United States Office of Water EPA 81 5-P-00-002
Environmental Protection Agency 4606 June 2001
Occurrence of Unregulated
Contaminants in Public Water
Systems-A National Summary
r?% Printed on Recycled Paper
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
TABLE OF CONTENTS
TABLES AND FIGURES iii
ACRONYMS v
EXECUTIVE SUMMARY vii
ACKNOWLEDGMENTS k
DISCLAIMER x
I. INTRODUCTION 1
I.A. Background 1
I.E. Unregulated and Regulated Contaminants, Databases, and Monitoring Timeframe 2
I.C. Data Analysis 7
II. DATA SOURCES AND DATA QUALITY REVIEW 8
II. A. URCIS (Round 1) Data 8
II. A. 1. Description of Data 8
II.A.2. Data Management and Data Quality 8
II.A.3. Further Data Review and Editing 9
II.B. SDWIS/FED (Round 2) Data 11
II.B.l. Description of Data 11
II.B.2. Data Management and Data Quality 11
II.B.3. Further Data Review and Editing 11
III. DEVELOPING A NATIONALLY REPRESENTATIVE PERSPECTIVE 13
III.A. Methods 14
III.A.1. Manufacturing Indicators 14
III.A.2. Agricultural Indicators 14
III.B. Representative Cross-Section of States 15
III.B.l. URCIS 24-State Cross-Section 15
III.B.2. Incremental National Cross-Sections 19
III.B.3. SDWIS/FED 20-State Cross-Section 19
IV DATA COVERAGE FOR THE NATIONAL OCCURRENCE OF
CONTAMINANTS IN DRINKING WATER 22
IVA. URCIS (Round 1) Data Coverage 22
IVB. SDWIS/FED (Round 2) Data Coverage 23
IVC. Comparing Data Coverage of URCIS (Round 1) and SDWIS/FED (Round 2) 23
IV D. Comparing Data Coverage Across Systems Sizes and Types 24
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
V. ANALYSIS OF NATIONAL OCCURRENCE 24
V.A. URCIS (Round 1) Contaminant Occurrence 24
V.B. SDWIS/FED (Round 2) Contaminant Occurrence 27
VI. ASSESSMENTS OF SELECT HIGH OCCURRENCE CONTAMINANTS 30
VI. A. Select High Occurrence Contaminants and Detailed Graphical and Spatial Analysis . . 30
VLB. Graphical and Spatial Assessments of Select High Occurrence Contaminants 33
VI.B.l. Ethylene Dibromide 33
VLB.2. Tetrachloroethylene 34
VLB.3. Trichloroethylene 34
VI.B.4. Aldicarb Sulfoxide 34
VI.B.5. Dieldrin 35
VI.B.6. Metolachlor 35
VI.B.7. 1,1-Dichloroethane 35
VI.B.8. Chloromethane 35
VI.B.9. Chloroform 36
VLB. 10. Comparison of Occurrence in URCIS (Round 1) and
SDWIS/FED (Round 2) 36
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
TABLES AND FIGURES
Figure I.B.I. Diagram of the Inter-Relationship of Various Databases, Monitoring
Rounds and Contaminant Lists Discussed in the Report ...................... 2
Table I.E. 1 . List and Description of Contaminants with Data in URCIS (Round 1)
(approximately 1987-1992) ........................................... 3
Table I.B.2. List and Description of Contaminants with Data in SDWIS/FED (Round 2)
(approximately 1993-1997) ........................................... 5
Table II.A.3.a. Summary of Data Quantity and Quality in URCIS (Round 1) for the States,
Tribes, and Territories ............................................... 9
Table II.B.3.a. Summary of Data Quantity and Quality in SDWIS/FED (Round 2) for the
States, Tribes, and Territories ........................................ 11
Table III.B. 1 . Ranking of States based on Number of Manufacturing Establishments
per Square Mile. URCIS (Round 1) 24 State Cross-Section in Bold ............. 14
Figure III.B. 1 .a. Distribution of State Rankings for Manufacturing Establishments /
Sq. Mile vs. Farm Ag. Chemical Expenses. Highlighting URCIS
(Round 1) 24 Cross-Section States .................................... 16
Figure III.B. l.b. 24 URCIS (Round 1) Representative Cross-Section States and States
Not Included in the Cross-Section ..................................... 17
Table III.B. 3. Ranking of States based on Number of Manufacturing Establishments
per Square Mile. SDWIS/FED (Round 2) 20 Cross-Section States in Bold ........ 18
Figure III.B. 3. b. Distribution of State Rankings for Manufacturing Establishments /
Sq. Mile vs. Farm Ag. Chemical Expenses. Highlighting SDWIS/FED
(Round 2) 20 Cross-Section States .................................... 20
Figure III.B.3.b. 20 SDWIS/FED (Round 2) Cross-Section States and States
Not Included in the Cross-Section ..................................... 21
Table V.A.I. URCIS (Round 1) 24-State Cross-Section Summary of Occurrence ............ 24
Table V.B. 1. SDWIS/FED (Round 2) Data - 20 State Cross-Section Summary of Occurrence ... 27
Table VI. A.I. Contaminant Occurrence Ranking of URCIS (Round 1) Data ................. 29
Table VI.A.2. Contaminant Occurrence Ranking of SDWIS/FED (Round 2) Data ............ 30
Table VI. A. 3. High Occurrence Contaminants Selected for Graphical and Spatial Assessments ... 31
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
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IV
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
ACRONYMS
Chemical Abstract Services (CAS)
Chemical Monitoring Reform (CMR)
Community Water System (CWS)
Dibromochloropropane (DBCP)
Environmental Protection Agency (EPA)
Ethylene Dibromide (EDB)
Ground Water (GW)
Ground Water - Purchased (GWP)
Ground Water Under Direct Influence (GUDI)
Ground Water Under Direct Influence - Purchased (GUP)
Health Advisory Level (HAL)
Health Reference Level (HRL)
Inorganic Chemical (IOC)
Maximum Contaminant Level (MCL)
Method Detection Limit (MDL)
micrograms per liter (• g/L)
milligrams per liter (mg/L)
Minimum Reporting Level (or Limit, MRL)
National Contaminant Occurrence Database (NCOD)
National Primary Drinking Water Regulations (NPDWRs)
National Water Quality Assessment Program (NAWQA)
Non-Transient Non-Community Water System (NTNCWS)
Office of Ground Water and Drinking Water (OGWDW)
Percentage of Systems with Exceedances (>MCL/ >HRL/ >HAL)
Percentage of Systems with Detections (>MRL)
Public Water System (PWS)
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
ACRONYMS (continued)
Public Water System Identifier (PWSID)
Safe Drinking Water Act (SDWA)
Safe Drinking Water Information System (SDWIS)
Safe Drinking Water Information System/Federal Version (SDWIS/FED)
Surface Water (SW)
Surface Water - Purchased (SWP)
Synthetic Organic Chemical (SOC)
Tetrachloroethylene (PCE)
Toxic Release Inventory (TRI)
Transient Non-Community Water System (TNCWS)
Trichloroethylene (TCE)
Trihalomethane (THM)
United States Geological Survey (USGS)
Unregulated Contaminant Monitoring Information System (URCIS)
Unregulated Contaminant Monitoring (UCM)
Unregulated Contaminant Monitoring Regulation (UCMR)
Volatile Organic Chemical (VOC)
VI
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
EXECUTIVE SUMMARY
This summary provides a condensed overview of the national occurrence report entitled
Occurrence of Unregulated Contaminants in Public Water Systems: An Initial Assessment (EPA
815-P-00-001). The complete, original report, referred to as the "complete National Occurrence report,"
includes a comprehensive overview of the management and initial assessment of the unregulated
contaminant occurrence data currently available to EPA. The data are from the required monitoring of
unregulated contaminants conducted by public drinking water systems prior to 1998. Specifically, the
assessments summarized here (and described in detail in the complete National Occurrence report
referenced above) are based on the occurrence data from the Unregulated Contaminant Information
System (URCIS) database and the Safe Drinking Water Information System/Federal Version
(SDWIS/FED) database. The objective of the occurrence assessment is to enhance the scientific
understanding of the occurrence of unregulated contaminants in public drinking water systems, and to
refine the approach of management and analysis of contaminant occurrence data.
The contaminant occurrence analyses and findings presented in this report are based on national
cross-sections of state data (i.e., a subset of representative state data) derived from the URCIS (Round
1) and SDWIS/FED (Round 2) databases. The occurrence findings presented here are not based on the
entire collection of state compliance monitoring data contained in the URCIS (Round 1) and SDWIS/FED
(Round 2) databases. The data that were used as the basis for the analyses in this report are available
upon request from EPA Office of Ground Water and Drinking Water. Requests for this data should be
sent to ucmr.report(g),epa. gov.
This summary report includes descriptions of Round 1 and Round 2 unregulated contaminant
monitoring data, reviews the extensive data quality management necessary to conduct occurrence
analyses, outlines the construction of a national cross-section of states from each of the two databases,
and summarizes the occurrence analyses (based on the cross-sections) of the 62 unregulated
contaminants in the Round 1 data set and the 48 unregulated contaminants in the Round 2 data set. The
Round 1 data are contained in the URCIS database, and the Round 2 data are contained in the
SDWIS/FED database.
The URCIS database (Round 1 data) contains public water system monitoring results, generally
from 1988 to 1992, for unregulated contaminants collected under the authority of the Safe Drinking Water
Act (SDWA). Forty states/primacy entities have submitted PWS monitoring data to URCIS. Round 2
monitoring data, generally collected from 1993 to 1997, were reported directly to the SDWIS/FED
database. Thirty-five states/primacy entities have submitted Round 2 PWS monitoring data to
SDWIS/FED. The raw data from these two databases were reviewed extensively and edited for data
quality considerations to ensure consistency and repeatability in the analyses.
A data management approach was used in this study to develop a national cross-section of states
that enables occurrence analyses that are indicative of national occurrence. All states with monitoring
data were evaluated according to their distribution across a range of pollution potential indicators and
spatial/hydrogeologic diversity. A select group of states, representing a balanced distribution across these
pollution-potential measures and across the nation geographically, were then used to construct national
cross-sections (one cross-section from Round 1 data, and another from Round 2 data) that would provide
reasonable representation of national occurrence. While the national cross-sections cannot be considered
"statistically representative," the constructed cross-sections are very large samples (24 and 20 states,
respectively), providing analytical occurrence results that are clear indications of central tendency of the
occurrence data, and are generally indicative of national contaminant occurrence.
Vll
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
The cross-sections have been constructed with a large number of occurrence data to broadly
reflect national coverage. The 24 cross-section states of URCIS (Round 1) data represent approximately
44% of public water systems nationally and 51% of the population served by public water systems. The
20 cross-section states of SDWIS/FED (Round 2) data represent approximately 41% of public water
systems nationally and 34% of the population served by public water systems. The data from these two
separate cross-sections are used to compute contaminant occurrence measures as an approximation of
national occurrence.
Summary assessments of data coverage and analyses of unregulated contaminant occurrence are
then presented. Comparisons of Round 1 and Round 2 data coverage were made to evaluate if
comparable states, public water systems, and contaminants are contained in both databases. Analytical
summaries of occurrence of all contaminants for the Round 1 and Round 2 cross-section states are
included. These occurrence assessments are based on measures such as the percent of public water
systems with at least one analytical result greater than the minimum reporting level, and the percent of
public water systems with at least one analytical result greater than the maximum contaminant limit (or
heath reference level).
This national summary concludes with a brief description of the more detailed spatial and
graphical assessments of select high occurrence contaminants.
The reader is referred to the complete National Occurrence report for full descriptions and more
details of the data quality assessments, cross-section development, and contaminant occurrence analyses
presented in this national summary.
vm
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
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) to enhance the scientific understanding of the
occurrence of unregulated chemical contaminants in public drinking water systems, and to refine the
approach of management and analysis of contaminant occurrence data. This effort was directed by Mr.
Guy Caruthers of OGWDW. This project began under the direction of Mr. Charles Job.
We would like to thank the many States, as well as the American Water Works Service
Company, that contributed data sets and valuable advice. Thanks also to the many public water systems
that conducted the monitoring that provided the contaminant occurrence data used in this report. Mr.
Lewis Summers and Mr. Guy Caruthers of OGWDW managed the access to EPA's URCIS and
SDWIS/FED databases, the repositories of data used in this project.
The Cadmus Group, Inc. served as the prime contractor for this project, supporting the data
management, analysis, and report development. Dr. George Hallberg and Dr. Jonathan Koplos served as
Cadmus Project Managers.
IX
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
DISCLAIMER
This report does not constitute U.S. Environmental Protection Agency Policy. Mention of trade
names or commercial products does not constitute endorsement or recommendation for use.
This document is designed to provide technical background for the Office of Ground Water and
Drinking Water's program. The document does not, however, substitute for the Safe Drinking Water Act
or EPA's regulations nor is this document a regulation itself. Thus, it cannot impose legally-binding
requirements on EPA, States, or the regulated community, and may not apply to a particular situation
based on the circumstances.
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
I. INTRODUCTION
This report provides a summary overview of the management and initial assessment of
unregulated contaminant occurrence data currently available to EPA. The data are from the required
compliance monitoring of unregulated contaminants conducted by public drinking water systems prior to
1998. Specifically, this report summarizes assessments based on occurrence data from the Unregulated
Contaminant Information System (URCIS) database (Round 1 monitoring data) and the Safe Drinking
Water Information System/Federal Version (SDWIS/FED) database (Round 2 monitoring data) that were
comprehensively presented and described in the report entitled Occurrence of Unregulated
Contaminants in Public Water Systems: An Initial Assessment (EPA 815-P-00-001; referred to as the
"complete National Occurrence report"). The "complete National Occurrence report" includes a
comprehensive overview of the assessment and initial analysis of the unregulated contaminant occurrence
data currently available to EPA.
This national summary, a condensed version of the complete National Occurrence report,
presents a description of URCIS (Round 1) and SDWIS/FED (Round 2) data, reviews the extensive data
quality management necessary to conduct occurrence analyses, outlines the construction of a national
cross-section of states from each of the two databases, and summarizes the occurrence analytical
findings for the 62 unregulated contaminants in the Round 1 data set and the 48 unregulated contaminants
in the Round 2 data set. For complete, detailed evaluations and extensive tabulations of all contaminant
occurrence findings for both Round 1 and Round 2 data, as well as spatial and graphical occurrence
assessments of select high-occurrence contaminants, the reader is directed to the complete National
Occurrence report referenced above (with the chapters in this national summary corresponding to the
same in the complete National Occurrence report).
I.A. Background
The Safe Drinking Water Act (SDWA), as amended in 1986, required Public Water Systems
(PWSs) to monitor for specified "unregulated" contaminants, on a five year cycle, and to report the
monitoring results to the states. Unregulated contaminants do not have an established or proposed
National Primary Drinking Water Regulation (NPDWR), but are formally listed and require monitoring
under federal regulations. The intent is to gather scientific information on the occurrence of these
contaminants to enable a decision regarding whether regulations were needed. All non-purchased
community water systems (CWSs), and non-purchased non-transient non-community water systems
(NTNCWSs), with greater than 150 service connections were required to conduct this unregulated
contaminant monitoring.
The 1993 amendments to SDWA added other contaminants to the unregulated contaminant list
for required monitoring, and the 1996 SDWA amendments directed EPA to develop a revised program for
such monitoring. This new program was formally published in the Federal Register on September 17,
1999 (64 FR 50556) as the Unregulated Contaminant Monitoring Regulation, now referred to as the
UCMR (1999). This new UCMR monitoring will begin in 2001, and must produce a new list of
unregulated contaminants for monitoring every 5-years.
To clarify the history of unregulated contaminant monitoring, a naming system is introduced to
distinguish between the different monitoring periods and the contaminant lists included in a specific
monitoring period. The first unregulated contaminant monitoring list was published in 1987 and will be
referred to as the UCM (1987) list. The UCM (1987) list was followed by the UCM (1993) list
(generated through the 1993 SDWA Amendments) and the recent UCMR (1999) list (generated through
the 1999 development of the Unregulated Contaminant Monitoring Regulation-UCMR-list of
contaminants. The occurrence analyses in this report are based on the historic data from the UCM
(1987) and UCM (1993) lists. Occurrence data for the UCM (1987) and UCM (1993) contaminants, as
well as for other contaminants listed in the following section, are contained in two databases. (To date,
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
there are no data yet available from the UCMR monitoring, which was initiated in January, 2001.) These
databases are briefly summarized in the following sections.
I.E. Unregulated and Regulated Contaminants, Databases, and Monitoring Timeframe
Figure I.B.I diagrams the inter-relationship of the various databases, monitoring rounds and
contaminant lists discussed in this report. Tables I.B.I and I.B.2 describe in more detail the specific
contaminants included in each database.
Figure I.B.I. Diagram of the Inter-Relationship of Various Databases, Monitoring Rounds and
Contaminant Lists Discussed in the Report
URCIS (Round 1)
(62 Contaminants)
* refer to Table I.B.I for a
complete list of contaminants
UCM
Phase I -21 VOCs
2 Regulated SOCs
5 Miscellaneous Contaminants
20 Mandatory VOCs (Group 3)
14 Discretionary VOCs (Group 4)
SDWIS/FED (Round 2)
(48 Contaminants)
* refer to Table I.B.2 for a
complete list of contaminants
I— 13 SOCs (Group 1)
UCM(1993)-
1 IOC (Group 2)
UCM(1987)
20 Mandatory VOCs (Group 3)
14 Discretionary VOCs (Group 4)
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Table I.B.I. List and Description of Contaminants with Data in URCIS (Round 1)
(approximately 1987-1992)
Contaminant
CAS
Number
SDWIS
ID
MCL
HAL *,
or
HRL"
uc
Round
UC
Group
Common Sources of Contaminant
Inorganic Chemicals
jNo Inorganic Chemicals in UCM (1987) data
Sl
nthetic Organic Chemicals - Regulated
Dibromochloropropane
( 1 ,2-Dibromo-3 -chloropropane;
or DBCP)
Ethylene Dibromide
(1,2-Dibromoethane; or EDB)
96-12-8
106-93-4
2931
2946
0.2
0.05
1
1
R
R
Soil fumigant on soybeans, cotton,
pineapple, orchards
Leaded gas additives; leaching of soil
fumigant
Volatile Organic Chemicals - Group 3
Bromobenzene
Bromodichlorom ethane
Bromoform
Bromomethane
(Methyl Bromide)
Chloroform
Chloroethane
Chloromethane
(Methyl Chloride)
Dibromochloromethane
Dibromom ethane
1 , 1 -Dichloroethane
1,3-Dichloropropane
2,2-Dichloropropane
1 , 1 -Dichloropropene
1,3-Dichloropropene
m-Dichlorobenzene
o-Chlorotoluene
p-Chlorotoluene
1,1, 1 ,2-Tetrachloroethane
1,1,2,2-Tetrachloroethane
1,2,3-Trichloropropane
108-86-1
75-27-4
75-25-2
74-83-9
67-66-3
70-00-3
74-87-3
124-48-1
74-95-3
75-34-3
142-28-9
594-20-7
563-58-6
542-75-6
541-73-1
95-49-8
106-43-4
630-20-6
79-34-5
96-18-4
2993
2943
2942
2214
2941
2216
2210
2944
2408
2978
2412
2416
2410
2413
2967
2965
2966
2986
2988
2414
-
60**
400**
10
600**
-
3
60**
-
5
-
-
—
40**
600*
100
100
70*
2*
40
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Solvent, organic synthesis
Disinfection-by-product, marine
microalgae
Disinfection-by-product, solvent for
waxes, greases, oils
Soil and space fumigant, extraction
solvent, oceans
Solvent, DBF, auto exhaust, chemical
intermediate
Chemical intermediate, solvent,
aerosol, solvent metabolite
Oceans, volcanoes, fires, smoke
exhaust, solvent, DBF
Organic synthesis, manufacture of fire
extinguishing agents, refrigerants,
aerosol propellants and pesticides.
Solvent, gage fluid, use in chemical
synthesis, marine algae
Leaded gasoline; fumigants, paints
Chemical intermediate for
cyclopropane
Solvent
Solvent
Solvent, used in fungicide
Dump leachate, fumigant, solvent,
chemical intermediate
Drain pipe solvent
Solvent, chemical intermediate for
dyes, organic chemicals
Product of manufacture of other
chloroethanes
Used in paint manufacturing; cement;
paint removers; moth-proofing
Paint/varnish remover, solvent,
degreasing agent
Volatile Organic Chemicals - Group 4
Bromochloromethane
Dichlorodifluoromethane
Hexachlorobutadiene
74-97-5
75-71-8
87-68-3
2430
2212
2246
10
1,000
0.9**
1
1
1
2
2
2
4
4
4
Organic synthesis and fire
extinguishers
Refrigerant, aerosol propellant, rocket
propellant, foaming agent, plastics
Solvent, synthetic rubber, pesticide,
insecticide, herbi- cide, chemical
intermediate
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Contaminant
Isopropylbenzene
n-Butylbenzene
n-Propylbenzene
Naphthalene
p-Isopropyltoluene
sec-Butylbenzene
tert-Butylbenzene
1,2,3-Trichlorobenzene
Trichlorofluorom ethane
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
CAS
Number
98-82-8
104-51-8
103-65-1
91-20-3
99-87-6
135-98-8
98-06-6
87-61-6
75-69-4
95-63-6
108-67-8
SDWIS
ID
2994
2422
2998
2248
2030
2428
2426
2420
2218
2418
2424
MCL
HAL *,
or
HRL"
-
-
-
140**
-
—
__
-
175*
-
—
UC
Round
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
UC
Group
4
4
4
4
4
4
4
4
4
4
4
Common Sources of Contaminant
Production of petroleum refining;
evaporation and combustion of
petroleum
Solvent, used in textile dyeing and
printing
Fungicide, moth repellant
Termite control; chemical
intermediate
Solvent, chemical intermediate,
lialocarbon aerosol propellant and
refrigerant
Chemical intermediate, solvent,
gasoline, coal tar, and petroleum
products
Volatile Organic Chemicals - Regulated
Benzene
Carbon tetrachloride
Chlorobenzene
cis- 1 ,2-Dichloroethylene
1,2-Dichloroethane
Dichloroethene
Dichloromethane
(Methyl ene chloride)
1,2-Dichloropropane
Ethyl benzene
o-Dichlorobenzene
p-Dichlorobenzene
Styrene
Tetrachloroethylene
Toluene
trans-l,2-Dichloroethylene
1 ,2, 4-Tri chlorobenzene
1,1,1 -Trichloroethane
1 , 1 ,2-Trichloroethane
Trichloroethene
(Trichloroethylene)
Vinyl chloride
71-43-2
56-23-5
108-90-7
156-59-2
107-06-2
75-35-4
75-09-2
78-87-5
100-41-4
95-50-1
106-46-7
100-42-5
127-18-4
108-88-3
156-60-5
120-82-1
71-55-6
79-00-5
79-01-6
75-01-4
2990
2982
2989
2380
2980
2977
2964
2983
2992
2968
2969
2996
2987
2991
2979
2378
2981
2985
2984
2976
5
5
100
70
5
7
5
5
700
600
75
100
5
1,000
100
70
200
5
5
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
Some foods; gas, drugs, pesticide,
paint, plastic industries
Solvents and their degradation
products
Waste solvent from metal degreasing
processes, discharge from chemical and
agricultural chemical factories
Waste industrial extraction solvents
Leaded gas, fumigants, paints
Plastics; dyes; perfumes; paints
Paint stripper, metal degreaser,
propellant, extraction
Soil fumigant; waste industrial solvents
Gasoline; insecticides; chemical
manufacturing wastes
Paints, engine cleaning compounds,
dyes, chemical wastes
Room and water deodorants, and
"mothballs"
Plastics, rubber, resin, drug industries;
leachate from city landfills
Improper disposal of dry cleaning and
other solvents
Gasoline additive; manufacturing and
solvent operations
Waste industrial extraction solvents
Herbicide production; dye carrier
Adhesives, aerosols, textiles, paints,
inks, metal degreasers
Solvent in rubber, other organic
products; chemical production wastes
Textiles, adhesives and metal
degreasers
May leach from PVC pipe; formed by
solvent breakdown
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Contaminant
Xylenes (Total)
m-Xylene
o-Xylene
D-Xvlene
CAS
Number
1330-20-7
108-38-3
95-47-6
106-42-3
SDWIS
ID
2955
2995
2997
2962
MCL
HAL *,
or
HRL"
10,000
—
—
uc
Round
1
1
1
1
2
UC
Group
R
Common Sources of Contaminant
By-product of gasoline refining;
paints, inks, detergents
Xylene Isomers
Volatile Organic Chemicals - Other
cis-l,3-Dichloropropylene
trans- 1,3-Dichloropropylene
10061-01-5
10061-02-6
2228
2224
-
-
1
1
Used in organic synthesis and soil
fumigants; used as a nematocide
Used in organic synthesis and soil
fumigants for control of nematodes
Includes some regulated SOCs and VOCs, and the unregulated contaminants from UCM (1987) List. UC Round = data included in
Round 1 and/or 2 monitoring and database; UC Group = contaminant group as specified in UCM (1993) Listing.
MCL=Maximum Contaminant Level
HAL=Health Advisory Level (as of December 2000)
HRL=Health Reference Level (concentration values used only as reference levels for analyses in this report)
The MCL, HAL, and HRL values are used in this report only as reference levels to facilitate occurrence assessments.
Table I.B.2. List and Description of Contaminants with Data in SDWIS/FED (Round 2)
(approximately 1993-1997)
Contaminant
CAS
Number
SDWIS
ID
MCL
HAL *, or
HRL"
(Hg/L)
UC
Round
UC
Group
Common Sources of Contaminant
Synthetic Organic Chemicals - Group 1
Aldicarb
Aldicarb Sulfone
Aldicarb Sulfoxide
Aldrin
Butachlor
Carbaryl
Dicamba
Dieldrin
3 -Hydroxycarbofuran
Methomyl
Metolachlor
Metribuzin
Propachlor
116-06-3
1646-88-4
1646-87-3
309-00-2
23184-66-9
63-25-2
1918-00-9
60-57-1
16655-82-6
16752-77-5
51218-45-2
21087-64-9
1918-16-7
2047
2044
2043
2356
2076
2021
2440
2070
2066
2022
2045
2595
2077
7**
7**
7**
0.002**
-
700
200
0.002**
-
200
70**
91**
90
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
Pesticide used with cotton, potatoes,
others (widely restricted)
Biodegradation of aldicarb
Biodegradation of aldicarb
Soil insecticide
Herbicide for rice, used on annual
grasses
Broad range pesticide (citrus,
vegetables, lawns, nuts)
Herbicide for agriculture, rangeland,
pasture, industry
Insecticide
Metabolite of carbofuran
Insecticide for soybeans, cotton, other
field and fruit crops
Herbicide for corn, soybeans, peanuts,
cotton, pod crops
Herbicide used on grass and broadleaf
weeds
Herbicide for corn and sorghum
Inorganic Chemicals - Group 2
Sulfate
14808-79-8
1055
500,000**
2
2
Fertilizer, natural occurrence, some
industrial uses
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Contaminant
CAS
Number
SDWIS
ID
MCL
HAL *, or
HRL"
(Hg/L)
uc
Round
UC
Group
Common Sources of Contaminant
Volatile Organic Chemicals - Group 3
Bromobenzene
Bromodichlorom ethane
Bromoform
Bromomethane
(Methyl Bromide)
Chloroethane
Chloroform
Chloromethane
(Methyl Chloride)
Dibromochloromethane
Dibromom ethane
1 , 1 -Dichloroethane
1,3-Dichloropropane
2,2-Dichloropropane
1 , 1 -Dichloropropene
1,3-Dichloropropene
m-Dichlorobenzene
o-Chlorotoluene
p-Chlorotoluene
1,1, 1 ,2-Tetrachloroethane
1,1,2,2-Tetrachloroethane
1,2,3-Trichloropropane
108-86-1
75-27-4
75-25-2
74-83-9
70-00-3
67-66-3
74-87-3
124-48-1
74-95-3
75-34-3
142-28-9
594-20-7
563-58-6
542-75-6
541-73-1
95-49-8
106-43-4
630-20-6
79-34-5
96-18-4
2993
2943
2942
2214
2216
2941
2210
2944
2408
2978
2412
2416
2410
2413
2967
2965
2966
2986
2988
2414
-
60**
400**
10
-
600**
3
60**
-
5
-
—
—
40**
600*
100
100
70*
2*
40
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Solvent, organic synthesis
Disinfection-by-product, marine
microalgae
Disinfection-by-product, solvent for
waxes, greases, oils
Soil and space fumigant, extraction
solvent, oceans
Chemical intermediate, solvent,
aerosol, solvent metabolite
Solvent, DBF, auto exhaust, chemical
intermediate
Oceans, volcanoes, fires, smoke
exhaust, solvent, DBF
Solvent, gage fluid, use in chemical
synthesis, marine algae
Leaded gasoline; fumigants, paints
Chemical intermediate for
cyclopropane
Solvent
Solvent
Solvent, used in fungicide
Dump leachate, fumigant, solvent,
chemical intermediate
Drain pipe solvent
Solvent, chemical intermediate for
dyes, organic chemicals
Product of manufacture of other
chloroethanes
Used in paint manufacturing; cement;
paint removers; moth-proofing
Paint/varnish remover, solvent,
degreasing agent
Volatile Organic Chemicals - Group 4
Bromochloromethane
Dichlorodifluoromethane
Hexachlorobutadiene
Isopropylbenzene
n-Butylbenzene
n-Propylbenzene
Naphthalene
p-Isopropyltoluene
sec-Butylbenzene
tert-Butylbenzene
1,2,3-Trichlorobenzene
74-97-5
75-71-8
87-68-3
98-82-8
104-51-8
104-51-8
91-20-3
99-87-6
135-98-8
98-06-6
87-61-6
2430
2212
2246
2994
2422
2998
2248
2030
2428
2426
2420
10
1,000
0.9**
-
—
-
140**
—
—
—
-
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
4
4
4
4
4
4
4
4
4
4
4
Organic synthesis and fire extinguishers
Refrigerant, aerosol propellant, rocket
propellant, foaming agent, plastics
Solvent, synthetic rubber, pesticide,
insecticide, herbi- cide, chemical
intermediate
Production of petroleum refining;
evaporation and combustion of
petroleum
Solvent, used in textile dyeing and
printing
Fungicide, moth repellant
Termite control; chemical intermediate
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Contaminant
Trichlorofluorom ethane
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
CAS
Number
75-69-4
95-63-6
108-67-8
SDWIS
ID
2218
2418
2424
MCL
HAL *, or
HRL"
175*
-
-
UC
Round
1
1
1
2
2
2
UC
Group
4
4
4
Common Sources of Contaminant
Solvent, chemical intermediate,
halocarbon aerosol propellant and
refrigerant
Chemical intermediate, solvent,
gasoline, coal tar, and petroleum
products
Includes the unregulated contaminants from UCM (1993) List. UC Round = data included in Round 1 and/or 2 monitoring and
database; UC Group = contaminant group as specified in UCM (1993) Listing.
MCL=Maximum Contaminant Level
HAL=Health Advisory Level (as of December 2000)
HRL=Health Reference Level (concentration values used only as reference levels for analyses in this report)
The MCL, HAL, and HRL values are used in this report only as reference levels to facilitate occurrence assessments.
I.C. Data Analysis
The contaminant occurrence analyses and findings presented in this report are based on national
cross-sections of state data (i.e., subsets of representative state data) derived from the URCIS (Round 1)
and SDWIS/FED (Round 2) databases. The occurrence findings presented here are not based on the
entire collection of state compliance monitoring data contained in the URCIS (Round 1) and SDWIS/FED
(Round 2) databases.
During initial URCIS and SDWIS/FED data quality assessments, significant data quality problems
were identified. The data sources, data quality reviews, and the necessary data editing are described in
detail in Section II of this report. Due to the data completeness and quality problems inherent in the raw
URCIS and SDWIS/FED data, cross-sections of state data (one using URCIS data, and a second cross-
section using SDWIS/FED data) were constructed to develop a nationally representative perspective for
contaminant occurrence assessments. The detailed efforts to develop the nationally representative state
cross-sections are described in Section III of this report.
An overview of data coverage (distribution of system types, months, years, etc. of the occurrence
data) of the two entire databases (and of the two cross-sections) is presented in Section IV. In Section
V, the contaminant occurrence analytical findings are presented. Note that the findings are based on the
constructed state cross-sections (not the entire URCIS and SDWIS/FED databases). The key summary
findings are presented in Table V.A.1 (for the URCIS 24-state representative cross-section; see
Appendix A for full detailed findings) and Table V.B.I (for the SDWIS/FED 20-state representative
cross-section; see Appendix B for full detailed findings). Finally, Section VI presents additional
occurrence assessments conducted for select high occurrence contaminants. The URCIS (Round 1) and
SDWIS/FED (Round 2) data that were used as the basis for the analyses in this report are available upon
request from EPA Office of Ground Water and Drinking Water. Requests for this data should be sent to
ucmr.report(g),epa. gov.
All statistical analyses, and most database manipulations were conducted with SAS® statistical
software. Some data formatting problems were corrected in Microsoft® Excel with the aid of specialized
programs written in Visual Basic® or were corrected directly in SAS before the analysis began. After
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
analysis, results were typically downloaded into Excel for secondary analysis, or sorting, or the
development of report tables.
II. DATA SOURCES AND DATA QUALITY REVIEW
II.A. URCIS (Round 1) Data
In this section of the summary, the unregulated contaminant monitoring data (from approximately
1988-1992) are reviewed for quantity, quality, and completeness. These Round 1 data were derived from
the Unregulated Contaminant Information System (URCIS). Significant data review, formatting, and data
quality checking and editing were required of this Round 1 data to enable the evaluations and analyses
conducted for this initial contaminant occurrence assessment.
II.A.1. Description of Data
URCIS is a compilation of public water system monitoring results for unregulated contaminants,
collected under the authority of SDWA, and reported to the states (as the primacy agents for SDWA).
EPA requested that the states submit these data to EPA in the early 1990s, but no formal protocol or
format had been established for reporting. Given the evolving nature of data management during this era,
various data problems were encountered. EPA has been working on quality assurance and analysis of
these data since 1992. Further data quality assessments and some preliminary analyses of the URCIS
data were conducted and presented in the occurrence and data report prepared for EPA-OGWDW's
Chemical Monitoring Revisions (CMR) project. This report,^ Review of Contaminant Occurrence in
Public Water Systems (EPA 816-R-99-006, 1999, USEPA, Office of Water), is referred to as the "CMR
Report".
In 1999, EPA also transferred the URCIS data into SDWIS/FED, to join these URCIS Round 1
data with Round 2 data being submitted by the states into SDWIS/FED. (SDWIS/FED is the official
database repository of data provided by public drinking water systems, and now includes data from an
earlier EPA public water system URCIS database.)
For the analyses described in this summary, the data from the original URCIS database was used.
URCIS contained data from only 40 states/primacy entities. The URCIS database includes data on 62
Round 1 contaminants: the 34 UCM (1987) VOCs; the 21 regulated Phase 1 VOCs; 2 regulated synthetic
organic contaminants (SOCs); and 5 miscellaneous contaminants.
II.A.2. Data Management and Data Quality
During the analytical work conducted for the CMR report in 1997-1998, the URCIS database
was reviewed for various data quality problems and subsequently edited to remove readily apparent
problematic data to ensure the quality of the data used in the analysis. Due to a variety of data quality
problems, including incorrect or incomplete data codes for source water type, system type, system size
(population-served), contaminant type, sample date, system identification, etc., some data records were
excluded from the analyses to maintain defensible data quality.
For some records, the data were of acceptable quality, but some system inventory information
was missing. To enable use of these URCIS data records, the URCIS data were merged by public water
system identification number (PWSID) with current SDWIS-Needs Survey PWS Inventory data to obtain
missing system inventory information data on the source water, system type and population served for the
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
PWSs. After these data management and editing efforts, there are 3,452,530 analytical records for the 62
contaminants for analysis of the Round 1 data. Even with this extensive data management effort, there
may still be data quality problems given the diverse sources of these data and the sheer size of the
database. Recent reviews of the original database indicate that this does not appear to affect many data.
II.A.3. Further Data Review and Editing
Subsequent to the major editing efforts on this database, a secondary review of the 3.5 million
records was undertaken. To begin, various descriptive statistics were compiled (state by state) to enable
a more detailed review for data bias and representativeness. Some state data, as will be described, are so
incomplete that their use would introduce bias into the analyses. These data are used in certain parts of
this report to provide context or reference, but not to make determinations based on their occurrence
analyses.
Table II.A.3.a. summarizes results from the state data review. The table presents the data
availability and data quality parameters assessed for 57 primacy entities considered under SDWA: the 50
states, 5 territories, the District of Columbia, and an aggregate entry for the Native American tribes.
Contained in URCIS are data for 38 states, the Virgin Islands, and Washington, D.C. No data were
reported for 17 primacy entities. An assessment of several parameters is used to determine if a state's
data are complete (or adequately complete), or incomplete and biased. Indicators of biased data are high
percent samples with detections (generally greater than 5 to 8 %), low number of samples per PWS
(significantly below the common range of 50 to 250 samples per PWS), and low number of PWSs per
state (as compared to the number of PWSs listed for a state in the SDWIS/FED inventory).
The last column on Table II.A.3.a lists states with data records that are not complete (i.e., less
than 100% of systems reported as compared to SDWIS/FED inventory listings), but have other
parameters (e.g., "Percent Sample Detections", or "Samples per PWS") that suggest that the data are
balanced and perhaps complete for the systems that did report. The last two columns, "States Usable for
Cross-Section," identify the 27 primacy entities with adequate and unbiased data that were further
considered for occurrence analyses.
Table II.A.3.a. Summary of Data Quantity and Quality in URCIS (Round 1) for the States, Tribes, and
Territories.
States/ Tribes/
Territories
1
9
3
4
5
6
7
8
9
10
11
12
13
Alabama
Alaska
American Samoa
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Guam
Hawaii
Total
Unique
PWSs
152
748
-
973
6
4,167
60
-
13
855
1,165
-
127
Percent
Sample
detections
5%
2%
1%
100%
7%
34%
6%
20%
2%
1%
Samples
per
PWS
136
132
151
5
111
38
1,207
14
120
370
No Data in
Database
American Samoa
Connecticut
Guam
Data sets
with 100%
Detects
Arkansas
Significantly
Too Few
Systems
Colorado
Delaware
States Usable for Cross-
Section
Most
Complete
Data sets
Alaska
Arizona
California
Georgia
Hawaii
Incomplete
but
Adequate
Data sets
Alabama
Florida
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
States/ Tribes/
Territories
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Marianna Islands
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Tribes
Utah
Vermont
Virgin Islands
Virginia
Washington
Washington, D.C.
West Virginia
Wisconsin
Wyoming
TOT4L
Total
Unique
PWSs
-
1,307
415
1,002
-
525
13
-
-
998
220
139
1,565
206
85
565
214
10
201
1,551
617
357
298
-
2,657
-
-
-
-
-
-
335
306
124
-
430
133
3
-
992
1
139
-
145
23,819
Percent
Sample
detections
5%
4%
5%
3%
3%
2%
91%
100%
1%
100%
1%
2%
100%
2%
100%
2%
0%
1%
2%
1%
4%
4%
98%
1%
82%
9%
1%
5%
6%
3%
2.9%
Samples
per
PWS
147
292
62
273
95
105
14
16
100
6
215
94
6
860
5
94
151
348
134
313
52
197
2
150
10
186
229
3,432
157
125
146
No Data in
Database
Idaho
Kansas
Maine
Marianna Islands
North Dakota
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
Tribes
Virginia
Wisconsin
17
Data sets
with 100%
Detects
Vlassachusetts
Michigan
Mississippi
Nebraska
New
Texas
Vermont
8
Significantly
Too Few
Systems
Louisiana
Missouri
Nevada
5
States Usable for Cross-
Section
Most
Complete
Data sets
Illinois
Indiana
Iowa
Kentucky
Maryland
Minnesota
Montana
New Jersey
New Mexico
Ohio
South Dakota
Tennessee
Utah
Washington
Washington,
Wyoming
21
Incomplete
but
Adequate
Data sets
New York
North
Virgin
West
6
10
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
II.B. SDWIS/FED (Round 2) Data
The monitoring data for the UCM (1993) list of unregulated contaminants (from Round 2,
approximately 1992-1997) are reviewed in this section of the summary. These Round 2 data were
derived from the Safe Drinking Water Information System/Federal Version (SDWIS/FED). Significant
data review, formatting, and data quality checking and editing were required of this Round 2 data to
enable the evaluations and analyses conducted for this contaminant occurrence assessment.
II.B.1. Description of Data
Data for this portion of the analysis were downloaded from the SDWIS/FED database. The
unregulated data include records from the second round of unregulated contaminant monitoring (referred
to as "Round 2") that were submitted directly into SDWIS/FED.
These data were generated through monitoring conducted during Round 2 of required unregulated
contaminant monitoring initiated in 1993. (Although second round monitoring was formally initiated in
1993, SDWIS/FED (Round 2) data can include older data that are comparable to, but predate, the formal
second round monitoring.) SDWIS/FED contained Round 2 data from 35 states/primacy entities. The
SDWIS/FED (Round 2) data includes information on 48 contaminants, including: 1 IOC, 13 SOCs, 20
mandatory VOCs, and 14 discretionary VOCs.
II.B.2. Data Management and Data Quality
The SDWIS/FED Round 2 data comprise 4,350,874 raw records. An important and substantial
component of this study consisted of the detailed and extensive review of these data records for
numerous data quality considerations including reporting consistencies, uniform and valid coding, data
completeness, correct and consistent use of analytical units, and any inherent bias in the raw records.
Common types of data problems that were addressed include records with invalid contaminant codes,
systems with unknown source water or system type codes, state records for specific contaminants that
reported only detections, or entire state records that appeared to have extremely and consistently low
analytical results. These types of records were either deleted (such as when water source or system type
codes were invalid) or converted (when a data units conversion appeared straightforward).
Another more general data management decision related to data from transient and "non-public"
water systems. To avoid the problems associated with transient sources in exposure studies, systems
with a system type recorded as "NC" (non-community, meaning transient) were not included in the
occurrence analyses. With these data management and quality improvements, the initial 4,350,874
analytical records decreased to 4,211,446 analytical records (which includes approximately 900,000
records with converted units).
II.B.3. Further Data Review and Editing
Subsequent to the initial editing and filtering of the data described above, a basic analysis of the
4.21 million records was undertaken. Similar to the URCIS (Round 1) data, various descriptive statistics
were compiled, by state, to enable a further, more detailed data review to assess data bias and
representativeness. Some state data, as will be described, are so incomplete that their use would
introduce bias into the analyses. These data are used in certain parts of this report to provide context or
reference, but not to make determinations based on their occurrence analyses.
ll
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Table II.B.S.a summarizes some key results from the Round 2 state data review. The table
presents the data availability and data quality parameters assessed for the 57 primacy entities considered
under SDWA. Of the 57 primacy entities in SDWIS/FED, 35 have reported Round 2 data and 22 have
not. An assessment of several parameters is used to determine if a state's data are complete (or
adequately complete), or incomplete and biased. Indicators of biased data are high percent samples with
detections (generally greater than 5 to 8%), low number of samples per PWS (significantly below the
common range of 50 to 250 samples per PWS), and low number of PWSs per state (as compared to the
number of PWSs listed for a state in the SDWIS/FED inventory).
The last column on Table II.B.S.a, "States Usable for Cross-Section," lists states with data
records that are reasonably balanced and perhaps complete for the systems that did report. These 20
Round 2 primacy entities with adequate and unbiased data were further considered for occurrence
analyses.
Table II.B.3.a. Summary of Data Quantity and Quality in SDWIS/FED (Round 2) for the States,
Tribes, and Territories.
State/ Tribes/
Territories
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
Alabama
Alaska
American Samoa
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Guam
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
\larianna Islands
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Mevada
Mew Hampshire
Mew Jersey
Mew Mexico
Total
Unique
PWSs
314
625
-
123
577
67
833
87
-
-
-
-
-
-
-
120
-
-
445
1,394
745
-
1,015
506
3,209
1,581
1,155
1,434
-
-
-
849
17
755
Percent
Sample
Detections
94.08%
3.10%
2.75%
7.29%
6.75%
3.72%
4.53%
2.26%
7.50%
0.00%
0.89%
0.62%
3.12%
7.26%
1.66%
71.27%
6.08%
5.45%
2.32%
0.75%
Samples
per PWS
2
194
55
118
44
143
921
58
125
118
163
140
125
97
198
4
109
23
28
277
No Data in
Database
American Samoa
Delaware
Florida
Georgia
Guam
Hawaii
Idaho
Illinois
Iowa
Kansas
Marianna Islands
Montana
Nebraska
Nevada
Data sets
with
100%
Detects
Alabama
Mississippi
Significantly
Too Few
Systems
Arizona
California
Connecticut
Indiana
New Jersey
)ata Quality
Problems
Louisiana
States
Usable for
Cross-
Section
Alaska
Arkansas
Colorado
Kentucky
Maine
Maryland
Massachusetts
Michigan
Minnesota
Missouri
New
New Mexico
12
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
State/ Tribes/
Territories
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Mew York
Morth Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Tribes
Utah
Vermont
Virgin Islands
Virginia
Washington
Washington, D.C.
West Virginia
Wisconsin
Wyoming
TOT4L
Total
Unique
PWSs
-
2,263
296
2,259
888
1,168
1,424
-
117
1,047
27
78
4,863
26
-
636
-
-
2,680
-
-
225
-
33,848
Percent
Sample
Detections
2.05%
7.73%
3.45%
3.99%
1.66%
10.19%
0.30%
0.33%
2.34%
9.31%
1.23%
1.22%
2.65%
2.23%
1.41%
2.95%
Samples
per PWS
55
59
291
180
75
16
136
147
40
147
124
57
74
123
51
124
No Data in
Database
New York
Puerto Rico
Utah
Virgin Islands
Virginia
Washington, D.C.
West Virginia
Wyoming
22
Data sets
with
100%
Detects
2
Significantly
Too Few
Systems
South Dakota
Tennessee
Tribes
Wisconsin
9
)ata Quality
Problems
Pennsylvania
South Carolina
Vermont
4
States
Usable for
Cross-
Section
North
North Dakota
Ohio
Oklahoma
Oregon
Rhode Island
Texas
Washington
20
III. DEVELOPING A NATIONALLY REPRESENTATIVE PERSPECTIVE
The data quality evaluation suggested that Round 1 data from 25 states (plus Washington, D.C.
and the Virgin Islands, totaling 27 primacy entities) were most complete and might be used to generate
national summary statistics on occurrence of the contaminants in URCIS. Data from 25 of the 50 states
is a substantial sample. However, even a 50 percent sample does not guarantee that the sample is
representative because the data were not collected in a systematic or random statistical framework.
Therefore, the state data were evaluated to assess how representative they were across the range, from
high to low, of likely contaminant occurrence and across the spatial/hydrologic diversity of the nation.
Based on these assessments, the construction of a cross-section of states from the available state data
sets provides a reasonable representation of national occurrence.
There are many sophisticated statistical methods that can be applied to analyze limited (and
biased) data. This development of a representative cross-section of data is undertaken to support this
initial occurrence analysis. The representative cross-section can also serve as the basis for subsequent,
more sophisticated analyses as deemed necessary and appropriate by the initial occurrence assessments
conducted in this report. For this initial analysis, the approach used was developed for the CMR report, A
Review of Contaminant Occurrence in Public Water Systems (EPA 816-R-99-006, 1999), to establish a
national cross-section from state SDWA contaminant databases. This approach was supported by peer
reviewers and by stakeholders as providing a clear, repeatable, and understandable approach. It cannot
provide a "statistically representative" sample, because the data were not selected in an appropriate
fashion. The resultant data should, however, provide a clear indication of the central tendency of the
national data.
13
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
III.A. Methods
For the CMR Report (referenced above), a protocol was developed for determining a
representative cross-section of states for occurrence analysis. In the CMR analysis, contaminant data
were available directly from 14 states. The state data were evaluated for completeness and quality
(similar to the data quality evaluations in this report). The balance of the states with adequately complete
and high quality data were evaluated to establish a national cross-section. In the CMR process, eight
states were selected for use in a national analysis as providing the best data quality and completeness, and
for providing a balanced national cross-section of occurrence data. The CMR process was based on
evaluating the states' pollution potential and geographic coverage in relation to all states. The URCIS and
SDWIS/FED states were evaluated using the same selection process.
Two broad factors were considered in the assessment of a representative cross-section: pollution
potential and geographic or spatial diversity. Pollution potential is considered to ensure that the selection
of cross-section states represents the range of likely high, medium, and low contaminant occurrence.
Geographic consideration is included so that the wide range of climatic and hydrogeologic conditions
across the United States are represented, again balancing the varied conditions that affect transport and
fate of contaminants.
For this analysis, two primary pollution potential indicators were used to evaluate the
representativeness of the states. One factor indicates the pollution potential from manufacturing
(generally related to VOC occurrence) and the second factor refers to pollution potential from agriculture
(generally related to SOC occurrence). States were ranked from 1 to 50 for each factor and divided into
quartiles based on the ranking. The rankings were reviewed to assess if states could be selected in
approximate balance from each quartile.
III.A.1. Manufacturing Indicators
Numerous factors were considered in the CMR analysis as potential indicators of manufacturing-
related pollution, including EPA's Toxic Release Inventory (TRI), the number of manufacturing
establishments, the number of manufacturing establishments per square mile, the number of
manufacturing employees, the product value added by manufacturers, and the value added per capita.
These factors were each considered in terms of their inherent value as pollution potential indicators, their
range and variance (in providing a relative ranking of the states), their inter-relationships, and consistency
in data collection. Based on these considerations, the number of manufacturing establishments per square
mile was used as the primary indicator for potential VOC pollution.
III.A.2. Agricultural Indicators
There is no complete measure of pesticide usage by states which is readily available. Therefore,
a variety of factors were considered to assess potential synthetic organic chemical pollution from
agriculture in each state. These included the percent of the state's population that is classified as rural,
the percent of land in the state that is crop land, the percent of land that is grassland pasture and
rangeland (a possible inverse indicator), and total farm agricultural chemical expenses. Like the
manufacturing factors, these agricultural variables were considered in terms of their value in indicating
potential sources of pollution and were plotted against one another to determine how closely they are
related. Of these factors, total farm agricultural chemical expenses was considered to be the most direct
indicator of potential pollution for SOCs.
14
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
III.B. Representative Cross-Section of States
Using the method and indicators described above, state cross-sections are developed from the
states with unbiased, complete, and relatively good quality data in URCIS and SDWIS/FED. The cross-
section states were selected to provide a relatively balanced distribution of pollution potential and
geography, so that the cross-sections approximate a representative national distribution.
III.B.l. URCIS 24-State Cross-Section
Table III.B.l summarizes the state pollution potential rankings, highlighting those included in
URCIS. Although data from 38 states (and Washington D.C. and Virgin Islands), are included in URCIS,
not all states were usable in a "representative" cross-section (as discussed in Section II). Thirteen states
contained only detections or too few analytical records, or records from too few PWSs and were
eliminated from consideration because of their inherent bias. The data from Washington, D.C. and Virgin
Islands were excluded from this state-level analysis because it was difficult to evaluate them in relation to
complete state data. The data quality screening left 25 states eligible for the national cross-section. New
York was excluded because of inherent data quality problems, leaving 24 states.
Table III.B.l. Ranking of States based on Number of Manufacturing Establishments per Square Mile.
URCIS (Round 1) 24 State Cross-Section in Bold.
State
Ihode Island
Vew Jersey
Connecticut
Vlassachusetts
4ew York
Ohio
Maryland
"ennsylvania
Delaware
llinois
California
i1 orida
Michigan
4ew Hampshire
ndiana
Vorth Carolina
Wisconsin
Tennessee
Georgia
Virginia
South Carolina
lawaii
Vermont
Washington
Alabama
Vlissouri
Kentucky
Minnesota
jOuisiana
Texas
Mississippi
Arkansas
Ranking of the Number of
Manufacturing Establishments/ Sq.
Mile
1
2
3
4
5
6
7
8
9
10
11
2
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Ranking of the Total Farm Ag.
Chemical Expenses
49
37
45
43
28
11
35
29
39
2
1
4
18
48
7
17
20
24
19
30
32
36
47
14
26
12
27
5
13
6
8
10
15
-------
EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
State
West Vireinia
Oregon
Vlaine
[owa
Oklahoma
Colorado
Kansas
Arizona
Utah
Nebraska
Idaho
New Mexico
South Dakota
Mevada
North Dakota
Montana
Wyoming
41aska
Ranking of the Number of
Manufacturing Establishments/ Sq.
Mile
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
l=highest
Ranking of the Total Farm Ag.
Chemical Expenses
44
22
38
3
33
31
16
25
42
9
23
40
21
46
15
34
41
50
l=highest
All 50 states are ranked based on the number of manufacturing establishments per square mile. Each state's rank in total farm
agricultural chemical expenses is also indicated. The 38 states in shaded rows are the states with data in the URCIS (Round 1)
database. The 24 states in bold are the selected URCIS (Round 1) cross-section states. Ranking quartiles are indicated by bold lines.
Figure III.B.l.a. summarizes the representativeness of the pollution potential distribution across
the ranking quartiles of the 24 cross-section states. Figure III.B.l.b. shows the geographic distribution of
these 24 cross-section states (and of the 26 excluded states). The consideration of a broad and diverse
geographic representation of states serves to address and include the potential range of naturally
occurring contaminants as represented by the inorganic chemicals, lOCs. As illustrated, the 24 states are
quite well distributed based on pollution potential indicators, with a uniform distribution from high to low
potential for both key pollution indicators (Figure III.B.l.a.). While geographic coverage is lacking from
the south-central U.S. and New England, the 24 cross-section states provide broad coverage from around
the country, from the major climatic regions, and include about 49% of the PWSs nationally and about
56% of population served by PWSs.
16
-------
EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Figure IILB.l.a. Distribution of State Rankings for Manufacturing Establishments / Sq. Mile
vs. Farm Ag. Chemical Expenses.
Highlighting URCIS (Round 1) 24 Cross-Section States
ing uf LIic NU. of Miiiiuf«iL.:l.iiiiiiy FiMjiljMiti CHIN' Sq. Mile
TOW TO TTTCiTT
i
o
0 e
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*
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O
0*
o
o
Q °
c
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a
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i
o
o
*
0 0
ft
•
o °
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o
o
o
TTIV«7T
TO
-LOW
53
a.
(£
• LRC1S (Round 1) 24-Stile
O 3i S luc-i :v OT ill LRCi S ( K.O mid 1) Cross- Sculk
17
-------
EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Figure IILB.l.b. 24 URCIS (Round 1) Representative Cross-Section States and States Not Included in
the Cross-Section
URCIS (Round 1)
URCIS (Round 1) States
I I States not in Cross-Section (no data)
I I States with biased data
I I 24 Cross-Section States
(data used in report)
In sum, the group of 24 cross-section states in URCIS (Round 1), should provide a balanced
representation, based on relative rankings for pollution potential (i.e., potential for contaminant
occurrence), geographic coverage, and data quality and completeness. The 24 cross-section state
distribution across pollution potential quartiles suggests that they should provide a valid indication of the
potential range and occurrence of contamination in public water systems nationally.
The data from the 24-state cross-section are used to compute aggregate contaminant occurrence
measures as an approximation of a national cross-section. While the data from these cross-section states
cannot be stated to be "statistically representative," their distribution should provide a representative view
and clear indication of national central tendency of occurrence.
In addition, the URCIS data, with 24 states in its cross-section, represent a relatively large
collection of state data for a cross-section. As noted, the CMR analysis developed a cross-section of 8
states. The data from the URCIS 24 cross-section states can also be used to evaluate and illustrate this
approach to constructing a national cross section by evaluating the data in aggregate steps, using
increments of the 24 states. This approach is described below.
18
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
III.B.2. Incremental National Cross-Sections
The data from the 24 URCIS cross-section states were used to build "incremental" national
cross-sections, by aggregating subsets of the 24 states using the same selection protocol for evaluating
representativeness. Each aggregate (e.g., 4 states, 8 states, etc.) provides some representation of all
quartiles of pollution potential indicators, a geographic balance, and, hence, hopefully, a balance in
potential occurrence. The data from the states in each aggregate were used to compute group
contaminant occurrence measures (such as percent systems with at least one analytical detection of a
particular contaminant). The results from the 4-state, 8-state, and 13-state cross-section (data
aggregations) were then compared to the same measures based on the 24-state cross-section.
The 8-state through the 24-state cross-sections provide comparable results. This consistency of
analytical results across the different number of state cross-section groups suggests that the criteria used
to construct the aggregations are valid. Again, while the data from these cross-section states cannot be
stated to be "statistically representative," their distribution should provide a clear indication of national
central tendency of occurrence. The results using the 24-state cross-section will be further described in
later sections of this report. The validity and value of the national cross-section sample could be further
tested if necessary.
III.B.3. SDWIS/FED 20-State Cross-Section
Table III.B.3. summarizes the pollution potential rankings for the 50 states, highlighting (in bold)
those included in SDWIS/FED. Although a total of 34 state data sets are included in SDWIS/FED Round
2 data, not all states were usable in constructing a "representative" cross-section (as discussed in Section
II). The data quality screening left 20 states eligible for the national cross-section. In Figure III.B.3.a,
the distribution of the pollution potential rankings of the 20 cross-section states illustrates how
representative the cross-section states are as based on these characteristics.
Table III.B.3. Ranking of States based on Number of Manufacturing Establishments per Square Mile.
SDWIS/FED (Round 2) 20 Cross-Section States in Bold.
State
Rhode Island
New Jersey
Connecticut
Massachusetts
New York
Ohio
Maryland
Pennsylvania
Delaware
Illinois
California
Florida
Michigan
New Hampshire
Indiana
North Carolina
Wisconsin
Tennessee
Georgia
Ranking of the Number of
Manufacturing Establishments/ Sq.
Mile
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Ranking of the Total Farm Ag.
Chemical Expenses
49
37
45
43
28
11
35
29
39
2
1
4
18
48
7
17
20
24
19
19
-------
EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
State
Virginia
South Carolina
Hawaii
Vermont
Washington
Alabama
Missouri
Kentucky
Minnesota
Louisiana
Texas
Mississippi
Arkansas
West Virginia
Oregon
Maine
Iowa
Oklahoma
Colorado
Kansas
Arizona
Utah
Nebraska
Idaho
New Mexico
South Dakota
Nevada
North Dakota
Montana
Wyoming
Alaska
Ranking of the Number of
Manufacturing Establishments/ Sq.
Mile
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
l=hiehest
Ranking of the Total Farm Ag.
Chemical Expenses
30
32
36
47
14
26
12
27
5
13
6
8
10
44
22
38
3
33
31
16
25
42
9
23
40
21
46
15
34
41
50
l=hiehest
All 50 states are ranked based on the number of manufacturing establishments per square mile. Each state's rank in total farm
agricultural chemical expenses is also indicated. The 34 states in shaded rows are the states with data in the SDWIS/FED database.
The 20 states in bold are the selected SDWIS/FED (Round 2) cross-section states. Ranking quartiles are indicated by bold lines.
20
-------
EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Figure III.B.3.b. Distribution of State Rankings for Manufacturing Establishments / Sq. Mile
vs. Farm Ag. Chemical Expenses.
Highlighting SDWIS/FED (Round 2) 20 Cross-Section States
Riiliking i.if LIic NU. of Miiiiuf«iL.:l.iiiiiiy FiMjiljMiti cnLiS'' Sq. Mile
IfiW
TO
VI. -
KILP-
TTTCiTT
o
* e
o
D
O
O
0 * 0
o
•
o
o
Q *
*
*
O
o
*
K
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•^
o
o
o
O Q
°o
">
.
_
o °
o
o
*
TO
-LOW
f£
"•3
• SU VVI &''! TD (Round 2> 2'J- Sutc C
O 3D State-, NOT ill SlJWlS.-T'liD Ctonnd 2j Crow Section
21
-------
EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
The geographic distribution of the 20 SDWIS/FED Round 2 cross-section states is presented in
Figure III.B.S.b. Geographically, the 20 Round 2 cross-section states are widely distributed across the
country. Although coverage is perhaps sparse in the south-east and along the western slope of the Rocky
Mountains, every major geographic region has some state representation.
Figure III.B.3.b. 20 SDWIS/FED (Round 2) Cross-Section States and States Not Included in the
Cross-Section
SDWIS/FED (Round 2)
SDWIS/FED (Round 2) States
I I States not in Cross-Section (no data)
I I States with biased data
20 Cross-Section States
(data used in report)
IV. DATA COVERAGE FOR THE NATIONAL OCCURRENCE OF CONTAMINANTS
IN DRINKING WATER
IV.A. URCIS (Round 1) Data Coverage
A descriptive overview of the Round 1 data is presented to provide additional insight and
perspective on the results. After data management and editing, 3.45 million records were available for
analysis representing over 24,000 PWSs from the 40 states/entities. For the 24 states comprising the
URCIS representative cross-section (see Section III for a discussion regarding the cross-section), the
analytical results total is 3.27 million records, from 22,034 PWSs.
Of the approximately 22,000 systems with data represented in the cross-section states, about 88%
are classified as ground water and 12% as using surface water. Approximately 65% of the cross-section
systems are categorized as Community Water Systems (CWSs ), 22% Non-Transient Non-Community
22
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Water Systems (NTNCWS), about 8% Non-Community Water Systems (NCWS), and 5% with unknown
system type designations.
The majority of data were collected during the 1987-1992 compliance cycle, with a peak of data
collection in 1991. Although in the month of March there is a slightly greater percentage of data, there is
no significant difference in the number of records from month to month, suggesting that there should be no
seasonal bias due to monthly differences in reporting.
IV.B. SDWIS/FED (Round 2) Data Coverage
After initial data management and editing, 4.21 million records were available for analysis from
over 33,000 PWSs in the 35 states/entities. The 20 SDWIS/FED Round 2 state cross-section totals 3.69
million records from slightly more than 27,000 PWSs. The Round 2 cross-section states, therefore,
contain nearly 88% of all Round 2 state contaminant occurrence data in SDWIS/FED.
Of the approximately 27,000 systems with data represented in the Round 2 cross-section states,
about 89% are classified as ground water and 11% as using surface water. These source water
percentages are essentially the same for the entire Round 2 data set for all 35 states/entities.
Approximately 70% of the cross-section systems are categorized as Community Water Systems (CWSs
), and 30% as Non-Transient Non-Community Water Systems (NTNCWS). This proportional distribution
of system types is very similar to that for all the Round 2 data.
The majority of data were collected during 1992-1997, with a peak of data collection in 1995.
Although there is a very slightly greater percentage of data in March, a fairly uniform distribution of
occurrence data by month suggests that there should be no inherent seasonal bias in the data.
IV.C. Comparing Data Coverage of URCIS (Round 1) and SDWIS/FED (Round 2)
The URCIS (Round 1) and SDWIS/FED (Round 2) data were evaluated to determine if
comparable states, public water systems (PWSs), and contaminants are contained in both databases. As
previously noted, URCIS contained data from 40 states/territories, and SDWIS/FED data consisted of
analytical results from 35 states/territories.
Of the 25 states with data in both URCIS (Round 1) and SDWIS/FED (Round 2), only 8 were
determined to be sufficiently complete for use in this comparison analysis. Alaska, Kentucky, Maryland,
Minnesota, North Carolina, New Mexico, Ohio, and Washington were contained in both databases and
have data of adequate quality for analyses and comparisons.
In addition, a determination was made regarding actual PWSs that are common to both
databases. Thirty-one percent of all PWSs in URCIS (Round 1) are also in SDWIS/FED (Round 2),
while only 22% of all SDWIS/FED (Round 2) PWSs are common to both rounds. This is, in part,
because there are many more systems reporting analytical results in SDWIS/FED (Round 2) than in
URCIS (Round 1).
Comparisons of contaminants in URCIS (Round 1) and SDWIS/FED (Round 2) indicated that
there were no common lOCs (Group 1) or SOCs (Regulated or Group 2) reported in both databases. In
contrast, all of the unregulated Group 3 and Group 4 VOCs reported in SDWIS/FED (Round 2) were also
reported in URCIS (Round 1). None of the regulated VOCs reported in URCIS (Round 1), however,
were reported in SDWIS/FED (Round 2).
23
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Changes in the percentages of samples and percentage of PWSs with at least one analytical
result greater than the MRL followed no consistent pattern either for the contaminants or states with data
in both rounds. The percentage of PWSs with at least one analytical result exceeding the concentration
of the MCL/HRL (or 1A MCL/HRL) also followed no apparent or consist pattern between URCIS
(Round 1) and SDWIS/FED (Round 2).
IV.D. Comparing Data Coverage Across Systems Sizes and Types
Data for select contaminants were also evaluated based on system type and size. Both the
URCIS (Round 1) and SDWIS/FED (Round 2) data were reviewed according to system size (with the
data stratified and assessed according to the five standard population-served categories) and according to
type (comparing community water systems and non-transient non-community water systems).
Generally, for both Round 1 and 2 data, the percentage of public water systems with analytical
results greater than the MRL and the MCL/HRL increases as the system size (population-served)
increases. Also, it appears to generally be the case that the percentage of public water systems with
analytical results greater than the MRL and the MCL/HRL is greater for community water systems than
for non-transient non-community water systems. Note that there is a much greater number of CWSs
than NTNCWSs in the databases.
V. ANALYSIS OF NATIONAL OCCURRENCE
In this section, general summaries of contaminant occurrence data from URCIS (Round 1) and
SDWIS/FED (Round 2) are presented. The summary data developed for the occurrence assessments in
this report are presented in detail in Appendices A, B, C, and D in the complete National Occurrence
report. Appendix A contains summary tables for the 62 URCIS (Round 1) contaminant data. Appendix
B contains summary tables for the 48 SDWIS/FED (Round 2) contaminant data. In Appendix C, data
coverage comparisons between URCIS (Round 1) and SDWIS/FED (Round 2) data are presented for
select states and contaminants. Data summaries of select contaminants by system type and population-
served for both URCIS (Round 1) and SDWIS/FED (Round 2) data are presented in Appendix D of the
complete National Occurrence report. A brief review of these findings is included the following sections
of this national summary.
V.A. URCIS (Round 1) Contaminant Occurrence
Table V.A.1 summarizes the occurrence data of the URCIS (Round 1) 24 state cross-section for
62 contaminants. The table presents the total number of unique public water systems, the percent of
public water systems with at least one monitoring sample analytical result greater than the MRL, the
percent of public water systems with at least one result greater than the estimated MCL/HRL/HAL and,
finally, the 99th percentile value in micrograms per liter (• g/L). (To review a map of the URCIS Round 1
cross-section states, refer to Figure III.B.l.b.)
The 24 URCIS cross-section states reflect significant national coverage: these states contain
approximately 44% of public water systems nationally and 51% of the population served by public water
systems. For the majority of contaminants evaluated here (35 out of 62), less than 1% of public water
systems in the cross-section states have analytical detections (any sample analytical result greater than
the MRL). Another 16 contaminants are detected in 1 to 2% of public water systems, as evidenced by
one or more sample analytical results greater than the MRL. Seven contaminants
24
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
(Dibromochloropropane, Dichloromethane, Tetrachloroethylene, Toluene, 1,1,1-Trichloroethane,
Trichloroethylene, and total Xylenes) are detected in 2 to 4% of public water systems, as evidenced by
one or more sample analytical results greater than the MRL. The four THMs have a considerably higher
percent of systems (ranging from 9.01% to 28.84%) with at least one sample analytical result greater than
the MRL. Select URCIS (Round 1) high occurrence contaminants are identified and assessed in Section
VI.
Table V.A.I. URCIS (Round 1) 24-State Cross-Section Summary of Occurrence
CHEMICAL NAME
(Threshold in ug/L)
Total #
PWS
#GW
PWS
#SW
PWS
%
PWS
>MRL
% GW
PWS
>MRL
% sw
PWS
>MRL
% PWS >
Threshold
% GW
PWS>
Threshold
% SW
PWS>
Threshold
99%
Value
(MS/L)
SOCs
Dibrom ochloropropane
(MCL=0.2)
Ethylene Dibrom ide
(MCL=0.05)
12,827
11,450
11,446
10,274
1,511
1,284
2.49%
1.14%
2.51%
1.01%
2 32%
2.10%
1.32%
0.16%
1.35%
0.12%
0.99%
0.47%
1.03
0.01
VOCs
Benzene
(MCL=5)
Bromobenzene
(N/A)
Bromochlorom ethane
(MCL=10)
Bromodichlorom ethane
(HRL=60)
Bromoform
(HRL=400)
Bromom ethane
(MCL=10)
Carbon Tetrachloride
(MCL=5)
Chlorobenzene
(MCL=100)
Chloroethane
(N/A)
Chloroform
(HRL=600)
Chlorom ethane
(MCL=3)
cis-l,2-Dichloroethene
(MCL=70)
cis-l,2-Dichloropropene
(N/A)
Dibromochlorom ethane
(HRL=60)
Dibrom om ethane
(N/A)
Dichlorodifluorom ethane
(MCL=1,000)
1 , 1 -Dichloroe thane
(MCL=5)
1 ,2-Dichloroe thane
(MCL=5)
Dichloroethene
(MCL=7)
Dichloromethane
(MCL=5)
1 ,2-Dichloropropane
(MCL=5)
14,910
16,450
12,881
20,024
19,582
20,198
15,266
20,038
20,236
20,039
20,246
16,705
9,211
19,750
16,549
16,076
20,483
15,282
15,430
19,287
19,591
13,919
14,862
11,576
17,917
17,773
18,472
14,176
18,337
18,507
17,874
18,513
15,026
8,438
17,785
14,953
14,617
18,758
14,192
14,180
17,602
17,908
1,119
1,726
1,386
2,324
1,979
1,886
1,214
1,859
1,882
2,385
1,894
1,832
836
2,158
1,720
1,588
1,876
1,215
1,380
1,836
1,820
1.14%
0.19%
0.50%
22.09%
9.01%
0.77%
1.32%
0.53%
0.39%
28.84%
1.22%
1.47%
0.61%
18.01%
0.36%
1.37%
1.14%
1.16%
1.17%
4.05%
0.67%
1.11%
0.14%
0.44%
14.84%
7.56%
0.71%
1.09%
0.26%
0.29%
21.69%
1.11%
1.45%
0.52%
12.41%
0.21%
1.38%
1.09%
1.10%
1.06%
3.31%
0.66%
5.18%
0.64%
1.08%
79.69%
22.13%
1.22%
3.95%
3.17%
1.33%
84.40%
2.27%
1.53%
1.44%
64.55%
1.69%
1.39%
1.55%
1.73%
1.45%
11.06%
0.77%
0.25%
0.25%
0.27%
N/A
0.03%
0.13%
0.01%
0.09%
0.16%
0.00%
0.03%
0.04%
0.01%
0.08%
0.15%
0.00%
0.07%
0.86%
0.00%
0.16%
0.25%
0.00%
N/A
0.02%
0.45%
0.03%
0.01%
0.41%
0.03%
0.17%
0.84%
0.00%
N/A
0.06%
0.02%
0.32%
N/A
0.00%
0.18%
0.19%
0.20%
0.77%
0.08%
0.00%
0.16%
0.17%
0.20%
0.52%
0.09%
0.00%
0.37%
0.41%
0.22%
3.27%
0.00%
<2.0
<2.0
<1.0
22.00
7.32
<4.0
1.60
<1.0
<2.0
87.00
<4.0
2.18
<1.0
12.70
<2.0
0.50
0.10
<5.0
1.80
1.30
<4.0
25
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
CHEMICAL NAME
(Threshold in u.g/L)
1 ,3-Dichloropropane
(N/A)
2,2-Dichloropropane
(N/A)
1 , 1 -Dichloropropene
(N/A)
1,3- Dichloropropene
(HRL=40)
Ethyl Benzene
(MCL=700)
Hexachlorobutadiene
(HRL=0.9)
Isopropylbenzene
(N/A)
m -Dichlorobenzene
(HAL=600)
m-Xylene
(N/A)
n-Butylbenzene
(N/A)
n-Propylbenzene
(N/A)
Naphthalene
(HRL=140)
o-Chlorotoluene
(MCL=100)
o-Dichlorobenzene
(MCL=600)
o-Xylene
(N/A)
p-Chlorotoluene
(MCL=100)
p-Dichlorobenzene
(MCL=750)
p-Isopropyltoluene
(N/A)
p-Xylene
(N/A)
sec-Butylbenzene
(N/A)
Styrene
(MCL=100)
tert-Butylbenzene
(N/A)
1,1,1,2- Tetrachloroethane
(HAL=70)
1 ,1 ,2,2-Tetrachloroethane
(HAL =2)
Tetrachloroethylene
(MCL=5)
Toluene
(MCL=100)
trans- 1,2-Dichloroethene
(MCL=100)
trans- 1,3-Dichloropropene
(N/A)
1 ,2,3-Trichlorobenzene
(N/A)
1 ,2,4-Trichlorobenzene
(MCL=70)
1,1,1 -Trichloroethane
(MCL=200)
Total #
PWS
16,947
16,757
16,947
9,164
20,081
12,284
12,771
20,429
11,329
12,763
12,724
13,452
15,721
19,953
13,987
15,612
15,494
12,167
10,127
12,343
16,623
12,353
16,956
20,407
19,814
20,089
19,945
9,883
12,876
13,449
15,279
#GW
PWS
15,338
15,138
15,332
8,303
18,355
10,980
11,480
18,752
10,145
11,471
11,440
12,034
14,154
18,300
12,638
14,057
14,284
10,953
8,956
11,071
14,938
11,081
15,338
18,693
18,298
18,364
18,267
9,017
11,567
11,996
14,191
#SW
PWS
1,748
1,754
1,749
898
1,884
1,385
1,359
1,819
1,276
1,371
1,363
1,502
1,702
1,795
1,450
1,689
1,334
1,282
1,230
1,337
1,832
1,337
1,753
1,867
1,652
1,887
1,825
959
1,389
1,539
1,213
%
PWS
>MRL
0.12%
0.15%
0.13%
0.16%
1.62%
0.35%
0.27%
0.25%
1.55%
0.35%
0.33%
1.18%
0.20%
0.28%
1.76%
0.17%
1.25%
0.25%
1.58%
0.23%
0.57%
0.19%
0.18%
0.45%
3.33%
3.50%
0.64%
0.25%
0.49%
0.49%
3.66%
% GW
PWS
>MRL
0.12%
0.14%
0.10%
0.12%
1.40%
0.30%
0.28%
0.20%
1.47%
0.29%
0.34%
1.08%
0.16%
0.20%
1.69%
0.15%
1.11%
0.26%
1.49%
0.23%
0.45%
0.19%
0.13%
0.39%
3.38%
3.10%
0.59%
0.13%
0.46%
0.45%
3.57%
% SW
PWS
>MRL
0.11%
0.23%
0.40%
0.56%
3.66%
0.72%
0.22%
0.77%
2.12/0
0.88%
0.22%
1.93%
0.53%
1.00%
2.41%
0.36%
2.70%
0.08%
2.36%
0.22%
1.53%
0.22%
0.63%
1.02%
2.66%
7.31%
1.10%
1.36%
0.72%
0.78%
4.62%
% PWS >
Threshold
% GW
PWS>
Threshold
% SW
PWS>
Threshold
N/A
N/A
N/A
0.00%
0.00%
0.11%
0.00%
0.00%
0.06%
0.00%
0.00%
0.51%
N/A
0.00%
0.00%
0.00%
N/A
N/A
N/A
0.01%
0.00%
0.00%
0.02%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
N/A
N/A
0.00%
0.00%
0.00%
N/A
0.00%
0.05%
0.91%
0.00%
0.01%
0.00%
0.05%
0.93%
0.00%
0.01%
0.00%
0.11%
0.67%
0.00%
0.00%
N/A
N/A
0.00%
0.03%
0.00%
0.03%
0.00%
0.00%
99%
Value
(MS/L)
<1.0
<2.0
<1.0
<1.0
<5.0
<5.0
<2.0
<5.0
<4.0
<2.0
<2.0
<5.0
<1.0
<5.0
<5.0
<1.0
<4.4
<2.0
<5.0
<2.0
<2.0
<2.0
<1.0
<1.0
13.2
0.7
<1.0
<1.0
<5.0
<5.0
3.7
26
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
CHEMICAL NAME
(Threshold in u.g/L)
1 , 1 ,2-Trichloroethane
(MCL=5)
Trichloroethylene
(MCL=5)
Trichlorofluorom ethane
(HAL=175)
1 ,2,3-Trichloropropane
(MCL=40)
1 ,2,4-Trim ethylbenzene
(N/A)
1, 3, 5-Trim ethylbenzene
(N/A)
Vinyl Chloride
(MCL=2)
Xylenes (Total)
(MCL=10,000)
Total #
PWS
19,964
15,290
16,851
17,392
12,755
12,671
15,184
9,463
#GW
PWS
18,253
14,198
15,347
15,771
11,462
11,379
14,099
8,841
#SW
PWS
1,853
1,220
1,637
1,758
1,372
1,370
1,209
670
%
PWS
>MRL
0.43%
3.54%
1.48%
0.25%
0.83%
0.61%
0.50%
3.04%
% GW
PWS
>MRL
0.29%
3.37%
1.39%
0.25%
0.76%
0.59%
0.44%
2.51%
% SW
PWS
>MRL
1.78%
5.66%
2 32%
0.23%
1.38%
0.66%
1.24%
10.75%
% PWS >
Threshold
0.04%
0.98%
0.01%
0.01%
% GW
PWS>
Threshold
0.02%
1.00%
0.01%
0.01%
% SW
PWS>
Threshold
0.16%
0.66%
0.00%
0.00%
N/A
N/A
0.28%
0.00%
0.23%
0.00%
0.83%
0.00%
99%
Value
(MS/L)
<1.0
20.8
0.6
<2.0
<2.0
<2.0
<2.0
0.6
1 The high occurrence of Ethylene Dibromide are, in part, considered false positives related to analytical methods problems.
MCL=Maximum Contaminant Level
HAL=Health Advisory Level (as of December 2000)
HRL=Health Reference Level (concentration values used only as reference levels for analyses in this report)
MRL=Minimum Reporting Level
The MCL, HAL, HRL, and MRL values are used in this report only as reference levels to facilitate occurrence assessments.
"% PWS > Threshold" indicates the proportion of systems with any analytical results exceeding the concentration value of the
HRL/MCL/HAL. (Note that results for % PWSs greater than an MCL value does not indicate a MCL violation. A formal MCL
violation occurs when the MCL is exceeded by the average of four consecutive quarterly samples or confirmation samples as required
by the primacy States.)
N/A= There is no HRL/MCL/HAL available
V.B. SDWIS/FED (Round 2) Contaminant Occurrence
Table V.B.I summarizes the occurrence data of the SDWIS/FED (Round 2) 20 cross-section
states for the 48 Round 2 contaminants. This table presents the total number of unique public water
systems, the percent of public water systems with at least one result greater than the MRL, the percent of
public water systems with at least one result greater than the MCL/HRL/HAL and, finally, the 99th
percentile value in micrograms per liter (• g/L). (To review a map of the SDWIS/FED Round 2 cross-
section states, refer to Figure III.B.S.b.)
The 20 SDWIS/FED (Round 2) cross-section states reflect a significant national coverage: these
states contain approximately 41% of public water systems nationally and 34% of the population served by
public water systems. For a significant majority of the contaminants evaluated here (40 out of 48), less
than 1% of public water systems in the cross-section states have analytical detections (any sample
analytical result greater than the MRL). Two contaminants (dichlorodifluoromethane and
trichlorofluoromethane) are detected in 1 to 2% of public water systems, as evidenced by one or more
sample analytical results greater than the MRL, and 1 contaminant (chloromethane) is detected in 2.25%
of public water systems, as evidenced by one or more sample analytical results greater than the MRL.
Five contaminants -4 THMs and sulfate- have a considerably higher percent of systems with one or
more sample analytical results greater than the MRL (ranging from 12.12% to 27.42% for the THMs and
88.11% for sulfate). Select SDWIS/FED (Round 2) high occurrence contaminants are identified and
briefly assessed in Section VI.
27
-------
EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Table V.B.I. SDWIS/FED (Round 2) Data - 20 State Cross-Section Summary of Occurrence
CHEMICAL NAME
(Threshold in ug/L)
Total
PWS
#GW
PWS
#SW
PWS
% PWS
>MRL
% GW
PWS
% sw
PWS
% PWS >
Threshol
% GW
PWS>
% SW
PWS>
99%
Value
IOCS
Sulfate
(HRL=500,000)
16,495
15,009
1,486
88.11%
87.76%
91.66%
1.79%
1.83%
1.41%
560000
SOCs
Aldicarb1
(HRL=7)
Aldicarb Sulfone1
(HRL=7)
Aldicarb Sulfoxide1
(HRL=7)
Aldrm1
(HRL =0.002)
Butachlor1
(N/A)
Carbaryl1
(MCL=700)
Dicamba1
(MCL=200)
Dieldrm1
(HRL =0.002)
3-Hydroxycarbofuran1
(N/A)
Methomyl1
(MCL=200)
Metolachlor1
(HRL =70)
Metribuzin1
(HRL=91)
Propachlor1
(MCL=90)
11,972
11,968
11,954
11,745
11,940
12,623
14,034
11,788
12,644
12,604
12,953
13,512
12,050
10,509
10,512
10,500
10,420
10,482
11,086
12,220
10,329
11,088
11,068
11,503
11,833
10,600
1,463
1,456
1,454
1,325
1,458
1,537
1,814
1,459
1,556
1,536
1,450
1,679
1,450
0.01%
0.08%
0.08%
0.01%
0.04%
0.03%
0.34%
0.09%
0.07%
0.07%
0.83%
0.01%
0.05%
0.00%
0.04%
0.03%
0.01%
0.01%
0.02%
0.21%
0.09%
0.02%
0.05%
0.11%
0.01%
0.02%
0.07%
0.41%
0.48%
0.00%
0.27%
0.13%
1.21%
0.14%
0.45%
0.20%
6.55%
0.00%
0.28%
0.00%
0.00%
0.01%
0.01%
0.00%
0.00%
0.01%
0.01%
0.00%
0.00%
0.00%
0.00%
N/A
0.00%
0.00%
0.09%
0.00%
0.00%
0.09%
0.00%
0.00%
0.14%
N/A
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
<3.0
<2.0
<4.0
<2.0
<10.0
<10.0
<10.0
<1.0
<10.0
<50.0
<5.0
<2.0
<5.0
VOCs
Bromobenzene
(N/A)
Bromochlorom ethane2
(MCL=10)
Bromodichlorom ethane
(HRL =60)
Bromoform
(HRL=400)
Bromom ethane
(MCL=10)
Chloroethane
(N/A)
Chloroform
(HRL=600)
Chlorom ethane
(MCL=3)
Dibromochlorom ethane
(HRL =60)
Dibromom ethane
(N/A)
Dichlorodifluorom ethane2
(MCL=1,000)
1 , 1 -Dichloroe thane
(MCL=5)
1 ,3-Dichloropropane
(N/A)
2,2-Dichloropropane
(N/A)
1 , 1 -Dichloropropene
(N/A)
24,125
22,974
23,858
18,461
23,328
24,433
23,737
23,478
23,750
23,006
22,141
24,808
24,065
24,096
24,069
21,461
20,507
21,152
16,348
20,872
21,925
21,021
21,030
21,059
20,454
19,836
22,114
21,430
21,445
21,438
2,664
2,467
2,706
2,113
2,456
2,508
2,716
2,448
2,691
2,552
2,305
2,694
2,635
2,651
2,631
0.13%
0.46%
21.97%
12.12%
0.75%
0.34%
27.42%
2.25%
18.37%
0.46%
1.27%
0.74%
0.06%
0.09%
0.07%
0.12%
0.32%
16.14%
11.08%
0.74%
0.32%
21.84%
2.04%
14.55%
0.32%
1.23%
0.67%
0.05%
0.07%
0.06%
0.23%
1.62%
67.52%
20.11%
0.86%
0.56%
70.54%
4.08%
48.23%
1.53%
1.65%
1.34%
0.11%
0.26%
0.15%
N/A
0.03%
0.08%
0.01%
0.06%
0.02%
0.05%
0.00%
0.05%
0.08%
0.30%
0.05%
0.08%
N/A
0.04%
0.58%
0.08%
0.01%
0.55%
0.05%
0.26%
0.78%
0.30%
N/A
0.00%
0.08%
0.00%
0.07%
0.00%
0.11%
N/A
N/A
N/A
<1.0
<1.0
18.8
6.5
<9.0
<2.5
110.0
<2.5
9.7
<1.0
<20.0
<1.0
<2.0
<1.0
<1.0
28
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
CHEMICAL NAME
(Threshold in ug/L)
1,3- Dichloropropene
(HRL=40)
Hexachlorobutadiene2
(HRL=0.9)
Isopropylbenzene2
(N/A)
m -Dichlorobenzene
(HAL=600)
n-Butylbenzene2
(N/A)
n-Propylbenzene2
(N/A)
Naphthalene2
(HRL=140)
o-Chlorotoluene
(MCL=100)
p-Chlorotoluene
(MCL=100)
p-Isopropyltoluene2
(N/A)
sec-Butylbenzene2
(N/A)
tert-Butylbenzene2
(N/A)
1,1, 1 ,2-Tetrachloroethane
(HAL=70)
1 ,1 ,2,2-Tetrachloroethane
(HAL =2)
1 ,2,3-Trichlorobenzene2
(N/A)
Trichlorofluorom ethane2
(HAL=175)
1 ,2,3-Trichloropropane
(MCL=40)
1 ,2,4-Trim ethylbenzene2
(N/A)
1, 3, 5-Trim ethylbenzene2
(N/A)
Total
PWS
16,787
22,736
22,995
24,119
22,972
22,969
22,923
24,118
21,378
22,617
22,973
22,973
24,127
24,800
22,532
22,659
24,088
22,965
22,974
#GW
PWS
15,178
20,380
20,524
21,457
20,509
20,501
20,524
21,457
18,808
20,320
20,509
20,508
21,462
22,106
20,144
20,329
21,441
20,504
20,513
#SW
PWS
1,609
2,356
2,471
2,662
2,463
2,468
2,399
2,661
2,570
2,297
2,464
2,465
2,665
2,694
2,388
2,330
2,647
2,461
2,461
% PWS
>MRL
0.35%
0.18%
0.24%
0.26%
0.13%
0.23%
0.75%
0.14%
0.12%
0.16%
0.14%
0.11%
0.21%
0.08%
0.19%
1 . 1 7%
0.08%
0.76%
0.43%
% GW
PWS
0.32%
0.13%
0.23%
0.22%
0.12%
0.19%
0.62%
0.11%
0.10%
0.15%
0.14%
0.10%
0.16%
0.05%
0.15%
0.93%
0.06%
0.63%
0.35%
% sw
PWS
0.62%
0.59%
0.32%
0.53%
0.20%
0.57%
1.92%
0.38%
0.27%
0.26%
0.20%
0.16%
0.64%
0.30%
0.50%
3.22 /o
0.23%
1.79%
1 . 1 0%
% PWS >
Threshol
0.00%
0.02%
% GW
PWS>
0.00%
0.00%
% sw
PWS>
0.00%
0.13%
N/A
0.00%
0.00%
0.00%
N/A
N/A
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
N/A
N/A
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
N/A
99%
Value
<0.5
<1.0
<2.0
<1.0
<2.0
<2.0
<2.0
<2.0
<2.0
<2.0
<2.0
<2.0
<1.0
<1.0
<2.0
<2.5
<1.0
<1.0
<2.0
1. Massachusetts data not included in summary statistics for this contaminant.
2. New Hampshire data not included in summary statistics for this contaminant.
MCL=Maximum Contaminant Level
HAL=Health Advisory Level (as of December 2000)
HRL=Health Reference Level (concentration values used only as reference levels for analyses in this report)
MRL=Minimum Reporting Level
The MCL, HAL, HRL, and MRL values are used in this report only as reference levels to facilitate occurrence assessments.
"% PWS > Threshold" indicates the proportion of systems with any analytical results exceeding the concentration value of the
HRL/MCL/HAL. (Note that results for % PWSs greater than an MCL value does not indicate a MCL violation. A formal MCL
violation occurs when the MCL is exceeded by the average of four consecutive quarterly samples or confirmation samples as required
by the primacy States.)
N/A= There is no HRL/MCL/HAL available
29
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
VI. ASSESSMENTS OF SELECT HIGH OCCURRENCE CONTAMINANTS
VI.A. Select High Occurrence Contaminants and Detailed Graphical and Spatial Analysis
The contaminants in URCIS (Round 1) and SDWIS/FED (Round 2) were ranked according to
their occurrence as a means to select a group of high occurrence contaminants for a more detailed
graphical and spatial assessments. These detailed assessments are included in Section VI of the compete
National Occurrence report (Occurrence of Unregulated Contaminants in Public Water Systems: An
Initial Assessment, EPA 815-P-00-001). This summary report provides only a description of the types of
assessments included in the complete report.
The ranking of the URCIS (Round 1) contaminant occurrence data is presented in Table VI. A. 1,
and the ranking of SDWIS/FED (Round 2) data is presented in Table VI.A.2. The contaminants were
ranked by percent of systems with at least one sample detection (at least one sample analytical result
greater than the minimum reporting level) and by percent of systems with at least one sample analytical
result greater than the MCL or HAL or HRL (whichever MCL/HAL/HRL health effects threshold is
relevant to the contaminant in question).
Table VI.A.3 identifies the high occurrence contaminants selected for detailed assessments.
High occurrence was the primary consideration for selection for the detailed assessments included in the
complete National Occurrence report, but consideration was also given to coverage across contaminant
groups, changing regulatory status between Rounds 1 and 2, and overlap between Rounds 1 and 2.
Table VI.A.1. Contaminant Occurrence Ranking of URCIS (Round 1) Data
Percent Systems With At Least One Sample
Analytical Detection
SOCs
iDibromochloropropane
X Ip.thvlene Dihromid^^^^ ^^_
2.49%
1 14%
VOCs
X
X
X
X
X
Chloroform
Bromodichlorom ethane
Dibromochloromethane
Bromoform
Dichloromethane
1,1,1 -Trichloroethane
Trichloroethylene
Toluene
Tetrachloroethylene
Xylenes (Total)
o-Xylene
Ethyl Benzene
p-Xylene
m-Xylene
rrichlorofluorom ethane
cis- 1 ,2-Dichloroethene
Dichlorodifluoromethane
Carbon Tetrachloride
p-Dichlorobenzene
Chloromethane
Naphthalene
Dichloroethene
1,2-Dichloroethane
Benzene
1 1 -nir.hlnrne: thane:
28.63%
22.09%
17.87%
8.95%
4.05%
3.66%
3.54%
3.50%
3.33%
3.04%
1.76%
1.62%
1.58%
1.55%
1.48%
1.47%
1.37%
1.32%
1.25%
1.22%
1.18%
1.17%
1.16%
1.14%
1 14%
Percent Systems With At Least One Sample
Analytical Result Greater than MCL/HAL/HRL
SOCs
Dibromochloropropane
X F.thvlene Dihromide
1.32%
0 16%
VOCs
X Trichloroethylene
X Tetrachloroethylene
Dichloromethane
X Chloromethane
Vinyl Chloride
Benzene
Dichloroethene
1,2-Dichloroethane
X 1,1-Dichloroethane
Carbon Tetrachloride
Bromodichloromethane
Hexachlorobutadiene
Bromomethane
1,2-Dichloropropane
Dibromochloromethane
1 , 1 ,2,2-Tetrachloroethane
1 , 1 ,2-Trichloroethene
Bromochlorom ethane
cis-l,2-Dichloroethene
1,1, 1 -Trichloroethane
X Chloroform
Naphthalene
Trichlorofluoromethane
1,2,3-Trichloropropane
Rrnm nfnrm
0.98%
0.91%
0.77%
0.45%
0.28%
0.25%
0.20%
0.19%
0.18%
0.16%
0.13%
0.11%
0.09%
0.08%
0.06%
0.05%
0.04%
0.03%
0.03%
0.03%
0.02%
0.01%
0.01%
0.01%
0 0 1 %
30
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Percent Systems With At Least One Sample
Analytical Detection
1,2,4-Trimethylbenzene
Bromomethane
1,2-Dichloropropane
trans- 1 ,2-Dichloroethene
cis- 1 ,2-Dichloropropene
1,3,5-Trimethylbenzene
Styrene
Chlorobenzene
Bromochloromethane
Vinyl Chloride
1 ,2, 4-Tri chlorobenzene
1, 2, 3-Tri chlorobenzene
1,1,2,2-Tetrachloroethane
1 , 1 ,2-Trichloroethene
Chloroethane
Dibromomethane
n-Butylbenzene
Hexachlorobutadiene
n-Propyulbenzene
o-Dichlorobenzene
Isopropyltoluene
1,2,3-Trichloropropane
trans- 1,3-Dichloropropene
m-Dichlorobenzene
p-Isopropyltoluene
sec-Butylbenzene
o-Chlorotoluene
Bromobenzene
tert-Butylbenzene
1,1, 1 ,2-Tetrachloroethane
p-Chlorotoluene
1,3-Dichloropropene
2,2-Dichloropropane
1 , 1 -Dichloropropene
1 ^-Fiir.lilnrnnrnnanR
0.83%
0.77%
0.67%
0.64%
0.61%
0.61%
0.57%
0.53%
0.50%
0.50%
0.49%
0.49%
0.45%
0.43%
0.39%
0.36%
0.35%
0.35%
0.33%
0.28%
0.27%
0.25%
0.25%
0.25%
0.25%
0.23%
0.20%
0.19%
0.19%
0.18%
0.17%
0.16%
0.15%
0.13%
ft 19%
X = Contaminants selected for graphical/spatial assessment in
N/A = There is no Health Reference Level (HRL), Maximum
the contaminants.
Percent Systems With At Least One Sample
Analytical Result Greater than MCL/HAL/HRL
trans- 1 ,2-Dichloroethene
Toluene
Xylenes (Total)
Ethyl Benzene
Dichlorodifluorom ethane
p-Dichlorobenzene
Styrene
Chlorobenzene
1,2,4-Trichlorobenzene
o-Dichlorobenzene
m-Dichlorobenzene
o-Chlorotoluene
1,1, 1 ,2-Tetrachloroethane
p-Chlorotoluene
1,3-Dichloropropene
1,3-Dichloropropane
1 , 1 -Dichloropropene
1,2,3-Trichlorobenzene
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
2,2-Dichloropropane
Bromobenzene
Chloroethane
cis-l,2-Dichloropropene
Dibromomethane
Isopropyltoluene
m-Xylene
n-Butylbenzene
n-Propyulbenzene
o-Xylene
p-Isopropyltoluene
p-Xylene
sec-Butylbenzene
tert-Butylbenzene
tran«-1 ^-Fiip.VilnrnnrnnpnR
0.01%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
XT/ A
complete National Occurrence report.
Contaminant Level (MCL), or Health Advisory Level (HAL) for
Table VI.A.2. Contaminant Occurrence Ranking of SDWIS/FED (Round 2) Data
Percent Systems With At Least One Sample
Analytical Detection
SOCs
X
X
X
Metolachlor
Dicamba
Dieldrin
Aldicarb Sulfoxide
Aldicarb Sulfone
Methomyl
3 -Hydroxycarbofuran
Propachlor
Butachlor
Carbaryl
Aldrin
Aldicarb
N/tfitrihiiyin
0.83%
0.34%
0.09%
0.08%
0.08%
0.07%
0.07%
0.05%
0.04%
0.03%
0.01%
0.01%
ft ft l %
Percent Systems With At Least One Sample
Analytical Result Greater than MCL/HAL/HRL
SOCs
X
X
X
Dieldrin
Aldrin
Aldicarb Sulfoxide
Metribuzin
Aldicarb
Carbaryl
Propachlor
Methomyl
Aldicarb Sulfone
Dicamba
Metolachlor
Butachlor
^-WvHrnwr.arhnfiiran
0.09%
0.01%
0.01%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
XT/ A
31
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Percent Systems With At Least One Sample
Analytical Detection
VOCs
X
X
X
Chloroform
Bromodichlorom ethane
Dibromochloromethane
Bromoform
Chloromethane
Dichlorodifluoromethane
rrichlorofluorom ethane
1,2,4-Trimethylbenzene
Naphthalene
Bromomethane
1 , 1 -Dichloroethane
Bromochloromethane
Dibromom ethane
1,3,5-Trimethylbenzene
1,3-Dichloropropene
Chloroethane
m-Dichlorobenzene
Isopropylbenzene
n-Propylbenzene
1,1, 1 ,2-Tetrachloroethane
1,2,3-Trichlorobenzene
Hexachlorobutadiene
p-Isopropyltoluene
sec-Butylbenzene
o-Chlorotoluene
Bromobenzene
n-Butylbenzene
p-Chlorotoluene
tert-Butylbenzene
2,2-Dichloropropane
1,2,3-Trichloropropane
1,1,2,2-Tetrachloroethane
1 , 1 -Dichloropropene
1 .3-Dichloronronane
27.42%
21.97%
18.37%
12.12%
2.25%
1.27%
1.17%
0.76%
0.75%
0.75%
0.74%
0.46%
0.46%
0.43%
0.35%
0.34%
0.26%
0.24%
0.23%
0.21%
0.19%
0.18%
0.16%
0.14%
0.14%
0.13%
0.13%
0.12%
0.11%
0.09%
0.08%
0.08%
0.07%
0.06%
Percent Systems With At Least One Sample
Analytical Result Greater than MCL/HAL/HRL
VOCs
X
X
X
Chloromethane
1 , 1 -Dichloroethane
Dibromochloromethane
Bromodichlorom ethane
Bromomethane
Chloroform
Bromochloromethane
Hexachlorobutadiene
Bromoform
1,2,3-Trichloropropane
1,1,1 ,2-Tetrachloroethane
1 , 1 ,2,2-Tetrachloroethane
1,3-Dichloropropene
Dichlorodifluoromethane
m-Dichlorobenzene
Naphthalene
o-Chlorotoluene
p-Chlorotoluene
Trichlorofluorom ethane
1 , 1 -Dichloropropene
1,2,3-Trichlorobenzene
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
1,3-Dichloropropane
2,2-Dichloropropane
Bromobenzene
Chloroethane
Dibromomethane
Isopropylbenzene
n-Butylbenzene
n-Propylbenzene
p-Isopropyltoluene
sec-Butylbenzene
tert-Butvlhen/ene
0.58%
0.08%
0.08%
0.08%
0.06%
0.04%
0.03%
0.02%
0.01%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
X= Contaminants selected for graphical/spatial assessment in
N/A = There is no Health Reference Level (HRL), Maximum
complete National Occurrence report.
Contaminant Level (MCL), or Health Advisory Level (HAL) for
Table VI.A.3. High Occurrence Contaminants Selected for Graphical and Spatial Assessments (and
some characteristics considered in the selection).
Contaminant
Trichloroethylene
Tetrachloroethylene
Chloromethane
1 , 1 -Dichloroethane
Chloroform
Ethylene Dibromide
Dieldrin
Aldicarb Sulfoxide
Metolachlor
Regulated
(Round 2)
(Round 2)
(Round 2)
Unregulated
•
•
•
.
.
•
•
•
•
voc
•
•
•
.
.
soc
•
•
•
•
THM
•
URCIS
(Round 1)
•
•
•
.
•
•
SDWIS/
FED
(Round 2)
•
.
.
•
•
•
32
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
VLB. Graphical and Spatial Assessments of Select High Occurrence Contaminants
The detailed graphical and spatial assessments of the high occurrence contaminants identified
above are included in Section VLB.of the complete National Occurrence report. These assessments,
evaluated together with the analytical results tables presented throughout the complete National
Occurrence report and report appendices, provide a comprehensive overview of the degree, distribution,
and temporal trends (if any) of contaminant occurrence. The graphical and spatial assessments are
conducted to provide additional analytical detail for the select high occurrence contaminants (of potentially
greater regulatory interest), and to provide examples of graphical and spatial assessments that can be
conducted for any other contaminants of interest. For contaminants of lower occurrence, however, the
data maybe too sparse to support these types of assessments.
One important aspect of the cross-section state data must be considered as part of any
conclusions drawn from the maps and graphs in the complete National Occurrence report and this
national summary. The national cross-sections have been developed from public water systems'
contaminant monitoring data with the intent that, in aggregate, the cross-section states' occurrence
findings are indicative of national occurrence. Given that half (or more) of the states are without
adequate data (and therefore could not be included in the cross-sections used for analyses), sub-national
occurrence findings, such as regional or multi-state patterns, may be difficult to characterize and must be
interpreted with caution. Supplemental information should be collected and used, whenever possible, to
assist in evaluating the significance of any apparent or suggested regional patterns.
To provide the broadest possible geographic coverage, some occurrence maps are presented that
use all available data from all states with data in URCIS (Round 1) and/or SDWIS/FED (Round 2) (see
the complete National Occurrence report Section V.I., Figures VI.B.I.a, VI.B.2.a, VLB.3.a, VLB.4.a,
VLB.5.a, VLB.6.a, VLB.7.a, and VLB.8.a). This use of all data, including incomplete state data sets,
and "biased" state data sets is only appropriate for broad, simple identifications of presence or absence of
a detection of a specific contaminant. This more extensive use of the data in the databases can be
appropriate when a simple identification of states with any PWS contaminant detection is of interest. The
biased data used in these figures are not and cannot be used for any national estimates of contaminant
occurrence.
The remaining, majority of figures presented in the complete National Occurrence report have
been based only on non-biased, representative cross-section state data, and are used to characterize the
distribution of contaminant occurrence. For example, the cross-section state data are used to develop
maps that categorize states as based on the range of percent of state PWSs with detections of a
particular contaminant (see Figures VI.B.l.b., VI.B.2.b, VI.B.S.b, VI.BAb, VI.B.5.b, VI.B.6.b,
VI.B.T.b, andVI.B.S.b).
Additionally, the temporal distribution of the percent of systems with contaminant detections, or
the percent of systems with sample results of contaminants identified above the MCL (or HRL) by year
are presented in Figures VLB.I.e., VI.B.2.C, VI.B.3.C, VI.BAc, VI.B.5.C, VI.B.6.C, VI.B.T.d, VI.B.S.d,
andVI.B.9.a.
VI.B.l. Ethylene Dibromide
A spatial assessment of contaminant occurrence using URCIS (Round 1) data for ethylene
dibromide suggests a widespread occurrence. However, there is no apparent spatial/geographic
occurrence pattern within the wide extent of occurrence.
33
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
In temporal assessments of ethylene dibromide occurrence, there appears to be a steady but slight
decrease in the percent of public water systems with ethylene dibromide detections (analytical results
greater than the MRL) from 1988 to 1992. There is also a less consistent, but apparent decrease in the
percent of public water systems with analytical results greater than the MCL during the same time period
(1988 to 1992).
VI.B.2. Tetrachloroethylene
Tetrachloroethylene (sometimes referred to as perchloroethylene, or 'perc', or PCE) is also of
very widespread occurrence and with no apparent spatial occurrence pattern. (Also noted is the well-
established co-occurrence of this contaminant with trichloroethylene.)
In temporal assessments of occurrence, there may be a decrease in the percent of public water
systems with detections and with analytical results greater than the MCL for the 1988 to 1992 period.
However, the percent of public water systems increases for both measures (detections and MCL
exceedances) in 1992. Note, however, that unavailable state data may affect interpretation of temporal
trends.
VI.B.3. Trichloroethylene
The occurrence overview of trichloroethylene (sometimes referred to as TCE) is similar to that of
tetrachloroethylene. Trichloroethylene is also of very widespread occurrence and with no apparent
spatial occurrence pattern. (Also noted is the well-established co-occurrence of this contaminant with
tetrachloroethylene.)
Also, in temporal assessments of occurrence, there may be a decrease in the percent of public
water systems with detections and with analytical results greater than the MCL for the 1988 to 1992
period. However, the percent of public water systems increases for both measures (detections and MCL
exceedances) in 1992. Note, however, the same caution regarding unavailable state data possibly
affecting interpretation of temporal trends.
VI.B.4. Aldicarb Sulfoxide
A review of the aldicarb sulfoxide illustrates some of the interpretive cautions mentioned
previously. The spatial assessment based on SDWIS/FED Round 2 data suggests that aldicarb sulfoxide
detections are more evident in northern states (likely related to specific farm crops and pesticide use).
Higher percentages of public water systems with detections (analytical results greater than the MRL) are
indicated in Michigan, Missouri, Washington, and Oregon. Only Oregon is present in the category of
highest percentage of public water systems with analytical results of aldicarb sulfoxide greater than the
HRL.
However, three states (Florida, New York, and Wisconsin) with known, historic problems with
aldicarb sulfoxide in groundwater do not have data in the SDWIS/FED (Round 2) database. Apparent
spatial and geographic patterns must be viewed and interpreted carefully. Any conclusions made
regarding the geographic patterns (or lack of patterns) of occurrence must consider this reality of missing
data coverage.
In the temporal assessment, a "spike" (a significant but short-lived increase) in 1996 in the
percent of public water systems with analytical results greater than the HRL appears significant, but
34
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
actually reflects a very small increase in the number of systems. Therefore, there is no temporal trend,
with occurrence remaining relatively low from 1992 to 1997.
VI.B.5. Dieldrin
Dieldrin detections appear to be limited to states south of a line extending between Texas and
Massachusetts (though there are many states without dieldrin data).
Although occurrence appears high in 1992 with a subsequent drop, occurrence data for 1992 was
sometimes inconsistently reported since that year marks the divide between the Round 1 and Round 2
monitoring periods. The implementation of the SDWA 1993 amendments may influence any occurrence
findings critically centered around the 1992 and 1993 data.
VI.B.6. Metolachlor
Metolachlor also appears to be of widespread, but generally low, occurrence. However, many
states did not report metolachlor data. This is especially important given that the cornbelt states with the
highest metolachlor use (Indiana, Illinois, and Iowa) do not have any metolachlor data in the SDWIS/FED
(Round 2) data. In this case, supplemental information is needed to more fully assess the national
occurrence of metolachlor.
VI.B.7. 1,1-Dichloroethane
Data are available from both Round 1 and Round 2 for 1,1-dichloroethane. Using only cross-
section state data, 32 of the 34 combined cross-section states have public water systems with at least one
detection of 1,1-dichloroethane. An expanded use of available data shows that 42 of the 46 states with
data (which includes cross-section as well as any available non-cross-section state data) have public
water systems with at least one detection of 1,1-dichloroethane. The biased (non-cross-section state)
data can be used here to expand the spatial coverage.
Based on the percentage of PWSs with analytical results greater than the detection limit, there
appears to be generally higher levels of occurrence in states east of the Mississippi River. Again,
supplemental information would be necessary to make definitive conclusions on 1,1-dichloroethane
occurrence distributions.
Regarding temporal trends, there appears to be a decrease in the occurrence of 1,1-
dichloroethane from 1986 to 1997 when based on either percent PWSs with analytical results greater then
the detection limit or greater than the MCL.
Comparisons were also made for 1,1-dichloroethane occurrence between Round 1 to Round 2 for
the 8 states with data in both sampling rounds. With occurrence based on the detection limit, no
consistent temporal trend is suggested. When occurrence is based on MCLs, there is an apparent
decreasing trend of 1,1-dichloroethane occurrence in 4 of the 8 states (with the other 4 states indicating
no occurrence in either rounds). These results seem to at least partially corroborate the decreasing
occurrence trend over time indicated above.
VI.B.8. Chloromethane
Detections and distribution of chloromethane are addressed with maps and graphs similar to those
for 1,1-dichloroethane. Chloromethane is of widespread and relatively high levels of occurrence.
35
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EPA - OGWDW Occurrence of Unregulated Contaminants in Public Water Systems - A National Summary
Temporally, occurrence may have decreased from 1988 to 1992, but in later years appears to be
increasing, based on percent public water systems with detections. The occurrence of chloromethane
appears to be stable, based on percent public water systems with analytical results greater than the MCL.
VI.B.9. Chloroform
Chloroform is evaluated only temporally. Occurrence for chloroform, as is typical of the THMs,
is relatively high based on the percent of systems with analytical detections. In contrast, the occurrence
of chloroform in public water systems greater than the HRL are relatively low. Also, chloroform
occurrence appears to increase from Round 1 to Round 2.
VLB. 10. Comparison of Occurrence in URCIS (Round 1) and SDWIS/FED (Round 2)
Occurrence data for three contaminants were contained in both Round 1 and Round data sets:
chloromethane, 1,1-dichloroethane, and chloroform. Review of the data suggest no distinct or apparent
temporal trends between occurrence of these three contaminants between the periods of URCIS (Round
1) and SDWIS/FED (Round 2) monitoring.
36
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