United States
Environmental Protecuon Office of Water EPA 833-8-94-QCP
Agency (4203) July 1994
WHOLE EFFLUENT TOXICITY
(WET) CONTROL POLICY
POLICY FOR THE DEVELOPMENT OF EFFLUENT LIMITATIONS IN
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM PERMITS
TO CONTROL WHOLE EFFLUENT TOXICITY FOR THE PROTECTION
OF AQUATIC LIFE
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July 1994
POLICY FOR THE DEVELOPMENT OF EFFLUENT LIMITATIONS IN
POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) PERMITS TO CQNTPnL
WHOLE EFFLUENT TOXICITY (WET) FOR THE PROTECTION OF AQUATIC T.TFtr
INTRODUCTION
EPA is today publishing a national policy on the control of
WET in NPDES permits. This policy is intended (i) to promote
uniform, nationwide compliance with statutory and regulatory
requirements for the control of WET, and (ii) to assist permit
writers in implementing these requirements.
This policy reflects EPA'a experience in implementing the
regulations at 40 C.F.R. § 122.44(d)(1), which were originally
published at 54 Fed. Reg. 23868 (June 2, 1989) {also referred to
as "the water quality permitting regulations"). In part, this
policy restates those regulations and reaffirms EPA's strong,
continuing commitment .to their prompt and complete
.implementation. The water quality permitting regulations, as
well as the statutory provisions restated in this policy
document, are fully binding on EPA Regions as well as States
authorized to administer the NPDES program.
This policy also provides guidance to permit writers on
implementation of the statutory and regulatory requirements for
the control of WET.1 EPA permit writers are expected to follow
the portions of this policy that provide such guidance, although
decisions on individual permit provisions should be made on *
case-by-case basis, applying the law and regulations to specific
facts and justifying decisions in the record for the permit.
Similarly, EPA Regions will consider this policy in determining
whether State-issued NPDES permits adequately implement the
statutory and regulatory requirements for the control of WET.
This policy addresses some specific areas where question*
have arisen regarding the implementation of statutory and
regulatory requirements. It does not address all areas wher« th«
regulatory agency will exercise judgment in the implementation of
statutory and regulatory requirements. For the questions
addressed, it provides EPA's view as to the best course of action
in most instances. This policy does not establish or affect
legal rights or obligations and is not finally determinative of
the issues addressed, Most importantly, nothing in this policy
should be interpreted as providing any relief from the statutory
and regulatory requirement -hat permits include conditions *•
necessary to assure attainment of water quality standards.
LA brief summary of existing Agency policy and guidance
addressing WET issues is contained in Appendix One to today
policy.
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SUMMARY OF STATEMENTS OF POLICY
Eight statements of policy appear below. Explanations of
each statement follow.
1. Basis for WET Controls
The permitting authority should evaluate WET water quality
criteria attainment for acute WET at the edge of the acute mixing
zone and for chronic WET at the edge of the chronic mixing zone
except where the State has different requirements for evaluating
WET criteria.2 The permitting authority will develop WET
effluent limitations based upon the more stringent of the acute
or chronic criterion applied at the edge of the respective mixing
zone, or, alternatively, on both.
2. Evaluation of Dischargers for Reasonable Potential
At a minimum, the permitting authority should review all
major dischargers for reasonable potential to cause or contribute
to exceedance of WET water quality criteria.
3. Evaluating Reasonable Potential
The permitting authority will consider available WET testing
data and other information in evaluating whether a discharger has
reasonable potential to cause or contribute to exceedance of WET
water quality criteria.
4. Consequences of Establishing Reasonable Potential
Upon finding reasonable potential to cause or contribute to
exceedance of WET water quality criteria, the permitting
authority will impose effluent limitations to control WET.
5. Whole Effluent Toxicitv Monitoring
Where appropriate, the permitting authority should impose
WET monitoring conditions upon dischargers that do not have
effluent limitations to control WET.
6. Compliance Schedules in NPDES Permits
Where allowed under State and federal law, NPDES permits
contain schedules for compliance with WET effluent limitations.
throughout this policy, the term "WET water quality
criteria" refers to State numeric water quality criteria for «CT
and State narrative water quality criteria for toxicity such as
"no toxics in toxics amounts" in State water quality standards.
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7. whole Effluent Toxicitv Controls and the Pollutants
and Chlorine
The requirements of the water quality permitting regulations
apply without regard to the pollutant(s) that may be causing
toxicity, including ammonia and chlorine.
8. Whole Effluent Toxicitv Controls and Publicly Owned
Treatment Works fPOTWsl
The requirements of the water quality permitting regulations
apply to all dischargers, including POTWs.
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EXPLANATION OF STATEMENTS OF POLICY3
1. Basis for WET Controls
The permitting authority should evaluate WET water
quality criteria attainment for acute WIT at the edge
of the acute mixing tone and for chronic WET at the
edge of the chronic mixing sone except where the state
has different requirements for evaluating WET criteria.
The permitting authority will develop WET effluent
limitations based upon the more stringent of the acute
or chronic criterion applied at the edge of the
respective mixing sone, or, alternatively, on both.
This policy statement describes the procedure permitting
authorities should use to evaluate WET water quality criteria
attainment and to develop effluent limitations to control WET.
In the absence of more specific State requirements, EPA believes
this approach most appropriately assures compliance with State
water quality standards. ,' The permitting authority must
•evaluate WET water quality criteria attainment according to the
applicable state water quality standard(s). Permitting
authorities should assess WET concentrations as diluted in the
receiving water at the edge of the acute and chronic mixing zones
JTo aid the reader in using this policy, Appendix Two
contains some background materials on WET testing, the State
water quality standards process and WET, and federal statutory
and regulatory requirements for development of water quality-
based permit limitations for WET.
4State water quality standards or implementation procedures
may (l) specify whether and how it is appropriate to account for
dilution in establishing WET controls; (2) require the applicable
criteria to apply at the outfall point of discharge or may
contain a specific policy approved by EPA allowing or prohibiting
mixing zones; as well as (3) specify exposure factors for WET
which are relevant to the application of this policy statement,
such as critical flow requirements for the receiving water,
appropriate modeling techniques for determining the fate of the
pollutant ear pollutant parameter in stream, or required
technique* for evaluating the mixing of the pollutant or
pollutant parameter in the stream.
5NPDES permitting authorities traditionally measure
compliance with effluent limitations at the outfall point of
discharge. By issuing this policy statement, EPA does not intend
to disturb this well-established permitting practice. Permittinq
authorities are familiar with procedures for determining the
concentration of toxicity in-streaa and establishing end-of-pxp*
effluent limitations on the basis of the information.
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and apply the more stringent of the acute criterion at the edge
of the acute mixing zone or the chronic criterion at the edge of
the chronic mixing zone in developing WET effluent limitations.
If there is uncertainty as to which of the two criterion so
applied is more stringent for the discharge, however, the
permitting authority will apply both.
The statement reflects the specific requirement of 40 c.F.R.
S 122.44(d)(1)(ii) that "where appropriate, [the permitting
authority will consider] the dilution of the effluent in the
receiving water" in determining whether a discharge causes, has
the reasonable potential to cause, or contributes to exceedance
of WET water quality criteria. This statement should assist
permitting authorities in establishing WET controls which meet
the requirements of sections 301(b)(l)(C) and 402 of the Clean
Water Act (CWA) and 40 C.F.R. S 122.44(d)(1).
40 C.F.R. S 122.44(d)(1)(iv) and (v) require the permitting
authority to impose effluent limitations to control WET where it
determines that a discharge causes, has the reasonable potential
to cause, or contributes to exceedance of WET water quality
criteria. 40 C.F.R. S I22.44(d)(1)(vii) also requires permitting
authorities to establish effluent limitations on point sources.
which are consistent with the requirements of applicable State
water quality standards. This is a •basic premise of this policy
statement. Where the applicable State water quality standard or
implementation procedure requires a different basis for
establishing WET controls, the permitting authority must follow
applicable State requirements.6
The second component of the policy statement also reflects
the principle of section 30l(b)(l)(C) of the CWA that effluent
limitations must assure compliance with all State water quality
standards. Hera, the permitting authority will establish Wt
controls for the particular discharge based upon the more
stringent of the acute or chronic criterion (or both) applied »t
the edge of their respective mixing zones in order to achieve
both criteria.
Consistent with this policy statement, the permitting
authority will establish two independent zones for controlling
'For example, some State water quality standards or
implementation procedures do not allow mixing zones at all or
restrict mixing zone use for certain dischargers. Where this is
the case, the permitting authority will not use the procedure
provided in policy statement one concerning the application of
mixing zones. The permitting authority must still ensure that
the permit includes WET limitations as necessary to achieve
applicable State requirements.
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acute and chronic WET.7 The first zone, the acute mixing zone,
immediately surrounds the discharge outfall. The acute mixing
zone is normally sized to prevent lethality (sometimes, also
described as "acute effects") to passing organisms. The permit
must include effluent limitations as necessary to meet numeric or
narrative water quality criteria for acute toxicity at the edge
of the acute mixing zone. The second zone, the chronic mixing
zone, is typically a larger zone which surrounds the acute mixing
zone. The chronic mixing zone is normally sized to protect the
ecology of the water body as a whole- from all point-source
related stresses including WET. The permit must include effluent
limitations as necessary to meet numeric or narrative water
quality criteria for chronic toxicity at the edge of the chronic
mixing zone.1
Once it is determined what the appropriate mixing zones are,
the permitting authority will take several additional steps
consistent with this policy statement. The permitting authority
will (l) evaluate the receiving water concentration of acute WET
at the edge of the acute mixing zone and of. chronic WET at the
edge of the chronic mixing zone for the particular discharge, (2)
determine which of the acute criterion or the chronic criterion .•
applied at the edge of the appropriate mixing zoim im the more
stringent'of the two for the particular discharge, and (3)
establish effluent limitations to assure attainment of the more
stringent criterion (or both where it is unclear which is more
stringent) . The Technical Support PogV,ffaiTtt for Water Quality—
based Toxics Control, as revised in March 1991 (EPA/505/2-90-001)
(the TSD1 at 3.3 and 5.4, illustrates how to apply this procedure
7This policy does not address what is acute or chronic WET.
40 C.F.R. S 122.2 defines "whole effluent toxicity.** Appendix
Two, which provides an overview of the water quality standards
process and WET, describes traditional acute and chronic toxicity
tests and EPA's recommended magnitudes for acute and chronic WTT.
states may interpret narrative water quality criteria for
toxicity in State implementation procedures. In the absence of
such implementation procedures, EPA's recommended magnitudes for
WET are .3 acute toxic unit and 1.0 chronic toxic unit at the
edge of th* appropriate mixing zone. Technical Support Document
for Waf«»r 9mii'tY"fra8ed Toxics Control, as revised in March 19»1
(EPA/505/2-90-001), at 2.3.3 and 2.3.4 (the
8The implementation of this policy requires permitting
authorities to establish mixing zones unless State standards or
implementation procedures direct otherwise; however, the specific
size of a particular mixing zone depends on a variety of factors
which can also be specified in the State water quality standard
or implementation procedure. See generally the Water Quality
Standards Handbook at 2-7 (1983); the XSfi at 2.2.2, for
discussions of this issue.
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to evaluate a particular discharge for reasonable potential and
to develop effluent limitations.
2. Evaluation of Dischargers for Reasonable Potential
At a minimum, the permitting authority should review all
major discharger* for reasonable potential to cause or
contribute to exceedance of WET water quality criteria.
40 C.F.R. SS 122.44(d)(1)(iv) and (v) require permitting
authorities to impose effluent limitations to control WET
whenever a discharge causes, has the reasonable potential to
cause, or contributes to an instream excursion of applicable
water quality criteria.* This policy statement identifies which
dischargers the permitting authority should, as a first priority,
assess for reasonable potential.10
The group of dischargers which the permitting authority
should evaluate first for reasonable potential are "major"
facilities. EPA defines a major POTW as a POTW having a design
flow of one million gallons per day or greater, a service
population of 10,000 or greater, or a significant impact on water
quality. EPA identifies a major industrial discharger on the
basis of a combination of factors, including size, toxic
pollutant potential, and stream flow volume.11 EPA believes that
these facilities (either POTWs or industrial facilities) have the
greatest opportunity for impacting surface water quality and
therefore should be evaluated for "reasonable potential" to
exceed an applicable State water quality standard.
Permitting authorities should continue to evaluate other
dischargers of concern for reasonable potential to exceed WET
water quality criteria. Factors which permitting authorities may
consider in deciding whether a particular discharge is "of
'Throughout this policy, any reference to "reasonable
potential" includes both reasonable potential to cause and
reasonable potential to contribute to an excursion of numeric
water quality criteria for WET or narrative water quality
criteria.
10Thi» policy statement continues to reflect EPA's position
on this matter articulated in the January 25, 1989, memorandum of
Rebecca W. Hanmer, Acting Assistant Administrator for Water, to
Regional Administrators entitled "Whole Effluent Toxicity Basic
Permitting Principles and Enforcement Strategy."
"See the June 27, 1990, memorandum "New NPDES Non-Municipal
Permit Rating System1* from James R. Elder, Director of the Office
of Water Enforcement and Permits, to Regional Water Management
Division Directors, which is Appendix Three to today's policy.
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concern" obviously would include those factors which are
described in Chapter 3 of the TSD as factors for assessing
reasonable potential (including WET data, chemical-specific data,
instream survey data, industry or publicly owned treatment work
type, compliance history, receiving water type,
designated/existing uses, and dilution calculations). Under
S 122.44(d)(l)(iv) and (v), permitting authorities must impose
effluent limitations to control WET where reasonable potential is
established. In addition, the permitting authority should
consider WET controls, where appropriate, in issuing general
permits.
3. Evaluating Reasonable Potential
The permitting authority will consider available WET
testing data and other information in evaluating
whether a discharger has reasonable potential to cause
or contribute to exceedance of WET water quality
criteria.
This policy statement describes what information is
considered in evaluating whether a specific discharger has the
reasonable potential to cause or contribute to excursion of WET
water quality criteria. The permitting authority first
determines whether valid WET testing data is available that is
relevant to the particular discharge.12 Whole effluent toxicity
data may be available from previous monitoring. Additionally,
under 40 C.F.R. $ 122.21(j), certain POTWs are required to submit
WET testing as part of the permit application. The permitting
authority may also decide to require the permittee to generate
WET data prior to permit issuance or as a condition of the
permit. See policy statement five below. If valid WET testing
data is available that is relevant to the particular discharge,
the permitting authority uses this data to determine if the
discharge exhibits reasonable potential under $S 122.44(d)(1)(iv)
or (v)." Where such WET data exist and demonstrate reasonable
potential, the permitting authority does not need to gather or
12The permitting authority determines whether available WET
testing is valid and addresses concerns relative to toxicity for
the particular discharge. For example, where a facility
discharges to a lov flow stream, submission of acute WET testing
data showing no toxicity is insufficient (absent conversion of
the acute results to chronic results using1 an acute-to-chronic
ratio, as explained in the TSD] to assess reasonable potential
for chronic toxicity.
13If additional factors also demonstrate reasonable potential
(see main text discussion below), the permitting authority should
also discuss these factors in the fact sheet or statement of
basis accompanying the permit.
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generate other information to verify or support the WET results.
EPA believes it is appropriate to assess reasonable potential on
the basis of WET testing. Whole effluent toxicity testing is
comparable in precision to chemical analytical measurements in
wide use. See discussions of these questions in 55 Fed. Reg.
30082, 30112-30115 (July 24, 1990); 54 Fed. Reg. 23868, 23874
(June 2, 1989); the TSD at 1.3 and 3.3.
The permitting authority should also consider whether other
factors establish reasonable potential for the discharge. The
TSD at 3.2 offers a discussion of factors other than facility-
specific WET monitoring data which a permitting authority may
consider in making a reasonable potential determination for a
particular discharge. These factors include 1) industry type
(primary, secondary, raw materials used, products produced, best
management practices, control equipment, treatment efficiencies,
etc.), 2) publicly owned treatment work type (pretreatment,
industrial loadings, number of taps, unit processes, treatment
efficiencies, chlorination/ammonia problems, etc.), 3) compliance
history, 4) existing chemical data from discharge monitoring
reports and applications, 5) available instream survey data, 6J
receiving water type and designated/existing uses, 7) available
dilution, etc. For each individual permit, the permitting
authority must include a clear explanation in the statement of
basis or fact sheet accompanying the permit of the specific
factors considered in evaluating reasonable potential for the
particular discharge.
EPA believes this approach to assessing reasonable potential
implements the requirements of sections 301(b)(l)(C) and 402 of
the CWA and 40 C.F.R. S 122.44
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the permitting authority will impose effluent
limitations to control WET.
This policy statement reiterates the requirements of
sections 301(b)(1)(C) and 402 of the CWA as well as 40 C.F.R.
§S 122.44(d)(1)(iv) and (v). 40 C.F.R. SS 122.44(d)(l)(iv) and
(v) require the permitting authority to establish effluent
limitations in a permit to control WET where it determines that a
discharge has the reasonable potential to cause or contribute to
an instream excursion above a numeric criterion for WET or a
narrative criterion.14
The permitting authority can either modify the permit or
reissue the permit upon expiration, as appropriate, to
incorporate effluent limitations to control WET. In no instance
will the permitting authority reissue the permit without
including appropriate effluent limitations to control WET. In
appropriate cases, the permitting authority may also require the
discharger to conduct a toxicity identification
evaluation/toxicity reduction evaluation to identify and
eliminate the cause of* the toxicity as part of a compliance
schedule to comply with effluent limitations to control WET.
5. Whole Effluent Toxicitv Monitoring
Where appropriate, the permitting authority should impose
WET monitoring conditions upon dischargers that do not have
effluent limitations to control WET.
Where appropriate, the permitting authority should impose
WET monitoring conditions upon those dischargers for which it
did not determine reasonable potential and did not impose
effluent limitations to control WET. Where the permitting
authority concludes that a continued monitoring requirement is
warranted based upon the particular circumstances of the
discharger, the permitting authority should require WET
monitoring for a reasonable period of time and evaluate the
monitoring results at the conclusion of this period.a
"Paragraph (v) provides that where the permitting authority
determine* tftat a discharge causes, has the reasonable potential
to cause, o* contributes to an instream excursion above a
narrative water quality criterion, the permit must contain (1) a
WET effluent limitation or (2) a pollutant-specific limitation,
where the permitting authority demonstrates that a pollutant-
specific limitation is sufficient to attain and maintain
applicable numeric and narrative water quality standards.
1540 C.F.R. S 122.21(j) requires many new and existing POTWs
to collect WET data for submission to the permitting authority at
time of application or reapplication for an NPDES permit. Where
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EPA and authorized NPDES States have broad authority under
the CWA to require continued monitoring to assure attainment of
water quality criteria. Under sections 308 and 402 of the CWA,
EPA or a State with an authorized NPDES program can require NPDES
permittees to provide WET testing data to assure State water
quality standards will be attained and maintained. The
permitting authority can impose a requirement on the discharger
to collect monitoring data through conditions in the NPDES permit
or through CWA section 308 letters. Under sections 301(b)(i)(c)
and 402 of the CWA as well as 40 C.F.R. SS 122.44(d)(1)(iv) and
(v) , EPA or a State with an authorized NPDES program must impose
effluent limitations to control WET where continued monitoring
results in a determination of reasonable potential to exceed WET
water quality criteria.
6. Compliance Schedules in NPDES Permits
Where allowed under State and federal law, NPDES permits may
contain schedules for compliance with WET effluent
limitations.
This policy statement reflects the principles for allowing
compliance schedules in NPDES permits which were articulated i~n
In re Star-Kist Caribe. Inc.. NPDES Appeal No. 88-5 (May 26,
1992) (order denying modification request}.1* Section
301 (b) (1) (C) of the CWA establishes a deadline of no later than
July l, 1977, for compliance with effluent limitations developed
to meet State water quality standards. In light of this CWA
provision, EPA has determined that all permits must reflect this
deadline, unless the following requirements are met.17 NPDES
permits may contain schedules'of compliance beyond July 1, 1977,
to meet water quality-based effluent limitations if two
requirements are met. The two requirements are: 1) the permit
appropriate, the permitting authority may, in its discretion,
require more frequent WET monitoring of POTWs or industrial
dischargers. For example, it may be appropriate to impose a
continued WET monitoring obligation upon a major industrial
discharger for which WET testing data is not available.
Similarly, it may be appropriate to impose a monitoring
obligation*upon a discharger for which available WET data is
limited or for which later information raises the possibility of
reasonable potential.
I640 C.F.R. S 122.2 defines a "schedule of compliance1* as •
"schedule of remedial measures included in a 'permit', includinq
an enforceable sequence of interim requirements . . . leading Co
compliance with the CWA and regulations."
17This entire discussion does not apply to permit limitation*
which are governed by section 304(1) of the CWA.
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effluent limitation must be based either on a post-July 1, 1977
State water quality standard or a new or revised interpretation
of a pre-July 1, 1977 State water quality standard; and (2) the
applicable State water quality standard or implementing
regulations must explicitly authorize schedules of compliance.
40 C.F.R. S 122.47 also governs compliance schedules in
NPDES permits. The regulation authorizes, where appropriate,
schedules requiring compliance with effluent limitations as soon
as possible and no later than the applicable CWA statutory
deadline. The regulation imposes certain restrictions on
allowing schedules of compliance for new sources, new
dischargers, and recommencing dischargers. The regulation
establishes requirements for interim dates for certain schedules
of compliance and for permittee reporting. Any compliance
schedules developed for WET limitations must also satisfy
S 122.47, if applicable.
Thus, to decide whether to allow a compliance schedule in an
NPDES permit for effluent limitations to control WET, the
permitting authority must answer these questions:
1. Was the Applicable state water quality criterion
promulgated or interpreted after July 1, 1177?
At this time, most permitting authorities
establish effluent limitations to control WET on the
basis of State narrative water quality criteria. Most
State narrative water quality criteria for toxicity
were adopted before July 1, 1977. Where this is the
case, the permitting authority can only allow a
schedule of compliance in the NPDES permit where the
State has made a new or revised interpretation of the
applicable narrative water quality criterion after
July 1, 1977. Where the permitting authority establishes *n
effluent limitation to control WET on the basis of a State
numeric water quality criterion for WET, it is more likely
that the criterion is a post-July 1, 1977 criterion.
2. Do th« State water quality standards or implementing
regulations explicitly authorise schedules of compliance?
Tn» State must include an explicit statement
authorizing compliance schedules in the State water quality
standard or implementing regulations. If the State water
quality standard or implementing regulations are silent on
whether schedules of compliance are authorized for NPDEJ
permits, the permitting authority cannot place a schedule of
compliance in the NPDES permit. Permit writers may find tn«
express authorization in the State statute or water quality
standards, water quality planning, or NPDES regulations.
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3. Do other relevant provisions of state or federal lav or
policy allow the schedule of compliance?
Here, for example, the permitting authority should
consider whether allowing a schedule of compliance for the
specific discharge meets the requirements of 40 C.F.R.
S 122.47, if applicable, or any other requirements of State
law.
Where the permitting authority answers yes to each of these
questions, it may allow a schedule of compliance in the NPDES
permit.
The permitting authority, however, is not compelled to
establish a schedule of compliance in the NPDES permit where so
authorized. The permitting authority should impose a schedule of
compliance only where appropriate under the specific conditions
of discharge. It has long been EPA's policy that EPA and
authorized NPDES States should require compliance with State
water quality standards as soon as possible in order to further
the goals of the CWA.
7. Whole Effluent Toxicity Controls and the Pollutants Apmonia
and Chlorine
The requirement* of the water quality permitting regulations
apply without regard to the pollutant(•> that may be causing
toxicity, including ammonia and chlorine.
This policy statement is designed to address several
questions which permitting authorities have encountered in
establishing WET controls where ammonia or chlorine is the
primary cause of toxicity. The questions typically arise on the
following set of facts: A permittee discharges to a stream for
which the State has not established numeric water quality
criteria for ammonia or chlorine; the State has adopted a
narrative water quality criterion for toxicity which is
applicable to the stream; the permittee conducts WET monitoring;
and the permittee exceeds the narrative criterion due to ammonia
or chlorine. Th« permitting authority must answer several
questions ilt permitting this discharge: What effluent
limitations*must, it establish in the permit? Will the permitting
authority require the permittee to control ammonia or chlorine,
so that the permittee does not exceed the narrative criterion due
to ammonia or chlorine? Is there a basis to treat ammonia or
chlorine differently from other pollutants in applying
§ 122.44(d)(l) to these facts?
The requirements of S 122.44(d)(l) apply to all pollutants
and pollutant parameters, including ammonia and chlorine. The
Agency sees no basis upon which to treat WET due to ammonia or
chlorine differently from WET due to other pollutants in applying
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the requirements of 40 C.F.R. S 122.44(d)(1) or other provisions
of federal law.11 Several provisions of 40 C.F.R. S 122.44(d)(i)
provide the answers to the questions posed in this policy
statement.
40 C.F.R. S 122.44(d)(1)(v) requires the permitting
authority to establish effluent limitations to control WET which
causes, has the reasonable potential to cause, or contributes to
an excursion above a state narrative water quality criterion.
Under S 122 .44 (d) (1) (v) , the permitting authority must establish
either a WET effluent limitation designed to meet the narrative
criterion or a pollutant-specific effluent limitation where the
permitting authority is satisfied it will assure compliance with
applicable narrative and numeric criteria to control the WET due
to ammonia or chlorine. 40 C.F.R. S 122.44(d)(1)(vi) allows the
permitting authority to use one of three options for developing
effluent limitations for a pollutant determined to cause an
exceedance of a State narrative criterion where the State has
developed no numeric water quality criterion for the specific
pollutant. These options are (1) establish an effluent
limitation using a calculated numeric water quality criterion
which will attain and maintain the applicable narrative criteria
and fully protect the designated use; (2) establish an effluent
limitation on a case-by-case basis using EPA criteria
supplemented by other relevant information where necessary; and
(3) establish an effluent limitation for an indicator parameter
provided certain factors are established.
8. Whole Effluent Toxicitv Controls and POTWs
The requirements of the water quality permitting
regulations apply to all dischargers, including POTWs.
This policy statement reaffirms EPA's longstanding policy of
treating all dischargers on an equal basis in imposing and
enforcing effluent limitations to control all pollutants and
pollutant parameters. Under sections 30l(b)(1)(C) and 402 of th«
"This policy statement does not mean that permitting
authorities^ may disregard technical factors which are unique to
ammonia and chlorine in implementing regulatory requirements.
For example, holding pH constant in the laboratory during a WIT
test may be necessary to assure a representative WET sample,
where WET is due to ammonia. The permitting authority may also
use judgment in interpreting testing results and setting limits
where temperature has a significant impact upon WET, which may ot
the case for ammonia discharges during winter. In addition, tn«
permitting authority may require WET testing prior to
chlorination if a facility is under a schedule to dechlorinat*.
Once dechlorination is implemented, then WET testing should b«
conducted on the final effluent.
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CWA as well as 40 C.F.R. S 122.44(d)(1), all dischargers must
meet effluent limitations designed to attain and maintain
applicable State water quality standards. Under the current
NPDES program, EPA exercises enforcement discretion where
appropriate for particular violations of effluent limitations
designed to meet State water quality standards, and provides
technical guidance and support to dischargers in seeking
solutions to water quality-permitting and compliance problems.
See Attachment 2 to the January 25, 1989, memorandum from Rebecca
w. Hanmer, Acting Assistant Administrator for Water, to EPA
Regional Administrators entitled "Whole Effluent Toxicity Basic
Permitting Principles and Enforcement Strategy." EPA's
Enforcement Management System for the National Pollutant
Discharge Elimination System (1989) also discusses how EPA
exercises such enforcement discretion.
Authorized NPDES States and EPA will work with
municipalities (as well as other permittees) to solve water
quality-related problems, including those resulting from WET. In
1991, EPA published the revised TSD. which provides comprehensive
technical guidance for assessing and regulating the discharge of
toxic substances to the waters of the United States. In 1989,
the Agency published a specific toxicity reduction manual for -the
municipal discharger, the Toxicity Reduction Evaluation Protocol
for Municipal Wastewater Treatment Plants (EPA 600/2-88/062 April
1989). Since 1985, EPA's National Effluent Toxicity Assessment
Center in Duluth, Minnesota has provided assistance to regulatory
authorities in connection with dischargers that have complex
toxicity problems. EPA has published the Toxicity Identification
Evaluation; characterization of Chronically Toxic Effluents^
Phase I (EPA-600/6-91/005F) (May 1992), a guidance document
designed to assist dischargers and their consultant laboratories
in conducting chronic aquatic toxicity identification
evaluations.
CONCLUSION
The fundamental premises of today's policy are not new.
Because of th« importance of WET controls, however, EPA is taXinq
this opportunity to reiterate key principles associated with
implementation of existing statutory and regulatory requirements
for WET. Th« publication of this policy is designed to foster
consistent nationwide compliance with existing statutory and
regulatory provisions for the control of WET, to facilitate th«
development of appropriate controls for WET in NPDES permits, «nd
to help assure attainment of water quality standards throughout
the nation.
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APPENDIX ONE
HISTORY OF FEDERAL. REGULATION OF WHOLE EFFLUENT TOXICITY
Since 1984, the Environmental Protection Agency, the .states,
and the regulated community have employed an integrated strategy
consisting of both biological and chemical means to control toxic
effects upon water quality beyond Clean Water Act (CWA)
technology-based requirements in order to achieve and maintain
State water quality standards. One method for measuring the
biological effects of toxic effluents upon aquatic life is WET
testing. EPA and the States have used the data derived from WET
testing to assess compliance with State water quality standards
and to establish National Pollutant Discharge Elimination System
(NPDES) permit effluent limitations necessary to attain and
maintain those standards.
In the past ten years, the Agency has published regulations,
policy statements, and guidance documents which address a variety
of issues associated with WET controls in NPDES permits. In
1984, EPA issued the "Policy for the Development of Water
Quality-Based Permit Limitations for Toxic Pollutants'* (published
at 49 Fed. Reg. 9016 (March 9, 1984)). This policy addresses the
use of biological and chemical methods to assure that toxic whole
effluent discharges are regulated consistent with federal and
State requirements. The document discusses such specific issues
as integration of chemical and biological approaches; chemical,
physical, and biological testing requirements (WET requirements);
use of data; setting of effluent limitations; and monitoring.
On January 25, 1989, Rebecca W. Hanmer, Acting Assistant
Administrator for Water, sent to EPA Regional Administrators the
memorandum entitled "Whole Effluent Toxicity Basic Permitting
Principles and Enforcement Strategy." A group of Regional and
State representatives developed the strategy, which discussed the
minimum acceptable national requirements for WET permitting.
In 1989, the Agency revised existing 40 C.F.R.
S 122.44(d)(1}, which previously required NPDES permits to
contain any more stringent requirements necessary to achieve
State water quality standards. See 54 Fed. Reg. 23868
(June 2, 1M9>. The revised regulation described in greater
detail requirements for NPDES permitting authorities to follow in
developing NPDES effluent limitations to assure compliance with
State water quality standards. On August 14, 1992, Michael B.
Cook, Director, Office of Wastewater Enforcement and Compliance,
and Robert H. Wayland, III, Director, Office of Wetlands, Oceans
and Watersheds, transmitted a memorandum to the Water Management
Division Directors, Regions I-X, entitled "Clarifications
Regarding Certain Aspects of EPA's Surface Water Toxics control
Regulations." (See Appendix Four.) In 1990,. EPA also published
new 40 C.F.R. S 122.21(j), which established a requirement for
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certain publicly owned treatment works (POTWs) to provide the
results of valid WET testing with applications for NPDES permits.
See 55 Fed. Reg. 30082 (July 24, 1990). The preambles to these
regulatory revisions and the 1984 policy provide a detailed
explanation of legal and policy support for WET testing and
effluent limitations.
Since 1984, the Agency has published various guidance
documents which address the subject of water quality-based toxics
control, including WET control. See, in particular, the
Technical Support Docyfflen^ for Water Quality—based Toxics
Control, which was originally published in September 1985 and was
revised in March 1991 (EPA/505/2-90-001) (the TSD1. The- revised
TSD provides an explanation of the technical support for WET
testing and gives detailed guidance on development of water
quality-based permit limitations for WET and toxic pollutants.
On June 19, 1991, EPA issued the "Policy on the Use of
Biological Assessments and Criteria in the Water Quality
Program." In discussing integration of various assessment
methods, the 1991 policy reflects a position of "independent
•application." In essence, "independent application" means that.
appropriate regulatory action should be taken when any one of
biosurvey, pollutant-specific, or WET testing methods indicates
that an applicable water quality standard is not attained.
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APPENDIX TWO
BACKGROUND MATERIALS ON WHOLE EFFLUENT TOXICITY
STATUTORY AND REGULATORY REQUIREMENTS FOR WET. AND WET REDUOTTOM
GUIDANCE
Overview^of WET Testing fo^-
Aquatic Life Protection.
The WET approach to toxic* control for the protection of
aquatic life involves the use of acute and chronic WET testing to
measure the toxicity of wastewaters. Whole effluent toxicity
testa typically use standardized, surrogate freshwater or marine
plants, vertebrates, or invertebrates to measure the aggregate
toxic effect of an effluent. An acute WET test is typically a
test of 96-hours or less in duration in which lethality is the
measured endpoint. A chronic WET test is typically a longer-term
test in which sublethal effects, such as fertilization, growth,
and reproduction can be measured in addition to lethality. On.
December 4, 1989, EPA published proposed Part 136 methods for
conducting short-term acute and chronic WET testing for marine
and freshwater species. See 54 Fed. Reg. 50216. Once these
methods are final, they will constitute approved Part 136 test
methods for the NPDES prograa.
overview of the State Water Quality Standards Process and WET
Section 303 of the Clean Water Act, (CWA) establishes the
statutory basis for the current State water quality standards
program. Under this provision of the CWA, States bear primary
responsibility for adopting water quality standards. State water
quality standards represent, the means by which EPA and authorized
NPDES States control point source discharges when technology-
based controls for point source discharges are inadequate.
A water quality standard defines the water quality of a
water body by designating the uses to be mad* of the water, by
setting criteria necessary to protect the uses, and by
establishing antidegradation policies and implementation
procedure* that serve to maintain and protect water quality, fie-p
section 3O9(c) of txi* CWA and 40 C.F.R. Part 131, States adopt
water quality standards to protect public health or welfare,
enhance the quality of the water, and serve the purposes of the
CWA. Among other requirements, State water quality criteria »ust
protect aquatic life.
Under section 303 of the CWA and 40 C.F.R. Part 131, EPA
must approve State water quality standards or disapprove State
water quality standards and overpromulgate with federal water
quality standards. State water quality standards are effective
until EPA overproasulgates with federal standards. Once
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promulgated, the federal standards are the applicable water
quality standards for the State.
State water quality criteria may be expressed as constituent
numeric concentrations of pollutants or pollutant parameters or
as narrative statements representing a quality of water that
supports a particular use. This is true of the pollutant
parameter WET. Several States have adopted numeric criteria for
WET. Most evaluation and control of WET at this time, however,
is based upon maintenance of the state's designated uses for the
water body through basic narrative water quality criteria for
toxicity. All States have narrative criteria for toxicity which
are statements of a desired water quality goal, such as "all
State waters must, at all times and flows, be free from
substances that are toxic to humans or aquatic life." EPA
considers narrative criteria to apply to all designated uses at
all flows unless specified otherwise in the State's water quality
standards. EPA regards narrative criteria for toxicity to cover
both short-term and long-term WET effects (acute and chronic
effects, respectively).
Section 303(d) of the CWA establishes requirements for
determining the specific pollutant reductions necessary to attain
water quality standards. Under section 303(d), the State (or,
upon the failure of the State, EPA) must establish a Total
Maximum Daily Load (TMDL) for water quality-limited waters. A
TMDL is an estimate of the total loading of a pollutant or
pollutant stressor that may be allowed within a receiving water
and an allocation of the total loading between the sources. See
40 C.F.R. Part 130. A TMDI* consists of Wasteload Allocations for
point sources, Load Allocations for other sources, and a Margin
of Safety to account for uncertainty in the relationship between
loadings and water quality. EPA has issued program guidance and
revised regulations pursuant to section 303(d) (see Guidance for
Water Quality-based Decisions; The TMDL Process, (EPA 440/4-91-
001 April 1991); 57 Fed. Rea. 33040-33050 (July 24, 1992); and
April 13, 1992, memorandum from Geoffrey H. Grubbe, Director,
Assessment and Watershed Protection Division, Office of Wetlands,
Oceans and Watersheds, entitled "Supplemental Guidance on Section
303 (d) Implementation"). TMDLs may be developed for a single
source to support the issuance of an NPDES permit or for a larger
water body tdten multiple sources need to be considered together.
State Implementation procedures may further explain how the
state implements the applicable narrative criterion to establish
effluent limitations to control WET. Many effluent limitations
to control WET, however, result from the permitting authority'*
case-by-case determination of what concentration of WET meets the
narrative criterion.
State WET criteria or the procedures implementing the state
criteria typically describe the magnitude, duration, and return
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frequency for WET. The duration and frequency of the discharge
nay also b« defined by the design stream flow appropriate to the
criterion. Magnitude is the maximum allowable concentration of
WET, which is typically expressed as a concentration of toxicity
instream; duration is the period of time over which the instream
concentration is averaged for comparison with criteria
concentrations, in order to limit the durations of concentrations
above the criterion; and return frequency is a designation of how
often the criterion may be exceeded without impacting the
organisms in the water body. This information is needed because
ambient water quality typically varies in response to changes in
effluent quality* stream flow, and other factors. Accordingly,
organisms in the receiving water typically experience fluctuating
exposure to pollutants, including some periods of exposure to
high pollutant concentrations, which may have adverse effects.
For this reason, criteria indicate a time period over which
exposure is to be averaged, as well as a maximum concentration,
thereby limiting the duration of exposure to elevated
concentrations. In addition, to predict or ascertain the
attainment of criteria it is necessary to specify the allowable
frequency for exceeding the WET criteria. The permitting
authority uses the magnitude, duration, and return frequency
provisions of WET criteria to develop wasteload allocations andL
effluent limitations to control the WET of the discharge.
Whole effluent toxicity criteria as adopted by the State or
as implemented by the permitting authority on a case-by-case
basis typically consist of two expressions of magnitude of
toxicity to surrogate test species, one to protect against acute
toxicity effects and one to protect against chronic toxicity
effects, along with a duration and return frequency for each. As
of the publication date of this policy, EPA has not developed a
recommended section 304(a) criterion for WET. The Technical
Support Docu.pgpt for Water Oualitv-baaed Toxics Control, which
was originally published in September 1985 and was revised in
March 1991 (EPA/505/2-90-001) (the TSD1. contains recommended
magnitudes, durations, and return frequencies for assessing acute
WET (.3 acute toxic unit to the most sensitive of at least three
species, with an averaging period of one hour and a once in
three-year return frequency) and chronic WET (l.o chronic tonic
unit to the> most sensitive of at least three species, with an
averaging; period of 4 days and a once in three-year return
frequency). See the Tgp at 2.3.3 to 2.3.5.
At their discretion, States may adopt certain policies for
implementation of water quality standards, such as critical low
flow and mixing zone policies. EPA has the authority to review
and approve or disapprove such policies. Sqe 40 C.F.R. S 131.1).
Additionally, EPA and States may establish a Technical Agreement.
describing procedures that will be used in developing TMDLs and
wasteload allocations. TMDLs, wasteload allocations, and persit
limitations developed consistent with Technical Agreements are
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subject to a lesser degree of EPA review. State water quality
standards protect water quality for designated uses in critical
low flow situations. Under S 131.13, States may designate
critical low flows below which numeric water quality criteria do
not apply. Mixing zones are small areas in the receiving water
near certain discharge outfalls where ambient concentrations
above the otherwise applicable State water quality criteria are
allowed. See generally the Water Quality Standards Handbook at
2-7 (1983); the TSD at 2.2.2. Some States prohibit mixing zones
entirely for all pollutants or pollutant parameters. Others may
allow mixing zones in general, but provide spatial dimensions to
limit the areal extent of the mixing zone*. Permitting
authorities may allow mixing zones on a case-by-case basis for
individual discharges. EPA strongly recommends that States have
a definitive statement in their water quality standards on
whether or not mixing zones are allowed and clearly explain the
procedures for defining mixing zones where allowed.
Overview of Federal Statutory and Regulatory Requirements for
Development of Water Quality-based Permit Limitations for WET
Section 101(a) of the CWA establishes a national policy of
restoring and maintaining the chemical, physical, and biological
integrity of the Nation's waters. In addition, section I0i(a)(3)
of the CWA states the national policy that the discharge of toxic
pollutants in toxic amounts is prohibited. Under sections 301
and 402 of the CWA, point source dischargers must obtain an NPOES
permit before discharging into waters of the United States.
Under sections 301 (b) (1) (C) and 402 of the CWA, dischargers with
NPDES permits must meet all of the technology-based requirements
of the CWA as well as any more stringent requirements necessary
to achieve State water quality standards established under
section 303 of the CWA.
In 40 C.F.R. § 122.2, EPA defines "whole effluent toxicity"
as "the aggregate toxic effect of an effluent measured directly
by a toxicity test." EPA has published 40 C.F.R. S 122.44(d)(L).
which describes requirements for NPDES permitting authorities to
follow in developing water quality-based effluent limitations,
including those necessary to control WET. The regulation
consists of seven subparagraphs:
1. Section 122.44fdl mfil
"Limitations must control all pollutants or pollutant
parameters (either conventional, nonconventional, or
toxic pollutants) which the Director determines are or
may be discharged at a level which will cause, have tn«
reasonable potential to cause, or contribute to an
excursion above any State water quality standard,
including State narrative criteria for water quality.
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2. Section 122.44 fd^(IV(
"When determining whether a discharge causes, has the
reasonable potential to cause, or contributes to an in-
stream excursion above a narrative or numeric criteria
within a State water quality standard, the permitting
authority shall use procedures which account for
existing controls on point and nonpoint sources of
pollution, the variability of the pollutant or
pollutant parameter in the effluent, the sensitivity of
the species to toxicity testing (when evaluating whole
effluent toxicity), and where appropriate, the dilution
of the effluent in the receiving water."
3. Section 122.44fdlmfiiil
"When the permitting authority determines, using the
procedures in paragraph (d)(l)(ii) of this section,
that a discharges causes, has the reasonable potential
to cause, or contributes to an in-stream excursion
above the allowable ambient concentration of a State
numeric criteria within a State water quality standard
for an individual pollutant, the permit must contain
effluent limits for that pollutant."
4. Section 132.44
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attain and maintain applicable numeric and narrative
State water quality standards."
6. Section 122 .44 fdl m fvii
"Where a State has not established a water quality
criterion for a specific chemical pollutant that is
present in an effluent at a concentration that causes,
has the reasonable potential to cause, or contributes
to an excursion above a narrative criterion within an
applicable State water quality standard, the permitting
authority must establish effluent limits using one or
more of the following options:
(A) Establish effluent limits using a calculated
numeric water quality criterion for the pollutant which
the permitting authority demonstrates will attain and
maintain applicable narrative water quality criteria
and will fully protect the designated use. Such a
criterion may be derived using a proposed State
criterion, or an explicit State policy or regulation
interpreting its narrative water quality criterion,
supplemented with other relevant information which may
include: EPA's Water Quality Standards Handbook,
October 1983, risk assessment data, exposure data,
information about the pollutant from the Food and Drug
Administration, and current EPA criteria documents; or
(B) Establish effluent limits on a case-by-cas«
basis, using EPA's water quality criteria, published
under section 304 (a) of the CWA, supplemented where
necessary by other relevant information; or
(C) Establish effluent limitations on an indicator
parameter for the pollutant of concern, provided:
(1) The permit identifies which pollutants are
intended to be controlled by the use of the effluent
limitation;
(2) The fact sheet required by S 124.56 s«t«
forth the basis for the limit, including a finding that
compliance with the effluent limit on the indicator
parameter will result in controls on the pollutant of
concern which are sufficient to attain and maintain
applicable water quality standards;
(3) The permit requires all effluent and
monitoring necessary to show that during the tern of
the permit the limit on the indicator parameter
continues to attain and maintain applicable wat«r
quality standards; and
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(4) The permit contains a reopener clause
allowing the permitting authority to modify or revoke
and reissue the permit if the limits on the indicator
parameter no longer attain and maintain applicable
water quality standards."
7. Section 122.44fdl mfviii
"When developing water quality-based effluent limits
under this paragraph the permitting authority shall
ensure that:
(A) The level of water quality to be achieved by
limits on point sources established under this
paragraph is derived from, and complies with all
applicable water quality standards; and
(B) Effluent limits developed to protect a
narrative water quality criterion, a numeric water
quality criterion, or both, are consistent with the
assumptions and requirements of any available wasteload
allocation for the discharge prepared by the State and
approved by EPA pursuant to 40 CFR 130.7."
Overview of Toxicity Reduction Guidance
The purpose of a toxicity reduction evaluation (TRE),
including a toxicity identification evaluation (TIE), is to
investigate the causes and determine corrective actions for WET
problems. The permitting authority may require the permittee to
conduct these evaluations in specific cases. Section 5.3 of the
TSD contains a detailed discussion of EPA's recommended approach
for conducting TIEs and TREs, including a list of guidance
documents EPA has developed describing methods and procedures for
conducting TIEs and TREs.
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