The State of California Inches Closer to Approving Toxicity Provisions and the Test of Significant Toxicity (TST)

November 10, 2020

By: Adrienne Cibor

After many years of drafts, comments, discussion, debate, consideration, and negotiation, the California Statewide Toxicity Provisions are expected to be considered for approval by the State Water Resources Control (State Board) on December 1, 2020. The toxicity provisions include a statewide standardization for how toxicity testing is measured and reported for National Pollutant Discharge Elimination System (NPDES) compliance purposes. Toxicity testing is one of the three main tools used by the USEPA to achieve the objective of “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters” stated in the Clean Water Act. To learn more about what toxicity testing is, check out Enthalpy’s previous blog post on Toxicity Testing 101.

Permitting Implications
The key change to note is how toxicity results will be handled under the new provisions. Toxicity test data will be analyzed with one single statistical test, the Test of Significant Toxicity (TST), for the purpose of determining permit compliance. The incorporation of the TST is meant to simplify and standardize the answer to a toxicity test – whether or not a discharge from a water treatment plant going into the receiving environment is toxic to the organisms living in the environment. Of course, in some cases, the answer is not that simple….

As we discussed in our previous blog post, toxicity tests are biological tests based on methods that vary depending on region, species, and test endpoints measured. The TST functions best with datasets where the variability is low, thus rewarding discharges who contract laboratories with a high level of precision.  However, some biological endpoints are more inherently variable than others.  Therefore, dischargers should work with their laboratory or environmental toxicology expert to understand the implications of the TST on their individual circumstances and use test designs that reduce their chance of producing a false-positive result.

What Happens Next?
Currently, these California provisions are only applicable for discharges to inland surface waters, enclosed bays, and estuaries. However, it is expected that similar provisions will be expanded to ocean discharges, groundwater, and stormwater runoff in the future.

As the Provisions are incorporated into new and existing NPDES permits, it is important for dischargers to understand how they can affect not only the toxicity test analyses, but also the frequency of testing, species sensitivity screening, and actions needed when limits are exceeded.

For More Information
You can learn more about the provisions, including all the background leading up to this point, and keep tabs on the upcoming December 2020 decision on the State Board website here.

Please note, The TST also has implications outside of California, as it is a USEPA method for determining test outcomes and has already been incorporated in permits outside of California.

Need help determining the impact of these provisions and the TST on your business? Want to consult with our experts to plan for future compliance in your testing needs? Our team can help, click here to start a conversation.

Adrienne Cibor
Senior Project Manager / Environmental Scientist
Adrienne Cibor is the Senior Project Manager in Enthalpy’s San Diego Environmental Toxicology lab. She leads a team of project managers and has over 18 years of experience in aquatic and sediment toxicology, regulatory affairs, risk assessment, and toxicity investigations. Adrienne is an enthusiastic community and environmental services professional with a Bachelor of Science focused in Marine Biology from San Diego State University.

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