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-09-002
www. epa. gov/waterscience
January 2009
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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 better 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. 2009. Guidance for Implementing the January 2001 Methylmercury Water Quality
Criterion. EPA 823-R-09-002. U.S. Environmental Protection Agency, Office of Water, Washington,
DC.
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FOREWORD
On January 8, 2001, the 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 the criterion be used as
guidance by states, territories, and authorized tribes 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 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 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, 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)
on how to use the new fish tissue-based criterion recommendation in developing their own 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.
For more information on the methylmercury criterion, see the criteria page on EPA's Web site at
http://www.epa.gov/waterscience/criteria/methvlmercurv/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.
Benjamin H. Grumbles
Assistant Administrator for Water
U.S. Environmental Protection Agency
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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? 10
2.2 What are the sources of mercury in fish? 12
2.3 How does methylmercury get into fish and shellfish? 14
2.4 Why is EPA publishing this document? 15
2.5 What is the effect of this document? 16
3 Water Quality Criteria and Standards Adoption 17
3.1 What must states and authorized tribes include as they adopt the
methylmercury criterion? 17
3.1.1 What do the CWA and EPA's regulations require? 17
3.1.2 What is the recommended form of the methylmercury criterion? 18
3.1.3 What approaches should states or authorized tribes consider when
developing a water column concentration criterion? 21
3.2 What options are available to address site-specific conditions and concerns? ...36
3.2.1 How can the methylmercury water quality criterion be modified for site-
specific conditions? 36
3.2.2 How do water quality standards variances apply? 41
3.2.3 How are use attainability analyses (UAAs) conducted? 45
4 Monitoring and Assessment 49
4.1 What are the analytical methods for detecting and measuring mercury and
methylmercury concentrations in fish and water? 49
4.1.1 Analytical Methods for Methylmercury 50
4.1.2 Analytical Methods for Mercury 50
4.1.3 Summary of Recommended Analytical Methods 51
4.2 What is the recommended guidance on field sampling plans for collecting fish
for determining attainment of the water quality standard? 52
4.2.1 What fish species should be monitored? 53
4.2.2 What sample types best represent exposure? 54
4.2.3 What is the recommended study design for site selection? 54
4.2.4 How often should fish samples be collected? 55
4.2.5 How many samples should be collected? 56
4.2.6 What form of mercury should be analyzed? 56
4.2.7 Other sampling considerations 56
4.3 How should waterbody impairment be assessed for listing decisions? 57
4.3.1 How should nondetections be addressed? 58
4.3.2 How should data be averaged across trophic levels? 59
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Contents
4.3.3 How should older data be assessed? 61
4.3.4 How should fish consumption advisories be used to determine
impairment? 61
5 Other Water Quality Standards Issues 63
5.1 How does this criterion relate to the criteria published as part of the Great
Lakes Initiative? 63
5.2 What is the applicable flow for a water column-based criterion? 64
5.3 How are mixing zones used for mercury? 65
5.3.1 What is a mixing zone? 65
5.3.2 How does a mixing zone apply for the fish tissue-based
methylmercury criterion? 65
5.3.3 Does the guidance for the fish tissue-based criterion change the Great
Lakes Initiative approach to mixing zones for bioaccumulative
pollutants? 66
5.4 How are fish consumption advisories and water quality standards
harmonized? 66
5.4.1 What is the role of state and tribal Fish Advisory Programs? 66
5.4.2 How are consumption limits for consumption advisories determined? 67
5.4.3 How does the criterion differ from the advisory level? 67
5.4.4 What if there is a difference between assessing criterion attainment
and issuance of a fish consumption advisory? 68
5.4.5 Should existing advisories be revised to reflect the new criterion? 69
5.4.6 What federal agencies issue advisories? 69
5.4.7 How is the criterion related to FDA action levels? 70
5.5 What public participation is recommended for implementing the
methylmercury criterion? 70
6 TMDLs 71
6.1 What is a TMDL? 71
6.2 How have states and tribes approached mercury TMDLs? 71
6.2.1 What geographic scales have been used for mercury TMDLs? 73
6.2.2 What are the considerations in developing mercury TMDLs? 74
7 National Pollutant Discharge Elimination System (NPDES)
Implementation Procedures 91
7.1 What are the general considerations in NPDES permitting? 91
7.2 What is the EPA-recommended NPDES permitting approach for
methylmercury? 92
7.2.1 Developing NPDES permit limits based on the fish tissue criterion 92
7.2.2 Determining reasonable potential 93
7.2.3 Implementing antidegradation 93
7.2.4 Establishing appropriate WQBELs 94
7.3 How does EPA recommend implementing the fish tissue criterion for NPDES
permits? 95
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Contents
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? 97
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? 99
7.5.1 How to determine the need for permit limits to control mercury (how to
determine reasonable potential) 100
7.5.2 Where reasonable potential exists, how can WQBELs be derived from
a fish tissue value? 110
8 Related Programs 121
8.1 What are EPA and others doing as a whole to address mercury? 121
8.2 How does pollution prevention play a role in the methylmercury criterion? 121
8.3 What regulations has EPA issued pursuant to the CAA to address air
emissions of mercury? 123
8.3.1 Municipal waste combustors 124
8.3.2 Hospital, medical, and infectious waste incinerators 124
8.3.3 Chlor-alkali plants 125
8.3.4 Hazardous waste combustors 125
8.3.5 Coal-fired power plants 126
8.3.6 Other 126
9 References 127
Appendix A. Methylmercury/Mercury Ratio Exhibited in Muscle
Tissue of Various Freshwater Fish Species 143
Appendix B. Tables from Methylmercury Criteria Document 145
Appendix C. Analytical Methods 149
Appendix D. Synopsized Mercury TMDLs Developed or Approved
by EPA 153
I. Ochlockonee Watershed, Georgia 154
Description of the Applicable Water Quality Standards 154
Source Assessment 155
Loading Capacity—Linking Water Quality and Pollutant Sources 156
Allocations 157
II. Arivaca Lake, Arizona 159
Description of the Applicable Water Quality Standards 159
Source Assessment 159
Loading Capacity—Linking Water Quality and Pollutant Sources 161
Allocations 163
III. McPhee and Narraguinnep Reservoirs, Colorado 166
Description of the Applicable Water Quality Standards 166
Source Assessment 166
Loading Capacity—Linking Water Quality and Pollutant Sources 167
in
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Contents
Allocations 167
IV. Clear Lake, California 168
Description of the Applicable Water Quality Standards 168
Source Assessment 168
Loading Capacity—Linking Water Quality and Pollutant Sources 170
Allocations 171
V. Cache Creek, California 174
Description of the Applicable Water Quality Standards 174
Source Assessment 175
Loading Capacity—Linking Water Quality Pollutant Sources 176
Allocations 177
VI. Minnesota Statewide Mercury Total Maximum Daily Load 179
Description of the Applicable Water Quality Standards and TMDL Target 179
Source Assessment 180
Loading Capacity 180
Allocations 182
Appendix E. Model Descriptions 183
BASS (Bioaccumulation and Aquatic System Simulator) 183
Community Multi-Scale Air Quality (CMAQ) Model 183
D-MCM (Dynamic Mercury Cycling Model) 185
EXAMS2 (Exposure Analysis Modeling System) 185
GBMM (Grid Based Watershed Mercury Model) 186
GEOS-CHEM Model 186
GWLF (Generalized Watershed Loading Function) 187
Mercury Maps screening analysis 187
MOBILE 188
NDMMF (National Descriptive Model of Mercury in Fish Tissue) 189
NONROAD 189
QEAFDCHN (Quantitative Environmental Analysis Food Chain) Model 190
Regional Modeling System for Aerosols and Deposition (REMSAD) 190
SERAFM (Spreadsheet-based Ecological Risk Assessment for the Fate of
Mercury) 191
TOXI5 192
WASP (Water Quality Analysis Simulation Program) 192
WCS (Watershed Characterization System) Mercury Loading Model 193
Example of Linking Models 193
Appendix F. Examples of National Deposition Monitoring Networks 195
Index 197
IV
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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 30
Table 3. Estimates of freshwater and estuarine combined finfish and shellfish
consumption from the combined 1994-1996 and 1998 CSFII surveys
(U.S. population) 40
Table 4. Recommended analytical methods for detecting and measuring low levels of
methylmercury and mercury in fish tissue and water 52
Table 5. Example data for calculating a weighted average fish tissue value 59
Table 6. Suggested content for MMPs based on the type of facility 117
Table B1. Exposure parameters used in derivation of the water quality criterion 146
Table B2. Average mercury concentrations in marine fish and shellfish 147
Table B3. Exposure estimates for methylmercury and percent of total exposure
based on adults in the general population 148
Table C1. Analytical methods for determining mercury and methylmercury in tissue ... 149
Table C2. Analytical methods for determining mercury and methylmercury in water,
sediment, and other nontissue matrices 150
Table D1. Annual average mercury load from each subbasin 156
Table D2. Predicted mercury for annual average load and flow 157
Table D3. Annual total mercury load to Arivaca Lake 162
Table D4. Predicted and observed mercury for annual average load and flow 163
Table D5. Summary of TMDL allocations and needed load reductions (in g-Hg/yr) 164
Table D6. Summary of mercury load estimates for McPhee Reservoir 166
Table D7. Summary of TMDL allocations and needed load reductions for McPhee
Reservoir 167
Table D8. Summary of TMDL allocations and needed load reductions for
Narraguinnep Reservoir 168
Table D9. Summary of mercury load allocations 172
Table D10. Sediment goals for mercury in Clear Lake 172
Table D11. Cache Creek methylmercury allocations 178
Table D12. Bear Creek Methylmercury Allocations 178
Table D13. Approved Northeast and Southwest Mercury TMDLs 182
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Contents
FIGURES
Figure 1. Average fish tissue concentrations by HUC watershed 11
Figure 2. Total number of state mercury fish consumption advisories 2006 12
Figure 3. Percentage of total mercury deposition attributable to global sources 76
Figure 4. Trends in mercury air emissions between 1990 and 1999 76
Figure 5. NPDES permitting approach for methylmercury 96
Figure 6. Implementing the fish tissue criterion in NPDES permits 97
Figure 7. Determining reasonable potential 99
Figure 8. Implementing tier2 antidegradation 107
Figure 9. Determining WQBEL requirements 111
Figure F-1. MDN data for 2005 196
VI
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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 2006, 48 states, 1 territory, and
2 tribes had issued fish consumption advisories for mercury covering 14.2 million lake
acres and 883,000 river miles (USEPA 2007a). 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. 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 their own 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.
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.
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Executive Summary
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).
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
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.
• Appendix A of Method 1631 for mercury in fish tissue.
• Method 1630 for methylmercury in water.
• Method 1630 (with 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 of fish 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).
• 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.
• Use of linked models without having explicit water
column criteria or translations.
FT or WC
6.2.2.2
FT
6.2.2.2.5
FT alone
6.2.2.2
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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 is available at time of permit
issuance, implement using the approaches described in
the Technical Support Document (TSD) for Water
Quality-based Controls (USEPA 1991).
• If a TMDL or water column translation is 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,
and
• Fish tissue from the receiving water 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)
Most
applicable
to criteria
expressed
as...
For a full
discussion
see
section...
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 discharger will not undertake an activity that could
result in an increase in receiving water or fish tissue
mercury concentration:
o Encourage the facility to voluntarily develop and
implement an MMP tailored to the facility's
potential to discharge mercury.
FT alone
7.5.1.2.2
Where fish tissue levels may be increasing
• EPA recommends that the permitting authority account
for situations where fish tissue levels are below but close
to the criterion and expected to be increasing. A finding
of RP could be made considering effects of current
discharges and other factors. The guidance provides
examples of how this could be accomplished.
FT alone
7.5.1.2.2
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.
FT or WC
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 may 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
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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,
include a numeric WQBEL.
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Introduction
2 Introduction
2A is the in
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.
2.1.1 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). 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 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).
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Introduction
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). 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 2006 303(d) listing cycle, 42 states and Puerto Rico reported at least one
waterbody as impaired due to mercury, and more than 9,000 specific waterbodies were
listed as impaired due to mercury, either solely or in combination with other pollutants. In
10
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Introduction
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 (figure 1). 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 200 Ib).
Figure 1 shows fish tissue mercury concentrations averaged by watershed (by 8-digit
hydrologic unit code, or HUC).
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
| 0.3-1
• 1-2.7
Note:
1 New Criterion tor methylmercury 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 fillel 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
western rivers (Peterson et al. 2007).
11
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Introduction
As of December 2006, 48 states, 1 territory, and 2 tribes had issued fish consumption
advisories1 for mercury covering 14.2 million lake acres and 883,000 river miles
(figure 2). Twenty-three states had issued advisories for mercury in all freshwater lakes
and rivers in the state, and 12 states had statewide advisories for mercury in their coastal
waters (USEPA 2007a). 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. mercury emissions have
declined by almost 50 percent since 1990 (USEPA 2007a).
^
NH(R,L)8
20 131
(R,L) (R,L)
CT(R,L)10
NJ (R,L) 85
rcury Advisories by Type:
ivisories exist for specific waterbodies only
atewide freshwater advisory
Statewide freshwater advisory and additional
advisories on specific waterbodies
"atewide coastal advisory
atewide advisory for marine fish included in count
No mercury advisories
American Samoa
R = All rivers under advisory
L - All lakes under advisory
Figure 2. Total number of state mercury fish consumption advisories 2006.
2.2 What are the sources of mercury in fish?
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
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. EPA and the Food and Drug
Administration (FDA) issue guidance on the level of contaminants in fish, which states and tribes may use in issuing their advisories.
12
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Introduction
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 an advanced, state-of-the-science modeling assessment of the atmospheric fate,
transport, and deposition of mercury conducted by EPA for the Clean Air Mercury Rule
(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 45 percent
since passage of the 1990 Clean Air Act (CAA) Amendments. 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. More
recent regulations, including regulation of mercury emissions from chlorine production
facilities that use mercury cells and regulation of industrial boilers, will further reduce
emissions of mercury.
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). In May 2005, EPA adopted the Clean Air Mercury Rule (CAMR) to regulate
mercury emissions from utilities. On February 8, 2008, the B.C. Circuit Court of Appeals
vacated the CAMR and remanded portions of it to EPA. See EPA's mercury Web site, at
On February 8,2008, the B.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.
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.
13
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Introduction
http://www.epa.gov/mercury. for information on current activities related to control of
power plant emissions.
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 discharges are 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 in
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.
2.3 How does methylmercury get into fish and shellfish?
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, Hg (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, Hg (Schroeder et al. 1989). Particulate and reactive
gaseous phases of Hgnare 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 Hg11
species or reactive gaseous mercury (ROM) and particulate mercury (Hgp) in the
atmosphere tend to be deposited more locally than Hg , differences in the species of
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 Hg11 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
14
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Introduction
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, Hg 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.
2.4 Why is EPA publishing this document?
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 enable 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
15
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Introduction
water quality criteria for methylmercury, on the basis of 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). 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.
EPA expects that, as a result of this revised methylmercury water quality criterion,
together with a more sensitive method for detecting mercury in effluent and the water
column and increased monitoring of previously unmonitored waterbodies, the number of
waterbodies that states report on CWA section 303(d) lists as impaired due to mercury
contamination might increase. 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.
2,5 is the of
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.
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Water Quality Criteria and Standards Adoption
3 Water Quality Criteria and Standards
Adoption
3.1 What must states and authorized tribes include as
they adopt the methylmercury criterion?
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 must 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)). 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
5
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.
• Option 3: States or authorized tribes may adopt a chemical-specific translator
procedure6 that can be used to develop numeric criteria as needed.
To protect human health from contaminants in fish, EPA considers the 2001
methylmercury criterion a sound, scientifically based approach for meeting human health
designated uses. Thus, EPA strongly encourages states and authorized tribes to adopt the
2001 methylmercury criterion or any sound, scientifically based approach for
4 The term -water quality 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).
5 CWA section 307(a) identifies a list of toxic pollutants that EPA has published at 40 CFR 401.15.
6 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.
17
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Water Quality Criteria and Standards Adoption
methylmercury or mercury into their water quality standards to fulfill the requirements of
40 CFR part 131.
Water quality criteria generally consist of three components: magnitude, duration, and
frequency (USEPA 1994). Water quality criteria for human health are typically expressed
as an allowable magnitude. A criterion is calculated to protect against long-term chronic,
human health effects. Thus, the duration of exposure assumed in deriving the criterion is
a lifetime exposure even though the criterion is expressed as a magnitude of contaminant
per day (USEPA 1991).
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 fish7 tissue concentration value (0.3 milligram
methylmercury per kilogram of wet-weight fish tissue, or 0.3 mg/kg). With the
publication of the 304(a) criterion, EPA withdrew the previous ambient 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).
States and authorized tribes that adopt a new or revised methylmercury criterion into their
water quality standards have several options. They may:
• Adopt the 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.
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, local or statewide fish
consumption, and exposure to mercury from other sources (relative source contribution,
or RSC). 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
7 The criterion applies to both finfish and shellfish. For purposes of simplifying language in this document, the term fish means both finfish
and shellfish.
18
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Water Quality Criteria and Standards Adoption
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, nor does it have a preference for or against such translation, except that
this is one approach EPA does recommend specifically for waters with relatively high
direct water inputs of mercury (see below). As noted above, criteria expressed as fish
tissue concentrations can be implemented directly, using approaches discussed in this
guidance, for most Clean Water Act applications. Section 3.1.3 provides information to
those states and tribes who choose to adopt a water column criterion.
For 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
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 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 criterion implementation plan to
ensure environmentally protective and effective administration of all water quality related
programs with respect to methylmercury. Developing an 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.
Developing an implementation plan could 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 during
triennial reviews or 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 an 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.
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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.
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:
BW x(R/D - RSC)
Z-J'=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 consumed8), estimated to be 0.027 ug/kg
body weight/day
BW = human body weight (default value of 70 kg for adults)
8 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.
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Water Quality Criteria and Standards Adoption
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 population9
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 2001c)). 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 develop a water quality criterion for
methylmercury using local or regional data to modify the fish consumption rate or the
RSC rather than using the default values if the state or authorized tribe believes that such
a water quality criterion would be more appropriate for its target population.
The TRC value is not based on any default breakout offish 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 (TL) 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 standards programs. Water
quality standards, water quality-based effluent limits10 (WQBELs), TMDLs, and other
9 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
activities generally employ a water column value. This section provides information for
states and authorized tribes that decide to adopt a criterion that is expressed as a water
column concentration.
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.
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 = TRCI BAF (Equation 2)
Where:
AWQC = water concentration-based ambient water quality criterion for
methylmercury in milligrams per liter (mg/L)
10 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
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
(Equation 3)
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
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
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Water Quality Criteria and Standards Adoption
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 chemicals11 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.
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 ite standard in this manner:
11 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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Water Quality Criteria and Standards Adoption
1. Use site-specific methylmercury BAFs derived from field studies.
2. Use a scientifically defensible bioaccumulation model.
3. As a last resort and only where appropriate, when deriving site-specific, field-
measured BAFs or using a model is not feasible, use BAFs derived using the
results of field studies that are not site-specific. Such BAFs may include the draft
national BAFs presented in appendix A of Water Quality Criterion for the
Protection of Human Health: Methylmercury (USEPA 200 la) 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 strongly 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 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)
• 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.
Where 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.
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Water Quality Criteria and Standards Adoption
Developing site-specific data to support approaches 1 and 2 can be facilitated by efforts
involving stakeholders, states, and authorized tribes. This 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
for bioaccumulation, such as largemouth bass. A field-measured site-specific BAF also
reflects biotic and abiotic factors at a location that influence the bioavailability and
metabolism of a chemical that might occur in the aquatic organism or its food web. 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 water12 (Equation 3). To predict the corresponding methylmercury
12 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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Water Quality Criteria and Standards Adoption
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 3 and 4 fish against
aqueous methylmercury concentrations (P < 0.001, R2 = 0.98, and P < 0.01, R2 = 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
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, such
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 increases 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
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Water Quality Criteria and Standards Adoption
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
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
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Water Quality Criteria and Standards Adoption
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, 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
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 fas 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 the BAF guidance in
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-
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Water Quality Criteria and Standards Adoption
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
(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
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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
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
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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
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), conducting studies to
develop a site-specific BAF (e.g., site-specific field studies or bioaccumulation
modeling), or not adopting the methylmercury criterion at all.
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. For fish tissue,
however, states and authorized tribes can estimate methylmercury concentrations 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
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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
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. 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
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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.
• 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.
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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
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.
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3.2 What options are available to address site-specific
conditions and concerns?
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 (sport or
subsistence, or both) that eat fish 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
• 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. To change the RSC
used by EPA, states and authorized tribes should review section 5 of the methylmercury
criterion document and modify the media-specific exposure estimates in table 5-30 using
local data that reflect the exposure patterns of their populations. Of the six exposure
media presented in table 5-30 (which does not include exposure from fresh and estuarine
fish), the exposure from ingestion of marine fish (including migratory species such as
salmonids - see table 5-14, USEPA 200 la) constituted greater than 99.9 percent of the
total exposure to methylmercury, and thus ingestion of fish would be the focus of any
modification to the RSC. To modify this factor, states and authorized tribes should
review the amount of marine fish and shellfish estimated to be consumed (table 5-1,
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USEPA 200la) and the concentration of methylmercury in the commonly consumed
marine species (table 5-14, USEPA 200la). States and authorized tribes should document
the modifications with data supporting the modifications and ideally should 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.
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/day , uncooked (USEPA 2001a). States and authorized tribes may use a
different intake rate based on local or regional consumption patterns. 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
their target population. However, states and authorized tribes should consider whether the
consumption rates reflect existing public concern about contamination offish 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.
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 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.
13 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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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).
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 offish 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
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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
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
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some
estimates. The survey does support interval estimates for the U.S. population and
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 of fish is delineated below in
table 3.
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.
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.
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
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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.14 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).
3.2.2 How do water quality standards variances apply?
A state or authorized tribe may provide NPDES dischargers temporary relief from a
water quality standard by adopting 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) where a state or authorized tribe believes the
water quality standard cannot be attained in the immediate future. 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. 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
human health 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).
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
14 See the discussion of the RSC in sections 3.1.2.3 and 3.2.1.1.
15 These six justifications are allowed for use attainability analyses under 40 CFR 131.10(g): (1) naturally occurring pollutant
concentrations prevent the attainment of the use; (2) natural, ephemeral, intermittent, or low-flow conditions or water levels prevent the
attainment of the use, unless these conditions may be compensated for by the discharge of sufficient volume of effluent discharges without
violating state water conservation requirements to enable uses to be met; (3) human-caused conditions or sources of pollution prevent the
attainment of the use and cannot be remedied or would cause more environmental damage to correct than to leave in place; (4) dams,
diversions, or other types of hydro logic modifications preclude 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; (5) 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, preclude attainment of aquatic life protection uses; and (6) controls more stringent than those required by sections 301(b) and
306 of the CWA would result in substantial and widespread economic and social impact.
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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
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). For example, atmospheric deposition
originating overseas could be the source of elevated mercury levels in a local
stream, yet the lack of an international agreement or treaty to cut mercury
emissions worldwide prevents attainment of the methylmercury criterion, despite
local reduction efforts. In this instance, if air deposition modeling shows that the
atmospheric deposition from outside the United States was a substantial cause of
the impairment, and there was no immediate expectation that those sources would
experience reductions, the variance may be warranted.
• 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?16
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 be set at a level that would not protect the 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
16 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 recommencing Great Lakes dischargers.
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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 regulations at 40 CFR 131.20 provide an opportunity to consider
new information every three years for the purpose of reviewing water quality
standards and, as appropriate, modifying and adopting standards. For this reason,
states typically limit the time frame of a variance to three to five years, with
renewals possible following a sufficient demonstration that the variance is still
necessary. Variances that extend longer than three years are traditionally revisited
in the context of a triennial review to justify their continuation. While the permittee
typically makes this demonstration, the permittee also should demonstrate that it
made reasonable progress to control mercury in the discharge during the period of
the previously approved variance. In terms of methylmercury, EPA anticipates a
time lag between implementing controls and seeing results (i.e., there may be
unaddressed sources, continual leaching of mercury from sediments, and so on).
For example, EPA modeled the response in fish tissue to a 50 percent reduction in
mercury loadings to four lakes and estimated that it would take 1 to 56 years for the
lakes to reach 90 percent of the estimated steady state fish tissue methylmercury
concentration (USEPA 2005a). To address this issue, states and authorized tribes
could develop an expedited variance adoption process, especially if legislative
deliberations or administrative procedures are necessary to adopt variances into
water quality standards. For example, a variance provision could allow for
mercury-specific demonstration for renewals by making use of information already
available. In the Great Lakes, renewal of a variance may be denied if a permittee
did not comply with the conditions of the original variance. (40 CFR part 132,
appendix F, procedure 2, section H).
Another perspective regarding the life span of a variance is that although three
years is the time frame for water quality standards reviews under the CWA, there is
no specific federal regulatory requirement for a variance to expire in three years.
Regardless, 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
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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.
• Pollutant Minimization Program. Pollutant Minimization Programs (PMPs) may
serve as a pollution prevention measure that states and authorized tribes could
require of dischargers receiving a variance. By reducing mercury sources up front,
as opposed to traditional reliance of treatment at the end of a pipe, diligent
implementation of PMPs might mitigate any adverse effects of a variance by
improving the 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, EPA encourages states and
authorized tribes to 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 any or some combination of the following:
• Similar discharge processes. A type of industry or effluent treatment process may
be targeted on the basis of similar treatment requirements and/or available
technology (e.g., publicly owned treatment works or POTWs, mining operations).
A state or authorized tribe may choose to adopt a variance with tiered requirements,
depending on the type of industry requesting coverage. For example, due to the
differing effluent matrices, one industry would be required to meet a variance of 10
parts per billion (ppb) above the criterion, whereas another industry would be
required to meet a variance of 20 ppb above the criterion, based on the availability
of technology to remove the pollutant from the different types of effluents.
• Watershed basis. A variance on a watershed scale might be a sensible approach,
particularly for states that issue NPDES permits on a watershed basis. As with
other pollutants, methylmercury concentrations can be monitored to gain site-
specific information (perhaps for calculating site-specific BAFs) in key watersheds
for a given year. A state or authorized tribe using a watershed approach to
permitting should have data available from a watershed in one year for the purpose
of issuing NPDES permits in the watershed(s) where permits would be issued in
the subsequent year. The state or authorized tribe could use these data for the
purpose of evaluating the continuing need for and potential for revision to a
previously approved water quality variance. Meanwhile, variances for other
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Water Quality Criteria and Standards Adoption
watersheds remain the same or are renewed with unchanged variance requirements
until monitoring occurs, with variance time frames coinciding with the permitting
cycle. This way, the variance-based limits will reflect a more "real-time" variance.
• Broader geographic basis. Analogous to a general NPDES permit, a multiple-
watershed, areawide, or statewide variance could be made available by the state or
authorized tribe using approaches similar to those above. Individual dischargers
could apply for coverage under such a variance upon fulfilling certain conditions.
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)).
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
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
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Water Quality Criteria and Standards Adoption
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.
• 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
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respect to establishing an attainable use. Of the six factors above, it is most likely that
human-caused conditions that cannot be remedied, naturally occurring pollutant
concentrations, or substantial and widespread social and economic impact resulting from
additional controls would be the reason cited in a UAA addressing methylmercury-
impacted waters. 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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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 What are the analytical methods for detecting and
measuring mercury and methylmercury
concentrations in fish and water?
Over the past two decades, EPA and other organizations have developed several
analytical methods for determining mercury and methylmercury concentrations in fish
and water. In 2001 EPA conducted a literature review to assess the availability of
different analytical methods and to determine which of the analytical methods would be
most useful for implementing the new methylmercury criterion. After the review, EPA
concluded that nearly all current research on low-level concentrations of mercury and
methylmercury is being performed using techniques that are based on procedures
developed by Bloom and Crecelius (1983) and refined by Bloom and Fitzgerald (1988),
Bloom (1989), Mason and Fitzgerald (1990), and Horvat et al. (1993).
To assist states and authorized tribes in selecting an analytical method to use, this chapter
describes selected analytical methods available (sections 4.1.1 and 4.1.2), and identifies
five specific methods that EPA recommends for use in implementing this guidance
(section 4.1.3). In addition, appendix C of this document presents a list of available
methods in more detail. Table Cl of the appendix summarizes 4 methods to analyze
mercury and methylmercury in fish tissue, and table C2 summarizes 18 methods for the
analysis of mercury and methylmercury in water and other nontissue matrices. Each table
identifies the forms and species of mercury targeted by each method, estimated or known
sensitivity, the techniques employed in the method, and any known studies or literature
references that use the techniques employed in the method.
The CWA establishes an EPA approval process for certain methods used in the NPDES
program and for section 401 certifications. As described in section 4.1.2 below, EPA has
approved two of the above methods for analysis of mercury in water under 40 CFR part
136: method 1631, revision E and method 245.7. EPA's regulations generally require that
these methods be used whenever such analyses are required for the NPDES program and
for CWA section 401 certifications issued by states and authorized tribes (40 CFR 136.1).
Sections 7.4 and 7.5.1.1 of this guidance provide additional information on appropriate
analytical methods for measuring mercury in water for NPDES permitting purposes.
There are no regulatory requirements for the use of particular methods in setting water
quality standards, evaluating the attainment of standards, or developing TMDLs,
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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
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 0.001 mg/kg in tissue and 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.
Modifications to method 1630, described in table Cl (see appendix C) and in Horvat et
al. (1993), allow for measurement of methylmercury in 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
tissue are desired.
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
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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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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)
Draft Method 1630 with
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.
4.2 What is the recommended guidance on field sampling
plans for collecting fish for determining attainment of
the water quality standard?
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. 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, a
monitoring sample could be composited to reflect this knowledge. For example, a
state might decide that 75 percent of the fish consumed by the general population
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
variability, so that consumption of larger (older) individuals correlates with greater
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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, the state or authorized tribe should consider including
the skin 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
probabilistic design can address the spatial variability of methylmercury levels in fish.
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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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4.3 How should waterbody impairment be assessed for
listing decisions?
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)17, 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.
17 See EPA's guidance for Integrated Reports described at http://www.epa.gov/owow/tmdl/2006IRG/.
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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
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 of fish 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
18 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 2005f). 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.
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.19 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 eight 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.
When reporting water quality conditions 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.
19 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
5.1 How does this criterion relate to the criteria published
as part of the Great Lakes Initiative?
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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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.
5.2 What is the applicable flow for a water column-based
criterion?
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).
20 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 (ig/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 How are mixing zones used for mercury?
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 (USPEA 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.
5.4 How are fish consumption advisories and water
quality standards harmonized?
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).
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
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
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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 RSC 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
demonstrate that a section 101(a) "fishable" use is not being attained in an
See discussion on the RSC in section 3.1.2.3 and 3.2.1.1.
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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. A state or tribe may choose to
revise existing advisories to mirror the methylmercury criterion. 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 data that are representative and of acceptable
quality.
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
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.
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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.
5.5 What public participation is recommended for
implementing the methylmercury criterion?
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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6 TMDLs
6.1 What is a TMDL?
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 2006 303(d) listing cycle, 42 states and Puerto Rico reported at least one
waterbody as impaired due to mercury, and more than 9,000 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.
6.2 How have states and tribes approached mercury
TMDLs?
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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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 December 2008, mercury TMDLs have been
approved for more than 6,600 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) (USEPA
2007b) (http://www.epa. gov/owow/tmdl/mercurv5m/Mercury5m .pdf). EPA is
recommending the voluntary approach for states that have in place a comprehensive
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 also 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 2008). 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
technical tools available to assist in mercury TMDL development. Technical tools
available to assist in the development of mercury TMDLs include screening-level
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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
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
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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.
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
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
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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 (RGM),
elemental mercury (Hg°), and particulate 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.
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 1999 and shows a 45 percent overall decrease.
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January 1,0 0:00:00
Min 14.076 at (21.84). Max- B8JBH(MW)
Figure 3. Percentage of total mercury deposition attributable to global sources
(USEPA 2005a).
U.S. Emissions of Anthropogenic Mercury Have Dropped 45% Since 1990
250
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1990 Emissions 1996 Emissions 1999 Emissions
Source: USEPA 1990,1996 NTI and EPA 1999 NEl. Snort ions per year. Adjusted for 9010 mines in 1990 em 1996.
'The 1990 and 1996 NE> did net inoude gold rrtining omissions data. Tno emissions shown hero tor gold mines in those years
are assumed to be equal to emissions for those mines in 1999
Figure 4. Trends in mercury air emissions between 1990 and 1999 (USEPA 1999a).
Additional decreases in mercury air emissions have occurred since 1999 as the result of
EPA's regulatory efforts under the CAA. At the same time, however, global emissions
might have increased.
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The 2002 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 2002 NEI is at http://www.epa.gov/ttn/chief/net/
2002inventory.html.
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
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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
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
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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.
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
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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)
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.,
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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?
• 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.
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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).
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
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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).
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 better 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.
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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
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.
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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.
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
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TMDLs
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.
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
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TMDLs
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/Files PDF/techguide/wpb/TMDL/
Savannah/EP A_Savannah_River_Watershed_Hg_TMDL.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
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 Hg TMDL.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
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TMDLs
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
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
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TMDLs
Colorado. Examples of such TMDLs can be found at http://iaspub.epa.gov/
tmdl waters 10/attains impaired waters.control?p state=CO&p_pollutant id=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
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 offish tissue and sediment (see appendix D, and the TMDL at
http://www.swrcb.ca.gov/rwqcb5/water_issues/tmdl/central_valley_projects/clear_lake_h
g/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
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TMDLs
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
7 National Pollutant Discharge Elimination
System (NPDES) Implementation
Procedures
7.1 What are the general considerations in NPDES
permitting?
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)).22
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 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
22 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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water quality standards) (see 40 CFR 122.44(d)(l)(ii)). The procedure specifies only
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.
7.2 What is the EPA-recommended NPDES permitting
approach for methylmercury?
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
122.44(d)(l)(vn)(B)).
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.
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 is 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 is available at the time of permit issuance, the permit limits based
on this criterion 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 is 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 procedures described below.
Section 7.3 contains additional information about expressing and developing permit
limits based on the methylmercury criterion.
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NPDES Implementation Procedures
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. 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 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 exceeds the criterion. If this
information 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 voluntarily develop and implement mercury minimization plans
(MMPs) to reduce mercury loading to the waterbody. If 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, 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
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.
To assist in preventing future impairments, in some situations a state or authorized tribe
may wish to 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 7.5.1.2.2 contains additional examples of other factors that could be
considered in a reasonable potential analysis.
7.2.3 Implementing antidegradation
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
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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,
include a numeric water quality-based limit.
• Where a water column translation is 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.
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NPDES Implementation Procedures
Other considerations and requirements may be necessary in developing permits. They
include the following, which are also explained in greater detail in section 7.5.2.1:
• Where a discharger undertakes an activity that could increase mercury loading to
the receiving water, the WQBEL 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.
The entire recommended NPDES permitting approach is summarized in figure 5 and
explained in greater detail in the following sections.
7.3 How does EPA recommend implementing the fish
tissue criterion for NPDES permits?
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
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NPDES Implementation Procedures
START
Is the criterion
expressed in terms of
fish tissue7
Is a water column
translation of the fish
tissue criterion
available?
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
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• Conduct tier Z
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and develop appropriate
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• 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,
include a numeric water quality-based limit
• Where a water column translation 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 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 CFR 132, Appendix F, Procedure 5.
Figure 5. NPDES permitting approach for methylmercury.
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NPDES Implementation Procedures
START
" Is the criterion • • Implement using the
I expressed in terms of { . approaches described
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NPDES Implementation Procedures
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
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).23
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.
23 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/mercurymemo analyticalmethods.pdf
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NPDES Implementation Procedures
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.
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?
This approach assumes that a state or authorized tribe decides to adopt a new or revised
water quality criterion for methylmercury in the form of a fish tissue concentration and
that a TMDL or water column translation of the fish tissue criterion is not available at the
time of permit issuance. As a result, the permitting authority will use a different approach
than it has previously used for determining reasonable potential and expressing
WQBELs. EPA recommends the approach described below, which is summarized in
figure 7.
Criterion is expressed in terns of fish tissue
AND
a water column translation of the fish tissue criterion is not available (Figure 6)
Determining Re
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
•asonable
^
^ J Is there a c
ii i mercuryd
Unknown
>
1 Does the fi
~* Unknown ^ \ exceed the
are there o
that woul
permitting
find rea
pote
No
f
uantifiabie
ischarge?
Yes
f
sh tissue in
ing water
criterion or
(her factors
i lead the
authority to
sonable
ilial?
^» 1 ff A'k*
Implement tier 2
No antidegraaanon (Mgure 8)
L
Yes
Determine WQBEL requirements {Figure 9)
Note:
* For Great Lakes states, implement using 40 CFR132, Appendix F, Procedure 5,
Figure 7. Determining reasonable potential.
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7.5.1 How to determine the need for permit limits to control
mercury (how to determine reasonable potential)
As discussed in section 3.1.2.2 of this document, EPA recommends that states and
authorized tribes adopt new or revised methylmercury water quality criteria in the form
of a fish tissue concentration. When criteria are adopted into standards as a fish tissue
value, 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. This section
provides recommendations for how a permitting authority can determine reasonable
potential in the absence of 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 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 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 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.
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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 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.
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:
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• 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
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).
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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., that the NPDES-permitted discharger has
mercury in 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 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.
• The fish tissue concentration of methylmercury exceeds 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 voluntarily 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
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NPDES Implementation Procedures
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
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.
Furthermore, 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 addition, in this situation EPA recommends that the permitting authority encourage the
permittee to voluntarily 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 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 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 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
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NPDES Implementation Procedures
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
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 are close to the
criterion and 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. Even where fish tissue concentrations are below the
criterion, a finding of reasonable potential could be made where the permitting authority
accounts for the effect of current discharges and other relevant factors that 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 alternative to this statistical approach,
the State of Idaho's implementation guidance24 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.
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 rising fish tissue concentrations
or the relative contribution of mercury or methylmercury from the source 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
24 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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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.
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.
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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
No
Implementing
Antidegradation
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.
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 voluntarily 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.
If future monitoring data demonstrate that a discharge does have reasonable potential,
development of a voluntary MMP could assist the permit writer in establishing
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appropriate permit conditions. Furthermore, EPA believes that simply developing an
MMP might provide dischargers of mercury with sufficient information to voluntarily
and 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).
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.
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
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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)).25 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.
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 dischargers 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.
25 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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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 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 exceed the fish
tissue water quality criterion. 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
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
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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
fish tissue in Ihe receiving water
exceeds the criterion (Figure 7)
1 Yes
T
Recommended WQBEL Requirements
• Where a TMDL has been developed, the WQBEL must be consistent with the wasteload allocation as required by
40CFR122.44(d)(1Xvii)(B})
• Where a TMDL has not been developed but a water column translation of the fish tissue criterion has been developed,
include a numeric water quality-based limit
• Where a water column translation is not available and the permit writer determines that a numeric limit is infeasible to
calculate
- 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 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
"For Greai Lakes states, implement ysing 40 CFR 132, Appendix F, 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 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:
• Where a water column translation of the fish tissue criterion has been developed,
include a numeric water quality-based limit.
• Where a water column translation is not available and the permit writer determines
that a numeric limit is infeasible to calculate.
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NPDES Implementation Procedures
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.
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
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,
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EPA recommends that states and authorized tribes specifically consider developing
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. 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.
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 is 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
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descriptions of TMDLs that have been developed using steady state models and the
proportionality approach.
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
(MGD) 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)).
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
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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 if a TMDL or water column translation of the fish
tissue criterion is available at the time of issuance. If neither a TMDL nor a water column
translation 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, 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
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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/mercuryjmp 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/
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
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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.
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.
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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.
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.
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
• 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 may 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
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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 could 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.
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Related Programs
8 Related Programs
8.1 What are EPA and others doing as a whole to address
mercury?
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.
8.2 How does pollution prevention play a role in the
methylmercury criterion?
Under the national pretreatment program, POTWs routinely control the volume and
concentration of pollutants contributed by significant industrial users (SIUs)26 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
26 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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District (WLSSD) determined that one SIU and many small non-SIUs (dental facilities)
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 What regulations has EPA issued pursuant to the
CAA to address air emissions of mercury?
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 45 percent reduction in domestic mercury air emissions between 1990
and 1999 (see figure 4 and http://www.epa.gov/ttn/chief/trends/index.html).
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 final regulations that apply to all new and existing waste-to-
energy plants and incinerators with the capacity to burn more than 250 tons of municipal
solid waste, including garbage, per day (see 60 FR 65,415 [December 19, 1995], codified
at 40 CFRpart 60, subparts Ea and Eb). 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 (see figure 4: 56.7 tons per year of mercury
emitted from domestic municipal waste combustors in 1990 versus 4.9 tons per year in
1999).
8.3.2 Hospital, medical, and infectious waste incinerators
Hospital/medical/infectious waste incinerators (HMIWIs) are used by hospitals, health
care facilities, and commercial waste disposal companies to dispose of hospital waste
and/or medical/infectious waste. EPA adopted regulations controlling mercury emissions
from HMIWIs on September 15, 1997 (62 FR 48,348, codified at 40 CFR part 60,
subparts Ce and EC). EPA estimated that the regulations would reduce mercury emissions
from HMIWIs at existing facilities by 93-95 percent, and all existing HMIWIs were
required to comply with the regulations by September 15, 2002 (see figure 4: 49.7 tons
per year of mercury emitted from domestic HMIWIs in 1990 versus 1.6 tons per year in
1999). In fact, the actual mercury emission reductions achieved as a result of
implementing the regulations were approximately 99 percent. At the time the regulations
were issued, EPA expected that 50 percent 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 final rule, few health care facilities are likely to install new
HMIWIs and approximately 97 percent of the 2,400 HMIWIs operating at health care
facilities in 1997 have shut down. Instead, the facilities have switched to other methods
of waste disposal, such as off-site commercial waste disposal. There are currently 57
existing HMIWIs at 52 facilities. EPA expected the standards to apply to between 10 and
70 new HMIWIs, most of which would employ mercury control technology by the
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compliance deadline; only 4 new HMIWI at 3 facilities began operating following the
1997 rulemaking.
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 8 such plants in the United States, compared to 20
when work on the rule began, with a further decrease to 5 plants expected for 2008. In
addition, EPA has initiated a study of fugitive mercury emissions at existing chlor-alkali
plants.
8.3.4 Hazardous waste combustors
In 1999 EPA established standards for HAPs, including air emission standards for
mercury, for incinerators, cement kilns, and lightweight aggregate kilns that burn
hazardous waste under CAA section 112 (70 FR 52828, 53011; September 30, 1999).
The 1999 standards were challenged by several parties and subsequently vacated by the
United States Court of Appeals for the District of Columbia Circuit (the Court) in 2001.
The parties to this proceeding subsequently filed a joint motion with the Court to delay
issuance of the mandate to vacate the challenged standards to allow time for EPA to
develop interim standards, which would replace the vacated standards temporarily, until
EPA could promulgate standards consistent with the Court's mandate. In 2002 EPA
published interim standards for these three source categories (67 FR 6792 [February 13,
2002]), which are under 40 CFR part 63, subpart EEE. The mercury standards for
existing and new sources, respectively, are under 40 CFR 63.1203(a)(2) and (b)(2) for
incinerators, 40 CFR 63.1204(a)(2) and (b)(2) for cement kilns, and 40 CFR
63.1205(a)(2) and (b)(2) for lightweight aggregate kilns. Affected sources were required
to comply with the interim standards by September 30, 2003.
In 2005 EPA published replacement standards (to replace the 2002 interim standards) for
hazardous waste-burning incinerators, cement kilns, and lightweight aggregate kilns. At
the same time, EPA also finalized emission standards for other types of hazardous waste
combustors, including liquid fuel boilers, solid fuel boilers, and hydrochloric acid
production furnaces (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. Sources are
required to comply with these emission standards by October 14, 2008.
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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). In May 2005, EPA adopted the Clean Air Mercury Rule (CAMR) to regulate
mercury emissions from utilities. On February 8, 2008, the B.C. Circuit Court of Appeals
vacated the CAMR and remanded portions of it to EPA. For information on current
activities related to control of power plant emissions, see EPA's mercury Web site, at
http: //www .epa. gov/mercury.
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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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.
143
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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 (http: //www. epa. gov/waterscience/
criteria/humanhealth/method/tsdvol2 .pdf).
144
-------
Appendix B. Tables from Methylmercury Criteria Document
Appendix B. Tables from Methylmercury
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.
145
-------
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).
c 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).
Pica child soil ingestion.
146
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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"
(M9 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).
147
-------
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.
148
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Appendix C. Analytical Methods
Appendix C. Analytical Methods
Table C1. Analytical methods for determining mercury and methylmercury in tissue
Method
Draft method
1630, with
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:
a . . ii- u- u. *+• i
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.
149
-------
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.
150
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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.
151
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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.
152
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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
153
-------
Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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-
154
-------
Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
specific data, EPA determined a representative weighted BAF. The BAF was calculated
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.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
diffusion. Sorbed variables can migrate downward or upward through net sedimentation
or erosion.
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
because EPA is not able to make the case-by-case judgments in this TMDL that EPA
believes are appropriate.
II.
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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.
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
derived for Arivaca were 5.3 ug/m2/yr by wet deposition and 7.1 ug/m2/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
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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
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.
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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.
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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.
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
III. McPhee and Narraguinnep Reservoirs, Colorado
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
Note: Measurements in g/year of mercury.
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.
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.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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
00
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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.
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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
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.
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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:
aThe 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.
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:
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 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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
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.
VI. Minnesota Statewide29 Mercury Total Maximum Daily
Load
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.
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
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
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
loading capacity was calculated by multiplying a regional reduction factor30 needed to
achieve the fish tissue mercury concentration target by the total source load for each
region, thus calculating a regional load reduction goal.32 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
30 The northeast regional reduction factor is 65 percent, and the southwest regional reduction factor is 51 percent.
31 The baseline load for the northeast region is 1153 kg/yr, and the baseline load for the southwest region is 1628 kg/yr.
32 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
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
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
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Appendix D. Synopsized Mercury TMDLs Developed or Approved by EPA
account for temporal and spatial comparisons of mercury concentrations in these top
predator fish, Minnesota used the standard-size top predator fish.33 Top predator fish that
are collected for fish tissue analysis vary in size and age. Because mercury concentrations
vary with the size offish and age offish, 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.
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
' 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 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
-14
3. The Hg° reaction with OH assumes the formation of 50 percent ROM 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
cm molecules" s" .
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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Appendix E. Model Descriptions
estimated.34 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.
34 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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Appendix E. Model Descriptions
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
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
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Appendix E. Model Descriptions
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
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
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Appendix E. Model Descriptions
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
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
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Appendix E. Model Descriptions
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
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.
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Appendix E. Model Descriptions
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
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 QEADFCHN 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
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Appendix E. Model Descriptions
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
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
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Appendix E. Model Descriptions
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).
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
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Appendix E. Model Descriptions
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.
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 (IEM 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/
wwqtsc/WCS-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
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Appendix E. Model Descriptions
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.
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.
194
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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).
195
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Appendix F. Examples of National Deposition Monitoring Networks
Total Mercury Concentration, 2005
v ^ iv *&&&
,
f M "
' '
f M
,D5 93, •' '
» ' . «V 10,1M . _^
..* .. -T "'j^:-
Sites not pictured:
Hidatgo, Mexico (HD01): 8.7 ng/L
National Atmospheric Deposition Pragram/Mercury Deposition Network
Figure F-1. MDN data for 2005.
196
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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, 34, 49-52, 98, 99,
149
antidegradation 44, 93-94, 105-9
atmospheric deposition.... 16, 74, 75-79,
87, 157, 160
AWQC 22, 30, 32, 57
BAF
and Great Lakes 64
and model selection 85
calculating 23
defined 23
draft national 25,29-32
sampling considerations 32-34
site-specific 2, 34, 37, 44, 66, 100
using 20-36
weighted 155
best management plan 118
best management practices See BMP
bioaccumulation 10
bioaccumulation factor See BAF
bioaccumulation model. 27-29, 80, 183,
193
biomagnification 14, 15, 53, 85
BMP
and designated use 46
andMMPs 109, 118
and variances 45
andWQBELs 91, 111
dental 117
emission 125
livestock 89, 165
CAA 13, 16, 71, 76, 123-26
CAMR
analysis supporting 24, 43, 61
and SERA FM model 192
andWCS 83
defined 13
modeling for 78
Clean Air Act See CAA
Clean Air Mercury Rule See CAMR
CMAQ 78, 183-85, 187
cold-vapor atomic fluorescence
spectrometry See CVAFS
Community Multi-Scale Air Quality.See
CMAQ
composite samples 3, 54-56
Consolidated Assessment and Listing
Methodology (CALM) 57
Continuing Survey of Food Intakes by
Individuals See CSFII
criterion, calculating 20, 21
CSFII 39,40, 147
CTR 64, 168, 174
CVAFS 50, 51, 149, 150, 151, 152
CWAlOl(a) 45,46,61
CWA304(a) 17, 18,68
demethylation 15, 23, 32, 82
designated use
andCWAlOl(a) 45
andUAA 45
and variances 41, 42, 43
changing 46
fishable 20
protecting 1, 17, 18,36
detection level 58
detection limit 50, 58, 150
dilution flow 64
D-MCM 28, 83, 84, 163, 166, 185
emissions
anthropogenic 12, 13, 14
controls 116
hourly estimates in models 184
mobility of 12
natural 1, 12, 13, 185
regulations 13, 121, 123-26
to air 75,77,83, 123-26
197
-------
Index
trends in 76-77, 75, 123, 124
environmental justice 70
EPA methods
1630 3,50,51,52,58, 149
1631
and measuring 3, 49, 50, 51, 52,
149
and nondetects 58, 98
andWQBELs 98
defined 49-52
inNPDES permits.. 98, 102, 101-2
inTMDLs 89
1669 50
245.7 3,49,50,51,98, 151
existing use 42,46, 106, 109
exposure
and BAFs 25, 26, 27, 32, 34
and consumption advisories 67
and fish 64
and humans 121, 168, 174, 179
and sample types 53, 54
andtheRSC 18,36,68
data in criterion calculation 20, 36, 40,
65, 68, 146
duration in criterion calculation 18
fish tissue concentration as proxy to
28
from drinking water 21
human health effects 1, 9-10
FDA action level 70
field sampling plan 52-56
fish advisories
and water quality standards 66-70
EPA guidance on 52, 61-62
issued 12,20,67
map (U.S.) 12
revising 69
statewide 12, 68
Fish Advisory Program 66
fish intake rate/estimate
and trophic levels 21, 33, 59
default 21,37,40
fish sampling guidance 52-56
fish tissue residue criterion... See TRC
in criterion calculation..21, 36, 37-41,
146,148
limits 66-70
modifying 37-41
of subsistence consumers 38
relative source criterion See RSC
RSC 18,21,26,36,68
TRC 20,21,37
fish sampling guidance 33
freshwater
and estuarine fish
age 24, 28, 31, 32, 33, 53, 159, 166,
182, 183, 190
and water quality criterion ...20, 21,
36, 37, 39, 40, 59, 60, 146
intake..See fish intake rate/estimate
mercury found in 15, 33, 56
ecosystem models 187
lakes and rivers 12
target species 38, 39, 143
Great Lakes Guidance 50
Great Lakes Water Quality Initiative
(GLI) 2,38,63
growth dilution 10, 15
health effects of methlymercury See
exposure: human health effects
human health
toxicological risk assessment 20
impairment
addressing 1, 62, 72
assessing 21, 57-62
identifying sources of 113, 116
listing decisions 57-62
Mercury Containing and Rechargeable
Battery Management Act 126
Mercury Deposition Network 77, 195
mercury emissions See emissions
Mercury Maps.73, 81, 181, 182, 187-88
mercury minimization plan See MMP
Mercury Study Report to Congress.... 10,
29,78,83, 115, 155, 160, 187, 192
mercury, forms of defined 24
methylation 15, 23, 28, 65, 73, 79
198
-------
Index
minimum level 106, 109
mixing zone 2, 63, 65-66
MMP
and antidegradation 94, 106-12
and reasonable potential 7, 93
and type of facility 117
as a permit condition 103, 115-19
guidance on 116
implementing 94, 115-19
model
D-MCM 28, 83, 84, 163, 166, 185
Dynamic Mercury Cycling Model.See
D-MCM
empirical bioaccumulation 28
mechanistic bioaccumulation 28
regression 28, 60, 61, 84
selecting 84
spatially detailed 83
steady state/mass balance 81-85
uncertainty 78, 85
monitoring and assessment. 3, 12, 49-62
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 51
National Toxics Rule 45, 64
NDMMF 24,33,61, 189
neurological effects 10
nondetections 54, 58, 98
normalizing factors 24, 33
NPDES
and antidegradation See
antidegradation
andWQBELs 91-95,97, 100-101,
103,106, 108-14, 119
documentation 115
effluents, measuring mercury in.... 94,
98,100-102, 108, 112
fish tissue criterion, implementing . 95
general considerations 91
new sources and new discharges,
mercury in 95, 109, 112
permit special condition 103
pollutant minimization plan
defined 44
recommended conditions ... 104-19
pollutant minimization program.... 44,
86,115
reasonable potential determination
and fish tissue data5, 93, 100, 103-
8, 110
and intakes 110
defined 91
how to 100-119
process 99
recommended permitting approach
92-95
reopener clause. 93-94, 102, 103, 112
Overview of P2 Approaches at POTWs
115
partition coefficient 157
persistency 116, 158
pollution prevention 44, 71, 94, 106,
115-16, 121-23
POTW 44, 75, 88, 114-18, 121-23
prenatal exposure 9
public participation 70
publicly owned treatment works See
POTW
quality control 61
quantitation level 50, 98, 149
recommended form of criterion 18
reference dose See RfD
regulations under CAA 123-26
relative source contribution See RSC
REMSAD 73,77, 190
RfD 9, 20, 36, 67, 148, 154, 155, 166
RSC 20,36,41,68, 155
sampling
and BAFs 23, 32-34
fish 52-56
guidance on 52-56
sediment 80,89
shellfish
199
-------
Index
advisories 62, 66
andCWAlOl(a) 45
in criterion calculation 20
intake rates 14, 39, 40
to be monitored 53
significant industrial users 121
site-specific conditions 36-47
site-specific procedure22-34, 64, 66, 80,
100
sources
atmospheric 9, 12-15, 41, 75-79,
187-88
human activity 13, 14, 80
in fish 12-14
mining 13, 47, 79
natural 13, 14, 42, 46, 74, 80
overseas 42, 184
point sources 14, 41, 47, 65, 74, 75
sediment 9, 15,79, 113
species 15, 26, 53-54, 144, 147
spill prevention and containment control
plan 118
tissue concentration-based standard.. 20,
22
tissue residue value 64, 95, 110
TMDL 71-90
allocation approaches 85
best uses 71
challenges 16
considerations 71-90
defined 71
examples See Appendix A
geographic scale 4, 72, 73
modeling tools 77-79, 80-85
monitoring provisions 89
pollutant loading scenario 86
Total Maximum Daily Load. See TMDL
translation factor 23-32,95-119
trophic levels
and BAFs 26, 27, 30-34, 194
and fish intake 20-23, 33, 37, 59
and fish species 144
and food webs 15, 53, 85
andGLI 64
andTMDLs.,154, 155, 166, 168, 174,
176
averaging data across 59-62
sampling in 3, 53, 56
UAA 45-46
uncertainty
and margin of safety 71, 163, 171, 178
assessing loadings 107
BAFs 29,31,33
from extrapolating results 28
in TMDL 71
model 31,78,85
reducing 22
RfD 9
use attainability analysis See UAA
variances
and controls 42, 43, 45
antidegradation 44
considerations 42, 43
how they apply 41-45
large-scale 44, 45
multiple discharger (group) 45
protocols 43
scenarios 42
time frames 43
when appropriate 2, 41
water column concentrations..30, 50, 65,
104
water quality criteria
and BAFs 20-36, 37
and fish advisories 68
and methods 1630, 1631 51,52
components 17, 18
water quality standards
and fish advisories 66-70
water quality-based effluent limits ....See
WQBEL
Watershed Characterization System . See
wcs
WCS 83, 156, 193
weighted consumption 154
WQBEL
200
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Index
andanti-backsliding....?, 95, 108, 115 and TMDLs ...94, 95, 99, 100, 111-14
and mercury in intake water 6, 110 and variances 41, 44
and NPDES permits.. 91-95, 97, 100- defined 91
101, 104, 106, 114, 115, 116 derivmg 97^ 91_95
and pretreatment 114 determining need for 100-110
and technology-based limits 7, 91,95, elements of 9495110-19
108,112,114 ff m
forms or 91
201
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