Ground-Water Quality Beneath an Urban 

Residential and Commercial Area, 

Montgomery, Alabama, 1999–2000

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

By James L. Robinson

Montgomery, Alabama

2002

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02–4052
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

The use of firm, trade, and brand names 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 can be purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

2350 Fairlane Drive, Suite 120 Box 25286, Federal Center

Montgomery, AL 36116 Denver, CO 80225

dc_al@usgs.gov 1-888-ASK-USGS

Information regarding the National Water-Quality Assessment (NAWQA) Program can be obtained from the NAWQA 

website <http://water.usgs.gov/nawqa> or the Mobile River Basin Study Unit website <http://tenn.er.usgs.gov/MOBL/

mobl.html>.
Foreword III

FOREWORD

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. 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 longterm 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. 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. 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. 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. 

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

Previous investigations................................................................................................................................................ 2

Acknowledgments....................................................................................................................................................... 4

Environmental setting............................................................................................................................................................ 4

Description of the study area....................................................................................................................................... 7

Hydrogeology of the shallow aquifer.......................................................................................................................... 7

Study design and methods..................................................................................................................................................... 11

Land-use selection....................................................................................................................................................... 11

Well network ............................................................................................................................................................... 11

Land-use classification................................................................................................................................................ 13

Water-quality samples ................................................................................................................................................. 14

Quality-assurance and quality-control procedures...................................................................................................... 14

Graphical and statistical methods................................................................................................................................ 16

Chemical and physical properties of the shallow aquifer ..................................................................................................... 17

Soil characteristics ...................................................................................................................................................... 17

Sediment core analyses ............................................................................................................................................... 17

Lithology of the shallow aquifer ................................................................................................................................. 18

Water quality in the shallow aquifer...................................................................................................................................... 18

Chemistry of natural ground water.............................................................................................................................. 18

Ground-water quality beneath an urban area of Montgomery, Alabama.................................................................... 24

Occurrence and distribution of major ions........................................................................................................ 25

Occurrence and distribution of nutrients........................................................................................................... 26

Occurrence and distribution of trace metals...................................................................................................... 27

Occurrence and distribution of pesticides ......................................................................................................... 28

Occurrence and distribution of volatile organic compounds............................................................................. 30

Age of ground water.......................................................................................................................................... 31

Relations among ground-water quality, ground-water age, land use, and geology............................................................... 33

Summary ............................................................................................................................................................................... 34

References ............................................................................................................................................................................. 35

FIGURES

1–5. Maps showing:

1. Locations of major rivers and cities in the Mobile River Basin....................................................................... 3

2. Physiographic units of the Mobile River Basin ............................................................................................... 5

3. Generalized geology of the Mobile River Basin.............................................................................................. 6

4. Locations of wells sampled in the Mobile River Basin for this study ............................................................. 8

5. Locations of urban wells sampled for the land-use study, line of section A–A', 

and the northern extent of the Selma confining unit, Montgomery, Alabama................................................. 9

6. Hydrogeologic section showing stratigraphic units underlying the urban land-use study area,

Montgomery, Alabama ............................................................................................................................................ 10

7. Diagram showing generalized section of stratigraphic and hydrogeologic units underlying 

Montgomery, Alabama ............................................................................................................................................ 10

8. Map showing locations of public water-supply wells, urban land-use study area, 

and line of section A–A', Montgomery County, Alabama...................................................................................... 11

9. Boxplot showing range and distribution of depth-to-open interval of rural wells in the Mobile 

River Basin and urban wells in Montgomery, Alabama, sampled for this study .................................................... 12

 10. Piper trilinear diagram showing major ion composition of ground-water samples collected from 

rural wells completed in the Coker, Gordo, and Eutaw Formations in the Mobile River Basin ............................. 20
VI Contents

11. Stiff diagrams representing water quality of samples collected from rural wells 

completed in the Coker, Gordo, and Eutaw Formations in the Mobile River Basin................................................ 21

12. Piper trilinear diagram showing major ion composition of ground water collected 

from urban wells in Montgomery, Alabama ............................................................................................................ 22

13. Piper trilinear diagram showing geochemical evolution of ground water in the 

Eutaw Formation beneath Montgomery, Alabama .................................................................................................. 23

14. Stiff diagrams representing water quality of samples collected from urban wells completed 

in the Eutaw Formation, alluvial deposits, and terrace deposits beneath Montgomery, Alabama........................... 24

15–18. Boxplots showing:

15. Concentrations of selected water-quality constituents in ground-water samples collected from 

rural wells in the Mobile River Basin, rural wells completed in the Eutaw Formation, and urban 

wells in Montgomery, Alabama........................................................................................................................ 25

16. Concentrations of chloride in ground-water samples collected from rural wells in the 

Mobile River Basin, rural wells completed in the Eutaw Formation, and urban wells in 

Montgomery, Alabama ..................................................................................................................................... 26

17. Concentrations of nitrite plus nitrate in ground-water samples collected from rural wells 

in the Mobile River Basin, rural wells completed in the Eutaw Formation, and urban wells 

in Montgomery, Alabama................................................................................................................................. 27

18. Concentrations of selected trace metals in ground-water samples collected from rural wells 

in the Mobile River Basin, rural wells completed in the Eutaw Formation, and urban wells 

in Montgomery, Alabama................................................................................................................................. 28

19–23. Graphs showing:

19. Range and distribution of concentrations of the most commonly detected pesticides 

in ground-water samples collected from rural wells in the Mobile River Basin and urban wells 

in Montgomery, Alabama................................................................................................................................. 29

20. Detection frequencies of pesticides in ground-water samples collected from urban wells in

Montgomery, Alabama ..................................................................................................................................... 29

21. Range and distribution of concentration of most commonly detected volatile organic 

compounds in ground-water samples collected from rural wells in the Mobile River Basin 

and urban wells in Montgomery, Alabama....................................................................................................... 31

22. Frequency of detection of volatile organic compounds, by compound class, in ground-water 

samples collected from rural wells in the Mobile River Basin and urban wells 

in Montgomery, Alabama ................................................................................................................................ 31

23. Detection frequencies of pesticides and volatile organic compounds in ground-water 

samples collected from urban wells in Montgomery, Alabama ....................................................................... 34

TABLES

1. Ground-water resources of the Mobile River Basin................................................................................................. 7

2. Percentages of predominant land-use types within a 0.3-mile radius around the urban wells in

Montgomery, Alabama............................................................................................................................................. 13

3. Constituents analyzed and analytical methods used in ground-water-quality samples collected 

during the urban land-use study in Montgomery, Alabama..................................................................................... 14

4. Summary of quality-assurance and quality-control samples collected during the urban land-use 

study in Montgomery, Alabama............................................................................................................................... 15

5. Descriptive statistics for quality-assurance and quality-control field spikes............................................................ 16

6. Minimum, median, and maximum values for physical properties and concentrations of selected 

chemical constituents in ground-water samples collected from rural wells in the Mobile River Basin 

and urban wells in Montgomery, Alabama .............................................................................................................. 19

7. Minimum and maximum concentrations of selected pesticides and volatile organic compounds 

in ground-water samples collected from rural wells in the Mobile River Basin and urban wells 

in Montgomery, Alabama......................................................................................................................................... 30

8. Ages of ground water in samples collected from urban wells in Montgomery, Alabama ....................................... 32

9. Spearman rank correlation coefficients for selected physical properties and parameters 

of ground-water samples collected from urban wells in Montgomery, Alabama .................................................... 33
Contents VII

CONVERSION FACTORS, VERTICAL DATUM, DEFINITIONS, AND ABBREVIATIONS 

and ACRONYMS

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

°C = (°F - 32) / 1.8

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD 

of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of both 

the United States and Canada, formerly called Sea Level Datum of 1929.

Altitude, as used in this report, refers to distance above or below sea level.

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).

Multiply By To obtain

Length

inch (in.) 2.54 centimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

square mile (mi2) 2.590 square kilometer 

Volume

gallon (gal) 3.785 liter

Flow rate

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

million gallons per day per square mile

 [(Mgal/d)/mi2] 1,460 cubic meter per day per square kilometer 

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day
VIII Contents

Additional abbreviations and acronyms used in this report:

CFC chlorofluorocarbon

CaCO3 calcium carbonate

CFC-11 trichlorofluoromethane (CFCl3)

CFC-12 dichlorodifluoromethane (CF2Cl2)

CFC-113 trichlorotrifluoroethane (C2F3Cl3)

CO2 carbon dioxide

CO3 carbonate ion

DCPA dacthal

ECD electron capture detector

E. coli Escherichia coli

FeS2 Iron sulfide

HCO3 bicarbonate ion

MCL U.S. EPA drinking water maximum contaminant level

MTBE methyl tert butyl ether

m-FC fecal coliform method

m-TEC Escherichia coli method

NAWQA National Water-Quality Assessment

NWQL National Water Quality Laboratory

p,p'-DDE dichlorodiphenyldichloroethylene

QA/QC quality assurance and quality control

RSD USEPA risk-specific dose health advisory for drinking water

SF6 sulfur hexafluoride

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

UV ultraviolet

VOC volatile organic compound
Abstract 1

Ground-Water Quality Beneath an Urban Residential and 

Commercial Area, Montgomery, Alabama, 1999–2000

By James L. Robinson

ABSTRACT

The Black Warrior River aquifer, which is 

composed of the Coker, Gordo, and Eutaw 

Formations, supplies more than 50 percent of the 

ground water used for public water supply in the 

Mobile River Basin. The city of Montgomery, 

Alabama, is partially built upon a recharge area for 

the Black Warrior River aquifer, and is one of many 

major population centers that depend on the Black 

Warrior River aquifer for public water supply. To 

represent the baseline ground-water quality in the 

Black Warrior River aquifer, water samples were 

collected from 30 wells located in a low-density 

residential or rural setting; 9 wells were completed 

in the Coker Formation, 9 wells in the Gordo 

Formation, and 12 wells in the Eutaw Formation. To 

describe the ground-water quality beneath 

Montgomery, Alabama, water samples also were 

collected from 30 wells located in residential and 

commercial areas of Montgomery, Alabama; 

16 wells were completed in the Eutaw Formation, 

8 wells in alluvial deposits, and 6 wells in terrace 

deposits. The alluvial and terrace deposits directly 

overlie the Eutaw Formation with little or no 

hydraulic separation. Ground-water samples 

collected from both the rural and urban wells were 

analyzed for physical properties, major ions, 

nutrients, metals, volatile organic compounds, and 

pesticides. Samples from the urban wells also were 

analyzed for bacteria, chlorofluorocarbons, 

dissolved gases, and sulfur hexafluoride. Groundwater quality beneath the urban area was compared 

to baseline water quality in the Black Warrior River 

aquifer.

Compared to the rural wells, ground-water 

samples from urban wells contained greater 

concentrations or more frequent detections of 

chloride and nitrate, and the trace metals aluminium, 

chromium, cobalt, copper, nickel, and zinc. 

Pesticides and volatile organic compounds were 

detected more frequently and in greater 

concentrations in ground-water samples collected 

from urban wells than in ground-water samples from 

rural wells.

The Spearman rho test was used to check for 

statistically significant covariance among urban 

ground-water quality and land-use type. The number 

of pesticides and volatile organic compounds 

detected and concentrations of nickel increased as 

the percentage of residential land use increased. 

Greater nickel concentrations also were associated 

with a greater number of volatile organic compounds 

detected. As the percentage of commercial land use 

increased, the numbers of pesticides and volatile 

organic compounds detected decreased. The number 

of pesticides detected in the urban ground-water 

samples increased as concentrations of nitrite plus 

nitrate increased; the number of pesticides detected 

and the concentrations of nitrite plus nitrate 

decreased as the age of the ground water increased. 

These correlations may indicate that, with time, 

pesticides and nitrate are removed from the groundwater system by physical, chemical, or biological 

processes. 

The effects of surficial geology on the 

occurrence of pesticides and volatile organic 

compounds was investigated by calculating 

frequencies of detection. The detection frequency for 

pesticides was greater for urban samples collected 

from wells where the surficial geology is sand than 
2 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

for urban samples collected from wells where the 

surficial geology is clay. The frequency of detection 

of volatile organic compounds did not show this 

relation.

INTRODUCTION

Ground water is the source of drinking water for 

approximately 50 percent of the Nation (U.S. Geological 

Survey, 1999a). Degradation of ground-water quality as a 

result of urban land use is a major concern not only 

because of its use for public water supply, but also 

because of the potential for ground water to affect 

surface-water quality, as well as ecological and 

recreational resources. The U.S. Geological Survey’s 

(USGS) National Water-Quality Assessment (NAWQA) 

Program was designed to assess the status of, and trends 

in, the quality of the ground- and surface-water resources 

in 59 of the Nation’s major river basins (also referred to 

as Study Units); and to link the status and trends with an 

understanding of the natural and human factors that affect 

the quality of water (Gilliom and others, 1995).

Ground-water studies performed for the NAWQA 

Program are classified as (1) major aquifer studies, 

designed to assess the water quality of major aquifer 

systems within the study unit; (2) land-use studies, which 

are intended to assess the quality of recently recharged 

shallow ground water associated with regionally 

extensive combinations of land use and hydrogeologic 

conditions; or (3) flowpath studies, designed to examine 

specific relations among land-use practices, ground-water 

flow, contaminant occurrence and transport, and surfaceand ground-water interactions (Gilliom and others, 1995). 

The land-use study described in this report is part of the 

NAWQA Program investigation of the Mobile River 

Basin in Alabama, Georgia, Mississippi, and Tennessee 

(fig. 1). 

Purpose and Scope

The objectives of this report are to (1) describe the 

quality of ground water beneath an urban area in 

Montgomery, Alabama, and compare it to regional 

ground-water quality in the same aquifer system; and 

(2) describe selected environmental factors that may be 

influencing ground-water quality beneath the urban area. 

Hydrologic and geologic data collected during the drilling 

of 30 wells were used to describe the hydrogeology of the 

shallow aquifer underlying the urban area. Water quality 

was determined in samples collected from the 30 urban 

wells. Ground-water quality in the urban area was 

compared and contrasted to the water quality of samples 

collected from 30 wells completed in the same aquifer but 

located in rural (low-density residential to forested land 

use) settings in Mississippi and Alabama. All groundwater samples were analyzed for physical properties, 

major ions, nutrients, metals, volatile organic compounds, 

and pesticides. Samples from the urban wells also were 

analyzed for bacteria, chlorofluorocarbons, dissolved 

gases, and sulfur hexafluoride. Ground-water samples 

were collected from the rural wells from June through 

September 1999, and from the urban wells from October 

1999 through January 2000. Correlation analysis was 

used to investigate possible relations between selected 

environmental factors and ground-water quality.

Previous Investigations

Reports that describe the geology of the study area 

date back approximately 140 years when Tuomey (1858) 

included a report on part of the Cretaceous Formations of 

Alabama in the second biennial report of the Geological 

Survey of Alabama. Bicker (1969) prepared the current 

geologic map of Mississippi; Osborne and others (1989) 

prepared the current geologic map of Alabama; and King 

and Biekman (1974) prepared a geologic map of the 

conterminous United States, which was used for this 

report. 

Reports describing the ground-water resources of 

the study area date back at least to Smith (1907) who 

published a report on the underground water resources of 

Alabama. The Layne Central Company (1941) prepared a 

report for the city of Montgomery describing groundwater conditions in and adjacent to the city as part of an 

exploratory drilling program to expand the municipal 

wellfield. Carlston (1942, 1944) authored reports on 

fluoride in the ground water of the Cretaceous area of 

Alabama and on the ground-water resources of the 

Cretaceous area of Alabama. Knowles and others (1960, 

1963) published the results of an exhaustive study of the 

geology and ground-water resources of Montgomery 

County. Ground-water resources of the Cretaceous 

aquifers in Mississippi were discussed in Crider and 

Johnson (1906); Stephenson and others (1928); Boswell 

(1963, 1977, 1978); Boswell and others (1965); Mallory 

(1993); and Strom and Mallory (1995). Scott and others 

(1987) prepared a report describing the geohydrology and 

susceptibility of major aquifers to surface contamination. 

Reports prepared by CH2M Hill, Inc. (1997a,b), describe 

the hydrogeology of the Cretaceous aquifers in the 

vicinity of Montgomery. The nomenclature documented
Introduction 3

Figure 1. Locations of major rivers and cities in the Mobile River Basin.
4 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

by Miller (1990) and Renken (1998) for the ground-water 

systems in the Mobile River Basin Study Unit is used 

herein.

Acknowledgments 

The author is grateful for the cooperation and 

assistance provided by the Montgomery Water Works and 

Sanitary Sewer Board and the City of Montgomery 

Engineering Department. The following organizations 

were helpful by allowing access to their properties for 

data collection: the State of Alabama, the Alabama 

Baptist State Convention, Alabama Christian Academy, 

Aldersgate Methodist Church, the First Assembly of God, 

Auburn University of Montgomery, Landmark Church of 

Christ, Montgomery County School Board, Trinity 

Presbyterian School, Vaughn Park Church of Christ, and 

YMCA of Montgomery. Finally, gratitude is expressed to 

the many private citizens of Alabama and Mississippi 

who allowed access to their wells and properties for data 

collection.

ENVIRONMENTAL SETTING

The Mobile River Basin includes about 

44,000 square miles (mi2) in Alabama, Georgia, 

Mississippi, and Tennessee (fig. 1). The major surfacewater systems are the Cahaba, Coosa, and Tallapoosa, 

which are tributary to the Alabama River; and the Black 

Warrior River, which is tributary to the Tombigbee River 

(fig. 1). The Alabama and Tombigbee Rivers join to form 

the Mobile River in the southern part of the basin (fig. 1). 

The Mobile River Basin Study Unit has diverse 

physiography (fig. 2) and geology (fig. 3). The study area 

is located in the Fall Line Hills, Alluvial-Deltaic Plain, 

and Black Prairie Belt physiographic districts (fig. 2). The 

geology of the study area is primarily unconsolidated 

clastic sediments, limestone, and chalk that dip to the 

southwest toward the coast and form gently curved, eastwest trending bands through Alabama and Mississippi. 

Ground water is an important resource in the 

Mobile River Basin. Total ground-water use in 1995 was 

estimated to be about 328 million gallons per day 

(Mgal/d; table 1) by Strom and Mallory (1995), Fanning 

(1997), and Mooty and Richardson (1998). This 

accounted for about 24 percent of the total water use in 

the basin. Ground-water withdrawals are concentrated in 

the Black Warrior River aquifer (166 Mgal/d), which is 

composed of clastic sediments of Cretaceous age, and in 

the Valley and Ridge aquifers (83 Mgal/d), which are 

solution-conduit aquifers developed in carbonate rocks of 

Devonian through Cambrian age (fig. 3). Fifty-one 

percent of the ground water used for public water supply 

in the Mobile River Basin is withdrawn from the Black 

Warrior River aquifer.
Environmental Setting 5

Figure 2. Physiographic units of the Mobile River Basin (modified from Sapp and Emplaincourt, 1975).
6 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

Figure 3. Generalized geology of the Mobile River Basin.
Hydrogeology of the Shallow Aquifer 7

Description of the Study Area

The rural wells sampled for this study (fig. 4) are 

randomly distributed following the outcrop of the 

Cretaceous clastic sediments that comprise the Black 

Warrior River aquifer (fig. 3). The urban wells sampled 

for this study are located in eastern Montgomery, 

Alabama (fig. 5). The population of the Montgomery 

metropolitan area in 1998 was approximately 321,000 

(U.S. Census Bureau, 2000). Land use in eastern 

Montgomery is primarily a mixture of high- to lowdensity residential, commercial, light industry, and 

forested areas.

Hydrogeology of the Shallow Aquifer

The city of Montgomery is underlain, north to 

south, by alluvial and terrace deposits of gravel, sand, and 

clay; sands and clays of the Eutaw Formation, which is 

the uppermost unit of the Black Warrior River aquifer; 

and by clay and clayey soils developed from the 

Mooreville Chalk (fig. 6). The alluvial and terrace 

deposits range from about 30 to more than 100 feet (ft) 

thick, and form a shallow aquifer (fig. 7) that overlies the 

Eutaw Formation with little or no hydraulic separation in 

the northern part of the urban study area (Scott and others, 

1987). In Montgomery County, the Eutaw Formation 

ranges from approximately 250 to 400 ft thick, and dips 

30 to 40 ft per mile (fig. 6) to the south, southeast, and 

southwest (Knowles and others, 1960, 1963; Scott and 

others, 1987). The Mooreville Chalk, part of the Selma 

confining unit, is the surficial geologic unit in the 

southern third of the urban study area (figs. 5 and 6).

Rainfall in Montgomery County averages 

55.4 inches (in.) annually (National Oceanic and 

Atmospheric Administration, 1995). There is a distinct 

seasonality to the distribution of rainfall, with the months 

of December through March having the highest rainfall 

(about 5–6 in. per month) and the months of August 

through October having the least (about 2–4 in. per 

month). Surface-water runoff in the city of Montgomery 

drains to the Alabama and Tallapoosa Rivers. North of the 

Selma confining unit (figs. 5 and 6), recharge to the Black 

Warrior River aquifer can occur directly from 

precipitation because the uppermost unit, the Eutaw 

Formation, is exposed at land surface or is overlain by 

permeable sand and gravel with no intervening unit of low 

permeability (Hinkle and others, 1983; Scott and others, 

1987). In the southern part of the study area, the Selma 

confining unit prevents direct recharge to the Black 

Warrior River aquifer. Ground water flows north away 

from the recharge area and toward the Tallapoosa River, 

west toward the Alabama River, and along dip to the south 

and southeast.

The Black Warrior River aquifer is heavily used for 

public and private water supply in Montgomery County. 

The Montgomery Water Works and Sanitary Sewer Board 

operates two well fields in the vicinity of Montgomery, 

Alabama, which utilize the Black Warrior River aquifer.

Table 1. Ground-water resources of the Mobile River Basin

[Modified from Miller (1990) and Renken (1998); Mgal/d, million gallons per day]

Physiographic

district

(fig. 2)

Regional

aquifer subunit

Primary

geology

(fig. 3)

Total 

population

served (1995),

in thousands

Total 

withdrawals

(1995),

in Mgal/d

Fall Line Hills Black Warrior River aquifer Cretaceous clastic 

sediments

885 166

Valley and Ridge Valley and Ridge aquifers Devonian through 

Cambrian carbonate 

rocks

429 83

Southern Hills Pearl River, Chickasawhay 

River, surficial aquifers

Oligocene, Eocene, and 

Paleocene clastic 

sediments and carbonate 

rocks

179 41

Blue Ridge and Piedmont Piedmont and Blue Ridge 

aquifers

Igneous and metamorphic 

rocks of various and 

uncertain age

192 21

Cumberland Plateau Appalachian Plateaus aquifers Pennsylvanian and 

Mississippian sandstone 

and carbonate rocks

130 17
8 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

Figure 4. Locations of wells sampled in the Mobile River Basin for this study.
Hydrogeology of the Shallow Aquifer 9 Figure 5. Location of urban wells sampled for the land-use study, line of section A

–A', and the northern extent of the Selma confining unit, Montgomery, Alabama.
10 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

Figure 6. Hydrogeologic section showing stratigraphic units underlying the urban land-use study area, Montgomery, Alabama (modified 

from Scott and others, 1987).

Figure 7. Generalized section of stratigraphic and hydrogeologic units underlying Montgomery, Alabama [from Knowles and others (1963), 

Scott and others (1987), Miller (1990)].

System Stratigraphic unit Major

lithology

Thickness

(feet)

Hydrogeologic

unit

Regional

aquifer

system

Quaternary Alluvial and terrace 

deposits

Sand, gravel, silt, and 

clay

30–100 + Shallow aquifer

Cretaceous

Selma 

Group

Mooreville 

Chalk

Chalk and limestone 0–500 + Selma confining 

unit

Southeastern Coastal Plain aquifer system

Eutaw Formation

Upper and lower marine 

sand separated by clay; 

consists of glauconitic 

sand interbedded with 

calcareous sandstone 

and sandy limestone

0–400 +

Black Warrior River aquifer

Tuscaloosa Group

Gordo 

Formation

Basal zone of gravel and 

sand overlain by 

lenticular beds of sand 

and clay

300 +

Coker 

Formation

Basal zone of non-marine 

sand, gravel, and clay; 

upper zone of marine 

sand and clay

500 +

Pre-Cretaceous Schist, gneiss 1,000 +

Base of freshwater flow 

system
Study Design and Methods 11

The Black Warrior River aquifer is also used by many 

other public water-supply systems (fig. 8) and domestic 

wells in Montgomery County. Total ground-water use in 

Montgomery County in 1995 was 34.8 Mgal/d (Mooty 

and Richardson, 1998).

STUDY DESIGN AND METHODS 

The urban land-use study was designed by using 

NAWQA guidelines (Gilliom and others, 1995; Squillace 

and Price, 1996). NAWQA ground-water protocols 

(Lapham and others, 1997; Koterba, 1998) were followed 

during data collection. Standardization of data-collection 

procedures is intended to produce a nationally consistent 

database that can be used to produce statistically valid 

interpretations. Modification of national protocols is 

sometimes necessary because of local conditions. The 

following sections describe how the national protocols 

were applied and, when necessary, modified for the urban 

land-use study.

Land-Use Selection 

The criteria used to select urban land-use study 

areas are outlined in Squillace and Price (1996). Of 

primary concern are the criteria specifying that the 

shallow aquifer in the study area be used as a source of 

drinking water, a potential source of drinking water, or 

hydraulically connected to surface water or deeper ground 

water that is used as a source of drinking water; and that 

land use within the study area be residential and 

commercial developed between 1970 and the 1990’s. The 

urban land-use study area in eastern Montgomery meets 

these criteria; however, the last criterion was modified to 

extend the period of residential development in the study 

area from 1960 to 1998. 

Well Network

Ground-water samples were collected from 

30 wells in rural areas and 30 wells in an urban area of the 

Mobile River Basin. The rural wells were sampled to

Figure 8. Locations of public water-supply wells, urban land-use study area, and line of section A–A', Montgomery County, 

Alabama
12 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

provide a regional assessment of baseline water-quality 

conditions in the Black Warrior River aquifer (Gilliom and 

others, 1995). The rural wells were selected from existing 

domestic or stock wells, and are randomly distributed 

throughout the Fall Line Hills and Black Prairie Belt physiographic districts (figs. 2 and 4). Nine rural wells are 

completed in the Coker Formation, 9 are completed in the 

Gordo Formation, and 12 wells are finished in the Eutaw 

Formation. 

The urban wells were designed to sample shallow 

ground water beneath a specific land-use type (Squillace 

and Price, 1996). The wells are located in eastern 

Montgomery, Alabama, in recharge areas or directly 

downgradient of recharge areas for the Black Warrior 

River aquifer. The urban wells are completed in the Eutaw 

Formation (16 wells), the alluvial deposits (8 wells), and 

the terrace deposits (6 wells; figs. 5 and 6).

The part of a well through which water is 

withdrawn from the ground is referred to as the “open” 

interval because it is open to the transmission of water. 

Screened wells have sections of pipe with thin slots cut in 

them through which water may flow into the well. In 

open-hole well construction, no pipe or screen is placed in 

the part of borehole through the aquifer, and a pipe or 

“surface casing” is installed in the borehole above the 

open-hole section. Water enters the well directly through 

the borehole. The depth-to-open interval of a well is the 

depth to the top of the screens or the open borehole. The 

importance of this measurement relates to the 

susceptibility of a well to contamination. The less the 

depth-to-open interval, the greater the susceptibility of the 

well to contamination from sources at land surface. The 

depth-to-open interval of the rural wells ranged from 

about 60 to 405 ft, with a median depth of 121 ft (fig. 9). 

The depth-to-open interval of the urban wells ranged from 

about 8 to 88 ft, with a median depth of 29 ft (fig. 9).

The urban wells were randomly distributed 

throughout the urban land-use study area to avoid biasing 

the data (fig. 5). NAWQA guidelines (Squillace and Price, 

1996) specify that land use within a 0.3-mile radius of the 

wells must be at least 75 percent residential and 

commercial and stable for approximately 5 years. Well 

locations are at least 0.6 mile from heavy industry or any 

known source of ground-water contamination. Although it 

is desirable that well locations be no closer than 0.6 mile 

to each other, two pairs of wells were located at a spacing 

slightly less than 0.6 mile. This was necessary to meet all 

other NAWQA requirements for urban land-use studies.

The 30 urban wells (fig. 5) were installed by the 

USGS in accordance with national NAWQA protocols 

(Lapham and others, 1997). A hollow-stem auger rig was 

used to drill 6-in.-diameter boreholes. The wells were

constructed within the hollow-stem augers using threaded, 

2-in.-diameter polyvinyl-chloride casing having 

10-ft-long, 0.010-in. slotted screens. A sand pack of 

washed 10/30 silica sand was placed around the screens 

where possible. The aquifer material flowed into the 

hollow-stem auger at some drill sites, making it impossible to place a sand pack around the well screens. The 10/

30 sand pack was placed to a depth of about 5 ft above the 

well screens. Bentonite was used to form a seal in the 

annulus around the well casing, and a cement grout and 

steel protective wellhead was installed to form a surface 

seal. All equipment used to drill the monitoring wells was 

decontaminated prior to the drilling of each well by scouring with a high pressure steam cleaner. Well casings and 

screens were cleaned with the high pressure steam cleaner 

and then rinsed with deionized water.

Sediment samples were collected from every major 

lithologic unit drilled during well installation, and 

geologist’s logs of the samples were prepared. When 

possible, sediment cores were collected from each 

lithologic unit present. Representative samples of each 

lithology cored were chilled and sent to the USGS 

National Water Quality Laboratory (NWQL) in Denver, 

Colorado, for organic carbon analyses. The methods 

Figure 9. Range and distribution of depth-to-open interval of rural 

wells in the Mobile River Basin and urban wells in Montgomery, 

Alabama, sampled for this study.

MINIMUM VALUE

EXPLANATION

MAXIMUM VALUE

NUMBER OF WELLS

 SAMPLED

(30)

25TH PERCENTILE

75TH PERCENTILE

MEDIAN

1

2

3

4

5

7

10

20

30

40

50

70

100

200

300

500

RURAL

WELLS 

(30)

URBAN

WELLS 

(30)

400

DEPTH-TO-OPEN-INTERVAL, IN FEET
Land-Use Classification 13

specified by Squillace and Price (1996) were used to 

determine soil pH values for sediment core samples. 

Representative sediment cores were taken to a 

geotechnical laboratory for grain-size and in situ 

sediment core analyses to determine the porosity and 

permeability of the material. 

Land-Use Classification

The type of land use within a 0.3-mile radius of 

each well (table 2) was determined by using aerial 

photography and field reconnaissance. The contributing 

area for a well is unlikely to be defined by the 0.3-mile

Table 2. Percentages of predominant land-use types within a 0.3-mile radius around the urban wells in 

Montgomery, Alabama

[Site identification number is latitude-longitude-well sequence number]

Map 

reference 

number

(fig. 5)

Site

identification

number

 Residential,

churches, 

schools, and 

developed 

parks

 Commercial

and 

light 

industry

 Undeveloped 

parks

 and

forests

Other

1 32242108611170 57 22 21

2 32223308614080 87 3 9 1

3 32235008612150 60 30 10 0

4 32233208613340 96 4

5 32234308614390 94 2 4

6 32232008613030 79 12 5 4

7 32195108611360 46 11 43

8 32234908611320 69 30 1

9 32230708611420 71 20 6 3

10 32223908608450 87 2 11

11 32232608609240 76 15 9

12 32231108608500 77 23

13 32225308614440 63 27 10

14 32230208614420 74 19 7

15 32224208612570 70 28 2

16 32224708612110 41 58 1

17 32223708611210 80 8 11 1

18 32221708610310 51 5 43 1

19 32243708611480 47 36 17

20 32224008608080 87 13

21 32214808612060 47 31 22

22 32221008612520 46 16 25 13

23 32205408614380 94 6

24 32205508610300 51 19 30

25 32211508610450 82 13 5

26 32210908608330 61 2 32 5

27 32204108611280 85 4 11

28 32204108611280 71 19 10

29 32211608614060 98 1 1

30 32231508614150 89 11
14 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

radius around the well; however, the land use within that 

area should have some affect on the ground-water quality 

(Squillace and Price, 1996). The land-use data were compared to ground-water-quality data to determine relations 

between land-use type and ground-water quality.

Water-Quality Samples

Ground-water samples collected during the urban 

land-use study were analyzed for major ions, nutrients, 

trace metals, pesticides, volatile organic compounds 

(VOCs), bacteria, chlorofluorocarbons (CFCs), dissolved 

gases, and sulfur hexafluoride (SF6). The constituents 

tested for and the laboratory analytical methods used are 

listed in table 3.

Sampling procedures were consistent with 

NAWQA ground-water sampling protocols (Koterba and 

others, 1995; U.S. Geological Survey, 1999c). All 

ground-water samples analyzed for organic compounds 

were collected by using sampling equipment constructed 

of stainless steel and Teflon. Before sampling began, at 

least three well volumes of water were purged, and field 

measurements of specific conductance, pH, water 

temperature, dissolved oxygen, and turbidity were stable 

within 10 percent for 15 minutes. Bacteriological samples 

were analyzed in the USGS Alabama District laboratory 

in Montgomery. Samples to be analyzed for CFCs, SF6, 

and dissolved gases were hand delivered to the CFC 

laboratory in Reston, Virginia. All other ground-water 

samples were chilled and shipped overnight to the USGS 

National Water Quality Laboratory (NWQL) in Denver, 

Colorado.

The USGS NWQL reports analysis values for 

constituent concentrations as measured or estimated 

(censored). These terms indicate the confidence the 

NWQL places in the accuracy of the measurement. 

Estimated values are reported for concentrations less than 

the reporting level but above the long-term method 

detection level (Childress and others, 1999) or for 

concentrations greater than the calibrated range of the 

apparatus. Measured values are reported for 

concentrations above the reporting level and within the 

calibration range of the apparatus.

Quality-Assurance and Quality-Control 

Procedures

Three types of quality-assurance and qualitycontrol (QA/QC) samples (table 4) were collected during 

sampling of the urban land-use study monitoring 

wells—blanks, spikes, and replicates. Seven field blanks, 

three source-water blanks, and one trip blank were 

collected. Three field spikes and three field-spike 

Table 3. Constituents analyzed and analytical methods used in ground-water-quality samples collected during 

the urban land-use study in Montgomery, Alabama

[UV, ultra-violet; C-18, octadecyl; E. coli, Escherichia coli; m-TEC, two-step membrane-filtration method for E. coli; 

m-FC, one-step membrane-filtration method for fecal coliform; CFC, chlorofluorocarbons; ECD, electron capture 

detector; SF6, sulfur hexafluoride]

Constituent Analysis method Reference

Major ions Atomic absorption spectrometry Fishman (1993)

Nutrients Various methods Fishman (1993)

Organic carbon UV-promoted persulfate oxidation 

and infrared spectrometry

Brenton and Arnett (1993)

Trace metals Atomic absorption spectrometry Fishman (1993)

Pesticides Solid-phase extraction using a C-18 

cartridge and gas chromatography/

mass spectrometry

Zaugg and others (1995)

Volatile organic 

compounds

gas chromatography/mass 

spectrometry

Connor and others (1998)

E. coli m-TEC Myers and Sylvester (1997)

Fecal coliform m-FC Myers and Sylvester (1997)

CFC gas chromatography with ECD 

detector

Busenberg and Plummer (1992)

SF6 gas chromatography with ECD 

detector

Busenberg and Plummer (2000)
Quality-Assurance and Quality-Control Procedures 15

(Mueller and others, 1997). Field blanks are used to test 

for all three of the sources of contamination listed above; 

equipment blanks are used to test for contamination 

sources 1 and 2 only. Source-water blanks are collected to 

determine if the sample-processing equipment is a source 

of contamination. A trip blank is prepared in the 

laboratory, taken to the field, and shipped with the 

environmental sample to test for contamination sources 2 

and 3 only. Spiked samples are environmental samples 

that are injected with a known mass of the analyte of 

interest for use in determining the accuracy and precision 

of organic analyses, the stability of analytes during typical 

holding times, and whether characteristics of the 

environmental sample may interfere with the analysis for 

analytes (Mueller and others, 1997). Replicates are two or 

more samples that are split or are collected in sequence or 

concurrently. They are considered to have identical 

composition. Replicates provide a measure of the 

variability resulting from sample collection, processing, 

and analysis (Mueller and others, 1997).

Interpretation of the data provided by the field 

blanks collected during the urban land-use study indicated 

no systematic bias or source of contamination attributable 

to the sampling equipment or procedures used to collect 

the ground-water samples. No detections were noted in the 

organic blank samples. Chromium, copper, and zinc were 

detected in two inorganic blank samples. With the 

exception of one copper detection, concentrations of these 

trace metals in the inorganic blank samples were less than 

10 percent of the chromium, copper, and zinc 

concentrations in the environmental sample collected the 

same day as the blank. Detections of copper are attributed 

to the copper tubing used to collect the CFC samples. 

Blank samples were collected from a glass cylinder in a 

procedure that exposed the inorganic blank water sample 

to the copper tubing. Environmental samples, however, 

did not come in contact with the copper tubing because 

they were collected directly from the well by using Teflon 

tubing. Detections of chromium and zinc in the inorganic 

blank samples are attributed to the stainless steel sample 

pump and line fittings.

Samples from three wells were spiked—one with 

VOCs and two with pesticides. Three field-spike 

replicates also were collected. Mean recovery of VOCs 

from the field spike and the field-spike replicate was 

78 and 71 percent, respectively (table 5). The mean 

difference in recovery between the field spike and the 

field-spike replicate was 14 percent. Analyses of the field 

spikes indicated that the results of analyses for VOCs in 

the urban samples may be conservative. Mean recovery of 

pesticides from the field spikes and the field-spike 

replicates ranged from 89 to 107 percent (table 5). The

Table 4. Summary of quality-assurance and qualitycontrol samples collected during the urban land-use 

study in Montgomery, Alabama

[TM, trace metals; I, major ions; N, nutrients; V, volatile 

organic compounds; P, pesticides; OC, organic carbon; A, 

alkalinity]

Map

 reference 

number

(fig. 5)

Quality-control

sample 

type

Date 

sampled

Analytical 

coverage

Inorganic blank

 6 Field blank 12/13/1999 TM, I, N

 7 Field blank 12/28/1999 TM, I, N

 12 Field blank 11/17/1999 TM, I, N

 17 Field blank 10/27/1999 TM, I, N

Organic blank

15 Source-water 

blank

12/07/1999 V

 15 Field blank 12/07/1999 P, V, OC

16 Field blank 11/08/1999 P, V, OC

 16 Source-water 

blank

11/08/1999 V

 19 Trip blank 01/05/2000 V

 19 Source-water 

blank

01/05/2000 V

19 Field blank 01/05/2000 P, V, OC

Spike

9 Field spike 12/02/1999 V

 20 Field spike 01/04/2000 P

28 Field spike 11/22/1999 P

Replicate

1 Environmental 11/15/1999 P, V, OC, TM, I, 

N, A

 3 Environmental 12/06/1999 P, V, OC, TM, I, 

N, A

 9 Field spike 12/02/1999 V

27 Environmental 12/01/1999 P, V, OC, TM, I, 

N, A

 20 Field spike 01/04/2000 P

 20 Pesticide 01/04/2000 P

28 Pesticide 11/22/1999 P

28 Field spike 11/22/1999 P

 29 Environmental 01/06/2000 P, V, OC, TM, I, 

N, A

replicates were collected in addition to four environmental 

replicate samples. 

A blank is a water sample that has no analytes of 

interest. A blank sample is analyzed to determine if 

contamination of the environmental sample has occurred 

during (1) sample collection and processing, (2) sample 

handling and transportation, and (or) (3) sample analysis 
16 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

mean difference in recovery between the field spikes and 

the field-spike replicates was 5 and 3 percent.

Four environmental replicate samples were 

collected. The variance between the environmental 

samples and the corresponding replicate samples 

typically was less than 7 percent. One set of 

environmental and replicate samples had variances of 

14 percent for manganese, 12 percent for organic carbon, 

and 19 percent for cobalt. Increased concentrations of 

copper in two replicate samples and nickel in one 

replicate sample are attributed to increased time of 

exposure of the sample water to the metal of the sample 

pump and fittings of the sample line. Interpretation of the 

data provided by the blanks, spiked samples, and replicate 

samples indicated no systematic bias in the sample 

analyses; therefore, none of the environmental data were 

adjusted based on interpretation of the results of the 

QA/QC samples. 

Graphical and Statistical Methods 

Three common graphical techniques were used to 

present and analyze results of water-quality sampling 

from the urban land-use study—the Piper (1944) trilinear 

diagram, boxplots (Tukey, 1977), and the Stiff (1951) 

diagram. The Piper (1944) diagram is used to graphically 

present water-quality data based on cation and anion 

content. Percentages of total milliequivalents per liter of 

cations or anions of interest are plotted in separate 

triangles. Each side of each triangle provides an axis to 

plot ions; a single point is plotted in each triangle. The 

two points are then projected as a single point onto a 

diamond-shaped diagram. Piper diagrams permit the 

ionic content of many samples to be represented on a 

single graph. The dominant ion type in each sample is 

easily determined by where the sample plots. However, 

because ion concentrations are converted to total 

composition percentages before plotting, waters with 

very different total concentrations may plot closely 

together. 

Boxplots are vertical rectangles the top of which 

represents the 75th percentile and the bottom the 

25th percentile for the range of values for a set of 

samples. The median value is represented as a line drawn 

across the rectangle. Vertical lines extend from the top 

and bottom of the rectangle to represent values that are 

outliers. Alley (1993) lists three ways boxplots illustrate 

the distribution of data: (1) the sample median is a robust 

measure of the central tendency of the data that is not 

influenced by outliers; (2) the difference between the top 

and bottom of the rectangle, the interquartile range, is a 

robust measure of the spread of the data; and (3) the 

distance from the top of the rectangle to the median 

compared to the distance from the bottom of the rectangle 

to the median is a measure of the skewness of the data. 

The top and bottom of a rectangle for normally distributed 

data are roughly equidistant from the median. Boxplots 

are useful in presenting data for individual constituents in 

large numbers of samples. Different groups of data can be 

compared and contrasted by placing boxplot analyses side 

by side.

A Stiff diagram is a polygon created by plotting 

cation and anion milliequivalents along a horizontal axis 

divided by a vertical center line. Cations are plotted on 

one side of the vertical center line; anions are plotted on 

the opposite side. Stiff diagrams are useful for rapid 

comparisons of water-quality analyses from different 

sources because the Stiff diagram for each source will be 

a distinctive graphical shape. They are not useful for large 

numbers of analyses.

Table 5. Descriptive statistics for quality-assurance and quality-control field spikes 

[V, volatile organic compounds; P, pesticides]

Map

reference

number

(fig. 5)

Sample 

type

Date 

sampled

Analytical

coverage

Mean

recovery

(percent)

Mean 

difference in 

recovery 

(percent)

 9 Field spike 12/02/1999 V 78

 9 Field-spike replicate 12/02/1999 V 71 14

 20 Field spike 01/04/2000 P 104

 20 Field-spike replicate 01/04/2000 P 107 5

 28 Field spike 11/22/1999 P 89

 28 Field-spike replicate 11/22/1999 P 91 3
Chemical and Physical Properties of the Shallow Aquifer 17

Descriptive statistics, such as the range, maximum, 

minimum, median, and interquartile range of data, were 

used in this study to summarize the distribution of 

chemical data for ground-water samples collected from 

wells completed in the same land-use setting or aquifer. 

Descriptive statistics for data sets that contained censored 

values were estimated by using log-probability regression 

(Maddy and others, 1990).

Nonparametric hypothesis tests were used to 

evaluate significant differences between water-quality 

variables in ground-water samples collected from 

different land-use settings or aquifers. Censored data are 

represented by ranks in nonparametric tests; estimation of 

data values below reporting limits is not necessary. The 

Wilcoxon rank-sum test was used to test the null 

hypothesis that independent, random ground-water 

samples from two populations were identical. Rejection 

of the null hypothesis, at a confidence level of 95 percent, 

supported the alternative hypothesis that the samples 

were drawn from different populations.

The relations between selected physical properties 

and chemical constituents in ground-water samples 

collected from the urban wells and land use surrounding 

the urban wells was examined by using statistical 

correlation. Correlation analysis assesses not only the 

relation between two variables, but also the strength of the 

relation (Ott, 1988, p. 319). The Spearman rho rank 

correlation test was chosen because the data are likely to 

be nonparametric and the number of samples was greater 

than 20 (Helsel and Hirsch, 1992, p. 217–218). 

Correlation tests calculate a probability statistic 

and a correlation coefficient. The probability statistic 

relates to the confidence level. A confidence level of 

95 percent, as used in this report, means that there is a 

95-percent probability that the correlation is statistically 

significant. The correlation coefficient describes the 

strength of the correlation and how the correlated 

parameters (physical properties and chemical constituents 

of the water and selected land use) vary. For this report, 

parameters with a correlation coefficient of 0.6 and 

greater is considered strongly correlated. Parameters with 

a correlation coefficient between 0.4 and 0.6 are 

considered somewhat correlated. Parameters with a 

correlation coefficient of 0.4 and less are considered 

weakly correlated. A positive correlation coefficient 

means that as the value of one parameter increases, the 

value of the other parameter also increases. A negative 

correlation means that the value of one parameter 

decreases as the value of the other parameter increases. 

Scatterplots were made of all correlated parameters to 

ensure that the parameters possessed a monotonic 

correlation (Helsel and Hirsh, 1992, p. 209–211).

CHEMICAL AND PHYSICAL PROPERTIES OF THE 

SHALLOW AQUIFER

The chemical and physical properties of sediments 

through which ground water flows can affect groundwater quality. Soils with low organic carbon content may 

increase the potential for nitrate (U.S. Geological Survey, 

1999c) and pesticides (Barbash and Resek, 1996) to enter 

ground water. Soils with low pH contribute to low pH 

conditions in ground water, which has been correlated 

with increased nitrate and trace element concentrations 

(van Duijvenbooden, 1993). Soil pH and organic carbon 

content also can affect concentrations of methyl tert-butyl 

ether (MTBE) and ethyl tert-butyl ether, which degrade 

only in soil having a low organic carbon content and a pH 

of about 5.5 (Yeh and Novak, 1994). Coarse-grained 

sediments permit more rapid infiltration of water than 

fine-grained sediments; therefore, aquifers overlain by 

coarse-grained sediments may be more vulnerable to 

contamination than aquifers overlain by fine-grained 

sediments.

Soil Characteristics 

The clayey soils that develop from weathering of 

the Selma confining unit are very poorly drained, have 

soil pH values ranging from 4.5 to 8.5, and have organic 

carbon content ranging from 0 to 7 percent (Burgess and 

others, 1960). This relatively high organic carbon content 

and moderate pH may reduce the potential for pesticides, 

nitrate, and trace elements to enter the Black Warrior 

River aquifer. The soils developed from the alluvial and 

terrace deposits and from the Eutaw Formation are well 

drained, have lower soil pH values ranging from 3.6 to 

6.5, and have comparatively low organic carbon content 

ranging from 0 to 4 percent (Burgess and others, 1960). 

These characteristics may increase the potential for 

pesticides, nitrate, and trace elements to enter the Black 

Warrior River aquifer; however, they may decrease the 

potential for MTBE and ethyl tert-butyl ether to enter the 

aquifer.

Sediment Core Analyses

Sediment core samples of the Selma confining unit, 

the shallow aquifer, and the Eutaw Formation were 

collected during the installation of the urban land-use 

monitoring wells. Core samples of the Selma confining 

unit had a soil pH range from 4.5 to 7.5, with a median 

value of 6.5. Organic carbon content ranged from less 

than 0.01 to 0.85 percent. The vertical hydraulic 
18 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

conductivity and porosity, determined for three core 

samples of the Selma confining unit, ranged from 

1.9 x 10-2 to 1.36 x 10-6 feet per day (ft/d) and 36.3 to 

46.9 percent, respectively. These analyses indicate that 

the Selma confining unit is likely to hydraulically isolate 

the underlying Black Warrior River aquifer from sources 

of contamination at land surface, and the moderate pH of 

the sediments may lessen the potential for nitrate and 

trace metals to enter the Black Warrior River aquifer (van 

Duijvenbooden, 1993).

Core samples from the shallow aquifer had a soil 

pH range from 5.5 to 6.0, with a median value of 5.5. 

Organic carbon content ranged from 0.03 to 0.16 percent. 

The vertical hydraulic conductivity, determined for two 

core samples, was 2.7 and 6.2 ft/d, and the porosity was 

26 and 35 percent. Core samples from the Eutaw 

Formation had a soil pH that ranged from 5.5 to 7.0, with 

a median value of 6.0. Organic carbon content ranged 

from less than 0.01 to 0.24 percent. The vertical hydraulic 

conductivity of six core samples ranged from 0.48 to 

35 ft/d. Porosity values of five samples ranged from 44 to 

47 percent. The results of these analyses indicate that 

there is little hydraulic separation between the ground 

water and sources of contamination where the shallow 

aquifer and Eutaw Formation are exposed at land surface. 

The relatively low pH and organic carbon content of the 

sediments have little potential to prevent the transport of 

nitrate, trace metals, and pesticides into the aquifer (van 

Duijvenbooden, 1993; Barbash and Resek, 1996; U.S. 

Geological Survey, 1999b); however, these properties 

may enhance the degradation of MTBE and ethyl tertbutyl ether (Yeh and Novak, 1994).

Lithology of the Shallow Aquifer

Representative sediment samples were collected 

from all materials drilled during the installation of the 

30 urban wells, and lithologic descriptions of the samples 

were prepared. Samples of the alluvial deposits typically 

were composed of very fine- to very coarse-grained 

quartz sand that was clear, white, red, and yellow in color. 

Pebbles were sometimes present. Muscovite was 

common. Red, brown, and gray silt and clay were mixed 

with the sand but also was present as separate layers. The 

lithology of the terrace deposits is similar, but quartz 

gravel up to 100 millimeters in diameter typically was 

present in the samples. 

Samples of the Eutaw Formation were composed 

of very fine- to medium-grained quartz sand, glauconite, 

calcium carbonate, and trace amounts of muscovite and 

pyrite. Where the Eutaw Formation is at or near land 

surface, the quartz sand has a clear, white, and tan color. 

Green and gold colored muscovite is commonly present, 

but the glauconite, calcium carbonate, and pyrite have 

been dissolved and transported (weathered) away by 

acidic rainwater as it enters the ground and moves 

downdip. The Eutaw Formation in the urban study area 

has been weathered as deep as 100 ft below land surface. 

The Eutaw Formation has not been weathered where it is 

overlain by the Selma confining unit, or is not near land 

surface. The presence of glauconite causes the quartz sand 

to appear deep to light green in color. Pyrite, calcium 

carbonate, and muscovite also are present. Gravel was not 

found in any of the Eutaw Formation samples. 

WATER QUALITY IN THE SHALLOW AQUIFER

During 1999–2000, ground-water samples were 

collected from 30 urban monitoring wells installed by the 

USGS in eastern Montgomery, Alabama. These samples 

were analyzed at the USGS NWQL for major ions, 

nutrients, trace metals, pesticides, and VOCs. The results 

of the analyses were compared to baseline water quality 

in the Black Warrior River aquifer.

Chemistry of Natural Ground Water

Natural ground-water quality is a term used to 

describe water quality unaffected by man. The natural 

water quality must be known before the effects of specific 

land-use practices can be determined. Natural waterquality conditions in the Black Warrior River aquifer were 

determined by analyzing ground-water samples collected 

from 30 wells (fig. 4) located in low-density residential 

and rural settings (Pearman and others, 2000). With the 

exception of bacteria, CFCs, and SF6, the ground-water 

samples were analyzed at the USGS NWQL for the 

constituents listed in table 3. Minimum, median, and 

maximum concentrations of selected chemical 

constituents in ground-water samples collected from the 

rural wells are listed in table 6.

The major ion composition of ground-water 

samples collected from the rural wells is illustrated by the 

Piper diagram in figure 10. The ion content of groundwater samples collected from the Gordo and Coker 

Formations plot near the center of the Piper diagram, 

indicating no dominant ion. The ion content of groundwater samples collected from the Eutaw Formation, 

however, plot primarily within the area of the Piper 

diagram indicating water quality dominated by calcium, 

bicarbonate (HCO3), and carbonate (CO3) ions. The 

sources of the calcium, HCO3, and CO3 ions in ground-
Water Quality in the Shallow Aquifer 19

Table 6. Minimum, median, and maximum values for physical properties and concentrations of selected chemical constituents in ground-water samples collected from rural wells 

in the Mobile River Basin and urban wells in Montgomery, Alabama

[MIN, minimum; MED, median; MAX, maximum; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; none, no drinking-water standard; mg/L, milligrams per liter; °C, degrees 

Celsius; <, less than; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit (Maddy and others, 1990); nd, not present above long_term 

detection level; μg/L, micrograms per liter; —, too few detections to estimate statistic; P, phosphorus; C, carbon]

Property or constituent

MCLa

SSb

ALc

a Maximum contaminant level for drinking water established by the U.S. Environmental Protection Agency.b Secondary drinking-water standard established by the U.S. Environmental Protection Agency.c Action level established by the U.S. Environmental Protection Agency.

Rural data set

(30 wells)

Rural data set

Eutaw Formation

(12 wells)

Urban data set

(30 wells)

Urban data set, by formation

Unweathered Eutaw

(8 wells)

Weathered Eutaw

(8 wells)

Alluvial and Terrace

(14 wells)

MIN MED MAX MIN MED MAX MIN MED MAX MIN MED MAX MIN MED MAX MIN MED MAX

Physical properties

pH (standard units) 6.5–8.5b 5.1 5.8 8.5 5.4 7.4 8.5 4.6 5.6 7.7 6.7 7.1 7.5 4.7 5.3 5.7 4.6 5.4 7.7Specific conductance (μS/cm at 25 °C) none 14 51 835 42 186 835 28 74 2,670 306 621 2,670 28 53 269 33 69 130Alkalinity (mg/L) none 3 14 290 5 88 290 2 8 380 88 214 381 3 7 15 2 6 17Dissolved solids residue 180 °C (mg/L) 500 19 46 455 46 129 455 27 48 2,240 192 406 2,240 27 42 148 29 42 79

Major Ions

Calcium (mg/L) none .4 1.9 110 1.6 13 110 1.2 3.4 520 29 105 523 1.3 2.6 16 1.2 2.7 10Magnesium (mg/L) none .3 .6 7.8 .4 2.2 7.8 .3 1.4 9 1 3 9 .3 1.2 7.1 .5 1.4 3.4Potassium (mg/L) none .1 2 8.6 .7 2.6 8.6 .2 1.4 2.8 1 2 3 .9 1.6 2.3 <.24 *1.4 2.8Sodium (mg/L) none .8 2.2 163 1.8 9.2 163 .9 4.6 228 9 25 228 .9 3.4 15 1.6 4.2 6.2Chloride (mg/L) 250b .5 2.5 150 1.7 3.2 150 1.3 6.8 120 6 28 123 1.3 4.6 30 2 6.4 12Fluoride (mg/L) 2b <.1 *.02 .9 <1 *.12 .9 <.1 *.09 .9 .2 .4 1 nd nd nd nd nd ndSilica (mg/L) none 8.3 14 55 10 20 36 8.2 14 42 23 29 42 11 15 25 8.2 12 17Sulfate (mg/L) 250b <.1 *.5 35 <.1 *4.3 35 <.1 *.6 1,100 9 53 1,100 <.1 *.4 .7 <.1 *.4 11Bromide (mg/L) none <.01 *.02 .9 .02 .05 .9 <.01 *.03 1 .04 .2 1 <.01 *.04 .1 <.01 *.02 .05Iron (μg/L) 300b <10 *17 17,900 <10 *205 14,300 <10 16 2,500 10 500 2,500 <10 *10 330 <10 *10 70

Nutrients

Nitrite plus nitrate (mg/L) 10a <.05 *.06 2.3 <.05 — 2.3 <.05 *1.3 15 <.05 — .11 .4 1.5 15 <.05 *2.6 7.1Phosphorus (mg/L as P) none <.006 *.01 .8 <.006 *.2 .8 <.006* *.005 .2 <.006 *.006 .2 nd nd nd <.006 *.005 .01Phosphate, ortho (mg/L as P) none <.01 *.02 .8 <.01 *.2 .8 <.01 *.002 .2 <.01 *.014 .2 nd nd nd <.01 — .02Dissolved organic carbon (mg/L) as C none <.33 *.15 .8 .1 .35 .8 <.33 *.28 1.2 .2 .6 1.2 <.33 *.3 .4 <.33 *.25 1.2

Metals

Aluminum (μg/L) 50–200b <1 *1.2 14 <1 *.8 2.4 1 12 136 <1 4 13 3 28 118 3 14 136Barium (μg/L) 2,000a 6.3 27 155 10 60 155 6 47 368 6 22 368 10 40 84 10 52 131Chromium (μg/L) 100a <1 — 2.3 nd nd nd <.8 *.569 1.8 nd nd nd <.8 — 1.4 <.8 *.5 1.8Cobalt (μg/L) none <1 — 9.6 nd nd nd <1 *1.5 7.3 <1 — 4 <1 *1 4 <1 *2.5 7Copper (μg/L) 1,000b <1 *1.8 29 <1 — 1.9 <1 *3.4 30 <1 — 4 1 4 30 <1 *6 13Lead (μg/L) 0a, 15c <1 *.5 2.8 nd nd nd <1 — 1.4 nd nd nd nd nd nd <1 — 1.4Manganese (μg/L) 50b 1 9.9 999 4.7 118 724 10 80 382 14 84 382 25 89 379 10 80 196Nickel (μg/L) none <1 *.3 12 <1 — 1.6 <1 *1.4 13 <1 — 13 <1 *2 3 <1 *1 4Zinc (μg/L) 5,000b <1 *1.5 216 <1 *1.1 5.5 <1 *4.8 23 <1 — 9 2 14 21 3 6 23
20 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

water samples collected from the Eutaw Formation are 

calcareous sandstone and limestone interbedded with 

glauconitic sand (Cook, 1993).

Concentrations of selected anions and cations in 

representative ground-water samples from the Coker, 

Gordo, and Eutaw Formations were used to create Stiff 

diagrams. The Stiff diagrams for ground-water samples 

collected from the Gordo and Coker Formations are 

elongated along the vertical central axis with no single 

ion producing a large horizontal departure from the 

central axis (fig. 11), indicating no dominant ion in the 

sample. The pattern generated by the ion content of 

ground-water samples collected from the Eutaw 

Formation is elongated along the bottom horizontal 

axis for the calcium, HCO3, and CO3 ions (fig. 11). 

This pattern indicates greater concentrations of these 

ions relative to the other ions plotted in the diagram. 

Analyses of water samples collected from urban 

wells completed in the unweathered Eutaw Formation 

indicate that the ground water is calcium-bicarbonate 

type (fig. 12), similar to samples collected from the 

rural wells completed in the Eutaw Formation (fig. 10). 

The ion content of ground-water samples collected 

from the alluvial and terrace deposits and the 

weathered Eutaw Formation plot near the center of the 

Piper diagram, indicating no dominant cation; 

however, ground water collected from these formations 

was dominated by chloride, fluoride, and nitrate 

anions. Minimum, median, and maximum 

concentrations of selected chemical constituents in 

ground-water samples collected from the urban wells 

are listed in table 6.

The chemical composition of water changes as it 

moves through the ground and interacts with soil and 

sediments. These changes often follow a predictable 

pattern. Recently recharged ground water is likely to 

have greater dissolved oxygen levels because it 

contains atmospheric oxygen; in addition, recharge 

water typically is acidic because atmospheric or 

microbial carbon dioxide (CO2) dissolved in the water 

produces a weak carbonic acid in solution. Recently 

recharged ground water also is typically low in 

dissolved solids because insufficient time has passed 

for the carbonic acid to dissolve minerals. As 

Figure 10. Piper trilinear diagram showing major ion composition of ground-water samples 

collected from rural wells completed in the Coker, Gordo, and Eutaw Formations in the Mobile 

River Basin.
Water Quality in the Shallow Aquifer 21

Figure 11. Stiff diagrams representing water quality of samples collected from rural wells completed in the Coker, Gordo, and Eutaw 

Formations in the Mobile River Basin.
22 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

Figure 12. Piper trilinear diagram showing major ion composition of ground water collected from urban wells in 

Montgomery, Alabama.
Water Quality in the Shallow Aquifer 23

Figure 13. Piper trilinear diagram showing geochemical evolution of ground water in the 

Eutaw Formation beneath Montgomery, Alabama.

ground water moves away from the recharge area, readily 

soluble minerals, such as carbonates and sulfides, are dissolved, increasing the dissolved solids content of the 

water. Dissolved oxygen concentration in the water also 

decreases as biological and chemical reactions consume 

the oxygen. Once dissolved oxygen in the water has been 

removed, denitrification may occur, causing nitrogen concentrations to decrease (Chapelle, 1993, p. 246). Iron concentrations may increase due to iron III reduction. The 

dissolved solids content of ground water increases with 

time as a result of the dissolution of readily soluble minerals, such as calcite (CaCO3) and pyrite (FeS2). Both of 

these minerals were found in drill cuttings collected during the installation of the urban wells sampled for this 

study. As a result of these natural chemical processes, 

ground water typically becomes less acidic and increases 

in alkalinity as it ages and moves away from the area of 

recharge.

The geochemical evolution of ground water in the 

urban study area is illustrated by the trilinear diagram of 

water-quality analyses of samples collected from the urban 

wells completed in the Eutaw Formation (fig. 13). Where 

the Eutaw Formation is exposed at or near land surface, 

recently recharged, acidic ground water has dissolved and 

transported away calcium-rich minerals, producing a 

major-ion composition similar to that of the alluvial and 

terrace deposits. As ground water flows downdip, the 

major-ion composition becomes more similar to that of 

ground-water samples collected from the rural wells 

completed in the Eutaw Formation. This geochemical 

evolution is further illustrated by the Stiff diagrams in 

figure 14.
24 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

Ground-Water Quality Beneath an Urban Area of 

Montgomery, Alabama

Urban ground-water quality, represented by 

samples collected from 30 wells in Montgomery, 

Alabama, was compared to regional ground-water quality 

represented by samples collected from 30 wells located in 

rural areas of the Mobile River Basin. All of the wells in 

the urban area produce water from the Eutaw Formation 

or from overlying deposits in direct hydraulic contact 

with the Eutaw Formation. Most of the urban wells are 

shallow relative to wells in the rural area (fig. 9), and 

many are completed in different formations. As a result, 

the direct effects of urbanization cannot be easily 

evaluated due to the complicating factors of position in 

the flow system and differing mineralogy. Despite these 

complicating factors, however, 12 rural wells completed 

in the Eutaw Formation, the same formation in which 16 

of the 30 urban wells are completed, allowed for a broad 

comparison based on these two data subsets. Graphical 

methods and the Wilcoxon rank-sum test were used to 

evaluate the significance of water-quality differences 

between the data sets.

Values of pH, dissolved solids, specific 

conductance, and alkalinity of the water samples from the 

30 rural wells, the 12 rural wells completed in the Eutaw 

Formation, and the 30 urban land-use study wells were 

illustrated and compared by using boxplots (fig. 15). The 

urban ground-water samples had lower median values but 

a larger range in values for pH, specific conductance, total 

dissolved solids, and alkalinity compared to the water 

quality of ground-water samples collected from the rural

Figure 14. Stiff diagrams representing water quality of samples collected from urban wells completed in the Eutaw 

Formation, alluvial deposits, and terrace deposits beneath Montgomery, Alabama.
Ground-Water Quality Beneath an Urban Area of Montgomery, Alabama 25

wells. The distribution of physical properties measured in 

the urban ground-water samples is consistent with those 

of samples collected from recently recharged ground 

water, the water-quality of which reflects diverse influences such as are found in an urban setting.

Occurrence and Distribution of Major Ions

A comparison of median values for major ions 

measured in rural water samples and urban water samples 

(table 6) indicated that the chloride concentration was 

greater in water samples collected from urban wells 

compared to rural wells (fig. 16). The apparent relation 

between greater chloride concentrations and the urban 

ground-water samples was tested by using the Wilcoxon 

rank-sum test. Three separate tests were run—the 

12 rural water samples collected from the Eutaw 

Formation were compared to all 30 urban water samples; 

the 12 rural water samples collected from the Eutaw 

Formation were compared to the 16 urban water samples 

collected from the Eutaw Formation; and all 30 rural 

water samples were compared to all 30 urban water 

samples. Results of these three tests indicated that 

chloride concentrations in urban water samples was 

statistically greater than in the rural water samples. 

Figure 15. Concentrations of selected water-quality constituents in ground-water samples collected from rural wells in 

the Mobile River Basin, rural wells completed in the Eutaw Formation, and urban wells in Montgomery, Alabama.
26 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

Figure 16. Concentrations of chloride in ground-water samples collected from rural wells in 

the Mobile River Basin, rural wells completed in the Eutaw Formation, and urban wells in 

Montgomery, Alabama.

Occurrence and Distribution of Nutrients

Comparison of nutrient concentrations in groundwater samples collected from the rural wells and the urban 

wells (table 6) suggests that concentrations of nitrite plus 

nitrate were greater in samples collected from the urban 

wells. The frequency of detection of nitrite plus nitrate in 

the urban water samples (22 detections) was greater than 

in the 30 rural water samples (16 detections) and greater 

than in the 12 rural water samples collected from the 

Eutaw Formation (1 detection). The apparent relation 

between greater concentrations of nitrite plus nitrate and 

urban ground-water samples (fig. 17) was tested by using 

the Wilcoxon rank-sum test. Two tests were run—the 

30 rural water samples were compared to the 30 urban 

water samples; and the 30 rural water samples were 

compared to the 16 urban water samples collected from 

the Eutaw Formation. Results of both tests indicated that 

concentrations of nitrite plus nitrate in the urban water 

samples were statistically greater than in the rural water 

samples.
Ground-Water Quality Beneath an Urban Area of Montgomery, Alabama 27

Figure 17. Concentrations of nitrite plus nitrate in ground-water samples collected from rural 

wells in the Mobile River Basin, rural wells completed in the Eutaw Formation, and urban wells 

in Montgomery, Alabama.

100

50

20

10

5

2

1

0.5

0.2

0.1

0.05

0.02

0.01

NITRITE PLUS NITRATE, IN MILLIGRAMS PER LITER

MINIMUM VALUE

EXPLANATION

MAXIMUM VALUE

NUMBER OF WELLS

 SAMPLED

25TH PERCENTILE

75TH PERCENTILE

MEDIAN

(30)

16 NUMBER OF DETECTIONS

RURAL 

(30)

EUTAW 

(12)

URBAN 

(30)

Maximum contaminant level 

(U.S. Environmental Protection Agency)

Method detection level 

(U.S. Geological Survey)

16 1

22

Occurrence and Distribution of Trace Metals

Median concentrations of some trace metals 

were greater in urban ground-water samples than in 

rural ground-water samples collected from the same 

aquifer (table 6). Boxplots of the data are of limited 

use, however, because of the large number of nondetections of trace metals (fig. 18). Aluminum, 

chromium, cobalt, copper, nickel, and zinc were 

detected more frequently in the urban ground-water 

samples than in the rural ground-water samples. The 

Wilcoxon rank-sum test was used to evaluate the 

apparent differences in concentrations of aluminum, 

cobalt, copper, zinc, and nickel in the urban and rural 

ground-water samples. No statistical analysis was 

performed on the occurrence and distributions of 

chromium because it was detected only twice in the 

rural wells; however, chromium was detected more 

frequently in the urban samples (11 detections).

The apparent differences in aluminum and zinc 

concentrations in three sets of ground-water samples 

were evaluated. The 30 rural water samples were 

compared to the 30 urban water samples; the 12 rural 

water samples collected from the Eutaw Formation were 

compared to 16 urban water samples collected from the 

Eutaw Formation; and the 12 rural water samples 

collected from the Eutaw Formation were compared to 

all 30 urban water samples (fig. 18). Results of these 

analyses indicated that the concentration of aluminum in 

the ground-water samples collected from the urban wells 

was statistically greater than in the rural samples. 

Concentrations of zinc in the ground-water samples 

collected from the urban wells were statistically greater 

than in water samples collected from the rural wells when 

all 30 samples were analyzed; but the zinc concentrations 

in the rural Eutaw samples were not significantly 

different from those in the urban Eutaw samples.
28 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

The apparent differences in cobalt, copper, and 

nickel concentrations also were evaluated. The 30 rural 

ground-water samples were compared to the 30 urban 

ground-water samples. The samples collected from the 

Eutaw Formation were not independently analyzed 

because cobalt, copper, and nickel were detected 

infrequently in ground-water samples collected from the 

rural wells (fig. 18). Results of the analysis indicated that 

concentrations of cobalt, copper, and nickel in groundwater samples collected from the urban wells were 

statistically greater than in ground-water samples 

collected from the rural wells.

Occurrence and Distribution of Pesticides

Pesticides were detected in greater variety and 

more frequently in ground-water samples collected from 

the urban land-use study wells than in ground-water 

samples from the rural wells. Samples from only two rural 

wells contained pesticides, and these two samples 

contained three different pesticides. Samples from 

21 urban wells contained pesticides, and these 21 samples 

contained 12 different pesticides. Pesticides were 

detected 3 times in the rural ground-water samples, but 

54 times in the urban ground-water samples. The most 

commonly detected compounds in the urban samples 

were deethyl atrazine (16 detections), atrazine 

(10 detections), dieldrin (7 detections), and simazine 

(6 detections). The range and distribution of 

concentrations of the most commonly detected pesticides 

in rural and urban wells are shown in figure 19; however, 

many of the concentrations are similar and when plotted 

do not appear as individual points on the graph. 

Herbicides were the most frequently detected class of 

pesticides in the urban samples (fig. 20). The highest 

measured concentration of any pesticide in the rural 

samples was 0.008 microgram per liter (μg/L) for 

atrazine. The highest measured concentration of any 

pesticide in the urban samples was also atrazine at 

0.55 μg/L. The minimum and maximum concentrations 

of selected pesticides detected in ground-water samples 

collected from the urban and rural wells are listed in 

table 7.

Figure 18. Concentrations of selected trace metals in ground-water samples collected from rural wells in the Mobile River Basin, 

rural wells completed in the Eutaw Formation, and urban wells in Montgomery, Alabama.
Ground-Water Quality Beneath an Urban Area of Montgomery, Alabama 29

Figure 19. Range and distribution of concentrations of the most commonly detected perticides in ground-water samples collected from rural 

wells in the Mobile River Basin and urban wells in Montgomery, Alabama.

Figure 20. Detection frequencies of pesticides in ground-water samples collected from urban wells in Montgomery, Alabama.
30 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

Occurrence and Distribution of Volatile Organic 

Compounds

Volatile organic compounds (VOCs) were detected 

in greater variety and more frequently in ground-water 

samples collected from the urban land-use study wells 

than in the ground-water samples from the rural wells. 

Seven different VOCs were detected in water samples 

from 19 of the rural wells. Twenty-nine different VOCs 

were detected in water samples from 29 of the urban 

wells. VOCs were detected a total of 25 times in the rural 

samples, but 121 times in the urban samples. Chloroform 

was the most commonly detected VOC in the rural 

samples (11 detections). The most commonly detected 

VOCs in the urban samples were chloroform 

(20 detections), toluene (12 detections), carbon disulfide 

(11 detections), tetrachloroethylene (9 detections), and 

benzene and 1,1,1-trichloroethane (8 detections). The 

range and distribution of concentrations of the most 

commonly detected VOCs in rural and urban wells are 

shown in figure 21; however, many of the concentrations 

are similar, and when plotted do not appear as individual 

points on the graph. Alkanes were the most frequently 

detected class of VOCs in the urban samples (fig. 22). 

Concentrations of all VOCs in the rural samples 

were reported as estimated because values were below the 

reporting limit but above the long-term method detection 

level. The highest measured concentration of any VOC in 

the urban land-use study samples was 45.5 μg/L for 

tetrachloroethylene. The minimum and maximum 

concentrations of selected VOCs detected in groundwater samples collected from the urban and rural wells are 

listed in table 7.

Table 7. Minimum and maximum concentrations of selected pesticides and volatile organic compounds in ground-water samples 

collected from rural wells in the Mobile River Basin and urban wells in Montgomery, Alabama

[MIN, minimum; MAX, maximum; μg/L, micrograms per liter; E, concentration less than the reporting level but above the long-term method 

detection level; p,p'-DDE, dichlorodiphenyldichloroethylene; none, no drinking-water standard]

Constituent

MCLa

RSDb

HAc

a Maximum contaminant level for drinking water established by the U.S. Environmental Protection Agency. b Risk-specific dose health advisory at 10E-6 level established by the U.S. Environmental Protection Agency. c Health advisory level established by the U.S. Environmental Protection Agency.

Number of detections Rural data set 

(30 wells)

Urban data set 

(30 wells)

Rural wells Urban wells MIN MAX MIN MAX

Pesticides

Atrazine (μg/L) 3a 1 10 0.008 0.008 E0.002 0.55

Dacthal (μg/L) 4,000c 1 3 E.0009 E.0009 .002 .01

Deethyl atrazine (μg/L) none 1 16 E.007 E.007 E.003 E.3

Dieldrin (μg/L) .002b 0 7 E.004 .06

Metolachlor (μg/L) 100c 0 3 E.003 .008

p,p'-DDE (μg/L) .1b 0 1 E.002 E.002

Simazine (μg/L) 4a 0 6 .009 .28

Terbacil (μg/L) 90c 0 4 E.007 E.009

Volatile organic compounds

Benzene (μg/L) 5a 0 8 E.008 E.06

Chloroform (μg/L) 100a 11 20 E.008 E.1 E.03 1.5

Tetrachloroethylene (μg/L) 5a 2 9 E.01 E.07 E.01 45.5

1,1,1-Trichloroethane (μg/L) 200a 1 8 E.007 E.007 E.008 .25

Toluene (μg/L) 1,000a 1 12 E.009 E.009 E.006 E.08

Carbon disulfide (μg/L) none 8 11 E.022 E.238 E.01 .13
Ground-Water Quality Beneath an Urban Area of Montgomery, Alabama 31

Age of Ground Water

Ground-water samples collected from the urban 

land-use study wells were analyzed for the environmental 

tracers, CFCs and SF6. Ground-water age is estimated by 

relating the measured concentration of the environmental 

tracer in ground-water samples to the reconstructed 

historical atmospheric concentration and(or) to calculated 

concentrations expected in water in equilibrium with air 

(Busenberg and Plummer, 1992, 2000; U.S. Geological 

Survey, 1999d). The age estimated for the water refers to 

the time period in which CFCs and SF6 are introduced into 

the water prior to entering the subsurface. Environmental 

processes, such as microbial degradation, sorption, and 

excess dissolved gases, may affect the concentration of 

environmental tracers in water.

Chlorofluorocarbons are synthetic compounds first 

produced in the early 1930’s (Cook and Herczeg, 2000). 

The presence of measurable concentrations of CFCs in a 

water sample indicates that the sample contains some 

post-1940 water. Sulfur hexafluoride is a trace 

atmospheric gas that occurs naturally in some minerals, 

igneous rocks, and volcanic and igneous fluids; however, 

SF6 is primarily of anthropogenic origin. Large-scale 

Figure 21. Range and distribution of concentration of most commonly detected volatile organic compounds in ground-water samples collected from 

rural wells in the Mobile River Basin and urban wells in Montgomery, Alabama.

Figure 22. Frequency of detection of volatile organic compounds, by 

compound class, in ground-water samples collected from rural wells in the 

Mobile River Basin and urban wells in Montgomery, Alabama.
32 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

production of SF6 began in the 1960’s, and dating is 

possible from about 1970 (Busenberg and Plummer, 

1997). Ground-water samples collected from the urban 

land-use study wells were analyzed for CFC-11 

(trichlorofluoromethane or CFCl3), CFC-12 

(dichlorodifluoromethane or CF2Cl2), CFC-113 

(trichlorotrifluoroethane or C2F3Cl3), and SF6.

The age of the ground water was determined for 

samples from all 30 urban land-use study wells (table 8). 

In addition to the CFC and SF6 age date estimates, the 

process of assigning an age to ground-water samples 

included consideration of the concentration of dissolved 

oxygen, the presence or absence of bacteria, the presence 

or absence of chemical compounds that can be used as 

date markers such as MTBE, and the hydrogeologic 

setting of the well. In general, factors that support a 

younger water age are the presence of fecal bacteria, 

which is assumed to be from a source at land surface, a 

dissolved oxygen concentration greater than 1 milligram 

per liter (mg/L), sandy surficial geology, and the presence

Table 8. Ages of ground water in samples collected from urban wells in Montgomery, Alabama

[SF6, sulfur hexafluoride; CFC, chlorofluorocarbon; CFC-11, trichlorofluoromethane; CFC-12, dichlorodifluoromethane; 

CFC-113, trichlorotrifluoroethane; mg/L, milligrams per liter; MTBE, methyl tert-butyl ether; contam., contaminated by 

contact with atmosphere during sampling; <, less than; ~, approximately; >, greater than; ns, no sample]

Map 

reference

number

(fig. 5)

Surficial 

geology

Open 

interval

(feet below

land surface)

SF6 age 

(years)

CFC age

(years) Dissolved 

oxygen

(mg/L)

Date marker 

chemical or 

bacteria 

present

 Age used 

in this 

report

(years) CFC-11 CFC-12 CFC-113

1 sand 12.5–22.5 14 42 37 45 0.24 MTBE 14

2 sand 87.9–97.9 17 contam. contam. 17 4.9 bacteria 17 

3 sand 17.0–27.0 6 contam. contam. contam. 5.5 bacteria 6

4 sand 30.0–40.0 22 contam. contam. 28 4.4 28

5 sand 22.5–32.5 9 12 < 1 2–5 2.3 2

6 sand 26.5–36.5 < 1 contam. contam. contam. 1.1 bacteria ~ 1

7 clay 70.0–80.0 22 45 52 > 45 .6 bacteria > 45

8 sand 8.3–18.3 12 contam. contam. 13 5.2 MTBE 12

9 sand 25.5–35.5 10 contam. contam. contam. 7.0 bacteria 10

10 sand 28.9–38.9 2 contam. contam. contam. 5.9 MTBE 2

11 sand 10.5–20.5 5 14 22 10 .8 bacteria 5

12 sand 52.5–62.5 8 4 contam. 9 5.1 8

13 sand 57.0–67.0 7 contam. contam. contam. 4.6 bacteria 7

14 sand 71.5–81.5 6 contam. contam. 11 4.2 11

15 sand 29.0–39.0 18 contam. < 1 contam. 4.5 ~ 1

16 sand 28.0–38.0 19 ns ns ns 4.0 MTBE 19

17 sand 21.0–31.0 6 contam. contam. 5 5.2 bacteria 6

18 clay 21.5–31.5 12 19 19 18 4.5 bacteria 18

19 gravel 16.2–26.2 5 14 12 8 1.4 5

20 sand 16.2–26.2 7 contam. 6 7 4.8 bacteria 7

21 sand 70.0–80.0 11 contam. contam. 14 1.4 14

22 sand 81.0–91.0 < 1 contam. contam. 10 5.5 10

23 clay 19.5–20.5 14 37 30 17 .31 bacteria 17

24 clay 76.0–86.0 2 20 50 21 .10 20

25 clay 50.0–60.0 20 ns ns ns .25 bacteria 20

26 clay 30.5–40.5 21 39 44 > 45 .49 > 40

27 clay 56.5–66.5 14 46 45 20 .07 bacteria 14

28 clay 21.0–31.0 12 45 31 > 45 .12 12

29 sand 74.4–84.4 12 contam. contam. 12 6.0 12

30 clay 47.0–57.0 25 contam. 53 22 .15 bacteria 22
Relations Among Ground-Water Quality, Ground-Water Age, Land Use, and Geology 33

of chemicals whose first manufacture and use is known to 

be recent. The opposite of these factors supports an older 

age for ground water.

The age assigned to the ground-water sample 

collected from urban land-use study well 1 (table 8) 

provides a useful example of the age dating process. The 

CFC data suggests a ground-water age of 37 to 45 years. 

The SF6 data, however, yields an age of 14 years. The 

sandy surficial geology and the detection in the sample of 

MTBE, which was first used in 1979 as an octane booster 

in gasoline, supports the SF6 age of less than 20 years. 

Urban ground water sampled for this study ranged in age 

from about 1 to greater than 45 years, with a median age 

of about 12 years. The ages estimated for the ground 

water are consistent with the geology and hydrology of 

the urban study area and the design of the urban wells. 

RELATIONS AMONG GROUND-WATER QUALITY, 

GROUND-WATER AGE, LAND USE, AND 

GEOLOGY

Selected factors that may influence ground-water 

quality in the shallow aquifer underlying the urban study 

area were examined using the Spearman rho correlation 

test. Analyses were run for covariance between physical 

properties, major ions, nutrients, trace metals, the number 

of pesticides and volatile organic compounds detected, 

depth-to-open interval, ground-water age, soil organic 

carbon content, soil pH, and land-use type. The Spearman 

rho correlation test is based on ranks. Concentrations of 

major ions and trace metals less than the reporting level 

were assigned a value of one-half the reporting level so 

they would not have a rank equal to that of a measured 

value at the reporting level. Correlated physical properties 

and parameters that relate to this study are listed in 

table 9.

Some of the correlations listed in table 9 reflect the 

natural geochemical evolution of ground water. The 

decrease in dissolved oxygen and in the concentration of 

nitrite plus nitrate as ground-water age increases, and the 

increase in pH and in the concentration of iron and sulfate 

as ground-water age increases, are common changes in 

ground-water quality that occur with time. These 

correlations support the accuracy of the ground-water age 

estimates in urban land-use areas.

Some correlations may reflect the fate of 

constituents in the ground-water system. The number of 

Table 9. Spearman rank correlation coefficients for selected physical properties and parameters of ground-water 

samples collected from urban wells in Montgomery, Alabama

[>, greater than; *, correlation test performed using only samples of ground water less than 20 years old; VOC, volatile organic 

compound]

Variables

Number

of 

sample

pairs

Correlation 

coefficient

Probability 

statistic

Ground-water age and dissolved oxygen 30 - 0.43 0.017

Ground-water age and concentration of nitrite plus nitrate 30 - .57 .001

Ground-water age and pH 30 .53 .002

Ground-water age and concentration of iron 30 .38 .038

Ground-water age and concentration of sulfate 29 .50 .005

Ground-water age and concentration of aluminum 30 - .54 .002

Ground-water age and concentration of copper 30 - .58 .001

Ground-water age and concentration of zinc 30 - .40 .026

Ground-water age and number of pesticides detected 30 - .56 .001

Number of pesticides detected and concentration of nitrite plus 30 .36 .049

Concentration of aluminum and pH 30 - .85 > .001

Concentration of zinc and pH 30 - .63 > .001

*Percentage of residential land use and concentration of nickel 24 .53 .007

*Percentage of residential land use and number of pesticides 24 .49 .013

*Percentage of residential land use and number of VOCs 24 .41 .047

*Percentage of commercial land use and number of pesticides 24 - .63 .001

*Percentage of commercial land use and number of VOCs 24 - .44 .033

*Number of VOCs detected and concentration of nickel 24 .47 .019
34 Ground-Water Quality Beneath an Urban Residential and Commercial Area, Montgomery, Alabama, 1999 – 2000

pesticides detected and the concentration of nitrite plus 

nitrate decreased as ground-water sample age increased. 

These data may indicate that, with time, pesticides and 

nitrogen are being removed from the ground-water system. Likewise, concentrations of aluminum, copper, and 

zinc decreased as the age of ground water and pH 

increased. These correlations may indicate that as water 

moves through sediments, changing pH and redox potential (Eh) conditions cause these elements to form insoluble 

compounds, removing them from solution. This may 

explain why the Wilcoxon test indicated that the greater 

median concentration of zinc in the urban samples was 

statistically significant when all 30 samples were tested, 

but not statistically significant for the rural and urban samples collected from the Eutaw Formation only. Although 

urban land use is indicated as a source of the greater 

median concentrations of aluminum, copper, and zinc in 

the urban ground-water samples, these trace metals were 

detected less frequently and in lower concentrations in 

ground-water samples collected from the unweathered 

portion of the Eutaw Formation (table 6).

Correlation between land use and ground-water 

quality beneath the urban study area was evaluated by 

applying the Spearman rho correlation test to the 

24 samples of ground water having an age of less than 

20 years (table 8). The concentration of nickel and the 

number of pesticides and VOCs detected increased 

somewhat as the percentage of residential land use 

increased. The number of pesticides and VOCs detected 

decreased as the percentage of commercial land use 

increased. No other statistically significant correlations 

were found between land use and the water quality of 

urban ground-water samples (table 9). 

The effect of surficial geology on the occurrence of 

pesticides and VOCs was investigated by calculating 

frequencies of detection. The detection frequency of 

pesticides and VOCs in the urban ground-water samples 

was compared to the surficial geology (fig. 23). The 

detection frequency for pesticides was greater for urban 

samples collected from wells where the surficial geology 

is sand than for urban samples collected from wells where 

the surficial geology is clay. The frequency of detection of 

VOCs did not show a similar relation (fig. 23).

SUMMARY

The city of Montgomery, Alabama, is underlain, 

north to south, by a shallow aquifer composed of alluvial 

and terrace deposits of gravel, sand, and clay; sands and 

clays of the Black Warrior River aquifer, and by the Selma 

confining unit, which consists of clay and clayey soils 

developed from the Mooreville Chalk. Montgomery is one 

of many major population centers in the Mobile River 

Basin that rely on the Black Warrior River aquifer for 

public supply. The chemical and physical characteristics 

of soils developed from the alluvial and terrace deposits 

and the Black Warrior River aquifer may increase the 

potential for nutrients, trace metals, and pesticides to enter 

the aquifer. The chemical and physical characteristics of 

soils developed from the Selma confining unit may 

decrease the potential for contamination of the aquifer. 

Thirty wells were installed in eastern Montgomery, 

where the Black Warrior River aquifer is overlain by 

residential and commercial land use. Ground-water 

samples collected during this urban land-use study were 

Figure 23. Detection frequencies of pesticides and volatile organic 

compounds in ground-water samples collected from urban well in 

Montgomery, Alabama.
References 35

analyzed for major ions, nutrients, trace metals, 

pesticides, volatile organic compounds (VOCs), bacteria, 

chlorofluorocarbons, dissolved gases, and sulfur 

hexafluoride. Ground-water quality beneath the urban 

area was compared to the water quality of ground-water 

samples collected from 30 wells located in low-density 

residential and rural areas, which represent regional 

ground-water quality in the Black Warrior River aquifer. 

The median concentrations of chloride, nitrite plus 

nitrate, aluminum, chromium, cobalt, copper, zinc, and 

nickel were greater in ground-water samples collected 

from the urban land-use study wells than in samples 

collected from the rural wells. Pesticides and VOCs were 

detected more frequently and in greater concentrations in 

ground-water samples collected from the urban wells 

compared to ground-water samples collected from the 

rural wells. The most commonly detected pesticides in the 

urban samples were deethyl atrazine (16 detections), 

atrazine (10 detections), dieldrin (7 detections), and 

simazine (6 detections). Herbicides were the most 

frequently detected class of pesticides. The most 

commonly detected VOCs in the urban samples were 

chloroform (20 detections), toluene (12 detections), 

carbon disulfide (11 detections), tetrachloroethylene 

(9 detections), and benzene and 1,1,1–trichloroethane 

(8 detections each). Alkanes were the most frequently 

detected class of VOCs in the urban samples.

Correlation analyses provided insight into the 

occurrence of chemical constituents in the ground-water 

system beneath the urban area. Concentrations of nitrite 

plus nitrate, aluminum, copper, zinc, and the number of 

pesticides decreased as the ground-water age increased. 

These correlations indicated that with time, these 

constituents may be removed from the ground-water 

system.

Statistically significant correlations were found 

between residential and commercial land use and three 

water-quality constituents. Concentrations of nickel and 

the number of pesticides and VOCs detected in a groundwater sample increased as the percentages of residential 

land use increased. The number of pesticides and VOCs 

detected decreased as the percentages of commercial land 

use increased.

The effect of surficial geology on the occurrence of 

pesticides and VOCs was investigated by calculating 

frequencies of detection. Pesticides were detected more 

frequently in urban ground-water samples collected 

where the surficial geology was sand than in urban 

ground-water samples collected where the surficial 

geology was clay. The frequency of detection of VOCs 

did not show a similar relation.

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