U.S. Department of the Interior

U.S. Geological Survey

Anthropogenic Constituents in Shallow Ground Water 

in the Upper Illinois River Basin

By William S. Morrow

Water-Resources Investigations Report 02-4293

Urbana, Illinois

2003
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. Government.

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

221 N. Broadway Avenue Box 25286

Urbana, IL 61801 Denver, CO 80225-0286
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 long-term availability of 

water that is clean and safe for drinking and recreation 

and that is suitable for industry, irrigation, and habitat 

for fish and wildlife. Escalating population growth and 

increasing demands for the multiple water uses make 

water availability, now measured in terms of quantity 

and quality, even more critical to the long-term 

sustainability of our communities and ecosystems.

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

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. 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, nongovernment 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

Description of Study Area........................................................................................................................... 2

Acknowledgments....................................................................................................................................... 5

Study Design, and Sampling and Analytical Methods......................................................................................... 5

Well Selection and Installation.................................................................................................................... 5

Sampling and Analysis Methods................................................................................................................. 7

Volatile Organic Compounds.............................................................................................................. 7

Pesticides ............................................................................................................................................ 7

Nitrate ................................................................................................................................................. 11

Age Dating of Ground-Water Samples ............................................................................................... 11

Quality-Assurance/Quality-Control Plan.................................................................................................... 11

Statistical Analysis...................................................................................................................................... 12

Anthropogenic Constituent Detections ................................................................................................................ 12

Volatile Organic Compounds ...................................................................................................................... 12

Pesticides..................................................................................................................................................... 16

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

Relations among Anthropogenic Constituents with Other Chemical 

Constituents and Physical Characteristics ................................................................................................ 23

Volatile Organic Compounds ...................................................................................................................... 23

Pesticides..................................................................................................................................................... 23

Nitrate.......................................................................................................................................................... 28

Significance of Results......................................................................................................................................... 28

Summary .............................................................................................................................................................. 31

References............................................................................................................................................................ 33

FIGURES

1-6. Maps showing:

1. Location of the upper Illinois River Basin.............................................................................................. 3

2. Physiography of the upper Illinois River Basin...................................................................................... 4

3. Urban land-use study area and well locations in urbanized areas in northern 

Illinois/southern Wisconsin ............................................................................................................... 6

4. Volatile organic compound detections in wells in urbanized areas in northern 

Illinois/southern Wisconsin ............................................................................................................... 15

5. Pesticide and pesticide transformation product detections in wells in urbanized 

areas in northern Illinois/southern Wisconsin.................................................................................... 21

6. Nitrate detections in wells in urbanized areas in northern Illinois/southern Wisconsin......................... 22
VI Contents

7-12. Graphs showing:

7. Concentration of chloroform as a function of (A) dissolved oxygen, (B) iron, 

(C) nitrate concentrations, and as a function of (D) well depth in ground water

from urbanized areas in northern Illinois/southern Wisconsin, with Spearman 

Rank Correlation ............................................................................................................................... 24

8. Concentration of total pesticides as a function of (A) the concentration of dissolved 

oxygen, (B) ground-water apparent recharge date, and (C) well depth, and 

concentration of total pesticides (with outlier removed) as a function of 

(D) ground-water apparent recharge date in ground water from urbanized 

areas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation ............................ 25

9. Concentration of the pesticides and pesticide transformation products (A) atrazine,

(B) deethylatrazine, (C) deethyldeisopropylatrazine, (D) deisopropylatrazine, 

(E) hydroxyatrazine, (F) metolachlor ethane sulfonic acid (ESA), and 

(G) prometon as a function of concentration of dissolved oxygen in ground 

water from urbanized areas in northern Illinois/southern Wisconsin, with 

Spearman Rank Correlation .............................................................................................................. 26

10. Concentration of the pesticides and pesticide transformation products (A) atrazine, 

(B) deethylatrazine, (C) deethyldeisopropylatrazine, (D) deisopropylatrazine, 

(E) hydroxyatrazine, (F) metolachlor ethane sulfonic acid (ESA), and 

(G) prometon as a function of well depth in ground water from urbanized 

areas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation ............................ 27

11. Concentration of the pesticides and pesticide transformation products (A) atrazine,

(B) deethylatrazine, (C) deethyldeisopropylatrazine, (D) deisopropylatrazine, 

(E) hydroxyatrazine, (F) metolachlor ethane sulfonic acid (ESA), and

(G) prometon as a function of ground-water apparent recharge date in ground 

water from urbanized areas in northern Illinois/southern Wisconsin, with 

Spearman Rank Correlation .............................................................................................................. 29

12. Concentration of nitrate as a function of (A) arsenic, (B) dissolved oxygen 

concentrations, (C) ground-water apparent recharge date, (D) iron concentration, 

(E) nitrogen as ammonia concentration, and (F) well depth in ground water from 

urbanized areas in northern Illinois/southern Wisconsin, with Spearman Rank 

Correlation......................................................................................................................................... 30

TABLES

1. Well dimensions for sampled wells in the upper Illinois River Basin......................................................... 5

2. List of pesticides, pesticide transformation products, and volatile organic compounds 

with associated laboratory reporting level (LRL) ranges for 1999-2001................................................. 8

3. List of volatile organic compound detections at or above laboratory reporting levels 

(LRLs) in 38 wells sampled in the upper Illinois River Basin, 2000-2001.............................................. 13

4. List of volatile organic compound detections at or above information-rich method 

levels in 38 wells sampled in the upper Illinois River Basin.................................................................... 14

5. List of pesticide and pesticide transformation product detections at or above laboratory 

reporting levels (LRLs) in 42 wells sampled in the upper Illinois River Basin ....................................... 17

6. List of pesticide and pesticide transformation product detections at or above

information-rich method levels in 42 wells sampled in the upper Illinois River Basin ........................... 19
Contents VII

CONVERSION FACTORS, ABBREVIATED WATER-QUALITY UNITS, AND OTHER ABBREVIATIONS

ABBREVIATED WATER-QUALITY UNITS

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

or micrograms per liter (μg/L).

ABBREVIATIONS

% percent

TU tritium unit

Multiply By To obtain

Length

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

square mile 2.59 square kilometer

Radioactivity

picocurie per liter (pCi/L) 0.037 becquerel per liter
Abstract 1

Anthropogenic Constituents in Shallow Ground Water in the 

Upper Illinois River Basin

By William S. Morrow

Abstract

The potential for anthropogenic effects on 

ground water is becoming of increasing concern as 

land throughout the Nation becomes more 

urbanized. The possible contamination of water 

resources by volatile organic compounds (VOCs), 

pesticides (including transformation products), 

and nitrate, from current urban land use and past 

agricultural land use, is of particular concern. As 

part of the U.S. Geological Survey's National 

Water-Quality Assessment program, water 

samples for analysis of VOCs, pesticides, and 

nitrate were collected from 43 wells in shallow 

(175 feet deep or less) ground water in glacial 

deposits overlying a major bedrock aquifer in 

recently urbanized areas in the Chicago, Ill. and 

Milwaukee, Wis. metropolitan counties.

Constituents were reported using two 

reporting levels. For the laboratory reporting level, 

the risk of a false positive or false negative 

detection is less than or equal to 1 percent. For

the information-rich method level, estimated 

concentrations are identified positively and are 

qualified to be present on the basis of qualitycontrol criteria, but have a higher risk of false 

positive detections.

VOCs were detected in 32 percent 

(12 of 38) of the well samples with 15 detections 

of 7 VOCs, based on laboratory reporting levels. 

Concentrations ranged from 0.03 (estimated) to 

4.6 micrograms per liter (μg/L), with a median 

concentration of 0.13 μg/L. Methyl tert-butyl ether 

(MTBE) and trichloromethane (chloroform) were 

the most common with detections in 10 percent (4 

of 38) of the well samples. Using information-rich 

method reporting levels, VOCs were detected in 74 

percent of the wells with 37 detections of 15 

VOCs. Chloroform was most common with 

detections in 24 percent (9 of 38) of the well 

samples.

Pesticides were detected in 62 percent (26 of 

42) of the well samples with 83 detections of 20 

pesticides, based on laboratory reporting levels for 

the respective constituent. Concentrations ranged 

from 0.003 (estimated) to 3.6 (estimated) μg/L, 

with a median concentration of 0.06 μg/L. 

Deethylatrazine was most common with detections 

in 43 percent (18 of 42) of the well samples. Using 

information-rich method reporting levels, 

pesticides were detected in 74 percent (31 of 42) of 

the well samples with 134 detections of 29 

pesticides. Deethylatrazine was most common 

with detections in 45 percent (19 of 42) of the well 

samples.

Nitrate concentrations ranged from less than 

0.047 to 12.5 milligrams per liter (mg/L) with a 

median concentration of 0.068 mg/L. Nitrate 

concentrations were greater than 2 mg/L in 30 

percent (13 of 43) of the wells sampled. 

Total VOC detections did not correlate well 

(less than Spearman Rank correlation value of plus 

or minus 0.10) with well depth, age, or dissolved 

oxygen. Total pesticide detections did correlate 

with dissolved oxygen and negatively correlated 

with well depth. Nitrate concentrations correlated 

with dissolved oxygen and apparent recharge date.

No VOC or pesticide concentrations 

exceeded U.S. Environmental Protection Agency 

drinking-water standards and only one nitrate 
2 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

detection exceeded the standards. However, of the 

43 wells sampled for VOCs or pesticides using 

information-rich methods, or nitrate at laboratory 

reporting levels, 40 of 43 (93 percent) well samples 

had at least one detection of a VOC or pesticide, or 

a detection of nitrate above 2.0 mg/L. This result 

indicates that most of these wells are 

anthropogenically affected, but presently not at 

U.S. Environmental Protection Agency drinkingwater regulation levels of concern. The wells 

sampled were not public drinking-water supplies; 

therefore, these wells were not subject to U.S. 

Environmental Protection Agency drinking-water 

regulations.

INTRODUCTION

In 1991, the U.S. Geological Survey (USGS) 

implemented the full-scale National Water-Quality 

Assessment (NAWQA) program to assess the quality of 

the ground- and surface-water resources of the United 

States, characterize the trends in the quality of these 

resources, and identify natural and anthropogenic 

(caused by humans) factors that affect water quality. 

The upper Illinois River Basin is one of more than 40 

study units throughout the United States, where waterquality data are being collected as part of the NAWQA 

program. 

The study area described here consists of 

selected rapidly expanding urban areas in and around 

Chicago, Ill. and Milwaukee, Wis. Urbanization of 

these once agricultural areas has affected ground-water 

quality (Kelly and Wilson, 2002). Anthropogenic 

effects on ground-water quality need to be evaluated in 

the basin because the shallow (less than 175 ft deep) 

ground-water resources are used as a drinking-water 

supply. Characterizing the extent and nature of 

anthropogenic effects, such as increased contamination, 

may be used in planning for the wise use of these 

resources.

Purpose and Scope

This report presents the results of sampling and 

analysis of ground water in the upper Illinois River 

Basin during 2000-01 for concentrations of volatile 

organic compounds (VOCs), pesticides, and nitrate. 

These constituents in ground water are anthropogenic 

indicators of effects on water chemistry. For the 

purposes of this report, the term "pesticide" will include 

both the pesticide and pesticide transformation 

products. Water samples were collected from 43 

randomly selected wells completed in glacial deposits 

in the upper Illinois River Basin. 

Description of the Study Area 

The upper Illinois River Basin covers an area 

of approximately 11,000 mi2 in northeastern Illinois 

(62 percent), northwestern Indiana (28 percent), 

southeastern Wisconsin (10 percent), and southwestern 

Michigan (less than 0.1 percent). The upper Illinois 

River Basin comprises the drainage areas upstream 

from Ottawa, Illinois of the Illinois River and its 

tributary streams (fig.1). The primary land use in the 

upper Illinois River Basin , in 1990, was approximately 

75 percent agricultural, mostly corn and soybeans. 

Urban land use accounted for about 17 percent in 1990, 

but is increasing rapidly because of recent urban 

expansion of the Chicago and Milwaukee metropolitan 

areas. The largest population increases from 1970 to 

1990 occurred in McHenry and DuPage Counties, Ill. 

(fig. 1) (Arnold and others, 1999).

The major aquifers underlying the basin are 

composed of, from youngest to oldest: Quaternary 

glacial deposits, Silurian-Devonian dolomite and 

limestone, and Cambrian-Ordovician sandstone and 

limestone (Arnold and others, 1999). The SilurianDevonian dolomite and limestone and the CambrianOrdovician sandstone and limestone are referred to in 

this report collectively as the bedrock aquifers. Shallow 

ground water from the Quaternary glacial deposits 

potentially can recharge the bedrock aquifers. Heavy 

use of the bedrock aquifers prior to 1970 has 

necessitated the use of surface-water supplies and 

potentially increased use of ground water from glacial 

deposits.

The upper Illinois River Basin lies within the 

Central Lowland physiographic province and consists 

of areas of the Great Lake Section and the Till Plains 

Section. The Great Lake Section is composed of the 

Chicago Lake Plain and the Wheaton Morainal Plain. 

The Till Plains Section is composed of the Bloomington 

Ridged Plain and the Kankakee Till Plain (fig. 2) 

(Arnold and others, 1999).
Introduction 3

Figure 1. Location of the upper Illinois River Basin.
4 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Figure 2. Physiography of the upper Illinois River Basin (modified from Fenneman, 1938; Leighton and 

others, 1948; and Schneider, 1966).
Study Design, and Sampling and Analytical Methods 5

The study area in northeastern Illinois and 

southeastern Wisconsin lies mostly within the Wheaton 

Morainal Plain (99 percent); a small part of the study 

area is in the Chicago Lake Plain (less than 1 percent) 

(fig. 3). The Wheaton Morainal Plain is composed of 

Wisconsinan Episode moraines and consists of clayey 

till of the Wadsworth Till Member/ Oak Creek 

Formation, and sand and gravel of the Haeger Till 

Member/New Berlin Formation. The Chicago Lake 

Plain is a flat, glacio-lacustrine deposit consisting 

primarily of clay and silt of the Carmi and Dolton 

members of the Equality/Atherton Formation (Arnold 

and others, 1999). Expanding population growth in the 

metropolitan areas of the upper Illinois River Basin will 

make the shallow glacial ground water more important 

as surface-water supplies and bedrock ground-water 

supplies are used to their maximum extent.

Acknowledgments

Thanks are extended to the private homeowners 

and land managers in the upper Illinois River Basin 

who allowed the USGS to sample their water-supply 

wells or allowed access to their land to install and 

sample monitoring wells. 

STUDY DESIGN, AND SAMPLING AND 

ANALYTICAL METHODS

Shallow ground water in the Quaternary deposits 

overlying a major bedrock aquifer located in the Great 

Lake Section underlies the study area that had recently 

changed from agricultural land use to urban land use 

(Vogelmann and others, 2001; Fegeas and others, 

1983). The bedrock aquifers underlying the study area 

are not included in the scope of this report. This 

recently urbanized study area was delineated based on 

the methods outlined in Squillace and Price (1996). 

Urban land use from the 1990 Geographical 

Information Retrieval and Analysis System (GIRAS) 

land-use/land-use change coverage (Hitt, 1995) 

originally was used to define the urban-land use area for 

this study. This urban land-use data was derived from 

1970's land-use information and updated based on 

increasing population density obtained from 1990 

population data. Because the 1990's land-use/land-use 

change data were dated, the urban areas defined around 

the rapidly urbanizing area of metropolitan Chicago 

were underrepresented. At a later time in the study, 

1993 land-use data (Vogelmann and others, 2001) 

became available. Although the land-use data were 

out-of-date by approximately 5 years, these 1993

land-use data defined urban areas temporally better 

than the 1990's land-use data. To better estimate the 

extent of urban areas around Chicago for the sampling 

time period of this study, a geographic information 

system (GIS) was used to combine these two land-use 

data sets and expand (buffer) the urban land-use areas 

by 500 meters (1,640 ft) on all sides (fig. 3). 

Well Selection and Installation

Water samples were collected from 26 

monitoring wells installed specifically for the study and 

17 private domestic-supply wells. All wells or well 

locations were confirmed visually to be within urban 

areas and selected for sampling on the basis of a 

random site-selection method developed by Scott 

(1990). Wells were chosen or installed within 0.5 mi of 

a randomly selected point as determined by the siteselection program. All wells were completed in glacial 

sediments at depths less than or equal to 175 ft, with 

93 percent (40 of 43) of the wells less than 100 ft deep. 

Domestic-supply wells selected for sampling 

must have been completed in the glacial deposits and 

constructed after 1980 to ensure that modern wellconstruction techniques were used. Water samples were 

obtained before, or by bypassing, residential watertreatment systems to avoid any chemical modifications 

introduced by these systems. The 17 domestic-supply 

wells were completed in sands and gravels of the glacial 

deposits. Well depths ranged from 31 to 175 ft, with a 

median depth of 72 ft. Well diameters ranged from 5 to 

7 in., with a median diameter of 6 in. Well-screen 

lengths ranged from 0 (open end) to 7 ft, with a median 

screen length of 3 ft (table 1). 

Table 1. Well dimensions for sampled wells in the upper Illinois River Basin

Type of well Number 

of wells

Well depth 

(feet below 

land surface)

Median 

well depth 

(in feet)

Well 

diameter 

(in inches)

Median well 

diameter 

(in inches)

Well screen 

length

(in feet)

Well screen 

median

(in feet)

Domestic supply 17 31-175 72 5-7 6 0-7 3 

Monitoring 26 13.2-58.5 28.6 2 2 5 5
6 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Figure 3. Urban land-use study area and well locations in urbanized areas in northern 

Illinois/southern Wisconsin (modified from Vogelman and others, 2001; and Hitt, 1995).
Study Design, and Sampling and Analytical Methods 7

The USGS constructed 26 monitoring wells for 

this study. The wells were completed in glacial deposits 

at the first water-producing layer. All monitoring wells 

were installed and constructed by the USGS on private 

land and on urban roadsides according to NAWQA 

protocols (Lapham and others, 1995) using hollowstem auger drilling methods. Wells were screened in 

deposits ranging from clayey-silt to sand and gravel. 

Well depths ranged from 13.2 to 58.5 ft, with a median 

depth of 28.6 ft. All monitoring wells were constructed 

of 2-in-diameter polyvinyl chloride (PVC) with 5-ft 

long screens (table 1). 

Sampling and Analysis Methods

Water samples were collected using standard 

NAWQA protocols (Koterba and others, 1995) using 

primarily Teflon and stainless-steel sampling 

equipment. The samples were collected after fieldmeasured parameters (pH, dissolved oxygen, water 

temperature, specific conductivity, and turbidity) had 

stabilized, usually after three well volumes were 

pumped, to ensure that a representative sample from the 

aquifer was obtained. Domestic-supply wells were 

sampled using the well owner's submersible pump. 

Monitoring wells were sampled using a Fultz 

submersible pump. In five of the monitoring wells, a 

Teflon bailer was used to collect the water sample, 

because flow into the well was too small to use the Fultz 

pump. In cases where bailing was necessary, the wells 

also were purged by bailing. No samples for analysis of 

VOCs were collected at these wells because of the 

potential for contaminating samples or loss of volatile 

organic compounds by aeration.

Two levels of reporting detections were used in 

this report. The highest censoring level of reporting 

used is the laboratory reporting level (LRL). The LRL 

is set at a level so that a risk of a false positive (analyte 

reported present when not in the sample) or false 

negative (analyte reported not present when present in 

sample at reporting level) detection is less than or equal 

to 1 percent. The LRL is twice the long-term method 

detection level (LT-MDL). The LT-MDL is set at a level 

that a risk of a false positive detection is no more than 1 

percent; however, the risk of a false negative detection 

is as great as 50 percent. A lower level of reporting, but 

less precise, is the information-rich method level. 

Detections using the information-rich method reporting 

level include, in addition to concentrations above the 

LRL, estimated concentrations above and below the LTMDL. These detections are reported if other qualitycontrol criteria, particularly laboratory blank data, are 

met. These data have an increased risk of false positive 

detections (Childress and others, 1999). LRLs for 

VOCs in this report vary widely, ranging from 0.02 to 7 

micrograms per liter (μg/L) with a median of 0.09 μg/

L. LRLs for pesticides in this report vary widely, 

ranging from 0.001 to 7.11 μg/L with a median of 0.013 

μg/L. LRLs vary among the different VOCs and 

pesticides. LRLs even can vary for the same VOC or 

pesticide, because of refinement of analysis methods 

and possible complications with individual analyses. 

LRLs for 

each constituent analyzed are listed in table 2.

Detections for VOC and pesticide analyses are 

reported using both the LRLs and information-rich 

method reporting levels. Nitrate is reported using the 

LRL.

Volatile Organic Compounds

Water samples for analysis of volatile organic 

compounds were obtained by collecting unfiltered 

water in a 40-ml amber bottle with a septum cap such 

that air bubbles are not present in the sample to allow 

degassing of VOCs. Samples were acidified with 

hydrochloric acid for preservation and shipped chilled 

to the USGS National Water-Quality Laboratory 

(NWQL) in Denver, Colo. The water samples were 

analyzed for 83 VOCs by purge-and-trap isolation 

and concentration, and capillary-column gas 

chromatography/mass spectrometry methods (Connor 

and others, 1998). 

Pesticides 

Water samples for analysis of pesticides and 

pesticide transformation products were obtained by 

filtering the sample into amber baked glass containers 

through glass-fiber filters with a 0.7-μm pore diameter. 

Samples for 94 pesticide and 4 transformation product 

analyses were shipped chilled to the USGS NWQL in 

Denver, Colo. for analysis by gas chromatography/mass 

spectrometry GCMS (Zaugg and others, 1995), and 

high-performance liquid chromatography/mass 

spectrometry (HPLC/MS) (Furlong and others, 2001). 

Samples for 10 ethane sulfonic acid (ESA) and oxanilic 

acid (OA) transformation product analyses were sent to 

the USGS Organic Geochemistry Research Laboratory 

in Lawrence, Kans. for analysis by HPLC/MS (Lee and 

others, 2001).
8 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Table 2. List of pesticides, pesticide transformation products, and volatile organic compounds with associated 

laboratory reporting level (LRL) ranges for 1999-2001

[<, less than]

Pesticide LRL range 

(micrograms per liter) Volatile organic compound LRL range (micrograms per liter)

2,4-D < 0.02 - < 0.15 1,1-Dichloroethane < 0.04 - < 0.066

2,4-D Methyl Ester < 0.009 - < 0.173 1,1-Dichloroethene < 0.04

2,4-DB < 0.02 - < 0.11 1,1-Dichloropropene < 0.026 - < 0.03

2,6-Diethylaniline < 0.002 - < 0.003 1,1,1-Trichloroethane < 0.03- < 0.032

3-Hydroxycarbofuran < 0.01 - < 0.12 1,1,1,2-Tetrachloroethane < 0.03

3-Ketocarbofuran < 0.072 - < 1.5 1,1,2-Trichloro-1,2,2-Trifluoroethane < 0.06

3,4-Chlorophenyl Methyl Urea < 0.0242 - < 0.183 1,1,2-Trichloroethane < 0.06

Acetochlor < 0.002 - < 0.004 1,1,2,2-Tetrachloroethane < 0.09

Acetochlor Ethane Sulfonic Acid < 0.05 1,2-Dibromo-3-Chloropropane < 0.2 - < 0.21

Acetochlor Oxanilic Acid < 0.05 1,2-Dibromoethane < 0.036 - < 0.04

Acifluorfen < 0.01 - < 0.12 1,2-Dichlorobenzene < 0.03 - < 0.048

Alachlor < 0.002 1,2-Dichloroethane < 0.1 - < 0.13

Alachlor Ethane Sulfonic Acid < 0.05 1,2-Dichloropropane < 0.03 - < 0.068

Alachlor Oxanilic Acid < 0.05 1,2-Dimethylbenzene < 0.038 - < 0.04

Aldicarb < 0.04 - < 0.16 1,2,3-Trichlorobenzene < 0.27 - < 0.3

Aldicarb Sulfone < 0.02 - < 0.32 1,2,3-Trichloropropane < 0.16 - < 0.2

Aldicarb Sulfoxide < 0.01 - < 0.05 1,2,3-Trimethylbenzene < 0.1 - < 0.12

Alpha BHC < 0.002 - < 0.005 1,2,3,4-Tetramethylbenzene < 0.2 - < 0.23

Atrazine < 0.001 - < 0.009 1,2,3,5-Tetramethylbenzene < 0.2

Bendiocarb < 0.025 - < 0.122 1,2,4-Trichlorobenzene < 0.19 - < 0.2

Benfluralin < 0.002 - < 0.01 1,2,4-Trimethylbenzene < 0.056 - < 0.06

Benomyl < 0.004 - < 0.044 1,3-Dichlorobenzene < 0.03 - < 0.054

Bensulfuron-methyl < 0.0158 - < 0.0964 1,3-Dichloropropane < 0.1 - < 0.12

Bentazon < 0.01 - < 0.04 1,3,5-Trimethylbenzene < 0.04 - < 0.044

Bromacil < 0.03 - < 0.16 1,4-Dichlorobenzene < 0.05

Bromoxynil < 0.02 - < 0.11 1,4-Dimethylbenzene < 0.06

Butylate < 0.002 2-Butanone < 1.6 - < 2

Caffeine (not a pesticide or

 transformation product) < 0.01 - < 0.081 2-Hexanone < 0.7

Carbaryl < 0.03 - < 0.13 2-Propenenitrile < 1 - < 1.2

Carbofuran < 0.01 - < 0.11 2,2-Dichloropropane < 0.05

Chloramben, Methyl Ester < 0.02 - < 0.23 2-Chlorotoluene < 0.03 - < 0.042

Chlorimuron < 0.01 - < 0.073 2-Ethyltoluene < 0.06

Chlorothalonil < 0.04 - < 0.1 3-Chloro-1-propene < 0.1 - < 0.2

Chlorpyrifos < 0.004 - < 0.005 4-Chlorotoluene < 0.06

Clopyralid < 0.01 - < 0.08 4-Methyl-2-Pentanone < 0.37 - < 0.4

Cyanazine < 0.004 - < 0.018 Acetone < 7

Cycloate < 0.01 - < 0.11 Benzene < 0.35 - < 0.04

Dacthal Mono-Acid < 0.01 - < 0.14 Bromobenzene < 0.036 - < 0.04
Study Design, and Sampling and Analytical Methods 9

DCPA < 0.002 - < 0.003 Bromochloromethane < 0.04 - < 0.044

Deethylatrazine < 0.002 - < 0.028 Bromodichloromethane < 0.048 - < 0.05

Deethyldeisopropylatrazine < 0.01 - < 0.12 Bromoethene < 0.1

Deisopropylatrazine < 0.04 - < 0.15 Bromomethane < 0.26 - < 0.3

Diazinon < 0.002 - < 0.005 Carbon Disulfide < 0.07

Dicamba < 0.01 - < 0.19 Chlorobenzene < 0.028 - < 0.03

Dichlorprop < 0.01 - < 0.1 Chlorodibromomethane < 0.18 - < 0.2

Dieldrin < 0.001 - < 0.005 Chloroethane < 0.1 - < 0.12

Dinoseb < 0.01 - < 0.09 Chloroethene < 0.1 - < 0.11

Dimethenamid Ethane Sulfonic Acid <0.05 Chloromethane < 0.2 - < 0.5

Dimethenamid Oxanilic Acid <0.05 Cis-1,2-Dichloroethene < 0.038 - < 0.4

Diphenamid < 0.03 - < 0.12 Cis-1,3-Dichloropropene < 0.09

Disulfoton < 0.017 - < 0.021 Dibromomethane < 0.05

Diuron < 0.01 - < 0.16 Dichlorodifluoromethane < 0.27 - < 0.03

EPTC < 0.002 Dichloromethane < 0.2 - <0.38

Ethalfluralin < 0.004 - < 0.009 Diethyl ether < 0.17 - < 0.2

Ethoprop < 0.003 - < 0.005 Diisopropyl Ether < 0.1

Fenuron < 0.03 - < 0.15 Ethylbenzene < 0.03

Flufenacet Ethane Sulfonic Acid <0.05 Ethyl Methacrylate < 0.18 - <0.2

Flufenacet Oxanilic Acid <0.05 Ethyl Tert-Butyl Ether < 0.05 - < 0.054

Flumetsulam < 0.011 - < 0.173 Hexachlorobutadiene < 0.1 - < 0.14

Fluometuron < 0.03 - < 0.12 Hexachloroethane < 0.19 - < 0.2

Fonofos < 0.003 Iodomethane < 0.1 - < 0.12

Hydroxyatrazine < 0.008 - < 0.385 Isopropylbenzene < 0.03 - < 0.032

Imazaquin < 0.016 - < 0.206 Methyl Acrylate < 1 - < 1.4

Imazethapyr < 0.017 - < 0.176 Methyl Acrylonitrile < 0.6

Imidacloprid < 0.0068 - < 0.2122 Methyl Methacrylate < 0.3 - < 0.35

Lindane < 0.004 Methyl Tert-Butyl Ether < 0.17 - < 0.2

Linuron < 0.01 - < 0.14 N-Butylbenzene < 0.19 - < 0.2

Malathion < 0.005 - < 0.027 N-Propylbenzene < 0.04 - < 0.042

MCPA < 0.02 - < 0.12 Naphthalene < 0.2 - < 0.25

MCPB < 0.01 - < 0.125 P-Isopropyltoluene < 0.07

Metalaxyl < 0.02 - < 0.114 Sec-Butylbenzene < 0.03 - < 0.032

Methiocarb <0.01 - < 0.159 Styrene < 0.04 - < 0.042

Methomyl < 0.0044 - < 0.154 Tert-Amyl Methyl Ether < 0.1 - < 0.11

Methomyl Oxime < 0.0102 - < 0.0204 Tert-Butylbenzene < 0.06

Methyl Azinphos < 0.001 - < 0.05 Tetrachloromethane < 0.06

Methyl Parathion < 0.006 Tetrahydrofuran < 2 - < 2.2

Metolachlor < 0.002 - < 0.013 Trans-1,2-Dichloroethene < 0.03 - < 0.032

Metolachlor Ethane Sulfonic Acid < 0.05 Trans-1,3-Dichloropropene < 0.09

Pesticide LRL range 

(micrograms per liter) Volatile organic compound LRL range (micrograms per liter)

Table 2. List of pesticides, pesticide transformation products, and volatile organic compounds with associated 

laboratory reporting level (LRL) ranges for 1999-2001—Continued
10 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Metolachlor Oxanilic Acid < 0.005 Trans-1,4-Dichloro-2-butene < 0.7

Metribuzin < 0.004 - < 0.006 Tribromomethane < 0.06

Metsulfuron-Methyl < 0.025 - < 0.228 Trichloroethene < 0.038 - < 0.04

Molinate < 0.002 - < 0.004 Trichlorofluoromethane < 0.09

Napropamide < 0.003 - < 0.007 Trichloromethane < 0.02 - < 0.052

Neburon < 0.01 - < 0.149

Nicosulfuron < 0.013 - < 0.131

Norflurazon < 0.02 - < 0.155

Oryzalin < 0.02 - < 0.14

Oxamyl < 0.01 - < 0.032

Oxamyl Oxime < 0.013 - < 0.129

P,P'-DDE < 0.003 - < 0.006

Parathion < 0.003 - < 0.004

Pebulate < 0.002 - < 0.004

Pendimethalin < 0.004 - < 0.01

Permethrin < 0.005 - < 0.006

Permethrin < 0.005 - < 0.006

Phorate < 0.002 - < 0.011

Picloram < 0.02 - < 0.142

Prometon < 0.015 - < 0.018

Pronamide < 0.003 - < 0.004

Propachlor < 0.007 - < 0.01

Propanil < 0.004 - < 0.011

Propargite < 0.013 - < 0.023

Propham < 0.01 - < 0.143

Propiconazole < 0.021 - < 0.129

Propoxur < 0.01 - < 0.119

Siduron < 0.017 - < 0.187

Simazine < 0.005 - < 0.011

Sulfometruron Methyl < 0.009 - < 0.078

Tebuthiuron < 0.006 - < 0.016

Terbacil < 0.007 - < 0.034

Terbufos < 0.013 - < 0.017

Thiobencarb < 0.002 - < 0.005

Triallate < 0.001 - < 0.002

Tribenuron < 0.01 - < 0.14

Triclopyr < 0.02 - < 0.2

Trifluralin < 0.002 - < 0.009

Pesticide LRL range 

(micrograms per liter) Volatile organic compound LRL range (micrograms per liter)

Table 2. List of pesticides, pesticide transformation products, and volatile organic compounds with associated 

laboratory reporting level (LRL) ranges for 1999-2001—Continued
Study Design, and Sampling and Analytical Methods 11

Nitrate

Water samples also were analyzed for nitrite 

and nitrate concentrations. These analyses are referred 

to as "nitrate", because the nitrite concentrations 

generally are negligible in ground water. Water samples 

for nitrate analysis were obtained by filtering the 

sample through a 0.45-μm high-capacity, tortuousflow, polysulfone-capsule filter. Samples were shipped 

chilled to the USGS NWQL in Denver, Colo. for 

analysis by colorimetric methods (Fishman and 

Friedman, 1989).

Age Dating of Ground-Water Samples

Shallow ground water usually is recharged faster 

and is younger (less than 50 years) than deeper ground 

water. Because of this fast recharge and resulting

young water, tritium/helium-3 and chlorofluorocarbon 

(CFC) samples, used to determine younger apparent 

ages, were analyzed to determine apparent ages of the 

ground-water samples. Tritium/helium-3 samples were 

obtained concurrently with CFC samples in 15 

monitoring wells. When samples were obtained 

concurrently, and if apparent ages differed, the analysis 

that was judged the least affected by factors affecting 

apparent age was used. Factors affecting CFC analyses 

include CFC contamination or degradation, whereas 

the tritium/helium-3 analyses could be affected by gas 

fractionation or excess terrigenic helium, among other 

factors. For statistical analysis, the apparent recharge 

date is used in this report, whereas apparent recharge 

date will decrease with an increase in apparent age.

CFCs are stable, non-toxic, nonflammable, 

synthetic constituents developed in the 1930's for 

refrigeration. Three CFC constituents were 

produced: trichlorofluoromethane (CFC-11), 

dichlorodifluoromethane (CFC-12), and 

trichlorotrifluoroethane (CFC-13). Production of CFCs 

ceased in the United States in 1996 (Plummer and 

Friedman, 1999). CFC dating is possible by 

reconstructing their estimated atmospheric amounts 

and, using the known solubilities of CFCs in water, 

calculating the concentration of CFCs in recharge water 

with respect to equilibrium with the air.

Samples for analysis of CFCs were obtained by 

collecting water through a closed system between the 

well and sampling apparatus. The boro-silicate glass 

sample bottles were purged with ultra-pure nitrogen gas 

before and during collection. The sample bottles then 

were welded shut, sealing the water from atmospheric 

contact. Samples were sent to the Reston, Va. 

Chlorofluorocarbon Laboratory and analyzed using 

purge and trap, gas chromatography techniques 

(Plummer and Busenberg, 2000; Plummer and 

Friedman, 1999). 

Tritium/helium-3 dating of young ground water 

is possible because of the additional input over natural 

sources by atmospheric testing of nuclear devices of 

tritium into the air, beginning in 1952 and peaking in 

1963-64. Tritium concentrations in recharge water, 

measured in tritium units (TU's), or picocuries per liter 

(pCi/L), approximately parallel this "bomb peak" in 

1963-64 and gradually decline to present. 

Concentrations of tritium in recently recharged ground 

water usually are under 10 TU's (Clark and Fritz, 1997). 

The tritium/helium-3 apparent age is calculated from 

the radioactive decay of tritium to helium-3 in the water 

sample. The decay of tritium to helium-3 is used to 

determine the amount of tritiogenic helium-3 based on 

a helium isotope mass balance (Schlosser and others, 

1988, 1989). 

Tritium/helium-3 samples were obtained by 

collecting water through a closed system between the 

well and the sampling apparatus. Copper sample tubes 

were flushed with sample water and then sealed shut 

while flowing to eliminate atmospheric contact. 

Samples were sent to the Lamont-Doherty Earth 

Observatory in Palisades, N.Y., where they were 

analyzed for measurement of helium isotopes and 

tritium by the helium ingrowth method (Schlosser and 

others, 1988, 1989).

Quality-Assurance/Quality-Control Plan

A quality-assurance plan for constituents 

analyzed in the study was developed and consisted of 

blanks, replicates, and (for VOCs and pesticides) 

spikes, in the field and laboratory to evaluate the bias 

and variability of the analytical results (Koterba and 

others, 1995; Connor and others, 1998; Zaugg and 

others, 1995).

Nine field and source blanks for VOCs were 

collected concurrently with source solution blanks. 

Toluene was deleted from the data set because of 

systematic contamination in the field blank and source 
12 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

blank. Trichloromethane (chloroform) was detected in 

three field blanks at or below the LT-MDL. One blank 

detection also had a concurrent environmental 

detection of chloroform. No source blanks had any 

chloroform detections. Based on these field blanks, 

source blanks, and environmental samples near the 

blank concentration, data quality from three samples 

are considered questionable for chloroform. The rest of 

the field-blank analyses for other constituents were 

good.

Nine field blanks were collected for pesticides. 

There were no detections of any pesticides in the field 

blank, except for caffeine. Caffeine, although not a 

pesticide, is included in the pesticides schedule because 

the same sampling and analytical methods are used for 

pesticides as well as caffeine because of similar 

chemical properties between the two constituent types. 

Caffeine is included in the dataset for this report 

because it also is indicative of anthropogenic effects. 

Caffeine was detected in two field blank samples at 

estimated values of 0.006 and 0.007 μg/L with a LRL 

of 0.080 μg/L. There were no corresponding 

environmental detections with these detections; 

therefore, for the purposes of this report, the 

environmental caffeine detections met data-quality 

objectives.

Concurrent environmental sample replicates 

were spiked in the field with known mixtures of 

pesticides and VOCs to determine recoverability of 

these constituents. Recoveries for four field-spiked 

pesticide samples ranged from 48 to 300 percent with 

an average of 92 percent. The recoveries for four fieldspiked VOC samples ranged from 32 to 113 percent, 

with an average of 69 percent. Laboratory spiked 

samples also were analyzed according to laboratory 

protocols for pesticides and VOCs (Zaugg and others, 

1995; Connor and others, 1998). No pesticide or VOC 

detections were deleted based on poor recoveries. 

Nine nitrate field blanks were collected and had 

no contamination. Four nitrate replicate samples were 

collected; nitrate concentrations in the replicate 

samples were within 2 percent of concentrations in 

the environmental samples. The rest of the constituents 

that were analyzed, and used in correlations and 

comparisons with VOCs, pesticides, and nitrate, met 

data-quality objectives based on their replicate and 

blank analyses.

Statistical Analysis

The number of wells sampled during the study 

consisted of 17 domestic wells and 26 monitoring 

wells, for a total well population of 43 wells. VOC, 

pesticide, and nitrate data were not normally distributed 

among the samples; therefore, nonparametric methods 

were used in the statistical analyses. The nonparametric 

Spearman Rank (Sr) correlation coefficient was 

calculated for VOC, pesticide, and nitrate data with 

inorganic constituents, field parameters, and well 

characteristics. Correlations are evaluated as to the 

degree of significance (p). If the p value was 0.05 or 

less, the correlation was reported as significant; if the 

p value was greater than 0.05, the p value is listed with 

the correlation.

ANTHROPOGENIC CONSTITUENT DETECTIONS

Two levels of reporting VOC and pesticide 

detection levels are used in this report; these are the 

LRL and the information-rich method reporting level. 

The LRL detections are suited for quantitative 

interpretations, whereas the information-rich methods 

are used in this report for qualitative interpretations, 

and general semi-quantitative interpretations and 

correlation statistics. 

Volatile Organic Compounds

Using LRLs, of the 38 wells (21 monitoring 

wells and 17 domestic-supply wells) sampled for 

VOCs, 12 wells (32 percent) had 15 detections of 7 

different VOCs with concentrations ranging from an 

estimated value of 0.03 to 4.6 μg/L with a median of 

0.13 μg/L. Of the domestic-supply wells, 7 samples 

had 10 detections of 6 different VOCs, whereas the 

monitoring wells had 5 samples with 5 detections of 

4 different VOCs (table 3).

All but one of the VOC detections were at 

concentrations less than or equal to 0.2 μg/L. Methyl 

tert-butyl ether (MTBE) in one sample had a 

concentration of 4.6 μg/L. The most common VOCs 

detected above LRLs were MTBE, a fuel oxygenate, 

and chloroform, a trihalomethane commonly formed as 

a disinfection by-product, each having four detections10 percent of the well samples. The other detections 
Anthropogenic Constituent Detections 13

above the LRLs were: the fuel oxygenates and 

octane enhancers tert-pentyl methyl ether (TAME) 

and diisopropyl ether (DIPE), the solvents 

1-1,dichloroethane, 1,1,1-trichlorethane, and carbon 

disulfide, which can occur naturally or from 

anthropogenic sources. 

Using information-rich method levels, of the 38 

wells sampled, 28 wells (74 percent) had 37 detections 

of 15 different VOCs. From the domestic-supply wells, 

14 samples (82 percent) had 18 detections of 10 

different VOCs. From the monitoring wells, 14 samples 

had 19 detections of 9 different VOCs (table 4). The 

most common VOC detected at the information-rich 

method reporting levels was chloroform, with nine 

detections, or 24 percent of the well samples. Well 

locations with VOC detections are shown in figure 4.

No detection for any VOC exceeded USEPA 

Maximum Contaminant Levels (MCLs), Health 

Advisories (HAs) or other USEPA drinking-water 

criteria. The highest detection, a 4.6 μg/L concentration 

of MTBE, was below the USEPA Margin of Exposure 

of 20 μg/L. All other VOC detections were at least two 

orders of magnitude below USEPA MCLs (U.S. 

Environmental Protection Agency, 2000).

Table 3. List of volatile organic compound detections at or above laboratory reporting levels (LRLs) in 38 

wells sampled in the upper Illinois River Basin, 2000-2001

[e, estimated concentration]

Volatile organic compound Well type Number of 

detections

Range 

(micrograms 

per liter)

Median 

(micrograms 

per liter)

Domestic 1 (e) 0.06 0.06

1,1-Dichloroethane Monitoring 0 0 0

Total 1 (e) 0.06 0.06

Domestic 2 0.11 0.11

1,1,1-Trichloroethane Monitoring 1 0.197 0.197

Total 3 0.11 - 0.197 0.11

Domestic 1 0.13 0.13

Carbon Disulfide Monitoring 0 0 0

Total 1 0.13 0.13

Domestic 0 0 0

Diisopropyl Ether Monitoring 1 0.105 0.105

Total 1 0.105 0.105

Domestic 3 0.2 - 4.6 0.2

Methyl Tert-Butyl Ether Monitoring 1 0.199 0.199

Total 4 0.199 - 4.6 0.2

Domestic 1 0.2 0.2

Tert-Amyl Methyl Ether Monitoring 0 0 0

Total 1 0.2 0.2

Domestic 2 (e) 0.03 0.03

Trichloromethane (chloroform) Monitoring 2 (e) 0.063 - 0.15 0.1065

Total 4 (e) 0.03 - 0.15 0.0465
14 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Table 4. List of volatile organic compound detections at or above information-rich method levels in 38 wells sampled 

in the upper Illinois River Basin

[e, estimated concentration]

Volatile organic compound Well type Number of 

detections

Concentration range 

(micrograms per liter)

Median concentration 

(micrograms per liter)

Domestic 1 (e) 0.06 0.06

1,1-Dichloroethane Monitoring 1 (e) 0.064 0.064

Total 2 (e) 0.06 - (e) 0.064 0.062

Domestic 4 (e) 0.01 - 0.11 0.06

1,1,1-Trichloroethane Monitoring 3 (e) 0.016 - 0.197 0.03

Total 7 (e) 0.01 - 0.197 0.03

Domestic 0 0 0

Benzene Monitoring 2 (e) 0.011 - (e) 0.016 0.0135

Total 2 (e) 0.011 - (e) 0.016 0.0135

Domestic 3 (e) 0.01 - 0.13 0.05

Carbon Disulfide Monitoring 0 0 0

Total 3 (e) 0.01 - 0.13 0.05

Domestic 0 0 0

Chloromethane Monitoring 2 (e) 0.06 - (e) 0.074 0.067

Total 2 (e) 0.06 - (e) 0.074 0.067

Domestic 1 (e) 0.1 0.1

Dichlorodifluoromethane Monitoring 0 0 0

Total 1 (e) 0.1 0.1

Domestic 1 (e) 0.1 0.1

Dichloromethane Monitoring 0 0 0

Total 1 (e) 0.1 0.1

Domestic 0 0 0

Diisopropyl Ether Monitoring 1 0.105 0.105

Total 1 0.105 0.105

Domestic 0 0 0

Ethylbenzene Monitoring 1 (e) 0.007 0.007

Total 1 (e) 0.007 0.007

Domestic 3 0.2 - 4.6 0.2

Methyl Tert-Butyl Ether Monitoring 1 0.199 0.199

Total 4 0.199 - 4.6 0.2

Domestic 1 (e) 0.02 0.02

Styrene Monitoring 0 0 0

Total 1 (e) 0.02 0.02

Domestic 1 0.2 0.2

Tert-Amyl Methyl Ether Monitoring 0 0 0

Total 1 0.2 0.2

Domestic 0 0 0

Tetrahydrofuran Monitoring 1 (e) 1.12 1.12

Total 1 (e) 1.12 1.12

Domestic 1 (e) 0.03 0.03

Trichloroethene Monitoring 0 0 0

Total 1 (e) 0.03 0.03

Domestic 2 (e) 0.03 0.03

Trichloromethane (chloroform) Monitoring 7 (e) 0.009 - 0.15 0.011

Total 9 (e) 0.009 - 0.15 0.016
Anthropogenic Constituent Detections 15

Figure 4. Volatile organic compound detections in wells in urbanized areas in northern 

Illinois/southern Wisconsin.
16 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Pesticides

Using LRLs, of 42 wells (25 monitoring wells 

and 17 domestic-supply wells) sampled for pesticides, 

26 samples (62 percent) had 83 detections of 20 

pesticides with concentrations ranging from 0.003 

(estimated) to 3.6 (estimated) μg/L with a median 

concentration of 0.06 μg/L. The domestic wells had

8 samples with 17 detections of 8 pesticides. The 

monitoring wells had 18 samples with 66 detections of 

20 pesticides (table 5).

 Pesticide concentrations at or above LRLs

were greater than 1.0 μg/L in 5 (6 percent) of the 

detections and 22 (29 percent) of the concentrations 

were greater than 0.2 μg/L. The most common pesticide 

detected above LRLs was deethylatrazine, a pesticide 

transformation product detected in 18 (43 percent) 

samples. Atrazine, the original pesticide, was 

detected in 13 (31 percent) samples. The pesticide 

transformation product metolachlor ESA was detected 

in 12 (29 percent) samples. The summed concentrations 

of all metolachlor ESA detection were higher than the 

sum total of any pesticide (original pesticide or 

transformation product), with median and average 

concentrations of 0.31 and 0.63 μg/L, respectively.

At information-rich method levels, 31 samples 

(74 percent) had 134 detections of 29 different 

pesticides. Of the domestic wells, 10 samples 

(59 percent) had 32 detections of 12 different 

pesticides, whereas 21 samples (84 percent) from 

monitoring wells had 102 detections of 27 different 

pesticides (table 6). The most common pesticide 

constituent, detected at information-rich method 

reporting levels, was deethylatrazine (a transformation 

product of atrazine), with 19 detections (45 percent) 

among the 42 samples. Atrazine was detected in 16 

samples (38 percent). Atrazine, and its transformation 

products deethylatrazine, deethyldeisopropylatrazine, 

deisopropylatrazine, and hydroxyatrazine, accounted 

for 63 of the 128 (49 percent) pesticide detections. 

Prometon was detected in 12 samples (29 percent). 

Prometon, although it is not used in crop pesticide 

applications, is used on industrial sites, non-crop areas 

of farms, in and under asphalt, and by homeowners. 

The frequent detections of prometon probably result 

because of its large use for non-agricultural purposes, 

persistence and solubility (Capel and others, 1999). 

Locations of wells where pesticides were sampled and 

detected are shown in figure 5. 

Pesticide transformation products were detected 

in 24 of the 42 samples. Of these 24 samples, 2 or 

more pesticide transformation products were detected 

concurrently in 18 (75 percent) of the samples with at 

least 1 detection. Three (12 percent) of these 24 

samples had 8 detections. Although ESA and OA 

concentrations were not reported below the LRL, 

combined concentrations of these transformation 

products were more than twice the sum of original 

pesticide products reported at information-rich method 

reporting levels (2.2 times) and LRLs (2.3 times). 

Pesticide transformation product detections at LRLs 

comprised 65 percent (50 of 77) of total pesticide 

detections.

No pesticide detection exceeded USEPA 

drinking water MCLs, HAs, or other USEPA drinkingwater criteria. The highest detection, an estimated 

3.6 μg/L concentration of MCPA, was near the lifetime 

HA level of 4 μg/L. All other pesticide detections were 

at least two orders of magnitude below USEPA MCLs 

(U.S. Environmental Protection Agency, 2000).

Nitrate 

Nitrate concentrations were reported above LRLs 

ranging from 0.047 to 0.05 milligrams per liter (mg/L). 

Nitrate concentrations ranged from less than 0.047 to 

12.5 mg/L with a median concentration of 0.068 mg/L. 

Of the 43 wells sampled for nitrate, 13 samples 

(30 percent) had nitrate concentrations exceeding the 

estimated national background concentration level 

of 2 mg/L (Mueller and Helsel, 1996). One sample 

exceeded the USEPA MCL of 10 mg/L (U.S. 

Environmental Protection Agency, 2000). Of the 

17 domestic wells, 5 samples (29 percent) had 

concentrations greater than 2.0 mg/L, whereas the 

26 monitoring wells had 8 samples (31 percent) with 

concentrations greater than 2.0 mg/L, with one sample 

exceeding 10 mg/L. Locations of wells where nitrate 

samples were collected and detected are shown in 

figure 6.
Anthropogenic Constituent Detections 17

Table 5. List of pesticide and pesticide transformation product detections at or above laboratory reporting levels 

(LRLs) in 42 wells sampled in the upper Illinois River Basin

[e, estimated concentration]

Pesticide or pesticide 

transformation product Well type Number of detections

Concentration range 

(micrograms per liter)

Median concentration 

(micrograms per liter)

Domestic 0 0 0

Acetochlor Monitoring 2 0.004 - 0.01 0.007

Total 2 0.004 - 0.01 0.007

Domestic 1 0.13 0.13

Acetochlor Ethane Sulfonic Acid Monitoring 1 0.06 0.06

Total 2 0.06 - 0.13 0.95

Domestic 0 0 0

Acetochlor Oxanilic Acid Monitoring 1 0.36 0.36

Total 1 0.36 0.36

Domestic 1 0.05 0.05

Alachlor Ethane Sulfonic Acid Monitoring 6 0.08 - 0.53 0.22

Total 7 0.05 - 0.43 0.22

Domestic 0 0 0

Alachlor Oxanilic Acid Monitoring 2 0.07 - 0.43 0.25

Total 2 0.07 - 0.43 0.25

Domestic 2 0.009 - 0.013 0.011

Atrazine Monitoring 11 0.004 - 0.03 0.007

Total 13 0.004 - 0.03 0.009

Domestic 0 0 0

Bromacil Monitoring 1 (e) 0.51 0.51

Total 1 (e) 0.51 0.51

Domestic 0 0 0

Butylate Monitoring 1 0.007 0.007

Total 1 0.007 0.007

Domestic 4 (e) 0.008 - (e) 0.02 0.0175

Deethylatrazine Monitoring 14 (e) 0.003 - (e) 0.108 0.0055

Total 18 (e) 0.003 - (e) 0.108 0.0085

Domestic 2 (e) 0.11 0.11

Deethyldeisopropylatrazine Monitoring 3 (e) 0.08 - 0.14 0.13

Total 5 (e) 0.08 - 0.14 0.11

Domestic 1 (e) 0.02 0.02

Hydroxyatrazine Monitoring 1 (e) 0.556 0.556

Total 2 (e) 0.02 - (e) 0.556 0.288
18 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Domestic 0 0 0

Imazaquin Monitoring 1 (e) 0.15 0.15

Total 1 (e) 0.15 0.15

Domestic 0 0 0

MCPA Monitoring 1 (e) 3.6 3.6

Total 1 (e) 3.6 3.6

Domestic 0 0 0

Metolachlor Monitoring 4 0.005 - 0.01 0.007

Total 4 0.005 - 0.01 0.007

Domestic 4 0.06 - 0.6 0.12

Metolachlor Ethane Sulfonic Acid Monitoring 8 0.1 - 2.86 0.53

Total 12 0.06 - 2.86 0.31

Domestic 0 0 0

Metolachlor Oxanilic Acid Monitoring 3 0.25 - 1.71 0.62

Total 3 0.25 - 1.71 0.62

Domestic 0 0 0

Oryzalin Monitoring 1 0.22 0.22

Total 1 0.22 0.22

Domestic 2 0.031 - 0.091 0.061

Prometon Monitoring 2 0.069 - 0.094 0.0815

Total 4 0.031 - 0.094 0.08

Domestic 0 0 0

Terbacil Monitoring 2 (e) 0.007 - (e) 0.008 0.0075

Total 2 (e) 0.007 - (e) 0.008 0.0075

Domestic 0 0 0

Triclopyr Monitoring 1 (e) 1.13 1.13

Total 1 (e) 1.13 1.13

Pesticide or pesticide 

transformation product Well type Number of detections

Concentration range 

(micrograms per liter)

Median concentration 

(micrograms per liter)

Table 5. List of pesticide and pesticide transformation product detections at or above laboratory reporting levels 

(LRLs) in 42 wells sampled in the upper Illinois River Basin—Continued
Anthropogenic Constituent Detections 19

Table 6. List of pesticide and pesticide transformation product detections at or above information-rich method 

levels in 42 wells sampled in the upper Illinois River Basin

[e, estimated concentration]

Pesticide or pesticide 

transformation product Well type Number of detections

Concentration range 

(micrograms per liter)

Median concentration 

(micrograms per liter)

Domestic 0 0 0

2,4-D Monitoring 1 (e) 0.05 0.05

Total 1 (e) 0.05 0.05

Domestic 0 0 0

Acetochlor Monitoring 2 0.004 - 0.01 0.007

Total 2 0.004 - 0.01 0.007

Domestic 1 0.13 0.13

Acetochlor Ethane Sulfonic Acid Monitoring 1 0.06 0.06

Total 2 0.06 - 0.13 0.95

Domestic 0 0 0

Acetochlor Oxanilic Acid Monitoring 1 0.36 0.36

Total 1 0.36 0.36

Domestic 0 0 0

Acifluorfen Monitoring 1 (e) 0.02 0.02

Total 1 (e) 0.02 0.02

Domestic 1 0.05 0.05

Alachlor Ethane Sulfonic Acid Monitoring 6 0.08 - 0.53 0.22

Total 7 0.05 - 0.43 0.22

Domestic 0 0 0

Alachlor Oxanilic Acid Monitoring 2 0.07 - 0.43 0.25

Total 2 0.07 - 0.43 0.25

Domestic 5 (e) 0.002 - 0.013 0.005

Atrazine Monitoring 11 (e) 0.004 - 0.03 0.006

Total 16 (e) 0.002 - 0.03 0.006

Domestic 0 0 0

Bromacil Monitoring 2 (e) 0.01 - (e) 0.51 0.26

Total 2 (e) 0.01 - (e) 0.51 0.26

Domestic 0 0 0

Butylate Monitoring 1 0.007 0.007

Total 1 0.007 0.007

Caffeine (not a pesticide or

 transformation product)

Domestic 0 0 0

Monitoring 4 (e) 0.004 - (e) 0.024 0.0095

Total 4 (e) 0.004 - (e) 0.024 0.0095

Domestic 5 (e) 0.002 - (e) 0.02 0.015

Deethylatrazine Monitoring 14 (e) 0.003 - (e) 0.108 0.0055

Total 19 (e) 0.002 - (e) 01.08 0.008

Domestic 2 0.11 0.11

Deethyldeisopropylatrazine Monitoring 9 (e) 0.01 - (e) 0.14 0.05

Total 11 (e) 0.01 - (e) 0.14 0.05

Domestic 2 (e) 0.01 - (e) 0.02 0.015

Deisopropylatrazine Monitoring 4 (e) 0.01 - (e) 0.04 0.02

Total 6 (e) 0.01 - (e) 0.04 0.015
20 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Domestic 0 0 0

Dicamba Monitoring 1 (e) 0.08 0.08

Total 1 (e) 0.08 0.08

Domestic 0 0 0

Diuron Monitoring 1 (e) 0.02 0.02

Total 1 (e) 0.02 0.02

Domestic 1 (e) 0.0068 0.0068

Flumetsulam Monitoring 0 0 0

Total 1 (e) 0.0068 0.0068

Domestic 2 (e) 0.011 - (e) 0.02 0.0155

Hydroxyatrazine Monitoring 9 (e) 0.004 - (e) 0.556 0.007

Total 11 (e) 0.004 - (e) 0.556 0.008

Domestic 0 0 0

Imazaquin Monitoring 3 (e) 0.025 - (e) 0.15 0.043

Total 3 (e) 0.025 - (e) 0.15 0.043

Domestic 0 0 0

MCPA Monitoring 1 (e) 3.6 3.6

Total 1 (e) 3.6 3.6

Domestic 0 0 0

Metolachlor Monitoring 4 0.005 - 0.01 0.007

Total 4 0.005 - 0.01 0.007

Domestic 4 0.06 - 0.6 0.12

Metolachlor Ethane Sulfonic Acid Monitoring 8 0.1 - 2.86 0.53

Total 12 0.06 - 2.86 0.31

Domestic 0 0 0

Metolachlor Oxanilic Acid Monitoring 3 0.25 - 1.71 0.62

Total 3 0.25 - 1.71 0.62

Domestic 0 0 0

Oryzalin Monitoring 1 0.22 0.22

Total 1 0.22 0.22

Domestic 0 0 0

P,P' DDE Monitoring 3 (e) 0.001 - (e) 0.002 0.002

Total 3 (e) 0.001 - (e) 0.002 0.002

Domestic 6 (e) 0.004 - 0.091 0.0075

Prometon Monitoring 6 (e) 0.004 - 0.094 0.014

Total 12 (e) 0.004 - 0.094 0.011

Domestic 2 (e) 0.001 - (e) 0.004 0.0025

Simazine Monitoring 0 0 0

Total 2 (e) 0.001 - (e) 0.004 0.0025

Domestic 0 0 0

Terbacil Monitoring 2 (e) 0.007 - (e) 0.008 0.0075

Total 2 (e) 0.007 - (e) 0.008 0.0075

Domestic 1 (e) 0.01 0.01

Triclopyr Monitoring 1 (e) 1.13 1.13

Total 2 (e) 0.01 - (e) 1.13 0.57

Pesticide or pesticide 

transformation product Well type Number of detections

Concentration range 

(micrograms per liter)

Median concentration 

(micrograms per liter)

Table 6. List of pesticide and pesticide transformation product detections at or above information-rich method levels 

in 42 wells sampled in the upper Illinois River Basin—Continued
Anthropogenic Constituent Detections 21

Figure 5. Pesticide and pesticide transformation product detections in wells in urbanized areas in 

northern Illinois/southern Wisconsin.
22 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Figure 6. Nitrate detections in wells in urbanized areas in northern Illinois/southern Wisconsin.
Relations Among Anthropogenic Constituents with Other Chemical Constituents and Physical Characteristics 23

RELATIONS AMONG ANTHROPOGENIC 

CONSTITUENTS WITH OTHER CHEMICAL 

CONSTITUENTS AND PHYSICAL 

CHARACTERISTICS 

Volatile Organic Compounds 

Because individual VOCs were detected with 

insufficient frequency in this study to use in correlation 

tests, summed concentrations of those compounds 

analyzed were calculated by summing the informationrich method concentrations for each well. These 

summed concentrations then were used in correlations 

with inorganic constituents, field parameters, and well 

characteristics. Summed concentrations did not 

correlate significantly with any inorganic constituent, 

field parameter, or well characteristic. The correlations 

of summed concentrations with well depth and 

dissolved oxygen were less than +0.10 with or without 

the large VOC (MTBE) outlier detection. VOC 

concentrations were detected in wells ranging from the 

shallowest to the deepest.

Chloroform, the VOC with the largest number 

of detections (9 detections from 38 samples, or 24 

percent), correlated significantly with dissolved oxygen 

(Sr = 0.49). This correlation may be because reductive 

dehalogenation of chloroform occurs more frequently 

in reducing conditions (Bouwer, 1994). Chloroform's 

significant correlations with iron (Sr = -0.52), more 

commonly found in reducing environments, and nitrate 

(Sr = 0.47), more commonly found in oxidizing 

environments, also are indicative of chloroform’s 

occurrence in oxidizing environments. Chloroform 

negatively correlated with well depth (Sr = -0.30, 

p = 0.07); no chloroform detections were found at 

depths greater than 50 ft (fig. 7). 

Pesticides

The sum of all pesticide concentrations 

analyzed in each sample was calculated by summing 

the information- rich reporting level concentrations 

for each sample. The summed total pesticide 

concentrations and individual pesticides with frequent 

detections were used in correlations with inorganic 

constituents, field parameters, and well characteristics. 

Summed total pesticide concentrations 

correlated significantly with dissolved oxygen 

concentrations (Sr = 0.46) and negatively correlated 

significantly with well depth (Sr = -0.32). Similarly to 

summed VOC concentrations, summed total pesticide 

concentrations substantially decreased at well depths 

greater than 62 ft. Summed pesticide concentrations 

correlated poorly with apparent recharge date 

(Sr = 0.24, p = 0.16), but this correlation is affected 

by one data point with a large pesticide concentration 

(MCPA)/older apparent recharge date outlier. With this 

outlier removed, summed pesticide concentrations 

correlated significantly with apparent recharge date (Sr 

= 0.34) (fig. 8). 

Seven pesticides accounted for 87 of the 

128 (68 percent) detections. The pesticides are 

atrazine, metolachlor ESA, prometon, and atrazine 

transformation products deethylatrazine, 

deethyldeisopropyl atrazine, deisopropylatrazine 

and hydroxyatrazine. Atrazine and its transformation 

products all correlated significantly with dissolved 

oxygen. Correlation values were atrazine (Sr = 0.50), 

deethylatrazine (Sr = 0.65), deethyldeisopropylatrazine 

(Sr = 0.47), deisopropylatrazine (Sr = 0.37), 

hydroxyatrazine (Sr = 0.36), prometon (Sr = 0.17, 

p = 0.86), and metolachlor ESA (Sr = 0.18, p = 0.13) 

(fig. 9). Because atrazine degrades more readily under 

oxidizing conditions, the correlation of atrazine with 

dissolved oxygen may not be causally related, but may 

be more closely associated with simultaneous losses of 

both atrazine, and its transformation products, and 

dissolved oxygen as the recharge waters move 

downgradient (Kolpin and others, 1994).

Correlation values were weak for most 

pesticides; however, a decrease with depth is apparent 

in all pesticides (fig. 10). For example, prometon, 

whereas having a weak correlation with depth, shows a 

distinct decrease of detections with depth, with no 

detection occurring greater than 62 ft. Of 128 

detections, only 4 (3 percent) were from samples from 

wells greater than 62 ft deep. Correlations with well 

depths ranged from -0.15 to -.0.41. Correlation values 

were: atrazine (Sr = -0.28, p = 0.07), deethylatrazine 

(Sr = -0.30, p = 0.06), deethyldeisopropylatrazine 

(Sr = -0.21, p = 0.18), deisopropylatrazine (Sr = -0.01, 

p = 0.95), hydroxyatrazine (Sr = -0.41, significant), 

metolachlor ESA (Sr = -0.15, p = 0.34), and prometon 

(Sr = -0.15, p = 0.37).
24 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Figure 7. Concentration of chloroform as a function of (A) dissolved oxygen, (B) iron, (C) nitrate concentrations, and as a function of (D) well depth in ground water from urbanized areas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation.
Relations Among Anthropogenic Constituents with Other Chemical Constituents and Physical Characteristics 25 Figure 8. Concentration of total pesticides as a function of (A) the concentration of dissolved oxygen, (B) ground-water apparent recharge date, and (C) well depth, and concentration of total pesticides (with outlier removed) as a function of (D) ground-water apparent recharge date in ground water from urbanized areas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation.
26 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Figure 9. Concentration of the pesticides and pesticide transformation products (A) atrazine, (B) deethylatrazine, (C) deethyldeisopropylatrazine, 

(D) deisopropylatrazine, (E) hydroxyatrazine, (F) metolachlor ethane sulfonic acid (ESA), and (G) prometon as a function of concentration of 

dissolved oxygen in ground water from urbanized areas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation.
Relations Among Anthropogenic Constituents with Other Chemical Constituents and Physical Characteristics 27 Figure 10. Concentration of the pesticides and pesticide transformation products (A) atrazine, (B) deethylatrazine, (C) deethyldeisopropylatrazine, (D) deisopropylatrazine, (E) hydroxyatrazine, (F) metolachlor ethane sulfonic acid (ESA), and (G) prometon as a function of well depth in ground water from urbanized areas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation.
28 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Correlation values were weak for some 

pesticides; however, an increase in pesticide 

concentration with more recent recharge dates visually 

is apparent in all pesticides except for metolachlor ESA 

(fig. 11). Of 128 detections, only 6 (5 percent) were 

from samples older than 1975. Metolachlor ESA 

accounted for three of the six detections older than 

1975, although metolachlor was not commercially 

applied until 1977. These detections are likely an 

example of mixing of ground water with different ages. 

Correlations with apparent recharge dates ranged from 

-0.03 to 0.59. Significant correlations were: 

atrazine (Sr = 0.44), deethylatrazine (Sr = 0.59), 

deethyldeisopropylatrazine (Sr = 0.40), and 

prometon (Sr = 0.34). Other correlations were 

deisopropylatrazine (Sr = 0.27, p = 0.10), 

hydroxyatrazine (Sr = 0.30, p = 0.08), and metolachlor 

ESA (Sr = -0.03, p = 0.86). 

Nitrate 

Concentrations of nitrate correlated significantly 

with those of dissolved oxygen (Sr = 0.58). This 

correlation was expected because dissolved oxygen is 

an indicator of oxidizing conditions, conditions 

favorable for nitrate to occur, as well as of recent 

recharge. Nitrate is mostly absent where indicators of 

reduced ground-water conditions are present. Nitrate 

concentrations have significant negative correlations 

with the constituents iron (Sr = -0.66), nitrogen 

(ammonia) (Sr = -0.52), and arsenic (Sr = -0.52) 

(fig. 12). Occurrence of nitrate usually is accompanied 

by a lack of the above constituents that are present in 

reducing conditions.

Concentrations of nitrate also were significantly 

correlated with apparent recharge date (Sr = .74) 

(fig. 12). No nitrate concentrations greater than 2.0 

mg/L occur earlier than 1975. This result may be an 

effect of young water from precipitation initially being 

oxic as it recharges the aquifer, creating an environment 

suitable for nitrate formation. It also is possible that 

the age in reducing water is skewed by anaerobic 

degradation of CFCs, which could decrease falsely the 

apparent recharge date (increase the ground-water age) 

in reducing conditions.

Nitrate did not correlate with depth (Sr = -0.22, 

p = 0.15), but a decrease with depth is evident on the 

plot. In depths ranging from 13-175 ft, no nitrate 

concentrations above 2.0 mg/L were detected deeper 

than 66 ft (fig. 12).

SIGNIFICANCE OF RESULTS

Using information-rich reporting levels, 37 VOC 

detections occurred in 28 of 38 (74 percent) of the well 

samples. Using LRLs, VOCs were detected in 32 

percent of the well samples. No VOCs exceeded 

USEPA drinking-water standards. Only one detection 

(3 percent) exceeded 1.0 μg/L. A study of VOC 

occurrence in urban wells across the United States 

indicated that VOCs were detected in 47 percent of the 

well samples (Squillace and others, 1999). This 

national study used a censoring level of 0.20 μg/L, 

higher than the 0.13 μg/L median detection value of 

VOCs at the LRLs in this report. This result indicates 

that VOCs may be found at a lower frequency in the 

upper Illinois River Basin than nationally. 

Using information-rich reporting levels, 134 

pesticide (or pesticide transformation product) 

detections occurred in 31 of 42 (74 percent) of the well 

samples. Using LRLs, pesticides were detected in 

62 percent of the samples. No pesticides exceeded 

USEPA drinking-water standards. Using LRLs, only 

five detections (6 percent) exceeded 1.0 μg/L. A study 

of pesticide occurrence in urban wells across the United 

States indicated that pesticides were detected in 46.6 

percent of the well samples (Kolpin and others, 1998). 

This national study had similar LRLs, but did not 

include pesticide transformation products (except 

deethylatrazine), the majority of detections in this 

report.

Of the 43 wells sampled for nitrate, 1 (2 percent) 

exceeded the USEPA drinking-water standard for 

nitrate of 10 mg/L. Of the 43 wells, 13 (30 percent) 

samples exceeded the national background 

concentration of 2 mg/L (Mueller and Helsel, 1996). 

A study of nutrient occurrence in shallow urban wells 

across the United States indicated a median nitrate 

concentration of 1.6 mg/L (Nolan and Stoner, 2000). 

This concentration was higher by an order of magnitude 

than the median concentration of 0.068 mg/L calculated 

here.
Significance of Results 29 Figure 11. Concentration of the pesticides and pesticide transformation products (A) atrazine, (B) deethylatrazine, (C) deethyldeisopropylatrazine, (D) deisopropylatrazine, (E) hydroxyatrazine, (F) metolachlor ethane sulfonic acid (ESA), and (G) prometon as a function of ground-water apparent recharge date in ground water from urbanized areas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation.
30 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Figure 12. Concentration of nitrate as a function of (A) arsenic, (B) dissolved oxygen concentrations, (C) ground-water apparent recharge date, (D) iron concentration, (E) nitrogen as ammonia concentration, and (F) well depth in ground water from urbanizedareas in northern Illinois/southern Wisconsin, with Spearman Rank Correlation.
Summary 31

Of the 42 wells sampled for VOCs or pesticides 

using information-rich methods, 38 of 42 (90 percent) 

had at least one detection. Of the 26 wells having 

water samples with detections below LT-MDLs, 22 

(85 percent) had at least one other VOC or pesticide 

detected above LRLs. If nitrate detections above

2.0 mg/L are taken into account, 40 of 43 (93 percent) 

had detections of a VOC or pesticide, or detections of 

nitrate above 2.0 mg/L. 

Occurrence of these constituents indicate that, 

although only one well sample exceeded any USEPA 

drinking-water standards, the majority of the wells are 

anthropogenically affected, but presently (2002) not at 

or above USEPA drinking-water regulation levels of 

concern. However, drinking-water standards have not 

been established for a number of these constituents, 

notably the pesticide transformation products. Pesticide 

transformation products frequently occur in samples 

with other pesticide transformation products, resulting 

in a mixture of multiple transformation products. Few 

health-risk studies have been completed concerning the 

effects of these mixtures.

SUMMARY

The upper Illinois River Basin is one of more 

than 40 study units throughout the United States where 

water-quality data are being collected by the U.S. 

Geological Survey National Water-Quality Assessment 

program to assess ground- and surface-water quality 

at a regional and national level. Increasing urbanization 

throughout the United States has made the occurrence 

and distribution of anthropogenic (caused by humans) 

constituents, such as volatile organic compounds 

(VOCs) and pesticides, in ground water a concern. 

The rapidly expanding growth in the Chicago, Ill. and 

Milwaukee, Wis. metropolitan areas in the upper 

Illinois River Basin may affect the ground-water 

resources of these areas.

VOCs, pesticides (and their pesticide 

transformation products), nitrate and other chemical 

constituents and physical characteristics were sampled 

in the ground water in Quaternary glacial till deposits 

overlying a bedrock aquifer in the recently urbanized 

areas in northeastern Illinois and southeastern 

Wisconsin. A total of 43 wells were sampled: 26 

monitoring wells installed specifically for the study, 

and 17 private domestic-supply wells.

Two levels of reporting detections were used in 

this report. The laboratory reporting level (LRL), in 

which the risk of a false positive or false negative 

detection is less than or equal to 1 percent (percent), 

was used for quantitative interpretations. The semiquantitative, information-rich method level, in which 

estimated concentrations are identified positively and 

are qualified to be present based on quality-control 

criteria, but have an increased risk of false positive 

detections was used for qualitative interpretations, and 

general semi-quantitative interpretations and 

correlation statistics.

Using LRLs, VOCs were detected in 12 of 

38 (32 percent) of the wells. Of the 15 detections of 

7 VOCs, concentrations ranged from 0.03 (estimated) 

to 4.6 micrograms per liter (μg/L), with a median 

concentration of 0.13 μg/L. Methyl tert-butyl ether 

(MTBE) and trichloromethane (chloroform) were the 

most common VOCs detected based on LRLs with 4 

(10 percent) detections.

Using information-rich reporting levels, VOCs 

were detected in 28 of 38 (74 percent) of the wells with 

37 detections of 15 compounds. Chloroform was the 

most commonly detected VOC with 9 (24 percent) 

detections.

Because of the relative infrequency of VOC 

detections compared to the number of samples taken, 

statistical correlation analyses only were conducted 

with sum of analyzed VOC concentrations and 

chloroform. The sum of VOC concentrations did not 

correlate with any of the sampled inorganic and 

physical parameters, including well depth, apparent 

ground-water recharge date, or dissolved oxygen 

concentrations. Chloroform concentrations correlated 

significantly with dissolved oxygen, and negatively 

correlated significantly with well depths, with no 

chloroform detections occurring at depths greater than 

50 ft.

Using LRLs, pesticides were detected in 26 of 

42 (62 percent) of the wells. Of the 83 detections of 

20 pesticides, concentrations ranged from 0.003 

(estimated) to 3.6 (estimated) μg/L, with a median 

concentration of 0.06 μg/L. Deethylatrazine, a 

transformation product of atrazine, was the most 

common pesticide detected using LRLs, with 18

(43 percent) detections.

Using information-rich reporting levels, 

pesticides were detected in 31 of 42 (74 percent) of 

the wells with 134 detections of 29 pesticides. 
32 Anthropogenic Constituents in Shallow Ground Water in the Upper Illinois River Basin

Deethylatrazine was the most commonly detected 

pesticide using information-rich methods, with 19 

(45 percent) detections. Atrazine and four atrazine 

transformation products accounted for 49 percent of 

all pesticide detections.

Summed concentrations of analyzed pesticides 

positively correlated with dissolved oxygen and 

negatively correlated with well depth. Seven pesticides 

accounted for 68 percent of the detections. These are 

the pesticides atrazine, prometon, and the pesticide 

transformation products deethylatrazine, 

deethyldeisopropyl atrazine, deisopropyl atrazine, 

hydroxyatrazine, and metolachlor ESA. Pesticide 

concentrations, except for metolachlor ESA, generally 

decreased with increasing well depth and decreasing 

apparent ground-water recharge date.

Nitrate concentrations ranged from less than 

0.047 to 12.5 mg/L with a median concentration of 

0.068 mg/L. Of the 43 wells sampled for nitrate, 

13 samples (30 percent) had nitrate concentrations 

exceeding the estimated national background 

concentration level of 2 mg/L. Nitrate concentrations 

correlated with dissolved oxygen and apparent groundwater recharge date.

Of the 42 wells sampled for VOCs or pesticides 

using information-rich methods, 38 of 42 (90 percent) 

had at least one detection. If nitrate detections above 

2.0 mg/L are taken into account, 40 of 43 (93 percent) 

had detections of a VOC or pesticide, or detections of 

nitrate above 2.0 mg/L. This result indicates that most 

of these wells are anthropogenically affected.

No individual VOC or pesticide concentrations 

exceeded U.S. Environmental Protection Agency 

(USEPA) drinking-water standards, and only one 

nitrate detection exceeded the standards. The 

percentage of these detections indicate that most of the 

wells are anthropogenically affected, but presently not 

at or above USEPA drinking-water regulation levels of 

concern. Health effects of many of these compounds, 

particularly pesticide transformation products, and 

mixtures of multiple pesticide transformation products, 

however, have not been determined. 
References 33

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