Occurrence Summary and Use

Support Document 

for the Six-Year Review of 

National Primary Drinking Water

Regulations
 Printed on Recycled Paper

Office of Water (4606)

EPA-815-D-02-006 

www.epa.gov 

March 2002
Occurrence Summary and Use Support Document March 2002

Disclaimer

This report is issued in support of the preliminary revise/not revise

decisions for the Six-Year Review Notice of Intent. It is intended for

public comment and does not represent final agency policy. EPA expects

to issue a final version of this report with the publication of the

final notice in 2002, reflecting corrections due to public comment on

the preliminary notice and the supporting documents.

Mention of trade names or commercial products does not constitute

endorsement or recommendation for use.
Occurrence Summary and Use Support Document March 2002 iii

ACKNOWLEDGMENTS

The compilation and analysis of the data summarized in this report were undertaken by EPA’s Office of

Ground Water and Drinking Water (OGWDW) in support of the Six-Year Review of National Primary

Drinking Water Regulations. This effort was directed by Mr. Peter Lassovszky, with contributions and

reviews by Ms. Wynne Miller, of OGWDW.

We would like to thank the many States and State staff who contributed data sets and valuable advice. 

Thank you also to the many public water systems and their staff who conducted the monitoring that

provided the extensive amount of contaminant occurrence data used in this report.

EPA also appreciates the technical support provided by The Cadmus Group, Inc., the prime contractor for

this project. Dr. Jonathan Koplos and Dr. George Hallberg served as Cadmus Project Managers in the

provision of support for background research, contaminant occurrence analyses, and report development. 

The major contributions of Erin Hartigan, Alison Kotros, and Jane Parkin are gratefully acknowledged.
Occurrence Summary and Use Support Document March 2002 iv

TABLE OF CONTENTS

1.0 Introduction ..................................................................... 1

1.1 Purpose and Scope ........................................................ 1

1.2 Review Process .......................................................... 1

1.3 Data Sources ............................................................ 2

1.4 Occurrence Analysis ...................................................... 9

1.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.0 Inorganic Contaminants (IOCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1 Beryllium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2 Chromium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.3 Fluoride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

2.4 Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

2.5 Thallium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

3.0 Synthetic Organic Contaminants (SOCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

3.1 Alachlor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

3.2 Bis(2-ethylhexyl)phthalate (DEHP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

3.3 Carbofuran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

3.4 Chlordane ............................................................ .151

3.5 1,2-Dibromo-3-chloropropane (DBCP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

3.6 Diquat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

3.7 Glyphosate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

3.8 Heptachlor & Heptachlor Epoxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

3.9 Hexachlorobenzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

3.10 Hexachlorocyclopentadiene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

3.11 Oxamyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

3.12 Picloram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

3.13 Simazine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

3.14 Toxaphene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

4.0 Volatile Organic Contaminants (VOCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

4.1 Benzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

4.2 Carbon Tetrachloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

4.3 1,4-Dichlorobenzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

4.4 1,2-Dichloroethane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346

4.5 1,1-Dichloroethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

4.6 Dichloromethane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382

4.7 1,2-Dichloropropane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

4.8 Tetrachloroethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406

4.9 1,1,2-Trichloroethane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

4.10 Trichloroethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

Abbreviations and Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
Occurrence Summary and Use Support Document March 2002 v

1.0 Introduction

Table of Contents

1.1 Purpose and Scope ............................................................... 1

1.2 Review Process .................................................................. 1

1.3 Data Sources .................................................................... 2

1.3.1 Agency for Toxic Substances and Disease Registry .............................. 2

1.3.2 Toxic Release Inventory ................................................... 2

1.3.3 National Water Quality Assessment .......................................... 3

1.3.4 The National Highway Runoff Data and Methodology Synthesis ................... 5

1.3.5 16-State Cross-Section Data ................................................ 5

1.3.5.1 Data Management ................................................ 6

1.3.6 Additional Data .......................................................... 8

1.4 Occurrence Analysis .............................................................. 9

1.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

List of Tables & Figures

Figure 1.3-1. Map of the 16 Cross-Section States .......................................... 6

Table 1.3-1. Contaminant Occurrence Data From the 16-State Cross-Section .................... 7
Occurrence Summary and Use Support Document March 2002 1

1.1 Purpose and Scope

This document summarizes contaminant occurrence findings for 30 regulated contaminants in support of

the Environmental Protection Agency’s (EPA’s) Six-Year Review of National Primary Drinking Water

Regulations (“Six-Year Review”). Included is detailed information regarding each contaminant’s

occurrence in drinking water and related information relevant to initial exposure assessments. Brief

reviews regarding each contaminant’s production, uses and occurrence in ambient water are also

included. To provide some regulatory context, the Six-Year Review process is briefly described.

This document is divided into four sections. This section (Section 1) contains general information

– applicable to all contaminants– which includes a description of all data sources used for this analysis

and the statistical methodology used to estimate national occurrence from the data that are national in

scope. The following three sections are organized by contaminant group. Section 2 provides information

for all inorganic contaminants (IOCs), Section 3 provides information for all synthetic organic

contaminants (SOCs), and Section 4 provides information for all volatile organic contaminants (VOCs). 

(See Page ii for a list of the contaminants included in each section.) Within each contaminant group

section there is a detailed Table of Contents specific to each contaminant. For a general overview or

summary of a particular contaminant’s occurrence findings, please refer to the conclusion section for that

specific contaminant.

1.2 Review Process

The Environmental Protection Agency’s Office of Ground Water and Drinking Water (OGWDW) is

responsible for implementing the provisions of the Safe Drinking Water Act (SDWA). The 1996 SDWA

amendments require the U.S. EPA to review existing National Primary Drinking Water Regulations

(NPDWRs) no less often than every six years and, if appropriate, revise them. As long as an NPDWR

revision maintains or provides for greater protection of public health, the SDWA 1996 amendments give

the Administrator discretion to determine if revision is appropriate. EPA believes the revision must

continue to meet the basic statutory requirements of the SDWA (e.g., generally setting the maximum

contaminant level as close to the maximum contaminant level goal as is feasible), to determine if a

revision is appropriate. EPA also believes the revision must present significant opportunities to improve

the level of public health protection and/or to achieve cost savings while maintaining, or improving, the

level of public health protection. The Six-Year Review workgroup is reviewing the factors relevant to

this formal re-assessment of each national primary drinking water regulation.

EPA developed a protocol document — EPA Protocol for the Review of Existing National Primary

Drinking Water Regulations (USEPA, 2001) — to describe the process and strategy for Review that EPA

will use to meet its statutory requirement. To most efficiently utilize limited resources, EPA plans to

perform a series of analyses at the beginning of each Review cycle, intended to target those NPDWRs

that are the most appropriate candidates for revision. The Agency plans to use available, scientificallysound data to make decisions regarding whether or not to revise a regulation. EPA will review the

following key information to make decisions regarding regulatory changes: current health risk

assessments, technology assessments (including reviews of laboratory analytical methods and treatment

techniques), and occurrence and exposure assessments. This current document presents information

specific to occurrence and exposure in support of the Six-Year Review. 

EPA will consider regulatory revisions based on the various components of each primary drinking water

regulation, including possible changes to Maximum Contaminant Levels (MCLs), Maximum

Contaminant Level Goals (MCLGs), treatment techniques, analytical method capabilities, and treatment

capabilities. In some cases, EPA may also consider revisions to monitoring or system reporting

requirements as part of the Six-Year Review; however, in most cases, these types of revisions will be

considered through other vehicles. In rare instances, EPA may consider dropping a contaminant from

regulation. For any NPDWR that is a potential candidate for revision based on its review, EPA will also

take economic considerations into account before making its “revise/not revise” decision. Moreover,

EPA will apply basic risk management principles to determine whether these candidate regulations
Occurrence Summary and Use Support Document March 2002 2

warrant regulatory revision to ensure that any revision will present a significant opportunity to improve

the level of public health protection and/or present a significant opportunity for cost savings while

maintaining, or improving, the level of public health protection.

1.3 Data Sources

Numerous data sources were used in this report to provide information on contaminant use, production,

occurrence, and potential exposure. The primary data sources used for background use, production, and

release reviews include the Agency for Toxic Substances and Disease Registry (ATSDR) and Toxics

Release Inventory (TRI). Information on contaminant occurrence in ambient water primarily derives

from the National Water Quality Assessment Program (NAWQA). Drinking water contaminant

occurrence analyses are generated from State drinking water compliance monitoring data from a national

cross-section comprised of occurrence data from 16 States. This 16-State national cross-section is the

largest compliance monitoring data set compiled to date by EPA. These primary data sources are

described in detail in the subsequent sections of this Introduction. In addition to the primary data

sources, supplemental contaminant occurrence information for drinking water and ambient water is also

reviewed whenever available. These supplemental data sources and findings are included in the

contaminant specific sections of this report. 

1.3.1 Agency for Toxic Substances and Disease Registry

In 1980, Congress created the Agency for Toxic Substances and Disease Registry (ATSDR) to

implement the health-related sections of laws that protect the public from hazardous wastes and

environmental spills of hazardous substances (ATSDR, 2001). The Comprehensive Environmental

Response, Compensation, and Liability Act of 1980 (CERCLA), commonly known as the “Superfund”

Act, provided the Congressional mandate to remove or clean up abandoned and inactive hazardous waste

sites and to provide federal assistance in toxic emergencies. As the lead Agency within the Public Health

Service for implementing the health-related provisions of CERCLA, ATSDR is charged under the

Superfund Act to assess the presence and nature of health hazards at specific Superfund sites, to help

prevent or reduce further exposure and the illnesses that result from such exposures, and to expand the

knowledge base about health effects from exposure to hazardous substances (ATSDR, 2001).

In the 1984 amendments to the Resource Conservation and Recovery Act of 1976 (RCRA), which

provides for the management of legitimate hazardous waste storage or destruction facilities, ATSDR was

authorized to conduct public health assessments at these sites, when requested by EPA, States, or

individuals. ATSDR was also authorized to assist EPA in determining which substances should be

regulated and the levels at which substances may pose a threat to human health (ATSDR, 2001).

With the passage of the Superfund Amendments and Reauthorization Act of 1986 (SARA), ATSDR

received additional responsibilities in environmental public health. This act broadened ATSDR's

responsibilities in the areas of public health assessments, establishment and maintenance of toxicologic

databases, information dissemination, and medical education (ATSDR, 2001). 

ATSDR issues Toxicological Profiles for over 250 substances, including 23 of the 30 contaminants

discussed in this report. These profiles contain exhaustive reports on the substances’ health effects,

chemical and physical properties, use and production, potential for human exposure, and analytical

methods. Whenever available, ATSDR was used as a primary source in this report for contaminant use

and production information.

1.3.2 Toxic Release Inventory

The Toxics Release Inventory (TRI) is a publicly available EPA database that contains information on

specific toxic chemical releases and other waste management activities reported annually by certain

covered industry groups as well as federal facilities. Facilities are required to use their best readily

available data to calculate their releases and waste management estimates. If facilities do not have actual
Occurrence Summary and Use Support Document March 2002 3

monitoring data, submitted values are derived from various estimation techniques. Reporting Year (RY)

1999 is the most recent TRI data available. 

In 1986, the Emergency Planning and Community Right-to-Know Act (EPCRA) established the TRI of

hazardous chemicals. Through EPCRA, Congress mandated that larger facilities publicly report when

TRI chemicals are released into the environment. TRI provides citizens with accurate information about

potentially hazardous chemicals and their use so that communities have more power to hold companies

accountable and make informed decisions about how toxic chemicals are to be managed. This public

reporting is required for facilities with more than 10 full-time employees that annually manufacture or

produce more than 25,000 pounds, or use more than 10,000 pounds, of TRI chemical (USEPA, 1996;

USEPA, 2000c). Under these conditions, facilities are required to report the pounds per year of the

contaminant released into the environment both on- and off-site. The on-site quantity is subdivided into

air emissions, surface water discharges, underground injections, and releases to land. 

Although the TRI data can be useful in giving a general idea of release trends, it is far from exhaustive

and has significant limitations. For example, only industries which meet TRI criteria (at least 10 fulltime employees and manufacture and processing of quantities exceeding 25,000 lbs/yr, or use of more

than 10,000 lbs/yr) are required to report releases. These reporting criteria, therefore, do not account for

releases from smaller industries. Threshold manufacture and processing quantities also changed from

1988 to 1990 (dropping from 75,000 lbs/yr in 1988 to 50,000 lbs/yr in 1989 to its current 25,000 lbs/yr in

1990) creating possibly misleading data trends. Also, reported releases are annual estimates. The

amounts reported could have been released evenly over the course of the year or, possibly, in a single

large burst. Finally, the TRI data is meant to reflect releases and should not be used to estimate general

exposure to a chemical (USEPA, 2000a; USEPA, 2000b). 

Twenty-six of the 30 contaminants discussed in this report are listed as Toxic Release Inventory (TRI)

chemicals. Whenever available, TRI data were used to describe environmental releases of each

contaminant; the distribution of these releases (with respect to the method of release and overall

geographic distribution); and the geographic distribution of the releases relative to the 16 cross-section

States.

1.3.3 National Water Quality Assessment

Although the Six-Year Review assesses contaminant occurrence in finished drinking water (assessing

occurrence in water sampled from within public water systems), an evaluation of contaminant occurrence

in ambient (raw, unfinished) water provides background information regarding the presence of a

contaminant in the environment. In a drinking water context, ambient water is source water existing in

surface waters and aquifers before treatment. The most comprehensive and nationally consistent data

describing ambient water quality in the United States are being collected and managed through the efforts

of the United States Geological Survey’s (USGS) and its National Water Quality Assessment (NAWQA)

program. (NAWQA, however, is a relatively young program and complete national data are not yet

available from their entire array of sites across the nation. Also, data is not yet available on all the

contaminants in this report. As the NAWQA program continues, important addition spatial and temporal

coverage of this ambient occurrence data will become available for occurrence analyzes.)

The USGS instituted the NAWQA program in 1991 to examine water quality status and trends in the

United States. NAWQA is designed and implemented in such a manner to allow consistency and

comparison between representative study basins located around the country, facilitating interpretation of

natural and anthropogenic factors affecting water quality (Leahy and Thompson, 1994).

The NAWQA program consists of 59 significant watersheds and aquifers referred to as “study units.” 

The study units represent approximately two thirds of the overall water usage in the United States and a

similar proportion of the population served by public water systems. Approximately one half of the

nation’s land area is represented (Leahy and Thompson, 1994).
Occurrence Summary and Use Support Document March 2002 4

To facilitate management and make the program cost-effective, approximately one third of the study

units at a time engage in intensive assessment for a period of 3 to 5 years. This is followed by a period of

less intensive research and monitoring that lasts between 5 and 7 years. This way all 59 study units

rotate through intensive assessment over a ten-year period (Leahy and Thompson, 1994). The first round

of intensive monitoring (1991-96) targeted 20 watersheds and the second round monitored 16 basins

beginning in 1994. 

Whenever available, ambient data for the inorganic contaminants were downloaded directly from the

USGS website. These data follow the parameters and guidelines discussed above. No particular

limitations apply specifically to the downloaded IOC data.

For pesticides (classified as SOCs), NAWQA includes analyses of 76 pesticides and 7 selected pesticide

degradation products in about 8,200 samples of ground water and surface water in 20 of the nation’s

major hydrologic basins (USGS, 1998). The 76 herbicides, insecticides, and fungicides targeted in the

study account for approximately 75 percent of the total amount (by weight) of pesticides used for

agriculture in the U.S., and also a substantial portion of urban and suburban use. The minimum reporting

limit (MRL) for the SOCs varied by contaminant.

For this Six-Year Review report, data for pesticide occurrence in ambient water was used from Pesticides

in Surface and Ground Water of the United States: Summary of Results of the National Water Quality

Assessment Program (USGS,1998). This published report includes the USGS analyzed NAWQA sample

data from 1992 to 1996. (More recent NAWQA sampling round results have recently become available

and include sample results data from 1996 to 1998. However, the data so far published are not as

comprehensive as the 1992-1996 data, and the more comprehensive data, while available on the USGS

website, has not been completely quality reviewed or analyzed by USGS. Therefore, this current SixYear Review occurrence assessment uses the data from the published 1998 report. In the subsequent

draft of this Six-Year Review report, the 1996 to 1998 NAWQA data will be reviewed and potentially

incorporated.)

For volatile organic chemicals (VOCs), the national synthesis will compile data from the first and second

rounds of intensive assessments. Study units assessed in the second round represent conditions in more

urbanized basins, but initial results are not yet available. However, VOCs were analyzed in the first

round of intensive monitoring and data are available for these study units (Squillace et al., 1999). The

minimum reporting limit (MRL) for all VOCs listed in this report was 0.2 μg/L (Squillace et al., 1999). 

Additional information on analytical methods used in the NAWQA study units, including method

detection limits, are described by Gilliom and others (1998).

Furthermore, the NAWQA program has compiled, by study unit, data collected from local, State, and

other Federal agencies to augment its own data. The data set provides an assessment of VOCs in

untreated ambient ground water of the conterminous United States for the period 1985-1995 (Squillace et

al., 1999). Data were included in the compilation if they met certain criteria for collection, analysis, well

network design, and well construction (Lapham et al., 1997). They represent both rural and urban areas,

but should be viewed as a progress report as NAWQA data continue to be collected that may influence

conclusions regarding occurrence and distribution of VOCs (Squillace et al., 1999).

In addition to the NAWQA studies/data described above, information is also presented regarding

pesticide concentrations in reservoirs and finished drinking water (Blomquist, et al., 2001) . In 1999, a

pilot monitoring program was initiated by USGS and EPA to provide information on pesticide

concentrations in drinking water. Prior to implementation of this pilot program, there were few available

datasets that contained information on pesticide concentrations in finished drinking water on a national

scale, as most available data sets generally cover only selected compounds or local areas. This pilot

program was implemented to begin to fill this important data gap, and to provide more information about

appropriate methods for a national monitoring of pesticides in drinking water. The NAWQA data sets

provide the only nationally consistent pesticide concentration data for a large suite of compounds. OPP

currently uses the NAWQA data in their drinking-water and aquatic-exposure assessments; however,
Occurrence Summary and Use Support Document March 2002 5

these data are not collected from public water supplies and, therefore, may not directly reflect human

exposure to pesticides via drinking water. 

Drinking water utilities that withdrew from reservoirs were sampled because reservoirs are vulnerable to

pesticide contamination, integrate pesticide loading from their watersheds, and show smaller temporal

variations than streams. Sampling frequencies were designed to measure long-term mean and short-term

peak concentrations of pesticides in drinking water. Samples were collected quarterly throughout the

year and at weekly or bi-weekly intervals following the primary pesticide application periods. Water

samples were collected from the raw-water intake and from the finished drinking-water tap prior to

entering the distribution system. At some sites, samples were also collected at the reservoir outflow. 

Three different laboratory methods were selected for use during the pilot monitoring program— a USGS

approved method and two developmental methods. Only results from the USGS approved method

(known as “method 2001” or “schedule 2001”) are presented in this report. 

Twelve water-supply reservoirs were sampled. The sites were in California, Indiana, Ohio, Oklahoma,

Louisiana, Missouri, South Carolina, South Dakota, New York, North Carolina, Pennsylvania, and

Texas. In 1999, drought conditions affected parts of the Eastern United States and California; therefore

sampling was extended through 2000 at nine sites. This report presents results for alachlor, carbofuran,

and simazine in both raw and finished water.

1.3.4 The National Highway Runoff Data and Methodology Synthesis

The National Highway Runoff Data and Methodology Synthesis has reviewed 44 highway and urban

runoff studies implemented since 1970 (Lopes and Dionne, 1998). Two national studies were included in

this review: the National Urban Runoff Program (NURP) and studies associated with the USEPA

National Pollution Discharge Elimination System (NPDES) municipal stormwater permits. NURP,

conducted in the 1970s and early 1980s, had the most extensive geographic distribution. The NPDES

studies took place in the early to mid- 1990s (Lopes and Dionne, 1998).

1.3.5 16-State Cross-Section Data

The State public water system (PWS) compliance monitoring occurrence data used in this analysis were

submitted by States for EPA review and study of the occurrence of regulated contaminants in PWSs (see

USEPA, 1999). In the USEPA (1999) review, all 50 States were evaluated through a methodology that

included ranking of States’ pollution potential, dividing States into quartiles based on these rankings, and

then selecting States that equally represent the four pollution potential quartiles. Another factor

considered (when selecting states equally across the four pollution potential quartiles) was selection of 

states distributed geographically to include a broad representation of climatic and hydrologic variability 

across the United States. In this way, a subset, or cross-section, of States could be selected to reflect a

national representation of pollution potentials and climatic/hydrologic difference. 

An initial national cross-section of 8 States was selected because it provided a balanced national crosssection of State occurrence data, was based only on high quality and adequately complete State

occurrence data sets, and that, in aggregate, is indicative of national contaminant occurrence. This

national cross-section development and use methodology was the subject of critical internal review and

external peer review in the USEPA (1999) study. An additional group of 8 States were added to build

upon and expand the coverage of the 8-State cross-section of occurrence data (USEPA, 2002). The

additional 8 States were selected using the same criteria for selection of the initial 8 cross-section States,

and therefore were added in a manner that maintained the pollution potential and geographic national

balance of the cross-section. The analyses presented in this report are based on data from the final group

of 16 States, including Alabama, California, Florida, Illinois, Indiana, Kentucky, Michigan, Montana,

Nebraska, New Jersey, New Mexico, Oregon, South Carolina, South Dakota, Texas, and Vermont (see

Figure 1.3-1).
Occurrence Summary and Use Support Document March 2002 6

Initial 8-State Cross-Section

Additional 8-State Cross-Section

States not included in Cross-Section

Figure 1.3-1. Map of the 16 Cross-Section States

The 8 initial plus 8 additional States that are shaded in the figure comprise the 16-State cross-section used for analysis.

1.3.5.1 Data Management

A brief discussion of data management is included below; for further detailed discussion of the extensive

data management of the State data sets used in the analyses included in this report, see USEPA (1999),

Cadmus (2000), Cadmus (2001), and USEPA (2002). The data used in the cross-section analyses were

limited to only those data with confirmed drinking water source and population served information. Only

standard SDWA compliance samples were used; samples identified as “special,” “duplicate,” or

“investigation,” or samples of unknown type were not used in the analyses. (For example, investigation

samples can signify an investigation of identified contamination at a particular PWS. Inclusion of the

investigation sample results would bias the calculation of mean concentration for the system, and

therefore the investigation samples are excluded.)

Raw data from the States were received in a very wide variety of formats, structures, and content. Each

data set was reviewed to ensure it contained the basic data elements (data fields) necessary to conduct a

consistent analysis for this study. These elements were reviewed with State data management staff both
Occurrence Summary and Use Support Document March 2002 7

before and after data were received and reviewed to ensure consistent and appropriate data set

interpretations. Every State data set reviewed for this study contained unique data elements or unique

treatment of common elements. Even after initial screening and conversion to roughly similar formats

and data set structure, unique factors were always uncovered during data analysis. Many of the

confounding factors were resolved only through direct consultation with the States. As a general rule,

when errors or ambiguities in various data elements could not be resolved, those particular data elements

were not included in the analyses to avoid problematic results or results based on data of questionable

quality. This data quality measure eliminated relatively very few observations (compared to the

thousands of analytical results included in the data sets).

Decisions also had to be made on how to quantitatively include “less-than” or “non-detection” data. 

Some states record the minimum reporting level (or limit) (MRL) in the analytical result column and also

include a “<“ in a corresponding column to identify an analytical result record for which no contaminant

was detected. (Such samples are often referred to as “no-detects” or “non-detections.” More precisely,

these samples can be referred to as “censored data,” meaning that there apparently is no quantitative

information for those records below the MRL, or censoring, concentration.) Other states simply include

a zero in the analytical result column to signify a non-detection. Although non-detection data do not play

a role in the Stage 1 analysis, the non-detection data did pose a problem within Stage 2 analysis

(described below in Section 1.4). 

Summary record counts were generated to determine what (and how many) MRLs were present in the

data for each contaminant. (There are sometimes multiple approved laboratory analytical methods that

can be used to analyze drinking water samples, and different analytical methods can have different

minimum reporting levels.) For the parametric statistical analysis conducted for the Six-Year Review,

each record must have a quantitative, non-zero value. Therefore, all non-detection data (often reported as

“zero” or simply “<“) were set equal to the non-zero modal MRL for the particular state reporting the

record in question. For the states that set all non-detections equal to zero, the non-detections were set

equal to the overall non-zero modal MRL for the entire 16 state cross-section. Table 1.3-1 describes the

number and type of public water systems, the population served by those systems, and the overall nonzero modal detection limit for each contaminant from the 16-State cross-section data set used for Stage 2

analysis.

Table 1.3-1. Contaminant Occurrence Data From the 16-State Cross-Section

Contaminant

Total

Number of

Systems

Number of

Ground

Water

Systems

Number of

Surface

Water

Systems

Total

Population

Served by

Systems

Non-Zero

Modal MRL

(mg/L)

IOCs

Beryllium 18,933 17,509 1,424 104,573,700 0.001

Chromium 19,695 18,169 1,526 105,380,000 0.01

Fluoride 20,803 19,210 1,593 107,075,700 0.1

Mercury 18,995 17,445 1,550 105,096,700 0.001

Thallium 17,972 16,504 1,468 104,291,600 0.001

SOCs

Alachlor 14,330 12,917 1,413 95,678,600 0.0002

Bis(2-ethylhexyl)phthalate 9,418 8,591 827 78,293,000 0.0006

Carbofuran 13,925 12,531 1,394 94,338,000 0.0009
Contaminant

Total

Number of

Systems

Number of

Ground

Water

Systems

Number of

Surface

Water

Systems

Total

Population

Served by

Systems

Non-Zero

Modal MRL

(mg/L)

Occurrence Summary and Use Support Document March 2002 8

Chlordane 13,184 11,854 1,330 97,459,900 0.0002

1,2-Dibromo-3-chloropropane 14,042 13,008 1,034 87,727,200 0.00002

Diquat 9,159 8,337 822 73,602,900 0.0004

Glyphosate 7,862 7,069 793 70,081,900 0.006

Heptachlor 14,245 12,835 1,410 96,563,400 0.00004

Heptachlor Epoxide 14,133 12,729 1,404 96,222,900 0.00002

Hexachlorobenzene 14,011 12,625 1,386 94,035,300 0.0001

Hexachlorocyclopentadiene 13,922 12,536 1,386 93,429,200 0.005

Oxamyl 13,157 11,798 1,359 92,345,800 0.002

Picloram 12,907 11,555 1,352 93,235,500 0.0001

Simazine 14,533 13,136 1,397 98,178,100 0.001

Toxaphene 13,805 12,408 1,397 95,108,100 0.001

VOC.

Benzene 23,266 21,670 1,596 110,866,600 0.0005

Carbon Tetrachloride 23,028 21,454 1,574 110,605,500 0.0005

1,4-Dichlorobenzene 18,961 17,615 1,346 72,994,500 0.0005

1,2-Dichloroethane 23,038 21,463 1,575 110,794,100 0.0005

1,1-Dichloroethylene 19,101 17,576 1,525 106,607,600 0.0005

Dichloromethane 21,530 20,019 1,511 110,146,100 0.0005

1,2-Dichloropropane 21,988 20,410 1,578 110,450,100 0.0005

Tetrachloroethylene 22,362 20,795 1,567 110,557,800 0.0005

1,1,2-Trichloroethane 22,284 20,758 1,526 110,366,500 0.0005

Trichloroethylene 23,035 21,461 1,574 110,612,900 0.0005

The reduced number of systems sampling for SOC data, as compared to IOC and VOC, may relate to state waivers for pesticides and herbicides. 

For example, New Jersey has an extensive SOC waiver protocol.

Note: All population values are rounded to the nearest hundred.

1.3.6 Additional Data

In addition to the primary data sources described above, previously compiled contaminant occurrence

information is also presented whenever available. This information generally includes reviews of

previous occurrence surveys and studies of contaminant occurrence in both ground water and surface

water drinking and non-drinking water sources. Furthermore, some of the information is national and

some regional in nature, providing additional, and sometimes historical, contaminant information that

supplements the other contaminant occurrence, use, and production information presented in this report. 

However, the detailed national estimates of contaminant occurrence, described in the following Section

1.4, were conducted only using the 16-state national cross-section data.
Occurrence Summary and Use Support Document March 2002 9

1.4 Occurrence Analysis

A two stage occurrence estimation approach has been developed to assess the 16-State cross-section data

of regulated contaminant occurrence. The initial stage, “Stage 1 Analysis,” provides a straight-forward,

clear, and conservative assessment of occurrence. Using the occurrence data aggregated from the 16-

State cross-section, calculations were made of the percent of PWSs with at least one analytical result

that exceeds a specified health threshold. These initial occurrence measures were developed for each

contaminant according to water system source water type (ground water, surface water) for the

aggregated 16-State cross-section data set. These “Stage 1 Analyses” are descriptive, non-parametric

statistics that provide a general characterization of contaminant occurrence. 

Similar estimates based on the population served by water system provide a “Stage 1” preliminary

characteristic of exposure potential. Stage 1 results are most closely representative of short term

exposure since the Stage 1 analyses are based on the single maximum analytical value recorded at each

water system. Assessed relative to MCLs (which reflect public health considerations for long-term

exposure to contaminants in drinking water), these Stage 1 analyses are conservative (cautious regarding

public health concerns) in the sense that they are descriptive statistics based on peak, rather than longterm mean, concentrations. For a complete description of the Stage 1 methodology and a comprehensive

presentation of the detailed Stage 1 findings, please refer to First Stage Occurrence and Exposure Report

for Six-Year Review (Cadmus, 2000).

The second “Stage 2 analysis,” a rigorous parametric statistical modeling approach, was developed to

enable more specific and detailed occurrence estimations. While Stage 1 analysis estimates, for example,

the percent of PWSs with at least one analytical result exceeding a specified health threshold, Stage 2

analysis estimates the percent of PWSs with an estimated system mean concentration exceeding a

specified health threshold. The Stage 2 analytical results are stratified by source water type and system

size. (For example, estimates can be made for the number of systems, with a mean concentration of a

contaminant greater than some specified concentration, that use ground water and serve fewer than 500

people, that use surface water and serve fewer than 500 people, that use ground water and serve 501 to

3300 people, etc.). These estimates are expressed as the probability of threshold exceedance. These

Stage 2 occurrence estimates also include quantified estimation errors for the values estimated. (These

quantified estimation errors are important because they provide a measure of the level of confidence in

an statistical estimation.) 

Since the Stage 2 occurrence estimations represent mean concentration values, they are more

representative of long-term exposure to contaminants in drinking water. These Stage 2 estimates

contribute to the initial assessments of health risks from exposure to contaminants through consumption

of drinking water. The Stage 2 estimates also can be used in assessments of the costs and benefits

associated with the establishment of a revised regulatory limit for any particular drinking water

contaminant. A general description of the Stage 2 analysis is presented below. For a complete

description of the Stage 2 methodology and a comprehensive presentation of the stratified Stage 2

findings, please refer to Occurrence Estimation Methodology and Occurrence Findings for Six-Year

Review of National Primary Drinking Water Regulations (USEPA, 2002). The entire two stage

occurrence estimation approach (including the development of the national cross-section of state data, as

well as the Stage 1 and Stage 2 analyses) was peer-reviewed and received generally favorable support. 

The statistical model developed for the Stage 2 analyses for the Six-Year Review is a Bayesian-based

hierarchical model. One advantage of this modeling approach is that it is able to fully use the occurrence

information contained in sample “non-detections” (all the analytical results with values less than the

MRL) in estimating system mean concentration. (This is important because the sample non-detections

typically comprise the majority of occurrence data for most drinking water contaminants.) The Bayesianbased model first estimates mean concentration values for each PWS in the 16-State cross-section. In

the process of generating the system means, a standard deviation associated with the mean is also

generated. (The standard deviation defines, in a general sense, the variability of the estimated system
Occurrence Summary and Use Support Document March 2002 10

mean concentrations.) Importantly, the Bayesian-based modeling approach also generates estimations of

error which enable a quantiative assessment of the uncertainty associated with all model estimates. 

The estimated system means and standard deviations are then used as input to a Markov chain Monte

Carlo method. The Monte Carlo method is, in general terms, any technique using a large number of

randomly selected values to determine a single estimated total. This method works well for estimating

the total number of public water systems with an (estimated) mean concentration greater than some

specified threshold concentration, because the underlying probability distributions –defined by the

individual estimated system means and standard deviations– are known, but the final results (the actual

total number of systems with actual contaminant means greater than some specified threshold) is more

difficult to determine. Approximately 500 Monte Carlo simulations (using the stratum-level mean and

standard deviation as model input) are used to estimate the number of systems for each source water type

and system-size category that are expected to exceed each specified concentration threshold. The

estimated number of systems that exceed each threshold for a given stratum is then divided by the total

number of systems in that stratum, resulting in the percent of systems estimated to exceed a specified

threshold for a specific stratum (the estimated mean “probability of threshold exceedance”). 

Once the probability of threshold exceedance has been estimated through the Stage 2 analysis, the

number of systems (and population served by systems) with potential threshold exceedances can be

estimated. The total number of systems in the 16-State cross-section with mean contaminant

concentrations that are expected to exceed specified threshold concentrations is calculated by multiplying

the percentage of systems with an estimated mean concentration threshold exceedance (estimated by the

statistical model) by the total number of systems in the 16-State cross-section with data for that particular

contaminant. The total population served by systems in the 16-State cross-section potentially exposed to

contaminant concentrations greater than the health threshold is estimated by multiplying the population

served by systems in the 16-State cross-section with data for that particular contaminant by the modelgenerated percentage of population served by systems with estimated mean concentration threshold

exceedance. (See Table 1.3-1 for the total number of systems and population served by systems in the

16-State cross-section for each of the 30 contaminants.)

Because the 16-State cross-section data set was developed to contain data on contaminant occurrence that

is indicative of national occurrence, national contaminant occurrence can be also estimated. The total

national number of systems (or population served by systems) estimated to exceed a specified threshold

is extrapolated by multiplying the representative cross-section probability of exceedance by the national

numbers for systems (and population served by systems) documented in the Water Industry Baseline

Handbook, Second Edition (USEPA, 2000d). The total number of ground and surface water community

water systems (CWSs) plus non-transient, non-community water systems (NTNCWSs) in the Baseline

Handbook is 65,030, and the total population served by ground and surface water CWSs plus NTNCWSs

is 213,008,182 persons. (The handbook presents the system and population served numbers stratified by

source water type and population served size categories as well.) 

To derive the national occurrence estimate for a specific threshold/source water type/population served

size category, the national number of PWSs (or population served by PWSs) from the handbook is simply

multiplied by the probability of exceedance (a percentage) estimated by the statistical model. In the

tables presented in this report, only the total number of systems (and population served by systems)

estimated to exceed each threshold are presented. For stratified contaminant occurrence findings, please

refer to Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of National

Primary Drinking Water Regulations (USEPA, 2002).

Contaminant occurrence findings based on the Stage 1 and Stage 2 analyses (using the 16-State crosssection data) are summarized in tables presented in the specific contaminant chapters that follow this

introductory chapter. All Stage 1 and Stage 2 occurrence findings (presented as percentages) are

displayed to 3 significant figures and all population values are rounded to the nearest hundred. 

Importantly, note that the Stage 2 findings are based on model estimations conducted separately for

ground water systems, surface water systems, and combined ground and surface water systems. Since
Occurrence Summary and Use Support Document March 2002 11

these groups of systems were modeled separately, the sum of occurrence estimates for ground water

systems and surface water systems will not equal the total occurrence estimate for combined ground and

surface water systems. For more information of the details of the Stage 2 Bayesian-based modeling,

please refer to USEPA (2002).

1.5 References

Agency for Toxic Substances and Disease Registry (ATSDR). 2001. About the Agency for Toxic

Substances and Disease Registry. Available on the Internet at: 

http://www.atsdr.cdc.gov/about.html (Last updated June 28, 2001).

Blomquist, J.D., J.M. Denis, J.L. Cowles, J.A. Hetrick, R.D. Jones, and N.B. Birchfield. 2001.

Pesticides in Selected Water-Supply Reservoirs and Finished Drinking Water, 1999-2000: 

Summary of Results from a Pilot Monitoring Survey. U.S. Geological Survey Open-File Report

01-456. 65 pp.

Cadmus. 2000. First Stage Occurrence and Exposure Report for Six-Year Review. Draft report

submitted to EPA for review May 12, 2000.

Cadmus. 2001. Data Quality Overview of Contaminant Occurrence Data - DRAFT. Draft report

submitted to EPA for review January 31, 2001.

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at: 

http://ca.water.usgs.gov/pnsp/rep/ofr97589 (Last updated October 09, 1998). 

Lapham, W.W., K.M. Neitzert, M.J. Moran, and J.S. Zogorski. 1997. USGS compiles data set for

national assessment of VOCs in ground water. G. Water Mon. Rem. 17(4):147-157.

Leahy, P.P., and T.H. Thompson. 1994. The National Water-Quality Assessment Program. U.S.

Geological Survey Open-File Report 94-70. 4 pp. Available on the Internet at:

http://water.usgs.gov/nawqa/NAWQA.OFR94-70.html (Last updated May 29, 2001). 

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 67

pp.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech.. 33(23):4176-4187.

USEPA. 1999. A Review of Contaminant Occurrence in Public Water Systems. EPA Report/816-R99/006, Office of Water, 78 pp.

USEPA. 2000a. TRI Explorer: Are Year-to-Year Changes Comparable? Available on the Internet at:

www.epa.gov/triexplorer/yearsum.htm (Last modified May 5, 2000).

USEPA. 2000b. The Toxic Release Inventory (TRI) and Factors to Consider when Using TRI Data.

Available on the Internet at: http://www.epa.gov/tri/tri98/98over.pdf (Last modified August 11,

2000).

USEPA. 2000c. What is the Toxic Release Inventory. Available on the Internet at: 

http://www.epa.gov/tri/general.htm (Last modified February 28, 2000).
Occurrence Summary and Use Support Document March 2002 12

USEPA. 2000d. Water Industry Baseline Handbook, Second Edition (Draft). March 17.

USEPA. 2001. EPA Protocol for the Review of Existing National Primary Drinking Water Regulations -

DRAFT. U.S. Environmental Protection Agency, Office of Drinking Water. May 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1998. Pesticides in Surface and Ground Water of the United States: Summary of Results of the

National Water Quality Assessment Program (NAWQA). PROVISIONAL DATA -- SUBJECT TO

REVISION. Available on the Internet at: http://water.wr.usgs.gov/pnsp/allsum/, last updated

October 9, 1998. 
Occurrence Summary and Use Support Document March 2002 13

2.0 INORGANIC CONTAMINANTS
Occurrence Summary and Use Support Document March 2002 14

2.1 Beryllium

Table of Contents

2.1.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.1.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.1.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.1.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . . 21

2.1.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.1.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Tables and Figures

Table 2.1-1: Imports of Beryllium to the United States (thousand metric tons, gross weight) . . . . . . . 16

Table 2.1-2: Beryllium and Beryllium Compound Manufacturers and Processors by State . . . . . . . . . 16

Table 2.1-3: Environmental Releases (in pounds) for Beryllium in the United States, 

1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 2.1-4: Environmental Releases (in pounds) for Beryllium Compounds in the 

United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 2.1-5: Beryllium Detections and Concentrations in Surface Water and Ground Water . . . . . . . . 18

Table 2.1-6: Beryllium Occurrence in Raw Water - National Surveys . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 2.1-7: Beryllium Occurrence in Raw Water - Regional Surveys . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 2.1-8: Stage 1 Beryllium Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . 22

Table 2.1-9: Stage 1 Beryllium Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . 22

Table 2.1-10: Stage 2 Estimated Beryllium Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Table 2.1-11: Stage 2 Estimated Beryllium Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Table 2.1-12: Estimated National Beryllium Occurrence - Systems and Population Served . . . . . . . . . 26

Table 2.1-13: Estimated Beryllium Exceedance as Reported in the NIRS - Systems . . . . . . . . . . . . . . 27

Table 2.1-14: Estimated Beryllium Exceedance as Reported in the NIRS - Population . . . . . . . . . . . . 27

Table 2.1-15: Beryllium Occurrence in 100 Largest U.S. Cities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Occurrence Summary and Use Support Document March 2002 15

2.1.1 Introduction, Use and Production

Beryllium (Be) is the lightest structural metal known. Pure beryllium is hard and grayish. Beryllium is

never found free in the environment but can be found in compounds in mineral rocks, coal, soil, and

volcanic dust (ATSDR, 1993). Beryllium compounds have no particular smell. Beryllium exists in the

environment in approximately 40 mineralized forms. The most common forms for beryllium are beryl, a

beryllium aluminum silicate (3BeO.Al2O3.6SiO2) and bertrandite, a hydrated disilicate

(4BeO.2SiO2.H2O). The most important commercial forms of beryllium are the metal itself, berylliumcopper alloys, and beryllium oxide (Ciccone & Associates, 1984). 

Most beryllium ore that is mined is converted into alloys. Most of these alloys are used in making

electrical and electronic parts or as construction materials for machinery and molds for plastics. Pure

beryllium metal is used in nuclear weapons and reactors, aircraft and space vehicle structures,

instruments, x-ray machines, and mirrors. Beryllium oxide is also made from beryllium ores and is used

to make specialty ceramics for electrical and high-technology applications (ATSDR, 2000).

Beryllium metal is used in aircraft disc brakes, x-ray transmission windows, space vehicle optics and

instruments, aircraft/satellite structures, missile guidance systems, nuclear reactor neutron reflectors,

nuclear warhead triggering devices, fuel containers, precision instruments, rocket propellants,

navigational systems, heat shields, mirrors, high speed computers, and audio components, with other

assorted miscellaneous uses (Cunningham, 1998, as cited in ATSDR, 2000). In 1998, the use of

beryllium (as an alloy, metal, or oxide) in the electronic and electrical components, aerospace, and

applications accounted for more than 80% of its consumption (Cunningham, 1999, as cited in ATSDR,

2000).

Beryllium oxide is used in high technology ceramics, electronic heat sinks, electrical insulators,

microwave oven components, gyroscopes, military vehicle armor, rocket nozzle crucibles, thermocouple

tubing, laser structural components, and substrates. Beryllium is also used for high-density electrical

circuits, automotive ignition systems, and radar electronic countermeasure systems (Cunningham, 1998,

as cited in ATSDR, 2000).

Beryllium-copper alloys are useful in a wide variety of applications because of their electrical and

thermal conductivity, high strength and hardness, good corrosion and fatigue resistance, and non

magnetic properties. Beryllium-copper alloys are manufactured into springs, electrical connectors and

relays, precision instruments, brushings and bearings in aircraft and heavy machinery, non sparking tools,

submarine cable housing and pivots, wheels and pinions, switches in automobiles, molds for injection

molded plastics, radar, telecommunications, factory automation, computers, home appliances,

instrumentation and control systems, tubing in oil and drilling equipment, connectors for fiber optics, and

integrated circuits, as well as many other uses (Cunningham, 1998, as cited in ATSDR, 2000).

Both anthropogenic and natural processes result in emissions of beryllium to the atmosphere. In addition

to ore processing, beryllium is also released into the atmosphere during the production and use of

beryllium alloys and chemicals. Beryllium is released into the atmosphere from anthropogenic sources

including the combustion of coal and fuel oil, the incineration of municipal and solid waste, the

production, use, and recycling of beryllium alloys and chemicals, and, to a minor extent, the burning of

solid rocket fuel. Emissions from coal and fuel oil combustion account for a majority of the United

States beryllium emissions from natural and anthropogenic sources. Natural emission sources include

windblown dusts and volcanic particles. However, the amount of beryllium released to the atmosphere

from these sources is small compared with anthropogenic sources.
Occurrence Summary and Use Support Document March 2002 16

Anthropogenic sources of beryllium release to water include industrial waste water effluents. Beryllium

concentrations are highest in waste waters from electric utility industries. Deposition of atmospheric

beryllium is also a source in surface waters. Beryllium also enters water from the weathering of rocks

and soils. Since coal contains beryllium, it is also likely that beryllium will enter surface water via

leaching of coal piles.

Beryllium is naturally present in soils and sediments. The majority of beryllium and beryllium

compound releases to land are by facilities that manufacture or process beryllium. Coal fly ash and

municipal solid waste containing beryllium are disposed of in landfills and used in building materials. 

This contributes to beryllium concentrations in soil. About 100 million tons of coal fly ash containing

various levels of beryllium are generated each year. Land application of sewage sludge containing higher

than background concentrations of beryllium can be a source of beryllium contamination of soil. 

Deposition of atmospheric aerosols on terrestrial surfaces is another source of beryllium in soil.

Table 2.1-1: Imports of Beryllium to the United States (thousand metric tons, gross weight)

Imports For Consumption 1995 1996 1997 1998 1999 

Beryllium Ore and Metal 32 20 20 50 20

 Source: USGS, 2000

Table 2.1-2: Beryllium and Beryllium Compound Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on 

site in thousands of poundsb Activities and usesc

AL 6 1,000-99,999 1,3,4,5,6,9,10,13

AZ 4 10,000-9,999,999 1,3,4,5,6,8,9,10

FL 2 1,000-9,999 1,4,5,6,10,13

GA 5 10,000-99,999 1,3,4,5,6,10,13

IL 1 1,000-9,999 1,5,10

IN 5 1,000-999,999 1,5,9,10

KY 4 0-99,999 1,5,6,10,13

MI 3 0-99,999 1,5,9,10

MO 1 1,000-9,999 8,10

MT 1 10,000-99,999 1,3,4,5,6,10,13

NC 4 10,000-99,999 1,3,4,5,6,9,10,13

NM 6 0-99,999 1,3,4,5,6,10,13

OH 8 1,000-99,999 1,3,4,5,6,10,13

OK 2 100-99,999 1,5,9

PA 5 100-999,999 1,2,3,4,5,6,7,9,10

SC 1 0-99 13

TN 3 10,000-99,999 1,5,8,9

TX 2 10,000-99,999 1,3,4,5,6,10,13

UT 4 100-49,999,999 1,4,7,8,10,13

WI 8 1,000-99,999 8,9

WV 1 1,000-99,999 1,3,4,5,6,10,13

WY 2 1,000-99,999 1,5,6,10,13

a

Post office State abbreviations used

b

 Range represents maximum amounts on site reported by facilities in each State

c

Activities/Uses

1. Produce 8. As a formulation component

2. Import 9. As an article component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

c

Number of facilities reporting “no data” regarding maximum amount of the substance on site

Source: ATSDR, 2000 compilation of 1998 TRI data
Occurrence Summary and Use Support Document March 2002 17

2.1.2 Environmental Release

Beryllium and beryllium compounds are listed as Toxics Release Inventory (TRI) chemicals (see Tables

2.1-3 and 2.1-4). For both beryllium and beryllium compounds, releases to land constitute most of the

on-site releases. Beryllium compounds have a gradual increase in releases to land until 1992, then

decrease from 1993 through 1999, while releases of beryllium decrease until 1993 and then increase in

1994. It is unclear whether these sharp beryllium decreases are real or a function of changes in TRI

reporting requirements in the late 1980s and early 1990s (see discussion in Introduction). Air emissions

are also an important mode of on-site release. Though the first several years of record for air emissions

of beryllium are markedly higher for certain years, no trend is apparent for the remainder. Also, air

emissions of beryllium compounds have fluctuated modestly with no trend evident. Surface water

discharges of beryllium and beryllium compounds are less significant on-site releases, with low levels

continuing until the present and no other trends apparent. There are no releases by underground injection

of either beryllium or beryllium compounds until 1999, where a high percentage of on-site releases of

beryllium compounds are attributed to underground injection.

 Increases in releases to land have contributed to increases in total on- and off-site releases in recent

years. Off-site releases of beryllium and beryllium compounds are considerable. Off-site releases of

beryllium are a large component of total releases. Though there is a large drop in beryllium releases in

1992 when compared to the previous year, the late 1990s show a steady increase in pounds released. 

Off-site releases of beryllium compounds fluctuate throughout the years, with highest releases in 1988

and 1998, although no other trends are apparent. These TRI data for beryllium were reported from 21

States, with only 3 States reporting data for all years (USEPA, 2000). Eight of these 21 States that

reported TRI data for beryllium are contained in the 16-State cross-section (used for analyses of

beryllium occurrence in drinking water; see Section 2.1.4). The TRI data for beryllium compounds were

reported from 17 States, with only two States reporting data for all years (USEPA, 2000). Six of the 17

States that reported TRI data for beryllium compounds are contained in the 16-State cross-section. (For a

map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.1-3: Environmental Releases (in pounds) for Beryllium in the United States, 

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Air Emissions Releases

Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 769 57 -- 53,271 20,081 74,178

1998 799 26 -- 57,818 20,404 79,047

1997 816 27 -- 56,123 5,741 62,707

1996 1,114 36 -- 31,245 4,852 37,247

1995 1,087 31 -- 21,255 7,595 29,968

1994 899 36 -- 22,860 9,632 33,427

1993 903 24 -- 14,594 5,142 20,663

1992 1,868 39 -- 21,358 14,774 38,039

1991 1,378 101 -- 29,023 117,582 148,084

1990 1,375 42 -- 6,517 1,371 9,305

1989 1,895 122 -- 31,522 1,199 34,738

1988 2,763 74 -- 37,000 3,160 42,997

 Source: USEPA, 2000 
Occurrence Summary and Use Support Document March 2002 18

Table 2.1-4: Environmental Releases (in pounds) for Beryllium Compounds in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 473 27 4,100 19 5,028 9,647

1998 383 6 -- -- 6,754 7,143

1997 365 1 -- 96 4,602 5,064

1996 395 1 -- 16,188 2,333 18,917

1995 360 2 -- 23,000 2,391 25,753

1994 610 2 -- 17,000 2,901 20,513

1993 363 4 -- 8,087 3,055 11,509

1992 511 5 -- 48,000 4,618 53,134

1991 242 9 -- 30,000 2,180 32,431

1990 212 88 -- 40,000 972 41,272

1989 962 25 -- 36,000 5,085 42,072

1988 862 17 – 12,000 8,261 21,140

 Source: USEPA, 2000 

2.1.3 Ambient Occurrence

Beryllium is an analyte for both surface and ground water NAWQA studies, with a method detection

limit (MDL) of 0.001 mg/L. Additional information on analytical methods used in the NAWQA study

units, including method detection limits, are described by Gilliom and others (1998). 

Beryllium was never detected in groundwater. A possible explanation for the higher detection

frequencies in surface water is its greater sensitivity to anthropogenic releases. Both the median and 99th

percentile concentrations of beryllium are below the MCL (0.001 mg/L and 0.002 mg/L, respectively). 

Beryllium detection frequencies in surface water greater than the MCL (0.004 mg/L) are approximately

10 times less than the percentage of all beryllium detections in surface water.

Table 2.1-5: Beryllium Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 > MDL* 

Detection frequency

 > MCL*

Concentration percentiles

(all samples; mg/L) 

% samples % sites % samples % sites median 99th

surface water 0.64% 3.83% 0.06% 0.55% 0.001 0.002

ground water 0.00% 0.00% 0.00% 0.00% N/A N/A

* The Method Detection Limit (MDL) for beryllium in water is 0.001 mg/L and the Maximum Contaminant Level (MCL) is 0.004 mg/L. 
Occurrence Summary and Use Support Document March 2002 19

2.1.3.2 Additional Ambient Occurrence Data

A summary document entitled “Beryllium in Water: An Assessment of Occurrence and Exposure”

(Ciccone & Associates, 1984), was previously prepared for past USEPA assessments of beryllium. This

document included various studies and information are presented regarding levels of beryllium in

ambient water on both the regional and national level. The following information is taken directly from

“Beryllium in Water: An Assessment of Occurrence and Exposure” (Ciccone & Associates, 1984).

2.1.3.2.1 National Surveys

Since 1967, no new information on beryllium concentrations in naturally occurring waters in the U.S. has

been cited in the literature. However, no drastic changes would be expected. A study by Kopp and

Kroner (1969, as cited in Ciccone & Associates, 1984) suggests a minimum beryllium concentration to

be 0 :g/L in raw surface water with a maximum positive value of 1.22 :g/L and a mean positive value of

0.19 :g/L (Table 2.1-6). It should be noted, however, that the authors used only positive values for

beryllium in calculating the average level of beryllium occurrence. Further, the frequency of occurrence

of beryllium in this study was only 5.4%. Thus, the average concentration of beryllium in raw water

suggested by Kopp and Kroner may be artificially inflated.

In a 1970 USGS survey of 143 surface water samples, beryllium levels were found to be mostly less than

1.0 :g/L (Table 2.1-6). The highest level detected was less than 40 :g/L in California Gulch of Malton,

Colorado. No detection limits were reported for this study. Therefore, the meaning of less than 1 or less

than 40 :g/L is unclear. Of the few actual numerical values reported by the USGS for beryllium, all

were in New Jersey. These values ranged from 0.1 - 2.4 :g/L (mean 0.65 :g/L), the highest value being

detected in the Delaware River of Trenton, NJ.

Durum and Haffty (1961, as cited in Ciccone & Associates, 1984) monitored 15 rivers in the U.S. and

Canada for the presence of beryllium (Table 2.1-6). At 13 sites, beryllium was below detection limits in

all samples examined. Beryllium was detected in 1 of 4 samples from the Apalachicola River, FL

(<0.058 :g/L) and in 2 of 4 samples from the Atchafalaya River, LA (for one sample no numerical value

reported; for the other, <0.22 :g/L). Detection limits for beryllium in this survey were not given. The

national surveys described above all indicate that beryllium occurrence is very low in naturally occurring

raw surface waters.

Table 2.1-6: Beryllium Occurrence in Raw Water - National Surveys

Survey Sampling

Site

# Samples/ Site Mean

Concentration

(Range) :g/L

System Size Survey

Area

Notes

Trace Metals in

Waters of the

United States.

Oct. 1, 1962-

Sept. 30, 1967

130 R, S Weekly samples

composited for 3

months

(occasionally 1

month). 

Composite

samples taken

twice yearly.

0.19

(0 - 1.22)

U; U.S.

divided into

15 major

river basins.

Nationwide 1,577 samples taken. 5.4%

frequency of occurrence
Survey Sampling

Site

# Samples/ Site Mean

Concentration

(Range) :g/L

System Size Survey

Area

Notes

Occurrence Summary and Use Support Document March 2002 20

Quality of

Surface Waters

in the United

States. USGS,

1970

181 R, S Samples

collected daily

and monthly at

143 locations.

0.65

(0.1 - 2.4)

U; U.S.

divided into

16 major

river basins.

Nationwide Highest concentrations of Be

detected in the Delaware River,

Trenton, NJ. No limits of

detection given.

Occurrence of

Minor Elements

in Water. 

Durum and

Haffty, 1961

15 R, S Variable, 2 to 7

samples/site.

<0.22 - <0.058 U, U.S. and

Canada 15

sampling

sites

Nationwide

and Canada

Apalachicola River, FL: 1 of 4

samples positive at < 0.058

:g/L. Atchafalaya River, LA: 2

of 4 samples positive at <0.22

:g/L. No detection limits

given. 

Public Water

Supplies of the

100 Largest

Cities in the

United States,

1962. Durfor

and Becker,

1962

100 G, S Variable ND - 0.75 U Nationwide

2.1.3.2.2 State and Regional Surveys

Regional studies of the occurrence of beryllium in natural waters show a spectrum of results (Table 2.1-

7). Silvey (1967, as cited in Ciccone & Associates, 1984) found no detectable beryllium in water

samples from the State of California in a study of groundwater, surface water, ocean water and oil wells. 

On the other hand, Page (1981, as cited in Ciccone & Associates, 1984) found beryllium in all 1,064

groundwater samples and all 590 surface water samples obtained from New Jersey. The highest

concentration of beryllium found by Page was 84 :g/L in groundwater. This same study showed that, in

surface water, the highest concentration of beryllium was 1 :g/L. For both surface and ground water, the

median level of beryllium was 1 :g/L. No detection limits were specified in this study.

Table 2.1-7: Beryllium Occurrence in Raw Water - Regional Surveys

Survey Sampling

Site

# Samples/

Site

Mean

Concentration

(Range) :g/L

System

Size

Survey

Area

Notes

Occurrence of Selected

Minor Elements in the

Waters of California.

Silvey, 1967.

72 Springs

63 Water

Wells

19 Oil Wells

One (3.51) ND U State of

California

Be limit of detection was 0.3

:g/L. No Be found at any

sampling site.
Survey Sampling

Site

# Samples/

Site

Mean

Concentration

(Range) :g/L

System

Size

Survey

Area

Notes

Occurrence Summary and Use Support Document March 2002 21

Comparison of Ground

Water and Surface

Water for Patterns and

Levels of

Contamination by

Toxic Substances,

1977-1979. Page,

1981.

1064 U, G

590 U, S

Usually one

grab

sample,

sometimes

more.

1-84 U State of

New Jersey

Median data reported. No limits

of detection reported. 84 :g/L

highest concentration found in

groundwater (median 1 :g/L). 1

:g/L highest concentration

found in surface water (median 1

:g/L). Be detected in all

samples.

2.1.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of beryllium occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.004 mg/L; 0.01 mg/L; and 0.001 mg/L.

All sixteen cross-section State data sets contained occurrence data for beryllium. These data represent

approximately 48,000 analytical results from more than 19,000 PWSs during the period from 1983 to

1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs vary by

State, although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limit for beryllium in the 16 cross-section States is equal to

0.001 mg/L. (For details regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)

2.1.4.1 Stage 1 Analysis Occurrence Findings

Table 2.1-8 illustrates the Stage 1 analysis of beryllium occurrence in drinking water for the public water

systems in the 16-State cross-section relative to three thresholds: 0.01 mg/L, 0.004 mg/L (the current

MCL), and 0.001 mg/L (the modal MRL). A total of 18 ground water and surface water PWSs

(approximately 0.0951%) had at least one analytical result exceeding 0.01 mg/L; 0.217% of systems (41

systems) had at least one analytical result exceeding the MCL (0.004 mg/L); and 1.28% of systems (243

systems) had at least one analytical result exceeding 0.001 mg/L. 

Approximately 0.0971% of ground water systems (17 systems) had at least one analytical result greater

than 0.01 mg/L. About 0.223% of ground water systems (39 systems) had at least one analytical result

above the MCL (0.004 mg/L). The percentage of ground water systems with at least one result greater

than 0.001 mg/L was equal to 1.27% (223 systems). 

Only 1 (0.0702% of) surface water systems had at least one analytical result greater than 0.01 mg/L. A

total of 2 (0.140% of) surface water systems had at least one analytical result greater than the MCL

(0.004 mg/L). Twenty surface water systems (1.40%) had at least one analytical result exceeding 0.001

mg/L.
Occurrence Summary and Use Support Document March 2002 22

Table 2.1-8: Stage 1 Beryllium Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.01 0.0971% 17

0.004 0.223% 39

0.001 1.27% 223

Surface Water

0.01 0.0702% 1

0.004 0.140% 2

0.001 1.40% 20

Combined Ground &

Surface Water

0.01 0.0951% 18

0.004 0.217% 41

0.001 1.28% 243

Reviewing beryllium occurrence in the 16 cross-section States by PWS population served (Table 2.1-9)

shows that approximately 0.0683% of the population (over 71,000 people) was served by PWSs with at

least one analytical result of beryllium greater than 0.01 mg/L. A total of 649,000 (0.621% of) people

were served by systems with an exceedance of the MCL. Approximately 3.2 million people (3.09%)

were served by systems in the 16-State cross-section with at least one analytical result greater than 0.001

mg/L.

The percentage of population served by ground water systems with analytical results greater than 0.01

mg/L was equal to 0.150% (almost 68,800 people). When evaluated relative to 0.004 mg/L and 0.001

mg/L, the percent of population exposed was equal to 1.38% (635,000 people) and 4.25% (almost 2

million people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.01 mg/L was equal

to 0.00441% (2,600 people). Approximately 0.0240% (about 14,100 people) of the population served by

surface water systems in the 16-State cross-section was exposed to beryllium concentrations greater than

0.004 mg/L. When evaluated relative to 0.001 mg/L, the percent of population exposed was equal to

2.18% (over 1.2 million people).

Table 2.1-9: Stage 1 Beryllium Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Ground Water

0.01 0.150% 68,800

0.004 1.38% 635,000

0.001 4.25% 1,954,500
Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 23

Surface Water

0.01 0.00441% 2,600

0.004 0.0240% 14,100

0.001 2.18% 1,277,600

Combined Ground &

Surface Water

0.01 0.0683% 71,400

0.004 0.621% 649,000

0.001 3.09% 3,232,100

2.1.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 2.1-10 and 2.1-

11. The statistically generated best estimate values, as well as the ranges around the best estimate value,

are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. 

For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology

and Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations -

DRAFT (USEPA, 2002)). 

A total of 2 (0.00809%) ground water and surface water PWSs in the 16 States had an estimated mean

concentration of beryllium exceeding 0.01 mg/L. Approximately 15 (0.0781% of) PWSs in the 16 States

had an estimated mean concentration exceeding 0.004 mg/L, and 203 (1.07%) had an estimated mean

concentration exceeding 0.001 mg/L. 

An estimated 2 ground water PWSs in the 16 cross-section States (0.00870%) had a mean concentration

greater than 0.01 mg/L, 15 (0.0833%) had a mean concentration greater than 0.004 mg/L, and 192

(1.10%) had a mean concentration greater than 0.001 mg/L. Approximately 1 (0.000562%), 1 (0.014%),

and 10 (0.731%) surface water PWSs in the 16 States had estimated mean concentrations exceeding 0.01

mg/L, 0.004 mg/L, and 0.001 mg/L, respectively. 
Occurrence Summary and Use Support Document March 2002 24

Table 2.1-10: Stage 2 Estimated Beryllium Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.01 0.00870% 0.000% - 0.0229% 2 0 - 4

0.004 0.0833% 0.0400% - 0.137% 15 7 - 24

0.001 1.10% 0.908% - 1.29% 192 159 - 225

Surface Water

0.01 0.000562% 0.000% - 0.000% 1 0 - 0

0.004 0.0140% 0.000% - 0.0702% 1 0 - 1

0.001 0.731% 0.351% - 1.19% 10 5 - 17

Combined Ground &

Surface Water

0.01 0.00809% 0.000% - 0.0211% 2 0 - 4

0.004 0.0781% 0.0370% - 0.127% 15 7 - 24

0.001 1.07% 0.882% - 1.25% 203 167 - 237

Reviewing beryllium occurrence by PWS population served (Table 2.1-11) shows that an estimate of

approximately 2,000 people (approximately 0.0019%) of population served by all PWSs in the 16 crosssection States were potentially exposed to beryllium levels above 0.01 mg/L. The percentage of

population served by PWSs in the 16 States with levels of beryllium above 0.004 mg/L and 0.001 mg/L

was 0.0208% (an estimated 21,800 people) and 0.699% (over 731,000 people), respectively. 

When the percent of population served by ground water systems was evaluated relative to a threshold of

0.01 mg/L, 0.004 mg/L, and 0.001 mg/L, the percentage of population exposed in the 16 cross-section

States was equal to 0.00403% (an estimated 1,900 people), 0.0430% (an estimated 19,800 people) and

1.17% (an estimated 538,500 people), respectively. 

The percentage of population served by surface water systems in the 16 States with levels above 0.01

mg/L was equal to 0.000227% (an estimated 100 people), while the percentage of population served with

levels above 0.004 mg/L was 0.00341% (an estimated 2,000 people). The percentage of the population

served by surface water systems in the 16 States with levels above 0.001 mg/L was 0.330% (almost

193,000 people). 
Occurrence Summary and Use Support Document March 2002 25

Table 2.1-11: Stage 2 Estimated Beryllium Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.01 0.00403% 0.000% - 0.0255% 1,900 0 - 11,700

0.004 0.0430% 0.00586% - 0.174% 19,800 2,700 - 79,900

0.001 1.17% 0.595% - 1.96% 538,500 273,800 - 903,400

Surface Water

0.01 0.000227% 0.000% - 0.000% 100 0 - 0

0.004 0.00341% 0.000% - 0.0427% 2,000 0 - 25,000

0.001 0.330% 0.0558% - 0.911% 192,900 32,600 - 533,200

Combined Ground &

Surface Water

0.01 0.00190% 0.000% - 0.0128% 2,000 0 - 13,400

0.004 0.0208% 0.00278% - 0.0781% 21,800 2,900 - 81,700

0.001 0.699% 0.356% - 1.18% 731,300 372,400 - 1,237,100

2.1.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 5 PWSs nationally serving approximately 4,100 people could be exposed to

beryllium concentrations above 0.01 mg/L. About 51 systems serving 44,400 people had estimated mean

concentrations greater than 0.004 mg/L. Approximately 696 systems serving about 1.5 million people

nationally were estimated to have beryllium concentrations greater than 0.001 mg/L. (See Section 1.4 for

a description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 5 PWSs serving about 3,500 people nationally had mean

concentrations greater than 0.01 mg/L. Approximately 50 systems serving about 36,800 people

nationally had estimated mean concentration values that exceeded 0.004 mg/L. About 653 ground water

systems serving just over 1 million people had estimated mean concentrations greater than 0.001 mg/L. 

Approximately 1 surface water system serving 300 people was estimated to have a mean concentration of

beryllium above 0.01 mg/L. An estimated 1 surface water system serving 4,300 people had an estimated

mean concentration greater than 0.004 mg/L. An estimated 41 surface water systems serving

approximately 419,500 people had mean concentrations greater than 0.001 mg/L.
Occurrence Summary and Use Support Document March 2002 26

Table 2.1-12: Estimated National Beryllium Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.01 5 0 - 14 3,500 0 - 21,900

0.004 50 24 - 81 36,800 5,000 - 148,700

0.001 653 540 - 764 1,002,500 509,700 - 1,681,900

Surface Water

0.01 1 0 - 0 300 0 - 0

0.004 1 0 - 4 4,300 0 - 54,400

0.001 41 20 - 67 419,500 71,000 - 1,159,600

Combined Ground &

Surface Water

0.01 5 0 - 14 4,100 0 - 27,200

0.004 51 24 - 82 44,400 5,900 - 166,300

0.001 696 574 - 814 1,489,600 758,500 - 2,519,900

2.1.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of beryllium in drinking water are also

reviewed. Beryllium data contained in the National Inorganics and Radionuclides Survey (NIRS)

database are summarized below. Previously compiled occurrence information, from an OGWDW

summary document entitled “Beryllium in Water: An Assessment of Occurrence and Exposure”

(Ciccone & Associates, 1984), is presented in Section 2.1.5.2. In that review, a literature search was

conducted and knowledgeable sources within the Office of Water were contacted. Only one study was

found that addressed the occurrence of beryllium in finished water. (All information in Section 2.1.5.2 is

taken directly from “Beryllium in Water: An Assessment of Occurrence and Exposure” (Ciccone &

Associates, 1984).) Note that the study presented in the following section does not provide the

quantitative analytical results or comprehensive coverage that would enable direct comparison to the

occurrence findings estimated with the cross-section occurrence data presented in Section 2.1.4. These

additional studies, however, do enable a broader assessment of the Stage 2 occurrence estimates

presented for this Six-Year Review. 

2.1.5.1 National Inorganics and Radionuclides Survey (NIRS)

In 1981, the USEPA's Office of Drinking Water (ODW) initiated the National Inorganics and

Radionuclides Survey (NIRS) to characterize the occurrence of various contaminants in community

drinking water supplies. The survey focused on the presence of 36 inorganics, including beryllium, and

four radionuclides in ground water supplies from throughout the United States. Implementation of the

survey and sampling were accomplished by ODW's Technical Support Division (TSD) between July

1984 and October 1986.

The NIRS sampling program was designed to reflect the national distribution of community ground water

supplies by size of population served as inventoried by the Federal Reporting Data System (FRDS). The
Occurrence Summary and Use Support Document March 2002 27

FRDS data was stratified into the following four population-size categories: very small (serving 25-500),

small (serving 501-3,300), medium (serving 3,301-10,000), and large/very large (serving >10,000). A

total of 1,000 sites were selected randomly from the FRDS data in proportion to the four size categories. 

Approximately 2.1% of the supplies in each size category were chosen for sampling. Of the 1,000

targeted sites, 990 were actually sampled in the NIRS.

Sample collection and location within each supply were designed to reflect the quality of water actually

received by the consumer. Samples were collected after three minutes of flushing in order to represent

the finished water in the distribution system. To the extent possible, the sampling location was chosen at

a point of maximum use in the distribution system. The method used to analyze for beryllium was not

reported. The minimum reporting limit (MRL) for beryllium was 0.001 mg/L.

Beryllium results are available for all of 989 sites sampled in the NIRS. The mean of the analytical

detections was 0.04 mg/L. The maximum value detected was 0.21 mg/L. Table 2.1-13 presents the

estimated percentages of beryllium exceedances and the total number of systems to exceed the given

threshold level. Table 2.1-14 shows the estimated percentages of beryllium exceedances and the total

number of population to exceed the given threshold level.

Table 2.1-13: Estimated Beryllium Exceedance as Reported in the NIRS - Systems

Threshold Percent of Systems That

Exceed Threshold

Number of Systems

Estimated to Exceed

Threshold

0.01 mg/L 0.101% 60

0.004 mg/L 0.101% 60

0.001 mg/L 0.506% 301

Table 2.1-14: Estimated Beryllium Exceedance as Reported in the NIRS - Population

Threshold

Percent of Population Served

by Systems That Exceed

Threshold

Total Population Served by

Systems Estimated to Exceed

Threshold

0.01 mg/L 0.038% 33,000

0.004 mg/L 0.038% 33,000

0.001 mg/L 0.106% 91,000

2.1.5.2 100 Largest Cities - Finished Water Survey

Only one study was identified which examined the concentration of beryllium in finished water from

treatment plants (Table 2.1-15). Durfor and Becker (1962, as cited in Ciccone & Associates, 1984)

studied the occurrence of beryllium in raw and finished water from the 100 largest U.S. cities (1960

census). No detectable beryllium (detection limits 0.0001% of dissolved solids) was found in finished

water in any of the cities. However, beryllium was detected in raw water from the Lock Raven

Reservoir, Baltimore, MD at a concentration of 0.75 :g/L. The treatment process yielded finished water

that contained no detectable beryllium.
Occurrence Summary and Use Support Document March 2002 28

Table 2.1-15: Beryllium Occurrence in 100 Largest U.S. Cities

Survey Sampling

Site

# Samples/

Site

Mean

Concentration

(Range) :g/L

System

Size

Survey Area Notes

Public Water

Supplies of the

100 Largest

Cities in the

U.S., 1962. 

Durfur and

Becker, 1962.

100 G, S Variable ND U Nationwide 1 sample of raw water from Lock Raven

Reservoir, Baltimore, MD contained 0.75

:g/L. No Be detected (detection limits:

0.0001% of dissolved solids) following

treatment, plain sedimentation,

prechlorination, coagulation with alum,

sedimentation, rapid sand filtration and

adjustment of pH to 7.8 with lime.

2.1.6 Conclusion

Beryllium and many of its compounds are naturally occurring and found at low levels in soil, water, and

air. Beryllium metal has a wide range of uses in nuclear weapons and reactors. Beryllium alloys are

used in making electrical and electronic parts. Industrial releases of beryllium and beryllium compounds

have been reported to TRI since 1988 from 21 States and 28 States, respectively. Releases to land, such

as spills or leaks within the boundaries of the reporting facility, constitute the greatest proportion of the

total on- and off-site releases of beryllium and beryllium compounds. Beryllium is also a national

NAWQA analyte. Only 4% of all surface water sites had analytical detections of beryllium, compared to

0% of ground water sites. The percentage of surface water sites with analytical detections of beryllium

greater than the MCL (0.004 mg/L) was equal to 0.55%. The Stage 2 analysis, based on the 16-State

cross-section, estimated that approximately 0.0781% of combined ground water and surface water

systems serving 0.0208% of the population had estimated mean concentrations of beryllium greater than

the MCL of 0.004 mg/L. Based on this estimate, approximately 51 PWSs nationally serving about

44,400 people are expected to have estimated mean concentrations of beryllium greater than 0.004 mg/L.

Beryllium is a naturally occurring element. Therefore, the balanced geographic distribution of the 16-

State cross-section should adequately cover the range of natural occurrence of beryllium from low to

high. The 16-State cross-section also contains a substantial proportion of the States with reported TRI

releases. Based on this use and release evaluation, the 16-State cross-section appears to adequately

represent beryllium occurrence nationally.

2.1.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1993. ToxFAQs for Beryllium. U.S.

Department of Health and Human Services, Public Health Service. Available on the Internet at:

http://atsdr.cdc.gov/tfacts4.html

Agency for Toxic Substances and Disease Registry (ATSDR). 2000. Toxicological Profile for

Beryllium. U.S. Department of Health and Human Services, Public Health Service. 239 pp. +

Appendices. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp4.pdf

Ciccone, V.J & Associates. 1984. Beryllium in Water: An Assessment of Occurrence and Exposure. 

Prepared for and submitted to EPA on August 8, 1984.
Occurrence Summary and Use Support Document March 2002 29

Cunningham, L.D. 1998. Beryllium, Mineral Yearbook. U.S. Geological Survey, pp. Kl-K4. 

Cunningham, L.D. 1999. Beryllium, Mineral Commodity Summary. U.S. Geological Survey, pp. 34-35.

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at:

http://ca.water.usgs.gov/pnsp/rep/ofr97589/, last updated October 9, 1998.

 

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 2000. Mineral Commodity Summaries, February, 2000 - Beryllium. Available on the Internet

at: http://minerals.usgs.gov/minerals/pubs/commodity.

Need references for: Kopp and Kroner; Duram and Haffty; Silvey; Page; Durfor and Decker
Occurrence Summary and Use Support Document March 2002 30

2.2 Chromium

Table of Contents

2.2.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.2.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.2.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

2.2.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . . 36

2.2.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

2.2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

2.2.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Tables and Figures

Table 2.2-1: Imports of Chromium to the United States (thousand metric tons, gross weight) . . . . . . . 33

Table 2.2-2: Chromium and Chromium Compound Manufacturers and Processors by State . . . . . . . . 33

Table 2.2-3: Environmental Releases (in pounds) for Chromium in the United States, 

1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Table 2.2-4: Environmental Releases (in pounds) for Chromium Compounds in the 

United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Table 2.2-5: Chromium Detections and Concentrations in Surface Water and Ground Water . . . . . . . 36

Table 2.2-6: Stage 1 Chromium Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . 37

Table 2.2-7: Stage 1 Chromium Occurrence Based on 16-State Cross-Section - Population . . . . . . . . 38

Table 2.2-8: Stage 2 Estimated Chromium Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Table 2.2-9: Stage 2 Estimated Chromium Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Table 2.2-10: Estimated National Chromium Occurrence - Systems and Population Served . . . . . . . . 42

Table 2.2-11: Cumulative Occurrence of Chromium as Reported in NIRS . . . . . . . . . . . . . . . . . . . . . . 43

Table 2.2-12: Estimated Chromium Exceedance as Reported in the NIRS - Systems . . . . . . . . . . . . . . 44

Table 2.2-13: Estimated Chromium Exceedance as Reported in the NIRS - Population . . . . . . . . . . . . 44

Table 2.2-14: National Summary of Chromium Violations in Ground Water Systems . . . . . . . . . . . . . 47
Occurrence Summary and Use Support Document March 2002 31

Table 2.2-15: Estimated Cumulative National Occurrence of Chromium in Community 

Ground Water Supplies Based on the Delta Lognormal Distribution Model . . . . . . . . . . . . . . . 49

Table 2.2-16: Estimated Cumulative Occurrence of Chromium in Surface Water Supplies 

Based on the Delta Lognormal Distribution Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Table 2.2-17: Population Exposed to Chromium at Levels Exceeding the Current MCL in 

Ground Water Supplies as Reported in FRDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Table 2.2-18: Estimated Cumulative Population (in thousands) Exposed to Chromium in 

Drinking Water Exceeding the Indicated Concentrations from Community 

Ground Water Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Table 2.2-19: Estimated Cumulative Population (in thousands) Exposed to Chromium in 

Drinking Water Exceeding the Indicated Concentrations from Community 

Surface Water Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Occurrence Summary and Use Support Document March 2002 32

2.2.1 Introduction, Use and Production

Chromium (Cr) is a member of Group VIA of the periodic table. It is a naturally occurring element

found in rocks, animals, plants, soil, and in volcanic dust and gases. Elemental chromium is a hard bluewhite metal that is generally obtained through reduction of the chromite ore (FeO-Cr2O3). Chromium is

present in the environment in several different forms. The primary valence states of chromium are +3

and +6, which are generally the only ones found in natural waters (Battelle, 1984; USEPA, 1979, as cited

in Wade Miller, 1990). Chromium(III) occurs naturally in the environment and is an essential nutrient. 

Chromium(VI) and chromium(0) are generally produced by industrial processes (ATSDR, 2001). No

taste or odor is associated with chromium compounds. 

The major source of chromium in ground water is through leaching from rocks, mineral deposits, and

mining and mill wastes. The major sources of chromium in surface waters are leaching from rocks,

mineral deposits, soil runoff, industrial effluents, and deposition/precipitation of airborne particulates

(Wade Miller, 1990).

Chromium has a wide range of uses in metals, chemicals, and refractories. Chromium is one of the

United States’ most important strategic and critical materials. Chromium use in iron, steel, and

nonferrous alloys enhances hardenability and resistance to corrosion and oxidation. The use of chromium

to produce stainless steel and nonferrous alloys are two of its more important applications. Chromium is

also used in bricks in furnaces, dyes and pigments, and for chrome plating, leather tanning, and wood

preserving. Other applications are in making pigments, leather processing, catalysts, surface treatments,

and refractories (USGS, 2001).

In the United States, most chromite ore is smelted to produce stainless steel and non-ferrous alloy

(ATSDR, 2000). The latter is used primarily in the production of steel to improve stiffness, hardness,

and strength. Almost all of the chromite ore used in steel production in the United States is imported (see

Table 2.2-1; USGS, 2001). Table 2.2-2 provides further information by State of the widespread

manufacture and processing of chromium (ATSDR, 2000).

Drinking water generally contains the same chromium levels as the surface and ground waters, which

serve as its source. Although some piping materials contain significant levels of chromium (corrosion

resistant steel, 8-14%; cement, 5-120 ppm chromium), little is leached into the water. However, it should

be noted that chromium (III) may be oxidized to chromium (VI) during the chlorination process (NLM,

2001).

The two largest sources of chromium emission in the atmosphere are from the chemical manufacturing

industry and combustion of natural gas, oil, and coal. Other sources include wind transport from road

dust, cement producing plants (since cement contains chromium), the wearing down of asbestos brake

linings from automobiles or similar sources of wind carried asbestos (since asbestos contains chromium),

incineration of municipal refuse and sewage sludge, exhaust emission from automotive catalytic

converters, emissions from cooling towers that use chromium compounds as rust inhibitors, waste waters

from electroplating, leather tanning, and textile industries when discharged into surface waters, and solid

wastes from chemical manufacture of chromium compounds or from municipal incineration when

disposed of improperly in landfill sites (NLM, 2001).
Occurrence Summary and Use Support Document March 2002 33

Table 2.2-1: Imports of Chromium to the United States (thousand metric tons, gross weight)

Import for Consumption 1995 1996 1997 1998 1999 

chromite ore 416 362 350 381 476

 Source: USGS, 2001

Table 2.2-2: Chromium and Chromium Compound Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on 

site in thousands of poundsb Activities and usesc

AK 1 0-99,999 11

AL 87 1,000-999,999 1,2,3,5,6,7,8,9,10,11,12,13

AR 49 100-999,999 1,2,3,4,5,8,9,11,12,13

AZ 31 100-999,999 1,2,3,4,5,6,8,9,11,12,13

CA 147 0-999,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

CO 33 100-999,999 1,2,3,4,5,7,8,9,11,12

CT 66 100-9,999,999 1,2,3,4,5,7,8,9,10,11,12,13

DE 6 1,000-999,999 1,2,3,4,5,7,8,9

FL 45 100-9,999,999 5,7,8,9,10,11,13

GA 90 0-49,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

HI 2 0-99,999 8

IA 55 100-9,999,999 1,2,3,5,7,8,9,10,12,13

ID 6 100,000-49,999,999 1,5,7,9

IL 212 0-9,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

IN 199 0-99,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

KS 38 0-999,999 2,3,7,8,9,11,12,13

KY 72 0-9,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

LA 34 100-9,999,999 1,2,3,4,5,7,8,9,10,11,12

MA 79 100-999,999 1,2,3,4,5,7,8,9,10,11,12,13

MD 32 100-49,999,999 1,2,3,4,5,6,7,8,9,10,11

ME 18 1,000-999,999,999 1,3,5,7,8,9,12,13

MI 162 0-9,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

MN 49 100-9,999,999 1,3,5,7,8,9,10,12,13

MO 74 100-99,99,999 1,2,5,7,8,9,10,11,12,13

MS 49 1,000-999,999 1,5,7,8,9,11,12,13

MT 4 10,000-99,999 7,8,13

NC 91 0-999,999,999 1,2,3,4,5,6,7,8,9,10,12,13

ND 5 1,000-999,999 2,3,9

NE 22 1,000-999,999 1,2,3,5,8,9,11,12,13

NH 20 1,000-99,999 8,9,11,12

NJ 48 100-9,999,999 1,2,3,4,5,7,8,9,10,11,12,13

NM 7 1,000-999,999 1,2,3,5,6,8,9,12

NV 6 10,000-99,999 4,8,9,10

NY 94 0-9,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

OH 333 0-999,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

OK 67 100-49,999,999 1,2,3,4,5,6,8,9,10,11,12,13

OR 37 1,000-999,999 1,2,3,5,8,9,10,12,13

PA 316 0-999,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

PR 4 0-99,999 1,5,9,11

RI 14 1,000-999,999 1,2,3,8,9,10,13

SC 72 0-999,999,999 1,2,3,4,5,7,8,9,10,11,12,13

SD 8 1,000-99,999 2,3,8,9

TN 81 0-9,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

TX 177 0-99,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

UT 28 0-999,999 1,2,3,4,5,7,8,9,11,13

VA 51 0-9,999,999 1,2,4,5,7,8,9,10,12,13

VT 4 0-999,999 3,4,9

WA 39 100-9,999,999 1,2,3,6,7,8,9,12,13
Statea Number of facilities Range of maximum amounts on 

site in thousands of poundsb Activities and usesc

Occurrence Summary and Use Support Document March 2002 34

WI 197 0-9,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

WV 27 100-9,999,999 1,2,3,5,6,7,8,9,10,12,13

WY 3 0-99,999 1,6,9

a

Post office State abbreviations used

b

 Range represents maximum amounts on site reported by facilities in each State

c

Activities/Uses

1. Produce 8. As a formulation component

2. Import 9. As an article component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

Source: ATSDR, 2000 compilation of 1997 TRI data

2.2.2 Environmental Release

Chromium and chromium compounds are listed as Toxics Release Inventory (TRI) chemicals. Table 2.2-

3 illustrates the environmental releases of chromium from 1988 to 1999. (There are only chromium data

for these years.) Releases to land, constituting most of the on-site releases of chromium, gradually

decreased from 1988 to 1995 and then dropped dramatically in 1996. It is unclear whether these sharp

chromium decreases are real or a function of changes in TRI reporting requirements in the late 1980s and

early 1990s (see discussion in the Introduction). Since 1995, land releases have fluctuated modestly for

chromium with no apparent trend. Air emissions are also an important mode of on-site release. Though

the first several years are markedly higher for air emissions of chromium, no trend is apparent for the

remaining years. Surface water discharges and underground injection of chromium are less significant

on-site releases. Off-site releases of chromium, a large component of total releases, are considerable. 

Though there was a large drop in total chromium releases in 1991 when compared to previous years, the

late 1990s show a steady increase in pounds released. The TRI data for chromium were reported from 49

States with the exception of Hawaii and included Puerto Rico (USEPA, 2000). All 16 of the crosssection States (used for analyses of chromium occurrence in drinking water; see Section 2.2.4) reported

releases of chromium. (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.2-3: Environmental Releases (in pounds) for Chromium in the United States, 

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 300,814 11,236 56 715,100 15,773,121 16,800,327

1998 478,733 13,112 9 685,766 12,938,825 14,116,445

1997 305,113 11,914 1 514,449 5,552,216 6,383,693

1996 434,107 574,456 7 535,711 6,022,527 7,566,808

1995 418,408 17,266 33 1,109,958 5,771,254 7,316,919

1994 622,337 20,566 48 1,176,881 5,877,781 7,697,613

1993 599,014 24,246 269 1,063,935 7,901,753 9,589,217

1992 492,851 23,341 333 1,138,756 6,047,944 7,703,225

1991 427,901 17,857 531 1,209,587 6,576,924 8,232,800

1990 434,330 41,265 95 2,738,681 10,585,379 13,799,750
Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

Occurrence Summary and Use Support Document March 2002 35

1989 945,625 69,681 693 3,369,485 9,865,483 14,250,967

1988 566,498 75,442 2,249 9,282,766 11,710,612 21,637,567

 Source: USEPA, 2000

Table 2.2-4 illustrates the environmental releases for chromium compounds. Releases to land, ranging

from about 20 to 30 million pounds, constitute most of the on-site releases of chromium compounds from

1988 to 1999. Though the first several years of recorded air emissions of chromium compounds are

slightly higher, no real trend is apparent. Surface water discharges and underground injection of

chromium compounds are less significant on-site releases. Surface water discharges of chromium

compounds have gradually decreased since 1988. Underground injections of chromium compounds

showed no discernable trend besides a sharp increase from 1995 to 1997. Off-site releases of chromium

compounds fluctuate throughout the years, with highest releases in 1995 and 1997, although no other

trends are apparent. The TRI data for chromium compounds were reported from 49 States with the

exception of Vermont and included Puerto Rico (USEPA, 2000). All 16 of the cross-section States (used

for analyses of chromium occurrence in drinking water; see Section 2.2.4) reported releases of chromium

compounds. (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.2-4: Environmental Releases (in pounds) for Chromium Compounds in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 467,071 97,379 816,717 29,591,378 14,203,028 45,175,573

1998 347,629 112,520 874,795 30,241,083 16,206,382 47,782,409

1997 382,843 100,082 1,131,559 29,271,102 21,003,330 51,888,916

1996 420,051 138,591 1,193,808 26,463,701 14,685,755 42,901,906

1995 650,311 138,551 1,084,747 22,090,165 20,389,031 44,352,805

1994 547,907 159,655 38,061 22,185,322 16,029,364 38,960,309

1993 405,083 230,548 42,493 24,634,864 12,975,431 38,288,419

1992 515,820 276,401 32,137 25,085,551 12,749,479 38,659,388

1991 606,278 343,298 34,603 26,267,556 13,735,176 40,986,911

1990 721,150 409,916 83,147 23,445,165 15,898,149 40,557,527

1989 1,398,526 475,850 59,110 31,081,444 18,526,178 51,541,108

1988 764,851 326,027 52,653 30,938,106 14,898,699 46,980,336

 Source: USEPA, 2000

2.2.3 Ambient Occurrence

Chromium is an analyte for both surface and ground water NAWQA studies, with a method detection

limit (MDL) of 0.01 mg/L. Additional information on analytical methods used in the NAWQA study

units, including method detection limits, are described by Gilliom and others (1998). 
Occurrence Summary and Use Support Document March 2002 36

Typical of many inorganic contaminants, chromium occurrence in ambient surface waters is high (Table

2.2-5). This is not surprising, considering that chromium and its compounds are used in many products. 

Contrary to occurrence of chromium in surface waters, no chromium was detected in ground waters. 

This is not surprising, however, considering the bonding tendencies of chromium with organic matter in

soil particles and the low tendency for chromium to be found in leachate because of its low mobility in

soil. Detection frequencies are also greater for surface water than for ground water, possibly because

surface waters are more sensitive to anthropogenic releases. For all surface water samples, the median

concentration is 0.001 mg/L and the 99th percentile concentration is 0.006 mg/L. However, chromium

detection frequencies exceeding the MCL (0.1 mg/L) do not occur for surface water samples. This

could be expected because surface waters subject to large anthropogenic inputs of chromium are more

easily diluted by waters integrated from other parts of the watershed where chromium concentrations

may be lower. 

Table 2.2-5: Chromium Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 > MDL* 

Detection frequency

 > MCL*

Concentration percentiles

(all samples; mg/L) 

% samples % sites % samples % sites median 99th

surface water 27.4% 66.0% 0.0% 0.0% 0.001 0.006

ground water 0.0% 0.0% 0.0% 0.0% N/A N/A

* The Minimum Reporting Level (MRL) for chromium in water is 0.01 mg/L and the Maximum Contaminant Level (MCL) is 0.1 mg/L.

2.2.3.2 Additional Ambient Occurrence Data

A summary document entitled “Occurrence and Exposure Assessment for Chromium in Public Drinking

Water Supplies” (Wade Miller, 1990), was previously prepared for past USEPA assessments of

chromium. However, no information on the ambient occurrence of chromium was included in that

document. (The document did include information regarding chromium occurrence in drinking water,

which is discussed in Section 2.2.5 of this report.)

2.2.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of chromium occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.1 mg/L; 0.07 mg/L; 0.05 mg/L; 0.02 mg/L; and

0.01 mg/L.

All sixteen cross-section State data sets contained occurrence data for chromium. These data represent

over 65,000 analytical results from approximately 20,000 PWSs during the period from 1983 to 1998

(with most analytical results from 1992 to 1997). The number of sample results and PWSs vary by State,

although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limit for chromium in the 16 cross-section States is equal to

0.01 mg/L. (For details regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)
Occurrence Summary and Use Support Document March 2002 37

2.2.4.1 Stage 1 Analysis Occurrence Findings

Table 2.2-6 illustrates the Stage 1 analysis of chromium occurrence in drinking water for the public water

systems in the 16-State cross-section relative to five thresholds: 0.1 mg/L (the current MCL), 0.07 mg/L,

0.05 mg/L, 0.02 mg/L, and 0.01 mg/L (the modal MRL). A total of 25 ground water and surface water

PWSs (approximately 0.127%) had at least one analytical result exceeding the MCL (0.1 mg/L); 0.513%

(101 systems) of PWSs had at least one analytical result exceeding 0.05 mg/L; and 2.83% (557 systems)

of PWSs had at least one analytical result exceeding 0.01 mg/L. 

Approximately 0.110% (20 systems) of ground water PWSs had at least one analytical result greater than

the MCL (0.1 mg/L). About 0.484% (88 systems) of ground water PWSs had at least one analytical

result above 0.05 mg/L. The percentage of ground water systems with at least one result greater than

0.01 mg/L was equal to 2.81% (511 systems). 

Only 5 (0.328% of) surface water systems had at least one analytical result greater than the MCL (0.1

mg/L). A total of 13 (0.852% of) surface water systems had at least one analytical result greater than

0.05 mg/L. Forty-six surface water systems (3.01%) had at least one analytical result exceeding 0.01

mg/L.

Table 2.2-6: Stage 1 Chromium Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold 

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.1 0.110% 20

0.07 0.352% 64

0.05 0.484% 88

0.02 1.33% 242

0.01 2.81% 511

Surface Water

0.1 0.328% 5

0.07 0.524% 8

0.05 0.852% 13

0.02 1.57% 24

0.01 3.01% 46

Combined Ground &

Surface Water

0.1 0.127% 25

0.07 0.366% 72

0.05 0.513% 101

0.02 1.35% 266

0.01 2.83% 557
Occurrence Summary and Use Support Document March 2002 38

Reviewing chromium occurrence in the 16 cross-section States by PWS population served (Table 2.2-7)

shows that approximately 0.666% (over 702,000 people) of the population was served by PWSs with at

least one analytical result of chromium greater than the MCL. Almost 10.5 million people (9.95%) were

served by systems with an exceedance of 0.05 mg/L. Approximately 14 million people (13.3%) were

served by systems with at least one analytical result greater than 0.01 mg/L.

The percentage of population served by ground water systems with analytical results greater than 0.1

mg/L was equal to 0.543% (244,300 people). When evaluated relative to 0.05 mg/L or 0.01 mg/L, the

percent of population exposed was equal to 1.76% (almost 789,000 people) and 8.83% (almost 4 million

people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.1 mg/L was equal

to 0.758% (about 458,000 people). The percentage of population served by surface water systems

dramatically increased to 16.1% (approximately 9.7 million people) when evaluated relative to 0.05

mg/L. The percentage of population exposed to concentrations greater than 0.01 mg/L was equal to

16.6% (over 10 million people).

Table 2.2-7: Stage 1 Chromium Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold 

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.1 0.543% 244,300

0.07 1.03% 462,500

0.05 1.76% 789,000

0.02 4.49% 2,020,400

0.01 8.83% 3,967,200

Surface Water

0.1 0.758% 457,800

0.07 13.0% 7,876,700

0.05 16.1% 9,699,800

0.02 16.2% 9,804,900

0.01 16.6% 10,055,100

Combined Ground &

Surface Water

0.1 0.666% 702,100

0.07 7.91% 8,339,100

0.05 9.95% 10,488,800

0.02 11.2% 11,825,300

0.01 13.3% 14,022,300
Occurrence Summary and Use Support Document March 2002 39

2.2.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 2.2-8 and 2.2-9. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

One (0.00424%) PWS in the 16 States was estimated to have a mean concentration of chromium above

0.1 mg/L (the current MCL). Approximately 7 (0.0366% of) PWSs in the 16-State cross-section are

estimated to have mean concentrations greater than 0.05 mg/L. The percentage of PWSs in the 16 States

with estimated mean concentrations exceeding 0.01 mg/L (the modal detection limit) was about 1.56%

(307) PWSs nationally.

A significantly greater proportion of ground water systems, as compared to surface water systems, were

estimated to exceed each threshold. Approximately 1 (0.00459% of) ground water system in the 16

States had an estimated mean concentration of chromium above 0.1 mg/L, compared to zero surface

water systems. About 0.0393% (an estimated 7 PWSs) of the 16 States’ ground water systems had

estimated mean concentrations greater than 0.05 mg/L. This compares with about 0.00406% (about 1

system) of the surface water systems with estimated mean concentrations greater than 0.05 mg/L. The

estimated mean concentration values for approximately 299 (1.65% of) ground water PWSs in the 16-

State cross-section exceed 0.01 mg/L, compared to only 7 (0.474% of) surface water systems with

estimated mean concentrations exceeding the modal detection limit.

Table 2.2-8: Stage 2 Estimated Chromium Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.1 0.00459% 0.000% - 0.0165% 1 0 - 3

0.07 0.0144% 0.000% - 0.0385% 3 0 - 7

0.05 0.0393% 0.011% - 0.0716% 7 2 - 13

0.02 0.396% 0.292% - 0.501% 72 53 - 91

0.01 1.65% 1.4% - 1.89% 299 255 - 343

Surface Water

0.1 0.000% 0.000% - 0.000% 0 0 - 0

0.07 0.000786% 0.000% - 0.000% 1 0 - 0

0.05 0.00406% 0.000% - 0.0655% 1 0 - 1

0.02 0.0696% 0.000% - 0.262% 1 0 - 4

0.01 0.474% 0.131% - 0.786% 7 2 - 12
Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 40

Combined Ground

& Surface Water

0.1 0.00424% 0.000% - 0.0152% 1 0 - 3

0.07 0.0133% 0.000% - 0.0355% 3 0 - 7

0.05 0.0366% 0.0152% - 0.0660% 7 3 - 13

0.02 0.371% 0.274% - 0.467% 73 54 - 92

0.01 1.56% 1.33% - 1.78% 307 262 - 350

Reviewing chromium occurrence by PWS population served (Table 2.2-9) shows that approximately

0.00139% (an estimate of approximately 1,500 people) of the population served by PWSs in the 16 States

were potentially exposed to chromium levels above 0.1 mg/L. When evaluated relative to a threshold of

0.05 mg/L, the percent of the population exposed estimated about 0.0108% (over 11,000 people served

by systems in the 16 cross-section States). The percentage of population served by PWSs with estimated

mean concentrations greater than 0.01 mg/L was approximately 0.431% (approximately 453,700 people).

About 1,500 people (0.00325% of the population served by ground water systems in the 16 States) were

served by systems with estimated mean concentrations of chromium above 0.1 mg/L. An estimated

0.0248% (over 11,000 people) of the 16-State population were served by ground water systems whose

mean concentration value exceeded 0.05 mg/L. The percentage of population served by ground water

PWSs with estimated mean concentration values exceeding 0.01 mg/L was approximately 0.893% (about

401,300 people).

Zero surface water PWSs (therefore, none of the population served by surface water systems) had

estimated mean concentrations of chromium above 0.1 mg/L. About 0.000336% (approximately 200

people in the 16 States) of the population served by surface water PWSs had mean concentrations greater

than 0.05 mg/L. An estimated 52,300 (0.0866% of) people served by surface water in the 16-State crosssection were served by systems with estimated mean concentrations of chromium above 0.01 mg/L. The

percentage (and estimated number) of population served by surface water systems that exceeded each

threshold was always less than the percentage of ground water systems that exceeded the threshold.

Table 2.2-9: Stage 2 Estimated Chromium Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.1 0.00325% 0.000% - 0.0186% 1,500 0 - 8,400

0.07 0.00987% 0.000% - 0.113% 4,400 0 - 50,700

0.05 0.0248% 0.00124% - 0.130% 11,100 600 - 58,600
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 41

0.02 0.228% 0.0959% - 0.357% 102,600 43,100 - 160,500

0.01 0.893% 0.635% - 1.32% 401,300 285,500 - 592,500

Surface Water

0.1 0.000% 0.000% - 0.000% 0 0 - 0

0.07 0.000104% 0.000% - 0.000% 100 0 - 0

0.05 0.000336% 0.000% - 0.00182% 200 0 - 1,100

0.02 0.00667% 0.000% - 0.0532% 4,000 0 - 32,100

0.01 0.0866% 0.00604% - 0.358% 52,300 3,700 - 216,100

Combined Ground &

Surface Water

0.1 0.00139% 0.000% - 0.00793% 1,500 0 - 8,400

0.07 0.00427% 0.000% - 0.0481% 4,500 0 - 50,600

0.05 0.0108% 0.000580% - 0.0559% 11,300 600 - 58,900

0.02 0.101% 0.0447% - 0.159% 106,600 47,100 - 167,700

0.01 0.431% 0.298% - 0.649% 453,700 313,700 - 683,900

2.2.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold (see Table 2.2-10), an estimated 3 PWSs serving approximately 3,000 people nationally could

be exposed to chromium concentrations above 0.1 mg/L. About 24 systems serving almost 23,000

people had estimated mean concentrations greater than 0.05 mg/L. Approximately 1,013 systems serving

about 917,000 people nationally were estimated to have chromium concentrations greater than 0.01

mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to national

values.)

For ground water systems, an estimated 3 PWSs serving about 2,800 people nationally had mean

concentrations greater than 0.1 mg/L. Approximately 23 ground water systems serving about 21,200

people nationally had estimated mean concentration values that exceeded 0.05 mg/L. About 980 ground

water systems serving almost 765,000 people had estimated mean concentrations greater than 0.01 mg/L. 

Zero surface water systems were estimated to have mean concentrations of chromium above 0.1 mg/L. 

An estimated 1 surface water system serving 400 people had an estimated mean concentration greater

than 0.05 mg/L. About 26 surface water systems serving approximately 110,200 people had estimated

mean concentrations greater than 0.01 mg/L.
Occurrence Summary and Use Support Document March 2002 42

Table 2.2-10: Estimated National Chromium Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.1 3 0 - 10 2,800 0 - 15,900

0.07 9 0 - 23 8,500 0 - 96,600

0.05 23 7 - 43 21,200 1,100 - 111,600

0.02 236 173 - 298 195,500 82,200 - 306,000

0.01 980 834 - 1,122 764,900 544,200 - 1,129,300

Surface Water

0.1 0 0 - 0 0 0 - 0

0.07 1 0 - 0 100 0 - 0

0.05 1 0 - 4 400 0 - 2,300

0.02 4 0 - 15 8,500 0 - 67,700

0.01 26 7 - 44 110,200 7,700 - 455,400

Combined Ground &

Surface Water

0.1 3 0 - 10 3,000 0 - 16,900

0.07 9 0 - 23 9,100 0 - 102,400

0.05 24 10 - 43 22,900 1,200 - 119,000

0.02 241 178 - 304 215,600 95,200 - 338,900

0.01 1,013 865 - 1,156 917,000 634,100 - 1,382,400

2.2.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of chromium in drinking water are also

reviewed. Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence and Exposure Assessment for Chromium in Public Drinking Water Supplies” (Wade Miller,

1990), is presented in this section. This variety of studies and information are presented regarding levels

of chromium in drinking water, with the scope of the reviewed studies ranging from national to regional. 

Note that none of the studies presented in the following section provide the quantitative analytical results

or comprehensive coverage that would enable direct comparison to the occurrence findings estimated

with the cross-section occurrence data presented in Section 2.2.4. These additional studies, however, do

enable a broader assessment of the Stage 2 occurrence estimates presented for this Six-Year Review. All

the following information in Section 2.2.5 is taken directly from “Occurrence and Exposure Assessment

for Chromium in Public Drinking Water Supplies” (Wade Miller, 1990).

2.2.5.1 National Inorganics and Radionuclides Survey (NIRS)

In 1981, the USEPA's Office of Drinking Water (ODW) initiated the National Inorganics and

Radionuclides Survey (NIRS) to characterize the occurrence of various contaminants in community

drinking water supplies. The survey focused on the presence of 36 inorganics, including chromium, and
Occurrence Summary and Use Support Document March 2002 43

four radionuclides in ground water supplies from throughout the United States. Implementation of the

survey and sampling were accomplished by ODW's Technical Support Division (TSD) between July

1984 and October 1986.

The NIRS sampling program was designed to reflect the national distribution of community ground water

supplies by size of population served as inventoried by the Federal Reporting Data System (FRDS). The

FRDS data was stratified into the following four population-size categories: very small (serving 25-500),

small (serving 501-3,300), medium (serving 3,301-10,000), and large/very large (serving >10,000). A

total of 1,000 sites were selected randomly from the FRDS data in proportion to the four size categories. 

Approximately 2.1% of the supplies in each size category were chosen for sampling. Of the 1,000

targeted sites, 990 were actually sampled in the NIRS.

Sample collection and location within each supply were designed to reflect the quality of water actually

received by the consumer. Samples were collected after three minutes of flushing in order to represent

the finished water in the distribution system. To the extent possible, the sampling location was chosen at

a point of maximum use in the distribution system. The method used to analyze for chromium was not

reported. The minimum reporting limit (MRL) for chromium was 0.002 mg/L.

Table 2.2-11 presents the NIRS results in terms of the cumulative number of systems exceeding the

indicated concentrations for each of the population size strata. Chromium results are available for all of

990 sites sampled in the NIRS. Approximately 94 percent of the samples had chromium concentrations

below the MRL of 0.002 mg/L. Six percent (63) of the samples contained chromium in concentrations

equal to or greater than 0.002 mg/L. The mean of the positives was 0.007 mg/L. The maximum value

detected was 0.041 mg/L which is below the current MCL of 0.05 mg/L and the proposed MCL of 0.1

mg/L. Table 2.2-12 presents the estimated percentages of chromium exceedances and the total number of

systems to exceed the given threshold level. Table 2.2-13 shows the estimated percentages of chromium

exceedances and the total number of population to exceed the given threshold level.

Table 2.2-11: Cumulative Occurrence of Chromium as Reported in NIRS

System size 

(population served)

Number of 

Systems Sampled

Cumulative Number of Supplies with Concentrations (mg/L) of:

> 0.002 > 0.05 > 0.1 > 0.2

Very Small

25 - 100 338 27 0 0 0

101 - 500 337 21 0 0 0

Small

501 - 1,000 113 2 0 0 0

1,001 - 3,300 120 4 0 0 0

Medium

3,301 - 10,000 54 8 0 0 0

Large/Very Large

10,001 - 25,000 22 1 0 0 0

25,001 - 50,000 3 0 0 0 0
System size 

(population served)

Number of 

Systems Sampled

Cumulative Number of Supplies with Concentrations (mg/L) of:

> 0.002 > 0.05 > 0.1 > 0.2

Occurrence Summary and Use Support Document March 2002 44

50,001 - 75,000 2 0 0 0 0

75,001 - 100,000 0 0 0 0 0

>100,000 1 0 0 0 0

Totals 990 63 0 0 0

Table 2.2-12: Estimated Chromium Exceedance as Reported in the NIRS - Systems

Threshold Percent of Systems That

Exceed Threshold

Number of Systems Estimated

to Exceed Threshold

0.10 mg/L 0.00% 0

0.07 mg/L 0.00% 0

0.05 mg/L 0.00% 0

0.02 mg/L 0.51% 301

0.01 mg/L 0.81% 481

Table 2.2-13: Estimated Chromium Exceedance as Reported in the NIRS - Population

Threshold

Percent of Population Served

by Systems That Exceed

Threshold

Total Population Served by

Systems Estimated to Exceed

Threshold

0.10 mg/L 0.00% 0

0.07 mg/L 0.00% 0

0.05 mg/L 0.00% 0

0.02 mg/L 0.16% 137,876

0.01 mg/L 0.48% 411,201

2.2.5.2 Federal Survey Data

Several national-scale surveys, in addition to the NIRS Survey, have been conducted that provide data on

chromium in public drinking water supplies. These include the 100 Largest Cities Study, the 1969

Community Water Supply Study, the 1978 Community Water Supply Survey, the Rural Water Survey,

and the National Organic Monitoring Survey. The following sections describe those surveys and present

the data on chromium levels in ground water and surface water supplies. It should be noted that none of

the surveys differentiate between chromium in the (III) and (VI) valence states.
Occurrence Summary and Use Support Document March 2002 45

2.2.5.2.1 100 Largest Cities Study

Durfor and Becker (1964, as cited in Wade Miller, 1990) reported on the water quality, use, and

treatment at public water supplies serving the 100 largest U.S. cities at the time of the 1960 census. 

Included were 66 cities that used only surface water, 20 that used only ground water, and 14 that used

mixed surface and ground water sources. Both raw and finished water samples were taken for most of

the locations.

Chromium was measured using a flame emission spectrographic technique. There was not sufficient

information provided to discern the minimum detectable or minimum quantifiable concentration. Only

very generalized results are available for chromium. Chromium concentrations ranged from undetectable

to 0.035 mg/L. The majority of finished water samples with chromium present had concentrations below

0.005 mg/L.

2.2.5.2.2 1969 Community Water Supply Study (1969 CWSS)

The U.S. Public Health Service (USPHS) conducted the Community Water Supply Study (CWSS) in

1969 to assess the Nation's water supply facilities and drinking water quality (McCabe et al., 1970;

USPHS, 1970; both as cited in Wade Miller, 1990). Finished water from 969 community supplies

located in 9 geographically distributed areas was studied. These areas were Vermont; New York, New

York; Charleston, West Virginia; Charleston, South Carolina; Cincinnati, Ohio; Kansas City, MissouriKansas; New Orleans, Louisiana; Pueblo, Colorado; and San Bernardino-Riverside-Ontario, California. 

Except for Vermont (in which all supplies in the State were sampled), the study locations are standard

metropolitan statistical areas (SMSAs). Water samples were taken at randomly selected sites in the

distribution system after flushing for several seconds.

Of the 969 systems studied, 678 were groundwater supplies; 109 were surface water supplies; and the

remaining 182 were mixed sources, purchased water, or of unspecified source. Analytical results for

chromium were provided for 676 ground water supplies and 109 surface water supplies.

Results were published in several volumes addressing each of the study areas and the national findings. 

The published report did not provide complete data on the water source, population served, or chromium

level measured for each system sampled. However, a computer file with the requisite data was prepared

by Science Applications International Corporation (SAIC, 1987, as cited in Wade Miller, 1990) using the

published data, and additional information was provided by Dr. Rolf Deininger of the University of

Michigan, and EPA staff.

The information does not specify a detection limit nor a minimum quantifiable concentration for

chromium. The “negative” findings for individual supplies were reported as having a value of 0 mg/L. 

Overall, chromium was observed in 107 of the 676 ground water supplies (16 percent) for which data are

available. Chromium was also present in 35 of the 109 surface water supplies sampled (32 percent) at

concentrations of 0.0005-0.21 mg/L.

2.2.5.2.3 1978 Community Water Supply Survey (1978 CWSS)

The 1978 Community Water Supply Survey (CWSS) was conducted by EPA to determine the occurrence

of organic and inorganic compounds in public water supplies throughout the U.S. Drinking water

samples were provided by approximately 500 supplies; however, due to analytical problems, reliable data
Occurrence Summary and Use Support Document March 2002 46

for chromium were available for only 47 ground water and 12 surface water supplies (USEPA, 1983, as

cited in Wade Miller, 1990).

Details on the analytical method used for chromium were not available; from the information provided by

Glick (1984, as cited in Wade Miller, 1990) the minimum quantifiable concentration appeared to be

0.005 mg/L. Supplies provided one to five samples of raw, finished, and/or distribution water. However,

Brass (1983, as cited in Wade Miller, 1990) indicated that reporting inconsistencies made it impossible to

distinguish between finished and distribution samples. Therefore, distribution and finished sample

results were averaged; raw water data were not used.

Chromium was not found above the (apparent) minimum quantifiable concentration of 0.005 mg/L in any

of the 47 ground water or 12 surface water supplies for which analytical data are available.

2.2.5.2.4 Rural Water Survey (RWS)

The Rural Water Survey (RWS) conducted between 1978 and 1980 evaluated the status of drinking water

in rural America as required by Section 3 of the Safe Drinking Water Act. More than 2,000 households

served by 648 public water supplies (494 ground water, 154 surface water) were surveyed. Many of

these households used private wells or very small systems serving fewer than 25 people, and only a

subsample of the supplies evaluated included analyses for chromium (71 ground water and 21 surface

water supplies). Results of the inorganic analyses were provided to Science Applications International

Corporation (SAIC, 1987, as cited in Wade Miller, 1990) as a computer file by Brower (1983, as cited in

Wade Miller, 1990).

A problem with the RWS was that the number of service connections associated with water systems was

reported in lieu of the actual populations served by the systems. Dr. Bruce Brower of Cornell University,

who collaborated in the National Statistical Assessment of Rural Water Conditions (based on the RWS

data), provided a factor to convert the data from service connections to the number of people served,

based on the average number of persons per household observed in the RWS. It must be noted, however,

that these population values are only approximations. Details were not available on the sample collection

nor the analytical methodology used. However, the minimum quantifiable concentration for chromium

appeared to be 0.005 mg/L. Of the 71 ground water supplies studied, 4 (6 percent) contained chromium,

all at levels of 0.005 mg/L.

For surface water supplies, 2 of the 21 supplies sampled had chromium present, also at levels of 0.005

mg/L.

2.2.5.2.5 National Organic Monitoring Survey (NOMS)

EPA conducted the National Organic Monitoring Survey (NOMS) in 1976 and 1977, primarily to provide

data for establishing MCLs for organic compounds in drinking water. A substudy of NOMS analyzed

samples for 27 trace elements in the 113 supplies sampled (91 surface water, 19 ground water, 3 mixed

sources) (USEPA, 1980, as cited in Wade Miller, 1990). Chromium data are available for 90 surface

water and 18 ground water supplies. Samples were taken of treated, finished water leaving the treatment

plant; occasionally, samples were taken of distribution system water in close proximity to the treatment

plant. The results of the inorganic analyses for NOMS were provided to SAIC by the Technical Support

Division of EPA's Office of Drinking Water (USEPA, 1985, as cited in Wade Miller, 1990). No

information on the analytical procedures used was available; the minimum quantifiable concentration

appeared to be approximately 0.003 mg/L.
Occurrence Summary and Use Support Document March 2002 47

Chromium was found in 3 of the 18 ground water supplies sampled (17 percent) at concentrations

ranging from 0.0045 to 0.0895 mg/L. Only one supply had a value exceeding the current MCL of 0.05

mg/L. Chromium was not detected in concentrations greater than the proposed MCL of 0.1 mg/L.

For surface water supplies, chromium was observed in 24 of the 90 supplies sampled (27 percent) at

concentrations ranging from 0.0032 mg/L to 0.0522 mg/L. Only one supply had a value exceeding the

current MCL of 0.05 mg/L and none of the concentrations were greater than the proposed MCL of 0.1

mg/L.

2.2.5.2.6 Compliance Monitoring Data

The Federal Reporting Data System (FRDS) provides information on public water supplies in violation

of current MCLs as determined through compliance monitoring of all supplies performed by the States

under the requirements of the National Interim Primary Drinking Water Regulations. Only violations of

current MCLs (i.e., 0.05 mg/L for chromium) and approved variances and exemptions from the standards

are recorded in FRDS. Monitoring is required annually for surface water supplies and every three years

for ground water supplies.

The FRDS database (FRDS, 1990, as cited in Wade Miller, 1990) was searched for ground water

violations reported during the three year period from 1987 through 1989. The data indicate that there are

5 public water supplies providing drinking water having chromium levels above the current MCL of 0.05

mg/L. As summarized in Table 2.2-14, all of those supplies have a ground water source and are in the

very small size categories. Four of the supplies in violation had chromium levels in the range of 0.05 to

0.075 mg/L and the fifth supply reported a value of 0.15 mg/L. No violations were reported for supplies

having a surface water source. Also, no variances or exemptions from the current chromium MCL of

0.05 mg/L have been granted.

Table 2.2-14: National Summary of Chromium Violations in Ground Water Systems

System size 

(population

served)

Unspecified

Concentration

Number of Supplies in Violation by Concentration Range (mg/L):

> 0.05 -

0.075

> 0.075 -

0.1

> 0.1 -

0.125 

> 0.125 -

0.15 > 0.15 Totals

Very Small

25 - 100 0 1 0 0 0 0 1

101 - 500 0 300104

Small

501 - 1,000 0 000000

1,001 - 3,300 0 000000

Medium

3,301 - 10,000 0 000000

Large/Very Large

10,001 - 25,000 0 000000

25,001 - 50,000 0 000000

50,001 - 75,000 0 000000
System size 

(population

served)

Unspecified

Concentration

Number of Supplies in Violation by Concentration Range (mg/L):

> 0.05 -

0.075

> 0.075 -

0.1

> 0.1 -

0.125 

> 0.125 -

0.15 > 0.15 Totals

Occurrence Summary and Use Support Document March 2002 48

75,001 - 100,000 0 000000

>100,000 0 000000

Totals 0 4 0 0 1 0 5

Source: FRDS 1990

2.2.5.3 Results of Survey Data

2.2.5.3.1 Estimated National Occurrence in Public Water Supplies

The preceding sections presented the results of several studies that provide information on the occurrence

of chromium in public drinking water supplies, as reported by Wade Miller (1990). This section presents

national estimates of chromium occurrence in public drinking water supplies based on those study

results. A document entitled Overview of methodology used to estimate national occurrence and

exposure to inorganic drinking water contaminants, describes the methodology used to estimate

chromium occurrence in drinking water (USEPA, 1986, as cited in Wade Miller, 1990).

In general, national survey data (presented in section 2.2.5.2) are used as the basis for the national

estimates. The most representative data sets are selected and combined, stratified appropriately by water

source and system size sampled, and applied to a "delta-lognormal" distribution model. Using that

model, the probability of contaminant occurrence above any given concentration is determined for each

source/size category of supplies and applied to the total number of water supplies in those groups. The

resulting national occurrence estimates are presented in tables that show the number of public water

supplies within various water source and size categories expected to have contaminant levels falling

within certain concentration ranges. Tables are also provided that show the cumulative number of

supplies, by source and size category, expected to exceed certain concentrations. The cumulative

estimates also include upper and lower bounds based on the 95 percent confidence intervals.

The chromium occurrence estimates are based on the results of the NIRS survey for ground water

supplies and the combined results of the 1969 CWSS, the 1978 CWSS, the RWS, and the NOMS for

surface water supplies. The NIRS data were the most current ground water data available at the time of

the study, and the analytical results are considered to be highly reliable because of the extensive quality

assurance program employed. None of the surveys that analyzed surface water supplies could be shown

to be any more or less representative of the universe of water supplies than the other surveys, and it was

therefore determined to be most appropriate to combine the results from all of the surveys to form the

basis of the national occurrence estimates. (There were insufficient details for the 100 Largest Cities

Survey to permit inclusion in the national estimates.)

Table 2.2-15 shows the estimated cumulative number of public ground water supplies, by system size,

having chromium levels exceeding various concentrations. It is estimated that more than 93 percent of

the water supplies have chromium levels below 0.002 mg/L. Because 0.002 mg/L was the minimum

quantifiable concentration for chromium, it is not known whether those supplies are free of chromium or

have chromium present at very low levels.
Occurrence Summary and Use Support Document March 2002 49

Table 2.2-15 indicates that two supplies, both serving small populations, are expected to have chromium

present at levels exceeding both the proposed MCL and MCLG of 0.1 mg/L. The FRDS compliance

data, given in Section 2.2.5.2.6, reported only one ground water supply as having chromium levels above

0.1 mg/L. The supply was listed as serving 200 people with a concentration of 0.15 mg/L chromium.

Table 2.2-15: Estimated Cumulative National Occurrence of Chromium in Community Ground

Water Supplies Based on the Delta Lognormal Distribution Model

System size 

(population served)

Number of 

Systems Sampled

Cumulative Number of Supplies with Concentrations (mg/L) of:

> 0.002 > 0.05 > 0.1 > 0.2

Very Small

25 - 100 17,079 1,216 2 0 0

101 - 500 15,354 1,093 2 0 0

Small

501 - 1,000 5,038 130 5 1 0

1,001 - 3,300 5,185 134 5 1 0

Medium

3,301 - 10,000 2,308 253 0 0 0

Large/Very Large

10,001 - 25,000 823 90 0 0 0

25,001 - 50,000 278 31 0 0 0

50,001 - 75,000 77 8 0 0 0

75,001 - 100,000 17 2 0 0 0

>100,000 43 4 0 0 0

Totals 46,202 2,961 14 2 0

* Number of systems in the United States includes those that purchase water.

Table 2.2-16 provides the national cumulative occurrence estimates for chromium from surface water

supplies. These estimates, based on the combined results of the 1969 CWSS, 1975 CWSS, NOMS and

RWS indicate that zero surface water supplies have chromium levels above the proposed MCL of 0.1

mg/L. This estimate is consistent with the FRDS data which also shows no supplies exceeding the 0.1

mg/L MCL.

It should be noted that the values shown in Tables 2.2-15 and 2.2-16 are rounded to the nearest whole

number. Because they are based on probabilities of occurrence at various concentrations, some partial

probability of occurrence may exist even when the value in the table indicates "0" systems in a particular

size category at or above a given concentration.
Occurrence Summary and Use Support Document March 2002 50

Table 2.2-16: Estimated Cumulative Occurrence of Chromium in Surface Water Supplies Based

on the Delta Lognormal Distribution Model

System size 

(population served)

Number of 

Systems Sampled

Cumulative Number of Supplies with Concentrations (mg/L) of:

> 0.002 > 0.05 > 0.1 > 0.2

Very Small

25 - 100 833 208 2 0 0

101 - 500 779 195 2 0 0

Small

501 - 1,000 754 189 2 0 0

1,001 - 3,300 1,040 260 2 0 0

Medium

3,301 - 10,000 1,156 289 3 0 0

Large/Very Large

10,001 - 25,000 569 142 1 0 0

25,001 - 50,000 328 82 1 0 0

50,001 - 75,000 157 39 0 0 0

75,001 - 100,000 108 27 0 0 0

>100,000 233 59 0 0 0

Totals 5,957 1,490 13 0 0

* Number of systems in the United States includes those that purchase water.

2.2.5.3.2 Estimated National Exposure from Public Water Supplies

The previous section noted that a separate methodology document has been prepared to describe the

approach used to estimate national occurrence of inorganic contaminants in public water supplies. That

document also addresses the approach to estimating the population exposed to contaminant levels in

public drinking water supplies. In summary, the occurrence probability density functions obtained from

the national survey data on supplies contaminated at various levels are applied to the number of people

using water supplies in the various size categories. The results of the population exposed estimates are

presented in tables similar to those in section 2.2.5.3.1 presenting the national occurrence estimates.

Table 2.2-17 presents the population exposed to chromium from ground water supplies exceeding the

current MCL of 0.05 mg/L as reported in FRDS (1990, as cited in Wade Miller, 1990). The data show

that 1,060 people are exposed to chromium at levels exceeding the current MCL of 0.05 mg/L. Of the

1,060 people, 806 are exposed to levels ranging from 0.05 to 0.075 mg/L and an additional 200 people

are exposed to chromium in ground water at levels above 0.1 mg/L. Table 2.2-18 gives the estimated

cumulative population exposed to chromium from ground water systems exceeding various

concentrations. This table indicates that 3,000 people are expected to be exposed to chromium at levels

above the proposed MCL of 0.1 mg/L.
Occurrence Summary and Use Support Document March 2002 51

National cumulative population exposure estimates based on the national survey data for chromium from

surface water supplies are shown in Table 2.2-19. An estimated 20,000 people are expected to be

exposed to chromium levels above the proposed MCL of 0.1 mg/L.

The apparent inconsistency between the estimate in Section 2.2.5.3.1 that there are no surface water

supplies exceeding the proposed MCL of 0.1 mg/L and the estimate here that 20,000 people using surface

water supplies are exposed to levels above this is a result of the application of the probability of

occurrence and exposure derived from the delta-lognormal distribution and applied to the universe of

water supplies and populations using those supplies. In the case of estimating supplies, the numbers are

rounded to the nearest whole number, whereas the population estimates are rounded to the nearest

thousand. Where very small probabilities of occurrence exist, the number of supplies may be rounded to

0, whereas the number of people exposed is rounded to some number greater than 0.

Using a drinking water consumption rate of 2 liters/day, the intake of chromium for an adult at the

proposed MCL is 0.200 mg/day. As indicated above from the national estimates, 23,000 people are

estimated to have an intake of that amount or more from drinking water. Typically, however, exposure to

chromium in drinking water is at levels below 0.002 mg/L, which would contribute less than 0.004

mg/day to chromium intake.

Table 2.2-17: Population Exposed to Chromium at Levels Exceeding the Current MCL in Ground

Water Supplies as Reported in FRDS

System size 

(population served)

Unspecified

Concentration

Number of Supplies in Violation by Concentration Range (mg/L):

> 0.05 -

0.075

> 0.075 -

0.1

> 0.1 -

0.125 

> 0.125 -

0.15 > 0.15 Totals

Very Small

25 - 100 0 40 0 0 0 0 40

101 - 500 0 820 0 0 200 0 1,020

Small

501 - 1,000 0 0 00000

1,001 - 3,300 0 0 00000

Medium

3,301 - 10,000 0 0 00000

Large/Very Large

10,001 - 25,000 0 0 00000

25,001 - 50,000 0 0 00000

50,001 - 75,000 0 0 00000

75,001 - 100,000 0 0 00000

>100,000 0 0 00000

Totals 0 860 0 0 200 0 1,060

Source: FRDS 1990
Occurrence Summary and Use Support Document March 2002 52

Table 2.2-18: Estimated Cumulative Population (in thousands) Exposed to Chromium in Drinking

Water Exceeding the Indicated Concentrations from Community Ground Water Supplies

System size 

(population served)

Number of 

Systems

Sampled

Cumulative Number of Supplies with Concentrations (mg/L) of:

> 0.002 > 0.05 > 0.1 > 0.2

Very Small

25 - 100 950 68 0 0 0

101 - 500 3,850 274 0 0 0

Small

501 - 1,000 3,910 101 4 1 0

1,001 - 3,300 10,000 258 10 2 0

Medium

3,301 - 10,000 13,310 1,461 0 0 0

Large/Very Large

10,001 - 25,000 13,110 1,439 0 0 0

25,001 - 50,000 9,540 1,047 0 0 0

50,001 - 75,000 4,770 524 0 0 0

75,001 - 100,000 1,360 149 0 0 0

>100,000 10,360 1,137 0 0 0

Totals 71,160 6,458 14 3 0

* Number of systems in the United States includes those that purchase water.

Table 2.2-19: Estimated Cumulative Population (in thousands) Exposed to Chromium in Drinking

Water Exceeding the Indicated Concentrations from Community Surface Water Supplies

System size 

(population served)

Number of 

Systems Sampled

Cumulative Number of Supplies with Concentrations (mg/L) of:

> 0.002 > 0.05 > 0.1 > 0.2

Very Small

25 - 100 90 23 0 0 0

101 - 500 570 143 1 0 0

Small

501 - 1,000 1,280 320 3 0 0

1,001 - 3,300 4,330 1,083 10 1 0

Medium

3,301 - 10,000 10,200 2,550 24 1 0
System size 

(population served)

Number of 

Systems Sampled

Cumulative Number of Supplies with Concentrations (mg/L) of:

> 0.002 > 0.05 > 0.1 > 0.2

Occurrence Summary and Use Support Document March 2002 53

Large/Very Large

10,001 - 25,000 12,640 3,160 30 2 0

25,001 - 50,000 15,910 3,978 37 2 0

50,001 - 75,000 10,310 2,578 24 1 0

75,001 - 100,000 10,090 2,523 24 1 0

>100,000 89,240 22,311 210 12 0

Totals 154,660 38,669 363 20 0

* Number of systems in the United States includes those that purchase water.

2.2.6 Conclusion

Chromium and many of its compounds are naturally occurring and found at low levels in soil, water, and

air. Furthermore, chromium compounds are produced in the United States from chromite ore and are in

widespread use. Chromium has a wide range of uses in metals, chemicals, and refractories. Chromium

use in iron, steel, and nonferrous alloys enhances hardenability and resistance to corrosion and oxidation. 

Recent statistics regarding import for consumption indicate production and use are robust. Industrial

releases of chromium and chromium compounds have been reported to TRI since 1988 from 49 of the 50

States. Off-site releases constitute a considerable amount of total releases, with releases to land the most

significant on-site releases. Chromium is also a national NAWQA analyte. Approximately 66% of all

surface water sites had analytical detections of chromium, compared to 0% of ground water sites. No

surface or ground water had any analytical detections of chromium greater than the MCL (0.1 mg/L). 

The Stage 2 analysis, based on the 16-State cross-section, estimated that approximately 0.00424% of

combined ground water and surface water systems serving 0.00139% of the population had estimated

mean concentrations of chromium greater than the MCL of 0.1 mg/L. Based on this estimate,

approximately 3 PWSs nationally serving about 3,000 people are expected to have estimated mean

concentrations of chromium greater than 0.1 mg/L.

Chromium is a naturally occurring element. Therefore, the balanced geographic distribution of the 16-

State cross-section should adequately cover the range of natural occurrence of chromium from low to

high. Fifteen of the 16 cross-section States, excluding Vermont, have reported TRI releases. Based on

this use and release evaluation, the 16-State cross-section appears to adequately represent chromium

occurrence nationally.

2.2.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 2000. Toxicological Profile for

Chromium. U.S. Department of Health and Human Services, Public Health Service. 419 pp. +

Appendices. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp7.pdf

Agency for Toxic Substances and Disease Registry (ATSDR). 2001. ToxFAQs for Chromium. U.S.

Department of Health and Human Services, Public Health Service. Available on the Internet at:

http://atsdr.cdc.gov/tfacts7.html
Occurrence Summary and Use Support Document March 2002 54

Battelle. 1984. Battelle, Pacific Northwest Laboratories. Chemical attenuation rates, coefficients, and

constants in leachate migration. Volume 1: A critical review. Prepared for the Electric Power

Research Institute. Research Project 2198-1.

Brass, H. 1983. U.S. Environmental Protection Agency, Office of Drinking Water, Technical Support

Division, Cincinnati, OH. Personal communication to author of SAIC, 1987.

Brower, B. 1983. Computer data file of analytical results for public water supplies sampled in the Rural

Water Survey. Cornell University, Department of Rural Sociology.

Durfor, C.N., and E. Becker. 1964. Public water supplies of the 100 largest cities in the United States,

1962. U.S. Geological Survey Water Supply Paper 1812. Washington, DC: U.S. Government

Printing Office.

Federal Reporting Data System (FRDS). 1990. Computer file extracts of compliance monitoring data

for the Safe Drinking Water Act.

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at:

http://ca.water.usgs.gov/pnsp/rep/ofr97589/, last updated October 9, 1998. 

Glick, E. 1984. U.S. Environmental Protection Agency, Office of Drinking Water, Technical Support

Division, Cincinnati, OH. Personal communication to author of SAIC, 1987.

McCabe, L.J., J.M. Symons, R.D. Lee, and G.G. Robeck. 1970. Survey of community water supply

systems. Journal of the American Water Works Association. v. 62, no. 9, pp. 670-687. 

Morel, F.M. 1983. Principles of aquatic chemistry. John Wiley and Sons, Inc.

National Library of Medicine (NLM). 2001. NLM Hazardous Substances Data Base Toxicology Data

Network. Available on the Internet at: http://toxnet.nlm.nih.gov/, last updated May 16, 2001.

Science Applications International Corporation (SAIC). 1987. Estimated National Occurrence and

Exposure to Chromium in Public Drinking Water Supplies (Revised Draft).

USEPA. 1979. Water-related environmental fate of 129 priority pollutants. Volume 1. Office of Water

Planning and Standards, USEPA. EPA-440/4-79-029a.

USEPA. 1980. Trace Elements in 113 U.S. Drinking Waters. A substudy of the National Organics

Monitoring Survey. Cincinnati, OH: Technical Support Division, Office of Drinking Water,

USEPA. January, 1980.

USEPA. 1983. Data on inorganics from the Community Water Supply Survey. Provided by E.M. Glick,

Drinking Water Quality Assessment Branch, Technical Support Division, Office of Drinking

Water, USEPA, Cincinnati, OH.
Occurrence Summary and Use Support Document March 2002 55

USEPA. 1985. Computerized listing of inorganics data for the National Organics Monitoring Survey

(NOMS). Provided to Science Applications International Corporation by E.B. Dotson, Water

Supply Technology Branch, Technical Support Division, Office of Drinking Water, USEPA,

Cincinnati, OH. November 12, 1985.

USEPA. 1986. Overview of methodology used to estimate national occurrence and exposure to

inorganic drinking water contaminants (Draft). Prepared by Science Applications International

Corporation for Science and Technology Branch, Office of Drinking Water, USEPA. October

30, 1986. 

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 2001. Mineral Commodity Summaries, January, 2001 - Chromium. Available on the Internet at:

http://minerals.usgs.gov/minerals/pubs/commodity/chromium/180300.pdf.

USPHS. 1970. Community water supply study. Analysis of national survey findings. Bureau of Water

Hygiene, Environmental Health Service, Department of Health, Education, and Welfare.

Wade Miller Associates, Inc. 1990. Occurrence and Exposure Assessment for Chromium in Public

Drinking Water Supplies. Prepared for and submitted to EPA on July 24, 1990.
Occurrence Summary and Use Support Document March 2002 56

2.3 Fluoride

Table of Contents

2.3.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

2.3.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

2.3.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

2.3.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . . 61

2.3.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

2.3.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

2.3.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Tables and Figures

Table 2.3-1: Imports of Fluorspar to the United States (thousand metric tons, gross weight) . . . . . . . . 57

Table 2.3-2: Hydrogen Fluoride Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . . . . 58

Table 2.3-3: Environmental Releases (in pounds) for Fluorine in the United States, 1995-1999 . . . . . 59

Table 2.3-4: Environmental Releases (in pounds) for Hydrogen Fluoride in the 

United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Table 2.3-5: Fluoride Detections and Concentrations in Surface Water and Ground Water . . . . . . . . . 61

Table 2.3-6: Stage 1 Fluoride Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . . 62

Table 2.3-7: Stage 1 Fluoride Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . . 63

Table 2.3-8: Stage 2 Estimated Fluoride Occurrence Based on 16-State Cross-Section - Systems . . . . 65

Table 2.3-9: Stage 2 Estimated Fluoride Occurrence Based on 16-State Cross-Section - Population . . 66

Table 2.3-10: Estimated National Fluoride Occurrence - Systems and Population Served . . . . . . . . . . 67
Occurrence Summary and Use Support Document March 2002 57

2.3.1 Introduction, Use and Production

Fluorine (F), the element, is a pale, yellow-green, irritating gas that has a strong, sharp odor. Because it

is so chemically reactive, it is almost always found naturally combined with metals as a salt. The term

“fluorides” is used to refer to the common salts of the element fluorine, with the most common salts

being sodium fluoride and calcium fluoride. Because toxic effects are due to the fluoride ion, the term

fluoride is most commonly used in discussing health effects and regulations.

Fluorides occur naturally in a variety of geologic settings (for example, in sedimentary and volcanic

rocks) in coal, clay, and certain minerals, and also are found in sea water. Ground water levels of

fluoride are typically higher than surface water levels because their content is influenced more by the

mineral and rock through which they flow (WHO, 1984, as cited in ATSDR, 1993). The biggest natural

source of fluorides released to the air is volcanic eruptions. Although the greatest total volume of

fluorides in the environment is released from natural sources (e.g., volcanoes and oceans), the highest

concentrations are found near anthropogenic point sources related to steel, aluminum, and glass

production.

Fluoride compounds are used in a wide range of industrial and other applications. The steel industry is

the largest consumer of fluorides, followed by the chemical industry and the glass and ceramics industry

(ATSDR, 1993).

In the United States, more than 80% of fluorspar, the primary source of fluorine and its compounds, is

imported (ATSDR, 1993). Fluorspar (a term sometimes used to refer to calcium fluoride) is used directly

or indirectly to manufacture products such as aluminum, gasoline, insulating foams, refrigerants, steel,

and uranium fuel. Byproduct fluorosilicic acid production from some phosphoric acid producers

supplements fluorspar as a domestic source of fluorine, but is not included in fluorspar production or

consumption calculations. The imports originate primarily from China, the Republic of South Africa,

and Mexico (USGS, 2000).

Table 2.3-1: Imports of Fluorspar to the United States (thousand metric tons, gross weight)

Imports For Consumption 1994 1995 1996 1997 1998 1999 

Acid grade 434 470 474 485 462 419

Metallurgical grade 59 88 39 51 41 59

Fluorspar equivalent from

hydrofluoric acid plus cryolite 108 114 131 175 204 192

Source: USGS, 2000

Usage of fluoride compounds are varied, implying potentially widespread environmental release. 

Molecular fluorine has been used as an oxidizer in rocket fuels, in the production of metallics and other

fluorides, and in glass, enamel, and brick production. Currently, molecular fluorine is used by most

manufacturers for the production of various inorganic fluorides. The main use of another fluoride

compound, sodium fluoride, is as a drinking water additive for prevention of dental caries (tooth decay). 

It is also used as a disinfectant for fermentation apparatus in breweries and distilleries, in wood
Occurrence Summary and Use Support Document March 2002 58

preservation, and in rimmed steel manufacturing. Calcium fluoride, the primary compound used by the

fluoride chemical industry, has been used as a flux in steel manufacturing. Other uses are frosting glass

and enamels, coating welding rods, fluoridation of drinking water, paint pigment, and as a catalyst in

wood preservation. Prior to 1930, hydrogen fluoride was used mainly for glass etching and polishing,

foundry scale removal, and minor production of metal fluorides. Other uses include uranium processing,

petroleum alkylation, and stainless steel pickling. A sharp decrease in demand for hydrogen fluoride

occurred in 1978 when the United States prohibited the use of chlorofluorocarbon gases in pressure

packaging (ATSDR, 1993).

Table 2.3-2 shows the number of facilities in each State that manufacture and process hydrogen fluoride,

the intended uses of the product, and the range of maximum amounts derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 1993). Because only certain types of facilities are required to report,

this is not an exhaustive list. Neither sodium fluoride nor any other fluoride salts are listed on TRI.

Table 2.3-2: Hydrogen Fluoride Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on 

site in thousands of poundsb Activities and usesc

AL 5 1-999 3,7,12

AR 1 100-999 7

AZ 8 (1) d 0.1-999 7,11,12,13

CA 60 (6) d 0-49,999 2,3,4,7,8,9,10,11,12,13

CO 6 (1) d 1-99 11,12,13

CT 9 0.1-99 1,5,8,11,12,13

DE 1 10-99 7,8

FL 11 0-999 1,3,5,6,7,12,13

GA 13 (1) d 0.1-999 8,9,11,12,13

HI 2 1-9 12

IA 3 0-99 3,7,9,11,13

ID 2 (1) d 0.1-0.9 1,5,12,13

IL 13 0-999 2,3,4,7,8,9,11,12

IN 14 (2) d 0-999 5,7,8,11,12,13

KS 8 1-9,999 7,10,11

KY 8 (1) d 0-9,999 1,2,3,4,5,7,10,11,12

LA 11 10-9,999 1,2,3,4,5,7,11,12,13

MA 15 0.1-99 8,11,12,13

MD 6 (1) d 1-999 5,11,12

ME 1 10-99 12

MI 12 0.1-9,999 2,7,8,11,12,13

MN 1 100-999 7,13

MO 12 (1) d 0-99 5,7,8,11,12,13

MS 1 1-9 13

MT 5 0-999 1,3,5,11

NC 13 0-99 1,5,7,11,12,13

ND 1 1-9 11

NJ 17 (2) d 0-999 1,2,3,4,5,7,8,10,11,12,13

NM 4 (1) d 0.1-99 11,12,13

NV 1 1-99 2,7

NY 21 (2) d 0-9,999 1,2,5,6,7,10,11,12,13

OH 38 (6) d 0-999 1,2,3,5,7,8,11,12,13

OK 8 (1) d 10-999 1,2,3,7,11,12

OR 8 0.1-999 1,5,11,12,13

PA 48 (2) d 0.1-9,999 2,5,7,8,10,11,12,13
Statea Number of facilities Range of maximum amounts on 

site in thousands of poundsb Activities and usesc

Occurrence Summary and Use Support Document March 2002 59

PR 7 (1) d 1-99 5,11,12,13

RI 3 (1) d 0.1-99 11,12

SC 6 0-999 5,7,11,12,13

TN 8 (1) d 0-9,999 1,3,4,5,6,7,11,12

TX 42 0-49,999 1,2,3,4,5,7,11,12,13

UT 7 0-999 2,3,5,8,11,12,13

VA 3 0-99 5,11,12

VT 1 100-999 12

WA 16 (1) d 0-999 1,5,7,11,12,13

WI 11 0.1-99 9,10,11,12,13

WV 3 0-9 2,5,12

WY 4 (1) d 10-99 5,11

a

Post office State abbreviations used

b

Data in TRI are maximum amounts on site at each facility

c

Activities/Uses include:

1. Produce 8. As a formulation component

2. Import 9. As an article component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

d

Number of facilities reporting “no data” regarding maximum amount of the substance on site

Source: ATSDR, 1993 compilation of 1989 TRI data

2.3.2 Environmental Release

Fluorine and hydrogen fluoride are both listed as Toxics Release Inventory (TRI) chemicals. Table 2.3-3

illustrates the environmental releases for fluorine from 1995 - 1999. (There are only fluorine data for

these years.) Air emissions constitute most of the on-site releases, with a steady increase over the years. 

The increase in air emissions, as well as in surface water discharges, have solely contributed to increases

in fluorine total on- and off-site releases in recent years. No underground injection, releases to land

(such as spills or leaks within the boundaries of the reporting facility), or off-site releases (including

metals or metal compounds transferred off-site) were reported for fluorine. These TRI release data for

fluorine were reported from 14 States and Puerto Rico (USEPA, 2000). Of the 14 States that reported

TRI data, 4 are contained within the 16-State cross-section (used for analyses of fluoride occurrence in

drinking water; see Section 2.3.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.3-3: Environmental Releases (in pounds) for Fluorine in the United States, 1995-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 86,302 54,153 -- -- -- 140,455

1998 81,938 49,857 -- -- -- 131,795

1997 30,091 54,200 -- -- -- 84,291

1996 25,460 48,300 -- -- -- 73,760

1995 18,319 15,000 -- -- -- 33,319

 Source: USEPA, 2000 
Occurrence Summary and Use Support Document March 2002 60

Table 2.3-4 illustrates the environmental releases for hydrogen fluoride between 1988 and 1999. Air

emissions constitute most of the on-site releases, with a moderate fluctuation over the years. No real

trend is suggested in the data. Surface water discharges have also fluctuated since 1988, but have stayed

considerably lower than the high levels observed in 1988. Underground injection and releases to land are

less significant on-site releases, with underground injections sharply decreasing to zero in 1998 after its

5-year long peak between 1993 and 1997. Off-site releases of hydrogen fluoride are considerable. From

1988 to 1998 there has been a general decrease in off-site releases, but in 1999 there was a large increase

in pounds released. The TRI data for hydrogen fluoride data were reported from 49 States and do not

include Alaska or Puerto Rico (USEPA, 2000). All 16 of the cross-section States (used for analyses of

fluoride occurrence in drinking water; see Section 2.3.4) reported releases of hydrogen fluoride. (For a

map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.3-4: Environmental Releases (in pounds) for Hydrogen Fluoride in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 14,434,432 16,983 0 5,353 522,159 14,978,927

1998 15,612,197 23,194 0 12,740 72,358 15,720,489

1997 13,235,977 31,680 2,879 15,047 110,848 13,396,431

1996 13,696,720 10,691 2,620 36,604 167,240 13,913,875

1995 11,616,575 8,702 3,845 24,078 1,020,034 12,673,234

1994 8,901,538 14,989 2,174 33,443 736,747 9,688,891

1993 9,388,840 10,340 3,520 33,260 856,706 10,292,666

1992 11,577,121 3,400 1 27,886 1,269,429 12,877,837

1991 11,345,059 5,469 1 25,259 1,080,205 12,455,993

1990 11,577,926 13,868 25 8,329 1,658,769 13,258,917

1989 13,066,004 35,918 0 10,943 1,398,278 14,511,143

1988 14,732,294 189,928 250 13,002 3,467,471 18,402,945

 Source: USEPA, 2000 

2.3.3 Ambient Occurrence

Fluoride is an analyte for both surface and ground water NAWQA studies, with a method detection limit

(MDL) of 0.1 mg/L. Additional information on analytical methods used in the NAWQA study units,

including method detection limits, is described by Gilliom and others (1998). 

Typical of many inorganic contaminants, fluoride occurrence in ambient surface and ground waters is

common (Table 2.3-5). This is not surprising, considering that the element and its compounds are used

in many products. Significantly, fluoride compounds are used in drinking water treatment. 

Detection frequencies are consistently greater for surface water than for ground water, possibly because

surface waters are more sensitive to anthropogenic releases. Median concentrations are also generally

higher for surface water (median concentration is 0.2 mg/L in surface water and 0.1 mg/L in ground

water). However, fluoride detection frequencies greater than the MCL (4 mg/L) are higher in ground

water, and 99th percentile ground water concentrations are two times larger than corresponding 99th

percentile surface water concentrations. Locally high concentrations in ground water, higher than any
Occurrence Summary and Use Support Document March 2002 61

seen in surface water, are not surprising given the possibility of long contact times between ground water

and rocks enriched in fluoride at a given location. Contact times between surface waters and naturally

occurring fluoride are orders of magnitude shorter, hence concentrations are lower. Furthermore, surface

waters subject to large anthropogenic inputs of fluoride are more easily diluted by waters integrated from

other parts of the watershed, where fluoride concentrations may be lower. 

Table 2.3-5: Fluoride Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 > MDL* 

Detection frequency

 > MCL*

Concentration percentiles

(all samples; mg/L) 

% samples % sites % samples % sites median 99th

surface water 65.7 % 69.0 % 0.02 % 0.05 % 0.2 1.3

ground water 60.3 % 67.0 % 0.4 % 0.5 % 0.1 2.6

* The Method Detection Limit (MDL) for fluoride in water is 0.1 mg/L and the Maximum Contaminant Level (MCL) is 4.0 mg/L. 

2.3.3.1 Additional Ambient Occurrence Data

A summary document entitled “Occurrence of Fluoride in Drinking Water, Food, and Air” (JRB

Associates, 1984), was previously prepared for past USEPA assessments of fluoride. However, no

information on the ambient occurrence of fluoride was included in that document. (The document did

include information regarding fluoride occurrence in drinking water, which is discussed in Section 2.3.5

of this report.)

2.3.4 Drinking Water Occurrence Based on the 16-State Cross-Section

Fluoride is unique as a drinking water constituent in that there are both a MCL to limit levels in drinking

water to protect the public from the adverse effects of fluoride, and a recommended Optimum Level for

protection against dental caries. A number of drinking water systems achieve the Optimum Level by the

addition of fluoride during the drinking water treatment process. The recommended optimum level

ranges from 0.7 mg/L for warmer climates to 1.2 mg/L for cooler climates. The current MCL of 4 mg/L

was promulgated by EPA in 1986. At the same time, a National Secondary Drinking Water Regulation

(NSDWR) was promulgated, establishing a Secondary Maximum Contaminant Level (SMCL) of 2.0

mg/L. (The SMCL was based upon the finding that a 2.0 mg/L concentration of fluoride in drinking

water would be protective against dental decay while preventing the majority of cases of water-related

dental fluorosis which is cosmetically objectionable.) 

The analysis of fluoride occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. Fluoride occurrence in

drinking water was assessed relative to several concentration thresholds of interest: 4 mg/L; 3 mg/L; 2

mg/L; 1.5 mg/L; 1.2 mg/L; 0.7 mg/L; 0.5 mg/L; and 0.1 mg/L. 
Occurrence Summary and Use Support Document March 2002 62

All sixteen cross-section State data sets contained occurrence data for fluoride. These data represent

more than 93,000 analytical results from approximately 21,000 PWSs during the period from 1983 to

1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs vary by

State, although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limit for fluoride in the 16 cross-section States is equal to 0.1

mg/L. (For details regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)

2.3.4.1 Stage 1 Analysis Occurrence Findings

The percentage of systems indicates the proportion of systems (or population served by systems) with

any analytical results exceeding the specified threshold of concern. Table 7 illustrates the Stage 1

analysis of fluoride occurrence in drinking water for the public water systems in the 16-State crosssection. The percentage of total ground and surface water PWSs with at least one analytical result

exceeding the MCL (4 mg/L) was equal to 1.28% (266 systems). Approximately 4.45% of total ground

and surface water systems (925 systems) had any analytical results greater than the 1⁄2 MCL (2 mg/L). 

Over 74.1% of PWSs (15,414 systems) had at least one analytical result greater than 0.1 mg/L (the modal

detection limit for fluoride).

Table 2.3-6: Stage 1 Fluoride Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Ground Water

4 1.26% 243

3 2.26% 434

2 4.51% 867

1.5 7.41% 1,424

1.2 10.7% 2,062

0.7 23.3% 4,475

0.5 31.1% 5,980

0.1 73.7% 14,164

Surface Water

4 1.44% 23

3 2.00% 32

2 3.64% 58

1.5 7.03% 112

1.2 15.6% 249

0.7 44.8% 713

0.5 50.4% 803

0.1 78.5% 1,250

Combined Ground &

Surface Water

4 1.28% 266

3 2.24% 466
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 63

2 4.45% 925

1.5 7.38% 1,536

1.2 11.1% 2,311

0.7 24.9% 5,188

0.5 32.6% 6,783

0.1 74.1% 15,414

Reviewing fluoride occurrence in the 16 cross-section States by PWS population served (Table 2.3-7)

shows over 4.56% of the total population (over 4.8 million people) was served by PWSs with at least one

analytical result greater than the MCL. Approximately 6.76% of the population served by all systems

(about 7.2 million people) had any analytical results greater than the 1⁄2 MCL. More than 93.5% of the

population (over 100 million people) was served by PWSs with analytical detections of fluoride greater

than 0.1 mg/L.

Table 2.3-7: Stage 1 Fluoride Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold 

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population 

Served by Systems

Exceeding Threshold

Ground Water

4 3.84% 1,685,400

3 5.29% 2,323,400

2 8.06% 3,539,100

1.5 12.2% 5,362,200

1.2 21.3% 9,363,800

0.7 52.5% 23,069,200

0.5 62.4% 27,432,700

0.1 93.0% 40,839,200

Surface Water

4 5.06% 3,195,800

3 5.09% 3,213,800

2 5.86% 3,700,100

1.5 9.34% 5,894,600

1.2 15.7% 9,921,200

0.7 62.4% 39,421,200

0.5 66.6% 42,022,900

0.1 93.9% 59,262,900
Source Water Type Threshold 

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population 

Served by Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 64

Combined Ground &

Surface Water

4 4.56% 4,881,200

3 5.17% 5,537,200

2 6.76% 7,239,200

1.5 10.5% 11,256,800

1.2 18% 19,285,000

0.7 58.4% 62,490,400

0.5 64.9% 69,455,600

0.1 93.5% 100,102,100

2.3.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 2.3-8 and 2.3-9. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

Approximately 106 (ground water and surface water) PWSs in the 16-State cross-section (0.511%) are

estimated to have mean concentrations of fluoride above 4 mg/L (the current MCL). Approximately 603

(2.90% of) PWSs in the 16 States are estimated to have mean concentrations greater than 2 mg/L. The

percentage of PWSs in the 16 States with estimated mean concentrations exceeding 0.1 mg/L (the modal

detection limit) was about 82.2% (17,098 PWSs).

A significantly greater proportion of ground water systems, as compared to surface water systems, was

estimated to exceed each threshold. Approximately 106 ground water systems in the 16-State crosssection (0.550%) had estimated mean concentrations of fluoride above 4 mg/L, compared to

approximately 1 surface water system (0.0491%). About 3.05% of ground water systems (an estimated

586 systems in the 16 States) had estimated mean concentrations greater than 2 mg/L. This compares

with about 1.11% of the surface water systems (about 18 systems) with estimated mean concentrations

greater than 2 mg/L. The estimated mean concentration values for approximately 15,846 ground water

PWSs in the 16 States (82.5%) exceed 0.1 mg/L. Approximately 1,251 surface water systems in the 16

States (78.6%) had estimated mean concentrations exceeding the modal detection limit.
Occurrence Summary and Use Support Document March 2002 65

Table 2.3-8: Stage 2 Estimated Fluoride Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

4 0.550% 0.469% - 0.635% 106 90 - 122

3 1.20% 1.07% - 1.33% 230 205 - 255

2 3.05% 2.85% - 3.23% 586 547 - 621

1.5 5.55% 5.29% - 5.78% 1,066 1,017 - 1,110

1.2 8.54% 8.24% - 8.80% 1,640 1,583 - 1,691

0.7 19.8% 19.4% - 20.2% 3,804 3,729 - 3,875

0.5 29.3% 28.8% - 29.7% 5,619 5,540 - 5,702

0.1 82.5% 82.1% - 82.9% 15,846 15,769 - 15,925

Surface Water

4 0.0491% 0.000% - 0.188% 1 0 - 3

3 0.193% 0.000% - 0.377% 3 0 - 6

2 1.11% 0.691% - 1.51% 18 11 - 24

1.5 3.91% 3.08% - 4.77% 62 49 - 76

1.2 9.37% 8.22% - 10.5% 149 131 - 167

0.7 30.2% 29.0% - 31.3% 481 462 - 499

0.5 39.6% 38.6% - 40.6% 631 615 - 646

0.1 78.6% 77.4% - 79.9% 1,251 1,233 - 1,272

Combined Ground

& Surface Water

4 0.511% 0.437% - 0.591% 106 91 - 123

3 1.12% 1.01% - 1.23% 233 209 - 256

2 2.90% 2.72% - 3.08% 603 566 - 640

1.5 5.42% 5.19% - 5.63% 1,128 1,079 - 1,172

1.2 8.60% 8.32% - 8.89% 1,789 1,730 - 1,849

0.7 20.6% 20.2% - 21.0% 4,283 4,208 - 4,358

0.5 30.0% 29.7% - 30.5% 6,249 6,170 - 6,337

0.1 82.2% 81.8% - 82.6% 17,098 17,017 - 17,177

Reviewing fluoride occurrence by PWS population served (Table 2.3-9) shows that approximately

96,000 (0.0897% of) the PWS population in the 16-State cross-section were served by systems with mean

fluoride concentrations above 4 mg/L. When evaluated relative to a threshold of 2 mg/L, the percent of

population exposed increased significantly to about 0.929% (about 994,600 people served in the 16

States). The percentage of population served by PWSs with estimated mean concentrations greater than

0.1 mg/L was approximately 89.4% (almost 96 million people).
Occurrence Summary and Use Support Document March 2002 66

For ground water systems, about 91,300 people in the 16 States (0.208% of the population served by

ground water systems) were served by systems with estimated mean concentrations of fluoride above 4

mg/L. An estimated 1.68% of the 16-State population (approximately 736,800 people) were served by

ground water systems whose mean concentration value exceeded 2 mg/L. The percentage of population

served by ground water PWSs with estimated mean concentration values exceeding 0.1 mg/L was

approximately 90.4% (almost 40 million people).

Approximately 0.00754% (about 4,800 people) of the population served by surface water PWSs in the

16-State cross-section were served by systems with an estimated mean concentration of fluoride above 4

mg/L. About 0.408% (about 257,800 people) of the population served by surface water PWSs were

served by systems with mean concentrations greater than 2 mg/L. Over 56 million people in the 16

States (88.7%) were served by PWSs with mean fluoride concentrations above 0.1 mg/L. The percentage

of population served by surface water systems that exceeded each threshold was generally always less

than the percentage of ground water systems that exceeded the threshold (except greater than 0.7 mg/L). 

However, the total population served by systems estimated to exceed each threshold was much greater

for surface water systems for thresholds less than 1.5 mg/L. 

Table 2.3-9: Stage 2 Estimated Fluoride Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

in the 16 States Estimated to Exceed

Threshold

Total Population served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

4 0.208% 0.131% - 0.314% 91,300 57,400 - 137,900

3 0.556% 0.393% - 0.771% 244,100 172,400 - 338,800

2 1.68% 1.35% - 2.04% 736,800 594,400 - 896,300

1.5 3.52% 2.87% - 4.18% 1,545,600 1,261,800 - 1,836,500

1.2 6.51% 5.59% - 7.57% 2,858,000 2,455,500 - 3,325,000

0.7 24.6% 20.8% - 27.4% 10,825,500 9,151,600 - 12,042,500

0.5 40.1% 38.3% - 42.0% 17,613,500 16,844,600 - 18,461,400

0.1 90.4% 89.6% - 91.3% 39,730,300 39,361,200 - 40,108,100

Surface Water

4 0.00754% 0.000% - 0.0687% 4,800 0 - 43,300

3 0.0400% 0.000% - 0.175% 25,300 0 - 110,300

2 0.408% 0.130% - 1.44% 257,800 81,800 - 908,600

1.5 1.92% 0.961% - 3.41% 1,212,900 606,900 - 2,153,100

1.2 5.59% 3.55% - 8.41% 3,527,700 2,244,000 - 5,309,500

0.7 28.3% 25.6% - 30.9% 17,837,300 16,189,300 - 19,491,600

0.5 37.8% 35.4% - 41.1% 23,892,500 22,364,500 - 25,938,300

0.1 88.7% 85.5% - 92.5% 56,012,300 53,953,900 - 58,392,700
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

in the 16 States Estimated to Exceed

Threshold

Total Population served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 67

Combined Ground &

Surface Water

4 0.0897% 0.0555% - 0.141% 96,000 59,400 - 151,300

3 0.252% 0.169% - 0.36% 269,400 181,000 - 387,300

2 0.929% 0.707% - 1.55% 994,600 756,600 - 1,655,400

1.5 2.58% 1.96% - 3.46% 2,758,300 2,093,300 - 3,707,000

1.2 5.96% 4.61% - 7.64% 6,384,900 4,937,300 - 8,179,500

0.7 26.8% 24.3% - 28.8% 28,664,200 26,040,800 - 30,837,800

0.5 38.8% 37.1% - 40.9% 41,502,600 39,671,600 - 43,794,000

0.1 89.4% 87.4% - 91.6% 95,736,400 93,573,500 - 98,102,800

2.3.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold (Table 2.3-10), an estimated 332 PWSs serving approximately 191,000 people nationally could

be exposed to fluoride concentrations above 4 mg/L. About 1,885 systems serving almost 2 million

people had estimated mean concentrations greater than 2 mg/L. Approximately 53,448 systems serving

over 190 million people nationally were estimated to have fluoride concentrations greater than 0.1 mg/L. 

(See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 327 PWSs serving about 178,000 people nationally had mean

concentrations greater than 4 mg/L. Approximately 1,812 ground water systems serving about 1.4

million people nationally had estimated mean concentration values that exceeded 2 mg/L. About 49,032

ground water systems serving over 77 million people had estimated mean concentrations greater than 0.1

mg/L. 

Three surface water systems serving 9,600 people were estimated to have mean concentrations of

fluoride above 4 mg/L. An estimated 62 surface water systems serving 519,900 people had estimated

mean concentrations greater than 2 mg/L. An estimated 4,392 surface water systems serving almost 113

million people had mean concentrations greater than 0.1 mg/L.

Table 2.3-10: Estimated National Fluoride Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems Nationally

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

4 327 278 - 378 178,000 112,000 - 268,900

3 711 634 - 789 476,000 336,300 - 660,800

2 1,812 1,692 - 1,922 1,436,900 1,159,300 - 1,747,900

1.5 3,297 3,147 - 3,434 3,014,300 2,460,800 - 3,581,500
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems Nationally

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 68

1.2 5,076 4,898 - 5,233 5,573,600 4,788,700 - 6,484,400

0.7 11,769 11,537 - 11,989 21,112,000 17,847,500 - 23,485,400

0.5 17,386 17,142 - 17,642 34,349,800 32,850,400 - 36,003,400

0.1 49,032 48,794 - 49,276 77,482,000 76,762,200 - 78,218,800

Surface Water

4 3 0 - 11 9,600 0 - 87,400

3 11 0 - 21 51,000 0 - 222,400

2 62 39 - 84 519,900 164,900 - 1,832,200

1.5 219 172 - 267 2,445,900 1,223,900 - 4,341,800

1.2 524 460 - 586 7,113,700 4,525,200 - 10,706,900

0.7 1,688 1,621 - 1,751 35,969,700 32,646,500 - 39,305,700

0.5 2,213 2,158 - 2,267 48,180,300 45,099,000 - 52,305,700

0.1 4,392 4,327 - 4,464 112,951,300 108,800,500 - 117,751,500

Combined Ground &

Surface Water

4 332 284 - 385 191,000 118,200 - 301,000

3 728 654 - 801 535,900 360,000 - 770,500

2 1,885 1,769 - 2,000 1,978,600 1,505,100 - 3,293,100

1.5 3,526 3,373 - 3,664 5,487,100 4,164,300 - 7,374,300

1.2 5,594 5,408 - 5,780 12,701,700 9,821,800 - 16,271,700

0.7 13,390 13,156 - 13,624 57,022,300 51,803,600 - 61,346,400

0.5 19,535 19,288 - 19,808 82,562,000 78,919,500 - 87,120,300

0.1 53,448 53,195 - 53,695 190,450,600 186,147,900 - 195,158,100

2.3.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of fluoride in drinking water are also reviewed. 

A preliminary comparison of the Stage 2 model findings to MCL violation records in SDWIS/FED was

conducted. The Stage 2 occurrence estimates for fluoride were also compared to fluoride occurrence

findings reported in the CDC Fluoridation Census 1992. Previously compiled occurrence information,

from an OGWDW summary document entitled “Occurrence of Fluoride in Drinking Water, Food, and

Air” (JRB Associates,1984), is presented in Sections 2.3.5.3 - 2.3.5.8. This variety of studies and

information are presented regarding levels of fluoride in drinking water, with the scope of the reviewed

studies ranging from national to regional. (All the information in Sections 2.3.5.3 - 2.3.5.8 is taken

directly from “Occurrence of Fluoride in Drinking Water, Food, and Air” (JRB Associates,1984).) Note

that none of the studies presented in the following section provide the quantitative analytical results or

comprehensive coverage that would enable direct comparison to the occurrence findings estimated with

the cross-section occurrence data presented in Section 2.3.4. These additional studies, however, do

enable a broader assessment of the Stage 2 occurrence estimates presented for this Six-Year Review.
Occurrence Summary and Use Support Document March 2002 69

2.3.5.1 SDWIS/FED Comparison

A preliminary comparison of Stage 2 model findings to MCL violation records in the Safe Drinking

Water Information System (SDWIS) was conducted. Due to many qualifying factors, this must be

regarded as a very general, indirect comparison. A primary reason inhibiting a direct comparison is the

somewhat incomplete State reporting to the SDWIS database over the time frame of interest (roughly

1993-1999). Also, the method for calculating a contaminant’s concentration in a system is somewhat

different for the Stage 2 analysis as compared to MCL violation determinations. A brief description of

some key topics related to MCL compliance information is presented below to provide background on

SDWIS MCL violation data. 

For systems that monitor more frequently than annually, compliance with the MCL is determined by a

running annual average of results from all samples taken at each sampling point. If this contaminant

mean concentration exceeds the MCL, then the system is out of compliance. For systems that monitor

annually or less frequently, if the level of a contaminant at any sampling point exceeds the MCL, the

system is out of compliance with the MCL. 

More systems have MCL exceedances than actual MCL violations. A system with an MCL violation

always has an MCL exceedance. However, a system with an MCL exceedance may not always incur an

MCL violation. For example, if a system on quarterly monitoring has one quarter in which the

concentration is above the MCL, but the running annual average of this high sample result and the three

preceding quarters are below the MCL, the system would have an MCL exceedance but not an MCL

violation. Also, if the State requires a confirmation sample, compliance with the MCL is calculated

using the average of the routine and confirmation sample. If the average is below the MCL, the system

would have an exceedance but not an MCL violation.

Many States experienced delays in implementation of the Phase II/V rule. In some cases, approval of

State primacy took many years. Laboratory capacity, resource and staffing levels, and waivers were

recurring issues. States are required to report MCL violations to SDWIS. However, delays in

determining MCL violations and reporting them to SDWIS were commonplace. States had to create new

databases or modify existing databases for Phase II/V compliance tracking and reporting. As a result,

many States had delays in reporting chemical violation data to SDWIS. Underreporting of violations for

chemicals may still be an issue for some States. SDWIS has the capability of storing data on MCL

exceedances; however, reporting of these is optional.

When comparing the modeled national occurrence estimates to the SDWIS MCL violation data, one must

also consider the different time frames at hand. The SDWIS MCL violation data are roughly from 1993-

1999. The Stage 2 estimate is based on compliance monitoring analytical results predominantly between

1992 and 1997. (Potentially more than five years of monitoring results are used to estimate a single

system mean concentration). The Stage 2 estimated number of systems with a mean concentration

greater than the MCL (based on data for many years) is an approximation of, though not directly

comparable to, the number of SDWIS MCL violations for a single year. 

Approximately 247 PWSs reported MCL violations to SDWIS/FED between January 1, 1993 and

December 31, 1999. The Stage 2 analysis estimated that approximately 332 PWSs nationally had mean

concentrations of fluoride greater than the MCL (See Table 2.3-10). (The Stage 2 estimate is based on

compliance monitoring analytical results predominantly between 1992 and 1997. Potentially more than

five years of monitoring results are used to estimate a single system mean concentration). Based on the

qualifying factors described above, it is not surprising that the Stage 2 estimates are higher than the

reported SDWIS MCL violations. Even given the inherent differences between the SDWIS MCL
1

 The optimum amount of fluoride in drinking water at PWSs is the range of fluoride that assists in the prevention of dental cavities. The

specific optimum level of fluoride for a given PWS is generally inversely proportional to temperature. It is assumed that individuals drink more

water in warmer climates and higher temperatures. The ingestion of fluoride via drinking water is directly related to the volume of water

consumed. Therefore, since high temperatures result in consumption of higher volumes of water, the amount of fluoride considered optimal is at

the low end of the optimal range (0.7 mg/L) in warmer regions (or warmer seasons) and at the high end of the optimum range (1.2 mg/L) in

cooler regions (or cooler seasons). For example, the optimum level of fluoride for PWSs in southern Florida is 0.7 mg/L and for PWSs in Maine

is 1.2 mg/L. The “control range” recommended by CDC for the optimum concentration is 0.1 mg/L below to 0.5 mg/L above the optimum. 

Occurrence Summary and Use Support Document March 2002 70

violation records and the Stage 2 analytical findings measured relative to the MCL, the comparison

between the two assessments of occurrence are quite comparable, providing additional measures that

suggest a validation of the Stage 2 modeling approach.

2.3.5.2 Centers for Disease Control and Prevention Fluoridation Census

This section provides a general comparative assessment between the Six-Year Review’s Stage 2 national

fluoride occurrence estimates (based on the 16-State national cross-section) primarily with public water

system fluoridation findings reported in the Centers for Disease Control and Prevention (CDC)

Fluoridation Census 1992 (CDC, 1992) as well as with findings provided by CDC staff from the

unpublished Fluoridation Census 2000 (CDC, 2002). A rigorous and direct comparison cannot be made

between the CDC Fluoridation Census 1992 (or 2000) findings and the EPA-OGWDW’s Six-Year

Review statistical model estimations. The CDC census findings report the voluntary provision of

qualitative/semi-quantitative information from public drinking water systems that identify if a particular

system is operating as a fluoridating system (with either natural or “adjusted” concentrations of fluoride

within the optimum range of fluoride). The OGWDW Six-Year Review Stage 2 findings are

quantitative, parametric statistical estimations of fluoride occurrence based on compliance monitoring

analytical results of fluoride concentrations in public drinking water systems from the 16-State crosssection (with the results from the 16-State cross-section then extrapolated to national occurrence

estimates). 

Despite the significant differences in the underlying sources of fluoride occurrence information, the

comparison between the CDC and OGWDW Stage 2 findings is informative. The comparison suggests

that the Stage 2 modeled national estimates are valid, broadly reflecting and correlating with the general

fluoride concentrations implied by the fluoridation census findings when considering details of the

differences between the census and statistical estimation approaches. Details of the comparative

assessment are included below. 

The CDC periodically conducts a national fluoridation census which records the total national number of

public water systems, and population served by those systems, that operate with natural or adjusted levels

of fluoride in drinking water at optimum levels. The “optimum range” of fluoride in drinking water

(regarding prevention of dental cavities) is from 0.7 mg/L to 1.2 mg/L (although a system can be

considered to be operating as a fluoridating system if it operates within the broader “control range” of

fluoride concentrations from 0.6 mg/L to 1.7 mg/L)1

. To complete the fluoridation census, States

voluntarily report: the name, location, and public water system identification number of each fluoridated

water system; the population served by each system; whether the system operates with adjusted, or

natural, levels of fluoride; the chemical used for fluoridation, if adjusted; and whether or not the system

purchased water. However, no quantitative analytical results are presented, no information is provided

for systems with fluoride occurrence less than 0.7 mg/L (the low end of the optimum range), and the

source water type is not specified. Therefore, the implication is that all systems that reported as

fluoridating (i.e., allsystemslisted in the CDC census) are considered for comparison purposes to have a

minimum (average) fluoride concentration of 0.7 mg/L, the low end of the optimum fluoridation range.
2

 The system and population totals listed here are equal to the exact system and population summations of the 50 States. These total sums do

not equal the sums presented in the CDC Fluoridation Census 1992, in part due to the inclusion of the District of Columbia.

Occurrence Summary and Use Support Document March 2002 71

Table VI.J.1.a shows a comparison between the quantitative results based on the 16-State cross-section

data and the qualitative reported findings of the CDC Fluoridation Census 1992 and the unpublished

CDC Fluoridation Census 2000. The table specifically presents the Stage 2 modeled estimates based on

the Six-Year Review 16-State cross-section compared to the number of fluoridating systems (and

population served by those systems) as reported to the CDC. 

Table VI.J.1.a. Comparison of the National Extrapolations of the Stage 2 Modeled Estimates with

the CDC Fluoridation Census Findings 

Stage 2 Modeled Estimates based on 

Compliance Monitoring Results of the 

16-State Cross-Section

CDC Fluoridation Census

1992 and unpublished 

2000 1

 Findings

Fluoride

Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems 

Nationally Estimated to 

Exceed Threshold

Total 

Number of

Systems

Fluoridating

Total Population

Served by

Systems

Fluoridating Best Estimate Range Best Estimate Range

4 332 284 - 385 191,000 118,200 - 301,000 145 1 152,527 1

2 1,885 1,769 - 2,000 1,978,600 1,505,100 - 3,293,100 746 1 849,591 1

0.7 13,390 13,156 - 13,624 57,022,300 2 51,803,600 - 61,346,400 2 14,496 3 141,107,164 3 

For a summary of how the Stage 2 modeled estimations are derived, please refer to Section 1.4 of this report. For a detailed description of the

Stage 2 method estimations, please refer to Occurrence Estimation Methodology and Occurrence Findings Report For Six-Year Review of 

National Primary Drinking Water Regulations, EPA-815-D-02-005, March 2002. 

1. The number of systems and population-served by systems with reported fluoride concentrations greater than 2 mg/L and 4 mg/L were

provided by the CDC from the unpublished Fluoridation Census 2000. (These measures of fluoride occurrence relative to these specific fluoride

thresholds are not included in the 1992 or earlier census publications.) 

2. There were no compliance monitoring records for fluoride for the Chicago Water System in the State of Illinois’ compliance monitoring data

set. Therefore, since Illinois is one of the states in the 16-state cross-section and the Chicago Water System is known to fluoridate, the Stage 2

modeled estimates presented here do not reflect the population served by the fluoridated water provided by the Chicago Water System (and its

consecutive systems). (The Chicago Water System fluoride were requested, but were received after the Stage 2 modeled estimates were

generated for this draft report.) 

3. This estimate includes public water systems that operate within the “control range” of optimum fluoride concentrations. Therefore, this

estimate includes systems that maintain fluoride concentrations as low as 0.6 mg/L while the Stage 2 model estimates are based on the 0.7 mg/L

fluoride concentration values which is the low end of the optimum (rather than control) range.

The CDC Fluoridation Census 1992 indicates that a total of 14,496 public water systems, serving

141,107,164 people, report that they operate as a fluoridated system2

. In comparison, the Stage 2

national occurrence estimates based on the 16-State cross-section indicate a total of 13,390 systems,

serving 57,022,300 people, with estimated mean concentrations of fluoride greater than 0.7 mg/L. (For a

detailed presentation of Stage 2 modeled estimations of fluoride occurrence, please refer to Appendix C,

Tables C.16.f and C.16.n). A system with a mean concentration of fluoride greater than 0.7 mg/L is

approximately equivalent to a “fluoridated” system (in the CDC census) that reports operation at

optimum fluoride levels, though systems are included in the CDC census as fluoridating if systems

operate within the broader control range and above 0.6 mg/L fluoride.
Occurrence Summary and Use Support Document March 2002 72

The differences between the national estimates for fluoridating systems (CDC–14,496 PWSs and national

cross-section–13,390 PWSs) and population served by fluoridating systems (CDC–141,107,164 people

and national cross-section–57,022,300 people) appear to relate to several factors. First, the lack of

fluoride occurrence data from the Chicago Water System certainly results in an underestimate for the

model estimated number of systems, and population served by those systems. (Fluoride data for Chicago

were not included in the original compliance monitoring data sets obtained directly from the state of

Illinois. Fluoride compliance monitoring data are reported to the state’s public health agency. These

fluoride data were subsequently requested, but were received after the Stage 2 estimations prepared for

this draft report.)

The size distribution of fluoridating systems (based on population served size categories) is a second

factor influencing the difference in population served between the State data and the CDC census data. 

Table VI.J.1.b illustrates the distribution of fluoridating systems based on six population served size

categories. Although the number of systems serving 1,000 people or less is similar in the State data and

CDC data (2,824 and 2,540 respectively), this equals a much larger percentage of the smallest systems in

the cross-section data set (66%) than are represented in the CDC census (only 42%). Therefore, the

cross-section data set (comprised of compliance monitoring data records acquired directly from the

States) has a proportionately larger amount of the smallest systems than does the CDC census (based on

voluntary reporting of which systems fluoridate). This differing system size profile can result in a

smaller population served by a similar number of systems (as is the case for the national extrapolations

based on the cross-section data).

Table VI.J.1.b. Distribution of Fluoridating Systems in the 16 Cross-Section States and the CDC

Fluoridation Census 1992 

Population

Served

Number of Systems

that Fluoridate -

State Data 1

Percent of State

 Total Number of

Fluoridating

Systems

Number of Systems

that Fluoridate -

CDC Data 2

Percent of CDC

 Total Number of

Fluoridating

Systems

# 1,000 2,824 66% 2,540 42%

1,001 - 5,000 750 18% 1,983 33%

5,001 - 10,000 244 6% 578 10%

10,001 - 50,000 347 8% 716 12%

50,001 - 100,000 54 1% 103 2%

> 100,000 42 1% 79 1%

Total 4,261 100% 5,999 100%

1. The State data results of “number of systems that fluoridate” are derived by using the cross-section data, calculating a simple arithmetic mean

fluoride concentration for each system in a particular population served system size category, and then counting all systems with a mean

concentration greater than 0.7 mg/L (which represents the low end of the range of optimum fluoride concentration for fluoridation).

2. CDC “number of systems that fluoridate” are derived from qualitative reported findings of the CDC 1992 Fluoridation Census.

A third factor influencing the system number and population differences between the CDC and national

cross-section estimates relates to systems that report as “fluoridated systems.” In the CDC Fluoridation

Census 1992, systems that operate within the control range (of optimum fluoride concentration) of 0.6

mg/L and 1.7 mg/L are considered to fluoridate. The Stage 2 statistical estimations and related national

extrapolations were based on a fluoride concentration threshold of 0.7 mg/L (the low end of the
Occurrence Summary and Use Support Document March 2002 73

optimum, not the control, range of fluoride levels). Therefore, the Six-Year Review Stage 2 estimates of

systems with estimated mean concentrations of fluoride greater than 0.7 mg/L will likely be lower the

CDC census number of systems reporting to operate within the control range (between 0.6 mg/L and 1.7

mg/L fluoride). 

Other factors relate to the type of systems included in EPA’s Six-Year Review and the CDC fluoridation

census. The Six-Year Review, based on compliance monitoring, does not include analytical results for

consecutive systems. Because consecutive systems compliance monitoring requirements are at the

discretion of the individual States, the consecutive system compliance monitoring record is not uniform

from state to state. Therefore, systems identified as consecutive (or, synonymously, as “purchased”)

were removed in the raw data sets prior to Stage 2 estimations. The CDC fluoridation census does

include consecutive systems. (CDC estimates that there may be approximately 1,696 consecutive

systems serving a population of 12,850,000 in the 16 states that comprise the 16-State cross-section used

in this Six-Year Review analysis.) Also, while the Six-Year Review 16-State cross-section (compliance

monitoring) data does include monitoring results from non-transient non-community water systems

(NTNCWSs), the CDC does not include NTNCWs in the fluoridation census.

In summary, given the differences between the CDC census numbers and the EPA model estimates, 

rigorous and systematic comparisons cannot be directly made between the two assessments of fluoride

occurrence in public water systems. However, general comparisons suggest that the EPA Six-Year Stage

2 modeling approach is valid in that it tracks relatively closely to CDC voluntarily reported qualitative

census findings. These comparisons are closer still when the underlying differences between the CDC

census findings and the Six-Year Review model estimates are considered. 

The comparison of the number of systems estimated by the Six-Year model to have an estimated mean

fluoride concentration greater than 0.7 mg/L compared to the number of systems reporting to the CDC

census as fluoridating exhibits the largest difference between the two fluoride occurrence assessments. 

However, the two differing estimates are likely much closer when considering that: the CDC fluoridating

systems include systems operating with the “control range” (as low as 0.6 mg/L); the Six-Year Review

estimates did not have data for the Chicago Water System, and; the Six-Year Review estimates generally

do not include systems considered to be “consecutive” (or purchasing water). 

The comparison between the Six-Year Review model estimates and the unpublished 2000 Census

numbers for systems with fluoride concentrations above 2 mg/L and 4 mg/L are generally good. For

example, relative to 4 mg/L, the Six-Year Review model estimates are not dramatically higher than the

CDC estimates, especially when comparing the total population served. The EPA system numbers are

modeled estimates, and therefore, it is appropriate to consider the estimated range of results rather than

the single “best estimate.” The modeled estimates indicate that from 118,200 people to 301,000 people

could be served by systems with a mean fluoride concentration greater than 4 mg/L. The CDC estimate

(of approximately 153,000 people) falls into this range. The other comparisons with the unpublished

2000 CDC census findings, while not within the statistical model estimate ranges, are relatively similar

(not orders of magnitude apart) given the differences between the two (CDC and EPA) sources of

information/data. The differences in hundreds of systems or hundreds of thousands of population served

by systems can be interpreted as somewhat close when considered relative to the total US population or

the total US population served by fluoridated water. 
Occurrence Summary and Use Support Document March 2002 74

2.3.5.3 1969 Community Water Supply Study

The U.S. Public Health Service (USPHS) conducted a Community Water Supply Study (CWSS) in 1969

to assess the status of the nation's water supply facilities and drinking water quality (USPHS 1970b, as

cited in JRB Associates,1984). Finished water from a total of 969 community supplies in nine

geographically distributed areas were studied. Except for the State of Vermont (in which all supplies

were sampled), the study locations were standard metropolitan statistical areas (SMSAs). Water samples

were reported to have been taken at various places in the distribution system of each supply studied. Of

the 969 systems, 678 were groundwater supplies, 109 were surface water supplies, and the remaining 182

were mixed sources, purchased water, or of unspecified source. A shortcoming in the 1969 CWSS data

file is that no distinction can be made between those systems for which fluoride was found not to be

present at the detection limit of 0.1 mg/L and those having an actual measured value of 0.1 mg/L. 

Therefore, all systems in the 1969 CWSS reporting a value of 0.1 mg/L were treated as though fluoride

were present at that level. 

Of the 678 groundwater supplies sampled, 628 (92.6%) had fluoride levels reported to be at or below 1.0

mg/L. Of the 50 supplies with higher levels, 34 (5.0 %) were found to have fluoride between 1.0 and 2.0

mg/L, 7 (1.0%) between 2.0 and 3.0 mg/L, and 9 (1.3%) between 3.0 and 4.0 mg/L. No groundwater

systems were observed in the 1969 CWSS to have fluoride levels exceeding 4.0 mg/L. Of the 16

groundwater systems exceeding 2.0 mg/L, 13 were small systems serving fewer than 500 people. The

mean value of fluoride levels in groundwater systems sampled in the 1969 CWSS was 0.39 mg/L; the

median was 0.17 mg/L.

In surface water, 102 (93.6%) of the 109 systems sampled had fluoride levels at or below 1.0 mg/L. Of

the remaining 7 systems, 6 (5.5%) were between 1.0 and 2.0 mg/L, and 1 (0.9%) was between 2.0 and 3.0

mg/L. The mean value of fluoride levels in surface water systems sampled in the 1969 CWSS was 0.30

mg/L; the median value was 0.18 mg/L.

These 1969 survey findings are generally consistent with the Stage 2 occurrence findings estimated for

this report. However, the different scopes of the two studies do not enable a direct comparison.

2.3.5.4 1978 Community Water Supply Survey

The 1978 CWSS, conducted by the USEPA, provided data on fluoride levels in a total of 157 surface

water and 345 groundwater supplies dispersed throughout the United States (USEPA, 1978, as cited in

JRB Associates,1984). The survey examined systems ranging in size from 25 people served to more than

100,000 people served. One to five samples were taken from each system. Water samples classified as

raw, finished (i.e., treated water sampled at the supply), and distribution (i.e., water sampled at a user's

tap) were all included. However, for the purpose of this analysis, distribution sample data were used

when available. When data for distribution samples were not available, data for finished water samples

were used. Data on raw water were not included in the analysis.

Of the 345 groundwater supplies sampled, 310 (89.9%) had fluoride levels reported to be at or below 1.0

mg/L. Of the remaining 35 systems, 23 (6.7%) were found to have fluoride levels between 1.0 and 2.0

mg/L, 5 (1.4%) between 2.0 and 3.0 mg/L, 3 (0.9%) between 3.0 and 4.0 mg/L, 2 (0.6%) between 4.0 and

5.0 mg/L, and 2 (0.6%) between 5.0 and 6.0 mg/L. Of the 12 groundwater systems exceeding 2.0 mg/L,

seven were small systems serving fewer than 500 people; the remaining five systems served between 500

and 2,500 people. The mean fluoride concentration in groundwater systems sampled in the 1978 CWSS

was 0.58 mg/L; the median value was 0.33 mg/L. 
Occurrence Summary and Use Support Document March 2002 75

In surface water, 134 (85.4%) of the 157 systems sampled had fluoride levels at or below 1.0 mg/L. Of

the remaining 23 systems, 22 (14.0%) were between 1.0 and 2.0 mg/L, and 1 (0.6%) was reported to be at

5.0 mg/L. This latter supply was a small system serving between 101-500 people. The mean fluoride

concentration in surface water systems in the 1978 CWSS was 0.69 mg/L; the median value was 0.79

mg/L.

These 1978 survey findings are generally consistent with the Stage 2 occurrence findings estimated for

this report. However, the different scope and coverage of the two studies prohibits a more direct

comparison.

2.3.5.5 Rural Water Survey

The Rural Water Survey (RWS) (USEPA, 1982, as cited in JRB Associates,1984) was conducted

between 1978 and 1980 to evaluate the status of drinking water in rural America as required by Section 3

of the Safe Drinking Water Act. Although the RWS examined drinking water from over 2,000

households in rural areas for a variety of water quality parameters, samples from only 91 public water

supplies were examined for fluoride levels (the sources of water for the remaining households were

private wells or very small systems serving fewer than 25 people). A second limitation regarding the

RWS was that the number of service connections associated with water systems was reported in lieu of

the actual population served by the systems. Dr. Bruce Brower of Cornell University, who collaborated

in the National Statistical Assessment of Rural Water Conditions (based on the RWS data) provided a

factor to convert the data from service connections to the number of people served, based on the average

number of persons per household observed in the RWS. It must be noted, however, that these population

values are only approximations.

Of the 70 groundwater supplies sampled, 62 (88.6%) had fluoride levels at or below 1 mg/L. Of the

remaining 8 systems, 6 (8.6%) had fluoride levels between 1.0 and 2.0 mg/L and 2 (2.9%) had fluoride

levels between 2.0 and 3.0 mg/L. The two systems with levels between 2.0 and 3.0 mg/L served between

501 and 2,500 people. The mean value of the fluoride levels in systems sampled in the RWS was 0.45

mg/L.

Of the 21 surface water systems sampled in the RWS, 19 (90.5%) had fluoride levels at or below 1.0

mg/L. The remaining 2 (9.5%) systems were reported to have fluoride between 1.0 and 2.0 mg/L. The

mean value of fluoride in surface water systems in the RWS was 0.67 mg/L.

2.3.5.6 Federal Reporting Data System

The Federal Reporting Data System (FRDS) was developed to provide information on public water

supplies with MCL violations as determined through monitoring of all supplies performed under the

requirements of the National Interim Primary Drinking Water Regulations. The FRDS was the

forerunner of the Safe Drinking Water Information System (SDWIS) database. The Wentworth (1983, as

cited in JRB Associates,1984) study on MCL violations recorded in the FRDS was conducted prior to the

1986 Fluoride Rule that set the MCL at 4 mg/L. Therefore, the Wentworth (1983, as cited in JRB

Associates,1984) study assessed violations in a different regulatory context, but the results are

summarized here for historical perspective. 

An estimated 558 groundwater supplies and 29 surface water supplies were delivering drinking water

with fluoride levels exceeding the MCL in place prior to the 1986 fluoride rule (Wentworth, 1983, as

cited in JRB Associates,1984). Because of the several different temperature-dependent standards

(ranging from 1.4-2.4 mg/L) for fluoride that were in place throughout the U.S. prior to 1986,
Occurrence Summary and Use Support Document March 2002 76

Wentworth’s results should be interpreted with caution. For example, in the fluoride concentration

ranges of 1.0-2.0 mg/L and 2.0-3.0 mg/L, the number of systems counted as exceeding the MCL is an

estimate of the number of systems that by virtue of having fluoride levels in those ranges are in violation

of the locally applicable fluoride standard. Other systems having fluoride concentrations in those ranges,

but not in violation of the local standard, are not included in the FRDS data. For the concentration

ranges greater than 3.0 mg/L, however, the FRDS data were considered to be a reasonably accurate

reflection of the total number of systems nationally, since fluoride present at such levels would always be

in violation of the MCL regardless of the local air temperature as based on the standards in place in 1983.

2.3.5.7 U. S. Public Health Service Reports on Optimum Levels

Two reports produced by the USPHS discuss fluoride in drinking water supplies, both of which deal with

systems operating at optimal fluoride levels. These two studies are earlier versions of the fluoridation

census. (The CDC Fluoridation Census 1992, for example, was described in Section 2.3.5.2) Note that

these studies are based on “communities” and “places” (see below) rather than on public water systems

and the direct population served by those water systems. These differences should be considered when

comparing the results of these two USPHS fluoridation studies to the results of the 1992 census and to

the result of the Stage 2 16-State cross-section fluoride analyses. Note also that the USPHS (1970a, as

cited in JRB Associates,1984) study is for communities served by natural fluoride levels at or above the

minimum optimal level of 0.7 mg/L.

The study titled National Fluoride Content of Community Water Supplies - 1969 (USPHS, 1970a, as

cited in JRB Associates,1984) was conducted to identify the number and location of community water

supplies in the United States that have natural fluoride levels at or above the minimum optimal level of

0.7 mg/L. This report provided the names of the communities, their populations, and the reported

concentration in the community water supplies. However, no information was given on the source of the

water (i.e., ground or surface) in those communities, nor was any information provided for communities

having natural levels less than 0.7 mg/L.

The results of the survey summarized indicated that 2,630 communities with a combined population of

8,106,435 (based on 1960 U.S. Census data) had natural fluoride levels above 0.7 mg/L. Of these, 1,517

communities (57.7%) with a combined population of 5,752,628 had drinking water supplies with natural

levels in the optimum range of 0.7-1.2 mg/L. There were 1,017 communities (38.7%) with a combined

population of 2,172,706 reported to have natural fluoride levels at or above 1.4 mg/L, the lowest

temperature based MCL value. Of these, 596 communities with 1,070,222 people were reported to have

levels above 2.0 mg/L. Only 138 communities were reported to have fluoride levels of 4 mg/L or more

and seven communities exceeded 8 mg/L.

The average community size in this survey was 3,082, ranging from less than 25 to one community of

313,900. Only eight communities had reported populations greater than 100,000; over 75% had fewer

than 2,500. There is some trend toward smaller average community size for those communities with

levels that exceed the current MCL. Communities reporting very high levels (e.g., 8 mg/L or more) all

had populations of about 500 persons or less.

The USPHS (1970a, as cited in JRB Associates,1984) indicated that most (62%) of the communities

having natural fluoride levels of 0.7 mg/L or more were located in the States of Arizona, Colorado,

Illinois, Iowa, New Mexico, Ohio, Oklahoma, South Dakota, and Texas. These same States account for

about 66% of the 1,017 communities exceeding the lowest MCL of 1.4 mg/L. Six States – Delaware,

Hawaii, Massachusetts, Pennsylvania, Tennessee, and Vermont – as well as the District of Columbia

were reported to have no communities with natural levels above 0.7 mg/L. Although this information
3

 “Place” refers to a geographic entity listed in the Worldwide Geographic Location Codes prepared by the General Services Administration.

Occurrence Summary and Use Support Document March 2002 77

indicates that there is a regional aspect to high natural fluoride levels in drinking water supplies, it is

important to note that in all but one State (other than those listed above as having no natural fluoride of

0.7 mg/L or more), at least one community had 1.4 mg/L or more. (The one exception to this, New

Hampshire, had one community at 1.3 mg/L.)

The second report by the U.S. Public Health Service that addressed optimum fluoride levels in drinking

water supplies is the 1975 Fluoridation Census (USPHS, 1977, as cited in JRB Associates,1984). This

report is similar to the USPHS report discussed above, although it includes locations and population data

for places having both natural and adjusted fluoride levels of 0.7 mg/L or more. However, this report

presents no data on the concentration of fluoride in these systems. Bock (1982, as cited in JRB

Associates,1984) indicates that, like the 1969 report, the 1975 census included all systems with levels

above 0.7 mg/L, not just those in the optimum fluoride range. Again, like the 1969 study, no information

was given on water source type nor for actual water sample analytical results.

The 1975 Fluoridation Census reported that 9,425 places3

 with a total population of 105,338,343 (using

1970 U.S. Census data) have drinking water with natural or adjusted fluoride levels of 0.7 mg/L or more. 

Of these, 2,630 places having a population of 10,711,049 have natural fluoride levels at 0.7 mg/L or

more. (The appearance of “2,630” in both the USPHS surveys is coincidental. The terms “community”

used in the 1969 study and “place” used in the 1975 Census do not appear to be synonymous. Some

States show significantly more “places” in the 1975 report than “communities” in the 1969 survey, while

others show fewer; States showing the same number in both studies often list different locations.)

Although of limited value for this discussion of fluoride occurrence in drinking water, the 1975

Fluoridation Census does indicate a higher population receiving natural fluoride levels of 0.7 mg/L or

more as compared to the 1969 study. Also, the Fluoridation Census supports the 1969 study conclusion

that the nine States listed earlier are responsible for most (60% in the 1975 fluoridation census) of the

places having natural levels of 0.7 mg/L or more.

2.3.5.8 Estimated National Occurrence of Fluoride in Public Drinking Water Supplies Based on

Survey Data

The JRB Associates (1984) study developed estimates of the number of drinking water supplies

nationally within each of the source/size categories expected to have fluoride present within various

concentration ranges. The study developed the national estimates using both Federal survey data and

compliance monitoring data. The Public Health Service data (briefly reviewed above in Section 2.3.5.7)

were reportedly not useful in the JRB Associates (1984) development of the national estimates for

several reasons. Those data were for “places” or “communities” rather than supplies, and there was no

indication as to the source of the water for those locations. The 1975 Fluoridation Census provided no

quantitative data on fluoride levels in the drinking water, indicating only whether the water had natural or

adjusted levels of 0.7 mg/L or more; the 1969 USPHS study addressed only communities with natural

levels at or above 0.7 mg/L.

The Federal survey data together with the compliance monitoring data provided information on water

source and system size for extrapolating to all public water supplies. The compliance monitoring data is

believed to provide a reasonably accurate picture of those supplies in the U.S. with high fluoride levels. 

However, because it addressed only supplies in violation of the current MCL, the compliance monitoring

data provided no information on supplies with lower levels of fluoride. The Federal survey data, which
Occurrence Summary and Use Support Document March 2002 78

provides some information on supplies at all concentrations, is of limited value for estimating the number

of systems nationally having high fluoride levels because of the small number of supplies sampled. That

is, because there are relatively few supplies in the U.S. having high levels, the chances of observing them

in the surveys is small. On the other hand, when a supply with a high fluoride level was observed in the

surveys, extrapolating to the national level results in a questionably high national estimate. It was,

therefore, decided that the compliance monitoring data would be used to describe national fluoride

occurrence at the higher concentrations and the survey data would be used to estimate national fluoride

occurrence at lower concentrations.

The estimates of supplies having > 3.0 mg/L are taken directly from the compliance monitoring data,

since systems having levels > 3.0 would always be reported through FRDS as MCL violations (at the

MCL in place prior to the 1986 fluoride rule). For lower levels (i.e., # 3.0 mg/L), national estimates

were calculated as follows. First, the results of the three surveys were combined for groundwater and

surface water, respectively, to determine the total number of systems sampled with values # 3.0 mg/l, as

well as the number falling within each concentration range of interest. National estimates of supplies

within each concentration range were then calculated in proportion to that observed in the combined

Federal survey data.

For the > 2.0-3.0 mg/L range for groundwater, the estimates calculated from the Federal survey data were

compared to the compliance monitoring data for each source/size category and the larger value was

chosen for the national estimates. This choice was based on the recognition that the compliance

monitoring data may underestimate the actual number of supplies in the > 2.0-3.0 mg/L range since not

all supplies having fluoride in that range are necessarily in violation of the MCL and, therefore, would

not be reported through FRDS. Higher estimates, computed from the survey data, were considered to be

more conservative. On the other hand, in those instances where the compliance data showed more

supplies in that range than the estimates from the survey data, the compliance data were considered more

representative of actual occurrence, since the lower estimates from the survey data probably resulted

from the small sample size. Specifically, for ground water in the > 2.0-3.0 mg/L ranges, the national

estimates for supplies serving 5,000 or fewer people are based on the Federal survey data and on the

compliance data for supplies serving more than 5,000 persons. For surface water, all values in the > 2.0-

3.0 mg/L range are from the compliance monitoring data. All estimates of ground water and surface

water supplies having # 2.0 mg/L of fluoride are based on the Federal survey data.

The estimates indicate that 82.8% of all public water supplies in the U.S. in the mid-1980s using ground

water had fluoride present in the range of 0.1 to 1.0 mg/L. About 8.6% of ground water supplies (4,214

total) were estimated to have fluoride levels > 1.0 mg/L, though most of these fall in the 1.0-2.0 mg/L

range. Most of the estimated 1,324 groundwater supplies with fluoride levels exceeding 2.0 mg/L are

expected to be small or medium sized supplies, while all of the supplies having very high levels (> 7.0

mg/L) are expected to be small systems serving fewer than 1,000 people.

For surface water, the majority of systems (78.5%) are also expected to have fluoride present in the 0.1-

1.0 mg/L range. Of the 726 surface water supplies estimated to have levels above 1.0 mg/L, almost all

(704) are estimated to be in the 1.0-2.0 mg/L range. As in the case of groundwater, most of the surface

water supplies expected to have levels exceeding 2.0 mg/L are small and medium sized systems.

2.3.6 Conclusion

The record of use, production and release of fluoride and its compounds suggest it is found at low levels

in soil, water, and air. Most fluorides are used in steel production, while other fluoride compounds are

used in a variety of applications including drinking water additives. Recent statistics regarding import
Occurrence Summary and Use Support Document March 2002 79

for consumption of fluorspar (the primary source of fluorine and its compounds) indicate production and

use are robust. Industrial releases of fluorine have occurred since 1995 in 11 States and Puerto Rico,

while releases of hydrogen fluoride have occurred since 1988 in 49 States. Air emissions constitute the

greatest proportion of the total on- and off-site releases of fluorine and hydrogen fluoride. Fluoride is

also a national NAWQA analyte. Fluoride occurrence in ambient surface and ground waters is high. 

Approximately 69.0% of all surface water sites had analytical detections of fluoride, compared to 67.0%

of ground water sites. The percentage of sites with fluoride detections greater than the MCL (4 mg/L)

drastically decreases, however, to 0.05% for surface water sites and 0.5% for ground water sites. The

Stage 2 analysis, based on the 16-State cross-section, estimated that approximately 0.511% of combined

ground water and surface water systems serving 0.0897% of the population had estimated mean

concentrations of fluoride greater than the MCL of 4 mg/L. Based on this estimate, approximately 332

PWSs nationally serving about 191,000 people are expected to have estimated mean concentrations of

fluoride greater than 4 mg/L.

Since fluoride and its compounds occur naturally occurring, the balanced geographic distribution of the

16-State cross-section should adequately cover the range of natural occurrence of fluoride from low to

high. The 16-State cross-section also contains a substantial proportion of the States with reported TRI

releases of fluorine and hydrogen fluoride. Based on this use and release evaluation, the 16-State crosssection appears to adequately represent fluoride occurrence nationally.

2.3.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1993. Toxicological Profile for

Fluorides, Hydrogen Fluoride, and Fluorine (F). U.S. Department of Health and Human

Services, Public Health Service. 244 pp. + Appendices. Available on the Internet at:

http://www.atsdr.cdc.gov/toxprofiles/tp11.pdf

Bock, W. 1982. Census Program, Center for Disease Control, U.S. Public Health Service, Athens, GA. 

Private Communication with author of JRB Associates,1984.

CDC. 1992. Fluoridation Census 1992. Atlanta, GA: Centers for Disease Control and Prevention,

Public Health Service, U.S. Department of Health and Human Services.

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at: 

http://ca.water.usgs.gov/pnsp/rep/ofr97589/, last updated October 9, 1998. 

JRB Associates. 1984. Occurrence of Fluoride in Drinking Water, Food, and Air. Prepared for and

submitted to EPA on February 9, 1984. 

USEPA. 1978. Community Water Supply Survey. Computer data files on inorganic contaminants.

USEPA. 1982. Rural Water Survey. Computer data provided by Department of Sociology, Cornell

University. 

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.
Occurrence Summary and Use Support Document March 2002 80

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 2000. Mineral Commodity Summaries, February, 2000 - Fluoride. Available on the Internet at:

http://minerals.usgs.gov/minerals/pubs/commodity.

USPHS. 1970a. Natural Fluoride Content of Community Water Supplies; 1969. Bethesda, MD:

National Institutes of Health, Public Health Service, Department of Health, Education, and

Welfare. 

USPHS. 1970b. Community Water Supply Survey. Washington, DC: Bureau of Water Hygiene, Public

Health Service, Department of Health, Education, and Welfare. 

USPHS. 1977. Fluoridation Census 1975. Atlanta, GA: Center for Disease Control, Public Health

Service, Department of Health, Education, and Welfare. 

Wentworth, N. 1983. Summary of fluoride drinking water violations data derived from: (a) FRDS24 of

FY82 (3/14/83); (b) FRDS Chemical Violation List of FY78-FY81; (c) Summary of Variances

and Exemptions Issued FY82; (d) Report on “Defluoridation Study for Suffolk Area of VA,”

(10/82); and (e) Region VIII report on “Solving Public Health Problems” (2/8/83). U.S.

Environmental Protection Agency, Office of Drinking Water. Personal communication to author

of JRB Associates, 1984 on March 24, 1983.

WHO. 1984. Fluorine and Fluorides. Geneve, Switzerland: World Health Organization, Distribution

and Sales Service, EHC Number 36.
Occurrence Summary and Use Support Document March 2002 81

2.4 Mercury

Table of Contents

2.4.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

2.4.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

2.4.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

2.4.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . . 85

2.4.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

2.4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

2.4.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Tables and Figures

Table 2.4-1: Facilities that Manufacture or Process Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Table 2.4-2: Environmental Releases (in pounds) for Mercury in the United States, 1988-1999 . . . . . 84

Table 2.4-3: Environmental Releases (in pounds) for Mercury Compounds in the 

United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Table 2.4-4: Stage 1 Mercury Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . . 86

Table 2.4-5: Stage 1 Mercury Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . . 87

Table 2.4-6: Stage 2 Estimated Mercury Occurrence Based on 16-State Cross-Section - Systems . . . . 88

Table 2.4-7: Stage 2 Estimated Mercury Occurrence Based on 16-State Cross-Section - Population . . 89

Table 2.4-8: Estimated National Mercury Occurrence - Systems and Population Served . . . . . . . . . . . 90
Occurrence Summary and Use Support Document March 2002 82

2.4.1 Introduction, Use and Production

Mercury (Hg) is a member of Group IIB of the periodic table. Mercury is a naturally occurring metal

which has several forms. The principal valence states of mercury are +1 (mercurous) and +2 (mercuric),

both of which are found in natural waters (USEPA, 1979, as cited in Wade Miller, 1990). The metallic

mercury is a shiny, silver-white, odorless liquid. If heated, it is a colorless, odorless gas. Mercury

combines with other elements, such as chlorine, sulfur, or oxygen, to form inorganic mercury compounds

or “salts,” which are usually white powders or crystals. Mercury also combines with carbon to make

organic mercury compounds (ATSDR, 1999b). 

The occurrence of mercury in surface and ground water is influenced by natural and anthropogenic

sources. Although mercury occurs in the environment as a result of human activities, the major source of

mercury in the environment results from geothermal activity, volatilization from mineral deposits, or

volcanic activity (Wade Miller, 1990). Mercury in surface water may be the result of human activities or

naturally occurring sources. Because mercury does not readily leach through soils, contamination of

ground water is believed to be unlikely. Therefore, most mercury in ground water is considered to be

natural in origin (Battelle, 1977; Perwak et al., 1980, all as cited in Wade Miller, 1990). 

Like all elements, the same amount of mercury has existed on the planet since the Earth was formed. 

However, the amount of mercury mobilized and released into the environment has increased since the

beginning of the industrial age. The human activities that are most responsible for causing mercury to

enter the environment are the burning of materials (such as batteries), use of fuels (such as coal) that

contain mercury, and certain industrial processes (USEPA, 2001).

Mercury has many applications in industry due to its unique properties, such as its fluidity, its uniform

volume expansion over the entire liquid temperature range, its high surface tension, and its ability to

alloy with other metals (ATSDR, 1999a). Mercury is used in its pure form in thermometers, barometers,

and other consumer products (NSC, 2001). However, domestic consumption of mercury has

demonstrated a downward trend since the early 1970s. In 1995, consumption was 102,000 pounds, down

10% from 1994. The largest commercial use of mercury in the United States was for electrolytic

production of chlorine and caustic soda in mercury cells, accounting for 35% of domestic consumption. 

Manufacture of wiring devices and switches accounted for 19%, measuring and control instruments for

9%, dental equipment and supplies used 7%, electric lighting used 7%, and other uses amounted to 21%

(USGS, 1997). Due to the high toxicity of mercury in most of its forms, many applications have been

canceled as a result of attempts to limit the amount of exposure to mercury waste (ATSDR, 1999a).

The canceled uses of mercury include use of phenylmercuric acetate as a fungicide in interior latex paints

and exterior paints. The former use was banned in 1990 and the latter in 1991. This occurred because

the paint released mercury vapors as it degraded. Most agricultural applications of mercury compounds

in bactericides and fungicides have been canceled due to the toxicity of mercury. Minor uses of mercury

in the production of felt hats and as a wood preservative have also been terminated (ATSDR, 1999a).

In electrical applications, mercury is a critical element in alkaline batteries. Due to its toxicity, the

amount of mercury in batteries is being reduced from 0.1% to 0.025%. Mercury vapors are used in

discharge tubes of some electrical lamps because this makes the lamps efficient, long-lasting, and more

energy efficient. In 1985, 64% of the mercury used in the U.S. was for electrical applications, and this

amount had fallen to 29% in 1992 (ATSDR, 1999a).

Probably one of mercury’s most familiar applications is in medicine in dental restorations. It is used in

dentistry because of its ability to alloy with other metals. Estimates of annual mercury usage by U.S.
Occurrence Summary and Use Support Document March 2002 83

dentists range from approximately 220,500 pounds in the 1970s to 154,300 pounds in 1995. Until 30

years ago, mercury was also used in pharmaceuticals. Mercury salts were used in antiseptics, diuretics,

skin lightening creams, and laxatives. Organic mercury compounds were used in antisyphilitic drugs and

some laxatives. Phenylmercury acetate was used in contraceptive gels and foams and as a disinfectant. 

Almost all of these uses have now been replaced by others that are more effective and less toxic

(ATSDR, 1999a).

In the chemical and mining industries, mercury is used as a catalyst in reactions to form polymers and in

the preparation of chlorine and caustic soda from brines. In mining, mercury is used in gold mining to

extract gold from ores through amalgamation (ATSDR, 1999a).

 Organic mercury (especially methyl mercury and dimethyl mercury) can imperil human welfare because

of its tendency to bioaccumulate in the flesh of certain fish. Low levels of mercury contamination in

oceans and lakes can lead to toxic contamination of fish, making it hazardous for human consumption,

especially for children and pregnant women (NSC, 2001).

The primary method of obtaining mercury is from mining. Ten percent of mercury mining is open pit

mining and 90% is from underground mining techniques. There are currently 34 facilities that produce

or process mercury in the U.S. (ATSDR, 1999a). U.S. production of mercury in 1985 was 1,254,000

pounds, and world production in 1986 was 13,376,000 pounds (NSC, 2001). As of 1995, eight mines in

California, Nevada, and Utah produced mercury as a by-product from gold mining operations. 

Approximately 127,900 pounds of mercury were produced from eight mines in 1991 and 141,100 pounds

were produced as a by-product from nine mines in 1992. Since then, production volumes have been

withheld to avoid disclosing Bureau of Mines company proprietary data (ATSDR, 1999a). 

Table 2.4-1 lists the facilities in each State that manufacture or process mercury, the intended use, and

the range of maximum amounts of mercury that are stored on site derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 1999a). 

Table 2.4-1: Facilities that Manufacture or Process Mercury

Facility Locationa

Range of maximum

amounts on site in

pounds

Activities and uses

Occidental Chemical Muscle Shoals, AL 100,000-999,999 Chemical processing aid

Tuscaloosa Steel Corp. Tuscaloosa, AL 0-99 Article component

Occidental Chemical New Castle, DE 100,000-999,999 Chemical processing aid

Olin Chlor-Alkali Prods. Augusta, GA 100,000-999,999 Chemical processing aid

Alexander Mfg. Co. Mason City, IA 0-99 Import, On-site use/processing, Article component

Micro Switch Freeport, IL 10,000-99,999 Article component

Valspar Corp. Rockford, IL 10,000-99,999 Formulation component

Durakool Inc. Elkhart, IN 10,000-99,999 Article component

Hermaseal Co. Elkhart, IN 10,000-99,999 Article component

U.S. Steel Gary, IN 10,000-99,999 Produce, Byproduct

United Techs. Edinburgh, IN 10,000-99,999 Article component

Koch Sulfur Prods. Co. De Soto, KS 0-99 Ancillary/other use

BF Goodrich Co. Calvert City, KY 100,000-999,999 Chemical processing aid

Du Pont Louisville, KY not available not available

Borden Chemicals & Geismar, LA 100,000-999,999 Import, On-site use/processing, Chemical processing aid

Dow Chemical Co. Plaquemine, LA 1,000-9,999 Produce, Byproduct

Pioneer Chlor Alkali Co. Saint Gabriel, LA 100,000-999,999 Chemical processing aid

PPG Ind. Inc. Lake Charles, LA 100,000-999,999 Chemical processing aid

Holtrachem Mfg. Orrington, ME 100,000-999,999 Chemical processing aid
Facility Locationa

Range of maximum

amounts on site in

pounds

Activities and uses

Occurrence Summary and Use Support Document March 2002 84

Elm Plating Co. Jackson, MI 0-99 Article component

Kerr Corp. Romulus, MI 1,000-9,999 Repackaging

Holtrachem Mfg. Co. Riegelwood, NC 100,000-999,999 Chemical processing aid

Mercury Refining Co. Albany, NY 10,000-99,999 Produce, Sale/Distribution, Repackaging, Ancillary/other use

Ashta Chemicals Inc. Ashtabula, OH 10,000-99,999 Chemical processing aid

Component Repair Mentor, OH not available not available

Sinclair Oil Corp. Tulsa, OK 100-999 Produce, Byproduct

Advanced Environmental Allentown, PA 10,000-99,999 Produce, Sale/distribution

Bethlehem Apparatus Hellertown, PA 100,000-999,999 Produce, Import, On-site use/processing, Sale/distribution,

Zinc Corp. of America Monaca, PA 10,000-99,999 Produce, Impurity

Olin Corp. Charleston, TN 100,000-999,999 Chemical processing aid

Occidental Chemical Deer Park, TX 100,000-999,999 Chemical processing aid

Georgia-Pacific West Bellingham, WA 100,000-999,999 Chemical processing aid

Vulcan Materials Co. Port Edwards, WI 100,000-999,999 Chemical processing aid

PPG Ind. Inc. New Martinsville, 100,000-999,999 Chemical processing aid a

Post office State abbreviations used

Source: ATSDR, 1999a compilation of TRI96 1998 data

2.4.2 Environmental Release

Mercury and mercury compounds are both listed as Toxics Release Inventory (TRI) chemicals. Table

2.4-2 illustrates the environmental releases for mercury from 1988 - 1999. (There are only mercury data

for these years.) Air emissions constitute most of the on-site releases, with the amount released

decreasing in earlier years and generally remaining constant in more recent years. The decrease in air

emissions, as well as decreases in surface water discharges and off-site releases (including metals or

metal compounds transferred off-site), have contributed to decreases in mercury total on- and off-site

releases in previous years. Releases to land decreased until 1996, at which point they began to rise. No

underground injection releases were recorded or reported for mercury. These TRI data for mercury were

reported from 31 States and Puerto Rico with 12 States reporting all 12 years (USEPA, 2000). Of the 31

States, 10 are included in the 16 State cross-section (used for analyses of mercury occurrence in drinking

water; see Section 2.4.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.4-2: Environmental Releases (in pounds) for Mercury in the United States, 1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 11,275 133 -- 2,419 7,070 20,897

1998 12,591 134 -- 3,069 15,721 31,515

1997 12,163 391 -- 1,016 26,346 39,916

1996 14,286 468 -- 537 13,012 28,303

1995 13,262 192 -- 1,016 14,228 28,698

1994 11,277 175 -- 1,351 14,097 26,900

1993 11,642 267 -- 1,801 18,355 32,065

1992 14,222 273 -- 3,122 43,854 61,471

1991 18,208 629 0 5,292 112,969 137,098

1990 22,391 751 0 4,184 177,015 204,341

1989 25,095 1,555 0 4,942 126,087 157,679

1988 22,905 1,397 0 13,279 258,718 296,299

 Source: USEPA, 2000 
Occurrence Summary and Use Support Document March 2002 85

Table 2.4-3 illustrates the environmental releases for mercury compounds between 1988 and 1999. Air

emissions constitute most of the on-site releases, with some fluctuation over the years. Both surface

water discharges and releases to land have also fluctuated, with releases to land dramatically increasing

in 1998-1999. Underground injections contribute relatively little to total releases, and have not been

registered since 1998. Off-site releases of mercury compounds are considerable. The levels of total onand off-site releases have generally followed the highs and lows of the levels of off-site releases, with no

discernible trend. These TRI data for mercury compounds were reported from 32 States with one State,

Pennsylvania, reporting every year (USEPA, 2000). Of the 32 States, 12 are included in the 16 State

cross-section (used for analyses of mercury occurrence in drinking water; see Section 2.4.4). (For a map

of the 16-State cross-section, see Figure 1.3-1.)

Table 2.4-3: Environmental Releases (in pounds) for Mercury Compounds in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 2,110 36 -- 5,700 53,051 60,897

1998 2,372 34 -- 2,550 19,858 24,814

1997 2,356 34 41 0 25,448 27,879

1996 2,916 73 9 0 29,437 32,435

1995 3,156 136 6 0 207,097 210,395

1994 2,716 151 7 0 26,166 29,040

1993 3,421 184 15 11 56,009 59,640

1992 3,249 307 9 17 191,945 195,527

1991 3,080 52 9 2 36,875 40,018

1990 1,158 58 21 15 36,041 37,293

1989 4,009 13 36 260 56,113 60,431

1988 2,376 9 27 0 17,916 20,328

 Source: USEPA, 2000 

2.4.3 Ambient Occurrence

The most comprehensive and nationally consistent data describing ambient water quality in the United

States are being produced through the United States Geological Survey’s (USGS) National Water Quality

Assessment (NAWQA) program. However, no national NAWQA data are available for mercury.

Also, there are no other ambient data available for mercury. A summary document entitled “Occurrence

and Exposure Assessment for Mercury in Public Drinking Water Supplies” (Wade Miller, 1990), was

previously prepared for past USEPA assessments of mercury. However, no information on the ambient

occurrence of mercury was included in that document. (The document did include information regarding

mercury occurrence in drinking water, which is discussed in Section 2.4.5 of this report.)

2.4.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of mercury occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most
Occurrence Summary and Use Support Document March 2002 86

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.002 mg/L; 0.001 mg/L; and 0.0005 mg/L.

All sixteen cross-section State data sets contained occurrence data for mercury. These data represent

more than 64,000 analytical results from approximately 19,000 PWSs during the period from 1984 to

1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs vary by

State, although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limit for mercury in the 16 cross-section States is equal to

0.001 mg/L. (For details regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)

2.4.4.1 Stage 1 Analysis Occurrence Findings

Table 2.4-4 illustrates the low occurrence of mercury in drinking water for the public water systems in

the 16-State cross-section relative to three thresholds: 0.002 mg/L (the current MCL), 0.001 mg/L (the

modal MRL), and 0.0005 mg/L. A total of 50 ground water and surface water PWSs (approximately

0.263%) had at least one analytical result exceeding the MCL; 0.900% (171 systems) of PWSs had at

least one analytical result exceeding 0.001 mg/L; and 2.90% (551 systems) of PWSs had at least one

analytical result exceeding 0.0005 mg/L. 

Approximately 0.252% (44 systems) of ground water PWSs had at least one analytical result greater than

the MCL. About 0.848% (148 systems) of ground water PWSs had at least one analytical result above

0.001 mg/L. The percentage of ground water systems with at least one result greater than 0.0005 mg/L

was equal to 2.68% (467 systems). 

Only 6 (0.387% of) surface water systems had at least one analytical result greater than the MCL. A total

of 23 (1.48% of) surface water systems had at least one analytical result greater than 0.001 mg/L. 

Eighty-four surface water systems (5.42%) had at least one analytical result exceeding 0.0005 mg/L.

Table 2.4-4: Stage 1 Mercury Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems Exceeding

Threshold

Ground Water

0.002 0.252% 44

0.001 0.848% 148

0.0005 2.68% 467

Surface Water

0.002 0.387% 6

0.001 1.48% 23

0.0005 5.42% 84

Combined Ground &

Surface Water

0.002 0.263% 50

0.001 0.900% 171

0.0005 2.90% 551
Occurrence Summary and Use Support Document March 2002 87

Reviewing mercury occurrence in the 16 cross-section States by PWS population served (Table 2.4-5)

shows that approximately 0.276% of the population (almost 300,000 people) was served by PWSs with at

least one analytical result of mercury greater than the MCL (0.002 mg/L). Approximately 4.5 million

(4.33% of) people were served by systems with an exceedance of 0.001 mg/L. A total of 9,268,500

people (8.82%) were served by systems with at least one analytical result greater than 0.0005 mg/L.

The percentage of population served by ground water systems with analytical results greater than the

MCL was equal to 0.538% (almost 232,000 people). When evaluated relative to 0.001 mg/L or 0.0005

mg/L, the percent of population exposed was equal to 4.18% (1,803,400 people) and 10.2%

(approximately 4.4 million people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.002 mg/L was

equal to 0.0937% (58,000 people). Approximately 4.43% (about 2.7 million people) of the population

served by surface water systems were served by systems with estimated mean concentrations of mercury

greater than 0.001 mg/L. When evaluated relative to 0.0005 mg/L, the percent of population exposed

was equal to 7.84% (almost 4.9 million people).

Table 2.4-5: Stage 1 Mercury Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems Exceeding

Threshold 

Total Population Served by

Systems Exceeding Threshold

Ground Water

0.002 0.538% 231,900

0.001 4.18% 1,803,400

0.0005 10.2% 4,409,500

Surface Water

0.002 0.0937% 58,000

0.001 4.43% 2,746,300

0.0005 7.84% 4,859,000

Combined Ground &

Surface Water

0.002 0.276% 290,000

0.001 4.33% 4,549,700

0.0005 8.82% 9,268,500

2.4.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 2.4-6 and 2.4-7. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 
Occurrence Summary and Use Support Document March 2002 88

A total of 13 (0.0672%) ground water and surface water PWSs in the 16 States had an estimated mean

concentration of mercury exceeding 0.002 mg/L. Approximately 73 (0.385% of) PWSs in the 16 States

had an estimated mean concentration exceeding 0.001 mg/L, and 431 (2.27%) had an estimated mean

concentration exceeding 0.0005 mg/L. 

An estimated 13 ground water PWSs in the 16 cross-section States (0.0727%) had a mean concentration

greater than 0.002 mg/L, 72 (0.411%) had a mean concentration greater than 0.001 mg/L, and 416

(2.38%) had a mean concentration greater than 0.0005 mg/L. Approximately 1 (0.00529%), 1

(0.0863%), and 16 (1.03%) surface water PWSs in the 16 States had estimated mean concentrations

exceeding 0.002 mg/L, 0.001 mg/L, and 0.0005 mg/L, respectively.

Table 2.4-6: Stage 2 Estimated Mercury Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.0727% 0.0459% - 0.103% 13 8 - 18

0.001 0.411% 0.321% - 0.504% 72 56 - 88

0.0005 2.38% 2.13% - 2.62% 416 372 - 457

Surface Water

0.002 0.00529% 0.000% - 0.0645% 1 0 - 1

0.001 0.0863% 0.000% - 0.258% 1 0 - 4

0.0005 1.03% 0.581% - 1.55% 16 9 - 24

Combined Ground

& Surface Water

0.002 0.0672% 0.0421% - 0.0948% 13 8 - 18

0.001 0.385% 0.300% - 0.474% 73 57 - 90

0.0005 2.27% 2.05% - 2.49% 431 390 - 473

Reviewing mercury occurrence by PWS population served (Table 2.4-7) shows that approximately

0.00627% (an estimate of approximately 6,600 people) of population served by all PWSs in the 16 crosssection States were potentially exposed to mercury levels above 0.002 mg/L. The percentage of

population served by PWSs in the 16 States with levels of mercury above 0.001 mg/L and 0.0005 mg/L

were 0.0987% (an estimated 103,700 people) and 1.56% (about 1.6 million people), respectively. 

When the percent of population served by ground water systems was evaluated relative to a threshold of

0.002 mg/L, 0.001 mg/L, and 0.0005 mg/L, the percentage of population exposed in the 16 cross-section

States was equal to 0.0147% (an estimated 6,300 people), 0.151% (an estimated 65,100 people) and

1.36% (an estimated 585,500 people), respectively. 

The percentage of population served by surface water systems with levels above 0.002 mg/L was equal to

0.000429% (an estimated 300 people served by systems in the 16 States), and the percentage of

population served with levels above 0.001 mg/L was 0.0624% (an estimated 38,700 people in the 16-

State cross-section). The percentage of the population served by surface water systems with levels above

0.0005 mg/L was 1.70% (just over 1 million people). 
Occurrence Summary and Use Support Document March 2002 89

Table 2.4-7: Stage 2 Estimated Mercury Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.0147% 0.00224% - 0.0535% 6,300 1,000 - 23,100

0.001 0.151% 0.0661% - 0.288% 65,100 28,500 - 124,100

0.0005 1.36% 0.923% - 2.26% 585,500 397,800 - 975,300

Surface Water

0.002 0.000429% 0.000% - 0.00921% 300 0 - 5,700

0.001 0.0624% 0.000% - 1.36% 38,700 0 - 840,400

0.0005 1.70% 0.473% - 2.27% 1,056,100 293,000 - 1,408,800

Combined Ground

& Surface Water

0.002 0.00627% 0.000924% - 0.0223% 6,600 1,000 - 23,400

0.001 0.0987% 0.0308% - 0.853% 103,700 32,300 - 896,900

0.0005 1.56% 0.946% - 2.06% 1,641,600 994,500 - 2,166,000

2.4.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 44 PWSs serving approximately 13,400 people nationally could be exposed to

mercury concentrations above 0.002 mg/L. About 250 systems serving 210,200 people had estimated

mean concentrations greater than 0.001 mg/L. Approximately 1,477 systems serving about 3.3 million

people nationally were estimated to have mean mercury concentrations greater than 0.0005 mg/L. (See

Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 43 PWSs serving about 12,600 people nationally had mean

concentrations greater than 0.002 mg/L. Approximately 244 systems serving about 129,300 people

nationally had estimated mean concentration values that exceeded 0.001 mg/L. About 1,416 ground

water systems serving over 1.1 million people had estimated mean concentrations greater than 0.0005

mg/L. 

Approximately 1 surface water system serving 500 people was estimated to have a mean concentration of

mercury above 0.002 mg/L. About 5 surface water systems serving 79,400 people had estimated mean

concentrations greater than 0.001 mg/L. An estimated 58 surface water systems serving approximately

2,169,600 people had mean concentrations greater than 0.0005 mg/L.
Occurrence Summary and Use Support Document March 2002 90

Table 2.4-8: Estimated National Mercury Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 43 27 - 61 12,600 1,900 - 45,900

0.001 244 191 - 300 129,300 56,700 - 246,600

0.0005 1,416 1,267 - 1,557 1,163,600 790,600 - 1,938,100

Surface Water

0.002 1 0 - 4 500 0 - 11,700

0.001 5 0 - 14 79,400 0 - 1,726,500

0.0005 58 32 - 87 2,169,600 601,900 - 2,894,100

Combined Ground

& Surface Water

0.002 44 27 - 62 13,400 2,000 - 47,400

0.001 250 195 - 308 210,200 65,500 - 1,817,800

0.0005 1,477 1,335 - 1,619 3,327,200 2,015,700 - 4,390,100

2.4.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of mercury in drinking water are also reviewed. 

Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence and Exposure Assessment for Mercury in Public Drinking Water Supplies” (Wade Miller,

1990), is presented in this section. This variety of studies and information are presented regarding levels

of mercury in drinking water, with the scope of the reviewed studies ranging from national to regional. 

Note that none of the studies presented in the following section provide the quantitative analytical results

or comprehensive coverage that would enable direct comparison to the occurrence findings estimated

with the cross-section occurrence data presented in Section 2.4.4. These additional studies, however, do

enable a broader assessment of the Stage 2 occurrence estimates presented for this Six-Year Review. All

the following information in Section 2.4.5 is taken directly from “Occurrence and Exposure Assessment

for Mercury in Public Drinking Water Supplies” (Wade Miller, 1990).

2.4.5.1 Reported Occurrence in Drinking Water

This section presents information on measured mercury levels in drinking water from public water

supplies. Section 2.4.5.1.1 provides the results from several national-scale surveys in which mercury

levels were measured in drinking water. Section 2.4.5.1.2 provides the most current information from the

U.S. Environmental Protection Agency's Federal Reporting Data System (FRDS) on the status of

drinking water supplies reported to be in violation of the current standard of 2 :g/L for mercury.

2.4.5.1.1 Federal Survey Data

Several national-scale surveys have been conducted that provide data on mercury in public drinking

water supplies. These include the 1978 Community Water Supply Survey, the Rural Water Survey, the

National Organic Monitoring Survey, and the National Inorganics and Radionuclides Survey. The
Occurrence Summary and Use Support Document March 2002 91

following sections describe these surveys and present the data on mercury levels in ground water and

surface water supplies.

1978 Community Water Supply Survey (1978 CWSS)

The 1978 Community Water Supply Survey (CWSS) was conducted by the USEPA to determine the

occurrence of organic and inorganic compounds in public water supplies. Drinking water samples were

provided by approximately 500 supplies; however, due to analytical problems, reliable data for mercury

were available for only 35 ground water and 10 surface water supplies (USEPA, 1983, as cited in Wade

Miller, 1990).

Details on the analytical method used for mercury were not available; from the information provided by

Glick (1984, as cited in Wade Miller, 1990) the minimum quantifiable concentration appeared to be 0.5

:g/L. Supplies provided one to five samples of raw, finished, and/or distribution water. However, Brass

(1983, as cited in Wade Miller, 1990) indicated that reporting inconsistencies made it impossible to

distinguish between finished and distribution samples. Therefore, distribution and finished sample

results were averaged; raw water data were not used.

Of the 35 ground water supplies sampled, nine (26 percent) contained mercury at concentrations ranging

from 0.5 to 175 :g/L. Except for the one high value of 175 :g/L, none of the samples exceeded 2 :g/L. 

None of the 10 surface water supplies sampled contained mercury above the minimum quantifiable

concentration of 0.5 :g/L.

Rural Water Survey (RWS)

The Rural Water Survey (RWS) conducted between 1978 and 1980 evaluated the status of drinking water

in rural America as required by Section 3 of the Safe Drinking Water Act. More than 2,000 households

served by 648 public water supplies (494 ground water, 154 surface water) were surveyed. Many of

these households used private wells or very small systems serving fewer than 25 people, and only a

subsample of the supplies evaluated included analyses for mercury (71 ground water and 21 surface

water supplies). Results of the inorganic analyses were provided to Science Applications International

Corporation (SAIC) as a computer file by Brower (1983, as cited in Wade Miller, 1990).

A problem with the RWS was that the number of service connections associated with water systems was

reported in lieu of the actual populations served by the systems. Dr. Bruce Brower of Cornell University,

who collaborated in the National Statistical Assessment of Rural Water Conditions (based on the RWS

data) provided a factor to convert the data from service connections to the number of people served,

based on the average number of persons per household observed in the RWS. It must be noted, however,

that these population values are only approximations.

Details were not available on the sample collection or analytical methodology used. However, the

minimum quantifiable concentration for mercury appeared to range from 0.2 to 0.5 :g/L. Of the 71

ground water supplies studied, 24 (34 percent) contained mercury at levels ranging from 0.3 to 12.3 :g/L. 

For surface water supplies, 11 of the 21 supplies sampled (52 percent) had mercury present at

concentrations ranging from 0.3 to 16.0 :g/L.

National Organic Monitoring Survey (NOMS)

The National Organic Monitoring Survey (NOMS), which was conducted by the USEPA in 1976 and

1977, was intended primarily to provide data for establishing MCLs for organic compounds in drinking
Occurrence Summary and Use Support Document March 2002 92

water. A substudy of NOMS analyzed samples for 27 trace elements in the 113 supplies sampled (91

surface water, 19 ground water, 3 mixed sources) (USEPA, 1980, as cited in Wade Miller, 1990). 

Mercury data are available for 86 surface water and 15 ground water supplies. Samples were taken of

treated, finished water leaving the treatment plant. Occasionally, samples were taken of distribution

system water in close proximity to the treatment plant. The results of the inorganic analyses for NOMS

were provided to SAIC by the Technical Support Division of EPA's Office of Drinking Water (USEPA,

1985, as cited in Wade Miller, 1990). No information on the analytical procedures used was available;

the minimum quantifiable concentration appeared to be approximately 0.5 :g/L.

Mercury was not found in any of the 15 ground water supplies sampled. For surface water supplies,

mercury was observed in two of the 86 supplies sampled (2 percent) at concentrations of 0.5 :g/L and 1.5

:g/L.

National Inorganics and Radionuclides Survey (NIRS)

In 1981 the USEPA's Office of Drinking Water (ODW) initiated the National Inorganics and

Radionuclides Survey (NIRS) to characterize the occurrence of various contaminants in community

drinking water supplies. The survey focused on the presence of 36 inorganics, including mercury, and

four radionuclides in ground water supplies from throughout the United States. Implementation of the

survey and sampling were accomplished by the ODW's Technical Support Division between July 1984

and October 1986.

The NIRS sampling program was designed to reflect the national distribution of community ground water

supplies by size of population served as inventoried by the Federal Reporting Data System (FRDS). The

FRDS data was stratified into the following four population-size categories: very small (serving 25-500),

small (serving 501-3,300) medium (serving 3,301-10,000), and large/very large (serving >10,000). A

total of 1,000 sites were selected randomly from the FRDS data in proportion to the four size categories. 

Approximately 2.1% of the supplies in each size category were chosen for sampling. Of the 1,000

targeted sites, 990 were actually sampled in the NIRS.

Sample collection and location within each supply were designed to reflect the quality of water actually

received by the consumer. Samples were collected after three minutes of flushing in order to represent

the finished water in the distribution system. To the extent possible, the sampling location was chosen at

a point of maximum use in the distribution system. The method used to analyze for mercury was not

reported. The minimum reporting limit (MRL) was 0.2 :g/L.

Mercury results are available for all of the 990 sites sampled in the NIRS. Approximately 98% of the

samples had mercury concentrations less than 0.5 :g/L. Of the 19 supplies (two percent) with higher

mercury concentrations, only one exceeded the current MCL of 2 :g/L. This maximum value was 2.1

:g/L for a small supply, serving between 501 and 3,300 people. The overall mean of the samples was

approximately 0.2 :g/L, which was the MRL.

2.4.5.1.2 Compliance Monitoring Data

The Federal Reporting Data System (FRDS) provides information on public water supplies in violation

of current MCLs as determined through compliance monitoring of all supplies performed by the States

under the requirements of the National Interim Primary Drinking Water Regulations. Only violations of

current MCLs (i.e., 2 :g/L for mercury) and approved variances and exemptions from the standards are

recorded in FRDS. Monitoring is required annually for surface water supplies and every three years for

ground water supplies.
Occurrence Summary and Use Support Document March 2002 93

The FRDS database (FRDS, 1990, as cited in Wade Miller, 1990) was searched for violations reported

during the three year period from 1987 through 1989. The data indicated that there were three public

ground water and three public surface water supplies providing drinking water which had mercury levels

above the current MCL of 2 :g/L. The ground water supplies were all in the very small and small size

categories. A maximum value of 4.3 :g/L was reported for a supply serving 70 people.

The three surface water violations were distributed between the very small, medium, and large/very large

size categories. A maximum value of 7 :g/L was reported for a system serving 8,000 people. 

Additionally, no variances or exemptions to the current mercury MCL of 2 :g/L were reported to have

been granted for surface water supplies.

2.4.5.2 Estimated National Occurrence in Public Water Supplies

Section 2.4.5.1 presented the results of several studies that provide information on the occurrence of

mercury in public drinking water supplies. This section presents national estimates of mercury

occurrence in public drinking water supplies based on those study results.

2.4.5.2.1 Methodology

National estimates of the occurrence of contaminants in drinking water supplies are needed to serve as

input to the analysis of regulatory costs and benefits. A draft document has been prepared that describes

the methodology used to estimate national occurrence of the inorganic drinking water contaminants

addressed under Phase II of the national primary drinking water regulations development process

(USEPA, 1986, as cited in Wade Miller, 1990). In general, national survey data are used as the basis for

the national estimates. The most representative data sets are selected and combined, stratified

appropriately by water source and system size sampled, and applied to a “delta-log normal” distribution

model. Using that model, the probability of contaminant occurrence above any given concentration is

determined for each source/size category of supplies and applied to the total number of water supplies in

those groups. The resulting national occurrence estimates are presented in tables that show the

cumulative number of public water supplies, within various water source and size categories, expected to

have certain concentrations.

The mercury occurrence estimates are based on the results of the NIRS survey for ground water supplies

and the combined results of the 1978 CWSS, the RWS, and the NOMS for surface water supplies. The

NIRS data are the most current ground water data available, and the analytical results are considered to

be highly reliable because of the extensive quality assurance program being employed. None of the

surveys that analyzed surface water supplies could be shown to be any more or less representative of the

universe of water supplies than the other surveys, and it was therefore determined to be most appropriate

to combine the results from all of the surveys to form the basis of the national occurrence estimates.

2.4.5.2.2 Results

Section 2.4.5.2.1 noted that the national estimates of mercury in finished water are based on the results

from NIRS for ground water supplies, and on the combined results from the 1978 CWSS, RWS and

NOMS for the surface water supplies.

For ground water, the model estimates that 45 public ground water supplies have mercury levels greater

than the proposed MCLG and MCL of 2 :g/L. Six of those supplies are estimated to have mercury levels

exceeding 3 :g/L. The majority of the supplies expected to have mercury concentrations above 2 :g/L
Occurrence Summary and Use Support Document March 2002 94

are in the small and very small size categories. FRDS reports only three systems in violation of the 2

:g/L MCL.

For surface water, the model predicts that approximately 7 percent or 395 surface water supplies contain

mercury in excess of 2 :g/L. An estimated 3 percent (189 supplies) are expected to contain greater than

6 :g/L mercury. The systems expected to exceed the proposed MCLG and MCL of 2 :g/L are

distributed throughout all size categories. FRDS reports only three systems in violation of the current

MCL of 2 :g/L, one of which contains mercury at levels greater than 6 :g/L.

The occurrence estimates formulated from the delta lognormal distribution model predict a larger number

of systems contain mercury in excess of 2 :g/L than reported by FRDS for both ground and surface water

supplies. It cannot be determined whether this is due to an over-estimate by the model or an underreporting of actual violations in FRDS. For the surface water estimates the higher number of supplies

predicted to exceed 2 :g/L are attributed to the use of the Rural Water Survey results. Six of the 21

samples from the RWS exceeded 2 :g/L and five of the six were above 6 :g/L. None of the surface

water samples from the 1978 CWSS or the NOMS contained mercury above 2 :g/L. The RWS data may

have significantly skewed the estimated occurrence numbers.

2.4.5.3 Estimated National Exposure from Public Water Supplies

2.4.5.3.1 Methodology

Section 2.4.5.2.1 noted that a separate methodology document has been prepared to describe the

approach used to estimate national occurrence of inorganic contaminants in public water supplies. That

document also addresses the approach to estimating the population exposed to contaminant levels in

public drinking water supplies. In summary, the occurrence probability density functions obtained from

the national survey data on supplies contaminated at various levels are applied to the number of people

using water supplies in the various size categories.

2.4.5.3.2 Results

Based on the national occurrence estimates derived from the national survey data, 72,000 people are

expected to be exposed to mercury from ground water supplied drinking water systems above the

proposed MCLG and MCL of 2 :g/L. The model also estimates that 6,000 of those people will be

exposed to mercury at levels greater than 3 :g/L. Zero people are expected to be exposed to mercury in

drinking water at levels greater than 4 :g/L. The FRDS data indicate that only 424 people are exposed to

mercury at levels exceeding the current MCL of 2 :g/L. Additionally, 70 people receive drinking water

with a mercury concentration between 4 and 5 :g/L.

Based upon the cumulative national population exposure estimates from the national survey data for

mercury in surface water supplies, the model predicts that approximately 10 million people are exposed

to mercury levels above 2 :g/L. Information regarding the population exposed to mercury at levels

exceeding the current MCL of 2 :g/L as reported in FRDS indicates that 18,766 people are exposed to

mercury levels above 2 :g/L.

The FRDS data and the modeled exposure estimates differ by several orders of magnitude. Once again,

this may be due to an over estimation by the mathematical model or an underreporting of FRDS

violations. It should also be noted that the higher national occurrence and exposure estimates for surface

water supplies are due to the fact that they are based on the (apparently) anomalous high results of the

RWS.
Occurrence Summary and Use Support Document March 2002 95

Overall, the model predicts that, of the estimated 219 million people using public drinking water

supplies, about 5 percent or 10.3 million are exposed to mercury at levels above 2 :g/L. The remaining

95 percent of the population (208.7 million people) are either not exposed to mercury or are receiving

levels less than 2 :g/L. Of the 10.3 million people exposed, approximately 5 million are expected to

receive drinking water with mercury levels in excess of 6 :g/L.

2.4.6 Conclusion

Mercury and many of its compounds are naturally occurring and found at low levels in soil, water, and

air. Furthermore, mercury is mined in the United States for widespread use. Most mercury is used in

production of mercury cells, while other uses for mercury include manufacture of wiring devices and

switches, dental equipment, and electric lighting. Recent statistics regarding production and use of

mercury indicate they are steady. Industrial releases of mercury and mercury compounds have been

reported to TRI since 1988 from 31 States and 32 States, respectively. Off-site releases constitute a

considerable amount of total releases, with releases to land the most significant on-site releases. No

national NAWQA data were available for mercury. The Stage 2 analysis, based on the 16-State crosssection, estimated that approximately 0.0672% of combined ground water and surface water systems

serving 0.00627% of the population had estimated mean concentrations of mercury greater than the MCL

of 0.002 mg/L. Based on this estimate, approximately 44 PWSs nationally serving about 13,400 people

are expected to have estimated mean concentrations of mercury greater than 0.002 mg/L.

Mercury is a naturally occurring element. Therefore, the balanced geographic distribution of the 16-State

cross-section should adequately cover the range of natural occurrence of mercury from low to high. The

16-State cross-section also contains a substantial proportion of the States with reported TRI releases of

mercury and mercury compounds. Based on this use and release evaluation, the 16-State cross-section

appears to adequately represent mercury occurrence nationally.

2.4.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1999a. Toxicological Profile for

Mercury. U.S. Department of Health and Human Services, Public Health Service. 617 pp. +

Appendices. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp46.pdf

Agency for Toxic Substances and Disease Registry (ATSDR). 1999b. ToxFAQs for Mercury. U.S.

Department of Health and Human Services, Public Health Service. Available on the Internet at:

http://atsdr.cdc.gov/tfacts46.html

Battelle. 1977. Multimedia levels: Mercury. Washington, DC: Office of Toxic Substances, USEPA. 

EPA-560/6-77-031.

Brass, H. 1983. U.S. Environmental Protection Agency, Office of Drinking Water, Technical Support

Division, Cincinnati, OH. Personal communication to Frank Letkiewicz, SAIC.

Brower, B. 1983. Computer data file of analytical results for public water supplies sampled in the Rural

Water Survey. Cornell University, Department of Rural Sociology.

Federal Reporting Data System (FRDS). 1990. Computer file extracts of compliance monitoring data

for the Safe Drinking Water Act. 1987-1989.
Occurrence Summary and Use Support Document March 2002 96

Glick, E. 1984. U.S. Environmental Protection Agency, Office of Drinking Water, Technical Support

Division, Cincinnati, OH. Personal communication to Frank Letkiewicz, SAIC.

National Safety Council (NSC). 2001. Mercury Chemical Backgrounder. Itasca, IL: National Safety

Council. Available on the Internet at:

http://www.crossroads.nsc.org/ChemicalTemplate.cfm?id=117&chempath=chemicals, accessed

July 23, 2001.

Perwak, J., M. Goyer, L. Nelken, K. Scow, M. Wald, and D. Wallace. 1980. An exposure and risk

assessment mercury. Final draft report prepared by A.D. Little submitted to Office of Water and

Waste Management, USEPA, Washington, DC. EPA Contracts 68-01-3857, 68-01-5949.

USGS. 1997. Mercury. United States Geological Survey.

USEPA. 1979. Water-related environmental fate of 129 priority pollutants. Volume 1. Office of Water

Planning and Standards, USEPA. EPA-440/4-79-029a.

USEPA. 1980. Trace elements in 113 U.S. drinking waters. A substudy of the National Organics

Monitoring Survey. Cincinnati, OH: Technical Support Division, Office of Drinking Water,

USEPA. 

USEPA. 1983. Data on inorganics from the Community Water Supply Survey. Provided by E.M. Glick,

Drinking Water Quality Assessment Branch, Technical Support Division, Office of Drinking

Water, Cincinnati, Ohio. 

USEPA. 1985. U.S. Environmental Protection Agency. Computerized listing of inorganics data for the

National Organics Monitoring Survey (NOMS). Provided to Science Applications International

Corporation by E.B. Dotson, Water Supply Technology Branch, Technical Support Division,

Office of Drinking Water, Cincinnati, Ohio. November 12, 1985.

USEPA. 1986. Overview of methodology used to estimate national occurrence and exposure to

inorganic drinking water contaminants (draft). Prepared by Science Applications International

Corporation for U.S. Environmental Protection Agency, Office of Drinking Water, Science and

Technology Branch.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: Mercury.

Office of Ground Water and Drinking Water, USEPA. Available on the Internet at:

http://www.epa.gov/safewater/dwh/c-ioc/mercury.html, last updated March 9, 2001.

Wade Miller Associates, Inc. 1990. Occurrence and Exposure Assessment for Mercury in Public

Drinking Water Supplies. Prepared for and submitted to EPA on July 26, 1990.
Occurrence Summary and Use Support Document March 2002 97

2.5 Thallium

Table of Contents

2.5.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

2.5.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

2.5.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

2.5.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 101

2.5.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

2.5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

2.5.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Tables and Figures

Table 2.5-1: Facilities that Manufacture or Process Thallium and Compounds . . . . . . . . . . . . . . . . . . . 98

Table 2.5-2: Environmental Releases (in pounds) for Thallium in the United States, 1989-1999 . . . . . 99

Table 2.5-3: Environmental Releases (in pounds) for Thallium Compounds in the 

United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Table 2.5-4: Stage 1 Thallium Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . 101

Table 2.5-5: Stage 1 Thallium Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . 102

Table 2.5-6: Stage 2 Estimated Thallium Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Table 2.5-7: Stage 2 Estimated Thallium Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Table 2.5-8: Estimated National Thallium Occurrence - Systems and Population Served . . . . . . . . . 104
Occurrence Summary and Use Support Document March 2002 98

2.5.1 Introduction, Use and Production

Pure thallium (Tl) is a bluish-white metal that is found in trace amounts in the earth’s crust. Thallium

metal forms alloys with other metals and readily amalgamates with mercury (Wade Miller, 1989). 

Thallium forms compounds in which it occurs in either the +1 (thallous) or +3 (thallic) valence states. 

The +1 salts are slightly to moderately soluble in water; however, trivalent thallium is reportedly the

predominant ionic species found in seawater and freshwater in equilibrium with atmospheric oxygen

(Wade Miller, 1989). 

Thallium is found mainly in several rare minerals, deposits of which are so small that they have not been

of commercial importance. The main commercial sources of thallium have been as by-products from the

production or processing of other materials, notably flue dusts from pyrites (FeS2), lead, zinc and

cadmium (Wade Miller, 1989). 

In its pure form, thallium is odorless and tasteless. It can also be found combined with other substances

such as bromine, chlorine, fluorine, and iodine. When it's combined, it appears colorless-to-white or

yellow (ATSDR, 1995). 

Thallium is a metal found in natural deposits in ores containing other elements. The greatest use of

thallium is in specialized electronic research equipment (USEPA, 2001). The domestic production of

thallium ceased in 1981. Prior to that, thallium had been recovered as a byproduct from the flue dust and

residuals that resulted from the smelting of zinc, copper, and lead ores. Based upon the estimated

thallium content of zinc ores, U.S. mine production of thallium was 992 pounds in 1986 and 1987,

compared to 31,000 pounds in the rest of the world (ATSDR, 1992).

Currently thallium can only be obtained by importation. In 1987, about 4,500 pounds of thallium were

imported (USEPA, 2001) and in 1990, approximately 1,540 pounds were imported (HSDB, 2000). 

About 60-70% of thallium use is concentrated in the semiconductor industry in the production of

switches and closures (ATSDR, 1992). Thallium is also used in the pharmaceutical industry for

myocardial imaging, in the manufacture of thallaphide cells, atomic beam clocks, photoelectric cells,

lamps, thermometers, alloys, scintillation counters (HSDB, 2000), and in highly refractive optical glass

(ATSDR, 1992). Thallium was formerly used as a rodenticide and ant killer, but it has not been available

for that function in the U.S. since 1975 and its use as such is restricted in many other parts of the world

(HSDB, 2000). 

Table 2.5-1 shows the six facilities that either import thallium, use thallium and its compounds in

manufacturing processes, or produce them as byproducts. The table also gives the uses of the product

and the range of maximum amounts on site. All information was derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 1992).

Table 2.5-1: Facilities that Manufacture or Process Thallium and Compoundsa

Facility Location Maximum amount on site in

pounds Use

Philips Industries, Inc., Dexter Axle Albion, IN 10,000-99,999 Import; as a manufacturing aid

Tenneco Oil Company Chalmette, LA 0-99 As a processing aid

Koch Refining Company Saint Paul, MN 1,000-9,999 As an impurity

River Cement Company Festus, MO 100,000,000-499,999,999 As a reactant
Facility Location Maximum amount on site in

pounds Use

Occurrence Summary and Use Support Document March 2002 99

Sohio Oil Company Toledo Refinery Oregon, OH 100-999 As an impurity

Dana Corporation Reading, PA 0-99 As an impurity

a

 Derived from TRI 1989

Source: ATSDR, 1992 compilation of 1989 TRI data

2.5.2 Environmental Release

Thallium and thallium compounds are both listed as Toxics Release Inventory (TRI) chemicals. Table

2.5-2 illustrates the environmental releases for thallium from 1989 - 1999. No thallium data were

reported in 1992 or 1996. Air emissions and releases to land are the only factors that have consistently

contributed to on-site releases. Air emissions decreased (from a high of 1,000 pounds in 1989 to a low of

15 pounds in 1998) until 1999, when they spiked to over 2,000 pounds. Total on- and off-site releases of

thallium remained relatively stable for many years until just recently. Off-site releases have been on an

upward trend since 1997, and releases to land went from 755 pounds to 4,355 pounds from 1995-1999. 

No underground injection releases and very few surface water discharges were reported for thallium. 

These TRI data for thallium were reported from 10 States (USEPA, 2000). Of the 10 States, four are

included in the 16 State cross-section (used for analyses of thallium occurrence in drinking water; see

Section 2.5.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.5-2: Environmental Releases (in pounds) for Thallium in the United States, 1989-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 2,137 -- -- 4,355 4,828 11,320

1998 15 -- -- 3,400 3,665 7,080

1997 256 -- -- 1,000 1,500 2,756

1995 255 -- -- 755 195 1,205

1994 255 -- -- 755 255 1,265

1993 255 -- -- 755 5 1,015

1991 30 1 -- -- 953 984

1990 750 5 -- -- 916 1,671

1989 1,000 -- -- 500 250 1,750

 Source: USEPA, 2000 

Table 2.5-3 illustrates the environmental releases for thallium compounds between 1988 and 1999. 

There were no data, however, reported in 1993 or 1995. Releases to land have generally constituted most

of the on-site releases, with dramatic increases in 1994 and 1998. No real trend is suggested in the data. 

Air emissions were relatively constant from 1988-1991, but since then have fluctuated from zero to over

1,000 pounds. Releases to land have fluctuated dramatically; from 1988-1991 they were constant, then

they increased to about 3,700 pounds in 1994 and over 400,000 pounds in 1998. Off-site releases of

thallium compounds vary from almost zero to under 2,000 pounds. No underground injection releases

and very few surface water discharges were reported for thallium compounds. Overall, total on- and offsite releases have ranged from 5 to over 400,000 pounds. The fluctuations are relatively modest except
Occurrence Summary and Use Support Document March 2002 100

for increases in 1998, mostly as a result of the increased releases to land. The TRI data for thallium

compounds were reported from 20 States (USEPA, 2000). Of the 20 States, eight are included in the 16

State cross-section (used for analyses of thallium occurrence in drinking water; see Section 2.5.4). (For a

map of the 16-State cross-section, see Figure 1.3-1.)

Table 2.5-3: Environmental Releases (in pounds) for Thallium Compounds in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 654 750 -- 252,800 1,838 256,042

1998 1,060 250 -- 409,000 759 411,069

1997 0 -- -- -- 180 180

1996 0 -- -- -- 5 5

1994 171 -- -- 3,695 5 3,871

1992 755 -- -- 505 255 1,515

1991 255 -- -- 255 5 515

1990 255 -- -- 255 5 515

1989 256 -- -- 250 504 1,010

1988 253 -- – 250 1,256 1,759

 Source: USEPA, 2000 

2.5.3 Ambient Occurrence

The most comprehensive and nationally consistent data describing ambient water quality in the United

States are being produced through the United States Geological Survey’s (USGS) National Water Quality

Assessment (NAWQA) program. However, no national NAWQA data are available for thallium.

2.5.3.1 Additional Ambient Occurrence Data

Information is very limited with regard to concentrations of thallium in ambient waters. A summary

document entitled “Occurrence and Exposure Assessment of Thallium in Public Drinking Water

Supplies” (Wade Miller, 1989), was previously prepared for past USEPA assessments of beryllium. No

additional national or regional studies on the occurrence of thallium in ground water were available. 

However, one additional study was presented regarding levels of thallium in ambient surface waters. The

following information is taken directly from that document.

V.J. Ciccone and Associates (USEPA, 1984, as cited in Wade Miller, 1989) provided information on a

study by Durum and Haffty (1961, as cited in Wade Miller, 1989) in which analyses of ambient water for

the occurrence of minor elements were reported. The study involved analysis of samples collected at 15

surface water sites throughout the United States and Canada. The number of samples collected varied

from two to seven per site. Samples were analyzed for thallium using the emission spectroscopy

technique. The results of this study revealed that thallium was below the analytical detection limit in all

samples collected; however, the detection limit was not provided.
Occurrence Summary and Use Support Document March 2002 101

2.5.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of thallium occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to two concentration thresholds of interest: 0.002 mg/L; and 0.001 mg/L.

All sixteen cross-section State data sets contained occurrence data for thallium. These data represent

more than 47,000 analytical results from approximately 18,000 PWSs during the period from 1985 to

1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs vary by

State, although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limit for thallium in the 16 cross-section States is equal to

0.001 mg/L. (For details regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)

2.5.4.1 Stage 1 Analysis Occurrence Findings

Table 2.5-4 illustrates the Stage 1 analysis of thallium occurrence in drinking water for the public water

systems in the 16-State cross-section relative to two thresholds of interest: 0.002 mg/L (the current

MCL) and 0.001 mg/L (the modal MRL). Approximately 0.679% (122 systems) of all ground water and

surface water PWSs had any analytical results of thallium exceeding the MCL. Approximately 1.89%

(340 systems) of PWSs had any exceedances of the modal MRL.

A greater proportion of surface water systems, as compared to ground water systems, exceeded each

threshold. However, the actual number of ground water systems with threshold exceedances was much

greater than the actual number of surface water systems with threshold exceedances. Over 100

(approximately 0.660% of) ground water PWSs had any analytical results exceeding the MCL, compared

to 13 (about 0.886% of) surface water PWSs. About 1.81% (299 systems) of ground water PWSs had

any analytical results exceeding 0.001 mg/L. This compares to about 2.79% (41 systems) of surface

water PWSs with any analytical results greater than the modal MRL.

Table 2.5-4: Stage 1 Thallium Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.002 0.660% 109

0.001 1.81% 299

Surface Water

0.002 0.886% 13

0.001 2.79% 41

Combined Ground &

Surface Water

0.002 0.679% 122

0.001 1.89% 340
Occurrence Summary and Use Support Document March 2002 102

Reviewing thallium occurrence in the 16 cross-section States by PWS population served (Table 2.5-5)

shows approximately 1.85% (a total of 1,927,200 people) of the population was served by PWSs with

any analytical results greater than the MCL. The percentage of population served by PWSs with any

exceedance of the modal MRL was 4.32% (4,500,600 people).

The number of people served by ground water systems with any analytical results greater than 0.002

mg/L was equal to 858,700 (about 2.01%). A total of 1,068,500 people (approximately 1.73%) were

served by surface water systems with any analytical results greater than 0.002 mg/L. About 4.46% of the

population served by ground water PWSs (1,903,500 people) had any exceedances of 0.001 mg/L,

compared to approximately 4.21% (2,597,100 people) of the population served by surface water systems.

Table 2.5-5: Stage 1 Thallium Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.002 2.01% 858,700

0.001 4.46% 1,903,500

Surface Water

0.002 1.73% 1,068,500

0.001 4.21% 2,597,100

Combined Ground &

Surface Water

0.002 1.85% 1,927,200

0.001 4.32% 4,500,600

2.5.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 2.5-6 and 2.5-7. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

Approximately 0.283% (51 systems) of all ground water and surface water PWSs in the 16-States are

estimated to have mean concentrations of thallium above 0.002 mg/L (the current MCL). The percentage

of PWSs in the 16 cross-section States with estimated mean concentrations exceeding 0.001 mg/L (the

modal detection limit) was about 1.20% (215 PWSs).

A greater proportion of ground water systems, as compared to surface water systems, were estimated to

exceed each threshold. Approximately 48 (0.292% of) ground water systems in the 16 cross-section

States had estimated mean concentrations of thallium above 0.002 mg/L, compared to approximately 3

(0.180% of) surface water systems. About 1.21% (an estimated 199 systems) of ground water systems in

the 16-State cross-section had estimated mean concentrations greater than 0.001 mg/L. This compares
Occurrence Summary and Use Support Document March 2002 103

with about 1.07% (about 16 systems) of the surface water systems with estimated mean concentrations

greater than 0.001 mg/L.

Table 2.5-6: Stage 2 Estimated Thallium Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.292% 0.206% - 0.382% 48 34 - 63

0.001 1.21% 1.01% - 1.41% 199 167 - 232

Surface Water

0.002 0.180% 0.000% - 0.409% 3 0 - 6

0.001 1.07% 0.545% - 1.64% 16 8 - 24

Combined Ground

& Surface Water

0.002 0.283% 0.195% - 0.367% 51 35 - 66

0.001 1.20% 1.01% - 1.39% 215 181 - 250

Reviewing thallium occurrence by PWS population served (Table 2.5-7) shows that approximately

77,500 (0.0743% of) the PWS population in the 16 States were served by systems with mean thallium

concentrations above 0.002 mg/L. When evaluated relative to a threshold of 0.001 mg/L, the percent of

population exposed increased significantly to about 0.527% (approximately 550,000 people served in the

16 States).

About 63,800 (0.150% of) people served by ground water systems in the 16 States were served by

systems with estimated mean concentrations of thallium above 0.002 mg/L. An estimated 0.887% of the

population (about 378,100 people) were served by ground water systems whose mean concentration

value exceeded 0.001 mg/L. 

Approximately 0.0222% of the population served by surface water PWSs (an estimated 13,700 people

nationally) had estimated mean concentrations of thallium above 0.002 mg/L. About 0.279% of the

population served by surface water PWSs had mean concentrations greater than 0.001 mg/L (almost

172,000 people).

Table 2.5-7: Stage 2 Estimated Thallium Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.150% 0.0319% - 0.573% 63,800 13,600 - 244,300

0.001 0.887% 0.383% - 1.41% 378,100 163,300 - 602,200
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 104

Surface Water

0.002 0.0222% 0.000% - 0.0866% 13,700 0 - 53,400

0.001 0.279% 0.0664% - 1.41% 171,900 40,900 - 869,800

Combined Ground

& Surface Water

0.002 0.0743% 0.0156% - 0.246% 77,500 16,300 - 256,900

0.001 0.527% 0.244% - 1.24% 550,000 254,600 - 1,296,300

2.5.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 184 PWSs serving approximately 158,300 people nationally could be exposed to

thallium concentrations above 0.002 mg/L. Approximately 778 systems serving about 1.1 million people

served nationally were estimated to have thallium concentrations greater than 0.001 mg/L. (See Section

1.4 for a description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 174 PWSs serving about 128,200 people nationally had mean

concentrations greater than 0.002 mg/L. Approximately 717 systems serving about 759,7000 people

nationally had estimated mean concentration values that exceeded 0.001 mg/L.

Approximately 10 surface water systems serving 28,300 people were estimated to have mean

concentrations of thallium above 0.002 mg/L. About 60 surface water systems serving 355,100 people

had estimated mean concentrations greater than 0.001 mg/L.

Table 2.5-8: Estimated National Thallium Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 174 122 - 227 128,200 27,300 - 490,900

0.001 717 602 - 836 759,700 328,100 - 1,209,800

Surface Water

0.002 10 0 - 23 28,300 0 - 110,300

0.001 60 30 - 91 355,100 84,500 - 1,796,600

Combined Ground

& Surface Water

0.002 184 127 - 239 158,300 33,300 - 524,600

0.001 778 655 - 905 1,123,400 520,000 - 2,647,700
Occurrence Summary and Use Support Document March 2002 105

2.5.5 Additional Drinking Water Occurrence Data

Additional data sources regarding the occurrence of thallium in drinking water are also reviewed. 

Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence and Exposure Assessment of Thallium in Public Drinking Water Supplies” (Wade Miller,

1989), is presented in this section. Only one national scale study – the National Inorganics and

Radionuclides Survey – provided data on the occurrence of thallium in drinking water sources. That

survey, however, is limited to ground water sources. No regional ground water or surface water studies

or national surface water studies were found. Note that none of the studies presented in the following

section provide the quantitative analytical results or comprehensive coverage that would enable direct

comparison to the occurrence findings estimated with the cross-section occurrence data presented in

Section 2.5.4. These additional studies, however, do enable a broader assessment of the Stage 2

occurrence estimates presented for this Six-Year Review. All the following information in Section 2.5.5

is taken directly from “Occurrence and Exposure Assessment of Thallium in Public Drinking Water

Supplies” (Wade Miller, 1989).

2.5.5.1 Ground Water Sources – National Studies

The National Inorganics and Radionuclides Survey (NIRS) was a two-year national sampling and

analytical study designed to gather information on the occurrence of selected inorganic compounds and

radionuclides in drinking water. From July 1984 through May 1986 approximately 1,000 samples of

finished drinking water from ground water supplies throughout the United States were collected. Of 989

utilities for which thallium data were reported, 28 systems served populations greater than 10,000 (large

and very large, combined), 54 served populations of 3,301 to 10,000 (medium), 233 served populations

of 501 to 3,300 (small), and 674 served populations of 25 to 500 (very small).

The analytical results of the NIRS were made available in printed form by EPA's Technical Support

Division, Office of Drinking Water. Additional information regarding the location and sources of

supplies, population served, methods, and detection limits was available in an EPA Status Report, also

provided by the Technical Support Division (USEPA, 1985, as cited in Wade Miller, 1989).

Samples were collected in the field by representatives of local utilities. Samplers were provided with

complete kits including detailed instructions, and a rigorous quality control procedure was developed to

ensure the representativeness of the samples. The samples collected for metals analyses were preserved

in the field with nitric acid and shipped to one of several EPA laboratories for testing.

Of the 989 utilities for which thallium data were reported, only one returned a sample that revealed a

thallium concentration above the minimum reporting level of 8 :g/L. That positive sample was collected

at a very small utility and was reported to contain 10 :g/L thallium.

2.5.5.2 Ground Water and Surface Water Sources – STORET

The EPA computerized water quality data base, known as STORET, was devised to help Federal and

State institutions meet the objectives of Public Law 92-500 to maintain and enhance the physical,

chemical, and biological quality of the nation's ambient waterways by providing for the collection and

dissemination of basic water quality data (Staples et al., 1985, as cited in Wade Miller, 1989). Data are

collected by States, EPA regional offices, and other government agencies and maintained in the STORET

system. STORET contains approximately 80 million pieces of data, including data for drinking water

from ground water and surface water sources.
Occurrence Summary and Use Support Document March 2002 106

Before presenting a summary of the drinking water data in STORET, it is important to note that there are

significant limitations in using the data base to estimate representative concentrations of a contaminant

such as thallium. Data entered into STORET are gathered from an array of studies conducted for various

purposes. Analyses are conducted in a number of different laboratories employing different

methodologies with a range of detection limits. In many cases, detection limits are not reported, making

the reliability of the data highly questionable. Where detection limits have been reported, STORET

assigns the detection limit value to those observations reported as not detected. This can lead to errors in

interpretation and overestimation of concentrations in cases in which there is a preponderance of

nondetectable values. Additionally, a few high values can inflate mean values and result in large

standard deviations relative to the means (Staples et al., 1985, as cited in Wade Miller, 1989). Very high

values may not be correct, as they may reflect sample contamination or analytical error, and can

significantly distort assessment of average concentrations. Staples et. al. (1985, as cited in Wade Miller,

1989) also notes that the use of data collected prior to the 1980s is not recommended, since such data was

obtained using less sensitive laboratory techniques and quality assurance procedures were not yet

mandated for the data entered into the system.

With these limitations in mind, a summary of STORET's most recently obtained data for drinking water

from ground water and surface water sources is presented here (USEPA, 1988, as cited in Wade Miller,

1989). For ground water, there were two positive observations for total thallium from February 1978 to

April 1979, with both values reported at 0.8 :g/L. There were 221 samples reported as undetected; the

apparent detection limit for these samples was 50 :g/L. Including the undetected samples and detections

known to be less than the reported value, there were 227 observations for total thallium in ground water

from February 1978 to November 1987. With detection limit value assigned to the undetected samples,

STORET reported an overall mean value of 48.7 :g/L and a range of 0.2 to 50 :g/L. The standard

deviation for all observations was 7.9 :g/L. Detection limits and other sampling information were not

reported.

For surface water, there were 11 positive observations for total thallium from April 1978 to September

1981, with an overall mean value of 3.4 :g/L and a range of 0.2 to 9.0 :g/L. The standard deviation for

these observations was 2.9 :g/L. Seven samples were reported as undetected, with a mean value of 30.3

:g/L, apparently reflecting a detection limit value range of 20 to 50 :g/L. Including the undetected

samples and the detections known to be less than the reported value, there were 54 observations for total

thallium in surface water from February 1978 to July 1987, with an overall mean value of 5.4 :g/L and a

range of 0.2 to 50 :g/L. The standard deviation for all observations was 12.9 :g/L. Detection limits and

other sampling information were not reported.

2.5.6 Conclusion

Thallium and some of its compounds are naturally occurring and found at low levels as natural deposits. 

Thallium is no longer produced domestically, and all thallium used in the United States is imported. 

Most thallium is used in production of specialized electronic research equipment. Some statistics

regarding import for consumption of thallium indicate that imports may be declining. Industrial releases

of thallium have occurred since 1989 in 10 States, while releases of thallium compounds have occurred

since 1988 in 20 States. Air emissions and off-site releases constitute the greatest proportion of the total

on- and off-site releases of thallium and thallium compounds. No national NAWQA data were available

for thallium. The Stage 2 analysis, based on the 16-State cross-section, estimated that approximately

0.283% of combined ground water and surface water systems serving 0.07439% of the population had

estimated mean concentrations of thallium greater than the MCL of 0.002 mg/L. Based on this estimate,

approximately 184 PWSs nationally serving about 158,300 people are expected to have estimated mean

concentrations of thallium greater than 0.002 mg/L.
Occurrence Summary and Use Support Document March 2002 107

Since thallium and its compounds occur naturally occurring, the balanced geographic distribution of the

16-State cross-section should adequately cover the range of natural occurrence of thallium from low to

high. The 16-State cross-section also contains a substantial proportion of the States with reported TRI

releases of thallium and thallium compounds. Based on this use and release evaluation, the 16-State

cross-section appears to adequately represent thallium occurrence nationally.

2.5.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1992. Toxicological Profile for Thallium.

U.S. Department of Health and Human Services, Public Health Service. 90 pp. + Appendices. 

Available on the Internet at: http://atsdr1.atsdr.cdc.gov/toxprofiles/tp54.pdf 

Agency for Toxic Substances and Disease Registry (ATSDR). 1995. ToxFAQs for Thallium. U.S.

Department of Health and Human Services, Public Health Service. Available on the Internet at:

http://atsdr.cdc.gov/tfacts54.html

Center for Disease Control and Prevention (CDC). 1992. Fluoridation Census 1992. Atlanta, GA:

Centers for Disease Control and Prevention, Public Health Service, U.S. Department of Health

and Human Services.

Center for Disease Control and Prevention (CDC). 2002. Written comments (including information

from the unpublished Fluoridation Census 2000) from CDC staff to OGWDW staff, January 8,

2002. 

Durum, W.H., and J. Haffty. 1961. Occurrence of minor elements in water. U.S. Geological Survey

Circular 445, U.S. Geological Survey, U.S. Department of the Interior, as cited in USEPA. 1984.

Hazardous Substances Data Bank (HSDB). 2000. Search for Thallium. Available on the Internet

through TOXNET, sponsored by the National Institute of Health’s National Library of Medicine. 

Available on the Internet at: http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB,

Staples, C.A., A.F. Werner, and T.J. Hoogheem. 1985. Assessment of priority pollutant concentrations

in the United States using STORET database. In: Environmental Toxicology and Chemistry. v.

4, pp. 131-142. New York, New York: Pergamon Press, Ltd.

USEPA. 1984. Thallium in water: An assessment of occurrence and exposure. First Draft. Prepared

by: V.J. Ciccone & Associates, Inc., Woodbridge, VA. Prepared for: Science and Technology

Branch, Criteria and Standards Division, Office of Drinking Water, USEPA, Washington, DC. 

September 28, 1984.

USEPA. 1985. Status report: National Inorganics and Radionuclides Survey. By Jon P. Longtin. 

Cincinnati, OH: Technical Support Division, Office of Drinking Water, USEPA. August 30,

1985.

USEPA. 1988. Computer printout of STORET water quality data base retrieval conducted March 23,

1988 by Science Applications International Corporation. Data available through the Office of

Water Regulations and Standards, USEPA.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.
Occurrence Summary and Use Support Document March 2002 108

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: Thallium.

Office of Ground Water and Drinking Water, USEPA. Available on the Internet at:

http://www.epa.gov/OGWDW/dwh/c-ioc/thallium.html, last updated March 9, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Thallium in Public

Drinking Water Supplies. Prepared for and submitted to EPA on February 24, 1989.
Occurrence Summary and Use Support Document March 2002 109

3.0 SYNTHETIC ORGANIC CONTAMINANTS
Occurrence Summary and Use Support Document March 2002 110

3.1 Alachlor

Table of Contents

3.1.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

3.1.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

3.1.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

3.1.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 116

3.1.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

3.1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

3.1.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Tables and Figures

Figure 3.1-1: Estimated Annual Agricultural Use for Alachlor (1992) . . . . . . . . . . . . . . . . . . . . . . . . 112

Table 3.1-1: Environmental Releases (in pounds) for Alachlor in the United States, 1995-1999 . . . . 113

Table 3.1-2: Alachlor Detections and Concentrations in Surface Water and Ground Water . . . . . . . . 113

Table 3.1-3: Stage 1 Alachlor Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . 116

Table 3.1-4: Stage 1 Alachlor Occurrence Based on 16-State Cross-Section - Population Served . . . 117

Table 3.1-5: Stage 2 Estimated Alachlor Occurrence Based on 16-State Cross-Section - Systems . . 118

Table 3.1-6: Stage 2 Estimated Alachlor Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

Table 3.1-7: Estimated National Alachlor Occurrence - Systems and Population Served . . . . . . . . . . 119

Table 3.1-8. Summary Alachlor Monitoring in Ground Water Conducted by the ARP . . . . . . . . . . . 121

Table 3.1-9. Summary of 1995 and 1996 Alachlor Monitoring in Surface Water Conducted 

by the ARP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Table 3.1-10. Summary of Wells with Detections of Alachlor from Various Studies Presented 

in the Alachlor RED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

Table 3.1-11. Summary of Major Surface Water Sources with Detections of Alachlor from 

Various Studies Presented in the Alachlor RED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Occurrence Summary and Use Support Document March 2002 111

3.1.1 Introduction, Use and Production

Alachlor [2-chloro-2', 6'-diethyl-N-(methoxymethyl) acetanilide] is a pre-emergent amide herbicide. It is

an odorless, white crystalline solid. Alachlor is found in a variety of commercial herbicides including

Lasso, Lariat, and Crop Star. It also mixes well with other herbicides such as Bullet, Freedom, and Rasta

and in mixed formulations with atrazine, glyphosate, trifluralin and imazaquin (EXTOXNET, 2001).

The greatest use of alachlor is as a herbicide for control of annual grasses and broadleaf weeds in crops,

primarily on corn, sorghum and soybeans. Alachlor is the second most widely used herbicide in the U.S.,

with particularly heavy use on corn and soybeans in Illinois, Indiana, Iowa, Minnesota, Nebraska, Ohio,

and Wisconsin (USEPA, 2001). It is a selective systemic herbicide, absorbed by germinating shoots and

by roots. The chemical works by interfering with a plant’s ability to produce protein and by interfering

with root elongation (EXTOXNET, 2001).

Recent national estimates of agricultural use for alachlor are available. The United States Geological

Survey (USGS, 1998a) estimates approximately 25.65 million pounds of alachlor active ingredient were

used in 1992. These estimates were derived using State-level data sets on pesticide use rates available

from the National Center for Food and Agricultural Policy (NCFAP) combined with county-level data on

harvested crop acreage from the Census of Agriculture (Thelin and Gianessi, 2000). Corn accounts for

the majority of usage (13.9 million pounds alachlor ai), while moderate use can be found on several other

crops as well (e.g., soybeans, sorghum, beans). According to EPA estimates, from 1993-1995 annual

alachlor use ranged between 29.3 and 44.6 million pounds, with 20.5 to 28.0 million acres treated

(number of acres times number of times treated) (USEPA, 1998). Although no production data is

available, Monsanto in St. Louis, MO is the basic manufacturer of alachlor (EXTOXNET, 2001).

Figure 3.1-1 shows the USGS (1998a) derived geographic distribution of estimated average annual

alachlor use in the United States for 1992. A breakdown of use by crop is also included. The greatest

amount of alachlor is used in corn production, with the largest concentration of alachlor use seen in the

Midwest, where corn and soybeans are plentiful. While non-agricultural uses are not reflected here and

any sharp spatial differences in use within a county are not well represented (USGS, 1998c), existing

data suggest that non-agricultural use of alachlor is minimal to non-existent (USEPA, 1998). A

comparison of this use map with the map of the 16 cross-section States (Figure 1.3-1) shows that States

across the range of high of low alachlor use are well represented in the cross-section.
Occurrence Summary and Use Support Document March 2002 112

Figure 3.1-1: Estimated Annual Agricultural Use for Alachlor (1992)

Source: USGS 1998a

3.1.2 Environmental Release

Alachlor is listed as a Toxics Release Inventory (TRI) chemical. Table 3.1-1 illustrates the

environmental releases for alachlor from 1995 to 1999. (There are only alachlor data for these years.) 

Air emissions constitute most of the on-site releases, with a decrease since 1997. Total on- and off-site

releases first increased from 1995 to 1998 and then dropped off dramatically in 1999, as both air

emissions and off-site releases (including metals or metal compounds transferred off-site) decreased in

1999. Surface water discharges have remained relatively stable over the five-year period. No

underground injection or releases to land (such as spills or leaks within the boundaries of the reporting

facility) were reported for alachlor. These TRI data for alachlor were reported from five States: Illinois,

Iowa, Nebraska, Ohio, and Texas, with only Iowa reporting every year (USEPA, 2000). Illinois,

Nebraska, and Texas are included in the 16-State cross-section (used for analyses of alachlor occurrence

in drinking water; see Section 3.1.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)
Occurrence Summary and Use Support Document March 2002 113

Table 3.1-1: Environmental Releases (in pounds) for Alachlor in the United States, 1995-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 755 390 -- -- 1,270 2,415

1998 1,510 220 -- -- 9,100 10,830

1997 2,700 290 -- -- 3,600 6,590

1996 2,340 330 -- -- 4,100 6,770

1995 756 280 -- -- 2,940 3,976

 Source: USEPA, 2000 

3.1.3 Ambient Occurrence

Alachlor is an analyte for both surface and ground water NAWQA studies, with a method detection limit

(MDL) of 0.002 :g/L. Additional information on analytical methods used in the NAWQA study units,

including method detection limits, are described by Gilliom and others (1998).

Alachlor concentrations at all of the ground and surface water sites exceed the detection limit, with the

exception of urban ground water sites. High percentages of surface water samples exceed detection

frequencies of 0.01 and 0.05 :g/L. Within surface water sites, urban sites have consistently lower

percentage exceeding the detection frequencies then agricultural or integrator sites. Within ground water

sites, agricultural sites have a slightly higher percentage exceeding the detection frequencies than urban

or integrator sites. The maximum concentration exceeds the detection limit in all ground and surface

water sites. The 95th percentile values exceed the detection limit for all surface water sites, while none of

the 95th percentile values exceed the detection limit for any ground water sites. None of the median

values exceed the detection limit in ground or surface water sites.

Table 3.1-2: Alachlor Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

all samples > 0.01 :g/L > 0.05 :g/L 10th median 95th max

surface water

agricultural 36.36% 27.37% 11.49% < MDL < MDL 0.22 5.4

urban 13.46% 8.87% 3.67% < MDL < MDL 0.019 3.8

integrator 39.02% 26.02% 10.16% < MDL < MDL 0.17 2.1

all sites 30.58% 22.62% 9.91% < MDL < MDL 0.19 25E
Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

Occurrence Summary and Use Support Document March 2002 114

ground water

agricultural 3.14% 1.49% 0.54% < MDL < MDL < MDL 0.55

urban 0.33% ND ND < MDL < MDL < MDL 0.007

major aquifers 1.61% 0.86% 0.54% < MDL < MDL < MDL 0.14

all sites 3.04% 1.95% 1.03% < MDL < MDL < MDL 10E

Note: Individual maximum values with an “E-code” have much greater uncertainty because the values were beyond the calibration range.

ND=No detect

Source: USGS, 1998b

Alachlor was also an analyte in the 1999 Pilot Monitoring Program (Blomquist, et al., 2001). Alachlor

was detected in almost 30% of the 323 raw water samples and in about 22.4% of the 228 finished water

samples. The 95th percentile value was equal to 0.002 :g/L and 0.027 :g/L for raw and finished water

samples, respectively. The maximum concentration of alachlor in raw water was 0.655 :g/L. In finished

water, the maximum concentration of alachlor was 0.148 :g/L.

3.1.3.2 Additional Ambient Occurrence Data

A summary document entitled “Occurrence and Human Exposure to Pesticides in Drinking Water, Food,

and Air in the United States of America” (USEPA, 1989), was previously prepared for past USEPA

assessments of alachlor. Eleven studies reviewed in that document provided data on concentrations of

alachlor in water other than drinking water. Three studies assessed levels of alachlor in ground water,

and eight studies provided information on levels of alachlor in surface water. The following information

is taken directly from “Occurrence and Human Exposure to Pesticides in Drinking Water, Food, and Air

in the United States of America” (USEPA, 1989).

3.1.3.2.1 Ground Water Sources

Spalding, et al., (1980, as cited in USEPA, 1989) presented data from a study conducted in atrazine highuse areas of Nebraska. Water samples from 14 wells, out of a total of more than 1,000 wells that were

studied in the area, were selected as representative of water in the area. Water samples from 2 of the 14

wells contained an average alachlor concentration of approximately 0.04 :g/L (range = 0.018 to 0.071

:g/L). No detection limit was reported.

In addition, ground water wells from Nebraska, as well as from Iowa, Maryland, and Pennsylvania, have

been found to have concentrations of alachlor typically in the range of 0.1 to 10.0 :g/L (Cohen, et al.,

1986, as cited in USEPA, 1989). No other information on these wells was available.

Ground water wells and spring water in the Big Spring Basin, Clayton County, Iowa, were sampled

during 1981-1982 for the occurrence of alachlor (Datta, no date, as cited in USEPA, 1989). Ninety-five

samples from 21 locations were analyzed for alachlor, and 4 positive samples were found. An overall

mean of 0.082 :g/L (range = 0.05 to 0.15 :g/L) was calculated.

A survey of alachlor in rural private wells was performed (Monsanto, 1986, as cited in USEPA, 1989). 

The survey analyzed for alachlor in 246 wells in 9 States. The wells sampled were selected from private
Occurrence Summary and Use Support Document March 2002 115

wells in areas where alachlor was extensively used. Of the 246 wells sampled, 10 wells had detectable

levels of alachlor. The highest level reported was 5.8 :g/L. The remaining nine wells had levels below 1

:g/L. The detection limit was 0.1 :g/L.

3.1.3.2.2 Surface Water Sources

Baker et al. (1981, as cited in USEPA, 1989) presented data from a study that examined concentrations of

alachlor in stream water in Ohio. A total of 292 samples were collected from 12 different streams during

the spring and summer of 1981 and analyzed for alachlor. The analysis identified 235 (80%) positive

samples. The maximum concentration observed was 104.6 :g/L. No detection limit for the analysis was

given.

Baker (1983, as cited in USEPA, 1989) reported on levels of alachlor in water samples collected from

two Ohio rivers. Between May 28, 1983, and July 27, 1983, a total of 46 samples were collected (23

samples from each river). The average alachlor concentrations for samples collected and analyzed from

each of the rivers were 1.24 :g/L and 3.11 :g/L, respectively. The number of positive values and the

detection limit for alachlor were not reported.

Another study examining surface waters in Ohio was reviewed for alachlor occurrence data. Datta (no

date, as cited in USEPA, 1989) reported analyses of a creek in southwest Ohio during 1981, and again in

1982. Mean concentrations of alachlor for the two years were 13.9 :g/L and 7.6 :g/L, respectively. No

other information was reported. The same source (Datta, no date, as cited in USEPA, 1989) also reported

that for 5 northwest Ohio rivers, 233 samples were found to have mean peak concentrations of 23.2 :g/L

(maximum concentration = 69.6 :g/L). The number of positives and the detection limit were not

reported.

River samples from the Little Sioux River in northwest Iowa and Big Spring Basin, Iowa, were analyzed

for alachlor by the Iowa Department of Water, Air, and Waste Management and as part of the Review of

Hydrogeology, Water Quality, and Land Management in the Big Spring Basin, respectively (Kelley and

Wnuk, 1986; Datta, no date, all as cited in USEPA, 1989). During the overall study period from 1981 to

1985, 18 samples from 5 locations were taken, and 10 proved positive for alachlor. These positive

samples represent a mean of 2.59 :g/1 (range = 0.06-20.0 :g/L). No detection limit was given. A

reservoir on the Des Moines River was sampled for alachlor during 1977-1978 by Leung et al. (1982, as

cited in USEPA, 1989). Three sites were sampled (upstream, within, and downstream of the reservoir). 

A mean concentration of 0.089 :g/L (range = 0 to 0.82 :g/L) was reported for positive samples. The

number of positives, number of samples, and detection limit were not reported.

Twenty-five samples from River Raisin, Michigan, were taken at U.S. Geological Survey stations during

1982 (Datta, no date, as cited in USEPA, 1989). A maximum concentration of 8.16 :g/L was reported

for alachlor. No other information was reported.

Dudley and Karr (1980, as cited in USEPA, 1989) analyzed levels of atrazine and alachlor in 45 samples

of water, sediment, and fish. The samples were collected in mid-July from a stream draining an

agricultural watershed (Black Creek) in Allen County, Indiana. No samples of water showed levels of

alachlor in excess of the detection limit of 100 :g/1. The exact number of water samples was not

reported.

Schepers et al. (1980, as cited in USEPA, 1989) assessed concentrations of alachlor in 30 samples of

water collected from a watershed in Nebraska. Concentrations of alachlor in the 30 samples ranged
Occurrence Summary and Use Support Document March 2002 116

between "non-detectable" and 1.41 :g/L. However, the period of collection, detection limit, and number

of positive samples for alachlor were not reported.

Lake Erie water samples were collected during a study by Konasevich et al. (1978, as cited in USEPA,

1989). Three samples were positive for alachlor at a mean concentration of 3.05 :g/L (range = 0.07 to

9.0 :g/L). The number of samples and detection limit were not reported.

3.1.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of alachlor occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to two concentration thresholds of interest: 0.002 mg/L; and 0.0002 mg/L.

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

alachlor. These data represent more than 58,000 analytical results from approximately 14,000 PWSs

during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The number of

sample results and PWSs vary by State, although the State data sets have been reviewed and checked to

ensure adequacy of coverage and completeness. The overall modal detection limit for alachlor in the 16

cross-section States is equal to 0.0002 mg/L. (For details regarding the 16-State cross-section, please

refer to Section 1.3.5 of this report.)

3.1.4.1 Stage 1 Analysis Occurrence Findings

Table 3.1-3 illustrates the Stage 1 analysis of alachlor occurrence in drinking water for the public water

systems in the 16-State cross-section relative to two thresholds: 0.002 mg/L (the current MCL), and

0.0002 mg/L (the modal MRL). Approximately 0.0419% of (a total of 6 systems) all ground water and

surface water PWSs had any analytical results of alachlor exceeding the MCL. Approximately 0.488%

(70 systems) of PWSs had any exceedances of the modal MRL.

A greater proportion of surface water systems, as compared to ground water systems, exceeded each

threshold. Only 1 (approximately 0.00774% of) ground water PWSs had any analytical results exceeding

the MCL, compared to 5 (about 0.354% of) surface water systems. About 0.132% (17 systems) of

ground water PWSs had any analytical results exceeding 0.0002 mg/L. This compares to about 3.75%

(53 systems) of surface water systems with any analytical results greater than the modal MRL.

Table 3.1-3: Stage 1 Alachlor Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.002 0.00774% 1

0.0002 0.132% 17

Surface Water

0.002 0.354% 5

0.0002 3.75% 53
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 117

Combined Ground &

Surface Water

0.002 0.0419% 6

0.0002 0.488% 70

Reviewing alachlor occurrence in the 16 cross-section States by PWS population served (Table 3.1-4)

shows approximately 0.259% of the population (a total of 247,300 people) was served by PWSs with any

analytical results greater than the MCL. The percentage of population served by PWSs with any

exceedance of the modal MRL was 1.19% (over 1.1 million people).

The number of people served by ground water systems with any analytical results greater than 0.002

mg/L was equal to 700 (about 0.00171%). A total of 246,700 (approximately 0.445% of) people were

served by surface water systems with any analytical results greater than 0.002 mg/L. About 0.249% of

the population served by ground water PWSs (100,200 people) had any exceedances of 0.0002 mg/L,

compared to approximately 1.87% of the population served by surface water systems (1,036,700 people).

Table 3.1-4: Stage 1 Alachlor Occurrence Based on 16-State Cross-Section - Population Served

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.002 0.00171% 700

0.0002 0.249% 100,200

Surface Water

0.002 0.445% 246,700

0.0002 1.87% 1,036,700

Combined Ground &

Surface Water

0.002 0.259% 247,300

0.0002 1.19% 1,136,900

3.1.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.1-5 and 3.1-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2002)). 

No ground water or surface water PWSs had an estimated mean concentration of alachlor exceeding

0.002 mg/L (the current MCL). Approximately 8 (0.0559% of) ground water and surface water PWSs in
Occurrence Summary and Use Support Document March 2002 118

the 16-States were estimated to have mean concentrations of alachlor above 0.0002 mg/L (the modal

detection limit).

A greater proportion of surface water systems, as compared to ground water systems, were estimated to

exceed 0.0002 mg/L. Approximately 3 (0.0266% of) ground water systems in the 16 States had

estimated mean concentrations of alachlor above 0.0002 mg/L, compared to approximately 5 (0.323% of)

surface water systems. As stated above, no ground water or surface water PWSs had an estimated mean

concentration of alachlor exceeding 0.002 mg/L. 

Table 3.1-5: Stage 2 Estimated Alachlor Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.0266% 0.0077% - 0.0542% 3 1 - 7

Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.323% 0.0708% - 0.566% 5 1 - 8

Combined Ground

& Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.0559% 0.0279% - 0.0907% 8 4 - 13

Reviewing alachlor occurrence by PWS population served (Table 3.1-6) shows that approximately

68,500 (0.0716% of) the PWS population in the 16 States were served by systems with mean alachlor

concentrations above 0.0002 mg/L. When evaluated relative to a threshold of 0.002 mg/L, the percent of

population exposed was equal to 0%.

For ground water systems, about 15,500 people nationally (0.0385% of the population served by ground

water systems in the 16 cross-section States) were exposed to alachlor levels above 0.0002 mg/L.

Approximately 0.0956% of the population served by surface water PWSs (about 53,000 people in the 16-

State cross-section) had estimated mean concentrations of alachlor above 0.0002 mg/L.

Table 3.1-6: Stage 2 Estimated Alachlor Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.0385% 0.00383% - 0.112% 15,500 1,500 - 45,200
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 119

Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.0956% 0.00250% - 0.408% 53,000 1,400 - 226,200

Combined Ground

& Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.0716% 0.0104% - 0.2576% 68,500 9,900 - 246,500

3.1.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, no PWSs (therefore, no population served by systems) had estimated mean concentrations of

alachlor above 0.002 mg/L. Approximately 36 systems serving about 152,500 people served nationally

were estimated to have alachlor concentrations greater than 0.0002 mg/L. An estimated 16 ground water

systems serving about 33,000 people nationally had mean concentration values that exceeded 0.0002

mg/L. Approximately 18 surface water systems serving 121,700 people had estimated mean

concentrations greater than 0.0002 mg/L. (See Section 1.4 for a description of how Stage 2 16-State

estimates are extrapolated to national values.)

Table 3.1-7: Estimated National Alachlor Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0 0 - 0 0 0 - 0

0.0002 16 5 - 32 33,000 3,300 - 96,200

Surface Water

0.002 0 0 - 0 0 0 - 0

0.0002 18 4 - 32 121,700 3,200 - 519,500

Combined Ground

& Surface Water

0.002 0 0 - 0 0 0 - 0

0.0002 36 18 - 59 152,500 22,100 - 548,700

3.1.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of alachlor in drinking water are also reviewed. 

Previously compiled alachlor occurrence information is presented in following section. Information from

the EPA’s Office of Pesticide Program’s (OPP’s) “Reregistration Eligibility Decision (RED): Alachlor”
Occurrence Summary and Use Support Document March 2002 120

(USEPA, 1988) is presented in Section 3.1.5.1, and information from an OGWDW summary document

entitled “Occurrence and Human Exposure to Pesticides in Drinking Water, Food, and Air in the United

States of America” (USEPA, 1989) is presented in Sections 3.1.5.2 - 3.1.5.5. The following variety of

studies and information is presented regarding levels of alachlor in drinking water, with the scope of the

reviewed studies ranging from national to regional. Note that none of the studies presented in the

following section provide the quantitative analytical results or comprehensive coverage that would

enable direct comparison to the occurrence findings estimated with the cross-section occurrence data

presented in Section 3.1.4. These additional studies, however, do enable a broader assessment of the

Stage 2 occurrence estimates presented for this Six-Year Review. The information in Section 3.1.5.1 is

taken directly from “Reregistration Eligibility Decision (RED): Alachlor” (USEPA, 1988). All the

information in Sections 3.1.5.2 - 3.1.5.5 is taken directly from “Occurrence and Human Exposure to

Pesticides in Drinking Water, Food, and Air in the United States of America” (USEPA, 1989).

3.1.5.1 Summary of Alachlor Monitoring Information from OPP’s Alachlor Reregistration

The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) states that “the Administrator shall

determine whether pesticides containing such active ingredient are eligible for reregistration,” before

either reregistering products or taking “other appropriate regulatory action.” Thus, reregistration

involves a thorough review of the scientific data base underlying a pesticide's registration. The purpose

of the Agency's review is to reassess the potential hazards arising from the currently registered uses of

the pesticide; to determine the need for additional data on health and environmental effects; and to

determine whether the pesticide meets the “no unreasonable adverse effects” criterion of FIFRA. 

In 1988, OPP published a “Reregistration Eligibility Decision” (RED) for alachlor (USEPA, 1988). 

Several sources of information on monitoring/detections of alachlor in ground water and surface water

were reviewed in the RED, and are summarized below. However, because most of these studies were

conducted in predominantly high atrazine use areas, the occurrence findings cannot be directly compared

to the Stage 2 national occurrence estimates for alachlor.

The most extensive review of alachlor occurrence data included in the RED was collected through the

Acetochlor Registration Partnership (ARP) Monitoring Program. This study included monitoring for

alachlor as part of Monsanto's conditional registration monitoring program for Acetochlor. Since 1995,

wells and surface waters in the major corn growing regions of the U.S. have been monitored.

The ARP Ground Water Monitoring Program involved the creation of a unique network of 175 ground

water monitoring wells. These wells are of great relevance to U.S. agriculture because they represent the

range of soil and agriculture in seven key Midwest states (Illinois, Indiana, Iowa, Kansas, Minnesota,

Nebraska, and Wisconsin) and are positioned directly next to treated corn fields. As a requirement for

the registration of acetochlor, the two acetochlor registrants are conducting a ground water monitoring

program in seven major use states. Analytes include alachlor, acetochlor, and atrazine, dimethenamid,

and metolachlor. Ground water samples are collected monthly from 175 wells located in corn producing

areas. The limits of detection and quantification for all analytes are 0.03 :g/L and 0.05 :g/L,

respectively. 

Results for alachlor are summarized in Table 3.1-8. Fourteen of the wells had alachlor detects greater

than limit of quantification (LOQ - 0.05 :g/L). Twenty-seven wells had alachlor detections above the

limit of detection (LOD) of 0.03 :g/L. Approximately 36% of the alachlor detections exceeded the MCL

(2.0 :g/L) and 54% exceeded a one-in-million cancer risk level of 0.4 :g/L. Approximately 75% of the

detections exceeded 0.11 :g/L. 
Occurrence Summary and Use Support Document March 2002 121

Table 3.1-8. Summary Alachlor Monitoring in Ground Water Conducted by the ARP

Statistic

Detection/Concentration

(:g/L)

Number of Samples with Detects $0.05 :g/L (% of samples) 30 (1.7%)

Number of Wells (% of 173) 14 (8.1%)

Number of Samples1 1,720

Mean 3.38

Minimum 0.05

Median 0.73

Maximum 15.89

The Acetochlor Registration Partnership also provides the most extensive data on alachlor concentrations

in finish surface drinking water available to OPP. Samples were collected at 179 different sites (drinking

water utilities) in the following 12 states: DE, IL, IN, IA, KS, MD, MN, MO, NE, OH, PA, and WI. 

Samples were collected approximately once every two weeks from April through early September. Two

to three additional samples were collected at most sites, one to two in the fall and one in the winter. 

Unfiltered samples were analyzed for total alachlor.

Additional detail is provided in a review and analysis of the data by R. David Jones (EFED memo dated

May 24, 1996 to B. Montague) and in an electronic spreadsheet (summary statistics) by S. Abel. These

analyses provide yearly summary statistics for peak, 96-hour time weighted mean concentrations

(TWMC), annual TWMC for 1995 (R. David Jones), and peak and annual TWMC for 1996 (S. Abel). 

Additionally, running peak and annual TWMC are provided for both years data. Based on the re-analysis

of data from 1995 through 1996, Table 3.1-9 provides maximum and 90th percentile (upper 10th

percentile) concentrations (peak and annual TWMC).

Table 3.1-9. Summary of 1995 and 1996 Alachlor Monitoring in Surface Water Conducted by the

ARP

Statistic Calculation for a given site

Summary Across Sites

Maximum Value for any Site (

:g/l)

Value Equaled/Exceeded

on 10% of Sites ( :g/l)

Peak

Concentrations

Highest Value Observed 1995-1996,

for any Site 4 0.63

Annual Time

Weighted Mean

Weighted Mean for 1995-1996,

for any Site (weight by time) 0.36 0.1

In addition to the ARP data, several other studies of alachlor monitoring data were summarized in the

Alachlor RED. Table 3.1-10 presents a summary of additional ground water occurrence findings and

Table 3.1-11 summarizes the major surface water studies contained in that report.
Occurrence Summary and Use Support Document March 2002 122

Table 3.1-10. Summary of Wells with Detections of Alachlor from Various Studies Presented in

the Alachlor RED

Study1 Well type

Number of Wells (%)

Sampled Alachlor

Detected

Concentration

< MCL

Concentration

$ MCL

USGS (1991 - 1994) drinking 303 10 (3.3%) 9 (3.0%) 1 (0.3%)

ARP-GWMP monitoring 173 27 (15.6%) 25 (14.5%) 2 (1.2%)

PGWDB mixed, most drinking 25,933 467 (1.8%) 368 (1.4%) 99 (0.4%)

NPS drinking 1300 1 (< 0.1%) 0 (0%) 1 (< 0.1%)

NAWWS drinking 1430 28 (2.0%) 26 (1.8%) 2 (0.1%)

1

 USGS = U.S. Geological Survey Midcontinent Study, ARP-GWMP = Acetochlor Registration Partnership Ground water Monitoring Program;

PGWDB = Pesticides in Ground Water Database; NPS = National Pesticide Survey; NAWWS = National Alachlor Water Well Survey.

Table 3.1-11. Summary of Major Surface Water Sources with Detections of Alachlor from

Various Studies Presented in the Alachlor RED

Study Number of Sites

Maximum Peak

(:g/l)

Maximum TWMC1

(:g/l)

ARP (1995-1996) 175-179 4.0 0.36

USGS - Midwestern Stream Recon. (1989) 48 51.3 11.6

USGS - Mississippi River Basin Study (1991-1992) 8 3.6 0.43

State of Illinois (1986-1988) 30 18 0.81

Monsanto Finished Surface Water Study (1986) 30 9.5 1.1

Monsanto Finished Surface Water Study 1985 30 12 1.5

USGS Cedar River basin Study (1984) 6 23 1.7

Ohio Tributaries to Lake Erie (1982-1985) 8 76 3.3 2

Lake Erie Basin Case Study (1983-1987) 7 91.47 1.74

1. TWMC: Time weighted mean concentrations, annual unless otherwise noted.

2. Time weighted mean concentration calculated over a 4 month period of the study; April 15 to August 15

3.1.5.2 Ground Water Sources – National Study

The National Screening Program for Organics in Drinking Water (NSP) (Boland, 1981, as cited in

USEPA, 1989) was conducted by SRI from June 1977 to March 1981. Samples of finished drinking

water were collected from 12 ground water systems of varying size throughout the United States and

analyzed for alachlor. None of the drinking water samples from the 12 ground water systems contained

levels of alachlor in excess of the quantification limit of 0.1 :g/L.
Occurrence Summary and Use Support Document March 2002 123

3.1.5.3 Ground Water Sources – Regional Studies

Drinking water wells from eight counties in Maryland were examined by the State of Maryland's Office

of Environmental Programs, Department of Health and Mental Hygiene, in the fall of 1983 (State of

Maryland, 1983, as cited in USEPA, 1989). Thirteen samples were collected from 11 locations and

analyzed for alachlor. Two samples were positive at concentrations of 0.1 and 0.8 :g/L. The detection

limit was 0.1 :g/L.

The Suffolk County Department of Health Services analyzed drinking water wells in Long Island, New

York, during 1984 (Holden, 1986, as cited in USEPA, 1989). Alachlor was not detected in any of 24

samples collected (detection limit not reported).

Drinking water wells throughout the State of Wisconsin were analyzed by Union Carbide during 1983-

1984 as part of a Wisconsin Department of Natural Resources program (Holden, 1986, as cited in

USEPA, 1989). Possible contamination may have occurred from both point and nonpoint sources. Of

the 377 samples analyzed, 47 were found positive for alachlor, with a maximum concentration of 88

:g/L. The mean concentration, range of values, and detection limit were not reported.

Two studies of drinking water wells in Iowa were available for information on the occurrence of

alachlor: one conducted by Iowa State University and the other by the Iowa Department of Water, Air,

and Waste Management (Baker and Austin, 1983: Kelley and Wnuk, 1986, all as cited in USEPA, 1989). 

Combined, the studies included six Iowa counties sampled between 1981 and 1985. Fifty-nine samples

were analyzed from 25 sites, with all but one positive sample coming from Humboldt County. The

overall range was 0 to 2.7 :g/L (the detection limit was 0.01 :g/L). The one positive sample from

outside Humboldt County was 0.18 :g/L. The mean for Humboldt County samples, all taken at one site,

was 0.08 :g/L (the detection limit was 0.01 :g/L). The total number of positives and other detection

limits were not reported.

3.1.5.4 Surface Water Sources – National Study

The National Screening Program for Organics in Drinking Water (NSP) (Boland, 1981, as cited in

USEPA, 1989) also contained information on alachlor contamination in drinking water from surface

water sources. Finished drinking water samples, collected from 104 surface water systems of varying

size throughout the United States, were analyzed for alachlor. Drinking water samples from four very

large systems (serving greater than 100,000 individuals) were found to contain levels of alachlor in

excess of the quantification limit of 0.1 :g/L, ranging between 0.1 and 0.9 :g/L, with an average value of

0.38 :g/L.

3.1.5.5 Surface Water Sources – Regional Studies

Alachlor was monitored in known high-use areas of Illinois, Indiana, Iowa, Michigan, Missouri, North

Carolina, and Ohio (Monsanto, 1986, as cited in USEPA, 1989). Sampling occurred at 24 community

water treatment plants in these seven States, which primarily or exclusively utilize surface water

supplies. Populations of the 24 communities ranged from 356 to 388,000 and, overall, the study is

representative of over 1.3 million people using public drinking water. Both raw and finished water

samples were collected daily from each location for 1 year, and were turned into weekly composites. 

Sampling took place between April 1985 and April 1986. The lower limit of method validation (LLMV)

was 0.02 :g/L.
Occurrence Summary and Use Support Document March 2002 124

Alachlor was not detected in any weekly sample of finished water from 10 of the 24 plants. Of the other

14 plants, the annualized mean concentration (AMC, i.e., a time-weighted average concentration) at 12

plants was less than 0.50 :g/L. The other two plants had AMCs of 0.69 :g/L and 1.4 :g/L. Rarely was

alachlor found above 2.0 :g/L in a weekly composite: only 2.6 percent of the weekly composites

exceeded 2.0 :g/L during the sampling year (Monsanto, 1986, as cited in USEPA, 1989). The weekly

composite maximum concentrations ranged from <0.20 to 10.7 :g/L for raw water samples and from

<0.20 to 10.9 :g/L for finished water samples. The AMCs ranged from 0 to 1.5 :g/L for raw water

samples, and from 0 to 1.4 :g/L for finished water samples. [Note: For the AMC range, the lower value

assumes that all non-detected = 0 :g/L and the higher value assumes that all non-detected = 0.20 :g/L.] 

Individual sample results were not presented in the report.

Baker (1983, as cited in USEPA, 1989) provided the results of analysis of finished drinking water

samples collected from a water supply in Ohio from 1981-1982. The supply obtained water from a river

draining an agricultural area. Between June 1981 and July 1982, 15 finished drinking water samples

were collected from this plant. Although no detection limits were given, 14 of the samples had positive

concentrations of alachlor that ranged between 0.03 and 14.3 :g/L, with an average of 4.5 :g/L.

In the study by Baker (1983, as cited in USEPA, 1989), 49 samples were collected from 3 water supplies

in Ohio and analyzed for alachlor. The supplies obtained their raw water from two rivers that drain

agricultural areas. Average concentrations for samples collected at each of the supplies between May 28

and July 27, 1983 were 1.08 (18 samples), 0.22 (15 samples), and 1.87 :g/L (16 samples). Peak

concentrations observed in 1983 were 2.73, 0.47, and 5.91 :g/L, respectively. Datta (no date, as cited in

USEPA, 1989) reported an overall mean concentration of 1.07 :g/L for these supplies. The detection

limit and number of positive samples were not reported.

Finished drinking water samples from New Orleans, Louisiana were analyzed by Keith et al. (1976, as

cited in USEPA, 1989). The range of positive samples for alachlor was 0.17 to 2.9 :g/L. The number of

samples analyzed, number of positive samples, mean, and detection limit were not reported.

3.1.6 Conclusion

Alachlor is a manufactured chemical that is the second most commonly used herbicide in the United

States. It is most often used for control of annual grasses and broadleaf weeds in crops, primarily on

corn, sorghum and soybeans. Recent statistics regarding use of alachlor indicate production and use are

considerable. Industrial releases of alachlor have been reported to TRI since 1995 from five States. 

Alachlor was also an analyte for the NAWQA occurrence studies. In the NAWQA study, alachlor was

detected in ground and surface water; however, none of the median values exceeded the detection limit. 

The Stage 2 analysis, based on the 16-State cross-section, estimated that zero percent of combined

ground water and surface water systems serving zero percent of the population exceeded the MCL of

0.002 mg/L. Based on this estimate, zero PWSs nationally are estimated to have levels greater than the

MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, TRI releases have been reported for alachlor from 5 States, including 3 of

16 cross-section States. According to information from USGS, all of the 16 cross-section States use

alachlor, although for most States in light to moderate amounts. Alachlor is used most heavily in the

Midwest, where there are six cross-section States. The cross-section should adequately represent the

occurrence of alachlor on a national scale based upon the use, production, and release patterns of the 16-

State cross-section in relation to the patterns observed for all 50 States.
Occurrence Summary and Use Support Document March 2002 125

3.1.7 References

Baker, D.B., K.A. Krieger, and J.V. Setzler. 1981. The Concentrations and Transport of Pesticides in

Northwestern Ohio Rivers. Prepared by Water Quality Laboratory, Heidelberg College, Tiffin,

Ohio, for Lake Erie Wastewater Management Study, U.S. Army Corps of Engineers, Buffalo,

New York.

Baker, D.B. 1983. Herbicide Contamination in Municipal Water Supplies of Northwestern Ohio. Draft

Final Report. Water Quality Laboratory, Heidelberg College, Tiffin, OH.

Baker, J.L., and T.A. Austin. 1983. Impact of Agricultural Drainage Wells on Groundwater Quality. 

Completion Report 1981-1983. Departments of Agricultural Engineering and Civil Engineering,

Iowa State University. EPA Grant No. G007228010.

Blomquist, J.D., J.M. Denis, J.L. Cowles, J.A. Hetrick, R.D. Jones, and N.B. Birchfield. 2001. 

Pesticides in Selected Water-Supply Reservoirs and Finished Drinking Water, 1999-2000: 

Summary of Results from a Pilot Monitoring Survey. U.S. Geological Survey Open-File Report

01-456. 65 pp.

Boland, P.A. 1981. National Screening Program for Organics in Drinking Water. Part II. Data.

Prepared by SRI International, Menlo Park, California, for Office of Drinking Water, U.S.

Environmental Protection Agency, Washington, DC. EPA Contract No. 68-01-4666. 

Cohen, S.Z., C. Eiden, and M.N. Lorder. 1986. Evaluation of Pesticides in Groundwater. W.Y. Garner,

R.C. Honeycutt, H.N. Nigg (eds.). American Chemical Society, Washington, DC. ACS

Symposium Series 315.

Datta, P.R. No date. Memorandum: Review of six documents regarding monitoring of pesticides in

Northwestern Ohio rivers. Sent to: D.J. Severn, Chief - Exposure Assessment Branch, HED. 

Washington, DC: Office of Pesticides and Toxic Substances, USEPA.

Dudley, D.R., and J.R. Karr. 1980. Pesticides and PCB residues in the Black Creek watershed, Allen

County, Indiana, 1977-1978. Pestic. Monit. J. v.13, no. 4, pp.155-157.

EXTOXNET. 2001. Pesticide Information Profile: Alachlor. Ithaca, NY: Extension Toxicology

Network, Pesticide Management Education Program. Available on the Internet at

http://pmep.cce.cornell.edu/profiles/extoxnet/24d-captan/alachlor-ext.html, last updated March 1,

2001.

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at: 

http://ca.water.usgs.gov/pnsp/rep/ofr97589, last updated October 9, 1998. 

Holden, P.W. 1986. Pesticides and Groundwater Quality. Issues and Problems in Four States.

Prepared for the Board of Agriculture, National Research Council. Washington, DC: National

Academy Press.
Occurrence Summary and Use Support Document March 2002 126

Keith, L.H., H.W. Garrison, F.R. Allen, et al. 1976. Identification of organic compounds in drinking

water from 13 U.S. cities. In: Identification and Analysis of Organic Pollutants in Water. Ann

Arbor, MI: Ann Arbor Sciences Publishers, Inc. pp. 329-373.

Kelley, R., and M. Wnuk. 1986. Little Synthetic Organic Compound Municipal Well Sampling Survey.

Des Moines, IA: Iowa Department of Water, Air, and Waste,.

Konasevich, D., W. Traversy, and H. Zar. 1978. Status Report on Organic and Heavy Metal

Contaminants in the Lakes Erie, Michigan, Huron and Superior Basins. Great Lakes Water

Quality Board. p. 37.

Leung, SY.Th., R.V. Bulkley, and J.J. Richard. 1982. Pesticide accumulation in a new impoundment in

Iowa. Water Res. Bull. v. 18, no. 3, pp. 485-493.

Monsanto Agricultural Company. 1986. Information to support the registration of Lasso herbicides. 

EAP Reg. Nos. 524-285, 524-296, 524-314, 524-329, 524-341, 524-344. Alachlor in raw and

finished drinking water derived from surface sources from 24 community water systems located

in regions of extensive Lasso use. Compiled by S.R. Muench, Monsanto Agricultural Company,

St. Louis, MO. 

Schepers, J.S., E.J. Vavricka, and G.E. Schuman. 1980. Agricultural runoff during a drought period. J.

WPCF v. 52, no. 4.

Spalding, R.F., G.A. Junk, and J.J. Richard. 1980. Pestic. Monit. J. v. 14, no. 2, pp. 70-73.

State of Maryland. 1983. Summary Report: Results of a Maryland ground water herbicide survey. Fall

1983. Office of Environmental Programs. Department of Health and Mental Hygiene.

Thelin, Gail P., and Leonard P. Gianessi. 2000. Method for Estimating Pesticide Use for County Areas

of the Conterminous United States. U.S. Geological Survey Open-File Report 00-250. 

62 pp. Available on the Internet at: http://water.wr.usgs.gov/pnsp/rep/ofr00250/ofr00250.pdf.

USEPA. 1989. Draft Final Report on the Occurrence and Human Exposure to Pesticides in Drinking

Water, Food, and Air in the United States of America. Office of Drinking Water, USEPA. 

September, 1989.

USEPA. 1998. Reregistration Eligibility Decision (RED): Alachlor. EPA Report 738-R-98-020. 

Washington, DC: Office of Prevention, Pesticides, and Toxic Substances, USEPA. Available on

the Internet at: http://www.epa.gov/oppsrrd1/REDs/0063red.pdf.

USEPA. 1998. R.E.D. Facts: Alachlor. EPA Report 738-F-98-018. Washington, DC: Office of

Prevention, Pesticides, and Toxic Substances, USEPA. 12 pp. Available on the Internet at:

http://www.epa.gov/oppsrrd1/REDs/factsheets/0063fact.pdf

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: Alachlor.

Office of Ground Water and Drinking Water, USEPA. Available on the Internet at

http://www.epa.gov/safewater/dwh/c-soc/alachlor.html, last updated April 12, 2001.
Occurrence Summary and Use Support Document March 2002 127

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1998a. Annual Use Maps. Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/,

last updated March 20, 1998.

USGS. 1998b. Pesticides in Surface and Ground Water of the United States: Summary of Results of the

National Water Quality Assessment Program (NAWQA). PROVISIONAL DATA -- SUBJECT TO

REVISION. Available on the Internet at: http://water.wr.usgs.gov/pnsp/allsum/, last updated

October 9, 1998. 

USGS. 1998c. Sources & limitations of data used to produce maps of annual pesticide use. Reston,

VA: United States Geological Survey. Available on the Internet at:

http://water.wr.usgs.gov/pnsp/use92/mapex.html (last updated March 20, 1998).
Occurrence Summary and Use Support Document March 2002 128

3.2 Bis(2-ethylhexyl)phthalate (DEHP)

Table of Contents

3.2.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

3.2.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

3.2.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

3.2.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 133

3.2.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

3.2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

3.2.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

Tables and Figures

Table 3.2-1: DEHP Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Table 3.2-2: Environmental Releases (in pounds) for DEHP in the United States, 1988-1999 . . . . . . 131

Table 3.2-3: Stage 1 DEHP Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . . . 133

Table 3.2-4: Stage 1 DEHP Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . . . 134

Table 3.2-5: Stage 2 Estimated DEHP Occurrence Based on 16-State Cross-Section - Systems . . . . 135

Table 3.2-6: Stage 2 Estimated DEHP Occurrence Based on 16-State Cross-Section - Population . . 136

Table 3.2-7: Estimated National DEHP Occurrence - Systems and Population Served . . . . . . . . . . . 137
Occurrence Summary and Use Support Document March 2002 129

3.2.1 Introduction, Use and Production

Bis(2-ethylhexyl)phthalate (also known as di(2-ethylhexyl)phthalate, or DEHP) is the most commonly

used chemical of a group of related synthetic organic chemicals called phthalates or phthalic acid esters. 

DEHP is a colorless liquid with almost no odor. It does not evaporate easily, and little will be present in

the air even near sources of production. It dissolves more easily in materials such as gasoline, than it

does in water. Trade names for DEHP are Platinol DOP, Octoil, Silicol 150, Bisoflex 81, and Eviplast 80

(ATSDR, 2000).

DEHP is a manufactured chemical that makes plastic more flexible. It is one of several plasticizers in

polyvinyl chloride (PVC) resins used to fabricate flexible vinyl products (NSC, 2001). At least 95% of

DEHP produced is used as a plasticizer for polyvinylchloride (PVC) and other polymers including

rubber, cellulose and styrene. PVC is used in many consumer products such as wall coverings,

tablecloths, floor tiles, furniture upholstery, shower curtains, garden hoses, swimming pool liners,

rainwear, baby pants, dolls, toys, shoes, automobile upholstery and tops. A number of packaging

materials and tubing used in the production of foods and beverages are PVC contaminated with phthalic

acid esters, primarily DEHP (USEPA, 2001). These materials include packaging film and sheet,

sheathing for wire and cable, medical tubing, and blood storage bags. 

Although DEHP does have uses as a non-plasticizer, they are very minor and relatively unimportant. It

can be used as a solvent in erasable ink, as an acaricide in orchards, as a component of dielectric fluids in

electrical capacitors, to detect leaks in respirators, and as an inert ingredient in pesticide products, in

cosmetics, in vacuum pump oil. DEHP can also be used in testing air filtration systems. In some cases,

its use has been discontinued because of concerns about health effects. Many toy manufacturers have

stopped using DEHP, and it is also no longer used for teethers and rattlers or in plastic food wrap

products (ATSDR, 2000).

DEHP is produced as part of a group of chemicals that are collectively known as phthalate esters, and, as

such, no production value for any single one of them is recorded. DEHP is included in a subgroup called

dioctyl phthalates, which also includes di-ethylhexyl phthalate, diisooctyl phthalate, and di-n-octyl

phthalate. Collective production amounts of dioctyl phthalates are as follows: 1990, 309 million pounds;

1994, 258 million pounds; 1995, 280 million pounds; 1996, 280 million pounds; 1997, 287 million

pounds, and 1998, 285 million pounds. Production of DEHP in coming years is expected to grow at a

slower rate than the economy because of limited growth in the PVC market. Demand for DEHP will also

continue to decrease due to health concerns (ATSDR, 2000).

Table 3.2-1 shows the number of facilities in each State that manufacture and process DEHP, the

intended uses of the product, and the range of maximum amounts derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 2000). 

Table 3.2-1: DEHP Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on site in

poundsb Activities and usesc

AL 4 1,000-99,999 8,11,13

AR 6 100-999,999 8,9,12,13

CA 15 1,000-999,999 2,3,8,9,12

CO 1 1,000-99,999 8,9

CT 4 1,000-99,999 8,9,10,12

DE 1 1,000-9,999 8

FL 3 1,000-99,999 8,9
Statea Number of facilities Range of maximum amounts on site in

poundsb Activities and usesc

Occurrence Summary and Use Support Document March 2002 130

GA 8 1,000-99,999 8,9,10

IA 1 10,000-99,999 9

IL 19 100-999,999 2,3,7,8,9,11

IN 8 1,000-99,999 7,8,9

KS 4 100-99,999 8,9,13

KY 3 100-99,999 8

LA 2 1,000-99,999 7,8

MA 12 100-999,999 1,6,8,9,10,11,13

MD 6 100-9,999,999 1,4,8,13

MI 11 100-99,999,999 8,9,12,13

MN 9 1,000-99,999 7,8,9

MO 12 1,000-999,999 7,8,9,13

MS 7 1,000-999,999 8,9

NC 17 100-999,999 1,2,3,5,8,9,11

NE 3 10,000-99,999 8,9

NH 4 1,000-99,999 8,9,13

NJ 11 1,000-999,999 2,3,8,9,11

NV 2 1,000-999,999 8

NY 11 1,000-9,999,999 1,3,5,7,8,9,13

OH 31 1,000-999,999 2,3,7,8,9,12

OK 3 1,000-999,999 7,9

PA 16 1,000-9,999,999 1,4,8,9,12,13

PR 8 10,000-999,999 8,9

RI 3 10,000-999,999 8,9

SC 7 100-999,999 8,9,12,13

SD 1 1,000-9,999 9

TN 13 1,000-9,999,999 1,3,4,5,6,7,8,9,10,11,12

TX 12 1,000-999,999 2,3,8,9,10,13

UT 1 1,000-9,999 2,5,8,12

VA 4 10,000-999,999 8,9

VT 1 10,000-99,999 8

WA 2 100-9,999 8

WI 9 1,000-999,999 8,9

WV 2 1,000-9,999 8

a

Post office State abbreviations used

b

Range represents maximum amounts on site reported by facilities in each State

c

Activities/Uses:

1. Produce 8. Formulation component

2. Import 9. Article component

3. On-site use/processing 10. Repackaging

4. Sale/distribution 11. Chemical processing aid

5. Byproduct 12. Manufacturing aid

6. Impurity 13. Ancillary/other uses

7. Reactant

Source: ATSDR, 2000 compilation of TRI97 2000 data

3.2.2 Environmental Release

DEHP is listed as a Toxics Release Inventory (TRI) chemical. Table 3.2-2 illustrates the environmental

releases for DEHP from 1988 to 1999. (There are only DEHP data for these years.) Air emissions

constitute most of the on-site releases, with a relatively steady decrease over the years. Other on-site

releases, such as surface water releases and releases to land (such as spills or leaks within the boundaries

of the reporting facility) do not display any discernable trend from 1988 to 1999. Underground injections

decreased from 1988 to1993, and have remained at zero ever since. Off-site releases (including metals or

metal compounds transferred off-site) have generally fallen over the years (with the exception of a brief

spike in 1995) from almost 4 million pounds to under 1 million pounds. The decrease in off-site releases,

as well as the decrease in air emissions, have contributed to decreases the total on- and off-site releases

of DEHP in recent years. These TRI data for DEHP were reported from 44 States, with 33 States

reporting every year (USEPA, 2000). Of the 44 States, 14 are included in the 16-State cross-section
Occurrence Summary and Use Support Document March 2002 131

(used for analyses of DEHP occurrence in drinking water; see Section 3.2.4). (For a map of the 16-State

cross-section, see Figure 1.3-1.)

Table 3.2-2: Environmental Releases (in pounds) for DEHP in the United States, 1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 226,926 2,629 0 4,685 917,024 1,151,264

1998 215,583 669 0 24,184 1,121,544 1,361,980

1997 240,523 595 0 71,009 1,087,976 1,400,103

1996 447,429 363 0 59,612 1,946,238 2,453,642

1995 504,167 921 0 19,705 3,041,389 3,566,182

1994 462,795 967 0 5,308 1,988,809 2,457,879

1993 571,014 1,248 0 7,192 2,894,667 3,474,121

1992 911,486 954 35 5,357 2,816,258 3,734,090

1991 1,161,162 3,849 370 87,625 2,955,417 4,208,423

1990 1,413,760 2,424 265 19,551 3,236,012 4,672,012

1989 1,173,021 2,987 600 25,937 3,723,521 4,926,066

1988 1,217,329 2,781 3,091 20,748 3,630,612 4,874,561

 Source: USEPA, 2000b

3.2.3 Ambient Occurrence

To understand the presence of a chemical in the environment, an examination of ambient occurrence is

useful. In a drinking water context, ambient water is untreated source water residing in surface waters

and aquifers. There are few available data on the occurrence of DEHP in ambient waters of the United

States. The most comprehensive and nationally consistent data describing ambient water quality in the

United States are being produced through the United States Geological Survey’s (USGS) National Water

Quality Assessment (NAWQA) program. However, national NAWQA data, as well as NPDES and

NURP data, are currently unavailable for DEHP.

3.2.3.1 Additional Ambient Occurrence Data

A summary document entitled Occurrence and Exposure of Phthalate Esters in Public Drinking Water

Supplies” (Wade Miller, 1989), was previously prepared for past USEPA assessments of DEHP. A

number of studies reviewed in that document provided data on concentrations of DEHP in water other

than drinking water. These studies, conducted on both regional and national levels, are summarized in

the following section. The following information is taken directly from “Occurrence and Exposure of

Phthalate Esters in Public Drinking Water Supplies” (Wade Miller, 1989).

3.2.3.1.1 Ground Water Sources

DEHP was detected in ground waters at infiltration sites of secondary effluents at Ft. Devens, MA;

Boulder, CO; Lubbock, TX; and Phoenix, AZ. The maximum reported concentration for DEHP was 1.40

:g/L (USEPA, 1987, as cited in Wade Miller, 1989).
Occurrence Summary and Use Support Document March 2002 132

Several phthalate esters have been detected in ground waters from landfill sites nationwide. DEHP was

detected at a maximum concentration of 100.0 :g/L at a landfill site in New Castle County, DE (USEPA,

1987, as cited in Wade Miller, 1989).

The USEPA's computerized water quality data base known as STORET was devised to assist Federal and

State institutions meet objectives of Public Law 92-500 to maintain and enhance the physical, chemical,

and biological quality of the nation's ambient waterways by providing for the collection and

dissemination of basic water quality data (Staples et al., 1985, as cited in Wade Miller, 1989). Data are

collected by States, EPA regional offices, and other government agencies and are maintained in the

STORET system.

Before presenting a summary of the ambient water data in STORET, it is important to note that there are

significant limitations in using the data base to estimate representative concentrations of a contaminant

such as hexachlorobenzene. Data entered into STORET are gathered from an array of studies conducted

for various purposes. Analyses are conducted in a number of different laboratories employing different

methodologies with a range of detection limits. In many cases, detection limits are not reported, making

the reliability of the data highly questionable. Where detection limits have been reported, STORET

assigns the detection limit value to those observations reported as not detected. This can lead to errors in

interpretation and overestimation of concentrations in cases in which there is a preponderance of

nondetectable values. Additionally, a few high values can inflate mean values and result in large

standard deviations relative to the means (Staples et al., 1985, as cited in Wade Miller, 1989). Very high

values may not be correct, as they may reflect sample contamination or analytical error and can

significantly distort assessment of average concentrations. Staples et al. (1985, as cited in Wade Miller,

1989) also notes that the use of data collected prior to the 1980s is not recommended, since such data was

obtained using less sensitive laboratory techniques and quality assurance procedures were not yet

mandated for the data entered into the system.

The STORET water quality data base provides information on the occurrence of contaminants at ambient

water stations in U.S. waterways. A summary of this information was obtained for DEHP in ambient

waters. Ambient sites include streams, lakes, ponds, wells, reservoirs, canals, estuaries, and oceans. 

While the preponderance of data were collected from surface water sources, the number of samples

collected from ground water wells, relative to the total number of samples collected from all ambient

sites combined, is unspecified (Staples et al., 1985, as cited in Wade Miller, 1989). Staples et al. (1985,

as cited in Wade Miller, 1989) have summarized data from the 1980's only; that is, data from 1980

through 1983. This was done based on the number of data points and the likelihood that better quality

assurance practices have been employed in more recent years. In the absence of sophisticated statistical

analyses to eliminate improbable data, median values have been reported. The median value is sensitive

to extreme values, and reflects a measure of central tendency more accurately than the mean value in the

presence of these extreme values (Staples et al., 1985, as cited in Wade Miller, 1989).

The median concentration of DEHP was 10.0 :g/L, with 24 percent of 901 observations reported as

detectable. Detection limits and other sampling information were not given for any of the contaminants.

3.2.3.1.2 Surface Water Sources

Phthalate esters have been detected in surface waters throughout the United States. DEHP was detected

in Delaware River water two miles downstream from a Philadelphia wastewater treatment plant at a

concentration of 1.0 :g/L (USEPA, 1987, as cited in Wade Miller, 1989). DEHP was detected in water

from Galveston Bay, TX at a mean concentration of 0.6 :g/L, and in Mississippi River water at a

(tentatively) maximum concentration of 600.0 :g/L (USEPA, 1987, as cited in Wade Miller, 1989). 
Occurrence Summary and Use Support Document March 2002 133

DEHP has also been detected in U.S. industrial water basins at concentrations ranging from 1.0 to 85.0

:g/L (USPHS, 1987, as cited in Wade Miller, 1989).

3.2.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of DEHP occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.006 mg/L; 0.003 mg/L; and 0.0006 mg/L.

Thirteen of the sixteen cross-section State data sets contained occurrence data for DEHP. (No data were

reported from New Jersey, New Mexico, or Oregon.) These data represent more than 41,000 analytical

results from approximately 9,400 PWSs during the period from 1984 to 1998 (with most analytical

results from 1992 to 1997). The number of sample results and PWSs vary by State, although the State

data sets have been reviewed and checked to ensure adequacy of coverage and completeness. The overall

modal detection limit for DEHP in the 16 cross-section States is equal to 0.0006 mg/L. (For details

regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)

3.2.4.1 Stage 1 Analysis Occurrence Findings

Table 3.2-3 illustrates the Stage 1 analysis of DEHP occurrence in drinking water for the public water

systems in the 16-State cross-section relative to three thresholds: 0.006 mg/L (the current MCL), 0.003

mg/L, and 0.0006 mg/L (the modal MRL). A total of 207 (approximately 2.20% of) ground water and

surface water PWSs had analytical results exceeding the MCL (0.006 mg/L); 3.81% of systems (359

systems) had results exceeding 0.003 mg/L. When evaluated relative to a threshold of 0.0006 mg/L, the

percentage of systems tripled to 11.7% (1,106 systems). 

Approximately 2.07% of ground water systems (178 systems) had any analytical results greater than the

MCL (0.006 mg/L). About 3.55% of ground water systems (305 systems) had results above 0.003 mg/L. 

The percentage of ground water systems with at least one result greater than 0.0006 mg/L was equal to

10.7% (921 systems). 

A total of 29 (3.51% of) surface water systems had results greater than 0.006 mg/L. Fifty-four (6.53%

of) surface water systems had at least one analytical result greater than 0.003 mg/L. Approximately

22.4% of surface water systems (185 systems) had results exceeding 0.0006 mg/L.

Table 3.2-3: Stage 1 DEHP Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.006 2.07% 178

0.003 3.55% 305

0.0006 10.7% 921

Surface Water

0.006 3.51% 29

0.003 6.53% 54
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 134

0.0006 22.4% 185

Combined Ground &

Surface Water

0.006 2.20% 207

0.003 3.81% 359

0.0006 11.7% 1,106

Table 3.2-4 illustrates DEHP occurrence in the 16 cross-section States by PWS population served. 

Approximately 3.20% of the 16-State population (over 2.5 million people) was served by PWSs with at

least one analytical result of DEHP greater than the MCL. Approximately 5.5 million people (7.06%)

were served by systems with an exceedance of 0.003 mg/L. Over 19 million people (24.6%) were served

by systems with at least one analytical result greater than 0.0006 mg/L.

The percentage of population served by ground water systems with analytical results greater than 0.006

mg/L was equal to 3.46% (about 1.1 million people). When evaluated relative to 0.003 mg/L and 0.0006

mg/L, the percent of population exposed was equal to 8.51% (approximately 2.7 million people) and

19.5% (over 6 million people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.006 mg/L was

equal to 3.01% (almost 1.4 million people). Approximately 6.05% of the population served by surface

water systems (almost 2.8 million people) were exposed to DEHP concentrations greater than 0.003

mg/L. When evaluated relative to 0.0006 mg/L, the percent of population exposed was equal to 28.2%

(over 13 million people).

Table 3.2-4: Stage 1 DEHP Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.006 3.46% 1,112,500

0.003 8.51% 2,735,100

0.0006 19.5% 6,265,300

Surface Water

0.006 3.01% 1,388,900

0.003 6.05% 2,792,100

0.0006 28.2% 13,028,100

Combined Ground &

Surface Water

0.006 3.20% 2,501,300

0.003 7.06% 5,527,200

0.0006 24.6% 19,293,400
Occurrence Summary and Use Support Document March 2002 135

3.2.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.2-5 and 3.2-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2002)). 

About 0.256% (approximately 24) of ground water and surface water PWSs had estimated mean

concentrations of DEHP greater than the MCL (0.006 mg/L). Approximately 89 systems (0.948%) in the

16 States had mean concentrations of DEHP exceeding 0.003 mg/L. When evaluated relative to 0.0006

mg/L, the percentage of systems exceeding the threshold increased by a factor of ten to 10.2% (an

estimated 957 systems).

Approximately 23 ground water systems in the 16 States (0.263%) have an estimated mean concentration

of DEHP greater than 0.006 mg/L. An estimated 0.944% of ground water systems (about 81 systems)

had mean concentration values greater than 0.003 mg/L. A total of 846 PWSs (9.85%) had estimated

mean concentration values of DEHP greater than 0.0006 mg/L. 

Only 2 (about 0.184% of) surface water systems in the 16 States had estimated mean concentrations

greater than the MCL. Eight (0.988% of) surface water systems had estimated mean concentration

values greater than 0.003 mg/L. Approximately 13.3% (about 110 systems) of surface water systems in

the 16 States had estimated mean concentration values of DEHP greater than 0.0006 mg/L.

Table 3.2-5: Stage 2 Estimated DEHP Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.006 0.263% 0.151% - 0.396% 23 13 - 34

0.003 0.944% 0.698% - 1.23% 81 60 - 106

0.0006 9.85% 8.93% - 10.8% 846 767 - 928

Surface Water

0.006 0.184% 0.000% - 0.484% 2 0 - 4

0.003 0.988% 0.363% - 1.69% 8 3 - 14

0.0006 13.3% 10.8% - 15.7% 110 89 - 130

Combined Ground

& Surface Water

0.006 0.256% 0.149% - 0.393% 24 14 - 37

0.003 0.948% 0.690% - 1.24% 89 65 - 117

0.0006 10.2% 9.22% - 11.1% 957 868 - 1,043
Occurrence Summary and Use Support Document March 2002 136

Reviewing DEHP occurrence by PWS population served (Table 3.2-6) shows that approximately 0.119%

of population served by all PWSs in the 16 cross-section States (an estimate of approximately 93,400

people) was served by systems with estimated mean concentrations of DEHP above 0.006 mg/L. The

percentage of population served by PWSs in the 16 States with levels of DEHP above 0.003 mg/L and

0.0006 mg/L were 0.652% (an estimated 510,100 people) and 9.82% (almost 7.7 million people),

respectively. 

When the percent of population served by ground water systems was evaluated relative to a threshold of

0.006 mg/L, 0.003 mg/L, and 0.0006 mg/L, the percentage of population exposed in the 16 cross-section

States was equal to 0.189% (an estimated 60,600 people), 0.676% (an estimated 217,400 people) and

7.22% (an estimated 2.3 million people), respectively. 

The percentage of population served by surface water systems with levels above 0.006 mg/L was equal to

0.0712% (an estimated 32,900 people), and the percentage of population served with levels above 0.003

mg/L was 0.634% (an estimated 292,700 people nationally). The percentage of the population served by

surface water systems with levels above 0.0006 mg/L was 11.6% (almost 5.4 million people). 

Table 3.2-6: Stage 2 Estimated DEHP Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.006 0.189% 0.0215% - 0.463% 60,600 6,900 - 148,700

0.003 0.676% 0.326% - 1.19% 217,400 104,600 - 382,400

0.0006 7.22% 5.45% - 9.92% 2,320,700 1,751,000 - 3,187,300

Surface Water

0.006 0.0712% 0.000% - 0.426% 32,900 0 - 196,600

0.003 0.634% 0.0312% - 3.00% 292,700 14,400 - 1,386,600

0.0006 11.6% 5.81% - 18.2% 5,363,700 2,679,600 - 8,410,200

Combined Ground

& Surface Water

0.006 0.119% 0.0186% - 0.363% 93,400 14,600 - 284,500

0.003 0.652% 0.220% - 2.02% 510,100 172,200 - 1,580,700

0.0006 9.82% 6.20% - 13.9% 7,686,000 4,852,600 - 10,851,400

3.2.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 166 PWSs serving approximately 254,100 people nationally could be exposed to

DEHP concentrations above 0.006 mg/L. About 616 systems serving almost 1.4 million people

nationally had estimated mean concentrations greater than 0.003 mg/L. Approximately 6,607 systems

serving almost 21 million people served nationally were estimated to have DEHP concentrations greater

than 0.0006 mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated

to national values.)
Occurrence Summary and Use Support Document March 2002 137

For ground water systems, an estimated 156 PWSs serving about 161,500 people nationally had mean

concentrations greater than 0.006 mg/L. Approximately 561 systems serving about 579,600 people

nationally had estimated mean concentration values that exceeded 0.003 mg/L. About 5,856 ground

water systems serving almost 6.2 million people nationally had estimated mean concentrations greater

than 0.0006 mg/L. 

Approximately 10 surface water systems serving 90,600 people nationally were estimated to have mean

concentrations of DEHP above 0.006 mg/L. An estimated 55 surface water systems serving 807,500

people had estimated mean concentrations greater than 0.003 mg/L. An estimated 745 surface water

systems serving almost 15 million people had mean concentrations greater than 0.0006 mg/L.

Table 3.2-7: Estimated National DEHP Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.006 156 90 - 235 161,500 18,400 - 396,400

0.003 561 415 - 733 579,600 278,900 - 1,019,600

0.0006 5,856 5,307 - 6,420 6,187,900 4,668,800 - 8,498,800

Surface Water

0.006 10 0 - 27 90,600 0 - 542,400

0.003 55 20 - 95 807,500 39,700 - 3,824,900

0.0006 745 601 - 879 14,795,300 7,391,300 - 23,198,900

Combined Ground

& Surface Water

0.006 166 97 - 256 254,100 39,700 - 774,100

0.003 616 449 - 808 1,387,700 468,600 - 4,300,600

0.0006 6,607 5,993 - 7,199 20,911,000 13,202,200 - 29,522,900

3.2.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of DEHP in drinking water are also reviewed. 

Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence and Exposure of Phthalate Esters in Public Drinking Water Supplies” (Wade Miller, 1989),

is presented in following section. This variety of regional studies and information are presented

regarding levels of DEHP in drinking water. (No national studies were included.) Note that none of the

studies presented in the following section provide the quantitative analytical results or comprehensive

coverage that would enable direct comparison to the occurrence findings estimated with the cross-section

occurrence data presented in Section 3.2.4. These additional studies, however, do enable a broader

assessment of the Stage 2 occurrence estimates presented for this Six-Year Review. All the following

information in Section 3.2.5 is taken directly from “Occurrence and Exposure of Phthalate Esters in

Public Drinking Water Supplies” (Wade Miller, 1989). 
Occurrence Summary and Use Support Document March 2002 138

3.2.5.1 Groundwater Studies

Thirty-nine public water wells in New York State were sampled and analyzed for the presence of

phthalate esters. DEHP was detected at a maximum concentration of 170.0 :g/L. The frequency of

occurrence for DEHP was 92 percent (USEPA, 1987, as cited in Wade Miller, 1989).

DEHP was detected in drinking water obtained from groundwater sources in Miami, FL at a

concentration of 30.0 :g/L. The number of positive detections was not reported (USEPA, 1987, as cited

in Wade Miller, 1989). DEHP was detected in five small water systems (wells with fewer than 200

connections) in Santa Cruz County, CA at concentrations ranging from 8.7 to 102.0 :g/L (California

Department of Health Services, Unpublished, as cited in Wade Miller, 1989).

3.2.5.2 Surface Water Studies

Water from three water treatment plants in New Orleans, LA was sampled and analyzed for the presence

of phthalate esters. DEHP was detected at concentrations ranging from 0.1 to 0.46 :g/L. The number of

positive detections was not reported (USEPA, 1987, as cited in Wade Miller, 1989). Water from a water

treatment plant in Philadelphia, PA was also sampled and analyzed for the presence of phthalate esters. 

DEHP was detected at a concentration of 0.6 :g/L. The number of positive detections was not reported

(USEPA, 1987, as cited in Wade Miller, 1989).

Drinking water from Seattle, WA; Ottumwa, IA; Philadelphia, PA: and Cincinnati, OH was sampled and

analyzed for the presence of phthalate esters. DEHP was not detected in the drinking water of any of the

four cities surveyed. The number of positive detections was not reported for any of the contaminants in

any of the cities (USEPA, 1987, as cited in Wade Miller, 1989).

3.2.5.5 Unspecified Water Sources

Tap water concentrations of phthalate esters in Cincinnati, OH: Hartford, CT; Atlanta, GA; and St.

Louis, MO were reported in USEPA (1987). DEHP was detected in Cincinnati at a concentration of 16.5

:g/L. The water sources were unspecified.

3.2.6 Conclusion

DEHP is a manufactured chemical that is part of a group of chemicals known as phthalate esters. Over

95% of DEHP is used as a plasticizer for PVC. Recent statistics regarding production and release of

DEHP indicate production and use are steady, but have the possibility of decline. Industrial releases of

DEHP have been reported to TRI since 1988 from 44 States. DEHP was not analyzed in any available

ambient studies. The Stage 2 analysis, based on the 16-State cross-section, estimated that approximately

0.256% of combined ground water and surface water systems serving 0.119% of the population exceeded

the MCL of 0.006 mg/L. Based on this estimate, approximately 166 PWSs serving approximately

254,100 people nationally are estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, DEHP is manufactured and/or processed in 40 States and has TRI releases

in 44 States. DEHP is manufactured and/or processed in 13 out of the 16 cross-section States and has

TRI releases in 14 of the 16 cross-section States. The cross-section should adequately represent the

occurrence of DEHP on a national scale based upon the use, production, and release patterns of the 16-

State cross-section in relation to the patterns observed for all 50 States. 
Occurrence Summary and Use Support Document March 2002 139

3.2.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 2000. Toxicological Profile for 

Di(2-ethylhexyl)phthalate. U.S. Department of Health and Human Services, Public Health

Service. 252 pp. + Appendices. Available on the Internet at

http://www.atsdr.cdc.gov/toxprofiles/tp9.pdf.

California Department of Health Services. Unpublished. Final Report on a Monitoring Program for

Organic Chemical Contamination of Small Public Water Systems in California. Summary

Version. Sacramento, CA.

National Safety Council (NSC). 2001. Di(2-ethylhexyl) Phthalate Chemical Backgrounder. Itasca, IL:

National Safety Council. Available on the Internet at:

http://www.crossroads.nsc.org/ChemicalTemplate.cfm?id=103&chempath=chemicals, accessed

July 23, 2001.

Staples, C.A., A.F. Werner, and T.J. Hoogheem. 1985. Assessment of Priority Pollutant Concentrations

in the United States Using STORET Data Base. Environmental Toxicology and Chemistry. v. 4,

pp. 131-142.

USEPA. 1987. Health and Environmental Effects Profile for Phthalic Acid Alkyl, Aryl, and Alkyl/Aryl

Esters. Final Draft. Cincinnati, OH: Environmental Criteria and Assessment Office, Office of

Health and Environmental Assessment. ECAO-CIN-P188.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on:

Di(2-ethylhexyl) Phthalate. Office of Ground Water and Drinking Water, USEPA. Available on

the Internet at http://www.epa.gov/safewater/dwh/c-SOC/DEHP.html, last updated April 12,

2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USPHS. 1987. Draft Toxicological Profile for Di(2-Ethylhexyl) Phthalate. Atlanta, GA: Agency for

Toxic Substances and Disease Registry.

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Phthalate Esters in Public

Drinking Water Supplies - DRAFT. Draft report submitted to EPA for review July 10, 1989.
Occurrence Summary and Use Support Document March 2002 140

3.3 Carbofuran

Table of Contents

3.3.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

3.3.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

3.3.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

3.3.4 Drinking Water Occurrence Based on the 16-State Cross Section . . . . . . . . . . . . . . . . . . . . . . . 147

3.3.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

3.3.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

3.3.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

Tables and Figures

Figure 3.3-1: Carbofuran Estimated Annual Agricultural Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

Table 3.3-1: Environmental Releases (in pounds) for Carbofuran in the United States, 1995-1999 . . 143

Table 3.3-2: Carbofuran Detections and Concentrations in Surface Water and Ground Water . . . . . . 143

Table 3.3-3. Results (:g/L) from the USGS NAWQA Surface Water Monitoring Program . . . . . . . . 145

Table 3.3-4. Results from the USGS NAWQA Ground Water Monitoring Program (for all wells

sampled) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

Table 3.3-5. Results from the USGS NAWQA Monitoring Program for Ground Water . . . . . . . . . . . 146

Table 3.3-3: Stage 1 Carbofuran Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . 147

Table 3.3-4: Stage 1 Carbofuran Occurrence Based on 16-State Cross-Section - Population . . . . . . . 148

Table 3.3-5: Stage 2 Estimated Carbofuran Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Table 3.3-6: Stage 2 Estimated Carbofuran Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Table 3.3-7: Estimated National Carbofuran Occurrence - Systems and Population Served . . . . . . . . 150
Occurrence Summary and Use Support Document March 2002 141

3.3.1 Introduction, Use and Production

Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) is a white crystalline solid with

a slightly phenolic odor. Carbofuran is available in liquid and granular formulations. Thermal

decomposition of carbofuran may include toxic oxides of nitrogen. Fires, and the runoff from fire

control, may produce irritating or poisonous gases. Some of its trade names are Furadan, Bay 70143,

Curaterr, D 1221, ENT 27164, Yaltox, Furacarb (EXTOXNET, 1998).

Carbofuran is a broad spectrum insecticide used primarily to exterminate insects, mites, nematodes and

rootworm on contact or after ingestion. Earlier uses were primarily on corn crops. The greatest use of

carbofuran is against foliar pests on alfalfa and rice, with turf and grapes making up most of the

remainder. It is sprayed directly onto soil and plants just after emergence to control beetles, nematodes

and rootworm. These insecticides work by blocking the normal functioning of cholinesterase, an

essential nervous system enzyme (EXTOXNET, 1998).

Glaze (1982, as cited in USEPA, 1989) estimated that in 1980 approximately 11 million pounds of

carbofuran active ingredient were available for domestic use and approximately 8 million pounds were

exported. Gianessi (1986, as cited in USEPA, 1989) estimated that of the approximately 30 million

pounds of carbofuran used nationwide from 1978 to 1982, 20 million pounds were applied to field corn

and 4 million pounds were applied to sorghum. The remaining production was used on a larger number

of crops, including alfalfa, tobacco, peanuts, rice, sugarcane, potatoes, soybeans, sweet corn, cotton,

grapes and small grains (USEPA, 1989).

The National Center for Food and Agricultural Policy (NCFAP) estimates total annual agricultural use at

about 5.1 million pounds per year (based on the 1992 agricultural census with updates from 1993 and

1995). The NCFAP estimates, combined with Census of Agriculture data on crop distributions can be

used to estimate the geographic distribution of carbofuran use (USGS, 1997). 

Carbofuran is used on about 30 crops -- the largest markets (in terms of pounds of active ingredient) are

for use on corn, alfalfa, rice, sorghum, potatoes, and cotton; followed by grapes, sugarbeets, soybeans,

wheat, tobacco, sunflowers, sweet corn, sugarcane, and peanuts (USGS, 1997). 

Figure 3.3-1 shows the United States Geological Survey (USGS, 1998a) derived geographic distribution

of estimated average annual carbofuran use in the United States for 1992. A breakdown of use by crop is

also included. The USGS (1998a) estimates almost 5 million pounds of carbofuran active ingredient

were used in 1992. The largest concentrations of carbofuran use are seen in the Midwest. A comparison

of this use map with the map of the 16 cross-section States (Figure 1.3-1) shows that States across the

range of high of low carbofuran use are well represented in the cross-section.
Occurrence Summary and Use Support Document March 2002 142

Figure 3.3-1: Carbofuran Estimated Annual Agricultural Use

Source: USGS, 1998a

3.3.2 Environmental Release

Carbofuran is listed as a Toxics Release Inventory (TRI) chemical. Table 3.3-1 illustrates the

environmental releases for carbofuran from 1995 to 1999. Air emissions constitute most of the on-site

releases. Carbofuran air emissions generally decreased over the years, with the exception of a sharp

increase in 1999. Surface water discharges also dramatically increased in 1999. However, before 1999,

surface water discharges were negligible. Underground injection and releases to land are less significant

on-site releases, with underground injections always equal to zero and the only releases to land occurring

in 1995. Off-site releases of carbofuran are minimal. The TRI data for carbofuran were reported from 10

States, with four reporting every year (USEPA, 2000). Four of the 10 States with TRI data are included

in the 16-State cross-section (used for analyses of carbofuran occurrence in drinking water; see Section

3.3.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)
Occurrence Summary and Use Support Document March 2002 143

Table 3.3-1: Environmental Releases (in pounds) for Carbofuran in the United States, 1995-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 13,999 112 -- -- -- 14,111

1998 2,921 1 -- -- -- 2,922

1997 3,903 1 -- -- 42 3,946

1996 3,854 1 -- -- -- 3,855

1995 4,187 2 -- 250 250 4,689

 Source: USEPA, 2000

3.3.3 Ambient Occurrence

Carbofuran is an analyte for both surface and ground water NAWQA studies, with a method detection

limit (MDL) of 0.003 :g/L. Additional information on analytical methods used in the NAWQA study

units, including method detection limits, are described by Gilliom and others (1998).

Carbofuran concentrations exceed the detection limit in all of the ground and surface sites. Detection

frequencies are consistently greater for surface water than for ground water, possibly because surface

waters are more sensitive to anthropogenic releases. High percentages of surface water samples exceed

detection frequencies of 0.01 and 0.05 :g/L. Within surface water sites, urban sites have consistently

lower percentage exceeding the detection frequencies then agricultural or integrator sites. Within ground

water sites, agricultural sites have slightly higher percentage exceeding the detection frequencies then

urban or major aquifer sites. The maximum concentration exceeds the detection limit in all ground and 

surface water sites. The 95th percentile values exceed the detection limit for all surface water sites except

urban sites, while none of the 95th percentile values exceed the detection limit for any ground water sites. 

None of the median values exceed the detection limit in ground or surface water sites.

Table 3.3-2: Carbofuran Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

all samples > 0.01 :g/L > 0.05 :g/L 10th median 95th max

surface water

agricultural 11.99% 10.79% 5.49% < MDL < MDL 0.059 7E

urban 2.75% 2.75% 0.31% < MDL < MDL < MDL 0.062E

integrator 9.35% 7.72% 2.85% < MDL < MDL 0.025 0.18E

all sites 7.96% 6.93% 3.08% < MDL < MDL 0.022 9.7E
Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

5

 For a more detailed description of the Reregistration Eligibility Decision (RED) process, please refer to Section 3.1.5.1.

Occurrence Summary and Use Support Document March 2002 144

ground water

agricultural 0.76% 0.65% 0.43% < MDL < MDL < MDL 1.3E

urban 0.66% 0.66% 0.33% < MDL < MDL < MDL 0.058E

major aquifers 0.54% 0.54% 0.21% < MDL < MDL < MDL 0.4E

all sites 0.50% 0.46% 0.26% < MDL < MDL < MDL 1.3E

Note: Carbofuran has more variable analytical performance than other analytes and usually lower recoveries. Individual maximum values with

an “E-code” have much greater uncertainty because the values were beyond the calibration range.

Source: USGS, 1998b

Carbofuran was also an analyte in the 1999 Pilot Monitoring Program (Blomquist et. al, 2001). 

Carbofuran was detected in less than 1% of the 323 raw water samples and approximately 1.3% of the

228 finished water samples. The 95th percentile value was reported as less than the MRL for both raw

and finished water samples. The maximum concentration of carbofuran in raw water was 0.050 :g/L. In

finished water, the maximum concentration of carbofuran was 0.030 :g/L.

3.3.3.2 Additional Ambient Data

Several additional data sources regarding the occurrence of carbofuran in non-drinking water are also

reviewed. Previously compiled carbofuran occurrence information is presented in following section. 

NAWQA summary data from EFED’s Risk Assessment for the carbofuran Reregistration Eligibility

Decision (RED) (USEPA, 2001) is presented in Section 3.3.3.2.1, while information from an OGWDW

summary document entitled “Occurrence and Human Exposure to Pesticides in Drinking Water, Food,

and Air in the United States of America” (USEPA, 1989) is presented in Sections 3.3.3.2.2 - 3.3.3.2.4. 

The following variety of studies and information is presented regarding levels of carbofuran in drinking

water, with the scope of the reviewed studies ranging from national to regional. The information in

Section 3.3.3.2.1 is taken directly from EFED's RED Science Chapter for carbofuran (USEPA, 2001). 

All the information in Sections 3.3.3.2.2 - 3.3.3.2.4 is taken directly from “Occurrence and Human

Exposure to Pesticides in Drinking Water, Food, and Air in the United States of America” (USEPA,

1989).

3.3.3.2.1 Summary of Carbofuran Monitoring Information from EFED's RED Science Chapter

As part of the Reregistration Eligibility Decision (RED) for carbofuran5

, the Environmental Fate and

Effects Division (EFED) of the Office of Pesticide Programs (OPP) put together a water resources

assessment to describe the occurrence of carbofuran in water resources of the United States. Table 3.3-3

summarizes results from all NAWQA sites where streams were sampled for carbofuran. These include

sites sampled many times over several years, as well as sites sampled only once or twice. The results

summarized in Table 3.3-3 are from all stream samples, including samples collected on a fixed sampling

frequency, high flow samples, low flow samples, diurnal and storm hydrograph samples, and samples

collected as part of special synoptic studies. Because all sites and samples are included, the summary

statistics shown in Table 3.3-3 are likely to be biased. The detection frequencies and concentration
Occurrence Summary and Use Support Document March 2002 145

percentiles shown will be biased high for commonly occurring conditions because more samples were

collected at sites where concentrations were high, or samples were collected more frequently during

periods of elevated concentrations. On the other hand, the values shown may be biased low because

sampling was not conducted during high-use periods. The maximum concentrations shown in Table 3.3-

3 are the highest concentrations observed in all NAWQA stream samples. Table 3.3-3 should not be

presumed to be a statistically representative summary of the NAWQA pesticide results. Samples were

collected between 4/20/92 and 12/16/96. The Level of Detection (LOD) for carbofuran was 0.003 :g/L.

Table 3.3-3. Results (:g/L) from the USGS NAWQA Surface Water Monitoring Program

Land Use Sites Samples Detects Range 1 Mean 95th

Percentile Median

Agricultural 506 2,996 297 9.70 - ND2 0.023 0.040 ND

Non-Agricultural 550 2,203 117 7.00 - ND 0.012 0.008 ND

1. Range, mean, median and 95th percentile are determined from all samples. Samples below the LOD were given a value one-half the LOD.

2. Below the LOD.

Table 3.3-4 summarizes data for every NAWQA ground water sample that was analyzed for carbofuran,

including newly drilled monitoring wells, production wells (such as domestic and public-supply wells),

springs, and tile drains. Although Table 3.3-4 provides a complete summary of all NAWQA results, it

should not be presumed to be a statistically representative summary of the NAWQA pesticide results. 

The data in the table contain a variety of spatial and temporal biases for which corrections must be

applied before any reliable statistical summaries can be compiled. For example, many of the sites were

sampled more than once. Failure to account for this would lead to an over-representation of these sites in

any statistical summary of chemistry data in which they were included. Samples were collected between

8/19/92 and 11/15/96. The LOD for carbofuran was 0.003 :g/L. 

Table 3.3-4. Results from the USGS NAWQA Ground Water Monitoring Program (for all wells

sampled)

Wells Samples Detects Range1

(:g/L) Mean 95th Percentile Median

2,550 3,024 15 1.30 - ND2 ND ND ND

1. Range, mean, median and 95th percentile are determined from all samples. Samples below the LOD were given a value one-half the LOD.

2. Below the LOD.

The USGS generated statistical summaries of the ground water data for three different settings: shallow

ground water in primarily agricultural areas, shallow ground water in primarily urban areas, and major

aquifers. The agricultural and urban land-use categories were represented by wells chosen or designed to

sample shallow, recently recharged (less than ten years old) ground water to determine the effects of

specific land uses on water quality. Sites comprising the “major aquifer” (an aquifer that is currently

being used as a source of drinking water) category had no such restrictions on land use or water age, and

thus, represent a broader mixture of land uses and ground water depths. The USGS followed the

following procedures to generate the relatively unbiased and comparable statistical summaries: tile
Occurrence Summary and Use Support Document March 2002 146

drains and springs were excluded to reduce the variability in site type; any well co-located with another

existing well was excluded; networks with fewer than 10 wells were excluded because they contained an

insufficient number of wells to be spatially representative of an area; wells that were included in more

than one type of network (e.g. a land-use study and an aquifer survey) were allowed to exist in both; one

sample from each well was selected.

Table 3.3-5. Results from the USGS NAWQA Monitoring Program for Ground Water

Setting/Land Use Wells Samples Detects Range1

(:g/L) Mean 95th

Percentile Median

Shallow

Ground Water

Urban 301 301 2 0.058 - ND2 NR3 ND ND

Agricultural 925 925 7 1.30 - ND NR ND ND

Major Aquifer 933 933 5 0.40 - ND NR ND ND

1. Range, mean, median and 95th percentile are determined from all samples. Samples below the LOD were given a value one-half the LOD.

2. Below the LOD.

3. Not Reported.

3.3.3.2.2 Groundwater Sources

Unpublished data summarized from EPA registration files and reported in Cohen et al. (1984, as cited in

USEPA, 1989) indicated that concentrations of carbofuran were present in samples of ground water

collected from private wells in areas with sandy soils and water table aquifers in Wisconsin and New

York. Concentrations ranged from 1 to 50 :g/L carbofuran. The number of samples, number of positive

samples, and detection limit were not reported.

Three studies were obtained examining ground water wells in California. These studies were conducted

by the California Department of Food and Agriculture in 1981, and again in 1982, and an evaluation in

1984 during the California State Board’s Toxics Special Project (Ramlit Associates, Inc., 1983; Holden,

1986; Cohen and Bowes, 1984, respectively, all as cited in USEPA, 1989). Overall, approximately 30

counties were sampled for the occurrence of carbofuran. Over 200 samples were collected from as many

sites, with only 2 proving positive. One concentration was 0.5 :g/L; the other was not reported. The

detection limit for the sample concentration given above was not reported.

3.3.3.2.3 Surface Water Sources

The Army Corps of Engineers sampled U.S. Geological Survey water stations along rivers of the Honey

Creek watershed in northwest Ohio during 1981 (Datta, no date, as cited in USEPA, 1989). Carbofuran

was sampled for at 12 locations and a maximum concentration of 45 :g/L was found. The number of

samples, number of positives, and detection limit were not reported.

Dudley and Karr (1980, as cited in USEPA, 1989) presented data on levels of carbofuran in water, fish,

and sediment samples collected from a stream draining the Black Creek agricultural watershed in Allen

County, Indiana, during 1977 to 1978. Although the detection limit and the number of water samples

collected and tested were not reported, none of the samples contained carbofuran in excess of the

detection limit.
Occurrence Summary and Use Support Document March 2002 147

Woodham et. al (1975, as cited in USEPA, 1989) presented monitoring data from a study to determine

whether significant pesticide accumulation had occurred in two counties in North Carolina. Samples of

pond water collected both inside and outside the study area contained no carbofuran in excess of the

detection limit of 0.05 :g/L. 

3.3.3.2.4 Unidentified Sources

Water samples of unidentified sources were collected nationally from various studies and entered in the

U.S. EPA’s STORET database (as reported in USEPA, 1984, as cited in USEPA, 1989) during 1979 to

1982. Of the 21 stations sampled for carbofuran, 11 had undetectable levels. However, 58 samples were

reported as positive. The total number of samples, detection limit(s), and range of positive values were

not reported.

3.3.4 Drinking Water Occurrence Based on the 16-State Cross Section

The analysis of carbofuran occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.04 mg/L; 0.007 mg/L; and 0.004 mg/L.

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

carbofuran. These data represent almost 52,000 analytical results from approximately 14,000 PWSs

during the period from 1983 to 1998 (with most analytical results from 1992 to 1997). The number of

sample results and PWSs vary by State, although the State data sets have been reviewed and checked to

ensure adequacy of coverage and completeness. The overall modal detection limit for carbofuran in the

16 cross-section States is equal to 0.0009 mg/L. (For details regarding the 16-State cross-section, please

refer to Section 1.3.5 of this report.)

3.3.4.1 Stage 1 Analysis Occurrence Findings

Table 3.3-3 illustrates the very low occurrence of carbofuran in public drinking water in drinking water

for the public water systems in the 16-State cross-section. Zero systems had any analytical results

exceeding the MCL (0.04 mg/L); 0.00718% of systems (1 system) had results exceeding 0.007 mg/L; and

0.0215% of systems (3 systems) had results exceeding 0.004 mg/L. 

Only 1 (0.00798% of) ground water system had any analytical results greater than 0.007 mg/L. No

surface water systems had results exceeding 0.007 mg/L. About 0.0160% of ground water systems (2

systems) had results above 0.004 mg/L. The percentage of surface water systems with at least one result

greater than 0.004 mg/L was equal to 0.0717% (1 system).

Table 3.3-3: Stage 1 Carbofuran Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems Exceeding

Threshold

Ground Water

0.04 0.000% 0

0.007 0.00798% 1

0.004 0.0160% 2
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 148

Surface Water

0.04 0.000% 0

0.007 0.000% 0

0.004 0.0717% 1

Combined Ground &

Surface Water

0.04 0.000% 0

0.007 0.00718% 1

0.004 0.0215% 3

Reviewing carbofuran occurrence in the 16 cross-section States by PWS population served (Table 3.3-4)

shows that approximately 0.000239% of the population (200 people) was served by PWSs with at least

one analytical result of carbofuran greater than 0.007 mg/L. A total of 2,100 (0.00218% of) people were

served by systems with an exceedance of 0.004 mg/L. As indicated above, no systems (therefore, no

population served by systems) had any analytical results greater than the MCL (0.04 mg/L).

The percentage of population served by ground water systems with analytical results greater than 0.007

mg/L was equal to 0.000576% (200 people). When evaluated relative to 0.004 mg/L, the percent of

population by ground water systems exposed was equal to 0.00105% (400 people). No surface water

systems had exceedances of 0.007 mg/L. The percentage of population served by surface water systems

with exceedances of 0.004 mg/L was equal to 0.00308% (1,700 people).

Table 3.3-4: Stage 1 Carbofuran Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.04 0.000% 0

0.007 0.000576% 200

0.004 0.00105% 400

Surface Water

0.04 0.000% 0

0.007 0.000% 0

0.004 0.00308% 1,700

Combined Ground &

Surface Water

0.04 0.000% 0

0.007 0.000239% 200

0.004 0.00218% 2,100
Occurrence Summary and Use Support Document March 2002 149

3.3.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.3-5 and 3.3-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2002)). 

No ground water or surface water PWSs in the 16 States had an estimated mean concentration of

carbofuran exceeding 0.04 mg/L or 0.007 mg/L. The percentage of total ground and surface water

systems in the 16 States with estimated mean concentration values of carbofuran greater than 0.004 mg/L

was equal to 0.000115% (an estimate of less than one system in the 16-State cross-section). The

percentage of ground water systems with estimated mean concentration values greater than 0.004 mg/L

was equal to 0.000112%. The percentage of surface water systems with estimated mean concentration

values greater than 0.004 mg/L was equal to 0.000144%.

Table 3.3-5: Stage 2 Estimated Carbofuran Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.000112% 0.000% - 0.000% 0 0 - 0

Surface Water

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.000144% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.000115% 0.000% - 0.000% 0 0 - 0

Reviewing carbofuran occurrence by PWS population served (Table 3.3-6) shows that approximately

0.00000461% of population served by all PWSs (less than 1 system in the 16 States) were potentially

exposed to carbofuran levels above 0.004 mg/L. The percentage of population served by ground water

systems potentially exposed to carbofuran levels above 0.004 mg/L was equal to 0.00000806%. The

percentage of population served by surface water systems with estimated mean concentration values

greater than 0.004 mg/L was equal to 0.00000217%. When evaluated relative to a threshold of 0.04

mg/L, and 0.007 mg/L, the percent of population exposed was equal to 0% for all system types.
Occurrence Summary and Use Support Document March 2002 150

Table 3.3-6: Stage 2 Estimated Carbofuran Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in

the 16 States Estimated to Exceed

Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.04 0.00000% 0.000% - 0.000% 0 0 - 0

0.007 0.00000% 0.000% - 0.000% 0 0 - 0

0.004 0.00000806% 0.000% - 0.000% 0 0 - 0

Surface Water

0.04 0.00000% 0.000% - 0.000% 0 0 - 0

0.007 0.00000% 0.000% - 0.000% 0 0 - 0

0.004 0.00000217% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.04 0.00000% 0.000% - 0.000% 0 0 - 0

0.007 0.00000% 0.000% - 0.000% 0 0 - 0

0.004 0.00000461% 0.000% - 0.000% 0 0 - 0

3.3.4.3 Estimated National Occurrence

As illustrated in Table 3.3-7, the Stage 2 analysis estimates zero systems serving none of the national

population have estimated mean concentration values of carbofuran greater than 0.04 mg/L, 0.007 mg/L,

or 0.004 mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to

national values.)

Table 3.3-7: Estimated National Carbofuran Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.04 0 0 - 0 0 0 - 0

0.007 0 0 - 0 0 0 - 0

0.004 0 0 - 0 0 0 - 0

Surface Water

0.04 0 0 - 0 0 0 - 0

0.007 0 0 - 0 0 0 - 0

0.004 0 0 - 0 0 0 - 0
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 151

Combined Ground

& Surface Water

0.04 0 0 - 0 0 0 - 0

0.007 0 0 - 0 0 0 - 0

0.004 0 0 - 0 0 0 - 0

3.3.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of carbofuran in drinking water are also

reviewed. Previously compiled occurrence carbofuran information, from an OGWDW summary

document entitled “Occurrence and Human Exposure to Pesticides in Drinking Water, Food and Air in

the United States of America” (USEPA, 1989), is presented in the following section. This variety of

studies and information are presented regarding levels of carbofuran in drinking water, with the scope of

the reviewed studies ranging from national to regional. Note that none of the studies presented in the

following section provide the quantitative analytical results or comprehensive coverage that would

enable direct comparison to the occurrence findings estimated with the cross-section occurrence data

presented in Section 3.3.4. These additional studies, however, do enable a broader assessment of the

Stage 2 occurrence estimates presented for this Six-Year Review. The information presented in the

following section is taken directly from “Occurrence and Human Exposure to Pesticides in Drinking

Water, Food and Air in the United States of America” (USEPA, 1989). 

3.3.5.1 Ground Water Sources – Regional Studies

In 1984, the Suffolk County Department of Health Services (Holden, 1986, as cited in USEPA, 1989)

examined drinking water wells in Long Island, New York, for various pesticides. The survey sampled

both public and private wells in close proximity to fields where carbofuran, aldicarb, and other pesticides

were used. Of the 5,083 wells sampled, 1,535 contained detectable levels of carbofuran and 250 to 300

wells contained levels greater than 15 :g/L. The maximum level reported was 65 :g/L. 

As part of a program of the Wisconsin Department of Natural Resources (Holden, 1986, as cited in

USEPA, 1989), drinking water wells were also analyzed for carbofuran during 1983-1984. This study

examined wells suspected of contamination by both point and nonpoint sources. Of 78 samples analyzed,

2 were positive, with a high concentration of 7 :g/L. No other information was reported.

Ground water wells were sampled near Richmond, Rhode Island, as part of a cooperative project between

the U.S. Geological Survey and the Rhode Island Water Resources Board to identify potential drinking

water sources for future water supply use (Offutt, 1984, as cited in USEPA, 1989). Eleven samples were

collected during 1984 from five locations and analyzed for carbofuran. Seven were positive, with a mean

concentration of 3.7 :g/L (range = 2 to 7 :g/L). The detection limit was 1.0 :g/L.
Occurrence Summary and Use Support Document March 2002 152

3.3.6 Conclusion

Carbofuran is a broad spectrum carbamate pesticide used primarily to exterminate insects, mites,

nematodes and rootworm on contact or after ingestion. It is used against soil and foliar pests of field,

fruit, vegetable and forest crops. The USGS (1998a) estimates almost 5 million pounds of carbofuran

active ingredient were used in 1992. The largest concentrations of carbofuran use are seen in the

Midwest. Industrial releases of carbofuran have been reported to TRI since 1995 from 10 States, with

four reporting every year. Carbofuran was also an analyte for the NAWQA occurrence studies. In the

NAWQA study, carbofuran was detected in ground and surface water; however, none of the median

values exceeded the detection limit. The Stage 2 analysis, based on the 16-State cross-section, estimated

that zero percent of combined ground water and surface water systems serving zero percent of the

population exceeded the MCL of 0.04 mg/L. Based on this estimate, zero PWSs nationally are estimated

to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. According to information from USGS, all of the 16 cross-section States use carbofuran,

although most States in light to moderate amounts. Carbofuran is used most heavily in the Midwest and

California, covered by seven cross-section States. Nationally, TRI releases have been reported for

carbofuran from 10 States, including 4 of 16 cross-section States. The cross-section should adequately

represent the occurrence of carbofuran on a national scale based upon the use, production, and release

patterns of the 16-State cross-section in relation to the patterns observed for all 50 States. 

3.3.7 References

Blomquist, J.D., J.M. Denis, J.L. Cowles, J.A. Hetrick, R.D. Jones, and N.B. Birchfield. 2001. 

Pesticides in Selected Water-Supply Reservoirs and Finished Drinking Water, 1999-2000: 

Summary of Results from a Pilot Monitoring Survey. U.S. Geological Survey Open-File Report

01-456. 65 pp.

Cohen, S.Z., S.M. Creeger, R.F. Carsel, and C.G. Enfield. 1984. Pesticide Contamination of

Groundwater from Agricultural Uses. American Chemical Society Symposium Series Treatment

and Disposal of Pesticide Wastes.

Cohen, D.B, and G.W. Bowes. 1984. Water Quality and Pesticides: A California Risk Assessment

Program (Volume 1). Sacramento, CA: State Water Resources Control Board, Toxic Substances

Control Program. 

Datta, P.R. No date. Memorandum: Review of six documents regarding monitoring of pesticides in

Northwestern Ohio rivers. Sent to: D.J. Severn, Chief - Exposure Assessment Branch, HED. 

Washington, DC: Office of Pesticides and Toxic Substances, U.S. Environmental Protection

Agency.

Dudley, D.R, and J.R. Karr. 1980. Pesticides and PCB residues in the Black Creek watershed, Allen

County, Indiana, 1977-1978. Pestic. Monit. J. v. 13, no. 4, pp. 155-157. 

EXTOXNET. 1998. Pesticide Information Profile: Carbofuran. Ithaca, NY: Extension Toxicology

Network, Pesticide Management Education Program. Available on the Internet at

http://pmep.cce.cornell.edu/profiles/extoxnet/metiram-propoxur/carbofuran-ext.html, last

updated March 1, 2001. 
Occurrence Summary and Use Support Document March 2002 153

Gianessi, L.P. 1986. A National Pesticide Usage Database. Prepared by Resources for the Future for

U.S. Environmental Protection Agency, Office of Standards and Regulations, Washington, DC. 

Cooperative Agreement CR 811858-01-0. 

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at: 

http://ca.water.usgs.gov/pnsp/rep/ofr97589, last updated October 9, 1998. 

Glaze, M.H. 1982. Preliminary Quantitative Usage of Carbofuran. Washington, DC: Office of

Pesticide Programs, U.S. Environmental Protection Agency.

Holden, P.W. 1986. Pesticides and Groundwater Quality. Issues and Problems in Four States. 

Prepared for the Board of Agriculture, National Research Council. Washington, DC: National

Academy Press.

JRB Associates. 1984. Occurrence of Carbofuran in Drinking Water, Food, and Air. Prepared for and

submitted to EPA on February 9, 1984. 

Offutt, C.K. 1984. Memorandum: Aldicarb in Rhode Island Groundwater. From: Carolyn K. Offutt,

Chief - Environmental Processes and Guidelines Section, Exposure Assessment Branch, HED. 

Sent to: Paul Lapsley, Chief - Special Review Branch, Registration Division. Washington, DC:

Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency.

Ramlit Associates, Inc. 1983. Groundwater Contamination by Pesticides: A California Assessment.

Submitted to: State Water Resources Control Board, Sacramento, California. Submitted by:

Ramlit Associates, Inc., Berkeley, California. Publication No. 83-4SP.

USEPA. 1984. Health and Environmental Effects Profile for Carbofuran. Prepared for Office of Solid

Waste and Emergency Response, Washington, DC, by Experimental Criteria and Assessment

Office, Cincinnati, OH.

USEPA. 1989. Draft Final Report on the Occurrence and Human Exposure to Pesticides in Drinking

Water, Food, and Air in the United States of America. Office of Drinking Water, USEPA. 

September, 1989.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. EFED Risk Assessment for the Reregistration Eligibility Decision on Carbofuran,

2/15/2001. Environmental Fate and Effects Division, Office of Pesticide Programs, USEPA. 

February, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1997. Carbofuran Occurrence and Distribution in Surface and Ground Waters 1991-1997 -

DRAFT. Pesticides National Synthesis Project, USGS. November 25, 1997.
Occurrence Summary and Use Support Document March 2002 154

USGS. 1998a. Annual Use Maps. Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/,

last updated 3/20/1998.

USGS. 1998b. Pesticides in Surface and Ground Water of the United States: Summary of Results of the

National Water Quality Assessment Program (NAWQA). PROVISIONAL DATA -- SUBJECT TO

REVISION. Available on the Internet at: http://water.wr.usgs.gov/pnsp/allsum/, last updated

October 9, 1998. 

Woodham, D.W., M.C. Ganyard, C.A. Bond, and R.G. Reeves. 1975. Monitoring of agricultural

pesticides in a cooperative pest management project in North Carolina, 1971, first year of study. 

In: Savage, E.P. (ed.). Environmental chemicals. Human and animal health. Proceedings of 4th

Annual Conference, Colorado State University, Fort Collins, CO.
Occurrence Summary and Use Support Document March 2002 155

3.4 Chlordane

Table of Contents

3.4.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

3.4.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

3.4.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

3.4.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 159

3.4.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

3.4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

3.4.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Tables and Figures

Table 3.4-1: Facilities that Manufacture or Process Chlordane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

Table 3.4-2: Environmental Releases (in pounds) for Chlordane in the United States, 1988-1996 . . . 157

Table 3.4-3: Stage 1 Chlordane Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . 159

Table 3.4-4: Stage 1 Chlordane Occurrence Based on 16-State Cross-Section - Population . . . . . . . . 160

Table 3.4-5: Stage 2 Estimated Chlordane Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

Table 3.4-6: Stage 2 Estimated Chlordane Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

Table 3.4-7: Estimated National Chlordane Occurrence - Systems and Population Served . . . . . . . . 162
Occurrence Summary and Use Support Document March 2002 156

3.4.1 Introduction, Use and Production

Chlordane (1,2,4,5,6,7,8,8-octachloro-2,3,3a,4,7,7a-hexahydro-4,7-methanoindene) does not occur

naturally in the environment. It is a thick nonpolar liquid with a mild, irritating odor whose color ranges

from colorless to amber. “Technical chlordane” (the contaminant described throughout this report) is

actually not a single chemical. It is a mixture of pure chlordane and about 10 major related chemicals

and numerous other components. Some of the major components are trans-chlordane, cis-chlordane,

beta-chlordene, heptachlor, and trans-nonachlor. Chlordane does not dissolve in water. Therefore, before

it can be used as a spray, it must be placed in water with emulsifiers (soap-like substances), resulting in a

milky-looking mixture. In the environment, chlordane tends to bind to soil and to degrade slowly. Some

of its trade names are Octachlor and Velsicol 1068 (ATSDR, 1994). 

Chlordane is a manufactured chemical that was used as a pesticide in the United States from 1948 to

1988 (ATSDR, 1994). It was used on corn, citrus, deciduous fruits and nuts, and vegetables. It was also

used on garden and ornamentals; lawns, turf, ditchbanks and roadsides. Chlordane was used to control a

variety of insect pests including parasitic roundworms and other nematodes, termites, cutworms,

chiggers, and leafhoppers (USEPA, 2001). In the mid 1970s the use pattern for chlordane was as

follows: 35% used by pest control operators, mostly on termites; 28% on agricultural crops, including

corn and citrus; 30% for home lawn and garden use; and 7% on turf and ornamentals (ATSDR, 1994).

On March 6, 1978, use of chlordane was suspended except for termite control and some application on

non-food plants. In 1983, its use on non-food plants was also banned (ATSDR, 1994). Its use and

production were ultimately banned on April 14, 1988 because of concern over cancer risk, evidence of

human exposure and accumulation in body fat, persistence in the environment, and danger to wildlife

(NSC, 2001). Currently, its only permitted commercial use is for fire ant control in power transformers

(USEPA, 2001).

Prior to 1983 the estimated annual usage of chlordane was over 3.6 million pounds (USEPA, 2001). 

Velsicol Chemical Company in Memphis, TN, is currently the only U.S. manufacturer of chlordane, and

it was the only domestic manufacturer when use of chlordane ceased in 1988 (ATSDR, 1994).

Table 3.4-1 shows the facilities that manufacture and process chlordane, the intended uses of the product,

and the range of maximum amounts derived from the Toxics Release Inventory (TRI) of EPA (ATSDR,

1994). 

Table 3.4-1: Facilities that Manufacture or Process Chlordanea

Facility Locationb Range of maximum amounts on site in

pounds Activities and uses

Stennis Space Center Stennis Space Cen, 0-99 In ancillary or other uses

Velsicol Chemical Corp. Memphis, TN 100,000-999,999 Produce; for sale/distribution

a

Derived from TRI90 (1992)

b

Post Office State abbreviations

Source: ATSDR, 1994 compilation of TRI90 1992 data
Occurrence Summary and Use Support Document March 2002 157

3.4.2 Environmental Release

Chlordane is listed as a Toxics Release Inventory (TRI) chemical. Table 3.4-2 illustrates the

environmental releases for chlordane from 1988 to 1996. (There are only chlordane data for these years.) 

Air emissions constitute most of the on-site releases, and emissions fluctuated from 1988 to 1993, before

decreasing from 1994 to 1996. Surface water increases have gradually increased, from 1 pound in 1991

to 95 pounds in 1996. The fluctuation in air emissions has been the major contributor to changes in

chlordane total on- and off-site releases in recent years. No releases to land (such as spills or leaks

within the boundaries of the reporting facility), or off-site releases (including metals or metal compounds

transferred off-site) were reported for chlordane. These TRI data for chlordane were reported from 10

States (USEPA, 2000). Five of the 16 cross-section Sates (used for analyses of chlordane occurrence in

drinking water; see Section 3.4.4) reported data for chlordane. (For a map of the 16-State cross-section,

see Figure 1.3-1.)

Table 3.4-2: Environmental Releases (in pounds) for Chlordane in the United States, 1988-1996

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1996 660 95 -- -- -- 755

1995 823 22 -- -- -- 845

1994 1,300 13 -- -- -- 1,313

1993 51 15 -- -- -- 66

1992 1,713 1 -- -- -- 1,714

1991 1,427 1 -- -- -- 1,428

1990 4,422 1 -- -- -- 4,423

1989 3,753 4 -- -- -- 3,757

1988 2,698 4 4,262 -- -- 6,964

 Source: USEPA, 2000b 

3.4.3 Ambient Occurrence

To understand the presence of a chemical in the environment, an examination of ambient occurrence is

useful. In a drinking water context, ambient water is untreated source water residing in surface waters

and aquifers. There are few available data on the occurrence of chlordane in ambient waters of the

United States. The most comprehensive and nationally consistent data describing ambient water quality

in the United States are being produced through the United States Geological Survey’s (USGS) National

Water Quality Assessment (NAWQA) program. However, national NAWQA data are currently

unavailable for chlordane.

3.4.3.1 Additional Ambient Occurrence Data

A summary document entitled “Occurrence and Human Exposure to Pesticides in Drinking Water, Food

and Air in the United States of America” (USEPA, 1989), was previously prepared for past USEPA

assessments of various pesticides. In that review, two national studies and seven regional studies

analyzed concentrations of chlordane in water other than drinking water. The following information is

taken directly from “Occurrence and Human Exposure to Pesticides in Drinking Water, Food and Air in

the United States of America” (USEPA, 1989).
Occurrence Summary and Use Support Document March 2002 158

3.4.3.1.1 Ground Water Sources – Regional Study

Tucker and Burke (1978, as cited in USEPA, 1989) reported the results of a Statewide groundwater

monitoring project conducted in New Jersey. For this study, samples of water were collected from 163

wells in nine counties. The analysis showed that samples of water from five wells contained levels of

chlordane in excess of the minimum reportable concentrations of 0.01 :g/L. The range of positive values

was 0.01 to 0.02 :g/L chlordane.

One California study of ground water wells found four samples, from as many counties, positive for

chlordane with a maximum value of 22 :g/L. No other data were presented for this study. One of three

well samples collected in the Barstow, California, area was found to have a chlordane concentration of

0.4 :g/L by the Victorville Regional Water Quality Board in 1980 (Ramlit Associates, Inc., 1983, as

cited in USEPA, 1989).

3.4.3.1.2 Surface Water Sources – National Study

The National Pesticide Monitoring Network (Gilliom et al., 1985, as cited in USEPA, 1989) examined

surface water samples from rivers nationwide during 1975-1980, and found no positive samples of

chlordane out of 2,943 samples analyzed from 177 locations. The detection limit was 0.15 :g/L.

The National Surface Water Monitoring Program (Carey and Kutz, 1983, as cited in USEPA, 1989)

presented data on levels of chlordane in surface water samples collected throughout the United States

between 1976 and 1980. Although no detection limit for chlordane was reported, 1.1 percent of the

samples analyzed had detectable concentrations of chlordane, with a maximum reported value of 0.23

:g/L. The number of samples taken was not reported. It is not known whether the samples were filtered

or unfiltered.

3.4.3.1.3 Surface Water Sources – Regional Studies

Truhlar and Reed (1976, as cited in USEPA, 1989) reported the results of analysis of water samples taken

from four streams in Pennsylvania. The streams drained four types of land use areas: forests, general

farms, orchards, and residential areas. None of the 19 samples collected and analyzed from April 1970 to

February 1971 contained chlordane in excess of the detection limit. The detection limit was not reported.

Benvenue et al. (1972b, as cited in USEPA, 1989) conducted extensive sampling of two canals on Oahu,

Hawaii, to determine the extent of organochlorine pesticide contamination. A total of nine samples was

collected from two canals and analyzed for residues of chlordane. The analyses showed an average

concentration of chlordane of 0.007 :g/L and a range of positive values of 0.003 to 0.018 :g/L. The

number of positive samples and the detection limit were not reported.

Barks (1978, as cited in USEPA, 1989) presented the results of a USGS water quality study conducted

from April 1973 to July 1974 in the Ozark National Scenic Riverways, Missouri. During the study, 20

surface water samples were collected from 3 sites on the Current River and 1 site on Jacks Fork and

analyzed for pesticide content. None of the unfiltered samples contained concentrations of chlordane in

excess of the detection limit (no detection limit was reported).

Englande et al. (1978, as cited in USEPA, 1989) presented the results of extensive chemical analyses of

six Advanced Wastewater Treatment (AWT) plant effluents. The plants were located in California, the

District of Columbia, and Texas. A mean concentration of less than 0.039 :g/L chlordane was identified
Occurrence Summary and Use Support Document March 2002 159

in one plant effluent; the other systems had no detectable levels of chlordane. The number of positive

samples and the detection limit were not reported.

3.4.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of chlordane occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.002 mg/L; 0.001 mg/L; and 0.0002 mg/L.

All sixteen cross-section State data sets, with the exception of Michigan, contained occurrence data for

chlordane. These data represent more than 59,000 analytical results from approximately 13,000 PWSs

during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The number of

sample results and PWSs vary by State, although the State data sets have been reviewed and checked to

ensure adequacy of coverage and completeness. The overall modal detection limit for chlordane in the

16 cross-section States is equal to 0.0002 mg/L. (For details regarding the 16-State cross-section, please

refer to Section 1.3.5 of this report.)

3.4.4.1 Stage 1 Analysis Occurrence Findings

Table 3.4-3 illustrates the Stage 1 analysis of chlordane occurrence in drinking water for the public water

systems in the 16-State cross-section relative to three thresholds: 0.002 mg/L (the current MCL), 0.001,

and 0.0002 mg/L (the modal MRL). A total of 2 (approximately 0.0152% of) ground water and surface

water PWSs had analytical results exceeding the MCL (0.002 mg/L); 0.303% of systems (4 systems) had

results exceeding 0.001 mg/L; and 0.106% of systems (14 systems) had results exceeding 0.0002 mg/L. 

Approximately 0.0167% of ground water systems had any analytical results greater than 0.002 mg/L. 

About 0.0337% of ground water systems had results above the MCL (0.002 mg/L). The percentage of

ground water systems with at least one result greater than 0.0002 mg/L was equal to 0.118%. No surface

water systems had any analytical results greater than 0.002 mg/L, 0.001 mg/L, or 0.0002 mg/L.

Table 3.4-3: Stage 1 Chlordane Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.002 0.0167% 2

0.001 0.0337% 4

0.0002 0.118% 14

Surface Water

0.002 0.000% 0

0.001 0.000% 0

0.0002 0.000% 0
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 160

Combined Ground &

Surface Water

0.002 0.0152% 2

0.001 0.0303% 4

0.0002 0.106% 14

Reviewing chlordane occurrence in the 16 cross-section States by PWS population served (Table 3.4-4)

shows that approximately 0.000477% of the population (about 500 people) was served by ground water

PWSs with at least one analytical result of chlordane greater than the MCL (0.002 mg/L). A total of 600

(0.000631% of) people in the 16-States were served by ground water systems with an exceedance of

0.001 mg/L. Approximately 0.0275% of the total 16-State population (26,800 people) was served by

ground water systems with at least one analytical result greater than 0.0002 mg/L. No surface water

systems exceeded any of the threshold levels.

Table 3.4-4: Stage 1 Chlordane Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Ground Water

0.002 0.00114% 500

0.001 0.00151% 600

0.0002 0.0658% 26,800

Surface Water

0.002 0.000% 0

0.001 0.000% 0

0.0002 0.000% 0

Combined Ground &

Surface Water

0.002 0.000477% 500

0.001 0.000631% 600

0.0002 0.0275% 26,800

3.4.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.4-5 and 3.4-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2002)). 
Occurrence Summary and Use Support Document March 2002 161

No ground or surface water systems had estimated mean concentrations of chlordane greater than the

MCL (0.002 mg/L). Approximately 0.0000910% of systems (less than 1 system in the 16 States) had

estimated mean concentration values greater than 0.001 mg/L. Approximately 0.0363% of systems

(about 5 systems) had estimated mean concentrations greater than 0.0002 mg/L. 

The percentage of ground water PWSs with an estimated mean concentration of chlordane exceeding

0.001 mg/L was equal to 0.000101% (less than 1 ground water system in the 16 States). Approximately

0.0403% of ground water systems (5 systems) had an estimated mean concentration of chlordane greater

than 0.0002 mg/L. A very small proportion (0.000301%) of surface water systems had estimated mean

concentration values greater than 0.0002 mg/L.

Table 3.4-5: Stage 2 Estimated Chlordane Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.000101% 0.000% - 0.000% 0 0 - 0

0.0002 0.0403% 0.0253% - 0.0591% 5 3 - 7

Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.000301% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.0000910% 0.000% - 0.000% 0 0 - 0

0.0002 0.0363% 0.0228% - 0.0531% 5 3 - 7

Table 3.4-6 illustrates chlordane occurrence by PWS population served. Approximately 0.00000146% of

population served by all PWSs in the 16 States were potentially exposed to chlordane levels above 0.001

mg/L. The percent of population exposed to levels of 0.0002 mg/L was 0.00147% (approximately 1,400

people in the 16 States). As stated above, no systems had estimated mean concentrations of chlordane

greater than the MCL (0.002 mg/L).

The percentage of population served by ground water systems in the 16 cross-section States with

estimated mean concentration values greater than 0.001 mg/L was equal to 0.00000350%. When

evaluated relative to a threshold of 0.0002 mg/L, the percent of population exposed was equal to

0.00346% (1,400 people). The percentage of population served by surface water systems with estimated

mean concentrations of chlordane greater than 0.0002 mg/L was equal to 0.0000479%.
Occurrence Summary and Use Support Document March 2002 162

Table 3.4-6: Stage 2 Estimated Chlordane Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in

the 16 States Estimated to Exceed

Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.00000350% 0.000% - 0.000% 0 0 - 0

0.0002 0.00346% 0.000945% - 0.0166% 1,400 400 - 6,700

Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0002 0.0000479% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.002 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.00000146% 0.000% - 0.000% 0 0 - 0

0.0002 0.00147% 0.000394% - 0.00701% 1,400 400 - 6,800

3.4.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 24 PWSs nationally serving approximately 3,100 people could be exposed to

chlordane concentrations above 0.0002 mg/L. No systems and population served by systems nationally

were estimated to have mean concentrations greater than 0.002 mg/L or 0.001 mg/L. (See Section 1.4 for

a description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 24 PWSs serving about 3,000 people nationally were expected to

have mean concentrations greater than 0.0002 mg/L. Approximately 1 surface water systems serving less

than 100 people was estimated to have mean concentrations of chlordane above 0.0002 mg/L. 

Table 3.4-7: Estimated National Chlordane Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.002 0 0 - 0 0 0 - 0

0.001 0 0 - 0 0 0 - 0

0.0002 24 15 - 35 3,000 800 - 14,200

Surface Water

0.002 0 0 - 0 0 0 - 0

0.001 0 0 - 0 0 0 - 0
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 163

0.0002 1 0 - 0 < 100 0 - 0

Combined Ground

& Surface Water

0.002 0 0 - 0 0 0 - 0

0.001 0 0 - 0 0 0 - 0

0.0002 24 15 - 35 3,100 800 - 14,900

3.4.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of chlordane in drinking water are also

reviewed. Previously compiled occurrence chlordane information, from an OGWDW summary

document entitled “Occurrence and Human Exposure to Pesticides in Drinking Water, Food and Air in

the United States of America” (USEPA, 1989), is presented in following section. This variety of regional

studies and information are presented regarding levels of chlordane in drinking water. (No national

studies were included in the review.) Note that none of the studies presented in the following section

provide the quantitative analytical results or comprehensive coverage that would enable direct

comparison to the occurrence findings estimated with the cross-section occurrence data presented in

Section 3.4.4. These additional studies, however, do enable a broader assessment of the Stage 2

occurrence estimates presented for this Six-Year Review. All the following information in Section 3.4.5

is taken directly from “Occurrence and Human Exposure to Pesticides in Drinking Water, Food and Air

in the United States of America” (USEPA, 1989). 

3.4.5.1 Ground Water Sources

Irwin and Healy (1978, as cited in USEPA, 1989) summarized data collected in 1976 during a water

quality reconnaissance of public water supplies in Florida. None of the 100 ground water supplies

sampled, representative of the 5 aquifers in Florida, contained measurable levels of chlordane (no

detection limit was reported).

Less than 8 percent of samples from 96 locations utilizing the Floridian aquifer were found positive for

chlordane in a 1984 study by the Florida Department of Environmental Resources and the U.S.

Geological Survey (Holden, 1986, as cited in USEPA, 1989). These supplies serve over 3 million

people. No other information from the study was reported.

No positive samples were found for chlordane in the following two studies; one involved the 1984-1985

sampling of 42 sites from 12 towns in Connecticut and the other involved the analysis of 67 samples

from Long Island, New York, in 1984 (Waggoner, 1985; Holden, 1986, all as cited in USEPA, 1989). 

The Connecticut drinking water wells serve a population of over 570,000, and the detection limit for that

study was 3.3 :g/L. No other information about either study was reported.

Two positive samples (one for alpha-chlordane and one for gamma-chlordane) out of 107 samples

analyzed were found for ground water wells in Idaho (Idaho Department of Health and Welfare, 1984, as

cited in USEPA, 1989). Monitoring for pesticides in drinking water wells is not routinely done; the

sampling performed was in response to a particular contamination incident, not for any comprehensive
Occurrence Summary and Use Support Document March 2002 164

monitoring program. A relatively low mean of 0.0002 :g/L was reported for these two samples, with one

sample having a chlordane concentration of 0.038 :g/L (no detection limit was reported). It appears that

“negative” samples, possibly assigned a detection limit value, were included in the calculation of the

mean.

Benvenue et al. (1972b, as cited in USEPA, 1989) conducted a study to determine the extent of

organochlorine pesticide contamination of drinking water in Hawaii. A total of 45 finished drinking

water samples were collected from February 1971 to May 1971. Concentrations of chlordane were

detected in four of the samples, with a range of positive values between 0.0005 and 0.005 :g/L, and an

average concentration of 0.001 :g/L (no detection limit was reported).

3.4.5.2 Surface Water Sources

Irwin and Healy (1978, as cited in USEPA, 1989), summarizing data collected during a water quality

reconnaissance of public water supplies in Florida, reported that none of the 16 surface water supplies

sampled contained chlordane in excess of the detection limit. No detection limit was reported.

In the New Orleans Water Supply Study conducted by USEPA Region VI (USEPA, 1975a, as cited in

USEPA, 1989), samples of drinking water were analyzed for levels of halogenated organics. Although

the number of positive samples was not reported, the concentrations of chlordane in three samples

analyzed ranged from “non-detected” to less than 0.1 :g/L. No detection limit for the analyses was

reported.

To assemble a database which would reflect the status of Great Lakes drinking water quality, the

Canadian Public Health Association gathered data from October 1984 through August 1985 (Canadian

Public Health Association, 1986, as cited in USEPA, 1989). The data collected covered the period from

the mid 1970s to early 1985. The study was funded by the Health Protection Branch of Health and

Welfare Canada and the Ontario Ministry of the Environment. A research team, appointed by the

Association, reviewed data on the quality of water at 31 representative Canadian and United States

communities and 24 offshore sites to evaluate the human health implications.

For each of the 31 communities, data consisted of: 1) background information on the community; 2)

treatment plant schematics and associated treatment process information; and 3) water quality data. 

Water sample types included raw water (treatment plant intake), distribution water (treated water), and

tap water. Water quality data collected included general parameters (e.g., alkalinity, turbidity),

microbiological and radiological parameters, inorganic parameters, and organic parameters (including

volatiles, base/neutrals, pesticides and PCBs, and phenols and acids). For each parameter, the water

type, time period, concentration (mean and range), number of samples, and detection limit are presented.

For most of the volatile organics, including chlordane, the available data indicated that there were very

low levels of these contaminants in the raw, treated, or tap water. Most of the values found were “not

detected” or near the detection limit (Canadian Public Health Association, 1986, as cited in USEPA,

1989).

3.4.5.3 Unspecified Sources

A Region V Survey (USEPA, 1975b, as cited in USEPA, 1989), conducted during the first three months

of 1975, assessed levels of organic chemicals in samples of raw and finished drinking water collected

from 83 utilities in Indiana, Illinois, Michigan, Minnesota, Ohio, and Wisconsin. Samples were analyzed
Occurrence Summary and Use Support Document March 2002 165

for various pollutants including gamma-chlordane. One sample of finished drinking water contained

gamma-chlordane at a level of 0.004 :g/L. No limits of detection for pesticides were reported.

In a study to identify the sources of pollutants entering a sewage treatment plant, Levins et al. (1979, as

cited in USEPA, 1989) collected samples from two drinking water sources. Although no detection limit

was reported, the analyses detected no chlordane in any of the samples.

Schafer et al. (1969, as cited in USEPA, 1989) reported concentrations of chlordane up to 8 :g/L for

finished drinking water, although no location(s) were given. No other information on this study was

reported.

3.4.6 Conclusion

Chlordane is a synthetic chemical that was used in the 1980s as a pesticide in agriculture and other areas. 

Today, chlordane’s only use is as fire ant control in power transformers. As of 1992, chlordane was

produced solely by Velsicol Chemical Corp., and its production has greatly decreased since its

cancellation. Industrial releases of chlordane were been reported to TRI from 1988 to 1996 from 10

States. Chlordane ambient occurrence was not analyzed in any available ambient studies. The Stage 2

analysis, based on the 16-State cross-section, estimated that zero percent of combined ground water and

surface water systems serving zero percent of the population exceeded the MCL of 0.002 mg/L. Based

on this estimate, zero PWSs nationally are estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, TRI releases have been reported for chlordane from 10 States, including 5

of 16 cross-section States. Chlordane use has been virtually eliminated throughout the U.S. The only

producer of chlordane is located in Tennessee, which is not one of the 16 cross-section States. However,

the cross-section should adequately represent the occurrence of chlordane on a national scale based upon

the use, production, and release patterns of the 16-State cross-section in relation to the patterns observed

for all 50 States.

3.4.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1994. Toxicological Profile for

Chlordane. U.S. Department of Health and Human Services, Public Health Service. 234 pp. +

Appendices. Available on the Internet at http://atsdr1.atsdr.cdc.gov/toxprofiles/tp31.pdf

Barks, J.H. 1978. Water Quality in the Ozark National Scenic Riverways, Missouri. Washington, DC:

U.S. Geological Survey, U.S. Department of Interior. Geological Survey Water-Supply Paper

2048.

Benvenue, A., J.N. Ogata, and J.W. Hylin. 1972b. Organochlorine pesticides in rainwater, Oahu,

Hawaii, 1971-1972. Bull. Environ. Contam. Toxicol. v. 8, no. 4, pp. 238-241.

Canadian Public Health Association. 1986. Comprehensive Survey of the Status of Great Lakes

Drinking Water. Prepared in cooperation with Health and Welfare Canada and the Ministry of

the Environment. Ottawa, Canada: Canadian Public Health Association. August 1986.
Occurrence Summary and Use Support Document March 2002 166

Carey, A.E., and F.W. Kutz. 1983. Trends in Ambient Concentrations of Agrochemicals in Humans and

the Environment of the United States. Presented at the International Conference on

Environmental Hazards of Agrochemicals in Developing Countries, Alexandria, Egypt,

November 8-12, 1983.

Englande, A.J., J.K. Smith, and J.N. English. 1978. Potable water quality of advanced wastewater

treatment plant effluents. Prog. Wat. Tech. v. 10, no. 1⁄2, pp. 17-39.

Gilliom, R.J., R.B. Alexander, and R.A. Smith. 1985. Pesticides in the Nation’s Rivers, 1975-1980, and

Implications for Future Monitoring. U.S. Geological Survey Water-Supply Paper 2271. U.S.

Government Printing Office, U.S. Department of Interior.

Holden, P.W. 1986. Pesticides and Groundwater Quality. Issues and Problems in Four States.

Prepared for the Board of Agriculture, National Research Council. Washington, DC: National

Academy Press.

Idaho Department of Health and Welfare. 1984. Letter to Charles Berry, Office of Drinking Water, U.S.

Environmental Protection Agency, summarizing data on groundwater contamination incidents. 

Sent by: Charles D. Brokopp, State Epidemiologist, Division of Health, Idaho Department of

Health and Welfare.

Irwin, G.A., and H.G. Healy. 1978. Chemical and Physical Quality of Selected Public Water Supplies in

Florida, August-September 1976. Tallahassee, FL: Water Resources Division, U.S. Geological

Survey. USGS/WRI 78-21.

Levins, P., J. Adams, P. Brenner, S. Coons, K. Thrun, and J. Varone. 1979. Sources of Toxic Pollutants

Found in Influents to Sewage Treatment Plants. IV. R.M. Clayton Drainage Basin, Atlanta

report. Prepared by Arthur D. Little, Inc., for Office of Water Planning and Standards, U.S.

Environmental Protection Agency, Washington, DC. EPA Contract No. 68-01-3857.

National Safety Council (NSC). 2001. Chlordane Chemical Backgrounder. Itasca, IL: National Safety

Council. Available on the Internet at:

http://www.crossroads.nsc.org/ChemicalTemplate.cfm?id=90&chempath=chemicals, accessed

July 18, 2001.

Ramlit Associates, Inc. 1983. Groundwater Contamination by Pesticides: A California Assessment.

Submitted to: State Water Resources Control Board, Sacramento, CA. Submitted by: Ramlit

Associates, Inc., Berkeley, CA. Publication No. 83-4SP.

Schafer, M.L., et al. 1969. Pesticides in drinking water. Environ. Sci. Technol. v. 3, p. 1261.

Truhlar, J.F., and L.A. Reed. 1976. Occurrence of pesticide residues in four streams draining different

land-use areas in Pennsylvania, 1969-1971. Pestic. Monit. J. v. 10, no.3, pp. 101-110.

Tucker, R.K., and T.A. Burke. 1978. A Second Preliminary Report on the Findings of the State

Groundwater Monitoring Project. New Jersey: Department of Environmental Protection.

USEPA. 1975a. Analytical Report: New Orleans Water Supply Study. Region VI, EPA. 

EPA-906/9-75-003.
Occurrence Summary and Use Support Document March 2002 167

USEPA. 1975b. Preliminary Assessment of Suspected Carcinogens in Drinking Water. Washington,

DC: Office of Toxic Substances, USEPA.

USEPA. 1989. Draft Final Report on the Occurrence and Human Exposure to Pesticides in Drinking

Water, Food, and Air in the United States of America. Office of Drinking Water, USEPA. 

September, 1989.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: Chlordane. 

Office of Ground Water and Drinking Water, USEPA. Available on the Internet at

http://www.epa.gov/safewater/dwh/c-SOC/chlordan.html, last updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Waggoner, P.E. 1985. Memorandum from the Connecticut Agricultural Experiment Station on

Pesticides in Connecticut Groundwater. P. Gough, (ed.). New Haven, CT: News of Science.
Occurrence Summary and Use Support Document March 2002 168

3.5 1,2-Dibromo-3-Chloropropane (DBCP)

Table of Contents

3.5.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

3.5.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

3.5.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

3.5.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 171

3.5.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

3.5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

3.5.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

Tables and Figures

Table 3.5-1: Environmental Releases (in pounds) for 1,2-Dibromo-3-Chloropropane in the 

United States, 1991-1992 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

Table 3.5-2: Stage 1 DBCP Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . . . 171

Table 3.5-3: Stage 1 DBCP Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . . . 172

Table 3.5-4: Stage 2 Estimated DBCP Occurrence Based on 16-State Cross-Section - Systems . . . . 173

Table 3.5-5: Stage 2 Estimated DBCP Occurrence Based on 16-State Cross-Section - Population . . 174

Table 3.5-6: Estimated National DBCP Occurrence - Systems and Population Served . . . . . . . . . . . 175
Occurrence Summary and Use Support Document March 2002 169

3.5.1 Introduction, Use and Production

1,2-Dibromo-3-chloropropane, also known as DBCP, is a manufactured chemical not found naturally in

the environment. It is a colorless liquid with a sharp smell that can be tasted in water at very low

concentrations. Most DBCP that enters surface water evaporates into the air within several days or a

week. Some of what is spilled on or applied to soil moves through the soil into the groundwater, where it

may remain for a long time. Trade names for pesticides containing DBCP are Nemagon, Nemafume,

Fumazone, Fumagon, and Nemazon (ATSDR, 1992).

1,2-Dibromo-3-chloropropane is a manufactured chemical and is not found naturally in the environment

(ATSDR, 1992). It is used as an intermediate in the synthesis of organic chemicals, such as the

brominated flame retardant tris[(2,3-dibromopropyl)phosphate] (Verschueren, 1983, as cited in ATSDR,

1992). Until 1977, DBCP was extensively used as a soil fumigant and nematocide on over 40 different

crops in the United States (Anonymous, 1988, as cited in ATSDR, 1992). The chemical was used to

protect field crops, vegetables, fruits and nuts, nursery and greenhouse crops, and turf from pests (NTP,

1985, as cited in ATSDR, 1992).

From 1977 to 1979, EPA suspended registration of products containing DBCP except for use on

pineapples in Hawaii (Anonymous 1988; USEPA 1977, 1979; all as cited in ATSDR, 1992). In 1985,

EPA issued an intent to cancel all registrations for DBCP-containing pesticide products, including use on

pineapples. Subsequently, the use of existing stocks of DBCP on pineapples was prohibited (USEPA

1985a, 1985b, all as cited in ATSDR, 1992).

Prior to the cancellation of pesticide uses, DBCP was used extensively; 9.8 million pounds of DBCP

were applied in 1974. In California, 831,000 pounds of the chemical were applied, mainly on grapes and

tomatoes, during 1977 (NTP, 1985, as cited in ATSDR, 1992). The volume of DBCP applied to

pineapple fields in Hawaii between 1979 and 1985 was probably high, since during much of that time,

the chemical was the preferred fumigant for use on pineapple fields (Albrecht, 1987, as cited in ATSDR,

1992).

DBCP was first produced commercially in the United States in 1955. In 1969, U.S. production was 8.58

million pounds (IARC, 1979, as cited in ATSDR, 1992). Estimates of annual production during 1974 to

1975 ranged from 18 to 20 million pounds (IARC, 1979; NTP, 1985, all as cited in ATSDR, 1992).

DBCP is no longer commercially manufactured in the United States (Hawley, 1981; Sax and Lewis,

1987, all as cited in ATSDR, 1992). R.W. Greeff & Co., Inc., in Old Greenwich, Connecticut, is listed as

a current supplier of DBCP for domestic research purposes (OPD, 1989, as cited in ATSDR, 1992). It is

not known whether this supplier produces DBCP in the United States or imports the chemical. 

Two companies were listed as producers of DBCP in 1977 (USEPA, 1989a, as cited in ATSDR, 1992).

The production volume of Columbia Organic Chemicals Co., in Columbia, South Carolina, was listed as

less than 1,000 pounds. No production volume was listed for the other producer, Velsicol Chemical

Corp., in El Dorado, Arkansas. As DBCP is no longer used as a fumigant and nematocide in the United

States, it is likely that its current production volume in the United States, if any, is very low.

3.5.2 Environmental Release

1,2-Dibromo-3-chloropropane is listed as a Toxics Release Inventory (TRI) chemical. Table 3.5-1

illustrates the environmental releases for DBCP from 1991 and 1992. (There are only DBCP data for

these years.) Air emissions are the only recorded releases of DBCP, and, given that the data is only for

two years, a trend is not self-evident. No surface water discharges, underground injection, releases to
Occurrence Summary and Use Support Document March 2002 170

land (such as spills or leaks within the boundaries of the reporting facility), or off-site releases (including

metals or metal compounds transferred off-site) were reported for DBCP. These TRI data for DBCP

were reported in Ohio and Rhode Island, neither of which are included in the 16-State cross-section (used

for analyses of DBCP occurrence in drinking water; see Section 3.5.4). (For a map of the 16-State crosssection, see Figure 1.3-1.)

Table 3.5-1: Environmental Releases (in pounds) for 1,2-Dibromo-3-Chloropropane in the United

States, 1991-1992

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1992 294 -- -- -- -- 294

1991 580 -- -- -- -- 580

 Source: USEPA, 2000 

3.5.3 Ambient Occurrence

To understand the presence of a chemical in the environment, an examination of ambient occurrence is

useful. In a drinking water context, ambient water is untreated source water residing in surface waters

and aquifers. There are few available data on the occurrence of DBCP in ambient waters of the United

States. The most comprehensive and nationally consistent data describing ambient water quality in the

United States are being produced through the United States Geological Survey’s (USGS) National Water

Quality Assessment (NAWQA) program. However, national NAWQA data are currently unavailable for

DBCP. Additional studies of ambient data are summarized below.

3.5.3.1 Additional Ambient Occurrence Data

A summary document entitled ““Occurrence and Human Exposure to Pesticides in Drinking Water,

Food, and Air in the United States of America” (USEPA, 1989b)), was previously prepared for past

USEPA assessments of pesticides. Regional studies reviewed in that document were the only

information found that addressed levels of DBCP in water other than drinking water or water not

specified as drinking water. The following information is taken directly from “Occurrence and Human

Exposure to Pesticides in Drinking Water, Food, and Air in the United States of America” (USEPA,

1989b).

Several regional studies (Peoples et al., 1980; Nelson et al., 1981; Pinto, 1980; Cohen, 1981; Carter and

Riley, 1981; and Mink, 1981, all as cited in Cohen et al, 1984 and all as cited in USEPA, 1989b) and the

EPA pesticide registration files (as reported in Cohen et al., 1984 and as cited in USEPA, 1989b)

provided monitoring data on levels of DBCP in ground water. Positive concentrations of DBCP ranging

from 0.02 :g/L to 20 :g/L were detected in samples of ground water in Hawaii, California, Arizona,

South Carolina, and Maryland. Areas with the highest concentrations were the San Joaquin Valley in

California and the region southwest of Phoenix, Arizona. The number of samples analyzed, the number

of positive samples detected, and the detection limit were not reported.

Holden (1986, as cited in USEPA, 1989b) reported that, in a massive survey of more than 8,000 public

and private wells in the San Joaquin Valley of California, detectable levels of DBCP were found in

approximately 25% of the wells tested. The highest level of DBCP found in the survey was 1,240 :g/L.
Occurrence Summary and Use Support Document March 2002 171

Samples of ground water collected from seven previously unsampled sites in Hawaii showed detectable

levels of DBCP in the range of 0.05 :g/L to 0.5 :g/L (USEPA, 1984, as cited in USEPA, 1989b). Some

of the sites have been used as drinking water supplies. The number of samples tested, the number of

positive samples, and the detection limit were not reported.

3.5.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of DBCP occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.0002 mg/L; 0.0001 mg/L; and 0.00002 mg/L.

All sixteen cross-section State data sets, with the exception of Texas, contained occurrence data for 1,2-

dibromo-3-chloropropane. These data represent more than 98,000 analytical results from approximately

14,000 PWSs during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The

number of sample results and PWSs vary by State, although the State data sets have been reviewed and

checked to ensure adequacy of coverage and completeness. The overall modal detection limit for DBCP

in the 16 cross-section States is equal to 0.00002 mg/L. (For details regarding the 16-State cross-section,

please refer to Section 1.3.5 of this report.)

3.5.4.1 Stage 1 Analysis Occurrence Findings

Table 3.5-2 illustrates the Stage 1 analysis of DBCP occurrence in drinking water for the public water

systems in the 16-State cross-section relative to three thresholds: 0.0002 mg/L (the current MCL),

0.0001, and 0.00002 mg/L (the modal MRL). A total of 128 (approximately 0.912% of) ground water

and surface water PWSs had analytical results exceeding the MCL (0.0002 mg/L); 1.08% of systems

(152 systems) had results exceeding 0.0001 mg/L. When evaluated relative to a threshold of 0.00002

mg/L, the percentage of systems increased to 1.50% (211 systems).

Approximately 0.861% of ground water systems (112 systems) had any analytical results greater than the

MCL (0.0002 mg/L). About 1.02% of ground water systems (132 systems) had results above 0.0001

mg/L. The percentage of ground water systems with at least one result greater than 0.00002 mg/L was

equal to 1.30% (169 systems). 

A total of 16 (1.55% of) surface water systems had results greater than 0.0002 mg/L. Twenty (1.93% of)

surface water systems had at least one analytical result greater than 0.0001 mg/L. Approximately 4.06%

of surface water systems (42 systems) had results exceeding 0.00002 mg/L.

Table 3.5-2: Stage 1 DBCP Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.0002 0.861% 112

0.0001 1.02% 132

0.00002 1.30% 169
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 172

Surface Water

0.0002 1.55% 16

0.0001 1.93% 20

0.00002 4.06% 42

Combined Ground &

Surface Water

0.0002 0.912% 128

0.0001 1.08% 152

0.00002 1.50% 211

Reviewing DBCP occurrence in the 16 cross-section States by PWS population served (Table 3.5-3)

shows that approximately 11.4% of the population served by PWSs in the 16 States (almost 10 million

people) was served by PWSs with at least one analytical result of DBCP greater than the MCL. 

Approximately 10.3 million (11.8% of) people were served by systems with an exceedance of 0.0001

mg/L. Over 11 million (13.0% of) people were served by systems with at least one analytical result

greater than 0.00002 mg/L.

The percentage of population served by ground water systems with at least one analytical result greater

than 0.0002 mg/L was equal to 3.41% (about 1.3 million people). When evaluated relative to 0.0001

mg/L and 0.00002 mg/L, the percent of population exposed was equal to 3.78% (almost 1.5 million

people) and 5.36% (over 2 million people), respectively. 

The percentages of population served by surface water systems with exceedances of all thresholds are

much greater than the ground water percentages of exceedance. About 17.7% of the population (over 8.6

million people) was served by surface water systems with at least one analytical result greater than the

MCL. Approximately 18.1% of the population served by surface water systems (over 8.8 million people)

were exposed to DBCP concentrations greater than 0.0001 mg/L. When evaluated relative to 0.00002

mg/L, the percent of population exposed was equal to 19.1% (almost 9.4 million people).

Table 3.5-3: Stage 1 DBCP Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.0002 3.41% 1,322,000

0.0001 3.78% 1,466,500

0.00002 5.36% 2,080,200

Surface Water

0.0002 17.7% 8,638,200

0.0001 18.1% 8,843,800

0.00002 19.1% 9,352,000
Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 173

Combined Ground &

Surface Water

0.0002 11.4% 9,960,300

0.0001 11.8% 10,310,200

0.00002 13.0% 11,432,200

3.5.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.5-4 and 3.5-5. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2002)). 

About 1.41% (approximately 199) of ground water and surface water PWSs had estimated mean

concentrations of DBCP greater than the MCL (0.0002 mg/L). Approximately 273 (1.94% of) systems in

the 16 States had mean concentrations of DBCP exceeding 0.0001 mg/L. When evaluated relative to

0.00002 mg/L, the percentage of systems exceeding the threshold increased to 4.09% (an estimated 574

systems).

Approximately 182 (1.40% of) ground water systems in the 16 States have an estimated mean

concentration of DBCP greater than 0.0002 mg/L. An estimated 1.91% of ground water systems (about

249 systems) had mean concentration values greater than 0.0001 mg/L. A total of 517 (3.97% of) PWSs

had estimated mean concentration values of DBCP greater than 0.00002 mg/L. 

Only 17 (about 1.64% of) surface water systems in the 16 States had estimated mean concentrations

greater than the MCL. Approximately 24 (2.33% of) surface water systems had estimated mean

concentration values greater than 0.0001 mg/L. Fifty-seven (approximately 5.56% of) surface water

systems in the 16 States had estimated mean concentration values of DBCP greater than 0.00002 mg/L.

Table 3.5-4: Stage 2 Estimated DBCP Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0002 1.40% 1.19% - 1.61% 182 155 - 210

0.0001 1.91% 1.65% - 2.18% 249 214 - 284

0.00002 3.97% 3.41% - 4.52% 517 443 - 588
Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 174

Surface Water

0.0002 1.64% 1.06% - 2.32% 17 11 - 24

0.0001 2.33% 1.55% - 3.19% 24 16 - 33

0.00002 5.56% 4.06% - 7.06% 57 42 - 73

Combined Ground

& Surface Water

0.0002 1.41% 1.22% - 1.65% 199 171 - 231

0.0001 1.94% 1.70% - 2.21% 273 238 - 310

0.00002 4.09% 3.53% - 4.63% 574 496 - 650

Reviewing DBCP occurrence by PWS population served (Table 3.5-5) shows that approximately 2.60%

of population served by all PWSs in the 16 cross-section States (an estimate of approximately 2.3 million

people) were potentially exposed to DBCP levels above 0.0002 mg/L. The percentage of population

served by PWSs in the 16 States with mean levels of DBCP above 0.0001 mg/L and 0.00002 mg/L were

3.22% (about 2.8 million people) and 5.75% (over 5 million people), respectively. 

When the percent of population served by ground water systems in the 16 States was evaluated relative to

a threshold of 0.0002 mg/L, 0.0001 mg/L, and 0.00002 mg/L, the percentage of population exposed in the

16 cross-section States was equal to 3.27% (an estimated 1.27 million people), 4.03% (an estimated 1.56

million people) and 6.21% (an estimated 2.4 million people), respectively. 

The percentage of population served by surface water systems in the 16 States with mean levels above

0.0002 mg/L was equal to 2.07% (over 1 million people), and the percentage of population served with

levels above 0.0001 mg/L was 2.58% (an estimated 1.26 million people). The percentage of the

population served by surface water systems with levels above 0.00002 mg/L was 5.39% (over 2.6 million

people). 

Table 3.5-5: Stage 2 Estimated DBCP Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the 16

States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0002 3.27% 2.71% - 4.20% 1,267,200 1,050,000 - 1,629,900

0.0001 4.03% 3.40% - 5.38% 1,563,900 1,318,400 - 2,086,000

0.00002 6.21% 4.92% - 9.98% 2,409,100 1,907,200 - 3,869,100

Surface Water

0.0002 2.07% 1.51% - 3.97% 1,011,100 738,000 - 1,941,900

0.0001 2.58% 1.60% - 5.24% 1,264,600 782,100 - 2,565,400

0.00002 5.39% 2.74% - 14.2% 2,637,300 1,340,000 - 6,929,800
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the 16

States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 175

Combined Ground

& Surface Water

0.0002 2.60% 2.11% - 3.77% 2,278,300 1,853,700 - 3,307,300

0.0001 3.22% 2.49% - 4.96% 2,828,300 2,182,700 - 4,353,900

0.00002 5.75% 3.99% - 10.4% 5,046,100 3,503,800 - 9,149,900

3.5.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 920 PWSs nationally serving approximately 5.5 million people could be exposed

to DBCP concentrations above 0.0002 mg/L. About 1,263 systems serving almost 6.9 million people

were estimated to have mean concentrations greater than 0.0001 mg/L. Approximately 2,658 systems

serving over 12 million people nationally were estimated to have DBCP concentrations greater than

0.00002 mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to

national values.)

For ground water systems, about 830 PWSs serving almost 2.8 million people nationally were estimated

to have mean concentrations greater than 0.0002 mg/L. Approximately 1,136 systems serving about 3.5

million people nationally were estimated to have a mean concentration value of DBCP that exceeded

0.0001 mg/L. About 2,360 ground water systems serving over 5.3 million people were estimated to have

mean concentrations greater than 0.00002 mg/L. 

Approximately 92 surface water systems serving about 2.6 million people were estimated to have mean

concentrations of DBCP above 0.0002 mg/L. An estimated 130 surface water systems serving almost 3.3

million people were estimated to have mean concentrations greater than 0.0001 mg/L. About 311 surface

water systems serving almost 6.9 million people were estimated to have mean concentrations greater than

0.00002 mg/L.

Table 3.5-6: Estimated National DBCP Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems Nationally

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0002 830 709 - 959 2,799,200 2,319,400 - 3,600,300

0.0001 1,136 978 - 1,298 3,454,700 2,912,300 - 4,608,000

0.00002 2,360 2,025 - 2,687 5,321,700 4,213,000 - 8,546,700

Surface Water

0.0002 92 59 - 130 2,630,600 1,920,100 - 5,052,300

0.0001 130 86 - 178 3,290,100 2,034,700 - 6,674,500

0.00002 311 227 - 395 6,861,600 3,486,200 - 18,029,400
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems Nationally

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 176

Combined Ground

& Surface Water

0.0002 920 792 - 1,070 5,531,800 4,500,900 - 8,030,400

0.0001 1,263 1,102 - 1,436 6,867,400 5,299,600 - 10,571,600

0.00002 2,658 2,297 - 3,010 12,252,200 8,507,500 - 22,216,800

3.5.5 Additional Drinking Water Occurrence Data

Several regional studies reviewed in the summary document entitled “Occurrence and Human Exposure

to Pesticides in Drinking Water, Food, and Air in the United States of America” (USEPA, 1989b)

addressed levels of DBCP in samples of drinking water obtained from ground water and surface water

sources. Note that the study presented in the following section does not provide the quantitative

analytical results or comprehensive coverage that would enable direct comparison to the occurrence

findings estimated with the cross-section occurrence data presented in Section 3.5.4. This additional

study, however, does enable a broader assessment of the Stage 2 occurrence estimates presented for this

Six-Year Review. All the following information in Section 3.5.5 is taken directly from “Occurrence and

Human Exposure to Pesticides in Drinking Water, Food and Air in the United States of America”

(USEPA, 1989b). 

3.5.5.1 Ground Water Sources

Carey and Kutz (1983, as cited in USEPA, 1989b) presented data collected in 1979 on levels of DBCP in

ground water samples collected in California, Arizona, Texas, South Carolina, and Alabama. Eight

positive ground water samples collected from California and South Carolina showed DBCP

concentrations ranging from 0.01 :g/L to 10.8 :g/L, and an average concentration of 2.8 :g/L. Seven of

the positive samples were from private wells; one sample containing 0.01 :g/L was from a municipal

well. The number of ground water samples tested was not reported.

3.5.5.2 Surface Water Sources

Carey and Kutz (1983, as cited in USEPA, 1989b) also reported on levels of DBCP in samples of surface

water collected in California, Arizona, Texas, South Carolina, and Alabama in 1979. Two positive

samples collected from municipal water supplies in California showed DBCP concentrations of 0.09

:g/L and 0.1 :g/L. The number of surface water samples tested was not reported.

To assemble a database which would reflect the status of Great Lakes drinking water quality, the

Canadian Public Health Association gathered data from October 1984 through August 1985 (Canadian

Public Health Association, 1986, as cited in USEPA, 1989b). The data collected covered the period from

the mid 1970s to early 1985. The study was funded by the Health Protection Branch of Health and

Welfare Canada and the Ontario Ministry of the Environment. A research team, appointed by the

Association, reviewed data on the quality of water at 31 representative Canadian and United States

communities and 24 offshore sites to evaluate the human health implications.
Occurrence Summary and Use Support Document March 2002 177

For each of the 31 communities, data consisted of: 1) background information on the community; 2)

treatment plant schematics and associated treatment process information; and 3) water quality data. 

Water sample types included raw water (treatment plant intake), distribution water (treated water), and

tap water. Water quality data collected included general parameters (e.g., alkalinity, turbidity),

microbiological and radiological parameters, inorganic parameters, and organic parameters (including

volatiles, base/neutrals, pesticides and PCBs, and phenols and acids). For each parameter, the water

type, time period, concentration (mean and range), number of samples, and detection limit were recorded.

For most of the volatile organics, including DBCP, the available data indicated that these contaminants

did not occur at significant levels in the raw, treated, or tap water. Most of the values found were “not

detected” or near the detection limit (Canadian Public Health Association, 1986, as cited in USEPA,

1989b).

3.5.6 Conclusion

DBCP is a pesticide that was used and produced extensively in the United States from 1955 to 1977,

when its use was restricted to pineapples in Hawaii. All uses were subsequently canceled in 1985. Until

its restriction and cancellation, DBCP was extensively used as a soil fumigant and nematocide on over 40

different crops in the United States. There are no recent statistics available regarding use or production

of DBCP, and any production is probably minimal. Industrial releases of DBCP were reported to TRI in

1991 and 1992 from two States. DBCP was not an analyte for any of the ambient occurrence studies. 

The Stage 2 analysis, based on the 16-State cross-section, estimated that approximately 1.41% of

combined ground water and surface water systems serving 2.60% of the population exceeded the MCL of

0.0002 mg/L. Based on this estimate, a national estimate of 920 PWSs, serving approximately 5,531,800

people, are estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, TRI releases have been reported for DBCP from 2 States, not including any

of the cross-section States. The use of DBCP has been canceled nationwide, and any production of

DBCP is projected to be very minimal. The cross-section should adequately represent the occurrence of

DBCP on a national scale based upon the use, production, and release patterns of the 16-State crosssection in relation to the patterns observed for all 50 States. 

3.5.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1992. Toxicological Profile for 1,2-

Dibromo-3-chloropropane. U.S. Department of Health and Human Services, Public Health

Service. 152 pp. + Appendices. Available on the Internet at

http://www.atsdr.cdc.gov/toxprofiles/tp36.pdf

Albrecht, W.N. 1987. Occupational exposure to 1,3-dichloropropene (Telone II@) in Hawaiian

pineapple culture. Archives of Environmental Health. v. 42, pp. 286-291.

Anonymous. 1988. DBCP. Reviews of Environmental Contamination and Toxicology. v. 104, 

pp. 73-91.

Canadian Public Health Association. 1986. Comprehensive Survey of the Status of Great Lakes

Drinking Water. Prepared in cooperation with Health and Welfare Canada and the Ministry of

the Environment. Ottawa, Canada: Canadian Public Health Association. August, 1986.
Occurrence Summary and Use Support Document March 2002 178

Carey, A.E., and F.W. Kutz. 1983. Trends in Ambient Concentrations of Agrochemicals in Humans and

the Environment of the United States. Presented at the International Conference on

Environmental Hazards of Agrochemicals in Developing Countries, Alexandria, Egypt,

November 8-12, 1983.

Carter, G.E., and M.B. Riley. 1981. Pestic. Monit. J. v. 15, pp. 139-142.

Cohen, S.Z. 1981. Summary Report – DBCP in Groundwater in the Southeast. Washington, DC:

Hazard Evaluation Division, U.S. Environmental Protection Agency.

Cohen, S.Z., S.M. Creeger, R.F. Carsel, and C.G. Enfield. 1984. Potential for Pesticide Contamination

in Groundwater Resulting from Agricultural Uses. In: Treatment and Disposal of Pesticide

Wastes. R.F. Kruger and J.W. Seiber (eds.). Washington, DC: American Chemical Society. 

ACS Symposium Series No. 259: pp. 247-325.

Hawley, G.G. 1981. The Condensed Chemical Dictionary. 10th ed. New York, NY: Van Nostrand

Reinhold Co., p. 325.

Holden, P.W. 1986. Pesticides and Groundwater Quality. Issues and Problems in Four States.

Prepared for the Board of Agriculture, National Research Council. Washington, DC: National

Academy Press.

International Agency for Research on Cancer (IARC). 1979. Monograph on the evaluation of the

carcinogenic risk of chemicals to humans. Vol. 20: Some halogenated hydrocarbons. Lyon,

France: World Health Organization, pp. l-40, 83-96.

Mink, J.F. 1981. DBCP and EDB in soil and water at Kuhia, Oahu, Hawaii. Prepared for Del Monte

Corp., Honolulu, Hawaii. 

National Toxicology Program (NTP). 1985. Fourth Annual Report on Carcinogens. National

Toxicology Program, pp. 179-182.

Nelson, S., M. Iskander, M. Volz, S. Khalifa, and R. Haberman. 1981. Sci. Total. Environ. v. 21, 

pp. 35-40.

OPD. 1989. OPD Chemical Buyers Directory. 76th ed. New York, NY: Schnell Publishing Co. Inc.,

pp. 235, 696. 

Peoples, S.A., K.T. Maddy, W. Cusick, T. Jackson, C. Cooper, and A.S. Frederickson. 1980. Bull.

Environ. Contam. Toxicol. v. 24, pp. 611-618.

Pinto, E. 1980. Report of Groundwater Contamination Study in Wicomico, Maryland. Wicomico

County Health Department, State of Maryland (plus 1981-1982 addenda).

Sax, N.I., and R.J. Lewis. 1987. Hawley's Condensed Chemical Dictionary. 10th Ed. New York, NY:

Van Nostrand Reinhold Co., p. 367.

USEPA. 1977. U.S. Environmental Protection Agency: Southern Agricultural Insecticides, Inc., et al.

Suspension order. Federal Register 42, pp. 57543-57548. 
Occurrence Summary and Use Support Document March 2002 179

USEPA. 1979. U.S. Environmental Protection Agency: Dibromochloropropane (DBCP); Suspension

order and notice of intent to cancel. Federal Register 44, pp. 65135-65176.

USEPA. 1984. Proposal for comment on intent to cancel use of dibromochloropropane in Hawaii. 

Federal Register 46, p. 19594.

USEPA. 1985a. U.S. Environmental Protection Agency: Dibromochloropropane; Intent to cancel

registrations of pesticide products containing dibromochloropropane (DBCP). Federal Register

50, pp. 1122-1123.

USEPA. 1985b. U.S. Environmental Protection Agency: Dibromochloropropane; Denial of use of

existing stocks. Federal Register 50, p. 46512.

USEPA. 1989a. Computer printout (CIS): 1977 Non-confidential production data from TSCA

inventory. Washington, DC: Office of Pesticides and Toxic Substances, CID, USEPA.

USEPA. 1989b. Draft Final Report on the Occurrence and Human Exposure to Pesticides in Drinking

Water, Food, and Air in the United States of America. Office of Drinking Water, USEPA. 

September, 1989.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Verschueren, K., ed. 1983. Handbook of Environmental Data on Organic Chemicals. New York, NY:

Van Nostrand Reinhold Co., pp. 464-465.
Occurrence Summary and Use Support Document March 2002 180

3.6 Diquat

Table of Contents

3.6.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181

3.6.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

3.6.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

3.6.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 183

3.6.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

3.6.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

3.6.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

Tables and Figures

Figure 3.6-1: Estimated Annual Agricultural Use for Diquat (1992) . . . . . . . . . . . . . . . . . . . . . . . . . . 182

Table 3.6-1: Stage 1 Diquat Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . . 183

Table 3.6-2: Stage 1 Diquat Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . . 184

Table 3.6-3: Stage 2 Estimated Diquat Occurrence Based on 16-State Cross-Section - Systems . . . . 185

Table 3.6-4: Stage 2 Estimated Diquat Occurrence Based on 16-State Cross-Section - Population . . 186

Table 3.6-5: Estimated National Diquat Occurrence - Systems and Population Served . . . . . . . . . . . 187
Occurrence Summary and Use Support Document March 2002 181

3.6.1 Introduction, Use and Production

Diquat [6,7-dihydrodipyrido (1,2-a:2',1'-c) pyrazinediium dibromide] is an organic solid of colorless or

yellow crystals. It is a quick-acting contact herbicide, causing injury only to the parts of the plant to

which it is applied. It is nonselective, meaning that it does not spare ‘nontarget’ plants from its

herbicidal effects. Diquat is referred to as a desiccant because it causes a leaf or an entire plant to dry out

quickly. It is not residual, so it does not leave any trace of herbicide on or in plants, soil, or water

(EXTOXNET, 2001). Diquat is persistent, but essentially immobile, in the environment, indicating that

it will most likely be associated with the soil and sediment rather than water (USEPA, 2001b). A trade

name for diquat is Reglone.

Diquat is widely used as a herbicide, algicide, and plant growth regulator (EXTOXNET, 2001). Usage in

1980 was estimated to be 200,000 pounds of active ingredient, and 1982 data indicates that diquat was

not produced domestically, but imports were nearly 835,000 pounds. Diquat has been in use since the

1950s to control both crop and aquatic weeds. It is used on potatoes; as an aid in harvesting cotton,

rapeseed and other oil seed crops; to wilt and dry out silage, standing hay, etc. for storage; a plant growth

regulator and sugar cane-flowering suppressant (USEPA, 2001a).

As a herbicide/algicide, diquat is used to control broadleaf and grassy weeds in non-crop (including

residential) and aquatic areas. As a desiccant/defoliant, it is used in seed crops and potatoes. Its largest

use is as a desiccant on potato crops (USEPA, 1995).

Figure 3.6-1 shows the United States Geological Survey (USGS, 1998a) derived geographic distribution

of estimated average annual diquat use in the United States for 1992. A breakdown of use by crop is also

included. The USGS (1998a) estimates approximately 230,000 pounds of diquat active ingredient were

used in 1992. The two largest concentrations of diquat use are seen in the West and the Northeast. Given

the amount of white space on the map, the possibility also exists that some States did not fully report

their diquat usage. While non-agricultural uses are not reflected here, and any sharp spatial differences

in use within a county are not well represented (USGS, 1998b), existing data suggest that nonagricultural use of diquat is minimal to non-existent (USEPA, 1995). A comparison of this use map with

the map of the 16 cross-section States (Figure 1.3-1) shows that States across the range of high of low

diquat use are well represented in the cross-section.
Occurrence Summary and Use Support Document March 2002 182

Figure 3.6-1: Estimated Annual Agricultural Use for Diquat (1992)

Source: USGS 1998a

3.6.2 Environmental Release

Diquat is released directly to the environment in its use as a herbicide, algicide, and plant growth

regulator and potentially during its manufacture, handling, and storage. EPA estimated that 200,000

pounds of diquat active ingredient were used in the United States in 1980 (USEPA, 2001a). Diquat is not

listed as a Toxics Release Inventory (TRI) contaminant, so no TRI release records are maintained. 

Therefore, the use of diquat (described in the previous section) may provide the primary indication of

where releases are most likely. The areas of highest diquat use are in various potato growing regions of

the U.S., including Idaho and other Western States, as well as Maine and other locations in the Northeast. 

In the Midwest it is most likely used on alfalfa hay crops. These and other use areas are illustrated in

Figure 3.6-1.

3.6.3 Ambient Occurrence

To understand the presence of a chemical in the environment, an examination of ambient occurrence is

useful. In a drinking water context, ambient water is untreated source water residing in surface waters

and aquifers. There are few available data on the occurrence of diquat in ambient waters of the United

States. The most comprehensive and nationally consistent data describing ambient water quality in the

United States are being produced through the United States Geological Survey’s (USGS) National Water

Quality Assessment (NAWQA) program. However, national NAWQA data are currently unavailable for

diquat.
Occurrence Summary and Use Support Document March 2002 183

A summary document entitled “Occurrence and Exposure Assessment of Diquat in Public Drinking

Water Supplies” (Wade Miler, 1989), was previously prepared for past USEPA assessments of diquat. 

However, no national or regional studies were included on the occurrence of diquat in water other than

drinking water from ground water or surface water sources.

3.6.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of diquat occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.02 mg/L; 0.004 mg/L; and 0.002 mg/L. 

All sixteen cross-section State data sets, with the exception of New Jersey and Texas, contained

occurrence data for diquat. These data represent more than 36,000 analytical results from approximately

9,000 PWSs during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The

number of sample results and PWSs vary by State, although the State data sets have been reviewed and

checked to ensure adequacy of coverage and completeness. The overall modal detection limit for diquat

in the 16 cross-section States is equal to 0.0004 mg/L. (For details regarding the 16-State cross-section,

please refer to Section 1.3.5 of this report.)

3.6.4.1 Stage 1 Analysis Occurrence Findings

Table 3.6-1 illustrates the low occurrence of diquat in drinking water for the public water systems in the

16-State cross-section relative to three thresholds: 0.02 mg/L (the current MCL), 0.004 mg/L (the modal

MRL), and 0.002 mg/L. A total of 2 (approximately 0.0218% of) ground water and surface water PWSs

had analytical results exceeding the MCL; 0.0655% of systems (6 systems) had results exceeding 0.004

mg/L; and 0.153% of systems (14 systems) had results exceeding 0.002 mg/L. 

Approximately 0.0120% of ground water systems (1 system) had any analytical results greater than the

MCL. About 0.0600% of ground water systems (5 systems) had results above 0.004 mg/L. The

percentage of ground water systems with at least one result greater than 0.002 mg/L was equal to 0.120%

(10 systems). 

Only 1 (0.122% of) surface water systems had results greater than the MCL. Also, approximately 1

(0.122% of) surface water systems had at least one analytical result greater than 0.004 mg/L. Four

(0.487% of) surface water systems had results exceeding 0.002 mg/L.

Table 3.6-1: Stage 1 Diquat Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.02 0.0120% 1

0.004 0.0600% 5

0.002 0.120% 10
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 184

Surface Water

0.02 0.122% 1

0.004 0.122% 1

0.002 0.487% 4

Combined Ground & 

Surface Water

0.02 0.0218% 2

0.004 0.0655% 6

0.002 0.153% 14

Reviewing diquat occurrence in the 16 cross-section States by PWS population served (Table 3.6-2)

shows that approximately 0.208% of the population (about 153,400 people) was served by PWSs with at

least one analytical result of diquat greater than the MCL (0.02 mg/L). Approximately 171,300 (0.233%

of) people were served by systems with an exceedance of 0.004 mg/L. Over 337,000 (0.458% of) people

were served by systems with at least one analytical result greater than 0.002 mg/L.

The percentage of population served by ground water systems with analytical results greater than the

MCL was equal to 0.441% (approximately 142,000 people). When evaluated relative to 0.004 mg/L and

0.002 mg/L, the percent of population exposed was equal to 0.497% (almost 160,000 people) and 0.664%

(almost 214,000 people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.02 mg/L and 0.004

mg/L was equal to 0.0275% (11,400 people). When evaluated relative to 0.002 mg/L, the percent of

population exposed was equal to 0.298% (over 123,000 people).

Table 3.6-2: Stage 1 Diquat Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.02 0.441% 142,000

0.004 0.497% 159,900

0.002 0.664% 213,817

Surface Water

0.02 0.0275% 11,400

0.004 0.0275% 11,400

0.002 0.298% 123,300
Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 185

Combined Ground &

Surface Water

0.02 0.208% 153,400

0.004 0.233% 171,300

0.002 0.458% 337,100

3.6.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.6-3 and 3.6-4. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2002)). 

No ground water or surface water PWSs had an estimated mean concentration of diquat exceeding 0.02

mg/L. The percentage of ground and surface water systems with estimated mean concentration greater

that 0.004 mg/L and 0.002 mg/L is equal to 0.00096% (less than 1 system) and 0.0202% (2 systems),

respectively. Only 1 (0.00101% of) ground water PWS in the 16 States was estimated to have a mean

concentration greater than 0.004 mg/L and 2 (0.0204%) are estimated to have a mean concentration

greater than 0.002 mg/L. The percentage of surface water systems with estimated mean concentration

values greater than 0.004 mg/L was equal to 0.000487% (less than 1 system in the 16 States). Only 1

(0.0173% of) surface water system in the 16 States had an estimated mean concentration value of diquat

greater than 0.002 mg/L. 

Table 3.6-3: Stage 2 Estimated Diquat Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.00101% 0.000% - 0.0120% 1 0 - 1

0.002 0.0204% 0.000% - 0.0600% 2 0 - 5

Surface Water

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.000487% 0.000% - 0.000% 0 0 - 0

0.002 0.0173% 0.000% - 0.122% 1 0 - 1
Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 186

Combined Ground

& Surface Water

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.000961% 0.000% - 0.0109% 1 0 - 1

0.002 0.0202% 0.000% - 0.0546% 2 0 - 5

Reviewing diquat occurrence by PWS population served (Table 3.6-4) shows that approximately

0.000470% of population served by all PWSs (an estimate of approximately 300 people in the 16 States)

were potentially exposed to diquat levels above 0.004 mg/L. When evaluated relative to a threshold of

0.002 mg/L, the percent of population exposed was equal to 0.0218% (approximately 16,300 people). 

The percent of population exposed was equal to 0% for all system types when evaluated relative to the

MCL (0.02 mg/L). 

The percentage of population served by ground water systems in the 16 States with estimated mean

concentration values greater than 0.004 mg/L was equal to 0.00101% (an estimate of approximately 300

people) and the percentage served by surface water systems in the 16 States was equal to 0.0000503%. 

Approximately 14,600 (0.0453% of) people in the 16 cross-section States were served by ground water

systems with estimated mean concentration values greater than 0.002 mg/L. The number of people in the

16 cross-section States served by surface water systems with estimated mean concentration values greater

than 0.002 mg/L was equal to about 1,500 (0.00356% of) people.

Table 3.6-4: Stage 2 Estimated Diquat Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.020 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.00101% 0.000% - 0.00621% 300 0 - 2,000

0.002 0.0453% 0.000% - 0.404% 14,600 0 - 130,000

Surface Water

0.020 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.0000503% 0.000% - 0.000% 0 0 - 0

0.002 0.00356% 0.000% - 0.0275% 1,500 0 - 11,400

Combined Ground

& Surface Water

0.020 0.000% 0.000% - 0.000% 0 0 - 0

0.004 0.000470% 0.000% - 0.00295% 300 0 - 2,200

0.002 0.0218% 0.000% - 0.177% 16,300 0 - 130,000
Occurrence Summary and Use Support Document March 2002 187

3.6.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, no systems had estimated mean concentration values of diquat greater than the MCL (0.02

mg/L). An estimated 1 system serving approximately 1,000 people had a mean concentration value of

diquat greater that 0.004 mg/L. About 13 systems serving about 46,500 people nationally were estimated

to have mean diquat concentrations greater than 0.002 mg/L. (See Section 1.4 for a description of how

Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, approximately 1 PWSs serving about 900 people nationally had mean

concentrations greater than 0.004 mg/L. An estimated 12 systems serving about 38,800 people nationally

had estimated mean concentration values that exceeded 0.002 mg/L.

Only 1 surface water system serving less than 100 people nationally was estimated to have mean

concentrations of diquat above 0.004 mg/L. Approximately 1 surface water systems serving 4,500

people had estimated mean concentrations greater than 0.002 mg/L.

Table 3.6-5: Estimated National Diquat Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.02 0 0 - 0 0 0 - 0

0.004 1 0 - 7 900 0 - 5,300

0.002 12 0 - 36 38,800 0 - 346,000

Surface Water

0.02 0 0 - 0 0 0 - 0

0.004 1 0 - 0 < 100 0 - 0

0.002 1 0 - 7 4,500 0 - 35,100

Combined Ground

& Surface Water

0.02 0 0 - 0 0 0 - 0

0.004 1 0 - 7 1,000 0 - 6,300

0.002 13 0 - 35 46,500 0 - 376,200

3.6.5 Additional Drinking Water Occurrence Data

A summary document entitled “Occurrence and Exposure Assessment of Diquat in Public Drinking

Water Supplies” (Wade Miler, 1989), was previously prepared for past USEPA assessments of diquat. 

However, no national or regional studies were included on the occurrence of diquat in drinking water

from ground water or surface water sources.
Occurrence Summary and Use Support Document March 2002 188

3.6.6 Conclusion

Diquat is widely used in agriculture and in non-agricultural applications as a herbicide, algicide, and

plant growth regulator. In 1982, imports of diquat active ingredient were 835,000 pounds. Information

from USGS indicates that use of diquat is most widespread in Western States and the Northeast, with

some scattered use in the Midwest. Diquat is not a TRI chemical, so there is no information available on

the environmental release of diquat. There are also no ambient data available. The Stage 2 analysis,

based on the 16-State cross-section, estimated that zero percent of combined ground water and surface

water systems serving zero percent of the population exceeded the MCL of 0.02 mg/L. Based on this

estimate, zero PWSs nationally are estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, according to information from USGS, approximately 25 States consumed

diquat for agricultural uses, including 8 of the 16 cross-section States. As there is no TRI or other data,

agricultural use seems to be the only basis for comparison between the 16 States and the nation. The

cross-section should adequately represent the occurrence of diquat on a national scale based upon the

use, production, and release patterns of the 16-State cross-section in relation to the patterns observed for

all 50 States. 

3.6.7 References

EXTOXNET. 2001. Pesticide Information Profile: Diquat Bromide. Ithaca, N Y: Extension

Toxicology Network, Pesticide Management Education Program. Available on the Internet at

http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/diquat-ext.html, last updated

March 1, 2001.

USEPA. 1995. R.E.D. Facts: Diquat Bromide. EPA Report 738-F-95-015. Washington, DC: Office of

Prevention, Pesticides, and Toxic Substances, USEPA. 10 pp. Available on the Internet at:

http://www.epa.gov/oppsrrd1/REDs/factsheets/0288fact.pdf

USEPA. 2001a. Consumer Factsheet on Diquat. Office of Ground Water and Drinking Water, 

USEPA. Available on the Internet at: http://www.epa.gov/OGWDW/dwh/c-SOC/diquat.html,

last updated April 12, 2001.

USEPA. 2001b. Memorandum: Tier I Drinking Water and Aquatic Ecological Exposure Assessments

for Diquat Dibromide. From: James Breithaupt, Environmental Risk Branch II/EFED. 

Washington, D.C., October 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1998a. Annual Use Maps. Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/,

last updated March 20, 1998.

USGS. 1998b. Sources & Limitations of Data Used to Produce Maps of Annual Pesticide Use. 

Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/mapex.html, last updated

March 20, 1998.
Occurrence Summary and Use Support Document March 2002 189

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Diquat in Public Drinking

Water Supplies - DRAFT. Draft report submitted to EPA for review April 24, 1989.
Occurrence Summary and Use Support Document March 2002 190

3.7 Glyphosate

Table of Contents

3.7.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

3.7.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

3.7.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

3.7.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 193

3.7.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

3.7.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

3.7.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Tables and Figures

Figure 3.7-1: Estimated Annual Agricultural Use for Glyphosate (1992) . . . . . . . . . . . . . . . . . . . . . . 192

Table 3.7-1: Stage 1 Glyphosate Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . 193

Table 3.7-2: Stage 1 Glyphosate Occurrence Based on 16-State Cross-Section - Population . . . . . . . 194

Table 3.7-3: Stage 2 Estimated Glyphosate Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

Table 3.7-4: Stage 2 Estimated Glyphosate Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

Table 3.7-5: Estimated National Glyphosate Occurrence - Systems and Population Served . . . . . . . . 196
Occurrence Summary and Use Support Document March 2002 191

3.7.1 Introduction, Use and Production

Glyphosate [N-(phosphonomethyl) glycine] is an organic solid of odorless white crystals that is usually

formulated as an isopropylamine salt. While it can be described as an organophosphorus compound,

glyphosate is not an organophosphate ester but a phosphanoglycine, and it does not inhibit cholinesterase

activity (EXTOXNET, 2001). Some trade names for glyphosate include Roundup, Sting, Rodeo,

Tumbleweed, Sonic, Glycel, and Rondo (USEPA, 2001).

Glyphosate is a non-selective herbicide used on many food and non-food crops as well as non-crop areas

where total vegetation control is desired, such as roadsides (USEPA, 1993). It is useful on essentially all

annual and perennial plants, including grasses, sedges, broad-leaved weeds and woody plants

(EXTOXNET, 2001). When applied at lower rates, glyphosate serves as a plant growth regulator. The

most common uses include control of broadleaf weeks and grasses in: hay and pasture, soybeans, field

corn, ornamentals, lawns, turf, forest plantings, greenhouses, and rights-of-way (USEPA, 2001).

Although production data seems to be unavailable, glyphosate is one of the most commonly used

pesticides in the U.S. by volume. In 1990 usage was estimated at 11.6 million pounds, and it ranked

eleventh in volume among conventional pesticides in 1990 and 1991 (USEPA, 2001). Use from 1989 to

1991 ranged between 11.4 and 18.7 million pounds of glyphosate per year for anywhere from 13 to 20

million acres (USEPA, 1993). Hay/pasture (20%), soybeans (20%), field corn (9%), and other

agricultural areas (20%) comprise 71% of the total acreage treated with glyphosate. Non-agricultural

areas (33%), soybeans (15%), hay/pasture (11%), and corn (8%) comprise 67% of the total pounds of ai

applied (USEPA, 1993). 

Figure 3.7-1 shows the USGS (1998) derived geographic distribution of estimated average annual

glyphosate use in the United States for 1992. The United States Geological Survey (USGS, 1998)

estimates approximately 16 million pounds of glyphosate active ingredient were used in 1992. These

estimates were derived using State-level data sets on pesticide use rates available from National Center

for Food and Agricultural Policy (NCFAP) combined with county-level data on harvested crop acreage

from the Census of Agriculture (Thelin and Gianessi, 2000). A breakdown of use by crop is also

included. Soybeans account for the majority of usage (about 6.5 million pounds glyphosate), while

intermediate use can be found on several other crops as well (e.g., corn, all citrus, cotton, almonds,

grapes). Glyphosate use appears to be geographically distributed across the U.S. The largest

concentrations of glyphosate use are seen in the soybean production region of the Midwest and the citrus

growing areas in California and Florida. A comparison of this use map with the map of the 16 crosssection States (Figure 1.3-1) shows that States across the range of high of low glyphosate use are well

represented in the cross-section.
Occurrence Summary and Use Support Document March 2002 192

Figure 3.7-1: Estimated Annual Agricultural Use for Glyphosate (1992)

Source: USGS 1998

3.7.2 Environmental Release

Glyphosate is released directly to the environment when used as a herbicide and potentially during its

manufacture, handling and storage. Unfortunately, glyphosate is not listed as a Toxics Release Inventory

(TRI) contaminant, so no TRI release records are maintained. The use of glyphosate (described in the

previous section) may provide the primary indication of where releases are most likely. The areas of

highest glyphosate use are in the soybean and corn production regions of the Midwest and Mid-Atlantic,

and on the citrus production areas in the Pacific Northwest, California, and Florida. Many of the highest

use States are contained in the 16-State cross-section (i.e., California, Florida, Illinois, Indiana,

Kentucky, Michigan, Oregon, and South Dakota).

3.7.3 Ambient Occurrence

To understand the presence of a chemical in the environment, an examination of ambient occurrence is

often useful. In a drinking water context, ambient water is untreated source water residing in surface

waters and aquifers. There are few available data on the occurrence of glyphosate in ambient waters of

the United States. The most comprehensive and nationally consistent data describing ambient water

quality in the United States are being produced through the United States Geological Survey’s (USGS)

National Water Quality Assessment (NAWQA) program. However, national NAWQA data are currently

unavailable for glyphosate.

Additional studies of ambient data are also unavailable. A summary document entitled ““Occurrence and

Exposure Assessment of Glyphosate in Public Drinking Water Supplies” (Wade Miler, 1989), was

previously prepared for past USEPA assessments of glyphosate. However, no national or regional
Occurrence Summary and Use Support Document March 2002 193

studies were included on the occurrence of glyphosate in water other than drinking water from ground

water or surface water sources.

3.7.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of glyphosate occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.7 mg/L; 0.06 mg/L; and 0.006 mg/L. 

Thirteen of the sixteen cross-section State data sets contained occurrence data for glyphosate. (There

were no glyphosate data from Nebraska, New Jersey or Texas.) These data represent more than 33,000

analytical results from approximately 7,800 PWSs during the period from 1984 to 1998 (with most

analytical results from 1992 to 1997). The number of sample results and PWSs vary by State, although

the State data sets have been reviewed and checked to ensure adequacy of coverage and completeness. 

The overall modal detection limit for glyphosate in the 16 cross-section States is equal to 0.006 mg/L. 

(For details regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)

3.7.4.1 Stage 1 Analysis Occurrence Findings

Table 3.7-1 illustrates the very low occurrence of glyphosate in drinking water for the public water

systems in the 16-State cross-section. No ground water or surface water PWSs in the 16 States had any

analytical results exceeding 0.7 mg/L or 0.06 mg/L. Only 0.0763% of total ground and surface water

systems (6 systems) had analytical results greater than 0.006 mg/L. Five (approximately 0.0707% of)

ground water systems had analytical results greater than 0.006 mg/L. The percentage of surface water

systems with at least one analytical result greater than 0.006 mg/L was equal to 0.126% (1 system).

Table 3.7-1: Stage 1 Glyphosate Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.7 0.000% 0

0.06 0.000% 0

0.006 0.0707% 5

Surface Water

0.7 0.000% 0

0.06 0.000% 0

0.006 0.126% 1

Combined Ground &

Surface Water

0.7 0.000% 0

0.06 0.000% 0

0.006 0.0763% 6
Occurrence Summary and Use Support Document March 2002 194

Table 3.7-2 illustrates glyphosate occurrence in the 16 cross-section States based on the PWS population

served. Approximately 0.0270% of the 16-State population was served by PWSs with analytical

detections of glyphosate greater than 0.006 mg/L (about 19,000 people). The percentage of population

served by ground water systems with at least one analytical result greater than 0.006 mg/L was equal to

0.0347% (almost 11,000 people). A total of 8,300 (0.0210% of) people served by surface water systems

were exposed to glyphosate levels greater than 0.006 mg/L. When evaluated relative to 0.7 mg/L and

0.06 mg/L, the percent of population exposed was equal to 0% for all system types.

Table 3.7-2: Stage 1 Glyphosate Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served 

by Systems Exceeding

Threshold

Ground Water

0.7 0.000% 0

0.06 0.000% 0

0.006 0.0347% 10,700

Surface Water

0.7 0.000% 0

0.06 0.000% 0

0.006 0.0210% 8,300

Combined Ground &

Surface Water

0.7 0.000% 0

0.06 0.000% 0

0.006 0.0270% 19,000

3.7.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.7-3 and 3.7-

4. The statistically generated best estimate values, as well as the ranges around the best estimate value,

are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. 

For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology

and Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations

(USEPA, 2002)). 

No ground water or surface water PWSs in the 16 cross-section States had an estimated mean

concentration of glyphosate exceeding 0.7 mg/L or 0.06 mg/L. Approximately 0.0000736% of ground

and surface water PWSs (less than 1 system in the 16-State cross-section) was estimated to have a mean

concentration greater than 0.006 mg/L. The percentage of ground water PWSs with estimated mean

concentrations greater than 0.006 mg/L was equal to approximately 0.0000849%. No surface water

PWSs had estimated mean concentration exceeding any of the three specified concentration thresholds.
Occurrence Summary and Use Support Document March 2002 195

Table 3.7-3: Stage 2 Estimated Glyphosate Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.7 0.000% 0.000% - 0.000% 0 0 - 0

0.06 0.000% 0.000% - 0.000% 0 0 - 0

0.006 0.0000849% 0.000% - 0.000% 0 0 - 0

Surface Water

0.7 0.000% 0.000% - 0.000% 0 0 - 0

0.06 0.000% 0.000% - 0.000% 0 0 - 0

0.006 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.7 0.000% 0.000% - 0.000% 0 0 - 0

0.06 0.000% 0.000% - 0.000% 0 0 - 0

0.006 0.0000763% 0.000% - 0.000% 0 0 - 0

Approximately 0.0000138% of population served by all PWSs in the 16 States was potentially exposed to

glyphosate levels above 0.006 mg/L. The percentage of population served by ground water systems

relative to 0.006 mg/L was equal to 0.0000313%. (No surface water systems exceeded any of the

specified health thresholds.) When evaluated relative to a threshold of 0.7 mg/L and 0.06 mg/L, the

percent of population exposed was equal to 0% for all system types.

Table 3.7-4: Stage 2 Estimated Glyphosate Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.7 0.000% 0.000% - 0.000% 0 0 - 0

0.06 0.000% 0.000% - 0.000% 0 0 - 0

0.006 0.0000313% 0.000% - 0.000% 0 0 - 0

Surface Water

0.7 0.000% 0.000% - 0.000% 0 0 - 0

0.06 0.000% 0.000% - 0.000% 0 0 - 0

0.006 0.000% 0.000% - 0.000% 0 0 - 0
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 196

Combined Ground

& Surface Water

0.7 0.000% 0.000% - 0.000% 0 0 - 0

0.06 0.000% 0.000% - 0.000% 0 0 - 0

0.006 0.0000138% 0.000% - 0.000% 0 0 - 0

3.7.4.3 Estimated National Occurrence

As illustrated in Table 3.7-5, the Stage 2 analysis estimates no PWSs nationally (therefore, no population

served) were estimated to have a mean concentration value of glyphosate greater than 0.7 mg/L, 0.06

mg/L, or 0.006 mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are

extrapolated to national values.)

Table 3.7-5: Estimated National Glyphosate Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.7 0 0 - 0 0 0 - 0

0.06 0 0 - 0 0 0 - 0

0.006 0 0 - 0 0 0 - 0

Surface Water

0.7 0 0 - 0 0 0 - 0

0.06 0 0 - 0 0 0 - 0

0.006 0 0 - 0 0 0 - 0

Combined Ground

& Surface Water

0.7 0 0 - 0 0 0 - 0

0.06 0 0 - 0 0 0 - 0

0.006 0 0 - 0 0 0 - 0

3.7.5 Additional Drinking Water Occurrence Data

Additional studies of ambient data are also unavailable. A summary document entitled “Occurrence and

Exposure Assessment of Glyphosate in Public Drinking Water Supplies” (Wade Miler, 1989), was

previously prepared for past USEPA assessments of glyphosate. However, no national or regional

studies were included on the occurrence of glyphosate in drinking water from ground water or surface

water sources.
Occurrence Summary and Use Support Document March 2002 197

3.7.6 Conclusion

Glyphosate is a non-selective herbicide used on many food and non-food crops as well as non-crop areas

such as roadsides. It is useful on essentially all annual and perennial plants, including grasses, sedges,

broad-leaved weeds and woody plants. Recent statistics regarding use of glyphosate indicate production

and use are steady, with glyphosate use concentrated in the Midwest, California, and Florida. Glyphosate

is not a TRI chemical, so there is no information available on the environmental release of glyphosate. 

There are also no ambient data available. The Stage 2 analysis, based on the 16-State cross-section,

estimated that zero percent of combined ground water and surface water systems serving zero percent of

the population exceeded the MCL of 0.7 mg/L. Based on this estimate, zero PWSs nationally are

estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, according to information from USGS, all 50 States used glyphosate for

agricultural purposes. The areas of most use are the Midwest, Florida, and California, represented by

eight cross-section States. As there is no TRI or other data, agricultural use seems to be the only basis

for comparison between the 16 States and the nation. The cross-section should adequately represent the

occurrence of glyphosate on a national scale based upon the use, production, and release patterns of the

16-State cross-section in relation to the patterns observed for all 50 States.

3.7.7 References

EXTOXNET. 2001. Pesticide Information Profile: Glyphosate. Ithaca, NY: Extension Toxicology

Network, Pesticide Management Education Program. Available on the Internet at

http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html,

accessed July 18, 2001.

Thelin, G.P., and L.P. Gianessi. 2000. Method for Estimating Pesticide Use for County Areas of the

Conterminous United States. U.S. Geological Survey Open-File Report 00-250. 

62 pp. Available on the Internet at: http://water.wr.usgs.gov/pnsp/rep/ofr00250/ofr00250.pdf

USEPA. 1993. Reregistration Eligibility Decision (RED): Glyphosate. EPA Report 738-R-93-014. 

Washington, DC: Office of Prevention, Pesticides, and Toxic Substances, USEPA. 74 pp. +

Appendices. Available on the Internet at:

http://www.epa.gov/oppsrrd1/REDs/old_reds/glyphosate.pdf

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: Glyphosate.

Office of Ground Water and Drinking Water, USEPA. Available on the Internet at

http://www.epa.gov/safewater/dwh/c-SOC/glyphosa.html, last updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1998. Annual Use Maps. Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/, last

updated March 20, 1998.

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Glyphosate in Public

Drinking Water Supplies - DRAFT. Draft report submitted to EPA for review April 12, 1989.
Occurrence Summary and Use Support Document March 2002 198

3.8 Heptachlor & Heptachlor Epoxide

Table of Contents

3.8.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

3.8.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

3.8.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

3.8.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 203

3.8.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

3.8.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

3.8.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

Tables and Figures

Table 3.8-1: Environmental Releases (in pounds) for Heptachlor in the United States, 

1988-1996 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

Table 3.8-2: Stage 1 Heptachlor Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . 203

Table 3.8-3: Stage 1 Heptachlor Occurrence Based on 16-State Cross-Section - Population . . . . . . . 204

Table 3.8-4: Stage 1 Heptachlor Epoxide Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

Table 3.8-5: Stage 1 Heptachlor Epoxide Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

Table 3.8-6: Stage 2 Estimated Heptachlor Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

Table 3.8-7: Stage 2 Estimated Heptachlor Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

Table 3.8-8: Stage 2 Estimated Heptachlor Epoxide Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

Table 3.8-9: Stage 2 Estimated Heptachlor Epoxide Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Table 3.8-10: Estimated National Heptachlor Occurrence - Systems and Population Served . . . . . . . 210

Table 3.8-11: Estimated National Heptachlor Epoxide Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
Occurrence Summary and Use Support Document March 2002 199

3.8.1 Introduction, Use and Production

Heptachlor is a synthetic chemical that does not occur naturally. It is both a breakdown product and a

component of the pesticide chlordane. Pure heptachlor is a white powder that smells like camphor

(mothballs). Technical-grade heptachlor is a tan powder and has a lower level of purity than pure

heptachlor. Technical-grade heptachlor was the form of heptachlor used most often as a pesticide. 

Heptachlor does not burn easily, does not explode, nor does it dissolve easily in water (ATSDR, 1993).

Heptachlor epoxide is a biodegradation product of heptachlor. It is not manufactured and was not used

as an insecticide like heptachlor. Heptachlor epoxide is made by bacteria in the environment. Like pure

heptachlor, heptachlor epoxide is a white powder that does not explode easily. Heptachlor epoxide is

frequently detected in areas of heptachlor use and is more likely to be found in the environment than

heptachlor. Animals and people also make heptachlor epoxide when heptachlor enters their bodies. 

About 20% of heptachlor is changed within hours to heptachlor epoxide in the environment and in the

body (ATSDR, 1993). 

Heptachlor is a chlorinated hydrocarbon insecticide, presently used in the United States only to control

fire ants, in buried, pad-mounted electric power transformers, and in underground cable television and

telephone cable boxes. The end use product, a granular formulation packaged in small plastic bags, is

applied by pouring the contents of the plastic bag directly into a metal or concrete enclosure, which is

rarely opened again (USEPA, 1992).

Heptachlor is a persistent dermal insecticide with some fumigant action. It is nonphytotoxic at

insecticidal concentrations (Worthing and Walker, 1987, as cited in ATSDR, 1993). Heptachlor is

present as an impurity in chlordane; typically, hepatchlor constitutes 10 percent of technical grade

chlordane (USEPA, 1980, as cited in USEPA, 1989). Because chlordane is applied by subsurface ground

injection, the potential for water contamination in some areas may be high (USEPA, 1989). Heptachlor

was used extensively from 1953 to 1974 as a soil and seed treatment to protect corn, small grains, and

sorghum from pests. It was used to control ants, cutworms, maggots, termites, thrips, weevils, and

wireworms in both cultivated and uncultivated soils. Heptachlor was also used nonagriculturally during

this time period to control termites and household insects (USEPA, 1986; Worthington and Walker,

1987, as cited in ATSDR, 1993). 

Heptachlor is converted to heptachlor epoxide, and other degradation products, in the environment. 

Heptachlor epoxide degrades more slowly and, as a result, is more persistent than heptachlor. Heptachlor

epoxide has been found in food crops grown in soils treated with heptachlor many years before (ATSDR,

1993). 

 In 1974, the EPA Administrator issued a notice of intent to suspend the registrations of certain pesticide

products containing heptachlor for subsurface control of termites and dipping of roots and tops of

nonfood plants (USEPA, 1983, as cited in USEPA, 1989). EPA proposed cancellation of nearly all

registered uses of heptachlor because of its potential cancer risk and its persistence and bioaccumulation

throughout the food chain. On March 6, 1978, EPA issued a final cancellation order putting into effect

the terms of settlement for the cancellation proceedings (USEPA, 1983, as cited in USEPA, 1989). 

Under this cancellation order, an agreement was outlined to phase out the nontermiticide uses of

heptachlor over a 5-year period. All uses permitted during the phase-out period were restricted to

treatment by certified applicators or professional commercial seed treatment companies. The few uses

that were not canceled in 1974, treatment of field corn, seed (for corn, wheat, oats, barley, rye, and

sorghum), citrus, pineapple, and narcissus bulbs, were phased out gradually over a 5-year period ending

on July 1, 1983 (USEPA, 1986, as cited in ATSDR, 1993). Certain uses of heptachlor were specifically
Occurrence Summary and Use Support Document March 2002 200

exempted from EPA’s suspension and cancellation actions because they were believed to result in

insignificant exposure and, consequently, insignificant risk. Registrations were retained for subsurface

termite control, fire ant control in buried cable closures, and dipping of roots or tops of nonfood plants (a

use subsequently canceled voluntarily by the registrant, Velsicol Chemical Corporation) (USEPA, 1986,

as cited in ATSDR, 1993).

Approximately 30 percent (or 550,000 pounds) of the heptachlor used in 1971 was applied to commercial

and residential structures for protection against termites and to nurseries, lawns, and gardens. By 1974,

domestic use of heptachlor for termite control had increased to 1.4 million pounds (USEPA, 1976, as

cited in USEPA, 1989). 

In the early 1980s, heptachlor was used to control subterranean termites. Nearly 10 million pounds of

chlordane was applied in the United States in 1980; approximately 1 million pounds of heptachlor would

have been present as an impurity in chlordane in that year. EPA (USEPA, 1983, as cited in USEPA,

1989) reported that the largest quantity of chlordane was initially distributed to EPA Region IV, which

includes Alabama, Georgia, Florida, Mississippi, North Carolina, South Carolina, Tennessee, and

Kentucky. 

In 1983, between 1 and 2 million pounds of heptachlor was used in the United States for termite control

(USEPA, 1983, as cited in USEPA, 1989). Between 0.75 and 1 million pounds of heptachlor were used

in 1986 (Kuch, 1986, as cited in USEPA, 1989). Heptachlor has limited use as a single active ingredient

and usually is applied in combination with chlordane (USEPA, 1983, as cited in USEPA, 1989). A

second approved use of heptachlor is to control fire ants in sugarcane and pineapple fields in Hawaii.

In 1988, EPA prohibited the sale, distribution, and shipment of existing stocks of all canceled chlordane

and heptachlor products. Subsequently, virtually all uses of heptachlor products were voluntarily

canceled by the registrant, Velsicol Chemical Corporation (USEPA, 1990, as cited in ATSDR, 1993). 

The only commercial use of heptachlor products still permitted is fire ant control in power transformers. 

Use of existing stocks of heptachlor-containing termicide products in the possession of homeowners is

also permitted (USEPA, 1990, as cited in ATSDR, 1993).

3.8.2 Environmental Release

Heptachlor is listed as a Toxics Release Inventory (TRI) chemical. Table 3.8-1 illustrates the

environmental releases for heptachlor from 1988 to 1996. (Heptachlor data are only available for these

years.) Air emissions constitute most of the on-site releases, with a general trend to decrease over the

years. Air emissions decreased drastically after 1988, which was the year EPA prohibited the sale,

distribution, and shipment of existing stocks of all canceled heptachlor products. The decrease in air

emissions are solely responsible for decreases in heptachlor total on- and off-site releases in recent years. 

Minimal surface water discharges were reported. No underground injection, releases to land (such as

spills or leaks within the boundaries of the reporting facility), or off-site releases (including metals or

metal compounds transferred off-site) were reported for heptachlor. These TRI data for heptachlor were

reported from 5 States (Georgia, Illinois, Tennessee, Florida, and Mississippi), although no more than 2

States reported releases in a given year. Only Tennessee reported releases after 1992 (USEPA, 2000). 

Of the five States, Illinois and Florida are included in the 16-State cross-section (used for analyses of

heptachlor occurrence in drinking water; see Section 3.8.4). (For a map of the 16-State cross-section, see

Figure 1.3-1.)
Occurrence Summary and Use Support Document March 2002 201

Table 3.8-1: Environmental Releases (in pounds) for Heptachlor in the United States, 

1988-1996

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1996 198 5 -- -- -- 203

1995 203 6 -- -- -- 209

1994 830 3 -- -- -- 833

1993 31 2 -- -- -- 33

1992 710 1 -- -- -- 711

1991 5 0 -- -- -- 5

1990 3,797 1 -- -- -- 3,798

1989 3,411 2 -- -- -- 3,413

1988 54,295 2 -- -- -- 54,297

 Source: USEPA, 2000

3.8.3 Ambient Occurrence

To understand the presence of a chemical in the environment, an examination of ambient occurrence is

useful. In a drinking water context, ambient water is untreated source water residing in surface waters

and aquifers. There are few available data on the occurrence of heptachlor in ambient waters of the

United States. The most comprehensive and nationally consistent data describing ambient water quality

in the United States are being produced through the United States Geological Survey’s (USGS) National

Water Quality Assessment (NAWQA) program. However, national NAWQA data are currently

unavailable for heptachlor.

3.8.3.1 Additional Ambient Occurrence Data

Additional studies of ambient data are summarized below. A summary document entitled “Occurrence

and Human Exposure to Pesticides in Drinking Water, Food and Air in the United States of America”

(USEPA, 1989), was previously prepared for past USEPA assessments of various pesticides. Three

national studies are summarized for the occurrence of heptachlor and heptachlor epoxide in surface

waters. Eight regional studies addressed levels of heptachlor and heptachlor epoxide in water other than

drinking water. Two of the regional studies addressed levels of heptachlor and heptachlor epoxide in

ground water, and six studies provided data on levels of heptachlor and heptachlor epoxide in surface

water. The following information is taken directly from “Occurrence and Human Exposure to Pesticides

in Drinking Water, Food and Air in the United States of America” (USEPA, 1989).

3.8.3.1.1 Ground Water Sources

Ground water wells in 25 California counties were analyzed as part of the California State Board’s

Toxics Special Project during 1984 (Cohen and Bowes, 1984, as cited in USEPA, 1989). Heptachlor was

found in three samples with a maximum concentration of 0.3 :g/L. The other positive values, total

number of samples, and detection limit were not reported.

Tucker and Burke (1978, as cited in USEPA, 1989) presented data on levels of heptachlor and heptachlor

epoxide in samples of water collected from 163 wells, including private and public drinking water

supplies, industrial sites, and wells in the vicinity of landfills in nine New Jersey counties. The analysis
Occurrence Summary and Use Support Document March 2002 202

showed that samples of water from three supply wells contained heptachlor and samples from seven

wells contained heptachlor epoxide in excess of the minimum reportable concentration of 0.01 :g/L. The

maximum values for heptachlor and heptachlor epoxide were 1.0 and 0.6 :g/L, respectively. The

maximum concentration for heptachlor epoxide occurred in a public drinking water supply well.

3.8.3.1.2 Surface Water Sources

National studies of surface water analyses for heptachlor and heptachlor epoxide were conducted by

USEPA (1976, as cited in USEPA, 1989) and Breidenbach et al. (1967, as cited in USEPA, 1989). The

overall mean as reported for both pesticides was 0.0063 :g/L. The minimum values determined for each

were 0.001 :g/L and the maximum values were 0.035 :g/L and 0.02 :g/L for heptachlor and heptachlor

epoxide, respectively. The number of positive values, total number of samples, and detection limit were

not reported.

The National Pesticide Monitoring Network examined rivers nationwide from 1975 to 1980 (Gilliom et

al., 1985, as cited in USEPA, 1989). Heptachlor epoxide was reported as being detected in 9 out of 2,946

samples analyzed from 177 locations (detection limit = 0.01 :g/L). The mean and range of values were

not reported.

Heptachlor and heptachlor epoxide were analyzed in rivers and streams in upstate New York

(Estabrooks, no date, as cited in USEPA, 1989) from 1982 to 1983. No samples for either pesticide were

found to be positive, out of 252 samples analyzed. The detection limit was 10.0 :g/L.

Barks (1978, as cited in USEPA, 1989) presented the results of a USGS water quality study conducted

from April 1973 to July 1974 in the Ozark National Scenic Riverways, Missouri. During the study, 20

surface water samples were collected from 3 sites on the Current River and 1 site on Jacks Fork and

analyzed for pesticide content. The analysis of unfiltered samples found no heptachlor or heptachlor

epoxide in excess of the detection limit (the detection limit was not reported).

Englande et al. (1978, as cited in USEPA, 1989) presented the results of extensive chemical analysis of

six Advanced Wastewater Treatment (AWT) plant effluents. Four plants were located in California, and

one each in the District of Columbia and Texas. None of the 63 AWT effluent samples contained

concentrations of heptachlor in excess of the detection limit (the detection limit was not reported).

Truhlar and Reed (1976, as cited in USEPA, 1989) reported on water samples collected from four

streams in Pennsylvania and analyzed for chlorinated hydrocarbon pesticides during the period from

April 1970 to February 1971. The streams drained four different types of land use areas. Concentrations

of heptachlor and heptachlor epoxide were not detected in any of the 25 stream samples.

Schacht (1974, as cited in USEPA, 1989) presented the results of a study to determine the levels of

pesticides in the surface water of Lake Michigan and its tributaries. During the period 1970 to 1972, a

total of 45 water samples was collected. Concentrations of heptachlor epoxide ranging from “nondetected” to 0.017 :g/L were found in the samples. The detection limit for heptachlor epoxide was

reported as less than 0.0002 :g/L

Dappen (1974, as cited in USEPA, 1989) reported the results of a study to determine the pesticide

content of urban storm runoff in Nebraska. Runoff samples were collected at three stations in a Nebraska

city during and after storms. A total of 80 samples was collected at the first station during 16 different

storms. Concentrations of heptachlor and heptachlor epoxide in samples from the first station ranged

from 0 to 0.059 :g/L and 0 to 0.2 :g/L, respectively. At the second sampling station, 55 samples were
Occurrence Summary and Use Support Document March 2002 203

collected during 9 different storms. Concentrations of heptachlor and heptachlor epoxide in samples

from the second station ranged from 0 to 0.176 :g/L and 0 to 0.194 :g/L respectively. A total of 14

samples was collected at the third station during 3 storms. Concentrations of heptachlor in samples from

the third station ranged from 0 to 0.055 :g/L. No heptachlor epoxide was detected. No detection limits

were reported for the study.

3.8.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of heptachlor and heptachlor epoxide occurrence presented in the following section is based

on State compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the

largest and most comprehensive compliance monitoring data set compiled by EPA to date. These data

were evaluated relative to several concentration thresholds of interest. Heptachlor was reviewed relative

to 0.0004 mg/L; 0.0001 mg/L; and 0.00004 mg/L. Heptachlor epoxide was reviewed relative to 0.0002

mg/L; 0.0001; and 0.00002 mg/L. 

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

heptachlor and heptachlor epoxide. Heptachlor and heptachlor epoxide data each represent more than

57,000 analytical results from approximately 14,000 PWSs during the period from 1984 to 1998 (with

most analytical results from 1992 to 1997). The number of sample results and PWSs vary by State,

although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limits for heptachlor and heptachlor epoxide in the 16 crosssection States are equal to 0.00004 mg/L and 0.00002 mg/L, respectively. (For details regarding the 16-

State cross-section, please refer to Section 1.3.5 of this report.)

3.8.4.1 Stage 1 Analysis Occurrence Findings

Table 3.8-2 illustrates the low occurrence of heptachlor in drinking water for the public water systems in

the 16-State cross-section relative to three thresholds: 0.0004 mg/L (the current MCL), 0.0001 mg/L, and

0.00004 mg/L (the modal MRL). Only 1 ground water PWS (approximately 0.00702% of PWSs in the

16 States) had analytical results exceeding the MCL; 0.0562% of systems (8 systems) had results

exceeding 0.0001 mg/L; and 0.0702% of systems (10 systems) had results exceeding 0.00004 mg/L. 

Approximately 0.00779% of ground water systems (1 system) had any analytical results greater than the

MCL. About 0.0545% of ground water systems (7 systems) had results above 0.0001 mg/L. The

percentage of ground water systems with at least one result greater than 0.00004 mg/L was equal to

0.0624% (8 systems). 

No surface water systems had results greater than the MCL. Only 1 (0.0709% of) surface water systems

had at least one analytical result greater than 0.0001 mg/L. Two (0.142% of) surface water systems had

results exceeding 0.00004 mg/L.

Table 3.8-2: Stage 1 Heptachlor Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.0004 0.00779% 1

0.0001 0.0545% 7
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 204

0.00004 0.0624% 8

Surface Water

0.0004 0.000% 0

0.0001 0.0709% 1

0.00004 0.142% 2

Combined Ground &

Surface Water

0.0004 0.00702% 1

0.0001 0.0562% 8

0.00004 0.0702% 10

Reviewing heptachlor occurrence in the 16 cross-section States by PWS population served (Table 3.8-3)

shows that approximately 0.000398% of the population (about 400 people) was served by PWSs with at

least one analytical result of heptachlor greater than the MCL (0.0004 mg/L). Approximately 160,400

(0.166% of) people were served by systems with an exceedance of 0.0001 mg/L. Over 170,000 (0.176%

of) people were served by systems with at least one analytical result greater than 0.00004 mg/L.

The percentage of population served by ground water systems with analytical results greater than the

MCL was equal to 0.000945% (approximately 400 people). When evaluated relative to 0.0001 mg/L and

0.00004 mg/L, the percent of population exposed was equal to 0.247% (over 100,000 people) and

0.252% (almost 103,000 people), respectively. 

The percent of population served by surface water systems exposed to heptachlor at levels greater than

0.0004 mg/L was equal to 0%. The percentage of population served by surface water systems with

exceedances of 0.0001 mg/L and 0.00004 mg/L was equal to 0.107% (60,000 people), and 0.121%

(67,800 people), respectively. 

Table 3.8-3: Stage 1 Heptachlor Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.0004 0.000945% 400

0.0001 0.247% 100,400

0.00004 0.252% 102,600

Surface Water

0.0004 0.000% 0

0.0001 0.107% 60,000

0.00004 0.121% 67,800
Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 205

Combined Ground &

Surface Water

0.0004 0.000398% 400

0.0001 0.166% 160,400

0.00004 0.176% 170,400

Table 3.8-4 illustrates the low occurrence of heptachlor epoxide in drinking water for the public water

systems in the 16-State cross-section relative to three thresholds: 0.0002 mg/L (the current MCL),

0.0001 mg/L, and 0.00002 mg/L (the modal MRL). Four (approximately 0.0283% of) ground and

surface water PWS had analytical results exceeding 0.0002 mg/L and 0.0001 mg/L. About 0.0566% of

systems (8 systems) had results exceeding 0.00002 mg/L. 

Approximately 0.0314% of ground water systems (4 systems) had any analytical results greater than

0.0002 mg/L and 0.0001 mg/L. The percentage of ground water systems with at least one result greater

than 0.00002 mg/L was equal to 0.0550% (7 systems). 

No surface water systems had results greater than 0.0002 mg/L and 0.0001 mg/L. Only 1 (0.0712% of)

surface water systems had at least one analytical result greater than 0.00002 mg/L.

Table 3.8-4: Stage 1 Heptachlor Epoxide Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.0002 0.0314% 4

0.0001 0.0314% 4

0.00002 0.0550% 7

Surface Water

0.0002 0.000% 0

0.0001 0.000% 0

0.00002 0.0712% 1

Combined Ground &

Surface Water

0.0002 0.0283% 4

0.0001 0.0283% 4

0.00002 0.0566% 8

Reviewing heptachlor epoxide occurrence in the 16 cross-section States by PWS population served

(Table 3.8-5) shows that approximately 0.0291% of the population (about 28,000 people) was served by

PWSs with at least one analytical result of heptachlor epoxide greater than the MCL (0.0002 mg/L), and

0.0001 mg/L. Approximately 91,600 (0.0952% of) people were served by systems with at least one

analytical result greater than 0.00002 mg/L.
Occurrence Summary and Use Support Document March 2002 206

The percentage of population served by ground water systems with analytical results greater than 0.0002

mg/L or 0.0001 mg/L was equal to 0.0695% (approximately 28,000 people). When evaluated relative to

0.00002 mg/L, the percent of population exposed was equal to 0.153% (almost 62,000 people). 

The percent of population served by surface water systems exposed to heptachlor epoxide at levels

greater than 0.0002 mg/L and 0.0001 mg/L was equal to 0%. The percentage of population served by

surface water systems with exceedances of 0.00002 mg/L was equal to 0.0537% (30,000 people). 

Table 3.8-5: Stage 1 Heptachlor Epoxide Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold 

Total Population Served 

by Systems Exceeding

Threshold

Ground Water

0.0002 0.0695% 28,000

0.0001 0.0695% 28,000

0.00002 0.153% 61,600

Surface Water

0.0002 0.000% 0

0.0001 0.000% 0

0.00002 0.0537% 30,000

Combined Ground &

Surface Water

0.0002 0.0291% 28,000

0.0001 0.0291% 28,000

0.00002 0.0952% 91,600

3.8.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings for heptachlor, based on the cross-section data, are presented in Tables

3.8-6 and 3.8-7. The statistically generated best estimate values, as well as the ranges around the best

estimate value, are presented. (For a review of the Stage 2 analytical approach, please refer to Section

1.4 of this report. For complete details regarding the Stage 2 analyses, please refer to Occurrence

Estimation Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking

Water Regulations (USEPA, 2002)). 

No ground water or surface water PWSs had an estimated mean concentration of heptachlor exceeding

0.0004 mg/L. Approximately 0.0000140% of PWSs (less than 1 system in the 16-State cross-section)

were estimated to have a mean concentration greater than 0.0001 mg/L. Only 1 (0.00119% of) system

had estimated mean concentration values of heptachlor greater than 0.00004 mg/L. 

The percentage of ground water systems with estimated mean concentration values of heptachlor greater

than 0.0001 mg/L was equal to 0.0000156% (less than 1 system in the 16 States). Approximately

0.00131% of ground water PWSs (about 1 system in the 16 States) had estimated mean concentration

values greater than 0.00004 mg/L. The percentage of surface water PWSs with estimated mean

concentration exceeding 0.00004 mg/L was equal to 0.000142% (less than 1 system).
Occurrence Summary and Use Support Document March 2002 207

Table 3.8-6: Stage 2 Estimated Heptachlor Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0004 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.0000156% 0.000% - 0.000% 0 0 - 0

0.00004 0.00131% 0.000% - 0.00779% 1 0 - 1

Surface Water

0.0004 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00004 0.000142% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.0004 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.0000140% 0.000% - 0.000% 0 0 - 0

0.00004 0.00119% 0.000% - 0.00702% 1 0 - 1

Reviewing heptachlor occurrence by PWS population served (Table 3.8-7) shows that approximately

0.000000242% of population served by all PWSs in the 16 States were potentially exposed to heptachlor

levels above 0.0001 mg/L. Approximately 0.000350% of the population served by PWSs in the 16 States

(about 300 people) was exposed to heptachlor at levels above 0.00004 mg/L. When evaluated relative to

a threshold of 0.0004 mg/L, the percent of population exposed was equal to 0%.

The percentage of population served by ground water systems relative to 0.0001 mg/L was equal to

0.000000576%. Approximately 0.000784% of the population was served by ground water systems

(about 300 people) with estimated mean concentration values of heptachlor greater than 0.00004 mg/L. 

The percentage of population served by surface water systems with estimated mean concentration values

greater than 0.00004 mg/L was equal to 0.0000341%.

Table 3.8-7: Stage 2 Estimated Heptachlor Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0004 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000000576% 0.000% - 0.000% 0 0 - 0

0.00004 0.000784% 0.000% - 0.0113% 300 0 - 4,600
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 208

Surface Water

0.0004 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00004 0.0000341% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.0004 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000000242% 0.000% - 0.000% 0 0 - 0

0.00004 0.000350% 0.000% - 0.00476% 300 0 - 4,600

The Stage 2 occurrence findings for heptachlor epoxide, based on the cross-section data, are presented in

Tables 3.8-8 and 3.8-9. No ground water or surface water PWSs had an estimated mean concentration of

heptachlor epoxide exceeding 0.0002 mg/L or 0.0001 mg/L. Approximately 0.00528% of PWSs (about 1

system in the 16-State cross-section) were estimated to have a mean concentration greater than 0.00002

mg/L.

The percentage of ground water systems with estimated mean concentration values of heptachlor epoxide

greater than 0.00002 mg/L was equal to 0.00583% (approximately 1 system in the 16 States). 

Approximately 0.000285% of surface water PWSs (about 1 system in the 16 States) had estimated mean

concentration values greater than 0.00002 mg/L.

Table 3.8-8: Stage 2 Estimated Heptachlor Epoxide Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0002 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00002 0.00583% 0.000% - 0.0236% 1 0 - 3

Surface Water

0.0002 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00002 0.000285% 0.000% - 0.000% 1 0 - 0

Combined Ground

& Surface Water

0.0002 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00002 0.00528% 0.000% - 0.0212% 1 0 - 3
Occurrence Summary and Use Support Document March 2002 209

Table 3.8-9 illustrates heptachlor epoxide occurrence by PWS population served in the 16-State crosssection. When evaluated relative to a threshold of 0.0002 mg/L and 0.0001 mg/L, the percent of

population exposed to heptachlor epoxide was equal to 0%. Approximately 0.00489% of the population

served by PWSs in the 16 States (about 4,700 people) was exposed to heptachlor epoxide at levels above

0.00002 mg/L. 

The percentage of population served by ground water systems relative to 0.00002 mg/L was equal to

0.0114% (approximately 4,600 people). The percentage of population served by surface water systems

with estimated mean concentration values of heptachlor epoxide greater than 0.00002 mg/L was equal to

0.000215% (about 100 people).

Table 3.8-9: Stage 2 Estimated Heptachlor Epoxide Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0002 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00002 0.0114% 0.000% - 0.0570% 4,600 0 - 23,000

Surface Water

0.0002 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00002 0.000215% 0.000% - 0.000% 100 0 - 0

Combined Ground

& Surface Water

0.0002 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.000% 0.000% - 0.000% 0 0 - 0

0.00002 0.00489% 0.000% - 0.0239% 4,700 0 - 23,000

3.8.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, zero systems nationally had estimated mean concentration values of heptachlor greater than the

MCL (0.0004 mg/L) and 0.0001 mg/L. An estimated 1 ground water system serving approximately 700

people was exposed to heptachlor concentrations greater than 0.00004 mg/L. (See Section 1.4 for a

description of how Stage 2 16-State estimates are extrapolated to national values.)
Occurrence Summary and Use Support Document March 2002 210

Table 3.8-10: Estimated National Heptachlor Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0004 0 0 - 0 0 0 - 0

0.0001 0 0 - 0 0 0 - 0

0.00004 1 0 - 5 700 0 - 9,700

Surface Water

0.0004 0 0 - 0 0 0 - 0

0.0001 0 0 - 0 0 0 - 0

0.00004 0 0 - 0 0 0 - 0

Combined Ground

& Surface Water

0.0004 0 0 - 0 0 0 - 0

0.0001 0 0 - 0 0 0 - 0

0.00004 1 0 - 5 700 0 - 10,100

The Stage 2 analysis estimated zero systems nationally with mean concentration values of heptachlor

epoxide greater than 0.0002 mg/L and 0.0001 mg/L. An estimated 3 ground water systems serving

approximately 9,800 people were exposed to heptachlor epoxide concentrations greater than 0.00002

mg/L. Approximately 1 surface water system serving 300 people nationally had estimated mean

concentration values of heptachlor epoxide greater than 0.00002 mg/L.

Table 3.8-11: Estimated National Heptachlor Epoxide Occurrence - Systems and Population

Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.0002 0 0 - 0 0 0 - 0

0.0001 0 0 - 0 0 0 - 0

0.00002 3 0 - 14 9,800 0 - 48,800

Surface Water

0.0002 0 0 - 0 0 0 - 0

0.0001 0 0 - 0 0 0 - 0

0.00002 1 0 - 0 300 0 - 0

Combined Ground

& Surface Water

0.0002 0 0 - 0 0 0 - 0

0.0001 0 0 - 0 0 0 - 0

0.00002 3 0 - 14 10,400 0 - 50,800
Occurrence Summary and Use Support Document March 2002 211

3.8.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of heptachlor and heptachlor epoxide in

drinking water are also reviewed. Previously compiled occurrence heptachlor and heptachlor epoxide

information, from an OGWDW summary document entitled “Occurrence and Human Exposure to

Pesticides in Drinking Water, Food and Air in the United States of America” (USEPA, 1989), is

presented in following section. This variety of studies and information are presented regarding levels of

heptachlor and heptachlor epoxide in drinking water, with the scope of the reviewed studies ranging from

national to regional. Note that none of the studies presented in the following section provide the

quantitative analytical results or comprehensive coverage that would enable direct comparison to the

occurrence findings estimated with the cross-section occurrence data presented in Section 3.8.4. These

additional studies, however, do enable a broader assessment of the Stage 2 occurrence estimates

presented for this Six-Year Review. All the following information in Section 3.8.5 is taken directly from

“Occurrence and Human Exposure to Pesticides in Drinking Water, Food and Air in the United States of

America” (USEPA, 1989). 

3.8.5.1 Ground Water Sources

Twelve towns in Connecticut were sampled during 1984 to 1985 for heptachlor and heptachlor epoxide

by the Connecticut Agricultural Experiment Station, New Haven, Connecticut (Waggoner, 1985, as cited

in USEPA, 1989). These towns, combined, serve a population of over 570,000 people. Drinking water

wells were sampled at 42 locations, and no samples were positive for either heptachlor or heptachlor

epoxide (detection limits were 0.2 :g/L and 0.47 :g/L, respectively).

Shallow drinking water wells in 10 counties in northwest Mississippi were analyzed from 1983 to 1984

during a Mississippi State University study on pesticide hazard assessment (MSU, 1984, as cited in

USEPA, 1989). No positive samples were found for either heptachlor or heptachlor epoxide out of 143

samples analyzed (detection limit = 0.001 :g/L).

Similarly, no positive results were obtained from 67 samples analyzed in Long Island, New York, for

either heptachlor or heptachlor epoxide. These results were from a 1984 study reported by the Suffolk

County Department of Health Services (Holden, 1986, as cited in USEPA, 1989). No detection limit(s)

was reported.

Drinking water supplies of the Floridian aquifer were analyzed at 96 locations in 1984 by the Florida

Department of Environmental Regulation and the U.S. Geological Survey (Holden, 1986, as cited in

USEPA, 1989). These supplies serve a combined population of over 3 million people. Less than 8

percent of the samples were positive for any of the pesticides sampled for, including heptachlor and

heptachlor epoxide. No other information was reported.

Irwin and Healy (1978, as cited in USEPA, 1989) summarized data collected in 1976 during a water

quality reconnaissance of public water supplies in Florida. None of the 100 water supplies sampled

using the five aquifers in Florida contained heptachlor and heptachlor epoxide in excess of the detection

limits. The detection limits were not reported.

Drinking water wells were sampled in Idaho for heptachlor epoxide by the Idaho Department of Health

and Welfare (1984, as cited in USEPA, 1989). One sample, out of 107, was positive, with a

concentration of 0.015 :g/L (no detection limit was reported).
Occurrence Summary and Use Support Document March 2002 212

Sandhu et al. (1978, as cited in USEPA, 1989) summarized the results from a study conducted in two

rural counties in South Carolina. Water supplies sampled were outside incorporated municipalities. 

Samples were taken randomly from wells where there was no pretreatment prior to use. It was not noted

whether these supplies were public or private. Also, data were collected on drinking water from different

land use areas in each county (i.e., agricultural, forest, and residential). The number of samples taken

and the number of positive samples were not reported: however, the percent of samples exceeding the

detection limit of 0.01 :g/L was reported by the county.

Results indicated that 62.5 percent of the samples taken in Chesterfield County had detectable levels of

heptachlor, and 42 percent had detectable levels of heptachlor epoxide. The sample means were 0.015

and 0.008 :g/L for heptachlor and heptachlor epoxide, respectively. In Hampton County, 45.5 percent of

the samples contained heptachlor and 64 percent of the samples contained heptachlor epoxide in excess

of the detection limit. The sample means for the Hampton County samples were 0.009 and 0.018 :g/L

for heptachlor and heptachlor epoxide, respectively. (These percentages included samples taken from

forest land use areas.) Concentrations of heptachlor in drinking water samples from agricultural areas in

Chesterfield and Hampton counties ranged from not detected to 0.16 :g/L with a mean of <0.01 :g/L

(not detected). For heptachlor epoxide, concentrations ranged from not detected to 0.09 :g/L with a

mean of <0.01 :g/L (not detected). In residential areas in both counties, concentrations of heptachlor

and heptachlor epoxide in drinking water samples ranged from not detected to 0.045 :g/L and not

detected to 0.01 :g/L respectively. Sample means were <0.01 :g/L (not detected) in all cases.

Tucker and Burke (1978, as cited in USEPA, 1989) reported that heptachlor epoxide was detected at a

level of 0.6 :g/L in water from a public drinking water supply well in Camden County, New Jersey.

3.8.5.2 Surface Water Sources

Irwin and Healy (1978, as cited in USEPA, 1989) reported that none of 16 surface water supplies

sampled in Florida contained heptachlor or heptachlor epoxide in excess of the detection limits. The

detection limits were not reported.

To assemble a database which would reflect the status of Great Lakes drinking water quality, the

Canadian Public Health Association gathered data from October 1984 through August 1985 (Canadian

Public Health Association, 1986, as cited in USEPA, 1989). The data collected covered the period from

the mid 1970s to early 1985. The study was funded by the Health Protection Branch of Health and

Welfare Canada, and the Ontario Ministry of the Environment. A research team, appointed by the

Association, reviewed data on the quality of water at 31 representative Canadian and United States

communities and 24 offshore sites to evaluate the human health implications.

For each of the 31 communities, data consisted of: 1) background information on the community; 2)

treatment plant schematics and associated treatment process information; and 3) water quality data. 

Water sample types included raw water (treatment plant intake), distribution water (treated water), and

tap water. Water quality data collected included general parameters (e.g., alkalinity, turbidity),

microbiological and radiological parameters, inorganic parameters, and organic parameters (including

volatiles, base/neutrals, pesticides and PCBs, and phenols and acids). For each parameter, the water

type, time period, concentration (mean and range), number of samples, and detection limit were recorded.

For most of the synthetic organics, including heptachlor and heptachlor epoxide, the available data

indicated that there were very low levels of these contaminants in the raw, treated, or tap water. Most of

the values found were “not detected” or near the detection limit (Canadian Public Health Association,

1986, as cited in USEPA, 1989).
Occurrence Summary and Use Support Document March 2002 213

3.8.5.3 Unspecified Sources

Pellizzari et al. (1979, as cited in USEPA, 1989) presented monitoring data on halogenated hydrocarbons

in drinking water from the northern New Jersey area and the Buffalo/Niagara, New York area. The

limits of detection ranged from 0.005 to 0.025 :g/L for both studies. Of 22 drinking water samples taken

from the northern New Jersey area, two samples (9%) contained heptachlor at levels of 0.007 and 0.02

:g/L, and none contained heptachlor epoxide. None of the 16 drinking water samples from the

Buffalo/Niagara area were found to contain heptachlor or heptachlor epoxide in excess of the detection

limits.

In a report on source identification of pollutants entering a sewage treatment plant, Levins et al. (1979, as

cited in USEPA, 1989) sampled two drinking water sources in a drainage basin in Georgia. Although

detection limits were not reported, heptachlor and heptachlor epoxide were not detected in either of the

drinking water samples.

3.8.6 Conclusion

Heptachlor is synthetically produced and exists at low levels in soil, water, air, and food. It was used as

an insecticide until 1988. Recent statistics regarding environmental release of heptachlor indicate use

has rapidly declined since the late 1980s, when it was banned for sale, distribution, and shipment. 

Reported industrial releases of heptachlor have been reported to TRI since 1988 in 5 States, with most

releases coming from Tennessee. Heptachlor ambient occurrence was not analyzed in any available

studies. Because heptachlor epoxide is a biodegradation product of heptachlor, it is frequently detected

in areas of heptachlor use and is more likely to be found in the environment than heptachlor. However,

little production and use information is available on heptachlor epoxide. 

The Stage 2 analysis of heptachlor, based on the 16-State cross-section, estimated that approximately

zero percent of combined ground water and surface water systems serving zero percent of the population

exceeded the MCL of 0.0004 mg/L. Based on this estimate, zero PWSs nationally are estimated to have

heptachlor levels greater than the MCL. The Stage 2 analysis of heptachlor epoxide, based on the 16-

State cross-section, estimated that approximately zero percent of combined ground water and surface

water systems serving zero percent of the population exceeded the MCL of 0.0002 mg/L. Based on this

estimate, zero PWSs nationally are estimated to have heptachlor epoxide levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOc, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, TRI releases have been reported for heptachlor from 5 States, including 2

of 16 cross-section States. Heptachlor use has been severely restricted, and its production has been

banned nationwide. The cross-section should adequately represent the occurrence of heptachlor and

heptachlor epoxide on a national scale based upon the use, production, and release patterns of the 16-

State cross-section in relation to the patterns observed for all 50 States.

3.8.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1993. Toxicological Profile for

Heptachlor and Heptachlor Epoxide. U.S. Department of Health and Human Services, Public

Health Service. 131 pp. + Appendices. Available on the Internet at:

http://www.atsdr.cdc.gov/toxprofiles/tp12.pdf
Occurrence Summary and Use Support Document March 2002 214

Barks, J.H. 1978. Water Quality in the Ozark National Scenic Riverways, Missouri. Washington, DC:

U.S. Geological Survey, U.S. Department of Interior. U.S. Geological Survey Water-Supply

Paper 2048. 

Breidenbach, A.W., et al. 1967. Chlorinated hydrocarbon pesticides in major river basins, 1957-65. 

Pub. Health Rep. v. 82, p. 139.

Canadian Public Health Association. 1986. Comprehensive Survey of the Status of Great Lakes

Drinking Water. Prepared in cooperation with Health and Welfare Canada and the Ministry of

the Environment. Ottawa, Canada: Canadian Public Health Association. August 1986.

Cohen, D.B., and G.W. Bowes. 1984. Water Quality and Pesticides: A California Risk Assessment

Program (Volume 1). Sacramento, CA: State Water Resources Control Board, Toxic Substances

Control Program.

Dappen, G. 1974. Pesticide Analysis from Urban Storm Runoff. Prepared by University of Nebraska,

Lincoln, Nebraska, for Office of Water Research and Technology, Nebraska Wesleyan

University. Project No. A-025-NEB(2).

Englande, A.J., J.K. Smith, and J.N. English. 1978. Potable water quality of advanced wastewater

treatment plant effluents. Prog. Wat. Tech. v. 10, no. 1⁄2, pp. 17-39.

Estabrooks, F. No date. Memorandum of pesticide information in New York surface water. From:

Frank Estabrooks, U.S. Department of Environmental Conservation. Albany, NY.

Gilliom, R.J., R.B. Alexander, and R.A. Smith. 1985. Pesticides in the Nation’s Rivers, 1975-1980, and

Implications for Future Monitoring. U.S. Geological Survey Water-Supply Paper 2271. U.S.

Government Printing Office, U.S. Department of Interior.

Holden, P.W. 1986. Pesticides and Groundwater Quality. Issues and Problems in Four States. 

Prepared for the Board of Agriculture, National Research Council. Washington, DC: National

Academy Press.

Idaho Department of Health and Welfare. 1984. Letter to Charles Berry, Office of Drinking Water, U.S.

Environmental Protection Agency, summarizing data on groundwater contamination incidents. 

Sent by: Charles D. Brokopp, State Epidemiologist, Division of Health, Idaho Department of

Health and Welfare.

Irwin, G.A., and H.G. Healy. 1978. Chemical and Physical Quality of Selected Public Water Supplies in

Florida, August-September 1976. Tallahassee, FL: Water Resources Division, U.S. Geological

Survey. USGS/WRI 78-21.

Kuch, P. 1986. Letter to Frederic A. Zafran, SAIC, McLean, VA. October 28, 1986.

Levins, P., J. Adams, P. Brenner, S. Coons, K. Thrun, and J. Varone. 1979. Sources of Toxic Pollutants

found in Influents to Sewage Treatment Plants. IV. R.M. Clayton Drainage Basin, Atlanta

report. Prepared by Arthur D. Little, Inc., for Office of Water Planning and Standards, U.S.

Environmental Protection Agency, Washington, DC. EPA Contract No. 68-01-3857.
Occurrence Summary and Use Support Document March 2002 215

Mississippi State University (MSU). 1984. Cooperative Agreement Progress Report: Mississippi

Pesticide Hazard Assessment Project. Pesticide Residue Monitoring of Drinking Water from

Shallow Wells in the Mississippi Delta. Prepared by: Larry Lane, Principal Investigator,

Mississippi State Chemical Laboratory, Mississippi State University

Pellizzari, E.D., M.D. Erickson, and R.A. Zweidinger. 1979. Formulation of a Preliminary Assessment

of Halogenated Organic Compounds in Man and Environmental Media. EPA Report 560-13-79-

006. Prepared by Research Triangle Institute, Research Triangle Park, North Carolina, for Office

of Toxic Substances, U.S. Environmental Protection Agency, Washington, DC. 

Sandhu, S.S., W.J. Warren, and P. Nelson. 1978. Pesticidal residue in rural potable water. Journal of

the American Water Works Association. v. 70, no. 1, pp. 41-45.

Schacht, R.A. 1974. Pesticides in the Illinois Waters of Lake Michigan. EPA Report 660-3-74-002. 

Prepared by Illinois Environmental Protection Agency, Chicago, Illinois, for Office of Research

and Development, Office of Ground Water and Drinking Water, U.S. Environmental Protection

Agency, Washington, DC. 

Truhlar, J.F., and L.A. Reed. 1976. Occurrence of pesticide residues in four streams draining different

land-use areas in Pennsylvania, 1969-1971. Pestic. Monit. J. v. 10, no. 3, pp. 101-110.

Tucker, R.K., and T.A. Burke. 1978. A Second Preliminary Report on the Findings of the State

Groundwater Monitoring Project. New Jersey: Department of Environmental Protection.

USEPA. 1976. EPA Actions to Cancel and Suspend Uses of Chlordane and Heptachlor as Pesticides –

Economic and Social Implications. EPA Report 540-4-76-004. Washington, DC: Office of

Pesticide Programs, USEPA. 

USEPA. 1980. Ambient Water Quality Criteria for Heptachlor. EPA Report 440-4-80-052. 

Washington, DC: Office of Water Regulations and Standards, USEPA. 

USEPA. 1983. Analysis of the risks and benefits of seven chemicals used for subterranean termite

control. EPA Report 540-9-83-005. Washington, DC: Office of Pesticide Programs, USEPA. 

USEPA. 1986. Guidance for the Reregistration of Pesticide Products Containing Heptachlor as the

Active Ingredient. EPA Report 540-RS-87-018. Washington, DC: Office of Pesticides and

Toxic Substances, USEPA. 

USEPA. 1989. Occurrence and Human Exposure to Pesticides in Drinking Water, Food and Air in the

United States of America (Draft Final Report). Office of Drinking Water, USEPA. September,

1989.

USEPA. 1990. Suspended, Canceled , and Restricted Pesticides. Office of Pesticides and Toxic

Substances, USEPA.

USEPA. 1992. R.E.D. Facts: Heptachlor. EPA Report 738-F-00-013. Washington, DC: Office of

Prevention, Pesticides, and Toxic Substances, USEPA. 4 pp. Available on the Internet at:

http://www.epa.gov/oppsrrd1/REDs/factsheets/0175fact.pdf, last updated June 21, 2001. 
Occurrence Summary and Use Support Document March 2002 216

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Waggoner, P.E. 1985. Memorandum from the Connecticut Agricultural Experiment Station on

Pesticides in Connecticut Groundwater. P. Gough, (ed.). New Haven, CT: News of Science. 

Worthing, C.R., Walker, S.B., eds. 1987. The Pesticide Manual: A World Compendium. 8th ed. 

Suffolk, Great Britain: The British Crop Protection Council. pp. 455-456. 
Occurrence Summary and Use Support Document March 2002 217

3.9 Hexachlorobenzene

Table of Contents

3.9.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

3.9.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

3.9.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

3.9.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 221

3.9.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

3.9.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

3.9.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Tables and Figures

Table 3.9-1: Hexachlorobenzene Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . . . 218

Table 3.9-2: Environmental Releases (in pounds) for Hexachlorobenzene in the 

United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

Table 3.9-3: Stage 1 Hexachlorobenzene Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

Table 3.9-4: Stage 1 Hexachlorobenzene Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

Table 3.9-5: Stage 2 Estimated Hexachlorobenzene Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

Table 3.9-6: Stage 2 Estimated Hexachlorobenzene Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

Table 3.9-7: Estimated National Hexachlorobenzene Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
Occurrence Summary and Use Support Document March 2002 218

3.9.1 Introduction, Use and Production

Hexachlorobenzene, also known as HCB, is a chlorinated hydrocarbon fungicide used as a seed

treatment, especially on wheat. It may be used with or without other seed treatments. 

Hexachlorobenzene is a white crystalline solid that is not very soluble in water. It does not occur

naturally in the environment. It is formed as a by-product while making other chemicals, in the waste

streams of chloralkali and wood-preserving plants, and when burning municipal waste (ATSDR, 2000). 

Currently, hexachlorobenzene is not manufactured as a commercial end product in the U.S. and also has

no commercial end uses. It does not occur naturally in the environment, and is mostly formed as a

byproduct in the manufacture of chlorinated solvents, in the waste streams of chloralkali and woodpreserving plants, in fly ash, and in flue gas effluents from municipal incineration. Hexachlorobenzene

has not been commercially produced since the late 1970s. In 1975 about 3,200 pounds were produced,

and in 1984 between 7,700 and 25,350 pounds were produced as a byproduct in chemical production

(ATSDR, 2000).

 

Until 1984 hexachlorobenzene was widely used as a pesticide to protect the seeds of onions, sorghum,

wheat and other grains against fungus. In 1984 the last registered use of hexachlorobenzene as a

pesticide was voluntarily canceled. It was also used to make fireworks, ammunition and synthetic

rubber; as a porosity controller in the manufacture of electrodes; as a chemical intermediate in dye

manufacturing; and as a wood preservative (ATSDR, 2000).

Table 3.9-1 shows the number of facilities in each State that manufacture and process

hexachlorobenzene, the intended uses of the product, and the range of maximum amounts derived from

the Toxics Release Inventory (TRI) of EPA (ATSDR, 2000). 

Table 3.9-1: Hexachlorobenzene Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on site in Activities and usesc

CA 3 100-99,999 1,4,5

IL 1 1,000-9,999 13

KS 1 100-199 13

KY 1 10,000-99,999 1,3,7

LA 4 0-99,999 1,2,3,5,7,8

NJ 1 1,000-9,999 13

TN 1 1,000-9,999 1,6

TX 4 1,000-999,999 1,5,6,10,13

a

Post office State abbreviations used

b

Data in TRI are maximum amounts on site at each facility

c

Activities/Uses include:

1. Produce 8. As a formulation component

2. Import 9. As an article component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

Source: ATSDR, 2000 compilation of TRI98 2000 data
Occurrence Summary and Use Support Document March 2002 219

3.9.2 Environmental Release

Hexachlorobenzene is listed as a Toxics Release Inventory (TRI) chemical. Table 3.9-2 illustrates the

environmental releases for hexachlorobenzene from 1988 through 1999. (There are only

hexachlorobenzene data for these years.) Although there is no detectable trend in virtually any category

of release for hexachlorobenzene, total on- and off-site releases have moderated and decreased in recent

years. Previous to 1995, levels had ranged from over 1 million pounds to around 30,000 pounds; recent

levels hover well under 20,000 pounds. Off-site releases comprise the vast majority of total releases, and

air emissions are, in most years, the most significant source of on-site releases. Releases to land

remained at or near zero until just recently, and both surface water discharges and underground injection

normally contributed less than 1,000 pounds to the overall total. These TRI data for hexachlorobenzene

were reported from 11 States, with four States (Texas, Tennessee, Louisiana, and California) reporting

every year (USEPA, 2000). Out of those 11 States, 6 are included in the 16-State cross section (used for

analyses of hexachlorobenzene occurrence in drinking water; see Section 3.9.4). (For a map of the 16-

State cross-section, see Figure 1.3-1.)

Table 3.9-2: Environmental Releases (in pounds) for Hexachlorobenzene in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 1,524 7 -- 23 13,550 15,104

1998 371 4 -- 96 13,251 13,722

1997 154 276 139 0 12,038 12,607

1996 220 274 717 0 23,449 24,660

1995 566 6,458 480 0 6,975 14,479

1994 458 269 204 0 940,478 941,409

1993 636 476 548 0 648,010 649,670

1992 4,471 227 794 0 28,380 33,872

1991 841 111 60 1 1,064,793 1,065,806

1990 1,468 124 220 -- 34,011 35,823

1989 4,613 338 710 0 1,008,186 1,013,847

1988 4,045 4 410 0 443,541 448,000

 Source: USEPA, 2000 

3.9.3 Ambient Occurrence

The most comprehensive and nationally consistent data describing ambient water quality in the United

States are being produced through the United States Geological Survey’s (USGS) National Water Quality

Assessment (NAWQA) program. However, national NAWQA data, as well as NURP and NPDES data,

are currently unavailable for hexachlorobenzene.

3.9.3.1 Additional Ambient Occurrence Data

Additional studies of ambient data are summarized below. A summary document entitled “Occurrence

and Exposure Assessment of Hexachlorobenzene in Public Drinking Water Supplies” (Wade Miller,
Occurrence Summary and Use Support Document March 2002 220

1989), was previously prepared for past USEPA assessments of hexachlorobenzene. Several studies

included in that document have addressed concentrations of hexachlorobenzene in ambient surface water. 

(No studies were found that addressed the occurrence of hexachlorobenzene in ambient ground water

sources.) The following information is taken directly from “Occurrence and Exposure Assessment of

Hexachlorobenzene in Public Drinking Water Supplies” (Wade Miller, 1989).

The USEPA's computerized water quality data base known as STORET was devised to assist Federal and

State institutions meet objectives of Public Law 92-500 to maintain and enhance the physical, chemical,

and biological quality of the nation's ambient waterways by providing for the collection and

dissemination of basic water quality data (Staples et al., 1985, as cited in Wade Miller, 1989). Data are

collected by States, EPA regional offices, and other government agencies and are maintained in the

STORET system.

Before presenting a summary of the ambient water data in STORET, it is important to note that there are

significant limitations in using the data base to estimate representative concentrations of a contaminant

such as hexachlorobenzene. Data entered into STORET are gathered from an array of studies conducted

for various purposes. Analyses are conducted in a number of different laboratories employing different

methodologies with a range of detection limits. In many cases, detection limits are not reported, making

the reliability of the data highly questionable. Where detection limits have been reported, STORET

assigns the detection limit value to those observations reported as not detected. This can lead to errors in

interpretation and overestimation of concentrations in cases in which there is a preponderance of

nondetectable values. Additionally, a few high values can inflate mean values and result in large

standard deviations relative to the means (Staples et al., 1985, as cited in Wade Miller, 1989). Very high

values may not be correct, as they may reflect sample contamination or analytical error and can

significantly distort assessment of average concentrations. Staples et al. (1985, as cited in Wade Miller,

1989) also notes that the use of data collected prior to the 1980s is not recommended, since such data was

obtained using less sensitive laboratory techniques and quality assurance procedures were not yet

mandated for the data entered into the system.

The STORET water quality data base provides information on the occurrence of contaminants at ambient

water stations in U.S. waterways. A summary of this information was obtained for hexachlorobenzene in

ambient waters. Ambient sites include streams, lakes, ponds, wells, reservoirs, canals, estuaries, and

oceans. While the preponderance of data were collected from surface water sources, the number of

samples collected from ground water wells, relative to the total number of samples collected from all

ambient sites combined, is unspecified (Staples et al., 1985, as cited in Wade Miller, 1989). Staples et al.

(1985, as cited in Wade Miller, 1989) have summarized data from the 1980's only; that is, data from 1980

through 1983. This was done based on the number of data points and the likelihood that better quality

assurance practices have been employed in more recent years. In the absence of sophisticated statistical

analyses to eliminate improbable data, median values have been reported. The median value is sensitive

to extreme values, and reflects a measure of central tendency more accurately than the mean value in the

presence of these extreme values (Staples et al., 1985, as cited in Wade Miller, 1989).

For a total of 1,786 observations from ambient water stations, the median concentration of

hexachlorobenzene was 0.020 :g/L. Of the total number of observations, 26.0% were reported as

detected. However, detection limits and other sampling information were not reported. Clark et al.

(1988, as cited in Wade Miller, 1989) reported that hexachlorobenzene concentrations ranging from

0.00001 to 0.00012 :g/L were detected in water samples collected from Lakes Ontario and Michigan. 

No other information was reported. 
Occurrence Summary and Use Support Document March 2002 221

3.9.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of hexachlorobenzene occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.001 mg/L; 0.0005 mg/L; and 0.0001

mg/L.

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

hexachlorobenzene. These data represent approximately 53,000 analytical results from more than 14,000

PWSs during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The

number of sample results and PWSs vary by State, although the State data sets have been reviewed and

checked to ensure adequacy of coverage and completeness. The overall modal detection limit for

hexachlorobenzene in the 16 cross-section States is equal to 0.0001 mg/L. (For details regarding the 16-

State cross-section, please refer to Section 1.3.5 of this report.)

3.9.4.1 Stage 1 Analysis Occurrence Findings

Table 3.9-3 illustrates the low occurrence of hexachlorobenzene in drinking water for the public water

systems in the 16-State cross-section relative to three thresholds: 0.001 mg/L (the current MCL), 0.0005

mg/L, and 0.0001 mg/L. One ground water PWSs (approximately 0.00714% of all PWSs in the 16

States) had at least one analytical result exceeding 0.001 mg/L, 0.0005 mg/L, and 0.0001 mg/L. No

surface water systems had any analytical results greater than any of the three thresholds.

Table 3.9-3: Stage 1 Hexachlorobenzene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.001 0.00792% 1

0.0005 0.00792% 1

0.0001 0.00792% 1

Surface Water

0.001 0.000% 0

0.0005 0.000% 0

0.0001 0.000% 0

Combined Ground &

Surface Water

0.001 0.00714% 1

0.0005 0.00714% 1

0.0001 0.00714% 1
Occurrence Summary and Use Support Document March 2002 222

Reviewing hexachlorobenzene occurrence in the 16 cross-section States by PWS population served

(Table 3.9-4) shows that approximately 0.0399% of the population (about 37,500 people) was served by

one ground water PWS with at least one analytical result of hexachlorobenzene greater than 0.001 mg/L,

0.0005 mg/L, and 0.0001 mg/L. No people served by surface water systems were exposed to

hexachlorobenzene at levels greater than any of the three thresholds.

Table 3.9-4: Stage 1 Hexachlorobenzene Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Ground Water

0.001 0.0951% 37,500

0.0005 0.0951% 37,500

0.0001 0.0951% 37,500

Surface Water

0.001 0.000% 0

0.0005 0.000% 0

0.0001 0.000% 0

Combined Ground &

Surface Water

0.001 0.0399% 37,500

0.0005 0.0399% 37,500

0.0001 0.0399% 37,500

3.9.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.9-5 and 3.9-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations (USEPA,

2002)). 

No ground water or surface water PWSs had an estimated mean concentration of hexachlorobenzene

exceeding 0.001 mg/L or 0.0005 mg/L. Approximately 1 (0.00307% of) ground water PWS and 1

(0.00101% of) surface water PWS in the 16 States were estimated to have a mean concentration greater

than 0.0001 mg/L. 
Occurrence Summary and Use Support Document March 2002 223

Table 3.9-5: Stage 2 Estimated Hexachlorobenzene Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.00307% 0.000% - 0.0158% 1 0 - 2

Surface Water

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.00101% 0.000% - 0.000% 1 0 - 0

Combined Ground

& Surface Water

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.00287% 0.000% - 0.0143% 1 0 - 2

Reviewing hexachlorobenzene occurrence by PWS population served (Table 3.9-6) shows that

approximately 0.0176% of population served by all PWSs in the 16 States (an estimate of approximately

16,600 people) were potentially exposed to hexachlorobenzene levels above 0.0001 mg/L. The percent

of population exposed was equal to 0% for all system types when evaluated relative to 0.001 mg/L and

0.0005 mg/L. 

The percentage of population served by ground water systems in the 16 States with estimated mean

concentration values greater than 0.0001 mg/L was equal to 0.0384% (an estimate of approximately

15,200 people). Approximately 1,400 (0.00260% of) people in the 16 cross-section States were served

by surface water systems with estimated mean concentration values greater than 0.0001 mg/L.

Table 3.9-6: Stage 2 Estimated Hexachlorobenzene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.0384% 0.000% - 0.214% 15,200 0 - 84,300
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 224

Surface Water

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.00260% 0.000% - 0.000% 1,400 0 - 0

Combined Ground

& Surface Water

0.001 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.000% 0.000% - 0.000% 0 0 - 0

0.0001 0.0176% 0.000% - 0.0896% 16,600 0 - 84,300

3.9.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, no systems had estimated mean concentration values of hexachlorobenzene greater than 0.001

mg/L or 0.0005 mg/L. An estimated 2 systems nationally serving approximately 37,600 people were

expected to have estimated mean concentrations of hexachlorobenzene greater than 0.0001 mg/L. (See

Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, approximately 2 PWSs serving about 32,900 people nationally were estimated

to have a mean concentration greater than 0.0001 mg/L. Only 1 surface water systems serving

approximately 3,300 people was estimated to have a mean concentration of hexachlorobenzene above

0.0001 mg/L.

Table 3.9-7: Estimated National Hexachlorobenzene Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.001 0 0 - 0 0 0 - 0

0.0005 0 0 - 0 0 0 - 0

0.0001 2 0 - 9 32,900 0 - 183,100

Surface Water

0.001 0 0 - 0 0 0 - 0

0.0005 0 0 - 0 0 0 - 0

0.0001 1 0 - 0 3,300 0 - 0

Combined Ground

& Surface Water

0.001 0 0 - 0 0 0 - 0

0.0005 0 0 - 0 0 0 - 0

0.0001 2 0 - 9 37,600 0 - 190,900
Occurrence Summary and Use Support Document March 2002 225

3.9.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of fluoride in drinking water are also reviewed. 

Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence and Exposure Assessment of Hexachlorobenzene in Public Drinking Water Supplies”

(Wade Miller, 1989), is presented in the following section. This variety of studies and information are

presented regarding levels of fluoride in drinking water nationally. (No regional studies were included.) 

Note that none of the studies presented in the following section provide the quantitative analytical results

or comprehensive coverage that would enable direct comparison to the occurrence findings estimated

with the cross-section occurrence data presented in Section 3.9.4. These additional studies, however, do

enable a broader assessment of the Stage 2 occurrence estimates presented for this Six-Year Review. All

the following information in Section 3.9.5 is taken directly from “Occurrence and Exposure Assessment

of Hexachlorobenzene in Public Drinking Water Supplies” (Wade Miller, 1989).

3.9.5.1 Ground Water Sources – National Studies

The National Screening Program for Organics in Drinking Water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water

systems in 33 States for 51 organic chemical contaminants, including hexachlorobenzene. Analyses were

made using gas chromatography/mass spectrometry (Boland, 1981, as cited in Wade Miller, 1989). The

NSP data extracted from Boland (1981, as cited in Wade Miller, 1989) showed that none of the 12

ground water supplies sampled contained detectable levels of hexachlorobenzene. The minimum

quantifiable concentration for hexachlorobenzene was 0.1 :g/L.

3.9.5.2 Surface Water Sources – National Studies

The National Screening Program for Organics in Drinking Water (NSP) (see section 3.9.5.1) also

reported the occurrence of hexachlorobenzene in finished drinking water from surface water sources. 

The NSP data extracted from Boland (1981, as cited in Wade Miller, 1989) showed that none of the 104

surface water supplies sampled contained detectable levels of hexachlorobenzene. The minimum

quantifiable concentration for hexachlorobenzene was 0.1 :g/L.

3.9.5.3 Unspecified Water Sources

Several studies provided data on the occurrence of hexachlorobenzene in drinking water supplies but

failed to specify water sources. Drinking water supplies from 83 locations in USEPA Region V were

analyzed for various pesticides and other organic chemicals. Hexachlorobenzene was detected in two

finished supplies at concentrations of 0.004 :g/L and 0.006 :g/L (USEPA, 1986, as cited in Wade

Miller, 1989).

In another study reported by USEPA (1986, as cited in Wade Miller, 1989), three samples of Lake

Ontario water were analyzed for the presence of hexachlorobenzene. Hexachlorobenzene was detected in

all three samples at concentrations ranging from 0.00006 to 0.0002 :g/L, with a mean concentration of

0.0001 :g/L. In Dade County, FL, hexachlorobenzene was detected in 4 out of 10 drinking water

samples analyzed for the presence of hexachlorobenzene. The mean and maximum concentrations were

0.014 and 0.68 :g/L, respectively. The detection limit was approximately 0.006 :g/L.
Occurrence Summary and Use Support Document March 2002 226

3.9.5.4 Ground Water and Surface Water Sources – STORET

The STORET system contains approximately 80 million pieces of data, including data for drinking water

from ground water and surface water sources. The limitations with these data are the same as described

for ambient water in Section 3.9.3.1. 

With these limitations in mind, a summary of the most recently obtained data for drinking water from

ground water sources is presented here (USEPA, 1988, as cited in Wade Miller, 1989). According to

STORET, there were a total of 1,053 observations for hexachlorobenzene in ground water from February

1978 to November 1987. In 27 of these samples, hexachlorobenzene was not detected; however, for

these the detection limit values were assigned. In the remaining 1,026 samples, hexachlorobenzene was

reported to have been detected, but known to have been present below the reporting value. Based on the

assigned and reported values for all 1,053 samples, STORET reported a mean value of 3.80 :g/L and a

range of 0.5 to 10.0 :g/L. The standard deviation for all observations was 1.90 :g/L. Detection limits

and other sampling information were not reported.

The USEPA STORET database similarly contains data on the occurrence of hexachlorobenzene in

drinking water from surface water sources (USEPA, 1988, as cited in Wade Miller, 1989). Between

February 1978 and July 1987, there were 54 observations for hexachlorobenzene in surface water. One

positive observation was reported in March 1978 at a value of 0.10 :g/L. In 5 samples,

hexachlorobenzene was not detected, but were assigned to the detection limit values. In the remaining 48

observations, hexachlorobenzene was reported as being detected but was known to be present at levels

below the reported value. Based on the reported and assigned values for all 54 samples, STORET

reported an overall mean value of 7.17 :g/L and a range of 0.1 to 10.0 :g/L. The standard deviation for

all observations was 3.03 :g/L. Detection limits and other sampling information were not reported.

3.9.6 Conclusion

In summary, hexachlorobenzene is not manufactured as a commercial end product in the U.S. and also

has no commercial end uses. It does not occur naturally in the environment, and is mostly formed as a

byproduct in the manufacture of chlorinated solvents, in the waste streams of chloralkali and woodpreserving plants, in fly ash, and in flue gas effluents from municipal incineration. Hexachlorobenzene

was at one time used as a pesticide, but that use was canceled in 1984. Although data indicates that there

are manufacturers and processors of hexachlorobenzene, it has not been commercially produced since the

1970s. Industrial releases of hexachlorobenzene have been reported to TRI from 11 States since 1988. 

There is no ambient occurrence survey data available for hexachlorobenzene. The Stage 2 analysis of

hexachlorobenzene, based on the 16-State cross-section, estimated that approximately zero percent of

combined ground water and surface water systems serving zero percent of the population exceeded the

MCL of 0.001 mg/L. Based on this estimate, zero PWSs nationally are estimated to have

hexachlorobenzene epoxide levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, TRI releases have been reported for hexachlorobenzene from 11 States,

including 6 of 16 cross-section States. The use and commercial production of hexachlorobenzene has

been eliminated nationwide. Five of the eight States listed in ATSDR as manufacturers and/or

processors of hexachlorobenzene are cross-section States. The cross-section should adequately represent

the occurrence of hexachlorobenzene on a national scale based upon the use, production, and release

patterns of the 16-State cross-section in relation to the patterns observed for all 50 States. 
Occurrence Summary and Use Support Document March 2002 227

3.9.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 2000. Toxicological Profile for

Hexachlorobenzene. U.S. Department of Health and Human Services, Public Health Service. 

308 pp. + Appendices. Available on the Internet at:

http://www.atsdr.cdc.gov/toxprofiles/tp90.pdf

Boland, P.A. 1981. National Screening Program for Organics in Drinking Water. Prepared by SRI

International for the Office of Drinking Water, U.S. Environmental Protection Agency,

Washington, DC. Contract No. 68-01-4666.

Clark, T., K. Clark, S. Paterson, D. MacKay, and R.J. Norstrom. 1988. Wildlife monitoring, modelling,

and fugacity. Environ. Sci. Technol. v. 22, no. 2, pp. 120-127.

Staples, C.A., A.F. Werner, and T.J. Hoogheem. 1985. Assessment of priority pollutant concentrations

in the United States using STORET data base. Environ. Toxicol. Chem. v. 4, pp. 131-142.

USEPA. 1986. Exposure Assessment for Hexachlorobenzene. Final Report. EPA Report 560-5-86-019. 

Washington, DC: Office of Pesticides and Toxic Substances, USEPA.

USEPA. 1988. Computer printout of STORET water quality data base. Retrieval conducted March 23,

1988 by Science Applications International Corporation. Data available through Office of Water

Regulations and Standards, USEPA, Washington, DC.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Hexachlorobenzene in

Public Drinking Water Supplies - DRAFT. Draft report submitted to EPA for review May 15,

1989.
Occurrence Summary and Use Support Document March 2002 228

3.10 Hexachlorocyclopentadiene

Table of Contents

3.10.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

3.10.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

3.10.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

3.10.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . 231

3.10.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235

3.10.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

3.10.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

Tables and Figures

Table 3.10-1: Facilities that Manufacture or Process Hexachlorocyclopentadiene . . . . . . . . . . . . . . . 229

Table 3.10-2: Environmental Releases (in pounds) for Hexachlorocyclopentadiene 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

Table 3.10-3: Stage 1 Hexachlorocyclopentadiene Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

Table 3.10-4: Stage 1 Hexachlorocyclopentadiene Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

Table 3.10-5: Stage 2 Estimated Hexachlorocyclopentadiene Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

Table 3.10-6: Stage 2 Estimated Hexachlorocyclopentadiene Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

Table 3.10-7: Estimated National Hexachlorocyclopentadiene Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Occurrence Summary and Use Support Document March 2002 229

3.10.1 Introduction, Use and Production

Hexachlorocyclopentadiene, also known as HEX or HCCPD, is a manufactured chemical that does not

occur naturally. It is a light, lemon-yellow liquid that has a sharp musty odor. 

Hexachlorocyclopentadiene easily evaporates into the air and its vapor looks like a blue haze. Most

hexachlorocyclopentadiene in the environment results from releases during its production and disposal

(ATSDR, 1999).

The greatest use of hexachlorocyclopentadiene is as a raw material in manufacturing other chemicals,

including pesticides, flame retardants, resins, dyes, pharmaceuticals, plastics, etc. 

Hexachlorocyclopentadiene has no end uses of its own (USEPA, 2001).

Hexachlorocyclopentadiene is a key intermediate in the production of chlorinated cyclodiene pesticides,

including aldrin, dieldrin, endrin, chlordane, hepachlor, kepone, endosulfan, pentac, isodrin, and mirex. 

It is also used as an intermediate in the manufacture of flame retardants and, to a lesser extent, in the

manufacture of nonflammable resins, polyester resins, pharmaceuticals, unbreakable plastics, acids,

esters, ketones, fluorocarbons, and dyes. It has previously been used as a biocide (ATSDR, 1999).

The only current commercial producer of hexachlorocyclopentadiene is the Velsicol Chemical Company

in Memphis, TN. Because production is limited to a single producer, information on the current

production volume of hexachlorocyclopentadiene is not available. Estimates of past production, based

on production volumes of chlorinated cyclodiene pesticides, indicate that production volume for

hexachlorocyclopentadiene was about 50 million pounds per year in the early 1970s. Due to regulatory

restrictions on many of the organochlorine pesticides using hexachlorocyclopentadiene as a chemical

intermediate, production volume dropped to between 8 to 15 million pounds per year in the late 1970s. It

has also been estimated that 18 million pounds of hexachlorocyclopentadiene were produced in 1983, but

more recent data is not available (ATSDR, 1999). Only two pesticides which use

hexachlorocyclopentadiene as an intermediate, endosulfan and pentac, are currently registered for use in

the U.S. 

Table 3.10-1 shows the facilities that manufacture or process hexachlorocyclopentadiene, the activities

and uses of the product, and the range of maximum amounts on site derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 1999). 

Table 3.10-1: Facilities that Manufacture or Process Hexachlorocyclopentadiene

Facility Locationa Range of maximum amounts 

on site in pounds Activities and uses

Occidental Chemical Niagra Falls, NY 100,000-999,999 Reactant

Morton Intl. Inc. West Alexandria, 10,000-99,999 Reactant

Velsicol Chemical Corp. Memphis, TN 1,000,000-9,999,999 Produce, on-site use/processing, sale/distribution,

Basf Corp. Beaumont, TX 10,000-99,999 Reactant

a

Post office State abbreviations used

Source: ATSDR, 1999 compilation of TRI96 1998 data

3.10.2 Environmental Release

Hexachlorocyclopentadiene is listed as a Toxics Release Inventory (TRI) chemical. Table 3.10-2

illustrates the environmental releases for hexachlorocyclopentadiene from 1988 - 1999. (There are only
Occurrence Summary and Use Support Document March 2002 230

hexachlorocyclopentadiene data for these years.) Air emissions, which constitute most of the on-site

releases, decreased substantially from 1989 through 1993, and then rose briefly before declining to their

lowest level on record in 1999. Surface water discharges have been consistently at very low levels, and

have been at or near zero since 1992. Although underground injection has varied from 5 to 2,131

pounds, levels remained at 250 pounds from 1993 to 1998. No information on releases to land was

reported prior to 1998, and since then readings have shown no trend. Off-site releases have generally

decreased, from a high of 28,000 pounds in 1988 to a low of 567 pounds in 1998. Overall, total on- and

off-site releases have mostly mirrored the changes in air emissions, with mild fluctuations and a declining

trend. These TRI data for hexachlorocyclopentadiene were reported from nine States, with three States

(Texas, Tennessee, and New York) reporting every year (USEPA, 2000). Four of the nine States are in

the 16-State cross-section (used for analyses of hexachlorocyclopentadiene occurrence in drinking water;

see Section 3.10.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 3.10-2: Environmental Releases (in pounds) for Hexachlorocyclopentadiene in the United

States, 1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 1,098 1 -- 0 903 2,002

1998 5,791 0 250 5,520 567 12,128

1997 6,927 3 250 -- 930 8,110

1996 7,966 0 250 -- 1,000 9,216

1995 8,311 6 250 -- 2,995 11,562

1994 8,923 1 250 -- -- 9,174

1993 3,765 1 250 -- -- 4,016

1992 8,380 0 5 -- 2,740 11,125

1991 25,461 23 5 -- 3,000 28,489

1990 84,585 10 5 -- 5,000 89,600

1989 89,246 6 250 -- 1,204 90,706

1988 78,317 6 2,131 -- 28,470 108,924

 Source: USEPA, 2000 

3.10.3 Ambient Occurrence

The most comprehensive and nationally consistent data describing ambient water quality in the United

States are being produced through the United States Geological Survey’s (USGS) National Water Quality

Assessment (NAWQA) program. However, national NAWQA data, as well as NURP and NPDES data,

are currently unavailable for hexachlorocyclopentadiene.

3.10.3.1 Additional Ambient Occurrence Data

Additional studies of ambient surface water data are summarized below. (No data were available on the

occurrence of hexachlorocyclopentadiene in ground water sources.) A summary document entitled

“Occurrence and Exposure Assessment of Hexachlorocyclopentadiene in Public Drinking Water

Supplies” (Wade Miller, 1989), was previously prepared for past USEPA assessments of

hexachlorocyclopentadiene. The following information is taken directly from that document. 

The USEPA's computerized water quality data base known as STORET was devised to assist Federal and

State institutions meet objectives of Public Law 92-500 to maintain and enhance the physical, chemical,
Occurrence Summary and Use Support Document March 2002 231

and biological quality of the nation's ambient waterways by providing for the collection and

dissemination of basic water quality data (Staples et al., 1985, as cited in Wade Miller, 1989). Data are

collected by States, EPA regional offices, and other government agencies and are maintained in the

STORET system.

Before presenting a summary of the ambient water data in STORET, it is important to note that there are

significant limitations in using the data base to estimate representative concentrations of a contaminant

such as hexachlorocyclopentadiene. Data entered into STORET are gathered from an array of studies

conducted for various purposes. Analyses are conducted in a number of different laboratories employing

different methodologies with a range of detection limits. In many cases, detection limits are not reported,

making the reliability of the data highly questionable. Where detection limits have been reported,

STORET assigns the detection limit value to those observations reported as not detected. This can lead

to errors in interpretation and overestimation of concentrations in cases in which there is a preponderance

of nondetectable values. Additionally, a few high values can inflate mean values and result in large

standard deviations relative to the means (Staples et al., 1985, as cited in Wade Miller, 1989). Very high

values may not be correct, as they may reflect sample contamination or analytical error and can

significantly distort assessment of average concentrations. Staples et al. (1985, as cited in Wade Miller,

1989) also notes that the use of data collected prior to the 1980s is not recommended, since such data was

obtained using less sensitive laboratory techniques and quality assurance procedures were not yet

mandated for the data entered into the system.

The STORET water quality data base provides information on the occurrence of contaminants at ambient

water stations in U.S. waterways. A summary of this information was obtained for

hexachlorocyclopentadiene in ambient waters. Ambient sites include streams, lakes, ponds, wells,

reservoirs, canals, estuaries, and oceans. While the preponderance of data were collected from surface

water sources, the number of samples collected from ground water wells, relative to the total number of

samples collected from all ambient sites combined, is unspecified (Staples et al., 1985, as cited in Wade

Miller, 1989). Staples et al. (1985, as cited in Wade Miller, 1989) have summarized data from the 1980's

only; that is, data from 1980 through 1983. This was done based on the number of data points and the

likelihood that better quality assurance practices have been employed in more recent years. In the

absence of sophisticated statistical analyses to eliminate improbable data, median values have been

reported. The median value is sensitive to extreme values, and reflects a measure of central tendency

more accurately than the mean value in the presence of these extreme values (Staples et al., 1985, as cited

in Wade Miller, 1989).

For a total of 854 observations from ambient water stations, the median concentration of

hexachlorocyclopentadiene was 10.0 :g/L. Of the total number of observations, 0.1 percent were

reported as detectable. Detection limits and other sampling information were not reported.

3.10.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of hexachlorocyclopentadiene occurrence presented in the following section is based on

State compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the

largest and most comprehensive compliance monitoring data set compiled by EPA to date. These data

were evaluated relative to several concentration thresholds of interest: 0.05 mg/L; 0.04 mg/L; and 0.005

mg/L.

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

hexachlorocyclopentadiene. These data represent more than 52,000 analytical results from

approximately 14,000 PWSs during the period from 1984 to 1998 (with most analytical results from 1992
Occurrence Summary and Use Support Document March 2002 232

to 1997). The number of sample results and PWSs vary by State, although the State data sets have been

reviewed and checked to ensure adequacy of coverage and completeness. The overall modal detection

limit for hexachlorocyclopentadiene in the 16 cross-section States is equal to 0.005 mg/L. (For details

regarding the 16-State cross-section, please refer to Section 1.3.5 of this report.)

3.10.4.1 Stage 1 Analysis Occurrence Findings

Table 3.10-3 illustrates the very low occurrence of hexachlorocyclopentadiene in drinking water for the

public water systems in the 16-State cross-section. No ground water or surface water PWSs had any

analytical results exceeding the MCL (0.05 mg/L) or 0.04 mg/L. Only 1 (0.0722% of) surface water

system had any analytical results greater than the modal detection limit (0.005 mg/L). No ground water

systems had analytical results greater than any of the three thresholds.

Table 3.10-3: Stage 1 Hexachlorocyclopentadiene Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.05 0.000% 0

0.04 0.000% 0

0.005 0.000% 0

Surface Water

0.05 0.000% 0

0.04 0.000% 0

0.005 0.0722% 1

Combined Ground &

Surface Water

0.05 0.000% 0

0.04 0.000% 0

0.005 0.00718% 1

Reviewing hexachlorocyclopentadiene occurrence in the 16 cross-section States by PWS population

served (Table 3.10-4) shows that approximately 0.0296% of the total 16-State population was served by

PWSs with analytical detections of hexachlorocyclopentadiene greater than 0.005 mg/L (about 27,700

people, all served by one surface water system).
Occurrence Summary and Use Support Document March 2002 233

Table 3.10-4: Stage 1 Hexachlorocyclopentadiene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

 by Systems Exceeding

Threshold

Ground Water

0.05 0.000% 0

0.04 0.000% 0

0.005 0.000% 0

Surface Water

0.05 0.000% 0

0.04 0.000% 0

0.005 0.0509% 27,700

Combined Ground &

Surface Water

0.05 0.000% 0

0.04 0.000% 0

0.005 0.0296% 27,700

3.10.4.3 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.10-5 and

3.10-6. The statistically generated best estimate values, as well as the ranges around the best estimate

value, are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this

report. For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation

Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water

Regulations (USEPA, 2002)). 

No ground water or surface water PWSs (therefore, no population served by systems) had an estimated

mean concentration of hexachlorocyclopentadiene exceeding 0.05 mg/L, 0.04 mg/L or 0.005 mg/L.

Table 3.10-5: Stage 2 Estimated Hexachlorocyclopentadiene Occurrence Based on 16-State CrossSection - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.05 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0
Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 234

Surface Water

0.05 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.05 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0

Table 3.10-6: Stage 2 Estimated Hexachlorocyclopentadiene Occurrence Based on 16-State CrossSection - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.05 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0

Surface Water

0.05 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.05 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0

3.10.4.3 Estimated National Occurrence

As illustrated in Table 3.10-7, the Stage 2 analysis estimated zero systems serving none of the national

population to have an estimated mean concentration values of hexachlorocyclopentadiene greater than

0.05 mg/L, 0.04 mg/L, or 0.005 mg/L. (See Section 1.4 for a description of how Stage 2 16-State

estimates are extrapolated to national values.)
Occurrence Summary and Use Support Document March 2002 235

Table 3.10-7: Estimated National Hexachlorocyclopentadiene Occurrence - Systems and

Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.05 0 0 - 0 0 0 - 0

0.04 0 0 - 0 0 0 - 0

0.005 0 0 - 0 0 0 - 0

Surface Water

0.05 0 0 - 0 0 0 - 0

0.04 0 0 - 0 0 0 - 0

0.005 0 0 - 0 0 0 - 0

Combined Ground

& Surface Water

0.05 0 0 - 0 0 0 - 0

0.04 0 0 - 0 0 0 - 0

0.005 0 0 - 0 0 0 - 0

3.10.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of fluoride in drinking water are also reviewed. 

For a previous summary document entitled “Occurrence and Exposure Assessment of

Hexachlorocyclopentadiene in Public Drinking Water Supplies” (Wade Miller, 1989), an extensive

search of the scientific and regulatory literature was conducted in an effort to obtain information on the

occurrence of hexachlorocyclopentadiene in drinking water from ground water and surface water

sources. In addition, knowledgeable sources within the Office of Drinking Water were contacted. 

Except for data obtained from the STORET data base, no national, regional or State studies were found

which analyzed the occurrence of hexachlorocyclopentadiene in drinking water supplies. The STORET

data are discussed below. Note that STORET data do not provide the quantitative analytical results or

comprehensive coverage that would enable direct comparison to the occurrence findings estimated with

the cross-section occurrence data presented in Section 3.10.4. These additional studies, however, do

enable a broader assessment of the Stage 2 occurrence estimates presented for this Six-Year Review. All

the following information in Section 3.1.5 is taken directly from “Occurrence and Exposure Assessment

of Hexachlorocyclopentadiene in Public Drinking Water Supplies” (Wade Miller, 1989).

3.10.5.1 Ground Water and Surface Water Sources - STORET

The STORET system contains approximately 80 million pieces of data, including data for drinking water

from ground water and surface water sources. The limitations with these data are the same as described

for ambient water in Section 3.10.3.1. 

With these limitations in mind, a summary of the most recently obtained data for drinking water from

ground water sources is presented here (USEPA, 1988, as cited in Wade Miller, 1989). According to

STORET, there were a total of 1,042 observations for hexachlorocyclopentadiene in ground water from

February 1978 to November 1987. In 27 of these samples, hexachlorocyclopentadiene was not detected;
Occurrence Summary and Use Support Document March 2002 236

however, for these the detection limit values were assigned. In the remaining 1,015 samples,

hexachlorocyclopentadiene was reported to have been detected, but known to have been present below

the reported value. Based on the assigned and reported values for all 1,042 samples, STORET reported a

mean value of 14.35 :g/L and a range of 1.0 to 40.0 :g/L. The standard deviation for all observations

was 7.23 :g/L. Detection limits and other sampling information were not reported.

STORET also contains data on the occurrence of hexachlorocyclopentadiene in drinking water from

surface water sources (USEPA, 1988, as cited in Wade Miller, 1989). Between February 1978 and July

1987, there were 62 observations for hexachlorocyclopentadiene in surface water. In 16 samples,

hexachlorocyclopentadiene was not detected, but were assigned the detection limit values. In the

remaining 46 observations hexachlorocyclopentadiene was reported as being detected but was known to

be present at levels below the reported values. Based on the reported and assigned values for all 62

samples, STORET reported an overall mean value of 8.95 :g/L and a range of 4.0 to 30.0 :g/L. The

standard deviation for all observations was 4.61 :g/L. Detection limits and other sampling information

were not reported.

3.10.5.2 National Estimates of the Occurrence of Hexachlorocyclopentadiene and Population

Exposure for Public Water Supplies

No Federal survey data on the occurrence of hexachlorocyclopentadiene in public drinking water

supplies are available. Information on the occurrence of hexachlorocyclopentadiene in public drinking

water supplies is available from the STORET data base; however, there are significant limitations

involved with utilizing these data. These limitations are discussed in detail in Section 3.10.5.1. 

Consequently, national estimates of occurrence and population exposure could not be made for

hexachlorocyclopentadiene.

3.10.6 Conclusion

Hexachlorocyclopentadiene is a manufactured chemical that does not occur naturally. Its greatest use is

as a raw material in manufacturing other chemicals, including pesticides, flame retardants, resins, dyes,

pharmaceuticals, plastics, etc. The only commercial producer of hexachlorocyclopentadiene is Velsicol

Chemical Corp. in Memphis, Tennessee, and other production or processing of

hexachlorocyclopentadiene is relatively limited. Industrial releases of hexachlorocyclopentadiene have

been reported to TRI from nine States since 1988. Ambient occurrence data was not available for

hexachlorocyclopentadiene. The Stage 2 analysis, based on the 16-State cross-section, estimated that

zero percent of combined ground water and surface water systems serving zero percent of the population

exceeded the MCL of 0.05 mg/L. Based on this estimate, zero PWSs nationally are estimated to have

hexachlorocyclopentadiene levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, hexachlorocyclopentadiene is manufactured and/or processed in 4 States

and has TRI releases in 9 States. Hexachlorocyclopentadiene is manufactured and/or processed in 1 out

of the 16 cross-section States and has TRI releases in 4 of the 16 cross-section States. The cross-section

should adequately represent the occurrence of hexachlorocyclopentadiene on a national scale based upon

the use, production, and release patterns of the 16-State cross-section in relation to the patterns observed

for all 50 States. 
Occurrence Summary and Use Support Document March 2002 237

3.10.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1999. Toxicological Profile for

Hexachlorocyclopentadiene. U.S. Department of Health and Human Services, Public Health

Service. 185 pp. + Appendices. Available on the Internet at: 

http://www.atsdr.cdc.gov/toxprofiles/tp112.pdf

Staples, C.A., A.F. Werner, and T.J. Hoogheem. 1985. Assessment of Priority Pollutant Concentrations

in the United States Using STORET Data Base. Environ. Toxicol. Chem. v. 4, pp. 131-142.

USEPA. 1988. Computer Printout of STORET Water Quality Data Base. Retrieval conducted March

23, 1988 by Science Applications International Corporation. Data available through Office of

Water Regulations and Standards, USEPA, Washington, DC.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on:

Hexachlorocyclopentadiene. Office of Ground Water and Drinking Water, USEPA. Available

on the Internet at: http://www.epa.gov/safewater/dwh/c-soc/hexachl2.html, last updated April 12,

2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of

Hexachlorocyclopentadiene in Public Drinking Water Supplies - DRAFT. Draft report submitted

to EPA for review May 15, 1989. 
Occurrence Summary and Use Support Document March 2002 238

3.11 Oxamyl

Table of Contents

3.11.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

3.11.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

3.11.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

3.11.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . 242

3.11.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

3.11.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

3.11.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

Tables and Figures

Figure 3.11-1: Estimated Annual Agricultural Use for Oxamyl (1992) . . . . . . . . . . . . . . . . . . . . . . . . 240

Table 3.11-1: Oxamyl Detections and Concentrations in Surface Water and Ground Water . . . . . . . 241

Table 3.11-2: Stage 1 Oxamyl Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . 242

Table 3.11-3: Stage 1 Oxamyl Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . 243

Table 3.11-4: Stage 2 Estimated Oxamyl Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

Table 3.11-5: Stage 2 Estimated Oxamyl Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

Table 3.11-6: Estimated National Oxamyl Occurrence - Systems and Population Served . . . . . . . . . 246
Occurrence Summary and Use Support Document March 2002 239

3.11.1 Introduction, Use and Production

Pure oxamyl, also known as Vydate (or methyl-N’,N’-dimethyl-N-[methylcarbamoyl)oxy]-1-thiooxamimidate) is an off-white crystalline powder or a white crystalline solid with a slight sulfurous odor. 

While oxamyl, a carbamate, is stable in solid form and in most solutions, it decomposes to innocuous

materials in natural waters and in soils. These insecticides work by blocking the normal functioning of

cholinesterase, an essential nervous system enzyme. Aeration, sunlight, alkalinity, and higher

temperatures increase its rate of decomposition. Toxic fumes of nitrogen oxides and sulfur oxides are

emitted if oxamyl is heated to decomposition. Oxamyl is noncorrosive. It is available in a variety of

formulations, such as a 24% water- soluble liquid and 10% granules (EXTOXNET, 1998). Oxamyl is

used to kill and control a broad spectrum of insects, as an acaricide to control mites and ticks, and as a

nematicide against roundworms. Its action is both systemic and contact. Oxamyl may be applied directly

on plants or on the soil surface (USEPA, 2001). 

In 1982, U.S. production of oxamyl was reported to be 400,000 pounds (USEPA, 2001), but production

appears to have dropped off by the late 1980s (Wade Miller, 1989). A systemic and contact

insecticide/acaricide and nematocide, oxamyl is a restricted use pesticide used on apples, bananas,

carrots, celery, citrus, cotton, cucumbers, eggplants, garlic, ginger, muskmelon (including cantaloupe and

honeydew melon), onion (dry bulb), peanuts, pears, peppers, peppermint, pineapples, plantains, potatoes,

pumpkins, soybeans, spearmint, squash, sweet potatoes, tobacco, tomatoes, watermelons, and yams. 

Oxamyl is also used on non-bearing apple, cherry, citrus, peach, pear, and tobacco (USEPA, 2001).

Recent national estimates of agricultural use for oxamyl are available. The United States Geological

Survey (USGS, 1998a) estimates approximately 750,000 pounds of oxamyl active ingredient were used

in 1992, and were applied to roughly 1.6 million acres (USGS, 2000). These estimates were derived

using State-level data sets on pesticide use rates available from National Center for Food and

Agricultural Policy (NCFAP) combined with county-level data on harvested crop acreage from the

Census of Agriculture (Thelin and Gianessi, 2000). EPA estimates that on average approximately

800,000 pounds of oxamyl active ingredient (ai) are used per year (USEPA, 2000a). Cotton accounts for

the majority of usage (600,000 pounds oxamyl ai), while intermediate use can be found on several other

crops as well (e.g., apples, celery, potatoes, and tomatoes, see Figure 3.11-1). Although cotton accounts

for most of the oxamyl usage, it is used on only 7% of cotton produced annually in the United States

(USEPA, 2000a). Cotton application is 1 to 2 times per season, usually at a rate of about 0.4 lb oxamyl

ai per acre. When oxamyl is used on other crops, it is generally applied 1 to 3 times per season at

between 0.2 and 1.0 lb ai per acre (the current label rates do allow for higher use rates on some crops)

(USEPA, 2000a). 

Figure 3.11-1 shows the USGS (1998a) derived geographic distribution of estimated average annual

oxamyl use in the United States for 1992. Oxamyl is used in cotton production as well as on a variety of

fruit and root crops, its use is geographically distributed across the United States. The two largest

concentrations of oxamyl use are seen in the cotton production regions of the Texas panhandle and the

lower Mississippi River Valley, including Alabama. Texas ranks as one of the largest producers of

cotton, and therefore has the highest oxamyl usage (USEPA, 2000a). Oxamyl’s application on potato,

fruit, and vegetable production is apparent with high oxamyl use identified in the Pacific Northwest,

California, and Florida (Figure 3.11-1). While non-agricultural uses are not reflected here (USGS,

1998b), existing data suggest that non-agricultural use of oxamyl is minimal to non-existent (USEPA,

2000b). In addition, the map does not provide any further resolution that county-level, obscuring any

intra-county usage differences (USGS, 1998b). A comparison of this use map with the map of the 16

cross-section States (Figure 1.3-1) shows that States across the range of high of low oxamyl use are well

represented in the cross-section.
Occurrence Summary and Use Support Document March 2002 240

Figure 3.11-1: Estimated Annual Agricultural Use for Oxamyl (1992)

Source: USGS 1998a

3.11.2 Environmental Release

Oxamyl is released directly to the environment when used as an insecticide and potentially during its

manufacture, handling and storage. EPA estimated that 400,000 pounds of oxamyl were produced in the

U.S. in 1982 (USEPA, 2001). Oxamyl is not listed as a Toxics Release Inventory (TRI) contaminant, so

no TRI release records are maintained. Therefore, the use of oxamyl (described in the previous section)

may provide the primary indication of where releases are most likely. The areas of highest oxamyl use

are in the cotton production regions of the Texas panhandle, the lower Mississippi River Valley, and on

the fruit and vegetable production areas in the Pacific Northwest, California, and Florida. These and

other agricultural use areas are illustrated in Figure 3.11-1. 

3.11.3 Ambient Occurrence

Oxamyl is an analyte for both surface and ground water NAWQA studies, with a method detection limit

(MDL) of 0.018 :g/L. Additional information on analytical methods used in the NAWQA study units,

including method detection limits, are described by Gilliom and others (1998). 

Oxamyl is an analyte for both surface and ground water NAWQA studies. Table 3.11-1 summarizes the

findings of USGS NAWQA sampling for oxamyl within the first 20 NAWQA study basins. Oxamyl

concentrations in all of the surface water samples were below the detection limit in most sites, although it

was detected in at least one sample. No oxamyl was detected in any of the ground water NAWQA study

sites.
Occurrence Summary and Use Support Document March 2002 241

Table 3.11-1: Oxamyl Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

all samples > 0.01 :g/L > 0.05 :g/L 10th median 95th max

surface water

agricultural ND -- ND <MDL <MDL <MDL <MDL

urban ND -- ND <MDL <MDL <MDL <MDL

integrator ND -- ND <MDL <MDL <MDL <MDL

all sites 0.03% -- 0.03% <MDL <MDL <MDL 0.07

ground water

agricultural ND -- ND <MDL <MDL <MDL --

urban ND -- ND <MDL <MDL <MDL --

major aquifers ND -- ND <MDL <MDL <MDL --

all sites ND -- ND <MDL <MDL <MDL –

ND=No detect

Source: USGS, 1998c

3.11.3.2 Additional Ambient Occurrence Data

A summary document entitled “Occurrence and Exposure Assessment of Oxamyl in Public Drinking

Water Supplies” (Wade Miller, 1989), was previously prepared for past USEPA assessments of oxamyl. 

One regional study was reviewed in that document that addressed levels of oxamyl in water withdrawn

from ground water sources. The following information is taken directly from that document.

Cohen et al. (1984, as cited in Wade Miller, 1989) summarized unpublished data from EPA’s pesticide

registration files. Oxamyl was detected in ground water samples collected from Long Island, New York,

at concentrations ranging from 5 to 65 :g/L. The detection limit, number of samples tested, and the

number of positive samples were not reported. 

The Pesticides in Groundwater Data Base, developed by EPA’s Offices of Pesticide Programs (OPP),

contains information derived from monitoring studies conducted by pesticide registrants, universities,

and government agencies. The data are presented in several categories, including all information

collected to date (excluding data known to be of poor quality and data that is from point source

contamination); data derived from scientifically confirmed agricultural use; and confirmed information

attributed to known point sources and documented misuse. While extreme care was taken to confirm

detections of pesticides in ground water , the authors caution that the studies investigated have not been

limited to drinking water supplies and some studies included samples from many types of wells including

observation and irrigation wells. In addition, many studies have focused on shallow ground water, which

may not be representative of drinking water sources in the area. As such, the results cannot be used to

estimate human exposure to pesticides in drinking water, but do provide an additional assessment of

possible oxamyl occurrence.
Occurrence Summary and Use Support Document March 2002 242

3.11.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of oxamyl occurrence in drinking water presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.2 mg/L; 0.04 mg/L; 0.03 mg/L; 0.02

mg/L; and 0.007 mg/L. 

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

oxamyl. These data represent more than 47,000 analytical results from approximately 13,000 PWSs

during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The number of

sample results and PWSs vary by State, although the State data sets have been reviewed and checked to

ensure adequacy of coverage and completeness. The overall modal detection limit for oxamyl in the 16

cross-section States is equal to 0.002 mg/L. (For details regarding the 16-State cross-section, please refer

to Section 1.3.5 of this report.)

3.11.4.1 Stage 1 Analysis Occurrence Findings

Table 3.11-2 illustrates the very low occurrence of oxamyl in drinking water for the public water systems

in the 16-State cross-section . No ground water or surface water PWSs had any analytical results greater

than 0.2 mg/L, 0.04 mg/L, or 0.03 mg/L. About 0.00760% of total ground and surface water systems had

analytical results greater than 0.02 mg/L (approximately 1 system). Approximately 0.0304% of systems

(4 systems) had any analytical detections greater than 0.007 mg/L. Only 1 (0.00848% of) ground water

system had any exceedances of 0.02 mg/L. Four (0.0339% of) ground water systems had at least one

analytical result greater than 0.007 mg/L. No surface water systems had analytical results greater than

any of the thresholds.

Table 3.11-2: Stage 1 Oxamyl Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.2 0.000% 0

0.04 0.000% 0

0.03 0.000% 0

0.02 0.00848% 1

0.007 0.0339% 4

Surface Water

0.2 0.000% 0

0.04 0.000% 0

0.03 0.000% 0

0.02 0.000% 0

0.007 0.000% 0
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 243

Combined Ground &

Surface Water

0.2 0.000% 0

0.04 0.000% 0

0.03 0.000% 0

0.02 0.00760% 1

0.007 0.0304% 4

Reviewing oxamyl occurrence in the 16 cross-section States by PWS population served (Table 3.11-3)

shows that approximately 0.00162% of the population (about 1,500 people) was served by PWSs with

analytical detections of oxamyl greater than 0.02 mg/L. The number of people exposed to oxamyl

drastically increased to about 51,300 (approximately 0.0555%) when evaluated relative to 0.007 mg/L. 

Approximately 0.00391% of people served by ground water systems were exposed to oxamyl at levels

greater than 0.02 mg/L. The percentage of population served by ground water systems exposed to

oxamyl at levels greater than 0.007 mg/L was equal to 0.134%. When evaluated relative to 0.2 mg/L,

0.04 mg/L, or 0.03 mg/L, the percent of population exposed to oxamyl was equal to 0% for all system

types. No surface water systems exceeded any of the specified health thresholds. 

Table 3.11-3: Stage 1 Oxamyl Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.2 0.000% 0

0.04 0.000% 0

0.03 0.000% 0

0.02 0.00391% 1,500

0.007 0.134% 51,300

Surface Water

0.2 0.000% 0

0.04 0.000% 0

0.03 0.000% 0

0.02 0.000% 0

0.007 0.000% 0

Combined Ground &

Surface Water

0.2 0.000% 0

0.04 0.000% 0

0.03 0.000% 0

0.02 0.00162% 1,500

0.007 0.0555% 51,300
Occurrence Summary and Use Support Document March 2002 244

3.11.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.11-4 and

3.11-5. The statistically generated best estimate values, as well as the ranges around the best estimate

value, are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this

report. For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation

Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water

Regulations (USEPA, 2002)). 

No ground water or surface water PWSs had an estimated mean concentration of oxamyl exceeding 0.2

mg/L, 0.04 mg/L, 0.03 mg/L, or 0.02 mg/L. Approximately 0.0000456% of all PWSs in the 16 States

(less than 1 system) had estimated mean concentration values of oxamyl greater than 0.007 mg/L. The

percentage of ground water PWSs in the 16 States estimated to have a mean concentration greater than

0.007 mg/L was equal to 0.0000509%. No surface water PWSs had estimated mean concentration

exceeding any of the five specified concentration thresholds.

Table 3.11-4: Stage 2 Estimated Oxamyl Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.2 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.03 0.000% 0.000% - 0.000% 0 0 - 0

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.0000509% 0.000% - 0.000% 0 0 - 0

Surface Water

0.2 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.03 0.000% 0.000% - 0.000% 0 0 - 0

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.2 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.03 0.000% 0.000% - 0.000% 0 0 - 0

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.0000456% 0.000% - 0.000% 0 0 - 0
Occurrence Summary and Use Support Document March 2002 245

Reviewing oxamyl occurrence by PWS population served (Table 3.11-5) shows that approximately

0.0000323% of population served by all PWSs in the 16-State cross-section were potentially exposed to

oxamyl levels above 0.007 mg/L. The percentage of population served by ground water systems in the

16 States relative to 0.007 mg/L was equal to 0.0000777%. (No surface water systems exceeded any of

the specified health thresholds.) When evaluated relative to a threshold of 0.2 mg/L, 0.04 mg/L, 0.03

mg/L, and 0.02 mg/L, the percent of population exposed was equal to 0% for all system types.

Table 3.11-5: Stage 2 Estimated Oxamyl Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.2 0.00000% 0.000% - 0.000% 0 0 - 0

0.04 0.00000% 0.000% - 0.000% 0 0 - 0

0.03 0.00000% 0.000% - 0.000% 0 0 - 0

0.02 0.00000% 0.000% - 0.000% 0 0 - 0

0.007 0.0000777% 0.000% - 0.000% 0 0 - 0

Surface Water

0.2 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.03 0.000% 0.000% - 0.000% 0 0 - 0

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.2 0.000% 0.000% - 0.000% 0 0 - 0

0.04 0.000% 0.000% - 0.000% 0 0 - 0

0.03 0.000% 0.000% - 0.000% 0 0 - 0

0.02 0.000% 0.000% - 0.000% 0 0 - 0

0.007 0.0000323% 0.000% - 0.000% 0 0 - 0

3.11.4.3 Estimated National Occurrence

As illustrated in Table 3.11-6, the Stage 2 analysis estimates zero systems serving none of the national

population have estimated mean concentration values of oxamyl greater than 0.2 mg/L, 0.04 mg/L, 0.03

mg/L, or 0.02 mg/L. Approximately 1 ground water system serving less than 100 people nationally was

estimated to have a mean concentration value of oxamyl greater than 0.007 mg/L. (See Section 1.4 for a

description of how Stage 2 16-State estimates are extrapolated to national values.)
Occurrence Summary and Use Support Document March 2002 246

Table 3.11-6: Estimated National Oxamyl Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.2 0 0 - 0 0 0 - 0

0.04 0 0 - 0 0 0 - 0

0.03 0 0 - 0 0 0 - 0

0.02 0 0 - 0 0 0 - 0

0.007 1 0 - 0 < 100 0 - 0

Surface Water

0.2 0 0 - 0 0 0 - 0

0.04 0 0 - 0 0 0 - 0

0.03 0 0 - 0 0 0 - 0

0.02 0 0 - 0 0 0 - 0

0.007 0 0 - 0 0 0 - 0

Combined Ground

& Surface Water

0.2 0 0 - 0 0 0 - 0

0.04 0 0 - 0 0 0 - 0

0.03 0 0 - 0 0 0 - 0

0.02 0 0 - 0 0 0 - 0

0.007 1 0 - 0 < 100 0 - 0

3.11.5 Additional Drinking Water Occurrence Data

For previously prepared USEPA assessments of oxamyl, discussed in Section 3.11.3.1, a literature search

was conducted and knowledgeable sources within the Office of Water were contacted. No national

studies were found on the occurrence of oxamyl in drinking water from ground water or surface water

sources nor were any regional or State studies found that addressed the occurrence of oxamyl in drinking

water from surface water sources (Wade Miller, 1989). Although the studies reviewed include oxamyl

occurrence information and/or data, none of the studies discussed provide the quantitative analytical

results or comprehensive coverage that would enable direct comparison to the occurrence findings

estimated with the cross-section occurrence data and presented in Section 3.11.4. All the following

information in Section 3.11.5 is taken directly from “Occurrence and Exposure Assessment of Oxamyl in

Public Drinking Water Supplies” (Wade Miller, 1989).

One county-level study was identified. Summary data were obtained from a drinking water well

pesticide sampling program conducted by Suffolk County Department of Health Services of

Massachusetts during 1980 to 1985. Oxamyl residues were detected at 0.001 to 0.049 mg/L in 2.9

percent (455) of the 15,535 samples tested. The average concentration was 0.01 mg/L. During the five

year period less than 0.1 percent (11) of the samples exceeded 0.05 mg/L (Dougherty, 1987, as cited in

Wade Miller, 1989). Additional summary data were obtained from a Massachusetts interagency

pesticide monitoring program of 341 public and private water sources in 27 communities. Of the 146
Occurrence Summary and Use Support Document March 2002 247

wells sampled for oxamyl, 1 was positive at the detection limit of 0.001 :g/L (Dougherty, 1987, as cited

in Wade Miller, 1989).

3.11.6 Conclusion

A systemic and contact insecticide/acaricide and nematocide, oxamyl is a restricted use pesticide used on

apples, bananas, carrots, celery, citrus, cotton, cucumbers, eggplants, garlic, ginger, muskmelon

(including cantaloupe and honeydew melon), onion (dry bulb), peanuts, pears, peppers, peppermint,

pineapples, plantains, potatoes, pumpkins, soybeans, spearmint, squash, sweet potatoes, tobacco,

tomatoes, watermelons, and yams. Oxamyl is also used on non-bearing apple, cherry, citrus, peach, pear,

and tobacco. Recent national estimates of agricultural use for oxamyl are available. The United States

Geological Survey estimates approximately 750,000 pounds of oxamyl active ingredient were used in

1992, and were applied to roughly 1.6 million acres. Oxamyl is not a TRI chemical, so there is no

information available on releases. Oxamyl was an analyte for the NAWQA ambient occurrence studies. 

In the NAWQA study, the median value of oxamyl for both ground water and surface water was less than

the detection limit. The Stage 2 analysis, based on the 16-State cross-section, estimated that zero percent

of combined ground water and surface water systems serving zero percent of the population exceeded the

MCL of 0.2 mg/L. Based on this estimate, zero PWSs nationally are estimated to have oxamyl levels

greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. According to information from USGS, 12 of the 16 cross-section States use oxamyl,

although most States in light to moderate amounts. Oxamyl is used most heavily in California, Texas,

Florida, and the Northeast; these States/regions are represented by five of the cross-section States. As

there is no TRI or other data, agricultural use seems to be the only basis for comparison between the 16

States and the nation. In the case of oxamyl, the cross-section should adequately represent the

occurrence of oxamyl on a national scale based upon the use, production, and release patterns of the 16-

State cross-section in relation to the patterns observed for all 50 States.

3.11.7 References

Cohen S.Z., S.M. Creeger, R.F. Carsel, and C.G. Enfield. 1984. Potential Pesticide Contamination of

Ground Water Resulting from Agricultural Uses. In: Treatment and Disposal of Pesticide

Wastes. Washington, DC. R.F. Kruger and J.W. Seiber (eds.). ACS Symposium Series No. 259: 

pp. 247-325.

Dougherty, T.M. 1987. Oxamyl - EAB science chapter for the registration standard. Memorandum from

Therese M. Dougherty, Exposure Assessment Branch, to Dennis Edwards, Insecticide - 

Rodenticide Branch, Office of Pesticide Programs, U.S. Environmental Protection Agency,

Arlington, VA. February 11, 1987.

EXTOXNET. 1996. Pesticide Information Profile: Oxamyl. Ithaca, NY: Extension Toxicology

Network, Pesticide Management Education Program. Available on the Internet at

http://ace.ace.orst.edu/info/extoxnet/pips/oxamyl.htm, revised June, 1996. 

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at: 

http://ca.water.usgs.gov/pnsp/rep/ofr97589, last updated October 9, 1998.
Occurrence Summary and Use Support Document March 2002 248

Thelin, G.P., and L.P. Gianessi. 2000. Method for Estimating Pesticide Use for County Areas of the

Conterminous United States. U.S. Geological Survey Open-File Report 00-250. 

62 pp. Available on the Internet at: http://water.wr.usgs.gov/pnsp/rep/ofr00250/ofr00250.pdf

USEPA. 2000a. Interim Reregistration Eligibility Decision (IRED): Oxamyl. EPA Report 738-R-00-

015. Washington, DC: Office of Prevention, Pesticides, and Toxic Substances, USEPA. 135 pp. 

October 2000. Available on the Internet at: http://www.epa.gov/REDs/0253ired.pdf

USEPA. 2000b. R.E.D. Facts: Oxamyl. EPA Report 738-F-00-013. Washington, DC: Office of

Prevention, Pesticides, and Toxic Substances, USEPA. 4 pp. November 2000. Available on the

Internet at: http://www.epa.gov/oppsrrd1/REDs/factsheets/0253iredfact.pdf, last updated June

21, 2001. 

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: OXAMYL

(VYDATE). Available on the Internet at: http://www.epa.gov/safewater/dwh/c-soc/oxamyl.html,

last updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1998a. Annual Use Maps. Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/,

last updated March 20, 1998.

USGS. 1998b. Sources & Limitations of Data Used to Produce Maps of Annual Pesticide Use. 

Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/mapex.html, last updated

March 20, 1998.

USGS. 1998c. Pesticides in Surface and Ground Water of the United States: Summary of Results of the

National Water Quality Assessment Program (NAWQA). PROVISIONAL DATA -- SUBJECT TO

REVISION. Available on the Internet at: http://water.wr.usgs.gov/pnsp/allsum/, last updated

October 9, 1998. 

USGS. 2000. PESTICIDES ANALYZED IN NAWQA SAMPLES: Use, Chemical Analyses, and

Water-Quality Criteria (PROVISIONAL DATA -- SUBJECT TO REVISION). Available on the

Internet at: http://water.wr.usgs.gov/pnsp/anstrat/, last updated August 20, 1999. 

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Oxamyl in Public

Drinking Water Supplies - DRAFT. Draft report submitted to EPA for review April 12, 1989.
Occurrence Summary and Use Support Document March 2002 249

3.12 Picloram

Table of Contents

3.12.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250

3.12.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

3.12.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

3.12.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . 253

3.12.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

3.12.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

3.12.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

Tables and Figures

Figure 3.12-1: Picloram Estimated Annual Agricultural Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

Table 3.12-1: Environmental Releases (in pounds) for Picloram in the United States, 1995-1999 . . . 252

Table 3.12-2: Picloram Detections and Concentrations in Surface Water and Ground Water . . . . . . . 252

Table 3.12-3: Stage 1 Picloram Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . 254

Table 3.12-4: Stage 1 Picloram Occurrence Based on 16-State Cross-Section - Population . . . . . . . . 254

Table 3.12-5: Stage 2 Estimated Picloram Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

Table 3.12-6: Stage 2 Estimated Picloram Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256

Table 3.12-7: Estimated National Picloram Occurrence - Systems and Population Served . . . . . . . . . 256
Occurrence Summary and Use Support Document March 2002 250

3.12.1 Introduction, Use and Production

Picloram, (4-amino-3,5,6-trichloropicolinic acid) in the pyridine family of compounds, is a crystalline

organic solid with a chlorine-like odor. Picloram is formulated either as an acid (technical product) or as

a potassium salt. In salt form, it is used as a systemic herbicide. It is used for controlling annual weeds

on crops, and in combination with 2,4-D or 2,4,5-T against perennials on non-croplands for brush

control. It also controls a wide range of broad-leaved weeds excepting mustards (crucifers). Most

grasses are resistant to picloram so it is used in range management programs. Picloram is used to control

bitterweed, knapweed, leafy spurge, locoweed, larkspur, mesquite, prickly pear, and snakeweed on

rangeland in the western States (USEPA, 2001). Commercial products containing picloram have trade

names including Grazon and Tordon. The compound may be used in formulations with other herbicides

such as bromoxynil, atropine, diuron, 2,4-D, MCPA, triclorpyr, and atrazine among others. Picloram is

also compatible with fertilizers (EXTOXNET, 2001). 

Picloram is a systemic herbicide used to control deeply rooted herbaceous weeds and woody plants in

rights-of-way, forestry, rangelands, pastures, and small grain crops (USEPA, 1995). It is applied in the

greatest amounts to pasture and rangeland, followed by forestry. Picloram acid is a manufacturing use

product with no end uses. Picloram products have no household or residential uses. All picloram

products are classified as Restricted Use Pesticides, based on hazard to nontarget plants, and may be

applied only by or under the direct supervision of certified applicators (USEPA, 1995).

No information was found that suggested any natural production of picloram. Picloram is produced

domestically for commercial markets by Dow Chemical USA, and by Union Carbide (Wade Miller,

1989). Picloram is produced by chlorination of a-picoline (2-methylpyridine) and reaction with

ammonia, followed by hydrolysis of the intermediate 4-amino-3,5,6, a, a, a-hexachloropicoline (KirkOthmer, 1980, as cited in Wade Miller, 1989). Domestic production of picloram was estimated to be

between 2.2 and 2.9 million pounds in 1981; approximately 1.4 to 1.9 million pounds were exported

(Schutte, 1982, as cited in Wade Miller, 1989).

Picloram is registered for use on pastureland and rangeland grasses in the following States: Alabama,

Arkansas, Colorado, Georgia, Kansas, Kentucky, Louisiana, Mississippi, Missouri, New Mexico, North

Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia (USEPA, 1981, as

cited in Wade Miller, 1989). Picloram is registered for use on uncultivated agricultural areas, rights-ofway, commercial and industrial premises, forests, and drainage ditch banks in the following States: 

California, Colorado, Hawaii, Idaho, Minnesota, Nebraska, Oregon, South Dakota, Utah, Washington,

West Virginia, and Wyoming (USEPA, 1981, as cited in Wade Miller, 1989).

Recent national estimates of agricultural use for picloram are available. The United States Geological

Survey (USGS) estimates approximately 1.7 million pounds of picloram active ingredient used for the

year 1992, with roughly 7 million acres treated (USGS, 1999). These estimates were derived using Statelevel data sets on pesticide use rates available from NCFAP combined with county-level data on

harvested crop acreage from the Census of Agriculture (CA) (Thelin and Gianessi, 2000). Figure 3.12-1

shows the geographic distribution of estimated average annual picloram use in the United States for 1992

(USGS, 1998a). A breakdown of use by crop is also included. By far, the greatest amount of picloram is

used in pasture (92%). A comparison of this use map with the map of the 16 cross-section States (Figure

1.3-1) shows that States across the range of high of low picloram use are well represented in the crosssection.
Occurrence Summary and Use Support Document March 2002 251

Figure 3.12-1: Picloram Estimated Annual Agricultural Use

Source: USGS, 1998a

3.12.2 Environmental Release

Picloram is listed as a Toxics Release Inventory (TRI) chemical. Table 3.12-1 illustrates the

environmental releases for picloram from 1995 - 1999. (There are only picloram data for these years.) 

Air emissions and surface water discharges are the sole contributors to total on- and off-site releases. 

Between 1995 and 1999, the releases of air emissions fluctuated greatly, with a dramatic increase in 1997

and 1999. Surface water discharges were generally very low, with the exception of a huge peak in 1998

(almost 400,000 pounds). No underground injection, releases to land (such as spills or leaks within the

boundaries of the reporting facility), or off-site releases (including metals or metal compounds

transferred off-site) were reported for picloram. These TRI data for picloram were reported from only

Michigan and Texas (USEPA, 2000), both of which are included in the 16-State cross-section (used for

analyses of picloram occurrence in drinking water; see Section 3.12.4). (For a map of the 16-State crosssection, see Figure 1.3-1.)
Occurrence Summary and Use Support Document March 2002 252

Table 3.12-1: Environmental Releases (in pounds) for Picloram in the United States, 1995-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 2,800 10 -- -- -- 2,810

1998 460 380,006 -- -- -- 380,466

1997 2,900 0 -- -- -- 2,900

1996 522 0 -- -- -- 522

1995 220 1 -- -- -- 221

 Source: USEPA, 2000 

3.12.3 Ambient Occurrence

Picloram is an analyte for both surface and ground water NAWQA studies, with a method detection limit

(MDL) of 0.05 :g/L. Table 3.12-2 summarizes the findings of USGS NAWQA sampling for picloram

within the first 20 NAWQA study basins. Picloram concentrations at all of the surface water sites were

below the detection limit in most sites, although it was detected in at least one sample. Also, picloram

concentrations at all of the ground water sites were below the detection limit in most sites, although it

was detected in at least one sample. 

Table 3.12-2: Picloram Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

all samples > 0.01 :g/L > 0.05 :g/L 10th median 95th max

surface water

agricultural ND -- ND <MDL <MDL <MDL <MDL

urban ND -- ND <MDL <MDL <MDL <MDL

integrator ND -- ND <MDL <MDL <MDL <MDL

all sites 0.15% -- 0.12% <MDL <MDL <MDL 2.7

ground water

agricultural 0.11% -- ND <MDL <MDL <MDL 2.2

urban ND -- ND <MDL <MDL <MDL --

major aquifers ND -- ND <MDL <MDL <MDL --

all sites 0.20% -- 0.20% <MDL <MDL <MDL 2.2

ND=No detect

Source: USGS, 1998b
Occurrence Summary and Use Support Document March 2002 253

3.12.3.2 Additional Ambient Occurrence Data

A summary document entitled “Occurrence and Exposure Assessment of Picloram in Public Drinking

Water Supplies” (Wade Miller, 1989), was previously prepared for past USEPA assessments of picloram. 

In that review, several national studies were included on the occurrence of picloram in both ground water

and surface water non-drinking water sources. The following information is taken directly from

“Occurrence and Exposure Assessment of Picloram in Public Drinking Water Supplies” (Wade Miller,

1989).

3.12.3.2.1 Groundwater Sources

Picloram was detected in five out of 77 groundwater samples collected at 49 locations throughout the

United States. Picloram was detected in seven States. The 85th percentile of all nonzero samples was

1.0 :g/1 in groundwater sources. The maximum concentration found was 1.0 :g/L (USEPA, 1987, as

cited in Wade Miller, 1989). No other sampling information was provided.

The Pesticides in Groundwater Data Base, developed by EPA’s Offices of Pesticide Programs (OPP),

contains information derived from monitoring studies conducted by pesticide registrants, universities,

and government agencies (Williams et al., 1988, as cited in Wade Miller, 1989). The data are presented

in several categories, including all information collected to date (excluding data known to be of poor

quality and data that is from point source contamination); data derived from scientifically confirmed

agricultural use; and confirmed information attributed to known point sources and documented misuse. 

Three States have confirmed detections of picloram in groundwater attributed to normal agricultural use

with a maximum concentration of 49 :g/L and a median concentration of 1.4 :g/L.

While extreme care was taken to confirm detections of pesticides in ground water, the reader is warned

that the studies investigated have not been limited to drinking water supplies. Some studies included

samples from many types of wells including observation and irrigation wells. In addition, many studies

have focused on shallow ground water which may not be representative of drinking water sources in the

area. As such, the results cannot be used to estimates human exposure to pesticides in drinking water,

but do provide an additional assessment of possible picloram occurrence.

3.12.3.2.2 Surface Water Sources

Picloram was detected in 359 out of 653 surface water samples collected at 124 locations throughout the

United States. Picloram was detected in seven States. The 85th percentile of all nonzero samples was

0.13 :g/L in surface water. The maximum concentration found was 4.6 :g/L (USEPA, 1987, as cited in

Wade Miller, 1989). No other sampling information was provided.

3.12.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of picloram occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 1 mg/L; 0.5 mg/L; and 0.05 mg/L.

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

picloram. These data represent almost 46,000 analytical results from approximately 13,000 PWSs during

the period from 1983 to 1998 (with most analytical results from 1992 to 1997). The number of sample

results and PWSs vary by State, although the State data sets have been reviewed and checked to ensure
Occurrence Summary and Use Support Document March 2002 254

adequacy of coverage and completeness. The overall modal detection limit for picloram in the 16 crosssection States is equal to 0.0001 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)

3.12.4.1 Stage 1 Analysis Occurrence Findings

Table 3.12-3 illustrates the very low occurrence of picloram in drinking water for the public water

systems in the 16-State cross-section. No ground water or surface water PWSs (therefore, no population

served by systems, as seen in Table 3.12-4) had any analytical results exceeding 1 mg/L, 0.5 mg/L, or

0.005 mg/L.

Table 3.12-3: Stage 1 Picloram Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

1 0.000% 0

0.5 0.000% 0

0.05 0.000% 0

Surface Water

1 0.000% 0

0.5 0.000% 0

0.05 0.000% 0

Combined Ground &

Surface Water

1 0.000% 0

0.5 0.000% 0

0.05 0.000% 0

Table 3.12-4: Stage 1 Picloram Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Ground Water

1 0.000% 0

0.5 0.000% 0

0.05 0.000% 0

Surface Water

1 0.000% 0

0.5 0.000% 0

0.05 0.000% 0
Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 255

Combined Ground &

Surface Water

1 0.000% 0

0.5 0.000% 0

0.05 0.000% 0

3.12.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.12-5 and

3.12-6. The statistically generated best estimate values, as well as the ranges around the best estimate

value, are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this

report. For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation

Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water

Regulations (USEPA, 2002)). 

No ground water or surface water PWSs (therefore, no population served by systems) had an estimated

mean concentration of picloram exceeding 1 mg/L, 0.5 mg/L or 0.05 mg/L.

Table 3.12-5: Stage 2 Estimated Picloram Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

1 0.000% 0.000% - 0.000% 0 0 - 0

0.5 0.000% 0.000% - 0.000% 0 0 - 0

0.05 0.000% 0.000% - 0.000% 0 0 - 0

Surface Water

1 0.000% 0.000% - 0.000% 0 0 - 0

0.5 0.000% 0.000% - 0.000% 0 0 - 0

0.05 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

1 0.000% 0.000% - 0.000% 0 0 - 0

0.5 0.000% 0.000% - 0.000% 0 0 - 0

0.05 0.000% 0.000% - 0.000% 0 0 - 0
Occurrence Summary and Use Support Document March 2002 256

Table 3.12-6: Stage 2 Estimated Picloram Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

1 0.000% 0.000% - 0.000% 0 0 - 0

0.5 0.000% 0.000% - 0.000% 0 0 - 0

0.05 0.000% 0.000% - 0.000% 0 0 - 0

Surface Water

1 0.000% 0.000% - 0.000% 0 0 - 0

0.5 0.000% 0.000% - 0.000% 0 0 - 0

0.05 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

1 0.000% 0.000% - 0.000% 0 0 - 0

0.5 0.000% 0.000% - 0.000% 0 0 - 0

0.05 0.000% 0.000% - 0.000% 0 0 - 0

3.12.4.3 Estimated National Occurrence

As illustrated in Table 3.12-7, the Stage 2 analysis estimates zero systems serving zero people nationally

have estimated mean concentration values of picloram greater than 1 mg/L, 0.5 mg/L, or 0.05 mg/L. (See

Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to national values.)

Table 3.12-7: Estimated National Picloram Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

1 0 0 - 0 0 0 - 0

0.5 0 0 - 0 0 0 - 0

0.05 0 0 - 0 0 0 - 0

Surface Water

1 0 0 - 0 0 0 - 0

0.5 0 0 - 0 0 0 - 0

0.05 0 0 - 0 0 0 - 0
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 257

Combined Ground

& Surface Water

1 0 0 - 0 0 0 - 0

0.5 0 0 - 0 0 0 - 0

0.05 0 0 - 0 0 0 - 0

3.12.5 Additional Drinking Water Occurrence Data

For a previous USEPA assessment of picloram occurrence in drinking water, a literature search was

conducted and knowledgeable sources within the Office of Water were contacted. No national studies

were found on the occurrence of picloram in drinking water from ground water or surface water sources,

nor were any regional or State studies found that addressed the occurrence of picloram in drinking water

from surface water sources (Wade Miller, 1989). However, some regional studies of ground water were

found. Note that none of the studies presented in the following section provide the quantitative analytical

results or comprehensive coverage that would enable direct comparison to the occurrence findings

estimated with the cross-section occurrence data presented in Section 3.12.4. These additional studies,

however, do enable a broader assessment of the Stage 2 occurrence estimates presented for this Six-Year

Review. All the following information in Section 3.12.5 is taken directly from “Occurrence and

Exposure Assessment of Picloram in Public Drinking Water Supplies” (Wade Miller, 1989).

EPA has developed contamination incidence surveys, which were subsequently distributed to States by

their Federal/State Toxicological and Regulatory Alliance Committee (FSTRAC). As of April 1988, the

contamination incidence surveys of 11 States have been returned and summarized by EPA, Region VII

(Schlachter, 1988, as cited in Wade Miller, 1989). These States include: California, Iowa,

Massachusetts, Michigan, Minnesota, Nebraska, Pennsylvania, Rhode Island, South Dakota, Texas, and

Wisconsin. The summary provided limited information on the occurrence of picloram in public ground

water supplies. Picloram was only detected in South Dakota in two samples from 17 sites, though at

values of 520 and 8,300 :g/L (mean = 4,410 :g/L). No detection limit or other sampling information

was reported.

From July 1985 to June 1987, the Minnesota Departments of Health (MDH) and Agriculture (MDA)

conducted cooperative surveys of observation, irrigation, and drinking water wells for selected pesticides

(MDH and MDA, 1988, as cited in Wade Miller, 1989). These studies were designed to provide

information on the extent of agricultural pesticide contamination in Minnesota's ground water and

drinking water. In the first survey (MDA), picloram was not detected in any of the 100 samples taken. 

The detection limit for the MDA survey was 1.8 :g/L. In the second survey (MDH), picloram was found

in five samples from three wells, out of 400 wells sampled, at a median concentration of 0.16 :g/L (range

= 0.08-0.63 :g/L). The detection limit for the MDH survey was 0.04 :g/L. The summary report did not

distinguish between observation, irrigation, and drinking water wells.
Occurrence Summary and Use Support Document March 2002 258

3.12.6 Conclusion

Picloram is a systemic herbicide used to control deeply rooted herbaceous weeds and woody plants in

rights-of-way, forestry, rangelands, pastures, and small grain crops. Picloram products are all restricted

use pesticides. Approximately 1.7 million pounds of picloram were used in 1992 on pastureland and for

other agricultural applications. The greatest concentrations of use are in Texas, New Mexico, and the

upper Midwest. Industrial releases of picloram have been reported to TRI from two States since 1995. 

Picloram was also an analyte for the NAWQA occurrence studies. In the NAWQA study, picloram was

detected in ground and surface water; however, none of the median values exceeded the detection limit. 

The Stage 2 analysis, based on the 16-State cross-section, estimated that zero percent of combined

ground water and surface water systems serving zero percent of the population exceeded the MCL of 0.5

mg/L. Based on this estimate, zero PWSs nationally are estimated to have picloram levels greater than

the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, according to information from USGS, 14 States use picloram agriculturally,

including 5 of the cross-section States. Picloram use is heaviest in Texas, New Mexico, and Kansas, two

of which are cross-section States. Nationally, TRI releases have been reported for picloram from 2

States, both of which are cross-section States. The cross-section should adequately represent the

occurrence of picloram on a national scale based upon the use, production, and release patterns of the 16-

State cross-section in relation to the patterns observed for all 50 States. 

3.12.7 References

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at: 

http://ca.water.usgs.gov/pnsp/rep/ofr97589/, last updated October 9, 1998. 

EXTOXNET. 2001. Pesticide Information Profile: Picloram. Ithaca, NY: Extension Toxicology

Network, Pesticide Management Education Program. Available on the Internet at

http://ace.ace.orst.edu/info/extoxnet/pips/picloram.htm, revised March, 2001. 

Kirk-Othmer. 1980. Herbicides. In: Kirk-Othmer Encyclopedia of Chemical Technology. Vol. 12, 3rd

ed. New York, NY: John Wiley and Sons. pp. 297-351.

Minnesota Department of Health (MDH) and Minnesota Department of Agriculture (MDA). 1988. 

Pesticides and Groundwater: Surveys of Selected Minnesota Wells. Prepared by Tomas G.

Klaseus (MDH), Greg C. Buzicky (MDA), and Edward C. Schneider (MDH) for Legislative

Commission on Minnesota Resources. February 1988.

Schlachter, J. 1988. Memorandum on Program Improvement Subcommittee, FSTRAC, Preparation for

April Meeting. Sent by Jacquelyn D. Schlachter, Chairman - Program Improvement

Subcommittee, U.S. Environmental Protection Agency, Region VII, Kansas City, KS. Sent to

Dennis Alt, IA; Pam Bonrud, SD; Bill Lee, NE; Kathy Miller, MT; Jennifer Orme, HQ; Sheila

Sullivan, EPA Region V; and Dan Wilson, WI.
Occurrence Summary and Use Support Document March 2002 259

Schutte, W.D. 1982. Preliminary Quantitative Usage Analysis of Picloram. Economic Analysis

Branch, Office of Pesticide Programs, U.S. Environmental Protection Agency, Arlington, VA. 

June, 1982.

Thelin, G.P., and L.P. Gianessi. 2000. Method for Estimating Pesticide Use for County Areas of the

Conterminous United States. U.S. Geological Survey Open-File Report 00-250. 

62 pp. Available on the Internet at: http://water.wr.usgs.gov/pnsp/rep/ofr00250/ofr00250.pdf

USEPA. 1981. EPA Index to Pesticide Chemicals. Picloram, Potassium, Salt. Washington, DC: Office

of Pesticide Programs, USEPA.

USEPA. 1987. Picloram Health Advisory. Washington, DC: Office of Drinking Water, USEPA. 

August, 1987.

USEPA. 1995. Registration Eligibility Decision (RED): Picloram. EPA Report 738-R-95-019. 

Washington, DC: Office of Prevention, Pesticides, and Toxic Substances, USEPA. 283 pp. 

Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/, last updated June 21, 2001. 

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USGS. 1998a. Annual Use Maps. Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/,

last updated March 20, 1998.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: PICLORAM. 

Available on the Internet at: http://www.epa.gov/safewater/dwh/c-soc/picloram.html, last

updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1998b. Pesticides in Surface and Ground Water of the United States: Summary of Results of the

National Water Quality Assessment Program (NAWQA). PROVISIONAL DATA -- SUBJECT TO

REVISION. Available on the Internet at: http://water.wr.usgs.gov/pnsp/allsum/ last updated

October 9, 1998. 

USGS. 1999. PESTICIDES ANALYZED IN NAWQA SAMPLES: Use, Chemical Analyses, and

Water-Quality Criteria (PROVISIONAL DATA -- SUBJECT TO REVISION). Available on the

Internet at: http://water.wr.usgs.gov/pnsp/anstrat/, last updated August 20, 1999. 

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Picloram in Public

Drinking Water Supplies. Prepared for and submitted to EPA on April 24, 1989. 

Williams, W.M., P.W. Holden, D.W. Parsons, and M.N. Lorber. 1988. Pesticides in groundwater Data

Base. Washington, DC: Office of Pesticide Programs, U.S. Environmental Protection Agency.
Occurrence Summary and Use Support Document March 2002 260

3.13 Simazine

Table of Contents

3.13.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

3.13.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

3.13.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263

3.13.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . 266

3.13.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

3.13.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274

3.13.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274

Tables and Figures

Figure 3.13-1: Estimated Annual Agricultural Use for Simazine (1992) . . . . . . . . . . . . . . . . . . . . . . . 262

Table 3.13-1: Environmental Releases (in pounds) for Simazine in the United States, 1995-1999 . . . 263

Table 3.13-2: Simazine Detections and Concentrations in Surface Water and Ground Water . . . . . . 263

Table 3.13-3: Stage 1 Simazine Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . 267

Table 3.13-4: Stage 1 Simazine Occurrence Based on 16-State Cross-Section - Population . . . . . . . . 267

Table 3.13-5: Stage 2 Estimated Simazine Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

Table 3.13-6: Stage 2 Estimated Simazine Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

Table 3.13-7: Estimated National Simazine Occurrence - Systems and Population Served . . . . . . . . 270

Table 3.13-8: Frequency of Surface Water Contamination by Simazine - National 

Screening Program for Organics in Drinking Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
Occurrence Summary and Use Support Document March 2002 261

3.13.1 Introduction, Use and Production

Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], is an organic white solid. It is available in wettable

powder, water dispersible granule, liquid, and granular formulations. It may also be soil-applied

(EXTOXNET, 1996). Simazine is used on a variety of deep-rooted crops such as artichokes, asparagus,

berry crops, broad beans, citrus, etc., and on non-crop areas such as farm ponds and fish hatcheries. Its

major use is on corn where it is often combined with AAtrex. Other herbicides with which simazine is

combined include: paraquat, on apples, peaches; Roundup or Oust for non-crop use; Surflan on

Christmas trees; Dual on corn and ornamentals (USEPA, 2001). 

Simazine is a selective triazine herbicide (EXTOXNET, 1996). It is used as a pre-emergence herbicide

for control of broad-leaved and grassy weeds on a variety of deep-rooted crops such as artichokes,

asparagus, berry crops, broad beans, citrus, etc., and on non-crop areas. Its major use is on corn

(USEPA, 2001). At higher rates, simazine is used for nonselective weed control in industrial areas. 

Before 1992, it was used to control submerged weeds and algae in large aquariums, farm ponds, fish

hatcheries, swimming pools, ornamental ponds, and cooling towers (EXTOXNET, 1996). In 1975, the

consumption pattern of simazine was approximately as follows: 49%, corn; 8%, citrus; 6%, deciduous

fruits; 5%, field crops; 3%, vegetables; 17%, industrial commercial uses; and 13%, aquatic uses (HSDB,

2001).

Two manufacturers of simazine are Drexel Chemical Company in Memphis, TN and Novartis

Corporation in Summit, NJ. Although production data is seemingly scarce, there is information on

consumption of simazine in the U.S. Agricultural use of simazine by year is approximately as follows: in

1989, 3.96 million pounds active ingredient (ai); 1982, 3.98 million pounds ai; 1976, 3.25 million pounds

ai; 1971, 1.74 million pounds ai; and 1966, 193,000 pounds ai (HSDB, 2001).

Recent national estimates of agricultural use for simazine are available. Figure 3.13-1 illustrates the

USGS (1998a) derived geographic distribution of estimated average annual simazine use in the United

States for 1992. USGS (1998a) estimates approximately 4.81 million pounds of simazine active

ingredient were used in 1992. A breakdown of use by crop is also included. Corn accounts for the

majority of usage (2.35 million pounds simazine active ingredient), while intermediate use can be found

on several other crops as well (e.g., citrus, grapes, alfalfa, apples, peaches, almonds, etc.) (USGS, 1998a). 

The two largest concentrations of simazine use are seen in the corn growing area of the Midwest and the

citrus areas in California and Florida, with some concentration also in the Mid-Atlantic States and

Washington State (Figure 3.13-1). Note that non-agricultural uses are not reflected here, and any sharp

spatial differences in use within a county may not be well represented (USGS, 1998b). A comparison of

this use map with the map of the 16 cross-section States (Figure 1.3-1) shows that States across the range

of high of low simazine use are well represented in the cross-section.
Occurrence Summary and Use Support Document March 2002 262

Figure 3.13-1: Estimated Annual Agricultural Use for Simazine (1992)

Source: USGS, 1998a

3.13.2 Environmental Release

Simazine is listed as a Toxics Release Inventory (TRI) chemical. Table 3.13-1 illustrates the

environmental releases for simazine from 1995 - 1999. (There are only simazine data for these years.) 

From 1995 to 1999, the releases of air emissions has generally decreased. Surface water discharges

generally hovered around 300 pounds. No underground injection or releases to land (with the exception

of 5 pounds reported in 1995) were reported for simazine. The amount of off-site releases (including

metals or metal compounds transferred off-site) has steadily decreased since 1995, with a dramatic

decrease in 1998. Decreases in air emissions and off-site releases have predominantly contributed to the

decreasing amount of total on- and off-site simazine releases. These TRI data for simazine were reported

from 8 States. Four of these 8 States reported TRI data every year (USEPA, 2000). Two of the 8 States

(Alabama and Nebraska) are included in the 16-State cross-section (used for analyses of simazine

occurrence in drinking water; see Section 3.13.4). (For a map of the 16-State cross-section, see Figure

1.3-1.)
Occurrence Summary and Use Support Document March 2002 263

Table 3.13-1: Environmental Releases (in pounds) for Simazine in the United States, 1995-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 3,928 385 -- 0 2,385 6,698

1998 3,321 332 -- 0 4,497 8,150

1997 2,939 348 0 0 48,629 51,916

1996 4,591 93 0 0 54,457 59,141

1995 4,990 232 -- 5 26,231 31,458

 Source: USEPA, 2000 

3.13.3 Ambient Occurrence

Simazine is an analyte for both surface and ground water NAWQA studies, with a method detection limit

(MDL) of 0.005 :g/L. Additional information on analytical methods used in the NAWQA study units,

including method detection limits, are described by Gilliom and others (1998). 

Table 3.13-2 summarizes the findings of USGS NAWQA sampling for simazine within the first 20

NAWQA study basins (USGS, 1998c). Simazine concentrations at ground and surface sites exceed the

detection limit in all sites. High percentages of both ground and surface water samples exceed detection

frequencies of 0.01 and 0.05 :g/L, although surface water sample percentages are notably higher than

ground water sample percentages. Within surface water sites, urban sites have consistently higher

percentage exceeding the detection frequencies then agricultural or integrator sites. Within ground water

sites, agricultural sites have consistently higher percentage exceeding the detection frequencies then

urban or integrator sites. The 95th percentile value and maximum concentration also exceed the detection

limit in all ground and surface water sites. The median concentration values exceed the detection limit

for all surface water sites, while none of the median concentration values exceed the detection limit for

any ground water sites.

Table 3.13-2: Simazine Detections and Concentrations in Surface Water and Ground Water

Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

all samples > 0.01 :g/L > 0.05 :g/L 10th median 95th max

surface water

agricultural 61.74% 44.76% 16.98% <MDL 0.007 0.27 5.76E

urban 87.77% 80.73% 40.67% <MDL 0.039 0.67 8.2E

integrator 82.93% 64.63% 27.64% <MDL 0.017 0.21 1.3

all sites 65.61% 53.86% 25.35% <MDL 0.012 0.38 20E
Detection frequency

 (% of samples)

Concentration percentiles

(all samples; :g/L) 

Occurrence Summary and Use Support Document March 2002 264

ground water

agricultural 22.38% 13.30% 4.54% <MDL <MDL 0.042 1.3

urban 15.28% 11.30% 3.65% <MDL <MDL 0.03 1.1

major aquifers 6.32% 3.00% 0.75% <MDL <MDL 0.003 0.11

all sites 15.91% 9.52% 3.27% <MDL <MDL 0.024 1.3

Note: Individual maximum values with an “E-code” have much greater uncertainty because the values were beyond the calibration range.

Source: USGS, 1998c

Simazine was also an analyte in the 1999 Pilot Monitoring Program (Blomquist et. al, 2001). Simazine

was detected in almost 30% of the 323 raw water samples and in about 84% of the 228 finished water

samples. The 95th percentile value was equal to 0.028 :g/L and 0.385 :g/L for raw and finished water

samples, respectively. The maximum concentration of simazine in raw water was 1.520 :g/L. In

finished water, the maximum concentration of simazine was 0.571 :g/L.

3.13.3.1 Additional Ambient Occurrence Data

A summary document entitled “Occurrence and Exposure Assessment of Simazine in Public Drinking

Water Supplies” (Wade Miller, 1989), was previously prepared for past USEPA assessments of simazine. 

In that review, several national and regional studies were included on the occurrence of simazine in both

ground water and surface water non-drinking water sources. The following information is taken directly

from “Occurrence and Exposure Assessment of Simazine in Public Drinking Water Supplies” (Wade

Miller, 1989).

3.13.3.1.1 Groundwater Sources – National Studies

Simazine has been found in 229 of 2,282 groundwater samples (USEPA, 1987, as cited in Wade Miller,

1989). Samples were collected at 1,730 groundwater locations, and simazine was detected in 22 States. 

The 85th percentile of all nonzero samples was 1.60 :g/L in groundwater sources. The maximum

concentration found in groundwater was 800 :g/L. No further information was provided.

The USEPA Office of Pesticide Programs developed a data base containing information derived from

monitoring studies conducted by pesticide registrants, universities, and government agencies (Williams et

al., 1988, as cited in Wade Miller, 1989). Six categories were designed to present the data; category 2

which includes all information collected except for data known to be of poor quality and data that is from

known point source contamination; category 5 which includes data derived from scientifically confirmed

studies where contamination is known to be solely due to normal agricultural use; and category 6 which

includes confirmed information attributed to known sources or documented misuse. Seven States are

reported to have confirmed detections of simazine in groundwater due to normal agricultural use. The

maximum concentration reported was 9.1 :g/L. The median concentration reported was 0.3 :g/L.

The authors (Wade Miller, 1989) note that because studies included in the data base have not been

confined to drinking water supplies, some studies include samples from many types of wells including

observation and irrigation wells. In addition, since many studies have focused on shallow ground water,
Occurrence Summary and Use Support Document March 2002 265

they may not be representative of drinking water sources in the area. For these reasons, use of these data

for the estimation of human exposure to pesticides in drinking water is not advised.

3.13.3.1.2 Groundwater Sources – Regional Studies

The U.S. Environmental Protection Agency has developed contamination incidence surveys, that have

been subsequently distributed to States by their Federal/State Toxicological and Regulatory Alliance

Committee (FSTRAC). As of April 1988, the contamination incidence surveys of 11 States had been

returned and summarized by EPA, Region VII (Schlachter, 1988, as cited in Wade Miller, 1989). These

States include: California, Iowa, Massachusetts, Michigan, Minnesota, Nebraska, Pennsylvania, Rhode

Island, South Dakota, Texas and Wisconsin. The summary provided limited information on the

occurrence of simazine in ground water. Simazine was only detected in Wisconsin in four samples from

28 sites, at a range of 1.0-15.0 :g/L. No other sampling information was reported. It is unclear whether

these detections are representative of ambient water or drinking water.

In a recent California study on the movement of pesticides and herbicides to groundwater (Cohen et al.,

1984, as cited in Wade Miller, 1989), collected samples to determine the levels of simazine in

groundwater. In analyses of samples collected from 166 wells, 6 wells were found to be contaminated

with simazine at levels between 0.5 :g/L and 3.5 :g/L. The limits of detection were not reported.

3.13.3.1.3 Surface Water Sources – National Studies

Simazine has been found in 877 of 5,067 surface water samples analyzed throughout the United States

(USEPA, 1987, as cited in Wade Miller, 1989). Samples were collected at 472 surface water locations,

and simazine was detected in 22 States. The 85th percentile of all nonzero samples was 2.18 :g/L. The

maximum concentration found in surface water was 1,300 :g/L.

Carey and Kutz (1983, as cited in Wade Miller, 1989) summarized a study on water samples collected

and analyzed for pesticides and herbicides as part of the National Surface Water Monitoring Program. 

During the collection period (1976 to 1980), 0.4 percent of the samples tested contained levels of

simazine in excess of the detection limit, with a maximum reported value of 1.13 :g/L. The detection

limits were not reported.

3.13.3.1.4 Surface Water Sources – Regional Studies

In a partial overview of activities performed by the International Joint Commission’s Pollution from

Land Use Activities Reference Group (PLUARG), Baker (1987, as cited in Wade Miller, 1989) reported

on rural nonpoint pollution in three northwest Ohio rivers. From 1983 to 1985, mean simazine values

were not detected, 0.12 and 0.18 :g/L, respectively. The number of samples taken for these three years

were 145, 183, and 188, respectively. Peak observed concentrations for the three years were 0.01, 1.25,

and 0.98 :g/L, all of which were from the Sandusky River. No other sampling information was reported.

In a study on sediment, nutrient, and pesticide transport in lower Great Lakes tributaries, Baker (1986, as

cited in Wade Miller, 1989) included a summary of an investigation of nonpoint source pollution of

tributaries for Lake Erie and Lake Ontario for the years 1982-1985. Biweekly samples were collected

each year between April 15 and August 15, when pesticide use was the greatest. The range of time

weighted mean values reported for simazine was 0.0 - 0.84 :g/L. The number of positive samples was

not reported; however, a total of 1,785 samples were taken from eight locations. The highest observed

concentrations for simazine were 10.77 :g/L in the Cuyahoga River in 1982 and 6.93 :g/L in the

Maumee River in 1982. The detection limit was reported to be 0.25 :g/L.
Occurrence Summary and Use Support Document March 2002 266

Baker (1983b, as cited in Wade Miller, 1989) assessed the results of a pesticide monitoring program

conducted in Ohio. A total of 258 samples were collected from six streams of different watershed size

during the April and August 1982 sampling period to compare peak pesticide concentrations. The range

of peak concentrations was 2.52 to 10.7 :g/L of simazine, with an average peak value of 4.65 :g/L.

In a subsequent related report, Baker (1983a, as cited in Wade Miller, 1989) reported the average

herbicide concentrations in samples collected from two rivers in Ohio from May 28 to July 27, 1983. Of

the 23 surface water samples collected from each river, the average reported concentrations of simazine

were 0.26 and 0.44 :g/L, respectively. The detection limits were not reported.

Baker et al. (1981, as cited in Wade Miller, 1989) assessed the results of a study to determine the

concentrations of various pesticides in Northwestern Ohio rivers. Samples were collected from June

1981 to September 1981 during periods of peak pesticide usage and maximum pesticide export due to

large amounts of runoff. The authors reported that the concentrations observed at the stream stations

were generally higher than those reported in other areas. Low levels of simazine were detected in 100%

of the 135 surface water samples collected from nine streams. The values ranged from 0.03 to 2.55 :g/L

for simazine, with an average value of 0.60 :g/L. The detection limit for the analysis was not reported.

3.13.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of simazine occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.004 mg/L; 0.002 mg/L; and 0.001 mg/L. 

All sixteen cross-section State data sets, with the exception of New Jersey, contained occurrence data for

simazine. These data represent more than 68,000 analytical results from approximately 15,000 PWSs

during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The number of

sample results and PWSs vary by State, although the State data sets have been reviewed and checked to

ensure adequacy of coverage and completeness. The overall modal detection limit for simazine in the 16

cross-section States is equal to 0.001 mg/L. (For details regarding the 16-State cross-section, please refer

to Section 1.3.5 of this report.)

3.13.4.1 Stage 1 Analysis Occurrence Findings

Table 3.13-3 illustrates the low occurrence of simazine in drinking water for the public water systems in

the 16-State cross-section relative to three thresholds: 0.004 mg/L (the current MCL), 0.002 mg/L, and

0.001 mg/L (the modal MRL). A total of 8 (approximately 0.0550% of) ground water and surface water

PWSs had analytical results exceeding the MCL; 0.144% of systems (21 systems) had results exceeding

0.002 mg/L; and 0.358% of systems (52 systems) had results exceeding 0.001 mg/L. 

Zero ground water systems had analytical results greater than the MCL. Approximately 0.0152% of

ground water systems (2 systems) had results above 0.002 mg/L. The percentage of ground water

systems with at least one result greater than 0.001 mg/L was equal to 0.129% (17 systems). 

The percentage of surface water systems with results greater than the MCL was equal to 0.573% (8

systems). Approximately 19 (1.36% of) surface water systems had at least one analytical result greater

than 0.002 mg/L. Thirty-five (2.51% of) surface water systems had results exceeding 0.001 mg/L.
Occurrence Summary and Use Support Document March 2002 267

Table 3.13-3: Stage 1 Simazine Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.004 0.000% 0

0.002 0.0152% 2

0.001 0.129% 17

Surface Water

0.004 0.573% 8

0.002 1.36% 19

0.001 2.51% 35

Combined Ground &

Surface Water

0.004 0.0550% 8

0.002 0.144% 21

0.001 0.358% 52

Reviewing simazine occurrence in the 16 cross-section States by PWS population served (Table 3.13-4)

shows that approximately 0.0471% of the 16-State population (about 46,300 people) was served by

PWSs with at least one analytical result of simazine greater than the MCL (0.004 mg/L). Approximately

113,000 (0.115% of) people were served by systems with an exceedance of 0.002 mg/L. Over 1 million

(1.06% of) people were served by systems with at least one analytical result greater than 0.001 mg/L.

The percentage of population served by ground water systems in the 16 States with analytical results

greater than the MCL was equal to 0%. When evaluated relative to 0.002 mg/L and 0.001 mg/L, the

percent of population exposed was equal to 0.0150% (about 6,200 people) and 0.823% (almost 342,000

people), respectively. 

The percentage of population served by surface water systems in the 16 States with exceedances of 0.004

mg/L and 0.002 mg/L was equal to 0.0817% (46,300 people) and 0.189% (106,800 people) respectively. 

When evaluated relative to 0.001 mg/L, the percent of population exposed was equal to 1.23% (over

697,000 people).

Table 3.13-4: Stage 1 Simazine Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems 

Exceeding Threshold

Ground Water

0.004 0.000% 0

0.002 0.0150% 6,200

0.001 0.823% 341,900
Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems 

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 268

Surface Water

0.004 0.0817% 46,300

0.002 0.189% 106,800

0.001 1.23% 697,100

Combined Ground &

Surface Water

0.004 0.0471% 46,300

0.002 0.115% 113,100

0.001 1.06% 1,039,000

3.13.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.13-5 and

3.13-6. The statistically generated best estimate values, as well as the ranges around the best estimate

value, are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this

report. For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation

Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water

Regulations (USEPA, 2002)). 

The percentages of ground water and surface water PWSs with estimated mean concentrations of

simazine exceeding 0.004 mg/L, 0.002 mg/L, and 0.001 mg/L are 0.0000413%, 0.000509%, and

0.00992%, respectively. 

Only 1 ground water PWS in the 16 States was estimated to have a mean concentration greater than 0.004

mg/L (0.0000305%), 0.002 mg/L (0.00289%) and 0.001 mg/L (0.00382%). The percentage of surface

water systems with estimated mean concentration values greater than 0.004 mg/L was equal to

0.000143%. One surface water system in the 16 States was estimated to have a mean concentration value

of simazine greater than 0.002 mg/L (0.00258%) and 0.001 mg/L (0.0673%). 

Table 3.13-5: Stage 2 Estimated Simazine Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.004 0.0000305% 0.000% - 0.000% 1 0 - 0

0.002 0.00289% 0.000% - 0.00761% 1 0 - 1

0.001 0.00382% 0.000% - 0.0152% 1 0 - 2

Surface Water

0.004 0.000143% 0.000% - 0.000% 0 0 - 0

0.002 0.00258% 0.000% - 0.0716% 1 0 - 1

0.001 0.0673% 0.000% - 0.215% 1 0 - 3
Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 269

Combined Ground

& Surface Water

0.004 0.0000413% 0.000% - 0.000% 1 0 - 0

0.002 0.000509% 0.000% - 0.00688% 1 0 - 1

0.001 0.00992% 0.000% - 0.0275% 1 0 - 4

Reviewing simazine occurrence by PWS population served (Table 3.13-6) shows that approximately

0.000107% of population served by all PWSs in the 16 States (an estimate of approximately 100 people)

were potentially exposed to simazine levels above 0.004 mg/L. When evaluated relative to a threshold of

0.002 mg/L, the percent of population exposed was equal to 0.000897% (approximately 900 people). 

The percent of potential population exposed equaled 0.0197% (over 19,000 people in the 16 States) when

evaluated relative to 0.001 mg/L. 

The percentage of population served by ground water systems in the 16 States with estimated mean

concentration values greater than 0.004 mg/L was equal to 0.000238% (an estimate of approximately 100

people) and the percentage served by surface water systems in the 16 States was equal to 0.0000106%. 

Approximately 700 (0.00178% of) people in the 16 cross-section States were served by ground water

systems with estimated mean concentration values greater than 0.002 mg/L. The number of people in the

16 cross-section States served by surface water systems with estimated mean concentration values greater

than 0.002 mg/L was equal to about 100 (0.000253% of) people. An estimated 4,100 (0.00991% of)

people served by ground water systems in the in the 16 States were exposed to simazine at concentrations

greater than 0.001 mg/L. Approximately 15,200 (0.0268% of) people were served by surface water

systems with mean concentrations of simazine greater than 0.001 mg/L.

Table 3.13-6: Stage 2 Estimated Simazine Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.004 0.000238% 0.000% - 0.000% 100 0 - 0

0.002 0.00178% 0.000% - 00733% 700 0 - 3,000

0.001 0.00991% 0.000% - 0.0668% 4,100 0 - 27,700

Surface Water

0.004 0.0000106% 0.000% - 0.000% 0 0 - 0

0.002 0.000253% 0.000% - 0.00382% 100 0 - 2,200

0.001 0.0268% 0.000% - 0.147% 15,200 0 - 83,300
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 270

Combined Ground

& Surface Water

0.004 0.000107% 0.000% - 0.000% 100 0 - 0

0.002 0.000897% 0.000% - 0.00310% 900 0 - 2,200

0.001 0.0197% 0.000% - 0.105% 19,300 0 - 68,000

3.13.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, 1 system serving approximately 200 people nationally was estimated to have a mean

concentration value of simazine greater than 0.004 mg/L. Approximately 1,900 people served by an

estimated 1 system were potentially exposed to simazine concentrations greater than 0.002 mg/L. About

6 systems serving about 41,900 people nationally were estimated to have mean simazine concentrations

greater than 0.001 mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are

extrapolated to national values.)

For ground water systems, approximately 1 PWSs serving about 200 people nationally was estimated to

have a mean concentration greater than 0.004 mg/L. One ground water system serving approximately

1,500 people was estimated to have mean concentration value of simazine greater than 0.002 mg/L. An

estimated 2 systems serving about 8,500 people nationally had estimated mean concentration values that

exceeded 0.001 mg/L.

Zero surface water systems had estimated mean concentration values of simazine greater than 0.004

mg/L. Only 1 surface water systems serving about 300 people was estimated to have a mean

concentration of simazine above 0.002 mg/L. Approximately 4 surface water systems serving 34,200

people had estimated mean concentrations greater than 0.001 mg/L.

Table 3.13-7: Estimated National Simazine Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.004 1 0 - 0 200 0 - 0

0.002 1 0 - 5 1,500 0 - 6,300

0.001 2 0 - 9 8,500 0 - 57,200

Surface Water

0.004 0 0 - 0 0 0 - 0

0.002 1 0 - 4 300 0 - 4,900

0.001 4 0 - 12 34,200 0 - 187,300
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 271

Combined Ground

& Surface Water

0.004 1 0 - 0 200 0 - 0

0.002 1 0 - 4 1,900 0 - 6,600

0.001 6 0 - 18 41,900 0 - 223,900

3.13.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of fluoride in drinking water are also reviewed. 

Previously compiled occurrence information, from an OGWDW summary document entitled Occurrence

and Exposure Assessment of Simazine in Public Drinking Water Supplies” (Wade Miller, 1989), is

presented in the following section. This variety of studies and information are presented regarding levels

of simazine in drinking water, with the scope of the reviewed studies ranging from national to regional. 

Note that none of the studies presented in the following section provide the quantitative analytical results

or comprehensive coverage that would enable direct comparison to the occurrence findings estimated

with the cross-section occurrence data presented in Section 3.13.4. All the following information in

Section 3.13.5 is taken directly from “Occurrence and Exposure Assessment of Simazine in Public

Drinking Water Supplies” (Wade Miller, 1989). 

3.13.5.1 Groundwater Sources – National Studies

The National Screening Program for Organics in Drinking Water (NSP) (Boland, 1981, as cited in Wade

Miller, 1989) was conducted by Stanford Research Institute (SRI) from June 1977 to March 1981. 

Finished drinking water samples, collected from 12 groundwater systems throughout the United States,

were analyzed for simazine. The 12 systems analyzed included 1 small system (serving 501-3,300

individuals), 1 medium system (serving 3,301-10,000 individuals), 1 large system (serving 10,001-

100,000 individuals), and 9 very large systems (serving greater than 100,000 individuals). Only 1 out of

the 12 systems sampled, a very large system, had a concentration of simazine in excess of the

quantification limit of 0.1 :g/L. The value of the positive sample was 1.0 :g/L.

3.13.5.2 Groundwater Sources – Regional Studies

The State of California conducted a monitoring program for organic chemical contamination of wells

used by large public water systems (California Department of Health Services, 1986, as cited in Wade

Miller, 1989). A total of 819 water systems were required to be monitored. Of the 5,650 wells that are

used as part of these systems, 2,947 (over 50%) were sampled. Simazine was found in only 26 wells, at a

mean concentration of 0.8 :g/L. The highest value found was 2.0 :g/L. The detection limit and other

sampling information were not reported. 

In addition, the California Department of Health Services provided unpublished data on results of

sampling from small water systems (i.e., systems with fewer than 200 service connections) (California

Department of Health Services, Unpublished, as cited in Wade Miller, 1989). A total of 304 systems and

608 samples were collected from 21 counties. Simazine was only found in two samples from one well in

Merced County, at levels of 0.4 and 0.8 :g/L. The detection limit was not reported.
Occurrence Summary and Use Support Document March 2002 272

From July 1985 to June 1987, the Minnesota Departments of Health (MDH) and Agriculture (MDA)

conducted cooperative surveys of observation, irrigation, and drinking water wells for selected pesticides

(MDH and MDA, 1988, as cited in Wade Miller, 1989). These studies were designed to provide

information on the extent of agricultural pesticide contamination in Minnesota’s ground water and

drinking water. In the first survey (MDA), simazine was detected in four samples from one well, out of

100 wells sampled, at a median concentration of 1.4 :g/L (range = 0.49 - 2.58 :g/L). The detection limit

was 0.08 :g/L. In the second survey (MDH), simazine was not detected in any of the 400 samples taken. 

The detection limit for the MDH survey was 0.3 :g/L. The summary report did not distinguish between

observation, irrigation, and drinking water wells.

3.13.5.3 Surface Water Sources – National Studies

The National Screening Program for Organics in Drinking Water (NSP) (Boland, 1981, as cited in Wade

Miller, 1989) also presented data on levels of simazine in drinking water obtained from surface water

systems. Finished drinking water samples, collected from 104 surface water systems throughout the

United States, were analyzed for the presence of simazine. Of the 104 systems sampled, 13 systems (or

12%) contained simazine in excess of the quantification limit of 0.1 :g/L (Table 3.13-8). The range of

positive values of simazine was 0.1 to 4.4 :g/L.

Table 3.13-8: Frequency of Surface Water Contamination by Simazine - National Screening

Program for Organics in Drinking Water

System Size

(Population

Served)

Number of

Systems in

U.S.

Number of

Systems Samples

Number of

Positive Systems1

Percent of

Positive Systems

Range of Values

for Positive

Systems

Unspecified -- 3 0 0 --

25-500 3,937 0 0 -- --

501-3,300 3,817 0 0 -- --

3,301-10,000 1,679 1 0 0 --

10,001-100,000 1,552 25 5 20 0.0001 - 0.0044

> 100,000 217 75 8 11 0.0001 - 0.0023

Total 11,202 104 13 12 0.0001 - 0.0044

1. Quantification limit = 0.0001 mg/L.

Source: Wade Miller 1989

3.13.5.4 Surface Water Sources – Regional Studies

Baker (1985, as cited in Wade Miller, 1989) reported on sampling conducted between 1980 and 1983

proximal to the Maumee River, Sundusky River, and Honey Creek. Finished tap water samples were

analyzed for the presence of simazine in Tiffin, Fremont, and Bowling Green, Ohio. The range of peak

concentrations reported was 0.13 - 1.9 :g/L. The highest value was from a sample in Tiffin, Ohio. No

other sampling information was reported.

Baker et al. (1981, as cited in Wade Miller, 1989) analyzed finished drinking water samples collected

from a water supply in Ohio between June 1980 and September 1981. Of five finished drinking water
Occurrence Summary and Use Support Document March 2002 273

samples analyzed, all were found to contain simazine in the range of 0.026 to 0.883 :g/L. The detection

limit was not reported.

Baker (1983a, as cited in Wade Miller, 1989) analyzed samples collected from three water supplies in

Ohio in 1983 for simazine. The supplies obtained their raw water from two rivers that drained

agricultural areas. Average concentrations of simazine in the samples collected at each of the supplies

between May 28 and July 27, 1983, were 0.30 :g/L (18 samples), 0.077 :g/L (15 samples), and 0.19

:g/L (16 samples). Peak concentrations of simazine observed in 1983 were 0.63, 0.13, and 0.35 :g/L,

respectively. The detection limit and the number of positive samples were not reported.

Pellizzari (1978, as cited in Wade Miller, 1989) summarized the results of the USEPA Region VI New

Orleans Water Supply Study. For the three samples analyzed for residues of simazine, a sample mean of

less than 0.1 :g/L was determined. The detection limit was not reported.

3.13.5.5 Groundwater and Surface Water Sources – STORET

The USEPA computerized water quality data base known as STORET was devised to assist Federal and

State institutions in meeting objectives of Public Law 92-500 to maintain and enhance the physical,

chemical, and biological quality of the nation’s ambient waterways by providing for the collection and

dissemination of basic water quality data (Staples et al., 1985, as cited in Wade Miller, 1989). Data are

collected by States, EPA regional offices, and other government agencies and are maintained in the

STORET system. STORET now contains approximately 80 million pieces of data, including data for

drinking water from ground water and surface water sources.

Before presenting a summary of the drinking water data in STORET, it is important to note that there are

significant limitations in using the data base to estimate representative concentrations of a contaminant

such as simazine. Data entered into STORET are gathered from an array of studies conducted for various

purposes. Analyses are conducted in a number of different laboratories employing different

methodologies with a range of detection limits. In many cases, detection limits are not reported, making

the reliability of the data highly questionable. Where detection limits have been reported, STORET

assigns the detection limit value to those observations reported as not detected. This could lead to errors

in interpretation and overestimation of concentrations in cases in which most values are nondetectable. 

Additionally, a few high values can inflate mean values and result in large standard deviations relative to

the means (Staples et al., 1985, as cited in Wade Miller, 1989). Very high values may not be correct, as

they may reflect sample contamination or analytical error and can significantly distort assessment of

average concentrations. Staples et al. (1985, as cited in Wade Miller, 1989) also notes that the use of

data collected prior to the 1980s is not recommended, since such data were obtained using less sensitive

laboratory techniques and quality assurance procedures were not yet mandated for the data entered into

the system.

With these limitations in mind, a summary of data for simazine is presented for drinking water from

groundwater sources (USEPA, 1988, as cited in Wade Miller, 1989). According to STORET, there were

68 positive observations for simazine in groundwater from June 1984 to June 1987, with an overall mean

value of 0.75 :g/L, and a range of 0.06 to 2.0 :g/L. The standard deviation for these observations was

0.42 :g/L. There were 112 samples reported as undetected, and assigned a detection limit value giving a

calculated mean value of 1.07 :g/L, a range of 0.5 to 1.0 :g/L, and a standard deviation of 0.32 :g/L. 

Forty-seven samples were reported as having the presence of simazine verified, but not quantified,

although a value of 0.5 :g/L was given as a mean. Including these samples, the undetected samples, and

the detections known to be below the reported value, there were 1,677 observations for simazine in

groundwater from February 1984 to November 1987, with an overall mean value of 0.58 and a range of
Occurrence Summary and Use Support Document March 2002 274

0.03 to 10.0 :g/L. The standard deviation for all observations was 0.94 :g/L. Detection limits and other

sampling information were not given.

The USEPA’s STORET data base similarly contains data on the occurrence of simazine in drinking

water from surface water sources (USEPA, 1988 , as cited in Wade Miller, 1989). There were three

positive observations for simazine in surface water during August 1986, with an overall mean value of

0.027 :g/L and a range of 0.02 to 0.04 :g/L. The standard deviation for these observations was 0.012

:g/L. One sample was reported as undetected, with a value of 0.001 :g/L. Including the undetected

sample and the detections known to be below the reported value, there were seven observations for

simazine in surface water from August 1986 to July 1987, with an overall mean value of 0.037 :g/L and

a range of 0.001 to 0.06 :g/L. The standard deviation for all observations was 0.024 :g/L. Detection

limits and other sampling information were not given.

3.13.6 Conclusion

Simazine is a triazine herbicide used to control deeply rooted herbaceous weeds. Its major use is on

corn. Approximately 4.8 million pounds of simazine were used in 1992 on corn and several other crops. 

The greatest concentrations of simazine use are in the Midwest, Mid-Atlantic, California, and Florida. 

Industrial releases of simazine have been reported to TRI from eight States since 1995. Simazine was

also an analyte for the NAWQA occurrence studies. In the NAWQA study, simazine was detected in

ground and surface water. The median concentration for simazine in surface water was 0.012 :g/L, and

for ground water, none of the median values exceeded the detection limit. The Stage 2 analysis, based on

the 16-State cross-section, estimated that approximately 0.0000413% of combined ground water and

surface water systems serving 0.000107% of the population exceeded the MCL of 0.004 mg/L. Based on

this estimate, zero PWSs nationally are estimated to have simazine levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, according to information from USGS, 44 States use simazine agriculturally,

including 14 of the 16 cross-section States. Most agricultural use is concentrated in the Midwest, MidAtlantic, California, and Florida. The areas of high use are represented by six cross-section States with

extensive use of simazine. TRI releases have been reported for simazine from 8 States nationally,

including 2 of 16 cross-section States. The cross-section should adequately represent the occurrence of

simazine on a national scale based upon the use, production, and release patterns of the 16-State crosssection in relation to the patterns observed for all 50 States.

3.13.7 References

Baker, D.B., K.A. Krieger, and J.V. Setzler. 1981. The Concentrations and Transport of Pesticides in

Northwestern Ohio Rivers. Prepared by Water Quality Laboratory, Heidelberg College, Tiffin,

OH, for Lake Erie Wastewater Management Study, U.S. Army Corps of Engineers, Buffalo, NY.

Baker, D.B. 1983a. Herbicide Contamination in Municipal Water Supplies of Northwestern Ohio. Draft

Final Report. Prepared by Water Quality Laboratory, Heidelberg College, Tiffin, OH, for Great

Lakes National Program Office, U.S. Environmental Protection Agency, Chicago, IL.

Baker, D.B. 1983b. Studies of Sediment, Nutrient, and Pesticide Loading in Selected Lake Erie and

Lake Ontario Tributaries. Prepared by Water Quality Laboratory, Heidelberg College, Tiffin,

OH, for U.S. Environmental Protection Agency, Region V, Chicago, IL.
Occurrence Summary and Use Support Document March 2002 275

Baker, D.B. 1985. Regional Water Quality Impacts of Intensive Row-Crop Agriculture: A Lake Erie

Basin Case Study. Reprinted from the Journal of Soil and Water Conservation. v. 40, no. 1, pp.

125-132.

Baker, D.B. 1986. Sediment, Nutrient and Pesticide Transport in Selected Lower Great Lakes

Tributaries. Prepared for Great Lakes National Program Office, U.S. Environmental Protection

Agency, Chicago, IL. Grant Nos. R005727 and R005817.

Baker, D.B. 1987. Overview of Rural Nonpoint Pollution in the Lake Erie Basin. In: Effects of

Conservation Tillage on Groundwater Quality: Nitrates and Pesticides. T.J. Logan et al. (eds.). 

Chelsea, MI: Lewis Publishers, Inc. pp. 65-91.

Blomquist, J.D., J.M. Denis, J.L. Cowles, J.A. Hetrick, R.D. Jones, and N.B. Birchfield. 2001. 

Pesticides in Selected Water-Supply Reservoirs and Finished Drinking Water, 1999-2000: 

Summary of Results from a Pilot Monitoring Survey. U.S. Geological Survey Open-File Report

01-456. 65 pp.

Boland, P.A. 1981. National Screening Program for Organics in Drinking Water. Part II. Data.

Prepared by SRI International, Menlo Park, CA, for U.S. Environmental Protection Agency,

Office of Drinking Water, Washington, DC. EPA Contract. No. 68-01-4666.

California Department of Health Services. 1986. Final Report on a Monitoring Program for Organic

Chemical Contamination of Large Public Water Systems in California. Summary Version. 

Sacramento, CA: Department of Health Services. April, 1986.

California Department of Health Services. Unpublished. Final Report on a Monitoring Program for

Organic Chemical Contamination of Small Public Water Systems in California. Summary

Version (tables). Sacramento, CA: Department of Health Services.

Carey, A.E., and F.W. Kutz. 1983. Trends in Ambient Concentrations of Agrochemicals in Humans and

the Environment of the United States. Presented at the International Conference on

Environmental Hazards of Agrochemicals in Developing Countries, Alexandria, Egypt,

November 8-12, 1983.

Cohen, S.Z., S.M. Creeger, R.F. Carsel, and C.G. Enfield. 1984. Potential for Pesticide Contamination

in Groundwater Resulting from Agricultural Uses. In: Treatment and Disposal of Pesticide

Wastes. R.F. Kruger and J.W. Seiber (eds.). Washington, DC: American Chemical Society. 

ACS Symposium Series No. 259: pp. 247-325.

EXTOXNET. 1996. Pesticide Information Profile: Simazine. Ithaca, NY: Extension Toxicology

Network, Pesticide Management Education Program. Available on the Internet at

http://ace.ace.orst.edu/info/extoxnet/pips/simazine.htm, revised June, 1996. 

Gilliom, R.J., D.K. Mueller, and L.H. Nowell. 1998. Methods for comparing water-quality conditions

among National Water-Quality Assessment Study Units, 1992-95. U.S. Geological Survey

Open-File Report 97-589. Available on the Internet at:

http://ca.water.usgs.gov/pnsp/rep/ofr97589, last updated October 9, 1998.

Hazardous Substances Data Bank (HSDB). 2001. Hazardous Substances Data Bank: Simazine. 

Available on the Internet at: http://toxnet.nlm.nih.gov/, last updated May 15, 2001.
Occurrence Summary and Use Support Document March 2002 276

Minnesota Department of Health (MDH) and Minnesota Department of Agriculture (MDA). 1988. 

Pesticides and Groundwater: Surveys of Selected Minnesota Wells. Prepared by Thomas G.

Klaseus (MDH), Greg C. Buzicky (MDA), and Edward C. Schneider (MDH) for Legislative

Commission on Minnesota Resources. February, 1988.

Pellizzari, E.D. 1978. Preliminary Assessment of Halogenated Organic Compounds in Man and

Environment Media. Monthly Technical Progress Report No. 5, April 1-30, 1978. Prepared by

Research Triangle Institute, Research Triangle Park, NC, for Office of Toxic Substances, U.S.

Environmental Protection Agency, Washington, DC. EPA Contract No. 68-01-4731.

Schlachter, J. 1988. Memorandum on Program Improvement Subcommittee, FSTRAC, Preparation for

April Meeting. Sent by: Jacquelyn D. Schlachter, Chairman - Program Improvement

Subcommittee, U.S. Environmental Protection Agency, Region VII, Kansas City, KS. Sent to: 

Dennis Alt, IA; Pam Bonrud, SD; Bill Lee, NE; Kathy Miller, MT; Jennifer Orme, HQ; Sheila

Sullivan, EPA Region V; and Dan Wilson, WI.

Staples, C.A., A.F. Werner, and T.J. Hoogheem. 1985. Assessment of Priority Pollutant Concentrations

in the United States Using STORET Data Base. In: Environmental Toxicology and Chemistry. 

v. 4, pp. 131-142. New York, New York: Pergamon Press, Ltd.

USEPA. 1987. Health Advisory for Simazine. Washington, D.C: Office of Drinking Water, USEPA. 

August, 1987.

USEPA. 1988. Computer Printout of STORET Water Quality Data Base Retrieval Conducted March

23, 1988 by Science Applications International Corporation. Data available through the Office

of Water Regulations and Standards.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: SIMAZINE. 

Available on the Internet at: http://www.epa.gov/safewater/dwh/c-soc/simazine.html, last

updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

USGS. 1998a. Annual Use Maps. Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/,

last updated March 20, 1998.

USGS. 1998b. Sources & Limitations of Data Used to Produce Maps of Annual Pesticide Use. 

Available on the Internet at: http://water.wr.usgs.gov/pnsp/use92/mapex.html, last updated

March 20, 1998.

USGS. 1998c. Pesticides in Surface and Ground Water of the United States: Summary of Results of the

National Water Quality Assessment Program (NAWQA). PROVISIONAL DATA -- SUBJECT TO

REVISION. Available on the Internet at: http://water.wr.usgs.gov/pnsp/allsum/, last updated

July 22, 1998. 
Occurrence Summary and Use Support Document March 2002 277

Wade Miller Associates, Inc. 1989. Occurrence and Exposure Assessment of Simazine in Public

Drinking Water Supplies - DRAFT. Draft report submitted to EPA for review April 12, 1989. 

Williams, W.M., P.W. Holden, D.W. Parsons, and M.N. Lorber. 1988. Pesticides in Groundwater Data

Base. 1988 Interim report. Washington, DC: Office of Pesticide Programs, USEPA.
Occurrence Summary and Use Support Document March 2002 278

3.14 Toxaphene

Table of Contents

3.14.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

3.14.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

3.14.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

3.14.3 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . 281

3.14.4 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

3.14.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

3.14.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

Tables and Figures

Table 3.14-1: Stage 1 Toxaphene Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . 282

Table 3.14-2: Stage 1 Toxaphene Occurrence Based on 16-State Cross-Section - Population . . . . . . 283

Table 3.14-3: Stage 2 Estimated Toxaphene Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

Table 3.14-4: Stage 2 Estimated Toxaphene Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

Table 3.14-5: Estimated National Toxaphene Occurrence - Systems and Population Served . . . . . . . 285
Occurrence Summary and Use Support Document March 2002 279

3.14.1 Introduction, Use and Production

Toxaphene is a manufactured insecticide containing over 670 chemicals. It does not occur naturally and

is usually found as a solid or gas. In its original form, toxaphene is a yellow to amber waxy solid that

smells like turpentine. It does not burn and evaporates when in solid form or when mixed with liquids. 

Toxaphene was one of the most heavily used insecticides in the United States until 1982, when it was

canceled for most uses; all uses were banned in 1990. It was used primarily in the southern United States

to control insect pests on cotton and other crops. It was also used to control insect pests on livestock and

to kill unwanted fish in lakes. Toxaphene is also known as camphechlor, chlorocamphene,

polychlorocamphene, and chlorinated camphene (ATSDR, 1996).

Toxaphene was formerly used as a nonsystemic stomach and contact insecticide. It was used to control

many insects that thrived on cotton, corn, fruit, vegetables, and small grains and to control the Cussia

obtusifola soybean pest. The principal use was for pest control on cotton crops. Toxaphene was also

used to control livestock ectoparasites such as lice, flies, ticks, mange, and scab mites. Its relatively low

toxicity to bees and its long-persisting insecticidal effect made it especially useful in the treatment of

flowering plants. At one time toxaphene was also used in the United States to eradicate fish. In 1974, an

estimated 44.1 million pounds was used in the United States, and was distributed as follows: 85% on

cotton; 7% on livestock and poultry; 5% on other field crops; 3% on soybeans; and less than 1% on

sorghum (ATSDR, 1996).

Through the early 1970s toxaphene or mixtures of toxaphene with rotenone were used widely in lakes

and streams by fish and game agencies to eliminate biologic communities that were considered

undesirable for sport fishing. Such uses of toxaphene by fish and game agencies have been discontinued

in the United States and Canada. Toxaphene use in this country has declined drastically since 1975, at

which time it was reported to be the most heavily used pesticide. The total amount consumed was

estimated to be 18.7 million pounds in 1980 and 10.8 million pounds in 1982 (ATSDR, 1996). 

In November 1982, EPA canceled the registrations of toxaphene for most of its uses as a pesticide or

pesticide ingredient. In the period following November 1982, its use was restricted to controlling scabies

on sheep and cattle; controlling grasshopper and army worm infestations on cotton, corn, and small

grains; controlling specific insects on banana and pineapple crops in Puerto Rico and the U.S. Virgin

Islands; and for emergency use only (to be determined on a case-by-case basis by EPA). Formulations

suitable for other purposes were to be sold or distributed until December 31, 1983, for use only on

registered sites. The distribution or sale of remaining stocks of toxaphene formulations was permitted

until December 31, 1986, for use on no-till corn, soybeans, and peanuts (to control sicklepod), and dry

and southern peas, and to control emergency infestations. All registered uses of toxaphene mixtures in

the United States and any of its territories were canceled in 1990 (ATSDR, 1996). 

In 1976, toxaphene was produced primarily by Hercules Incorporated, Wilmington, Delaware. 

Production during 1976 by three U.S. companies (Hercules Incorporated, Tenneco, and Vicksburg

Chemical Co., a division of Vertac) totaled 41.9 million pounds, which was a 29% decline from the

production level of 59.5 million pounds in 1975 (ATSDR, 1996). 

Total U.S. production in 1977 was estimated to be 39.9 million pounds. The most recent production

volumes are from 1982, when it was estimated that 3.7 million pounds were produced in the United

States. This represents a decline of more than 90% from 1972, when toxaphene was the most heavily

manufactured insecticide in the United States with a production volume of 46.0 million pounds (ATSDR,

1996). By 1982, when EPA canceled most of its uses, consumption was reported at 12 million pounds

(USEPA, 2001).
Occurrence Summary and Use Support Document March 2002 280

3.14.2 Environmental Release

Toxaphene is released directly to the environment primarily in its use as an insecticide. Total U.S.

production in 1982 was estimated to be 3.7 million pounds (ATSDR, 1996). Toxaphene is not listed as a

Toxics Release Inventory (TRI) contaminant, so no TRI release records are maintained. Therefore, the

use of toxaphene (described in the previous section) may provide the primary indication of where

releases are most likely. 

3.14.3 Ambient Occurrence

To understand the presence of a chemical in the environment, an examination of ambient occurrence is

useful. In a drinking water context, ambient water is untreated source water residing in surface waters

and aquifers. There are few available data on the occurrence of toxaphene in ambient waters of the

United States. The most comprehensive and nationally consistent data describing ambient water quality

in the United States are being produced through the United States Geological Survey’s (USGS) National

Water Quality Assessment (NAWQA) program. However, national NAWQA data are currently

unavailable for toxaphene.

3.14.3.1 Additional Ambient Occurrence Data

Additional studies of ambient data are summarized below. A summary document entitled “Occurrence

and Human Exposure to Pesticides in Drinking Water, Food and Air in the United States of America”

(USEPA, 1989), was previously prepared for past USEPA assessments of various pesticides. In that

review, one national and several regional studies were included on the occurrence of toxaphene in

surface water non-drinking water sources. Barbash and Resek (1996) also conducted reviews of

pesticides in ground water non-drinking water sources, including a national review and a compilation of

various monitoring studies on the occurrence of toxaphene. The following information for the surface

water studies only is taken directly from “Occurrence and Human Exposure to Pesticides in Drinking

Water, Food and Air in the United States of America” (USEPA, 1989).

3.14.3.1.1 Surface Water Sources – National Studies

The National Surface Water Monitoring Program presented data on levels of toxaphene in surface water

samples collected throughout the U.S. during the period 1975 to 1979 (USEPA, 1989). During this time,

2,479 samples were collected and analyzed for toxaphene. Although no detection limit was given for

toxaphene, 11 positive samples (or 0.4%) were found during testing. The range of positive values was

0.0 to 1.65 :g/L.

3.14.3.1.2 Surface Water Sources – Regional Studies

Mattraw (1975, as cited in USEPA, 1989) did not detect toxaphene in any surface water samples

collected and analyzed during an organochlorine residue survey in Florida. The number of samples

analyzed and the detection limit were not reported.

Toxaphene was detected in 11 (or 55%) of 20 Mississippi Delta lakes sampled by Herring and Cotton

(1970, as cited in USEPA, 1989). The maximum reported concentration was 1.92 :g/L (the detection

limit was not reported).
Occurrence Summary and Use Support Document March 2002 281

3.14.3.1.3 Ground Water Sources – National Studies

The Pesticides in Ground Water Data Base (PGWDB), developed by EPA’s Offices of Pesticide

Programs (OPP), contains information derived from monitoring studies conducted by pesticide

registrants, universities, and government agencies. The data are presented in several categories,

including all information collected to date (excluding data known to be of poor quality and data that is

from point source contamination); data derived from scientifically confirmed agricultural use; and

confirmed information attributed to known point sources and documented misuse. While extreme care

was taken to confirm detections of pesticides in ground water, the authors caution that the studies

investigated have not been limited to drinking water supplies and some studies included samples from

many types of wells including observation and irrigation wells. In addition, many studies have focused

on shallow ground water which may not be representative of drinking water sources in the area. As such,

the results cannot be used to estimate human exposure to pesticides in drinking water, but do provide an

additional assessment of possible toxaphene occurrence. The PGWDB is the most comprehensive

summary available on pesticide occurrence in ground water, including data from a total of 68,824 wells

sampled for pesticide analytes from 45 States (Barbash and Resek, 1996).

Results of the review of the PGWDB indicate that toxaphene was detected in 9 of the 4,273 wells

sampled. The maximum concentration reported was 0.0180 :g/L. The minimum concentration reported

was 0.00115 :g/L. The frequency of exceedances of the MCL (or Health Advisory Level [HAL], if the

MCL unavailable) among sampled wells is 0.070% (Barbash and Resek, 1996).

3.14.3.1.4 Ground Water Sources – Regional Studies

Several monitoring studies, including results from various multistate, State and local monitoring studies

of pesticides, are reviewed in Barbash and Resek (1996). Results from these studies indicate that

toxaphene was detected in at least one study reviewed, although it was not possible to determine the

exact number of studies for which toxaphene was an analyte, or exactly how many studies did detect

toxaphene. In the summary information reviewed, details were provided regarding the geographic

distribution and the total number of systems collected, although further detail is beyond the scope of this

report.

3.14.3 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of toxaphene occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.003 mg/L; 0.0015 mg/L; and 0.001 mg/L. 

All sixteen cross-section State data sets, with the exception of Alabama, contained occurrence data for

toxaphene. These data represent over 52,000 analytical results from approximately 14,000 PWSs during

the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The number of sample

results and PWSs vary by State, although the State data sets have been reviewed and checked to ensure

adequacy of coverage and completeness. The overall modal detection limit for toxaphene in the 16 crosssection States is equal to 0.001 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)
Occurrence Summary and Use Support Document March 2002 282

3.14.3.1 Stage 1 Analysis Occurrence Findings

Table 3.14-1 illustrates the low occurrence of toxaphene in drinking water for the public water systems in

the 16-State cross-section relative to three thresholds: 0.003 mg/L (the current MCL), 0.0015 mg/L, and

0.001 mg/L (the modal MRL). Only 1 PWS (approximately 0.00724%) had analytical results exceeding

the MCL; 0.0290% of systems (4 systems) had results exceeding 0.0015 mg/L; and 0.0362% of systems

(5 systems) had results exceeding 0.001 mg/L. 

No ground water systems had any analytical results greater than the MCL. Only 1 ground water system

(0.00806%) had results above 0.0015 mg/L or 0.001 mg/L. 

One (0.0716% of) surface water systems had results greater than the MCL. Approximately 3 (0.215%

of) surface water systems had at least one analytical result greater than 0.0015 mg/L. Four (0.286% of)

surface water systems had results exceeding 0.001 mg/L.

Table 3.14-1: Stage 1 Toxaphene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Ground Water

0.003 0.000% 0

0.0015 0.00806% 1

0.001 0.00806% 1

Surface Water

0.003 0.0716% 1

0.0015 0.215% 3

0.001 0.286% 4

Combined Ground &

Surface Water

0.003 0.00724% 1

0.0015 0.0290% 4

0.001 0.0362% 5

Reviewing toxaphene occurrence in the 16 cross-section States by PWS population served (Table 3.14-2)

shows that approximately 0.131% of the population (125,000 people) was served by PWSs with at least

one analytical result of toxaphene greater than the MCL (0.003 mg/L). Approximately 150,900 (0.159%

of) people were served by systems with an exceedance of 0.0015 mg/L. Almost 206,000 (0.216% of)

people were served by systems with at least one analytical result greater than 0.001 mg/L.

The percentage of population served by ground water systems with analytical results greater than the

MCL was equal to 0%. When evaluated relative to 0.0015 mg/L and 0.001 mg/L, the percent of

population exposed was equal to 0.0436% (approximately 17,500 people). 

The percentage of population served by surface water systems with exceedances of the MCL (0.003

mg/L) was equal to 0.227% (125,000 people). When evaluated relative to 0.0015 mg/L and 0.001 mg/L,
Occurrence Summary and Use Support Document March 2002 283

the percent of population exposed was equal to 0.243% (about 133,400 people) and 0.343% (about

188,400 people), respectively.

Table 3.14-2: Stage 1 Toxaphene Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Ground Water

0.003 0.000% 0

0.0015 0.0436% 17,500

0.001 0.0436% 17,500

Surface Water

0.003 0.227% 125,000

0.0015 0.243% 133,400

0.001 0.343% 188,400

Combined Ground &

Surface Water

0.003 0.131% 125,000

0.0015 0.159% 150,900

0.001 0.216% 205,900

3.14.3.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 3.14-3 and

3.14-4. The statistically generated best estimate values, as well as the ranges around the best estimate

value, are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this

report. For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation

Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water

Regulations (USEPA, 2002)). 

No ground water or surface water PWSs had an estimated mean concentration of toxaphene exceeding

0.003 mg/L, or 0.0015 mg/L. Approximately 0.000145% of PWSs (approximately 1 system in the 16-

State cross-section) were estimated to have a mean concentration greater than 0.001 mg/L. The

percentage of ground water PWSs with estimated mean concentration exceeding 0.001 mg/L was equal to

0.0000967% (less than 1 system in the 16 States). Approximately 0.000573% of surface water systems

(about 1 system in the 16 States) had estimated mean concentration values of toxaphene greater than

0.001 mg/L.
Occurrence Summary and Use Support Document March 2002 284

Table 3.14-3: Stage 2 Estimated Toxaphene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.003 0.000% 0.000% - 0.000% 0 0 - 0

0.0015 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.0000967% 0.000% - 0.000% 0 0 - 0

Surface Water

0.003 0.000% 0.000% - 0.000% 0 0 - 0

0.0015 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.000573% 0.000% - 0.000% 1 0 - 0

Combined Ground

& Surface Water

0.003 0.000% 0.000% - 0.000% 0 0 - 0

0.0015 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.000145% 0.000% - 0.000% 1 0 - 0

Reviewing toxaphene occurrence by PWS population served (Table 3.14-4) shows that approximately

0.000833% of population served by all PWSs in the 16 States (an estimated 800 people in the 16 States)

were potentially exposed to toxaphene levels above 0.001 mg/L. The percentage of population served by

ground water systems relative to 0.001 mg/L was equal to 0.0000376%. Approximately 0.00141% of the

population served by surface water systems (about 800 people) were exposed to toxaphene at levels

greater than 0.001 mg/L. When evaluated relative to a threshold of 0.003 mg/L and 0.0015 mg/L, the

percent of population exposed was equal to 0% for all system types.

Table 3.14-4: Stage 2 Estimated Toxaphene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.003 0.000% 0.000% - 0.000% 0 0 - 0

0.0015 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.0000376% 0.000% - 0.000% 0 0 - 0

Surface Water

0.003 0.000% 0.000% - 0.000% 0 0 - 0

0.0015 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.00141% 0.000% - 0.000% 800 0 - 0
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 285

Combined Ground

& Surface Water

0.003 0.000% 0.000% - 0.000% 0 0 - 0

0.0015 0.000% 0.000% - 0.000% 0 0 - 0

0.001 0.000833% 0.000% - 0.000% 800 0 - 0

3.14.3.3 Estimated National Occurrence

As illustrated in Table 3.14-5, the Stage 2 analysis estimates zero systems serving zero people nationally

have estimated mean concentration values of toxaphene greater than 0.003 mg/L or 0.0015 mg/L. Only 1

surface water system serving approximately 1,800 people nationally had an estimated mean concentration

value of toxaphene greater than 0.001 mg/L. (See Section 1.4 for a description of how Stage 2 16-State

estimates are extrapolated to national values.)

Table 3.14-5: Estimated National Toxaphene Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.003 0 0 - 0 0 0 - 0

0.0015 0 0 - 0 0 0 - 0

0.001 0 0 - 0 0 0 - 0

Surface Water

0.003 0 0 - 0 0 0 - 0

0.0015 0 0 - 0 0 0 - 0

0.001 1 0 - 0 1,800 0 - 0

Combined Ground

& Surface Water

0.003 0 0 - 0 0 0 - 0

0.0015 0 0 - 0 0 0 - 0

0.001 1 0 - 0 1,800 0 - 0

3.14.4 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of toxaphene in drinking water are also

reviewed. Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence and Human Exposure to Pesticides in Drinking Water, Food and Air in the United States of

America” (USEPA, 1989), is presented in the following section. This variety of studies and information

are presented regarding levels of toxaphene in drinking water, with the scope of the reviewed studies
Occurrence Summary and Use Support Document March 2002 286

ranging from national to regional. Note that none of the studies presented in the following section

provide the quantitative analytical results or comprehensive coverage that would enable direct

comparison to the occurrence findings estimated with the cross-section occurrence data presented in

Section 3.14.4. These additional studies, however, do enable a broader assessment of the Stage 2

occurrence estimates presented for this Six-Year Review. All the following information in Section

3.14.5 is taken directly from “Occurrence and Human Exposure to Pesticides in Drinking Water, Food

and Air in the United States of America” (USEPA, 1989).

3.14.4.1 Ground Water Sources – National Studies

The Federal Reporting Data System (FRDS, 1984, as cited in USEPA, 1989) provides information on

public water supplies found to be in violation of current Maximum Contaminant Levels (MCLs). Data

are not available on the number of ground water systems in the U.S. that have monitoring requirements

for toxaphene; however, no violations of the current MCL of 5 :g/L were reported for toxaphene during

the years 1979-1983.

The 1978 Rural Water Survey (USEPA, 1984, as cited in USEPA, 1989) involved the collection of

samples from 267 households (the majority using private water supplies) in rural locations throughout the

U.S. and analyses for toxaphene. A total of 71 public drinking water systems of varying sizes using

ground water were covered by the survey. None of the samples from the 71 ground water systems

studied exceeded the minimum quantification limit of 0.17 :g/L for toxaphene.

3.14.4.2 Ground Water Sources – Regional Studies

Irwin and Healy (1978, as cited in USEPA, 1989) summarized a study of data collected in 1976 during a

water quality reconnaissance of public water supplies in Florida. None of the 100 water supplies

sampled utilizing the five aquifers in Florida contained toxaphene in excess of the detection limit (the

detection limit was not reported).

Tucker and Burke (1978, as cited in USEPA 1989) presented the results of analyses of samples collected

from wells in nine New Jersey counties. None of the samples tested contained concentrations of

toxaphene in excess of the minimum reportable concentration of 0.06 :g/L for this study.

3.14.4.3 Surface Water Sources – National Studies

Data were obtained from the Federal Reporting Data System (FRDS, 1984, as cited in USEPA, 1989) on

violations of the current MCL of 5 :g/L for toxaphene. The data were obtained for the years 1979 to

1983 and include information for all surface water systems in the United States. The analysis indicated

that none of the samples from the surface water systems studied contained toxaphene in excess of the

current MCL.

The 1978 Rural Water Survey (USEPA, 1984, as cited in USEPA, 1989) also presented data on drinking

water samples obtained from surface water systems of varying sizes. None of the samples from the 21

public drinking water systems contained concentrations of toxaphene in excess of the minimum

quantification limit of 0.17 :g/L.

3.14.4.4 Surface Water Sources – Regional Studies

Irwin and Healy (1978, as cited in USEPA, 1989), summarizing data collected during a water quality

reconnaissance of public water supplies in Florida, reported that none of the samples from the 16 surface
Occurrence Summary and Use Support Document March 2002 287

water supplies studied contained concentrations of toxaphene in excess of the detection limit. The

detection limit was not reported.

In a study on the effects of forest runoff on the quality of a public water supply in Oregon, Elliot (1979,

as cited in USEPA, 1989) observed a concentration of toxaphene of 3 :g/L.

To assemble a database which would reflect the status of Great Lakes drinking water quality, the

Canadian Public Health Association gathered data from October 1984 through August 1985 (Canadian

Public Health Association, 1986, as cited in USEPA, 1989). The data collected covered the period from

the mid 1970s to early 1985. The study was funded by the Health Protection Branch of Health and

Welfare Canada and the Ontario Ministry of the Environment. A research team, appointed by the

Association, reviewed data on the quality of water at 31 representative Canadian and United States

communities and 24 offshore sites to evaluate the human health implications.

For each of the 31 communities, data consisted of: 1) background information on the community; 2)

treatment plant schematics and associated treatment process information; and 3) water quality data. 

Water sample types included raw water (treatment plant intake), distribution water (treated water), and

tap water. Water quality data collected included general parameters (e.g., alkalinity, turbidity),

microbiological and radiological parameters, inorganic parameters, and organic parameters (including

volatiles, base/neutrals, pesticides and PCBs, and phenols and acids). For each parameter, the water

type, time period, concentration (mean, range), number of samples and detection limit are presented.

For most of the volatile organics, including toxaphene, the available data indicate that there were very

low levels of these contaminants in the raw, treated, or tap water. Most of the values found were “not

detected” or near the detection limit (Canadian Public Health Association, 1986, as cited in USEPA,

1989).

3.14.4.5 Unspecified Sources – National Study

In an EPA survey (USEPA, 1977, as cited in USEPA, 1989) of pesticide contamination in commercial

drinking water sampled during 1975 and 1976, 27 of 58 samples analyzed were found to be positive for

toxaphene. The levels of toxaphene were at or below 0.05 :g/L. The detection limit was not reported.

3.14.4.6 Unspecified Sources – Regional Study

In a report on source identification of pollutants entering a sewage treatment plant, Levins et al. (1979, as

cited in USEPA 1989) two drinking water sources in a drainage basin were tested in Georgia. Although

the detection limits were not reported, toxaphene was not detected in either of the samples tested.

3.14.5 Conclusion

Toxaphene was formerly used as a nonsystemic stomach and contact insecticide. The principal use was

for pest control on cotton crops. In the U.S., toxaphene use has declined drastically since 1975, at which

time it was reported to be the most heavily used pesticide. In November 1982, EPA canceled the

registrations of toxaphene for most of its uses as a pesticide or pesticide ingredient. All registered uses

of toxaphene mixtures in the United States and any of its territories were canceled in 1990. Toxaphene is

not a TRI chemical, so there is no information available on releases of toxaphene. There are also no

ambient data available. The Stage 2 analysis, based on the 16-State cross-section, estimated that zero

percent of combined ground water and surface water systems serving zero percent of the population
Occurrence Summary and Use Support Document March 2002 288

exceeded the MCL of 0.003 mg/L. Based on this estimate, zero PWSs nationally are estimated to have

levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. The cross-section should adequately represent the occurrence of toxaphene on a

national scale based upon the fact that toxaphene is no longer produced or used in any state and that there

are no documented releases for toxaphene. 

3.14.6 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1996. Toxicological Profile for

Toxaphene. U.S. Department of Health and Human Services, Public Health Service. 215 pp. +

Appendices. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp94.pdf

Barbash, J. E., and E. A. Resek. 1996. Pesticides in Ground Water: Distribution, Trends, and 

Governing Factors. Volume two of Pesticides in the Hydrologic System. Chelsea, MI: Ann

Arbor Press, Inc. 588 pp.

Canadian Public Health Association. 1986. Comprehensive Survey of the Status of Great Lakes

Drinking Water. Prepared in cooperation with Health and Welfare Canada and the Ministry of

the Environment. Ottawa, Canada: Canadian Public Health Association. August 1986.

Elliot, W.M. 1979. Portland’s Public Water Supply -- Pure and Simple. Proceedings of the National

Conference on Environmental Engineering. New York, NY: American Society of Civil

Engineers.

Federal Reporting Data System (FRDS). 1984. Computer printout containing data on organic chemical

MCL violations, FY 1979-1983. Washington, DC: USEPA. April 4, 1984.

Herring, J., and D. Cotton. 1970. Pesticide residues of 20 Mississippi delta lakes. Proceedings of the.

4th Annual Conference of S.E. Assoc. Game Fish Comm. 482.

Irwin, G.A., and H.G. Healy. 1978. Chemical and Physical Quality of Selected Public Water Supplies in

Florida, August-September 1976. Tallahassee, FL: Water Resources Division, U.S. Geological

Survey. USGS/WRI 78-21.

Levins, P., J. Adams, P. Brenner, S. Coons, K. Thrun, and J. Varone. 1979. Sources of Toxic Pollutants

Found in Influents to Sewage Treatment Plants. IV. R.M. Clayton Drainage Basin, Atlanta

report. Prepared by Arthur D. Little, Inc., for Office of Water Planning and Standards, U.S.

Environmental Protection Agency, Washington, DC. EPA Contract No. 68-01-3857.

Mattraw, H.C. 1975. Occurrence of chlorinated hydrocarbon insecticides, southern Florida, 1968-1972.

Pestic. Monit. J. v. 9, p. 106.

Tucker, R.K., and T.A. Burke. 1978. A Second Preliminary Report on the Findings of the State

Groundwater Monitoring Project. New Jersey: Department of Environmental Protection.

USEPA. 1977. Toxaphene: Position document 1. Washington, DC: Special Pesticide Review Division,

USEPA. EPA/SPRD-80/55.
Occurrence Summary and Use Support Document March 2002 289

USEPA. 1984. Rural Water Survey. Computer data provided by Department of Sociology, Cornell

University, Ithaca, New York. 

USEPA. 1989. Draft Final Report on the Occurrence and Human Exposure to Pesticides in Drinking

Water, Food, and Air in the United States of America. Office of Drinking Water, USEPA. 

September, 1989. 202 pp.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: TOXAPHENE. 

Available on the Internet at: http://www.epa.gov/OGWDW/dwh/c-soc/toxaphen.html, last

updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.
Occurrence Summary and Use Support Document March 2002 290

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Occurrence Summary and Use Support Document March 2002 291

4.0 VOLATILE ORGANIC CONTAMINANTS
Occurrence Summary and Use Support Document March 2002 292

4.1 Benzene

Table of Contents

4.1.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

4.1.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

4.1.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

4.1.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 296

4.1.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301

4.1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

4.1.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

Tables and Figures

Table 4.1-1: Benzene Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

Table 4.1-2: Environmental Releases (in pounds) for Benzene in the United States, 1988-1999 . . . . 295

Table 4.1-3: Stage 1 Benzene Occurrence Based on 16-State Cross-Section - Systems . . . . . . . . . . . 297

Table 4.1-4: Stage 1 Benzene Occurrence Based on 16-State Cross-Section - Population . . . . . . . . . 298

Table 4.1-5: Stage 2 Estimated Benzene Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

Table 4.1-6: Stage 2 Estimated Benzene Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

Table 4.1-7: Estimated National Benzene Occurrence - Systems and Population Served . . . . . . . . . . 301
Occurrence Summary and Use Support Document March 2002 293

4.1.1 Introduction, Use and Production

Benzene, also known as benzol, has the chemical formula C6H6 and is a colorless liquid with a sweet

odor. Benzene evaporates into air very quickly and dissolves slightly in water. It is also highly

flammable. Benzene is found in the environment as a result of both anthropogenic and natural processes. 

It is also a part of crude oil and gasoline and cigarette smoke. Benzene was first discovered and isolated

from coal tar in the 1800s. Today, benzene is made mostly from petroleum sources. Because of its wide

use, benzene ranks in the top 20 in production volume for chemicals produced in the United States

(ATSDR, 1997).

Benzene is produced naturally by volcanoes and forest fires and is present in many plants and animals. It

is also a major industrial chemical made from coal and oil (NSC, 2001). 

The greatest use of benzene is as a building block for making plastics, rubber, resins and synthetic fabrics

like nylon and polyester (USEPA, 2001). Benzene is also used in the following manufacturing

processes: medicines, dyes, artificial leather, linoleum, oil cloth, pesticides, plastics and resins, PCB,

aviation fuel, detergents, flavors and perfumes, paints and coatings, airplane dope, varnishes, lacquers,

explosives and other organics. It is used in photogravure printing and as a component of high octane

gasoline. In organic synthesis, it is used to make ethylbenzene, isopropyl-benzene, cyclohexane, aniline,

maleic anhydride and alkylbenzenes (NTP, 2001).

Benzene is also a component of gasoline since it occurs naturally in crude oil and it is a byproduct of oil

refining processes. The percentage by volume of benzene in unleaded gasoline is approximately 1-2%. 

In the past, certain consumer products, such as some types of paint strippers and carpet glue, carburetor

cleaners, denatured alcohol, textured carpet liquid detergent, furniture wax, and rubber cement used in

tire patch kits and arts and crafts supplies contained small amounts of benzene (ATSDR, 1997). 

The use of benzene in certain pesticides has been canceled. Under the Federal Insecticide, Fungicide,

and Rodenticide Act (FIFRA), the USEPA has established a voluntary cancellation of registered products

containing benzene as an active ingredient. Benzene was once used alone or in formulations to control

screwworms on animals and as an early fumigant for grain. Under the Food, Drug, and Cosmetics Act,

benzene is regulated as an indirect food additive and restricted for use only as a component of adhesives

used on articles intended for packaging, transport, or holding foods (ATSDR, 1997). 

More than 98% of the benzene produced in the U.S. is derived from the petrochemical and petroleum

refining industries. Catalytic reformat is the major source of benzene; between 1978 and 1981, catalytic

reformats accounted for approximately 44-50% of the total U.S. benzene production. In 1994, benzene

was the 17th highest volume chemical produced in the US, with 14.7 billion pounds produced. Other

production data are as follows: 12.3 billion pounds in 1993, 12.0 billion pounds in 1992, and 11.5 billion

pounds in 1991 (ATSDR, 1997).

Table 4.1-1 shows the number of facilities in each State that manufacture and process benzene, the

intended uses of the product, and the range of maximum amounts derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 1997). 
Occurrence Summary and Use Support Document March 2002 294

Table 4.1-1: Benzene Manufacturers and Processors by State

Statea Number of

facilities

Range of maximum amounts on site in

thousands of poundsb Activities and usesc

AK 4 0-10,000 1,3,4,8,10

AL 18 0-50,000 1,2,3,4,5,6,7,8,9,11,13

AR 4 1-10,000 1,3,4,7,13

AZ 2 10-1,000 1,6,10,13

CA 35 0-50,000 1,2,3,4,5,6,7,8,9,10,13

CO 2 1,000-10,000 1,3,4,6,7

DE 4 1-50,000 1,6,7,9,12,13

GA 6 0-10,000 1,2,4,8,9,10,11

HI 2 1,000-10,000 1,2,6

IA 1 1,000-10,000 1,4

IL 26 1-100,000 1,2,3,4,5,6,7,8,9,10,11,12,13

IN 18 1-100,000 1,2,3,4,5,6,8,9,10,11,13

KS 10 0-50,000 1,3,4,5,6,7,8,9,10,13

KY 12 1-50,000 1,3,4,5,6,7,8,9,10,11,13

LA 40 0-500,000 1,2,3,4,5,6,7,8,9,10,11,13

MD 3 1-10,000 7,8,9

MI 28 0-10,000 1,2,3,4,5,6,7,8,9,10,11,13

MN 3 1-100,000 1,3,4,6,8,9

MO 7 0-100 8,9,13

MS 6 10-50,000 1,3,4,6,7,8

MT 4 100-500,000 1,2,3,4,6,7,8,9

NC 3 0-1,000 1,5,11

ND 1 10,000-50,000 1,2,3,4,7

NE 1 0-1 11

NJ 12 1-50,000 1,2,3,4,6,7,8,9,10,11,13

NM 4 1-10,000 1,3,4,6,8,13

NY 5 1-1,000 1,2,4,5,9,11,13

OH 25 0-100,000 1,2,3,4,5,6,8,9,10,11,13

OK 6 1-50,000 1,2,3,4,5,6,7,8,9,13

OR 1 1,000-10,000 10

PA 21 0-50,000 1,2,3,4,5,6,7,8,10,11,13

PR 5 100-50,000 1,2,3,5,6,7,8

SC 3 0-1,000 1,5,7,12

TN 9 0-10,000 1,3,5,6,7,8,9,12,13

TX 94 0-500,000 1,2,3,4,5,6,7,8,9,10,11,12,13

UT 8 10-50,000 1,2,3,4,6,7,8,9,10,13

VA 5 1-1,000 1,2,3,5,6,7,9,11

VT 1 100,000-500,000 1,2,3,4,7

WA 6 100-100,000 1,2,3,4,6,7,8

WI 4 1-10,000 1,6,9,12,13

WV 8 1-10,000 1,4,5,6,7,8,9,13

WY 5 0-10,000 1,3,4,5,6,7,8,10

a

Post office State abbreviations used

b

Data in TRI are maximum amounts on site at each facility

c

Activities/Uses:

1. Produce 8. As a formulation component

2. Import 9. As a product component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

Source: ATSDR, 1997 compilation of TRI93 1995 data

4.1.2 Environmental Release

Benzene is listed as a Toxics Release Inventory (TRI) chemical. Table 4.1-2 illustrates the

environmental releases for benzene from 1988 to 1999. (Benzene data are only available for these years.) 

Air emissions constitute most of the on-site releases, with a steady decrease over the years, except for
Occurrence Summary and Use Support Document March 2002 295

small increases in 1997 and 1999. The decrease in air emissions has been the major contributor to

decreases in benzene total on- and off-site releases, as the release total declined every year but 1997. 

Surface water discharges have also generally decreased, and averaged around 15,000 pounds for 1997-

1999. Underground injection declined until 1994, and has been rising ever since. Releases to land (such

as spills or leaks within the boundaries of the reporting facility) have varied between levels of 717,000

pounds and 18,000 pounds between 1988 and 1999, with no discernable trend. Off-site releases

(including metals or metal compounds transferred off-site) also span a wide range of values, although

releases between 1988 and 1990 were greater than any releases since. These TRI data for benzene were

reported from 49 States (except Vermont), Puerto Rico, Washington D.C., the Virgin Islands, Guam,

American Samoa, and the Northern Mariana Islands (USEPA, 2000). Fifteen of the 16 cross-section

States (used for analyses of benzene occurrence in drinking water; see Section 4.1.4) reported releases of

benzene, the exception being Vermont. (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 4.1-2: Environmental Releases (in pounds) for Benzene in the United States, 1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 7,287,778 13,647 617,825 18,732 147,994 8,085,976

1998 7,239,578 15,070 504,109 237,544 185,440 8,181,741

1997 8,777,297 12,226 363,100 62,474 83,476 9,298,573

1996 8,219,965 27,357 312,766 51,178 66,246 8,677,512

1995 9,410,086 21,290 282,642 18,583 71,391 9,803,992

1994 9,853,271 22,294 223,103 25,555 203,685 10,327,908

1993 11,362,776 19,450 356,660 31,220 94,171 11,864,277

1992 13,236,803 24,347 355,683 342,241 93,486 14,052,560

1991 19,032,803 27,238 824,342 113,153 140,989 20,138,525

1990 25,846,649 25,303 689,066 717,008 264,685 27,542,711

1989 27,422,786 169,170 668,610 114,132 241,518 28,616,216

1988 32,341,184 46,732 825,035 126,728 396,880 33,736,559

 Source: USEPA, 2000 

4.1.3 Ambient Occurrence

Benzene was detected in 14 out of 398 wells (3.5%) in urban areas of the local, State, and federal data set

compiled by NAWQA. The minimum and maximum concentrations detected were 0.2 :g/L and 290

:g/L, respectively. The median value of detection concentrations was 1.0 :g/L. Benzene was also

detected in 24 of the 2,504 wells (0.96%) with analysis in rural areas. The minimum and maximum

concentrations detected were 0.2 :g/L and 73 :g/L, respectively. The median value of detection

concentrations was 0.7 :g/L. These data (urban and rural) represent untreated ambient ground water of

the conterminous United States for the years 1985-1995 (Squillace et al., 1999).

Benzene was also an analyte in both the NURP and NPDES data. The NURP study found benzene in

urban runoff. The minimum and maximum concentrations detected were 3.5 :g/L and 13 :g/L,

respectively, with no mean value reported. The use of the land from which the samples were taken was

unspecified. The NPDES related investigations analyzing urban and highway runoff detected benzene. 
Occurrence Summary and Use Support Document March 2002 296

The maximum concentration of benzene in NPDES samples of stormwater was 0.8 :g/L, and the

drinking water standard (MCL) is 5 :g/L (Lopes and Dionne, 1998).

4.1.3.1 Additional Ambient Occurrence Data

A summary document entitled “Benzene: Occurrence in Drinking Water, Food, and Air” (JRB

Associates, 1983), was previously prepared for past USEPA assessments of benzene. However, no

information on the ambient occurrence of benzene was included in that document. (The document did

include information regarding benzene occurrence in drinking water, which is discussed in Section 4.1.5

of this report.)

4.1.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of benzene occurrence presented in the following section is based on State compliance

monitoring data from the 16 cross-section States. The 16-State cross-section is the largest and most

comprehensive compliance monitoring data set compiled by EPA to date. These data were evaluated

relative to several concentration thresholds of interest: 0.005 mg/L; 0.0005 mg/L; and 0.0004 mg/L.

All sixteen cross-section State data sets contained occurrence data for benzene. These data represent

more than 194,000 analytical results from approximately 23,000 PWSs during the period from 1984 to

1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs vary by

State, although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limit for benzene in the 16 cross-section States is equal to

0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to Section 1.3.5 of this

report.)

4.1.4.1 Stage 1 Analysis Occurrence Findings

Table 4.1-3 illustrates the occurrence of benzene in drinking water for the public water systems in the 16-

State cross-section relative to three thresholds: 0.005 mg/L (the current MCL), 0.0005 mg/L (the modal

MRL), and 0.0004 mg/L. Based on the 16-State cross-section data, a total of 44 (approximately 0.189%

of) ground water and surface water PWSs had analytical results exceeding the MCL; 1.02% of systems

(237 systems) had results exceeding 0.0005 mg/L; and 1.24% of systems (288 systems) had results

exceeding 0.0004 mg/L. 

Approximately 0.185% of ground water systems (40 systems) had any analytical results greater than the

MCL. About 0.941% of ground water systems (204 systems) had results above 0.0005 mg/L. The

percentage of ground water systems with at least one result greater than 0.0004 mg/L was equal to 1.10%

(239 systems). 

Only 4 (0.251% of) surface water systems had results greater than the MCL. A total of 33 (2.07% of)

surface water systems had at least one analytical result greater than 0.0005 mg/L. Forty-nine (3.07% of)

surface water systems had results exceeding 0.0004 mg/L.
Occurrence Summary and Use Support Document March 2002 297

Table 4.1-3: Stage 1 Benzene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.185% 40

0.0005 0.941% 204

0.0004 1.10% 239

Surface Water

0.005 0.251% 4

0.0005 2.07% 33

0.0004 3.07% 49

Combined Ground &

Surface Water

0.005 0.189% 44

0.0005 1.02% 237

0.0004 1.24% 288

Reviewing benzene occurrence by PWS population served (Table 4.1-4) shows that approximately

0.581% (almost 575,000 people) of the 16-State population was served by PWSs with at least one

analytical result of benzene greater than the MCL (0.005 mg/L). The percentage of population exposed

dramatically increased when evaluated relative to 0.0005 mg/L and 0.0004 mg/L. Approximately 12.4

million (11.2% of) people were served by systems with an exceedance of 0.0005 mg/L. A total of about

13.2 million (11.9% of) people were served by systems with at least one analytical result greater than

0.0004 mg/L.

The percentage of population served by ground water systems with analytical results greater than the

MCL was equal to 0.980% (about 486,300 people). When evaluated relative to 0.0005 mg/L or 0.0004

mg/L, the percent of population exposed was equal to 6.20% (3,074,800 people) and 6.74%

(approximately 3.3 million people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.005 mg/L was

equal to 0.144% (88,300 people). Approximately 15.2% of the population served by surface water

systems (about 9.3 million people) was exposed to benzene concentrations greater than 0.0005 mg/L. 

When evaluated relative to 0.0004 mg/L, the percent of population exposed was equal to 16.0% (over 9.8

million people).
Occurrence Summary and Use Support Document March 2002 298

Table 4.1-4: Stage 1 Benzene Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.005 0.980% 486,300

0.0005 6.20% 3,074,800

0.0004 6.74% 3,346,200

Surface Water

0.005 0.144% 88,300

0.0005 15.2% 9,289,900

0.0004 16.0% 9,823,500

Combined Ground &

Surface Water

0.005 0.518% 574,700

0.0005 11.2% 12,364,700

0.0004 11.9% 13,169,800

4.1.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.1-5 and 4.1-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

A total of 7 (0.0312% of) ground water and surface water PWSs in the 16 States had an estimated mean

concentration of benzene exceeding 0.005 mg/L. Approximately 65 (0.279% of) PWSs in the 16 States

had an estimated mean concentration exceeding 0.0005 mg/L, and 80 (0.343%) had an estimated mean

concentration exceeding 0.0004 mg/L. 

An estimated 7 (0.0332% of) ground water PWSs in the 16 cross-section States had a mean concentration

greater than 0.005 mg/L, 61 (0.282%) had a mean concentration greater than 0.0005 mg/L, and 75

(0.344%) had a mean concentration greater than 0.0004 mg/L. Approximately 1 (0.00363% of), 4

(0.237% of), and 5 (0.323% of) surface water PWSs in the 16 States had estimated mean concentrations

exceeding 0.005 mg/L, 0.0005 mg/L, and 0.0004 mg/L, respectively.
Occurrence Summary and Use Support Document March 2002 299

Table 4.1-5: Stage 2 Estimated Benzene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.0332% 0.0138% - 0.0554% 7 3 - 11

0.0005 0.282% 0.198% - 0.369% 61 43 - 80

0.0004 0.344% 0.249% - 0.452% 75 54 - 98

Surface Water

0.005 0.00363% 0.000% - 0.0627% 1 0 - 1

0.0005 0.237% 0.0627% - 0.501% 4 1 - 8

0.0004 0.323% 0.125% - 0.627% 5 2 - 10

Combined Ground

& Surface Water

0.005 0.0312% 0.0172% - 0.0516% 7 4 - 12

0.0005 0.279% 0.198% - 0.370% 65 46 - 86

0.0004 0.343% 0.245% - 0.456% 80 57 - 106

Reviewing benzene occurrence by PWS population served (Table 4.1-6) shows that approximately

0.00947% of population served by all PWSs in the 16 cross-section States (an estimate of about 10,500

people) was potentially exposed to benzene levels above 0.005 mg/L. The percentage of population

served by PWSs in the 16 States with levels of benzene above 0.0005 mg/L and 0.0004 mg/L were

0.260% (about 288,000 people) and 0.309% (over 342,000 people), respectively. 

When the percent of population served by ground water systems was evaluated relative to a threshold of

0.005 mg/L, 0.0005 mg/L, and 0.0004 mg/L, the percentage of population exposed in the 16 cross-section

States was equal to 0.0204% (an estimated 10,100 people), 0.481% (an estimated 238,700 people) and

0.546% (an estimated 271,100 people), respectively. 

The percentage of population served by surface water systems with levels above 0.005 mg/L was equal to

0.000625% (an estimated 400 people in the 16 States), and the percentage of population served with

levels above 0.0005 mg/L was 0.0805% (over 49,000 people). The percentage of the population served

by surface water systems with levels above 0.0004 mg/L was 0.117% (about 71,400 people in the 16

States). 
Occurrence Summary and Use Support Document March 2002 300

Table 4.1-6: Stage 2 Estimated Benzene Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.0204% 0.00407% - 0.0629% 10,100 2,000 - 31,200

0.0005 0.481% 0.340% - 0.632% 238,700 168,900 - 313,500

0.0004 0.546% 0.399% - 0.758% 271,100 197,900 - 376,000

Surface Water

0.005 0.000625% 0.000% - 0.0220% 400 0 - 13,500

0.0005 0.0805% 0.0194% - 0.283% 49,300 11,900 - 173,100

0.0004 0.117% 0.0244% - 0.451% 71,400 15,000 - 276,200

Combined Ground

& Surface Water

0.005 0.00947% 0.00188% - 0.0300% 10,500 2,100 - 33,200

0.0005 0.260% 0.176% - 0.389% 288,000 194,700 - 431,400

0.0004 0.309% 0.211% - 0.514% 342,500 234,200 - 570,100

4.1.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 20 PWSs nationally serving approximately 20,200 people could be exposed to

benzene concentrations above 0.005 mg/L. About 181 systems serving 553,400 people nationally had

estimated mean concentrations greater than 0.0005 mg/L. Approximately 223 systems serving about

658,000 people nationally were estimated to have mean benzene concentrations greater than 0.0004

mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to national

values.)

For ground water systems, an estimated 20 PWSs serving about 17,500 people nationally had mean

concentrations greater than 0.005 mg/L. Approximately 168 systems serving about 412,100 people

nationally had estimated mean concentration values that exceeded 0.0005 mg/L. About 204 ground

water systems serving almost 468,200 people had estimated mean concentrations greater than 0.0004

mg/L. 

Approximately 1 surface water systems serving 800 people was estimated to have mean concentration of

benzene above 0.005 mg/L. About 13 surface water systems serving 102,500 people had estimated mean

concentrations greater than 0.0005 mg/L. An estimated 18 surface water systems serving approximately

148,500 people had mean concentrations greater than 0.0004 mg/L.
Occurrence Summary and Use Support Document March 2002 301

Table 4.1-7: Estimated National Benzene Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 20 8 - 33 17,500 3,500 - 53,900

0.0005 168 118 - 219 412,100 291,700 - 541,300

0.0004 204 148 - 269 479,900 341,800 - 649,200

Surface Water

0.005 1 0 - 4 800 0 - 28,000

0.0005 13 4 - 28 102,500 24,700 - 359,800

0.0004 18 7 - 35 151,400 31,100 - 574,200

Combined Ground

& Surface Water

0.005 20 11 - 34 20,200 4,000 - 63,800

0.0005 181 129 - 240 553,400 374,000 - 828,800

0.0004 223 159 - 296 658,000 449,900 - 1,095,300

4.1.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of benzene in drinking water are also reviewed. 

Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence of Benzene in Drinking Water, Food, and Air” (JRB Associates, 1983), is presented in this

section. This variety of studies and information are presented regarding levels of benzene in drinking

water, with the scope of the reviewed studies ranging from national to regional. Note that none of the

studies presented in the following section provide the quantitative analytical results or comprehensive

coverage that would enable direct comparison to the occurrence findings estimated with the cross-section

occurrence data presented in Section 4.1.4. These additional studies, however, do enable a broader

assessment of the Stage 2 occurrence estimates presented for this Six-Year Review. All the following

information in Section 4.1.5 is taken directly from “Occurrence of Benzene in Drinking Water, Food, and

Air” (JRB Associates, 1983).

4.1.5.1 Overview and Quality Assurance Assessment of Federal Drinking Water Surveys

Four national drinking water surveys provide data on benzene: the National Organic Monitoring Survey

(NOMS), the National Screening Program for Organics in Drinking Water (NSP), the 1978 Community

Water Supply Survey (CWSS), and the Groundwater Supply Survey (GWSS). The terms used in this

report are those used in the individual surveys, recognizing that they may not always correspond to strict

technical definitions.

The National Organic Monitoring Survey (NOMS) was conducted to identify contaminant sources, to

determine the frequency of occurrence of specific drinking water contaminants, and to provide data for

the establishment of maximum contaminant levels (MCL's) for various organic compounds in drinking

water (Brass et al., 1977, as cited in JRB Associates, 1983). The NOMS was conducted in three phases:

March-April 1976, May-July 1976, and November 1976-January 1977. Finished drinking water samples
Occurrence Summary and Use Support Document March 2002 302

from 113 communities were analyzed for 21 different compounds. Of the 113 community supplies

sampled, 18 had groundwater sources, 91 had surface water sources, and 4 had a mixed

groundwater/surface water source.

The analytical results of the NOMS were made available in printed form by EPA's Technical Support

Division, Office of Drinking Water. Additional information on the locations and source of the supplies,

and on the populations served by the supplies in the NOMS were provided by Wayne Mello (1983) at

EPA's Technical Support Division, Office of Drinking Water. A single value for benzene was reported

for each supply studied in the NOMS. 

The National Screening Program for Organics in Drinking Water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water

systems in 33 States for 51 organic chemical contaminants. Data are available for benzene on finished

water samples from 12 groundwater and 100 surface water supplies. However, the data for three of the

groundwater supplies and 27 of the surface water supplies were indicated by Boland (1981, as cited in

JRB Associates, 1983) to be suspect due to potential interference by chlorodibromomethane and

trichloroethylene.

In the Community Water Supply Survey (CWSS), carried out in 1978, 106 surface water supplies, 330

groundwater supplies, and 16 supplies with mixed sources were examined for volatile organic chemical

contamination. Fourteen purgeable organic compounds were analyzed and total organic carbon levels

were determined. Samples were taken of raw, finished, and distribution water. Only the latter two types

of water are considered here. Data for benzene in finished and/or distribution samples were obtained

from a total of 289 groundwater and 97 surface water supplies.

The Groundwater Supply Survey (GWSS) was conducted from December 1980 to December 1981 to

develop additional data on the occurrence of volatile organic chemicals in the nation's groundwater

supplies (Westrick et al., 1983, as cited in JRB Associates, 1983). It was hoped that this study would

stimulate State efforts toward the detection and control of groundwater contamination and the

identification of potential chemical "hot spots." A total of 945 systems were sampled, of which 466 were

chosen at random. The remaining 479 systems were chosen nonrandomly based on information from

States encouraged to identify locations believed to have a higher than normal probability of VOC

contamination (e.g., locations near landfills or industrial activity). The file provided a single analytical

result for each supply sampled. One sample of finished water was collected from each supply at a point

near the entrance to the distribution system. 

Each of the drinking water surveys was evaluated with respect to the validity of the reported occurrence

data for a number of organic chemicals, including benzene. The evaluations were carried out by

analyzing information about the procedures used for collection and analysis of samples as well as the

quality control protocols used. The reported results for the compounds studied in each survey were

judged with respect to their qualitative acceptability (i.e., was the substance correctly identified as

benzene), and their quantitative acceptability (i.e., are the reported measurements reliable). In the case of

benzene, a qualitatively acceptable but quantitatively unacceptable rating was given for data from the

NOMS, NSP and CWSS due to suspected biodegradation of the samples, which were held unrefrigerated

for prolonged periods before analysis (particularly the CWSS). Benzene values in excess of the

quantitation limit reported for some samples in these studies are qualitatively valid and can be taken as

minimum values, representative of samples which probably originally contained benzene at higher

concentrations. In the case of the GWSS, all data were rated both quantitatively and qualitatively

acceptable.
Occurrence Summary and Use Support Document March 2002 303

4.1.5.2 Groundwater – Federal Surveys

The National Organic Monitoring Survey (NOMS), the National Screening Program for Organics in

Drinking Water (NSP), the Community Water Supply Survey (CWSS), and the Groundwater Supply

Survey (GWSS) all contain data concerning the levels of benzene in groundwater supplies from across

the country.

Eighteen groundwater systems were analyzed for benzene during Phase I of NOMS (March to April

1976); the Phase I data are not reported here because of sample contamination invalidating the results. 

Eighteen groundwater systems were sampled during Phase II of the study (May to July 1976) with one

containing benzene at a concentration of 0.1 :g/L. Only one supply was analyzed during Phase III of the

study (November 1976 to January 1977) for benzene; none was observed. The minimum quantifiable

limits for benzene were 0.1-0.2 :g/L in Phase II and 0.2 :g/L in Phase III.

Twelve groundwater supplies were tested for benzene contamination in the NSP. Data for three of these

were indicated by Boland (1981, as cited in JRB Associates, 1983) to be suspect because of a potential

analytical interference. Of the remaining 9 systems, none were found to be contaminated with benzene

above the quantification limit of 0.1 :g/L.

The 1978 CWSS provided information on benzene levels in 289 groundwater systems. Of these systems,

5 contained detectable levels of benzene, with values ranging from 0.51-21.8 :g/L. The mean value was

5.0 :g/L with a standard deviation of 9.3 :g/L; the median value was 0.95 :g/L. The minimum

quantitation limits for benzene in the CWSS ranged from 0.50-1 :g/L.

In the GWSS, 3 of the 456 randomly chosen water systems serving 25 or more individuals were

contaminated with benzene, at concentrations of 0.61, 3, and 15 :g/L. Of the 473 nonrandom locations

sampled serving 25 or more individuals, 8 were contaminated with benzene, at concentrations between

0.5-12 :g/L, the highest values being 1.6, 2.7, and 12 :g/L. The average benzene level for the

nonrandom systems was 4.1 :g/L with a standard deviation of 4.9 :g/L; the median value was 2.2 :g/L. 

The minimum quantitation limit for benzene was 0.5 :g/L.

4.1.5.3 Groundwater – State Data

Data supplied to the U.S. Environmental Protection Agency by Connecticut and Delaware, showed

relatively small amounts of benzene in the groundwater supplying one of four cities examined. Six

samples from this site had benzene concentrations ranging from nondetectable to 4.0 :g/L, with an

average of 1.8 :g/L. In Elkhart, Indiana, five samples had benzene concentrations ranging from 0.3-

3,500 :g/L, with an average of 2,200 :g/L. Benzene was detected in drinking water samples from

Lunenberg, Massachusetts, where 10 samples had benzene levels from undetectable to 145 :g/L (average

of 70 :g/L). Finally, in Nassau County, New York, eight of 165 wells tested for benzene showed

positive results, but were not quantified.

4.1.5.4 Surface Water – Federal Surveys

The National Organic Monitoring Survey (NOMS), the National Screening Program for Organics in

Drinking Water (NSP), and the Community Water Supply Survey (CWSS) all contain data concerning

the levels of benzene in surface water supplies from across the country.

In Phase I of the National Organic Monitoring Survey (March to April 1976), water samples from 89

surface water systems were analyzed for benzene; the Phase I data are not reported here because of
Occurrence Summary and Use Support Document March 2002 304

sample contamination invalidating the results. Ninety-one systems were sampled during the second

phase of the survey and 5 were found to be contaminated, at levels ranging from 0.1-1.8 :g/L. The

average benzene concentration among the positive Phase II samples was 0.5 :g/L with a standard

deviation of 0.7 :g/L; the median concentration was 0.3 :g/L. During the third phase of the NOMS

(November 1976 to January 1977), analyses revealed benzene contamination in 4 out of a total of 14

systems sampled. The contamination levels for these systems ranged from 0.1-1.5 :g/L. The mean

concentration was 0.9 :g/L with a standard deviation of 0.6 :g/L; the median level was 1.0 :g/L. The

minimum quantifiable limits for benzene ranged from 0.1-0.4 :g/L in Phase II and 0.1-0.2 :g/L in Phase

III.

Surface water samples from 100 drinking water systems were analyzed for benzene during the National

Screening Program (NSP) between June 1977 and March 1981. Data for 27 of these were indicated by

Boland (1981, as cited in JRB Associates, 1983) to be suspect because of a potential analytical

interference. Of the remaining 73 systems, 23 contained detectable levels of benzene, ranging from 0.1-

1.8 :g/L. The average concentration among the 23 positive systems was 0.2 :g/L with a standard

deviation of 0.4 :g/L; the median level was 0.1 :g/L. The quantification limit for the NSP was 0.1 :g/L.

One of the 97 surface water systems sampled during the Community Water Supply Survey (CWSS)

contained benzene, at a concentration of 0.56 :g/L. The minimum quantitation limit for benzene in the

CWSS was 0.5 :g/L.

4.1.5.5 Surface Water – State Data

Three States provided data to the EPA on levels of benzene in drinking water supplies derived from

surface water. Connecticut and Delaware reported data for a total of four cities, none of which had any

positive samples. In New York, one of two cities supplying surface water data had detectable benzene

concentrations. Of five samples from Waterford, New York, four were positive for benzene, with levels

of 1.0-4.7 :g/L (average of 2.2 :g/L).

4.1.5.6 Projected National Occurrence of Benzene in Public Water Supplies

As reported in the JRB Associates (1983) report, public water systems in the United States fall into two

major categories with respect to water source (surface water and groundwater) and into five size

categories and twelve subcategories according to the number of individuals served. The JRB 1983 report

presented estimates of both the number of drinking water supplies nationally within each of the

source/size categories expected to have benzene present, and of the concentration of benzene expected to

be present in those supplies.

The key features of the methodology used and assumptions made to develop the national estimates are

summarized here. The estimates are based on the data from the Federal surveys only. The State data

were not included for several reasons. Generally, these data are from a few States and were not

considered to be geographically representative. There was also a general lack of data on the population

served by systems measured, the type of water sampled, and the methodologies used to sample, identify,

and measure benzene.

The Federal survey data from the NOMS, NSP, CWSS, and GWSS were pooled together for developing

the national projections. It was assumed in combining these surveys that the resulting data base would be

representative of the nation's water supplies. In the case of the GWSS data, both the random and

nonrandom samples were included in the projections because a statistical test of the GWSS data showed
Occurrence Summary and Use Support Document March 2002 305

no statistically significant difference in the frequency of occurrence of positive values or the mean of the

positive values between the random and nonrandom samples.

Ideally, adequate data would be available to develop the national projections separately for each of the

twelve system size categories within the groundwater and surface water groups; however, the available

data were too limited for this. JRB (1983) consolidated some of the size categories to have sufficient

data for developing the projections. In consolidating data from various size categories, consideration was

given to the potential for there being statistically significant differences in the frequency of occurrence of

benzene as a function of system size. The consolidation of size categories therefore involved a balancing

of the need to group size categories together to have an adequate data base for developing the national

projections against the need to treat size categories separately in order to preserve the influence of system

size as a determinant of contamination potential. The consolidation of size categories also took into

account EPA's classification of systems into the five major groups as very small (25-500), small (501-

3,300), medium (3,301-10,000), large (10,001-100,000), and very large (> 100,000) (Kuzmack, 1983, as

cited in JRB Associates, 1983).

Once the data were consolidated, statistical models for extrapolating to the national level were tested and

an appropriate model selected. In the case of benzene, the delta distribution was used for groundwater

and the multinominal method was used for surface water. The frequency of contamination of

groundwater and surface water systems at various concentrations was determined for each consolidated

size category. For completing the national estimates, it was assumed that the frequency of contamination

observed for each consolidated category was directly applicable to each of the system sizes comprising it.

In the JRB Associates (1983) report, it is noted that some of the data used in computing the national

estimates are from samples held for a prolonged period of time prior to analysis, with possible

biodegradation of benzene. Therefore, they concluded that these projections of national occurrence may

underestimate actual contaminant levels.

4.1.5.6.1 Groundwater Supplies

The combined benzene groundwater data from the NOMS, NSP, CWSS, and GWSS surveys are

available. JRB Associates (1983) also reported that data were available for a total of 1,223 supplies from

the combined surveys. Of these, 17 supplies were reported to have benzene present, at concentrations

ranging from 0.13 :g/L to 15 :g/L. Based on the overall distribution of positive values and maximum

possible values for those supplies in which benzene was not found, 0.5 :g/L was selected as the common

minimum quantifiable concentration for the combined survey data. That is, quantitative projections are

made of supplies at several concentration ranges > 0.5 :g/L, while only a total number for supplies

expected to have either no benzene or levels below 0.5 :g/L can be determined. Although some data

indicate the presence of benzene in groundwater supplies at levels < 0.5 :g/L, it is not possible to

determine the proportion of supplies that have benzene present and the proportion that are actually free of

benzene contamination.

Of the 1,206 supplies reporting no benzene to be present, 1,202 were assumed to have maximum possible

levels of < 0.5 :g/L based on the minimum quantifiable concentrations reported for the various surveys. 

The other 4 supplies reporting no benzene to be present had maximum possible levels ranging from 0.6

:g/L to 1.0 :g/L. It is assumed, based on the overall distribution of values, that benzene if present in

these 4 supplies is so at a concentration of < 0.5 :g/L, although a rigorous, conservative argument could

be made for assuming a level equal to the maximum possible value.
Occurrence Summary and Use Support Document March 2002 306

Sixteen of the 1,223 supplies examined had measured values of benzene > 0.5 :g/L. When the twelve

size categories were consolidated into the five major EPA groupings, there was no apparent trend in the

frequency of values > 0.5 :g/L as a function of size:

Very small 0.3% (1/362)

Small 1.4% (4/293)

Medium 1.6% (3/186)

Large 2.4% (8/338)

Very large 0% (0/44)

Overall 1.3% (16/1,223)

A test for statistical significance revealed that at the 0.05 level, the difference among the five categories

was not significant; therefore, all supplies were grouped together for the analysis. As noted previously,

the frequency of occurrence of benzene at various concentrations was determined for the consolidated

group and then applied to the number of supplies nationally within each of the individual size categories

comprising the group.

No groundwater supplies are estimated to have benzene present in any of the 10 :g/L ranges above 50

:g/L, but it can be estimated that there are two supplies with benzene present at levels exceeding 50

:g/L. This apparent discrepancy is due to the rounding of fractional numbers of supplies resulting from

the delta distribution to the nearest integer. That is, the fractional numbers of supplies estimated to have

benzene above 50 :g/L were rounded to 0 within each individual 10 :g/L range, while the sum of all the

fractional numbers above 50 :g/L was rounded to 2. The cumulative estimates are probably more

descriptive of the national occurrence than are the estimates within each 10 :g/L range. An estimated

635 groundwater supplies (range of 330-939), approximately 1.3% of the total groundwater supplies in

the United States, are expected to have benzene at levels of > 0.5 :g/L; the remaining 47,823 supplies

have either no benzene or levels < 0.5 :g/L.

It is estimated that 60 supplies (range of 0-154) are expected to have benzene levels > 10 :g/L; while 2

supplies (range of 0-23) are expected to have levels > 50 :g/L. Most of the supplies with high benzene

levels are expected to be in the smaller size categories. Although, as noted previously, the frequency of

benzene occurrence appears to be independent of system size, the number of systems affected nationally

is greater for the small sizes because there are many more small systems in existence.

4.1.5.6.2 Surface Water Systems

Data are available for a total of 223 surface water supplies. Of these, 29 supplies were reported by JRB

Associates (1983) to have benzene present at concentrations ranging from 0.1 :g/L to 1.4 :g/L.

Based on the overall distribution of positive values and maximum possible values for those supplies in

which benzene was not found, 0.5 :g/L was selected as the common minimum quantifiable concentration

for the combined survey data. That is, quantitative projections are made of supplies at several

concentration ranges > 0.5 :g/L, while only a total number for supplies expected to have either no

benzene or levels below 0.5 :g/L can be determined. Although some data indicate the presence of

benzene in surface water supplies at levels < 0.5 :g/L, it is not possible to determine the proportion that

have benzene present and the proportion that are free of benzene contamination.

Only 6 of the 223 supplies examined had measured values of benzene > 0.5 :g/L. The twelve size

categories were consolidated into the five major EPA groupings, showing the following frequency of

occurrence of values > 0.5 :g/L as a function of size:
Occurrence Summary and Use Support Document March 2002 307

Very small 0% (0/18)

Small 2.9% (1/34)

Medium 4.2% (1/24)

Large 1.9% (1/52)

Very large 3.2% (3/95)

Overall 2.7% (6/223)

A test for statistical significance revealed that at the 0.05 level, there was no difference in the frequency

of occurrence of benzene at levels > 0.5 :g/L among these groups. Therefore, the data from all sizes

were consolidated to develop the national estimates. As noted previously, the frequency of occurrence of

benzene at various concentrations was determined for the consolidated group and then applied to the

number of supplies nationally within each of the individual size categories comprising it.

An estimated 301 surface water supplies (range of 64-537), approximately 2.7% of the total surface water

systems in the United States, are expected to have benzene at levels > 0.5 :g/L; the remaining 10,901

supplies have either no benzene or levels < 0.5 :g/L. It is estimated that no surface water supplies will

have levels > 5 :g/L.

4.1.6 Conclusion

Benzene is a manufactured organic chemical that is used heavily in several industries and (in 1994) was

the 17th highest volume chemical produced in the U.S. Most benzene is used as a building block for

making plastics, rubber, resins and synthetic fabrics like nylon and polyester. It is also used in the

manufacture of medicines, dyes, artificial leather, linoleum, oil cloth, pesticides, plastics and resins,

PCB, aviation fuel, other organics, and in organic synthesis. Recent statistics regarding production and

use indicate that benzene is a very abundant chemical. Industrial releases of benzene have been reported

to TRI since 1988 in 49 States, Puerto Rico, Washington D.C., the Virgin Islands, Guam, American

Samoa, and the Northern Mariana Islands. Benzene was also an analyte for the NAWQA, NURP, and

NPDES ambient occurrence studies. In the NAWQA study, benzene was detected in 3.5% of urban wells

and 0.96% of rural wells, with median detection values of 1.0 :g/L and 0.7 :g/L, respectively. The Stage

2 analysis, based on the 16-State cross-section, estimated that approximately 0.0313% of combined

ground water and surface water systems serving 0.0105% of the population had estimated mean

concentrations of benzene greater than the MCL of 0.005 mg/L. Based on this estimate, approximately

20 PWSs nationally serving approximately 22,500 people are expected to have estimated mean

concentrations of benzene greater than the MCL. 

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, benzene is manufactured and/or processed in over 40 States and has TRI

releases in every state except for Vermont. Benzene is manufactured and/or processed in 14 out of the 16

cross-section States and has TRI releases in 15 of the 16 cross-section States. The cross-section should

adequately represent the occurrence of benzene on a national scale based upon the use, production, and

release patterns of the 16-State cross-section in relation to the patterns observed for all 50 States. 

4.1.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1997. Toxicological Profile for Benzene.

U.S. Department of Health and Human Services, Public Health Service. 423 pp. + Appendices. 

Available on the Internet at http://www.atsdr.cdc.gov/toxprofiles/tp3.pdf
Occurrence Summary and Use Support Document March 2002 308

Boland, P.A. 1981. National Screening Program for Organics in Drinking Water. Prepared by SRI

International, Menlo Park, California, for Office of Drinking Water, U.S. Environmental

Protection Agency, Washington, DC. EPA Contract No. 68-01-4666. 

Brass, H.J., M.A. Feige, T. Halloran, J.W. Mello, D. Munch, and R.F. Thomas. 1977. The National

Organic Monitoring Survey: A sampling and analysis for purgeable organic compounds. 

Drinking water quality enhancement through source protection. R.B. Pojasek (ed.). Ann Arbor,

MI: Ann Arbor Science, pp. 393-416.

JRB Associates. 1983. Benzene: Occurrence in Drinking Water, Food, and Air. Draft report submitted

to EPA for review November 23, 1983.

Kuzmack, A.M. 1983. Memorandum: Characterization of the water supply industry (FY82). 

Washington, D.C.: Office of Water, U.S. Environmental Protection Agency. May 16, 1983. 

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 

67 pp.

Mello, Wayne. 1983. Personal communication between Wayne Mello, Technical Support Division,

Office of Drinking Water, U.S. Environmental Protection Agency, and author of JRB Associates,

1983, March 10, 1983.

National Safety Council (NSC). 2001. Benzene Chemical Backgrounder. Itasca, IL: National Safety

Council. Available on the Internet at:

http://www.crossroads.nsc.org/ChemicalTemplate.cfm?id=83&chempath=chemicals, accessed

July 23, 2001.

National Toxicology Program (NTP). 2001. National Toxicology Program Health and Safety

Information Sheet - Benzene. Available on the Internet at

http://ntp-server.niehs.nih.gov/htdocs/CHEM_H&S/NTP_Chem7/Radian71-43-2.html, last

updated August 13, 2001.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: Benzene. 

Office of Ground Water and Drinking Water, USEPA. Available on the Internet at 

http://www.epa.gov/safewater/dwh/c-voc/benzene.html, last updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.
Occurrence Summary and Use Support Document March 2002 309

Westrick, J.J., J.W. Mello, and R.F. Thomas. 1983. The Ground Water Supply Survey summary of

volatile organic contaminant occurrence data. EPA Technical Support Division, Office of

Drinking Water, Cincinnati, Ohio.
Occurrence Summary and Use Support Document March 2002 310

4.2 Carbon Tetrachloride

Table of Contents

4.2.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

4.2.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

4.2.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

4.2.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 313

4.2.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

4.2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

4.2.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

Tables and Figures

Table 4.2-1: Carbon Tetrachloride Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . 312

Table 4.2-2: Environmental Releases (in pounds) for Carbon Tetrachloride 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

Table 4.2-3: Stage 1 Carbon Tetrachloride Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

Table 4.2-4: Stage 1 Carbon Tetrachloride Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

Table 4.2-5: Stage 2 Estimated Carbon Tetrachloride Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

Table 4.2-6: Stage 2 Estimated Carbon Tetrachloride Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

Table 4.2-7: Estimated National Carbon Tetrachloride Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
Occurrence Summary and Use Support Document March 2002 311

4.2.1 Introduction, Use and Production

Carbon tetrachloride (CCl4) is a clear liquid that evaporates very easily. It has a sweet odor and does not

easily burn. Most carbon tetrachloride that escapes to the environment is, therefore, found as a gas. 

Carbon tetrachloride does not occur naturally but has been produced in large quantities to make

refrigeration fluid and propellants for aerosol cans (ATSDR, 1994). Its major routes of entry to drinking

water are a consequence of its industrial production and use (JRB Associates, 1983). It is expected that

discharges to surface water during production and use, and leaching into groundwater from wastes

deposited in landfills are primary causes of carbon tetrachloride contamination of drinking water (JRB

Associates, 1983). Carbon tetrachloride is also known as carbona, carbon chloride, carbon tet, methane

tetrachloride, perchloromethane, tetrachloromethane, and benzinoform (ATSDR, 1994).

With few exceptions, production of carbon tetrachloride has been eliminated in developed nations,

including the U.S. As an ozone-depleting substance (ODS), carbon tetrachloride falls under the auspices

of the Montreal Protocol, which mandated the cessation of production of carbon tetrachloride as of

January 1, 2000. The only exceptions to this rule are for “transformation” and “destruction”.

Under the transformation exemption, the Protocol excludes from phase-out those ODSs that are used as

feedstocks during the manufacturing process. The rationale for this exemption is that no ODS is released

into the atmosphere after transformation, and thus it is unnecessary for the Protocol to prohibit such use. 

To qualify for the exemption under international law, an ODS must be nearly 100% transformed into a

non-ODS product and any residual must be destroyed as provided under the destruction exemption

(McKenna and Cuneo, 2001). 

Under the destruction exemption, controlled substances that are destroyed rather than emitted to the

atmosphere are not subject to the ban. This exemption is based on the Protocol's definition of

“production” which is “the amount of controlled substances produced, minus the amount destroyed by

technologies approved by the Parties” (McKenna and Cuneo, 2001).

Prior to the enactment of the Montreal Protocol, use of carbon tetrachloride was already heavily

restricted. All consumer uses, such as use in the production of refrigeration fluid and propellants for

aerosols, as a pesticide, as a cleaning fluid, and in fire extinguishers, were prohibited, and its application

was limited to some industrial applications. The major use of carbon tetrachloride in the early 1990s was

in the production of chlorofluorocarbons, such as dichlorodifluoromethane and trichlorofluoroemthane

(ATSDR, 1994).

The decrease in use of carbon tetrachloride has led to a similar decrease in the amount produced. 

According to the latest figures available before the ban on production, the U.S. produced between 573

and 761 million pounds each year from 1981-1988. Production was 413 million pounds in 1990 and 315

million pounds in 1991. Because of the continual phasing out of most uses of carbon tetrachloride,

production was expected to lessen to an even greater extent in the 1990s, although no data is available to

corroborate that assumption (ATSDR, 1994).

Table 4.2-1 shows the number of facilities in each State that manufactured and processed carbon

tetrachloride as of 1992, the intended uses of the product, and the range of maximum amounts derived

from the Toxics Release Inventory (TRI) of EPA (ATSDR, 1994). 
Occurrence Summary and Use Support Document March 2002 312

Table 4.2-1: Carbon Tetrachloride Manufacturers and Processors by Statea

Stateb Number of facilities Range of maximum amounts on site in thousands of

poundsc Activities and usesd

AL 4 10-49,999 1,4,5,11

AR 2 10-99 7,11

CA 8 0-49,999 1,3,4,5,7,8,11,12,13

CO 1 1-9 1,5,11

DE 1 100-999 7

GA 2 0-0.09 8,9,12

IL 3 10-9,999 7,11

IN 2 10-99 1,5,6,11

KS 5 10-9,999 1,3,4,7,11

KY 6 (1)e 10-9,999 1,3,5,7,10,11,13

LA 16 0-49,999 1,3,4,5,6,7,11,12,13

MD 1 10-99 7

MI 2 10-999 7,11

MN 2 1-99 11,13

MO 2 10-99 13

MS 2 0.1-99 11,13

MT 1 0.1-0.9 11

ND 1 10-99 11

NJ 4 0-9,999 3,7,8,9,11

NY 1 (1)e No Data 11

OH 6 1-999 1,5,10,11,12,13

OK 2 10-99 11

PA 2 10-99 11

TN 2 1-999 11

TX 14 1-49,999 1,4,5,6,7,8,10,11,12,13

VA 1 10-99 13

VI 1 10-99 11

WV 2 0.1-999 1,4,6

WY 1 1-9 11

a

Derived from TRI90 (1992)

b

Post office State abbreviations used 

c

Data in TRI are maximum amounts on site at each facility

d

Activities/Uses include:

1. Produce 8. As a formulation component

2. Import 9. As an article component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

e

Number of facilities reporting “no data” regarding maximum amount of the substance on site

Source: ATSDR, 1994 compilation of TRI90 1992 data

4.2.2 Environmental Release

Carbon tetrachloride is listed as a Toxics Release Inventory (TRI) chemical. Table 4.2-2 illustrates the

environmental releases for carbon tetrachloride from 1988 to 1999. (Carbon tetrachloride data are only

available for these years.) Air emissions constitute the vast majority of the on-site releases, with a steady

decrease over the years. Surface water discharges have generally decreased from 1988 to 1999, with the

exception of an increase in 1998. Releases to land (such as spills or leaks within the boundaries of the

reporting facility) decreased from 1988 to 1993, remained at zero for three years, and then began

increasing in 1997. Off-site releases (including metals or metal compounds transferred off-site) have

generally decreased from 1988 to 1999. The decrease in air emissions, as well as underground injection,

have predominantly contributed to decreases in carbon tetrachloride total on- and off-site releases in

recent years. These TRI data for carbon tetrachloride were reported from 38 States, Puerto Rico, and the

Virgin Islands (USEPA, 2000). Sixteen of the 38 States reported every year. Twelve of the cross-section
Occurrence Summary and Use Support Document March 2002 313

States (used for analyses of carbon tetrachloride occurrence in drinking water; see Section 4.2.4) reported

releases. (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 4.2-2: Environmental Releases (in pounds) for Carbon Tetrachloride in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 237,235 84 27,548 938 7,307 273,112

1998 274,291 2,586 23,163 1,679 9,956 311,675

1997 357,902 315 32,958 135 18,697 410,007

1996 363,681 215 44,515 0 9,245 417,656

1995 420,754 717 53,966 0 7,735 483,172

1994 651,098 1,223 12,654 0 50,791 715,766

1993 2,243,590 1,453 34,332 79 121,363 2,400,817

1992 1,399,490 2,444 45,984 333 11,955 1,460,206

1991 1,549,782 2,849 42,475 2,157 39,111 1,636,374

1990 1,753,340 4,718 31,557 1,005 10,163 1,800,783

1989 3,465,179 15,656 122,030 1,616 24,996 3,629,477

1988 3,795,248 15,627 98,050 14,759 49,703 3,973,387

 Source: USEPA, 2000

4.2.3 Ambient Occurrence

National NAWQA data, as well as NURP and NPDES data, are currently unavailable for carbon

tetrachloride. Additional studies of ambient data are also unavailable. A summary document entitled

“Occurrence of Carbon Tetrachloride in Drinking Water, Food and Air” (JRB Associates, 1983), was

previously prepared for past USEPA assessments of carbon tetrachloride. However, no information on

the ambient occurrence of carbon tetrachloride was included in that document. (The document did

include information regarding carbon tetrachloride occurrence in drinking water, which is discussed in

Section 4.2.5 of this report.)

4.2.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of carbon tetrachloride occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.005 mg/L; 0.0025 mg/L; and 0.0005

mg/L.

All sixteen cross-section State data sets contained occurrence data for carbon tetrachloride. These data

represent more than 182,000 analytical results from approximately 23,000 PWSs during the period from

1984 to 1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs

vary by State, although the State data sets have been reviewed and checked to ensure adequacy of

coverage and completeness. The overall modal detection limit for carbon tetrachloride in the 16 crosssection States is equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)
Occurrence Summary and Use Support Document March 2002 314

4.2.4.1 Stage 1 Analysis Occurrence Findings

Table 4.2-3 illustrates the occurrence of carbon tetrachloride in drinking water for the public water

systems in the 16-State cross-section relative to three thresholds: 0.005 mg/L (the current MCL), 0.0025

mg/L, and 0.0005 mg/L (the modal MRL). Based on the 16-State cross-section data, a total of 47

(approximately 0.204% of) ground water and surface water PWSs had analytical results exceeding the

MCL; 0.386% of systems (89 systems) had results exceeding 0.0025 mg/L; and 1.56% of systems (359

systems) had results exceeding 0.0005 mg/L. 

Approximately 0.205% of ground water systems (44 systems) had any analytical results greater than the

MCL. About 0.350% of ground water systems (75 systems) had results above 0.0025 mg/L. The

percentage of ground water systems with at least one result greater than 0.0005 mg/L was equal to 1.32%

(283 systems). 

Only 3 (0.191% of) surface water systems had results greater than the MCL. A total of 14 (0.889% of)

surface water systems had at least one analytical result greater than 0.0025 mg/L. Seventy-six (4.83% of)

surface water systems had results exceeding 0.0005 mg/L.

Table 4.2-3: Stage 1 Carbon Tetrachloride Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.205% 44

0.0025 0.350% 75

0.0005 1.32% 283

Surface Water

0.005 0.191% 3

0.0025 0.889% 14

0.0005 4.83% 76

Combined Ground &

Surface Water

0.005 0.204% 47

0.0025 0.386% 89

0.0005 1.56% 359

Reviewing carbon tetrachloride occurrence in the 16 cross-section States by PWS population served

(Table 4.2-4) shows that approximately 7.35% of the 16-State population (over 8 million people) was

served by PWSs with at least one analytical result of carbon tetrachloride greater than the MCL (0.005

mg/L). Approximately 9.2 million (8.32% of) people were served by systems with an exceedance of

0.0025 mg/L. Over 13.6 million (12.3% of) people were served by systems with at least one analytical

result greater than 0.0005 mg/L.

The percentage of population served by ground water systems with analytical results greater than the

MCL was equal to 0.830% (about 411,200 people). When evaluated relative to 0.0025 mg/L and 0.0005
Occurrence Summary and Use Support Document March 2002 315

mg/L, the percent of population exposed was equal to 2.14% (1,060,200 people) and 7.64%

(approximately 3.8 million people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.005 mg/L was

equal to 12.6% (over 7.7 million people). Approximately 13.3% of the population served by surface

water systems in the 16 States (almost 8.2 million people) was exposed to carbon tetrachloride

concentrations greater than 0.0025 mg/L. When evaluated relative to 0.0005 mg/L, the percent of

population exposed was equal to 16.1% (over 9.8 million people).

Table 4.2-4: Stage 1 Carbon Tetrachloride Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold

Total Population Served

by Systems Exceeding

Threshold

Ground Water

0.005 0.830% 411,200

0.0025 2.14% 1,060,200

0.0005 7.64% 3,783,200

Surface Water

0.005 12.6% 7,721,100

0.0025 13.3% 8,147,200

0.0005 16.1% 9,818,800

Combined Ground &

Surface Water

0.005 7.35% 8,132,300

0.0025 8.32% 9,207,300

0.0005 12.3% 13,602,000

4.2.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.2-5 and 4.2-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

A total of 4 (0.0159% of) ground water and surface water PWSs in the 16 States had an estimated mean

concentration of carbon tetrachloride exceeding 0.005 mg/L. Approximately 6 (0.0256% of) PWSs in

the 16 States had an estimated mean concentration exceeding 0.0025 mg/L, and 48 (0.210%) had an

estimated mean concentration exceeding 0.0005 mg/L. 

An estimated 4 (0.0171% of) ground water PWSs in the 16 cross-section States had a mean concentration

greater than 0.005 mg/L, 6 (0.0273%) had a mean concentration greater than 0.0025 mg/L, and 41

(0.193%) had a mean concentration greater than 0.0005 mg/L. Approximately 0.000381% (less than 1),
Occurrence Summary and Use Support Document March 2002 316

0.00267% (about 1), and 0.441% of (approximately 7 ) surface water PWSs in the 16 States had

estimated mean concentrations exceeding 0.005 mg/L, 0.0025 mg/L, and 0.0005 mg/L, respectively.

Table 4.2-5: Stage 2 Estimated Carbon Tetrachloride Occurrence Based on 16-State Cross-Section

- Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.0171% 0.00932% - 0.0233% 4 2 - 5

0.0025 0.0273% 0.0186% - 0.0373% 6 4 - 8

0.0005 0.193% 0.140% - 0.242% 41 30 - 52

Surface Water

0.005 0.000381% 0.000% - 0.000% 0 0 - 0

0.0025 0.00267% 0.000% - 0.0635% 1 0 - 1

0.0005 0.441% 0.254% - 0.699% 7 4 - 11

Combined Ground

& Surface Water

0.005 0.0159% 0.00869% - 0.0217% 4 2 - 5 

0.0025 0.0256% 0.0174% - 0.0347% 6 4 - 8

0.0005 0.210% 0.161% - 0.265% 48 37 - 61

Reviewing carbon tetrachloride occurrence by PWS population served (Table 4.2-6) shows that

approximately 0.0316% of population served by all PWSs in the 16 cross-section States (an estimate of

approximately 35,000 people) was potentially exposed to carbon tetrachloride levels above 0.005 mg/L. 

The percentage of population served by PWSs in the 16 States with levels of carbon tetrachloride above

0.0025 mg/L was 0.0474% (approximately 52,500 people). Approximately 7.37% of the population

served in the 16 States (over 8.1 million people) was exposed to carbon tetrachloride concentrations

above 0.0005 mg/L. 

When the percent of population served by ground water systems was evaluated relative to a threshold of

0.005 mg/L, 0.0025 mg/L, and 0.0005 mg/L, the percentage of population exposed in the 16 cross-section

States was equal to 0.0705% (an estimated 34,900 people), 0.104% (an estimated 51,600 people) and

0.764% (an estimated 378,500 people), respectively. 

The percentage of population served by surface water systems with levels above 0.005 mg/L was equal to

0.0000713%, and the percentage of population served with levels above 0.0025 mg/L was 0.00139%

(about 800 people). The percentage of the population served by surface water systems dramatically

increased to about 12.7% (about 7.8 million people in the 16 States) when evaluated relative to 0.0005

mg/L. 
Occurrence Summary and Use Support Document March 2002 317

Table 4.2-6: Stage 2 Estimated Carbon Tetrachloride Occurrence Based on 16-State Cross-Section

- Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.0705% 0.00158% - 0.0950% 34,900 800 - 47,000

0.0025 0.104% 0.0938% - 0.191% 51,600 46,500 - 94,400

0.0005 0.764% 0.627% - 1.05% 378,500 310,600 - 521,700

Surface Water

0.005 0.0000713% 0.000% - 0.000% 0 0 - 0

0.0025 0.00139% 0.000% - 0.00104% 800 0 - 600

0.0005 12.7% 12.4% - 13.9% 7,779,500 7,571,900 - 8,487,800

Combined Ground

& Surface Water

0.005 0.0316% 0.000707% - 0.0429% 35,000 800 - 47,500

0.0025 0.0474% 0.0420% - 0.0865% 52,500 46,500 - 95,700

0.0005 7.37% 7.16% - 8.00% 8,154,900 7,916,000 - 8,849,500

4.2.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 10 PWSs serving approximately 67,400 people nationally could be exposed to

carbon tetrachloride concentrations above 0.005 mg/L. About 17 systems serving 101,100 people had

estimated mean concentrations greater than 0.0025 mg/L. Approximately 137 systems serving about 15.7

million people nationally were estimated to have mean carbon tetrachloride concentrations greater than

0.0005 mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to

national values.)

For ground water systems, an estimated 10 PWSs serving about 60,400 people nationally had mean

concentrations greater than 0.005 mg/L. Approximately 16 systems serving about 89,300 people

nationally had estimated mean concentration values that exceeded 0.0025 mg/L. About 115 ground

water systems serving almost 654,600 people had estimated mean concentrations greater than 0.0005

mg/L. 

Approximately 1 surface water system serving less than 100 people was estimated to have a mean

concentration of carbon tetrachloride above 0.005 mg/L. One surface water system serving about 1,800

people nationally had an estimated mean concentration greater than 0.0025 mg/L. An estimated 25

surface water systems serving over 16 million people had mean concentrations greater than 0.0005 mg/L.
Occurrence Summary and Use Support Document March 2002 318

Table 4.2-7: Estimated National Carbon Tetrachloride Occurrence - Systems and Population

Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 10 6 - 14 60,400 1,400 - 81,400

0.0025 16 11 - 22 89,300 80,400 - 163,300

0.0005 115 83 - 144 654,600 537,200 - 902,200

Surface Water

0.005 1 0 - 0 < 100 0 - 0

0.0025 1 0 - 4 1,800 0 - 1,300

0.0005 25 14 - 39 16,221,400 15,788,500 - 17,698,400

Combined Ground

& Surface Water

0.005 10 6 - 14 67,400 1,500 - 91,400

0.0025 17 11 - 23 101,100 89,500 - 184,300

0.0005 137 105 - 172 15,705,100 15,245,000 - 17,042,800

4.2.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of carbon tetrachloride in drinking water are

also reviewed. Previously compiled occurrence information, from an OGWDW summary document

entitled “Occurrence of Carbon Tetrachloride in Drinking Water, Food, and Air” (JRB Associates, 1983),

is presented in the following section. This variety of studies and information are presented regarding

levels of carbon tetrachloride in drinking water, with the scope of the reviewed studies ranging from

national to regional. Note that none of the studies presented in the following section provide the

quantitative analytical results or comprehensive coverage that would enable direct comparison to the

occurrence findings estimated with the cross-section occurrence data presented in Section 4.2.4. These

additional studies, however, do enable a broader assessment of the Stage 2 occurrence estimates

presented for this Six-Year Review. All the following information in Section 4.2.5 is taken directly from

“Occurrence of Carbon Tetrachloride in Drinking Water, Food, and Air” (JRB Associates, 1983).

JRB Associates (1983) found three major types of data available that were potentially useful for

describing the occurrence of carbon tetrachloride in the nation’s public drinking water supplies. First,

there are several Federal surveys in which a number of public water supplies from throughout the U.S.

were selected for analysis of chemical contamination, including carbon tetrachloride. Second, data are

available from State surveys and from State investigations of specific incidents of known or suspected

contamination of a supply. Third, there are miscellaneous published data which, like some of the State

data, tend to be from studies in response to suspected contamination of specific sites. For accomplishing

the basic objectives of this study, namely to estimate the number of public water supplies nationally

within the various source and size categories contaminated with carbon tetrachloride, the distribution of

carbon tetrachloride concentrations in those supplies, and the number of individuals exposed to those

concentrations, it was determined that the Federal survey data provides the most suitable data base. The

State and miscellaneous data tend to be poorly described with respect to the source and size categories of

the supplies examined and the sampling and analysis methods used for determining contaminant levels. 
Occurrence Summary and Use Support Document March 2002 319

The lack of source and system size information precludes using the data for estimating levels in public

water supplies of similar characteristics. The absence of details on sampling and analysis methods

precludes evaluating those data for their qualitative and quantitative reliability. Also, because much of

the State and miscellaneous data are from investigations in response to incidents of known or suspected

contamination (e.g., spills), they were judged to be not representative of contaminant levels in the

nation’s water supplies in general. Although they are not used with the Federal data for the purpose of

estimating contamination levels nationally, the available State and miscellaneous data are presented here

to provide some additional perspective on carbon tetrachloride occurrence in drinking water.

Data are presented only on drinking water samples taken from a consumer's tap (i.e., distribution water

samples) or on treated water samples taken at the water supply (i.e., finished water samples) because

these are considered to be most representative of the water consumed by the public. No data on raw (i.e.,

untreated) water are presented. It is recognized that for some groundwater supplies where no treatment

of the water occurs, samples identified as raw may be representative of water consumed by the users of

the supply. However, it was generally not possible to differentiate between those groundwater supplies

that do and those that do not treat raw water from the available survey data.

4.2.5.1 Overview and Quality Assurance Assessment of Federal Drinking Water Surveys

Six Federal drinking water surveys provide data on carbon tetrachloride: the National Organics

Reconnaissance Survey (NORS), the National Organic Monitoring Survey (NOMS), the National

Screening Program for Organics in Drinking Water (NSP), the 1978 Community Water Supply Survey

(CWSS), the Rural Water Survey (RWS), and the Groundwater Supply Survey (GWSS). The terms used

in this report are those used in the individual surveys, recognizing that they may not always correspond to

strict technical definitions.

The National Organics Reconnaissance Survey (NORS) was conducted in 1975 to determine the extent

of the presence of carbon tetrachloride, 1,2-dichloroethane, and four trihalomethanes in drinking water

supplies from 80 cities across the country (Symons et al., 1975, as cited in JRB Associates, 1983). The

effect of the water sources and treatment practices on the formation of these compounds were also

examined in NORS. Of the 80 supplies studied, 16 were indicated as having a groundwater source and

64 as having a surface water source. Symons et al. (1975, as cited in JRB Associates, 1983) did not

provide data on the population served by the supplies studied in the NORS; the populations served were

estimated by JRB based on information available from other sources for the supplies studied and from

census data for the locations of the supplies.

The National Organic Monitoring Survey (NOMS) was conducted to identify contaminant sources, to

determine the frequency of occurrence of specific drinking water contaminants, and to provide data for

the establishment of maximum contaminant levels (MCLs) for various organic compounds in drinking

water (Brass et al. 1977, as cited in JRB Associates, 1983). The NOMS was conducted in three phases:

March to April 1976, May to July 1976, and November 1976 to January 1977. Finished drinking water

samples from 113 communities were analyzed for 21 different compounds. Of the 113 community

supplies sampled, 18 had groundwater sources, 91 had surface water sources, and 4 had a mixed

groundwater/surface water source. For carbon tetrachloride, data are available for 18 groundwater

sources and 89 surface water sources.

The analytical results of the NOMS were made available in printed form by EPA’s Technical Support

Division, Office of Drinking Water. Additional information on the locations and source of the supplies,

and on the populations served by the supplies in the NOMS were provided by Wayne Mello (1983, as
Occurrence Summary and Use Support Document March 2002 320

cited in JRB Associates, 1983) at EPA’s Technical Support Division, Office of Drinking Water. A single

value for carbon tetrachloride was reported for each supply studied in the NOMS.

The National Screening Program for Organics in Drinking Water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water

systems in 33 States for 51 organic chemical contaminants. Data are available for carbon tetrachloride

on finished water samples from 12 groundwater and 106 surface water supplies.

In the Community Water Supply Survey (CWSS), carried out in 1978, 106 surface water supplies, 330

groundwater supplies, and 16 supplies with mixed sources were examined for volatile organic chemical

contamination. Fourteen purgeable organic compounds were analyzed and total organic carbon levels

were determined. Samples were taken of raw, finished, and distribution water. Only the latter two types

of water are considered here. Data for carbon tetrachloride in finished and/or distribution samples were

obtained from a total of 316 groundwater and 105 surface water supplies.

The Rural Water Survey (RWS), conducted in 1978, was carried out in response to Section 3 of the Safe

Drinking Water Act, which mandated that EPA “conduct a survey of the quantity, quality, and

availability of rural drinking water supplies.” Drinking water samples were collected for analysis of

inorganic chemicals, pesticides, and VOCs from 2,655 households throughout the United States located

in areas defined in the survey as rural. Of these, a total of 855 household samples were examined for

VOCs. The majority of these samples were obtained from households receiving water from private wells

or small supplies serving fewer than 25 people. For carbon tetrachloride, data are available in the RWS

for 207 groundwater and 45 surface water supplies serving 25 or more people.

The RWS did not obtain data on the number of persons in each household served by the supplies. 

However, data were obtained on the number of service connections at each supply. With the input of Dr.

Bruce Brower at Cornell University, who participated in the statistical analysis of the RWS for

parameters other than VOCs, the population served by each supply was estimated from the average

number of persons per household (3.034) observed in the survey. A single value was reported for each

household; in some cases it was necessary to average two or three households obtaining water from the

same supply. Brass (1981, as cited in JRB Associates, 1983) cautions that the RWS water samples were

analyzed 6 to 27 months after collection and that degradation of some VOCs may have occurred during

this holding period.

The Groundwater Supply Survey (GWSS) was conducted from December 1980 to December 1981 to

develop additional data on the occurrence of volatile organic chemicals in the nation’s groundwater

supplies (Westrick et al., 1983, as cited in JRB Associates, 1983). It was hoped that this study would

stimulate State efforts toward the detection and control of groundwater contamination and the

identification of potential chemical “hot spots.” A total of 945 systems were sampled, of which 466 were

chosen at random. The remaining 479 systems were chosen nonrandomly based on information from

States encouraged to identify locations believed to have a higher than normal probability of VOC

contamination (e.g., locations near landfills or industrial activity). One sample of finished water was

collected from each supply at a point near the entrance to the distribution system.

Each of the drinking water surveys was evaluated with respect to the validity of the reported occurrence

data for a number of organic chemicals, including carbon tetrachloride. The evaluations were carried out

by analyzing information about the procedures used for collection and analysis of samples as well as the

quality control protocols used. The analyzed compounds dealt with in each study were assigned one of

three possible ratings: quantitatively acceptable, qualitatively acceptable (i.e., the substance measured

was carbon tetrachloride), and totally unacceptable. In the case of carbon tetrachloride, a qualitatively
Occurrence Summary and Use Support Document March 2002 321

acceptable rating was given for data from the CWSS and RWS because of suspected biodegradation of

the samples, which were held unrefrigerated for prolonged periods before analysis, although it is

recognized that biodegradation of carbon tetrachloride is less likely to occur than it is for unsaturated and

aromatic VOCs. Carbon tetrachloride values in excess of the quantitation limit reported for some

samples in these studies are qualitatively valid and can be taken as minimum values, representative of

samples which probably originally contained carbon tetrachloride at higher concentrations. In the case of

the NORS, NOMS, NSP, and GWSS, all data were rated both quantitatively and qualitatively acceptable.

4.2.5.2 Groundwater – Federal Surveys

The National Organics Reconnaissance Survey (NORS), the National Organic Monitoring Survey

(NOMS), the National Screening Program for Organics in Drinking Water (NSP), the Community Water

Supply Survey (CWSS), the Rural Water Survey (RWS), and the Groundwater Supply Survey (GWSS)

all contain data concerning the levels of carbon tetrachloride in groundwater supplies from across the

country.

In the NORS, finished water samples were analyzed for 16 groundwater systems. Only one system was

reported to have carbon tetrachloride present, although the level of contamination was below the

minimum quantifiable concentration of 2 :g/L for that analysis. All other groundwater supplies were

indicated as having “none found,” with the minimum quantifiable concentration ranging from 1-2 :g/L.

Eighteen groundwater systems were analyzed for carbon tetrachloride during Phase I of NOMS (March

to April 1976); only one system contained detectable carbon tetrachloride, at a concentration of 4.0 :g/L. 

None of the 18 systems resampled during Phase II of the study (May to July 1976) contained quantifiable

levels of carbon tetrachloride. Samples analyzed during Phase III of the study (November 1976 to

January 1977) were negative for all 14 systems examined. The minimum quantifiable limits for carbon

tetrachloride ranged from 1.0-2.0 :g/L in Phase 1, 0.2-0.4 :g/L in Phase II, and 0.2-0.4 :g/L in Phase III.

Twelve groundwater supplies were tested for carbon tetrachloride contamination in the NSP. Of these 12

systems, two were found to be contaminated with carbon tetrachloride at levels of 0.2 and 0.5 :g/L. The

quantification limit for carbon tetrachloride was 0.1 :g/L.

The 1978 CWSS provided information on carbon tetrachloride levels in 316 groundwater systems. Of

these systems, 6 contained detectable levels of carbon tetrachloride, with values ranging from 0.67-2.15

:g/L. The mean value was 1.4 :g/L with a standard deviation of 0.50 :g/L; the median value was 1.4

:g/L. The minimum quantitation limit for carbon tetrachloride in the CWSS was 0.50 :g/L.

The RWS examined 207 groundwater supplies for carbon tetrachloride and found 2 to have levels above

the minimum quantification limit of 0.5 :g/L. The two positive values were 0.8 to 0.88 :g/L.

In the GWSS, 15 of the 456 randomly chosen water systems serving 25 or more individuals were

contaminated with carbon tetrachloride, at concentrations ranging from 0.21-16 :g/L. The three systems

with the highest values were contaminated at 1.7, 2.8, and 16 :g/L. Ten of the 15 systems with

detections of carbon tetrachloride served populations in excess of 10,000 people. The average for all

randomly chosen systems was 1.7 :g/L with a standard deviation of 4.0 :g/L; the median was 0.37 :g/L. 

Of the 473 nonrandom locations sampled serving 25 or more individuals, 15 were contaminated with

carbon tetrachloride, at concentrations between 0.21-15 :g/L, the highest values being 1.8, 9.4, and 15

:g/L. Six of the 15 systems with detections of carbon tetrachloride served populations in excess of

10,000 people. The average carbon tetrachloride level for the nonrandom systems was 2.2 :g/L with a
Occurrence Summary and Use Support Document March 2002 322

standard deviation of 4.2 :g/L; the median value was 0.45 :g/L. The minimum quantitation limit for

carbon tetrachloride was 0.2 :g/L.

4.2.5.3 Groundwater – State Data

Eight States (California, Connecticut, Delaware, Indiana, Maine, Massachusetts, New Jersey, and New

York) provided the U.S. Environmental Protection Agency with information concerning carbon

tetrachloride contamination in groundwater supplies. Analytical results for carbon tetrachloride in

samples from four locations in California ranged from undetectable to greater than 20 :g/L. Of 33

locations sampled in Connecticut, carbon tetrachloride levels ranged from undetectable to 66 :g/L; 70 of

the 85 samples contained less than 5.0 :g/L. Indiana provided data on eight samples from one location,

all with undetectable carbon tetrachloride. A total of 84 groundwater samples from 57 locations in

Maine and four samples from one location in Massachusetts proved to be free of detectable carbon

tetrachloride. Data on 235 samples from 12 unidentified counties in New Jersey indicated that 190 had

no detectable carbon tetrachloride; another 35 samples contained carbon tetrachloride at less than 1.0

:g/L. In another study, 18 locations in New Jersey reported carbon tetrachloride levels ranging from not

detectable to 863 :g/L. Finally, 20 of 365 groundwater samples taken in New York contained detectable

carbon tetrachloride.

4.2.5.4 Groundwater – Miscellaneous Data

Region V of the U.S. Environmental Protection Agency conducted a study in early 1975 in which

drinking water samples from 50 cities were analyzed for carbon tetrachloride (USEPA, 1975, as cited in

JRB Associates, 1983). Of 16 groundwater systems sampled, seven contained carbon tetrachloride, at

levels ranging from 1.0-13.0 :g/L (averaging 4.6 :g/L). In a survey by Bush et al. (1977, as cited in JRB

Associates, 1983) of New York State drinking water supplies, 7 of 11 groundwater samples from the

Buffalo area and Long Island contained carbon tetrachloride, at levels of less than 0.2 :g/L.

4.2.5.5 Surface Water – Federal Surveys

The National Organics Reconnaissance Survey (NORS), the National Organic Monitoring Survey

(NOMS), the National Screening Program for Organics in Drinking Water (NSP), the Community Water

Supply Survey (CWSS), and the Rural Water Survey (RWS) all contain data concerning the levels of

carbon tetrachloride in surface water supplies from across the country.

In the NORS, finished water from 64 surface water systems were studied, of which nine were found to

have carbon tetrachloride present. Five of the nine positive systems reported carbon tetrachloride to be

present but below the minimum quantifiable concentration of 2 :g/L. Of those with quantifiable levels,

two were reported as 2 :g/L and two as 3 :g/L. The 55 negative surface water supplies were indicated as

having “none found,” with the minimum quantifiable concentration from 1-2 :g/L. It should be noted

that confirmatory quantitative analyses were performed for 8 surface water supplies in NORS, using a

method able to quantify carbon tetrachloride at 0.05 :g/L. Three of these eight supplies were originally

reported as having carbon tetrachloride present, but below the minimum quantifiable concentration of 2

:g/L; the presence of carbon tetrachloride was confirmed in all three cases at concentrations ranging

from 0.4 to 0.8 :g/L. Of the five supplies originally reported as having none found, four were observed

in the confirmatory analysis to have carbon tetrachloride present at levels ranging from 0.2 to 0.3 :g/L.

In Phase I of the National Organic Monitoring Survey (March to April 1976), water samples from 89

surface water systems were analyzed for carbon tetrachloride. Of these 89 systems, only two were found

to contain carbon tetrachloride, at levels of 1.8 and 2.9 :g/L. Eighty-eight systems were sampled during
Occurrence Summary and Use Support Document March 2002 323

the second phase of the survey (May to July 1976) and 10 were found to be contaminated, at levels

ranging from 0.19-10 :g/L, including the two systems identified as positive in the first phase of the

study. The average carbon tetrachloride concentration among the positive Phase II samples was 2.4 :g/L

with a standard deviation of 2.9 :g/L; the median concentration was 1.4 :g/L. During the third phase of

the NOMS (November 1976 to January 1977), analyses revealed carbon tetrachloride contamination in

11 out of a total of 87 systems. The contamination levels for these systems ranged from 0.2-29 :g/L. 

The mean concentration averaged 4.3 :g/L with a standard deviation of 8.4 :g/L; the median level was

1.3 :g/L. Only two systems had concentrations above 4.9 :g/L. The minimum quantifiable limits for

carbon tetrachloride ranged from 1.0-3.0 :g/L in Phase I, 0.2-0.4 :g/L in Phase II, and 0.2-0.4 :g/L in

Phase III.

Surface water samples from 106 drinking water systems were analyzed for carbon tetrachloride during

the National Screening Program (NSP) between June 1977 and March 1981. Of these, 36 systems

contained detectable levels of carbon tetrachloride, ranging from 0.1-30 :g/L. Only two of these systems

were contaminated at levels greater than 1.8 :g/L (8.4 and 30 :g/L). The average concentration among

the 36 positive systems was 1.6 :g/L with a standard deviation of 5.1 :g/L; the median level was 0.4

:g/L. The quantification limit for the NSP was 0.1 :g/L.

Of the 105 surface water systems sampled during the Community Water Supply Survey (CWSS), three

contained quantifiable levels of carbon tetrachloride. These three positive values were 0.52, 0.64, and

0.925. The mean concentration averaged 0.70 with a standard deviation of 0.21 :g/L and a median of

0.64 :g/L. The minimum quantitation limit for carbon tetrachloride in the CWSS was 0.50 :g/L.

The RWS examined drinking water from 45 surface water supplies; only 1 supply was found to have

carbon tetrachloride present above the minimum quantification limit of 0.5 :g/L (0.8 :g/L).

4.2.5.6 Surface Water – State Data

Only two States, Connecticut and New York, provided carbon tetrachloride data from surface water

sources. In 11 samples from 9 locations in Connecticut, carbon tetrachloride concentrations ranged from

undetectable to 1.5 :g/L. Of 23 samples from three locations in New York, only one was found to

contain detectable carbon tetrachloride (0.1 :g/L).

4.2.5.7 Surface Water – Miscellaneous Data

In 34 surface water systems analyzed during the EPA Region V study, carbon tetrachloride levels ranged

from 0.9-26.0 :g/L (averaging 4.8 :g/L) (USEPA, 1975, as cited in JRB Associates, 1983). In the Bush

et al. (1977, as cited in JRB Associates, 1983) study, 16 drinking water samples from surface water were

analyzed, 13 from Lake Erie and 3 from Niagara Falls, New York. Seven of the samples from Lake Erie

were contaminated with carbon tetrachloride, at 0.2-4.8 :g/L (averaging 2.4 :g/L). Two of the samples

from Niagara Falls were contaminated, with levels of 0.3 and 1.1 :g/L.

4.2.5.8 Projected National Occurrence of Carbon Tetrachloride in Public Water Supplies

As reported in the JRB Associates (1983) report, public water systems fall into two major categories with

respect to water source (surface water and groundwater) and into five size categories and twelve

subcategories according to the number of individuals served. The JRB (1983) report presented estimates

of both the number of drinking water supplies nationally within each of the source/size categories

expected to have carbon tetrachloride present, and of the concentration of carbon tetrachloride expected

to be present in those supplies.
Occurrence Summary and Use Support Document March 2002 324

The key features of the methodology used and assumptions made to develop the national estimates are

summarized here. The estimates are based on the data from the Federal surveys only. The State data and

miscellaneous information were not included for several reasons. Generally, these data are from a few

States and were not considered to be geographically representative. There was also a general lack of data

on the population served by systems measured, the type of water sampled, and the methodologies used to

sample, identify, and measure carbon tetrachloride. Furthermore, since much of these data were

apparently obtained in response to incidents of recognized contamination problems, they may not be

representative of typical conditions existing nationally. However, while these data were not used for

computing the national projections, they do provide a valuable and necessary perspective for evaluating

those projections, especially with respect to the projected high levels of contamination of carbon

tetrachloride.

The Federal survey data from the NORS, NOMS, NSP, CWSS, RWS, and GWSS were pooled together

for developing the national projections. It was assumed in combining these surveys that the resulting

data base would be representative of the nation’s water supplies. In the case of the GWSS data, both the

random and nonrandom samples were included in the projections because a test of the GWSS data

showed no statistically significant difference in the frequency of occurrence of positive values or the

mean of the positive values of carbon tetrachloride.

Ideally, adequate data would be available to develop the national projections separately for each of the

twelve system size categories within the groundwater and surface water groups; however, the available

data were too limited for this. JRB (1983) consolidated some of the size categories to have sufficient

data for developing the projections. In consolidating data from various size categories, consideration was

given to the potential for there being statistically significant differences in the frequency of occurrence of

carbon tetrachloride as a function of system size. The consolidation of size categories therefore involved

a balancing of the need to group size categories together to have an adequate data base for developing the

national projections against the need to treat size categories separately in order to preserve the influence

of system size as a determinant of contamination potential. The consolidation of size categories also took

into account EPA’s classification of systems into the five major groups as very small (25-500), small

(501-3,300), medium (3,301-10,000), large (10,001-100,000), and very large (> 100,000) (Kuzmack,

1983, as cited in JRB Associates, 1983).

Once the data were consolidated, statistical models for extrapolating to the national level were tested and

an appropriate model selected. In the case of carbon tetrachloride, the multinominal method was used. 

The frequency of contamination of groundwater and surface water systems at various concentrations was

determined for each consolidated size category. For completing the national estimates, it was assumed

that the frequency of contamination observed for each consolidated category was directly applicable to

each of the system sizes comprising it.

4.2.5.8.1 Groundwater Systems

Data are available for a total of 1,466 supplies from the combined surveys (NORS, NOMS, NSP, CWSS,

RWS, and GWSS). Of these, 42 supplies were reported to have carbon tetrachloride present, at

concentrations ranging from 0.2 :g/L to 16 :g/L.

Based on the overall distribution of positive values and maximum possible values for those supplies in

which carbon tetrachloride was not found, 0.5 :g/L was selected as the common minimum quantifiable

concentration for the combined survey data. That is, quantitative projections are made of supplies at

several concentration ranges > 0.5 :g/L, while only a total number for supplies expected to have either

no carbon tetrachloride or levels below 0.5 :g/L can be determined. Although some data indicate the
Occurrence Summary and Use Support Document March 2002 325

presence of carbon tetrachloride in groundwater supplies at levels < 0.5 :g/L, it is not possible to

determine the proportion of supplies that have carbon tetrachloride present and the proportion that are

actually free of carbon tetrachloride contamination.

Of the 1,424 supplies reporting no carbon tetrachloride to be present, 1,402 were assumed to have

maximum possible levels of < 0.5 :g/L based on the minimum quantifiable concentrations reported for

the various surveys (885 of these had maximum levels of < 0.2 :g/L). The other 22 supplies reporting no

carbon tetrachloride to be present had maximum possible levels ranging from approximately 0.6 :g/L to

2 :g/L. It is assumed, based on overall distribution of values, that carbon tetrachloride if present in the

22 supplies is so at a concentration of < 0.5 :g/L, although a rigorous conservative argument could be

made for assuming a level equal to the maximum possible value. The impact of this assumption is

notable both in terms of the national projection of groundwater systems above 0.5 :g/L and in terms of

the population exposed.

Twenty-three of the 1,466 supplies examined had measured values of carbon tetrachloride $ 0.5 :g/L. 

When the twelve size categories were consolidated into the five major EPA groupings, there was an

apparent relationship between the frequency of values $ 0.5 :g/L and system size:

Very small 0.2% (1/423)

Small 1.9% (8/417)

Medium 1.4% (3/214)

Large 1.9% (7/363)

Very large 8.2% (4/49)

Overall 1.6% (23/1,466)

A test for statistical significance revealed that at the " = 0.05 level, a statistically significant difference

was found between the very small and small categories, as well as between the large and very large

categories. No further consolidation of these five categories was done. As noted previously, the

frequency of occurrence of carbon tetrachloride at various concentrations was determined for the

consolidated groups and then applied to the number of supplies nationally within each of the size

categories comprising each group.

About 335 groundwater supplies (range of 124-545), approximately 0.7% of the total groundwater

supplies in the United States, are expected to have carbon tetrachloride at levels of $ 0.5 :g/L; the

remaining 48,123 supplies have either no carbon tetrachloride or levels < 0.5 :g/L.

It is estimated that 110 supplies (range of 0-277) are expected to have carbon tetrachloride levels > 5

:g/L, while 107 supplies (range of 0-273) are expected to have levels > 10 :g/L. Most of the supplies

with high carbon tetrachloride levels are expected to be in the smaller size categories. Although, as noted

previously, the frequency of carbon tetrachloride occurrence is greater in the very large system size, the

number of systems affected nationally is greater for the small sizes because there are many more small

systems in existence.

It is interesting to note the impact on the national projections of the assumption made that the 22 supplies

with undetected but maximum potential values of 0.6-2 :g/L had < 0.5 :g/L. Had it been assumed that

carbon tetrachloride was present in those supplies at their maximum possible values, the national

projection of supplies with carbon tetrachloride levels $ 0.5 :g/L would have increased to 417 (200-633)

with no differences in levels > 5 :g/L. These differences in the 0.5-5 :g/L range would be found in

systems serving > 500 people.
Occurrence Summary and Use Support Document March 2002 326

4.2.5.8.2 Surface Water Systems

Data are available for a total of 312 surface water supplies. Of these, 51 supplies were reported by JRB

Associates (1983) to have carbon tetrachloride present at concentrations ranging from 0.1 :g/L to 30

:g/L, although this high value is the only one reported above 10 :g/L.

Based on the overall distribution of positive values and maximum possible values for those supplies in

which carbon tetrachloride was not found, 0.5 :g/L was selected as the common minimum quantifiable

concentration for the combined survey data. That is, quantitative projections are made of supplies at

several concentration ranges > 0.5 :g/L, while only a total number for supplies expected to have either

no carbon tetrachloride or levels below 0.5 :g/L can be determined. Although some data indicate the

presence of carbon tetrachloride in surface water supplies at levels < 0.5 :g/L, it is not possible to

determine the proportion that have carbon tetrachloride present and the proportion that are free of carbon

tetrachloride contamination.

Of the 261 supplies reporting no carbon tetrachloride to be present, 186 had maximum possible levels of

< 0.5 :g/L based on the minimum quantifiable concentrations reported for the various surveys. The other

75 supplies reporting no carbon tetrachloride to be present had maximum possible levels ranging from

0.53 :g/L to 2 :g/L. It is assumed, based on the overall distribution of values, that carbon tetrachloride if

present in these 75 supplies is so at a concentration of < 0.5 :g/L, although a rigorous conservative

argument could be made for assuming a level equal to the maximum possible value. As will be noted

further below, the difference between these alternatives is considerable for the estimate of the number of

surface water supplies with carbon tetrachloride > 0.5 :g/L; also the impact on the estimated population

exposed to carbon tetrachloride at levels > 0.5 :g/L in surface water supplies is very large.

Forty of the 312 supplies examined had measured values of carbon tetrachloride > 0.5 :g/L. When the

twelve size categories were consolidated into the five major EPA groupings, there was a general trend in

the frequency of values > 0.5 :g/L as a function of size:

Very small 0% (0/20)

Small 3.3% (2/60)

Medium 2.4% (1/42)

Large 12.2% (9/74)

Very large 24.1% (28/116)

Overall 12.8% (40/312)

A test for statistical significance revealed that at the " = 0.05 level, the very small, small, and medium

groups were not different from one another and that the large and very large groups are not different;

however, the combined very small, small, and medium groups and the combined large and very large

groups are different. These two consolidated categories were selected for developing the national

estimates:

Very small/small/medium (25-10,000)

Large/very large (> 10,000)

As noted previously, the frequency of occurrence of carbon tetrachloride at various concentrations was

determined for the consolidated groups and then applied to the number of supplies nationally within each

of the size categories comprising each group.
Occurrence Summary and Use Support Document March 2002 327

About 575 surface water supplies (range of 299-850), approximately 5.10% of the total surface water

systems in the United States, are expected to have carbon tetrachloride at levels > 0.5 :g/L; the

remaining 10,627 supplies have either no carbon tetrachloride or levels < 0.5 :g/L. It is estimated that 26

surface water supplies (range of 0-55) will have levels > 5 :g/L and 9 (range of 0-26) will have levels > 2

:g/L. None are projected to have levels above 30 :g/L.

JRB Associates (1983) reported that a notable impact on the national projections by the assumption made

that the 75 supplies with undetected but maximum potential values of 0.53-2 :g/L had < 0.5 :g/L. Had it

been assumed that carbon tetrachloride was present in these supplies at their maximum possible values,

the national projections of supplies with carbon tetrachloride levels > 0.5 :g/L would be 1,819 (range of

1,326-2,311) supplies. However, there would be no difference in the projected number of surface water

supplies with levels > 5 :g/L.

4.2.6 Conclusion

With few exceptions, production of carbon tetrachloride has been eliminated in developed nations,

including the U.S. The major use of carbon tetrachloride in the early 1990s was in the production of

chlorofluorocarbons, such as dichlorodifluoromethane and trichlorofluoromethane. According to the

latest figures available before the production ban, the U.S. produced between 573 and 761 million

pounds each year from 1981 to 1988. Industrial releases of carbon tetrachloride have been reported to

TRI since 1988 in 38 States, Puerto Rico, and the Virgin Islands. The Stage 2 analysis, based on the 16-

State cross-section, estimated that approximately 0.0159% of combined ground water and surface water

systems serving 0.0316% of the population had estimated mean concentrations of carbon tetrachloride

greater than the MCL of 0.005 mg/L. Based on this estimate, approximately 10 PWSs nationally serving

about 67,400 people are expected to have estimated mean concentrations of carbon tetrachloride greater

than the MCL. 

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, TRI releases have been reported for carbon tetrachloride from 38 States,

including 12 of 16 cross-section States. Except for certain exemptions, carbon tetrachloride is no longer

produced or used in any State, including the cross-section States. The cross-section should adequately

represent the occurrence of carbon tetrachloride on a national scale based upon the use, production, and

release patterns of the 16-State cross-section in relation to the patterns observed for all 50 States. 

4.2.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1994. Toxicological Profile for Carbon

Tetrachloride. U.S. Department of Health and Human Services, Public Health Service. 229 pp.

+ Appendices. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp30.pdf.

Brass, H.J., M.A. Feige, T. Halloran, J.W. Mello, D. Munch, and R.F. Thomas. 1977. The National

Organic Monitoring Survey: A sampling and analysis for purgeable organic compounds. 

Drinking water quality enhancement through source protection. R.B. Pojasek (ed.). Ann Arbor,

MI: Ann Arbor Science, pp. 393-416.

Brass, H.J. 1981. Rural Water Survey organics data. Memorandum of March 17, 1981 to Hugh Hanson,

Chief, Science and Technology Branch, Office of Drinking Water, and David Schnare, Office of

Drinking Water, U.S. Environmental Protection Agency, Washington, DC. 
Occurrence Summary and Use Support Document March 2002 328

Bush, B., R.S. Narang, and S. Syrotynski. 1977. Screening for halo organics in New York State drinking

water. Bull. Envir. Contam. Toxicol. 18(4): October 1977.

JRB Associates. 1983. Occurrence of Carbon Tetrachloride in Drinking Water, Food and Air - DRAFT. 

Draft report submitted to EPA for review November 17, 1983. 

Kuzmack, A.M. 1983. Memorandum: Characterization of the water supply industry (FY82). 

Washington, DC: Office of Water, U.S. Environmental Protection Agency. May 16, 1983. 

McKenna and Cuneo, L.L.P. 2001. Montreal Protocol to limit the use of the ‘transformation’ exemption

from the ODS Ban. McKenna and Cuneo, L.L.P. Client Bulletin. Available on the Internet at:

http://www.mckennacuneo.com/articles/archive/ENV04019970620.html

Mello, Wayne. 1983. Personal communication between Wayne Mello, Technical Support Division,

Office of Drinking Water, U.S. Environmental Protection Agency, and author of JRB Associates,

1983, March 10, 1983.

Symons, J.M., T.A. Bellar, and J.K. Carswell et al. 1975. National Organics Reconnaissance Survey for

Halogenated Organics. J. Amer. Water Works Assoc. 667(11): 634-647.

USEPA. 1975. Sources of organic, metal, and other inorganic parameter concentrations in selected

Region V drinking water supplies. Chicago IL: Water Division and Surveillance and Analyses

Division, USEPA. 

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Westrick, J.J., J.W. Mello, and R.F. Thomas. 1983. The Ground Water Supply Survey summary of

volatile organic contaminant occurrence data. EPA Technical Support Division, Office of

Drinking Water, Cincinnati, Ohio.
Occurrence Summary and Use Support Document March 2002 329

4.3 1,4-Dichlorobenzene

Table of Contents

4.3.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330

4.3.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

4.3.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

4.3.4 Drinking Water Occurrence Based on the 16-State Cross-Section Data . . . . . . . . . . . . . . . . . . . 332

4.3.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337

4.3.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342

4.3.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343

Tables and Figures

Table 4.3-1: Facilities that Manufacture or Process 1,4-Dichlorobenzene . . . . . . . . . . . . . . . . . . . . . . 330

Table 4.3-2: Environmental Releases (in pounds) for 1,4-Dichlorobenzene 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

Table 4.3-3: Stage 1 1,4-Dichlorobenzene Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

Table 4.3-4: Stage 1 1,4-Dichlorobenzene Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334

Table 4.3-5: Stage 2 Estimated 1,4-Dichlorobenzene Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335

Table 4.3-6: Stage 2 Estimated 1,4-Dichlorobenzene Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335

Table 4.3-7: Estimated National 1,4-Dichlorobenzene Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
Occurrence Summary and Use Support Document March 2002 330

4.3.1 Introduction, Use and Production

1,4-Dichlorobenzene (chemical formula C6H4Cl2) is usually called para-DCB or p-DCB; however, there

are about 20 additional names for it, including para crystals and paracide. It is also called paramoth

because it is one of two chemicals commonly used to make mothballs. At room temperature, 1,4-

dichlorobenzene is a white solid with a strong odor that one would probably recognize as the smell of

mothballs. Most of the 1,4-dichlorobenzene that is released to the general environment is present as a

vapor. 1,4-Dichlorobenzene does not occur naturally, but is produced by chemical companies to make

products for home use and other chemicals such as resins (ATSDR, 1998). 1,4-Dichlorobenzene can

burn, but not easily. Its major routes of entry to drinking water are a consequence of industrial activity. 

It is expected that discharges to the environment during production of the dichlorobenzenes and the use

of a variety of solvents, pesticides, and deodorants containing dichlorobenzene are primary causes of

dichlorobenzene contamination of drinking water (JRB Associates, 1983). 

For over 20 years, 1,4-dichlorobenzene has been primarily used as a space deodorant for toilets and

refuse containers, and as a fumigant for control of moths, molds, and mildews. When exposed to air, it

slowly changes from a solid to a vapor. It is the vapor that acts as a deodorizer or insect killer. Most

people recognize the odor as the smell of mothballs, and can smell 1,4-dichlorobenzene in the air at very

low levels (ATSDR, 1998).

About half to a third of the 1,4-dichlorobenzene produced is used as a deodorant and fumigant, 37% is

exported, 27% is used to produce polyphenylene sulfide resin, and another 10% is used as an

intermediate in the production of other chemicals, such as 1,2,4-trichlorobenzene (ATSDR, 1998) and

2,5-dichloroaniline (NTP, 1991). 1,4-Dichlorobenzene is also used in the control of certain tree-boring

insects and ants; in the control of blue mold in tobacco seed beds (ATSDR, 1998); as a disintegrating

paste for molding concrete and stoneware; as a lubricant (NTP, 1991); and in the manufacture of plastics,

dyes, and pharmaceuticals (USEPA, 2001).

Estimates for the production of 1,4-dichlorobenzene in the U.S. are as follows: 1972, 77.2 million

pounds; 1975, 45.9 million pounds; 1977, 16-116 million pounds; 1981, 15 million pounds (ATSDR,

1998). (More recent data is unavailable.) The three primary manufacturers of 1,4-dichlorobenzene are

Monsanto Company in Sauget, Illinois; PPG Industries, Inc., in Natrium, West Virginia; and Standard

Chlorine of Delaware, Inc., in Delaware City, Delaware; with annual production capacities of 33, 36, and

75 million pounds, respectively (ATSDR, 1998).

Table 4.3-1 lists the facilities in each State that manufacture and process 1,4-dichlorobenzene, the

intended uses of the product, and the range of maximum amounts that are stored on site. The data were

derived from the Toxics Release Inventory (TRI) of EPA (ATSDR, 1998).

Table 4.3-1: Facilities that Manufacture or Process 1,4-Dichlorobenzene

Facility Location a Range of maximum

amount on site in pounds Activities and uses

Bay State Sterling North Manchester, IN 1,000-9,999 Manufacturing Aid

Bay State Sterling Westborough, MA 1,000-9,999 Manufacturing Aid

Caroline Solite Corp. Norwood, NC 1,000-9,999 Ancillary/Other Use

Coughlan Prods. Corp. Clifton, NJ 10,000-99,999 Formulation Component

Coughlan Prods. Corp. Wayne, NJ 10,000-99,999 Formulation Component

Coughlan Prods. Corp. Paterson, NJ 10,000-99,999 Formulation Component

Crest Prods. Inc. Oldsmar, FL 10,000-99,999 Formulation Component

Dow Chemical Co. Plaquemine, LA 1,000-9,999 Produce, Impurity

Fortron Ind. Wilmington, NC 100,000-999,999 Reactant
Facility Location a Range of maximum

amount on site in pounds Activities and uses

Occurrence Summary and Use Support Document March 2002 331

Fresh Prods. Inc. Toledo, OH 10,000-99,999 Import, Sale/Dist., Repackaging, Ancillary/Other

Fuller Brush Co. Great Bend, KS 100,000-999,999 Reactant

Heartland Cement Co. Independence, KS 100-999 Ancillary/Other Use

Hospital Specialty Co. Cleveland, OH 100,000-999,999 Article Component

I. Schneid Inc. Atlanta, GA 10,000-99,999 Article Component, Repackaging

Monsanto Sauget, IL 1,000,000-9,999,999 Produce, Sale/Distribution

Nipa Hardwicke Inc. Elgin, SC 10,000-99,999 Reactant

Phillips Chemical Co. Borger, TX 100,000-999,999 Reactant

Phillips Research Center Bartlesville, OK 1,000-9,999 Reactant

PPG Ind. Inc. New Martinsville, WV 1,000,000-9,999,999 Produce, Sale/Distribution

Standard Chlorine of Delaware City, DE 10,000,000-49,999,999 Produce, On-site Use/Processing, Sale/Dist.,

Willert Home Prods. Saint Louis, MO 100,000-999,999 Article Component

a

Post office State abbreviations used

Source: ATSDR, 1998 compilation of TRI96 1998 data

4.3.2 Environmental Release

1,4-Dichlorobenzene is listed as a Toxics Release Inventory (TRI) chemical. Table 4.3-2 illustrates the

environmental releases for 1,4-dichlorobenzene from 1988 to 1999. (1,4-Dichlorobenzene data are only

available for these years.) Air emissions constitute most of the on-site releases, with a steady decrease

that has moderated in recent years. The decrease in air emissions has been the primary contributor to

decreasing levels of total on- and off-site releases. Surface water discharges have slightly decreased from

the high in 1989, although levels have been rising since 1995. Underground injection has remained

relatively constant, except for a considerable increase from 1997 to 1999. Releases to land (such as spills

or leaks within the boundaries of the reporting facility) and off-site releases (including metals or metal

compounds transferred off-site) have no discernable trend in the amounts released, as they range from

almost zero to a few thousand pounds in any given year. These TRI data for 1,4-dichlorobenzene were

reported from 22 States, with six States reporting every year (USEPA, 2000). Nine of the 22 States are in

the 16-State cross-section (used for analyses of 1,4-dichlorobenzene occurrence in drinking water; see

Section 4.3.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 4.3-2: Environmental Releases (in pounds) for 1,4-Dichlorobenzene in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 178,210 1,880 7,300 1,370 0 188,760

1998 181,899 1,706 3,100 460 -- 187,165

1997 262,266 1,728 2,000 1,960 289 268,243

1996 236,502 1,881 2,000 480 -- 240,863

1995 242,372 1,287 -- 3,100 3,328 250,087

1994 257,211 1,595 2,000 1,100 -- 261,906

1993 357,891 1,265 2,000 1,112 213 362,481

1992 337,946 2,021 2,000 622 751 343,340

1991 344,254 2,146 2,000 420 770 349,590
Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

Occurrence Summary and Use Support Document March 2002 332

1990 818,133 3,912 255 38 4,006 826,344

1989 1,592,229 6,621 250 250 1 1,599,351

1988 1,891,419 6,153 4,000 1,300 750 1,903,622

 Source: USEPA, 2000 

4.3.3 Ambient Occurrence

1,4-Dichlorobenzene was detected in 6 out of 330 wells (1.8%) in urban areas of the local, State, and

federal data set compiled by NAWQA. The minimum and maximum concentrations detected were 0.3

:g/L and 56 :g/L, respectively. The median value of detection concentrations was 1 :g/L. 1,4-

Dichlorobenzene was also detected in 4 of the 2,434 wells (0.16%) with analysis in rural areas. The

minimum and maximum concentrations detected were 0.8 :g/L and 6.7 :g/L, respectively. The median

value of detection concentrations was 1.3 :g/L. These data (urban and rural) represent untreated ambient

ground water of the conterminous United States for the years 1985-1995 (Squillace et al., 1999).

4.3.3.1 Additional Ambient Occurrence Data

A summary document entitled “Dichlorobenzenes: Occurrence in Drinking Water, Food, and Air” (JRB

Associates, 1983), was previously prepared for past USEPA assessments of 1,4-dichlorobenzene. 

However, no information on the ambient occurrence of 1,4-dichlorobenzene was included in that

document. (The document did include information regarding 1,4-dichlorobenzene occurrence in drinking

water, which is discussed in Section 4.3.5 of this report.)

4.3.4 Drinking Water Occurrence Based on the 16-State Cross-Section Data

The analysis of 1,4-dichlorobenzene occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.075 mg/L; 0.005 mg/L; and 0.0005

mg/L.

Fourteen of the sixteen cross-section State data sets contained occurrence data for 1,4-dichlorobenzene. 

(There were no 1,4-dichlorobenzene data from California or Montana.) These data represent more than

123,000 analytical results from approximately 19,000 PWSs during the period from 1984 to 1998 (with

most analytical results from 1992 to 1997). The number of sample results and PWSs vary by State,

although the State data sets have been reviewed and checked to ensure adequacy of coverage and

completeness. The overall modal detection limit for 1,4-dichlorobenzene in the 16 cross-section States is

equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to Section 1.3.5 of

this report.)
Occurrence Summary and Use Support Document March 2002 333

4.3.4.1 Stage 1 Analysis Occurrence Findings

Table 4.3-3 illustrates the Stage 1 analysis of 1,4-dichlorobenzene in drinking water for the public water

systems in the 16-State cross-section. Based on the 16-State cross-section data, no ground water or

surface water PWSs had any analytical results exceeding the MCL (0.075 mg/L). Only 0.0844% of all

PWSs in the 16 States (a total of 16 systems) had any analytical results greater than 0.005 mg/L. 

Approximately 1.32% of PWSs (250 systems) had analytical detections of 1,4-dichlorobenzene greater

than 0.0005 mg/L.

Approximately 0.0908% of ground water PWSs (16 systems) had any analytical results exceeding the

0.005 mg/L, compared to 0% of surface water systems. Over 1.2% of ground water PWSs (217 systems)

had at least one analytical result greater than 0.0005 mg/L. About 2.45% of surface water systems (33

systems) had any analytical results of 1,4-dichlorobenzene greater than 0.0005 mg/L.

Table 4.3-3: Stage 1 1,4-Dichlorobenzene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Ground Water

0.075 0.000% 0

0.005 0.0908% 16

0.0005 1.23% 217

Surface Water

0.075 0.000% 0

0.0050 0.000% 0

0.0005 2.45% 33

Combined Ground &

Surface Water

0.075 0.000% 0

0.005 0.0844% 16

0.0005 1.32% 250

Reviewing 1,4-dichlorobenzene occurrence in the 16 cross-section States by PWS population served

(Table 4.3-4) shows that no ground water or surface water systems had any analytical detections greater

than the MCL (0.075 mg/L). Approximately 0.230% of the population (almost 168,000 people) was

served by systems with at least one analytical results greater than 0.005 mg/L. Approximately 2.53% of

the population (over 1.8 million people) was served by PWSs with analytical detections of 1,4-

dichlorobenzene greater than 0.0005 mg/L. 

The percentage of population served by ground water systems in the 16 States with analytical results

greater than 0.005 mg/L was equal to 0.464% (about 168,000 people). When evaluated relative to 0.0005

mg/L, the percent of population exposed by ground water systems was equal to 3.16% (over 1.1 million

people). The percentage of population served by surface water systems with exceedances of 0.0005

mg/L was equal to 1.90% (700,400 people).
Occurrence Summary and Use Support Document March 2002 334

Table 4.3-4: Stage 1 1,4-Dichlorobenzene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Ground Water

0.075 0.000% 0

0.005 0.464% 167,800

0.0005 3.16% 1,143,000

Surface Water

0.075 0.000% 0

0.005 0.000% 0

0.0005 1.90% 700,400

Combined Ground &

Surface Water

0.075 0.000% 0

0.005 0.230% 167,800

0.0005 2.53% 1,843,400

4.3.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.3-5 and 4.3 -

6. The statistically generated best estimate values, as well as the ranges around the best estimate value,

are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. 

For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology

and Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations -

DRAFT (USEPA, 2002)). 

No ground water or surface water PWSs in the 16 States had an estimated mean concentration of 1,4-

dichlorobenzene exceeding 0.075 mg/L (the current MCL). The percentage of PWS in the 16 States with

estimated mean concentration values of 1,4-dichlorobenzene greater than 0.005 mg/L was equal to

0.000253%. The percentage of PWSs with estimated mean concentrations exceeding 0.0005 mg/L (the

modal detection limit) was about 0.114% PWSs (22 systems) in the 16 States. 

A greater proportion of ground water systems, as compared to surface water systems, were estimated to

exceed the modal detection limit. Approximately 0.000273% of ground water systems in the 16 States

had estimated mean concentrations greater than 0.005 mg/L, as compared to 0% of surface water

systems. About 0.117% of ground water systems (an estimated 21 systems in the 16 States) had

estimated mean concentrations greater than 0.0005 mg/L. This compares with about 0.0746% of the

surface water systems (about 1 system) with estimated mean concentrations greater than 0.0005.
Occurrence Summary and Use Support Document March 2002 335

Table 4.3-5: Stage 2 Estimated 1,4-Dichlorobenzene Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.075 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000273% 0.000% - 0.00568% 0 0 - 1

0.0005 0.117% 0.0738% - 0.170% 21 13 - 30

Surface Water

0.075 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.0746% 0.000% - 0.223% 1 0 - 3

Combined Ground

& Surface Water

0.075 0.0000% 0.000% - 0.000% 0 0 - 0

0.005 0.000253% 0.000% - 0.00527% 0 0 - 1

0.0005 0.114% 0.0738% - 0.164% 22 14 - 31

Reviewing 1,4-dichlorobenzene occurrence by PWS population served (Table 4.3-6) shows that

approximately 0.00000206% of the population in the 16 States was served by PWSs with mean

concentrations greater than 0.005 mg/L. Approximately 0.0379% of population served by all PWSs in

the 16 States (an estimate of approximately 27,700 people) was potentially exposed to 1,4-

dichlorobenzene levels above 0.0005 mg/L. When evaluated relative to a threshold of 0.075 mg/L, the

percent of population exposed was equal to 0%.

For ground water systems, about 0.00000416% of the population served by ground water systems in the

16 States was exposed to 1,4-dichlorobenzene levels above 0.005 mg/L. An estimated 0.0505% of the

population (about 18,300 people) was served by systems in the 16 States whose mean concentration

value exceeded 0.0005 mg/L.

No surface water systems had mean concentrations that exceeded 0.005 mg/L. Approximately 0.0255%

of the 16-State population was served by surface water PWSs (about 9,400 people) with estimated mean

concentrations of 1,4-dichlorobenzene above 0.0005 mg/L.

Table 4.3-6: Stage 2 Estimated 1,4-Dichlorobenzene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.075 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.00000416% 0.000% - 0.0000691% 0 0 - < 100
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 336

0.0005 0.0505% 0.00580% - 0.187% 18,300 2,100 - 67,600

Surface Water

0.075 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.0005 0.0255% 0.000% - 0.193% 9,400 0 - 70,900

Combined Ground

& Surface Water

0.075 0.000% 0.000% - 0.000% 0 0 - 0

0.005 0.00000206% 0.000% - 0.0000343% 0 0 - < 100

0.0005 0.0379% 0.00390% - 0.167% 27,700 2,800 - 121,800

4.3.4.3 Estimated National Occurrence

As illustrated in Table 4.3-7, the Stage 2 analysis estimated zero PWSs nationally were estimated to have

mean concentration values of 1,4-dichlorobenzene greater than 0.075 mg/L or 0.005 mg/L. 

Approximately 74 systems serving about 80,700 people nationally were estimated to have mean 1,4-

dichlorobenzene concentrations greater than 0.0005 mg/L. An estimated 69 ground water PWSs serving

about 43,300 people nationally had mean concentrations greater than 0.0005 mg/L. Approximately 4

surface water systems serving 32,400 people was estimated to have mean concentrations of 1,4-

dichlorobenzene above 0.0005 mg/L. (See Section 1.4 for a description of how Stage 2 16-State

estimates are extrapolated to national values.)

Table 4.3-7: Estimated National 1,4-Dichlorobenzene Occurrence - Systems and Population

Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.075 0 0 - 0 0 0 - 0

0.005 0 0 - 3 0 0 - < 100

0.0005 69 44 - 101 43,300 5,000 - 160,000

Surface Water

0.075 0 0 - 0 0 0 - 0

0.005 0 0 - 0 0 0 - 0

0.0005 4 0 - 12 32,400 0 - 245,400
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 337

Combined Ground

& Surface Water

0.075 0 0 - 0 0 0 - 0

0.005 0 0 - 3 0 0 - < 100

0.0005 74 48 - 106 80,700 8,300 - 355,500

4.3.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of 1,4-dichlorobenzene in drinking water are

also reviewed. Previously compiled occurrence information on one of the three isomers of

dichlorobenzene, para-dichlorobenzene (1,4-dichlorobenzene), from an OGWDW summary document

entitled “Dichlorobenzenes: Occurrence in Drinking Water, Food, and Air” (JRB Associates, 1983), is

presented in the following section. This variety of studies and information are presented regarding levels

of 1,4-dichlorobenzene in drinking water, with the scope of the reviewed studies ranging from national to

regional. Note that none of the studies presented in the following section provide the quantitative

analytical results or comprehensive coverage that would enable direct comparison to the occurrence

findings estimated with the cross-section occurrence data presented in Section 4.3.4. These additional

studies, however, do enable a broader assessment of the Stage 2 occurrence estimates presented for this

Six-Year Review. All the following information in Section 4.3.5 is taken directly from

“Dichlorobenzenes: Occurrence in Drinking Water, Food, and Air” (JRB Associates, 1983).

The JRB Associates (1983) report found three major types of data available that were potentially useful

for describing the occurrence of dichlorobenzene in the nation's public drinking water supplies. First,

there are several Federal surveys in which a number of public water supplies from throughout the U.S.

were selected for analysis of chemical contamination, including dichlorobenzene. Second, data are

available from State surveys and from State investigations of specific incidents of known or suspected

contamination of a supply. Third, there are miscellaneous published data which, like some of the State

data, tend to be from studies in response to suspected contamination of specific sites. For accomplishing

the basic objectives of this study, namely to estimate the number of public water supplies nationally

within the various source and size categories contaminated with dichlorobenzene, the distribution of

dichlorobenzene concentrations in those supplies, and the number of individuals exposed to those

concentrations, it was determined that the Federal survey data provides the most suitable data base. The

State and miscellaneous data tend to be poorly described with respect to the source and size categories of

the supplies examined and the sampling and analysis methods used for determining contaminant levels. 

The lack of source and system size information precludes using the data for estimating levels in public

water supplies of similar characteristics. The absence of details on sampling and analysis methods

precludes evaluating those data for their qualitative and quantitative reliability. Also, because much of

the State and miscellaneous data are from investigations in response to incidents of known or suspected

contamination (e.g., spills), they were judged to be not representative of contaminant levels in the

nation's water supplies in general. Although they are not used with the Federal data for the purpose of

estimating contamination levels nationally, the available State and miscellaneous data are presented here

to provide some additional perspective on dichlorobenzene occurrence in drinking water.
Occurrence Summary and Use Support Document March 2002 338

Data are presented only on drinking water samples taken from a consumer's tap (i.e., distribution water

samples) or on treated water samples taken at the water supply (i.e., finished water samples) because

these are considered to be most representative of the water consumed by the public. No data on raw (i.e.,

untreated) water are presented. It is recognized that for some groundwater supplies where no treatment

of the water occurs, samples identified as raw may be representative of water consumed by the users of

the supply. However, it was generally not possible to differentiate between those groundwater supplies

that do and do not treat raw water from the available survey data.

4.3.5.1 Overview and Quality Assurance Assessment of Federal Drinking Water Surveys

Three Federal drinking water surveys provide data on dichlorobenzene: the National Organic Monitoring

Survey (NOMS), the National Screening Program for Organics in Drinking Water (NSP), and the

Groundwater Supply Survey (GWSS). The terms used in this report are those used in the individual

surveys, recognizing that they may not always correspond to strict technical definitions.

The National Organic Monitoring Survey (NOMS) was conducted to identify contaminant sources, to

determine the frequency of occurrence of specific drinking water contaminants, and to provide data for

the establishment of maximum contaminant levels (MCLs) for various-organic compounds in drinking

water (Brass et al., 1977, as cited in JRB Associates, 1983). The NOMS was conducted in three phases:

March-April 1976, May-July 1976, and November 1976-January 1977. Finished drinking water samples

from 113 communities were analyzed for 21 different compounds. Of the 113 community supplies

sampled, 18 had groundwater sources, 91 had surface water sources, and 4 had a mixed

groundwater/surface water source.

The analytical results of the NOMS were made available in printed form by EPA's Technical Support

Division, Office of Drinking Water. Additional information on the locations and source of the supplies,

and on the populations served by the supplies in the NOMS were provided by Wayne Mello (1983) at

EPA's Technical Support Division, Office of Drinking Water. A single value for dichlorobenzenes was

reported for each supply studied in the NOMS.

The National Screening Program for Organics in Drinking Water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water

systems in 33 States for 51 organic chemical contaminants. Data are available only for pdichlorobenzene (1,4-dichlorobenzene) on finished water samples from 12 groundwater and 103 surface

water supplies.

The Groundwater Supply Survey (GWSS) was conducted from December 1980 to December 1981 to

develop additional data on the occurrence of volatile organic chemicals in the nation's groundwater

supplies (Westrick et al., 1983, as cited in JRB Associates, 1983). It was hoped that this study would

stimulate State efforts toward the detection and control of groundwater contamination and the

identification of potential chemical “hot spots.” A total of 945 systems were sampled, of which 466 were

chosen at random. The remaining 479 systems were chosen nonrandomly based on information from

States encouraged to identify locations believed to have a higher than normal probability of VOC

contamination (e.g., locations near landfills or industrial activity).

Each of the drinking water surveys was evaluated with respect to the validity of the reported occurrence

data for a number of organic chemicals, including dichlorobenzene. The evaluations were carried out by

analyzing information about the procedures used for collection and analysis of samples as well as the

quality control protocols used. The analyzed compounds dealt with in each study were assigned one of

three possible ratings: quantitatively acceptable, qualitatively acceptable (i.e., the substance measured
Occurrence Summary and Use Support Document March 2002 339

was dichlorobenzene), and totally unacceptable. In the case of dichlorobenzene, a qualitatively

acceptable rating was given for data from the NOMS (Phases II and III) because of suspected

biodegradation of the samples, which were held unrefrigerated for prolonged periods before analysis. 

Dichlorobenzene values in excess of the quantitation limit reported for some samples in these studies are

qualitatively valid and can be taken as minimum values, representative of samples which probably

originally contained dichlorobenzene at higher concentrations. In the case of the NOMS (Phase I), NSP,

and GWSS, all data were rated both quantitatively and qualitatively acceptable.

4.3.5.2 Groundwater – Federal Surveys

Three Federal surveys contain data concerning the levels of one or more of the three dichlorobenzene

isomers in groundwater supplies from across the country. The National Organics Monitoring Survey

(NOMS) and Groundwater Supply Survey (GWSS) contain data on all three isomers. The National

Screening Program for Organics in Drinking Water (NSP) contains data on p-dichlorobenzene only.

Eighteen groundwater systems were analyzed for p-dichlorobenzene during Phase I of NOMS (March to

April 1976), with none of the systems containing quantifiable levels. These 18 systems were sampled

again during Phase II of the study (May to July 1976) for all three isomers of dichlorobenzene. Four

systems contained p-dichlorobenzene at levels ranging from 0.006-0.41 :g/L. The average of the

positive values was 0.13 :g/L with a standard deviation of 0.19 :g/L; the median value was 0.04 :g/L. 

Two of the 17 systems analyzed for p-dichlorobenzene proved positive, with levels of 0.09 and 0.1 :g/L. 

The minimum quantifiable limit for p-dichlorobenzene was1.0 :g/L in Phase I and 0.005 :g/L in Phases

II and III.

Twelve groundwater supplies were tested for p-dichlorobenzene contamination in the NSP. Of these 12

systems, one was contaminated with p-dichlorobenzene at a level of 0.5 :g/L. The quantification limit

for p-dichlorobenzene was 0.1 :g/L.

In the GWSS, 5 of the 456 randomly chosen water systems serving 25 or more individuals were positive

for p-dichlorobenzene, at concentrations ranging from 0.52-1.3:g/L. The three systems with the highest

values were contaminated at 0.66, 0.68, and 1.3 :g/L. Of the 5 positive p-dichlorobenzene systems, 3

were from systems serving populations in excess of 10,000 people. The average for all randomly chosen

systems was 0.8 :g/L with a standard deviation of 0.3 :g/L; the median was 0.7 :g/L. Of the 473

nonrandom locations sampled serving 25 or more individuals, 4 were contaminated with p-dichlorobenzene at levels ranging from 0.7-0.9 :g/L. All 4 positive p-dichlorobenzene samples were from

systems serving populations under 10,001 people. The average p-dichlorobenzene concentration for the

nonrandom systems was 0.8 :g/L with a standard deviation of 0.09 :g/L; the median value was 0.7 :g/L. 

The minimum quantitation limit for dichlorobenzene was 0.5 :g/L.

4.3.5.3 Groundwater – State Data

Dichlorobenzene data (undifferentiated by isomer) on groundwater from 274 wells, supplied to the EPA

by New Jersey, contained only one positive value (between 1-10 :g/L).

Data from California, Indiana, and New Jersey revealed a low incidence of p-dichlorobenzene

contamination. Groundwater supplies from four locations in California (unspecified water type) were

sampled with only one containing a quantifiable amount of p-dichlorobenzene (0.4 :g/L from Morada). 

Analytical results from seven groundwater samples from Elkhart, Indiana proved negative for pdichlorobenzene. One hundred seventy-five groundwater samples were taken from New Jersey with only

one positive value between the detection limit and 9.9 :g/L (unquantified).
Occurrence Summary and Use Support Document March 2002 340

4.3.5.4 Surface Water – Federal Surveys

Two Federal studies, the National Organic Monitoring Survey (NOMS) and the National Screening

Program for Organics in Drinking Water (NSP), contain data concerning dichlorobenzene levels in

surface water supplies from across the country. The NOMS contains information on all three isomers of

dichlorobenzene, while the NSP provides data for p-dichlorobenzene only.

In Phase I of the National Organic Monitoring Survey (March to April 1976), water samples from 89

surface water systems were analyzed only for p-dichlorobenzene. Of these 89 systems, only two were

found to contain p-dichlorobenzene, at levels of 1.0 and 3.0 :g/L. Ninety-one systems were sampled

during the second phase of the survey (May to July 1976) and sixteen of the 91 systems were

contaminated with p-dichlorobenzene, at levels ranging from 0.007-1.6 :g/L, including the three systems

identified as positive in the first phase of the study. The average p-dichlorobenzene concentration among

the positive Phase II samples was 0.14 :g/L with a standard deviation of 0.39 :g/L; the median

concentration was 0.03 :g/L. During the third phase of the NOMS (November 1976 to January 1977),

analyses revealed contamination by all three isomers of dichlorobenzene. Of the 89 systems analyzed, 27

systems showed p-dichlorobenzene contamination, at levels ranging from 0.01-0.75 :g/L. The average

concentration among the 27 positive systems was 0.06 :g/L ± 0.14; the median value was 0.02 :g/L. For

p-dichlorobenzene, the minimum quantifiable limit was 1.0 :g/L in Phase I, 0.1 :g/L in Phase II, and

0.005 :g/L in Phase III.

Surface water samples from 106 drinking water systems were analyzed for p-dichlorobenzene during the

National Screening Program (NSP) between June 1977 and March 1981. Of these, 5 systems contained

detectable levels of p-dichlorobenzene, ranging from 0.1-0.9 :g/L. Only two of these systems were

contaminated at levels greater than 0.1 :g/L (0.2 and 0.9 :g/L). The average concentration among the 5

positive systems was 0.3 :g/L with a standard deviation of 0.3 :g/L; the median level was 0.15 :g/L. 

The quantification limit for the NSP was 0.1 :g/L.

4.3.5.5 Surface Water – State Data

The levels of dichlorobenzene in surface water systems at Niagara Falls were monitored. Eight surface

water samples were analyzed for p-dichlorobenzene with four containing quantities ranging from 0.01 to

0.18 :g/L, the average being 0.05 :g/L. Of five surface water samples analyzed for dichlorobenzene

undifferentiated as to isomer, three had concentrations of 0.02-0.26 :g/L (average of 0.16 :g/L for

positive samples).

4.3.5.6 Surface Water – Miscellaneous Data

Drinking water samples from surface water sources, collected from three cities on Lake Ontario, were

analyzed for the three isomers of dichlorobenzene. Positive results were found for each isomer. In the

case of p-dichlorobenzene, concentrations ranged from 0.008-0.020 :g/L, with an average of 0.013 :g/L

(Oliver and Nicol, 1982, as cited in JRB Associates, 1983).

4.3.5.7 Projected National Occurrence of Dichlorobenzene in Public Water Supplies

As reported in the JRB Associates (1983) report, public water systems fall into two major categories with

respect to water source (surface water and groundwater) and into five size categories and twelve

subcategories according to the number of individuals served. The JRB Associates (1983) report

presented estimates of both the number of drinking water supplies nationally within each of the
Occurrence Summary and Use Support Document March 2002 341

source/size categories expected to have dichlorobenzene present, and of the concentration of

dichlorobenzene expected to be present in those supplies.

The key features of the methodology used and assumptions made to develop the national estimates are

summarized here. The estimates are based on the data from the Federal surveys only. The State data and

miscellaneous information were not included for several reasons. Generally, these data are from a few

States and were not considered to be geographically representative. There was also a general lack of data

on the population served by systems measured, the type of water sampled, and the methodologies used to

sample, identify, and measure dichlorobenzene.

The Federal survey data from the NOMS, NSP, and GWSS were pooled together for developing the

national projections. It was assumed in combining these surveys that the resulting data base would be

representative of the nation's water supplies. In the case of the GWSS data, both the random and

nonrandom samples were included in the projections because statistical test of the GWSS data showed

that neither the frequency of occurrence of positive values nor the mean of the positive values for any of

the three dichlorobenzene isomers was significantly different between the two samples.

Ideally, adequate data would be available to develop the national projections separately for each of the

twelve system size categories within the groundwater and surface water groups; however, the available

data were too limited for this. JRB Associates (1983) consolidated some of the size categories to have

sufficient data for developing the projections. In consolidating data from various size categories,

consideration was given to the potential for there being statistically significant differences in the

frequency of occurrence of dichlorobenzene as a function of system size. The consolidation of size

categories therefore involved a balancing of the need to group size categories together to have an

adequate data base for developing the national projections against the need to treat size categories

separately in order to preserve the influence of system size as a determinant of contamination potential. 

The consolidation of size categories also took into account EPA's classification of systems into the five

major groups as very small (25500), small (501-3,300), medium (3,301-10,000), large (10,001-100,000),

and very large (> 100,000) (Kuzmack, 1983, as cited in JRB Associates, 1983).

Once the data were consolidated, statistical models for extrapolating to the national level were tested and

an appropriate model selected. In the case of the dichlorobenzenes, the multinomial method was used. 

The frequency of contamination of groundwater and surface water systems at various concentrations was

determined for each consolidated size category. For completing the national estimates, it was assumed

that the frequency of contamination observed for each consolidated category was directly applicable to

each of the system sizes comprising it.

In the JRB Associates (1983) report, it is noted some of the data used in computing the national estimates

are from samples held for a prolonged period of time prior to analysis, with possible biodegradation of

the dichlorobenzenes. Therefore, these projections of national occurrence may underestimate actual

contaminant levels.

4.3.5.7.1 Groundwater Supplies

Fourteen of 948 groundwater supplies sampled were found to have p-dichlorobenzene present at levels

ranging from 0.34 to 1.3 :g/L. Based on the overall distribution of positive values and maximum

possible values for those supplies in which the dichlorobenzenes were not found, 0.5 :g/L was selected

as the common minimum quantifiable concentration for the combined survey data. That is, quantitative

projections are made of supplies at several concentration ranges > 0.5 :g/L, while only a total number for

supplies expected to have either no dichlorobenzene or levels below 0.5 :g/L can be determined. 
Occurrence Summary and Use Support Document March 2002 342

Although some data indicate the presence of dichlorobenzene (specifically p-dichlorobenzene) in

groundwater supplies at levels < 0.5 :g/L, it is not possible to determine the proportion of supplies that

have dichlorobenzene present and the proportion that are actually free of dichlorobenzene contamination.

The survey data was combined across all system sizes for each of the dichlorobenzene isomers in order to

develop the national estimates. The frequency of occurrence of each of the dichlorobenzenes that was

determined on the basis of data for all size supplies was then applied to each of the separate size

categories to complete the national estimates.

An estimated 510 groundwater supplies (range of 197-822), approximately 1.1% of the total groundwater

supplies in the United States, are expected to have p-dichlorobenzene levels of > 0.5 :g/L; the remaining

47,948 supplies have either no p-dichlorobenzene or levels < 0.5 :g/L. No groundwater supplies are

expected to have p-dichlorobenzene at levels above 5 :g/L.

4.3.5.7.2 Surface Water Systems

P-dichlorobenzene was observed in 38 of 150 supplies sampled. The concentrations ranged from 0.1 to

1.6 :g/L. Based on the overall distribution of positive values and maximum possible values for those

supplies in which the dichlorobenzenes were not found, 0.5 :g/L was selected as the common minimum

quantifiable concentration for the combined survey data. That is, quantitative projections are made of

supplies at several concentration ranges > 0.5 :g/L, while only a total number for supplies expected to

have either no dichlorobenzene or levels below 0.5 :g/L can be determined. Although some data

indicate the presence of dichlorobenzene in surface water supplies at levels < 0.5 :g/L, it is not possible

to determine the proportion that have dichlorobenzene present and the proportion that are free of

dichlorobenzene contamination.

Twelve surface water supplies (range of 0-34), approximately 0.1% of the total surface water supplies in

the United States, are expected to have p-dichlorobenzene levels of > 0.5 :g/L; the remaining 11,190

supplies have either no p-dichlorobenzene or levels < 0.5 :g/L. No surface water supplies are expected

to have p-dichlorobenzene at levels > 5 :g/L.

4.3.6 Conclusion

1,4-Dichlorobenzene is primarily used as a space deodorant for toilets and refuse containers, and as a

fumigant for control of moths, molds, and mildews. According to the latest data available, production of

1,4-dichlorobenzene was 78.8 million pounds in 1994, and production has generally increased over time. 

Industrial releases of 1,4-dichlorobenzene have been reported to TRI since 1988 from 22 States. 1,4-

Dichlorobenzene was also an analyte for the NAWQA ambient occurrence studies. In the NAWQA

study, 1,4-dichlorobenzene was detected in 1.8% of urban wells and 0.16% of rural wells, with median

detection values of 1.0 :g/L and 1.3 :g/L, respectively. The Stage 2 analysis, based on the 16-State

cross-section, estimated that 0% of combined ground water and surface water systems serving 0% of the

population exceeded the MCL of 0.075 mg/L. Based on this estimate, no PWSs nationally are expected

to have estimated mean concentrations of 1,4-dichlorobenzene greater than MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, 1,4-dichlorobenzene is manufactured and/or processed in 16 States and has

TRI releases in 22 States. 1,4-Dichlorobenzene is manufactured and/or processed in 6 out of the 16

cross-section States and has TRI releases in 9 of the 16 cross-section States. The cross-section should

adequately represent the occurrence of 1,4-dichlorobenzene on a national scale based upon the use,
Occurrence Summary and Use Support Document March 2002 343

production, and release patterns of the 16-State cross-section in relation to the patterns observed for all

50 States. 

4.3.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1998. Toxicological Profile for 1,4-

Dichlorobenzene. U.S. Department of Health and Human Services, Public Health Service. 253

pp. + Appendices. Available on the Internet at http://www.atsdr.cdc.gov/toxprofiles/tp10.pdf

Brass, H.J., M.A. Feige, T. Halloran, J.W. Mello, D. Munch, and R.F. Thomas. 1977. The National

Organic Monitoring Survey: A sampling and analysis for purgeable organic compounds. 

Drinking water quality enhancement through source protection. R.B. Pojasek (ed.). Ann Arbor,

MI: Ann Arbor Science, pp. 393-416.

JRB Associates. 1983. Dichlorobenzenes: Occurrence in Drinking Water, Food, and Air. Draft report

submitted to EPA for review November 17, 1983.

Kuzmack, A.M. 1983. Memorandum: Characterization of the water supply industry (FY82). 

Washington, D.C.: Office of Water, USEPA. May 16, 1983. 

Mello, Wayne. 1983. Personal communication between Wayne Mello, Technical Support Division,

Office of Drinking Water, USEPA, and author of JRB Associates, 1983, March 10, 1983.

National Toxicology Program (NTP). 1991. National Toxicology Program Health and Safety

Information Sheet - 1,4-Dichlorobenzene. Available on the Internet at

http://ntp-db.niehs.nih.gov/NTP_Reports/NTP_Chem_H&S/NTP_Chem1/Radian106-46-7.txt

Oliver, B.G., K.D. Nicol. 1982. Chlorobenzenes in sediments, water, and selected fish from Lakes

Superior, Huron, Erie, and Ontario. Envir. Sci. Technol. 16:532-536.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: Paradichlorobenzene. Office of Ground Water and Drinking Water, USEPA. Available on the

Internet at http://www.epa.gov/safewater/dwh/c-voc/p-dichlo.html (Last updated 04/12/2001)

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Westrick, J.J., J.W. Mello, and R.F. Thomas. 1983. The Ground Water Supply Survey summary of

volatile organic contaminant occurrence data. EPA Technical Support Division, Office of

Drinking Water, Cincinnati, Ohio.
Occurrence Summary and Use Support Document March 2002 344

4.4 1,2-Dichloroethane

Table of Contents

4.4.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

4.4.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

4.4.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

4.4.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 348

4.4.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353

4.4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

4.4.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

List of Tables

Table 4.4-1: 1,2-Dichloroethane Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . . . 345

Table 4.4-2: United States Production of 1,2-Dichloroethane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346

Table 4.4-3: Environmental Releases (in pounds) for 1,2-Dichloroethane 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

Table 4.4-4: Stage 1 1,2-Dichloroethane Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

Table 4.4-5: Stage 1 1,2-Dichloroethane Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

Table 4.4-6: Stage 2 Estimated 1,2-Dichloroethane Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

Table 4.4-7: Stage 2 Estimated 1,2-Dichloroethane Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352

Table 4.4-8: Estimated National 1,2-Dichloroethane Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
Occurrence Summary and Use Support Document March 2002 345

4.4.1 Introduction, Use and Production

1,2-Dichloroethane is a clear, manufactured liquid with the chemical formula C2H4Cl2. It evaporates

quickly at room temperature and has a pleasant smell and a sweet taste. 1,2-Dichloroethane burns with a

smoky flame (ATSDR, 1999). The major routes of entry of 1,2-dichloroethane to drinking water are a

consequence of industrial activity. It is expected that discharges to surface water and leaching from solid

waste are the primary causes of 1,2-dichloroethane contamination of drinking water. Most discharges of

1,2-dichloroethane ultimately reach the atmosphere because of its high volatility (JRB Associates, 1983). 

Other names for 1,2-dichloroethane are ethylene dichloride, dichloroethane, and EDC. 

Although large amounts of 1,2-dichloroethane are produced today, most of it is used as a chemical

intermediate for vinyl chloride (ATSDR, 1999). This is, by far, the dominant use of 1,2-dichloroethane. 

(Ninety-eight percent of the 1,2-dichloroethane produced is produced for this use.) It is used in smaller

amounts to synthesize other organic compounds such as vinylidene chloride, 1,1,1-trichloroethane,

trichloroethylene, tetrachloroethylene, aziridines, ethylene diamines, and various chlorinated solvents. It

can also be added to leaded gasoline to remove lead (ATSDR, 1999).

Some uses of 1,2-dichloroethane have been discontinued, especially in many consumer products. It is no

longer used in varnish and finish removers, soaps and scouring compounds, metal degreasers, ore

flotation, or paints, coatings, and adhesives; or in organic synthesis for extraction and cleaning purposes. 

It was also formerly used as a grain, household, and soil fumigant (ATSDR, 1999).

Most of the 1,2-dichloroethane produced is used captively by the manufacturers. In 1986 only 6% of the

1,2-dichloroethane produced was sold on the open market, and the most recent information indicates that

about 85% of total 1,2-dichloroethane produced is used captively. Production totals for past years are as

follows: 1984, 7.3 billion pounds; 1985, 12.1 billion pounds; 1986, 12.9 billion pounds; 1990, 13.8

billion pounds; 1992, 15.2 billion pounds; 1993, 17.9 billion pounds; and 1994, 16.8 billion pounds

(ATSDR, 1999).

Table 4.4-1 shows the number of facilities in each State that manufacture and process 1,2-dichloroethane,

the intended uses of the product, and the range of maximum amounts derived from the Toxics Release

Inventory (TRI) of EPA. Table 4.4-2 shows the company names and locations of facilities that produce

1,2-dichloroethane and their annual capacities as of February 1, 1998 (ATSDR, 1999).

Table 4.4-1: 1,2-Dichloroethane Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on site in

poundsb Activities and usesc

AL 2 1,000-99,999 11

AR 3 10,000-999,999 7,11

CA 2 10,000-99,000 8

HI 1 10,000-99,999 8,11

IA 2 1,000-9,999 1,6

IL 3 0-99,999 7,11

IN 3 10,000-999,999 11,12

KS 4 100-999,999 2,4,10,11,13

KY 3 10,000-49,999,999 1,3,5,7,10

LA 15 1,000-499,999,999 1,3,4,5,6,7,10,11,13

MI 2 1,000-9,999 1,5,7,12,13

MO 2 100,000-9,999,999 1,3,5,7,8,11

MS 1 100,000-999,999 7,11

NC 3 1,000-999,999 11,13

NJ 2 10,000-99,999 10,11,13

NM 1 1,000-9,999 11
Statea Number of facilities Range of maximum amounts on site in

poundsb Activities and usesc

Occurrence Summary and Use Support Document March 2002 346

NY 1 10,000-99,999 11

PA 6 10,000-999,999 1,5,11,13

PR 2 0-99,999 11,13

SC 2 10,000-999,999 7,11

TX 19 0-499,999,999 1,2,3,4,5,6,7,8,10,11,13

a

Post office State abbreviations used

b

Data in TRI are maximum amounts on site at each facility

c

Activities/Uses include:

1. Produce 8. As a formulation component

2. Import 9. As a product component

3. For on-site use/processing 10. For repackaging

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

Source: ATSDR, 1999 compilation of TRI96 1999 data

Table 4.4-2: United States Production of 1,2-Dichloroethanea,b

Manufacturer Location Annual capacity (millions of pounds)

Borden Chemicals and Plastics Geismar, LA 745

CONDEA Vista Company Lake Charles, LA 1,400

Dow Chemical USA Freeport, TX

Plaquemine, LA

4,500

2,300

Formosa Plastics Corporation USA Baton Rouge, LA

Point Comfort, TX

525

1,900

Geon Company LaPorte, TX 4,000

Georgia Gulf Corporation Plaquemine, LA 1,760

Occidental Chemical Corporation

 Electrochemicals and Proprietary Products

Division

 Electrochemicals

Convent, LA

Deer Park, TX

Ingleside, TX

1,500

1,950

3,300

Oxymar Ingleside, TX 3,000

PHH Monomers Lake Charles, LA 1,400

PPG Industries, Inc. Chemicals Group Lake Charles, LA 1,600

Vulcan Materials Company

 Vulcan Chemicals Division

Geismar, LA 500

Westlake Monomers Corporation Calvert City, KY 1,950

TOTAL 32,330

a

Derived from Anonymous 1998

b

Estimates as of February 1, 1998

Source: ATSDR, 1999
Occurrence Summary and Use Support Document March 2002 347

4.4.2 Environmental Release

1,2-Dichloroethane is listed as a Toxics Release Inventory (TRI) chemical. Table 4.4-3 illustrates the

environmental releases of 1,2-dichloroethane from 1988 - 1999. (1,2-Dichloroethane data are only

available for these years.) Air emissions constitute most of the on-site releases, with a steady decrease

over the years, except for a minor upturn in 1990. Surface water discharges have fluctuated with a

decreasing trend, as releases have remained below 10,000 pounds since 1993. Underground injection has

also generally declined, from a high of almost 1.5 million pounds in 1988 to about 1,200 pounds in 1999. 

Releases to land (such as spills or leaks within the boundaries of the reporting facility) have ranged from

near zero to over 7,000 pounds, with no apparent trend. Off-site releases (including metals or metal

compounds transferred off-site) decreased from 1988-1991, but have since risen, with by far the greatest

release reported in 1999. The decreases in air emissions, underground injection, and surface water

discharges have contributed to an overall decreasing trend of total 1,2-dichloroethane on- and off-site

releases. These TRI data for 1,2-dichloroethane were reported from 37 States and Puerto Rico, with 18

States reporting every year (USEPA, 2000). Of the 37 States that reported, 11 are in the 16 State crosssection (used for analyses of 1,2-dichloroethane occurrence in drinking water; see Section 4.4.4). (For a

map of the 16-State cross-section, see Figure 1.3-1.)

Table 4.4-3: Environmental Releases (in pounds) for 1,2-Dichloroethane in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 545,225 833 1,171 2,983 679,749 1,229,961

1998 708,117 2,337 2,178 886 162,677 876,195

1997 910,890 1,826 4,549 27 120,476 1,037,768

1996 1,051,183 1,848 5,126 250 91,249 1,149,656

1995 1,292,842 5,194 24,339 256 23,671 1,346,302

1994 1,930,617 7,501 34,296 15 75,642 2,048,071

1993 2,382,308 9,871 5,198 303 61,675 2,459,355

1992 3,307,692 12,760 85,750 1,858 20,530 3,428,590

1991 4,089,523 26,264 6,334 7,051 6,789 4,135,961

1990 5,609,152 49,513 826,672 7,351 33,279 6,525,967

1989 4,251,586 225,824 1,046,661 714 110,085 5,634,870

1988 4,615,179 40,527 1,452,084 2,166 166,131 6,276,087

 Source: USEPA, 2000 

4.4.3 Ambient Occurrence

The local, State, and federal data set compiled by NAWQA reports that 1,2-dichloroethane was detected

in 7 out of 351 urban wells (2.0%). The minimum and maximum concentrations detected were 0.2 :g/L

and 3 :g/L, respectively. The median value of detection concentrations was 0.5 :g/L. 1,2-

Dichloroethane was also detected in 18 of the rural 2,539 wells (0.71%) analyzed. The minimum and

maximum concentrations detected were 0.2 :g/L and 2.8 :g/L, respectively. The median value of

detection concentrations was 0.55 :g/L. These data (urban and rural) represent untreated ambient ground

water of the conterminous United States for the years 1985-1995 (Squillace et al., 1999).
Occurrence Summary and Use Support Document March 2002 348

1,2-Dichloropropane was also an analyte in the NURP data. The NURP study found 1,2-dichloroethane

in urban runoff (Lopes and Dionne, 1998). The minimum concentration detected was not reported, and

the maximum concentration detected was 4 :g/L, with no mean value reported. The use of the land from

which the samples were taken was unspecified. 

4.4.3.1 Additional Ambient Occurrence Data

A summary document entitled “Occurrence of 1,2-Dichloroethane in Drinking Water, Food, and Air”

(JRB Associates, 1983), was previously prepared for past USEPA assessments of 1,2-dichloroethane. 

However, no information on the ambient occurrence of 1,2-dichloroethane was included in that

document. (The document did include information regarding 1,2-dichloroethane occurrence in drinking

water, which is discussed in Section 4.4.5 of this report.)

4.4.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of 1,2-dichloroethane occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.0005 mg/L; 0.0025 mg/L; and 0.005

mg/L.

All sixteen cross-section State data sets contained occurrence data for 1,2-dichloroethane. These data

represent more than 180,000 analytical results from approximately 23,000 PWSs during the period from

1984 to 1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs

vary by State, although the State data sets have been reviewed and checked to ensure adequacy of

coverage and completeness. The overall modal detection limit for 1,2-dichloroethane in the 16 crosssection States is equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)

4.4.4.1 Stage 1 Analysis Occurrence Findings

Table 4.4-4 illustrates the occurrence of in drinking water for the public water systems in the 16-State

cross-section relative to three thresholds: 0.005 mg/L (the current MCL), 0.0025 mg/L, and 0.0005 mg/L

(the modal MRL). Based on the 16-State cross-section data, less than one percent of all ground water

and surface water systems had any threshold exceedances. A total of 29 (approximately 0.126% of)

PWSs had analytical results exceeding the MCL; 0.239% of systems (55 systems) had results exceeding

0.0025 mg/L; and 0.977% of systems (225 systems) had results exceeding 0.0005 mg/L. 

Approximately 0.112% of ground water systems (24 systems) had any analytical results greater than the

MCL. About 0.214% of ground water systems (46 systems) had results above 0.0025 mg/L. The

percentage of ground water systems with at least one result greater than 0.0005 mg/L was equal to

0.909% (195 systems). 

Only 5 (0.317% of) surface water systems had results greater than the MCL. A total of 9 (0.571% of)

surface water systems had at least one analytical result greater than 0.0025 mg/L. Thirty (1.91% of)

surface water systems had results exceeding 0.0005 mg/L.
Occurrence Summary and Use Support Document March 2002 349

Table 4.4-4: Stage 1 1,2-Dichloroethane Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.112% 24

0.0025 0.214% 46

0.0005 0.909% 195

Surface Water

0.005 0.317% 5

0.0025 0.571% 9

0.0005 1.91% 30

Combined Ground &

Surface Water

0.005 0.126% 29

0.0025 0.239% 55

0.0005 0.977% 225

Reviewing 1,2-dichloroethane occurrence in the 16 cross-section States by PWS population served

(Table 4.4-5) shows that approximately 8.40% of the population (over 9 million people) was served by

PWSs (ground and surface water systems) with at least one analytical result of 1,2-dichloroethane greater

than the MCL. Approximately 8.98% of the population (almost 10 million people) was exposed to 1,2-

dichloroethane concentrations greater than 0.0025 mg/L. The percentage of population served by all

PWSs with at least one analytical result of 1,2-dichloroethane greater than 0.0005 mg/L was equal to

11.2% (over 12 million people).

The percentage of population served by surface water systems with threshold exceedances was

considerably greater than the percentage of population served by ground water systems with threshold

exceedances. Approximately 0.789% of the population served by ground water systems (391,200

people) had at least one analytical result of 1,2-dichloroethane greater than 0.005 mg/L, compared to

14.6% of the population served by surface water systems (over 8.9 million people) with results greater

than 0.005 mg/L. When evaluated relative to 0.0025 mg/L, the percent of population exposed by ground

water systems was 1.30% (641,600 people) and the percent of population exposed by surface water

systems was 15.2% (over 9.3 million people). Approximately 4.64% of the population was served by

ground water systems (over 2.3 million people) with analytical detections greater than 0.0005 mg/L, as

compared to 16.5% of the population served by surface water systems (about 10.1 million people) with

analytical detections greater than 0.0005 mg/L.

Table 4.4-5: Stage 1 1,2-Dichloroethane Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold

Total Population Served

by Systems Exceeding

Threshold

Ground Water 0.005 0.789% 391,200
Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold

Total Population Served

by Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 350

0.0025 1.30% 641,600

0.0005 4.64% 2,300,500

Surface Water

0.005 14.6% 8,916,000

0.0025 15.2% 9,311,400

0.0005 16.5% 10,113,500

Combined Ground &

Surface Water

0.005 8.40% 9,307,200

0.0025 8.98% 9,953,000

0.0005 11.2% 12,414,000

4.4.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.4-6 and 4.4-7. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

Only 1 PWS in the 16 States (approximately 0.00479% of all systems in the 16 States) had an estimated

mean concentration of 1,2-dichloroethane exceeding 0.005 mg/L. Four (about 0.0175% of) PWSs were

estimated to have mean concentrations greater than 0.0025 mg/L. Approximately 30 (0.132% of) PWSs

had estimated mean concentrations of 1,2-dichloroethane greater than 0.0005 mg/L. 

The estimated number of ground water PWSs in the 16 States with mean concentrations exceeding the

thresholds of 0.005 mg/L, 0.0025 mg/L, and 0.0005 mg/L was 1 (about 0.00514%), 4 (about 0.0187%),

and 29 (about 0.135%), respectively. No surface water PWSs had estimated mean concentration

exceeding 0.005 mg/L. One (approximately 0.000762% of) surface water PWSs in the 16 States was

estimated to have a mean concentration greater than 0.0025 mg/L. The percentage of surface water

PWSs in the 16 States with estimated mean concentration exceeding 0.0005 mg/L was equal to 0.0974%

(approximately 2 systems).
Occurrence Summary and Use Support Document March 2002 351

Table 4.4-6: Stage 2 Estimated 1,2-Dichloroethane Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.00514% 0.000% - 0.0140% 1 0 - 3

0.0025 0.0187% 0.00932% - 0.0326% 4 2 - 7

0.0005 0.135% 0.0932% - 0.177% 29 20 - 38

Surface Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.0025 0.000762% 0.000% - 0.000% 1 0 - 0

0.0005 0.0974% 0.0635% - 0.191% 2 1 - 3

Combined Ground

& Surface Water

0.005 0.00479% 0.000% - 0.0130% 1 0 - 3

0.0025 0.0175% 0.00868% - 0.0304% 4 2 - 7

0.0005 0.132% 0.0955% - 0.174% 30 22 - 40

Reviewing 1,2-dichloroethane occurrence by PWS population served (Table 4.4-7) shows that

approximately 0.0003341% of population served by all PWSs in the 16 States (an estimate of

approximately 400 people) were potentially exposed to 1,2-dichloroethane levels above 0.005 mg/L. 

About 39,400 (approximately 0.0357% of) people and about 370,300 (0.334% of) people served by the

combined total of surface and ground water systems were potentially exposed to levels above 0.0025

mg/L and 0.0005 mg/L, respectively. 

The percentage of population served by ground water systems in the 16 States with levels greater than

0.005 mg/L was approximately 0.000740% (over 400 people). When evaluated relative to thresholds of

0.0025 mg/L and 0.0005 mg/L, the population exposed was about 37,700 (0.0760%) and 189,200

(0.382%), respectively. 

No surface water systems had estimated mean concentrations of 1,2-dichloroethane greater than 0.005

mg/L. About 0.00297% (approximately 1,800 people) of the population served by surface water in the

16 States were potentially exposed to levels above 0.0025 mg/L. When evaluated relative to thresholds

of 0.0005 mg/L, the population exposed was equal to 0.296% (about 181,000 people).
Occurrence Summary and Use Support Document March 2002 352

Table 4.4-7: Stage 2 Estimated 1,2-Dichloroethane Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.000740% 0.000% - 0.00155% 400 0 - 800

0.0025 0.0760% 0.00107% - 0.118% 37,700 500 - 58,400

0.0005 0.382% 0.212% - 0.616% 189,200 105,100 - 305,000

Surface Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.0025 0.00297% 0.000% - 0.000% 1,800 0 - 0

0.0005 0.296% 0.246% - 0.548% 181,000 150,800 - 335,500

Combined Ground

& Surface Water

0.005 0.000331% 0.000% - 0.000692% 400 0 - 800

0.0025 0.0357% 0.000478% - 0.0542% 39,400 500 - 60,000

0.0005 0.334% 0.231% - 0.518% 370,300 255,900 - 573,600

4.4.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 3 PWSs nationally serving approximately 700 people could be exposed to 1,2-

dichloroethane concentrations above 0.005 mg/L. About 11 systems serving almost 76,000 people had

estimated mean concentrations greater than 0.0025 mg/L. Approximately 86 systems serving about

711,900 people nationally were estimated to have mean 1,2-dichloroethane concentrations greater than

0.0005 mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to

national values.)

For ground water systems, an estimated 3 PWSs serving about 600 people nationally had mean

concentrations greater than 0.005 mg/L. Approximately 11 systems serving about 65,200 people

nationally had estimated mean concentration values that exceeded 0.0025 mg/L. About 80 ground water

systems serving almost 327,200 people had estimated mean concentrations greater than 0.0005 mg/L. 

Zero surface water systems had estimated mean concentrations of 1,2-dichloroethane above 0.005 mg/L. 

About 1 surface water systems serving 3,800 people had estimated mean concentrations greater than

0.0025 mg/L. An estimated 5 surface water systems serving approximately 376,300 people had mean

concentrations greater than 0.0005 mg/L.
Occurrence Summary and Use Support Document March 2002 353

Table 4.4-8: Estimated National 1,2-Dichloroethane Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 3 0 - 8 600 0 - 1,300

0.0025 11 6 - 19 65,200 900 - 101,000

0.0005 80 55 - 105 327,200 181,700 - 527,400

Surface Water

0.005 0 0 - 0 0 0 - 0

0.0025 1 0 - 0 3,800 0 - 0

0.0005 5 4 - 11 376,300 313,600 - 697,500

Combined Ground

& Surface Water

0.005 3 0 - 8 700 0 - 1,500

0.0025 11 6 - 20 75,900 1,000 - 115,400

0.0005 86 62 - 113 711,900 492,000 - 1,102,700

4.4.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of 1,2-dichloroethane in drinking water are also

reviewed. Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence of 1,2-Dichloroethane in Drinking Water, Food, and Air” (JRB Associates, 1983), is

presented in the following section. This variety of studies and information are presented regarding levels

of 1,2-dichloroethane in drinking water, with the scope of the reviewed studies ranging from national to

regional. Note that none of the studies presented in the following section provide the quantitative

analytical results or comprehensive coverage that would enable direct comparison to the occurrence

findings estimated with the cross-section occurrence data presented in Section 4.4.4. These additional

studies, however, do enable a broader assessment of the Stage 2 occurrence estimates presented for this

Six-Year Review. All the following information in Section 4.4.5 is taken directly from “Occurrence of

1,2-Dichloroethane in Drinking Water, Food, and Air” (JRB Associates, 1983).

JRB Associates (1983) found two major types of data available that were potentially useful for

describing the occurrence of 1,2-dichloroethane in the nation’s public drinking water supplies. First,

there are several Federal surveys in which a number of public water supplies from throughout the U.S.

were selected for analysis of chemical contamination, including 1,2-dichloroethane. Second, data are

available from State surveys and from State investigations of specific incidents of known or suspected

contamination of a supply. For accomplishing the basic objectives of this study, namely to estimate the

number of public water supplies nationally within the various source and size categories contaminated

with 1,2-dichloroethane, the distribution of 1,2-dichloroethane concentrations in those supplies, and the

number of individuals, exposed to those concentrations, it was determined that the Federal survey data

provides the most suitable data base. The State data tend to be poorly described with respect to the

source and size categories of the supplies examined and the sampling and analysis methods used for

determining contaminant levels. The lack of source and system size information precludes using the data

for estimating levels in public water supplies of similar characteristics. The absence of details on

sampling and analysis methods precludes evaluating those data for their qualitative and quantitative
Occurrence Summary and Use Support Document March 2002 354

reliability. Although they are not used with the Federal data for the purpose of estimating contamination

levels nationally, the available State data are presented here to provide some additional perspective on

1,2-dichloroethane occurrence in drinking water.

Data are presented only on drinking water samples taken from a consumer's tap (i.e., distribution water

samples) or on treated water samples taken at the water supply (i.e., finished water samples) because

these are considered to be most representative of the water consumed by the public. No data on raw (i.e.,

untreated) water are presented. It is recognized that for some groundwater supplies where no treatment

of the water occurs, samples identified as raw may be representative of water consumed by the users of

the supply. However, it was generally not possible to differentiate between those groundwater supplies

that do and those that do not treat raw water from the available survey data.

4.4.5.1 Overview and Quality Assurance Assessment of Federal Drinking Water Surveys

Six Federal drinking water surveys provide data on 1,2-dichloroethane: the National Organics

Reconnaissance Survey (NORS), the National Organic Monitoring Survey (NOMS), the National

Screening Program for Organics in Drinking Water (NSP), the 1978 Community Water Supply Survey

(CWSS), the Rural Water Survey (RWS), and the Groundwater Supply Survey (GWSS). The terms used

in this report are those used in the individual surveys, recognizing that they may not always correspond to

strict technical definitions.

The National Organics Reconnaissance Survey (NORS) was conducted in 1975 to determine the extent

of the presence of 1,2-dichloroethane, carbon tetrachloride, and four trihalomethanes in drinking water

supplies from 80 cities across the country (Symons et al., 1975, as cited in JRB Associates, 1983). The

effect of the water source and treatment practices on the formation of these compounds were also

examined in the NORS. Of the 80 supplies studied, 16 were indicated as having a groundwater source

and 64 as having a surface water source. Symons et al. (1975, as cited in JRB Associates, 1983) did not

provide data on the population served by the supplies studied in NORS; the populations served were

estimated by JRB based on information available from other sources for the supplies studied and from

census data for the locations of the supplies.

The National Organic Monitoring Survey (NOMS) was conducted to identify contaminant sources, to

determine the frequency of occurrence of specific drinking water contaminants, and to provide data for

the establishment of maximum contaminant levels (MCL’s) for various organic compounds in drinking

water (Brass et al., 1977, as cited in JRB Associates, 1983). The NOMS was conducted in three phases:

March-April 1976, May-July 1976, and November 1976-January 1977. Finished drinking water samples

from 113 communities were analyzed for 21 different compounds. Of the 113 community supplies

sampled, 18 had groundwater sources, 91 had surface water sources, and 4 had a mixed

groundwater/surface water source. For 1,2-dichloroethane, 18 groundwater supplies were examined in

Phases I and II, and 14 groundwater supplies in Phase III; for surface water, 88, 91, and 87 supplies were

analyzed for 1,2-dichloroethane in Phases I, II, and III, respectively.

The analytical results of the NOMS were made available in printed form by EPA's Technical Support

Division, Office of Drinking Water. Additional information on the locations and source of the supplies,

and on the populations served by the supplies in the NOMS were provided by Wayne Mello (1983, as

cited in JRB Associates, 1983) at EPA's Technical Support Division, Office of Drinking Water. A single

value for 1,2-dichloroethane was reported for each supply studied in the NOMS. 

The National Screening Program for Organics in Drinking Water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water
Occurrence Summary and Use Support Document March 2002 355

systems in 33 States for 51 organic chemical contaminants. Data are available for 1,2-dichloroethane on

finished water samples from 12 groundwater and 103 surface water supplies.

In the Community Water Supply Survey (CWSS), carried out in 1978, 106 surface water supplies, 330

groundwater supplies, and 16 supplies with mixed sources were examined for volatile organic chemical

contamination. Samples were taken of raw, finished, and distribution water. Only the latter two types of

water are considered here. Data for 1,2-dichloroethane in finished and/or distribution samples were

obtained from a total of 315 groundwater and 104 surface water supplies.

The Rural Water Survey (RWS), conducted in 1978, was carried out in response to Section 3 of the Safe

Drinking Water Act, which mandated that EPA “conduct a survey of the quantity, quality, and

availability of rural drinking water supplies.” Drinking water samples were collected for analysis of

inorganic chemicals, pesticides, and VOCs from 2,655 households throughout the United States located

in areas defined in the survey as rural. Of these, a total of 855 household samples were examined for

VOCs. The majority of these samples were obtained from households receiving water from private wells

or small supplies serving fewer than 25 people. For 1,2-dichloroethane, data are available in the RWS

for 206 groundwater and 35 surface water supplies serving 25 or more people.

The RWS did not obtain data on the number of persons in each household served by the supplies. 

However, data were obtained on the number of service connections at each supply. With the input of Dr.

Bruce Brower at Cornell University, who participated in the statistical analysis of the RWS for

parameters other than VOCs, the population served by each supply was estimated from the average

number of persons per household (3.034) observed in the survey. A single value was reported for each

household; in some cases it was necessary to average two or three households obtaining water from the

same supply. Brass (1981, as cited in JRB Associates, 1983) cautions that the RWS water samples were

analyzed 6 to 27 months after collection and that degradation of some VOCs may have occurred during

this holding period.

The Groundwater Supply Survey (GWSS) was conducted from December 1980 to December 1981 to

develop additional data on the occurrence of volatile organic chemicals in the nation’s groundwater

supplies (Westrick et al., 1983, as cited in JRB Associates, 1983). It was hoped that this study would

stimulate State efforts toward the detection and control of groundwater contamination and the

identification of potential chemical “hot spots.” A total of 944 systems were sampled for 1,2-

dichloroethane, of which 466 were chosen at random. The remaining 478 systems were chosen non

randomly based on information from States encouraged to identify locations believed to have a higher

than normal probability of VOC contamination (e.g., locations near landfills or industrial activity). The

file provided a single analytical result for each supply sampled. One sample of finished water was

collected from each supply at a point near the entrance to the distribution system. 

Each of the drinking water surveys was evaluated with respect to the validity of the reported occurrence

data for a number of organic chemicals, including 1,2-dichloroethane. The evaluations were carried out

by analyzing information about the procedures used for collection and analysis of samples as well as the

quality control protocols used. The analyzed compounds dealt with in each study were assigned one of

three possible ratings: quantitatively acceptable, qualitatively acceptable (i.e., the substance measured

was 1,2-dichloroethane), and totally unacceptable. In the case of 1,2-dichloroethane, a qualitatively

acceptable rating was given for data from the CWSS and RWS because of suspected biodegradation of

the samples, which were held unrefrigerated for prolonged periods before analysis. 1,2-Dichloroethane

values in excess of the quantitation limit reported for some samples in these studies are qualitatively

valid and can be taken as minimum values, representative of samples which probably originally
Occurrence Summary and Use Support Document March 2002 356

contained 1,2-dichloroethane at higher concentrations. In the case of the NORS, NOMS, NSP, and

GWSS, all data were rated both quantitatively and qualitatively acceptable.

4.4.5.2 Groundwater – Federal Surveys

The National Organics Reconnaissance Survey (NORS), the National Organic Monitoring Survey

(NOMS), the National Screening Program for Organics in Drinking Water (NSP), the Community Water

Supply Survey (CWSS), the Rural Water Survey (RWS), and the Groundwater Supply Survey (GWSS)

all contain data concerning the levels of 1,2-dichloroethane in groundwater supplies from across the

country.

In the NORS, finished water samples were taken from 16 groundwater systems from across the country. 

Of these, 4 supplies were reported to have 1,2-dichloroethane present, although the level of

contamination in these 4 supplies was below the minimum quantifiable concentration of 0.2 :g/L for

those analyses. All other groundwater supplies were indicated as having “none found,” with the

minimum quantifiable concentration ranging from 0.2 to 0.4 :g/L.

Eighteen groundwater systems were analyzed for 1,2-dichloroethane during Phase I of NOMS (March to

April 1976), with none of the systems containing quantifiable levels. These 18 systems were sampled

again during Phase II of the study (May to July 1976) with one containing 1,2-dichloroethane at 0.2 :g/L. 

Samples analyzed during Phase III of the study (November 1976 to January 1977) proved negative for all

of the 14 systems examined. The minimum quantifiable limits for 1,2-dichloroethane ranged from 1-2

:g/L in Phase I, 0.05-1 :g/L in Phase II, and 0.05-1 :g/L in Phase III.

Twelve groundwater supplies were tested for 1,2-dichloroethane contamination in the NSP. Of these 12

systems, one was found to be contaminated with 1,2-dichloroethane at 0.2 :g/L. The quantification limit

for 1,2-dichloroethane was 0.1 :g/L.

The 1978 CWSS provided information on 1,2-dichloroethane levels in 315 groundwater systems. Of

these systems, 4 contained detectable levels of 1,2-dichloroethane, with values ranging from 0.56-1.1

:g/L. The mean value was 0.9 :g/L with a standard deviation of 0.3 :g/L; the median value was 0.9

:g/L. The minimum quantitation limit for 1,2-dichloroethane in the CWSS was 0.5 :g/L.

The RWS examined 206 groundwater supplies for 1,2-dichloroethane and found none to have levels

above the minimum quantification limit of 0.5 :g/L.

In the GWSS, 3 of the 456 randomly chosen water systems serving 25 or more individuals were

contaminated with 1,2-dichloroethane, at concentrations of 0.53, 0.57, and 0.95 :g/L. Of the 472

nonrandom locations sampled serving 25 or more individuals, 7 were contaminated with 1,2-

dichloroethane, at concentrations between 1.1-9.8 :g/L, the highest values being 2.9, 3.4, and 9.8 :g/L. 

Of the 7 positive samples, 4 were from systems serving populations in excess of 10,000 people. The

average 1,2-dichloroethane level for the nonrandom systems was 3.4 :g/L with a standard deviation of

2.9 :g/L; the median value was 2.5 :g/L. The minimum quantitation limit for 1,2-dichloroethane was

0.2 :g/L.

4.4.5.3 Groundwater – State Data

Six States (California, Connecticut, Delaware, Indiana, Massachusetts, and New Jersey) provided EPA

with information concerning 1,2-dichloroethane contamination in groundwater supplies. Analytical

results for samples from four locations in California ranged from undetectable to 21 :g/L. Samples from
Occurrence Summary and Use Support Document March 2002 357

two locations in Connecticut gave 1,2-dichloroethane readings of not detectable and 7.8 :g/L. Delaware

reported data from three locations, with four samples having no detectable 1,2-dichloroethane. Data on

26 samples from two cities in Indiana showed 17 samples with undetectable 1,2-dichloroethane and nine

samples with concentrations ranging from 19-2,100 :g/L (averaging 624 :g/L). In data from

Massachusetts, there was no detectable 1,2-dichloroethane in five groundwater samples from two cities,

while levels ranging from 10.1-19.1 :g/L (averaging 14.7 :g/L) were reported in samples taken from two

other cities. In New Jersey data, 405 samples showed no detectable 1,2-dichloroethane and 26 additional

samples were contaminated at 0.1-100 :g/L (ranges were the only data reported for groups of samples, so

no averages can be taken).

4.4.5.4 Surface Water – Federal Surveys

The National Organics Reconnaissance Survey (NORS), the National Organic Monitoring Survey

(NOMS), the National Screening Program for Organics in Drinking Water (NSP), the Community Water

Supply Survey (CWSS), and the Rural Water Survey (RWS) all contain data concerning the levels of 1,2-

dichloroethane in surface water supplies from across the country.

In the NORS, finished water from 64 surface water systems were studied, 22 of which were found to

have 1,2-dichloroethane present. Sixteen of the 22 positive systems reported 1,2-dichloroethane to be

present, but below the minimum quantifiable concentration range of 0.2 to 0.4 :g/L. Of six systems with

quantifiable levels, the concentrations ranged from 0.2-6 :g/L. The 42 negative surface water systems

were indicated as having “none found,” with the minimum quantifiable concentration ranging from 0.2 to

0.4 :g/L. It should be noted that confirmatory quantitative analyses were performed for 8 surface water

supplies in NORS, using a method able to quantify 1,2-dichloroethane at 0.1 :g/L. Three of these 8

supplies were originally reported as having 1,2-dichloroethane present, but below the minimum

quantifiable concentration of 0.2 :g/L in 2 cases and 0.4 :g/L in the third case; 1,2-dichloroethane was

not observed in any of these 3 systems in the confirmatory analysis. Of the 5 supplies originally reported

as having “none found,” one was observed in the confirmatory analysis to have 1,2-dichloroethane

present at 0.2 :g/L.

In Phase I of the National Organic Monitoring Survey (March to April 1976), water samples from 88

surface water systems were analyzed for 1,2-dichloroethane. Of these 88 systems, only one was found to

contain 1,2-dichloroethane, at 2 :g/L. Ninety-one systems were sampled during the second phase of the

survey (May to July 1979) and one was found to be contaminated at 1.8 :g/L. During the third phase of

the NOMS (November 1976 to January 1977), analyses revealed 1,2-dichloroethane contamination in

one out of a total of 87 systems, at 1.2 :g/L. The minimum quantifiable limits for 1,2-dichloroethane

ranged from 1-3 :g/L in Phase I, 0.05-1 :g/L in Phase II, and 0.05-2 :g/L in Phase III.

Surface water samples from 106 drinking water systems were analyzed for 1,2-dichloroethane during the

National Screening Program (NSP) between June 1977 and March 1981. Of these, only one system

contained a detectable level of 1,2-dichloroethane, at 4.8 :g/L. The quantification limit for the NSP was

0.1 :g/L.

None of the 104 surface water systems sampled during the Community Water Supply Survey (CWSS)

contained quantifiable levels of 1,2-dichloroethane. The minimum quantitation limit for 1,2-

dichloroethane in the CWSS was 0.5 :g/L.

The RWS examined drinking water from 35 surface water supplies; only one supply was found to have

1,2-dichloroethane present above the minimum quantification limit range of 0.5-2.0 :g/L. The

concentration of 1,2-dichloroethane observed in that supply was 19 :g/L.
Occurrence Summary and Use Support Document March 2002 358

4.4.5.5 Surface Water – State Data

The only State supplied surface water information on 1,2-dichloroethane was from New York. One

sample from Poughkeepsie assayed for 1,2-dichloroethane was positive at 5.9 :g/L.

4.4.5.6 Projected National Occurrence of 1,2-Dichloroethane in Public Water Supplies

As reported in the JRB Associates (1983) report, public water systems fall into two major categories with

respect to water source (surface water and groundwater) and into five size categories and twelve

subcategories according to the number of individuals served. The JRB Associates (1983) report

presented estimates of both the number of drinking water supplies nationally within each of the

source/size categories expected to have 1,2-dichloroethane present, and of the concentration of 1,2-

dichloroethane expected to be present in those supplies.

The key features of the methodology used and assumptions made to develop the national estimates are

summarized here. The estimates are based on the data from the Federal surveys only. The State data

were not included for several reasons. These data are from a few States and were not considered to be

geographically representative. There was also a general lack of data on the population served by systems

measured, the type of water sampled, and the methodologies used to sample, identify, and measure 1,2-

dichloroethane.

The Federal survey data from the NORS, NOMS, NSP, CWSS, RWS, and GWSS (random only) were

pooled together for developing the national projections. It was assumed in combining these surveys that

the resulting data base would be representative of the nation’s water supplies. In the case of the GWSS

data, only the randomly selected samples were included in the projections because a statistical test of the

GWSS data showed that the mean of the positive values for 1,2-dichloroethane was significantly higher

in the nonrandom portion. Therefore, these data were not included in the national projections to avoid

biasing the results. Ideally, adequate data would be available to develop the national projections

separately for each of the twelve system size categories within the groundwater and surface water groups;

however, the available data were too limited for this. It was, therefore, necessary to consolidate some of

the size categories to have sufficient data for developing the projections. In consolidating data from

various size categories, consideration was given to the potential for there being statistically significant

differences in the frequency of occurrence of 1,2-dichloroethane as a function of system size. The

consolidation of size categories therefore involved a balancing of the need to group size categories

together to have an adequate data base for developing the national projections against the need to treat

size categories separately in order to preserve the influence of system size as a determinant of

contamination potential. The consolidation of size categories also took into account EPA’s classification

of systems into the five major groups as very small (25-500), small (501-3,300), medium (3,301-10,000),

large (10,001-100,000), and very large (> 100,000) (Kuzmack, 1983, as cited in JRB Associates, 1983).

Once the data were consolidated, statistical models for extrapolating to the national level were tested and

an appropriate model selected. In the case of 1,2-dichloroethane, the multinominal method was used. 

The frequency of contamination of groundwater and surface water systems at various concentrations was

determined for each consolidated size category. For completing the national estimates, it was assumed

that the frequency of contamination observed for each consolidated category was directly applicable to

each of the system sizes comprising it.

In the JRB Associates (1983) report, it is noted that some of the data used in computing the national

estimates are from samples held for a prolonged period of time prior to analysis, with possible
Occurrence Summary and Use Support Document March 2002 359

biodegradation of 1,2-dichloroethane. Therefore, these projections of national occurrence may

underestimate actual contaminant levels.

4.4.5.6.1 Groundwater Supplies

JRB Associates (1983) reported that data were available for a total of 1,001 supplies from the combined

surveys (NORS, NOMS, NSP, CWSS, RWS, and GWSS (random)). Of these, 12 supplies were reported

to have 1,2-dichloroethane present, at concentrations ranging from 0.2 :g/L to 1.1 :g/L.

Based on the overall distribution of positive values and maximum possible values for those supplies in

which 1,2-dichloroethane was not found, 0.5 :g/L was selected as the common minimum quantifiable

concentration for the combined survey data. An estimate is made of supplies having concentrations > 0.5

:g/L, while only a total number for supplies expected to have either no 1,2-dichloroethane or levels

below 0.5 :g/L can be determined. Although some data indicate the presence of 1,2-dichloroethane in

groundwater supplies at levels < 0.5 :g/L, it is not possible to determine the proportion of supplies that

have 1,2-dichloroethane present and the proportion that are actually free of 1,2-dichloroethane

contamination.

Of the 989 supplies reporting no 1,2-dichloroethane to be present, 968 were assumed to have maximum

possible levels of < 0.5 :g/L based on the minimum quantifiable concentrations reported for the various

surveys. The other 21 supplies reporting no 1,2-dichloroethane to be present had maximum possible

levels ranging from approximately 0.53 :g/L to 1.5 :g/L. It is assumed, based on the overall distribution

of values, that 1,2-dichloroethane if present in these 21 supplies is so at a concentration of < 0.5 :g/L,

although a rigorous, conservative argument could be made for assuming a level equal to the maximum

possible value. The impact of this assumption is considerable both in terms of the national projection of

groundwater systems above 0.5 :g/L, and in terms of the population exposed.

Nine of the 1,001 supplies examined had measured values of 1,2-dichloroethane > 0.5 :g/L. When the

twelve size categories were consolidated into the five major EPA groupings, there was an apparent relationship between the frequency of values > 0.5 :g/L and system size:

Very small 0% (0/352)

Small 0.7% (2/290)

Medium 0% (0/100)

Large 2.7% (6/225)

Very large 3.0% (1/34)

Overall 0.9% (9/1,001)

A test for statistical significance revealed that at the " = 0.05 level, the difference among the very small,

small, and medium categories was not significant; nor was the difference between the large and very

large categories. However, the combined very small, small, and medium categories were different from

the combined large and very large categories. Two consolidated categories were, therefore, selected for

developing the national estimates:

Very small/small/medium (< 10,000)

Large/Very large (> 10,000)

As noted previously, the frequency of occurrence of 1,2-dichloroethane at various concentrations was

determined for the consolidated groups and then applied to the number of supplies nationally within each

of the size categories comprising each group.
Occurrence Summary and Use Support Document March 2002 360

About 161 groundwater supplies (range of 0-337), approximately 0.3% of the total groundwater supplies

in the United States, are expected to have 1,2-dichloroethane at levels of > 0.5 :g/L; the remaining

48,297 supplies have either no 1,2-dichloroethane or levels < 0.5 :g/L. It is estimated that no

groundwater supplies will have levels exceeding 5 :g/L.

It is interesting to note the impact on the national projections of the assumption made that the 21 supplies

with undetected but maximum potential values of 0.53-1.5 :g/L had < 0.5 :g/L. Had it been assumed

that 1,2-dichloroethane was present in those supplies at their maximum possible values, the national

projection of supplies with 1,2-dichloroethane levels of 0.5-5 :g/L would have increased to 791 (381-

1,200) with no differences in levels > 5 :g/L. These differences would be found primarily in systems

serving < 2,500 people.

It is also interesting to compare these national estimates to estimates that include the nonrandom portion

of the GWSS. Inclusion of the nonrandom data results in an estimated 258 supplies exceeding 0.5 :g/L. 

Of these, 3 supplies are estimated to exceed 5 :g/L, based on one observation in the 25,001-50,000

category. None, however, are expected to have levels > 10 :g/L. These data indicate that, while the

projections for levels > 5 :g/L based on the random data only may underestimate actual conditions, the

error is very small.

4.4.5.6.2 Surface Water

Data are available for a total of 301 surface water supplies. Of these, 25 supplies were reported by JRB

Associates (1983) to have 1,2-dichloroethane present at concentrations ranging from 0.2 :g/L to 19 :g/L,

although this high value is the only one reported above 4.8 :g/L.

Based on the overall distribution of positive values and maximum possible values for those supplies in

which 1,2-dichloroethane was not found, 0.5 :g/L was selected as the common minimum quantifiable

concentration for the combined survey data. That is, quantitative projections are made of supplies at

several concentration ranges $ 0.5 :g/L, while only a total number for supplies expected to have either

no 1,2-dichloroethane or levels below 0.5 :g/L can be determined. Although some data indicate the

presence of 1,2-dichloroethane in surface water supplies at levels < 0.5 :g/L, it is not possible to

determine the proportion that have 1,2-dichloroethane present and the proportion that are free of 1,2-

dichloroethane contamination.

Of the 276 supplies reporting no 1,2-dichloroethane to be present, 129 had maximum possible levels of <

0.5 :g/L based on the minimum quantifiable concentrations reported for the various surveys. The other

147 supplies reporting no 1,2-dichloroethane to be present had maximum possible levels ranging from

approximately 0.52 :g/L to 2 :g/L. It is assumed, based on the overall distribution of values, that 1,2-

dichloroethane if present in these 147 supplies is so at a concentration of < 0.5 :g/L, although a rigorous

conservative argument could be made for assuming a level equal to the maximum possible value. As will

be noted further below, the difference between these alternatives is very large for both the estimate of the

number of surface water supplies with 1,2-dichloroethane $ 0.5 :g/L and for the estimated population

exposed to 1,2-dichloroethane at levels > 0.5 :g/L in surface water supplies.

Eighteen of the 301 supplies examined had measured values of 1,2,-dichloroethane $ 0.5 :g/L. When the

twelve size categories were consolidated into the five major EPA groupings, there was an apparent

relationship between the frequency of values > 0.5 :g/L and system size:

Very smal l0% (0/20)

Small 0% (0/55)
Occurrence Summary and Use Support Document March 2002 361

Medium 5.0% (2/40)

Large 5.6% (4/71)

Very large 10.4% (12/115)

Overall 6.0% (18/301)

A test for statistical significance revealed that at the " = 0.05 level, the very small, small, and medium

groups were not different from one another and that the large and very large groups are not different;

however, the combined very small, small, and medium groups and the combined large and very large

groups are different. These two consolidated categories were selected for developing the national

estimates:

Very small/small/medium (< 10,000)

Large/very large (> 10,000)

As noted previously, the frequency of occurrence of 1,2-dichloroethane at various concentrations was

determined for the consolidated groups and then applied to the number of supplies nationally within each

of the size categories comprising each group.

About 317 surface water supplies (range of 82-551), approximately 2.8% of the total surface water

systems in the United States, are expected to have 1,2-dichloroethane at levels > 0.5 :g/L; the remaining

10,885 supplies have either no 1,2-dichloroethane or levels < 0.5 :g/L. It is estimated that 82 surface

water supplies (range of 0-241) will have levels > 10 :g/L and none are projected to have levels above 20

:g/L.

There was a notable impact on the national projections by the assumption made that the 147 supplies

with undetected but maximum potential values of 0.52-2 :g/L had < 0.5 :g/L. Had it been assumed that

1,2-dichloroethane was present in these supplies at their maximum possible values, the national

projections of supplies with 1,2-dichloroethane levels $0.5 :g/L would be 5,993 (range of 5,125-6,860)

supplies. However, there would be no difference in the projected number of surface water supplies with

levels > 5 :g/L. 

4.4.5.7 Drinking Water Intake - Estimated Population Exposed

The values given here were obtained using Federal Reporting Data Systems data on populations served

by primary water supply systems and the estimated number of these water systems that contain a given

level of 1,2-dichloroethane. An estimated 12,232,000 individuals (5.7% of the population of

214,419,000 using public water supplies) are exposed to levels of 1,2-dichloroethane in drinking water at

or above 0.5 :g/L, while 143,000 individuals (0.1%) are exposed to levels above 5 :g/L. It is estimated

that no individuals are exposed to levels greater than 20 :g/L. Of the approximately 12 million people

exposed to levels ranging from 0.5 to 5 :g/L, 11 million (90%) obtain water from surface water supplies. 

All exposure to 1,2-dichloroethane in drinking water at levels above 5 :g/L is expected to be from

surface water sources.

The previous section also presented estimates of the number of public water supplies exceeding various

concentrations when the GWSS nonrandom data was included in the analysis. Had the GWSS

nonrandom data been included, an increased estimate in the population exposed to 1,2-dichloroethane at

levels below 10 :g/L would be seen, notably an increase of 104,000 individuals at levels between 5 and

10 :g/L.
Occurrence Summary and Use Support Document March 2002 362

Also presented in the previous section were estimates of the number of public water supplies exceeding

various concentrations using an alternative assumption for 168 supplies in which no 1,2-dichloroethane

was observed, but which may have contained concentrations exceeding 0.5 :g/L owing to relatively high

minimum quantifiable levels in the analysis of those supplies. Had it been assumed that the 168 supplies

sampled had been contaminated at the maximum quantifiable level, the national projections would have

indicated that 82 million individuals were exposed to levels at or above 0.5 :g/L. This population

represents an increase of about 70 million individuals over the estimate used here that assumes the

supplies do not have contamination at the maximum quantifiable level but rather at a level less than 0.5

:g/L. Note, however, that no change occurs in the estimated population exposed to levels exceeding 5

:g/L.

4.4.6 Conclusion

1,2-Dichloroethane is used primarily to manufacture other organic compounds. Ninety-eight percent of

the 1,2-dichloroethane produced in the U.S. is used to make vinyl chloride. Most 1,2-dichloroethane

produced in the United States is used captively by the manufacturers. Data from the 1990s indicates that

production is increasing, with almost 17 billion pounds of 1,2-dichloroethane being produced in 1994. 

1,2-Dichloroethane is also a TRI chemical. Industrial releases of 1,2-dichloroethane have been reported

from 1988-1999 in 37 States and Puerto Rico. 1,2-Dichloroethane was an analyte for the NAWQA and

NURP ambient occurrence studies. In the NAWQA study, 1,2-dichloroethane was detected in 2.0% of

urban wells and 0.71% of rural wells, with median detection values of 0.5 :g/L and 0.55 :g/L,

respectively. In the Stage 2 analysis of 16-State occurrence of 1,2-dichloroethane, 0.00479% of

combined ground water and surface water systems serving 0.000331% of the population exceeded the

MCL of 0.005 mg/L. Nationally, 3 ground water and/or surface water systems (serving approximately

700 people) are estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, 1,2-dichloroethane is manufactured and/or produced in 21 States and has

TRI releases in 37 States. 1,2-dichloroethane is manufactured and/or processed in 10 out of the 16 crosssection States and has TRI releases in 11 of the 16 cross-section States. The cross-section should

adequately represent occurrence of 1,2-dichloroethane on a national scale based upon the use,

production, and release patterns in the 16-State cross-section in relation to the patterns observed for all

50 States. 

4.4.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1999. Toxicological Profile for 1,2-

Dichloroethane. U.S. Department of Health and Human Services, Public Health Service. 239

pp. + Appendices. Available on the Internet at http://www.atsdr.cdc.gov/toxprofiles/tp38.pdf

Anonymous. 1998. Chemical profile: Ethylene dichloride. Chem Mark Rep. February 16, 1998.

Brass, H.J., M.A. Feige, T. Halloran, J.W. Mello, D. Munch, and R.F. Thomas. 1977. The National

Organic Monitoring Survey: A sampling and analysis for purgeable organic compounds. 

Drinking water quality enhancement through source protection. R.B. Pojasek (ed.). Ann Arbor,

MI: Ann Arbor Science, pp. 393-416.
Occurrence Summary and Use Support Document March 2002 363

Brass, H.J. 1981. Rural Water Survey organics data. Memorandum of March 17, 1981 to Hugh Hanson,

Chief, Science and Technology Branch, Office of Drinking Water, and David Schnare, Office of

Drinking Water, USEPA, Washington, DC.

JRB Associates. 1983. Occurrence of 1,2-Dichloroethane in Drinking Water Food and Air. Draft

report submitted to EPA for review November 18, 1983.

Kuzmack, A.M. 1983. Memorandum: Characterization of the water supply industry (FY82). 

Washington, D.C.: Office of Water, USEPA. May 16, 1983. 

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 

67 pp.

Mello, Wayne. 1983. Personal communication between Wayne Mello, Technical Support Division,

Office of Drinking Water, USEPA, and author of JRB Associates, 1983, March 10, 1983.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

Symons, J.M., T.A. Bellar, J.K. Carswell, et al. 1975. National Organics Reconnaissance Survey for

Halogrenated Organics. Journal of the American Water Works Association. 667(11): 634-647. 

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Westrick, J.J., J.W. Mello, and R.F. Thomas. 1983. The Ground Water Supply Survey summary of

volatile organic contaminant occurrence data. EPA Technical Support Division, Office of

Drinking Water, Cincinnati, Ohio.
Occurrence Summary and Use Support Document March 2002 364

4.5 1,1-Dichloroethylene

Table of Contents

4.5.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

4.5.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

4.5.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

4.5.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 367

4.5.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

4.5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378

4.5.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378

Tables and Figures

Table 4.5-1: Facilities that Manufacture or Process 1,1-Dichloroethylene . . . . . . . . . . . . . . . . . . . . . 365

Table 4.5-2: Environmental Releases (in pounds) for 1,1-Dichloroethylene 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

Table 4.5-3: Stage 1 1,1-Dichloroethylene Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368

Table 4.5-4: Stage 1 1,1-Dichloroethylene Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369

Table 4.5-5: Stage 2 Estimated 1,1-Dichloroethylene Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370

Table 4.5-6: Stage 2 Estimated 1,1-Dichloroethylene Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

Table 4.5-7: Estimated National 1,1-Dichloroethylene Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
Occurrence Summary and Use Support Document March 2002 365

4.5.1 Introduction, Use and Production

1,1-Dichloroethylene (chemical formula C2H2Cl2) is a man-made chemical known that is never found

naturally in the environment. It is a colorless liquid that evaporates quickly at room temperature, has a

mild sweet smell, and burns quickly. 1,1-Dichloroethylene can be found in landfills as the result of the

breakdown of polyvinylidene chloride products. Its major routes of entry to drinking water are a

consequence of industrial activity. Quantities of 1,1-dichloroethylene in water may result from industrial

discharge, atmospheric fallout, or the release of quantities remaining as impurities in products (JRB

Associates, 1983). Other names for 1,1-dichloroethylene include vinylidene chloride, 1,1-

dichloroethene, and DCE. 

Although 1,1-dichloroethylene is manufactured in large quantities, most of it is used to make other

substances or products such as polyvinylidene chloride (ATSDR, 1994). Single molecules of 1,1-

dichloroethylene are used in the production of polyvinylidene chloride copolymers and as intermediates

for captive organic chemical synthesis and (ATSDR, 1994). Ninety-six percent of the 1,1-

dichloroethylene produced is used in the production of copolymers with vinyl chloride or acrylonitrile

(USEPA, 2001). The polymers, which have been commercially important since their introduction in the

early 1940s, are used extensively in many types of flexible packing materials, as flame retardant coatings

for fiber and carpet backing, and in piping, coating for steel pipes, and adhesive applications. The major

application of polyvinylidene chloride copolymers is the production of flexible films for food packaging

(SARAN and VELON wraps). At one time, SARAN wrap was found to contain up to 30 parts per

million (ppm) 1,1-dichloroethylene. Currently, the plastic packaging films can contain no more than 10

ppm 1,1-dichloroethylene (ATSDR, 1994).

The two major producers of 1,1-dichloroethylene are Dow Chemical and Pittsburgh Paint and Glass

(PPG) Industries. Production capacity in 1977 was 270 million pounds/year, but by 1985, production

capacity had declined to 178 million pounds/year. In 1989, production was estimated at 230 million

pounds (ATSDR, 1994). 

Table 4.5-1 shows the number of facilities in each State that manufacture or process 1,1-

dichloroethylene, the activities and uses of the product, and the range of maximum amounts on site

derived from the Toxics Release Inventory (TRI) of EPA (ATSDR, 1994). 

Table 4.5-1: Facilities that Manufacture or Process 1,1-Dichloroethylenea

Facility Locationb Range of maximum

amounts on site in Activities and uses

3M Decatur, AL 1,000-9,999 As a reactant

Monsanto Co. Chemical Decatur, AL 100,000-999,999 As a reactant

Eastman Kodak Co. Windsor, CO 1,000-9,999 As a reactant

Dow Chemical Dalton Site Dalton, GA 0-99 As a reactant

Morton International Inc. Ringwood, IL 1,000,000-9,999,999 As a reactant

BF Goodrich Co. Louisville Louisville, KY 10,000-99,999 As a reactant

W.R. Grace & Co. Owensboro, KY 100,000-999,999 As a reactant

Marine Shale Processors Inc. Amelia, LA 10,000-99,999 As a reactant

Vulcan Materials Co. 

 Chemical Div.

Geismar, LA 10,000-99,999 Produce; as a byproduct; as an impurity; as a reactant

Dow Chemical Co. Louisiana Plaquemine, LA 1,000-9,999 Produce; as a byproduct; as a reactant; in ancillary or

PPG Industries Inc. Westlake, LA 10,000,000-49,999,999 Produce; for sale/distribution; as a byproduct; as an

Dow Chemical USA Midland Midland, MI 10,000,000-49,999,999 As a reactant; in ancillary or other uses

Rhone-Poulenc Inc. Walsh Gastonia, NC 10,000-99,999 As a reactant

Allied-Signal Inc. Elizabeth Elizabeth, NJ 10,000-99,999 As a reactant
Facility Locationb Range of maximum

amounts on site in Activities and uses

Occurrence Summary and Use Support Document March 2002 366

Du Pont Parlin Plant Parlin, NJ 1,000-9,999 As a reactant

Allied Signal Inc. Buffalo, NY 10,000,000-49,999,999 As a reactant

Eastman Kodak Co. Kodak Rochester, NY 1,000-9,999 As a reactant

Gencorp Polymer Products Mogadore, OH 100,000-999,999 As a reactant

Occidental Chemical Corp. 

 VCM Plant

Deer Park, TX 10,000-99,999 Produce; as a byproduct

Dow Chemical Co. Texas

Operations

Freeport, TX 1,000,000-9,999,999 Produce; for sale/distribution; as a byproduct; as an

impurity; in repackaging; as a processing aid; in

Occidental Chemical Co.

 Corpus Christi Plant

Gregory, TX 100-999 Produce; as a byproduct

Hercules Inc. Covington, VA 100,000-999,999 As a reactant

Arco Chemical Co. South Charleston, 100,000-999,999 As a reactant

a

Derived from TRI91 (1993)

b

Post Office State abbreviations used

Source: ATSDR, 1993 compilation of TRI91 1993 data

4.5.2 Environmental Release

1,1-Dichloroethylene is listed as a Toxics Release Inventory (TRI) chemical (as vinylidene chloride). 

Table 4.5-2 illustrates the environmental releases for 1,1-dichloroethylene from 1988 - 1999 (1,1-

dichloroethylene data are only available for these years). Air emissions constitute most of the on-site

releases, with a downward trend in emissions. The decrease in air emissions has contributed to decreases

in 1,1-dichloroethylene total on- and off-site releases in recent years. Releases to land (such as spills or

leaks within the boundaries of the reporting facility) decreased significantly from 1988-1991, and they

have been at or near zero from 1994-1999. Releases from surface water discharges and underground

injection have fluctuated over the years with no discernable trends; also, underground injections data are

incomplete because they were not monitored from 1991-1996. Since 1989, off-site releases (including

metals or metal compounds transferred off-site) have fluctuated, from zero to over 6,000 pounds, with no

apparent trend. These TRI data for 1,1-dichloroethylene were reported from 19 States and Puerto Rico,

with 11 States reporting every year (USEPA, 2000). Of the 19 States that reported, 10 are included in the

16 State cross-section (used for analyses of 1,1-dichloroethylene occurrence in drinking water; see

Section 4.5.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 4.5-2: Environmental Releases (in pounds) for 1,1-Dichloroethylene in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 155,891 132 99 0 8 156,130

1998 179,391 311 218 0 3 179,923

1997 199,243 662 323 -- 104 200,332

1996 192,815 466 -- 1 33 193,315

1995 193,550 642 -- 0 260 194,452

1994 165,743 215 -- 0 2,031 167,989

1993 204,814 192 -- 20 1 205,027

1992 253,920 1,306 -- 14 0 255,240
Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

Occurrence Summary and Use Support Document March 2002 367

1991 287,640 794 -- 15 7 288,456

1990 305,686 251 150 463 12 306,562

1989 222,738 2,691 720 540 6,307 232,996

1988 296,353 3,462 170 429 44,281 344,695

 Source: USEPA, 2000 

4.5.3 Ambient Occurrence

The local, State, and federal data set compiled by NAWQA reports that 1,1-dichloroethylene was

detected in 12 out of 397 urban wells (3.0%). The minimum and maximum concentrations detected were

0.2 :g/L and 11 :g/L, respectively. The median value of detection concentrations was 0.9 :g/L. 1,1-

Dichloroethylene was also detected in 7 of the 2,414 rural wells (0.29%) analyzed The minimum and

maximum concentrations detected were 0.4 :g/L and 39 :g/L, respectively. The median value of

detection concentrations was 1.0 :g/L. These data (urban and rural) represent untreated ambient ground

water of the conterminous United States for the years 1985-1995 (Squillace et al., 1999).

1,1-Dichloroethylene was also an analyte in the NURP data. The NURP study found 1,1-

dichloroethylene in urban runoff (Lopes and Dionne, 1998). The minimum and maximum concentrations

detected were 1.5 :g/L and 4 :g/L, respectively, with no mean value reported. The use of the land from

which the samples were taken was unspecified. 

4.5.3.1 Additional Ambient Occurrence Data

A summary document entitled “Occurrence of 1,1-Dichloroethylene in Drinking Water, Food, and Air”

(JRB Associates, 1983), was previously prepared for past USEPA assessments of 1,1-dichloroethylene. 

However, no information on the ambient occurrence of 1,1-dichloroethylene was included in that

document. (The document did include information regarding 1,1-dichloroethylene occurrence in

drinking water, which is discussed in Section 4.5.5 of this report.)

4.5.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of 1,1-dichloroethylene occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.007 mg/L; 0.005 mg/L; 0.001 mg/L;

and 0.0005 mg/L.

All sixteen cross-section State data sets contained occurrence data for 1,1-dichloroethylene. These data

represent more than 146,000 analytical results from approximately 19,000 PWSs during the period from

1984 to 1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs

vary by State, although the State data sets have been reviewed and checked to ensure adequacy of

coverage and completeness. The overall modal detection limit for 1,1-dichloroethylene in the 16 crosssection States is equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)
Occurrence Summary and Use Support Document March 2002 368

4.5.4.1 Stage 1 Analysis Occurrence Findings

Table 4.5-3 illustrates the occurrence of 1,1-dichloroethylene in drinking water for the public water

systems in the 16-State cross-section. Based on the 16-State cross-section data, 0.236% of ground water

or surface water PWSs (45 systems) had analytical results of 1,1-dichloroethylene exceeding the MCL

(0.007 mg/L). Approximately 0.309% of PWSs (59 systems) had at least one analytical result greater

than 0.005 mg/L. The percentage of PWSs with results greater than 0.001 mg/L was equal to 0.869%

(166 systems). Approximately 1.18% of PWSs (225 systems) in the 16 States had at least one analytical

result greater than 0.0005 mg/L.

Less than 1% of ground water systems had analytical results greater than any of the four thresholds. 

Approximately 0.211% of ground water systems (37 systems) had results exceeding the MCL. The

percentage of ground water systems in the 16 States with at least one analytical result greater than 0.005

mg/L was equal to 0.273% (48 systems). Approximately 0.819% of ground water systems (144 systems),

and 0.944% of ground water systems (166 systems) had any analytical results exceeding 0.001 mg/L, and

0.0005 mg/L, respectively.

For surface water PWSs, 0.525% (8 systems) had analytical results exceeding 0.007 mg/L. 

Approximately 0.721% of surface water systems (11 systems) had results exceeding 0.005 mg/L. The

percentage of surface water systems with at least one analytical result greater than 0.001 mg/L was equal

to 1.44% (22 systems). Approximately 1.90% of surface water systems (29 systems) had analytical

results of 1,1-dichloroethylene 0.0005 mg/L.

Table 4.5-3: Stage 1 1,1-Dichloroethylene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Ground Water

0.007 0.211% 37

0.005 0.273% 48

0.001 0.819% 144

0.0005 0.944% 166

Surface Water

0.007 0.525% 8

0.005 0.721% 11

0.001 1.44% 22

0.0005 1.90% 29

Combined Ground &

Surface Water

0.007 0.236% 45

0.005 0.309% 59

0.001 0.869% 166

0.0005 1.18% 225
Occurrence Summary and Use Support Document March 2002 369

Reviewing 1,1-dichloroethylene occurrence in the 16 cross-section States by PWS population served

(Table 4.5-4) shows that approximately 8.69% of the population (almost 9.3 million people) was served

by PWSs with analytical detections of 1,1-dichloroethylene greater than the MCL (0.007 mg/L). 

Approximately 9.44% of the population (over 10 million people) was served by PWSs with at least one

analytical result greater than 0.005 mg/L. The percentage of population served by systems with results

greater than 0.001 mg/L was equal to 12.8% (about 13.6 million people). Approximately 14.4% of the

population (about 15.3 million people) was exposed to levels of 1,1-dichloroethylene greater than 0.0005

mg/l. 

A much greater proportion of population was served by surface water systems with threshold

exceedances, as compared to ground water systems with threshold exceedances. The percentage of

population served by ground water systems and surface water systems with analytical detections of 1,1-

dichloroethylene greater than the MCL was equal to 2.53% (almost 1.2 million people), and 13.3% (over

8 million people), respectively. Relative to 0.005 mg/L, 3.42% of the ground water population (over 1.5

million people) was served by systems exceeding that limit, whereas 13.9% of the surface water

population (approximately 8.5 million people) was served by systems exceeding 0.005 mg/L. In

addition, 7.75% of the population was served by ground water systems with results that exceeded 0.001

mg/L, while 16.5% of the population was served by surface water systems with results exceeding 0.001

mg/L. Approximately 9.30% of the population served by ground water systems was exposed to levels of

1,1-dichloroethylene greater than 0.0005 mg/L, compared to 18.2% of the population served by surface

water systems exposed to levels greater than 0.0005 mg/L.

Table 4.5-4: Stage 1 1,1-Dichloroethylene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population 

Served by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding Threshold

Ground Water

0.007 2.53% 1,152,600

0.005 3.42% 1,556,600

0.001 7.75% 3,528,900

0.0005 9.30% 4,237,200

Surface Water

0.007 13.3% 8,114,700

0.005 13.9% 8,506,200

0.001 16.5% 10,088,600

0.0005 18.2% 11,098,300

Combined Ground &

Surface Water

0.007 8.69% 9,267,400

0.005 9.44% 10,062,800

0.001 12.8% 13,617,500

0.0005 14.4% 15,335,500
Occurrence Summary and Use Support Document March 2002 370

4.5.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.5-5 and 4.5-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

Seventeen (0.0911% of) systems nationally were estimated to have a mean concentration greater than

0.007 mg/L. Twenty-one (0.111% of) systems nationally were estimated to exceed a mean concentration

of 0.005 mg/L. Approximately 67 (0.350% of) systems were estimated to exceed 0.001 mg/L, while 118

(0.616% of) systems had estimated mean concentrations exceeding 0.0005 mg/L. 

Approximately 15 (0.0875% of) ground water systems had estimated mean concentrations of 1,1-

dichloroethylene greater than 0.007 mg/L. An estimated 19 (0.109% of) ground water systems had

estimated mean concentrations greater than 0.005 mg/L. Approximately 62 (0.351% of) ground water

systems and 108 (0.613% of) ground water systems had estimated mean concentrations exceeding 0.001

mg/L and 0.0005 mg/L, respectively.

Only 2 (0.132% of) surface water systems in the 16 States was estimated to have a mean concentration

greater than 0.007 mg/L. Two (0.134% of) surface water systems had an estimated mean concentration

greater than 0.005 mg/L. Approximately 5 (0.329% of) surface water systems had estimated mean

concentrations of 1,1-dichloroethylene greater than 0.001 mg/L. Ten (about 0.657% of) surface water

systems had estimated mean concentration values greater than 0.0005 mg/L. 

Table 4.5-5: Stage 2 Estimated 1,1-Dichloroethylene Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.007 0.0875% 0.0626%-0.120% 15 11 - 21

0.005 0.1090% 0.0740%-0.148% 19 13 - 26

0.001 0.351% 0.273%-0.433% 62 48 - 76

0.0005 0.613% 0.507%-0.723% 108 89 - 127

Surface Water

0.007 0.132% 0.131% - 0.1311% 2 2 - 2

0.005 0.134% 0.131% - 0.197% 2 2 - 3

0.001 0.329% 0.262% - 0.459% 5 4 - 7

0.0005 0.657% 0.459% - 0.92% 10 7 - 14

Combined Ground

& Surface Water

0.007 0.0911% 0.0681% - 0.120% 17 13 - 23

0.005 0.1110% 0.0786% - 0.147% 21 15 - 28
Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 371

0.001 0.350% 0.272% - 0.424% 67 52 - 81

0.0005 0.616% 0.513% - 0.717% 118 98 - 137

Reviewing 1,1-dichloroethylene occurrence by PWS population served (Table 4.5-6) shows that

approximately 0.331% of population served by all PWSs in the 16 States (an estimate of approximately

352,700 people) was potentially exposed to 1,1-dichloroethylene levels above 0.007 mg/L. 

Approximately 0.340% of the total population served by PWSs in the 16 States (exposure to an estimated

362,900 people) was exposed to levels of 1,1-dichloroethylene exceeding the limit of 0.005 mg/L, and

0.898% of the population served by PWSs in the 16 States (exposure to an estimated 956,800 people)

was potentially exposed to levels exceeding 0.001 mg/L. The percentage of population exposed

substantially increased to 8.58% (over 9.1 million people) when evaluated relative to 0.0005 mg/L. 

When the ground water PWSs were evaluated relative to a thresholds of 0.007 mg/L, 0.005 mg/L, 0.001

mg/L, and 0.0005 mg/L, the percentages of population exposed in the 16 States were equal to 0.398% (an

estimated 181,200 people), 0.417% (an estimated 190,000 people), 0.973% (an estimated 443,000

people), and 2.08% (an estimated 945,000 people), respectively. 

The percentage of population served by surface water systems in the 16 States that exceeded the limit of

0.007 mg/L was 0.281% (exposure to an estimated 171,400 people). The percentage that exceeded 0.005

mg/L was 0.283% (exposure to an estimated 172,900 people in the 16 States). Approximately 0.841% of

the population served by surface water systems was potentially exposed to 1,1-dichloroethylene levels

greater than 0.001 mg/L (exposure to an estimated 513,800 people). The percentage of surface water

systems that exceeded the limit of 0.0005 mg/L was 13.4% (exposure to an estimated 8.2 million people

in the 16 States). 

Table 4.5-6: Stage 2 Estimated 1,1-Dichloroethylene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.007 0.398% 0.370% - 0.459% 181,200 168,600 - 209,000

0.005 0.417% 0.385% - 0.479% 190,000 175,400 - 218,300

0.001 0.973% 0.727% - 1.435% 443,000 331,100 - 653,900

0.0005 2.08% 1.593% - 2.68% 945,000 725,900 - 1,222,200

Surface Water

0.007 0.281% 0.280% - 0.280% 171,400 171,700 - 171,700

0.005 0.283% 0.280% - 0.291% 172,900 171,700 - 178,300

0.001 0.841% 0.611% - 1.762% 513,800 374,400 - 1,079,100
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 372

0.0005 13.4% 13.0% - 14.5% 8,195,300 7,986,100 - 8,861,900

Combined Ground

& Surface Water

0.007 0.331% 0.319%-0.357% 352,700 340,400 - 381,100

0.005 0.340% 0.325%-0.380% 362,900 347,200 - 405,500

0.001 0.898% 0.673%-1.326% 956,800 719,000 - 1,416,300

0.0005 8.58% 8.24%-9.19% 9,141,600 8,797,000 - 9,811,700

4.5.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 59 PWSs nationally serving approximately 704,600 people could be exposed to

1,1-dichloroethylene concentrations above 0.007 mg/L. About 72 systems serving almost 725,100 people

had estimated mean concentrations greater than 0.005 mg/L. Approximately 227 systems serving over

1.9 million people nationally were estimated to have mean 1,1-dichloroethylene concentrations greater

than 0.001 mg/L. A total of 401 systems serving over 18 million people had estimated mean

concentrations greater than 0.0005 mg/L. (See Section 1.4 for a description of how Stage 2 16-State

estimates are extrapolated to national values.)

For ground water systems, an estimated 52 PWSs serving about 341,000 people nationally had mean

concentrations greater than 0.007 mg/L. Approximately 65 systems serving about 357,500 people

nationally had estimated mean concentration values that exceeded 0.005 mg/L. About 209 ground water

systems serving almost 833,500 people had estimated mean concentrations greater than 0.001 mg/L. An

estimated 364 ground water PWSs nationally exposed over 1.7 million people to concentrations of 1,1-

dichloroethylene greater than 0.0005 mg/L.

Approximately 1 surface water system serving 357,400 people was estimated to have a mean

concentration of 1,1-dichloroethylene above 0.007 mg/L. About 7 surface water systems serving 360,500

people had estimated mean concentrations greater than 0.005 mg/L. An estimated 18 surface water

systems serving approximately 1.1 million people had mean concentrations greater than 0.001 mg/L. 

Approximately 73 surface water PWSs serving over 17 million people had estimated mean

concentrations of 1,1-dichloroethylene greater than 0.0005 mg/L.

Table 4.5-7: Estimated National 1,1-Dichloroethylene Occurrence - Systems and Population

Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.007 52 37 - 71 341,000 317,100 - 392,900

0.005 65 44 - 88 357,500 329,800 - 410,500
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 373

0.001 209 162 - 257 833,500 622,600 - 1,229,500

0.0005 364 301 - 430 1,777,900 1,364,900 - 2,298,000

Surface Water

0.007 1 7 - 7 357,400 357,000 - 357,000

0.005 7 7 - 11 360,500 357,000 - 370,600

0.001 18 15 - 26 1,071,200 778,500 - 2,243,500

0.0005 37 26 - 51 17,087,200 16,603,400 - 18,424,100

Combined Ground

& Surface Water

0.007 59 44 - 78 704,600 678,900 - 760,000

0.005 72 51 - 95 725,100 692,500 - 808,600

0.001 227 177 - 276 1,911,700 1,433,800 - 2,824,500

0.0005 401 334 - 467 18,265,500 17,543,400 - 19,566,900

4.5.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of 1,1-dichloroethylene in drinking water are

also reviewed. Previously compiled occurrence information, from an OGWDW summary document

entitled “Occurrence of 1,1-Dichloroethylene in Drinking Water, Food, and Air” (JRB Associates, 1983),

is presented in the following section. This variety of studies and information are presented regarding

levels of 1,1-dichloroethylene in drinking water, with the scope of the reviewed studies ranging from

national to regional. Note that none of the studies presented in the following section provide the

quantitative analytical results or comprehensive coverage that would enable direct comparison to the

occurrence findings estimated with the cross-section occurrence data presented in Section 4.5.4. These

additional studies, however, do enable a broader assessment of the Stage 2 occurrence estimates

presented for this Six-Year Review. All the following information in Section 4.5.5 is taken directly from

“Occurrence of 1,1-Dichloroethylene in Drinking Water, Food, and Air” (JRB Associates, 1983).

JRB Associates (1983) found two major types of data available that are potentially useful for describing

the occurrence of 1,1-dichloroethylene in the nation's public drinking water supplies. First, there are

several Federal surveys in which a number of public water supplies from throughout the U.S. were

selected for analysis of chemical contamination, including 1,1-dichloroethylene. Second, data are

available from State surveys and from State investigations of specific incidents of known or suspected

contamination of a supply. For accomplishing the basic objectives of this study, namely to estimate the

number of public water supplies nationally within the various source and size categories contaminated

with 1,1-dichloroethylene, the distribution of 1,1-dichloroethylene concentrations in those supplies, and

the number of individuals exposed to those concentrations, it was determined that the Federal survey data

provides the most suitable data base. The State data tend to be poorly described with respect to the

source and size categories of the supplies examined and the sampling and analysis methods used for

determining contaminant levels. The lack of source and system size information precludes using the data

for estimating levels in public water supplies of similar characteristics. The absence of details on

sampling and analysis methods precludes evaluating those data for their qualitative and quantitative
Occurrence Summary and Use Support Document March 2002 374

reliability. Also, because much of the State data are from investigations in response to incidents of

known or suspected contamination (e.g., spills), they were judged to be not representative of contaminant

levels in the nation's water supplies in general. Although they are not used with the Federal data for the

purpose of estimating contamination levels nationally, the available State data are presented here to

provide some additional perspective on 1,1-dichloroethylene occurrence in drinking water.

Data are presented only on drinking water samples taken from a consumer's tap (i.e., distribution water

samples) or on treated water samples taken at the water supply (i.e., finished water samples) because

these are considered to be most representative of the water consumed by the public. No data on raw (i.e.,

untreated) water are presented. It is recognized that for some groundwater supplies where no treatment

of the water occurs, samples identified as raw may be representative of water consumed by the users of

the supply. However, it was generally not possible to differentiate between those groundwater supplies

that do and those that do not treat raw water from the available survey data

4.5.5.1 Overview and Quality Assurance Assessment of Federal Drinking Water Surveys

Two Federal drinking water surveys provide data on 1,1-dichloroethylene: the National Screening

Program for Organics in Drinking Water (NSP) and the Groundwater Supply Survey (GWSS). The terms

used in this report are those used in the individual surveys, recognizing that they may not always

correspond to strict technical definitions.

The National Screening Program for Organics in Drinking Water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water

systems in 33 States for 51 organic chemical contaminants. Data are available for 1,1-dichloroethylene

on finished water samples from 12 groundwater and 103 surface water supplies.

The Groundwater Supply Survey (GWSS) was conducted from December 1980 to December 1981 to

develop additional data on the occurrence of volatile organic chemicals in the nation's groundwater

supplies (Westrick et al. 1983, as cited in JRB Associates, 1983). It was hoped that this study would

stimulate State efforts toward the detection and control of groundwater contamination and the

identification of potential chemical “hot spots.” A total of 945 systems were sampled, of which 466 were

chosen at random. The remaining 479 systems were chosen nonrandomly based on information from

States encouraged to identify locations believed to have a higher than normal probability of VOC

contamination (e.g., locations near landfills or industrial activity). The file provided a single analytical

result for each supply sampled. One sample of finished water was collected from each supply at a point

near the entrance to the distribution system.

Each of the drinking water surveys was evaluated with respect to the validity of the reported occurrence

data for a number of organic chemicals, including 1,1-dichloroethylene. The evaluations were carried

out by analyzing information about the procedures used for collection and analysis of samples as well as

the quality control protocols used. The analyzed compounds dealt with in each study were assigned one

of three possible ratings: quantitatively acceptable, qualitatively acceptable (i.e., the substance measured

was 1,1-dichloroethylene), and totally unacceptable. In the case of 1,1-dichloroethylene, a qualitatively

acceptable rating was given for data from the NSP because of suspected biodegradation of the samples,

which were held unrefrigerated for prolonged periods before analysis. 1,1-Dichloroethylene values in

excess of the quantitation limit reported for some samples in these studies are qualitatively valid and can

be taken as minimum values, representative of samples which probably originally contained 1,1-

dichloroethylene at higher concentrations. In the case of the GWSS, all data were rated both

quantitatively and qualitatively acceptable.
Occurrence Summary and Use Support Document March 2002 375

4.5.5.2 Groundwater – Federal Surveys

The National Screening Program for Organics in Drinking Water (NSP) and the Groundwater Supply

Survey (GWSS) both contain data concerning the levels of 1,1-dichloroethylene in groundwater supplies

from across the country.

Twelve groundwater supplies were tested for ,1,1-dichloroethylene contamination in the NSP. Of these

12 systems, only one was found to be contaminated with 1,1-dichloroethylene at a level of 0.2 :g/L. The

quantification limit for 1,1-dichloroethylene was 0.1 :g/L.

In the GWSS, 9 of the 456 randomly chosen water systems serving 25 or more individuals were

contaminated with 1,1-dichloroethylene, at concentrations ranging from 0.22-6.3 :g/L. The three

systems with the highest values were contaminated at 2.1, 2.2, and 6.3 :g/L. Of the 9 positive systems, 5

were from systems serving populations in excess of 10,000 people. The average for all randomly chosen

systems was 1.4 :g/L with a standard deviation of 2.0 :g/L; the median was 0.28 :g/L. Of the 473

nonrandom locations sampled serving 25 or more individuals, 15 were contaminated with 1,1-

dichloroethylene, at concentrations between 0.22-3 :g/L, the highest values being 0.04, 1.2, and 3 :g/L. 

Of the 15 positive samples, 10 were from systems serving populations in excess of 10,000 people. The

average 1,1-dichloroethylene level for the nonrandom systems was 0.59 :g/L with a standard deviation of

0.71 :g/L; the median value was 0.35 :g/L. The minimum quantitation limit for 1,1-dichloroethylene

was 0.2 :g/L.

4.5.5.3 Groundwater – State Data

Three States (California, Massachusetts, and New Jersey) provided the USEPA with information

concerning 1,1-dichloroethylene contamination in groundwater supplies. Analytical results for samples

from three locations in California ranged from undetectable to 50 :g/L. 

1,1-Dichloroethylene levels ranged from undetectable to 261 :g/L in 22 samples from six Massachusetts

cities. New Jersey provided data from 19 samples from Fair Lawn and Mahwah; 12 of the samples

contained undetectable 1,1-dichloroethylene while the other seven samples ranged from 2.7-3.5 :g/L at

Mahwah and 0.9-27 :g/L at Fair Lawn.

4.5.5.4 Surface Water – Federal Surveys

Only one federal survey, the National Screening Program (NSP), contains data concerning 1,1-

dichloroethylene levels in surface water supplies. During this survey, 106 drinking water systems were

analyzed for 1,1-dichloroethylene between June 1977 and March 1981. Of these, two systems contained

detectable levels of 1,1-dichloroethylene, with concentrations of 0.2 and 0.51 :g/L.

4.5.5.5 Surface Water – State Data

Data from two surface water samples were reported from Niagara Falls, New York. Of the two finished

water samples, one contained no detectable 1,1-dichloroethylene. The other sample was contaminated

with 1,1-dichloroethylene at 0.22 :g/L.

4.5.5.6 Projected National Occurrence of 1,1-Dichloroethylene in Public Water Supplies

As reported by the JRB Associates (1983) report, public water systems fall into two major categories

with respect to water source (surface water and groundwater) and into five size categories and twelve
Occurrence Summary and Use Support Document March 2002 376

subcategories according to the number of individuals served. The JRB Associates (1983) report

presented estimates of both the number of drinking water supplies nationally within each of the

source/size categories expected to have 1,1-dichloroethylene present, and of the concentration of 1,1-

dichloroethylene expected to be present in those supplies.

The key features of the methodology used and assumptions made to develop the national estimates are

summarized here. The estimates are based on the data from the Federal surveys only. The State data

were not included for several reasons. Generally, these data are from a few States and were not

considered to be geographically representative. There was also a general lack of data on the population

served by systems measured, the type of water sampled, and the methodologies used to sample, identify,

and measure 1,1-dichloroethylene.

The Federal survey data from the NSP and GWSS were pooled together for developing the national

projections. It was assumed in combining these surveys that the resulting data base would be

representative of the nation's water supplies. In the case of the GWSS data, both the random and

nonrandom samples were included in the projections because a statistical test of the GWSS data showed

no statistically significant difference in the frequency of occurrence of positive values or the mean of the

positive values of vinyl chloride between the random and nonrandom samples.

Ideally, adequate survey data would be available to develop the national projections separately for each

of the twelve system size categories within the groundwater and surface water groups; however, the

available data were too limited for this. JRB (1983) consolidated some of the size categories to have

sufficient data for developing the projections. In consolidating data from various size categories,

consideration was given to the potential for there being statistically significant differences in the

frequency of occurrence of 1,1-dichloroethylene as a function of system size. The consolidation of size

categories therefore involved a balancing of the need to group size categories together to have an

adequate data base for developing the national projections against the need to treat size categories

separately in order to preserve the influence of system size as a determinant of contamination potential. 

The consolidation of size categories also took into account EPA's classification of systems into the five

major groups as very small (25-500), small (501-3,300), medium (3,301-10,000), large (10,001-100,000),

and very large (> 100,000) (Kuzmack, 1983, as cited in JRB Associates, 1983).

Once the data were consolidated, statistical models for extrapolating to the national level were tested and

an appropriate model selected. In the case of 1,1-dichloroethylene, the multinominal method was used. 

The frequency of contamination of groundwater and surface water systems at various concentrations was

determined for each consolidated size category. For completing the national estimates, it was assumed

that the frequency of contamination observed for each consolidated category was directly applicable to

each of the system sizes comprising it.

In the JRB Associates (1983) report, it is noted that some of the data used in computing the national

estimates are from samples held for a prolonged period of time prior to analysis, with possible

biodegradation of 1,1-dichloroethylene. Therefore, these projections of national occurrence may

underestimate actual contaminant levels.

4.5.5.6.1 Groundwater Supplies

JRB Associates (1983) reported data that were available for a total of 938 supplies from the combined

surveys. Of these, 25 supplies were reported to have 1,1-dichloroethylene present, at concentrations

ranging from 0.2 :g/L to 6.3 :g/L. Based on the overall distribution of positive values and maximum
Occurrence Summary and Use Support Document March 2002 377

possible values for those supplies in which 1,1-dichloroethylene was not found, 0.2 :g/L was selected as

the common minimum quantifiable concentration for the combined survey data. That is, quantitative

projections are made of supplies at several concentration ranges > 0.2 :g/L, while only a total number for

supplies expected to have either no 1,1-dichloroethylene or levels below 0.2 :g/L can be determined.

When the twelve size categories were consolidated into the five major EPA groupings, there was an

apparent trend in the frequency of values > 0.2 :g/L as a function of size:

Very small 0.9% (2/230)

Small 2.0% (4/203)

Medium 2.6% (4/154)

Large 4.5% (14/312)

Very large 2.6% (1/39)

Overall 2.7% (25/938)

A test for statistical significance revealed that at the " = 0.05 level, the difference among the very small,

small, and medium categories was not significant; nor was the difference between the large and very

large size categories. However, the combined very small, small, and medium categories and the

combined large and very large categories were found to be different. Therefore, two consolidated

categories were selected for developing the national estimates:

Very small/small/medium (25-10,000)

Large/very large (> 10,000)

As noted previously, the frequency of occurrence of 1,1-dichloroethylene at various concentrations was

determined for the two consolidated groups and then applied to the number of supplies nationally within

each of the size categories comprising each group.

Approximately 1.8% of the total groundwater supplies in the United States (858 supplies, with a range of

366-1,349), are expected to have 1,1-dichloroethylene at levels of > 0.2 :g/L; the remaining 47,600

supplies have either no 1,1-dichloroethylene or levels < 0.2 :g/L. It is estimated that 81 supplies (range

of 0-237) are expected to have 1,1-dichloroethylene levels > 5 :g/L; while no supplies are expected to

have levels > 10 :g/L. Most of the supplies with 1,1-dichloroethylene levels > 0.2 :g/L are expected to

be in the smaller size categories. Although, as noted previously, the frequency of 1,1-dichloroethylene

occurrence appears to increase with increasing system size, the number of systems affected nationally is

greater for the small sizes because there are many more small systems in existence.

4.5.5.6.2 Surface Water Systems

Data are available for a total of 103 surface water supplies. Of these, 2 supplies were reported by JRB

Associates (1983) to have 1,1-dichloroethylene present at concentrations of 0.2 :g/L and 0.5 :g/L. All

but one of the 103 surface water supplies sampled in the NSP fall in the large and very large size

categories (i.e., serving > 10,000 people). Consequently, it was not possible to evaluate the frequency of

occurrence of 1,1-dichloroethylene as a function of system size for the very small, small, and medium

size categories. In the large size category (serving 10,001-100,000), none of the 19 supplies were found

to have 1,1-dichloroethylene present, while 2 of 83 in the very large category (serving > 100,000) had

1,1-dichloroethylene present. The difference in the frequency of occurrence between the large and very

large groups was not statistically significant at the " = 0.05 level. For the purpose of the national

estimates, the groundwater supplies were consolidated into two groups:
Occurrence Summary and Use Support Document March 2002 378

Very small/small/medium (25-10,000)

Large/very large (> 10,000)

Again, the frequency of occurrence of 1,1-dichloroethylene at various concentrations was determined for

the two consolidated groups and then applied to the number of supplies nationally within each of the size

categories comprising each group.

Thirty-five surface water supplies (range of 0-81), approximately 0.3% of the total surface water systems

in the United States, are expected to have 1,1-dichloroethylene at levels > 0.2 :g/L; the remaining 11,167

supplies have either no 1,1-dichloroethylene or levels < 0.2 :g/L. It is estimated that no surface water

supplies will have levels > 5 :g/L. Note that all of the supplies with levels in the 0.2-5 :g/L range are in

the large and very large category. The estimate of no occurrence in the smaller categories is based on

only one sample and is probably not a reliable estimate.

4.5.6 Conclusion

1,1-Dichloroethylene does not occur naturally, but it is found as the result of the breakdown of

polyvinylidene chloride products in landfills. Virtually all 1,1-dichloroethylene produced is used in the

production of copolymers with vinyl chloride or acrylonitrile, and only a small percentage (4%) is used

as chemical intermediates. The primary producers of 1,1-dichloroethylene are Dow Chemical and

Pittsburgh Paint and Glass (PPG) Industries, and the most recent data available suggests that production

is relatively stable. 1,1-Dichloroethylene is also a TRI chemical. Under the TRI program, industrial

releases of 1,1-dichloroethylene have been recorded since 1988 in 19 States and Puerto Rico. 1,1-

Dichloroethylene was an analyte for the NAWQA and NURP ambient occurrence studies. In the

NAWQA study, 1,1-dichloroethylene was detected in 3.0% of urban wells and 0.29% of rural wells, with

median detection values of 0.9 :g/L and 1.0 :g/L, respectively. In the Stage 2 analysis of 16-State

occurrence of 1,1-dichloroethylene, 0.0144% of combined ground water and surface water systems

serving 0.0135% of the population exceeded the MCL of 0.007 mg/L. Nationally, 9 ground water and

surface water systems combined (serving approximately 28,800 people) are estimated to have levels

greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, 1,1-dichloroethylene is manufactured and/or processed in 14 States and has

TRI releases have been reported in 19 States. 1,1-Dichloroethylene is manufactured and/or processed in

6 out of the 16 cross-section States and has TRI releases in 10 of the 16 cross-section States. The crosssection should adequately represent occurrence of 1,1-dichloroethylene on a national scale based upon

the use, production, and release patterns of the 16-State cross-section in relation to the patterns observed

for all 50 States. 

4.5.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1994. Toxicological Profile for 1,1-

Dichloroethene. U.S. Department of Health and Human Services, Public Health Service. 174

pp. + Appendices. Available on the Internet at http://www.atsdr.cdc.gov/toxprofiles/tp39.pdf

JRB Associates. 1983. Occurrence of 1,1-Dichloroethylene in Drinking Water, Food and Air - DRAFT. 

Draft report submitted to EPA for review December 18, 1983. 
Occurrence Summary and Use Support Document March 2002 379

Kuzmack, A.M. 1983. Memorandum: Characterization of the water supply industry (FY82). 

Washington, D.C.: Office of Water, USEPA. May 16, 1983. 

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 67

pp.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: 1,1-

Dichloroethylene. Office of Ground Water and Drinking Water, USEPA. Available on the

Internet at http://www.epa.gov/safewater/dwh/c-voc/11-dichl.html (Last updated 04/12/2001)

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Westrick, J.J., J.W. Mello, and R.F. Thomas. 1983. The Ground Water Supply Survey summary of

volatile organic contaminant occurrence data. EPA Technical Support Division, Office of

Drinking Water, Cincinnati, Ohio.
Occurrence Summary and Use Support Document March 2002 380

4.6 Dichloromethane

Table of Contents

4.6.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381

4.6.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382

4.6.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

4.6.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 384

4.6.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389

4.6.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389

4.6.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390

Tables and Figures

Table 4.6-1: Dichloromethane Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . . . . . 381

Table 4.6-2: Environmental Releases (in pounds) for Dichloromethane 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

Table 4.6-3: Stage 1 Dichloromethane Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

Table 4.6-4: Stage 1 Dichloromethane Occurrence Based on 16-State Cross-Section -

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385

Table 4.6-5: Stage 2 Estimated Dichloromethane Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

Table 4.6-6: Stage 2 Estimated Dichloromethane Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388

Table 4.6-7: Estimated National Dichloromethane Occurrence - Systems and Population Served . . . 389
Occurrence Summary and Use Support Document March 2002 381

4.6.1 Introduction, Use and Production

Dichloromethane, also known as methylene chloride, has the chemical formula CH2Cl2. It is a colorless

liquid that has a mild sweet odor, evaporates easily, and does not burn easily. Dichloromethane does not

appear to occur naturally in the environment. It is made from methane gas or wood alcohol. Most of the

dichloromethane released to the environment results from its use as an end product by various industries

and the use of aerosol products and paint removers in the home (ATSDR, 2000).

The breakdown of dichloromethane use is as follows: paint strippers and removers, 25%; propellant in

aerosols, 25%; as a process solvent in the manufacture of drugs, pharmaceuticals, and film coatings,

20%; as a metal cleaning and finishing solvent, 10%; in electronics manufacturing, 10%; and as an agent

in urethane foam blowing, 10% (ATSDR, 2000). Dichloromethane has been the primary substitute for

Chlorofluorocarbon 11 as a flexible polyurethane foam blowing agent (Chemexpo, 2001).

Dichloromethane is also used as a solvent in the production of polycarbonate resins and triacetate fibers,

in film processing, in ink formulation, and as an extraction solvent for spice oleoresin, caffeine and hops. 

It is registered in the U.S. as an insecticide for commodity fumigation of strawberries, citrus fruits, and a

variety of grains (NSC, 2001). 

Many consumer products may also contain dichloromethane. These include spray shoe polish, water

repellant/protectors, spot removers, wood floor and panel cleaners, contact cement, superglue, spray

adhesives, adhesive removers, silicone lubricants, specialized electronic cleaners, wood stains, paint

thinners, aerosol rust removers, and glass frosting/artificial snow (NSC, 2001). Concerns over health and

environmental issues have led to a decrease in use of dichloromethane in some products, such as

consumer aerosol products and as a decaffeinator. Its use in hair sprays was banned in 1989 (ATSDR,

2000).

Production of dichloromethane increased steadily through the 1970s and early 1980s, with a peak

production volume of about 620 million pounds in 1984. Demand has declined in the years since the

early 1980s, primarily because manufacturers have moved towards water-based aerosol systems in

anticipation of further regulation of dichloromethane. In 1994, the most recent year for which

information is available, production of dichloromethane was 403 million pounds. Dichloromethane is

produced in a number of States, and the major manufacturers are Dow Chemical in Freeport, TX and

Plaquemine, LA and Vulcan Materials Company in Geismar, LA and Wichita, KS (ATSDR, 2000).

Table 4.6-1 shows the number of facilities in each State that manufacture and process dichloromethane,

the intended uses of the product, and the range of maximum amounts derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 2000). 

Table 4.6-1: Dichloromethane Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on site in

thousands of poundsb Activities and usesc

AL 12 100-999,999 1,4,7,8,10,11,12,13

AR 7 1,000-999,999 2,3,7,10,11,12,13

AZ 5 100-999,999 8,10,11,12,13

CA 23 0-9,999,999 2,3,4,8,9,10,11,12,13

CO 4 1,000-999,999 8,10,11,13

CT 8 1,000-99,999 2,3,10,11,12,13

DE 2 10,000-99,999 8,11

FL 12 100-999,999 8,10,11,12,13
Statea Number of facilities Range of maximum amounts on site in

thousands of poundsb Activities and usesc

Occurrence Summary and Use Support Document March 2002 382

GA 18 0-999,999 2,3,8,9,10,11,12,13

IA 10 100-999,999 8,10,11,12,13

IL 23 0-9,999,999 1,2,3,5,7,8,9,10,11,12,13

IN 21 100-9,999,999 1,2,3,5,8,9,10,11,12,13

KS 8 100-999,999 1,2,3,4,8,10,11,12,13

KY 9 100-99,999 1,5,7,8,10,11,13

LA 8 1,000-9,999,999 1,4,5,6,7,8,10,12,13

MA 10 1,000-999,999 2,3,8,9,10,11,12,13

MD 5 1,000-99,999 8,10,12,13

ME 1 1,000-9,999 13

MI 17 100-999,999 1,2,3,4,5,7,8,10,11,12,13

MN 8 100-99,999 2,3,8,11,12,13

MO 13 1,000-999,999 4,8,10,11,12,13

MS 11 100-999,999 1,2,3,8,11,12,13

MT 1 1,000-9,999 12

NC 17 100-999,999 1,2,4,5,7,8,10,11,12,13

NE 3 1,000-999,999 11,13

NH 3 1,000-99,999 8,12,13

NJ 19 0-999,999 1,2,3,4,7,8,9,10,11,12,13

NM 2 1,000-99,999 8,12

NV 3 100-9,999 1,2,3,8,11,13

NY 14 1,000-9,999,999 2,3,4,7,8,9,10,11,12,13

OH 17 100-9,999,999 2,3,7,8,10,11,12,13

OK 9 100-999,999 8,10,11,13

OR 6 1,000-999,999 2,4,8,10,11,12,13

PA 17 1,000-999,999 8,9,10,11,12,13

PR 12 1,000-9,999,999 1,2,5,6,8,9,10,11,12,13

RI 2 10,000-99,999 10,13

SC 14 100-999,999 7,8,10,11,12,13

TN 15 100-9,999,999 8,9,10,11,12,13

TX 27 0-49,999,999 1,2,3,4,5,6,7,8,9,10,11,12,13

UT 6 1,000-999,999 8,10,11,12,13

VA 10 1,000-999,999 8,10,11,12,13

WA 10 0-99,999 1,6,7,10,11,12,13

WI 14 1,000-999,999 1,4,5,8,10,11,12,13

WV 5 0-9,999,999 8,11,13

a

Post office State abbreviations used

b

Data in TRI are maximum amounts on site at each facility

c

Activities/Uses include:

1. Produce 8. As a formulation component

2. Import 9. As an article component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

Source: ATSDR, 2000 compilation of TRI98 2000 data

4.6.2 Environmental Release

Dichloromethane is listed as a Toxics Release Inventory (TRI) chemical. Table 4.6-2 illustrates the

environmental releases for dichloromethane from 1988 - 1999. (Dichloromethane data are only

available for these years.) Air emissions constitute the vast majority of the on-site releases, with a

substantial decrease over the years. Surface water discharges have also generally declined, with a slight

upturn since 1997. Underground injection fluctuated between about 1 and 2 million pounds from 1988-

1995, and releases have steadily decreased since. Releases to land (such as spills or leaks within the

boundaries of the reporting facility) have fluctuated and show no apparent trend. Off-site releases

(including metals or metal compounds transferred off-site) have declined from the releases of 1988-1991,

and numbers since have remained between about 150,000 and 300,000 pounds. The decrease in air
Occurrence Summary and Use Support Document March 2002 383

emissions has contributed to a considerable decrease in dichloromethane total on- and off-site releases

over the course of monitoring. These TRI data for dichloromethane were reported from 46 States and

Puerto Rico. Forty-one States and Puerto Rico reported TRI data every year (USEPA, 2000). Of the 46

States, 15 are included in the 16 State cross-section (used for analyses of dichloromethane occurrence in

drinking water; see Section 4.6.4). (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 4.6-2: Environmental Releases (in pounds) for Dichloromethane in the United States, 1988-

1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 35,556,474 12,056 107,386 8,344 154,374 35,838,634

1998 40,302,462 15,492 456,962 173,592 267,633 41,216,141

1997 48,315,635 9,493 528,030 11,180 230,405 49,094,743

1996 54,143,761 10,064 749,507 4,957 168,475 55,076,764

1995 58,305,923 28,620 1,140,335 2,064 180,137 59,657,079

1994 63,714,204 52,289 960,942 41,645 314,976 65,084,056

1993 65,499,529 62,909 956,098 69,467 144,479 66,732,482

1992 75,011,911 233,786 1,183,867 77,208 209,916 76,716,688

1991 84,224,528 99,220 1,317,706 96,559 502,795 86,240,808

1990 101,000,812 194,764 850,018 21,024 1,001,707 103,068,325

1989 125,604,691 227,025 1,937,469 15,894 1,530,916 129,315,995

1988 129,124,529 349,960 1,478,833 157,156 7,806,328 138,916,806

 Source: USEPA, 2000 

4.6.3 Ambient Occurrence

Dichloromethane was detected in 8 out of 336 wells (2.4%) in urban areas of the local, State, and federal

data set compiled by NAWQA. The minimum and maximum concentrations detected were 0.2 :g/L and

1.5 :g/L, respectively. The median value of detection concentrations was 0.45 :g/L. Dichloromethane

was also detected in 20 of the 2,345 wells (0.86%) with analysis in rural areas. The minimum and

maximum concentrations detected were 0.2 :g/L and 4 :g/L, respectively. The median value of

detection concentrations was 0.45 :g/L. These data (urban and rural) represent untreated ambient ground

water of the conterminous United States for the years 1985-1995 (Squillace et al., 1999).

Dichloromethane was also an analyte in both the NURP and NPDES programs (Lopes and Dionne,

1998). A comparison of the results of the NURP and NPDES studies found that the frequency of

detection of dichloromethane in the NURP data was 11%, whereas for the NPDES data it was 7%. The

NURP study found dichloromethane in urban runoff. The minimum and maximum concentrations

detected were 4 :g/L and 14.5 :g/L, respectively, with no mean value reported. The NPDES related

investigations analyzing urban and highway runoff detected dichloromethane. The minimum and

maximum concentrations detected were <0.2 :g/L and 13 :g/L, respectively, with no mean value

reported. The use of the land from which both sets of samples were taken was unspecified.

4.6.3.1 Additional Ambient Occurrence Data

Additional studies of ambient data are unavailable for dichloromethane.
Occurrence Summary and Use Support Document March 2002 384

4.6.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of dichloromethane occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.005 mg/L; 0.0025 mg/L; 0.0005

mg/L; and 0.00025 mg/L.

All sixteen cross-section State data sets, with the exception of Montana, contained occurrence data for

dichloromethane. These data represent more than 170,000 analytical results from approximately 22,000

PWSs during the period from 1984 to 1998 (with most analytical results from 1992 to 1997). The

number of sample results and PWSs vary by State, although the State data sets have been reviewed and

checked to ensure adequacy of coverage and completeness. The overall modal detection limit for

dichloromethane in the 16 cross-section States is equal to 0.0005 mg/L. (For details regarding the 16-

State cross-section, please refer to Section 1.3.5 of this report.)

4.6.4.1 Stage 1 Analysis Occurrence Findings

Table 4.6-3 illustrates the occurrence of dichloromethane in drinking water for the public water systems

in the 16-State cross-section. About 0.669% of all PWSs in the 16 States (144 systems) had analytical

results of dichloromethane exceeding the MCL (0.005 mg/L). Approximately 1.72% of PWSs (370

systems) had at least one analytical result greater than 0.0025 mg/L. The percentage of PWSs with

results greater than 0.0005 mg/L was equal to 7.72% (1,663 systems). Approximately 8.51% of PWSs in

the 16 States (1,832 systems) had at least one analytical result greater than 0.00025 mg/L.

Approximately 0.569% of ground water systems (114 systems) had results exceeding the MCL. The

percentage of ground water systems in the 16 States with at least one analytical result greater than 0.0025

mg/L was equal to 1.46% (292 systems). Approximately 7.15% of ground water systems (1,432

systems), and 7.93% of ground water systems (1,587 systems) had any analytical results exceeding

0.0005 mg/L, and 0.00025 mg/L, respectively.

For surface water PWSs, 1.99% (30 systems) had analytical results exceeding 0.005 mg/L. 

Approximately 5.16% of surface water systems (78 systems) had results exceeding 0.0025 mg/L. The

percentage of surface water systems with at least one analytical result greater than 0.0005 mg/L was

equal to 15.3% (231 systems). Approximately 16.2% of surface water systems (245 systems) had

analytical results of dichloromethane 0.00025 mg/L.

Table 4.6-3: Stage 1 Dichloromethane Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.569% 114

0.0025 1.46% 292

0.0005 7.15% 1,432

0.00025 7.93% 1,587
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 385

Surface Water

0.005 1.99% 30

0.0025 5.16% 78

0.0005 15.3% 231

0.00025 16.2% 245

Combined Ground &

Surface Water

0.005 0.669% 144

0.0025 1.72% 370

0.0005 7.72% 1,663

0.00025 8.51% 1,832

Reviewing dichloromethane occurrence by PWS population served (Table 4.6-4) shows that

approximately 9.50% of the 16-State population (about 10.5 million people) was served by PWSs with

analytical detections of dichloromethane greater than the MCL. Approximately 17.7% of the population

(almost 19.5 million people) was served by PWSs with at least one analytical result greater than 0.0025

mg/L. The percentage of population served by systems with results greater than 0.0005 mg/L was equal

to 27.6% (over 30 million people). Approximately 28.5% of the population (over 31 million people) was

exposed to levels of dichloromethane greater than 0.00025 mg/L. 

A much greater proportion of the 16-State population was served by surface water systems with threshold

exceedances, as compared to ground water systems with threshold exceedances. The percentage of

population served by ground water systems and surface water systems with analytical detections of

dichloromethane greater than the MCL was equal to 3.91% (almost 2 million people), and 14.0%

(approximately 8.5 million people), respectively. Relative to 0.0025 mg/L, 6.16% of the population

(about 3 million people) was served by ground water systems with threshold exceedances, whereas

26.9% of the population (over 16 million people) was served by surface water systems with threshold

exceedances. In addition, 16.9% of the population was served by ground water systems with results that

exceeded 0.0005 mg/L, while 36.2% of the population was served by surface water systems with results

exceeding 0.0005 mg/L. Approximately 17.5% of the population served by ground water systems was

exposed to levels of dichloromethane greater than 0.00025 mg/L, compared to 37.3% of the population

served by surface water systems exposed to levels greater than 0.00025 mg/L.

Table 4.6-4: Stage 1 Dichloromethane Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.005 3.91% 1,916,200

0.0025 6.16% 3,019,600

0.0005 16.9% 8,315,100
Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 386

0.00025 17.5% 8,599,000

Surface Water

0.005 14.0% 8,548,400

0.0025 26.9% 16,434,700

0.0005 36.2% 22,125,500

0.00025 37.3% 22,769,400

Combined Ground &

Surface Water

0.005 9.50% 10,464,600

0.0025 17.7% 19,454,400

0.0005 27.6% 30,440,600

0.00025 28.5% 31,368,400

4.6.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.6-5 and 4.6-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

Dichloromethane occurs in a small proportion of PWSs when evaluated relative to the MCL. Only 3

(about 0.0131% of) ground water and surface water PWSs had an estimated mean concentration of

dichloromethane exceeding 0.005 mg/L, the MCL. Approximately 13 (0.0601% of) systems were

estimated to have mean concentrations greater than 0.0025 mg/L. An estimated 348 (1.62% of) systems

had estimated mean concentration values greater than 0.0005 mg/L. About 1,067 (4.96% of) systems in

the 16 States were estimated to have mean concentrations greater than 0.00025 mg/L. 

For ground water systems, 3 (about 0.0130% of) systems were estimated to have a mean concentration

greater than 0.005 mg/L. About 11 (0.0564% of) ground water systems in the 16 States had an estimated

mean concentration exceeding 0.0025 mg/L. An estimated 303 (1.51% of) ground water systems in the

16 States had an estimated mean concentration above 0.0005 mg/L, and 954 (4.77% of) ground water

systems had an estimated mean concentration greater than 0.00025 mg/L. 

Only 1 surface water system in the 16-State cross-section had an estimated mean concentration value of

dichloromethane greater than 0.005 mg/L. Approximately 2 (about 0.133% of) surface water systems

had estimated mean concentrations greater than 0.0025 mg/L. In addition, 44 (2.94% of) surface water

systems, and 113 (7.50% of) surface water systems were estimated to have mean concentrations above

0.0005 mg/L, and 0.00025 mg/L, respectively.
Occurrence Summary and Use Support Document March 2002 387

Table 4.6-5: Stage 2 Estimated Dichloromethane Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.0130% 0.00500% - 0.0300% 3 1 - 6

0.0025 0.0546% 0.0250% - 0.0849% 11 5 - 17

0.0005 1.51% 1.31% - 1.73% 303 262 - 346

0.00025 4.77% 4.36% - 5.19% 954 872 - 1,038

Surface Water

0.005 0.0142% 0.000% - 0.0662% 1 0 - 1

0.0025 0.133% 0.000% - 0.331% 2 0 - 5

0.0005 2.94% 2.25% - 3.84% 44 34 - 58

0.00025 7.50% 6.22% - 8.93% 113 94 - 135

Combined Ground

& Surface Water

0.005 0.0131% 0.00465% - 0.0279% 3 1 - 6

0.0025 0.0601% 0.0325% - 0.0929% 13 7 - 20

0.0005 1.62% 1.41% - 1.84% 348 304 - 395

0.00025 4.96% 4.54% - 5.37% 1,067 977 - 1,157

Reviewing dichloromethane occurrence in the 16 cross-section States by PWS population served (Table

4.6-6) shows that approximately 0.119% of the 16-State population (over 131,000 people) was served by

PWSs with estimated mean concentrations of dichloromethane greater than the 0.005 mg/L. 

Approximately 1.36% of the population (just over 1.5 million people) was served by PWSs with an

estimated mean concentration greater than 0.0025 mg/L. The percentage of population served by systems

with estimated mean concentrations of dichloromethane greater than 0.0005 mg/L was equal to 6.59%

(about 7.3 million people). Approximately 9.40% of the population (over 10 million people) was

potentially exposed to levels of dichloromethane greater than 0.00025 mg/l. 

Although fewer surface water systems than ground water systems had estimated mean concentration

values greater than the thresholds, a much larger population was served by surface water systems with

threshold exceedances because surface water systems tend to serve much larger populations. The

percentage of the 16-State population served by ground water systems and surface water systems with

estimated mean concentrations of dichloromethane greater than the MCL was equal to 0.00203%

(approximately 1,000 people), and 0.213% (over 130,000 people), respectively. Relative to 0.0025 mg/L,

0.0189% of the population (about 9,300 people) was served by ground water systems with estimated

mean concentrations exceeding that limit, whereas 2.44% of the population (almost 1.5 million people)

was served by surface water systems with estimated mean concentrations exceeding 0.0025 mg/L. In

addition, 1.06% of the population served by ground water systems was potentially exposed to levels of

dichloromethane that exceeded 0.0005 mg/L, while 11.0% of the population was served by surface water

systems with estimated mean concentrations of dichloromethane exceeding 0.0005 mg/L. Approximately

3.56% of the population served by ground water systems was potentially exposed to levels of

dichloromethane greater than 0.00025 mg/L, compared to 14.1% of the population served by surface

water systems potentially exposed to levels greater than 0.00025 mg/L.
Occurrence Summary and Use Support Document March 2002 388

Table 4.6-6: Stage 2 Estimated Dichloromethane Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.00203% 0.000357% - 0.0103% 1,000 200 - 5,000

0.0025 0.0189% 0.00242% - 0.0815% 9,300 1,200 - 40,000

0.0005 1.06% 0.720% - 1.91% 518,100 353,000 - 938,000

0.00025 3.56% 2.85% - 4.83% 1,748,000 1,396,700 - 2,368,600

Surface Water

0.005 0.213% 0.000% - 0.449% 130,100 0 - 274,500

0.0025 2.44% 0.000% - 8.98% 1,490,500 0 - 5,483,700

0.0005 11.0% 9.93% - 12.3% 6,737,800 6,063,400 - 7,531,900

0.00025 14.1% 12.7% - 16.2% 8,600,900 7,739,600 - 9,895,900

Combined Ground

& Surface Water

0.005 0.119% 0.000159% - 0.250% 131,200 200 - 275,300

0.0025 1.36% 0.00221% - 4.99% 1,500,200 2,400 - 5,494,100

0.0005 6.59% 5.92% - 7.34% 7,256,400 6,518,400 - 8,089,100

0.00025 9.40% 8.52% - 10.6% 10,350,400 9,383,400 - 11,642,400

4.6.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 9 PWSs nationally serving approximately 253,700 people could be exposed to

dichloromethane concentrations above 0.005 mg/L. About 39 systems serving almost 3 million people

nationally were estimated to have mean concentrations greater than 0.0025 mg/L. Approximately 1,050

systems serving over 14 million people nationally were estimated to have mean dichloromethane

concentrations greater than 0.0005 mg/L. A total of 3,224 systems serving over 20 million people were

estimated to have mean concentrations greater than 0.00025 mg/L. (See Section 1.4 for a description of

how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 8 PWSs serving about 1,700 people nationally had mean

concentrations greater than 0.005 mg/L. Approximately 32 systems serving about 16,200 people

nationally were estimated to have mean concentration values that exceeded 0.0025 mg/L. About 900

ground water systems serving almost 905,200 people were estimated to have mean concentrations greater

than 0.0005 mg/L. An estimated 2,833 ground water PWSs nationally could potentially expose over 3

million people to concentrations of dichloromethane greater than 0.00025 mg/L.

Approximately 1 surface water system serving 271,200 people nationally was estimated to have mean

concentrations of dichloromethane above 0.005 mg/L. About 7 surface water systems serving

approximately 3.1 million people were estimated to have mean concentrations greater than 0.0025 mg/L. 

An estimated 164 surface water systems serving approximately 14 million people had mean
Occurrence Summary and Use Support Document March 2002 389

concentrations greater than 0.0005 mg/L. Approximately 419 surface water PWSs serving almost 18

million people were estimated to have mean concentrations of dichloromethane greater than 0.00025

mg/L.

Table 4.6-7: Estimated National Dichloromethane Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 8 3 - 18 1,700 300 - 8,800

0.0025 32 15 - 50 16,200 2,100 - 69,800

0.0005 900 778 - 1,027 904,800 616,600 - 1,638,200

0.00025 2,833 2,589 - 3,082 3,052,800 2,439,400 - 4,136,700

Surface Water

0.005 1 0 - 4 271,200 0 - 572,200

0.0025 7 0 - 18 3,106,800 0 - 11,430,100

0.0005 164 126 - 215 14,044,100 12,638,400 - 15,699,400

0.00025 419 348 - 499 17,927,600 16,132,300 - 20,626,900

Combined Ground

& Surface Water

0.005 9 3 - 18 253,700 300 - 532,300

0.0025 39 21 - 60 2,901,200 4,700 - 10,624,800

0.0005 1,050 918 - 1,193 14,033,000 12,605,800 - 15,643,300

0.00025 3,224 2,951 - 3,495 20,016,400 18,146,200 - 22,515,000

4.6.5 Additional Drinking Water Occurrence Data

Additional studies of drinking water occurrence data are unavailable for dichloromethane.

4.6.6 Conclusion

Dichloromethane is used in paint strippers and removers, as a propellant in aerosols, as a process solvent

in the manufacture of drugs, pharmaceuticals, and film coatings, as a metal cleaning and finishing

solvent, in electronics manufacturing, and as an agent in urethane foam blowing. It is also used in many

consumer products. Production of dichloromethane has declined since the early 1980s, and the most

recent data indicates that 403 million pounds of dichloromethane were produced in 1994. 

Dichloromethane is also a TRI chemical. Industrial releases of dichloromethane have occurred since

1988 in 46 States and Puerto Rico. Dichloromethane was an analyte for the NAWQA, NURP, and

NPDES ambient occurrence studies. In the NAWQA study, dichloromethane was detected in 3.0% of

urban wells and 0.29% of rural wells, with a median detection value of 0.45 :g/L for all wells. In the

Stage 2 analysis of 16-State occurrence of dichloromethane, 0.0131% of combined ground water and

surface water systems serving 0.119% of the population exceeded the MCL of 0.005 mg/L. Nationally, 9
Occurrence Summary and Use Support Document March 2002 390

ground water and surface water systems combined (serving approximately 253,700 people) are estimated

to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, dichloromethane is manufactured and/or processed in 43 States and has

TRI releases in 46 States. Dichloromethane is manufactured and/or processed in 14 out of the 16 crosssection States and has TRI releases in 15 of the 16 cross-section States. The cross-section should

adequately represent the occurrence of dichloromethane on a national scale based upon the use,

production, and release patterns of the 16-State cross-section in relation to the patterns observed for all

50 States. 

4.6.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 2000. Toxicological Profile for

Methylene Chloride. U.S. Department of Health and Human Services, Public Health Service. 

268 pp. + Appendices. Available on the Internet at

http://www.atsdr.cdc.gov/toxprofiles/tp14.pdf..

Chemexpo. 2001. Methylene Chloride Chemical Profile. Available on the Internet at

http://www.chemexpo.com/news/PROFILE001009.cfm.

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 67

pp.

National Safety Council (NSC). 2001. Dichloromethane Chemical Backgrounder. Itasca, IL: National

Safety Council. Available on the Internet at:

http://www.crossroads.nsc.org/ChemicalTemplate.cfm?id=104&chempath=chemicals, accessed

July 23, 2001.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.
Occurrence Summary and Use Support Document March 2002 391

4.7 1,2-Dichloropropane

Table of Contents

4.7.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392

4.7.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

4.7.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

4.7.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 395

4.7.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400

4.7.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402

4.7.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402

Tables and Figures

Table 4.7-1: Environmental Releases (in pounds) for 1,2-Dichloropropane 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

Table 4.7-2: Stage 1 1,2-Dichloropropane Occurrence Based on 16-State Cross-Section - Systems . 396

Table 4.7-3: Stage 1 1,2-Dichloropropane Based on 16-State Cross-Section - Population . . . . . . . . . 396

Table 4.7-4: Stage 2 Estimated 1,2-Dichloropropane Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397

Table 4.7-5: Stage 2 Estimated 1,2-Dichloropropane Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

Table 4.7-6: Estimated National 1,2-Dichloropropane Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
Occurrence Summary and Use Support Document March 2002 392

4.7.1 Introduction, Use and Production

1,2-Dichloropropane (chemical formula C3H6Cl2) is a colorless liquid that has a chloroform-like odor and

evaporates quickly at room temperature. It is a man-made chemical, whose releases are almost all

anthropogenic in nature. 1,2-Dichloropropane is now used in the United States only in research and

industry. 1,2-Dichloropropane is also known as propylene dichloride and DCP. 

Based on 1982 production data supplied by Dow Chemical (USEPA, 1986, as cited in ATSDR, 1989), it

has been estimated that over 95% of the isolated 1,2-dichloropropane manufactured by Dow was used

on-site as a captive intermediate in the production of perchloroethylene and other chlorinated products by

their ‘per-tet’ process (USEPA, 1986; Dow Chem. Co., 1983, all as cited in ATSDR, 1989). 

Approximately 3 million pounds per year of 1,2-dichloropropane were marketed by Dow Chemical in

1982 for minor uses as an industrial solvent for oils, fats, resins, waxes, and rubber, in ion exchange

manufacture, in toluene diisocyanate (TDI) production, in photographic film manufacture, for paper

coating, and for petroleum catalyst regeneration (HSDB, 1988; IARC, 1986; USEPA, 1986, all as cited in

ATSDR, 1989). Outside of its use as a chemical intermediate, Dow Chemical Company's use pattern for

1,2-dichloropropane in 1982 was as follows: 41% in ion exchange manufacturing, 34% in toluene

diisocyanate (TDI) production, 19% in photographic film production, 4% in paper coating, and 2% in

petroleum catalyst regeneration (Dow Chem. Co., 1983, as cited in ATSDR, 1989). 

Production for sale, as opposed to internal consumption by manufacturers, was greatly curtailed in the

early 1980s. By 1983, 1,2-dichloropropane was no longer sold for consumer use in paint strippers, paint

varnish, and furniture finish removers (USEPA, 1986; Dow Chem. Co., 1983, all as cited in ATSDR,

1989). By the end of 1983, its use as a solvent for film production was to be phased out in favor of l,l,ltrichloroethane (Dow, 1983, as cited in ATSDR, 1989). According to comments submitted by Dow to

ATSDR (USEPA, 1989, as cited in ATSDR, 1989), the phaseout of use of 1,2-dichloropropane as a

solvent for film production had not occurred as of June, 1989, although it is still planned. They further

stated that the use of 34% of 1,2-dichloropropane in TDI production has now been discontinued. 

Before the early 1980s, it was used in farming as a soil fumigant and was found in some paint strippers,

varnishes, and furniture finish removers (ATSDR, 1989). An estimated 20 million pounds/year of

dichloropropane were produced as a by-product in a mixture marketed as a soil fumigant which was used

in the cultivation of a variety of crops, including citrus fruits, pineapple, soy beans, cotton, tomatoes, and

potatoes (IARC, 1986; HSDB, 1988, all as cited in ATSDR, 1989). Dow has discontinued production of

soil fumigants containing 1,2-dichloropropane, and pesticidal formulations containing this chemical are

no longer available in the U.S. (Meister, 1987, as cited in ATSDR, 1989). Other uses of 1,2-

dichloropropane include use as an intermediate in the synthesis of carbon tetrachloride, lead scavenger in

gasoline, textile stain remover, oil and paraffin extractant, scouring compound, and metal degreasing

agent, especially prior to electroplating (IARC, 1986, as cited in ATSDR, 1989).

1,2-Dichloropropane was produced by Columbia Organics in Cassatt, SC, Dow Chemical in Freeport, TX

and Dow Chemical in Plaquemine, LA (SRI, 1988; USITC, 1987, all as cited in ATSDR, 1989);

however, Dow Chemical Company was the only manufacturer of the isolated chemical in the United

States (USEPA, 1986, as cited in ATSDR, 1989), and Dow discontinued the production of 1,2-

dichloropropane in 1991 (USEPA, 2001). The total output of 1,2-dichloropropane by U.S. manufacturers

remained relatively stable until 1984 when a major manufacturer, Mannsville Chemical Products

Corporation, discontinued production. Production of 1,2-dichloropropane in 1980 was 77 million pounds

(USEPA, 2001), and domestic production volume during 1984 was 59.8 million pounds (IARC, 1986, as

cited in ATSDR, 1989).
Occurrence Summary and Use Support Document March 2002 393

4.7.2 Environmental Release

1,2-Dichloropropane is listed as a Toxics Release Inventory (TRI) chemical. Table 4.7-1 illustrates the

environmental releases for 1,2-dichloropropane from 1988 - 1999. (1,2-Dichloropropane data are only

available for these years.) Air emissions constitute most of the on-site releases, with a relatively steady

decrease over the years. Surface water discharges decreased from a high of over 23,000 pounds in 1988

to under 4,000 pounds in 1994, but have since fluctuated between 1,000-9,000 pounds. The significant

decrease in air emissions, as well as a decrease in surface water discharges, has contributed to decreases

in 1,2-dichloropropane total on- and off-site releases from 1988-1999. Underground injection has not

been monitored for most of the years, and otherwise registers zero, with the exception of a measurement

in 1994. Releases to land (such as spills or leaks within the boundaries of the reporting facility) show no

apparent trend, ranging from zero to over 3,000 pounds. However, releases to land have been 150

pounds or less since 1993. Off-site releases (including metals or metal compounds transferred off-site)

vary between under 300 pounds to over 12,000 pounds, displaying no discernable trend. These TRI data

for 1,2-dichloropropane were reported from 15 States, with five States reporting every year (USEPA,

2000). Five of the 16 cross-section States (used for analyses of 1,2-dichloropropane occurrence in

drinking water; see Section 4.7.4) reported releases of 1,2-dichloropropane. (For a map of the 16-State

cross-section, see Figure 1.3-1.)

Table 4.7-1: Environmental Releases (in pounds) for 1,2-Dichloropropane in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 249,656 9,242 -- 30 6,856 265,784

1998 298,150 1,122 -- 32 267 299,571

1997 378,454 2,609 -- 30 12,375 393,468

1996 514,428 1,855 -- 150 5,337 521,770

1995 616,470 4,344 -- 20 1,371 622,205

1994 709,547 3,609 215 12 699 714,082

1993 577,439 4,749 0 19 567 582,774

1992 619,917 6,755 -- 1,206 1,952 629,830

1991 772,543 6,570 -- 0 2,073 781,186

1990 1,038,614 10,453 -- 300 1,639 1,051,006

1989 1,280,220 11,577 0 5 1,446 1,293,248

1988 1,395,304 23,785 -- 3,400 1,131 1,423,620

 Source: USEPA, 2000 

4.7.3 Ambient Occurrence

1,2-Dichloropropane was detected in 3 out of 359 wells (0.84%) in urban areas of the local, State, and

federal data set compiled by NAWQA. The minimum and maximum concentrations detected were 0.2

:g/L and 1.3 :g/L, respectively. The median value of detection concentrations was 0.2 :g/L. 1,2-

Dichloropropane was also detected in 23 of the 2,508 wells (0.92%) analyzed in rural areas. The

minimum and maximum concentrations detected were 0.2 :g/L and 7.5 :g/L, respectively. The median

value of detection concentrations was 0.5 :g/L. These urban and rural data represent untreated ambient

ground water of the conterminous United States for the years 1985-1995 (Squillace et al., 1999).
Occurrence Summary and Use Support Document March 2002 394

1,2-Dichloropropane was also an analyte in the NPDES data. NPDES-related investigations analyzing

urban and highway runoff detected 1,2-dichloropropane (Lopes and Dionne, 1998). The minimum

concentration detected was not reported, and the maximum concentration detected was 3 :g/L, with no

mean value reported. The use of the land from which the samples were taken was unspecified. 

4.7.3.1 Additional Ambient Occurrence Data

A summary document entitled “Occurrence of Synthetic Organic Chemicals in Drinking Water, Food,

and Air” (USEPA, 1987), was previously prepared for past USEPA assessments of 1,2-dichloropropane. 

Several studies were included that addressed levels of 1,2-dichloropropane in water other than drinking

water. The following information is taken directly from “Occurrence of Synthetic Organic Chemicals in

Drinking Water, Food, and Air” (USEPA, 1987).

4.7.3.1.1 Ground Water Sources

Five State studies from California were obtained, including a study of various shallow and deep wells in

Kern County, California (near Bakersfield) for DCP (Cohen and Bowes, 1984, as cited in USEPA, 1987).

Seventeen positive samples were reported with a range of concentrations from 0.1 to 7.9 :g/L. No other

information on the study was reported.

Another State study of wells in Lathrop, California (San Joaquin County), near the Occidental Chemical

Company, was conducted in 1979, and again in 1983 (Cohen and Bowes, 1984, as cited in USEPA,

1987). In 1979, seven of 14 samples from seven locations were positive for DCP with a range of

concentrations from 0.2 to 5.0 :g/L. The mean concentration and detection limit were not reported.

Analyzed subsequently in 1983, none of the samples from the seven locations had detectable levels of

DCP.

Ground water wells in 25 counties from California were analyzed as part of a toxics special project by

the California Water Resources Control Board (Cohen and Bowes, 1984; Holden, 1986, all as cited in

USEPA, 1987). Positive results for DCP were found in 68 out of 266 samples taken from as many sites.

A high value of 1,200 :g/L was reported for a sample from Crescent City, California. No further

information was presented in either report on this study.

Ground water from 24 feet below surface level was sampled in 1982 as part of the California State Board

Toxic Substances Control Program (Cohen and Bowes, 1984, as cited in USEPA, 1987). One sample was

reported to have a concentration of 4.6 :g/L. No other information was reported on this study.

Ground water well samples from California, Maryland, New York, and Washington were reported by the

USEPA Office of Pesticide Programs (Cohen et al., 1986, as cited in USEPA, 1987) to show typical

positive concentrations for DCP in the range of 1.0 to 50 :g/L. No further information was reported.

4.7.3.1.2 Surface Water Sources

Urban stormwater runoff in Eugene, Oregon, was sampled as part of USEPA's Nationwide Urban Runoff

Program (Cole et al. 1984, as cited in USEPA, 1987). Of the 15 sites sampled, only 1 of 86 samples was

positive for DCP, at a concentration of 3.0 :g/L. The detection limit was not reported.

Surface water from rivers in Delaware, Ohio, and West Virginia, as well as 14 other U.S. river basins,

were sampled during various studies reported in USEPA (1985, as cited in USEPA, 1987). In total, more
Occurrence Summary and Use Support Document March 2002 395

than 8 samples from over 207 sites tested positive, with some reported levels between “trace” and 2.0

:g/L. No other specific information was reported.

4.7.3.1.3 Unidentified Sources

Water samples have been compiled by USEPA's STORET data base from national studies without

specification as to type of source (USEPA, 1985, as cited in USEPA, 1987). For a total of 22,670

“observations,” DCP concentrations ranged from 0 to 25,000 :g/L, with a mean concentration of 10.0

:g/L. Whether “observations” referred to positive samples or to the total samples collected was

unspecified. No other information on the studies was reported.

4.7.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of 1,2-dichloropropane occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.005 mg/L; 0.0005 mg/L; and 0.0004

mg/L.

All sixteen cross-section State data sets contained occurrence data for 1,2-dichloropropane. These data

represent more than 180,000 analytical results from approximately 22,000 PWSs during the period from

1984 to 1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs

vary by State, although the State data sets have been reviewed and checked to ensure adequacy of

coverage and completeness. The overall modal detection limit for 1,2-dichloropropane in the 16 crosssection States is equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)

4.7.4.1 Stage 1 Analysis Occurrence Findings

Table 4.7-2 illustrates the occurrence of in drinking water for the public water systems in the 16-State

cross-section relative to three thresholds: 0.005 mg/L (the current MCL), 0.0005 mg/L (the modal

MRL), and 0.0004 mg/L. According to the 16-State cross-section data, a total of 15 (approximately

0.0682% of) ground water and surface water PWSs had analytical results exceeding the MCL; 0.432% of

systems (95 systems) had results exceeding 0.0005 mg/L; and 0.637% of systems (140 systems) had

results exceeding 0.0004 mg/L. 

Approximately 0.0588% of ground water systems (12 systems) had any analytical results greater than the

MCL. About 0.402% of ground water systems (82 systems) had results above 0.0005 mg/L. The

percentage of ground water systems with at least one result greater than 0.0004 mg/L was equal to

0.539% (110 systems). 

Approximately 3 (0.190% of) surface water systems had results greater than the MCL. A total of 13

(0.824% of) surface water systems had at least one analytical result greater than 0.0005 mg/L. Thirty

(1.90% of) surface water systems had results exceeding 0.0004 mg/L.
Occurrence Summary and Use Support Document March 2002 396

Table 4.7-2: Stage 1 1,2-Dichloropropane Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.0588% 12

0.0005 0.402% 82

0.0004 0.539% 110

Surface Water

0.005 0.190% 3

0.0005 0.824% 13

0.0004 1.90% 30

Combined Ground &

Surface Water

0.005 0.0682% 15

0.0005 0.432% 95

0.0004 0.637% 140

Reviewing 1,2-dichloropropane occurrence in the 16 cross-section States by PWS population served

(Table 4.7-3) shows that approximately 1.18% of the 16-State population (over 1.3 million people) was

served by PWSs with at least one analytical result of 1,2-dichloropropane greater than the MCL (0.005

mg/L). Over 11 million (10.1% of) people were served by systems with an exceedance of 0.0005 mg/L. 

A total of about 12 million (10.9% of) people were served by systems with at least one analytical result

greater than 0.0004 mg/L.

The percentage of population served by ground water systems in the 16 States with analytical results

greater than the MCL was equal to 2.22% (approximately 1 million people). When evaluated relative to

1, 2-dicloropropane detections of 0.0005 mg/L or 0.0004 mg/L, the percent of population exposed was

equal to 3.48% (over 1.7 million people) and 3.80% (almost 1.9 million people), respectively. 

The percentage of population served by surface water systems with exceedances of 0.005 mg/L was

equal to 0.347% (approximately 212,200 people). Approximately 15.4% of the population served by

surface water systems (about 9.4 million people) was exposed to 1,2-dichloropropane concentrations

greater than 0.0005 mg/L. When evaluated relative to 0.0004 mg/L, the percent of population exposed

was equal to 16.7% (over 10 million people).

Table 4.7-3: Stage 1 1,2-Dichloropropane Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.005 2.22% 1,091,000

0.0005 3.48% 1,715,000
Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding

Threshold

Occurrence Summary and Use Support Document March 2002 397

0.0004 3.80% 1,871,100

Surface Water

0.005 0.347% 212,200

0.0005 15.4% 9,443,700

0.0004 16.7% 10,216,500

Combined Ground &

Surface Water

0.005 1.18% 1,303,200

0.0005 10.1% 11,158,700

0.0004 10.9% 12,087,600

4.7.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.7-4 and 4.7-5. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

One (0.00358% of) PWS in the 16 States had an estimated mean concentration of 1,2-dichloropropane

exceeding 0.005 mg/L, while 8 (0.0382% of) systems in the 16 States had an estimated mean

concentration exceeding 0.0005 mg/L and 11 (0.0506% of) systems had an estimated mean concentration

exceeding 0.0004 mg/L. 

Zero ground water PWSs in the 16 States were estimated to have a mean concentration greater than 0.005

mg/L. Seven (0.0347% of) ground water PWSs were estimated to exceed a mean concentration of

0.0005 mg/L and 10 (0.0472% of) systems are estimated to exceed a mean concentration of 0.0004 mg/L. 

For surface water PWSs in the 16 States, 0.0176%, 0.0837%, and 0.0947% had estimated mean

concentrations exceeding 0.005 mg/L, 0.0005 mg/L, and 0.0004 mg/L, respectively.

Table 4.7-4: Stage 2 Estimated 1,2-Dichloropropane Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated to Exceed

Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.00250% 0.000% - 0.00980% 0 0 - 2

0.0005 0.0347% 0.0196% - 0.0539% 7 4 - 11

0.0004 0.0472% 0.0245% - 0.0686% 10 5 - 14
Source Water Type Threshold

(mg/L)

Percent of Systems Estimated to Exceed

Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Occurrence Summary and Use Support Document March 2002 398

Surface Water

0.005 0.0176% 0.000% - 0.0634% 1 0 - 1

0.0005 0.0837% 0.0634% - 0.127% 1 1 - 2

0.0004 0.0947% 0.0634% - 0.190% 1 1 - 3

Combined Ground

& Surface Water

0.005 0.00358% 0.000% - 0.00910% 1 0 - 2

0.0005 0.0382% 0.0227% - 0.0546% 8 5 - 12

0.0004 0.0506% 0.0318% - 0.0728% 11 7 - 16

Reviewing 1,2-dichloropropane occurrence by PWS population served (Table 4.7-6) shows that

approximately 0.0358% of population served by all PWSs in the 16 States (an estimate of approximately

39,500 people) was potentially exposed to 1,2-dichloropropane levels above 0.005 mg/L. For all PWSs,

an estimated 0.137% of population served (an estimate of over 151,000 people served in the 16 States)

was exposed to levels above 0.0005 mg/L and 0.150% (an estimated 165,700 people in the 16-State

cross-section) was exposed to levels above 0.0004 mg/L.

When the population exposed by ground water systems in the 16 States was evaluated relative to

thresholds of 0.005 mg/L, 0.0005 mg/L, and 0.0004 mg/L, the percentages of population exposed were

equal to 0.0000401%, 0.0167% (8,200 people), and 0.0446% (22,000 people), respectively.

 The percentage of population served by surface water systems in the 16 States with levels above 0.005

mg/L was 0.0645% (an estimated 39,500 people in the 16 States), while the population served with levels

above 0.0005 mg/L and 0.0004 mg/L was 0.234% (an estimated 143,200 people in the 16 States) and

0.235% (an estimate of 143,700 people in the 16 States), respectively. 

Table 4.7-5: Stage 2 Estimated 1,2-Dichloropropane Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.0000401% 0.000% - 0.000136% 0 0 - 100

0.0005 0.0167% 0.00205% - 0.0649% 8,200 1,000 - 32,000

0.0004 0.0446% 0.00466% - 0.0962% 22,000 2,300 - 47,400

Surface Water

0.005 0.0645% 0.000% - 0.232% 39,500 0 - 142,000

0.0005 0.234% 0.232% - 0.235% 143,200 142,000 - 143,500

0.0004 0.235% 0.232% - 0.250% 143,700 142,000 - 153,000
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Occurrence Summary and Use Support Document March 2002 399

Combined Ground

& Surface Water

0.005 0.0358% 0.000% - 0.129% 39,500 0 - 142,000

0.0005 0.137% 0.130% - 0.158% 151,400 143,000 - 174,700

0.0004 0.150% 0.131% - 0.179% 165,700 145,000 - 197,400

4.7.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) with mean 1,2-

dichloropropane occurrence exceeding each threshold, an estimated 2 PWSs nationally, serving over

76,000 people total could be exposed to 1,2-dichloropropane concentrations above 0.005 mg/L. About

25 systems, serving a total of about 292,000 people, had estimated mean concentrations greater than

0.0005 mg/L. Approximately 33 systems, serving a total of about 319,500 people nationally, were

estimated to have mean 1,2-dichloropropane concentrations greater than 0.0004 mg/L. (See Section 1.4

for a description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 1 PWS in the nation, serving less than 100 people, had a mean

concentration greater than 0.005 mg/L. Approximately 21 systems serving 14,300 people nationally had

estimated mean concentration values that exceeded 0.0005 mg/L. About 28 ground water systems

serving about 38,200 people had estimated mean concentrations greater than 0.0004 mg/L. 

Although fewer surface water systems than ground water systems nationally had estimated mean

concentration values greater than the thresholds, a much larger population was served by surface water

systems with threshold exceedances because surface water systems tend to serve much larger

populations. Approximately 1 surface water system, serving about 82,100 people, was estimated to have

mean concentrations of 1,2-dichloropropane above 0.005 mg/L. About 5 surface water systems serving

almost 298,000 people had estimated mean concentrations greater than 0.0005 mg/L. An estimated 5

surface water systems, serving approximately 299,000 people, had mean concentrations greater than

0.0004 mg/L.

Table 4.7-6: Estimated National 1,2-Dichloropropane Occurrence - Systems and Population

Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 1 0 - 6 < 100 0 - 100

0.0005 21 12 - 32 14,300 1,800 - 55,600

0.0004 28 15 - 41 38,200 4,000 - 82,400

Surface Water

0.005 1 0 - 4 82,100 0 - 295,500

0.0005 5 4 - 7 297,900 295,500 - 298,600
Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Occurrence Summary and Use Support Document March 2002 400

0.0004 5 4 - 11 299,000 295,500 - 318,300

Combined Ground

& Surface Water

0.005 2 0 - 6 76,200 0 - 273,900

0.0005 25 15 - 35 292,000 275,800 - 337,000

0.0004 33 21 - 47 319,500 279,700 - 380,600

4.7.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of 1,2-dichloropropane in drinking water are

also reviewed. Previously compiled occurrence information on 1,2-dichloropropane, from an OGWDW

summary document entitled “Occurrence of Synthetic Organic Chemicals in Drinking Water, Food, and

Air” (USEPA, 1987), is presented in this section. This variety of studies and information are presented

regarding levels of 1,2-dichloropropane in drinking water, with the scope of the reviewed studies ranging

from national to regional. Note that none of the studies presented in the following section provide the

quantitative analytical results or comprehensive coverage that would enable direct comparison to the

occurrence findings estimated with the cross-section occurrence data presented in Section 4.7.4. These

additional studies, however, do enable a broader assessment of the Stage 2 occurrence estimates

presented for this Six-Year Review. All the following information in Section 4.7.5 is taken directly from

“Occurrence of Synthetic Organic Chemicals in Drinking Water, Food, and Air” (USEPA, 1987).

4.7.5.1 Groundwater – National Studies

The Ground Water Supply Survey was conducted from December 1980 to December 1981 to develop

data on the occurrence of volatile organic chemicals in the nation's ground water supplies (USEPA, 1983;

Westrick et al., 1983, all as cited in USEPA, 1987). The GWSS involved the sampling of 945 water

supply- systems, of which 466 were selected randomly while the remaining 479 systems were chosen by

the States as having a high potential for contamination. DCP was observed in 6 of the 466 randomly

selected systems. One of the six positive values obtained came from a supply serving fewer than 10,000

persons; the positive value was 0.75 :g/L. The other five positive values, found in supplies serving

greater than 10,000 people, had a median value of 0.86 :g/L (range = 0.48 to 21 :g/L). In the nonrandom

portion of the GWSS, DCP was detected in 7 of 479 systems sampled. Three positives were from systems

serving fewer than 10,000 people, and had values of 0.51, 1.2, and 1.4 :g/L. The four positive values

from supplies serving more than 10,000 people had a median value of 0.7 :g/L (range = 0.21 to 18 :g/L).

The quantitation limit for both random and nonrandom systems was 0.2 :g/L.

The American Water Works Association (AWWA) surveyed water utilities nationwide that were

monitoring for unregulated contaminants including 1,2-dichloropropane in raw and finished water from

ground and surface water sources. Of the 114 utilities monitoring for 1,2-dichloropropane, 3 utilities

whose primary water source is ground water detected 1,2-dichloropropane in 1 of 1,382 raw water

samples and 5 of 5 finished water samples. Concentrations ranged from less than 1.0 to 4.0 in finished

water. The concentration detected in raw water was 3.0 :g/L. No detection limits were reported

(AWWA, 1988, as cited in USEPA, 1987). The American Water Works Association advises caution in

utilizing this data as it appears there are discrepancies in the units reported by some utilities

(Achtermann, 1990, as cited in USEPA, 1987).
Occurrence Summary and Use Support Document March 2002 401

4.7.5.2 Groundwater – Regional Studies

Twelve towns in Connecticut were examined by the Connecticut Agricultural Experiment Station in New

Haven, Connecticut (Waggoner, 1985, as cited in USEPA, 1987). Drinking water wells representing the

major drinking water sources for those 12 towns were analyzed during 1984-1985. The population served

by the wells sampled exceeded 570,000 persons. None of the wells, at a total of 42 locations, were

positive for DCP. The detection limit was 0.05 :g/L.

Community ground water wells were sampled during 1982 in Visalia (Tulare County) and Reedley

(Fresno County), California, as part of the USEPA National Groundwater Monitoring Program (Cohen

and Bowes, 1984, as cited in USEPA, 1987). DCP was found in three samples, at a mean concentration

of 9.93 :g/L (range = 1.0 to 25.9 :g/L). The total number of samples, number of locations, and detection

limit were not reported.

Domestic and irrigation wells were sampled for DCP on Long Island, New York, by the Suffolk County

Department of Health Services (Holden, 1986, as cited in USEPA, 1987). Out of 1,000 samples taken,

about 500 were contaminated with DCP at concentrations ranging from 30 to 300 :g/L. More specific

information was not reported.

Community wells in Del Norte County, California, were sampled in 1983 for DCP (Cohen and Bowes,

1984, as cited in USEPA, 1987). Twenty-five of 37 samples were found positive, with a maximum

concentration of greater than 10.0 :g/L. No other information on this study was reported.

Private domestic wells from three other California counties were analyzed as part of the California State

Board Toxic Substances Control Program during 1982 (Cohen and Bowes, 1984, as cited in USEPA,

1987). DCP was found in 12 out of 95 samples, with a range of concentrations between 0.4 and 16 :g/L.

The mean concentration and detection limit were not reported.

4.7.5.3 Surface Water – National Study

The American Water Works Association (AWWA) surveyed water utilities nationwide that were

monitoring for unregulated contaminants including 1,2-dichloropropane in raw and finished water from

ground and surface water sources. Of the 114 utilities monitoring for 1,2-dichloropropane, 10 utilities

whose primary water source is surface water detected 1,2-dichloropropane in 793 of 11,394 raw water

samples and 257 of 885 finished water samples. Concentrations ranged from 0.1 :g/L to 15.0 :g/L in raw

water samples and less than 0.1 :g/L to 9.0 :g/L in finished water samples. No detection limits were

reported (AWWA, 1988, as cited in USEPA, 1987). The American Water Works Association advises

caution in utilizing this data as it appears there are discrepancies in the units reported by some utilities

(Achtermann, 1990, as cited in USEPA, 1987).

4.7.5.4 Surface Water – Regional Studies

To assemble a database which would reflect the status of Great Lakes drinking water quality, the

Canadian Public Health Association gathered data from October 1984 through August 1985. The data

collected covered the period from the mid 1970s to early 1985. A research team, appointed by the

Association, reviewed data on the quality of water at 31 representative Canadian and United States

communities and 24 offshore sites to evaluate the human health implications.
Occurrence Summary and Use Support Document March 2002 402

For each of the 31 communities, data consisted of: 1) background information on the community; 2)

treatment plant schematics and associated treatment process information; and 3) water quality data.

Water sample types included raw water (treatment plant intake), distribution water (treated water), and

tap water. Water quality data collected included general parameters (e.g., alkalinity, turbidity),

microbiological and radiological parameters, inorganic parameters, and organic parameters (including

volatiles, base/neutrals, pesticides and PCBs, and phenols and acids). For each parameter, the water type,

time period, concentration (mean, range), number of samples, and detection limit were recorded.

For most of the volatile organics, including DCP, the available data indicated that these contaminants did

not occur at significant levels in the raw, treated, or tap water. Most of the values found were “not

detected” or near the detection limit (Canadian Public Health Association, 1986, as cited in USEPA,

1987).

4.7.5.5 Unidentified Sources

Drinking water samples were collected and analyzed in the Love Canal area, New York, during 1980 by

Barkley et al. (1980, as cited in USEPA, 1987). The only information reported was that one sample

contained a DCP concentration of 1,200 :g/L (detection limit not given).

4.7.6 Conclusion

1,2-Dichloropropane was mostly used captively by manufacturers as a chemical intermediate in the

production of chlorinated products. At one time, it was also used in various consumer products such as

paint and finish removers and was found in soil fumigants as a processing byproduct. Domestic

production of 1,2-dichloropropane as an isolated chemical ceased in 1991. 1,2-Dichloropropane is also a

TRI chemical. Industrial releases of 1,2-dichloropropane have occurred since 1988 in 15 States. 1,2-

Dichloropropane was an analyte for the NAWQA and NPDES ambient occurrence studies. In the

NAWQA study, 1,2-dichloropropane was detected in 0.84% of urban wells and 0.92% of rural wells,

with median detection values of 0.2 :g/L and 0.5 :g/L, respectively. In the Stage 2 analysis of 16-State

occurrence of 1,2-dichloropropane, 0.00358% of combined ground water and surface water systems

serving 0.0358% of the population exceeded the MCL of 0.005 mg/L. Nationally, 2 ground water and

surface water systems combined (serving approximately 76,200 people) are estimated to have levels

greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, TRI releases have been reported for 1,2-dichloropropane from 15 States,

including 5 of 16 cross-section States. As an isolated chemical, 1,2-Dichloropropane is no longer

produced in any State. The cross-section should adequately represent the occurrence of 1,2-

dichloropropane on a national scale based upon the use, production, and release patterns of the 16-State

cross-section in relation to the patterns observed for all 50 States. 

4.7.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1989. Toxicological Profile for 1,2-

Dichloropropane. U.S. Department of Health and Human Services, Public Health Service. 118

pp. + Appendices. Available on the Internet at http://www.atsdr.cdc.gov/toxprofiles/tp134.pdf.
Occurrence Summary and Use Support Document March 2002 403

Dow Chem Co. 1983. Letter summarizing the EPA/DOW Chemical Co. meeting regarding the

manufacture of 1,2-dichloropropane. OTS Section 4 submission by Dow Chemical Co.

Document No. 40-8367072. Microfiche No, OTS 0511731.

Hazardous Substances Data Bank (HSDB). 1988. Hazard Substances Data Bank. 

On-line: July 27, 1988.

International Agency for Research on Cancer (IARC). 1986. IARC Monograph on the Evaluation of

Carcinogenic Risks to Humans: Some halogenated hydrocarbon and pesticide exposure. v. 41,

pp. 131-147.

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 

67 pp.

Meister, R.T. 1987. Farm chemicals handbook '87. Willoughby, OH: Meister Publishing Co.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

SRI. 1988. Directory of Chemical Producers: United States of America. p. 921.

USEPA. 1986. Toxic substances; 1,2-dichloropropane; testing requirements. Final rule. Fed Reg

51:32079-32087.

USEPA. 1987. Occurrence of Synthetic Organic Chemicals in Drinking Water, Food, and Air. Office

of Drinking Water, USEPA. July 1987.

USEPA. 1989. Comments of the Dow Chemical Company on ATSDR's Toxicology Profile for 1,2-

Dichloride. Submitted to ATSDR May 1, 1989.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. Consumer Factsheet on: 1,2-Dichloropropane. Available on the Internet at:

http://www.epa.gov/safewater/dwh/c-voc/12-dich3.html, last updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

United States International Trade Commission (USITC). 1987. Synthetic Organic Chemicals: United

States Production and Sales, 1986. USITC Pub 2009. pp. 233; 238.

Still need references cited in USEPA, 1987
Occurrence Summary and Use Support Document March 2002 404

4.8 Tetrachloroethylene

Table of Contents

4.8.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405

4.8.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

4.8.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

4.8.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 408

4.8.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412

4.8.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420

4.8.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421

Tables and Figures

Table 4.8-1: Tetrachloroethylene Manufacturers and Processors by State . . . . . . . . . . . . . . . . . . . . . 406

Table 4.8-2: Environmental Releases (in pounds) for Tetrachloroethylene 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

Table 4.8-3: Stage 1 Tetrachloroethylene Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

Table 4.8-4: Stage 1 Tetrachloroethylene Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

Table 4.8-5: Stage 2 Estimated Tetrachloroethylene Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

Table 4.8-6: Stage 2 Estimated Tetrachloroethylene Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

Table 4.8-7: Estimated National Tetrachloroethylene Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
Occurrence Summary and Use Support Document March 2002 405

4.8.1 Introduction, Use and Production

Tetrachloroethylene is a manufactured organic compound with the chemical formula C2Cl4. It is a

nonflammable liquid at room temperature, evaporates easily into the air, and has a sharp, sweet odor. 

The major routes of entry of tetrachloroethylene to drinking water are a consequence of its production

and industrial use. It is expected that discharges into surface water would volatilize into the atmosphere

fairly rapidly. It is expected that discharges during production and use, and leaching into groundwater

from wastes deposited in landfills are primary causes of tetrachloroethylene contamination of drinking

water. Additionally, tetrachloroethylene may enter drinking water through the use of vinyl-lined A/C

pipe (JRB Associates, 1983). Other names for tetrachloroethylene include 1,1,2,2,-tetrachloroethylene,

perchloroethylene, PCE, perc, tetrachloroethene, perclene, and perchlor (ATSDR, 1997). 

Tetrachloroethylene is a commercially important chlorinated hydrocarbon solvent and chemical

intermediate in the production of chlorofluorocarbons. It is used as a dry cleaning and textile-processing

solvent and for vapor degreasing in metal-cleaning operations. Tetrachloroethylene was first

commercially produced in the U.S. in 1925. There has been an overall decline in production of about

50% between 1983 and 1993, from 547 to 271 million pounds (ATSDR, 1997). In 1986, production of

tetrachloroethylene totaled 405 million pounds (USEPA, 2001) and 1991 production has been reported as

310 million pounds. The major reasons for the decline in production are solvent recycling and reduced

demand for chlorofluorocarbons (USEPA, 1994). 

The 1995 Directory of Chemical Producers in the U.S. lists three major manufacturers of

tetrachloroethylene with a total annual capacity of 490 million pounds. Tetrachloroethylene is also

produced naturally by various temperate and subtropical marine macroalgae at the rate of 0.0026-8.2 ng/g

fresh weight/hour, a potentially significant amount in the global chlorine budget (ATSDR, 1997).

It is widely used for dry cleaning of fabrics and for metal-degreasing operations and is also used as a

starting material (building block) for making other chemicals and in some consumer products (ATSDR,

1997). In 1995, the estimated end-use breakdown for tetrachloroethylene was as follows: 55% as a

chemical intermediate, 25% for metal cleaning and vapor degreasing, 15% for dry cleaning and textile

processing, and 5% miscellaneous (ATSDR, 1997). In small amounts, tetrachloroethylene is used in

rubber coatings, solvent soaps, printing inks, adhesives and glues, sealants, polishes, lubricants, and

pesticides (NSC, 2001). 

Other uses of tetrachloroethylene include use in veterinary medicine as an anthelmintic; as a fumigant for

insects and rodents; as a vermifuge; as a heat-transfer medium; in copying machines; in the manufacture

of paint removers; and in removing soot from industrial boilers (NTP, 1991). Formerly

tetrachloroethylene was used as an anthelmintic against hookworms, intestinal flukes, and nematodes; but

it has since been supplanted by drugs that are less toxic and easier to administer (ATSDR, 1997).

Table 4.8-1 shows the number of facilities in each State that manufacture and process

tetrachloroethylene, the intended uses of the product, and the range of maximum amounts derived from

the Toxics Release Inventory (TRI) of EPA (ATSDR, 1997). 
Occurrence Summary and Use Support Document March 2002 406

Table 4.8-1: Tetrachloroethylene Manufacturers and Processors by State

Statea Number of facilities Range of maximum amounts on

site in thousands of poundsb Activities and usesc

AL 5 1-100 2,3,4,10,13

AR 4 1-100 2,3,8,12,13

AZ 2 1-10 13

CA 63 0-10,000 2,3,4,7,8,9,10,11,12,13

CO 2 1-100 12,13

CT 16 1-1,000 11,12,13

FL 11 1-1,000 8,11,12,13

GA 12 0-1,000 2,3,5,8,10,11,13

IA 7 0-1,000 11,12,13

IL 35 0-10,000 2,3,4,8,10,11,12,13

IN 26 0-100 2,3,8,10,11,12,13

KS 8 1-10,000 1,3,4,7,8,11,12,13

KY 10 1-1,000 1,3,7,8,11,12,13

LA 16 0-50,000 1,3,4,5,6,7,8,9,11,12,13

MA 7 1-1,000 8,10,12,13

MD 2 1-10 12,13

ME 1 1-10 12

MI 10 1-1,000 7,8,10,11,12,13

MN 11 1-100 2,3,11,12,13

MO 12 1-1,000 8,11,12,13

MS 5 10-1,000 8,11,12,13

MT 2 1-100 11,13

NC 20 0-1,000 2,3,5,7,8,11,12,13

NE 4 1-100 12,13

NH 4 1-100 13

NJ 6 0-100 8,11,12,13

NY 20 0-1,000 8,10,11,12,13

OH 48 0-1,000 2,3,8,10,11,12,13

OK 8 1-1,000 11,12,13

OR 1 10-100 11

PA 18 0-10,000 8,10,11,12,13

PR 2 0-10 2,5,8,13

SC 12 1-100 8,12,13

TN 8 1-1,000 8,11,12,13

TX 25 1-50,000 1,2,3,4,5,6,7,8,10,11,12,13

UT 3 1-100 11,13

VA 7 0-1,000 2,3,9,11,13

VT 1 100-1,000 12

WA 1 1-10 12

WI 12 1-100 7,8,10,12,13

WY 1 0-1 11,13

a

Post office State abbreviations used

b

Data in TRI are maximum amounts on site at each facility

c

Activities/Uses include:

1. Produce 8. As a formulation component

2. Import 9. As an article component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a by-product 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

Source: ATSDR, 1997 compilation of TRI93 1995 data
Occurrence Summary and Use Support Document March 2002 407

4.8.2 Environmental Release

Tetrachloroethylene is listed as a Toxics Release Inventory (TRI) chemical. Table 4.8-2 illustrates the

environmental releases for tetrachloroethylene from 1988 - 1999. (Tetrachloroethylene data are only

available for these years.) Air emissions constitute the vast majority of the on-site releases, with a steady

decrease over the years. The decrease in air emissions, as well as surface water discharges and a general

decrease in off-site emissions (including metals or metal compounds transferred off-site), have

contributed to decreases in tetrachloroethylene total on- and off-site releases in recent years. Releases to

land (such as spills or leaks within the boundaries of the reporting facility) display no particular trend,

and underground injection has fluctuated between 5,000 and 20,000 pounds, with the exception of high

levels of releases in 1988-1989. These TRI data for tetrachloroethylene were reported from 48 States

(with the exceptions of Alaska and Wyoming), Puerto Rico, and the Virgin Islands (USEPA, 2000). 

Thirty-one of the 48 States reported every year. All 16 of the cross-section States (used for analyses of

tetrachloroethylene occurrence in drinking water; see Section 4.8.4) reported releases of

tetrachloroethylene. (For a map of the 16-State cross-section, see Figure 1.3-1.)

Table 4.8-2: Environmental Releases (in pounds) for Tetrachloroethylene in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 3,648,732 1,793 8,897 19,885 27,966 3,707,273

1998 5,463,597 1,490 5,916 2,992 130,927 5,604,922

1997 7,213,469 2,282 15,118 5,074 29,228 7,265,171

1996 7,995,845 1,561 13,436 5,472 23,212 8,039,526

1995 9,674,185 2,407 20,481 6 78,953 9,776,032

1994 10,826,150 3,877 4,051 4,349 80,255 10,918,682

1993 11,357,864 10,157 15,041 618,026 56,340 12,057,428

1992 12,816,529 10,322 12,780 9,754 113,324 12,962,709

1991 17,384,881 7,453 14,005 23,309 115,933 17,545,581

1990 23,000,633 21,510 11,012 1,260 796,846 23,831,261

1989 27,813,294 53,940 50,000 10,791 1,044,249 28,972,274

1988 36,124,485 33,314 72,250 82,144 1,385,378 37,697,571

 Source: USEPA, 2000 

4.8.3 Ambient Occurrence

Tetrachloroethylene was detected in 67 out of 403 wells (16.6%) in urban areas of the local, State, and

federal data set compiled by NAWQA. The minimum and maximum concentrations detected were 0.2

:g/L and 260 :g/L, respectively. The median value of detection concentrations was 1.1 :g/L. 

Tetrachloroethylene was also detected in 64 of the 2,526 wells (2.5%) with analysis in rural areas. The

minimum and maximum concentrations detected were 0.2 :g/L and 250 :g/L, respectively. The median

value of detection concentrations was 0.8 :g/L. These data (urban and rural) represent untreated ambient

ground water of the conterminous United States for the years 1985-1995 (Squillace et al., 1999).
Occurrence Summary and Use Support Document March 2002 408

Tetrachloroethylene was also an analyte in both the NURP and NPDES data (Lopes and Dionne, 1998). 

In a comparison of the two data sets, the frequency of detection of tetrachloroethylene for NURP was

5%, while the frequency of detection for NPDES was 8%. The NURP study found tetrachloroethylene in

urban runoff. The minimum and maximum concentrations detected were 4.5 :g/L and 43 :g/L,

respectively, with no mean value reported. The NPDES related investigations analyzing urban and

highway runoff detected tetrachloroethylene. The minimum and maximum concentrations detected were

<0.2 :g/L and 42 :g/L, respectively, with no mean value reported. The use of the land from which the

samples were taken was unspecified.

4.8.3.1 Additional Ambient Occurrence Data

A summary document, entitled “Occurrence of Tetrachloroethylene in Drinking Water, Food and Air”

(JRB Associates, 1983), was previously prepared for past USEPA assessments of tetrachloroethylene. 

However, no information on the ambient occurrence of tetrachloroethylene was included in that

document. (The document did include information regarding tetrachloroethylene occurrence in drinking

water, which is discussed in Section 4.8.5 of this report.)

4.8.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of tetrachloroethylene occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to two concentration thresholds of interest: 0.005 mg/L; and 0.0005 mg/L.

All sixteen cross-section State data sets contained occurrence data for tetrachloroethylene. These data

represent more than 195,000 analytical results from approximately 22,000 PWSs during the period from

1984 to 1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs

vary by State, although the State data sets have been reviewed and checked to ensure adequacy of

coverage and completeness. The overall modal detection limit for tetrachloroethylene in the 16 crosssection States is equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)

4.8.4.1 Stage 1 Analysis Occurrence Findings

Table 4.8-3 illustrates the occurrence of tetrachloroethylene in drinking water for the public water

systems in the 16-State cross-section. The percentage of total ground and surface water PWSs with any

analytical results exceeding the MCL (0.005 mg/L) was equal to 0.778% (a total of 174 systems). 

Approximately 2.89% of total ground and surface water systems (646 PWSs) had any analytical results

greater than the modal detection limit (0.0005 mg/L). 

A greater proportion of surface water systems, as compared to ground water systems, exceeded each

threshold. Yet, a greater number of ground water systems exceeded each threshold, as compared to

surface water systems. Approximately 0.692% of ground water PWSs (144 systems) had any analytical

results exceeding the MCL, compared to 1.91% of surface water systems (30 systems). The percentage

of ground water PWSs with any analytical results exceeding 0.0005 mg/L was equal to about 2.72% (565

ground water systems). Close to 5.2% of surface water PWSs (a total of 81 systems) had at least one

analytical result greater than 0.0005 mg/L.
Occurrence Summary and Use Support Document March 2002 409

Table 4.8-3: Stage 1 Tetrachloroethylene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.692% 144

0.0005 2.72% 565

Surface Water

0.005 1.91% 30

0.0005 5.17% 81

Combined Ground &

Surface Water

0.005 0.778% 174

0.0005 2.89% 646

Reviewing tetrachloroethylene occurrence by PWS population served (Table 4.8-4) shows approximately

13.5% of the total 16-State cross-section population (almost 15 million people) was served by PWSs with

at least one analytical result greater than the MCL. Approximately 22.9% of the population (over 25

million people) was served by systems with analytical results greater than 0.0005 mg/L.

About 7.13% of the population served by ground water systems (over 3.5 million people) was exposed to

tetrachloroethylene levels above the MCL. Approximately 19.5% of the population (almost 10 million

people) was served by ground water systems with at least one analytical result greater than 0.0005 mg/L.

Approximately 18.6% of the population (over 11 million people) was served by surface water PWSs with

at least one analytical results greater than the MCL. About 25.7% of the population (almost 16 million

people) was served by surface water PWSs with any analytical results greater than 0.0005 mg/L.

Table 4.8-4: Stage 1 Tetrachloroethylene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served

by Systems

Exceeding Threshold 

Total Population Served 

by Systems Exceeding

Threshold

Ground Water

0.005 7.13% 3,524,300

0.0005 19.5% 9,633,800

Surface Water

0.005 18.6% 11,390,000

0.0005 25.7% 15,717,500

Combined Ground &

Surface Water

0.005 13.5% 14,914,300

0.0005 22.9% 25,351,400
Occurrence Summary and Use Support Document March 2002 410

4.8.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.8-5 and 4.8-6. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

Approximately 45 (0.202% of all) ground water and surface water PWSs in the 16 States were estimated

to have mean concentrations of tetrachloroethylene above 0.005 mg/L. The percentage of PWSs with

estimated mean concentrations exceeding 0.0005 mg/L was about 1.62% of PWSs in the 16 States (362

systems).

Similar to the Stage 1 analysis, Stage 2 analysis estimated a greater proportion of surface water systems,

as compared to ground water systems, exceeding each threshold, but a greater number of ground water

systems exceeding each threshold. Approximately 40 (0.194% of) ground water systems in the 16 States

had estimated mean concentrations of tetrachloroethylene above 0.005 mg/L, compared to approximately

5 (0.317% of) surface water systems in the 16 States. The estimated mean concentration values for

approximately 324 (1.56%) ground water PWSs in the 16 States exceeded 0.0005 mg/L. About 39

(2.48% of) surface water systems in the 16 States had estimated mean concentrations exceeding the

modal detection limit.

Table 4.8-5: Stage 2 Estimated Tetrachloroethylene Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.194% 0.154% - 0.231% 40 32 - 48

0.0005 1.56% 1.43% - 1.68% 324 297 - 349

Surface Water

0.005 0.317% 0.191% - 0.447% 5 3 - 7

0.0005 2.48% 2.17% - 2.87% 39 34 - 45

Combined Ground

& Surface Water

0.005 0.202% 0.166% - 0.237% 45 37 - 53

0.0005 1.62% 1.50% - 1.74% 362 335 - 390

Reviewing tetrachloroethylene occurrence by PWS population served (Table 4.8-6) shows that over

757,000 (0.685% of) people in the 16 States were served by systems with mean tetrachloroethylene

concentrations above 0.005 mg/L. When evaluated relative to a threshold of 0.0005 mg/L, the percent of

population exposed increased significantly to about 12.2% (approximately 13.5 million people served in

the 16 States).
Occurrence Summary and Use Support Document March 2002 411

Of the 16-State cross-section population served by ground water, approximately 0.833% of the

population was served by PWSs (almost 412,000 people served in the 16 States) with estimated mean

concentrations of tetrachloroethylene above 0.005 mg/L. An estimated 3.6 million (7.36% of) people

served by ground water systems in the 16 States were exposed to tetrachloroethylene above 0.0005 mg/L. 

Approximately 0.565% of the population (345,600 people in the 16 States) was served by surface water

PWSs with estimated mean concentrations greater than 0.005 mg/L. The percentage of population served

by surface water PWSs with estimated mean concentrations greater than 0.0005 mg/L increased

dramatically to approximately 16.2% (almost 10 million people in the 16 States).

Table 4.8-6: Stage 2 Estimated Tetrachloroethylene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.833% 0.642% - 1.10% 411,600 317,200 - 544,500

0.0005 7.36% 6.72% - 8.32% 3,636,800 3,319,200 - 4,112,100

Surface Water

0.005 0.565% 0.218% - 0.777% 345,600 133,500 - 475,400

0.0005 16.2% 15.2% - 18.6% 9,875,900 9,288,800 - 11,392,400

Combined Ground

& Surface Water

0.005 0.685% 0.470% - 0.873% 757,200 519,700 - 965,100

0.0005 12.2% 11.5% - 13.7% 13,510,200 12,747,300 - 15,102,200

4.8.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 132 PWSs serving almost 1.5 million people nationally could be exposed to

tetrachloroethylene concentrations above 0.005 mg/L. About 1,053 systems serving over 26 million

people nationally had estimated mean concentrations greater than 0.0005 mg/L. (See Section 1.4 for a

description of how Stage 2 16-State estimates are extrapolated to national values.)

For ground water systems, an estimated 115 PWSs serving about 713,800 people nationally had mean

concentrations greater than 0.005 mg/L. Approximately 925 systems serving about 6.3 million people

nationally had estimated mean concentration values that exceeded 0.0005 mg/L. 

Approximately 18 surface water systems serving about 719,500 people nationally were estimated to have

mean concentrations of tetrachloroethylene above 0.005 mg/L. About 139 surface water systems serving

almost 21 million people had estimated mean concentrations greater than 0.0005 mg/L.
Occurrence Summary and Use Support Document March 2002 412

Table 4.8-7: Estimated National Tetrachloroethylene Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 115 91 - 137 713,800 550,200 - 944,200

0.0005 925 849 - 997 6,307,000 5,756,100 - 7,131,300

Surface Water

0.005 18 11 - 25 719,500 278,000 - 989,800

0.0005 139 121 - 161 20,563,200 19,340,900 - 23,720,900

Combined Ground

& Surface Water

0.005 132 108 - 154 1,458,900 1,001,400 - 1,859,300

0.0005 1,053 974 - 1,134 26,029,600 24,559,800 - 29,096,900

4.8.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of tetrachloroethylene in drinking water are also

reviewed. Previously compiled occurrence information, from an OGWDW summary document entitled

“Occurrence of Tetrachloroethylene in Drinking Water, Food, and Air” (JRB Associates, 1983), is

presented in this section. This variety of studies and information are presented regarding levels of

tetrachloroethylene in drinking water, with the scope of the reviewed studies ranging from national to

regional. Note that none of the studies presented in the following section provide the quantitative

analytical results or comprehensive coverage that would enable direct comparison to the occurrence

findings estimated with the cross-section occurrence data presented in Section 4.8.4. These additional

studies, however, do enable a broader assessment of the Stage 2 occurrence estimates presented for this

Six-Year Review. All the following information in Section 4.8.5 is taken directly from “Occurrence of

Tetrachloroethylene in Drinking Water, Food, and Air” (JRB Associates, 1983). 

JRB Associates (1983) found two major types of data available that are potentially useful for describing

the occurrence of tetrachloroethylene in the nation's public drinking water supplies. First, there are

several Federal surveys in which a number of public water supplies from throughout the U.S. were

selected for analysis of chemical contamination, including tetrachloroethylene. Second, data are

available from State surveys and from State investigations of specific incidents of known or suspected

contamination of a supply. For accomplishing the basic objectives of this study, namely to estimate the

number of public water supplies nationally within the various source and size categories contaminated

with tetrachloroethylene, the distribution of tetrachloroethylene concentrations in those supplies, and the

number of individuals exposed to those concentrations, it was determined that the Federal survey data

provides the most suitable data base. The State data tend to be poorly described with respect to the

source and size categories of the supplies examined and the sampling and analysis methods used for

determining contaminant levels. The lack of source and system size information precludes using the data

for estimating levels in public water supplies of similar characteristics. The absence of details on

sampling and analysis methods precludes evaluating those data for their qualitative and quantitative

reliability. Also, because much of the State data are from investigations in response to incidents of

known or suspected contamination (e.g., spills), they were judged to be not representative of contaminant
Occurrence Summary and Use Support Document March 2002 413

levels in the nation's water supplies in general. Although they are not used with the Federal data for the

purpose of estimating contamination levels nationally, the available State data are presented here to

provide some additional perspective on tetrachloroethylene occurrence in drinking water.

Data are presented only on drinking water samples taken from a consumer's tap (i.e., distribution water

samples) or on treated water samples taken at the water supply (i.e., finished water samples) because

these are considered to be most representative of the water consumed by the public. No data on raw (i.e.,

untreated) water are presented. It is recognized that for some groundwater supplies where no treatment

of the water occurs, samples identified as raw may be representative of water consumed by the users of

the supply. However, it was generally not possible to differentiate between those groundwater supplies

that do and those that do not treat raw water from the available survey data.

4.8.5.1 Overview and Quality Assurance Assessment of Federal Drinking Water Surveys

Five Federal drinking water surveys provide data on tetrachloroethylene: the National Organic

Monitoring Survey (NOMS), the National Screening Program for Organics in Drinking Water (NSP), the

1978 Community Water Supply Survey (CWSS), the Rural Water Survey (RWS), and the Groundwater

Supply Survey (GWSS). The terms used in this report are those used in the individual surveys,

recognizing that they may not always correspond to strict technical definitions.

The National Organic Monitoring Survey (NOMS) was conducted to identify contaminant sources, to

determine the frequency of occurrence of specific drinking water contaminants, and to provide data for

the establishment of maximum contaminant levels (MCL's) for various organic compounds in drinking

water (Brass et al., 1977, as cited in JRB Associates, 1983). The NOMS was conducted in three phases:

March-April 1976, May-July 1976, and November 1976-January 1977. For tetrachloroethylene,

qualitative results are available for Phase II and quantitative results for Phase III. Tetrachloroethylene

was not analyzed for in Phase I. Finished drinking water samples from 113 communities were analyzed

for 21 different compounds. Of the 113 community supplies sampled, 18 had groundwater sources, 91

had surface water sources, and 4 had a mixed groundwater/surface water source. In Phase III, only 14

groundwater supplies had data available for tetrachloroethylene.

The analytical results of the NOMS were made available in printed form by EPA's Technical Support

Division, Office of Drinking Water. Additional information on the locations and source of the supplies,

and on the populations served by the supplies in the NOMS were provided by Wayne Mello (1983, as

cited in JRB Associates, 1983) at EPA's Technical Support Division, Office of Drinking Water. A single

value for tetrachloroethylene was reported for each supply studied in the NOMS. 

The National Screening Program for Organics in Drinking Water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water

systems in 33 States for 51 organic chemical contaminants. Data are available for tetrachloroethylene on

finished water samples from 12 groundwater and 106 surface water supplies. 

In the Community Water Supply Survey (CWSS), carried out in 1978, 106 surface water supplies, 330

groundwater supplies, and 16 supplies with mixed sources were examined for volatile organic chemical

contamination. Samples were taken of raw, finished, and distribution water. Only the latter two types of

water are considered here. Data for tetrachloroethylene in finished and/or distribution samples were

obtained from a total of 316 groundwater and 105 surface water supplies.
Occurrence Summary and Use Support Document March 2002 414

The Rural Water Survey (RWS), conducted in 1978, was carried out in response to Section 3 of the Safe

Drinking Water Act, which mandated that EPA “conduct a survey of the quantity, quality, and

availability of rural drinking water supplies.” Drinking water samples were collected for analysis of

inorganic chemicals, pesticides, and VOCs from 2,655 households throughout the United States located

in areas defined in the survey as rural. Of these, a total of 855 household samples were examined for

VOCs. The majority of these samples were obtained from households receiving water from private wells

or small supplies serving fewer than 25 people. For tetrachloroethylene, data are available in the RWS

for 207 groundwater and 45 surface water supplies serving 25 or more people.

The RWS did not obtain data on the number of persons in each household served by the supplies. 

However, data were obtained on the number of service connections at each supply. With the input of Dr.

Bruce Brower at Cornell University, who participated in the statistical analysis of the RWS for

parameters other than VOCs, the population served by each supply was estimated from the average

number of persons per household (3.034) observed in the survey. A single value was reported for each

household; in some cases it was necessary to average two or three households obtaining water from the

same supply. Brass (1981, as cited in JRB Associates, 1983) cautions that the RWS water samples were

analyzed 6 to 27 months after collection and that degradation of some VOCs may have occurred during

this holding period.

The Groundwater Supply Survey (GWSS) was conducted from December 1980 to December 1981 to

develop additional data on the occurrence of volatile organic chemicals in the nation's groundwater

supplies (Westrick et al., 1983, as cited in JRB Associates, 1983). It was hoped that this study would

stimulate State efforts toward the detection and control of groundwater contamination and the

identification of potential chemical “hot spots.” A total of 945 systems were sampled, of which 466 were

chosen at random. The remaining 479 systems were chosen non-randomly based on information from

States encouraged to identify locations believed to have a higher than normal probability of VOC

contamination (e.g., locations near landfills or industrial activity). The file provided a single analytical

result for each supply sampled. One sample of finished water was collected from each supply at a point

near the entrance to the distribution system. 

Each of the drinking water surveys was evaluated with respect to the validity of the reported occurrence

data for a number of organic chemicals, including tetrachloroethylene. The evaluations were carried out

by analyzing information about the procedures used for collection and analysis of samples as well as the

quality control protocols used. The analyzed compounds dealt with in each study were assigned one of

three possible ratings: quantitatively acceptable, qualitatively acceptable (i.e., the substance measured

was tetrachloroethylene), and totally unacceptable. In the case of tetrachloroethylene, a qualitatively

acceptable rating was given for data from the NOMS, NSP, CWSS, and RWS because of suspected

biodegradation of the samples, which were held unrefrigerated for prolonged periods before analysis

(particularly CWSS and RWS). Tetrachloroethylene values in excess of the quantitation limit reported

for some samples in these studies are qualitatively valid and can be taken as minimum values,

representative of samples which probably originally contained tetrachloroethylene at higher

concentrations. In the case of the GWSS, all data were rated both quantitatively and qualitatively

acceptable.

4.8.5.2 Groundwater – Federal Surveys

The National Organic Monitoring Survey (NOMS), the National Screening Program for Organics in

Drinking Water (NSP), the Community Water Supply Survey (CWSS), the Rural Water Survey (RWS),
Occurrence Summary and Use Support Document March 2002 415

and the Groundwater Supply Survey (GWSS) all contain data concerning the levels of

tetrachloroethylene in groundwater supplies from across the country.

Tetrachloroethylene was not analyzed for in Phase I of NOMS (March to April 1976). In NOMS Phase

II (May to July 1976), a qualitative assessment that tetrachloroethylene was present in 6 of the 18

groundwater supplies sampled was made on the basis of the presence of a peak on the gas chromatograph

at the appropriate retention time for tetrachloroethylene. As indicated previously, a rigorous analysis of

all samples was not made, and some samples with smaller tetrachloroethylene peaks may have been

overlooked. Samples analyzed during Phase III of the study (November 1976 to January 1977) proved

positive for two of the 14 systems for which data are available, with levels of 1.1 and 3.1 :g/L. The

minimum quantifiable limit for tetrachloroethylene was 0.2 :g/L in Phase III.

Twelve groundwater supplies were tested for tetrachloroethylene contamination in the NSP. Of these 12

systems, three were found to be contaminated with tetrachloroethylene at levels of 0.1, 0.2, and 0.7 :g/L. 

The quantification limit for tetrachloroethylene was 0.1 :g/L.

The 1978 CWSS provided information on tetrachloroethylene levels in 316 groundwater systems. Of

these systems, 18 contained detectable levels of tetrachloroethylene, with values ranging from 0.51-15.3

:g/L. The two highest values were 3.1 :g/L and 15.3 :g/L; all other values were less than 3.0 :g/L. The

mean value was 2.1 :g/L with a standard deviation of 3.4 :g/L; the median value was 1.2 :g/L. The

minimum quantitation limit for tetrachloroethylene in the CWSS was 0.5 :g/L.

The RWS examined 207 groundwater supplies for tetrachloroethylene and found 7 to have levels above

the minimum quantification limit range of 0.5-1.5 :g/L. The range of positive values was 1.0 to 8.2

:g/L. The mean of the positive values was 3.2 :g/L with a standard deviation of 2.5 :g/L; the median

concentration was 2.1 :g/L. In the GWSS, 34 of the 456 randomly chosen water systems serving 25 or

more individuals were contaminated with tetrachloroethylene, at concentrations ranging from 0.21-23

:g/L. The three systems with the highest values were contaminated at 2.9, 5.9, and 23 :g/L. Twenty-one

of the 34 positive systems served populations in excess of 10,000 people. The average for all randomly

chosen systems was 1.5 :g/L with a standard deviation of 4 :g/L; the median was 0.5 :g/L. Of the 473

nonrandom locations sampled serving 25 or more individuals, 43 were contaminated with

tetrachloroethylene, at concentrations between 0.22-69 :g/L, the highest values being 20, 21, and 69

:g/L. Of the 43 positive samples, 18 were from systems serving populations in excess of 10,000 people. 

The average tetrachloroethylene level for the nonrandom systems was 4.7 :g/L with a standard deviation

of 11 :g/L; the median value was 0.73 :g/L. The minimum quantitation limit for tetrachloroethylene

was 0.2 :g/L.

4.8.5.3 Groundwater – State Data

Seven States (California, Connecticut, Delaware, Indiana, Massachusetts, New Jersey, and New York)

provided the USEPA with information concerning tetrachloroethylene contamination in groundwater

supplies. Analytical results for 407 samples from 16 areas in California revealed 257 positive samples

with tetrachloroethylene concentrations from 0.03 to “greater than 20" :g/L. Monitoring data from 55

locations in Connecticut revealed a wide range of contamination levels. Fifteen cities were supplied with

water containing no detectable tetrachloroethylene. Of the 40 systems with detectable

tetrachloroethylene, 20 had levels of 2.5 :g/L or less, 13 had levels between 2.5-10 :g/L, and seven were

contaminated at 10-640 :g/L. Data from Delaware indicated that of eight samples taken from finished

groundwater supplies in two counties, five contained tetrachloroethylene at 0.79-7.1 :g/L. Information

supplied by Indiana showed that eight samples from one system were free of detectable
Occurrence Summary and Use Support Document March 2002 416

tetrachloroethylene contamination. Of five systems sampled in Massachusetts, four were free of

detectable contamination while another had between 24-49 :g/L. Data from New Jersey showed a large

variation in the concentration of measured tetrachloroethylene contamination, ranging from undetectable

to 870 :g/L. Finally, of 421 samples from Nassau County, New York, 67 reported tetrachloroethylene to

be present qualitatively.

4.8.5.4 Surface Water – Federal Surveys

The National Organic Monitoring Survey (NOMS), the National Screening Program for Organics in

Drinking Water (NSP), the Community Water Supply Survey (CWSS), and the Rural Water Survey

(RWS) all contain data concerning the levels of tetrachloroethylene in surface water supplies from across

the country.

Tetrachloroethylene was not analyzed for in Phase I of NOMS. In NOMS Phase II (May to July 1976), a

qualitative assessment that tetrachloroethylene was present in 40 of 91 surface water supplies sampled

(and in one of the mixed source supplies using surface water ,during Phase II) was made on the basis of

the presence of a peak on the gas chromatograph at the appropriate retention time for tetrachloroethylene. 

As indicated previously, a rigorous analysis of all samples was not made, and some samples with smaller

tetrachloroethylene peaks may have been overlooked. During Phase III of NOMS (November 1976 to

January 1977), analyses revealed tetrachloroethylene contamination in 7 out of a total of 87 systems. 

The contamination levels for these systems ranged from 0.2-0.82 :g/L. The mean concentration was 0.4

:g/L with a standard deviation of 0.2 :g/L; the median level was 0.45 :g/L. The minimum quantifiable

limit for tetrachloroethylene was 0.2 :g/L in Phase III.

Surface water samples from 106 drinking water systems were analyzed for tetrachloroethylene during the

National Screening Program (NSP) between June 1977 and March 1981. Of these, 16 systems contained

detectable levels of tetrachloroethylene, ranging from 0.1-3.2 :g/L. Only two of these systems were

contaminated at levels greater than 1.0 :g/L (1.1 and 3.2 :g/L). The average concentration among the 16

positive systems was 0.6 :g/L with a standard deviation of 0.8 :g/L; the median level was 0.4 :g/L. The

quantification limit for the NSP was 0.1 :g/L.

Of the 105 surface water systems sampled during the Community Water Supply Survey (CWSS), 2

contained quantifiable levels of tetrachloroethylene. The positive values were 0.5 and 1.7 :g/L. The

minimum quantitation limit for tetrachloroethylene in the CWSS was 0.5 :g/L. The RWS examined

drinking water from 45 surface water supplies; none were found to have tetrachloroethylene present

above the minimum quantification limit range of 0.5-5 :g/L.

4.8.5.5 Surface Water – State Data

Three States provided the USEPA with data on tetrachloroethylene from surface water sources. Of 12

cities sampled in Connecticut, 10 had tetrachloroethylene contamination, with one mean concentration

higher than 10 :g/L (at 31 :g/L). Two of three locations sampled in New York had detectable

tetrachloroethylene ranging from 0.49 to 2.8 :g/L. One location in California was sampled twice,

revealing no detectable tetrachloroethylene.
Occurrence Summary and Use Support Document March 2002 417

4.8.5.6 Projected National Occurrence of Tetrachloroethylene in Public Water Supplies

As reported in the JRB Associates study, public water systems fall into two major categories with respect

to water source (surface water and groundwater) and into five size categories and twelve subcategories

according to the number of individuals served. The JRB Associates (1983) report presented estimates of

both the number of drinking water supplies nationally within each of the source/size categories expected

to have tetrachloroethylene present, and of the concentration of tetrachloroethylene expected to be

present in those supplies.

The key features of the methodology used and assumptions made to develop the national estimates are

summarized here. The estimates are based on the data from the Federal surveys only. The State data

were not included for several reasons. Generally, these data are from a few States (e.g., California and

Connecticut provide most of the data) and were not considered to be geographically representative. 

There was also a general lack of data on the population served by systems measured, the type of water

sampled, and the methodologies used to sample, identify, and measure tetrachloroethylene. Furthermore,

since much of these data were apparently obtained in response to incidents of recognized contamination

problems, they may not be representative of typical conditions existing nationally. However, while these

data were not used for computing the national projections, they do provide a valuable and necessary

perspective for evaluating those projections, especially with respect to the projected high levels of

contamination of tetrachloroethylene.

The Federal survey data from the NOMS, NSP, CWSS, RWS, and GWSS were pooled together for

developing the national projections. It was assumed in combining these surveys that the resulting data

base would be representative of the nation's water supplies. In the case of the GWSS data, both the

random and nonrandom samples were included in the projections because a statistical test of the GWSS

data showed that neither the frequency of occurrence of positive values nor the mean of the positive

values for tetrachloroethylene was significantly different in the two samples.

Ideally, adequate data would be available to develop the national projections separately for each of the

twelve system size categories within the groundwater and surface water groups; however, the available

data were too limited for this. JRB Associates (1983) consolidated some of the size categories to have

sufficient data for developing the projections. In consolidating data from various size categories,

consideration was given to the potential for there being statistically significant differences in the

frequency of occurrence of tetrachloroethylene as a function of system size. The consolidation of size

categories therefore involved a balancing of the need to group size categories together to have an

adequate data base for developing the national projections against the need to treat size categories

separately in order to preserve the influence of system size as a determinant of contamination potential. 

The consolidation of size categories also took into account EPA's classification of systems into the five

major groups as very small (25-500), small (501-3,300), medium (3,301-10,000), large (10,001-100,000),

and very large (> 100,000) (Kuzmack, 1983, as cited in JRB Associates, 1983).

Once the data were consolidated, statistical models for extrapolating to the national level were tested and

an appropriate model selected. In the case of tetrachloroethylene, the multinominal method was used. 

The frequency of contamination of groundwater and surface water systems at various concentrations was

determined for each consolidated size category. For completing the national estimates, it was assumed

that the frequency of contamination observed for each consolidated category was directly applicable to

each of the system sizes comprising it.
Occurrence Summary and Use Support Document March 2002 418

In the JRB Associates (1983) report, it is noted that some of the data used in computing the national

estimates are from samples held for a prolonged period of time prior to analysis, with possible

biodegradation of tetrachloroethylene. Therefore, these projections of national occurrence may

underestimate actual contaminant levels.

4.8.5.6.1 Groundwater Supplies

JRB Associates (1983) reported that data were available for a total of 1,457 supplies from the combined

surveys. Of these, 103 supplies were reported to have tetrachloroethylene present, at concentrations

ranging from 0.20 :g/L to 69 :g/L.

Based on the overall distribution of positive values and maximum possible values for those supplies in

which tetrachloroethylene was not found, 0.5 :g/L was selected as the common minimum quantifiable

concentration for the combined survey data. That is, quantitative projections are made of supplies at

several concentration ranges $ 0.5 :g/L, while only a total number for supplies expected to have either

no tetrachloroethylene or levels below 0.5 :g/L can be determined. Although some data indicate the

presence of tetrachloroethylene in groundwater supplies at levels < 0.5 :g/L, it is not possible to

determine the proportion of supplies that have tetrachloroethylene present and the proportion that are

actually free of tetrachloroethylene contamination.

Of the 1,354 supplies reporting no tetrachloroethylene to be present, 1,244 were assumed to have

maximum possible levels of < 0.5 :g/L based on the minimum quantifiable concentrations reported for

the various surveys (857 of these had maximum levels of < 0.2 :g/L). The other 110 supplies reporting

no tetrachloroethylene to be present had maximum possible levels ranging from 1.0 :g/L to 1.5 :g/L. It

is assumed, based on the overall distribution of values, that tetrachloroethylene if present in these 110

supplies is so at a concentration of < 0.5 :g/L, although a rigorous, conservative argument could be made

for assuming a level equal to the maximum possible value. The impact of this assumption is considerable

both in terms of the national projection of groundwater systems between 0.5 and 5 :g/L and the size of

the population exposed to that concentration range.

The data indicate that 68 of 1,457 supplies examined had measured values of tetrachloroethylene > 0.5

:g/L. When the twelve size categories were consolidated into the five major EPA groupings, there was

an apparent general trend in the frequency of values > 0.5 :g/L as a function of size:

Very small 3.6% (15/423)

Small 2.2% (9/416)

Medium 8.5% (18/213)

Large 5.6% (20/358 )

Very large 12.8% (6/47)

Overall 4.7% (68/1,457)

A test for statistical significance revealed that, at the " = 0.05 level, the difference between the very

small and small categories was not significant; nor was the difference between the large and very large

groups. The medium category showed a statistically significant difference from the combined very small

and small categories. Three consolidated categories were, therefore, selected for developing the national

estimates:

Very small/small (25-3,300)

Medium (3,301-10,000)
Occurrence Summary and Use Support Document March 2002 419

Large/very large (> 10,000)

As noted previously, the frequency of occurrence of tetrachloroethylene at various concentrations was

determined for the consolidated groups and then applied to the number of supplies nationally within each

of the size categories comprising each group.

An estimated 1,557 groundwater supplies (range of 1,047-2,066), approximately 3.2% of the total

groundwater supplies in the United States, are expected to have tetrachloroethylene at levels of $ 0.5

:g/L; the remaining 46,901 supplies have either no tetrachloroethylene or levels < 0.5 :g/L. It is

estimated that 325 supplies (range of 89-560) are expected to have tetrachloroethylene levels > 5 :g/L;

while only 3 supplies (range of 0-187) are expected to have levels > 30 :g/L. None are expected at

levels above 70 :g/L. Most of the supplies with high tetrachloroethylene levels are expected to be in the

smaller size categories. Although, as noted previously, the frequency of tetrachloroethylene occurrence

increases with increasing system size, the number of systems affected nationally is greater for the small

sizes because there are many more small systems in existence.

It is interesting to note the impact on the national projections of the assumption made that the 110

supplies with undetected but maximum potential values of 1.0-1.5 :g/L had < 0.5 :g/L. Had it been

assumed that tetrachloroethylene was present in those supplies at their maximum possible values, the

national projection of supplies with tetrachloroethylene levels > 0.5 :g/L would have increased to 6,278

(5,258-7,297) with no differences in levels > 5 :g/L. These differences in the 0.5-5 :g/L range would be

found predominantly in systems serving < 10,000 people.

4.8.5.6.2 Surface Water Systems

Data are available for a total of 296 surface water supplies. Of these, 24 supplies were reported by JRB

Associates (1983) to have tetrachloroethylene present at concentrations ranging from 0.1 :g/L to 3.2

:g/L.

Based on the overall distribution of positive values and maximum possible values for those supplies in

which tetrachloroethylene was not found, 0.5 :g/L was selected as the common minimum quantifiable

concentration for the combined survey data. That is, quantitative projections are made of supplies at

several concentration ranges $ 0.5 :g/L, while only a total number for supplies expected to have either

no tetrachloroethylene or levels below 0.5 :g/L can be determined. Although some data indicate the

presence of tetrachloroethylene in surface water supplies at levels < 0.5 :g/L, it is not possible to

determine the proportion that have tetrachloroethylene present and the proportion that are free of

tetrachloroethylene contamination.

Of the 272 supplies reporting no tetrachloroethylene to be present, 243 had maximum possible levels of <

0.5 :g/L based on the minimum quantifiable concentrations reported for the various surveys. The other

29 supplies reporting no tetrachloroethylene to be present had maximum possible levels ranging from 1.0

:g/L to 1.5 :g/L. It is assumed, based on the overall distribution of values, that tetrachloroethylene if

present in these 29 supplies is so at a concentration of < 0.5 :g/L, although a rigorous conservative

argument could be made for assuming a level equal to the maximum possible value. As will be noted

further below, the difference between these alternatives is considerable for the estimate of the number of

surface water supplies with tetrachloroethylene at 0.5-5 :g/L; also, the impact on the estimated

population exposed to tetrachloroethylene at levels of 0.5-5 :g/L in surface water supplies is very large.
Occurrence Summary and Use Support Document March 2002 420

The data also indicates that 11 of the 296 supplies examined had measured values of tetrachloroethylene

$0.5 :g/L. When the twelve size categories are consolidated into the five major EPA groupings, the

frequency of values > 0.5 :g/L as a function of size are:

Very small 0% (0/20)

Small 1.7% (1/58)

Medium 0% (0/39)

Large 6.1% (4/66)

Very large 5.3% (6/113)

Overall 3.7% (11/296)

A test for statistical significance revealed that, at the " = 0.05 level, the very small, small, and medium

groups were not different from one another and that the large and very large groups are not different;

however, the combined very small, small, and medium groups and the combined large and very large

groups are different. These two consolidated categories were selected for developing the national

estimates:

Very small/small/medium (25-10,000)

Large/very large (> 10,000)

As noted previously, the frequency of occurrence of tetrachloroethylene at various concentrations was

determined for the consolidated groups and then applied to the number of supplies nationally within each

of the size categories comprising each group.

About 180 surface water supplies (range of 13-346), approximately 1.6% of the total surface water

systems in the United States, are expected to have tetrachloroethylene at levels between 0.5 and 5 :g/L;

the remaining 11,022 supplies have either no tetrachloroethylene or levels < 0.5 :g/L. It is estimated that

no surface water supplies will have levels > 5 :g/L.

There was a notable impact on the national projections by the assumption made that the 29 supplies with

undetected but maximum potential values of 1.0-1.7 :g/L had < 0.5 :g/L. Had it been assumed that

tetrachloroethylene was present in these supplies at their maximum possible values, the national

projections of supplies with tetrachloroethylene levels of 0.5-5 :g/L would be 1,953 (range of 1,282-

2,623) supplies. However, there would still be no surface water supplies expected to have levels > 5

:g/L.

4.8.6 Conclusion

 Tetrachloroethylene is a commercially important chlorinated hydrocarbon solvent and chemical

intermediate in the production of chlorofluorocarbons. It is used as a dry cleaning and textile-processing

solvent and for vapor degreasing in metal-cleaning operations. Production of tetrachloroethylene has

decreased in recent years, although it is still widely produced and processed. Tetrachloroethylene is also

a TRI chemical. Industrial releases of tetrachloroethylene have occurred since 1988 in 48 States, Puerto

Rico, and the Virgin Islands. Tetrachloroethylene was an analyte for the NAWQA, NURP, and NPDES

ambient occurrence studies. In the NAWQA study, tetrachloroethylene was detected in 16.6% of urban

wells and 2.5% of rural wells, with median detection values of 1.1 :g/L and 0.8 :g/L, respectively. The

frequency of detection of tetrachloroethylene for NURP was 5%, while the frequency of detection for

NPDES was 8%. In the Stage 2 analysis of 16-State occurrence of tetrachloroethylene, 0.202% of

combined ground water and surface water systems serving 0.685% of the population exceeded the MCL
Occurrence Summary and Use Support Document March 2002 421

of 0.005 mg/L. Nationally, 132 ground water and surface water systems combined (serving

approximately 1,458,900 people) are estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, tetrachloroethylene is manufactured and/or processed in 40 States and has

TRI releases in 48 States. Tetrachloroethylene is manufactured and/or processed in 14 out of the 16

cross-section States and has TRI releases in all of the 16 cross-section States. The cross-section should

adequately represent the occurrence of tetrachloroethylene on a national scale based upon the use,

production, and release patterns of the 16-State cross-section in relation to the patterns observed for all

50 States. 

4.8.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1997. Toxicological Profile for

Tetrachloroethylene. U.S. Department of Health and Human Services, Public Health Service. 

278 pp. + Appendices. Available on the Internet at: 

http://www.atsdr.cdc.gov/toxprofiles/tp18.pdf.

Brass, H.J., M.A. Feige, T. Halloran, J.W. Mello, D. Munch, and R.F. Thomas. 1977. The National

Organic Monitoring Survey: A sampling and analysis for purgeable organic compounds. 

Drinking water quality enhancement through source protection. R.B. Pojasek (ed.). Ann Arbor,

MI: Ann Arbor Science, pp. 393-416.

Brass, H.J. 1981. Rural Water Survey organics data. Memorandum of March 17, 1981 to Hugh Hanson,

Chief, Science and Technology Branch, Office of Drinking Water, and David Schnare, Office of

Drinking Water , USEPA, Washington, DC. 

JRB Associates. 1983. Occurrence of Tetrachloroethylene in Drinking Water, Food and Air - DRAFT. 

Draft report submitted to EPA for review June 22, 1983. 

Kuzmack, A.M. 1983. Memorandum: Characterization of the water supply industry (FY82). 

Washington, D.C.: Office of Water, USEPA. May 16, 1983. 

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 

67 pp.

Mello, Wayne. 1983. Personal communication between Wayne Mello, Technical Support Division,

Office of Drinking Water, USEPA, and author of JRB Associates, 1983, March 10, 1983.

National Safety Council (NSC). 2001. Tetrachloroethylene Chemical Backgrounder. Itasca, IL:

National Safety Council. Available on the Internet at:

http://www.crossroads.nsc.org/ChemicalTemplate.cfm?chempath=chemicals&id=137, accessed

July 17, 2001.

National Toxicology Program (NTP). 1991. National Toxicology Program Health and Safety

Information Sheet - Tetrachloroethylene. Available on the Internet at

http://ntp-db.niehs.nih.gov/NTP_Reports/NTP_Chem_H&S/NTP_Chem1/Radian127-18-4.txt.
Occurrence Summary and Use Support Document March 2002 422

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

USEPA. 1994. R.E.D. Facts: Tetrachloroethylene. EPA Report/749-F-94-020. Washington, DC:

Office of Prevention, Pesticides, and Toxic Substances. Available on the Internet at:

http://www.epa.gov/opptintr/chemfact/f_perchl.txt

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on:

Tetrachloroethylene. Office of Ground Water and Drinking Water, USEPA. Available on the

Internet at: http://www.epa.gov/safewater/dwh/c-voc/tetrachl.html, Last updated April 12, 2001.

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Westrick, J.J., J.W. Mello, and R.F. Thomas. 1983. The Ground Water Supply Survey summary of

volatile organic contaminant occurrence data. EPA Technical Support Division, Office of

Drinking Water, Cincinnati, Ohio.
Occurrence Summary and Use Support Document March 2002 423

4.9 1,1,2-Trichloroethane

Table of Contents

4.9.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424

4.9.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424

4.9.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

4.9.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . . 426

4.9.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

4.9.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433

4.9.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433

Tables and Figures

Table 4.9-1: Environmental Releases (in pounds) for 1,1,2-Trichloroethane 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

Table 4.9-2: Stage 1 1,1,2-Trichloroethane Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427

Table 4.9-3: Stage 1 1,1,2-Trichloroethane Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427

Table 4.9-4: Stage 2 Estimated 1,1,2-Trichloroethane Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428

Table 4.9-5: Stage 2 Estimated 1,1,2-Trichloroethane Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428

Table 4.9-6: Estimated National 1,1,2-Trichloroethane Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
Occurrence Summary and Use Support Document March 2002 424

4.9.1 Introduction, Use and Production

1,1,2-Trichloroethane (chemical formula C2H3Cl3) is a colorless, sweet-smelling liquid. It does not burn

easily, but does boil at a higher temperature than water. 1,1,2-Trichloroethane is also known as ethane

trichloride, $-trichloroethane, vinyl trichloride, and 1,2,2-trichloroethane (ATSDR, 1989).

The principal use of 1,1,2-trichloroethane is as a chemical intermediate in the production of 1,1-

dichloroethylene (also known as vinylidene chloride), which is in turn used to make synthetic fibers and

plastic wraps (ATSDR, 1989; USEPA, 2001). 1,1,2-Trichloroethane has limited use as a solvent, where

its high solvency is useful. It may also be used as a solvent for fats, oils, waxes, and resins. Information

indicates that 1,1,2-trichloroethane has been sold for use in consumer products, but it is not known for

which products, nor how extensive the use. A Dow Chemical spokesman, as cited in ATSDR, stated that

the company had no knowledge of any consumer uses of 1,1,2-trichloroethane and that the company

screens potential customers to determine how they intend to use it (ATSDR, 1989).

1,1,2-Trichloroethane is produced exclusively by Dow Chemical in Freeport, TX, and Olin Corporation

in Seward, IL. No recent information on production volumes is available. Dow Chemical was formerly

the sole manufacturer of 1,1,2-trichloroethane, and therefore manufacturing volumes from that time

period are proprietary information and are unavailable. The only estimates of production of 1,1,2-

trichloroethane are based upon the production of 1,1-dichloroethylene. In 1974, the production volume

of 1,1,2-trichloroethane was estimated at 124 million pounds (USEPA, 2001), and in 1979, 412 million

pounds (ATSDR, 1989).

It should be noted that ATSDR indicates that information on 1,1,2-trichloroethane is wholly inadequate

and does not provide sufficient information to determine how widespread this chemical is, or what

potential exists for exposure in the general population. It is emphasized that information is especially

needed on the commercial uses of 1,1,2-trichloroethane and what types of consumer products, if any,

contain it. That information is requisite in determining exposure to 1,1,2-trichloroethane, and for

determining which groups in the population are occupationally, or generally, exposed (ATSDR, 1989). 

4.9.2 Environmental Release

1,1,2-Trichloroethane is listed as a Toxics Release Inventory (TRI) chemical. Table 4.9-1 illustrates the

environmental releases for 1,1,2-trichloroethane from 1988 - 1999. (1,1,2-Trichloroethane data are only

available for these years.) Air emissions constitute the vast majority of the on-site releases, with a

relatively steady decrease over the years. The decrease in air emissions, as well as surface water

discharges, have contributed to decreases in 1,1,2-trichloroethane total on- and off-site releases over the

years. Except for releases in 1989-1991, no underground injection was reported for 1,1,2-

trichloroethane. Releases to land (such as spills or leaks within the boundaries of the reporting facility),

except for an upturn in 1999, decreased to at or near zero from 1992-1998. Off-site releases (including

metals or metal compounds transferred off-site) have also declined from large amounts recorded from

1988-1991, as releases since then have, with one exception, remained below 600 pounds. These TRI data

for 1,1,2-trichloroethane were reported from 29 States, with six States reporting every year (USEPA,

2000). Twelve of the 16 cross-section States (used for analyses of 1,1,2-trichloroethane occurrence in

drinking water; see Section 4.9.4) reported release of 1,1,2-trichloroethane. (For a map of the 16-State

cross-section, see Figure 1.3-1.)
Occurrence Summary and Use Support Document March 2002 425

Table 4.9-1: Environmental Releases (in pounds) for 1,1,2-Trichloroethane in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 198,539 925 0 123 91 199,678

1998 279,470 540 0 1 1,203 281,214

1997 296,348 621 0 0 141 297,110

1996 339,055 516 0 16 114 339,701

1995 280,352 870 0 0 113 281,335

1994 310,112 914 0 0 166 311,192

1993 315,152 2,030 0 5 592 317,779

1992 562,085 1,163 0 7 219 563,474

1991 527,866 1,382 2 256 8,580 538,086

1990 588,464 2,231 1,091 265 25,498 617,549

1989 744,618 6,395 2,090 130 75,990 829,223

1988 1,741,442 5,303 0 89 19,810 1,766,644

 Source: USEPA, 2000 

4.9.3 Ambient Occurrence

1,1,2-Trichloroethane was not detected in rural or urban wells in the local, State, and federal data set

compiled by NAWQA. These data represent untreated ambient ground water of the conterminous United

States for the years 1985-1995 (Squillace et al., 1999).

The NURP study found 1,1,2-trichloroethane in urban runoff (Lopes and Dionne, 1998). The minimum

and maximum concentrations detected were 2 :g/L and 3 :g/L, respectively, with no mean value

reported. The use of the land from which the samples were taken was unspecified. 

4.9.3.1 Additional Ambient Occurrence Data

A summary document entitled “Estimated National Occurrence and Exposure Assessment of 1,1,2-

Trichloroethane in Public Drinking Water Supplies” (Wade Miller, 1989), was previously prepared for

past USEPA assessments of 1,1,2-trichloroethane. Various information was presented regarding levels

of 1,1,2-trichloroethane in water other than drinking water. The following information is taken directly

from “Estimated National Occurrence and Exposure Assessment of 1,1,2-Trichloroethane in Public

Drinking Water Supplies” (Wade Miller, 1989). 

4.9.3.1.1 Groundwater Sources

In an effort to obtain information on the occurrence of 1,1,2-TCE in water other than drinking water from

ground water sources, an extensive search of the literature was conducted. In addition, knowledgeable

sources within the Office of Drinking Water were contacted. No data are available on the occurrence of

1,1,2-TCE in non-drinking ground water sources.
Occurrence Summary and Use Support Document March 2002 426

4.9.3.1.2 Surface Water Sources

The STORET water quality data base provides information on the occurrence of contaminants at ambient

water stations in U.S. waterways. A summary of this information was obtained for 1,1,2-TCE in ambient

waters. Ambient sites include streams, lakes, ponds, wells, reservoirs, canals, estuaries, and oceans. 

Since the preponderance of data were collected from surface water sources, the data are presented in this

section. However, the number of samples collected from ground water wells, relative to the total number

of samples collected from all ambient sites combined, is unspecified (Staples et al. 1985, as cited in

Wade Miller, 1989). The limitations with these data are the same as those described for drinking water

(see Section 4.9.5.6). Staples et al. (1985, as cited in Wade Miller, 1989) have summarized data from the

1980s only; that is, data from 1980 through 1983. This was done based on the number of data points and

the likelihood that better quality assurance practices have been employed in more recent years. In the

absence of sophisticated statistical analyses to eliminate improbable data, median values have been

reported. The median value is less sensitive to extreme values, and reflects a measure of central tendency

more accurately than the mean value in the presence of these extreme values (Staples et al. 1985, as cited

in Wade Miller, 1989).

For a total of 1,047 observations from ambient water stations, the median concentration of 1,1,2-TCE

was < 5.0 :g/L. Of the total number of observations, two percent were reported as detectable. Detection

limits and other sampling information were not reported.

4.9.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of 1,1,2-trichloroethane occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to two concentration thresholds of interest: 0.005 mg/L; and 0.003 mg/L.

All sixteen cross-section State data sets contained occurrence data for 1,1,2-trichloroethane. These data

represent approximately 174,000 analytical results from over 22,000 PWSs during the period from 1984

to 1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs vary

by State, although the State data sets have been reviewed and checked to ensure adequacy of coverage

and completeness. The overall modal detection limit for 1,1,2-trichloroethane in the 16 cross-section

States is equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to Section

1.3.5 of this report.)

4.9.4.1 Stage 1 Analysis Occurrence Findings

Table 4.9-2 illustrates the low occurrence of in drinking water for the public water systems in the 16-

State cross-section relative to two thresholds: 0.005 mg/L (the current MCL), and 0.003 mg/L. Based on

the 16-State cross-section data, a total of 9 (approximately 0.0404% of) ground water and surface water

PWSs had analytical results exceeding the MCL. Twice as many (0.0808% of) systems had results

exceeding 0.003 mg/L. 

Approximately 0.0385% of ground water systems (8 systems) had any analytical results greater than the

MCL. Only 1 (0.0655% of) surface water system had results greater than the MCL. About 0.0626% of

ground water systems (13 systems) had results above 0.003 mg/L. A total of 5 (0.328% of) surface water

systems had at least one analytical result greater than 0.003 mg/L. 
Occurrence Summary and Use Support Document March 2002 427

Table 4.9-2: Stage 1 1,1,2-Trichloroethane Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold 

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.0385% 8

0.003 0.0626% 13

Surface Water

0.005 0.0655% 1

0.003 0.328% 5

Combined Ground &

Surface Water

0.005 0.0404% 9

0.003 0.0808% 18

Reviewing 1,1,2-trichloroethane occurrence in the 16 cross-section States by PWS population served

(Table 4.9-3) shows that approximately 6.97% of the population (almost 7.7 million people) was served

by PWSs with at least one analytical result of 1,1,2-trichloroethane greater than the MCL (0.005 mg/L). 

Approximately 8.0 million (7.21% of) people were served by systems with an exceedance of 0.003 mg/L.

A much larger percentage of population served by surface water systems had MCL exceedances as

compared to the population served by ground water systems. Approximately 0.556% of people served by

ground water systems in the 16 States (about 274,900 people) were exposed to levels of 1,1,2-

trichloroethane greater than 0.005 mg/L. The percentage of population served by surface water systems

with exceedances of 0.005 mg/L was equal to 12.2% (approximately 7.4 million people). When

evaluated relative to 0.003 mg/L, the percent of population served by ground water exposed was equal to

0.627% (309,700 people). Approximately 12.6% of the population served by surface water systems

(almost 7.7 million people) was exposed to 1,1,2-trichloroethane concentrations greater than 0.003 mg/L.

Table 4.9-3: Stage 1 1,1,2-Trichloroethane Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold 

Total Population Served

by Systems Exceeding

Threshold

Ground Water

0.005 0.556% 274,900

0.003 0.627% 309,700

Surface Water

0.005 12.2% 7,415,200

0.003 12.6% 7,652,100

Combined Ground &

Surface Water

0.005 6.97% 7,690,100

0.003 7.21% 7,961,800
Occurrence Summary and Use Support Document March 2002 428

4.9.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.9-4 and 4.9-5. 

The statistically generated best estimate values, as well as the ranges around the best estimate value, are

presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this report. For

complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation Methodology and

Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations - DRAFT

(USEPA, 2002)). 

No ground water or surface water PWSs (therefore, no population served by systems) had an estimated

mean concentration of 1,1,2-trichloroethane exceeding 0.005 mg/L or 0.003 mg/L.

Table 4.9-4: Stage 2 Estimated 1,1,2-Trichloroethane Occurrence Based on 16-State Cross-Section

- Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.003 0.000% 0.000% - 0.000% 0 0 - 0

Surface Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.003 0.000% 0.000% - 0.000% 0 0 - 0

Combined Ground

& Surface Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.003 0.000% 0.000% - 0.000% 0 0 - 0

Table 4.9-5: Stage 2 Estimated 1,1,2-Trichloroethane Occurrence Based on 16-State Cross-Section

- Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.003 0.000% 0.000% - 0.000% 0 0 - 0

Surface Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.003 0.000% 0.000% - 0.000% 0 0 - 0
Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Occurrence Summary and Use Support Document March 2002 429

Combined Ground

& Surface Water

0.005 0.000% 0.000% - 0.000% 0 0 - 0

0.003 0.000% 0.000% - 0.000% 0 0 - 0

4.9.4.3 Estimated National Occurrence

As illustrated in Table 4.9-6, the Stage 2 analysis estimates zero systems serving zero people nationally

have estimated mean concentration values of 1,1,2-trichloroethane greater than 0.005 mg/L, or 0.003

mg/L. (See Section 1.4 for a description of how Stage 2 16-State estimates are extrapolated to national

values.)

Table 4.9-6: Estimated National 1,1,2-Trichloroethane Occurrence - Systems and Population

Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0 0 - 0 0 0 - 0

0.003 0 0 - 0 0 0 - 0

Surface Water

0.005 0 0 - 0 0 0 - 0

0.003 0 0 - 0 0 0 - 0

Combined Ground

& Surface Water

0.005 0 0 - 0 0 0 - 0

0.003 0 0 - 0 0 0 - 0

4.9.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of 1,1,2-trichloroethane in drinking water are

also reviewed. Previously compiled occurrence information, from an OGWDW summary document

entitled “Estimated National Occurrence and Exposure Assessment of 1,1,2-Trichloroethane in Public

Drinking Water Supplies” (Wade Miller, 1989), is presented in this section. This variety of studies and

information are presented regarding levels of 1,1,2-trichloroethane in drinking water, with the scope of

the reviewed studies ranging from national to regional. Note that none of the studies presented in the

following section provide the quantitative analytical results or comprehensive coverage that would

enable direct comparison to the occurrence findings estimated with the cross-section occurrence data

presented in Section 4.9.4. These additional studies, however, do enable a broader assessment of the

Stage 2 occurrence estimates presented for this Six-Year Review. All the following information in
Occurrence Summary and Use Support Document March 2002 430

Section 4.9.5 is taken directly from “Estimated National Occurrence and Exposure Assessment of 1,1,2-

Trichloroethane in Public Drinking Water Supplies” (Wade Miller, 1989).

4.9.5.1 Groundwater Sources – National Studies

The Ground Water Supply Survey (GWSS) was conducted from December 1980 to December 1981 to

develop additional data on the occurrence of volatile organic chemicals (VOCs) in the Nation’s ground

water supplies (Westrick et al. 1983, as cited in Wade Miller, 1989). A total of 929 finished drinking

water supplies serving 25 or more individuals were sampled. Four hundred and fifty-six systems were

chosen at random, while the remaining 473 systems were chosen non-randomly based on information

from States encouraged to identify locations believed to have a higher than normal probability of VOC

contamination (e.g., locations near landfills or industrial activity). None of the supplies sampled

contained 1,1,2-TCE in excess of the minimum quantifiable concentration of 0.5 :g/L.

The National Screening Program for organics in drinking water (NSP), conducted by SRI International

from June 1977 to March 1981, examined both raw and finished drinking water samples from 166 water

systems in 33 States for 51 organic chemical contaminants, including 1,1,2-TCE. Analyses were made

using gas chromatography with electrolytic conductivity detection. In this procedure,

chlorodibromomethane and 1,1,2-TCE coelute and are not distinguishable. Reported levels should be

considered “as either compound or a combination of the two with maximum concentrations as indicated.”

In summarizing the results of this survey for 1,1,2-TCE, SAIC has presented a worst case assessment by

assuming all of the coelute to be 1,1,2-TCE. The values reported are thus taken to be maximum

(potential) contamination levels in the sampled finished drinking water supplies.

The NSP data extracted from Boland (1981, as cited in Wade Miller, 1989) indicated that for ground

water systems (5 samples), concentrations ranged from 0.2 to 12.0 :g/L (mean = 3.82 :g/L; median = 0.3

:g/L). The minimum quantifiable concentration for 1,1,2-TCE was 0.1 :g/L.

4.9.5.2 Groundwater Sources – Regional Studies

The State of California’s Department of Health Services (DHS) analyzed samples from 2,947 drinking

water wells used by large public water systems (having 200 connections) between 1984 and 1985. 1,1,2-

TCE was detected in four of the wells sampled with concentrations ranging from 0.7 to 1.1 :g/L. The

median concentration was 1.0 :g/L (California Department of Health Services, 1986, as cited in Wade

Miller, 1989). The California DHS also reported that one drinking water well used by a small public

water system (< 200 connections) tested positive twice for 1,1,2-TCE at concentrations of 3.2 :g/L and

1.1 :g/L (California Department of Health Services, unpublished, as cited in Wade Miller, 1989). In an

earlier study, the State of California (1980, as cited in Wade Miller, 1989) reported that 1,1,2-TCE was

detected in two of four wells (1 well sampled at 4 separate California Water Utilities), both at

concentrations of 0.2 :g/L. The other two samples were reported as less than the detection limit, which

was not provided.

The State of Minnesota’s Department of Health (MDH) sampled 1,801 community water supply wells for

VOCs between 1982 and 1985. 1,1,2-TCE was detected in one well at a median and maximum

concentration of 0.3 :g/L. The minimum quantifiable concentration was 0.2 :g/L (Minnesota

Department of Health, 1985, as cited in Wade Miller, 1989). One hundred and seven additional wells

were tested after the 1985 MDH survey was completed, but 1,1,2-TCE was not detected in any of them

(detection limit not specified) (FSTRAC, 1988, as cited in Wade Miller, 1989).
Occurrence Summary and Use Support Document March 2002 431

Four hundred and fifty-nine actual or potential drinking water wells in Nebraska were tested for the

presence of 1,1,2-TCE. One well tested positive, with multiple samples showing concentrations ranging

from 2.3 to 32.1 :g/L. The average concentration of 1,1,2-TCE was 13.7 :g/L (FSTRAC, 1988, as cited

in Wade Miller, 1989).

The results of a Statewide New Jersey ground water quality survey revealed that through March 1981,

two percent of the 1,118 well water samples collected contained 1,1,2-TCE at concentrations exceeding

the minimum reportable quantity of 1.0 :g/L. Although the maximum concentration reported was 31.1

:g/L, no other sample exceeded a concentration of 10.0 :g/L (Tucker, 1981, as cited in Wade Miller,

1989). USEPA (1981, as cited in Wade Miller, 1989) reported that of 399 ground water samples

collected in New Jersey, 203 samples had concentrations of < 1.0 :g/L, 141 samples had concentrations

ranging from 1.0 to 10.0 :g/L, 55 samples had concentrations ranging from 10.0 to 1,000.0 :g/L, and one

sample had a concentration > 1,000.0 :g/L.

In 1978, 372 drinking water wells in Nassau County, Long Island, New York were tested for the presence

of 1,1,2-TCE. Thirteen percent of the wells tested positive, with a maximum concentration of 300.0 :g/L

detected (USEPA, 1981, as cited in Wade Miller, 1989).

4.9.5.3 Surface Water Sources – National Studies

The National Screening Program for Organics in Drinking Water (NSP) (see Section 4.9.5.1) also

contained information on the occurrence of 1,1,2-TCE in finished drinking water from surface water

sources. The NSP data extracted from Boland (1981, as cited in Wade Miller, 1989) indicated that, for

surface water systems (82 samples), concentrations ranged from 0.1 to 52.0 :g/L (mean = 1.92 :g/L;

median = 0.55 :g/L). The minimum quantifiable concentration for 1,1,2-TCE was 0.1 :g/L.

4.9.5.4 Surface Water Sources – Regional Studies

In an effort to obtain information from regional and State surveys on the occurrence of 1,1,2-TCE in

drinking water from surface water sources, an extensive literature search was conducted. In addition,

knowledgeable sources within the Office of Drinking Water were contacted. No regional survey data are

available on the occurrence of 1,1,2-TCE in surface water supplies.

4.9.5.5 Unspecified Water Sources

The results of two studies which analyzed the quality of finished water at three Puerto Rico water utilities

were available as data base output. Samples were collected during September of 1980 and August of

1981. None of the finished water, from any of the utilities sampled, contained detectable levels of 1,1,2-

TCE. The detection limit, sampling and analytical methodology employed, and water source were

unspecified (Puerto Rico, 1980 and 1981, as cited in Wade Miller, 1989).

The results of a study which analyzed the quality of finished water at ten New York water utilities were

available as data base output. Samples were collected during November and December of 1980. The

results of this study revealed that none of the finished water from any of the utilities sampled contained

detectable levels of 1,1,2-TCE. The detection limit, sampling and analytical methodology employed, and

water source were unspecified (State of New York, 1980, as cited in Wade Miller, 1989).

The results of a study which analyzed the quality of finished water at fourteen New Jersey water utilities

were available as data base output. Samples were collected during July of 1980. The detection limit for
Occurrence Summary and Use Support Document March 2002 432

1,1,2-TCE was reported at 20.0 :g/L for this study. None of the finished water collected at any of the

utilities sampled exceeded this value. The sampling and analytical methodology employed and the water

source were unspecified (State of New Jersey, 1980, as cited in Wade Miller, 1989). The results of

another study which analyzed the quality of finished water at twelve New Jersey water utilities were also

available as data base output. Samples were collected in 1981. The results of this study revealed that

none of the finished water, from any of the utilities sampled, contained detectable levels of 1,1,2-TCE. 

The detection limit, sampling and analytical methodology employed, and water source were unspecified

(State of New Jersey, 1981, as cited in Wade Miller, 1989).

4.9.5.6 Occurrence in Groundwater and Surface Water Sources – STORET

The EPA computerized water quality data base known as STORET was devised to assist Federal and

State institutions in meeting objectives of Public Law 92-500 to maintain and enhance the physical,

chemical, and biological quality of the Nation’s ambient waterways by providing for the collection and

dissemination of basic water quality data (Staples et al., 1985, as cited in Wade Miller, 1989). Data are

collected by States, EPA regional offices, and other government agencies and are maintained in the

STORET system. STORET contains approximately 80 million data entries including data on drinking

water from ground water and surface water sources.

Before presenting a summary of the drinking water data in STORET, it is important to note that there are

significant limitations in using this data base to estimate representative concentrations of a contaminant

such as 1,1,2-TCE. Data entered into STORET are gathered from an array of studies conducted for

various purposes. Analyses are conducted in a number of different laboratories employing different

methodologies with a range of detection limits. In many cases, detection limits are not reported, making

the reliability of the data highly questionable. In cases in which the detection limits have been reported,

STORET assigns the detection limit value for those observations reported as not detected. This can lead

to errors in interpretation and overestimation of concentrations in a particular medium. Additionally, a

few high values can inflate mean values and result in large standard deviations relative to the means

(Staples et al., 1985, as cited in Wade Miller, 1989). Very high values may not be correct, as they may

reflect sample contamination or analytical error and can significantly distort assessment of average

concentrations. Staples et al. (1985, as cited in Wade Miller, 1989) also notes that use of data collected

prior to the 1980s is not recommended since some data were obtained using less sensitive laboratory

techniques than are currently available and since quality assurance procedures were not yet mandated for

the data entered into the system.

With these limitations in mind, a summary of the most recently obtained data for 1,1,2-TCE is presented

for drinking water from ground water sources (USEPA, 1988, as cited in Wade Miller, 1989). According

to STORET, there were 16 positive observations for 1,1,2-TCE in ground water from December 1984 to

March 1987, with an overall mean value of 1.97 :g/L and a range of 0.1 to 5.8 :g/L. The standard

deviation for these observations was 2.06 :g/L. There were 237 samples reported as undetected and

assigned detection limit values, resulting in a mean value of 0.76 :g/L, a range of 0.1 to 1.0 :g/L and a

standard deviation of 0.26 :g/L. Including the undetected samples, the 10,069 observations with actual

values less than the reported values, and the 3 detections that were verified but not quantified, there were

a total of 10,325 observations for 1,1,2-TCE in ground water from February 1978 to November 1987,

with an overall mean value of 0.42 :g/L and a range of 0.01 to 10.0 :g/L. The standard deviation for all

observations was 0.35 :g/L. Detection limits and other sampling information were not reported.

The STORET data base similarly contains data on the occurrence of 1,1,2-TCE in drinking water from

surface water sources (USEPA, 1988, as cited in Wade Miller, 1989). According to STORET, there were
Occurrence Summary and Use Support Document March 2002 433

89 observations for 1,1,2-TCE in surface water from February 1978 to July 1987, with an overall mean

value of 5.51 :g/L and a range of 0.5 to 10.0 :g/L. The standard deviation for all observations was 4.44

:g/L. Detection limits and other sampling information were not reported. It is important to note that of

the 89 total observations for 1,1,2-TCE, 40 observations were reported as undetected and assigned

detection limit values resulting in a mean of 2.07 :g/L (range = 1.0 - 10.0 :g/L) and a standard deviation

of 2.58 :g/L. The remaining 49 observations had actual values less than the reported values.

4.9.5.7 National Estimate of the Occurrence of 1,1,2-Trichloroethane and Population Exposure for

Public Water Supplies

Although Federal survey data on the occurrence of 1,1,2-trichloroethane in public drinking water

supplies are available, there are few detectable concentration values. Information on the occurrence of

1,1,2-TCE in public drinking water supplies is available in STORET; however, as discussed above, there

are significant limitations involved with utilizing these data. The available State data are usually poorly

described with respect to the source and size categories of the supplies examined and the sampling and

analysis methods used for determining contaminant levels. Consequently, national estimates of

occurrence and population exposure were not made for 1,1,2-TCE.

4.9.6 Conclusion

The primary use of 1,1,2-trichloroethane is as a chemical intermediate in the production of 1,1-

dichloroethylene. It is also used as a solvent, and it is unknown whether or not it may be present in any

consumer products. Virtually no production data about 1,1,2-trichloroethane is available due to

proprietary concerns of Dow Chemical. 1,1,2-Trichloroethane is also a TRI chemical. Industrial releases

of 1,1,2-trichloroethane have occurred in 29 States since 1988. 1,1,2-Trichloroethane was an analyte for

the NURP ambient occurrence studies. In the NURP study, 1,1,2-trichloroethane was detected at a

maximum concentration of 3 :g/L and a minimum concentration of 2 :g/L, with no median value

reported. In the Stage 2 analysis of 16-State occurrence of 1,1,2-trichloroethane, zero percent of

combined ground water and surface water systems serving zero percent of the population exceeded the

MCL of 0.005 mg/L. Nationally, zero ground water and surface water systems combined (serving

approximately zero people) are estimated to have levels greater than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. All production information for 1,1,2-trichloroethane is unavailable for comparison due

to proprietary restrictions. Nationally, 29 States have reported TRI releases of 1,1,2-trichloroethane,

including 12 of the 16 cross-section States. The cross-section should adequately represent the occurrence

of 1,1,2-trichloroethane on a national scale based upon the use, production, and release patterns of the

16-State cross-section in relation to the patterns observed for all 50 States. 

4.9.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1989. Toxicological Profile for 1,1,2-

Trichloroethane. U.S. Department of Health and Human Services, Public Health Service. 108

pp. + Appendices. Available on the Internet at http://atsdr1.atsdr.cdc.gov/toxprofiles/tp148.pdf

Boland, P.A. 1981. National Screening Program for Organics in Drinking Water. Prepared by SRI

International, Menlo Park, California, for Office of Drinking Water, USEPA, Washington, DC. 

EPA Contract No. 68-01-4666. 
Occurrence Summary and Use Support Document March 2002 434

California Department of Health Services. 1986. Final Report on a Monitoring Program for Organic

Chemical Contamination of Large Public Water Systems in California. Summary Version. 

Sacramento, CA.

California Department of Health Services. Unpublished. Final Report on a Monitoring Program for

Organic Chemical Contamination of Small Public Water Systems in California. Summary

Version. Sacramento, CA.

FSTRAC. 1988. Federal/State Toxicological and Regulatory Alliance Committee. FSTRAC Survey

Results - April 1988. Survey results obtained from Ralph Langemeier, Chief of Drinking Water

Branch, USEPA, Region VII.

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 

67 pp.

Minnesota Department of Health. 1985. Volatile Organic Survey of Community Water Supplies. Report

to the Legislative Commission on Minnesota Resources. Minneapolis, MN.

Puerto Rico. 1980. Results of Puerto Rico Water Supply Study for 1,1,2-Trichloroethane. Data obtained

from Arthur Perler, Branch Chief, Science and Technology Branch, Office of Drinking Water,

USEPA, Washington, D.C.

Puerto Rico. 1981. Results of Puerto Rico Water Supply Study for 1,1,2-Trichloroethane. Data obtained

from Arthur Perler, Branch Chief, Science and Technology Branch, Office of Drinking Water,

USEPA, Washington, D.C.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

Staples, C.A., A.F. Werner, and T.J. Hoogheem. 1985. Assessment of Priority Pollutant Concentrations

in the United States Using STORET Data Base. Environmental Toxicology and Chemistry,

4:131-142.

State of California. 1980. Memorandum: Analysis of California Department of Health Services Well

Water Samples for 1,1,2-Trichloroethane. Data obtained from Arthur Perler, Branch Chief,

Science and Technology Branch, Office of Drinking Water, USEPA, Washington, D.C. 1/30/80. 

State of New Jersey. 1980. Results of New Jersey Water Supply Sampling for 1,1,2-Trichloroethane. 

Report date 9/24/80. Data obtained from Arthur Perler, Branch Chief, Science and Technology

Branch, Office of Drinking Water, USEPA, Washington, D.C.

State of New Jersey. 1981. Results of New Jersey Water Supply Sampling for 1,1,2-Trichloroethane. 

Report date 10/8/81. Data obtained from Arthur Perler, Branch Chief, Science and Technology

Branch, Office of Drinking Water, USEPA, Washington, D.C.
Occurrence Summary and Use Support Document March 2002 435

State of New York. 1980. Results of New York Water Supply Sampling for 1,1,2-Trichloroethane. 

Report date 2/26/81. Data obtained from Arthur Perler, Branch Chief, Science and Technology

Branch, Office of Drinking Water, USEPA, Washington, D.C.

Tucker, R.K. 1981. Groundwater Quality in New Jersey: An Investigation of Toxic Contaminants. State

of New Jersey Department of Environmental Protection. Office of Cancer and Toxic Substances

Research, Trenton, NJ.

USEPA. 1981. USEPA. An Exposure and Risk Assessment for Trichloroethanes. Final Draft Report. 

Office of Water Regulations and Standards, Office of Water, Washington, D.C. (Revised July

1982).

USEPA. 1988. Computer Printout of STORET Water Quality Data Base. Retrieval conducted March

23, 1988 by Science Applications International Corporation. Data available through Office of

Water Regulations and Standards, Washington, D.C.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. National Primary Drinking Water Regulations - Consumer Factsheet on: 1,1,2-

Trichloroethane. Office of Ground Water and Drinking Water, USEPA. Available on the

Internet at http://www.epa.gov/safewater/dwh/c-voc/112-tric.html (Last updated 04/12/2001)

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.

Wade Miller Associates, Inc. 1989. Estimated National Occurrence and Exposure Assessment of 1,1,2-

Trichloroethane in Public Drinking Water Supplies. Prepared for and submitted to EPA on

September 29, 1989.

Westrick, J.J., J.W. Mello, and R.F. Thomas. 1983. The Ground Water Supply Survey summary of

volatile organic contaminant occurrence data. EPA Technical Support Division, Office of

Drinking Water, Cincinnati, Ohio.
Occurrence Summary and Use Support Document March 2002 436

4.10 Trichloroethylene

Table of Contents

4.10.1 Introduction, Use and Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437

4.10.2 Environmental Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

4.10.3 Ambient Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439

4.10.4 Drinking Water Occurrence Based on the 16-State Cross-Section . . . . . . . . . . . . . . . . . . . . . . 440

4.10.5 Additional Drinking Water Occurrence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444

4.10.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

4.10.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

Tables and Figures

Table 4.10-1: Facilities that Manufacture or Process Trichloroethylene . . . . . . . . . . . . . . . . . . . . . . . 437

Table 4.10-2: Environmental Releases (in pounds) for Trichloroethylene 

in the United States, 1988-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439

Table 4.10-3: Stage 1 Trichloroethylene Occurrence Based on 16-State Cross-Section - 

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440

Table 4.10-4: Stage 1 Trichloroethylene Occurrence Based on 16-State Cross-Section - 

Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441

Table 4.10-5: Stage 2 Estimated Trichloroethylene Occurrence Based on 16-State 

Cross-Section - Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442

Table 4.10-6: Stage 2 Estimated Trichloroethylene Occurrence Based on 16-State 

Cross-Section - Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443

Table 4.10-7: Estimated National Trichloroethylene Occurrence - Systems and 

Population Served . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
Occurrence Summary and Use Support Document March 2002 437

4.10.1 Introduction, Use and Production

Trichloroethylene (chemical formula C2HCl3) is a nonflammable, colorless liquid at room temperature

that has a somewhat sweet odor, and a sweet, burning taste. It is also known as acetylene trichloride, 1-

chloro-2,2-dichloroethylene, 1,1-dichloro-2-chloroethylene, ethylene trichloride, trichloride, TCE, 1,1,2-

trichloroethylene, and trichloroethene. Trichloroethylene is also known as Triclene, Vitran, and by other

trade names in industry (ATSDR, 1997). 

The end use pattern of trichloroethylene in the U.S. in 1987 was estimated as follows: vapor degreasing

of fabricated metal parts, 80%; chemical intermediates, 5%; miscellaneous uses, 5%; and exports, 10%

(Spectrum Laboratories, 2001). Trichloroethylene is an excellent extraction solvent for greases, oils,

fats, waxes, and tars and is used by the textile processing industry to scour cotton, wool, and other

fabrics. As a general solvent, or as a component of solvent blends, trichloroethylene is used with

adhesives, lubricants, paints, varnishes, paint strippers, pesticides, and cold metal cleaners (ATSDR,

1997).

Trichloroethylene is used as a chemical intermediate for the production of polyvinyl chloride,

pharmaceuticals, polychlorinated aliphatics, flame retardant chemicals, and insecticides. 

Trichloroethylene is used as a refrigerant for low-temperature heat transfer, and in the aerospace industry

for flushing liquid oxygen. Some consumer products that contain trichloroethylene are typewriter

correction fluids, paint removers and strippers, adhesives, spot removers, and rug cleaning fluids

(ATSDR, 1997).

Use of trichloroethylene has declined due to its toxicity (NTP, 2001). It had been used as a general and

obstetrical anesthetic; a grain fumigant; a skin, wound, and surgical disinfectant; pet food additive, and

extractant of spice oleoresins in food and of caffeine for the purpose of making decaffeinated coffee. 

These uses were banned by the U.S. Food and Drug Administration in 1977 (ATSDR, 1997).

The only U.S. manufacturers of trichloroethylene are Dow Chemical in Freeport, TX, and PPG Industries

in Lake Charles, LA, with a combined annual production capacity of 320 million pounds. Because there

are currently only two manufacturers, recent production data is not available. In previous years,

production volumes of trichloroethylene have been reported as follows: 1978, 299 million pounds; 1979,

319 million pounds; 1980, 266 million pounds; 1981, 258 million pounds; and 1982, 200 million pounds. 

U.S. demand for trichloroethylene was estimated at 235 million pounds in 1983, 180 million pounds in

1985, and 170 million pounds in 1986 (ATSDR, 1997).

Table 4.10-1 shows the number of facilities in each State that manufacture and process trichloroethylene,

the intended uses of the product, and the range of maximum amounts derived from the Toxics Release

Inventory (TRI) of EPA (ATSDR, 1997). 

Table 4.10-1: Facilities that Manufacture or Process Trichloroethylene

Statea Number of facilities Range of maximum amounts on 

site in thousands of poundsb Activities and usesc

AL 12 1-1,000 2,3,7,8,12,13

AR 11 1-1,000 8,9,11,12,13

AZ 4 1-10 12,13

CA 5 1-10,000 1,5,8,10,11,13

CO 1 10-100 12

CT 15 1-100 11,12,13
Statea Number of facilities Range of maximum amounts on 

site in thousands of poundsb Activities and usesc

Occurrence Summary and Use Support Document March 2002 438

DE 1 100-1,000 13

FL 14 0-100 11,12,13

GA 12 1-1,000 8,12,13

IA 5 1-10 12,13

IL 99 0-100,000 1,4,8,9,10,11,12,13

IN 50 0-10,000 7,8,10,11,12,13

KS 12 0-1,000 8,10,11,12,13

KY 17 1-50,000 1,3,7,10,12,13

LA 11 1-10,000 1,3,4,5,6,7,8,12,13

MA 36 0-1,000 8,10,11,12,13

MD 4 1-100 2,3,12,13

ME 2 10-100 13

MI 41 1-1,000 2,3,8,10,11,12,13

MN 28 0-100 11,12,13

MO 28 0-1,000 2,3,8,10,12,13

MS 6 1-1,000 12,13

NC 19 0-100 10,11,12,13

NE 10 1-100 11,12,13

NH 4 1-100 11,13

NJ 11 1-1,000 8,12,13

NY 55 0-1,000 3,7,10,11,12,13

OH 55 0-1,000 8,10,11,12,13

OK 5 1-100 2,3,13

OR 7 0-1,000 11,12,13

PA 54 1-1,000 3,8,10,11,12,13

PR 1 10-100 13

RI 5 0-100 8,12,13

SC 12 1-1,000 7,12,13

SD 2 10-100 13

TN 14 1-1,000 2,3,7,11,12,13

TX 34 1-50,000 1,3,4,5,6,7,8,10,12,13

VA 12 1-1,000 12,13

VT 3 1-100 11,13

WA 9 0-100 12,13

WI 42 0-1,000 8,10,11,12,13

a

Post office State abbreviations used

b

Data in TRI are maximum amounts on site at each facility

c

Activities/Uses include:

1. Produce 8. As a formulation component

2. Import 9. As a product component

3. For on-site use/processing 10. For repackaging only

4. For sale/distribution 11. As a chemical processing aid

5. As a byproduct 12. As a manufacturing aid

6. As an impurity 13. Ancillary or other uses

7. As a reactant

Source: ATSDR, 1997 compilation of TRI93 1995 data

4.10.2 Environmental Release

Trichloroethylene is listed as a Toxics Release Inventory (TRI) chemical. Table 4.10-2 illustrates the

environmental releases for trichloroethylene from 1988 - 1999. (Trichloroethylene data are only

available for these years.) Air emissions constitute the vast majority of the on-site releases, with a steady

decrease over the years. The decrease in air emissions, as well as surface water discharges and off-site

releases (including metals or metal compounds transferred off-site), have contributed to decreases in

trichloroethylene total on- and off-site releases in the years covered by the TRI data. Underground

injection and releases to land (such as spills or leaks within the boundaries of the reporting facility) have

fluctuated over the years, but usually do not make a very significant contribution to overall releases. 

These TRI data for trichloroethylene were reported from 46 States and Puerto Rico. (No data were

reported from Wyoming, North Dakota, Hawaii, or Alaska). Of the 46 States, 37 reported every year
Occurrence Summary and Use Support Document March 2002 439

(USEPA, 2000). All of 16 cross-section States (used for analyses of trichloroethylene occurrence in

drinking water; see Section 4.10.4) reported TRI data for trichloroethylene. (For a map of the 16-State

cross-section, see Figure 1.3-1.)

Table 4.10-2: Environmental Releases (in pounds) for Trichloroethylene in the United States,

1988-1999

Year

On-Site Releases

Off-Site Releases

Total On- & 

Off-site 

Releases Air Emissions Surface Water

Discharges

Underground

Injection

Releases 

to Land

1999 10,510,064 1,043 0 138,522 115,587 10,765,216

1998 13,137,700 867 588 800 98,774 13,238,729

1997 18,143,968 563 986 3,975 182,423 18,331,915

1996 21,880,624 541 1,291 9,740 89,527 21,981,723

1995 26,265,512 1,477 550 3,577 74,145 26,345,261

1994 30,945,977 1,671 288 4,070 96,312 31,048,318

1993 31,007,030 5,220 460 8,212 233,561 31,254,483

1992 30,838,983 8,606 466 20,726 248,714 31,117,495

1991 36,356,277 12,784 800 62,991 115,973 36,548,825

1990 40,028,932 14,285 805 12,554 753,864 40,810,440

1989 49,798,528 15,849 390 8,686 1,250,933 51,074,386

1988 55,943,736 13,801 390 21,186 1,466,469 57,445,582

 Source: USEPA, 2000 

4.10.3 Ambient Occurrence

Trichloroethylene was detected in 47 out of 405 wells (11.6%) in urban areas of the local, State, and

federal data set compiled by NAWQA. The minimum and maximum concentrations detected were 0.2

:g/L and 80 :g/L, respectively. The median value of detection concentrations was 0.9 :g/L. 

Trichloroethylene was also detected in 41 of the 2,542 wells (1.6%) with analysis in rural areas. The

minimum and maximum concentrations detected were 0.2 :g/L and 63 :g/L, respectively. The median

value of detection concentrations was 0.6 :g/L. These data (urban and rural) represent untreated ambient

ground water of the conterminous United States for the years 1985-1995 (Squillace et al., 1999).

Trichloroethylene was also an analyte in the NURP study. The NURP study found trichloroethylene in

urban runoff (Lopes and Dionne, 1998). The minimum and maximum concentrations detected were 0.3

:g/L and 10 :g/L, respectively, with no mean value reported. The use of the land from which the

samples were taken was unspecified.

4.10.3.1 Additional Ambient Occurrence Data

A summary document entitled “Sources, Emission and Exposure for Trichloroethylene (TCE) and

Related Chemicals” (USEPA, 2001), was previously prepared for past USEPA assessments of

trichloroethylene. Various studies and information are presented regarding levels of TCE in water, both

ambient and drinking. These studies are summarized in Section 4.10.5. 
Occurrence Summary and Use Support Document March 2002 440

4.10.4 Drinking Water Occurrence Based on the 16-State Cross-Section

The analysis of trichloroethylene occurrence presented in the following section is based on State

compliance monitoring data from the 16 cross-section States. The 16-State cross-section is the largest

and most comprehensive compliance monitoring data set compiled by EPA to date. These data were

evaluated relative to several concentration thresholds of interest: 0.005 mg/L; 0.0025 mg/L; and 0.0005

mg/L.

All sixteen cross-section State data sets contained occurrence data for trichloroethylene. These data

represent more than 201,000 analytical results from approximately 23,000 PWSs during the period from

1984 to 1998 (with most analytical results from 1992 to 1997). The number of sample results and PWSs

vary by State, although the State data sets have been reviewed and checked to ensure adequacy of

coverage and completeness. The overall modal detection limit for trichloroethylene in the 16 crosssection States is equal to 0.0005 mg/L. (For details regarding the 16-State cross-section, please refer to

Section 1.3.5 of this report.)

4.10.4.1 Stage 1 Analysis Occurrence Findings

Table 4.10-3 illustrates the occurrence of trichloroethylene in drinking water for the public water systems

in the 16-State cross-section relative to three thresholds: 0.005 mg/L (the current MCL), 0.0025 mg/L,

and 0.0005 mg/L (the modal MRL). A total of 149 (approximately 0.647% of) ground water and surface

water PWSs had analytical results exceeding the MCL; 1.02% (234 systems) of systems in the 16 States

had results exceeding 0.0025 mg/L; and 2.24% of systems (516 systems) had results exceeding 0.0005

mg/L. 

Approximately 0.596% (128 systems) of ground water systems had any analytical results greater than the

MCL. About 0.951% (204 systems) of ground water systems had results above 0.0025 mg/L. The

percentage of ground water systems with at least one result greater than 0.0005 mg/L was equal to 2.12%

(455 systems). 

Approximately 21 (1.33% of) surface water systems had results greater than the MCL. A total of 30

(1.91% of) surface water systems had at least one analytical result greater than 0.0025 mg/L. Sixty-one

(3.88% of) surface water systems had results exceeding 0.0005 mg/L.

Table 4.10-3: Stage 1 Trichloroethylene Occurrence Based on 16-State Cross-Section - Systems

Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Ground Water

0.005 0.596% 128

0.0025 0.951% 204

0.0005 2.12% 455

Surface Water

0.005 1.33% 21

0.0025 1.91% 30

0.0005 3.88% 61
Source Water Type Threshold

(mg/L)

Percent of Systems

Exceeding Threshold

Number of Systems

Exceeding Threshold

Occurrence Summary and Use Support Document March 2002 441

Combined Ground &

Surface Water

0.005 0.647% 149

0.0025 1.02% 234

0.0005 2.24% 516

Reviewing trichloroethylene occurrence by PWS population served (Table 4.10-4) shows that

approximately 13.3% of the population served in the 16 States (almost 15 million people) was served by

PWSs with at least one analytical result of trichloroethylene greater than the MCL (0.005 mg/L). Over

17 million (15.6% of) people in the 16 States were served by systems with an exceedance of 0.0025

mg/L. A total of about 25.6 million (23.1% of) people were served by systems with at least one

analytical result greater than 0.0005 mg/L.

The percentage of 16-State population served by ground water systems with analytical results greater

than the MCL was equal to 8.01% (almost 4 million people). When evaluated relative to 0.0025 mg/L or

0.0005 mg/L, the percent of population exposed was equal to 11.2% (over 5.5 million people) and 18.6%

(approximately 9.2 million people), respectively. 

The percentage of 16-State population served by surface water systems with exceedances of 0.005 mg/L

was equal to 17.5% (approximately 10.7 million people). Approximately 19.2% of the population served

by surface water systems (about 11.7 million people) was exposed to trichloroethylene concentrations

greater than 0.0025 mg/L. When evaluated relative to 0.0005 mg/L, the percent of population exposed

was equal to 26.8% (over 16 million people).

Table 4.10-4: Stage 1 Trichloroethylene Occurrence Based on 16-State Cross-Section - Population

Source Water Type Threshold

(mg/L)

Percent of Population

Served by Systems

Exceeding Threshold

Total Population Served by

Systems Exceeding

Threshold

Ground Water

0.005 8.01% 3,971,100

0.0025 11.2% 5,539,500

0.0005 18.6% 9,219,500

Surface Water

0.005 17.5% 10,710,100

0.0025 19.2% 11,713,300

0.0005 26.8% 16,357,500

Combined Ground &

Surface Water

0.005 13.3% 14,681,200

0.0025 15.6% 17,252,900

0.0005 23.1% 25,577,000
Occurrence Summary and Use Support Document March 2002 442

4.10.4.2 Stage 2 Analysis Occurrence Findings

The Stage 2 occurrence findings, based on the cross-section data, are presented in Tables 4.10-5 and

4.10-6. The statistically generated best estimate values, as well as the ranges around the best estimate

value, are presented. (For a review of the Stage 2 analytical approach, please refer to Section 1.4 of this

report. For complete details regarding the Stage 2 analyses, please refer to Occurrence Estimation

Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water

Regulations - DRAFT (USEPA, 2002)). 

A combined total of 54 (0.236% of) ground water and surface water PWSs in the 16 States had an

estimated mean concentration of trichloroethylene exceeding 0.005 mg/L, while 103 (0.445% of) systems

in the 16 States had an estimated mean concentration exceeding 0.0025 mg/L and 299 (1.30% of)

systems had an estimated mean concentration exceeding 0.0005 mg/L. 

About 47 (0.221% of) ground water PWSs in the 16 States were estimated to have a mean concentration

greater than 0.005 mg/L. Additionally, 90 (0.420% of) ground water PWSs were estimated to exceed a

mean concentration of 0.0025 mg/L and 272 (1.27% of) systems were estimated to exceed a mean

concentration of 0.0005 mg/L. For surface water PWSs in the 16 States, 7 (0.450%), 13 (0.795%), and

27 (1.71%) had estimated mean concentrations exceeding 0.005 mg/L, 0.0025 mg/L, and 0.0005 mg/L,

respectively.

Table 4.10-5: Stage 2 Estimated Trichloroethylene Occurrence Based on 16-State Cross-Section -

Systems

Source Water Type Threshold

(mg/L)

Percent of Systems Estimated 

to Exceed Threshold

Number of Systems in the 16 States

Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 0.221% 0.186% - 0.256% 47 40 - 55

0.0025 0.420% 0.368% - 0.466% 90 79 - 100

0.0005 1.27% 1.17% - 1.39% 272 252 - 299

Surface Water

0.005 0.450% 0.381% - 0.572% 7 6 - 9

0.0025 0.795% 0.699% - 0.953% 13 11 - 15

0.0005 1.71% 1.46% - 2.03% 27 23 - 32

Combined Ground

& Surface Water

0.005 0.236% 0.204% - 0.274% 54 47 - 63

0.0025 0.445% 0.399% - 0.491% 103 92 - 113

0.0005 1.30% 1.21% - 1.42% 299 279 - 326

Reviewing trichloroethylene occurrence by PWS population served (Table 4.10-6) shows that

approximately 8.19% of population served by all PWSs in the 16 States (an estimate of over 9 million

people) were potentially exposed to trichloroethylene levels above 0.005 mg/L. For all PWSs in the 16

States, an estimated 9.17% of population served (an estimate of over 10 million people served in the 16
Occurrence Summary and Use Support Document March 2002 443

States) was exposed to levels above 0.0025 mg/L, and 12.5% (an estimated 13.8 million people in the 16-

State cross-section) was exposed to levels above 0.0005 mg/L.

When the population exposed for ground water systems was evaluated relative to thresholds of 0.005

mg/L, 0.0025 mg/L, and 0.0005 mg/L, the percentages of population exposed were equal to 1.94% (an

estimated 962,700 people), 3.30% (an estimate of over 1.6 million people), and 7.90% (an estimated 3.9

million people), respectively.

 The percentage of population served by surface water systems in the 16 States with levels above 0.005

mg/L was 13.3% (an estimated 8 million people), while the population served with levels above 0.0025

mg/L and 0.0005 mg/L was 13.9% (an estimated 8.5 million people) and 16.2% (an estimate of almost

9.9 million people), respectively. 

Table 4.10-6: Stage 2 Estimated Trichloroethylene Occurrence Based on 16-State Cross-Section -

Population

Source Water Type Threshold

(mg/L)

Percent of Population Served by Systems

Estimated to Exceed Threshold

Total Population Served by Systems in the

16 States Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 1.94% 1.56% - 2.33% 962,700 772,500 - 1,153,500

0.0025 3.30% 2.91% - 3.82% 1,634,100 1,442,900 - 1,890,800

0.0005 7.90% 7.26% - 8.69% 3,914,900 3,597,800 - 4,305,300

Surface Water

0.005 13.3% 13.0% - 13.7% 8,097,000 7,950,500 - 8,377,900

0.0025 13.9% 13.8% - 14.5% 8,512,300 8,408,400 - 8,823,700

0.0005 16.2% 15.0% - 18.6% 9,886,200 9,165,600 - 11,351,700

Combined Ground

& Surface Water

0.005 8.19% 7.98% - 8.41% 9,062,500 8,828,000 - 9,302,500

0.0025 9.17% 8.95% - 9.53% 10,147,600 9,894,300 - 10,535,900

0.0005 12.5% 11.7% - 13.8% 13,804,500 12,952,800 - 15,242,500

4.10.4.3 Estimated National Occurrence

Based on the Stage 2 estimated percent of systems (and population served by systems) exceeding each

threshold, an estimated 154 PWSs nationally, serving over 17 million people, could be exposed to

trichloroethylene concentrations above 0.005 mg/L. About 290 systems, serving almost 20 million

people nationally, had estimated mean concentrations greater than 0.0025 mg/L. Approximately 844

systems, serving about 26.6 million people nationally, were estimated to have mean trichloroethylene

concentrations greater than 0.0005 mg/L. (See Section 1.4 for a description of how Stage 2 16-State

estimates are extrapolated to national values.)

For ground water systems, an estimated 131 PWSs, serving about 1.7 million people nationally, had

mean concentrations greater than 0.005 mg/L. Approximately 250 systems, serving over 2.8 million
Occurrence Summary and Use Support Document March 2002 444

people nationally, had estimated mean concentration values that exceeded 0.0025 mg/L. About 754

ground water systems, serving almost 6.8 million people, had estimated mean concentrations greater than

0.0005 mg/L. 

Although fewer surface water systems than ground water systems nationally had estimated mean

concentration values greater than the thresholds, a much larger population was served by surface water

systems with threshold exceedances because surface water systems tend to serve much larger

populations. Approximately 25 surface water systems, serving almost 17 million people, were estimated

to have mean concentrations of trichloroethylene above 0.005 mg/L. About 44 surface water systems,

serving almost 18 million people, had estimated mean concentrations greater than 0.0025 mg/L. An

estimated 95 surface water systems, serving approximately 20.6 million people, had mean concentrations

greater than 0.0005 mg/L.

Table 4.10-7: Estimated National Trichloroethylene Occurrence - Systems and Population Served

Source Water Type Threshold

(mg/L)

Total Number of Systems Nationally

Estimated to Exceed Threshold

Total Population Served by Systems

Nationally Estimated to Exceed Threshold

Best Estimate Range Best Estimate Range

Ground Water

0.005 131 111 - 152 1,664,800 1,335,800 - 1,994,700

0.0025 250 219 - 277 2,825,800 2,495,100 - 3,269,600

0.0005 754 698 - 828 6,769,700 6,221,300 - 7,444,900

Surface Water

0.005 25 21 - 32 16,883,500 16,577,900 - 17,469,200

0.0025 44 39 - 53 17,749,300 17,532,900 - 18,398,700

0.0005 95 82 - 114 20,614,200 19,111,700 - 23,670,000

Combined Ground

& Surface Water

0.005 154 133 - 178 17,451,800 17,000,200 - 17,914,000

0.0025 290 260 - 319 19,541,400 19,053,600 - 20,289,000

0.0005 844 788 - 920 26,583,400 24,943,300 - 29,352,500

4.10.5 Additional Drinking Water Occurrence Data

Several additional data sources regarding the occurrence of trichloroethylene in drinking water are also

reviewed. Previously compiled occurrence information, from an OGWDW summary document entitled

“Sources, Emission and Exposure for Trichloroethylene (TCE) and Related Chemicals” (USEPA, 2001),

is presented in this section. This variety of studies and information are presented regarding levels of

trichloroethylene in drinking water, with the scope of the reviewed studies ranging from national to

regional. Note that none of the studies presented in the following section provide the quantitative

analytical results or comprehensive coverage that would enable direct comparison to the occurrence

findings estimated with the cross-section occurrence data presented in Section 4.10.4. These additional

studies, however, do enable a broader assessment of the Stage 2 occurrence estimates presented for this

Six-Year Review. All the following information in Section 4.10.5 is taken directly from “Sources,

Emission and Exposure for Trichloroethylene (TCE) and Related Chemicals” (USEPA, 2001).
Occurrence Summary and Use Support Document March 2002 445

4.10.5.1 Levels of Trichloroethylene (TCE) in Various Water Sources

According to IARC (1995, as cited in USEPA, 2001), the reported median concentrations of TCE in

1983-84 were 0.5 :g/L in industrial effluents and 0.1 :g/L in ambient water. ATSDR (1997, as cited in

USEPA, 2001) has reported that TCE is the most frequently reported organic contaminant in

groundwater and the one present in the highest concentration in a summary of ground water analyses

reported in 1982. It has been estimated that somewhere between 9 and 34 percent of the drinking water

supply sources tested in the U.S. may have some trichloroethylene contamination. This estimate is based

on available Federal and State surveys (ATSDR, 1997, as cited in USEPA, 2001). Results from an

analysis of the EPA STORET Data Base (1980-1982) showed that TCE was detected in 28 percent of

9,295 surface water reporting stations nationwide (ATSDR, 1997, as cited in USEPA, 2001).

More recently, the USEPA Office of Ground Water and Drinking Water reposed that most water supplies

are in compliance with the maximum contaminant level (maximum contaminant level (MCL), 5 :g/L),

and that only 407 samples out of many thousands taken from community and other water supplies

throughout the country over the past 11 years (1987-1997) have exceeded the MCL limit for TCE

(USEPA, 1998, as cited in USEPA, 2001). 

TCE concentrations in ground water have been measured extensively in California. The data were

derived from a survey of large water utilities (i.e. utilities with more than 200 service connections). The

survey was conducted by the California Department of Health Services (DHS, 1986, as cited in USEPA,

2001). From January 1984 through December 1985, wells in 819 water systems were sampled for organic

chemical contamination. The water systems use a total of 5,550 wells, 2,947 of which were sampled.

TCE was found in 187 wells, at concentrations up to 440 :g/L, with a median concentration of 3.0 :g/L.

Generally, the most contaminated wells and the wells with the highest concentrations were found in the

heavily urbanized areas of the State. Los Angeles County registered the greatest number of contaminated

wells (149).

4.10.5.2 Human Exposure and Population Estimates

4.10.5.2.1 General U.S. Population

Because of the pervasiveness of TCE in the environment, most people are exposed to it through ingestion

of drinking water, inhalation of ambient air, or ingestion of food (ATSDR, 1997, as cited in USEPA,

2001). Contamination of drinking water with TCE varies according to location and with the drinking

water source (whether source is surface water or groundwater). TCE readily volatilizes from water and

inhalation of indoor air may be a major route of exposure in homes with contaminated water supply

(ATSDR, 1997, as cited in USEPA, 2001).

The California survey of large water utilities in 1984 found a median concentration of 3.0 :g/L (DHS,

1986). Using this value and a 2 L/day water consumption rate yields an estimate of 6 :g/day. This is

consistent with ATSDR (ATSDR, 1997, as cited in USEPA, 2001) which reported an average daily water

intake for the general population of 2 to 20 :g/day.

The use of ambient air data to estimate inhalation exposure does not account for possible differences

between contaminant levels in indoor vs. outdoor air. TCE readily volatilizes from water and indoor

inhalation exposure may be comparable or greater than ingestion exposures in homes where the water

supply contains TCE (ATSDR, 1997; Andelman, et al., 1985; Giardino, et al., 1992; Andelman et al.,

1986a; Andelman et al., 1986b, as cited in USEPA, 2001). For example, in two homes using well water 
Occurrence Summary and Use Support Document March 2002 446

with TCE levels averaging 22 to 128 :g/L, the TCE levels in bathroom air ranged from <0.5 to 40 mg/m3

when the shower was run less than 30 minutes (Andelman et al., 1985, as cited in USEPA, 2001). In one

study, the transfer of TCE from shower water to air had a mean efficiency of 61% (independent of water

temperature); it was concluded that a 10-minute shower in TCE-contaminated water could result in a

daily inhalation exposure comparable to that expected from drinking TCE-contaminated tap water

(ATSDR, 1997, as cited in USEPA, 2001). TCE in bathing water can also cause dermal exposure. A

modeling study has suggested that a significant fraction of the total dose associated with exposure to

volatile organics in drinking water results from dermal absorption (Brown, et al., 1984, as cited in

USEPA, 2001).

Pharmacokinetic modeling can be used to gain further understanding of general population exposure.

Clewell et al. (1995, as cited in USEPA, 2001) developed a physiologically based pharmacokinetic model

for TCE that can be used to estimate the long-term average ingested dose that would result in a measured

blood concentration, assuming no other TCE exposure. This dose can be converted to a TCE water

concentration assuming an ingestion rate such as 2 L/day. This model was applied to the range of TCE

levels in blood as measured in NHANES 111. The TCE environmental concentrations modeled from

blood levels exceeded the range of measured values for air and water: modeled mean concentration in

drinking water was 59.5 :g/L (measured range was trace to 50 :g/L) and the modeled mean air

concentration was 4.2 :g/m3

 (measured range was for 0.01 to 3.9 :g/m3) . This implies that neither

inhalation nor water ingestion dominate exposure; rather both contribute to the total exposure. Exposure

estimates derived from blood cannot distinguish among exposure routes and sources. It is generally

believed that TCE exposure occurs primarily via water consumption and air inhalation, but it is

impossible to use the blood data to directly estimate how much of the total exposure is attributable to

each. A wide range of combinations of exposures from air and water could have produced the measured

blood levels. As noted earlier, most water supplies have TCE levels under the MCL of 5 :g/L. The

modeling suggests that exposure at the MCL would correspond to a very low blood level. This implies

that the TCE exposure via the air and other nonwater pathways may generally be more important than

water ingestion.

4.10.5.2.2 Extent of General Population Exposure

Because of the pervasiveness of TCE in the environment. most people are likely to have some exposure

via one or more of the following pathways: ingestion of drinking water, inhalation of ambient air, or

ingestion of food (ATSDR, 1997, as cited in USEPA, 2001). As noted earlier, the NHANES survey

suggests that about 10% of the population has detectable levels of TCE in their blood. The exposures in

these individuals may be higher than those in others in the general population, as a result of a number of

factors. Some members of the general population may have increased TCE exposure via their drinking

water. The extent of TCE exposure via drinking water is difficult to estimate; but the following

discussion provide some perspective on this issue.

TCE is the most frequently reported organic contaminant in ground water (ATSDR, 1997, as cited in

USEPA, 2001). Ninety-three percent of the public water systems in the United States obtain water from

groundwater (USEPA, 1995, as cited in USEPA, 2001), and between 9% and 34% of the drinking water

supply sources tested in the United States may have some TCE contamination (ATSDR, 1997, as cited in

USEPA, 2001). Although commonly detected in water supplies, the levels are generally low, since, as

discussed earlier, MCL violations for TCE in public water supplies are relatively rare for any extended

period (USEPA, 1998, as cited in USEPA, 2001). Private wells, however, are often not closely

monitored, and, if located near TCE disposal/contamination sites where leaching occurs, may have

undetected contamination levels. About 10% of Americans (27 million people) obtain water from sources
Occurrence Summary and Use Support Document March 2002 447

other than public water systems, primarily private wells (USEPA, 1995, as cited in USEPA, 2001). TCE

is a common contaminant at Superfund sites. It has been identified in at least 861 of the 1,428 hazardous

waste sites proposed for inclusion on the EPA National Priorities List (NPL) (ATSDR, 1997, as cited in

USEPA, 2001). Studies have shown that many people live near these sites: 41 million people live less

than 4 miles from one or more of the nation's NPL sites, and, on average, 3,325 people live within 1 mile

of any given NPL site (ATSDR, 1996, as cited in USEPA, 2001). Thus, although exact estimates cannot

be made, many people are probably exposed to TCE via drinking water from private wells. It is not

known how often such exposures would be above the MCL.

4.10.6 Conclusion

Trichloroethylene is primarily used for vapor degreasing of fabricated metal parts. It is also used as a

chemical intermediate and as a product for export. The use of trichloroethylene has also declined due to

its toxicity. Recent statistics regarding production are not available, but according to TRI data,

trichloroethylene is widely manufactured and processed in substantial amounts. Trichloroethylene is also

a TRI chemical. Industrial releases of trichloroethylene have occurred since 1988 in 46 States and Puerto

Rico. Trichloroethylene was an analyte for the NAWQA and NURP ambient occurrence studies. In the

NAWQA study, trichloroethylene was detected in 11.6% of urban wells and 1.6% of rural wells, with

median detection values of 0.9 :g/L and 0.6 :g/L, respectively. In the Stage 2 analysis of 16-State

occurrence of trichloroethylene, 0.236% of combined ground water and surface water systems serving

8.19% of the population exceeded the MCL of 0.005 mg/L. Nationally, 154 ground water and surface

water systems combined (serving approximately 17,451,800 people) are estimated to have levels greater

than the MCL.

The 16-State cross-section was designed to be nationally representative based upon VOC, SOC, and IOC

pollution potentials as suggested by considerations of manufacturing, agriculture, and geographic

diversity factors. Nationally, trichloroethylene is manufactured and/or processed in 40 States and has

TRI releases in 46 States. Trichloroethylene is manufactured and/or processed in 14 out of the 16 crosssection States and has TRI releases in all of the 16 cross-section States. The cross-section should

adequately represent the occurrence of trichloroethylene on a national scale based upon the use,

production, and release patterns of the 16-State cross-section in relation to the patterns observed for all

50 States.

4.10.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1996. Biennial Report to Congress (1991

and 1992). Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease

Control and Prevention, ATSDR. Internet site: www.dhhs.gov. 

Agency for Toxic Substances and Disease Registry (ATSDR). 1997. Toxicological Profile for

Trichloroethylene. U.S. Department of Health and Human Services, Public Health Service. 298

pp. + Appendices. Available on the Internet at http://www.atsdr.cdc.gov/toxprofiles/tp19.pdf 

Andelman, J.B. 1985. Human exposure to volatile halogenated organic chemicals in indoor and outdoor

air. Environ Health Perspect 62:313-318.

Andelman, J., A. Couch, W.W. Thurston. 1986a. Inhalation exposures in indoor air to trichloroethylene

from shower water. Chapter 16. Environmental epidemiology. Kopfler, F.C. and G.C. Craun

(eds.). Chelsea, MI: Lewis Publishers.
Occurrence Summary and Use Support Document March 2002 448

Andelman, J.B., S.M. Meyers, L.C. Wilder. 1986b. Volatilization of organic chemicals from indoor uses

of water. Chemicals in the environment. Lester, J.N., R. Perry, and R.M. Sterritt (eds.). 

London: Selper Ltd.

Brown, H.S., D.R. Bishop, C.A. Rowan. 1984. The role of skin absorption as a route of exposure for

volatile organic compounds in drinking water . Am. J. Publ. Health 74(5): 479-484. 

Clewell, H.J., P.R. Gentry, J.M. Gearhart et al. 1995. Considering pharmacokinetic and mechanistic

information in cancer risk assessments for environmental contaminants: examples with vinyl

chloride and trichloroethylene. Chemosphere. 31(1): 2561-2578.

DHS. 1986. Organic chemical contamination of large public water systems in California. Sacramento,

CA: California Department of Health Services.

Giardino, N.J., E. Gumerman, N.A. Esmen, et al. 1992. Shower volatilization exposures in homes using

tap water contaminated with TCE. J. Exposure Analysis Environ Epidemiol (Suppl. 1): 147-158.

International Agency for Research on Cancer (IARC). 1995. IARC monographs on the evaluation of

carcinogenic risks to humans: dry cleaning, some chlorinated solvents and other industrial

chemicals. Vol.63. Lyon, France: IARC.

Lopes, T.J. and S.G. Dionne. 1998. A Review of Semivolatile and Volatile Organic Compounds in

Highway Runoff and Urban Stormwater. U.S. Geological Survey Open-File Report 98-409. 

67 pp.

National Toxicology Program (NTP). 2001. National Toxicology Program Health and Safety

Information Sheet - Trichloroethylene. Available on the Internet at

http://ntp-server.niehs.nih.gov/htdocs/CHEM_H&S/NTP_Chem7/Radian79-01-6.html, accessed

July 23, 2001.

Spectrum Laboratories. 2001. Chemical Fact Sheet - Trichloroethylene. Available on the Internet at

http://www.speclab.com/compound/c79016.htm, accessed July 23, 2001.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges, and J.S. Zogorski. 1999. 

Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995. 

Env. Sci. and Tech. 33(23):4176-4187.

USEPA. 1995. The National Public Water Systems Supervision Program. The FY 1994 Compliance

Report. EPA 812-R-94-001. Washington, DC: Office of Water, USEPA.

USEPA. 1998. EPA data file. Office of Groundwater and Drinking Water. Washington, D.C.: U.S.

Environmental Protection Agency.

USEPA. 2000. TRI Explorer: Trends. Available on the Internet at:

http://www.epa.gov/triexplorer/trends.htm, last updated May 5, 2000.

USEPA. 2001. Sources, Emissions and Exposure for Trichloroethylene (TCE) and Related Chemicals. 

Office of Research and Development, USEPA. March 2001.
Occurrence Summary and Use Support Document March 2002 449

USEPA. 2002. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of

National Primary Drinking Water Regulations - DRAFT. EPA Report/815-D-02-005, Office of

Water, 55 pp.
Occurrence Summary and Use Support Document March 2002 450

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Occurrence Summary and Use Support Document March 2002 451

Abbreviations and Acronyms

>MRL - analytical results greater than the Minimum Reporting Limit (or Level)

1,1,2-TCE - 1,1,2-trichloroethane

ai - active ingredient

AMC - annualized mean concentration

ARP - Acetochlor Monitoring Partnership

ARP-GWMP - Acetochlor Monitoring Partnership Ground water Monitoring Program

ATSDR - Agency for Toxic Substances and Disease Registry

AWT - Advanced Wastewater Treatment

AWWA - American Water Works Association

CA - Census of Agriculture

CAS - Chemical Abstract Service

CASRN - Chemical Abstract Service Registry Number

CDC - Centers for Disease Control and Prevention

CERCLA - Comprehensive Environmental Response, Compensation & Liability Act

CMR - Chemical Monitoring Reform

CWS - Community Water System

CWSS - Community Water Supply Survey

DBCP - 1,2-Dibromo-3-chloropropane

DCE - dichloroethylene

DCP - dichloropropane

DEHP - di(2-ethylhexyl)phthalate

DHS - Department of Health Services, California

EFED - Environmental Fate and Effects Division

EPA - Environmental Protection Agency

EPCRA - Emergency Planning and Community Right-to-Know Act

FIFRA - Federal Insecticide, Fungicide, and Rodenticide Act

FR - Federal Register

FRDS - Federal Reporting Data Systems

FSTRAC - Federal/State Toxicological and Regulatory Alliance Committee

g/mol - grams per mole

GW - ground water

GWSS - Groundwater Supply Survey

HAL - Health Advisory Level

HSDB - Hazardous Substances Data Bank

IARC - International Agency for Research on Cancer

IOC - inorganic compound

LLMV - lower limit of method validation

LOD - level of detection
Occurrence Summary and Use Support Document March 2002 452

MCL - Maximum Contaminant Level

MCLG - Maximum Contaminant Level Goal

MDA - Minnesota Department of Agriculture

MDH - Minnesota Department of Health

MDL - Method Detection Limit

mg/L - milligrams per liter

MRL - Minimum Reporting Level

NAWQA - National Water Quality Assessment Program

NAWQA - National Alachlor Water Well Survey

NCFAP - National Center for Food and Agricultural Policy

NHANES - National Health and Nutrition Examination Survey

NIRS - National Inorganics and Radionuclides Survey

NLM - National Library of Medicine

NOMS - National Organic Monitoring Survey

NORS - National Organics Reconnaissance Survey

NPS - National Pesticide Survey

NPDES - National Pollution Discharge Elimination System

NPDWR - National Primary Drinking Water Regulations

NPL - National Priorities List

NSC - National Safety Council

NSDWR - National Secondary Drinking Water Regulation

NSP - National Screening Program for organics in drinking water

NTNCWS - Non-Transient Non-Community Water System

NTP - National Toxicology Program

NURP - National Urban Runoff Program

ODS - ozone depleting substance

ODW - Office of Drinking Water

OGWDW - Office of Ground Water and Drinking Water

OL - Optimum Level

OPP - Office of Pesticide Programs

OSHA - Occupational Safety and Health Administration

PCBs - polychlorinated biphenyls

PEL - permissible exposure limit

PGWDB - Pesticides in Ground Water Data Base

pH - the negative log of the concentration of H+

 ions

PLUARG - Pollution from Land Use Activities Reference Group

PPG - Pittsburgh Paint and Glass Industries

PVC - polyvinyl chloride

PWS - Public Water System

PWSID - Public Water System Identifier 

QA - quality assurance

QC - quality control

RCRA - Resource Conservation and Recovery Act

RED - Reregistration Eligibility Decision

RWS - Rural Water Survey
Occurrence Summary and Use Support Document March 2002 453

RY - Reporting Year

SAIC - Science Applications International Corporation

SARA Title III - Superfund Amendments and Reauthorization Act

SDWA - Safe Drinking Water Act

SDWIS/FED - Safe Drinking Water Information System/Federal version

SMCL - Secondary Maximum Contaminant Level

SMSA - standard metropolitan statistical areas

SOC - synthetic organic compound

SRI - formerly the Stanford Research Institute

STORET - STOrage and RETrieval

SW - surface water 

TCE - trichloroethylene

TDI - toluene diisocyanate

TRI - Toxics Release Inventory

TSD - Technical Support Division (ODW)

TWMC - time weighted mean concentration

USEPA - United States Environmental Protection Agency

USGS - United States Geological Survey

USITC - United States International Trade Commission

USPHS - United States Public Health Service

VOC - volatile organic compound

WHO - World Health Organization

μg/L - micrograms per liter