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 ------- ------- 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 ------- 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." ------- 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 ------- 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. ------- 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 ------- 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 6 ------- 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 ------- 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 8 ------- 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. ------- 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 10 ------- 12 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. 11 ------- 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 12 ------- 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. 13 ------- 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 14 ------- 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. 15 ------- 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 16 ------- 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. 17 ------- 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 18 ------- 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 19 ------- 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 20 ------- 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. 21 ------- 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 22 ------- 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 23 ------- 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. 24 ------- 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. 25 ------- ------- |