U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5267

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

SOURCE WATER-QUALITY ASSESSMENT

Anthropogenic Organic Compounds in Ground Water 

and Finished Water of Community Water Systems 

in the Northern Tampa Bay Area, Florida, 2002–04
Cover: Aerial photograph of Clearwater, Florida, May 8, 2002 (photograph courtesy of U.S. Geological Survey).
Anthropogenic Organic Compounds in 

Ground Water and Finished Water of 

Community Water Systems in the 

Northern Tampa Bay Area, Florida, 

2002–04

By Patricia A. Metz, Gregory C. Delzer, Marian P. Berndt, Christy A. Crandall, 

and Patricia L. Toccalino

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

SOURCE WATER-QUALITY ASSESSMENT

Scientific Investigations Report 2006–5267

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: 2007

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Suggested citation:

Metz, P.A., Delzer, G.C., Berndt, M.P., Crandall, C.A., and Toccalino, P.L., 2007, Anthropogenic organic compounds in 

ground water and finished water of community water systems in the northern Tampa Bay area, Florida, 2002–04: 

U.S. Geological Survey Scientific Investigations Report 2006–5267, 48 p.
iii

FOREWORD

The U.S. Geological Survey (USGS) is committed to providing the Nation with 

accurate and timely scientific information that helps 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 quality of the 

Nation’s water resources is critical to assuring the long-term availability of water that 

is safe for drinking and recreation and suitable for industry, irrigation, and habitat for 

fish and wildlife. Population growth and increasing demands for multiple water uses 

make water availability, 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, and local information needs and decisions related 

to water-quality management and policy (http://water.usgs.gov/nawqa). Shaped by 

and coordinated with ongoing efforts of other Federal, State, and local agencies, 

the NAWQA Program is designed to answer: What is the condition of our Nation’s 

streams and ground water? How are the conditions changing over time? How do 

natural features and human activities affect the quality of streams and ground water, 

and where are those effects most pronounced? By combining information on water 

chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA 

Program aims to provide science-based insights for current and emerging water issues 

and priorities. 

From 1991–2001, the NAWQA Program completed interdisciplinary assessments in 

51 of the Nation’s major river basins and aquifer systems, referred to as Study Units 

(http://water.usgs.gov/nawqa/studyu.html). Baseline conditions were established for 

comparison to future assessments, and long-term monitoring was initiated in many of 

the basins. During the next decade, 42 of the 51 Study Units will be reassessed so that 

10 years of comparable monitoring data will be available to determine trends at many 

of the Nation’s streams and aquifers. The next 10 years of study also will fill in critical 

gaps in characterizing water-quality conditions, enhance understanding of factors that 

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.
iv

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

to inform 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 

a fully integrated understanding of watersheds and 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, 

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
Contents

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

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

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

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

Description of Study Area ............................................................................................................................4

Land Use.................................................................................................................................................4

Hydrogeology.........................................................................................................................................4

Ground-Water Withdrawals and Distribution..................................................................................6

Site Selection, Methods, and Human-Health Benchmarks....................................................................8

Site Selection and Methods................................................................................................................8

Human-Health Benchmarks................................................................................................................9

Consumer Confidence Reports and Source Water-Quality Assessments.......................10

Anthropogenic Organic Compounds in Ground Water during Phase 1..............................................10

Volatile Organic Compounds.............................................................................................................10

Pesticides.............................................................................................................................................13

Other Anthropogenic Organic Compounds ....................................................................................13

Effects of Hydrogeology on Ground-Water Quality.......................................................................13

Effects of Land Use and Population Density on Ground-Water Quality ....................................14

Comparison of Source-Water Results to Results from Other Studies .......................................16

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

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

Other Anthropogenic Organic Compounds ....................................................................................17

Anthropogenic Organic Compounds in Ground Water and Finished Water during Phase 2..........18

Volatile Organic Compounds.............................................................................................................18

Pesticides.............................................................................................................................................19

Other Anthropogenic Organic Compounds ....................................................................................24

Summary........................................................................................................................................................26

References Cited..........................................................................................................................................27

Appendixes ...................................................................................................................................................31
vi

Figures

1-2. Maps showing:

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

Ground-Water Source Water-Quality Assessments......................................................3

2. Location and land use of the study area..........................................................................5

3. Graph showing generalized hydrogeologic section of the study area................................6

4. Map showing distribution of the intermediate confining unit overlying the Upper 

Floridan aquifer and location of wells sampled in phase 1 and source-water wells 

where the associated finished water also was sampled in phase 2 of the study .............7

5. Photographs showing example of two treatment facilities located in the study area .....8

6-11. Graphs showing:

6. Concentrations, number of detections, and benchmark quotient values for 

volatile organic compounds, pesticides, and other anthropogenic organic 

compounds from 30 source-water wells during phase 1............................................12

7. Concentrations of all detected anthropogenic organic compounds in source 

water from semiconfined and unconfined areas of the Upper Floridan aquifer 

during phase 1....................................................................................................................14

8. Number of anthropogenic organic compound detections in source-water 

samples collected during phase 1 in comparison to population surrounding 

source-water wells in unconfined or semiconfined areas, and statistical 

relations with population..................................................................................................15

9. Detected volatile organic compounds in source water and associated finished

water (non-blended and blended) during phase 2 showing concentrations 

and number of detections, and benchmark quotient values......................................22

10. Detected pesticides in source water and associated finished water (nonblended and blended) during phase 2 showing concentrations and 

number of detections, and benchmark quotient values..............................................23

11. Detected anthropogenic organic compounds in source water and associated

finished water (blended) during phase 2 showing concentrations and 

number of detections, and benchmark quotient values..............................................25

Tables

1. Maximum concentration, detection frequency, and maximum benchmark 

quotient for regulated and unregulated compounds detected in samples from 

30 source-water wells of community water systems in the northern Tampa 

Bay area .......................................................................................................................................11

2. Summary of locally conducted ground-water quality studies that evaluated the

occurrence of volatile organic compounds, pesticides, and (or) other

anthropogenic organic compounds ........................................................................................16

3 Maximum concentrations, detection frequency, and maximum benchmark quotient

for regulated and unregulated compounds detected in samples collected during

phase 2 from 11 source-water wells and the associated finished water of

community water systems in the northern Tampa Bay Area ..............................................20
vii

Conversion Factors, Datum, Abbreviations, Acronyms, and 

Definitions

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.4047 square hectometer (hm2)

acre 0.004047 square kilometer (km2)

square miles (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.7854 liter (L)

Flow rate

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

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

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

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

Concentration

parts per billion (ppb) 1.0 micrograms per liter (μg/L)

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

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 

(NGVD 29).

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

Appendixes 1–8.

1. Volatile organic compounds analyzed in this study.....................................................33

2. Pesticides and pesticide degradates analyzed in this study .....................................36

3. Other anthropogenic organic compounds analyzed in this study.............................40

4. Descriptions of human-health benchmarks related to drinking water.....................42

5. Comparison of volatile organic compounds (VOCs) detected in the source 

water during phase 1 of the Source Water-Quality Assessment (SWQA) with 

VOCs detected in other local and regional studies......................................................43

6. Comparison of pesticides detected in the source water during phase 1 of the 

Source Water-Quality Assessment (SWQA) with pesticides detected in other 

local and regional studies ................................................................................................44

7. Comparison of other anthropogenic organic compounds (OAOCs) detected 

in the source water during phase 1 of the Source Water-Quality Assessment 

(SWQA) with OAOCs detected in a local study ............................................................45

8. Comparison between source and associated finished water for anthropogenic 

organic compounds detected during phase 2 of the Source Water-Quality 

Assessment ........................................................................................................................46
viii

Abbreviations and Acronyms

< less than

> greater than

μg/L micrograms per liter

AOC anthropogenic organic compound

BQ benchmark quotient

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

CASR Chemical Abstracts Service Registry

CCR Consumer Confidence Report

CWS community water system

DBP disinfection by-product

DEET N,N-diethyl-meta-toluamide

E estimated concentration

GAFL Georgia-Florida Coastal Plain

GC/MS gas chromatography-mass spectrometry

GIS geographic information system

HBSL Health-Based Screening Level

MAS major aquifer study

MCL Maximum Contaminant Level

MRL maximum reporting level

MTBE methyl tert-butyl ether

NAWQA National Water-Quality Assessment

NWQL National Water Quality Laboratory

OAOC other anthropogenic organic compound

PCE perchloroethene

SWQA Source Water-Quality Assessment

TCEP tri(2-chloroethyl)phosphate

TCPP tri(dichloroisopropyl)phosphate

ULUS urban land-use study

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound
ix

Definitions

Terms for which definitions are provided below are presented in boldface type when first used 

in the text

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

Contaminant Level (MCL) value for a regulated compound or to its 

Health-Based Screening Level (HBSL) value for an unregulated 

compound. BQs greater than 1 identify concentrations of 

potential human-health concern. BQs greater than 0.1 identify 

compounds that may warrant inclusion in a low-concentration, 

trends-monitoring program.

BQmax Ratio of the maximum concentration of a contaminant to its MCL 

or HBSL value.

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

one or more different ground-water sources. Finished water 

blended with surface water was not sampled as part of this study.

Concentration of potential 

human-health concern

As used in this report: (1) for a regulated compound with a 

U.S. Environmental Protection Agency (USEPA) drinkingwater standard, a concentration greater than the Maximum 

Contaminant Level; and (2) for an unregulated compound, a 

concentration greater than the Health-Based 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 is subject to USEPA 

regulations enforcing the Safe Drinking Water Act. A community 

water system serves a residential population, such as a 

municipality, mobile home park, or nursing home.

Drinking-water guideline As used in this report, a threshold concentration that has no 

regulatory status, but is issued in an advisory capacity by the 

USEPA or State agencies.

Drinking-water standard As used in this report, a threshold concentration that is legally 

enforceable (such as MCLs) by the 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)

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 

U.S. Geological Survey (USGS) in collaboration with USEPA and 

others using USEPA methodologies for establishing drinkingwater guidelines and the most current, USEPA peer-reviewed, 

publicly available human-health toxicity information.

Human-health benchmarks As used in this report, these include USEPA and Florida 

Department of Environmental Protection (FDEP) MCL values and 

HBSL values developed collaboratively by the USGS, USEPA, 

New Jersey Department of Environmental Protection, and Oregon 

Health & Science University.
Maximum Contaminant 

Level (MCL)

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 non-enforceable public health goals that take into 

account the best available technology, treatment techniques, 

cost considerations, expert judgment, and public comments.

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

State drinking-water standard has been established.

Source water Source water is 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 

Northern Tampa Bay Area, Florida, 2002–04

By Patricia A. Metz, Gregory C. Delzer,Marian P. Berndt, Christy A. Crandall, and Patricia L. Toccalino

chloroform) and pesticides were highest in residential land-use 

areas.

The results of source-water samples from the 30 CWS 

wells monitored during phase 1 of this SWQA study were 

compared to four locally conducted studies. These general 

comparisons indicate that the occurrence of VOCs in other 

studies is similar to their occurrence in source water of 

CWSs monitored as part of this SWQA. However, pesticide 

compounds, especially atrazine and its breakdown products, 

occurred more frequently in the SWQA study than in the other 

four studies.

Phase 2 of the SWQA assessed AOCs in samples from 

11 of the 30 CWS wells and the associated finished water. 

Overall, 42 AOCs were detected in either source water or 

finished water and more compounds were detected in finished 

water than in source water. Specifically, 22 individual AOCs 

were detected in source water and 27 AOCs were detected in 

finished water. The total number of detections was greater in 

the finished water (80) than in the source water (49); however, 

this was largely due to the creation of disinfection by-products 

(DBPs) during water treatment. Excluding DBPs, about the 

same number of total detections was observed in source water 

(40) and finished water (44).

During phase 2, AOC detected concentrations ranged 

from E0.003 (estimated) to 1,140 μg/L in the source water and 

from E0.003 to 36.3 μg/L in the finished water. Concentrations 

of 24 of the 42 compounds were compared to human-health 

benchmarks and were about 1 to 5 orders of magnitude below 

their human-health benchmarks indicating that concentrations 

are unlikely to be of potential human-health concern, 

excluding DBPs. Concentrations of carbon tetrachloride, 

however, were within 10 percent of its human-health 

benchmark, which is considered a level that may warrant 

inclusion of the compound in a low-concentration, trendsmonitoring program. The potential human-health relevance 

for the remaining 18 detected unregulated AOCs could not 

be evaluated because no human-health benchmarks were 

available for these compounds.

The source-water results were compared with the 

associated finished water results. On the basis of this 

Abstract

As part of the U.S. Geological Survey’s (USGS’s) 

National Water-Quality Assessment (NAWQA) Program, a 

Source Water-Quality Assessment (SWQA) was conducted 

in the unconfined and semiconfined portions of the Upper 

Floridan aquifer system during 2002–04. SWQAs are twophased sampling activities, wherein phase 1 was designed 

to evaluate the occurrence of 258 anthropogenic organic 

compounds (AOCs) in ground water used as source water for 

30 of the largest-producing community water system (CWS) 

wells in the northern Tampa Bay area, Florida. The 258 AOCs 

included volatile organic compounds (VOCs), pesticides, and 

other anthropogenic organic compounds (OAOCs). Phase 2 

was designed to monitor concentrations in the source water 

and also the finished water of CWSs for compounds most 

frequently detected during phase 1.

During phase 1 of the SWQA study, 31 of the 258 AOCs 

were detected in source-water samples collected from CWS 

wells at low concentrations (less than 1.0 microgram per liter 

(μg/L)). Twelve AOCs were detected in at least 10 percent of 

samples. Concentrations from 16 of the 31 detected AOCs 

were about 2 to 5 orders of magnitude below human-health 

benchmarks indicating that concentrations were unlikely to 

be of potential human-health concern. The potential humanhealth relevance for the remaining 15 detected unregulated 

AOCs could not be evaluated because no human-health 

benchmarks were available for these compounds.

Hydrogeology, population, and land use were examined 

to evaluate the effects of these variables on the source water 

monitored. Approximately three times as many detections 

of VOCs (27) and pesticides (34) occurred in unconfined 

areas than in the semiconfined areas (8 VOCs, 14 pesticides). 

In contrast, 1 OAOC was detected in unconfined areas, and 

13 OAOCs were detected in semiconfined areas with 9 of the 

OAOC detections occurring in samples from two wells located 

near septic systems. Analyses of population and land use 

indicated that the number of compounds detected increased 

as the population surrounding each well increased. Detection 

frequencies and concentrations for VOCs (particularly 
comparison, it appears that additional data are needed to 

determine how source water compares to finished water. In 

this study, the occurrence of VOCs in source water does not 

necessarily characterize the occurrence of VOCs in finished 

water, especially because 14 of 18 detected VOCs occurred in 

the source water or finished water, but not both. In contrast, 

monitoring selected pesticides in source water (especially 

atrazine and its breakdown products) may approximate the 

occurrence of these pesticides in finished water. However, 

the effect of blending makes it difficult to compare source 

water to finished water without monitoring all CWS wells that 

contribute to blended finished water.

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 more than 50 of the largest and 

most important river basins and aquifers across the Nation; 

(2) define long-term trends in water quality; and (3) identify, 

describe, and explain, as possible, the major factors that 

affect observed water-quality conditions and trends. This 

information, which is obtained on a continuing basis, is made 

available to water managers, policy makers, and the public to 

help address and prioritize the multitude of issues related to 

managing and protecting our water resources.

Beginning in 2001, the NAWQA Program began its 

second decade of intensive assessment activities by returning 

to 42 of the original river basins and aquifers studied during 

the first decade (fig. 1). The second decade of assessments is 

designed to build upon the initial assessments of water-quality 

conditions and establish links between sources, transport, and 

the potential effects of contaminants on humans and aquatic 

ecosystems. This will be accomplished through a variety of 

new, focused study components within the NAWQA Program. 

One such new assessment activity focuses on characterizing 

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

of supply to larger community water systems (CWSs)

located in many of the original 42 basins studied. These 

activities are called Source Water-Quality Assessments 

(SWQAs) and are intended to complement drinking-water 

monitoring required by Federal, State, and local programs, 

which focus primarily on post-treatment compliance 

monitoring. Through SWQAs, NAWQA is increasing its 

emphasis on characterizing water-quality of rivers and aquifers 

that are major sources of drinking water and will continue to 

collaborate with other agencies and organizations involved 

with supplying and managing drinking water.

One ground-water SWQA study was completed in the 

Georgia-Florida Coastal Plain (GAFL) Study Unit during 

2002–04. The GAFL Study Unit (fig. 1) includes northern 

Florida and central Georgia, which covers an area about 

61,000 square miles (mi2). In 2000, approximately 3 billion 

gallons per day of ground water was withdrawn in the Study 

Unit with more than 90 percent of withdrawals from the 

Floridan aquifer system (R.L. Marella, U.S. Geological 

Survey, written commun., 2005). As a result, the northern 

Tampa Bay area (fig. 2) was chosen for an SWQA because of 

the large population that relies heavily on the ground-water 

resources from the Upper Floridan aquifer system.

The water-quality sampling for SWQAs consists of two 

phases. Phase 1 focuses on determining the occurrence of 

258 anthropogenic organic compounds (AOCs) (Appendixes 

1, 2, and 3) in the source water of some of the largest CWS 

wells in the Study Units. The occurrence of AOCs in the 

source water and the associated finished water is assessed 

during phase 2 for those AOCs detected most frequently 

during phase 1. Currently (2006), 12 ground-water SWQAs 

have been completed and 3 more will be completed by 

NAWQA during the year.

The AOCs monitored as part of SWQAs include 

volatile organic compounds (VOCs), pesticides, and other 

anthropogenic organic compounds (OAOCs). VOCs are a 

subset of organic chemicals that have been produced and 

used in a variety of commercial, industrial, and household 

applications for many decades and are a major component 

or additive to gasoline, paints, varnishes, glues, dyes, and 

plastics. Pesticides are used extensively throughout the United 

States to increase crop yields; enhance the aesthetics of lawns, 

gardens, golf courses, and recreational areas; and protect 

the safety of the public from insect-associated diseases. The 

widespread use of pesticides over the past several decades has 

led to their frequent detection in ground water (Barbash and 

Resek, 1996). OAOCs represent a 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. Little is known about the environmental 

occurrence, transport, and ultimate fate of OAOCs after their 

intended 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 low concentrations that might be expected 

in the environment.

The purpose of many USGS water-quality studies is to 

assess the occurrence of contaminants in the Nation’s water 

resources (ambient water-quality assessments, hereafter 

referred to as other studies) and little emphasis is placed 

specifically on source water and even less emphasis is placed 

on finished water. In SWQAs, source water includes waters 

from CWS wells, and finished water represents source water 

that has been treated (at least disinfected) prior to distribution. 

Finished water may be composed of water from multiple CWS 

wells (blended water) or it may be composed only of water 

from one CWS well and treated at (or near) the well (nonblended).

   Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Georgia-Florida

NAWQA Study Unit

Ground-Water Source Water-Quality

 Assessment location 

EXPLANATION

NAWQA Study Units—Scheduled

 to begin in fiscal year: 

2001

2004

2007

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

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

Because most other studies do not provide direct linkage 

to source water of CWSs due to the type of well sampled 

(such as monitoring and domestic wells), a need exists to, at 

minimum, qualitatively determine how representative results 

from other studies conducted by the USGS are of source 

water used by large and very large CWSs. This qualitative 

representation may be accomplished by comparison of results 

from other studies with those from SWQAs. Similarly, 

because the application of various treatment technologies 

alters the water chemistry of source water to meet various 

Federal and State drinking-water requirements, a need exists 

to better understand how representative source-water results 

are of finished water prior to distribution. A sequential 

comparison of results from other studies with source water 

and a separate comparison of source water with finished 

water may begin to characterize the overall representative 

nature of other studies conducted by USGS on the quality of 

finished water prior to distribution. Linking these types of 

studies is important, especially considering the documented 

occurrence of AOCs in finished water at concentrations similar 

to those found in source water (Stackelberg and others, 2004; 

Loraine and Pettigrove, 2006) and in simulated drinking-water 

treatment processes (Westerhoff and others, 2005). Thus, data 

obtained through SWQAs characterize not only the quality of 

source water and finished water of some of the larger CWSs 

prior to distribution but also begin to provide a mechanism 

to bring results obtained from other studies into context with 

water used for human consumption.

Purpose and Scope

The purpose of this report is to describe the occurrence 

of AOCs in ground water and finished water of CWSs in the 

northern Tampa Bay area during 2002–04. The SWQA results 

are compared to findings from selected ambient water-quality 

assessments that monitored the same compounds using the 

same field and analytical techniques.

For the assessment of ground water, this report describes 

the occurrence of 258 AOCs in source water obtained from 

30 of the largest producing CWS wells (source-water wells) in 

the northern Tampa Bay area. One-half of the CWS wells were 

screened in unconfined areas, and one-half were screened in 

semiconfined areas of the Upper Floridan aquifer. In addition, 

Introduction 
the effects of hydrogeology, as well as land use and population 

density, on the water quality in these settings are described for 

the 30 CWS wells.

This report also presents a comparison of the SWQA 

results from the source-water samples from 30 CWS wells to 

results from four other locally conducted studies. Specifically, 

results are compared to three studies of the Upper Floridan 

aquifer and one study of the Biscayne aquifer in Miami-Dade, 

Broward, and Palm Beach Counties, Florida.

Finally, this report describes the occurrence of selected 

AOCs in samples from 11 of the 30 CWS wells and in the 

associated finished water. Concentrations are compared 

to USEPA Maximum Contaminant Levels (MCLs) and 

Health-Based Screening Levels (HBSLs) developed by the 

USGS in collaboration with USEPA and others to evaluate the 

potential relevance of the findings to human health.

Acknowledgments

The authors are grateful to the many public and private 

organizations for providing information pertaining to the 

wells used in this study and for permitting the collection of 

samples for water-quality analyses. The authors also express 

their appreciation for the technical discussions with John 

Troutt from Tampa Bay Water, Dave Slonena from Pinellas 

County Utilities, and Dave DeWitt from Southwest Florida 

Water Management District. The authors acknowledge USGS 

employees Jessica Hopple and Yvonne Stoker for their 

constructive review comments and Scott McBride, Terry 

Petrosky, and Darlene Blum for their help with field collection 

and data compilation.

Description of Study Area

The study area is approximately 2,000 mi2 and includes 

all of Pasco County and parts of Hernando, Pinellas, 

Hillsborough, and Polk Counties (fig. 2). The topography 

of the study area is characterized by flat, marshy lowlands 

along the coast, low rolling hills in the central region, and 

sand ridges and terraces that vary more than 200 feet (ft) in 

elevation in the northern and eastern regions. Hundreds of 

lakes, wetlands, and marshes are interspersed throughout 

the study area, ranging from less than an acre to more than 

2,500 acres. Six rivers and their tributaries and several springs 

that discharge inland and along the coast are located within the 

study area.

Warm, wet summers and relatively mild, dry springs 

characterize the subtropical climate of the study area. Rainfall 

varies seasonally with more than one-half the annual rainfall 

typically occurring during June through September. Long-term 

average rainfall for the south-central Georgia and peninsular 

Florida is about 53 inches per year (Bush and Johnston, 1988).

Land Use

The northern Tampa Bay area has experienced an 

increase in urbanization during the last 20 years, which has 

resulted in substantial land-use changes. The population 

increased from 1.1 million in 1980 to an estimated 2 million 

in 2003 (U.S. Census Bureau, 2002). Many of the land-use 

changes in the last 20 years can be attributed to increases in 

residential land use.

Geographic information system (GIS) land-use coverages 

were used to determine the land-use distribution within 

the study area (Vogelmann and others, 2001). Land use 

was grouped into six categories with the percentage of the 

total area occupied by each category as follows: residential 

(25 percent); wetlands and surface water (25 percent); open 

land and recreational (20 percent); agricultural (pasture and 

tree plantations, 18 percent); commercial, industrial, and 

transportation (8 percent); and agricultural (nurseries and 

farms, 4 percent) (fig. 2). The majority of residential and 

commercial land use is concentrated along the coast and in the 

southern area near Tampa Bay, whereas many of the wetlands, 

open-land and recreational, and agricultural land-use areas 

are located in the northern, central, and eastern regions of the 

study area.

Hydrogeology

The geologic units underlying the study area consist of 

sand, clay, and carbonate rocks that were deposited primarily 

in a marine environment. Deposition of each geologic 

formation was followed by a period of erosion that resulted 

in the development of surface irregularities and solution 

cavities in the limestone. The hydrogeologic setting of the 

study area is characterized by limited confinement between the 

land surface and underlying karst limestone, springs, several 

sinking streams, and more than 800 documented sinkholes. 

Principal hydrogeologic units include the surficial aquifer, the 

intermediate confining unit, and the Upper Floridan aquifer 

(fig. 3).

The uppermost unit, the surficial aquifer, is an unconfined 

sand and clay aquifer. The thickness of these surficial 

sediments ranges from about 10 to 60 ft. The water table of 

the surficial aquifer is at a relatively shallow depth below land 

surface (approximately 1 to 10 ft). Because of the shallow 

depth to the water table and the permeable sand deposits, the 

ground water in the surficial aquifer is affected by localized 

land-use practices (Metz and Sacks, 2002).

The intermediate confining unit is a nonwater-yielding 

layer that impedes the downward flow from the surficial 

aquifer. The confining unit consists of dense, marine, plastic 

clay that contains varying amounts of sand, chert, and 

carbonate mud (Sinclair, 1974). The clay confining unit is 

variable in extent, thickness, and permeability throughout the 

study area.

   Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Weeki

Wachee

River

GULF OF MEXICO

OLD

TAMPA

BAY Alafia River

River

River

River

River

Anclote

Pithlachascotee

Withlacoochee

Hillsborough

Brooksville

Weeki Wachee

Spring Hill

Hudson Dade City

Port Richey

Zephyrhills

Lutz

Citrus Park

Dunedin Temple Terrace

Tampa Brandon

Lakeland

Clearwater

PINELLAS

COUNTY

PASCO COUNTY

HILLSBOROUGH COUNTY

POLK COUNTY

HERNANDO COUNTY

PASCO COUNTY

A

A‘

A A‘

FLORIDA

82°45’ 30’ 82°00’

28°30’

28°00’

15’

 15’

0 5 10

0 5 10

MILES

KILOMETERS

Base from U.S. Geological Survey digital data 1:2,000,000, 1987

Universal Transverse Mercator projection, Zone 17

Land use from Vogelmann and others, 2001

Residential

Commercial, industrial, and transportation

Wetlands and surface water 

Open land and recreational

Agriculture (nurseries and farms) 

Agriculture (pasture and tree plantations)

EXPLANATION

General location of springs

Hydrogeologic section—Referenced in figure 3 

Land use

Figure 2. Location and land use of the study area.

Description of Study Area 
A A‘

South North

ELEVATION, IN FEET ABOVE OR

BELOW NGVD OF 1929

100

50

 0

50

100

150

Surficial aquifer

Intermediate confining unit

Upper Floridan aquifer Hillsborough River

Figure 3. Generalized hydrogeologic section of the study area. Location of section is shown in figure 2.

Underlying the intermediate confining unit is the Upper 

Floridan aquifer, which is the major source of water supply 

within the study area. The aquifer is contained in a thick 

sequence of limestone and dolomite, which has many solutionenlarged fractures and cavities. Public-supply wells that tap 

this limestone and dolomite unit commonly yield several 

hundred to several thousand gallons per minute. For the 

purpose of this report, the following two areas of confinement 

for the Upper Floridan aquifer are distinguished within the 

study area: (1) an unconfined area, for which the intermediate 

confining unit ranges in thickness from zero to less than 

5 ft; and (2) a semiconfined area for which the intermediate 

confining unit ranges in thickness from 5 ft to more than 100 ft 

(fig. 4).

Ground-Water Withdrawals and Distribution

The northern Tampa Bay area relies heavily on ground 

water for public supply. More than 700 public-supply wells are 

permitted for use within the study area. Public-supply water is 

used for a variety of purposes, such as domestic, commercial, 

industrial, and agricultural uses. These supply wells may be 

publicly or privately owned and operated, and the source water 

may be treated prior to distribution.

As used in this study, source water is the raw (ambient) 

water collected at the supply well prior to water treatment, 

blended water is a mixture of water from several ground-water 

sources, and finished water is the source water or blended 

water that is treated and ready to be delivered to consumers. 

Blended water, by definition, also could include a mixture of 

ground water and surface water; however, this study (as well 

as other ground-water SWQAs) only included systems that 

blended with other ground waters.

Much of the ground water supplied by CWSs within 

the study area is obtained from a regional system of 

11 interconnected well fields. Withdrawals during 2000 were 

approximately 200 million gallons per day (Mgal/d) (R.L. 

Marella, U.S. Geological Survey, written commun., 2005). 

In this study, blended water typically was treated by several 

processes, including the addition of hypochlorous acid and 

ammonia to form chloramines (fig. 5A). Non-blended ground 

water typically is treated only with chlorine (fig. 5B) prior to 

entering the distribution system.

In addition to the well fields, hundreds of wells are 

permitted for small communities and municipalities within 

the study area. These wells cumulatively pump approximately 

80 Mgal/d and range from serving less than 500 residents 

to the larger municipality wells serving more than 150,000 

residents (R.L. Marella, U.S. Geological Survey, written 

commun., 2005). Water from these CWS wells are treated 

prior to distribution by a variety of methods including 

disinfection using chlorine gas, coagulation and filtration, 

adsorption, lime softening, addition of corrosion and pH 

control additives, and reverse osmosis.

 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
GULF OF MEXICO

OLD

TAMPA

BAY

Brooksville

Weeki Wachee

Spring Hill

Hudson Dade City

Port Richey

Zephyrhills

Lutz

Citrus Park

Dunedin Temple Terrace

Tampa Brandon

Lakeland

Clearwater

PINELLAS

COUNTY

PASCO COUNTY

HILLSBOROUGH COUNTY

POLK COUNTY

HERNANDO COUNTY

PASCO COUNTY

6

17

3

8

1

15

12

13

2

4

9

10

28

18

30

24

16

19 20

21

22

27

26

25

11

5

7

14

23

29

6

17

A

A‘

A A‘

30’ 82°00’

28°30’

28°00’

15’

82°45’ 15’

0 5 10

0 5 10

MILES

KILOMETERS

Unconfined area, confining unit 0 to 5 feet thick 

Semiconfined area, confining unit 5 to more than

 100 feet thick 

EXPLANATION

Upper Floridan aquifer

Inferred geologic contact

Phase-one sampling—30 source-water wells. Number is 

 well identification

Phase-two sampling—Resampling of 11 source-water and 

 associated finished-water wells. Number is well 

 identification

Hydrogeologic section—Referenced in figure 3 

Base from U.S. Geological Survey digital data 1:2,000,000, 1987

Universal Transverse Mercator projection, Zone 17

Figure 4. Distribution of the intermediate confining unit overlying the Upper Floridan aquifer and location of wells sampled 

in phase 1 and source-water wells where the associated finished water also was sampled in phase 2 of the study.

Description of Study Area 
A

B

(A) Treatment plant that blends ground water from several source wells. 

Treatment is then performed on the blended water and distributed. 

(B) Example of a non-blended well site where ground water is disinfected at 

the well and distributed to the nearby community.

Figure 5. Example of two treatment facilities located in the study 

area.

Site Selection, Methods, and HumanHealth Benchmarks

This section describes the process used to select the 

sampled wells and the methods for sample collection and 

analyses. Regulatory and non-regulatory human-health 

benchmarks used in this report also are described, and a 

description of how water-quality results are interpreted in a 

human-health context is provided.

Site Selection and Methods

In phase 1 of the study, 30 public-supply wells serving 

CWSs were sampled to characterize the occurrence of 

anthropogenic compounds that may exist in ground water. 

To characterize the effects of hydrogeology on the groundwater quality, 15 wells in the unconfined areas and 15 wells 

in the semiconfined areas of the Upper Floridan aquifer were 

selected (fig. 4). The wells were selected from more than 

700 CWS wells using a random computerized statistical 

process (Statistical Analysis System, 1989). The well 

selection process included selecting only wells in the upper 

25th percentile of pumping volume (withdrawals greater than 

about 200,000 gallons per day) with a minimum distance 

of 0.62 mile (1 kilometer) between well sites to minimize 

sampling the same volume of water from the aquifer. These 

highest producing wells (based on pumping volume) tend 

to stress the ground-water systems more, have a larger 

cone of depression, and hence are more likely to capture 

anthropogenic contaminants than lower producing wells. 

Wells were sampled in October 2002 through January 2003 for 

88 VOCs, 120 pesticides, and 50 OAOCs (Appendixes 1, 2, 

and 3, respectively).

During phase 2 of the study, 11 of the 30 wells were 

selected for resampling in August and September 2004 on 

the basis of the occurrence of AOCs detected most frequently 

in phase 1 (fig. 4). Samples of both source water and the 

associated finished water from 10 wells were analyzed for 

VOCs, 6 wells for pesticides, and 2 wells for OAOCs.

Ground-water samples were collected using established 

USGS protocols (Koterba and others, 1995), and finishedwater samples were collected after treatment and prior to the 

water entering 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 (Winslow and others, 2001). 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 these dechlorination reagents to 

water samples was tested in a laboratory setting, and results 

indicated that they did not interfere with the analytical 

 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
performance (Mark Sandstrom, USGS National Water Quality 

Laboratory, oral commun., 2004).

All samples were analyzed at the USGS National Water 

Quality Laboratory (NWQL) in Denver, Colorado. Water 

samples were analyzed for VOCs using purge and trap 

capillary column gas chromatography/mass spectrometry 

(GC/MS) (Connor and others, 1998) and for pesticides using 

capillary column GC/MS (Zaugg and others, 1995; Lindley 

and others, 1996; Furlong and others, 2001; Sandstrom and 

others, 2001; Madsen and others, 2003). Water samples 

were analyzed for OAOCs using solid-phase extraction and 

capillary-column GC/MS (Zaugg and others, 2002). Data are 

presented in Carter and others (2007).

The minimum reporting level (MRL) is the smallest 

measured concentration of a constituent that may be reliably 

reported using a given analytical method (Timme, 1995). 

Concentrations greater than (>) the MRL are reported 

as detected concentrations. Some analyte concentrations 

were flagged with an “E” to indicate estimated values. 

Concentrations are estimated when a compound is found to be 

present in a water sample but the concentration is less than the 

lowest-daily calibration standard.

Quality-assurance/quality-control samples were collected 

following methods by Koterba and others (1995). All SWQA 

data are reviewed on an annual basis to evaluate systematic 

contamination. If systematic contamination is identified, those 

data are removed from the data set and not used in subsequent 

data analyses (D.A. Bender (VOCs), J.A. Hopple (pesticides), 

and J.A. Kingsbury (OAOCs), U.S. Geological Survey, written 

commun., 2006). Field-blank samples collected as part of the 

GAFL SWQA did not contain any compounds detected in 

source or finished water with the exception of N,N-diethylmeta-toluamide (DEET). DEET was detected in one fieldblank sample collected during phase 1; however, it was not 

detected in any blanks collected during phase 2. Because the 

DEET detection in one blank sample was not considered to 

be representative of systematic contamination, DEET results 

were retained in the data set. However, the overall effect of the 

DEET detection in one blank sample is not fully understood, 

and needs to be considered in subsequent interpretations.

Human-Health Benchmarks

The USGS began an interagency pilot effort in 1998 to 

communicate the importance of water-quality findings of the 

NAWQA Program in a human-health context. Historically, the 

USGS has assessed water-quality conditions by comparing 

measured concentrations with human-health benchmarks 

such as established Federal or State drinking-water 

standards and guidelines. The drinking-water standards for 

regulated compounds are called MCLs, which are legally 

enforceable standards that set 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 the maximum level of a contaminant at which no known 

or anticipated adverse effects on human health would occur, 

taking into account the best available technology, treatment 

techniques, cost considerations, expert judgment, and public 

comments (U.S. Environmental Protection Agency, 2006).

Federal drinking-water standards and guidelines currently 

(2006) are not available for nearly one-half of the organic 

compounds most frequently analyzed by the NAWQA 

Program and other USGS studies (Toccalino and others, 

2005). In order to provide a more complete understanding of 

the human-health relevance of water-quality data collected, 

existing Federal drinking-water standards and guidelines are 

supplemented by HBSL values calculated for unregulated 

compounds (compounds without Federal drinking-water 

standards). HBSLs were calculated using an approach that was 

developed collaboratively by the USGS, U.S. Environmental 

Protection Agency (USEPA), New Jersey Department of 

Environmental Protection, and Oregon Health & Science 

University (Toccalino and others, 2003, 2004).

HBSLs are not legally enforceable regulatory standards, 

and water utilities are not required to compare contaminant 

monitoring results to HBSLs. HBSLs are benchmark 

concentrations of contaminants in water that may be of 

potential concern for human health, if exceeded, and can 

be used as threshold values against which contaminant 

concentrations in water samples 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 potential 

human-health concern in water resources (Toccalino and 

others, 2005). Appendix 4 provides descriptions of the humanhealth 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 was 

used to identify concentrations of potential human-health 

concern (hereafter referred to as concentrations of potential 

concern). A BQmax threshold value greater than or equal 

to 0.1 was used to identify compounds that may warrant 

inclusion in a low-concentration, trends-monitoring program; 

frequently occurring compounds (in this report, frequently 

occurring indicates an occurrence of an AOC in 10 percent 

or more of samples) also may warrant inclusion in such a 

monitoring program. Such monitoring allows for analyzing 

trends in their occurrence, may provide an early indication of 

contaminant levels that approach human-health benchmarks, 

and consequently, approach concentrations of potential 

human-health concern.

Site Selection, Methods, and Human-Health Benchmarks 
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/ccrfact.html). 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 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 raw (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; therefore, contaminant detection frequencies 

reported in SWQA reports 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), 

respectively. HBSLs are benchmark concentrations of 

contaminants in water that may be of potential humanhealth concern, if exceeded, 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 during Phase 1

A total of 31 of the 258 individual AOCs were detected 

(11 VOCs, 12 pesticides, and 8 OAOCs) in ground-water 

(source-water) samples collected from 30 CWS wells sampled 

between October 2002 and January 2003 during phase 1 of 

the SWQA study (table 1). The 10 most frequently occurring 

AOCs were detected in at least 13 percent of the 30 sourcewater samples and included chloroform, deethylatrazine, 

atrazine, 2-hydroxyatrazine, bentazon, carbon disulfide, 

prometon, DEET, perchloroethene (PCE), and simazine. 

Sam­ples generally contained a mixture of compounds (average 

of three compounds per sample), and 70 percent of the 

samples contained at least one AOC.

Concentrations for compounds detected in the source 

water were low (defined in this report as concentrations less 

than 1.0 microgram per liter (μg/L)). Concentrations were 

compared to their respective human-health benchmarks 

(MCLs for regulated compounds or HBSLs for unregulated 

compounds), which were available for 16 of the 31 detected 

compounds. Concentrations were about 2 to 5 orders 

of magnitude less than their human-health benchmarks, 

indicating that these concentrations are unlikely to be of 

potential human-health concern (table 1). The potential 

human-health relevance of the remaining 15 detected 

unregulated contaminants could not be evaluated because 

human-health toxicity information necessary to calculate 

HBSLs for these contaminants was not available. Additional 

monitoring may be warranted for frequently occurring AOCs 

(defined in this report as occurring in 10 percent or more of 

samples) that do not have human-health benchmarks, such as 

1,2,4-trimethylbenzene, to better understand their spatial and 

temporal distribution, as well as sources, transport, and fate.

When comparing analytical results among different 

AOCs, it is important to consider the analytical MRL of each 

AOC. That is, an AOC may have a higher detection frequency 

in comparison to other AOCs that have higher MRLs. A true 

comparison is possible, however, when comparing individual 

compounds analyzed using the same analytical method 

(same MRL). For the purposes of this report, comparisons of 

AOCs are made among AOCs and between studies regardless 

of varying MRLs (Appendixes 1, 2, and 3) to characterize 

general occurrence rates and similarities, or the lack thereof, 

between these studies.

Volatile Organic Compounds

Eleven VOCs were detected in the source-water samples 

(table 1, fig. 6A). Chloroform, the most frequently detected 

compound (43 percent of samples), may enter the hydrologic 

system from recharge of chlorinated water, direct releases 

10 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Table 1. Maximum concentration, detection frequency, and maximum benchmark quotient for regulated and unregulated compounds 

detected in samples from 30 source-water wells of community water systems in the northern Tampa Bay area.

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

Level; BQmax, maximum benchmark quotient = ratio of maximum compound concentration to MCL or HBSL value; DEET, N,N,-diethyl-meta-toluamide; E, 

estimated value; μg/L, micrograms per liter; <, less than; NA, not applicable; --, not available. A regulated compound is a compound for which Federal and (or) 

State drinking-water standards have been established; an unregulated compound is a compound for which no Federal and (or) State drinking-water standards 

have been established]

Regulated (R) or

unregulated (U)

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 MCL1 

or HBSL3

(μg/L)

BQmax for 

source water

Volatile organic compounds

Chloroform (R) 67–66–3 13 43 0.024 0.957 280 0.01

Carbon disulfide (U) 75–15–0 5 17 .038 .131 700 .0002

Perchloroethene (PCE) (R) 127–18–4 4 13 .03 .190 5 .04

Bromodichloromethane (R) 75–27–4 3 10 .028 E.043 280 .0005

1,2,4-Trimethylbenzene (U) 95–63–6 3 10 .056 E.030 -- --

Bromoform (R) 75–25–2 2 7 .1 E.038 280 .0005

1,1-Dichloroethane (U) 75–34–3 1 3 .035 E.021 -- --

cis-1,2-Dichloroethene (R) 156–59–2 1 3 .024 E.022 70 .0003

Methyl tert-butyl ether (MTBE) (U) 1634–04–4 1 3 .1 E.035 -- --

Trichloroethene (R) 79–01–6 1 3 .038 .142 5 .03

Trichlorofluoromethane (U) 75–69–4 1 3 .08 E.047 2,000 .00002

Total number of VOC detections NA 35 NA NA NA NA NA

Pesticides

Deethylatrazine (U) 6190–65–4 10 33 0.014 E0.048 -- --

Atrazine (R) 1912–24–9 7 23 .007 .036 3 0.01

2-Hydroxyatrazine (U) 2163–68–0 7 23 .032 E.025 70 .0004

Bentazon (U) 25057–89–0 6 20 .024 E.027 200 .0001

Prometon (U) 1610–18–0 5 17 .01 .018 100 .0002

Simazine (R) 122–34–9 4 13 .005 .010 4 .003

Deisopropylatrazine (U) 1007–28–9 2 7 .08 E.008 -- --

Imidacloprid (U) 105827–78–9 2 7 .02 .023 400 .00006

Tebuthiuron (U) 34014–18–1 2 7 .026 E.030 1,000 .00003

Bromacil (U) 314–40–9 1 3 .018 E.087 70 .001

3,4-Dichloroaniline (U) 95–76–1 1 3 .0045 E.002 -- --

Fonofos, oxygen analog (U) 944–21–8 1 3 .0029 .002 -- --

Total number of pesticide detections NA 48 NA NA NA NA NA

Other anthropogenic organic compounds

DEET (U) 134–62–3 5 17 0.5 E0.021 -- --

Cholesterol (U) 57–88–5 2 7 2 E.530 -- --

3-beta-Coprostanol (U) 360–68–9 2 7 2 E.340 -- --

p-Cresol (U) 106–44–5 1 3 1 E.054 -- --

Indole (U) 120–72–9 1 3 .5 E.080 -- --

4-Octylphenol diethoxylate (U) 26636–32–8 1 3 1 E.010 -- --

beta-Sitosterol (U) 83–46–5 1 3 2 E.390 -- --

beta-Stigmastanol (U) 19466–47–8 1 3 2 E.360 -- --

Total number of other anthropogenic 

organic compound detections

NA 14 NA NA NA NA NA

Total number of detections for all 

compounds

NA 97 NA NA NA NA NA

1

U.S. Environmental Protection Agency (2003, 2004).

2

MCL is for total trihalomethanes.

3

Denotes HBSL (Toccalino and others, 2006a).

Anthropogenic Organic Compounds in Ground Water during Phase 1 11
Chloroform

Carbon disulfide

Perchloroethene (PCE)

1,2,4-Trimethybenzene

Bromodichloromethane

Bromoform

1,1-Dichloroethane

Trichlorofluoromethane

Trichloroethene

cis-1,2-Dichloroethene

Methyl tert-butyl ether

(MTBE)

13

5

4

3

3

2

1

1

1

1

1

NUMBER OF DETECTIONS NUMBER OF DETECTIONS NUMBER OF DETECTIONS

Deethylatrazine

Atrazine

2-Hyroxyatrazine

Bentazon

Prometon

Simazine

Tebuthiuron

Deisopropylatrazine

Imidacloprid

Bromacil

3,4-Dichloroaniline

Funofos, oxygen analog

10

7

7

6

5

4

2

2

2

1

1

1

N,N,-Diethyl-meta-toluamide

(DEET)

3-beta-Coprostanol

beta-Sitosterol

beta-Stigmastanol

Indole

4-Octylphenol diethoxylate

p-Cresol

Cholesterol

5

2

2

1

1

1

1

1

0.00001 0.0001 0.001 0.01 0.1 1 10

CONCENTRATION, IN MICROGRAMS PER LITER BENCHMARK QUOTIENT VALUE

[Bold type indicates an unregulated compound; underlined indicates the unregulated compound does not have an 

HBSL; 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)]

0.00001 0.0001 0.001 0.01 0.1 1 10

A

B

C

Benchmark quotient value of 0.1—

 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

EXPLANATION

No human-health

benchmarks

available

Figure 6. Concentrations, number of detections, and benchmark quotient values for (A) volatile organic compounds, 

(B) pesticides, and (C) other anthropogenic organic compounds from 30 source-water wells during phase 1.

12 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
(air emissions, discharges to surface water, underground 

injections, and releases to land), dehalogenation of carbon 

tetrachloride, and a variety of natural sources (Ivahnenko and 

Barbash, 2004). Chloroform is one of the four disinfection 

by-products (DBPs; bromodichloromethane, bromoform, 

chloroform, and dibromochloromethane) produced in the 

highest concentrations during the chlorination of drinking 

water and wastewater. Detection of chloroform in ground 

water along with associated DBPs provides a means for 

distinguishing between the input of chlorinated water to the 

hydrologic system and the input of other chloroform sources 

to the environment (Ivahnenko and Barbash, 2004).

The frequent detection of chloroform in the study area 

may be from several sources such as chlorinated or reclaimed 

water to irrigate lawns and gardens; leakage from distribution 

lines for treated water and wastewater; spas; pools; and 

leachate from septic-system drainfields (Thiros, 2000). 

Several lines of evidence indicate that chloroform in the study 

area is associated with the by-product of chlorination and 

not from natural sources. For example, the associated DBPs 

(bromodichloromethane and bromoform) also were detected in 

the source water, and chloroform was only found in residential 

and commercial areas and not detected in undeveloped areas 

(as discussed further in subsequent sections). Other frequently 

detected VOCs include the solvents carbon disulfide (also 

occurs naturally) and PCE (also known as tetrachloroethene or 

tetrachloroethylene), which is primarily used as a dry-cleaning 

agent.

Concentrations for VOCs detected in the source water 

were low (fig. 6A). Of the 11 VOCs detected, human-health 

benchmarks were available for 8 compounds. BQmax values 

for these 8 VOCs typically were several orders of magnitude 

below 1 and none were greater than 0.1 (table 1). This 

indicates that the concentrations of these VOCs are unlikely 

to be of potential human-health concern or warranted to be 

included in a low-concentration, trends-monitoring program. 

An HBSL was not available for 1,2,4-trimethylbenzene 

because human-health toxicity information was not available; 

however, additional monitoring of this VOC may be warranted 

on the basis of its frequent occurrence (10 percent of samples) 

to better understand its spatial and temporal distribution as 

well as its sources, transport, and fate.

Pesticides

Twelve pesticide compounds were detected in the source 

water (table 1, fig. 6B). Although the number of individual 

pesticides detected (12) was roughly about the same as for 

VOCs (11), pesticides were detected more frequently in 

comparison to VOCs (48 pesticide detections compared to 

35 VOC detections). However, the analytical methods allow 

pesticides to be detected at lower concentrations than VOCs 

(Appendixes 1 and 2).

Of the 48 pesticide detections, most (54 percent) were 

derived from atrazine (7 detections) and its breakdown 

products deethylatrazine (10 detections), 2-hydroxyatrazine 

(7 detections), and deisopropylatrazine (2 detections). Several 

reasons exist for the high detection frequency for atrazine 

and deethylatrazine including high mobility in sandy soils, 

widespread use, 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 were low (fig. 6B). Of the 12 pesticides detected, 

human-health benchmarks were available for 8 of these 

compounds. BQmax values for these 8 pesticides typically 

were several orders of magnitude below 1 and none were 

greater than 0.1 (table 1). Human-health benchmarks were 

not available for deethylatrazine and, as such, additional 

monitoring may be warranted on the basis of its frequent 

occurrence (33 percent of samples).

Other Anthropogenic Organic Compounds

Eight OAOCs were detected in the source-water samples, 

and concentrations were low (table 1, fig. 6C). Of the eight 

OAOCs detected, none had human-health benchmarks to 

compare with measured concentrations.

Effects of Hydrogeology on Ground-Water 

Quality

Fifteen wells were sampled in this study in both the 

unconfined and semiconfined areas of the Upper Floridan 

aquifer due to the importance of each area as a source of 

drinking-water supply (fig. 4). Water-quality results obtained 

from the unconfined and semiconfined areas were compared to 

characterize the differences, or lack thereof, between these two 

types of hydrogeologic settings.

Of 31 AOCs detected a total of 97 times (table 1), almost 

twice as many detections occurred in the unconfined areas (62) 

as in the semiconfined areas of the Upper Floridan aquifer (35) 

(fig. 7). There were 27 detections of VOCs in the unconfined 

areas and 8 detections of VOCs in the semiconfined areas of 

the Upper Floridan aquifer (fig. 7). Sixteen of the 27 VOCs 

detected were DBPs. This included 11 detections of 

chloroform, 3 of bromodichloromethane, and 2 of bromoform. 

Only two detections of chloroform occurred in semiconfined 

areas. The higher detection frequency of DBPs in unconfined 

areas than in semiconfined areas may be related to less clay 

confinement where unconfined, which may increase the 

potential for transport of DBPs, or may be due to a greater 

population density around the wells in the unconfined areas 

(as described in the following section).

Pesticide detections also were more frequent in 

unconfined areas (34) than in semiconfined areas (14) of 

the Upper Floridan aquifer (fig. 7). Atrazine and the 

Anthropogenic Organic Compounds in Ground Water during Phase 1 13
VOCs

(semiconfined)

VOCs

(unconfined)

Pesticides

(semiconfined)

Pesticides

(unconfined)

OAOCs

(semiconfined)

OAOCs

(unconfined)

0.001

0.01

0.1

1

CONCENTRATION, IN MICROGRAMS PER LITER

8 27 14 34 13 1

8

75th percentile

Average

Number of observations

OAOC concentration

Data value less than or equal to 1.5 times the 

 interquartile range outside the quartile

50th percentile

25th percentile

Outlier data value more than 1.5 times the 

 interquartile range outside the quartile

EXPLANATION

Interquartile

range

[VOCs, volatile organic compounds; OAOCs, other anthropogenic 

organic compounds]

Figure 7. Concentrations of all detected anthropogenic organic 

compounds in source water from semiconfined and unconfined 

areas of the Upper Floridan aquifer during phase 1.

breakdown products deethylatrazine, 2-hydroxyatrazine, 

and deisopropylatrazine were detected a total of 19 times in 

unconfined areas compared to 7 times in semiconfined areas. 

Deethylatrazine, which was detected 8 times in the unconfined 

areas and only 2 times in the semiconfined areas, is the most 

mobile of the atrazine breakdown products and is more mobile 

in sandy soils than in clayey soils (Kruger and others, 1995). 

Other pesticide compounds were cumulatively detected 

15 times in unconfined areas and 7 times in semiconfined 

areas.

In contrast to what was observed for VOCs and 

pesticides, OAOCs were detected more frequently in semiconfined areas than in unconfined areas (fig. 7). One OAOC 

was detected in one well sample from the unconfined areas, 

and 13 OAOCs were detected in semiconfined areas. Little 

is known about the transport and fate of these compounds in 

ground water, but many of the detections in this study appear 

to be more site specific than regionally widespread. Nine of 

the 14 detections of OAOCs occurred in source-water samples 

from two wells in the semiconfined area of the Upper Floridan 

aquifer; 6 OAOCs in one well sample and 3 OAOCs in the 

other well sample. These wells were located near facilities that 

utilize septic systems. DEET was detected in 4 well samples 

from semiconfined areas and 1 well sample from unconfined 

areas.

On the basis of these results, hydrogeology plays an 

important role in the detection of AOCs in CWS wells, 

especially for VOCs and pesticides. These compounds are 

used extensively and have a potential to reach ground water 

by direct application to the land surface or through a variety 

of sources from the primary use of the product. OAOCs, 

on the other hand, may have more specific sources and (or) 

pathways to enter the environment, such as by wastewater 

from a wastewater-treatment plant and septic tank effluent. 

As described in more detail in the following section, the 

population density surrounding wells in unconfined areas was 

twice the population surrounding wells in semiconfined areas, 

thereby magnifying the susceptibility of the ground-water 

quality in the unconfined areas. However, the more populous 

areas surrounding the wells in unconfined areas (figs. 2 and 4) 

typically use municipal sewer systems, and the less populous 

areas surrounding the wells in semiconfined areas use more 

septic systems. This may result in a higher potential for OAOC 

occurrence in the areas using septic systems and, in part, may 

help explain why OAOCs were detected more frequently in the 

less populated, semiconfined areas.

Effects of Land Use and Population Density on 

Ground-Water Quality

GIS land-use coverages were evaluated to characterize 

the effects of land use on ground-water quality. For this 

analysis, land use was categorized within a 500-meter (m) 

(1,640-ft) radius for each sampled well. Land use surrounding 

the 30 wells varied and was categorized as follows: residential 

(37 percent); open land and recreational (26 percent); wetlands 

and surface water (18 percent); agricultural (pasture and 

tree plantations, 11 percent); commercial, industrial, and 

transportation (7 percent); and agricultural (nurseries and 

farms, 1 percent) (fig. 2). Population also was determined 

within a 500-m radius for each well. Satellite land-use imagery 

was used to determine the population surrounding each well 

by assigning 2.5 residents per household.

The population within a 500-m radius of the CWS well 

compared to the number of detected compounds for each 

well is shown in figure 8A. At least one AOC was detected 

in 22 of the 30 source-water samples. In general, the number 

of compounds detected in each well sample decreased as the 

population surrounding each well decreased. AOCs were 

not detected in 8 of the well samples, 7 of which were from 

well fields where residential and commercial development is 

prohibited.

14 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
1,500

0

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

17

15

30

22

21

23

20

18

4 29

25 24

2

10

1

3

16

11

9

12

8

26

27

28

14

13 7

19

6

5

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

WELL NUMBER

NUMBER OF ANTHROPOGENIC ORGANIC COMPOUND DETECTIONS

POPULATION, WITHIN A 500-METER RADIUS OF WELL POPULATION, WITHIN A 500-METER RADIUS OF WELL 

Number of detections

Population, unconfined area

0

200

400

600

800

1,000

1,200

1,400

1,600

0 1 2 3 4 5 6 7 8 9 10 11

NUMBER OF DETECTIONS

Population, semiconfined area

r2 = 0.72

A

B

Well in unconfined areas

Well in semiconfined area

Figure 8. Number of anthropogenic organic compound detections in source-water samples collected during phase 1 

in (A) comparison to population surrounding source-water wells in unconfined or semiconfined areas, and (B) statistical 

relations with population.

Anthropogenic Organic Compounds in Ground Water during Phase 1 15
Linear and multiple linear regression analyses were 

used to mathematically relate the number of anthropogenic 

compounds detected in the 30 source-water samples to 

land use, population, hydrogeology, well depth, and well 

screen depth. With a regression significant to an alpha of 

0.05 (95-percent confidence interval), population was the 

parameter that provided the best regression estimate (r2 = 0.72; 

fig. 8B). As the population surrounding the well increases, the 

number of AOCs increased. Relations improved (r2 = 0.82) 

when OAOCs were removed from the analysis. OAOCs, 

as described previously, were detected in areas where the 

population was low and relied on the use of septic systems.

Chloroform detections and concentrations were highest 

beneath areas where residential land use was greater than 

60 percent and 73 percent, respectively. Pesticides were 

detected in areas where the residential land use was greater 

than 68 percent, except deethylatrazine, where two detections 

occurred in a mixed land-use area.

Comparison of Source-Water Results to Results 

from Other Studies

Results from the source-water samples from the 30 CWS 

wells monitored in this study were compared to results from 

four locally conducted studies that characterized VOCs, 

pesticides, and (or) OAOCs in the Upper Floridan aquifer in 

the northern Tampa Bay area or in the Biscayne aquifer in 

Miami-Dade, Broward, and Palm Beach Counties (table 2). 

These studies were conducted by USGS personnel using 

the same field and analytical techniques as were used in the 

SWQA study. Three of the five studies (studies A, B, and 

C) listed in table 2 were conducted as part of the NAWQA 

Program. As such, these studies incorporated a “nested” 

design for sampling that allows information to be applied at 

several spatial scales in the same hydrologic unit because all 

samples were collected within the confines of one geographic 

boundary. Although not conducted by the NAWQA Program, 

studies D and E provide valuable information for comparison 

to different aquifers and (or) types of wells in the area. 

However, differences in compounds monitored for this SWQA 

study (study A) and those compounds monitored for other 

studies do not allow for a direct comparison among all five 

studies.

For study B, 34 shallow monitoring wells in urban 

areas in the northern Tampa Bay area were sampled during 

2002 as part of the NAWQA Program’s urban land-use study 

(ULUS) component that monitors shallow ground water under 

residential and commercial areas. Sixty domestic wells in the 

Upper Floridan aquifer were sampled as part of the NAWQA 

Program’s major aquifer study (MAS) effort (study C), which 

was a study designed to broadly characterize the quality of 

water representing current or future sources of drinking water. 

For study D, 30 public-supply wells in the Biscayne aquifer 

were sampled in Miami-Dade, Broward, and Palm Beach 

Counties, Florida. For study E, 38 wells of varying types were 

Table 2. Summary of locally conducted ground-water quality studies that evaluated the occurrence of volatile organic compounds, 

pesticides, and (or) other anthropogenic organic compounds.

[NAWQA, National Water-Quality Assessment; GAFL, Georgia-Florida Coastal Plain; GW, ground water; SWQA, Source Water-Quality Assessment; VOCs, 

volatile organic compounds; OAOCs, other anthropogenic organic compounds; ULUS, urban land-use study; MAS, major aquifer study]

Study 

identifier

Ground-water

quality study

Comparison

data Types of wells sampled

Number 

of wells 

sampled

Median 

well depth

(feet)

Sampling 

frequency and 

period

A NAWQA GAFL 

GW SWQA1

VOCs, 

pesticides, 

and OAOCs

Existing large capacity public-supply wells 

in the unconfined and semi-confined areas 

of Upper Floridan aquifer in the northern 

Tampa Bay area, Florida

30 563 Once in 2002.

B NAWQA ULUS2 VOCs and 

pesticides

Shallow monitoring wells in the northern 

Tampa Bay area, Florida

34 42 Once in 2002.

C NAWQA MAS2 VOCs and 

pesticides

Domestic wells in the Upper Floridan aquifer 

in central Florida to southern Georgia

60 83 Once in 2002.

D Bradner and 

others (2005)

VOCs and 

pesticides

Public-supply wells in the Biscayne aquifer 

in Miami-Dade, Broward, and Palm Beach 

Counties, Florida

30 105 Once during 

1996–98.

E Phelps (2004) OAOCs Domestic, monitoring, and drinking-water 

wells and three springs in the Upper 

Floridan aquifer in the Silver Springs 

Basin, Florida

38 107 Once during 

2001–02.

1

Topic of this report.

2

W.S. McBride, U.S. Geological Survey, written commun., 2005.

16  Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
sampled in areas thought to be susceptible to contamination 

from human or animal waste. The comparisons conducted 

herein are only intended to provide initial and general insight 

on how representative other studies may, or may not be, of 

source water used by CWSs and to set the stage for future, 

more detailed comparisons.

Volatile Organic Compounds

Eleven VOCs were detected in samples from CWS 

wells monitored in the northern Tampa Bay area as part 

of this SWQA (table 1, study A in Appendix 5). A total of 

15 VOCs were detected in each of the locally nested studies 

B and C. Many of these VOCs, however, were detected 

in only one sample. Five of the VOCs detected once in 

study A (1,1-dichloroethane, trichlorofluoromethane, 

cis-1,2-dichloroethene, trichloroethene, and MTBE) and 

bromoform (which was detected in only 2 samples) also were 

detected infrequently (less than about 5 percent) in studies B 

and C.

Chloroform, carbon disulfide, and PCE were the first, 

second, and third most frequently detected VOCs in this 

SWQA, respectively. With the exception of carbon disulfide 

in study D, these three compounds also were among the top 

five most frequently detected VOCs in each of the comparison 

studies. Although not detected in this SWQA, toluene was 

the second most frequently detected VOC in nested studies 

B (detected in 18 percent of samples) and C (detected in 

25 percent of samples) of the Upper Floridan aquifer.

Results for study D, for which 30 public-supply 

wells in the Biscayne aquifer were sampled, showed that 

proportionately more VOCs were detected from these well 

samples in comparison to any other locally conducted study 

(Appendix 5). This may be explained, in part, by the high 

permeability of the sand and limestone sediments and shallow 

water table of the Biscayne aquifer, in comparison to the 

Upper Floridan aquifer, which makes these ground waters 

more vulnerable to contamination by human activities. The 

VOCs that occurred infrequently in studies A, B, and C 

occurred in as many as 40 percent of samples in study D. The 

VOCs cis-1,2-dichloroethene and MTBE occurred in 40 and 

30 percent, respectively, of public-supply well samples from 

the Biscayne aquifer, and 1,1-dichloroethane and bromoform 

were detected in 13 and 10 percent of these samples, 

respectively.

These general comparisons indicate that VOCs that 

occurred relatively infrequently in other studies of the Upper 

Floridan aquifer also tend to be found infrequently in source 

water of large CWSs in the area. Similarly, those VOCs 

that occurred most frequently in other studies also occurred 

relatively frequently (on a ranking basis) in source water; 

particularly chloroform, carbon disulfide, and PCE. Thus, the 

results of other locally conducted studies described herein tend 

to be similar to source-water results from CWSs monitored 

in this SWQA. However, the larger number and frequency of 

detection of VOCs detected in the Biscayne aquifer (study D) 

in comparison to studies A, B, and C do document their 

occurrence and, thus, potential to be present in other source 

waters in the area.

Pesticides

Twelve pesticides were detected in CWS wells monitored 

in the northern Tampa Bay area as part of this SWQA 

(table 1, study A in Appendix 6). Three of these pesticides 

(bromacil, fonofos, oxygen analog, and 3,4-dichloroanaline) 

were detected in only one sample and three pesticides 

(deisopropylatrazine, imidacloprid, and tebuthiuron) were 

detected in only two samples. Each of these five pesticides 

also were detected relatively infrequently (in less than 

13 percent of samples) or not analyzed in locally nested 

studies B and C.

The five most frequently detected pesticides in this 

SWQA were deethylatrazine, atrazine, 2-hydroxyatrazine, 

bentazon, and prometon. Each of these pesticides also was 

typically among the top six most frequently detected pesticides 

in each of the comparison studies (if analyzed). Interestingly, 

atrazine and its breakdown products, deethylatrazine and 

2-hydroxyatrazine, were detected more frequently in this 

SWQA (in 23 to 33 percent of samples) than in studies B and 

C (equal to or less than 3 percent of samples). However, 

atrazine and deethylatrazine were detected more frequently 

in study D, occurring in 73 and 63 percent of samples, 

respectively.

As was observed for VOCs, proportionately more 

pesticides were detected in samples from the Biscayne aquifer 

(study D) in comparison to studies A, B, and C. Tebuthiuron 

was detected in 77 percent of public-supply well samples 

(study D), and other pesticides detected frequently in study 

D but detected infrequently or not detected in studies A, B, 

and C include diuron (53 percent), fenuron (30 percent), and 

metolachlor (27 percent).

These general comparisons indicate that pesticides, 

especially atrazine and its breakdown products 

(deethylatrazine and 2-hydroxyatrazine), occur more 

frequently in the source water monitored as part of this 

SWQA in comparison to studies B and C. However, the large 

difference in both the number and frequency of detection 

of pesticides detected in the Biscayne aquifer (study D) 

documents their occurrence and potential to be present in other 

source waters in the area.

Other Anthropogenic Organic Compounds

SWQAs are the only component of the NAWQA Program 

to monitor OAOCs, therefore it is not possible to compare 

SWQA results with locally nested studies of the Upper 

Floridan aquifer. However, one other study (study E) was 

conducted by the USGS Florida Water Science Center (table 1, 

Appendix 7). Because study E was conducted in areas thought 

to be susceptible to wastewater contamination, it seems likely 

Anthropogenic Organic Compounds in Ground Water during Phase 1 17
that a greater number of OAOCs would be detected more 

frequently in study E in comparison to this SWQA. This was 

found to be true (Appendix 7). In contrast to the comparison 

of VOCs and pesticides to other studies, comparison of OAOC 

results to other studies is difficult due to the relative newness 

of analytical methods for these compounds, which results in 

fewer completed studies.

Eight OAOCs were detected in samples from CWS wells 

monitored as part of this SWQA. Five of these compounds 

were detected in only one SWQA sample, and two of these 

compounds were detected in only two samples. Although 

OAOCs were detected infrequently, these results indicate 

that some OAOCs have sufficient persistence and mobility to 

be transported to CWS wells at detectable quantities. DEET 

occurred most frequently (5 samples, 17 percent). Other 

studies have found DEET in rivers, streams, ground water, 

springs, and seawater (Weigel and others, 2002; Sandstrom 

and others, 2005); it occurred most frequently in study E 

(30 of the 38 samples; 79 percent) (Appendix 7). Toxicological 

data do not show DEET to be carcinogenic, significantly 

developmentally toxic, or mutagenic (U.S. Environmental 

Protection Agency, 1998).

In general, most (7 of 8) of the OAOCs detected in this 

SWQA also were detected in study E. Ten additional OAOCs 

occurred in the Upper Floridan aquifer in study E that were 

not detected in CWS wells sampled for this SWQA. The 

similarities between those OAOCs detected in study E and 

those detected as part of this SWQA indicate that these 

compounds are sometimes present in source water. Additional 

monitoring of these compounds to further characterize their 

occurrence in source water and finished water is needed to 

more fully understand their temporal patterns and potential 

sources, fate, and transport.

Anthropogenic Organic Compounds 

in Ground Water and Finished Water 

during Phase 2

Eleven of the original 30 CWS wells that had the highest 

number of detections of AOCs were resampled during phase 2 

of this SWQA along with the associated finished water 

during August and September 2004. For the 11 finished-water 

samples, 5 were blended with ground water from other CWS 

wells, and 6 were not blended. Because these CWSs were 

sampled only for those AOCs that occurred most frequently 

during phase 1, not all pairs of CWS wells and associated 

finished water were sampled for the same AOCs. That is, 

10 pairs of source water and the associated finished water 

were analyzed for VOCs, 6 for pesticides, and 2 for OAOCs. 

The process used to select CWS wells was biased to those 

compounds that occurred most frequently, and because this 

process resulted in a small number of samples (especially for 

OAOCs), characterization of the overall occurrence of these 

compounds in source water and finished water is not feasible. 

Thus, a general comparison of these compounds in source 

water and finished water is presented.

For interpretive purposes, select finished-water results 

were separated as blended and non-blended waters. This 

differentiation provides additional insight about the effect of 

blending on finished-water quality and allows for examination 

of occurrence findings separately for CWSs that do not blend 

with those that do blend. Concentrations of each AOC detected 

in source water and the associated blended or non-blended 

finished water are presented in Appendix 8 and number of 

detections, maximum concentrations, and BQmax values are 

presented in table 3.

Overall, 35 AOCs were detected in either source water or 

finished water and more compounds were detected in finished 

water than in source water. Specifically, 22 individual AOCs 

(8 VOCs, 10 pesticides, and 4 OAOCs) were detected in 

source water and 27 (14 VOCs, 8 pesticides, and 5 OAOCs) 

were detected in finished water. The total number of detections 

also were greater in the finished water (80) than in the source 

water (49); however, this was largely due to the creation of 

disinfection by-products in the finished water. Excluding 

DBPs, about the same number of total detections was observed 

in source water (40) as in finished water (44). Sam­ples 

generally contained a mixture of compounds with an average 

of 4 compounds in source water and 7 compounds in finished 

water.

Volatile Organic Compounds

Samples from 10 CWS wells and the associated finished 

water were analyzed for VOCs. Four of the finished-water 

samples represented water blended with ground water from 

other CWS wells prior to treatment, and six were not blended. 

A total of 18 VOCs were detected in either the source water or 

the finished water. Specifically, 8 and 14 VOCs were detected 

in the source- and finished-water samples, respectively 

(table 3). However, four of the VOCs detected in finished 

water were DBPs. Chloroform was detected in 8 source-water 

and in all 10 finished-water samples. Other DBPs typically 

were not detected in the source water but were detected in all 

or most of the finished-water samples, including bromodichloromethane (10 of 10 samples), dibromochloromethane (9 of 

10 samples), and bromoform (8 of 10 samples).

Four VOCs (acetone, methyl ethyl ketone, 

tetrahydrofuran, chloroethane, and trichloroethene) were 

detected in only one source-water sample, albeit at fairly large 

concentrations (as much as 1,140 μg/L), but were not detected 

in the finished water (table 3). Ten additional VOCs were 

not detected in the source water but were detected in at least 

one finished-water sample. Five of these 11 VOCs (methyl 

isobutyl ketone, ethylbenzene, o-xylene, m- and p-xylene, and 

chloromethane) occurred in non-blended finished water of the 

same well (CWS well 29), whereas carbon tetrachloride and 

toluene each occurred in blended finished water of different 

18  Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
wells (Appendix 8). With the exception of the DBPs, the 

detection of compounds in the finished water and not in the 

source water may be due to several reasons. For example, 

compounds detected in the non-blended finished water of 

well 29 may have been introduced to the water from a CWS 

pump as a result of normal lubrication and service, or from 

pipe gaskets or other materials used between the sourceand finished-water sample location. The detection of other 

compounds in the blended finished water may be due to their 

presence in other source waters blended with the source water 

monitored as part of this study, which in turn composes the 

sampled finished water.

Concentrations of detected VOCs ranged from E0.033 to 

1,140 μg/L in the source water and from E0.018 to 36.3 μg/L 

in the finished water. Concentrations of the four DBPs were 

higher in finished water than in source water, and concentrations tended to be greater in blended finished water than in 

non-blended finished water (fig. 9A, Appendix 8).

Concentrations of 15 of the 18 VOCs detected in either 

source water or finished water typically were well below 

their human-health benchmark and, as such, BQmax values 

were typically several orders of magnitude below 1 (table 3, 

fig. 9B). This indicates that none of these 15 individual VOCs 

were detected at concentrations of potential human-health 

concern.

BQmax values for methyl ethyl ketone detected 

in source water and BQmax values for chloroform, 

dibromochloromethane, and carbon tetrachloride detected 

in finished water were greater than or equal to 0.1. It should 

be noted, however, that the MCL used to calculate BQmax 

values for chloroform and dibromochloromethane is intended 

for the summation of concentrations of these two compounds 

plus the other DBPs bromoform and bromodichloromethane. 

Although not in table 3, summing all maximum concentrations 

of these four DBPs in source water and finished water results 

in BQmax values equal to 0.012 and 0.72, respectively, further 

indicating concentrations were not greater than the MCL. 

Disinfection by-products already are monitored routinely 

by CWSs. Methyl ethyl ketone was detected only in one 

source-water sample, so additional monitoring may not be 

necessary. However, carbon tetrachloride, which was detected 

in 3 of 10 finished-water samples and at concentrations 

within 10 percent of its human-health benchmark may 

warrant inclusion in a low-concentration, trends-monitoring 

program to better understand temporal and spatial patterns, 

and its potential sources, fate, and transport. HBSLs were not 

available for two detected unregulated VOCs (methyl isobutyl 

ketone and tetrahydrofuran) because human-health toxicity 

information was not available.

These results indicate that monitoring VOCs in source 

water does not necessarily characterize the occurrence of 

VOCs in finished water. This is especially true for DBPs that 

are formed as a result of disinfection. In addition, 14 of the 

18 (12 of 16 if DBPs are excluded) VOCs were detected in 

either the source water or finished water, but not both. These 

differences may be due largely to blending. That is, VOCs 

present in source water but not the finished water may have 

been diluted to undetectable concentrations in the finished 

water by blending with other source water that didn’t contain 

those VOCs. Similarly, VOCs present in the finished water but 

not the source water sampled may have been present in the 

source water from other wells.

Pesticides

Samples from six CWS wells and associated finished 

water were analyzed for pesticides. Two of the finishedwater samples represented water blended with ground water 

from other CWS wells prior to treatment and four were not 

blended. A total of 10 individual pesticides were detected 

in either the source water or finished water, and all 10 of 

these pesticides were detected in at least one source-water 

sample. Eight pesticides were detected in finished-water 

samples (table 3). The most frequently detected compounds 

in both the source and the finished water were atrazine and its 

breakdown products 2-hydroxyatrazine and deethylatrazine. 

These compounds, if detected in source water, also generally 

were detected in the associated finished water, whether it was 

blended or not blended (Appendix 8). 2-Hydroxyatrazine 

was present in all 6 source-water and finished-water samples, 

whereas atrazine and deethylatrazine were each detected in 

5 source-water and 5 finished-water samples (Appendix 8). 

It should be noted that 2-hydroxyatrazine, atrazine, and 

deethylatrazine also were among the most frequently detected 

pesticides in finished water from 12 community surface-water 

supply sites sampled across the Nation (Coupe and Blomquist, 

2004). Bentazon also was detected frequently in the source 

water (5 of 6 source-water samples); however, it was only 

detected in 1 finished-water sample. Two pesticides, bromacil 

and deisopropylatrazine, were detected in 1 and 2 source-water 

samples, respectively, but were not detected in any finishedwater samples.

Concentrations of detected pesticides in source water 

and finished water were similar and low, ranging from 

E0.001 to E0.059 μg/L in the source water and from E0.003 to 

E0.035 μg/L in finished water (fig. 10, Appendix 8). Concentrations of 8 of the 10 pesticides detected were compared to 

human-health benchmarks, and BQmax values were about 

four orders of magnitude below 0.1. HBSLs were not available 

for deethylatrazine and deisopropylatrazine; however, their 

frequent occurrence in both source and finished water may 

warrant additional monitoring.

These results indicate that monitoring pesticides in 

source water may reflect the occurrence of pesticides in 

finished water, especially for atrazine and its breakdown 

products. However, the effect of blending makes it difficult 

to characterize how representative source water is of finished 

water because many pesticides were detected more frequently 

in source water than in finished water. More data are needed 

to better characterize the representative nature of pesticides in 

source water compared to finished water.

Anthropogenic Organic Compounds in Ground Water and Finished Water during Phase 2 19
Table 3. Maximum concentrations, detection frequency, and maximum benchmark quotient for regulated and unregulated compounds detected in s

phase 2 from 11 source-water wells and the associated finished water of community water systems in the northern Tampa Bay area.—Continued[MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contamination Level; HBSL, Health-Based Screening Level; μg/L, microgrmark quotient = ratio of maximum detected compound concentration to MCL or HBSL value; DEET, N,N,-diethyl-meta-toluamide; TCEP, tri(2-chloroethyl)phosphate; TCPP, trE, estimated value; <, less than; --, not available. A regulated compound is a compound for which Federal and (or) State drinking-water standards have been established; an unrepound for which no Federal and (or) State drinking-water standards have been established]

Regulated (R) or

unregulated (U)

compound

Chemical 

Abstracts 

Service 

Registry 

Number

Number of 

samples 

collected

Number of detections

MRL 

(μg/L)

Maximum concentration 

(μg/L)

USEPA 

MCL1 or 

HBSL3

(μg/L)

Source 

water

Finished 

water

Source 

water

Finished 

water

Volatile organic compounds

Bromodichloromethane (R) 75–27–4 10 1 10 0.028 E0.040 7.48 280 

Carbon disulfide (U) 75–15–0 10 1 1 .038 .116 E.040 700 

Chloroform (R) 67–66–3 10 8 10 .024 .948 36.3 280 Perchloroethene (PCE) (R) 127–18–4 10 1 3 .03 E.033 E.080 5 

Bromoform (R) 75–25–2 10 0 8 .1 -- 5.52 280 

Carbon tetrachloride (R) 56–23–5 10 0 3 .06 -- .500 5 Chloromethane (U) 74–87–3 10 0 1 .17 -- E.116 30 

Dibromochloromethane (R) 124–48–1 10 0 9 .1 -- 7.95 280 Ethylbenzene (R) 100–41–4 10 0 1 .03 -- .593 700 

Methyl isobutyl ketone (U) 108–10–1 10 0 1 .37 -- 3.30 -- Methyl tert-butyl ether (MTBE) (U) 1634–04–4 10 0 1 .1 -- E.100 -- 

Toluene (R) 108–88–3 10 0 1 .02 -- E.020 1,000 

o-Xylene (R) 95–47–6 10 0 1 .038 -- 1.03 410,000 

m- and p-Xylene (R) 108–38–3 10 0 1 .06 -- 2.26 410,000 Acetone (U) 67–64–1 10 1 0 6 68.4 -- 6,000 

Methyl ethyl ketone (MEK) (U) 78–93–3 10 1 0 2 1,140 -- 4,000 

Tetrahydrofuran (U) 109–99–9 10 1 0 1.2 279 -- -- Trichloroethene (R) 79–01–6 10 1 0 .038 E.046 -- 5 

Total number of VOC detections NA NA 15 51 NA NA NA NA 

Pesticides

Atrazine (R) 1912–24–9 6 5 5 0.007 0.023 0.012 3 

Bentazon (U) 25057–89–0 6 5 1 .024 E.057 E.035 200 

Deethylatrazine (U) 6190–65–4 6 5 5 .014 E.025 E.020 -- 

2-Hydroxyatrazine (U) 2163–68–0 6 6 6 .032 .029 E.013 70 
Table 3. Maximum concentrations, detection frequency, and maximum benchmark quotient for regulated and unregulated compounds detected in s

phase 2 from 11 source-water wells and the associated finished water of community water systems in the northern Tampa Bay area.—Continued[MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contamination Level; HBSL, Health-Based Screening Level; μg/L, microgrmark quotient = ratio of maximum detected compound concentration to MCL or HBSL value; DEET, N,N,-diethyl-meta-toluamide; TCEP, tri(2-chloroethyl)phosphate; TCPP, trE, estimated value; <, less than; --, not available. A regulated compound is a compound for which Federal and (or) State drinking-water standards have been established; an unrepound for which no Federal and (or) State drinking-water standards have been established]

Regulated (R) or

unregulated (U)

compound

Chemical 

Abstracts 

Service 

Registry 

Number

Number of 

samples 

collected

Number of detections

MRL 

(μg/L)

Maximum concentration 

(μg/L)

USEPA 

MCL1 or 

HBSL3

(μg/L)

Source 

water

Finished 

water

Source 

water

Finished 

water

Pesticides—Continued

Imidacloprid (U) 138261–41–3 6 2 3 0.02 0.017 0.016 400 

Prometon (U) 1610–18–0 6 1 1 .01 .009 .010 100 Simazine (R) 122–34–9 6 1 1 .005 .010 .007 4 Tebuthiuron (U) 34014–18–1 6 1 1 .026 .034 .030 1,000 Bromacil (U) 314–40–9 6 1 0 .018 E.059 -- 70 Deisopropylatrazine (U) 1007–28–9 6 2 0 .08 E.004 -- -- Total number of pesticide detections NA NA 29 23 NA NA NA NA 

Other anthropogenic organic compounds

Caffeine (U) 58–08–2 10 2 2 0.018 E0.006 E0.004 -- DEET (U) 134–62–3 2 1 1 .5 E.08 E.08 -- Camphor (U) 76–22–2 2 0 1 .5 -- E.013 -- 1-Methylnaphthalene (U) 90–12–0 2 0 1 .5 -- E.014 -- 2-Methylnaphthalene (U) 91–57–6 2 0 1 .5 -- E.025 30 TCEP (U) 115–96–8 2 1 0 .5 E.110 -- -- TCPP (U) 13674–87–8 2 1 0 .5 E.081 -- -- Total number of other anthropogenic 

organic compound detections

NA NA 5 6 NA NA NA NA 

Total detections for all compounds NA NA 49 80 NA NA NA NA 

1U.S. Environmental Protection Agency (2003, 2004).2MCL is for total trihalomethanes.3Denotes HBSL (Toccalino and others, 2006a).4MCL is for the sum of concentrations for mixed isomers of xylene.
0.00001 0.0001 0.001 0.01 0.1 1 10 100 1,000 10,000

CONCENTRATION, IN MICROGRAMS PER LITER

0.00001 0.0001 0.001 0.01 0.1 1 10

BENCHMARK QUOTIENT VALUE

Methyl isobutyl ketone (0,1)

Compounds

detected in

source and

finished

water

Compounds

detected only

in finished

water—

non-blended

and blended

water

Compounds

detected only

in source

water

Compounds

detected in

source and

finished

water

Compounds

detected only

in finished

water—

non-blended

and blended

water

Compounds

detected only

in source

water

Perchloroethene (PCE) (1,3)

Chloroform (8,10)

Bromodichloromethane (1,10)

Ethylbenzene (0,1)

o-Xylene (0,1)

m- and p-Xylene (0,1)

Chloromethane (0,1)

Methyl tert-butyl ether (0,1)

Acetone (1,0)

Methyl ethyl ketone (1,0)

Tetrahydrofuran (1,0)

Trichloroethene (1,0)

Toluene (0,1)

Dibromochloromethane (0,9)

Carbon disulfide (1,1)

A

B

Methyl isobutyl ketone (0,1)

Perchloroethene (PCE) (1,3)

Chloroform (8,10)

Bromodichloromethane (1,10)

Ethylbenzene (0,1)

o-Xylene (0,1)

m- and p-Xylene (0,1)

Chloromethane (0,1)

Methyl tert-butyl ether (0,1)

Acetone (1,0)

Methyl ethyl ketone (1,0)

Tetrahydrofuran (1,0)

Trichloroethene (1,0)

Toluene (0,1)

Dibromochloromethane (0,9)

Bromoform (0,8)

Carbon tetrachloride (0,3)

Bromoform (0,8)

Carbon tetrachloride (0,3)

Carbon disulfide (1,1)

Chloroform (8,10)—Number of

 compounds detected for

 source water (8) and finished

 water (10); 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

Non-blended

Finished water—Some values

 are equal and therefore 

 plotted values overlap 

Blended

[Benchmark quotient value is the ratio of the detected concentration of a particular compound to its Maximum Contamination Level, MCL; 

or Health Based Screening Level, HBSL]

Figure 9. Detected volatile organic compounds in source water and associated finished water (non-blended and blended) 

during phase 2 showing (A) concentrations and number of detections, and (B) benchmark quotient values.

22 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
0.00001 0.0001 0.001 0.01 0.1 1 10 100 1,000 10,000

CONCENTRATION, IN MICROGRAMS PER LITER

0.00001 0.0001 0.001 0.01 0.1 1 10

BENCHMARK QUOTIENT VALUE

Compounds

detected in

source and

finished

water

Compounds

detected only

in source

water

Compounds

detected in

source and

finished

water

Compounds

detected only

in source

water

2-Hydroxyatrazine (6,6)

Atrazine (5,5)

Deethylatrazine (5,5)

Imidacloprid (2,3)

Tebuthiuron (1,1)

Bentazon (5,1)

Simazine (1,1)

Prometon (1,1)

Deisopropylatrazine (2,0)

Bromacil (1,0)

A

B

2-Hydroxyatrazine (6,6)

Atrazine (5,5)

Deethylatrazine (5,5)

Imidacloprid (2,3)

Tebuthiuron (1,1)

Bentazon (5,1)

Simazine (1,1)

Prometon (1,1)

Deisopropylatrazine (2,0)

Bromacil (1,0)

Benchmark quotient value of 0.1—

 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

Atrazine (5,5)—Number of

 compounds detected for

 source water (5) and finished

 water (5); bold type indicates 

 an unregulated compound;

 underlined indicates the 

 unregulated compound

 does not have an HBSL

EXPLANATION

Source water

[Benchmark quotient value is the ratio of the detected concentration of a particular compound to its Maximum Contamination Level, MCL; 

or Health Based Screening Level, HBSL]

Non-blended

Finished water—Some values

 are equal and therefore 

 plotted values overlap

Blended

Figure 10. Detected pesticides in source water and associated finished water (non-blended and blended) during 

phase 2 showing (A) concentrations and number of detections, and (B) benchmark quotient values.

Anthropogenic Organic Compounds in Ground Water and Finished Water during Phase 2 23
Other Anthropogenic Organic Compounds

Samples from two CWS wells and associated finishedwater were analyzed for OAOCs. A total of seven OAOCs 

were detected in the source water and (or) finished water 

(table 3, Appendix 8). It is important to note, however, that 

caffeine is listed on table 3 and Appendix 8 as an OAOC. 

Caffeine was actually analyzed as part of other analytical 

methods; thus, it was monitored at more than two CWS wells. 

Four of the seven compounds were detected in the source 

water, and five were detected in the finished water. Of the 

seven OAOCs detected in either source or finished water, 

DEET was the only compound that also was detected during 

phase 1 sampling of source water. Caffeine was detected in 

both source-water samples and the associated finished water, 

and DEET was detected in source-water and the associated 

finished-water sample (table 3, Appendix 8). Three OAOCs—

camphor, 1-methylnaphthalene, and 2-methylnaphthalene—

were not detected in source water but were detected in one 

finished-water sample. Because the finished water was 

blended, it is possible that the source of these compounds 

could be from water from other CWS wells containing 

these compounds that were not monitored for this SWQA. 

Two OAOCs—tri(2-chloroethyl)phosphate (TCEP) and 

tri(dichloroisopropyl)phosphate (TCPP) (flame retardants)—

were detected in source water but not in the finished water 

(table 2). It is possible that the compounds present in the 

source water could have been diluted to levels below detection 

when blended with waters from other CWS wells.

Concentrations of detected OAOCs were low, ranging 

from E0.006 to E0.11 μg/L in the source water and from 

E0.004 to E0.075 μg/L in the finished water (fig. 11, table 3, 

Appendix 8). Concentrations from only 1 of these 7 OAOCs 

(2-methylnaphthalene) were compared to human-health 

benchmarks, and BQmax values were 2 orders of magnitude 

below 0.1. HBSLs were not calculated for the remaining six 

detected unregulated OAOCs. However, additional monitoring 

of DEET may be warranted due to its frequent occurrence in 

source water (table 1) and presence in finished water (table 3, 

Appendix 8). More data are needed to determine how OAOCs 

in source water compare to finished water. However, these 

limited results indicate that OAOCs in source water are not 

necessarily representative of those in finished water because 

5 of 7 OAOCs were detected in source water or finished water, 

but not both.

24 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Benchmark quotient value of 0.1—

 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

Compounds

detected in

source and

finished

water

Compounds

detected only

in finished

water—

non-blended

and blended

water

Compounds

detected only

in source

water

Compounds

detected in

source and

finished

water

Compounds

detected only

in finished

water—

non-blended

and blended

water

Compounds

detected only

in source

water

0.00001 0.0001 0.001 0.01 0.1 1 10 100 1,000 10,000

CONCENTRATION, IN MICROGRAMS PER LITER

0.00001 0.0001 0.001 0.01 0.1 1 10

BENCHMARK QUOTIENT VALUE

EXPLANATION

[Benchmark quotient value is the ratio of the detected concentration of a particular compound to its Maximum Contamination Level, MCL; 

or Health Based Screening Level, HBSL]

Caffeine (2,2)—Number of

 compounds detected for

 source water (2) and finished

 water (2); bold type indicates 

 an unregulated compound;

 underlined indicates the

 unregulated compound

 does not have an HBSL

A

B

Caffeine (2,2)

1-Methylnaphthalene (0,1)

2-Methylnaphthalene (0,1)

Camphor (0,1)

N,N-Diethyl-meta-toluamide

(DEET) (1,1)

Tri(2-chloroethyl)phosphate

(TCEP) (1,0)

Tri(dichlorisopropyl)phosphate

(TCPP) (1,0)

Caffeine (2,2)

1-Methylnaphthalene (0,1)

2-Methylnaphthalene (0,1)

Camphor (0,1)

N,N-Diethyl-meta-toluamide

(DEET) (1,1)

Tri(2-chloroethyl)phosphate

(TCEP) (1,0)

Tri(dichlorisopropyl)phosphate

(TCPP) (1,0)

Source water

Non-blended

Finished water—Some values

 are equal and therefore 

 plotted values overlap 

Blended

Figure 11. Detected anthropogenic organic compounds in source water and associated finished water (blended) during 

phase 2 showing (A) concentrations and number of detections, and (B) benchmark quotient values.

Anthropogenic Organic Compounds in Ground Water and Finished Water during Phase 2 25
Summary

As part of the U.S. Geological Survey (USGS) National 

Water-Quality Assessment (NAWQA) Program, a new 

sampling activity called Source Water-Quality Assessments 

(SWQAs) commenced in 2002. SWQAs consist of two 

sampling phases. Phase 1 was designed to evaluate the 

occurrence of 258 anthropogenic organic compounds 

(AOCs) in the ground water used as source water for some 

of the highest producing community water system (CWS) 

wells in the sampling area. The AOCs monitored include 

volatile organic compounds (VOCs), pesticides, and other 

anthropogenic organic compounds (OAOCs). Phase 2 was 

designed to monitor those AOCs that occurred most frequently 

during phase 1 sampling and characterizes AOC occurrence in 

source water as well as in the associated finished water prior 

to distribution. This report presents the results of an SWQA 

conducted in the unconfined and semiconfined portions of the 

Upper Floridan aquifer system through monitoring 30 of the 

largest producing CWS wells in the northern Tampa Bay area, 

Florida.

During phase 1 of the SWQA, 31 of the 258 AOCs were 

detected (11 VOCs, 12 pesticides, and 8 OAOCs) in sourcewater samples collected between October 2002 and January 

2003. The 10 most frequently detected AOCs in source water 

occurred in at least 13 percent of samples and 12 AOCs 

occurred in at least 10 percent of samples. Samples generally 

contained a mixture of compounds (average of three AOCs 

per sample), and 70 percent of samples contained at least one 

detected compound.

Concentrations of 16 of the 31 detected compounds 

were compared to human-health benchmarks (Maximum 

Contaminant Levels (MCLs) for regulated compounds and 

Health-Based Screening Levels (HBSLs) for unregulated 

compounds). For these 16 compounds, concentrations were 

well below their human-health benchmarks, are unlikely to 

be of potential human-health concern, and may not warrant 

consideration in a low-concentration, trends-monitoring 

program. HBSLs were not available for the remaining 

15 detected unregulated AOCs because human-health 

toxicity information was not available. However, additional 

monitoring may be warranted for 2 of these 15 unregulated 

AOCs—1,2,4-trimethylbenzene and deethylatrazine—to 

better understand their temporal and spatial occurrence and 

their sources, transport, and fate because they were frequently 

detected in source-water samples.

Population density was determined to provide the best 

estimate of the number of AOCs in source water. However, 

hydrogeology also plays an important role in the detection of 

AOCs in source-water samples from CWS wells, especially 

for VOCs and pesticides. OAOCs, on the other hand, may 

have more specific sources and (or) pathways to enter the 

environment, such as wastewater from wastewater-treatment 

plants and (or) septic tank effluent. Of 31 AOCs detected a 

total of 97 times, there were almost twice as many detections 

in the unconfined areas (62) as in the semiconfined areas of 

the Upper Floridan aquifer (35). There were 27 detections 

of VOCs in the unconfined areas, and 8 detections of VOCs 

in the semiconfined areas of the Upper Floridan aquifer. 

Similarly, there were 34 detections of pesticides in the 

unconfined areas, and 14 detections in the semiconfined 

areas of the Upper Floridan aquifer. In contrast to VOCs 

and pesticides, one OAOC was detected in one source-water 

sample from the unconfined areas, and 13 OAOCs were 

detected in semiconfined areas. Little is known about the 

persistence and mobility of OAOCs in ground water, but many 

of the detections in this study appear to be more site specific 

than regionally widespread. Nine of the 14 detections of 

OAOCs occurred in two well samples from semiconfined areas 

of the Upper Floridan aquifer; 6 in one well sample and 3 in 

the other sample. These wells were located near facilities that 

utilize septic systems.

Results from the 30 CWS wells sampled during phase 1 

in this SWQA study were compared to four locally conducted 

studies that characterized VOCs, pesticides, and (or) OAOCs 

in the Upper Floridan aquifer in the northern Tampa Bay area 

or in the Biscayne aquifer in Miami-Dade, Broward, and Palm 

Beach Counties. These general comparisons indicate that 

VOCs that occurred relatively infrequently in other studies of 

the Upper Floridan aquifer also tend to be found infrequently 

in source water of large CWSs in the area. Similarly, those 

VOCs found to occur most frequently in other studies also 

tend to be found relatively frequently in source water; 

particularly chloroform, carbon disulfide, and perchloroethene 

(PCE). However, pesticide compounds, especially atrazine and 

its breakdown products deethylatrazine and 2-hydroxyatrazine, 

occurred more frequently in the source water monitored in 

the SWQA study than in other studies. Thus, the VOC results 

from other studies may be somewhat representative of the 

quality of source water used by CWSs in the area but are not 

necessarily representative for selected pesticides. Several 

VOCs and pesticides were detected more frequently in a 

study of the Biscayne aquifer than in this SWQA. This may 

be explained, in part, by the high permeability of the sand and 

limestone sediments and shallow water table of the Biscayne 

aquifer, in comparison to the Upper Floridan aquifer, which 

makes these ground waters more vulnerable to contamination 

by human activities. In contrast VOCs and pesticides, which 

have been monitored for several years, comparison of OAOC 

results to other studies is difficult because the analytical 

methods were more recently developed.

Eleven of the 30 CWS wells along with their associated 

finished water were resampled during phase 2, and samples 

were analyzed for those AOCs that occurred most frequently 

during phase 1 sampling. For the 11 finished-water samples, 

5 were blended with ground water from other CWS wells. Ten 

pairs of source water and finished water were analyzed for 

VOCs, 6 for pesticides, and 2 for OAOCs. Overall, 42 AOCs 

were detected in either source water or finished water and 

more compounds were detected in finished water than in 

source water. Specifically, 22 individual AOCs (8 VOCs, 

26  Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
10 pesticides, and 4 OAOCs) were detected in source water 

and 27 (14 VOCs, 8 pesticides, and 5 OAOCs) were detected 

in finished water. The total number of detections also were 

greater in the finished water (80) than in the source water (49); 

however, this was largely due to the creation of disinfection 

by-products in the finished water. Excluding DBPs, about the 

same number of total detections was observed in source water 

(40) as in finished water (44). Sam­ples generally contained 

a mixture of compounds with an average of 4 compounds in 

source water and 7 compounds in finished water.

AOC concentrations ranged from E0.001 (estimated) 

to 1,140 μg/L in source water and from E0.003 to 36.3 μg/L 

in finished water. Human-health benchmarks were available 

for 24 of the 42 compounds detected in either source 

water or finished water. Concentrations were about 1 to 

5 orders of magnitude less than human-health benchmarks, 

indicating that these concentrations are unlikely to be of 

potential human-health concern. The potential human-health 

relevance for the remaining 18 detected unregulated AOCs 

could not be evaluated at this time because human-health 

toxicity information necessary to calculate HBSLs for these 

compounds was not available.

Concentrations for 3 AOCs detected in finished water and 

1 AOC in source water were within a factor of 10 of humanhealth benchmarks, which is considered a level that may 

warrant inclusion in a low-concentration, trends-monitoring 

program. However, two of these AOCs—chloroform and 

dibromochloromethane—are disinfection by-products already 

monitored routinely by CWSs, and methyl ethyl ketone 

was detected in only one source-water sample. Carbon 

tetrachloride was detected in three finished-water samples 

and, thus, may be warranted for inclusion in such a monitoring 

program.

More data are needed to determine how source water 

compares to finished water. However, in this study, VOCs 

monitored in source water does not necessarily reflect the 

occurrence of VOCs in finished water. This is especially true 

for compounds that are formed as a result of disinfection. In 

addition, 14 of the 18 VOCs were detected in either the source 

water or finished water, but not both. These differences may 

be largely due to blending. That is, VOCs present in source 

water but not the finished water may have been diluted to 

undetectable concentrations in the finished water by blending 

with other source water that did not contain those VOCs. 

Similarly, VOCs present in the finished water but not the 

source water sample, in part, may have been present in the 

source water from other wells that composed the blended 

finished water. However, these results indicate that monitoring 

pesticides in source water may approximate the occurrence 

of pesticides in finished water, especially for atrazine and its 

breakdown products. Although the effect of blending makes 

it difficult to quantitatively characterize how representative 

source water is of finished water without monitoring each 

CWS well contributing to the blended finished water, this 

study determined that many pesticides were detected more 

frequently in source water than finished water.

References Cited

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.

Bradner, Anne, McPherson, B.F., Miller, R.L., Kish, George, 

and Bernard, Bruce, 2005, Quality of ground water in 

the Biscayne aquifer in Miami-Dade, Broward, and Palm 

Beach Counties, Florida, 1996–1998, with emphasis on 

contaminants: U.S. Geological Survey Open-File Report 

2004–1438, 20 p.

Bush, P.W., and Johnston, R.H., 1988, Ground-water 

hydraulics, regional flow, and ground-water development 

of the Floridan aquifer system in Florida and in parts of 

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Appendixes
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Appendix 1. Volatile organic compounds analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, 

Maximum Contaminant Level; Gasoline, compounds that include gasoline hydrocarbons, oxygenates, and oxygenate degradates]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Primary use or source

Acetone (U) 67–64–1 6 HBSL Solvent.

Acrylonitrile (U) 107–13–1 .8 HBSL Organic synthesis compound.

tert-Amyl alcohol (U) 75–85–4 1 NA Gasoline.

tert-Amyl methyl ether (U) (TAME) 994–05–8 .04 NA Gasoline.

Benzene (R) 71–43–2 .021 MCL Gasoline.

Bromobenzene (U) 108–86–1 .028 NA Solvent.

Bromochloromethane (U) 74–97–5 .12 HBSL Personal care and domestic use 

products.

Bromodichloromethane (R) 75–27–4 .028 MCL1 Disinfection by-product.

Bromoform (R) 75–25–2 .1 MCL1 Disinfection by-product.

tert-Butyl alcohol (U) 75–65–0 1 NA Gasoline.

n-Butylbenzene (U) 104–51–8 .14 NA Gasoline.

sec-Butylbenzene (U) 135–98–8 .06 NA Gasoline.

tert-Butylbenzene (U) 98–06–6 .08 NA Gasoline.

Carbon disulfide (U) 75–15–0 .038 HBSL Organic synthesis compound.

Carbon tetrachloride (R) 56–23–5 .06 MCL Solvent.

Chlorobenzene (R) 108–90–7 .028 MCL Solvent.

Chloroethane (U) 75–00–3 .12 NA Solvent.

Chloroform (R) 67–66–3 .024 MCL1 Disinfection by-product.

Chloromethane 74–87–3 .17 HBSL Organic synthesis compound.

3-Chloro-1-propene (U) 107–05–1 .5 NA Organic synthesis compound.

2-Chlorotoluene (U) 95–49–8 .04 HBSL Solvent.

4-Chlorotoluene (U) 106–43–4 .05 HBSL Solvent.

Dibromochloromethane (R) 124–48–1 .1 MCL1 Disinfection by-product.

1,2-Dibromo-3-chloropropane (R) (DBCP) 96–12–8 .51 MCL Fumigant related compound.

1,2-Dibromoethane (R) (EDB) 106–93–4 .036 MCL Fumigant related compound.

Dibromomethane (U) 74–95–3 .05 NA Solvent.

1,2-Dichlorobenzene (R) (o-dichlorobenzene) 95–50–1 .048 MCL Solvent.

1,3-Dichlorobenzene (U) (m-dichlorobenzene) 541–73–1 .03 HBSL Solvent.

1,4-Dichlorobenzene (R) (p-dichlorobenzene) 106–46–7 .034 MCL Fumigant related compound.

Dichlorodifluoromethane (U) (Freon 12) 75–71–8 .18 HBSL Refrigerants and propellants.

trans-1,4-Dichloro-2-butene (U) 110–57–6 .7 NA Organic synthesis compound.

1,1-Dichloroethane (U) 75–34–3 .035 NA Solvent.

1,2-Dichloroethane (ethylene dichloride) (R) 107–06–2 .13 MCL Solvent.

1,1-Dichloroethene (R) 75–35–4 .024 MCL Solvent.

cis-1,2-Dichloroethene (R) 156–59–2 .024 MCL Solvent.

trans-1,2-Dichloroethene (R) 156–60–5 .032 MCL Solvent.

1,2-Dichloropropane (R) 78–87–5 .029 MCL Fumigant related compound.

Appendixes  33
Appendix 1. Volatile organic compounds analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, 

Maximum Contaminant Level; Gasoline, compounds that include gasoline hydrocarbons, oxygenates, and oxygenate degradates]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Primary use or source

1,3-Dichloropropane (U) 142–28–9 0.06 NA Fumigant related compound.

2,2-Dichloropropane (U) 594–20–7 .05 NA Fumigant related compound.

1,1-Dichloropropene (U) 563–58–6 .026 NA Organic synthesis compound.

cis-1,3-Dichloropropene (U) 10061–01–5 .05 NA Fumigant related compound.

trans-1,3-Dichloropropene (U) 10061–02–6 .09 NA Fumigant related compound.

Diethyl ether (U) 60–29–7 .08 HBSL Solvent.

Diisopropyl ether (U) (DIPE) 108–20–3 .1 NA Gasoline.

Ethylbenzene (R) 100–41–4 .03 MCL Gasoline.

Ethyl methacrylate (U) 97–63–2 .18 NA Organic synthesis compound.

1-Ethyl-2-methylbenzene (U) 611–14–3 .06 NA Gasoline.

Ethyl tert-butyl ether (U) (ETBE) 637–92–3 .03 NA Gasoline.

Hexachlorobutadiene (U) 87–68–3 .14 HBSL Organic synthesis compound.

Hexachloroethane (U) 67–72–1 .14 HBSL Solvent.

2-Hexanone (U) 591–78–6 .4 NA Solvent.

Iodomethane (U) 74–88–4 .5 NA Organic synthesis compound.

Isopropylbenzene (U) 98–82–8 .038 HBSL Gasoline.

p-Isopropyltoluene (U) (p-cymene) 99–87–6 .08 NA Gasoline.

Methyl acetate(U) 79–20–9 .43 NA Solvent.

Methyl acrylate (U) 96–33–3 1 NA Organic synthesis compound.

Methyl acrylonitrile (U) 126–98–7 .4 HBSL Organic synthesis compound.

Methyl bromide (U) 74–83–9 .33 HBSL Fumigant related compound.

Methyl ethyl ketone (U) (MEK) 78–93–3 2 HBSL Solvent.

Methyl isobutyl ketone (U) (MIBK) 108–10–1 .37 NA Solvent.

Methyl methacrylate (U) 80–62–6 .2 HBSL Organic synthesis compound.

Methyl tert-butyl ether (U) (MTBE) 1634–04–4 .1 NA Gasoline.

Methylene chloride (R) 75–09–2 .06 MCL Solvent.

Naphthalene (U) 91–20–3 .52 HBSL Gasoline.

34 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Appendix 1. Volatile organic compounds analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, 

Maximum Contaminant Level; Gasoline, compounds that include gasoline hydrocarbons, oxygenates, and oxygenate degradates]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Primary use or source

Perchloroethene (R) (PCE) 127–18–4 0.03 MCL Solvent.

n-Propylbenzene (U) 103–65–1 .042 NA Solvent.

Styrene (R) 100–42–5 .042 MCL Gasoline.

1,1,1,2-Tetrachloroethane (U) 630–20–6 .03 HBSL Solvent.

1,1,2,2-Tetrachloroethane (U) 79–34–5 .08 HBSL Solvent.

Tetrahydrofuran (U) 109–99–9 1.2 NA Solvent.

1,2,3,4-Tetramethylbenzene (U) 488–23–3 .14 NA Gasoline.

1,2,3,5-Tetramethylbenzene (U) 527–53–7 .18 NA Gasoline.

Toluene (R) 108–88–3 .02 MCL Gasoline.

1,2,3-Trichlorobenzene (U) 87–61–6 .18 NA Organic synthesis compound.

1,2,4-Trichlorobenzene (R) 120–82–1 .12 MCL Solvent.

1,1,1-Trichloroethane (R) 71–55–6 .032 MCL Solvent.

Trichloroethene (R) 79–01–6 .038 MCL Solvent.

Trichlorofluoromethane (U) (CFC–11) 75–69–4 .08 HBSL Refrigerants and propellants.

1,2,3-Trichloropropane (U) 96–18–4 .18 HBSL Organic synthesis compound.

1,1,2-Trichloroethane (R) 79–00–5 .04 MCL Solvent.

1,1,2-Trichloro-1,2,2-trifluoroethane (U) 

(Freon 113) 

76–13–1 .038 HBSL Refrigerants and propellants.

1,2,3-Trimethylbenzene (U) 526–73–8 .09 NA Gasoline.

1,2,4-Trimethylbenzene (U) 95–63–6 .056 NA Gasoline.

1,3,5-Trimethylbenzene (U) 108–67–8 .044 NA Organic synthesis compound.

Vinyl bromide (U) 593–60–2 .1 NA Organic synthesis compound.

Vinyl chloride (R) 75–01–4 .08 MCL Organic synthesis compound.

m- & p-Xylene (R) m=106–42–3

p=108–38–3

.06 MCL2 Gasoline.

o-Xylene (R) 95–47–6 .038 MCL2 Gasoline.

1 MCL is for sum of the trihalomethanes.

2 MCL is for total xylene.

Appendixes  35
Appendix 2. Pesticides and pesticide degradates analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, Maximum Contaminant Level]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Type of pesticide

Acetochlor (U) 34256–82–1 0.006 HBSL Herbicide.

Acifluorfen (U) 50594–66–6 .028 HBSL Herbicide.

Alachlor (R) 15972–60–8 .005 MCL Herbicide.

Aldicarb (U) 116–06–3 .15 HBSL Insecticide.

Aldicarb sulfone (U) 1646–88–4 .018 HBSL Insecticide degradate.

Aldicarb sulfoxide (U) 1646–87–3 .1 HBSL Insecticide degradate.

Atrazine (R) 1912–24–9 .007 MCL Herbicide.

Azinphos-methyl (U) 86–50–0 .05 HBSL Insecticide.

Azinphos-methyl-oxon (U) 961–22–8 .042 NA Insecticide degradate.

Bendiocarb (U) 22781–23–3 .08 HBSL Insecticide.

Benfluralin (U) 1861–40–1 .01 HBSL Herbicide.

Benomyl (U) 17804–35–2 .022 HBSL Fungicide.

Bensulfuron-methyl (U) 83055–99–6 .018 HBSL Herbicide.

Bentazon (U) 25057–89–0 .024 HBSL Herbicide.

Bromacil (U) 314–40–9 .018 HBSL Herbicide.

Bromoxynil (U) 1689–84–5 .044 HBSL Herbicide.

Carbaryl (U) 63–25–2 .018 HBSL Insecticide.

Carbofuran (U) 1563–66–2 .016 MCL Insecticide.

Chloramben, methyl ester (U) 7286–84–2 .024 NA Herbicide.

Chlorimuron-ethyl (U) 90982–32–4 .032 HBSL Herbicide.

2-Chloro-2,6-diethylacetanilide (U) 6967–29–9 .0065 NA Herbicide degradate.

4-Chloro-2-methylphenol (U) 1570–64–5 .005 NA Herbicide degradate.

3(4-Chlorophenyl)-1-methyl urea (U) 5352–88–5 .036 NA Herbicide degradate.

Chlorothalonil (U) 1897–45–6 .035 HBSL Fungicide.

Chlorpyrifos (U) 2921–88–2 .005 HBSL Insecticide.

Chlorpyrifos, oxygen analog (U) 5598–15–2 .0562 NA Insecticide degradate.

cis-Permethrin (U) 54774–45–7 .006 NA Insecticide.

Clopyralid (U) 1702–17–6 .067 NA Herbicide.

Cycloate (U) 1134–23–2 .014 HBSL Herbicide.

Cyfluthrin (U) 68359–37–5 .053 HBSL Insecticide.

Cypermethrin (U) 52315–07–8 .046 HBSL Insecticide.

2,4–D (R) 94–75–7 .038 MCL Herbicide.

36  Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Appendix 2. Pesticides and pesticide degradates analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, Maximum Contaminant Level]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Type of pesticide

2,4–D methyl ester (U) 1928–38–7 0.19 NA Herbicide.

Dacthal (U) 1861–32–1 .003 HBSL Herbicide.

Dacthal monoacid (U) 887–54–7 .028 NA Herbicide degradate.

2,4–DB (U) 94–82–6 .02 HBSL Herbicide.

Deethylatrazine (U) 6190–65–4 .014 NA Herbicide degradate.

Deisopropylatrazine (U) 1007–28–9 .08 NA Herbicide degradate.

Desulfinylfipronil (U) NA .012 NA Insecticide degradate.

Desulfinylfipronil amide (U) NA .029 NA Insecticide degradate.

Diazinon (U) 333–41–5 .005 HBSL Insecticide.

Diazinon, oxygen analog (U) 962–58–3 .006 NA Insecticide degradate.

Dicamba (U) 1918–00–9 .036 HBSL Herbicide.

3,4-Dichloroaniline (U) 95–76–1 .0045 NA Herbicide degradate.

Dichlorprop (U) 120–36–5 .028 NA Herbicide.

Dichlorvos (U) 62–73–7 .013 HBSL Insecticide.

Dicrotophos (U) 141–66–2 .0843 HBSL Insecticide.

Didealkyatrazine (U) 3397–62–4 .04 NA Herbicide degradate.

Dieldrin (U) 60–57–1 .009 HBSL Insecticide.

2,6-Diethylaniline (U) 579–66–8 .006 NA Herbicide degradate.

Dimethoate (U) 60–51–5 .0061 HBSL Insecticide.

Dinoseb (R) 88–85–7 .038 MCL Herbicide.

Diphenamid (U) 957–51–7 .01 HBSL Herbicide.

Diuron (U) 330–54–1 .016 HBSL Herbicide.

Ethion (U) 563–12–2 .016 HBSL Insecticide.

Ethion monoxon (U) 17356–42–2 .021 NA Insecticide degradate.

2-Ethyl-6-methylaniline (U) 24549–06–2 .01 NA Herbicide degradate.

Fenamiphos (U) 22224–92–6 .029 HBSL Insecticide.

Fenamiphos sulfone (U) 31972–44–8 .053 NA Insecticide degradate.

Fenamiphos sulfoxide (U) 31972–43–7 .04 NA Insecticide degradate.

Fenuron (U) 101–42–8 .1 NA Herbicide.

Fipronil (U) 120068–37–3 .016 NA Insecticide.

Fipronil sulfide (U) 120067–83–6 .013 NA Insecticide degradate.

Fipronil sulfone (U) 120068–36–2 .024 NA Insecticide degradate.

Appendixes  37
Appendix 2. Pesticides and pesticide degradates analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, Maximum Contaminant Level]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Type of pesticide

Flumetsulam (U) 98967–40–9 0.04 HBSL Herbicide.

Fluometuron (U) 2164–17–2 .016 HBSL Herbicide.

Fonofos (U) 944–22–9 .0053 HBSL Insecticide.

Fonofos, oxygen analog (U) 944–21–8 .0029 NA Insecticide degradate.

Hexazinone (U) 51235–04–2 .026 HBSL Herbicide.

2-Hydroxyatrazine (U) 2163–68–0 .032 HBSL Herbicide degradate.

3-Hydroxycarbofuran (U) 16655–82–6 .008 NA Insecticide degradate.

Imazaquin (U) 81335–37–7 .036 HBSL Herbicide.

Imazethapyr (U) 81335–77–5 .038 HBSL Herbicide.

Imidacloprid (U) 138261–41–3 .02 NA Insecticide.

Iprodione (U) 36734–19–7 .026 HBSL Fungicide.

Isofenphos (U) 25311–71–1 .011 HBSL Insecticide.

3-Ketocarbofuran (U) 16709–30–1 1.5 NA Insecticide degradate.

Linuron (U) 330–55–2 .014 HBSL Herbicide.

Malaoxon (U) 1634–78–2 .039 NA Insecticide degradate.

Malathion (U) 121–75–5 .027 HBSL Insecticide.

MCPA (U) 94–74–6 .07 HBSL Herbicide.

MCPB (U) 94–81–5 .1 HBSL Herbicide.

Metalaxyl (U) 57837–19–1 .007 HBSL Fungicide.

Methidathion (U) 950–37–8 .0087 HBSL Insecticide.

Methiocarb (U) 2032–65–7 .034 HBSL Insecticide.

Methomyl (U) 16752–77–5 .07 HBSL Insecticide.

Metolachlor (U) 51218–45–2 .006 HBSL Herbicide.

Metribuzin (U) 21087–64–9 .028 HBSL Herbicide.

Metsulfuron methyl (U) 74223–64–6 .067 HBSL Herbicide.

Myclobutanil (U) 88671–89–0 .033 HBSL Fungicide.

1-Naphthol (U) 90–15–3 .0882 NA Insecticide degradate.

Neburon (U) 555–37–3 .012 NA Herbicide.

38  Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Appendix 2. Pesticides and pesticide degradates analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, Maximum Contaminant Level]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Type of pesticide

Nicosulfuron (U) 111991–09–4 0.04 HBSL Herbicide.

Norflurazon (U) 27314–13–2 .02 HBSL Herbicide.

Oryzalin (U) 19044–88–3 .023 HBSL Herbicide.

Oxamyl (R) 23135–22–0 .05 MCL Insecticide.

Paraoxon-methyl (U) 950–35–6 .019 NA Insecticide degradate.

Parathion-methyl (U) 298–00–0 .015 HBSL Insecticide.

Pendimethalin (U) 40487–42–1 .022 HBSL Herbicide.

Phorate (U) 298–02–2 .055 HBSL Insecticide.

Phorate oxon (U) 2600–69–3 .027 NA Insecticide degradate.

Phosmet (U) 732–11–6 .0079 HBSL Insecticide.

Phosmet oxon (U) 3735–33–9 .0511 NA Insecticide degradate.

Picloram (U) 1918–02–1 .032 NA Herbicide.

Prometon (U) 1610–18–0 .01 HBSL Herbicide.

Prometryn (U) 7287–19–6 .0059 HBSL Herbicide.

Propham (U) 122–42–9 .03 HBSL Herbicide.

Propiconazole (U) 60207–90–1 .01 HBSL Fungicide.

Propoxur (U) 114–26–1 .008 HBSL Insecticide.

Propyzamide (U) 23950–58–5 .004 HBSL Herbicide.

Siduron (U) 1982–49–6 .02 NA Herbicide.

Simazine (R) 122–34–9 .005 MCL Herbicide.

Sulfometuron-methyl (U) 74222–97–2 .09 NA Herbicide.

Tebuthiuron (U) 34014–18–1 .026 HBSL Herbicide.

Terbacil (U) 5902–51–2 .026 HBSL Herbicide.

Terbufos (U) 13071–79–9 .017 HBSL Insecticide.

Terbufos-O-analogue sulfone (U) 56070–15–6 .045 NA Insecticide degradate.

Terbuthylazine (U) 5915–41–3 .0083 HBSL Herbicide.

Triclopyr (U) 55335–06–3 .026 HBSL Herbicide.

Trifluralin (U) 1582–09–8 .009 HBSL Herbicide.

Appendixes  39
Appendix 3. Other anthropogenic organic compounds analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, Maximum Contaminant Level; Gasoline, compounds that include gasoline hydrocarbons, oxygenates, and oxygenate degradates; Pavement & combustion, includes 

polyaromatic hydrocarbon compounds present in pavement and released from the combustion of fossil fuels]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Primary use or source

Acetophenone (U) 98–86–2 0.5 HBSL Personal care and domestic use products.

Acetyl hexamethyl tetrahydronaphthalene (U) 

(AHTN)

21145–77–7 .5 NA Personal care and domestic use products.

Anthracene (U) 120–12–7 .5 HBSL Pavement & combustion.

Anthraquinone (U) 84–65–1 .5 NA Organic synthesis compound.

Benzo[a]pyrene 50–32–8 .5 MCL Pavement & combustion.

Benzophenone (U) 119–61–9 .5 NA Personal care and domestic use products.

Bisphenol-A (U) 80–05–7 1 HBSL Manufacturing additive.

3-tert-Butyl-4-hydroxy anisole (U) (BHA) 25013–16–5 5 NA Personal care and domestic use products.

Caffeine (U) 58–08–2 .018 NA Personal care and domestic use products.

Camphor (U) 76–22–2 .5 NA Personal care and domestic use products.

Carbazole (U) 86–74–8 .5 NA Organic synthesis compound.

Cholesterol (U) 57–88–5 2 NA Plant- or animal-derived biochemical.

3-beta-Coprostanol (U) 360–68–9 2 NA Plant- or animal-derived biochemical.

Cotinine (U) 486–56–6 1 NA Personal care and domestic use products.

p-Cresol (U) 106–44–5 1 NA Solvent.

4-Cumylphenol (U) 599–64–4 1 NA Personal care and domestic use products.

N,N-Diethyl-meta-toluamide (U) (DEET) 134–62–3 .5 NA Personal care and domestic use products.

2,6-Dimethylnaphthalene (U) 581–42–0 .5 NA Gasoline.

Fluoranthene (U) 206–44–0 .5 HBSL Pavement & combustion.

Hexadydrohexamethylcyclopentabenzopyran (U) (HHCB)1222–05–5 .5 NA Personal care and domestic use products.

Indole (U) 120–72–9 .5 NA Personal care and domestic use products.

Isoborneol (U) 124–76–5 .5 NA Personal care and domestic use products.

Isophorone (U) 78–59–1 .5 HBSL Solvent.

Isoquinoline (U) 119–65–3 .5 NA Personal care and domestic use products.

d-Limonene (U) 5989–27–5 .5 NA Personal care and domestic use products.

40 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Appendix 3. Other anthropogenic organic compounds analyzed in this study.—Continued

[CASRN, Chemical Abstracts Service Registry Number; μg/L, micrograms per liter; NA, not available; HBSL, Health-Based Screening Level; MCL, Maximum Contaminant Level; Gasoline, compounds that include gasoline hydrocarbons, oxygenates, and oxygenate degradates; Pavement & combustion, includes 

polyaromatic hydrocarbon compounds present in pavement and released from the combustion of fossil fuels]

Regulated (R) or unregulated (U) 

compound (alternate name) CASRN

Minimum 

reporting 

level, 

in μg/L

Type of 

human-health 

benchmark

Primary use or source

Menthol (U) 89–78–1 0.5 NA Personal care and domestic use products.

5-Methyl-1H-benzotriazole (U) 136–85–6 2 NA Manufacturing additive.

3-Methyl-1(H)-indole (U) (Skatole) 83–34–1 1 NA Plant- or animal-derived biochemical.

1-Methylnaphthalene (U) 90–12–0 .5 NA Gasoline.

2-Methylnaphthalene (U) 91–57–6 .5 HBSL Gasoline.

Methyl salicylate (U) 119–36–8 .5 NA Personal care and domestic use products.

4-Nonylphenol (U) 84852–15–3 5 NA Personal care and domestic use products.

4-Nonylphenol, diethoxylate (U) 

(NPEO2-total)

26027–38–2 5 NA Personal care and domestic use products.

4-n-Octylphenol (U) 1806–26–4 1 NA Personal care and domestic use products.

4-tert-Octylphenol (U) 140–66–9 1 NA Personal care and domestic use products.

4-Octylphenol diethoxylate (U) (OPEO2) 26636–32–8 1 NA Personal care and domestic use products.

4-Octylphenol monoethoxylate (U) (OPEO1) 26636–32–8 1 NA Personal care and domestic use products.

Pentachlorophenol (R) 87–86–5 2 MCL Fungicide.

Phenanthrene (U) 85–01–8 .5 NA Pavement & combustion.

Phenol (U) 108–95–2 .5 NA Personal care and domestic use products.

Pyrene (U) 129–00–0 .5 HBSL Pavement & combustion.

beta-Sitosterol (U) 83–46–5 2 NA Plant- or animal-derived biochemicals.

beta-Stigmastanol (U) 19466–47–8 2 NA Plant- or animal-derived biochemicals.

Tributyl phosphate (U) 126–73–8 .5 NA Manufacturing additive.

Tri(2-butoxyethyl)phosphate (U) 78–51–3 .5 NA Manufacturing additive.

Tri(2-chloroethyl)phosphate (U) (TCEP) 115–96–8 .5 NA Manufacturing additive.

Triclosan (U) 3380–34–5 1 NA Personal care and domestic use products.

Tri(dichlorisopropyl)phosphate (U) (TCPP) 13674–87–8 .5 NA Manufacturing additive.

Triethyl citrate (U) (ethyl citrate) 77–93–0 .5 NA Personal care and domestic use products.

Triphenyl phosphate (U) 115–86–6 .5 NA Manufacturing additive.

Appendixes 41
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

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 peerreviewed, publicly available human-health toxicity 

information.

Toccalino and others, 

2003 and 2006a.

Maximum 

Con­taminant 

Level (Federal)

USEPA 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 non-enforceable 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, 

2003 and 2006.

42 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Appendix 5. Comparison of volatile organic compounds (VOCs) detected in the source water during phase 1 of the Source WaterQuality Assessment (SWQA) with VOCs detected in other local and regional studies.

[ULUS, urban land-use study; MAS, major aquifer study; VOC, volatile organic compound; n, number of samples; ND, not detected; --, not analyzed, reported, 

and (or) not able to calculate a ranking because compound was not detected]

Regulated (R) or 

unregulated (U) 

compound

Study identifier (from table 2)

A 

(SWQA)

B 

(ULUS)

C 

(MAS)

D 

(Bradner and others, 2005)

Percent 

detection 

n=30

VOC 

Rank

Percent 

detection 

n=34

VOC 

Rank

Percent 

detection 

n=60

VOC 

Rank

Percent 

detection 

n=30

VOC 

Rank

Chloroform (R) 43 1 12 3 35 1 27 4

Carbon disulfide (U) 17 2 35 1 10 4 3.3 19

Perchloroethene (R) (PCE) 13 3 12 3 1.7 5 23 5

Bromodichloromethane (R) 10 4 3 7 1.7 5 23 5

1,2,4-Trimethylbenzene (U) 10 4 ND -- ND -- ND --

Bromoform (R) 6.7 6 ND -- ND -- 10 11

1,1-Dichloroethane (U) 3.3 7 ND -- 1.7 5 13 10

cis-1,2-Dichloroethene (R) 3.3 7 2.9 7 1.7 5 40 1

Methyl tert-butyl ether (U) 

(MTBE) 3.3 7 2.9 7 1.7 5 30 2

Trichlorofluoromethane (U) 3.3 7 ND -- ND -- ND --

Trichloroethene (R) 3.3 7 2.9 8 1.7 5 20 7

Toluene (R) ND -- 18 2 25 2 17 9

Isopropylbenzene (U) ND -- 5.9 5 ND -- ND --

Tetrahydrofuran (U) ND -- 5.9 5 ND -- ND --

Dichloromethane (R) ND -- 3.1 7 1.7 5 ND --

Bromochloromethane (U) ND -- 2.9 8 ND -- ND --

Dichlorodifluoromethane (U) ND -- 2.9 8 1.7 5 6.7 13

1,2-Dichloropropane (U) ND -- 2.9 8 23 3 ND --

1-Methyl-4-isopropylbenzene (U) ND -- 2.9 8 ND -- ND --

1,1-Dichloroethene (R) ND -- ND -- 1.7 5 ND --

Ethylbenzene (R) ND -- ND -- 1.7 5 ND --

Styrene (R) ND -- ND -- 1.7 5 ND --

1,4-Dichlorobenzene (R) ND -- ND -- ND -- 30 2

Chlorobenzene (R) ND -- ND -- ND -- 20 7

1,2-Dichlrobenzene (R) ND -- ND -- ND -- 10 11

Benzene (R) ND -- ND -- ND -- 6.7 13

Dibromochloromethane (R) ND -- ND -- ND -- 6.7 13

trans-1,2-Dichloroethene (R) ND -- ND -- ND -- 6.7 13

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

trifluoroethane (R)

ND -- ND -- ND -- 6.7 13

Vinyl chloride (R) ND -- ND -- ND -- 6.7 13

Chloromethane (R) ND -- ND -- ND -- 3.3 19

Appendixes 43
Appendix 6. Comparison of pesticides detected in the source water during phase 1 of the Source Water-Quality Assessment (SWQA) 

with pesticides detected in other local and regional studies.

[ULUS, urban land-use study; MAS, major aquifer survey; n, number of samples; ND, not detected; --, not analyzed, reported, and (or) not able to calculate a 

ranking because compound was not detected; p,p’-DDE, dichlorodiphenyldichloroethylene]

Regulated (R) or 

unregulated (U) 

compound

Study identifier (from table 2)

A 

(SWQA)

B 

(ULUS)

C 

(MAS)

D 

(Bradner and others, 2005)

Percent 

detection 

n=30

Pesticide 

rank

Percent 

detection 

n=34

Pesticide 

rank

Percent 

detection 

n=60

Pesticide 

rank

Percent 

detection 

n=30

Pesticide 

rank

Deethylatrazine (U) 33 1 3 6 1.7 2 63 3

Atrazine (R) 23 2 3 6 1.7 2 73 2

2-Hydroxyatrazine (U) 23 2 3 6 ND -- ND --

Bentazon (U) 20 4 15 1 ND -- -- --

Prometon (U) 17 5 3 6 1.7 2 47 5

Simazine (R) 13 6 ND -- 3.3 1 27 7

Deisopropylatrazine (U) 6.7 7 ND -- ND -- ND --

Imidacloprid (U) 6.7 7 3 6 ND -- ND --

Tebuthiuron (U) 6.7 7 12 2 1.7 2 77 1

Bromacil (U) 3.3 10 9 3 ND -- -- --

3,4-Dichloroaniline (U) 3.3 10 ND -- ND -- ND --

Fonofos, oxygen analyge (U) 3.3 10 ND -- ND -- ND --

Hexazinone (U) ND -- 6 4 ND -- ND --

Imazaquin (U) ND -- 6 4 ND -- ND --

2-Amino-n-isopropylbenzamide ND -- 3 6 ND -- ND --

Chlordiamino-s-triazine (U) ND -- 3 6 ND -- ND --

2,4–DB (U) ND -- 3 6 ND -- ND --

Fenuron (U) ND -- 3 6 ND -- 30 6

Imazethapyr (U) ND -- 3 6 ND -- ND --

Metsulfuron methyl (U) ND -- 3 6 ND -- ND --

Oryzalin (U) ND -- 3 6 ND -- ND --

Picloram (U) ND -- 3 6 ND -- ND --

Propoxur (U) ND -- 3 6 ND -- ND --

Diazinon (U) ND -- ND -- 3.3 1 -- --

Diuron (U) ND -- ND -- ND -- 53 4

Metolachlor (U) ND -- ND -- ND -- 27 7

2,6-Diethylaniline (U) ND -- ND -- ND -- 13 9

Butylate (U) ND -- ND -- ND -- 6.7 10

p,p ́-DDE (U) -- -- -- -- -- -- 6.7 10

Dieldrin (U) ND -- ND -- ND -- 6.7 10

EPTC (U) ND -- ND -- ND -- 6.7 10

Norflurazon (U) ND -- ND -- ND -- 3.3 14

44 Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Appendix 7. Comparison of other anthropogenic organic compounds (OAOCs) detected in the source water during phase 1 of the 

Source Water-Quality Assessment (SWQA) with OAOCs detected in a local study.

[n, number of samples; ND, not detected; --, not analyzed, reported, and (or) not able to calculate a ranking because compound was not detected]

Compound Name (all are unregulated

compounds)

Study Identifier (from table 2)

A 

(SWQA)

E 

(Phelps, 2004)

Percent detection 

n=30

OAOC 

rank

Percent detection 

n=38

OAOC 

rank

N,N,-diethyl-meta-toluamide (DEET) 17 1 79 1

Cholesterol 6.7 2 11 4

3-beta-Coprostanol 6.7 2 2.6 14

p-Cresol 3.3 4 7.9 8

Indole 3.3 4 2.6 14

4-Octylphenol diethoxylate 3.3 4 2.6 14

beta-Sitosterol 3.3 4 2.6 14

beta-Stigmastanol 3.3 4 ND --

Bisphenol-A ND -- 29 2

Triclosan ND -- 16 3

Isophorone ND -- 11 4

4-Nonylphenol (total) ND -- 11 4

Tri(2-chloroethyl)phosphate (TCEP) ND -- 11 4

Caffeine ND -- 7.9 8

Benzophenone ND -- 5.3 10

Diethoxynonylphenone ND -- 5.3 10

2-Methylnaphthalene ND -- 5.3 10

Tributyl phosphate ND -- 5.3 10

Appendixes 45
Appendix 8. Comparison between source and associated finished water for anthropogenic organic compounds detected during 

phase 2 of the Source Water-Quality Assessment.—Continued

[Shaded cells indicate blended water. μg/L, micrograms per liter; E, estimated value; ND, not detected]

Well identifier

Detected anthropogenic 

organic compound 

(regulated (R) or unregulated (U))

Source water 

(μg/L)

Finished water, 

nonblended or 

blended 

(μg/L)

Volatile organic compounds

22 Acetone (U) 68.4 ND

20 Bromoform (R) ND 0.482

21 Bromoform (R) ND .156

23 Bromoform (R) ND .546

29 Bromoform (R) ND E.127

2 Bromoform (R) ND .18 

10 Bromoform (R) ND E.02 

15 Bromoform (R) ND .93 

17 Bromoform (R) ND 5.52 

18 Bromodichloromethane (R) E.04 .371

20 Bromodichloromethane (R) ND 1.78 

21 Bromodichloromethane (R) ND .571

22 Bromodichloromethane (R) ND E.053

23 Bromodichloromethane (R) ND 2.94 

29 Bromodichloromethane (R) ND 3.13 

2 Bromodichloromethane (R) ND 7.48 

11 Bromodichloromethane (R) ND 3.19 

15 Bromodichloromethane (R) ND .74 

17 Bromodichloromethane (R) ND 3.72 

2 Carbon disulfide (U) .116 ND 

11 Carbon disulfide (U) ND .04 

23 Carbon tetrachloride (R) ND E.018

2 Carbon tetrachloride (R) ND E.06 

15 Carbon tetrachloride (R) ND .50 

18 Chloroform (R) .948 1.35 

20 Chloroform (R) .269 1.23 

21 Chloroform (R) E.051 .453 

22 Chloroform (R) .304 .356

23 Chloroform (R) .504 3.18 

29 Chloroform (R) E.035 3.64 

2 Chloroform (R) ND 36.3 

11 Chloroform (R) ND 24.6 

15 Chloroform (R) .151 .82

17 Chloroform (R) .36 1.43 

29 Chloromethane (U) ND E.116

46  Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Appendix 8. Comparison between source and associated finished water for anthropogenic organic compounds detected during 

phase 2 of the Source Water-Quality Assessment.—Continued

[Shaded cells indicate blended water. μg/L, micrograms per liter; E, estimated value; ND, not detected]

Well identifier

Detected anthropogenic 

organic compound 

(regulated (R) or unregulated (U))

Source water 

(μg/L)

Finished water, 

nonblended or 

blended 

(μg/L)

Volatile organic compounds—Continued

18 Dibromochloromethane (R) ND 0.207

20 Dibromochloromethane (R) ND 1.84

21 Dibromochloromethane (R) ND .612 

23 Dibromochloromethane (R) ND 2.45 

29 Dibromochloromethane (R) ND 1.64 

2 Dibromochloromethane (R) ND 1.37 

11 Dibromochloromethane (R) ND .27 

15 Dibromochloromethane (R) ND 1.59 

17 Dibromochloromethane (R) ND 7.95

29 Ethylbenzene (R) ND .593 

22 Methyl ethyl ketone (U) (MEK) 1,140 ND 

29 Methyl isobutyl ketone (U) ND 3.3 

15 Methyl tert-butyl ether (U) (MTBE) ND E.100

10 Naphthalene (R) ND E.06 

20 Perchloroethene (R) (PCE) ND E.023

15 Perchloroethene (R) (PCE) E.033 E.04 

17 Perchloroethene (R) (PCE) ND E.08 

22 Tetrahydrofuran (U) 279 ND 

17 Trichloroethene (U) E.046 ND 

11 Toluene (R) ND E.02 

29 o-Xylene (R) ND 1.03 

29 m- and p-Xylene (R) ND 2.26

Pesticides

20 Atrazine (R) 0.023 0.01 

21 Atrazine (R) E.003 E.003 

22 Atrazine (R) .012 .012 

15 Atrazine (R) E.001 E.008 

17 Atrazine (R) E.004 .004 

20 Bentazon (U) E.026 ND 

21 Bentazon (U) E.021 ND 

22 Bentazon (U) E.036 E.035

23 Bentazon (U) E.009 ND 

17 Bentazon (U) .057 ND 

15 Bromacil (U) E.059 ND 

20 Deethylatrazine (U) E.021 E.008

Appendixes 47
Appendix 8. Comparison between source and associated finished water for anthropogenic organic compounds detected during 

phase 2 of the Source Water-Quality Assessment.—Continued

[Shaded cells indicate blended water. μg/L, micrograms per liter; E, estimated value; ND, not detected]

Well identifier

Detected anthropogenic 

organic compound 

(regulated (R) or unregulated (U))

Source water 

(μg/L)

Finished water, 

nonblended or 

blended 

(μg/L)

Pesticides—Continued

22 Deethylatrazine (U) E0.025 E0.02 

21 Deethylatrazine (U) E.006 E.004 

23 Deethylatrazine (U) E.004 E.004 

15 Deethylatrazine (U) E.016 E.012 

15 Deisopropylatrazine (U) E.004 ND 

22 Deisopropylatrazine (U) E.004 ND 

20 2-Hydroxyatrazine (U) E.011 E.006

21 2-Hydroxyatrazine (U) E.006 E.006

22 2-Hydroxyatrazine (U) E.01 E.007 

23 2-Hydroxyatrazine (U) E.006 E.005

15 2-Hydroxyatrazine (U) E.011 .012 

17 2-Hydroxyatrazine (U) E.029 E.013 

22 Imidacloprid (U) .017 .01

15 Imidacloprid (U) ND .01 

17 Imidacloprid (U) .007 .016 

15 Prometon (U) .009 .01 

15 Simazine (R) .01 .007

23 Tebuthiuron (U) .034 .03 

Other anthropogenic organic compounds

23 Caffeine (U) E0.006 E0.004 

17 Caffeine (U) E.006 E.004 

10 Camphor (U) ND E.013

10 1-Methylnaphthalene (U) ND E.014

10 2-Methylnaphthalene (U) ND E.025

10 N,N,-diethyl-meta-toluamide (U) (DEET) E.084 E.075 

10 Tri(2-chloroethyl)phosphate (R) (TCEP) E.110 ND 

10 Tri(dichlorisopropyl)phosphate (R) (TCPP) E.081 ND 

48  Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04
Prepared by the USGS Publishing Network,

 Helena Publishing Service Center.

For more information concerning the research in this report, contact:

 National Water-Quality Assessment Program,

 The University Center for Business

 10500 University Center Drive, Suite 215

 Tampa, Florida 33612–6427

Information regarding the National Water-Quality Assessment 

Program is available at http://fl.water.usgs.gov/nawqa/
Metz and others—Anthropogenic Organic Compounds in Ground and Finished Water in the Northern Tampa Bay Area, 2002–04—SIR 2006–5267

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