U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5273

National Water-Quality Assessment Program

Source Water-Quality Assessment

Anthropogenic Organic Compounds in Ground Water 

and Finished Water of Community Water Systems in 

the Greater Twin Cities Metropolitan Area, Minnesota 

and Wisconsin, 2004–05
Cover. Photograph shows a pump house for a municipal well that is typical for wells sampled for this 

study. Photograph by Michael Menheer, U.S. Geological Survey, 2005
Anthropogenic Organic Compounds in 

Ground Water and Finished Water of 

Community Water Systems in the Greater 

Twin Cities Metropolitan Area, Minnesota 

and Wisconsin, 2004–05

By Lan H. Tornes, James R. Stark, Christopher J. Hoard, and Erik A. Smith

National Water-Quality Assessment Program

Source Water-Quality Assessment

Scientific Investigations Report 2007–5273

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Tornes, L.H., Stark, J.R., Hoard, C.J., and Smith, E.A., 2007, Anthropogenic organic compounds in ground water and 

finished water of community water systems in the Greater Twin Cities metropolitan area, Minnesota and Wisconsin, 

2004–05: U.S. Geological Survey Scientific Investigations Report 2007–5273, 42 p.
iii

Foreword

The U.S. Geological Survey (USGS) is committed to providing the Nation with credible scientific information that helps to enhance and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the 

Nation’s water resources is critical to ensuring long-term availability of water that is safe for drinking and 

recreation and is suitable for industry, irrigation, and fish and wildlife. Population growth and increasing 

demands for water make the availability of that water, now measured in terms of quantity and quality, 

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

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

national, regional, State, and local information needs and decisions related to water-quality management 

and policy (http://water.usgs.gov/nawqa). The NAWQA Program is designed to answer: What is the condition of our Nation’s streams and ground water? How are conditions changing over time? How do natural 

features and human activities affect the quality of streams and ground water, and where are those effects 

most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, 

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

water issues and priorities. From 1991–2001, the NAWQA Program completed interdisciplinary assessments and established a baseline understanding of water-quality conditions in 51 of the Nation’s river 

basins and aquifers, referred to as Study Units (http://water.usgs.gov/nawqa/studyu.html).

Multiple national and regional assessments are ongoing in the second decade (2001–2012) of the 

NAWQA Program as 42 of the 51 Study Units are reassessed. These assessments extend the findings in 

the Study Units by determining status and trends at sites that have been consistently monitored for more 

than a decade, and filling critical gaps in characterizing the quality of surface water and ground water. 

For example, increased emphasis has been placed on assessing the quality of source water and finished 

water associated with many of the Nation’s largest community water systems. During the second decade, 

NAWQA is addressing five national priority topics that build an understanding of how natural features 

and human activities affect water quality, and establish links between sources of contaminants, the 

transport of those contaminants through the hydrologic system, and the potential effects of contaminants 

on humans and aquatic ecosystems. Included are topics on the fate of agricultural chemicals, effects of 

urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, effects of nutrient 

enrichment on aquatic ecosystems, and transport of contaminants to public-supply wells. These topical 

studies are conducted in those Study Units most affected by these issues; they comprise a set of multiStudy-Unit designs for systematic national assessment. In addition, national syntheses of information on 

pesticides, volatile organic compounds (VOCs), nutrients, selected trace elements, and aquatic ecology 

are continuing.

The USGS aims to disseminate credible, timely, and relevant science information to address practical and 

effective water-resource management and strategies that protect and restore water quality. We hope this 

NAWQA publication will provide you with insights and information to meet your needs, and will foster 

increased citizen awareness and involvement in the protection and restoration of our Nation’s waters.

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

issues of interest. External coordination at all levels is critical for cost-effective management, regulation, 

and conservation of our Nation’s water resources. The NAWQA Program, therefore, depends on advice 

and information from other agencies—Federal, State, regional, interstate, Tribal, and local—as well as 

nongovernmental organizations, industry, academia, and other stakeholder groups. Your assistance and 

suggestions are greatly appreciated.

Robert M. Hirsch

Associate Director for Water

v

Contents

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

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

Purpose and Scope ..............................................................................................................................3

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

Description of Study Area ...................................................................................................................3

Methods...........................................................................................................................................................5

Anthropogenic Organic Compounds in Ground Water and Finished Water of Community 

Supply Wells....................................................................................................................................15

Anthropogenic Organic Compounds in Ground Water Used as Source Water for 

Community Supply Wells......................................................................................................15

Volatile Organic Compounds.............................................................................................................17

Pesticide Compounds ........................................................................................................................19

Other Anthropogenic Organic Compounds ....................................................................................19

Comparison of Source and Finished Ground Water ..............................................................................19

Volatile Organic Compounds.............................................................................................................19

Pesticide Compounds ........................................................................................................................20

Other Anthropogenic Organic Compounds ....................................................................................20

Study Implications Related to Hydrogeologic Setting, Land Use, and Aquifer Productivity...........24

Summary........................................................................................................................................................25

References Cited..........................................................................................................................................26

Appendixes ...................................................................................................................................................29

Appendix 1. Volatile organic compounds analyzed in this study, 2004–05...............................30

Appendix 2. Pesticide compounds analyzed in this study, 2004–05 ..........................................33

Appendix 3. Other anthropogenic organic compounds analyzed in this study, 

2004–05....................................................................................................................................37

Appendix 4. Descriptions of human-health benchmarks related to drinking water...............39

Appendix 5. Comparison between source and associated finished water for anthropogenic organic compounds detected during this study, 2005 .....................................40

Figures

1–2. Maps showing:

1. Location of National Water-Quality Assessment Study Units and Ground-Water 

Source Water-Quality Assessments in contiguous United States.......................................2

2. Location of study area. ................................................................................................................4

3. Generalized hydrogeologic column showing aquifers and confining units in the 

Upper Mississippi River Basin Study Unit................................................................................6

4–5. Maps showing:

4. Surficial glacial aquifer and wells sampled in study area, 2004–05. ...................................7

5. Extent of unconfined Prairie du Chien-Jordan aquifer and wells sampled in study 

area, 2004–05.................................................................................................................................8

6. Example of a pump house and well where water is disinfected at the well 

before being distributed ..............................................................................................................9
vi

7–11. Graphs showing:

7. Anthropogenic organic compound concentrations, number of detections, 

and benchmark quotient values for source-water samples from the study for 

volatile organic compounds, pesticides, and other anthropogenic organic 

compounds from 30 source-water wells in glacial aquifer and unconfined 

part of Prairie du Chien-Jordan aquifer, 2004. .......................................................................16

8. Concentrations of all detected compounds in source-water samples from 

study area, 2004. .........................................................................................................................17

9. Detected volatile organic compounds showing concentrations and number 

of detections, and benchmark quotient values for source and associated 

finished water (blended and nonblended) in samples from study area, 2005. .................21

10. Detected pesticides showing concentrations and number of detections, and 

benchmark quotient values for source and associated finished water 

(blended and nonblended) in samples from study area 2005..............................................22

11. Dectected other anthropogenic organic compounds showing concentrations 

and number of detections, and benchmark quotients for source and associated 

finished water (blended and nonblended) in samples from study area, 2005. .................23

Tables

1. Maximum concentrations, detection frequencies, and maximum benchmark 

quotients for compounds detected in source water from community water 

systems in studied aquifers in the Greater Twin Cities metropolitan area, 

Minnesota and Wisconsin, 2004. .............................................................................................10

2. Maximum concentrations, detection frequencies, and maximum benchmark 

quotients for compounds detected in source-water wells and in associated 

finished water from community water systems in studied aquifers in the 

Greater Twin Cities metropolitan area, Minnesota and Wisconsin, 2005. ........................12
 vii

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

gallon (gal) 3.785 cubic decimeter (dm3) 

Flow rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

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

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

Concentrations of chemical constituents in water are given in micrograms per liter (μg/L).

Fiscal year is the accounting period of the Federal government. It begins on October 1 and ends 

on September 30 of the next calendar year.

Conversion Factors
viii

< less than

μg/L microgram per liter

AHTN acetyl hexamethyl tetrahydronaphthalene

AOC anthropogenic organic compound

BGD billion gallons per day

BHA 3-tert-butyl-4-hydroxy anisole

BQ benchmark quotient

BQmax ratio of the maximum concentration to a drinking-water benchmark 

(benchmark quotient)

CASR Chemical Abstract Services Registry

CAAT chlordiamino-s-triazine

CEAT 2-chloro-6-ethylamino-4-amino-s-triazine

CIAT 2-chloro-4-isopropylamino-6-amino-s-triazine

CCRs Consumer Confidence Reports

CWSs community water systems

DBP disinfection by-product

DOC dissolved organic carbon

E estimated value

ESA ethanesulfonic acid

HHCB hexahydrohexamethylcyclopentabenzopyran 

HBSL Health-Based Screening Level

MRL minimum reporting level

MCL Maximum Contaminant Level

MCLG Maximum Contaminant Level Goal

MTBE methyl tert-butyl ether

NAWQA National Water-Quality Assessment

NJDEP New Jersey Department of Environmental Protection

NWQL National Water Quality Laboratory

OA oxanilic acid

OHSU Oregon Health & Science University

QA/QC quality assurance and quality control

OIET 2-hydroxy-4-isopropylamino-6-ethylamino-s-triazine

SA second amide

SWQAs Source Water-Quality Assessments

TCEP tris(2-chloroethyl)phosphate

TCMA Twin Cities metropolitan area

TCPP tris(dichloroisopropyl)phosphate 

UMIS Upper Mississippi River Basin Study Unit

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound

Abbreviations and Acronyms
 ix

Definitions

Benchmark quotient (BQ) Ratio of the concentration of a contaminant to its Maximum 

Contaminant Level (MCL) for a regulated compound or to its HealthBased Screening Level (HBSL) value for an unregulated compound. 

BQs greater than 1.0 identify concentrations of potential concern. BQs 

greater than 0.1 identify compounds that may warrant inclusion in a 

low-concentration, trends-monitoring program.

BQmax Maximum benchmark quotient, which is the ratio of the maximum 

concentration of a contaminant to its MCL or HBSL.

Blended water As used in this report, finished water that has been blended with one 

or more different ground waters. Finished water blended with surface 

water was not sampled as part of this study.

Concentration of humanhealth concernAs used in this report: (1) for a regulated compound with a U.S. 

Environmental Protection Agency (USEPA) drinking-water standard, a 

concentration greater than the Maximum Contaminant Level; and (2) 

for an unregulated compound, a concentration greater than the HealthBased Screening Level.

Community water system 

(CWS)

A public water system with 15 or more connections and serving 25 

or more year-round residents and thus subject to USEPA regulations 

enforcing the Safe Drinking Water Act. A CWS serves a residential 

population, such as a municipality, mobile-home park, or nursing home.

Drinking-water guideline As used in this report, a concentration that has no regulatory status but 

is issued in an advisory capacity by USEPA or State agencies.

Drinking-water standard As used in this report, a concentration that is legally enforceable (such 

as MCLs) by USEPA or State agencies.

Finished water Water is “finished” when it has passed through all the processes in a 

water-treatment plant and is ready to be delivered to consumers.

Health-Based Screening 

Level (HBSL)

An estimate of a concentration (for a noncarcinogen) or concentration 

range (for a carcinogen) in water that (1) may be of human-health 

concern; (2) can be used as a value against which measured 

concentrations of contaminants in water samples can be compared; 

and (3) is consistent with USEPA Office of Water methodologies.

Human-health 

benchmarks

As used in this report, these include USEPA MCL values and HBSL 

values developed collaboratively by the U.S. Geological Survey, 

USEPA, New Jersey Department of Environmental Protection, and 

Oregon Health & Science University.

Maximum Contaminant 

Level (MCL)

As used in this report, a USEPA drinking-water standard that is legally 

enforceable and that sets the maximum permissible concentration of 

a contaminant in water that is delivered to any user of a public water 

system at which no known or anticipated adverse effect on the health 

of persons occurs and which allows an adequate margin of safety.

Regulated compound As used in this report, a compound for which a Federal and (or) State 

drinking-water standard has been established.

Source water The raw (ambient) water collected at the supply well or surface-water 

intake prior to water treatment used to produce finished water.

Unregulated compound As used in this report, a compound for which no Federal and (or) State 

drinking-water standard has been established. Note that a compound 

that is unregulated under the Safe Drinking Water Act may be 

regulated in other contexts and under other statutes.
 
Anthropogenic Organic Compounds in Ground Water 

and Finished Water of Community Water Systems in the 

Greater Twin Cities Metropolitan Area, Minnesota and 

Wisconsin, 2004–05

By Lan H. Tornes, James R. Stark, Christopher J. Hoard, and Erik A. Smith

Abstract

As part of the U.S. Geological Survey’s National 

Water-Quality Assessment (NAWQA) Program, two Source 

Water-Quality Assessments (SWQAs) were conducted during 

2004–05 in unconfined parts of the glacial aquifer system and 

in unconfined parts of the Prairie du Chien-Jordan aquifer in 

the Greater Twin Cities metropolitan area of Minnesota and 

Wisconsin. SWQAs are two-phased sampling activities in 

the NAWQA Program. The first phase evaluated the occurrence of 265 (258 are included in this report) anthropogenic 

organic compounds (AOCs) through monitoring source water 

in 30 of the largest-producing community water system wells 

completed in the aquifers underlying the Greater Twin Cities metropolitan area. The AOCs included volatile organic 

compounds (VOCs), pesticides, and other AOCs. During the 

second phase of the study, 15 of the original community water 

system wells, those with the greatest number of AOC detections, were resampled along with associated finished water. 

Results from the first phase of sampling indicated that 

40 AOCs were detected, and 83 percent of the samples had 

at least one detected AOC. Concentrations of AOCs detected 

in the source water generally were low (defined in this report 

as concentrations less than 1.0 microgram per liter). Humanhealth benchmarks for these compounds (Maximum Contaminant Levels for regulated compounds or Health-Based Screening Levels for unregulated compounds, when they existed) 

typically were not exceeded. Fifteen VOCs were detected in 

the source-water samples. However, concentrations were low. 

Seventeen pesticide compounds were detected generally at 

concentrations less than concentrations for VOCs. Most of the 

pesticide compounds detected were triazine- or alachlor-parent 

compounds or their breakdown products. Eight other AOCs 

were detected in the source-water samples but generally at low 

concentrations.

Results from the second phase of sampling indicated a 

total of 13 and 12 VOCs were detected in source-water and 

in finished-water samples, respectively. Most of the VOCs, 

except for those associated with disinfection by-products, were 

detected more frequently in source-water samples than in finished-water samples. Concentrations of most VOCs detected 

in either source water or finished water were less than humanhealth benchmarks. Twenty-one pesticide compounds were 

detected in either source water or finished water. Concentrations of detected pesticides in source-water and finished-water 

samples were low. The most frequently detected compounds in 

both the source and finished water were triazine-parent pesticides or their breakdown products and breakdown products of 

alachlor and metolachlor. In general, pesticides, if detected in 

source water, also were detected in the corresponding finished 

water. Concentrations of pesticides detected were less than 

human-health benchmarks in both source and finished water. 

A total of nine other AOCs were detected in the source-water 

or finished-water samples, and about the same number of 

compounds was detected in each of the sample groups in 

either source water or finished water. Detected concentrations 

of other AOCs were low. 

Water-quality results from source-water samples were 

compared to characterize differences between aquifers. VOC 

and other AOC detections were more frequent in water from 

the Prairie du Chien-Jordan aquifer compared to the glacial 

aquifer. Pesticides, however, were detected more frequently in 

the glacial aquifer. On the basis of study results, the hydrogeologic setting, land use, and aquifer productivity are important 

in explaining the occurrence of AOCs in community water 

system wells. Results of this study indicate that monitoring 

for pesticides in source water generally indicates the potential 

occurrence of pesticides in finished water but that this is not 

necessarily true of VOCs. Additional monitoring is needed to 

better understand the occurrence of other AOCs in source and 

finished waters.
2 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Introduction

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

National Water-Quality Assessment (NAWQA) Program to 

(1) provide a nationally consistent description of current 

water-quality conditions for the largest and most important 

river basins and aquifers across the Nation; (2) define longterm trends in water quality; and (3) identify, describe, and 

explain major factors that affect observed water-quality conditions and trends (fig. 1). This information was intended to 

allow water managers, policymakers, and the public to address 

and prioritize issues related to managing and protecting the 

Nation’s water resources. 

During the initial period of data collection (1995–98) 

in the Upper Mississippi River Basin NAWQA Study Unit 

(UMIS), water quality was measured in hundreds of groundwater and surface-water samples (Stark and others, 2001). 

These samples represented water quality in different environmental media and at various spatial and temporal scales. 

Samples included ground water, stream water, streambed 

sediment, fish tissue, and aquatic biology. To develop an integrated assessment, data were analyzed in various combinations 

and interpreted in relation to natural and human factors that 

can affect water quality. The most significant contaminants 

detected in ground water and surface water included nutrients, 

pesticides, and volatile organic compounds (VOCs) (Stark and 

others, 2001). This intensive phase of data collection was an 

initial step in a long-term integrated water-quality assessment. 

In 2001, NAWQA began a second period of intensive 

assessments by returning to 42 of the Study Units studied 

during the first decade. These assessments built on the initial 

assessments by establishing links between sources, transport, 

and effects of contaminants on humans and aquatic ecosystems. One of the second-phase activities involved characterizing the quality of major aquifers and rivers used as sources 

of water to large community water systems (CWSs). Previous 

NAWQA studies had focused on ambient (present conditions 

of untreated water) water quality rather than on the quality of 

water used as sources of drinking water (source water) or on 

water treated for delivery to the public (finished water). The 

new Source Water-Quality Assessments (SWQAs) begun during the second phase complement drinking-water monitoring 

required by Federal, State, and local programs that focused 

primarily on post-treatment compliance monitoring. 

Figure 1. Location of National Water-Quality Assessment (NAWQA) Study Units and Ground-Water Source Water-Quality Assessments 

in contiguous United States.

0 200 400 MILES

0 200 400 KILOMETERS

Base modified from U.S. Geological Survey 

digital data, 1:2,000,000, 1990

Albers Equal-Area Projection

North American Datum of 1983

Upper Mississippi River Basin

NAWQA Study Unit

Ground-Water Source Water-Quality

 Assessment location 

EXPLANATION

NAWQA Study Units—Studies

begun in fiscal year: 

2001

2004

2007

Figure 1. Location of National Water-Quality Assessment (NAWQA) Study Units and Ground-Water Source Water-Quality 

Assessments in contiguous United States.
Introduction 3

Purpose and Scope

This report describes the occurrence of anthropogenic 

organic compounds (AOCs) in ground-water source water as 

well as the occurrence of selected AOCs in a subset of associated finished water during 2004–05. The report summarizes 

results from ground-water SWQAs of two important watersupply aquifers in the unconfined part of the glacial aquifer 

system and the unconfined part of the Prairie du Chien-Jordan 

aquifer system that underlie the Greater Twin Cities metropolitan area (TCMA) in Minnesota and Wisconsin. The aquifers 

are considered susceptible to anthropogenic contamination 

because of their direct hydraulic connection with the land surface. The glacial aquifer system, as used in this report, refers 

to unconfined, coarse-grained glacial deposits that yield water 

to wells. These deposits are part of the glacial aquifer system as defined by the NAWQA Program for the Nation. The 

term “system” does not imply that there is a good hydrologic 

connection between individual wells completed in the glacial 

aquifer system. For this report, wells sampled from the glacial 

aquifer system (termed glacial aquifer in this report) were 

selected from parts of the aquifer system that are unconfined. 

Water-quality samples were collected and analyzed from 

a random selection of 30 of the largest CWS wells completed 

in unconfined parts of the glacial aquifer and the Prairie du 

Chien-Jordan aquifer. Results are compared to human-health 

benchmarks, which consist of U.S. Environmental Protection 

Agency (USEPA) Maximum Contaminant Levels (MCLs) and 

Health-Based Screening Levels (HBSLs) (U.S. Environmental 

Protection Agency, 2002). 

AOCs analyzed included VOCs, pesticides, and other 

AOCs (Appendixes 1, 2, and 3). VOCs are a subset of organic 

chemicals that have been produced and used in commercial, 

industrial, and household applications. Pesticides are used 

extensively throughout the Nation to increase crop yields, 

to enhance the aesthetics of lawns, gardens, golf courses, 

and recreational areas, and to protect crops and the public 

from insects. The widespread use of pesticides over the past 

several decades has led to their frequent detection in ground 

water (Barbash and Resek, 1996). Other AOCs represent a 

select group of compounds that are present in a wide variety 

of products commonly used in homes, industry, and agriculture, including personal-care and domestic-use products, 

plant- or animal-derived biochemicals, and fumigants, for 

which analytical methods are available. Little is known about 

the environmental occurrence, transport, and ultimate fate of 

other AOCs after their use. However, it is known that these 

compounds often are released directly to the environment 

after passing through wastewater treatment plants or domestic 

septic systems, which often are not designed to remove these 

compounds from the effluent (Herberer, 2002; Ternes and 

others, 2002). Until recently, few analytical methods were 

capable of detecting these compounds at the low concentrations expected in the environment. Linking ground-water 

source water and finished water from CWSs to ambient waterquality data and to drinking-water monitoring required by Federal, State, and local programs is important, considering the 

documented occurrence of organic contaminants in finished 

water at concentrations similar to those found in source water 

(Stackelberg and others, 2004; Westerhoff and others, 2005; 

Loraine and Pettigrove, 2006). 

Acknowledgments 

The authors are grateful to staff from the participating 

municipalities for providing information pertaining to the 

wells used for this study and for permitting the collection of 

samples. The authors also express appreciation for technical 

assistance from Bruce Olsen and other staff from the Minnesota Department of Health and thank the following USGS 

employees for their help with data collection and compilation: 

Allan Arntson (retired), Robert Borgstede (retired), Timothy 

Cowdery, Gregory Delzer, Landon Gryczkowski, Michael 

Menheer, Thomas Reppe, Chris Sanocki, and Greg Stratton 

(retired).

Description of Study Area

The study area (fig. 2) covers approximately 11,000 mi2

and includes parts of the TCMA. The study area is part of the 

47,000-mi2 UMIS Study Unit that includes the Mississippi 

River Basin upstream from Lake Pepin and the tributary basins 

of the Minnesota and St. Croix Rivers. Ground-water quality 

in the study area is affected by natural and human factors (precipitation, evaporation, geology, drainage, population density, 

and land use). The environmental and hydrologic setting of the 

study area is complex, and natural and human factors, in addition to ground-water withdrawals from wells, affect the areal 

distribution and flow of ground water and the distribution and 

concentration of water-quality constituents in the aquifers. 

The environmental setting of the study area is described 

in detail by Stark and others (1996). The TCMA consists of 

13 counties located in both Minnesota and Wisconsin. The 

counties are Anoka, Carver, Chisago, Dakota, Hennepin, 

Isanti, Ramsey, Scott, Sherburne, Washington, and Wright in 

Minnesota and Pierce and St. Croix in Wisconsin. Increased 

urbanization of the study area has resulted in substantial landuse change. The TCMA, which includes most of the population of the study area, is the 15th largest metropolitan area in 

the Nation according to population figures from the last two 

censuses. The area grew by 16.9 percent from 2,538,834 in 

1990 to 2,968,806 in 2000 (Minnesota State Demographic 

Center, 2002). The most significant ground-water-quality concerns in the study area are related to nutrients, pesticides, and 

VOCs (Stark and others, 2001).
4 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

EXPLANATION

Greater Twin Cities 

metropolitan area

River

Minnesota

River

River

St.

Croix

Vermillion

River

River

River

River

River

River

River

River

Canon

Crow

Rum

Snake

Apple

Rush

Chippewa

Lake

Pepin

Mississippi

M I N N E S O T A

W I S C O N S I N

35

35

35E

35W

94

94

494

694

RICE

GOODHUE

ISANTI

KANABEC

DAKOTA

WRIGHT

SCOTT

SIBLEY

ANOKA

HENNEPIN

WABASHA

MILLE LACS

CARVER

CHISAGO

PINE

LE SUEUR

SHERBURNE

BENTON

MORRISON

WASHINGTON

RAMSEY

POLK

BURNETT

DUNN

ST. CROIX

BARRON

PIERCE

WASHBURN

BUFFALO

PEPIN

Minneapolis St. Paul

Plymouth

River Falls Bloomington

St. Croix

Falls

Hudson

Stillwater

Hastings

Red Wing

93o30' 93o 92o30' 92o

44o30'

45o

45o30'

MINNESOTA

WISCONSIN

0 20 40 Miles

0 20 40 Kilometers

Base from Minnesota Department of Natural Resources

Digital data 1:24,000, 1993. 

ESRI Data & Maps 1999 (WI interstate 94)

Wisconsin Department of Natural Resources

Digital data 1:24,000, 2004 (county boundaries)

Universal Transverse Mercator

projection, Zone 15, Central Meridian -93o.

MINNESOTA RIVER BASIN

MISSISSIPPI

RIVER BASIN ST. CROIX RIVER

BASIN

CANNON/

VERMILLION

RIVER

BASINS

Study

Area

Figure 2. Location of study area.
Methods 5

Hydrogeologic units (fig. 3), integral parts of the hydrologic setting, underlie the study area and consist of glacial till 

and glacial sand and gravel of Quaternary age and underlying 

sandstone, shale, and carbonate rocks of Paleozoic and Precambrian age. The uppermost unconsolidated deposits consist 

of sand and gravel of Quaternary age. (Norvitch and others, 

1973; Bloomgren and others, 1989; Meyer and Hobbs, 1989; 

Meyer, 1993; Andrews and others, 1998). Sand and gravel 

deposits of the surficial glacial aquifer commonly are overlain 

or underlain by sandy to clayey glacial till (fig. 4). Ground 

water in the glacial aquifer generally flows toward the Mississippi River or to its tributaries (Kanivetsky, 1989; Palen and 

others, 1989). Within the aquifer, the water table generally is 

within 20 ft of land surface (Helgesen and Lindholm, 1977). 

Estimated recharge to the aquifer can be as great as 11 in/yr 

based on analyses of hydrographs of water levels in shallow 

wells. The surficial part of the aquifer is highly susceptible to 

contamination from activities at the land surface (Piegat, 1989; 

Meyer, 1993). 

Quaternary deposits are underlain by as much as 

1,000 ft of sedimentary rock of Cretaceous through Cambrian 

age (fig. 3). These sedimentary rocks are, in turn, underlain by 

“basement” rocks (metamorphic and igneous) of Precambrian 

age. The primary bedrock aquifer underlying the study area 

is the Prairie du Chien-Jordan aquifer (fig. 5). The aquifer 

consists of fractured sandy dolomite (Prairie du Chien Group 

of Ordovician age) and underlying quartz sandstone (Jordan 

Sandstone of Cambrian age) (Setterholm and others, 1991). 

The Prairie du Chien Group of rocks is karstic, and ground 

water flows mainly through joints, fractures, and solution cavities. Flow in the Jordan Sandstone is primarily through intergranular pore spaces and joint partings (Delin and Woodward, 

1984). The Prairie du Chien Group and the Jordan Sandstone 

are in good hydraulic connection and have traditionally been 

considered a single aquifer although recent research indicates 

that the aquifers are less hydraulically well connected in some 

areas (Delin and Woodward, 1984; Young, 1992a, 1992b; 

Tipping and others, 2006). In some areas, the aquifer is in 

good hydraulic connection with the overlying glacial deposits, 

especially through flow in glacial valleys cut into the bedrock, 

and later filled with glacial sand and gravel. Ground water in 

the aquifer generally flows toward major rivers.

Public water suppliers in the study area rely on ground 

water and on the Mississippi River. Ground water is particularly important in the suburbs of Minneapolis and St. Paul. 

More than 276 public-supply wells are permitted for use 

within the study area (A.D. Arntson, U.S. Geological Survey, 

oral commun., 2006). These wells are publicly owned, and 

source water generally is treated prior to distribution. In 2003, 

approximately 1.45 billion gallons per day (BGD) of ground 

water were withdrawn from the study area. Figure 6 shows a 

typical pump house and well where water is disinfected at the 

well before being distributed.

Methods

Wells sampled were selected at random from the largest producing CWS wells (upper 25th percentile of pumping 

volume) completed in the unconfined parts of each of the two 

aquifers (figs. 4 and 5). Because of this random selection, 

the wells generally represent the variability in hydrogeology 

and land use and land cover across the study area. As used 

in this report, source water is the untreated (ambient) water 

from a supply well prior to water treatment, blended water is 

a mixture of water from several wells, and finished water is 

the source water or blended water that is treated and delivered 

to consumers. Individual well names and locations are not 

included in this report to protect the security of these wells. 

The wells are approximately located on figures in this report.

Fifteen wells were selected from unconfined parts of the 

glacial aquifer, and 15 wells were selected from unconfined 

parts of the Prairie du Chien-Jordan aquifer (figs. 4 and 5). 

Wells were selected at random from the upper 25th percentile 

of pumping volume while maintaining a minimum distance 

of 0.62 mi (1 kilometer) between sampled wells. The initial 

sampling occurred during November and December 2004. 

The second phase of sampling in 2005 focused on wells where 

AOCs were detected most frequently during the first phase. 

The second phase evaluated the occurrence of these compounds in source water and associated finished water. During the second phase, samples of source water were obtained 

from 15 wells. Samples of finished waters were obtained at 

14 sites (figs. 4 and 5) because two of the wells were in the 

same municipality and had potential to be blended, depending 

on pumping schedules, prior to the point where the finished 

water could be sampled. Chemical compounds analyzed varied 

among sites based on results from the first phase of sampling. 

Ground-water samples were collected using established 

USGS and USGS-NAWQA protocols described in the USGS 

“National Field Manual for the Collection of Water-Quality 

Data” available at http://water.usgs.gov/owq/FieldManual/

(last accessed on February 14, 2007). Additional samplecollection and processing information can be found in Koterba 

and others (1995) and Menheer and Brigham (1997). Finishedwater samples were collected after treatment and prior to the 

entry to transport pipelines. Finished-water samples typically 

contain free chlorine, which has been documented to degrade 

certain organic compounds that may be present in the water 

samples. Therefore, a dechlorination reagent (ascorbic acid) 

and, for certain contaminant groups, pH buffers, were added 

to finished-water samples during sample collection to stabilize 

them prior to analyses. The addition of dechlorination reagents 

to water samples has been tested in a laboratory setting, and 

results indicated that they do not interfere with the analytical 

performance (Sandstrom and Delzer, 2007). 
6 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Glacial

deposits

Galena

Dolomite

Galena

Dolomite

Decorah

Shale

FORMATION

OR

GROUP

GENERAL

LITHOLOGY

HYDROGEOLOGIC UNIT 

Platteville

Formation

Platteville

Formation

Glenwood

Formation

Glenwood

Formation

St. Peter

Sandstone

St. Peter

Sandstone

Prairie du

Chien

Group

Prairie du

Chien

Group

Jordan

Sandstone

St. Lawrence

Formation

St. Lawrence

Formation

Franconia

Formation

Franconia

Sandstone

Ironton

Sandstone

Galesville

Sandstone

Eau Claire

Formation

Eau Claire

Sandstone

Mount Simon

Sandstone

Mt. Simon

Sandstone

Hinckley

Sandstone

Fond du Lac

Formation

Solor Church

Formation

Igneous/

metamorphic

rocks

Igneous/

metamorphic

rocks

ERATHEMSYSTEM ORSERIES O R D O V I C I A N C A

M B R I A N QUATERNARY P R E C A

M B R I A N

P A L E O Z O I C MESO- ZOIC

CRETACEOUS

P R O T E R O Z O I C CENOZOIC

Figure 3. Generalized hydrogeologic column showing aquifers and confining units in the Upper Mississippi River Basin

 Study Unit (modified from Green, 1977; Delin and Woodward, 1984; Olcott, 1992).

Till Limestone Sandstone Shale Silty Calcareous

Cedar Valley

Formation

Carlisle Shale

Greenhorn Fm.

Graneros Shale

Dakota Fm.

--

Maquoketa

Shale

DEVONIAN

MINNESOTA MINNESOTA

Glacial

deposits

Bayfield

Group

Oronto Group

Wonewoc

Formation

Trempealeau

Formation

--

--

--

--

WISCONSIN WISCONSIN

0-450

0-500

0-50?

0-110?

0-50?

0-90

0-30

0-16

0-130

0-65

0-335

0-130

0-70

0-200

0-200

0-200

0-650

0-1,100

UP TO

20,000 

0-100 THICKNESS (IN FEET) 

St. Lawrence

confining unit

St. Lawrence

confining unit

Franconia-IrontonGalesville aquifer Tunnel City-WonewocEau Claire aquifer

Eau Claire confining unit

Mt. Simon-HinckleyFond du Lac aquiferMt. Simon-HinckleyFond du Lac aquifer

 Undifferentiated Precambrian 

sandstone aquifer

 Undifferentiated Precambrian 

sandstone aquifer

Precambrian igneous/

metamorphic aquifers

Precambrian igneous/

metamorphic aquifers

Prairie du ChienTrempealeau aquifer

Prairie du ChienJordan aquifer

Basal St. Peter confining unit

St. Peter aquifer St. Peter aquifer

Glenwood confining unit

Decorah-PlattevilleGlenwood confining unit

Galena-Platteville aquifer

Upper carbonate aquifer Maquoketa shale

confining unit

Devonian aquifer

Cretaceous aquifer

Surficial sand and gravel

aquifer,

till and clay confining 

unit, and

buried sand and gravel

aquifer

Surficial sand and gravel

aquifer,

till and clay confining 

unit, and

buried sand and gravel

aquifer

Sand and Dolomite

gravel

Igneous/

metamorphic

EXPLANATION OF GENERAL LITHOLOGY

Figure 3. Generalized hydrogeologic column showing aquifers and confining units in the Upper Mississippi River Basin Study Unit 

(modified from Green, 1977; Delin and Woodward, 1984; Olcott, 1992).
Methods 7

Hydrogeology from Soller and 

Packard (1998) 

M I N N E S O T A

W I S C O N S I N

RICE

GOODHUE

ISANTI

KANABEC

DAKOTA

WRIGHT

SCOTT

SIBLEY

ANOKA

HENNEPIN

WABASHA

MILLE LACS

CARVER

CHISAGO

PINE

LE SUEUR

SHERBURNE

BENTON

MORRISON

WASHINGTON

RAMSEY

POLK

BURNETT

DUNN

ST. CROIX

BARRON

PIERCE

WASHBURN

BUFFALO

PEPIN

93o30' 93o 92o30' 92o

44o30'

45o

45o30'

Figure 4. Surficial glacial aquifer and wells sampled in study area, 2004–05.

0 20 40 MILES

0 20 40 KILOMETERS

Base from Minnesota Department of Natural Resources

Digital data 1:24,000, 1993. 

Wisconsin Department of Natural Resources

Digital data 1:24,000, 2004 (county boundaries)

Universal Transverse Mercator

projection, Zone 15, Central Meridian -93o.

Course-grained, stratified sediment1

Fine-grained, stratified sediment

Till

Patchy Quaternary sediment

Organic-rich sediment

Exposed bedrock, residuum, or

 alluvium or colluvium not derived

 from glacial deposits

Well — source water

Well — source and finished water

1

Generalized extent of surficial glacial aquifer. Some wells are located in areas

 of the surficial aquifer that are not identified on maps by Soller and Packard (1998)

EXPLANATION

Figure 4. Surficial glacial aquifer and wells sampled in study area, 2004–05.
8 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Figure 5. Extent of unconfined Prairie du Chien-Jordan aquifer and wells samples in study area, 2004–05.

M I N N E S O T A

W I S C O N S I N

RICE

GOODHUE

ISANTI

KANABEC

DAKOTA

WRIGHT

SCOTT

SIBLEY

ANOKA

HENNEPIN

WABASHA

MILLE LACS

CARVER

CHISAGO

PINE

LE SUEUR

SHERBURNE

BENTON

MORRISON

WASHINGTON

RAMSEY

POLK

BURNETT

DUNN

ST. CROIX

BARRON

PIERCE

WASHBURN

BUFFALO

PEPIN

93o30' 93o 92o30' 92o

44o30'

45o

45o30'

0 20 40 MILES

0 20 40 KILOMETERS

Base from Minnesota Department of Natural Resources

Digital data 1:24,000, 1993. 

Wisconsin Department of Natural Resources

Digital data 1:24,000, 2004 (county boundaries)

Universal Transverse Mercator

projection, Zone 15, Central Meridian -93o.

Hydrogeology modified from Morey and

Meints, 2000 (Minnesota); Cannon and 

others, 1999 (Wisconsin)

EXPLANATION

Ordovician, Galena-Maquoketa Fm

Mid-Ordovician; Decorah Shale

Ordovician; St. Peter-Glenwood-Platteville

Ordovician; Prairie du Chien Group1

Upper Cambrian; Mt. Simon-Jordan Sandstone1

Well — source water

Well — source and finished water

1

The Prairie du Chien-Jordan aquifer is comprised of the Prairie du Chien Group

of rocks and the Jordan Sandstone. No geologic or hydrogeologic maps are

available that identify this aquifer for Minnesota and Wisconsin. The extent of the

aquifer is included within, but is smaller than, the area defined by the Mt. SimonJordan Sandstone and the Prairie du Chien Group of rocks.

Ol

Ol

Om

Om

Om

Ol Ol

Ol

Oum

Om

Om

Ol

Ol

Ol

Cu

Om

Oum

Om

Ol

Ol

Om

Ol

Om

Omd

Ol

Om

Om

Om

Om

Ol

Om

Ol

Ol

Oum

Om

Om

Om

Om

Ol

Ol

Omd

Om

Omd

Ol

Ol

Ol

Ol

Ol

Ol

Ol

Ol

Omd

Om

Om

Om

Om

Omd

Cu

Cu

Cu

Cu

Cu

Cu

Ol

Om

Oum

Cu

Omd

Cu
Methods 9

Most samples were analyzed at the USGS National 

Water Quality Laboratory (NWQL) in Lakewood, Colorado. 

For documentation pertaining to the analytical methods see 

Zaugg and others (1995), Lindley and others (1996), Connor 

and others (1998), Furlong and others (2001), Sandstrom and 

others (2001), Zaugg and others (2002), and Madsen and others (2003). Pesticide metabolites were analyzed at the USGS 

Organic Geochemistry Research Laboratory in Lawrence, 

Kansas. The methods used are documented in Lee and Strahan 

(2003). Analytical results of samples are reported by Carter 

and others (2007).

The constituents are described in this report by the group 

the constituent belonged to (VOCs, pesticides, or other AOCs). 

Within each group, the individual constituents are sorted by 

the total number of detections. The constituents detected in 

source water are ranked in descending order with the highest number of detections at the top and the lowest number of 

detections at the bottom (table 1). In table 2, the constituents 

are placed in their respective groups, and constituents with 

the highest number of detections, in both finished and source 

waters, are placed first, followed by constituents detected only 

in finished waters, then by constituents detected only in source 

waters. 

Analytical results in this report are sometimes censored; 

that is, they are qualified with a less than (<) symbol. A 

“ < ” symbol means that the compound was not detected but 

may be present at a concentration below the level at which 

a concentration can be accurately reported. These censoring 

limits are developed over time and are subject to change as 

analytical refinements are made. Another qualifier is an “E” to 

designate an estimated value. This frequently is applied when 

interferences or degradation during analysis results in uncertain recoveries so that the reported value has a large degree of 

uncertainty. An “E” qualifier also may be applied when the 

presence of a compound is identified at a concentration below 

the reporting level, but it is not in the range where the value 

provided by the analysis instrument is considered reliable and 

able to be confirmed by multiple lines of evidence.

Figure 6. Example of a pump house and well where water is disinfected at the well before being distributed (photographs by Michael 

Menheer, U.S. Geological Survey, 2005).
10 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Table 1. Maximum concentrations, detection frequencies, and maximum benchmark quotients for compounds detected in source 

water from community water systems in studied aquifers in the Greater Twin Cities metropolitan area, Minnesota and Wisconsin, 2004.

—Continued

[MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contaminant Level; HBSL, Health-Based Screening 

Level; BQmax, benchmark quotient = ratio of maximum compound concentration to MCL or HBSL value; ESA, ethanesulfonic acid; SA, second amide; OA, 

oxanilic acid; E, estimated value; μg/L, micrograms per liter; --, not available; bold type indicates unregulated compound for which no Federal and (or) State 

drinking-water standards have been established]

Regulated or

unregulated

compound

Chemical 

Abstracts 

Service Registry 

number

Number of 

detections

for source 

water

Detection

frequency

(percent)

MRL 

(μg/L)

Maximum 

concentration

for source 

water

(μg/L)

USEPA MCL 

(or HBSL) 

concentration

(μg/L)

BQmax 

for source 

water

Volatile organic compounds (VOCs)

cis-1,2-Dichloroethene 156–59–2 7 23 0.038 1.496 70 0.02

Trichloroethene 79–01–6 5 17 .038 69.52 5 10

Chloroform 67–66–3 3 10 .024 E.097 180 .001

trans-1,2-Dichloroethene 156–60–5 3 10 .032 E.110 100 .001

Vinyl chloride 75–01–4 2 7 .08 .677 2 .3

Perchloroethene 127–18–4 2 7 .03 .285 5 .06

Benzene 71–43–2 2 7 .021 .101 5 .02

1,1-Dichloroethene 75–35–4 2 7 .024 6.533 7 .9

1,1-Dichloroethane 75–34–3 2 7 .035 4.878 -- --

1,1,1-Trichloroethane 71–55–6 2 7 .032 5.306 200 .03

Methyl tert-butyl ether 

(MTBE)

1634–04–4 1 3 .1 .1035 -- --

1,2-Dichloroethane 107–06–2 1 3 .13 .1651 5 .03

Dichlorodifluoromethane 

(Freon 112)

75–71–8 1 3 .18 E.068 1,000 

 (HBSL)

.00007

1,1,2-Trichloro-1,2,2-

trifluoroethane 

(Freon 113)

76–13–1 1 3 .038 .195 200,000

 (HBSL)

.000001

1,1,2-Trichloroethane 79–00–5 1 3 .04 E.079 5 .02

Total number of VOC detections 35

Pesticides

Alachlor ESA 140939–15–7 9 30 0.02 0.32 -- --

Fenuron 101–42–8 6 20 .018 .019 -- --

Deethylatrazine (CIAT)2 6190–65–4 6 20 .006 E.018 -- --

Atrazine 1912–24–9 5 17 .007 .034 3 0.01

Prometon 1610–18–0 4 13 .01 .019 100 

 (HBSL)

.0002

Metolachlor ESA -- 4 13 .02 .25 -- --

Alachlor ESA SA -- 4 13 .02 .05 -- --

Metolachlor OA 152019–73–3 3 10 .02 .40 -- --

Didealkyatrazine (CAAT)3 3397–62–4 2 7 .022 E.068 -- --
Methods 11

Table 1. Maximum concentrations, detection frequencies, and maximum benchmark quotients for compounds detected in source 

water from community water systems in studied aquifers in the Greater Twin Cities metropolitan area, Minnesota and Wisconsin, 2004.

—Continued

[MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contaminant Level; HBSL, Health-Based Screening 

Level; BQmax, benchmark quotient = ratio of maximum compound concentration to MCL or HBSL value; ESA, ethanesulfonic acid; SA, second amide; OA, 

oxanilic acid; E, estimated value; μg/L, micrograms per liter; --, not available; bold type indicates unregulated compound for which no Federal and (or) State 

drinking-water standards have been established]

Regulated or

unregulated

compound

Chemical 

Abstracts 

Service Registry 

number

Number of 

detections

for source 

water

Detection

frequency

(percent)

MRL 

(μg/L)

Maximum 

concentration

for source 

water

(μg/L)

USEPA MCL 

(or HBSL) 

concentration

(μg/L)

BQmax 

for source 

water

Pesticides—Continued

Bromacil 314–40–9 2 7 0.018 0.337 70 

 (HBSL)

0.005

Alachlor OA 140939–14–6 2 7 .02 .04 -- --

Sulfometuron-methyl 74222–97–2 1 3 .038 E.004 -- --

2-Hydroxyatrazine 

(OIET)4

2163–68–0 1 3 .032 E.013 70

 (HBSL)

.0002

Metolachlor 51218–45–2 1 3 .006 E.003 70

 (HBSL)

.00004

Imazethapyr 81335–77–5 1 3 .038 E.007 100 

 (HBSL)

.00007

Diuron 330–54–1 1 3 .014 .018 2 

 (HBSL)

.009

Deisopropylatrazine 

(CEAT)5

1007–28–9 1 3 .08 E.058 -- --

Total number of pesticide detections 53

Other anthropogenic organic compounds (OAOCs)

Menthol 89–78–1 6 20 0.5 E0.21 -- --

Hexahydrohexamethylcyclopentabenzopyran 

(HHCB)

1222–05–5 5 17 .5 E.005 -- --

Tributyl phosphate 126–73–8 4 13 .5 E.065 -- --

Methyl salicylate 119–36–8 3 10 .5 E.11 -- --

Triphenyl phosphate 115–86–6 1 3 E.002 -- --

Acetyl hexamethyl 

tetrahydronaphthalene 

(AHTN)

21145–77–7 1 3 .5 E.036 -- --

Octylphenol, (monoethoxy)26636–32–8 1 3 1 E.11 -- --

2,6-Dimethylnaphthalene 581–42–0 1 3 .5 E.003 -- --

Total number of OAOC detections 22

Total number of detections for all compounds 110

1

1998 Final Rule for Disinfectants and Disinfection By-products: The total for trihalomethanes is 80 micrograms per liter.

2

CIAT = 2-Chloro-4-isopropylamino-6-amino-s-triazine.

3

CAAT = Chlorodiamino-s-triazine.

4

OIET = 2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine.

5

CEAT = 2-Chloro-6-ethylamino-4-amino-s-triazine.
12 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Table 2. Maximum concentrations, detection frequencies, and maximum benchmark quotients for compounds detected in sourcewater wells and in associated finished water from community water systems in studied aquifers in the Greater Twin Cities metropolitan 

area, Minnesota and Wisconsin, 2005.—Continued

[MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contaminant Level; HBSL, Health-Based Screening Level; 

BQmax, benchmark quotient = ratio of maximum compound concentration to MCL or HBSL value; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic 

acid; E, estimated value; μg/L, micrograms per liter; --, not available; bold type indicates unregulated compound for which no Federal and (or) State drinkingwater standards have been established]

Regulated or 

unregulated

compound

Chemical 

Abstracts 

Service 

Registry 

Number 

Number of 

detections 

for source 

water 

out of 15 

samples

Number of 

detections 

for finished

water 

out of 14 

samples

MRL 

(μg/L)

Maximum 

concentration for 

source 

water

 (μg/L)

Maximum 

concentration for 

finished 

water 

 (μg/L)

USEPA 

MCL 

(or HBSL) 

(μg/L)

BQmax 

for 

source 

water

BQmax

for 

finished 

water

Volatile organic compounds (VOCs)

Trichloroethene 79–01–6 4 4 0.038 64 0.63 5 10 0.13

cis-1,2-Dichloroethene 156–59–2 4 4 .024 2.4 1.8 70 .03 .026

trans-1,2-Dichloroethene 156–60–5 3 3 .032 .18 .15 100 .002 .002

Chloroform 67–66–3 1 4 .024 E.069 1.8 180 .001 .002

Perchloroethene 127–18–4 2 2 .03 E.14 E.092 5 .02 .018

Benzene 71–43–2 3 1 .021 .13 .12 5 .03 .024

1,1-Dichloroethane 75–34–3 2 2 .035 5.1 .14 -- -- --

1,1-Dichloroethene 75–35–4 2 1 .024 7.0 E.018 7 1 .003

Bromoform 75–25–2 0 4 .1 -- E8.9 180 -- .11

Dibromochloromethane 124–48–1 0 3 .1 -- .84 180 -- .011

Bromodichloromethane 75–27–4 0 3 .028 -- 1.2 180 -- .010

Chloromethane 74–87–3 0 1 .17 -- E.15 30

 (HBSL)

-- .005

Vinyl chloride 75–01–4 1 0 .08 .39 -- 2 .2 --

Methyl tert-butyl ether 1634–04–4 1 0 .1 .10 -- -- -- --

Dichlorodifluoromethane 

(Freon-112)

75–71–8 1 0 .18 E.050 -- 1,000 

 (HBSL)

.00005 --

1,1,2-Trichloro-1,2,2-

trifluoroethane 

(Freon-113)

76–13–1 1 0 .038 E.18 -- 200,000 

 (HBSL)

.000001 --

1,1,1-Trichloroethane 71–55–6 1 0 .032 5.1 -- 200 .03 --

Total number of VOC detections 26 32

Pesticides

Alachlor ESA 140939–15–7 6 5 0.02 0.54 0.53 -- -- --

Metolachlor ESA -- 5 4 .02 .14 .23 -- -- --

Atrazine 1912–24–9 5 3 .007 .05 .047 3 0.02 0.02

Metolachlor OA 152019–73–3 3 3 .02 .41 .62 -- -- --

Alachlor OA 140939–14–6 3 3 .02 .14 .32 -- -- --

Deethylatrazine (CIAT)2 6190–65–4 4 2 .006 .041 .033 -- -- --

3-Ketocarbofuran 16709–30–1 3 2 .02 E.25 E.25 -- -- --

Metsulfuron methyl 74223–64–6 2 2 .025 E.07 E.07 2,000 

 (HBSL)

.00004 .00004

Alachlor ESA SA -- 3 1 .02 .13 .21 -- -- --

Deisopropylatrazine 

(CEAT)3 

1007–28–9 2 2 .08 E.052 E.006 -- -- --

Acetochlor ESA 187011–11–3 2 1 .02 .04 .02 -- -- --
Methods 13

Table 2. Maximum concentrations, detection frequencies, and maximum benchmark quotients for compounds detected in sourcewater wells and in associated finished water from community water systems in studied aquifers in the Greater Twin Cities metropolitan 

area, Minnesota and Wisconsin, 2005.—Continued

[MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contaminant Level; HBSL, Health-Based Screening Level; 

BQmax, benchmark quotient = ratio of maximum compound concentration to MCL or HBSL value; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic 

acid; E, estimated value; μg/L, micrograms per liter; --, not available; bold type indicates unregulated compound for which no Federal and (or) State drinkingwater standards have been established]

Regulated or 

unregulated

compound

Chemical 

Abstracts 

Service 

Registry 

Number 

Number of 

detections 

for source 

water 

out of 15 

samples

Number of 

detections 

for finished

water 

out of 14 

samples

MRL 

(μg/L)

Maximum 

concentration for 

source 

water

 (μg/L)

Maximum 

concentration for 

finished 

water 

 (μg/L)

USEPA 

MCL 

(or HBSL) 

(μg/L)

BQmax 

for 

source 

water

BQmax

for 

finished 

water

Pesticides—Continued

Prometon 1610–18–0 1 1 0.01 E0.009 E0.008 100 

 (HBSL)

0.00009 0.00008

Acetochlor OA -- 0 1 .02 -- .04 -- -- --

N(Ethmethphen)ox ESA -- 0 1 .02 -- .02 -- -- --

Flufenacet 142459–58–3 2 0 .02 .02 -- -- -- --

Bromacil 314–40–9 2 0 .018 .258 -- 70 

 (HBSL)

.004 --

Oryzalin 19044–88–3 1 0 .012 E.01 -- 4 

 (HBSL)

.002 --

Metolachlor 51218–45–2 1 0 .006 .02 -- 70 

 (HBSL)

.0003 --

Hexazinone 51235–04–2 1 0 .0129 .017 -- 400 

 (HBSL)

.00004 --

Fenuron 101–42–8 1 0 .018 .019 -- -- -- --

Didealkyatrazine (CAAT)4 3397–62–4 1 0 .022 E.052 -- -- -- --

Total number of pesticide detections 48 31

Other anthropogenic organic compounds (OAOCs)

Caffeine 58–08–2 2 2 0.012 E0.097 E0.065 -- -- --

Methyl salicylate 119–36–8 1 1 .5 E.014 E.011 -- -- --

Triphenyl phosphate 115–86–6 0 1 .5 -- E.017 -- -- --

Menthol 89–78–1 0 1 .5 -- E.033 -- -- --

Tributyl phosphate 126–73–8 3 0 .5 E.13 -- -- -- --

Tris(2-chloroethyl) phosphate (TCEP)115–96–8 1 0 .5 E.04 -- -- -- --

Tris(2-butoxyethyl) phosphate78–51–3 1 0 .5 E.18 -- -- -- --

Octylphenol, (monoethoxy)26636–32–8 1 0 1 E.066 -- -- -- --

HHCB5 1222–05–5 1 0 .5 E.012 -- -- -- --

Total number of OAOC detections 10 5

Total detections for all compounds 84 68

1

1998 Final Rule for Disinfectants and Disinfection By-products: The total for trihalomethanes is 80 micrograms per liter.

2

CIAT = 2-Chloro-4-isopropylamino-6-amino-s-triazine.

3

CEAT = 2-Chloro-6-ethylamino-4-amino-s-triazine.

4

CAAT = Chlorodiamino-s-triazine.

5

HHCB = Hexahydrohexamethylcyclopentabenzopyran.
14 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Environmental-sample data were compared to qualityassurance data to document sample integrity. The effectiveness 

of cleaning methods of sampling equipment was quantified 

using blank samples. Replicate samples were collected from 

selected wells to verify the stability of water quality and 

efficacy of purging procedures, to assess the reproducibility of 

sampling and analytical methods, and to quantify the resulting 

variability. Spiked samples were submitted for selected VOC 

and pesticide samples to measure changes in concentrations 

during shipment and to check analytical recoveries from the 

sample matrix.

Eight quality-assurance/quality-control (QA/QC) samples 

were collected during this study. These samples include two 

field-equipment blank, two field-spiked, and three replicate 

samples. Standard NAWQA QA/QC procedures are described 

in Koterba and others (1995). Field-equipment blanks consisted of three types of water prepared and tested to be free of 

organic and inorganic compounds that were pumped through 

the sampling systems. Field-equipment blanks were used to 

determine whether cleaning procedures prevented contamination between sites and to ensure that field methods, sample 

shipment, and laboratory procedures had not contaminated 

samples. The field-equipment blanks for pesticides, VOCs, 

and other AOCs were collected after a full cleaning and 

methanol and de-ionized water rinses of the equipment and 

sampling lines. A few compounds were detected at concentrations below reporting-level concentrations in blank QA/QC 

samples. These blank-sample concentrations were much 

less than those generally reported in ground-water samples, 

indicating a low likelihood of cross-contamination of groundwater samples. When ground-water samples were collected 

from spigots located near the well prior to any water treatment, 

large volumes (typically greater than 30 gal) of water were 

passed through the sampling system prior to blank-sample 

collection, which substantially minimizes the possibility of 

contamination to samples by the sampling equipment. 

Pervasive detection of compounds in field-equipment 

blanks processed as part of this study, as well as from other 

SWQAs conducted across the Nation, resulted in the removal 

of all data for 7 of the 265 compounds. Specifically, data 

for phenol, N,N-diethy-meta-toluamide (DEET), benzophenone, 4-nonylphenol, isophorone, acetone, and toluene were 

removed from inclusion in this report. In addition, data for 

caffeine and p-cresol were censored to their highest blank concentration of 0.012 μg/L and 0.013 μg/L, respectively. Therefore, only concentrations greater than these levels are reported.

Field-spiked samples were used to assess the recovery 

bias and precision or variability in recoveries of pesticides 

and VOCs. Field-spiked samples were submitted for four 

schedules (groups of associated constituents) analyzed by the 

NWQL during this study. One spike each was submitted for 

schedules 1433 (wastewater compounds), 2003 (triazine and 

related pesticides with degradates), 2020 (VOCs), and 2060 

(polar pesticides with metabolites). Review of the results 

showed that most of the analyses provided good results, 

although certain constituents showed poor recovery. 

The recoveries of spiked concentrations of wastewater 

Consumer Confidence Reports and 

Source Water-Quality Assessments

Since 1999, the U.S. Environmental Protection 

Agency (USEPA) has required water suppliers to provide annual drinking-water quality reports called Consumer Confidence Reports (CCRs) to their customers 

(http://www.epa.gov/safewater/ccr/). CCRs are the 

centerpiece of the right-to-know provisions of the 1996 

Amendments to the Safe Drinking Water Act. Each 

CCR provides consumers with fundamental information about their drinking water including 

(1) the source of the drinking water, (2) a brief summary of the susceptibility to contamination of the 

local drinking-water source, (3) the concentrations (or 

range of concentrations) of any selected contaminants 

found in local drinking water, as well as their USEPA 

Maximum Contaminant Levels (MCLs), which are 

legally enforceable drinking-water standards and are 

the highest allowed concentrations of contaminants in 

drinking water, for comparison, and (4) phone numbers 

for additional sources of information.

Information in CCRs is specific to a particular 

water utility. Water utilities analyze finished-water 

samples primarily for regulated contaminants (that is, 

those with MCLs) using USEPA analytical methods 

for the purpose of compliance monitoring. In contrast, 

Source Water-Quality Assessments (SWQAs) performed by the USGS are not conducted for compliance 

monitoring and encompass data from multiple water 

utilities spatially distributed across the Nation. As part 

of SWQAs, both source- and finished-water samples 

are analyzed using USGS analytical methods, where 

source water is the untreated (ambient) water collected at the surface-water intake or supply well prior 

to water treatment and finished water is the treated 

water sampled prior to entering the distribution system. 

USGS analytical methods used in SWQAs typically 

have lower analytical reporting levels than those used 

in compliance monitoring; contaminant detection 

frequencies reported in SWQA reports, therefore, 

may be higher than detection frequencies for the same 

contaminants reported in CCRs. In SWQAs, concentrations of regulated and unregulated contaminants in 

source and finished water are compared to MCLs and 

Health-Based Screening Levels (HBSLs). HBSLs are 

estimates of concentrations of contaminants in water 

that may be of human-health concern and are consistent with USEPA Office of Water methodologies 

for setting nonenforceable drinking-water guideline 

values. HBSLs are not legally enforceable regulatory 

standards, and water utilities are not required to compare contaminant monitoring results to HBSLs. 
Anthropogenic Organic Compounds in Ground Water and Finished Water of Community Supply Wells 15

compounds generally were within 20 percent of the target 

concentration. Five of the spiked compounds analyzed had 

concentrations less than one-half or more than twice the target 

concentration, and dichlorvos was not detected. The recoveries of spiked samples for schedule 2003 generally were within 

20 percent of the target concentration. However, 22 of the 

recovered concentrations were less than one-half of the spiked 

target concentration, and the insecticide phosmet and its oxon 

degradate were not detected. VOCs recovered from spiked 

samples showed some problems in their recoveries. Of the 80 

VOCs spiked and analyzed, 52 were detected at less than onehalf or more than twice the target concentration. Because most 

recoveries were below the target concentrations and surrogate 

recoveries ranged from 94 to 106 percent, it is suspected that 

spiked compounds may have been lost during the field-spiking 

procedure. Schedule 2060, polar pesticides and metabolites, 

showed spike recoveries close to the expected values, with 

only 6 of the 61 constituents detected at less than one-half of 

the target concentration.

The mean recoveries for the 2060 surrogates (diazinond10, a-HCH-d6, and terbuthylazine) ranged from 103 to 

133 percent. Mean recoveries in VOC spiked samples ranged 

from 69.3 to 115 percent. Mean VOC surrogate recoveries 

ranged from 77.7 to 111 percent for 1,2-dichloroethane d-4, 

toluene d-8, and p-bromofluorobenzene. Spike and surrogate 

recoveries for both pesticides and VOCs generally were within 

acceptable ranges. Concentrations of pesticides or VOCs in 

the environmental samples were not adjusted for surrogate 

recoveries.

Replicate samples were collected sequentially with 

environmental samples and both were analyzed for the same 

groups of compounds. Replicate samples determine the 

sample variability resulting from sample collection and laboratory analysis. The differences in concentrations between the 

environmental sample and replicate sample for these constituents were 0.001 μg/L or less for pesticides, 0.1 μg/L or less for 

VOCs, and 0.9 μg/L or less for other AOCs, which were all 

qualified as estimated.

Anthropogenic Organic Compounds in 

Ground Water and Finished Water of 

Community Supply Wells

SWQAs were conducted for the unconfined parts of the 

glacial and Prairie du Chien-Jordan aquifers. The first phase 

during 2004 measured the concentrations of 265 AOCs (258 

are included in this report) in source water from 30 wells completed in the two aquifers underlying TCMA. In the second 

phase, 15 of the original 30 CWS wells, those with the greatest number of AOC detections, were re-sampled along with 

finished water from 14 associated CWS wells. Water-quality 

results from source-water samples were compared among 

wells completed in the two aquifers to characterize differences 

between the aquifers.

Anthropogenic Organic Compounds in Ground 

Water Used as Source Water for Community 

Supply Wells

A total of 40 of the 258 individual AOCs (Appendixes 1, 

2, and 3) were detected (15 VOCs, 17 pesticides, and 8 other 

AOCs) in phase-1 samples collected during November and 

December 2004 (table 1, figs. 7 and 8). The most frequently 

occurring AOCs detected, those detected in 10 percent or more 

of the source-water samples, were (table 1): alachlor ethanesulfonic acid (ESA) (30 percent), cis-1-2-dichloroethene 

(23 percent), menthol (20 percent), fenuron (20 percent), 

deethylatrazine (CIAT) (20 percent), trichloroethene 

(17 percent), atrazine (17 percent), hexahydrohexamethylcyclopentabenzopyran (HHCB) (17 percent), prometon 

(13 percent), metolachlor ESA (13 percent), alachlor ESA second amide (SA) (13 percent), tributyl phosphate (13 percent), 

methyl salicylate (10 percent), metolachlor oxanilic acid (OA) 

(10 percent), chloroform (10 percent), and trans1,2-dichloroethene (10 percent). Samples generally contained 

a mixture of AOC compounds (average of three compounds 

per sample), and at least one AOC was detected in 83 percent 

of the samples.

Concentrations of AOCs detected in source waters generally were low (defined in this report as concentrations less than 

1.0 μg/L). Human-health benchmarks were available for 20 of 

the 40 detected compounds. For most of these AOC compounds, concentrations from untreated source-water samples 

were several orders of magnitude less than their human-health 

benchmark standards. Benchmarks include USEPA MCLs and 

USGS HBSLs. The human-health relevance of the remaining 

detected, but unregulated, contaminants cannot be evaluated 

because human-health toxicity information is not available. 

Because compounds with established benchmarks typically 

were detected at concentrations that were several orders of 

magnitude less than their established benchmark standards, 

additional monitoring for those compounds may not be warranted. However, additional monitoring for frequently occurring AOCs without established benchmark standards may 

be warranted to better understand their spatial and temporal 

distribution, as well as sources, transport, and fate and the 

synergetic effects of mixtures of compounds detected. 

When comparing analytical results among different 

AOCs, it is important to consider the analytical reporting level 

of each AOC. For example, an AOC with a lower reporting 

level may be expected to be detected more frequently than 

an AOC with a higher reporting level. A true comparison is 

possible only when comparing individual compounds analyzed 

using the same analytical method (same reporting level). For 

the purposes of this report, comparisons are made among 

AOCs, regardless of varying reporting levels (Appendixes 1, 

2, and 3) to characterize general occurrence rates and similarities, or the lack thereof, between source water and finished 

waters. 
16 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Figure 7. Anthropogenic organic compound concentrations, number of detections, and benchmark quotient values for source-water 

samples from the study for (A) volatile organic compounds, (B) pesticides, and (C) other anthropogenic organic compounds from 30 

source-water wells in glacial aquifer and unconfined part of Prairie du Chien-Joran aquifer (see table 1), 2004. 

A

B

C

[Bold type indicates an unregulated compound; benchmark quotient value is the ratio of the detected 

concentration of a particular compound to its Maximum Contaminant Level (regulated compounds) 

or Health-Based Screening Level (unregulated compounds) (U.S. Environmental Protection Agency, 2002)]

BENCHMARK QUOTIENT VALUE OF 0.1—

 Values equal to or greater than may 

 warrant inclusion of the compound in 

 a low-concentration, trends-monitoring 

 program

BENCHMARK QUOTIENT VALUE OF 1.0—

 Values greater than this line indicates 

 concentrations of potential human-health 

 concern

EXPLANATION

Figure 7. Anthropogenic organic compound concentrations, number of detections, and benchmark quotient values for water 

samples from the study (A) volatile organic compounds, (B) pesticides, and (C) other anthropogenic organic compounds from 

30 source-water wells in glacial aquifer and in unconfined part of Prairie du Chien-Jordan aquifer (see table 1), 2004.

NUMBER OF DETECTIONS

9

6

6

5

4

4

4

3

2

2

2

1

1

1

1

1

1

Alachlor ESA

Fenuron

Deethylatrazine

Atrazine

Prometon

Metolachlor ESA

Alachlor ESA SA

Metolachlor OA

Didealkyatrazine

Bromacil

Alachlor OA

Sulfometuron-methyl

2-Hydroxyatrazine

Metolachlor

Imazethapyr

Diuron

Deisopropylatrazine

CONCENTRATION, IN MICROGRAMS PER LITER

NUMBER OF DETECTIONS

BENCHMARK QUOTIENT VALUE

6

5

4

3

1

1

1

1

 1 10 10 100 -7 10-6 10-5 10-4 10-3 10-2 10-1

A

cis-1,2-Dichloroethene

Trichloroethene

Chloroform

trans-1,2-Dichloroethene

Vinyl chloride

Perchloroethene

Benzene

1,1-Dichloroethene

1,1-Dichloroethane

1,1,1-Trichloroethane

Methyl tert-buyl ether

1,2-Dichloroethane

Freon 112

Freon 113

1,1,2-Trichloroethane

NUMBER OF DETECTIONS

7

5

3

3

2

2

2

2

2

2

1

1

1

1

1

10-4 10-3 10-2 10-1 1 10 100

Menthol

HHCB

Tributyl phosphate

Methyl salicylate

Triphenyl phosphate

AHTN

Monoethoxyoctylphenol

2,6-Dimethylnaphthalene
Anthropogenic Organic Compounds in Ground Water and Finished Water of Community Supply Wells 17

Volatile Organic Compounds

VOCs are carbon-containing compounds that readily 

evaporate at normal temperatures and pressures. VOCs are 

present in many commercial products including gasoline, 

paints, adhesives, solvents, wood preservatives, dry-cleaning 

agents, pesticides, cosmetics, correction fluids, and refrigerants. VOCs may leach to ground water from spills and leaks 

at or near land surface, from atmospheric dispersion to ground 

water, and through recharge of rainwater that contains VOCs 

sorbed from the atmosphere. Fifteen VOCs were detected in 

source-water samples (table 1, fig. 7). The compounds 

cis-1,2-dichloroethene, trichloroethene, chloroform, and 

trans-1,2-dichloroethene were the most frequently detected 

VOCs, each detected in 10 percent or more of the samples. 

These compounds may enter the hydrologic system from air 

emissions, discharges to surface water, and releases to land 

and from a variety of other anthropogenic sources (Ivahnenko 

and Barbash, 2004). Other frequently detected VOCs included 

vinyl chloride, perchloroethene, benzene, 1,1-dichloroethene, 

1,1-dichloroethane, and 1,1,1-trichloroethane.

Chloroform is one of many disinfection by-products 

(DBPs) typically produced during the disinfection of drinking 

water and wastewater. DBPs may enter the ground water from 

recharge of treated wastewater, chlorinated or reclaimed water 

used to irrigate lawns and gardens, leakage from distribution 

lines for treated water and wastewater, spas, pools, leachate 

from septic-system drainfields, air emissions, and releases to 

the atmosphere (Thiros, 2000; Ivahnenko and Barbash, 2004). 

Detection of chloroform in ground water, along with other 

associated DBPs, provides a means for distinguishing between 

the inputs of chlorinated water and inputs of other chloroform 

sources to the environment (Ivahnenko and Barbash, 2004). 

VOC concentrations in source water generally were less 

than human-health benchmarks (table 1, fig. 7). Of the 

15 VOCs detected, human-health benchmarks were available 

for 13 compounds. BQmax values for these 13 compounds 

typically were several orders of magnitude less than 1.0, and 

three were greater than the 0.1 criteria (table 1, fig. 7). 

Trichloroethene, vinyl chloride, and 1,1-dichloroethene in one 

well likely are related to a known source of VOC contamination; the Twin Cities Army Ammunition Plant (TCAAP) 

located in Arden Hills, Minn. (City of New Brighton, 2008). 

Water from that well is treated to reduce VOC concentrations 

prior to being used as a source of public supply.

Results indicate that VOCs are of possible concern in 

specific areas and may warrant consideration for continued 

low-concentration trends monitoring. An MCL or HBSL has 

Figure 8. Concentrations of all detected compounds in source-water samples from study area, 2004. CONCENTRATION, IN MICROGRAMS PER LITER

100

10

1

0.1

0.01

0.001

VOLATILE ORGANIC

COMPOUNDS

PESTICIDES ANTHROPOGENIC ORGANIC

COMPOUNDS

Figure 8. Concentrations of all detected compounds in water samples from study area, 2004.

Number of values

Upper outside

Upper adjacent

75th percentile

Median

25th percentile

Lower adjacent

Prairie du Chien-Jordan aquifer Glacial aquifer

EXPLANATION

5

x

x

x

 5 30 35 18 7 15 
18 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Relating Study Results to Human-Health Benchmarks, Consumer 

Confidence Reports, and Source Water-Quality Assessments

Results from this study were compared to U.S. Environmental Protection 

Agency (USEPA) Maximum Contaminant Levels (MCLs) and U.S. Geological 

Survey (USGS) Health-Based Screening Levels (HBSLs) to evaluate the relevance 

of the findings to human health (Appendix 4).

The USGS began an interagency pilot effort in 1998 to communicate the 

significance of water-quality findings of the NAWQA Program in a human-health 

context. Historically, the USGS has assessed water-quality conditions by comparing 

water concentration data with human-health benchmarks such as established Federal or State drinking-water standards and guidelines. The drinking-water standards 

for regulated compounds are called Maximum Contaminant Levels (MCLs), which 

protect drinking-water quality by limiting the concentration of specific compounds 

delivered to any user of a public water system that can adversely affect public health 

(U.S. Environmental Protection Agency, 2002). However, drinking-water standards 

and guidelines do not exist for nearly one-half of the compounds analyzed by the 

NAWQA Program and other USGS studies. To provide a more complete understanding of the significance of water-quality data collected, existing Federal drinkingwater standards and guidelines are supplemented by HBSL concentrations or ranges 

calculated for unregulated compounds (compounds without Federal drinking-water 

standards) monitored by the NAWQA Program using an approach that was developed collaboratively by the USGS, USEPA, New Jersey Department of Environmental Protection (NJDEP), and Oregon Health & Science University (OHSU) (Toccalino and others, 2003, 2004).

HBSLs are not regulatory standards and are not enforceable, and water systems 

are not required to monitor for any unregulated compounds for which HBSLs have 

been developed. HBSLs are estimates of benchmark concentrations that can be used 

as thresholds against which contaminant concentrations in water can be compared to 

evaluate water-quality data in a human-health context. HBSLs can be used as planning tools to help prioritize contaminants that may merit further study or monitoring 

and to provide an early indication of contaminant concentrations of human-health 

concern in water resources (Toccalino and others, 2005). 

Appendix 4 provides descriptions of the human-health benchmarks that were 

used in this study. 

To aid in evaluating water-quality data in the context of human health, benchmark quotient (BQ) values were calculated. A BQ value is the ratio of a measured 

concentration of a detected compound to its MCL (for a regulated compound) or 

HBSL (for an unregulated compound). For this study, the maximum concentration detected for each compound was used to calculate this ratio, called BQmax. 

A BQmax value greater than or equal to 1.0 was used to identify concentrations of 

potential human-health concern (hereafter referred to as concentrations of potential 

concern). A BQmax value greater than or equal to 0.1 is used to identify compounds 

that may warrant inclusion in a low-concentration, trends-monitoring program; 

especially frequently occurring compounds (in this report, an anthropogenic organic 

compound detected in 10 percent or more of samples) also may warrant inclusion in 

such a monitoring program. Such monitoring can provide an early indication of contaminant levels that approach human-health benchmarks, and consequently, concentrations of concern (or potential concern for those compounds with HBSLs).
Comparison of Source and Finished Water Ground Water 19

not been developed for methyl tert-butyl ether (MTBE) and 

1,1-dichloroethane, and additional monitoring of these compounds may be warranted because they often were detected. 

VOCs were more frequently detected, and detected at higher 

concentrations, in the Prairie du Chien-Jordan aquifer compared to the glacial aquifer (fig. 8). 

Pesticide Compounds

Pesticide compounds are used to control plants, insects, 

and other pests. They are applied primarily to cropland in rural 

areas but also for lawns, rights-of-way, and gardens in urban 

areas. Seventeen pesticide compounds were detected in source 

water (table 1, fig. 7). The number of individual pesticides 

detected was roughly the same as for VOCs. However, pesticides were detected more frequently (53 pesticide detections 

compared to 35 VOC detections, table 1). Pesticides generally 

were detected at lower concentrations than VOCs (table 1, 

fig. 7).

Of the pesticide compounds detected, most were triazineparent and alachlor-parent pesticides and their breakdown 

products. Several reasons exist for the higher detection 

frequencies for triazine-parent and alachlor-parent compounds 

and their breakdown products compared to other pesticides. 

These reasons include widespread use, high mobility in sandy 

soils, and persistence in ground water (Kruger and others, 

1995; Barbash and others, 1999). The half-life for atrazine in 

soils can be more than 100 days, and in ground water, atrazine 

and deethylatrazine can persist for almost 6 years and more 

than 25 years, respectively (Denver and Sandstrom, 1991; 

Gaus, 2000).

Concentrations of pesticides detected in the source water 

generally were low (less than 0.1 μg/L) (table 1, figs. 7 and 8). 

Of the 17 pesticides detected, human-health benchmarks were 

available for seven compounds. BQmax values for these seven 

pesticides typically were several orders of magnitude less than 

1.0 and none were greater than 0.1 (table 1, fig. 7). Humanhealth benchmarks were not available for many of the pesticide compounds, and additional monitoring may be warranted 

on the basis of their frequencies of occurrence. Pesticides 

were more frequently detected, and detected at higher concentrations, in the glacial aquifer as compared to the Prairie 

du Chien-Jordan aquifer (fig. 8). This probably is because 

pesticides have widespread use on the landscape and are more 

easily transported to the shallow glacial aquifer.

Other Anthropogenic Organic Compounds

Eight other AOCs were detected in source water during 

this study. Of those, menthol, HHCB, tributyl phosphate, and 

methyl salicylate were each detected in 10 percent or more of 

the samples. Concentrations generally were low (0.21 μg/L 

or less) (table 1, fig. 7). A human-health benchmark was not 

available for any of the eight other AOCs detected. Additional 

monitoring may be warranted for several of the compounds 

detected based on their frequent occurrence. Other AOCs 

were detected more frequently in the Prairie du Chien-Jordan 

aquifer but concentrations were higher in the glacial aquifer 

(fig. 8). 

Comparison of Source and Finished 

Ground Water

In the second phase of sampling, 15 of the original 

30 CWS sampled wells (seven in the glacial aquifer and eight 

in the Prairie du Chien–Jordan aquifer, figs. 4 and 5), those 

with the greatest number of AOC detections during the first 

phase, were re-sampled in August 2005. In addition, 14 corresponding finished-water samples were collected. Fourteen 

finished-water wells were sampled instead of 15 because two 

of the sampled CWS wells had potential to contain blended 

water. Only one-half as many wells were resampled during the 

second phase, resulting in a smaller number of samples. Consequently, the characterization of the occurrence of these compounds in source water and finished water is less well defined, 

so only a general comparison of these compounds in source 

water and finished water can be presented. In addition, of the 

14 finished-water sampling sites, nine had potential to contain 

water that could be blended with water from one or more other 

wells. Five sites did not have the potential for blended water. 

The CWS wells and associated finished water were not 

all sampled for the same AOCs. Five of the source-water 

CWS wells and associated finished water pairs were analyzed 

for VOCs, 6 pairs were analyzed for pesticides, and 12 pairs 

were sampled for other AOCs. Concentrations of each AOC 

detected in source water and the associated blended or nonblended finished water are presented in Appendix 5.

Volatile Organic Compounds

Five of the 30 original CWS wells were analyzed for 

VOCs. Seventeen VOCs were detected in either source water 

or finished water. Specifically, 13 and 12 VOC compounds 

were detected in source-water and finished-water samples, 

respectively (table 2, fig. 9). Four of the VOCs detected in 

finished water were common chlorination DBPs. For example, 

chloroform was detected in one source-water sample and in 

four finished-water samples. The DBPs typically detected 

in finished-water samples, but not in source-water samples, 

included bromodichloromethane, bromoform, and dibromochloromethane. In addition, DBP concentrations were 

greater in finished-water samples than in source-water samples 

in all but one case (fig. 9, Appendix 5). Most of the VOCs, 

except for the DBPs, were detected more frequently in sourcewater samples than in finished-water samples. 

Maximum concentrations of detected VOCs ranged from 

E0.050 to 64 μg/L in source water and from E0.018 to 

E8.9 μg/L in finished water (table 2). Concentrations of most 
20 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

VOCs detected in either source water or finished water were 

well below their human-health benchmarks, and as such, 

BQmax values typically were several orders of magnitude 

less than 1.0 (table 2, fig. 9). BQmax values for 1,1-dichloroethene, trichloroethene, and vinyl chloride were 0.10 or greater 

in samples of source water, and BQmax values for bromoform 

and trichloroethene were greater than 0.10 in some samples 

of finished water. Most of these detections are associated with 

one well that is part of a gradient-control system and a watertreatment system related to a known source of contamination 

(City of New Brighton, 2008). Water from wells in these 

systems is treated and routinely tested by the utilities prior to 

discharge to the municipal-supply distribution system. 

The DBPs bromoform and chloroform are routinely 

analyzed by the NWQL as part of the suite of VOCs. When 

samples of treated water are collected, they are treated with a 

dechlorination reagent to deactivate free bromine and chlorine, 

effectively stopping the formation of DBPs in the collected 

sample. Although bromine and chlorine may continue forming DBPs after collection and processing, this does not explain 

the large bromoform concentration (E8.9 μg/L) in the VOC 

sample shown in table 2. A similarly high bromoform concentration was measured in the replicate sample collected 

during the environmental sampling. DBPs also were present in 

other VOC-suite analyses of source water, but at much lower 

concentrations. 

Results indicate that monitoring VOCs in source water 

does not necessarily identify the potential occurrence of VOCs 

in finished water. Some VOCs are removed during water treatment and some appear to be introduced to finished water as a 

result of disinfection. Eight of the 17 VOCs were detected in 

either the source-water samples or finished-water samples but 

not both. VOCs present in source-water samples, but not in 

finished-water samples, may be diluted to undetectable concentrations in the finished water by blending with other source 

water. Similarly, VOCs present in the finished-water samples, 

but not the source-water samples, may have been present in 

the source water from other wells or may be the result of disinfection processes.

Pesticide Compounds

Six of the original 30 CWS wells and six associated finished waters were re-sampled for pesticides in August 2005. 

Of the six finished waters sampled for pesticides, five potentially contained water blended from other wells. A total of 

21 individual pesticide compounds were detected in either the 

source water or finished water. The most frequently detected 

compounds in both the source and the finished water were 

atrazine and breakdown products of triazine-based herbicides 

as well as breakdown products of alachlor and metolachlor. 

Generally, pesticides detected in source-water samples also 

were detected in corresponding finished water (table 2). 

However, seven pesticide compounds were detected in sourcewater samples but not in finished-water samples, and two 

compounds were detected in finished-water samples but not in 

source-water samples. 

Maximum concentrations of detected pesticides in 

source-water samples and in finished-water samples were 

similar and low, ranging from E0.009 to 0.54 μg/L in source 

water and from E0.006 to 0.62 μg/L in finished water (table 2, 

fig. 10). Concentrations of seven of the pesticides detected in 

source-water samples or in finished-water samples could be 

compared to human-health benchmarks, and BQmax values 

were several orders of magnitude less than 0.1. HBSLs were 

not available for many of the pesticide compounds, and the 

occurrence of these unregulated compounds in both source and 

finished water may warrant additional monitoring. 

Results indicate that monitoring for pesticides in source 

water generally helps to identify the potential occurrence of 

pesticides in finished water and that water treatment used by 

the CWSs participating in this study does not substantially 

remove many pesticide compounds from finished water. 

However, these systems are not designed to remove these 

compounds, and blending of source waters makes it difficult 

to characterize how representative source water is of finished 

water. Pesticides present in source-water samples, but not in 

finished-water samples, may be diluted to undetectable concentrations in the finished water by blending with other source 

waters. Similarly, pesticide compounds present in the finishedwater samples, but not the source-water samples, may have 

been present in the source water from other wells.

Other Anthropogenic Organic Compounds 

Twelve of the 30 original CWS wells and associated finished water were re-sampled for other AOCs in August 2005. 

Seven of the finished-water samples could have contained 

water blended from more that one well (these samples do not 

sum to 12 because one of the finished-water samples could 

contain water from two source-water wells). A total of nine 

other AOCs were detected in source-water samples or in 

finished-water samples; however, none were detected frequently (table 2, fig. 11). Caffeine occurred most frequently 

but only in two of the source-water and finished-water 

samples. Seven compounds were detected in source-water 

samples, and four compounds were detected in finished-water 

samples. Five compounds were detected in only source-water 

samples, and two compounds were detected only in finishedwater samples. Two compounds were detected in both sourcewater samples and finished-water samples (table 2, fig. 11, 

and Appendix 5).

Concentrations of other detected AOCs generally were 

low, with maximum concentrations ranging from E0.012 to 

E0.18 μg/L in the source water and from E0.011 to 

E0.065 μg/L in finished water (table 2, fig. 11). A humanhealth benchmark was not available for any of the nine other 

AOCs detected. Additional monitoring of some compounds 

may be warranted due to their occasional detection in source 

water and in finished water (table 2, Appendix 5).
Comparison of Source and Finished Ground Water 21

Figure 9. Detected volatile organic compounds showing (A) concentrations and number of detections, and (B) benchmark quotient 

values for source and associated finished water (blended and nonblended) in samples from study area, 2005.

Compounds

detected only

in finished water—

blended and 

nonblended water 

Compounds

detected only

in finished water—

blended and 

nonblended water 

Compounds

detected only

in source water

Compounds

detected only

in source water

A Concentrations of volatile organic compounds

B Benchmark quotient values

0.0000001 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100

0.001 0.01 0.1 1 10 100

BENCHMARK QUOTIENT VALUE

CONCENTRATION, IN MICROGRAMS PER LITER

TRICHLOROETHENE (4,4)—Number of

 detections for source (4) and finished 

 water (4); bold type indicates an

 unregulated compound; underlined 

 indicates the unregulated compound 

 does not have an HBSL 

EXPLANATION

BENCHMARK QUOTIENT VALUE OF 0.1— SOURCE WATER

 Values equal to or greater than this 

 line may warrant inclusion of the 

 compound in a low-concentration, 

 trends-monitoring program

BENCHMARK QUOTIENT VALUE OF 1.0—

 Values greater than this line indicate 

 concentrations of potential human-

 health concern

FINISHED WATER

 (nonblended) 

FINISHED WATER

 (blended) 

[Benchmark quotient value is the ratio of the detected concentration of a particular compound

to its Maximum Contaminant Level, MCL; or Health-Based Screening Level, HBSL (U.S. Environmental

Protection Agency, 2002)]

Trichloroethene (4,4)

cis-1,2-Dichloroethene (4,4)

trans-1,2-Dichloroethene (3,3)

Chloroform (1,4)

Perchloroethene (2,2)

Benzene (3,1)

1,1-Dichloroethane (2,2)

1,1-Dichloroethene (2,1)

Bromoform (0,4)

Dibromochloromethane (0,3)

Bromodichloromethane (0,3)

Chloromethane (0,1)

Vinyl chloride (1,0)

Methyl tert-buyl ether (1,0)

Freon 112 (1,0)

Freon 113 (1,0)

1,1,1-Trichloroethane (1,0)

Compounds

detected in

source and

finished water

Compounds

detected in

source and

finished water

Trichloroethene (4,4)

cis-1,2-Dichloroethene (4,4)

trans-1,2-Dichloroethene (3,3)

Chloroform (1,4)

Perchloroethene (2,2)

Benzene (3,1)

1,1-Dichloroethane (2,2)

1,1-Dichloroethene (2,1)

Bromoform (0,4)

Dibromochloromethane (0,3)

Bromodichloromethane (0,3)

Chloromethane (0,1)

Vinyl chloride (1,0)

Methyl tert-buyl ether (1,0)

Freon 112 (1,0)

Freon 113 (1,0)

1,1,1-Trichloroethane (1,0)
22 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Figure 10. Detected pesticides showing (A) concentrations and number of detections, and (B) benchmark quotient values for 

source and associated finished water (blended and nonblended) in samples from study area, 2005.

BENCHMARK QUOTIENT VALUE

Compounds

detected in

source and

finished

water

Compounds

detected only

in source

water

0.001 0.01 0.1 1 10

0.00001 0.0001 0.001 0.01 0.1 1

CONCENTRATION, IN MICROGRAMS PER LITER

Compounds

detected only 

in finished 

water—

blended and 

nonblended

water 

Alachlor ESA (6,5)

Metolachlor ESA (5,4)

Atrazine (5,3)

Metolachlor OA (3,3)

Alachlor OA (3,3)

Deethylatrazine (4,2)

3-Ketocarbofuran (3,2)

Metsulfuron-methyl (2,2)

Alachlor ESA SA (3,1)

Deisopropylatrazine (2,2)

Acetochlor ESA (2,2)

Prometon (1,1)

Acetochlor OA (0,1)

N(Ethmethphen)ox ESA (0,1)

Flufenacet (2,0)

Bromacil (2,0)

Oryzalin (1,0)

Metolachlor (1,0)

Hexazinone (1,0)

Fenuron (1,0)

Didealkyatrazine (1,0)

Compounds

detected in

source and

finished

water

Compounds

detected only

in source

water

Compounds

detected only 

in finished 

water—

blended and 

nonblended

water 

ATRAZINE (5,3)—Number of compounds 

 detected for source (5) and finished-

 water (3); bold type indicates an

 unregulated compound; underlined 

 indicates the unregulated compound 

 does not have an HBSL 

EXPLANATION

BENCHMARK QUOTIENT VALUE OF 0.1— SOURCE WATER

 Values equal to or greater than this 

 line may warrant inclusion of the 

 compound in a low-concentration, 

 trends-monitoring program

BENCHMARK QUOTIENT VALUE OF 1.0—

 Values greater than this line indicate 

 concentrations of potential human-

 health concern

Benchmark quotient value of 1.0

FINISHED WATER

 (non-blended) 

FINISHED WATER

 (blended) 

[Benchmark quotient value is the ratio of the detected concentration of a particular compound

to its Maximum Contaminant Level, MCL; or Health-Based Screening Level, HBSL]

A Concentration of pesticides

B Benchmark quotient values 

Alachlor ESA (6,5)

Metolachlor ESA (5,4)

Atrazine (5,3)

Metolachlor OA (3,3)

Alachlor OA (3,3)

Deethylatrazine (4,2)

3-Ketocarbofuran (3,2)

Metsulfuron-methyl (2,2)

Alachlor ESA SA (3,1)

Deisopropylatrazine (2,2)

Acetochlor ESA (2,2)

Prometon (1,1)

Acetochlor OA (0,1)

N(Ethmethphen)ox ESA (0,1)

Flufenacet (2,0)

Bromacil (2,0)

Oryzalin (1,0)

Metolachlor (1,0)

Hexazinone (1,0)

Fenuron (1,0)

Didealkyatrazine (1,0)
Comparison of Source and Finished Ground Water 23

Figure 11. Detected other anthropogenic organic compounds showing (A) concentrations and number of detections, and (B) 

benchmark quotient values for source and associated finished-water (blended and nonblended) in samples from study area, 2005.

BENCHMARK QUOTIENT VALUE

Compounds

detected in

source and

finished

water

Compounds

detected only

in source

water

CONCENTRATION, IN MICROGRAMS PER LITER

Compounds

detected only 

in finished 

water—

non-blended

and blended

water 

Compounds

detected in

source and

finished

water

Compounds

detected only

in source

water

Compounds

detected only 

in finished 

water—

non-blended

and blended

water 

CAFFEINE (2,2)—Number of compounds 

 detected for source (2) and finished-

 water (2); bold type indicates an

 unregulated compound; underlined 

 indicates the unregulated compound 

 does not have an HBSL 

EXPLANATION

BENCHMARK QUOTIENT VALUE OF 0.1— SOURCE WATER

 Values equal to or greater than this 

 line may warrant inclusion of the 

 compound in a low-concentration, 

 trends-monitoring program

BENCHMARK QUOTIENT VALUE OF 1.0—

 Values greater than this line indicate 

 concentrations of potential human-

 health concern

FINISHED WATER

 (non-blended) 

FINISHED WATER

 (blended) 

[Benchmark quotient value is the ratio of the detected concentration of a particular compound

to its Maximum Contaminant Level, MCL; or Health-Based Screening Level, HBSL (U.S. Environmental

Protection Agency, 2002)]

A Concentrations of other anthropogenic organic compounds

B Benchmark quotient values

0.001 0.01 0.1 1 10 100

0.00001 0.0001 0.001 0.01 0.1 1 10

Caffeine (2,2)

Methyl salicylate (1,1)

Triphenyl phosphate (0,1)

Menthol (0,1)

Tributyl phosphate (3,0)

Tris(2-chloroethyl)phosphate (1,0)

Tris(2-butoxyethyl)phosphate (1,0)

Monoethoxyoctylphenol (1,0)

HHCB (1,0)

Caffeine (2,2)

Methyl salicylate (1,1)

Triphenyl phosphate (0,1)

Menthol (0,1)

Tributyl phosphate (3,0)

Tris(2-chloroethyl)phosphate (1,0)

Tris(2-butoxyethyl)phosphate (1,0)

Monoethoxyoctylphenol (1,0)

HHCB (1,0)
24 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Results indicate that additional monitoring for other 

AOCs in source water is needed to better understand their 

potential occurrence in source water and in finished water. 

Blending of source water makes it difficult to characterize how 

representative source water is of finished water. Other AOCs 

present in source-water samples, but not in finished-water 

samples, may be diluted to undetectable concentrations in the 

finished water by blending with other source water. Similarly, 

other AOC compounds present in the finished-water samples, 

but not in the source-water samples, may have been present in 

the source water from other wells.

Study Implications Related to 

Hydrogeologic Setting, Land Use, and 

Aquifer Productivity

Water-quality results were compared to characterize 

differences between the aquifers. Of the 40 AOCs detected 

(a total of 110 individual detections) in source-water samples 

during phase-1 sampling, detections were more frequent in 

samples from the Prairie du Chien-Jordan aquifer than in 

samples from the glacial aquifer (fig. 8). Concentrations of 

AOC compounds detected in the source water generally were 

less than concentrations of potential concern (BQmax values greater than or equal to 1.0). Water-quality results from 

source-water samples were compared to characterize differences between aquifers. There were 30 detections of VOCs in 

samples from the Prairie du Chien-Jordan aquifer and 

5 detections in samples from the glacial aquifer (fig. 8). Pesticide detections, however, were more frequent in samples from 

the glacial aquifer (35) than in samples from the Prairie du 

Chien-Jordan aquifer (18). Similar to results for VOCs, other 

AOCs were detected more frequently in samples from the 

Prairie du Chien-Jordan aquifer (15 times compared to 

7 times in samples from the glacial aquifer) although the 

median of the concentrations was greater in samples from the 

glacial aquifer (fig. 8). 

These data indicate that hydrogeologic and land-use 

settings, as well as the productivity of aquifers, play a role 

in the presence of AOCs in CWS wells. Greater numbers of 

compounds were detected in samples from the deeper Prairie 

du Chien-Jordan aquifer compared to samples from the glacial 

aquifer (Appendix 5). This may indicate that water pumped 

from wells in the deeper Prairie du Chien-Jordan aquifer 

integrates larger contributing areas and longer flow paths 

compared to water pumped from the glacial aquifer. In addition, fracture flow and bedrock valleys incised in the Prairie du 

Chien-Jordan aquifer and filled with transmissive glacial drift 

and fracture flow also may enhance transport of anthropogenic 

compounds in the Prairie du Chien-Jordan aquifer relative to 

the glacial aquifer. In contrast, median AOC concentrations 

were greater in samples from the glacial aquifer, possibly 

because some of these compounds, like pesticides, are used 

extensively on the land surface and have a potential to reach 

ground water through a variety of primary uses and nonpoint 

applications that exert a greater effect on shallow aquifers. 

Other AOCs, on the other hand, may have more specific 

sources and (or) pathways to enter the environment, such as 

nonpoint source contamination. 

VOCs detected in source water do not necessarily help to 

identify the potential occurrence of VOCs in finished water. 

Some VOCs are removed during water treatment, and some 

appear to be introduced to finished water as the result of 

disinfection. VOCs present in source-water samples, but not in 

finished-water samples, may be diluted to undetectable concentrations in the finished water by blending with other source 

water. Similarly, VOCs present in the finished-water samples, 

but not the source-water samples, may be present in the source 

water from other wells or may be the result of disinfection 

processes. 

Pesticide compounds detected in source-water samples 

generally were detected in corresponding finished-water 

samples (Appendix 5). Results indicate that monitoring for 

pesticides in source water helps to identify potential occurrence of pesticides in finished water and that water treatment 

may not remove many of the pesticide compounds. Blending 

of source water, however, makes it difficult to characterize 

how representative source water is of finished water. Pesticide compounds detected in source-water samples, but not in 

finished-water samples, may be diluted to undetectable concentrations in the finished water by blending with other source 

water. Similarly, pesticide compounds present in finishedwater samples, but not in source-water samples, may have 

been introduced from other wells. 

Other AOCs detected in source-water samples also generally help to identify the potential occurrence of other AOCs in 

finished-water samples and consequently that water treatment 

may not remove many of the compounds from finished water. 

Like for pesticides, blending of source water makes it difficult 

to characterize how representative source water is of finished 

water. Although HBSLs are not available for some other 

detected and unregulated AOCs, additional monitoring may be 

warranted due to their frequent occurrence in source water and 

presence in finished water. 
Summary 25

Summary

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

National Water-Quality Assessment (NAWQA) Program to 

collect and interpret water-quality information and to make 

this information available to help address and prioritize 

issues related to managing and protecting the Nation’s water 

resources. In 2001, the NAWQA Program began its second 

decade of intensive assessment activities. During its second 

decade, the NAWQA Program returned to 42 of the original river basin and aquifer study areas to build on the initial 

assessments and to establish links between sources, transport, 

and the potential effects of contaminants on humans and 

aquatic ecosystems. This was accomplished through focused 

studies. One assessment activity focused on characterizing 

the quality of major rivers and aquifers used as a source of 

supply to large community water systems (CWSs). This activity, called a Source Water-Quality Assessment (SWQA), was 

intended to complement drinking-water monitoring required 

by Federal, State, and local programs, which focused primarily 

on post-treatment compliance monitoring.

This report summarizes results from ground-water 

SWQAs of two important water-supply aquifers—the unconfined part of the glacial aquifer system and the unconfined 

part of the Prairie du Chien-Jordan aquifer system underlying 

the Greater Twin Cities metropolitan areas in Minnesota and 

Wisconsin. Ground-water SWQAs consisted of two sampling 

phases. The first phase focused on determining the occurrence 

of 265 (258 are included in this report) anthropogenic organic 

compounds (AOCs) in the source water of 30 of the largest 

producing CWS wells in the study area. Forty individual 

AOCs were detected. AOCs monitored during the first phase 

included volatile organic compounds (VOCs), pesticides, and 

other AOCs. The second phase focused on those AOCs that 

occurred most frequently during the first phase of sampling 

and characterized their occurrence in source water as well as 

in the associated finished water of 14 of the CWS wells prior 

to distribution. 

During the first phase of sampling in November and 

December 2004, concentrations of AOCs detected in the 

source water generally were low (defined in this report as 

concentrations less than 1.0 microgram per liter) and generally 

were less than human-health benchmarks, which include U.S. 

Environmental Protection Agency Maximum Contaminant 

Levels for regulated compounds and USGS Health-Based 

Screening Levels for unregulated compounds. Fifteen VOCs 

were detected. The compounds cis-1,2-dichloroethene, trichloroethene, chloroform, and trans-1,2-dichloroethene were 

the most frequently detected VOC compounds, each being 

detected in at least 10 percent of the samples. Concentrations of VOCs in source water were low. Seventeen pesticide 

compounds were detected in source water. Pesticides generally 

were detected at lower concentrations than VOCs, and most 

were derived from atrazine and alachlor and their breakdown 

products. Human-health benchmarks were available for seven 

of these compounds. Maximum benchmark quotients for these 

pesticides typically were several orders of magnitude less 

than 1.0. Eight other AOCs were detected in the source-water 

samples, and concentrations generally were low.

During the second phase of sampling, 15 of the original 30 CWS wells, those with the greatest number of AOC 

detections, were re-sampled along with associated finished 

water in 2005. Thirteen and 12 VOCs were detected in the 

source-water and finished-water samples, respectively. Most 

of the VOCs, except for disinfection by-products, were 

detected more frequently in source-water samples than in 

finished-water samples. Disinfection by-products generally 

had higher concentrations in finished water than in source 

water. Concentrations of most VOCs detected in either source 

water or finished water were well below their human-health 

benchmarks. Twenty-one pesticide compounds were detected 

in either source water or finished water. The most frequently 

detected compounds in both the source and the finished water 

were atrazine and its breakdown products and the breakdown 

products of alachlor and metolachlor. In general pesticides, if 

detected in source water, also were detected in the corresponding finished water. Concentrations of detected pesticides in 

source-water and finished-water samples were low. Concentrations of seven of the pesticides detected in source or finished 

waters could be compared to human-health benchmarks, and 

concentrations generally were several orders of magnitude less 

than the benchmark quotients. Nine other AOCs were detected 

in the source-water and (or) finished-water samples. Caffeine 

occurred most frequently but in only two of the source- and 

finished-water samples. Concentrations of other detected 

AOCs were low. A human-health benchmark was not available 

for any of the nine other AOCs detected. Results indicate that 

monitoring for pesticides in source water generally reflects the 

occurrence of pesticides in finished water but that this is not 

necessarily true of VOCs. Additional monitoring is needed to 

better understand the occurrence of other AOCs in source and 

finished waters.

Water-quality results were compared to characterize 

differences between the two aquifers. VOC and other AOC 

detections were more frequent in the Prairie du Chien-Jordan 

aquifer compared to the glacial aquifer. However, pesticide 

detections were more frequent in the glacial aquifer compared 

to the Prairie du Chien-Jordan aquifer. On the basis of results 

from this study, the hydrogeologic setting, land use, and aquifer productivity seem to play an important role in the detection 

of AOCs in CWS wells. 
26 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

References Cited

Andrews, W.J., Fong, A.L., Harrod, L., and Dittes, M.E., 1998, 

Water-quality assessment of part of the Upper Mississippi 

River Basin, Minnesota and Wisconsin—Ground-water 

quality in an urban part of the Twin Cities metropolitan 

area, Minnesota, 1996: U.S. Geological Survey WaterResources Investigations Report 97–4248, 54 p.

Barbash, J.E., and Resek, E.A., 1996, Pesticides in ground 

water—distribution, trends, and governing factors: Chelsea, 

Mich., Ann Arbor Press, Pesticides in the Hydrologic 

System Series, v. 2, 590 p.

Barbash, J.E., Thelin, G.P., Kolpin, D.W., and Gilliom, R.J., 

1999, Distribution of major herbicides in ground water of 

the United States: U.S. Geological Survey Water-Resources 

Investigations Report 98–4245, 57 p. 

Bloomgren, B.A., Cleland, J.M., and Olsen, B.M., 1989, 

Depth to bedrock and bedrock topography, in Balaban, 

N.H., ed., Geologic atlas—Hennepin County, Minnesota: 

Minnesota Geological Survey, County Atlas Series C–4, 

8 pls.

Cannon, W.F., Kress, T.H., Sutphin, D.M., Morey, G.B., and 

Meints, Joyce, 1999, Digital geologic map and mineral 

deposits of the Lake Superior region—Minnesota, Wisconsin, Michigan: U.S. Geological Survey Open-File Report 

97–455, accessed March 17, 2008, at http://pubs.usgs.gov/

of/1997/of97-455/.

Carter, J.M., Delzer, G.C., Kingsbury, J.A., and Hopple, 

J.A., 2007, Concentration data for anthropogenic organic 

compounds in ground water, surface water, and finished 

water of selected community water systems in the United 

States, 2002–05: U.S. Geological Survey Data Series 268, 

30 p., accessed March 20, 2008, at http://pubs.usgs.gov/

ds/2007/268/.

City of New Brighton, 2008, History of water system and 

ground contamination: accessed January 31, 2008, at 

http://www.ci.new-brighton.mn.us/index.asp

Connor, B.F., Rose, D.L., Noriega, M.C., Murtagh, L.K., and 

Abney, S.R., 1998, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of 86 volatile organic compounds in water by gas 

chromatography/mass spectrometry, including detections 

less than reporting limits: U.S. Geological Survey Open-File 

Report 97–829, 78 p.

Delin, G.N., and Woodward, D.G., 1984, Hydrogeologic 

setting and the potentiometric surface of regional aquifers 

in the Hollandale Embayment, southeastern Minnesota, 

1970–1980: U.S. Geological Survey Water-Supply Paper 

2219, 56 p.

Denver, J.M., and Sandstrom, M.W., 1991, Distribution of 

dissolved atrazine and two metabolites in the unconfined 

aquifer, southeastern Delaware, in Mallard, G.E., and Aronson, D.A., eds., U.S. Geological Survey Toxic Substances 

Hydrology Program—Proceedings of the technical meeting, 

Monterey, California, March 11–15, 1991: U.S. Geological 

Survey Water-Resources Investigations Report 91–4034, 

p. 314–318. 

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of pesticides in water 

by graphitized carbon-based solid-phase extraction and 

high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations 

Report 01–4134, 73 p.

Gaus, Irena, 2000, Effects of water extraction in a vulnerable 

phreatic aquifer-consequences for groundwater contamination by pesticides, Sint-Jansteen area, The Netherlands: 

Journal of Hydrology, v. 8, p. 218–229.

Green, J.C., 1977, Keweenawan plateau volcanism in the Lake 

Superior region, in Baragen, W.R., Coleman, L.C., and Hall, 

J.M., eds., Volcanic regimes in Canada: Geological Association of Canada, Special Paper 15, p. 407–422.

Helgesen, J.O., and Lindholm, G.F., 1977, Geology and watersupply potential of the Anoka Sand Plain aquifer, Minnesota: Minnesota Department of Natural Resources Technical 

Paper 6, 17 p. 

Herberer, T., 2002, Occurrence, fate, and removal of pharmaceutical residues in the aquatic environment—A review of 

recent research data: Toxicology Letters, v. 131, p. 5–17.

Ivahnenko, Tamara, and Barbash, J.E., 2004, Chloroform in 

the hydrologic system—Sources, transport, fate, occurrence, and effects on human health and aquatic organisms: 

U.S. Geological Survey Scientific Investigations Report 

2004–5137, 34 p.

Kanivetsky, Roman, 1989, Water-table system, in Balaban, 

N.H., ed., Geologic atlas—Hennepin County, Minnesota: 

Minnesota Geological Survey, County Atlas Series C–4, 

8 pls.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, 

Ground-water data-collection protocols and procedures for 

the National Water-Quality Assessment Program, collection 

and documentation of water quality samples and related 

data: U.S. Geological Survey Open-File Report 95–399, 

113 p.

Kruger, E.L., Zhu, Beilei, and Coats, J.R., 1995, Relative 

mobilities of atrazine, five atrazine degradates, metolachlor, 

and simazine in soils of Iowa: Environmental Toxicology 

and Chemistry, v. 15, no. 5, p. 691–695.
References Cited 27

Lee, E.A., and Strahan, A.P., 2003, Methods of analysis by the 

U.S. Geological Survey Organic Geochemistry Research 

Group—Determination of acetamide herbicides and their 

degradation products in water using online solid-phase 

extraction and liquid chromatography/mass spectrometry: 

U.S. Geological Survey Open-File Report 2003–173, 17 p.

Lindley, C.E., Stewart, J.T., and Sandstrom, M.W., 1996, 

Determination of low concentrations of acetochlor in water 

by automated solid-phase extraction and gas chromatography with mass selective detection: Journal of Association of 

Official Analytical Chemists International, v. 79, no. 4, 

p. 962–966.

Loraine, G.A., and Pettigrove, M.E., 2006, Seasonal variations in concentrations of pharmaceuticals and personal 

care products in drinking water and reclaimed wastewater 

in southern California: Environmental Science and Technology, v. 40, p. 687–695.

Madsen, J.E., Sandstrom, M.W., and Zaugg, S.D., 2003, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—A method supplement for the 

determination of fipronil and degradates in water by gas 

chromatography/mass spectrometry: U.S. Geological 

Survey Open-File Report 02–462, 11 p.

Menheer, M.A., and Brigham, M.E., 1997, Ground-water sampling methods and quality-control data for the Red River 

of the North Basin, Minnesota, North Dakota, and South 

Dakota, 1993–95: U.S. Geological Survey Water-Resources 

Investigation Report 96–4317, 34 p. 

Meyer, G.N., 1993, Geological sensitivity of the uppermost 

aquifer to pollution, in Meyer, G.N., Falteisek, J., Meints, J., 

and Dahlman, B., eds., Regional hydrogeologic assessment, 

Anoka Sand Plain, Anoka, Chisago, Isanti, and Sherburne 

Counties, Minnesota: Minnesota Department of Natural 

Resources Regional Hydrogeological Assessment, RHA–1, 

3 pl.

Meyer, G.N., and Hobbs, H.C., 1989, Surficial geology, in

Balaban, N.H., ed., Geologic atlas—Hennepin County, Minnesota: Minnesota Geological Survey, County Atlas Series 

C–4, 8 pls.

Minnesota State Demographic Center, 2002, Minneapolis–

St. Paul metropolitan area comparison: Fact Sheet, April 

2002, 4 p.

Morey, G.B., and Meints, Joyce, 2000, Geological Map of 

Minnesota: Bedrock Geology: Minnesota Geological Survey, Map Series S–20 (3rd edition). 

Norvitch, R.F., Ross, T.G., and Brietkrietz, A., 1973, Water 

resources outlook for the Minneapolis-Saint Paul metropolitan area, Minnesota: Twin Cities Metropolitan Council, 

219 p.

Olcott, P.G., 1992, Ground-water atlas of the United States, 

segment 9, Iowa, Michigan, Minnesota, and Wisconsin: 

U.S. Geological Survey Hydrologic Investigation Atlas 

730–J, 31 p., scales 1:250,000 and 1:500,000.

Palen, B.M., Kanivetsky, Roman, and Christopher, R.A., 1989, 

Water-table hydrogeology, in Balaban, N.H., ed., Geologic 

atlas—Hennepin County, Minnesota: Minnesota Geological 

Survey, County Atlas Series C–4, 8 pls.

Piegat, James, 1989, Sensitivity of ground-water systems to 

pollution, in Balaban, N.H., ed., Geologic atlas—Hennepin 

County, Minnesota: Minnesota Geological Survey, County 

Atlas Series C–4, 8 pls. 

Sandstrom, M.W., and Delzer, G.C., 2007, Field methods—

Dechlorination reagent for organic compounds tested 

resulting in new preservation requirement for water samples 

containing residual chlorine: U.S. Geological Survey 

Water-Quality Information Note 2007.04, 2 p., available at 

http://water.usgs.gov/usgs/owq/WaQI/WaQI07.04.pdf

Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and 

Schroeder, M.P., 2001, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

Determination of moderate-use pesticides and selected 

degradates in water by C–18 solid-phase extraction and gas 

chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations Report 01–4098, 70 p.

Setterholm, D.R., Runkel, A.C., Cleland, J.M., Tipping, R.G., 

Mossler, J.H., Kanivetsky, R., and Hobbs, H.C., 1991, 

Geologic factors affecting the sensitivity of the Prairie du 

Chien-Jordan aquifer: Minnesota Geological Survey Open 

File Report 91–5, 18 p., 12 pls.

Soller, D.R., and Packard, P.H., 1998, Digital representation 

of a map showing the thickness and character of Quaternary 

sediments in the glaciated United States east of the Rocky 

Mountains: U.S. Geological Survey Digital Data Series 

DDS–38, accessed March 20, 2008, at http://pubs.usgs.gov/

dds/dds38/.

Stackelberg, P.E., Furlong, E.T., Meyer, M.T., Zaugg, S.D., 

Henderson, A.K., and Reissman, D.B., 2004, Persistence of 

pharmaceutical compounds and other organic wastewater 

contaminants in a conventional drinking-water-treatment 

plant: Science of the Total Environment, v. 329, no. 1–3, 

p. 99–113.

Stark, J.R., Andrews, W.J., Fallon, J.D., Fong, A.L., Goldstein, 

R.M., Hanson, P.E., Kroening, S.E., and Lee, K.E., 1996, 

Water-quality assessment of part of the Upper Mississippi 

River Basin, Minnesota and Wisconsin—Environmental 

setting and study design: U.S. Geological Survey WaterResources Investigations Report 96–4098, 62 p.
28 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Stark, J.R., Hanson, P.E., Goldstein, R.M., Fallon, J.D., Fong, 

A.L., Lee, K.E., Kroening, S.E., and Andrews, W.J., 2001, 

Water quality in the Upper Mississippi River Basin, Minnesota and Wisconsin, South Dakota, Iowa, and North Dakota, 

1995–98: U.S. Geological Survey Circular 1211, 35 p. 

Ternes, T.A., Meisenheimer, M., McDowell, D., Sacher, F., 

Branch H.J., Hsiate-Guide, B., Preuss, G., Wilme, U., and 

Zulei-Seibert, N., 2002, Removal of pharmaceuticals during 

drinking water treatment: Environmental Science and 

Technology, v. 36, p. 3,855–3,863.

Thiros, S.A., 2000, Quality of shallow ground water in areas 

of recent residential and commercial development in Salt 

Lake Valley, Utah, 1999: U.S. Geological Survey Fact Sheet 

106–00, 6 p.

Tipping, R.G., Runkel, A.C., Alexander, E.C., Jr., Alexander, 

S.C., and Green, J.A., 2006, Evidence for hydraulic heterogeneity and anisotropy in the mostly carbonate Prairie du 

Chien Group, southeastern Minnesota, USA: Sedimentary 

Geology, v. 184, nos. 3–4, p. 305–330.

Toccalino, P.L., Norman, J.E., Phillips, R.H., Kauffman, L.J., 

Stackelberg, P.E., Nowell, L.H., Krietzman, S.J., and Post, 

G.B., 2004, Application of Health-Based Screening Levels 

to ground-water quality data in a State-scale pilot effort: 

U.S. Geological Survey Scientific Investigations Report 

2004–5174, 64 p.

Toccalino, P.L., Nowell, Lisa, Wilber, W.G., Zogorski, J.S., 

Donohue, Joyce, Eiden, C., Krietzman, S., and Post, G., 

2003, Development of Health-Based Screening Levels for 

use in State- or local-scale water-quality assessments: U.S. 

Geological Survey Water-Resources Investigations Report 

03–4054, 22 p.

Toccalino, P.L., Zogorski, J.S., and Norman, J.E., 2005, 

Health-Based Screening Levels and their application to 

water-quality data: U.S. Geological Survey Fact Sheet 

2005–3059, 2 p. 

U.S. Environmental Protection Agency, 2002, Setting standards for safe drinking water: U.S. Environmental Protection Agency, Office of Ground Water and Drinking Water, 

Washington, D.C., updated November 26, 2002, accessed 

January 7, 2005, at http://www.epa.gov/safewater/standard/

setting.html

U.S. Environmental Protection Agency, 2008, Drinking water 

contaminants: accessed March 4, 2008, at http://www.epa.

gov/safewater/contaminants/index.html

Westerhoff, Paul, Yoon, Yeomin, Snyder, Shane, and Wert, 

Eric, 2005, Fate of endocrine-disruptor, pharmaceutical, and 

personal care product chemicals during simulated drinking

water treatment processes: Environmental Science and 

Technology, v. 39, no. 17, p. 6,649–6,663.

Young, H.L., 1992a, Summary of ground-water hydrology of 

the Cambrian-Ordovician aquifer system in the Northern 

Midwest, United States: U.S. Geological Survey Professional Paper 1405–A, 55 p. 

Young, H.L., 1992b, Hydrology of the Cambrian-Ordovician 

aquifer system in the Northern Midwest, United States: 

U.S. Geological Survey Professional Paper 1405–B, 99 p. 

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—Determination 

of pesticides in water by C–18 solid-phase extraction and 

capillary-column gas chromatography/mass spectrometry 

with selected-ion monitoring: U.S. Geological Survey 

Open-File Report 95–181, 60 p. 

Zaugg, S.D., Smith, S.G., Schroeder, M.P., Barber, L.B., and 

Burkhardt, M.R., 2002, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

Determination of wastewater compounds by polystyrenedivinylbenzene solid-phase extraction and capillary-column 

gas chromatography/mass spectrometry: U.S. Geological 

Survey Water-Resources Investigations Report 01–4186, 

37 p.
Appendixes
30 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Appendix 1. Volatile organic compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source or finished water in this study; 

bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting level

(μg/L)

Remarks

1,1,1,2-Tetrachloroethane 630–20–6 0.03 --

1,1,1-Trichloroethane 71–55–6 .032 --

1,1,2,2-Tetrachloroethane 79–34–5 .08 --

1,1,2-Trichloro-1,2,2-trifluoroethane 76–13–1 .038 Also known as Freon 113.

1,1,2-Trichloroethane 79–00–5 .04 --

1,1-Dichloroethane 75–34–3 .035 Used to make other chemicals; solvent.

1,1-Dichloroethene 75–35–4 .024 --

1,1-Dichloropropene 563–58–6 .026 --

1,2,3,4-Tetramethylbenzene 488–23–3 .14 --

1,2,3,5-Tetramethylbenzene 527–53–7 .14 --

1,2,3-Trichlorobenzene 87–61–6 .18 --

1,2,3-Trichloropropane 96–18–4 .18 --

1,2,3-Trimethylbenzene 526–73–8 .06 --

1,2,4-Trichlorobenzene 120–82–1 .12 --

1,2,4-Trimethylbenzene 95–63–6 .056 Used in foam insulation, paints, and thinners.

1,2-Dibromo-3-chloropropane 96–12–8 .51 --

1,2-Dibromoethane 106–93–4 .036 --

1,2-Dichlorobenzene 95–50–1 .048 --

1,2-Dichloroethane 107–06–2 .13 --

1,2-Dichloropropane 78–87–5 .029 --

1,3,5-Trimethylbenzene 108–67–8 .044 --

1,3-Dichlorobenzene 541–73–1 .03 --

1,3-Dichloropropane 142–28–9 .06 --

1,4-Dichlorobenzene 106–46–7 .034 --

1-Ethyl-2-methylbenzene 611–14–3 .06 Also known as o-ethyl toluene.

2,2-Dichloropropane 594–20–7 .05 --

2-Chlorotoluene 95–49–8 .04 --

2-Hexanone 591–78–6 .4 --

3-Chloropropene 107–05–1 .5 --

4-Chlorotoluene 106–43–4 .05 --

4-Methyl-2-pentanone 108–10–1 .37 Used as a solvent, used in paints, varnishes, and lacquers.

Acetone1 67–64–1 6 Occurs naturally; manufactured chemical is used to make 

plastics and other chemicals; a solvent.

Acrylonitrile 107–13–1 .8 --

Benzene 71–43–2 .021 --

Bromobenzene 108–86–1 .028 --

Bromochloromethane 74–97–5 .12 --

Bromodichloromethane 75–27–4 .028 Also known as dichlorobromomethane; by-product when 

chlorine is added to water-supply systems.
Appendix 1 31

Appendix 1. Volatile organic compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source or finished water in this study; 

bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting level

(μg/L)

Remarks

Bromoform 75–25–2 0.1 By-product when chlorine is added to water-supply 

systems.

Bromomethane 74–83–9 .26 --

Carbon disulfide 75–15–0 .038 Occurs naturally; manufactured chemical is used as a 

solvent in industrial processes.

Carbon tetrachloride 56–23–5 .06 Used as a solvent in dry cleaning; used in fire extinguishers. 

Also known as tetrachloromethane.

Chlorobenzene 108–90–7 .028 --

Chloroethane 75–00–3 .12 Gasoline additive; used in cellulose, dyes, and medical drugs.

Chloroform 67–66–3 .024 Also known as trichloromethane, by-product when chlorine is 

added to water-supply systems; used as a solvent.

Chloromethane 74–87–3 .17 Used as a chemical intermediate and in agricultural 

chemicals (methyl chloride).

cis-1,2-Dichloroethene 156–59–2 .024 Used as a solvent for waxes and resins; used as a 

refrigerant.

cis-1,3-Dichloropropene 10061–01–5 .05 --

Dibromochloromethane 124–48–1 .1 Also known as chlorodibromomethane; by-product when 

chlorine is added to water-supply systems.

Dibromomethane 74–95–3 .05 --

Dichlorodifluoromethane 75–71–8 .18 Also known as Freon 112.

Diethyl ether 60–29–7 .08 --

Diisopropyl ether 108–20–3 .1 --

Ethylbenzene 100–41–4 .03 Used in the production of synthetic rubber; a solvent.

Ethyl methacrylate 97–63–2 .18 --

Ethyl tert-butyl ether 637–92–3 .03 Also known as ETBE.

Hexachlorobutadiene 87–68–3 .14 --

Hexachloroethane 67–72–1 .14 --

Iodomethane 74–88–4 .5 Also known as methyl iodide.

Isopropylbenzene 98–82–8 .038

m- and p-Xylene m=108–38–3 

p=106–42–3 .06 Occurs naturally in petroleum; manufactured chemical is used 

in chemical processes and pesticides.

Methyl acrylate 96–33–3 1 --

Methyl acrylonitrile 126–98–7 .4 --

Methylene chloride 75–09–2 .06 Also known as dichloromethane.

Methyl ethyl ketone 78–93–3 2

Occurs naturally; manufactured chemical is used in paints and 

coatings; cleaning agent; exhaust from cars and trucks. Also 

known as 2-butanone.

Methyl methacrylate 80–62–6 .2 --

Methyl tert-butyl ether 1634–04–4 .1 Also known as MTBE. Gasoline additive.

Naphthalene 91–20–3 .52 Used in the making of polyvinyl chloride (PVC) plastics, moth 

repellents, and toilet deodorant blocks.

n-Butylbenzene 104–51–8 .12 --

n-Propylbenzene 103–65–1 .042 --
32 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Appendix 1. Volatile organic compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source or finished water in this study; 

bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting level

(μg/L)

Remarks

o-Xylene 95–47–6 0.038 Used in the production of plastics, dyes, and insecticides.

Perchloroethene 127–18–4 .03 Also known as tetrachloroethene and PCE; primarily used as 

dry cleaning agent.

p-Isopropyltoluene 99–87–6 .08 Also known as 4-isopropyl-1-methylbenzene.

sec-Butylbenzene 135–98–8 .06 --

tert-Amyl methyl ether 994–05–8 .04 --

tert-Butylbenzene 98–06–6 .06 --

Tetrahydrofuran 109–99–9 1 Industrial solvent and chemical intermediate.

Toluene1 108–88–3 .02 --

trans-1,2-Dichloroethene 156–60–5 .032 --

trans-1,3-Dichloropropene 10061–02–6 .09 --

trans-1,4-Dichloro-2-butene 110–57–6 .7 --

Trichloroethene 79–01–6 .038 Also known as TCE; solvent.

Trichlorofluoromethane 75–69–4 .08 Used in refrigeration and air conditioning; foam blowing 

agents.

Vinyl bromide 593–60–2 .1 Also known as bromoethene.

Vinyl chloride 75–01–4 .08 --

1

Results not included in this report.
Appendix 2 33

Appendix 2. Pesticide compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source water or finished water 

in this study; bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, 

none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting level

(μg/L)

Remarks

1-Naphthol 90–15–3 0.0882 --

2,4–D 94–75–7 .038 Herbicide.

2,4–D methyl ester 1928–38–7 .016 --

2,4–DB 94–82–6 .02 --

2,6-Diethylaniline 579–66–8 .006 --

2-Chloro-2,6-diethylacetanilide 6967–29–9 .005 --

2-Ethyl-6-methylaniline 24549–06–2 .0045 --

2-Hydroxyatrazine (OIET) 2163–68–0 .032

Breakdown product of triazines; also referred to 

as 2-hydroxy-4-isopropylamino-6-ethylamino-striazine. 

3(4-Chlorophenyl)-1-methyl urea 5352–88–5 .036 --

3,4-Dichloroaniline 95–76–1 .0045 Herbicide.

3-Hydroxycarbofuran 16655–82–6 .008 --

3-Ketocarbofuran 16709–30–1 .02 --

4-Chloro-2-methylphenol 1570–64–5 .0057 --

Acetochlor 34256–82–1 .006 Herbicide.

Acetochlor ESA 187011–11–3 .02 --

Acetochlor OA -- .02 --

Acifluorfen 50594–66–6 .028 --

Alachlor 15972–60–8 .005 Herbicide.

Alachlor ESA 14039–15–7 .02 --

Alachlor ESA SA -- .02 --

Alachlor OA 140939–14–6 .02 --

Aldicarb 116–06–3 .04 --

Aldicarb sulfone 1646–88–4 .018 --

Aldicarb sulfoxide 1646–87–3 .022 --

Atrazine 1912–24–9 .007 Herbicide.

Azinphos-methyl 86–50–0 .05 --

Azinphos-methyl-oxon 961–22–8 .07 --

Bendiocarb 22781–23–3 .02 --

Benfluralin 1861–40–1 .01 Herbicide.

Benomyl 17804–35–2 .022 --

Bensulfuron-methyl 83055–99–6 .018 --

Bentazon 25057–89–0 .012 Herbicide.

Bromacil 314–40–9 .018 Herbicide.

Bromoxynil 1689–84–5 .028 --

Carbaryl 63–25–2 .018 --

Carbofuran 1563–66–2 .016 --
34 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Appendix 2. Pesticide compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source water or finished water 

in this study; bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, 

none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting level

(μg/L)

Remarks

Chloramben, methyl ester 7286–84–2 0.024 --

Chlorimuron-ethyl 90982–32–4 .032 --

Chlorothalonil 1897–45–6 .035 --

Chlorpyrifos 2921–88–2 .005 Herbicide.

Chlorpyrofos, oxygen analog 5598–15–2 .0562 --

cis-Permethrin 54774–45–7 .006 --

Clopyralid 1702–17–6 .024 --

Cycloate 1134–23–2 .014 --

Cyfluthrin 68359–37–5 .008 --

Cypermethrin 52315–07–8 .0086 --

Dacthal 1861–32–1 .003 --

Dacthal monoacid 887–54–7 .028 --

Deethylatrazine (CIAT) 6190–65–4 .006 Breakdown product of triazines; also referred to as 

2-chloro-4-isopropylamino-6-amino-s-triazine.

Deisopropylatrazine (CEAT) 1007–28–9 .08 Breakdown product of triazines; also referred to as 

2-chloro-6-ethylamino-4-amino-s-triazine.

Desulfinylfipronil -- .012 --

Desulfinylfipronil amide -- .029 --

Diazinon 333–41–5 .005 Insecticide.

Diazinon, oxygen analog 962–58–3 .006 --

Dicamba 1918–00–9 .036 --

Dichlorprop 120–36–5 .028 --

Dichlorvos 62–73–7 .0118 --

Dicrotophos 141–66–2 .0843 --

Didealkylatrazine (CAAT) 3397–62–4 .022 Breakdown product of triazines; also referred to as

chlordiamino-s-triazine.

Dieldrin 60–57–1 .009 --

Dimethoate 60–51–5 .0061 --

Dinoseb 88–85–7 .038 --

Diphenamid 957–51–7 .01 --

Diuron 330–54–1 .014 --

Ethion 563–12–2 .004 --

Ethion monoxon 17356–42–2 .002 --

Fenamiphos 22224–92–6 .029 --

Fenamiphos sulfone 31972–44–8 .0491 --

Fenamiphos sulfoxide 31972–43–7 .0387 --

Fenuron 101–42–8 .018 --

Fipronil 120068–37–3 .016 --

Fipronil sulfide 120067–83–6 .013 --
Appendix 2 35

Appendix 2. Pesticide compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source water or finished water 

in this study; bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, 

none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting level

(μg/L)

Remarks

Fipronil sulfone 120068–36–2 0.024 --

Flufenacet 142459–58–3 .02 --

Flumetsulam 98967–40–9 .04 --

Fluometuron 2164–17–2 .016 --

Fonofos 944–22–9 .003 --

Fonofos, oxygen analog 944–21–8 .0029 --

Hexazinone 51235–04–2 .0129 --

Imazaquin 81335–37–7 .036 --

Imazethapyr 81335–77–5 .038 Herbicide.

Imidacloprid 138261–41–3 .02 Insecticide.

Iprodione 36734–19–7 .387 --

Isofenphos 25311–71–1 .0034 --

Linuron 330–55–2 .014 --

Malaoxon 1634–78–2 .0298 --

Malathion 121–75–5 .027 Insecticide.

MCPA 94–74–6 .03 Herbicide.

MCPB 94–81–5 .01 Herbicide.

Metalaxyl 57837–19–1 .0051 --

Methidathion 950–37–8 .0058 --

Methiocarb 2032–65–7 .01 --

Methomyl 16752–77–5 .02 --

Metolachlor 51218–45–2 .006 --

Metolachlor ESA -- .02 --

Metolachlor OA 152019–73–3 .02 --

Metribuzin 21087–64–9 .006 --

Metsulfuron methyl 74223–64–6 .025 --

Myclobutanil 88671–89–0 .008 --

N(Ethmethphen)ox ESA -- .02 --

Neburon 555–37–3 .012 --

Nicosulfuron 111991–09–4 .04 --

Norflurazon 27314–13–2 .02 --

Oryzalin 19044–88–3 .012 Herbicide.

Oxamyl 23135–22–0 .03 --

Paraoxon-methyl 950–35–6 .0299 --

Parathion-methyl 298–00–0 .015 --

Pendimethalin 40487–42–1 .022 --

Phorate 298–02–2 .011 --

Phorate oxygen analog 2600–69–3 .1048 --
36 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Appendix 2. Pesticide compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source water or finished water 

in this study; bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, 

none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting level

(μg/L)

Remarks

Phosmet 732–11–6 0.0079 --

Phosmet oxon 3735–33–9 .0511 --

Picloram 2/1/1918 .032 Herbicide.

Prometon 1610–18–0 .01 Herbicide.

Prometryn 7287–19–6 .0054 --

Propham 122–42–9 .03 --

Propiconazole 60207–90–1 .01 --

Propoxur 114–26–1 .008 --

Propyzamide 23950–58–5 .004 --

Siduron 1982–49–6 .02 --

Simazine 122–34–9 .005 Herbicide.

Sulfometuron-methyl 74222–97–2 .038 --

Tebuthiuron 34014–18–1 .016 Herbicide.

Terbacil 5902–51–2 .016 --

Terbufos 13071–79–9 .017 --

Terbufos oxygen analog sulfone 56070–15–6 .0676 --

Terbuthylazine 5915–41–3 .0102 --

Tribenuron-methyl 101200–48–0 .0088 --

Triclopyr 55335–06–3 .026 --

Trifluralin 1582–09–8 .009 --
Appendix 3 37

Appendix 3. Other anthropogenic organic compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source water or finished water in 

this study; bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; --, none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting 

level

(μg/L)

Remarks

1-Methylnaphthalene 90–12–0 0.5 Used in the manufacture of PVC, 

pharmaceuticals, and insecticides.

2,6-Dimethylnaphthalene 581–42–0 .5 --

2-Methylnaphthalene 91–57–6 .5 Used in the manufacture of PVC, 

pharmaceuticals, and insecticides.

3-beta-Coprostanol 360–68–9 2 Human and animal waste indicator.

3-Methyl-1(H)-indole 83–34–1 1 Also known as Skatole.

3-tert-Butyl-4-hydroxy anisole (BHA) 25013–16–5 5 --

4-Cumylphenol 599–64–4 1 --

4-Nonylphenol (total)1 84852–15–3 5 Used as a surfactant in detergents.

4-n-Octylphenol 1806–26–4 1 --

4-tert-Octylphenol 140–66–9 1 --

5-Methyl-1H-benzotriazole 136–85–6 2 --

Acetophenone 98–86–2 .5 --

Acetyl hexamethyl tetrahydronaphthalene 

(AHTN) 21145–77–7 .5 --

Anthracene 120–12–7 .5 --

Anthraquinone 84–65–1 .5 --

Benzo[a]pyrene 50–32–8 .5 --

Benzophenone1 119–61–9 .5 --

beta-Sitosterol 83–46–5 2 Eukaryotic sterol.

beta-Stigmastanol 19466–47–8 2 Plant sterol; hormone to lower cholesterol.

Bisphenol A 80–05–7 1 --

Caffeine 58–08–2 .012 Stimulant found in coffee and tea.

Camphor 76–22–2 .5 Widely used as a plasticizer in celluloid and 

lacquers.

Carbazole 86–74–8 .5 --

Cholesterol 57–88–5 2 Sterol found in human and animal body tissue 

and fat.

Cotinine 486–56–6 1 --

d-Limonene 5989–27–5 .5 --

Fluoranthene 206–44–0 .5 --

Hexahydrohexamethylcyclopentabenzopyran 

(HHCB) 1222–05–5 .5 --

Indole 120–72–9 .5 Fertilizer; stimulates root growth.

Isoborneol 124–76–5 .5 --

Isophorone1 78–59–1 .5 --

Isoquinoline 119–65–3 .5 --

Menthol 89–78–1 .5 --
38 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Appendix 3. Other anthropogenic organic compounds analyzed in this study, 2004–05.—Continued

[CASR, Chemical Abstracts Service Registry; μg/L, micrograms per liter; shading represents compound detected in source water or finished water in 

this study; bold type indicates unregulated compound for which no Federal and (or) State drinking-water standards have been established; —, none]

Regulated or unregulated

compound

CASR

number

Minimum 

reporting 

level

(μg/L)

Remarks

Methyl salicylate 119–36–8 0.5 --

N,N,-diethy-meta-toluamide (DEET) 1 134–62–3 .5 Insect repellant.

Nonylphenol, diethoxy- (total) 26027–38–2 5 --

Octylphenol, diethoxy- 26636–32–8 1 Grouped as ethoxyoctylphenol.

Octylphenol, monoethoxy- 26636–32–8 1 Grouped as ethoxyoctylphenol.

p-Cresol 106–44–5 1 Wood preservative; cleaning agent; solvent.

Pentachlorophenol 87–86–5 2 --

Phenanthrene 85–01–8 .5 --

Phenol1 108–95–2 .5 --

Pyrene 129–00–0 .5 --

Tributyl phosphate 126–73–8 .5 --

Triclosan 3380–34–5 1 --

Triethyl citrate (ethyl citrate) 77–93–0 .5 --

Triphenyl phosphate 115–86–6 .5 --

Tris(2-butoxyethyl)phosphate 78–51–3 .5 --

Tris(2-chloroethyl)phosphate (TCEP) 115–96–8 .5 Used as a flame retardant in plastics and 

foams.

Tris(dichloroisopropyl)phosphate (TCPP) 13674–87–8 .5 Used as a flame retardant in plastics and 

foams.

1

Results not included in this report.
Appendix 4 39

Appendix 4. Descriptions of human-health benchmarks related to drinking water.

[Maximum Contaminant Levels (MCLs) (Federal and State) are enforceable standards; Health-Based Screening Levels (HBSLs) are not enforceable guidelines; 

USGS, U.S. Geological Survey; USEPA, U.S. Environmental Protection Agency; OW, Office of Water]

Human-health

benchmark Acronym Agency Description References

Maximum 

Contaminant 

Level 

MCL USEPA (OW) Legally enforceable standard that sets the 

maximum permissible level of a contaminant in water that is delivered to any user 

of a public water system. MCLs are set as 

close as feasible to Maximum Contaminant 

Level Goals (MCLGs). An MCLG is the 

maximum level of a contaminant in drinking water at which no known or anticipated 

adverse effect on the health of persons 

would occur, and which allows an adequate 

margin of safety. MCLGs are nonenforceable public health goals that take 

into account the best available technology, 

treatment techniques, cost considerations, 

expert judgment, and public comments.

U.S. Environmental 

Protection Agency, 2008.

Health-Based 

Screening Level

HBSL USGS Benchmark concentrations of contaminants 

in water that may be of potential concern 

for human health, if exceeded. HBSLs are 

non-enforceable benchmarks that were developed by the USGS in collaboration with 

USEPA and others using USEPA methodologies for establishing drinking-water 

guidelines and the most current, USEPA 

peer-reviewed, publicly available humanhealth toxicity information.

Toccalino and others, 

2003 and 2006.
40 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Appendix 5. Comparison between source and associated finished water for anthropogenic organic compounds detected during this 

study, 2005.—Continued

[E, estimated value; ND, no detection; μg/L, micrograms per liter; bold type indicates unregulated compound for which no Federal and (or) State drinkingwater standards have been established; * indicates blended water; PDCJ, Prarie du Chien-Jordan aquifer; GLAC, glacial aquifer]

Aquifer Detected anthropogenic

organic compound (regulated or unregulated)

Source-water 

concentration

(μg/L)

Finished-water 

concentration

(blended and nonblended)

(μg/L)

Volatile organic compounds

PDJC 1,1,1-Trichloroethane 5.066 ND*

PDJC 1,1,2-Trichloro-1,2,2-trifluoroethane (Freon-113) E.184 ND*

PDJC 1,1-Dichloroethane .131 0.142*

PDJC 1,1-Dichloroethane 5.110 ND*

PDJC 1,1-Dichloroethane ND E.052*

PDJC 1,1-Dichloroethene E.039 ND*

PDJC 1,1-Dichloroethene 7.018 ND*

PDJC 1,1-Dichloroethene ND E.018*

PDJC Benzene E.016 ND 

PDJC Benzene E.016 ND*

PDJC Benzene .133 .121*

PDJC Bromodichloromethane1 ND .316 

GLAC Bromodichloromethane1 ND .825 

PDJC Bromodichloromethane1 ND 1.206*

PDJC Bromoform1 ND E.068*

GLAC Bromoform1 ND E.470*

PDJC Bromoform1 ND E2.000

GLAC Bromoform1 ND E8.900

PDJC Chloroform1 E.069 ND*

PDJC Chloroform1 ND E.054*

PDJC Chloroform1 ND .491 

GLAC Chloroform1 ND .492 

PDJC Chloroform1 ND 1.828*

PDJC Chloromethane ND E.150*

PDJC cis-1,2-Dichloroethene E.077 .944*

PDJC cis-1,2-Dichloroethene .296 .266 

PDJC cis-1,2-Dichloroethene 1.166 ND*

PDJC cis-1,2-Dichloroethene 2.401 1.789* 

GLAC cis-1,2-Dichloroethene ND E.026

PDJC Dibromochloromethane1 ND .213 

PDJC Dibromochloromethane1 ND .445*

GLAC Dibromochloromethane1 ND .841 

GLAC Dichlorodifluoromethane (Freon-112) E.050 ND 

GLAC Methyl tert-butyl ether (MTBE) .103 ND 

PDJC Perchloroethene E.019 E.019

PDJC Perchloroethene E.136 ND*

GLAC Perchloroethene ND E.092

PDJC trans-1,2-Dichloroethene E.029 ND*

PDJC trans-1,2-Dichloroethene .167 .154* 

PDJC trans-1,2-Dichloroethene .177 .149 

PDJC trans-1,2-Dichloroethene ND E.084*
Appendix 5 41

Appendix 5. Comparison between source and associated finished water for anthropogenic organic compounds detected during this 

study, 2005.—Continued

[E, estimated value; ND, no detection; μg/L, micrograms per liter; bold type indicates unregulated compound for which no Federal and (or) State drinkingwater standards have been established; * indicates blended water; PDCJ, Prarie du Chien-Jordan aquifer; GLAC, glacial aquifer]

Aquifer Detected anthropogenic

organic compound (regulated or unregulated)

Source-water 

concentration

(μg/L)

Finished-water 

concentration

(blended and nonblended)

(μg/L)

Volatile organic compounds—Continued

PDJC Trichloroethene E0.018 E.015

PDJC Trichloroethene E.044 .631* 

PDJC Trichloroethene .322 .253* 

PDJC Trichloroethene 63.970 ND*

GLAC Trichloroethene ND E.048

PDJC Vinyl chloride .387 ND* 

Pesticides

PDJC 3-Ketocarbofuran E0.250 E0.250*

PDJC 3-Ketocarbofuran E.250 ND*

PDJC 3-Ketocarbofuran E.250 ND*

GLAC 3-Ketocarbofuran ND E.250*

GLAC Acetochlor ESA .020 ND*

GLAC Acetochlor ESA .040 ND*

PDJC Acetochlor ESA ND .020* 

PDJC Acetochlor OA ND .040* 

PDJC Alachlor ESA .020 .070* 

GLAC Alachlor ESA .090 .030* 

GLAC Alachlor ESA .130 .110 

PDJC Alachlor ESA .140 .120* 

GLAC Alachlor ESA .170 2.530* 

GLAC Alachlor ESA .540 2.530* 

PDJC Alachlor ESA SA .020 ND*

GLAC Alachlor ESA SA .100 2.210* 

GLAC Alachlor ESA SA .130 2.210* 

PDJC Alachlor OA .020 .020* 

GLAC Alachlor OA .090 2.320* 

GLAC Alachlor OA .140 2.320* 

PDJC Alachlor OA ND .020* 

GLAC Atrazine E.007 E.004*

GLAC Atrazine 0.008 E.005

PDJC Atrazine .010 ND*

PDJC Atrazine .034 .047* 

PDJC Atrazine .050 ND*

PDJC Bromacil .028 ND*

GLAC Bromacil .258 ND

PDJC Deethylatrazine (CIAT) E.006 ND*

GLAC Deethylatrazine (CIAT) E.009 E.004*

PDJC Deethylatrazine (CIAT) E.016 ND*

PDJC Deethylatrazine (CIAT) .041 .033* 

PDJC Deisopropylatrazine (CEAT) E.005 E.006*

GLAC Deisopropylatrazine (CEAT) E.052 E.006*
42 Organic Compounds in Community Ground-Water Systems, Twin Cities Area, Minnesota and Wisconsin

Appendix 5. Comparison between source and associated finished water for anthropogenic organic compounds detected during this 

study, 2005.—Continued

[E, estimated value; ND, no detection; μg/L, micrograms per liter; bold type indicates unregulated compound for which no Federal and (or) State drinkingwater standards have been established; * indicates blended water; PDCJ, Prarie du Chien-Jordan aquifer; GLAC, glacial aquifer]

Aquifer Detected anthropogenic

organic compound (regulated or unregulated)

Source-water 

concentration

(μg/L)

Finished-water 

concentration

(blended and nonblended)

(μg/L)

Pesticides—Continued

GLAC Didealkyatrazine (CAAT) E0.052 ND*

PDJC Fenuron .019 ND*

PDJC Flufenacet .020 ND*

GLAC Flufenacet .020 ND*

PDJC Hexazinone .017 ND*

PDJC Metolachlor .020 ND*

PDJC Metolachlor ESA .020 0.080*

PDJC Metolachlor ESA .020 .080* 

GLAC Metolachlor ESA .040 2.230* 

GLAC Metolachlor ESA .100 2.230* 

GLAC Metolachlor ESA .140 .030* 

GLAC Metolachlor OA .020 ND*

GLAC Metolachlor OA .120 2.620* 

GLAC Metolachlor OA .410 2.620* 

PDJC Metolachlor OA ND .020*

PDJC Metolachlor OA ND .040* 

PDJC Metsulfuron methyl E.070 E.070*

PDJC Metsulfuron methyl E.070 ND*

GLAC Metsulfuron methyl ND E.070*

PDJC N(Ethmethphen)ox ESA ND 0.020*

GLAC Oryzalin E.010 ND*

GLAC Prometon E.009 E.008

Other anthropogenic organic compounds

GLAC Caffeine E0.032 E0.026

GLAC Caffeine E.097 E.065*

GLAC Monoethoxyoctylphenol E.066 ND 

PDJC Hexahydrohexamethylcyclopentabenzopyran (HHCB) E.012 ND

GLAC Menthol ND E.033*

GLAC Methyl salicylate E.014 E.011*

GLAC Tributyl phosphate E.019 ND*

PDJC Tributyl phosphate E.067 ND

GLAC Tributyl phosphate E.130 ND

PDJC Triphenyl phosphate ND E.017*

GLAC Tris(2-butoxyethyl)phosphate E.180 ND

GLAC Tris(2-chloroethyl)phosphate (TCEP) E.040 ND

1

Disinfection by-product (DBP).

2

One finished-water sample was collected that was paired with two source-water samples due to blending. The same finished-water concentration is shown for 

both source-water samples.

Tornes, Stark, Hoard, and Smith—Anthropogenic Organic Compounds in Ground Water and Finished Water of Community Water Systems in the Greater Twin 

Cities Metropolitan Area, Minnesota and Wisconsin, 2004–05—Scientific Investigations Report 2007–5273

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