1. Update on Whole Effluent Toxicity (WET)

2. Reasonable Potential
40 CFR § (d)(1)(v) “(W)hen the permitting authority determines. . . that a discharge causes, has the reasonable potential to cause an in-stream excursion above a narrative criterion within an applicable State water quality standard, the permit must contain limits for whole effluent toxicity.”

3. RP for WQBELs
A single sample approaching or in excess of the calculated limit does not automatically require a limit
Samples may be averaged
Different than federal methodology

4. RP History
Originally, RP was not determined for WET during the application process
WET was a monitoring requirement
A TRE was required for persistent significant lethality
At the end of a TRE a WET limit could be included in the permit

5. Sublethal Toxicity
In 2007 EPA began to objecting to permits being issued with no additional requirements for permittees that had a history of sublethal failures
Added a “trigger” for a sublethal TRE
Eventually lead to SL WET limits

6. RP Dilemma
How many failures are a reasonable prediction for instream toxicity?
Zero?
One or two?
Three or more?

7. AGREEMENT
On December 28, 2015, EPA and TCEQ concurrently signed letters agreeing to a new procedure for making RP determinations. This agreement will allow the avoidance of the interim objection letters for draft permits that didn’t include WET limits after one or two failures.

8. RP for WET Zero failures, standard 5 year permit
One or two failures, 3 year permit, monthly testing after a failure
Three or more failures, 5 year permit with a WET limit, optional compliance period

9. IMPLEMENTATION PROCEDURES
With an agreement on RP in place, TCEQ is now drafting a new WET section of the IPs. The WET section of the 2010 IPs were never approved by the EPA, so they never went into effect.

10. IPs
Some of the other WET issues we are looking to address in the revised WET section of the IPs are:
Eliminating formal Toxicity Reduction Evaluations (TREs)
Switching to IC25 statistical methodology for test results
Other miscellaneous items

11. IPs and Stakeholders
We value the input of our Stakeholders. Now is the time to start thinking about any changes you would like to see.

12. Water Effects Ratios
Not technically a WET issue, but… Site-specific studies referenced in IPs increasingly popular as aquatic life criteria become more stringent Biotic Ligand Model (BLM)

13. SUMMARY
An RP agreement with EPA has been in place with EPA for over two years ago, IO letters now rare for WET.
TCEQ is drafting new WET IPs, with stakeholders input encouraged and welcome.
Michael Pfeil
(512)