xvEPA
United States
Environmental Protection
Agency
Office Of Water
(EN-336)
-5- 91-100
Technical Support Document
For Water Quality-based
Toxics Control
RESPONSIVENESS SUMMARY
Printed on Recycled Paper
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RESPONSIVENESS SUMMARY
General
The TSD needs to be peer reviewed.
EPA Response: We feel EPA has provided ample opportunity for
review of the TSD. The Williamsburg workgroup met in
December, 1988, and was composed of a diverse group of people
from EPA Regions, States, environmental groups, trade
associations, academia, private industry, and municipalities.
This group was formed to determine what changes were needed
in the document. Based on the workgroup's inputs, EPA
produced a first draft TSD in November, 1990. This draft was
sent out to workgroup members, and anyone else upon request,
for review and comment. EPA considered each comment and made
changes to the document. A second revised draft TSD was
noticed in the Federal Register on May 11, 1990. Over 2500
copies of the new draft were sent out. Between the two
drafts, we received 120 comments from a diverse group of
people. EPA considered each individual comment and made
changes to the document where necessary.
The TSD doesn't apply to CSO discharges.
EPA Response: We acknowledge that the TSD was written with
continuous discharges in mind. However, there is no reason
why the general concepts and some of the recommendations of
the TSD cannot be extended to CSO or other rainfall related
discharges. The dynamic model applications .in the TSD have
been used over the last 10 years to address water quality
problems related to CSOSo EPA believes that this model can
also be applied to address toxic problems with CSOs.
Chapter 1; Approaches to Water Quality-based Toxics Control
Overview: Added more information and clarification to support
EPA's position with regard to the major issues addressed in the
comments.
1. The cause and effect relationship between effluent toxicity
and instream impacts is not adequately documented, and other
factors that may cause instream impacts have not been
addressed. EPA's use of the CETTP studies was criticized.
EPA Response: The revised draft TSD has been changed to
include more documentation to support our position on the
cause and effect relationship between effluent toxicity and
instream impacts. Supporting information on a study con-
ducted on the Trinity River in Texas was added as well as more
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detailed explanation of the CETTP studies. EPA evaluated the
results of the CETTP studies, the North Carolina studies, and
the Trinity River study and found that if toxicity is present
after considering dilution, instream impact will also be
present. EPA's finding is now clearly stated in the TSD and
referenced. The TSD now includes a discussion of Parkhurst's
major criticisms of the CETTP studies and why EPA feels those
criticisms are unfounded. The TSD also acknowledges that
biological, physical, and chemical factors of the community
can influence the actual effects that effluent toxicity may
cause in the receiving water.
2. Toxicity test method precision is too variable to be used in
NPDES permits.
EPA Response: The revised draft includes all available
precision data for both acute and chronic toxicity tests; this
includes intralaboratory and all available interlaboratory
test results. Raw precision data is presented in table form
in Appendix A and discussed within the chapter. EPA
evaluations, as well as published literature reviews which
include estimates of whole effluent precision data are
presented. EPA is comfortable with the conclusion that whole
effluent toxicity tests are no more variable than chemical
analytical methods and therefore stands behind the
recommendation that toxicity test methods be used in NPDES
permits.
The same data contained in the TSD has been used by EPA in
proposing adoption of the toxicity methods into EPA's reg-
ulations at 40 CFR 136. The toxicity methods were proposed
for adoption on December 4, 1989. Comments were received and
will be answered upon notice of EPA's decision regarding these
methods. The decision is expected in April 1991.
3. The biological criteria/bioassessment approach is not yet part
of EPA's water quality regulations and should not yet be used
in the regulatory process. For the best assessment of sources
and causes, EPA should use a "weight-of-evidence approach."
EPA Response: As previously stated in the TSD (per section
131.11(b)(2) of the Water Quality Standards Regulation),
biological criteria can supplement existing chemical-specific
criteria and provide an alternative to chemical-specific
criteria where such criteria cannot be established. To
acknowledge the current evolving status of the use of bio-
criteria, EPA's statement in the TSD has been revised to read:
"To better protect the biological integrity of aquatic
communities, EPA recommends that States begin to develop and
implement biological criteria in their water quality stand-
ards."
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4.
EPA does not agree with use of the "weight-of -evidence"
approach in this context because biosurveys are too complex
to override the other two methods (i.e., chemical-specific
and whole effluent toxicity). The TSD now explains EPA's
position that the concept of "independent application" be
applied to water quality-based situations. Since each method
has unique as well as overlapping attributes, sensitivities,
and program applications, no single approach for detecting
impact should be considered uniformly superior to any other
approach. For example, the inability to detect receiving
water impacts using a biosurvey alone is insufficient evidence
to waive or relax a permit limit established using either of
the other methods. The most protective results from each
assessment conducted should be used in the effluent
characterization process (Chapter 3) . The results of one
assessment technique should not be used to contradict or
overrule the results of the other(s).
However, EPA recognizes that there are instances when the
whole effluent, chemical specific, and biological criteria
approaches will give disparate results. The TSD was revised
to recommend that permitting authorities use a more complex
way to assess excursions beyond standards and establishing
permit limits to provide assurance that simplifying assump-
tions are not the cause of the apparent discrepancy. The TSD
also now includes examples of where the whole effluent
toxicity test protocols may conflict with critical environ-
mental parameters to lead to an apparent disparity between
the whole effluent toxicity and chemical specific approaches.
The problem of false positives (i.e., instream impact pre-
dicted by toxicity test where none exists) is not addressed.
EPA Response: The revised draft TSD now addresses the problem
of toxicity test interferences caused by environmental
parameters and explains that there may be a few unusual
situations where the pH, temperature, hardness, salinity, and
solids requirements of the testing procedures differ greatly
from the worst environmental conditions for these parameters.
In these situations, the effluent toxicity tests may either
over or under predict the toxicity in the ambient receiving
water. An example of this is where ammonia is present and the
highest expected ambient water temperature is 20°C whereas the
chronic toxicity test must be conducted at 25°C. Since a
higher temperature causes more ammonia toxicity, the
temperature requirements of the test may induce toxicity not
found in the ambient water. In such an instance, the
regulatory authority must carefully look at the test protocols
and all the data collected to determine if the facility is
actually contributing to toxicity in the ambient water. A
toxicity identification evaluation (TIE) may be necessary to
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make this determination. If this analysis shows a toxicity
test result to be artificial due to environmental parameters,
then that test should be overridden by subsequent toxicity
tests conducted.
5. Current standard algal toxicity test methods lack the ability
to provide useful data on the ecological impact of a discharge
and should not be recommended as a test species. EPA should
recommend three species representing two different phyla be
used for toxicity testing. EPA's recommendation to use
surrogate (rather than resident) species in toxicity testing
as being more protective seems contrary to the site specific
nature of the permitting process.
EPA Response: To address concerns with the algal test and to
allow more flexibility in testing, the recommendation in the
TSD has been changed to "fish, invertebrate, and plant." EPA
will not modify its recommendation to include only 2 phyla.
EPA's objective in requiring 3 species from 3 different phyla
is to be predictively protective.
The TSD's discussion of the use of surrogate species was
expanded to explain that to use a resident organism, a
facility would have to develop a protocol to culture the
organism and to assess intra- and inter-laboratory variabil-
ity. Such testing is more costly, more difficult, and
potentially subject to more variability (disease, age, etc.)
than standardized testing. In any case, organisms collected
directly from the receiving water itself should never be used
because their health cannot be assured.
6. More documentation is needed for the statement that the "IC25
is approximately the analogue of an NOEC." Before EPA makes
such a broad ranging recommendation, there must be sufficient
data to establish an overall relationship.
EPA Response: The language in the revised draft has been
clarified to better explain what an IC25 is and how it is
calculated. EPA believes that there is sufficient data to
support the statement that the "IC25 is approximately the
analogue of an NOEC." The data in Appendix A is presented so
that both hypothesis testing and IC25 calculations of an NOEC
can be compared. A statistical analysis using minimum
significant differences is graphically presented in Figure 1-
1. Figure 1-1 shows that an NOEC calculated using the IC25
is comparable to an NOEC calculated using hypothesis testing,
and that the relationship is statistically sound.
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7. The data in the TSD shows that whole effluent toxicity is not
additive.
EPA Response: The cited article in the TSD and the TIE data
were reviewed. These data support EPA's position that acute
toxicity is additive. However, the data do not support
additivity of chronic toxicity. Therefore, the TSD was
changed to reflect this.
8. There are insufficient chemical-specific field data to support
that exceedances of the criteria cause instream impacts.
EPA Response: The field studies referenced in Chapter 1 for
chemical specific criteria investigations were conducted over
twenty years ago. The field investigators dosed a stream with
toxicants to measure the response. This approach is not
possible today because it would violate the States water
quality standards. Since that time, EPA has developed a
method of using laboratory toxicity data on specific chemicals
to derive data.
Chapter 2: Water Quality Criteria and Standards
Overview: Revised introduction to summarize key regulatory
requirements; reorganized into clearly defined aquatic life and
human health discussions; added more information on what should be
considered when allowing mixing zones; added more in-depth
discussion of criteria for human health protection.
1. Water quality criteria are not reliable due to data gaps or
errors in derivation. Site-specific criteria should not be
limited to being more stringent than the national criteria.
EPA Response: Changing the general procedure for deriving WQ
criteria is not within the scope of the TSD. In the near
future EPA expects to re-examine the general procedures for
deriving aquatic life criteria, and will request public
comment thereon. While EPA requests public comment on all WQ
criteria documents before publishing them in final form, EPA
accepts comment on criteria at any time and can correct errors
through criteria summary documents that it distributes from
time to time. Finally, there is no Agency policy, set forth
in the TSD or elsewhere, that prevents state-wide or site-
specific criteria from being less stringent than the national
criteria.
2.
Provide more clarity on how to prohibit lethality within the
mixing zones?
EPA Response: The TSD has been amended to clarify the goals
of EPA's recommendations on mixing zones. It now states that
mixing zone conditions should not be lethal to organisms
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passing through it. Survival of organisms that might wish to
reside permanently in a mixing zone is not assured by past or
current policy.
Because the chronic criteria may be exceeded at the end of
the pipe there is a potential for lethality to sensitive
organisms that attempt to reside permanently in the mixing
zone. Part of the intent of the recommendations of the 1985
TSD and 1991 TSD is to protect the survival of organisms
passing through the mixing zone. In all cases, exposures to
concentrations above the CCC and CMC cannot be correctly
interpreted without accounting for the duration of exposure.
The TSD is flawed because it assumes that mixing zones exist.
The Great Lakes Water Quality Agreement precludes use of flow
augmentation as a substitute for adequate treatment.
EPA Response: The TSD recommendations in no way authorize
mixing zones where otherwise prohibited. In addition, the
recommendations on mixing zones do not advocate management of
reservoirs for flow augmentation.
TSD should at a minimum be against mixing zones for per-
sistent and bioacccumulative toxicants, and the burden of
justifying mixing zones for non-persistent and non-bio-
acccumulative toxicants should be on the discharger. The
Great Lakes Water Quality Agreement calls for zero discharge
of pollutants and elimination of persistent and bioaccumu-
lative toxicants. The Clean Water Act also has a goal of zero
discharge of pollutants.
EPA Response: The TSD continues to note that EPA regulations
allow mixing zones at the discretion of the State. The TSD
also discusses options that should be considered when
determining whether to allow mixing zones for aquatic life and
human health protection. For protection of aquatic life, a
mixing zone may be permitted as long as its size is
sufficiently limited that it does not significantly impair
the integrity of the water body as a whole, and it does not
cause lethality to organisms passing through the mixing zone.
For protection of human health, mixing zones should be
restricted such that they do not encroach on areas often used
by the public for fishing, and particularly where stationary
species such as shellfish are harvested; mixing zones may also
be restricted to compensate for uncertainties in the
protectiveness of the water quality criteria or uncertainties
in the assimilative capacity (TMDL) of the water body.
Bioaccumulative pollutant problems are not fundamentally
caused by mixing zones. Bioaccumulation is generally a
system-wide problem that occurs when the appropriate TMDL for
a water body as a whole is exceeded. Consequently, EPA does
not consider mixing zone restrictions to be the best mechanism
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for addressing such problems. However, eliminating mixing
zones can be used as a device to further reduce the loading
below the TMDL, although the results are not as predictable
as a direct reduction of the TMDL would be. Chapter 2 has
been now been modified to state the factors that should be
considered in judging whether a mixing zone causes significant
health or ecological risks.
It sliould be noted that the TSD deals with WQ based effluent
limits (i.e., those needed to protect aquatic life and human
health), implemented primarily under the specific require-
ments of Sections 301, 303, and 304 of the CWA. Under this
framework, zero discharge of pollutants is generally required
where the water quality standard or the Total Maximum Daily
Load is set at zero.
5. The TSD should allow mixing zones for all toxicants includ-
ing bioaccumulative pollutants. Furthermore, fate processes
(such as sedimentation or decay) that occur within mixing
zones should be taken into consideration.
EPA Response: The TSD now sets forth specific conditions
under which denial of mixing zones would be appropriate. EPA
regulations also allow (while neither encouraging nor
discouraging) States to use mixing zones. The recommenda-
tions of the TSD implicitly discourage consideration of fate
processes such as sedimentation or decay. Mixing zones are
an allowance for variations in concentration due to incom-
plete mixing, over small spatial scales, usually too small
for fate processes to significantly reduce concentrations.
6. Limiting all dischargers to 0.3 TUa is akin to a technology
based approach such as a 30 mg/L BOD or suspended solids
limit. The TSD should consider the resulting instream water
quality.
EPA Response: The mixing zone discussion has been modified
to provide different alternatives for assuring that instream
goals and standards are met. Not exceeding 0.3 TUa at the
end of the pipe is one of the recommended ways to assure
survival of organisms passing through the mixing zone.
Nevertheless, the discussion has been modified to de-
emphasize the technological requirements and emphasize the
attainment of instream goals.
7. EPA should provided more information on the tests it used to
arrive at an LC50/LC1 ratio of 0.3. According to the data
presented in the TSD, the 0.3 ratio is overly conservative in
most cases.
EPA Response: The magnitude of the acute WET criterion is
based on data collected from a number of facilities in EPA
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Region 4. These data show that 90% of the facilities
exhibited an LCI which was no less than 0.3 times the LC50.
This is different from the 0.5 factor used to derive a
chemical specific acute criterion.
8. The acute toxicity criterion of 0.3 TUa is below detection.
How would it be implemented?
EPA Response: The implementation of this criterion would be
identical to that used for specific chemicals. This imple-
mentation is expressed in Chapter 5.
9. The 1-hour averaging period for the acute criteria (CMC) is
overly restrictive, does not correspond to the 48-96 hour
toxicity tests, and cannot be modeled with existing EPA WQ
models. Elsewhere in the document, EPA indicates that 24
hours is an appropriate averaging period for modeling
purposes. Both concentration and exposure time are import-
ant, since for many toxicants the 96-hour LC50 is dramati-
cally higher than the l-hour LC50. The 1-hour averaging
period is technically unsupported by the limited information
presented. EPA appears to have edited the data presented in
Appendix D to include only those data that support the 1-hour
averaging period. EPA should present all available data on
the effect of exposure duration on toxicity.
EPA Response: EPA agrees that both concentration and exposure
time are important. The TSD has now been modified to note
that the 1-hour averaging period is based on ammonia, a fast-
acting toxicant. As the 1-hour averaging period was intended
to be protective even for the fastest acting toxicants, it may
be overly conservative for many pollutants. Consequently, the
TSD recommends allowance for site-specific (or chemical-
specific) modification of the averaging periods. Alternative
averaging periods can be developed from data on the time
course of mortality in acute toxicity tests.
EPA expects that for many pollutants, such site-specific_or
state-wide alternative averaging periods, if developed using
adequate data, may be greater than the period recommended for
national criteria. Furthermore, EPA recognizes that a 24-
hour acute averaging period may be appropriate in some
modeling contexts, where concentrations do not change rapidly
over short time periods.
While Appendix D of the TSD presents some examples of
pollutants for which a short averaging period, on the order
of hours, might be appropriate, the TSD was not intended as
the mechanism by which EPA would develop a rationale for the
acute averaging period. The averaging periods were set forth
in 1985 in the "Guidelines for Deriving...National Criteria".
In the near future EPA intends to review and perhaps modify
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the Guidelines, and may at that time consider the feasibility
of different acute averaging periods for different chemicals.
10. The rationale for the 4-day averaging period is weak. Chronic
toxicity tests for most species require much longer than four
days. The field studies presented in Chapter 1 indicate that
longer term excursions are needed to produce ecological
effects. EPA inappropriately picked examples of pollutants
with low acute-chronic ratios to justify the 4-day averaging
period. A 30-day averaging period (per the freshwater ammonia
criteria document) should be acceptable, particularly in cases
where concentrations do not change rapidly.
EPA Response: The TSD has been modified to note that EPA
selected the 4-day chronic averaging period based on the
shortest period that chronic effects may be observed for
certain chemicals.
As the 4-day period was selected for provide adequate
protection in all cases, EPA recognizes that longer averag-
ing periods may be appropriate for many pollutants, and
recommends using site-specific or state-wide pollutant-
specific alternative averaging periods, where scientifically
supported. EPA believes that selection of an appropriate
chronic averaging period is technically difficult, with less
applicable data than is available for selecting the acute
averaging period. EPA agrees that the acute-chronic ratio is
a confounding influence in interpreting the duration needed
to produce a chronic effect endpoint. Where an appropriate
acute criterion is in force, the chronic averaging period need
not be shortened simply because the acute-chronic ratio is
low.
The TSD does not supersede the freshwater ammonia criteria
document, and thus EPA still recommends an averaging period
of as long as 30 days for ammonia, where concentrations do
not vary excessively.
11. EPA's recommended once in three year return frequency for
criteria excursions is overly conservative. Appendix D
presents time periods needed for ecological recovery from
severe or catastrophic stresses, not slight stresses caused
by marginal criteria excursions. The frequency of signif-
icant criteria excursions, comparable to those that caused
the measurable ecological impacts set forth in Chapter 1,
would be much less than for marginal criteria excursions.
EPA should present data on the ecological differences between
sites with different excursion frequencies. EPA should
develop guidance on how to establish site-specific allowable
frequencies.
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EPA Response: EPA has used Appendix D to set forth informa-
tion on time periods needed for ecological recovery from
severe or catastrophic stresses. EPA's recommended 3-year
return interval was set forth in the 1985 "Guidelines for
Deriving Numeric National Criteria...", and a review or
revision of this recommended frequency was not within the
scope of the TSD. Nevertheless, EPA intends to address the
excursion frequency during the. upcoming revision of the
Guidelines.
EPA expects that criteria exceedances can cause adverse
effects and that the magnitude of the effect will depend on
many things including the magnitude and duration of the
exceedance. EPA believes that all adverse effects are not
necessarily unacceptable, but that pollution should not be
allowed to subject aquatic communities to long-term or regular
short-term adverse effects. All dramatic adverse effects are
certainly unacceptable.
EPA believes that the 3-year return interval can be justified
by the Appendix D data if one makes the assumption that the
type of ecological impact shown in Appendix D could be caused
by fairly small criteria excursions. The concentrations
causing the Appendix D impacts were in fact not known. EPA
recognizes that the chemical and ecological field data
summarized in Chapter 1 suggest that successive excursions
well above the criteria would be needed to cause severe
impacts. EPA also recognizes that the probability of large
excursions can be calculated to be extremely small compared
to the probability of marginal excursions.
EPA does not have information to allow direct comparisons of
ecological quality versus criteria excursion frequency, except
possibly as could be inferred from the field data shown in
Chapter 1. EPA does not intend at this time to set forth
guidance on developing site-specific allowable frequencies.
Nevertheless, in general, EPA recommends that ecosystems not
spend a substantial portion of time in a state of recovery
from pollution stresses, and that pollution stresses not
significantly increase the total stress experienced by
organisms in the ecosystem. If the criteria are set appro-
priately, a marginal excursion might be expected to have
little or no measurable impact, and little or no time period
needed for recovery. The probability of a marginal criteria
excursion nevertheless has a calculable relationship with the
probabilities of severe criteria excursions. Consequently,
a scientifically justified site-specific or state-wide
frequency could be developed by considering (a) the
probability (estimated by simulation or by statistical
calculation) of a range of excursions of differing severity,
coupled with (b) the estimated ecological recovery period for
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13,
14,
15,
the corresponding different degrees of impact. Based on the
total period of recovery from a full range of possible events,
compared with the sum of return intervals for such events, the
allowable frequency for the marginal criteria excursion could
be established.
The once in three year excursion frequency does not take into
consideration the likelihood of apparent excursions caused by
the inherent variability of the analytical tests.
EPA Response: The allowable frequency for criteria excur-
sions should refer to true excursions of the criteria, not to
spurious excursions caused by analytical variability or error.
In evaluating data on chemical concentrations or toxicity
units, it is desirable to subtract the analytical error log
variance from the observed log variance in order to arrive at
the true log variance contributing to criteria excursions.
The IRIS (Integrated Risk Information System) data base should
be peer reviewed before it is used to update and generate
RACs. The TSD should not imply that a State can update its
standards simply by inserting the latest IRIS information into
the equation used to calculate the criteria.
EPA Response: EPA's IRIS data base reflects the latest
information about the Agency's health assessments for specific
chemicals. While the material in the data base is internally
reviewed, the Agency does not plan to have it undergo external
peer review. Use of IRIS information for developing state
water quality standards or discharge permits in no way
relieves the State of applicable requirements for public
notice and comment.
The fish consumption rates used to derive residue-based
criteria and RACs are unrealistically high for many waters.
EPA Response: EPA recommends using site-specific fish
consumption rates whenever such information can be obtained.
The harmonic mean is not an appropriate design flow.
arithmetic mean flow should be used.
The
EPA Response: For carcinogens it is appropriate to determine
the long-term arithmetic mean exposure concentration. Because
flow is not normally distributed, using the arithmetic mean
flow for design purposes will underestimate the mean
concentration.
Using the downstream harmonic mean flow will result in closely
estimating the mean concentration, providing that the
streamflow is not dominated by the effluent flow, and provided
that the effluent input is not correlated to the streamflow.
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16. Discussion of sediment criteria and biological criteria is
premature. The TSD should not advocate that states and
regions implement regulatory controls based on such criteria.
EPA Response: The biological criteria and sediment criteria
sections have been modified. EPA has undertaken development
of biological criteria and sediment criteria with the intent
that they would, after development, have regulatory applica-
tions .
EPA does not intend to imply that these approaches can or
should necessarily be used at this time to implement con-
trols. Nevertheless, EPA believes that the states, the
regulated community, and the interested general public need
to know how EPA is proceeding with these criteria, and what
the future regulatory implications may be. EPA is not
advocating that sediment criteria, by themselves, be used to
establish remediation target levels. EPA also recognizes that
sediment criteria cannot be used for setting discharge limits
without first developing a scientifically sound basis for
predicting the effect of effluent quality on sediment quality.
EPA is not suggesting that sediment quality concerns would
necessarily be more limiting on dischargers than water quality
concerns.
17. Aquatic life protection as measured by whole effluent toxicity
and chemical specific criteria are not applicable to waters
without aquatic life designated uses.
EPA Response: The TSD explains that numeric water quality
criteria are developed by States to protect the designated
uses within the water quality standards. However, the TSD
also reiterated EPA's position, as expressed in the June 2,
1989, Federal Register preamble on the 304(1) promulgation
was added, that the narrative criteria apply to all waters to
prohibit acute toxicity.
18. The food chain multiplier factors in the RAC calculation
should be deleted because it is contrary to measured levels
and BCF estimations.
EPA Response: The differences between bioconcentration and
bioaccumulation have been recognized in the scientific
literature for a number of years. Data published by Thomann
in Environmental Science and Technology (June 1989) show that
bioaccumulation can be over 100 times higher than
bioconcentration. Published critiques on EPA's dioxin
criterion have also expressed that bioaccumulation is more
important than bioconcentration for pollutants with log water
octanol partition coefficients greater than 6. EPA believes
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that consideration of bioaccumulation through use of the food
chain multiplier is consistent with the existing knowledge of
bioconcentration factors.
Chapter 3; Effluent Characterization
Overview: Simplified the chapter organization; cited regulatory
requirements (40 CFR 122. 44 (d) ) ; revised the discussion on effluent
bioconcentration evaluation to conform with the new draft document.
1. Determining the need for an effluent limit in the absence of
effluent monitoring data does not address the required factors
of 40 CFR § 122.44(d) (1)
EPA Response: EPA maintains the position that regulatory
authorities may make a finding of reasonable potential even
where effluent monitoring data is not available. EPA
disagrees with the commenter on the issue of whether the
required factors can be addressed in the absence of effluent
monitoring data. Box 3-1 of the TSD was revised to illustrate
how the recommended procedure for making reasonable potential
determinations in the absence of effluent monitoring data will
address each of the 4 rec[uired factors.
2 . Including bioconcentration and bioaccumulation recommenda-
tions in the TSD is premature. Approaches to this problem
require much more peer review, input and development.
EPA Response: EPA agrees with this comment. The draft
bioconcentration guidance that was referenced in the draft
chapter 3 has not yet been released for public comment and
does require additional peer review. The majority of the
chapter 3 discussion on the specifics of this guidance was
removed; the remaining sections specifically state that the
procedures in the draft guidance should not be used by
regulatory authorities until the guidance is finalized by EPA.
3. In determining reasonable potential, the cumulative effluent
discharge to a receiving water should be considered instead
of single discharges.
EPA Response: EPA agrees with this comment. The draft of
chapter 3 did not draw a clear enough distinction between the
terms "cause" and "contributes to" in the context of the
reasonable potential determination. Chapter 3 now states that
where multiple discharges collectively are causing or show the
reasonable potential to cause or contribute to an excursion
of water quality standards, limits must be developed for each
discharger to protect against such collective excursions.
This is underscored by adding the exact regulatory language
of 122. 44 (d). Finally, the document now has recommendations
on the use of toxicity testing in multiple discharge
situations.
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4. Guidance is needed on how to demonstrate that chemical-
specific limits alone are sufficient to achieve applicable
water quality standards, thus obviating the need for a WET
limit.
EPA Response: EPA agrees with this comment. Regulations at
122.44 (d) (1) (v) provide that WET limits are not necessary
where the permitting authority demonstrates that chemical-
specific limits are sufficient to protect water quality
standards. The draft of chapter 3 did not clearly recognize
this point and provided no guidance on how to make this
demonstration. Chapter 3 now reiterates this regulatory
provision with a new section entitled "Using a Chemical-
specific Limit to Control Toxicity." This new section
recommends that the discharger conduct a TIE to identify
causative toxicants. Where the causative toxicants are
controlled by chemical-specific limits, the permitting
authority may make the determination that WET limits are not
necessary.
5. The multiple conservative assumptions in the effluent
characterization methodology (the effluent is most toxic to
the most sensitive life stage at the time of lowest stream
flow and peak design flow) are overkill.
EPA Response: EPA does not agree that multiple conservative
assumptions amount to overkill. This comment implies that
EPA recommends establishing effluent limits to protect against
toxic impacts that are never projected to occur. In truth,
EPA only recommends establishing effluent limits where toxic
impacts are projected to occur. Estimates of toxic impact
should be made assuming that the effluent is most toxic to the
most sensitive species or lifestage at the time of lowest
available dilution because these are conditions that can be
expected to occur. For the most part chapter 3 remains
unchanged as a result of this comment. However, EPA has added
a short discussion that suggests that the regulatory authority
may choose to assess reasonable potential using a stochastic
dilution model which incorporates both ambient dilution and
effluent variability to project toxic impact.
6. EPA should not recommend a 3 species minimum. The algae test
and the marine tests are not sufficiently studied.
EPA Response: Chapter 3 continues to recommend as a minimum
that 3 species be tested quarterly for a minimum of 1 year
where toxicity tests are used to make decisions regarding the
need for WET limits. Experience indicates that algal tests
can be a highly sensitive test species for some pollutants.
Furthermore, using a plant adds another trophic level to the
test regimen. EPA rejects the assertion that the algal tests
are not sufficiently studied. For both freshwater and marine
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waters, the use of 3 species is more protective than 2 species
since a wider range of species sensitivity can be measured.
7. EPA should not recommend that ambient toxicity tests be
conducted at worst case low flow conditions.
EPA Response: EPA disagrees with this comment. Chapter 3
continues to recommend that ambient toxicity testing be
conducted during appropriate low flow or worst case design
periods. In order for the results of ambient toxicity tests
to form the basis for decisions about whether toxicity
controls are needed, the test must reflect the conditions that
such controls would be designed to protect. If a regulatory
authority's policy is to protect at the 7Q10 flow, than the
ambient tests must be conducted at flows that are very near
the 7Q10. Otherwise, the regulatory authority will learn very
little from the ambient test about whether toxicity limits are
necessary for a particular discharge.
8. Reasonable potential determinations should not be based on
whole effluent toxicity data alone. Toxicity data and
instream survey data should be used together in a weight of
evidence approach.
EPA Response: We disagree. As discussed in the response to
comment no. 2 in Chapter 1, EPA considers that water quality
standards apply independently of each other. Whole effluent
toxicity measures a different biological endpoint than do
instream survey data.
9. One piece of effluent data projecting an excursion above a
water quality standard is insufficient to justify setting an
effluent limit.
EPA Response: EPA disagrees. EPA's position is that where
even one data point shows that an excursion of a state water
quality standard is projected, the Director may determine that
permit limits for whole effluent toxicity or for specific
chemicals are necessary. In making such a determination,
NPDES regulations requires that the Director also account for
existing controls on point and nonpoint sources, the
variability of the pollutant parameter in the effluent, the
sensitivity of the species to toxicity testing (for whole
effluent), and where appropriate the dilution of the effluent
in the receiving water. In addition, the Director should
consider all other available information pertaining to the
discharger to assist in making an informed judgement.
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Chapter 4; Exposure Assessment and Wasteload Allocation
Overview: Clarified terminology for mixing zone and design flow
conditions.
1. Clarify or reevaluate Agency's position with respect to key
mixing zone issues: including how to establish geographical
boundaries of mixing zones and point of application of
criterion for persistent bioaccumulative pollutants, and how
to prevent lethality in the mixing zone.
EPA Response: The revised TSD states as it did in previous
drafts that the mixing zone size should be minimized and the
dimensions should be based on the site-specific conditions.
As previously stated, site-specific evaluations should also
be conducted by the permitting agency to determine whether to
allow a mixing zone for discharge of bioaccumulative
pollutants. The TSD was revised to expand the three
approaches for preventing lethality in the mixing zone to four
approaches. The new approach includes submission of actual
data to show that a drifting organism would not be exposed to
1-hour average concentrations exceeding the CMC. In addition,
clarification was provided on the approach not requiring the
use of a high velocity discharge to show that the CMC is met.
Approaches for preventing lethality in the mixing zone conform
with the position taken in Chapter 2.
2. Clarify or reevaluate Agency's position on appropriate
critical flows for toxicants which have potential human health
impacts and/or aquatic life impacts.
EPA Response: It was determined that the harmonic mean flow
was appropriate for evaluation of human health impacts that
are of concern due to long-term exposures (e.g., cancer).
The TSD was revised to clarify the use of harmonic mean flow
and its appropriateness for use in water quality modeling to
evaluate human health impacts (e.g., a step-by-step calcula-
tion procedure was added). Additional clarification was
provided for the use of hydrologically-based 7Q10 and 1Q10
flows for the evaluation of "worst case" scenarios for
determining potential aquatic life impacts. .
3. EPA should present all valid modeling approaches and deter-
mine the best water quality model for each water quality
condition.
EPA Response: The models described in the text were those
EPA considers to be comprehensive to evaluate most water
quality conditions. Because of all the potential site-
specific scenarios, it is beyond the scope of the document to
present all of the valid approaches that could be used for
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water quality modeling. The permitting authority needs to
evaluate the data available for the site and select the water
quality model that is best for calculating the receiving water
concentrations and the TMDLs.
4. Specific caveats should be added to the model descriptions.
EPA Response: It is beyond the scope of the document to
provide all of the caveats that are applicable for each of
the "models. Although the commenters presented specific
caveats for a model, they were not incorporated since it was
beyond the scope of revising the document to determine all
the cases that the caveat could apply.
5. Commenters want additional explanation or justification for
the assumptions and applications for the equations presented
in the TSD.
EPA Response: The TSD already contained a sufficient explan-
ation or referenced the documents which contained the
rationale.
6. The water quality model "DYNTOX" and the software program HHD
FLOW are not available.
EPA Response: DYNTOX is not currently available but should
be accessible by early 1991. HHD FLOW is not available, but
DFLOW is available, and the TSD has been changed to reference
this software package.
7. Guidance on regulating nonpoint sources should be included in
the TSD.
EPA Response: It is beyond the scope of the document to
include information on regulating non-point sources.
8. Guidance should be given in the discussion on design flow for
persistent pollutants.
EPA Response: Persistent pollutants should be assessed in
the same way as bioaccumulative pollutants.
9. The human health section does not provide direction regard-
ing the percentage of fish that are taken from a given area.
EPA Response: The percentage of fish should be determined
based on site-conditions. The WLA criteria are conservative
estimates based on heavy consumption of fish or a potentially
large contaminated area.
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10. The TSDs discussion on mixing zones' contribution to human
health is overemphasized.
EPA Response: The TSDs discussion on mixing zones has been
revised and does not overemphasize the contributions to human
health.
11. EPA should revise its discussion of modeling WLAs for human
health toxicants because it is misleading since it suggests
that the method should be used whether the applicable
criterion is a drinking water standard intended to prevent
acute effects on humans or criterion established for Deriv-
ing Numerical National Water Quality Criteria.
EPA Response: The TSD does not discuss acute human health
effects; therefore, it was determined that the discussion is
not misleading.
Chapter 5; Permit Requirements
Overview: Added clarifications and examples to support the
existing text; gave equal weight to developing limits based on a
dynamic and steady state wasteload allocations; added discussion
on metals, average and maximum permit limits, single dilution
tests, variability, and mass-based limits.
1. The two value, steady-state model approach to permit limit
derivation is overly conservative with too many built-in
safety factors. As a result the limits derived are too
stringent.
EPA Response: EPA has revised Chapter 5 of the TSD to
emphasize the development of permit limits that are as exact
as possible to attain and maitain water quality standards.
Chapter 5 now recommends the use of the statistical limit
derivation procedure which provides for two options. The
first option uses a steady state model approach for develop-
ment of the wasteload allocation (WLA) and long term average
(LTA). Since this approach relies on critical condition
assumptions regarding effluent characteristics and receiving
water characteristics, this approach may derive limits that
are more restrictive than the second option. The effluent
characteristics of importance are pollutant concentrations,
pollutant concentration variation, and effluent flow. The
receiving water characteristics of importance are pollutant
concentrations and receiving water flow.
Where a discharger or permitting authority believes that the
steady state model approach results in overly restrictive
permit limits, under the revised TSD the discharger or
permitting authority has the alternative of using a dynamic
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model approach. Under the dynamic model approach worst case
assumptions are minimized and more accurate receiving water
concentrations of a pollutant can be calculated. In general,
dynamic models account for the daily variations of and
relationships between flow, effluent and environmental
conditions and therefore directly determine the probability
that a water quality standards exceedance will occur. Because
of this, dynamic models can be used to develop wasteload
allocations which more exactly maintain the water quality
standards at the return frequency requirements of the
standards. The WLA is first developed by iteratively running
the dynamic model with successively lower LTAs until the model
shows compliance with the water quality standards. With this
approach now a recommended option in the TSD, this major issue
is resolved. A disadvantage of using dynamic model outputs
to develop permit limits is the lack of necessary data for
effluent variability and receiving water flows.
2. The discussion of below detection levels is confusing. EPA
should not be setting water quality-based limits below
detection levels, especially since variability of a test
method is greater the closer the results are to the detection
level.
EPA Responses The discussion of below detection level limits
in the draft TSD was unclear. Since the time of the draft
TSD, EPA issued its guidance on setting permit limits below
the detection level for dioxin. This guidance uses a minimum
level (ML) to ascertain compliance with limits set below
detection levels. The TSD was revised to follow the dioxin
guidance (May 21, 1990 Memorandum from LaJuana Wilcher,
"Strategy for the Regulation of Discharges of PHDDs and PHDFs
from Pulp and Paper Mills to Waters of the United States").
Specific values for the minimum level are found in the
description of methods 1624 and 1625 for some organic
compounds. (See the appendix to 40 CFR 136.)
3. EPA's criteria recommend that limits be derived for toxicant
in the soluble form or biologically available form, yet many
permit limits are being written and compliance being based
upon the total recoverable form of metals. The TSD should
address this issue and give guidance on developing limits only
for bioavailable forms of pollutants.
EPA Response: The TSD has been revised to cite the regula-
tory requirements at 40 CFR 122.45 (c) and to provide three
options for use where a state has not developed a method for
determining total recoverable permit limits based on a
dissolved or acid soluble water quality criterion. The three
options are 1) assume complete availability of the total
recoverable metal, 2) use the method in the EPA wasteload
allocation guidance manual for toxics in rivers to relate the
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two, and 3) use site specific data to develop a relationship.
4. EPA's regulations do not allow permit limits based on one day
maximum concentrations for POTWs.
EPA Response: The NPDES regulation at 40 CFR 122.45(d)
require the use of a 7-day average unless impractical. The
discussion on the expression of permit limits now states that
EPA considers the 7-day average limit for POTWs to be
impractical for the purposes of controlling the discharge of
toxics. The reason for this statement is that control of the
7-day average in lieu of control of the 1-day maximum will
allow for unmeasured short-term excursions of an acute water
quality standard.
5. TREs should not be required as a permit condition to respond
to a violation of a whole effluent toxicity limit. The proper
response by the permitting authority is through use of
enforcement mechanisms.
EPA Response: The discussion on TREs was changed to not
recommend that the TRE or accelerated monitoring be included
in the permit to respond to permit limit violations but rather
be part of the enforcement response. This was done to help
distinguish between monitoring only provisions and enforcement
of permit limits. This should reduce confusion about the
difference between enforcement on a single event violation of
a limit and the need for multiple violations before a TRE is
warranted.
6. Permit limits should be increased to consider analytical
variability. EPA should consider using the approach it
proposed in the Amelia River study.
EPA Response: EPA disagrees with the proposal. A discussion
was added to explain how EPA considers analytical variability
in developing permit limits. The discussion states that since
this variability is an intrinsic part of all data collection
(effluent monitoring, wasteload allocation development, and
water quality standards development) , and that the variability
can go both ways (higher or lower) , that EPA does not separate
it out from all other variability factors. EPA's Amelia River
study is not final; the approach cited may not be included in
the final report.
Although difficult, it may be possible to determine what
proportion of the observed variability can be attributed to
sampling error, and what proportion can be attributed to the
method of measurement. Regardless, the TSD makes use of a
coefficient of variation that includes both sources of
variability. This is not unreasonable since sampling for
monitoring purposes also results in the inclusion of these
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two sources of variability. Any consideration of upstream
concentrations in the WLA will also include analytical
variability. There is rio "true" calculation in the process
of developing permit limits because there is analytical
uncertainty throughout the process. Instead, LTAs should be
calculated from the WLAs using the same CV that is also used
to calculate permit limits from the most limiting LTA. It is
unimportant exactly what CV is used because the most
restrictive LTA itself is used only for determining the
desired treatment performance level. However, this procedure
assures (99 or 95% confident) that the permit limits will be
less than or equal to the more limiting LTA.
7. Since permit limits were derived based on 95th and 99th
percentile probabilities, that occasional exceedances of
permit limits should be allowed on the same basis.
EPA Response: In statistics, the selection of an acceptable
probability level reflects the level of confidence that is
desired of the results. As such, an acceptable level must be
defined prior to performing any statistical procedure. As
stated in the TSD, the probability basis of 0.99 for the daily
maximum limit, and 0.95 for the average monthly limit have
been used historically in connection with development of the
effluent guideline limitations and have been well accepted
upheld in legal challenges to the guidelines. These values
are tied to monitoring frequencies that are required for each
limit. There is no mixing of two probability bases since they
are distinct and separate limits. The goal in establishing
these levels is to allow the regulatory agency to distinguish
between adequately operated wastewater treatment plants with
normal variability from poorly operated treatment plants.
8. Permit limits should vary with flow conditions in the
receiving waters since exposure is based on dilution with
receiving water flow.
EPA Response: EPA partially agrees but only to the extent
that the limits are seasonally based. The seasonal approach
has been used by permitting authorities for setting permit
limits to protect against excursions of dissolved oxygen and
ammonia standards. However, seasonal limits are different
than limits which vary dciily based on river flow. EPA is not
convinced that a daily variable approach would be universally
practical given wastewater treatment response and performance;
for this reason EPA has not included procedures for this
approach. In addition, the discharger has the option of using
dynamic modeling to develop permit limits. Since dynamic
modeling considers all receiving water flows, this option
would provide the discharger a less restrictive permit limit
than would be obtained by using steady state modeling.
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9. If limits were derived that were overly stringent due to the
worst case assumption of the steady state model, and if in
the future the permittee conducted dynamic modeling which
resulted in less stringent limits, permittees would be bound
to the previous limits due to the anti-backsliding require-
ments .
EPA Response: There is no absolute prohibition. EPA's
September 1989 guidance document on antibacksliding contains
EPA's. interpretation of the Clean Water Act provisions in
§402(o) and §303(d)(4). This guidance also does not contain
an absolute prohibition. It is EPA's position that the CWA's
anti-backsliding provision and EPA's existing regulations do
not uniformly prohibit the incorporation into a permit of less
stringent limits, standards, or conditions. In certain
situations (i.e., under Sections 402(o) and 303(d)(4) of the
CWA) , less stringent limits or conditions may be permissible.
Section 402(o)(l) provides that backsliding from water
quality-based limits is prohibited except in compliance with
Section 303(d)(4). Section 303(d)(4)(A) only allows estab-
lishment of less stringent limits in a permit for discharge
into a non-attainment water only if two conditions are met:
1) the existing permit limit must have been based on a TMDL
or other WLA established under Section 303, and 2) attainment
of water quality standards must be assured. Section
303(d)(4)(B) allows establishment of less stringent limits in
a permit for discharge into an attained water only where
relaxation is consistent with a State's antidegradation
policy.
Section 402(o)(2) also outlines exceptions to the general
prohibition against backsliding from water quality-based
permit limitations. Under Section 402(o)(3), backsliding may
be allowed: 1) where there have been material and substantial
alterations or additions to the facility; 2) where good cause
exists due to events beyond the permittee's control and for
which there is no reasonably available remedy; 3) where the
permittee has installed and properly operated and maintained
required treatment facilities; and 4) where new information
justifies backsliding from water quality-based permit
limitations and other Section 301(b)(1)(C) limitations.
10. EPA does not have guidance on how to conduct a chronic TRE
and therefore limits should not be derived based upon chronic
endpoints.
EPA Response: EPA is aware of the need for guidance on
conducting TREs for chronic toxicity. EPA's Duluth labora-
tory is near completion of a draft guidance document. The
guidance document will be widely available when finished.
Regardless, the lack of a finished guidance document is not
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a valid reason to allow for excursions above a narrative
standard as measured by chronic whole effluent toxicity.
Some dischargers have been able to comply with chronic
toxicity limits and identify and control sources of chronic
toxicity. EPA experience has shown that portions of the
published TRE procedures for solving incidences of acute
toxicity (EPA/600/2-88/070, EPA/600/2-88/062, EPA/600/3-
88/034) can be used for resolving incidences of chronic
toxicity.
11. EPA should allow adequate time for facilities to come into
compliance with water quality-based permit limits.
EPA Response: EPA is aware that facilities may need time to
comply with newly established effluent limits. This has been
accomplished in the past in NPDES permits by allowing
compliance schedules within the permit. Regulatory agencies
use of compliance schedules for water quality-based effluent
limits are governed by recent decisions regarding the Star-
Kist Caribe ruling by EPA's Chief Judicial Officer (CJO). On
March 8, 1989, in review of the evidentiary hearing request
by Star-Kist Caribe, the CJO ruled that compliance schedules
for water quality-based effluent limits may not be included
in NPDES permits unless explicitly authorized by the State in
its water quality standards or implementation regulations.
The ruling was based on an interpretation of section
301(b)(1)(C) of the Clean Water Act. Later, on Septermber 4,
1990, the CJO granted a stay of the ruling to allow EPA and
States to use compliance schedules for water quality-based
limits where such schedules are consistent with State policy.
In any case, the allowance for compliance schedules is a State
decision which may ultimately need to be expressed in water
quality standards.
12. Effluent limits should be set within the ability of treatment
technology.
EPA Response: EPA is aware that there may be a number of
water quality-based permit limits for toxics which may be
presently unachievable with existing wastewater treatment
technology. However, the NPDES regulations at 40 CFR
122.44(d) require that effluent limits more stringent than
those established based on a treatment technology basis must
be set to achieve water quality standards.
13. The limit derivation procedures for human health should use
the same statistical procedures as used for deriving limits
for aquatic life. Permit limits should be derived from the
harmonic mean effluent concentration.
EPA Response: Since compliance with permit limitations is by
regulation determined on a daily and monthly basis, it is
necessary to set permit limitations expressed in these
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contexts that meet a given WLA every month. The statistical
procedures for permit limit derivation in the TSD are designed
to accomplish this for aquatic life protection where the use
of shorter term averaging periods is consistent with two
number aquatic life criteria.
However, if the TSD procedures were directly used for setting
permit limits on bioconcentratable pollutants, both maximum
daily and average monthly permit limits could exceed the
wasteload allocation necessary to meet the criterion. These
two permit limits would assure that the long term average
effluent discharge would comply with the human health derived
WLA only if the assessment of the effluent variability was
precise. With bioconcentratable pollutants where exposure
duration ranges up to 70 years, EPA believes that effluent
variability cannot be reliably estimated from existing data
for exposure periods a year. If the effluent variability was
over-estimated when establishing the permit limits, then a
facility could be discharging in compliance with the permit
limits but would be exceeding the wasteload allocation for
human health protection. This approach is clearly
unacceptable.
This problem does not arise when using the TSD statistical
procedure for setting permit limits for protecting against
aquatic toxicity. In this case, the monthly average and daily
maximum permit limits are more closely related to the four day
average and one hour maximum used as exposure periods for the
criteria. Any imprecision in assessing effluent variability
would therefore not have as great an effect on the permit
limits.
14. Effluents may not always demonstrate a log-normal distribu-
tion. The TSD should present procedures for using other
distributions.
EPA Response: EPA believes, after reviewing the database used
to establish effluent guidelines, that the log-normal
distribution best characterizes effluents. EPA's analysis of
these data are provided in Appendix E. The general
characteristics of the lognormal distribution (it is only
positive and is skewed towards extreme high values) make it
an appropriate distribution for dealing with effluent
concentrations. According to Gilbert (1987), the lognormal
distribution is the only available 2-parametric distribution
that can routinely be applied to environmental data. Since
the Agency is not providing derivation procedures for
alternate data distributions, it is not necessary to test for
lognormality of effluent data. Permitting authorities can
develop their own methods using other probabilistic
distributions.
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Chapter 6; Enforcement
Overview: No major changes made in recommendations; added
clarifications and explanations.
1. One effluent test failure should not equal a violation;
provisions should be made to delay punitive enforcement action
where legitimate efforts are being made; permittees should not
be held in violation of their toxicity limit while conducting
a TRE.
EPA Response: The current draft still emphasizes the
principle that any single exceedance is a violation and is
subject to a full range of enforcement responses. However,
the draft has been caveated with discussion on EPA's guidance
which outlines a systematic review of all violations to
determine the appropriate level of enforcement. EPA's
enforcement guidance is included in an appendix.
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