Transcript www.tceq.state.tx.us

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.
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
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-04-003),
released December 2004, which reiterates
information found in the
Technical Support Document for Water-Quality
Based Toxics Control (EPA-505-2-90-001, 1991).
EPA Permitting Strategy for WET

Applicability

Reasonable Potential (RP)
Regulatory basis - 40 CFR 122.44(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.
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 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
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 assessment
• Minimum number of failures
• “x” number within “y” timeframe
• 95% 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 RP
• 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 email 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 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?
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?