Guidance for Implementing
the January 2001 Methyl mercury
Water Quality Criterion
EPA 823-R-10-001 • April 2010
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Guidance for Implementing the
January 2001 Methyl mercury
Water Quality Criterion
Final
United States Environmental Protection Agency
Office of Science and Technology (4305T)
1200 Pennsylvania Ave., NW
Washington, DC 20460
EPA-823-R-10-001
www. epa. gov/waterscience
April 2010
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Contents
DISCLAIMER
This guidance provides advice on how to implement the water quality criterion
recommendation for methylmercury that the U.S. Environmental Protection Agency
(EPA) published in January 2001. This guidance does not impose legally binding
requirements on EPA, states, tribes, other regulatory authorities, or the regulated
community, and may not apply to a particular situation based upon the circumstances.
EPA, state, tribal, and other decision makers retain the discretion to adopt approaches on
a case-by-case basis that differ from those in the guidance where appropriate. EPA may
update this guidance in the future as belter information becomes available.
The Office of Science and Technology, Office of Water, U.S. Environmental Protection
Agency has approved this guidance for publication. Mention of trade names, products, or
services does not convey and should not be interpreted as conveying official EPA
approval, endorsement, or recommendation for use.
The suggested citation for this document is:
USEPA. 2010. Guidance for Implementing the January 2001 Methylmercury Water Quality
Criterion. EPA 823-R-10-001. U.S. Environmental Protection Agency, Office of Water, Washington,
DC.
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Contents
FOREWORD
On January 8, 2001, the U.S. Environmental Protection Agency (EPA) announced the
availability of its recommended Clean Water Act (CWA) section 304(a) water quality
criterion for methylmercury. This water quality criterion, 0.3 milligram (mg)
methylmercury per kilogram (kg) fish tissue wet weight, describes the concentration of
methylmercury in freshwater and estuarine fish and shellfish tissue that should not be
exceeded to protect consumers offish and shellfish among the general population. EPA
recommends that states, territories, and authorized tribes use the criterion and this
guidance in establishing or updating water quality standards for waters of the United
States and in issuing fish and shellfish consumption advisories. States and authorized
tribes remain free to adjust EPA's recommended criterion, provided that their new or
revised water quality criteria protect the designated uses and are based on scientifically
defensible methodology.
The publication of the 2001 methylmercury criterion was the first time EPA issued a
water quality criterion expressed as a fish and shellfish tissue value rather than as a water
column value. EPA recognizes that this approach differs from traditional water column
criteria and might pose implementation challenges. In the January 8, 2001 Federal
Register notice, EPA stated that it planned to develop more detailed guidance to help
states, territories, and authorized tribes with implementation of the methylmercury
criterion in water quality standards and related programs. This document provides that
detailed guidance.
EPA wrote the Guidance for Implementing the January 2001 Methylmercury Water
Quality Criterion to provide technical guidance to states, territories, and authorized tribes
exercising responsibility under CWA section 303(c), which provides for state review and
revision of water quality standards every three years, and adoption of criteria for toxic
pollutants, such as mercury, for which EPA has published criteria under CWA section
304(a). The document provides guidance on how to use the new fish tissue-based
criterion recommendation in developing water quality standards for methylmercury and
in implementing those standards in Total Maximum Daily Loads (TMDLs) and National
Pollutant Discharge Elimination System (NPDES) permits. EPA also wrote the guidance
to discuss approaches for managing the development of TMDLs for waterbodies
impaired by mercury and to recommend an approach for directly incorporating the
methylmercury tissue criterion into NPDES permits.
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For more information on the methylmercury criterion, see the criteria page on EPA's
Web site at http://www.epa.gov/waterscience/criteria/methylmercurv/index.html. For
more information on EPA's water quality standards program, see the standards page on
EPA's Web site at http://www.epa.gov/waterscience/standards. For more information
about this guidance document, contact U.S. Environmental Protection Agency, Office of
Science and Technology (4305T), 1200 Pennsylvania Avenue, NW, Washington, DC
20460.
Peter S. Silva
Assistant Administrator for Water
U.S. Environmental Protection Agency
in
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Contents
CONTENTS
1 Executive Summary 1
2 Introduction 9
2.1 What is the interest in mercury? 9
2.1.1 What are the health effects of methylmercury? 9
2.1.2 How frequent are the environmental problems? 11
2.2 What are the sources of mercury in fish? 14
2.3 How does methylmercury get into fish and shellfish? 15
2.4 Why is EPA publishing this document? 17
2.5 What is the effect of this document? 18
3 Water Quality Criteria and Standards Adoption 19
3.1 What must states and authorized tribes include as they adopt the
methylmercury criterion? 19
3.1.1 What do the CWA and EPA's regulations require? 19
3.1.2 What is the recommended form of the methylmercury criterion? 20
3.1.3 What approaches should states or authorized tribes consider when
developing a water column concentration criterion? 24
3.2 What options are available to address site-specific conditions and concerns? ...38
3.2.1 How can the methylmercury water quality criterion be modified for site-
specific conditions? 38
3.2.2 How do water quality standards variances apply? 44
3.2.3 How are use attainability analyses conducted? 47
4 Monitoring and Assessment 51
4.1 What are the analytical methods for detecting and measuring mercury and
methylmercury concentrations in fish and water? 51
4.1.1 Analytical Methods for Methylmercury 52
4.1.2 Analytical Methods for Mercury 52
4.1.3 Summary of Recommended Analytical Methods 53
4.2 What is the recommended guidance on field sampling plans for collecting fish
for determining attainment of the water quality standard? 54
4.2.1 What fish species should be monitored? 55
4.2.2 What sample types best represent exposure? 56
4.2.3 What is the recommended study design for site selection? 56
4.2.4 How often should fish samples be collected? 57
4.2.5 How many samples should be collected? 58
4.2.6 What form of mercury should be analyzed? 58
4.2.7 Other sampling considerations 58
4.3 How should waterbody impairment be assessed for listing decisions? 59
4.3.1 How should nondetections be addressed? 59
4.3.2 How should data be averaged across trophic levels? 61
IV
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4.3.3 How should older data be assessed? 63
4.3.4 How should fish consumption advisories be used to determine
impairment? 63
5 Other Water Quality Standards Issues 65
5.1 How does this criterion relate to the criteria published as part of the Great
Lakes Initiative? 65
5.2 What is the applicable flow for a water column-based criterion? 66
5.3 How are mixing zones used for mercury? 67
5.3.1 What is a mixing zone? 67
5.3.2 How does a mixing zone apply for the fish tissue-based
methylmercury criterion? 67
5.3.3 Does the guidance for the fish tissue-based criterion change the Great
Lakes Initiative approach to mixing zones for bioaccumulative
pollutants? 68
5.4 How are fish consumption advisories and water quality standards
harmonized? 68
5.4.1 What is the role of state and tribal Fish Advisory Programs? 68
5.4.2 How are consumption limits for consumption advisories determined? 69
5.4.3 How does the criterion differ from the advisory level? 69
5.4.4 What if there is a difference between assessing criterion attainment
and issuance of a fish consumption advisory? 70
5.4.5 Should existing advisories be revised to reflect the new criterion? 71
5.4.6 What federal agencies issue advisories? 71
5.4.7 How is the criterion related to FDA action levels? 72
5.5 What public participation is recommended for implementing the
methylmercury criterion? 72
6 TMDLs 73
6.1 What is a TMDL? 73
6.2 How have states and tribes approached mercury TMDLs? 73
6.2.1 What geographic scales have been used for mercury TMDLs? 75
6.2.2 What are the considerations in developing mercury TMDLs? 76
7 National Pollutant Discharge Elimination System (NPDES)
Implementation Procedures 93
7.1 What are the general considerations in NPDES permitting? 93
7.2 What is the EPA-recommended NPDES permitting approach for
methylmercury? 94
7.2.1 Developing NPDES permit limits based on the fish tissue criterion 94
7.2.2 Determining reasonable potential 95
7.2.3 Implementing antidegradation 96
7.2.4 Establishing appropriate WQBELs 96
7.3 How does EPA recommend implementing the fish tissue criterion for NPDES
permits? 99
7.4 What are the procedures for developing permit limits when the criterion is
adopted as a water column value or when the criterion is adopted as a fish
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tissue value and the permitting authority uses a water column translation of
the fish tissue value? 101
7.5 What are the procedures for developing permit limits when the criterion is
adopted as a fish tissue value and the permitting authority does not use a
water column translation of the fish tissue value? 103
7.5.1 How to determine the need for permit limits to control mercury (how to
determine reasonable potential) 103
7.5.2 Where reasonable potential exists, how can WQBELs be derived from
a fish tissue value? 114
8 Related Programs 125
8.1 What are EPA and others doing as a whole to address mercury? 125
8.2 How does pollution prevention play a role in the methylmercury criterion? 125
8.3 What regulations has EPA issued pursuant to the CAA to address air
emissions of mercury? 127
8.3.1 Municipal waste combustors 128
8.3.2 Hospital, medical, and infectious waste incinerators 128
8.3.3 Chlor-alkali plants 129
8.3.4 Hazardous waste combustors 129
8.3.5 Coal-fired power plants 130
8.3.6 Other 130
9 References 131
Appendix A. Methylmercury/Mercury Ratio Exhibited in Muscle
Tissue of Various Freshwater Fish Species 149
Appendix B. Tables from Methylmercury Criteria Document 151
Appendix C. Analytical Methods 155
Appendix D. Synopsized Mercury TMDLs Developed or Approved
by EPA 159
I. Ochlockonee Watershed, Georgia 160
Description of the Applicable Water Quality Standards 160
Source Assessment 161
Loading Capacity—Linking Water Quality and Pollutant Sources 161
Allocations 163
II. Arivaca Lake, Arizona 165
Description of the Applicable Water Quality Standards 165
Source Assessment 165
Loading Capacity—Linking Water Quality and Pollutant Sources 167
Allocations 169
III. McPhee and Narraguinnep Reservoirs, Colorado 171
Description of the Applicable Water Quality Standards 171
Source Assessment 172
Loading Capacity—Linking Water Quality and Pollutant Sources 173
Allocations 173
VI
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IV. Clear Lake, California 174
Description of the Applicable Water Quality Standards 174
Source Assessment 174
Loading Capacity—Linking Water Quality and Pollutant Sources 176
Allocations 177
V. Cache Creek, California 180
Description of the Applicable Water Quality Standards 180
Source Assessment 180
Loading Capacity—Linking Water Quality Pollutant Sources 182
Allocations 182
VI. Minnesota Statewide Mercury Total Maximum Daily Load 185
Description of the Applicable Water Quality Standards and TMDL Target 185
Source Assessment 185
Loading Capacity 186
Allocations 188
Appendix E. Model Descriptions 189
BASS (Bioaccumulation and Aquatic System Simulator) 189
Community Multi-Scale Air Quality (CMAQ) Model 189
D-MCM (Dynamic Mercury Cycling Model) 191
EXAMS2 (Exposure Analysis Modeling System) 191
GBMM (Grid Based Watershed Mercury Model) 192
GEOS-CHEM Model 192
GWLF (Generalized Watershed Loading Function) 193
Mercury Maps screening analysis 193
MOBILE 194
NDMMF (National Descriptive Model of Mercury in Fish Tissue) 195
NONROAD 195
QEAFDCHN (Quantitative Environmental Analysis Food Chain) Model 195
Regional Modeling System for Aerosols and Deposition (REMSAD) 196
SERAFM (Spreadsheet-based Ecological Risk Assessment for the Fate of
Mercury) 197
TOXI5 198
WASP (Water Quality Analysis Simulation Program) 198
WCS (Watershed Characterization System) Mercury Loading Model 199
Example of Linking Models 199
Appendix F. Examples of National Deposition Monitoring Networks 201
Index 203
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Contents
TABLES
Table 1a. Recommendations for water quality standards adoption 2
Table 1b. Recommendations for monitoring and assessment 3
Table 1c. Recommendations fortotal maximum daily loads (TMDLs) 4
Table 1d. Recommendations for permitting procedures 5
Table 2. Draft national BAFs fordissolved methylmercury 32
Table 3. Estimates of freshwater and estuarine combined finfish and shellfish
consumption from the combined 1994-1996 and 1998 CSFII surveys
(U.S. population) 43
Table 4. Recommended analytical methods for detecting and measuring low levels of
methylmercury and mercury in fish tissue and water 54
Table 5. Example data for calculating a weighted average fish tissue value 61
Table 6. Suggested content for MMPs based on the type of facility 122
Table B1. Exposure parameters used in derivation of the water quality criterion 152
Table B2. Average mercury concentrations in marine fish and shellfish 153
Table B3. Exposure estimates for methylmercury and percent of total exposure
based on adults in the general population 154
Table C1. Analytical methods for determining mercury and methylmercury in tissue ....155
Table C2. Analytical methods for determining mercury and methylmercury in water,
sediment, and other nontissue matrices 156
Table D1. Annual average mercury load from each subbasin 162
Table D2. Predicted mercury for annual average load and flow 163
Table D3. Annual total mercury load to Arivaca Lake 168
Table D4. Predicted and observed mercury for annual average load and flow 169
Table D5. Summary of TMDL allocations and needed load reductions (in g-Hg/yr) 170
Table D6. Summary of mercury load estimates for McPhee Reservoir 172
Table D7. Summary of TMDL allocations and needed load reductions for McPhee
Reservoir 173
Table D8. Summary of TMDL allocations and needed load reductions for
Narraguinnep Reservoir 174
Table D9. Summary of mercury load allocations 177
Table D10. Sediment goals for mercury in Clear Lake 178
Table D11. Cache Creek methylmercury allocations 183
Table D12. Bear Creek methylmercury allocations 184
Table D13. Approved northeast and southwest mercury TMDLs 188
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FIGURES
Figure 1. Average fish tissue concentrations by HUC watershed 12
Figure 2. Fish Consumption Advisories for Mercury 2008 13
Figure 3. Percentage of total mercury deposition attributable to global sources 78
Figure 4. Trends in mercury air emissions between 1990 and 2005 79
Figure 5. NPDES permitting approach for methylmercury 100
Figure 6. Implementing the fish tissue criterion in NPDES permits 101
Figure 7. Determining reasonable potential 103
Figure 8. Implementing tier2 antidegradation 111
Figure 9. Determining WQBEL requirements 115
Figure F-1. MDN data for 2005 204
IX
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Executive Summary
1 Executive Summary
In January 2001 EPA published ambient water quality criteria (AWQC)
recommendations for methylmercury for the protection of people who eat fish and
shellfish. This criterion, 0.3 milligram (mg) methylmercury per kilogram (kg) fish tissue
wet weight, marks EPA's first issuance of a water quality criterion expressed as a fish
and shellfish tissue value rather than as an ambient water column value.
Research shows that exposure to mercury and its compounds can cause certain toxic
effects in humans and wildlife (USEPA 1997a). As of 2008, 50 states, 1 territory, and
3 tribes had issued fish consumption advisories for mercury covering 16.8 million lake
acres and 1.3 million river miles (USEPA 2009a). Mercury is widely distributed in the
environment and originates from natural and human-induced (anthropogenic) sources,
including combustion and volcanoes. Methylmercury is highly bioaccumulative,
especially in aquatic food webs. Nearly 100 percent of the mercury that bioaccumulates
in upper-trophic-level fish (predator) tissue is methylmercury (Akagi et al. 1995; Becker
and Bigham 1995; Bloom 1992; Kim 1995).
Under section 303(c) of the Clean Water Act (CWA), states and authorized tribes must
adopt water quality criteria that protect designated uses. Section 303(c )(1) provides that
states and authorized tribes review their water quality standards every three years and
modify and adopt water quality standards as appropriate. In light of the new science used
to develop the 2001 methylmercury fish tissue criterion, EPA believes that states should
consider reviewing and revising their mercury human health criteria during their next
triennial review. This document provides technical guidance to states and authorized
tribes that exercise responsibility under CWA section 303(c) on how to use the new fish
tissue-based criterion recommendation as they develop water quality standards for
methylmercury.
EPA expects that, as states adopt methylmercury water quality criteria and as monitoring
of effluents, receiving waters, and fish tissue with the more sensitive methods
recommended by EPA increases, the number of waterbodies that states report on CWA
section 303(d) lists as impaired due to methylmercury contamination might increase. This
guidance is designed to assist states and authorized tribes to address those impairments.
Furthermore, this guidance addresses coordination across various media and program
areas in implementing the criterion, which will be important because atmospheric
deposition and multimedia cycling of mercury are significant in many waterbodies.
EPA recognizes the complexity and comprehensive nature of this guidance. As is always
the case when EPA issues technical guidance, EPA will provide outreach and technical
assistance to states and authorized tribes in implementing this guidance.
The following tables (tables la through Id) provide a brief summary of the most
important recommendations applicable to states and authorized tribes that are contained
in the guidance.
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Executive Summary
NOTE: These tables are provided as a convenience to the reader, but are not
comprehensive and are not a substitute for the full content of the guidance contained in
the other chapters of this document.
Table 1a. Recommendations for water quality standards adoption
Recommended form of a methylmercury criterion
EPA recommends that states and authorized tribes adopt a
methylmercury criterion expressed as a fish tissue value.
When adopting a fish tissue criterion, states and authorized
tribes will need to decide whether to:
• Implement the fish tissue criterion without water column
translation, or
• Translate the fish tissue criterion to a water column
value using bioaccumulation factors (BAFs). Three
approaches include:
1. Site-specific BAFs
2. Modeled BAFs
3. BAFs derived using the results of field studies that
are not site-specific (in limited circumstances); or
• Combination (fish tissue criterion for some or all waters,
combined with water column criteria for some or all
waters).
• States and authorized tribes may consider retaining their
existing water column criteria, on a temporary basis,
particularly for waters where there is a relatively high
direct water input of mercury.
Adoption considerations
• When adopting a fish tissue criterion, EPA encourages
states and authorized tribes to develop implementation
procedures.
• This guidance does not supersede requirements in
EPA's Great Lakes Initiative (GLI) regulation for waters
in the Great Lakes system.
Criterion adjustments
• Adjusting for local fish consumption rates.
• Adjusting for other sources of mercury (marine fish).
Mixing zones
• Not relevant when applying a fish tissue criterion that
has not been translated to a water column value.
• If the fish tissue criterion is converted to water column
values, EPA advises caution in the use of any mixing
zones for mercury. Restricting or eliminating mixing
zones may be appropriate.
Variances
• Guidance on when variances are appropriate.
• Considerations before granting a variance.
Most
applicable
to criteria
expressed
as...
FT (fish
tissue value)
WC (water
column
value)
Both FT and
WC
FT alone
FTorWC
FT or WC
FT alone
WC
WC
For a full
discussion
see
section...
3. 1.2 and
3.1.3
3.1.2.1
5.1
3.2.1
5.3
3.2.2
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Executive Summary
Table 1b. Recommendations for monitoring and assessment
Recommended analytical methods
• Methods 1631, revision E and 245.7 for mercury in
water.
• Draft Appendix A of Method 1631 for mercury in fish
tissue.
• Method 1630 for methylmercury in water.
• Method 1630 (with draft modifications) for
methylmercury in fish tissue.
Other available methods are listed in appendix C of this
guidance.
Field sampling recommendations
• Select fish for monitoring that are commonly eaten in the
study area.
• Choose large fish because these are typically highest in
methylmercury.
• If local consumption data are not available, match
assumed consumption pattern to sampled species, or
sample trophic level 4 species.
• Use composite samples offish fillets.
• EPA recommends biennial sampling if resources allow,
otherwise waterbodies should be screened a minimum
of every 5 years.
Assessing non-attainment offish tissue criterion
• Use statistical tests if enough data, or consider sample-
by-sample comparisons if very limited data.
Most
applicable
to criteria
expressed
as...
we
FT
we
FT
FT or WC
FT alone
FT alone
For a full
discussion
see
section...
4.1
App. C
4.2
4.3
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Executive Summary
Table 1c. Recommendations for total maximum daily loads (TMDLs)
Most
applicable
to criteria
expressed
as...
For a full
discussion
see
section...
States' timing of TMDL development
• States with comprehensive mercury reduction programs
in place may defer TMDLs for waters impaired by
mercury mainly from atmospheric sources.
(Summarizing EPA's voluntary "5m" category for listing
impaired waters.)
• The greater the relative contribution to a waterbody from
mercury sources other than air deposition, such as
water point sources, the more appropriate it may be to
use the TMDL process to characterize and address
those sources sooner, rather than deferring TMDL
development.
FT or WC
6.2 and
7.5.2.2
Approaches in approved mercury TMDLs
Examples in guidance text and appendix D discuss:
• Types of mercury sources; tools for assessing point
sources, atmospheric deposition, past metals mining
activity, sediments, and natural sources.
• Example allocation scenarios involving waters where
predominant sources are air deposition or mining.
• Post-TMDL monitoring.
FT or WC
6.2
Geographic scale
Describes scales that have been used for developing
mercury TMDLs:
• Waterbody-specific.
• Watershed-level.
• Statewide or regional.
FT or WC
6.2.1
Available models and example TMDL applications
• Example models for different situations (steady state,
dynamic, detail geometry, regression).
• Factors leading to model selection (methylation, BAFs,
sediments).
• Use of linked models without having explicit water
column criteria or translations.
• Other analytical approaches, e.g., proportionality
approach: Where air deposition is the only significant
mercury source and steady-state conditions apply,
TMDLs have been developed to meet fish tissue targets
by relying on a proportional relationship between
mercury deposition and fish tissue methylmercury
concentration.
FTorWC
6.2.2.2
FT alone
FT
6.2.2.2.1
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Executive Summary
Table 1d. Recommendations for permitting procedures
Two implementation approaches
• If a TMDL or a water column translation derived from a
fish tissue criterion or site-specific data to translate is
available at time of permit issuance, implement using
the approaches described in the Technical Support
Document (TSD) for Water Quality-based Controls
(USEPA1991).
• If a TMDL or water column translation or site-specific
data to translate are not available, implement
approaches described below.
Finding "reasonable potential" (RP)a
Depending on the particular facts, a permitting authority may
reasonably conclude that a facility has RP if:
• There is a quantifiable level of mercury in the discharge,
using a sufficiently sensitive EPA-approved analytical
method and
• Fish tissue from the receiving water is close to or
exceeds the criterion.
Where mercury effluent levels are unknown
EPA recommends that permitting authorities:
• Require effluent monitoring using a sufficiently sensitive
EPA-approved analytical method.
• Include a reopener clause in the permit to allow permit
to be modified if effluent data indicate a water quality-
based effluent limit (WQBEL) is necessary.
Where quantifiable amounts of mercury are not found
• If the permitting authority believes the monitoring data
are representative of the discharge, no further permit
conditions may be necessary.
Where fish tissue concentrations are unknown
EPA recommends that permitting authorities:
• Include a special permit condition to conduct a mercury
fish tissue survey for the receiving waterbody.
• Include a reopener clause in the permit to allow permit
to be modified if fish tissue data become available
indicating a WQBEL is necessary.
• Encourage the permittee to develop and implement a
mercury minimization plan (MMP) tailored to the facility's
potential to discharge mercury.
Most
applicable
to criteria
expressed
as...
we
FT alone
FT alone
FT alone
FT alone
FT alone
For a full
discussion
see
section...
7.4
7.5
7.5.1
7.5.1.1.1
7.5.1.1.2
7.5.1.2.1
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Executive Summary
Table 1d. Recommendations for permitting procedures (continued)
Permits with quantifiable mercury but without RP
Where a discharge contains a quantifiable amount of
mercury but fish tissue in the receiving water does not
exceed the criterion:
• If the discharger will undertake an activity that could
result in an increase in receiving water or fish tissue
mercury concentration
o Conduct tier 2 antidegradation analysis and
develop appropriate permit conditions.
o Require permittee to implement an MMP
tailored to the facility's potential to discharge
mercury.
o Require effluent monitoring.
• If the discharqer will not undertake an activity that could
result in an increase in receiving water or fish tissue
mercury concentration:
o Encourage the facility to develop and implement
an MMP tailored to the facility's potential to
discharge mercury.
Other factors in determining RP
• EPA recommends that the permitting authority account
for other factors that may constitute the basis for a
finding of RP. These include rising fish tissue
concentrations and the impact on downstream waters.
Mercury in intake water
• Where the only source of mercury in a discharge may
be the intake water taken directly from the same body of
water, and where there are no known sources or
additional contributions of mercury at the facility, the
permitting authority may reasonably conclude, based on
the particular facts, that there is no RP to exceed water
quality standards.
Most
applicable
to criteria
expressed
as...
FT alone
FT alone
FT or WC
For a full
discussion
see
section...
7.5.1.2.2
7.5.1.2.2
7.5.1.3
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Executive Summary
Table 1d. Recommendations for permitting procedures (continued)
Most
applicable
to criteria
expressed
as...
For a full
discussion
see
section...
WQBELs where there is a finding of RP
EPA recommends that permitting authorities:
• Require the permittee to implement an MMP tailored to
its potential to discharge mercury.
• Depending on the particular facts, the permitting
authority should consider including in an MMP an
effluent trigger level, a mercury reduction goal, or an
enforceable numeric level representing existing effluent
quality or some increment of the mercury reduction
determined achievable as a result of the measures and
practices specified in the MMP.
• Require effluent monitoring using a sufficiently sensitive
EPA-approved method to enable evaluation of the
effectiveness and implementation of the MMP.
• Include a reopener clause to modify the permit
conditions if the MMP is found to be not effective or if a
water column translation of the criterion is developed.
Other considerations and requirements may be necessary:
• Where a discharger undertakes an activity that could
result in an increase in receiving water or fish tissue
mercury concentrations, it must be consistent with
applicable antidegradation requirements. Additional
requirements may also be necessary under the CWA
and EPA's NPDES regulations.
• Include appropriate technology-based limits pursuant to
CWA section 301(b) and 40 CFR sections 125.3 and
122.44(a)(1).
• For modified or reissued permits with existing effluent
limits for mercury, any less stringent effluent limit must
be consistent with anti-backsliding requirements.
FT alone
7.5.2.1
7.2.4
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Executive Summary
Table 1d. Recommendations for permitting procedures (continued)
Permits with RP where direct water inputs are relatively high
In addition to the above:
• EPA recommends that states and authorized tribes
specifically consider developing TMDLs in the short
term.
• Where a state or tribe chooses not to develop a TMDL
in the short term, the state or tribe should develop an
analysis of sources and loading capacity similar to what
a TMDL would provide, or a water column translation of
the fish tissue criterion.
• EPA recommends that permitting authorities work
together with mercury dischargers in the watershed to
collect data necessary to develop:
o A TMDL, or
o An analysis of sources and loading capacity similar
to what a TMDL would provide, or
o A water column translation of the fish tissue criterion
for future permitting.
One approach is for the permitting authority to invoke its
authority under CWA section 308 (or comparable state
authority).
Additional requirements that may apply
• Additional requirements for: POTWs with pretreatment
programs; technology-based limits; anti-backsliding;
permit documentation.
Mercury minimization plans (MMPs)
This section provides guidance on appropriate MMPs.
Most
applicable
to criteria
expressed
as...
FT alone
FT or WC
FT
For a full
discussion
see
section...
7.5.2.2
7.5.2.3
7.5.2.4
Notes:
"Reasonable potential" refers to the reasonable potential to cause or contribute to an excursion above a
numeric or narrative criterion for water quality. 40 CFR 122.44(d)(1 )(i). NPDES permits for discharges with
"reasonable potential" must include water quality-based effluent limits (WQBELs).
As noted at the beginning of table 1d, this section refers to situations where neither a TMDL nor a water
column translation is available at time of permit issuance. Where a TMDL has been developed, the
WQBEL for that discharge must be consistent with the TMDL's wasteload allocation. Where a TMDL is not
available at the time of permit discharge, but where a water column translation of the fish tissue criterion
has been developed, or where site-specific data to do so are readily available, include a numeric WQBEL.
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Introduction
2 Introduction
2,1 . .• ;;••.•: -i;f ire TTV. :. y::
Mercury occurs naturally in the earth's crust and cycles in the environment as part of
natural and human-induced activities. The amount of mercury mobilized and released
into the biosphere has increased since the beginning of the industrial age. Most of the
mercury in the atmosphere is elemental mercury vapor, which circulates in the
atmosphere for up to a year and therefore can be widely dispersed and transported
thousands of miles from sources of emission (USEPA 1997b). Most of the mercury in
water, soil, sediments, plants, and animals is in the form of inorganic mercury salts and
organic forms of mercury (e.g., methylmercury). Inorganic mercury salts, when bound to
airborne particles, are readily removed from the atmosphere by precipitation and are also
dry deposited. Even after mercury deposits, it commonly returns to the atmosphere, as a
gas or associated with particles, and then redeposits elsewhere. As it cycles between the
atmosphere, land, and water, mercury undergoes a series of complex chemical and
physical transformations, many of which are not completely understood (USEPA 1997b).
This guidance focuses on an organic mercury compound known as methylmercury.
Methylmercury most often results from microbial activity in wetlands, the water column,
and sediments, and it is the form of mercury that presents the greatest environmental risks
to human health (66 FR 1344; January 8, 2001). The methylation process and
methylmercury bioaccumulative patterns are discussed in more detail in section 2.3.
2.7.7 What are the health effects of methylmercury?
Exposure to methylmercury can result in a variety of health effects in humans. Children
that are exposed to low concentrations of methylmercury prenatally might be at risk of
poor performance on neurobehavioral tests, such as those measuring attention, fine motor
function, language skills, visual-spatial abilities, and verbal memory (NRC 2000; USEPA
2002a). Mercury and its compounds are listed as a "toxic" pollutant under section
307(a) of the Clean Water Act (see 40 CFR401.15).
In 2000 the National Academy of Sciences (NAS)/National Research Council (NRC)
reviewed the health studies on mercury (NRC 2000). EPA's assessment of the
methylmercury reference dose (RfD) relied on the quantitative analyses performed by the
NRC (USEPA 2002a). The RfD is an estimate (with uncertainty spanning perhaps an
order of magnitude) of a daily exposure of the human population, including sensitive
subgroups, that is likely to be without an appreciable risk of deleterious effects during a
lifetime (USEPA 2002a). In its review of the literature, NRC found neurodevelopmental
effects to be the most sensitive endpoints and appropriate for establishing a
methylmercury RfD (NRC 2000).
On the basis of the NRC report, EPA established an RfD of 0.0001 mg/kg-day (0.0001
milligram of methylmercury per day for each kilogram of a person's body mass) (USEPA
2002a). EPA believes that exposures at or below the RfD are unlikely to be associated
with an appreciable risk of deleterious effects. It is important to note, however, that the
RfD does not define an exposure level corresponding to zero risk; mercury exposure near
-------
Introduction
or below the RfD could pose a very low level of risk that EPA deems nonappreciable. It
is also important to note that the RfD does not define a bright line above which
individuals are at risk of adverse effects (USEPA 2005a).
The primary route by which the U.S. population is exposed to methylmercury is through
the consumption offish containing methylmercury. The exposure levels at which
neurological effects have been observed in children can occur through maternal
consumption offish (rather than high-dose poisoning episodes) (USEPA 2005a).
In 2005 the National Health and Nutrition Examination Survey (NHANES) published the
results of a study of blood mercury levels in a representative sample of U.S. women of
childbearing age (CDC 2005). The report data for the period 1999-2002 show that all
women of childbearing age had blood mercury levels below 58 (ig/L, a concentration
associated with neurological effects in the fetus. These data show that 5.7 percent of
women of childbearing age had blood mercury levels between 5.8 and 58 (ig/L; that is,
levels within an order of magnitude of those associated with neurological effects. Typical
exposures for women of childbearing age were generally within two orders of magnitude
of exposures associated with these effects, according to data from NHANES (CDC 2005;
USEPA 2005a).
With regard to other health effects of methylmercury, some recent epidemiological
studies in men suggest that methylmercury is associated with a higher risk of acute
myocardial infarction, coronary heart disease, and cardiovascular disease in some
populations (Salonen et al. 1995, as cited in USEPA 200la). Other recent studies have
not observed this association. The studies that have observed an association suggest that
the exposure to methylmercury might offset the beneficial effects of fish consumption
(USEPA 2005a). There also is some recent evidence that exposures to methylmercury
might result in genotoxic or immunotoxic effects ([Amorim et al. 2000; ATSDR 1999;
Silva at al. 2004], as cited in USEPA 2005a). Other research with less corroboration
suggests that reproductive, renal, and hematological impacts could be of concern. There
are insufficient human data to evaluate whether these effects are consistent with
methylmercury exposure levels in the U.S. population (USEPA 2005a).
Deposition of mercury to waterbodies can also have an adverse impact on ecosystems
and wildlife. Plant and aquatic life, as well as birds and mammalian wildlife, can be
affected by mercury exposure; however, overarching conclusions about ecosystem health
and population effects are difficult to make. Mercury contamination is present in all
environmental media; aquatic systems experience the greatest exposures because of
bioaccumulation. Bioaccumulation refers to the net uptake of a contaminant from all
possible pathways. It includes the accumulation that might occur by direct exposure to
contaminated media, as well as uptake from food. Elimination of methylmercury from
fish is so slow that long-term reductions of mercury concentrations in fish are often due
to growth of the fish ("growth dilution"), whereas other mercury compounds are
eliminated relatively quickly. Piscivorous avian and mammalian wildlife are exposed to
mercury mainly through consuming contaminated fish, and as a result they accumulate
mercury to levels greater than those in their prey (USEPA 1997a).
10
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Introduction
EPA's mercury Web site, at http://www.epa.gov/mercury. provides a broad range of
information about mercury, including a full discussion of potential human health and
ecosystem effects.
2.1.2 How frequent are the environmental problems?
As of the 2008 listing of impaired waters (i.e.: water not attaining water quality
standards) under section 303(d) of the clean Water Act, 43 states and Puerto Rico
reported at least one waterbody as impaired due to mercury, and more than 8,800 specific
waterbodies were listed as impaired due to mercury, either solely or in combination with
other pollutants. All states have numeric criteria for mercury. About seven states, plus
Washington B.C. and two territories have adopted a fish tissue criterion for
methylmercury. Once additional states, tribes and territories begin to adopt EPA's
recommended fish tissue criterion, the number of waterbodies listed as impaired for
methylmercury is expected to increase since the revised criterion is more stringent than
the water concentration criteria most states currently have in their water quality
standards.
In 2001 EPA mapped concentrations of mercury in fish tissue from fish collected from
waterbodies all over the country (i.e., not limited to the waters identified by the states as
impaired) and compared them to the 2001 national recommended water quality criterion,
0.3 mg methylmercury/kg fish tissue wet weight. These data were not randomly or
systematically collected, but rather reflect fish tissue information that states had collected
as part of their fish consumption advisory programs. Approximately 40 percent of the
watershed-averaged fish tissue concentrations exceeded 0.3 mg methylmercury/kg fish
tissue wet weight (USEPA 200Ib).
Figure 1 shows fish tissue mercury concentrations averaged by watershed (by 8-digit
hydrologic unit code, or HUC).
11
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Introduction
Fish Tissue Mercury Concentrations
Averaged by Watershed
Average Fish Cone, (ppm)
No data
Less than 0.1
0.1-0.2
B 0.2-0.3
H 0.3-1
• 1-2.7
Note:
I.New Criterion for melhylmercury in fish is 0.3 ppm. Point of departure in fish advisories is often in 0.15 to 0.3 ppm range.
Average value based on fiilet samples only.
2. For HUCs shown in white, data do not exist to estimate mercury concentrations.
Figure 1. Average fish tissue concentrations by HUC watershed (USEPA 2005a).
In EPA's Environmental Monitoring and Assessment Project (EMAP) Western Streams
and Rivers Statistical Study (USEPA 2005b), 626 streams and rivers were sampled in 12
states of the western United States. Mercury was detected at 100 percent of sites and
samples in the study. The 0.3 mg/kg criterion (equivalent to 0.3 parts per million, ppm)
was exceeded in 56.8 percent of waters surveyed, which represent 20-30 percent of all
western rivers (Peterson et al. 2007). Results from the 2009 National Lake Fish Tissue
Study, a statistically-based survey conducted by EPA, showed that 49% of the sampled
population of lakes (76,559 lakes in the lower 48 states with surface areas greater than or
equal to 1 hectare or about 2.5 surface acres) had mercury concentrations that exceeded
the 0.3 ppm tissue-based mercury criterion (USEPA 2009b).
12
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Introduction
As of December 2008, 50 states, 1 territory, and 3 tribes had issued fish consumption
advisories1 for mercury covering 16.8 million lake acres and 1.3 million river miles
(figure 2). Twenty-seven states had issued advisories for mercury in all freshwater lakes
and rivers in the state, 13 states had statewide advisories for mercury in their coastal
waters and one state had a deep sea advisory (USEPA 2009a). The thresholds for the
levels of mercury in fish that trigger the issuance of an advisory for women of
childbearing age vary among the states and authorized tribes, but generally range from
0.07 to 1 ppm, with most threshold values in the range of 0.1 to 0.3 ppm.
Although states, territories, tribes, and local governments continue to issue new fish
advisories and most new fish advisories involve mercury, EPA believes that the increase
in advisories is a result of increased monitoring and assessment of previously untested
waters rather than increased domestic releases of mercury or increased levels or
frequency of contamination. In fact, U.S. releases of mercury to the air have declined by
more than 58 percent between 1990 and 2005 (USEPA 2008b).
Figure 2. Fish Consumption Advisories for Mercury 2008 (USEPA 2009a).
1 States and tribes issue their advisories and guidelines voluntarily and have flexibility in which criteria they use and how they collect data.
As a result, there are significant variations in the numbers of waters tested, the pollutants tested for, and the threshold for issuing advisories.
Based on self-reporting, the national trend is for states to monitor different waters each year, generally without retesting waters monitored
in previous years. Note that EPA does not issue fish advisories; states and tribes issue advisories (with the exception of national advisories,
regional advisories, and Superfund-related advisories). EPA issues guidance on the level of contaminants in fish, which states and tribes
may use in issuing their advisories.
13
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Introduction
Mercury is emitted from both natural and anthropogenic sources. Its residence time in the
atmosphere is much longer than that of most other metals because mercury can circulate
for up to a year (USEPA 1997b). Such mobility enables elemental mercury to disperse
and be transported over thousands of miles from likely sources of emission, across
regions, and around the globe. As a result, the mercury detected in fish in U.S. surface
waters is from both U.S. and international sources (USEPA 2005c). EPA estimates that
approximately 83 percent of the atmospheric mercury deposited on land and water in the
country is from a combination of sources outside the United States and Canada, as well as
from natural and re-emitted sources. EPA's current air quality modeling indicates a
substantial variation across the country: domestic sources influence mercury deposition
much more in the East, and global sources are a more significant contributor to mercury
deposition in the West, where relatively few domestic sources exist. This estimate was
based on a modeling assessment of the atmospheric fate, transport, and deposition of
mercury conducted by EPA for the Clean Air Mercury Rule2 (USEPA 2005d).
Natural sources of mercury include geothermal emissions from volcanoes and crustal
degassing in the deep ocean, as well as dissolution of mercury from other geologic
sources (Rasmussen 1994). Anthropogenic sources of mercury in the United States
include combustion (e.g., utility boilers; municipal waste combustors;
commercial/industrial boilers; hospital, medical, and infectious waste incinerators),
manufacturing sources (e.g., chlor-alkali and cement manufacturers), and mining
(USEPA 1997b).
U.S. anthropogenic emissions of mercury to the air have declined more than 58 percent
from the passage of the 1990 Clean Air Act (CAA) Amendments to 2005 (most recent
data available). These amendments provided EPA new authority to reduce emissions of
mercury and other toxic pollutants to the air. In 1990 more than two-thirds of U.S.
human-caused mercury emissions came from just three source categories: coal-fired
power plants; municipal waste combustion; and hospital, medical, and infectious waste
incineration (figure 4, section 6.2.2.1). Regulations were issued in the 1990s to control
mercury emissions from waste combustion. In addition, actions to limit the use of
mercury—most notably voluntary and Congressional action to limit the use of mercury in
batteries and EPA regulatory limits on the use of mercury in paint—contributed to the
reduction of mercury emissions from waste combustion during the 1990s by reducing the
mercury content of waste. Regulation of mercury emissions from chlorine production
facilities that use mercury cells and regulation of industrial boilers will further reduce
emissions of mercury.
2 On February 8,2008, the D.C. Circuit Court of Appeals vacated the Section 112(n) Revision Rule and the Clean Air Mercury Rule.
Rules controlling mercury emissions, which implement the 1990 CAA amendments, include standards for municipal waste combustors
(40 CFR part 60, subpart Da, and parts 72 and 75); standards for hospital, medical, and infectious waste incinerators (40 CFR part 60,
subpart Ce); standards for chlor-alkali plants (40 CFR part 63, subpart IIIII); standards for existing and new hazardous waste-burning
incinerators (40 CFR 63.1203 [a][2] and [b][2]); standards for existing and new hazardous waste-burning cement kilns (40 CFR 63.1204
[a][2] and [b][2]); and standards for existing and new hazardous waste-burning lightweight aggregate kilns (40 CFR 63.1205 [a][2] and
[b][2]). See also section 8.3 of this document.
14
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Introduction
At present, the largest single source of anthropogenic mercury emissions to the air in the
country is coal-fired power plants. Mercury emissions from U.S. power plants are
estimated to account for about one percent of total global mercury emissions (70 FR
15994; March 29, 2005). In May 2005, EPA adopted the Clean Air Act Section 112(n)
Revision Rule and the Clean Air Mercury Rule (CAMR). CAMR regulated mercury
emissions from coal-fired utilities. On February 8, 2008, the B.C. Circuit Court of
Appeals vacated the Section 112(n) Revision Rule and CAMR. EPA is developing air
toxics emissions standards for power plants under Clean Air Act (Section 112(d). EPA
currently intends to propose and finalize air toxics standards for coal- and oil-fired
electric generating units by the end of 2011. Point sources of mercury discharging into
waters are also regulated by NPDES permits. Chlor-alkali facilities are subject to effluent
guidelines that impose treatment levels reflective of the Best Available Technology
Economically Achievable (40 CFR part 415). All NPDES permits must ensure that
permitted discharges achieve water quality standards (40 CFR 122.44(d)). Nonpoint
source runoff is not regulated under federal regulations, but to the extent that these
sources cause a water to exceed its water quality standards, states will develop TMDLs
that identify the necessary reductions from these sources for achieving the water quality
standards.
Anthropogenic emissions, however, are only one part of the mercury cycle. Releases
from human activities today add to the mercury reservoirs that already exist in land,
water, and air, both naturally and as a result of previous human activity.
i.] •.:*•. .•••:• "•'.. ?,:-••: ,.' o^/'L :":'
Mercury is widely distributed in the environment. Understanding the distribution and
cycling of mercury among the abiotic (nonliving) and biotic (living) compartments of
aquatic ecosystems is essential to understanding the factors that govern methylmercury
uptake in fish and shellfish tissue. The following is a synopsis of the current
understanding of mercury cycling in the environment.
Mercury occurs naturally in the environment as several different chemical species. Most
mercury in the atmosphere (95-97 percent) is present in a neutral, elemental state, Hg°
(Lin and Pehkonen 1999). In water, sediments, and soils, most mercury is found in the
oxidized, divalent state, Hgn (Morel et al. 1998). A small fraction of this pool of divalent
mercury is transformed by microbes into methylmercury (CH3Hgn) (Jackson 1998).
Methylmercury is retained in fish tissue and is the only form of mercury that
biomagnifies in aquatic food webs (Kidd et al. 1995). Transformations among mercury
species within and between environmental media result in a complicated chemical cycle.
The relative contributions of local, regional, and long-range sources of mercury to fish
mercury levels in a given waterbody are strongly affected by the speciation of natural and
anthropogenic emission sources. Elemental mercury is oxidized in the atmosphere to
form the more soluble mercuric ion, Hgn (Schroeder et al. 1989). Particulate and reactive
gaseous phases of Hgn are the principal forms of mercury deposited onto terrestrial and
aquatic systems because they are more efficiently scavenged from the atmosphere
through wet and dry deposition than is Hg° (Lindberg and Stratton 1998). Because Hgn
species or reactive gaseous mercury (RGM) and particulate mercury (Hgp) in the
atmosphere tend to be deposited more locally than Hg°, differences in the species of
15
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Introduction
mercury emitted affect whether the mercury is deposited locally or travels longer
distances in the atmosphere (Landis et al. 2004).
A portion of the mercury deposited in terrestrial systems is re-emitted to the atmosphere.
On soil surfaces, sunlight might reduce deposited Hgn to Hg°, which might then escape
back to the atmosphere (Carpi and Lindberg 1997, Frescholtz and Gustin 2004, Scholtz et
al. 2003). Significant amounts of mercury can be co-deposited to soil surfaces in
throughfall and litterfall of forested ecosystems (St. Louis et al. 2001), and exchange of
gaseous Hg by vegetation has been observed (e.g., Gustin et al. 2004). Hg has a strong
affinity for organic compounds such that inorganic mercury in soils and wetlands is
predominantly bound to dissolved organic matter (Mierle and Ingram 1991).
Concentrations of methylmercury in soils are generally very low. In contrast, wetlands
are areas of enhanced methylmercury production and account for a significant fraction of
the external methylmercury inputs to surface waters that have watersheds with a large
portion of wetland coverage (e.g., St. Louis et al. 2001).
In the water column and sediments, Hg11 partitions strongly to silts and biotic solids, sorbs
weakly to sands, and complexes strongly with dissolved and particulate organic material.
Hg11 and methylmercury sorbed to solids settle out of the water column and accumulate
on the surface of the benthic sediment layer. Surficial sediments interact with the water
column through resuspension and bioturbation. The amount of bioavailable
methylmercury in water and sediments of aquatic systems is a function of the relative
rates of mercury methylation and demethylation. In the water, methylmercury is degraded
by two microbial processes and sunlight (Barkay et al. 2003; Sellers et al. 1996). Mass
balances for a variety of lakes and coastal ecosystems show that in situ production of
methylmercury is often one of the main sources of methylmercury in the water and
sediments (Benoit et al. 1998; Bigham and Vandal 1994; Gbundgo-Tugbawa and Driscoll
1998; Gilmour et al. 1998; Mason et al. 1995). Changes in the bioavailability of inorganic
mercury and the activity of methylating microbes as a function of sulfur, carbon, and
ecosystem-specific characteristics mean that ecosystem changes and anthropogenic
"stresses" that do not result in a direct increase in mercury loading to the ecosystem, but
alter the rate of methylmercury formation, might also affect mercury levels in organisms
(e.g., Griebetal. 1990).
Dissolved Hg11 and methylmercury accumulate in aquatic vegetation, phytoplankton, and
benthic invertebrates. Unlike Hg11, methylmercury biomagnifies through each successive
trophic level in the benthic and pelagic food chains such that mercury in predatory,
freshwater fish is found almost exclusively as methylmercury (Bloom 1992; Watras et al.
1998). In fish, methylmercury bioaccumulation is a function of several uptake pathways
(diet, gills) and elimination pathways (excretion, growth dilution) (Gilmour et al. 1998;
Greenfield et al. 2001). Factors such as pH, length of the aquatic food chain, temperature,
and dissolved organic carbon (DOC) can affect bioaccumulation (Ullrich et al. 2001). As
a result, the highest mercury concentrations for a given fish species correspond to
smaller, long-lived fish that accumulate methylmercury over their life span with minimal
growth dilution (e.g., Doyon et al. 1998). In general, higher mercury concentrations are
expected in top predators, which are often large fish relative to other species in a
waterbody.
16
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Introduction
. : , : • • : .>•: " •: •.-; •, •; .-. .
In a January 8, 2001, Federal Register notice (66 FR 1344), EPA announced the
availability of its recommended water quality criterion for methylmercury. In that notice,
EPA also stated that development of the associated implementation procedures and
guidance documents would begin by the end of 2001. Therefore, EPA makes this
guidance available to fulfill that commitment to assist states and authorized tribes to
adopt into their water quality standards the recommendations set forth in Water Quality
Criterion for the Protection of Human Health: Methylmercury (USEPA 200 la), or other
water quality criteria for methylmercury where such other criteria are based on
scientifically defensible methods.
This nontraditional approach—developing a water quality criterion as a fish and shellfish
tissue value—raises several implementation questions on both technical and
programmatic fronts. Development of water quality standards, NPDES permits, and
TMDLs presents many challenges because these activities have usually been based on a
water concentration (e.g., as a measure of mercury levels in effluent or receiving waters).
This guidance addresses issues associated with states' and authorized tribes' adoption of
the new water quality criterion into their water quality standards programs and
implementation of the revised water quality criterion in TMDLs and NPDES permits.
Furthermore, because atmospheric deposition is a large source of mercury for many
waterbodies, implementation of this criterion involves coordination across various media
and program areas, which is also addressed in this guidance.
At this time, about seven states, plus Washington D.C. and two territories have adopted a
fish tissue criterion for methylmercury with EPA approval. EPA expects that with the
publication of this guidance, states and authorized tribes will include new or revised
criteria for methylmercury in their waters as part of the next three year review of
standards required by section 303(c ) of the Clean Water Act. This expanded adoption
of the 2001 methylmercury fish tissue criterion, together with a more sensitive method
for detecting mercury in effluent and the water column and increased monitoring of
previously unmonitored waterbodies, is expected to result in an increase in the number of
waterbodies that states identify as impaired by mercury on CWA section 303(d) lists.
This guidance includes recommended approaches for relating a concentration of
methylmercury in fish tissue to a concentration of mercury in ambient water (see chapter
3); a recommended approach for directly using the methylmercury tissue criterion as a
basis for issuing NPDES permits (see chapter 7); and approaches that have been used in
approved TMDLs for waterbodies impaired by mercury. This guidance includes
examples of TMDL approaches for waterbodies where much of the mercury comes from
atmospheric sources, as well as examples of TMDLs for waterbodies where the mercury
is predominantly from past mining activity. Finally, the guidance describes ongoing EPA
efforts to address sources of mercury, such as programs under the CAA and pollution
prevention activities.
EPA recognizes the complexity and comprehensive nature of this guidance. As is always
the case when EPA issues technical guidance, EPA will provide outreach and technical
assistance to states and authorized tribes in implementing this guidance.
17
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Introduction
This guidance document presents suggested approaches—but not the only technically
defensible approaches—to criteria adoption and implementation. The guidance is not a
substitute for applicable sections of the CWA or EPA's regulations; nor is it a regulation
itself. Thus, it cannot impose legally binding requirements on EPA, states, authorized
tribes, or the regulated community and may not apply to a particular situation. EPA, state,
territorial, and tribal decision makers retain the discretion to adopt other scientifically
defensible approaches that differ from this guidance. EPA may change this guidance in
the future.
18
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Water Quality Criteria and Standards Adoption
3 Water Quality Criteria and Standards
Adoption
3.1.1 What do the CWA and EPA's regulations require?
The CWA and EPA's regulations specify the requirements for adoption of water quality
criteria into state or tribal water quality standards. States and authorized tribes must adopt
water quality criteria4 that protect designated uses. See CWA section 303(c)(2)(A). Water
quality criteria must be based on a sound scientific rationale and must contain sufficient
parameters or components to protect the designated uses (see 40 CFR 131.11). States and
authorized tribes are required to review standards every three years and submit changes
to EPA for approval.
Whenever they review or revise standards, states and authorized tribes are to adopt
numeric criteria for all toxic pollutants for which EPA has established national
recommended ambient water quality criteria (AWQC) and where the discharge or
presence of these pollutants could reasonably interfere with the designated uses (see
CWA section 303(c)(2)(B)). Mercury and related compounds are identified as toxic
pollutants in EPA regulations (40 CFR 401.15) and EPA published a criterion under
304(a) for methylmercury in 2001. EPA issued guidance on how states and authorized
tribes may comply with CWA section 303(c)(2)(B), which is now contained in the Water
Quality Standards Handbook: Second Edition (USEPA 1994). This document provides
three options for compliance:
• Option 1: States and authorized tribes may adopt statewide or reservation-wide
numeric chemical-specific criteria for all toxic pollutants for which EPA has issued
CWA section 304(a) criteria guidance.
• Option 2: States and authorized tribes may adopt numeric chemical-specific criteria
for those stream segments where the state or tribe determines that the priority toxic
pollutants for which EPA has issued CWA section 304(a) criteria guidance are
present and can reasonably be expected to interfere with designated uses (e.g., a
designated use of "fishing" is interfered with by nonattainment of the mercury
water quality criterion).
4 The term water qualify criteria has two different definitions under the CWA. Under CWA section 304(a), EPA publishes recommended
water quality criteria guidance that consists of scientific information regarding concentrations of specific chemicals or levels of parameters
in water that protect aquatic life and human health. The 2001 methylmercury criterion is an example of a recommended section 304(a)
criterion. States may use these recommended criteria as the basis for developing water quality standards. Water quality criteria are also
elements of state water quality standards adopted under CWA section 303(c).
19
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Water Quality Criteria and Standards Adoption
• Option 3: States or authorized tribes may adopt a chemical-specific translator
procedure that can be used to develop numeric criteria as needed.
EPA considers the 2001 methylmercury criterion a sound, scientifically based approach
for meeting human health designated uses. In addition, this guidance addresses a range of
complex technical issues and responds to the questions that states and authorized tribes
have raised. Thus, EPA strongly encourages states and authorized tribes to adopt the
2001 methylmercury criterion or any sound, scientifically based approach for
methylmercury or mercury, into their water quality standards at the upcoming triennial
review of standards to fulfill the requirements of section 303(c) (2)(B) of the Clean
Water Act and 40 CFR part 131. Numerical criteria for mercury in water, rather than fish
tissue, published by EPA and in effect prior to 2001, may be included temporarily as part
of revised mercury criteria at the next triennial review as provided for below.
3.1.2 What is the recommended form of the methylmercury
criterion?
EPA's current recommended CWA section 304(a) water quality criterion for
methylmercury is expressed as a fish6 tissue concentration value (0.3 milligram
methylmercury per kilogram of wet-weight fish tissue, or 0.3 mg/kg). With the
publication of the fish tissue criterion, EPA withdrew the previous human health water
quality criterion for mercury as the recommended section 304(a) water quality criterion
for states and authorized tribes to use as guidance in adopting water quality standards
(USEPA 200Ic). These water column criteria, however, may be temporarily part of
revised mercury criteria until the triennial review that follows the criterion adoption to
help the transition in implementing the fish tissue criterion.
States and authorized tribes have several options for adopting a new or revised
methylmercury criterion into their water quality standards. They may:
• Adopt the 2001 criterion or other scientifically defensible criterion as a fish tissue
residue concentration, and implement it without water column translation; or
• Adopt a water column concentration, using the translation methodologies outlined
in section 3.1.3.1, and implement it using traditional approaches; or
• Use a combination of the above approaches. For example, states and tribes could
adopt a fish tissue criterion and implement it without water column translation for
some or all waters, and translate the criterion to water column values for some or
all waters.
Site-specific data for translating the fish tissue criterion to water column concentration,
where needed, may take time to collect. Accordingly, states and authorized tribes may
5 A translator procedure is simply the detailed process adopted by a state or authorized tribe, that explains how the state or authorized tribe
will interpret its narrative criteria for toxics so that a quantifiable term can be used in assessment, permitting, and TMDL development. For
example, a state or tribe could use EPA's water quality criteria as the means for interpreting its narrative criteria.
6 The criterion applies to both finfish and shellfish. For purposes of simplifying language in this document, the term fish means both finfish
and shellfish.
20
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Water Quality Criteria and Standards Adoption
consider retaining their existing water column criteria, on a temporary basis, particularly
for waters where there is a relatively high direct water input of mercury. In such a case,
where the state has retained the existing water column criteria, permits must include both
a limit based on the existing numeric water column criterion and other requirements
based on the fish tissue criterion (see chapter 7).
Where a water column translation of the fish tissue criterion has been developed or where
site-specific data to do so are readily available using one of the options in Section 3.1.3.1,
states and authorized tribes should translate the fish tissue criterion, and implement using
traditional approaches. If site-specific data are not available to translate, the state or
authorized tribe may design data collection activities to obtain the necessary data. States
and authorized tribes should focus data collection activities on water bodies where
methylmercury impairments are high priorities for action because of high direct water
inputs. EPA recommends that states and tribes not only focus on data collection but also
on the development of translators for waters with high direct water inputs of mercury.
Additionally, EPA recommends that states and tribes include such translators in their
criterion implementation plans.
States and authorized tribes remain free not to use EPA's current recommendations,
provided that their new or revised water quality criteria for methylmercury protect the
designated uses and are based on a scientifically defensible methodology. In doing this,
states and authorized tribes should consider bioaccumulation and local or statewide fish
consumption. EPA will evaluate criteria submitted by states and authorized tribes case by
case.
If states and authorized tribes decide to adopt the tissue criterion expressed as a fish
tissue concentration without translating it to a traditional water column concentration, this
decision will lead to choices on how to implement the tissue criterion. A state or
authorized tribe could decide to develop TMDLs and to calculate WQBELs in NPDES
permits directly without first measuring or calculating a BAF. This guidance provides
options for such approaches in chapters 6 and 7.
EPA does not require states and tribes to translate the fish tissue criterion into water
column criteria. For waters with relatively high direct water inputs of mercury (mercury
from point sources and nonpoint sources other than air deposition), EPA does
recommend developing TMDLs, an analysis of sources and loading capacity similar to
what would be provided in a TMDL, or a water column translation of the fish tissue
criterion, to provide important information for developing appropriate permit limits. See
section 7.5.2.2 for a further discussion of this situation.
3.1.2.1 Developing a methylmercury criterion implementation plan
Regardless of the approach a state decides to use to implement its criterion, EPA
encourages states and authorized tribes to develop a methylmercury criterion
implementation plan to ensure environmentally protective and effective administration of
all water quality related programs with respect to methylmercury. Developing a
methylmercury implementation plan can facilitate adoption of the tissue-based criterion
and provide transparency on state or tribal approaches to the numerous implementation
issues associated with this type of criterion. This benefits not only the state or tribe but
the regulated community and the public.
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Water Quality Criteria and Standards Adoption
Examples of potential implementation issues the plan could cover include criterion
adoption into the water quality standards (e.g., tissue or water column value with
translators, BAF development methods), reasonable potential and permitting decisions,
ambient monitoring strategies, and impairment determinations.
Developing an implementation plan could also facilitate subsequent regulatory decisions.
Working with stakeholders and the public to develop an appropriate implementation plan
concurrent with adoption of a tissue-based criterion could facilitate subsequent
implementation decisions (e.g., application of the criterion in the context of 303(d) listing
decisions or NPDES permitting actions) and decrease the likelihood of legal challenges.
It may be most useful to states and tribes to develop such an implementation plan prior to
the adoption of the fish tissue criterion. States and tribes could propose draft plans when
they are developing updates or revisions to their water quality standards. Additionally,
EPA encourages states and tribes to take public comment on their draft plan during the
time when the state or tribe is proposing to adopt the fish tissue criterion.
If a state or tribe develops a methylmercury implementation plan during adoption of its
criterion, the state or tribe should submit the plan to EPA with the state's new criterion.
Although the plan itself is not subject to EPA review and approval, the plan could
facilitate EPA's review of the new criterion.
3.1.2.2 Why is the fish tissue concentration criterion recommended?
EPA recommends that when states and authorized tribes adopt new or revised
methylmercury water quality criteria, they adopt the criteria in the form of a fish tissue
methylmercury concentration. This is the preferred form for the following reasons:
• A criterion expressed as a fish tissue concentration is closely tied to the "fishable"
designated use goal applied to nearly all waterbodies in the United States.
• A fish tissue concentration value is expressed in the same form (fish tissue) through
which humans are exposed to methylmercury.
• A fish tissue concentration value is more consistent with how fish advisories are
issued.
• At environmentally relevant concentrations, methylmercury is currently easier to
detect in fish tissue than in water samples.
3.1.2.3 How is the fish tissue concentration criterion calculated?
The derivation of a methylmercury water quality criterion uses a human health
toxicological risk assessment (e.g., a reference dose [RfD]), exposure data (e.g., the
amount of pollutant ingested, inhaled, or absorbed per day), and data about the target
population to be protected. The methylmercury fish tissue residue criterion (TRC) for the
protection of human health is calculated as:
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Water Quality Criteria and Standards Adoption
BW x(RfD -RSC)
1 KU - ~^
1=2 (Equation 1)
Where:
TRC = fish tissue residue criterion (in mg/kg) for freshwater and estuarine fish
and shellfish
RfD = reference dose (based on noncancer human health effects); for
methylmercury, it is 0.1 ug/kg body weight/day
RSC = relative source contribution (subtracted from the RfD to account for
methylmercury in marine fish consumed7), estimated to be 0.027 ug/kg
body weight/day
BW = human body weight (default value of 70 kg for adults)
FI = fish intake at trophic level (TL)/ (/' = 2, 3, 4); total default intake of
uncooked freshwater and estuarine fish is 17.5 g fish/day for the general
U.S. adult population8
This equation and all values used in the equation are described in Water Quality Criterion
for the Protection of Human Health, Methylmercury (USEPA 200 la). This equation is
essentially the same equation used in the 2000 Human Health Methodology (USEPA
2000b) to calculate a water quality criterion for a pollutant that may cause noncancerous
health effects. Here, it is rearranged to solve for a protective concentration in fish tissue
rather than in water. Thus, it does not include a BAF or drinking water intake value
(methylmercury exposure from drinking water is negligible (USEPA 200lc)).
When all the numeric values are put into the generalized equation, the TRC of 0.3 mg
methylmercury/kg fish is the concentration in fish tissue that should not be exceeded on
the basis of a consumption rate of 17.5 g fish/day of freshwater or estuarine fish.
EPA encourages states and authorized tribes to collect, as quickly as possible, local or
regional data to modify the fish consumption rate rather than using the default values if
the state or authorized tribe believes that such a fish consumption rate would be more
appropriate for its target population. This gives states and tribes the flexibility to develop
criteria that provide additional protection appropriate for highly exposed populations that
may be at greater risk than the general population protected by the 304(a) criterion
(USEPA 2000b). Where states do not have site-specific data, but intend to collect this
7 The RSC accounts for exposures from all anticipated sources so that the entire RfD is not apportioned to freshwater/estuarine fish and
shellfish consumption alone. In the assessment of human exposure in the methylmercury water quality criterion document, EPA found that
human exposures to methylmercury were negligible except from freshwater/estuarine and marine fish. Therefore, in developing the
criterion on the basis of consumption of freshwater/estuarine fish, EPA subtracted the exposure due to consumption of marine fish. See 66
FR 1354-1355; January 8,2001.
8 The consumption rate value of 17.5 grams uncooked fish per day is the 90th percentile of freshwater and estuarine fish consumed by the
public according to the 1994—96 Continuing Survey of Food Intakes by Individuals (USEPA 2000a). EPA uses this value as the default
consumption rate in development of water quality criteria. The default trophic level values for the general population are 3.8 g fish/day for
TL2, 8.0 g fish/day for TL3, and 5.7 g fish/day for TL4. The rationale behind the selection of this value is described in the Human Health
Methodology (USEPA 2000b).
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Water Quality Criteria and Standards Adoption
data over time to develop a more appropriate criterion, states should use EPA's default
fish consumption rate on a temporary basis to be able to adopt and implement the fish
tissue criterion in a timely manner.
The TRC value is not based on any default breakout of fish consumption by trophic
level.The trophic levels assigned to the fish consumption value should reflect those that
each target population consumes. For assessing impairment or attainment of the TRC, a
state or authorized tribe may choose to assign the TRC value to only trophic level 4 or to
the highest trophic level consumed. This approach is conservative in that it assumes that
all fish consumed are at the highest trophic level, and it will likely protect most, if not all,
populations at an uncooked freshwater or estuarine fish consumption rate of 17.5
grams/day. If a state or authorized tribe wishes to calculate the TRC value on the basis of
consumption at each trophic level for monitoring and compliance purposes, it would first
determine consumption patterns at each trophic level for the target population(s). (For
information on determining consumption patterns, see chapter 4.) This approach might be
more precise and is less likely to be overprotective; however, developing it could be
resource-intensive.
3.1.3 What approaches should states or authorized tribes consider
when developing a water column concentration criterion?
As described in section 3.1.2 above, there may be situations where it is appropriate to
adopt a criterion expressed as a water column concentration. EPA recognizes that a fish
tissue residue water quality criterion is new to states and authorized tribes and might pose
implementation challenges for traditional water quality programs. Water quality
standards, water quality-based effluent limits (WQBELs), total maximum daily loads
(TMDLs), and other activities generally employ a water column value. This section
provides information for states and authorized tribes that decide to adopt a water
concentration criterion derived from a fish tissue criterion.
Alternatively, a state or authorized tribe may decide to adopt a fish tissue criterion with a
site-specific procedure for translating the tissue criterion to a water column concentration.
Because methylmercury bioaccumulation can vary substantially from one location to
another, this option allows for the tissue criterion to be translated to a water concentration
using site-specific information on methylmercury bioaccumulation (i.e., site-specific
BAFs). Administratively, this option might be more efficient compared to adopting a
water concentration criterion for an entire state or tribal jurisdiction or adopting or
approving site-specific criteria on an individual waterbody basis. Approaches for
translating a tissue concentration-based criterion to a water concentration are provided in
the following section (section 3.1.3.1).
Developing a water column translation of the fish tissue criterion requires assessment of
methylmercury bioaccumulation at an appropriate geographic scale. The uncertainty
associated with differential bioaccumulation of methylmercury across sites within a state
or tribal jurisdiction will be embedded in the state or tribal water-based criterion.
9 A WQBEL is a requirement in an NPDES permit that is derived from, and complies with, all applicable water quality standards and is
consistent with the assumptions and requirements of any approved wasteload allocation (see 40 CFR 122.44(d)( 1 )(vii)).
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Water Quality Criteria and Standards Adoption
Reducing such uncertainty is one of the primary reasons EPA chose to express its
national recommended criterion for methylmercury as a tissue concentration rather than
as a water concentration.
To express the methylmercury tissue concentration-based criterion as a water
concentration, a state or authorized tribe would translate the methylmercury criterion
concentration in fish tissue to methylmercury concentrations in the water column. To
accomplish this, the state or authorized tribe would develop BAFs. In the 2001 Federal
Register notice of the methylmercury criterion, EPA identified three different possible
approaches for developing a BAF. These approaches are discussed in more detail in
section 3.1.3.1. The basic equations used in developing a water column criterion are
presented below, and additional discussion of calculating BAFs is presented in the
following section.
The following equation may be used to translate the tissue concentration-based human
health AWQC to a water concentration-based methylmercury criterion using a BAF as
A WQC = TRC I BAF (Equation 2)
Where:
A WQC = water concentration-based ambient water quality criterion for
methylmercury in milligrams per liter (mg/L)
TRC = tissue residue concentration; the water quality criterion for
methylmercury in fish tissue in mg/kg
BAF = bioaccumulation factor for trophic levels 2, 3, and 4, weighted on the
basis offish consumption rates for each trophic level in liters per
kilogram (L/kg)
The BAF is the ratio of the concentration of the chemical in the appropriate tissue of the
aquatic organism and the concentration of the chemical in ambient water at the site of
sampling. BAFs are trophic-level-specific . EPA recommends that they be derived from
site-specific, field-measured data as
u» (Equation3)
Where:
BAF = bioaccumulation factor, derived from site-specific field-collected
samples of tissue and water in L/kg
Ct = concentration of methylmercury in fish tissue in mg/kg, wet tissue
weight
Cw = concentration of methylmercury in water in mg/L
When such data are unavailable, other approaches for deriving BAFs may be used, as
outlined in section 3.1.3.1.
In the calculation to derive an AWQC as a water column concentration, the BAFs for the
different trophic levels are combined to provide a weighted BAF value. For example, if a
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Water Quality Criteria and Standards Adoption
state wants to protect a population that eats on average 17.5 grams per day of uncooked
fish from a waterbody, and 75 percent of the fish eaten are in trophic level 4 and 25
percent of the fish eaten are in trophic level 3, the weighted BAF would be the sum of
0.25 times the trophic level 3 BAF and 0.75 times the trophic level 4 BAF. Section
3.2.1.2 provides guidance on estimating fish intake rates.
3.1.3.1 How is the methylmercury fish tissue concentration translated to
a water concentration?
Should a state or authorized tribe decide to translate the methylmercury fish tissue
criterion into a water column concentration, it would assess the extent to which
methylmercury is expected to bioaccumulate in fish tissue for the site(s) of interest.
Assessing and predicting methylmercury bioaccumulation in fish is complicated by a
number of factors that influence bioaccumulation. These factors include the age or size of
the organism; food web structure; water quality parameters such as pH, DOC, sulfate,
alkalinity, and dissolved oxygen; mercury loadings history; proximity to wetlands;
watershed land use characteristics; and waterbody productivity, morphology, and
hydrology. In combination, these factors influence the rates of mercury bioaccumulation
in various—and sometimes competing—ways. For example, these factors might act to
increase or decrease the delivery of mercury to a waterbody, alter the net production of
methylmercury in a waterbody (through changes in methylation and/or demethylation
rates), or influence the bioavailability of methylmercury to aquatic organisms. Although
bioaccumulation models have been developed to address these and other factors for
mercury, their broad application can be limited by the site- or species-specific nature of
many of the factors that influence bioaccumulation and by limitations in the data
parameters necessary to run the models.
The bioaccumulation of nonionic organic chemicals10 such as methylmercury can also be
affected by a number of these same physicochemical factors (e.g., loading history, food
web structure, dissolved oxygen, DOC). However, a substantial portion of the variability
in bioaccumulation for nonionic organic chemicals can be reduced by accounting for lipid
content in tissues and organic carbon content in water and "normalizing" BAFs using
these factors (Burkhard et al. 2003; USEPA 2003). Normalizing to the age or size
(length, weight) offish has been shown to reduce variability in measures of
bioaccumulation (Brumbaugh et al. 2001; Glass et al. 2001; Sonesten 2003; Sorensen et
al. 1990; Wente 2004).
The United States Geological Survey (USGS) developed a procedure called the National
Descriptive Model for Mercury in Fish Tissue (NDMMF) (Wente 2004). This model
provides a translation factor to convert a mercury concentration taken from one
species/size/sample method to an estimated concentration for any other user-predefined
species/size/sample method.
10 Nonionic organic compounds are those organic compounds that do not ionize substantially when dissolved in water and therefore are
more likely to associate with sediment compounds, lipids, or other compounds in water (USEPA 2000b).
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Mercury Terminology
For the purposes of this document, the following definitions apply:
Mercury (or total mercury): The sum of all forms of mercury, including methylmercury, other
organic forms, inorganic, and elemental mercury. All of these are toxic, and inorganic and
elemental mercury can be methylated in the environment.
Methylmercury: The organic form of mercury, that bioaccumulates in the food chain. (Other
organic forms of mercury exist, but exposure to them through environmental pathways is not
significant.)
Dissolved mercury (or filtered mercury): The portion of mercury that passes through a
filter.
Dissolved methylmercury (or filtered methylmercury): The portion of methylmercury
which passes through a filter.
Total recoverable mercury (or unfiltered mercury): The dissolved portion plus the
particulate portion of mercury in a water sample.
Total recoverable methylmercury (or unfiltered methylmercury): The dissolved portion
plus the particulate portion of methylmercury in a water sample.
Taking into account the previous discussion, EPA has outlined in this document three
different approaches that could be considered for relating a concentration of
methylmercury in fish tissue to a concentration of methylmercury in ambient water,
should a state decide to develop or implement its standard in this manner:
1. Use site-specific methylmercury BAFs derived from field studies.
2. Use a scientifically defensible bioaccumulation model.
3. Where appropriate, use BAFs derived using the results of field studies that are not
site-specific. Appropriate situations for using such BAFs include waters where
direct water inputs are relatively high and where ambient fish tissue data are
unavailable, where deriving site-specific, field-measured BAFs is not feasible, or
where using a model is not feasible. Such BAFs may include the draft national
BAFs presented in appendix A of Water Quality Criterion for the Protection of
Human Health: Methylmercury (USEPA 200la) and discussed in more detail
below. Alternatively, BAFs may be derived using other approaches, such as a
combination of national and site-specific data in conjunction with other, non-site-
specific data, to create better estimates.
Of these approaches, 1 and 2 are preferred over 3. Because of the significant uncertainties
inherent in non-site-specific estimates of BAFs (including the draft national BAFs), they
should be used as defaults only in limited circumstances such as:
• When a state determines that use of the draft national BAFs are appropriate (for
example, where direct water inputs are relatively high, where no other data are
available to derive site-specific field-measured BAFs, and use of an appropriate
BAF model is not feasible)
• When a state can show that such BAFs are appropriate for its situation (e.g., a state
has data or analyses that demonstrate that the draft national BAFs would be
appropriate)
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• As an interim approach until more appropriate BAFs can be developed using other
data and/or an alternate approach
The reasons for preferring approaches 1 and 2 are discussed in more detail below.
However, the hierarchy assigned to the approaches is not intended to be inflexible. For
example, in some cases, the site-specific information available may be so limited in
quality or quantity that BAFs derived using other data may be preferable. In other cases,
there might be enough site-specific information to indicate that the local conditions
approximate the draft national values.
In situations where the state or tribe has some data available on fish tissue and water
column levels in its jurisdiction, but data are insufficient to support broad development of
site-specific translations, the state or tribe may be able to use these data in combination
with an evaluation of the draft national BAFs to help develop water column translations.
For example, California's Office of Environmental Health Hazard Assessment compiled
mercury concentration data for water and biota, and calculated state-specific BAFs for
different types of waters and different trophic levels. The office found enough similarities
between the state-specific BAFs and EPA's draft national BAFs that it recommended
using EPA's draft national values as an interim approach until more complete state-
specific data becomes available (Sanborn and Brodberg 2006). The state is in the process
of deciding whether to adopt this approach.
If the state or tribe chooses to derive BAFs using the third approach above, the state or
tribe should provide an accompanying rationale that acknowledges an understanding of
the potential limitations of the approach.
Developing site-specific data to support approaches 1 and 2 can be facilitated by efforts
involving stakeholders, states, and authorized tribes. Developing site-specific data is one
possible approach EPA recommends permitting authorities consider to help develop
NPDES permits in watersheds where mercury loadings from point sources are relatively
high. See section 7.5.2.2.
3.1.3.1.1 Site-specific bioaccumulation factors derived from field studies
The use of site-specific BAFs based on data obtained from field-collected samples of tissue
from aquatic organisms that people eat and water from the waterbody of concern—referred
to as a "field-measured site-specific BAF"—is the most direct and most relevant measure
of bioaccumulation. This approach is consistent with EPA's bioaccumulation guidance
contained in the 2000 Human Health Methodology (USEPA 2000b) and the Technical
Support Document for developing national BAFs (USEPA 2003). Although a BAF is
actually a simplified form of a bioaccumulation model, the field-measured site-specific
BAF approach is discussed separately here because of its widespread use and application.
A field-measured site-specific BAF is derived from measurements of methylmercury
concentrations in tissues of aquatic organisms and the ambient water they inhabit.
Because the data are collected from a natural aquatic ecosystem, a field-measured BAF
reflects an organism's exposure to a chemical through all relevant exposure routes (e.g.,
water, sediment, diet). Although a BAF can be measured for the aggregate offish in a
location, site-specific BAFs are often specific to trophic level and species offish. The
BAF can also be measured based on a predatory indicator species with a high propensity
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Water Quality Criteria and Standards Adoption
for bioaccumulation, such as largemouth bass. A field-measured site-specific BAF also
reflects biotic and abiotic factors that influence the bioavailability and metabolism of a
chemical that might occur in the aquatic organism or its food web at a given location. By
incorporating these factors, field-measured site-specific BAFs account for the actual
uptake and accumulation of the chemical.
States and authorized tribes should exercise caution, however, in developing a site-
specific BAF for a migratory fish because its exposure to methylmercury occurred in part
in areas other than where the fish was caught and therefore might not accurately predict
the water column mercury concentrations associated with the fish tissue concentration of
mercury. States and tribes should consider the life history of the migratory fish and the
consumption patterns of the local population when considering BAFs for migratory
species. States and tribes should also review how the applicable RSC considers migratory
fish when considering including those species in BAF calculations (see section 3.2.1.1).
For the purposes of developing a criterion expressed as a water concentration, states and
authorized tribes should calculate the BAF as the ratio of the concentration of
methylmercury in the tissue of aquatic organisms that people eat to the concentration of
methylmercury in water11 (Equation 3). To predict the corresponding methylmercury
concentration in water for a site, the tissue-based methylmercury criterion would then be
divided by the site-specific BAF (Equation 2). Using the site-specific BAF approach
assumes that at steady state, the accumulation of methylmercury by the aquatic organism
varies in proportion to the methylmercury concentration in the water column.
As an example, California is currently employing a site-specific BAF approach in its
Central Valley Region. In this approach, the state evaluated graphs of average
concentrations of methylmercury in water and the corresponding concentrations in fish at
multiple sites in a watershed. Researchers found statistically significant, positive
relationships between concentrations of unfiltered methylmercury in water and in various
trophic levels of the aquatic food chain (Slotton et al. 2004). California linearly regressed
fish tissue methylmercury concentrations for specific trophic level (TL) 3 and 4 fish
against aqueous methylmercury concentrations (P < 0.001, R = 0.98, and P < 0.01, R =
0.9, respectively) and determined methylmercury concentrations in unfiltered water that
correspond to the fish tissue criteria used in the TMDL analyses (0.15 ng/L for TL3 fish
and 0.14 ng/L for TL4 fish) (Central Valley Water Board 2005). California assumed that
sites that fit in a statistically significant regression have similar processes controlling
methylmercury accumulation. In other words, site-specific BAFs for such sites are nearly
identical.
Strengths associated with using a site-specific BAF approach include simplicity,
widespread applicability (i.e., site-specific BAFs can be derived for any waterbody, fish
species, and the like), and that the net effects of biotic and abiotic factors that affect
11 Although BAFs are sometimes calculated to represent the relationship between methylmercury in fish tissue and dissolved
methylmercury in the water column, data can be collected to determine the relationship between methylmercury in fish tissue and total
recoverable methylmercury or dissolved or total recoverable mercury in the water column. The Great Lakes Water Quality Initiative (GLI)
used site-specific BAFs to convert directly from methylmercury in fish to total recoverable mercury in the water column. See 40 CFR part
132, and appendix B to part 132, Methodology for Deriving Bioaccumulation Factors.
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bioaccumulation are incorporated within the measurements used to derive the BAF.
Specifically, it is not required that the exact relationship between methylmercury
accumulation and the factors that can influence it be understood or quantified to derive a
site-specific BAF. By measuring the methylmercury concentrations empirically, these
factors have been incorporated such that site-specific BAFs provide an accounting of the
uptake and accumulation of methylmercury for an organism in a specific location and at a
specific point in time.
Limitations to the site-specific BAF approach relate primarily to its cost and empirical
nature. For example, the level of effort and associated costs of developing site-specific
BAFs increase as the spatial scale of the site of interest increases. Furthermore, the
amount of data necessary to obtain a representative characterization of methylmercury in
the water and fish might take considerable time to gather. (For a discussion on sampling
considerations for developing a site-specific BAF, see section 3.1.3.2.) The strictly
empirical nature of this approach is also a barrier to extrapolating BAFs among species,
across space, and over time because the site-specific factors that might influence
bioaccumulation are integrated within the tissue concentration measurement and thus
cannot be individually adjusted to extrapolate to other conditions.
3.1.3.1.2 Bioaccumulation models
Bioaccumulation models for mercury vary in the technical foundation on which they are
based (empirically or mechanistically based), spatial scale of application (specific to
waterbodies, watersheds or regions, and species offish), and level of detail in which they
represent critical bioaccumulation processes (simple, mid-level, or highly detailed
representations). Thus, it is critical that states and tribes use a model that is appropriately
developed, validated, and calibrated for the species and sites of concern.
Empirical bioaccumulation models that explicitly incorporate organism-, water-
chemistry-, and waterbody/watershed-specific factors that might affect methylmercury
bioaccumulation (e.g., fish species, age, length, pH, DOC, sulfate, alkalinity, sediment
acid-volatile sulfide concentration, proximity to wetlands, land use, morphology,
hydrology, productivity) usually take the form of multivariate regression models. Many
examples of such models are available in the literature (e.g., Brumbaugh et al. 2001;
Kamman et al. 2004; Sorensen et al. 1990). The model developed by Brumbaugh et al.
(2001) is based on a national pilot study of mercury in 20 watersheds throughout the
United States. Specifically, Brumbaugh et al. (2001) developed a multiple regression
relationship between five factors: length-normalized mercury concentration in fish,
methylmercury concentration in water, percentage of wetland area in the watershed, pH,
and acid-volatile sulfide concentration in sediments (r =0.45; all fish species). When
data were restricted to a single species (e.g., largemouth bass) and a single explanatory
variable (e.g., methylmercury in water), a highly significant relationship was found
(p < 0.001) with a similar degree of correlation (r = 0.50). This demonstrates the
importance of species specificity in the strength of such regression relationships and, in
this case, methylmercury in water as an explanatory variable.
States and tribes should consider several important issues when using regression-based
bioaccumulation models for translating from a tissue concentration to a water column
concentration. First, a number of such regression models have been developed without
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explicitly incorporating methylmercury (or mercury) concentrations in the water column.
Instead, the models relate fish tissue methylmercury concentrations to variables that serve
as proxies for methylmercury exposure (e.g., atmospheric deposition rates, ratio of the
watershed drainage to the wetland area, pH, lake trophic status), often because of the
costs associated with obtaining accurate measurements of mercury in the water column.
Obviously, such models cannot be directly solved for the parameter of interest
(methylmercury in water). Second, correlation among independent or explanatory
variables in these multiple regressions is common and expected (e.g., pH and
methylmercury concentration in water). Such correlations among explanatory variables
can cause bias and erroneous estimates of an explanatory variable (in this case,
methylmercury concentration in water) when back-calculated from the regression
equation (Neter et al. 1996). In such cases, using the underlying data set to develop a
separate regression model with methylmercury concentration in water as the dependent
variable is more appropriate. Last, because these regression models are based on
empirical data, uncertainty is introduced when the results are extrapolated to aquatic
ecosystems with different conditions. Only in a few cases have such models been tested
using independent data sets (e.g., Kamman et al. 2004).
Mechanistic bioaccumulation models are mathematical representations of the natural
processes that influence methylmercury bioaccumulation. The process of methylation
itself is incompletely understood, and general models for reliably predicting rates of
methylation do not exist, although EPA's WASP model might be useful in some
environments. Three examples of mechanistic bioaccumulation models are the Dynamic
Mercury Cycling Model, or D-MCM (EPRI 2002); the Bioaccumulation and Aquatic
System Simulator, or BASS (Barber 2002), and the Quantitative Environmental Analysis
Food Chain model, or QEAFDCHN (QEA 2000). A conceptual advantage of
mechanistically based bioaccumulation models is that methylmercury bioaccumulation
can be predicted under different conditions (e.g., different growth rates offish, different
water chemistry conditions, and different mercury loading scenarios) because the models
include mathematical representations of various processes that affect bioaccumulation.
This advantage comes at the cost of additional input data necessary to run the model.
Notably, only a few models have been used to predict methylmercury bioaccumulation.
Such models have not been widely used and have been applied only to mercury in a few
aquatic ecosystems under specific environmental conditions. Of the examples listed
above, only the D-MCM was developed specifically for mercury. The D-MCM has not
been applied to lotic systems (i.e. streams, rivers, estuaries) and therefore probably
should be used only for static environments (lakes) at this time. The other models have
been developed more generally, for nonionic organic chemicals that bioaccumulate, and
require substantial modification and validation for application to mercury.
Most mechanistic bioaccumulation models use a chemical mass balance approach to
calculate bioaccumulation in fish or other aquatic organisms. This approach requires
considerable understanding of mercury loadings to and cycling within the environment.
None of the example models presented can predict bioaccumulation without considerable
site-specific information, at least some degree of calibration to the waterbody of interest,
and, in some cases, considerable modification of the model. The amount and quality of
data necessary for proper model application may equal or exceed that necessary to
develop site-specific methylmercury BAFs, although these models might also help in
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determining BAFs if the kinetic condition in the waterbody is not steady state. Because of
the need for site-specific data and calibration, these models are likely to cost as much to
implement as a site-specific BAF. Their value comes from the ability to represent a wider
range of explanatory and policy-relevant variables.
Regardless of the type of model used, states' and authorized tribes' methodologies should
be consistent with the Methodology for Deriving Ambient Water Quality Criteria for the
Protection of Human Health (section 5.6: National Bioaccumulation Factors for
Inorganic and Organometallic Chemicals; USEPA 2000b) and Technical Support
Document Volume 2: Derivation of National Bioaccumulation Factors (USEPA 2003).
These documents provide detailed discussion of topics such as BAF derivation
procedures, bioavailability, and the steps involved in procedures 5 and 6 of the Human
Health Methodology. States and tribes should document how they derive the site-specific
parameters used in the bioaccumulation models and should describe the uncertainty
associated with the BAFs derived using any of the models.
3.1.3.1.3 Draft national bioaccumulation factors
EPA acknowledges that using site-specific BAFs or model-derived BAFs might not be
feasible in all situations. Without site-specific methylmercury bioaccumulation data or an
appropriate bioaccumulation model, another approach is to use EPA's empirically
derived draft national methylmercury BAFs as defaults. EPA used Technical Support
Document Volume 3: Development of Site-Specific Bioaccumulation Factors of the 2000
Human Health Methodology (USEPA 2000b, 2003) and the BAF methods in volume III,
appendix D, of the Mercury Study Report to Congress (USEPA 1997c) to derive draft
methylmercury BAFs as part of its initial efforts to derive a water column-based
recommended section 304(a) ambient water quality criterion for methylmercury. These
draft national BAFs were developed from field data collected from across the United
States and reported in the published literature. The draft national BAFs and the
uncertainties associated with them are discussed in appendix A, section I, of Water
Quality Criterion for the Protection of Human Health: Methylmercury (USEPA 200 la).
The draft national BAFs (50th percentile values) are listed by trophic level in table 2.
Table 2. Draft national BAFs for dissolved methylmercury
BAF trophic
level 2
(L/kg)
120,000
BAF trophic
level 3
(L/kg)
680,000
BAF trophic
level 4
(L/kg)
2,700,000
Source: USEPA 2001 a.
Note: Expressed as milligrams methylmercury/kilogram fish tissue per milligram methylmercury/liter
water, or liters per kilogram (L/kg).
To develop the draft national BAFs for each trophic level, EPA calculated the geometric
mean of the field-measured BAFs obtained from the published literature. EPA believes
the geometric mean BAFs are the best available central tendency estimates of the
magnitude of BAFs nationally, understanding that the environmental and biological
conditions of the waters of the United States are highly variable. Specifically, the data
presented in Water Quality Criterion of the Protection of Human Health: Methylmercury
(USEPA 200la) indicate that BAFs for trophic levels 3 and 4 vary by a factor of 100
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(two orders of magnitude) between the 5th and 95th percentiles. EPA does not
recommend basing an AWQC on BAF values associated with the extremes of the
distribution (e.g., 10th or 90th percentile), unless supported by site-specific data. Such
values might introduce an unacceptable level of uncertainty into the calculation of a
water column-based AWQC. States and authorized tribes should consider the magnitude
of the potential error when proposing to use the draft national BAFs.
When states and authorized tribes calculate a water column-based criterion using draft
national BAFs that differ greatly from the BAFs for the waterbody of concern, the
resulting water column-based criterion will be either over- or under-protective. As a
result, evaluation of the results of the analysis of water samples might result in the false
conclusion that a fish tissue concentration has been exceeded (when it actually has not) or
a false conclusion that a fish tissue concentration has not been exceeded (when it actually
has). For more information on the draft national BAFs, see chapter 6 and appendix A,
section I, of EPA's 304(a) water quality criterion for methylmercury (USEPA 200 la).
The following examples illustrate the potential impact of calculating a water quality
criterion using a BAF that is substantially different from the actual BAF.
• Underprotective scenario
A state uses the draft national BAF of 2,700,000 L/kg for trophic level 4 fish, but
the BAF based on site-specific data for the trophic level 4 fish in the waterbody is
three times that, or 8,100,000 L/kg. In using the draft national BAF, a state would
consider water column concentrations up to 0.11 nanogram per liter (ng/L)
(0.3 mg/kg / 2,700,000 L/kg) to indicate attainment of the water quality column
criterion. Using the BAF based on site-specific data, however, a water column
criterion of 0.11 ng/L would correspond to a fish tissue concentration of 0.9 mg/kg,
which is three times the 0.3 mg/kg criterion recommended to protect human health.
Thus, load reductions or permits using the draft national BAF of 2,700,000 L/kg
would be underprotective.
• Overprotective scenario
A state uses the draft national BAF of 2,700,000 L/kg for trophic level 4 fish, but
the BAF based on site-specific data for the trophic level 4 fish in the waterbody is
one-third that, or 900,000 L/kg. As a result, a state would consider water column
concentrations up to 0.11 ng/L (0.3 mg/kg / 2,700,000 L/kg) to indicate attainment
of the water quality criterion. Using the BAF based on site-specific data, however,
attainment of the water quality criterion could be achieved at a higher water
column concentration, 0.33 ng/L. Thus, load reductions or permits using the draft
national BAF of 2,700,000 L/kg would be Overprotective.
EPA cautions water quality managers that methylmercury bioaccumulation is generally
viewed as a site-specific process and that BAFs can vary greatly across ecosystems. The
uncertainty in the estimates of a draft national BAF comes from uncertainty arising from
natural variability, such as size of individual fish, and from uncertainty due to
measurement error, such as error in measurements of mercury in water or lack of
knowledge of the true variance of a process (e.g., methylation). Users of the draft national
BAFs are encouraged to review appendix A of Water Quality Criterion for the Protection
of Human Health: Methylmercury (USEPA 200 la), which describes the uncertainties
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inherent in these values. The following is a synopsis of the discussion of uncertainty in
that appendix.
• Uncertainty due to sampling and chemical analysis: In many cases, water
methylmercury concentrations reported in the available studies incorporated limited
or no cross-seasonal variability, incorporated little or no spatial variability, and
were often based on a single sampling event. Because fish integrate exposure of
mercury over a lifetime, comparing fish concentrations to a single sample or mean
annual concentrations introduces bias to the estimates. The geographic range
represented by the waterbodies was also limited.
• Uncertainty due to estimation method: The approaches used to estimate the draft
national BAFs have their own inherent uncertainties. The approaches assume that
the underlying process and mechanisms of mercury bioaccumulation are the same
for all species in a given trophic level and for all waterbodies. They are also based
on a limited set of data.
• Uncertainty due to biological factors: With the exception of deriving BAFs on the
basis of river or lake waterbody type, there were no distinctions in the BAFs as to
the size or age offish, waterbody trophic status, or underlying mercury uptake
processes. In reality, methylmercury bioaccumulation for a given species can vary
as a function of the age (body size) of the organisms examined.
• Uncertainty due to universal application of BAFs: There is uncertainty introduced
by failure of a single trophic-level-specific BAF to represent significant real-world
processes that vary from waterbody to waterbody. The simple linear BAF model
relating methylmercury in fish to mercury in water simplifies a number of
nonlinear processes that lead to the formation of bioavailable methylmercury in the
water column and subsequent accumulation. Much of the variability in field data
applicable to the estimation of mercury BAFs can be attributed to differences in
biotic factors (e.g., food chain, organism age or size, primary production,
methylation or demethylation rates) and abiotic factors (e.g., pH, organic matter,
mercury loadings, nutrients, watershed type or size) between aquatic systems.
Unfortunately, although the concentration of methylmercury in fish tissue is
presumably a function of these varying concentrations, published BAFs are
typically estimated from a small number of measured water values whose
representativeness of long-term exposure is not completely understood.
Furthermore, although it is known that biotic and abiotic factors control mercury
exposure and bioaccumulation, the processes are not well understood, and the
science is not yet available to accurately model bioaccumulation on a broad scale.
Peer reviewers expressed concerns about the use of the draft national BAFs as defaults to
predict bioaccumulation across all ecosystems and about using them to derive a national
recommended section 304(a) water quality criterion for methylmercury that would
suitably apply to waterbodies across the nation. EPA recognized the peer reviewers'
concerns and acknowledges that these draft national BAF values might significantly
over- or underestimate site-specific bioaccumulation. As a result, EPA decided not to use
the draft national BAFs to develop a national water-column-based AWQC for
methylmercury. Furthermore, the draft national BAFs are EPA's least preferred means
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Water Quality Criteria and Standards Adoption
for assessing the BAF. States and tribes should also consider whether more recent data
and/or data that are more reflective of local conditions are available to supplant or
supplement the limited database used to derive the draft national BAFs.
Risk managers should also understand that in using the draft national BAFs as defaults,
one assumes that the biotic and abiotic processes affecting mercury fate and
bioaccumulation are similar across different waterbodies, and therefore using the draft
national BAFs does not address site-specific factors that might increase or decrease
methylation and bioaccumulation. A state's or tribe's decision to use the draft national
BAFs would be a risk management decision. The decision would reflect the state's or
tribe's judgment that, for specific reasons, translating the fish tissue criterion to a water
column value using such a BAF is preferable to implementing the fish tissue criterion
directly (e.g., using the approaches discussed in this guidance), or conducting studies to
develop a site-specific BAF (e.g., site-specific field studies or bioaccumulation
modeling).
3.1.3.2 What are the sampling considerations for deriving site-specific
field-measured BAFs?
For both fish tissue and water, states and authorized tribes should analyze for
methylmercury when deriving site-specific BAFs. EPA has not yet published analytical
methods to measure methylmercury in water or fish in 40 CFR part 136. A discussion of
analytical methods for mercury and methylmercury can be found in section 4.1. For fish
tissue, however, states and authorized tribes can estimate methylmercury concentrations
and determine attainment by using the same analytical method used to measure for
mercury, at least for upper-trophic-level fish (levels 3 and 4). This is because 80 to 100
percent of the mercury found in the edible portions of freshwater fish greater than three
years of age from these two trophic levels is in the form of methylmercury (USEPA
2000c). In fish greater than approximately three years of age, mercury has had sufficient
time to bioaccumulate to roughly steady levels in the fish. Appendix A summarizes eight
studies of the relative proportion of the mercury concentration in North American
freshwater fish that is in the form of methylmercury. In six of the eight studies,
methylmercury on average accounted for more than 90 percent of the mercury
concentration in fish tissue. In the remaining two studies, methylmercury on average
accounted for 80 to 90 percent of the mercury concentration in trophic level 3 and 4 fish.
States and tribes should consider a number of issues when sampling aquatic organism
tissue and water to derive a site-specific BAF. The goal of deriving site-specific
methylmercury BAFs is to reflect or approximate the long-term bioaccumulation of
methylmercury in commonly consumed aquatic organisms of a specified trophic level.
Hence, an important sample design consideration is how to obtain samples of tissue and
water that represent long-term, average accumulation of methylmercury. Methylmercury
is often slowly eliminated from fish tissue. Therefore, concentrations of methylmercury
in fish tissue tend to fluctuate much less than the concentration of methylmercury in
water. Thus, for calculating representative site-specific BAFs, states and tribes should
consider how to integrate spatial and temporal variability in methylmercury
concentrations in both water and tissue. States and tribes should address the variability in
methylmercury concentrations in fish tissue with age or size of the organism either by
restricting sample collection to organisms of similar age or size classes or by using
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Water Quality Criteria and Standards Adoption
appropriate normalization techniques. EPA's fish sampling guidance recommends that
fish should be of similar size so that the smallest individual in a composite is no less than
75 percent of the total length (size) of the largest individual (USEPA 2000c). One way of
normalizing data is by using the National Descriptive Model for Mercury in Fish Tissue,
or NDMMF (Wente 2004). The NDMMF is a statistical model that normalizes Hg fish
tissue concentration data to control for species, size, and sample type variability. An
example use of the NDMMF is in the combination of mercury fish tissue data from two
databases (USEPA 2005a).
States and tribes should assess the fish consumption patterns of the exposed human
population when designing a site-specific sampling plan. Because the age and size of
aquatic organisms are correlated with the magnitude of methylmercury accumulation, the
types and sizes of aquatic organisms being consumed should be considered when
determining which fish to sample for deriving BAFs. States and tribes should consider
the fish being consumed by various subpopulations (e.g., sport anglers, subsistence
fishers) as well as culturally and economically diverse communities. This information
should also guide the decision on whether the site-specific BAF should be based on a
single trophic level (e.g., trophic level 4) or on multiple trophic levels.
States and authorized tribes should review site-specific data used to calculate field-
measured BAFs and thoroughly assess the quality of the data and the overall uncertainty
in the BAF values. States and authorized tribes should also consider the following general
factors when determining the acceptability of field-measured BAFs reported in the
published scientific literature. The same general issues and questions should also be
addressed when designing a field study to generate site-specific field-measured BAFs.
• Calculate a field-measured BAF using aquatic organisms that are representative of
the aquatic organisms commonly consumed at the site of interest (e.g., river, lake,
ecoregion, state). Review information on the ecology, physiology, and biology of
the target organisms when assessing whether an organism is a reasonable surrogate
of a commonly consumed organism.
• Determine the trophic level of the study organism by taking into account its life
stage, its diet, and the food web structure at the study location. Information from
the study site (or similar sites) is preferred when evaluating trophic status. If such
information is lacking, states and authorized tribes can find general information for
assessing the trophic status of aquatic organisms in Guidance for Assessing
Chemical Contaminant Data for Use in Fish Advisories, volume 1, Fish Sampling
and Analysis (USEPA 2000c).
• Collect length, weight, and age data for any fish used in deriving a field-measured
BAF because current information suggests that variability in methylmercury
accumulation is dependent on fish age and size (USEPA 200la). This information
helps normalize the BAF to a standardized fish size within the range of fish sizes
and species known to be consumed by the human population of interest.
• Verify that the study used to derive the field-measured BAF contains sufficient
supporting information from which to determine that tissue and water samples were
collected and analyzed using appropriate, sensitive, accurate, and precise analytical
methods.
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Water Quality Criteria and Standards Adoption
• Verify that the water concentrations used to derive a BAF reflect the average
exposure of the aquatic organism of concern that resulted in the concentration
measured in its tissue. Concentrations of methylmercury in a waterbody vary
seasonally and diurnally (Cleckner et al. 1995) because of a variety of biological
and physical factors.
• Attempt to design a field sampling program that addresses potential temporal and
spatial variability and that allows estimation of average exposure conditions. The
study should be designed to sample an area large enough to capture the more
mobile organisms and also to sample across seasons or multiple years when
methylmercury concentrations in waters are expected to have large fluctuations.
Longer sampling durations are necessary for waters experiencing reductions in
mercury loadings, changes in water chemistry that affect methylation, and changes
in the composition of the food web.
Volume I of the Guidance for Assessing Chemical Contaminant Data for Use in Fish
Advisories (USEPA 2000c) provides additional guidance on selecting target species to
sample, specific sampling design procedures, analytical measurement procedures, and
quality assurance guidance. Chapter 10 of EPA's Exposure Factors Handbook provides
additional guidance on collecting information about local species (USEPA 1997d).
Additional guidance on evaluating existing site-specific bioaccumulation studies for use
in deriving trophic-level-specific BAFs and designing sampling plans for obtaining data
for deriving site-specific BAFs is provided in Technical Support Document—Volume 2:
Developing National Bioaccumulation Factors (USEPA 2003). A publication by
Burkhard (2003) is also a good source of information on designing BAF field studies and
on deriving field-measured site-specific BAFs.
3.1.3.3 How is methylmercury in water translated into its mercury
equivalent in water?
Given that permit limits are often derived using a mercury water column concentration
criterion, a state or tribe may wish to take another step after using a BAF to determine a
methylmercury water concentration criterion to derive a mercury water column
concentration criterion. Although not necessary to develop a water quality criterion, a
state can translate a methylmercury water concentration into a mercury water
concentration criterion by converting the concentration of methylmercury in water to the
equivalent concentration of mercury in water. This step might be necessary because
although the BAF is typically based on the concentration of methylmercury in water, the
assessment of water quality is typically based on an evaluation of mercury concentrations
since other forms of mercury are converted to methylmercury in the environment. As a
result, a relationship between (dissolved or total recoverable) methylmercury and
(dissolved or total recoverable) mercury in the water needs to be developed. NPDES
permits and other water quality-based pollution control activities traditionally rely on the
total recoverable concentration of mercury, not the dissolved methylmercury form.
Many of the issues surrounding the uncertainty in predicting and transferring
methylmercury BAFs across different waterbodies also apply to translating
methylmercury concentrations to mercury concentrations. As with BAFs, one approach
for translating between methylmercury and mercury concentrations is for states and
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Water Quality Criteria and Standards Adoption
authorized tribes to measure site-specific concentrations of methylmercury and mercury
to determine the relative amounts of each form. This field-measured, site-specific
approach is the most direct and the most appropriate approach to the translation.
Where a site-specific approach is not feasible, states and authorized tribes may consider
applying EPA's draft national methylmercury-to-mercury translator factors. In the 2001
methylmercury criterion document (USEPA 200Ic), EPA derived these translator factors
for rivers/streams and lakes as geometric means from data collected from the literature
reporting concentrations of mercury in aquatic environments. Thus, like the draft national
BAFs, the methylmercury-to-mercury translators were empirically derived based on
various water data from across the United States. As with the draft national BAFs, the
draft national methylmercury-to-mercury translator factors vary greatly across
ecosystems and are subject to many of the same uncertainties. Therefore, EPA suggests
that states and tribes that may be considering using the draft national translator values as
defaults carefully review the discussion in the 2001 criterion document, particularly the
discussions concerning uncertainty and limitations, before deciding to apply them in a
regulatory context (see appendix A, section II, USEPA 200la). States and tribes should
consider whether more recent data and/or data that are more reflective of local conditions
are available to supplant or supplement the limited database used to derive the draft
national translators.
Alternatively, states and tribes that choose to develop water column criteria can consider
collecting data to develop BAFs that relate methylmercury in fish tissue directly to total
mercury in the water column. See the footnote to section 3.1.3.1.1 for more information.
3.2 ., ": : :";> ' •;•-.•. ,
1 - ":
3.2.1 How can the methylmercury water quality criterion be
modified for site-specific conditions?
The 2000 Human Health Methodology (USEPA 2000b) describes how states and
authorized tribes can adopt site-specific modifications of a section 304(a) criterion to
reflect local environmental conditions and human exposure patterns. "Local" may refer to
any appropriate geographic area where common aquatic environmental or exposure
patterns exist. Thus, it may signify a statewide or regional area, a river reach, or an entire
river. Such site-specific criteria may be developed as long as the site-specific data, either
toxicological or exposure-related, are justifiable. For example, when using a site-specific
fish consumption rate, a state or authorized tribe should use a value that represents at
least the central tendency for the consumption rate of the population surveyed. When
defining a target population, a state or authorized tribe should focus on protecting
populations with high rates offish consumption from the local area.
States and authorized tribes may modify EPA's recommended 304(a) criterion for
methylmercury by using different assumptions for certain components of EPA's criterion
to derive a criterion that maintains and protects the designated uses. For example, states
and authorized tribes may:
• Use an alternative RSC factor or
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Water Quality Criteria and Standards Adoption
• Use a daily uncooked freshwater and estuarine fish consumption rate that is more
reflective of local or regional consumption patterns than the 17.5 grams/day default
value. EPA encourages states and authorized tribes to consider using local or
regional consumption rates instead of the default values if the former would better
reflect the target population.
If a state or authorized tribe intends to modify both the RSC and the fish consumption
rate, it might find collecting the data at the same time advantageous.
3.2.1.1 How does one modify the RSC?
Section 5 of the methylmercury criterion document (USEPA 200 la) provides detailed
discussions on how EPA assessed exposure to methylmercury and how EPA derived the
RSC factor used in calculating the criterion. The methylmercury RSC is an exposure,
subtracted from the RfD to account for exposure to methylmercury from sources other
than freshwater or estuarine fish. By accounting for other known exposures, the RSC
seeks to ensure that methylmercury exposures do not exceed the RfD.
If a state or tribe proposes to change the RSC, it should document the modifications with
data supporting the modifications and share the proposed modifications to the RSC with
EPA prior to recalculating the criterion. See appendix B for the tables from the
methylmercury criterion document. States and authorized tribes should review section 5
of the methylmercury criterion document and modify the media-specific exposure
estimates using local data that reflect the exposure patterns of their populationsTo modify
this factor, states and authorized tribes should review the amount of marine fish and
shellfish estimated to be consumed (table 5-1, USEPA 200la) and the concentration of
methylmercury in the commonly consumed marine species (table 5-14, USEPA 2001a).
3.2.1.2 How does one modify the daily fish intake rate?
EPA derived the recommended methylmercury water quality criterion on the basis of a
default fish intake rate for the general population (consumers and nonconsumers) of
17.5 grams/day12, uncooked (USEPA 2001a). States and authorized tribes may use a
different intake rate based on local or regional consumption patterns and are encouraged
to use consumption rates that are protective of a range of culturally and economically
diverse communities. The fish consumption value in the TRC equation may be changed
if the target population eats a higher or lower amount offish. For example, if the 90th
percentile of a target population eats approximately 15 grams/day of freshwater and
estuarine fish of various trophic levels, the fish intake value in equation 1 would simply
be 15 grams/day, rather than the national default value of 17.5 grams/day used in
calculating the 0.3 mg/kg TRC.
EPA encourages states and authorized tribes to develop a water quality criterion for
methylmercury using local or regional fish consumption data rather than the default
values if they believe that such a water quality criterion would be more appropriate for
12 This value represents the 90th percentile of freshwater and estuarine finfish and shellfish consumption reported by the 1994-1996
Continuing Survey of Food Intakes by Individuals. For more information, see Methodology for Deriving Ambient Water Quality Criteria
for the Protection of Human Health (USEPA 2000b).
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Water Quality Criteria and Standards Adoption
their target population. However, states and authorized tribes should consider whether the
fish consumption rates reflect existing public concern about contamination of fish when
collecting survey data, rather than local preference for fish consumption (i.e., the
presence offish advisories limits the consumption offish). In this instance, the state or
authorized tribe should take this into account and try to conduct surveys in a manner that
accounts for the effects offish advisories on the consumption offish. Where there is afish
consumption advisory, surveys should be designed to evaluate how much fish a local
population would consume if the fish were safe to eat and incorporate that consumption
level into the criterion.
EPA suggests that states and authorized tribes follow a hierarchy when deriving fish
intake estimates (USEPA 2000b). From highest preferred to lowest preferred, this
hierarchy is as follows (1) use local data protective of culturally and economically
diverse communities when available, (2) use data reflecting similar geography or
population groups, (3) use data from national surveys, and (4) use EPA's default fish
intake rates. Additional discussion of these four preferences is provided below.
When a state or authorized tribe develops a site-specific criterion on the basis of local
fish consumption, site-specific BAFs, or a site-specific RSC, states and authorized tribes
might want to include EPA in the development of the study plan and submit the data
supporting the site-specific criterion for EPA's consideration when EPA approves or
disapproves state or tribal water quality standards under CWA section 303(c). Including
EPA at the study plan development stage may help to avoid problems and facilitate
development of a defensible site-specific criterion.
3.2.1.2.1 Use local data
If a state or authorized tribe believes a fish consumption rate other than the default would
be appropriate for their target population, EPA's first preference is that they use fish
intake rates derived from studies of consumption of local fish. Such studies could include
results of surveys designed to obtain information on the consumption of freshwater or
estuarine species caught from local watersheds within the state or tribal jurisdiction.
When estimating the fish intake rate, all freshwater fish, whether caught recreationally or
bought commercially, should be included. States and authorized tribes may choose to
develop either fish intake rates for the local population as a whole, or individual fish
intake rates for various subpopulations (e.g., sport anglers, subsistence fishers) as well as
culturally and economically diverse consumers.
States and authorized tribes might wish to conduct their own surveys offish intake.
Guidance for Conducting Fish and Wildlife Consumption Surveys (USEPA 1998a)
provides EPA guidance on methods for conducting such studies. States and authorized
tribes should take care to ensure that the local data are of sufficient quality and scope to
support development of a criterion and are representative of the population of people that
eat local fish. EPA's consumption survey guidance offers recommendations on how to
develop appropriate quality assurance and quality control procedures to help ensure the
quality of the survey. Results of studies of the broader geographic region in which the state
or authorized tribe is located can also be used, but they might not be as applicable as study
results for local watersheds. Because such studies would ultimately form the basis of a
state's or authorized tribe's methylmercury criterion, EPA would consider any surveys of
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Water Quality Criteria and Standards Adoption
fish intake as part of its review of the methylmercury criterion's scientific defensibility as
part of the Agency's review of water quality standards under CWA section 303(c).
States and authorized tribes may use either high-end (such as 90th or 95th percentile) or
central tendency (such as median or mean) consumption values for the population of
interest (e.g., subsistence fishers, sport fishers, or the general population). EPA generally
recommends that a central tendency value be the lowest value states or authorized tribes
should use when deriving a criterion. When considering median values from fish
consumption studies, states and tribes should ensure that the distribution is based on
survey respondents that reported consuming fish because surveys of both consumers and
nonconsumers can often result in median values of zero. EPA believes the approach
described above is a reasonable procedure and is also consistent with other Agency
positions such as that of the Great Lakes Water Quality Initiative, known as the GLI
(USEPA 1995a).
3.2.1.2.2 Use similar geography or population groups
If surveys conducted in the geographic area of the state or authorized tribe are not
available, EPA's second preference is that states and authorized tribes consider results
from existing surveys offish intake in similar geographic areas and population groups
(e.g., from a neighboring state or authorized tribe or a similar watershed type) and follow
the method described above regarding target values to derive a fish intake rate. For
instance, states or tribes with subsistence fisher populations might wish to use
consumption rates from studies that focus specifically on these groups, or use rates that
represent high-end values from studies that measured consumption rates for a range of
types of fishers (e.g., recreational or sport fishers, subsistence fishers, minority
populations). A state or authorized tribe in a region of the country might consider using
rates from studies that surveyed the same region; for example, a state or authorized tribe
that has a climate that allows year-round fishing might underestimate consumption if it
uses rates from studies taken in regions where people fish for only one or two seasons per
year. A state or authorized tribe that has a high percentage of an age group (such as older
persons, who have been shown to have higher rates in certain surveys) might wish to use
age-specific consumption rates, which are available from some surveys. For additional
information on the use offish consumption rates, see EPA's 2000 Human Health
Methodology (USEPA 2000b). Again, EPA recommends that states and tribes use only
uncooked weight intake values and freshwater or estuarine species data.
3.2.1.2.3 Use national surveys
If applicable consumption rates are not available from local, state, or regional surveys,
EPA's third preference is that states and authorized tribes select intake rate assumptions
for different population groups from national food consumption surveys. EPA has
analyzed two such national surveys, the 1994-1996 and 1998 Continuing Survey of Food
Intakes by Individuals (CSFII). These surveys, conducted by the U.S. Department of
Agriculture (USDA), include food consumption information from a probability sample of
the population of all 50 states. Respondents to the survey provided 2 days of dietary
recall data. A separate EPA report provides a detailed description of the combined 1994-
1996 and 1998 CSFII surveys, the statistical methodology, and the results and
uncertainties of the EPA analyses (USEPA 2002b). The estimated fish consumption rates
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in the CSFII report are presented by fish habitat (i.e., freshwater or estuarine, marine, and
all habitats) for the following population groups: (1) all individuals, (2) individuals age
18 and over, (3) women ages 15-44, and (4) children age 14 and under. Three kinds of
estimated fish consumption rates are provided: (1) per capita rates (rates based on
consumers and nonconsumers offish from the survey period), (2) by consumers-only
rates (rates based on respondents that reported consuming finfish or shellfish during the
2-day reporting period), and (3) per capita consumption by body weight (per capita rates
reported as mg/kg-day). For purposes of revising the fish consumption rate in the
methylmercury criterion, EPA recommends using the rates for freshwater and estuarine
fish and shellfish.
The CSFII surveys (USDA/ARS 1998, 2000) have advantages and limitations for
estimating per capita fish consumption. The primary advantage of the CSFII surveys is
that USDA designed and conducted them to support unbiased estimation of food
consumption across the population in the United States and the District of Columbia. One
limitation of the CSFII surveys is that individual food consumption data were collected
for only 2 days—a brief period that does not necessarily depict "usual intake." Usual
dietary intake is defined as "the long-run average of daily intakes by an individual."
Upper percentile estimates might differ for short-term and long-term data because short-
term food consumption data tend to be inherently more variable. It is important to note,
however, that variability due to duration of the survey does not result in bias of estimates
of overall mean consumption levels. Also, the multistage survey design does not support
interval estimates for many of the subpopulations because of sparse representation in the
sample. Subpopulations with sparse representation include American Indians on
reservations and certain ethnic groups. Although these persons were participants in the
survey, they were not present in sufficient numbers to support fish consumption
estimates. The survey does support interval estimates for the U.S. population and some
large subpopulations (USEPA 2002b).
3.2.1.2.4 Use EPA default fish intake rates
EPA's fourth preference is that states and authorized tribes use as fish intake assumptions,
default rates on the basis of the 1994-1996 CSFII data for the U.S. population, which EPA
believes are representative of freshwater and estuarine fish and shellfish intake for different
population groups. The 1994-1996 CSFII data for U.S. fish consumption among both
consumers and nonconsumers offish is delineated below in table 3.
Because the combined 1994-1996 CSFII survey is national in scope, EPA uses the results
from it to estimate fish intake for deriving national criteria. EPA applies a default rate of
17.5 grams/day for the general adult population. EPA selected an intake rate that is
protective of a majority of the population (the 90th percentile of consumers and
nonconsumers, according to the 1994-1996 CSFII survey data) (USEPA 2000b). EPA
also recommends a default rate of an average of 17.5 grams/day for sport fishers.
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Water Quality Criteria and Standards Adoption
Table 3. Estimates of freshwater and estuarine combined finfish and shellfish
consumption from the combined 1994-1996 and 1998 CSFII surveys
(U.S. population)
All ages
Age 18 and over
Women ages 15-44
Children age 14 and under
Mean
6.30
7.50
5.78
2.64
Median
N/a
0.00*
N/a
0.00
90th
percentile
11.65
17.53
6.31
0.00
95th
percentile
41.08
49.59
32.37
13.10
99th
percentile
123.94
142.41
109.79
73.70
Note: All values expressed as grams per day for uncooked fish.
* The median value of 0 grams/day might reflect the portion of persons in the population that never eat
fish, as well as the limited reporting period (2 days) during which intake was measured.
Similarly, EPA believes the 99th percentile of 142.4 grams/day is within the range of
consumption estimates for subsistence fishers, according to the studies reviewed, and that
it represents an average rate for subsistence fishers. EPA knows that some local and
regional studies indicate greater consumption among American Indian, Pacific Asian
American, and other subsistence consumers and recommends the use of those studies in
appropriate cases, as indicated by the first and second preferences. Again, states and
authorized tribes have the flexibility to choose intake rates higher than the average values
for these population groups. If a state or authorized tribe has not identified a separate
well-defined population of exposed consumers and believes that the national data from
the 1994-1996 CSFII are representative, the state or tribe may choose these
recommended rates.
EPA has made these risk management decisions after evaluating numerous fish intake
surveys. These values represent the uncooked weight intake of freshwater and estuarine
finfish and shellfish. As with the other preferences, EPA requests that states and
authorized tribes routinely consider whether a substantial population of sport fishers or
subsistence fishers exists in the area when establishing water quality criteria rather than
automatically using data for the general population.
The CSFII surveys also provide data on marine species, but EPA considered only
freshwater and estuarine fish intake values for determining default fish consumption rates
because EPA considered exposure from marine species offish in calculating an RSC for
dietary intake.13 States and authorized tribes should ensure that when evaluating overall
exposure to a contaminant, marine fish intake is not double-counted with the other dietary
intake estimate used. Coastal states and authorized tribes that believe accounting for total
fish consumption (fresh or estuarine and marine species) is more appropriate for
protecting the population of concern may do so, provided that the marine intake
component is not double-counted with the RSC estimate (USEPA 2000b).
See the discussion of the RSC in sections 3.1.2.3 and 3.2.1.1.
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Water Quality Criteria and Standards Adoption
3.2.2 How do water quality standards variances apply?
Where a discharger or waterbody cannot meet a water quality standard, a state or
authorized tribe may adopt a temporary water quality standard through a variance
process. The variance would then, in effect, serve as a substitute standard for a point
source, and the WQBEL contained in an NPDES permit would then be based on the
variance. As a revision to the otherwise applicable water quality standard (designated use
and criteria), water quality standards variances must be supported by one of the six
justifications under 40 CFR 131.10(g) (see section 3.2.3.4 below). Variances are
generally determined based on the discharger's ability to meet a WQBEL and, therefore,
are considered after an evaluation of controls necessary to implement water quality
standards. In addition, EPA recommends that the permitting authority require the facility
seeking a variance to develop and implement a mercury minimization plan (MMP) to
both reduce mercury loading and to determine the highest level of water quality
achievable to inform future permit decisions (see section 7.5.2.4 for more discussion of
MMPs).
Variances typically apply for a limited period but may be reviewed at the time of the state
triennial review of water quality standards, and require the same procedural steps that are
required of a change in the standards. Where the term of a variance extends beyond
three years, as for example in an NPDES permit, the variance must still be reassessed as
part of the state's three year triennial review to confirm that the underlying attainability
analysis remains relevant and accurate. A variance must continue to protect "existing
uses" (defined in 40 CFR 131.3(e) as uses actually attained in the waterbody on or after
November 28, 1975). Typically, variances apply to specific pollutants and facilities,
which would mean that a water quality standards variance for mercury would apply to
only the new methylmercury criterion in a stated waterbody and specifically to the
discharger requesting the variance. The state or authorized tribe, however, may provide
justification for more than one discharger or for an entire waterbody or segment to
receive a variance (as discussed in section 3.2.2.3 of this document). See section 3.2.3
for a discussion of the requirement to conduct a use attainability analysis for changes to
water quality standards, including the prohibition on removing existing uses.
3.2.2.1 When is a variance appropriate?
Some regulated point sources discharging mercury might apply for variances for their
discharges into impaired waters where the largest source of mercury is atmospheric
deposition. In other cases, limits to technology or naturally elevated levels of
methylmercury in a waterbody could preclude attainment of standards. To address these
types of issues, the following scenarios are examples of demonstrations that could satisfy
the requirements under 40 CFR 131.10(g). The demonstrations are more thoroughly
explained below and in the Water Quality Standards Handbook (USEPA 1994).
• Economic or social impacts (131.10(g)(6)). Demonstrate that, in the short term, the
costs of constructing controls necessary to meet the methylmercury criterion
(beyond those required by sections 301(b)(l)(A) and (B) and 306 of the CWA)
would result in substantial and widespread economic and social impact.
• Human-caused conditions that cannot be remedied (131.10(g)(3)). Demonstrate
that, in the short term, none of the present technologies for improving the quality of
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Water Quality Criteria and Standards Adoption
an effluent are capable of bringing methylmercury levels in the discharge down to a
level as stringent as necessary to meet the criterion (i.e., there is no technological
remedy or it is technologically infeasible).
• Natural conditions that preclude attainment (131.10(g)(l)). Demonstrate that local
conditions of an aquatic system result in high methylmercury levels. For example,
elevated methylmercury concentrations might occur naturally in a system because
of a short-term condition.
During the period the variance applies, any permit issued must be consistent with
applicable water quality standards (40 CFR 122.44(d)(l)(vii)), which in this case would
be the temporary standard approved in the variance. The permit would need to be
modified to derive from and comply with the underlying standard if the variance is not
re-issued.
3.2.2.2 What should a state or tribe consider before granting a
variance?14
In general, the temporary revised standard established by a variance should be set at a
level representing the highest attainable water quality (like all water quality standards).
Variances may not interfere with existing uses, and variances should ensure progress
toward ultimate attainment of the designated use for the waterbody. Regarding procedural
considerations, the same requirements apply for a variance as for a new or revised
standard (e.g., public review and comment, EPA approval or disapproval) because a
variance is a change to the water quality standards. In addition, the following describes
more specific issues that states and authorized tribes should take into account when
considering granting a variance.
• Variance protocols. If a state or authorized tribe anticipates receiving a number of
variance requests for mercury discharges, it could consider establishing a mercury
variance protocol, with EPA's participation and agreement. The protocol would
govern the development and processing of variance requests. It would specify the
information needed and the criteria the state would use in considering whether to
adopt the variance. Although the state or tribe would need to submit each variance
to EPA for approval (40 CFR 131.20), EPA's advance agreement to the protocol
could streamline EPA's review of any variances developed in accordance with the
protocol. Public notice requirements for variances could be satisfied through the
process of issuing the NPDES permit that incorporates limits based on such
temporary standards, as long as the variance is identified and all the necessary
information pertaining to the variance is included.
• Time frames. A variance is typically a time-limited change in the water quality
standards. Although EPA part 131 regulations do not specify a time limit for
variances, EPA's triennial review regulations at 40 CFR 131.20 require that
variances, as part of water quality standards, are reexamined every three years to
14 Federal or state regulations also govern the granting of a variance. For example, regulations promulgated under 40 CFR part 132,
appendix F, procedure 2, specify the conditions for granting variances in the Great Lakes and prohibit the granting of variances to new
dischargers or recommending Great Lakes dischargers.
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Water Quality Criteria and Standards Adoption
determine if new information has become available and modified as appropriate.
Variances that extend longer than three years are traditionally revisited in the
context of a triennial review. Once a variance has expired, to justify the
continuation of the variance, the state must demonstrate that meeting the standard
is still unattainable based on one of the factors at 131.10(g). The state should also
ensure that the permittee has made reasonable progress to control mercury in the
discharge during the period of the previously approved variance (i.e. has adopted a
mercury minimization plan.)
As with any other revision to the water quality standards, the permit and permit
conditions implementing the variance do not automatically change back to the
previous permit conditions if the variance expires, unless that is a condition of a
variance and permit. Although water quality standards can change with every
triennial review, states and authorized tribes are not obliged to reopen and modify
permits immediately to reflect those changes, but may do so where the permit
contains a reopener condition to address such revised water quality standards. In
the Great Lakes, however, permits with limits based on variances must include a
provision enabling the permitting authority to reopen and modify the permit based
on triennial revisions to water quality standards. (40 CFR part 132, appendix F,
procedure 2, section F.4). Any new or reissued permit must implement the water
quality standards applicable at time of permit issuance. 40 CFR 122.44(d)(l).
• Antidegradation. Permits with effluent limits based on a variance for
methylmercury must conform, as do all permits, to the state or authorized tribe's
antidegradation policy.
• Mercury Minimization Plans (MMPs). EPA recommends that states and authorized
tribes require dischargers receiving a variance to adopt and implement an MMP as
described in section 7.5.2.4. By reducing mercury sources up front, as opposed to
traditional reliance on treatment at the end of a pipe, diligent implementation of
MMPs might mitigate any adverse effects of a variance by improving the water
quality. As noted above, MMPs also serve to inform the evaluation of controls
needed to grant a variance and to determine the highest attainable water quality
3.2.2.3 What is involved in granting a variance on a larger scale?
Traditionally, variances are specific to a pollutant and a facility. However, for situations
where a number of NPDES dischargers are located in the same area or watershed and the
circumstances for granting a variance are the same, states and authorized tribes may
consider administering a multiple-discharger variance for a group of dischargers
collectively. Such a group variance can be based on various scales and may depend
largely on the rationale for adopting a variance for methylmercury. Possible applications
of a group variance may include facilities with similar discharge processes, a watershed
basis, particularly for states that issue NPDES permits on a watershed basis, or a broader
geographic basis, analogous to a general NPDES permit.
For example, Ohio adopted a statewide mercury variance applicable to point source
dischargers in the state that meet specified criteria. In addition, Michigan has authorized
multiple discharger variances for mercury with permit requirements, including
development and implementation of an MMP.
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Water Quality Criteria and Standards Adoption
It is important to note that, despite the coverage of a multiple-source variance, an
individual discharger must still demonstrate that the underlying criterion is not attainable
with the technology-based controls identified by CWA sections 301(b) and 306 and with
cost-effective and reasonable best management practices (BMPs) for nonpoint sources
(40CFR131.10(h)(2)).
3.2.3 How are use attainability analyses conducted?
3.2.3.1 What is a use attainability analysis?
A use attainability analysis (UAA) is defined in 40 CFR 131.3(g) as a structured
scientific assessment of the factors affecting the attainment of a use, which may include
physical, chemical, biological, and economic factors, that must be conducted whenever a
state wishes to remove a designated use specified in section 101(a)(2) of the CWA, or to
adopt subcategories of uses specified in section 101(a)(2) of the CWA, which require less
stringent criteria (see 40 CFR 131.3 and 40 CFR 131.10(g)).
Where a UAA indicates that the current use is unattainable, the state or tribe will need to
identify and assign the "highest attainable use," which should reflect the factors and
constraints on the attainability of a use that were evaluated as part of the UAA process.
Once the state or tribe has determined the highest attainable use, it should propose
adopting this designated use in place of the designated use deemed unattainable. For
example, to the extent allowed by state or tribal law, the state or tribe could refine its
designated use from "fish consumption" to "mercury-limited fish consumption." That
way the waterbody would still be expected to meet other pollutant criteria designed to
protect fish consumption.
3.2.3.2 What is EPA's interpretation of CWA section 101 (a)?
CWA section 101(a) (2) establishes as a national goal "water quality [that] provides for
the protection and propagation offish, shellfish, and wildlife and provides for recreation
in and on the water," wherever attainable. These goals are commonly referred to as the
"fishable/swimmable" goals of the CWA. EPA interprets these goals as providing for the
protection of aquatic communities and human health related to the consumption offish
and shellfish. In other words, EPA views "fishable" to mean that fish and shellfish can
thrive in a waterbody and, when caught, can also be safely eaten by humans. This
interpretation also satisfies the CWA section 303(c)(2)(A) requirement that water quality
standards protect public health. Including human consumption offish and shellfish as the
appropriate interpretation of the definition of section 101(a)(2) uses is not new. For
example, in the 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 (57 FR 60859, December 22, 1992).
3.2.3.3 When is a UAA needed for a "fishable" use?
Under 40 CFR 131.10(j) of the Water Quality Standards Regulation, states and
authorized tribes are required to conduct a UAA whenever the state or authorized tribe
designates or has designated uses that do not include the "fishable/swimmable" use
specified in CWA section 101 (a)(2); or the state or authorized tribe wishes to remove a
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Water Quality Criteria and Standards Adoption
designated use that is specified in CWA section 101(a)(2) or adopt subcategories of the
uses specified in that section that require less stringent criteria.
An important caveat to the process of removing a designated use is that states and
authorized tribes may not remove an "existing use" as defined by the Water Quality
Standards Regulation. An existing use is defined in 40 CFR 131.3(c) as any use that has
been actually attained on or after November 28, 1975, when the CWA regulations
regarding use designation were originally established. In practical terms, waters widely
used for recreational fishing would not be good candidates for removing a "fishable" use,
especially if the associated water quality supports, or has until recently supported, the
fishable use, on the basis, in part, of the "existing use" provisions of EPA's regulations.
In addition, EPA considers designated uses attainable, at a minimum, if the use can be
achieved (1) through effluent limitations under CWA sections 301(b)(l)(A) and (B) and
306 and (2) through implementation of cost-effective and reasonable BMPs for nonpoint
sources. The federal regulations at 40 CFR 131.10(g) further establish the basis for
finding that attaining the designated use is not feasible, as long as the designated use is
not an existing use. EPA emphasizes that when adopting uses and appropriate criteria,
states and authorized tribes must ensure that such standards provide for the attainment
and maintenance of the downstream uses (40 CFR part 131.10(b)). States and tribes are
not required to conduct UAAs when designating uses that include those specified in
CWA section 101(a) (2), although they may conduct these or similar analyses when
determining the appropriate subcategories of uses.
3.2.3.4 What conditions justify changing a designated use?
EPA's regulations at 40 CFR 131.10(g) list the following six reasons for states or
authorized tribes to use to support removal of a designated use or adoption of a
subcategory of use that carries less stringent criteria:
• Naturally occurring pollutant concentrations prevent the attainment of the use.
• 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 discharges without violating state water
conservation requirements to enable uses to be met.
• 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.
• Dams, diversions, or other types of hydrologic modifications prevent the
attainment of the use, and it is not feasible to restore the waterbody to its original
condition or to operate such modification in a way that would result in attainment
of the use.
• Physical conditions related to the natural features of the waterbody, such as the lack
of a proper substrate, cover, flow, depth, pools, riffles, and the like, unrelated to
water quality, prevent attainment of aquatic protection uses.
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Water Quality Criteria and Standards Adoption
• Controls more stringent than those required by CWA sections 301(b) and 306
would result in substantial and widespread economic and social impact.
In addition to citing one or more of these factors to support removal of a use, states and
authorized tribes use the same six factors to guide analysis and decision-making with
respect to establishing an attainable use.
In all cases, states and authorized tribes must obtain scientifically sound data and
information to make a proper assessment. It is also recommended that they conduct
pollutant source surveys to define the specific dominant source of mercury in the
waterbody. Sources may include point source loadings, air deposition, mining waste or
runoff, legacy levels (e.g., mercury resulting from historical releases), and geologic
"background levels." This is similar to source assessments under the TDML program.
Existing documents provide guidance on obtaining data and conducting analyses for the
other components of a UAA. These documents are at http://www.epa.gov/waterscience/
standards/uaa/info.htm. The Technical Support Manual: Waterbody Surveys and
Assessments for Conducting Use Attainability Analyses (USEPA 1983) covers the
physical and chemical components of UAAs. Technical support for assessing economic
and social impacts is offered through the Interim Economic Guidance for Water Quality
Standards Workbook (USEPA 1995b).
EPA recognizes that there may be naturally occurring concentrations of methylmercury
which may exceed the national recommended 304(a) criterion. However, EPA policy,
whereby criterion may be set at ambient conditions if contaminant levels are due only to
non-anthropogenic sources, applies only to aquatic life uses. The policy does not apply to
human health uses. The policy states that for human health uses, where the natural
background concentration is documented, this new information should result in, at a
minimum, a re-evaluation of the human health use designation (USEPA 1997e).
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Monitoring and Assessment
4 Monitoring and Assessment
Water quality monitoring and assessment are essential elements in implementing the
CWA at the local, state, and national levels. In implementing the water quality-based
approach, the most obvious uses of monitoring information are in determining attainment
of water quality standards and in developing TMDLs and permits. In the case of mercury,
analyzing for mercury and methylmercury in water and fish is particularly important for
states and tribes that choose to develop BAFs and methylmercury-to-mercury translators.
This chapter provides guidance on analytical methods, field sampling, and assessment
considerations for mercury. Additional information on developing site-specific BAFs and
translators is provided in section 3.1.3 of this guidance.
4,1 VV-.v.: -. : -.'•; :-. .:- '
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Monitoring and Assessment
although any methods used need to be scientifically defensible. Although this chapter
provides recommendations for methods that can be used for these purposes, states and
tribes are not precluded from using other methods, including those in appendix C.
4.1.1 Analytical Methods for Methylmercury
For measuring methylmercury in water, EPA method 1630 (USEPA 200Id), developed
by EPA's Office of Water, reflects the techniques developed by Bloom and Crecelius
(1983) and refined by Bloom and Fitzgerald (1988), Bloom (1989), Mason and Fitzgerald
(1990), and Horvat (1993). This method has a quantitation level of 0.06 ng/L.
Draft modifications to method 1630, described in table Cl (see appendix C) and in
Horvat et al. (1993), allow for measurement of methylmercury in fish tissue as low as
0.001 to 0.002 mg/kg, well below the water quality criterion for methylmercury in tissue
(0.3 mg/kg). EPA recommends using these techniques when direct measurements of
methylmercury in fish tissue are desired.
Three additional methods for measuring methylmercury in water are listed in table C2
(see appendix C). These methods are UW-Madison's standard operating procedure, or
SOP (Hurley et al. 1996), used by the Great Lakes National Program Office for its Lake
Michigan Mass Balance Study; USGS Wisconsin-Mercury Lab SOPs 004 (DeWild et al.
2002), used by USGS and EPA in the Aquatic Cycling of Mercury in the Everglades
study; and a recently released USGS method (DeWild et al. 2002). All these procedures
are based on the same techniques and have detection limits of 0.01 ng/L, 0.05 ng/L and
0.04 ng/L, respectively.
Because the four methods are nearly identical test procedures, they are expected to
produce very similar results with sensitivity as low as 0.01 to 0.06 ng/L in water. These
levels are well below the expected range of water column concentrations associated with
the methylmercury fish tissue criterion.
4.1.2 Analytical Methods for Mercury
For measuring low level mercury in water, EPA method 1631, revision E (USEPA
2002c), developed by EPA's Office of Water, reflects the techniques developed by
researchers mentioned previously. It has a quantitation level of 0.5 ng/L. EPA made this
revision to clarify method requirements, increase method flexibility, and address
frequently asked questions. The revision includes recommendations for using the clean
techniques contained in EPA's Method 1669: Sampling Ambient Water for Trace Metals
at EPA Water Quality Criteria Levels (USEPA 1996a). The benefits of using method
1631 are that it has been fully validated, numerous laboratories are routinely using the
method, and it is sensitive enough to measure at the water concentrations expected to be
associated with the criterion. This method was approved in 2002 under 40 CFR part 136
for NPDES permitting and other purposes under the CWA (67 FR 65876).
In addition, EPA method 245.7 (USEPA 2005e), which has a quantitation level of
5.0 ng/L, was approved under part 136 in 2007 (72 FR 11200). Developed by EPA's
Office of Water, method 245.7 is similar to EPA method 163 IE because both methods
require use of a cold-vapor atomic fluorescence spectrometry (CVAFS) detector to
measure low levels of mercury. Method 245.7 has been validated in two EPA
52
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Monitoring and Assessment
laboratories, one university laboratory, and an interlaboratory validation study. Results
from these studies indicate that the method is capable of producing reliable measurements
of mercury at some toxic criteria levels (40 CFR 136).
Appendix A to method 1631 (64 FR 10596) details the researcher's techniques for
determining total and dissolved mercury in tissue, sludge, and sediments. The appendix
was developed for processing fish tissue samples to be analyzed for mercury using the
previously validated and approved method 1631 analytical procedures. The procedures
are expected to be capable of measuring mercury in the range of 0.002 to 5.0 mg/kg.
EPA recognizes that some users might find Method 1631 (appendix A) costly or difficult
to implement. Appendix C summarizes three other methods available for analyzing
mercury in fish tissue that are less costly and less difficult to implement, but they have
not undergone the same extensive interlaboratory validation studies as Method 1631
(appendix A). Two are listed in table Cl (Methods 245.6 and 7474). The third—Method
7473 for analyzing mercury in water, listed in table C2—has been adapted by some users
for analyzing mercury in fish tissue; this approach has been used to measure mercury in
fish tissue to support state fish consumption advisories.
Because researchers have found that nearly all mercury in fish tissue is in the form of
methylmercury (USEPA 2000c), EPA also suggests that analysis of tissue for mercury, as
a surrogate for methylmercury, might be a useful means for implementing the
methylmercury criterion. If mercury concentrations in tissue exceed the criterion, further
investigation of the methylmercury component might be desired.
4.1.3 Summary of Recommended Analytical Methods
In summary, on the basis of the available information, EPA believes that the most
appropriate methods for measuring low levels of mercury concentrations in the water
column are method 1631, revision E (mercury in water by CVAFS) and method 245.7
(mercury in water by CVAFS). Likewise, EPA believes that the most appropriate method
for measuring methylmercury concentrations in the water column is method 1630
(methylmercury in water by CVAFS), and the most appropriate methods for measuring
mercury concentrations in fish tissue are appendix A to method 1631 (mercury in tissue
by CVAFS) and modifications to method 1630 for handling tissues. EPA recommends
these procedures for the following reasons:
• EPA developed methods 1631 and 1630 to support implementation of water quality
criteria for mercury and methylmercury, respectively. Both are already in the
appropriate EPA format and include all standardized quality control elements
needed to demonstrate that results are reliable enough to support CWA
implementation.
• EPA developed method 245.7 specifically to address state needs for measuring
mercury at ambient water quality criteria levels, when such measurements are
necessary to protect designated uses. In addition, it has been validated in two EPA
laboratories, one university laboratory, and an interlaboratory validation study.
• EPA developed appendix A to method 1631 to support its National Study of
Chemical Residues in Lake Fish Tissue. Appendix A provides information on
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Monitoring and Assessment
preparing a fish tissue sample for analysis using method 1631. The method was
validated by Brooks Rand (USEPA 1998b) and was used by Battelle Marine
Sciences to analyze more than a thousand tissue samples collected during EPA's
national study (USEPA 2000d). Successful use of these techniques also has been
widely reported in the literature. This history, combined with the fact that appendix
A supplements the already well-characterized and approved method 1631, makes
this method a good candidate for use with the new fish tissue criterion.
• Method 1630 already has been used in several studies, including EPA's Cook Inlet
Contaminant Study (USEPA 200 le) and the Savannah River TMDL study
(USEPA 200If). The techniques described in the method and in the recommended
method modifications also have been successfully applied in numerous studies
described in the published literature. Furthermore, the procedures in method 1630
are nearly identical to those given in the USGS method and in the University of
Wisconsin SOP (Hurley et al., 1996), listed in table C2. The University of
Wisconsin SOP was used in EPA's Lake Michigan Mass Balance Study (USEPA
2001g).
Table 4 summarizes the recommendations discussed above.
Table 4. Recommended analytical methods for detecting and measuring low levels
of methylmercury and mercury in fish tissue and water
Recommended for analysis of:
...in fish tissue
(for additional available methods,
see appendix C, table C1)
...in water
(for additional available methods,
see appendix C, table C2)
Methylmercury...
(see section 4.1.1)
Method 1630 with draft
modifications for tissue
Method 1630
Mercury...
(see section 4.1.2)
Method 1631, draft Appendix
A
Method 1631, revision E*
Method 245.7*
'Approved under 40 CFR part 136. See sections 7.4 and 7.5.1.1 for further information on appropriate
methods for NPDES permitting purposes.
EPA has published guidance providing information on sampling strategies for a fish
contaminant monitoring program in volume 1, Fish Sampling and Analysis, of a
document series, Guidance for Assessing Chemical Contaminant Data for Use in Fish
Advisories (USEPA 2000c). This guidance provides scientifically sound
recommendations for obtaining a representative sample for issuing fish consumption
advisories, and can be applied for obtaining a representative sample for determining
attainment. The guidance also includes recommendations for quality control and quality
assurance considerations. In all cases, states and authorized tribes should develop data
quality objectives for determining the type, quantity, and quality of data to be collected
(USEPA 2000e).
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4.2.1 What fish species should be monitored?
EPA's fish sampling guidance (USEPA 2000c) provides recommendations for selecting
finfish and shellfish species for monitoring to assess human consumption concerns.
According to the guidance, the most important criterion for selecting fish is that the
species are commonly eaten in the study area and have commercial, recreational, or
subsistence fishing value. States and tribes also should ensure that the species monitored
reflect the fish species consumed by culturally and economically diverse communities.
Fish creel data (from data gathered by surveying recreational fishers) from state fisheries
departments are a justifiable basis for estimating types and amounts offish consumed
from a given waterbody. States and authorized tribes should ensure that the creel data are
of sufficient quality and are representative of the local population of people that eat fish.
The fish sampling guidance also identifies recommended target species for inland fresh
waters and for Great Lakes waters. Walleye and largemouth bass have been identified as
freshwater fish that accumulate high levels of methylmercury. Reptiles, such as turtle
species and alligators, are recommended as target species for mercury if they are part of
the local diet. Larger reptiles can also bioaccumulate environmental contaminants in their
tissues from exposure to contaminated sediments or consumption of contaminated prey.
The fish sampling guidance further recommends that the size range of the sampled target
fish ideally should include the larger fish individuals harvested at each sampling site
because larger (older) fish within a population are usually the most contaminated with
methylmercury (Phillips 1980, Voiland et al. 1991). In addition, the methylmercury
concentrations in migratory species are likely to reflect exposures both inside and outside
the study area, and the state or authorized tribe should take this into account when
determining whether to sample these species. For migratory species, EPA's fish sampling
guidance recommends that neither spawning populations nor undersized juvenile stages
be sampled in fish contaminant monitoring programs (USEPA 2000c). States and
authorized tribes should consider the life history of migratory species and the
consumption patterns of the local population when including migratory species in their
fish sampling protocols. Sampling of target finfish species during their spawning period
should be avoided because contaminant tissue concentrations might decrease at that time.
If states and authorized tribes do not have local information about the types of fish that
people eat, the following two options provide an alternative for identifying which fish to
sample:
• Match assumed or known consumption pattern to sampled species. If the state has
some knowledge of the fish species consumed by the general population or by
individuals in another target population, a monitoring sample could be composited
to reflect this knowledge. For example, a state might decide that 75 percent of the
fish consumed are trophic level 4 species, 20 percent are trophic level 3 species,
and 5 percent are trophic level 2 species. A composite sample (see section 4.2.2)
would reflect the determined trophic level breakout.
• Use trophic level 4 fish only. Predator species (e.g., trout, walleye, largemouth
bass, and smallmouth bass) are good indicators for mercury and other persistent
pollutants that are biomagnified through several trophic levels of the food web.
Increasing mercury concentrations correlate with an increase in fish age, with some
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variability, so that consumption of larger (older) individuals correlates with greater
risks to human health. Increasing mercury concentrations also correlate with higher
trophic levels, and thus consumption of higher-trophic-level species would provide
greater risks to human health. Therefore, targeting trophic level 4 species should
serve as a conservative approach (depending on the species most frequently
consumed by recreational fishers) for addressing waterbodies with highly varying
concentrations of methylmercury.
4.2.2 What sample types best represent exposure?
EPA recommends using composite samples offish fillets from the types offish that
people in the local area eat because methylmercury is found primarily in fish muscle
tissue (USEPA 2002c). Using skinless fillets is a more appropriate approach for
addressing mercury exposures for members of the general population and most
recreational fishers because fish consumers typically eat the fillets without skin. Because
mercury is differentially concentrated in muscle tissue, leaving the skin on the fish fillet
actually results in a lower mercury concentration per gram of skin-on fillet than per gram
of skinless fillet (USEPA 2000c). Analysis of skinless fillets might also be more
appropriate for some target species, such as catfish and other scaleless finfish species.
Some fish consumers, however, do eat fish with the skin on. In areas where the local
population eats fish with the skin or eats other parts of fish, the state or authorized tribe
should consider including these parts offish in the sample.
Composite samples are homogeneous mixtures of samples from two or more individual
organisms of the same species collected at a site and analyzed as a single sample.
Because the costs of performing individual chemical analyses are usually higher than the
costs of sample collection and preparation, composite samples are most cost-effective for
estimating average tissue concentrations in target species populations. In compositing
samples, EPA recommends that composites be of the same species and of similar size so
that the smallest individual in a composite is no less than 75 percent of the total length
(size) of the largest individual (USEPA 2000c). Composite samples can also overcome
the need to determine how nondetections will be factored into any arithmetical averaging
because the composite represents a physical averaging of the samples. However,
depending on the objectives of a study, compositing might be a disadvantage because
individual concentration values for individual organisms are lost. Guidance for Assessing
Chemical Contaminant Data for Use in Fish Advisories, volume 1, at sections 6.1.1.6 and
6.1.2.6, provides additional guidance for sampling recommendations.
4.2.3 What is the recommended study design for site selection?
Ideally, states and authorized tribes should collect samples over a geographic area that
represents the average exposure to those who eat fish from the waterbody. However, if
there are smaller areas where people are known to concentrate fishing, those areas should
be used as the sampling area. Fish sampled in locations with mercury point sources
should be included in the average concentration if fishing occurs in those areas but not
included if the areas are not used for fishing.
Once the state or tribe identifies the geographic area, EPA recommends that they use a
probabilistic sampling design to select individual sites or sampling locations. Use of a
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probabilistic design can address the spatial variability of methylmercury levels in fish.
This approach allows statistically valid inferences to be drawn about tissue levels in the
area as a whole. EPA's Guidance on Choosing a Sampling Design for Environmental
Data Collection, for Use in Developing a Quality Assurance Project Plan (USEPA
2002d) contains information about probabilistic site selection.
4.2.4 How often should fish samples be collected?
EPA's Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories,
volume 1 (USEPA 2000c), at section 6.1.1.5, provides recommendations for how
frequently to sample fish tissue. If program resources are sufficient, this guidance
recommends biennial sampling offish in waterbodies where recreational or subsistence
harvesting is commonly practiced. If biennial screening is not possible, waterbodies
should be screened at least once every five years. Also, the state or authorized tribe
should sample during the period when the target species is most frequently harvested or
caught.
In fresh waters, the guidance recommends that the most desirable sampling period is from
late summer to early fall (August to October). Water levels are typically lower during that
time, simplifying collection procedures. Also, the fish lipid content is generally higher,
allowing the data to also provide information for other contaminant levels. The guidance
does not recommend the late summer to early fall sampling period if it does not coincide
with the legal harvest season of the target species or if the target species spawns during
that period. In estuarine and coastal waters, the guidance recommends that the most
appropriate sampling time is during the period when most fish are caught and consumed
(usually summer for recreational and subsistence fishers).
EPA recommends that states and authorized tribes sample consistently in a season to
eliminate seasonal variability as a confounding factor when analyzing fish monitoring
data. Moreover, focused seasonality studies could be used both to assess the impact of
seasonal variability on fish concentrations and to normalize concentrations to a standard
season(s). Several studies have measured seasonality in the mercury concentrations in
fish fillet muscle in estuaries and reservoirs (Kehrig et al. 1998; Park and Curtis 1997;
Szefer et al. 2003). In these studies, concentrations were generally higher in cold seasons
than in warm seasons by as much as two to three times. Slotten et al. (1995) showed that
the uptake of methylmercury in zooplankton and fish increased dramatically during the
fall mixing of Davis Creek Reservoir, a California reservoir contaminated by mercury
mining activities.
No studies of seasonality of mercury concentrations in fish were found for rivers or
natural lakes. On the basis of literature-reported fish mercury depuration rates, EPA does
not expect seasonal fluctuations in fish mercury levels. Though reported mercury
elimination half-lives cover a wide range of rates, from a few days to several years, the
central tendency is 100-200 days (Burrows and Krenkel 1973; Giblin and Massaro 1973;
Huckabee et al. 1979 [literature review]; McKim et al. 1976; Rodgers and Beamish
1982). Such slow depuration rates are expected to dampen strongly any fluctuations in
methylmercury concentrations in fish. Instead, seasonal variations in fish tissue are likely
linked to seasonal nutrition variability that affects fish body conditions but not mercury
body burden.
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4.2.5 How many samples should be collected?
EPA's Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories,
volume 1 (USEPA 2000c), at section 6.1.2.7.2, provides information to help determine
the number of composite samples needed for comparing fish tissue information to a target
value. The guidance does not recommend a single set of sample size requirements (e.g.,
number of replicate composite samples per site and number of individuals per composite
sample) for all fish contaminant monitoring studies, but rather presents a more general
approach that is both scientifically defensible and cost-effective. The guidance provides
the means for determining an optimal sampling design that identifies the minimum
number of composite samples and of individuals per composite necessary to detect a
minimum difference between a target (in this case, the water quality criterion) and the
mean concentration of composite samples at a site. Under optimal field and laboratory
conditions, at least two composite samples are needed at each site to estimate the
variance. To minimize the risk of a destroyed or contaminated composite sample's
preventing the site-specific statistical analysis, at least three replicate composite samples
should be collected at each site.
4.2.6 What form of mercury should be analyzed?
Because of the higher cost of methylmercury analysis (two to three times greater than that
for mercury analysis), one approach for the states and authorized tribes could be to first
measure mercury in fish tissue. States and tribes may find that more labs have the
capability for mercury analysis and that the analysis time may be quicker.
When measuring only mercury, the state or authorized tribe might make the conservative
assumption that all mercury in fish tissue is methylmercury. Appendix A summarizes
eight studies of the relative proportion of the mercury concentration in North American
freshwater fish that is in the form of methylmercury. In six of the eight studies,
methylmercury, on average, accounted for more than 90 percent of the mercury
concentration in fish tissue. In the remaining two studies, methylmercury, on average,
accounted for 80 to 90 percent of the mercury concentration in trophic level 3 and 4 fish.
If the measured mercury level exceeds the methylmercury criterion, states and tribes may
wish to repeat the sampling (if sufficient tissue is not left) and analyze for
methylmercury.
4.2.7 Other sampling considerations
EPA recommends that states and tribes routinely collect both weight and length data
when assessing the potential influence of fish nutritional state on mercury concentration,
and potentially for normalizing fish concentrations to a standard body condition.
Greenfield et al. (2001), Cizdziel et al. (2002, 2003), and Hinners (2004) reported a
negative correlation between fish body condition (a ratio of weight to cubed length) and
fish tissue mercury concentration. Regardless of the exact mechanism, body condition
offers a useful method to explain variability in fish mercury.
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•i for
Section 303(d)(l) of the CWA and EPA's implementing regulations require states and
authorized tribes to identify and establish priority ranking for waters that do not, or are
not expected to, achieve or maintain water quality standards. In accordance with this
ranking, a TMDL for such waters must then be established. For purposes of determining
impairment of a waterbody and whether to include it on section 303(d) lists, or in
category 5 of the Integrated Report under sections 303(d) and 305(b)15, states and
authorized tribes must consider all existing and readily available data and information
(see 40 CFR 130.7).
States and authorized tribes determine attainment of water quality standards by
comparing ambient concentrations to the numeric and narrative AWQC (40 CFR 130.7
(b)(3)). Where a fish tissue criterion has been adopted, states and tribes should consider
observed concentrations in fish tissue in comparison to the criterion. Where a water
column translation of the fish tissue criterion has been developed and is adopted as part
of the state's or tribe's water quality standards, states and tribes should consider ambient
water concentrations in comparison to the translation.
For assessment of concentrations in fish tissue, resources may typically be unavailable to
collect an adequate number of replicate composite samples to support rigorous statistical
testing, especially where it is desirable to evaluate each individual target species
separately. In these situations, states should make direct comparisons between composite
sample concentrations and the criterion, as each composite effectively represents the
average concentration observed in several fish.
Statistical tests for comparing the average concentration from multiple replicate
composite samples to the criterion may be conducted where a sufficient number of
replicates have been collected. EPA's Guidance for Assessing Chemical Contaminant
Data for Use in Fish Advisories, volume 1 (USEPA 2000c), at section 6.1.2.7.2,
recommends using the t-test to determine whether the mean concentration of mercury in
composite fish tissue samples exceeds the screening value. This test involves a statistical
comparison of the mean of all fish tissue data to the criterion. States and authorized tribes
can evaluate whether the t-test statistic of the mean exceeds the water quality standards.
This procedure could also be used to determine impairment, provided it is consistent with
a state's water quality standards. States and authorized tribes might also want to consider
the guidance in appendixes C and D of the Consolidated Assessment and Listing
Methodology: Toward a Compendium of Best Practices (USEPA 2002e). Ultimately, the
method that states and authorized tribes choose depends on how they express their water
quality standards and apply their water quality assessment methodology.
4.3.1 How should nondetections be addressed?
When computing the mean of mercury in fish tissue, a state or authorized tribe might
encounter a data set that includes analyzed values below the detection level. EPA does
15
See EPA's guidance for Integrated Reports described at http://www.epa.gov/owow/tmdl/2006IRG/.
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not expect this to occur frequently for two reasons. First, if the samples are physically
composited (see section 4.2.2.), the composite itself provides the average, and there is no
need to mathematically compute an average. Second, the newer analytical methods 1630
and 1631 can quantify mercury at 0.002 mg/kg, which should be lower than the observed
mercury in most fish tissue samples being analyzed.
If, however, a state or authorized tribe is mathematically computing an average of a data
set that includes several values below the detection level, the water quality standards
and/or assessment methodology should discuss how it will evaluate these values. The
convention recommended in EPA's Guidance for Assessing Chemical Contaminant Data
for Use in Fish Advisories, volume 1, at section 9.1.2, is to use one-half of the method
detection limit for nondetects in calculating mean values (USEPA 2000c). The guidance
also recommends that measurements that fall between the method detection limit and the
method quantitation limit be assigned a value of the detection limit plus one-half the
difference between the detection limit and the quantitation limit. EPA notes, however,
that these conventions provide a biased estimate of the average concentration (Gilbert
1987) and, where the computed average is close to the criterion, might suggest an
impairment when one does not exist or, conversely, suggest no impairment when one
does exist.
States or authorized tribes can calculate the average of a data set that includes values
below the detection level using other statistical methods (e.g., sample median and
trimmed means) (Gilbert 1987). EPA has published a review of several methods and
analyzed the potential bias each can introduce into the calculation of the mean (USEPA
2001h).
One approach that a state or authorized tribe could take is to conduct a sensitivity
analysis to ascertain the consequence of what value is used to quantify samples below the
detection level. In a sensitivity analysis, the state or authorized tribe would compute the
mean concentration by first using the value of the detection level to quantify samples
below the detection level and then using a zero value for samples below the detection
level. If both calculated means are above or below the criterion, it is clear that the choice
of how to quantify samples below the detection level does not affect the decision.
However, if one calculated mean is below the criterion and the other is above, it is clear
that the choice of how to quantify samples below the detection level does affect the
decision, and a more sophisticated approach such as the ones in Robust Estimation of
Mean and Variance Using Environmental Data Sets with Below Detection Limit
Observations (USEPA 200 Ih) should be used.
All methods have advantages and disadvantages. A state or authorized tribe should
understand the consequences of which method it uses, especially if the choice makes a
difference as to whether a waterbody is considered impaired or not. Furthermore, a state
or authorized tribe should be clear about which approach it used. Again, the selected
methodology must be consistent with the state's water quality standards and their
published assessment method.
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4.3.2 How should data be averaged across trophic levels?
If target populations consume fish from different trophic levels, the state or authorized
tribe should consider factoring the consumption by trophic level when computing the
average methylmercury concentration in fish tissue. To take this approach, the state or
authorized tribe would need some knowledge of the fish species consumed by the general
population so that the state or authorized tribe could perform the calculation using only
data for fish species that people commonly eat. (For guidance on gathering this
information, see section 3.2.1.2.) States and authorized tribes can choose to apportion all
the fish consumption, either a value reflecting the local area or the 17.5 grams fish/day
national value for freshwater and estuarine fish if a local value is not available, to the
highest trophic level consumed for their population or modify it using local or regional
consumption patterns. Fish creel data from state fisheries departments are one reasonable
basis for estimating types and amounts offish consumed from a given waterbody. The
state or authorized tribe must decide which approach to use.
As an example of how to use consumption information to calculate a weighted average
fish tissue concentration, see table 5 and equation 4.
Table 5. Example data for calculating a weighted average fish tissue value
Species
Cutthroat trout
Kokanee
Yellow perch
Smallmouth bass
Pumpkinseed
Brown bullhead
Signal crayfish
Trophic level
3
3
3
4
3
3
2
Number of samples
30
30
30
95
30
13
45
Geometric mean
methylmercury
concentration (mg/kg)
0.07
0.12
0.19
0.45
0.13
0.39
0.07
These concentrations are used to compute a weighted average of tissue methylmercury
concentrations for comparison to the 0.3 mg/kg criterion. All fish measured are classified
as trophic level 3 except signal crayfish, which are trophic level 2, and smallmouth bass,
which are trophic level 4. The mean methylmercury concentration in trophic level 3 fish
in this example is 0.15 mg/kg. This is calculated by weighting the geometric mean
methylmercury concentration in each trophic level 3 species by the number of samples of
each of the trophic level 3 species, and then averaging the weighted geometric means.
Had the concentrations been averaged without weighting for the number of samples, the
average concentration would have been 0.18 mg/kg and would have given more weight to
the methylmercury concentrations in brown bullhead than to the concentrations in the
other species. (Note that this averaging approach does not consider that the trophic level
3 fish in this sample are of different sizes, or that some fish might be consumed more or
less frequently than is represented by the number of samples.) Equation 4 shows how the
total (all trophic levels) weighted concentration is calculated using the 0.15 mg/kg value
as representative of trophic level 3 fish and the default consumption for each trophic
level:
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Qvg = 3.8 * C2 + 8.0* Q + 5.7* Q = 0.23 mg/kg (Equation 4)
(3.8 + 8.0 + 5.7)
Where:
C2 = average mercury concentration for trophic level 2
C3 = average mercury concentration for trophic level 3
C4 = average mercury concentration for trophic level 4
This calculation is based on apportioning the 17.5 grams/day national default
consumption rate for freshwater and estuarine fish and shellfish by trophic level
(5.7 grams/day of trophic level 4 fish, 8.0 grams/day of trophic level 3 fish, and
3.8 grams/day of trophic level 2 fish ). As noted throughout this document, however, the
consumption pattern of the target population should be used if available.
If fish tissue concentration data from a trophic level are missing, one would drop the
consumption factor for that trophic level from both the numerator and denominator. For
example, if there were no tissue concentration data for trophic level 2 fish in the previous
example, equation 5 shows the revised calculation:
Qvg = 8.0*C, + 5.7*Q = 0.27 mg/kg (Equations)
(8.0 + 5.7)
This revised calculation preserves the relative contribution of each trophic level to
consumption patterns. This approach (i.e., dropping a trophic level from Equation 4),
however, should not be used if there are no fish tissue data for trophic level 4 fish. Since
level 4 fish are the type offish that people most often consume, dropping trophic level 4
from Equation 4 may result in underprotection if trophic level 4 fish are actually
consumed at the site. Instead, the state or authorized tribe should collect information to
determine the consumption rate for fish in trophic level 4. If the state or authorized tribe
finds that no trophic level 4 fish are eaten, the state or tribe may drop trophic level 4 from
Equation 4.
If the state or authorized tribe has developed a site-specific fish consumption rate for the
criterion, the state or authorized tribe should incorporate this site-specific rate into
equation 4. In this case, the state or authorized tribe would replace the values of 5.7
grams/day of trophic level 4 fish, 8.0 grams/day of trophic level 3 fish, and 3.8 grams/day
of trophic level 2 fish with the values that the state or authorized tribe developed.
As an alternative approach, states or authorized tribes might wish to translate fish tissue
sample data to a standard size, length, or species offish that is more commonly
consumed or is representative of the risk considerations of the state. Regression models
16 The values for each trophic level are the same as those discussed in section 3.2.1.2; they can be found in Methodology for Deriving
Ambient Water Quality Criteria for the Protection of Human Health (USEPA 2000b).
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have been developed for this purpose (Rae 1997; Wente 2003). An inherent assumption is
that concentrations will differ between samples of two different species/lengths/sample
cuts in a fixed equilibrium distribution relationship among all fish. If this relationship is
known and at least one tissue sample concentration is measured from a
species/length/sample cut that is accurately described by this relationship, fish
consumption risk analyses could be performed for any species/lengths/sample cuts
described by the relationship at this site.
Such regression models may include independent variables that account for species,
aquatic environment (e.g., lotic vs. lentic, or other waterbody characteristics), sample cut
(e.g., whole fish, skin-on fillet, skinless fillet), specific characteristics (e.g., age and
retention time) of reservoirs, temporal trends, and fish length. The response variable is
fish mercury concentration, which is typically assumed to be lognormally distributed. In a
graphic sense, the model shows the covariance of each combination of nominal scale
variables (e.g., whole fish, lentic waterbody) with fish length, with the slope representing
the concentration/length ratio. Regression slopes can vary from lake to lake, resulting in
models that inappropriately retain some fish size covariation (Soneston 2003).
EPA used the USGS National Descriptive Model for Mercury in Fish Tissue in various
analyses (USEPA 2005a). This model is a statistical model related to covariance, and it
allows the prediction of methylmercury concentrations in different species, cuts, and
lengths offish for sampling events, even when those species, lengths, or cuts offish were
not sampled during those sampling events. The model can also prove useful to states and
authorized tribes in averaging fish tissue across trophic levels.
4.3.3 How should older data be assessed?
For purposes of determining waterbody impairment and inclusion on section 303(d) lists
or category 5 of the Integrated Report, states and authorized tribes must consider all
existing and readily available water quality-related data and information (40 CFR 130.7).
Ideally, a state or authorized tribe would have collected fish tissue information within the
past five years, as recommended in section 4.2.4. Such recent information might not
always be available, however, and the available data often includes mercury samples
collected and analyzed several years in the past. When the state or authorized tribe
evaluates this information, it should take into account the reliability of this information
and its compliance with applicable data collection or quality assurance/quality control
program requirements.
4.3.4 How should fish consumption advisories be used to
determine impairment?
On October 24, 2000, EPA issued guidance on the use offish advisories in CWA section
303(d) listing and 305(b) reporting decisions (USEPA 2000J). This guidance notes EPA's
general interpretation that fish consumption advisories on the basis of waterbody-specific
information can demonstrate impairment of CWA section 101 (a) "fishable" uses.
Although the CWA does not explicitly direct the use offish consumption advisories to
determine attainment of water quality standards, states and authorized tribes must
consider all existing and readily available data and information to identify impaired
waterbodies on their section 303(d) lists. For purposes of determining waterbody
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impairment and inclusion on a section 303(d) list or in an Integrated Report, EPA
considers a fish consumption advisory and the supporting data existing and readily
available data and information.
When listing waters under CWA sections 303(d) or in the Integrated Reporting format on
the basis of a fish advisory for a migratory fish species, the state or authorized tribe
should include the waters the migratory fish are known to inhabit because those are the
waters where the fish potentially would be exposed to mercury. In addition, a state or
authorized tribe has the discretion to include any other water having a fish consumption
advisory as impaired on its section 303(d) list if the state or authorized tribe believes
inclusion is appropriate.
A state or authorized tribe should include on its section 303(d) list or in its Integrated
Report, at a minimum, those waters for which waterbody-specific data that were the basis
of a fish or shellfish consumption advisory demonstrate nonattainment of water quality
standards. EPA believes that a fish or shellfish advisory demonstrates nonattainment
when the advisory is based on tissue data, the data are from the specific waterbody in
question, and the risk assessment parameters of the advisory or classification are
cumulatively equal to or less protective than those in the water quality standards.17
For example, consider a state or authorized tribe that bases its water quality criterion on
eating two fish meals a month. If the state or authorized tribe finds fish tissue information
showing that the level of mercury is at a level where it decides to advise people not to eat
more than one fish meal a month and all other risk assessment factors are the same, the
advisory also may serve to demonstrate a water quality standard exceedance and that the
waterbody should be placed on the 303(d) list or in the Integrated Report. In contrast, if
this same state or authorized tribe finds the level of mercury in fish in another waterbody
is at a level at which it would advise people to eat no more than three meals a month, and
all other risk assessment factors are the same, the advisory is not necessarily the same as
an impairment and the waterbody might not need to be listed.
17 The October 2000 EPA guidance assumes that the fish tissue monitoring that supports the advisory is sufficiently robust to provide a
representative sample of mercury in fish tissue. EPA's fish tissue guidance (USEPA 2000c) provides recommendations on how public
health officials can collect sufficient information about contaminants in fish.
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5 Other Water Quality Standards Issues
•:.'" ," •• "• ." "• - ' :•' '
The 2001 recommended methylmercury fish tissue criterion and EPA's recommendations
for its implementation do not supersede the requirements applicable to the Great Lakes at
40 CFR part 132. The Great Lakes regulatory requirements, known as the Great Lakes
Initiative, or GLI, apply to all the streams, rivers, lakes and other bodies of water within
the U.S. portion of the Great Lakes drainage basin. For those waters, a state or authorized
tribe must adopt requirements (including water quality criteria) that are consistent with
(as protective as) regulations EPA promulgated on March 23, 1995. See 60 FR 15366 and
40 CFR 132.l(b) and 132.4.
Under these regulations, if a state or authorized tribe adopts a fish tissue residue
methylmercury criterion for the protection of human health, EPA, in its review of the new
state or tribal criterion, must determine whether it is as protective as the mercury water
column criterion for human health protection promulgated at 40 CFR 132.6, table 3, and
whether all implementation procedures are as protective as the implementation
procedure. See 40 CFR 132.5(g).
As described below, it is unlikely that adoption of EPA's 2001 recommended
methylmercury fish tissue-based criterion of 0.3 mg/kg to protect human health would
result in TMDLs or NPDES permit limits addressing mercury impairments in the Great
Lakes basin less stringent than those that would be required under the existing GLI
regulations. The reasons for this include the following:
• The GLI requires all states and authorized tribes to adopt the GLI wildlife water
column criterion. The GLI wildlife criterion has a significantly more stringent
methylmercury fish tissue basis than either the 2001 criterion or the GLI human
health criteria and would therefore likely be the controlling basis for any TMDLs
or NPDES permit limits addressing mercury pollution.
• Even if that were not the case, the 2001 criterion is more stringent than the
methylmercury fish tissue basis for the GLI human health water column criteria for
mercury.
Furthermore, using the 2001 fish tissue criterion would not necessarily result in lower
transaction costs than the GLI. The GLI implementation procedures (e.g., the mixing
zone prohibition, 40 CFR part 132, appendix F, procedure 3) require the use of water
column criteria, so the 2001 methylmercury fish tissue criterion would need to be
converted to a water column criterion following the GLI site-specific modification
procedures before it could be approved by EPA and implemented using other GLI
implementation procedures.
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Other Water Quality Standards Issues
18
The human health criterion for mercury established by the GLI is 3.1 ng/L . This water
column criterion for mercury is equivalent to a methylmercury fish tissue residue value of
0.35 mg/kg using the Great Lakes-specific BAFs for mercury—27,900 L/kg for trophic
level 3 and 140,000 L/kg for trophic level 4—as well as other Great Lakes-specific
information (USEPA 1995c). Because EPA's 2001 methylmercury criterion (0.30 mg/kg)
is more stringent than the GLI fish tissue residue value, the 2001 criterion would result in
more stringent water column concentrations than the GLI human health criteria unless
other, site-specific factors were significantly less stringent. This could occur, for
example, if a state or authorized tribe applied the GLI site-specific modification
procedures and found that the current, local BAF is significantly lower than the one used
to develop the GLI criterion. In that case, the state or tribe could use the lower, local BAF
and EPA's recommended fish tissue-based criterion to recalculate the water column
criterion using the GLI site-specific modification procedures and submit it to EPA for
review and approval. If the site-specific water column criterion was approved by EPA,
the state or authorized tribe could use it and the GLI implementation procedures to
develop TMDLs and NPDES permits.
Finally, as indicated above, if a state or authorized tribe were to adopt the 2001 human
health criterion in the Great Lakes basin, this action most likely would not result in a
change to TMDLs or NPDES permits. The GLI also includes a 1.3 ng/L criterion for the
protection of wildlife, and in most instances, this more stringent criterion will drive the
calculation of TMDLs or NPDES permit limits.
•'•' • ', •' " " '
If a state or authorized tribe adopts new or revised methylmercury criteria based on a
water column value rather than a fish tissue value, it should consider the dilution flow
specified in the state's or tribe's water quality standards when applying the new mercury
criterion. Where a state's or authorized tribe's water quality standards do not specify the
appropriate flow for use with the mercury criterion, EPA recommends using a harmonic
mean flow. EPA used this flow for application of the human health criteria for mercury in
the Great Lakes (40 CFR part 132). EPA also used this flow for application to the human
health criteria in the National Toxics Rule (40 CFR 131.36) and the California Toxics
Rule, or CTR (40 CFR 131.38). The Agency considers this flow to better reflect the
exposure offish to mercury. The technical means for calculating a harmonic mean is
described in section 4.6.2.2.a of the Technical Support Document for Water Quality-
based Toxics Control (USEPA 1991).
18 EPA promulgated the GLI human health criteria of 1.8 ng/L in 40 CFR part 132, table 3, in March 1995, based on an RiD of 0.06
Hg/kg/d. In May 1995 EPA revised the RiD to the current 0.1 ng/kg/d, which would result in GLI criteria of 3.1 ng/L. In October 1996
EPA issued guidance indicating that the 3.1 ng/L criteria were considered as protective as the promulgated 1.8 ng/L.
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5,3 .:-"..-.. '. ' ..•....•; .. ~'
5.3.1 What is a mixing zone?
A mixing zone is the area beyond a point source outfall (e.g., a pipe) in which
concentrations of a pollutant from a wastewater discharge mix with receiving waters.
Under 40 CFR 131.13, states and authorized tribes may, at their discretion, include
mixing zones in their water quality standards. Within a mixing zone, the water may be
allowed to exceed the concentration-based water quality criterion for a given pollutant.
The theory of allowing mixing zones is based on the belief that by mixing with the
receiving waters within the zone, the concentration of the pollutant being discharged will
become sufficiently diluted to meet applicable water quality criteria beyond the borders
of that zone and fully protect the designated use of the waterbody as a whole. More
information on mixing zones is available in the Technical Support Document for Water
Quality-based Toxics Control (USEPA 1991) and the Water Quality Standards
Handbook (USEPA 1994). States and authorized tribes often authorize mixing zone
provisions and methodologies for calculating mixing zones for later application to
NPDES point source discharge points.
5.3.2 How does a mixing zone apply for the fish tissue-based
methylmercury criterion?
The question of mixing zones is not relevant when applying the fish tissue-based
criterion, which refers to the level of mercury found in fish flesh. The criterion is fish
tissue-based, not water column-based. The criterion reflects the exposure of the fish to
mercury in the water column and food over the life of the fish, and thus it reflects an
integration of the exposure over time and over spatially varying water column
concentrations. The total load of mercury in the waterbody, taking into account the
methylation rate and bioaccumulation of mercury in fish, affects the level of
methylmercury in the fish tissue.
Some states and authorized tribes, however, might choose to adopt a water column
criterion based on the fish tissue criterion and thus have a criterion for which a mixing
zone might apply. In this situation, a state or authorized tribe should follow its existing
procedures for determining appropriate mixing zones. EPA advises caution in the use of
mixing zones for mercury. While fish tissue contamination tends to be a far field problem
affecting entire waterbodies, rather than a narrow scale problem confined to mixing
zones, EPA's guidance recommends restricting or eliminating mixing zones for
bioaccumulative pollutants such as mercury so that they do not encroach on areas often
used for fish harvesting (particularly for stationary species such as shellfish). Restriction
or elimination might also be used to compensate for uncertainties regarding the ability of
aquatic life or the aquatic system to tolerate excursions above the criteria, uncertainties
inherent in estimating bioaccumulation, or uncertainties in the assimilative capacity of the
waterbody. See the Water Quality Standards Handbook, section 5.1.3 (USEPA 1994).
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5.3.3 Does the guidance for the fish tissue-based criterion change
the Great Lakes Initiative approach to mixing zones for
bioaccumulative pollutants?
To reduce the adverse effects from bioaccumulative chemicals of concern (BCCs) in the
Great Lakes, on November 13, 2000, EPA promulgated an amendment to the Final Water
Quality Guidance for the Great Lakes System (40 CFRpart 132, appendix F, procedure
3). The regulation requires prohibition of mixing zones for bioaccumulative pollutants
from existing discharges in the Great Lakes to the greatest extent technically and
economically feasible. Specifically, existing discharges of BCCs are not eligible for a
mixing zone after November 10, 2010 (although under certain circumstances mixing
zones may be authorized). For new BCC discharges, the rule essentially prohibits mixing
zones of bioaccumulatives immediately upon commencing discharge. This means that
NPDES permit limitations for mercury discharged to the Great Lakes system must not
exceed the water quality criterion. This also limits the flexibility that states and
authorized tribes would otherwise have to adjust point source controls on the basis of
nonpoint source contributions.
EPA reiterates that the new methylmercury criterion, and EPA's recommendations on its
implementation, does not supersede the requirements applicable to the Great Lakes at 40
CFR part 132. The criteria for the Great Lakes are water column-based, and therefore
they can be applied as an effluent requirement at the end of a pipe. EPA continues to
view the prohibition of a mixing zone for mercury and other bioaccumulative pollutants
for the Great Lakes as appropriately protective for water column-based water quality
criteria applied to these waters.
If a state or authorized tribe adopts the new fish tissue-based criterion for a Great Lake or
tributary to the Great Lake, the state or tribe would do this using the site-specific
modification procedures of part 132 (see section 5.1 of this document). The state ortribe
would have determined a site-specific BAF in this process and therefore would have the
means for calculating a water column-based criterion. Under the part 132 regulations,
EPA in its review of the new state or tribal implementation procedures would determine
whether they are as protective as the Great Lakes procedures for human health protection
(40 CFR 132.5(g)(3)). Specifically, EPA would determine whether the implementation
procedures are as protective as applying the table 3 (in 40 CFRpart 132) criterion for
protection of human health without a mixing zone, consistent with the prohibition on
mixing zones for BCCs (40 CFR 132, appendix F.3.C.). In addition, if the state's or
tribe's implementation procedures involve converting the fish tissue-based criterion into
an equivalent water column-based number, the mixing zone prohibition requirements of
40 CFR part 132 still apply.
-..• :r: -• ,-, ...:: „ " •. i::1 :./•-.
5.4.1 What is the role of state and tribal Fish Advisory Programs?
States and authorized tribes have the primary responsibility of estimating the human
health risks from the consumption of chemically contaminated, noncommercially caught
finfish and shellfish (e.g., where water quality standards are not attained). They do this by
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issuing consumption advisories for the general population, including recreational and
subsistence fishers, and for sensitive subpopulations (such as pregnant women, nursing
mothers and their infants, and children). These advisories are nonregulatory and inform
the public that high concentrations of chemical contaminants, such as mercury, have been
found in local fish. The advisories recommend either limiting or avoiding consumption of
certain fish from specific waterbodies or, in some cases, from specific waterbody types
(e.g., all lakes). In the case of mercury, many states and authorized tribes have calculated
a consumption limit to determine the maximum number offish meals per unit of time that
the target population can safely eat from a defined area.
5.4.2 How are consumption limits for consumption advisories
determined?
EPA has published guidance for states and authorized tribes to use in deriving their
recommended fish consumption limits, titled Guidance for Assessing Chemical
Contaminant Data for Use in Fish Advisories, volumes 1 and 2 (USEPA 2000c, 2000f).
This guidance describes the two main equations necessary to derive meal consumption
limits on the basis of the methylmercury RfD. Basically, the first equation is used to
calculate the daily consumption limits of grams of edible fish (in g/day); a second
equation is used to convert daily consumption limits to meal consumption limits over a
specified period of time. Variables used to calculate the advisory consumption limits
include fish meal size and frequency, consumer body weight, contaminant concentration
in the fish tissue, the time-averaging period selected, and the reference dose for
methylmercury health endpoints.
In the absence of site-specific fish consumption data, EPA recommends using a fish
consumption rate of 17.5 grams/day offish (uncooked) eaten from the local water as a
screening level. This consumption rate equates to approximately two 8-ounce meals per
month. Using this consumption rate, and assuming a 70-kg body weight (the same
assumption used to derive the methylmercury criterion), the concentration of
methylmercury in locally caught fish that would result in exposures that do not exceed
the RfD (0.0001 mg/kg-day) is about 0.4 mg/kg and lower ([0.001 mg/kg-day x 70 kg
bw]/0.0175 kg fish/day). This means that you can safely consume approximately two 8-
ounce meals per month of locally-caught fish, where concentrations in such fish are 0.4
mg/kg or lower, and where there is no additional exposure (i.e., consumption of store
bought or marine-caught fish).
Advisory limits can differ from one state or tribe to another. This inconsistency is due to
a host of reasons, some of which speak to the flexibility states and authorized tribes have
to use different assumptions (chemical concentrations, exposure scenarios and
assumptions) to determine the necessity for issuing an advisory. The nonregulatory nature
offish advisories allows such agencies to choose the risk level deemed appropriate to
more accurately reflect local fishing habits or to safely protect certain subpopulations
(e.g., subsistence fishers).
5.4.3 How does the criterion differ from the advisory level?
Although EPA derived its recommended screening value for a fish advisory limit for
mercury and human health methylmercury criterion from virtually identical
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methodologies, it is important to clarify the distinctions between the two values. They are
consistently derived, but because each value differs in purpose and scope, they diverge at
the risk management level. Fish advisories are intended to inform the public about how
much consumers should limit their intake of individual fish species from certain
waterbodies. Alternatively, the Agency uses its methylmercury criterion, like other CWA
section 304(a) criteria, as a basis for both nonregulatory and regulatory decisions. The
criterion can serve as guidance to states and authorized tribes for use in establishing water
quality standards, which, in turn, serve as a benchmark for attainment, compliance, and
enforcement purposes.
The main risk management difference between EPA's recommended methylmercury
water quality criterion and the fish advisory default screening value for mercury is that
the criterion includes an RSC19 and the screening value does not. In deriving the
criterion, EPA assumed an RSC value of 2.7xlO~5 mg/kg-day to account for exposure
from marine fish and shellfish. The guidance for setting fish consumption limits also
discusses using an RSC to account for exposures other than those from noncommercially
caught fish, but the guidance may be applied without using an RSC. The RSC guidance
in the 2000 Human Health Methodology (USEPA 2000b) provides more detail and
specific quantitative procedures to account for other exposure pathways. EPA's advisory
guidance recommends that states and authorized tribes consider using an RSC to account
for exposure from other sources of pollutants (such as mercury) when deriving a fish
consumption limit and setting a fish advisory for mercury.
5.4.4 What if there is a difference between assessing criterion
attainment and issuance of a fish consumption advisory?
In many states and authorized tribes, numeric water quality criteria and fish and shellfish
consumption limits differ because of inherent differences in the technical and risk
assumptions used to develop them. As discussed in section 4.2, EPA considers a fish
consumption advisory to demonstrate nonattainment of water quality standards when the
advisory is based on tissue data, the data are from the specific waterbody in question, and
the risk assessment parameters of the advisory or classification are cumulatively equal to
or less protective than those in the water quality standards. Two situations in which the
presence of an advisory might not imply an exceedance of the water quality standard
(USEPA 2005f) are as follows:
• Statewide or regional advisory. States have issued statewide or regional warnings
regarding fish tissue contaminated with mercury, on the basis of data from a subset
of waterbodies, as a precautionary measure. In these cases, fish consumption
advisories might not demonstrate that a CWA section 101(a) "fishable" use is not
being attained in an individual waterbody and might not be appropriate for
determining attainment based on exceedance of water quality criteria.
• Local advisory. States have issued local advisories using a higher fish consumption
value than that which they use in establishing water quality criteria for protection
of human health. Again, in this case the fish consumption advisories might not
See discussion on the RSC in section 3.1.2.3 and 3.2.1.1.
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demonstrate that a section 101(a) "fishable" use is not being attained in an
individual waterbody and might not be as appropriate as comparison with water
quality criteria as a basis for determining attainment.
For example, consider a state or authorized tribe that adopts EPA's methylmercury
criterion of 0.3 mg/kg, which is based on eating approximately two 8-ounce fish meals a
month. If the state or authorized tribe finds that a waterbody has fish with a mercury level
of 0.2 mg/kg, this water would not be exceeding the water quality criterion. Yet, this
mercury concentration is sufficient for the state or authorized tribe to issue a fish
consumption advisory recommending that people eat no more than four 8-ounce meals a
month. In this case, because the fish consumption advisory uses a higher fish
consumption value than that used to develop the water quality criterion (and the fish
tissue concentration does not exceed the criterion), consistent with EPA's 2000 guidance,
the waterbody is not necessarily impaired (USEPA 2005f).
In the case where a local advisory is based on a higher fish consumption value which is
considered representative of local consumption, the state or authorized tribe should
consider whether it should adopt a site-specific criterion for the waterbody. A local
advisory generally reflects actual contaminant monitoring data and may reflect local fish
consumption patterns, and it might identify more representative fish species. The
information gathered in developing the advisory might provide valid grounds for revising
the level of a numeric water quality criterion to match that of the advisory.
5.4.5 Should existing advisories be revised to reflect the new
criterion?
Although EPA's screening value for fish advisory studies and the recommended 304(a)
criterion for mercury are based on similar methodologies and are intended to protect
people who consume mercury-contaminated fish, they do not necessarily have to be the
same value. As explained above, each limit is predicated on different risk-management
decisions and thus incorporates different assumptions. However, recognizing that
differences in consumption advisories and waterbody impairment for the methylmercury
criterion can be confusing to the public, states may wish to consider explaining the
differences in the information that these two types of listings provide. Likewise, there is
merit in adopting a site-specific methylmercury criterion on the basis of a local fish
advisory, if that advisory is supported by sufficient fish tissue and fish consumption data
that are representative and of acceptable quality. Alternatively, states may wish to
consider issuing a fish consumption advisory, where appropriate, if a waterbody is
considered impaired based on the methylmercury 304(a) criterion and no such
consumption warning exists.
5.4.6 What federal agencies issue advisories?
The Food and Drug Administration's (FDA's) mission is to protect the public health with
respect to levels of chemical contaminants in all foods, including fish and shellfish, sold
in interstate commerce. To address the levels of contamination in foods, FDA has
developed both action levels and tolerances. An action level is an administrative
guideline that defines the extent of contamination at which FDA may regard food as
adulterated and represents the limit at or above which FDA may take legal action to
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remove products from the marketplace. It is important to emphasize that FDA's
jurisdiction in setting action levels is limited to contaminants in food shipped and
marketed in interstate commerce; it does not include food that is caught locally by
recreational or subsistence fishers. FDA also issues fish consumption advice on fish and
shellfish sold in commerce in cases where contaminants have been detected at levels that
may pose public health concerns for some consumers.
As described in section 5.4.2, EPA provides guidance to states, tribes, local governments
and others on scientifically sound, cost-effective methods for developing and managing
noncommercial fish consumption advisories on local waters. See EPA's Guidance for
Assessing Chemical Contaminant Data for Use in Fish Advisories (USEPA 2000c,
2000f). In addition, EPA has issued advice under CWA section 104(b)(6) to supplement
state and/or tribal advice on local waters.
In March 2004, EPA and FDA issued a joint national fish advisory about mercury in fish
and shellfish. The purpose of the advisory is to inform women who may become
pregnant, pregnant women, nursing mothers, and parents of young children how to get
the positive health benefits from eating fish and be confident that they have reduced their
exposure to the harmful effects of mercury. The 2004 advisory lists fish sold in interstate
commerce that are known to be high in mercury as well as fish that that are low in
mercury to help consumers choose the most appropriate fish. The advisory also contains
recommendations about eating fish harvested from local waters where no advice has been
provided by state or tribal authorities. Information regarding the national advisory is at
http://www.epa.gov/waterscience/fish/.
5.4.7 How is the criterion related to FDA action levels?
The current FDA action level for mercury in fish is 1 mg/kg. Generally, an action level is
different from a fish advisory limit—and even more different from a CWA section 304(a)
criterion. FDA action levels are intended for members of the general population who
consume fish and shellfish typically purchased in supermarkets or fish markets that sell
products harvested from a wide geographic area. The underlying assumptions used in the
FDA methodology were never intended, as local fish advisories are, to be protective of
recreational, tribal, ethnic, and subsistence fishers who typically consume fish and
shellfish from the same local waterbodies repeatedly over many years. EPA and FDA
have agreed that the use of FDA action levels for the purposes of making local advisory
determinations is inappropriate. Furthermore, it is EPA's belief that FDA action levels
and tolerances should not be used as a basis for establishing a state's or tribe's
methylmercury criterion.
- .- '•; r. .. • ',. : '
By applicable regulations, water quality standards, TMDL, and NPDES permit decisions
require public notice and the opportunity for the public to comment on tentative
decisions. Some public interest groups might have an interest in decisions related to
mercury, especially in areas where local citizens rely heavily on locally caught fish as a
food source. EPA recommends that organizations with an interest in environmental
justice issues be included in the public notice.
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TMDLs
6 TMDLs
••-.•: - ?
CWA section 303(d)(l) and EPA's implementing regulations require states and
authorized tribes to identify and establish priority rankings for waters that do not, or are
not expected to, achieve or maintain water quality standards with existing or anticipated
required controls. This list is known as the state's or tribe's list of "impaired"
waterbodies or 303(d) list. States and authorized tribes then must establish TMDLs for
the impaired waterbodies.
A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can
receive and still meet water quality standards. A TMDL also allocates the pollutant loads
among the contributing sources, both point and nonpoint. The TMDL calculation must
include a margin of safety to take into account any uncertainty in the TMDL calculation
and must account for seasonal variation in water quality. The current statutory and
regulatory framework governing TMDLs includes CWA section 303(d) and the TMDL
regulations published in 1985 at 40 CFR 130.2 and 130.7 and amended in 1992 (see 50
FR 1774 (Jan. 11, 1985); 57 FR 33040 (July 24, 1992)).
As of the 2008 303(d) listing cycle, 43 states and Puerto Rico reported at least one
waterbody as impaired due to mercury, and more than 8,800 specific waterbodies were
listed as impaired due to mercury, either solely or in combination with other pollutants.
As mentioned previously in section 2.4, with the implementation of the new
methylmercury fish tissue criterion, monitoring of previously unmonitored waterbodies,
and use of more sensitive analytical methods, EPA expects that the number of
waterbodies listed as impaired due to mercury might increase.
'-'. ' • • •- • .- s -.- •'•' '; • s • • •:•.' :; ":
Developing TMDLs for waters impaired by mercury raises a number of technical and
policy issues. For example, air deposition is the predominant source of mercury to many
waterbodies, especially in the eastern United States. The mercury deposited from air
comes from local, regional, and international sources, and identifying how each of these
sources contributes to the mercury load in the waterbody is challenging. In other
waterbodies, significant loadings might come from other sources, such as past metal-
mining activity or geologic sources. Frequently, states and authorized tribes do not have
the authority to address all the sources that contribute mercury to their waterbodies and
rely on efforts conducted under a variety of programs, such as regulations under the
CAA, pollution prevention programs, and international efforts to reduce releases and
emissions from mercury sources. States and EPA have found that, in many cases, it is
important to coordinate closely with programs other than those under the CWA to
address these mercury sources.
Given these challenges, EPA is working with states, tribes, and stakeholders to determine
how best to use TMDLs and the 303(d) listing process to provide a basis for reducing
mercury releases to water, including consideration of air deposition, to meet applicable
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TMDLs
water quality standards and CWA goals. In areas where large numbers of waterbodies are
impaired due to mercury derived from air deposition, some states have begun to explore
ways to address mercury impairments efficiently, such as through development of
TMDLs on various geographic scales. As of April 2010, mercury TMDLs have been
approved for more than 6,700 waterbodies, including a "statewide" mercury TMDL in
Minnesota and a multi-state mercury TMDL for the Northeast states (see below).
On March 8, 2007, EPA issued a memorandum describing a voluntary approach for
listing waters impaired by atmospheric mercury under CWA section 303(d) and
managing the development of mercury TMDLs. (USEPA 2007)
(http://www.epa.gov/owow/tmdl/mercurv5m/Mercury5m.pdf). EPA recommends this
approach for states that have in place a comprehensive statewide mercury reduction
program with elements recommended by EPA. These states may separate their waters
impaired by mercury predominantly from atmospheric sources in a subcategory of their
impaired waters list ("5m") and defer the development of TMDLs for those waters. A
state using the 5m subcategory may continue to defer the development of mercury
TMDLs where the state demonstrates continuing progress in reducing in-state mercury
sources. Recommended elements of a mercury reduction program include identification
of air and multimedia sources within a state and programs to address those sources;
mercury reduction goals and target dates; multimedia monitoring; public reporting on the
state's mercury reduction efforts; and multistate coordination. The 5m subcategory is
intended to recognize states with comprehensive mercury programs and to allow states to
focus on early implementation actions.
Because the 5m subcategory is focused primarily on waterbodies impaired by mercury
from air deposition, EPA recommends that the 5m subcategory include waters where the
proportion of mercury from air deposition is high compared to other mercury sources. In
the 5m memorandum, EPA recommends that states describe how such waterbodies were
identified. Such information will help determine whether the 5m approach is appropriate.
EPA also believes that, as the relative contribution to a waterbody from sources other
than air deposition increases, such as water point sources, it may be more appropriate to
use the TMDL process to characterize and address those sources sooner, rather than
deferring TMDL development. As stated in the 5m memorandum, states have the option
to continue developing mercury TMDLs sooner, whether or not they place waterbodies in
subcategory 5m.
On September 29, 2008, EPA issued a document titled Elements of Mercury TMDLs
Where Mercury Loadings Are Predominantly from Air Deposition, to assist states, EPA
regional staff, and other stakeholders in identifying approaches for the development of
mercury TMDLs (USEPA 2008a). Compiled in a checklist format, approaches described
in the document are drawn largely from approaches and best practices used in approved
mercury TMDLs. The checklist summarizes considerations in addressing the required
and recommended TMDL elements described in the Guidelines for Reviewing TMDLs
under Existing Regulations Issued in 1992 (USEPA 2002f) when developing mercury
TMDLs on geographic scales ranging from waterbody-specific to multi-state.
While the checklist is based on existing guidance for reviewing TMDLs, this guidance
document supplements the checklist by providing additional information and case studies
on approaches that have been used in approved mercury TMDLs to date, and examples of
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technical tools available to assist in mercury TMDL development. Technical tools
available to assist in the development of mercury TMDLs include screening-level
analyses of mercury loadings and sources using the Mercury Maps tool and more
complex water and air models. Many of these tools are discussed in the sections below.
EPA recommends that states continue to develop TMDLs for mercury-impaired waters
where appropriate, taking into account the considerations and approaches described in
this guidance. States may also consider using the 5m subcategory for waters impaired by
mercury predominantly from air deposition if the state has a comprehensive mercury
reduction program as described in the 5m memorandum.
6.2.1 What geographic scales have been used for mercury TMDLs?
Many mercury TMDLs approved to date were developed on a waterbody-specific basis.
They include some of the first approved mercury TMDLs, such as those developed for
waterbodies in middle and south Georgia. Other examples include TMDLs developed for
waterbodies in Louisiana, such as the Ouachita River, the Narraguinnup and McPhee
reservoirs in Colorado, and Pena Blanca and Arivaca lakes in Arizona. Various aspects of
these TMDLs are described further in appendix D.
In areas of the country where many waterbodies are listed as impaired due to mercury
primarily from atmospheric sources, some states have begun to explore the development
of mercury TMDLs on a watershed scale or on the basis of a large geographic area, such
as a state or region. One example of a regional or grouped approach is the mercury
TMDL for the Coastal Bays and Gulf Waters of Louisiana, approved in June 2005. The
TMDL covers six segments of coastal Louisiana. Because of the large geographic extent
of mercury in the coastal waters and the similar extent of mercury contributions from air
deposition, the TMDL was developed on a watershed basis rather than waterbody by
waterbody. The TMDL used air deposition modeling results from the Regional Modeling
System for Aerosols and Deposition (REMSAD) to estimate wet and dry deposition of
mercury for the six segments. The air deposition modeling results, in turn, were used to
model runoff or nonpoint source mercury loadings. As described in the following section,
mercury loadings can include direct deposition to waterbodies and deposition to the
watershed that is subsequently transported to the waterbody via runoff and erosion.
Additional information on this TMDL can be found on EPA's TMDL webpage at
http://iaspub.epa. gov/tmdl/waters list.tmdl report?p tmdl id= 11642.
A "statewide" mercury TMDL developed by Minnesota was approved by EPA on
March 27, 2007. The TMDL report covers 998 mercury impairments and is the first
approved mercury TMDL covering such a large number of waterbodies and large
geographic area. (Note: Although called statewide, the TMDL does not cover all
mercury-impaired waterbodies in the state.) Minnesota used a statewide approach
because the predominant mercury source in those waterbodies—air deposition—is
relatively uniform across the state. The final TMDL report includes two TMDLs—one
for the northeast region of the state and the other for the southwest region of the state.
Waterbodies were grouped into the two regions on the basis of differences in fish tissue
concentrations, with higher fish mercury concentrations in the northeast region compared
to the southwest region. The difference in mercury concentrations is thought to be due to
the effect of land use and other factors on the methylation of mercury. For example, the
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TMDLs
northeast region is dominated by wetlands, where mercury tends to be methylated more
readily; the southwest is dominated by cultivated lands. A summary of the Minnesota
mercury TMDL approach is provided in appendix D, and the allocation approach is
described further below. The final TMDL and EPA decision document are at
http://www.pca.state.mn.us/water/tmdl/tmdl-ercurvplan.htmltfapproval.
On December 20, 2007, EPA approved the Northeast Regional Mercury TMDL
covering waterbodies in Connecticut, Maine, Massachusetts, New Hampshire, New York,
Rhode Island and Vermont. In using a regional approach, the TMDL document provides
aggregate wasteload allocations and load allocations for the region. The regional
approach was based on an analysis of data showing similar levels of mercury in fish
throughout waterbodies in the region, and the states' finding that air deposition is the
predominant mercury source. The TMDL document focuses on waters impaired by
mercury primarily from atmospheric sources; it excludes coastal and marine waters and
a few areas of high localized deposition and high fish mercury levels. The number of
individual waterbodies covered by the regional TMDL document amounts to over
5,300 (the specific number of waterbodies covered by the TMDL document vary from
state to state and are cited in EPA's approval documents). The TMDL target is EPA's
recommended fish tissue criterion of 0.3 ppm methylmercury for each of the states
except for Connecticut and Maine, where the targets are 0.1 ppm and 0.2 ppm,
respectively. The TMDL allocates approximately 2.0 percent of the loading capacity
to point sources and 98 percent to nonpoint sources (predominantly atmospheric
deposition). The TMDL assumes that most of the reductions would need to come
from atmospheric sources. The Northeast Regional Mercury TMDL are at
http://www.epa.gov/regionl/eco/tmdl/assets/pdfs/ne/Northeast-Regional-Mercury-
TMDL.pdf. and the EPA approval documents for each of the states are at
http://www.epa.gov/regionl/eco/tmdl/approved.html.
6.2.2 What are the considerations in developing mercury TMDLs?
A TMDL must identify the applicable water quality standards for each listed segment and
identify the loading capacity of a water (40 CFR 130.2). In addition, a TMDL must
allocate the pollutant loads among the sources, both point and nonpoint (40 CFR
130.2(i)). EPA guidance further notes that a TMDL should identify the pollutant sources,
both point and nonpoint, including the location of the sources and quantity of the loading.
Where feasible, states are encouraged to consider waterbodies affecting disadvantaged
communities and tribal issuses in setting priorities for TMDL development. Some of the
considerations in developing a mercury TMDL and approaches used in approved mercury
TMDLs are described in more detail in the text below.
6.2.2.1 What are potential mercury sources to waterbodies?
An important step in TMDL development is an evaluation of the loadings from various
sources. The potential sources of mercury to waterbodies include the following: (1) direct
discharges of mercury from water point sources, including industrial dischargers and
wastewater treatment plants; (2) atmospheric deposition, including direct deposition to
the waterbody surface and deposition to the watershed, which subsequently is transported
to the waterbody via runoff and erosion, including via stormwater; (3) runoff, ground
water flow, acid mine drainage, and erosion from mining sites or mining wastes, and
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other waste disposal sites such as landfills and land application units; (4) sediments,
which might have mercury contamination or hot spots resulting from past discharges; and
(5) "naturally occurring" mercury in soils and geologic materials. Sediments containing
mercury from past discharges might continue to contribute mercury to the overlying
waterbody. Further discussion of each of these types of sources follows.
Point sources. Point source discharges of mercury include POTWs, electric utilities, and
other industrial facilities. Sources of data on point source discharges of mercury include
the Permit Compliance System, as well as a study of domestic mercury sources by the
Association of Metropolitan Sewerage Agencies (AMSA 2000), now called the National
Association of Clean Water Agencies (NACWA). Without accurate discharge data, a
sample of a representative portion of dischargers has been used in mercury TMDLs to
estimate the mercury discharges from point sources. In addition, some point source
dischargers, such as chlor-alkali plants and POTWs, might have permits requiring
monitoring for mercury, although most dischargers, especially smaller dischargers, are
not likely to have such monitoring requirements. NPDES-permitted stormwater sources
might also include mercury discharges, which in turn might include mercury originating
from atmospheric deposition.
Atmospheric deposition. Deposition of mercury from the air can be a significant source
of mercury in many waterbodies. Some waterbodies have been identified as receiving as
much as 99 percent of their total loading from atmospheric deposition, either directly or
indirectly via runoff and erosion. (See Ochlockonee, Georgia, TMDL in appendix D.)
The mercury in atmospheric deposition originates from anthropogenic sources, including
U.S. and international sources, as well as natural sources. Examples of specific
anthropogenic sources that emit mercury to the air include medical and municipal waste
incinerators, electric utilities, chlor-alkali plants, and active metals mining, among others.
Mercury is emitted to the air in several chemical forms or species. Common
measurements of mercury in air differentiate between reactive gaseous mercury (ROM),
elemental mercury (Hg°), and participate mercury (Hgp). Some chemical forms of
mercury emissions to air deposit relatively close to their sources, while others are
transported over longer distances and even globally. The mix of chemical forms or
species emitted from a given source determines what fraction of the mercury from that
source is depositing locally and what proportion is transported over longer distances,
making the task of identifying sources of deposition to a waterbody challenging. At any
given location, the mercury deposited from air can originate from several sources.
Figure 3 depicts the current understanding of deposition from U.S. and international
sources. It shows that in many parts of the United States, the source of deposited mercury
is not a U.S. source.
Of the approved mercury TMDLs involving atmospheric loadings, most have
characterized the contributions from air deposition in terms of total or aggregate loadings.
Atmospheric mercury loadings include both direct deposition to the waterbody surface
and indirect deposition to the watershed. Indirect deposition is that which is deposited to
the watershed and then transported to the waterbody via runoff and erosion. Atmospheric
mercury loadings include both wet and dry deposition of mercury.
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It is important to use the most current information about deposition because U.S. mercury
emissions into the air have decreased over time. Older data on deposition might not
reflect current deposition conditions. For example, figure 4 depicts a summary of U.S.
mercury air emissions between 1990 and 2005 and shows a 58 percent overall decrease.
95.000112
January 1,0 0:00 00
Mln- 14.076 at(21,84^ Max- 99.985*1(148,1)
Figure 3. Percentage of total mercury deposition attributable to global sources
(USEPA 2005a).
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Exhibit 2-39. Mercury emissions in the U.S. by source category,
1990-1993, 2002, and 2005a-b
250
200
£. 150
I
t/3
E
100
50
r
Industrial processes
DGold mining
D Hazardous waste incineration
D Electric arc furnaces
D Chlorine production
n Medical waste incinerators
D Municipal waste combustors
D Other industrial processes
Fuel combustion
D Industrial, commercial, and
institutional boilers
D Utility coal boilers
1990-1993
2002
Year
2005
d1990-1993 is considered the baseline period for mercury emissions. The baseline period
spans multiple years due to the availability of emissions data for various source
categories. The data presented for the baseline period are annual emissions (tons per
year) and are therefore comparable to the 2002 and 2005 data.
bMercury emissions from mobile sources are not depicted because they have been
estimated only for inventory years 2002 (0.8 tons) and 2005 (1.1 tons), not for the
baseline period.
Data source: U.S. EPA, 2009
Figure 4. Trends in mercury air emissions between 1990 and 2005 (USEPA 2008b).
Additional decreases in mercury air emissions may have occurred since 2005 as the result
of EPA's regulatory efforts under the CAA. At the same time, however, global emissions
might have increased.
The 2005 National Emissions Inventory (NEI) is EPA's latest comprehensive national
emission inventory. It contains emission measurements and estimates for 7 criteria
pollutants and 188 hazardous air pollutants (HAPs). The NEI contains emissions for all
major contributors to air pollution, including point sources (large industrial sources such
as electric utilities and petroleum refineries), mobile sources (both onroad sources such as
cars and trucks and nonroad engines such as those in construction equipment and
agricultural equipment), and nonpoint sources (small stationary sources such as
residential fuel use and various types of fires). The NEI includes emission estimates for
the entire United States. For point sources, the NEI inventories emissions for each
individual process at an industrial facility. For mobile and nonpoint sources, the NEI
contains county-level emission estimates. The NEI is developed using the latest data and
best estimation methods, including data from Continuous Emissions Monitors; data
collected from all 50 states, as well as many local and tribal air agencies; and data
generated using EPA's latest models such as the MOBILE and NONROAD models.
More information on the 2005 NEI is at
http://www.epa.gov/ttn/chief/net/2005inventory.html.
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Some approved mercury TMDLs have identified the types or categories of sources likely to
contribute to mercury deposition in a waterbody. An example of this type of source analysis
is included in the Savannah River mercury TMDLs issued February 28, 2001, and a series
of mercury TMDLs issued February 28, 2002, for a number of watersheds in middle and
south Georgia (see http://gaepd.org/Documents/TMDL_page.html). These TMDLs
included an analysis of the categories of air sources contributing deposition to the
waterbodies and the reductions in loadings expected from controls in place when the
TMDL was approved. To estimate the total contributions from air deposition, data from
the Mercury Deposition Network (MDN) were used. Modelers also used the existing
Regional Langrangian Model of Air Pollution (RELMAP) deposition results developed
for the 1997 Mercury Report to Congress to estimate the relative contributions from local
sources within a 100-kilometer airshed.
EPA has evaluated water and air deposition modeling tools as part of two mercury
TMDL pilot projects in Wisconsin and Florida. In particular, the pilots examined
approaches for combining the results of air deposition and water quality modeling, which
in turn might be used in a TMDL context. In the Florida pilot, air modelers used a
combination of modeling tools to predict the amount of mercury deposition to the study
area from local sources in southern Florida. Using the Mercury Cycling Model, aquatic
modelers then used results from the atmospheric modeling and other data to examine how
mercury levels in fish might respond to reductions in deposition. The Florida pilot report
is complete (see ftp://ftp.dep.state.fl.us/pub/labs/assessment/mercurv/tmdlreport03.pdf)
(Atkeson et al. 2002).
In the Wisconsin pilot project, EPA evaluated modeling tools such as the Regional
Modeling System for Aerosols and Deposition (REMSAD) for identifying the sources or
categories of sources contributing mercury deposition to a waterbody, as well as how to
use the deposition results as input to aquatic models, similar to the approach used in the
Florida pilot. REMSAD is a three-dimensional grid model designed to calculate the
concentrations of both inert and chemically reactive pollutants by simulating the physical
and chemical processes in the atmosphere that affect pollutant concentrations (ICF
International 2006). REMSAD simulates both wet and dry deposition of mercury. (See
appendix E for further information on REMSAD.) In the Wisconsin pilot, the results of
the air deposition modeling were used as input to the Mercury Cycling Model to examine
how mercury levels in fish might respond to potential changes in deposition.
Other TMDLs in which the results of REMSAD modeling were used include the mercury
TMDL for the Coastal Bays and Gulf Waters of Louisiana approved in 2005. The results
of earlier air modeling for the Mercury Study Report to Congress were used in the
mercury TMDLs for middle and south Georgia approved in 2002 (see Ochlockonee
TMDL in appendix D). EPA plans to provide each state or authorized tribe with modeled
estimates of mercury deposition from sources within the state or on the tribal land and
contributions from sources outside the state or tribe. The modeling results will help EPA
and the states and authorized tribes develop TMDLs and determine the appropriate
strategies for addressing mercury deposition from sources within their jurisdictions.
Additional tools available for determining mercury deposition loadings include the
Community Multi-Scale Air Quality (CMAQ) model. The CMAQ modeling system is a
comprehensive, three-dimensional, grid-based Eulerian air quality model designed to
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estimate pollutant concentrations and depositions over large spatial scales (Dennis et al.
1996; Byun and Ching 1999; Byun and Schere 2006). The CMAQ model is a publicly
available, peer-reviewed, state-of-the-science model with a number of science attributes
that are critical for simulating the oxidant precursors and nonlinear chemical relationships
associated with mercury formation. Version 4.3 of CMAQ (Bullock and Brehme 2002;
Byun and Schere 2006) reflects updates to earlier versions in a number of areas to
improve the underlying science and address comments from peer review. Further
information on the CMAQ model is provided in appendix E.
As with any analysis based on limited data, uncertainty is inherent in the estimates of all
analytical outputs of modeling. Model uncertainty results from the fact that models and
their mathematical expressions are simplifications of reality used to approximate
real-world conditions, processes, and their relationships. Models do not include all
parameters or equations necessary to express real-world conditions because of the
inherent complexity of the natural environment and the lack of sufficient data to describe
the natural environment. Consequently, models are based on numerous assumptions and
simplifications and reflect an incomplete understanding of natural processes. As a result,
there will be some uncertainty when using models to quantify the sources of air-deposited
mercury.
Other tools available to help states characterize mercury deposition include existing
national monitoring networks and modeling tools, such as the MDN. Examples of these
tools are provided in appendix F. Published results of national modeling studies could
also be available to help estimate atmospheric deposition loadings. Further information
on tools and approaches for characterizing atmospheric deposition to waterbodies can be
found in the Frequently Asked Questions about Atmospheric Deposition section of
EPA's Web site at http://www.epa.gov/oar/oaqps/gr8water/handbook/.
An analysis of deposition should take into account both direct deposition to the
waterbody, as well as mercury deposited within the watershed (indirect deposition). In
addition, fires, flooding, and other landscape disturbances could re-mobilize mercury
previously deposited within the watershed and cause an increase in mercury transported
to the waterbody. Studies are underway to examine the extent to which mercury
deposited to a watershed is transported to a waterbody. For example, the Mercury
Experiment to Assess Atmospheric Loading in Canada and the United States
(METAALICUS) project is a mercury loading experiment to examine the timing and
magnitude of the relationship between mercury loading to ecosystems and mercury
concentrations in fish (Harris et al. 2006). Using stable mercury isotopes, researchers are
examining the fate of mercury deposited to uplands, wetlands, and directly to lakes. It is
being carried out at the Experimental Lakes Area (ELA) in northwestern Ontario by U.S.
and Canadian researchers. A discussion of factors affecting mercury transport and
bioavailability is included in chapter 2 of this guidance.
As part of a source evaluation, EPA encourages states to conduct a careful analysis to
verify and quantify the contributions of air deposition as compared to other sources. Such
information is important for determining the appropriate management approaches. For
example, an analysis of the contribution from air sources is the basis for determining
whether it may be appropriate to defer TMDLs under the 5m approach, or whether it is
more appropriate to develop TMDLs to address significant local sources.
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Although not required for a TMDL, states may wish to examine the contributions to the
watershed from local air sources within the state as compared to out-of-state sources.
Such information provides a basis for determining the appropriate allocations. In turn,
such source information can help to develop a meaningful TMDL implementation plan
and identify the extent to which state and local programs may be appropriate for
addressing the mercury sources.
Metals mining activity. Loadings from metals mining activities might reflect both
historical and recent mining activity within the watershed. Mining areas of interest are
those involving "placer" deposits, in which mercury itself is present in the ore, or those
deposits for which mercury is used to extract other metals such as gold. For example,
sulfide replacement deposits are often associated with mercury. Locations at mining sites
that might serve as sources of mercury include direct seeps, as well as leachate from
tailings or spoil piles. In the Clear Lake TMDL (see appendix E), ground water from an
abandoned mining site was reported to contain mercury that is readily methylated. In
Clear Lake, acid mine drainage was found to contain high sulfate concentrations, which
might enhance methylation by sulfate-reducing bacteria. Sources of data on potential
mercury deposits associated with mining activity include USGS, the U.S. Bureau of
Mines (for a list of major deposits of gold and silver), the State Inactive Mine Inventory,
and the EPA Superfund program. Examples of TMDLs involving mercury associated
with mining are provided in appendix E.
Sediments. A TMDL analysis should account for any mercury present in sediments as a
result of current and past mercury loadings. Mercury in sediments may be the result of
past metals mining activity as described above, past industrial activity, and historical air
deposition. Data on levels of mercury in sediments are important in determining which
sources are most significant, the most appropriate approach for addressing the sources
and how long it will take to achieve water quality standards. For example, development
of appropriate allocations, and in turn development of management strategies, may need
to address both current sources of deposition as well as legacy sources. An examination
of past industrial practices in the watershed could include whether sediments might serve
as a reservoir for mercury. Various national databases, such as the National Sediments
Database (USEPA 2002g) and data collected by USGS might help to identify isolated
locations of elevated mercury in sediments. EPA has also developed a detailed guide on
sediment source analysis in the first edition of Protocol for Developing Sediment TMDLs:
http://www.epa.gov/owow/tmdl/sediment/pdf/sediment.pdf
In the absence of sediment data for a waterbody, site-specific monitoring might be
needed to confirm the levels of mercury in sediments to use as input to water quality
models. In the sediment TMDL for Bellingham Bay, Washington, site-specific sediment
analyses for mercury and other pollutants were conducted, including sediment sampling
and toxicity analyses. Two kinds of modeling were also conducted:
• Modeling of contaminant transport and mixing to determine whether loadings from
a location were contributing to water quality standards violations
• Screening modeling to identify other potential sources of sediment
contamination (see the TMDL at http://www.epa.gov/waters/tmdldocs/
1991 Bellingham%20Bav%20TMDL.pdf)
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Other examples of TMDLs involving an analysis of mercury contributions from
sediments include the TMDLs for Pena Blanca, Arizona, and the Cache Creek watershed
in California (see appendix D). As described in the section on allocations, the Cache
Creek watershed TMDL also accounts for methylmercury production in sediments.
Natural or background levels of mercury in soils. Soils and sediments can include
mercury of geologic origin or mercury produced by the weathering of geologic materials,
together with mercury of anthropogenic origin (mercury emitted over time from human
sources and then deposited on soils). Mercury in soils can also re-emit or become re-
suspended and subsequently redeposit to soils. Local studies have been used in some
TMDLs to estimate the geologic contributions of mercury to waterbodies. For example, a
TMDL developed for the Ouachita watershed in Arkansas relied on a study of mercury
concentrations in the rocks of the Ouachita Mountains (FTN 2002). The mercury
concentration estimated to be of geologic origin was then subtracted from the total
concentration of mercury measured in soils to estimate the nongeologic concentration of
mercury in soils.
6.2.2.2 What modeling tools are available to link mercury sources and
water quality?
When developing a TMDL, states and authorized tribes should characterize the
association between the concentration of methylmercury in fish tissue and the identified
sources of mercury in a watershed. The association is defined as the cause-and-effect
relationship between the selected targets, in this case the fish tissue-based criterion and
the sources. The association provides the basis for estimating the total assimilative
capacity of the waterbody and any needed load reductions. TMDLs for mercury typically
link models of atmospheric deposition, watershed loading, and mercury cycling with
bioaccumulation. For example, a watershed model (e.g., Grid Based Watershed Mercury
Model, GBMM) might be linked with a receiving water mercury model (e.g., Water
Quality Analysis Simulation Program, WASP) and a bioaccumulation model (e.g.,
Bioaccumulation and Aquatic Simulator, BASS). These models are described further in
appendix E. Linking models together can enable a translation between the endpoint for
the TMDL (expressed as a fish tissue concentration of methylmercury) and the mercury
loads to the water without having explicit water column criteria or translations. The
analysis determines the loading capacity as a mercury loading rate consistent with
meeting the endpoint fish tissue concentration. This section describes some of the
modeling tools available for use in mercury TMDLs.
When selecting a model or models for developing a mercury TMDL, states and
authorized tribes should first consider whether the models will effectively simulate the
management action(s) under consideration. If a percent reduction in mercury load to the
waterbody is the sole action considered, a simple model might suffice; to answer more
complex questions, a more complex or detailed model might be needed. Some questions
decision makers should address include:
• How much do specific mercury loads need to be reduced to meet the criterion?
• What are the relative sources of the mercury load to the segment?
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• Are mercury loads to the waterbody from sediments and watershed runoff and
concentrations in fish at equilibrium with respect to current deposition levels? If
not, how much will an equilibrium assumption affect the accuracy of predicted
future fish concentrations?
• Could other pollution-control activities reduce mercury loads to the waterbody or
affect the mercury bioaccumulation rate?
• After regulatory controls are implemented, how long will it take for fish tissue
levels to meet the criterion?
Depending on the types of questions states and authorized tribes ask and the management
approaches they consider, appropriate models could range from a very simple steady state
model to a comprehensive dynamic simulation model, as described below. In addition,
models are often used in TMDL analyses but are not required. For more information on
the specific models described here, see http ://www.epa.gov/athens and
http://www.epa.gov/crem.
6.2.2.2.1 Steady state models and the proportionality approach
Steady state modeling describes the dynamic equilibrium between environmental media
established in response to constant loads over the long term. Consequently, complex
mercury cycling processes can be compressed into simple equations. One such approach,
assumes that a ratio of current to future fish tissue concentration equals the ratio of
current to future mercury loads to the waterbody. This approach, often referred to as the
proportionality approach and explained in detail in the Mercury Maps report (USEPA
200 Ib), assumes that where air deposition is the sole significant source, factors affecting
methylation remain unchanged. As a result, the ratio of current to future fish tissue
concentrations can be assumed to equal the ratio of current to future air deposition loads
in this situation. Mercury Maps, and the situations in which the proportionality
assumption may or may not apply, are described further in appendix E.
A number of mercury TMDLs where air deposition is the predominant mercury source
have been developed using an assumption of proportionality between mercury deposition
and fish tissue methylmercury concentration. Specifically, such TMDLs have reasoned
that a reduction in deposition will result in a proportional reduction in mercury
concentrations in fish overtime. Such an approach applies to situations where air
deposition is the only significant mercury source and relies on steady-state conditions.
This approach may also be used to estimate the reductions needed to meet a fish tissue
target without necessarily calculating a water column target.
Mercury TMDLs which applied a proportional relationship between reductions in
deposition and reductions in fish tissue methylmercury concentration include TMDLs for
waterbodies in Louisiana, such as the Ouachita Basin (FTN 2002), the Mermentau and
Vermillion-Teche River Basins (USEPA 200li, 200Ij) and the Coastal Bays and Gulf
Waters of Louisiana (Parsons 2005). Using the Everglades Mercury Cycling Model, the
pilot mercury TMDL study in the Florida Everglades also reported a linear relationship
between mercury deposition and the concentrations of mercury in largemouth bass
(Atkeson et al. 2002).
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More recently, the Minnesota statewide mercury TMDL applied the proportionality
approach. As described in section 6.2.1 above, waterbodies within the state were grouped
into two regions, and a TMDL developed for each region. Minnesota calculated a
reduction factor for each region, or the percent reduction in total mercury load needed in
each region to achieve the fish tissue target of 0.2 mg/kg for the 90th percentile of the
standard-length fish (MPCA 2007). Using the proportionality assumption, Minnesota
applied the regional reduction factor (51 percent for the southwest region and 65 percent
for the northeast region) to the total source loadings to determine the load reduction goal.
The Minnesota TMDL explains in further detail the basis for using the proportionality
approach.
Mass balance models are somewhat more complex implementations of the steady state
approach. In place of a simple ratio, such models describe fluxes of mercury in and out of
the model domain (e.g., impaired segment) and, optionally, balance fluxes (e.g.,
methylation and demethylation) within the model domain. The advantage provided by
this approach is that individual fate processes can also be simulated. For example, if soil
erosion and sediment runoff are modeled, decreased mercury soil erosion load can be
related to decreased fish tissue concentrations (AZDEQ 1999). Where all other aspects of
a watershed and waterbody remain unchanged, steady state models can produce as
accurate an estimate of the necessary load reductions as a dynamic model, generally with
less-intensive data collection and analysis. In addition, such simple approaches might be
less prone to calculation error and are much easier for the public to understand.
6.2.2.2.2 Continuous-simulation and dynamic models
Continuous-simulation and dynamic models take into account time-varying effects such
as variable pollutant inputs, precipitation, hydrologic responses, seasonal ecosystem
changes, and effects on fish tissue concentrations. For mercury, they might also include a
variety of physical and chemical fate and transport processes such as oxidation,
demethylation, volatilization, sedimentation, resuspension, and adsorption and
desorption. Dynamic models can be important in establishing cause-and-effect
relationships. They assemble available scientific knowledge on mercury fate and
transport into a single picture. Such models have been used to demonstrate how mercury
moves from air emission to deposition to watershed runoff to subsequent
bioaccumulation in fish at observed levels in remote waterbodies (USEPA 1997c).
Dynamic models could be used to describe waterbodies in dis-equilibrium (e.g., a recent
surface water impoundment with elevated methylation rates). The Everglades Mercury
TMDL pilot project (USEPA 2000g) simulated the amount of time necessary to attain
equilibrium in response to reduced mercury loads using the Everglades Mercury Cycling
Model. The model results predicted that sediments would continue to supply as much as
5 percent of the mercury load 100 years after air deposition reductions occurred. The
Dynamic Mercury Cycling Model (D-MCM) was used in the mercury TMDLs for
McPhee and Narraguinnep reservoirs in Colorado and the TMDLs for Arivaca and Pena
Blanca lakes in Arizona (see appendix D) (Tetra Tech 2001).
The SERAFM model incorporates more recent advances in scientific understanding and
implements an updated set of the IEM-2M solids and mercury fate algorithms described
in the 1997 Mercury Study Report to Congress (USEPA 1997c).
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Dynamic models can also describe how fish tissue concentrations are expected to respond
to environmental variability, such as seasonal or year-to-year changes in meteorology.
Thus, they can be used to belter interpret how samples collected in a specific season of a
specific year would be expected to vary relative to other seasons or years with mercury
loads being constant.
6.2.2.2.3 Spatially detailed models
Spatially detailed models, such as that used in the Savannah River mercury TMDL
(USEPA 200 Ij), can demonstrate how mercury fish tissue concentrations are expected to
vary with distance downstream of the impaired segment(s). For the Savannah River, EPA
used the Water Quality Analysis Simulation Program (WASP) model. WASP is a
dynamic, mass balance framework for modeling contaminant fate and transport in surface
water systems. The model helps users interpret and predict water quality responses to
natural phenomena and man-made pollution for various pollution management decisions.
Another model that has been used for mercury TMDLs is the EPA Region 4 Watershed
Characterization System (WCS). WCS is a geographic information system (GlS)-based
modeling system for calculating soil particle transport and pollutant fate in watersheds
(Greenfield et al. 2002).
As with the steady state mass balance model, including additional processes can allow a
modeler to determine the impact of different environmental regulatory or management
controls on mercury fish tissue concentrations. For example, where mercury transport to a
waterbody occurs predominantly through soil erosion, erosion control might be identified
as a useful nonpoint source control on mercury to waterbodies (Balogh et al. 1998). As
another example, controls on acid deposition and, thus, changes in lake pH and their
effect on fish tissue mercury concentrations can also be modeled (Gilmour and Henry
1991, Hrabik and Watras 2002). Finally, spatially detailed landscape models
hypothetically could be used to reflect the local effects of wetlands and their impacts on
mercury methylation rates.
6.2.2.2.4 Regression models
In general, a regression model is a statistical model describing how a parameter, such as
mercury levels in fish, is related to one or more variables. Regression models provide
only approximations of real trends.
One example of a regression model for mercury is the regression-based model under
development for New England. The model, known as MERGANSER (Mercury
Geospatial Assessments for the New England Region), is being developed by EPA and
several partners. The partners include USGS, the Biodiversity Research Institute, the
State of Vermont, the Clean Air Association of the Northeast States, and the New
England Interstate Water Pollution Control Commission. The model will integrate recent
atmospheric mercury-deposition models with many databases on mercury sources,
mercury levels in fish and bird tissue, and ecosystem features that might be associated
with the risk of mercury contamination in biota and, ultimately, humans.
The intent of the project is to identify, by using regression modeling, explanatory
variables that contribute to elevated mercury levels in fish and wildlife in New England.
The model can then be applied in a predictive mode to lakes throughout New England
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that have no mercury fish tissue or loon blood data. Specifically, the model will
(1) identify watershed and other factors associated with high mercury levels in fish and
wildlife; (2) identify likely sources of mercury; (3) provide estimates of mercury levels in
fish and wildlife at any lake or stream in New England; (4) provide estimates of mercury
reductions needed from air deposition to meet water-quality criteria; and (5) identify
optimal locations for long-term monitoring. Modeling will be done within a GIS
environment so that the spatial distribution of data is retained and results can be displayed
watershed by watershed. Maps from MERGANSER will show the areas in New England
that are susceptible to high mercury levels in biota and that are, therefore, areas where
human health impacts (through fish consumption) and ecological impacts (bird tissue
mercury levels) are potentially occurring. In addition, the model can be used to produce
maps that identify mercury sources and show the relative magnitude of mercury loading
from those sources.
6.2.2.2.5 Model selection
When selecting a model, a state or authorized tribe should be aware of the assumptions
inherent in each type of model and consider the potential effects of those assumptions on
relationships between loadings and fish tissue levels or water quality. The first
consideration for model assumptions is methylation. Several factors, including pH, redox,
potential sulfate concentrations, temperature, dissolved organic carbon (DOC)
concentrations, salinity, and microbial populations, influence the speciation of mercury
(Ullrich et al. 2001). If these factors fluctuate seasonally around an average condition, a
waterbody could be at a dynamic equilibrium and the steady state assumption would still
apply over the long term. If these factors change overtime such that they might have a
significant impact on fish tissue concentrations, the equilibrium assumptions inherent in
steady state modeling might not hold, and a dynamic model like the D-MCM (EPRI
1999) should be used. In using this model, the state or authorized tribe should consider
the amount of environmental media concentration data needed to initialize the model to
represent its non-equilibrium state.
The second consideration for model assumptions is the BAF. As discussed in section
3.1.3.1, the BAF assumes a constant proportionality between fish tissue methylmercury
concentrations, water column methylmercury concentrations, and water column mercury
concentrations. Mercury in a waterbody might not be at a steady state because of ongoing
reductions in mercury emissions, changes in water chemistry that affect methylation,
changes in aquatic ecosystem makeup, or changes in fish biomass. If these factors change
with time, the equilibrium assumptions inherent in steady state modeling might not hold,
and a dynamic model should be used.
The third consideration for model assumptions is the relative importance of the mercury
in aquatic sediments to the concentrations in fish tissue. Depending on previous loadings
to the watershed, the deposition pattern of solids, and the chemistry in the aquatic
sediments, the mercury in sediments can significantly influence the mercury
concentrations in fish tissue. Sediments are repositories, and the loading that caused
sediment mercury could be a legacy source. If so, a simplified steady state approach
cannot simulate changes in mercury concentrations in fish tissue due to external loading
reductions, and a dynamic model should be used.
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6.2.2.2.6 Model limitations
To effectively estimate fish methylmercury concentrations in an ecosystem, it is
important to understand that the behavior of mercury in aquatic ecosystems is a complex
function of the chemistry, biology, and physical dynamics of different ecosystems. The
majority (95 to 97 percent) of the mercury that enters lakes, rivers, and estuaries from
direct atmospheric deposition is in an inorganic form (Lin and Pehkonen 1999). Microbes
convert a small fraction of the pool of inorganic mercury in the water and sediments of
these ecosystems into methylmercury. Methylmercury is the only form of mercury that
biomagnifies in organisms (Bloom 1992). Ecosystem-specific factors that affect both the
bioavailability of inorganic mercury to methylating microbes (e.g., sulfate, DOC) and the
activity of the microbes themselves (e.g., temperature, organic carbon, redox status)
determine the rate of methylmercury production and subsequent accumulation in fish
(Benoit et al. 2003). The extent of methylmercury bioaccumulation is also affected by the
number of trophic levels in the food web (e.g., piscivorous fish populations) because
methylmercury biomagnifies as large piscivorous fish eat smaller organisms (Watras and
Bloom 1992; Wren and MacCrimmon 1986). These and other factors can result in
considerable variability in fish methylmercury levels among ecosystems at the regional
and local scales.
The lack of complete knowledge about key mercury process variables, such as the
functional form of equations used to quantify methylation rate constants, is a major
contributor to overall uncertainty in models that cannot be quantified at this time.
6.2.2.3 What are the allocation approaches in mercury TMDLs?
A requirement for an approvable TMDL is that the state or authorized tribe allocate the
pollutant load necessary to achieve water quality standards among point and nonpoint
sources. EPA's regulations, however, leave the decision regarding how to allocate
loadings to the state or authorized tribe developing the TMDL. States and authorized
tribes have discretion in selecting a method or system for allocating pollutant loads
among sources, provided that the allocations will result in attainment of water quality
standards represented by the loading capacity (40 CFR 130.2). States and authorized
tribes could reasonably consider the relative contribution of each source as one factor in
developing allocations. Other factors might include cost-effectiveness, technical and
programmatic feasibility, previous experience with the approach being considered,
likelihood of implementation, and past commitments to load reductions. These same
considerations apply to mercury TMDLs.
A number of pollutant loading and allocation scenarios have occurred in mercury
TMDLs, each with a different mix of point and nonpoint sources. The scenarios have
ranged from situations where mercury loadings are predominantly from air deposition,
with small loadings from point sources or other sources, to situations where mercury
loadings are predominantly from past mining activity. In addition, allocation approaches
in mercury TMDLs have included allocations to individual sources as well as allocations
to sectors and regions where appropriate. Examples of scenarios involving different
source mixes and allocation approaches in approved mercury TMDLs are provided
below.
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Mercury loadings predominantly from air deposition, with very small loadings from
point sources or other sources
Contributions from air deposition, such as direct deposition to the waterbody and
deposition to the watershed transported to the waterbody by runoff and erosion, are
typically included as part of the load allocation. As discussed in EPA guidance on
reviewing TMDLs, allocations for nonpoint sources may range from reasonably accurate
estimates to gross allotments (USEPA 2002f). TMDLs where air deposition is the
predominant mercury source have usually allocated only a small portion of the reductions
to the point sources or wasteload allocation, as described in the examples below. Many
mercury TMDLs have included an allocation to air deposition as a whole; in some
mercury TMDLs, the contributions from air deposition are further allocated to within-
state and out-of-state sources, and contributions from anthropogenic and natural
contributions are distinguished.
The Savannah River mercury TMDL is one of the first examples of an approach to
allocating loadings where the predominant mercury source is atmospheric deposition. Many
of the TMDLs developed to date are for situations where air deposition is the predominant
mercury source. The Savannah River mercury TMDL indicated that NPDES point sources
contribute 1 percent of the mercury loadings, while atmospheric deposition contributes 99
percent of the loadings. The TMDL identified only one point source on the Georgia side of
the river that has a permit to discharge mercury to the Savannah River. It identified 28 point
sources in Georgia that might have the potential to discharge larger amounts of mercury in
their effluent according to the nature of the discharge or the mercury levels that have been
found in their effluents above the water quality standard level.
The Savannah River mercury TMDL assigned 99 percent of the load reductions to the air
sources and 1 percent of the reductions to point sources. The TMDL provides specific
wasteload allocations for these 28 sources on the basis of meeting the water quality
criterion at the end of a pipe or, alternatively, implementing a pollutant minimization
program. In addition, the TMDL identifies about 50 other point sources expected, on the
basis of their size and nature, to discharge mercury at levels below the water quality
standard or not add mercury in concentrations above the concentrations in their intake
water. Individual wasteload allocations are given to these point sources on the basis of
their holding their effluents at current levels. The wasteload allocations for these point
sources are expressed in the TMDL as a sum or aggregate allocation.
Note: After the Savannah River mercury TMDL was issued, Georgia adopted a new
interpretation of its narrative water quality criteria that used EPA's new recommended
fish tissue criterion for methylmercury. On the basis of the new interpretation, Georgia
determined, and EPA agreed, that the Savannah River was meeting water quality
standards for mercury. EPA therefore withdrew the TMDL. EPA believes, however, that
the decisions, policies, and interpretations set forth in the TMDL are still valid and
provide an example of a possible approach to mercury TMDLs. The Savannah River
mercury TMDL is at http: //www .gaepd. org/File s PDF/techguide/wpb/TMDL/
Savannah/EPA Savannah River Watershed HgTMDL.pdf.
The series of mercury TMDLs issued February 28, 2002, for watersheds in middle and
south Georgia, such as the Ochlockonee watershed, also illustrate the first scenario. In
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these basins, point source loadings contribute very little to the mercury loadings (the
cumulative loading of mercury from all point sources is less than 1 percent of the total
estimated current loading), with the vast majority of loading to the basins as air
deposition.
The Ochlockonee mercury TMDL assigns most of the load reductions to the air sources,
with a load allocation of 1.16 kg/yr and a wasteload allocation of 0.06 kg/yr. Although
point sources collectively contribute a very minute share of the mercury load, the
Ochlockonee and other mercury TMDLs for middle and south Georgia include wasteload
allocations for the point sources. The TMDLs include wasteload allocations for each
facility identified as a significant discharger of mercury, with the remainder of the
allocation assigned collectively to the remaining point sources, considering that these
smaller point sources would reduce their mercury loadings using appropriate, cost-
effective minimization measures. The TMDL was written so that all NPDES-permitted
facilities would achieve the wasteload allocation through discharging mercury at
concentrations below the applicable water quality standard or through implementing a
pollutant minimization program. A summary of the Ochlockonee mercury TMDL is
provided in appendix D and is at http://gaepd.org/Files_PDF/techguide/wpb/
TMDL/Ochlockonee/EPA Ochlockonee River HgTMDL.pdf
The Minnesota "statewide" mercury TMDL document takes a regional approach to
allocations, providing a single wasteload allocation and a single load allocation that
applies to each region rather than to individual waterbodies. The TMDL document
indicates that such a regional allocation serves as a regional "cap." The predominant
source is atmospheric deposition, with a small contribution (about 1.2 percent of the total
source load for both regions combined) from point sources. The wasteload allocation is
set at 1 percent of the TMDL or the 1990 baseline load, whichever is lower, with the
remainder allocated to nonpoint sources. Point sources, including NPDES-permitted
stormwater sources, municipal treatment facilities, and industrial dischargers that impact
the waterbodies covered by the TMDL, are subject to the wasteload allocation. For the
load allocation, the Minnesota TMDL estimates the contributions to air deposition from
within-state and out-of state sources, as well as from global sources and anthropogenic
sources. A summary of the Minnesota mercury TMDL is included in appendix D. The
TMDL and related documents can be found at http://www.pca.state.mn.us/water/tmdl/
tmdl-mercuryplan.html.
Mercury loadings predominantly from past mining activity, with small or no
contributions from atmospheric deposition and/or NPDES point source contributions
One example of a TMDL for this scenario is the Cache Creek Watershed TMDL. Cache
Creek is a tributary to the Sacramento-San Joaquin Delta in California. Sources of
mercury entering the Cache Creek watershed include leaching from waste rock and
tailings from historical mercury and gold mines, erosion of naturally mercury-enriched
soils, geothermal springs, and atmospheric deposition. There are multiple inactive
mercury and gold mines in the Cache Creek watershed and no NPDES-permitted
discharges. Methylmercury is also produced in situ in the streambed of Cache Creek. The
TMDL analysis provides load allocations for Cache Creek, as well as each of the
tributaries. For each waterbody, load reductions are provided for both methylmercury and
total mercury. Allocations are expressed as a percentage of the existing methylmercury
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loads. Estimated atmospheric contributions of mercury, from direct deposition and runoff
after deposition, are very small compared to loads of mercury from mine sites or erosion
of the stream bed and banks, and thus no allocations are made to air deposition. Reducing
the methylmercury loads will require a multifaceted approach that includes controlling
inorganic mercury loads and limiting the entry of inorganic mercury into sites with high
rates of methylmercury production. The Cache Creek watershed mercury TMDL and the
allocation approach are summarized further in appendix D.
Mercury loadings from a combination of different sources, including atmospheric
deposition, past mining, and point sources
The Mercury TMDL for the Willamette Basin, Oregon, identifies atmospheric deposition
(direct plus indirect deposition: 47.7 percent) and erosion of mercury-containing soils (47.8
percent) as the top sources, along with small contributions from legacy mining (0.6 percent)
and NPDES-permitted point sources (3.9 percent). The point source loadings consist of 2.7
percent from POTWs and 1.2 percent from industrial discharges. The TMDL assigns
interim allocations to each of the source categories or sectors, rather than individual
sources, based on the considerable uncertainty in the loading estimates and other factors.
The TMDL specifies an across-the-board reduction of 27 percent in each source. After the
27 percent reduction to each source, the allocations for the Willamette mainstem are
approximately similar to their relative contribution to the total loadings: 44.7 kg/yr for air
deposition, 44.8 kg/yr for erosion, 0.6 kg/yr for legacy mine discharges, 2.6 kg/yr for
POTWs, 1.1 kg/yr for industrial discharges, and 0.8 kg/yr for reserved capacity. Allocations
are also provided for other waterbodies in the basin. The TMDL is at
http://www.deq.state.or.us/wq/tmdls/docs/willamettebasin/willamette/chpt3mercurv.pdf
Mercury loadings from point sources predominate or are not insignificant compared to
other sources
A small number of approved TMDLs have been developed for situations where mercury
is primarily or exclusively from point sources, including TMDLs for waterbodies in
Colorado. Examples of such TMDLs can be found at http://iaspub.epa.gov/
tmdl waters 10/attains impaired waters.control?pstate=CO&p_pollutantid=693.
6.2.2.4 What kinds of monitoring provisions have been associated with
approved TMDLs?
Monitoring provisions in approved TMDLs have included point source effluent and
influent monitoring, as well as water column, fish tissue, sediment, and air deposition
monitoring. Examples of mercury TMDLs with post-TMDL monitoring are the middle
and south Georgia mercury TMDLs approved in 2002. For facilities with the potential to
discharge significant amounts of mercury on the basis of their large flow volume or other
factors, the TMDL provides the permitting authority with two options for the wasteload
allocation:
• Implement the criteria-end-of-pipe (i.e., apply the TMDL water quality target to a
discharger's effluent at the outfall point).
• Monitor for mercury in the facilities' influent and effluent using more sensitive
analytical techniques (e.g., EPA method 1631) and implement cost-effective
mercury minimization if mercury is present in effluent at concentrations greater
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than source water concentrations and if the discharge exceeds the water quality
target.
Other facilities expected to discharge at levels below the water quality target will be
expected to verify through monitoring whether or not they are significant dischargers of
mercury. Other follow-up activities include further characterization of the air sources and
additional ambient monitoring of mercury concentrations in water, sediment, and fish.
The mercury TMDL for the coastal bays and gulf waters of Louisiana (approved July
2005) includes similar monitoring provisions for point source dischargers with flows
above a specified discharge volume. The TMDL also indicates that Louisiana will
conduct water, fish tissue, and air deposition monitoring and that the state will develop a
statewide mercury risk reduction program, including an assessment of all mercury
sources. (See the TMDL and supporting documents at http://iaspub.epa.gov/tmdl/
waters list.tmdl report?p tmdl id= 11642.)
TMDLs involving past mining activity have also included follow-up monitoring;
examples include three of the TMDLs described in appendix D (Clear Lake, California;
Arivaca Lake, Arizona; and Cache Creek, California). The mercury TMDL for Arivaca
Lake lists several follow-up actions and monitoring activities, such as additional
watershed investigations to identify other potential mine-related mercury sources,
including sediment sampling; evaluation of livestock BMPs to reduce erosion of soils
containing mercury and follow-up monitoring; and fish tissue monitoring to
evaluate progress toward the TMDL target (see the TMDL at http://www.epa.gov/waters/
tmdldocs/17.pdf). The Clear Lake, California, mercury TMDL also identifies the need for
follow-up monitoring of fish tissue and sediment (see appendix D, and the TMDL at
http://www.swrcb.ca.gov/rwqcb5/water issues/tmdl/centralvallev_projects/
clear_lake_hg/cl_final_tmdl .pdf. The Cache Creek TMDL indicates that monitoring will
be conducted to determine whether mercury loads have been reduced and to measure
progress toward the TMDL target, as well as to better characterize areas of
methylmercury production and mercury loadings from tributaries. Monitoring will
include fish tissue, sediment, and water monitoring.
EPA recommends that states and authorized tribes periodically review TMDLs during
implementation to ensure that progress is being made toward achieving water quality
standards. Such "adaptive implementation" provides the flexibility to refine and improve
a TMDL as data on the success of implementation activities are collected. States may
refine information on the contributions from sources such as runoff from abandoned
mining sites, sediment loading of mercury-laden sediments, and air deposition as data and
modeling tools improve. States should consider the application of adaptive
implementation in determining load allocations for these sources. Although a monitoring
plan is not required in a TMDL, EPA guidance documents recommend using a
monitoring plan to track the effectiveness of a TMDL; see Guidance for Water Quality-
Based Decisions: the TMDL Process (EPA 440/4-91-001). Post-TMDL monitoring is an
important tool for evaluating implementation success and, if necessary, refining the
TMDL. Follow-up monitoring may include monitoring of water quality, fish tissue, air
deposition, and sediments.
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NPDES Implementation Procedures
National Pollutant Discharge Elimination
System (NPDES) Implementation
Procedures
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Section 301 (a) of the CWA prohibits the discharge of any pollutant, including mercury,
from a point source into waters of the United States except in compliance with certain
enumerated provisions of the CWA, among them section 402. CWA section 402
establishes the NPDES program, under which EPA or states and tribes authorized to
administer the program issue permits that allow the discharge of pollutants into waters of
the United States, notwithstanding the general prohibition established by section 301(a).
These permits must contain (1) technology-based effluent limitations, which represent the
degree of control that can be achieved by point sources using various levels of pollution
control technology (see CWA sections 301, 304, and 306) and (2) more stringent
limitations, commonly known as water quality-based effluent limitations (WQBELs),
when necessary to ensure that the receiving waters achieve applicable water quality
standards (see CWA section 301(b)(l)(C)).20
Most WQBELs are expressed as numeric limits on the amounts of specified pollutants
that may be discharged. However, WQBELs may also be expressed in narrative form
such as best management practices (BMPs) or pollutant minimization measures (e.g.,
practices or procedures that a facility follows to reduce pollutants to waters of the United
States) when it is infeasible to calculate a numeric limit (see 40 CFR 122.44(k)(3)). In
addition, BMPs may be imposed in the form of NPDES permit conditions to supplement
numeric effluent limitations when the permitting authority determines that such
requirements are necessary to carry out the purposes and intent of the CWA (see CWA
section 402(a)(l)(B) and 40 CFR 122.44(k)(4)).
As noted above, NPDES permits must contain WQBELs when necessary to achieve
applicable water quality standards. The procedure for determining the need for WQBELs
is called a "reasonable potential" analysis. Under EPA's regulations at 40 CFR
122.44(d)(l)(i), effluent limitations must control all pollutants that the permitting
authority determines "are or may be discharged at a level that will cause, have the
reasonable potential to cause, or contribute to an exceedance of any applicable water
quality standard." Thus, if a pollutant discharge has the reasonable potential to cause or
contribute to an exceedance of applicable water quality standards, the discharger's
NPDES permit must contain a WQBEL for that pollutant (see 40 CFR 122.44(d)(l)(iii)-
(vi)). The procedure for determining reasonable potential must consider the variability of
the pollutant in the effluent, other loading sources, and dilution (when allowed by the
water quality standards) (see 40 CFR 122.44(d)(l)(ii)). The procedure specifies only
20 When developing WQBELs, the permitting authority must ensure that the level of water quality achieved by such limits derives from and
complies with water quality standards (see 40 CFR 122.44(d)(l)(vii)(A)).
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whether a discharge must have a WQBEL; it does not specify the actual permit limits.
The NPDES regulations at 40 CFR 122.44(d)(l)(vii) specify that the level of water
quality to be achieved by the WQBEL must derive from and comply with water quality
standards, as required by CWA section 301(b)(l)(C) (requiring "any more stringent
limitation... necessary to meet water quality standards"). This would necessarily be a
permit-by-permit determination.
The recommendations below assume that an approved TMDL is not available at the time
of permit issuance. If EPA has approved or established a TMDL containing wasteload
allocations for the discharge of mercury (and methylmercury where appropriate), the
WQBEL for that discharge must be consistent with the wasteload allocation (see 40 CFR
EPA believes, depending on the particular facts, that a permit writer may reasonably
conclude that limits on point sources consistent with this guidance are likely to be as
stringent as necessary to achieve water quality standards. As described in more detail
below, the permit writer should conduct a reasonable potential analysis to determine
whether a discharger will cause or contribute to the exceedance of applicable water
quality standards. Once such a determination is made, limits can be imposed consistent
with this guidance. In circumstances where waters are not yet impaired, the permit writer
should consider other factors or conditions when determining whether a facility has
reasonable potential with the goal of preventing future impairments. (See Sections 7.2.2,
7.5. 1.2.2 and 7.5. 1.2.3).
7.2.1 Developing NPDES permit limits based on the fish tissue
criterion
The first component of the recommended NPDES permitting approach for
methylmercury is to determine how the methylmercury criterion is expressed in the
applicable water quality standard and to determine whether a water column translation of
the fish tissue criterion or site-specific data to translate are available at the time of permit
issuance. This will inform the selection of the appropriate recommended implementation
option. If the methylmercury criterion is expressed as a water column value, the permit
writer should develop permit limits based on this criterion according to procedures
described in section 5.4.4 of the Technical Support Document for Water Quality-based
Toxics Control, or TSD (USEPA 1991). If the criterion is expressed as a fish tissue value
and a water column translation of the fish tissue criterion or site-specific data to translate
are available at the time of permit issuance, the permit limits based on the translated
water concentration value should again be developed according to procedures described
in section 5.4.4 of the TSD.
If, however, the criterion is expressed as a fish tissue value and a water column
translation of the fish tissue criterion or site-specific data to translate are not available at
the time of permit issuance, the permitting authority may reasonably conclude that a
numeric WQBEL is infeasible to calculate. In that instance, EPA recommends that the
permitting authority develop NPDES permit limits based on the criterion using the
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procedures described below. Section 7.3 contains additional information about expressing
and developing permit limits based on the methylmercury criterion.
7.2.2 Determining reasonable potential
The second component of the recommended NPDES permitting approach for
methylmercury is to conduct a reasonable potential analysis to determine whether the
discharge will cause or contribute to an exceedance of applicable water quality standards.
The recommended reasonable potential analysis consists of two steps. Step one is to
determine whether there is a quantifiable amount of mercury in the discharge using a
sufficiently sensitive analytical method (see sections 7.4 and 7.5.1.1 for more information
on sufficiently sensitive methods.) If this information is unknown, EPA recommends
including a monitoring requirement in the permit to collect this information and a
reopener clause to allow establishment of appropriate requirements if the permitting
authority determines that the discharge has reasonable potential. If, using a sufficiently
sensitive analytical method, there is not a quantifiable amount of mercury in the
discharge, depending on the particular facts, the permitting authority may reasonably
conclude that the discharge does not have reasonable potential and that no water quality-
based limits are necessary. If there is a quantifiable amount of mercury, however, the
permitting authority should move to step two of the reasonable potential analysis. Section
7.5.1.1 contains additional information on step one of the reasonable potential analysis.
Step two of the reasonable potential analysis is to determine whether the fish tissue
concentration of methylmercury in the receiving water is close to or exceeds the criterion.
If the fish tissue concentration of methylmercury in the receiving water is below and not
close to the criterion, depending on the particular facts, the permitting authority may
reasonably conclude that the discharge does not have reasonable potential, but tier 2
antidegradation provisions should be considered. This situation is described below in the
third component of the NPDES permitting approach.
If the fish tissue concentration of methylmercury in the receiving water is close to or
exceeds the criterion, depending on the particular facts, the permitting authority may
reasonably conclude that the discharger has reasonable potential, and a WQBEL must be
included in the permit. Recommended WQBELs for this situation are described below in
the fourth component of the NPDES permitting approach. Section 7.5.1.2 contains
additional information on step two of the reasonable potential analysis. If information for
step two is unknown, EPA recommends including in the permit a special permit condition
to conduct a fish tissue survey of the receiving waterbody and a reopener clause so that
reasonable potential can be determined when the fish tissue data become available. EPA
further recommends that in this situation the permitting authority encourage permittees to
develop and implement mercury minimization plans (MMPs) to reduce mercury loading
to the waterbody.
In order to prevent future impairments, EPA recommends that a state or authorized tribe
consider other factors or conditions such as rising fish tissue concentrations or the
relative contribution of mercury or methylmercury from the source when determining
whether a facility has reasonable potential in waters that are not yet impaired. Section
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7.5.1.2.2 contains additional examples of other factors, such as downstream impacts, that
should be considered in a reasonable potential analysis.
7.2.3 Implementing ant/degradation
The third component of the recommended NPDES permitting approach for
methylmercury is to determine whether the discharger will undertake an activity that can
increase mercury loading to the waterbody. If the discharger will not undertake such an
activity, no additional permit conditions are necessary. EPA recommends, however, that
in this situation the facility voluntarily develop and implement an MMP to reduce the
facility's mercury loading to the receiving water. If the discharger will undertake such an
activity, EPA recommends that a tier 2 antidegradation analysis be conducted in
accordance with the state or tribe's antidegradation policy and that permit conditions
consistent with the analysis be included in the permit.
As part of conducting a tier 2 antidegradation analysis, the state or authorized tribe would
evaluate the activity's potential to lower water quality, whether there are alternatives that
would avoid lowering water quality, and whether lowering of water quality would be
necessary to accommodate important economic or social development in the area of the
discharge. EPA considers analyses of potential pollution prevention and enhanced
treatment alternatives as an appropriate starting point for the antidegradation review for
both industrial and municipal dischargers. See 67 FR 68971, 68979. The results of such
an analysis of potential alternatives could provide the basis for developing an MMP.
EPA further recommends that the permit contain a special condition requiring the
permittee to implement an MMP and conduct effluent monitoring to allow for evaluation
of the effectiveness and implementation of the MMP. Section 7.5.1.2.2 contains
additional information on antidegradation considerations.
7.2.4 Establishing appropriate WQBELs
The fourth component of the recommended NPDES permitting approach for
methylmercury is to develop appropriate WQBEL requirements. Where a TMDL
containing wasteload allocations for the discharge of mercury (and methylmercury where
appropriate) has been developed, the WQBEL for that discharge must be consistent with
the wasteload allocation (see 40 CFR 122.44(d)(l)(vii)(B)). Where a TMDL is not
available at the time of permit issuance, to satisfy 122.44(d)(l)(vii)(A), EPA recommends
the following WQBEL requirements, which are explained in greater detail in section
7.5.2.1:
• Where a water column translation of the fish tissue criterion has been developed, or
where site-specific data to do so are readily available, include a numeric water
quality-based limit.
• Where a water column translation or site-specific data are not available and the
permit writer determines that a numeric limit is infeasible to calculate:
o Require the permittee to implement an MMP tailored to the facility's potential
to discharge mercury. Depending on the particular facts, the permitting
authority may include in the MMP a trigger level, reduction goal, or
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enforceable numeric level (e.g., existing effluent quality) to further manage
mercury discharges.
o Require effluent monitoring using a sufficiently sensitive EPA-approved
method to enable evaluation of the effectiveness and implementation of the
MMP. (See sections 7.4 and 7.5.1.1 for more information on sufficiently
sensitive methods.)
o Include a reopener clause to modify the permit conditions if the MMP is not
found to be effective or if a water column translation of the fish tissue
criterion is developed.
Since permitting authorities need to establish and maintain WQBELs as stringent as
necessary to meet water quality standards, if a state or tribe has yet to complete the
transition from an existing water column criterion to a fish tissue-based criterion, states
may consider retaining their existing water column criteria until translators are
developed. Alternatively, until a translator is available, EPA recommends that one of the
approaches outlined in this document for relating a concentration of methylmercury in
fish tissue to a concentration of methylmercury in ambient water be considered,
especially for waters with relatively high direct water inputs of mercury. (See section
3.1.3.1.)
In modifying or reissuing permits with existing WQBELs for mercury, permit writers
must also ensure compliance with CWA anti-backsliding requirements. As described
elsewhere in this Guidance, CWA section 402(o)(l) prohibits the revision of WQBELs to
make them less stringent than existing permit limits unless a specific exception applies
under 402(o)(2) or 303(d)(4).
Exceptions under Section 402(o)(2), which would allow for the establishment of less
stringent limits are:
(1) There have been material and substantial alterations or additions to the permitted
facility which justify the less stringent limit.
(2) New information (other than revised regulations, guidance, or test methods) is
available that was not available at the time of permit issuance, and that would have
justified a less stringent limit.
(3) Good cause exists due to events beyond the permittee's control (e.g., natural
disasters) and for which there is no reasonably available remedy.
(4) The permit has been modified under 301(c), 301(g), 301(h), 310(i), 301(k), 301(n),
or316(a).
CWA section 303(d)(4) provides additional exceptions to the anti-backsliding
prohibition: paragraph (A), which applies to "non-attainment waters," and paragraph (B),
which applies to "attainment waters".
• Non-attainment water: CWA section 303(d)(4)(A) allows the establishment of a
less stringent effluent limitation when the receiving water does not meet applicable
water quality standards (i.e., a "non-attainment water") if the permittee meets two
conditions. First, the existing effluent limitation must have been based on a total
maximum daily load (TMDL) or other wasteload allocation established under
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CWA section 303. Second, relaxation of the effluent limitation is allowed only if
the cumulative effect of all revised limitations would assure the attainment of water
quality standards, or the designated use not being attained is removed in
accordance with the water quality standards regulations.
• Attainment water: CWA section 303(d)(4)(B) applies to waters where the water
quality equals or exceeds levels necessary to protect the designated use, or to
otherwise meet applicable water quality standards (i.e., an "attainment water").
Under CWA section 303(d)(4)(B), a limitation based on a TMDL, wasteload
allocation, other water quality standard, or any other permitting standard may only
be relaxed where the action is consistent with the state's antidegradation policy.
The application of these exceptions is limited under 402(o)(3), which prohibits the
relaxation of effluent limitations in all cases if a revised effluent limitation would result
in a violation of applicable effluent limitation guidelines or water quality standards,
including antidegradation requirements.
In establishing WQBELs for mercury, permit writers will need to ensure that the CWA
anti-backsliding requirements are met. The first step of the inquiry is to determine
whether the WQBEL based on the fish tissue criterion is "less stringent" than the
WQBEL in the previous permit. If the new permit limit is not less stringent (e.g., if the
prior numeric WQBEL is included in the MMP as an enforceable numeric level (see
section 7.5.2.4 for additional information)), then the anti-backsliding prohibition should
not be triggered and it should be appropriate to include the new limit in the permit. If the
WQBEL based on the new fish tissue criterion is in fact less stringent than the prior
WQBEL, then the permit writer must retain the existing numeric WQBEL unless there is
an available exception to the anti-backsliding prohibition.
Because CWA section 402(o)(2)(B)(i) does not allow backsliding solely because
regulations are revised (e.g., adoption of the fish tissue criterion), any applicable
exceptions to the anti-backsliding prohibition for impaired waters would be found under
section 303(d)(4)(A). In this case, permit limits based on TMDLs or other wasteload
allocations established under section 303 can be made less stringent only if: a) the
cumulative effect of all loadings meets the WQS or b) the designated use is removed.
Anti-backsliding requirements are further described in EPA's NPDES Permit Writers'
Manual (USEPA 1996a) and in EPA's Technical Support Document for Water Quality-
Based Toxics Control (USEPA 1991).
Other considerations and requirements may be necessary in developing permits. They
include the following:
• Where a discharger undertakes an activity that could increase mercury loading to
the receiving water, the WQBEL must be consistent with applicable
antidegradation requirements (see section 7.5.1.2.2). Additional requirements may
also be necessary under the CWA and EPA's NPDES regulations (see section
7.5.2.3).
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• The permitting authority would need to include appropriate technology-based
limits pursuant to CWA section 301(b) and 40 CFR sections 125.3 and
122.44(a)(l) (see section 7.5.2.3).
The entire recommended NPDES permitting approach is summarized in figure 5 and
explained in greater detail in the following sections.
As discussed in section 3.1, states and authorized tribes that decide to use the
recommended criterion as the basis for new or revised methylmercury water quality
standards have the option of adopting the criterion into their water quality standards as a
fish tissue concentration, a traditional water column concentration, or both. If states or
authorized tribes choose to use both approaches, they should clearly describe in their
standards how each will be used for specific applications and describe applicable
implementation procedures.
EPA recommends two approaches for implementing the fish tissue-based methylmercury
water quality criterion in NPDES permits, depending on the form in which the state or
authorized tribe expresses the criterion—as a fish tissue concentration or as a water
column concentration. In addition, states and authorized tribes that adopt the
recommended criterion as a fish tissue value may choose to implement it through NPDES
permitting as a water column translation of the fish tissue value. Each of these
approaches is summarized in figure 6 and discussed in more detail in sections 7.4 and 7.5.
The recommendations below assume that an approved TMDL is not available. If EPA has
approved or established a TMDL containing a wasteload allocation for the discharge of
mercury (and methylmercury where appropriate), the WQBEL for that discharge must be
consistent with the wasteload allocation (see 40 CFR 122.44(d)(l)(vii)(B)).
This chapter provides EPA's guidance on how a permitting authority could implement
the fish tissue criterion in NPDES permits consistent with the CWA and its implementing
regulations. States and authorized tribes retain the discretion to develop and use
procedures for determining reasonable potential and establishing effluent limits in
NPDES permits that differ from those in the guidance. Such procedures may use other
information relevant to determining reasonable potential and establishing effluent limits,
where appropriate. If a state or authorized tribe develops its own such permitting
procedures, EPA recommends that states and authorized tribes make the procedures
public so that all stakeholders can be aware of the requirements and expectations of the
permit program. In addition, the permit's fact sheet or statement of basis should also
explain the basis of the permit conditions and effluent limitations and how these are
consistent with the state's or authorized tribes' permitting procedures, the CWA, and
applicable federal regulations.
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START
Implementing t..
Fish Tissue Criterion
in NPDES Permits
Implement the water
concentration criteria using
the approaches described in
section 5.4,4 of the TSD
(USEPA1991a)a
In addition to a fish tissue
criterion, does the state
have hold-over water
concentration criteria?
Implement the water
concentration criteria using
the approaches described
in section 5.4.4 of the TSD
(USEPA1991a)'
Is a water column concentration
of the fish tissue criterion or the
site-specific data to translate available?
No
Determining Reasonable
Potential
Monitoring requirement
Permit reopener clause
to assess reasonable
potential after data are
collected
Special condition to
conduct a fish tissue
survey
Permit reopener clause
to assess reasonable
potential after fish tissue
data are collected
Recommend voluntary
MMP
For fish tissue criterion
continue to the next box
No necessary conditions
Recommend voluntary MMP
Implementing
Antidegradation
No
Will the discharger undertake
an activity that could result
in an increase in receiving
water or fish tissue mercury
concentration?
Yes
Conduct tier 2
antidegradation analysis
and develop appropriate
permit conditions
Require permittee to
develop and implement
MMP tailored to facility
Require effluent monitoring
Recommended WQBEL Requirements
• Where a TMDL has been developed, the WQBEL must be consistent with the wasteload allocation as required by
40CFR122.44(d)(1)(vii)(B))
• Where a TMDL has not been developed but a water column translation of the fish tissue criterion has been developed, or
the site-specific data to translate is readily available, include a numeric water quality-based limit
• Where a water column translation or data to translate is not available and the permit writer determines that a numeric limit
is infeasible to calculate:
- Require the permittee to develop and implement an MMP tailored to the facility's potential to discharge mercury.
Depending on the particular facts, the permitting authority may include in the MMP a trigger level, reduction goal, or
enforceable numeric level (e.g., existing effluent quality) to further manage mercury discharges
- Require effluent monitoring using a sufficiently sensitive EPA-approved method to determine whether the MMP is
effective (See sections 7.4 and 7.5.1.1 for more information on sufficiently sensitive methods)
- Include a reopener clause to modify the permit conditions if the MMP is not found to be effective or if a water column
translation of the fish tissue criterion is developed
• Where a discharger undertakes an activity that could increase mercury loading to the receiving water, it must be
consistent with applicable antidegradation requirements. Additional requirements may also be necessary under the
CWAand EPA's NPDES regulations.
Note:
' For Great Lakes states, implement using 40 CFR132, Appendix F, Procedure 5.
Figure 5. NPDES permitting approach for methylmercury.
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START
Implementing the
Fish Tissue Criterion
in NPDES Permits
In addition to a fish tissue
criterion, does the state
have hold-over water
concentration criteria?
Implement the water
concentration criteria using
the approaches described in
section 5.4.4 of the TSD
(USEPA 1991a)B
Is a water column concentration
of the fish tissue criterion or the
site-specific data to translate available?
Implement the water
concentration criteria using
the approaches described
in section 5.4.4 of the TSD
(USEPA 1991a)"
For fish tissue criterion
continue to the next box
No
Implement using the
approaches described
in this guidance
Note:
' For Great Lakes states, implement using 40 CFR132, Appendix F, Procedure 5.
Figure 6. Implementing the fish tissue criterion in NPDES permits.
7.4 What are the procedures for developing permit limits
when the criterion is adopted as a water column value
or when the criterion is adopted as a fish tissue value
and the permitting authority uses a water column
translation of the fish tissue value?
This approach assumes that a state or authorized tribe decides to adopt a new or revised
water quality criterion for methylmercury in one of the following forms:
• Water column concentration value. Expressing a criterion as a water column value
is very common, and permitting authorities have considerable historical experience
in developing permit limits based on such criteria in NPDES permits.
• Fish tissue concentration value that is translated into a water column value.
Sections 3.1.3.1 through 3.1.3.3 of this guidance discuss the procedures for
translating the fish tissue criterion into a water column value for water quality
standards purposes. These procedures may also be used to translate a fish tissue
criterion into a water column value for determining reasonable potential and for
deriving numeric WQBELs.
In either case described above, the permitting authority should determine reasonable
potential and calculate numeric WQBELs using the procedures described in section 5.4.4
of the TSD (USEPA 1991) to derive a numeric WQBEL.
This approach relies on the measurement of mercury in effluent, often at concentrations
below the quantitation levels of some analytical methods. Therefore, the permitting
authority should specify that the NPDES regulated discharger use a sufficiently sensitive
EPA-approved method for the measurement of mercury in the discharge. An analytical
method is sufficiently sensitive when (1) its method quantitation level is at or below the
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level of the applicable water quality criterion or (2) its method quantitation level is above
the applicable water quality criterion, but the amount of mercury in a discharge is high
enough that the method detects and quantifies the level of mercury in the discharge. To
illustrate the latter, if the water column criterion or water column translation of a fish
tissue criterion for mercury in a particular waterbody is 2.0 parts per trillion (ppt), method
245.7 (with a quantitation level of 5.0 ppt) would be sufficiently sensitive when it reveals
that the level of mercury in a discharge is 5.0 ppt or greater. In contrast, method 245.7
would not be sufficiently sensitive when it resulted in a level of nondetection for that
discharge because it could not be known whether mercury existed in the discharge at a
level between 2.0 and 5.0 ppt (less than the quantitation level but exceeding the water
quality criterion).21
The selection of a sufficiently sensitive method relates method quantitation levels to the
water column criterion value. If a water column criterion or a water column translation of
a fish tissue criterion is not available to allow for selecting an alternate sufficiently
sensitive method, EPA recommends the use of the most recent version of method 1631 to
characterize discharges from all facilities for which the mercury levels are unknown or
undetected. Method 1631 is relatively new, and the facilities may not have used it to
analyze their effluent discharges. As a result, previous monitoring may show
undetectable levels of mercury when use of method 1631 shows detectable or
quantifiable amounts. Therefore, EPA recommends monitoring using the most recent
version of method 1631 to help identify all facilities that contribute to mercury water
quality impairment, unless another EPA-approved method can be justified as being
sufficiently sensitive.
EPA's regulations require that measurements included on NPDES permit applications
and on reports required to be submitted under the permit must generally be made using
analytical methods approved by EPA under 40 CFR part 136. Because EPA has approved
methods for analyzing mercury in water, these approved methods must be used in water
analyses for NPDES permits involving mercury. See 40 CFR sections 122.21(g)(7),
122.41(j), 136.1, 136.3, and 136.6. Selection of an approved method should take into
account the above discussion of method sensitivity. For metals, such as mercury, the
federal regulations at 40 CFR 122.45(c) generally require effluent monitoring for the total
form of the metal.
The discussion above describes analytical methods for measuring mercury in water. Refer
to section 4.1 and appendix C for information on analytical methods for measuring
mercury in fish tissue and for measuring methylmercury in water or fish tissue.
21 For more information on choosing a sufficiently sensitive method, see the memorandum Analytical Methods for Mercury in National
Pollutant Discharge Elimination System (NPDES) Permits from James A. Hanlon, Director of the Office of Wastewater Management,
dated August 23, 2007, at http://www.epa.gov/npdes/pubs/mercurvmemo_analvticalmethods.pdf
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f.$
the is, j;lcjpte*l as a
the poi/ri!
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NPDES Implementation Procedures
tissue value to a traditional water column value using BAFs or translators. This section
provides recommendations for how a permitting authority can determine reasonable
potential in the absence of site-specific data to translate the fish tissue value into a water
column value.
When determining reasonable potential, the permitting authority must determine whether
the discharge "causes, has reasonable potential to cause, or contributes" to an exceedance
of the applicable water quality criterion (see 40 CFR 122.44(d)(l)(ii)). The NPDES
permit fact sheet should provide the rationale and assumptions used in determining
whether WQBELs proposed in the associated draft permit are appropriate. The
recommendations in this guidance could be applied on a permit-by-permit basis where
appropriate to support the reasonable potential determination that satisfies 40 CFR
122.44(d)(l)(ii) with respect to a water quality criterion for methylmercury expressed as
a fish tissue value in the absence of a TMDL and a water column translation of that value
at the time of permit issuance.
EPA believes that, depending on the particular facts, a permitting authority could
reasonably conclude that reasonable potential exists if two conditions are present: (1) the
NPDES permitted discharger has mercury in its effluent at a quantifiable level and (2) the
methylmercury level in fish tissue from the receiving waterbody is close to or exceeds the
fish tissue water quality criterion. Under these circumstances, the effluent data indicate
that the mercury load in the effluent contributes to the mercury load in the waterbody,
and the fish tissue concentration indicates that the mercury load in the waterbody causes
or has the potential to cause an exceedance of the water quality criterion. This approach is
consistent with federal regulations pertaining to the Great Lakes Basin, which contained
an approach for determining reasonable potential using fish tissue data (see 40 CFR part
132, appendix F, procedure 5.F.4). The reasonable potential approach for mercury
described in this guidance has the advantage of significantly reducing environmental
monitoring costs and does not involve developing a site-specific BAF for each waterbody
in a state.
EPA recognizes that the mere presence of mercury at a quantifiable level in an effluent is
not necessarily an indication that the mercury discharge is the sole cause of the fish
contamination or even a substantial contributor of such contamination. However, mercury
in an effluent discharge may contribute to the methylmercury present in fish tissue at
levels close to or above the fish tissue criterion, and therefore the discharge may be found
to exhibit the reasonable potential to cause or contribute to the exceedance of applicable
water quality standards. EPA notes that the reasonable potential procedures as a whole
are intended as conservative screening procedures to determine when a permit should
contain a WQBEL to reduce the contribution to existing contamination or to prevent
further possible degradation.
EPA notes that, unlike typical water quality criteria that are expressed as water column
values, the fish tissue water quality criterion integrates spatial and temporal complexity
and the cumulative effects of mercury loading from point and nonpoint sources that affect
methylmercury bioaccumulation in aquatic systems. As discussed further in section
7.5.1.2.2, EPA believes that comparing the fish tissue concentration in steady state
systems directly to the applicable fish tissue criterion appropriately accounts for the
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factors specified in 40 CFR 122.44(d)(l)(ii) for a criterion expressed as a fish tissue
value.
Finally, EPA further notes that because of the sensitivity of Method 163 IE or other
sufficiently sensitive methods (as described in section 7.4), it is reasonable to conclude
that a discharge below quantitation does not have reasonable potential to exceed the
criterion.
7.5.1.1 Step one of the reasonable potential analysis: Determining
whether the NPDES-permitted discharger has mercury in its
effluent at quantifiable levels
The first step in the reasonable potential analysis is to determine whether the discharge
contains a quantifiable amount of mercury. To determine this, EPA recommends that
permitting authorities require monitoring using a sufficiently sensitive analytical method
approved for use by EPA under 40 CFR part 136. Section 7.4 contains additional
information about sufficiently sensitive EPA-approved methods. If an alternate EPA-
approved method cannot be justified as being sufficiently sensitive, EPA recommends
monitoring using the most recent version of method 1631 to help identify all facilities
that contribute to mercury water quality impairment. EPA recognizes that using method
1631 will likely result in a large majority of facilities showing quantifiable mercury
discharges. This approach, however, is intended to allow permitting authorities to
determine that facilities without quantifiable levels of mercury may not need step two of
the reasonable potential analysis (determining whether the fish tissue criterion is being
attained).
One of three outcomes will be reached in answering the first condition of the reasonable
potential analysis:
• It is unknown whether the discharge includes a quantifiable amount of mercury.
• The discharge does not include a quantifiable amount of mercury.
• The discharge includes a quantifiable amount of mercury.
The recommended reasonable potential determination and recommended permit
conditions for each of the outcomes is described in detail below.
7.5.1.1.1 What are the recommended permit conditions when it is unknown whether
the discharge includes quantifiable amounts of mercury because there are
limited or no effluent data to characterize the discharge of mercury?
In this situation, EPA recommends that the permitting authority include permit conditions
that include the following elements:
• Effluent monitoring using a sufficiently sensitive EPA-approved analytical method
to characterize the discharger's effluent for mercury (see sections 7.4 and 7.5.1.1
for information on sufficiently sensitive methods)
• A reopener clause to identify the actions that the permitting authority may take
should the monitoring information indicate that a WQBEL for mercury is necessary
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EPA recommends that permitting authorities require monitoring, using a sufficiently
sensitive EPA-approved method, by all facilities for which the mercury levels are
unknown or previously undetected (using less sensitive methods) to characterize the
discharger's effluent for mercury. EPA recommends this monitoring to help identify all
facilities that contribute to mercury loads in the waterbody. The permitting authority
could obtain these monitoring data as part of the permit application, by requiring periodic
(e.g., quarterly to annually) monitoring as part of the permit, or by invoking its authority
under CWA section 308 (or equivalent state authority) to require NPDES facilities to
collect information necessary for developing NPDES permit limits. The permit should
include a reopener clause so that as soon as there is complete information and an
indication that a more stringent limit is required, the permitting authority can establish the
necessary requirements. The permitting authority may also decide to no longer require
the monitoring if the information shows that the facility is not discharging mercury at
quantifiable levels.
EPA recommends that when selecting the monitoring frequency, permitting authorities
consider the factors in section 5.7.5 of the TSD (USEPA 1991). This section
acknowledges that EPA has not recommended a specific monitoring frequency. However,
the TSD recognizes that the choice of a monitoring frequency is a site-specific decision
and provides the permitting authority with a number of factors to consider when making
these decisions.
Until the permitting authority has sufficient data to determine whether the discharge has
reasonable potential, and depending on the particular facts, the permit writer may
reasonably conclude that the permit conditions described in this section are as stringent as
necessary to achieve water quality standards, as required by CWA section 301(b)(l)(C).
7.5.1.1.2 What are the recommended permit conditions when the discharge does not
include quantifiable amounts of mercury?
In this situation, EPA recommends that the permitting authority first review the
monitoring data to determine whether they are representative of the effluent. If the
permitting authority believes the monitoring data are representative of the discharge, no
further permit conditions may be necessary. In contrast, if the permitting authority
believes the data are not representative, the authority should consider requiring additional
monitoring, as described in section 7.5.1.1.1.
7.5.1.1.3 What are the recommended actions for discharges that include quantifiable
amounts of mercury?
In this case, the permitting authority should move to step two of the reasonable potential
analysis and evaluate data on the concentrations of methylmercury in the fish tissue from
the receiving waterbody to determine appropriate permit conditions (see section 7.5.1.2).
7.5.1.2 Step two of the reasonable potential analysis: Determining
whether the fish tissue concentration of methylmercury in the
receiving waterbody exceeds the fish tissue criterion
In step two of EPA's recommended fish tissue criterion reasonable potential procedure,
the permitting authority has concluded that the first condition of the two-part reasonable
potential analysis has been satisfied (i.e., the NPDES-permitted discharger has mercury in
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its effluent at a quantifiable level). The permitting authority should then address the
second condition of the reasonable potential analysis—determining whether the fish
tissue from the receiving waterbody exceeds (or is close to exceeding) the fish tissue
water quality criterion.
One of three outcomes will be reached in answering this question:
• The fish tissue concentration of methylmercury is unknown.
• The fish tissue concentration of methylmercury does not exceed the criterion or is
not close to the criterion.
• The fish tissue concentration of methylmercury exceeds the criterion or is close to
exceeding the criterion.
For discharges with quantifiable levels of mercury, the recommended reasonable
potential determination and recommended permit conditions for each outcome is
described in detail below.
EPA recognizes that when evaluating reasonable potential, the permitting authority
should exercise discretion and careful judgment in determining whether fish tissue data
are representative of current ambient conditions. EPA guidance for sampling strategies
for fish tissue monitoring is provided in section 4.2 of this document.
7.5.1.2.1 What are the recommended permit conditions when a facility discharges
quantifiable amounts of mercury but the fish tissue concentrations of
methylmercury in the receiving waterbody are unknown?
In waterbodies for which there are insufficient fish tissue data available, a permitting
authority cannot determine whether there is reasonable potential using a fish tissue
approach. Therefore, in this case, EPA recommends that the permitting authority take the
following actions:
• Include a special permit condition to conduct a mercury fish tissue survey for the
receiving waterbody, unless such information will be available from another source
in a timely manner.
• Include as a permit condition a reopener clause to identify the actions that the
permitting authority may take should fish tissue monitoring information become
available and indicate that a WQBEL for mercury is necessary.
• Encourage the permittee to develop and implement an MMP tailored to the
facility's potential to discharge mercury.
In this instance, the permitting authority should start a process for collecting fish tissue
data in the waterbodies where point source discharges of mercury exist. One approach for
collecting this information is for the permitting authority to invoke its authority under
CWA section 308 (state permitting authorities would use comparable state authorities) to
require NPDES facilities to collect information necessary for the development of NPDES
permit limits. In this case, the permitting authority could issue a section 308 letter or
include special conditions in the permit to require the permittee to conduct a
methylmercury fish tissue monitoring study. EPA recommends that the study design be
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consistent with the recommendations on conducting ambient monitoring in section 4.2 of
this guidance.
EPA also recommends that the permitting authority require only one study per
waterbody. The permitting authority could do this by contacting all facilities that
discharge into the waterbody and encouraging them to work jointly to conduct the study,
because the outcomes of the study may affect the permit limits of those facilities. For
example, the State of Idaho has developed a statewide fish tissue monitoring program for
mercury that provides a standardized approach for collecting reliable data while
recognizing limited resources for monitoring.
In waterbodies where the permitting authority expects to find high mercury
concentrations in the water column or believes it will need a site-specific BAF to finish
issuing the permits, the permitting authority should consider requiring the facility to
include measurement of water column concentrations of mercury as part of the study.
EPA further recommends that the permit include a reopener clause so that as soon as
there is complete information, the permitting authority can establish any additional
requirements that are necessary. In this situation EPA recommends that the permitting
authority encourage the permittee to develop and implement an MMP for the reasons
discussed in section 7.5.1.2.2.1.
7.5.1.2.2 What are the recommended permit conditions when a facility discharges
quantifiable amounts of mercury but the fish tissue concentrations of
methylmercury in the receiving waterbody do not exceed and are not close
to the criterion ?
Once the permitting authority has determined that a facility discharges quantifiable
amounts of mercury and that the concentration of methylmercury in fish tissue in the
receiving waterbody does not exceed and is not close to the criterion, depending on the
particular facts, the permitting authority may reasonably conclude that the discharge does
not have reasonable potential to cause or contribute to an exceedance of the applicable
fish tissue water quality criterion.
To assist in preventing future impairments, in some situations as outlined below, EPA
recommends that states and authorized tribes also consider other factors or conditions
such as a trend of rising fish tissue concentrations or the relative contribution of mercury
or methylmercury from the source when determining whether a facility has reasonable
potential in waters that are not yet impaired.
EPA notes that, unlike typical water quality criteria that are expressed as water column
values, the fish tissue water quality criterion integrates spatial and temporal complexity
as well as the cumulative effects of variable mercury loading from point and nonpoint
sources that affect methylmercury bioaccumulation in aquatic systems. EPA believes that
comparing the fish tissue concentration in steady state systems directly to the applicable
criterion expressed as a fish tissue value appropriately accounts for the factors specified
in 40 CFR 122.44(d)(l)(ii) for a criterion expressed as a fish tissue value. Existing tissue-
based data are indicators of accumulation that has already occurred. Thus, where fish
tissue concentrations in a watershed are expected to be constant (i.e., steady state
conditions) or decreasing over time, data that indicate that the fish tissue criterion is
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currently being attained may be effective indicators of current and potential continued
future attainment.
However, in dynamic systems where the levels in tissue in a watershed may be expected
to increase, EPA recommends that the permitting authority account for this as part of the
reasonable potential determination that is designed to prevent potential future
impairments.
Another factor that permitting authorities may consider is the impact of permitted
discharges to downstream waters (e.g., a discharge to a river that flows into a lake where
mercury is a concern). In such a circumstance, it may be appropriate to conclude that the
discharge has reasonable potential on the grounds that its discharge causes or contributes
to the excursion of the fish tissue criterion in the downstream water.
The presence of these other factors or conditions such as the relative contribution of
mercury or methylmercury from the source, rising fish tissue concentrations, or potential
excursion of the criterion downstream, could constitute a basis for concluding that an
effluent limit is necessary depending on the particular facts.
As discussed in section 7.5.1.2.2.2, for discharges to waters that are not impaired, EPA
recommends that states and tribes regard any activity that could result in an increase in
receiving water or fish tissue mercury concentration as a significant lowering of water
quality for the purposes of triggering an antidegradation review.
Implementing tier 2 antidegradation
If the facility undertakes any activity that could increase mercury loading to the receiving
waterbody, an antidegradation review may be necessary. Such increases must be
consistent with the applicable antidegradation policy. Federal regulations at 40 CFR
131.6 specify that tribal or state water quality standards must include an antidegradation
policy, and federal regulations at 40 CFR 131.12 identify the elements of an acceptable
antidegradation policy. Section 303(d)(4)(B) requires that applicable antidegradation
requirements be satisfied prior to modifying NPDES permits (for example, prior to
removing a WQBEL or including less stringent effluent limitations).
The federal antidegradation policy is composed of three levels of protection commonly
referred to as tiers. The first tier, identified at 40 CFR 131.12(a)(l), protects the minimum
level of water quality necessary to support existing uses and applies to all waters. This
tier prohibits lowering water quality to the point where existing uses are impaired. The
second tier, found at 40 CFR 131.12(a)(2), protects water quality where water quality is
better than that needed to support "fishable/swimmable" uses of the water. Where these
conditions exist, the waterbody is typically considered not impaired, and water quality
must be maintained and protected unless it is demonstrated that lowering water quality is
necessary to support important social and economic development and that existing uses
will be fully protected. The third tier, at 40 CFR 131.12(a)(3), involves the protection of
water quality in waterbodies that are of exceptional ecological, aesthetic, or recreational
significance. Water quality in such waterbodies, identified and specifically designated by
states or authorized tribes as Outstanding National Resource Waters, must be maintained
and protected.
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States and authorized tribes should determine whether the discharger will undertake an
activity that can result in an increase in mercury loading to the receiving waterbody.
One of two outcomes will be reached in answering this question:
• The discharger will not undertake an activity that can increase mercury loading to
the waterbody.
• The discharger will undertake an activity that can increase mercury loading to the
waterbody.
As part of conducting a tier 2 antidegradation analysis, the permitting authority would
evaluate the activity's potential to lower water quality, whether there are alternatives that
would avoid lowering water quality, and whether lowering of water quality would be
necessary to accommodate important economic or social development in the area of the
discharge. EPA considers analyses of potential pollution prevention and enhanced
treatment alternatives as an appropriate starting point for the antidegradation review for
both industrial and municipal dischargers. See 67 FR 68971, 68979. The results of such
an analysis of potential alternatives could provide the basis for developing an MMP.
EPA's recommendations for implementing antidegradation provisions and addressing
increases in mercury loads are summarized in figure 8 and explained in sections
7.5.1.2.2.1 and 7.5.1.2.2.2. EPA recognizes, however, that states and tribes have the
flexibility to interpret their antidegradation policies differently. For example, some states
use limits established at existing effluent quality to implement their antidegradation
provisions.
7.5.1.2.2.1 What are the recommended permit conditions when a facility discharges
quantifiable amounts of mercury into a waterbody in which the fish tissue
concentration of methylmercury does not exceed the criterion and the
facility will not undertake an activity that could increase mercury loading to
the waterbody?
If the facility discharges a quantifiable amount of mercury and the fish tissue
concentration of methylmercury in the receiving water does not exceed the criterion,
depending on the particular facts, the permitting authority may reasonably conclude that
the discharge does not have reasonable potential to cause or contribute to an exceedance
of the applicable fish tissue water quality criterion. In such situations, however, EPA
recommends that the permitting authority encourage the facility to develop and
implement an MMP.
An MMP helps ensure that the discharge will continue to have no reasonable potential to
cause or contribute to an exceedance of applicable water quality standards. The
recommendation to develop a voluntary MMP is also based on the extent of potential
mercury impairment across the country and the scientific complexities of and
uncertainties associated with assessing mercury loadings and evaluating their effects.
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NPDES Implementation Procedures
Recommend voluntary MMP
Discharge contains a
quantifiable amount of mercury
but fish tissue in the receiving
water does not exceed the
criterion (Figure 7)
Yes
Implementing
Antidegradation
No
Will the discharger undertake
an activity that could result
in an increase in receiving
water or fish tissue mercury
concentration?
Yes
Conduct tier 2
antidegradation analysis
and develop appropriate
permit conditions
Require permittee to
develop and implement
MMP tailored to facility
Require effluent monitoring
Figure 8. Implementing tier 2 antidegradation.
If future monitoring data demonstrate that a discharge does have reasonable potential,
development of a MMP could assist the permit writer in establishing appropriate permit
conditions. Furthermore, EPA believes that simply developing an MMP might provide
dischargers of mercury with sufficient information to economically reduce the discharge
of mercury into our Nation's waters by voluntarily implementing the mercury
minimization measures identified in the plan. Section 7.5.2.1 provides additional
information on MMPs.
7.5.1.2.2.2 What are the recommended permit conditions when a facility discharges
quantifiable amounts of mercury into a waterbody in which the fish tissue
concentration ofmethylmercury does not exceed the criterion but the facility
will undertake an activity that could result in an increase in receiving water
or fish tissue mercury concentration?
In this situation, the receiving water does not currently exceed the fish tissue criterion.
EPA believes that increases in mercury loading to a waterbody should be allowed at
levels determined appropriate by an antidegradation analysis and that such dischargers
should be required to implement MMPs under the authority of CWA section 402(a)(l)(B)
and 40 CFR 122.44(k)(4).
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NPDES Implementation Procedures
EPA recommends the following WQBEL requirements:
• Include permit conditions consistent with antidegradation requirements.
• Require the permittee to implement an MMP tailored to the facility's potential to
discharge mercury. Depending on the particular facts, the permitting authority may
include in the MMP a trigger level, reduction goal, or enforceable numeric level to
further manage mercury discharges.
• Require the permittee to monitor its effluent using a sufficiently sensitive EPA-
approved method (see sections 7.4 and 7.5.1.1 for information on sufficiently
sensitive methods).
Other considerations and requirements might be necessary in developing permits:
• The permitting authority would need to include appropriate technology-based
limits pursuant to CWA section 301(b) and 40 CFR sections 125.3 and
122.44(a)(l) .
• For modified or reissued permits with existing effluent limits for mercury, any less
stringent effluent limit must be consistent with anti-backsliding requirements (see
section 7.2.4).
Activities that would lower water quality in a high-quality water must be consistent with
the applicable antidegradation provisions of a state's or authorized tribe's water quality
standards. Consistent with EPA's antidegradation regulations for water quality standards,
state and tribal antidegradation regulations are to provide that the quality of waters at
levels better than the levels necessary to support "fishable/swimmable" uses of the water
may be lowered only if the state or authorized tribe determines that allowing lower water
quality is necessary to accommodate important economic or social development in the
area in which the waters are located (see 40 CFR 131.12(a)(2)). EPA recommends that
states and authorized tribes regard any activity that could result in an increase in
receiving water or fish tissue mercury concentration as a significant lowering of water
quality for the purposes of triggering a tier 2 antidegradation review. If the state's or
authorized tribe's antidegradation analysis determines that the proposed lowering of
water quality should not be allowed, the permitting authority would not authorize or
allow any such discharge to occur. If the state's or authorized tribe's antidegradation
analysis determines that a lowering of water quality is allowable, the level to which the
discharger is ultimately allowed to lower water quality (on the basis of the applicable
antidegradation requirements) would then be subject to a reasonable potential analysis.
Also, EPA's antidegradation regulations for water quality standards require state and
tribal antidegradation regulations to protect the minimum level of water quality necessary
to support existing uses by prohibiting lowering of water quality to the point where
existing uses are impaired (see 40 CFR 131.12(a)(l)).22 For new and increased
discharges, states have the flexibility to interpret their antidegradation policies
differently. For example, some states use limits established at existing effluent quality.
22 This part of the antidegradation analysis is similar to the reasonable potential determination and WQBEL development process that a
permitting authority conducts for an existing discharger.
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EPA expects that fluctuations in mercury loadings arising from normal industrial
production fluctuations, or loading fluctuations that are not results of change in existing
POTW service areas, would generally not trigger a tier 2 antidegradation analysis. EPA
expects that increases in mercury loadings from a POTW arising from adding a new
subdivision or an unsewered neighborhood to a sewer service area would generally
trigger a tier 2 antidegradation review. If an antidegradation review is triggered, the
review should consider the source of the increased mercury loading, the potential for
source reduction through either treatment, pretreatment or pollution prevention, and the
expected benefits likely to accrue to the affected community as a result of the activities
that result in increased mercury loadings. EPA recommends that states and tribes tailor
the level of detail and documentation for antidegradation demonstrations to the specific
circumstances. For example, in some instances, as with diffuse domestic sources of
mercury, available treatment and pollution prevention alternatives may be limited or
lacking, leaving only the importance of social and/or economic development as the
primary focus of the review.
EPA recognizes that an increase in the discharge of mercury might be due to mercury
present in stormwater or input process water that does not originate with and is not under
the reasonable control of a facility. While an MMP, to the extent that there are available
BMPs to minimize mercury discharges, might still be appropriate in such circumstances,
EPA would not generally expect that such discharges would trigger the need for an
antidegradation review, or numeric WQBELs.
In addition to permit conditions consistent with antidegradation requirements, EPA
recommends that the permit require the dischargers to implement an MMP under the
authority of CWA section 402(a)(l)(B) and 40 CFR 122.44(k)(4). The MMP should be
tailored to the individual facility's potential to discharge mercury. For more information
on MMPs, see section 7.5.2.1.
7.5.1.2.3 What are the recommended permit conditions when a facility discharges
quantifiable amounts of mercury and the fish tissue concentrations of
methylmercury in the receiving waterbody are close to or exceed the
criterion ?
EPA believes that, depending on the particular facts, a permitting authority may
reasonably conclude that reasonable potential exists if two conditions are present: (1) the
NPDES-permitted discharger has mercury in its effluent at quantifiable levels, and (2) the
fish tissue concentrations of methylmercury from the receiving waterbody are close to or
exceed the fish tissue water quality criterion.
Where fish tissue concentrations are below but close to the criterion, EPA recommends
that a finding of reasonable potential be made since the effect of current discharges and
other relevant factors may not yet be reflected in fish tissue concentrations. For example,
where the tissue data are below the water quality criterion, the permitting authority may
consider applying an appropriate confidence interval (e.g., 95 percent upper confidence
limit on the mean) to such values and compare that value to the fish tissue criterion to the
extent necessary to account for variability in fish tissue data. As an example of an
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23
alternative to this statistical approach, the State of Idaho's implementation guidance for
its methylmercury fish tissue criterion of 0.3 mg/kg recommends that where the levels in
fish exceed 0.24 mg/kg, the permitting authority should determine that reasonable
potential exists. Where methylmercury levels in fish tissue are thought to be relatively
sensitive to a water point source load of mercury or methylmercury, the permitting
authority may take that into account in the reasonable potential determination.
When reasonable potential exists, it is necessary to establish an appropriately protective
WQBEL in the permit. For guidance on recommended WQBELs, see section 7.5.2.1.
7.5.1.3 How to consider mercury in intake water with a reasonable
potential approach
For some facilities, the only source of mercury in a discharge may be the intake water
taken directly from the same body of water to which the facility discharges. An example
of this is a discharge of cooling water where the source of the cooling water is upstream
of the discharge. In these situations where there are no known sources or additional
contributions of mercury at the facility, the permitting authority could reasonably
conclude, based on the particular facts, that there is no reasonable potential to cause or
contribute to an exceedance of water quality standards. Furthermore, any slight increase
in concentration after discharge (due to evaporation or other water loss) should not have
an effect on the bioaccumulation of methylmercury in fish tissue unless the fish are
known to frequently inhabit the water in the area immediately adjacent to the discharge.
In making this decision, the permitting authority should consider the monitoring data
from both the intake and discharge to verify that there are no known sources of additional
contributions of mercury at the facility. EPA also recommends that permitting authorities
consider evaluating whether the methylmercury concentration in fish tissue significantly
increases for facilities with anaerobic conditions in the discharge. This procedure
represents a comprehensive approach for conducting a site-specific analysis of the
potential for a discharge to cause or contribute to an excursion above a water quality
standard, which can lead to a decision to not require a WQBEL. This approach is
consistent with the rationale for the federal regulations pertaining to the Great Lakes
Basin, which included consideration of intake pollutants in finding reasonable potential
(see 40 CFRpart 132, appendix F, procedure 5.D).
7.5.2 Where reasonable potential exists, how can WQBELs be
derived from a fish tissue value?
As discussed in section 3.1.2.2 of this document, EPA recommends that states and
authorized tribes adopt a new or revised methylmercury water quality criterion in the
form of a fish tissue concentration. When the criterion is adopted into standards as a fish
tissue value, some states and authorized tribes may not have sufficient data to translate
from a fish tissue value to a traditional water column value using BAFs or translators.
When developing WQBELs, the permitting authority must ensure that the level of water
quality to be achieved by such limits derives from and complies with water quality
23 Implementation Guidance for the Idaho Mercury Water Quality Criteria is available at http: //www. deq. state .id. us/water/data reports/
surface water/monitoring/idaho mercury wq guidance.pdf.
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standards (see 40 CFR 122.44(d)(l)(vii)). This section provides recommendations on
how a permitting authority could derive appropriate WQBELs in the absence of a TMDL
and a water column translation of the fish tissue criterion at the time of permit issuance.
The information discussed in this section is summarized in figure 9.
Discharge contains a quantifiable amount
of mercury
AND
the fish tissue in the receiving water is
dose to or exceeds the criterion (Figure 7)
Tves
Recommended WQBEL Requirements
• Where a TMDL has been developed, the WQBEL must be consistent with the wasteload allocation as required by
40CFR122.44(d)(1J(vii)(B))
• Where a TMDL has not been developed but a water column translation of the fish tissue criterion has been developed, or
the site-specific data to translate is readily available, include a numeric water quality-based limit
• Where a water column translation or data to translate is not available and the permit writer determines that a numeric limit
is infeasible to calculate:
- Require the permittee to develop and implement an MMP tailored to the facility's potential to discharge mercury.
Depending on the particular facts, the permitting authority may include in the MMP a trigger level, reduction goal, or
enforceable numeric level (e.g., existing effluent quality) to further manage mercury discharges
- Require effluent monitoring using a sufficiently sensitive EPA-approved method to determine whether the MMP is
effective (See sections 7.4 and 7.5.1.1 for more information on sufficiently sensitive methods)
- Include a reopener clause to modify the permit conditions if the MMP is not found to be effective or if a water column
translation of the fish tissue criterion is developed
• Where a discharger undertakes an activity that could increase mercury loading to the receiving water, it must be
consistent with applicable antidegradation requirements. Additional requirements may also be necessary under the
CWA and EPA's NPDES regulations.
Note:
aFor Greal Lakes states, implement using 40 CFR 132, Appendix Fs Procedure 5,
Figure 9. Determining WQBEL requirements.
7.5.2.1 What are the recommended WQBELs?
If the facility has a quantifiable amount of mercury in its discharge and the concentration
of methylmercury in fish tissue in the receiving water is close to or exceeds the criterion,
depending on the particular facts, the permitting authority may reasonably conclude that
the discharge has reasonable potential to cause or contribute to an exceedance of the
applicable fish tissue water quality criterion. In this situation, in the absence of a TMDL
and a water column translation of the fish tissue criterion, it may be appropriate to
conclude that it is infeasible to calculate a numeric WQBEL at the time of permit
issuance and to instead express the WQBEL as narrative BMPs, as provided in
122.44(k)(3).
Where a TMDL containing wasteload allocations for the discharge of mercury (and
methylmercury where appropriate) has been developed, the WQBEL for that discharge
must be consistent with the wasteload allocation (see 40 CFR 122.44(d)(l)(vii)(B)).
Where a TMDL is not available at the time of permit issuance, to satisfy
122.44(d)(l)(vii)(A), EPA recommends that the WQBEL consist of the following
elements:
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• Where a water column translation of the fish tissue criterion has been developed, or
site-specific data to do so are readily available, include a numeric water quality-
based limit.
• Where a water column translation or site-specific data are not available and the
permit writer determines that a numeric limit is infeasible to calculate:
o Require the permittee to implement an MMP tailored to the facility's potential
to discharge mercury. Depending on the particular facts, the permitting
authority may include in the MMP a trigger level, reduction goal, or
enforceable numeric level to further manage mercury discharges.
o Require effluent monitoring using a sufficiently sensitive EPA-approved
method to enable evaluation of the effectiveness and implementation of the
MMP. (See sections 7.4 and 7.5.1.1 for more information on sufficiently
sensitive methods.)
o Include a reopener clause to modify the permit conditions if the MMP is not
found to be effective or if a water column translation of the fish tissue
criterion is developed.
Other considerations and requirements may be necessary in developing permits:
• Where a discharger undertakes an activity that could increase mercury loading to
the receiving water, it must be consistent with applicable antidegradation
requirements. Additional requirements may also be necessary under the CWA and
EPA's NPDES regulations.
• The permitting authority would need to include appropriate technology-based
limits pursuant to CWA section 301(b) and 40 CFR sections 125.3 and
122.44(a)(l) .
• For modified or reissued permits with existing effluent limits for mercury, any less
stringent effluent limit must be consistent with anti-backsliding requirements (see
section 7.2.4).
7.5.2.2 What does EPA recommend where direct water inputs are
relatively high?
This section describes EPA's recommendations where direct water inputs of mercury are
relatively high. In this section, EPA discusses the recently developed "5m" listing
approach for waters impaired by mercury from primarily atmospheric sources, as well as
approaches for developing TMDLs, analyses of sources and loading capacity similar to
what would be provided in a TMDL, or water column translations of the fish tissue
criterion, to serve as the basis for permit limits.
As described in section 6.2, EPA recently developed an optional voluntary approach for
deferring TMDL development for waters impaired by mercury predominantly from
atmospheric sources pursuant to CWA section 303(d). Under this approach, states with
comprehensive mercury reduction programs may consider waters appropriate for
inclusion in a subcategory of their impaired waters lists (category 5m under the
Integrated Report Guidance) and defer the development of TMDLs for those waters.
EPA's 5m guidance states that in deciding on the scope of waterbodies proposed for
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subcategory 5m, a contribution for states to consider would be approximately 90 to 95
percent of the loadings or higher from air deposition to the waterbody; the specific
percent may vary, however. A full description of the 5m approach is at
http://www.epa.gov/owow/tmdl/mercury5m/.
In watersheds where direct water inputs (mercury from point sources and nonpoint
sources other than air deposition) represent a relatively high contribution of mercury,
EPA recommends that states and authorized tribes specifically consider developing
numeric permit limits for mercury dischargers to these waterbodies. States and authorized
tribes may develop TMDLs for these waterbodies in the short term to provide important
information for developing appropriate permit limits. Where a state or authorized tribe
chooses not to develop a TMDL in the short term for such a waterbody, EPA
recommends that the state or tribe develop an analysis of sources and loading capacity
similar to what would be provided in a TMDL or a water column translation of the fish
tissue criterion using the methods outlined in 3.1.3.1. Consistent with the 5m approach
for establishing priorities for mercury TMDL development, in deciding whether there is a
relatively high contribution from direct water inputs, a contribution for states to consider
would be approximately 5 to 10 percent or more of mercury loadings from direct water
inputs, taking into account that the specific percent may vary by state. At the same time,
states may consider other factors, such as the complexity of the TMDL, in determining
schedules for developing TMDLs.
Cumulative loads from point sources and localized nonpoint sources such as abandoned
mines, contaminated sediments, and naturally occurring sources can potentially combine
to cause localized mercury impairment. These situations are more complicated because
the specific location and magnitude of each source could significantly affect fish tissue
concentrations. In these situations, a TMDL provides the best basis for developing the
appropriate permit limits.
Once EPA has approved or established a TMDL containing a wasteload allocation for the
discharge of mercury (and methylmercury where appropriate), the permitting authority
develops a WQBEL for a point source discharge that is consistent with the requirements
and assumptions of the wasteload allocation in the TMDL (see 40 CFR
122.44(d)(l)(vii)(B)). In addition to developing a WQBEL, the permitting authority
specifies monitoring requirements for the WQBEL (see 40 CFR 122.44(i) and 122.48).
EPA recommends that permitting authorities require the permittee to use a sufficiently
sensitive EPA-approved method for monitoring purposes.
In such watersheds where direct water inputs represent a relatively high mercury loading,
EPA recommends that the permitting authority and the mercury dischargers in the
watershed work together to collect the data necessary to develop a TMDL, an analysis of
sources and loading capacity similar to what would be provided in a TMDL, or a water
column translation of the fish tissue criterion. One approach for collecting information
for a source analysis described above or a water column translation of the fish tissue
criterion is for the permitting authority to invoke its authority under CWA section 308
(state permitting authorities would use comparable state authorities) to require NPDES
facilities to collect information necessary for the development of NPDES permit limits.
In the absence of a final TMDL, EPA recommends that a permitting authority conduct an
analysis of sources and loading capacity similar to what would be provided in a TMDL.
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Such an analysis that applied factors similar to those considered in a TMDL could be
included in the fact sheet of the draft permit as a justification for the effluent limit being
as stringent as necessary to attain the water quality standard. The permitting authority
may also use a water column translation of the fish tissue criterion to derive numeric
permit limits if such a translation or site-specific data to translate are available.
A water column translation of the fish tissue criterion may not always be necessary in
developing a TMDL or an analysis of sources and loading capacity similar to what a
TMDL would provide. For example, section 6.2.2.2.1 of this guidance provides
descriptions of TMDLs that have been developed using steady state models and the
proportionality approach.
Since permitting authorities need to establish and maintain WQBELs as stringent as
necessary to meet water quality standards, if a state or tribe has yet to complete the
transition from an existing water column criterion to a fish tissue-based criterion, states
may consider retaining their existing water column criteria until translators are
developed. Alternatively, until a translator is available, EPA recommends that one of the
approaches outlined in this document for relating a concentration of methylmercury in
fish tissue to a concentration of methylmercury in ambient water be considered (see
section 3.1.3.1.)
7.5.2.3 What additional requirements may apply?
Activities that could increase mercury loadings to a receiving waterbody
Permits for sources that are seeking authorization to increase their discharge of mercury
(or commence the discharge of mercury) must be consistent with applicable
antidegradation requirements. See discussions of antidegradation elsewhere in this
chapter, including sections 7.2.3 and 7.5.1.2.2.
The permitting authority may consider whether an offset of such discharges by other
pollutant source reductions would support the development of a WQBEL that would
ensure that the level of water quality to be achieved by such effluent limitation is derived
from and complies with the water quality standards, as required by 40 CFR
122.44(d)(l)(vii)(A) and any other applicable NPDES regulations.
Pretreatment
A POTW is required to prohibit discharges from industrial users in amounts that result in
or cause a violation of any requirement of the POTW's NPDES permit (see 40 CFR
403.2(a) and (b), 403.3(i) and 403.3(n)). A POTW that accepts mercury in its collection
systems may need to ensure that its pretreatment program prevents its effluent from
contributing to exceedance of the fish tissue criterion. The general pretreatment
regulations (at 40 CFR part 403) require that each POTW, or combination of POTWs
operated by the same water authority, with a design flow of 5.0 million gallons per day
(MOD) or more develop an approved pretreatment program that protects against pass-
through and interference, which may be caused by industrial discharges to the treatment
facilities, by developing local limits for mercury and other pollutants or demonstrating
that limits are not necessary for these pollutants. The POTW is also required to prohibit
discharges from industrial users in amounts that result in or cause a violation of any
requirement of the POTW's NPDES permit (see 403.2(a) and (b), 403.3(i) and 403.3(n)).
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Federal categorical pretreatment standards, which are applicable to certain classes of
industries, establish technology-based minimum pretreatment standards. The categorical
standards, however, do not address POTW-specific problems that may arise from
discharges by categorically regulated industries. In addition, many types of industries that
discharge significant quantities of pollutants are not regulated by the categorical
standards. Hence, there is a need for many POTWs to establish site-specific discharge
limits to protect the treatment facilities, receiving water quality, and worker health and
safety and to allow for the beneficial use of sludge.
Technology-based limits
When developing effluent limits for an NPDES permit, a permit writer must impose
limits based on the technology available to treat mercury (technology-based limits) as a
minimum level of control, as required by CWA section 301(b) and 40 CFR sections
125.3 and 122.44(a)(l). There are two general approaches for developing technology-
based effluent limits for industrial facilities: national effluent limitation guidelines
(ELGs) and best professional judgment (BPJ) on a case-by-case basis (in the absence of
ELGs). Technology-based effluent limits for municipal facilities (POTWs) are derived
from secondary treatment standards.
Anti-backsliding
Where a facility has a currently effective effluent limit for mercury and seeks a less
stringent limit, the permitting authority must also comply with anti-backsliding
requirements (see CWA section 402(o) and 40 CFR 122.44(1); see also CWA section
303(d)(4)). These requirements are described in EPA's NPDES Permit Writers' Manual
(USEPA 1996b).
Permit documentation
Documentation is an important part of the permit development process. The NPDES
permit fact sheet should provide an explanation of how the limit proposed in the
associated draft permit is as stringent as necessary to achieve water quality standards
(40 CFR 124.8 and 124.56). The recommendations in this guidance could be applied on a
permit-by-permit basis, where appropriate, to support effluent limitations and other
conditions that satisfy CWA section 301(b)(l)(C) and 40 CFR 122.44(d)(l) with respect
to mercury.
7.5.2.4 Mercury minimization plans
EPA recommends that the permit contain a special condition requiring the permittee to
implement an MMP that includes effluent monitoring using a sufficiently sensitive EPA-
approved method (see sections 7.4 and 7.5.1.1 for information on sufficiently sensitive
methods), with the expectation that effluent monitoring will allow for evaluation of the
effectiveness and implementation of the plan. The MMP would be included in the permit
in addition to a numeric WQBEL in cases where a TMDL, a water column translation of
the fish tissue criterion, or other water concentration criterion is available at the time of
issuance. If neither a TMDL nor a water column translation (or other water criterion) is
available at the time of permit issuance, however, the MMP would be included in the
permit as part of a narrative WQBEL in lieu of a numeric WQBEL. EPA believes that,
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depending on the particular facts, a permit writer may reasonably conclude that such
MMPs are as stringent as necessary to achieve water quality standards, for the reasons
discussed below.
EPA believes that mercury reductions achieved through implementing MMPs tailored to
the facility's potential to discharge mercury could result in important reductions in
mercury loadings. EPA's basis for this conclusion is its study of pollutant minimization
programs and their success in reducing mercury loadings to the environment. The reports
Mercury Study Report to Congress (USEPA 1997c) and draft Overview ofP2
Approaches at POTWs (USEPA 1999b) show that POTWs and industrial dischargers
have implemented source controls, product substitution, process modification, and public
education programs with great success. These minimization practices focus on sources
and wastes that originate with and are under the reasonable control of a facility, not on
pollutants in rainwater or source water.
As an example, POTWs can educate the public to prevent pollution by avoiding
household products that contain high levels of mercury or substituting for those products
ones that are mercury-free or more environmentally friendly. The most cost-effective
approach for POTWs to substantially reduce mercury discharges appears to be pollution
prevention and waste minimization programs that focus on high-concentration, high-
volume discharges to the collection system, with considerable effort also directed at high-
concentration, low-volume discharges such as those from medical and dental facilities.
Using pollutant minimization or prevention programs can also reduce the transfer from
wastewater to other media through disposal of mercury-containing sludge from which
mercury may subsequently reenter the environment. For example, mercury removed at a
POTW through treatment is likely to reenter the environment through POTW sludges that
are then incinerated or applied to land (although some is captured by air emission
controls on incineration). EPA believes that a better approach for reducing mercury
releases to the environment is to prevent mercury from entering the wastewater collection
system at the source through product substitution, waste minimization or process
modification, or removing and recycling mercury at the source (source controls) using
state-of-the-art technology. These measures aimed at reducing influent loads to POTWs
also reduce the use of mercury in the community, which could reduce the amount of
mercury entering the environment through other media or sources. (For example,
products that contain low levels of mercury may be disposed of as a nonhazardous solid
waste and incinerated, releasing mercury to the air.) Where pollution prevention
approaches have been implemented, substantial reductions in mercury concentrations in
POTW influents, sludges, and effluents have been achieved. For a discussion of this
approach, see the draft Overview of P2 Approaches at POTWs (USEPA 1999a). For an
example of guidance on developing an MMP, see the EPA Region 5 final document
Mercury Pollutant Minimization Program Guidance, dated November 2004
(http://www.epa.gov/region5/water/npdestek/mercury_pmp_nov_04_guidance.pdf).
Many of the recommendations contained in the document are drawn from existing
guidance and practice of state permitting authorities in EPA's Regional Office in
Chicago. See also the City of Superior's document, Mercury Pollutant Minimization
Program Guidance Manual for Municipalities, at http://www.ci.superior.wi.us/
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index.asp?NID=129. and EPA's Local Limits Development Guidance (USEPA 2004) at
http://www.epa.gov/npdes/pubs/final local limits guidance.pdf.
Finally, as explained in section 2.1.1, mercury is a bioaccumulative, persistent pollutant
that can cause adverse health effects. Given this fact, EPA believes that point sources that
can cost-effectively reduce their mercury discharges should do so. The fact that air
sources or historical contamination are likely dominant causes of impairment does not
mean that point sources should not implement cost-effective, feasible pollution
prevention measures to reduce their contribution of mercury to the environment, however
small those contributions may be. In short, EPA believes that it is reasonable to expect
NPDES permittees to implement cost-effective, feasible, and achievable measures to
reduce the amount of mercury they discharge into the environment and that, depending
on the particular facts, permit writers may reasonably conclude that permit limits that
require such measures derive from and comply with water quality standards as required
by EPA regulations at 40 CFR 122.44(d)(l)(vii)(A).
In cases where a permittee believes it may have reasonable potential, EPA recommends
that the permittee provide information that the permitting authority can use in developing
appropriate permit conditions and would encourage the permittee to provide a draft
MMP. Alternatively, where a draft MMP is not initially submitted by the permittee, the
permitting authority may request that the permittee provide a draft MMP. The permitting
authority retains the final responsibility for determining reasonable potential, and for
incorporating the appropriate permit conditions, including an effective MMP and its
implementation, in the permit.
Developing an MMP need not be an intensive or burdensome activity. The content of an
MMP should be determined on a case-by-case basis and tailored to the individual
facility's potential to discharge mercury and implement reasonable controls. The MMP
could be as little as one or two pages or as much as a major engineering study. Table 6
contains suggestions for the content of an MMP based on the type of facility. Of course,
MMPs should vary in their level of detail and degree of stringency on the basis of site-
specific factors and the degree to which the facility has the ability to reduce
environmental releases of mercury. For example, if the mercury analysis performed for
the permit application shows a much higher concentration than would be expected for the
type of facility, further investigation would be appropriate and could lead to increased
requirements. On the other hand, EPA recognizes that MMPs may not be effective in
certain cases such as when an increase in the discharge of mercury may be due to the
presence in stormwater or input process water that does not originate with and is not
under the reasonable control of a facility.
If a permittee has several of the types of sources listed in table 6, each of these sources
should be considered in developing an appropriate MMP. For example, if the service area
of a POTW contains dental offices and medical facilities, the MMP should contain
appropriate measures for both. The mercury minimization measures suggested in table 6
are expected to reduce mercury levels in the wastewater discharge as well as other waste
streams and media. Most of the mercury discharged to POTWs, for example, ends up in
biosolids that may be incinerated or disposed on the land, thus contributing to the overall
mercury burden in the environment. In addition, any measures that reduce releases to the
atmosphere should be encouraged.
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Table 6. Suggested content for MMPs based on the type of facility
Type of facility
Publicly (or privately) owned treatment
works serving a purely residential area.
No dental or medical offices or hospitals.
No industrial users.
POTW whose service area contains
dental offices.
POTW whose service area contains one
or more hospitals.
POTW whose service area contains
schools or medical offices.
Industrial direct or indirect dischargers
that use mercury as an intentional
component of their process or recover
mercury as a by-product of their process.
Industrial direct or indirect dischargers
that do not use mercury as an intentional
component of their process and do not
recover mercury as a by-product of their
process.
Suggested content
Recommended distribution of outreach materials on
fish-consumption advisories and properly disposing of
mercury-containing products.
Recommend or require that dental offices follow
American Dental Association BMPs.a Collect any bulk
mercury in the offices. Develop an approach for using
amalgam separators.
Recommend or require that hospitals follow the
practices recommended by the American Hospital
Association.
Recommend or require that schools and medical
offices properly dispose of bulk mercury in their
possession (including, for example, mercury-containing
sphygmomanometers).
Generally, such a case would involve a thorough
analysis of opportunities to reduce their releases of
mercury.
Such facilities should investigate opportunities to
reduce their incidental releases of mercury such as
recycling fluorescent lamps, switches, thermostats, etc.
and replacing them with low-mercury or non-mercury
products.
Notes:
For more information on the American Dental Association BMPs, see Best Management Practices for
Amalgam Waste (September 2005) at http://www.ada.org/prof/resources/topics/
topics amalaamwaste.pdf.
For more information on American Hospital Association practices, see Replacing Mercury in Healthcare
Facilities—A Step-by-Step Approach at http://www.h2e-online.ora/hazmat/mercguide.html.
When developing MMPs, EPA recommends beginning with any existing best
management plans and spill prevention and containment control plans for that facility.
Many of the activities covered by those plans can also reduce mercury sources to
wastewater. After reviewing many pollutant minimization programs, EPA recommends
that a plan include at least the following elements:
• Identification and evaluation of current and potential mercury sources
• For POTWs, identification of both large industrial sources and other commercial or
residential sources that could contribute large mercury loads to the POTW
• Monitoring to confirm current or potential sources of mercury
• Identification of potential methods for reducing or eliminating mercury, including
requiring BMPs or assigning limits to all potential sources of mercury to a
collection system, material substitution, material recovery, spill control and
collection, waste recycling, process modifications, housekeeping and laboratory
use and disposal practices, and public education
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• Implementation of appropriate minimization measures identified in the plan
• Effluent monitoring to verify the effectiveness of pollution minimization efforts
EPA believes that these minimum permit conditions may be appropriate because they
help to ensure that the discharge does not cause or contribute to an exceedance of water
quality standards to protect against possible localized impacts and to minimize the
discharge of mercury. EPA also believes that, depending on the particular facts, a permit
writer may reasonably conclude that such an MMP is as stringent as necessary to achieve
water quality standards.
To further manage mercury discharges, the permitting authority should consider
including an effluent trigger level or reduction goal in an MMP. Such a trigger level or
goal could be set at a level that would provide a basis for evaluating whether the mercury
minimization measures or BMPs specified in the MMP are working as anticipated. The
level or goal could be expressed numerically or in narrative form. For example, the MMP
might provide a trigger level equal to the existing effluent quality that, if exceeded, would
indicate that mercury minimization measures may not be effective. Alternately, the MMP
might provide goals for mercury reductions that are expected to occur as a result of the
implementation of mercury minimization efforts specified in the MMP. As explained in
this section and in section 7.5.2.1, an MMP includes a set of BMPs that would be part of
an enforceable special condition of the permit. The MMP might specify that exceeding a
trigger level or failing to achieve a mercury reduction goal would prompt actions such as
reevaluation of the MMP, additional monitoring, or the implementation of additional
BMPs. In this case, the failure of the permittee to undertake the additional actions
identified in the MMP would be a violation of the permit special condition.
Even where it is infeasible to calculate a numeric WQBEL (for the reasons discussed in
section 7.5.2.1), a permitting authority should consider including in the MMP an
enforceable numeric level on the discharge of mercury. In this case, the enforceable
numeric level would not constitute a stand-alone water quality-based effluent limit, but
rather, a baseline for achieving mercury reductions that, combined with the other
measures and practices in the MMP, would together constitute the water quality-based
effluent limit. Such an enforceable numeric level could represent either existing effluent
quality or a level representing some increment of the mercury reduction determined
achievable as a result of the measures and practices specified in the MMP. Depending on
the particular facts, the permit writer may reasonably conclude that the enforceable
numeric level combined with the other measures and practices in the MMP will result in
a level of mercury discharge that is controlled as stringently as necessary to meet water
quality standards. Where the MMP contains an enforceable numeric level for mercury
and/or methylmercury in the effluent, exceeding that value would be a violation of the
permit special condition.
The permitting authorities should consider use of effluent trigger levels, effluent
reduction goals, and enforceable numeric levels in any discharge permits that are based
on MMPs as water quality-based effluent limits. EPA recommends that permitting
authorities include such levels or goals in permits where direct water inputs are relatively
high.
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8 Related Programs
Ci
A wide variety of actions are under way in the United States and internationally to
address mercury contamination. EPA's mercury Web site, at http://www.epa.gov/
mercury, provides a broad range of information about mercury: actions by EPA and
others, including international actions, effects on people and the environment, and how
people can protect themselves and their families.
With respect to EPA's actions, on July 5, 2006, EPA issued a report titled EPA 's
Roadmap for Mercury ^Roadmap"). It is at http://www.epa.gov/mercury/roadmap .htm.
EPA's Roadmap describes the Agency's progress to date in addressing mercury issues
domestically and internationally, and it outlines EPA's major ongoing and planned
actions to address risks associated with mercury. The Roadmap describes the Agency's
most important actions to reduce both mercury releases and human exposure to mercury.
Creating the Roadmap has enabled EPA to maximize coordination of its many diverse
efforts, with the goal of improving its mercury program. In addition to providing a
roadmap for EPA, the report provides important information about mercury to other
federal agencies; to EPA's partners in state, tribal, and local governments; and to the
public.
•"•',; ; ; ^ ; < '
Under the national pretreatment program, POTWs routinely control the volume and
concentration of pollutants contributed by significant industrial users (SIUs)24 to their
collection system and wastewater treatment plant. However, as water quality criteria,
sludge standards, and air emissions standards become more restrictive, even low levels of
pollutants like mercury might cause noncompliance with these standards. Therefore,
POTWs must expand pollutant control efforts or install treatment technologies to remove
the problem pollutants.
In many cases, large-scale treatment technology is either not yet available or not
economically feasible for controlling mercury at POTWs. Instead, POTWs are choosing
to develop and implement pollution prevention (P2) strategies to reduce the amount of
mercury received by the wastewater treatment plant. Although SIUs can contribute a
significant mercury load to the treatment plant, non-SIU sources can also be identified as
causing or contributing to the problem. For example, the Western Lake Superior Sanitary
District (WLSSD) determined that one SIU and many small non-SIUs (dental facilities)
24 EPA defines an SIU as (1) any industrial user (IU) subject to a categorical pretreatment standard (national effluent guidelines); (2) any
user that discharges an average of 25,000 gallons per day or more of process wastewater or that contributes a process waste stream making
up 5 percent or more of the average dry weather hydraulic or organic capacity of the POTW treatment plant; or (3) any other user
designated by the Control Authority (POTW) to be an SIU on the basis that it has a reasonable potential for adversely affecting the
POTWs operation or for violating a pretreatment standard or requirement (40 CFR 403.4(v)).
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contribute a major portion of the mercury in its wastewater. Sectors historically more
difficult to control (e.g., residential) or beyond the POTW's direct control (e.g., pollutants
in contaminated inflow/rainfall) can also contribute substantial loadings.
Effective mercury source reduction relies on the POTW's effectively communicating to
sector entities that minimal individual efforts can collectively reduce the mercury loading
to the environment. Forming partnerships and working with sector representatives to
investigate mercury sources, explore alternatives, and assist in implementing selected
options is integral to a successful reduction strategy. Permitting authorities developing a
P2 plan should consider a POTW's role in compliance assistance. The sections below
provide summary-level guidance for developing a POTW P2 plan.
Through the pretreatment program, POTWs should communicate with their permitting
authority, as well as maintain close contact with local sewer dischargers and have a good
understanding of specific industrial process operations. Thus, they can uniquely promote
P2 to numerous facilities and provide public awareness and education. In general, the
success of a POTW P2 effort depends on a behavioral change on the part of the POTW
and the community. As noted by the City of Palo Alto, "Experience shows that people are
more likely to change their behaviors if they fully understand environmental problems
and the range of possible solutions, if they have participated in the process leading to a
policy decision, and if they believe regulators are dealing with them in good faith...."
(City of Palo Alto 1996). A POTW might minimize community resistance and apathy by
undertaking the following activities prior to developing its plan:
• Conduct a preliminary investigation of the problem and potential sources. Verify
that the problem is not a wastewater treatment plant operational issue. Identify
internal sources and any area government facilities in addition to industrial,
commercial, and uncontrollable sources that could be contributing to or causing the
problem.
• Meet with upper management (e.g., utility director, mayor, council) and discuss the
problem, preliminary findings, and potential ramifications. Upper management
support will be essential for obtaining necessary resources, funding, equipment,
and authority for implementing a P2 plan. Their support will also be necessary for
resolving any wastewater treatment plant and government facility issues. Upper
management may also advise development of a POTW mission statement that
declares goals and the chosen approach. Exhibit 1 provides an example of the
WLSSD mission statement (WLSSD 1997).
• Establish a workgroup composed of representatives from government, industry,
community, and environmental organizations, preferably those that are familiar
with P2 strategies or with the pollutant of concern. The workgroup likely will
develop or help develop the plan, guide plan implementation, and measure plan
success. Therefore, findings from the preliminary investigation will guide the
POTW to select appropriate committee members and experts. Bear in mind that the
workgroup size should ensure representation of most interests but not grow so large
as to be counterproductive. This group could also prove valuable in disseminating
information.
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With the support and expertise needed, the POTW and
workgroup can draft a plan by doing the following:
• State the problem to provide background information
about the POTW, problems caused by mercury, and
why the POTW is taking action (described in terms that
most people can understand).
• Identify the goals to determine whether the POTW
intends to help minimize mercury introduced to all
environmental media (air, water, solid waste), known as
"front-end" P2 or merely to minimize the amount of
mercury discharged to the wastewater treatment plant.
The latter option ignores mercury transfers to other
media (e.g., air, solid waste) and is the less
environmentally sound option. It may be essential for
the POTW to implement a front-end P2 approach and
establish waste collection programs for the proper
recycling or disposal of mercury-bearing wastes (e.g.,
thermometers, fluorescent light bulbs).
Exhibit 1. Example Mission Statement
The WLSSD Commitment to Zero Discharge
The WLSSD as a discharger to Lake Superior is
committed to the goal of zero discharge of
persistent toxic substances and will establish
programs to make continuous progress toward
that goal. The District recognizes step-wise
progress is only possible when pollution
prevention strategies are adopted and
rigorously pursued. These approaches will focus
upon our discharge as well as indirect sources.
WLSSD will work with its users to implement
programs, practices, and policies which will
support the goal. We will call upon the
resources and assistance of the State and
federal governments for support, including
financial support of the programs to ensure that
our users are not penalized unfairly.
WLSSD recognizes that airborne and other
indirect sources beyond District control must be
addressed in order for significant reductions to
occur.
• Define an approach that outlines the sectors selected for
P2 efforts, the criteria for targeting efforts (e.g., size of
the source loading, authority available to control the
source or sector, time necessary to produce desired results), where efforts will be
voluntary or mandatory, who will execute the various program efforts, and how the
POTW will proceed where mercury introduction is beyond its control (e.g.,
contaminated stormwater).
• Identify resources necessary to implement the plan such as staffing, equipment, and
funding.
• Create contingency plans that describe actions to be taken if the planned efforts do
not succeed, such as obtaining the authority to mandate and enforce P2 or other
source control requirements or installing wastewater treatment plant technology.
Plans might develop in response to a specific problem (e.g., elevated mercury levels in
wastewater treatment plant effluent) or proactively to minimize potential problems. Plans
will vary in complexity and in resources necessary to achieve goals. Plan updates should
detail successful and failed efforts, such as in the form of lessons learned.
8,3 V:' .; . -,- • ', '•' , ., . .••-/•.
As rules and standards pursuant to the CAA have been developed, proposed, and
promulgated since the Amendments of 1990, compliance by emitting sources and actions
taken voluntarily have already begun to reduce mercury emissions to the air across the
country. EPA expects that a combination of ongoing activities will continue to reduce
such emissions over the next decade.
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EPA has made substantial progress in addressing mercury air emissions under the CAA. In
particular, EPA has issued regulations addressing the major contributors of mercury to the
air (including, for example, municipal waste combustors; hospital, medical, and infectious
waste incinerators; chlor-alkali plants; and hazardous waste combustors). EPA issued
regulations for these source categories under different sections of the CAA, including
sections 111, 112, and 129. Indeed, as the result of EPA's regulatory efforts, the United
States achieved a 58 percent reduction in domestic mercury air emissions between 1990
and 2005 (see figure 4 and http://cfpub.epa.gov/eroe/index.cfm?fuseaction=
detail.viewMidImg&lShowInd=0&subtop=341 &lv=list.listByAlpha&r=216615# 11215).
The relevant regulations that EPA has issued to date under the CAA are described briefly
below. For more information about other CAA actions to control mercury, see
http://www.epa.gov/mercury under "What EPA and Others Are Doing."
8.3.1 Municipal waste combustors
In 1995 EPA promulgated new source performance standards (NSPS) that apply to all
new municipal waste combustor units (both waste-to-energy plants and incinerators) with
the capacity to burn more than 250 tons of municipal solid waste, including garbage, per
day and emission guidelines that apply to existing units with the same capacity through
either an EPA-approved State plan or a promulgated Federal plan (see 60 FR 65,415
[December 19, 1995], codified at 40 CFRpart 60, subparts Eb and Cb). These regulations
cover approximately 130 existing waste-to-energy plants and incinerators, as well as any
new plants and incinerators built in the future. The regulations have reduced emissions of
a number of HAPs, including mercury, by approximately 145,000 tons per year. The
regulations have resulted in about a 90 percent reduction in mercury emissions from
domestic municipal waste combustors from 1990 emission levels (57 tons per year of
mercury emitted from domestic municipal waste combustors in 1990 versus 2.3 tons per
year in 2005). In 2000, EPA promulgated NSPS and emission guidelines establishing
similar requirements for small municipal waste combustor units (units with a capacity of
35 to 250 tons per day) (see 65 FR 76,355 [December 6, 2000], codified at 40 CFR part
60, subparts AAAA and BBBB).
8.3.2 Hospital, medical, and infectious waste incinerators
Hospital/medical/infectious waste incinerators (HMIWIs) are used by hospitals, health
care facilities, research laboratories, universities, and commercial waste disposal
companies to dispose of hospital waste and/or medical/infectious waste. EPA adopted
regulations controlling mercury and other emissions from HMIWIs on September 15,
1997 (62 FR 48,348, codified at 40 CFR part 60, subparts Ce and EC). All existing
HMIWIs were required to comply with the regulations by September 15, 2002. EPA
estimated that the regulations would reduce mercury emissions from HMIWIs at existing
facilities by 93-95 percent (from 16.5 to 0.9-1.2 tons per year). In fact, the actual
mercury emission reductions achieved as a result of implementing the regulations were
approximately 98 percent. At the time the regulations were issued, EPA expected that 50
to 80 percent of the 2,400 then-existing HMIWIs would close in response to the rule.
EPA's rule resulted in a significant change in medical waste disposal practices in the
United States. Because of the increased cost of on-site incineration under the 1997 rule,
approximately 98 percent of the 2,400 HMIWIs operating at health care facilities in 1997
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have shut down or obtained exemptions, and few facilities have installed new HMIWIs (5
new HMIWIs at 4 facilities). Instead, many facilities have switched to other methods of
waste treatment and disposal, such as autoclaving and off-site commercial waste disposal.
There are currently 57 existing HMIWIs operating at 52 facilities. EPA adopted revised
regulations for HMIWIs on October 6, 2009 (74 FR 51,368). The revisions were issued in
order to respond to a court remand of the 1997 rule and to satisfy the Clean Air Act
section 129(a)(5) requirement to conduct a review of the standards every 5 years. EPA
estimates that the revised regulations will reduce mercury emissions at existing HMIWIs
by 89 percent (from 0.3 to 0.04 tons per year). The revised mercury standards are
estimated to impact 20 HMIWIs, which are expected to employ mercury control
technology (e.g., installing activated carbon injection systems or increasing current use of
activated carbon). All existing HMIWIs are required to comply with the revised
regulations by October 6, 2014.
8.3.3 Chlor-alkali plants
On December 19, 2003, EPA issued final regulations to reduce mercury emissions from
chlorine production plants that rely on mercury cells (see 68 FR 70,904, codified at 40
CFR part 63, subpart IIIII). These air regulations have reduced mercury air emissions
from existing chlor-alkali plants by approximately 50 percent since the compliance date
of December 19, 2006. The regulation requires a combination of controls for point
sources, such as vents, and BMPs to address fugitive air emissions, that are more
stringent work practices than those required by a preexisting regulation that covered this
source category. Today, there are four (4) such plants in the United States, compared to
20 when work on the rule began. In addition, EPA completed a study of fugitive mercury
emissions at existing chlor-alkali plants and found the levels of elemental mercury
emissions much lower than previously thought. Current total emissions from the four
plants are estimated to be approximately 0.3 tons per year of mostly (>98%) elemental
mercury.
8.3.4 Hazardous waste combustors
In 2005, EPA published standards under Section 112(d) of the CAA for hazardous waste
combustors (HWCs)--incinerators, cement kilns, lightweight aggregate kilns, liquid fuel
boilers, solid fuel boilers, and hydrochloric acid production furnaces that burn hazardous
waste (70 FR 59402 (October 12, 2005)). The mercury standards for existing and new
sources, respectively, are under 40 CFR 63.1216(a)(2) and (b)(2) for solid fuel boilers,
40 CFR 63.1217(a)(2) and (b)(2) for liquid fuel boilers, 40 CFR 63.1218(a)(2) and (b)(2)
for hydrochloric acid production furnaces, 40 CFR 63.1219(a)(2) and (b)(2) for
incinerators, 40 CFR 63.1220(a)(2) and (b)(2) for cement kilns, and 40 CFR
63.1221(a)(2) and (b)(2) for lightweight aggregate kilns. Approximately 200 HWCs are
complying with these standards.
EPA will be reviewing these standards as a result of the D.C Circuit Court of Appeals'
approval in June 2009 of EPA's motion for voluntary remand of the emission standards.
Any revised standards would be no less stringent than the current standards.
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8.3.5 Coal-fired power plants
At present, the largest single source of anthropogenic mercury emissions in the country is
coal-fired power plants. Mercury emissions from U.S. power plants are estimated to
account for about one percent of total global mercury emissions (70 FR 15994; March 29,
2005). EPA has initiated a rulemaking effort to develop emission standards under Clean
Air Act section 112(d) for emissions of hazardous air pollutants (including mercury) from
coal- and oil-fired electric utility steam generating units. Consistent with a Consent
Decree, the Agency intends to issue final emission standards for these units by the end of
2011.
8.3.6 Other
In addition to EPA's regulatory efforts under the CAA, in 1996 the United States
eliminated the use of mercury in most batteries under the Mercury Containing and
Rechargeable Battery Management Act. This action reduces the mercury content of the
waste stream, which further reduces mercury emissions from waste combustion. In
addition, voluntary measures to reduce use of mercury-containing products, such as the
voluntary measures to which the American Hospital Association has committed, will
contribute to reduced emissions from waste combustion.
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References
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1992. Memorandum from Charles Sutfin, May 20, 2002. Washington, DC:
U.S. Environmental Protection Agency, Office of Wetlands, Oceans and
Watersheds ..
USEPA (U.S. Environmental Protection Agency). 2002g. National Sediment Quality
Survey Database, 1980-1999. Washington, DC: U.S. Environmental Protection
Agency, Office of Water,
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. Washington, DC: U.S. Environmental Protection Agency, Office of
Water,
USEPA (U.S. Environmental Protection Agency). 2004. Local Limits Development
Guidance. EPA-833-R-04-002A. U.S. Environmental Protection Agency, Office of
Wastewater Management. July 2004.
144
-------
References
USEPA (U.S. Environmental Protection Agency). 2005a. Regulatory Impact Analysis of
the Clean Air Mercury Rule. Final report. EPA-452/R-05-003. Research Triangle
Park, NC: U.S. Environmental Protection Agency, Office of Air Quality Planning
and Standards, Air Quality Strategies and Standards Division.
25
USEPA (U.S. Environmental Protection Agency). 2005b. Environmental Monitoring and
Assessment Project (EMAP) Western Streams and Rivers Statistical Study.
EPA-620-R-05-006. Washington, DC: U.S. Environmental Protection Agency,
Office of Research and Development.
USEPA (U.S. Environmental Protection Agency). 2005c. Technical Support Document,
Revision of December 2000 Regulatory Finding on the Emissions of Hazardous Air
Pollutants From Electric Utility Steam Generating Units and the Removal ofCoal-
and Oil-Fired Electric Utility Steam Generating Units from the Section 112(c) List:
Reconsideration, October 21, 2005.
USEPA (U.S. Environmental Protection Agency). 2005d. Technical Support Document
for the Final Clean Air Mercury Rule: Air Quality Modeling. Research Triangle
Park, NC: U.S. Environmental Protection Agency, Office of Air Quality Planning
and Standards, 26
USEPA (U.S. Environmental Protection Agency). 2005e. Method 245.7, Revision 2.0.
Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry. EPA-821-R-
05-001. Washington, DC: U.S. Environmental Protection Agency.
USEPA (U.S. Environmental Protection Agency). 2005f. Standards of Performance for
New and Existing Stationary Sources: Electric Utility Steam Generating Units.
U.S. Environmental Protection Agency. Fed. Regist., May 18, 2005, 70:28606.
USEPA (U.S. Environmental Protection Agency). 2005g. Method 245.7, Revision 2.0.
Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry. EPA-821-R-
05-001. Washington, DC: U.S. Environmental Protection Agency.
USEPA (U.S. Environmental Protection Agency). 2005h. Presentation for the Meeting
with National Mining Association, Robert J. Wayland, Ph.D., Office of Air Quality
Planning and Standards, September 28, 2005. EPA-HQ-OAR-2002-0056-6447.
USEPA (U.S. Environmental Protection Agency). 2007. Listing Waters Impaired by
Atmospheric Mercury Under Clean Water Act Section 303(d): Voluntary
Subcategory 5m for States with Comprehensive Mercury Reduction Programs, Craig
Hooks, March 8, 2007.
On February 8, 2008, the D.C. Circuit Court of Appeals vacated the Clean Air Mercury Rule and remanded portions of it to EPA, for
reasons unrelated to the technical analyses in this document.
26 On February 8, 2008, the D.C. Circuit Court of Appeals vacated the Clean Air Mercury Rule and remanded portions of it to EPA, for
reasons unrelated to the technical analyses in this document.
145
-------
References
USEPA (U.S. Environmental Protection Agency). 2008a. Elements of Mercury TMDLs
Where Mercury Loadings Are Predominantly from Air Deposition, Craig E. Hooks,
September 29, 2008. at
and
USEPA (U.S. Environmental Protection Agency). 2008b. EPA 's 2008 Report on the
Environment. EPA 600-R-07-045F. Washington, DC: U.S. Environmental
Protection Agency, http://www.epa.gov/roe/downloads.htm and
http://crpub.epa.gov/eroe/index.cfm?fuseaction=detail.viewMidImg&lShowInd=0&
subtop=341 &lv=list.listByAlpha&r=216615# 11215 (last updated April 13,2010.
USEPA (U.S. Environmental Protection Agency). 2009a. 2008 Biennial National Listing
of Fish Advisories. EPA 823-F-09-007. Washington, DC: U.S. Environmental
Protection Agency, Office of Water.
http://www.epa.gov/waterscience/fish/advisories/tech2008.pdf>
USEPA (U.S. Environmental Protection Agency). 2009b. The National Study of
Chemical Residues in Lake Fish Tissue. EPA 823-R-09-006. Washington, DC: U.S.
Environmental Protection Agency, Office of Water.
http://www.epa.gov/waterscience/fish/study/data/finalreport.pdf
Voiland, M.P., K.L. Gall, D.J. Lisk, and D.B. MacNeill. 1991. Effectiveness of
recommended fat-trimming procedures on the reduction of PCB and Mirex levels in
Brown trout (Salmo trutta) from Lake Ontario. J. Great Lakes Res. 17(4):454-460.
Wagemann, R., E. Trebacz, R. Hunt, and G. Boila. 1997. Percent methylmercury and
organic mercury in tissues of marine mammals and fish using different experimental
and calculation methods. Environ. Toxicol. Chem. 16(9): 1859-1866.
Watras, C.J., R.C. Back, S. Halvorsen, R.J.M. Hudson, K.A. Morrison, and S.P. Wente.
1998. Bioaccumulation of mercury in pelagic freshwater food webs. Sci. Total
Environ. 219(2-3): 183-208.
Watras, C.J. and N.S. Bloom. 1992. Mercury and methylmercury in individual
zooplankton: Implications for bioaccumulation. Limnol. Oceanogr. 37:1313-1318.
Watras, C.J., K.A. Morrison, J.S. Host, and N.S. Bloom. 1995. Concentration of mercury
species in relationship to other site-specific factors in the surface waters of northern
Wisconsin lakes. Limnol. Oceanogr. 40:556-565.
Wente, S.P. 2003. A Spatially and Temporally Variable Model of Mercury
Concentrations in Aquatic Communities with Applications to Public Health
Protection and Water Quality Assessment. Ph.D. thesis, Purdue University, West
Lafayette, Indiana.
Wente, S.P. 2004.^4 Statistical Model and National Data Set for Partitioning Fish-Tissue
Mercury Concentration Variation Between Spatiotemporal and Sample
Characteristic Effects. Scientific Investigation Report 2004-5199. Reston, Virginia:
U.S. Geological Survey.
146
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References
WLSSD (Western Lake Superior Sanitary District). 1997. The WLSSD Commitment to
Zero Discharge. Duluth, MN: Western Lake Superior Sanitary District.
Wren, C.D. and H.R. MacCrimmon. 1986. Comparative bioaccumulation of mercury in
two adjacent freshwater ecosystems. Water Res. 6:763-769.
Yantosca, B. 2004. GEOS-CHEMv7-01-02 User's Guide. Cambridge, MA: Atmospheric
Chemistry Modeling Group, Harvard University.
147
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-------
Appendix A. Methylmercury/Mercury Ratio Exhibited in Muscle Tissue
of Various Freshwater Fish Species
Appendix A. Methylmercury/Mercury Ratio Exhibited in
Muscle Tissue of Various Freshwater Fish
Species
Source
Ecosystem type
Fish species
MethylHg/
total Hg ratio
Hammerschmidt et al.
1999
Freshwater lakes
in Wisconsin, USA
Yellow perch (Perca flavescens)
mean: 0.95
range: 0.84 to 0.97
Becker and Bigham 1995
Onondaga Lake, a
chemically
contaminated lake
in New York, USA
Gizzard shad (Dorosoma cepedianum)
White perch (Morone americana)
Carp (Cyprinus carpio)
Channel catfish (Ictalurus punctatus)
Bluegill (Lepomis macrochirus)
Smallmouth bass (Micropterus dolomieui)
Walleye (Stizostedion vitreum)
>0.90
Note: Authors did not provide
specific percentages for
individual species.
Grieb et al. 1990
Lakes in the Upper
Michigan
Peninsula, USA
Yellow perch (Perca flavescens)
Northern pike (Esox lucius)
Largemouth bass (Micropterus salmoides)
White sucker (Catostomus commersoni)
0.99
Note: Authors did not provide
data for each species
separately—only mean value
observed over all species.
Bloom 1992
Freshwater fish
species collected
from remote
midwestern lakes
and one mercury
contaminated site
USA
Yellow perch (Perca flavescens)
Northern pike (Esox lucius)
White sucker (Catostomus commersoni)
Largemouth bass (Micropterus salmoides)
0.99
1.03
0.96
0.99
Lasorsa and Allen-Gil
1995
3 lakes in the
Alaskan Arctic,
USA
Arctic grayling
Lake trout
Arctic char
Whitefish
1.00 all for species
Note: Authors did not provide
species-specific information on
MeHg/total Hg ratio.
Kannan, et al. 1998
Estuaries in South
Florida
Hardhead catfish (Arius felis)
White grunt (Haemulon plumieri)
Sand perch (Diplectrum formosum),
Lane snapper (Lutjanus synagris)
Gafftopsail catfish (Bagre marinus)
Pinfish (Lagodon rhomboides)
Spot (Leiostomus xanthurus)
Pigfish (Orthopristis chrysoptera)
Sand seatrout (Cynoscion arenarius)
Brown shrimp (Penaeus aztecus)
0.90
0.91
0.91
0.97
0.71
0.78
0.75
0.82
0.85
0.72
Note: Author sampled the 10
fish species at 20 locations.
Jackson 1991
Lakes and
reservoirs in
northern Manitoba,
Canada
Walleye (Stizostedion vitreum)
Northern pike (Esox lucius)
Lake whitefish (Coregonus clupeaformis)
range: 0.806% to 0.877%
range: 0.824% to 0.899%
range: 0.781% to 0.923%
Note: Author sampled the 3 fish
species at 4 lake locations.
149
-------
Appendix A. Methylmercury/Mercury Ratio Exhibited in Muscle Tissue
of Various Freshwater Fish Species
Source
Wagemann et al. 1997
Ecosystem type
Sampling location
not provided;
presumed to be
from Canadian
waters
Fish species
Walleye (Stizostedion vitreum)
MethylHg/
total Hg ratio
mean 1.00
Note: Authors did not provide
more specific information.
For trophic level assignments for specific fish species, refer to tables 6-4 and 6-6 of the
2000 Human Health BAF guidance (USEPA 2003). Additional information on trophic
level assignments is in the appendix of that guidance Oittp: //www. epa. gov/waterscience/
criteria/humanhealth/method/tsdvol2 .pdf).
150
-------
Appendix B. Tables from Metkylmercury Criteria Document
Appendix B. Tables from Methyl mercury
Criteria Document
This appendix contains several tables taken directly from the 2001 methylmercury
criteria document. They are repeated here to help the reader understand the development
of the 2001 criterion.
151
-------
Appendix B. Tables from Methylmercury Criteria Document
Table B1. Exposure parameters used in derivation of the water quality criterion.
(References cited in this table can be found in the 2001 methylmercury criterion document.)
Parameter
Body Weight, kg
Drinking Water Intake, L/day
Freshwater/Estuarine Fish Intake,
g/day
Inhalation, m /day
Soil Ingestion, g/day
Mean Marine Fish Intake, g/day
Median Marine Fish intake, g/day
90th Percentile Marine Fish Intake,
g/day
Population
Children
(0-1 4 years)
30
1.0
156.3a
10.4
0.0001, 0.01e
74. 9a
59.71a
152.293
Women of
Childbearing Age
(15-44 years)
67
2.0
165.5a
11
0.00005
91.04a
75.48a
188.353
Adults in the
General
Population
70
2.0
17.5b'c
20
0.00005
12.46b
Ob
49.16b
Source
USEPA (2000f)
USEPA (2000f)
USEPA (2000f)
USEPA (1994, 1997d)d
USEPA (1997d)
USEPA (2000a)
USEPA (2000a)
USEPA (2000a)
Notes:
For children and women of Childbearing age, intake rates are estimates of "consumers only" data (as described in USEPA 2000a).
For adults in the general population, intake rates are estimates of all survey respondents to derive an estimate of long-term
consumption (USEPA).
This is the 90th percentile freshwater and estuarine fish consumption value.
Inhalation rates for children and women of Childbearing age from USEPA, 1997d. Inhalation rates for adults in the general population
from USEPA (1994).
ePica child soil ingestion.
152
-------
Appendix B. Tables from Metkylmercury Criteria Document
Table B2. Average mercury concentrations in marine fish and shellfish3
(References cited in this table can be found in the 2001 methylmercury criteria document.)
Species
Concentration
[Mg Hg/g Wet Wt.)
Species
Concentration
Mg Hg/g Wet Wt.)
Finfish
Anchovy
Barracuda, Pacific
Cod*
Croaker, Atlantic
Eel, American
Flounder*'0
Haddock*
Hake
Halibut*
Herring
Kingfish
Mackerel*
Mullet
Ocean Perch*
Pollock*
0.047
0.177
0.121
0.125
0.213
0.092
0.089
0.145
0.25
0.013
0.10
0.081
0.009
0.116
0.15
Pompano*
Porgy*
Ray
Salmon*
Sardines*
Sea Bass*
Shark*
Skate
Smelt, Rainbow*
Snapper*
Sturgeon
Swordfish*
Tuna*
Whiting (silver hake)*
Whitefish*
0.104
0.522d
0.176
0.035
0.1
0.135
1.327
0.176
0.1
0.25
0.235
0.95e
0.206
0.041
0.054f
Shellfish
Abalone
Clam*
Crab*
Lobster
0.016
0.023
0.117
0.232
Oysters
Scallop*
Shrimp
Other shellfish*
0.023
0.042
0.047
0.012d
Molluscan Cephalopods
Octopus*
0.029
I Squid*
0.026
Notes:
'Denotes species used in calculation of methylmercury intake from marine fish for one or more populations of concern, based
on existence of data for consumption in the CSFII (USEPA 2000a).
a More current information on commercial fish and shellfish is provided by the Food and Drug Administration at
http://www.cfsan.fda.aov/%7Efrf/sea-mehg.html.
Mercury concentrations are from NOAA (1978) as referenced in the NMFS database, as reported in USEPA (1997c) unless
otherwise noted, measured as micrograms (ug) of mercury per gram (g) wet weight offish tissue.
c Mercury data for flounder were used to estimate mercury concentration in marine flatfish for intake calculations.
d Mercury concentration data are from Stern et al. (1996) as cited in USEPA (1997f).
Mercury concentration data are from U.S. FDA Compliance Testing as cited in USEPA (1997f).
Mercury concentration data are from U.S. FDA (1978) compliance testing as described in the NMFS database, as cited in
USEPA (1997f).
153
-------
Appendix B. Tables from Methylmercury Criteria Document
Table B3. Exposure estimates for methylmercury and percent of total exposure based on adults in
the general population
Exposure Source
Ambient water intake
Drinking water intake3
Nonfish dietary intake
Marine fish intake
Air intake
Soil intake
Exposure Estimate
(mg/kg-day)
4.3 x10"9
5.6 x10"8
0
2.7 x10"5
4.6 x10"9
1.3x10"9
Percent of Total Exposure
0.0047
0.0605
0
29.33
0.005
0.0014
Percent of RfD
0.004
0.006
0
27
0.005
0.001
Note:
3 This represents the high-end of the range of estimates. Because the contribution of ambient water or drinking water intake
to total exposure is so negligible in comparison to the sum of intake from other sources, there is not difference in the total
exposure estimated using either of these two alternatives.
154
-------
Appendix C. Analytical Methods
Appendix C. Analytical Methods
Table C1. Analytical methods for determining mercury and methylmercury in tissue
Method
Method 1630,
with draft
modifications for
tissue
(Recommended
method - see
section 4.1.3)
Method 1631,
draft appendix A
(Recommended
method - see
section 4.1.3)
Method 245.6
Draft method
7474
(SW-846)
Form/species
and applicable
matrices
Methylmercury
in tissue
Total mercury in
tissue, sludge,
and sediment
Total mercury in
tissue
Total mercury in
sediment and
tissue
Quantitation
Level or MLa
0.001 mg/kg
0.002 mg/kg
0.002 mg/kg
0.020 mg/kg
40 mg/kg
Technique
Tissue modification: digest tissue with
acid solution, neutralize with acetate
buffer, and analyze as per Method 1630,
i.e., distillation with heat and N2 flow to
separate methylHg from sample,
etnylation with sodium tetraethyl borate,
N2 purging of methylethylHg onto
graphite carbon (Carbotrap) column,
thermal desorption of methylethylHg and
reduction to Hg°, followed by CVAFS
detection.
Digest tissue with HNO3/H2SO4. Dilute
digestate with BrCI solution to destroy
remaining organic material. Analyze
digestate per method 1631: Add BrCI to
oxidize all Hg compounds to Hg(ll).
Sequentially pre-reduced with
hydroxylamine hydrochloride to destroy
the free halogens and reduced with
SnCI2 to convert Hg(ll) to Hg(0). Hg(0) is
purged from solution onto gold-coated
sand trap and thermally desorbed from
trap for detection by CVAFS.
Sulfuric and nitric acid digestion,
oxidation with potassium permanganate
and potassium persulfate, SnCl2
reduction, CVAAS detection
Microwave digestion of sample in nitric
and hydrochloric acids, followed by cold
digestion with bromate/bromide in HCI.
Hg purged from sample and determined
by CVAFS.
Known studies or literature
references using the techniques in
this method
• EPA Cook Inlet Contaminant Study
• Lake Michigan fish and
invertebrates, Mason and Sullivan
1997
• Northeastern Minnesota lake
plankton, Monson and Brezonik
1998b
• Method performance testing in
freshwater and marine fish, Bloom
1989
• EPA National Fish Tissue Study
(>1 ,000 samples over 4-year period)
• EPA Cook Inlet Contaminant Study
• Lake Michigan fish and
invertebrates, Mason and Sullivan
1997
• Northeastern Minnesota lake
plankton, Monson and Brezonik
1998b
• Method performance testing in
freshwater and marine fish, Bloom
1989
Unknown
Reference materials cited in method.
Niessen et al. 1999.
Notes:
3 Quantitation level or minimum level (ML) is considered the lowest concentration at which a particular
contaminant can be quantitatively measured using a specified laboratory procedure for monitoring of the
contaminant.
Used similar techniques but used a methylene chloride extraction instead of the distillation.
155
-------
Appendix C. Analytical Methods
Table C2. Analytical methods for determining mercury and methylmercury in water, sediment, and other
nontissue matrices
Method
EPA 1630a
(Recommended
method - see
section 4.1.3)
UW-Madison
SOPforMeHg
Analysis3
USGS
Wisconsin -
Mercury Lab
SOPs 004a
USGS Open-
File Report 01-
445a
Forms/species
and applicable
matrices
Methylmercury
in water
Methylmercury
in water
Methylmercury
in water
Methylmercury
in water
Quantitation
Level or ML
0.06 ng/L
0.01 ng/L
0.05 ng/L
0.04 ng/L
Sample preparation
Distillation with heat and N2 flow, addition
of acetate buffer and ethylation with
sodium tetraethyl borate. Purge with N2
onto Carbotrap. Thermal desorption and
GC separation of ethylated mercury
species, reduction to Hg followed by
CVAFS detection.
Distillation with heat and N2 flow, with
potassium chloride, sulfuric acid, and
copper sulfate. Ethylation with sodium
tetraethyl borate. Purge with N2 onto
Carbotrap. Thermal desorption and GC
separation of ethylated mercury species,
reduction to Hg° followed by CVAFS
detection.
Distillation (heat), APDC solution, N2
flow, potassium chloride, sulfuric acid,
and copper sulfate. Ethylation with
sodium tetraethyl borate. Purge with N2
onto Carbotrap. Thermal desorption and
GC separation of ethylated species,
reduction to Hg , and CVAFS detection.
Distillation (heat) and N2 flow, HCI and
copper sulfate. Addition of acetate buffer
and ethylation with sodium tetraethyl
borate. Purge with N2 onto Carbotrap.
Thermal desorption and GC separation of
ethylated mercury species, reduction to
Hg(0) followed by CVAFS detection.
Known studies or literature
references using the techniques in
this method
• USEPA Cook Inlet Study
• USEPA Savannah River TMDL study
• Northern Wisconsin Lakes, Watras et
al. 1995
• Lake Michigan waters, Mason and
Sullivan 1997
• Anacostia River Study, Mason and
Sullivan 1998
• Northeastern Minnesota lakes,
Monson and Brezonik 1998
• Poplar Creek, TN CERCLA Remedial
Investigation of surface water,
sediment, and pore water, Cambell et
al. 1998C
• Scheldt estuary study of water,
polychaetes, and sediments,
Baeyensetal. 1998
• Lake Michigan tributaries to support
GLNPO's LMMB Study
• Fox River, Wl, waters and sediments,
Hurley etal. 1998
Aquatic Cycling of Mercury in the
Everglades (ACME), cofunded by
USGS, EPA, and others
Formalized USGS method version of
USGS Wisconsin Lab SOP 004. Report
title is Determination of Methyl Mercury
by Aqueous Phase Ethylation, Followed
by GC Separation with CVAFS
Detection.
156
-------
Appendix C. Analytical Methods
Table C2. Analytical methods for determining mercury and methylmercury in water, sediment, and other
nontissue matrices (continued)
Method
EPA 1631,
revision E
(CVAFS)
(Recommended
method - see
section 4.1.3)
EPA 245. 1d
(CVAAS)
EPA 245.2d
(CVAAS)
EPA 245.5
(CVAAS)
EPA 245.7d
(CVAFS)
(Recommended
method - see
section 4.1.3)
EPA 7470A
(CVAAS)
Forms/species
and applicable
matrices
Total or
dissolved
mercury in
water
Total or
dissolved
mercury in
wastewater
Total or
dissolved
mercury in
wastewater and
sewage
Total or
dissolved
mercury in
soils, sludge
and sediment
Total or
dissolved
mercury in
water
Total or
dissolved
mercury in
liciuid wastes
and
ground water
Quantitation
Level or ML
ML = 0.5 ng/L
(MDL = 0.2
ng/L)
200 ng/L
200 ng/L
200 ng/L
ML = 5 ng/L;
(MDL=1.8
ng/L) e
200 ng/L
(IDL)
Sample preparation
Oxidize all Hg compounds to Hg(ll)
with BrCI. Sequentially pre-reduce with
hydroxylamine hydrochloride to
destroy the free halogens and reduce
with SnCI2 to convert Hg(ll) to Hg(0).
Hg(0) is purged from solution with N2
onto gold coated sand trap and
thermally desorbed from trap for
detection by CVAFS.
H2SO4 and HNO3 digestion, KMnO4 ,
K2S2C>8 oxidation + heat, cool +NaCI-
(NH2OH)2-H2SO4, SnSO4, aeration.
Detection by CVAAS.
H2SO4 and HNO3 added, SnSO4,
NaCI-(NH2OH)2-H2S04, KMnO4,
K2S2O8 , heat. Detection by CVAAS.
Dry sample, aqua regia, heat, KMnO4
added, cool +NaCI-(NH2OH)2-H2SO4,
SnSO4, aeration. Detection by CVAAS.
HCI, KBr03/KBr, NH2OH-HCI, SnCI2 ,
liquid-vapor separation. CVAFS
detection
H2S04 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI-(NH2OH)2-H2S04, SnSO4,
aeration of sample. CVAAS detection.
Known studies or literature references
using the techniques in this method
• USEPA Cook Inlet Study
• State of Maine studies
• USEPA Savannah River TMDL study
• USEPA/U.S. Navy study for
development of Uniform National
Discharge Standards
• Watraset al. 1995
• Anacostia River Study, Mason and
Sullivan 1998
• Northeastern Minnesota lakes, Monson
and Brezonik1998
• Poplar Creek, TN, CERCLA Remedial
Investigation Study, Cambell etal. 1998
• Scheldt Estuary Study, Baeyens et al.
1998
Effluent guideline development studies for
the Meat Products Industry, Metal
Products and Machinery Industry, and
Waste Incinerators
MPM Industry effluent guideline
development study
Pharmaceutical industry effluent guideline
development study
Interlaboratory validation completed
Method is similar to and cites performance
data given in EPA 245.5.
157
-------
Appendix C. Analytical Methods
Table C2. Analytical methods for determining mercury and methylmercury in water, sediment, and other
nontissue matrices (continued)
Method
EPA 7471 B
(CVAAS)
EPA 7472
(Anodic
stripping
voltametry)
EPA 7473
(Thermal
decomposition,
amalgamation,
and CVAA )
Draft Method
7474
(SW-846/
EPA 1620
(CVAAS)
SM3112B
(CVAAS)
ASTM D3223-
97, 02 (CVAAS)
AOAC 977.22
(Atomic
absorption
spectrometry)
Forms/species
and applicable
matrices
Total or
dissolved
mercury in solid
wastes and
semisolid
wastes
Total or
dissolved
mercury in water
Mercury in
water, soil, and
sediment
Total mercury in
sediment and
tissue
Mercury in
water, sludge,
and soil
Total or
dissolved
mercury in water
Total or
dissolved
mercury in water
Total or
dissolved
mercury in water
Quantitation
Level of M L
200 ng/L
(IDL)
100-300 ng/L
estimated to
be as low as
20 ng/ L or
20 ng/kg
20 ng/g
200 ng/L
500 ng/L
500 ng/L
200 ng/L
Sample preparation
H2SO4 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI-(NH2OH)2-H2SO4, SnSO4,
aeration of sample. CVAAS detection.
Acidify and chlorinate sample, GCE
electrode
Sample aliquot decomposed at 750°C
in oxygen atmosphere. Decomposition
products carried into catalytical furnace
for completed oxidations, then to
algamated trap. Mercury is thermally
desorbed and determined by CVAA.
Microwave digestion of sample in nitric
and hydrochloric acids, followed by
cold digestion with bromate/bromide in
HCI. Hg purged from sample and
determined by CVAFS.
H2SO4 and HNO3 added, KMnO4 ,
K2S2O8 + heat, cool +NaCI-
(NH2OH)2-H2SO4, SnSO4, aeration.
CVAAS detection.
H2SO4 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI (NH2OH)2-H2SO4, SnCI2 or
SnSO4, aeration. CVAAS
determination.
H2S04 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI (NH2OH)2-H2S04, SnSO4,
aeration. CVAAS determination.
H2SO4 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI (NH2OH)2-H2SO4, SnSO4,
aeration. Determine mercury by CVAA.
Known studies or literature references
using the techniques in this method
Method is similar to and cites performance
data given in EPA 245.5.
Unknown
Unknown
Reference materials cited in method.
Niessen et al. 1999.
Industry effluent guideline development
studies
Unknown
Unknown
Unknown
Notes: (1) CVAAS = cold vapor atomic absorption spectrometry.
(2) CVAFS = cold-vapor atomic fluorescence spectrometry.
(3) ASTM and AOAC analytical methods are available from the respective organization.
a All four methylmercury methods above are based on the work of Bloom 1989, as modified by Horvat et al. 1993, and are virtually
identical as a result.
Used similar techniques but used a methylene chloride extraction instead of the distillation.
c Used similar techniques but omitted the distillation procedure.
Promulgated and approved under 40 CFR part 136, Table 1B.
e The method detection level (MDL) is the minimum concentration of an analyte (substance) that can be measured and reported
with a 99 percent confidence that the analyte concentration is greater than zero as determined by the procedure set forth in
appendix B of 40 CFR part 136.
Provided for reference purposes only. EPA recommends using method 1631 for analyzing mercury for water and fish tissue.
158
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Appendix D. Synopsized Mercury TMDLs
Developed or Approved by EPA
I. Ochlockonee Watershed, Georgia
II. Arivaca Lake, Arizona
III. McPhee and Narraguinnep Reservoirs, Colorado
IV. Clear Lake, California
V. Cache Creek, California
VI. Minnesota Statewide Mercury Total Maximum Daily Load
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
I, ..•'. -•: :"' "'• .
Description of the Applicable Water Quality Standards
TMDLs are established to attain and maintain the applicable narrative and numerical
water quality standards. The State of Georgia's Rules and Regulations for Water Quality
Control do not include a numeric criterion for the protection of human health from
methylmercury, but they do provide a narrative "free from toxics" water quality standard.
Because mercury can cause toxicity in humans, Georgia has used a numeric
"interpretation" of its narrative water quality standard for toxic substances to ensure that
a TMDL will protect human health. The numeric interpretation of its narrative water
quality standard is a concentration of no more than 0.3 mg/kg methylmercury in fish
tissue. This numeric interpretation protects the "general population," which is the
population that consumes 17.5 g/day or less of freshwater fish.
This approach is consistent with EPA's recommended water quality criterion for the
protection of human health from methylmercury, described in the document Water
Quality Criterion for the Protection of Human Health: Methylmercury (USEPA 2001a).
The methodology uses a "weighted consumption" approach. When only trophic level 3
and 4 fish have been collected, the methodology assumes that 8 g/day (58.4 percent) of
the total fish consumption is trophic level 3 fish (e.g., catfish and sunfish) and 5.7 g/day
(41.6 percent) is trophic level 4 fish (e.g., largemouth bass). EPA collected site-specific
data from the Ochlockonee River on ambient mercury in fish tissue and in the water
column in the summer of 2000 and in March and April 2001 at two locations. Using a
weighted consumption approach, site-specific fish tissue concentration data collected in
the Ochlockonee River yields a weighted fish tissue concentration of 0.6 mg/kg, which is
greater than the state's current applicable water quality criterion of 0.3 mg/kg. This was
calculated as
Weighted fish tissue concentration = (avg. trophic 4 cone, x .416) +
(avg. trophic 3 cone, x .584)
where:
average trophic level 3 concentration = 0.2 mg/kg
average trophic level 4 concentration =1.0 mg/kg
weighted fish tissue concentration = 0.6 mg/kg
To establish the TMDL, EPA determined the maximum allowable concentration of
mercury in the ambient water that will prevent accumulation of methylmercury in fish
tissue above the applicable water quality standard, 0.3 mg/kg. To determine this
concentration, EPA used the Methodology for Deriving Ambient Water Quality Criteria
for the Protection of Human Health (USEPA 2000b). EPA also used the recommended
national values from the Methodology, including the reference dose of 0.0001 mg/kg-day
methylmercury, a standard average adult body weight of 70 kg, and the consumption rate
for the general population of 17.5 g/day. For the other factors in the calculation,
bioaccumulation and fraction of methylmercury, EPA used site-specific data from the
Ochlockonee River collected in summer 2000 and March and April 2001. From this site-
specific data, EPA determined a representative weighted BAF. The BAF was calculated
160
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
by taking the average calculated BAF from each of the two trophic levels. The BAF
calculation also used 0.17 as the measured fraction of the total mercury as
methylmercury. Using this approach, an allowable concentration of mercury in the
ambient water of Ochlockonee River for the protection of human health is 1.6 ng/L. This
concentration was calculated as
WQS = ((reference dose - RSC) x body weight x units conversion)
(consumption rate x weighted BAF x fraction MeHg)
Where:
WQS = water quality standard =1.6 ng/L
reference dose = 0.0001 mg/kg-day MeHg
RSC = relative source contribution from other fish species =
0.000027 mg/kg-day MeHg
body weight = 70 kg
units conversion = 1,000,000 mg/kg
consumption rate = 0.0175 kg/day fish
weighted bioaccumulation factor = 1,063,270 I/kg
fraction of the mercury as methylmercury = 0.17 as measured
Source Assessment
A TMDL evaluation must examine all known potential sources of the pollutant in the
watershed, including point sources, nonpoint sources, and background levels. The source
assessment was used as the basis of development of a model and the analysis of TMDL
allocation options. This TMDL analysis includes contributions from point sources,
nonpoint sources, and background levels. Sixteen water point sources in the Ochlockonee
River watershed could have mercury in their discharges.
According to a review of the Mercury Study Report to Congress (USEPA 1997c),
significant potential air emission sources include coal-fired power plants, waste
incinerators, cement and lime kilns, smelters, and chlor-alkali factories. In the report, a
national airshed model (RELMAP) was applied to the continental United States. This
model provides a distribution of wet and dry deposition of mercury as a function of air
emissions and global sources, and it was used to calculate wet and dry deposition rates
for south Georgia.
The MDN includes a national database of weekly concentrations of mercury in
precipitation and the seasonal and annual flux of mercury in wet deposition. EPA
reviewed the MDN data for a sampling station near south Georgia. The MDN data were
compared with the RELMAP deposition predictions and the MDN data were found to be
substantially higher. Using the MDN data, the average annual wet deposition rate was
determined to be 12.75 ug/square meter. The dry deposition rate was determined to be
6.375 ug/square meter on the basis of the RELMAP results.
Loading Capacity—Linking Water Quality and Pollutant Sources
The link between the fish tissue endpoint and the identified sources of mercury was the
basis for the development of the TMDL. The linkage analysis helped estimate the total
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
assimilative capacity of the river and any needed load reductions. In this TMDL, models
of watershed loading of mercury were combined with a model of mercury cycling and
bioaccumulation in the water. This approach enabled a translation between the endpoint
for the TMDL (expressed as a fish tissue concentration of mercury) and the mercury
loads to the water. The loading capacity was then determined by the linkage analysis as a
mercury loading rate that was consistent with meeting the endpoint fish tissue
concentration.
Watershed-scale loading of water and sediment was simulated using the WCS. The
complexity of this loading function model falls between that of a detailed simulation
model (which attempts a mechanistic, time-dependent representation of pollutant load
generation and transport) and simple export coefficient models (which do not represent
temporal variability). The WCS provides a mechanistic, simplified simulation of
precipitation-driven runoff and sediment delivery, yet it is intended to be applicable
without calibration. Solids load, runoff, and ground water can then be used to estimate
pollutant delivery to the receiving waterbody from the watershed. This estimate is based
on pollutant concentrations in wet and dry deposition, processed by soils in the watershed
and ultimately delivered to the receiving waterbody by runoff, erosion, and direct
deposition. The WCS-calculated loads for each subbasin are shown in table Dl.
Table D1. Annual average mercury load from each subbasin
Watershed
Barnett Creek
Middle/Lower
Ochlocklonee
Tired Creek
Lower Ochlockonee
Little Ochlockonee
Bridge Creek
Upper/Middle
Ochlockonee
Upper Ochlockonee
Total Hg
load
(mg)
786098.4
307965.8
827172.8
359317.5
873773.4
454417.5
627746.1
766396.8
Area!
load
(mg/ha)
25.6
21.24
22.03
15.62
19.89
23.11
20.67
20.1
Impervious
area
(mg/yr)
116614.69
125771.73
252386.89
100125.11
140023.69
53496.45
152881.42
164465.44
Sediment
(mg/yr)
422879.88
89440.3
317969.16
130407.68
433136.75
261042.44
254746.48
320337
Runoff
(mg/yr)
177553.9
54786.29
194751.7
97802.16
219614.2
98468.66
182250.7
186825.6
Deposition
on water
(mg/yr)
68850
37867.5
61965
30982.5
80898.75
41310
37867.5
94668.75
WASPS (Ambrose et al. 1988) was chosen to simulate mercury fate in the Ochlockonee
River. WASPS is a general, dynamic mass balance framework for modeling contaminant
fate and transport in surface waters. Environmental properties and chemical
concentrations are modeled as spatially constant within segments. Each variable is
advected and dispersed among water segments and exchanged with surficial benthic
segments by diffusive mixing. Sorbed or particulate fractions can settle through water
column segments and deposit to or erode from surficial benthic segments. Within the bed,
dissolved variables can migrate downward or upward through percolation and pore water
diffusion. Sorbed variables can migrate downward or upward through net sedimentation
or erosion.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
The toxics WASP model, TOXI5, combines a kinetic structure adapted from EXAMS2
with the WASPS transport structure and simple sediment balance algorithms to predict
dissolved and sorbed chemical concentrations in the bed and overlying waters. TOXI5
simulates the transport and transformation of chemicals as a neutral compound and up to
four ionic species, as well as particulate material. Local equilibrium is assumed so that
the distribution of the chemical among the species and phases is defined by distribution
or partition coefficients. The predicted mercury concentrations are shown in table D2.
Table D2. Predicted mercury for annual average load and flow
Calculated concentrations
Total Hg: water column (ng/L)
Total Hg: sediment (ng/g)
Methyl Hg: water column (ng/L)
River reach
1
6.33
7.05
0.90
2
5.84
9.07
0.82
3
5.55
9.81
0.77
4
5.76
8.17
0.79
5
5.65
7.63
0.77
6
5.17
6.97
0.71
Allocations
To determine the total maximum load that can enter the Ochlockonee River, the current
loading conditions were evaluated and the instream concentration was determined using
the modeling approach described above. This allowed the development of a relationship
between load and instream mercury concentrations. Using this developed relationship, the
total maximum load could be determined. Because the water column mercury
concentration response is linear with respect to changes in load, a proportion could be
developed to calculate the total maximum mercury load from the watershed that would
achieve the derived water quality target of 1.6 ng/L. The TMDL was calculated as the
ratio of the water quality target to the highest segment concentration (1.6 ng/L divided by
6.3 ng/L) applied to the current annual average load of 5.00 kg/yr. This gave a TMDL
load of 1.22 kg/yr mercury, which represents a 76 percent reduction from the current
annual average load.
In a TMDL assessment, the total allowable load is divided and allocated to the various
pollutant sources. The calculated allowable load of mercury that can come into the
Ochlockonee River without exceeding the applicable water quality target of 1.6 ng/L is
1.22 kg/yr. Because EPA's assessment indicates that over 99 percent of the current
loading of mercury is from atmospheric sources, 99 percent of the allowable load is
assigned to the load allocation and 1 percent of the allowable load is assigned to the
wasteload allocation. Therefore, the load allocation and the wasteload allocation for the
Ochlockonee River are:
Load allocation (atmospheric sources) =1.16 kilograms/year
Wasteload allocation (NPDES sources) = 0.06 kilograms/year
EPA estimates that atmospheric deposition contributes over 99 percent of current
mercury loadings to the river; therefore, significant reductions in atmospheric deposition
will be necessary if the applicable water quality standard is to be attained. On the basis of
the total allowable load of 1.22 kg/year, a 76 percent reduction of mercury loading is
needed to achieve the applicable water quality standard. EPA believes that an estimated
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
31 percent to 41 percent reduction in mercury deposition to the Ochlockonee River
watershed can be achieved by 2010 through full implementation of existing CAA
requirements. In addition, a number of activities to address remaining sources of mercury
are planned or under way, and EPA expects that further reductions in mercury loadings
will occur over time as a result of those activities. EPA is not able to estimate the
reductions in mercury deposition to the Ochlockonee River watershed that will be
achieved from future activities. As contemplated by CWA section 303(d)(l)(C),
however, this TMDL quantifies the water quality problem facing the Ochlockonee River
watershed and identifies the needed reductions in loadings from atmospheric
deposition—by CAA initiatives or under other authorities—for the watershed to achieve
applicable standards for mercury. In addition, as EPA collects additional data and
information for the Ochlockonee River watershed and as new legal requirements are
imposed under the CAA, EPA will continue to evaluate the effectiveness of regulatory
and nonregulatory air programs in achieving the TMDL's water quality target.
The analysis of NPDES point sources in the watershed indicates that the cumulative
loading of mercury from these facilities is less than 1 percent of the total estimated
current loading. Even if this TMDL allocated none of the calculated allowable load to
NPDES point sources (a wasteload allocation of zero), the waterbody would not attain the
applicable water quality standards for mercury because of the very high mercury loadings
from atmospheric deposition. At the same time, however, EPA recognizes that mercury is
an environmentally persistent bioaccumulative toxic with detrimental effects on human
fetuses even at minute quantities and that it should be eliminated from discharges to the
extent practicable. Taking these two considerations into account, this TMDL provides a
wasteload allocation applicable to all Georgia NPDES-permitted facilities in the
watershed in the amount of 0.06 kg/year. The TMDL was written so that all NPDES-
permitted facilities will achieve this wasteload allocation by discharging mercury only at
concentrations below the applicable water quality standard, 1.6 ng/L, or by implementing
a pollutant minimization program.
In the context of this TMDL, EPA believes it can reasonably offer the choice of the two
approaches to the permitting authority for the following reasons. First, on the basis of
EPA's analysis, the Agency expects either wasteload allocation option, in the aggregate,
to result in point source mercury loadings lower than the wasteload allocation. Second,
EPA believes this flexibility is the best way of ensuring that the necessary load reductions
are achieved without causing significant social and economic disruption. EPA recognizes
that NPDES point sources contribute a small share of the mercury contributions to the
Ochlockonee River. EPA also recognizes, however, that mercury is a highly persistent
toxic pollutant that can bioaccumulate in fish tissue at levels harmful to human health.
Therefore, EPA has determined, as a matter of policy, that NPDES point sources known
to discharge mercury at levels above the amount present in their source water should
reduce their loadings of mercury using appropriate, cost-effective mercury minimization
measures to ensure that the total point source discharges are at a level equal to or less
than the wasteload allocation specified in this TMDL. The point sources' waste load
allocation will be applied to the increment of mercury in their discharge that is above the
amount of mercury in their source water. EPA recommends that the permitting authority
make this choice between the two options in consultation with the affected dischargers
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
because EPA is not able to make the case-by-case judgments in this TMDL that EPA
believes are appropriate.
Description of the Applicable Water Quality Standards
Authorities develop TMDLs to meet applicable water quality standards. These standards
may include numeric water quality standards, narrative standards describing designated
uses, and other associated indicators supporting designated uses (beneficial uses apply
only to California). A numeric target identifies the specific goals or endpoints for the
TMDL that equate to attainment of the water quality standard. The numeric target may be
equivalent to a numeric water quality standard (where one exists), or it may represent a
quantitative interpretation of a narrative standard.
The applicable numeric targets for the Arivaca TMDL are the Arizona water quality
standard of 0.2 ug/L mercury in the water column and the Arizona Fish Consumption
Guideline criterion of 1 mg/kg mercury concentration in fish tissue. Arizona has adopted
water quality standards for mercury that apply to a number of the designated uses
specified for Arivaca Lake, including protection of aquatic life and wildlife and
protection of human and agricultural uses. Of these numeric criteria, the most stringent is
the chronic aquatic life criterion of 0.01 ug/L dissolved mercury (see table 7 on page 15
in the TMDL). Arizona has also issued a fish consumption advisory for this lake because
mercury concentrations in fish tissue exceed 1 mg/kg.
Mercury bioaccumulates in the food chain. Within a lake fish community, top predators
usually have higher mercury concentrations than forage fish, and tissue concentrations
generally increase with age class. Top predators (such as largemouth bass) are often
target species for sport fishermen. Arizona bases its Fish Consumption Guideline on
average concentrations in a sample of sport fish. Therefore, the criterion should not apply
to the extreme case of the most-contaminated age class offish within a target species;
instead, the criterion is most applicable to an average-age top predator. Within Arivaca
Lake, the top predator sport fish is the largemouth bass. The selected target for the
TMDL analysis is an average tissue concentration in 5-year-old largemouth bass of 1.0
mg/kg.
Source Assessment
A TMDL evaluation must examine all known potential sources of the pollutant in the
watershed, including point sources, nonpoint sources, and background levels. The source
assessment is used as the basis for developing a model and analyzing TMDL allocation
options. There are no permitted point source discharges and no known sources of
mercury-containing effluent in the Arivaca watershed. External sources of the mercury
load to the lake include natural background load from the watershed, atmospheric
deposition, and possible nonpoint load from past mining activities.
Watershed background load. The watershed background load of mercury was derived
from mercury in the parent rock and from the net effects of atmospheric deposition of
mercury on the watershed. Some mercury is also present within the parent rock
formations of the Arivaca watershed, although no concentrated ore deposits are known.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
The net contributions of atmospheric deposition and weathering of native rock were
assessed by measuring concentrations in sediment of tributaries to Arivaca Lake. EPA
collected 25 sediment and rock samples from dry tributaries in the Arivaca watershed and
analyzed them for mercury. These data show that most of the sediment samples from the
Arivaca watershed were considered at or near background mercury levels.
Nonpoint loadings from mining. No known mining for mercury itself has occurred in the
watershed. However, mining activities for minerals other than mercury, especially
historical mining practices for gold, might contribute to mercury loading in the
watershed. Gold and silver mining commonly occurred in the area surrounding Arivaca
Lake but apparently not within the watershed itself. The U.S. Bureau of Mines identified
only one exploratory prospect, for manganese and uranium, within the Arivaca
watershed.
Ruby Dump. Ruby Dump is in the southern portion of Arivaca watershed at the very
upstream end of Cedar Canyon Wash. The dump apparently served the town of Ruby and
the Montana Mine. The waste is characterized by numerous mining artifacts (e.g.,
crucibles) but also includes many common household items like bottles and plates.
Samples were taken at three different locations of the Ruby Dump: the top of the hill (just
below the fire pit), the middle of the hill, and the base of the dump. The mercury results
for these samples, from the top of the hill to the bottom, were 1,467 ppb, 1,244 ppb (blind
duplicate was 495 ppb), and 486 ppb. The average of these four samples is 918 ppb,
which is the number used in the watershed modeling to represent the mercury
concentration in sediment eroding from this site.
Near-field atmospheric deposition. Significant atmospheric point sources of mercury
often cause locally elevated areas of near-field atmospheric deposition downwind. A
review of Mercury Study Report to Congress (USEPA 1997c) and a search of EPA's
AIRS database of permitted point sources found no significant U.S. sources of airborne
mercury within or near the Arivaca watershed. Also, the most nearby parts of Mexico
immediately to the southwest (prevailing wind direction) of the watershed are sparsely
populated. Because of the lack of major nearby sources, especially sources along the axis
of the prevailing wind, EPA does not believe that near-field atmospheric deposition of
mercury attributable to individual emitters is a major component of mercury loading to
the Arivaca watershed. Because no significant near-field sources of mercury deposition
were identified, mercury from atmospheric deposition onto the watershed is treated as
part of a general watershed background load in this analysis.
Far-field atmospheric deposition. In May 1997 the MDN began collecting deposition
data at a new station in Caballo, in the southwestern quadrant of New Mexico. This
station is the closest MDN station to the Arivaca Lake and was used to estimate loads to
Arivaca Lake. Because the climate at Arivaca is wetter than that at Caballo, the
distribution of wet and dry deposition is likely to be different. Monthly wet deposition
rates at Arivaca were estimated as the product of the volume-weighted mean
concentration for wet deposition at Caballo times the rainfall depth at Arivaca. This
approach was used because volume-weighted mean concentrations are usually much
more stable between sites than wet deposition rates, which are sensitive to rainfall
amount. Dry deposition at Arivaca was then calculated as the difference between the total
deposition rate at Caballo and the estimated Arivaca wet deposition rate. The estimates
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
derived for Arivaca were 5.3 ug/m /yr by wet deposition and 7.1 ug/m /yr by dry
deposition. In sum, mercury deposition at Arivaca is assumed to be equivalent to that
estimated for Caballo, New Mexico, but Arivaca is estimated to receive more wet
deposition and less dry deposition than Caballo because more of the particulate mercury
and reactive gaseous mercury that contribute to dry deposition are scavenged at a site
with higher rainfall.
Loading Capacity—Linking Water Quality and Pollutant Sources
The linkage analysis in a TMDL defines the connection between numeric targets and
identified sources. The linkage is defined as the cause-and-effect relationship between the
selected indicators, the associated numeric targets, and the identified sources. This
linkage analysis provides the basis for estimating total assimilative capacity and any
needed load reductions. Specifically, for the linkage analysis in the Arivaca TMDL,
models of watershed loading of mercury were used together with a model of mercury
cycling and bioaccumulation in the lake. This approach enabled a translation between the
numeric target (expressed as a fish tissue concentration of mercury) and mercury loading
rates. The loading capacity was then determined through the linkage analysis as the
mercury loading rate that is consistent with meeting the target fish tissue concentration.
Watershed model, Watershed-scale loading of water and sediment was simulated using
the Generalized Watershed Loading Function (GWLF) model. The complexity of this
loading function model falls between that of detailed simulation models (which attempt a
mechanistic, time-dependent representation of pollutant load generation and transport)
and simple export coefficient models (which do not represent temporal variability).
GWLF provides a mechanistic, simplified simulation of precipitation-driven runoff and
sediment delivery, yet it is intended to be applicable without calibration. Solids load,
runoff, and ground water seepage can then be used to estimate particulate and dissolved-
phase pollutant delivery to a stream, on the basis of pollutant concentrations in soil,
runoff, and ground water. Applying the GWLF model to the period from October 1985
through September 1998 yielded an average of 11.0 cm/year runoff and 2,520,000 kg
sediment yield by sheet and rill erosion. The sediment yield estimate is likely to be less
than the actual yield rate from the watershed because mass wasting loads were not
accounted for; however, mass wasting loads are thought to be of minor significance for
loading of bioavailable mercury to the lake.
Estimates of watershed mercury loading were based on the sediment loading estimates
generated by GWLF by applying a sediment potency factor. These estimates are shown in
table D3. A background loading estimate was first calculated and then combined with
estimates of loads from individual hot spots. Most of the EPA sediment samples showed
no clear spatial patterns, with the exception of the hot spot area identified at Ruby Dump.
Therefore, background loading was calculated using the central tendency of sediment
concentrations from all samples excluding Ruby Dump. The background sediment
mercury concentrations were assumed to be distributed lognormally, as is typical for
environmental concentration samples, and an estimate of the arithmetic mean of 70.9 ppb
was calculated from the observed geometric mean and coefficient of variation. Applying
this assumption to the GWLF estimates of sediment transport yields an estimated rate of
mercury loading from watershed background of 178.9 g/yr.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Table D3. Annual total mercury load to Arivaca Lake
Watershed year
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
Grand total
Annual average
Mercury loading to lake (g/year)
From
watershed
170.16
184.34
205.61
70.9
198.52
99.26
163.07
233.97
141.8
219.79
170.16
191.43
276.51
2,325.52
178.89
From Ruby
Dump
0.65
0.7
0.79
0.27
0.76
0.38
0.62
0.89
0.54
0.84
0.65
0.73
1.06
8.88
0.68
From direct
atmospheric
deposition to lake
4.208
4.208
4.208
4.208
4.208
4.208
4.208
4.208
4.208
4.208
4.208
4.208
4.208
54.704
4.21
Total
175.018
189.248
210.608
75.378
203.488
103.848
167.898
239.068
146.548
224.838
175.018
196.368
281.778
2,389.10
183.78
Loading from the Ruby Dump was calculated separately, but it was also based on the
GWLF estimate of sediment load generated per hectare of rangeland (the land use
surrounding the hot spots), as reduced by the sediment delivery ratio for the watershed.
The extent of the hot spot was observed to be 200 feet by 50 feet. The mercury
concentration assigned to surface sediments at the dump was the arithmetic average of
the four EPA samples taken in October 1997, or 918 ppb. From these assumptions, less
than 1 percent of the watershed mercury load to Arivaca Lake appears to originate from
Ruby Dump, which is the only identified hot spot in the watershed.
The direct deposition of mercury from the atmosphere onto the Arivaca Lake surface was
calculated by multiplying the estimated atmospheric deposition rates times the lake
surface area, resulting in a load of 4.2 g/yr.
Lake hydrology model. The water level in Arivaca Lake is not actively managed, and
releases occur only when storage capacity is exceeded. Therefore, lake hydrology was
represented by a simple monthly water balance. Applying the water balance model
requires pan evaporation data as an input, in addition to the watershed meteorological
data. Because no evaporation data were available at the local Cooperative Summary of
the Day meteorological station, pan evaporation data for Tucson were used. Pan
evaporation data for 1980 through 1995 were obtained from the BASINS 2.0 Region 9
data files. Later pan evaporation data were not available for Tucson, so monthly averages
were used for the 1996 through 1998 water balance. The water balance model was run for
the period 1985 through 1998. This water balance approach provides a rough
approximation of the seasonal cycle of changes in volume and surface area of Arivaca
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Lake and of the amount of water released downstream over the spillway. It cannot
capture daily or event-scale movement of water in and out of the lake.
Mercury cycling and bioaccumulation model. Cycling and bioaccumulation of mercury
within the lake were simulated using the D-MCM (EPRI 1999). D-MCM predicts the
cycling and fate of the major forms of mercury in lakes, including methylmercury,
Hg(II), and elemental mercury. D-MCM is a time-dependent mechanistic model,
designed to consider the most important physical, chemical, and biological factors
affecting fish mercury concentrations in lakes. It can be used to develop and test
hypotheses, scope field studies, improve understanding of cause/effect relationships,
predict responses to changes in loading, and help design and evaluate mitigation options.
Because strong anoxia in the hypolimnion is a prominent feature during summer
stratification for the Arizona lakes simulated in this study, D-MCM was modified to
explicitly allow significant methylation to occur in the hypolimnion. In previous
applications of D-MCM, the occurrence of methylation was restricted to primarily within
surficial sediments. That the locus of methylation likely includes or is even largely within
the hypolimnion is supported by (1) the detection of very high methylmercury
concentrations in the hypolimnia of Arivaca Lake and (2) almost complete losses of
sulfate in Arivaca Lake in the hypolimnion resulting from sulfate reduction. An input was
added to the model to specify the rate constant for hypolimnetic methylation, distinct
from sediment methylation.
The results of the model calibration are shown in table D4. The model calculations are
the predicted annual ranges after the model has reached steady state. The observed
concentrations are from July 1997.
Table D4. Predicted and observed mercury for annual average load and flow
Methyl Hg: Water column (ng/L)
Hg II: Water column (ng/L)
Methyl Hg: 5-year-old largemouth bass (mg/kg)
Predicted
0.00-12.07
0.00-6.28
1.18
Observed
14.3
1.46-8.3
1.18
Allocations
A TMDL represents the sum of all individual allocations of portions of the waterbody's
loading capacity. Allocations may be made to point sources (wasteload allocations) or
nonpoint sources (load allocations). The TMDL (sum of allocations) must be less than or
equal to the loading capacity; it is equal to the loading capacity only if the entire loading
capacity is allocated. In many cases, it is appropriate to hold a portion of the loading
capacity in reserve to provide a margin of safety (MOS), as provided for in the TMDL
regulation. The allocations and MOS are shown in table D5. These allocations, from the
best currently available information, predict attainment of acceptable fish tissue
concentrations within a time horizon of approximately 10 years. A delay in achieving
standards is unavoidable because time will be required for mercury to cycle through the
lake and food chain after load reductions occur.
169
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Table D5. Summary of TMDL allocations and needed load reductions (in g-Hg/yr)
Source
Wasteload allocations
Allocation
0.0
Existing load
0.0
Needed
reduction
0.0
Load allocations
Atmospheric deposition
Ruby Dump
Watershed background
Total
Unallocated reserve
Loading capacity
4.2
0.7
111.2
116.1
38.7
154.8
4.2
0.7
178.9
183.8
0
0
67.7
67.7
The model was used to evaluate the load reductions necessary to meet the numeric target.
The response of concentrations of mercury in 5-year-old largemouth bass to changes in
external mercury loads is nearly linear. This is because the sediment burial rates are high
and sediment recycling is low, with most of the methylmercury that enters the food chain
being created in the anoxic portion of the water column. The model calculates that the
numeric target of 1 mg/kg in 5-year-old largemouth bass is predicted to be met with a 16
percent reduction in total watershed loads to Arivaca Lake, which results in a loading
capacity of 154.8 g/year of mercury.
There are uncertainties associated with mercury sources and the linkage between mercury
sources and fish tissue concentrations in Arivaca Lake. As a result, the TMDL reserves
38.7 g-Hg/yr (25 percent of the loading capacity) for the MOS and allots the remaining
load of 116.1 g-Hg/yr for sources. Because no permitted point source discharges occur
within the Arivaca watershed, the wasteload allocation is zero and the load allocation is
116.1 g-Hg/yr.
The load allocation provides loads for three general sources: direct atmospheric
deposition onto the lake surface, hot spot loading from Ruby Dump, and generalized
background watershed loading, including mercury derived from parent rock and soil
material, small amounts of residual mercury from past mining operations, and the net
contribution of atmospheric deposition onto the watershed. Direct deposition to the lake
surface is a small part of the total load and is believed to derive from long-range transport
of global sources, which are not readily controllable. The load from Ruby Dump is also
small. As a result, the TMDL does not require reductions from these sources, and their
load allocations are their existing loads.
Background watershed loading appears to be the major source of mercury to Arivaca
Lake. The intensive watershed survey conducted for this TMDL did not identify any
significant terrestrial sources of mercury. Regarding air deposition to the watershed land
surface, insufficient data were available to calculate reliable estimates of the proportion
of mercury deposited from the air that actually reaches Arivaca Lake. Therefore, a load
allocation of 111.2 g-Hg/yr was established for overall background watershed loading.
This requires a 38 percent reduction from existing estimated loads from this source. This
reduction is believed feasible for several reasons.
170
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Potential for erosion control. Reduction of mercury loading from the watershed to
Arivaca Lake depends on reduction in sediment erosion rates. Improved livestock
management practices could obtain significant reductions in erosion rates. As a side
benefit, implementation of livestock BMPs could result in significant reductions in
loadings of DOC and nutrients to the lake. The availability of high levels of DOC and
nutrients in the lake appears to affect the methylation process. Reduction of DOC and
nutrient levels should reduce the efficiency of the methylation process at Arivaca Lake,
effectively increasing the lake's mercury loading capacity.
Reductions in atmospheric deposition of mercury. Although no reliable estimates are
available, new mercury air emissions to the environment appear to be declining. U.S.
mercury emissions have declined significantly since 1990 and are expected to decline
further upon implementation of new emission limits on incinerators as required by recent
EPA regulations. Reductions in air deposition in Arivaca Lake watershed would
eventually result in decreases in mercury loading to the lake itself.
Potential location and remediation of undiscovered mercury sources. Although
investigation of the watershed did not reveal any significant localized sources of mercury
in the watershed (with the possible exception of Ruby Dump), additional site
investigation is warranted to ensure that no significant sources were missed. From past
experience with mine site remediation in similar circumstances in Arizona, newly
discovered sites could be effectively eliminated as ongoing mercury sources.
Alternative management strategies. Any alterations in rates of methylation or in rates of
mercury loss to deep sediments will change the relationship between external mercury
load and fish tissue concentration and would thus result in a change in the loading
capacity for external mercury loads. The loading capacity could be increased by
management intervention methods that decrease rates of bacterial methylmercury
production within the lake or increase rates of burial and sequestration of mercury in lake
sediment. Selection of such an approach would require further research and feasibility
studies. Some alternative strategies that might be suitable for further investigation include
the following:
• Hypolimnion aeration or mixing
• Sulfur chemistry modification
• Alum treatment
• Reduction of DOC and nutrient levels
• Dredging of lake sediments
[[[. •-• . -.".,. : . ." , '(•'-. ".•:.'• « . .*,_ :
Description of the Applicable Water Quality Standards
The TMDL for McPhee and Narraguinnep Reservoirs in southwestern Colorado was
based on the Fish Consumption Advisory action level of 0.5 mg/kg mercury
concentration in fish tissue. Colorado Department of Public Health and the Environment
listings are based on the risk analysis presented in the May 6, 1991, Disease Control and
171
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Epidemiology Division position paper for Draft Colorado Health Advisory for
Consumption of Fish Contaminated with Methylmercury. This paper, using atoxicity
value RfD of 0.3 ug/kg/day, establishes a fish tissue concentration of 0.5 mg/kg as the
approximate center of the range at which the safe consumption level is four meals per
month for nonpregnant adults and one meal per month for women who are pregnant,
nursing, or planning to become pregnant and children nine years of age or younger. The
criterion is applied to an average-age top predator. In McPhee Reservoir, the top predator
among sport fish regularly taken is the smallmouth bass (19 percent of the total catch in
1993); the top predator sport fish in Narraguinnep Reservoir is the walleye. The lake
water quality model D-MCM (EPRI 1999) is capable of predicting mercury
concentrations in fish tissue for each age class at each trophic level. Average mercury
concentrations in fish tissue of target species are assumed to be approximated by the
average concentration in 15-inch smallmouth bass in McPhee and the 18-inch walleye in
Narraguinnep. Therefore, the selected target for the TMDL analysis in McPhee Reservoir
is an average tissue concentration in 15-inch smallmouth bass of 0.5 mg/kg or less. The
selected target in Narraguinnep Reservoir is the 18-inch walleye of 0.5 mg/kg or less.
Source Assessment
McPhee and Narraguinnep reservoirs have several sources of mercury. The sources
external to the reservoirs separate into direct atmospheric deposition onto the lakes (from
both near- and far-field sources) and transport into the lakes from the watershed. The
watershed loading occurs in both dissolved and sediment-sorbed forms. Ultimate sources
in the watershed include mercury in parent rock, mercury residue from mine tailings and
mine seeps, point source discharges, and atmospheric deposition onto the watershed,
including deposition and storage in snowpack. A summary of the mercury load estimates
for McPhee Reservoir is presented in table D6.
Table D6. Summary of mercury load estimates for McPhee Reservoir
Reservoir
McPhee
Narraguinnep
Water-
shed
runoff
(g/yr)
2,576
2.7
Water-
shed
sediment
(g/yr)
222
22.7
Inter-
basin
transfer
(g/yr)
15.9
Atmos.
deposition
(g/yr)
251
36.8
Total
(g/yr)
3,049
78.1
Load per
volume
(mg/ac-ft)
4.66
4.59
Load per
surface
area
(mg/m2)
0.098
0.035
Past mining activities likely provide an important source of mercury load to the McPhee
and Narraguinnep watershed. There are large mining districts in the Dolores River
watershed, the LaPlata, the Rico, and the area around Dunton on the West Dolores River.
The quantity of mercury loading from mining operations has been estimated through a
combination of observed data in the water column and sediment coupled with the
watershed linkage analysis.
Significant atmospheric point sources of mercury often cause locally elevated areas of near-
field atmospheric deposition downwind. Two large coal-fired power plants are in the Four
Corners area within about 50 miles of the McPhee and Narraguinnep reservoirs. The plants
in the Four Corners area (2,040 megawatt (MW) capacity) and the Navajo plant (1,500
MW capacity) are upwind of McPhee and Narraguinnep reservoirs. It is likely that the
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
mercury emitted from these plants contributes to the mercury loading of the two reservoirs.
Because no direct measurements of atmospheric deposition of mercury are available, EPA
cannot assess the significance of this loading and must await further investigation,
including the establishment of a mercury deposition monitoring site in the area.
Loading Capacity—Linking Water Quality and Pollutant Sources
Models of watershed loading of mercury are combined with a model of mercury cycling
and bioaccumulation in the lake to translate the numeric target, expressed as a fish tissue
concentration of mercury, to mercury loading rates. The coupled models estimate mercury
loading to the reservoirs and predict mercury cycling and speciation within the reservoir.
An estimated load reduction of 52 percent is needed for long-term average mercury
concentrations in a standardized 15-inch smallmouth bass to drop to 0.5 mg/kg wet muscle.
Allocations
The loading capacity for McPhee Reservoir was estimated to be 2,592 g/year of mercury.
Narraguinnep Reservoir's loading capacity was estimated at 39.1 g/year of mercury. This
is the maximum rate of loading consistent with meeting the numeric target of 0.5 mg/kg
in fish tissue. Because of the uncertainties regarding the linkage between mercury sources
and fish tissue concentrations in McPhee and Narraguinnep reservoirs, an allocation of 70
percent of the loading capacity was used for this TMDL. The TMDL calculated for
McPhee Reservoir is equivalent to a total annual mercury loading rate of 1,814 g/yr (70
percent of the loading capacity of 2,592 g/yr), while that for Narraguinnep Reservoir is
equivalent to a total annual mercury loading rate of 27.3 g-Hg/yr (70 percent of 39.1 g-
Hg/yr). Summaries of the TMDL allocations and needed load reductions for the McPhee
and Narraguinnep Reservoirs are presented in tables D7 and D8, respectively.
Table D7. Summary of TMDL allocations and needed load reductions for
McPhee Reservoir
Source
Atmospheric deposition
Rico/Silver Creek mining area
Dunton mining area
La Plata mining area
Watershed background
Total
Unallocated reserve
Loading capacity
Allocation
63
507
348
69
827
1,814
778
2,592
Existing load
251
1030
708
141
919
3,049
Needed reduction
188
523
360
72
92
1,235
Note: Measurements in g/year of mercury.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Table D8. Summary of TMDL allocations and needed load reductions for
Narraguinnep Reservoir
Source
Atmospheric deposition
Interbasin transfer from
McPhee Reservoir
Watershed background
Total
Unallocated reserve
Loading capacity
Allocation
9.2
9.5
8.6
27.3
11.8
39.1
Existing load
36.8
15.9
25.4
78.1
Needed reduction
27.6
6.4
16.8
50.8
Note: Measurements in g/year of mercury.
IV. -'•••-. •,:•: "j - -
Description of the Applicable Water Quality Standards
EPA promulgated the California Toxics Rule (CTR) in May 2000 (65 FR 31682). The
CTR contains a water quality criterion of 50 ng/L total recoverable mercury for water and
organism consumption and is intended to protect humans from exposure to mercury in
drinking water and through fish and shellfish consumption. This criterion is enforceable
in California for all waters with a municipal or domestic water supply designated use and
is applicable to Clear Lake. However, the state of California does not consider this
criterion sufficiently protective of the consumers offish from Clear Lake.
The water quality management plan or Basin Plan for the Central Valley Regional Water
Quality Control Board adopted new water quality standards for mercury for Clear Lake at
the same time it adopted mercury TMDLs for Clear Lake. The state's water quality
criteria are for fish tissue and are intended to protect designated uses for fishing and
wildlife habitat. The applicable criteria are 0.09 mg/kg and 0.19 mg/kg of mercury in fish
tissue for trophic levels 3 and 4 fish, respectively. These levels were recommended by the
U.S. Fish and Wildlife Service to protect wildlife, including osprey and bald eagles, at
Clear Lake; these levels allow adults to safely consume about 3.5 fish meals per month
(26 grams/day) if eating mainly trophic level 4 fish such as catfish and bass. The 26
grams/day assumes a diet composed of 70 percent trophic level 4 fish and 30 percent
trophic level 3 fish. The 90th percentile consumption rate of a small group of residents of
Clear Lake, primarily members of the Elem Porno Indian Tribe, is 30 grams/day of Clear
Lake fish, as reported in 1997.
Source Assessment
Clear Lake is in Lake County in northern California. It is a shallow, eutrophic waterbody
that consists of three basins—the Upper, Lower, and Oaks Arms. It is the largest natural
lake entirely within California's boundaries. Tourism and sport fishing are important
sectors of the local economy. Five American Indian tribes use the resources of the lake
and its watershed.
The Clear Lake watershed lies within a region naturally enriched in mercury. The
Sulphur Bank Mercury Mine (SBMM) site, on the shores of Oak Arm, was a highly
productive source of mercury between 1872 and 1957. Similar smaller mines were
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
present in the Clear Lake watershed, all of which are now inactive. Levels of mercury in
Clear Lake sediments rose significantly after 1927, when open-pit operations became the
dominant mining method at SBMM. EPA declared the SBMM a federal Superfund site in
1991, and since then several remediation projects have been completed, including
regrading and vegetation of mine waste piles along the shoreline and construction of a
diversion system for surface water runoff. EPA is conducting a remedial investigation to
fully characterize the SBMM site to propose final remedies.
Inorganic mercury loads entering Clear Lake come from ground water and surface water
from the SBMM site; tributaries and other surface water that flows directly into the lake;
and atmospheric deposition, including atmospheric flux from SBMM. Some mercury
deposited historically in the lake due to mining operations or erosion at SBMM might
also contribute to mercury concentrations in fish today.
Ground water and surface water from the SBMM site. SBMM covers approximately 1
square mile on the east shore of the Oaks Arm of Clear Lake. The site contains
approximately 120 acres of exposed mine overburden and tailings (referred to as waste
rock). Two small unprocessed ore piles are also on the site. Mercury in samples of mine
materials ranged from 50 to 4,000 mg/kg. All piles of mine materials exhibit the potential
to generate acid rock drainage. The abandoned mine pit, the Herman Impoundment, is
filled with 90 feet of acidic water (pH 3) and has a surface area of about 20 acres. The
average concentrations in the Herman Impoundment of water and sediment are around
800 ng/L and 26 mg/kg, respectively. A geothermal vent at the bottom of the
impoundment continues to discharge gases, minerals (including mercury), and fluids into
the pit.
A large pile of waste rock, known as the waste rock dam (WRD), stretches about 2,000
feet along the shore of the western side of the SBMM site. The WRD lies between
Herman Impoundment and Clear Lake. The surface water in the impoundment is 10-14
feet above the surface of Clear Lake, which creates a gradient of ground water flow
toward the lake. Surface runoff from the northern side of the site is bounded by a wetland
that drains to Clear Lake. Surface runoff from the northern waste rock piles is directed
through culverts into the northern wetland. In 1990 rock and geofabric barriers were
installed at the culverts to reduce the transport of suspended solids. The northern wetland
is used for cattle grazing and as a source offish, tules, and other resources used by the
members of the Elem Porno Tribe. Waste rock piles extend into the wetlands.
Inputs of mercury from SBMM are estimated to be between 1 and 568 kg/year. EPA
Superfund program's estimate of mercury transported in ground water from the WRD is
used as the lower-bound input. Regional Board staff estimate that 568 kg/year is the
maximum upper-bound estimate of all inputs from SBMM, including past and continuing
contributions to the active sediment layer. This is approximately 96.5 percent of total
sources.
Ground water from SBMM appears to contribute mercury that is readily methylated,
relative to mercury from other inputs. Ground water flow from the mine site has been
detected entering Clear Lake by subsurface flow through lake sediments. Mercury in
ground water from the WRD is solubilized and likely in chemical forms that are easily
taken up by methylating bacteria. Acidic drainage from the mine site also contains high
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
sulfate concentrations that enhance the rates of methylation by sulfate-reducing bacteria.
This assertion is supported by data showing that methylation rates near the mine site are
significantly higher than those in other parts of Clear Lake. In contrast to the mercury in
SBMM ground water, the mercury in lakebed and tributary sediments originates
primarily as cinnabar, which has low solubility in water.
Tributaries and other surface water flowing directly into the lake. Mercury entering Clear
Lake from its tributaries originates in runoff from naturally mercury-enriched soils, sites
of historical mining activities, and mercury deposited in the watershed from the
atmosphere. Geothermal springs might contribute to tributary loads, especially in the
Schindler Creek tributary to Oaks Arm. Tributary and watershed runoff loads of mercury
range from 1 to 60 kg/year, depending on flow rates. Loads in average water years are 18
kg/year, approximately 3 percent of the total sources.
Geothermal springs and lava tubes that directly discharge to Clear Lake do not appear to
be significant sources of mercury. Mercury concentrations in surficial sediment samples
collected near lakebed geothermal springs were not elevated relative to levels in sediment
away from geothermal springs.
Atmospheric deposition, including flux from the SBMM site. Small amounts of mercury
deposit directly on the surface of Clear Lake from the global atmospheric pool and
potentially from local, mercury-enriched sources. Atmospheric loads to the lake surface
from the global pool were estimated using data from MDN monitoring stations in
Mendocino County and San Jose. Estimates ranged from 0.6 to 2.0 kg/year,
approximately 0.3 percent of the total sources.
Loading Capacity—Linking Water Quality and Pollutant Sources
The Regional Board staff assumes that there is a directly proportional relationship
between methylmercury in fish and mercury in the surficial sediment. This is a
simplification of a highly complex process. Many factors, such as sulfide and sulfate
concentrations, temperature, and organic carbon, affect methylation or concentrations of
methylmercury. Factors that affect accumulation of methylmercury in fish include
species, growth rate, prey availability, and the like. To reduce levels of methylmercury in
fish, loads of mercury to the lake must be reduced. Section 5.3.1 of the Staff Report
provides examples of remediation projects demonstrating that removal of inorganic
mercury from a range of aquatic environments has been effective in reducing
concentrations of mercury in fish.
A set of first-order relationships, each controlled by a single variable of concentration of
mercury or methylmercury, provide the basis for the assumption of a directly
proportional relationship between mercury in fish and in surficial sediment in Clear Lake.
Concentrations of methylmercury in water and methylmercury in biota are related by
BAFs. Relationships between methylmercury in the water column and in sediment can be
described as a flux rate of methylmercury from sediment. Concentrations of
methylmercury and mercury in sediment are related through calculation of a methylation
efficiency index (ratio of methylmercury to mercury in surficial sediment).
In each of these steps in the linkage analysis, one variable is related to another by a
simple ratio or linear equation. For example, BAFs are calculated by dividing the
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
concentration of methylmercury in fish by the concentration of methylmercury in the
water. Data are available to determine BAF and methylation indices that are specific for
Clear Lake. With the current understanding of the transport, methylation, and uptake
processes in Clear Lake, the Regional Board staff was unable to refine these relationships
to incorporate the effects of other factors. The end result was that methylmercury in biota
was related linearly to mercury in surficial sediment.
Meeting the recommended water quality standards would require reducing existing fish
tissue concentrations by 60 percent. Using the linear relationship, the linkage analysis
indicates that overall mercury loads to Clear Lake sediment must be reduced by 60
percent to reduce methylmercury concentrations in fish tissue by the proportional
amount. The Regional Board is establishing the assimilative capacity of inorganic
mercury in Clear Lake sediments as 70 percent of existing levels to include a margin of
safety of 10 percent to account for the uncertainties in the linkage analysis.
Allocations
The strategy for meeting the fish tissue criteria is to reduce the inputs of mercury to the
lake from tributaries and the SBMM site, combined with active and passive remediation
of contaminated lake sediments. The load allocations for Clear Lake will result in a
reduction in the overall mercury sediment concentration by 70 percent of existing
concentrations. The load allocations are assigned to the active sediment layer of the
lakebed, the SBMM terrestrial site, the tributary creeks and surface water runoff to Clear
Lake, and atmospheric deposition. Table D9 summarizes the load allocations. The load
allocation to the active sediment layer is expressed as reducing concentrations of mercury
in the active sediment layer to 30 percent of current concentrations. The load allocation to
the SBMM terrestrial site is 5 percent of the ongoing loads from the terrestrial mine site.
The load allocation for the mine also includes reducing mercury concentrations in
surficial sediment to achieve the sediment compliance goals for Oaks Arm, shown in
table DIG. The load allocation to tributary and surface water runoff is 80 percent of
existing loads. These load allocations account for seasonal variation in mercury loads,
which vary with water flow and rainfall. The analysis includes an implicit margin of
safety in the reference doses for methylmercury that were used to develop the fish tissue
objectives. It also includes an explicit margin of safety of 10 percent to account for
uncertainty in the relationship between fish tissue concentrations and loads of mercury.
The reductions in loads of mercury from all sources are expected to result in attainment
of water quality objectives.
Table D9. Summary of mercury load allocations
Source
Clear Lake sediment
Sulphur Bank Mercury
Mine
Tributaries
Atmosphere
Existing load
(kg/year)
695
18
2
Needed reduction
70% of existing concentration
95% of existing load
20% of existing load
no change
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Table D10. Sediment goals for mercury in Clear Lake
Site designation
Upper Arm
UA-03
Lower Arm
LA-03
Oaks Arm
OA-01b
OA-02b
OA-03b
OA-04b
Narrows O1
Location
Center of Upper Arm on transect from
Lakeportto Lucerne
Center of Lower Arm, north and west of
Monitor Point
0.3 km from SBMM 0.3 km from SBMM
0.8 km from SBMM
1.8 km from SBMM
3.0 km from SBMM
7.7 km from SBMM
Sediment mercury goal
(mg/kg dry weight)3
OP
1.0
16C
16C
16
10
3
Notes:
aSediment goals are 30 percent of existing concentrations. Existing concentrations are taken as the
average mercury concentrations in samples collected in 1996-2000 (Clear Lake Basin Plan Amendment
Staff Report).
Sediment goal is part of the load allocation for SBMM.
cDue to the exceptionally high concentrations existing at the eastern end of Oaks Arm, sediment goals at
OA-01 and OA-02 are not 70 percent of existing concentrations. These goals are equal to the sediment
goal established for OA-03.
Clear Lake sediment. Reducing mercury concentrations in surficial sediment by 70
percent is an overall goal for the entire lake. To achieve water quality objectives,
extremely high levels of mercury in the eastern end of Oaks Arm near SBMM must be
reduced by more than 70 percent. To evaluate progress in lowering sediment
concentrations, the following sediment compliance goals are established at sites that have
been sampled previously.
Sulphur Bank Mercury Mine. Current and past releases from SBMM are a significant
source of mercury loading to Clear Lake. Ongoing annual loads from the terrestrial mine
site to the lakebed sediments occur through ground water, surface water, and atmospheric
routes. Loads from ongoing releases from the terrestrial mine site should be reduced to 5
percent of existing inputs. Because of its high potential for methylation relative to
mercury in lakebed sediments, mercury entering the lake through ground water from the
mine site should be reduced to 0.5 kg/year.
Past releases from the mine site are a current source of exposure through remobilization
of mercury that exists in the lakebed sediments as a result of past releases to the lake
from the terrestrial mine site. Past active mining operations, erosion, and other mercury
transport processes at SBMM have contaminated sediment in Oaks Arm. The load
allocation assigned to SBMM includes reducing surficial sediment concentrations in
Oaks Arm by 70 percent (more at sites nearest the mine site) to meet the sediment
compliance goals in table DIG.
EPA anticipates implementing additional actions to address the ongoing surface and
ground water releases from SBMM over the next several years. These actions are
expected to lead to significant reductions in the ongoing releases from the mine pit, the
mine waste piles, and other ongoing sources of mercury releases from the terrestrial mine
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
site. EPA also plans to investigate what steps are appropriate under the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) to address the
existing contamination in the lakebed sediments from past releases from SBMM. The
Regional Board will continue to work closely with EPA on these important activities. In
addition, the Regional Board will coordinate monitoring activities to investigate other
sources of mercury loads to Clear Lake. These investigations by EPA and the Regional
Board should reduce the uncertainty that exists regarding the annual load of mercury to
the lake, the contribution of each source to that load, and the degree to which those
sources lead to methylmercury exposure of and mercury uptake by fish in the lake. This
information should lead to more refined decisions about what additional steps are
appropriate and feasible to achieve the applicable water quality criteria.
Tributaries and surface water runoff. Past and current loads of mercury from the
tributaries and direct surface water runoff are also a source of mercury loading to the lake
and to the active sediment layer in the lakebed. This section excludes loads from surface
water runoff associated with SBMM, which are addressed separately above. The loads of
mercury from the tributaries and surface water runoff to Clear Lake should be reduced by
20 percent of existing levels. In an average water year, existing loads are estimated to be
18 kg/year. Loads range from 1 to 60 kg/year, depending on water flow rates and other
factors. The load allocation applies to tributary inputs as a whole, instead of to individual
tributaries. Efforts should be focused on identifying and controlling inputs from hot spots.
The U.S. Bureau of Land Management, U.S. Forest Service, other land management
agencies in the Clear Lake Basin, and Lake County will submit plans for monitoring and
implementation to achieve the necessary load reductions. The Regional Board will
coordinate with those agencies and other interested parties to develop the monitoring and
implementation plans. The purpose of the monitoring is to refine load estimates and
identify potential hot spots of mercury loading from tributaries or direct surface runoff
into Clear Lake. Hot spots can include erosion of soils with concentrations of mercury
above the average for the rest of the tributary. If significant sources are identified, the
Regional Board will coordinate with the agencies to develop and implement load
reductions. The implementation plans will include a summation of existing erosion
control efforts and a discussion of feasibility and proposed actions to control loads from
identified hot spots. The agencies will provide monitoring and implementation plans
within five years after the effective date of this amendment and implement load reduction
plans within five years thereafter. The goal is to complete the load reductions within 10
years of implementation plan approval.
The Regional Board will work with the American Indian tribes in the Clear Lake
watershed on mercury reduction programs for the tributaries and surface water runoff. It
will solicit the tribes' participation in developing monitoring and implementation plans.
Wetlands. The Regional Board is concerned about the potential for wetland areas to be
significant sources of methylmercury. Loads and fate of methylmercury from wetlands
that drain to Clear Lake are not fully understood. The potential for production of
methylmercury should be assessed during the planning of any wetlands or floodplain
restoration projects within the Clear Lake watershed. The Regional Board established a
goal of no significant increases of methylmercury to Clear Lake resulting from such
activities. As factors contributing to mercury methylation are better understood, the
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Regional Board should examine the possible control of existing methylmercury
production within tributary watersheds.
Atmospheric deposition. Atmospheric loads of mercury originating outside the Clear
Lake watershed and depositing locally are minimal. Global and regional atmospheric
inputs of mercury are not under the jurisdiction of the Regional Water Board. Loads of
mercury from outside the Clear Lake watershed and depositing from air onto the lake
surface are established at the existing input rate, estimated to be 1 to 2 kg/year.
Description of the Applicable Water Quality Standards
EPA promulgated the California Toxics Rule (CTR) in May 2000 (65 FR 31682). The
CTR contains a water quality criterion of 50 ng/L total recoverable mercury for waters
designated for water and organism consumption, and it was intended to protect humans
from exposure to mercury in drinking water and through fish and shellfish consumption.
This criterion is enforceable in California for all waters with a municipal or domestic
water supply designated use, and it is applicable to all waters in the Cache Creek
watershed. The State of California, however, does not consider this criterion sufficiently
protective of human and wildlife consumers offish in the watershed.
The water quality management plan or Basin Plan for the Central Valley Regional Water
Quality Control Board adopted new water quality standards for mercury for Cache Creek,
Bear Creek, and Harley Gulch at the same time it adopted mercury TMDLs for those
waterbodies. The state's water quality criteria are expressed as concentrations in fish
tissue and are intended to protect designated uses, which include human and wildlife fish
consumption. The applicable criteria are as follows: for Cache Creek and Bear Creek, the
average methylmercury concentration shall not exceed 0.23 mg methylmercury/kg wet
weight of muscle tissue in trophic level 4 fish 250-350 mm (piscivorous species,
including bass and catfish), and 0.12 mg methylmercury/kg wet weight of muscle tissue
in trophic level 3 fish 250-350 mm, or if not available, a minimum of 125 mm (bluegill,
sunfish, and sucker); for Harley Gulch, the average methylmercury concentration shall
not exceed 0.05 mg methylmercury/kg wet weight in whole, trophic level 2 and 3 fish
75-100 mm total length (hardhead, California roach, or other small resident species).
Because Harley Gulch does not support larger, trophic level 3 and 4 fish, no water quality
criteria for these larger fish were proposed in that waterbody.
These water quality standards permit safe consumption of about 22-40 g/day of Cache or
Bear Creek fish (3 to 5.4 meals/month). In Cache and Bear creeks, the standards protect
wildlife species, including bald eagle, peregrine falcon (state endangered), river otter,
American mink, mergansers, grebes, and kingfishers. In Harley Gulch, the standards
protect wildlife species, including small mammals, herons, and kingfishers.
Source Assessment
The Cache Creek watershed is impaired due to elevated levels of mercury in the water
and in fish tissue. Because Cache Creek is a primary source of mercury to the
Sacramento-San Joaquin Delta Estuary, lowering mercury levels in the Cache Creek
watershed will assist in protecting human and wildlife health in the delta. The TMDL
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
encompasses the 81-mile reach of Cache Creek between Clear Lake Dam and the outflow
of the Cache Creek Settling Basin, Bear Creek from its headwaters to its confluence with
Cache Creek, and the 8-mile length of Harley Gulch.
Sources of mercury entering the watershed include waste rock and tailings from historical
mercury mines, erosion of naturally mercury-enriched soils, geothermal springs, and
atmospheric deposition. There are multiple inactive mercury mines in the Cache Creek
watershed. The Sulphur Bank Mercury Mine contributes mercury to Cache Creek at the
Clear Lake outflow. The Sulphur Creek mining district includes eight mines that drain
predominately to Bear Creek via Sulphur Creek and four mines in the Bear Creek Basin.
Harley Gulch receives inputs from the Turkey Run and Abbott mines. The Reed Mine
drains to Davis Creek, a tributary to Cache Creek.
Historical mining activities in the Cache Creek watershed discharged and continue to
discharge large volumes of inorganic mercury (termed total mercury) to creeks in the
watershed. Much of the mercury discharged from the mines is now distributed in the
creek channels and floodplain downstream from the mines. Natural erosion processes can
be expected to slowly move the mercury downstream out of the watershed over the next
several hundred years. However, current and proposed activities in and around the creek
channel can enhance mobilization of this mercury. Activities in upland areas, such as
road maintenance and grazing and timber activities, can add to the mercury loads
reaching Cache Creek, particularly when the activities take place in areas that have
elevated mercury levels. Mercury can be transformed to methylmercury in sediment by
sulfate-reducing bacteria.
Cache Creek. In Cache Creek the watershed above Rumsey is the major source of
methylmercury. The highest concentrations and production rates were observed below
the mercury mines in Harley Gulch, in Sulphur and Bear creeks, and in the canyon above
Rumsey. Lower methylmercury concentrations in water were measured in the North Fork
and Cache Creek below Clear Lake Dam, which have lower inorganic mercury
concentrations in sediment.
The sources of total mercury in Cache Creek largely parallel the sources of methylmercury.
Most mercury derives from the watershed upstream of Rumsey. On a five-year average,
mercury loads from the mine-related tributaries (Bear Creek, Harley Gulch, and Davis
Creek), North Fork Cache Creek and Clear Lake contributed about 15 percent of the
mercury loads measured in Cache Creek at Rumsey. In years with high degrees of runoff or
extreme erosional events, inputs from the inactive mines would be much greater. The
majority of the inorganic mercury loads were from unnamed sources, which include
smaller, unmeasured tributaries and mercury in the Cache Creek bed and banks. Clean
sediment entering the watershed below Rumsey diluted sediment mercury concentrations.
Bear Creek. The Bear Creek watershed upstream of all mine inputs contributes less than
10 percent to each of the loads of methylmercury and total mercury in Bear Creek.
Sulphur Creek contributes about half of each of the methylmercury and total mercury
loads in Bear Creek. The remainder of the Bear Creek methylmercury likely comes from
production within the channel and seepage of underground springs. The rest of the
mercury load in Bear Creek likely derives from the remobilization of mine waste
deposited in the floodplain.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Harley Gulch. Much of the methylmercury in Harley Gulch is likely produced in a
wetland area in the West Branch Harley Gulch, downstream of the inactive mercury
mines. Over 90 percent the total mercury load in Harley Gulch is estimated to come from
the West Branch, where the mines are. Total mercury loads from the mines may be
underestimated due to a lack of data collected during heavy rainfall events. An alluvial
fan, likely containing mine waste, at the confluence of Harley Gulch and Cache Creek,
might contribute to the unknown source of mercury in the Cache Creek canyon.
Loading Capacity—Linking Water Quality Pollutant Sources
Total mercury in the creeks is converted to methylmercury by bacteria in the sediment.
The concentration of methylmercury in fish tissue is directly related to the concentration
of methylmercury in the water. The concentration of methylmercury in the water column
is controlled in part by the concentration of total mercury in the sediment and the rate at
which the total mercury is converted to methylmercury. The rate at which total mercury
is converted to methylmercury varies from site to site; some sites (wetlands and marshes)
having greatly enhanced methylation rates.
The linkage analysis describes the relationship between methylmercury concentrations in
water and in large fish. Data collected in 2000 and 2001 show statistically significant
relationships between concentrations of aqueous unfiltered methylmercury in water and
large trophic level 3 and 4 fish. In Cache Creek, large trophic level 3 fish tissue
concentrations (Sacramento sucker), normalized to 290 mm (from Slotten et al. 2004),
were regressed against aqueous unfiltered methylmercury concentrations (Y= 584.8X +
30.2; P < 0.001, R2 = 0.98). In Cache Creek, large trophic level 4 fish tissue
concentrations (largemouth bass, small mouth bass, and pikeminnow, depending on site),
normalized to 305 mm (from Slotton et al. 2004), were regressed against aqueous
unfiltered methylmercury concentrations (Y = 2970.8X - 180.6; P < 0.01, R2 = 0.9).
Using these relationships, staff determined concentrations of unfiltered methylmercury in
water that correspond to the proposed criteria for trophic levels 3 and 4 fish (0.12 mg/kg
and 0.23 mg/kg, respectively). These concentrations are 0.15 ng/1 for trophic level 3 fish
and 0.14 ng/L for trophic level 4 fish. To ensure meeting both fish tissue criteria, staff
selected 0.14 ng/L as the aqueous unfiltered methylmercury goal for Cache Creek.
For Bear Creek, the methylmercury goal of 0.06 ng/L represents the best estimate of the
annual, median aqueous (unfiltered) concentration of methylmercury needed to attain the
target of 0.23 mg/kg wet weight in trophic level 4 fish. Harley Gulch has no trophic level
4 fish, so the above relationships could not be used. Based on bioaccumulation factors
specific to Harley Gulch, the aqueous methylmercury goal for Harley Gulch is 0.09 ng/L.
Allocations
The TMDL presents a plan to reduce mercury and methylmercury loads. Reducing the
methylmercury loads will require a multi-faceted approach that includes controlling
inorganic mercury loads and limiting the entry of inorganic mercury into sites with high
rates of methylmercury production. Inorganic mercury loads may be controlled through
remediation of mercury mines, erosion control, removal of highly contaminated
sediment, and other activities. In addition to addressing inorganic mercury loads, the
TMDL discusses limits to the production of methylmercury in constructed
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
impoundments, such as gravel pits and water storage facilities. Identification and
evaluation of the unknown mercury source(s) in the upper basin are essential to attain the
Cache Creek methylmercury targets in fish tissue and to help reduce mercury in sediment
of the Sacramento-San Joaquin Delta Estuary.
Since methylmercury in the water column is directly related to mercury levels in fish, the
following methylmercury load allocations are assigned to tributaries and the main stem of
Cache Creek.
Methylmercury Load Allocations. Tables Dll and D12 provide methylmercury load
allocations for Cache Creek, its tributaries, and instream methylmercury production.
Allocations are expressed as a percent of existing methylmercury loads. The
methylmercury allocations will be achieved by reducing the annual average
methylmercury (unfiltered) concentrations to site- specific, aqueous methylmercury
goals, which are 0.14 ng/L in Cache Creek, 0.06 ng/L in Bear Creek, and 0.09 ng/L in
Harley Gulch. The allocations in tables Dll and D12 apply to sources of methylmercury
entering each tributary or stream segment. In aggregate, the sources to each tributary or
stream segment must have reductions of methylmercury loads as shown below.
Table D12 provides the load allocation within Bear Creek and its tributaries to attain the
allocation for Bear Creek described in table Dll. The inactive mines listed in the
implementation summary are assigned a 95 percent total mercury load reduction. These
mines include mines in the Harley Gulch Sulphur Creek and Bear Creek watersheds.
Reductions in mercury loads from mines, erosion, and other sources in the Sulphur Creek
watershed are expected to reduce in-channel production of methylmercury to meet the
Sulphur Creek methylmercury allocation.
Table D11. Cache Creek methylmercury allocations
Source
Cache Creek (Clear Lake to
North Fork confluence)
North Fork Cache Creek
Harley Gulch
Davis Creek
Bear Creek at Highway 20
Within-channel production
and ungauged tributaries
Total of loads
Cache Creek at Yolob
Cache Creek Settling Basin
Outflow0
Existing annual load
(g/yr)
36.8
12.4
1.0
1.3
21.1
49.5
122
72.5
87
Acceptable annual
load (g/yr)
11
12.4
0.04
0.7
3
32
7a
66
39
12
Allocation (% of
existing load)
30%
100%
4%
50%
15%
65%
10%a
54%
54%
14%
Notes:
The allocation includes a margin of safety, which is set to 10% of the acceptable loads. In terms of
acceptable annual load estimates, the margin of safety is 7 g/yr.
Cache Creek at Yolo is the compliance point for the tributaries and Cache Creek channel for meeting the
allocations and aqueous goals. Agricultural water diversions upstream of Yolo remove methylmercury (50
g/yr existing load).
The Settling Basin Outflow is the compliance point for methylmercury produced in the Settling Basin.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Table D12. Bear Creek methylmercury allocations
Source
Bear Creek at Bear Valley
Road
Sulphur Creek
In-channel production and
ungauged tributaries
Total of loads
Bear Creek at Highway 20b
Existing Annual
Load (g/yr)
1.7
8
11.4
21.1
21.1
Acceptable Annual
Load (g/yr)
0.9
0.8
1
0.3a
3
3
Allocation (% of
existing load)
50%
10%
10%
10%a
15%
15%
Notes:
acceptable annual load estimates, the margin of safety is 0.3 g/yr.
Bear Creek at Highway 20 is the compliance point for Bear Creek and its tributaries.
To achieve the water quality objectives and the methylmercury allocations listed in tables
Dl 1 and D12, the following actions are needed: (1) reduce loads of total mercury from
inactive mines; (2) where feasible, implement projects to reduce total mercury inputs
from existing mercury-containing sediment deposits in creek channels and creek banks
downstream from historical mine discharges; (3) reduce erosion of soils with enriched
total mercury concentrations; (4) limit activities in the watershed that will increase
methylmercury discharges to the creeks and, where feasible, reduce discharges of
methylmercury from existing sources; and (5) evaluate other remediation actions that are
not directly linked to activities of a discharger. Because methylmercury is a function of
total mercury, reductions in total mercury loads are needed to achieve the methylmercury
load allocations. Methylmercury allocations will be achieved in part by natural erosion
processes that remove mercury that has deposited in creek beds and banks since the start
of mining.
The proposed Basin Plan Amendment for mercury in San Francisco Bay assigns a
reduction in total mercury loads from the Sacramento-San Joaquin River Delta of 110
kg/yr. Cache Creek is a major source of mercury to the Delta. To attain the San Francisco
Bay reduction, loads of total mercury exiting Cache Creek should be reduced. Reductions
in total mercury loads to the inactive mines in Harley Gulch and the Bear Creek
watershed assigned by this TMDL and proposed changes to the Cache Creek Settling
Basin, which would increase the mass of mercury retained in the basin, would create
significant reductions in loads from Cache Creek.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
:'
Description of the Applicable Water Quality Standards and TMDL
Target
Minnesota Rules Chapters 7050.0222 and 7052.0100 set forth chronic numeric water
quality standards based on total mercury concentrations in the water column. The
wildlife-based standard applicable to only the waters of the Lake Superior Basin is 1.3
ng/L, while the human health-based standard applicable to waters outside the Lake
Superior Basin is 6.9 ng/L. In addition to these numeric standards, Chapter 7050.0150,
subpart 7, provides a narrative standard for assessing the contaminants in fish tissue. The
narrative standard states that a waterbody is impaired when the Minnesota Department of
Health recommends a consumption frequency of less than one meal per week for any
member of the population.
To establish the two regional TMDLs, Minnesota selected a target of 0.2 mg/kg fish
tissue mercury concentration. Fish tissue mercury concentration was selected as the water
quality target for the TMDLs because it was consistent with EPA's 2001 methylmercury
fish tissue criterion. In the 2001 guidance, EPA chose to express the water quality
criterion as a fish tissue concentration rather than as a water column value because fish
consumption is the primary route of human exposure. Two aspects of EPA's criterion are
toxicity and exposure. Minnesota relied on EPA's assessments of toxicity to humans but
selected a more state-specific exposure rate. For purposes of calculating its recommended
human health-based fish tissue criterion, EPA assumes that people consume 17.5 g/day of
fish. Minnesota selected a higher consumption rate, 30 g/day offish, based on several
surveys of the fish-eating habits of upper-Midwest recreational fishers.
Since Minnesota's water quality standards are water column chronic standards for total
mercury, not fish tissue concentration standards, Minnesota demonstrated a link from the
fish tissue mercury concentration TMDL target to the numeric water column water
quality standards. Bioaccumulation factors for 14 lakes representing agricultural areas,
urban areas, and forested areas were used to calculate the water column concentration
that would be equivalent to the 0.2 mg/kg fish tissue mercury concentration target.
Source Assessment
Sources that Minnesota considered in developing the two regional TMDLs included
atmospheric deposition, wastewater treatment plants, non-municipal waste discharges,
and stormwater. Atmospheric deposition was the only significant nonpoint source of
mercury identified by Minnesota. The state identified 99 percent of the total mercury load
to the state as coming from atmospheric deposition. Both natural and anthropogenic
As described in Section 6 of this guidance, Minnesota divided the state into two regions, a northeast region and a southwest region, and
developed a TMDL for each region. Although Minnesota's report is called a "statewide TMDL," the two regional TMDLs do not address
all the mercury impairments in the state. The TMDLs address 511 of the lake and river reach impairments in Category 5 of Minnesota's
2006 Integrated Report.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
sources contribute to the atmospheric deposition mercury load. Minnesota identified
natural sources as contributing 30 percent to the atmospheric deposition mercury load,
while the remaining 70 percent is from worldwide anthropogenic sources. Point sources
that Minnesota considered included wastewater treatment plants, pulp and paper mills,
taconite mines, coal-fired power plants, and one refinery. The state recognized that
stormwater is considered a point source and therefore subject to wasteload allocations;
however, for purposes of estimating a baseline mercury load (referred to in the TMDL
report as the total source load), the mercury loadings from stormwater were included in
the estimate of loadings from atmospheric deposition. Using data from two studies in
Minnesota, the state concluded that the primary source of mercury to stormwater is
atmospheric deposition rather than specific anthropogenic sources.
Loading Capacity
Minnesota established a loading capacity for each of the two regional TMDLs. Each
28
loading capacity was calculated by multiplying a regional reduction factor needed to
achieve the fish tissue mercury concentration target by the total source load29 for each
region, thus calculating a regional load reduction goal.30 The load reduction goal was
subtracted from the total source load to arrive at the loading capacities.
The total source load was considered the baseline condition from which reductions would
be needed to achieve water quality standards. Minnesota selected the year 1990 as the
baseline to which reductions would be applied. Minnesota selected 1990 as the baseline
for three reasons. First, the total source load is the sum of the point source load and the
nonpoint source load. The nonpoint source load is represented by total (wet and dry)
mercury deposition. Minnesota's estimate of both wet and dry deposition is from lake
sediment cores collected in a study conducted from 1988 to 1990. The second reason for
selecting 1990 was to remain consistent with other mercury reduction baselines. The state
uses 1990 as its mercury emission inventory baseline, and other state and federal plans,
such as the Great Lakes Binational Toxics Strategy and the Lake Superior Lakewide
Management Plan, use 1990 as a baseline for assessing mercury reductions. Minnesota
selected a baseline year that was consistent with other reduction goals and targets. Last,
Minnesota selected 1990 because prior to 1990 mercury use was relatively high, and then
beginning in around 1990, mercury use dropped precipitously as mercury was removed
from many products. For this reason Minnesota concluded that 1990 represents the end of
a period when mercury emissions and fish tissue concentrations were in a steady state.
The sum of the point source load and nonpoint source load are the total source load for
each region. The total source load for each region simply defines the 1990 baseline
condition for the region to which the applicable reduction factor is applied.
The existing point source contribution to the total source load was calculated based on the
sum of design flows for point sources within each region and mean effluent mercury
concentrations. The design flows were current-day design flows, while the mean effluent
28 The northeast regional reduction factor is 65 percent, and the southwest regional reduction factor is 51 percent.
The baseline load for the northeast region is 1153 kg/yr, and the baseline load for the southwest region is 1628 kg/yr.
30 The load reduction goal for the northeast region is 749 kg/yr, and the load reduction goal for the southwest region is 830 kg/yr.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
mercury concentrations were "typical" mercury concentrations unless actual facility
effluent concentrations were available. Actual facility effluent concentrations were used
for the coal-fired power plants, the one refinery, and the Metro and Western Lake
Superior Sanitary District wastewater treatment plants. For all other point sources, typical
mercury concentrations were used. A typical effluent concentration of 5 ng/L was used
for wastewater treatment plants. It was based on a study by the Association of
Metropolitan Sewerage Agencies, a state study of 37 NPDES facilities, and the Mercury
Maps report. Minnesota relied on the Mercury Maps report in support of the mean
effluent mercury concentration of 13 ng/L for pulp and paper mills, although effluent
reports from one Wisconsin and one Minnesota facility show effluent concentrations in
the range of 1.6 ng/L to 2 ng/L. Minnesota used its discharge monitoring database to
calculate 1.5 ng/L as the mean mercury effluent concentration for taconite mines.
The existing nonpoint source contribution to the total source load was based on total
mercury deposition to the state. Minnesota used sediment cores from Minnesota lakes to
estimate total statewide mercury deposition as 12.5 g km" yr" . Minnesota used the
regional surface areas for each of the two regions, along with the total mercury
deposition, to estimate the nonpoint source contribution to the total source load.
The reduction factor for each region is the percent reduction in total mercury load needed
to achieve the fish tissue target of 0.2 mg/kg for the 90th percentile of the standard-length
fish. Fish tissue data were reviewed for the standard-size top predator fish in each region.
The 90th percentile fish tissue mercury concentration and median concentrations were
calculated for each region for top predator fish (walleye and northern pike). Minnesota
used the difference between the 90th percentile mercury concentration in top predator
fish within each region and the 0.2 mg/kg target to calculate the reduction factors.
Minnesota used fish tissue data from 1988 to 1992 to establish the reduction factors. The
state looked at fish tissue data from 1970 to 2002; however, to be consistent with the
baseline year of 1990, fish tissue data from 1988 to 1992 were selected. Multiyear data
better represent real conditions over time because they account for year-to-year
variability in weather, fish populations, and sampling locations. Data for the standard-size
top predator fish were used to calculate the reduction factor. Mercury bioaccumulates in
fish; therefore, mercury concentrations are typically highest in the top predator fish. To
account for temporal and spatial comparisons of mercury concentrations in these top
predator fish, Minnesota used the standard-size top predator fish.31 Top predator fish that
are collected for fish tissue analysis vary in size and age. Because mercury concentrations
vary with the size of fish and age of fish, it is difficult to make comparisons regarding
mercury concentrations in fish without establishing a standard of comparison. Use of the
standard-size fish accounted for differences in mercury concentrations due to age and size
and allowed Minnesota to compare mercury concentrations across waterbodies.
' Minnesota uses a standard size of 40 cm (approximately 22 inches) for walleye and 55 cm (approximately 16 inches) for northern pike.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Allocations
Consistent with the regional approach used to establish the loading capacities, Minnesota
did not assign waterbody-specific allocations; rather, the state established gross
allocations for each region.
Minnesota assigned 1 percent of the loading capacity to point sources as the wasteload
allocation for each regional TMDL. Minnesota chose 1 percent of the loading capacity
based on an approach used in the Mercury Maps report to screen watersheds for
significant point source impacts to identify waterbodies impaired primarily by
atmospheric mercury (see appendix E on Mercury Maps). The northeast region wasteload
allocation was set at 1 percent of the loading capacity, while the southwest region's
wasteload allocation was set equal to the point source load portion of the total source
load. The state set the southwest region's wasteload allocation equal to the point source
load portion of the total source load because it was slightly less than 1 percent of the
southwest region's loading capacity and the state chose the more restrictive allocation.
Load allocations for each region were established by subtracting the wasteload allocation
and any explicit margin of safety from the established loading capacity. The remaining
load within each region was assigned to the load allocation. The approved loading
capacity and allocations for both regional TMDLs are shown in table D13.
Table D13. Approved northeast and southwest mercury TMDLs
Region
Northeast
Southwest
Loading
capacity
1.10 kg/day
2. 18 kg/day
Load
allocation
1.09 kg/day
1.55 kg/day
Wasteload
allocation
0.01 kg/day
0.02 kg/day
Margin of
safety
Implicit
0.61 kg/day
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Appendix E. Model Descriptions
Appendix E. Model Descriptions
This appendix describes currently available models discussed in this guidance. These
models aid in developing bioaccumulation factors and modifying fish tissue criteria (see
chapter 3), making assessments (see chapter 4), developing total maximum daily loads
(TMDLs) (see chapter 6), and in carrying out related programs such as 319 Nonpoint
Source Program activities, watershed management, stormwater permits, and National
Pollutant Discharge Elimination System (NPDES) discharge evaluations. This appendix
provides a description of each model, some examples of how or where it has been used,
and a Web site for further information about each model.
BASS (Bioaccumulation and Aquatic System Simulator)
The Bioaccumulation and Aquatic System Simulator (BASS) is a model that simulates
the population and bioaccumulation dynamics of age-structured fish communities.
Although BASS was specifically developed to investigate the bioaccumulation of
chemical pollutants within a community or ecosystem context, it can also be used to
explore population and community dynamics offish assemblages that are exposed to a
variety of non-chemical stressors such as altered thermal regimes associated with
hydrological alterations or industrial activities, commercial or sports fisheries, and
introductions of non native or exotic fish species.
BASS is being used to investigate methylmercury bioaccumulation in the Florida
Everglades and to predict population and community dimensions offish health" for a
regional analysis of the ecological sustainability of the Albemarle Pamlico drainage basin
in North Carolina and Virginia.
Information on BASS can be found at: http://www.epa.gov/athens/research/
modeling/bass .html.
Community Multi-Scale Air Quality (CMAQ) Model
The CMAQ modeling system is a comprehensive, three-dimensional, grid-based Eulerian
air quality model designed to estimate pollutant concentrations and depositions over large
spatial scales (Byun and Ching 1999; Byun and Schere 2006; Dennis et al. 1996). The
CMAQ model is a publicly available, peer-reviewed, state-of-the-science model
consisting of a number of science attributes that are critical for simulating the oxidant
precursors and nonlinear chemical relationships associated with the formation of
mercury. Version 4.3 of CMAQ (Bullock and Brehme 2002; Byun and Schere 2006)
reflects updates to earlier versions in a number of areas to improve the underlying science
and address comments from peer review. The updates in mercury chemistry in version
4.3 from that described in Bullock and Brehme (2002) are as follows:
1. The elemental mercury (Hg°) reaction with H2O2 assumes the formation of
100 percent reactive gaseous mercury (RGM) rather than 100 percent particulate
mercury (HgP).
2. The Hg reaction with ozone assumes the formation of 50 percent RGM and
50 percent Hgp rather than 100 percent HgP.
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Appendix E. Model Descriptions
o
-14
3. The Hg reaction with OH assumes the formation of 50 percent RGM and
50 percent HgP rather than 100 percent HgP.
4. The rate constant for the Hg + OH reaction was lowered from 8.7 to 7.7 x 10
cm3 molecules"1 s"1.
CMAQ simulates every hour of every day of the year and requires a variety of input files
that contain information pertaining to the modeling domain and simulation period. These
include hourly emissions estimates and meteorological data in every grid cell and a set of
pollutant concentrations to initialize the model and to specify concentrations along the
modeling domain boundaries.
Meteorological data, such as temperature, wind, stability parameters, and atmospheric
moisture content influence the formation, transport, and removal of air pollution. The
CMAQ model requires a specific suite of meteorological input files to simulate these
physical and chemical processes. For recent CMAQ modeling, meteorological input files
were derived from a simulation of the Pennsylvania State University's National Center
for Atmospheric Research Mesoscale Model (Grell et al. 1994) for the entire year of
2001. This model, commonly referred to as MM5, is a limited-area, nonhydrostatic,
terrain-following system that solves for the full set of physical and thermodynamic
equations that govern atmospheric motions. For this analysis, version 3.6.1 of MM5 was
used. A complete description of the configuration and evaluation of the 2001
meteorological modeling is provided by McNally (2003).
These initial and boundary concentrations were obtained from the output of a global
chemistry model, Harvard's GEOS-CHEM model (Yantosca 2004), to provide the
boundary concentrations and initial concentrations. The global GEOS-CHEM model
simulates atmospheric chemical and physical processes driven by assimilated
meteorological observations from NASA's Goddard Earth Observing System (GEOS).
This model was run for 2001 with a grid resolution of 2 degrees x 2.5 degrees (latitude-
longitude) and 20 vertical layers.
The CMAQ modeling domain encompasses all the lower 48 states and extends from 126
degrees west longitude to 66 degrees west longitude and from 24 degrees north latitude to
52 degrees north latitude. The modeling domain is segmented into rectangular blocks
referred to as grid squares. The model predicts pollutant concentrations and depositions
for each grid cell. For this application the horizontal domain consisted of 16,576 grid
cells that are roughly 36 km by 36 km. The modeling domain contains 14 vertical layers,
with the top of the modeling domain at about 16,200 meters, or 100 millibar. The height
of the surface layer is 38 meters.
A CMAQ modeling run was performed to estimate the impact of global sources on U.S.
deposition estimates. For this analysis, all non-U.S. mercury input species to the model
were set to zero. By comparing the results of this analysis with the 2001 Clean Air
Mercury Rule (CAMR) base case run, which included all U.S. and global mercury
species, the percent of total mercury deposition attributable to global sources can be
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3
estimated. The model estimated that over 80 percent on average of total mercury
deposition in the United States is attributable to global sources.
Due to the evolving nature of mercury modeling science, such deposition estimates have
associated uncertainties. For example, it remains difficult to distinguish between the
natural emissions of mercury and the re-emission of previously deposited anthropogenic
mercury and there remains uncertainty in the scientific community concerning the
atmospheric processes that control the oxidation state of atmospheric mercury. Thus,
further advances in the current understanding of mercury chemistry could potentially lead
to changes in the modeling parameters and assumptions governing the mercury chemistry
in the models and therefore, changes in the estimate of the fraction deposited in the U.S.
attributable to global sources.
For more information on CMAQ, see http://www.epa.gov/asmdnerl/CMAQ.
D-MCM (Dynamic Mercury Cycling Model)
D-MCM is a food web simulation of mercury accumulation in lakes. It predicts the
cycling and fate of major forms of mercury in lakes, including methylmercury, Hg (II),
elemental mercury, and total mercury. It is a time-dependent mechanistic model which
considers the most important physical, chemical, and biological factors affecting fish
mercury concentrations in lakes. D-MCM is meant for lotic (lake) systems, and is not
meant to be used for lentic (streams, rivers, etc.) systems.
D-MCM can be used to develop and test hypotheses, scope field studies, improve
understanding of cause and effect relationships, predict responses to changes in loading,
and support design and evaluation of mitigation options. It was used in the development
of mercury TMDLs for McPhee and Narraguinnep Reservoirs in Colorado and for the
TMDLs for Arivaca and Pena Blanca Lakes in Arizona. The Everglades Mercury Cycling
Model (E-MCM) was developed off of D-MCM and added vegetation processes and the
ability to simulate multiple sediment layers for wetlands.
Information on D-MCM can be found at: http://rd.tetratech.com/DraftHgBrochurev2 .pdf.
EXAMS2 (Exposure Analysis Modeling System)
EXAMS2 is a model for creating aquatic ecosystem models which can evaluate the fate,
transport, and exposure concentrations of chemicals. Chemicals include synthetic organic
chemicals like pesticides, industrial materials, and leachates from disposal sites.
EXAMS2 core is a set of modules that link chemical properties to limnological
characteristics that control the fate and transport of chemicals in aquatic systems. This
model allows for both long-term analysis of chronic chemical discharges at constant
release and varying release overtime, and short-term analysis of chemical releases.
EXAMS2 has commonly been used to predict pesticide fate in water and soil. This model
has been used to evaluate the role of hydroxyl radicals in degrading pesticides by
32 On February 8, 2008, the D.C. Circuit Court of Appeals vacated the Clean Air Mercury Rule and remanded portions of it to EPA, for
reasons unrelated to the technical analyses cited in this guidance.
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researchers at the University of Georgia. EXAMS2 was also used to simulate mercury
fate in the Withlacoochee River watershed and the Ohoopee River watershed in Georgia.
Information on EXAMS2 can be found at: http://www.epa.gov/ceampubl/swater/exams/.
GBMM (Grid Based Watershed Mercury Model)
EPA's Grid Based Watershed Mercury Model (GBMM) is a continuous grid-based
watershed mercury loading model using the latest ArcGIS platform. It simulates the
spatial and temporal dynamics of mercury from both point and non-point sources on a
daily basis. The model calculates the water balance, sediment generation and transport,
and mercury dynamics within a watershed. The mercury transport and transformation
module simulates the following key processes:
• Mercury input from atmospheric deposition.
• Mercury assimilation and accumulation in forest canopy and release from forest
litter.
• Mercury input from bedrock weathering.
• Mercury transformation in soils.
• Mercury transformation in lakes and wetlands including reduction and net
methylation.
• Mercury transport through sediment and runoff.
• Mercury transport in stream channels.
GBMM accepts input data from atmospheric deposition, point sources, and natural
background in time series or in digital spatial maps. By using the grid-based technology,
flow and mercury dynamics can be examined at any of several points in the watershed.
The software has been peer reviewed and tested on two watersheds in Georgia, where it
was used to calculate mercury TMDLs. GBMM has been used to investigate the mercury
fate and transport in Brier Creek watershed located in the coastal plain of Georgia.
GBMM was used to investigate detailed watershed mercury processes. The findings of
this study were presented in Eighth International Conference on Mercury as a Global
Pollutant (August 2006), Madison, Wisconsin, USA.
For more information on GBMM please visit: http://www.epa. gov/athens/research/
modeling/mercury/gbmm.html.
GEOS-CHEM Model
The Global GEOS-CHEM model simulates physical and chemical atmospheric processes
driven by observations by NASA's Goddard Earth Observing System (GEOS). This
model is managed and supported by the atmospheric chemistry modeling group at
Harvard University. This model is used as a tool for atmospheric composition problems.
This model was run for the 2001 CMAQ model with a grid resolution of 2 degree x 2.5
degree (latitude-longitude) and 20 vertical layers. GEOS-Chem is a major contributor to
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the NASA Global Model Initiative (GMI). GEOS-Chem has been interfaced with the
NASA/GISS general circulation model to investigate the effects of climate change. This
work contributes to the multi-institutional Global Change and Air Pollution (GCAP)
project. GEOS-Chem provides chemical modules for data assimilation of tropospheric
composition at the NASA GMAO.
For more information on GEOS-CHEM please visit: http://www-as.harvard.edu/
chemistry/trop/geos/geos_overview.html.
GWLF (Generalized Watershed Loading Function)
GWLF simulates mixed land use watersheds to evaluate the effect of land use practices
on downstream loads of sediment and nutrients (N, P). As a loading function model, it
simulates runoff and sediment transport using the curve number (CN) and Universal Soil
Loss Equation (USLE), combined with average nutrient concentration, based on land use.
Recently, a GIS-interface has been integrated which can use national land use and soil
GIS data. Also GWLF models in-stream routing using the Muskingum-Cunge method
and simulates three particle classes of sediment transport.
GWLF has been used in studies and TMDL development nationally. It is suitable for
application to generalized watershed loading, source assessment, and seasonal and
interannual variability. It has been extensively used in northeast and mid-Atlantic
regions. It has been adopted by Pennsylvania as state system for TMDL development and
agricultural land management. GWLF was used to calculate mercury load from the
watershed to a lake in several TMDLs in Arizona (e.g., TMDL for Pena Blanca Lake,
Arizona). GWLF is also applied in West Virginia TMDL projects by Tetra Tech, Inc.
Information on GWLF can be found at: http://www.epa.gov/nrmrl/pubs/
600r05149/600r05149gwlf.pdf and http://www.vims.edu/bio/models/basinsim.html.
Mercury Maps screening analysis
A simple screening-level analysis of the mercury sources affecting a waterbody or
waterbodies can assist in determining what type of approach to TMDLs is most
appropriate. EPA's Mercury Maps (USEPA 2001b) is a geographic information system
(GlS)-based analysis using national data coverage for watersheds, fish tissue
concentrations, and non-air deposition source locations.
Mercury Maps uses a simplified form of the IEM-2M model applied in EPA's Mercury
Study Report to Congress (USEPA 1997a). By simplifying the assumptions inherent in
the freshwater ecosystem models described in the report to Congress, Mercury Maps
showed that these models converge at a steady state solution for methylmercury
concentrations in fish that are proportional to changes in mercury inputs from
atmospheric deposition (e.g., over the long term, fish concentrations are expected to
decline proportionally to declines in atmospheric loading to a waterbody). This analytical
approach applies only to situations where air deposition is the only significant source of
mercury to a waterbody and the physical, chemical, and biological characteristics of the
ecosystem remain constant over time. To predict reductions in fish concentrations,
Mercury Maps requires estimates of percent air deposition reductions by watershed, as
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Appendix E. Model Descriptions
generated from a regional air deposition model, and georeferenced measurements of
mercury concentrations in fish.
A state or authorized tribe can apply Mercury Maps on a state or watershed scale. For
example, it could apply Mercury Maps on a statewide scale, using state- or tribe-defined
watershed boundaries. The state might have its own data on point source effluent loads
and more detailed information on other significant sources of mercury in the state, e.g.,
erosion of mine tailings or natural geology.
Because Mercury Maps is a simplified approach, it has several limitations.
1. The Mercury Maps approach is based on the assumption of a linear, steady state
relationship between concentrations of methylmercury in fish and present-day air
deposition mercury input. This condition might not be met in many waterbodies
because of recent changes in mercury inputs and other environmental variables that
affect mercury bioaccumulation. For example, the United States has recently
reduced human-caused emissions, and international emissions have increased.
2. Environmental conditions might not remain constant over the time required to
reach steady state inherent in the Mercury Maps methodology, particularly in
systems that respond slowly to changes in mercury inputs.
3. Many waterbodies, particularly in areas of historical gold and mercury mining in
western states, contain significant non-air sources of mercury. Mercury Maps'
methodology should not be applied to such waterbodies.
4. Finally, Mercury Maps does not provide for a calculation of the time lag between
a reduction in mercury deposition and a reduction in the methylmercury
concentrations in fish.
Despite the limitations of Mercury Maps, for those watersheds where mercury comes
almost exclusively from air deposition, Mercury Maps can be used as a simple screening
tool to show the watersheds across a region where the current fish tissue concentration on
average exceeds the new methylmercury fish tissue criterion and, thus, to estimate the
atmospheric load reductions needed to meet the new criterion. Further information on
Mercury Maps is at http://www.epa.gov/waterscience/maps and from the Office of Air
Quality Planning and Standards at http: //www. epa. gov/ttn/atw/utilitv/ria final .pdf.
MOBILE
MOBILE is an EPA model for estimating air pollution from highway vehicles. MOBILE
predicts emissions (grams/mile) of air pollutants from cars, trucks, and motorcycles under
various conditions. MOBILE models emissions of several air toxics, hydrocarbons (HC),
carbon monoxide (CO), oxides of nitrogen (NOX), carbon dioxide (CO2), and particulate
matter (PM). MOBILE is based on emissions testing of tens of thousands of vehicles. The
model accounts for the impact on emissions of factors such as legislative changes in
vehicle emission standards, variation in local conditions such as temperature, humidity,
and fuel quality, and changes in the types and use of the vehicles being driven.
MOBILE has been used to calculate national and local inventories of current and future
levels of highway vehicle emissions. The inventories are used to inform decision-making
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about air pollution policy and programs at the national, state and local level. Inventories
based on MOBILE are also used to meet requirement of federal statutes like the Clean
Air Act (CAA) and the National Environmental Protection Act (NEPA). MOBILE
contributed to the creation of the National Emissions Inventory (NEI).
Information on MOBILE can be found at: http ://www.epa. gov/otaq/mobile .htm.
NDMMF (National Descriptive Model of Mercury in Fish Tissue)
NDMMF is a statistical model which simulates mercury accumulation in varying species
offish. It simulates factors representing differences in species, size, and sampling
method. This model has the ability to control for site factors specific to a location that
influence mercury concentrations in fish tissue. For example, all fish tissue samples can
be scaled to a standardized 14" bass for a specific location. The model works in
association with a national dataset of over 30,000 samples offish tissue for calibration.
NDMMF could be useful for evaluating spatial and temporal trends in fish mercury
concentrations and developing fish-consumption advisories. The U.S. Geological Survey
recently applied this model to study spatial variation in fish-tissue mercury
concentrations in the St. Croix River Basin, Minnesota and Wisconsin.
Information on NDMMF can be found at: http://emmma.usgs.gov/fishHgAbout.aspx.
NONROAD
NONROAD is an EPA model for estimating air pollution from all engines, equipment,
and vehicles that is considered "nonroad". This includes recreational vehicles,
agricultural equipment, industrial equipment, residential equipment, and construction
equipment. The NONROAD model is used to predict past, present, and future emissions
of air pollutants like hydrocarbons (HC), oxides of nitrogen (NOX), carbon monoxide
(CO), carbon dioxide (CO2), sulfur oxides (SOX), and particulate matter (PM). It has been
shown that "nonroad" sources contribute a significant amount of air pollutants to the
environment.
Used in complement to MOBILE, NONROAD has been used to calculate national and
local inventories of current and future levels of "nonroad" emissions. This model has
become critical over the past several years in providing state and local pollution control
agencies the ability to create accurate and consistent inventories of "nonroad" emissions
to satisfy the requirements of the Clean Air Act Amendments of 1990. NONROAD
contributed to the creation of the National Emissions Inventory (NEI). The Lake
Michigan Air Directors Consortium (LADCO) used NONROAD to forecast emissions in
their region and make appropriate policy recommendations.
Information on NONROAD can be found at: http://www.epa.gov/otaq/nonrdmdl .htm.
QEAFDCHN (Quantitative Environmental Analysis Food Chain) Model
The QEAFDCHN model is a tool for predicting chemical residues in aquatic organisms
given the concentrations of chemicals in water and sediment. To predict chemical
residues, the model requires information on the individual species (bioenergetic and
physiological) and their diets. The model is designed to determine chemical residue in
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Appendix E. Model Descriptions
aquatic organisms given varying chemical concentrations in both water and sediment
overtime.
The QEAFDCHN model can be used in a steady-state or dynamic application. The model
allows the specification of complex food webs, e.g., fish preying on multiple species
including smaller fish, and even age classes of fishes. The model treats individual
segments of the greater ecosystem as individual ecosystems and the model has an aquatic
organism migration feature. QEAFDCHN has been applied to the Lavaca Bay, Texas,
chlor-alkali facility mercury contamination study by Quantitative Analysis, LLC.
Information on QEADFCFIN can be found at: http://www.epa.gOv/superfund//health/
conmedia/sediment/pdfs/bsafissue.pdf
Regional Modeling System for Aerosols and Deposition (REMSAD)
REMSAD is a three-dimensional grid model designed to calculate the concentrations of
both inert and chemically reactive pollutants by simulating the physical and chemical
processes in the atmosphere that affect pollutant concentrations (ICF International 2006).
REMSAD has been peer-reviewed and is designed to support an understanding of the
distributions, sources, and removal processes relevant to fine particles and other airborne
pollutants, including soluble acidic components and several toxic species (mercury,
cadmium, dioxin, poly cyclic organic matter [POM], atrazine, and lead).
Mercury can be present in the atmosphere in both the gas and particulate phases. The
mercury species included in REMSAD are Hg° (elemental mercury vapor), Hg2+ (divalent
mercury compounds in gas phase), and Hgp (divalent mercury compounds in particulate
phase). These species represent the oxidation state of mercury, and the gas and particulate
phases. The reactions in REMSAD, which are based on the studies of Lin and Pehkonen
(1999) and other recently published studies, simulate the transfer of mercury mass from
one of these states to another. REMSAD Version 8 uses the full Carbon Bond-V
mechanism to simulate gas-phase photochemical processes in the atmosphere (micro-CB
is still available as an option), and it also includes a chemical mechanism to calculate the
transformations of mercury.
REMSAD simulates both wet and dry deposition of mercury. Wet deposition occurs as a
result of precipitation scavenging. Dry deposition is calculated for each species based on
land-use characteristics and meteorological parameters. REMSAD also includes
algorithms for the reemission of previously deposited mercury (originating from
anthropogenic and natural sources) into the atmosphere from land and water surfaces due
to naturally occurring (e.g., microbial) processes.
REMSAD provides estimates of the concentrations and deposition of mercury and all
other simulated pollutants at each grid location in the modeling domain. Post-processing
can provide concentration averages and deposition totals for any subset of the time span
of the simulation for any location within the domain.
The mercury treatment in REMSAD can be expanded to include additional, tagged
mercury species. The Particle and Precursor Tagging Methodology (PPTM) feature
allows the user to tag or track emissions from selected sources or groups of sources and
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Appendix E. Model Descriptions
to quantify their contribution to mercury deposition throughout the modeling domain and
simulation period.
The REMSAD model is capable of "nesting" one or more finer-scale subgrids within a
coarser overall grid. This feature uses a fully interactive two-way nesting capability that
permits high resolution over selected source and/or receptor regions of interest. The
modeling system can be applied at scales ranging from a single metropolitan area to a
continent containing multiple urban areas.
REMSAD has been used in identifying the sources contributing mercury deposition to a
waterbody. In an EPA Wisconsin pilot project, REMSAD was used to input the air
pollutant deposition results to aquatic models like the Mercury Cycling Model, to
examine how mercury levels in fish might respond to potential changes in deposition.
REMSAD has been used to develop TMDLs and determine strategies for addressing
mercury and other air pollutant deposition. REMSAD was used in developing the
mercury TMDL for the Coastal Bays and Gulf Waters of Louisiana (approved in 2005)
and the mercury TMDLs for middle and south Georgia (approved in 2002).
Information on REMSAD can be found at: http://remsad.saintl.com/.
SERAFM (Spreadsheet-based Ecological Risk Assessment for the
Fate of Mercury)
The SERAFM model is a spreadsheet-based risk assessment tool specifically designed
for mercury contaminated ecosystems. SERAFM uses a steady-state simplifying
assumption and includes a series of sequentially linked modules presented on separate
spreadsheets. These modules include:
• Atmospheric deposition
• Watershed soil erosion
• Watershed mercury loading
• Waterbody solids balance
• Equilibrium partitioning (DOC complexation, solids partitioning)
• Mercury speciation
• Waterbody mercury calculations (historic sediment contamination, background,
and remedial goal)
• Fish tissue concentrations
• Wildlife hazard quotients
The SERAFM model incorporates more recent advances in scientific understanding and
implements an updated set of the IEM-2M solids and mercury fate algorithms that were
described in the 1997 Mercury Study Report to Congress (USEPA 1997c).
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Appendix E. Model Descriptions
For more information on SERAFM please visit: http://www.epa. gov/athens/research/
modeling/mercury/serafm.html and http://www.epa.gov/nerl/news/forum2005/
knightes.pdf
TOXI5
TOXI5 is one of two submodels of WASP (Water Quality Analysis Simulation Model),
the other being EUTRO5, which deals with eutrophication. TOXI5 is a sediment
transport model which can also simulate the transport and transformation of chemicals.
The transport of up to three types of sediment and up to three chemicals can be simulated.
The chemicals may react independently or they may be linked with reaction yields which
predict the fate of the interaction. Dissolved and sorbed chemical concentrations in the
waterbody bed and overlying waters can be predicted using TOXI5.
TOXI5 was used to simulate the fate of mercury in the Ochlockonee Watershed in
Georgia, to help develop mercury TMDLs for the Southeast U.S., and to evaluate the
feasibility of dam release of water on the Nakdong River in Korea to mitigate frequent
accidental spills of toxic chemicals.
For more information on TOXI5 please visit: http://smig.usgs.gov/cgi-bin/SMIC/
model home_pages/modelhome?selection=wasp.
WASP (Water Quality Analysis Simulation Program)
The Water Quality Analysis Simulation Program (WASP) is a dynamic compartment-
modeling program for aquatic systems, including both the water column and the
underlying benthos. It has detailed mercury transformation processes for the water
column and benthic sediments. The mercury module simulates the following key
processes:
• Volatilization of Hg° (aq) to Hg° (air)
• Oxidation of Hg° ^ Hgn
• Reduction of Hgn ^ Hg°
• Methylation of Hgll -» MeHg
• Demethylation of MeHg -> Hgn
• Photoreduction of MeHg -> Hg°
WASP has been used to examine eutrophication of Tampa Bay, Florida; phosphorus
loading to Lake Okeechobee, Florida; eutrophication of the Neuse River Estuary, North
Carolina; eutrophication of the Coosa River and Reservoirs, Alabama; PCB pollution of
the Great Lakes; eutrophication of the Potomac Estuary; kepone pollution of the James
River Estuary; volatile organic pollution of the Delaware Estuary; heavy metal pollution
of the Deep River, North Carolina; and mercury in the Savannah River, Georgia.
Information on WASP can be found at: http://www.epa.gov/athens/research/
modeling/wasp .html.
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Appendix E. Model Descriptions
WCS (Watershed Characterization System) Mercury Loading Model
The WCS Mercury Loading model is a GIS-based (Arc View 3.x) extension of the WCS
model based on a soil-mercury mass balance model (IBM v 2.05). The soil-mercury mass
balance model calculates surface soil concentrations in dissolved, sorbed, and gas phases.
The model accounts for three routes of contaminant entry into the soil:
• Deposition of particle-bound contaminant through dry fall
• Deposition through wet fall
• Diffusion of gas phase contaminant into the soil surface
The model also accounts for four dissipation processes that remove mercury from the
surface soils:
• Volatilization (movement of gas phase out of the soil surface)
• Runoff of dissolved phase from the soil surface
• Leaching of dissolved phase through the soil horizon
• Erosion of particulate phase from the soil surface
The model assumes that the diffusion and volatilization processes are roughly balanced
on an annual basis. The WCS Mercury Loading model was used to develop many
TMDLs in EPA Region 4 including a mercury TMDL for the Middle and Lower
Savannah River.
Information on the WCS model can be found at: http://www.epa.gov/athens/
wwqtscAVCS-toolbox.pdf
Example of Linking Models
Since there is no single model that can simulate all processes involved in TMDLs, some
TMDLs for mercury have linked together models of atmospheric deposition, watershed
loading, and mercury cycling with bioaccumulation. For example, a watershed mercury
model such as GBMM, or the watershed module within SERAFM could be linked to a
receiving water mercury model such as WASP, and a bioaccumulation model such as
BASS.
GBMM is a spatially discrete, dynamic watershed mercury loading model which was
designed for direct linkage to the EPA receiving waterbody model, WASP. GBMM can
simulate mercury fate and transport within the watershed landscape and transport
mercury and soils to the receiving waters through the tributaries. WASP can in turn
simulate mercury dynamics in the receiving water. To predict bioaccumulation of the
resulting mercury concentrations into fish tissues, WASP can then be linked to BASS.
SERAFM is a more simplified approach and captures the processes from watershed to
waterbody to fish bioaccumulation; however, it makes simplifying assumptions such as
the waterbodies are steady state and it uses the national BAFs presented by EPA for
trophic level fish.
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Appendix E. Model Descriptions
Linkage of such models may be a workable solution in some situations. One of the
limitations of the GBMM-WASP-BASS approach is that it is not an "off-the-shelf
model and a high level of expertise might be required to link the models together.
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Appendix F. Examples of National Deposition Monitoring Networks
Appendix F. Examples of National
Deposition Monitoring Networks
A number of national deposition monitoring networks might be useful for developing
TMDLs. The networks include the National Atmospheric Deposition Program-National
Trends Network (NADP/NTN) and the Mercury Deposition Network (MDN, a subset of
the NADP network). The NADP/NTN is a nationwide network of precipitation
monitoring stations. Operating since 1978, it collects data on the chemistry of
precipitation for monitoring of geographic patterns and temporal long-term trends.
NADP/NTN measures weekly average concentrations of sulfate, nitrate, ammonium, base
cations, and acidity at approximately 230 monitoring stations across the United States.
The MDN measures concentrations of total mercury in precipitation at approximately 45
monitoring stations across the United States and Canada. NADP/NTN results for 2003
are shown in figure F-l. For more information about NADP, see
http: //nadp. sws .uiuc. edu.
Used in conjunction with NADP/NTN, the Clean Air Status and Trends Network
(CASTNET) is the nation's primary source of atmospheric data on the dry deposition
component of total acid deposition, ground-level ozone, and other forms of atmospheric
pollution that enters the environment as particles and gases. CASTNET measures weekly
average atmospheric concentrations of sulfate, nitrate, ammonium, sulfur dioxide, and
nitric acid, as well as hourly concentrations of ambient ozone levels in rural areas. Dry
deposition rates are calculated using the measured atmospheric concentrations,
meteorological data, and information on land use, surface conditions, and vegetation.
Seventy-nine monitoring stations operate across the United States. For more information
about CASTNET, see http://www.epa.gov/castnet and http://nadp.sws.uiuc.edu.
Note that these national monitoring networks generally provide only estimates of wet
deposition; estimates of dry deposition can be obtained from the literature. For more
information on deposition monitoring networks, see Deposition of Air Pollutants to
the Great Waters: Third Report to Congress (USEPA 2000h) (http://www.epa.gov/
oar/oaqps/gr8water/3rdrpt) and the Air-Water Interface Plan (http://www.epa.gov/ttn/
caaa/t3/reports/combined.pdf).
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Appendix F. Examples of National Deposition Monitoring Network
Total Mercury Concentration, 2005
,vv KB
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117 " . •!"? ioi100 9-
Sites rot pictured:
Hidalgo, Mexico (HD01): 8.7 ng/L
National Atmospheric Deposition Program/Mercury Deposition Network
Hg (ng/L)
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8-10
10-12
12-14
14-16
16-18
Figure F-1. MDN data for 2005.
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Index
Index
Note: Bold numbers indicate where the term is defined (if applicable). If the term has been broken
into subcategories, this is noted with a defined entry.
ambient water quality criteria See
AWQC
analytical methods 3, 36, 51-54, 101,
102,155
antidegradation 46, 95, 96, 109-13
atmospheric deposition.... 17, 76, 77-82,
90, 164, 167
AWQC 25, 33, 34, 59
BAF
and Great Lakes 66
and model selection 87
calculating 25
defined 25
draft national 27,32-35
sampling considerations 35-37
site-specific 2,37,40,68, 104
using 22-38
weighted 162
best management plan 122
best management practices See BMP
bioaccumulation 10
bioaccumulation factor See BAF
bioaccumulation model. 30-32, 83, 190,
200
biomagnification 15, 16, 55, 88
BMP
and designated use 48
andMMPs 113, 122
and variances 47
andWQBELs 93, 115
dental 122
emission 129
livestock 92, 172
CAA 14, 17, 73, 79, 127-30
CAMR
analysis supporting 26, 63
and SERA FM model 198
andWCS 86
defined 14
modeling for 81
Clean Air Act See CAA
Clean Air Mercury Rule See CAMR
CMAQ 80-81, 190-92, 193
cold-vapor atomic fluorescence
spectrometry See CVAFS
Community Multi-Scale Air Quality.See
CMAQ
composite samples 3, 56-58
Consolidated Assessment and Listing
Methodology (CALM) 59
Continuing Survey of Food Intakes by
Individuals See CSFII
criterion, calculating 22, 23
CSFII 41,42, 153
CTR 66, 175, 181
CVAFS 52, 53, 155, 156, 157, 158
CWAlOl(a) 47,48,63
CWA304(a) 19,20,70
demethylation 16, 26, 34, 85
designated use
andCWAlOl(a) 47
andUAA 47
and variances 44, 45
changing 48
fishable 22
protecting 1, 19,38
detection level 59, 60
detection limit 52, 60, 156
dilution flow 66
D-MCM 31, 85, 87, 170, 173, 192
emissions
anthropogenic 14, 15
controls 120
hourly estimates in models 191
mobility of 14
natural 1, 14, 192
regulations 14, 125, 127-30
to air 77, 79, 85, 127-30
203
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Index
trends in 79, 78, 127, 128
environmental justice 72
EPA methods
1630 3,52,53,54,60, 155
1631 3, 51, 52, 53, 54, 60, 91, 102,
105, 141, 144, 155, 157, 158
and measuring 3, 51, 52, 53, 54,
155
and nondetects 60, 102
andWQBELs 102
defined 51-54
in NPDES permits
102,106, 105-6
inTMDLs 91
1669 52
245.7 3,51,52,53, 102, 157
existing use 45,48, 109, 112
exposure
and BAFs 27, 29, 30, 35, 37
and consumption advisories 69
and fish 66
and humans 125, 175, 181, 186
and sample types 55, 56
andtheRSC 39,70
data in criterion calculation
22,38,42,67,70, 152
fish tissue concentration as
proxy to 31
from drinking water 23
human health effects 1, 9-11
FDA action level 72
field sampling plan 54-58
fish advisories
and water quality standards 68-72
EPA guidance on 54, 63-64
issued 13,22,69
map (U.S.) 13
revising 71
statewide 13, 70
Fish Advisory Program 68
fish intake rate/estimate
and trophic levels 24, 36, 61
default 23,39,42
fish sampling guidance 54-58
fish tissue residue criterion... See TRC
in criterion calculation
23,38,39-43, 152, 154
limits 68-72
modifying 39-43
of subsistence consumers 40
RSC 29,38,39,70
TRC 22,24,39
fish sampling guidance 36
freshwater
and estuarine fish
age 26,30,34,35,36,55, 166,
173, 188, 190, 197
and water quality criterion ...23, 39,
42,43,61,62, 152
intake..See fish intake rate/estimate
mercury found in 16, 35, 58
ecosystem models 194
lakes and rivers 13
target species 40, 41, 149
Great Lakes Guidance 52
Great Lakes Water Quality Initiative
(GLI) 2,41,65
growth dilution 10, 16
health effects of methlymercury See
exposure: human health effects
human health
toxicological risk assessment 22
impairment
addressing 1, 64, 74
assessing 24, 59-64
identifying sources of 117, 121
listing decisions 59-64
Mercury Containing and Rechargeable
Battery Management Act 130
Mercury Deposition Network 80, 201
mercury emissions See emissions
Mercury Maps 75,84, 188, 189,
194-95
mercury minimization plan See MMP
Mercury Study Report to Congress.... 11,
32, 80, 85, 120, 162, 167, 194, 198
mercury, forms of defined 27
204
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Index
methylation 16, 26, 31, 67, 75, 82
minimum level 109, 112
mixing zone 2, 65, 67-68
MMP
and antidegradation 96, 110-16
and reasonable potential 7, 95
and type of facility 121
as a permit condition 107, 119-23
guidance on 120
implementing 96, 119-23
model
D-MCM 31,85,87, 170, 173, 192
Dynamic Mercury Cycling Model
See D-MCM
empirical bioaccumulation 30
mechanistic bioaccumulation 31
regression 30, 31, 62, 63, 86
selecting 87
spatially detailed 86
steady state/mass balance 84-87
uncertainty 81, 88
monitoring and assessment. 3, 13, 51-64
National Descriptive Model for Mercury
in Fish Tissue See NDMMF
National Health and Nutrition
Examination Survey 10
National Pollutant Discharge
Elimination System See NPDES
National Study of Chemical Residues in
Fish Tissue 53
National Toxics Rule 47, 66
NDMMF 26,36,63, 196
neurological effects 10
nondetections 56, 59, 60, 102
normalizing factors 26, 36
NPDES
and antidegradation See
antidegradation
andWQBELs 93-99, 101, 104-5,
107,109, 112-19, 123
documentation 119
effluents, measuring mercury in.... 96,
101,104-6, 112, 116
fish tissue criterion, implementing ...99
general considerations 93
new sources and new discharges,
mercury in 99, 112, 116
permit special condition 107
pollutant minimization plan
recommended conditions ... 108-23
pollutant minimization program.... 89,
120
reasonable potential determination
and fish tissue data 5,95, 104,
106-11,114
and intakes 114
defined 93
how to 104-23
process 103
recommended permitting
approach 94-99
reopener clause
95-97, 105, 106, 107, 116
Overview of P2 Approaches at
POTWs 120
partition coefficient 164
persistency 121, 165
pollution prevention ... 73, 96, 110, 120-
21, 125-27
POTW 77,91, 118-22, 125-27
prenatal exposure 9
public participation 72
quality control 63
quantitation level 52, 101, 155
recommended form of criterion 20
reference dose See RfD
regulations under CAA 127-3 0
REMSAD 75, 80, 197
RfD 9, 23, 39, 69, 154, 161, 162, 173
RSC 23, 39, 43, 70, 162
sampling
and BAFs 25, 35-37
fish 54-58
guidance on 54-58
sediment 82, 92
shellfish
advisories 64, 68
and CWA 101(a) 47
205
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Index
in criterion calculation 23
intake rates 15, 42, 43
to be monitored 55
significant industrial users 125
site-specific conditions 38-49
site-specific procedure 24-37, 66,
68,82, 104
sources
atmospheric 9, 14-16, 44, 77-82,
194-95
human activity 14, 15, 83
in fish 14-15
mining 14, 49, 82
natural 14, 15, 45, 48, 77, 83
overseas 191
point sources 15, 44, 49, 67, 76, 77
sediment 9, 16,82, 117
species 16, 28, 55-56, 150, 153
spill prevention and containment control
plan 122
tissue concentration-based standard.. 22,
24
tissue residue value 66, 99, 114
TMDL 73-92
allocation approaches 88
best uses 73
challenges 17
considerations 73-92
defined 73
examples See Appendix A
geographic scale 4, 74, 75
modeling tools 80-81, 83-88
monitoring provisions 91, 92
pollutant loading scenario 88
Total Maximum Daily Load ...See TMDL
translation factor 26-35, 99-123
trophic levels
and BAFs 28, 29, 32-36, 200
and fish intake 23-26, 36, 39, 61
and fish species 150
and food webs 16, 55, 88
and GLI 66
andTMDLs
161, 162, 173, 175, 181,183
averaging data across 61-64
sampling in 3, 55, 58
UAA 47-48
uncertainty
and margin of safety 73, 170, 178
184
assessing loadings 110
BAFs 32,34,36
from extrapolating re suits 31
in TMDL 73
model 33,81,88
reducing 25
RfD 9
use attainability analysis See UAA
variances
and controls 44, 47
antidegradation 46
considerations 45
how they apply 44-47
large-scale 46
multiple discharger (group) 47
protocols 45
scenarios 45
time frames 45
when appropriate 2, 44
water column concentrations
33,52,67, 108
water quality criteria
and BAFs 22-38, 40
and fish advisories 70
and methods 1630, 1631 53,54
components 19
water quality standards
and fish advisories 68-72
water quality-based effluent limits ....See
WQBEL
Watershed Characterization System
See WCS
WCS 86, 163,200
weighted consumption 161
206
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Index
WQBEL and TMDLs 96, 99, 103, 104,
and anti-backsliding 7, 112, 119 115-19
and mercury in intake water 6, 114 and variances 44
and NPDES permits 93-99, 101, defined 93
103-5, 107, 109, 118, 119, 121 deriving 101, 93-99
and pretreatment 118, 119 determining need for 103-14
and technology-based limits 7, 93, elements of 96, 98, 114-23
99,112,116,119 formsof 93
207
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