Presentation on theme: "Whole Effluent Toxicity (WET) Testing Water Quality Standards Workgroup Meeting June 26, 2007."— Presentation transcript:
Whole Effluent Toxicity (WET) Testing Water Quality Standards Workgroup Meeting June 26, 2007
Introduction of WET Staff Jim Davenport, Team Leader Michael Pfeil Lynda Clayton Debbie Miller Jason Godeaux
WET Basics – Current TCEQ Policy WET testing: The purpose of WET testing is to assess the effect that a permitted wastewater discharge may have on the aquatic organisms in the receiving waters. Regulatory Authority: 40 Code of Federal Regulations §122.44(d)(1)30 Texas Administrative Code §307.6(e)
WET Basics – Current TCEQ Policy, cont. Applicability: Domestic wastewater dischargers with: -Permitted wastewater flow of 1 MGD or greater -EPA-approved pretreatment program -Potential to effect toxicity in receiving waters Industrial wastewater dischargers with: -EPA-classified majors -Continuously-discharged process wastewater -Potential to effect toxicity in receiving waters
WET Basics – Current TCEQ Policy, cont. Three Types of WET testing -24-hour acute: measures lethality to specified invertebrate/vertebrate species -48-hour acute: measures lethality to specified invertebrate/vertebrate species -7-day chronic: measures lethality and sublethality (growth/reproduction) to specified invertebrate/vertebrate species
WET Basics – Current TCEQ Policy, cont. Test Organisms Used Passing vs. Failing WET Passing: When the difference between the critical dilution (% effluent at the mixing zone) and the control is not statistically significant, the test is considered to have passed. Failing: When the difference between the critical dilution (% effluent at the mixing zone) and the control is statistically significant, the test is considered to be a failure.
WET Basics – Current TCEQ Policy, cont. After a failure, TCEQ policy requires the permittee to conduct 2 additional consecutive monthly tests for LETHALITY ONLY to determine persistent toxicity. After a failure, TCEQ policy requires the permittee to conduct 2 additional consecutive monthly tests for LETHALITY ONLY to determine persistent toxicity. A Toxicity Reduction Evaluation (TRE) is required when persistent toxicity is demonstrated after the initial failure and when both subsequent retests fail.
WET Basics – Current TCEQ Policy, Cont. Toxicity Reduction Evaluation (TRE): A test method to try to determine the source of the lethal toxicity. There are three possible outcomes to a TRE: -Chemical specific limit: If an actual toxicant was identified as causing the test failure, then a limit is placed in the permit for that particular toxicant. This limit is enforceable. -Whole Effluent Toxicity limit (WET limit): If no single toxicant was identified, then a limit is placed in the permit for the toxicity of the entire effluent. This limit is enforceable.
WET Basics – Current TCEQ Policy, cont. -Best Management Practice (BMP): Very rarely used; assessed in situations were a BMP will clearly prevent the toxicant from ever entering the wastewater treatment system. The current Implementation Procedures also indicate that persistent sublethal effects may have to be addressed by a TRE to attempt to determine a source of sublethal toxicity. Currently, there are no stipulations indicating this may lead to a sublethal WET limit.
EPA Permitting Strategy for WET EPA proposes the following strategy to further: Regulatory policy and requirements established in 1989 and Regulatory policy and requirements established in 1989 and Guidance developed since that time as outlined in the EPA draft guidance document Guidance developed since that time as outlined in the EPA draft guidance document National Whole Effluent Toxicity (WET) Implementation Guidance Under The NPDES Program (EPA-832-B ), released December 2004, which reiterates information found in the Technical Support Document for Water-Quality Based Toxics Control (EPA , 1991).
EPA Permitting Strategy for WET Applicability Reasonable Potential (RP) Regulatory basis - 40 CFR (d)(1)(i) requires limitations on any parameter that has a “reasonable potential to cause, or contributes to an in-stream excursion...above any state water quality standard, including state narrative criteria...” EPA uses a statistical analysis described in Technical Support Document (EPA 1991) to determine reasonable potential. Historical data is used to determine if a WET effluent limit is appropriate. Assessed WET limit would simply be for “toxicity”, which includes lethal and sublethal effects.
EPA Permitting Strategy for WET Reasonable Potential Calculation as outlined in 2004 draft guidance document:
EPA Permitting Strategy for WET Results of RP Calculation: If the calculation resulted in a number greater than or equal to 1, the reasonable potential is said to exist and a WET limit is assessed. Toxicity Units (TUs): Reporting NOECs as TUs to simplify the RP determinations. TUs =100/NOEC. TUs =100/NOEC.
EPA Permitting Strategy for WET WET Limits Included in the newly-issued permit when RP is determined. Issued for lethal and sublethal effects (“toxicity”). The guidance document, however, does not specifically address sublethal toxicity. Monitoring Frequencies Permits with WET limits: once per quarter for five years. Majors: once per quarter for the first year, after which the frequency may be reduced. Minors: case-by-case. All dischargers: once per month for the next three months after a test failure.
Region 6 WET Permitting Strategy Reasonable Potential During the permitting process, determine if reasonable potential (RP) exists. “Toxicity” equals both lethal and sublethal effects. If RP exists, WET limits must be included in the permit. A chemical specific (CS) limit may be substituted for a WET limit if the permitting authority demonstrates that the CS limit will preclude toxicity.
Region 6 WET Permitting Strategy For 7-day chronic tests, RP analysis will be performed for both lethal and sublethal effects. During the permitting process, if it is determined that the permittee will not alter the effluent quality or quantity during the permit term and has conducted quarterly testing with no significant toxicity demonstrated for the previous five years, and has a critical dilution equal to or greater than 90% then a finding of no RP may be made.
Region 6 WET Permitting Strategy WET Limits WET limits may be removed from a permit after the first five years in effect as long as there has been no demonstration of significant toxicity. All data will be evaluated to ensure that the data is valid and mitigating circumstances (such as if there are failures but they were reported more than 2-3 years prior with several passing tests since) will be considered before automatically issuing a WET limit. Sublethal WET limits will only be implemented at the 80% effluent level at this time.
Region 6 WET Permitting Strategy Toxicity Reduction Evaluations (TREs) Trigger language is only included in permits where an RP is not determined. For lethal effects, TREs are implemented. This has been done historically. For sublethal effects, a graduated approach - after initial failure, 2 of 3 additional sublethal test failures trigger TRE requirements. Sublethal TREs are implemented only when failures have NOECs (No Observable Effect Concentration) below 75%.
Definitions LOEC (Lowest Observed Effect Concentration): the lowest effluent dilution at which a significant effect is demonstrated. Magnitude: the resultant NOEC of a test failure. NOEC (No Observed Effect Concentration): the greatest effluent dilution at which no significant effect is demonstrated. Significant effect: a statistically significant difference at the 95% confidence level between the survival, reproduction, or growth of the test organism(s) in a specified effluent dilution compared to the survival, reproduction, or growth of the test organism(s) in the control (0% effluent). Test failure: a significant statistical difference in test results between the control and the critical dilution.
Sublethal Toxicity Sublethal toxicity (failure) is a significant statistical difference between the control and the critical dilution for the reproduction and/or growth endpoints. Currently, the TCEQ Implementation Procedures indicate that sublethal TREs may be required for persistent significant sublethal toxicity. Successful TREs to determine the causes of sublethal toxicity depend greatly on: The frequency of significant sublethal toxicity occurrences, and The frequency of significant sublethal toxicity occurrences, and The magnitude (NOEC) of the failure (the lower the NOEC the greater the magnitude of failure). The magnitude (NOEC) of the failure (the lower the NOEC the greater the magnitude of failure).
Possible Factors That May Affect Reasonable Potential (RP) WET testing history Staff currently evaluates five-year test history when making WET recommendations Staff currently evaluates five-year test history when making WET recommendations Other suggestions for period of history to assess? Other suggestions for period of history to assess? Frequency of test failures – below are some possible methods for assessing the frequency of lethal or sublethal test failures Percent of failures of total test results – binomial assessmentPercent of failures of total test results – binomial assessment Minimum number of failuresMinimum number of failures “x” number within “y” timeframe“x” number within “y” timeframe 95% versus 99% confidence interval95% versus 99% confidence interval
Possible Factors That May Affect Reasonable Potential (RP), cont. Magnitude For lethal or sublethal failures: NOEC less than or equal to 50%, for example, may indicate RPFor lethal or sublethal failures: NOEC less than or equal to 50%, for example, may indicate RP Other NOEC values appropriate?Other NOEC values appropriate? Effluent flow - the higher the flow, the higher the potential for toxicity Pretreatment program – does facility have one and is it likely to increase reasonable potential? Compliance record – does it indicate exceedances of chemicals of concern? Other?
Discussion Topics For routine WET testing for permits, should sublethal persistent toxicity be addressed with the same approach as for persistent lethal toxicity? Existing Procedures: Under the existing implementation procedures, if a lethal failure occurs, two consecutive monthly retests are conducted to determine if persistent lethal toxicity is occurring. If one of those two retests fails, a TRE is initiated. Permits are amended to impose WET limits only 1) after a TRE has been completed, 2) if no BMP is applicable, and 3) if no specific chemical was identified as the cause of toxicity. Currently, TCEQ does not assign WET limits due to persistent significant sublethal toxicity.
Discussion Topics, cont. Options to address sublethal toxicity, for discussion purposes: A. Continue current process. B.Don’t require TREs or WET limits for sublethal toxicity during a permit cycle, but address long-term sublethal toxicity through an assessment of reasonable potential when the next permit is issued (as discussed below). C.Address sublethal toxicity with the same procedures as for lethal toxicity. D.Consider using a different endpoint to define sublethal WET test failure, such as conducting three additional retests, and entering a TRE if two of the three retests fail. E. Other suggestions?
Discussion Topics, cont. How should reasonable potential for toxicity be assessed? Factors to consider [see separate handout for further explanation]: WET testing history Frequency of test failures Magnitude of test failures Effluent flow relative to instream dilution Pretreatment program in place, indicating higher potential for commercial loadings Compliance history concerning chemical-specific effluent limits Other factors?
Discussion Topics, cont. Examples of options to assess reasonable potential, for discussion purposes: A.Use a straight percentage of failures. For instance, for the history of representative WET data, if ≥ 30% are failures, then there is reasonable potential for toxicity. B.Use a “Weight of Evidence” approach with “Lines of Evidence” such as: For demonstrations of sublethal toxicity, the NOEC must be equal to or less than 50%, and at least 25% failures (lethal and/or sublethal) with at least 7 test failures over the past 5 year period, and a demonstration of recent significant toxicity, representative of current conditions, such as at least 2 failures in the last 2 years and 1 in the last year.
Discussion Topics, cont. C.Modify EPA’s RP calculation to consider facility history and toxicity magnitude. An example: If a facility has a total of six failures** in a five-year period, then reasonable potential for toxicity might be indicated. **If there is a Ceriodaphnia dubia sublethal failure included in the six failures identified above, the permittee may resubmit the test data for evaluation of test validity to determine if the reported failure may have been due to anomalous data (especially for data submitted prior to May 2004). If a reported sublethal failure was at an NOEC of 76% or greater, then that failure will not be considered as one of the six failures identified. This is because the magnitude of toxicity is not likely to be high enough for successful identification of the toxicant.
Discussion Topics, cont. D. As in option C, except evaluate lethal and sublethal failures independently. This option could allow for different numbers of lethal and sublethal failures being used to define reasonable potential. Note: with this option there is the possibility of developing a mathematical formula for determining reasonable potential as opposed to using the EPA formula proposed in the 2004 draft guidance document. E. Conduct a reasonable potential calculation as presented in EPA’s draft guidance document (December 2004) which considers toxicity in general with no distinction between lethal and sublethal effects. F.Other Options? NOTE: Additionally, EPA Region 6 has indicated, via dated June 6, 2007, that a compliance period would be granted for permittees assessed up front WET limits.
Discussion Topics, cont. If reasonable potential is determined for toxicity, what are the appropriate steps? Examples of options to address reasonable potential, for discussion purposes: A. Increased testing frequency - monthly If toxicity is shown, initiate a TRE or establish a WET limit If toxicity is shown, initiate a TRE or establish a WET limit If no toxicity is shown for a minimum of twelve consecutive months, reduce frequency to quarterly If no toxicity is shown for a minimum of twelve consecutive months, reduce frequency to quarterly B. Initiate TRE upon permit issuance C.Up-front WET limits in the permit with a three-year compliance period D.Establish procedures to remove WET limits if lack of toxicity proves this is warranted. E. Initiate a TRE to address sublethal toxicity; but require the permittee to implement a plan to reduce sublethal toxicity, rather than impose WET limits. F. Other Options?
Break Out Group Questions Topic 1 for Break Out Group Discussion Reasonable Potential: 1)Do you think Reasonable Potential (RP) should be determined by using EPA's model, which uses the worst-test result of the past 5 years? 1)Do you think Reasonable Potential (RP) should be determined by using EPA's model, which uses the worst-test result of the past 5 years? a)Why or why not? b)If not, what would you propose instead to determine RP? c) Are there additional factors you would like considered in assessing RP? d)Should different factors contributing to assessment of RP be weighted differently? 2)Should RP lead directly to WET limits (lethal and/or sublethal) without a TRE being performed? If not, what would you propose as an alternative? 3)What would be appropriate justification for removing effective WET limits?
Break Out Group Questions Topic 2 for Break Out Group Discussion Sublethal Toxicity Issues: 1) Do you think sublethal TREs are ever appropriate? a)Why or why not? b)If not, what would you propose instead to address sublethal toxicity? 2) TRE triggers a)How many sublethal failures should a facility have before a TRE is triggered? b)Over what time period? c)What NOEC would be appropriate to use to trigger a TRE? d)Could anything else trigger a TRE? 3)If a TRE is performed and a toxicant is not identified, what should happen next?