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What exactly is WET? (Whole Effluent Toxicity / Biomonitoring)

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Whole Effluent Toxicity (WET) “The Canary in Your Coal Mine” 27 th Annual Region VI Pretreatment Workshop Irving, TX August 1-4, 2011 Paul Juarez, 6WQ-PP Whole Effluent Toxicity Coordinator US Environmental Protection Agency 214.665.7247. What exactly is WET?

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Whole Effluent Toxicity (WET)“The Canary in Your Coal Mine”27th Annual Region VI Pretreatment WorkshopIrving, TXAugust 1-4, 2011Paul Juarez, 6WQ-PPWhole Effluent Toxicity CoordinatorUS Environmental Protection Agencyjuarez.paul@epa.gov214.665.7247


What exactly is WET?

(Whole Effluent Toxicity / Biomonitoring)

WET, or biomonitoring, is the use of live test

organisms to determine the potential toxic

impacts of wastewater effluents, stormwater,

or other water discharges, on aquatic life in

receiving streams and lakes.


Pimephales promelas

Fathead minnow

Ceriodaphnia dubia

Daphnid - water flea

is wet required if so why
Is WET required? If so, why?

EPA (and State governments) require wastewater permits to include WET testing to ensure compliance with objectives of the Clean Water Act, federal regulations for NPDES permitting 40 CFR 122.44(d)(1), and State narrative water quality standards to protect aquatic life.


State Water Quality Standard for the Protection of Aquatic Life

After allowing for mixing with receiving water upstream, there shall be no chronic toxicity outside the edge of the defined mixing zone.

Chronic Toxicity — Toxicity which, after long-term exposure, exerts sublethal negative effects, or which is lethal to representative, sensitive organisms.


A facility must obtain a permit to

  • discharge its wastewater.
  • The permit defines what chemicals
  • may be discharged, how much over
  • what time period (mass limits and/or
  • concentration limits).
  • Permits also require whole effluent
  • toxicity (WET) testing to determine if the
  • effluent is toxic to aquatic life. If the
  • effluent is toxic, permit limits on WET may
  • be required.
but how can wet benefit my facility
But how can WET benefit my facility?

Failing a WET test usually signals something has gone wrong with the treatment system – either a change in chemicals added, process, OR that the toxicity of your influent has increased for some reason – possibly a new discharger or a change in the effluent discharged by an existing customer. But, while the initial WET test failure may be a negative sign, WET is also a basic tool to find and correct the problem.

pretreatment wet testing requirements
Pretreatment WET Testing Requirements

Pretreatment permits issued by municipalities to their industrial users now include WET monitoring. Such permits usually include quarterly testing with increased frequency following a failure. A failure is defined as a significant lethal or sublethal effect at a critical concentration. That critical concentration is based on the industrial user’s proportion of the POTW’s influent.

pretreatment primary defense
Pretreatment – Primary Defense
  • Can add additional levels of protection and influent/effluent toxicity control(s)
  • User survey analysis when performing a Toxicity Reduction Evaluation (TRE)
  • Provides initial points of reference outside the POTW
  • Systematic examination of the user collection system
local limits
Local Limits

The goal in developing local limits is to implement pretreatment regulations that are technically and legally defensible. Local limits can include provisions for equitable recovery of costs associated with the toxicity source evaluations and local limits development.

wet tools
WET Tools
  • Historical WET test data review – “barely” passing/failing tests?
  • Internal/external surveys for new dischargers/chemicals/processes
  • Toxicity data review for new/altered treatment compounds or suppliers
  • Upstream Sampling (no advance notice – toxicity may temporarily disappear)
  • Streamlined WET tests (cheap, use to find toxic samples for toxicant analysis)
facility specific information
Facility-Specific Information
  • Industrial waste surveys
  • Industrial user self-monitoring reports
  • Industrial user operational schedules and flow patterns
  • Waste hauler monitoring and manifests
  • Hazardous waste inventories

System Inspections/Sampling

  • System inspections
  • Microtox, ELISA
  • Streamlined WET tests
  • Onsite facility inspections
  • Advance notice to users?
detective work
Detective Work
  • What else is going on? Are there records that correlate WWTP / SIU activities and reduced/increased toxicity?
  • Develop chemical usage profile for SIUs
  • Batch or seasonal processes/chemicals?
  • Communicate Communicate Communicate
tre t oxicity reduction evaluation
TRE - Toxicity Reduction Evaluation

A study to identify causes and controls for effluent toxicity – begin by gathering information:

  • Historical effluent toxicity data
  • Treatment plant design capabilities
  • Operation and maintenance practices
  • Industrial user permits
  • Pretreatment inspection reports
  • Monitoring and compliance reports
toxicity reduction evaluations tres
Toxicity Reduction Evaluations (TREs)
  • Resolution depends on toxicity magnitude / duration
  • Many facilities have worked aggressively and
  • resolved both lethal and sub-lethal toxicity issues
  • Unresolved toxicity usually related to inexperience or
  • sloppy work, sampling or lab
  • Success is usually a result of good communications and
  • coordinated efforts between the TRE/WET testing
  • consultant, the permittee and the permitting authority

Commonly Found Toxicants:

Chlorine Ammonia

Copper Zinc

Nickel Tributyltin

Total Dissolved Solids (TDS)

(Potassium, Bicarbonate, Calcium)

Organophosphate Pesticides

(Diazinon, OXO-Diazinon, Chlorpyrifos)

Pathogenic Interference – Not acceptable for

POTWs, which are designed to treat for pathogens.

pretreatment tre example
Pretreatment TRE Example

POTW was in violation of its WET limits >>> TRE

In-house processes were reviewed and corrected, and toxicity was reduced but not eliminated

A toxicant identification evaluation (TIE) revealed high levels of pesticides in the effluent and a pretreatment user review showed treatment inefficiencies at a pesticide manufacturer.

The pesticide facility eventually found it had 2 problems:

example cont
Example (Cont.)

1) Dye studies showed the settling pond with 4-7 days retention actually had only 1.5 hours retention

2) Storage barrel rinse water was dumped directly to the retention pond. Pesticide slugs were passed from the settling pond directly to the POTW influent

The TRE established two control strategies:

1) Dredge the pond and install a baffle system to increase the retention time

2) Reroute storage barrel rinse water to treatment cycle

tre tie
  • A TRE is a study to determine the source(s) of toxicity in an effluent and identify potential treatment options.
  • A TIE is a set of effluent manipulations designed to identify pollutants. EPA recommends TIEs as part of a TRE.
  • The presence of toxicity in samples is a cornerstone of TRE success – this means increased testing frequency and obtaining adequate amount of sample for WET and chemical testing.
  • TRE duration should be sufficient to perform the work.
  • Concerned parties should meet at start and end of the TRE.
  • Most R6 TREs have been successful. Inconclusive TREs occur – but even those have eventually been resolved.

WET Test

Data Review


Your permit explains your various WET reporting codes. A good WET test lab report should contain a page showing the results for each reporting code as well, plus the bench sheets raw data and the statistical analysis, for review by you or the permit authority.

  • Example Permit, Part II, WET language, Reporting Section (Section 3 or 4)
  • Ceriodaphnia dubia
  • If the NOEC for survival is less than the critical dilution, enter a ‘1’;
  • otherwise, enter a ‘0’ for Parameter No. TLP3B
  • Report the NOEC value for survival, Parameter No. TOP3B
  • Report the LOEC value for survival, Parameter No. TXP3B
  • Report the NOEC value for reproduction, Parameter No. TPP3B
  • Report the LOEC value for reproduction, Parameter No. TYP3B
  • If the No Observed Effect Concentration (NOEC) for reproduction is less
  • than the critical dilution, enter a ‘1’; otherwise, enter a ‘0’ for
  • Parameter No. TGP3B
  • Report the higher (critical dilution or control) Coefficient of Variation,
  • Parameter No. TQP3B

Your lab’s WET

report should

always include a

full statistical

analysis of your

WET data!


Your lab’s WET report

should also always

include the

actual raw data sheets.

Does your lab provide

a full statistical analysis

and the raw data sheets

for each test?

Permitting authorities

will be looking for these

any time they are

reviewing your files.

example of graphed chronic test data

% Effluent


# of young

(Total = 33)

Example of Graphed Chronic Test Data















Note: As the


of effluent







Adjusted Number of Young








Percent Effluent (log scale)


Now let’s look at some

of the basic information

you should be able to dig

out of that 30-page WET

test report…


Note CVs in Performance v Dilution Water v Low-Flow

Concentrations: lower CVs = lower variability


All effluent concentrations passed,

1 organism died (56% effluent)


IC25 analysis may or may not agree with

NOEC analysis. Permits in Region 6 States

stipulate NOEC as the test endpoint.


Example of a failed

test. While the dose

response isn’t pretty,

it is obvious that

something is going

on with this effluent.


Example of a

false positive.

The data here

was very tight.

As a result, the

effluent failed but it should not have.

This situation was corrected by increasing to 5 replicates.


25% effluent


‘passed’ with

only 50%

survival in 15%


Example of a

false negative,

rarely reported.

Corrected by

revising the concentration series.

Thank you for your attention today. Please feel free to ask any questions or contact me at:

(214) 665-7247