v>EPA
United States
Environmental Protection
Agency
The Analysis of Regulated Contaminant
Occurrence Data from Public Water Systems in
Support of the Third Six-Year Review of
National Primary Drinking Water Regulations:
Chemical Phase Rules and Radionuclides Rules

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Office of Water (4607M)
EP A-810-R-16-014
December 2016
www. epa. gov/ safewater

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Disclaimer
This report is in support of the revise/take no action decisions for EPA's Third Six-Year Review
of Existing Drinking Water Standards Federal Register Notice. This report is intended to provide
technical background for the third Six-Year Review.
This document is not a regulation itself and it does not substitute for the Safe Drinking Water
Act (SDWA) or EPA's regulations. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.

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Executive Summary
The 1996 Amendments to the Safe Drinking Water Act (SDWA) require that the U.S.
Environmental Protection Agency (EPA) "shall, at least once every six years, review and revise,
as appropriate, each National Primary Drinking Water Regulation (NPDWR)." The NPDWRs
are often referred to as the national drinking water contaminant regulations or drinking water
standards. The 'Six-Year Review' process is an assessment of new information on the health
effects and national occurrence of the regulated contaminants, as well as new capabilities of
treatment technologies and laboratory analytical methods. Through this process, EPA determines
whether the new information and technical capabilities provide a scientific basis to support a
revision of existing regulations that will improve public health protection.
This report presents the national contaminant occurrence assessments conducted in support of
EPA's third Six-Year Review of NPDWRs. Included are detailed descriptions of the national
contaminant occurrence dataset, the data management procedures conducted to develop the
national dataset and the statistical analytical methods employed to generate national estimates of
regulated contaminant occurrence in public drinking water systems.
Because there is no national database that receives and stores all relevant data on the occurrence
of regulated contaminants in public drinking water systems, EPA conducted a voluntary data
call-in from the states, territories and tribes to obtain the data. EPA worked with the states and
primacy agencies to receive the states' and agencies' complete records of compliance monitoring
data (public drinking water system regulated contaminant occurrence data) for 2006 through
2011. The compliance monitoring data were obtained through the Information Collection
Request (ICR) process.
EPA conducted data management and quality assurance (QA) evaluations on the data received
for contaminants evaluated for the Third Six-Year Review to establish a high quality, national
contaminant occurrence dataset consisting of data from 54 states/primacy agencies (46 states
plus Washington, D.C. and the tribal data). The contaminant occurrence data for the these 54
states/primacy agencies comprise almost 13 million analytical records from approximately
139,000 public water systems (PWSs), which serve approximately 290 million people nationally.
This dataset, the Third Six-Year Review (SYR3) ICR Dataset for the third Six-Year Review (or
"SYR3 ICR Dataset"), is the largest and most comprehensive contaminant occurrence dataset
ever compiled and analyzed by EPA's Drinking Water Program.
To estimate national contaminant occurrence using the SYR3 ICR Dataset, EPA used a two-
stage analytical approach. In the first stage of analysis (the "Stage 1 analysis"), the occurrence
data were reviewed, quality-checked, characterized and then analyzed to generate simple, non-
parametric estimates of national contaminant occurrence in PWSs. Simple counts were made of
the number and percentage of systems and of the population served by systems that report at
least one compliance monitoring sample result greater than a specified contaminant
concentration threshold, such as the contaminant's Maximum Contaminant Level (MCL) (the
contaminant's drinking water standard). This Stage 1 analysis, based on maximum sample
concentration values, is inherently conservative. It is designed to ensure that contaminant
occurrence is not underestimated for the consideration of public health protection. The Stage 1
analysis provides occurrence assessments that may be more reflective of potential acute
exposure. Additional parametric statistical estimations (the "Stage 2 analyses") were conducted
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on a set of contaminants selected by EPA on the basis of the Six-Year Review Protocol. The
Stage 2 analysis estimates long-term mean concentrations of contaminants in all systems
nationwide, generating occurrence analyses that are less conservative than the Stage 1 analysis.
The Stage 2 analysis also provides occurrence assessments that may be more reflective of
potential chronic exposure.
EPA used the Stage 1 analyses of approximate peak concentration measures to assess the
national occurrence of 61 regulated contaminants (57 chemical and 4 radiologicals). Ten
regulated chemical contaminants (lead, copper, 1,2-dichloroethane, 1,2-dichloropropane,
benzene, carbon tetrachloride, dichloromethane, tetrachloroethylene, trichloroethylene and vinyl
chloride), as well as disinfection byproducts (DBPs) and microbial contaminants were being
reviewed or revised under other regulatory actions, or included in separate regulatory reviews.
EPA also conducted additional Stage 2 analyses using mean concentration measures for 17 of the
61 regulated chemical contaminants. Several different variations of the Stage 1 and Stage 2
analyses were conducted to broadly characterize national occurrence and are described and
presented in this report and its appendices.
Additionally, two synthetic organic chemicals (SOCs) were assessed using a more detailed Stage
1 analysis while four inorganic chemicals (IOCs), nine SOCs and five volatile organic chemicals
(VOCs) were assessed using the Stage 2 analytical approach. The Stage 2 occurrence analyses
conducted in this report, based roughly on long-term, multi-year average contaminant
occurrence, are not the same as the occurrence analyses formally conducted to assess compliance
with contaminant drinking water standards (which for most contaminants are based on annual
average contaminant occurrence; see Section 7 for details).
Background information regarding the national contaminant occurrence data and data
management is presented in Sections 1 through 5 of this report. The summary of the Stage 1
analytical findings is presented in Section 6, with more detailed Stage 1 analyses for two
contaminants in Appendix A. The summary of the Stage 2 analytical findings for 17 select
contaminants is presented in Section 7, with complete detailed Stage 2 occurrence findings for
the 17 contaminants included in Appendix B.
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Table of Contents
1	Introduction	1-1
1.1	Purpose and Scope	1-2
1.2	Data Sources	1-2
1.3	Data Analysis	1-4
2	The National Compliance Monitoring ICR Dataset for the Third Six-Year
Review	2-6
2.1	Completeness and Representativeness of the Six-Year Review ICR Dataset	2-7
3	Data Management	3-13
3.1	Dataset Consistency and Restructuring	3-13
3.2	Review of Dataset Content	3-14
3.3	Establishing Consistent Data Fields for Analytical Results	3-17
4	Data Quality Assurance/Quality Control	4-19
4.1	Quality Assurance Measures	4-19
4.2	Adjustments of Population Served by Public Water Systems	4-21
4.3	Adjustments of Source Water Type for Public Water Systems	4-22
5	Summary of the Compliance Monitoring Data	5-23
5.1	Characteristics of the Data - States, Systems and Records	5-23
5.2	Occurrence Variability Assessment	5-31
5.3	Threshold Evaluations	5-32
6	Stage 1 Analysis	6-35
6.1	Summary of Stage 1 Contaminant Occurrence Findings	6-35
6.2	Comparison of Stage 1 Analysis of First, Second and Third Six-Year Reviews	6-41
6.3	System Sample Point Level Analysis	6-44
7	Stage 2 Analysis	7-49
7.1	Preparing the Data for the Stage 2 Analysis	7-50
7.2	Summary of Stage 2 Contaminant Occurrence Estimations	7-50
8	References	8-52
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Exhibits
Exhibit 1.1: States Compliance Monitoring Waivers	1-3
Exhibit 2.1: States with Compliance Monitoring Data Included in the SYR3 ICR Dataset	2-6
Exhibit 2.2: Comparison of the Total Number of Non-Purchased Systems and Retail Population
Served in SDWIS/Fed and the SYR3 ICR Dataset, By State	2-9
Exhibit 2.3: Comparison of the Total Number of Systems and Retail Population Served in
SDWIS/Fed and the SYR3 ICR Dataset, By Source Water Type and
System Type	2-11
Exhibit 3.1: Summary of Compliance Monitoring Data Provided by States for the Third Six-Year
Review	3-13
Exhibit 3.2: Data Elements Requested by EPA for the Third Six-Year Review	3-14
Exhibit 3.3: List of Contaminants for Which Data Were Requested from States	3-16
Exhibit 4.1: Chemical Group Monitoring Requirements	4-19
Exhibit 5.1: Number of Systems and Population Served by Systems in the SYR3 ICR Dataset,
by Source Water Type	5-23
Exhibit 5.2: Number of Systems and Population Served by Systems in the SYR3 ICR Dataset, by
System Size	5-24
Exhibit 5.3: Number of Systems and Retail Population Served by Systems in the SYR3 ICR
Dataset, by System Type	5-25
Exhibit 5.4: An Inventory of Contaminant Occurrence Data in the SYR3 ICR Dataset, by
State	5-25
Exhibit 5.5: An Inventory of the Contaminant Occurrence Data in the SYR3 ICR Dataset, by
Contaminant	5-28
Exhibit 5.6: List of Contaminant Thresholds used in Stage 2 Occurrence Analysis1	5-33
Exhibit 6.1: Summary of Stage 1 Contaminant Occurrence Findings - Systems and Population
Served by Systems	6-35
Exhibit 6.2: Number and Percent of Systems and Population Served by Systems with Detections
Greater than the MCL Concentration	6-38
Exhibit 6.3: Comparison of Stage 1 Analyses of the First, Second and Third Six-Year Reviews
based on the Percent of Systems	6-41
Exhibit 6.4: Summary of Stage 1 Contaminant Occurrence Findings - Sample Points and
Population Served by Sample Points	6-46
Exhibit 7.1: Comparison of Stage 1 and Stage 2 Analytical Results - Percent of Systems and
Population Served by Systems Greater than the MCL Concentration	7-51
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Appendices
APPENDIX A. Background Information and Detailed Stage 1 Analysis Occurrence Measures
for 2 Select Regulated Chemical Contaminants
APPENDIX B. Background Information and Detailed Stage 2 Analysis Occurrence Measures
for 17 Select Regulated Chemical Contaminants
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Acronyms
CAS
Chemical Abstracts Service
CWS
Community Water System
DBCP
l,2-Dibromo-3-chloropropane
DBP
Disinfection Byproduct
DBPR
Disinfection Byproduct Rule
DEHA
Di(2-ethylhexyl)adipate
DEHP
Di(2-ethylhexyl)phthalate
EDB
Ethylene dibromide
EPA
Environmental Protection Agency (United States)
EQL
Estimated Quantitation Level
FBRR
Filter Backwash Recycling Rule
GW
Ground Water
GWR
Ground Water Rule
GWUDI
Ground Water Under Direct Influence (of Surface Water)
HPC
Heterotrophic Plate Count
ICR
Information Collection Request
IOC
Inorganic Chemical
LCR
Lead and Copper Rule
MCL
Maximum Contaminant Level
MCLG
Maximum Contaminant Level Goal
MDL
Method Detection Limit
MFL
Million Fibers per Liter
mg/L
Milligrams per Liter
MOR
Monthly Operating Report
mrem/yr
Millirem per year
MRL
Minimum Reporting Level
ND
Non-detect or Non-detection
NPDWR
National Primary Drinking Water Regulation
NTNCWS
Non-Transient Non-Community Water System
OGWDW
Office of Ground Water and Drinking Water
PCBs
Polychlorinated Biphenyls
pCi/L
Picocuries per Liter
PQL
Practical Quantitation Level
PWS
Public Water System
PWSID
Public Water System Identification Number
QA
Quality Assurance
QC
Quality Control
RfD
Reference Dose
SDWA
Safe Drinking Water Act
SDWIS/Fed
Safe Drinking Water Information System / Federal Versio
SD WIS/State
Safe Drinking Water Information System / State Version
soc
Synthetic Organic Chemical
SP
Sample Point
sw
Surface Water
SWP
Purchased Surface Water
SWTR	Surface Water Treatment Rule
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SYR3
Third Six-Year Review
TCR
Total Coliform Rule
TNCWS
Transient Non-Community Water System
TOC
Total Organic Carbon
USEPA
United States Environmental Protection Agency
^g/L
Micrograms per Liter
voc
Volatile Organic Chemical
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1 Introduction
Pursuant to the 1996 Safe Drinking Water Act (SDWA) Amendments, the U.S. Environmental
Protection Agency (EPA) conducts, at least every six years, a review of the National Primary
Drinking Water Regulations (NPDWRs). For this "Six-Year Review" of the nation's public
drinking water standards, EPA assesses the occurrence of regulated contaminants in public water
systems (PWSs or "systems") in conjunction with other assessments of health effects, analytical
feasibility and treatment feasibility. Assessments are conducted to determine if revisions to the
existing NPDWRs (public drinking water standards) are appropriate. EPA completed and
published the results of its first and second Six-Year Reviews of NPDWRs (68 FR 42908,
USEPA, 2003a; 75 FR 15499, USEPA, 2010a) using a systematic approach, or protocol, for the
reviews. EPA has applied the same protocol to the current, third Six-Year Review of NPDWRs
("Six-Year Review 3"). This report presents the assessments of national contaminant occurrence
in PWSs in the United States in support of EPA's third Six-Year Review of NPDWRs.
Because there is no national database of regulated drinking water contaminant occurrence data
for public drinking water systems, EPA conducted a voluntary data call-in from the states,
primacy agencies, territories and tribes ("states" throughout the remainder of the report) to obtain
the data using the Information Collection Request (ICR) process. EPA worked with states to
obtain their complete compliance monitoring data for 2006 through 2011; state data management
staff were consulted to resolve any questions about the data submitted. EPA conducted data
management and quality assurance (QA) evaluations to establish a high quality, national
contaminant occurrence database consisting of data from 54 states/primacy agencies (46 states
plus Washington, D.C., American Samoa and tribal data from Region 1, Region 4, Region 5,
Region 8, Region 9 and Navajo Nation). This dataset, referred to as the National Compliance
Monitoring ICR Dataset for the Third Six-Year Review (or "SYR3 ICR Dataset"), is the largest
and most comprehensive compliance monitoring dataset ever compiled and analyzed by EPA's
Drinking Water Program. Using this dataset, EPA employed a two-stage analytical approach to
estimate a variety of occurrence measures to characterize the national occurrence of regulated
contaminants in systems to support the third Six-Year Review process.
As part of this ICR effort, EPA requested voluntary submission of States' SDWA compliance
monitoring data for chemical contaminants regulated under Phase I, II, lib and V Rules; the
Arsenic Rule; and the Radionuclides Rule. This report presents occurrence assessments for those
contaminants with the exception of contaminants currently evaluated under other regulatory
actions or included in separate regulatory reviews. Lead and copper occurrence assessments are
not included in this report because of ongoing efforts on long-term revisions to the Lead and
Copper Rule. Eight chemicals - 1,2-dichloroethane, 1,2-dichloropropane, benzene, carbon
tetrachloride, dichloromethane, tetrachloroethylene, trichloroethylene and vinyl chloride - are
not included in this review because these chemicals are being evaluated as part of the Group
Regulation of Carcinogenic Volatile Organic Compound (VOCs) (USEPA, 201 la; USEPA,
2014).
Acrylamide and epichlorohydrin are not included because there are currently no acceptable
laboratory analytical methods for detecting these contaminants in drinking water. Additionally,
no states submitted SYR3 data for these two contaminants; however, for the treatment technique
review for these two contaminants, see Support Document for Third Six Year Review of Drinking
Water Regulations for Acrylamide and Epichlorohydrin (USEPA, 2016a).
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The microbial contaminant regulations covered in this Six-Year Review include: the Surface
Water Treatment Rule (SWTR), the Interim Enhanced Surface Water Treatment Rule
(IESWTR), the Long-Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR), the Long-
Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), the Filter Backwash Recycling
Rule (FBRR) and the Ground Water Rule (GWR). Occurrence analyses related to these
contaminants' data are not included in this report; for more detailed information on the microbial
contaminants' occurrence analysis, refer to USEPA (2016b). Based on the Initial Review
Branch, EPA excluded the revised Total Coliform Rule (RTCR) from the remaining steps in this
Six-Year Review because it was promulgated on February 13, 2013. Furthermore, since most of
the 1989 Total Coliform Rule (TCR) requirements are being replaced by the 2013 RTCR, the
1989 rule was excluded from review. EPA is also reviewing the Stage 1 and Stage 2 Disinfectant
and Disinfection Byproducts Rules (DBPRs) (USEPA, 1998; USEPA, 2006) as part of the third
Six-Year Review. For more information see the technical support document for DBPRs
(USEPA, 2016c).
This report describes the extensive data management and data quality checks conducted as part
of the development of the SYR3 ICR Dataset; explains the analytical approach used to estimate
the various measures of national contaminant occurrence for the 61 contaminants included in this
report; and presents and describes the resulting national contaminant occurrence estimates for
those contaminants. This report presents many different measures and estimates of national
occurrence. Some of the contaminant occurrence measures are presented in this report as
"preliminary exposure estimates" meaning they are not formal exposure estimates, but estimates
of the population served by systems found to have some degree of contaminant occurrence in
their drinking water samples.
1.1	Purpose and Scope
EPA's Office of Ground Water and Drinking Water (OGWDW) is responsible for implementing
the provisions of SDWA. Under SDWA, OGWDW develops both regulations to address the
public health risks from contaminated drinking water and related programs to protect ground
water (GW) and surface water (SW) supplies. The 1996 Amendments to SDWA require that
EPA shall, at least once every six years, review and revise, as appropriate, each NPDWR
promulgated by the Agency. SDWA specifies that revision of a NPDWR shall maintain, or
provide for greater, protection of public health. Any revision of the regulations will be partially
dependent on contaminant occurrence findings, on the reevaluation of the public's exposure to
the contaminants and the potential adverse health effects from that exposure. The purpose of this
report is to describe the contaminant occurrence data, data management and statistical methods
used to develop the national contaminant occurrence estimations in support of EPA's Six-Year
Review 3. This report presents occurrence assessments for 61 contaminants regulated under the
Phase I, II, lib and V Rules, the Arsenic Rule and the Radionuclides Rule. As noted above,
SDWA compliance monitoring data for some of the regulated contaminants collected under
SYR3 (i.e., lead, copper, carcinogenic VOCs, microbials and DBPs) are being assessed
separately under other regulatory actions or included in separate regulatory reviews.
1.2	Data Sources
PWSs must meet health-based federal standards for contaminants, including performing regular
monitoring and reporting. Water systems are required to sample and test their water and report
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the results to the Agency with primacy for implementing the SDWA. These systems, which may
be publicly- or privately-owned, serve at least 15 service connections or 25 persons.
EPA established nine-year fixed compliance cycles to standardize monitoring requirements for
the various contaminant rules. Each nine-year compliance cycle is divided into three three-year
compliance periods. The first Compliance Period ran from January 1, 1993 to December 31,
1995. The second Compliance Period ran from 1996 to 1998 and the third Compliance Period
ran from 1999 to 2001. Together, these nine years comprise one Compliance Cycle (Compliance
Cycle 1). The second compliance cycle began January 1, 2002 and ended December 31, 2010;
the third compliance cycle began January 1, 2011 and ends December 31, 2019. The SYR3
period of review (2006 through 2011) falls within the second and third compliance cycles.
All non-purchased community water systems (CWSs) and non-transient non-community water
systems (NTNCWSs) are required to sample for the Inorganic Contaminants (IOCs), Synthetic
Organic Contaminants (SOCs) and Volatile Organic Contaminants (VOCs).1 States may grant
waivers to PWSs to reduce sampling (Exhibit 1.1). Reduced monitoring requirements for
contaminants are based on both a vulnerability assessment and previous analytical results. It is
possible that systems that had been granted waivers may not have sampled at all during the
SYR3 period of review.
Exhibit 1.1: States Compliance Monitoring Waivers
Contaminant Group /
System Source Water Type
Waiver
Monitoring
Frequency
Waiver Renewal
Frequency
Notes1
Inorganic Contaminants (IOC)2 -
Ground Water/Surface Water
Once every
nine years
Every nine years
Dependent on previous sample
results.
Volatile Organic Contaminants
(VOC)3 - Ground Water
Once every
six years
Every six years
Vulnerability Assessment must be
renewed every three years.
Volatile Organic Contaminants
(VOC)3 - Surface Water
None
Every three years
Vulnerability Assessment must be
renewed every three years.
Synthetic Organic Contaminants
(SOC) - Ground Water/Surface
Water
None
Every three years
Vulnerability Assessment must be
renewed every three years.
Source: EPA Chemical Contaminant Rules Compliance for Primacy Agencies
1	There are two bases for vulnerability assessments: (1) The PWS can prove that the contaminant has not been used in the area, or
(2) the PWS can prove it is not susceptible to contamination from that contaminant.
2	There are no waivers allowed for nitrate or nitrite monitoring. Asbestos waiver conditions are different than the rest of the IOCs.
3	Vinyl chloride is an exception to this waiver policy.
The Federal Safe Drinking Water Information System database (SDWIS/Fed) contains
information about PWSs and their violations of EPA's drinking water regulations. However,
SDWIS/Fed does not receive or store complete compliance monitoring data (called parametric
data), which includes non-detections as well as detections. To estimate national occurrence of
regulated contaminants in PWSs, it is necessary to have results from all contaminant occurrence
samples, including samples which showed analytical detections and non-detections. These data
1 Transient non-community water systems are also required to sample for nitrate and nitrite.
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are collected by states but are not required to be submitted to SDWIS/Fed. Therefore, to obtain
the necessary compliance monitoring data to support national occurrence assessments for the
Six-Year Review 3, EPA conducted the voluntary data call-in described in this report from the
states and through the ICR process. For more information on the process undertaken to request
the voluntary submission of compliance monitoring data by the states, see the third Six-Year
Review ICR renewal (75 FR 6023, USEPA, 2010b).
Through the ICR process, EPA requested that states voluntarily submit compliance monitoring
data with records of all sample detections and non-detections collected between January 2006
and December 2011. Forty-six states and eight other primacy agencies provided compliance
monitoring data that included contaminant monitoring records. Through extensive data
management efforts and quality assurance evaluations, as well as through communications and
consultations with state data management staff, EPA established a high quality contaminant
occurrence dataset (the SYR3 ICR Dataset) that consists of data from 54 states/primacy agencies
(46 states plus data from Washington, D.C. and the tribes). See Section 2 for additional details on
states included in the SYR3 ICR Dataset.
1.3 Data Analysis
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. The first stage of analysis provides a simple, straightforward evaluation
of occurrence of all contaminants. The "Stage 1 analysis" assesses the sources, quality and
characteristics of the occurrence data and then uses the data to generate summary statistics of
each contaminant's occurrence, as well as national estimates of occurrence that are simple, non-
parametric and conservative.2 For each contaminant, analyses are conducted focusing on
samples, water systems, population served by water systems and system sample point (SP)
locations. A typical Stage 1 analysis is a simple count of the number or percentage of systems
reporting at least one sample detection of a specific contaminant, or at least one sample detection
with a concentration greater than the Maximum Contaminant Level (MCL) of the contaminant.
The details of the Stage 1 analysis methods are described in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants for which additional parametric statistical
estimations were warranted (referred to as the "Stage 2 analysis"). The Stage 2 analysis estimates
national contaminant occurrence by generating estimated long-term mean concentrations of
contaminants for each water system. This Stage 2 long-term mean analysis is less conservative
than the Stage 1 analysis, which reflects a rough approximation of peak occurrence. This
fundamental difference between the two analytical approaches has a very direct implication:
regardless of the contaminant concentration value assessed, the Stage 1 analysis findings will
always exceed, or at most be approximately equal to, the Stage 2 analysis findings. For example,
the Stage 1 analysis of the number of systems with at least one detection of toxaphene greater
than the MCL concentration will always be greater than, or at most equal to, the Stage 2 analysis
2 The Stage 1 analyses are conservative in the sense that they are protective of human health (i.e., because they are
based on a single, maximum sample detection value rather than an average value for each system, the Stage 1
analyses are more likely to overestimate occurrence and potential risks to human health than underestimate them).
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showing the number of systems with a mean concentration of toxaphene greater than the MCL
concentration.
Because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for
contaminant occurrence at systems, the analyses can support assessments of population served
by water systems with detections (or "preliminary exposure" assessments) that may be more
reflective of potential chronic exposure than the assessments from the Stage 1 analyses, which
reflect a one-time peak. Section 7 describes the details of the Stage 2 analysis.
This two-stage analytical approach was previously developed for other EPA national occurrence
studies, including those conducted for the first Six-Year Review of NPDWRs (USEPA, 2003b)
and the first and second Regulatory Determinations for Contaminants from the Drinking Water
Contaminant Candidate List (USEPA, 2002, 2008a and 2008b). The approach was also used for
the second Six-Year Review of NPDWRs and the third Regulatory Determinations for
Contaminants from the Drinking Water Contaminant Candidate List. The overall data
management and general two-stage occurrence analytical approach used for these OGWDW
projects was peer-reviewed for use under the first Six-Year Review, which assessed regulated
contaminant occurrence data collected from 1993 to 1997. The Stage 2 analysis used for this
third Six-Year Review is consistent with the simplified version of the Stage 2 analysis that was
used for the second Six-Year Review (USEPA, 2010c). This was possible because, similar to the
second Six-Year Review, a large number of states provided contaminant occurrence data for the
third Six-Year Review. See Section 7 for a complete description of the Stage 2 analysis; a
selection of contaminants are presented in Appendix B.
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2 The National Compliance Monitoring ICR Dataset for
the Third Six-Year Review
Through the ICR process, EPA conducted a voluntary data call-in for states' compliance
monitoring records and received data from a total of 54 states/primacy agencies: 46 states;
American Samoa; Washington, D.C.; Region 1 tribes; Region 4 tribes; Region 5 tribes; Region 8
tribes; Region 9 tribes and the Navajo Nation. Through extensive data management efforts,
quality assurance evaluations and communications with state data management staff, EPA
established the SYR3 ICR Dataset (see Exhibit 2.1 below).
Exhibit 2.1: States with Compliance Monitoring Data Included
in the SYR3 ICR Dataset
r*.
£
i^Cvvti AmericsnSamoa
jPjj District of Columbia
| | Guam-
| 	j Northern Marianalsiands
| | Puerto Rica
| j Virgin Islands
11 Tribes
~
Region? Tribes
| | Region 2Tribes

RegionBTribss
| | Region 3 Tribes
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Region 9 Navajo Nation
14Trifoes
¦
Region 9 Tribes
n S Tribes.
~
Region lOTribes
| | Region 6Tribes


~
State Did Not Submit D=
Stats Submitted Data
The compliance monitoring contaminant occurrence data from these 54 states/primacy agencies
for contaminants evaluated in this report for comprise more than 13 million analytical records
from approximately 139,000 water systems. Approximately 290 million people are served by
these systems nationally.
Data quality, completeness and representativeness are key considerations for the dataset. Given
the size, scope and variety of formats of the datasets received from the states, EPA conducted
extensive data management and quality assurance/quality control (QA/QC) assessments on the
data to be included in the SYR3 ICR Dataset. A review of completeness and representativeness,
details of data management and details of quality assessments are presented in the following
three sections. Additional details of the data management measures can be found in the report
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titled The Data Management and Quality Assurance/Quality Control Process for the Third Six-
Year Review Information Collection Rule Dataset (USEPA, 2016d).
2.1 Completeness and Representativeness of the Six-Year Review ICR Dataset
The final SYR3 ICR Dataset consists of compliance monitoring data received from 54 out of 67
states/primacy agencies. It represents a very large sample and the largest compliance monitoring
dataset ever compiled and analyzed by EPA's Drinking Water Program (Exhibit 2.1). The 54
states/primacy agencies that provided data for the SYR3 ICR Dataset comprise 95 percent of all
PWSs and 92 percent of the total population served by PWSs nationally and are geographically
representative of PWSs nationwide.
The absence of data from the four states and nine primacy agencies in the final SYR3 ICR
Dataset could potentially bias the dataset's representation of the national occurrence of particular
contaminants. The four states, representing about five percent of PWSs and eight percent of
population served by PWSs nationally, have a fairly small influence relative to the PWSs and
populations represented by the states that did submit data. The four states that did not provide
compliance monitoring contaminant occurrence data (Colorado, Delaware, Georgia and
Mississippi) are generally geographically distributed across the United States and reflect a
diverse mix of urban, agricultural and industrial areas. No regional geologic terrain, climatic or
hydrologic zone, geography or socio-economic activity is unrepresented in the dataset. Although
two states in the southeastern U.S., Georgia and Mississippi, did not provide data, all other
southeast states did provide data, allowing for significant regional coverage, especially from a
population-based perspective. All other regions had at most one state not included in the dataset.
The SYR3 ICR Dataset, with 46 of the 50 states represented, is therefore considered reasonably
complete and nationally representative as the basis of the contaminant occurrence estimates
presented in this report. To further address the issue of potential bias, though, EPA conducted an
assessment for each contaminant by comparing occurrence in the 4 states to that in the 46 states.
Because a complete compliance monitoring dataset of all 50 states does not exist, it is not
possible to know the true national occurrence for a particular contaminant or how occurrence
rates for a particular contaminant in the 4 missing states compare to occurrence in the other 46
states. Therefore, an indicator of occurrence was developed using data available from the
SDWIS/Fed database, which does not have complete compliance monitoring data but does
include all 50 states. EPA compiled SDWIS/Fed records of MCL violations, used here as an
indicator of contaminant occurrence, by state for the same years (2006-2011) as the SYR3 ICR
Dataset.3 The MCL violation records were used to determine if the violation rate in the 4 missing
states was significantly different than the violation rate in the 46 states in the dataset, or if the
violation rate in the 46 states could be considered representative (from the same statistical
population). EPA conducted this assessment for the IOCs, SOCs, VOCs and radionuclides
evaluated under Six-Year Review 3.
3 While the SDWIS/Fed database does not store complete compliance monitoring parametric records, the database
does maintain the most current and complete national and state records of contaminant MCL violations. Annual
MCL data were extracted from SDWIS/Fed by EPA in March 2014.
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The mean MCL violation rate for each contaminant (i.e., the percentage of systems with at least
one MCL violation) was calculated for the 46 states in the dataset and separately for the 4 states
not in the SYR3 ICR Dataset. For each contaminant, a statistical t-test was used to determine
whether these two estimated mean MCL violation rates (46-state vs. 4-state) were significantly
different; the t-test had an alpha (a) level of 0.05 and assumed unequal variance.4 If the p-value
resulting from the t-test was less than 0.05, EPA rejected the null hypothesis that the two mean
MCL violation rates were from the same population and accepted the alternative hypothesis that
they were from different populations.
Of the 61 contaminants evaluated, only nine contaminants had at least one MCL violation listed
in the SDWIS/Fed database for the 2006-2011 time period; thus, t-tests were conducted on only
these nine contaminants. For five contaminants (fluoride, nitrate, gross alpha, uranium and
combined radium), the t-test resulted in a p-value > 0.05 (EPA failed to reject the null
hypothesis). This suggests, but does not prove, that the mean MCL violation rates for the 46
states and the 4 states were not statistically different (were from the same population). For three
additional contaminants, only one of the four states had MCL violations so the t-test could not be
applied.
Arsenic was the only contaminant for which the t-test resulted in a p-value < 0.05 (EPA rejected
the null hypothesis); thus, the mean arsenic MCL violation rate for the 46 states appears to be
statistically different (come from a different population) than the mean arsenic MCL violation
rate for the four states. This suggests that the absence of system compliance monitoring data
from the four states might result in some amount of over-estimation of occurrence for that
contaminant. These findings, however, are most appropriately used as context or background for
the quantitative occurrence findings presented in Sections 6 and 7 of this report.
To further evaluate the completeness of each state's dataset, EPA used the SDWIS/Fed database
as a reference and compared the number of water systems by state in the SYR3 ICR Dataset to
the number of systems by state in the SDWIS/Fed database (frozen fourth quarter 2011). Only
the SDWIS/Fed database records from the 46 states also in the SYR3 ICR Dataset were included.
(As described in Section 4.2, systems that purchase 100 percent of their water are accounted for
differently than non-purchased water system. To simplify this comparison of number of systems
by state, only non-purchased systems were included in the counts.) The SDWIS/Fed version
accessed to obtain this inventory data was the fourth quarter of 2011. Although the system
inventory information represented in the two data sources is very similar, it is not equivalent.
The main difference is that the SYR3 ICR Dataset reflects the total number of systems with
compliance monitoring data in any of the six years represented in the dataset (2006-2011), while
the SDWIS/Fed 2011 data freeze reflects the number of systems with compliance monitoring
data in a single year (2011). Since systems open, close and consolidate over time, the number of
systems in each state will understandably be somewhat different between the two data sources.
Population changes in system service areas over time could also contribute to differences in
population served numbers for systems between the two data sources. This comparison is
presented in Exhibit 2.2. In order to be consistent with the SDWIS/Fed counts, the population
4 The t-test calculation used considered the variance, mean and sample size of each of the two groups of states to
estimate the probability that the observed difference in sample means represents an actual difference in contaminant
occurrence and not just a statistical inconsistency resulting from low sample sizes.
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values listed for the SYR3 ICR Dataset include only the populations directly served by non-
purchased systems (retail populations); total adjusted populations are discussed in Section 4.2.
The comparison between the counts of systems in the two data sources indicate that the data in
the SYR3 ICR Dataset are reasonably complete. Overall, there is an approximately 11 percent
difference between the number of systems listed in a December 2011 SDWIS/Fed freeze
compared to the number of systems in the third SYR3 ICR Dataset. (The percent difference is
calculated by subtracting the number of systems in SDWIS/Fed from the number in SYR3 ICR
and then dividing by the number of systems in the SYR3 ICR Dataset.) In Exhibit 2.2, positive
values for percent difference indicate that more systems are reported in the SYR3 ICR Dataset,
which negative values indicate that more systems are reported in the 2011 SDWIS/Fed Freeze.
Comparing the number of systems for each state, the absolute percentage difference between
SDWIS/Fed and the SYR3 ICR Dataset ranges from a zero percent difference (e.g., Region 1
Tribes and Utah) to an approximately 26 percent difference (e.g., Region 5 Tribes) in the number
of systems. Based on the population served by systems, there is a three percent difference
between the total population served by systems listed in SDWIS/Fed and the population served
by systems listed in the SYR3 ICR Dataset. Comparing individual state population served
values, the absolute percentage differences between SDWIS/Fed and the Six-Year states ranges
from less than a one percent difference (e.g., Alabama and New Mexico) to approximately a 20
percent difference (e.g., Nebraska).
Exhibit 2.2: Comparison of the Total Number of Non-Purchased Systems and
Retail Population Served in SDWIS/Fed and the SYR3 ICR Dataset, By State
State
Total Number of Non-Purchased
Systems1
Retail Population Served by Non-
Purchased Systems
2011
SDWIS/Fed
Freeze
SYR3 ICR
Data
Percent
Difference2
2011
SDWIS/Fed
Freeze
SYR3 ICR
Data
Percent
Difference2
Alabama
399
415
4%
4,270,460
4,269,317
0.0%
Alaska
1,429
1,403
-2%
718,776
762,190
6%
American Samoa
19
17
-11%
60,958
61,309
1%
Arizona
1,511
1,493
-1%
6,414,815
6,431,456
0.3%
Arkansas
643
639
-1%
1,808,219
1,782,034
-1%
California
7,215
7,540
5%
28,781,357
28,528,121
-1%
Connecticut
2,523
2,971
18%
2,676,429
2,716,577
2%
Florida
5,295
6,350
20%
16,742,435
17,383,116
4%
Hawaii
108
118
9%
1,421,758
1,452,737
2%
Idaho
1,936
1,907
-1%
1,315,860
1,360,791
3%
Illinois
4,097
4,625
13%
8,228,681
8,296,918
1%
Indiana
4,012
4,397
10%
4,886,097
4,946,190
1%
Iowa
1,660
1,763
6%
2,365,619
2,380,108
1%
Kansas
647
642
-1%
2,281,561
2,292,280
0.5%
Kentucky
261
257
-2%
3,268,613
3,299,397
1%
Louisiana
1,287
1,390
8%
4,844,307
4,868,351
0.5%
Maine
1,851
2,198
19%
903,130
964,872
7%
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State
Total Number of Non-Purchased
Systems1
Retail Population Served by Non-
Purchased Systems
2011
SDWIS/Fed
Freeze
SYR3 ICR
Data
Percent
Difference2
2011
SDWIS/Fed
Freeze
SYR3 ICR
Data
Percent
Difference2
Maryland
3,390
3,886
15%
5,022,871
5,711,914
14%
Massachusetts
1,545
1,674
8%
7,154,525
7,117,276
-1%
Michigan
10,873
13,078
20%
4,809,937
5,087,202
6%
Minnesota
6,943
7,753
12%
4,617,552
4,689,328
2%
Missouri
2,458
2,768
13%
4,463,766
4,515,797
1%
Montana
1,899
1,856
-2%
894,851
902,225
1%
Navajo Nation
146
152
4%
131,031
140,818
7%
Nebraska
1,155
1,283
11%
1,545,502
1,861,572
20%
Nevada
531
584
10%
942,651
984,355
4%
New Hampshire
2,394
2,610
9%
1,124,928
1,156,828
3%
New Jersey
3,686
4,295
17%
7,428,858
7,534,923
1%
New Mexico
1,109
1,089
-2%
1,899,344
1,896,614
-0.1%
New York
8,206
8,945
9%
16,731,989
18,127,928
8%
North Carolina
5,684
6,806
20%
6,945,228
7,131,934
3%
North Dakota
301
279
-7%
513,800
508,028
-1%
Ohio
4,543
5,363
18%
9,056,572
9,232,856
2%
Oklahoma
960
1,102
15%
3,002,063
3,091,513
3%
Oregon
2,484
2,705
9%
2,831,651
2,767,113
-2%
Pennsylvania
8,779
10,128
15%
10,699,485
10,814,930
1%
Region 1 - Tribes
5
5
0%
49,031
49,031
0.0%
Region 4 - Tribes
31
32
3%
28,387
27,889
-2%
Region 5 - Tribes
100
126
26%
139,916
154,489
10%
Region 8 - Tribes
103
101
-2%
91,321
92,432
1%
Region 9 - Tribes
284
314
11%
367,252
353,335
-4%
Rhode Island
459
487
6%
775,182
778,796
0.5%
South Carolina
1,104
1,064
-4%
2,681,749
2,683,477
0.1%
South Dakota
447
463
4%
603,361
609,007
1%
Tennessee
700
673
-4%
5,616,106
5,704,724
2%
Texas
5,635
5,528
-2%
16,682,616
17,119,034
3%
Utah
892
892
0%
1,443,051
1,470,928
2%
Vermont
1,273
1,414
11%
489,778
503,324
3%
Virginia
2,519
2,917
16%
4,769,127
5,340,030
12%
Washington
3,902
4,309
10%
5,038,297
5,149,128
2%
Washington, D.C.
1
1
0%
0
0
0.0%
West Virginia
822
988
20%
1,292,503
1,314,496
2%
Wisconsin
11,345
12,563
11%
4,468,486
4,576,227
2%
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State
Total Number of Non-Purchased
Systems1
Retail Population Served by Non-
Purchased Systems
2011
SDWIS/Fed
Freeze
SYR3 ICR
Data
Percent
Difference2
2011
SDWIS/Fed
Freeze
SYR3 ICR
Data
Percent
Difference2
Wyoming
698
682
-2%
380,269
378,901
-0.4%
Total
132,299
147,040
11%
225,722,111
231,374,166
3%
1	As indicated in Exhibit 5-3, approximately 57 percent of the total number of water systems whose data were submitted by states for
the third Six-Year Review are transient non-community water systems. Because only the nitrate/nitrite regulations require
compliance monitoring by these transient systems (Exhibit 4.1), data from the transient systems were included only for the nitrate
and nitrite occurrence analyses and were excluded for all occurrence analyses for lOCs, SOCs, VOCs and radiological
contaminants.
2	The 'percent difference' was calculated by subtracting the 2011 SDWIS/Fed Freeze total number of non-purchased systems (or
retail population served by systems) from the SYR3 ICR Dataset total number of non-purchased systems (or retail population served
by systems). That difference was then divided by the total number of non-purchased systems (or retail population served by
systems) from the SYR3 ICR Dataset. The 'percent difference' is less than zero if the SYR3 ICR Dataset indicated a smaller number
of systems (or retail population served by systems).
Exhibit 2.3 compares the number of systems and population served by these systems in the
December 2011 SDWIS/Fed freeze and the SYR3 ICR Dataset stratified by source water type
and system type. (For consistency with SDWIS/Fed data, non-purchased systems and the only
the direct or retail population served are included in this comparison. See Section 4.2 for more
information.) The overall national 46 state totals indicate about 11 percent more systems and a
three percent greater population served is reported in the SYR3 ICR Dataset than is represented
in SDWIS/Fed. For community water systems (CWSs), there is about a four percent difference
based on the number of systems and a two percent difference based on the population served by
systems. Percentage differences were larger for ground water systems than surface water
systems. For non-transient non-community water systems (NTNCWSs), there is about a 13
percent difference based on the number of systems and an 8 percent difference based on the
population served by systems. For transient non-community water systems (TNCWSs), there is
about a 12 percent difference based on the number of systems and a 7 percent difference based
on the population served by systems. CWSs account for approximately 93 percent of the total
population served by systems in the United States.
Exhibit 2.3: Comparison of the Total Number of Systems and Retail Population
Served in SDWIS/Fed and the SYR3 ICR Dataset, By Source Water Type and
System Type
Source
Water Type
2011 SDWIS/Fed Freeze
SYR3 ICR Dataset
CWS
NTNCWS
TNCWS
Total
CWS
NTNCWS
TNCWS
Unknown1
Total
Number of Non-Purchased Systems
Ground
Water (GW)
33,247
16,325
77,221
126,793
34,576
18,802
87,816
123
141,317
Surface
Water (SW)
4,226
322
958
5,506
4,327
335
1,058
3
5,723
Total
37,473
16,647
78,179
132,299
38,903
19,137
88,874
126
147,040
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Source
Water Type
2011 SDWIS/Fed Freeze
SYR3 ICR Dataset
CWS
NTNCWS
TNCWS
Total
CWS
NTNCWS
TNCWS
Unknown1
Total
Retail Population Served
Ground
Water (GW)
77,175,728
4,734,551
9,552,196
91,462,475
79,082,376
5,148,753
10,332,691
2,573
94,566,393
Surface
Water (SW)
133,813,746
153,948
291,942
134,259,636
136,398,900
137,898
270,751
224
136,807,773
Total
210,989,474
4,888,499
9,844,138
225,722,111
215,481,276
5,286,651
10,603,442
2,797
231,374,166
1 Systems with unknown system type (i.e., system type not reported by the state) were included in the third Six-Year Review
analyses.
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3 Data Management
The data received from the states were in a variety of formats and data structures and required
reformatting to a uniform structure to enable the national contaminant occurrence analyses. This
section provides an overview of the data management efforts that were conducted to enable and
facilitate the contaminant occurrence analyses. Additional details of the data management
measures can be found in USEPA (2016d).
3.1 Dataset Consistency and Restructuring
About 75 percent of all states currently store and manage at least portions of their compliance
monitoring data in the Safe Drinking Water Information System/State Version (SDWIS/State).
The majority of states using SDWIS/State that submitted data to EPA used a SDWIS Query
Extract Tool, developed and provided by EPA, to extract and compile the EPA-requested
compliance monitoring data. The Extract Tool enabled a streamlined effort by states to select,
compile and format the requested data and generally resulted in state submission of complete
datasets that were uniform in format. The states not using SDWIS/State submitted their
compliance monitoring data "as is," resulting in a variety of formats of datasets submitted to
EPA.
Exhibit 3.1 lists the states that did and did not use the SDWIS Query Extract Tool. Thirty-three
states and three tribes used the SDWIS Query Extract Tool to extract all or some of their
chemical data; therefore, those datasets were all submitted in a similar format. States that did not
use the SDWIS Query Extract Tool were restructured into a format similar to the data structure
achieved by the EPA tool. The SDWIS Query Extract Tool pulls the SDWIS/State data into
Microsoft (MS) Access. The 18 states/ primacy agencies that did not use the SDWIS Query
Extract Tool submitted data in a variety of file types, including dBase, MS Access, comma
delimited, tab delimited, Text and Excel. However, all of these datasets were converted to MS
Access to enable a detailed QA/QC review.
Exhibit 3.1: Summary of Compliance Monitoring Data Provided by States for the
Third Six-Year Review

State Name

Alabama
Maine
Oregon

Alaska
Missouri
Region 4 tribes

Arizona
Montana
Region 5 tribes

Arkansas
Nebraska
Region 8 tribes

Connecticut
Nevada
Rhode Island
States/Entities that DID use
Idaho
New Jersey1
South Carolina
the SDWIS Extract Tool
Illinois
New Mexico
Texas1

Indiana
New York
Utah

Iowa
North Carolina1
Vermont

Kansas
North Dakota
Virginia

Kentucky
Ohio
West Virginia

Louisiana
Oklahoma
Wyoming
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State Name

American Samoa
Michigan
Region 9 tribes

California
Minnesota
South Dakota
States/Entities that DID NOT
Florida
Navajo Nation
Tennessee
use the SDWIS Extract Tool
Hawaii
New Hampshire
Washington

Maryland
Pennsylvania
Washington, D.C.

Massachusetts
Region 1 tribes
Wisconsin
1 North Carolina, New Jersey and Texas submitted their SDWIS/State data in an Oracle database. EPA applied the SDWIS Query
Extract Tool to their databases to extract and compile the compliance monitoring data requested by EPA for the Third Six-Year
Review.
3.2 Review of Dataset Content
One of the first reviews of the submitted data sets was to verify that all of the necessary data
elements were included. Many of the states not using the SDWIS Query Extract Tool submitted
datasets with more data elements than necessary. In those cases, EPA determined which data
elements were and were not needed for the Six-Year Review 3 occurrence analyses. Exhibit 3.2
provides a detailed list of the data elements requested by EPA for Six-Year Review 3.
Although data dictionaries were not necessary for the review of data from states that used the
SDWIS Query Extract Tool, these files (or any other available supporting information provided
by the states) were very useful when trying to interpret the data submitted by the states that did
not use the SDWIS Query Extract Tool. Data dictionary and supporting information files were
reviewed for a definition of the various data elements, field/row headings, codes and acronyms,
among others. In addition, field names were standardized and data types were changed to similar
formats. Data reported for each field were also standardized.
Exhibit 3.2: Data Elements Requested by EPA for the Third Six-Year Review
Data Category
Description
System-Specific Information
Public Water System
Identification Number
(PWSID)
The code used to identify each PWS. The code begins with the standard 2-character postal state
abbreviation or Region code; the remaining seven numbers are unique to each PWS in the state.
System Name
Name of the PWS.
Federal Public Water
System Type Code
A code to identify whether a system is:
•	Community Water System,
•	Non-transient Non-community Water System, or
•	Transient Non-community Water System.
Population Served
Highest average daily number of people served by a PWS, when in operation.
Federal Source Water
Type
Type of water at the source. Source water type can be:
•	Ground water, or
•	Surface water, or
•	Ground water under the direct influence of surface water (GWUDI) (Note: Some states may not
distinguish GWUDI from surface water sources. In those states, a GWUDI source should be
reported as a surface water source type.)
Sanitary Survey
Information
Site visit information for Total Coliform Rule (TCR), Ground Water Rule (GWR) and Surface Water
Treatment Rules (SWTRs), including: site visit type, date completed, associated deficiencies
identified, corrective actions taken.
Treatment Information
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Data Category
Description
Water System Facility
System facility data, including: treatment plant identification number, treatment plant information,
treatment unit process/objectives, facility flow, treatment train (train or flow of water through
treatment units within the treatment plant).
Filtration Type
Information relating to system filtration, including: filtration status, types of filtration (e.g., unfiltered,
conventional filtration and other permitted values)
Treatment Technique
Information
Information pertaining to treatment processes. Types of treatment technique information including:
coagulant/coagulant aid type and dose, disinfectant concentration (amounts, types, primary and
secondary types of disinfection, disinfection profile/bench mark data), log of viral
inactivation/removal, contact time, contact value, pH, temperature.
Filter Backwash
Information
Information about filter backwash that is returned to the treatment plant influent (e.g., information
on: recycle/schematic status, alternative return location, corrective action requirements and recycle
flows and frequency).
Sample-Specific Information
Sampling Point
Identification Code
A sampling point identifier established by the state, unique within each applicable facility, for each
applicable sampling location (e.g., entry point to the distribution system). This information enables
occurrence assessments that address intra-system variability.
Sample Identification
Number
Identifier assigned by state or the laboratory that uniquely identifies a sample.
Sample Collection Date
Date the sample is collected, including month, day and year.
Sample Type
Indicates why the sample is being collected (e.g., compliance, routine, repeat, confirmation,
additional routine samples, duplicate, special, special duplicate, etc.).
Sample Analysis Type
Code
Code for type of water sample collected.
•	Raw (Untreated) water sample, • Finished (Treated) water sample
For lead and copper only:
•	Source, • Tap
For TCR, Repeats only; indicator of sampling location relative to sample point where positive
sample was originally collected:
•	Upstream, • Downstream, • Original
Contaminant
Contaminant name, 4-digit SDWIS contaminant identification number or Chemical Abstracts
Service (CAS) Registry Number for which the sample is being analyzed.
Sample Analytical Result
- Sign
The sign indicates whether the sample analytical result was:
•	(<) "less than" means the contaminant was not detected or was detected at a level "less than" the
minimum reporting level (MRL).
•	(=) "equal to" means the contaminant was detected at a level "equal to" the value reported in
"Sample Analytical Result - Value."
(Not required for TCR data)
Sample Analytical Result
- Value
Actual numeric (decimal) value of the analysis for the chemical results, or the MRL if the analytical
result is less than the contaminant's MRL.
For the TCR, results will indicate presence/absence.
Sample Analytical Result
- Unit of Measure
Unit of measurement for the analytical results reported (usually expressed in either |jg/L or mg/L for
chemicals; or pCi/L or mrem/yrfor radiological contaminants).
(Not required for TCR data)
Sample Analytical Method
Number
EPA identification number of the analytical method used to analyze the sample for a given
contaminant.
Minimum Reporting Level
(MRL) - Value
MRL refers to the lowest concentration of an analyte that may be reported.
(Not required for TCR data)
MRL - Unit of Measure
Unit of measure to express the concentration value of a contaminant's MRL.
(Not required for TCR data)
Source Water Monitoring
Information
Total organic carbon (TOC), including percent TOC removal, TOC removal summary, pH, alkalinity,
monitoring data entered as individual results or included in DBP (or monthly operating report
(MOR)) summary records, alternative compliance criteria.
Sample Summary Reports
Sample summaries for Disinfection Byproduct Rules (DBPRs), SWTRs, TCR and Lead and Copper
Rule (LCR) associated with analytical result records. Values used for compliance determination
[e.g., turbidity (combined effluent/individual effluent), disinfectant residual levels in treatment plant
and distribution system, treatment technique information, Heterotrophic Plate Count (HPC), etc.]
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It was also necessary to confirm that all of the requested contaminants were included in each
state dataset. EPA requested voluntary submission of compliance monitoring information for
chemical contaminants regulated under Phase I, II, lib and V Rules; the Arsenic Rule; and the
Radionuclides Rule. In addition, EPA requested data collected for the Ground Water Rule,
Surface Water Treatment Rules, Disinfection Byproduct Rules and Filter Backwash Recycling
Rule (FBRR).
Exhibit 3.3 below lists the specific contaminants for which EPA requested monitoring data. Note
that all contaminants whose data were requested are listed in the table, though not all were not
analyzed as part of this report because they are being evaluated under other regulatory actions or
included in separate regulatory reviews. The following contaminants/contaminant groups are not
evaluated in this report: lead and copper, cVOCs, acrylamide and epichlorohydrin, disinfectants
and their byproducts and microbial contaminants. See Section 1 for more details on the
contaminants addressed in this report.
Exhibit 3.3: List of Contaminants for Which Data Were Requested from States
Chemical Contaminants (Phase 1, II, IIB and V Rules; Arsenic Rule; Lead and Copper Rule)
Acrylamide
1,1-Dichloroethylene
Methoxychlor
Alachlor
cis-1,2-Dichloroethylene
Monochlorobenzene
(Chlorobenzene)
Antimony
trans-1,2-Dichloroethylene
Nitrate (as N)
Arsenic
Dichloromethane (Methylene chloride)
Nitrite (as N)
Asbestos
1,2-Dichloropropane
Oxamyl (Vydate)
Atrazine
Di(2-ethylhexyl) adipate (DEHA)
Pentachlorophenol
Barium
Di(2-ethylhexyl) phthalate (DEHP)
Picloram
Benzene
Dinoseb
Polychlorinated biphenyls (PCBs)
Benzo[a]pyrene
Diquat
Selenium
Beryllium
Endothall
Simazine
Cadmium
Endrin
Styrene
Carbofuran
Epichlorohydrin
2,3,7,8-TCDD (Dioxin)
Carbon tetrachloride
Ethyl benzene
Tetrachloroethylene
Chlordane
Ethylene dibromide (EDB)
Thallium
Chromium (total)
Fluoride
Toluene
Copper
Glyphosate
Toxaphene
Cyanide
Heptachlor
2,4,5-TP (Silvex)
2,4-Dichlorophenoxyacetic acid (2,4-D)
Heptachlor epoxide
1,2,4-T richlorobenzene
Dalapon
Hexachlorobenzene
1,1,1-Trichloroethane
1,2-Dibromo-3-chloropropane (DBCP)
Hexachlorocyclopentadiene
1,1,2-T richloroethane
1,2-Dichlorobenzene (o-Dichlorobenzene)
Lead
Trichloroethylene
1,4-Dichlorobenzene (p-Dichlorobenzene)
Lindane
Vinyl chloride
1,2-Dichloroethane (Ethylene dichloride)
Mercury (inorganic)
Xylenes (total)
Radiological Contaminants
Combined Radium-226/228; and
Radium-226 & Radium-228 (if available)
Gross beta
Tritium
lodine-131
Uranium
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Chemical Contaminants (Phase 1, II, IIB and V Rules; Arsenic Rule; Lead and Copper Rule)
Gross alpha
Strontium-90

Microbiological Contaminants
Total coliforms
Fecal coliforms
Escherichia coli (E. coli)
Disinfectants and Disinfection Byproducts Rules (DBPRs)1
Total Trihalomethanes (TTHMs):
Haloacetic Acids (HAA5):
Bromate
Chloroform
Monochloroacetic acid
Chlorite
Bromodichloromethane
Dichloroacetic acid
Chlorine
Dibromochloromethane
Trichloroacetic acid
Chloramines
Bromoform
Bromoacetic acid
Chlorine dioxide

Dibromoacetic acid

Ground Water Rule (GWR)
Escherichia coli (E. coli)
Enterococci
Coliphage
Surface Water Treatment Rules (SWTRs)2
Chlorine
Cryptosporidium
Heterotrophic Plate Count (HPC)
Chloramines
Giardia lamblia

Filter Backwash Recycling Rule (FBRR)
No specific occurrence data collected; see Exhibit 3.2 for data elements for FBRR
1	Including both Disinfection Byproducts/Treatment Rules: Stage 1 (December 1998) and Stage 2 (January 2006).
2	Including: Surface Water Treatment Rule (June 1989); Interim Enhanced SWTR (December 1998); Long-Term 1 Enhanced SWTR
(January 2002); and, Long-Term 2 Enhanced SWTR (January 2006).
3.3 Establishing Consistent Data Fields for Analytical Results
When preparing the data for the occurrence analysis, as well as a review for potential outliers,
etc., it was essential to get the following three data elements into a consistent format: the sample
analytical result (sign), sample analytical result (value) and sample analytical result (unit of
measure). Many of the state datasets included analytical results signs (e.g., "<" for non-
detections or "=" for detections), detection limits and analytical results data in multiple fields. A
"DETECT" field was added to all of the state datasets to identify the results sign. Wherever the
analytical result was greater than zero and the result sign indicated a detection, then DETECT
was set equal to 1, representing a detection. When the analytical result was equal to zero and/or
the result sign indicated a non-detection, then DETECT was set equal to 0 (i.e., a non-detect).
Finally, data were received in a variety of units of measure. It was important that all data for each
individual contaminant be expressed in a single unit in order to facilitate analysis. Chemical
monitoring data were received in both milligrams per liter (mg/L) and micrograms per liter
(|ig/L). For this analysis, all data for IOCs were converted to mg/L, while all data for the SOCs,
VOCs and uranium were converted to |ig/L. Data for alpha particles, beta particles and combined
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radium-226/228 were analyzed in picocuries per liter (pCi/L).5 Note that with the exception of
asbestos and the radionuclides, all thresholds and concentrations in this report are expressed in
Hg/L.
5 Although the MCL for beta particles, 4 mrem/yr, is in the unit of measure of millirem per year (mrem/yr), the
primary unit of analytical measure is picocuries per liter (pCi/L). This unit of measure relates to screening thresholds
of 15 pCi/L and 50 pCi/L that are defined in the 2000 Radionuclides Rule. More than 99 percent of all compliance
monitoring data for beta particles submitted by the states to EPA were in units of pCi/L. The analyses presented here
are based on compliance monitoring data represented in units of pCi/L and are conducted relative to the screening
threshold of 50 pCi/L.
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4 Data Quality Assurance/Quality Control
After the state data sets were converted into a consistent format, a significant effort was
undertaken to ensure the quality of the data submitted. This QA/QC effort encountered a range of
data quality across the different contaminants and different states. Included below is a summary
description of the QA/QC measures that were conducted on the state datasets prior to analysis.
Not all QA/QC measures described were conducted on all states, as noted below. For complete
details of the data QA/QC measures, refer to USEPA (2016d).
4.1 Quality Assurance Measures
Before the analyses of contaminant occurrence could begin, EPA performed an initial QA/QC
review of each state's data. EPA sent emails to each state, asking general questions about their
data set, if necessary. Question topics included descriptions of non-intuitive data element names,
definitions of field headings, or non-standard codes that were not described in any
documentation files from the state. It was also necessary to confirm that all of the requested
contaminants were included in each state dataset. When a state was missing data for any of the
contaminants listed in Exhibit 3.3, EPA asked the state to identify the reason for the omission,
such as a statewide waiver for the contaminant(s).
States were asked to provide data for all contaminants listed in Exhibit 3.3, but individual PWSs
may be required to sample for a subset of those contaminants depending on the type of system.
Exhibit 4.1 lists the systems that are required to monitor for the contaminants within each
chemical group. All required data that passed the QA/QC process, given the type of system, were
included in the third Six-Year Review analyses. Some systems provided monitoring data that
were not required given their system type (e.g., SOC data from transient systems or radionuclide
data from transient or non-transient non-community systems), however this data was available
inconsistently. To ensure consistent monitoring and to avoid bias, this non-required data were
maintained in the SY3 ICR database but were excluded from the third Six-Year Review
analyses.
Exhibit 4.1: Chemical Group Monitoring Requirements
Chemical Group
System Types Required to Sample
(sample data included in analyses)
System Types Not Required to Sample
(sample data excluded from analyses)
Inorganic
Chemicals (lOCs)
All non-purchased community water systems and
non-transient non-community water systems are
required to sample for lOCs.
All purchased systems and transient non-
community water systems are not required
to sample for lOCs.
Nitrate and Nitrite
Non-purchased community water systems, non-
transient non-community water systems and
transient non-community water systems are all
required to sample for nitrate and nitrite.
All purchased systems are not required to
sample for nitrate and nitrite
Synthetic Organic
Chemicals
(SOCs)
All non-purchased community water systems and
non-transient non-community water systems are
required to sample for SOCs.
All purchased systems and transient non-
community water systems are not required
to sample for SOCs.
Volatile Organic
Chemicals
(VOCs)
All non-purchased community water systems and
non-transient non-community water systems are
required to sample for VOCs.
All purchased systems and transient non-
community water systems are not required
to sample for VOCs.
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Chemical Group
System Types Required to Sample
(sample data included in analyses)
System Types Not Required to Sample
(sample data excluded from analyses)
Radiological
Contaminants
All non-purchased community water systems are
required to sample for the radionuclides.
All purchased systems and non-purchased
non-transient non-community and non-
purchased transient non-community water
systems are not required to sample for
radionuclides.
EPA created several automated data QA checks to identify potential common data entry errors or
numerical inconsistencies. These QA checks flagged records with potential data quality
concerns. EPA sent out a detailed report to each state describing its flagged records, which
included the counts of flagged records by category (described below) as well as specific
questions for each of these categories. An attachment identified the specific records that were
flagged; EPA requested that each state provide the appropriate disposition (delete, make
corrections, etc.) of these flagged records. For all flagged records, input from the states was
always used as the initial criteria in deciding on the appropriate action or decision to include /
exclude the record from analysis. When states did not provide a response or action, EPA made a
decision on what to do with the data in question. Below is a general description of the various
QA measures that were used to identify records of potential data quality concerns.
Of these flagged records, a number of categories addressed sampling concerns. For example,
samples that were taken outside of the SYR3 date range, collected from non-public water
systems, or identified as non-compliance were excluded from the occurrence analysis. All data
from purchased systems were excluded from the occurrence analysis, as well as any sample
types other than routine or confirmation. Non-nitrate or nitrite data collected from transient
systems were excluded unless a state responded to say that the system in question was previously
a CWS and NTNCWS at the time of sampling.
Other categories of flagged records included reporting concerns, such as use of correct units,
inclusion of duplicates and missing system inventory data. Samples with reported units that were
not one of the standard units used for the particular contaminant were excluded unless there was
strong evidence of the correct standard unit to use. Potential duplicates were included in the
occurrence analysis for consistency with the second Six-Year Review unless the state confirmed
that the records were in fact duplicates and should be excluded. Samples from systems that did
not specify inventory data were supplemented by a 4th quarter 2011 SDWIS/Fed data freeze and
were included in the occurrence analysis. However, all records from systems whose inventory
data were still missing after filling gaps with SDWIS/Fed data were excluded from the analysis.
For all samples, any detected concentrations that were greater than four times the contaminant's
MCL and any that were greater than 10 times the MCL were flagged and sent to states for
comment. Any changes suggested by the states were implemented for these records. For the
states that did not respond, all concentrations less than or equal to 100 times the MCL were
included; any greater than 100 times the MCL were excluded. Similarly, all detected
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concentrations less than the contaminant's method detection limit (MDL)6 and all less than one
tenth of the MDL were sent to states for comment and any changes suggested by the states were
implemented. For states that did not respond, all detected concentrations greater than or equal to
1/100 of the MDL were included in the analysis and any with concentrations less than 1/100 of
the MDL were excluded. In addition, data collected from raw water samples were considered
based on corresponding finished water samples and compliance status.
The review of states responses on these flagged records was a critical QA step prior to the data
analysis. EPA documented all changes made to the compliance monitoring data and suggested to
the states that they make corrections in their data system as well, if appropriate. To resolve data
quality issues that required significant corrections to the raw data, such as identifying and
deleting outliers or identifying and changing incorrect units, state data management staff were
consulted when appropriate before data corrections were completed.
The initial SYR3 ICR Dataset included more than 47 million analytical records from
approximately 167,000 PWSs that serve approximately 290 million people nationally.7 More
than two-thirds of these records (more than 33 million) were for contaminants that were not
analyzed as part of this current Six-Year Review 3 effort (including lead, copper, cVOCs, total
coliform, DBPs and others). More than 13 million analytical records underwent QA/QC review
in order to be included in the SYR3 ICR Dataset for contaminants evaluated in this report for the
Six-Year Review 3. After the QA/QC review was completed on these analytical records and a
small percentage of records that did not meet quality standards were omitted from analyses, the
final SYR3 ICR Dataset comprise almost 13 million analytical records from approximately
139,000 PWSs that serve approximately 290 million people nationally.8
4.2 Adjustments of Population Served by Public Water Systems
"Purchased" water systems are the systems that purchase 100 percent of their water from other
systems ("seller" or "wholesaler" systems). Compliance monitoring requirements are different
for purchased water systems compared to non-purchased systems because purchased water
systems do not have their own water sources (e.g., wells or intakes). As described above, EPA
excluded from the analysis data from systems that purchase 100 percent of their water. However,
EPA did adjust the population values of the wholesale systems to include the population of the
systems that they sell to (the purchased water systems). The population served directly by these
wholesale systems is known as the "retail population," while the population served indirectly
6	The Method Detection Limit, MDL, is defined as the minimum concentration of a substance that can be measured
and reported with 99 percent confidence, based on an analyte concentration being greater than zero as determined
from analysis of a sample in a given matrix containing the analyte. In other words, the MDL is the concentration at
which presence or absence of an analyte can be dependably determined. This contrasts with the MRL, which is a
concentration above the MDL, typically set 2 to 10 times the MDL and enables reporting at specified levels of
precision and accuracy of the actual concentration of the analyte present in the sample.
7	This count of 167,000 PWSs represents all water systems that submitted any SYR3 data (including purchased
water systems). In this case, 290 million is the population served directly (retail) by these purchased and non-
purchased systems (see Section 4.2).
8	This count of 139,000 PWSs represents non-purchased systems only. The population served remains at 290
million; however, the number now reflects the total population served directly (retail) and indirectly (wholesale) by
non-purchased systems only.
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through the purchased systems is known as the "wholesale population." This adjustment ensured
that all relevant population were included in the exposure estimates.
For some systems, a slightly more complicated adjustment to the wholesalers' total population
served values was required. Many purchased water systems buy water from more than one
wholesaler. Because of this, their entire population should not be attributed to a single wholesale
system and EPA must instead distribute the population across the wholesale systems. There are
no data available on the actual relative quantities of water purchased from the different
wholesalers. In the cases of multiple wholesalers, the population served by the purchased system
was assumed to be uniformly distributed across the wholesalers.
To make adjustments across the SYR3 ICR data, EPA compiled a list of all wholesale and
purchased systems. This list of buyer-wholesaler relationships was from SDWIS/Fed, fourth
quarter of 2010. EPA then created a crosswalk linking the purchased systems to the wholesale
systems from which they purchased 100 percent of their water. The population served by each
purchased system was then distributed evenly across the relevant wholesale system populations,
according to the calculations described above. As a result, the contaminant occurrence measures
are associated with the total (retail plus wholesale) population served by these non-purchased
systems included in the Six-Year Review data.
4.3 Adjustments of Source Water Type for Public Water Systems
For the third Six-Year Review analysis, each system must have a single source water type and
population served designation to define each system in a unique source water type/population
size strata. Systems using both ground water and surface water and systems using ground water
under direct influence of surface water, were considered surface water systems for analysis.
Systems with more than one specified value of their population served in the original data were
included using their most frequently occurring population served value.
An additional adjustment to source water type was necessary for a select group of systems whose
water came from a mix of consecutive connections and their own sources. Specifically, these
were systems that do not have their own intake or other SW facilities but do purchase some SW;
however, in addition, they do have some of their own GW wells. In these cases, because the
system does include some purchased surface water (SWP) sources, the federal source water type
is listed as SWP in SDWIS/Fed and in the states' compliance monitoring data. This is the case
even if the system only purchases a very small portion of their water and the rest of the water
comes from GW wells. Based on the QA criteria described in Section 4.1, data from these
systems should be excluded from the SYR3 data analyses since data from purchased water
systems were excluded. However, the GW sources from these systems did provide legitimate
(and required) compliance monitoring data. Thus, it was necessary in the SYR3 analyses to
consider these SWP systems as GW systems as the compliance monitoring data that were
provided by these systems were from GW sources.
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5 Summary of the Compliance Monitoring Data
This section provides an overview of the data that were received, passed the QA/QC process and
were analyzed for Six-Year Review 3. Also provided is information on the total number of
systems in the final SYR3 ICR Dataset; characteristics of the systems such as system types,
source water types, population served; the number of records from each state and the number of
records for each contaminant. An assessment of contaminant occurrence variability over the six
years was also conducted and is described below.
5.1 Characteristics of the Data - States, Systems and Records
Exhibit 5.1 shows the number and percent of systems and population served by systems
according to source water type in the SYR3 ICR Dataset. Exhibit 5.2 shows the number and
percent of systems and the population served by systems according to source water type and
system size. As discussed in Sections 4.1 and 4.2, purchased water systems were excluded and
the populations served by these systems were accounted for in the occurrence analyses for the
contaminants evaluated in this report. Population served values and occurrence estimates in all
tables in Section 5, 6 and 7 were generated using the total (adjusted) population served, as is
described in Section 4.2. Source water types stratified by all classifications, including GWUDI as
well as GW and SW groupings, are presented in Exhibit 5.1. For analysis of these data, however,
EPA followed its standard practice of treating GWUDI as surface water.
Exhibit 5.1: Number of Systems and Population Served by Systems in the
SYR3 ICR Dataset, by Source Water Type
Source Water Type
Systems
Total Population Served by
Systems
Number
Percent of Total
Number
Percent of Total
Ground Water (GW)
133,516
96%
125,617,215
43%
Ground Water Under the Direct Influence of
Surface Water (GWUDI)
775
1%
2,075,138
1%
Surface Water (SW)
4,769
3%
162,885,819
56%
Total Number of Systems
139,060
100%
290,578,172
100%
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Exhibit 5.2: Number of Systems and Population Served by Systems in the
SYR3 ICR Dataset, by System Size
System Size
(Population Served
by the System)
Ground Water (GW)
Surface Water (SW)
Total
Number of
Systems
Total Population
Served by
Systems
Number of
Systems
Total
Population
Served by
Systems
Number of
Systems
Total Population
Served by
Systems
<50
43,588
1,230,003
573
13,343
44,161
1,243,346
50-100
35,646
2,611,071
436
32,921
36,082
2,643,992
101 -500
36,323
8,464,729
891
235,031
37,214
8,699,760
501 -1,000
7,074
5,194,327
383
294,985
7,457
5,489,312
1,001 -3,300
6,066
11,206,423
821
1,694,222
6,887
12,900,645
3,301 -10,000
2,859
16,418,571
944
5,898,160
3,803
22,316,731
10,001 -50,000
1,600
34,484,799
969
22,454,312
2,569
56,939,111
50,001 -100,000
229
15,675,332
252
17,594,243
481
33,269,575
100,001 -1 million
127
23,968,963
255
69,329,070
382
93,298,033
> 1 million
4
6,362,997
20
47,414,670
24
53,777,667
Total
133,516
125,617,215
5,544
164,960,957
139,060
290,578,172
Exhibit 5.3 shows the number and percent of systems in the SYR3 ICR Dataset by system type.
Although more than 57 percent of the systems are transient water systems they serve only 3.3
percent of the population; almost 95 percent of the population is served by CWSs. Only a small
fraction of transient systems collected data for most of the contaminants requested in the SYR3
ICR data call-in, as transient systems are only required to collect nitrate and nitrite samples.
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Exhibit 5.3: Number of Systems and Retail Population Served by Systems in the
SYR3 ICR Dataset, by System Type
System Type
Systems
Total Population Served by Systems
Number
Percent of Total
Number
Percent of Total
Community Water System (CWS)
40,196
28.9%
275,436,560
94.8%
Non-Transient Non-Community
Water System (NTNCWS)
18,941
13.6%
5,572,922
1.9%
Transient Non-Community Water
System (TNCWS)1
79,804
57.4%
9,566,002
3.3%
Unknown2
119
0.1%
2,688
0.0%
Total Number of Systems
139,060
100%
290,578,172
100%
1	Only the nitrate/nitrite regulations require compliance monitoring by these transient systems; thus, data from the transient systems
were included only for the nitrate and nitrite occurrence analyses and were excluded for all occurrence analyses for lOCs, SOCs,
VOCs and radiological contaminants.
2	Systems with unknown system type were included in the Six-Year Review 3 analyses. None of the occurrence analyses conducted
for the Six-Year Review 3 required specifying the system type.
Exhibit 5.4 lists the total number of records, systems and population served by systems in each of
the 54 state/tribal datasets used in the Six-Year Review 3 analyses. In addition, the last column
of the table lists any contaminant(s) for which the state did not provide data. States might not
have submitted data for certain contaminants if they have monitoring waivers for the
contaminant. States may grant waivers to PWSs to reduce monitoring frequencies; thus, it is
possible that no samples were collected by systems during the SYR3 period of review. See
Section 1.2 for more information on compliance monitoring and waivers. States may have
submitted data for these contaminants under the ICR; however, the data were not in a format
compatible with the SYR3 ICR data set. See Exhibit 5.5 for the list of regulated contaminants
evaluated for the third Six-Year Review.
Exhibit 5.4: An Inventory of Contaminant Occurrence Data in
the SYR3 ICR Dataset, by State
State
Number of
Records for
Regulated
Contaminants 1
Number of
Systems with
Data for
Regulated
Contaminants
Population
Served by
Systems with
Data for
Regulated
Contaminants
Did not submit useable data for
the following regulated contaminants:
Alabama
191,413
452
5,346,899

Alaska
53,315
1,365
817,479

American Samoa
5,208
11
62,196
Combined Radium-226 & -228
Arizona
332,193
1,739
6,813,243

Arkansas
141,835
517
2,643,519
Asbestos; 2,3,7,8-TCDD (Dioxin); Alpha
Particles; Uranium; Combined Radium-226 &-
228
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State
Number of
Records for
Regulated
Contaminants 1
Number of
Systems with
Data for
Regulated
Contaminants
Population
Served by
Systems with
Data for
Regulated
Contaminants
Did not submit useable data for
the following regulated contaminants:
California
2,224,544
7,728
42,332,069

Colorado
133
2
2,047
The State of Colorado did not provide data for
any contaminants for the 3rd Six-Year Review.
The counts in this row reflect data from two tribal
systems located in Colorado.
Connecticut
321,895
2,971
3,018,503

Florida
550,332
6,338
19,889,742

Hawaii
50,400
118
1,489,566
Alpha Particles; Combined Radium-226 & -228
Idaho
114,635
1,907
1,364,144

Illinois
387,634
4,500
11,448,122
2,3,7,8-TCDD (Dioxin)
Indiana
132,072
4,267
5,482,894

Iowa
76,870
1,828
2,873,105
2,3,7,8-TCDD (Dioxin)
Kansas
75,653
696
2,661,362

Kentucky
77,124
265
4,244,786

Louisiana
217,092
1,120
4,978,104
Asbestos
Maine
109,766
2,182
978,294
Glyphosate; 2,3,7,8-TCDD (Dioxin); Beta
Particles
Maryland
163,019
3,695
5,421,969
Asbestos; Ethylene Dibromide (EDB)
Massachusetts
259,042
1,666
9,484,435
2,3,7,8-TCDD (Dioxin); Combined Radium-226 &
-228
Michigan
400,333
12,934
8,647,270

Minnesota
261,926
7,808
4,988,096

Mississippi
1,085
5
6,176
The State of Mississippi did not provide data for
any contaminants for the 3rd Six-Year Review.
The counts in this row reflect data from five tribal
systems located in Mississippi.
Missouri
230,179
2,660
5,463,242
Asbestos; 2,3,7,8-TCDD (Dioxin);
Polychlorinated biphenyls (PCBs)
Montana
126,612
966
873,923
2,3,7,8-TCDD (Dioxin)
Nebraska
182,390
740
1,668,159
Nitrate; Nitrite; 2,3,7,8-TCDD (Dioxin);
Polychlorinated biphenyls (PCBs)
Nevada
143,882
615
2,725,079

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State
Number of
Records for
Regulated
Contaminants 1
Number of
Systems with
Data for
Regulated
Contaminants
Population
Served by
Systems with
Data for
Regulated
Contaminants
Did not submit useable data for
the following regulated contaminants:
New Hampshire
243,533
2,606
1,201,039
Asbestos; 2,3,7,8-TCDD (Dioxin);
Polychlorinated biphenyls (PCBs); Beta Particles
New Jersey
369,861
4,337
9,757,926
Toxaphene; Dalapon; Diquat; Endothall;
Glyphosate; 2,3,7,8-TCDD (Dioxin);
Polychlorinated biphenyls (PCBs); Chlordane;
Beta Particles
New Mexico
185,680
902
2,003,572

New York
799,621
8,844
20,833,578

North Carolina
646,516
6,747
8,274,437

North Dakota
10,496
192
610,974
Asbestos; 2,3,7,8-TCDD (Dioxin); Beta Particles
Ohio
265,231
5,343
10,703,302

Oklahoma
127,513
963
3,617,365
Asbestos; 2,3,7,8-TCDD (Dioxin); Di(2-
ethylhexyl)phthalate (DEHP)
Oregon
178,962
2,699
3,652,679

Pennsylvania
626,314
10,130
12,102,084
Combined Radium-226 & -228
Rhode Island
52,092
493
1,098,288
Diquat; Endothall; Glyphosate; 2,3,7,8-TCDD
(Dioxin)
South Carolina
126,052
1,092
3,719,705
Asbestos; Cyanide; Endothall; 2,3,7,8-TCDD
(Dioxin); Polychlorinated biphenyls (PCBs); Beta
Particles
South Dakota
52,126
488
780,472
2,3,7,8-TCDD (Dioxin)
Tennessee
43,478
667
6,628,308
Beta Particles; Combined Radium-226 & -228
Texas
563,231
6,011
26,068,814
Asbestos; Diquat; Glyphosate; 2,3,7,8-TCDD
(Dioxin); Endothall; Polychlorinated biphenyls
(PCBs)
Utah
295,231
951
2,909,712

Vermont
72,624
1,360
590,755
Diquat; Endothall; Glyphosate; 2,3,7,8-TCDD
(Dioxin); Beta Particles
Virginia
209,608
1,860
6,964,718

Washington
342,363
4,170
5,715,708
2,3,7,8-TCDD (Dioxin)
Washington, D.C.
1,335
1
761,124
Combined Radium-226 & -228
West Virginia
60,722
956
1,633,025

Wisconsin
389,849
8,708
4,732,724

Wyoming
59,384
443
493,316
2,3,7,8-TCDD (Dioxin)
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State
Number of
Records for
Regulated
Contaminants 1
Number of
Systems with
Data for
Regulated
Contaminants
Population
Served by
Systems with
Data for
Regulated
Contaminants
Did not submit useable data for
the following regulated contaminants:
Unknown
5
2
124

Total
12,552,409
139,060
290,578,172

1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. The number of
records presented in this table reflect the number of fluoride records before the exclusion of fluoridated systems.
Exhibit 5.5 summarizes the SYR3 ICR Dataset by contaminant. For each contaminant, this table
includes MCL concentration values, the number of states with data, total number of records,
number of systems with data and the population served by systems that have data represented in
the SYR3 ICR Dataset. Also presented are the modal MRL values for each contaminant, derived
as the mode of state modal MRLs. See Section 7.1 for details regarding modal MRL values.
Exhibit 5.5: An Inventory of the Contaminant Occurrence Data in
the SYR3 ICR Dataset, by Contaminant
Contaminant
(MCL Concentration)
Number of
States with
Data
Total Number
of Records
Total Number
of Systems
Total
Population
Served by
Systems
MRL
Inorganic Chemicals
Antimony
(6 Mg/L)
49
164,961
50,532
254,359,720
1 Mg/L
Arsenic
(10 |jg/L)
50
297,354
54,845
267,062,633
1 Mg/L
Asbestos
(7 MFL)
39
12,084
5,785
94,380,829
0.2 MFL
Barium
(2,000 Mg/L)
49
165,387
50,711
254,501,602
100 Mg/L
Beryllium
(4 Mg/L)
49
164,392
50,195
253,512,318
1 Mg/L
Cadmium
(5 Mg/L)
49
165,247
50,583
254,433,966
1 Mg/L
Chromium (Total)
(100 Mg/L)
49
167,251
50,597
254,405,306
1 Mg/L
Cyanide
(200 Mg/L)
49
119,659
36,907
210,427,981
10 Mg/L
Fluoride1
(4,000 Mg/L)
49
256,237
47,227
189,186,454
100 Mg/L
Mercury (Inorganic)
(2 Mg/L)
49
164,558
50,552
254,397,552
0.2 Mg/L
Nitrate (as N)
(10,000 Mg/L)
49
1,157,522
132,176
266,378,543
100 Mg/L
Nitrite (as N)
(1,000 Mg/L)
49
445,544
85,742
224,146,056
100 Mg/L
Selenium
(50 Mg/L)
49
165,672
50,568
254,428,296
5 Mg/L
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Contaminant
(MCL Concentration)
Number of
States with
Data
Total Number
of Records
Total Number
of Systems
Total
Population
Served by
Systems
MRL
Thallium
(2 Mg/L)
49
164,156
50,522
254,265,115
1 Mg/L
Synthetic Organic Chemicals2
Alachlor
(2 Mg/L)
50
153,083
42,955
245,844,381
0.2 Mg/L
Atrazine
(3 Mg/L)
50
162,134
44,310
251,501,740
0.1 Mg/L
Benzo(a)pyrene
(0.2 ra/L)
50
131,437
34,341
220,684,857
0.02 Mg/L
Carbofuran
(40 Mg/L)
50
122,110
34,614
228,717,933
0.9 Mg/L
Chlordane
(2 Mg/L)
49
128,870
35,685
217,637,369
0.2 Mg/L
Dalapon
(200 Mg/L)
49
146,702
36,005
222,985,164
1 Mg/L
Di(2-ethylhexyl)adipate (DEHA)
(400 Mg/L)
50
133,169
34,628
221,563,794
0.6 Mg/L
Di(2-ethylhexyl)phthalate (DEHP)
(6 Mg/L)
49
133,523
33,923
216,841,935
0.6 Mg/L
1,2-Dibromo-3-chloropropane (DBCP)
(0.2 Mg/L)
50
188,597
37,226
217,765,167
0.02 Mg/L
2,4-Dichlorophenoxyacetic acid
(2,4-D) (70 Mg/L)
50
131,047
37,690
233,873,578
0.1 Mg/L
Dinoseb
(7 Mg/L)
50
126,014
36,701
230,831,397
0.2 Mg/L
Diquat
(20 Mg/L)
46
69,829
17,906
146,939,794
0.4 Mg/L
Endothall
(100 Mg/L)
45
61,972
15,538
136,801,729
9 Mg/L
Endrin
(2 Mg/L)
50
136,623
38,453
229,199,508
0.01 Mg/L
Ethylene Dibromide (EDB)
(0.05 Mg/L)
49
184,784
37,499
221,781,780
0.01 Mg/L
Glyphosate
(700 Mg/L)
45
70,016
18,502
145,203,976
6 Mg/L
Heptachlor
(0.4 Mg/L)
50
137,286
38,691
229,832,285
0.04 Mg/L
Heptachlor Epoxide
(0.2 Mg/L)
50
137,081
38,625
229,832,890
0.02 Mg/L
Hexachlorobenzene
(1 Mg/L)
50
137,816
38,498
230,197,968
0.04 Mg/L
Hexachlorocyclopentadiene
(50 Mg/L)
50
140,004
38,743
229,902,564
0.1 Mg/L
Lindane (gamma-
Hexachlorocyclohexane) (0.2 Mg/L)
50
139,076
39,260
231,972,432
0.02 Mg/L
Methoxychlor
(40 Mg/L)
50
139,744
39,187
233,030,961
0.1 Mg/L
Oxamyl (Vydate)
(200 Mg/L)
50
121,508
34,518
227,520,373
2 Mg/L
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Contaminant
(MCL Concentration)
Number of
States with
Data
Total Number
of Records
Total Number
of Systems
Total
Population
Served by
Systems
MRL
Pentachlorophenol
(1 Mg/L)
50
140,486
40,322
234,008,187
0.04 Mg/L
Picloram
(500 |jg/L)
50
128,401
37,445
233,036,908
0.1 Mg/L
Polychlorinated biphenyls (PCBs)
(0.5 Mg/L)
44
86,405
21,571
153,248,065
0.1 Mg/L
Simazine
(4 Mg/L)
50
156,862
43,240
247,063,728
0.07 Mg/L
Toxaphene
(3 pg/L)
49
127,187
37,043
223,888,971
1 Mg/L Mg/L
2,3,7,8-TCDD (Dioxin)
(0.00003 Mg/L)
30
20,244
3,216
74,077,780
0.000005 Mg/L
2,4,5-Trichlorophenoxypropionic Acid
(Silvex) (50 Mg/L)
50
126,887
36,897
230,214,788
0.2 Mg/L
Volatile Organic Chemicals
1,2-Dichlorobenzene
(600 Mg/L)
50
370,929
55,732
263,055,936
0.5 Mg/L
1,4-Dichlorobenzene
(75 Mg/L)
50
371,276
55,739
263,060,364
0.5 Mg/L
1,1-Dichloroethylene
(7 Mg/L)
50
379,522
55,728
263,336,047
0.5 Mg/L
cis-1,2-Dichloroethylene
(70 Mg/L)
50
376,300
55,734
263,344,982
0.5 Mg/L
trans-1,2-Dichloroethylene
(100 Mg/L)
50
371,580
55,633
263,180,210
0.5 Mg/L
Ethylbenzene
(700 Mg/L)
50
372,709
55,754
263,388,439
0.5 Mg/L
Monochlorobenzene
(100 Mg/L)
50
371,311
55,676
262,721,516
0.5 Mg/L
Styrene
(100 Mg/L)
50
370,368
55,731
263,371,533
0.5 Mg/L
Toluene
(1,000 Mg/L)
50
373,021
55,748
263,497,932
0.5 Mg/L
1,2,4-Trichlorobenzene
(70 Mg/L)
50
369,032
55,725
263,373,653
0.5 Mg/L
1,1,1-Trichloroethane
(200 Mg/L)
50
374,181
55,735
263,367,902
0.5 Mg/L
1,1,2-Trichloroethane
(5 Mg/L)
50
371,877
55,733
263,373,568
0.5 Mg/L
Xylenes (Total)
(10,000 Mg/L)
50
323,477
51,074
248,916,224
0.5 Mg/L
Radiological Contaminants
Alpha Particles
(15 pCi/L)
47
60,803
13,309
107,091,381
3 pCi/L
Beta Particles
(screening level = 50 pCi/L)3
41
43,278
11,531
109,503,691
4 pCi/L
Combined Radium-226 & -228
(5 pCi/L)
42
73,018
15,805
120,504,165
1 pCi/L
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Contaminant
(MCL Concentration)
Number of
States with
Data
Total Number
of Records
Total Number
of Systems
Total
Population
Served by
Systems
MRL
Uranium
(30 Mg/L)
49
86,208
12,155
121,747,100
1 i-ig/i
1	Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems.
2	The reduced number of systems sampling for SOC data, as compared to lOCs and VOCs, likely relates to state waivers for
pesticides and herbicides.
3	Although the MCL for beta particles, 4 millirem per year (mrem/yr), is in the unit of measure of mrem/yr, the primary unit of
analytical measure is picocuries per liter (pCi/L). This unit of measure relates to screening thresholds of 15 pCi/L and 50 pCi/L that
are defined in the 2000 Radionuclides Rule. More than 95 percent of all compliance monitoring data for beta particles submitted by
the states to EPA were in units of pCi/L. The analyses presented here are based on compliance monitoring data represented in
units of pCi/L and are conducted relative to the screening threshold of 50 pCi/L.
5.2 Occurrence Variability Assessment
The six years of data collected through the SYR3 ICR were used to develop aggregate measures
of occurrence (i.e., a single measure of occurrence that is based on all six years of data). For
example, a typical measure is the percent of systems with at least one detection of a particular
contaminant greater than its MCL concentration. This single measure would not differentiate
between years, but would reflect detections in any of the six years considered. Recognizing that
occurrence of a particular contaminant might vary over a six -year period, EPA conducted
assessments to determine if the compliance monitoring data in the SYR3 ICR Dataset exhibit
significant variability over time.
To make these assessments, it was not possible to simply evaluate yearly sample detection rates
for each contaminant at the national level. Monitoring schedules for a particular contaminant can
differ from system-to-system and year-to-year (e.g., not all surface water systems monitor all
contaminants quarterly). Therefore, a national comparison of system monitoring data from
different years will likely result in a comparison of data from different subsets of systems
nationally.
The variation in compliance monitoring schedules generally corresponds to the assessed chance
of contaminant occurrence based on historic monitoring results at each system. If a contaminant
is shown not to occur at a system through a specified period of routine compliance monitoring,
that system is authorized to conduct a reduced monitoring schedule for that contaminant. Some
systems monitor contaminants as infrequently as once every year, every three years, or even
every nine years. Because of this variability in monitoring schedules and its implications (i.e., the
frequency and timing of sampling are not random), a simple year-to-year assessment of
occurrence across all systems does not provide a clear, unambiguous assessment of occurrence
variability. For this variability assessment, EPA identified systems that collected at least one
sample in each of the six years of 2006 through 2011. This allowed the evaluation to focus on the
observed variability in the occurrence measures due to changes in contaminant occurrence rather
than differences or changes in monitoring schedules.
There is no single measure of occurrence for assessing variability. Contaminant occurrence
variability can be based on a number of different measures such as contaminant detection rates,
concentration averages, or the frequency at which systems find a contaminant above some
concentration threshold. Occurrence is also defined by a relatively small number of samples from
each system, as expected given compliance monitoring requirements. Because of the small
sample size, EPA compared detection rates in two, three-year groups rather than the detection
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rates for each individual year. EPA quantified contaminant occurrence at the system level (i.e.,
calculating the detection rate at each system) for the first three years of data (2006-2008) and
then the second three years of data (2009-2011). EPA then used standard statistical t-tests to
determine whether system level occurrence in the first three years was significantly different
from system level occurrence in the second three years.
EPA conducted variability assessments on a subset of 15 contaminants. The 15 contaminants
were: carbofuran; cis-l,2-dichloroethylene; cyanide; DBCP; dioxin; heptachlor; heptachlor
epoxide; hexachlorocyclopentadiene; oxamyl; pentachlorophenol; selenium; thallium; toluene;
toxaphene and xylenes (total). For each of these 15 select contaminants, the mean detection rate
for each system (i.e., the percentage of detections for each system) for each time period was
calculated. Results for ground water systems were evaluated separately from the results for
surface water systems. For each contaminant, a t-test (paired two sample for means) was used
with an alpha (a) level of 0.05 to determine whether these two estimated mean system detection
rates were significantly different between the first time period and the second time period. (If the
p-value resulting from the t-test was greater than 0.05, EPA did not reject the null hypothesis that
the two time periods' mean system detection rates were from the same population.) If so, this
would suggest, but does not prove, that the mean system detection rates of that contaminant for
2006-2008 and 2009-2011 were not significantly different (were from the same population).
For 11 of the 15 contaminants assessed, there was no statistically significant variability in system
detection rates (for ground water or surface water systems) between the 2006-2008 and 2009-
2011 time periods (i.e., the p-value was greater than 0.05 and EPA failed to reject the null
hypothesis). For the other four contaminants, either the ground water or surface water systems'
detection rates were found to be statistically different in the two time periods (i.e., the p-value
was less than 0.05, EPA accepted the alternative hypothesis that the system detection rates were
from different populations). Most of the contaminants with occurrence variability over time had
a decrease in occurrence over the six-year period including DBCP in GW; xylenes (total) in GW
and toluene in GW. Hexachlorocyclopentadiene in SW showed an increase in occurrence over
the six-year period. For the four contaminants with at least some statistically significant measure
of increasing or decreasing occurrence, these findings are most appropriately used as context or
background for the quantitative occurrence findings presented in Sections 6 and 7 of this report.
5.3 Threshold Evaluations
EPA assessed the occurrence of the regulated contaminants relative to several different
thresholds. Stage 1 and Stage 2 assessments of occurrence were made relative to the MRL,
identifying the simple presence/absence of a detection of a contaminant. A sample analytical
result is defined as a "detection" if the quantified sample concentration of the contaminant is
equal to or greater than that contaminant's MRL. Contaminant occurrence was also evaluated
relative to multiple contaminant concentration thresholds including a contaminant's MCL
concentration. For Stage 1 and Stage 2 assessments of occurrence relative to the MCL
concentration, the criterion is that the sample concentration of the contaminant is greater than
that contaminant's MCL. The Stage 1 analyses would identify any single result greater than the
MCL concentration and the Stage 2 analyses would identify system estimated long-term (multi-
year) average concentrations greater than the MCL concentration.
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The Stage 1 and Stage 2 analyses conducted relative to the MCL concentration are not equivalent
to the analyses conducted to estimate a potential MCL violation. Calculations of MCL violations
from the sample data are not conducted in this report. Both these Stage 1 and Stage 2 analyses
are based on sample detection and non-detection results from all years with data in the SYR3
ICR Dataset. The Stage 2 analysis (based on an estimated long-term average concentration) is
similar but not identical to the calculation conducted to determine an MCL violation. For most
regulated drinking water contaminants, an MCL violation occurs when the concentration
threshold equal to a contaminant's MCL is exceeded by the estimated system annual average
concentration, based on a limited number of consecutive quarterly compliance monitoring
samples (typically four samples for surface water systems and two samples for ground water
systems).9 In contrast, a "Stage 2 MCL exceedance" occurs when the concentration threshold
equal to a particular contaminant's MCL is exceeded by the estimated system long-term average
concentration, based on multiple years (not two or four consecutive quarters) of compliance
monitoring samples.
In accordance with the Six-Year Review 3 Protocol, EPA selected a set of contaminants for
which an MCL revision might be feasible: the current MCL is limited by analytical capability
(i.e., the MCL equals a practical quantitation level or PQL) and there is new information
indicating improved analytical capability; or the current MCL is set equal to the Maximum
Contaminant Level Goal (MCLG) and a new health effects assessment indicates it is possible to
revise the MCLG. For the 61 contaminants considered in the third Six-Year Review, EPA
identified 19 contaminants for which to derive other thresholds (in addition to the MCL). Two of
the 19 chemical contaminants (oxamyl and carbofuran) have acute health effects and only the
Stage 1 analysis was conducted. (For more details on the Stage 1 analysis, refer to Section 6 of
this report.) The remaining 17 contaminants have chronic health effects and were analyzed using
the Stage 2 occurrence analysis. (For more details on the Stage 2 analysis, refer to Section 7 of
this report.) For 10 contaminants, EPA generated occurrence estimates relative to the estimated
quantitation level (EQL). The EQL represents the potential quantitation capabilities below a PQL
(USEPA, 2016e). For eight contaminants, EPA generated occurrence estimates relative to the
potential MCLG. For one contaminant, EPA generated occurrence estimates relative to the
(existing) MCLG and one other contaminant, EPA generated occurrence estimates relative to the
PQL. Occurrence analyses relative to these additional thresholds are presented in Appendix A for
oxamyl and carbofuran and Appendix B for the remaining 17 contaminants for which Stage 2
analysis was warranted. Exhibit 5.6 presents the list of thresholds used to conduct the Stage 2
occurrence analysis. For more information on the new potential thresholds of concern used in the
SYR3 analyses, refer to USEPA (2016e) and (2016f).
Exhibit 5.6: List of Contaminant Thresholds used in Stage 2 Occurrence Analysis1
Contaminant
MCL
Alternate
Threshold Type
Alternate Threshold
Concentration
Carbofuran1
40 |jg/L
EQL
5 |jg/L
Chlordane
2 pg/L
EQL
1 hq/l
9 For nitrate and nitrite, if a single sample result is greater than or equal to the MCL, the system must collect a
confirmation sample and average it with the original sample. If that average is greater than the MCL, then an MCL
violation has occurred.
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Contaminant
MCL
Alternate
Threshold Type
Alternate Threshold
Concentration
cis-1,2-Dichloroethylene
70 pg/L
Potential MCLG
10 pg/L
Cyanide
200 pg/L
EQL
50 pg/L
Endothall
100 pg/L
Potential MCLG
50 pg/L
Fluoride
4,000 pg/L
Potential MCLG
900 pg/L
Heptachlor
0.4 pg/L
EQL
0.1 pg/L
Heptachlor Epoxide
0.2 pg/L
EQL
0.04 pg/L
Hexachlorobenzene
1 pg/L
EQL
0.1 pg/L
Hexachlorocyclopentadiene
50 pg/L
Potential MCLG
40 pg/L
Methoxychlor
40 pg/L
EQL
1 pg/L
Oxamyl (Vydate)1
200 pg/L
Potential MCLG
9, 10 pg/L
Selenium
50 pg/L
Potential MCLG
40 pg/L
Styrene
100 pg/L
EQL
0.5 pg/L
2,3,7,8-TCDD (Dioxin)
0.00003 pg/L
EQL
0.000005 pg/L
Toluene
1,000 pg/L
Potential MCLG
600 pg/L
Toxaphene
3 pg/L
EQL
1 pg/L
1,1,2-Trichloroethane
5 pg/L
MCLG
3 pg/L
Xylenes (Total)
10,000 pg/L
Potential MCLG
1,000 pg/L
1 Oxamyl and carbofuran have health endpoints that are associated with acute exposure; thus, the Stage 2 analysis was
not appropriate. The thresholds presented in this table were used to conduct more detailed Stage 1 occurrence analyses
presented in Appendix A.
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6 Stage 1 Analysis
The Stage 1 statistical analysis of the SYR3 ICR Dataset consists of simple counts and
descriptive statistics of the occurrence data for each of the regulated contaminants assessed.
National contaminant occurrence estimates were conducted relative to contaminant MRLs and
MCL concentrations and Section 6.1 presents the results by systems and population served by
systems. A comparison of the summary Stage 1 analysis results from the first Six-Year Review
with data from 1993-1997, the second Six-Year Review with data from 1998-2005 and the
current Six-Year Review with data from 2006-2011, is presented in Section 6.2. A supplemental
measure of occurrence, based on occurrence at sample point locations within each system, using
the 2006-2011 data is described in Section 6.3 with summary sample point estimates presented in
Exhibit 6.3.
6.1	Summary of Stage 1 Contaminant Occurrence Findings
Several Stage 1 analyses were conducted to characterize national occurrence of regulated
contaminants in public drinking water systems and are summarized in Exhibit 6.1 and Exhibit
6.2. Stage 1 analyses generated general system-level assessments of occurrence, for population
served by systems and for a preliminary assessment of potential exposure to contaminants in
drinking water. Exhibit 6.1 shows occurrence measures conducted relative to a contaminant's
MRL, identifying analytical detections for a broad assessment of the rate of occurrence; Exhibit
6.2	shows occurrence measures relative to each contaminant's MCL concentration, making a
preliminary estimate of occurrence and exposure at or above a contaminant's health-based
drinking water standard. The percent of systems and population served by systems with at least
one detection greater than the MCL concentration indicates the proportion of the number of
systems or the proportion of population served by systems with any analytical results exceeding
the concentration value of the MCL. Note that this does not indicate an MCL violation. An MCL
violation occurs when the MCL is exceeded by the average results from four consecutive
quarterly confirmation samples. These Stage 1 analytical findings are organized by contaminant
group.
Exhibit 6.1: Summary of Stage 1 Contaminant Occurrence Findings - Systems
and Population Served by Systems
Contaminant
Total
Number
of
Systems
Systems With
Detections > MRL
Total
Population
Served by
Systems
Population Served by
Systems With
Detections > MRL
Range of Detected
Concentrations
(5lh percentile - 95lh
percentile)
Number
Percent
Number
Percent
Inorganic Chemicals
Antimony
50,532
2,243
4.44%
254,359,720
35,557,081
13.98%
0.06 - 6.4 |jg/L
Arsenic
54,845
21,850
39.84%
267,062,633
142,045,436
53.19%
1.00 - 25.4 |jg/L
Asbestos
5,785
214
3.70%
94,380,829
7,011,486
7.43%
0.10-6.8 MFL
Barium
50,711
37,328
73.61%
254,501,602
215,824,476
84.80%
5.00- 310 |jg/L
Beryllium
50,195
1,051
2.09%
253,512,318
18,768,223
7.40%
0.01 - 4.0 |jg/L
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Contaminant
Total
Number
of
Systems
Systems With
Detections > MRL
Total
Population
Served by
Systems
Population Served b\
Systems With
Detections > MRL
Range of Detected
Concentrations
(5lh percentile - 95lh
percentile)
Number
Percent
Number
Percent
Cadmium
50,583
1,826
3.61%
254,433,966
23,767,870
9.34%
0.05 -4.0 |jg/L
Chromium (Total)
50,597
13,609
26.90%
254,405,306
102,850,010
40.43%
0.73 - 20.0 |jg/L
Cyanide
36,907
1,580
4.28%
210,427,981
29,827,337
14.17%
1.62-150 |jg/L
Fluoride 1
47,227
33,478
70.89%
189,186,454
164,918,799
87.17%
100.0-2,550 |jg/L
Mercury (Inorganic)
50,552
1,610
3.18%
254,397,552
31,509,568
12.39%
0.02-1.4 |jg/L
Nitrate (as N)
132,176
84,347
63.81%
266,378,543
237,542,569
89.17%
84.00 - 8,339 (jg/L
Nitrite (as N)
85,742
10,064
11.74%
224,146,056
72,846,518
32.50%
2.00-1,150 Mg/L
Selenium
50,568
8,754
17.31%
254,428,296
92,506,459
36.36%
0.60 - 27.0 jjg/L
Thallium
50,522
1,828
3.62%
254,265,115
25,659,625
10.09%
0.01 -2.0 Mg/L
Synthetic Organic Chemicals
Alachlor
42,955
68
0.16%
245,844,381
2,409,101
0.98%
0.03-1.30 Mg/L
Atrazine
44,310
1,144
2.58%
251,501,740
46,065,991
18.32%
0.10-1.73 Mg/L
Benzo(a)pyrene
34,341
143
0.42%
220,684,857
8,066,622
3.66%
0.02 - 0.53 Mg/L
Carbofuran
34,614
23
0.07%
228,717,933
83,512
0.04%
0.32-31.42 Mg/L
Chlordane
35,685
61
0.17%
217,637,369
1,959,885
0.90%
0.03 - 2.00 Mg/L
Dalapon
36,005
650
1.81%
222,985,164
22,843,243
10.24%
0.45 - 5.3 Mg/L
Di (2-ethyl hexy l)adi pate
(DEHA)
34,628
511
1.48%
221,563,794
9,960,923
4.50%
0.12-8.74 Mg/L
Di(2-ethylhexyl)phthalate
(DEHP)
33,923
4,042
11.92%
216,841,935
55,983,264
25.82%
0.29 - 6.84 Mg/L
1,2-Dibromo-3-
chloropropane (DBCP)
37,226
379
1.02%
217,765,167
11,331,048
5.20%
0.01 - 0.22 Mg/L
2,4-Dichlorophenoxyacetic
acid (2,4-D)
37,690
193
0.51%
233,873,578
8,842,605
3.78%
0.05 - 2.40 Mg/L
Dinoseb
36,701
94
0.26%
230,831,397
878,035
0.38%
0.09 - 5.52 Mg/L
Diquat
17,906
106
0.59%
146,939,794
2,804,725
1.91%
0.22 - 6.68 Mg/L
Endothall
15,538
25
0.16%
136,801,729
210,779
0.15%
2.70 - 66.2 Mg/L
Endrin
38,453
48
0.12%
229,199,508
2,093,675
0.91%
0.002 - 0.77 Mg/L
Ethylene Dibromide (EDB)
37,499
155
0.41%
221,781,780
4,779,841
2.16%
0.01 -0.17 Mg/L
Glyphosate
18,502
20
0.11%
145,203,976
238,876
0.16%
3.20 - 32.64 Mg/L
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December 2016

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Contaminant
Total
Number
of
Systems
Systems With
Detections > MRL
Total
Population
Served by
Systems
Population Served b\
Systems With
Detections > MRL
Range of Detected
Concentrations
(5lh percentile - 95lh
percentile)
Number
Percent
Number
Percent
Heptachlor
38,691
62
0.16%
229,832,285
3,729,607
1.62%
0.01 - 0.19 (jg/L
Heptachlor Epoxide
38,625
135
0.35%
229,832,890
2,882,874
1.25%
0.01 -0.11 |jg/L
Hexachlorobenzene
38,498
45
0.12%
230,197,968
1,071,688
0.47%
0.00 - 0.84 |jg/L
Hexachlorocyclopentadiene
38,743
172
0.44%
229,902,564
9,511,658
4.14%
0.02-1.14 Mg/L
Lindane (gamma-
1—la va 1 r* rr* r*\/r* 1 r* ava no \
39,260
44
0.11%
231,972,432
3,391,071
1.46%
0.01 - 0.24 jjg/L
Methoxychlor
39,187
68
0.17%
233,030,961
2,319,414
1.00%
0.01 - 0.93 Mg/L
Oxamyl (Vydate)
34,518
37
0.11%
227,520,373
994,043
0.44%
0.35 - 37.00 Mg/L
Pentachlorophenol
40,322
226
0.56%
234,008,187
7,810,865
3.34%
0.01 - 0.98 Mg/L
Picloram
37,445
98
0.26%
233,036,908
1,773,249
0.76%
0.01 - 4.59 Mg/L
Polychlorinated biphenyls
(PCBs)
21,571
32
0.15%
153,248,065
216,797
0.14%
0.02-1.17 Mg/L
Simazine
43,240
365
0.84%
247,063,728
24,110,287
9.76%
0.07 -1.30 Mg/L
Toxaphene
37,043
28
0.08%
223,888,971
1,097,044
0.49%
0.13-6.89 Mg/L
2,3,7,8-TCDD (Dioxin)
3,216
8
0.25%
74,077,780
124,178
0.17%
0.000001 - 0.0007 Mg/L
2,4,5-
T richlorophenoxypropionic
Acid (Silvex)
36,897
59
0.16%
230,214,788
5,445,631
2.37%
0.04 - 4.57 Mg/L
Volatile Organic Chemicals
1,2-Dichlorobenzene
55,732
145
0.26%
263,055,936
5,684,614
2.16%
0.13-9.64 Mg/L
1,4-Dichlorobenzene
55,739
644
1.16%
263,060,364
7,214,920
2.74%
0.10-4.53 Mg/L
1,1-Dichloroethylene
55,728
379
0.68%
263,336,047
15,927,038
6.05%
0.50 - 4.70 Mg/L
cis-1,2-Dichloroethylene
55,734
516
0.93%
263,344,982
22,180,279
8.42%
0.50 - 11.00 Mg/L
trans-1,2-Dichloroethylene
55,633
149
0.27%
263,180,210
5,567,372
2.12%
0.02-6.13 Mg/L
Ethyl benzene
55,754
1,744
3.13%
263,388,439
17,798,704
6.76%
0.29 - 8.70 Mg/L
Monochlorobenzene
55,676
217
0.39%
262,721,516
4,740,559
1.80%
0.04 - 2.71 Mg/L
Styrene
55,731
387
0.69%
263,371,533
4,932,664
1.87%
0.01 - 6.60 Mg/L
Toluene
55,748
2,485
4.46%
263,497,932
24,438,509
9.27%
0.27-10.85 Mg/L
1,2,4-Trichlorobenzene
55,725
147
0.26%
263,373,653
4,700,300
1.78%
0.02 -1.90 Mg/L
1,1,1-Trichloroethane
55,735
400
0.72%
263,367,902
12,878,782
4.89%
0.50- 11.50 Mg/L
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Contaminant
Total
Number
of
Systems
Systems With
Detections > MRL
Total
Population
Served by
Systems
Population Served b\
Systems With
Detections > MRL
Range of Detected
Concentrations
(5lh percentile - 95lh
percentile)
Number
Percent
Number
Percent
1,1,2-Trichloroethane
55,733
116
0.21%
263,373,568
8,374,139
3.18%
0.03 - 2.36 |jg/L
Xylenes (Total)
51,074
3,241
6.35%
248,916,224
34,901,941
14.02%
0.50-18.42 |jg/L
Radiological Contaminants
Alpha Particles
13,309
8,126
61.06%
107,091,381
77,231,268
72.12%
0.50 - 22 pCi/L
Beta Particles
11,531
6,894
59.79%
109,503,691
76,615,844
69.97%
1.23-20.7 pCi/L
Combined Radium-226 & -
228
15,805
11,092
70.18%
120,504,165
96,765,143
80.30%
0.20 - 8.2 pCi/L
Uranium
12,155
6,785
55.82%
121,747,100
83,230,946
68.36%
0.49-41 |jg/L
1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems.
Exhibit 6.2: Number and Percent of Systems and Population Served by Systems
with Detections Greater than the MCL Concentration
Contaminant
(MCL Concentration)
Systems With Detections
> MCL Concentration
Population Served by Systems With
Detections > MCL Concentration
Number
Percent
Number
Percent
Inorganic Chemicals
Antimony
(6 |jg/L)
93
0.184%
899,395
0.354%
Arsenic
(10 |jg/L)
3,478
6.342%
19,619,428
7.346%
Asbestos
(7 MFL)
8
0.138%
190,895
0.202%
Barium
(2,000 |jg/L)
62
0.122%
1,312,318
0.516%
Beryllium
(4 |jg/L)
33
0.066%
576,710
0.227%
Cadmium
(5 |jg/L)
63
0.125%
239,604
0.094%
Chromium (Total)
(1 oo |jg/L)
22
0.043%
106,717
0.042%
Cyanide
(200 |jg/L)
38
0.103%
502,135
0.239%
Fluoride 1
(4,000 |jg/L)
343
0.726%
6,156,091
3.254%
Mercury (Inorganic)
(2 |jg/L)
50
0.099%
1,111,902
0.437%
Nitrate (as N)
(10,000 |jg/L)
3,016
2.282%
10,406,882
3.907%
Nitrite (as N)
(1,000 |jg/L)
523
0.610%
2,658,267
1.186%
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December 2016

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Contaminant
(MCL Concentration)
Systems With Detections
> MCL Concentration
Population Served by Systems With
Detections > MCL Concentration

Number
Percent
Number
Percent
Selenium
(50 Mg/L)
88
0.174%
626,607
0.246%
Thallium
(2 (jg/L)
98
0.194%
1,021,116
0.402%
Synthetic Organic Chemicals
Alachlor
(2 (jg/L)
4
0.009%
12,793
0.005%
Atrazine
(3 pg/L)
64
0.144%
3,507,861
1.395%
Benzo(a)pyrene
(0.2 |Jg/L)
16
0.047%
1,322,607
0.599%
Carbofuran
(40 Mg/L)
0
0.000%
0
0.000%
Chlordane
(2 (jg/L)
6
0.017%
2,621
0.001%
Dalapon
(200 |jg/L)
1
0.003%
125
0.000%
Di(2-ethylhexyl)adipate (DEHA)
(400 |jg/L)
0
0.000%
0
0.000%
Di(2-ethylhexyl)phthalate (DEHP)
(6 (jg/L)
352
1.038%
9,060,445
4.178%
1,2-Dibromo-3-chloropropane
(DBCP) (0.2 Mg/L)
103
0.277%
2,671,550
1.227%
2,4-Dichlorophenoxyacetic acid
(2,4-D) (70 Mg/L)
1
0.003%
125
0.000%
Dinoseb
(7 Mg/L)
5
0.014%
68,933
0.030%
Diquat
(20 Mg/L)
1
0.006%
993
0.001%
Endothall
(100 Mg/L)
1
0.006%
993
0.001%
Endrin
(2 Mg/L)
1
0.003%
993
0.000%
Ethylene Dibromide (EDB)
(0.05 Mg/L)
40
0.107%
810,484
0.365%
Glyphosate
(700 Mg/L)
0
0.000%
0
0.000%
Heptachlor
(0.4 Mg/L)
3
0.008%
1,643
0.001%
Heptachlor Epoxide
(0.2 Mg/L)
7
0.018%
2,503
0.001%
Hexachlorobenzene
(1 Mg/L)
1
0.003%
6,916
0.003%
Hexachlorocyclopentadiene
(50 Mg/L)
1
0.003%
10,018
0.004%
Lindane (gamma-
Hexachlorocyclohexane)
(0.2 Mg/L)
5
0.013%
20,440
0.009%
Methoxychlor
(40 Mg/L)
0
0.000%
0
0.000%
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December 2016

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Contaminant
(MCL Concentration)
Systems With Detections
> MCL Concentration
Population Served by Systems With
Detections > MCL Concentration
Number
Percent
Number
Percent
Oxamyl (Vydate)
(200 |jg/L)
0
0.000%
0
0.000%
Pentachlorophenol
(1 (jg/L)
11
0.027%
88,756
0.038%
Picloram
(500 |jg/L)
0
0.000%
0
0.000%
Polychlorinated biphenyls (PCBs)
(0.5 |Jg/L)
5
0.023%
36,354
0.024%
Simazine
(4 (jg/L)
5
0.012%
14,816
0.006%
Toxaphene
(3 pg/L)
5
0.013%
714,581
0.319%
2,3,7,8-TCDD (Dioxin)
(0.00003 |jg/L)
1
0.031%
550
0.001%
2,4,5-T richlorophenoxypropionic
Acid (Silvex) (50 |jg/L)
1
0.003%
125
0.000%
Volatile Organic Chemicals
1,2-Dichlorobenzene
(600 |jg/L)
0
0.000%
0
0.000%
1,4-Dichlorobenzene
(75 Mg/L)
2
0.004%
4,574
0.002%
1,1-Dichloroethylene
(7 |jg/L)
28
0.050%
694,929
0.264%
cis-1,2-Dichloroethylene
(70 Mg/L)
1
0.002%
54
0.000%
trans-1,2-Dichloroethylene
(100 Mg/L)
0
0.000%
0
0.000%
Ethyl benzene
(700 Mg/L)
2
0.004%
282
0.000%
Monochlorobenzene
(100 Mg/L)
0
0.000%
0
0.000%
Styrene
(100 Mg/L)
1
0.002%
100
0.000%
Toluene
(1,000 Mg/L)
2
0.004%
583
0.000%
1,2,4-Trichlorobenzene
(70 Mg/L)
0
0.000%
0
0.000%
1,1,1-Trichloroethane
(200 Mg/L)
2
0.004%
1,403
0.001%
1,1,2-Trichloroethane
(5 Mg/L)
3
0.005%
7,839
0.003%
Xylenes (Total)
(10,000 Mg/L)
0
0.000%
0
0.000%
Radiological Contaminants
Alpha Particles
(15 pCi/L)
719
5.402%
7,353,592
6.867%
Beta Particles
(50 pCi/L)
54
0.468%
725,062
0.662%
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December 2016

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Contaminant
(MCL Concentration)
Systems With Detections
> MCL Concentration
Population Served by Systems With
Detections > MCL Concentration
Number
Percent
Number
Percent
Combined Radium-226 & -228
(5 pCi/L)
788
4.986%
5,023,247
4.169%
Uranium
(30 |Jg/L)
523
4.303%
8,462,624
6.951%
1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems.
6.2 Comparison of Stage 1 Analysis of First, Second and Third Six-Year Reviews
Exhibit 6.3 presents a comparison of contaminant occurrence estimates from the first Six-Year
Review (based on compliance monitoring data from 1993-1997), the second Six-Year Review
(1998-2005) and the third Six-Year Review (2006-2011). Some of the contaminants assessed for
the second and third Six-Year Reviews were not assessed for the first Six-Year Review (noted in
Exhibit 6.3 by a hyphen in the "Six-Year 1" columns). The occurrence estimates from the three
rounds of Six-Year Review appear to be broadly similar. Note, however, that comparisons or
apparent occurrence changes over time must be somewhat qualified given the differences
between the three datasets. The first Six-Year Review dataset consisted of data from 16 states
that were assembled into a "national cross-section" that was indicative, though not statistically
representative, of national occurrence. In contrast, the SYR2 and SYR3 ICR Datasets consist of
data from 45 and 46 states, respectively, that serve as a very large sample that is, essentially,
nationally representative. Therefore, it is possible that differences in occurrence measures
between the first and second or between the first and third Six-Year Review Stage 1 findings
summarized in Exhibit 6.3 reflect differences in the respective datasets rather than differences in
actual occurrence. Nonetheless, each of the three datasets provide sound assessments of national
contaminant occurrence in systems, so significant differences in occurrence estimates generated
for the first, second and third Six-Year Reviews may provide information on changes in
occurrence over time. Occurrence evaluations specifically designed to assess occurrence trends
over time might assess occurrence changes for a particular contaminant only in all the systems
that were included in the first, second and third Six-Year Review datasets. These temporal
analyses of contaminant occurrence were not conducted for this current assessment.
Exhibit 6.3: Comparison of Stage 1 Analyses of the First, Second and Third Six-
Year Reviews based on the Percent of Systems
Contaminant
(MCL Concentration)
Percent of Systems With
Detections > MRL
Percent of Systems With Detections
> MCL Concentration
Six-Year 11
Six-Year 22
Six-Year 3
Six-Year 11
Six-Year 22
Six-Year 3
Inorganic Chemicals
Antimony
(6 |jg/L)
14.40%
5.98%
4.44%
0.62%
0.27%
0.18%
Arsenic
(io |jg/L)3
13.70%
37.33%
39.84%
0.87%
0.75%
6.34%
Asbestos
(7 MFL)
-
3.24%
3.70%
-
0.17%
0.14%
Barium
(2,000 |jg/L)
71.20%
72.02%
73.61%
0.17%
0.13%
0.12%
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Contaminant
(MCL Concentration)
Percent of Systems With
Detections > MRL
Percent of Systems With Detections
> MCL Concentration
Six-Year 11
Six-Year 22
Six-Year 3
Six-Year 11
Six-Year 22
Six-Year 3
Beryllium
(4 (jg/L)
3.32%
3.12%
2.09%
0.22%
0.11%
0.07%
Cadmium
(5 (jg/L)
17.60%
5.61%
3.61%
0.54%
0.27%
0.12%
Chromium (Total)
(1 oo |jg/L)
18.30%
24.21%
26.90%
0.13%
0.09%
0.04%
Cyanide
(200 |jg/L)
17.00%
4.14%
4.28%
0.17%
0.14%
0.10%
Fluoride 4
(4,000 |jg/L)
83.80%
79.28%
70.89%
1.28%
1.07%
0.73%
Mercury (Inorganic)
(2 |jg/L)
17.30%
3.96%
3.18%
0.26%
0.17%
0.10%
Nitrate (as N)
(10,000 |jg/L)
-
69.94%
63.81%
-
2.49%
2.28%
Nitrite (as N)
(1,000 |jg/L)
-
22.32%
11.74%
-
0.74%
0.61%
Selenium
(50 |jg/L)
22.10%
17.28%
17.31%
0.11%
0.13%
0.17%
Thallium
(2 kig/L)
4.22%
3.49%
3.62%
0.68%
0.26%
0.19%
Synthetic Organic Chemicals
Alachlor
(2 kig/L)
0.67%
0.33%
0.16%
0.00%
0.02%
0.01%
Atrazine
(3 kig/L)
3.83%
2.39%
2.58%
0.68%
0.26%
0.14%
Benzo(a)pyrene
(0.2 |Jg/L)
0.44%
0.49%
0.42%
0.05%
0.05%
0.05%
Carbofuran
(40 |jg/L)
0.06%
0.14%
0.07%
0.00%
0.00%
0.00%
Chlordane
(2 kig/L)
1.19%
0.21%
0.17%
0.01%
0.01%
0.02%
Dalapon
(200 |jg/L)
1.10%
1.83%
1.81%
0.00%
0.00%
0.00%
Di(2-ethylhexyl)adipate (DEHA) (400
Mg/L)
7.31%
1.75%
1.48%
0.01%
0.01%
0.00%
Di(2-ethylhexyl)phthalate (DEHP) (6
Mg/L)
12.50%
11.20%
11.92%
2.20%
1.66%
1.04%
1,2-Dibromo-3-chloropropane
(DBCP)
(0.2 |Jg/L)
1.61%
1.03%
1.02%
0.91%
0.39%
0.28%
2,4-Dichlorophenoxyacetic acid (2,4-
D) (70 |jg/L)
0.12%
0.90%
0.51%
0.02%
0.00%
0.00%
Dinoseb
(7 |jg/L)
0.24%
0.27%
0.26%
0.02%
0.02%
0.01%
Diquat
(20 |Jg/L)
0.49%
0.44%
0.59%
0.02%
0.00%
0.01%
Endothall
(100 |jg/L)
0.15%
0.23%
0.16%
0.03%
0.02%
0.01%
Endrin
(2 kig/L)
0.18%
0.14%
0.12%
0.02%
0.00%
0.00%
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Contaminant
(MCL Concentration)
Percent of Systems With
Detections > MRL
Percent of Systems With Detections
> MCL Concentration
Six-Year 11
Six-Year 22
Six-Year 3
Six-Year 11
Six-Year 22
Six-Year 3
Ethylene Dibromide (EDB)
(0.05 |jg/L)
1.06%
0.54%
0.41%
0.72%
0.24%
0.11%
Glyphosate
(700 |jg/L)
0.10%
0.18%
0.11%
0.00%
0.00%
0.00%
Heptachlor
(0.4 |Jg/L)
0.08%
0.80%
0.16%
0.01%
0.01%
0.01%
Heptachlor Epoxide
(0.2 |Jg/L)
0.09%
0.22%
0.35%
0.03%
0.02%
0.02%
Hexachlorobenzene
(1 (jg/L)
0.09%
0.34%
0.12%
0.01%
0.01%
0.00%
Hexachlorocyclopentadiene
(50 Mg/L)
0.89%
0.69%
0.44%
0.00%
0.00%
0.00%
Lindane (gamma-
Hexachlorocyclohexane)
(0.2 |Jg/L)
0.16%
0.25%
0.11%
0.04%
0.01%
0.01%
Methoxychlor
(40 Mg/L)
0.19%
0.16%
0.17%
0.01%
0.00%
0.00%
Oxamyl (Vydate)
(200 |jg/L)
0.08%
0.23%
0.11%
0.00%
0.00%
0.00%
Pentachlorophenol
(1 (jg/L)
0.43%
0.73%
0.56%
0.03%
0.02%
0.03%
Picloram
(500 |jg/L)
0.41%
0.41%
0.26%
0.00%
0.00%
0.00%
Polychlorinated biphenyls (PCBs)
(0.5 |Jg/L)
0.09%
0.16%
0.15%
0.03%
0.01%
0.02%
Simazine
(4 pg/L)
1.80%
0.72%
0.84%
0.06%
0.04%
0.01%
Toxaphene
(3 pg/L)
0.08%
0.13%
0.08%
0.01%
0.02%
0.01%
2,3,7,8-TCDD (Dioxin)
(0.00003 Mg/L)
-
0.71%
0.25%
-
0.04%
0.03%
2,4,5-T richlorophenoxypropionic
Acid (Silvex) (50 Mg/L)
0.40%
0.24%
0.16%
0.00%
0.00%
0.00%
Volatile Organic Chemicals
1,2-Dichlorobenzene
(600 Mg/L)
0.61%
0.23%
0.26%
0.00%
0.00%
0.00%
1,4-Dichlorobenzene
(75 Mg/L)
1.76%
1.50%
1.16%
0.00%
0.01%
0.00%
1,1-Dichloroethylene
(7 Mg/L)
1.58%
0.69%
0.68%
0.24%
0.07%
0.05%
cis-1,2-Dichloroethylene
(70 Mg/L)
1.37%
0.96%
0.93%
0.03%
0.01%
0.00%
trans-1,2-Dichloroethylene
(100 Mg/L)
0.53%
0.19%
0.27%
0.00%
0.00%
0.00%
Ethyl benzene
(700 Mg/L)
3.62%
3.91%
3.13%
0.00%
0.00%
0.00%
Monochlorobenzene
(100 Mg/L)
0.75%
0.27%
0.39%
0.00%
0.00%
0.00%
Styrene
(100 Mg/L)
0.99%
1.05%
0.69%
0.00%
0.01%
0.00%
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Contaminant
(MCL Concentration)
Percent of Systems With
Detections > MRL
Percent of Systems With Detections
> MCL Concentration
Six-Year 11
Six-Year 22
Six-Year 3
Six-Year 11
Six-Year 22
Six-Year 3
Toluene
(1,000 Mg/L)
4.73%
5.76%
4.46%
0.00%
0.00%
0.00%
1,2,4-Trichlorobenzene
(70 Mg/L)
0.61%
0.32%
0.26%
0.00%
0.00%
0.00%
1,1,1-Trichloroethane
(200 Mg/L)
2.50%
1.07%
0.72%
0.01%
0.00%
0.00%
1,1,2-Trichloroethane
(5 Mg/L)
0.62%
0.18%
0.21%
0.04%
0.01%
0.01%
Xylenes (Total)
(10,000 Mg/L)
4.16%
7.59%
6.35%
0.00%
0.00%
0.00%
Radiological Contaminants
Alpha Particles
(15 pCi/L)
-
68.08%
61.06%
-
4.58%
5.40%
Beta Particles
(50 pCi/L)
-
74.51%
59.79%
-
0.53%
0.47%
Combined Radium-226 & -228 (5
pCi/L)
-
69.97%
70.18%
-
11.46%
4.99%
Uranium
(30 Mg/L)
-
69.26%
55.82%
-
7.57%
4.30%
1	The first Six-Year Review occurrence estimate values presented in this table are from the report titled Occurrence Estimation
Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations. EPA Report 815-R-03-
006, Office of Water (USEPA, 2003b).
2	The second Six-Year Review occurrence estimate values presented in this table are from the report titled The Analysis of
Regulated Contaminant Occurrence Data from Public Water Systems in Support of the Second Six-Year Review of National Primary
Drinking Water Regulations. EPA Report 815-B-09-006, Office ofWater (USEPA, 2010c).
3	For the third Six-Year Review, there was a different MCL for arsenic (0.01 mg/L) compared to the earlier MCL (0.05 mg/L) for the
first and second Six-Year Reviews.
4	For the third Six-Year Review, quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water
systems.
6.3 System Sample Point Level Analysis
The basic Stage 1 analytical methodology is a conservative approach; occurrence measures are
based on simple counts of whether or not a system has at least one monitoring sample identified
with a contaminant detection greater than a specified concentration threshold. The approach
includes another implicit conservative assumption; if a detection is found in a single entry point
to the distribution system or other formal system sample point (SP), then the entire population
served by the system is assumed to be potentially exposed to the detected contaminant at the
system. For example, if a system serves a population of 30,000 and identified a detection of a
contaminant in one of its two SPs, the primary Stage 1 analytical methodology would estimate
that the entire population served by the system (30,000) was potentially exposed to the maximum
detected levels of the contaminant found in the one SP. In this context, sample points (SPs) are
defined as the authorized drinking water sample locations for compliance monitoring of
regulated contaminants. SPs primarily are entry points to the distribution system, but a small
number of states allow for sampling of raw, untreated ground water wells or surface water
intakes as well.
In reality, many systems get water from multiple water sources, such as a mix of purchased and
non-purchased water, ground water wells and surface water source intakes, among others. In
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systems with multiple SPs, such as multiple surface water intakes, multiple wells and/or multiple
entry points to the distribution system, contaminant occurrence in one source or one SP does not
necessarily mean contaminant occurrence in all sources or SPs that distribute water to
consumers. Given this, additional Stage 1 analyses were conducted at the SP-level to provide
supplementary details of contaminant occurrence.
The SP analysis is a less conservative estimate of the population served by systems with
contaminant detections. To derive this SP-level measure, an assumption was necessary regarding
population served by individual SPs at drinking water systems. The population served by each
SP and/or entry point to the distribution system is often difficult to know and is rarely, if ever,
reported along with other compliance monitoring records. Therefore, EPA assumed for the
analysis that the total population served by a particular system is equally distributed across all
SPs at the system.10 With this assumption, the population served all SPs with a detection of a
particular contaminant is calculated by dividing the system's total population served by the
number of that system's SPs with a contaminant detection. For example, if a system serves a
population of 30,000 and found detections of a contaminant in one of its two SPs, then a
population of 15,000 (or 30,000 x V2) would be estimated to be potentially exposed to the
contaminant.
This the total number of entry points and/or other SPs for each system must be determined in
order to calculate the proportional population potentially exposed. This was done by counting the
total number of unique SPs for each system over the entire six years of data. These counts were
done separately for each contaminant at every system. While conducting these counts, it
appeared that some systems may have changed their sample point numbering conventions (i.e.,
their "SP identification codes" or formal sample point identification number) at some point over
the six years of data, which would result in a higher number of apparent SPs than the number of
actual SPs. If so, this approach to sample point counting could potentially overestimate the total
number of SPs for a system, thereby resulting in an underestimate of the population served by
each SP.11 Exhibit 6.4 presents a summary of the Stage 1 findings based on SPs and population
served by SPs.
10	This "proportional population" assumption is based on the idea that for every PWS, each sample point serves an
equal portion of the system's total population. How well this assumption reflects actual populations potentially
exposed to contaminant occurrence at a system will depend on the distribution system and service population
configurations at individual systems.
11	Another method was explored for counting the number of SPs. This other method used the maximum number of
SPs that sampled in a given year as the system's "total number of SPs." This approach likely avoids the issue of
changing SP numbering conventions over time. However, this method has the potential to underestimate the total
number of SPs for the system and therefore overestimate the population served by each SP. For example, a system
could truly have a total of three SPs but those three SPs might not all sample within the same year, so the number of
actual SPs sampled over the six-year period might be underestimated. If a system is on reduced monitoring, each SP
might only need to sample as often as once every three years.
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Exhibit 6.4: Summary of Stage 1 Contaminant Occurrence Findings - Sample
Points and Population Served by Sample Points
Contaminant
(MCL Concentration)
Percent of Sample Points
Percent of Population-
Served by Sample Points
With Detections
> MRL
With Detections
> MCL
Concentration
With Detections
> MRL
With Detections
> MCL
Concentration
Inorganic Chemicals
Antimony
(6 |jg/L)
3.397%
0.126%
5.956%
0.068%
Arsenic
(10 |jg/L)
38.314%
5.840%
37.218%
1.739%
Asbestos
(7 MFL)
2.769%
0.086%
3.423%
0.038%
Barium
(2,000 |jg/L)
69.377%
0.083%
76.789%
0.138%
Beryllium
(4 |jg/L)
1.653%
0.040%
3.045%
0.024%
Cadmium
(5 |jg/L)
2.561%
0.079%
3.574%
0.020%
Chromium (Total)
(1 oo |jg/L)
25.561%
0.026%
28.044%
0.009%
Cyanide
(200 |jg/L)
2.973%
0.064%
7.260%
0.209%
Fluoride 1
(4,000 |jg/L)
70.639%
0.568%
78.228%
0.313%
Mercury (Inorganic)
(2 |jg/L)
2.521%
0.062%
4.113%
0.029%
Nitrate (as N)
(10,000 |jg/L)
61.987%
1.878%
81.103%
0.723%
Nitrite (as N)
(1,000 |jg/L)
9.622%
0.497%
16.965%
0.601%
Selenium
(50 |jg/L)
15.896%
0.140%
20.489%
0.059%
Thallium
(2 |jg/L)
2.817%
0.120%
4.656%
0.137%
Synthetic Organic Chemicals
Alachlor
(2 |jg/L)
0.097%
0.006%
0.392%
0.005%
Atrazine
(3 kig/L)
2.008%
0.086%
12.350%
0.481%
Benzo(a)pyrene
(0.2 |Jg/L)
0.267%
0.027%
0.702%
0.122%
Carbofuran
(40 |jg/L)
0.038%
0.000%
0.025%
0.000%
Chlordane
(2 |jg/L)
0.117%
0.010%
0.337%
0.001%
Dalapon
(200 |jg/L)
1.475%
0.002%
3.535%
0.000%
Di(2-ethylhexyl)adipate (DEHA)
(400 |jg/L)
1.080%
0.000%
1.830%
0.000%
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Contaminant
(MCL Concentration)
Percent of Sample Points
Percent of Population-
Served by Sample Points
With Detections
> MRL
With Detections
> MCL
Concentration
With Detections
> MRL
With Detections
> MCL
Concentration
Di(2-ethylhexyl)phthalate (DEHP)
(6 (jg/L)
10.209%
0.640%
12.034%
0.849%
1,2-Dibromo-3-chloropropane (DBCP)
(0.2 |Jg/L)
1.426%
0.213%
1.151%
0.114%
2,4-Dichlorophenoxyacetic acid (2,4-D)
(70 Mg/L)
0.352%
0.002%
1.925%
0.000%
Dinoseb
(7 (jg/L)
0.170%
0.008%
0.123%
0.004%
Diquat
(20 Mg/L)
0.400%
0.003%
0.424%
0.000%
Endothall
(100 |jg/L)
0.100%
0.003%
0.048%
0.000%
Endrin
(2 (jg/L)
0.074%
0.002%
0.122%
0.000%
Ethylene Dibromide (EDB)
(0.05 |jg/L)
0.317%
0.080%
0.436%
0.022%
Glyphosate
(700 |jg/L)
0.073%
0.000%
0.051%
0.000%
Heptachlor
(0.4 |Jg/L)
0.098%
0.005%
0.236%
0.000%
Heptachlor Epoxide
(0.2 |Jg/L)
0.264%
0.011%
0.202%
0.001%
Hexachlorobenzene
(1 (jg/L)
0.075%
0.002%
0.084%
0.001%
Hexachlorocyclopentadiene
(50 Mg/L)
0.289%
0.002%
1.292%
0.004%
Lindane (gamma-Hexachlorocyclohexane)
(0.2 |Jg/L)
0.067%
0.008%
0.490%
0.002%
Methoxychlor
(40 Mg/L)
0.104%
0.000%
0.132%
0.000%
Oxamyl (Vydate)
(200 |jg/L)
0.063%
0.000%
0.055%
0.000%
Pentachlorophenol
(1 (jg/L)
0.389%
0.016%
0.742%
0.016%
Picloram
(500 |jg/L)
0.174%
0.000%
0.217%
0.000%
Polychlorinated biphenyls (PCBs)
(0.5 |Jg/L)
0.085%
0.013%
0.060%
0.015%
Simazine
(4 (jg/L)
0.612%
0.007%
5.603%
0.006%
Toxaphene
(3 pg/L)
0.048%
0.008%
0.089%
0.048%
2,3,7,8-TCDD (Dioxin)
(0.00003 |jg/L)
0.107%
0.013%
0.107%
0.001%
2,4,5-Trichlorophenoxypropionic Acid (Silvex)
(50 Mg/L)
0.103%
0.002%
0.614%
0.000%
Volatile Organic Chemicals
1,2-Dichlorobenzene
(600 |jg/L)
0.212%
0.000%
0.472%
0.000%
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Contaminant
(MCL Concentration)
Percent of Sample Points
Percent of Population-
Served by Sample Points
With Detections
> MRL
With Detections
> MCL
Concentration
With Detections
> MRL
With Detections
> MCL
Concentration
1,4-Dichlorobenzene
(75 Mg/L)
0.771%
0.002%
0.900%
0.000%
1,1-Dichloroethylene
(7 (jg/L)
0.737%
0.030%
1.535%
0.011%
cis-1,2-Dichloroethylene
(70 Mg/L)
1.083%
0.001%
2.058%
0.000%
trans-1,2-Dichloroethylene
(100 Mg/L)
0.181%
0.000%
0.489%
0.000%
Ethyl benzene
(700 Mg/L)
1.949%
0.002%
1.672%
0.000%
Monochlorobenzene
(100 Mg/L)
0.263%
0.000%
0.528%
0.000%
Styrene
(100 Mg/L)
0.408%
0.001%
0.639%
0.000%
Toluene
(1,000 Mg/L)
2.778%
0.002%
2.483%
0.000%
1,2,4-Trichlorobenzene
(70 Mg/L)
0.154%
0.000%
0.434%
0.000%
1,1,1-Trichloroethane
(200 Mg/L)
0.587%
0.002%
0.980%
0.000%
1,1,2-Trichloroethane
(5 Mg/L)
0.129%
0.004%
0.425%
0.001%
Xylenes (Total)
(10,000 Mg/L)
4.112%
0.000%
3.586%
0.000%
Radiological Contaminants
Alpha Particles
(15 pCi/L)
57.551%
4.248%
60.478%
2.976%
Beta Particles
(50 pCi/L)
54.782%
0.319%
59.160%
0.237%
Combined Radium-226 & -228
(5 pCi/L)
67.174%
4.305%
69.367%
2.045%
Uranium
(30 Mg/L)
57.952%
3.399%
57.905%
0.971%
1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems.
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7 Stage 2 Analysis
Based on the initial review under the Third Six-Year Review Protocol, EPA determined that 10
chemical contaminants (lead, copper, 1,2-dichloroethane, 1,2-dichloropropane, benzene, carbon
tetrachloride, dichloromethane, tetrachloroethylene, trichloroethylene and vinyl chloride) were
being reviewed or revised under other regulatory actions and, therefore, no further action was
taken under Six-Year Review 3. EPA reviewed the remaining chemical contaminants for new
health effects and analytical feasibility information and 19 chemical contaminants were
identified for additional analysis. Two of the 19 chemical contaminants (oxamyl and carbofuran)
have health endpoints associated with acute exposure and, therefore, did not require the Stage 2
analysis which is most appropriate for contaminants for which chronic health effects are of
concern. (Detailed Stage 1 analyses for oxamyl and carbofuran are included in Appendix A of
this report.) The remaining 17 contaminants have chronic health effects and were evaluated via
the Stage 2 occurrence analysis. These 19 contaminants fall into two groups: (1) contaminants
with analytical limitations - carbofuran; chlordane; cyanide; heptachlor; heptachlor epoxide;
hexachlorobenzene; methoxychlor; styrene; 2,3,7,8-TCDD (dioxin); toxaphene; 1,1,2-
trichloroethane and (2) non-carcinogens with updated health assessments - cis-1,2-
dichloroethylene; endothall; fluoride; hexachlorocyclopentadiene; oxamyl; selenium; toluene and
xylenes (total).
The SYR3 ICR Dataset is as large and robust as the dataset used for the second Six-Year
Review; thus, similar to SYR2, it was again possible for SYR3 to use a simple analytical
approach to estimate system means. System means were calculated using a simple arithmetic
average of all detection and non-detection records for each system. The Stage 2 analysis system
contaminant long-term mean estimates provide a less conservative contaminant occurrence
estimate than does the Stage 1 analysis, which is based on a single maximum sample result
exceeding a certain contaminant threshold. As described above, the Stage 2 analyses also provide
better occurrence estimates for contaminants for which chronic health effects are of concern.
In order to calculate a contaminant arithmetic mean for each system, a numeric value was
substituted for each non-detection record. This "simple substitution method" for the non-
detections is a straight-forward and standard data management approach for this type of analysis
(e.g., Helsel and Hirsch, 1991). PWSs use this approach for calculating annual, rolling, four-
quarter average contaminant concentrations and can substitute zero for each sample non-
detection record when generating average concentration values. For the third Six-Year Review,
three different substitution values were applied-zero, one-half the MRL value and the full MRL
value. Since the true, but unknown, concentration of a contaminant for each non-detection is
theoretically between zero and the MRL, using a substitution value of zero for each non-
detection generates a lower bound estimated average, substituting the full MRL generates an
upper bound estimate and substituting the V2 MRL value generates a mid-range estimate. EPA
calculated three arithmetic means for each contaminant at each system using the zero, one-half
MRL and full MRL substitution values. For each of these three substitution values, system
contaminant means were calculated for all systems with data in the SYR3 ICR Dataset, then the
percent of all systems with a long-term mean concentration greater than each contaminant's
MCL concentration was calculated.
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7.1	Preparing the Data for the Stage 2 Analysis
As was described in Section 3.3, in order to conduct the Stage 1 and Stage 2 occurrence analysis,
each contaminant sample analytical result must specify a sample analytical result (value) and a
sample analytical result (sign) to indicate whether that result is a detection (sample analytical
result greater than or equal to the MRL) or a non-detection. Sample records reported as non-
detections tend to be less uniform and less complete than sample records for analytical
detections. Some states reported MRL data, recording it in the analytical result field and also
including a "<" in a corresponding field to identify the record as a non-detection. Other states
simply included a zero or negative result in the analytical result field to signify a non-detection
and did not include any MRL data. The Stage 1 analyses are not affected by how non-detections
are specifically recorded. However, since the Stage 2 analyses were conducted using a "simple
substitution" approach that substitutes MRL values for reported analytical non-detections, non-
zero MRL numeric values needed to replace all analytical results that were reported either as
zero, "non-detection," "ND," etc.
A convention was established where EPA replaced any missing non-detect results with the most
common modal MRL value for the state in which the system was located (derived directly from
the PWS compliance monitoring data submitted to EPA in the SYR3 ICR Dataset). In some
cases, though, all MRL data for a specific contaminant's data from an entire state were missing.
The missing values were replaced with the national modal MRL derived as the mode of all the
state modal MRL values for that contaminant. If state-modal MRL values were extremely low or
high, a process was developed to identify and replace such values with more reasonable MRL
values. Reported MRL values that were below the minimum MDL, greater than the national
modal MRL, or missing were replaced with the national modal MRL. For complete details of the
data management measures, including the methods used to identify and replace non-numeric or
incorrect non-detection records, see USEPA (2016d).
7.2	Summary of Stage 2 Contaminant Occurrence Estimations
The results from these Stage 2 analyses presented below in Exhibit 7.1 reflect the percentage of
systems and population served by systems, with an estimated system contaminant mean
exceeding the respective MCL concentration for each contaminant over the six-year period of
data in the SYR3 ICR Dataset. The results using the zero substitution value are shown because
they are equivalent to how states are authorized to calculate system means for compliance
determinations. (For comparison, the Stage 1 results relative to the MCL concentration are also
included.) Note: The results in Exhibit 7.1 do not necessarily indicate an MCL violation. The
long-term mean in the Stage 2 analysis differs from compliance assessments that calculate a
system mean concentration over four consecutive quarters. An MCL violation occurs, for
example, when the MCL is exceeded at a sampling point by the average results from the
consecutive samples at that sampling point.
Please see Appendix B for additional measures of contaminant occurrence based on the Stage 2
analyses, including presentations of the numbers of systems and population served generated
using the V2 MRL and full MRL substitution values, which supplement the calculations using
zero substitution values presented in Exhibit 7.1. The appendix summary tables present findings
separately for ground water vs. surface water and present occurrence measures that identify the
total number of systems and total population served by systems with estimated system
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contaminant means greater than the MCL concentration, as well as many other thresholds. For
more information on the potential thresholds of concern used in the SYR3 Stage 2 analyses, refer
to Section 5.3.
Exhibit 7.1: Comparison of Stage 1 and Stage 2 Analytical Results - Percent of
Systems and Population Served by Systems Greater than the MCL Concentration
Contaminant
(MCL Concentration)
Percent of Systems > MCL
Concentration
Percent of Population Served by
Systems > MCL Concentration
Stage 11
(one detect
Stage 22
(mean > MCL
Stage 11
(one detect
Stage 22
(mean > MCL
Chlordane
(2 Mg/L)
0.017%
0.003%
0.001 %
0.0005%
cis-1,2-Dichloroethylene
(70 Mg/L)
0.002%
0.000%
0.00002%
0.000%
Cyanide
(200 |jg/L)
0.103%
0.019%
0.239%
0.038%
Endothall
(100 |jg/L)
0.006%
0.006%
0.001 %
0.001%
Fluoride 3
(4,000 jjg/L)
0.726%
0.284%
3.254%
0.032%
Heptachlor
(0.4 Mg/L)
0.008%
0.005%
0.001 %
0.001%
Heptachlor Epoxide
(0.2 Mg/L)
0.018%
0.005%
0.001 %
0.001%
Hexachlorobenzene
(1 Mg/L)
0.003%
0.000%
0.003%
0.000%
Hexachlorocyclopentadiene
(50 Mg/L)
0.003%
0.000%
0.004%
0.000%
Methoxychlor
(40 Mg/L)
0.000%
0.000%
0.000%
0.000%
Selenium
(50 Mg/L)
0.174%
0.061%
0.246%
0.008%
Styrene
(100 Mg/L)
0.002%
0.000%
0.00004%
0.000%
2,3,7,8-TCDD (Dioxin)
(0.00003 Mg/L)
0.031 %
0.031%
0.001 %
0.001%
Toluene
(1,000 Mg/L)
0.004%
0.000%
0.0002%
0.000%
Toxaphene
(3 M9/L)
0.013%
0.005%
0.319%
0.104%
1,1,2-Trichloroethane
(5 Mg/L)
0.004%
0.000%
0.001 %
0.000%
Xylenes
(10,000 Mg/L)
0.000%
0.000%
0.000%
0.000%
1	The Stage 1 results represent the percent of systems with at least one sample analytical result greater than a contaminant's MCL
concentration.
2	The Stage 2 results represent the percent of systems with an estimated long-term mean concentration greater than a
contaminant's MCL concentration. The Stage 2 results presented here are based on long-term means generated by substituting
zero for each non-detection record. For the Stage 2 results based on substituting the value of the full MRL or % MRL (instead of
zero), please refer to Appendix B.
3	Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems.
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8 References
Helsel, D.R. and R.M. Hirsch. 1991. "Statistical Methods in Water Resources," Chapter A3,
Book 4 of Techniques of Water-Resources Investigations of the United States Geologic Survey.
United States Environmental Protection Agency (USEPA). 1986. National Primary and
Secondary Drinking Water Regulations; Fluoride; Final Rule. 51 FR 11396. April 2, 1986.
USEPA. 1991a. National Primary Drinking Water Regulations—Synthetic Organic Chemicals
and Inorganic Chemicals; Monitoring for Unregulated Contaminants; National Primary Drinking
Water Regulations Implementation; National Secondary Drinking Water Regulations; Final
Rule. 56 FR 3526. January 30, 1991.
USEPA. 1991b. Integrated Risk Information System (IRIS) - Selenium. Oral RfD. Last modified
October 2016. Available online at: http://www.epa.gov/iris/subst/0472.htm
USEPA. 1992. Drinking Water; National Primary Drinking Water Regulations—Synthetic
Organic Chemicals and Inorganic Chemicals; National Primary Drinking Water Regulations
Implementation; Final Rule. 57 FR 31776. July 17, 1992.
USEPA. 1998. National Primary Drinking Water Regulations: Disinfectants and Disinfection
Byproducts; Final Rule. 63 FR 69390. December 16, 1998.
USEPA. 2002. Analysis of National Occurrence of the 1998 Contaminant Candidate List (CCL)
Regulatory Determination Priority Contaminants in Public Water Systems. EPA Report 815-D-
01-002. May 2002.
USEPA. 2003a. National Primary Drinking Water Regulations; Announcement of Completion of
EPA's Review of Existing Drinking Water Standards. 68 FR 42907. July 18, 2003.
USEPA. 2003b. Occurrence Estimation Methodology and Occurrence Findings for Six-Year
Review of National Primary Drinking Water Regulations. EPA Report 815-R-03-006. June 2003.
USEPA. 2006. National Primary Drinking Water Regulations: Stage 2 Disinfectants and
Disinfection Byproducts Rule; Final Rule. 71 FR 388. January 4, 2006.
USEPA. 2008a. The Analysis of Occurrence Data from the Unregulated Contaminant
Monitoring (UCM) Program and National Inorganics and Radionuclides Survey (NIRS) in
Support of Regulatory Determinations for the Second Drinking Water Contaminant Candidate
List. EPA Report 815-R-08-014. June 2008.
USEPA. 2008b. The Analysis of Occurrence Data from the First Unregulated Contaminant
Monitoring Regulation (UCMR 1) in Support of Regulatory Determinations for the Second
Drinking Water Contaminant Candidate List. EPA Report 815-R-08-013. June 2008.
USEPA. 2010a. National Primary Drinking Water Regulations; Announcement of the Results of
EPA's Review of Existing Drinking Water Standards and Request for Public Comment and/or
Information on Related Issues. 75 FR 15499. March 29, 2010.
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USEPA. 2010b. Agency Information Collection Activities; Submission to OMB for Review and
Approval; Contaminant Occurrence Data in Support of EPA's Third Six-Year Review of
National Primary Drinking Water Regulations (Renewal). 75 FR 6023. February 5, 2010.
USEPA. 2010c. The Analysis of Regulated Contaminant Occurrence Data from Public Water
Systems in Support of the Second Six-Year Review of National Primary Drinking Water
Regulations. EPA Report 815-B-09-006. September 2010.
USEPA. 201 la. National Primary Drinking Water Regulations: Group Regulation of
Carcinogenic Volatile Organic Compounds (VOCs). 40 CFR 141 40 CFR 142.
USEPA. 201 lb. Exposure Factors Handbook 2011 Edition (Final). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-09/052F, 2011.
USEPA. 2014. National Drinking Water Advisory Council Meeting Summary, November 6-7,
2014.
USEPA. 2016a. Support Document for Third Six-Year Review of Drinking Water Regulations
for Acrylamide and Epichlorohydrin. EPA- 810-R-16-019. December 2016.
USEPA. 2016b. Six-Year Review 3 Technical Support Document for Microbial Contaminant
Regulations. EPA-810-R16-010. December 2016.
USEPA. 2016c. Six-Year Review 3 Technical Support Document for Disinfectants/Disinfection
Byproducts Rules. EPA-810-R-16-012. December 2016.
USEPA. 2016d. The Data Management and Quality Assurance/Quality Control Process for the
Third Six- Year Review Information Collection Rule Dataset. EPA-810-R-16-015. December
2016.
USEPA. 2016e. Development of Estimated Quantitation Levels for the Third Six-Year Review
of National Primary Drinking Water Regulations (Chemical Phase Rules). EPA-810-R-16-002.
December 2016.
USEPA. 2016f. Six- Year Review 3-Health Effects Assessment for Existing Chemical and
Radionuclide National Primary Drinking Water Regulations-Summary Report. December 2016.
Yang, G., R. Zhou, S. Yin, L. Gu, B. Yan, Y. Liu, Y. Liu, and X. Li. 1989a. Studies of safe
maximal daily dietary selenium intake in a seleniferous area in China. I. Selenium intake and
tissue levels of the inhabitants. Journal of Trace Elements and Electrolytes in Health and
Disease. 3(2): 77-87.
Yang, G., S. Yin, R. Zhou, L. Gu, B. Yan, Y. Liu, and Y. Liu. 1989b. Studies of safe maximal
daily dietary Se-intake in a seleniferous area in China. II. Relation between Se- intake and the
manifestation of clinical signs and certain biochemical alterations in blood and urine. Journal of
Trace Elements and Electrolytes in Health and Disease. 3(3): 123-130.
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Appendices
APPENDIX A. Background Information and Detailed Stage 1 Analysis Occurrence Measures
for 2 Select Regulated Chemical Contaminants
APPENDIX B. Background Information and Detailed Stage 2 Analysis Occurrence Measures
for 17 Select Regulated Chemical Contaminants

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A Background Information and Detailed Stage 1 Analysis Occurrence
Measures for 2 Select Regulated Chemical Contaminants
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A.l Carbofuran
This chapter on carbofuran includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
A.l.l Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for carbofuran on January 30, 1991 (56 FR
3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG)
and a maximum contaminant level (MCL) of 40 |ig/L. EPA based the MCLG on a reference dose
(RfD) of 5 |ig/kg-day (0.005 mg/kg-day) and a cancer classification of E, evidence of non-
carcinogenicity for humans.
Carbofuran is regulated as a synthetic organic chemical (SOC) in drinking water. All non-
purchased community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.1 If all 4 samples are non-detections, then
a system serving less than 3,300 people may reduce its collection frequency to 1 sample during
each consecutive compliance period; a system serving more than 3,300 people may reduce its
collection frequency to 2 quarterly samples within a 12-month period during each repeat
compliance period. If a chemical is detected, the system must monitor quarterly until results are
reliably and consistently below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems). If all quarterly samples are below
the MCL, the system may return to annual sampling. If a chemical is detected at a level greater
than the MCL, the system (whether ground water or surface water) must take quarterly samples
until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL,
the system may return to annual sampling.
A.1.2 Occurrence in Drinking Water
The analysis of carbofuran occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 122,110
analytical results from 34,614 public water systems (PWSs) during the period from 2006 to
1 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the State. The system must also comply with the
initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the
MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Carbofuran has health endpoints associated with acute
exposure and, therefore, did not require the Stage 2 analysis. Details on the Stage 1 analysis are
presented in Section 6. For carbofuran, EPA generated additional Stage 1 occurrence estimates
relative to the MCL and the estimated quantitation level (EQL).
Stage 1 Occurrence Estimates
Stage 1 analyses for carbofuran are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 40 |ig/L (the MCL) and 5 |ig/L (the EQL). The
EQL represents the potential quantitation capabilities below a practical quantitation level
(PQL).2 For more information on the new potential thresholds of concern used in the SYR3
analyses for carbofuran, refer to USEPA (2016d) and (2016e).
Exhibit A-l presents the system-level Stage 1 analysis of carbofuran occurrence in drinking
water. Exhibit A-2 presents similar information based on population served by the systems.
Based on the Stage 1 analysis, no systems had any detections greater than the MCL
concentration of 40 |ig/L. Three systems, serving 24,258 people, had at least 1 detection greater
than the EQL concentration of 5 |ig/L.
Exhibit A-1: Carbofuran Stage 1 Analysis - Summary of Systems with a Threshold
Exceedance
Source Water Type
(Number of Systems)
Threshold
Number of Systems with
Detections That Are
Greater Than the
Threshold
Percent of Systems with
Detections That Are Greater
Than the Threshold
Ground Water
> 40 |jg/L
0
0.000%
(31,375)
> 5 |jg/L1
1
0.003%

2 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical
feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year
Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced.
The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to
evaluate occurrence and exposure for the Stage 1 analyses.
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Source Water Type
(Number of Systems)
Threshold
Number of Systems with
Detections That Are
Greater Than the
Threshold
Percent of Systems with
Detections That Are Greater
Than the Threshold
Surface Water
(3,239)
> 40 |jg/L
0
0.000%
> 5 |jg/L1
2
0.062%

Combined Ground &
Surface Water
(34,614)
> 40 |jg/L
0
0.00%
> 5 |jg/L1
3
0.009%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Exhibit A-2: Carbofuran Stage 1 Analysis - Summary of Population Served by
Systems with a Threshold Exceedance
Source Water Type
(Population Served by
Systems)
Threshold
Population Served by
Systems with Detections
That Are Greater Than the
Threshold
Percent of Population Served
by Systems with Detections
That Are Greater Than the
Threshold
Ground Water
(90,319,675)
> 40 |jg/L
0
0.000%
> 5 |jg/L1
993
0.001%

Surface Water
(138,398,258)
> 40 |jg/L
0
0.000%
> 5 |jg/L1
23,265
0.017%

Combined Ground &
Surface Water
(228,717,933)
> 40 |jg/L
0
0.00%
> 5 |jg/L1
24,258
0.011%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Data for carbofuran were available from 50 states/entities. Four states did not submit data for use
in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the count of 50 states because a handful of tribal water systems
located within these 2 states did submit carbofuran data.
Exhibit A-3 presents the total number of systems in each state that submitted data for carbofuran.
In addition, the geographic distribution of carbofuran occurrence in drinking water is illustrated
by showing states with systems with at least one detection greater than the EQL and the MCL
concentrations. No systems had detections greater than the MCL. Three systems (one in New
Mexico and two in New York) had at least one detection greater than the EQL of 5 |ig/L.
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Exhibit A-3: Carbofuran Stage 1 Analysis - Summary of Systems with Threshold
Exceedances by State1

Total Number of
Systems with Detections
Systems with Detections

Systems
> 5 |ig/L2
> 40 |jg/L


Number
Percent
Number
Percent
AK
9




AL
383




AR
459




AS
11




AZ
868




CA
1,320




CO
1




CT
1,136




DC
1




FL
2,088




HI
115




IA
2




ID
325




IL
1,467




IN
1,210




KS
86




KY
225




LA
1,104




MA
562




MD
882




ME
127




Ml
2,423




MN
921




MO
1,321




MS
5




MT
857




NC
2,347




ND
23




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State
Total Number of
Systems
Systems with Detections
> 5 |ig/L2
Systems with Detections
> 40 |jg/L
Number
Percent
Number
Percent
NE
656




NH
1,146




NJ
80




NM
718
1
0.14%
0
0.00%
NV
303




NY
2,115
2
0.09%
0
0.00%
OH
178




OK
91




OR
1,118




PA
1,289




Rl
74




SC
497




SD
258




TN
8




TX
1,535




UT
428




VA
228




VT
382




WA
700




Wl
1,912




WV
302




WY
318




Total
34,614
3
0.009%
0
0.00%
1	Blank cells within the table indicate that there were no systems with any detections that exceeded either threshold.
2	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Exhibit A-4 presents the population served by systems with at least one detection greater than the
MCL concentration by state (40 |ig/L). As described above, no systems had any detections
greater than the MCL. Three systems, serving 24,258 people, had at least 1 detection greater than
the EQL of 5 |ig/L.
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Exhibit A-4: Carbofuran Stage 1 Analysis - Summary of Population Served by
Systems with Threshold Exceedances by State1
State
Total
Population
Population Served by Systems
with Detections
> 5 jjg/L2
Population Served by
Systems with Detections
> 40 jjg/L
Population
Percent
Population
Percent
AK
39,228




AL
5,333,035




AR
2,635,934




AS
62,196




AZ
6,473,687




CA
35,686,301




CO
2,020




CT
2,883,135




DC
761,124




FL
18,943,131




HI
1,487,191




IA
165,864




ID
885,855




IL
10,998,351




IN
4,769,597




KS
1,685,226




KY
4,225,473




LA
4,964,671




MA
9,163,574




MD
4,939,512




ME
362,333




Ml
7,218,130




MN
3,752,615




MO
5,232,592




MS
6,176




MT
845,014




NC
7,832,302




ND
66,229




NE
1,653,596




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State
Total
Population
Population Served by Systems
with Detections
> 5 jjg/L2
Population Served by
Systems with Detections
> 40 jjg/L
Population
Percent
Population
Percent
NH
949,308




NJ
5,123,511




NM
1,940,795
993
0.05%
0
0.00%
NV
2,681,118




NY
10,480,579
23,265
0.22%
0
0.00%
OH
2,473,669




OK
338,082




OR
3,432,212




PA
10,891,371




Rl
1,017,507




SC
3,622,250




SD
678,171




TN
1,176,648




TX
22,373,743




UT
2,752,741




VA
5,295,906




VT
387,092




WA
3,822,877




Wl
4,236,667




WV
1,499,884




WY
469,710




Total
228,717,933
24,258
0.011%
0
0.00%
1	Blank cells within the table indicate that there were no systems with any detections that exceeded either threshold.
2	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
A.1.3 Summary of Data
A total of 122,110 analytical results from 34,614 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for carbofuran. The Stage 1 analysis of occurrence in drinking water
indicated that zero systems had any detections of carbofuran greater than the MCL concentration
of 40 |ig/L. Three systems (one served by ground water and two served by surface water),
serving 24,258 people, had at least 1 detection greater than the EQL (5 |ig/L).
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A.2 Oxamyl
This chapter on oxamyl includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
A.2.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for oxamyl on July 17, 1992 (57 FR 31776;
USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) and a
maximum contaminant level (MCL) of 200 |ig/L. EPA based the MCLG on a reference dose
(RfD) of 25 |ig/kg-day (0.025 mg/kg-day) and a cancer classification of E, evidence of non-
carcinogenicity for humans.
Oxamyl is regulated as a synthetic organic chemical (SOC) in drinking water. All non-purchased
community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.3 If all 4 samples are non-detections, then
a system serving less than 3,300 people may reduce its collection frequency to 1 sample during
each consecutive compliance period; a system serving more than 3,300 people may reduce its
collection frequency to 2 quarterly samples within a 12-month period during each repeat
compliance period. If a chemical is detected (but is less than the MCL), the system must monitor
quarterly until results are reliably and consistently below the MCL (minimum of two quarterly
samples for ground water systems and four quarterly samples for surface water systems). If all
quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is
detected at a level greater than the MCL, the system (whether ground water or surface water)
must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly
samples are below the MCL, the system may return to annual sampling.
A.2.2 Occurrence in Drinking Water
The analysis of oxamyl occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 121,508
analytical results from 34,518 public water systems (PWSs) during the period from 2006 to
3 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Oxamyl has health endpoints associated with acute
exposure and, therefore, did not require the Stage 2 analysis. Details on the Stage 1 analysis are
presented in Section 6.
For oxamyl, since there were no analytical method limitations at the potential MCLG, EPA
generated additional Stage 1 occurrence estimates relative to the MCL and two potential
MCLGs.
Stage 1 Occurrence Estimates
Stage 1 analyses for oxamyl are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 200 |ig/L (the MCL), 10 |ig/L (one potential
MCLG value) and 9 |ig/L (the other potential MCLG value).4 The potential MCLG is due to
changes in the RfD based on new health effects information. For more information on the new
potential thresholds of concern used in the SYR3 analyses, refer to USEPA (2016d) and (2016e).
Exhibit A-5 presents the system-level estimates for oxamyl occurrence in drinking water. Exhibit
A-6 presents similar information based on population served by the systems. Based on the Stage
1 analyses, no systems had any detections greater than the MCL concentration of 200 |ig/L.
Three systems, serving 28,146 systems, had at least 1 detection greater than the potential MCLG
of 10 |ig/L. Four systems, serving 42,662 systems, had at least 1 detection greater than the
potential MCLG of 9 |ig/L.
4 The MCLG for oxamyl can be derived using a normalized drinking water intake per unit body weight from birth to
less than 12 months at the 90th percentile of 0.15 L/Kg (based on Table 3-19 in USEPA (201 lb)). The alternate
MCLG for children derived using the normalized exposure factors is 0.009 mg/L (0.0069 mg/kg/day x 0.2/ 0.15 =
0.009 mg/L). There was no difference in the Stage 1 occurrence analysis results between the 9 |ig/L and 10 |ig/L
threshold.
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Exhibit A-5: Oxamyl Stage 1 Analysis - Summary of Systems with a Threshold
Exceedance
Source Water Type
(Number of Systems)
Threshold
Systems with Detections
That Are Greater Than the
Threshold
Systems with Detections
That Are Greater Than the
Threshold
Ground Water
(31,355)
> 200 |jg/L
0
0.00%
> 10 |jg/L1
2
0.01%
> 9 |jg/L1
2
0.01%

Surface Water
(3,163)
> 200 |jg/L
0
0.00%
> 10 |jg/L1
1
0.03%
> 9 |jg/L1
2
0.06%

Combined Ground &
Surface Water
(34,518)
> 200 |jg/L
0
0.00%
> 10 |jg/L1
3
0.01%
> 9 |jg/L1
4
0.01%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit A-6: Oxamyl Stage 1 Analysis - Summary of Population Served by
Systems with a Threshold Exceedance
Source Water Type
(Population Served by
Systems)
Threshold
Population Served by Systems
with Detections That Are
Greater Than the Threshold
Percent of Population Served
by Systems with Detections
That Are Greater Than the
Threshold
Ground Water
(90,279,553)
> 200 |jg/L
0
0.00%
> 10 |jg/L1
19,397
0.02%
> 9 |jg/L1
19,397
0.02%

Surface Water
(137,240,820)
> 200 |jg/L
0
0.000%
> 10 |jg/L1
8,749
0.01%
> 9 |jg/L1
23,265
0.02%

Combined Ground &
Surface Water
> 200 |jg/L
0
0.000%
> 10 |jg/L1
28,146
0.01%
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Source Water Type
(Population Served by
Systems)
Threshold
Population Served by Systems
with Detections That Are
Greater Than the Threshold
Percent of Population Served
by Systems with Detections
That Are Greater Than the
Threshold
Combined Ground &
Surface Water, cont.
(227,520,373)
> 9 |jg/L1
42,662
0.02%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Data for oxamyl were available from 50 states/entities. Four states did not submit data for use in
the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the count of 50 states because a handful of tribal water systems
located within these 2 states did submit oxamyl data.
Exhibit A-7 presents the total number of systems in each state that submitted data for oxamyl. In
addition, the geographic distribution of oxamyl occurrence in drinking water is illustrated by
showing states with systems with any detections greater than the potential MCLG and the MCL
concentrations. Detection rates of oxamyl were low; no systems had any detections greater than
the MCL. Three systems in three states (Florida, New Mexico and New York) had detections
greater than the potential MCLG of 10 |ig/L. Four systems in three states (Florida, New Mexico
and New York) had detections greater than the potential MCLG of 9 |ig/L.
Exhibit A-7: Oxamyl Stage 1 Analysis - Summary of Systems with Threshold
Exceedances by State12
State
Total
Number of
Systems
Systems with
Detections > 9 jjg/L3
Systems with
Detections >10 jjg/L3
Systems with
Detections > 200 jjg/L
Number
Percent
Number
Percent
Number
Percent
AK
9






AL
383






AR
459






AS
11






AZ
856






CA
1,336






CO
1






CT
1,136






DC
1






FL
2,087
1
0.05%
1
0.05%
0
0.00%
HI
115






IA
2






ID
323






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State
Total
Number of
Systems
Systems with
Detections > 9 jjg/L3
Systems with
Detections >10 jjg/L3
Systems with
Detections > 200 jjg/L
Number
Percent
Number
Percent
Number
Percent
IL
1,459






IN
1,210






KS
3






KY
225






LA
1,104






MA
564






MD
873






ME
126






Ml
2,424






MN
921






MO
1,321






MS
5






MT
857






NC
2,346






ND
23






NE
656






NH
1,146






NJ
80






NM
718
1
0.14%
1
0.14%
0
0.00%
NV
304






NY
2,115
2
0.09%
1
0.05%
0
0.00%
OH
178






OK
90






OR
1,118






PA
1,290






Rl
74






SC
497






SD
258






TN
7






TX
1,535






UT
428






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State
Total
Number of
Systems
Systems with
Detections > 9 jjg/L3
Systems with
Detections >10 jjg/L3
Systems with
Detections > 200 jjg/L
Number
Percent
Number
Percent
Number
Percent
VA
228






VT
382






WA
700






Wl
1,914






WV
302






WY
318






Total
34,518
4
0.01%
3
0.01%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit A-8 presents the population served by systems with detections greater than the MCL and
MCLG concentrations by state. As described above, no systems had any detections greater than
the MCL. Three systems in 3 states (Florida, New Mexico and New York), serving 28,146
people, had detections greater than the potential MCLG of 10 |ig/L. Four systems in three states
(Florida, New Mexico and New York), serving 42,662 people, had detections greater than the
potential MCLG of 9 |ig/L.
Exhibit A-8: Oxamyl Stage 1 Analysis - Summary of Population Served by
Systems with Threshold Exceedances by State12
State
Total
Population
Population Served by
Systems with Detections
> 9 jjg/L3
Population Served by
Systems with Detections
>10 mq/l3
Population Served by
Systems with Detections
> 200 Mg/L
Population
Percent
Population
Percent
Population
Percent
AK
39,228






AL
5,333,035






AR
2,635,934






AS
62,196






AZ
6,470,039






CA
35,698,949






CO
2,020






CT
2,883,135






DC
761,124






FL
18,943,101
18,404
0.10%
18,404
0.10%
0
0.00%
HI
1,487,191






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State
Total
Population
Population Served by
Systems with Detections
> 9 jjg/L3
Population Served by
Systems with Detections
>10 mq/l3
Population Served by
Systems with Detections
> 200 Mg/L
Population
Percent
Population
Percent
Population
Percent
IA
165,864






ID
884,736






IL
10,997,092






IN
4,769,597






KS
482,056






KY
4,225,473






LA
4,964,671






MA
9,163,674






MD
4,936,864






ME
362,303






Ml
7,218,255






MN
3,752,615






MO
5,232,592






MS
6,176






MT
845,014






NC
7,832,272






ND
66,229






NE
1,653,596






NH
949,308






NJ
5,123,511






NM
1,940,795
993
0.05%
993
0.05%
0
0.00%
NV
2,681,738






NY
10,480,579
23,265
0.22%
8,749
0.08%
0
0.00%
OH
2,473,669






OK
337,997






OR
3,432,307






PA
10,895,086






Rl
1,017,507






SC
3,622,250






SD
678,171






TN
1,173,584






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State
Total
Population
Population Served by
Systems with Detections
> 9 jjg/L3
Population Served by
Systems with Detections
>10 mq/l3
Population Served by
Systems with Detections
> 200 Mg/L
Population
Percent
Population
Percent
Population
Percent
TX
22,373,743






UT
2,752,741






VA
5,295,906






VT
387,092






WA
3,822,877






Wl
4,236,887






WV
1,499,884






WY
469,710






Total
227,520,373
42,662
0.02%
28,146
0.01%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
A.2.3 Summary of Data
A total of 121,508 analytical results from 34,518 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for oxamyl. The Stage 1 analysis of occurrence in drinking water indicated
that zero systems had any detections of oxamyl greater than the MCL concentration of 200 |ig/L.
Three water systems (two ground water systems and one surface water system), serving a total of
28,146 people, had at least 1 detection greater than the potential MCLG of 10 |ig/L. Four water
systems (two ground water systems and two surface water systems), serving a total of 42,662
people, had at least 1 detection greater than the potential MCLG of 9 |ig/L. These four water
systems were located in Florida, New Mexico and New York.
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B Background Information and Detailed Stage 2 Analysis Occurrence
Measures for 17 Select Regulated Chemical Contaminants
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B.l Chlordane
This chapter on chlordane includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.l.l Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for chlordane on January 30, 1991 (56 FR 3526;
USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) of zero
based on a cancer classification of B2, probable human carcinogen. The NPDWR also
established a maximum contaminant level (MCL) of 2 |ig/L based on analytical feasibility.
Chlordane is regulated as a synthetic organic chemical (SOC) in drinking water. All non-
purchased community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.5 If all 4 samples are non-detections, then
a system serving less than 3,300 people may reduce its collection frequency to 1 sample during
each consecutive compliance period; a system serving more than 3,300 people may reduce its
collection frequency to 2 quarterly samples within a 12-month period during each repeat
compliance period. If a chemical is detected, the system must monitor quarterly until results are
reliably and consistently below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems). If all quarterly samples are below
the MCL, the system may return to annual sampling. If a chemical is detected at a level greater
than the MCL, the system (whether ground water or surface water) must take quarterly samples
until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL,
the system may return to annual sampling.
B.1.2 Occurrence in Drinking Water
The analysis of chlordane occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 128,870
analytical results from 35,685 public water systems (PWSs) during the period from 2006 to
5 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including chlordane, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Two different substitution values -zero and V2 the
minimum reporting level (MRL) value- were used to replace each non-detection record. (The
national modal MRL for chlordane in the dataset is 0.2 |ig/L.) Two arithmetic mean chlordane
concentrations were calculated at each system using the zero and V2 MRL substitution values.
These mean calculations were performed for all systems with chlordane data in the SYR3 ICR
dataset. Then, the percentages of all systems with a mean concentration greater than each
threshold were calculated. For chlordane, EPA generated Stage 2 occurrence estimates relative to
the MCL and the estimated quantitation level (EQL).
Stage 2 Occurrence Estimates
Stage 2 analyses for chlordane are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 2 |ig/L (the MCL) and 1 |ig/L (EQL). Note that
the EQL is equivalent to V2 the MCL. The EQL represents the potential quantitation capabilities
below a practical quantitation level (PQL).6For more information on the new potential
thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e).
6 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical
feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year
Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced.
The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to
evaluate occurrence and exposure for the Stage 2 analyses.
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Exhibit B-l presents the system-level Stage 2 analysis of estimated mean concentrations for
chlordane occurrence in drinking water. Exhibit B-2 presents similar information based on
population served by the systems. Based on the Stage 2 analyses, 1 system (0.003 percent of all
systems), serving 993 people, had an estimated system mean greater than the MCL concentration
of 2 |ig/L. Three water systems (approximately 0.008 percent of all systems) had an estimated
mean greater than the EQL concentration of 1 |ig/L. These 3 systems serve approximately 1,353
people.
Exhibit B-1: Chlordane Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Ground Water
(32,472)
> 2 |jg/L
1
1
0.003%
0.003%
> 1 |jg/L1
3
3
0.009%
0.009%

Surface Water
(3,213)
> 2 |jg/L
0
0
0.000%
0.000%
> 1 |jg/L1
0
0
0.000%
0.000%



Combined Ground &
Surface Water
(35,685)
> 2 |jg/L
1
1
0.003%
0.003%
> 1 |jg/L1
3
3
0.008%
0.008%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Exhibit B-2: Chlordane Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold


Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Ground Water
> 2 |jg/L
993
993
0.001%
0.001%
(89,347,451)
> 1 |jg/L1
1,353
1,353
0.002%
0.002%

Surface Water
> 2 |jg/L
0
0
0.000%
0.000%
(128,289,918)
> 1 |jg/L1
0
0
0.000%
0.000%
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Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0

Combined Ground &
Surface Water
(217,637,369)
> 2 |jg/L
993
993
0.000%
0.000%
> 1 |jg/L1
1,353
1,353
0.001%
0.001%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Data for chlordane were available from 49 states/entities. Four states did not submit data for use
in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the table below because a handful of tribal water systems located
within these two states did submit chlordane data. New Jersey did submit Six-Year data for most
contaminants. There is a statewide waiver for chlordane in New Jersey, however, so no
chlordane data were available from that state.
Exhibit B-3 presents the total number of systems in each state that submitted data for chlordane.
In addition, the geographic distribution of chlordane occurrence in drinking water is illustrated
by showing states with systems with a mean concentration greater than the EQL and MCL
concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.)
Detection rates were low; only one system in New Mexico had an estimated mean concentration
greater than the MCL. Three systems in three states (North Carolina, New Hampshire and New
Mexico) had estimated mean concentrations greater than the EQL of 1 |ig/L.
Exhibit B-3: Chlordane Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a
Mean Concentration
> 1 mq/l3
Systems with a
Mean Concentration
> 2 jjg/L
Number
Percent
Number
Percent
AK
12




AL
383




AR
459




AS
11




AZ
873




CA
1,243




CO
1




CT
1,136




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State
Total Number
of Systems
Systems with a
Mean Concentration
> 1 mq/l3
Systems with a
Mean Concentration
> 2 jjg/L
Number
Percent
Number
Percent
DC
1




FL
2,087




HI
111




IA
3




ID
385




IL
1,467




IN
1,212




KS
87




KY
225




LA
946




MA
565




MD
881




ME
160




Ml
13




MN
920




MO
1,332




MS
5




MT
857




NC
2,348
1
0.04%
0
0.00%
ND
157




NE
696




NH
1,146
1
0.09%
0
0.00%
NJ
0




NM
718
1
0.14%
1
0.14%
NV
309




NY
2,119




OH
31




OK
36




OR
1,118




PA
1,267




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State
Total Number
of Systems
Systems with a
Mean Concentration
> 1 mq/l3
Systems with a
Mean Concentration
> 2 jjg/L
Number
Percent
Number
Percent
Rl
73




SC
497




SD
269




TN
6




TX
3,925




UT
428




VA
254




VT
380




WA
1,998




Wl
1,914




WV
303




WY
318




Total
35,685
3
0.01%
1
0.003%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Exhibit B-4 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for chlordane is presented, as well. New Mexico was the only state with an
estimated system mean concentration greater than the MCL. This system served a total
population of 993 people. Three systems in 3 states, serving 1,353 people, had estimated mean
concentrations greater than EQL (1 |ig/L).
Exhibit B-4: Chlordane Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by
Systems with a Mean
Concentration> 1 H9"-3
Population Served by
Systems with a Mean
Concentration> 2 jjg/L
Population
Percent
Population
Percent
AK
39,530




AL
5,333,035




AR
2,635,934




AS
62,196




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State
Total
Population
Population Served by
Systems with a Mean
Concentration> 1 H9"-3
Population Served by
Systems with a Mean
Concentration> 2 jjg/L
Population
Percent
Population
Percent
AZ
6,487,524




CA
35,723,529




CO
2,020




CT
2,883,135




DC
761,124




FL
18,943,101




HI
1,479,317




IA
166,302




ID
976,042




IL
10,997,826




IN
4,969,942




KS
1,817,722




KY
4,225,473




LA
4,709,163




MA
9,163,377




MD
4,939,436




ME
356,698




Ml
34,902




MN
3,752,545




MO
5,233,314




MS
6,176




MT
845,294




NC
7,832,371
310
0.004%
0
0.00%
ND
592,232




NE
1,659,899




NH
949,308
50
0.01%
0
0.00%
NJ
0




NM
1,940,795
993
0.05%
993
0.05%
NV
2,682,358




NY
10,481,646




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State
Total
Population
Population Served by
Systems with a Mean
Concentration> 1 H9"-3
Population Served by
Systems with a Mean
Concentration> 2 jjg/L
Population
Percent
Population
Percent
OH
755,924




OK
130,809




OR
3,432,307




PA
10,887,488




Rl
989,530




SC
3,623,380




SD
708,340




TN
1,168,508




TX
23,277,937




UT
2,752,741




VA
5,685,070




VT
386,948




WA
4,947,604




Wl
4,236,887




WV
1,500,920




WY
469,710




Total
217,637,369
1,353
0.001%
993
0.0005%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
B.1.3 Summary of Data
A total of 128,870 analytical results from 35,685 PWSs in 49 states/entities were available in the
SYR3 ICR Dataset for chlordane. The Stage 2 analysis of occurrence in drinking water indicated
that 1 ground water system in New Mexico, serving 993 people, had an estimated system mean
concentration of chlordane greater than the MCL concentration of 2 |ig/L. Three ground water
systems, serving 1,353 people, had an estimated mean concentration greater than the EQL of 1
jig/L.
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B.2 cis-l,2-Dichloroethylene
This chapter on cis-l,2-dichloroethylene includes background information such as the regulatory
history and a summary of monitoring requirements, as well as occurrence and exposure estimates
in drinking water. All drinking water occurrence estimates are based on data from the National
Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year
Review (the "SYR3 ICR Dataset").
B.2.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for cis-l,2-dichloroethylene on January 30,
1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level
goal (MCLG) and maximum contaminant level (MCL) of 70 |ig/L. The Agency developed the
MCLG based on a reference dose (RfD) of 10 |ig/kg-day (0.01 mg/kg-day) and a cancer
classification of D, not classifiable as to human carcinogenicity.
cis-l,2-Dichloroethylene is regulated as a volatile organic compound (VOC) in drinking water.
All non-purchased community water systems (CWSs) and non-transient non-community water
systems (NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs
is two compliance periods for ground water systems and one compliance period for surface water
systems.
All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial
three-year compliance period.7 If all four samples are non-detections, then the system may
reduce to annual sampling. After three annual samples without a detection, and upon conducting
a vulnerability assessment, a system may be granted a waiver. During the waiver period, the
ground water system must sample at least once, while surface water system must sample at the
frequency specified by the state. If a compound is detected, the system must take one sample per
quarter until results are below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems). If all quarterly samples are
reliably and consistently below the MCL, the system may return to annual sampling. If a
compound is detected at a level greater than the MCL, the system (whether ground water or
surface water) must take four consecutive quarterly samples until all are below the MCL. If all
quarterly samples are below the MCL, the system may return to annual sampling. If a compound
is detected, the system must also monitor in a similar fashion for vinyl chloride.
B.2.2 Occurrence in Drinking Water
The analysis of cis-l,2-dichloroethylene occurrence presented in the following section is based
on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 376,300
7 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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analytical results from 55,734 public water systems (PWSs) during the period from 2006 to
2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including cis-l,2-dichloroethylene, for
which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant
occurrence by generating estimated long-term mean concentrations of contaminants for each
system. This provides occurrence analyses that are less conservative than the Stage 1 analysis,
since the Stage 2 analysis is based on estimated mean concentrations rather than on a single
maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year)
mean concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for cis-l,2-dichloroethylene in the dataset is 0.5 |ig/L.) Three
arithmetic mean cis-l,2-dichloroethylene concentrations were calculated at each system using
the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for
all systems with cis-l,2-dichloroethylene data in the SYR3 ICR dataset. Then, the percentages of
all systems with a mean concentration greater than each threshold were calculated. For cis-1,2-
dichloroethylene, since there were no analytical method limitations at the potential MCLG, EPA
generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG.
Stage 2 Occurrence Estimates
Stage 2 analyses for cis-l,2-dichloroethylene are summarized in this section. Occurrence
estimates were generated relative to the following thresholds: 70 |ig/L (the MCL) and 10 |ig/L
(the potential MCLG). The potential MCLG is due to changes in the RfD based on new health
effects information. Since the practical quantitation level (PQL) for cis-l,2-dichloroethylene is
less than the possible MCLG, EPA designated the possible MCLG as the threshold for the
occurrence analysis. For more information on the new potential thresholds of concern used in the
SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-5 presents the system-level Stage 2 analysis of estimated mean concentrations for cis-
1,2-dichloroethylene occurrence in drinking water. Exhibit B-6 presents similar information
based on population served by the systems. Based on the Stage 2 analyses, no systems had an
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estimated system mean greater than the MCL concentration of 70 |ig/L. Four systems, serving
5,569 people, had an estimated system mean greater than the potential MCLG concentration of
10 |ig/L.
Exhibit B-5: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Systems
with a Mean Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(51,302)
> 70 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 10 |jg/L1
4
4
4
0.008%
0.008%
0.008%

Surface Water
(4,432)
> 70 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 10 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground &
Surface Water
(55,734)
> 70 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 10 |jg/L1
4
4
4
0.007%
0.007%
0.007%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit B-6: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(110,779,859)
> 70 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 10 |jg/L1
5,569
5,569
5,569
0.005%
0.005%
0.005%

Surface Water
(152,565,123)
> 70 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 10 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground &
Surface Water
> 70 |jg/L
0
0
0
0.000%
0.000%
0.000%
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Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold


Non-detect
Non-detect
Non-detect
Non-detect
Non-detect
Non-detect


values
values
values
values
values
values


= MRL
= 1/2 MRL
= 0
= MRL
= 1/2 MRL
= 0
(263,344,982)
> 10 |jg/L1
5,569
5,569
5,569
0.002%
0.002%
0.002%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Data for cis-l,2-dichloroethylene were available from 50 states/entities. Four states did not
submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi).
Although the States of Colorado and Mississippi did not provide data for any contaminants for
the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of
tribal water systems located within these 2 states did submit cis-l,2-dichloroethylene data.
Exhibit B-7 presents the total number of systems in each state that submitted data for cis-1,2-
dichloroethylene. In addition, the geographic distribution of cis-l,2-dichloroethylene occurrence
in drinking water is illustrated by showing states with systems with a mean concentration greater
than the potential MCLG and MCL concentrations. (Note: Only the V2 MRL substitution results
are presented in this exhibit.) No systems had an estimated mean concentration greater than the
MCL. Four systems in three states (Illinois, North Carolina and Virginia) had estimated mean
concentrations greater than the potential MCLG of 10 |ig/L.
Exhibit B-7: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Systems
with a Mean Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a Mean
Concentration >10 H9"-3
Systems with a Mean
Concentration > 70 jjg/L
Number
Percent
Number
Percent
AK
595




AL
384




AR
461




AS
11




AZ
1,109




CA
3,811




CO
1




CT
1,202




DC
1




FL
2,633




HI
110




IA
1,045




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State
Total Number
of Systems
Systems with a Mean
Concentration >10 H9"-3
Systems with a Mean
Concentration > 70 jjg/L
Number
Percent
Number
Percent
ID
839




IL
1,493
2
0.13%
0
0.00%
IN
1,196




KS
602




KY
227




LA
1,102




MA
721




MD
1,054




ME
784




Ml
2,419




MN
1,462




MO
1,445




MS
5




MT
897




NC
2,356
1
0.04%
0
0.00%
ND
160




NE
705




NH
1,185




NJ
1,434




NM
744




NV
350




NY
2,498




OH
1,922




OK
685




OR
1,132




PA
3,166




Rl
152




SC
494




SD
313




TN
366




TX
4,532




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State
Total Number
of Systems
Systems with a Mean
Concentration >10 H9"-3
Systems with a Mean
Concentration > 70 jjg/L
Number
Percent
Number
Percent
UT
471




VA
1,630
1
0.06%
0
0.00%
VT
634




WA
2,468




Wl
2,026




WV
385




WY
317




Total
55,734
4
0.01%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit B-8 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for cis-l,2-dichloroethylene is presented, as well. As described above, no systems
had an estimated mean concentration greater than the MCL. The 4 systems in 3 states (Illinois,
North Carolina and Virginia with an estimated mean concentration greater than the potential
MCLG (10 |ig/L) serve 5,569 people.
Exhibit B-8: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration >
10 mq/l3
Population Served by Systems
with a Mean Concentration >
70 jjg/L
Population
Percent
Population
Percent
AK
719,561




AL
5,334,584




AR
2,637,712




AS
62,196




AZ
6,669,227




CA
40,601,783




CO
2,020




CT
2,937,643




DC
761,124




FL
19,280,091




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
10 mq/l3
Population Served by Systems
with a Mean Concentration >
70 jjg/L
Population
Percent
Population
Percent
HI
1,402,969




IA
2,743,404




ID
1,219,635




IL
11,019,196
5,490
0.05%
0
0.00%
IN
4,940,108




KS
2,605,030




KY
4,225,914




LA
4,966,653




MA
9,329,953




MD
5,120,409




ME
757,984




Ml
3,470,708




MN
4,373,668




MO
5,293,851




MS
6,176




MT
856,529




NC
7,827,828
54
0.00%
0
0.00%
ND
592,539




NE
1,664,802




NH
961,134




NJ
9,273,130




NM
1,962,298




NV
2,697,555




NY
10,637,039




OH
10,209,121




OK
3,588,559




OR
3,434,191




PA
11,234,684




Rl
1,040,737




SC
3,637,408




SD
757,925




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
10 mq/l3
Population Served by Systems
with a Mean Concentration >
70 jjg/L
Population
Percent
Population
Percent
TN
6,578,052




TX
23,863,702




UT
2,802,068




VA
6,908,704
25
0.00%
0
0.00%
VT
486,604




WA
5,535,827




Wl
4,273,462




WV
1,570,171




WY
469,314




Total
263,344,982
5,569
0.00%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
B.2.3 Summary of Data
A total of 376,300 analytical results from 55,734 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for cis-l,2-dichloroethylene. The Stage 2 analysis of occurrence in drinking
water indicated that zero systems had an estimated system mean concentration of cis-1,2-
dichloroethylene greater than the MCL concentration of 70 |ig/L. Four ground water systems,
serving 5,569 people, had an estimated mean concentration greater than the potential MCLG (10
Hg/L).
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B.3 Cyanide
This chapter on cyanide includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.3.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for cyanide on July 17, 1992 (57 FR 31776;
USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) and
maximum contaminant level (MCL) of 200 |ig/L. The MCLG was developed based on a
reference dose (RfD) of 20 |ig/kg-day and a cancer classification of D, not classifiable as to
human carcinogenicity.
Cyanide is regulated as an inorganic chemical (IOC) in drinking water. All community water
systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to
sample for the IOCs. Cyanide waivers may be granted if a state determines that a system is not
vulnerable to cyanide contamination due to a lack of industrial cyanide sources. The maximum
waiver period for cyanide is one compliance cycle. During this cycle, the system must sample at
least once. (Statewide waivers for cyanide may be granted if all systems in the state are required
to chlorinate.)
Ground water systems must sample once during the initial three-year compliance period. Surface
water systems must sample annually during the initial three-year compliance period. If all
analytical results are less than the MCL, and upon considering other factors which may affect
contaminant concentration, a ground water and surface water system may be granted waiver. If
the results are greater than the MCL, the public water system (PWS) must take one sample per
quarter until results are below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems).8 If all quarterly samples are
reliably and consistently below the MCL, the system may continue at initial monitoring
indefinitely until the state or EPA establishes an alternate schedule.
B.3.2 Occurrence in Drinking Water
The analysis of cyanide occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 119,659
analytical results from 36,907 PWSs during the period from 2006 to 2011. The number of
sample results and systems vary by state, although the state datasets have been reviewed and
checked to ensure adequacy of coverage and completeness.
8 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including cyanide, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for cyanide in the dataset is 10 |ig/L.) Three arithmetic mean
cyanide concentrations were calculated at each system using the zero, V2 MRL and full MRL
substitution values. These mean calculations were performed for all systems with cyanide data in
the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater
than each threshold were calculated. For cyanide, EPA generated Stage 2 occurrence estimates
relative to the MCL and the estimated quantitation level (EQL).
Stage 2 Occurrence Estimates
Stage 2 analyses for cyanide are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 200 |ig/L (the MCL) and 50 |ig/L (the EQL). The
EQL represents the potential quantitation capabilities below a practical quantitation level
(PQL).9 For more information on the new potential thresholds of concern used in the SYR3
Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-9 presents the system-level Stage 2 analysis of estimated mean concentrations for
cyanide occurrence in drinking water. Exhibit B-10 presents similar information based on
population served by the systems. Based on the Stage 2 analyses using the V2 MRL substitution
9 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical
feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year
Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced.
The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to
evaluate occurrence and exposure for the Stage 2 analyses.
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for non-detections, 8 systems (0.022 percent of all systems), serving 80,826 people, had an
estimated system mean greater than the MCL concentration of 200 |ig/L. A total of 98 systems
(0.266 percent of all systems), serving 574,038 people, had an estimated system mean greater
than the EQL concentration of 50 |ig/L.
Exhibit B-9: Cyanide Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Ground Water
(33,842)
> 200 |jg/L
7
7
6
0.021%
0.021%
0.018%
> 50 |jg/L1
93
91
83
0.275%
0.269%
0.245%

Surface Water
(3,065)
> 200 |jg/L
1
1
1
0.033%
0.033%
0.033%
> 50 |jg/L1
7
7
7
0.228%
0.228%
0.228%

Combined Ground &
Surface Water
(36,907)
> 200 |jg/L
8
8
7
0.022%
0.022%
0.019%
> 50 |jg/L1
100
98
90
0.271%
0.266%
0.244%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Exhibit B-10: Cyanide Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served
by Systems with Mean
Concentrations That Are
Greater Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
> 200 |jg/L
2,521
2,521
2,287
0.003%
0.003%
0.003%
(87,768,998)
> 50 |jg/L1
157,428
157,231
154,877
0.179%
0.179%
0.176%

Surface Water
(122,658,983)
> 200 |jg/L
78,305
78,305
78,305
0.064%
0.064%
0.064%
> 50 |jg/L1
416,807
416,807
416,807
0.340%
0.340%
0.340%

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Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served
by Systems with Mean
Concentrations That Are
Greater Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Combined Ground &
Surface Water
(210,427,981)
> 200 |jg/L
80,826
80,826
80,592
0.038%
0.038%
0.038%
> 50 |jg/L1
574,235
574,038
571,684
0.273%
0.273%
0.272%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Data for cyanide were available from 49 states/entities. Four states did not submit data for use in
the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the table below because a handful of tribal water systems located
within these two states did submit cyanide data. South Carolina did submit Six-Year data for
most contaminants. There is a statewide waiver for cyanide in South Carolina, however, so no
cyanide data were available from that state.
Exhibit B-l 1 presents the total number of systems in each state that submitted data for cyanide.
In addition, the geographic distribution of cyanide occurrence in drinking water is illustrated by
showing states with systems with a mean concentration greater than the EQL and MCL
concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) The
distribution of systems with mean concentrations of cyanide is geographically dispersed.
Detection rates were generally low; only four states had an estimated mean concentration greater
than the MCL. (Massachusetts, Minnesota, North Carolina and Nebraska each contained a single
system with a mean concentration greater than the MCL in each state.) A total of 98 systems in
23 states had estimated mean concentrations greater than the EQL of 50 |ig/L.
Exhibit B-11: Cyanide Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a Mean
Concentration > 50 jjg/L3
Systems with a Mean
Concentration > 200 jjg/L
Number
Percent
Number
Percent
AK
491




AL
385
1
0.26%
0
0.00%
AR
460
6
1.30%
0
0.00%
AS
11




AZ
1,057




CA
1,781
6
0.34%
0
0.00%
CO
1




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State
Total Number
of Systems
Systems with a Mean
Concentration > 50 jjg/L3
Systems with a Mean
Concentration > 200 jjg/L
Number
Percent
Number
Percent
CT
1,173
1
0.09%
0
0.00%
DC
1




FL
2,608
4
0.15%
0
0.00%
HI
110




IA
10




ID
126




IL
1,358
1
0.07%
0
0.00%
IN
1,128
2
0.18%
0
0.00%
KS
5




KY
226




LA
1,108




MA
666
2
0.30%
1
0.15%
MD
8




ME
742




Ml
1,847
1
0.05%
0
0.00%
MN
1,143
27
2.36%
5
0.44%
MO
832




MS
5




MT
54




NC
2,182
7
0.32%
1
0.05%
ND
23




NE
689
2
0.29%
1
0.15%
NH
1,155




NJ
1,401
1
0.07%
0
0.00%
NM
742
4
0.54%
0
0.00%
NV
294
1
0.34%
0
0.00%
NY
2,514
11
0.44%
0
0.00%
OH
1,893
1
0.05%
0
0.00%
OK
187




OR
856




PA
1,425




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State
Total Number
of Systems
Systems with a Mean
Concentration > 50 jjg/L3
Systems with a Mean
Concentration > 200 jjg/L
Number
Percent
Number
Percent
Rl
153




SC
0




SD
33




TN
242
1
0.41%
0
0.00%
TX
470
13
2.77%
0
0.00%
UT
479




VA
1,373
1
0.07%
0
0.00%
VT
410




WA
2,198
3
0.14%
0
0.00%
Wl
145
1
0.69%
0
0.00%
WV
391
1
0.26%
0
0.00%
WY
316




Total
36,907
98
0.27%
8
0.02%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Exhibit B-12 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for cyanide is presented, as well. As described above, Massachusetts, Minnesota,
North Carolina and Nebraska were the only four states with an estimated mean concentration
greater than the MCL. A total of 574,038 people were served by the 98 systems in 23 states that
had estimated mean concentrations of cyanide greater than the EQL (50 |ig/L).
Exhibit B-12: Cyanide Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration >
50 jjg/L3
Population Served by Systems
with a Mean Concentration >
200 \iglL
Population
Percent
Population
Percent
AK
673,570




AL
5,336,667
1,800
0.03%
0
0.00%
AR
2,636,302
6,366
0.24%
0
0.00%
AS
62,196




AZ
6,588,496




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
50 jjg/L3
Population Served by Systems
with a Mean Concentration >
200 Mg/L
Population
Percent
Population
Percent
CA
37,838,435
16,380
0.04%
0
0.00%
CO
2,020




CT
2,933,337
50
0.00%
0
0.00%
DC
761,124




FL
19,124,265
1,295
0.01%
0
0.00%
HI
1,471,730




IA
172,941




ID
515,565




IL
10,983,267
80
0.00%
0
0.00%
IN
4,555,819
898
0.02%
0
0.00%
KS
627,486




KY
4,225,513




LA
4,968,920




MA
9,275,574
78,353
0.84%
78,305
0.84%
MD
756




ME
749,486




Ml
982,862
350
0.04%
0
0.00%
MN
3,684,296
11,510
0.31%
2,223
0.06%
MO
2,941,901




MS
6,176




MT
95,088




NC
7,765,979
7,346
0.09%
64
0.00%
ND
66,229




NE
1,659,463
261
0.02%
234
0.01%
NH
958,187




NJ
9,150,992
65
0.00%
0
0.00%
NM
1,955,107
3,160
0.16%
0
0.00%
NV
2,678,248
25
0.00%
0
0.00%
NY
10,465,711
107,749
1.03%
0
0.00%
OH
10,202,452
50
0.00%
0
0.00%
OK
592,288




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
50 jjg/L3
Population Served by Systems
with a Mean Concentration >
200 Mg/L
Population
Percent
Population
Percent
OR
3,141,979




PA
9,952,670




Rl
1,019,797




SC
0




SD
53,644




TN
4,734,392
34,106
0.72%
0
0.00%
TX
6,343,868
301,414
4.75%
0
0.00%
UT
2,816,488




VA
5,599,685
633
0.01%
0
0.00%
VT
385,881




WA
5,389,854
443
0.01%
0
0.00%
Wl
2,238,852
1,162
0.05%
0
0.00%
WV
1,573,115
542
0.03%
0
0.00%
WY
469,308




Total
210,427,981
574,038
0.27%
80,826
0.04%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
B.3.3 Summary of Data
A total of 119,659 analytical results from 36,907 PWSs in 49 states/entities were available in the
SYR3 ICR Dataset for cyanide. The Stage 2 analysis of occurrence in drinking water indicated
that 8 (0.02 percent of all) systems serving 80,826 people (0.038 percent of the population) had
an estimated system mean concentration of cyanide greater than the MCL concentration of 200
|ig/L. A total of 98 systems, serving 574,038 people, had an estimated mean concentration
greater than the EQL (50 |ig/L). The majority of systems with mean concentrations greater than
the MCL and EQL were ground water systems.
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B.4 Endothall
This chapter on endothall includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.4.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for endothall on July 17, 1992 (57 FR 31776;
USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) and a
maximum contaminant level (MCL) of 100 |ig/L. EPA developed the MCLG based on a
reference dose (RfD) of 20 |ig/kg-day (0.02 mg/kg-day) and a cancer classification of D, not
classifiable as to human carcinogenicity.
Endothall is regulated as a synthetic organic chemical (SOC) in drinking water. All non-
purchased community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.10 If all 4 samples are non-detections,
then a system serving less than 3,300 people may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 people may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a chemical is detected, the system must monitor quarterly until
results are reliably and consistently below the MCL (minimum of two quarterly samples for
ground water systems and four quarterly samples for surface water systems). If all quarterly
samples are below the MCL, the system may return to annual sampling. If a chemical is detected
at a level greater than the MCL, the system (whether ground water or surface water) must take
quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are
below the MCL, the system may return to annual sampling.
B.4.2 Occurrence in Drinking Water
The analysis of endothall occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 61,972 analytical
results from 15,538 public water systems (PWSs) during the period from 2006 to 2011. The
10 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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number of sample results and systems vary by state, although the state datasets have been
reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including endothall, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for endothall in the dataset is 9 |ig/L.) Three arithmetic mean
endothall concentrations were calculated at each system using the zero, V2 MRL and full MRL
substitution values. These mean calculations were performed for all systems with endothall data
in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater
than each threshold were calculated. For endothall, since there were no analytical method
limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the
MCL and the potential MCLG.
Stage 2 Occurrence Estimates
Stage 2 analyses for endothall are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 100 |ig/L (the MCL) and 50 |ig/L (the potential
MCLG). The potential MCLG is due to changes in the RfD based on new health effects
information. For more information on the new potential thresholds of concern used in the SYR3
Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-13 presents the system-level Stage 2 analysis of estimated mean concentrations for
endothall occurrence in drinking water. Exhibit B-14 presents similar information based on
population served by the systems. Based on the Stage 2 analyses, one water system
(approximately 0.006 percent of all systems) had an estimated mean greater than 50 |ig/L and
100 |ig/L. This system serves 993 people.
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Exhibit B-13: Endothall Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are
Greater Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(14,033)
> 100 |jg/L
1
1
1
0.007%
0.007%
0.007%
> 50 |jg/L1
1
1
1
0.007%
0.007%
0.007%

Surface Water
(1,505)
> 100 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 50 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground
& Surface Water
(15,538)
> 100 |jg/L
1
1
1
0.006%
0.006%
0.006%
> 50 |jg/L1
1
1
1
0.006%
0.006%
0.006%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit B-14: Endothall Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(61,307,038)
> 100 |jg/L
993
993
993
0.002%
0.002%
0.002%
> 50 |jg/L1
993
993
993
0.002%
0.002%
0.002%

Surface Water
(75,494,691)
> 100 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 50 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground &
Surface Water
(136,801,729)
> 100 |jg/L
993
993
993
0.001%
0.001%
0.001%
> 50 |jg/L1
993
993
993
0.001%
0.001%
0.001%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
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Data for endothall were available from 45 states/entities. Four states did not submit data for use
in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the table below because a handful of tribal water systems located
within these two states did submit endothall data. New Jersey, Rhode Island, South Carolina,
Texas and Vermont did submit Six-Year data for most contaminants. There is a statewide waiver
for endothall in those states, however, so no endothall data were available from them.
Exhibit B-15 presents the total number of systems in each state that submitted data for endothall.
In addition, the geographic distribution of endothall occurrence in drinking water is illustrated by
showing states with systems with a mean concentration greater than the potential MCLG and
MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.)
Only one system had an estimated mean concentration greater than the MCL and the potential
MCLG. This system is located in New Mexico.
Exhibit B-15: Endothall Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a Mean
Concentration > 50 jjg/L3
Systems with a Mean
Concentration >100 jjg/L
Number
Percent
Number
Percent
AK
9




AL
383




AR
459




AS
11




AZ
863




CA
1,157




CO
1




CT
29




DC
1




FL
2,091




HI
115




IA
2




ID
351




IL
1,452




IN
1,210




KS
2




KY
225




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State
Total Number
of Systems
Systems with a Mean
Concentration > 50 jjg/L3
Systems with a Mean
Concentration >100 jjg/L
Number
Percent
Number
Percent
LA
1,091




MA
4




MD
11




ME
12




Ml
22




MN
27




MO
21




MS
5




MT
47




NC
5




ND
23




NE
11




NH
4




NJ
0




NM
717
1
0.14%
1
0.14%
NV
301




NY
80




OH
177




OK
4




OR
1,118




PA
1,249




Rl
0




SC
0




SD
258




TN
6




TX
0




UT
13




VA
8




VT
0




WA
25




Wl
1,914




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State
Total Number
of Systems
Systems with a Mean
Concentration > 50 jjg/L3
Systems with a Mean
Concentration >100 jjg/L


Number
Percent
Number
Percent
WV
18




WY
6




Total
15,538
1
0.01%
1
0.01%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit B-16 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for endothall is presented, as well. As described above, only 1 system in New
Mexico, serving 993 people, had an estimated mean concentration and the potential MCLG.
Exhibit B-16: Endothall Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration >
50 jjg/L3
Population Served by Systems
with a Mean Concentration >
100 Mg/L
Population
Percent
Population
Percent
AK
39,228




AL
5,333,035




AR
2,635,934




AS
62,196




AZ
6,468,762




CA
36,137,032




CO
2,020




CT
245,905




DC
761,124




FL
18,991,343




HI
1,487,191




IA
165,864




ID
903,523




IL
10,996,262




IN
4,769,597




KS
482,004




KY
4,225,473




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
50 jjg/L3
Population Served by Systems
with a Mean Concentration >
100 Mg/L
Population
Percent
Population
Percent
LA
4,961,515




MA
108,884




MD
1,959,910




ME
48,749




Ml
225,565




MN
25,573




MO
1,380,996




MS
6,176




MT
25,192




NC
534,572




ND
66,229




NE
933,101




NH
1,461




NJ
0




NM
1,940,555
993
0.05%
993
0.05%
NV
2,681,616




NY
3,370,044




OH
2,423,043




OK
7,343




OR
3,432,307




PA
10,883,210




Rl
0




SC
0




SD
680,381




TN
1,168,508




TX
0




UT
6,459




VA
839,004




VT
0




WA
695,302




Wl
4,236,887




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
50 jjg/L3
Population Served by Systems
with a Mean Concentration >
100 Mg/L
Population
Percent
Population
Percent
WV
379,363




WY
73,291




Total
136,801,729
993
0.001%
993
0.001%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
B.4.3 Summary of Data
A total of 61,972 analytical results from 15,538 PWSs in 45 states/entities were available in the
SYR3 ICR Dataset for endothall. The Stage 2 analysis of occurrence in drinking water indicated
that 1 ground water system in New Mexico, serving 993 people, had an estimated system mean
concentration of endothall greater than the MCL concentration of 100 |ig/L and the potential
MCLG of 50 |ig/L.
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B.5 Fluoride
This chapter on fluoride includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.5.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for fluoride on April 2, 1986 (51 FR 11396;
USEPA, 1986). The NPDWR established a maximum contaminant level goal (MCLG) and a
maximum contaminant level (MCL) of 4,000 |ig/L. EPA based the MCLG on a reference dose
(RfD) of 0.11 mg/kg-day (0.025 mg/kg-day) to avoid skeletal fluorosis; fluoride was not
classified as carcinogenicity for humans. EPA also established a secondary MCL of 2,000 |ig/L
to protect against severe dental fluorosis. The secondary MCL is not enforceable, but triggers a
public notification requirement.
Fluoride is regulated as an inorganic chemical (IOC) in drinking water. All community water
systems (CWSs) and non-transient non-community water systems (NTNCWSs) must sample for
the regulated IOCs. The maximum waiver period for IOCs is one compliance cycle. During this
cycle, the system must sample at least once.
Ground water systems must sample once during the initial three-year compliance period. Surface
water systems must sample annually during the initial three-year compliance period. If all
analytical results are less than the MCL, and upon considering reported concentrations, degrees
of variation in reported concentration and other factors which may affect contaminant
concentration, a ground water and surface water system may be granted a waiver. If the results
are greater than the MCL, the public water system (PWS) must take one sample per quarter until
results are below the MCL (minimum of two quarterly samples for ground water systems and
four quarterly samples for surface water systems).11 If all quarterly samples are reliably and
consistently below the MCL, the system may continue at initial monitoring indefinitely until the
state or EPA establishes an alternate schedule.
B.5.2 Occurrence in Drinking Water
The analysis of fluoride occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 256,237
analytical results from regulated public water systems (PWSs) during the period from 2006 to
2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
11 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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EPA used a two-stage analytical approach to estimate the national contaminant occurrence of
fluoride in drinking water using the SYR3 ICR Dataset. The "Stage 1" analysis is a simple non-
parametric analysis with accompanying descriptive statistics of national contaminant occurrence
among regulated public water systems. The results are simple counts of the number and
percentage of systems and population served by systems that have at least one compliance
monitoring sample result exceeding a specified concentration threshold. The Stage 1 analysis
provides occurrence assessments that are more conservative and may be more reflective of
potential acute exposure than the assessments from the Stage 2 analyses. Section 6 provides the
details for the Stage 1 analysis.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including fluoride, for which Stage 2
analyses were warranted. The Stage 2 analysis is an assessment of national contaminant
occurrence based on estimates of long-term mean concentrations of contaminants for each
system. This analysis method provides occurrence estimates that are less conservative than the
Stage 1 analysis, which relies on a single maximum concentration. Also, because the Stage 2
analyses generate long-term (multi-year) mean concentration estimates for contaminant
occurrence at systems, the analyses can support assessments of population served by systems that
may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, EPA calculated system arithmetic means using all sample detection
records and all non-detection records, excluding samples for fluoridated water (i.e., water to
which a system adds fluoride to maintain a concentration in the 700 to 1,200 |ig/L range).12
There are three different substitution values -zero, V2 the minimum reporting level (MRL) value
and the full MRL value-to replace each non-detection record. (The national modal MRL for the
fluoride dataset is 50 |ig/L.) Thus, there are three arithmetic mean fluoride concentrations
calculated for each system using the zero, V2 MRL and full MRL substitution values. There are
mean estimates for all systems with fluoride data in the SYR3 ICR dataset. There are
corresponding percentages that reflect the share of all systems with a mean concentration greater
than each threshold. For fluoride, since there were no analytical method limitations at the
potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the
potential MCLG.
Stage 2 Occurrence Estimates
This section provides summary results of the Stage 2 analyses for fluoride. Occurrence estimates
were generated relative to several thresholds: 4,000 |ig/L (the MCL), 900 |ig/L (the potential
MCLG value) and four interim values - 3,000 |ig/L, 2,000 |ig/L, 1,500 |ig/L and 1,000 |ig/L.
The potential MCLG is due to changes in the RfD based on new health effects information. For
more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses,
refer to USEPA (2016d) and (2016e).
12 The fluoridation range during the sample period was 700 to 1,200 |ig/L. but the current fluoridation target is 700
|ig/L. Thus, historical samples of fluoridated water could exceed of the fluoride concentration thresholds that
overlap the fluoridation range, whereas samples that reflect the current target would not. Therefore, EPA excluded
samples for fluoridated water to remove an upward bias in the occurrence estimates.
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Exhibit B-17 presents the system-level Stage 2 results of estimated mean concentrations for
fluoride occurrence in drinking water relative to various thresholds. Exhibit B-18 presents
similar information based on population served by the systems. Based on the Stage 2 analyses,
134 systems serving almost 60,000 people had an estimated system mean greater than the MCL
concentration of 4,000 |ig/L. More than 5,000 systems, serving 13 million people, had an
estimated system mean greater than the potential MCLG of 900 |ig/L.
Exhibit B-17: Fluoride Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are
Greater Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(44,033)
>4,000 |jg/L
134
134
134
0.30%
0.30%
0.30%
>3,000 |jg/L
330
330
330
0.75%
0.75%
0.75%
>2,000 |jg/L
964
964
964
2.19%
2.19%
2.19%
>1,500 |jg/L
1,952
1,951
1,950
4.43%
4.43%
4.43%
>1,000 |jg/L
4,218
4,210
4,205
9.58%
9.56%
9.55%
>900 |jg/L1
4,898
4,892
4,884
11.12%
11.11%
11.09%

Surface Water
(3,194)
>4,000 |jg/L
0
0
0
0.00%
0.00%
0.00%
>3,000 |jg/L
3
3
3
0.09%
0.09%
0.09%
>2,000 |jg/L
8
8
8
0.25%
0.25%
0.25%
>1,500 |jg/L
21
20
20
0.66%
0.63%
0.63%
>1,000 |jg/L
139
138
137
4.35%
4.32%
4.29%
>900 |jg/L1
163
161
160
5.10%
5.04%
5.01%

Combined Ground &
Surface Water
(47,227)
>4,000 |jg/L
134
134
134
0.28%
0.28%
0.28%
>3,000 |jg/L
333
333
333
0.71%
0.71%
0.71%
>2,000 |jg/L
972
972
972
2.06%
2.06%
2.06%
>1,500 |jg/L
1,973
1,971
1,970
4.18%
4.17%
4.17%
>1,000 |jg/L
4,357
4,348
4,342
9.23%
9.21%
9.19%
>900 |jg/L1
5,061
5,053
5,044
10.72%
10.70%
10.68%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
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Exhibit B-18: Fluoride Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Ground Water
(96,498,333)
>4,000 |jg/L
59,911
59,911
59,911
0.06%
0.06%
0.06%
>3,000 |jg/L
582,629
582,629
582,629
0.60%
0.60%
0.60%
>2,000 |jg/L
1,503,017
1,503,017
1,503,017
1.56%
1.56%
1.56%
>1,500 |jg/L
2,755,639
2,743,439
2,743,029
2.86%
2.84%
2.84%
>1,000 |jg/L
8,121,680
8,114,433
8,112,955
8.42%
8.41%
8.41%
>900 |jg/L1
10,059,180
10,006,942
9,926,430
10.42%
10.37%
10.29%

Surface Water
(92,688,121)
>4,000 |jg/L
0
0
0
0.00%
0.00%
0.00%
>3,000 |jg/L
20,512
20,512
20,512
0.02%
0.02%
0.02%
>2,000 |jg/L
33,297
33,297
33,297
0.04%
0.04%
0.04%
>1,500 |jg/L
119,381
102,529
102,529
0.13%
0.11%
0.11%
>1,000 |jg/L
2,223,360
2,222,803
2,219,484
2.40%
2.40%
2.39%
>900 |jg/L1
3,522,836
3,397,425
3,394,742
3.80%
3.67%
3.66%

Combined Ground &
Surface Water
(189,186,454)
>4,000 |jg/L
59,911
59,911
59,911
0.03%
0.03%
0.03%
>3,000 |jg/L
603,141
603,141
603,141
0.32%
0.32%
0.32%
>2,000 |jg/L
1,536,314
1,536,314
1,536,314
0.81%
0.81%
0.81%
>1,500 |jg/L
2,875,020
2,845,968
2,845,558
1.52%
1.50%
1.50%
>1,000 |jg/L
10,345,040
10,337,236
10,332,439
5.47%
5.46%
5.46%
>900 |jg/L1
13,582,016
13,404,367
13,321,172
7.18%
7.09%
7.04%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Data for fluoride were available from 49 states/entities. Four states did not submit data for use in
the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the State of
Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, this state is
included in the state-level results shown below because a handful of tribal water systems located
within this state submitted fluoride data.
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Exhibit B-19 presents the total number of systems in each state that submitted data for fluoride,
excluding systems that only submitted data for fluoridated water. It also shows the exceedance
values for the potential MCLG (900 |ig/L) and the next two highest thresholds (1,000 |ig/L and
1,500 |ig/L), (Note: These results reflect the '/2 MRL substitution case).
Exhibit B-19: Fluoride Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total
Number of
Systems
Systems with a
Mean Concentration
> 1,500 jjg/L
Systems with a
Mean Concentration
> 1,000 jjg/L
Systems with a
Mean Concentration
> 900 jjg/L3
Number
Percent
Number
Percent
Number
Percent
AK
489
1
0.20%
7
1.43%
7
1.43%
AL
343
4
1.17%
16
4.66%
18
5.25%
AR
420
7
1.67%
13
3.10%
14
3.33%
AS
11






AZ
899
90
10.01%
164
18.24%
197
21.91%
CA
3,902
74
1.90%
145
3.72%
176
4.51%
CT
1,168
11
0.94%
25
2.14%
27
2.31%
DC
1
0
0.00%
0
0.00%
1
100.00%
FL
2,589
38
1.47%
88
3.40%
112
4.33%
HI
113






IA
370
41
11.08%
78
21.08%
84
22.70%
ID
680
18
2.65%
38
5.59%
45
6.62%
IL
653
80
12.25%
223
34.15%
268
41.04%
IN
942
54
5.73%
201
21.34%
251
26.65%
KS
564
18
3.19%
52
9.22%
62
10.99%
KY
73
6
8.22%
17
23.29%
17
23.29%
LA
1,100
21
1.91%
42
3.82%
51
4.64%
MA
639
9
1.41%
28
4.38%
37
5.79%
MD
164
3
1.83%
9
5.49%
9
5.49%
ME
755
13
1.72%
60
7.95%
75
9.93%
Ml
2,259
41
1.81%
167
7.39%
204
9.03%
MN
615
14
2.28%
206
33.50%
216
35.12%
MO
1,386
41
2.96%
113
8.15%
133
9.60%
MS
5
0
0.00%
3
60.00%
5
100.00%
MT
785
39
4.97%
66
8.41%
75
9.55%
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State
Total
Number of
Systems
Systems with a
Mean Concentration
> 1,500 jjg/L
Systems with a
Mean Concentration
> 1,000 jjg/L
Systems with a
Mean Concentration
> 900 jjg/L3
Number
Percent
Number
Percent
Number
Percent
NC
2,121
45
2.12%
107
5.04%
130
6.13%
ND
146
19
13.01%
56
38.36%
59
40.41%
NE
685
3
0.44%
37
5.40%
47
6.86%
NH
1,170
103
8.80%
168
14.36%
192
16.41%
NJ
1,396
5
0.36%
17
1.22%
22
1.58%
NM
748
78
10.43%
131
17.51%
161
21.52%
NV
330
21
6.36%
39
11.82%
50
15.15%
NY
2,389
15
0.63%
36
1.51%
49
2.05%
OH
1,711
149
8.71%
396
23.14%
436
25.48%
OK
599
26
4.34%
45
7.51%
52
8.68%
OR
847
16
1.89%
25
2.95%
31
3.66%
PA
1,369
3
0.22%
10
0.73%
14
1.02%
Rl
151
3
1.99%
10
6.62%
11
7.28%
SC
537
32
5.96%
51
9.50%
55
10.24%
SD
158
21
13.29%
31
19.62%
37
23.42%
TN
126
0
0.00%
12
9.52%
13
10.32%
TX
4,596
507
11.03%
898
19.54%
1,011
22.00%
UT
477
5
1.05%
11
2.31%
12
2.52%
VA
1,524
204
13.39%
260
17.06%
273
17.91%
VT
417
1
0.24%
6
1.44%
7
1.68%
WA
2,196
32
1.46%
53
2.41%
65
2.96%
Wl
1,997
22
1.10%
101
5.06%
138
6.91%
WV
297
4
1.35%
13
4.38%
16
5.39%
WY
315
34
10.79%
74
23.49%
88
27.94%
Total
47,227
1,971
4.17%
4,348
9.21%
5,053
10.70%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded the threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Exhibit B-20 provides the corresponding state-level populations served by systems that have a
mean concentration greater than the thresholds show above. Again, these estimates exclude
population served by systems that provided only samples for fluoridated water.
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Exhibit B-20: Fluoride Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by
Systems with a
Mean Concentration
> 1,500 jjg/L
Population Served by
Systems with a
Mean Concentration
> 1,000 jjg/L
Population Served by
Systems with a
Mean Concentration
> 900 jjg/L1
Population
Percent
Population
Percent
Population
Percent
AK
653,758
173
0.03%
16,978
2.60%
16,978
2.60%
AL
3,951,346
22,703
0.57%
106,577
2.70%
107,762
2.73%
AR
2,154,639
7,179
0.33%
25,198
1.17%
25,228
1.17%
AS
62,196






AZ
6,507,196
144,530
2.22%
473,064
7.27%
663,864
10.20%
CA
41,166,323
326,394
0.79%
708,080
1.72%
804,725
1.95%
CT
2,848,818
1,627
0.06%
3,220
0.11%
3,405
0.12%
DC
761,124
0
0.00%
0
0.00%
761,124
100.00%
FL
18,078,815
15,387
0.09%
90,117
0.50%
135,945
0.75%
HI
1,486,472






IA
905,648
41,299
4.56%
205,076
22.64%
222,603
24.58%
ID
1,152,093
31,922
2.77%
69,957
6.07%
70,542
6.12%
IL
3,702,273
173,654
4.69%
1,365,422
36.88%
1,864,804
50.37%
IN
1,913,536
195,536
10.22%
701,799
36.68%
754,671
39.44%
KS
1,871,086
14,295
0.76%
116,603
6.23%
129,838
6.94%
KY
528,053
12,876
2.44%
184,200
34.88%
184,200
34.88%
LA
4,312,127
108,424
2.51%
144,272
3.35%
155,410
3.60%
MA
7,821,027
676
0.01%
117,086
1.50%
274,799
3.51%
MD
35,504
260
0.73%
3,035
8.55%
3,035
8.55%
ME
445,391
1,537
0.35%
135,959
30.53%
137,673
30.91%
Ml
3,038,489
13,690
0.45%
219,941
7.24%
230,257
7.58%
MN
788,703
5,432
0.69%
687,349
87.15%
692,644
87.82%
MO
2,663,227
55,819
2.10%
285,286
10.71%
446,999
16.78%
MS
6,176
0
0.00%
2,092
33.87%
6,176
100.00%
MT
740,136
16,446
2.22%
25,633
3.46%
27,817
3.76%
NC
3,927,168
77,947
1.98%
278,606
7.09%
315,742
8.04%
ND
412,916
8,139
1.97%
317,175
76.81%
318,479
77.13%
NE
1,652,769
2,138
0.13%
116,350
7.04%
163,539
9.89%
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State
Total
Population
Population Served by
Systems with a
Mean Concentration
> 1,500 jjg/L
Population Served by
Systems with a
Mean Concentration
> 1,000 jjg/L
Population Served by
Systems with a
Mean Concentration
> 900 jjg/L1
Population
Percent
Population
Percent
Population
Percent
NH
776,183
15,863
2.04%
47,122
6.07%
51,738
6.67%
NJ
9,129,229
14,346
0.16%
117,773
1.29%
157,843
1.73%
NM
1,974,790
127,596
6.46%
234,708
11.89%
315,293
15.97%
NV
2,418,044
16,184
0.67%
89,040
3.68%
97,135
4.02%
NY
4,916,027
11,627
0.24%
71,637
1.46%
77,711
1.58%
OH
1,873,754
97,603
5.21%
513,809
27.42%
544,330
29.05%
OK
2,418,323
23,683
0.98%
86,054
3.56%
192,024
7.94%
OR
2,928,203
11,605
0.40%
13,179
0.45%
14,260
0.49%
PA
5,307,038
173
0.00%
19,316
0.36%
19,837
0.37%
Rl
1,019,737
1,678
0.16%
3,008
0.29%
3,931
0.39%
SC
2,376,386
103,163
4.34%
135,290
5.69%
153,744
6.47%
SD
107,316
15,669
14.60%
24,356
22.70%
27,900
26.00%
TN
1,822,566
0
0.00%
102,634
5.63%
124,741
6.84%
TX
23,510,681
928,382
3.95%
1,951,430
8.30%
2,351,648
10.00%
UT
2,816,964
29,158
1.04%
31,543
1.12%
31,813
1.13%
VA
2,653,609
86,467
3.26%
183,087
6.90%
241,509
9.10%
VT
345,674
32
0.01%
787
0.23%
812
0.23%
WA
4,094,793
27,121
0.66%
91,164
2.23%
225,593
5.51%
Wl
4,251,831
43,181
1.02%
100,169
2.36%
117,987
2.77%
WV
389,087
2,489
0.64%
66,177
17.01%
74,770
19.22%
WY
469,210
11,865
2.53%
55,878
11.91%
61,489
13.10%
Total
189,186,454
2,845,968
1.50%
10,337,236
5.46%
13,404,367
7.09%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded the threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
B.5.3 Summary of Data
A total of 256,237 analytical results from 47,227 PWSs in 49 states/entities were available in the
SYR3 ICR Dataset for fluoride. The Stage 2 analysis of occurrence in drinking water indicated
that 134 systems had an estimated system mean concentration of fluoride greater than the MCL
concentration of 4,000 |ig/L. More than 5,000 water systems, serving more than 13 million
people had an estimated mean concentration greater than the potential MCLGs of 900 |ig/L.
These water systems are located in almost every state.
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B.6 Heptachlor
This chapter on heptachlor includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.6.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for heptachlor on January 30, 1991 (56 FR
3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) of
zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also
established a maximum contaminant level (MCL) of 0.4 |ig/L based on analytical feasibility.
Heptachlor is regulated as a synthetic organic chemical (SOC) in drinking water. All non-
purchased community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.13 If all 4 samples are non-detections,
then a system serving less than 3,300 people may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 people may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a chemical is detected, the system must monitor quarterly until
results are reliably and consistently below the MCL (minimum of two quarterly samples for
ground water systems and four quarterly samples for surface water systems). If all quarterly
samples are below the MCL, the system may return to annual sampling. If a chemical is detected
at a level greater than the MCL, the system (whether ground water or surface water) must take
quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are
below the MCL, the system may return to annual sampling.
B.6.2 Occurrence in Drinking Water
The analysis of heptachlor occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 137,286
analytical results from 38,691 public water systems (PWSs) during the period from 2006 to
13 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including heptachlor, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Two different substitution values -zero and V2 the
minimum reporting level (MRL) value- were used to replace each non-detection record. (The
national modal MRL for heptachlor in the dataset is 0.04 |ig/L.) Two arithmetic mean heptachlor
concentrations were calculated at each system using the zero and V2 MRL substitution values.
These mean calculations were performed for all systems with heptachlor data in the SYR3 ICR
dataset. Then, the percentages of all systems with a mean concentration greater than each
threshold were calculated. For heptachlor, EPA generated Stage 2 occurrence estimates relative
to the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL.
Stage 2 Occurrence Estimates
Stage 2 analyses for heptachlor are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 0.4 |ig/L (the MCL), 0.2 |ig/L (V2 the MCL and
two times the EQL) and 0.1 |ig/L (the EQL). The EQL represents the potential quantitation
capabilities below a practical quantitation level (PQL).14For more information on the new
14 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical
feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year
Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL
represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and
exposure for the Stage 2 analyses.
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potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and
(2016e).
Exhibit B-21 presents the system-level Stage 2 analysis of estimated mean concentrations for
heptachlor occurrence in drinking water. Exhibit B-22 presents similar information based on
population served by the systems. Based on the Stage 2 analyses, three water systems
(approximately 0.008 percent of all systems) had an estimated mean greater than the MCL of 0.4
|ig/L, as well as the EQL of 0.1 |ig/L. These 3 systems serve approximately 1,643 people.
Exhibit B-21: Heptachlor Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Ground Water
(35,408)
> 0.4 |jg/L
3
2
0.008%
0.006%
> 0.2 |jg/L1
3
3
0.008%
0.008%
>0.1 |jg/L2
3
3
0.008%
0.008%

Surface Water
(3,283)
> 0.4 |jg/L
0
0
0.000%
0.000%
> 0.2 |jg/L1
0
0
0.000%
0.000%
>0.1 |jg/L2
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(38,691)
> 0.4 |jg/L
3
2
0.008%
0.005%
> 0.2 |jg/L1
3
3
0.008%
0.008%
>0.1 |jg/L2
3
3
0.008%
0.008%
1	This threshold is equal to % the MCL and two times the EQL.
2	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
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Exhibit B-22: Heptachlor Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Ground Water
(92,583,244)
> 0.4 |jg/L
1,643
1,543
0.002%
0.002%
> 0.2 |jg/L1
1,643
1,643
0.002%
0.002%
>0.1 |jg/L2
1,643
1,643
0.002%
0.002%

Surface Water
(137,249,041)
> 0.4 |jg/L
0
0
0.000%
0.000%
> 0.2 |jg/L1
0
0
0.000%
0.000%
>0.1 |jg/L2
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(229,832,285)
> 0.4 |jg/L
1,643
1,543
0.001%
0.001%
> 0.2 |jg/L1
1,643
1,643
0.001%
0.001%
>0.1 |jg/L2
1,643
1,643
0.001%
0.001%
1	This threshold is equal to % the MCL and two times the EQL.
2	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Data for heptachlor were available from 50 states/entities. Four states did not submit data for use
in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the count of 50 states because a handful of tribal water systems
located within these 2 states did submit heptachlor data.
Exhibit B-23 presents the total number of systems in each state that submitted data for
heptachlor. In addition, the geographic distribution of heptachlor occurrence in drinking water is
illustrated by showing states with systems with a mean concentration greater than the EQL, V2
MCL (or two times the EQL) and MCL concentrations. (Note: Only the V2 MRL substitution
results are presented in this exhibit.) Detection rates of heptachlor were low; three states each
had a single system with an estimated mean concentration greater than the MCL (Maryland, New
Mexico and New York). The same three systems had estimated mean concentrations greater than
V2 the MCL and EQL, as well.
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Exhibit B-23: Heptachlor Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total
Number of
Systems
Systems with a
Mean Concentration
>0.1 mq/l3
Systems with a
Mean Concentration
> 0.2 jjg/L4
Systems with a
Mean Concentration
> 0.4 jjg/L


Number
Percent
Number
Percent
Number
Percent
AK
13






AL
383






AR
459






AS
11






AZ
872






CA
1,279






CO
1






CT
1,136






DC
1






FL
2,091






HI
111






IA
3






ID
390






IL
1,468






IN
1,213






KS
87






KY
225






LA
1,102






MA
566






MD
881
1
0.11%
1
0.11%
1
0.11%
ME
173






Ml
2,439






MN
920






MO
1,332






MS
5






MT
857






NC
2,348






ND
157






NE
703






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State
Total
Number of
Systems
Systems with a
Mean Concentration
>0.1 mq/l3
Systems with a
Mean Concentration
> 0.2 jjg/L4
Systems with a
Mean Concentration
> 0.4 jjg/L
Number
Percent
Number
Percent
Number
Percent
NH
1,146






NJ
46






NM
718
1
0.14%
1
0.14%
1
0.14%
NV
310






NY
2,121
1
0.05%
1
0.05%
1
0.05%
OH
33






OK
36






OR
1,119






PA
1,048






Rl
102






SC
497






SD
269






TN
6






TX
4,422






UT
428






VA
254






VT
380






WA
1,996






Wl
1,914






WV
302






WY
318






Total
38,691
3
0.01%
3
0.01%
3
0.01%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
4	This threshold is equal to % the MCL and two times the EQL.
Exhibit B-24 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for heptachlor is presented, as well. Three states (Maryland, New Mexico and
New York) contained a single system with an estimated mean concentration greater than the
MCL, V2 MCL and EQL. These 3 systems served a total of 1,643 people.
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Exhibit B-24: Heptachlor Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by
Systems with a
Mean Concentration
>0.1 mq/l3
Population Served by
Systems with a
Mean Concentration
> 0.2 jjg/L4
Population Served by
Systems with a
Mean Concentration
> 0.4 jjg/L
Population
Percent
Population
Percent
Population
Percent
AK
40,300






AL
5,333,035






AR
2,635,934






AS
62,196






AZ
6,484,144






CA
35,713,404






CO
2,020






CT
2,883,135






DC
761,124






FL
18,991,343






HI
1,479,317






IA
166,302






ID
980,149






IL
10,998,526






IN
5,017,598






KS
1,817,722






KY
4,225,473






LA
4,966,772






MA
9,164,737






MD
4,939,436
100
0.00%
100
0.00%
100
0.00%
ME
367,408






Ml
7,221,983






MN
3,752,545






MO
5,233,314






MS
6,176






MT
845,294






NC
7,832,371






ND
592,232






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State
Total
Population
Population Served by
Systems with a
Mean Concentration
>0.1 mq/l3
Population Served by
Systems with a
Mean Concentration
> 0.2 jjg/L4
Population Served by
Systems with a
Mean Concentration
> 0.4 jjg/L
Population
Percent
Population
Percent
Population
Percent
NE
1,662,774






NH
949,308






NJ
4,123,518






NM
1,940,795
993
0.05%
993
0.05%
993
0.05%
NV
2,682,465






NY
10,481,222
550
0.01%
550
0.01%
550
0.01%
OH
756,016






OK
145,992






OR
3,432,424






PA
10,847,346






Rl
1,002,727






SC
3,623,380






SD
708,340






TN
1,168,508






TX
23,814,787






UT
2,752,741






VA
5,685,070






VT
386,948






WA
4,947,453






Wl
4,236,887






WV
1,499,884






WY
469,710






Total
229,832,285
1,643
0.00%
1,643
0.00%
1,643
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
4	This threshold is equal to % the MCL and two times the EQL.
B.6.3 Summary of Data
A total of 137,286 analytical results from 38,691 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for heptachlor. The Stage 2 analysis of occurrence in drinking water
indicated that 3 ground water systems, serving 1,643 people, had an estimated system mean
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concentration of heptachlor greater than the MCL concentration of 0.4 |ig/L. The same three
systems also had an estimated mean concentration greater than V2 the MCL (0.2 |ig/L) and the
EQL (0.1 |ig/L). These systems were located in Maryland, New Mexico and New York.
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B.7 Heptachlor Epoxide
This chapter on heptachlor epoxide includes background information such as the regulatory
history and a summary of monitoring requirements, as well as occurrence and exposure estimates
in drinking water. All drinking water occurrence estimates are based on data from the National
Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year
Review (the "SYR3 ICR Dataset").
B.7.1 Background
On January 30, 1991, the United States Environmental Protection Agency (EPA) published the
current National Primary Drinking Water Regulations (NPDWR) for heptachlor epoxide, a
product of heptachlor degradation (56 FR 3526; USEPA, 1991a). The NPDWR established a
maximum contaminant level goal (MCLG) of zero based on a cancer classification of B2,
probable human carcinogen. The NPDWR also established a maximum contaminant level
(MCL) of 0.2 |ig/L based on analytical feasibility.
Heptachlor epoxide is regulated as a synthetic organic chemical (SOC) in drinking water. All
non-purchased community water systems (CWSs) and non-transient non-community water
systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon
a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.15 If all 4 samples are non-detections,
then a system serving less than 3,300 persons may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 persons may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a chemical is detected, the system must monitor quarterly until
results are reliably and consistently below the MCL (minimum of two quarterly samples for
ground water systems and four quarterly samples for surface water systems). If all quarterly
samples are below the MCL, the system may return to annual sampling. If a chemical is detected
at a level greater than the MCL, the system (whether ground water or surface water) must take
quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are
below the MCL, the system may return to annual sampling.
B.7.2 Occurrence in Drinking Water
The analysis of heptachlor epoxide occurrence presented in the following section is based on
state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 137,081
analytical results from 38,625 public water systems (PWSs) during the period from 2006 to
2011. The number of sample results and systems vary by state, although the state datasets have
15 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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been reviewed and checked to ensure adequacy of coverage and completeness. The national
modal minimum reporting level (MRL) for heptachlor epoxide in the dataset is 0.02 |ig/L.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including heptachlor epoxide, for which
Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant
occurrence by generating estimated long-term mean concentrations of contaminants for each
system. This provides occurrence analyses that are less conservative than the Stage 1 analysis,
since the Stage 2 analysis is based on estimated mean concentrations rather than on a single
maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year)
mean concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means that were calculated using all sample
detection records and all non-detection records. Two different substitution values -zero and V2
the MRL value- were used to replace each non-detection record. (The national modal MRL for
heptachlor epoxide in the dataset is 0.02 |ig/L.) Two arithmetic mean heptachlor epoxide
concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution
values. These mean calculations were performed for all systems with data in the SYR3 ICR
dataset. Then, the percentages of all systems with a mean concentration greater than each
threshold were calculated. For heptachlor epoxide, EPA generated Stage 2 occurrence estimates
relative to the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL.
Stage 2 Occurrence Estimates
Stage 2 analyses for heptachlor epoxide are summarized in this section. Occurrence estimates
were generated relative to the following thresholds: 0.2 |ig/L (the MCL), 0.1 |ig/L (1/2 the
MCL), 0.08 |ig/L (two times the EQL) and 0.04 |ig/L (the EQL). The EQL represents the
potential quantitation capabilities below a practical quantitation level (PQL).16For more
16 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical
feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year
Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced.
The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to
evaluate occurrence and exposure for the Stage 2 analyses.
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information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer
to USEPA (2016d) and (2016e).
Exhibit B-25 presents the system-level Stage 2 analysis of estimated mean concentrations for
heptachlor epoxide occurrence in drinking water. Exhibit B-26 presents similar information
based on population served by the systems. Based on the Stage 2 analyses, 2 water systems
(approximately 0.005 percent of all systems) had an estimated mean greater than 0.2 |ig/L (the
MCL). These 2 systems serve 1,543 people. Fourteen systems (0.036 percent of all systems),
serving 11,659 persons, had an estimated system mean greater than the EQL concentration of
0.04 |ig/L.
Exhibit B-25: Heptachlor Epoxide Stage 2 Analysis - Summary of Systems with a
Mean Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= 1/2 MRL
Non-detect values
= 0
Non-detect
values
= 1/2 MRL
Non-detect values
= 0
Ground Water
(35,355)
> 0.2 |jg/L
2
2
0.006%
0.006%
> 0.1 |jg/L
6
6
0.017%
0.017%
> 0.08 |jg/L
7
7
0.020%
0.020%
> 0.04 |jg/L1
14
14
0.040%
0.040%

Surface Water
(3,270)
> 0.2 |jg/L
0
0
0.000%
0.000%
> 0.1 |jg/L
0
0
0.000%
0.000%
> 0.08 |jg/L
0
0
0.000%
0.000%
> 0.04 |jg/L1
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(38,625)
> 0.2 |jg/L
2
2
0.005%
0.005%
> 0.1 |jg/L
6
6
0.016%
0.016%
> 0.08 |jg/L
7
7
0.018%
0.018%
> 0.04 |jg/L1
14
14
0.036%
0.036%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
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Exhibit B-26: Heptachlor Epoxide Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect values
= 0
Ground Water
(92,692,937)
> 0.2 |jg/L
1,543
1,543
0.002%
0.002%
> 0.1 |jg/L
2,461
2,461
0.003%
0.003%
> 0.08 |jg/L
2,700
2,700
0.003%
0.003%
> 0.04 |jg/L1
11,659
11,659
0.013%
0.013%

Surface Water
(137,139,953)
> 0.2 |jg/L
0
0
0.000%
0.000%
> 0.1 |jg/L
0
0
0.000%
0.000%
> 0.08 |jg/L
0
0
0.000%
0.000%
> 0.04 |jg/L1
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(229,832,890)
> 0.2 |jg/L
1,543
1,543
0.001%
0.001%
> 0.1 |jg/L
2,461
2,461
0.001%
0.001%
> 0.08 |jg/L
2,700
2,700
0.001%
0.001%
> 0.04 |jg/L1
11,659
11,659
0.005%
0.005%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Data for heptachlor epoxide were available from 50 states/entities. Four states did not submit
data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although
the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3
ICR Dataset, these states are included in the count of 50 states because a handful of tribal water
systems located within these 2 states did submit heptachlor epoxide data.
Exhibit B-27 presents the total number of systems in each state that submitted data for heptachlor
epoxide. In addition, the geographic distribution of heptachlor epoxide occurrence in drinking
water is illustrated by showing states with systems with a mean concentration greater than the
EQL, two times the EQL, V2 MCL and MCL concentrations. (Note: Only the V2 MRL substitution
results are presented in this exhibit.) Detection rates of heptachlor epoxide were low; only two
systems in states (New Mexico and New York) had an estimated mean concentration greater than
the MCL. Six systems in six states had estimated mean concentrations greater than V2 the MCL.
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Exhibit B-27: Heptachlor Epoxide Stage 2 Analysis - Summary of Systems with a
Mean Threshold Exceedance by State1
State
Total
Number of
Systems
Systems with a
Mean
Concentration
> 0.04 jjg/L2
Systems with a
Mean Concentration
> 0.08 jjg/L
Systems with a
Mean Concentration
> 0.1 jjg/L
Systems with a
Mean Concentration
> 0.2 jjg/L
Number
Percent
Number
Percent
Number
Percent
Number
Percent
AK
13








AL
383
1
0.26%
1
0.26%
1
0.26%
0
0.00%
AR
459








AS
11








AZ
872








CA
1,280








CO
1








CT
1,136








DC
1








FL
2,090
3
0.14%
0
0.00%
0
0.00%
0
0.00%
HI
111








IA
3








ID
391








IL
1,467








IN
1,214








KS
87








KY
225








LA
1,078








MA
564








MD
881
1
0.11%
1
0.11%
1
0.11%
0
0.00%
ME
135








Ml
2,439








MN
920








MO
1,332








MS
5








MT
857








NC
2,348
4
0.17%
1
0.04%
0
0.00%
0
0.00%
ND
157








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State
Total
Number of
Systems
Systems with a
Mean
Concentration
> 0.04 jjg/L2
Systems with a
Mean Concentration
> 0.08 jjg/L
Systems with a
Mean Concentration
> 0.1 jjg/L
Systems with a
Mean Concentration
> 0.2 jjg/L
Number
Percent
Number
Percent
Number
Percent
Number
Percent
NE
703
2
0.28%
1
0.14%
1
0.14%
0
0.00%
NH
1,146








NJ
80








NM
718
1
0.14%
1
0.14%
1
0.14%
1
0.14%
NV
309








NY
2,121
1
0.05%
1
0.05%
1
0.05%
1
0.05%
OH
33








OK
1








OR
1,119








PA
1,047
1
0.10%
1
0.10%
1
0.10%
0
0.00%
Rl
102








SC
497








SD
269








TN
6








TX
4,422








UT
428








VA
254








VT
380








WA
1,996








Wl
1,914








WV
302








WY
318








Total
38,625
14
0.04%
7
0.02%
6
0.02%
2
0.01%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Exhibit B-28 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for heptachlor epoxide is presented, as well. As described above, New Mexico
and New York were the only states with an estimated mean concentration greater than the MCL.
These 2 systems served a total of 1,543 people. Six systems, serving a population of 2,461
people, had estimated mean concentrations greater than V2 the MCL.
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Exhibit B-28: Heptachlor Epoxide Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance by State
State
Total
Population
Population Served
by Systems with a
Mean Concentration
> 0.04 |jg/L2
Population Served
by Systems with a
Mean Concentration
> 0.08 jjg/L
Population Served
by Systems with a
Mean Concentration
> 0.1 |jg/L
Population Served
by Systems with a
Mean Concentration
> 0.2 jjg/L
Population
Percent
Population
Percent
Population
Percent
Population
Percent
AK
40,300








AL
5,333,035
200
0.004%
200
0.004%
200
0.004%
0
0.00%
AR
2,635,934








AS
62,196








AZ
6,484,144








CA
35,713,444








CO
2,020








CT
2,883,135








DC
761,124








FL
18,991,163
8,522
0.045%
0
0.00%
0
0.00%
0
0.00%
HI
1,479,317








IA
166,302








ID
980,519








IL
10,998,201








IN
5,018,298








KS
1,817,722








KY
4,225,473








LA
4,901,263








MA
9,164,462








MD
4,939,436
60
0.001 %
60
0.001 %
60
0.001 %
0
0.00%
ME
356,040








Ml
7,221,983








MN
3,752,545








MO
5,233,314








MS
6,176








MT
845,294








NC
7,832,371
584
0.007%
239
0.003%
0
0.00%
0
0.00%
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State
Total
Population
Population Served
by Systems with a
Mean Concentration
> 0.04 |jg/L2
Population Served
by Systems with a
Mean Concentration
> 0.08 jjg/L
Population Served
by Systems with a
Mean Concentration
> 0.1 |jg/L
Population Served
by Systems with a
Mean Concentration
> 0.2 jjg/L
Population
Percent
Population
Percent
Population
Percent
Population
Percent
ND
592,232








NE
1,662,774
669
0.040%
577
0.035%
577
0.035%
0
0.00%
NH
949,308








NJ
4,346,209








NM
1,940,795
993
0.051 %
993
0.051 %
993
0.051 %
993
0.051 %
NV
2,682,358








NY
10,481,222
550
0.005%
550
0.005%
550
0.005%
550
0.005%
OH
756,016








OK
464








OR
3,432,424








PA
10,847,442
81
0.001 %
81
0.001 %
81
0.001 %
0
0.00%
Rl
1,002,727








SC
3,623,380








SD
708,340








TN
1,168,508








TX
23,814,787








UT
2,752,741








VA
5,685,070








VT
386,948








WA
4,947,453








Wl
4,236,887








WV
1,499,884








WY
469,710








Total
229,832,890
11,659
0.005%
2,700
0.001%
2,461
0.001%
1,543
0.001%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
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B.7.3 Summary of Data
A total of 137,081 analytical results from 38,625 PWSs in 50 states/entities were available for
the SYR3 ICR Dataset for heptachlor epoxide. The Stage 2 analysis of occurrence in drinking
water indicates that 2 (0.005 percent of all) systems (serving 0.001 percent of the population) had
an estimated system mean concentration of heptachlor epoxide greater than the MCL
concentration of 0.2 |ig/L. Both of the systems, serving a total of 1,543 people, with an estimated
mean greater than the MCL concentration were ground water systems. Six systems, serving
2,461 people, had an estimated mean concentration greater than V2 the MCL (0.1 |ig/L). These
six systems were all served by ground water.
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B.8 Hexachlorobenzene
This chapter on hexachlorobenzene includes background information such as the regulatory
history and a summary of monitoring requirements, as well as occurrence and exposure estimates
in drinking water. All drinking water occurrence estimates are based on data from the National
Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year
Review (the "SYR3 ICR Dataset").
B.8.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for hexachlorobenzene on July 17, 1992 (57 FR
31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) of
zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also
established a maximum contaminant level (MCL) of 1 |ig/L based on analytical feasibility.
Hexachlorobenzene is regulated as a synthetic organic chemical (SOC) in drinking water. All
non-purchased community water systems (CWSs) and non-transient non-community water
systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon
a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.17 If all 4 samples are non-detections,
then a system serving less than 3,300 persons may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 persons may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a chemical is detected, the system must monitor quarterly until
results are reliably and consistently below the MCL (minimum of two quarterly samples for
ground water systems and four quarterly samples for surface water systems). If all quarterly
samples are below the MCL, the system may return to annual sampling. If a chemical is detected
at a level greater than the MCL, the system (whether ground water or surface water) must take
quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are
below the MCL, the system may return to annual sampling.
B.8.2 Occurrence in Drinking Water
The analysis of hexachlorobenzene occurrence presented in the following section is based on
state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 137,816
analytical results from 38,498 public water systems (PWSs) during the period from 2006 to
17 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including hexachlorobenzene, for which
Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant
occurrence by generating estimated long-term mean concentrations of contaminants for each
system. This provides occurrence analyses that are less conservative than the Stage 1 analysis,
since the Stage 2 analysis is based on estimated mean concentrations rather than on a single
maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year)
mean concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Two different substitution values -zero and 1/2 the
minimum reporting level (MRL) value- were used to replace each non-detection record. (The
national modal MRL for hexachlorobenzene in the dataset is 0.04 |ig/L.) Two arithmetic mean
hexachlorobenzene concentrations were calculated at each system using the zero, V2 MRL and
full MRL substitution values. These mean calculations were performed for all systems with
hexachlorobenzene data in the SYR3 ICR dataset. Then, the percentages of all systems with a
mean concentration greater than each threshold were calculated. For hexachlorobenzene, EPA
generated Stage 2 occurrence estimates relative to the MCL, twice the estimated quantitation
level (EQL) and the EQL.
Stage 2 Occurrence Estimates
Stage 2 analyses for hexachlorobenzene are summarized in this section. Occurrence estimates
were generated relative to the following thresholds: 1 |ig/L (the MCL), 0.2 |ig/L (two times the
EQL) and 0.1 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below
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a practical quantitation level (PQL).18 For more information on the new potential thresholds of
concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-29 presents the system-level Stage 2 analysis of estimated mean concentrations for
hexachlorobenzene occurrence in drinking water. Exhibit B-30 presents similar information
based on population served by the systems. Based on the Stage 2 analyses, no systems had an
estimated system mean greater than the MCL concentration of 1 |ig/L. Six systems, serving
8,703 people, had an estimated system mean greater than the EQL of 0.1 |ig/L.
Exhibit B-29: Hexachlorobenzene Stage 2 Analysis - Summary of Systems with a
Mean Threshold Exceedance
Source Water Type
(Number of Systems)
Threshold
Number of Systems with
Mean Concentrations That
Are Greater Than the
Threshold
Percent of Systems with Mean
Concentrations That Are
Greater Than the Threshold
Non-detect
values
= 1/2 MRL
Non-detect
values = 0
Non-detect
values
= 1/2 MRL
Non-detect
values = 0
Ground Water
(35,255)
> 1 MQ/L
0
0
0.000%
0.000%
> 0.2 |jg/L
3
3
0.009%
0.009%
>0.1 |jg/L1
6
5
0.017%
0.014%

Surface Water
(3,243)
> 1 mq/l
0
0
0.000%
0.000%
> 0.2 |jg/L
0
0
0.000%
0.000%
>0.1 |jg/L1
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(38,498)
> 1 mq/l
0
0
0.000%
0.000%
> 0.2 |jg/L
3
3
0.008%
0.008%
>0.1 |jg/L1
6
5
0.016%
0.013%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
18 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical
feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year
Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced.
The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to
evaluate occurrence and exposure for the Stage 2 analyses.
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Exhibit B-30: Hexachlorobenzene Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served
by Systems with Mean
Concentrations That Are
Greater Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect
values
= 1/2 MRL
Non-detect
values = 0
Ground Water
(92,988,313)
> 1 Mg/L
0
0
0.000%
0.000%
> 0.2 |jg/L
7,546
7,546
0.008%
0.008%
>0.1 |jg/L1
8,703
8,589
0.009%
0.009%

Surface Water
(137,209,655)
> 1 mq/l
0
0
0.000%
0.000%
> 0.2 |jg/L
0
0
0.000%
0.000%
>0.1 |jg/L1
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(230,197,968)
> 1 mq/l
0
0
0.000%
0.000%
> 0.2 |jg/L
7,546
7,546
0.003%
0.003%
>0.1 |jg/L1
8,703
8,589
0.004%
0.004%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Data for hexachlorobenzene were available from 50 states/entities. Four states did not submit
data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although
the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3
ICR Dataset, these states are included in the table below because a handful of tribal water
systems located within these two states did submit hexachlorobenzene data.
Exhibit B-31 presents the total number of systems in each state that submitted data for
hexachlorobenzene. In addition, the geographic distribution of hexachlorobenzene occurrence in
drinking water is illustrated by showing states with systems with a mean concentration greater
than the EQL, two times the EQL and MCL concentrations. (Note: Only the V2 MRL substitution
results are presented in this exhibit.) No systems had estimated mean concentrations greater than
the MCL. Six systems in five different states had an estimated mean concentration greater than
the EQL of 0.1 |ig/L.
Exhibit B-31: Hexachlorobenzene Stage 2 Analysis - Summary of Systems with a
Mean Threshold Exceedance by State12
State
Total
Number of
Systems
Systems with a
Mean Concentration >
0.1 mq/l3
Systems with a
Mean Concentration >
0.2 ng/L
Systems with a
Mean Concentration >
1 mq/l
Number
Percent
Number
Percent
Number
Percent
AK
10






AL
383






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State
Total
Number of
Systems
Systems with a
Mean Concentration >
0.1 mq/l3
Systems with a
Mean Concentration >
0.2 Mg/L
Systems with a
Mean Concentration >
1 mq/l
Number
Percent
Number
Percent
Number
Percent
AR
459






AS
11






AZ
869






CA
1,317
2
0.152%
1
0.076%
0
0.00%
CO
1






CT
1,135






DC
1






FL
2,090






HI
112






IA
3






ID
522






IL
1,261






IN
1,213






KS
87






KY
225






LA
1,102
1
0.091%
1
0.091%
0
0.00%
MA
565






MD
881






ME
173






Ml
2,439






MN
920






MO
1,332






MS
5






MT
857






NC
2,348






ND
23






NE
703






NH
1,146






NJ
82






NM
718
1
0.139%
0
0.00%
0
0.00%
NV
312






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State
Total
Number of
Systems
Systems with a
Mean Concentration >
0.1 mq/l3
Systems with a
Mean Concentration >
0.2 \iglL
Systems with a
Mean Concentration >
1 mq/l
Number
Percent
Number
Percent
Number
Percent
NY
2,123
1
0.047%
1
0.047%
0
0.00%
OH
34






OK
1






OR
1,120






PA
1,049






Rl
103






SC
497






SD
269






TN
6






TX
4,422
1
0.023%
0
0.000%
0
0.00%
UT
428






VA
254






VT
382






WA
1,994






Wl
1,914






WV
279






WY
318






Total
38,498
6
0.016%
3
0.008%
0
0.000%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Exhibit B-32 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for hexachlorobenzene is presented, as well. As described above, no systems had
estimated mean concentrations greater than the MCL. Six systems, serving 8,703 people, had an
estimated mean concentration greater than the EQL of 0.1 |ig/L.
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Exhibit B-32: Hexachlorobenzene Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Served by
Systems
Population Served by
Systems with a
Mean Concentration >
0.1 mq/l3
Population Served by
Systems with a
Mean Concentration >
0.2 Mg/L
Population Served by
Systems with a
Mean Concentration
> 1 mq/l
Number
Percent
Number
Percent
Number
Percent
AK
39,878






AL
5,333,035






AR
2,635,934






AS
62,196






AZ
6,471,242






CA
36,681,076
130
0.000%
80
0.000%
0
0.000%
CO
2,020






CT
2,882,395






DC
761,124






FL
18,945,034






HI
1,479,717






IA
166,302






ID
1,052,952






IL
10,925,340






IN
5,017,598






KS
1,817,722






KY
4,225,473






LA
4,966,772
6,916
0.139%
6,916
0.139%
0
0.000%
MA
9,164,636






MD
4,939,436






ME
367,408






Ml
7,221,983






MN
3,752,545






MO
5,233,314






MS
6,176






MT
845,294






NC
7,832,371






ND
66,229






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State
Total
Population
Served by
Systems
Population Served by
Systems with a
Mean Concentration >
0.1 mq/l3
Population Served by
Systems with a
Mean Concentration >
0.2 \iglL
Population Served by
Systems with a
Mean Concentration
> 1 mq/l
Number
Percent
Number
Percent
Number
Percent
NE
1,662,774






NH
949,308






NJ
4,366,309






NM
1,940,795
993
0.051%
0
0.000%
0
0.000%
NV
2,688,765






NY
10,481,573
550
0.005%
550
0.005%
0
0.000%
OH
758,784






OK
464






OR
3,432,479






PA
10,854,480






Rl
1,003,245






SC
3,623,380






SD
708,340






TN
1,168,508






TX
23,814,787
114
0.000%
0
0.000%
0
0.000%
UT
2,752,741






VA
5,685,070






VT
387,157






WA
4,949,076






Wl
4,236,887






WV
1,368,134






WY
469,710






Total
230,197,968
8,703
0.004%
7,546
0.003%
0
0.000%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
B.8.3 Summary of Data
A total of 137,816 analytical results from 38,498 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for hexachlorobenzene. The Stage 2 analysis of occurrence in drinking water
indicated that no systems had an estimated system mean concentration of hexachlorobenzene
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greater than the MCL concentration of 1 |ig/L. Six systems had an estimated mean concentration
greater than the EQL of 0.1 |ig/L.
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B.9 Hexachlorocyclopentadiene
This chapter on hexachlorocyclopentadiene includes background information such as the
regulatory history and a summary of monitoring requirements, as well as occurrence and
exposure estimates in drinking water. All drinking water occurrence estimates are based on data
from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the
Third Six-Year Review (the "SYR3 ICR Dataset").
B.9.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for hexachlorocyclopentadiene on July 17, 1992
(57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal
(MCLG) and a maximum contaminant level (MCL) of 50 |ig/L. EPA based the MCLG on a
reference dose (RfD) of 7 |ig/kg-day (0.007 mg/kg-day) and a cancer classification of D, not
classifiable as to human carcinogenicity.
Hexachlorocyclopentadiene is regulated as a synthetic organic chemical (SOC) in drinking
water. All non-purchased community water systems (CWSs) and non-transient non-community
water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all
systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum
waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is
reconfirmed that the source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.19 If all 4 samples are non-detections,
then a system serving less than 3,300 people may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 people may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a chemical is detected, the system must monitor quarterly until
results are reliably and consistently below the MCL (minimum of two quarterly samples for
ground water systems and four quarterly samples for surface water systems). If all quarterly
samples are below the MCL, the system may return to annual sampling. If a chemical is detected
at a level greater than the MCL, the system (whether ground water or surface water) must take
quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are
below the MCL, the system may return to annual sampling.
B.9.2 Occurrence in Drinking Water
The analysis of hexachlorocyclopentadiene occurrence presented in the following section is
based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of
140,004 analytical results from 38,743 public water systems (PWSs) during the period from
19 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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2006 to 2011. The number of sample results and systems vary by state, although the state
datasets have been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including hexachlorocyclopentadiene, for
which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant
occurrence by generating estimated long-term mean concentrations of contaminants for each
system. This provides occurrence analyses that are less conservative than the Stage 1 analysis,
since the Stage 2 analysis is based on estimated mean concentrations rather than on a single
maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year)
mean concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for hexachlorocyclopentadiene in the dataset is 0.1 |ig/L.)
Three arithmetic mean hexachlorocyclopentadiene concentrations were calculated at each system
using the zero, V2 MRL and full MRL substitution values. These mean calculations were
performed for all systems with hexachlorocyclopentadiene data in the SYR3 ICR dataset. Then,
the percentages of all systems with a mean concentration greater than each threshold were
calculated. For hexachlorocyclopentadiene, since there were no analytical method limitations at
the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the
potential MCLG.
Stage 2 Occurrence Estimates
Stage 2 analyses for hexachlorocyclopentadiene are summarized in this section. Occurrence
estimates were generated relative to the following thresholds: 50 |ig/L (the MCL) and 40 |ig/L
(the potential MCLG). The potential MCLG is due to changes in the RfD based on new health
effects information. Since the practical quantitation level (PQL) for hexachlorocyclopentadiene
is less than the possible MCLG, EPA designated the possible MCLG as the threshold for the
occurrence analysis. For more information on the new potential thresholds of concern used in the
SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e).
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Exhibit B-33 presents the system-level Stage 2 analysis of estimated mean concentrations for
hexachlorocyclopentadiene occurrence in drinking water. Exhibit B-34 presents similar
information based on population served by the systems. Based on the Stage 2 analyses, no
systems had estimated system means greater than the MCL concentration of 50 |ig/L or the
potential MCLG concentration of 40 |ig/L.
Exhibit B-33: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of
Systems with a Mean Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are
Greater Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Ground Water
(35,479)
> 50 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 40 |jg/L1
0
0
0
0.000%
0.000%
0.000%


Surface Water
(3,264)
> 50 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 40 |jg/L1
0
0
0
0.000%
0.000%
0.000%


Combined Ground
& Surface Water
(38,743)
> 50 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 40 |jg/L1
0
0
0
0.000%
0.000%
0.000%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit B-34: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of
Population Served by Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by
Systems with Mean
Concentrations That Are
Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(92,695,520)
> 50 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 40 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Surface Water
(137,207,044)
> 50 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 40 |jg/L1
0
0
0
0.000%
0.000%
0.000%

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Source Water Type
(Population Served
by Systems)
Threshold
Population Served by
Systems with Mean
Concentrations That Are
Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Combined Ground
& Surface Water
(229,902,564)
> 50 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 40 |jg/L1
0
0
0
0.000%
0.000%
0.000%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Data for hexachlorocyclopentadiene were available from 50 states/entities. Four states did not
submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi).
Although the States of Colorado and Mississippi did not provide data for any contaminants for
the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of
tribal water systems located within these 2 states did submit hexachlorocyclopentadiene data.
Exhibit B-35 presents the total number of systems in each state that submitted data for
hexachlorocyclopentadiene. In addition, the geographic distribution of
hexachlorocyclopentadiene occurrence in drinking water is illustrated by showing states with
systems with a mean concentration greater than the potential MCLG and the MCL
concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) As is
described above, no systems had estimated system means greater than the MCL concentration of
50 |ig/L or the potential MCLG concentration of 40 |ig/L.
Exhibit B-35: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of
Systems with a Mean Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a Mean
Concentration > 40 jjg/L3
Systems with a Mean
Concentration > 50 jjg/L
Number
Percent
Number
Percent
AK
10




AL
383




AR
459




AS
11




AZ
869




CA
1,318




CO
1




CT
1,135




DC
1




FL
2,089




HI
112




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State
Total Number
of Systems
Systems with a Mean
Concentration > 40 jjg/L3
Systems with a Mean
Concentration > 50 jjg/L
Number
Percent
Number
Percent
IA
3




ID
521




IL
1,261




IN
1,214




KS
86




KY
225




LA
1,102




MA
566




MD
881




ME
173




Ml
2,439




MN
920




MO
1,332




MS
5




MT
857




NC
2,348




ND
23




NE
703




NH
1,146




NJ
38




NM
718




NV
312




NY
2,123




OH
34




OK
1




OR
1,120




PA
1,317




Rl
103




SC
497




SD
269




TN
6




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State
Total Number
of Systems
Systems with a Mean
Concentration > 40 jjg/L3
Systems with a Mean
Concentration > 50 jjg/L
Number
Percent
Number
Percent
TX
4,420




UT
428




VA
254




VT
382




WA
1,994




Wl
1,914




WV
302




WY
318




Total
38,743
0
0.00%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
Exhibit B-36 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for hexachlorocyclopentadiene is presented, as well. No systems had estimated
system means greater than the MCL concentration of 50 |ig/L or the potential MCLG
concentration of 40 |ig/L.
Exhibit B-36: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of
Population Served by Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration >
40 jjg/L3
Population Served by Systems
with a Mean Concentration >
50 Mg/L
Population
Percent
Population
Percent
AK
39,878




AL
5,333,035




AR
2,635,934




AS
62,196




AZ
6,471,242




CA
36,666,576




CO
2,020




CT
2,882,395




DC
761,124




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
40 jjg/L3
Population Served by Systems
with a Mean Concentration >
50 Mg/L
Population
Percent
Population
Percent
FL
18,944,969




HI
1,479,717




IA
166,302




ID
1,052,868




IL
10,925,340




IN
5,032,598




KS
1,685,226




KY
4,225,473




LA
4,966,772




MA
9,164,737




MD
4,939,436




ME
367,408




Ml
7,221,983




MN
3,752,545




MO
5,233,314




MS
6,176




MT
845,294




NC
7,832,371




ND
66,229




NE
1,662,774




NH
949,308




NJ
4,027,741




NM
1,940,795




NV
2,688,765




NY
10,481,569




OH
758,784




OK
464




OR
3,432,479




PA
10,898,082




Rl
1,003,245




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State
Total
Population
Population Served by Systems
with a Mean Concentration >
40 jjg/L3
Population Served by Systems
with a Mean Concentration >
50 Mg/L
Population
Percent
Population
Percent
SC
3,623,380




SD
708,340




TN
1,168,508




TX
23,814,647




UT
2,752,741




VA
5,685,070




VT
387,157




WA
4,949,076




Wl
4,236,887




WV
1,499,884




WY
469,710




Total
229,902,564
0
0.00%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information.
B.9.3 Summary of Data
A total of 140,004 analytical results from 38,743 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for hexachlorocyclopentadiene. The Stage 2 analysis of occurrence in
drinking water indicated that zero systems had an estimated system mean concentration of
hexachlorocyclopentadiene greater than the MCL concentration (50 |ig/L) or the potential
MCLG (40 |ig/L).
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B.10 Methoxychlor
This chapter on methoxychlor includes background information such as the regulatory history
and a summary of monitoring requirements, as well as occurrence and exposure estimates in
drinking water. All drinking water occurrence estimates are based on data from the National
Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year
Review (the "SYR3 ICR Dataset").
B.10.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for methoxychlor on January 30, 1991 (56 FR
3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG)
and a maximum contaminant level (MCL) of 40 |ig/L. The Agency based the MCLG on a
reference dose (RfD) of 5 |ig/kg-day (0.005 mg/kg-day) and a cancer classification of D, not
classifiable as to human carcinogenicity.
Methoxychlor is regulated as a synthetic organic chemical (SOC) in drinking water. All non-
purchased community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.20 If all 4 samples are non-detections,
then a system serving less than 3,300 persons may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 persons may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a chemical is detected, the system must monitor quarterly until
results are reliably and consistently below the MCL (minimum of two quarterly samples for
ground water systems and four quarterly samples for surface water systems). If all quarterly
samples are below the MCL, the system may return to annual sampling. If a chemical is detected
at a level greater than the MCL, the system (whether ground water or surface water) must take
quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are
below the MCL, the system may return to annual sampling.
B.10.2 Occurrence in Drinking Water
The analysis of methoxychlor occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 139,744
analytical results from 39,187 public water systems (PWSs) during the period from 2006 to
20 All new systems or systems using a new water source that began operation after January 22, 2004 must
demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply
with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with
the MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including methoxychlor, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for methoxychlor in the dataset is 0.1 |ig/L.) Three arithmetic
mean methoxychlor concentrations were calculated at each system using the zero, V2 MRL and
full MRL substitution values. These mean calculations were performed for all systems with
methoxychlor data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean
concentration greater than each threshold were calculated. For methoxychlor, EPA generated
Stage 2 occurrence estimates relative to the MCL, twice the estimated quantitation level (EQL)
and the EQL.
Stage 2 Occurrence Estimates
Stage 2 analyses for methoxychlor are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 40 |ig/L (the MCL), 2 |ig/L (two times the EQL)
and 1 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a
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practical quantitation level (PQL).21 For more information on the new potential thresholds of
concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-37 presents the system-level Stage 2 analysis of estimated mean concentrations for
methoxychlor occurrence in drinking water. Exhibit B-38 presents similar information based on
population served by the systems. Based on the Stage 2 analyses, no systems had an estimated
system mean greater than the MCL concentration of 40 |ig/L. One system, serving 993 people,
had an estimated system mean greater than the EQL of 1 |ig/L.
Exhibit B-37: Methoxychlor Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(35,867)
> 40 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 2 |jg/L
1
1
1
0.003%
0.003%
0.003%
> 1 |jg/L1
1
1
1
0.003%
0.003%
0.003%

Surface Water
(3,320)
> 40 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 2 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 1 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground &
Surface Water
(39,187)
> 40 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 2 |jg/L
1
1
1
0.003%
0.003%
0.003%
> 1 |jg/L1
1
1
1
0.003%
0.003%
0.003%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
21 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility
level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA
evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation
capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2
analyses.
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Exhibit B-38: Methoxychlor Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(92,942,500)
> 40 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 2 |jg/L
993
993
993
0.001 %
0.001%
0.001%
> 1 |jg/L1
993
993
993
0.001 %
0.001%
0.001%

Surface Water
(140,088,461)
> 40 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 2 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 1 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground &
Surface Water
(233,030,961)
> 40 |jg/L
0
0
0
0.0000%
0.0000%
0.0000%
> 2 |jg/L
993
993
993
0.0004%
0.0004%
0.0004%
> 1 |jg/L1
993
993
993
0.0004%
0.0004%
0.0004%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Data for methoxychlor were available from 50 states/entities. Four states did not submit data for
use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States
of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR
Dataset, these states are included in the table below because a handful of tribal water systems
located within these two states did submit methoxychlor data.
Exhibit B-39 presents the total number of systems in each state that submitted data for
methoxychlor. In addition, the geographic distribution of methoxychlor occurrence in drinking
water is illustrated by showing states with systems with a mean concentration greater than the
EQL, two times the EQL and MCL concentrations. (Note: Only the V2 MRL substitution results
are presented in this exhibit.) No systems had estimated mean concentrations greater than the
MCL. One system in New Mexico had an estimated mean concentration greater than the EQL of
l^g/L.
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Exhibit B-39: Methoxychlor Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total
Number of
Systems
Systems with a
Mean Concentration
> 1 |ig/L3
Systems with a
Mean Concentration
> 2 |jg/L
Systems with a
Mean Concentration
> 40 |jg/L
Number
Percent
Number
Percent
Number
Percent
AK
13






AL
383






AR
459






AS
11






AZ
872






CA
1,327






CO
1






CT
1,137






DC
1






FL
2,088






HI
111






IA
8






ID
392






IL
1,468






IN
1,214






KS
87






KY
225






LA
1,102






MA
564






MD
881






ME
173






Ml
2,439






MN
920






MO
1,332






MS
5






MT
857






NC
2,348






ND
157






NE
703






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State
Total
Number of
Systems
Systems with a
Mean Concentration
> 1 |ig/L3
Systems with a
Mean Concentration
> 2 |jg/L
Systems with a
Mean Concentration
> 40 |jg/L
Number
Percent
Number
Percent
Number
Percent
NH
1,146






NJ
42






NM
718
1
0.139%
1
0.139%
0
0.000%
NV
311






NY
2,121
0
0.000%
0
0.000%
0
0.000%
OH
228






OK
39






OR
1,119






PA
1,320






Rl
103






SC
497






SD
269






TN
6






TX
4,422






UT
428
0
0.000%
0
0.000%
0
0.000%
VA
254






VT
380






WA
1,998






Wl
1,914






WV
276






WY
318






Total
39,187
1
0.003%
1
0.003%
0
0.000%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Exhibit B-40 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for methoxychlor is presented, as well. As described above, no systems had
estimated mean concentrations greater than the MCL. One system in New Mexico, serving 993
people, had an estimated mean concentration greater than the EQL of 1 |ig/L.
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Exhibit B-40: Methoxychlor Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Served by
Systems
Population Served by
Systems with a
Mean Concentration
> 1 |ig/L3
Population Served by
Systems with a
Mean Concentration
> 2 |jg/L
Population Served by
Systems with a
Mean Concentration >
40 |jg/L
Number
Percent
Number
Percent
Number
Percent
AK
40,300






AL
5,333,035






AR
2,635,934






AS
62,196






AZ
6,484,144






CA
36,060,067






CO
2,020






CT
2,925,135






DC
761,124






FL
18,944,904






HI
1,479,317






IA
301,990






ID
980,589






IL
10,998,526






IN
5,032,598






KS
1,817,722






KY
4,225,473






LA
4,966,772






MA
9,164,462






MD
4,939,436






ME
367,408






Ml
7,221,983






MN
3,752,545






MO
5,233,314






MS
6,176






MT
845,294






NC
7,832,371






ND
592,232






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State
Total
Population
Served by
Systems
Population Served by
Systems with a
Mean Concentration
> 1 |ig/L3
Population Served by
Systems with a
Mean Concentration
> 2 |jg/L
Population Served by
Systems with a
Mean Concentration >
40 |jg/L
Number
Percent
Number
Percent
Number
Percent
NE
1,662,774






NH
949,308






NJ
4,006,631






NM
1,940,795
993
0.051%
993
0.051%
0
0.000%
NV
2,682,815






NY
10,481,222
0
0.000%
0
0.000%
0
0.000%
OH
3,536,843






OK
152,140






OR
3,432,424






PA
10,900,135






Rl
1,003,245






SC
3,623,380






SD
708,340






TN
1,168,508






TX
23,814,787






UT
2,752,741
0
0.000%
0
0.000%
0
0.000%
VA
5,685,070






VT
386,948






WA
4,947,604






Wl
4,236,887






WV
1,481,587






WY
469,710






Total
233,030,961
993
0.000%
993
0.000%
0
0.000%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
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B.10.3 Summary of Data
A total of 139,744 analytical results from 39,187 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for methoxychlor. The Stage 2 analysis of occurrence in drinking water
indicated that no systems had an estimated system mean concentration of methoxychlor greater
than the MCL concentration of 40 |ig/L. The only system with an estimated mean concentration
greater than the EQL of 1 |ig/L was a ground water system in New Mexico.
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B.ll Selenium
This chapter on selenium includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.ll.l Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for selenium on January 30, 1991 (56 FR 3526;
USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a
maximum contaminant level (MCL) of 50 |ig/L. EPA based the MCLG on a maximum safe
intake22 of 400 |ig/person/day and a cancer classification of D, not classifiable as to human
carcinogenicity.
Selenium is regulated as an inorganic chemical (IOC) in drinking water. All community water
systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to
sample for the IOCs. The maximum waiver period for IOCs is one compliance cycle. During this
cycle, the system must sample at least once.
Ground water systems must sample once during the initial three-year compliance period. Surface
water systems must sample annually during the initial three-year compliance period. If all
analytical results are less than the MCL, and upon considering reported concentrations, degrees
of variation in reported concentration and other factors which may affect contaminant
concentration, a ground water and surface water system may be granted a waiver. If the results
are greater than the MCL, the public water system (PWS) must take one sample per quarter until
results are below the MCL (minimum of two quarterly samples for ground water systems and
four quarterly samples for surface water systems).23 If all quarterly samples are reliably and
consistently below the MCL, the system may continue at initial monitoring indefinitely until the
state or EPA establishes an alternate schedule.
B.11.2 Occurrence in Drinking Water
The analysis of selenium occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 165,672
analytical results from 50,568 PWSs during the period from 2006 to 2011. The number of
22	The 400 ng/day safe level was based on data (Yang etal., 1989a and 1989b) that extrapolated from blood selenium levels to
estimated dietary intake in the studied population. As described in USEPA (1991a), EPA partially considered selenium's status as
a nutrient and did not use the typical procedure for deriving the MCLG. Hence, there is no specific reference to a reference dose
(RiD) for selenium in the 1991 FR notice. After the publication of the regulation, IRIS (USEPA, 1991b) posted an RfD of 5
(ig/kg-day for selenium using the same data that are the basis of the regulation.
23	All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling
frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL.
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sample results and systems vary by state, although the state datasets have been reviewed and
checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including selenium, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for selenium in the dataset is 5 |ig/L.) Three arithmetic mean
selenium concentrations were calculated at each system using the zero, V2 MRL and full MRL
substitution values. These mean calculations were performed for all systems with selenium data
in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater
than each threshold were calculated. For selenium, since there were no analytical method
limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the
MCL and the potential MCLG.
Stage 2 Occurrence Estimates
Stage 2 analyses for selenium are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 50 |ig/L (the MCL) and 40 |ig/L (the potential
MCLG). The potential MCLG is due to changes in the reference dose (RfD) based on new health
effects information. Since the practical quantitation level (PQL) for selenium is less than the
possible MCLG, EPA designated the possible MCLG as the threshold for the occurrence
analysis. For more information on the new potential thresholds of concern used in the SYR3
Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-41 presents the system-level Stage 2 analysis of estimated mean concentrations for
selenium occurrence in drinking water. Exhibit B-42 presents similar information based on
population served by the systems. Based on the Stage 2 analyses using the V2 MRL substitution
for non-detections, 31 systems (0.061 percent of all systems), serving 21,489 people, had an
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estimated system mean greater than the MCL concentration of 50 |ig/L. Forty-nine systems
(0.097 percent of all systems), serving 135,685 people, had an estimated system mean greater
than the potential MCLG concentration of 40 |ig/L.
Exhibit B-41: Selenium Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(46,378)
> 50 |jg/L
31
30
30
0.067%
0.065%
0.065%
> 40 |jg/L1
49
48
48
0.106%
0.103%
0.103%

Surface Water
(4,190)
> 50 |jg/L
1
1
1
0.024%
0.024%
0.024%
> 40 |jg/L1
1
1
1
0.024%
0.024%
0.024%

Combined Ground &
Surface Water
(50,568)
> 50 |jg/L
32
31
31
0.063%
0.061 %
0.061 %
> 40 |jg/L1
50
49
49
0.099%
0.097%
0.097%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Exhibit B-42: Selenium Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served by
Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean Concentrations
That Are Greater Than the Threshold
Non-
detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Ground Water
(105,367,702)
> 50 |jg/L
21,101
21,039
21,039
0.020%
0.020%
0.020%
> 40 |jg/L1
135,421
135,235
135,235
0.129%
0.128%
0.128%

Surface Water
(149,060,594)
> 50 |jg/L
450
450
450
0.000%
0.000%
0.000%
> 40 |jg/L1
450
450
450
0.000%
0.000%
0.000%

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Source Water Type
(Population Served by
Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean Concentrations
That Are Greater Than the Threshold
Non-
detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Combined Ground &
Surface Water
(254,428,296)
> 50 |jg/L
21,551
21,489
21,489
0.008%
0.008%
0.008%
> 40 |jg/L1
135,871
135,685
135,685
0.053%
0.053%
0.053%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Data for selenium were available from 49 states/entities. Four states did not submit data for use
in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the State of
Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, this state is
included in the table below because a handful of tribal water systems located within this state did
submit selenium data. There were no selenium data submitted by tribal communities in
Colorado.
Exhibit B-43 presents the total number of systems in each state that submitted data for selenium.
In addition, the geographic distribution of selenium occurrence in drinking water is illustrated by
showing states with systems with a mean concentration greater than the potential MCLG and the
MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.)
The distribution of systems with mean concentrations of selenium is geographically dispersed.
Detection rates were generally low; only 14 states had systems with an estimated mean
concentration greater than the MCL. Forty-nine systems in 15 states had estimated mean
concentrations greater than the potential MCLG.
Exhibit B-43: Selenium Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total Number of
Systems
Systems with a Mean
Concentration > 40 |jg/L3
Systems with a Mean
Concentration > 50 |jg/L


Number
Percent
Number
Percent
AK
508




AL
385




AR
460




AS
11




AZ
1,097
1
0.09%
1
0.09%
CA
3,978
5
0.13%
3
0.08%
CO
0




CT
1,173




DC
1




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State
Total Number of
Systems
Systems with a Mean
Concentration > 40 |jg/L3
Systems with a Mean
Concentration > 50 |jg/L
Number
Percent
Number
Percent
FL
2,605




HI
112




IA
350




ID
721




IL
1,358




IN
1,191




KS
601
4
0.67%
2
0.33%
KY
226




LA
1,110




MA
665




MD
595




ME
780




Ml
2,126




MN
1,144




MO
1,444
1
0.07%
1
0.07%
MS
5




MT
774




NC
2,180
2
0.09%
2
0.09%
ND
181




NE
687
10
1.46%
7
1.02%
NH
1,167




NJ
1,402




NM
750
4
0.53%
3
0.40%
NV
307
1
0.33%
1
0.33%
NY
2,528
1
0.04%
1
0.04%
OH
1,893




OK
625
2
0.00%
2
0.32%
OR
856




PA
1,408




Rl
153




SC
559




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State
Total Number of
Systems
Systems with a Mean
Concentration > 40 |jg/L3
Systems with a Mean
Concentration > 50 |jg/L


Number
Percent
Number
Percent
SD
201




TN
242
1
0.41%
0
0.00%
TX
4,580
13
0.28%
5
0.11%
UT
481
1
0.21%
1
0.21%
VA
1,609
1
0.06%
1
0.06%
VT
429




WA
2,203




Wl
1,998




WV
394




WY
315
2
0.63%
1
0.32%
Total
50,568
49
0.10%
31
0.06%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Exhibit B-44 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for selenium is presented, as well. As described above, 14 states had systems with
an estimated mean concentration greater than the MCL. These systems served a total of 21,489
people. A total of 49 systems in 15 states, serving 135,685 people, had estimated mean
concentrations greater than the potential MCLG (40 |ig/L).
Exhibit B-44: Selenium Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration
> 40 |Jg'L3
Population Served by Systems
with a Mean Concentration
> 50 |jg/L
Population
Percent
Population
Percent
AK
677,666




AL
5,336,667




AR
2,636,302




AS
62,196




AZ
6,659,383
144
0.00%
144
0.00%
CA
41,064,051
169
0.00%
119
0.00%
CO
0




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State
Total
Population
Population Served by Systems
with a Mean Concentration
> 40 |Jg'L3
Population Served by Systems
with a Mean Concentration
> 50 |jg/L
Population
Percent
Population
Percent
CT
2,933,337




DC
761,124




FL
19,110,546




HI
1,481,171




IA
1,320,723




ID
1,157,142




IL
10,983,227




IN
4,934,479




KS
2,605,369
1,245
0.05%
614
0.02%
KY
4,225,513




LA
4,970,924




MA
9,274,922




MD
163,520




ME
757,647




Ml
6,079,096




MN
3,684,918




MO
5,278,387
145
0.00%
145
0.00%
MS
6,176




MT
795,027




NC
7,759,220
6,941
0.09%
6,941
0.09%
ND
582,630




NE
1,656,731
10,527
0.64%
10,178
0.61%
NH
959,233




NJ
9,151,032




NM
1,973,494
777
0.04%
412
0.02%
NV
2,684,168
110
0.00%
110
0.00%
NY
10,481,957
450
0.00%
450
0.00%
OH
10,202,691




OK
3,512,817
1,026
0.00%
1,026
0.03%
OR
3,141,336




PA
9,935,296




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State
Total
Population
Population Served by Systems
with a Mean Concentration
> 40 |Jg'L3
Population Served by Systems
with a Mean Concentration
> 50 |jg/L
Population
Percent
Population
Percent
Rl
1,019,797




SC
3,653,359




SD
406,820




TN
4,734,392
65
0.00%
0
0.00%
TX
23,797,890
113,626
0.48%
990
0.00%
UT
2,818,359
240
0.01%
240
0.01%
VA
6,907,783
30
0.00%
30
0.00%
VT
405,823




WA
5,384,657




Wl
4,256,823




WV
1,573,265




WY
469,210
190
0.04%
90
0.02%
Total
254,428,296
135,685
0.05%
21,489
0.01%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
B.11.3 Summary of Data
A total of 165,672 analytical results from 50,568 PWSs in 49 states/entities were available in the
SYR3 ICR Dataset for selenium. The Stage 2 analysis of occurrence in drinking water indicated
that 31 systems, serving 21,489 people, had an estimated system mean concentration of selenium
greater than the MCL concentration of 50 |ig/L. A total of 49 systems, serving 135,685 people,
had an estimated mean concentration greater than the potential MCLG of 40 |ig/L. All but one of
the systems with a mean concentrations exceeding the MCL and potential MCLG were ground
water systems.
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B.12 Styrene
This chapter on styrene includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.12.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for styrene on January 30, 1991 (56 FR 3526;
USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a
maximum contaminant level (MCL) of 100 |ig/L. The Agency based the MCLG on a reference
dose (RfD) of 200 |ig/kg-day (0.2 mg/kg-day).
Styrene is regulated as a volatile organic compound (VOC) in drinking water. All non-purchased
community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two
compliance periods for ground water systems and one compliance period for surface water
systems.
All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial
three-year compliance period.24 If all four samples are non-detections, then the system may
reduce to annual sampling. After three annual samples without a detection, and upon conducting
a vulnerability assessment, a system may be granted a waiver. During the waiver period, the
ground water system must sample at least once, while surface water system must sample at the
frequency specified by the state. If a compound is detected, the system must take one sample per
quarter until results are below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems). If all quarterly samples are
reliably and consistently below the MCL, the system may return to annual sampling. If a
compound is detected at a level greater than the MCL, the system (whether ground water or
surface water) must take four consecutive quarterly samples until all are below the MCL. If all
quarterly samples are below the MCL, the system may return to annual sampling.
B.12.2 Occurrence in Drinking Water
The analysis of styrene occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 370,368
analytical results from 55,731 public water systems (PWSs) during the period from 2006 to
2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
24 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling
frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL.
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EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including styrene, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for styrene in the dataset is 0.5 |ig/L.) Three arithmetic mean
styrene concentrations were calculated at each system using the zero, V2 MRL and full MRL
substitution values. These mean calculations were performed for all systems with styrene data in
the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater
than each threshold were calculated. For styrene, EPA generated Stage 2 occurrence estimates
relative to the MCL, twice the estimated quantitation level (EQL) and the EQL.
Stage 2 Occurrence Estimates
Stage 2 analyses for styrene are summarized in this section. Occurrence estimates were generated
relative to the following thresholds: 100 |ig/L (the MCL), 1 |ig/L (two times the EQL) and 0.5
|ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical
quantitation level (PQL).25 For more information on the new potential thresholds of concern used
in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-45 presents the system-level Stage 2 analysis of estimated mean concentrations for
styrene occurrence in drinking water. Exhibit B-46 presents similar information based on
population served by the systems. Based on the Stage 2 analyses, one ground water system had
25 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility
level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA
evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation
capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2
analyses.
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an estimated system mean greater than the MCL concentration of 100 |ig/L. A total of 117
systems, serving 571,425 people, had an estimated system mean greater than the EQL of 0.5
Hg/L.
Exhibit B-45: Styrene Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(51,299)
> 100 |jg/L
1
1
0
0.002%
0.002%
0.000%
> 1 |Jg/L
59
48
43
0.115%
0.094%
0.084%
> 0.5 |jg/L1
235
114
84
0.458%
0.222%
0.164%

Surface Water
(4,432)
> 100 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 1 |Jg/L
0
0
0
0.000%
0.000%
0.000%
> 0.5 |jg/L1
19
3
0
0.429%
0.068%
0.000%

Combined Ground &
Surface Water
(55,731)
> 100 |jg/L
1
1
0
0.002%
0.002%
0.000%
> 1 |Jg/L
59
48
43
0.106%
0.086%
0.077%
> 0.5 |jg/L1
254
117
84
0.456%
0.210%
0.151%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Exhibit B-46: Styrene Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Ground Water
(110,770,943)
> 100 |jg/L
100
100
0
0.000%
0.000%
0.000%
> 1 |Jg/L
26,448
20,242
17,199
0.024%
0.018%
0.016%
> 0.5 |jg/L1
602,074
80,116
36,835
0.544%
0.072%
0.033%

Surface Water
> 100 |jg/L
0
0
0
0.000%
0.000%
0.000%
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Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Surface Water, cont.
(152,600,590)
> 1 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 0.5 |jg/L1
930,047
491,309
0
0.609%
0.322%
0.000%

Combined Ground &
Surface Water
(263,371,533)
> 100 |jg/L
100
100
0
0.000%
0.000%
0.000%
> 1 |Jg/L
26,448
20,242
17,199
0.010%
0.008%
0.007%
> 0.5 |jg/L1
1,532,121
571,425
36,835
0.582%
0.217%
0.014%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation
capabilities below a PQL (USEPA, 2016d).
Data for styrene were available from 50 states/entities. Four states did not submit data for use in
the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the table below because a handful of tribal water systems located
within these two states did submit styrene data.
Exhibit B-47 presents the total number of systems in each state that submitted data for styrene. In
addition, the geographic distribution of styrene occurrence in drinking water is illustrated by
showing states with systems with a mean concentration greater than the EQL, two times the EQL
and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this
exhibit.) No systems had estimated mean concentrations greater than the MCL. One system in
Michigan had an estimated mean concentration greater than the MCL of 100 |ig/L. A total of 117
systems had an estimated mean concentration greater than the EQL of 0.5 |ig/L.
Exhibit B-47: Styrene Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a
Mean Concentration
> 0.5 |jg/L3
Systems with a
Mean Concentration
> 1 Hg'L
Systems with a
Mean Concentration
>100 |jg/L
Number
Percent
Number
Percent
Number
Percent
AK
595
0
0.000%
0
0.000%
0
0.000%
AL
384






AR
461
0
0.000%
0
0.000%
0
0.000%
AS
11






AZ
1,110
2
0.180%
1
0.090%
0
0.00%
CA
3,811
1
0.026%
0
0.000%
0
0.00%
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State
Total Number
of Systems
Systems with a
Mean Concentration
> 0.5 |jg/L3
Systems with a
Mean Concentration
> 1 H9'L
Systems with a
Mean Concentration
>100 |jg/L
Number
Percent
Number
Percent
Number
Percent
CO
1






CT
1,202
0
0.000%
0
0.000%
0
0.00%
DC
1






FL
2,633
0
0.000%
0
0.000%
0
0.00%
HI
110






IA
1,043
0
0.000%
0
0.000%
0
0.00%
ID
839
0
0.000%
0
0.000%
0
0.00%
IL
1,493
2
0.134%
0
0.000%
0
0.00%
IN
1,196
7
0.585%
4
0.334%
0
0.00%
KS
602
0
0.000%
0
0.000%
0
0.000%
KY
227






LA
1,102
3
0.272%
0
0.000%
0
0.00%
MA
721
1
0.139%
0
0.000%
0
0.00%
MD
1,054
3
0.285%
2
0.190%
0
0.00%
ME
784
8
1.020%
5
0.638%
0
0.00%
Ml
2,419
41
1.695%
13
0.537%
1
0.04%
MN
1,463
8
0.547%
6
0.410%
0
0.00%
MO
1,445
1
0.069%
0
0.000%
0
0.00%
MS
5






MT
897
0
0.000%
0
0.000%
0
0.00%
NC
2,356
7
0.297%
3
0.127%
0
0.00%
ND
160






NE
705
1
0.142%
1
0.142%
0
0.00%
NH
1,185
1
0.084%
0
0.000%
0
0.00%
NJ
1,434
5
0.349%
3
0.209%
0
0.00%
NM
744
1
0.134%
0
0.00%
0
0.00%
NV
350






NY
2,498
2
0.080%
2
0.080%
0
0.00%
OH
1,922
14
0.728%
6
0.312%
0
0.00%
OK
685
0
0.000%
0
0.000%
0
0.000%
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State
Total Number
of Systems
Systems with a
Mean Concentration
> 0.5 |jg/L3
Systems with a
Mean Concentration
> 1 H9'L
Systems with a
Mean Concentration
>100 |jg/L
Number
Percent
Number
Percent
Number
Percent
OR
1,132
1
0.088%
0
0.000%
0
0.00%
PA
3,166
2
0.063%
0
0.000%
0
0.00%
Rl
152
0
0.000%
0
0.000%
0
0.00%
SC
494
0
0.000%
0
0.000%
0
0.00%
SD
313
0
0.000%
0
0.000%
0
0.00%
TN
366






TX
4,532
0
0.000%
0
0.000%
0
0.00%
UT
468
0
0.000%
0
0.000%
0
0.00%
VA
1,630
2
0.123%
0
0.000%
0
0.00%
VT
634
0
0.000%
0
0.000%
0
0.00%
WA
2,468
0
0.000%
0
0.000%
0
0.00%
Wl
2,026
4
0.197%
2
0.099%
0
0.00%
WV
385
0
0.000%
0
0.000%
0
0.00%
WY
317






Total
55,731
117
0.210%
48
0.086%
1
0.002%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Exhibit B-48 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for styrene is presented, as well. As described above, 1 system in Michigan,
serving 100 people, had an estimated mean concentration greater than the MCL of 100 |ig/L. A
total of 117 systems, serving 571,425, had an estimated mean concentration greater than the
EQL of 0.5 |ig/L.
Exhibit B-48: Styrene Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Served by
Systems
Population Served by
Systems with a
Mean Concentration
> 0.5 |jg/L3
Population Served by
Systems with a
Mean Concentration
> 1 H9'L
Population Served by
Systems with a
Mean Concentration
>100 |jg/L
Number
Percent
Number
Percent
Number
Percent
AK
719,561
0
0.000%
0
0.000%
0
0.000%
AL
5,334,584






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State
Total
Population
Served by
Systems
Population Served by
Systems with a
Mean Concentration
> 0.5 |jg/L3
Population Served by
Systems with a
Mean Concentration
> 1 H9'L
Population Served by
Systems with a
Mean Concentration
>100 |jg/L
Number
Percent
Number
Percent
Number
Percent
AR
2,637,712
0
0.000%
0
0.000%
0
0.000%
AS
62,196






AZ
6,669,277
398
0.006%
348
0.005%
0
0.000%
CA
40,638,035
564
0.001%
0
0.000%
0
0.000%
CO
2,020






CT
2,937,643
0
0.000%
0
0.000%
0
0.000%
DC
761,124






FL
19,280,091
0
0.000%
0
0.000%
0
0.000%
HI
1,402,969






IA
2,734,678
0
0.000%
0
0.000%
0
0.000%
ID
1,219,635
0
0.000%
0
0.000%
0
0.000%
IL
11,019,196
775
0.007%
0
0.000%
0
0.000%
IN
4,940,108
1,452
0.029%
268
0.005%
0
0.000%
KS
2,605,030
0
0.00%
0
0.00%
0
0.00%
KY
4,225,914






LA
4,966,653
2,483
0.050%
0
0.000%
0
0.000%
MA
9,329,953
100
0.001%
0
0.000%
0
0.000%
MD
5,120,409
3,295
0.064%
2,950
0.058%
0
0.000%
ME
757,984
613
0.081%
463
0.061%
0
0.000%
Ml
3,470,708
102,788
2.962%
5,761
0.166%
100
0.003%
MN
4,374,468
441,937
10.103%
1,226
0.028%
0
0.000%
MO
5,293,851
200
0.004%
0
0.000%
0
0.000%
MS
6,176






MT
856,529
0
0.000%
0
0.000%
0
0.000%
NC
7,827,828
2,585
0.033%
971
0.012%
0
0.000%
ND
592,539






NE
1,664,802
390
0.023%
390
0.023%
0
0.000%
NH
961,134
485
0.050%
0
0.000%
0
0.000%
NJ
9,273,130
1,032
0.011%
825
0.009%
0
0.000%
NM
1,962,298
993
0.051%
0
0.000%
0
0.000%
NV
2,697,555






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State
Total
Population
Served by
Systems
Population Served by
Systems with a
Mean Concentration
> 0.5 |jg/L3
Population Served by
Systems with a
Mean Concentration
> 1 H9'L
Population Served by
Systems with a
Mean Concentration
>100 |jg/L
Number
Percent
Number
Percent
Number
Percent
NY
10,637,039
4,725
0.044%
4,725
0.044%
0
0.000%
OH
10,209,121
4,641
0.045%
1,825
0.018%
0
0.000%
OK
3,588,559
0
0.000%
0
0.000%
0
0.000%
OR
3,434,191
90
0.003%
0
0.000%
0
0.000%
PA
11,234,684
484
0.004%
0
0.000%
0
0.000%
Rl
1,040,737
0
0.000%
0
0.000%
0
0.000%
SC
3,637,408
0
0.000%
0
0.000%
0
0.000%
SD
757,925
0
0.000%
0
0.000%
0
0.000%
TN
6,578,052






TX
23,863,702
0
0.000%
0
0.000%
0
0.000%
UT
2,800,243
0
0.000%
0
0.000%
0
0.000%
VA
6,908,704
700
0.010%
0
0.000%
0
0.000%
VT
486,604
0
0.000%
0
0.000%
0
0.000%
WA
5,535,827
0
0.000%
0
0.000%
0
0.000%
Wl
4,273,462
695
0.016%
490
0.011 %
0
0.000%
WV
1,570,171
0
0.000%
0
0.000%
0
0.000%
WY
469,314






Total
263,371,533
571,425
0.217%
20,242
0.008%
100
0.000%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
B.12.3 Summary of Data
A total of 370,368 analytical results from 55,731 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for styrene. The Stage 2 analysis of occurrence in drinking water indicated
that one system in Michigan had an estimated system mean concentration of styrene greater than
the MCL concentration of 100 |ig/L. A total of 117 systems, serving 571,425 people, had an
estimated mean concentration greater than the EQL of 0.5 |ig/L. All but three of those systems
were served by ground water.
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B.13 2,3,7,8-TCDD (Dioxin)
This chapter on 2,3,7,8-TCDD (dioxin) includes background information such as the regulatory
history and a summary of monitoring requirements, as well as occurrence and exposure estimates
in drinking water. All drinking water occurrence estimates are based on data from the National
Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year
Review (the "SYR3 ICR Dataset").
B.13.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for dioxin on July 17, 1992 (57 FR 31776;
USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) of zero
based on a cancer classification of B2, probable human carcinogen. The NPDWR also
established a maximum contaminant level (MCL) of 0.00003 |ig/L based on analytical
feasibility.
Dioxin is regulated as a synthetic organic chemical (SOC) in drinking water. All non-purchased
community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.26 If all 4 samples are non-detections,
then a system serving less than 3,300 people may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 people may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a chemical is detected, the system must monitor quarterly until
results are reliably and consistently below the MCL (minimum of two quarterly samples for
ground water systems and four quarterly samples for surface water systems). If all quarterly
samples are below the MCL, the system may return to annual sampling. If a chemical is detected
at a level greater than the MCL, the system (whether ground water or surface water) must take
quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are
below the MCL, the system may return to annual sampling.
B.13.2 Occurrence in Drinking Water
The analysis of dioxin occurrence presented in the following section is based on state compliance
monitoring data from the SYR3 ICR Dataset. These data consist of 20,244 analytical results from
3,216 public water systems (PWSs) during the period from 2006 to 2011. The number of sample
26 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling
frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL.
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results and systems vary by state, although the state datasets have been reviewed and checked to
ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including dioxin, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Two different substitution values -zero and V2 the
minimum reporting level (MRL) value- were used to replace each non-detection record. (The
national modal MRL for dioxin in the dataset is 0.000005 |ig/L.) Two arithmetic mean dioxin
concentrations were calculated at each system using the zero and V2 MRL substitution values.
These mean calculations were performed for all systems with dioxin data in the SYR3 ICR
dataset. Then, the percentages of all systems with a mean concentration greater than each
threshold were calculated. For dioxin, EPA generated Stage 2 occurrence estimates relative to
the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL.
Stage 2 Occurrence Estimates
Stage 2 analyses for dioxin are summarized in this section. Occurrence estimates were generated
relative to four thresholds: 0.00003 |ig/L (the MCL), 0.000015 |ig/L (V2 the MCL), 0.00001 |ig/L
(two times the EQL) and 0.000005 |ig/L (the EQL). The EQL represents the potential
quantitation capabilities below a practical quantitation level (PQL).27For more information on
27 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility
level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA
evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation
capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2
analyses.
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the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA
(2016d) and (2016e).
Exhibit B-49 presents the system-level Stage 2 analysis of estimated mean concentrations for
dioxin occurrence in drinking water. Exhibit B-50 presents similar information based on
population served by the systems. Based on the Stage 2 analyses using the V2 MRL substitution
for non-detections, one water system (approximately 0.031 percent of all systems) had an
estimated mean greater than the MCL of 0.00003 |ig/L. This system serves approximately 550
people. Two water systems (approximately 0.062 percent of all systems) had estimated means
greater than the EQL of 0.000005 |ig/L. These 2 systems serve approximately 1,450 people.
Exhibit B-49: Dioxin Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of Systems)
Threshold
Number of Systems with Mean
Concentrations That Are
Greater Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect
values = 1/2 MRL
Non-detect
values = 0
Ground Water
(2,653)
> 0.00003 |jg/L
1
1
0.038%
0.038%
> 0.000015 |jg/L
1
1
0.038%
0.038%
> 0.00001 |jg/L
1
1
0.038%
0.038%
> 0.000005 |jg/L1
2
1
0.075%
0.038%

Surface Water
(563)
> 0.00003 |jg/L
0
0
0.000%
0.000%
> 0.000015 |jg/L
0
0
0.000%
0.000%
> 0.00001 |jg/L
0
0
0.000%
0.000%
> 0.000005 |jg/L1
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(3,216)
> 0.00003 |jg/L
1
1
0.031 %
0.031 %
> 0.000015 |jg/L
1
1
0.031 %
0.031 %
> 0.00001 |jg/L
1
1
0.031 %
0.031 %
> 0.000005 |jg/L1
2
1
0.062%
0.031 %
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
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Exhibit B-50: Dioxin Stage 2 Analysis - Summary of Population Served by
Systems with a Threshold Exceedance
Source Water Type
(Population Served by
Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Ground Water
(27,816,835)
> 0.00003 |jg/L
550
550
0.002%
0.002%
> 0.000015 |jg/L
550
550
0.002%
0.002%
> 0.00001 |jg/L
550
550
0.002%
0.002%
> 0.000005 |jg/L1
1,450
550
0.005%
0.002%

Surface Water
(46,260,945)
> 0.00003 |jg/L
0
0
0.000%
0.000%
> 0.000015 |jg/L
0
0
0.000%
0.000%
> 0.00001 |jg/L
0
0
0.000%
0.000%
> 0.000005 |jg/L1
0
0
0.000%
0.000%

Combined Ground &
Surface Water
(74,077,780)
> 0.00003 |jg/L
550
550
0.001%
0.001%
> 0.000015 |jg/L
550
550
0.001%
0.001%
> 0.00001 |jg/L
550
550
0.001%
0.001%
> 0.000005 |jg/L1
1,450
550
0.002%
0.001%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Data for dioxin were available from 30 states/entities. (There were no dioxin data from 20
states/entities.) Four states did not submit data for use in the Six-Year Review (Colorado,
Delaware, Georgia and Mississippi). Although the State of Mississippi did not provide data for
any contaminants for the SYR3 ICR Dataset, this state is included in the table below because a
handful of tribal water systems located within Mississippi did submit dioxin data. Twenty
states/entities included in the table below did provide Six-Year data for most contaminants but
did not submit dioxin data because waivers had been granted.
Exhibit B-51 presents the total number of systems in each state that submitted data for dioxin. In
addition, the geographic distribution of dioxin occurrence in drinking water is illustrated by
showing states with systems with a mean concentration greater than the EQL, two times the
EQL, '/2 MCL and MCL concentrations. (Note: Only the V2 MRL substitution results are
presented in this exhibit.) Detection rates were low; only one system in Maryland an estimated
mean concentration greater than the MCL. Two systems (one in Florida and one in Maryland)
had an estimated mean concentration greater than the EQL of 0.000005 |ig/L.
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Exhibit B-51: Dioxin Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total
Number of
Systems
Systems with a
Mean
Concentration
> 0.000005 |jg/L3
Systems with a
Mean
Concentration
> 0.00001 |jg/L
Systems with a
Mean
Concentration
> 0.000015 |jg/L
Systems with a
Mean Concentration
> 0.00003 |jg/L
Number
Percent
Number
Percent
Number
Percent
Number
Percent
AK
6








AL
1








AR
0








AS
11








AZ
829








CA
534








CO
0








CT
10








DC
1








FL
264
1
0.38%
0
0.00%
0
0.00%
0
0.00%
HI
115








IA
0








ID
1








IL
0








IN
55








KS
2








KY
56








LA
4








MA
0








MD
2
1
50.00%
1
50.00%
1
50.00%
1
50.00%
ME
0








Ml
13








MN
27








MO
0








MS
5








MT
0








NC
6








ND
0








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State
Total
Number of
Systems
Systems with a
Mean
Concentration
> 0.000005 |jg/L3
Systems with a
Mean
Concentration
> 0.00001 |jg/L
Systems with a
Mean
Concentration
> 0.000015 |jg/L
Systems with a
Mean Concentration
> 0.00003 |jg/L
Number
Percent
Number
Percent
Number
Percent
Number
Percent
NE
0








NH
0








NJ
0








NM
60








NV
117








NY
60








OH
18








OK
0








OR
6








PA
895








Rl
0








SC
0








SD
0








TN
3








TX
0








UT
12








VA
4








VT
0








WA
0








Wl
98








WV
1








WY
0








Total
3,216
2
0.06%
1
0.03%
1
0.03%
1
0.03%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the
thresholds.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Exhibit B-52 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for dioxin is presented, as well. As described above, 1 system in Maryland had an
estimated mean concentration greater than the MCL; this system served 550 people. Two
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systems, serving a total population of 1,450 people, had an estimated mean concentration greater
than the EQL of 0.000005 |ig/L.
Exhibit B-52: Dioxin Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served
by Systems with a
Mean Concentration
> 0.000005 |jg/L3
Population Served
by Systems with a
Mean
Concentration
> 0.00001 |jg/L
Population Served
by Systems with a
Mean
Concentration
> 0.000015 |jg/L
Population
Served by
Systems with a
Mean
Concentration
> 0.00003 |jg/L
Population
Percent
Population
Percent
Population
Percent
Population
Percent
AK
36,711








AL
750








AR
0








AS
62,196








AZ
6,395,030








CA
29,120,942








CO
0








CT
49,751








DC
761,124








FL
9,131,313
900
0.01%
0
0.00%
0
0.00%
0
0.00%
HI
1,487,191








IA
0








ID
30








IL
0








IN
2,343,163








KS
482,004








KY
2,771,859








LA
32,844








MA
0








MD
1,800,550
550
0.03%
550
0.03%
550
0.03%
550
0.03%
ME
0








Ml
34,902








MN
25,573








MO
0








MS
6,176








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State
Total
Population
Population Served
by Systems with a
Mean Concentration
> 0.000005 |jg/L3
Population Served
by Systems with a
Mean
Concentration
> 0.00001 |jg/L
Population Served
by Systems with a
Mean
Concentration
> 0.000015 |jg/L
Population
Served by
Systems with a
Mean
Concentration
> 0.00003 |jg/L
Population
Percent
Population
Percent
Population
Percent
Population
Percent
MT
0








NC
15,984








ND
0








NE
0








NH
0








NJ
0








NM
82,348








NV
2,577,238








NY
1,822,971








OH
1,099,358








OK
0








OR
910,206








PA
9,393,195








Rl
0








SC
0








SD
0








TN
954,057








TX
0








UT
6,159








VA
785,888








VT
0








WA
0








Wl
1,888,147








WV
120








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State
Total
Population
Population Served
by Systems with a
Mean Concentration
> 0.000005 |jg/L3
Population Served
by Systems with a
Mean
Concentration
> 0.00001 |jg/L
Population Served
by Systems with a
Mean
Concentration
> 0.000015 |jg/L
Population
Served by
Systems with a
Mean
Concentration
> 0.00003 |jg/L


Population
Percent
Population
Percent
Population
Percent
Population
Percent
WY
0








Total
74,077,780
1,450
0.002%
550
0.001%
550
0.001%
550
0.001%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the
thresholds.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
B.13.3 Summary of Data
A total of 20,244 analytical results from 3,216 PWSs in 30 states/entities were available in the
SYR3 ICR Dataset for dioxin. The Stage 2 analysis of occurrence in drinking water indicated
that 1 ground water system in Maryland, serving 550 people, had an estimated system mean
concentration of dioxin greater than the MCL concentration of 0.00003 |ig/L. Two ground water
systems, serving a total population of 1,450 people, had an estimated mean concentration greater
than the EQL of 0.000005 |ig/L. These two ground water systems were located in Florida and
Maryland.
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B.14 Toluene
This chapter on toluene includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.14.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for toluene on January 30, 1991 (56 FR 3526;
USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a
maximum contaminant level (MCL) of 1,000 |ig/L. The Agency based the MCLG on a reference
dose (RfD) of 200 |ig/kg-day (0.2 mg/kg-day) and a cancer classification of D, not classifiable as
to human carcinogenicity.
Toluene is regulated as a volatile organic compound (VOC) in drinking water. All non-purchased
community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two
compliance periods for ground water systems and one compliance period for surface water
systems.
All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial
three-year compliance period.28 If all four samples are non-detections, then the system may
reduce to annual sampling. After three annual samples without a detection, and upon conducting
a vulnerability assessment, a system may be granted a waiver. During the waiver period, the
ground water system must sample at least once, while surface water system must sample at the
frequency specified by the state. If a compound is detected, the system must take one sample per
quarter until results are below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems). If all quarterly samples are
reliably and consistently below the MCL, the system may return to annual sampling. If a
compound is detected at a level greater than the MCL, the system (whether ground water or
surface water) must take four consecutive quarterly samples until all are below the MCL. If all
quarterly samples are below the MCL, the system may return to annual sampling.
B.14.2 Occurrence in Drinking Water
The analysis of toluene occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 373,021
analytical results from 55,748 public water systems (PWSs) during the period from 2006 to
28 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling
frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including toluene, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for toluene in the dataset is 0.5 |ig/L.) Three arithmetic mean
toluene concentrations were calculated at each system using the zero, V2 MRL and full MRL
substitution values. These mean calculations were performed for all systems with toluene data in
the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater
than each threshold were calculated. For toluene, since there were no analytical method
limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the
MCL and the potential MCLG.
Stage 2 Occurrence Estimates
Stage 2 analyses for toluene are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 1,000 |ig/L (the MCL) and 600 |ig/L (the potential
MCLG). The potential MCLG is due to changes in the RfD based on new health effects
information. Since the practical quantitation level (PQL) for toluene is less than the possible
MCLG, EPA designated the possible MCLG as the threshold for the occurrence analysis. For
more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses,
refer to USEPA (2016d) and (2016e).
Exhibit B-53 presents the system-level Stage 2 analysis of estimated mean concentrations for
toluene occurrence in drinking water. Exhibit B-54 presents similar information based on
population served by the systems. No systems had an estimated system mean greater than the
MCL concentration of 1,000 |ig/L or the potential MCLG concentration of 600 |ig/L.
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Exhibit B-53: Toluene Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water
Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(51,316)
> 1,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 600 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Surface Water
(4,432)
> 1,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 600 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined
Ground &
Surface Water
(55,748)
> 1,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 600 |jg/L1
0
0
0
0.000%
0.000%
0.000%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Exhibit B-54: Toluene Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water
Type (Population
Served by
Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(110,897,342)
> 1,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 600 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Surface Water
(152,600,590)
> 1,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 600 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined
Ground &
Surface Water
> 1,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
Combined
Ground &
Surface Water,
cont.
> 600 |jg/L1
0
0
0
0.000%
0.000%
0.000%
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Source Water
Type (Population
Served by
Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
(263,497,932)







1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Data for toluene were available from 50 states/entities. Four states did not submit data for use in
the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the count of 50 states because a handful of tribal water systems
located within these 2 states did submit toluene data.
Exhibit B-55 presents the total number of systems in each state that submitted data for toluene.
In addition, the geographic distribution of toluene occurrence in drinking water is illustrated by
showing states with systems with a mean concentration greater than the potential MCLG and
MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.)
No water systems had an estimated mean greater than 1,000 |ig/L (the MCL) or the potential
MCLG of 600 |ig/L.
Exhibit B-55: Toluene Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total Number of
Systems
Systems with a Mean
Concentration > 600 |jg/L3
Systems with a Mean
Concentration > 1,000 |jg/L
Number
Percent
Number
Percent
AK
596




AL
384




AR
461




AS
11




AZ
1,110




CA
3,814




CO
1




CT
1,202




DC
1




FL
2,633




HI
111




IA
1,048




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State
Total Number of
Systems
Systems with a Mean
Concentration > 600 |jg/L3
Systems with a Mean
Concentration > 1,000 |jg/L
Number
Percent
Number
Percent
ID
839




IL
1,493




IN
1,196




KS
604




KY
227




LA
1,102




MA
721




MD
1,056




ME
784




Ml
2,419




MN
1,462




MO
1,445




MS
5




MT
897




NC
2,356




ND
160




NE
705




NH
1,186




NJ
1,434




NM
744




NV
350




NY
2,498




OH
1,922




OK
685




OR
1,131




PA
3,166




Rl
152




SC
494




SD
313




TN
366




TX
4,532




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State
Total Number of
Systems
Systems with a Mean
Concentration > 600 |jg/L3
Systems with a Mean
Concentration > 1,000 |jg/L
Number
Percent
Number
Percent
UT
471




VA
1,629




VT
634




WA
2,469




Wl
2,026




WV
386




WY
317




Total
55,748
0
0.00%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Exhibit B-56 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. As stated above, no water systems had an estimated mean
greater than the MCL or the potential MCLG.
Exhibit B-56: Toluene Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration
> 600 |jg/L3
Population Served by Systems
with a Mean Concentration
> 1,000 |jg/L
Population
Percent
Population
Percent
AK
719,618




AL
5,334,584




AR
2,637,712




AS
62,196




AZ
6,669,277




CA
40,642,888




CO
2,020




CT
2,937,643




DC
761,124




FL
19,280,091




HI
1,479,317




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State
Total
Population
Population Served by Systems
with a Mean Concentration
> 600 |jg/L3
Population Served by Systems
with a Mean Concentration
> 1,000 |jg/L
Population
Percent
Population
Percent
IA
2,753,930




ID
1,219,635




IL
11,019,196




IN
4,940,108




KS
2,628,748




KY
4,225,914




LA
4,966,653




MA
9,329,953




MD
5,120,669




ME
757,984




Ml
3,470,708




MN
4,373,668




MO
5,293,851




MS
6,176




MT
856,529




NC
7,827,828




ND
592,539




NE
1,664,802




NH
962,134




NJ
9,273,130




NM
1,962,298




NV
2,697,555




NY
10,637,039




OH
10,209,121




OK
3,588,559




OR
3,434,141




PA
11,234,684




Rl
1,040,737




SC
3,637,408




SD
757,925




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State
Total
Population
Population Served by Systems
with a Mean Concentration
> 600 |jg/L3
Population Served by Systems
with a Mean Concentration
> 1,000 |jg/L
Population
Percent
Population
Percent
TN
6,578,052




TX
23,863,702




UT
2,802,068




VA
6,908,525




VT
486,604




WA
5,535,917




Wl
4,273,462




WV
1,570,196




WY
469,314




Total
263,497,932
0
0.00%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
B.14.3 Summary of Data
A total of 373,021 analytical results from 55,748 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for toluene. The Stage 2 analysis of occurrence in drinking water indicated
that zero systems had an estimated system mean concentration of toluene greater than the MCL
concentration of 1,000 |ig/L or the potential MCLG of 600 |ig/L.
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B.15 Toxaphene
This chapter on toxaphene includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.15.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for toxaphene on January 30, 1991 (56 FR
3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) of
zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also
established a maximum contaminant level (MCL) of 3 |ig/L based on analytical feasibility.
Toxaphene is regulated as a synthetic organic chemical (SOC) in drinking water. All non-
purchased community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a
favorable vulnerability assessment and/or prior analytical results. The maximum waiver period
for SOCs is three years, but waivers can be renewed indefinitely, if it is reconfirmed that the
source is not vulnerable.
All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly
samples during the initial three-year compliance period.29 If all 4 samples are non-detections,
then a system serving less than 3,300 people may reduce its collection frequency to 1 sample
during each consecutive compliance period; a system serving more than 3,300 people may
reduce its collection frequency to 2 quarterly samples within a 12-month period during each
repeat compliance period. If a contaminant is detected, the system must monitor quarterly to
demonstrate that results are reliably and consistently below the MCL (minimum of two quarterly
samples for ground water systems and four quarterly samples for surface water systems). If all
quarterly samples are below the MCL, the system may return to annual sampling. If a
contaminant is detected at a concentrations greater than the MCL, the system (whether ground
water or surface water) must take quarterly samples until four consecutive quarters are below the
MCL. If all quarterly samples are below the MCL, the system may return to annual sampling.
B.15.2 Occurrence in Drinking Water
The analysis of toxaphene occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 127,187
analytical results from 37,043 public water systems (PWSs) during the period from 2006 to
2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
29 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the state. The system must also comply with the initial sampling
frequencies specified by the state to ensure that a system can demonstrate compliance with the MCL.
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EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including toxaphene, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Two different substitution values -zero and V2 the
minimum reporting level (MRL) value- were used to replace each non-detection record. (The
national modal MRL for toxaphene in the dataset is 1 |ig/L.) Two arithmetic mean toxaphene
concentrations were calculated at each system using the zero and V2 MRL substitution values.
These mean calculations were performed for all systems with toxaphene data in the SYR3 ICR
dataset. Then, the percentages of all systems with a mean concentration greater than each
threshold were calculated. For toxaphene, EPA generated Stage 2 occurrence estimates relative
to the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL.
Stage 2 Occurrence Estimates
Stage 2 analyses for toxaphene are summarized in this section. Occurrence estimates were
generated relative to four thresholds: 3 |ig/L (the MCL), 1.5 |ig/L (1/2 the MCL), 2 |ig/L (two
times the EQL) and 1 |ig/L (the EQL). The EQL represents the potential quantitation capabilities
below a practical quantitation level (PQL).30For more information on the new potential
thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e).
Exhibit B-57 presents the system-level Stage 2 analysis of estimated mean concentrations for
toxaphene occurrence in drinking water. Exhibit B-58 presents similar information based on
population served by the systems. Two systems (0.005 percent of all systems), serving 233,219
30 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility
level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA
evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation
capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2
analyses.
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people, had an estimated system mean greater than the MCL concentration of 3 |ig/L. Based on
the Stage 2 analyses using the V2 MRL substitution for non-detections, six water systems
(approximately 0.016 percent of all systems) had an estimated mean greater than the EQL of 1
|ig/L. These 6 systems serve 715,106 people.
Exhibit B-57: Toxaphene Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Ground Water
(33,812)
> 3 |jg/L
1
1
0.003%
0.003%
> 1.5 |jg/L
2
2
0.006%
0.006%
> 2 |jg/L
2
2
0.006%
0.006%
> 1 |jg/L1
4
2
0.012%
0.006%

Surface Water
(3,231)
> 3 |jg/L
1
1
0.031%
0.031%
> 1.5 |jg/L
2
2
0.062%
0.062%
> 2 |jg/L
2
1
0.062%
0.031%
> 1 |jg/L1
2
2
0.062%
0.062%

Combined Ground &
Surface Water
(37,043)
> 3 |jg/L
2
2
0.005%
0.005%
> 1.5 |jg/L
4
4
0.011%
0.011%
> 2 |jg/L
4
3
0.011%
0.008%
> 1 |jg/L1
6
4
0.016%
0.011%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
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Exhibit B-58: Toxaphene Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served by
Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the Threshold
Percent of Population Served by
Systems with Mean Concentrations
That Are Greater Than the
Threshold
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Non-detect values
= 1/2 MRL
Non-detect
values = 0
Ground Water
> 3 |jg/i
993
993
0.001%
0.001%
Ground Water, cont.
(91,710,210)
> 1.5 |jg/L
1,298
1,298
0.001%
0.001%
> 2 |jg/L
1,298
1,298
0.001%
0.001%
> 1 |jg/L1
8,739
1,298
0.010%
0.001%

Surface Water
(132,718,761)
> 3 |jg/L
232,226
232,226
0.175%
0.175%
> 1.5 |jg/L
706,367
706,367
0.532%
0.532%
> 2 |jg/L
706,367
232,226
0.532%
0.175%
> 1 |jg/L1
706,367
706,367
0.532%
0.532%

Combined Ground &
Surface Water
(223,888,971)
> 3 |jg/L
233,219
233,219
0.104%
0.104%
> 1.5 |jg/L
707,665
707,665
0.316%
0.316%
> 2 |jg/L
707,665
233,524
0.316%
0.104%
> 1 |jg/L1
715,106
707,665
0.319%
0.316%
1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Data for toxaphene were available from 49 states/entities. Four states did not submit data for use
in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the table below because a handful of tribal water systems located
within these two states did submit toxaphene data. New Jersey did submit Six-Year data for most
contaminants. There is a statewide waiver for toxaphene in New Jersey, however, so no
toxaphene data were available from that state.
Exhibit B-59 presents the total number of systems in each state that submitted data for
toxaphene. In addition, the geographic distribution of toxaphene occurrence in drinking water is
illustrated by showing states with systems with a mean concentration greater than the EQL, two
times the EQL, V2 MCL and MCL concentrations. (Note: Only the V2 MRL substitution results
are presented in this exhibit.) The distribution of systems with mean concentrations of toxaphene
is geographically dispersed. Detection rates were generally low; only two states had an estimated
mean concentration greater than the MCL. (New Mexico and North Carolina each contained a
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single system with a mean concentration greater than the MCL in each state.) Six systems in five
states had estimated mean concentrations greater than the EQL.
Exhibit B-59: Toxaphene Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total
Number of
Systems
Systems with a
Mean
Concentration
> 1 mq/l3
Systems with a
Mean
Concentration
> 2 jjg/L
Systems with a
Mean
Concentration
>1.5 jjg/L
Systems with a
Mean
Concentration
> 3 jjg/L
Number
Percent
Number
Percent
Number
Percent
Number
Percent
AK
12








AL
382








AR
459








AS
11








AZ
872








CA
1,271
1
0.08%
1
0.08%
1
0.08%
0
0.00%
CO
1








CT
1,137








DC
1








FL
2,086








HI
111








IA
1








ID
386








IL
1,466








IN
1,212








KS
87








KY
225








LA
946
1
0.11%
0
0.00%
0
0.00%
0
0.00%
MA
565








MD
45








ME
160








Ml
2,439








MN
920








MO
1,332








MS
5








MT
857








NC
2,347
2
0.09%
2
0.09%
2
0.09%
1
0.04%
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State
Total
Number of
Systems
Systems with a
Mean
Concentration
> 1 mq/l3
Systems with a
Mean
Concentration
> 2 jjg/L
Systems with a
Mean
Concentration
>1.5 jjg/L
Systems with a
Mean
Concentration
> 3 jjg/L
Number
Percent
Number
Percent
Number
Percent
Number
Percent
ND
157








NE
639








NH
1,146








NJ
0








NM
718
1
0.14%
1
0.14%
1
0.14%
1
0.14%
NV
303








NY
2,117








OH
18








OK
38








OR
1,118








PA
1,045
1
0.10%
0
0.00%
0
0.00%
0
0.00%
Rl
73








SC
497








SD
269








TN
6








TX
3,981








UT
428








VA
254








VT
380








WA
1,996








Wl
1,914








WV
292








WY
318








Total
37,043
6
0.02%
4
0.01%
4
0.01%
2
0.01%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the
thresholds.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
Exhibit B-60 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for toxaphene is presented, as well. As described above, North Carolina and New
Mexico were the only two states with an estimated mean concentration greater than the MCL of
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3 jug/L. Six systems in 5 states, serving 715,106 people, had estimated mean concentrations
greater than the EQL of 1 |ig/L.
Exhibit B-60: Toxaphene Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by
Systems with a Mean
Concentration
> 1 |ig/L3
Population Served by
Systems with a
Mean Concentration
> 2 |jg/L
Population Served by
Systems with a
Mean Concentration
> 1.5 |jg/L
Population Served by
Systems with a
Mean Concentration
> 3 |jg/L
Population
Percent
Population
Percent
Population
Percent
Population
Percent
AK
39,530








AL
5,332,585








AR
2,635,934








AS
62,196








AZ
6,487,437








CA
35,717,333
474,141
1.33%
474,141
1.33%
474,141
1.33%
0
0.00%
CO
2,020








CT
2,925,135








DC
761,124








FL
18,943,061








HI
1,479,317








IA
438








ID
976,182








IL
10,997,746








IN
4,969,942








KS
1,817,722








KY
4,225,473








LA
4,709,163
6,916
0.15%
0
0.00%
0
0.00%
0
0.00%
MA
9,163,377








MD
3,991,250








ME
356,698








Ml
7,221,983








MN
3,752,545








MO
5,233,314








MS
6,176








MT
845,294








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State
Total
Population
Population Served by
Systems with a Mean
Concentration
> 1 |ig/L3
Population Served by
Systems with a
Mean Concentration
> 2 |jg/L
Population Served by
Systems with a
Mean Concentration
> 1.5 |jg/L
Population Served by
Systems with a
Mean Concentration
> 3 |jg/L
Population
Percent
Population
Percent
Population
Percent
Population
Percent
NC
7,832,302
232,531
2.97%
232,531
2.97%
232,531
2.97%
232,226
2.96%
ND
592,232








NE
1,646,746








NH
949,308








NJ
0








NM
1,940,795
993
0.05%
993
0.05%
993
0.05%
993
0.05%
NV
2,681,668








NY
10,480,954








OH
676,533








OK
136,313








OR
3,432,307








PA
10,853,332
525
0.00%
0
0.00%
0
0.00%
0
0.00%
Rl
989,530








SC
3,622,250








SD
708,340








TN
1,168,508








TX
23,671,855








UT
2,752,741








VA
5,685,070








VT
386,948








WA
4,942,339








Wl
4,236,887








WV
1,379,328








WY
469,710








Total
223,888,971
715,106
0.32%
707,665
0.32%
707,665
0.32%
233,219
0.10%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the
thresholds.
3	The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential
quantitation capabilities below a PQL (USEPA, 2016d).
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B.15.3 Summary of Data
A total of 127,187 analytical results from 37,043 PWSs in 49 states/entities were available in the
SYR3 ICR Dataset for toxaphene. The Stage 2 analysis of occurrence in drinking water indicated
that 2 water systems (1 ground water system and 1 surface water system), serving a total
population of 233,219 people, had an estimated system mean concentration of toxaphene greater
than the MCL concentration of 3 |ig/L. Six water systems, serving 715,106 people, had an
estimated mean concentration greater than the EQL of 1 |ig/L.
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B.16 l,l?2-Trichloroethane
This chapter on 1,1,2-trichloroethane includes background information such as the regulatory
history and a summary of monitoring requirements, as well as occurrence and exposure estimates
in drinking water. All drinking water occurrence estimates are based on data from the National
Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year
Review (the "SYR3 ICR Dataset").
B.16.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for 1,1,2-trichloroethane on July 17, 1992 (57
FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal
(MCLG) of 3 |ig/L based on a reference dose (RfD) of 4 |ig/kg-day (0.004 mg/kg-day) and a
cancer classification of C, possible human carcinogen. The NPDWR also established a maximum
contaminant level (MCL) of 5 |ig/L based on analytical feasibility.
1,1,2-Trichloroethane is regulated as a volatile organic compound (VOC) in drinking water. All
non-purchased community water systems (CWSs) and non-transient non-community water
systems (NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs
is two compliance periods for ground water systems and one compliance period for surface water
systems.
All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial
three-year compliance period.31 If all four samples are non-detections, then the system may
reduce to annual sampling. After three annual samples without a detection, and upon conducting
a vulnerability assessment, a system may be granted a waiver. During the waiver period, the
ground water system must sample at least once, while surface water system must sample at the
frequency specified by the state. If a compound is detected, the system must take one sample per
quarter until results are below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems). If all quarterly samples are
reliably and consistently below the MCL, the system may return to annual sampling. If a
compound is detected at a level greater than the MCL, the system (whether ground water or
surface water) must take four consecutive quarterly samples until all are below the MCL. If all
quarterly samples are below the MCL, the system may return to annual sampling.
B.16.2 Occurrence in Drinking Water
The analysis of 1,1,2-trichloroethane occurrence presented in the following section is based on
state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 371,877
analytical results from 55,733 public water systems (PWSs) during the period from 2006 to
2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
31 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling
frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL.
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EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including 1,1,2-trichloroethane, for which
Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant
occurrence by generating estimated long-term mean concentrations of contaminants for each
system. This provides occurrence analyses that are less conservative than the Stage 1 analysis,
since the Stage 2 analysis is based on estimated mean concentrations rather than on a single
maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year)
mean concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means that were calculated using all sample
detection records and all non-detection records. Three different substitution values -zero, V2 the
minimum reporting level (MRL) value and the full MRL value- were used to replace each non-
detection record. Three arithmetic mean 1,1,2-trichloroethane concentrations were calculated at
each system using the zero, V2 MRL and full MRL substitution values. These mean calculations
were performed for all systems with data in the SYR3 ICR dataset. Then, the percentages of all
systems with a mean concentration greater than each threshold were calculated. For 1,1,2-
trichloroethane, EPA generated Stage 2 occurrence estimates relative to the MCL and the
MCLG. Note: The national modal MRL for 1,1,2-trichloroethane in the dataset is 0.5 |ig/L.
Stage 2 Occurrence Estimates
Stage 2 analyses for 1,1,2-trichloroethane are summarized in this section. Occurrence estimates
were generated relative to the following thresholds: 5 |ig/L (the MCL) and 3 |ig/L (the MCLG).
Because the current MCLG of 3 |ig/L is lower than the PQL for 1,1,2-trichloroethane of 5 |ig/L,
the threshold of interest for the occurrence analysis is the current MCLG of 3 |ig/L. For more
information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer
to USEPA (2016d) and (2016e).
Exhibit B-61 presents the system-level Stage 2 analysis of estimated mean concentrations for
1,1,2-trichloroethane occurrence in drinking water. Exhibit B-62 presents similar information
based on population served by the systems. Based on the Stage 2 analyses, zero water systems
had an estimated system mean greater than the MCL concentration of 5 |ig/L or the MCLG of 3
Hg/L-
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Exhibit B-61: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Systems with
a Mean Threshold Exceedance
Source Water
Type
(Number of
Systems)
Threshold
Number of Systems with Mean
Concentrations That Are Greater
Than the Threshold
Percent of Systems with Mean
Concentrations That Are Greater Than
the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(51,300)
> 5 |jg/i
0
0
0
0.000%
0.000%
0.000%
> 3 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Surface Water
(4,433)
> 5 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 3 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined
Ground &
Surface Water
(55,733)
> 5 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 3 |jg/L1
0
0
0
0.000%
0.000%
0.000%
1 The threshold of interest for this contaminant is the current MCLG.
Exhibit B-62: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems with
Mean Concentrations That Are
Greater Than the Threshold
Percent of Population Served by
Systems with Mean Concentrations
That Are Greater Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(110,769,873)
> 5 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 3 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Surface Water
(152,603,695)
> 5 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 3 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground &
Surface Water
(263,373,568)
> 5 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 3 |jg/L1
0
0
0
0.000%
0.000%
0.000%
1 The threshold of interest for this contaminant is the current MCLG.
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Data for 1,1,2-trichloroethane were available from 50 states/entities. Four states did not submit
data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although
the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3
ICR Dataset, these states are included in the table below because a handful of tribal water
systems located within these two states did submit 1,1,2-trichloroethane data.
Exhibit B-63 presents the total number of systems in each state that submitted data for 1,1,2-
trichloroethane. In addition, the geographic distribution of 1,1,2-trichloroethane occurrence in
drinking water is illustrated by showing states with systems with a mean concentration greater
than the MCLG and MCL concentrations. (Note: Only the V2 MRL substitution results are
presented in this exhibit.) As is described above, no systems had an estimated mean
concentration greater than the MCL or the MCLG.
Exhibit B-63: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Systems with
a Mean Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a Mean Concentration
> 3 |ig/L3
Systems with a Mean Concentration
> 5 |jg/L
Number
Percent
Number
Percent
AK
595




AL
384




AR
461




AS
11




AZ
1,109




CA
3,814




CO
1




CT
1,202




DC
1




FL
2,633




HI
110




IA
1,043




ID
839




IL
1,493




IN
1,196




KS
602




KY
227




LA
1,102




MA
721




MD
1,053




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State
Total Number
of Systems
Systems with a Mean Concentration
> 3 |ig/L3
Systems with a Mean Concentration
> 5 |jg/L
Number
Percent
Number
Percent
ME
784




Ml
2,419




MN
1,462




MO
1,445




MS
5




MT
897




NC
2,356




ND
160




NE
705




NH
1,185




NJ
1,434




NM
743




NV
350




NY
2,498




OH
1,922




OK
685




OR
1,132




PA
3,166




Rl
152




SC
494




SD
313




TN
366




TX
4,532




UT
471




VA
1,630




VT
634




WA
2,468




Wl
2,026




WV
385




WY
317




Total
55,733
0
0.00%
0
0.00%
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1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The threshold of interest for this contaminant is the current MCLG.
Exhibit B-64 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. As described above, no systems had an estimated mean
concentration greater than the MCL or the MCLG.
Exhibit B-64: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Population
Served by Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration
> 3 |ig/L3
Population Served by Systems
with a Mean Concentration
> 5 |jg/L
Population
Percent
Population
Percent
AK
719,561




AL
5,334,584




AR
2,637,712




AS
62,196




AZ
6,669,227




CA
40,641,146




CO
2,020




CT
2,937,643




DC
761,124




FL
19,280,091




HI
1,402,969




IA
2,734,678




ID
1,219,635




IL
11,019,196




IN
4,940,108




KS
2,605,030




KY
4,225,914




LA
4,966,653




MA
9,329,953




MD
5,120,409




ME
757,984




Ml
3,470,708




MN
4,373,668




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State
Total
Population
Population Served by Systems
with a Mean Concentration
> 3 |ig/L3
Population Served by Systems
with a Mean Concentration
> 5 |jg/L
Population
Percent
Population
Percent
MO
5,293,851




MS
6,176




MT
856,529




NC
7,827,828




ND
592,539




NE
1,664,802




NH
961,134




NJ
9,273,130




NM
1,960,247




NV
2,697,555




NY
10,637,039




OH
10,209,121




OK
3,588,559




OR
3,434,191




PA
11,234,684




Rl
1,040,737




SC
3,637,408




SD
757,925




TN
6,578,052




TX
23,863,702




UT
2,802,068




VA
6,908,704




VT
486,604




WA
5,535,827




Wl
4,273,462




WV
1,570,171




WY
469,314




Total
263,373,568
0
0.00%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The threshold of interest for this contaminant is the current MCLG.
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B.16.3 Summary of Data
A total of 371,877 analytical results from 55,733 PWSs in 50 states/entities were available in the
SYR3 ICRDataset for 1,1,2-trichloroethane. The Stage 2 analysis of occurrence in drinking
water indicated that zero systems had an estimated system mean concentration of 1,1,2-
trichloroethane greater than the MCL concentration of 5 |ig/L or the MCLG concentration of 3
Hg/L-
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B.17 Xylenes
This chapter on xylenes includes background information such as the regulatory history and a
summary of monitoring requirements, as well as occurrence and exposure estimates in drinking
water. All drinking water occurrence estimates are based on data from the National Compliance
Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the
"SYR3 ICR Dataset").
B.17.1 Background
The United States Environmental Protection Agency (EPA) published the current National
Primary Drinking Water Regulations (NPDWR) for total xylenes on January 30, 1991 (56 FR
3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG)
and a maximum contaminant level (MCL) of 10,000 |ig/L. The Agency based the MCLG on a
reference dose (RfD) of 2,000 |ig/kg-day (2 mg/kg-day) and a cancer classification of D, not
classifiable as to human carcinogenicity.
Xylenes are regulated as volatile organic compounds (VOCs) in drinking water. All non-
purchased community water systems (CWSs) and non-transient non-community water systems
(NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two
compliance periods for ground water systems and one compliance period for surface water
systems.
All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial
three-year compliance period.32 If all four samples are non-detections, then the system may
reduce to annual sampling. After three annual samples without a detection, and upon conducting
a vulnerability assessment, a system may be granted a waiver. During the waiver period, the
ground water system must sample at least once, while surface water system must sample at the
frequency specified by the state. If a compound is detected, the system must take one sample per
quarter until results are below the MCL (minimum of two quarterly samples for ground water
systems and four quarterly samples for surface water systems). If all quarterly samples are
reliably and consistently below the MCL, the system may return to annual sampling. If a
compound is detected at a level greater than the MCL, the system (whether ground water or
surface water) must take four consecutive quarterly samples until all are below the MCL. If all
quarterly samples are below the MCL, the system may return to annual sampling.
B.17.2 Occurrence in Drinking Water
The analysis of xylenes occurrence presented in the following section is based on state
compliance monitoring data from the SYR3 ICR Dataset. These data consist of 323,477
analytical results from 51,074 public water systems (PWSs) during the period from 2006 to
32 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate
compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling
frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL.
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2011. The number of sample results and systems vary by state, although the state datasets have
been reviewed and checked to ensure adequacy of coverage and completeness.
EPA used a two-stage analytical approach to estimate the national contaminant occurrence using
the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate
simple non-parametric estimates and descriptive statistics of national contaminant occurrence in
public water systems. Simple counts were made of the number and percentage of systems and
population served by systems with at least one compliance monitoring sample result greater than
a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that
are more conservative and may be more reflective of potential acute exposure than the
assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6.
Based on the evaluation of the health effects and analytical methods as part of the Six-Year
Review protocol, EPA selected a set of contaminants, including xylenes, for which Stage 2
analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by
generating estimated long-term mean concentrations of contaminants for each system. This
provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage
2 analysis is based on estimated mean concentrations rather than on a single maximum
concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean
concentration estimates for contaminant occurrence at systems, the analyses can support
assessments of population served by systems with detections or potential exposure assessments
that may be more reflective of potential chronic exposure than the assessments from the Stage 1
analyses.
For the Stage 2 analyses, system arithmetic means were calculated using all sample detection
records and all non-detection records. Three different substitution values -zero, V2 the minimum
reporting level (MRL) value and the full MRL value- were used to replace each non-detection
record. (The national modal MRL for xylenes in the dataset is 0.5 |ig/L.) Three arithmetic mean
xylenes concentrations were calculated at each system using the zero, V2 MRL and full MRL
substitution values. These mean calculations were performed for all systems with xylenes data in
the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater
than each threshold were calculated. For xylenes, since there were no analytical method
limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the
MCL and the potential MCLG.
Stage 2 Occurrence Estimates
Stage 2 analyses for xylenes are summarized in this section. Occurrence estimates were
generated relative to the following thresholds: 10,000 |ig/L (the MCL) and 1,000 |ig/L (the
potential MCLG). The potential MCLG is due to changes in the RfD based on new health effects
information. Since the practical quantitation level (PQL) for xylenes is less than the possible
MCLG, EPA designated the possible MCLG as the threshold for the occurrence analysis. For
more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses,
refer to USEPA (2016d) and (2016e).
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Exhibit B-65 presents the system-level Stage 2 analysis of estimated mean concentrations for
xylenes occurrence in drinking water. Exhibit B-66 presents similar information based on
population served by the systems. Based on the Stage 2 analyses, no systems had an estimated
system mean greater than the MCL concentration of 10,000 |ig/L. Two systems, serving 825
people, had an estimated system mean greater than the potential MCLG concentration of 1,000
Hg/L-
Exhibit B-65: Xylenes Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance
Source Water Type
(Number of Systems)
Threshold
Number of Systems with Mean
Concentrations That Are
Greater Than the Threshold
Percent of Systems with Mean
Concentrations That Are
Greater Than the Threshold
Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Non-
detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
(47,037)
> 10,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 1,000 |jg/L1
2
2
2
0.004%
0.004%
0.004%

Surface Water
(4,037)
> 10,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 1,000 |jg/L1
0
0
0
0.000%
0.000%
0.000%

Combined Ground &
Surface Water
(51,074)
> 10,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
> 1,000 |jg/L1
2
2
2
0.004%
0.004%
0.004%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Exhibit B-66: Xylenes Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance
Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the
Threshold
Percent of Population Served
by Systems with Mean
Concentrations That Are
Greater Than the Threshold


Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Non-
detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0
Ground Water
> 10,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
(106,335,621)
> 1,000 |jg/L1
825
825
825
0.0008%
0.0008%
0.0008%

Surface Water
> 10,000 |jg/L
0
0
0
0.000%
0.000%
0.000%

> 1,000 |jg/L1
0
0
0
0.000%
0.000%
0.000%
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Source Water Type
(Population Served
by Systems)
Threshold
Population Served by Systems
with Mean Concentrations That
Are Greater Than the
Threshold
Percent of Population Served
by Systems with Mean
Concentrations That Are
Greater Than the Threshold


Non-detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-
detect
values
= 0
Non-
detect
values
= MRL
Non-detect
values
= 1/2 MRL
Non-detect
values
= 0

Combined Ground &
Surface Water
> 10,000 |jg/L
0
0
0
0.000%
0.000%
0.000%
(248,916,224)
> 1,000 |jg/L1
825
825
825
0.0003%
0.0003%
0.0003%
1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Data for xylenes were available from 50 states/entities. Four states did not submit data for use in
the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of
Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset,
these states are included in the count of 50 states because a handful of tribal water systems
located within these 2 states did submit xylenes data.
Exhibit B-67 presents the total number of systems in each state that submitted data for xylenes.
In addition, the geographic distribution of xylenes occurrence in drinking water is illustrated by
showing states with systems with a mean concentration greater than the potential MCLG and
MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.)
As was stated above, no systems had an estimated mean concentration greater than the MCL.
Two systems in two states (Michigan and Pennsylvania) had estimated mean concentrations
greater than the potential MCLG of 1,000 |ig/L.
Exhibit B-67: Xylenes Stage 2 Analysis - Summary of Systems with a Mean
Threshold Exceedance by State12
State
Total Number
of Systems
Systems with a Mean
Concentration > 1,000 |jg/L3
Systems with a Mean
Concentration > 10,000 |jg/L
Number
Percent
Number
Percent
AK
596




AL
384




AR
461




AS
11




AZ
1,111




CA
3,790




CO
1




CT
5




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State
Total Number
of Systems
Systems with a Mean
Concentration > 1,000 |jg/L3
Systems with a Mean
Concentration > 10,000 |jg/L
Number
Percent
Number
Percent
DC
1




FL
2,633




HI
18




IA
1,085




ID
839




IL
1,493




IN
1,196




KS
608




KY
227




LA
1,102




MA
721




MD
1,055




ME
749




Ml
2,419
1
0.04%
0
0.00%
MN
1,466




MO
1,445




MS
5




MT
897




NC
2,356




ND
160




NE
705




NH
1,185




NJ
1,428




NM
744




NV
350




NY
20




OH
1,922




OK
685




OR
1,132




PA
3,166
1
0.03%
0
0.00%
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State
Total Number
of Systems
Systems with a Mean
Concentration > 1,000 |jg/L3
Systems with a Mean
Concentration > 10,000 |jg/L
Number
Percent
Number
Percent
Rl
152




SC
494




SD
313




TN
366




TX
3,826




UT
471




VA
1,629




VT
465




WA
2,458




Wl
2,026




WV
386




WY
317




Total
51,074
2
0.004%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
Exhibit B-68 presents the population served by systems with a mean concentration greater than
the MCL concentration by state. The total population served by systems in each state that
submitted data for xylenes is presented, as well. As described above, no systems had an
estimated mean concentration greater than the MCL. Two systems, serving 825 people, had
estimated mean concentrations greater than the potential MCLG (1,000 |ig/L).
Exhibit B-68: Xylenes Stage 2 Analysis - Summary of Population Served by
Systems with a Mean Threshold Exceedance by State12
State
Total
Population
Population Served by Systems
with a Mean Concentration
> 1,000 |jg/L3
Population Served by Systems
with a Mean Concentration
> 10,000 |jg/L
Population
Percent
Population
Percent
AK
719,618




AL
5,334,584




AR
2,637,712




AS
62,196




AZ
6,669,311




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State
Total
Population
Population Served by Systems
with a Mean Concentration
> 1,000 |jg/L3
Population Served by Systems
with a Mean Concentration
> 10,000 |jg/L
Population
Percent
Population
Percent
CA
40,638,016




CO
2,020




CT
193,473




DC
761,124




FL
19,280,091




HI
1,094,345




IA
2,759,457




ID
1,219,635




IL
11,019,196




IN
4,940,108




KS
2,608,108




KY
4,225,914




LA
4,966,653




MA
9,329,953




MD
5,120,434




ME
754,554




Ml
3,470,708
25
0.001 %
0
0.00%
MN
4,375,774




MO
4,975,051




MS
6,176




MT
856,529




NC
7,827,828




ND
592,539




NE
1,664,802




NH
961,134




NJ
9,272,654




NM
1,962,298




NV
2,697,555




NY
32,600




OH
10,209,121




OK
3,588,559




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State
Total
Population
Population Served by Systems
with a Mean Concentration
> 1,000 |jg/L3
Population Served by Systems
with a Mean Concentration
> 10,000 |jg/L
Population
Percent
Population
Percent
OR
3,434,191




PA
11,234,684
800
0.01%
0
0.00%
Rl
1,040,737




SC
3,637,408




SD
757,925




TN
6,578,052




TX
23,407,822




UT
2,802,068




VA
6,908,536




VT
436,629




WA
5,535,245




Wl
4,273,462




WV
1,570,321




WY
469,314




Total
248,916,224
825
0.0003%
0
0.00%
1	Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset.
2	Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold.
3	The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects
information.
B.17.3 Summary of Data
A total of 323,477 analytical results from 51,074 PWSs in 50 states/entities were available in the
SYR3 ICR Dataset for xylenes. The Stage 2 analysis of occurrence in drinking water indicated
that zero systems had an estimated system mean concentration of xylenes greater than the MCL
concentration of 10,000 |ig/L. Two ground water systems, serving a total of 825 people, had an
estimated mean concentration greater than the potential MCLG (1,000 |ig/L). These two systems
were located in Michigan and Pennsylvania.
SYR3 Occurrence Support Document
B-143
December 2016

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