United States Office of Water EPA 822-R-15-001
Environmental Protection Office of Science and June 2015
Agency Technology
EPA Response to Scientific Views from the Public
on
Draft Updated National Recommended Water Quality Criteria
for the Protection of Human Health
(Docket ID No. EPA-HQ-OW-2014-0135)
June 2015
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TABLE OF CONTENTS
INTRODUCTION 3
LIST OF COMMENTERS 4
1 OVERALL IMPRESSIONS 6
1.1 GENERAL SUPPORT 6
1.2 GENERAL OPPOSITION 6
2 PUBLIC COMMENT PERIOD 9
2.1 REQUEST FOR EXTENSION 9
3 AWQC INPUT PARAMETERS 9
3.1 BODY WEIGHT 9
3.2 DRINKING WATER INTAKE 11
3.3 FISH CONSUMPTION RATE 15
3.4 BIOACCUMULATION FACTORS 18
3.5 HUMAN HEALTH TOXICITY VALUES 21
3.6 RELATIVE SOURCE CONTRIBUTION 23
4 CHEMICAL-SPECIFIC ISSUES 26
4.1 BIOACCUMULATION FACTORS 26
4.2 HUMAN HEALTH TOXICITY VALUES 29
4.3 RELATIVE SOURCE CONTRIBUTION 33
5 IMPLEMENTATION 34
5.1 STATE FLEXIBILITY 34
5.2 IMPAIRED WATER BODIES 36
5.3 ECONOMIC IMPACTS 36
6 MISCELLANEOUS 38
7 REFERENCES 39
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INTRODUCTION
EPA has updated its national recommended ambient water quality criteria (AWQC) for human
health for 94 chemical pollutants to reflect the latest scientific information and implementation
of existing EPA policies found in Methodology for Deriving Ambient Water Quality Criteria for
the Protection of Human Health (2000). EPA issued the draft updated human health criteria on
May 13, 2014 and accepted written scientific views from the public until August 13, 2014. EPA
considered those scientific views during finalization of the AWQC and prepared the following
responses to those public comments.
The final updated human health criteria were developed pursuant to Section 304(a) of the
Clean Water Act. EPA's recommended Section 304(a) criteria provide technical information for
states and authorized tribes to consider and use in adopting water quality standards that
ultimately provide the basis for assessing water body health and controlling discharges of
pollutants into waters of the United States.
The public comments (scientific views) summarized in this document are condensed versions of
the original comments provided in the Public Docket (EPA-HQ-OW-2014-0135).
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LISTOFCOMMENTERS
Alaska Department of Environmental Conservation
Alcoa Inc.
American Chemistry Council
American Forest & Paper Association
American Water Works Association
Association of Clean Water Administrators
Association of Missouri Cleanwater Agencies
Central Valley Clean Water Association
City of Everett, Public Works, Everett, Washington
Clearwater Paper Corporation
County of San Diego, Department of Public Works, Watershed Protection Program
Department of Defense
District Department of the Environment
Federal Water Quality Coalition
Florida Department of Environmental Protection
Florida Water Environment Association Utility Council
Hampton Roads Sanitation District
Idaho Department of Environmental Quality
Integral Consulting Inc, on behalf of Syngenta
J.R. Simplot Company
Lower Elwha Klallam Tribe
Minnesota Pollution Control Agency
National Association of Clean Water Agencies
North American Metals Council
North Carolina Conservation Network and Clean Water Action
North Carolina Water Quality Association, Inc.
Northwest Indian Fisheries Commission
Northwest Pulp & Paper Association
Ohio Environmental Protection Agency
Oregon Department of Environmental Quality
Pennsylvania Department of Environmental Protection
Pentachlorophenol Task Force
South Carolina Water Quality Association, Inc.
State of Washington Department of Ecology
Steven Rudnick, Public Citizen
Texas Commission on Environmental Quality
The Boeing Company
Transportation and Storm Water Department, City of San Diego, California
Treated Wood Council
Utility Water Act Group
West Virginia Department of Environmental Protection
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West Virginia Municipal Water Quality Association, Inc.
Wet Weather Partnership
Wisconsin Department of Natural Resources
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1 OVERALL IMPRESSIONS
1.1 GENERAL SUPPORT
1.1.1 Comment: Several commenters noted that they appreciated EPA's efforts to update and
maintain the national recommended human health ambient water quality criteria (AWQC).
Some commenters supported EPA's use of the most recent health effects toxicity values
(reference doses, cancer slope factors) from various sources for developing ambient water
quality criteria instead of relying solely on toxicity information from EPA's Integrated Risk
Information System (IRIS). Several commenters also supported EPA's decision to use
bioaccumulation factors (BAFs) instead of bioconcentration factors (BCFs).
EPA Response: EPA appreciates the support. The Clean Water Act (CWA) section 304(a) requires
EPA to develop, and from time to time, revise AWQC that will protect and maintain designated
uses, including safe drinking water supplies. EPA updated 94 AWQC to reflect the latest scientific
information and EPA policies. The updates take into account current exposure factors (body
weight, drinking water intake, and fish consumption rate), bioaccumulation factors, and toxicity
factors (reference dose, cancer slope factor) and follow the approach described in the EPA
Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health
("2000 Methodology") (USEPA 2000a).
In addition, refer to EPA's responses to the Exposure Input Parameters (section 3 of this
response to comments) - body weight (3.1), drinking water intake (3.2), fish consumption rate
(3.3), bioaccumulation factors (3.4), human health toxicity values (3.5), and relative source
contribution (3.6) for specific responses.
1.2 GENERAL OPPOSITION
1.2.1 Comment: Some commenters suggested that the draft updated AWQC may be based on
changes in policy rather than changes in science and requested that EPA identify and
distinguish policy choices from changes in scientific information. Several commenters
questioned whether the proposed numeric AWQC were appropriately peer reviewed.
EPA Response: The updated AWQC reflect implementation of existing EPA policies found in the
2000 Methodology (USEPA 2000a).
In addition, EPA updated the AWQC for 94 chemical pollutants to reflect the latest scientific
information and to take into account current exposure factors (body weight, drinking water
intake, fish consumption rate), bioaccumulation factors, and toxicity factors (reference dose,
cancer slope factor). See additional clarifications in section 3 of this document.
EPA based these revised criteria recommendations on sound science and policies that have been
externally peer reviewed and thoroughly vetted publicly, including:
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• USEPA (U.S. Environmental Protection Agency). 2000. Methodology for Deriving
Ambient Water Quality Criteria for the Protection of Human Health (2000). EPA-822-B-
00-004. U.S. Environmental Protection Agency, Office of Water, Office of Science and
Technology, Washington, DC.
• USEPA (U.S. Environmental Protection Agency). 2000. Methodology for Deriving
Ambient Water Quality Criteria for the Protection of Human Health (2000), Technical
Support Document. Vol. 1, Risk Assessment. EPA-822-B-00-005. U.S. Environmental
Protection Agency, Office of Water, Office of Science and Technology, Washington, DC.
• USEPA (U.S. Environmental Protection Agency). 2003. Methodology for Deriving
Ambient Water Quality Criteria for the Protection of Human Health (2000), Technical
Support Document. Vol. 2, Development of National Bioaccumulation Factors. EPA-822-
R-03-030. U.S. Environmental Protection Agency, Office of Water, Office of Science and
Technology, Washington, DC.
• USEPA (U.S. Environmental Protection Agency). 2011. Exposure Factors Handbook: 2011
Edition. EPA-600-R-09-052F. U.S. Environmental Protection Agency, Office of Research
and Development, Washington, DC.
• USEPA (U.S. Environmental Protection Agency). 2012. Estimation Programs Interface
(EPI) Suite™ for Microsoft® Windows, v 4.10. U.S. Environmental Protection Agency,
Office of Pollution Prevention and Toxics, Washington, DC.
• USEPA (U.S. Environmental Protection Agency). 2014. Estimated Fish Consumption Rates
for the U.S. Population and Selected Subpopulations (NHANES 2003-2010). EPA-820-R-
14-002. U.S. Environmental Protection Agency, Off ice of Water, Washington, DC.
1.2.2 Comment: A commenter noted that, according to the EPA Framework for Human Health
Risk Assessment to Inform Decision Making ("Framework;" USEPA 2014a), the AWQC's problem
formulation section should consist of analytical considerations of the issues that are major
factors influencing the technical approach; EPA failed to include the problem formulation
information, including a conceptual model and chemical specific analysis plan, for each
chemical.
EPA Response: In updating the criteria, EPA relied upon the policies and processes outlined in
the 2000 Methodology (USEPA 2000a). Although the 2000 Methodology predates the EPA
Framework (USEPA 2014a), many of the steps, in effect, apply the same approaches outlined in
that document. The structure of each of the 94 criteria documents is intended to be consistent
with general concepts of effects assessments as described in the EPA Framework (USEPA
2014a). The 2000 Methodology includes steps that are, effectively, a problem formulation, a
conceptual model, etc. These analyses were applied uniformly to all chemicals in the context of
the crtieria update. The updated AWOC relied on peer reviewed information and were
submitted to public comment during development.
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1.2.3 Comment: Some commenters suggested that EPA revise the 2000 Methodology prior to
revising the AWQC.
EPA Response: The 2000 Methodology was developed over more than eight years and included
scientific review by EPA's Science Advisory Board (1993), a four-month public comment period
(1998), a public meeting (1999), an external peer review workshop (1999), and multiple
stakeholder review processes. For these reasons, EPA reasonably chose to update the AWQC
following this peer-reviewed, publicly vetted methodology.
1.2.4 Comment: Several commenters suggested that EPA's assumptions used to calculate the
proposed AWQC are overly conservative for the protection of human health.
EPA Response: EPA based the revised AWQC recommendations on sound science and policies
that have been thoroughly vetted publicly (see above). The exposure and toxicity inputs used to
derive the AWQC follow the approach described in the 2000 Methodology (USE PA 2000a).
AWQC for the protection of human health are designed to minimize the risk of adverse effects
occurring to humans from chronic (lifetime) exposure to substances through the ingestion of
drinking water and consumption offish obtained from surface water. Following the 2000
Methodology, EPA used a combination of median values, mean values, and percentile estimates
for the parameter value defaults to calculate its updated AWQC. EPA's assumptions afford an
overall level of protection targeted at the high end of the general population (i.e., the target
population or the criteria-basis population) (USEPA 2000a). This approach is reasonably
conservative and appropriate to meet the goals of the CWA and the 304(a) criteria program
(USEPA 2000a).
EPA made the following standard assumptions for the updated AWQC (USEPA 2000a). The
default body weight (80 kg) is an arithmetic mean. National BAFs were computed using mean
lipid values and median (i.e., 50th percentile) values for dissolved organic carbon and particulate
organic carbon. The default drinking water intake rate and fish consumption rate are 90th
percentile estimates. The use of these values result in 304(a) AWQC that are protective of a
majority of the population; this is EPA's goal (USEPA 2000a). See additional clarifications in
section 3 of this document.
1.2.5 Comment: Commenters noted that there was a lack of transparency in the technical
record underlying the draft AWQC. Commenters requested that EPA provide additional
documentation on the development of the proposed AWQC.
EPA Response: EPA has provided documentation of the data and process used to develop each
updated AWQC in the final 94 criteria documents. In particular, EPA has added text in each of
the criteria documents that describes in a clear, transparent manner the selection process for
toxicity values, the approach for development of the bioaccumulation factors (BAFs), and the
approach for development of the relative source contributions (RSCs). The documents can be
accessed on EPA's website at
http://water.epa.Qov/scitech/swQuidance/standards/criteria/health/.
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1.2.6 Comment: Several commenters recommended the use of a probabilistic risk assessment
approach rather than using a deterministic approach to derive numeric AWQC.
EPA Response: EPA has not implemented probabilistic risk assessment approaches in this
update to the AWQC. The use of probabilistic techniques was not reflected in the 2000
Methodology (USEPA 2000o), which served as the guide for the current revisions (for the
reasons described above in EPA response to comment 1.2.3). EPA intends to consider
probabilistic techniques in future updates of the 2000 Methodology.
1.2.7 Comment: Some commenters requested that EPA evaluate the potential economic
impacts on affected entities before finalizing the criteria and issue additional technical support
documents on implementation for CWA purposes before issuing the AWQC as final.
EPA Response: Water quality criteria developed by EPA under section 304(a) are based solely on
data and scientific judgments on the relationship between pollutant concentrations and
environmental and human health effects. As a result, section 304(a) criteria do not reflect
consideration of economic impacts or the technological feasibility of meeting pollutant
concentrations in ambient water (see also section 5).
2 PUBLIC COMMENT PERIOD
2.1 REQUEST FOR EXTENSION
2.1.1 Comment: Several commenters requested an extension of the public comment period to
allow them to perform a comprehensive review and analysis of the draft updated AWQC and to
consider potential impacts. These commenters requested extension times ranging from 30 to
90 days past the original July 14, 2014 public comment period end date.
EPA Response: In response to stakeholder requests, on June 23, 2014, EPA announced in the
Federal Register (79 FR 35545) an extension of the public comment period for an additional
30 days, until August 13, 2014. This extension allowed the public to comment on the draft
updated AWQC for a total of 90 days.
3 AWQC INPUT PARAMETERS
3.1 BODY WEIGHT
3.1.1 Comment: Several commenters noted that some populations may not be adequately
protected by criteria derived using an assumed body weight of 80 kilograms (kg) (e.g., adults
weighing less than 80 kg (particularly women), children, and infants). The commenters
requested that EPA clarify how states and tribes should consider calculating or applying criteria
to be protective of these populations, including being fully protective of children. One
commenter suggested that EPA does not explicitly consider life stage (from preconception to
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adult) differences to health risks from water and fish pollutants and suggested normalization of
the drinking water and fish consumption rates per body weight.
EPA Response: EPA has updated the default body weight assumption for AWQC to 80.0 kg
based on National Health and Nutrition Examination Survey (NHANES) data from 1999 to 2006
as recommended in EPA's Exposure Factors Handbook (USEPA 2011). This represents the mean
body weight for adults ages 21 and older. EPA's previously recommended body weight
assumption was 70 kilograms, which was based on the mean body weight of adults from the
NHANES III database (1988-1994).
Regarding protection of individuals weighing less than 80 kg, EPA set the updated AWQC at a
level intended to be adequately protective of a human population over a lifetime (USEPA
2000a). For this update, as in previous updates (in 2002 and 2003), exposure factors were
chosen for the general adult population only. Also, EPA did not normalize drinking water and
fish consumption rates per body weight, which is consistent with the 2000 Methodology (USEPA
2000a).
However, states and tribes may modify EPA's recommendations (including normalization of
drinking water intake and fish consumption), as appropriate, for various lifestages. If pregnant
women/fetuses or young children are the target populations, then EPA recommends criteria
development using specific exposures for those groups (for acute or subchronic toxicity only).
For more information on exposure considerations for children and sensitive target populations,
see EPA's 2000 Methodology (USEPA 2000a). Updated exposure parameters for sensitive
populations may also be found in EPA's Exposure Factors Handbook (USEPA 2011) and EPA's
updated fish consumption report, Estimated Fish Consumption Rates for the U.S. Population
and Selected Subpopulations (NHANES 2003-2010) (USEPA 2014b).
3.1.2 Comment: One commenter noted that the updated body weight assumption of 80 kg
creates two groups of AWQC, those calculated with the updated body weight (80 kg) and those
criteria that were not updated and remain calculated with the previous body weight
assumption (70 kilograms). The commenter asked EPA to clarify what, if anything, should be
done to address this discrepancy.
EPA Response: For the criteria that are not being updated at this time, EPA acknowledges that
the AWQC for these pollutants continue to rely on previously recommended exposure
assumptions, including a 70-kilogram body weight assumption. Due to outstanding technical
issues, EPA did not update the following chemical pollutants: antimony, arsenic, asbestos,
barium, beryllium, cadmium, chromium (III or VI), copper, manganese, methylmercury, nickel,
nitrates, nitrosamines, N-nitrosodibutylamine, N-nitrosodiethylamine, N-nitrosopyrrolidine,
N-nitrosodimethylamine, N-nitrosodi-n-propylamine, N-nitrosodiphenylamine, polychlorinated
biphenyls (PCBs), selenium, thallium, zinc, or 2,3,7,8-TCDD (dioxin).
EPA intends to update AWQC for additional pollutants as sufficient information becomes
available to address technical issues, such as the bioaccumulation of metals, and some non-
lipophilic compounds in a scientifically defensible manner. In the meantime, states should
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consider adopting the existing criteria recommendations for those compounds that were not
addressed in this update. In addition, states or tribes can modify EPA's AWQC to reflect site-
specific conditions and inputs, such as body weight, drinking water intake, and fish consumption
rates that are protective of specific populations identified by a state or tribe, or adopt different
AWQC based on other scientifically defensible methods. EPA must, however, approve any new
water quality standards adopted by a state before they can be used for CWA purposes.
3.2 DRINKING WATER INTAKE
3.2.1 Comment: Several commenters suggested that EPA's draft drinking water intake
assumption (3 liters per day [L/d]) presented an unrealistic or overly conservative exposure
scenario for most of the population. Some commenters questioned the inclusion of "indirect"
sources of water in the intake rate and asked EPA to further justify its selection of the drinking
water intake rate.
EPA Response: In light of the comments received, EPA revised the drinking water intake rate
used in the final 2015 updated AWQC. EPA revised the default drinking water intake rate from
the proposed 3 L/d to 2.4 L/d, rounded from 2.414 L/d, based on NHANES data from 2003 to
2006 as reported in EPA's Exposure Factors Handbook (USEPA 2011, Table 3-23). This rate
represents the per capita estimate of combined direct and indirect community water1 ingestion
at the 90th percentilefor adults ages 21 and older. EPA selected the per capita rate for the
updated drinking water intake rate because it represents the average daily dose estimates; that
is, it includes people who reported that they drank water during the survey period and those
who reported that they did not, which is appropriate for a national-scale assessment such as
CWA section 304(a) AWQC development (USEPA 2011, section 3.2.1).
In the 2014 draft AWQC, EPA chose a default drinking water intake rate assumption of 3 L/d,
which represented a consumer-only estimate of combined direct and indirect water ingestion
based on NHANES data from 2003 to 2006 as reported in EPA's Exposure Factors Handbook
(USEPA 2011, Table 3-36) for all sources2 of water at the 90th percentilefor adults ages 21 and
older. Consumer-only estimated intake rates may be appropriate for more site-specific or local-
scale assessments, such as those conducted by EPA Office of Solid Waste and Emergency
Response (OSWER), because they represent the quantity of water consumed only by individuals
who reported water intake during the survey period, resulting in a higher (more conservative)
intake rate (USEPA 2011, section 3.2.1).
1 Community water includes direct and indirect use of tap water for household uses and excludes bottled water
and other sources (USEPA 2011, section 3.3.1.2). Direct ingestion is defined as direct consumption of water as a
beverage, while indirect ingestion includes water added during food preparation (e.g., cooking, rehydration of
beverages) but not water intrinsic to purchased foods (USEPA 2011, section 3.1).
2 "All sources" includes water from all supply sources such as community water supply (tap water), bottled water,
other sources, and missing/unknown sources.
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EPA's updated drinking water intake rate of 2.4 L/d is consistent with the methodology
described in the 2000 Methodology (USEPA 2000a). In that document, EPA recommended a
default drinking water intake rate of 2 L/d, which represented the per capita ingestion rate of
community water at the 86th percentilefor adults surveyed in the U.S. Department of
Agriculture's 1994-1996 Continuing Survey of Food Intake by Individuals (CSFII) analysis (USEPA
2000a, section 4.3.2.1).
3.2.2 Comment: Commenters noted that most of the population does not drink water from
untreated surface water sources. A commenter noted that the default water consumption rates
(both the previously recommended 2 L/d and the updated rate of 3 L/d) do not represent a
consideration of actual health risk but rather were selected in support of larger goals related to
pollution prevention and maintenance of designated uses.
EPA Response: Since at least the 1980s, EPA has included the drinking water exposure pathway
in the development ofAWQC in order to provide information to states to protect water bodies
designated for drinking water use. The rationale for inclusion of drinking water in the criteria
are cited in the 2000 Methodology (USEPA 2000a) as follows:
EPA recommends inclusion of the drinking water exposure pathway where drinking
water is a designated use for the following reasons: (1) Drinking water is a designated
use for surface waters under the CWA and, therefore, criteria are needed to assure that
this designated use can be protected and maintained. (2) Although rare, there are some
public water supplies that provide drinking water from surface water sources without
treatment. (3) Even among the majority of water supplies that do treat surface waters,
existing treatments may not necessarily be effective for reducing levels of particular
contaminants. (4) In consideration of the Agency's goals of pollution prevention, ambient
waters should not be contaminated to a level where the burden of achieving health
objectives is shifted away from those responsible for pollutant discharges and placed on
downstream users to bear the costs of upgraded or supplemental water treatment.
3.2.3 Comment: The NHANES data cited in EPA's Exposure Factors Handbook (USEPA 2011) are
potentially biased because the drinking water intake values in the NHANES study are based on
self-reporting data.
EPA Response: EPA analyzed the data provided from NHANES 2003 to 2006 to develop
distributions of drinking water intake for different age groups and bias has been adequately
addressed in the analytical methods applied. Studies presented in the Exposure Factors
Handbook (USEPA 2011) were carefully selected based on a number of considerations, including
first and foremost, study soundness (adequacy of the approach and minimal or defined bias).
The NHANES study soundness was rated medium to high (USEPA 2011, Table 3-2). EPA's
analysis was peer reviewed and found to be a sound basis for estimation of drinking water
intake (Eastern Research Group 2010).
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3.2.4 Comment: There is a divergence in the exposure assumptions used for the AWQC and the
exposure assumptions used to calculate maximum contaminant level goals (MCLGs) under the
Safe Drinking Water Act (SDWA).
EPA Response: The CWA's AWQC and the SDWA regulatory programs offer complementary
protection to the U.S. population, are carried out under different statutory authorities with
differing regulatory processes, and are administered separately under different timelines.
Section 304(a) of the CWA requires the Agency to develop AWQC that will protect and maintain
designated uses, including waters defined by states in their designated uses as drinking water
supplies. AWQC are not intended to reflect consideration of non-human health endpoints or
economic impacts, nor do they consider the technological feasibility of meeting the chemical
concentrations in ambient water. The SDWA is directed to incorporate technological constraints,
including analytical method and water treatment limitations, as well as toxicological
information in the development of MCLGs for individual chemicals.
EPA acknowledges and agrees that the best available drinking water intake and body weight
data should be used in evaluating drinking water contaminants. EPA considers new data on
human exposures as it would other new scientific data to evaluate regulated and unregulated
contaminants under the SDWA. EPA will consider the updated exposure assumptions as it
develops drinking water health advisories, revises existing drinking water regulations and
develops future drinking water regulations.
The SDWA requires EPA to review each National Primary Drinking Water Regulation (NPDWR) at
least once every six years and revise them, if appropriate. The purpose of the review, called the
Six Year Review, is to identify those NPDWRsfor which current health effects assessments,
changes in technology, and/or other factors provide a health or technical basis to support a
regulatory revision that will maintain or strengthen public health protection. EPA does not
intend to use the updated exposure assumptions to conduct the Six Year Review, however, the
updated exposure assumptions would be applied during the development of any proposed
revision to a NPDWR resulting from the review.
3.2.5 Comment: One commenter noted that assuming a person's water source would remain
the same for 70 years does not reflect U.S. Census data that indicate a person moves 11.7 times
in their lifetime. EPA should consider this information in the exposure estimate.
EPA Response: EPA has not attempted to adjust for duration of residence in its criteria update.
Adjustment for this factor is not appropriate because an individual moving to an alternative
location may be exposed to similar contaminants at that site. Additionally, the criteria are
intended to protect the water quality at a given site regardless of which individual is exposed.
3.2.6 Comment: A commenter noted that groundwater comprises about 35 - 44 percent of the
water consumed in the United States and bottled water comprises about 10 percent, and
therefore the Agency should conclude that more than 50 percent of drinking water is derived
from sources other than surface water. A commenter noted that bottled water comprises
about half of the drinking water consumed away from home (and about 15 percent of the total
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drinking water consumed) and that bottled water is subject to Food and Drug Administration
(FDA) regulations, which include standards of quality, identity, and good manufacturing
practices. EPA should revise its drinking water intake estimates to subtract the amount
obtained from bottled drinking water.
EPA Response: The revised drinking water rate is 2.4 L/d, which represents the per capita
estimate of combined direct and indirect community water ingestion at the 90th percentilefor
adults ages 21 and older based on NHANES data from 2003 to 2006 as reported in EPA's
Exposure Factors Handbook (USEPA 2011, Table 3-23). "Community water" includes direct and
indirect use of tap water for household uses and excludes bottled water and other sources
(USEPA 2011, section 3.3.1.2). The per capita rate is representative of the national average
regardless of source and is preferred for national-level assessments, such as national AWQC
development.
3.2.7 Comment: One commenter suggested that EPA should apply a "removal factor" to surface
water concentrations to reflect the fact that surface water sources are treated. For example,
compounds with high partition coefficients and very low water solubility would be sorbed to
suspended solids in surface water and would have high removal efficiencies by most public
water supply treatment systems.
EPA Response: EPA does not apply a removal factor in its AWQC development because the
values reflect ambient water column values. EPA's longstanding policy is that ambient waters
should not be contaminated to a level where the burden of achieving health objectives is shifted
away from those responsible for pollutant discharges and placed on water utilities or
downstream users to bear the costs of upgraded or supplemental water treatment (USEPA
2000a; see EPA response to comment 3.2.2).
3.2.8 Comment: A commenter noted that EPA's Supplemental Guidance for Superfund (OSWER
Directive 9200.1-120, February 6, 2014) recommends a 90th percentile adult drinking water
intake value of 2.5 L/d, whereas the updated AWQC uses a 90th percentile value of 3.0 L/d. For
decades the recommended drinking water values used for AWQC development and Superfund
risk assessment have been the same value (i.e., 2 L/d). EPA needs to explain why the two new
(i.e., 2014) drinking water values differ from each other and the rationale for selecting the value
of 3 L/d for AWQC development versus the value of 2.5 L/d.
EPA Response: EPA's Supplemental Guidance for Superfund (OSWER Directive 9200.1-120,
February 6, 2014) recommends a 90th percentile adult drinking water intake value of 2.5 L/d,
which represents the consumer-only estimate of combined direct and indirect water ingestion
based on NHANES data from 2003 to 2006 as reported in EPA's Exposure Factors Handbook
(USEPA 2011, Table 3-33) for community water at the 90th percentilefor adults ages 21 and
older. The consumer-only rate is slightly higher than the per capita rate (2.4 L/d) because it only
includes individuals who reported water intake during the survey period (and does not include
those who reported no intake). The consumer-only rate is recommended for site-specific
assessments, whereas the per capita rate is representative of the national average and is
preferred for national-level assessments, such as national human health criteria development.
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3.3 FISH CONSUMPTION RATE
3.3.1 Comment: Several commenters requested that EPA provide greater transparency as to
how the external peer review comments on its model were addressed and the extent to which
the modified EPA model deviates from the National Cancer Institute (NCI) model. One
commenter asserted that EPA did not adequately validate the model or address peer review
comments related to potential bias. Some commenters requested clarification regarding EPA's
modifications to the NCI method and requested access to the model and data.
EPA Response: EPA updated the default fish consumption rate (FCR) to 22 grams per day (g/d)
from 17.5 g/d. This rate represents the 90th percentile consumption rate of fish from inland and
nearshore waters for the U.S. adult population 21 years of age and older, based on NHANES data
collected from 2003 to 2010 and calculated using a modification of the NCI model (USEPA 2014b).
EPA's previously recommended rate of 17.5 g/d was based on the 90th percentile consumption
rate of fish from inland and nearshore waters for the U.S. adult population 21 years of age and
older, based on CSFII data from 1994-1996, calculated using ratio estimation methods.
EPA's FCR Report, Estimated Fish Consumption Rates for the U.S. Population and Selected
Subpopulations (NHANES 2003-2010) ("FCR report;" USEPA 2014b), provides a description of
the differences between the EPA and NCI models, includes the equations used by both models,
and establishes the consistency of the results obtained using the EPA model with those from the
NCI model. EPA modified the NCI method so that the model could process and manage the large
NHANES dataset. Modifications were made to allow the model to run at the minimum penalty
to robustness, while maintaining model accuracy, as described in the FCR report (USEPA 2014b).
A comparison of the results of calculations of FCR percentiles using the NCI and EPA methods is
described in section 4.6.2 of the FCR report (USEPA 2014b).
EPA's method (including the modification to the NCI method) has been externally peer reviewed.
EPA's FCR report, the external peer review report, and EPA's responses to the peer review
comments are available on EPA's website:
http://water.epa.Qov/scitech/swQuidance/fishshellfish/fishadvisories/technical.cfmfftabs-4.
With regard to accessibility of the NHANES data, Metadata from the modeling have been
released by EPA and are accessible at the above website. The model and primary data are
available from the U.S. Department of Health and Human Services, Centers for Disease Control
and Prevention.
3.3.2 Comment: Some commenters suggested that EPA's default FCR (22 grams per day) may
not protect highly exposed populations that have a significantly higher FCR, such as subsistence
fishers and tribes.
EPA Response: The fish consumption rate used by EPA to update the AWQC reflects the national
rate for the U.S. adult population. As stated in the 2000 Methodology, "because the level offish
intake in highly exposed populations varies by geographical location, EPA suggests a four
preference hierarchy for states and authorized tribes to follow when deriving consumption rates
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that encourages use of the best local, state, or regional data available...EPA strongly
emphasizes that states and authorized tribes should consider developing criteria to protect
highly exposed population groups and use local or regional data over the default values as more
representative of their target population group(s). The four preference hierarchy is: (1) use of
local data; (2) use of data reflecting similar geography/population groups; (3) use of data from
national surveys; and (4) use of EPA's default intake rates" (USEPA 2000a).
3.3.3 Comment: Commenters suggested that EPA's selection of an FCR at the 90th percentile is
overly conservative and represents a change in EPA policy.
EPA Response: EPA followed the 2000 Methodology (USEPA 2000a), which recommends using
a 90th percentile FCR to derive AWQC, and is thus not a change in policy. In the 2000
Methodology, the default fish consumption rate, which is protective of 90 percent of the general
population, is a risk management decision. This default assumption helps achieve EPA's target
goal of protecting the majority of the population, without being inordinately conservative
(USEPA 2000a; see also EPA response to comment 1.2.4).
3.3.4 Comment: Commenters suggested that EPA's FCR is not reflective of the actual
consumption of fish for most of the U.S. population, particularly of fish caught and eaten from
waters where the AWQC are applicable (i.e., inland and nearshore U.S. waters). Commenters
suggested that much of the fish eaten in the U.S. is imported and that apportioning the entire
FCR to fish from inland and nearshore waters is not reflective of human exposure to
contaminants in fish that most people eat.
EPA Response: As stated in the October 24, 2000 Memorandum from EPA Office of Science and
Technology (OST) Director Geoffrey Grubbs and EPA Office of Wetlands, Oceans, and
Watersheds (OWOW) Director Robert Wayland, "EPA interprets 'fishable' uses under section
101(a) of the CWA to include, at a minimum, designated uses providing for the protection of
aquatic communities and human health related to consumption offish and shellfish. In other
words, EPA views 'fishable' to mean that not only can fish and shellfish thrive in a waterbody,
but when caught, can also be safely eaten by humans. This interpretation also satisfies the
section 303(c)(2)(A) requirement that water quality standards protect public health. Including
human consumption offish and shellfish in the definition of section 101(a) 'fishable' uses is not
new. For example, in EPA's National Toxics Rule, all waters designated for even minimal aquatic
life protection (and therefore a potential fish and shellfish consumption exposure route) are
protected for human health (see 57 FR 60859, December 22,1992)" (USEPA 2000b).
For the purposes of developing a default national FCR, EPA assumed that all consumed fish were
harvested from inland and nearshore U.S. waters (which encompasses EPA's jurisdiction under
the CWA). It is unknown whether the proportion offish harvested from non-U.S. waters is
equally distributed across fish consumers. For example, it is possible that high fish consumers
eat more locally caught fish as they may be recreational or subsistence fishers. In the case of
shrimp, the most commonly consumed fish by U.S. consumers, 82.4 percent were considered to
be from nearshore waters and were included in EPA's FCR model, whereas the 17.6 percent of
shrimp from ocean waters were not included (USEPA 2014b, Table 1).
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3.3.5 Comment: Commenters disagreed with EPA's apportionment offish consumption across
fresh, marine, and coastal waters. One commenter stated that including marine fish caught in
near-coastal waters in determining FCR represents a change in EPA policy.
EPA Response: EPA apportioned fish species consumed by habitat, including inland (freshwater)
and nearshore (estuarine and a fraction of marine fish caught in near shore areas) to derive its
FCR. This policy is consistent with the 2000 Methodology (USEPA 2000a) and EPA's longstanding
interpretation of the "fishable" uses under section 101 (a) of the CWA (USEPA 2000b and EPA
response to Comment 3.3.4). EPA developed the apportionments based on catch data from the
National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service
(NMFS), Fisheries Statistics Division.3 Species apportionments were applied on a global basis to
represent what is actually consumed per habitat by the general U.S. population. The final
apportionments were compared to earlier apportionments in the previous FCR (USEPA 2002a)
and discrepancies were verified. EPA's FCR method, including the apportionment offish species,
was externally peer reviewed (see EPA response to Comment 3.3.1).
3.3.6 Comment: Several commenters requested that EPA clarify how the fish consumption
rates compare in developing AWQC and fish consumption advisories.
EPA Response: With few exceptions, fish consumption advisories are the responsibility of states
and tribes. State and tribal fish advisories identify how much fish can be safely consumed based
on the site-specific concentrations of pollutants in those fish.
3.3.7 Comment: Commenters expressed that, with respect to suppression offish consumption,
concepts of "availability" of fish and "contamination" of fish get mixed up and that it would be
helpful to acknowledge the difficulty in accurately quantifying suppression.
EPA Response: EPA acknowledges that it is important to avoid any suppression effect that may
occur when a fish consumption rate for a given subpopulation reflects an artificially diminished
level of consumption from an appropriate baseline level of consumption for that subpopulation.
See Human Health Ambient Water Quality Criteria and Fish Consumption Rates: Frequently
Asked Questions (January 18, 2013) (USEPA 2013). EPA notes that the AWQC update does not
directly address suppression because the updated national default FCR is based on actual
consumption. EPA acknowledges that there are many possible causes of suppressed
consumption and that information is often lacking to accurately quantify suppression.
Consistent with EPA's 2000 Methodology, states and tribes should consider local data, where
available, in determining which FCR to use in deriving human health criteria, and consider
whether such data represent a suppressed level of consumption either because of a perception
of contamination, lack of access, or other factors.
3 NOAA NMFS "Commercial Fisheries Statistics" http://www.st.nmfs.noaa.gov/commercial-fisheries/commercial-
landings/annual-landings/index and "Fisheries of the United States (FUS)"
http://www.st.nmfs.noaa.gov/commercial-fisheries/.
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3.3.8 Comment: Commenters questioned whether it is EPA or the states who have
responsibility for making risk management decisions with regard to risk level and FCR.
EPA Response: States and tribes must establish scientifically sound criteria that protect
designated uses. If EPA finds that water quality standards do not meet this requirement, then
EPA may specify changes that would remedy the deficiency. Thus, the CWA and its
implementing regulations make this a shared responsibility. Consistent with EPA's 2000
Methodology, states have the initial duty to choose an appropriate FCR and cancer risk level,
taking into consideration EPA's 2000 Methodology and any other applicable requirements, but
EPA is then charged with an oversight approval/disapproval of the resulting criteria, and, as
mentioned above, EPA must disapprove such criteria if they are not protective of applicable
designated uses and based on sound science.
3.4 BIOACCUMULATION FACTORS
3.4.1 Comment: Commenters requested clarification about why EPA used bioaccumulation
factors (BAFs) instead of bioconcentration factors (BCFs) to derive the updated AWQC. Several
commenters requested that EPA include more discussion of the benefits and limitations of both
BCFs and BAFs in the final AWQC.
EPA Response: Several attributes of the bioaccumulation process are important to understand
when deriving national BAFs for use in developing national recommended section 304(a) AWQC.
First, the term bioaccumulation refers to the uptake and retention of a chemical by an aquatic
organism from all surrounding media, such as water, food, and sediment. The term
bioconcentration refers to the uptake and retention of a chemical by an aquatic organism from
water only. For some chemicals (particularly those that are highly persistent and hydrophobia),
the magnitude of bioaccumulation by aquatic organisms can be substantially greater than the
magnitude of bioconcentration. Thus, an assessment of bioconcentration alone might
underestimate the extent of accumulation in aquatic biota for those chemicals. Accordingly, the
EPA guidelines presented in the 2000 Methodology emphasize using, when possible, measured
or estimated BAFs, which account for chemical accumulation in aquatic organisms from all
potential exposure routes (USEPA 2000a).
3.4.2 Comments: Some commenters suggested that measured bioaccumulation data should
have preference over estimated or modeled data to derive BAFs. There were many comments
on the appropriateness of using EPI Suite compared to other models, in particular given the
underlying assumptions associated with EPI Suite (e.g., EPI Suite was developed using data from
temperate waters). Several commenters noted that EPA did not follow the recommendations of
EPA's Scientific Advisory Board (SAB) review of EPI Suite and the SAB comments on model
verification. On the other hand, several commenters supported EPA's decision to use the EPI
Suite model-derived BAFs instead of laboratory-derived BCFs.
EPA Response: In light of the public comments, national BAFs used to update the criteria
followed EPA's 2000 Methodology and its Technical Support Document, Volume 2:
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Development of National Bioaccumulation Factors (USEPA 2003a). Specifically, these
documents provide a framework for identifying alternative procedures to derive national trophic
level-specific BAFsfor a chemical based on the chemical's properties (e.g., ionization and
hydrophobicity), metabolism, and biomagnification potential (USEPA 2000a; USEPA 2003a).
EPA followed the approach described in Figure 3-1 of the Technical Support Document,
Volume 2 (USEPA 2003a). EPA used peer-reviewed, publicly available information to classify
each chemical using this framework to derive the most appropriate BAFs according to EPA's
2000 Methodology (USEPA 2000a). The framework provides six alternatives, or procedures,
resulting in up to four possible methods for each chemical, based on the chemical's properties.
These four methods are:
• BAF Method. This method uses measured BAFs derived from data obtained from field
studies. Field-measured BAFs are normalized by adjusting for the water-dissolved
portions of the chemical and the lipid fraction offish tissue for each species, as well as
the fraction of the total concentration of chemical in water that is freely dissolved. EPA
averaged multiple field BAFs using the geometric mean of the normalized BAFs by
species and trophic level; then EPA further averaged the BAFs across species to compute
trophic-level baseline BAFs. The national-level BAF adjusts the trophic-level baseline
BAFs by national default values for lipid content, dissolved and particulate organic
carbon content, and the n-octanol-water partition coefficient (Kow). EPA chose the
recommended 50th percentile dissolved and particulate organic carbon content for the
national-level default values, as described in section 6.3 of the Technical Support
Document, Volume 2 (USEPA 2003a).
• BSAF Method. This method uses biota-sediment accumulation factors (BSAFs) to
estimate BAFs. EPA did not use measured BSAFs to calculate national BAFs because the
two major compilations of these data—EPA's Biota-Sediment Accumulation Factor Data
Set, Version 1.0 (USEPA 2015a), and the U.S. Army Corps of Engineers' BSAF database
(USACE 2015)—have not been peer-reviewed.
• BCF Method. This method uses BAFs estimated from laboratory-measured BCFs with or
without adjustment by a food chain multiplier. Similar to field BAFs, laboratory-
measured BCFs are normalized with the lipid fraction and the fraction of the total
concentration of chemical in water that is freely dissolved, then multiplied by the food
chain multiplier where applicable. Multiple values are averaged using a geometric mean
across species and then across trophic level to compute baseline BAFs. The national-level
BAF adjusts the trophic-level baseline BAFs by national default values for lipid content,
dissolved and particulate organic carbon content, and the Kow. EPA chose the
recommended 50th percentile dissolved and particulate organic carbon content for the
national-level default values, as described in section 6.3 of the Technical Support
Document, Volume 2 (USEPA 2003a).
• Kow Method. This method predicts BAFs based on a chemical's Kow, with or without
adjustment using a food chain multiplier, as described in section 5.4 of the Technical
Support Document, Volume 2 (USEPA 2003a).
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Following the decision framework presented in Figure 3-1 of the Technical Support Document,
Volume 2 (USEPA 2003a), EPA selected the method that provided BAF estimates for all three
trophic levels (TL2-TL4) in the following priority:
1. BAF estimates using the BAF method (i.e., based on field-measured BAFs) if possible.
2. BAF estimates using the BCF method if (a) the BAF method did not produce estimates for
all three trophic levels and (b) the BCF method produced national-level BAF estimates for
all three trophic levels.
3. BAF estimates using the Kow method if (a) Procedure 1 or 3 was applicable (see Figure 3-1
of the Technical Support Document, Volume 2 [USEPA 2003a]) and (b) the BAF and BCF
methods did not produce BAF estimates for all three trophic levels.
In cases where the procedure called for the BAF method but there were fewer than three trophic
level estimates and the Kow method did not apply (i.e., Procedures 2, 4, 5, and 6), EPA used the
BAF method estimate for the reported trophic levels by averaging the estimates using a
geometric mean when there were two BAFs and using the single estimate when only one was
available. EPA did not mix values from the BAF and BCF methods. If the BAF method did not
have sufficient reliable data for any trophic levels, EPA used the BCF method estimates in the
same manner. If none of the four methods provided sufficient data, or if none were appropriate
for the procedure, EPA used the BCF from the previously recommended 2002/2003 criteria
(USEPA 2002b; USEPA 2003b).
EPA used field-measured BAFs and laboratory-measured BCFs available from peer-reviewed,
publicly available databases (Arnot and Gobas 2006; Environment Canada 2006) to develop
national BAFs. If field-measured BAFs and laboratory-measured BCFs were not available from
those sources, EPA selected Kow values from peer-reviewed sources (i.e., Agency for Toxic
Substances and Disease Registry [ATSDR] preferentially, followed by U.S. Department of Health
and Human Services' Hazardous Substances Data Bank) for use in calculating national BAFs
using the Kow method described in EPA's Technical Support Document, Volume 2 (USEPA 2003a).
For those chemicals for which the Kow method was not applicable, based on the Technical Support
Document, Volume 2 (USEPA 2003a), EPA performed open literature searches of peer-reviewed
journal articles to find field-measured BAFs or laboratory-measured BCFs.
EPA provided model-estimated BAFs from the EPI Suite (USEPA 2012a) to allow for
characterization of field-measured or predicted BAFs developed using the four methods
described above. These EPI Suite-based BAFs are provided as an additional line of evidence only.
The BCFBAF program within EPI Suite estimates fish bioaccumulation factors by using Kow and
biotransformation data from a model designed by Arnot and Gobas (2003). The model includes
mechanistic processes for bioaccumulation, such as chemical uptake from the water at the gill
surface and from the diet, chemical elimination at the gill surface, fecal egestion, growth
dilution, and metabolic biotransformation. Other processes included in the calculations are
bioavailability in the water column (only the freely dissolved fraction can bioconcentrate) and
absorption efficiencies at the gill and in the gastrointestinal tract. The model requires the Kow of
the chemical and the normalized whole-body metabolic biotransformation rate constant as
input parameters to predict BAF values.
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3.4.3 Comment: Some commenters suggested that EPA should cap the upper bound of a BAF at
500 or 1000 L/kg.
EPA Response: EPA recommends following the approach described in EPA's 2000 Methodology
and its Technical Support Document, Volume 2: Development of National Bioaccumulation
Factors (USEPA 2003a). Capping the BAF at an arbitrary value would not reflect the true
bioaccumulation potential of a particular chemical and could result in under-protective AWQC.
3.4.4 Comment: A commenter requested clarification on whether EPA intends the same trophic
level breakdown be used for subsistence fishers as for the general population.
EPA Response: States and tribes may modify EPA's recommendations (including trophic level
breakdown), as appropriate. EPA recommends that when choosing exposure factors for criteria
development, states should consider values that are relevant to population(s) that is (are) most
susceptible to that pollutant (USEPA 2000a).
3.5 HUMAN HEALTH TOXICITY VALUES
3.5.1 Comment: Several commenters said that EPA's process for selecting among different
toxicity values was not clear. A commenter suggested that EPA relied heavily on the results of
California's toxicity assessments and outdated EPA guidance and noted that EPA should give
preference to its most recent guidance and clearly document and justify the use of other
sources of toxicity information.
EPA Response: In light of the public comments, EPA has expanded the description of how
toxicity values were selected to derive the final updated criteria in a manner that is clear and
transparent. EPA conducted a systematic search of eight peer-reviewed, publicly available
sources to obtain the toxicity value (reference dose or cancer slope factor) for use in developing
the updated criteria. EPA's primary source of toxicity values for developing human health
criteria is EPA's Integrated Risk Information System (IRIS) program. EPA also systematically
searched for toxicological assessments from the following EPA program offices, other national
and international programs, and state programs:
• EPA, Office of Pesticide Programs (USEPA 2015b)
• EPA, Office of Pollution Prevention and Toxics (USEPA 2015c)
• EPA, Office of Water (USEPA 2015d)
• EPA, Office of Solid Waste and Emergency Response (USEPA 2015e)
• U.S. Department of Health and Human Services, Agency for Toxic Substances and
Disease Registry (ATSDR 2015)
• Health Canada (HC 2015a)
• California Environmental Protection Agency, Office of Environmental Health Hazard
Assessment (CalEPA 2014)
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After identifying and documenting all available toxicity values, EPA followed a systematic
process to select the toxicity values used to derive the AWQCfor noncarcinogenic and
carcinogenic effects. EPA selected IRIS toxicity values to derive the updated AWQC if any of the
following conditions were met:
1. EPA's IRIS toxicological assessment was the only available source of a toxicity value.
2. EPA's IRIS toxicological assessment was the most current source of a toxicity value.
3. EPA's IRIS program was reassessing the chemical in question and had published the draft
Toxicological Review for public review and comment, discussion at a public meeting, and
subsequent expert peer review.4
4. The toxicity value from a more current toxicological assessment from a source other
than EPA IRIS was based on the same principal study and was numerically the same as
an older EPA IRIS toxicity value.
5. A more current toxicological assessment from a source other than EPA IRIS was available,
but it did not include the relevant toxicity value (chronic-duration oral RfD or CSF).
6. A more current toxicological assessment from a source other than EPA IRIS was
available, but it did not introduce new science (e.g., the toxicity value was not based on a
newer principal study) or use a more current modeling approach compared to an older
EPA IRIS toxicological assessment.
EPA selected the toxicity value from a peer-reviewed, publicly available source other than EPA
IRIS to derive the updated AWQC if any of the following conditions were met:
1. The chemical is currently used as a pesticide, and EPA Office of Pesticide Programs had a
toxicity value that was used in pesticide registration decision-making.
2. A toxicological assessment from a source other than EPA IRIS was the only available
source of a toxicity value.
3. A more current toxicological assessment from a source other than EPA IRIS introduced
new science (e.g., the toxicity value was based on a newer principal study) or used a
more current modeling approach compared to an older EPA IRIS toxicological
assessment.
3.5.2 Comment: A commenter suggested that EPA's use of adult exposure factors (i.e., lifetime
exposure) for chemicals with toxicity values based on developmental effects results in AWQC
that are not protective of children. A commenter suggested that EPA should be examining all of
the chemicals included in the AWQC updates characterized as carcinogens for the Age-
Dependent Adjustment Factor (ADAF) or chemical-specific Adjustment Factor.
EPA Response: EPA derived the updated AWQC at a level intended to be adequately protective
of a human population over a lifetime (USEPA 2000a). For this update, as in previous updates
(in 2002 and 2003), exposure factors were chosen for the general adult population only.
4 Equivalent to Step 4 in the July 2013 EPA Process for Developing IRIS Health Assessments. Available online at
http://www.epa.gov/iris/process.htm.
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3.5.3 Comment: Several commenters noted that the Cancer Slope Factor-based AWQC ("CSF")
the numeric CSF used is an upper bound, approximating a very conservative 95 percent
confidence level.
EPA Response: EPA applied previously developed and externally peer-reviewed cancer slope
factors in the update of the AWQC. The use of a 95th percent! le upper confidence bound is
consistent with EPA risk assessment policy, which is provided in detail in the 2005 EPA
Guidelines for Carcinogen Risk Assessment (USEPA 2005a).
3.5.4 Comment: Some commenters noted that EPA allows states to choose 10~5 or 10~6 risk
range; EPA has said that both are acceptable. EPA should clarify this policy. One commenter
expressed concern that allowing 10~4 risk for high consuming groups is inconsistent with
environmental justice practices.
EPA Response: For this update, EPA followed the 2000 Methodology and calculated its AWQC at
a 10~6 (one in one million) cancer risk level. EPA recommends cancer risk levels of 10~6 or 10~5
(one in one hundred thousand) for the general population and notes that states and authorized
tribes can choose a more stringent risk level, such as 10~7 (one in ten million), when deriving
human health criteria. EPA's 2000 Methodology also states, "Criteria based on a 10~5 risk level
are acceptable for the general population as long as states and authorized tribes ensure that
the risk to more highly exposed subgroups (sport fishers or subsistence fishers) does not exceed
the 10-4 level."
3.5.5 Comment: A commenter noted that EPA states the RfD has uncertainty spanning an order
of magnitude; however, some RfDs include an uncertainty factor (UF) up to 3000. A commenter
noted that some uncertainty factors used in reference dose calculations appear to be rounded
(e.g., 3 x 3 x 10 x 10 = 1000) and asked whether there is an EPA policy about this practice.
EPA Response: The default UFs used by EPA typically cover a single order of magnitude
(i.e., 101). By convention, EPA uses a value of 3 in place of one-half power (i.e., 10as) when
appropriate (USEPA 2002c). These half-power values are factored as whole numbers when they
occur singly but as powers or logs when they occur in tandem. For example, EPA expresses a
composite uncertainty factor of 3 and 10 as 30 (3 x 101), whereas a composite uncertainty
factor of 3 and 3 is expressed as 10 (10°-5 x 10°-5 = 101) (USEPA 2002c).
3.6 RELATIVE SOURCE CONTRIBUTION
3.6.1 Comment: Several commenters noted that the basis for EPA's use of the default relative
source contribution (RSC) value of 20 percent for all criteria was not justified and/or was too
conservative. Several commenters urged EPA to clarify terms and use the Decision Tree
approach described in the 2000 Methodology, using data from available sources (e.g., Food and
Drug Administration, National Marine Fisheries Service) to determine appropriate chemical-
specific RSCs rather than using the default of 20 percent. Several commenters noted that an
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RSC should not be used in cases where there is no reasonable anticipation of other significant
exposures to that chemical.
EPA Response: The 2000 Methodology describes the RSC component of the AWQC calculation.
The RSC allows a percentage of the RfD to be attributed to the consumption of ambient water
and fish and shellfish from inland and nearshore waters when there are other potential
exposure sources. The RSC describes the portion of the RfD available for AWQC-related sources
(USEPA 2000a); the remainder of the RfD is allocated to other sources of the pollutant. The
rationale for this approach is that for pollutants exhibiting threshold effects, the objective of the
AWQC is to ensure that an individual's total exposure from all sources does not exceed that
threshold level. Exposures outside the RSC include, but are not limited to, exposure to a
particular pollutant from ocean fish and shellfish consumption (which is not included in the fish
consumption rate), non-fish food consumption (e.g., fruits, vegetables, grains, meats, and
poultry), dermal exposure, and respiratory exposure (USEPA 2000a).
In response to public comments, EPA described how the RSC was derived for each chemical
included in this 2015 update referencing the Exposure Decision Tree described in the 2000
Methodology (USEPA 2000a). To use the Exposure Decision Tree, EPA compiled information for
each chemical on its uses, chemical and physical properties, occurrences in other potential
sources (e.g., air, food), and releases to the environment, as well as regulatory restrictions on
other sources that are specific to the chemical (e.g., air quality standards, food tolerance levels).
The ATSDR "Toxicological Profiles" (ATSDR 2015) were the primary source for this information.
EPA used the Hazardous Substance Data Bank (HSDB) (USDHHS 2015) from the National Library
of Medicine's Toxicology Data Network (TOXNET) as the primary source for chemicals without
ATSDR Toxicological Profiles. Both sources are peer-reviewed compilations of chemical
information.
EPA used additional references, including the following, to obtain specific types of information
and to supplement the information from ATSDR and the HSDB:
• EPA's Six-Year Reviews (drinking water data) (USEPA 2009a; USEPA 2009b).
• FDA Total Diet Study (USFDA 2015).
• FDA Everything Added to Food in the United States (USFDA 2013).
• EPA National Lake Fish Tissue Study (USEPA 2009c).
• EPA Toxic Release Inventory (USEPA 2015f).
• International Bottled Water Association Standards of Quality (IBWA 2012).
• NOAA Mussel Watch (NOAA 2014).
• Additional sources as needed.
To determine the RSC to be used in the AWQC calculation, EPA then used the information
compiled for each chemical to address the questions posed in the Exposure Decision Tree. Some
of the important items evaluated in the Exposure Decision Tree are:
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• The adequacy of the data available for each relevant exposure source and pathway.
• The availability of sufficient information to characterize the likelihood of exposure to
relevant sources.
• Whether there are significant known or potential uses/sources other than the source of
concern (i.e., ambient water and fish/seafood from those waters).
• Whether information on each source is available to make a characterization of exposure.
In cases where there is a lack of environmental or exposure data, or both, the Exposure Decision
Tree approach results in a recommended RSC of 20 percent. This 20 percent value for the RSC
may be replaced where sufficient data are available to develop a scientifically defensible
alternative value. When appropriate, if scientific data demonstrating that sources and routes of
exposure other than water and fish from inland and nearshore waters are not anticipated for
the pollutant in question, the RSC may be raised to 80 percent based on the available data
(USEPA 2000a).
3.6.2 Comment: One commenter requested EPA provide a scientific explanation as to why RSCs
are included for nonlinear carcinogens (e.g., chloroform) but not linear carcinogens.
EPA Response: As stated in the 2000 Methodology, "In the case of substances for which the
AWQC is set on the basis of a carcinogen based on a nonlinear low-dose extrapolation or for a
noncancer endpoint where a threshold is assumed to exist, non-water exposures are considered
when deriving the AWQC using the RSC approach. The rationale for this approach is that for
pollutants exhibiting threshold effects, the objective of the AWQC is to ensure that an
individual's total exposure does not exceed that threshold level" (USEPA 2000a).
3.6.3 Comment: Commenters disagreed with EPA's assumption of a 20 percent default RSC for
states that include anadromous fish in the FCR.
EPA Response: RSCs may need to be modified for a variety of local, state, or regional issues,
including depending on which fish species are included in the FCR (e.g., fish from inland,
nearshore, and/or ocean waters).
3.6.4 Comment: Commenters expressed that the "20 percent/80 percent" RSC approach, as a
means of "harmonizing" SDWA and CWA, fails to recognize that MCLs may be adjusted to
reflect available treatment and available analytical methods, yet CWA criteria must be enforced
in the ambient water through permits and has potentially large economic consequences.
EPA Response: EPA recognizes the differences in regulatory approaches between SDWA and
CWA and notes that while the CWA and its implementing regulations do not allow for cost to be
considered in adopting scientifically sound water quality criteria that protect applicable
designated uses, the Act and regulations do include the means to address economic
consequences through use attainability analyses, variances, compliance schedules, etc. EPA's
primary consideration in establishing recommendations for protective criteria are to ensure
human health protection consistent with designated uses that meet CWA goals, and this
consideration leads to addressing other sources of exposure through use of RSC.
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4 CHEMICAL-SPECIFIC ISSUES
4.1 BIOACCUMULA TION FACTORS
4.1.1 Comment: A commenter questioned EPA's use of the EPI Suite model to estimate a
national BAF for anthracene in the proposed updated AWQC.
EPA Response: EPA selected a national BAF value of 610 L/kgfor anthracene for the final
updated AWQC. EPA followed the framework for selection of methods for deriving national BAFs
in Figure 3-1 of the Technical Support Document, Volume 2 (USEPA 2003a). Based on the
characteristics of this chemical, EPA selected Procedure 2 for deriving a national BAF value.
Anthracene has the following characteristics:
• Nonionic organic chemical (USDHHS 2011)
• Moderate-high hydrophobicity (log Kow > 4); log Kow = 4.45 (ATSDR 1995)
• High metabolism (NOAA n.d.)
EPA was not able to locate peer-reviewed, field-measured BAFs, BSAFs, or lab-measured BCFs
for all three TLs (2, 3, and 4). Therefore, EPA used the BCF method estimate for the reported TLs
by calculating the geometric mean of the TL2 and TL3 BCF values available for anthracene
(Arnot and Gobas 2006; Environment Canada 2006) to derive the national BAF value of 610 L/kg
for this chemical. This national BAF replaces EPA's previously recommended BCF of 30 L/kg.
4.1.2 Comment: Several commenters questioned EPA's use of the EPI Suite model to estimate a
national BAF for bis(2-ethylhexyl) phthalate in the proposed updated AWQC.
EPA Response: EPA selected a national BAF value of 710 L/kgfor bis(2-ethylhexyl) phthalate for
the final updated AWQC. EPA followed the framework for selection of methods for deriving
national BAFs in Figure 3-1 of the Technical Support Document, Volume 2 (USEPA 2003a). Based
on the characteristics of this chemical, EPA selected Procedure 2 for deriving a national BAF
value. Bis(2-ethylhexyl) phthalate has the following characteristics:
• Nonionic organic chemical (USDHHS 201 Oa)
• Moderate-high hydrophobicity (log Kow > 4); log Kow = 7.5 (ATSDR 2002)
• High metabolism (Gobas et a I. 2003; Mankidya et al. 2013)
EPA was not able to locate peer-reviewed, field-measured BAFs, BSAFs or lab-measured BCFs for
all three TLs (2, 3, and 4). Therefore, EPA used the BAF method estimate for the reported TLs by
calculating the geometric mean of the TL 3 and TL 4 BAF values available for bis(2-ethylhexyl)
phthalate (Arnot and Gobas 2006; Environment Canada 2006) to derive the national BAF value
of 710 L/kgfor this chemical. This national BAF replaces EPA's previously recommended BCF of
130 L/kg.
4.1.3 Comment: A commenter suggested that EPA should use field or laboratory data instead of
the EPI Suite model to develop the BAF for chloroform.
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EPA Response: EPA selected national BAF values of 2.8 L/kg (TL2), 3.4 L/kg (TLS), and 3.8 L/kg
(TL4)for chloroform for the final updated AWQC. EPA followed the framework for selection of
methods for deriving national BAFs in Figure 3-1 of the Technical Support Document, Volume 2
(USEPA 2003a). Based on the characteristics of this chemical, EPA selected Procedure 3 for
deriving a national BAF value. Chloroform has the following characteristics:
• Nonionic organic chemical (USDHHS 2014)
• Low hydrophobicity (log Kow < 4); log Kow = 1.97 (ATSDR 1997)
• Low/unknown metabolism
EPA was not able to locate peer-reviewed, field-measured BAFs or lab-measured BCFsfor TLs 2,
3, and 4. Therefore, EPA used the Kow method to derive the national BAF values for this
chemical:
TL2 = 2.8L/kg
TLS = 3.4 L/kg
TL4 = 3.8L/kg
These national TL BAFs replace EPA's previously recommended BCF of 3.75 L/kg.
4.1.4 Comment: Commenters suggested that EPA should use field or laboratory data instead of
the EPI Suite model to develop the BAF for benzo(a)pyrene.
EPA Response: EPA selected a national BAF value of 3,900 L/kg for benzo(a)pyrenefor the final
updated AWQC. EPA followed the framework for selection of methods for deriving national BAFs
in Figure 3-1 of the Technical Support Document, Volume 2 (USEPA 2003a). Based on the
characteristics of this chemical, EPA selected Procedure 2 for deriving a national BAF value.
Benzo(a)pyrene has the following characteristics:
• Nonionic organic chemical (USDHHS 201 Ob)
• Moderate-high hydrophobicity (log Kow > 4); log Kow = 6.06 (ATSDR 1995)
• High metabolism (NOAA n.d.)
EPA was not able to locate peer-reviewed, field-measured BAFs, BSAFs, or lab-measured BCFs
for all three TLs (2, 3, and 4). Therefore, EPA used the BCF method estimate for the reported TLs
by calculating the geometric mean of the TL 2 and TL 3 BCF values available for benzo(a)pyrene
(Arnot and Gobas 2006; Environment Canada 2006) to derive the national BAF value of 3,900
L/kg for this chemical. This national BAF replaces EPA's previously recommended BCF of 30 L/kg.
4.1.5 Comment: A commenter noted that there is large disparity between the previously used
BCF measured values for pentachlorophenol and the proposed EPI Suite estimated BAFs.
Another commenter noted that the bioaccumulation of acidic compounds like
pentachlorophenol is sensitive to changes in pH because of changes in chemical speciation,
questioned the accuracy of EPI Suite estimates, and urged EPA to revise the national BAFs.
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EPA Response: EPA selected national BAF values of 44 L/kg (TL2), 290 L/kg (TL3), and 520 L/kg
(TL4) for pentachlorophenol for the final updated AWQC. EPA followed the framework for
selection of methods for deriving national BAFs in Figure 3-1 of the Technical Support
Document, Volume 2 (USEPA 2003a). Based on the characteristics of this chemical, EPA selected
Procedure 5 for deriving a national BAF value. Pentachlorophenol has the following
characteristics:
• Ionic organic chemical, with ionization not negligible (USDHHS 2010c)
• Biomagnification unlikely (ATSDR 2001a)
EPA was able to locate peer-reviewed, lab-measured BCFsfor trophic levels 2, 3, and 4 (Arnot
and Gobas 2006; Environment Canada 2006). Therefore, EPA used the Lab BCF method (USEPA
2003a) to derive the national BAF values for this chemical:
TL2 = 44 L/kg
TL3 = 290 L/kg
TL4 = 520 L/kg
These national trophic level BAFs replace EPA's previously recommended BCF of 11 L/kg.
4.1.6 Comment: Several commenters indicated EPA used an incorrect Kow (1.62) rather than
1.38 for vinyl chloride and did not take its high volatility into account. Commenters noted that
vinyl chloride is a highly volatile organic compound that does not bioaccumulate or transfer
through food chains, and therefore, it would be expected to be metabolized and eliminated
rather than accumulate in tissues for human consumption.
EPA Response: EPA selected national BAF values of 1.4 L/kg (112), 1.6 L/kg (113), and 1.7 L/kg
(TL4)for vinyl chloride. EPA followed the framework for selection of methods for deriving
national BAFs in Figure 3-1 of the Technical Support Document, Volume 2 (USEPA 2003a). Based
on the characteristics of this chemical, EPA selected Procedure 3 for deriving a national BAF
value. Vinyl chloride has the following characteristics:
• Nonionic organic chemical (USDHHS 2013)
• Low hydrophobicity (log Kow < 4); log Kow = 1.36 (ATSDR 2006)
• Low/unknown metabolism
EPA was not able to locate peer-reviewed, field-measured BAFs or lab-measured BCFsfor TLs 2,
3, and 4. Therefore, EPA used the Kow method to derive the national BAF values for this
chemical:
TL2 = 1.4 L/kg
TLS = 1.6 L/kg
TL4 = 1.7 L/kg
These national TL BAFs replace EPA's previously recommended BCF of 1.17 L/kg.
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4.2 HUMAN HEALTH TOXICITY VALUES
4.2.1 Comment: Some commenters noted that EPA should ensure that it uses the best available
science for specific chemicals (e.g., chloroform, 1,2-dichloroethane, toluene, vinyl chloride) and
criticized EPA's reliance on IRIS values that are more than a decade old.
EPA Response: EPA followed the systematic selection process described above (see response to
comment 3.5.1). Relevant toxicity values for the chemicals mentioned in this comment are
summarized below (full text is available in the 94 final AWQC documents):
Chloroform: EPA selected an RfD of1 x 10~2 mg/kg-d (0.01 mg/kg-d) for chloroform based on a
2001 EPA IRIS assessment (USEPA 2001). EPA identified two other RfD sources based on the
systematic search: a 2006 EPA Office of Water (OW) assessment (USEPA 2006) and a 1997
ATSDR assessment (ATSDR 1997). Based on the selection process, the 2001 EPA IRIS assessment
is preferred for use in AWQC development at this time. The EPA OW assessment is based on the
same principal study and is numerically the same as the IRIS assessment. The 2001 IRIS
assessment is more current than the 1997 ATSDR assessment.
1,2-Dichloroethane: EPA selected an RfD of 7.8 x 10~2 mg/kg-d (0.078 mg/kg-d) for
1,2-dichloroethane based on a 2015 Health Canada assessment (HC 2015b). EPA identified two
other RfD sources through the systematic search: a 1999 California EPA assessment (CalEPA
1999a) and a 2001 ATSDR assessment (ATSDR 2001b). Based on the selection process, the 2015
Health Canada RfD is preferred for use in AWQC development at this time. Health Canada
evaluated the same principal study considered in the other two assessments, but used more
current benchmark dose (BMD) modeling in order to identify the point of departure for the RfD
derivation. According to EPA guidance, when data are amenable to modeling, the BMD
approach is the preferred approach (USEPA 2012b).
EPA selected a CSF of 3.3 x 10~3 per mg/kg-d5 (0.0033 per mg/kg-d) for 1,2-dichloroethane
based on a 2015 Health Canada assessment (HC 2015b). EPA identified two other CSF sources
through the systematic search described in section 5: a 1986 EPA IRIS assessment (USEPA 1986)
and a 1999 California EPA assessment (CalEPA 1999a). Based on the selection process, the 2015
Health Canada CSF is preferred for use in AWQC development at this time. The Health Canada
assessment is based on a more recent critical study and applied more current guidance and
modeling approaches. Specifically, the LEDw (the lower 95 percent confidence limit on the
estimated dose associated with 10 percent extra risk) was selected by Health Canada as the
point of departure for derivation of the slope factor in place of a linear multistage (LMS) slope
factor. Additionally, the Health Canada CSF uses a cross-species scaling approach based on
BW3/4, which is consistent with current EPA practice (HC 2015b; USEPA 2005a).
5 This CSF was calculated by dividing the cancer risk level (10"s) by the human external dose (PBPK approach)
(0.0003 mg/kg-d) (see Table 3 in HC 2015b).
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Toluene: EPA selected an RfD of 9.7 x 10~3 mg/kg-d (0.0097 mg/kg-d) for toluene based on a
2015 Health Canada assessment (HC 2015c). EPA identified three other RfD sources for toluene:
a 2005 EPA IRIS assessment (USEPA 2005b), a 2000 ATSDR assessment (ATSDR 2000), and a
1999 California EPA assessment (CalEPA 1999b). Based on the selection process, the Health
Canada RfD is preferred for use in AWQC development at this time. The 2015 Health Canada
assessment is the most current available RfD source and is based on more recent critical studies
than the IRIS assessment.
Vinyl Chloride: EPA selected an RfD of 3 x 10~3 mg/kg-d (0.003 mg/kg-d) for vinyl chloride based
on a 2000 EPA IRIS assessment (USEPA 2000c). In 2003, EPA's IRIS program conducted a
screening-level review of the more recent toxicology literature pertinent to the RfD for vinyl
chloride and did not identify any critical new studies. EPA identified two other RfD sources
through the systematic search: a 2006 ATSDR assessment (ATSDR 2006) and a 2000 CalEPA
assessment (CalEPA 2000). Based on the selection process, the 2000 EPA IRIS RfD is preferred for
use in AWQC development at this time. Both of the other assessments are based on the same
principal studies as the IRIS assessment and use the same toxicity endpoint to derive an RfD.
EPA selected a CSF of 1.5 per mg/kg-d for vinyl chloride based on a 2000 EPA IRIS assessment
(USEPA 2000d). In 2003, EPA's IRIS program conducted a screening-level review of the more
recent toxicology literature pertinent to the cancer assessment for vinyl chloride and did not
identify any critical new studies. EPA identified one other potential CSF source through the
systematic search described in section 5: a 2000 CalEPA assessment (CalEPA 2000). The CalEPA
assessment is an inhalation assessment and does not include an oral CSF. Based on the selection
process, the EPA IRIS CSF is preferred for use in AWQC development at this time.
4.2.2 Comment: A commenter noted the 2000 IRIS assessment for benzene does not follow
EPA's 2005 Guidelines for Carcinogen Risk Assessment (USEPA 2005a), specifically that there is
no generally applicable method for accounting for uptake differences in a quantitative route-to-
route extrapolation of dose-response data in absence of good data on the agent of interest.
EPA Response: EPA selected a CSF range of 1.5 x 10~2 per mg/kg-d (0.015 per mg/kg-d) to
5.5 x 10~2 per mg/kg-day (0.055 per mg/kg-day) for benzene based on a 2000 EPA IRIS
assessment (USEPA 2000e). EPA's IRIS program derived the CSF using principal studies by Rinsky
et al. (1981; 1987), Paustenbach et al. (1993), Crump (1994), and USEPA (1998a; 1999) based on
the development of leukemia in humans with occupational inhalation exposure to benzene
(USEPA 2000e).
EPA identified one other CSF source through the systematic search described in section 3.5 of
this document: a 2001 California EPA assessment (CalEPA 2001). Based on that selection
process, the 2000 EPA IRIS CSF is preferred for use in AWQC development at this time. The
CalEPA CSF is based on studies that IRIS considered in their assessment but did not use
quantitatively (Paxton et al. 1994; Hayes et al. 1997). EPA will consider new toxicological
assessments on benzene for AWQC development as they become available.
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4.2.3 Comment: One commenter noted that the proposed draft update AWQC document for
chlorophenoxy herbicide (2,4-D) (USEPA 2014c) incorrectly cites a reference to USEPA (2005c)
on page 7. The commenter notes that the 2005 document refers to an RfD of 0.005 mg/kg-day
whereas the USEPA (2012c) document provides the oral RfD of 0.05 mg/kg-day that is used as
the basis for the draft updated criterion value.
EPA Response: EPA has corrected the reference in the final updated 2015 AWQC.
4.2.4 Comment: Several commenters had questions about the critical study and uncertainty
factors used for cyanide. One commenter requested that EPA address method issues with the
40 CFR Part 136 analytical method for cyanide at levels of 3 to 5 u.g/L. The commenter also
noted that the new proposed EPA criterion is lower than the existing section 304(a) criterion for
protection of aquatic life (5 u.g/L). Another commenter noted that the analytical method that
should be used for determining compliance with any cyanide standard should be measuring
free and not total cyanide because the toxicological assessment is based on free cyanide; the
commenter requested that EPA update the AWQC to be based on free cyanide instead of total
cyanide.
EPA Response: EPA selected an RfD ofSxlCT4 mg/kg-d (0.0006 mg/kg-d) for free cyanide based
on a 2010 EPA IRIS assessment for hydrogen cyanide and cyanide salts (USEPA 2010a). EPA IRIS
states that the "use of the RfD for free cyanide to calculate RfDs of other cyanide compounds
may be merited, but the ability of the individual cyanogenic species to dissociate and release
free cyanide in aqueous solution (and at physiological pHs) should be taken into consideration. If
dissociation of the compound is expected, then liberated cations should be considered for
potential toxicity independent ofCN~. Also, some metallocyanides, such as copper cyanide, have
chemical-specific data and are not included in this (IRIS) analysis" (USEPA 2010b).
Consistent with EPA's previously published criteria for cyanide (USEPA 2003b), the final updated
2015 AWQC are expressed as total cyanide, even though the IRIS RfD used to derive the criterion
is based on free cyanide. The multiple forms of cyanide that are present in ambient water have
significant differences in toxicity due to their differing abilities to liberate the CN-moiety. Some
complex cyanides require even more extreme conditions than refluxing with sulfuric acid to
liberate the CN-moiety. Thus, these complex cyanides are expected to have little or no
bioavailability to humans. If a substantial fraction of the cyanide present in a water body is
present in a complexedform (e.g., Fe4[Fe(CN)6]3), EPA's recommended criteria may be overly
conservative (USEPA 2003b).
4.2.5 Comment: A commenter noted that EPA's decision to use the cancer slope factor derived
from a mixture of 2,4-dinitrotoluene (2,4-DNT) and 2,6-DNT for 2,4-DNT does not incorporate
updates to body weight and drinking water intake values, uses outdated methods to derive
human equivalent doses, and relies on a principle study that utilized a mixture of isomers of
DNT despite 20 years of data indicating that only 2,6-DNT is carcinogenic.
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EPA Response: EPA selected a CSF of 6.67 x 10~1per mg/kg-d (0.667 per mg/kg-d) for the final
AWQCfor 2,4-dinitrotolulene based on a 2008 EPA Office of Water assessment (USEPA 2008).
EPA Office of Water program identified a study by Ellis et al. (1979) as the critical study and
development of mammary gland tumors as the critical effect in female rats orally exposed to a
mixture of 98 percent 2,4-dinitrotoluene and 2 percent 2,6-dinitrotoluene (USEPA 2008). The
benchmark dose (BMD) is estimated using the numbers of female rats with mammary gland
tumors. For a benchmark risk (BMR) level of 0.10, the estimated BMD value is 0.25 mg/kg-d
with a lower bound (95 percent) (BMDL) of 0.15 mg/kg-d using the multistage model. The BMDL
is used as the point of departure selected for the quantification of cancer risk (USEPA 2008).
EPA identified one other CSF source for 2,4-dinitrotolulene through the systematic search
described in section 3.5 of this document: a 1989 EPA IRIS assessment (USEPA 1989). Based on
that selection process, the 2008 Office of Water CSF is preferred for use in AWOC development
at this time. The Office of Water assessment uses the same principal study (Ellis et al. 1979), but
uses a more current BMD modeling approach than was used in the IRIS assessment.
4.2.6 Comment: One commenter requested that EPA assess precursors to toxic disinfection
byproducts (DBFs) when setting AWQC, especially where downstream impacts could occur.
They also note that EPA should look at the cumulative impact of DBFs, in particular to children
and other sensitive populations.
EPA Response: EPA added the following statement in the problem formulation section of the
final criteria documents for each of the four trihalomethanes (THM) - chloroform, bromoform,
chlorodibromomethane, and dichlorobromomethane - that were regulated in EPA's Stage 1 and
Stage 2 Disinfection Byproduct (DBF) Rule (USEPA 1998b; USEPA 2006): "DBFs are formed by
the reaction of disinfectants with constituents in the water, especially natural organic matter
(NOM), but also inorganic constituents such as bromide and iodide. The concentration of DBFs
within a public water system can vary depending on source water quality, treatment (e.g., type
of disinfectant), and distribution system conditions. For example, THM concentrations might be
lower when chloramine is used as the disinfectant compared to when chlorine is used."
EPA does not have adequate data to evaluate precursors to DBFs at this time. EPA agrees that
DBFs create an environmental challenge, and CWA programs are working with SDWA programs
to develop complimentary approaches to reduce the impacts associated with DBFs, especially to
sensitive lifestages.
4.2.7 Comment: A commenter requested that EPA identify whether hexachlorocyclohexane
(HCH) technical (CAS #608-73-1) is a priority pollutant or a non-priority pollutant.
EPA Response: Hexachlorocyclohexane (HCH) technical (CAS #608-73-1) is not a priority
pollutant. However, four of its isomers are on the priority pollutant list: alpha-HCH (CAS #319-
84-6), beta-HCH (CAS #319-85-7), gamma-HCH (CAS #58-89-9), and delta-HCH (CAS #319-86-8).
4.2.8 Comment: One commenter noted that the updated criteria do not currently include
N-nitrosodimethylamine (NDMA).
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EPA Response: EPA elected not to update theAWQCfor NDMA at this time due to the EPA's
ongoing evaluation of nitrosamines for the SDWA Six Year Review (see 79 FR 62715) (USEPA
2014d).
4.2.9 Comment: One commenter questioned EPA's use of the state of California's Office of
Environmental Health Hazard Assessment (OEHHA) cancer potency factor for benzo(a)pyrene.
EPA Response: EPA did not use the OEHHA CSF to derive the final updated AWQC for
benzo(a)pyrene. Due to EPA's ongoing IRIS reassessment of benzo(a)pyrene, EPA used the
current IRIS CSF to derive AWQC at this time. EPA selected a CSF of 7.3 per mg/kg-dfor
benzo(a)pyrene based on a 1991 EPA IRIS assessment (USEPA 1991).
4.2.10 Comment: One commenter noted that an uncertainty factor of 10,000 was used in the
proposed AWQC for pentachlorobenzene.
EPA Response: EPA selected an RfD ofSxlCT4 mg/kg-d (0.0008 mg/kg-d) for pentachlorobenzene
based on a 1985 EPA IRIS assessment (USEPA 1985). In deriving the RfD, EPA's IRIS program
applied a composite uncertainty factor of 10,000 (USEPA 2002c) to account for interspecies
extrapolation (10), intraspecies variation (10), subchronic-to-chronic study extrapolation (10),
and extrapolation of the NOAELfrom the LOAEL (10) (USEPA 1985). EPA identified no other RfD
sources for pentachlorobenzene.
4.2.11 Comment: One commenter noted that there are a few EPA-funded studies which found
reasonable correlations between various polycyclic aromatic hydrocarbons (PAHs) in the
natural environment and urged the use of surrogates for some of the measurements.
EPA Response: EPA used benzo(a)pyrene as a surrogate (index chemical) for toxicity values used
in the final AWQC derivations for six other PAHs: benzo(a)anthracene, benzo(b)fluoranthene,
benzo(k)fluoranthene, chrysene, dibenzo(a,h)anthracene, indeno(l,2,3-cd)pyrene.
4.3 RELATIVE SOURCE CONTRIBUTION
4.3.1 Comment: Several commenters noted that Oregon (2011) recently developed an RSC of
80 percent for endrin using EPA's 2000 Methodology (USEPA 2000a) that had been approved by
EPA Region 10. The commenters noted that Oregon had cited the U.S. Department of Health
and Human Services' Toxicological Profile for endrin, which concludes that there is no
significant source of human exposure to endrin other than water and fish consumption.
EPA Response: EPA recommends an RSC of 80 percent (0.80) for endrin in its final updated
AWQC. Based on the available exposure information for endrin, and given that the chemical is
no longer produced or used in the United States, EPA does not anticipate that there will be
significant sources and routes of exposure of endrin other than fish and shellfish from inland and
nearshore waters. Based on EPA's 2000 Methodology, "If it can be demonstrated that other
sources and routes of exposure are not anticipated for the pollutant in question (based on
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information about its known/anticipated uses and chemical/physical properties), then EPA
would use the 80 percent ceiling" (USEPA 2000a, section 4.2.3).
5 IMPLEMENTATION
5.1 STATE FLEXIBILITY
5.1.1 Comment: Commenters requested clarification from EPA on whether states would be
expected to adopt AWQC for those substances contained in EPA's proposal for which they do
not currently have AWQC.
EPA Response: Section 303(a)-(c) of the CWA requires states and authorized tribes to adopt
water quality standards for their waters. As part of the water quality standards triennial review
process set forth in section 303(c) of the CWA, states and authorized tribes are required to
review and revise, as appropriate, their water quality standards at least once every three years.
States and authorized tribes must adopt water quality criteria that protect designated uses.
40 CFR 131.11(a)(l). Criteria must be based on a sound scientific rationale and contain sufficient
parameters or constituents to protect the designated uses. Id. Criteria may be expressed in
either narrative or numeric form. EPA's regulations provide that states and authorized tribes
should adopt numeric water quality criteria based on:
(1) EPA's recommended section 304(a) criteria; or
(2) EPA's recommended section 304(a) criteria modified to reflect site-specific
conditions; or
(3) Other scientifically defensible methods. (40 CFR 131.11(b)).
It is important for states and authorized tribes to consider any new or updated section 304(a)
recommended criteria as part of their triennial review process to ensure that state or tribal
water quality criteria reflect sound science and protect applicable designated uses. EPA recently
proposed revisions to its water quality standards regulations that would, if finalized without
substantive change, require states during their triennial reviews to consider new or updated
section 304(a) recommended criteria and, if they do not adopt new or revised criteria for such
pollutants, provide an explanation to EPA and the public as to why the state did not do so. These
final 2015 updated section 304(a) human health criteria recommendations supersede EPA's
previous recommendations.
5.1.2 Comment: Several commenters noted that the AWQC and associated documents should
more clearly reflect the states' options in adopting state water quality standards and more
clearly define the respective federal and state roles. Additionally, although the 2000
Methodology (USEPA 2000a) is clear in its intent to provide states with flexibility in adjusting
levels in accordance to local or regional data, the guidance does not include specific guidelines
regarding type, amount, and quality of additional data required to adjust AWQC.
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EPA Response: As stated above, states may adopt the AWQC that EPA publishes, modify EPA's
A WQC to reflect site-specific conditions, or adopt different A WQC based on other scientifically
defensible methods. EPA must, however, approve any new water quality standards adopted by
a state before they can be used for CWA purposes. Water quality criteria developed by EPA
under section 304(a) are based solely on data and scientific judgments on the relationship
between pollutant concentrations and environmental and human health effects. Section 304(a)
criteria do not reflect consideration of economic impacts or the technological feasibility of
meeting pollutant concentrations in ambient water. However, there are a number of
implementation approaches available for state consideration, including variances, revisions to
designated uses, and compliance schedules.
Variances
A discharger may be interested in a variance where 1) the permitting authority has determined
that there is reasonable potential for the discharger to cause or contribute to an excursion
above a newly adopted criterion and 2) the state and discharger can show, based on §131.10(g),
that the designated use and criteria for the particular waterbody or segment are unattainable
immediately or within a limited period of time because the discharger cannot meet its new
Water Quality-Based Effluent Limits (WQBELs). In such a case, the state may adopt a discharger-
specific variance as long as the variance is consistent with the CWA and implementing
regulations.
Revision to Designated Uses
The water quality standards (WQS) regulation at 40 CFR §131.10(g) provides that "[s]tates may
remove a designated use... or establish sub-categories of a use if the [s]tate can demonstrate
that attaining the designated use is not feasible..." because of at least one of the six factors
specified at §131.10(g)(l)-(6):
(1) Naturally occurring pollutant concentrations prevent the attainment of the use; or
(2) Natural, ephemeral, intermittent or low flow conditions or water levels prevent the
attainment of the use, unless these conditions may be compensated for by the
discharge of sufficient volume of effluent without violating state water conservation
requirements to enable uses to be met; or
(3) Human caused conditions or sources of pollution prevent the attainment of the use
and cannot be remedied or would cause more environmental damage to correct than
to leave in place; or
(4) Dams, diversions or other types of hydrologic modifications preclude the attainment
of the use, and it is not feasible to restore the water body to its original condition or
to operate such modification in a way that would result in the attainment of the use;
or
(5) Physical conditions related to the natural features of the water body, such as the lack
of a proper substrate, cover, flow, depth, pools, riffles, and the like, unrelated to
water quality, preclude attainment of aquatic life protection uses; or
(6) Controls more stringent than those required by sections 301(b) and 306 of the Act
would result in substantial and widespread economic and social impact.
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Compliance Schedules
EPA's regulations at 40 CFR 122.47 govern the use of schedules of compliance in NPDES permits.
A schedule of compliance means a schedule of remedial measures in a permit, including an
enforceable sequence of interim actions or milestones leading to compliance with the CWA and
its regulations. 40 CFR 122.2. Section 122.47 provides that, "when appropriate/' a permit may
include a schedule of compliance with a permit's WQBEL, provided that schedule requires
compliance "as soon as possible." Schedules of compliance are often used when the discharger
requires time to install treatment technology or implement other controls necessary to meet a
new or revised WQBEL.
5.2 IMPAIRED WATER BODIES
5.2.1 Comment: A commenter noted that the AWQC will become regulatory limits once they
are adopted by state as water quality standards and many, if not most, surface water bodies
will fail to meet all of the AWQC. Another commenter noted that use of the new AWQC will
result in many new impaired waters, many new TMDLs, many new stringent permit limits, and
result in high compliance costs for regulated facilities, with little or no public health benefit.
EPA Response: Water quality criteria developed by EPA under section 304(a) are based solely on
data and scientific judgments on the relationship between pollutant concentrations and
environmental and human health effects. Section 304(a) criteria do not reflect consideration of
economic impacts or the technological feasibility of meeting pollutant concentrations in
ambient water. There are many existing tools in water quality standards to help states adjust
water quality standards in cases of economic hardship, or to give dischargers appropriate time
to comply with more stringent limits. EPA is not aware of any evidence supporting the assertion
of widespread additional listings of impaired waters. Ambient monitoring data from the past 10
years indicate an overall 94 percent non-detection rate nationwide for the pollutants with
updated AWQC, and only a few pollutants with measurements that exceed the updated
recommended criteria compared to previous recommendations, many of which are likely from
the same waters.
5.3 ECONOMIC IMPACTS
5.3.1 Comment: Commenters noted that given the potential economic cost of implementing
these AWQC, EPA should promulgate this action as a rulemaking and EPA should analyze the
feasibility of implementing the AWQC and ensuring that it does not cause unnecessary burden
to State, local and tribal governments.
EPA Response: AWQC are scientific recommendations to states and tribes authorized to
establish water quality standards under the CWA, regarding ambient concentrations of
pollutants that protect human health. Under the CWA, states and authorized tribes must
establish water quality criteria to protect designated uses. State and tribal decision makers
retain the discretion to adopt criteria on a case-by-case basis that differ from this guidance
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provided that the criteria are scientifically defensible and protective of the applicable use(s).
EPA's AWQC are not regulations, and thus, do not impose legally binding requirements on EPA,
states, tribes, or the regulated community. Moreover, water quality criteria developed by EPA
under section 304(a) are based solely on data and scientific judgments on the relationship
between pollutant concentrations and environmental and human health effects. Section 304(a)
criteria do not reflect consideration of economic impacts or the technological feasibility of
meeting pollutant concentrations in ambient water.
5.3.2 Comment: A commenter indicated that the updated criteria include many that did not
previously have criteria and asks if EPA will be updating their priority pollutant list and permit
requirements to require monitoring.
EPA Response: All 94 of the A WQC included in this update are pollutants that previously had
AWQC; no new AWQC were developed. EPA has no plans to update the list of priority pollutants.
The permitting authority, which is the state in most cases, determines monitoring requirements
in permits on a case-by-case basis.
5.3.3 Comment: EPA should address analytical issues of measuring chemicals accurately in
ambient waters. For example, commenters noted that EPA's proposed AWQC value for
bis (2-ethylhexyl) phthalate is approximately two orders of magnitude lower than the current
standard identified in the California Toxics Rule (CTR) and permitting programs will have
difficulties accurately measuring this compound.
EPA Response: Where there is reasonable potential for a proposed discharge to cause or
contribute to an exceedance of water quality standards, National Pollutant Discharge
Elimination System (NPDES) permit limits must derive from and ensure compliance with all
applicable water quality criteria in state water quality standards. If a permit limit derived from
the water quality criteria is below the analytical Minimum Level (ML) (i.e., the level at which the
pollutant can be accurately quantified by an analytical method), then the limit as calculated
must be included in the NPDES permit, and additional permit language would be included
prescribing how monitoring data should be reported and how compliance would be assessed.
Typically, this additional permit language would indicate that sample analysis must be
conducted using the most sensitive of the EPA approved methods, and that results below the ML
would demonstrate compliance with the effluent limit. While not common, permitting
authorities do periodically encounter this situation and have developed standard procedures
and permit language to address limits established below analytical MLs.
5.3.4 Comment: Several commenters asked EPA to be explicit about the exposure duration of
the AWQC. A commenter suggested that EPA should clearly identify those pollutants and AWQC
for which long-term exposure is the basis for the AWQC derivation and long-term average
application of the AWQC is appropriate. EPA should identify an appropriate averaging period,
given the assumptions associated with long-term exposure.
Page | 37
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EPA Response: EPA's current guidance that addresses averaging period for purposes of deriving
wasteload allocations for human health criteria can be accessed on EPA's website:
http://water.epa.aov/scitech/datait/models/upload/2002 10 25 npdes pubs owm0264.pdf.
6 MISCELLANEOUS
6.1 Comment: A commenter suggested that for each AWQC document, EPA should perform the
following:
• Update the reference to the EPA "Framework for Human Health Risk Assessment to
Inform Decision Making" and corresponding citation in the "Problem Formulation"
section, so that the date is 2014.
• Include a website link to the reference for the USEPA 2014 Estimated Fish Consumption
Rates for U.S. Population and Selected Subpopulations (NHANES 2003-2010) (i.e.,
http://water.epa.gov/scitech/swguidance/fishshellfish/fishadvisories/technical.cfm.
• Conduct a thorough technical edit of all documents to ensure that the correct chemicals
are matched with their chemical specific information.
EPA Response: EPA has updated the reference for the EPA Framework (USEPA 2014a) and
added the website link for the USEPA 2014 report Estimated Fish Consumption Rates for U.S.
Population and Selected Subpopulations (NHANES 2003-2010) in the final AWQC documents.
EPA has made every effort to ensure that the final documents are technically accurate, clear,
and transparent.
6.2 Comment: A commenter requested clarification regarding whether EPA will update the
methods and parameters used to derive AWQC as defined in Water Quality Guidance for the
Great Lakes System (40 CFR 132) to reflect the proposed changes to the AWQC.
EPA Response: EPA has no plans to revise the Water Quality Guidance for the Great Lakes
System (40 CFR 132) at this time.
Page | 38
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USEPA. 2014c. Draft Update of Human Health Ambient Water Quality Criteria: Chlorophenoxy
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4-D.pdf.
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