian carbonate aquifer. The water-quality data collected from the shallow monitoring wells in this study 

represent water in the aquifer that should be most 

affected by activities associated with agricultural land 

use. Much of the recharge to the bedrock part of the 

aquifer is from water moving through the regolith. The 

monitoring well data are compared to data collected 

from 25 of the drinking-water wells that are completed 

in the Fort Payne Chert, Tuscumbia Limestone, and 
24 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

Monteagle Limestone to characterize the effect of 

cropland on parts of the Mississippian carbonate aquifer used for water supply. These drinking-water wells 

ranged from 44 to 157 ft deep, with a median depth of 

87 ft (Kingsbury and Shelton, 2002).

Concentrations of inorganic constituents in the 

agricultural land-use monitoring wells are similar to 

concentrations in the drinking-water wells from the 

previous study. Although drinking-water wells are 

completed in bedrock and generally are deeper than 

the monitoring wells, both groups of wells have similar ranges in DO, pH, and specific conductance 

(fig. 18). With the exception of a slightly higher 

median concentration of potassium in samples from 

the land-use monitoring wells, the land-use monitoring 

wells and the drinking-water wells are not statistically 

different with respect to major inorganic constituent 

concentrations. Potassium is a plant nutrient and is 

applied to agricultural lands, which may account for 

the slightly higher median concentration for samples 

from the land-use monitoring wells.

Nitrate concentrations generally were low in 

both well networks; the median nitrate concentration 

for the drinking-water wells was about 1.5 mg/L compared to 1 mg/L for the monitoring wells (fig. 19). 

Nitrate concentrations greater than 5 mg/L were infrequent in both networks (fig. 19). The drinking-water 

wells had two samples that exceeded the maximum 

contaminant level of 10 mg/L. Point sources of nitrate 

(an animal feedlot and a small cooperative fertilizer 

storage facility) near these wells may have contributed 

to these high concentrations (Kingsbury and Shelton, 

2002). The generally low concentrations of nitrate in 

samples from the land-use monitoring wells support 
Shallow Ground-Water Quality in Agricultural Areas 25

the interpretation that point sources and rapid transport 

of nitrate to the bedrock part of the aquifer likely contributed to these high concentrations (greater than 

13 mg/L). 

Although the amount of cropland in buffer areas 

around the drinking-water wells was less than around 

the land-use monitoring wells (fig. 20), pesticides 

detected frequently in samples from the land-use monitoring wells corresponded to those detected frequently in the samples from the drinking-water wells 

(fig. 21). The most frequently detected pesticides in 

both networks were atrazine and its degradates, fluometuron, and norflurazon (fig. 21). The degradates of 

fluometuron and norflurazon were not analyzed in 

samples collected from the drinking-water wells. 

Metolachlor, deethylatrazine, and the degradates of 

aldicarb had similar detection frequencies in samples 

from both networks. Although several pesticides were 

detected more frequently in the land-use monitoring 

wells than in the drinking-water wells, median concentrations for several pesticides were similar (fig. 21). 

The higher detection frequencies in samples from the 

land-use monitoring wells may be related to the higher 

percentage of cropland in buffer areas around the wells 
26 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001
Shallow Ground-Water Quality in Agricultural Areas 27
28 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

(fig. 20). A number of the samples analyzed for pesticides by HPLC/MS (fluometuron, norflurazon, and 

aldicarb degradates) from the drinking-water wells 

exceeded the sample holding time. The concentrations 

and detection frequencies for these pesticides may be 

biased low, and the holding time exceedances could 

contribute to the lower detection frequencies in samples from the drinking-water wells than detection frequencies in samples from the land-use monitoring 

wells.

Tebuthiuron, prometon, and dieldrin, which 

have non-agricultural uses, were detected in samples 

from the drinking-water wells but were not detected 

above 0.01 μg/L in samples from the land-use monitoring wells. The concentrations of these pesticides 

were comparable to the concentrations of the pesticides detected that are used on cropland; however, 

their detection frequency is somewhat lower (fig. 21). 

Tebuthiuron and prometon are herbicides that are used 

predominantly for weed control along rights-of-way 

and roadsides, and they were detected in samples from 

drinking-water wells having large amounts of urban 

land use in the buffer areas or that were near railroads 

and highways (Kingsbury and Shelton, 2002). 

Although dieldrin had agricultural use until the 1970s, 

detections only in samples from the drinking-water 

wells suggest that the principal source of dieldrin to 

the aquifer is residue remaining from its use for termite control around homes.

No individual pesticide concentrations from 

either well network exceeded drinking-water standards, but drinking-water standards typically do not 

exist for degradates, which may have toxicological 

characteristics similar to the parent pesticide. The 

potential health effects of mixtures of low-level pesticides and their degradates are not known. A high percentage of samples from both networks contained at 

least one pesticide. More than 60 percent of samples 

from the land-use monitoring wells and about 25 percent of samples from the drinking-water wells had five 

pesticide or pesticide-degradate detections (fig. 22). 

The high percentage of samples with multiple pesticide detections is a result of the co-occurrence of fluometuron, norflurazon, aldicarb degradates (cotton 

pesticides), and atrazine and its degradates. Few samples from either network (about 15 percent) had more 

than eight pesticides in a sample, but the frequency of 

samples with a large number of detections was greater 

in the drinking-water wells (fig. 22). The higher percentage of samples with eight or more pesticides and 

the greater number of pesticides detected in samples 

from the drinking-water wells may be a result of the 

larger contributing areas for these wells than for the 

land-use monitoring wells. The larger contributing 

areas for the drinking-water wells likely integrate 

more land uses and crop types, which increases the 

maximum number of pesticides detected but generally 

lowers concentrations (fig. 23).

The total pesticide concentration was more than 

an order of magnitude higher in the land-use monitoring wells than in the drinking-water wells for 50 percent of samples (fig. 23). The total pesticide 

concentration was less than 1 μg/L in 60 percent of the 

land-use monitoring wells and in about 80 percent of 

the drinking-water wells (fig. 23). Similar to the number of pesticides detected in a sample, the total pesticide concentration for the two networks converge for 

about the upper 15 percent of samples. The likelihood 

of a well having a total pesticide concentration greater 

than 2 μg/L (not including the cotton herbicide degradates) was about the same for both networks.
Summary and Conclusions 29

SUMMARY AND CONCLUSIONS

Thirty-two monitoring wells were installed in 

regolith in the Mississippian carbonate aquifer and 

sampled for major inorganic constituents, nutrients, 

and selected pesticides and pesticide degradates to 

characterize the effect of row-crop agriculture on the 

quality of recently recharged ground water. Land use 

and soil characteristics within a 1,640-ft radius buffer 

area around each well were delineated, and pesticide 

use was estimated based on crop acreages. A close 

association among land use, soil characteristics (cropland in areas with well-drained soils), and hydrology 

in this area limited the analysis of how these factors 

affect nitrate and pesticide occurrence. The interdependence of these variables in this study suggests that 

ground-water reconnaissance studies that attempt to 

relate ground-water quality to factors such as soil 

properties without considering possible correlation 

between soil properties and land use may attribute 

movement of pesticides into ground water to differences in soils, when in fact, differences in land use and 

pesticide use are related to soil characteristics.

Nitrate concentrations in the land-use monitoring wells generally were low, with a maximum concentration of about 8 mg/L and a median of 1 mg/L. 

The principal factor affecting nitrate concentrations 

was dissolved-oxygen concentrations. Low dissolvedoxygen concentrations in wells likely indicate longer 

average ground-water residence times, slow rates of 

recharge, or some degree of confinement in the 

regolith. Ratios of chloride (which is conserved in 

ground water) to nitrate suggest that nitrate concentrations in at least a third of the samples were affected by 

denitrification. Although nitrate concentrations were 

not correlated to the amount of cropland in the buffer 

areas, a correlation between nitrate and total pesticide 

concentrations suggests that cropland is the probable 

source of nitrate to the these wells. Nitrate concentrations in this study generally were lower than concentrations measured in similar agricultural land-use well 

networks sampled for the National Water-Quality 

Assessment Program throughout the Nation.

Agricultural land in the Eastern Highland Rim 

typically occurs in areas with well-drained soils and 

low organic matter content, which likely contributes to 

the frequent detection of the most heavily used pesticides in the land-use monitoring wells. With the 

exception of glyphosate, which sorbs tightly to soil, 

pesticides with the highest use, such as fluometuron, 

atrazine, and their degradates, were detected most frequently and at the highest concentrations. Fluometuron and atrazine were detected in 83 and 70 percent, 

respectively, of the samples from wells that had applications of these pesticides in the surrounding buffer 

areas. Those samples without atrazine and fluometuron detections, but with estimated use in buffer areas, 

were from wells with dissolved-oxygen concentrations 

less than 1.5 mg/L. Generally, pesticide concentrations 

were less than 1 μg/L, and the maximum concentration 

measured was 3.21 μg/L of demethylnorflurazon, a 

degradate of the cotton herbicide norflurazon. The 

highest concentrations of pesticides generally were 

associated with short average ground-water residence 

time as indicated by high dissolved-oxygen concentrations and low calcite saturation indices. Pesticide degradates usually were detected in association with the 

parent pesticide, and concentrations generally were 

comparable to or greater than the parent pesticide concentrations.

Nitrate concentrations in samples in this study 

generally were lower than in samples from similar 

well networks in agricultural areas across the country; 

however, pesticides were detected more frequently in 

samples in this study. For example, atrazine and its 

degradate, deethylatrazine, were detected in 62 and 

47 percent, respectively, of samples in this study and 

were detected in about 25 percent of the 851 wells 

sampled for agricultural land-use studies conducted by 

the National Water-Quality Assessment Program. In 

those study areas with atrazine use greater than in the 

lower Tennessee River Basin, atrazine was detected in 

about 30 percent of the samples. Cotton pesticides 

were detected much more frequently in this study, but 

many of the study areas nationwide had small amounts 

of cotton acreage.

Similar nitrate and pesticide concentrations in 

samples from these shallow monitoring wells and 

samples collected in an earlier study from deeper 

drinking-water wells completed in bedrock indicate 

that the Mississippian carbonate aquifer is susceptible 

to nonpoint-source contamination associated with 

cropland. Nitrate concentrations generally were low in 

both well networks, and concentrations greater than 

5 milligrams per liter were infrequent. The finegrained texture of the regolith likely slows the rate of 

nitrate transport throughout much of the area and 

allows for some denitrification to occur, keeping concentrations low. Pesticide detection frequencies and 

maximum concentrations were higher in the land-use 

monitoring wells than in the drinking-water wells; 

however, the median concentrations of pesticides 
30 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

detected in both networks were similar. The lower frequency of detection in the drinking-water wells may 

result from a smaller percentage of cropland in the 

contributing areas of these wells. Pesticides with noncropland uses were detected in the drinking-water 

wells at lower frequencies than pesticides used on 

cropland, but at similar concentrations. Similarities in 

water quality of ground water collected from the landuse monitoring wells and the drinking-water wells 

probably reflect the karst hydrology of the aquifer, 

which allows for substantial movement of nonpointsource contaminants away from agricultural areas 

once water has moved through the regolith to conduits 

in bedrock. Rapid movement of nonpoint-source contaminants also can occur when recharge enters the 

conduit flow system through sinkholes or macropores 

where the regolith is thin.

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APPENDIXES

Appendix 1 35

Appendix 1. Pesticides and pesticide degradates analyzed, common name, and use

[MRL, minimum reporting level; μg/L, micrograms per liter; CAS, chemical abstracts reference number; H, herbicide; I, insecticide; F, fungicide; 

Degr., pesticide degradate; N/A, not applicable; --, no CAS number; pesticides in italics were analyzed before analytical method approval, and data 

in this report are provisional; *, pesticides denoted with an asterisk have had low or inconsistent recoveries throughout method development, and 

concentrations always are reported as estimated; pesticides denoted with a "+" were analyzed at the U.S. Geological Survey Organic Geochemistry 

Research Laboratory in Lawrence, Kansas]

Compound Common name MRL, in μg/L CAS number Use

Pesticides detected

2,4-D methyl ester N/A 0.086 1928-38-7 H

3(4-chlorophenyl) methyl urea N/A 0.092 1897-46-6 H-Degr.

Acetochlor Acenit, Guardian, Harness 0.002 34256-82-1 H

Aldicarb* Temik 0.082 116-06-3 I 

Aldicarb sulfone* Standak, aldoxycarb 0.16 1646-88-4 I-Degr.

Aldicarb sulfoxide* Temik sulfoxide 0.027 1646-87-3 I-Degr.

Atrazine Aatrex 0.001 1912-24-9 H

Deethylatrazine* N/A 0.002 6190-65-4 H-Degr.

Deisopropylatrazine* N/A 0.074 1007-28-9 H-Degr.

Deethyldeisopropylatrazine* N/A 0.06 3397-62-4 H-Degr.

Hydroxyatrazine N/A 0.193 2163-68-0 H-Degr.

Bentazon* Basagran, Adagio, Galaxy, Storm 0.019 25057-89-0 H

Carbaryl* Sevin 0.003 63-25-2 I

Carbofuran* Furadan 0.003 1563-66-2 I

Diphenamid Dymid, Enide, Rideon, Dyfen 0.058 957-51-7 H

Diuron DCMU, Diurex, Aguron, Karmex 0.079 330-54-1 H

Fluometuron Cortoran, Lanex, Cottonex, Flo-met 0.062 2164-17-2 H

Demethylfluometuron+ N/A 0.05 -- H-Degr.

3-(trifluromethyl) aniline (TFMA)+ N/A 0.05 -- H-Degr.

Imazethapyr* Pursuit, Pursuit DG 0.088 81335-77-5 H

Metalaxyl Apron, Subdue, Ridomil 0.057 94-81-5 F

Methiocarb* Draza, Mesurol, Slug-geta 0.08 57837-19-1 I

Metolachlor Dual, Pennant 0.002 51218-45-2 H

Methomyl* Nudrin, Lannate, Lanox 0.077 2032-65-7 I

Metribuzin Sencor, Lexone 0.004 21087-64-9 H

p,p’-DDE N/A 0.006 72-55-9 I-Degr.

Norflurazon Solicam, Telok, Evital, Zorial 0.077 27314-13-2 H

Demethylnorflurazon+ N/A 0.05 -- H-Degr.

Pendimethalin Prowl, Stomp 0.004 40487-42-1 H

Prometon Pramitol, Princep 0.018 1610-18-0 H

Trifluralin Treflan, Gowan 0.002 1582-09-8 H

Siduron Tupersan, Trey 0.093 1982-49-6 H

Simazine Princep 0.005 122-34-9 H

Sulfometuron-methyl Oust, DPX-T5648 0.039 74222-97-2 H
36 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

Compound Common name MRL, in μg/L CAS number Use

Pesticides not detected

2,4-D Aqua Kleen, Weedone-2,4-DP 0.077 94-75-7 H

2,6-Diethylaniline N/A 0.003 579-66-8 H-Degr.

3-Hydroxycarbofuran N/A 0.062 16655-82-6 I-Degr.

3-Ketocarbofuran* N/A 0.072 16709-30-1 I-Degr.

3-(trifluromethyl)phenylurea 

(TFMPU)+

N/A 0.05 -- H-Degr.

2,4-DB Butyrac, Butoxone, Legumex D 0.054 94-82-6 H

Acifluorfen, sodium salt Tackle, Blazer 0.062 62476-59-9 H

Alachlor Lasso, Bronco 0.002 15972-60-8 H

alpha-BHC HCH-alpha 0.002 319-84-6 I

Bendiocarb Ficam, Tattoo 0.061 22781-23-3 I

Benfluralin Balan, Benefin 0.002 1861-40-1 H

Benomyl Benlate 0.022 17804-35-2 F

Bensulfuron-methyl Londax 0.048 83055-99-6 H

Bromacil* Bromax, Hyvar, Uragon 0.081 314-40-9 H

Bromoxynil* Bromanil, Buctril, Torch 0.057 1689-84-5 H

Butylate Sutan + 0.002 2008-41-5 H

Chloramben methyl ester* Amiben, methyl ester 0.114 7286-84-2 H

Chlorimuron-ethyl Classic 0.037 90982-32-4 H

Chlorothalonil* Bravo, Forturf 0.048 1897-45-6 H

Chlorpyrifos Lorsban, Dursban 0.004 2921-88-2 I

Clopyralid Stinger, Lontrel 0.041 1702-17-6 H

Cyanazine Bladex 0.004 21725-46-2 H

Cyanazineamide+ N/A 0.05 -- H-Degr.

Cycloate* Ro-Neet, Marathon 0.054 1134-23-2 H

Dacthal monoacid DCPA Monoacid 0.072 887-54-7 H-Degr.

DCPA Dacthal 0.002 19719-28-9 H

Diazinon Spectracide 0.002 333-41-5 I

Dicamba Banvel, Marksman, Clarity 0.096 1918-00-9 H

Dichlorprop Seritox 50, Weedone 0.05 120-36-5 H

Dieldrin Dieldrin, Panoram D-31 0.001 60-57-1 I

Dimethenamid Frontier 0.05 87674-68-8 H

Dinoseb DNPB, Caldon, Dynamite 0.043 88-85-7 H

Disulfoton Di-Syston 0.017 298-04-4 I

EPTC Eradicane, Eptam 0.002 759-94-4 H

Ethalfluralin Sonalan 0.004 55283-68-6 H

Ethoprop Mocap 0.003 13194-48-4 I

Fenuron Beet-Klean, Fenidim 0.074 101-42-8 H

Appendix 1. Pesticides and pesticide degradates analyzed, common name, and use—Continued
Appendix 1 37

Compound Common name MRL, in μg/L CAS number Use

Pesticides not detected—Continued

Flumetsulam* DE 498, XRD 498 0.087 98967-40-9 H

Fonofos Dyfonate 0.003 944-22-9 I

Glyphosate+ Round-up 0.1 1071-83-6 H

Imazaquin* Image 1.5LC; Scepter 1.5L 0.103 81335-37-7 H

Imidacloprid Admire, Gaucho, Merit 0.106 105827-78-9 I

Lindane Isotox 0.004 58-89-9 I

Linuron Lorox 0.002 330-55-2 H

Malathion Cythion 0.005 121-75-5 I

MCPA Bordermaster, Metaxon, Rhomene 0.058 86-50-0 H

MCPB* Tropotox, Can-Trol, PDQ 0.062 94-74-6 H

Methomyl oxime* N/A 0.01 16752-77-5 I-Degr.

Azinphos-methyl* Guthion 0.001 13749-94-5 I

Methyl parathion Penncap-M 0.006 298-00-0 I

Metsulfuron-methyl * Escort, Gropper, Ally 0.114 74223-64-6 H

Molinate Ordram 0.004 2212-67-1 H

Napropamide Devrinol 0.003 15299-99-7 H

Neburon Granurex, Herbalt, Kloben 0.075 555-37-3 H

Nicosulfuron Accent, Accent DF 0.065 111991-09-4 H

Oryzalin Ryzelan, Surflan, Dirimal 0.071 19044-88-3 H

Oxamyl Vydate L, Thioxamyl 0.016 23135-22-0 I

Oxamyl oxime* N/A 0.064 30558-43-1 I-Degr.

Parathion Phoskil 0.004 56-38-2 I

Pebulate Tillam 0.004 1114-71-2 H

cis-Permethrin Pounce, Ambush 0.005 54774-45-7 I

Phorate Thimet 0.002 298-02-2 I

Picloram Tordon, Amdon, Grazon 0.071 191802-1 H

Prometryn+ Caparol 0.05 7287-19-6 H

Pronamide Kerb 0.003 23950-58-5 H

Propachlor Ramrod 0.007 1918-16-7 H

Propanil Stam, Stampede 0.004 709-98-8 H

Propargite Comite 0.013 2312-35-8 I

Propiconazole Tilt, Orbit, Banner, Proconazole, Wocosin 0.064 60207-90-1 F

Propoxur Baygon, PHC, Suncide, Unden 0.059 114-26-1 I

Tebuthiuron Graslan, Spike, Perflan 0.01 34014-18-1 H

Terbacil* Sinbar, DPX-D732, Geonter 0.007 5902-51-2 H

Terbufos Counter 0.013 13071-79-9 I

Thiobencarb Bolero 0.002 28249-77-6 H

Triallate Far-Go 0.001 2303-17-5 H

Tribenuron-methyl* Express, tribenuron methyl ester, DPX-L5300 0.068 101200-48-0 H

Triclopyr Garlon, Curtail, Redeem, Remedy 0.101 55335-06-3 H

Appendix 1. Pesticides and pesticide degradates analyzed, common name, and use—Continued
38 Shallow Ground-Water Quality in Agricultural Areas of Northern Alabama

and Middle Tennessee, 2000-2001

Appendix 2. Chlorofluorocarbon concentrations, calculated atmospheric partial pressures, and model recharge dates for 

sampled wells

[temp., temperature; °C, degrees Celsius; pg/kg, picograms per kilogram; pptv, parts per trillion by volume; CFC, chlorofluorocarbon; Contam., CFC concentrations in samples were greater than air-water atmospheric equilibrium concentrations; Modern, CFC concentrations indicative of 2000 atmospheric concentrations]

Well 

number

Sampling

date Time

Recharge 

temp.

(

οC)

Elev. 

(feet 

above 

NGVD 29)

Concentration in solution, 

in pg/kg

Calculated Atmospheric

partial pressure, in pptv

Model CFC recharge dates,

in years

CFC-11 CFC-12 CFC-113 CFC-11 CFC-12 CFC-113 CFC-11 CFC-12 CFC-113

35 05/25/00 1450 16.2 640 546.5 261.5 64.9 270.2 546.8 78.6 1990.5/

1998.0

1997.0 1990.5 

35 05/25/00 1515 16.2 640 542.3 245.2 67.2 268.2 512.7 81.5 1990.0/

1998.5

1992.5 1991.0 

35 05/25/00 1525 16.2 640 539.3 251.8 66.9 266.6 526.5 81.1 1989.5 1994.0 1991.0 

14 05/31/00 1555 13.8 822 525.3 261.0 62.4 231.6 493.0 66.7 1986.5 1990.5 1988.5 

14 05/31/00 1615 13.8 822 527.1 267.8 64.5 232.4 505.8 68.9 1986.5 1991.5 1988.5 

14 05/31/00 1620 13.8 822 518.9 241.9 62.5 228.8 456.8 66.7 1986.0 1988.0 1988.5 

11 06/06/00 1635 14.8 860 976.5 320.0 74.5 453.8 633.6 84.3 Contam. Contam. 1992.0/

1997.0

11 06/06/00 1640 14.8 860 544.2 269.4 66.8 252.9 533.4 75.6 1988.0 1994.5 1989.5 

11 06/06/00 1700 14.8 860 547.9 271.3 66.2 254.6 537.2 74.9 1988.0 1995.5 1989.5 

7 06/05/00 1450 13.7 950 655.1 301.2 95.3 288.7 569.0 101.7 Modern Modern Contam.

7 06/05/00 1510 13.7 950 649.3 289.8 94.7 286.2 547.5 101.0 Modern 1997.0 Contam.

7 06/05/00 1520 13.7 950 639.4 266.4 88.8 281.8 503.2 94.7 Modern 1991.5 Modern

25 05/24/00 1100 17.5 550 24.2 56.4 0.0 12.7 124.5 0.0 1961.0 1969.5 <1955

25 05/24/00 1115 17.5 550 23.3 50.3 0.0 12.2 111.0 0.0 1960.5 1968.5 <1955

25 05/24/00 1120 17.5 550 23.5 52.1 0.0 12.4 115.0 0.0 1960.5 1969.0 <1955

20 05/25/00 1015 14.7 580 520.4 295.4 71.1 238.1 576.2 79.2 1987.0 Modern 1990.5 

20 05/25/00 1030 14.7 580 4,010.7 279.4 67.7 1,835.3 544.9 75.3 Contam. 1997.0 1989.5 

20 05/25/00 1050 14.7 580 1,384.0 306.6 73.3 633.3 598.1 81.6 Contam. Contam. 1991.0 

12 06/07/00 1220 15.1 765 750.1 285.6 63.3 352.7 571.2 72.6 Contam. Modern 1989.0 

12 06/07/00 1250 15.1 765 849.6 348.1 79.0 399.5 696.2 90.6 Contam. Contam. Modern

12 06/07/00 1300 15.1 765 909.2 301.6 74.9 427.5 603.2 85.9 Contam. Contam. 1994.0 

13 06/01/00 1445 15.0 705 560.0 260.2 69.8 261.4 516.9 79.3 1989.0 1992.5 1990.5 

13 06/01/00 1455 15.0 705 562.2 266.2 71.8 262.4 528.8 81.7 1989.0 1994.0 1991.0 

13 06/01/00 1500 15.0 705 567.3 262.7 70.2 264.8 521.8 79.8 1989.5 1993.5 1990.5 

33 05/22/00 1530 13.4 540 215.0 155.3 25.4 91.9 284.9 26.3 1973.0 1978.0 1981.0 

33 05/22/00 1550 13.4 540 219.8 129.5 23.7 93.9 237.6 24.4 1973.0 1975.5 1980.0 

33 05/22/00 1600 13.4 540 229.3 133.4 26.2 98.0 244.7 27.0 1973.5 1976.0 1981.0