Update on Whole Effluent Toxicity (WET)

Reasonable Potential 40 CFR § 122.44(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.”

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

Reasonable Potential 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

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

Reasonable Potential How many failures are a reasonable prediction for instream toxicity? Zero? One or two? Three or more?

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.

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

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.

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

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

SUMMARY An RP agreement is now in place with EPA. Next is drafting new WET IPs. As always, Stakeholders will be allowed input during this development process. Michael Pfeil (512) 239-4592