State Water Board Briefs POTWs on Latest Developments Regarding Statewide Toxicity Approach

  • by BPC Staff
  • on August 29, 2013



CASA Alert




State Water Board Briefs POTWs on Latest Developments Regarding Statewide Toxicity Approach


On August 27, 2013, the State Water Resources Control Board staff conducted a briefing for public wastewater and industry representatives on the status of the proposed policy for Toxicity Assessment and Control. CASA participated in the half-day small group session, which was convened to update the regulated community on proposed changes to the draft policy and provide the opportunity to weigh in on key issues. Similar briefings are planned for other stakeholders including stormwater, agriculture and non governmental organizations.

Much of the discussion focused on two specific issues where the Water Board is seeking stakeholder input. 


  • Maximum Daily Effluent Limitations for Chronic Toxicity: The options included retaining the proposed effluent limitations, eliminating the MDEL and imposing only monthly effluent limitations, or phasing the limitations in by using the numeric values as triggers for accelerated monitoring for the first three years of the policy.
  • Acute Toxicity Effluent Limitations: The options discussed included allowing the regional water boards to retain some discretion to impose acute limitations in addition to chronic limits where justified by findings in the permit, or requiring all permit holders to conduct reasonable potential analyses for acute toxicity.


Though no new language has yet been released, Water Board staff summarized key proposed revisions since the 2012 draft, including several requested by CASA and other clean water associations. These include: 


  • Increased threshold for monthly toxicity monitoring from one to 5 million gallons per day (MGD). POTWs with permitted discharges of 5 MGD or more would be subject to numeric effluent limits and conduct monthly chronic toxicity monitoring. POTWs below five MGD would be required to conduct a reasonable potential (RP) analysis for chronic toxicity and would receive effluent limits and a quarterly monitoring schedule if RP is demonstrated.
  • Changed calendar month requirement to allow the applicable regional water board to define when a calendar month begins and ends for each individual discharger (to avoid overwhelming labs with testing the first week of the month).
  • Extended time for Toxicity Reduction Evaluations (TRE). The six-month time period for completing a TRE would start upon initiation of the TRE instead of from the date of the violation. In addition, language has been clarified so that dischargers may be granted longer than six months to complete a TRE if warranted, without incurring violations.


Toxicity tests measure the acute (mortality) effects of effluent on a group of test organisms during specified exposure periods, or the chronic (reduced growth or reproduction) effects on those organisms. The Board expects to have a revised draft of the toxicity requirements (which will incorporated into a water quality control plan rather than a stand alone policy) out for public review and comment in October. CASA will continue to be actively engaged in the process, with the goal of ensuring that a new statewide toxicity policy does not place wastewater treatment agencies in violation of their permits due to false determinations of toxicity.