823B04001
Draft Guidance for Implementing the
January 2001 Methyl mercury
Water Quality Criterion
United States Environmental Protection Agency
Office of Science and Technology (4305T)
1200 Pennsylvania Ave., NW
Washington, D.C. 20460
EPA-823-B-04-001
www.epa.gov/waterscience
August 2006
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Draft Guidance for Implementing the
January 2001 Methyl mercury
Water Quality Criterion
United States Environmental Protection Agency
Office of Science and Technology (4305T)
1200 Pennsylvania Ave., NW
Washington, DC 20460
EPA-823-B-04-001
www. epa. gov/waterscience
August 2006
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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. 2006. Draft Guidance for Implementing the January 2001 Methylmercury Water
Quality Criterion. EPA 823-B-04-001. 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 mg methylmercury/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 of fish and shellfish among the
general population. EPA recommends the criterion to 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.
This is the first time EPA has 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
may 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
the 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 these 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 in 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/methylmercurv/criteria.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 3
2.1 What is the interest in mercury? 3
2.1.1 What are the health effects of mercury? 3
2.1.2 How frequent are the environmental problems? 5
2.2 What are the sources of mercury in fish? 6
2.3 How does methylmercury get into fish and shellfish? 8
2.4 Why is EPA publishing this document? 10
2.5 What is the effect of this document? 10
3 Water Quality Criteria and Standards Adoption 11
3.1 What must states and authorized tribes include as they adopt the
methylmercury criterion? 11
3.1.1 What do the CWA and EPA's regulations require? 11
3.1.2 What is the recommended form of the methylmercury criterion? 12
3.1.3 Can states or authorized tribes adopt a water column concentration
criterion? 14
3.2 What options are available to address for site-specific conditions and
concerns? 26
3.2.1 How can the methylmercury water quality criterion be modified for site-
specific conditions? 26
3.2.2 How do water quality variances apply? 31
3.2.3 How are use attainability analyses conducted? 37
4 Monitoring and Assessment 41
4.1 What are the analytical methods for detecting and measuring
methylmercury concentrations in fish and water? 41
4.1.1 What is Method 1631 for determination of mercury in water? 43
4.1.2 What analytical methods are available for determination of
methylmercury? 43
4.2 What is the recommended guidance on field sampling plans for collecting
fish for determining attainment of the water quality standard? 44
4.2.1 What fish species should be monitored? 44
4.2.2 What sample types best represent exposure? 45
4.2.3 What is the recommended study design for site selection? 46
4.2.4 How often should fish samples be collected? 46
4.2.5 How many samples should be collected? 48
4.2.6 What form of mercury should be analyzed? 48
4.3 How should waterbody impairment be assessed for listing decisions? 49
4.3.1 How should nondetections be addressed? 49
4.3.2 How should data be averaged across trophic levels? 50
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4.3.3 How should older data be assessed? 53
4.3.4 How should fish consumption advisories be used to determine
impairment? 53
5 Other Water Quality Standards Issues 55
5.1 How does this criterion relate to the criteria published as part of the Great
Lakes Initiative? 55
5.2 What is the applicable flow for a water column-based criterion? 55
5.3 How are mixing zones used for mercury? 56
5.3.1 What is a mixing zone? 56
5.3.2 How does a mixing zone apply for the fish tissue-based
methylmercury criterion? 56
5.3.3 Does the guidance for the fish tissue-based criterion change the Great
Lakes Initiative approach to mixing zones for bioaccumulative
pollutants? 56
5.4 How are fish consumption advisories and water quality standards
harmonized? 57
5.4.1 What is the role of the Fish Advisory Program? 57
5.4.2 How are consumption limits for consumption advisories determined? 58
5.4.3 How does the criterion differ from the advisory level? 58
5.4.4 What if there is a difference between the attainment of a criterion and
issuance of a fish consumption advisory? 59
5.4.5 Should existing advisories be revised to reflect the new criterion? 60
5.4.6 How is the criterion related to FDA action levels? 60
5.5 What public participation is recommended for implementing the
methylmercury criterion? 61
6 TMDLs 63
6.1 What is a TMDL? 63
6.2 How have states and tribes approached mercury TMDLs? 63
6.2.1 How have large-scale approaches been used for mercury TMDLs? 64
6.2.2 What is the Mercury Maps screening analysis? 65
6.2.3 What are considerations in developing mercury TMDLs? 67
7 NPDES Implementation Procedures 81
7.1 What are the general considerations in NPDES permitting? 81
7.2 How does EPA recommend implementing the fish tissue criterion for
NPDES permits? 82
7.3 What are the implementation procedures when the criterion is adopted as
a water column value? 83
7.4 What are the implementation procedures when the criterion is adopted as
a fish tissue value and the permitting authority uses a water column
translation of a fish tissue value? 83
7.5 What are the implementation procedures 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? 84
7.5.1 How to determine the need for permit limits to control mercury (i.e.,
how to determine reasonable potential) 85
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7.5.2 Where reasonable potential exists, how can WQBELs be derived from
a tissue value? 91
7.6 What are the recommended analyses for new sources or new dischargers
discharging quantifiable amounts of mercury? 99
7.6.1 What are the recommendations for permitting authorities when
considering issuing permits for new sources or new dischargers
where the fish tissue concentrations in the receiving waterbody are
unknown? 99
7.6.2 What are the recommended permit conditions for new sources or new
dischargers where the fish tissue in the receiving water does not
exceed the criterion? 100
7.6.3 What are recommended permit conditions for new sources or new
dischargers where the fish tissue in the receiving water exceeds the
criterion? 102
7.7 What are the special conditions for mercury in a facility's intake? 103
7.7.1 How to consider mercury intakes with a reasonable potential approach. 103
7.7.2 How to consider mercury in intakes in WQBELs 103
8 Related Programs 105
8.1 How does pollution prevention play a role in the methylmercury criterion? 105
8.2 What regulations has EPA issued pursuant to the CAA to address air
emissions of mercury? 107
8.2.1 Municipal Waste Combustors 108
8.2.2 Medical Waste Incinerators 108
8.2.3 Chlor-Alkali Plants 108
8.2.4 Industrial Boilers 109
8.2.5 Hazardous Waste Combustors 109
8.2.6 Coal-fired Power Plants 109
9 References 113
Appendix A. Synopsized Mercury TMDLs Developed or Approved by
EPA 127
I. Ochlockonee Watershed, Georgia 128
Description of the Applicable Water Quality Standards 128
Source Assessment 129
Loading Capacity—Linking Water Quality and Pollutant Sources 130
Allocations 131
II. Arivaca Lake, Arizona 133
Description of the Applicable Water Quality Standards 133
Source Assessment 133
Loading Capacity—Linking Water Quality and Pollutant Sources 135
Allocations 137
III. McPhee and Narraguinnep Reservoirs, Colorado 140
Description of the Applicable Water Quality Standards 140
Source Assessment 140
Loading Capacity—Linking Water Quality and Pollutant Sources 141
in
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Allocations 141
IV. Clear Lake, California 142
Description of the Applicable Water Quality Standards 142
Source Assessment 143
Loading Capacity-Linking Water Quality and Pollutant Sources 144
Allocations 145
Appendix B. Tables from Methylmercury Criteria Document 149
Appendix C. Analytical Methods 153
Appendix D. Examples of National Deposition Monitoring Networks 157
Appendix E. Methylmercury/Mercury Ratio Exhibited in Muscle Tissue
of Various Freshwater Fish Species 159
Index 163
IV
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TABLES
Table 1. National draft BAFs for dissolved methylmercury 21
Table 2. Estimates of freshwater and estuarine combined finfish and shellfish
consumption from the combined 1994-96 and 1998 CSFII surveys 29
Table 3. Example data for calculating a weighted average fish tissue value 51
Table A1. Annual average mercury load from each subbasin 130
Table A2. Predicted mercury for annual average load and flow 131
Table A3. Annual total mercury load to Arivaca Lake 136
Table A4. Predicted and observed mercury for annual average load and flow 137
Table A5. Summary of TMDL allocations and needed load reductions (in g-Hg/yr) 138
Table A6. Summary of mercury load estimates for McPhee Reservoir 140
Table A7. Summary of TMDL allocations and needed load reductions for McPhee
Reservoir 142
Table A8. Summary of TMDL allocations and needed load reductions for
Narraguinnep Reservoir 142
Table A9. Summary of mercury load allocations 146
Table A10. Sediment goals for mercury in Clear Lake 146
Table 5-1. Exposure parameters used in derivation of the water quality criterion 150
Table 5-14. Average Mercury Concentrations in Marine Fish and Shellfish 151
Table 5-30. Exposure estimates for methylmercury and percent of total exposure
based on adults in the general population 152
Table C1. Analytical methods for determining mercury and methylmercury in tissue ... 153
Table C2. Analytical methods for determining mercury and methylmercury in water,
sediment, and other nontissue matrices 154
FIGURES
Figure 1. Fish Tissue Mercury Concentrations Averaged by Watershed
(USEPA2001d) 5
Figure 2 Total Number of State Mercury Fish Consumption Advisories 2004 6
Figure 3. Percent of total mercury deposition attributable to global sources
(USEPA2005C) 66
Figure 4. Trends in mercury air emissions between 1990 and 1999 69
Figure 5. Implementing the fish tissue criterion in NPDES permits 82
Figure 6. Determining reasonable potential 85
Figure 7. Process for determining the WQBEL 92
Figures. Procedures for addressing new sources and new discharges 100
Figure 9. Mercury deposition in the United States following CAMR and CAIR 110
Figure D-1 Mercury Deposition Network data for 2003 158
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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 mg methylmercury/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 1997c). As of 2004, 44 states, 1 territory, and
2 tribes have issued fish consumption advisories for mercury covering 13.2 million lake
acres and 765,000 river miles (USEPA 2005a). Mercury is widely distributed in the
environment and originates from both natural and anthropogenic processes, including
combustion and volcanoes. Methylmercury is highly bioaccumulative and is the form of
mercury that bioaccumulates most efficiently in the food web.
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 exercising responsibility under section
CWA 303(c) on how to use the new fish tissue-based criterion recommendation as they
develop their own water quality standards for methylmercury. One approach that States
and authorized tribes may decide to use is to translate the tissue residue value to a water
column value through use of methylmercury bioaccumulation factors (BAFs). If a state or
authorized tribe decides to use this approach, EPA recommends three potential
approaches for relating a concentration of methylmercury in fish tissue to a concentration
of mercury in ambient water. The approaches are:
• Deriving site-specific methylmercury BAFs
• Using bioaccumulation models
• Using EPA's draft default methylmercury BAFs
All three approaches have limitations, especially in the amount of data necessary to
develop a BAF. This guidance discusses the advantages and limitations of each approach.
States and authorized tribes may also consider calculating their own fish tissue criteria or
adopting site-specific criteria for methylmercury to reflect local or regional fish
consumption rates or relative source contributions. EPA encourages states and authorized
tribes to develop a water quality criterion for methylmercury using local or regional data
rather than the default values if they believe that such a water quality criterion would be
more appropriate for their target population. This guidance also discusses variances and
use attainability analyses (UAAs) relating to methylmercury.
This document describes methods for measuring mercury and methylmercury in both
tissue and water. These methods can analyze mercury and methylmercury in tissue and
water at very low levels—well below the previous criterion for mercury in water and the
current criterion of methylmercury in fish tissue. This document also provides guidance
for field sampling plans, laboratory analysis protocols, and data interpretation on the
basis of previously published EPA guidance on sampling strategies for contaminant
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Executive Summary
monitoring. This document also describes how states can assess the attainment of water
quality criteria and protection of designated uses by comparing sampling data to water
quality criteria.
EPA expects that, as states and authorized tribes adopt the methylmercury criterion, the
number of waterbodies states report as impaired due to mercury contamination might
increase. EPA expects this to occur because the number of river miles and lake acres
under fish consumption advisories due to methylmercury in fish tissue greatly exceeds
the number of waters listed by states as impaired. 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 may increase. Thus,
this guidance also discusses approaches for managing the development of Total
Maximum Daily Loads (TMDLs) for waterbodies impaired by mercury. This includes
approaches for addressing waterbodies where much of the mercury is from atmospheric
sources and how TMDLs can take into account ongoing efforts to address sources of
mercury, such as programs under the Clean Air Act (CAA) and pollution prevention
activities. This guidance also includes a recommended approach for directly
incorporating the methylmercury tissue criterion in National Pollutant Discharge
Elimination System (NPDES) permits.
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Introduction
2 Introduction
2.1 What is the interest in mercury?
Mercury occurs naturally in the earth's crust and cycles in the environment as part of
both 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 hence can be widely dispersed and transported
thousands of miles from sources of emission. 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). Divalent mercury, when bound to airborne
particles, is readily removed from the atmosphere by precipitation and is also dry
deposited. Even after it deposits, mercury commonly returns to the atmosphere either as a
gas or associated with particles, and 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.
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 is the form of mercury that presents the greatest risks to human health.
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 mercury?
Exposure to methylmercury can result in a variety of health effects in humans. Children
who 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 2002e, USEPA 2005b). In 2000, the National Academy of Sciences
(NAS)/National Research Council (NRC) reviewed the health studies on mercury (NRC
2000). EPA's current assessment of the methylmercury reference dose (RfD) relied on
the quantitative analyses performed by the NRC (USEPA 2002e). The RfD is an estimate
(with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the
human population, including sensitive subgroups, that is likely to be without an
appreciable risk of deleterious effects during a lifetime (USEPA 2002e). 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 per day (0.1 microgram of
methylmercury per day for each kilogram of a person's body mass) in 2001 (USEPA
2002e). EPA believes that exposures at or below the RfD are unlikely to be associated
with 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 to be non-appreciable.
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 2005b).
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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 via maternal consumption
offish (rather than high-dose poisoning episodes) (USEPA 2005b). In 2005, the National
Health and Nutrition Examination Survey (NHANES) published 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 neurologic 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 2005b).
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. Other recent studies have not observed this association. The studies that
have observed an association suggest that the exposure to methylmercury might attenuate
the beneficial effects offish consumption (USEPA 2005b). There also is some recent
evidence that exposures of methylmercury might result in genotoxic or immunotoxic
effects. 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 2005b).
Deposition of mercury to waterbodies can also have an adverse impact on ecosystems
and wildlife. Plant and aquatic life, as well as fish, 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 with aquatic systems experiencing the greatest exposures due to
bioaccumulation. Bioaccumulation refers to the net uptake of a contaminant from all
possible pathways and 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 the consumption of contaminated fish and, as a result,
accumulate mercury to levels greater than those in their prey (USEPA 1997c). The
Regulatory Impact Analysis of the Clean Air Mercury Rule (USEPA 2005b) provides a
full discussion of potential ecosystem effects updated since publication of the 1997
Mercury Study Report to Congress (USEPA 1997c). Thus, the approach outlined in the
Clean Air Mercury Rule provides states an alternative methodology for designing their
site-specific TMDL analyses.
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Introduction
2.1.2 How frequent are the environmental problems?
As of 2004, 42 states reported at least one waterbody as being impaired due to mercury,
and over 8,500 specific waterbodies were listed as being impaired due to mercury, either
solely or in combination with other pollutants. In 2001, EPA mapped concentrations of
mercury in fish tissue from fish collected from waterbodies all over the country (i.e., not
limited to the 595 waters identified by the states) and compared these to the 2001 national
recommended water quality criterion of 0.3 mg methylmercury/kg fish tissue wet weight
(see 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 200Id).
A statistical comparison of the data presented in Figure 1 (from the National Listing of Fish
Advisories (NLFA) fish tissue database), versus data from the National Lake Fish Tissue
Study (NLFTS), a national random sample offish tissue in 500 lakes and reservoirs
throughout the United States, showed the NLFA data to be biased high (USEPA 2005b).
The bias was found to be the result of sampling bias in the NLFA toward fish of species
and sizes that tended to bioaccumulate more mercury. When data from the NLFA and
NLFTS were normalized to a set of standard species and lengths, the bias was removed.
(See USEPA 2005b, Figure 4-11, page 5-16 which shows fish tissue data averaged by
watershed (i.e., hydrologic unit codes, or HUCs.) As a result, the NLFA data suggest that
fewer watersheds contain fish with methylmercury that exceed the criterion.
Fish Tissue Mercury Concentrations
Averaged by Watershed
Average Fish Cone (pom)
0.001 -0.149
0.150 - 0.299
B 0.300 - 0.440
0.450 - 0.5&S
0.6-33
No Data
Suies
Note: New Cntenon for mercury in fish is 0.3 pom Po^rt of departure in fish aoVisoHes often r 0.15 ppm to 03 pom rarge
Average value Qased on Me: sarnies only. See report text for ct:a s
3:xr;~: Lateral Ls:>r§ o*ris" ,5-ic '.\ 3lfe Ad-.nsi'es (NLrV.'A: Me-s^ry =is* ~issi.* Datata?* iJune CCC1;
Figure 1. Fish Tissue Mercury Concentrations Averaged by Watershed (USEPA 2001 d)
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Introduction
As of December 2004, 44 states, 1 territory, and 2 tribes have issued fish consumption
advisories1 for mercury covering 13.2 million lake acres and 765,000 river miles (see
Figure 2). Twenty-one states have issued advisories for mercury in all freshwater lakes
and rivers in their state, and 12 states have statewide advisories for mercury in their
coastal waters (USEPA 2005a). EPA believes that the increase in advisories is primarily
due to increased sampling of previously untested waters and not necessarily due to
increased levels or frequency of contamination. Although states, territories, tribes, and
local governments also continue to issue new fish advisories, most new fish advisories
involve mercury and are a result of increased monitoring and assessment rather than
increased domestic releases of mercury. In fact, U.S. mercury emissions have declined by
more than 45 percent since 1990 (USEPA 2005a).
Fish Consumption Advisories for Mercury
- NH (R,L)
WA(R.L)
-RKR.LI
NOTE: ThEira
depicts the prese
arid type offish
the states far mercury
us of December 2004.
Because only selected
wateibodies are
Mercury Advisories by Type:
• AMuriw tar sp*cinc wiUirtJodlo*
does not reflect the
fall eiieri of chemic al
rnmtflir.TnjHnn cdf fitli
tissues in each state or
province.
**n5Grt*f specific
- AM ntm uiMfer «Mwry
iSEPA NatbiaiFkl aidnitmRCaitamliatei Pronran
soiree: 2DDt Nattaial Lhflig err Fkl Adttkorlei
Figure 2. Total Number of State Mercury Fish Consumption Advisories 2004
2.2 What are the sources of mercury in fish?
Mercury is emitted from both natural and anthropogenic sources. Mercury's residence
time in the atmosphere is much longer than that of most metals, because mercury can
1 States issue their advisories and guidelines voluntarily and have flexibility in what criteria they use and how the data are collected. 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.
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Introduction
circulate for up to a year (USEPA 1997a). 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 derived from both U.S. and international sources. EPA estimates that
approximately 83 percent of the atmospheric mercury deposited on land and water in the
country is from a combination of sources outside the United States and Canada, as well as
natural and re-emitted sources. EPA's current air quality modeling does indicate a
substantial variation across the country, with domestic sources influencing mercury
deposition much more in the east and global sources being a more significant contributor
to mercury deposition in the west, where relatively few domestic sources exist. This
estimate was based on the 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 (CAMR) (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, MWIs), manufacturing sources (e.g., chlor-alkali, cement,
pulp and paper manufacturing), and mining (USEPA 1997a).
U.S. anthropogenic emissions of mercury to the air have declined more than 45 percent
since passage of the 1990 CAA Amendments. These amendments provided new authority
to EPA 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 medical
waste incineration (see Figure 4). Regulations were issued in the 1990s to control
mercury emissions from waste combustion. In addition, actions to limit the use of
mercury, most notably 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.2
The largest single source of anthropogenic mercury emissions in the country currently 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. In March 2005, EPA
signed the CAMR to permanently cap and reduce mercury emissions from coal-fired
power plants (USEPA 2005e). This rule makes the United States the first country in the
world to regulate mercury emissions from utilities. CAMR builds on EPA's Clean Air
2 EPA has issued several regulations pursuant to the CAA to address these air emissions, including recent regulations covering coal-fired
power plants. For example, see Title 40 of the Code of Federal Regulations (CFR) Part Cb (standards for municipal waste combustors); 40
CFR Part 60, subpart Ce (standards for MWIs); 40 CFR Part 63 subpart IIIII (standards for chlor-alkali plants); 40 CFR 63.1203 (a)(2) and
(b)(2) (standards for existing and new hazardous waste-burning incinerators), 40 CFR 63.1204 (a)(2) and (b)(2) (standards for existing and
new hazardous waste-burning cement kilns), and § 63.1205 (a)(2) and (b)(2) (standards for existing and new hazardous waste-burning
lightweight aggregate kilns); 40 CFR Part 63, Subpart DDDDD (standards for industrial boilers); and 70 Federal Register 28,606 (May 18,
2005) (codified at 40 CFR Parts 60, 72 and 75) (standards for power plants). See also section 8.2 of this document.
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Introduction
Interstate Rule (CAIR) to significantly reduce emissions from coal-fired power plants.
When fully implemented, these rules will reduce utility emissions of mercury nearly 70
percent.
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 CFRPart
415). All NPDES permits must assure that permitted discharges achieve water quality
standards (40 CFR 122.42(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 are only one part of the mercury cycle, however. 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.
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 governing methylmercury
uptake in fish and shellfish tissue. The following is a synopsis of the current
understanding of mercury cycling in the environment as described in the Regulatory
Impact Analysis of the Clean Air Mercury Rule (USEPA 2005b).
Mercury occurs naturally in the environment as several different chemical species. The
majority of mercury in the atmosphere (95-97 percent) is present in a neutral, elemental
state (Hgo) (Lin and Pehkonen 1999), while in water, sediments, and soils, the majority of
mercury is found in the oxidized, divalent state (Hg(II)) (Morel et al. 1998). A small
fraction of this pool of divalent mercury is transformed by microbes into methylmercury
(CH3Hg(II) (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 emissions sources. Elemental mercury is oxidized in the atmosphere to
form the more soluble mercuric ion (Hg(II)) (Schroeder et al. 1989). Particulate and
reactive gaseous phases of Hg(II) are the principle forms of mercury deposited onto
terrestrial and aquatic systems because they are more efficiently scavenged from the
atmosphere through wet and dry deposition than Hgo (Lindberg and Stratton 1998).
Because Hg(II) species or reactive gaseous mercury (ROM) and particulate mercury
(Hg(p)) in the atmosphere tend to be deposited more locally than Hgo, differences in the
species of mercury emitted affect whether it is deposited locally or travels longer
distances in the atmosphere (Landis et al. 2004).
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Introduction
A portion of the mercury deposited in terrestrial systems is re-emitted to the atmosphere.
On soil surfaces, sunlight might reduce deposited Hg(II) to Hgo, which might then evade
back to the atmosphere (Carpi and Lindberg 1997, Frescholtz and Gustin 2004, Scholtz et
al. 2003). Significant amounts of mercury can be codeposited to soil surfaces in
throughfall and litterfall of forested ecosystems (St. Louis et al. 2001), and exchange of
gaseous Hgoby vegetation has been observed (e.g., Gustin et al. 2004). Hg(II) 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(II) partitions strongly to silts and biotic solids,
sorbs weakly to sands, and complexes strongly with dissolved and particulate organic
material. Hg(II) 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 via 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. 1999). 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 Hg(II) and methylmercury accumulate in aquatic vegetation, phytoplankton,
and benthic invertebrates. Unlike Hg(II), methylmercury biomagnifies through each
successive trophic level in both 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 (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.
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Introduction
In a January 8, 2001, Federal Register notice (66 FR 1344), EPA announced the
availability of its recommended water quality criterion for methylmercury. In that notice,
EPA also stated that development of the associated implementation procedures and
guidance documents would begin by the end of 2001. As such, EPA makes this guidance
available to fulfill that commitment to enable states and authorized tribes to adopt the
recommendations set forth in Water Quality Criterion for the Protection of Human
Health: Methylmercury (USEPA 200Ic), or other water quality criteria for
methylmercury on the basis of scientifically defensible methods, into their water quality
standards.
This nontraditional approach in 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 present
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 adopting the new water quality
criterion into their water quality standards programs and implementation of the revised
water quality criterion in TMDLs and NPDES permits. Further, because atmospheric
deposition serves as a large source of mercury for many waterbodies, implementation of
this criterion involves coordination across various media and program areas.
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 discusses approaches for managing the
development of TMDLs for waterbodies impaired by mercury. This includes approaches
for addressing waterbodies where much of the mercury comes from atmospheric sources
and how TMDLs can take into account ongoing efforts to address sources of mercury,
such as programs under the CAA and pollution prevention activities. This guidance also
includes a recommended approach for directly incorporating the methylmercury tissue
criterion in NPDES permits.
This guidance document presents suggested approaches, but not the only technically
defensible approaches, to criteria adoption and implementation. The guidance does not
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 approaches on a case-
by-case basis that differ from this guidance where appropriate. EPA may change this
guidance in the future.
10
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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. 2006. Draft Guidance for Implementing the January 2001 Methylmercury Water
Quality Criterion. EPA 823-B-04-001. U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
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Water Quality Criteria and Standards Adoption
3 Water Quality Criteria and Standards
Adoption
3.1.1 What do the CWA and EPA's regulations require?
The CWA and EPA's regulations specify the requirements for adoption of water quality
criteria. States and authorized tribes must adopt water quality criteria3 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
criteria for all toxic pollutants for which EPA has established AWQC where the
discharge or presence of these pollutants could reasonably interfere with the designated
uses (see CWA 303(c)(2)(B)). EPA issued guidance on how states and authorized tribes
may comply with section 303(c)(2)(B), which is now contained in the Water Quality
Standards Handbook: Second Edition (USEPA 1994). This document provides three
options for compliance:
Option 1—states and authorized tribes may adopt statewide or reservation-wide
numeric chemical-specific criteria for all toxic pollutants4 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
procedure 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 into their water
quality standards to fulfill the requirements of 40 CFR Part 131.
The term "water quality criteria" has two different definitions under the CWA. Under section 304(a), EPA publishes water quality criteria
that consist 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 section 304(a) criterion. States may use these 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).
4 CWA section 307(a) identifies a list of toxic pollutants that EPA has published at 40 CFR 401.16.
5 A translator procedure is simply the detailed process, published 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.
11
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Water Quality Criteria and Standards Adoption
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 304(a) water quality criterion for methylmercury is
expressed as a fish6 tissue concentration value (0.3 milligram methylmercury per
kilogram of wet-weight fish tissue, or 0.3 mg/kg). With the publication of this 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 200 Ib).
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 as a fish tissue residue concentration into their water quality standards, or
adopting it as a traditional water column concentration. However, if states and authorized
tribes choose to use both approaches, they should clearly describe how each will be used
for specific applications in their standards and describe applicable implementation
procedures. 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 (RSC)). EPA will evaluate criteria submitted by states and authorized
tribes on a case-by-case basis.
3.1.2.1 Why is the fish tissue concentration criterion recommended?
EPA recommends that states and authorized tribes adopt new or revised methylmercury
water quality criteria in the form of a fish tissue methylmercury concentration. The
following reasons make this the preferred form:
• A fish tissue concentration value water quality criterion 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) that
humans are exposed to methylmercury.
• A fish tissue concentration value is more consistent with how fish advisories are
issued.
6 The criterion applies to both finfish and shellfish. For purposes of simplifying language in this document, the term "fish" means both
finfish and shellfish.
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Water Quality Criteria and Standards Adoption
• A fish tissue sample is currently easier to analyze for methylmercury and analysts
are more experienced in analyzing methylmercury in fish tissue than in water
samples.
• A fish tissue concentration avoids the need for BAFs7 that are necessary to translate
between a tissue concentration and water concentration when deriving a water
concentration-based criterion. This is significant because bioaccumulation of
methylmercury by aquatic organisms is temporally and spatially variable such that
site-specific BAFs, which can be costly to develop, are the preferred approach for
translating tissue concentrations into water concentrations.
3.1.2.2 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 criterion for the protection of
human health is calculated as:
BWx(Rfl) -RSC)
^4
2-«=iFI (Equation 1)
Where:
TRC = Fish tissue residue criterion (mg methylmercury/kg fish tissue) 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).
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 population.9
This equation and all values used in the equation are described in Water Quality Criterion
for the Protection of Human Health, Methylmercury (USEPA 200 Ic). This equation is
7 A BAF is a ratio (in milligrams/kilogram per milligrams/liter, or liters per kilogram) that relates the expected concentration of a chemical
in commonly consumed aquatic organisms in a specified trophic level to the concentration of the chemical in water (USEPA 2001c).
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
Federal Register 1354-1355.
9 The 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 2000i). 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, nd 5.7 g fish/day for TL4. The rationale behind the selection of this value is described in the Human Health Methodology
(USEPA 2000e).
13
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Water Quality Criteria and Standards Adoption
essentially the same equation used in the 2000 Human Health Methodology 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 200lb)). 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 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
rather than the default values if they believe that such a water quality criterion would be
more appropriate for their 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 4 or to the
highest trophic level consumed. This will result in a conservative assumption, thereby
protecting 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 guidance on determining consumption patterns see
section 4.)
EPA acknowledges that implementation of a TRC entails more technical steps than
implementation of a water column criterion. Although water quality standards programs
traditionally use water column values, states and authorized tribes may not find it
necessary to translate this fish tissue based-criterion into a water column value for all
implementation methodologies. Later chapters on TMDLs and NPDES permits in this
guidance offer some methodologies that use the fish tissue value without translating from
fish tissue to water column values.
3.1.3 Can states or authorized tribes adopt a water column
concentration criterion?
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 limits
(WQBELs), TMDLs, and other activities generally employ a water column value. If
states and authorized tribes decide to adopt the tissue criterion expressed as fish tissue
concentration, per EPA recommendation, without translating to a traditional water
column concentration, they will make a choice on how to implement the tissue criterion.
A state or authorized tribe could decide to directly develop TMDLs and to calculate
WQBELs in NPDES permits without first measuring or calculating a BAF. This
guidance provides some options for such approaches in sections 6 and 7.
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
Alternatively, a state or authorized tribe may decide to adopt a tissue concentration-based
standard with a site-specific procedure for translating the tissue concentration-based
standard to a water column concentration. Because methylmercury bioaccumulation can
vary substantially from one location to another, this option allows for the tissue
concentration-based standard to be translated to water concentration-based standards
using site-specific information on methylmercury bioaccumulation (i.e., site-specific
BAFs) while ensuring that a water-expressed standard is ultimately developed for the
waterbodies of interest. Administratively, this option might be more efficient when
compared to adopting a water concentration-based standard for an entire state or tribal
jurisdiction adopting or approving site-specific standards on an individual waterbody
basis. Approaches for translating a tissue concentration-based criterion to a water
concentration-based criterion are provided in the following section.
States or authorized tribes may also choose to adopt a standard that is expressed as a
water column concentration. Conversion of the tissue concentration-based criterion to a
water concentration-based criterion may be desirable for various reasons, such as
achieving consistency with traditional water column-based AWQCs and/or regulatory
simplicity. However, note that this approach requires assessment of methylmercury
bioaccumulation on a state or tribal geographic scale. Thus, the uncertainty associated
with differential bioaccumulation of methylmercury across sites within a state or
authorized tribe 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 AWQC
for methylmercury as a tissue concentration rather than as a water concentration.
To express the methylmercury concentration-based criterion as a water concentration, a
state or authorized tribe would translate the methylmercury concentrations in fish tissue
to methylmercury concentrations in the water column. To accomplish this, the state or
authorized tribe will develop BAFs. In the Federal Register notice of the methylmercury
criterion, EPA identified three possible different 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.
States and authorized tribes would translate the tissue concentration-based human health
AWQC to a water concentration-based methylmercury criterion using a BAF as
A WQC = TRC • >BAF (Equation 2)
Where:
A WQC = Water concentration-based ambient water quality criterion for
methylmercury in mg/L
TRC = Tissue concentration (residue)-based ambient water quality criterion for
methylmercury 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 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
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Water Quality Criteria and Standards Adoption
sampling. BAFs are trophic level-specific. EPA recommends that they be derived from
site-specific, field-measured data as
w (Equation 3)
Where:
BAF = Bioaccumulation factor, derived from site-specific field-collected
samples of tissue and water in L/kg fish
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 the following section.
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 methylmercury 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. Some of 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 (i.e., via changes in methylation and/or
demethylation rates), or influence the bioavailability of methylmercury to aquatic
organisms. Although bioaccumulation models have been developed to address these and
other factors for mercury, their broad application can be limited by the site- or species-
specific nature of many of the factors and by limitations in the data parameters necessary
to run the models.
The bioaccumulation of nonionic organic chemicals can also be affected by a number of
these same physico-chemical factors (e.g., loading history, food web structure, dissolved
oxygen, DOC). However, a substantial portion of the variability in bioaccumulation for
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Water Quality Criteria and Standards Adoption
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 2003b). Normalizing to the age or size (length, weight) offish has
been shown to reduce variability in measures of bioaccumulation (Sorensen et al. 1990,
Glass et al. 2001, Brumbaugh et al. 2001, Sonesten 2003, Wente 2004). The United
States Geological Survey (USGS) developed a procedure called the National Descriptive
Model of Mercury and Fish Tissue (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;
EPA used this model to normalize national data sets offish tissue for analysis supporting
the CAMR (USEPA 2005a).
Taking into account the previous discussion, EPA recommends three different
approaches for relating a concentration of methylmercury in fish tissue to a concentration
of methylmercury in ambient water:
1. Use site-specific methylmercury BAFs derived from field studies.
2. Use a scientifically defensible bioaccumulation model.
3. When derivation of site-specific field-measured BAFs or use of a model are not
feasible, use national methylmercury BAFs derived from empirical data.
Of these approaches, 1 and 2 are preferred over 3 for reasons discussed below. However,
the hierarchy assigned to the approaches is not intended to be inflexible. Some situations
might indicate that greater uncertainty is likely to occur when applying a BAF derived
from a "more highly preferred" approach (e.g., a field-measure BAF) than with a "less
preferred" approach, for example, when data from the more preferred method have less
representativeness, quantity, or quality relative to the less preferred approach. In these
situations, data from the less preferred, but less uncertain, approach would be used to
derive BAFs.
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 2000e) and its
Technical Support Document for developing national BAFs (USEPA 2003b). 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 that
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). The BAF can be measured for the aggregate
offish in a location or specific to each trophic level. 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.
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Water Quality Criteria and Standards Adoption
However, states should exercise caution in developing a site-specific BAF for a
migratory fish because its exposure to methylmercury reflects areas other than where the
fish was caught. By incorporating these factors, field-measured site-specific BAFs
account for the uptake and accumulation of the chemical.
For the purposes of developing a human health water quality criterion, states and 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 water
(Equation 3). To predict the corresponding methylmercury concentration in water for a
site, the tissue-based methylmercury criterion would then be divided by the site-specific
BAF. 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 (specifically methylmercury) and that
the site-specific BAF is independent of water column concentration.
As an example, the State of California is currently employing a site-specific BAF
approach in its Central Valley Region. In this approach, California 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, 2004). California linearly regressed fish
tissue methylmercury concentrations for specific trophic level 3 and 4 fish against
aqueous methylmercury concentrations (PO.001, R2=0.98, and PO.01, R2=0.9,
respectively), and determined methylmercury concentrations in unfiltered water that
correspond to the fish tissue criteria (0.15 ng/1 for TL3 fish and 0.14 ng/1 for TL4 fish)
that were used in the TMDL analyses. (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 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
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,
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Water Quality Criteria and Standards Adoption
across space, and over time because the site-specific factors that might influence
bioaccumulation are integrated within the tissue concentration measurement and thus,
cannot be individually adjusted to extrapolate to other conditions.
3.1.3.1.2 Bioaccumulation models
Bioaccumulation models for mercury vary in the technical foundation on which they are
based (empirically or mechanistically based), spatial scale of application (specific to
waterbodies, watersheds or regions, and species offish), and level of detail in which they
represent critical bioaccumulation processes (simple, mid-level, or highly detailed
representations). Thus, it is critical that states and tribes use a model that is appropriately
developed, validated, and calibrated for the species and sites of concern.
Empirical bioaccumulation models that explicitly incorporate organism-, water
chemistry-, 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., Sorensen et al. 1990,
Kamman et al. 2004, Brumbaugh et al. 2001). 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, percent 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 on 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 due to 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, use of 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
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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 bioaccumulation. Three examples of mechanistic type
bioaccumulation models are: the Dynamic Mercury Cycling Model (D-MCM) (EPRI
2002), BA (BASS) (Barber 2002), and the Quantitative Environmental Analysis Food
Chain model (QEAFDCHN) (QEA 2000). The conceptual advantage of mechanistically
based bioaccumulation models is that predictions of methylmercury bioaccumulation can
be made under different conditions (e.g., different growth rates offish, different water
chemistry conditions, different mercury loading scenarios), because the models include
mathematical representations of the 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
yet been applied to lotic systems. The other models have been developed more generally,
for nonionic organic chemicals that bioaccumulate and that require substantial
modification and validation for application to mercury.
Most mechanistic bioaccumulation models use a chemical mass balance approach to
calculate bioaccumulation into 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.
Regardless of the type of model used, states' and authorized tribes' methodologies should
be consistent with the Methodology for Deriving Ambient Water Quality Criteria for the
Protection of Human Health (section 5.6: National Bioaccumulation Factors for
Inorganic and Organometallic Chemicals; USEPA 2000e) and Technical Support
Document Volume 2: Derivation of National Bioaccumulation Factors (USEPA 2003b).
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 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. EPA used the BAF guidance in the 2000 Human
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Health Methodology (USEPA 2000e, 2003b) and the BAF methods in Volume III,
Appendix D of the Mercury Study Report to Congress (USEPA 1997b) to derive draft
methylmercury BAFs as part of its initial efforts to derive a water column-based
recommended section 304(a) ambient water quality criterion for methylmercury. These
draft national BAFs were developed from field data collected from across the United States
and reported in the published literature. These 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 2001c). The draft national BAFs
(50th percentile values) are listed by trophic level in Table 1. The 5th and 95th percentile
values are also provided to show the distribution of national BAF values.
Table 1. National draft BAFs for dissolved methylmercury
5th Percentile
50th Percentile (Geometric mean)
95th Percentile
BAF trophic
level 2
(L/kg)
18,000
117,000
770,000
BAF trophic
level 3
(L/kg)
74,300
680,000
6,230,000
BAF trophic
level 4
(L/kg)
250,000
2,670,000
28,400,000
(USEPA 2001 c)
(mg methylmercury/kg fish tissue per mg methylmercury/L water)
To develop the 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. EPA generally does not recommend
basing an AWQC on BAF values near the extremes of the distribution (e.g., 10th or 90th
percentile) because such values might introduce an unacceptable level of uncertainty into
the calculation of a water column-based AWQC.
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). 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 2,670,000 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 • «2,670,000 L/kg) to indicate attainment of the water quality column
criterion. However, using the BAF based on site-specific data, a water column
criterion of 0.11 ng/L would correspond to a fish tissue concentration of 0.9
mg/kg, which is three times the 0.3 mg/kg criterion recommended to protect
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human health. Thus, load reduction or permits using the national BAF of
2,670,000 L/kg would be under-protective.
Overprotective scenario
A state uses the draft national BAF of 2,670,000 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 of 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 • *2,670,000 L/kg) to indicate
attainment of the water quality criterion. However, using the BAF based on site-
specific data, attainment of the water quality criterion could be achieved at a
higher water column concentration of 0.33 ng/L. Thus, load reductions or permits
using the national BAF of 2,670,000 L/kg would be over-protective.
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 Ic) that 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 ages (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 total mercury in water simplifies a number of
nonlinear processes that lead to the formation of bioavailable methylmercury in the
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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, while the concentration of methylmercury in fish tissue is
presumably a function of these varying concentrations, published BAFs are
generally 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.
The peer reviewers of the draft national BAFs expressed concerns about the use of the
draft national BAFs 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 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. However, EPA may revise its
guidance should significant new information become available to support developing a
final national BAF.
EPA believes that the draft national methylmercury BAFs in Table 1 sufficiently
represent bioaccumulation such that they may be used to implement a fish tissue-based
methylmercury water quality criterion in a state's or authorized tribe's water quality
standards in the absence of any other site-specific bioaccumulation data. Thus, EPA is
likely to approve water quality standards for mercury on the basis of these draft national
BAFs in the absence of information indicating that the water quality criteria do not
protect human health in the waters to which the standards apply. Risk managers should
also understand that in using the draft national BAFs, 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. The decision to
allow the use of the draft national BAFs is a risk management decision. It reflects
judgment that human health is better protected if the water quality criteria reflect the new
science associated with methylmercury, even if that means using a draft national BAF
value, rather than not adopting a criterion because the state or authorized tribe lacks
resources to conduct site-specific studies or to run an appropriate bioaccumulation model.
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 either water or fish in 40 CFR Part 136. However,
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for fish tissue, states and authorized tribes can measure methylmercury concentrations
using the same analytical method used to measure for total mercury at least for upper
trophic level fish (i.e., levels 3 and 4). This is because 80 to 100 percent of the mercury
found in the edible portions of freshwater fish greater than 3 years of age from these two
trophic levels is in the form of methylmercury (USEPA 2000c). In fish greater than
approximately 3 years of age, mercury has had sufficient time to bioaccumulate to
roughly steady levels in the fish. Appendix E summarizes seven 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 seven studies, methylmercury on average accounted
for more than 90 percent of the mercury concentration in fish tissue.
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 through
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 use of the National Descriptive Model for Mercury in Fish Tissue
(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 2005b).
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 is correlated with the magnitude of methylmercury accumulation, the
types and sizes of aquatic organisms being consumed should be considered when
determining what 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 tribes should review site-specific data used to calculate a field-measured
BAFs, and thoroughly assess the quality of the data and the overall uncertainty in the
BAF values. Consider the following general factors when determining the acceptability
of field-measured BAFs reported in the published scientific literature. Address the same
general issues and questions also when designing a field study to generate site-specific
field-measured BAFs.
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• Calculate a field-measured BAF using aquatic organisms that are representative of
those aquatic organisms that are commonly consumed at the site of interest (e.g.,
river, lake, ecoregion, state). Review information on the ecology, physiology, and
biology of the target organisms when assessing whether an organism is a
reasonable surrogate of a commonly consumed organism.
• Determine the trophic level of the study organism by taking into account its life
stage, 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 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 200Ic). 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) due to 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 1997e).
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 2003b). In addition, EPA
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expects to publish specific guidance for deriving site-specific BAFs from field studies in
the future. Until then, the EPA guidance cited above and a recent publication by
Burkhard (2003) are good sources of information on the design of BAF field studies and
on deriving field-measured site-specific BAFs.
3.2 What options are available to address for 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 2000e) describes how states and
authorized tribes can adopt site-specific modifications of a 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, local 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, is 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 of the population surveyed (either sport or subsistence, or both)
to eat fish from the local area. 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, EPA will likely review the data supporting the site-specific criterion when EPA
approves or disapproves state or tribal water quality standards under section 303(c).
States and authorized tribes may modify EPA's recommended 304(a) criteria for
methylmercury by using other scientifically defensible methods, or by using different
assumptions for certain components of EPA's criterion to derive a criterion that maintains
and protects the designated uses. For example:
• Use an alternative RSC factor
• 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 these would better reflect
the target population.
If a state or authorized tribe intends to modify both the RSC and fish consumption rate, it
may find it advantageous to collect the data at the same time.
3.2.1.1 How does one modify the RSC?
Section 5 of the methylmercury criterion document (USEPA 200 Ic) 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 reference dose 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
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methylmercury criterion document and modify the media specific exposure estimates
found 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, the exposure from
ingestion of marine fish comprised greater than 99.9 percent of the total exposure to
methylmercury, and thus ingestion offish 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; USEPA 200Ic) and the
concentration of methylmercury in the commonly consumed marine species (Table 5-14;
USEPA 200Ic). 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
included 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/day11 (uncooked) (USEPA 2001c). States and authorized Tribes can choose to
apportion an intake rate to the highest trophic level consumed for their population or use
a different intake rate based on local or regional consumption patterns. The fish
consumption value in the TRC equation can be changed if the target population eats a
higher or lower amount offish. For example, if the 90* percentile of a target population
eats approximately 15 grams/day of freshwater and estuarine fish of various trophic
levels, the fish intake value in the above equation 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. In this instance,
the state or authorized tribe should not use the survey data because it does not represent
what the local population would eat if the fish was not already contaminated.
EPA suggests that states and authorized tribes follow a hierarchy when deriving fish
intake estimates (USEPA 2000e). 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.
11 This value represents the 90th percentile of freshwater and estuarine finfish and shellfish consumption reported by the 1994-96
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 2000e).
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3.2.1.2.1 Use local data
EPA's first preference is that states and authorized tribes modify the water quality
criterion using fish intake rates derived from studies of consumption of local fish, such as
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. EPA
recognizes that states and authorized tribes may choose to develop a fish intake rate for
highly exposed subpopulations (e.g., sport anglers, subsistence fishers), and if this is the
case, the states and authorized tribes should collect the intake rates from these
subpopulations.
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 who
eat local fish. EPA's consumption survey guidance offers recommendations on how to
develop appropriate quality assurance and control procedures to help assure the quality of
the survey. Results of studies of broader geographic regions in which the state or
authorized tribe is located can also be used, but might not be as applicable as study
results for local watersheds. Because such studies would ultimately form the basis of a
state or authorized tribe's methylmercury criterion, EPA would review any surveys of
fish intake for consistency with the principles of EPA's guidance 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 authorized tribes should ensure that the distribution is
based on survey respondents who 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 the recent
Great Lakes Water Quality Initiative (known as the "GO") (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, at a minimum,
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, minority
populations). A state or tribe in a region of the country might consider using rates from
studies that surveyed the same region; for example, a state or tribe that has a climate that
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Water Quality Criteria and Standards Adoption
allows year-round fishing may underestimate consumption if rates are used from studies
taken in regions where individuals fish for only one or two seasons per year. A state or
tribe that has a high percentage of an age group (such as elderly individuals, who have
been shown to have higher rates in certain surveys) may wish to use age-specific
consumption rates, which are available from some surveys. EPA has published guidance
for selecting a study from a similar geographic area or population group (USEPA 1998c)
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 n ation al 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 1994-96 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-
96 and 1998 CSFII surveys, the statistical methodology, and the results and uncertainties
of the EPA analyses (USEPA 2002f). The estimated fish consumption rates in the CSFII
report are 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 (i.e., rates based on consumers and
nonconsumers offish from the survey period), (2) by consumers-only rates (i.e., rates
based on respondents who reported consuming finfish or shellfish during the 2-day
reporting period), and (3) per capita consumption by body weight (i.e., per capita rates
reported as milligrams offish per kilogram of body weight per 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.
Table 2. Estimates of freshwater and estuarine combined finfish and shellfish
consumption from the combined 1994-96 and 1998 CSFII surveys
All Ages
Age 18 and Over
Women Ages 15-44
Children Ages 14 and Under
Mean
6.30
7.50
5.78
2.64
Median
N/a
O.OO12
N/a
0.00
90tn
11.65
17.37
6.31
0.00
95tn
41.08
49.59
32.37
13.10
99tn
123.94
143.35
109.79
73.70
Note: (all values as g/day for uncooked fish)
The CSFII surveys 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
12 The median value of 0 grams/day may reflect the portion of individuals in the population who never eat fish as well as the limited
reporting period (2 days) during which intake was measured.
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Water Quality Criteria and Standards Adoption
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 Native Americans on reservations and certain ethnic
groups. While these individuals were participants in the survey, they were not present in
sufficient numbers to support fish consumption estimates. The survey does support interval
estimates for the U.S. population and some large subpopulations (USEPA 2002f).
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
the following default rates, on the basis of the 1994-96 CSFII data, which EPA believes
are representative of freshwater and estuarine fish and shellfish intake for different
population groups: 17.5 grams/day for the 90th percentile of the general adult population,
an average of 17.5 grams/day for sport fishers, and an average of 142.4 grams/day for
subsistence fishers. EPA has made these risk management decisions after evaluating
numerous fish intake surveys. These values represent the uncooked weight intake of
freshwater and estuarine finfish and shellfish. As with the other preferences, EPA
requests that states and authorized tribes routinely consider whether a substantial
population of sport fishers or subsistence fishers exists in the area when establishing
water quality criteria rather than automatically using data for the general population.
The CSFII surveys also provide data on marine species, but EPA considered only
freshwater and estuarine fish intake values for determining default fish consumption
rates, because EPA considered exposure from marine species offish in calculating an
RSC for dietary intake.13 States and 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 (i.e., fresh or estuarine a«J 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 2000e).
Because the combined 1994-96 CSFII survey is national in scope, EPA uses the results
from it to estimate fish intake for deriving national criteria. The estimated mean of
freshwater and estuarine uncooked fish intake for adults from the CSFII study is 7.5
grams/day, and the median is 0 grams/day. The estimated 90th percentile is 17.53
grams/day; the estimated 95th percentile is 49.59 grams/day; and the estimated 99th
percentile is 142.41 grams/day. The median value of 0 grams/day reflects the portion of
individuals in the population who never eat fish as well as the limited reporting period (2
13 See the discussion of the RSC in sections 3.1.2.2. and 3.2.1.1.
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Water Quality Criteria and Standards Adoption
days) during which intake was measured. By applying as a default 17.5 grams/day for the
general adult population, EPA selected an intake rate that is protective of a majority of
the population (again, the 90th percentile of consumers and nonconsumers according to
the 1994-96 CSFII survey data). In apportioning the default consumption rate to fish in
different trophic levels, EPA uses the following breakout: TL2 = 3.8 grams/day; TL3 =
8.0 grams/day; and TL4 = 5.7 grams/day (USEPA 2000e)
Similarly, EPA believes that the 99* percentile of 142.4 grams/day is within the range of
consumption estimates for subsistence fishers according to the studies reviewed, and
represents an average rate for subsistence fishers. EPA knows that some local and
regional studies indicate greater consumption among Native American, 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 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
1994-96 CSFII are representative, they may choose these recommended rates.
3.2.2 How do water quality variances apply?
A state or authorized tribe may provide NPDES dischargers temporary relief from a
water quality standard by granting a temporary variance to that standard. 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 change to the
otherwise applicable water quality standard (designated use and criteria), water quality
variances must be supported by one of the six justifications under 40 CFR 131.10(g)
where a state or authorized tribe believes the standard cannot be attained in the immediate
future. Variances are tied to 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 means
that a water quality standard variance for mercury would apply only to the new human
health methylmercury criterion in a stated waterbody and specifically to the discharger
requesting the variance, but the State 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?
Typically, variances provide a bridge when a state or authorized tribe needs additional
data or analyses before making a determination of whether the designated use is
14 These six justifications are the ones allowed for use attainability analyses (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 hydrologic 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 the 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; or (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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attainable and when the state or authorized tribe adopts an alternative use on the basis of
a determination under 40 CFR 131.10(g). In the case of methylmercury, such a variance
might also be appropriate where implementation tools are not available or feasible,
particularly where a state or authorized tribe has not yet developed a TMDL. With EPA's
belief that a number of waterbodies will be added to CWA section 303(d) listings for
mercury following adoption of the new methylmercury criterion, variances could provide
a short-term solution until development of the TMDL. Further, given limited resources, a
state or authorized tribe might decide to focus on controlling significant mercury sources
one at a time, beginning with a source other than effluent discharges (e.g., sediment,
atmospheric deposition) and employing variances in the interim.
EPA believes that a large number of regulated point sources discharging mercury may
apply for variances because they discharge into impaired waters where the largest source
of mercury comes from atmospheric deposition, and expects there to be commonality in
the grounds for these variances. The most likely scenarios to prompt a variance request
are listed below. Many point source dischargers contribute a relatively small percentage
of the mercury in an aquatic system. These scenarios are examples of demonstrations that
could satisfy the requirements under 40 CFR 131.10(g). These demonstrations are more
thoroughly explained below and in the Water Quality Standards Handbook (USEPA
1994).
Economic or social impacts—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—Demonstrate that, in the
short term, none of the present technologies for improving the quality of an
effluent are capable of bringing methylmercury levels down to the criterion (i.e.,
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 mercury
criterion, despite local efforts of reduction. In this instance, if air deposition
modeling shows that the atmospheric deposition from outside the United States
was a substantial cause of the impairment, the variance may be warranted.
Natural conditions preclude attainment—Demonstrate that local conditions of an
aquatic system result in high methylmercury levels. This could result from two
conditions. The first is that elevated mercury concentrations occur naturally. The
second is that conditions of the area or the waterbody itself—whether it be the
soil or sediment composition, microbial community, or the aquatic biota
interactions—might favor a high level of methylation such that low levels of
atmospherically-derived or ambient water column levels of mercury can amplify
into high concentrations in fish tissues. In other words, bioaccumulation might
occur at a higher rate under certain natural conditions and prevent the criterion
from being attained.
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3.2.2.2 What considerations should a state or tribe consider before
granting a variance?15
In general, the temporary standard established by a variance is set as close as possible to
the numerical criterion for the designated use and is always retained at the level needed to
preserve the existing use. This is done to protect the existing uses, and to ensure progress
toward ultimate attainment of the designated use. 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 in the
water quality standards. In addition, the following describes more specific issues that
states and authorized tribes should take into account when considering granting a
variance.
Performance-based approach—Unlike the typical numeric chemical criterion,
EPA based the recommended methylmercury criterion on a fish tissue
concentration, thus requiring a nontraditional expression of the criterion. States
and authorized tribes have flexibility in how a variance is expressed in their
water quality standard regulations. One approach is to incorporate the temporary
fish tissue-based criterion established by the variance directly in the standards,
and another is to use a performance-based approach. In the performance-based
approach, the state or authorized tribe adopts into its water quality standards the
procedure for calculating a new criterion on the basis of the variance. Such a
procedure should fully lay out the calculations and default values necessary to
derive an alternative fish tissue criterion using more site-specific numbers. To
implement a performance-based approach, a state or tribe would maintain a
publicly available, comprehensive list of all site-by-site decisions made using the
procedures; however, such decisions would not, as a federal matter, have to be
codified in state or tribal regulations. In addition, the public notice requirements
for adopting variances could be satisfied through the process of issuing the
NPDES permit that incorporates such temporary limits.
States and authorized tribes may find a performance-based approach
advantageous in the case of variances to the methylmercury criterion because
once the state or authorized tribe has submitted—and EPA has approved—these
procedures, performance-based variances could be issued without subsequent
individual approvals. The key advantage of this approach is that adoption of
sufficiently detailed implementation procedures, with suitable safeguards, does
not require EPA approval of every application of the variance.
Time frames—A variance is typically a time-limited change in the water quality
standards. Although EPA 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 3 to 5 years, with renewals
15 Federal or state regulations also govern the granting of a variance. For example, regulations promulgated under 40 CFR Part 132,
Appenidx F, Procedure 2 specifies the conditions for granting variances in the Great Lakes, and prohibits the granting of variances to new
dischargers or recommencing Great Lakes dischargers.
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Water Quality Criteria and Standards Adoption
possible following a sufficient demonstration that the variance is still necessary.
Variances that extend longer than 3 years are traditionally revisited in the context
of a triennial review to justify their continuation. While the discharger makes this
demonstration, the discharger also shows that it made reasonable progress to
control mercury in the discharge during the period of the previous variance. In
terms of methylmercury, there will likely be 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). EPA modeled the response in
fish tissue to a 50 percent reduction in mercury loadings to four lakes as part of
the analysis supporting the CAMR and estimated that it would take between 1 to
56 years for the lakes to reach 90 percent of the estimated steady state fish tissue
methylmercury concentration (USEPA 2005b). 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. Namely, a specific provision
within a variance for methylmercury could describe a less comprehensive
demonstration for renewals by making use of information already available.
Another perspective regarding the life span of a variance is that a 3-year timeframe
is mainly associated with a triennial review; there is no specific federal regulatory
requirement for a variance to expire in 3 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 triennial
review, states and authorized tribes are not obliged to reopen and modify permits
immediately to reflect those changes before issuance of a new permit.
Antidegradation—Permits with effluent limits based on a variance for
methylmercury must conform to the state or authorized tribe's antidegradation
policy.
Pollutant Minimization Plans—Pollution Minimization Plans (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-pipe, PMPs might
partially counter the 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:
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Water Quality Criteria and Standards Adoption
Case study:
Ohio statewide variance for mercury
Ohio adopted a statewide mercury variance applicable to any point source dischargers in
the state that meet several criteria. Specifically, Ohio adopted, and EPA approved, a rule
that finds complying with a mercury WQBEL on the basis of the Great Lakes Guidance
criteria applied at the end-of-pipe (i.e., without a mixing zone) would result in widespread
adverse social and economic impacts, relieving individual permittees of the burden of
making this demonstration on an individual basis. However, to obtain individual coverage
under the Ohio group variance, a permittee must do the following:
1. Demonstrate that it can (or will within 5 years) achieve an average annual
effluent concentration no greater than 12 ng/L mercury
2. Document that it is currently unable to comply with what would be the WQBEL
for mercury in the absence of a variance (based on the guidance wildlife
criterion of 1.3 ng/L)
3. Provide a plan of study to document known and suspected sources of mercury
4. Describe control measures taken to date as well as planned future measures to
reduce or eliminate mercury from the discharger's effluent
5. Explain why there are not readily available means of complying with the
WQBEL for mercury without construction of end-of-pipe controls
As a condition for receiving the variance, the discharger must accept permit conditions needed
to implement the plan of study regarding the identification and evaluation of mercury sources
and potential control measures. Further, the rule requires public notice of the preliminary
decision and the supporting materials (including the plan of study). Ohio also requires
monitoring as necessary to assess the impacts of the variance on public health, safety, and
welfare. If the discharger still cannot meet the standard following completion of actions
addressed in the plan of study and in the PMP, Ohio may take action (through permit
modification or permit reissuance) to delete the variance or impose additional pollutant
minimization steps (after consideration of public comment). Ohio also retains the right to
request that a discharger submit an individual variance application.
Similar costs, discharge processes —A type of industry or effluent treatment
process may be targeted on the basis of the associated costs or available
technology (i.e., publicly owned treatment works (POTWs), mining operations,
and so on). A state or authorized tribe can choose to adopt a variance with tiered
requirements, depending on the type of industry requesting coverage. For
example, due to the differing cost implications, 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.
Case study:
Michigan's mercury multiple discharger variance
Until recently, analytical methods for detecting mercury in effluents at levels below the
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Water Quality Criteria and Standards Adoption
water quality criterion (1.3 ng/L for the protection of wildlife) were lacking. Due to the
inability to quantify effluent mercury concentrations at low levels, most monitoring resulted
in no detects. Because of these monitoring results, facilities did not receive effluent limits
for mercury or were considered in compliance with effluent limits. EPA's new method
(1631) makes possible quantification of effluent mercury concentrations to levels less than
the criterion (quantification level = 0.5 ng/L).
Application of EPA's new method is expected to result in additional permit limits for
mercury and better detection of noncompliance with permit limits. Michigan expects that
many facilities with mercury limits will be unable to comply with the limits. No known,
demonstrated treatment technologies for removing mercury from effluents at low
nanogram per liter levels exist. Consequently, efforts intended to achieve compliance with
water quality-based effluent limits for mercury focus on the identification and reduction of
sources of mercury to a wastewater treatment system. Often, it is difficult to identify such
sources and to quantify the expected effects of source controls on effluent mercury
concentrations. Given the uncertainty in the ability to comply and the timing of compliance,
Michigan invoked a provision of this water quality standards (R 323.1103(9)) that
authorizes multiple-discharger variances where the Michigan Department of
Environmental Quality determines, "that a multiple discharger variance is necessary to
address widespread UQS compliance issues, including the presence of ubiquitous
pollutants or naturally high background levels of pollutants in a watershed" for mercury.
Where the available data indicate that a limit on mercury is needed, Michigan imposes a
limit that reflects the level currently achievable (10 ng/L expressed as a rolling 12 month
average). The permit requires reasonable progress towards achieving the limit on the
basis of the water quality criterion over the course of the permit. The permit requires the
permittee to develop and implement a pollutant minimization plan to identify and eliminate
sources of mercury. Effluent data will be generated using Method 1631. The variance is
not available to new dischargers.
Rather than having each of these individual facilities apply for and receive an individual
variance, the multiple discharger variance allows Michigan to respond to this issue
consistently and efficiently and to get in place permits that require pollutant minimization
plans that produce reductions in mercury effluent concentrations.
Watershed basis—A variance on a watershed scale might be a sensible approach,
particularly for those 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 will be collecting data from a watershed in 1 year for the
purpose of issuing NPDES permits in a subsequent year. The state or authorized
tribe could use these data for the purpose of revising a previously issued water
quality variance. Meanwhile, variances for other 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
WQBELs will reflect a more "real-time" variance limit.
Statewide—Analogous to a general NPDES permit, a statewide variance is made
available by the state or authorized tribe. Individual dischargers may apply for
coverage under the variance upon fulfillment of certain conditions. One example
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Water Quality Criteria and Standards Adoption
of this approach is Ohio's statewide variance for mercury, which is described
below.
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 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
and40CFR131.10(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 fishable/swimmable as
providing for the protection of aquatic communities and human health related to
consumption offish and shellfish. In other words, EPA views fishable/swimmable 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) fishable/swimmable 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 What is the rebuttable presumption of CWA section 101 (a)?
EPA regulations effectively establish a rebuttable presumption that fishable/swimmable
uses are attainable and therefore should apply to a waterbody unless it is affirmatively
demonstrated that such uses are not attainable. The rebuttable presumption approach
preserves states' and authorized tribes' paramount role in establishing water quality
standards in weighing any available evidence regarding the attainable uses of a
waterbody. If the water quality goals articulated by Congress cannot be met in a
waterbody, the regulations simply require that such a determination be based upon a
credible structured scientific assessment (e.g., a UAA). EPA believes that the rebuttable
presumption policy reflected in the federal regulations is an essential foundation for
effective implementation of the CWA as a whole. The use of a waterbody is the most
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Water Quality Criteria and Standards Adoption
fundamental articulation of its role in the aquatic and human environments, and all the
water quality protections established by the CWA follow from the water's designated
use. If a use lower than a fishable/swimmable use is designated on the basis of inadequate
information or superficial analysis, water quality-based protections that might have
enabled the water to achieve the goals articulated by Congress in section 101 (a) may not
be put in place.
3.2.3.4 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
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. Existing
uses are 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, designated uses
are considered by EPA to be 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 on nonpoint sources. The
federal regulation 40 CFR 131.10(g) further establishes 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. States 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.
3.2.3.5 What conditions justify changing a designated use?
EPA's regulations at 40 CFR 131.10(g) lists 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
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• 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 serve the purpose of guiding analysis and
decision making with 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. 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).
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4 Monitoring and Assessment
4.1 What are the analytical methods for detecting and
measuring methylmercury concentrations in fish and
water?
Over the last 2 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 protocols
and to determine which of these protocols would be most useful for implementing the
new methylmercury criterion. After its 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).
EPA Methods 1630 and 1631, developed by EPA's Office of Water, reflect the
techniques developed by these researchers for analyzing methylmercury and mercury in
water, respectively. Appendix A to Method 1631 (64 FR 10596) details the researcher's
techniques for determining total and dissolved mercury in tissue, sludge, and sediments.
These methods, which are written in EPA Environmental Monitoring Management
Council (EMMC) format, include all quality control elements that EPA's Office of Water
considers necessary to adequately define data quality.
In Appendix C, Table Cl summarizes these and other methods that EPA knows have
been used to analyze mercury and methylmercury in fish tissue, and Table C2
summarizes methods available for the analysis of mercury and methylmercury in water
and other nontissue matrices. Each table identifies the forms and species 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.
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 use of these techniques when direct measurements of methylmercury
in tissue are desired.
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, is 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. Appendix A to Method 1631 allows for
measurement of mercury in tissue at approximately 0.002 mg/kg, well below the tissue
criterion.
Several options are also available for measuring mercury concentrations in water (Table
D2). Because Method 1631 has already been promulgated for use in CWA applications,
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EPA strongly recommends use of this method when measuring all species of mercury in
water, especially when low-level measurements are expected. When measuring
methylmercury in water, three options are Method 1631, developed by the Office of
Water (USEPA 2002d); UW-Madison's SOP (Hurley et al. 1996), used by the Great
Lakes National Program Office for its Lake Michigan Mass Balance Study; and a
recently released USGS method (DeWild et al. 2002). All these procedures are based on
the same techniques, and each can meet the most stringent (i.e., Great Lakes Guidance)
mercury water quality criterion of 1.3 ng/L for wildlife protection in water. While any of
these methods are acceptable, EPA recommends the use of Method 1631, which is
documented in EMMC format and includes all quality control criteria considered
necessary to define data quality.
In summary, on the basis of the available information, EPA believes that the most
appropriate methods for measuring compliance with new or revised methylmercury
criteria are Method 1631 (mercury in water by cold vapor atomic fluorescence
spectrometry (CVAFS)), Method 1630 (methylmercury in water by CVAFS), Appendix
A to Method 1631 (mercury in tissue by CVAFS), and modifications to Method 1630 for
handling tissues (described in Table Cl—see Appendix C). EPA recommends these
procedures for the following reasons:
• Methods 1630 and 1631 were developed by EPA to support implementation of
water quality criteria for mercury and methylmercury. Both are already in the
appropriate EPA format and include all standardized quality control (QC) elements
needed to demonstrate that results are reliable enough to support permitting and
enforcement programs.
• Appendix A to Method 1631 was developed by EPA to support its National Study
of Chemical Residues in Fish Tissue. Appendix A provides information on
preparing a fish tissue sample for analysis using Method 1631. The method was
validated by Brooks Rand (USEPA 1998b) and is currently being used by Battelle
Marine Sciences to analyze more than a thousand tissue samples collected during
EPA's National Fish Tissue Survey (USEPA 2000J). 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 Ig) and the Savannah River TMDL study
(USEPA 200 le). 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. The procedures in Method 1630 also are
nearly identical to those given in the USGS method and in the University of
Wisconsin SOP, listed in Table D2 (Hurley et al. 1996). The University of
Wisconsin SOP was used in EPA's Lake Michigan Mass Balance Study (USEPA
2001f).
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4.1.1 What is Method 1631 for determination of mercury in water?
In May 1998, EPA proposed Method 1631 at 40 CFR Part 136 for use in determining
mercury concentrations at AWQC levels in EPA's CWA programs, and subsequently
published a Notice of Data Availability (64 FR 10596) that included additional data
supporting application of the method to effluent matrices. On June 8, 1999, EPA
responded to numerous public comments on the proposed method and promulgated EPA
Method 1631, Revision B: Mercury in Water by Oxidation, Purge and Trap, and Cold
Vapor Atomic Fluorescence Spectrometry at 40 CFR Part 136 for use in EPA's CWA
monitoring programs. EPA promulgated the method on the basis of extensive validation
of the procedures, including four single-laboratory studies and an interlaboratory
validation involving 12 participating laboratories and 1 referee laboratory. The highest
method detection limit (MDL) determined by all laboratories in reagent water was 0.18
ng/L, indicating that this method is capable of producing reliable measurements of
mercury in aqueous matrices at AWQC levels.
EPA has revised Method 1631 after its promulgation to clarify method requirements,
increase method flexibility, and address frequently asked questions. The current method
(Method 1631, Revision E) includes recommendations for use of clean techniques
contained in EPA's Method 1669: Sampling Ambient Water for Trace Metals at EPA
Water Quality Criteria Levels (USEPA 1996b). The benefits of using Method 1631 are
that it is an approved method under EPA's CWA monitoring programs, has been fully
validated, and numerous laboratories are routinely using this method. However, Method
1631 measures only mercury (total and dissolved) in aqueous samples and is not capable
of measuring the methylmercury species.
Method 1631, Appendix A 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 2 to 5,000 ng/g (0.002 to 5.0 mg/kg). The expected method detection limit
for mercury in fish tissue is 0.002 mg/kg, well below the new water quality criterion for
methylmercury. The procedures in the appendix are not published in the Code of Federal
Regulations, but were implemented in EPA's National Study of Chemical Residues in
Fish Tissue (USEPA 2000J). Although Appendix A of Method 1631 has not been fully
validated (i.e., via an interlaboratory validation study), it was validated by EPA in a
single laboratory study, and the techniques have been widely reported in the literature.
Also, as discussed above, the analytical component of the method (Method 1631) has
been fully validated and approved for measurement of total or dissolved mercury in
aqueous matrices.
4.1.2 What analytical methods are available for determination of
methylmercury?
EPA has not published an analytical method specifically for measuring methylmercury.
As technical guidance to assist States and authorized tribes in their selection of an
analytical method to use, Tables C1 and C2 in Appendix C include four methods that
EPA has seen investigators successfully use for the determination of methylmercury.
Other methods may be acceptable for use under the appropriate circumstances. As
written, all four of the methods are specific to aqueous matrices and are based on almost
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identical analytical procedures (i.e., distillation, ethylation, GC separation, and CVAFS
detection). These methods have been or are being used in several national or regional
studies, but none are yet published in 40 CFR Part 136. Modifications to adapt these
procedures for fish tissue have been reported in the literature (e.g., Bloom 1989, and
modified by Horvat et al. 1993) and used in EPA's Cook Inlet contaminant study
(USEPA 200Ig), the 4-year Lake Michigan Mass Balance study (USEPA 200If), and an
extensive study of the Everglades (USEPA 2000b).
Because the four methods are nearly identical, they are expected to produce very similar
results with sensitivity as low as 0.002 mg/kg in tissue and 0.01 to 0.05 ng/L in water.
These levels are well below the methylmercury criterion for fish and the most stringent
(i.e., Great Lakes Guidance) mercury water quality criterion of 1.3 ng/L for wildlife
protection in water.
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 (2000c) 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, thus, offers EPA's current guidance for obtaining a representative sample
for determining attainment. This guidance also includes recommendations for quality
control and quality assurance considerations. In all cases, states should develop data
quality objectives for determining the type, quantity, and quality of data to be collected
(USEPA 2000h).
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 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 through surveying anglers) from state fisheries
departments is one justifiable basis for estimating types and amounts of fish 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 who eat fish.
The fish sampling guidance also identifies recommended target species for inland fresh
waters and for Great Lakes waters. Seabass, walleye, king mackerel, tilefish, and
largemouth bass have been identified as accumulating 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
via consumption of contaminated prey.
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The fish sampling guidance recommends that the size range of the sampled fish ideally
should include, from the species of fish that people in the area eat, the larger fish
individuals harvested at each sampling site, because larger (older) fish within a
population are generally the most contaminated with methylmercury (Phillips 1980,
Voiland et al. 1991). This means that small fish such as minnows should be avoided as
target species. 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, for migratory
species, that neither spawning populations nor undersized juvenile stages be sampled in
fish contaminant monitoring programs (USEPA 2000c). Sampling of target finfish
species during their spawning period should be avoided as contaminant tissue
concentrations may decrease during this time and because the spawning period is
generally outside the legal harvest period.
If states and authorized tribes do not have local information about the types of fish
present 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 would reflect the determined
trophic level breakout. Fish creel data (from data gathered through surveying
anglers) from state fisheries departments is one 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 who eat fish. The state or
authorized tribe should decide which approach to use.
Trophic level 4 fish only—Predator species (e.g., trout, walleye, largemouth bass,
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 higher trophic level species correlates with
greater risks to human health. (This correlation is less evident in estuarine and
marine species.) Therefore, targeting trophic level 4 species should serve as a
conservative approach (depending upon the species most frequently consumed by
anglers) 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 people in
the local area eat because methylmercury binds to proteins and is found primarily in fish
muscle. Using skinless fillets is a more appropriate approach for addressing mercury
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exposures for members of the general population and most recreational fishers because
fish consumers generally eat the fillets. 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. However, some fish consumers 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. Besides being cost
effective, composite samples also ensure adequate sample mass to allow analyses for all
recommended contaminants. 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 upon 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?
To address spatial variability of methylmercury levels in fish, EPA recommends that
states and tribes design a probabilistic sampling by randomly selecting sites or sampling
locations. This approach allows statistically valid inferences to be drawn on an area as a
whole.
Ideally, samples should be collected 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, these 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 these areas but not included if the area is
not used for fishing.
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 sufficient program resources exist, this guidance
recommends biennial sampling offish in waterbodies where recreational or subsistence
harvesting is commonly practiced. If biennial screening is not possible, waterbodies
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should be screened at least once every 5 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 (i.e., August to October). Water levels are typically lower during
this time, thus simplifying collection procedures. Also, the fish lipid content is generally
higher, thus allowing these 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 this period. However, if the target species can be legally harvested during
its spawning period, sampling to determine contaminant concentrations should be
conducted during that time. 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 tribes sample consistently in a season to eliminate
seasonal variability as a confounding factor when analyzing fish monitoring data.
Additionally, 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 fish-fillet muscle mercury
concentrations 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
by as much as a factor of two to three times that in warm seasons. 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 in fish mercury 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. 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 (Giblin and Massaro 1973, Rodgers and Beamish 1982, Huckabee et al. 1979
[literature review], Burrows and Krenkel 1973, McKim et al. 1976). Such slow
depuration rates are expected to dampen strongly any fluctuations in methylmercury
concentrations in fish. Instead, season variations in fish tissue are likely linked to
seasonal nutrition variability that impact fish body conditions but not mercury body
burden.
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. These studies support the concept of starvation
concentration—whereby loss of muscle mass during periods of starvation occurs quicker
than loss of mercury. Burrows and Krenkel (1973) found mercury elimination rate to be
the same for fish that were starved relative to nonstarved fish. The converse phenomenon
of growth dilution, where lower fish-mercury concentrations correlate with higher growth
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rates, has been described by a number of researchers (Simoneau et al. 2005, Doyon et al.
1998, Park and Curtis 1997). The authors of the first two papers hypothesize that slower-
growing fish allocate more energy towards maintenance and less to flesh production
while faster growing fish add flesh at a lower energy cost and, thus, with proportionally
less mercury intake. Park and Curtis (1997) proposed an alternative hypothesis that
growth dilution occurs when high growth coincides with periods of low methylmercury
concentration. Regardless of the exact mechanism, body condition offers a useful method
to explain variability in fish mercury.
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 6.1.2.7.1 provides information to help determine
the number of composite samples for comparing fish tissue information to a target value.
This guidance does not recommend a single set of sample size requirements (e.g., number
of replicate composite samples per site and the 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
preventing the site-specific statistical analysis, a minimum of 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 for
mercury analysis), states and authorized tribes should first measure mercury in fish tissue.
This approach assumes that all mercury in fish tissue is methylmercury and is, thus, a
conservative assessment. This approach does not pose a risk of a false positive decision
(considering the tissue to exceed the criterion when it does not) where the measured
mercury in fish tissue is less than the 0.3 mg/kg criterion (or a site-specific criterion
adopted by a state) nor should it pose a realistic risk of a false positive when the
measured mercury exceeds the criterion by 10 percent. Appendix E summarizes seven
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 seven studies,
methylmercury, on average, accounted for more than 90 percent of the mercury
concentration in fish tissue. If the measured mercury level is within 10 percent of the
methylmercury criterion, states might wish to repeat the sampling (if sufficient tissue is
not left) and analyze for methylmercury.
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Section 303(d)(l) of the CWA requires 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 with existing or anticipated required controls. In
accordance to 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, 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 AWQC. EPA's Guidance for Assessing
Chemical Contaminant Data for Use in Fish Advisories, Volume 1, at section 6.1.2.7.1
recommends using the t-test to determine whether the mean concentration of mercury in
composite fish tissue samples exceeds the screening value. This involves a statistical
comparison of the mean of all fish tissue data to the criterion. If the t-test statistic of the
mean exceeds the water quality standards, there is an exceedence. EPA recommends that
this procedure also be used for determining impairment. States and authorized tribes
might also want to consider the guidance in Appendices C and D of the Consolidated
Assessment and Listing Methodology, Toward a Compendium of Best Practices (USEPA
2002b). Ultimately, the method that states choose depends on how they express their
water quality standards.
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 will
be no need to mathematically compute an average. Second, the newer analytical Methods
1630 and 1631 are able to quantify mercury at 0.002 mg/kg, which should be lower than
the observed mercury in fish tissue samples being analyzed.
However, if a state or authorized tribe is mathematically computing an average of a data
set that does include 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). This 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 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 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)
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(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 200 li).
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 using first the value of the detection level to quantify samples below
the detection level and then again using a zero value for samples below the detection
level. If both calculated means are either 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 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 200li) 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.
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 performs 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 3.
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Table 3. 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
Methyl mercury
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 for 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 be 0.18 mg/kg, and would have given more weight to the
methylmercury concentrations in brown bullhead than 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:
Qvg = 3.8 * C2 + 8.0* Q + 5.7* Q = 0.23 mg/kg (Equation 4)
Where:
C2
C4
(3.8 + 8.0 + 5.7)
average mercury concentration for trophic level 2
average mercury concentration for trophic level 3
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 ). However, as noted throughout this document, the consumption
pattern of the target population should be used if available
16 The values for each trophic level are the same as discussed in section 3.2.1.2., and are found in Methodology for Deriving Ambient Water
Quality Criteria for the Protection of Human Health (USEPA 2000e).
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If fish tissue 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 data for trophic level 2 fish in the previous example, Equation 5 shows the
revised calculation:
Cavg = 8.0* C2 + 5.7* Q = 0.27mg/kg (Equations)
(8.0 + 5.7)
This revised calculation preserves the relative contribution of each trophic level to
consumption patterns. However, this approach should not be used if there are no data for
trophic level 4 fish, which is the type offish that is most often eaten. 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 approach can be applied to trophic level 4.
If the state or authorized tribe has developed a site-specific fish consumption rate for the
criterion, then the state or authorized tribe should incorporate this site-specific rate in
Equation 4 above. 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 are representative of the risk considerations of the state. Regression models
have been developed for this purpose (Wente 2003, Rae 1997). 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 log-normally 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 of Mercury and Fish to analyze two
data sets for use in analysis supporting the CAMR (USEPA 2005a). This model is a
statistical model related to covariance and 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
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events. This 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,
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 last 5 years, as recommended in section
4.2.4. However, such information might not be available, and states and authorized tribes
will often consider mercury from samples collected and analyzed several years in the
past. Although the state and authorized tribe should consider this information, they
should also determine the reliability of this information and its accordance with
applicable data collection or quality assurance/quality control (QA/QC) program
requirements before using these data for listing assessments.
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 2000g). 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
impairment and inclusion on a section 303(d) list, EPA considers a fish consumption
advisory and the supporting data as existing and readily available data and information.
A state or authorized tribe should include on its section 303(d) list, at a minimum, those
waters where waterbody-specific data that was the basis of a fish or shellfish
consumption advisory demonstrates nonattainment of water quality standards. EPA
believes that a fish or shellfish advisory would demonstrate nonattainment when the
advisory is based on tissue data, the data are from the specific waterbody in question, and
the risk assessment parameters of the advisory or classification are cumulatively equal to
or less protective than those in the water quality standards.17 For example, consider a
state or authorized tribe that bases its water quality criterion on eating two fish meals a
month. If the state or authorized tribe finds fish tissue information showing that the level
of mercury is at a level where it decides to advise people to not 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 exceedence and that the waterbody should
be placed on the 303(d) list. In contrast, if this same state or authorized tribe finds the
level of mercury in fish in another waterbody is at a level where it would advise people to
17 The October 2000 EPA guidance assumes that the fish tissue monitoring that supports the advisory is sufficiently robust to provide a
representative sample of mercury in fish tissue. EPA's fish tissue guidance (USEPA 2000c) provides recommendations on how public
health officials can collect sufficient information about contaminants in fish.
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eat no more than 8 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 may not need
to be listed.
When reporting water quality conditions under CWA sections 303(d) or 305(b) on the
basis of a fish advisory for a migratory fish species, the state or authorized tribe should
include the waters where the migratory fish are known to inhabit because these are the
waters where the fish would become potentially 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 it is appropriate.
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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?
As stated in the January 8, 2001, Federal Register notice, EPA encourages states and
authorized tribes to adopt the fish tissue residue water quality criterion for methylmercury
into their water quality standards to protect CWA section 101(a) designated uses related
to human consumption offish. With respect to waterbodies within the Great Lakes basin,
a state or authorized tribe must also follow the requirements promulgated on March 23,
1995, at 40 CFR Part 132. Under these regulations, if a state or authorized tribe adopts
the new methylmercury criterion, EPA, in its review of the new state or tribal criterion,
must determine if it is as protective as the mercury criterion for human health protection
published in Table 3 at 40 CFR 132.5(g)(l) or on the basis of improved science (40 CFR
132.4(h)).
The human health criterion for mercury established by the methodology contained at Part
132 and adopted by the Great Lakes states is 3.1 ng/L. This water column criterion for
mercury is equivalent to a fish tissue residue value of 0.35 ug methylmercury/g fish tissue
using the Great Lakes-specific BAFs for mercury of 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). Therefore, a state or authorized tribe would apply the site-specific
modification procedures of Part 132 to show that the current, local BAF is lower than the
one used to develop the criterion in Part 132 before it could adopt the new fish tissue-
based criterion and methodology.
Also, EPA believes that if a state or authorized tribe adopts the new tissue-based criterion
for protection of human health in the Great Lakes, this action may not always result in a
change to TMDLs or NPDES permits. Part 132 also includes a 1.3 ng/L criterion for the
protection of wildlife, and in some instances, this criterion may 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 a 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 California Toxics Rule (CTR) (40 CFR 131.38) and the National
Toxics Rule (40 CFR 131.36). 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).
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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 is 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. 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 in their water quality
standards plans for later application to NPDES point sources 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 both the water column and food over the life of the fish and, thus, 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.
However, some states and authorized tribes may choose to adopt a water column criterion
based on the fish tissue criterion and, thus, have a criterion where a mixing zone may
apply. In this situation, a state or authorized tribe should follow its existing procedures
for mixing zones.
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 CFR Part 132, Appendix F, Procedure
3). This 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
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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 through the phased approach to TMDL development.
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, thus, 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 or
authorized tribe would have determined a site-specific BAF in this process and, thus,
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 if they are as protective as the Great Lakes procedures for human health
protection (40 CFR 132.5(g)(3)). Specifically, EPA would determine if the
implementation procedures are as protective as applying the Table 3 (in 40 CFR Part 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 authorized 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 the Fish Advisory Program?
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
issuing consumption advisories for the general population, including recreational and
subsistence fishers, and 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.
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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, Volume 1 and 2 (USEPA 2000c, 2000d).
This guidance describes the two main equations necessary to derive meal consumption
limits on the basis of the methylmercury RfD. Basically, a first equation is used to
calculate the daily consumption limits of grams of edible fish (in grams per day (gd)); 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.
As a default screening-level approach, EPA recommends basing fish consumption
advisories on a consumption rate of 17.5 grams/day offish (uncooked) eaten from the
local water. 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 (i.e., 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
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 fish consumption limit for mercury is that the criterion
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includes an RSC18 and EPA's recommended tissue value for a fish advisory does not. In
deriving the criterion, EPA assumed an RSC value of 2.7x10" 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 noncommercially caught
fish, but the guidance can be applied without using an RSC. The RSC guidance in the
2000 Human Health Methodology (USEPA 2000e) 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 the attainment of a
criterion and issuance of a fish consumption advisory?
In many states and authorized tribes, numeric water quality criteria and fish and shellfish
consumption limits differ due to inherent differences in the technical and risk
assumptions used to their development. 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 where the
presence of an advisory may not imply an exceedence of the water quality standard
(USEPA 2000g) 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 may not demonstrate that a CWA section 101(a)
"fishable" use is not being attained in an individual waterbody and may not be
appropriate for determining attainment based on exceedence of water quality
criteria.
Local advisory—States have issued local advisories using a higher fish
consumption value than they use in establishing water quality criteria for
protection of human health. Again, in this case the fish consumption advisories
may not demonstrate that a section 101(a) "fishable" use is not being attained in
an individual waterbody and may not as appropriate as 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 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 eight meals a month. In this case,
See discussion on the RSC in section 3.1.2.2.
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because the fish consumption advisory uses a higher fish consumption value than was
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 2000g).
In the case where a local advisory is based on a higher fish consumption value, 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, local
fish consumption patterns, and may identify more representative fish species. The
information gathered in developing the advisory may 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 a fish consumption limit and 304(a) criterion for
mercury are based on similar methodologies and are intended to protect human health
from consumption of 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 How is the criterion related to FDA action levels?
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, not food that is caught locally by recreational or
subsistence fishers
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 the general population who consume fish
and shellfish typically purchased in supermarkets or fish markets that sell products that
are 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
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and tolerances should not be used as a basis for establishing a state'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 are more reliant upon 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?
Section 303(d)(l) of the CWA requires 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 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 those 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 2004, 42 states reported at least one waterbody as being impaired due to mercury,
and over 8,500 specific waterbodies were listed as being impaired due to mercury, either
solely or in combination with other pollutants. With the implementation of the new
methylmercury fish tissue criterion, EPA expects that the number of waterbodies listed as
impaired due to mercury is likely to increase, although the waterbodies might also be
impaired due to other contaminants.
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 mining 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 to provide a basis for reducing mercury releases to water,
including through air deposition, to meet applicable water quality standards and Clean
Water Act goals. In areas where large numbers of waterbodies are impaired due to
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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. EPA plans to develop further information on approaches to listing
mercury impaired waters and developing mercury TMDLs at a later date.
In the meantime, states continue to develop mercury TMDLs, with mercury TMDLs
approved for over 280 waterbodies. This guidance provides examples of approaches that
have been used in approved mercury TMDLs and examples of technical tools available to
assist in mercury TMDL development. Note that there are examples beyond those cited in
this document. Approaches in approved TMDLs range from waterbody-specific TMDLs
to regional-scale approaches. Technical tools available to assist in the development of
mercury TMDLs include screening level analyses of mercury loadings and sources using
the Mercury Maps tool and more complex water and air models. Many of these tools are
discussed in the sections below.
6.2.1 How have large-scale approaches been used for mercury
TMDLs?
In areas of the country where many waterbodies are listed as impaired for mercury, some
states have begun to explore the development of mercury TMDLs either as a group or on
a larger geographic scale, such as statewide or regionally. 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.
Due to the large extent of mercury from air deposition, the TMDL was developed on a
regional rather than a waterbody-by-waterbody basis. The TMDL used air deposition
modeling results to estimate wet and dry deposition of mercury for the six segments. 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, which is subsequently
transported to the waterbody via runoff and erosion. Additional information on this
TMDL can be found on EPA's detailed TMDL report at http ://oaspub .epa.gov/pls/tmdl/
waters list.tmdl report?p tmdl id= 11642.
In New England, EPA is conducting a pilot project to test the feasibility of taking a
regionwide approach to mercury contamination. Mercury contamination throughout New
England has resulted in statewide fish consumption advisories and the inclusion of almost
all fresh surface water on state lists of impaired waters. The pilot project will involve
development of a system to show regionwide information on mercury levels in fish,
loadings and sources of mercury, and mercury reductions needed to meet water quality
standards. The New England pilot project will consist of two levels of analyses or
models—fish tissue concentration predictions and mercury load reduction predictions.
EPA will use the regional model to identify factors that contribute to high levels of
mercury in fish and to predict the risk of mercury contamination for waterbodies with no
fish tissue data. EPA will use the Mercury Maps system, described above, to estimate
needed fish tissue concentration reductions.
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6.2.2 What is the Mercury Maps screening analysis?
A simple screening level analysis of the mercury sources impacting a waterbody or
waterbodies can assist in determining what type of approach to TMDLs is most
appropriate. One tool available to help states with such an analysis is EPA's Mercury
Maps (USEPA 200Id). Mercury Maps is a peer-reviewed geographic information system
(GIS) based analysis with 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 that were described in the report to Congress, Mercury Maps showed that these
models converge at a steady-state solution for methylmercury concentrations in fish that
are proportional to changes in mercury inputs from atmospheric deposition (e.g., over the
long term, fish concentrations are expected to decline proportionally to declines in
atmospheric loading to a waterbody). This analytical approach applies only to situations
where air deposition is the only significant source of mercury to a waterbody, and the
physical, chemical, and biological characteristics of the ecosystem remain constant over
time. To predict reductions in fish concentrations, Mercury Maps requires estimates of
percent air deposition reductions by watershed, as generated from a regional air
deposition model, and georeferenced measurements of mercury concentrations in fish.
Because Mercury Maps is a simplified approach, it has several limitations. First, Mercury
Maps is based on the assumption of a linear, steady-state relationship between
concentrations of methylmercury in fish and present day air deposition mercury inputs.
This condition will likely 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 (see Figure 3).
A second limitation is that the Mercury Maps methodology inherently requires that
environmental conditions remain constant over the time required to reach steady states.
This methodology might not be met, especially in systems that respond slowly to changes
in mercury inputs. For example, fish tissue data might not represent average, steady-state
concentrations for two major reasons. Fish tissue and deposition rate data for the base
period are not at steady state. Where deposition rates have recently changed, the
watershed or waterbody might not have had sufficient time to fully respond. Also, fish
tissue data do not represent average conditions (or conditions of interest for forecast fish
levels). Methylation and bioaccumulation are variable and dynamic processes. If fish are
sampled during a period of high or low methylation or bioaccumulation, they would not
be representative of the average, steady-state or dynamic equilibrium conditions of the
waterbody. Other examples include areas in which seasonal fluctuations in fish mercury
levels are significant, for example due to seasonal runoff of contaminated soils from
abandoned gold and mercury mines or areas geologically rich in mercury. In such a case,
Mercury Maps predictions would be valid for similar conditions (e.g., wet year, dry year,
or season) in the future, rather than typical or average conditions. Alternatively, sufficient
fish tissue should be collected to get an average concentration that represents a baseline
dynamic equilibrium.
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January 1,00:00:00
Mill- 14.076 at (21,84), Max- 99.985dt(I48,1)
Figure 3. Percent of total mercury deposition attributable to global sources
(USEPA2005C)
Other ecosystem conditions might cause projections from the Mercury Maps approach to
be inaccurate for a particular ecosystem. Watershed and waterbody conditions can
undergo significant changes in capacity to transport, methylate, and bioaccumulate
mercury. Examples of this include regions where sulfate or acid deposition rates are
changing (in turn, affecting methylmercury production independently of mercury
loading), and where the trophic status of a waterbody is changing. A number of other
water quality parameters have been correlated with increased fish tissue concentrations
(e.g., low pH, high DOC, lower algal concentrations), but these relationships are highly
variable among different waterbodies. Mercury Maps will be biased when waterbody
characteristics change between when fish were initially sampled and the new conditions
of the waterbody.
Third, states should be aware that many waterbodies, particularly in areas of historic gold
and mercury mining or areas with known natural mercury deposits, contain significant
non-air sources of mercury. The Mercury Maps methodology cannot be applied to these
waterbodies.
Fourth, 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. If a state or authorized tribe wants know the time over which the methylmercury
concentrations would change, they should use a dynamic model to estimate the recovery
during the period in which waterbody response lags reductions in mercury loads. A
dynamic model is also essential for understanding seasonal fluctuations and year-to-year
fluctuations due to meteorological variability.
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Finally, another source of uncertainty in the Mercury Maps forecasts are the atmospheric
deposition rates used to forecast changes in fish mercury concentrations. In the analysis
for the CAMR, EPA compared deposition rates in the Community Multiscale Air Quality
(CMAQ) and Regulatory Modeling System for Aerosols and Deposition (REMSAD) grid
cells to empirically derived loading rates (USEPA 2005b). At the locations chosen for the
analysis, site-specific data suggest somewhat higher deposition rates than the CMAQ and
REMSAD models. In evaluating the importance of differences in absolute deposition
rates from air quality models and site-specific data, it is important to consider how the
results will be applied. If the results from air quality models are used as inputs to
ecosystem models such as the Dynamic Mercury Cycling Model and the BASS model
then the absolute deposition rates are used and so differences in absolute deposition is
important. However, if the results are used as inputs into models like Mercury Maps then
relative changes in deposition are used. In the latter case, differences in absolute
deposition rates are not directly relevant although such differences are important in model
validation.
EPA recognizes that methylmercury concentrations in fish across all ecosystems might
not reach steady state and that ecosystem conditions affecting mercury dynamics are
unlikely to remain constant over time. EPA further recognizes that many waterbodies,
especially in areas of historic gold and mercury mining in western states, contain
significant non-air sources of mercury. Finally, EPA recognizes that 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, EPA is unaware of any other tool for performing a regional-scale
assessment of the change in fish methylmercury concentrations resulting from reductions
in atmospheric deposition of mercury. Mercury Maps can show the watersheds across a
region where the current fish tissue concentration on average exceeds the new
methylmercury fish tissue criterion and, thus, where mercury load reductions will be
necessary to achieve the criterion. Mercury Maps also can group watersheds by their
major mercury sources, such as those watersheds where air deposition of mercury
predominates and those watersheds where other mercury sources besides air deposition
(e.g., POTWs, mining, pulp and paper mills, chlor-alkali chemical plants) have
significant impacts. For those watersheds where mercury comes almost exclusively from
air deposition, Mercury Maps can estimate the atmospheric load reductions needed to
meet the new criterion.
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 tribal-defined
watershed boundaries. The state may have its own data on point source effluent loads and
more detailed information on other significant sources of mercury in their state, e.g.,
erosion of mine tailings or natural geology. Further information on Mercury Maps is
available at http://www.epa.gov/waterscience/maps.
6.2.3 What are 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 sources (40 CFR
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130.2(i)). EPA guidance further notes that a TMDL should identify the pollutant sources,
both point and nonpoint sources, including the location of the sources and quantity of the
loading. Some of the considerations in developing a mercury TMDL are described in
more detail in the text below.
6.2.3.1 What are potential mercury sources to waterbodies?
Some of the potential sources of mercury to waterbodies include direct discharges of
mercury from water point sources, including industrial dischargers and wastewater
treatment plants; 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; 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; sediments, which might have mercury contamination
or hot spots resulting from past discharges; and "naturally occurring" mercury in soils
and geologic materials. Sediments containing mercury from past discharges might
continue to contribute mercury to the overlying waterbody. Below is further discussion of
examples of TMDLs involving each of these types of sources.
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 (PCS) as well as a study of domestic mercury sources by
the National Association of Clean Water Agencies (NACWA), formerly known as the
Association of Metropolitan Sewerage Agencies (AMSA 2000). 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.
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 the total loadings from atmospheric deposition, either directly or
indirectly via runoff and erosion. (See various mercury TMDLs developed by EPA
Region 4 at http://www.epa.gov/region4/water/tmdl/georgia/index.htm.) The mercury in
atmospheric deposition originates from natural sources and from facilities such as
medical and waste incinerators, electric utilities, and chlor-alkali plants, among others.
Mercury is emitted to the air in several chemical forms or species. 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 will determine 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,
showing that in many parts of the United States the source of deposited mercury is not
from a U.S. source.
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In 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.
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, global emissions might have
increased.
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Figure 4. Trends in mercury air emissions between 1990 and 1999
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
electric utilities and petroleum refineries), mobile sources (both onroad sources such as
cars and trucks, and nonroad engines such as construction equipment, agricultural
equipment, and so on), 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 using EPA's
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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://www.epa.gov/region4/water/tmdl/
georgia/index.htm). 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.
EPA has evaluated water and air deposition modeling approaches as part of two mercury
TMDL pilot projects in Wisconsin and Florida. 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
REMSAD model for identifying the sources or categories of sources contributing
mercury deposition to a waterbody.19 The modeling and peer review for the Wisconsin
pilot are completed, and a final report is expected in 2006. The Agency also 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
determine the appropriate strategies for addressing mercury deposition from sources
within their jurisdictions.
Air quality modeling for the CAMR was conducted using the CMAQ. 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 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 (Byun and Schere 2006, Bullock and Brehme 2002) was used for CAMR. This
version 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 used
for CAMR from that described in (Bullock and Brehme 2002) are as follows:
1. The elemental mercury (HgO) reaction with H2O2 assumes the formation of
100 percent ROM rather than 100 percent particulate mercury (HgP).
2. The HgO reaction with ozone assumes the formation of 50 percent RGM and
50 percent HgP rather than 100 percent HgP.
3. The HgO reaction with OH assumes the formation of 50 percent RGM and
50 percent HgP rather than 100 percent HgP.
19 The air deposition modeling using REMSAD used an older emissions inventory than was used in CMAQ modeling conducted as part of
the CAMR analysis.
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TMDLs
4. The rate constant for the HgO + OH reaction was lowered from 8.7 to
7.7 x ICT^cn^molecules'V1.
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 contents 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 the CAMR CMAQ modeling, meteorological input
files were derived from a simulation of 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 in McNally (2003).
These initial and boundary concentrations were obtained from 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 the NASA's Goddard Earth Observing System
(GEOS). This model was run for 2001 with a grid resolution of 2 degree x 2.5 degree
(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 of these grid cells. 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.
As with any analysis based on limited data, there is inherent uncertainty 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 that are 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.
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Other tools available to help states characterize mercury deposition include existing
national monitoring networks and modeling tools, such as the Mercury Deposition
Network (MDN). Examples of these are provided in Appendix D. 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 at http://www.epa.gov/owow/oceans/airdep/air7.html.
Mining activity—Loadings from mining activities might include 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 (e.g., 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 A), 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 may 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 A.
Sediments—A TMDL analysis should account for any mercury present in sediments as a
result of current or past mercury loadings. Data on levels of mercury in sediments are
important in determining the extent to which controls on other sources will be effective
and how long it will take to achieve water quality standards. An examination of past
industrial practices in the watershed could include whether sediments may serve as a
reservoir for mercury. Various national databases, such as the National Sediments
Database (USEPA 2002c) and data collected by USGS might also identify isolated
locations of elevated mercury in sediments. 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 if loadings from a
location were contribution to water quality standards violations
• Screening modeling to determine other potential sources of sediment
contamination (see the TMDL at http://www.epa.gov/waters/tmdldocs/
1991 Bellingham%20Bav%20TMDL.pdf)
Natural or "background" levels of mercury in soils—Soils and sediments can include
mercury of geologic origin or mercury produced by the weathering of geological
materials, together with mercury of anthropogenic origin (i.e., mercury emitted overtime
from human sources and then deposited on soils). Mercury in soils can also re-emit and
subsequently redeposit to soils. Local studies have been used in some TMDLs to estimate
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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.
6.2.3.2 What modeling tools are available to link mercury sources and
water quality?
When developing a TMDL states or 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 will typically link
together models of atmospheric deposition, watershed loading, and mercury cycling with
bioaccumulation. This enables a translation between the endpoint for the TMDL
(expressed as a fish tissue concentration of methylmercury) and the mercury loads to the
water. The analysis determines the loading capacity as a mercury loading rate consistent
with meeting the endpoint fish tissue concentration.
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 may 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 accuracy of predicted future
fish concentrations?
• Could other pollution control activities reduce mercury loads to the waterbody or
affect the mercury bioaccumulation rate?
• After implementing regulatory controls, how long will it take for fish tissue levels
to meet the criterion?
Depending on the types of questions states and 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. For more
information on the specific models described below, see http://www.epa.gov/athens and
http://www.epa.gov/crem.
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6.2.3.2.1 Steady state models
Steady state modeling describes the dynamic equilibrium between environmental media
established in response to constant loads over the long term. As such, complex mercury
cycling processes can be compressed into simple equations. One such approach,
discussed in the Mermentau/Vermillion Mercury TMDL (USEPA 200Ih), 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, derived in detail in the Mercury Maps
report (USEPA 2001a), assumes that where air deposition is the sole significant source,
the ratio of current to future fish tissue concentrations equals the ratio of current to future
air deposition loads. For the Clean Air Mercury Rule the assumptions of the Mercury
Maps steady state model were implemented. CMAQ modeled percentage changes in air
deposition under the rule were used to predict changes in fish tissue concentrations. For
example, if the air deposition model showed that the rule would result in a 10 percent
reduction air mercury deposition at a given fish tissue sample location, that sample
concentration was reduced by 10 percent. An advantage of this method is the ability to
use measured fish tissue concentrations which, by default, reflect potential variability in
bioaccumulation rates between ecosystems. Examples of the application of the Mercury
Maps assumptions can be found in the Clean Air Mercury Rule (USEPA 2005b and
USEPA 2005c).
Mass balance models are somewhat more complex implementations of the steady state
modeling approach. In place of a simple ratio, the model would describe fluxes of
mercury in and out of the model domain (e.g., impaired segment), and optionally,
balancing fluxes (e.g., methylation and demethylation) within the model domain. The
advantage of this approach is that individual fate processes, which could additionally be
controlled in a management setting, 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 the
watershed and waterbody remain unchanged, steady state models can produce as accurate
an estimate of the necessary load reductions as a dynamic model at a fraction of the cost.
Additionally, simple approaches, such as those discussed above, are less prone to
calculation errors and much easier to communicate to the public.
6.2.3.2.2 Continuous simulation and dynamic models
Continuous simulation or dynamic models take into account time varying effects such as
variable pollutant inputs, precipitation, hydrologic response, seasonal ecosystem changes,
and other effects on fish tissue concentrations. They might also include a variety of
physical and chemical fate and transport processes such as methylation, demethylation,
volatilization, sedimentation, re suspension, adsorption and desorption and so on. Such
dynamic models are important in establishing cause and effect relationships. They
assemble all available scientific knowledge on mercury fate and transport into a single
picture. Thus, they have been used to demonstrate how mercury moves from air
emissions to deposition to watershed runoff to subsequent bioaccumulation in fish at
observed levels in remote waterbodies (USEPA 1997b).
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
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TMDL pilot project (USEPA 2000b) simulated the amount of time necessary to attain
equilibrium in response to reduced mercury loads using the Everglades Mercury Cycling
Model. The model results showed sediments continued to supply as much as 5 percent of
the mercury load 100 years after air deposition reductions occurred. The 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 A) (Tetra Tech
2001).
The SERAFM model incorporates more recent advances in scientific understanding
described above and implements an updated set of the IEM-2M solids and mercury fate
algorithms that were described in the 1991 Mercury Study Report to Congress (USEPA
1997b). This model was also used in the watershed characterizations to support the
CAMR (USEPA 2005b).
Dynamic models can also describe how fish tissue concentrations are expected to respond
to environmental variability, such as seasonal or year-to-year changes in meteorology.
Thus, they can be used to belter interpret how samples collected in a specific season of a
specific year would be expected to vary relative to other seasons or years with mercury
loads being constant.
6.2.3.2.3 Spatially detailed models
Spatially detailed models, such as that used in the Savannah River TMDL (USEPA
200la), 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 WASP (Water Quality Analysis Simulation Program) model. WASP is a dynamic,
mass balance framework for modeling contaminant fate and transport in surface water
systems. This model helps users interpret and predict water quality responses to natural
phenomena and man-made pollution for various pollution management decisions.
Another model used for both mercury TMDLs and watershed characterization in the
CAMR is the EPA Region 4 Watershed Characterization System (WCS). This is a GIS-
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 the
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 is predominantly through soil erosion, erosion control might be identified as a
valid nonpoint source control on mercury to waterbodies (Balogh et al. 1998).
Additionally, controls on acid deposition and, thus, changes in lake pH and its effect on
fish tissue mercury concentrations, might also be modeled (Gilmour and Henry 1991,
Hrabik and Watras 2002). Finally, spatially detailed models can be used to reflect the
local effects of wetlands, which produce significantly more methylmercury per unit area
than other types of land use.
6.2.3.2.4 Model selection
When selecting a model, the state or authorized tribe should be aware of the assumptions
inherent in each type of model and consider what effect that assumption has on
determining the relationship between loadings and fish tissue levels or water quality. The
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TMDLs
first consideration is methylation. Several factors including pH, redox, sulfide
concentrations, temperature, DOC concentrations, salinity, and microbial populations
influence the speciation of mercury (Ullrich et al. 2001). If these factors vary seasonally
or around an average condition, the waterbody could be at a dynamic equilibrium and the
steady state assumption still apply. If these factors change with time such that they may
have a significant impact on fish tissue concentrations, the equilibrium assumptions
inherent in steady state modeling might not hold, and a dynamic model such as 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 out of equilibrium state.
The second consideration is the BAF. As discussed in section 3.1.2.2., 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 due to 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 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.
6.2.3.2.5 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 the 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., sulfide,
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 scale.
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TMDLs
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. In
addition, the expected effect of land-use changes on fish mercury concentrations for a
watershed dominated system illustrates changes like urbanization within a watershed can
alter the magnitude and timing offish mercury concentrations.
6.2.3.3 What are the allocation approaches in mercury TMDLs?
A requirement for an approvable TMDL is that the state or tribe allocate the pollutant
load necessary to achieve water quality standards among point and nonpoint sources.
However, EPA's regulations leave the decision regarding how to allocate loadings to the
state or authorized tribe developing the TMDL. States and authorized tribes may use any
method or system for allocating pollutant loads among sources, provided that the
allocations will result in attainment of water quality standards represented by the loading
capacity (40 CFR 130.2). States and authorized tribes could reasonably consider the
relative contribution of each source as one factor in developing allocations. Other factors
may 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 scenarios have occurred in mercury TMDLs, each with a
different mix of point and nonpoint sources. These scenarios have included the following:
• Point source loadings are small compared to loadings from nonpoint sources (e.g.,
atmospheric deposition), but the expected load reductions in the nonpoint sources,
together with modest reductions from the point sources, are sufficient to achieve
water quality standards.
• Point source loadings are small compared to nonpoint sources, but the expected
nonpoint source reductions are not adequate to achieve water quality standards
even if point sources cease to discharge.
• Point source loadings are not small compared to nonpoint source loadings.
Point source loadings small; nonpoint sources expected to achieve WQS—The Savannah
River mercury TMDL provides an example of the first scenario. On the basis of an
analysis of air loadings for the Savannah TMDL, CAA regulations in place when the
TMDL was developed are expected to achieve the reductions from air loadings needed to
achieve the water quality target in the TMDL. The TMDL determined that a 44 percent
reduction in mercury loadings would be needed to reach the water quality target, and a
38-48 percent reduction in mercury loadings from air sources is expected by 2010 under
air regulations in existence at that time. The air regulations identified in the TMDL
address mercury emissions from medical, municipal, and hazardous waste incinerators.
The TMDL identifies only one point source on the Georgia side of the river that has a
permit to discharge mercury to the Savannah River. It identifies 28 point sources in
Georgia that may have the potential to discharge larger amounts of mercury in their
effluent according to the nature of the discharge or on mercury levels that have been
found in their effluents above the water quality standard level.
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TMDLs
The TMDL provides specific wasteload allocations for these sources on the basis of
meeting the water quality criterion at the end of pipe or alternatively implementing a
pollutant minimization program. In addition, the TMDL identifies about 50 other point
sources expected, according to their size and nature, to either discharge mercury 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 them holding their effluents at current levels. The wasteload allocations are
expressed in the TMDL by their sum. This TMDL can be found at http://www.epa.gov/
region4/water/tmdl/georgia/index.htm.
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. However, EPA believes that
the decisions, policies, and interpretations set forth in the TMDL are still valid and serve
as one example of an approach to mercury TMDLs.
Point source loadings small; nonpoint sources not expected to achieve WQS under
current regulations—The series of mercury TMDLs issued February 28, 2002 for
watersheds in middle and south Georgia illustrate the second scenario. In these basins,
point source loadings contribute very little to the mercury loadings (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. In five out of
seven basins where load reductions are needed to meet the water quality target, the
analysis indicates that CAA air regulations in place at the time the TMDL was developed
will not achieve sufficient load reductions in the air sources to achieve the target. In the
Ochlockonee Basin, for example, a 76 percent reduction in mercury loadings is needed to
achieve the water quality target, but an analysis conducted for the TMDL indicated that a
31-41 percent reduction in air loadings would likely be achieved under air regulations in
place at that time (USEPA 2002a). In comparison, the aggregate of point sources is only
1 percent of the total load to the basin. The TMDL anticipates that there would be
additional reductions in mercury loadings due to current and planned activities. However,
as provided for under section 303(d), the TMDL quantifies the reductions needed to meet
the water quality standards.
Although point sources collectively contributed a very minute share of the mercury load,
the Ochlockonee and other mercury TMDLs for middle and south Georgia included
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 middle and south Georgia mercury TMDLs issued
February 28, 2002, can be found at http://www.epa.gov/region4/water/tmdl/
georgia/index.htm.
Point sources loadings are not small—For these TMDLs, the reductions in point source
loadings, alone or in combination with nonpoint sources, can sufficiently achieve water
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TMDLs
quality standards. In this situation, the TMDL should consider reductions in both the
point sources and nonpoint sources to achieve the water quality standard. Appendix A
provides an example of a TMDL where point source loadings of mercury from mining
areas are large.
6.2.3.4 What kind 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 criteria-end-of-pipe.
• Monitor for mercury in their influent and effluent using more sensitive analytical
techniques (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.
For other facilities expected to be discharging below the water quality target, the TMDL
expects that they will verify through monitoring whether 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 by the end of 2005, including an assessment of
all mercury sources. (See the TMDL and supporting documents at
http://oaspub.epa.gov/pls/tmdl/waters list.tmdl report?p tmdl id= 11642.)
TMDLs involving past mining activity have also included follow-up monitoring;
examples include two of the TMDLs described in Appendix A (Clear Lake, California
and Arivaca Lake, Arizona). The mercury TMDL for Arivaca Lake lists several follow-
up actions and monitoring activities, including 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 A, and the TMDL at http: //www.waterboards. ca. gov/
centralvallev/programs/tmdl/ClearLake/ClkTMDLfinal .pdf).
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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 is collected on the success of implementation activities. States may
refine information on the contributions from sources, such as runoff from abandoned
mining sites, sediment loading of mercury-laden sediments, or air deposition as data and
modeling tools improve. Thus, states should consider the application of adaptive
implementation in determining load allocations for these sources. Post-TMDL monitoring
is an important tool for evaluating implementation success and, if necessary, making
refinements in the TMDL.
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7 NPDES Implementation Procedures
The CWA prohibits the discharge of any pollutant including mercury from a point source
into waters of the United States except in compliance with an NPDES or other CWA
permit (see CWA sections 301 (a) and 402). EPA or states and tribes authorized to
administer the NPDES program issue NPDES permits. 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 WQBELs, when necessary to ensure that the receiving waters achieve applicable water
quality standards (see CWA section 301(b)(l)(C)).20
Most WQBELs are expressed as numerical 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 that result in a reduction of 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 Act (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" determination. 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 excursion above any [applicable] water
quality standard." Thus, if a pollutant discharge has the reasonable potential to cause or
contribute to an exceedence of applicable water quality standards, the discharger's
NPDES permit must contain a WQBEL for that pollutant (See 40 CFR 122.44(d)(l)(iii)-
(vi)). The procedure for determining reasonable potential must consider the variability of
the pollutant in the effluent, other loading sources, and dilution (when allowed by the
water quality standards) (See 40 CFR 122.44(d)(l)(ii)). The procedure, while specifying
whether a discharge must have WQBELs, does not specify the actual value of the permit
limitation. The Technical Support Document for Water Quality-based Toxics Control
(TSD) (USEPA 1991) contains EPA's guidance on determining reasonable potential.
20 When developing WQBELs, the permitting authority must ensure that the level of water quality achieved by such limits is "derived from
and complies with water quality standards (see 40 CFR 122.44(d)(l)(vii)(A)).
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7.2 How 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 as a fish tissue residue concentration
into their water quality standards, adopting it as a traditional water column concentration,
or adopting both the criterion as a fish tissue residue concentration and a traditional water
column translation. If states or authorized tribes choose to use both approaches, they
should clearly describe how each will be used for specific applications in their standards
and describe applicable implementation procedures.
EPA recommends three different 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 expressed the criterion (i.e., as a fish tissue value or as
a water column concentration). Additionally, states and authorized tribes that adopt the
recommended criterion as a fish tissue residue value may choose to implement it through
NPDES permitting as a water column translation of the fish tissue value. Each of these
approaches is discussed in more detail below and is summarized in Figure 5.
Is the criterion
expressed in
terms offish
tissue?
Is the criterion
implemented
in terms of
fish tissue?
Implement
using the
approaches in
the TSD (EPA,
1991a)
•Must develop
a BAP
Implement
using the
approaches in
the TSD (EPA,
199 la)
•Must develop
a BAP
Implement using the
approaches in this guidance
•Does not require developing
a BAP
Figure 5. Implementing the fish tissue criterion in NPDES permits
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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, the WQBEL for that mercury discharge must be consistent with the wasteload
allocation's assumptions (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
implementation 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 that is relevant to determining reasonable potential and establishing
effluent limits, where appropriate. If a state or authorized tribe develops its own permit
implementation procedures, EPA recommends that states and authorized tribes should
make the procedures public so that all stakeholders can be aware of the requirements and
expectations of the permit program. In addition, the permit's fact sheet or statement of
basis should also explain the basis of the permit conditions and effluent limitations and
how these are consistent with the state's or authorized tribes' implementation procedures,
the CWA, and applicable federal regulations.
7.3 What are the implementation procedures when the
criterion is adopted as a water column 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 water column concentration
value. Expressing a criterion as a water column value is very common, and permitting
authorities have considerable historical experience in implementing such criteria in
NPDES permits. Under this approach, EPA recommends that the permitting authority
make reasonable potential determinations and calculate numeric effluent limitations using
procedures consistent with those described in the TSD (USEPA 1991) or equivalent state
procedures.
This approach relies upon the measurement of mercury in effluents. Because the level of
mercury in many effluents is often very small, the permitting authority should specify
that the NPDES regulated discharger use the most sensitive analytical method approved
under 40 CFR Part 136 and report the quantitation level associated with that test.
Mercury levels in effluents can often be below the quantitation levels of some analytical
methods. By specifying the most sensitive method, the permitting authority minimizes
the chance that it would not require a WQBEL when one is actually necessary.
7.4 What are the implementation procedures when the
criterion is adopted as a fish tissue value and the
permitting authority uses a water column translation
of a 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 offish tissue, but translates it into a
water column value for use in making reasonable potential determinations and
developing appropriate numeric WQBEL when necessary. Section 3.1.2.2 of this
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guidance discusses the procedures for translating the fish tissue criterion into a water
column value for water quality standards purposes. These procedures may also be used to
translate a fish tissue criterion into a water column value for reasonable potential
determinations and numeric WQBELs. Once the criterion has been translated into a water
column value, the TSD (USEPA 1991) or equivalent state procedures can be used to
complete a reasonable potential determination and develop numeric WQBELs.
Because the level of mercury in many effluents is often very small, the permitting
authority should specify that the NPDES regulated discharger use the most sensitive
analytical method approved under 40 CFR Part 136 for total mercury and report the
quantitation level associated with that test. Federal regulations at 40 CFR 122.45(c)
generally require effluent monitoring for metal using the total form of the metal.
In addition, the permitting authority may also specify effluent monitoring using draft
EPA Method 1630 where the permitting authority is concerned about the level of
methylmercury (as opposed to total mercury) being discharged. Federal regulations at
122.41(j)(4) generally require that effluent monitoring results must be conducted
according to the test procedures approved under Part 136, unless other test procedures
have been specified in the permit.
7.5 What are the implementation procedures 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 offish tissue and directly
implements the criterion without translating it into a water column concentration. As a
result, the permitting authority will use a different approach than it has used before for
determining reasonable potential and expressing effluent limits. EPA recommends the
approach described below, which is summarized in Figure 6.
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NPDES Implementation Procedures
START of Process for Determining
Reasonable Potential Directly from a
Fish Tissue Criterion
• Monitor-asing Method
1631
• Permit re opener to
assess Reasonable
Potential after data is
collected
• Special condition to
conduct fish tissue
survey
• Permit re opener to
assess RP once fish
tissue is collected
•Develop MMP
(facilities that use or
accept mercury
Unknown
Is there
quantifiable
mercury
discharge?
Ho
•Ho necessary
conditions
Does feciliry
use or accept
mercury?
Yes
Permit needs a
WQEELfcr
Mercury
(see Figure 7)
• Consider a MMP for
facilities that use cc
ac cept mercury
Figure 6. Determining reasonable potential
7.5.1 How to determine the need for permit limits to control
mercury (i.e., how to determine reasonable potential)
As discussed in section 3.1.2.1. 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 residue concentration. When adopted in standards as a tissue value, states
and authorized tribes do not translate from a traditional water column value to a tissue
residue value using BAFs, which can vary highly by location and can be expensive. This
section provides recommendations for how a permitting authority could determine
reasonable potential in the absence of an available translation of the fish tissue value to 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 excursion
above the applicable water quality criterion (see 40 CFR 122.44(d)(l)(ii)). The NPDES
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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 CWA section
301(b)(l)(C) and 40 CFR 122.44(d)(l)(ii) with respect to a water quality criteria for
methylmercury expressed as fish tissue value, in the absence of a water column
translation of that value.
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)
fish tissue from the waterbody into which the discharger discharges exceeds the fish
tissue water quality criterion. Under these circumstances, the effluent data indicates that
the mercury loadings in the effluent contribute to the mercury load to the waterbody, and
the fish tissue indicates that the mercury load causes a water quality criterion excursion.
This approach is also consistent with federal regulations pertaining to the Great Lakes
Basin that contained an approach for determining reasonable potential using fish tissue
data (see 40 CFR Part 132, Appendix F, Procedure 5.F.4). EPA recommends that
permitting authorities use this approach because it 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 mercury present in fish tissue at levels
above the fish tissue criterion, and therefore the discharge may be found, in some
circumstances, to exhibit the reasonable potential to cause or contribute to the excursion
above applicable water quality standards. EPA notes that the reasonable potential
procedures as a whole are intended as conservative screening procedures to determine
when a permit should contain a WQBEL to reduce the contribution to existing
contamination or to prevent further possible degradation.
EPA notes that, unlike typical water quality criteria that are expressed as water column
values, the fish tissue residue water quality criterion integrates spatial and temporal
complexity and the cumulative effects of loadings from point and nonpoint sources that
occur in aquatic systems that affect methylmercury bioaccumulation, including the
effluent variability of point sources. Therefore, EPA believes that comparing the fish
tissue residue concentration in receiving water 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 residual value.
7.5.1.1 How to determine that the NPDES permitted discharger has
mercury in its effluent at quantifiable levels
EPA recommends that permitting authorities require some monitoring using the
appropriate version of Method 1631 to characterize the discharger's effluent for mercury
from all facilities for which the mercury levels are unknown or undetected. Method 1631
is relatively new, and the facility might not have used it to analyze its effluent. As a
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result, previous monitoring might show undetectable levels of mercury when use of
Method 1631 would show detectable or quantifiable amounts. As a result, EPA
recommends monitoring using Method 1631 to help identify all facilities that contribute
to mercury water quality impairment. At time of permit issuance, the permitting authority
should have at least one data point using Method 1631 as part as the permit application
submitted by the facility.
One of three outcomes will be reached in answering the first condition of the above
described reasonable potential analysis:
• It is unknown whether the discharge includes quantifiable amounts of mercury.
• The discharge does not include quantifiable amounts of mercury.
• The discharge includes quantifiable amounts.
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 using
Method 1631?
In this situation, EPA recommends the permitting authority include permit conditions
comprised of:
• Effluent monitoring using the appropriate version of Method 1631 to characterize
the discharger's effluent for mercury
• A reopener clause to identify the actions that the permitting authority may take
should the monitoring information indicate that a mercury effluent limit is
necessary
EPA recommends that permitting authorities require some monitoring, using the
appropriate version of Method 1631, by all facilities for which the mercury levels are
unknown or previously undetected to characterize the discharger's effluent for mercury,
unless prior testing was done using Method 1631. Method 1631 is relatively new, and the
facility might not have used it to analyze its effluent. As a result, the previous monitoring
might show undetectable levels of mercury when using Method 1631 would show
detectable or quantifiable amounts. As a result, EPA recommends this additional
monitoring to help identify all facilities that contribute to mercury water quality
impairment. The permitting authority could obtain this monitoring data either as part of
the permit application, by requiring periodic (e.g., quarterly to annually) monitoring as
part of the permit, or the permitting authority could invoke its authority under CWA
section 308 to require NPDES facilities to collect information necessary for the
development of NPDES permit limits. The permit should include a reopener clause such
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.
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EPA recommends that when selecting the monitoring frequency, permitting authorities
consider the factors in section 5.7.5 of the Technical Support Document for Water
Quality-based Toxics Control (USEPA 1991). This section acknowledges that EPA has
not recommended a specific monitoring frequency, but recognizes that the choice of a
monitoring frequency is a site-specific decision and provides the permitting authority a
number of factors to consider when making these decisions.
Until the permitting authority has sufficient data to determine whether there is reasonable
potential, and depending on the particular facts, these permit conditions might be
considered as being as stringent as necessary to meet 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 is
analyzed using Method 1631 and does not include quantifiable amounts of
mercury?
In this situation, EPA recommends the permitting authority first review the monitoring
data to determine if it is representative of the effluent. If the permitting authority believes
the monitoring data are representative and all data are below the level of quantification,
no further permit conditions may be necessary. If the discharge is below the level of
quantification, EPA does not consider the discharge to have reasonable potential to cause
or contribute to an excursion of the applicable fish tissue water quality criterion. 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 above.
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 evaluate data on the concentrations of
mercury in the fish tissue from the waterbody into which the discharger discharges and
determine appropriate permit conditions (see section 7.5.1.2 below).
7.5.1.2 How to determine appropriate permit conditions for facilities
discharging quantifiable amounts of mercury
When applying EPA's recommended fish tissue reasonable potential procedure, once 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. That is, does the fish tissue from the waterbody into which
the discharger discharges exceed the fish tissue water quality criterion?
One of three outcomes will be reached in answering this question:
• The fish tissue concentration of mercury is unknown.
• The fish tissue concentration of mercury does not exceed the criterion.
• The fish tissue concentration of mercury exceeds the criterion.
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For discharges with quantifiable levels of mercury, the recommended reasonable
potential determination and recommended permit conditions for each of the outcomes 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 guidance.
7.5.1.2.1 What are the recommended permit conditions for facilities discharging
quantifiable amounts of mercury but the concentrations of mercury in
tissue offish in the receiving waterbody are unknown?
In waterbodies for which there are no fish tissue data, a permitting authority cannot
determine whether there is reasonable potential using a fish tissue approach. Therefore,
EPA recommends the permitting authority include permit conditions comprised of:
• A permit special condition to conduct a mercury fish tissue survey for the receiving
water
• A reopener clause to identify the actions that the permitting authority may take
should the monitoring information indicate that a mercury effluent limit is
necessary
• A permit special condition under the authority of CWA section 402(a)(l)(B) and
40 CFR 122.44(k)(4) to develop a mercury minimization plan for facilities that use
mercury in any aspect of their operations or accept waste waters that may contain
mercury
In this instance, the permitting authority should start a process for collecting fish tissue
data in the vicinity of the facility. One approach for collecting this information is for the
permitting authority to invoke its authority under CWA section 308 (state permitting
authorities would use comparable state authorities) to require NPDES facilities to collect
information necessary for the development of NPDES permit limits. In this case, the
permitting authority could issue a section 308 letter or include special conditions in the
permit to require the permittee to conduct a methylmercury fish tissue monitoring study.
EPA recommends that the permitting authority require that the study design be consistent
with the recommendations on conducting ambient monitoring in section 4.2 of this
guidance.
EPA recommends that the permitting authority require only one study per waterbody.
The authority could do this by contacting all facilities that discharge into the waterbody
and encourage them to jointly work to conduct the study. Additionally, in waterbodies
where the permitting authority expects to find high water column values or believes it
will need a site-specific BAF to complete issuing the permits, the authority should
consider requiring the facility to measure water column concentrations of mercury as part
of the study.
EPA further recommends that the permit should include a reopener clause such 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.
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Additionally, in this situation EPA recommends that the permit should also include a
pollutant minimization plan for the reasons as described in section 7.5.1.2.2 below.
7.5.7.2.2 What are the recommended permit conditions for facilities discharging
quantifiable amounts of mercury but the concentrations of mercury in
tissue offish in the receiving waterbody do not exceed the criterion?
If the concentration of mercury in tissue offish in the receiving water does not exceed the
criterion, depending on the particular facts, the permitting authority might reasonably
conclude that the discharge does not have reasonable potential to cause or contribute to
an excursion of the applicable fish tissue water quality criterion.
In such situations, EPA recommends the permitting authority consider including permit
conditions comprised of a permit special condition under the authority of CWA section
402(a)(l)(B) and 40 CFR 122.44(k)(4) to develop a mercury minimization plan for
facilities that use mercury in any aspect of their operations or accept wastewaters that
may contain mercury.
A mercury minimization plan helps ensure that the discharge continues to have no
reasonable potential to cause or contribute to an exceedence of water quality standards.
The recommendation to consider including in the permit a requirement to develop a
mercury minimization plan is also based on the extent of potential mercury impairment
across the country and the scientific complexities of and uncertainties when assessing
mercury loadings and evaluating these effects. Given these uncertainties, a permit
requirement that a permittee at least develop a plan to minimize the discharge of mercury
would ensure that if the monitoring data demonstrates that a discharge does have
reasonable potential, the permittee and the permit writer are prepared to establish a limit
as stringent as necessary. Furthermore, EPA believes that a requirement simply to
develop a mercury minimization plan may provide dischargers of mercury with sufficient
information to voluntarily and economically reduce the discharge of mercury into our
nation's waters.
EPA recommends that facilities, when developing mercury minimization plans, start with
their existing best management plans and spill prevention and containment control plans.
Many of the activities covered by these plans can also serve to reduce mercury sources to
wastewater. In addition, for facilities that do not use mercury in any aspect of their
operations or accept wastewaters that may contain mercury, EPA does not believe these
facilities have pollution prevention opportunities and, thus, should not be required to
develop a mercury minimization plan.
The facility should determine the content of a mercury minimization plan on a case-by-
case basis. After reviewing many PMPs, EPA recommends that a plan include at least the
following elements:
• The identification and evaluation of current and potential mercury sources
• For POTWs, the 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
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• The 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, materials 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
• Monitoring to verify the results of pollution minimization efforts
7.5.1.2.3 What are the recommended permit conditions for facilities discharging
quantifiable amounts of mercury and the concentrations of mercury in
tissue offish in the receiving waterbody exceed the criterion ?
EPA believes that, depending on the particular facts, a permitting authority might
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
concentrations of mercury in tissue offish from the waterbody into which the discharger
discharges 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 how to develop appropriate WQBELs, see the following section.
7.5.2 Where reasonable potential exists, how can WQBELs be
derived from a tissue value?
As discussed in section 3.1.2.1 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 residue concentration. When adopted in standards as a tissue value, states
and authorized tribes do not translate from a tissue residue value to a traditional water
column value using BAFs, which can vary highly by location and can entail extensive
costs to develop. When developing WQBELs, the permitting authority must ensure that
the level of water quality to be achieved by such limits is "derived from and complies
with water quality standards" (see 40 CFR 122.44(d)(l)(vii)). This section provides
recommendations for how a permitting authority could derive appropriate WQBELs in
the absence of an available translation of the fish tissue value to a water column value.
The process described in this section is shown in Figure 7.
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S TART of Process for Det*nninmg the
Water Quality-based Effluent Limit
• Use sere ening tool or
TMDL analysis!*!
determine relative
contribution from point
and non-point sources
/" t the \
/' discharge i \
Unknown \ mercury / j^Q
source ? /
•Numeric limit at
existing effluent
kvels
•Compliance
monitoring using
Method 1631
MMP
•Numeric limit based on water
quality standards (either water
column, translation and applying
criteria as limit; or offset; or
based OIL TMDL or TMDL-like
anafysis
• Compliance monitoring using
Method 1631
Does the facility
use mercury in
its process or
accept
wastewater
Figure 7. Process for determining the WQBEL
EPA recommends that the permitting authority, when establishing appropriate WQBELs,
first determine whether the discharge is a significant source of mercury. EPA
recommends different WQBELs depending on whether the discharge is considered to be
significant or not significant, as described in 7.5.2.3 and 7.5.2.2, respectively. EPA's
guidance on how to determine whether a discharge is significant is described in section
7.5.2.1 below. Additionally, EPA recommends that the permitting authority, when
establishing appropriate WQBELs for a significant discharger, consider whether the
facility uses or accepts mercury in its process.
The NPDES permit fact sheet must provide an explanation that how the 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
effluent limitations and other conditions that satisfy CWA section 301(b)(l)(C) and 40
CFR 122.44(d)(l) with respect to mercury.
7.5.2.1 How to determine if the discharge is a "significant" source of
mercury
When determining the sufficiency of a WQBEL to attain and maintain water quality
standards, the permitting authority may consider the effluent controls in conjunction with
the other point and nonpoint source controls (including expected mercury reductions
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from airborne deposition as a result of existing or expected controls on air emissions) and
their cumulative effect on water quality standards attainment. Because air deposition and
other nonpoint sources are expected to play a significant role in the mercury loading to
many waters, EPA recommends that permitting authorities take into account these
loadings—and their potential change—when determining what WQBELs are appropriate.
One way of doing this is to use a screening level approach, such as that used in Mercury
Maps21 (USEPA 200Id). The Mercury Maps report identified watersheds where EPA
believed mercury air deposition likely contributed greater than 95 percent of mercury
concentrations in fish tissue. For example, mercury mines, large-producer gold mines,
and mercury-cell chlor-alkali facilities were considered significant sources on the basis of
simple presence in the watershed. Municipal wastewater treatment plants and pulp and
paper mills were considered significant when their estimated cumulative load contributed
greater than 5 percent of the estimated waterbody-delivered air deposition load. Another
option for determining the relative significance of point source discharges is to do a
TMDL, or TMDL-like analysis, as part of the permit. Depending on the facts in each
case, permitting authorities should determine what sources are potentially large sources
of mercury other than air deposition.
For a discharge not to be considered "significant," under existing loading conditions,
EPA recommends that the loading of the point source (or cumulative loading of all point
sources) to the receiving water are expected to account for a small or negligible
component of the current total mercury loadings and that, upon implementation of the
permit's mercury minimization program requirements, any further reductions from the
point source(s) would result in no discernable improvement in water quality. This is not a
situation where a wasteload allocation to a point source is increased because of an
assumption that loads from nonpoint sources will be reduced. To the contrary, this is a
situation where mercury minimization activities will maintain or reduce current point
source loadings of mercury to levels at which there are no discernible impacts to water
quality.
If permitted discharges are regulated consistent with the recommendations described in
this guidance, EPA believes that the discharge is likely to have no discernible effect on
water quality. EPA believes that discharger mercury loadings that remain following
implementation of the minimization program requirements would have no discernible
impact to water quality because, due to the large contribution of mercury from
nonpermitted sources, even entirely eliminating the point source discharges of mercury
would cause no discernible improvement to water quality. Therefore, EPA believes,
depending on the particular facts, limits on these point sources consistent with this
guidance are likely to be as stringent as necessary to implement water quality standards.
EPA notes that point source discharges of bioaccumulative chemicals like mercury might
have particular local significance apart from their contribution to the cumulative load.
Point source discharges by their nature could create hot spots where observed elevated
concentrations have potential impact on human health if fish stay in the immediate area.
Consequently, comparing contributions from the air and water sources at long distances
downstream from the point source could conceal the real impact of mercury from point
21 For more information about Mercury Maps see section 4.2.2.
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NPDES Implementation Procedures
source discharges. Instead, permitting authorities should evaluate the relative
contributions of point sources to the total load at the point of discharge. In some cases,
elevated receiving water concentrations may be dictated caused solely by the mercury
concentration in the effluent as opposed to the mercury delivered from air deposition.
7.5.2.2 What are EPA's recommended permit conditions for discharges
that are not significant sources of mercury?
Here, a permitting authority is addressing the situation where there are data showing that
there is reasonable potential and thus a WQBEL is necessary. However, if one's mercury
discharge is determined to be insignificant, EPA believes that an appropriate WQBEL
could be comprised of both of the following:
• A numeric effluent limit for the mass loading of mercury established at the existing
effluent level (or any existing numeric limit, whichever is more stringent) including
compliance monitoring using the appropriate version of Method 1631
• A permit condition to implement appropriate mercury minimization measures
identified in a mercury minimization plan
EPA believes these minimum permit conditions may be appropriate because they help to
ensure the discharge does not cause or contribute to an exceedence 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, when the discharge is
not a significant source of mercury, permit numeric effluent limits established at the
existing effluent quality (or any existing numeric limit, whichever is more stringent) and
implementation of a mercury minimization plan are likely to be as stringent as necessary
to meet water quality standards.
EPA believes that mercury reductions achieved through implementation of mercury
minimization programs could potentially result in important reductions in mercury
loadings. EPA bases this belief on its study of pollutant minimization programs and their
success in reducing loadings of mercury to the environment. See the Mercury Report to
Congress (USEPA 1997b) and draft Overview of P2 Approaches atPOTWs (USEPA
1999). These reports 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, and not 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 those products for
ones that are mercury-free or more environmentally friendly. The most cost-effective
approach for POTWs to substantially reduce mercury discharges appears to be pollution
prevention and waste minimization programs that focus on high concentration, high
volume discharges to the collection system, with considerable effort also directed at high
concentration, low volume discharges such as medical and dental facilities.
Using pollutant minimization or prevention programs can also reduce the transfer from
wastewater to other media via disposal of mercury-containing sludge that may reenter the
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environment. For example, mercury removed at a POTW through treatment is likely to
reenter the environment through POTW sludges that are then either 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 remove and recycle
mercury at the source (i.e., 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 also reduce the amount of mercury entering the environment
through other media or sources (e.g., 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, see the draft Overview of P2 Approaches at POTWs (USEPA
1999). For an example of guidance on how to develop a mercury minimization plan, see
the EPA Region 5 final document Mercury Minimization Program Guidance dated
November 2004 (http://www.epa.gov/region5/water/npdestek/
mercury_pmp nov 04 guidance .pdf). Many of the recommendations contained in the
document are drawn from existing guidance and practice of the state permitting
authorities in Region 5.
Finally, mercury is a bioaccumulative, persistent pollutant that has been linked to adverse
health effects. For example, children who 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. In this scenario, EPA believes, as a matter of policy, that
point sources that can cost effectively reduce their mercury discharges should do so.
Because air sources or historical contamination are likely dominant causes of impairment
this does not mean that point sources should not implement cost-effective, feasible
pollution prevention measures to reduce their contribution of mercury, however small, to
the environment. In short, EPA believes it is reasonable to expect that NPDES permittees
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 limits that require such implementation are likely to derive from and comply with
water quality standards as required by EPA regulations at 40 CFR 122.44(d)(vii)(A).
7.5.2.3 What are EPA's recommended permit conditions for discharges
that are significant sources of mercury?
If a facility is a significant source of mercury, the permitting authority should first
consider whether or not the facility uses mercury in its process or accepts wastewater
containing mercury when deciding on appropriate WQBELs.
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7.5.2.3.1 What are appropriate WQBELsfor significant dischargers that do not use
mercury and do not accept wastewater containing mercury in their
processes?
For significant dischargers that do not use mercury in their processes and do not accept
wastewater containing mercury, EPA believes that the permitting authority may express
the WQBEL that is comprised of the following:
• A numeric effluent limit for the mass loading of mercury established at the existing
effluent level of mercury (or any existing numeric limit, whichever is more
stringent) including compliance monitoring using the appropriate version of
Method 1631
• A permit condition to implement appropriate mercury minimization measures
identified in a mercury minimization plan
If such a discharge has the reasonable potential to cause or contribute to an exceedence of
water quality standards and the discharge is significant, EPA believes that during the first
term of the permit and depending on the particular facts, permit terms that limit the
discharge of mercury to existing effluent quality (or any existing numeric limit,
whichever is more stringent), require the facility to develop and implement a mercury
minimization plan, and require monitoring are likely to be as stringent as necessary to
meet water quality standards. Given the extent of mercury impairment across the United
States mostly due to nonpoint sources such as air deposition or previous contamination,
and that assuming these dischargers do not use or accept mercury in their processes but
rather receive it from diffuse sources, EPA believes that, depending on the particular
facts, permit conditions that prohibit an increase of mass loadings of mercury and
mandate a reduction of loadings when consistent with a mercury minimization plan are
likely to be as stringent as necessary to meet standards as required by CWA section
301(b)(l)(C). EPA generally believes these minimum permit conditions are appropriate
and sufficient to ensure the discharge does not cause or contribute to an exceedence of
water quality standards, protect against possible localized impacts, and minimize the
discharge of mercury. EPA believes these permit terms are appropriate in cases where the
facility itself does not use mercury in its processes. EPA expects that the implementation
of a mercury minimization plan will reduce the discharge of mercury. However, if at the
end of the first permit term, data and information indicate that a more stringent limit is
necessary to ensure that the discharge does not cause or contribute to an exceedence of
water quality standards, including localized effects, the permit should be revised at
renewal.
7.5.2.3.2 What are appropriate WQBELsfor significant dischargers that use
mercury in their processes or accept wastewater containing mercury?
For significant dischargers that use mercury in their processes or accept wastewater
containing mercury, EPA believes that the permitting authority may express the WQBEL
that is comprised of the following:
• A numeric WQBEL for the mass loading of mercury. Such a limit could be based
on a TMDL, a TMDL-like analysis, an offset, or established using the criteria as
the effluent limit (through development of a site-specific BAF) including
compliance monitoring using the appropriate version of EPA Method 1631
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• A permit condition to implement appropriate mercury minimization measures
identified in a mercury minimization plan
Because there are significant direct water inputs of mercury from these facilities, states
and authorized tribes should carefully consider making these watersheds a priority for
TMDL development so that the TMDL can provide the basis for the appropriate permit
limits. 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 impairment due to mercury. These situations are
more complicated because the specific location and magnitude of each source could be
significant as to its effect on fish tissue concentrations. For these situations, a TMDL
provides the best basis for developing the appropriate permit limits, and thus, these
situations should receive a higher priority for completion.
Once EPA has approved or established a TMDL containing a wasteload allocation for the
discharge of mercury, 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)). Besides developing a
WQBEL, the permitting authority also 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 the version of Method 1631 then in effect to
assure that even trace levels of mercury are quantified.
In addition, EPA recommends that the permit require the dischargers to implement
appropriate mercury minimization measures identified through the mercury minimization
plan if the monitoring data shows that mercury is present in the final effluent. In many
instances, the mercury minimization plan may be a recommended part of the wasteload
allocation. Where it is not, EPA believes that implementing the plan should help the
facility achieve the WQBEL.
In the absence of a final TMDL, a permitting authority could develop an analysis similar
to what would be provided in a TMDL. Such a TMDL-like analysis that applied similar
factors used 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.
It is also possible for the permitting authority to issue a discharger a permit prior to
TMDL development where it is demonstrated that other pollutant source reductions (such
as nonpoint source reductions implemented by the discharger or other sources) will offset
the discharge in a manner consistent with water quality standards. The ultimate result of
this type of "offset" may be a net decrease in the loadings of the pollutant of concern in
the CWA section 303(d) listed water, and therefore, the point source being permitted
might be considered as not causing or contributing to a violation of water quality
standards.
Establishing the proper WQBEL in a specific permit is a fact-based determination. There
are a number of ways to develop a permit that ensure that a discharge does not cause or
contribute to an exceedence of water quality standards. Historically, EPA has not
considered a discharge with effluent limitations at or below either the numeric water
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quality criteria or a quantification of a narrative water quality criterion to "cause or
contribute to a violation of water quality standards."
For these significant dischargers, a state or authorized tribe may decide to translate the
fish tissue criterion into a water column value for use in making reasonable potential
determinations and developing appropriate numeric WQBELs. Section 3.1.2.2 of this
guidance discusses the procedures for translating the fish tissue criterion into a water
column value for water quality standards purposes. These procedures may also be used to
translate a fish tissue criterion into a water column value for reasonable potential
determinations and numeric WQBELs. Once the criterion has been translated into a water
column value that accounts for the effects of bioaccumulation, the TSD (USEPA 1991) or
equivalent state procedures can be used to complete a reasonable potential determination
and develop numeric WQBELs. Once such a water column criteria concentration value is
developed, a WQBEL established at the criterion concentration would be appropriate for
receiving waters that exceed the fish tissue criterion.
7.5.2.4 What are EPA's recommendations for indirect dischargers to
POTWs that are significant sources of mercury?
POTWs are 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)). POTWs that accept mercury in their collections
systems may need to ensure that their pretreatment program protects the POTW's effluent
from contributing to excursions of the fish tissue criterion. The General Pretreatment
Regulations (40 CFR 403) require that each POTW required to develop an approved
pretreatment program must protect 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. POTWs are 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(1) and 403.3(n)).
Federal categorical pretreatment standards, which are applicable to certain classes of
industries, establish technology-based minimum pretreatment standards. However, the
categorical standards do not address POTW-specific problems which 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 in order to protect the treatment facilities, receiving water quality, and worker
health and safety, and to allow for beneficial use of sludge.
As described above, this guidance typically recommends that permit limits for POTWs
consist of a numeric effluent limit and a requirement to develop and implement
appropriate mercury minimization measures. EPA expects that a POTW's numeric limit
for mercury would be the basis for the development of local limits in the pretreatment
program consistent with guidance on the development of local limits. The mercury
minimization program requirements could also be the basis for establishing pollutant
minimization program requirements for dischargers to the collection system.
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7.6 What are the recommended analyses for new sources
or new dischargers discharging quantifiable amounts
of mercury?
Additional permitting requirements apply to new sources or new dischargers that will be
discharging new or increasing concentrations of pollutants. The NPDES regulations at 40
C.F.R. §122.4(i) currently prohibit the issuance of a permit to a new source or new
discharger whose discharge will cause or contribute to a violation of water quality
standards.
In addition, such increased discharges of mercury must be consistent with the applicable
antidegradation policy. Federal regulations at 40 CFR 131.6 specify that tribal or state
water quality standards must include an antidegradation policy. Federal Regulations at 40
CFR 131.12 identify the elements of an acceptable antidegradation policy. The Federal
antidegradation policy is composed of three levels of protection commonly referred to as
tiers. The first element 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 element
prohibits lowering water quality to the point where existing uses are impaired. The
second element is found at 40 CFR 131.12(a)(2), and protects water quality where water
quality is better than that needed to support designated uses in and on the water. Where
these conditions exist, the water body is 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 element at 40 CFR 131.12(a)(3) involves the protection
of water quality in water bodies that are of exceptional ecological, aesthetic or
recreational significance. Water quality in such water bodies, identified and specifically
designated by States as Outstanding National Resource Waters must be maintained and
protected.
One potential means of satisfying antidegradation (and 40 CFR 122.4(i) for new sources
or new dischargers to water quality limited segments) may be a demonstration that other
mercury source reductions (such as nonpoint source reductions implemented by the
discharger) will offset the new or increased discharge. The ultimate result of this type of
"offset" might be a net decrease in the loadings of mercury to the receiving water, and
therefore, depending on the particular facts, the discharge might not be considered an
increased loading. EPA's recommendations for addressing mercury in new sources and
new discharges are summarized in Figure 8.
7.6.1 What are the recommendations for permitting authorities
when considering issuing permits for new sources or new
dischargers where the fish tissue concentrations in the
receiving waterbody are unknown?
In waterbodies for which there are no fish tissue data, a permitting authority cannot
determine the applicable antidegradation requirements. In these instances, the permitting
authority should start a process for collecting such data in the vicinity of the facility. One
approach for collecting this information is for the permitting authority to invoke its
authority under CWA section 308 to require point sources to collect information
necessary for the development of NPDES permit limits. In this case, the permitting
authority could issue a section 308 letter to require the permittee to conduct a
methylmercury fish tissue monitoring study prior to issuance of a permit. EPA
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NPDES Implementation Procedures
recommends that the permitting authority require that the study design be consistent with
the recommendations on conducting ambient monitoring in section 4.2 of this guidance.
START Process for New Sources
New Dischargers Expected to
Discharge Mercury
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/
• C onduct a fish tis sue
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v<
•Numeric limit to prevent new or
increased loads to the waterbody that
would cause or contribute to the
impairment
•Compliance monitoring using
Method 1631
•Develop andimplementMMP
(facilities that use mercury in their
process or accept wastewater
containing mercury)
•Numeric limit based on
antide gradation
requirements (both
prevent significant
degradation and protect
designated use)
•Compliance Monitor
using Method 1631
•Develop and implement
MMP (facilities that use
mercury in their process
or accept wastewater
containing mercury)
Figure 8. Procedures for addressing new sources and new discharges
Once the permitting authority has determined the appropriate antidegradation
requirements on the basis of the fish tissue concentrations in the receiving water, the
permitting authority can then determine the appropriate permit requirements for new
sources or new dischargers, as described below.
7.6.2 What are the recommended permit conditions for new
sources or new dischargers where the fish tissue in the
receiving water does not exceed the criterion?
In this situation, EPA believes that the permitting authority may establish permit
conditions that are comprised of the following:
« A numeric effluent limitation, the level to which the discharger is ultimately
allowed to lower water quality (on the basis of the applicable antidegradation
requirements) including compliance monitoring using the appropriate version of
Method 1631
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NPDES Implementation Procedures
• A permit condition to implement appropriate mercury minimization measures
identified through the mercury minimization plan if the facility uses mercury in its
process or accepts wastewater containing mercury
In this case, the receiving water does not currently exceed the fish tissue criterion. EPA
believes that new sources or new dischargers that increase the discharge of mercury
should be required to implement mercury minimization plans and should be allowed to
discharge at levels as determined by the antidegradation analysis.
Permits for proposed new sources or new dischargers of mercury 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. Under EPA's
antidegradation regulations for water quality standards, the quality of waters belter than
levels necessary to protect human health can 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 encourages states and authorized tribes to regard any
increase in mercury used in a discharger's process or in wastewater accepted by a
discharger as a significant lowering of water quality for the purposes of triggering a tier 2
antidegradation review. If the state's or authorized tribe's antidegradation analysis
determines that the proposed lowering of water quality should not be allowable, the
permitting authority would not authorize or allow any such new or increased discharge.
Where 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 protect the minimum level of
water quality necessary to support existing uses by prohibiting lowering water quality to
the point where existing uses are impaired (see 40 CFR 131.12(a)(l).
EPA recognizes that 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. While an mercury minimization plan, to the extent that
there are available BMPs to minimize mercury discharges, may 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, unless they were causing
or contributing to a significant lowering of water quality.
In addition, EPA recommends that the permit require the dischargers to implement
appropriate mercury minimization measures identified through the mercury minimization
plan if the facility uses mercury in its process or accepts wastewater containing mercury.
22 This part of the antidegradation analysis is similar to the reasonable potential determination and WQBEL development process that a
permitting authority conducts for an existing discharger. See sections 7.5.1.2.2 and 7.5.2 for more details.
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NPDES Implementation Procedures
7.6.3 What are recommended permit conditions for new sources or
new dischargers where the fish tissue in the receiving water
exceeds the criterion?
In this situation, EPA believes that the WQBEL may be comprised of the following:
• A numeric WQBEL for the mass loading of mercury established at levels
consistent with 40 CFR 122.4(i) and 122.44(d)(l)(vii). Such a limit could be based
on a TMDL, a TMDL like analysis, or via an offset, including compliance
monitoring using the appropriate version of Method 1631
• A permit condition to implement appropriate mercury minimization measures
identified through the mercury minimization plan if the facility uses mercury in its
process or accepts wastewater containing mercury
Existing EPA regulations do not establish an absolute prohibition on new or increasing
discharges for point sources on water quality limited segments. Instead, the NPDES
regulations at 40 CFR 122.4(i) prohibit the issuance of a permit to a new source or new
discharger whose discharge will cause or contribute to a violation of water quality
standards, including the applicable antidegradation policy. A permit may be issued if the
discharge would not cause or contribute to the exceedence of the water quality standards.
For example, it is possible for a discharger to be issued a permit, under appropriate
circumstances, where it is demonstrated that other pollutant source reductions will offset
the discharge in a manner consistent with water quality standards. The ultimate result of
this type of offset may be a net decrease in the loadings of the pollutant of concern in the
impaired water and, therefore, be considered not to "cause or contribute to a violation of
water quality standards." This regulation applies only to "new sources" and "new
dischargers" as defined in sections 122.2 and 122.29 of the NPDES regulations. Existing
dischargers and increases in existing discharges are not subject to this regulation.
Existing dischargers, as well as new sources and new dischargers, are subject to the
regulation at 40 CFR 122.44(d)(l)(vii) (A). That regulation provides that when
developing water quality-based permit effluent limitations, the permitting authority is to
set the limitations to ensure that the level of water quality to be achieved "is derived
from, and complies with all applicable water quality standards." This would necessarily
be a permit-by-permit determination. After a TMDL has been established, the regulation
provides that the effluent limitations must be consistent with the assumptions and
requirements of any approved wasteload allocation (see 40 CFR 122.44(d)(l)(vii)(B)).
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 1996a).
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NPDES Implementation Procedures
7.7 What are the special conditions for mercury in a
facility's intake?
7.7.1 How to consider mercury intakes with a reasonable potential
approach
For some dischargers, the only source of mercury in a facility's discharge might be the
intake water from the same body of water as where 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 decide that there is
no reasonable potential for the discharge to exceed 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 the fish
unless the fish are known to frequently inhabit the water immediately in the area of the
discharge. In making this decision, the permitting authority should conduct monitoring of
both the intake and discharge to verify that there are no known sources of additional
contributions of mercury at the facility. Also, EPA recommends that permitting
authorities consider requiring an evaluation of whether the methylmercury concentration
significantly increases for facilities with anaerobic conditions in the discharge. This
approach is also consistent with federal regulations pertaining to the Great Lakes Basin
that contained an approach for determining reasonable potential using fish tissue data (see
40 CFR Part 132, Appendix F, Procedure 5.D).
7.7.2 How to consider mercury in intakes in WQBELs
For facilities that take in water from the same body of water that they discharge into, a no
net increase limit may be appropriate. This type of effluent limit allows a facility to
discharge into a waterbody no more mercury than it takes out of the waterbody when the
concentration of mercury in the waterbody above the facility already exceeds the water
quality criterion. EPA recommends that permits for these type of facilities contain:
• Effluent limits that constrain the mass discharges to not exceed the mass intake of
mercury from the waterbody, or if proper operation and maintenance of a facility's
treatment system results in removal of a pollutant, effluent limits that reflect these
reductions from the influent loading
• Monitoring of the influent and effluent using the current version of EPA Method
1631 to quantify the amount of mercury entering and exiting the facility
• A requirement to develop a mercury minimization plan
This approach is also consistent with federal regulations pertaining to the Great Lakes
Basin that contained an approach for determining reasonable potential using fish tissue
data (see 40 CFR Part 132, Appendix F, Procedure 5.E).
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8 Related Programs
8.1 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)23 to their
collection system and wastewater treatment plant. However, as water quality criteria,
sludge standards, and air emissions become more restrictive, even low levels of pollutants
such as mercury might cause noncompliance with these standards. As such, POTWs must
either expand pollutant control efforts or install treatment technologies to remove the
problem pollutants.
In many cases, large-scale treatment technology is either not yet available or not
economically feasible for controlling mercury at POTWs. Instead, POTWs are choosing
to develop and implement pollution prevention (P2) strategies to reduce the amount of
mercury received by the wastewater treatment plant. Although SIUs can contribute a
significant mercury load to the treatment plant, non-SIU sources can also be identified as
causing or contributing to the problem. For example, the Western Lake Superior Sanitary
District (WLSSD) determined that one SIU and many small non-SIUs (dental facilities)
contribute a major portion of the mercury in their 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 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 implementation of selected
options is integral to a successful reduction strategy. Permitting authorities developing a
P2 plan should consider a POTWs role in compliance assistance. The sections below
provide summary level guidance for developing a POTW P2 plan.
Through the pretreatment program, POTWs should 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, success of a POTW P2 effort depends upon 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). By undertaking the
23 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 a SIU on the basis that it has a reasonable potential for adversely affecting the POTW's
operation or for violating a pretreatment standard or requirement (40 CFR 403.3(t)).
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following activities prior to developing its plan, the POTW might minimize community
resistance and apathy:
• Conduct a preliminary investigation of the problem and potential sources. Verify
that the problem is not a wastewater treatment plant operational issue. Further,
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).
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.
• Establish a workgroup composed of representatives from government, industry,
community, and environmental organizations, preferably those that are either
familiar with P2 strategies or familiar 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.
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 the
most people can understand).
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Identify the goals to determine if the POTW intends to help minimize mercury
introduced to all environmental media (air, water, solid waste), known as "front-
end" P2, or merely 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/disposal of mercury-bearing wastes (e.g.,
thermometers, fluorescent light bulbs).
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 assessment techniques that identify how the POTW will monitor influent,
effluent, sludge, and sources to assess success and that identify possible follow-up
activities to ensure P2 measures continue to be implemented.
Create contingency plans that describe actions to be taken if planned efforts do not
succeed, such as obtaining 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 wastewater
treatment plant effluent mercury levels) 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.
As rules and standards pursuant to the CAA have been developed, proposed, and
promulgated since 1990, compliance by emitting sources and actions taken voluntarily
have already begun to reduce emissions of mercury to the air across the country. EPA
expects a combination of ongoing activities will continue to reduce mercury emissions to
the air over the next decade.
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, medical waste incinerators,
chlor-alkali plants, industrial boilers, 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). Most
recently, EPA issued a regulation under CAA section 111 that directly regulates mercury
emissions from coal-fired power plants (see 70 FR. 28,606 (May 18, 2005) (codified at
40 CFR Parts 60, 72, and 75) (standards for power plants)).
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The relevant regulations that EPA has issued to date under the CAA are described briefly
below.
8.2.1 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 (Dec. 19, 1995), codified at 40
CFR Part 60). These regulations cover approximately 130 existing waste-to-energy plants
and incinerators, and any new plants and incinerators built in the future. The regulations
have reduced emissions of a number of F£APs, 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 emissions
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)).
8.2.2 Medical Waste Incinerators
Medical waste incinerators (MWIs) are used by hospitals, health care facilities, and
commercial waste disposal companies to dispose of hospital waste and medical or
infectious waste. EPA adopted regulations controlling mercury emissions from MWIs on
September 15, 1997 (62 FR 48,348, codified at 40 CFR Part 60, subpart Ce). EPA
estimated that the regulations would reduce mercury emissions from these facilities by
about 90 percent, with all existing MWIs required to comply with the regulations by
September 15, 2002 (see Figure 4 (49.7 tons per year of mercury emitted from domestic
municipal waste incinerators in 1990 versus 1.6 tons per year in 1999)). At the time the
regulations were issued, EPA expected that 50 percent to 80 percent of the 2,400 then-
existing MWIs would close in response to the rule. In fact, 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 MWIs and many health care facilities have discontinued use of their
existing MWIs. Instead they have switched to other methods of waste disposal such as
off-site commercial waste disposal. EPA expected the standards to apply to between 10
and 70 new MWIs, most of which would employ mercury control technology by the
compliance deadline.
8.2.3 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). The regulations impose requirements for more stringent work
practice limits, representing the best practices from the industry, than were required by a
preexisting regulation that covered this source category. Today, there are 9 such plants in
the United States, as compared to 20 when work on the rule began. The regulations, which
require a combination of controls for point sources, such as vents and management
practices to address fugitive air emissions, will reduce mercury air emissions from existing
chlor-alkali plants by about 50 percent by the compliance date of December 19, 2006. In
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Related Programs
addition, EPA is initiating a study of fugitive mercury emissions at existing chlor-alkali
plants, which could result in the proposal of further regulatory changes in the future.
8.2.4 Industrial Boilers
In September 2004, EPA issued a final rule to limit emissions of HAP, including
mercury, from new and existing industrial, commercial, and institutional boilers and
process heaters (ICI boiler and process heaters) at major stationary sources (see 69 FR
55,218 (Sept. 13, 2004), codified at 40 CFR Part 63, Subpart DDDDD). ICI boilers and
process heaters burn coal and other substances such as wood to produce steam to generate
electricity or mechanical energy and to provide heat. ICI boilers and process heaters are
used at facilities such as refineries, chemical and manufacturing plants, and paper mills.
In addition, boilers can stand alone to provide heat for shopping malls and university
heating systems. EPA promulgated emissions limitations for mercury for all new solid
fuel boilers and process heaters and for large existing solid fuel units. EPA expects that
this rule will reduce total emissions of HAP from regulated sources by 50,000 to 58,000
tons per year (see 69 FR 55,218, 55,244). The largest segment of emissions and projected
emissions reductions from these sources involve hydrogen chloride. However, EPA
expects that the standards will reduce mercury emissions from new and existing facilities
by about 2 tons per year.
8.2.5 Hazardous Waste Combustors
In 1999, EPA established standards for HAPs, including mercury, for incinerators,
cement kilns, and lightweight aggregate kilns that burn hazardous waste under CAA
section 112 (64 FR 52,828, 53,011 (September 30, 1999)). The 1999 standards were
challenged and subsequently vacated by the United States Court of Appeals for the
District of Columbia Circuit. In 2002, EPA issued interim emission standards, which are
found at 40 CFR 63.1203 (a)(2) and (b)(2) (mercury standards for existing and new
hazardous waste burning incinerators), section 63.1204 (a)(2) and (b)(2) (mercury
standards for existing and new hazardous waste-burning cement kilns), and section
63.1205 (a)(2) and (b)(2) (mercury standards for existing and new hazardous waste-
burning lightweight aggregate kilns). Recently, EPA issued a rule that supersedes the
interim standards issued in 2002 (see 70 FR 59,402 (Oct. 12, 2005) (final standards for
hazardous air pollutants from hazardous waste combustors: Phase 1 Final Replacement
Standards and Phase II)). The October 2005 rule sets mercury standards under CAA
section 112 for specific types of sources, including some sources that were not covered
by the interim standards (e.g., liquid fuel fired boilers and solid fuel fired boilers).
8.2.6 Coal-fired Power Plants
On March 15, 2005, EPA issued the first-ever federal rule to permanently cap and reduce
mercury emissions from coal-fired power plants (see 70 FR 28606 (May 18, 2005)
(CAMR)). This rule makes the United States the first country in the world to regulate
mercury emissions from coal-fired power plants. The CAMR, which builds on EPA's
CAIR (70 FR 25,162 (May 12, 2005)), will significantly reduce mercury emissions from
coal-fired power plants. When fully implemented, CAIR and CAMR will reduce coal-
fired utility emissions of mercury from 48 tons a year to 15 tons, a reduction of nearly 70
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percent. EPA expects that air deposition from these utilities will also decrease by nearly
70 percent (see Figure 9).
Mercury Deposition in the U.S.
_«;•
'.-
e
c
i—
Total Deposition in 2001
144
Deposition from U.S. Power Plants
12
"
• 2301 depssllHin In tie L S. *oir SQLHCSS sutEtoe :f
•he L .3. ard Canada
- 2301 total deposltlwi Ir We U.S. Tram Carac 51 aid
r: L
220" deposition
ffarn U.S power ps/ils
2121 deposition
frcrn U.S p
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Related Programs
global total, and U.S. coal-fired power plants are estimated to account for only about 1
percent.
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 committed to by the American Hospital Association, will contribute
to reduced emissions from waste combustion.
For more information about CAMR and other CAA actions to control mercury, see
http://www.epa.gov/mercury/control emissions/decision.htm.
Ill
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References
9 References
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Byun, D.W., and J.K.S. Ching, Eds, 1999. Science algorithms ofEPAModels-3
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USEPA (U.S. Environmental Protection Agency). 2005a. 2004 National Listing of Fish
Advisories. EPA-823-F-05-004. U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
USEPA (U.S. Environmental Protection Agency). 2005b. Regulatory Impact Analysis of
the Clean Air Mercury Rule. Final Report. EPA-452/R-05-003. U.S. Environmental
Protection Agency, Office of Air Quality Planning and Standards, Air Quality
Strategies and Standards Division, Research Triangle Park, NC.
USEPA (U.S. Environmental Protection Agency). 2005c. Technical Support Document.
Revision of December 2000 Regulatory Finding on the Emissions of Hazardous Air
Pollutants From Electric Utility Steam Generating Units and the Removal of Coal
and Oil-Fired Electric Utility Steam Generating Units from the section 112(c) List:
Reconsideration. U.S. Environmental Protection Agency.
USEPA (U.S. Environmental Protection Agency). 2005d. Technical Support Document
for the Final Clean Air Mercury Rule: Air Quality Modeling. U.S. Environmental
Protection Agency, Office of Air Quality Planning and Standards, Research Triangle
Park, NC.
USEPA (U.S. Environmental Protection Agency). 2005e. Standards of Performance for
New and Existing Stationary Sources: Electric Utility Steam Generating Units. U.S.
Environmental Protection Agency. Fed. Regist., May 18, 2005, 70:28606.
125
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References
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Wagemann, R., E. Trebacz, R. Hunt, R., and G. Boila. 1997. Percent methylmercury and
organic mercury in tissues of marine mammals and fish using different experimental
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Watras, C.J., and N.S. Bloom. 1992. Mercury and methylmercury in individual
zooplankton: implications for bioaccumulation. Limnol. Oceanogr. 37:1313-1318.
Watras, C.J., K.A. Morrison, J.S. Host, and N.S. Bloom. 1995. Concentration of Mercury
Species in Relationship to Other Site-Specific Factors in the Surface Waters of
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Watras, C.J., R.C. Back, S. Halvorsen, R.J.M. Hudson, K.A. Morrison, and S.P. Wente.
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Environ. 219(2-3): 183-208.
WLSSD (Western Lake Superior Sanitary District). 1997. The WLSSD Commitment to
Zero Discharge. Western Lake Superior Sanitary District, Duluth, MN.
Wente, S. P. 2003. A Spatially and Temporally Variable Model of Mercury
Concentrations in Aquatic Communities with Applications to Public Health
Protection and Water Quality Assessment, Ph.D. Thesis, Purdue University.
Wente, S.P. 2004. A Statistical Model and National Data Set for Partitioning Fish-Tissue
Mercury Concentration Variation Between Spatiotemporal and Sample
Characteristic Effects. Scientific Investigation Report 2004-5199. U.S. Geological
Survey, Reston, VA.
Wren, C.D., and H.R. MacCrimmon. 1986. Comparative bioaccumulation of mercury in
two adjacent freshwater ecosystems. Water Res. 6:763-769.
Yantosca, B. 2004. GEOS-CHEMv7-01-02 User's Guide. Atmospheric Chemistry
Modeling Group, Harvard University, Cambridge, MA.
126
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
Appendix A. Synopsized Mercury TMDLs
Developed or Approved by EPA
I. Ochlockonee Watershed, Georgia
II. Arivaca Lake, Arizona
III. McPhee and Narraguinep Reservoirs, Colorado
VI. Clear Lake, California
127
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
I. Ochlockonee Watershed, Georgia
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, a numeric "interpretation" of the
narrative water quality standard was used to assure that a TMDL will protect human
health. The state of Georgia has made a numeric interpretation of their narrative water
quality standard for toxic substances at a numeric 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 grams per day or less of
freshwater fish.
This approach is consistent with EPA's recently adopted guidance value for the
protection of human health from methylmercury described in the document titled, Water
Quality Criterion for the Protection of Human Health: Methylmercury (USEPA 2001c).
The methodology uses a "weighted consumption" approach. When only trophic level 3
and 4 fish have been collected, the methodology assumes that 8 grams per day (58.4
percent) of the total fish consumption is trophic level 3 fish (e.g., catfish and sunfish) and
5.7 grams per day (41.6 percent) are 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:
Avg. Trophic Level 3 Concentration = 0.2 mg/kg
Avg. 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 of 0.3 mg/kg level. To determine this
EPA used the Methodology for Deriving Ambient Water Quality Criteria for the
Protection of Human Health (USEPA 2000e). EPA also used the recommended national
values from the Human Health 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 grams per day. For the other factors
in the calculation, bioaccumulation and fraction of methylmercury, EPA used site-
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specific data from the Ochlockonee River collected in summer of 2000 and March and
April of 2001. From this site-specific data, EPA determined a representative weighted
BAF. This BAF was calculated by taking the average calculated BAF from each of the
two trophic levels to determine a "weighted" BAF on the basis of the different
consumption rates for trophic levels and a median measured fraction methylmercury of
0.17. 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 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. There are 16 water point sources in the
Ochlockonee River watershed that could potentially have mercury in their discharge.
According to a review of the Mercury Study Report to Congress (USEPA 1997a),
significant potential air emission sources include coal-fired power plants, waste
incinerators, cement and limekilns, smelters, pulp and paper mills, 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 both wet and dry
deposition of mercury as a function of air emissions and global sources and was used to
calculate dry and wet deposition rates for south Georgia as derived by RELMAP.
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. This data was
compared with the RELMAP deposition predictions and was 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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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. This helped estimate 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 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 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 and 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 Al.
Table A1. Annual average mercury load from each subbasin
Watershed name
Barnett Creek
Middle/Lower Ochloclonee
Tired Creek
Lower Ochlockonee
Little Ochlockonee
Bridge Creek
Upper/Middle Ochlockonee
Upper Ochlockonee
Total Hg
load
(mg)
786098.4
307965.8
827172.8
359317.5
873773.4
454417.5
627746.1
766396.8
Area!
load
(mg/ha)
25.6
21.24
22.03
15.62
19.89
23.11
20.67
20.1
Impervious
area
(mg/yr)
116614.69
125771.73
252386.89
100125.11
140023.69
53496.45
152881.42
164465.44
Sediment
(mg/yr)
422879.88
89440.3
317969.16
130407.68
433136.75
261042.44
254746.48
320337
Runoff
(mg/yr)
177553.9
54786.29
194751.7
97802.16
219614.2
98468.66
182250.7
186825.6
Deposition
on water
(mg/yr)
68850
37867.5
61965
30982.5
80898.75
41310
37867.5
94668.75
WASPS (Ambrose, et al. 1988) was chosen to simulate mercury fate in the Ochlockonee
River. WASPS is a general, dynamic mass balance framework for modeling contaminant
fate and transport in surface waters. Environmental properties and chemical
concentrations are modeled as spatially constant within segments. Each variable is
advected and dispersed among water segments and exchanged with surficial benthic
segments by diffusive mixing. Sorbed or particulate fractions can settle through water
column segments and deposit to or erode from surficial benthic segments. Within the bed,
dissolved variables can migrate downward or upward through percolation and pore water
diffusion. Sorbed variables can migrate downward or upward through net sedimentation
or erosion.
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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, also for particulate material. Local equilibrium is assumed so that the
distribution of the chemical between each of the species and phases is defined by
distribution or partition coefficients. The predicted mercury concentrations are shown in
Table A2.
Table A2. 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 come into the Ochlockonee River, the
current loading conditions are evaluated and the instream concentration is determined
using the modeling approach described above. This allows 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 gives
a TMDL load of 1.22 kg/yr mercury. This 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 kilograms/year. Because EPA's assessment indicates that over 99 percent of the
current loading of mercury is from atmospheric sources, all the load reduction is being
assigned to the load allocation and no reduction is required of the wasteload allocation.
Therefore, the load allocation and the wasteload allocation for the Ochlockonee River
are:
Load allocation (atmospheric sources) = 1.16 kilograms/year
Wasteload allocation (NPDES sources) = 0.06 kilograms/year
EPA estimates that atmospheric deposition contributes over 99 percent of current
mercury loadings to the river; therefore, significant reductions in atmospheric deposition
will be necessary if the applicable water quality standard is to be attained. On the basis of
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
the total allowable load of 1.22 kilograms per 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, there are a number of activities planned or underway to address
remaining sources of mercury, and EPA expects that further reductions in mercury
loadings will occur overtime as a result of these activities. EPA is not able to estimate
the reductions in mercury deposition to the Ochlockonee River watershed that will be
achieved from future activities. However, as contemplated by CWA section 303(d)(l)(C),
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 (i.e., 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 to human fetuses even at minute quantities, and 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 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 either through the discharge of
mercury at concentrations below the applicable water quality standard of 1.6 ng/L or
through the implementation of a pollutant minimization plan.
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 less 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. However, EPA also recognizes 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' WLA will be
applied to the increment of mercury in their discharge that is above the amount of
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
mercury in their source water. EPA recommends that the permitting authority make this
choice between the two options in consultation with the affected discharger because EPA
is not able to make the case-by-case judgments in this TMDL that EPA believes are
appropriate.
II. Arivaca Lake, Arizona
Description of the Applicable Water Quality Standards
Authorities develop TMDLs to meet applicable water quality standards. These 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.
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 of development of a model and the analysis of 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 mercury
load to the lake include natural background load from the watershed, atmospheric
deposition, and possible nonpoint loading from past mining activities.
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
Watershed background load: The watershed background load of mercury was derived
from mercury in the parent rock and from the net effects of atmospheric deposition of
mercury on the watershed. Some mercury also exists within the parent rock formations of
the Arivaca watershed, although no concentrated ore deposits are known. The net
contributions of both 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. From these data, 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
itself.
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 such as bottles and plates.
Samples were taken at three different locations of the Ruby Dump: 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 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. After a
review of Mercury Study Report to Congress (USEPA 1997a) and a search of EPA's
AIRS database of permitted point sources, there are 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 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
134
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
deposition at Caballo times the rainfall depth at Arivaca. This approach was used because
volume-weighted mean concentrations are usually much more stable between sites than
wet deposition rates, which are sensitive to rainfall amount. Dry deposition at Arivaca
was then calculated as the difference between the total deposition rate at Caballo and the
estimated Arivaca wet deposition rate. The estimates derived for Arivaca were 5.3
ug/m /yr by wet deposition and 7.1 ug/m /yr by dry deposition. In sum, mercury
deposition at Arivaca is assumed to be equivalent to that estimated for Caballo, New
Mexico, but Arivaca is estimated to receive greater wet deposition and less dry deposition
than Caballo because more of the particulate mercury and reactive gaseous mercury that
contribute to dry deposition will be scavenged at a site with higher rainfall.
Loading Capacity—Linking Water Quality and Pollutant Sources
The linkage analysis defines the connection between numeric targets and identified
sources. The linkage is defined as the cause-and-effect relationship between the selected
indicators, associated numeric targets, and the identified sources. This provided the basis
for estimating total assimilative capacity and any needed load reductions. Specifically,
models of watershed loading of mercury were combined with a model of mercury cycling
and bioaccumulation in the lake. This 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 via 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 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 estimate are shown in
Table A3. A background loading estimate was first calculated, then combined with
estimates of loads from individual hot spots. The majority of the EPA sediment samples
showed no clear spatial patterns, with the exception of the hot spot area identified at
Ruby Dump. Therefore, background loading was calculated using the central tendency of
sediment concentrations from all samples excluding Ruby Dump. The background
sediment mercury concentrations were assumed to be distributed lognormally, as is
typical for environmental concentration samples, and an estimate of the arithmetic mean
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
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 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.
Table A3. 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 (grams per 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
The direct deposition of mercury from the atmosphere onto the Arivaca Lake surface was
calculated by multiplying the estimated atmospheric deposition rates times the lake
surface area, resulting in a load of 4.2 g/yr.
Lake hydrology model: The water level in Arivaca Lake is not actively managed, and
releases occur only when storage capacity is exceeded. Therefore, lake hydrology was
represented by a simple monthly water balance. Applying the water balance model
requires pan evaporation data as an input in addition to the watershed meteorological
data. Because no evaporation data were available at the local Cooperative Summary of
the Day meteorological station, pan evaporation data for Tucson were used. Pan
evaporation for 1980 through 1995 was 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
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
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 significant 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.
Results of the model calibration are shown in Table A4. The model calculations are the
predicted annual ranges after the model has reached steady state. The observed
concentrations are from July 1997.
Table A4. 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 in reserve a portion of the
loading capacity to provide a margin of safety (MOS), as provided for in the TMDL
regulation. The allocations and MOS are shown in Table A5. These allocations, from the
best currently available information, predict attainment of acceptable fish tissue
concentrations within a time horizon of approximately 10 years. A delay in achieving
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standards is unavoidable because time will be required for mercury to cycle through the
lake and food chain after load reductions occur.
Table AS. 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 the majority 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 grams mercury per year.
There are uncertainties associated with mercury sources and the linkage between mercury
sources and fish tissue concentrations in Arivaca Lake. As a result, the TMDL reserves
38.7 g-Hg/yr (25 percent of the loading capacity) for the MOS and allots the remaining
load of 116.1 g-Hg/yr for sources. Because no permitted point source discharges occur
within the Arivaca watershed, the wasteload allocation is zero and the load allocation is
116.1 g-Hg/yr.
The load allocation provides loads for three general sources: direct atmospheric
deposition onto the lake surface, hot spot loading from Ruby Dump, and generalized
background watershed loading, including mercury derived from parent rock and soil
material, small amounts of residual mercury from past mining operations, and the net
contribution of atmospheric deposition onto the watershed. Direct deposition to the lake
surface is a small part of the total load and is believed to derive from long-range transport
of global sources which are not readily controllable. The load from Ruby Dump is also
small. As a result, the TMDL does not require reductions from these sources, and their
load allocations are their existing loads.
Background watershed loading appears to be the major source of mercury to Arivaca
Lake. The intensive watershed survey conducted for this TMDL did not identify any
significant terrestrial sources of mercury. Regarding air deposition to the watershed land
surface, insufficient data were available to calculate reliable estimates of the proportion
of mercury deposited from the air that actually reaches Arivaca Lake. Therefore, a load
allocation of 111.2 g-Hg/yr was established for overall background watershed loading.
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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 reliable estimates are
unavailable, 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 may be suitable for further investigation include
the following:
• Hypolimnion aeration or mixing
• Sulfur chemistry modification
• Alum treatment
• Reduce DOC and nutrient levels
• Dredge lake sediments
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Appendix A. SynopsizedMercury 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 4 meals per month
for nonpregnant adults and 1 meal per month for women who are pregnant, nursing, or
planning to become pregnant and children 9 years of age or younger. The criterion is
applied to an average-age top predator. Within 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 on to the watershed,
including deposition and storage in snowpack.
Table A6. Summary of mercury load estimates for McPhee Reservoir
Reservoir
McPhee
Narraguinnep
Watershed
runoff
(g/yr)
2,576
2.7
Watershed
sediment
(g/yr)
222
22.7
Interbasin
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. Three large mining districts exist 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 A. SynopsizedMercury 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
McPhee and Narraguinnep Reservoirs. No direct measurements of atmospheric
deposition of mercury are available, therefore 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 O.g mg/kg
wet muscle.
Allocations
The loading capacity for McPhee Reservoir was estimated to be 2.59 kilograms mercury
per year. Narraguinnep Reservoir loading capacity was estimated at 39.1 grams of
mercury per year. This is the maximum rate of loading consistent with meeting the
numeric target of 0.5 mg/kg in fish tissue. Due to 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 kg/yr), while
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).
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Table A7. 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
2,590
Existing load
251
1030
708
141
919
3,049
Needed reduction
188
523
360
72
92
1,235
Measurements in g-Hg/yr
Table A8. 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
Measurements in g-Hg/yr
IV. Clear Lake, California
Description of the Applicable Water Quality Standards
The EPA promulgated the 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 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 to be
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 comprised of 70 percent trophic level 4 fish and 30 percent
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
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 is comprised 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 Native American Indian Tribes use
resources of the lake and its watershed.
The Clear Lake watershed lies within a region naturally enriched in mercury. The
Sulphur Bank Mercury Mine (SBMM) site, on the shores of Oak Arm, was a highly
productive source of mercury between 1872 and 1957. Similar smaller mines were 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 located 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 transport of suspended solids. The northern wetland is
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
used for cattle grazing and as a source offish, tules, and other resources used by the
members of the Elem Porno Tribe. Waste rock piles extend into the wetlands.
Inputs of mercury from SBMM are estimated to be between 1 and 568 kg/year. EPA
Superfund Program's estimate of mercury transported in ground water from the WRD is
used as the lower bound input. Regional Board staff estimate that 568 kg/year is the
maximum upper bound estimate of all inputs from SBMM, including past and continuing
contributions to the active sediment layer. This is approximately 96.5 percent of total
sources.
Ground water from SBMM appears to contribute mercury that is readily methylated,
relative to mercury from other inputs. Ground water flow from the mine site has been
detected entering Clear Lake by subsurface flow through lake sediments. Mercury in
ground water from the WRD is solubilized and likely in chemical forms that are easily
taken up by methylating bacteria. Acidic drainage from the mine site also contains high
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 in other parts of the Clear Lake. In contrast to mercury in
SBMM ground water, 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 upon flow rates. Loads in average water years are
18 kg/year. This is approximately 3 percent of 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. This is
approximately 0.3 percent of 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 affect methylation or
concentrations of methylmercury, including sulfide and sulfate concentrations,
temperature, organic carbon, and so on. Factors that affect accumulation of
methylmercury in fish include species, growth rate, prey availability, and the like. To
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
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 that
demonstrate 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 basis for the assumption of a directly proportional
relationship between mercury in fish and in surficial sediment in Clear Lake.
Concentrations of methylmercury in water and methylmercury in biota are related by
BAFs. Relationships between methylmercury in the water column and in sediment can be
described as a flux rate of methylmercury from sediment. Concentrations of
methylmercury and mercury in sediment are related through calculation of a methylation
efficiency index (ratio of methylmercury to mercury in surficial sediment).
In each of these steps in the linkage analysis, one variable is related to another by a
simple ratio or linear equation. For example, BAFs are calculated by dividing the
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, staff is unable to refine these relationships to incorporate 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 reduction of 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 in order 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 A9 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 A10. 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
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
safety in the reference doses for methylmercury that were used to develop the fish tissue
objectives. It also includes an explicit margin of safety of 10 percent to account for
uncertainty in the relationship between fish tissue concentrations and loads of mercury.
The reductions in loads of mercury from all sources are expected to result in attainment
of water quality objectives.
Table A9. Summary of mercury load allocations
Source
Clear Lake sediment
Sulphur Bank 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 A10. Sediment goals for mercury in Clear Lake
Site designation
Upper Arm
UA-03
Lower Arm
LA-03
Oaks Arm
OA-01C
OA-02C
OA-03C
OA-04C
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
0.8
1.0
16b
16b
16
10
3
a. Sediment 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).
b. Due 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.
c. Sediment goal is part of the load allocation for SBMM.
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 the 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.
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Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
Past releases from the mine site are a current source of exposure through remobilization
of mercury that exists in the lakebed sediments as a result of past releases to the lake
from the terrestrial mine site. Past active mining operations, erosion, and other mercury
transport processes at SBMM have contaminated sediment in Oaks Arm. The load
allocation assigned to SBMM includes reducing surficial sediment concentrations in
Oaks Arm by 70 percent (more at sites nearest the mine site) to meet the sediment
compliance goals in Table A10.
EPA anticipates implementing additional actions to address the ongoing surface and
ground water releases from the 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 Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) to address the
existing contamination in the lakebed sediments from past releases from the 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 currently 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 to 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 the 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 upon 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 5 years after the effective date of this amendment and
147
-------
Appendix A. SynopsizedMercury TMDLs Developed or Approved by EPA
implement load reduction plans within 5 years thereafter. The goal is to complete the load
reductions within 10 years of implementation plan approval.
The Regional Board will work with the Native American Tribes in the Clear Lake
watershed on mercury reduction programs for the tributaries and surface water runoff.
They will solicit the tribes' participation in the development of 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 of 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 of the Clear Lake watershed and depositing from air onto the lake
surface are established at the existing input rate, which is estimated to be 1 to 2 kg/year.
148
-------
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. These are repeated here to help the reader understand the development
of the 2001 criterion.
149
-------
Appendix B. Tables from Methylmercury Criteria Document
Table 5-1. Exposure parameters used in derivation of the water quality criterion. (References cited in this
table can be found in the 2001 methylmercury criteria document.)
Parameter
Body Weight, kg
Drinking Water Intake, L/day
Freshwater/Estuarine Fish Intake,
g/day
Inhalation, m3/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
(0-14 years)
30
1.0
156.3b
10.4
0.0001,0.01s
74. 9b
59.71b
152.29b
Women of
Childbearing
Age
(15-44 years)
67
2.0
165.5b
11
0.00005
91.04b
75.48b
188.35b
Adults in the
General
Population
70
2.0
17.5c24
20
0.00005
12.46C
Oc
49.16C
Source
U.S. EPA
(2000a)
U.S. EPA
(2000a)
U.S. EPA
(2000a)
U.S. EPA
(1994, 1997h)d
U.S. EPA
(1997h)
U.S. EPA
(2000b)
U.S. EPA
(2000b)
U.S. EPA
(2000b)
aPica child soil ingestion
bFor children and women of childbearing age, intake rates are estimates of "consumers only" data (as described in U.S. EPA,
2000b)
Tor adults in the general population, intake rates are estimates of all survey respondents to derive an estimate of long-term
consumption (U.S. EPA).
dlnhalation rates for children and women of childbearing age from U.S. EPA, 1997h. Inhalation rates for adults in the general
population from U.S. EPA (1994).
24 This is the 90th percentile freshwater and estuarine fish consumption value.
150
-------
Appendix B. Tables from Methylmercury Criteria Document
Table 5-14. Average Mercury Concentrations in Marine Fish and Shellfish25
(References cited in this table can be found in the 2001 methylmercury criteria
document)
Species
Concentration"
(jigHg/gWetWt.)
Species
Concentration
(jigHg/gWetWt.)
Finfish
Anchovy
Barracuda, Pacific
Cod*
Croaker, Atlantic
Eel, American
Flounder*'6
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, Rainbot
Snapper
Sturgeon
Swordfish*
Tuna*
Whiting (silver hake)*
Whitefish*
0.104
0.522b
0.176
0.035
0.1
0.135
1.327
0.176
0.1
0.25
0.235
0.95C
0.206
0.041
0.054d
Shellfish
Abalone
Clam*
Crab*
Lobster
0.016
0.023
0.117
0232
Oysters
Scallop*
Shrimp
Other shellfish*
0.023
0.042
0.047
0.012b
Molluscan Cephalopods
Octopus
0.029
Squid
0.026
'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 (U.S. EPA, 2000b).
a Mercury concentrations are fromNMFS (1978) as reported in U.S. EPA (1997d) unless otherwise noted, measured as jig of
mercury per gram wet weight of fish tissue.
b Mercury concentration data are from Stem et al. (1996) as cited in U.S. EPA (1997c).
0 Mercury concentration data are from U.S. FDA Compliance Testing as cited in U.S. EPA (1997c).
d Mercury concentration data are from U.S. FDA (1978) as cited in U.S. EPA (1997c).
e Mercury data for flounder were used to estimate mercury concentration in marine flatfish for intake calculations.
25 More current information on commercial fish and shellfish is provided by the Food and Drug Administration at
http: //www.cfsan. fda. go v/%7Efrf/sea-mehg .html
151
-------
Appendix B. Tables from Methylmercury Criteria Document
Table 5-30. 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 x ID'9
5.6 xlO'8
0
2.7 xlO'5
4.6 xlO'9
1.3 xlO'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
a 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.
152
-------
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
Method 1631,
Draft
Appendix A
Method
245. 628
Draft Method
7474
(SW-846)29
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
Sensitivity
Methylmercury
in tissue
Total mercury in
tissue, sludge,
and sediment
Total mercury in
tissue
Total mercury in
sediment and
tissue
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 (i.e., 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, SnCb
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
• NE Minnesota lake plankton,
Monson and Brezonik 199826
• 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
• NE Minnesota lake plankton,
Monson and Brezonik 199827
• Method performance testing in
freshwater and marine fish, Bloom
1989
unknown
Reference materials cited in method.
Niessen etal. 1999.
26 Used similar techniques but used a methylene chloride extraction instead of the distillation.
27 Used similar techniques but used a methylene chloride extraction instead of the distillation.
28 Provided for reference purposes only. EPA recommends use of Method 1631 for mercury for analyzing water and fish tissue.
29 Provided for reference purposes only. EPA recommends using Method 1631 for analyzing mercury for water and fish tissue.
153
-------
Appendix C. Analytical Methods
Table C2. Analytical methods for determining mercury and methylmercury in water, sediment, and other
nontissue matrices
Method
EPA 1630
UW-Madison
SOPforMeHg
Analysis
USGS
Wisconsin -
Mercury Lab
SOPs 004
USGS Open-
File Report 01-
445:
Forms/species
and applicable
matrices
Methylmercury
in water
Methylmercury in
water
Methylmercury in
water
Methylmercury in
water
Sensitivity
0.02 ng/L
0.01 ng/L
0.05 ng/L
Detection
limit cited as
0.04 ng/L
Sample preparation
Distillation with heat and N2 flow,
addition of acetate buffer and etnylation
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
• NE Minnesota lakes, Monson and
Brezonik199830
• Poplar Creek, TN CERCLA Remedial
Investigation of surface water,
sediment, and pore water, Cambell et
al. 199831
• Scheldt estuary study of water,
polychaetes, and sediments, Baeyens
etal. 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.
Note: The four methylmercury methods above are all based on the work of Bloom 1989 as modified by Horvat et al. 1993, and are
virtually identical as a result.
30 Used similar techniques but used a methylene chloride extraction instead of the distillation.
31 Used similar techniques but omitted the distillation procedure
154
-------
Appendix C. Analytical Methods
Table C2. (continued)
Method
EPA 1631
(CVAFS)
EPA 245.1
(CVAAS)
EPA 245.2
(CVAAS)
EPA 245.5
(CVAAS)
EPA 245.7
(CVAFS)
EPA 7470A
(CVAAS)
EPA 7471 B
(CVAAS)
EPA 7472
(Anodic
Stripping
Voltametry)
EPA 7473
(Thermal
decomposition,
amalgamation,
and CVAA )
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 liquid
wastes and
Ground water
Total or
dissolved
mercury in solid
wastes
semisolid wastes
Total or
dissolved
mercury in water
Mercury in water,
soil, and
sediment
Sensitivity
MDL=0.2 ng/L
ML=0.5 ng/L
200 ng/L
200 ng/L
200 ng/L
ML = 5 ng/L;
MDL= 1.8
ng/L
200 ng/L
(IDL)
200 ng/L
(IDL)
100-300 ng/L
estimated to
be as low as
20 ng/L or 20
ng/kg
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)2H2SO4, SnSO4, aeration.
Detection by CVAAS.
H2SO4 and HNO3 added, SnSO4,
NaCI-(NH2OH)2H2SO4, 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
H2SO4 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI-(NH2OH)2H2S04, SnSO4,
aeration of sample. CVAAS detection.
H2SO4 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI-(NH2OH)2H2SO4, 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 AA.
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
• Watrasetal. 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
Method is similar to and cites performance
data given in EPA 245.5
Unknown
Unknown
155
-------
Appendix C. Analytical Methods
Table C2. (continued)
Method
EPA 1620
(CVAAS)
SM3112B
(CVAAS)
*ASTM D3223-
91 (CVAAS)
*AOAC 977.22
(Atomic
absorption
spectrometry)
Forms/species
and applicable
matrices
Mercury in water,
sludge, and soil
Total or
dissolved
mercury in water
Total or
dissolved
mercury in water
Total or
dissolved
mercury in water
Sensitivity
200 ng/L
500 ng/L
500 ng/L
200 ng/L
Sample preparation
H2S04 and HNO3 added, KMnO4 ,
K2S2O8 + heat, cool +NaCI-
(NH2OH)2H2SO4, SnSO4, aeration.
CVAAS detection.
H2SO4 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI (NH2OH)2 H2S04, SnCI2 or
SnSO4, aeration. CVAAS
determination.
H2SO4 and HNO3 added, KMnO4
added, K2S2Os added + heat, cool
+NaCI (NH2OH)2 H2S04, SnSO4,
aeration. CVAAS determination.
H2S04 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
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
156
-------
Appendix D. Examples of National Deposition Monitoring Networks
Appendix D. Examples of National
Deposition Monitoring Networks
There are a number of national deposition monitoring networks that may be useful for
developing TMDLs. Networks include the National Atmospheric Deposition Program -
National Trends Network (NADP/NTN) and the 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
geographical 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 NADP/NTN results for 2003 are shown in Figure D-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, and 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 2000f)
(http ://www.epa.gov/oar/oaqps/gr8water/3rdrpt) and the Air-Water Interface Plan
Oittp ://www. epa. gov/owow/oceans/airdep/airwater_plan 16 .pdf).
157
-------
Appendix D. Examples of National Deposition Monitoring Networks
Total Mercury Concentration, 2003
n 1 • *».
'V'v -
f
Natoonal Atmosphenc Depositor PrograrrVMercury Deposition Network
184
Figure D-1 MDN data for 2003
158
-------
Appendix E. Methylmercury/Mercury Ratio Exhibited in Muscle Tissue of Various Freshwater Fish Species
Appendix E. Methylmercury/Mercury Ratio Exhibited in
Muscle Tissue of Various Freshwater Fish
Species
Source
Ecosystem type
Fish species
MethylHg/
total Hg ratio
C.R. Hammerschmidt,
J.G. Wiener, B.E.
Frazier and R.G.
Rada(1999)
Freshwater lakes in
Wisconsin, USA
Yellow perch (Perca flavescens)
mean 0.95; range from 0.84 to
0.97
D.S. Becker and G.N.
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
T.M. Grieb, C.T.
Driscoll, S.P. Gloss,
C.L Schofield, G.L
Bowie, and D.B.
Porcella(1990)
Lakes in the Upper
Michigan Peninsula,
USA
Yellow perch (Perca flavescens)
Northern pike (Esoxlucius)
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
N.S. 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
B. Lasorsa and S.
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
T. A. 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
R. Wagemann, E.
Trebacz, R. Hunt, and
G. Boila(1997)
Sampling location not
provided; presumed
to be from Canadian
waters
Walleye (Stizostedion vitreum)
mean 1.00
Note: authors did not provide
more specific information
159
-------
-------
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.
Index
ambient water quality criteria See
AWQC
antidegradation
AWQC
BAF
and Great Lakes
and model selection
and WQBEL
calculating
defined
using
weighted
best management plan
34,97-99
15,21,23,48
55
75
95
15
15
13-26
125
89
best management practices See BMP
bioaccumulation factor See BAF
biomagnification 8, 9, 45, 76
BMP 37,38,79,81
CAA 2, 69, 77, 103-7
CAIR 7, 105, 106
CAMR
analysis supporting 17, 33, 52, 67
and coal-fired power plants 105-7
and SERA FM model 74
and WCS 75
defined 7
modeling for 70
Clean Air Act See CAA
Clean Air Interstate Rule See CAIR
Clean Air Mercury Rule See CAMR
CMAQ 67,70-71
cold vapor atomic fluorescence
spectrometry (CVAFS) 42
Community Multiscale Air Quality See
CMAQ
composite samples
45, 46, 48
Consolidated Assessment and Listing
Methodology (CALM) 49
Continuing Survey of Food Intakes by
Individuals See CSFII
CSFII 27, 29, 30, 147
designated use
andCWAlOl(a) 37,55
and UAA 37
and variances 31,32
changing 38
fishable 12
protecting 1, 11, 26
detection level 2, 49
dilution flow 55
emissions
anthropogenic 7,77
controls 92,93
hourly estimates in models 70
mobility of 6
natural 7
regulations
to air
trends in
environmental justice
EPA Method 1630
EPA Method 1631
and nondetects
101, 103-7
3, 68, 74, 103-7
69
61
41,42,49
49
161
-------
Index
defined 41-43
in Michigan case study 36
in NPDES permits 86-87, 93, 99
in TMDLs 79
inWQBELs 100
EPA Method 1669 43
existing use 32, 38
exposure
and sample types 45
and the RSC 26
data in criterion calculation 13
duration in criterion calculation 12
fish tissue concentration as proxy to
19
from drinking water 14
human health effects 1, 3-4
to fish 18,22,55
to humans 26, 46, 59
facility intake 100
FDA action level 60
FDA tolerances 60
field sampling plan 25, 44-48
fish advisories
and water quality standards 57-61
EPA guidance on 44, 52-53
issued 1,6
national listing of 5
statewide 64
updating 60
fish intake rate/estimate
and trophic levels 14, 24, 50
in criterion calculation 13, 26, 27-31
limits 57-61
fish sampling guidance 24, 44-45
freshwater
and estuarine fish
age 23
and water quality criterion 13
intake See fish intake rate/estimate
mercury found in 9, 23, 48
ecosystem models 65
lakes and rivers 6
Great Lakes Guidance 35, 42, 44
human health toxicological risk
assessment 13
impairment
addressing 64
assessing 14,48-53
identifying sources of 2, 86, 94, 95
nationwide 89,95
laboratory analysis protocols 41-44
listing decisions 48-53
market-based cap-and-trade program 106
Mercury Deposition Network 71
mercury emissions
anthropogenic 7,77
controls 92,93
hourly estimates in models 70
mobility of 6
natural 7, 32, 38, 68
regulations 101, 103-7
to air 3, 68, 74, 103-7
trends in 69
Mercury Maps 64, 65-67, 73, 92
Mercury Study Report to Congress 4,
20, 34, 65, 74
mixing zone 56-57
model
continuous simulation/dynamic 66, 74
Dynamic Mercury Cycling Model (D-
MCM) 19,74
empirical bioaccumulation
18
162
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Index
mechanistic bioaccumulation 19
regression 19,51
selection of 75
spatially detailed 75
steady state/mass balance 73, 76
uncertainty 22, 71, 76
monitoring and assessment 6,41-53
National Descriptive Model of Mercury
and Fish 17,52
National Health and Nutrition
Examination Survey 4
National Lake Fish Tissue Study 5
National Listing of Fish Advisories 5
National Pollutant Discharge
Elimination System See NPDES
Overview of P2 Approaches at POTWs
93
neurological effects
nondetections
normalizing factors
NPDES
4
46,49
17, 24, 47
effluents, measurement of mercury in
36,83
fish tissue criterion, implementing 82
new sources and new discharges,
mercury in 97-99
permit special condition 88
pollutant minimization plan
defined 34
in case study 36
recommended conditions 89-90
reasonable potential determination
and fish tissue data 100
and intakes 100
defined 81
how to 84-97
process 83, 84
reopener clause 86, 87, 88
partition coefficient
127
persistent, bioaccumulative, and toxic
128
persistent, bioaccumulative, and toxic
(PBT) 94
pollution prevention 34,94,101-3
POTW 35, 68, 90, 93, 101-3
prenatal 3,94
public participation 61
publicly owned treatment works See
POTW
quality control 41,42,52
reference dose 3, 13, 26, 58
REMSAD 67,70
sampling
and BAFs 16, 23-25
and increased advisories 6
bias 5
guidance on 44-48
sediment 72,79
shellfish
advisories 53,57
andCWAlOl(a) 37
in criterion calculation 13
intake rates 29, 30
to be monitored 44
significant industrial users 101
site-specific procedure 15-25, 55, 57, 72,
85
sources
atmospheric3, 6-9, 32, 65-67, 68-71,
106
background levels in soil 39, 72
human activity 7, 8, 72, 77
mining 7, 39, 66, 67, 72, 78
163
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Index
natural
7, 8, 32, 38, 68, 72
use attainability analysis (UAA) 37-39
point sources 8, 31, 39, 56, 67, 68, 77,
92
variances
sediment
3, 9, 72-76, 95
spill prevention and containment control
plan 89
tissue concentration-based standard 12,
13, 15
tissue residue value
TMDL
allocation approaches
best uses
challenges
defined
examples
1,55,82,85,90
63-79
76
63
10
63
See Appendix A
monitoring provisions 78
pollutant loading scenario 77
Total Maximum Daily Loads See TMDL
translation factor 1, 16-23, 82-97
uncertainty
accuracy 13
assessing loadings 89
BAFs 17, 20, 22, 24
from extrapolating results 19
in TMDL 63
Mercury Maps 67
model 22, 71, 76
precision 13
reducing 15
RfD 3
34
31
34
36
33
34
33
31
34
antidegradation
how they apply
large-scale
multiple discharger
performance-based approach
pollutant minimization plans
time frames
when appropriate
wildlife
water column concentrations 21, 56, 89
water quality criteria See also AWQC
and BAFs 23
and fish advisories 59
and Methods 1630, 1631 42, 43
components 12
defined 11
recommendation 12, 30, 84
water quality limited segments 97, 99
water quality-based effluent limits See
WQBEL
WQBEL
and mercury intakes
and variances
components
defined
deriving
determining need for
forms of
100
31
99
14
90-97
84-86
81
164
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