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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 firstname.lastname@example.org 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.email@example.com
(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.
Daphnid - water flea
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.
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.
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 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.
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.
A study to identify causes and controls for effluent toxicity – begin by gathering information:
Total Dissolved Solids (TDS)
(Potassium, Bicarbonate, Calcium)
(Diazinon, OXO-Diazinon, Chlorpyrifos)
Pathogenic Interference – Not acceptable for
POTWs, which are designed to treat for pathogens.
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:
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
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.
always include a
analysis of your
should also always
actual raw data sheets.
Does your lab provide
a full statistical analysis
and the raw data sheets
for each test?
will be looking for these
any time they are
reviewing your files.
of the basic information
you should be able to dig
out of that 30-page WET
Concentrations: lower CVs = lower variability
1 organism died (56% effluent)
NOEC analysis. Permits in Region 6 States
stipulate NOEC as the test endpoint.
test. While the dose
response isn’t pretty,
it is obvious that
something is going
on with this effluent.
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.
survival in 15%
Example of a
revising the concentration series.