Office of Water

EPA 823-B-94-005a

August 1994

Water Quality Standards Handbook 

Chapter 3: Water Quality Criteria
Water Quality Standards Handbook 

CHAPTER 3: WATER QUALITY CRITERIA 

 

 

(40 CFR 131.11 ) 

 

CHAPTER 3 WATER QUALITY CRITERIA .............................................................................................. 1

3.1 EPA Section 304(a) Guidance.................................................................................................. 1

3.1.1 State Use of EPA Criteria Documents............................................................................... 1

3.1.2 Criteria for Aquatic Life Protection.................................................................................. 2

Magnitude for Aquatic Life Criteria ............................................................................................. 3

Duration for Aquatic Life Criteria ................................................................................................ 3

Frequency for Aquatic Life Criteria.............................................................................................. 3

3.1.3 Criteria for Human Health Protection .............................................................................. 4

Magnitude and Duration............................................................................................................. 4

Human Exposure Considerations ................................................................................................ 5

Fish Consumption Values ........................................................................................................... 5

Bioaccumulation Considerations................................................................................................. 6

Table 3-1. Estimated Food Chain Multipliers (FMs) ................................................................... 8

Updating Human Health Criteria Using IRIS .................................................................................... 9

Figure 3-1. Procedure for determining an updated criterion using IRIS data. ........................... 10

Calculating Criteria for Non-carcinogens.................................................................................. 10

Exhibit 3-1. Equation for Deriving Human Health Criteria Based on Noncarcinogenic Effects ...... 11

Calculating Criteria for Carcinogens ......................................................................................... 11

Exhibit 3-2. Equation for Deriving Human Health Criteria Based on Carcinogenic Effects ............ 12

Deriving Quantitative Risk Assessments in the Absence of IRIS Values ...................................... 13

3.2 Section 304(a) Criteria to State Designated Uses .................................................................. 13

3.2.1 Recreation.................................................................................................................... 13

3.2.2 Aquatic Life .................................................................................................................. 14

3.2.3 Agricultural and Industrial Uses.................................................................................... 14
3.2.4 Public Water Supply ...................................................................................................... 14

3.3 State Criteria Requirements ................................................................................................. 15

3.4 Criteria for Toxicants........................................................................................................... 16

3.4.1 Priority Toxic Pollutant Criteria ..................................................................................... 17

General Requirements .............................................................................................................. 17

State Options............................................................................................................................ 19

OPTION 1: ................................................................................................................................ 20

OPTION 3: ................................................................................................................................ 23

Criteria Based on Biological Monitoring .................................................................................... 28

3.4.2 Criteria for Nonconventional Pollutants ........................................................................ 29

3.5 Forms of Criteria.................................................................................................................. 29

3.5.1 Numeric Criteria ........................................................................................................... 29

3.5.2 Narrative Criteria .......................................................................................................... 30

All waters, including those within mixing zone, shall be free from substances attributable to 

wastewater discharge or other pollutant sources that: .............................................................. 30

1. Settle to form objectionable deposits; .............................................................................. 30

2. Float as debris, scum, oil, or other matter forming nuisances;.......................................... 30

3. Produce objectionable color, odor, taste, or turbidity;...................................................... 30

4. Cause injury to or are toxic to, or produce adverse physiological responses in humans, 

animals, or plants; or ............................................................................................................... 30

5. Produce undesirable or nuisance aquatic life (54 F.R.28627, July 6, 1989). ...................... 30

Exhibit 3-3. Components of a State Implementation Procedure for Narrative Toxics Criteria..... 30

3.5.3 Biological Criteria ......................................................................................................... 32

Regulatory Bases for Biocriteria ................................................................................................ 32

Development and Implementation of Biocriteria........................................................................... 33

3.5.4 Sediment Criteria.......................................................................................................... 34

Chemical Approach to Sediment Criteria Development................................................................. 35

Application of Sediment Criteria ............................................................................................... 35

Specific Applications ................................................................................................................ 36

Sediment Criteria Status .............................................................................................................. 37

Science Advisory Board Review ................................................................................................. 37

Sediment Criteria Documents and Application Guidance ........................................................... 37

Methodology for Developing Sediment Criteria for Metal Contaminants.................................... 37
Biological Approach to Sediment Criteria Development............................................................. 37

3.5.5 Wildlife Criteria............................................................................................................. 38

Statutory and Regulatory Authority........................................................................................... 38

Wildlife Protection in Current Aquatic Criteria........................................................................... 38

3.5.6 Numeric Criteria for Wetlands....................................................................................... 40

3.6 Policy on Aquatic Life Criteria for Metals .............................................................................. 41

3.6.1 Background .................................................................................................................. 41

3.6.2 Expression of Aquatic Life Criteria................................................................................ 42

Dissolved Criteria ..................................................................................................................... 43

Site-Specific Criteria Modifications ........................................................................................... 43

3.6.3 Total Maximum Daily Loads (TMDLs) and National Pollutant Discharge Elimination System 

(NPDES) Permits........................................................................................................................... 44

Dynamic Water Quality Modeling .............................................................................................. 44

Dissolved-Total Metal Translators ............................................................................................ 44

3.6.4 Guidance on Monitoring ............................................................................................... 45

Use of Clean Sampling and Analytical Techniques..................................................................... 45

Use of Historical Data ............................................................................................................... 46

3.7 Site-Specific Aquatic Life Criteria ......................................................................................... 46

3.7.1 History of Site-Specific Criteria Guidance ..................................................................... 47

3.7.2 Preparing to Calculate Site-Specific Criteria.................................................................. 48

3.7.3 Definition of a Site........................................................................................................ 49

3.7.4 The Recalculation Procedure......................................................................................... 50

3.7.5 The Water-Effect Ratio (WER) Procedure........................................................................ 52

Water-Effect Ratios in the Derivation of Site-Specific Criteria.................................................... 52

Option 1:.................................................................................................................................. 52

Option 2:.................................................................................................................................. 53

3.7.6 The Resident Species Procedure ................................................................................... 53

Endnotes ........................................................................................................................................ 54
1 

CHAPTER 3 WATER QUALITY CRITERIA 

The term "water quality criteria" has two different definitions under the Clean Water Act (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 (see section 3.1 of this Handbook). The States may use these contents as the 

basis for developing enforceable water quality standards. Water quality criteria are also elements of 

State water quality standards adopted under section 303(c) of the CWA (see sections 3.2 through 3.6 

of this Handbook). States are required to adopt water quality criteria that will protect the designated 

use(s) of a water body. These criteria must be based on sound scientific rationale and must contain 

sufficient parameters or constituents to protect the designated use. 

3.1 EPA Section 304(a) Guidance 

EPA and a predecessor agency have produced a series of scientific water quality criteria guidance 

documents. Early Federal efforts were the "Green Book" (FWPCA, 1968) and the "Red Book" (USEPA, 

1976). EPA also sponsored a contract effort that resulted in the "Blue Book" (NAS/NAE, 1973). These 

early efforts were premised on the use of literature reviews and the collective scientific judgment of 

Agency and advisory panels. However, when faced with the need to develop criteria for human 

health as well as aquatic life, the Agency determined that new procedures were necessary. 

Continued reliance solely on existing scientific literature was deemed inadequate because essential 

information was not available for many pollutants. EPA scientists developed formal methodologies 

for establishing scientifically defensible criteria. These were subjected to review by the Agency's 

Science Advisory Board of outside experts and the public. This effort culminated on November 28, 

1980, when the Agency published criteria development guidelines for aquatic life and for human 

health, along with criteria for 64 toxic pollutants (USEPA, 1980a,b). Since that initial publication, the 

aquatic life methodology was amended (Appendix H), and additional criteria were proposed for 

public comment and finalized as Agency criteria guidance. EPA summarized the available criteria 

information in the "Gold Book" (USEPA, 1986a), which is updated from time to time. However, the 

individual criteria documents (see Appendix I), as updated, are the official guidance documents.

EPA's criteria documents provide a comprehensive toxicological evaluation of each chemical. For 

toxic pollutants, the documents tabulate the relevant acute and chronic toxicity information for 

aquatic life and derive the criteria maximum concentrations (acute criteria) and criteria continuous 

concentrations (chronic criteria) that the Agency recommends to protect aquatic life resources. The 

methodologies for these processes are described in Appendices H and J and outlined in sections 

3.1.2 and 3.1.3 of this Handbook

3.1.1 State Use of EPA Criteria Documents 

EPA's water quality criteria documents are available to assist States in: 
2 

 adopting water quality standards that include appropriate numeric water quality 

criteria; 

 interpreting existing water quality standards that include narrative "no toxics in toxic 

amounts" criteria; 

 making listing decisions under section 304(1) of the CWA; 

 writing water quality-based NPDES permits and individual control strategies; and 

 providing certification under section 401 of the CWA for any Federal permit or license 

(e.g., EPA-issued NPDES permits, CWA section 404 permits, or Federal Energy 

Regulatory Commission licenses). 

In these situations, States have primary authority to determine the appropriate level to protect 

human health or welfare (in accordance with section 303(c)(2) of the CWA) for each water body. 

However, under the Clean Water Act, EPA must also review and approve State water quality 

standards; section 304(1) listing decisions and draft and final State-issued individual control 

strategies; and in States where EPA writes NPDES permits, EPA must develop appropriate water 

quality-based permit limitations. The States and EPA therefore have a strong interest in assuring 

that the decisions are legally defensible, are based on the best information available, and are subject 

to full and meaningful public comment and participation. It is very important that each decision be 

supported by an adequate record. Such a record is critical to meaningful comment, EPA's review of 

the State's decision, and any subsequent administrative or judicial review. 

Any human health criterion for a toxicant is based on at least three interrelated considerations: 

 cancer potency or systemic toxicity, 

 exposure, and 

 risk characterization. 

States may make their own judgments on each of these factors within reasonable scientific bounds, 

but documentation to support their judgments, when different from EPA's recommendation, must be 

clear and in the public record. If a State relies on EPA's section 304(a) criteria document (or other 

EPA documents), the State may reference and rely on the data in these documents and need not 

create duplicative or new material for inclusion in their records. However, where site-specific issues 

arise or the State decides to adopt an approach to any one of these three factors that differs from 

the approach in EPA's criteria document, the State must explain its reasons in a manner sufficient for 

a reviewer to determine that the approach chosen is based on sound scientific rationale (40 CFR 

131.11(b)). 

3.1.2 Criteria for Aquatic Life Protection 

The development of national numerical water quality criteria for the protection of aquatic organisms 

is a complex process that uses information from many areas of aquatic toxicology. (See Appendix H 

for a detailed discussion of this process.) After a decision is made that a national criterion is needed 
3

for a particular material, all available information concerning toxicity to, and bioaccumulation by, 

aquatic organisms is collected and reviewed for acceptability. If enough acceptable data for 48- to 

96-hour toxicity tests on aquatic plants and animals are available, they are used to derive the acute 

criterion. If sufficient data on the ratio of acute to chronic toxicity concentrations are available, they 

are used to derive the chronic or long-term exposure criteria. If justified, one or both of the criteria 

may be related to other water quality characteristics, such as pH, temperature, or hardness. 

Separate criteria are developed for fresh and salt waters.

The Water Quality Standards Regulation allows States to develop numerical criteria or modify EPA's 

recommended criteria to account for site-specific or other scientifically defensible factors. Guidance 

on modifying national criteria is found in sections 3.6 and 3.7. When a criterion must be developed

for a chemical for which a national criterion has not been established, the regulatory authority 

should refer to the EPA guidelines (Appendix H).

Magnitude for Aquatic Life Criteria 

Water quality criteria for aquatic life contain two expressions of 

allowable magnitude: a criterion maximum concentration (CMC) to 

protect against acute (short-term) effects; and a criterion continuous 

concentration (CCC) to protect against chronic (long-term) effects. 

EPA derives acute criteria from 48- to 96-hour tests of lethality or 

immobilization. EPA derives chronic criteria from longer term (often 

greater than 28-day) tests that measure survival, growth, or reproduction. Where appropriate, the 

calculated criteria may be lowered to be protective of commercially or recreationally important 

species.

Duration for Aquatic Life Criteria 

The quality of an ambient water typically varies in response to variations of effluent quality, stream 

flow, and other factors. Organisms in the receiving water are not experiencing constant, steady 

exposure but rather are experiencing fluctuating exposures, including periods of high 

concentrations, which may have adverse effects. Thus, EPA's criteria indicate a time period over 

which exposure is to be averaged, as well as an upper limit on the average concentration, thereby 

limiting the duration of exposure to elevated concentrations. For acute criteria, EPA recommends an 

averaging period of 1 hour. That is, to protect against acute effects, the 1-hour average exposure 

should not exceed the CMC. For chronic criteria, EPA recommends an averaging period of 4 days. 

That is, the 4-day average exposure should not exceed the CCC.

Frequency for Aquatic Life Criteria 

To predict or ascertain the attainment of criteria, it is necessary to specify the allowable frequency 

for exceeding the criteria. This is because it is statistically impossible to project that criteria will 

never be exceeded. As ecological communities are naturally subjected to a series of stresses, the 
4 

allowable frequency of pollutant stress may be set at a value that does not significantly increase the 

frequency or severity of all stresses combined. 

EPA recommends an average frequency for excursions of both acute and chronic criteria not to 

exceed once in 3 years. In all cases, the recommended frequency applies to actual ambient 

concentrations, and excludes the influence of measurement imprecision. EPA established its 

recommended frequency as part of its guidelines for deriving criteria (Appendix H). EPA selected the 

3-year average frequency of criteria exceedence with the intent of providing for ecological recovery 

from a variety of severe stresses. This return interval is roughly equivalent to a 7Q10 design flow 

condition. Because of the nature of the ecological recovery studies available, the severity of criteria 

excursions could not be rigorously related to the resulting ecological impacts. Nevertheless, EPA 

derives its criteria intending that a single marginal criteria excursion (i.e., a slight excursion over a 

1-hour period for acute or over a 4-day period for chronic) would require little or no time for 

recovery. If the frequency of marginal criteria excursions is not high, it can be shown that the 

frequency of severe stresses, requiring measurable recovery periods, would be extremely small. EPA 

thus expects the 3-year return interval to provide a very high degree of protection. 

3.1.3 Criteria for Human Health Protection 

This section reviews EPA's procedures used to develop assessments of human health effects in 

developing water quality criteria and reference ambient concentrations. A more complete human 

health effects discussion is included in the Guidelines and Methodology Used in the Preparation of 

Health Effects Assessment Chapters of the Consent Decree Water Documents (Appendix J). The 

procedures contained in this document are used in the development and updating of EPA water 

quality criteria and may be used in updating State criteria and in developing State criteria for those 

pollutants lacking EPA human health criteria. The procedures may also be applied as site-specific 

interpretations of narrative standards and as a basis for permit limits under 40 CFR 122.44 (d)(1)(vi). 

Magnitude and Duration 

Water quality criteria for human health contain only a single expression of allowable magnitude; a 

criterion concentration generally to protect against long-term (chronic) human health effects. 

Currently, national policy and prevailing opinion in the expert community establish that the duration 

for human health criteria for carcinogens should be derived assuming lifetime exposure, taken to be 

a 70-year time period. The duration of exposure assumed in deriving criteria for noncarcinogens is 

more complicated owing to a wide variety of endpoints: some developmental (and thus age-specific 

and perhaps gender-specific), some lifetime, and some, such as organoleptic effects, not durationrelated at all. Thus, appropriate durations depend on the individual noncarcinogenic pollutants and 

the endpoints or adverse effects being considered. 

 
5

Human Exposure Considerations 

A complete human exposure evaluation for toxic pollutants of concern for bioaccumulation would 

encompass not only estimates of exposures due to fish consumption but also exposure from 

background concentrations and other exposure routes, The more important of these include 

recreational and occupational contact, dietary intake from other than fish, intake from air inhalation, 

and drinking water consumption. For section 304(a) criteria development, EPA typically considers 

only exposures to a pollutant that occur through the ingestion of water and contaminated fish and 

shellfish. This is the exposure default assumption, although the human health guidelines provide 

for considering other sources where data are available (see 45 F.R. 79354). Thus the criteria are 

based on an assessment of risks related to the surface water exposure route only (57 F.R. 60862-3).

The consumption of contaminated fish tissue is of serious concern because the presence of even 

extremely low ambient concentrations of bioaccumulative pollutants (sublethal to aquatic life) in 

surface waters can result in residue concentrations in fish tissue that can pose a human health risk. 

Other exposure route information should be considered and incorporated in human exposure 

evaluations to the extent available.

Levels of actual human exposures from consuming contaminated fish vary depending upon a 

number of case-specific consumption factors. These factors include type of fish species consumed, 

type of fish tissue consumed, tissue lipid content, consumption rate and pattern, and food 

preparation practices. In addition, depending on the spatial variability in the fishery area, the 

behavior of the fish species, and the point of application of the criterion, the average exposure of 

fish may be only a small fraction of the expected exposure at the point of application of the 

criterion. If an effluent attracts fish, the average exposure might be greater than the expected 

exposure.

With shellfish, such as oysters, snails, and mussels, whole-body tissue consumption commonly 

occurs, whereas with fish, muscle tissue and roe are most commonly eaten. This difference in the 

types of tissues consumed has implications for the amount of available bioaccumulative 

contaminants likely to be ingested. Whole-body shellfish consumption presumably means ingestion 

of the entire burden of bioaccumulative contaminants. However, with most fish, selective cleaning 

and removal of internal organs, and sometimes body fat as well, from edible tissues, may result in 

removal of much of the lipid material in which bioaccumulative contaminants tend to concentrate.

Fish Consumption Values 

EPA's human health criteria have assumed a human body weight of 70 kg and the consumption of 

6.5 g of fish and shellfish per day. Based on data collected in 1973-74, the national per capita 

consumption of freshwater and estuarine fish was estimated to average 6.5 g/day. Per capita 

consumption of all seafood (including marine species) was estimated to average 14.3 g/day. The 

95th percentile for consumption of all seafood by individuals over a period of 1 month was 
6

estimated to be 42 g/day. The mean lipid content of fish and shellfish tissue consumed in this study 

was estimated to be 3.0 percent (USEPA, 1980c). 

Currently, four levels of fish and shellfish consumption are provided in EPA guidance (USEPA, 1991a):

 6.5 g/day to represent an estimate of average consumption of fish and shellfish from 

estuarine and freshwaters by the entire U.S. population. This consumption level is 

based on the average of both consumers and nonconsumers of.

 20 g/day to represent an estimate of the average consumption of fish and shellfish 

from marine, estuarine, and freshwaters by the U.S. population. This average 

consumption level also includes both consumers and nonconsumers of.

 165 g/day to represent consumption of fish and shellfish from marine, estuarine, 

and freshwaters by the 99.9th percentile of the U.S. population consuming the most 

fish or seafood.

 180 g/day to represent a "reasonable worst case" based on the assumption that 

some individuals would consume fishand shellfish at a rate equal to the combined 

consumption of red meat, poultry, fish, and shellfish in the United States. 

EPA is currently updating the national estuarine and freshwater fish and shellfish consumption 

default values and will provide a range of recommended national consumption values. This range 

will include: 

 mean values appropriate to the population at large; and 

 values appropriate for those individuals who consume a relatively large proportion of 

fish and shellfish in their diets (maximally exposed individuals). 

Many States use EPA's 6.5 g/day consumption value. However, some States use the abovementioned 20 g/day value and, for saltwaters, 37 g/day. In general, EPA recommends that the 

consumption values used in deriving criteria from the formulas in this chapter reflect the most 

current, relevant, and/or site-specific information available.

Bioaccumulation Considerations 

The ratio of the contaminant concentrations in fish tissue versus that in water is termed either the 

bioconcentration factor (BCF) or the bioaccumulation factor (BAF). Bioconcentration is defined as 

involving contaminant uptake from water only (not from food). The bioaccumulation factor (BAF) is 

defined similarly to the BCF except that it includes contaminant uptake from both water and food. 

Under laboratory conditions, measurements of tissue/water partitioning are generally considered to 

involve uptake from water only. On the other hand, both processes are likely to apply in the field 

since the entire food chain is exposed.

The BAF/BCF ratio ranges from 1 to 100, with the highest ratios applying to organisms in higher 

trophic levels, and to chemicals with logarithm of the octanol-water partitioning coefficient (log P) 

close to 6.5.
7

Bioaccumulation considerations are integrated into the criteria equations by using food chain 

multipliers (FMs) in conjunction with the BCF. The bioaccumulation and bioconcentration factors for 

a chemical are related as follows:

BAF = FM x BCF

By incorporating the FM and BCF terms into the criteria equations, bioaccumulation can be 

addressed.

*These recommended FMs are conservative estimates; FMs for log P values greater than 6.5 may 

range from the values given to as low as 0.1 for contaminants with very low bioavailability.

In Table 3-1, FM values derived from the work of Thomann (1987, 1989) are listed according to log 

P value and trophic level of the organism. For chemicals with log P values greater than about 7, 

there is additional uncertainty regarding the degree of bioaccumulation, but generally, trophic level 

effects appear to decrease due to slow transport kinetics of these chemicals in fish, the growth rate 

of the fish, and the chemical's relatively low bioavailability. Trophic level 4 organisms are typically 

the most desirable species for sport fishing and, therefore, FMs for trophic level 4 should generally 

be used in the equations for calculating criteria. In those very rare situations where only lower 

trophic level organisms are found, e.g., possibly oyster beds, an FM for a lower trophic level might 

be considered. 

Measured BAFs (especially for those chemicals with log P values above 6.5) reported in the literature 

should be used when available. To use experimentally measured BAFs in calculating the criterion, 

the (FM x BCF) term is replaced by the BAF in the equations in the following section. Relatively few 

BAFs have been measured accurately and reported, and their application to sites other than the 

specific ecosystem where they were developed is problematic and subject to uncertainty. The option 

is also available to develop BAFs experimentally, but this will be extremely resource intensive if done 

on a site-specific basis with all the necessary experimental and quality controls.

 

 
8 

Table 3-1. Estimated Food Chain Multipliers (FMs) 

Trophic Levels

Log P 2 3 4

3.5 1.0 1.0 1.0

3.6 1.0 1.0 1.0

3.7 1.0 1.0 1.0

3.8 1.0 1.0 1.0

3.9 1.0 1.0 1.0

4.0 1.1 1.0 1.0

4.1 1.1 1.1 1.1

4.2 1.1 1.1 1.1

4.3 1.1 1.1 1.1

4.4 1.2 1.1 1.1

4.5 1.2 1.2 1.2

4.6 1.2 1.3 1.3

4.7 1.3 1.4 1.4

4.8 1.4 1.5 1.6

4.9 1.5 1.8 2.0

5.0 1.6 2.1 2.6

5.1 1.7 2.5 3.2

5.2 1.9 3.0 4.3

5.3 2.2 3.7 5.8

5.4 2.4 4.6 8.0

5.5 2.8 5.9 11

5.6 3.3 7.5 16

5.7 3.9 9.8 23

5.8 4.6 13 33

5.9 5.6 17 47

6.0 6.8 21 67

6.1 8.2 25 75

6.2 10 29 84

6.3 13 34 92

6.4 15 39 98

6.5 19 45 100

≥6.5 19.2* 45* 100*

 
9

Updating Human Health Criteria Using IRIS 

EPA recommends that States use the most current risk information in the process of updating human 

health criteria. The Integrated Risk Information System (IRIS) (Barns and Dourson, 1988; Appendix 

N) is an electronic data base of the USEPA that provides chemical-specific risk information on the 

relationship between chemical exposure and estimated human health effects. Risk assessment 

information contained in IRIS, except as specifically noted, has been reviewed and agreed upon by an 

interdisciplinary group of scientists representing various Program Offices within the Agency and 

represent an Agency-wide consensus. Risk assessment information and values are updated on a 

monthly basis and are approved for Agency-wide use. IRIS is intended to make risk assessment 

information readily available to those individuals who must perform risk assessments and also to 

increase consistency among risk assessment/risk management decisions.

IRIS contains two types of quantitative risks values: the oral Reference Dose (RfD) and the 

carcinogenic potency estimate or slope factor. The RfD (formerly known as the acceptable daily 

intake or ADI) is the human health hazard assessment for noncarcinogenic (target organ) effects. 

The carcinogenic potency estimate (formerly known as q1*) represents the upper bound cancercausing potential resulting from lifetime exposure to a substance. The RfD or the oral carcinogenic 

potency estimate is used in the derivation of EPA human health criteria. 

EPA periodically updates risk assessment information, including RfDs, cancer potency estimates, and 

related information on contaminant effects, and reports the current information on IRIS. Since IRIS 

contains the Agency's most recent quantitative risk assessment values, current IRIS values should be 

used by States in updating or developing new human health criteria. This means that the 1980 

human health criteria should be updated with the latest IRIS values. The procedure for deriving an 

updated human health water quality criterion would require inserting the current Rfd or carcinogenic 

potency estimate on IRIS into the equations in Exhibit 3.1 or 3.2, as appropriate. 

Figure 3-1 shows the procedure for determining an updated criterion using IRIS data. If a chemical 

has both carcinogenic and non-carcinogenic effects, i.e., both a cancer potency estimate and a RfD, 

both criteria should be calculated. The most stringent criterion applies
10

Figure 3-1. Procedure for determining an updated criterion using IRIS data. 

Calculating Criteria for Non-carcinogens 

The RfD is an estimate of the daily exposure to the human population that is likely to be without 

appreciable risk of causing deleterious effects during a lifetime. The RfD is expressed in units of mg 

toxicant per kg human body weight per day. 

RfDs are derived from the "no-observed-adverse-effect level" (NOAEL) or the "lowest-observedadverse-effect level" (LOAEL) identified from chronic or subchronic human epidemiology studies or 

animal exposure studies. (Note: "LOAEL" and "NOAEL" refer to animal and human toxicology and are 

therefore distinct from the aquatic toxicity terms "no-observed-effect concentration" (NOEC) and 

"lowest-observed-effect concentration" (LOEC).) Uncertainty factors are then applied to the NOAEL 

or LOAEL to account for uncertainties in the data associated with variability among individuals, 

extrapolation from nonhuman test species to humans, data on other than long-term exposures, and 

the use of a LOAEL (USEPA, 1988a). An additional uncertainty factor may be applied to account for 

significant weakness or gaps in the database.

Start

Calculate

criterion Use current criterion

EPA's water quality

criterion

available

?

IRIS

data

updated

? Data

exist

in IRIS

?

Yes No Yes No No Evaluate other sources of data, e.g., FDA action

levels, MCLs, risk assessment, fish

consumption

advisory levels
11

The RfD is a threshold below which systemic toxic effects are unlikely to occur. While exposures 

above the RfD increase the probability of adverse effects, they do not produce a certainty of adverse 

effects. Similarly, while exposure at or below the RfD reduces the probability, it does not guarantee 

the absence of effects in all persons. The RfDs contained in IRIS are values that represent EPA's 

consensus (and have uncertainty spanning perhaps an order of magnitude). This means an RfD of 

1.0 mg/kg/day could range from 0.3 to 3.0 mg/kg/day.

For noncarcinogenic effects, an updated criterion can be derived using the equation in Exhibit 3-1.

 

Exhibit 3-1. Equation for Deriving Human Health Criteria Based on Noncarcinogenic Effects 

C (mg/l) = (RfD x WT) - (DT + IN) x WT

WI + [FC x L x FM x BCF]

Where:

C= updated water quality criterion (mg/l)

RfD = oral reference dose (mg toxicant/kg human body weight/day)

WT = weight of an average human adult (70 kg)

DT = dietary exposure (other than fish) (mg toxicant/kg body human weight/day)

IN = inhalation exposure (mg toxicant/kg body human weight/day)

WI = average human adult water intake (2 l/day)

FC = daily fish consumption (kg fish/day)

L = ratio of lipid fraction of fish tissue consumed to 3%

FM = food chain multiplier (from Table 3-1)

BCF = bioconcentration factor (mg toxicant/kg fish divided by mg toxicant/L water) for fish 

with 3% lipid content

If the receiving water body is not used as a drinking water source, the factor WI can be deleted. 

Where dietary and/or inhalation exposure values are unknown, these factors may be deleted from 

the above calculation.

Calculating Criteria for Carcinogens 

Any human health criterion for a carcinogen is based on at least three interrelated considerations: 

cancer potency, exposure, and risk characterization. When developing State criteria, States may 

make their own judgments on each of these factors within reasonable scientific bounds, but 

documentation to support their judgments must be clear and in the public record. 

Maximum protection of human health from the potential effects of exposure to carcinogens through 

the consumption of contaminated fish and/or other aquatic life would require a criterion of zero. 

The zero level is based upon the assumption of non-threshold effects (i.e., no safe level exists below 

which any increase in exposure does not result in an increased risk of cancer) for carcinogens. 

However, because a publicly acceptable policy for safety does not require the absence of all risk, a 
12

numerical estimate of pollutant concentration (in μg/l) which corresponds to a given level of risk for 

a population of a specified size is selected instead. A cancer risk level is defined as the number of 

new cancers that may result in a population of specified size due to an increase in exposure (e.g., 

10-6 risk level = 1 additional cancer in a population of 1 million). Cancer risk is calculated by 

multiplying the experimentally derived cancer potency estimate by the concentration of the chemical 

in the fish and the average daily human consumption of contaminated fish. The risk for a specified 

population (e.g., 1 million people or 10-6) is then calculated by dividing the risk level by the specific 

cancer risk. EPA's ambient water quality criteria documents provide risk levels ranging from 10-5 to 

10-7 as examples.

The cancer potency estimate, or slope factor (formerly known as the q1*), is derived using animal 

studies. High-dose exposures are extrapolated to low-dose concentrations and adjusted to a 

lifetime exposure period through the use of a linearized multistage model. The model calculates the 

upper 95 percent confidence limit of the slope of a straight line which the model postulates to occur 

at low doses. When based on human (epidemiological) data, the slope factor is based on the 

observed increase in cancer risk and is not extrapolated. For deriving criteria for carcinogens, the 

oral cancer potency estimates or slope factors from IRIS are used.

It is important to note that cancer potency factors may overestimate or underestimate the actual risk. 

Such potency estimates are subject to great uncertainty because of two primary factors:

 adequacy of the cancer data base (i.e., human vs. animal data); and

 limited information regarding the mechanism of cancer causation.

Risk levels of 10-5, 10-6, and 10-7 are often used by States as minimal risk levels in interpreting their 

standards. EPA considers risks to be additive, i.e., the risk from individual chemicals is not 

necessarily the overall risk from exposure to water. For example, an individual risk level of 10-6 may 

yield a higher overall risk level if multiple carcinogenic chemicals are present.

For carcinogenic effects, the criterion can be determined by using the equation in Exhibit 3-2.

 

Exhibit 3-2. Equation for Deriving Human Health Criteria Based on Carcinogenic Effects 

C (mg/l) = (RL x WT)

ql* [WI + FC x L x (FM x BCF)] 

Where:

C = updated water quality criterion (mg/l)

RL = risk level (10-x) where x is usually in the range of 4 to 6

WT = weight of an average human adult (70 kg)

q1* = carcinogenic potency factor (kg day/mg)

WI = average human adult water intake (2 l/day)

FC = daily fish consumption (kg fish/day)
13

C (mg/l) = (RL x WT)

ql* [WI + FC x L x (FM x BCF)] 

L = ratio of lipid fraction of fish tissue consumed to 3% assumed by EPA

FM = food chain multiplier (from Table 3-1)

BCF = bioconcentration factor (mg toxicant/kg fish divided by mg toxicant/L water) for fish 

with 3% lipid content

If the receiving water body is not designated as a drinking water source, the factor WI can be 

deleted. 

Deriving Quantitative Risk Assessments in the Absence of IRIS Values 

The RfDs or cancer potency estimates comprise the existing dose-response factors for developing 

criteria. When IRIS data are unavailable, quantitative risk level information may be developed 

according to a State's own procedures. Some States have established their own procedures whereby 

dose-response factors can be developed based upon extrapolation of acute and/or chronic animal 

data to concentrations of exposure protective of fish consumption by humans. 

here owing to the complexity of the subject. 

3.2 Section 304(a) Criteria to State Designated Uses 

The section 304(a)(1) criteria published by EPA from time to time can be used to support the 

designated uses found in State standards. The following sections briefly discuss the relationship 

between certain criteria and individual use classifications. Additional information on this subject 

also can be found in the "Green Book" (FWPCA, 1968); the "Blue Book" (NAS/NAE, 1973); the "Red 

Book" USEPA, 1976); the EPA Water Quality Criteria Documents (see Appendix I); the"Gold Book" 

(USEPA, 1986a); and future EPA section 304(a)(1) water quality criteria publications. 

Where a water body is designated for more than one use, criteria necessary to protect the most 

sensitive use must be applied. The following four sections discuss the major types of use 

categories. 

3.2.1 Recreation 

Recreational uses of water include activities such as swimming, wading, boating, and fishing. Often 

insufficient data exist on the human health effects of physical and chemical pollutants, including 

most toxics, to make a determination of criteria for recreational uses. However, as a general 

guideline, recreational waters that contain chemicals in concentrations toxic or otherwise harmful to 

man if ingested, or irritating to the skin or mucous membranes of the human body upon brief 

immersion, should be avoided. The section 304(a)(1) human health effects criteria based on direct 

human drinking water intake and fish consumption might provide useful guidance in these 

circumstances. Also, section 304(a)(1) criteria based on human health effects may be used to 
14

support this designated use where fishing is included in the State definition of "recreation." In this 

latter situation, only the portion of the criterion based on fish consumption should be used. Section 

304(a)(1) criteria to protect recreational uses are also available for certain physical, microbiological, 

and narrative "free from" aesthetic criteria. 

Research regarding bacteriological indicators has resulted in EPA recommending that States use 

Escherichia coli or enterococci as indicators of recreational water quality (USEPA, 1986b) rather than 

fecal coliform because of the better correlation with gastroenteritis in swimmers. 

The "Green Book" and "Blue Book" provide additional information on protecting recreational uses 

such as pH criteria to prevent eye irritation and microbiological criteria based on aesthetic 

considerations. 

3.2.2 Aquatic Life 

The section 304(a)(1) criteria for aquatic life should be used directly to support this designated use. 

If subcategories of this use are adopted (e.g., to differentiate between coldwater and warmwater 

fisheries), then appropriate criteria should be set to reflect the varying needs of such subcategories. 

3.2.3 Agricultural and Industrial Uses 

The "Green Book" (FWPCA, 1968) and "Blue Book" (NAS/NAE, 1973) provide some information on 

protecting agricultural and industrial uses. Section 304(a)(1) criteria for protecting these uses have 

not been specifically developed for numerous parameters pertaining to these uses, including most 

toxics. 

Where criteria have not been specifically developed for these uses, the criteria developed for human 

health and aquatic life are usually sufficiently stringent to protect these uses. States may also 

establish criteria specifically designed to protect these uses. 

3.2.4 Public Water Supply 

The drinking water exposure component of the section 304(a)(1) criteria based on human health 

effects can apply directly to this use classification. The criteria also may be appropriately modified 

depending upon whether the specific water supply system falls within the auspices of the Safe 

Drinking Water Act's (SDWA) regulatory control and the type and level of treatment imposed upon 

the supply before delivery to the consumer. The SDWA controls the presence of contaminants in 

finished ("at-the-tap") drinking water. 

A brief description of relevant sections of the SDWA is necessary to explain how the Act will work in 

conjunction with section 304(a)(1) criteria in protecting human health from the effects of toxics due 

to consumption of water. Pursuant to section 1412 of the SDWA, EPA has promulgated "National 

Primary Drinking Water Standards" for certain radionuclide, microbiological, organic, and inorganic 
15

substances. These standards establish maximum contaminant levels (MCLs), which specify the 

maximum permissible level of a contaminant in water that may be delivered to a user of a public 

water system now defined as serving a minimum of 25 people. MCLs are established based on 

consideration of a range of factors including not only the health effects of the contaminants but also 

treatment capability, monitoring availability, and costs. Under section 1401(1)(D)(i) of the SDWA, 

EPA is also allowed to establish the minimum quality criteria for water that may be taken into a 

public water supply system.

Section 304(a)(1) criteria provide estimates of pollutant concentrations protective of human health, 

but do not consider treatment technology, costs, and other feasibility factors. The section 304(a)(1) 

criteria also include fish bioaccumulation and consumption factors in addition to direct human 

drinking water intake. These numbers were not developed to serve as "at-the-tap" drinking water 

standards, and they have no regulatory significance under the SDWA. Drinking water standards are 

established based on considerations, including technological and economic feasibility, not relevant 

to section 304(a)(1) criteria. Section 304(a)(1) criteria are more analogous to the maximum 

contaminant level goals (MCLGs) (previously known as RMCLs) under section 1412(b)(1)(B) of the 

SDWA in which, based upon a report from the National Academy of Sciences, the Administrator 

should set target levels for contaminants in drinking water at which "no known or anticipated 

adverse effects occur and which allow an adequate margin of safety." MCLGs do not take treatment, 

cost, and other feasibility factors into consideration. Section 304(a)(1) criteria are, in concept, 

related to the health-based goals specified in the MCLGs.

MCLs of the SDWA, where they exist, control toxic chemicals in finished drinking water. However, 

because of variations in treatment, ambient water criteria may be used by the States as a supplement 

to SDWA regulations. When setting water quality criteria for public water supplies, States have the 

option of applying MCLs, section 304(a)(1) human health effects criteria, modified section 304(a)(1) 

criteria, or controls more stringent than these three to protect against the effects of contaminants by 

ingestion from drinking water.

For treated drinking water supplies serving 25 people or greater, States must control contaminants 

down to levels at least as stringent as MCLs (where they exist for the pollutants of concern) in the 

finished drinking water. However, States also have the options to control toxics in the ambient water 

by choosing section 304(a)(1) criteria, adjusted section 304(a)(1) criteria resulting from the reduction 

of the direct drinking water exposure component in the criteria calculation to the extent that the 

treatment process reduces the level of pollutants, or a more stringent contaminant level than the 

former three options.

3.3 State Criteria Requirements 

Section 131.11(a)(1) of the Regulation requires States to adopt water quality criteria to protect the 

designated use(s). The State criteria must be based on sound scientific rationale and must contain 

sufficient parameters or constituents to protect the designated use(s). For waters with multiple use 

designations, the criteria must support the most sensitive use. 
16

In section 131.11, States are encouraged to adopt both numeric and narrative criteria. Aquatic life 

criteria should protect against both short-term (acute) and long-term (chronic) effects. Numeric 

criteria are particularly important where the cause of toxicity is known or for protection against 

pollutants with potential human health impacts or bioaccumulation potential. Numeric water quality 

criteria may also be the best way to address nonpoint source pollution problems. Narrative criteria

can be the basis for limiting toxicity in waste discharges where a specific pollutant can be identified 

as causing or contributing to the toxicity but where there are no numeric criteria in the State 

standards. Narrative criteria also can be used where toxicity cannot be traced to a particular 

pollutant. 

Section 131.11(a)(2) requires States to develop implementation procedures which explain how the 

State will ensure that narrative toxics criteria are met.

To more fully protect aquatic habitats, it is EPA's policy that States fully integrate chemical-specific, 

whole-effluent, and biological assessment approaches in State water quality programs (see Appendix 

R). Specifically, each of these three methods can provide a valid assessment of non-attainment of 

designated aquatic life uses but can rarely demonstrate use attainment separately. Therefore, EPA 

supports a policy of independent application of these three water quality assessment approaches. 

Independent application means that the validity of the results of any one of the approaches does not 

depend on confirmation by one or both of the other methods. This policy is based on the unique 

attributes, limitations, and program applications of each of the three approaches. Each method 

alone can provide valid and independently sufficient evidence of non-attainment of water quality 

standards, irrespective of any evidence, or lack thereof, derived from the other two approaches. The 

failure of one method to confirm impacts identified by another method does not negate the results 

of the initial assessment.

It is also EPA's policy that States should designate aquatic life uses that appropriately address 

biological integrity and adopt biological criteria necessary to protect those uses (see section 3.5.3 

and Appendices C, K, and R).

3.4 Criteria for Toxicants 

Applicable requirements for State adoption of water quality criteria for toxicants vary depending 

upon the toxicant. The reason for this is that the 1983 Water Quality Standards Regulation 

(Appendix A) and the Water Quality Act of 1987 which amended the Clean Water Act (Public Law 

100-4) include more specific requirements for the particular toxicants listed pursuant to CWA 

section 307(a). For regulatory purposes, EPA has translated the 65 compounds and families of 

compounds listed pursuant to section 307(a) into 126 more specific substances, which EPA refers to 

as "priority toxic pollutants." The 126 priority toxic pollutants are listed in the WQS regulation and 

in Appendix P of this Handbook. Because of the more specific requirements for priority toxic 

pollutants, it is convenient to organize the requirements applicable to State adoption of criteria for 

toxicants into three categories:
17

 requirements applicable to priority toxic pollutants that have been the subject of 

CWA section 304(a)(1) criteria guidance (see section 3.4.1); 

 requirements applicable to priority toxic pollutants that have not been the subject of 

CWA section 304(a)(1) criteria guidance (see section 3.4.1); and 

 requirements applicable to all other toxicants (e.g., non-conventional pollutants like 

ammonia and chlorine) (see section 3.4.2). 

3.4.1 Priority Toxic Pollutant Criteria 

The criteria requirements applicable to priority toxic pollutants (i.e., the first two categories above) 

are specified in CWA section 303(c)(2)(B). Section 303(c)(2)(B), as added by the Water Quality Act of 

1987, provides that: 

Whenever a State reviews water quality standards pursuant to paragraph (1) of this subsection, or 

revises or adopts new standards pursuant to this paragraph, such State shall adopt criteria for all 

toxic pollutants listed pursuant to section 307(a)(1) of this Act for which criteria have been published 

under section 304(a), the discharge or presence of which in the affected waters could reasonably be 

expected to interfere with those designated uses adopted by the State, as necessary to support such 

designated uses. Such criteria shall be specific numerical criteria for such toxic pollutants. Where 

such numerical criteria are not available, whenever a State reviews water quality standards pursuant 

to paragraph (1), or revises or adopts new standards pursuant to this paragraph, such State shall 

adopt criteria based on biological monitoring or assessment methods consistent with information 

published pursuant to section 304(a)(8). Nothing in this section shall be construed to limit or delay 

the use of effluent limitations or other permit conditions based on or involving biological monitoring 

or assessment methods or previously adopted numerical criteria. 

EPA, in devising guidance for section 303(c)(2)(B), attempted to provide States with the maximum 

flexibility that complied with the express statutory language but also with the overriding 

congressional objective: prompt adoption and implementation of numeric toxics criteria. EPA 

believed that flexibility was important so that each State could comply with section 303(c)(2)(B) and 

to the extent possible, accommodate its existing water quality standards regulatory approach. 

General Requirements 

To carry out the requirements of section 303(c)(2)(B), whenever a State revises its water quality 

standards, it must review all available information and data to first determine whether the discharge 

or the presence of a toxic pollutant is interfering with or is likely to interfere with the attainment of 

the designated uses of any water body segment. 

If the data indicate that it is reasonable to expect the toxic pollutant to interfere with the use, or it 

actually is interfering with the use, then the State must adopt a numeric limit for the specific 

pollutant. If a State is unsure whether a toxic pollutant is interfering with, or is likely to interfere 
18

with, the designated use and therefore is unsure that control of the pollutant is necessary to support 

the designated use, the State should undertake to develop sufficient information upon which to 

make such a determination. Presence of facilities that manufacture or use the section 307(a) toxic 

pollutants or other information indicating that such pollutants are discharged or will be discharged 

strongly suggests that such pollutants could be interfering with attaining designated uses. If a State 

expects the pollutant not to interfere with the designated use, then section 303(1)(2)(B) does not 

require a numeric standard for that pollutant.

Section 303(c)(2)(B) addresses only pollutants listed as "toxic" pursuant to section 307(a) of the Act, 

which are codified at 40 CFR 131.36(b). The section 307(a) list contains 65 compounds and families 

of compounds, which potentially include thousands of specific compounds. The Agency has 

interpreted that list to include 126 "priority" toxic pollutants for regulatory purposes. Reference in 

this guidance to toxic pollutants or section 307(a) toxic pollutants refers to the 126 priority toxic 

pollutants unless otherwise noted. Both the list of priority toxic pollutants and recommended 

criteria levels are subject to change.

The national criteria recommendations published by EPA under section 304(a) (see section 3.1, 

above) of the Act include values for both acute and chronic aquatic life protection; only chronic 

criteria recommendations have been established to protect human health. To comply with the 

statute, a State needs to adopt aquatic life and human health criteria where necessary to support the 

appropriate designated uses. Criteria for the protection of human health are needed for water 

bodies designated for public water supply. When fish ingestion is considered an important activity, 

then the human health-related water quality criteria recommendation developed under section 

304(a) of the CWA should be used; that is, the portion of the criteria recommendation based on fish 

consumption. For those pollutants designated as carcinogens, the recommendation for a human 

health criterion is generally more stringent than the aquatic life criterion for the same pollutant. In 

contrast, the aquatic life criteria recommendations for noncarcinogens are generally more stringent 

than the human health recommendations. When a State adopts a human health criterion for a 

carcinogen, the State needs to select a risk level. EPA has estimated risk levels of 10-5, 10-6, and 10-

7 in its criteria documents under one set of exposure assumptions. However, the State is not limited 

to choosing among the risk levels published in the section 304(a) criteria documents, nor is the State 

limited to the base case exposure assumptions; it must choose the risk level for its conditions and 

explain its rationale.

EPA generally regulates pollutants treated as carcinogens in the range of 10-6 to 10-4 to protect 

average exposed individuals and more highly exposed populations. However, if a State selects a 

criterion that represents an upper bound risk level less protective than 1 in 100,000 (e.g., 10-5), the 

State needs to have substantial support in the record for this level. This support focuses on two 

distinct issues. First, the record must include documentation that the decision maker considered the 

public interest of the State in selecting the risk level, including documentation of public participation 

in the decision making process as required by the Water Quality Standards Regulation at 40 CFR 

131.20(b). Second, the record must include an analysis showing that the risk level selected, when 

combined with other risk assessment variables, is a balanced and reasonable estimate of actual risk 
19

posed, based on the best and most representative information available. The importance of the 

estimated actual risk increases as the degree of conservatism in the selected risk level diminishes. 

EPA carefully evaluates all assumptions used by a State if the State chose to alter any one of the 

standard EPA assumption values (57 F.R. 60864, December 22, 1993).

EPA does not intend to propose changes to the current requirements regarding the bases on which a 

State can adopt numeric criteria (40 CFR 131.11(b)(1)). Under EPA's regulation, in addition to basing 

numeric criteria on EPA's section 304(a) criteria documents, States may also base numeric criteria on 

site-specific determinations or other scientifically defensible methods. 

EPA expects each State to comply with the new statutory requirements in any section 303(c) water 

quality standards review initiated after enactment of the Water Quality Act of 1987. The structure of 

section 303(c) is to require States to review their water quality standards at least once each 3 year 

period. Section 303(c)(2)(B) instructs States to include reviews for toxics criteria whenever they 

initiate a triennial review. Therefore, even if a State has complied with section 303(c)(2)(B), the State 

must review its standards each triennium to ensure that section 303(c)(2)(B) requirements continue 

to be met, considering that EPA may have published additional section 304(a) criteria documents 

and that the State will have new information on existing water quality and on pollution sources. 

It should be noted that nothing in the Act or in the Water Quality Standards Regulation restricts the 

right of a State to adopt numeric criteria for any pollutant not listed pursuant to section 307(a)(1), 

and that such criteria may be expressed as concentration limits for an individual pollutant or for a 

toxicity parameter itself as measured by whole-effluent toxicity testing. However, neither numeric 

toxic criteria nor whole-effluent toxicity should be used as a surrogate for, or to supersede the 

other.

State Options 

States may meet the requirements of CWA section 303(c)(2)(B) by choosing one of three scientifically 

and technically sound options (or some combination thereof):

1. Adopt statewide numeric criteria in State water quality standards for all section 

307(a) toxic pollutants for which EPA has developed criteria guidance, regardless of 

whether the pollutants are known to be present;

2. Adopt specific numeric criteria in State water quality standards for section 307(a) 

toxic pollutants as necessary to support designated uses where such pollutants are 

discharged or are present in the affected waters and could reasonably be expected to 

interfere with designated uses;

3. Adopt a "translator procedure" to be applied to a narrative water quality standard 

provision that prohibits toxicity in receiving waters. Such a procedure is to be used 

by the State in calculating derived numeric criteria, which shall be used for all 

purposes under section 303(c) of the CWA. At a minimum, such criteria need to be 

developed for section 307(a) toxic pollutants, as necessary to support designated 
20

uses, where these pollutants are discharged or present in the affected waters and 

could reasonably be expected to interfere with designated uses.

Option 1 is consistent with State authority to establish water quality standards. Option 2 most 

directly reflects the CWA requirements and is the option recommended by EPA. Option 3, while 

meeting the requirements of the CWA, is best suited to supplement numeric criteria from option 1 or 

2. The three options are discussed in more detail below.

OPTION 1: 

Adopt statewide numeric criteria in State water quality standards for all section 307(a) toxic 

pollutants for which EPA has developed criteria guidance, regardless of whether the pollutants are 

known to be present.

Pro:

 simple, straightforward implementation 

 ensures that States will satisfy statute 

 makes maximum uses of EPA recommendations 

 gets specific numbers into State water quality standards fast, at first

Con:

 some priority toxic pollutants may not be discharged in State

 may cause unnecessary monitoring by States 

 might result in "paper standards"

Option 1 is within a State's legal authority under the CWA to adopt broad water quality standards. 

This option is the most comprehensive approach to satisfy the statutory requirements because it 

would include all of the priority toxic pollutants for which EPA has prepared section 304(a) criteria 

guidance for either or both aquatic life protection and human health protection. In addition to a 

simple adoption of EPA's section 304(a) guidance as standards, a State must select a risk level for 

those toxic pollutants which are carcinogens (i.e., that cause or may cause cancer in humans). 

Many States find this option attractive because it ensures comprehensive coverage of the priority 

toxic pollutants with scientifically defensible criteria without the need to conduct a resourceintensive evaluation of the particular segments and pollutants requiring criteria. This option also 

would not be more costly to dischargers than other options because permit limits would be based 

only on the regulation of the particular toxic pollutants in their discharges and not on the total 

listing in the water quality standards. Thus, actual permit limits should be the same under any of 

the options.

The State may also exercise its authority to use one or more of the techniques for adjusting water 

quality standards: 
21

 establish or revise designated stream uses based on use attainability analyses (see 

section 2.9); 

 develop site-specific criteria; or 

 allow short-term variances (see section 5.3) when appropriate.

All three of these techniques may apply to standards developed under any of the three options 

discussed in this guidance. It is likely that States electing to use option 1 will rely more on variances 

because the other two options are implemented with more site-specific data being available. It 

should be noted, however, that permits issued pursuant to such water quality variances still must 

comply with any applicable antidegradation and antibacksliding requirements.

OPTION 2: 

Adopt specific numeric criteria in State water quality standards for section 307(a) toxic pollutants as 

necessary to support designated uses where such pollutants are discharged or are present in the 

affected waters and could reasonably be expected to interfere with designated uses.

Pro:

 directly reflects statutory requirement 

 standards based on demonstrated need to control problem pollutants

 State can use EPA's section 304(a) national criteria recommendations or other 

scientifically acceptable alternative, including site-specific criteria

 State can consider current or potential toxic pollutant problems

 State can go beyond section 307(a) toxics list, as desired

Con:

 may be difficult and time consuming to determine if, and which, pollutants are 

interfering with the designated use

 adoption of standards can require lengthy debates on correct criteria limit to be 

included in standards 

 successful State toxic control programs based on narrative criteria may be halted or 

slowed as the State applies its limited resources to developing numeric standards

 difficult to update criteria once adopted as part of standards

 to be absolutely technically defensible, may need site-specific criteria in many 

situations, leading to a large workload for regulatory agency

EPA recommends that a State use this option to meet the statutory requirement. It directly reflects 

all the Act's requirements and is flexible, resulting in adoption of numeric water quality standards as 

needed. To assure that the State is capable of dealing with new problems as they arise, EPA also 

recommends that States adopt a translator procedure the same as, or similar to, that described in 
22

option 3, but applicable to all chemicals causing toxicity and not just priority pollutants as is the 

case for option 3.

Beginning in 1988, EPA provided States with candidate lists of priority toxic pollutants and water 

bodies in support of CWA section 304(l) implementation. These lists were developed because States 

were required to evaluate existing and readily available water-related data to comply with section 

304(l), 40 CFR 130.10(d). A similar "strawman" analysis of priority pollutants potentially requiring 

adoption of numeric criteria under section 303(c)(2)(B) was furnished to most States in September or 

October of 1990 for their use in ongoing and subsequent triennial reviews. The primary differences 

between the "strawman" analysis and the section 304(l) candidate lists were that the "strawman" 

analysis (1) organized the results by chemical rather than by water body, (2) included data for 

certain STORET monitoring stations that were not used in constructing the candidate lists, (3) 

included data from the Toxics Release Inventory database, and (4) did not include a number of data 

sources used in preparing the candidate lists (e.g., those, such as fish kill information, that did not 

provide chemical-specific information).

EPA intends for States, at a minimum, to use the information gathered in support of section 304(l) 

requirements as a starting point for identifying (1) water segments that will need new and/or revised 

water quality standards for section 307(a) toxic pollutants, and (2) which priority toxic pollutants 

require adoption of numeric criteria. In the longer term, EPA expects similar determinations to occur 

during each triennial review of water quality standards as required by section 303(c).

In identifying the need for numeric criteria, EPA is encouraging States to use information and data 

such as: 

 presence or potential construction of facilities that manufacture or use priority toxic 

pollutants;

 ambient water monitoring data, including those for sediment and aquatic life (e.g., 

fish tissue data); 

 NPDES permit applications and permittee self-monitoring reports; 

 effluent guideline development documents, many of which contain section 307(a)(1) 

priority pollutant scans; 

 pesticide and herbicide application information and other records of pesticide or 

herbicide inventories; 

 public water supply source monitoring data noting pollutants with Maximum 

Contaminant Levels (MCLs); and 

 any other relevant information on toxic pollutants collected by Federal, State, 

interstate agencies, academic groups, or scientific organizations. 

States are also expected to take into account newer information as it became available, such as 

information in annual reports from the Toxic Chemical Release Inventory requirements of the 

Emergency Planning and Community Right-To-Know Act of 1986 (Title III, Public Law 99-499).
23

Where the State's review indicates a reasonable expectation of a problem from the discharge or 

presence of toxic pollutants, the State should identify the pollutant(s) and the relevant segment(s). 

In making these determinations, States should use their own EPA-approved criteria or existing EPA 

water quality criteria for purposes of segment identification. After the review, the State may use 

other means to establish the final criterion as it revises its standards.

As with option 1, a State using option 2 must follow all its legal and administrative requirements for 

adoption of water quality standards. Since the resulting numeric criteria are part of a State's water 

quality standards, they are required to be submitted by the State to EPA for review and either 

approval or disapproval.

EPA believes this option offers the State optimum flexibility. For section 307(a) toxic pollutants 

adversely affecting designated uses, numeric criteria are available for permitting purposes. For 

other situations, the State has the option of defining site-specific criteria.

OPTION 3: 

Adopt a procedure to be applied to the narrative water quality standard provision that prohibits 

toxicity in receiving waters. Such a procedure would be used by a State in calculating derived 

numeric criteria to be used for all purposes of water quality criteria under section 303(c) of the CWA. 

At a minimum such criteria need to be derived for section 307(a) toxic pollutants where the 

discharge or presence of such pollutants in the affected waters could reasonably be expected to 

interfere with designated uses, as necessary to support such designated uses.

Pro:

 allows a State flexibility to control priority toxic pollutants

 reduces time and cost required to adopt specific numeric criteria as water quality 

standards regulations 

 allows immediate use of latest scientific information available at the time a State 

needs to develop derived numeric criteria

 revisions and additions to derived numeric criteria can be made without need to 

revise State law 

 State can deal more easily with a situation where it did not establish water quality 

standards for the section 307(a) toxic pollutants during the most recent triennial 

review

 State can address problems from non-section 307(a) toxic pollutants

Con:

 EPA is currently on notice that a derived numeric criterion may invite legal challenge
24

 once the necessary procedures are adopted to enhance legal defensibility (e.g., 

appropriate scientific methods and public participation and review), actual savings in 

time and costs may be less than expected

 public participation in development of derived numeric criteria may be limited when 

such criteria are not addressed in a hearing on water quality standards

EPA believes that adoption of a narrative standard along with a translator mechanism as part of a 

State's water quality standard satisfies the substantive requirements of the statute. These criteria 

are subject to all the State's legal and administrative requirements for adoption of standards plus 

review and either approval or disapproval by EPA, and result in the development of derived numeric 

criteria for specific section 307(a) toxic pollutants. They are also subject to an opportunity for public 

participation. Nevertheless, EPA believes the most appropriate use of option 3 is as a supplement to 

either option 1 or 2. Thus, a State would have formally adopted numeric criteria for toxic pollutants 

that occur frequently; that have general applicability statewide for inclusion in NPDES permits, total 

maximum daily loads, and waste load allocations; and that also would have a sound and predictable 

method to develop additional numeric criteria as needed. This combination of options provides a 

complete regulatory scheme.

Although the approach in option 3 is similar to that currently allowed in the Water Quality Standards 

Regulation (40 CFR 131.11(a)(2)), this guidance discusses several administrative and scientific 

requirements that EPA believes are necessary to comply with section 303(c)(2)(B).

1. The Option 3 Procedure Must Be Used To Calculate Derived Numeric Water Quality 

Criteria

States must adopt a specific procedure to be applied to a narrative water quality criterion. To satisfy 

section 303(c)(2)(B), this procedure shall be used by the State in calculating derived numeric criteria, 

which shall be used for all purposes under section 303(c) of the CWA. Such criteria need to be 

developed for section 307(a) toxic pollutants as necessary to support designated uses, where these 

pollutants are discharged or are present in the affected waters and could reasonably be expected to 

interfere with the designated uses.

To assure protection from short-term exposures, the State procedure should ensure development of 

derived numeric water quality criteria based on valid acute aquatic toxicity tests that are lethal to 

half the affected organisms (LC50) for the species representative of or similar to those found in the 

State. In addition, the State procedure should ensure development of derived numeric water quality 

criteria for protection from chronic exposure by using an appropriate safety factor applicable to this 

acute limit. If there are saltwater components to the State's aquatic resources, the State should 

establish appropriate derived numeric criteria for saltwater in addition to those for freshwater.

The State's documentation of the tests should include a detailed discussion of its quality control and 

quality assurance procedures. The State should also include a description (or reference existing 

technical agreements with EPA) of the procedure it will use to calculate derived acute and chronic 
25

numeric criteria from the test data, and how these derived criteria will be used as the basis for 

deriving appropriate TMDLs, WLAs, and NPDES permit limits.

As discussed above, the procedure for calculating derived numeric criteria needs to protect aquatic 

life from both acute and chronic exposure to specific chemicals. Chronic aquatic life criteria are to 

be met at the edge of the mixing zone. The acute criteria are to be met (1) at the end-of-pipe if 

mixing is not rapid and complete and a high rate diffuser is not present; or (2) after mixing if mixing 

is rapid and complete or a high rate diffuser is present. (See EPA's Technical Support Document for 

Water Quality-based Toxics Control, USEPA 1991a.) 

EPA has not established a national policy specifying the point of application in the receiving water to 

be used with human health criteria. However, EPA has approved State standards that apply human 

health criteria for fish consumption at the mixing zone boundary and/or apply the criteria for 

drinking water consumption, at a minimum, at the point of use. EPA has also proposed more 

stringent requirements for the application of human health criteria for highly bioaccumulative 

pollutants in the Water Quality guidance for the Great Lakes System (50 F.R. 20931, 21035, April 16, 

1993) including elimination of mixing zones.

In addition, the State should also include an indication of potential bioconcentration or 

bioaccumulation by providing for: 

 laboratory tests that measure the steady-state bioconcentration rate achieved by a 

susceptible organism; and/or 

 field data in which ambient concentrations and tissue loads are measured to give an 

appropriate factor. 

In developing a procedure to be used in calculating derived numeric criteria for the protection of 

aquatic life, the State should consider the potential impact that bioconcentration has on aquatic and 

terrestrial food chains.

The State should also use the derived bioconcentration factor and food chain multiplier to calculate 

chronically protective numeric criteria for humans that consume aquatic organisms. In calculating 

this derived numeric criterion, the State should indicate data requirements to be met when dealing 

with either threshold (toxic) or non-threshold (carcinogenic) compounds. The State should describe 

the species and the minimum number of tests, which may generally be met by a single mammalian 

chronic test if it is of good quality and if the weight of evidence indicates that the results are 

reasonable. The State should provide the method to calculate a derived numeric criterion from the 

appropriate test result.
26

Both the threshold and non-threshold 

criteria for protecting human health should 

contain exposure assumptions, and the State 

procedure should be used to calculate 

derived numeric criteria that address the 

consumption of water, consumption of fish, 

and combined consumption of both water 

and fish. The State should provide the 

assumptions regarding the amount of fish 

and the quantity of water consumed per 

person per day, as well as the rationale used 

to select the assumptions. It needs to 

include the number of tests, the species necessary to establish a dose-response relationship, and 

the procedure to be used to calculate the derived numeric criteria. For non-threshold contaminants, 

the State should specify the model used to extrapolate to low dose and the risk level. It should also 

address incidental exposure from other water sources (e.g., swimming). When calculating derived 

numeric criteria for multiple exposure to pollutants, the State should consider additive effects, 

especially for carcinogenic substances, and should factor in the contribution to the daily intake of 

toxicants from other sources (e.g., food, air) when data are available.

2. The State Must Demonstrate That the Procedure Results in Derived Numeric Criteria 

Are Protective

The State needs to demonstrate that its procedures for developing criteria, including translator 

methods, yield fully protective criteria for human health and for aquatic life. EPA's review process 

will proceed according to EPA's regulation of 40 CFR 131.11, which requires that criteria be based on 

sound scientific rationale and be protective of all designated uses. EPA will use the expertise and 

experience it has gained in developing section 304(a) criteria for toxic pollutants by application of its 

own translator method (USEPA, 1980b; USEPA, 1985b).

Once EPA has approved the State's procedure, the Agency's review of derived numeric criteria, for 

example, for pollutants other than section 307(a) toxic pollutants resulting from the State's 

procedure, will focus on the adequacy of the data base rather than the calculation method. EPA also 

encourages States to apply such a procedure to calculate derived numeric criteria to be used as the 

basis for deriving permit limitations for nonconventional pollutants that also cause toxicity.

3. The State Must Provide Full Opportunity for Public Participation in Adoption of the 

Procedure

The Water Quality Standards Regulation requires States to hold public hearings to review and revise 

water quality standards in accordance with provisions of State law and EPA's Public Participation 

Regulation (40 CFR 25). Where a State plans to adopt a procedure to be applied to the narrative 
27

criterion, it must provide full opportunity for public participation in the development and adoption of 

the procedure as part of the State's water quality standards.

While it is not necessary for the State to adopt each derived numeric criterion into its water quality 

standards and submit it to EPA for review and approval, EPA is very concerned that all affected 

parties have adequate opportunity to participate in the development of a derived numeric criterion 

even though it is not being adopted directly as a water quality standard.

A State can satisfy the need to provide an opportunity for public participation in the development of 

derived numeric criteria in several ways, including:

 a specific hearing on the derived numeric criterion;

 the opportunity for a public hearing on an NPDES permits as long as public notice is 

given that a criterion for a toxic pollutant as part of the permit issuance is being 

contemplated; or

 a hearing coincidental with any other hearing as long as it is made clear that 

development of a specific criterion is also being undertaken.

For example, as States develop their lists and individual control strategies (ICSs) under section 

304(1), they may seek full public participation. NPDES regulations also specify public participation 

requirements related to State permit issuance. Finally, States have public participation requirements 

associated with Water Quality Management Plan updates. States may take advantage of any of these 

public participation requirements to fulfill the requirement for public review of any resulting derived 

numeric criteria. In such cases, the State must give prior notice that development of such criteria is 

under consideration.

4. The Procedure Must Be Formally Adopted and Mandatory

Where a State elects to supplement its narrative criterion with an accompanying implementing 

procedure, it must formally adopt such a procedure as a part of its water quality standards. The 

procedure must be used by the State to calculate derived numeric criteria that will be used as the 

basis for all standards' purposes, including the following: developing TMDLs, WLAs, and limits in 

NPDES permits; determining whether water use designations are being met; and identifying potential 

nonpoint source pollution problems.

5. The Procedure Must Be Approved by EPA as Part of the State's Water Quality 

Standards Regulation

To be consistent with the requirements of the Act, the State's procedure to be applied to the 

narrative criterion must be submitted to EPA for review and approval, and will become a part of the 

State's water quality standards. (See 40 CFR 131.21 for further discussion.) This requirement may be 

satisfied by a reference in the standards to the procedure, which may be contained in another 
28

document, which has legal effect and is binding on the State, and all the requirements for public 

review, State implementation, and EPA review and approval are satisfied.

Criteria Based on Biological Monitoring 

For priority toxic pollutants for which EPA has not issued section 304(a)(1) criteria guidance, CWA 

section 303(c)(2)(B) requires States to adopt criteria based on biological monitoring or assessment 

methods. The phrase "biological monitoring or assessment methods" includes: 

 whole-effluent toxicity control methods;

 biological criteria methods; or 

 other methods based on biological monitoring or assessment. 

The phrase "biological monitoring or assessment methods" in its broadest sense also includes 

criteria developed through translator procedures. This broad interpretation of that phrase is 

consistent with EPA's policy of applying chemical-specific, biological, and whole-effluent toxicity 

methods independently in an integrated toxics control program. It is also consistent with the intent 

of Congress to expand State standards programs beyond chemical-specific approaches.

States should also consider developing protocols to derive and adopt numeric criteria for priority 

toxic pollutants (or other pollutants) where EPA has not issued section 304(a) criteria guidance. The 

State should consider available laboratory toxicity test data that may be sufficient to support 

derivation of chemical-specific criteria. Existing data need not be as comprehensive as that required 

to meet EPA's 1985 guidelines in order for a State to use its own protocols to derive criteria. EPA has 

described such protocols in the proposed Water Quality Guidance for the Great Lakes System (58 F.R. 

20892, at 21016, April 16, 1993.) This is particularly important where other components of a State's 

narrative criterion implementation procedure (e.g., WET controls or biological criteria) may not 

ensure full protection of designated uses. For some pollutants, a combination of chemical-specific 

and other approaches is necessary (e.g., pollutants where bioaccumulation in fish tissue or water 

consumption by humans is a primary concern).

Biologically based monitoring or assessment methods serve as the basis for control where no 

specific numeric criteria exist or where calculation or application of pollutant-by-pollutant criteria 

appears infeasible. Also, these methods may serve as a supplemental measurement of attainment of 

water quality standards in addition to numeric and narrative criteria. The requirement for both 

numeric criteria and biologically based methods demonstrates that section 303(c)(2)(B) contemplates 

that States develop a comprehensive toxics control program regardless of the status of EPA's section 

304(a) criteria. 

The whole-effluent toxicity (WET) testing procedure is the principal biological monitoring guidance 

developed by EPA to date. The purpose of the WET procedure is to control point source dischargers 

of toxic pollutants. The procedure is particularly useful for monitoring and controlling the toxicity of 

complex effluents that may not be well controlled through chemical-specific numeric criteria. As 
29

such, biologically based effluent testing procedures are a necessary component of a State's toxics 

control program under section 303(c)(2)(B) and a principal means for implementing a State's 

narrative "free from toxics" standard. 

Guidance documents EPA considers to serve the purpose of section 304(a)(8) include the Technical 

Support Document for Water Quality-based Toxics Control (USEPA, 1991a; Guidelines for Deriving 

National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses (Appendix H); 

Guidelines and Methodology Used in the Preparation of Health Effect Assessment Chapters of the 

Consent Decree Water Criteria Documents (Appendix J); Methods for Measuring Acute Toxicity of 

Effluents to Freshwater and Marine Organisms (USEPA, 1991d); Short-Term Methods for Estimating 

the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms (USEPA, 1991e); and 

Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Marine 

and Estuarine Organisms (USEPA, 1991f). 

3.4.2 Criteria for Nonconventional Pollutants 

Criteria requirements applicable to toxicants that are not priority toxic pollutants (e.g., ammonia and 

chlorine), are specified in the 1983 Water Quality Standards Regulation (see 40 CFR 131.11). Under 

these requirements, States must adopt criteria based on sound scientific rationale that cover 

sufficient parameters to protect designated uses. Both numeric and narrative criteria (discussed in 

sections 3.5.1 and 3.5.2, below) may be applied to meet these requirements. 

3.5 Forms of Criteria 

States are required to adopt water quality criteria, based on sound scientific rationale, that contain 

sufficient parameters or constituents to protect the designated use. EPA believes that an effective 

State water quality standards program should include both parameter-specific (e.g., ambient 

numeric criteria) and narrative approaches. 

3.5.1 Numeric Criteria 

Numeric criteria are required where necessary to protect designated uses. Numeric criteria to 

protect aquatic life should be developed to address both short-term (acute) and long-term (chronic) 

effects. Saltwater species, as well as freshwater species, must be adequately protected. Adoption of 

numeric criteria is particularly important for toxicants known to be impairing surface waters and for 

toxicants with potential human health impacts (e.g., those with high bioaccumulation potential). 

Human health should be protected from exposure resulting from consumption of water and fish or 

other aquatic life (e.g., mussels, crayfish). Numeric water quality criteria also are useful in 

addressing nonpoint source pollution problems. 

In evaluating whether chemical-specific numeric criteria for toxicants that are not priority toxic 

pollutants are required, States should consider whether other approaches (such as whole-effluent 

toxicity criteria or biological controls) will ensure full protection of designated uses. As mentioned 
30

above, a combination of independent approaches may be required in some cases to support the 

designated uses and comply with the requirements of the Water Quality Standards Regulation (e.g., 

pollutants where bioaccumulation in fish tissue or water consumption by humans is a primary 

concern). 

3.5.2 Narrative Criteria 

To supplement numeric criteria for toxicants, all States have also adopted narrative criteria for 

toxicants. Such narrative criteria are statements that describe the desired water quality goal, such as 

the following: 

All waters, including those within mixing zone, shall be free from substances attributable to 

wastewater discharge or other pollutant sources that: 

1. Settle to form objectionable deposits; 

2. Float as debris, scum, oil, or other matter forming nuisances; 

3. Produce objectionable color, odor, taste, or turbidity; 

4. Cause injury to or are toxic to, or produce adverse physiological responses in 

humans, animals, or plants; or 

5. Produce undesirable or nuisance aquatic life (54 F.R.28627, July 6, 1989). 

EPA considers that the narrative criteria apply to all designated uses at all flows and are necessary to 

meet the statutory requirements of section 303(c)(2)(A) of the CWA. 

Narrative toxic criteria (No. 4, above) can be the basis for establishing chemical-specific limits for 

waste discharges where a specific pollutant can be identified as causing or contributing to the 

toxicity and the State has not adopted chemical-specific numeric criteria. Narrative toxic criteria are 

cited as a basis for establishing whole-effluent toxicity controls in EPA permitting regulations at 40 

CFR 122.44(d)(1)(v). 

To ensure that narrative criteria for toxicants are attained, the Water Quality Standards Regulation 

requires States to develop implementation procedures (see 40 CFR 131.11(a)(2)). Such 

implementation procedures. 

Exhibit 3-3. Components of a State Implementation Procedure for Narrative Toxics Criteria 

State implementation procedures for narrative toxics criteria should describe the following: 

 Specific, scientifically defensible methods by which the State will implement its 

narrative toxics standard for all toxicants, including: 

o methods for chemical-specific criteria, including methods for applying 

chemical-specific criteria in permits, developing or modifying chemicalspecific criteria via a "translator procedure" (defined and discussed below), 
31

and calculating site-specific criteria based on local water chemistry or 

biology);

o methods for developing and implementing whole-effluent toxicity criteria 

and/or controls; and

o methods for developing and implementing biological criteria.

 How these methods will be integrated in the State's toxics control program (i.e., how 

the State will proceed when the specified methods produce conflicting or inconsistent 

results).

 Application criteria and information needed to apply numerical criteria, for example:

o methods the State will use to identify those pollutants to be regulated in a 

specific discharge;

o an incremental cancer risk level for carcinogens;

o methods for identifying compliance thresholds in permits where calculated 

limits are below detection;

o methods for selecting appropriate hardness, pH, and temperature variables 

for criteria expressed as functions;

o methods or policies controlling the size and in-zone quality of mixing zones

o design flows to be used in translating chemical-specific numeric criteria for 

aquatic life and human health into permit limits; and

o other methods and information needed to apply standards on a case-by-case 

basis.

(Exhibit 3-3) should address all mechanisms to be used by the State to ensure that narrative criteria 

are attained. Because implementation of chemical-specific numeric criteria is a key component of 

State toxics control programs, narrative criteria implementation procedures must describe or 

reference the State's procedures to implement such chemical-specific numeric criteria (e.g., 

procedures for establishing chemical-specific permit limits under the NPDES permitting program). 

Implementation procedures must also address State programs to control whole-effluent toxicity 

(WET) and may address programs to implement biological criteria, where such programs have been 

developed by the State. Implementation procedures therefore serve as umbrella documents that 

describe how the State's various toxics control programs are integrated to ensure adequate 

protection for aquatic life and human health and attainment of the narrative toxics criterion. In 

essence, the procedure should apply the "independent application" principle, which provides for 

independent evaluations of attainment of a designated use based on chemical-specific, wholeeffluent toxicity, and biological criteria methods (see section 3.5.3 and Appendices C, K, and R).

EPA encourages, and may ultimately require, State implementation procedures to provide for 

implementation of biological criteria. However, the regulatory basis for requiring whole-effluent 

toxicity (WET) controls is clear. EPA regulations at 40 CFR 122.44(d)(1)(v) require NPDES permits to 

contain WET limits where a permittee has been shown to cause, have the reasonable potential to 

cause, or contribute to an in-stream excursion of a narrative criterion. Implementation of chemicalspecific controls is also required by EPA regulations at 40 CFR 122.44(d)(1). State implementation 

procedures should, at a minimum, specify or reference methods to be used in implementing 
32

chemical-specific and whole-effluent toxicity-based controls, explain how these methods are 

integrated, and specify needed application criteria.

In addition to EPA's regulation at 40 CFR 131, EPA has regulations at 40 CFR 122.44 that cover the 

National Surface Water Toxics Control Program. These regulations are intrinsically linked to the 

requirements to achieve water quality standards, and specifically address the control of pollutants 

both with and without numeric criteria. For example, section 122.44(d)(1)(vi) provides the 

permitting authority with several options for establishing effluent limits when a State does not have a 

chemical-specific numeric criterion for a pollutant present in an effluent at a concentration that 

causes or contributes to a violation of the State's narrative criteria.

3.5.3 Biological Criteria 

The Clean Water Act of 1972 directs EPA to develop programs that will evaluate, restore, and 

maintain the chemical, physical, and biological integrity of the Nation's waters. In response to this 

directive, States and EPA have implemented chemically based water quality programs that address 

significant water pollution problems. However, over the past 20 years, it has become apparent that 

these programs alone cannot identify and address all surface water pollution problems. To help 

create a more comprehensive program, EPA is setting a priority for the development of biological 

criteria as part of State water quality standards. This effort will help States and EPA (1) achieve the 

biological integrity objective of the CWA set forth in section 101, and (2) comply with the statutory 

requirements under sections 303 and 304 of the Act (see Appendices C and K).

Regulatory Bases for Biocriteria 

The primary statutory basis for EPA's policy that States should develop biocriteria is found in 

sections 101(a) and 303(c)(2)(B) of the Clean Water Act. Section 101(a) of the CWA gives the general 

goal of biological criteria. It establishes as the objective of the Act the restoration and maintenance 

of the chemical, physical, and biological integrity of the Nation's waters. To meet this objective, 

water quality criteria should address biological integrity. Section 101(a) includes the interim water 

quality goal for the protection and propagation of fish, shellfish, and wildlife.

Section 304(a) of the Act provides the legal basis for the development of informational criteria, 

including biological criteria. Specific directives for the development of regulatory biocriteria can be 

found in section 303(c), which requires EPA to develop criteria based on biological assessment 

methods when numerical criteria are not established. 

Section 304(a) directs EPA to develop and publish water quality criteria and information on methods 

for measuring water quality and establishing water quality criteria for toxic pollutants on bases other 

than pollutant-by-pollutant, including biological monitoring and assessment methods that assess:
33

 the effects of pollutants on aquatic community components (". . . plankton, fish, 

shellfish, wildlife, plant life . . .") and community attributes (". . . biological 

community diversity, productivity, and stability . . .") in any body of water; and

 factors necessary " . . . to restore and maintain the chemical, physical, and biological 

integrity of all navigable waters . . ." for " . . . the protection of shellfish, fish, and 

wildlife for classes and categories of receiving waters ..."

Once biocriteria are formally adopted into State standards, biocriteria and aquatic life use 

designations serve as direct, legal endpoints for determining aquatic life use attainment/nonattainment. CWA section 303(c)(2)(B) provides that when numeric criteria are not available, States 

shall adopt criteria for toxics based on biological monitoring or assessment methods; biocriteria can 

be used to meet this requirement.

Development and Implementation of Biocriteria 

Biocriteria are numerical values or narrative expressions that describe the expected reference 

biological integrity of aquatic communities inhabiting waters of a designated aquatic life use. In the 

most desirable scenario, these would be waters that are either in pristine condition or minimally 

impaired. However, in some areas these conditions no longer exist and may not be attainable. In 

these situations, the reference biological communities represent the best attainable conditions. In 

either case, the reference conditions then become the basis for developing biocriteria for major 

surface water types (streams, rivers, lakes, wetlands, estuaries, or marine waters). 

Biological criteria support designated aquatic life use classifications for application in State 

standards (see chapter 2). Each State develops its own designated use classification system based 

on the generic uses cited in the Act (e.g., protection and propagation of fish, shellfish, and wildlife). 

Designated uses are intentionally general. However, States may develop subcategories within use 

designations to refine and clarify the use class. Clarification of the use class is particularly helpful 

when a variety of surface waters with distinct characteristics fit within the same use class, or do not 

fit well into any category. 

For example, subcategories of aquatic life uses may be on the basis of attainable habitat (e.g., 

coldwater versus warmwater stream systems as represented by distinctive trout or bass fish 

communities, respectively). Special uses may also be designated to protect particularly unique, 

sensitive, or valuable aquatic species, communities, or habitats. 

Resident biota integrate multiple impacts over time and can detect impairment from known and 

unknown causes. Biological criteria can be used to verify improvement in water quality in response 

to regulatory and other improvement efforts and to detect new or continuing degradation of waters. 

Biological criteria also provide a framework for developing improved best management practices and 

management measures for nonpoint source impacts. Numeric biological criteria can provide 

effective monitoring criteria for more definitive evaluation of the health of an aquatic ecosystem. 
34

The assessment of the biological integrity of a water body should include measures of the structure 

and function of the aquatic community within a specified habitat. Expert knowledge of the system is 

required for the selection of appropriate biological components and measurement indices. The 

development and implementation of biological criteria requires: 

 selection of surface waters to use in developing reference conditions for each 

designated use;

 measurement of the structure and function of aquatic communities in reference 

surface waters to establish biological criteria;

 measurement of the physical habitat and other environmental characteristics of the 

water resource; and

 establishment of a protocol to compare the biological criteria to biota in comparable 

test waters to determine whether impairment has occurred. 

These elements serve as an interactive network that is particularly important during early 

development of biological criteria where rapid accumulation of information is effective for refining 

both designated uses and developing biological criteria values and the supporting biological 

monitoring and assessment techniques.

3.5.4 Sediment Criteria 

While ambient water quality criteria are playing an important role in assuring a healthy aquatic 

environment, they alone have not been sufficient to ensure appropriate levels of environmental 

protection. Sediment contamination, which can involve deposition of toxicants over long periods of 

time, is responsible for water quality impacts in some areas.

EPA has authority to pursue the development of sediment criteria in streams, lakes and other waters 

of the United States under sections 104 and 304(a)(1) and (2) of the CWA as follows:

 section 104(n)(1) authorizes the Administrator to establish national programs that 

study the effects of pollution, including sedimentation, in estuaries on aquatic life;

 section 304(a)(1) directs the Administrator to develop and publish criteria for water 

quality, including information on the factors affecting rates of organic and inorganic 

sedimentation for varying types of receiving waters;

 section 304(a)(2) directs the Administrator to develop and publish information on, 

among other issues, "the factors necessary for the protection and propagation of 

shellfish, fish, and wildlife for classes and categories of receiving waters. . . ."

To the extent that sediment criteria could be developed that address the concerns of the section 

404(b)(1) Guidelines for discharges of dredged or fill material under the CWA or the Marine 

Protection, Research, and Sanctuaries Act, they could also be incorporated into those regulations.
35

EPA's current sediment criteria development effort, as described below, focuses on criteria for the 

protection of aquatic life. EPA anticipates potential future expansion of this effort to include 

sediment criteria for the protection of human health.

Chemical Approach to Sediment Criteria Development 

Over the past several years, sediment criteria development activities have centered on evaluating and 

developing the Equilibrium Partitioning Approach for generating sediment criteria. The Equilibrium 

Partitioning Approach focuses on predicting the chemical interaction between sediments and 

contaminants. Developing an understanding of the principal factors that influence the 

sediment/contaminant interactions will allow predictions to be made regarding the level of 

contaminant concentration that benthic and other organisms may be exposed to. Chronic water 

quality criteria, or possibly other toxicological endpoints, can then be used to predict potential 

biological effects. In addition to the development of sediment criteria, EPA is also working to 

develop a standardized sediment toxicity test that could be used with or independently of sediment 

criteria to assess chronic effects in fresh and marine waters.

Equilibrium Partitioning (EqP) Sediment Quality Criteria (SQC) are the U.S. Environmental Protection 

Agency's best recommendation of the concentration of a substance in sediment that will not 

unacceptably affect benthic organisms or their uses.

Methodologies for deriving effects-based SQC vary for different classes of compounds. For nonionic organic chemicals, the methodology requires normalization to organic carbon. A methodology 

for deriving effects-based sediment criteria for metal contaminants is under development and is 

expected to require normalization to acid volatile sulfide. EqP SQC values can be derived for varying 

degrees of uncertainty and levels of protection, thus permitting use for ecosystem protection and 

remedial programs.

Application of Sediment Criteria 

SQC would provide a basis for making more informed decisions on the environmental impacts of 

contaminated sediments. Existing sediment assessment methodologies are limited in their ability to 

identify chemicals of concern, responsible parties, degree of contamination, and zones of impact. 

To make the most informed decisions, EPA believes that a comprehensive approach using SQC and 

biological test methods is preferred.

Sediment criteria will be particularly valuable in site-monitoring applications where sediment 

contaminant concentrations are gradually approaching a criterion over time or as a preventive tool to 

ensure that point and nonpoint sources of contamination are controlled and that uncontaminated 

sediments remain uncontaminated. Also comparison of field measurements to sediment criteria will 

be a reliable method for providing early warning of a potential problem. An early warning would 

provide an opportunity to take corrective action before adverse impacts occur. For the reasons 
36

mentioned above, it has been identified that SQC are essential to resolving key contaminated 

sediment and source control issues in the Great Lakes.

Specific Applications 

Specific applications of sediment criteria are under development. The primary use of EqP-based 

sediment criteria will be to assess risks associated with contaminants in sediments. The various 

offices and programs concerned with contaminated sediment have different regulatory mandates 

and, thus, have different needs and areas for potential application of sediment criteria. Because 

each regulatory need is different, EqP-based sediment quality criteria designed specifically to meet 

the needs of one office or program may have to be implemented in different ways to meet the needs 

of another office or program. 

One mode of application of EqP-based numerical sediment quality criteria would be in a tiered 

approach. In such an application, when contaminants in sediments exceed the sediment quality 

criteria the sediments would be considered as causing unacceptable impacts. Further testing may or 

may not be required depending on site-specific conditions and the degree in which a criterion has 

been violated. (In locations where contamination significantly exceeds a criterion, no additional 

testing would be required. Where sediment contaminant levels are close to a criterion, additional 

testing might be necessary.) Contaminants in a sediment at concentrations less than the sediment 

criterion would not be of concern. However, in some cases the sediment could not be considered 

safe because it might contain other contaminants above safe levels for which no sediment criteria 

exist. In addition, the synergistic, antagonistic, or additive effects of several contaminants in the 

sediments may be of concern. 

Additional testing in other tiers of an evaluation approach, such astoxicity tests, could be required to 

determine if the sediment is safe. It is likely that such testing would incorporate site-specific 

considerations. Examples of specific applications of sediment criteria after they are developed 

include the following:

 Establish permit limits for point sources to ensure that uncontaminated sediments 

remain uncontaminated or sediments already contaminated have an opportunity to 

cleanse themselves. Of course, this would occur only after criteria and the means to 

tie point sources to sediment contamination are developed.

 Establish target levels for nonpoint sources of sediment contamination.

 For remediation activities, SQC would be valuable in identifying:

o need for remediation, 

o spatial extent of remediation area,

o benefits derived from remediation activities,

o responsible parties,

o impacts of depositing contaminated sediments in water environments, and

o success of remediation activities.
37

In tiered testing sediment evaluation processes, sediment criteria and biological testing procedures 

work very well together.

Sediment Criteria Status 

Science Advisory Board Review 

The Science Advisory Board has completed a second review of the EqP approach to deriving sediment 

quality criteria for non-ionic contaminants. The November 1992 report (USEPA, 1992c) endorses the 

EqP approach to deriving criteria as ". . . sufficiently valid to be used in the regulatory process if the 

uncertainty associated with the method is considered, described, and incorporated," and that "EPA 

should establish criteria on the basis of present knowledge within the bounds of uncertainty”

The Science Advisory Board also identified the need for ". . . a better understanding of the 

uncertainty around the assumptions inherent in the approach, including assumptions of equilibrium, 

bioavailability, and kinetics, all critical to the application of the EqP."

Sediment Criteria Documents and Application Guidance 

EPA efforts at producing sediment criteria documents are being directed first toward phenanthrene, 

fluoranthene, dieldrin, acenaphthene, and endrin. Efforts are also being directed towards producing 

a guidance document on the derivation and interpretation of sediment quality criteria. The criteria 

documents were announced in the Federal Register in January 1994; the public comment period 

ended June 1994. Final documents and implementation guidance should be available in early 1996.

Methodology for Developing Sediment Criteria for Metal Contaminants 

EPA is proceeding to develop a methodology for calculating sediment criteria for benthic toxicity to 

metal contaminants, with key work focused on identifying and understanding the role of acid volatile 

sulfides (AVS), and other binding factors, in controlling the bioavailability of metal contaminants. A 

variety of field and laboratory verification studies are under way to add additional support to the 

methodology. Standard AVS sampling and analytical procedures are under development. 

Presentation of the metals methodology to the SAB for review is anticipated for Fall 1994.

Biological Approach to Sediment Criteria Development 

Under the Contaminated Sediment Management Strategy, EPA programs have committed to using 

consistent biological methods to determine if sediments are contaminated. In the water program, 

these biological methods will be used as a complement to the sediment-chemical criteria under 

development. The biological methods consist of both toxicity and bioaccumulation tests. 

Freshwater and saltwater benthic species, selected to represent the sensitive range of species' 

responses to toxicity, are used in toxicity tests to measure sediment toxicity. Insensitive freshwater 

and saltwater benthic species that form the base of the food chain are used in toxicity tests to 
38

measure the bioaccumulation potential of sediment. In FY 1994, acute toxicity tests and 

bioaccumulation tests selected by all the Agency programs should be standardized and available for 

use. Training for States and EPA Regions on these methods is expected to begin in FY1995.

In the next few years, research will be conducted to develop standardized chronic toxicity tests for 

sediment as well as toxicity identification evaluation (TIE) methods. The TIE approach will be used to 

identify the specific chemicals in a sediment causing acute or chronic toxicity in the test organisms. 

Under the Contaminated Sediment Management Strategy, EPA's programs have also agreed to 

incorporate these chronic toxicity and TIE methods into their sediment testing when they are 

available.

3.5.5 Wildlife Criteria 

Terrestrial and avian species are useful as sentinels for the health of the ecosystem as a whole. In 

many cases, damage to wildlife indicates that the ecosystem itself is damaged. Many wildlife species 

that are heavily dependent on the aquatic food web reflect the health of aquatic systems. In the case 

of toxic chemicals, terminal predators such as otter, mink, gulls, terns, eagles, ospreys, and turtles 

are useful as integrative indicators of the status or health of the ecosystem.

Statutory and Regulatory Authority 

Section 101(a)(2) of the CWA sets, as an interim goal of, 

...wherever attainable...water quality which provides for the protection and 

propagation of fish, shellfish, and wildlife...(emphasis added). 

Section 304(a)(1) of the Act also requires EPA to:

...develop and publish... criteria for water quality accurately reflecting...the kind and 

extent of all identifiable effects on health and welfare including...wildlife.

The Water Quality Standards Regulation reflect the statutory goals and requirements by requiring 

States to adopt, where attainable, the CWA section 101(a)(2) goal uses of protection and propagation 

of fish, shellfish, and wildlife (40 CFR 131.10), and to adopt water quality criteria sufficient to protect 

the designated use (40 CFR 131.11).

Wildlife Protection in Current Aquatic Criteria 

Current water quality criteria methodology is designed to protect fish, benthic invertebrates, and 

zooplankton; however, there is a provision in the current aquatic life criteria guidelines (Appendix H) 

that is intended to protect wildlife that consume aquatic organisms from the bioaccumulative 

potential of a compound. The final residue value can be based on either the FDA Action Level or a 

wildlife feeding study. However, if maximum permissible tissue concentration is not available from a
39

wildlife feeding study, a final residue value cannot be derived and the criteria quantification 

procedure continues without further consideration of wildlife impacts. Historically, wildlife have 

been considered only after detrimental effects on wildlife populations have been observed in the 

environment (this occurred with relationship to DDT, selenium, and PCBs).

Wildlife Criteria Development 

EPA's national wildlife criteria effort began following release of a 1987 Government Accounting 

Office study entitled Wildlife Management - National Refuge Contamination Is Difficult To Confirm 

and Clean Up (GAO, 1987). After waterfowl deformities observed at Kesterson Wildlife Refuge were 

linked to selenium contamination in the water, Congress requested this study and recommended 

that "the Administrator of EPA, in close coordination with the Secretary of the Interior, develop water 

quality criteria for protecting wildlife and their refuge habitat."

In November of 1988, EPA's Environmental Research Laboratory in Corvallis sponsored a workshop 

entitled Water Quality Criteria To Protect Wildlife Resources, (USEPA, 1989g) which was co-chaired by 

EPA and the Fish and Wildlife Service (FWS). The workshop brought together 26 professionals from a 

variety of institutions, including EPA, FWS, State governments, academia, and consultants who had 

expertise in wildlife toxicity, aquatic toxicity, ecology, environmental risk assessment, and 

conservation. Efforts at the workshop focused on evaluating the need for, and developing a strategy 

for production of wildlife criteria. Two recommendations came out of that workshop:

1. The process by which ambient water quality criteria are established should be 

modified to consider effects on wildlife; and

2. chemicals should be prioritized based on their potential to adversely impact 

wildlife species.

Based on the workshop recommendations, screening 

level wildlife criteria (SLWC) were calculated for priority 

pollutants and chemicals of concern submitted by the 

FWS to gauge the extent of the problem by:

1. evaluating whether existing 

water quality criteria for aquatic 

life are protective of wildlife, 

and 

2. prioritizing chemicals for their 

potential to adversely impact 

wildlife species.

There were 82 chemicals for which EPA had the necessary toxicity information as well as ambient 

water quality criteria, advisories, or lowest-observed-adverse-effect levels (LOAELs) to compare 

with the SLWC values.
40

As would be expected, the majority of chemicals had SLWC larger than existing water quality criteria, 

advisories, or LOAELs for aquatic life. However, the screen identified classes of compounds for 

which current ambient water quality criteria may not be adequately protective of wildlife: chlorinated 

alkanes, benzenes, phenols, metals, DDT, and dioxins. Many of these compounds are produced in 

very large amounts and have a variety of uses (e.g., solvents, flame retardants, organic syntheses of 

fungicides and herbicides, and manufacture of plastics and textiles. The manufacture and use of 

these materials produce waste byproduct). Also, 5 of the 21 are among the top 25 pollutants 

identified at Superfund sites in 1985 (3 metals, 2 organics).

Following this initial effort, EPA held a national meeting in April 1992 to constructively discuss and 

evaluate proposed methodologies for deriving wildlife criteria to build consensus among the 

scientific community as to the most defensible scientifically approach(es) to be pursued by EPA in 

developing useful and effective wildlife criteria.

The conclusions of this national meeting were as follows: 

 wildlife criteria should have a tissue-residue component when appropriate;

 peer-review of wildlife criteria and data sets should be used in their derivation

 wildlife criteria should incorporate methods to establish site-specific wildlife criteria;

 additional amphibian and reptile toxicity data are needed;

 further development of inter-species toxicological sensitivity factors are needed; and

 criteria methods should measure biomarkers in conjunction with other studies.

On April 16, 1993, EPA proposed wildlife criteria in the Water Quality Guidance for the Great Lakes 

System (58 F.R. 20802). The proposed wildlife criteria are based on the current EPA noncancer 

human health criteria approach. In this proposal, in addition to requesting comments on the 

proposed Great Lakes criteria and methods, EPA also requested comments on possible modifications 

of the proposed Great Lakes approach for consideration in the development of national wildlife 

criteria.

3.5.6 Numeric Criteria for Wetlands 

Extension of the EPA national 304(a) numeric aquatic life criteria to wetlands is recommended as part 

of a program to develop standards and criteria for wetlands. Appendices D and E provide an 

overview of the need for standards and criteria for wetlands. The 304(a) numeric aquatic life criteria 

are designed to be protective of aquatic life for surface waters and are generally applicable to most 

wetland types. Appendix E provides a possible approach, based on the site-specific guidelines, for 

detecting wetland types that might not be protected by direct application of national 304(a) criteria. 

The evaluation can be simple and inexpensive for those wetland types for which sufficient water 

chemistry and species assemblage data are available, but will be less useful for wetland types for 

which these data are not readily available. In Appendix E, the site-specific approach is described 

and recommended for wetlands for which modification of the 304(a) numeric criteria are considered 

necessary. The results of this type of evaluation, combined with information on local or regional 
41

environmental threats, can be used to prioritize wetland types (and individual criteria) for further 

site-specific evaluations and/or additional data collection. Close coordination among regulatory 

agencies, wetland scientists, and criteria experts will be required. 

3.6 Policy on Aquatic Life Criteria for Metals 

It is the policy of the Office of Water that the use of dissolved metal to set and measure compliance 

with water quality standards is the recommended approach, because dissolved metal more closely 

approximates the bioavailable fraction of metal in the water column than does total recoverable 

metal. This conclusion regarding metals bioavailability is supported by a majority of the scientific 

community within and outside EPA. One reason is that a primary mechanism for water column 

toxicity is adsorption at the gill surface which requires metals to be in the dissolved form. 

Until the scientific uncertainties are better resolved, a range of different risk management decisions 

can be justified by a State. EPA recommends that State water quality standards be based on 

dissolved metal--a conversion factor must be used in order to express the EPA criteria articulated as 

total recoverable as dissolved. (See the paragraph below for technical details on developing 

dissolved criteria.) EPA will also approve a State risk management decision to adopt standards based 

on total recoverable metal, if those standards are otherwise approvable as a matter of law. (Office of 

Water Policy and Technical Guidance on Interpretation and Implementation of Aquatic Life Metals 

Criteria USEPA, 1993f) 

3.6.1 Background 

The implementation of metals criteria is complex due to the site-specific nature of metals toxicity. 

This issue covers a number of areas including the expression of aquatic life criteria; total maximum 

daily loads (TMDLs), permits, effluent monitoring, and compliance; and ambient monitoring. The 

following Sections, based on the policy memorandum referenced above, provide additional guidance 

in each of these areas. Included in this Handbook as Appendix J are three guidance documents 

issued along with the Office of Water policy memorandum with additional technical details. They 

are: Guidance Document on Expression of Aquatic Life Criteria as Dissolved Criteria (Attachment 

#2), Guidance Document on Dynamic Modeling and Translators (Attachment #3), and Guidance 

Document on Monitoring (Attachment #4). These will be supplemented as additional information 

becomes available. 

Since metals toxicity is significantly affected by site-specific factors, it presents a number of 

programmatic challenges. Factors that must be considered in the management of metals in the 

aquatic environment include: toxicity specific to effluent chemistry; toxicity specific to ambient 

water chemistry; different patterns of toxicity for different metals; evolution of the state of the 

science of metals toxicity, fate, and transport; resource limitations for monitoring, analysis, 

implementation, and research functions; concerns regarding some of the analytical data currently on 

record due to possible sampling and analytical contamination; and lack of standardized protocols for 

clean and ultraclean metals analysis. The States have the key role in the risk management process of 
42

balancing these factors in the management of water programs. The site-specific nature of this issue 

could be perceived as requiring a permit-by-permit approach to implementation. However, EPA 

believes that this guidance can be effectively implemented on a broader level, across any waters with 

roughly the same physical and chemical characteristics, and recommends that States work with the 

EPA with that perspective in mind. 

3.6.2 Expression of Aquatic Life Criteria 

Dissolved vs. Total Recoverable Metal 

A major issue is whether, and how, to use dissolved metal concentrations ("dissolved metal") or total 

recoverable metal concentrations ("total recoverable metal") in setting State water quality standards. 

In the past, States have used both approaches when applying the same EPA Section 304(a) criteria 

guidance. Some older criteria documents may have facilitated these different approaches to 

interpretation of the criteria because the documents were somewhat equivocal with regards to 

analytical methods. The May 1992 interim guidance continued the policy that either approach was 

acceptable. 

The position that the dissolved metals approach is more accurate has been questioned because it 

neglects the possible toxicity of particulate metal. It is true that some studies have indicated that 

particulate metals appear to contribute to the toxicity of metals, perhaps because of factors such as 

desorption of metals at the gill surface, but these same studies indicate the toxicity of particulate 

metal is substantially less than that of dissolved metal. 

Furthermore, any error incurred from excluding the contribution of particulate metal will generally 

be compensated by other factors which make criteria conservative. For example, metals in toxicity 

tests are added as simple salts to relatively clean water. Due to the likely presence of a significant 

concentration of metals binding agents in many discharges and ambient waters, metals in toxicity 

tests would generally be expected to be more bioavailable than metals in discharges or in ambient 

waters. 

If total recoverable metal is used for the purpose of specifying water quality standards, the lower 

bioavailability of particulate metal and lower bioavailability of sorbed metals as they are discharged 

may result in an overly conservative water quality standard. The use of dissolved metal in water 

quality standards gives a more accurate result in the water column. However, total recoverable 

measurements in ambient water have value, in that exceedences of criteria on a total recoverable 

basis are an indication that metal loadings could be a stress to the ecosystem, particularly in 

locations other than the water column (e.g., in the sediments). 

The reasons for the potential consideration of total recoverable measurements include risk 

management considerations not covered by evaluation of water column toxicity alone. The ambient 

water quality criteria are neither designed nor intended to protect sediments, or to prevent effects in 

the food webs containing sediment dwelling organisms. A risk manager, however, may consider 
43

sediments and food chain effects and may decide to take a conservative approach for metals, 

considering that metals are very persistent chemicals. This conservative approach could include the 

use of total recoverable metal in water quality standards. However, since consideration of sediment 

impacts is not incorporated into the criteria methodology, the degree of conservatism inherent in the 

total recoverable approach is unknown. The uncertainty of metal impacts in sediments stem from 

the lack of sediment criteria and an imprecise 

understanding of the fate and transport of 

metals. EPA will continue to pursue research 

and other activities to close these knowledge 

gaps.

Dissolved Criteria 

In the toxicity tests used to develop EPA 

metals criteria for aquatic life, some fraction 

of the metal is dissolved while some fraction 

is bound to particulate matter. The present 

criteria were developed using total 

recoverable metal measurements or measures expected to give equivalent results in toxicity tests, 

and are articulated as total recoverable. Therefore, in order to express the EPA criteria as dissolved, 

a total recoverable to dissolved conversion factor must be used. Attachment #2 in Appendix J 

provides guidance for calculating EPA dissolved criteria from the published total recoverable criteria. 

The data expressed as percentage metal dissolved are presented as recommended values and 

ranges. However, the choice within ranges is a State risk management decision. EPA has recently 

supplemented the data for copper and is proceeding to further supplement the data for copper and 

other metals. As testing is completed, EPA will make this information available and this is expected 

to reduce the magnitude of the ranges for some of the conversion factors provided. EPA also 

strongly encourages the application of dissolved criteria across a watershed or waterbody, as 

technically sound and the best use of resources.

Site-Specific Criteria Modifications 

While the above methods will correct some site-specific factors affecting metals toxicity, further 

refinements are possible. EPA has issued guidance for three site-specific criteria development 

methodologies: recalculation procedure, water-effect ratio (WER) procedure (called the indicator 

species procedure in previous guidance) and resident species procedure. (See Section 3.7 of this 

Chapter.)

In the National Toxics Rule (57 FR 60848, December 22, 1992), EPA recommended the WER as an 

optional method for site-specific criteria development for certain metals. EPA committed in the NTR 

preamble to provide additional guidance on determining the WERs. The Interim Guidance on the 

Determination and Use of Water-Effect Ratios for Metals was issued by EPA on February 22, 1994 

and is intended to fulfill that commitment. This interim guidance supersedes all guidance 
44

concerning water-effect ratios and the recalculation procedure previously issued by EPA. This 

guidance is included as Appendix L to this Handbook.

In order to meet current needs, but allow for changes suggested by protocol users, EPA issued the 

guidance as "interim." EPA will accept WERs developed using this guidance, as well as by using other 

scientifically defensible protocols.

3.6.3 Total Maximum Daily Loads (TMDLs) and National Pollutant Discharge Elimination System 

(NPDES) Permits 

Dynamic Water Quality Modeling 

 

Although not specifically part of the reassessment of water quality criteria for metals, dynamic or 

probabilistic models are another useful tool for implementing water quality criteria, especially for 

those criteria protecting aquatic life. These models provide another way to incorporate site-specific 

data. The Technical Support Document for Water Quality-based Toxics Control (TSD) (USEPA, 1991a) 

describes dynamic, as well as static (steady-state) models. Dynamic models make the best use of 

the specified magnitude, duration, and frequency of water quality criteria and, therefore, provide a 

more accurate representation of the probability that a water quality standard exceedence will occur. 

In contrast, steady-state models frequently apply a number of simplifying, worst case assumptions 

which makes them less complex but also less accurate than dynamic models.

Dynamic models have received increased attention over the last few years as a result of the 

widespread belief that steady-state modeling is over-conservative due to environmentally 

conservative dilution assumptions. This belief has led to the misconception that dynamic models 

will always lead to less stringent regulatory controls (e.g., NPDES effluent limits) than steady-state 

models, which is not true in every application of dynamic models. EPA considers dynamic models to 

be a more accurate approach to implementing water quality criteria and continues to recommend 

their use. Dynamic modeling does require a commitment of resources to develop appropriate data. 

(See Appendix J, Attachment #3 and the USEPA, 1991a for details on the use of dynamic models.)

Dissolved-Total Metal Translators 

Expressing ambient water quality criteria for metals as the dissolved form of a metal poses a need to 

be able to translate from dissolved metal to total recoverable metal for TMDLs and NPDES permits. 

TMDLs for metals must be able to calculate: (1) dissolved metal in order to ascertain attainment of 

water quality standards, and (2) total recoverable metal in order to achieve mass balance necessary 

for permitting purposes.

EPA's NPDES regulations require that limits of metals in permits be stated as total recoverable in 

most cases (see 40 CFR §122.45(c)) except when an effluent guideline specifies the limitation in 

another form of the metal, the approved analytical methods measure only dissolved metal, or the 

permit writer expresses a metals limit in another form (e.g., dissolved, valent specific, or total) when 
45

required to carry out provisions of the Clean Water Act. This is because the chemical conditions in 

ambient waters frequently differ substantially from those in the effluent, and there is no assurance 

that effluent particulate metal would not dissolve after discharge. The NPDES rule does not require 

that State water quality standards be expressed as total recoverable; rather, the rule requires permit 

writers to translate between different metal forms in the calculation of the permit limit so that a total 

recoverable limit can be established. Both the TMDL and NPDES uses of water quality criteria require 

the ability to translate between dissolved metal and total recoverable metal. Appendix J, Attachment 

#3 provides guidance on this translation.

3.6.4 Guidance on Monitoring 

Use of Clean Sampling and Analytical Techniques 

In assessing waterbodies to determine the potential for toxicity problems due to metals, the quality 

of the data used is an important issue. Metals data are used to determine attainment status for 

water quality standards, discern trends in water quality, estimate background loads for TMDLs, 

calibrate fate and transport models, estimate effluent concentrations (including effluent variability), 

assess permit compliance, and conduct research. The quality of trace level metal data, especially 

below 1 ppb, may be compromised due to contamination of samples during collection, preparation, 

storage, and analysis. Depending on the level of metal present, the use of "clean" and "ultraclean" 

techniques for sampling and analysis may be critical to accurate data for implementation of aquatic 

life criteria for metals.

The significance of the sampling and analysis contamination problem increases as the ambient and 

effluent metal concentration decreases and, therefore, problems are more likely in ambient 

measurements. "Clean" techniques refer to those requirements (or practices for sample collection 

and handling) necessary to produce reliable analytical data in the part per billion (ppb) range. 

"Ultraclean" techniques refer to those requirements or practices necessary to produce reliable 

analytical data in the part per trillion (ppt) range. Because typical concentrations of metals in surface 

waters and effluents vary from one metal to another, the effect of contamination on the quality of 

metals monitoring data varies appreciably.

EPA plans to develop protocols on the use of clean and ultra-clean techniques and is coordinating 

with the United States Geological Survey (USGS) on this project, because USGS has been doing work 

on these techniques for some time, especially the sampling procedures. Draft protocols for clean 

techniques were presented at the Norfolk, VA analytical methods conference in the Spring of 1994 

and final protocols are expected to be available in early 1995. The development of comparable 

protocols for ultra-clean techniques is underway and are expected to be available in late 1995. In 

developing these protocols, we will consider the costs of these techniques and will give guidance as 

to the situations where their use is necessary. Appendix L, pp. 98-108 provide some general 

guidance on the use of clean analytical techniques. We recommend that this guidance be used by 

States and Regions as an interim step, while the clean and ultra-clean protocols are being 

developed.
46

Use of Historical Data 

The concerns about metals sampling and analysis discussed above raise corresponding concerns 

about the validity of historical data. Data on effluent and ambient metal concentrations are collected 

by a variety of organizations including Federal agencies (e.g., EPA, USGS), State pollution control 

agencies and health departments, local government agencies, municipalities, industrial dischargers, 

researchers, and others. The data are collected for a variety of purposes as discussed above.

Concern about the reliability of the sample collection and analysis procedures is greatest where they 

have been used to monitor very low level metal concentrations. Specifically, studies have shown data 

sets with contamination problems during sample collection and laboratory analysis, that have 

resulted in inaccurate measurements. For example, in developing a TMDL for New York Harbor, 

some historical ambient data showed extensive metals problems in the harbor, while other historical 

ambient data showed only limited metals problems. Careful resampling and analysis in 1992/1993 

showed the latter view was correct. The key to producing accurate data is appropriate quality 

assurance (QA) and quality control (QC) procedures. EPA believes that most historical data for 

metals, collected and analyzed with appropriate QA and QC at levels of 1 ppb or higher, are reliable. 

The data used in development of EPA criteria are also considered reliable, both because they meet 

the above test and because the toxicity test solutions are created by adding known amounts of 

metals.

With respect to effluent monitoring reported by an NPDES permittee, the permittee is responsible for 

collecting and reporting quality data on a Discharge Monitoring Report (DMR). Permitting authorities 

should continue to consider the information reported to be true, accurate, and complete as certified 

by the permittee. Where the permittee becomes aware of new information specific to the effluent 

discharge that questions the quality of previously submitted DMR data, the permittee must promptly 

submit that information to the permitting authority. The permitting authority will consider all 

information submitted by the permittee in determining appropriate enforcement responses to 

monitoring/reporting and effluent violations. (See Appendix J, Attachment #4 for additional details.)

3.7 Site-Specific Aquatic Life Criteria 

The purpose of this section is to provide guidance for the development of site-specific water quality 

criteria which reflect local environmental conditions. Site-specific criteria are allowed by regulation 

and are subject to EPA review and approval. The Federal water quality standards regulation at 

section 131.11(b)(1)(ii) provides States with the opportunity to adopt water quality criteria that are 

"...modified to reflect site-specific conditions." Site-specific criteria, as with all water quality criteria, 

must be based on a sound scientific rationale in order to protect the designated use. Existing 

guidance and practice are that EPA will approve site-specific criteria developed using appropriate 

procedures.
47

A site-specific criterion is intended to come closer than the national criterion to providing the 

intended level of protection to the aquatic life at the site, usually by taking into account the 

biological and/or chemical conditions (i.e., the species composition and/or water quality 

characteristics) at the site. The fact that the U.S. EPA has made these procedures available should 

not be interpreted as implying that the agency advocates that states derive site-specific criteria 

before setting state standards. Also, derivation of a site-specific criterion does not change the 

intended level of protection of the aquatic life at the site. 

3.7.1 History of Site-Specific Criteria Guidance 

National water quality criteria for aquatic life may be under- or over-protective if: 

1. the species at the site are more or less sensitive than those included in the national 

criteria data set (e.g., the national criteria data set contains data for trout, salmon, 

penaeid shrimp, and other aquatic species that have been shown to be especially 

sensitive to some materials), or 

2. physical and/or chemical characteristics of the site alter the biological availability 

and/or toxicity of the chemical (e.g., alkalinity, hardness, pH, suspended solids and 

salinity influence the concentration(s) of the toxic form(s) of some heavy metals, 

ammonia and other chemicals). 

Therefore, it is appropriate that site-specific procedures address each of these conditions separately 

as well as the combination of the two. In the early 1980's, EPA recognized that laboratory-derived 

water quality criteria might not accurately reflect site-specific conditions and, in response, created 

three procedures to derive site-specific criteria. This Handbook contains the details of these 

procedures, referenced below. 

1. The Recalculation Procedure is intended to take into account relevant 

differences between the sensitivities of the aquatic organisms in the national 

dataset and the sensitivities of organisms that occur at the site (see Appendix 

L, pp. 90-97). 

2. The Water-Effect Ratio Procedure (called the Indicator Species Procedure in 

USEPA, 1983a; 1984f ) provided for the use of a water-effect ratio (WER) that 

is intended to take into account relevant differences between the toxicities of 

the chemical in laboratory dilution water and in site water (see Appendix L). 

3. The Resident Species Procedure intended to take into account both kinds of 

differences simultaneously (see Section 3.7.6). 

These procedures were first published in the 1983 Water Quality Standards Handbook (USEPA, 

1983a) and expanded upon in the Guidelines for Deriving Numerical Aquatic Site-Specific Water 

Quality Criteria by Modifying National Criteria (USEPA, 1984f). Interest has increased in recent years 

as states have devoted more attention to chemical-specific water quality criteria for aquatic life. In 

addition, interest in water-effect ratios increased when they were integrated into some of the aquatic 
48

life criteria for metals that were promulgated for several states in the National Toxics Rule (57 FR

60848, December 22, 1992). The Office of Water Policy and Technical Guidance on Interpretation 

and Implementation of Aquatic Life Criteria for Metals (USEPA, 1993f) (see Section 3.6 of this 

Handbook) provided further guidance on site-specific criteria for metals by recommending the use 

of dissolved metals for setting and measuring compliance with water quality standards. 

The early guidance concerning WERs (USEPA, 1983a; 1984f) contained few details and needed 

revision, especially to take into account newer guidance concerning metals. To meet this need, EPA 

issued Interim Guidance on the Determination and Use of Water-Effect Ratios for Metals in 1994 

(Appendix L). Metals are specifically addressed in Appendix L because of the National Toxics Rule 

and because of current interest in aquatic life criteria for metals; although most of this guidance also 

applies to other pollutants, some obviously applies only to metals. Appendix L supersedes all 

guidance concerning water-effect ratios and the Indicator Species Procedure given in Chapter 4 of 

the Water Quality Standards Handbook (USEPA, 1983a) and in Guidelines for Deriving Numerical 

Aquatic Site-Specific Water Quality Criteria by Modifying National Criteria (USEPA, 1984f). Appendix 

L (p. 90-98) also supersedes the guidance in these earlier documents for the Recalculation Procedure 

for performing site-specific criteria modifications. The Resident Species Procedure remains 

essentially unchanged since 1983 (except for changes in the averaging periods to conform to the 

1985 aquatic life criteria guidelines (USEPA, 1985b) and is presented in Section 3.7.6, below. 

The previous guidance concerning sitespecific procedures did not allow the 

Recalculation Procedure and the WER 

procedure to be used together in the 

derivation of a site-specific aquatic life 

criterion; the only way to take into 

account both species composition and 

water quality characteristics in the 

determination of a site-specific 

criterion was to use the Resident 

Species Procedure. A specific change 

contained Appendix L is that, except in 

jurisdictions that are subject to the National Toxics Rule, the Recalculation Procedure and the WER 

Procedure may now be used together provided that the recalculation procedure is performed first. 

Both the Recalculation Procedure and the WER Procedure are based directly on the guidelines for 

deriving national aquatic life criteria (USEPA 1985 ) and, when the two are used together, use of the 

Recalculation Procedure must be performed first because the Recalculation Procedure has specific 

implications concerning the determination of the WER. 

3.7.2 Preparing to Calculate Site-Specific Criteria 

Adopting site-specific criteria in water quality standards is a State option--not a requirement. 

Moreover, EPA is not advocating that States use site-specific criteria development procedures for 
49

setting all aquatic life criteria as opposed to using the National Section 304(a) criteria 

recommendations. Site-specific criteria are not needed in all situations. When a State considers the 

possibility of developing site-specific criteria, it is essential to involve the appropriate EPA Regional 

office at the start of the project. 

 

This early planning is also essential if it appears that data generation and testing may be conducted 

by a party other than the State or EPA. The State and EPA need to apply the procedures judiciously 

and must consider the complexity of the problem and the extent of knowledge available concerning 

the fate and effect of the pollutant under consideration. If site-specific criteria are developed 

without early EPA involvement in the planning and design of the task, the State may expect EPA to 

take additional time to closely scrutinize the results before granting any approval to the formally 

adopted standards. 

The following sequence of decisions need to be made before any of the procedures are initiated: 

 verify that site-specific criteria are actually needed (e.g., that the use of clean 

sampling and/or analytical techniques, especially for metals, do not result in 

attainment of standards.) 

 Define the site boundaries. 

 Determine from the national criterion document and other sources if physical and/or 

chemical characteristics are known to affect the biological availability and/or toxicity 

of a material of interest. 

 If data in the national criterion document and/or from other sources indicate that the 

range of sensitivity of the selected resident species to the material of interest is 

different from the range for the species in the national criterion document, and 

variation in physical and/or chemical characteristics of the site water is not expected 

to be a factor, use the Recalculation Procedure (Section 3.7.4). 

 If data in the national criterion document and/or from other sources indicate that 

physical and/or chemical characteristics of the site water may affect the biological 

availability and/or toxicity of the material of interest, and the selected resident 

species range of sensitivity is similar to that for the species in the national criterion 

document, use the Water-Effect Ratio Procedure (Section 3.7.5). 

 If data in the national criterion document and/or from other sources indicated that 

physical and/or chemical characteristics of the site water may affect the biological 

availability and/or toxicity of the material of interest, and the selected resident 

species range of sensitivity is different from that for the species in the national 

criterion document, and if both these differences are to be taken into account, use 

the Recalculation Procedure in conjunction with the Water-Effect Ratio Procedure or 

use the Resident Species Procedure (Section 3.7.6). 

3.7.3 Definition of a Site 
50

Since the rationales for site-specific criteria are usually based on potential differences in species 

sensitivity, physical and chemical characteristics of the water, or a combination of the two, the 

concept of site must be consistent with this rationale. 

In the general context of site-specific criteria, a "site" may be a state, region, watershed, waterbody, 

or segment of a waterbody. The site-specific criterion is to be derived to provide adequate 

protection for the entire site, however the site is defined. 

If water quality effects on toxicity are not a consideration, the site can be as large as a generally 

consistent biogeographic zone permits. For example, large portions of the Chesapeake Bay, Lake 

Michigan, or the Ohio River may be considered as one site if their respective aquatic communities do 

not vary substantially. However, when a site-specific criterion is derived using the Recalculation 

Procedure, all species that "occur at the site" need to be taken into account when deciding what 

species, if any, are to be deleted from the dataset. Unique populations or less sensitive uses within 

sites may justify a designation as a distinct site. 

If the species of a site are toxicologically comparable to those in the national criteria data set for a 

material of interest, and physical and/or chemical water characteristics are the only factors 

supporting modification of the national criteria, then the site can be defined on the basis of 

expected changes in the material's biological availability and/or toxicity due to physical and 

chemical variability of the site water. However, when a site-specific criterion is derived using a WER, 

the WER is to be adequately protective of the entire site. If, for example, a site-specific criterion is 

being derived for an estuary, WERs could be determined using samples of the surface water obtained 

from various sampling stations, which, to avoid confusion, should not be called "sites". If all the 

WERs were sufficiently similar, one site-specific criterion could be derived to apply to the whole 

estuary. If the WERs were sufficiently different, either the lowest WER could be used to derive a sitespecific criterion for the whole estuary, or the data might indicate that the estuary should be divided 

into two or more sites, each with its own criterion. 

3.7.4 The Recalculation Procedure 

The Recalculation Procedure is intended to cause a site-specific criterion to appropriately differ from 

a national aquatic life criterion if justified by demonstrated pertinent toxicological differences 

between the aquatic species that occur at the site and those that were used in the derivation of the 

national criterion. There are at least three reasons why such differences might exist between the 

two sets of species. 

 First, the national dataset contains aquatic species that are sensitive to many 

pollutants, but these and comparably sensitive species might not occur at the site. 

 Second, a species that is critical at the site might be sensitive to the pollutant and 

require a lower criterion. (A critical species is a species that is commercially or 

recreationally important at the site, a species that exists at the site and is listed as 

threatened or endangered under section 4 of the Endangered Species Act, or a 
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species for which there is evidence that the loss of the species from the site is likely 

to cause an unacceptable impact on a commercially or recreationally important 

species, a threatened or endangered species, the abundances of a variety of other 

species, or the structure or function of the community.)

 Third, the species that occur at the site might represent a narrower mix of species 

than those in the national dataset due to a limited range of natural environmental 

conditions. 

The procedure presented in Appendix L, pp. 90-98 is structured so that corrections and additions 

can be made to the national dataset without the deletion process being used to take into account 

taxa that do not occur at the site; in effect, this procedure makes it possible to update the national 

aquatic life criterion. All corrections and additions that have been approved by EPA are required, 

whereas use of the deletion process is optional. The deletion process may not be used to remove 

species from the criterion calculation that are not currently present at a site due to degraded 

conditions.

The Recalculation Procedure is more likely to result in lowering a criterion if the net result of 

addition and deletion is to decrease the number of genera in the dataset, whereas the procedure is 

more likely to result in raising a criterion if the net result of addition and deletion is to increase the 

number of genera in the dataset.

For the lipid soluble chemicals whose national Final Residue Values are based on Food and Drug 

Administration (FDA) action levels, adjustments in those values based on the percent lipid content of 

resident aquatic species is appropriate for the derivation of site-specific Final Residue Values. For 

lipid-soluble materials, the national Final Residue Value is based on an average 11 percent lipid 

content for edible portions for the freshwater chinook salmon and lake trout and an average of 10 

percent lipids for the edible portion for saltwater Atlantic herring. Resident species of concern may 

have higher (e.g., Lake Superior siscowet, a race of lake trout) or lower (e.g., many sport fish) 

percent lipid content than used for the national Final Residue Value.

For some lipid-soluble materials such as polychlorinated biphenyls (PCB) and DDT, the national Final 

Residue Value is based on wildlife consumers of fish and aquatic invertebrate species rather than an 

FDA action level because the former provides a more stringent residue level. See the National 

Guidelines (USEPA, 1985b) for details.

For the lipid-soluble materials whose national Final Residue Values are based on wildlife effects, the 

limiting wildlife species (mink for PCB and brown pelican for DDT) are considered acceptable 

surrogates for resident avian and mammalian species (e.g., herons, gulls, terns, otter, etc.) 

Conservatism is appropriate for those two chemicals, and no less restrictive modification of the 

national Final Residue Value is appropriate. The site-specific Final Residue Value would be the same 

as the national value.
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3.7.5 The Water-Effect Ratio (WER) Procedure 

The guidance on the Water-Effect Ratio Procedure presented in Appendix L is intended to produce 

WERs that may be used to derive site-specific aquatic life criteria from most national and state 

aquatic life criteria that were derived from laboratory toxicity data. 

As indicated in Appendix L, the determination of a water-effect ratio may require substantial 

resources. A discharger should consider cost-effective, preliminary measures described in this 

Appendix L (e.g., use of "clean" sampling and chemical analytical techniques especially for metals, or 

in non-NTR States, a recalculated criterion) to determine if an indicator species site-specific criterion 

is really needed. In many instances, use of these other measures may eliminate the need for 

deriving water-effect ratios. The methods described in the 1994 interim guidance (Appendix L) 

should be sufficient to develop site-specific criteria that resolve concerns of dischargers when there 

appears to be no instream toxicity but, where (a) a discharge appears to exceed existing or proposed 

water quality-based permit limits, or (b) an instream concentration appears to exceed an existing or 

proposed water quality criterion. 

WERs obtained using the methods described in Appendix L should only be used to adjust aquatic life 

criteria that were derived using laboratory toxicity tests. WERs determined using the methods 

described herein cannot be used to adjust the residue-based mercury Criterion Continuous 

Concentration (CCC) or the field-based selenium freshwater criterion. 

Except in jurisdictions that are subject to the NTR, the WERs may also be used with site-specific 

aquatic life criteria that are derived using the Recalculation Procedure described in Appendix L 

(p.90). 

 

Water-Effect Ratios in the Derivation of Site-Specific Criteria 

A central question concerning WERs is whether their use by a State results in a site-specific criterion 

subject to EPA review and approval under Section 303(c) of the Clean Water Act? 

Derivation of a water-effect ratio by a State is a site-specific criterion adjustment subject to EPA 

review and approval/disapproval under Section 303(c). There are two options by which this review 

can be accomplished. 

Option 1: 

A State may derive and submit each individual water-effect ratio determination to EPA for review and 

approval. This would be accomplished through the normal review and revision process used by a 

State. 

 
53

Option 2: 

A State can amend its water quality standards to provide a formal procedure which includes 

derivation of water-effect ratios, appropriate definition of sites, and enforceable monitoring 

provisions to assure that designated uses are protected. Both this procedure and the resulting 

criteria would be subject to full public participation requirements. EPA would review and 

approve/disapprove this protocol as a revised standard as part of the State's triennial 

review/revision. After adoption of the procedure, public review of a site-specific criterion could be 

accomplished in conjunction with the public review required for permit issuance. For public 

information, EPA recommends that once a year the State publish a list of site-specific criteria.

An exception to this policy applies to the waters of the jurisdictions included in the National Toxics 

Rule. The EPA review is not required for the jurisdictions included in the National Toxics Rule where 

EPA established the procedure for the State for application to the criteria promulgated. The National 

Toxics Rule was a formal rulemaking process (with notice and comment) in which EPA preauthorized the use of a correctly applied water-effect ratio. That same process has not yet taken 

place in States not included in the National Toxics Rule. 

However, the National Toxics Rule does not affect State authority to establish scientifically defensible 

procedures to determine Federally authorized WERs, to certify those WERs in NPDES permit 

proceedings, or to deny their application based on the State's risk management analysis. 

As described in Section 131.36(b)(iii) of the water quality standards regulation (the official regulatory 

reference to the National Toxics Rule), the water-effect ratio is a site-specific calculation. As 

indicated on page 60866 of the preamble to the National Toxics Rule, the rule was constructed as a 

rebuttable presumption. The water-effect ratio is assigned a value of 1.0 until a different watereffect ratio is derived from suitable tests representative of conditions in the affected waterbody. It is 

the responsibility of the State to determine whether to rebut the assumed value of 1.0 in the National 

Toxics Rule and apply another value of the water-effect ratio in order to establish a site-specific 

criterion. The site-specific criterion is then used to develop appropriate NPDES permit limits. The 

rule thus provides a State with the flexibility to derive an appropriate site-specific criterion for 

specific waterbodies.

As a point of emphasis, although a water-effect ratio affects permit limits for individual dischargers, 

it is the State in all cases that determines if derivation of a site-specific criterion based on the watereffect ratio is allowed and it is the State that ensures that the calculations and data analysis are done 

completely and correctly.

3.7.6 The Resident Species Procedure 

The resident Species Procedure for the derivation of a site-specific criterion accounts for differences 

in resident species sensitivity and differences in biological availability and/or toxicity of a material 

due to variability in physical and chemical characteristics of a site water. Derivation of the site-
54

specific criterion maximum concentration (CMC) and site-specific criterion continuous concentration 

(CCC) are accomplished after the complete acute toxicity minimum data set requirements have been 

met by conducting tests with resident species in site water. Chronic tests may also be necessary. 

This procedure is designed to compensate concurrently for any real differences between the 

sensitivity range of species represented in the national data set and for site water which may 

markedly affect the biological availability and/or toxicity of the material of interest.

Certain families of organisms have been specified in the National Guidelines acute toxicity minimum 

data set (e.g., Salmonidae in fresh water and Penaeidae or Mysidae in salt water); if this or any other 

requirement cannot be met because the family or other group (e.g., insect or benthic crustacean) in 

fresh water is not represented by resident species, select a substitute(s) from a sensitive family 

represented by one or more resident species and meet the 8 family minimum data set requirement. 

If all the families at the site have been tested and the minimum data set requirements have not been 

met, use the most sensitive resident family mean acute value as the site-specific Final Acute Value.

To derive the criterion maximum concentration divide the site-specific Final Acute Value by two. 

The site-specific Final Chronic Value can be obtained as described in the Appendix L. The lower of 

the site-specific Final Chronic Value (as described in the recalculation procedure - Appendix L, p. 

90) and the recalculated site-specific Final Residue Value becomes the site-specific criterion 

continuous concentration unless plant or other data (including data obtained from the site-specific 

tests) indicates a lower value is appropriate. If a problem is identified, judgment should be used in 

establishing the site-specific criterion.

The frequency of testing (e.g., the need for seasonal testing) will be related to the variability of the 

physical and chemical characteristics of site water as it is expected to affect the biological availability 

and/or toxicity of the material of interest. As the variability increases, the frequency of testing will 

increase. Many of the limitations discussed for the previous two procedures would also apply to this 

procedure.

Endnotes 

1. Proceedings in production.

Contact: Ecological Risk Assessment Branch (4304)

U.S. Environmental Protection Agency

401 M Street, S.W.

Washington, DC 20460

Telephone (202) 260-1940