By Darien Key
In an August 5, 2025, published opinion from the Fifth Appellate District Court of Appeal, in Camarillo Sanitary District et al. v. State Water Resources Control Board the court addressed the legality of California’s newly adopted water quality policy known as the “Toxicity Provisions.” Central to the case was California’s effort to modernize its approach to measuring whole effluent toxicity (WET) in discharged waters, a metric not defined by a single chemical, but by the overall toxic effect on aquatic life. [Camarillo Sanitary District et al. v. State Water Resources Control Board, ___Cal.App.5th___, Case No. F087362 (5th Dist. Aug. 5, 2025).]
The controversy stemmed from the State Water Resources Control Board’s (State Water Board) decision to adopt the Test of Significant Toxicity (TST), a statistical model developed by the U.S. Environmental Protection Agency (EPA) in 2010 but never formally codified under federal law. While the State Water Board asserted the TST provided a more scientifically robust method for analyzing water toxicity, plaintiffs, including public wastewater treatment entities, challenged its legality under both federal and state law.
A major focus of the litigation was compliance with the California Environmental Quality Act (CEQA), especially given the policy’s environmental and procedural ramifications.
The Toxicity Provisions: A Statewide Shift in Policy
The Toxicity Provisions were initially adopted in December 2020 and revised in October 2021. They apply to all inland surface waters, enclosed bays, estuaries, and coastal lagoons in California, including both waters of the United States and state surface waters. The policy mandates that effluent toxicity be analyzed using the TST, regardless of which EPA-approved bioassay method is used.
Unlike traditional toxicity testing, which used statistical endpoints like the No Observed Effect Concentration (NOEC) or the 25 percent Inhibition Concentration (IC25), the TST redefined toxicity in a binary “pass/fail” framework based on bioequivalence testing. It reversed the traditional null hypothesis by presuming toxicity unless disproven and set a toxicity threshold of a 25 percent difference in biological response (e.g., growth or survival) between a test sample and control.
This had major implications for National Pollutant Discharge Elimination System (NPDES) permits, which are issued under the federal Clean Water Act and require the use of federally approved test procedures. The core legal question became whether the TST could lawfully substitute for NOEC and IC25 under federal standards.
The Court of Appeal’s Decision
CEQA Review and the Use of a Substitute Environmental Document
The State Water Board used a Substitute Environmental Document (SED) instead of a full Environmental Impact Report (EIR), invoking its certified regulatory program under CEQA. Appellants contended this was improper because they believed a statewide water policy did not fall within the basin planning exemption.
The court disagreed, affirming that California’s basin planning program under CEQA includes both regional and statewide water policies. The court cited prior administrative findings and the Board’s own regulations (Title 23, Cal. Code Regs., § 3777) to support this conclusion.
While the SED acknowledged potentially significant impacts in areas like agriculture, air quality, and hydrology, especially if new toxicity controls were implemented, it classified these impacts as too speculative for full analysis. The court upheld this approach, drawing from precedent in Ebbetts Pass Forest Watch v. California Dept. of Forestry & Fire Protection and emphasizing that CEQA does not require analysis of uncertain future actions where parameters are unknown. The SED’s qualitative review of sample projects and mitigation measures satisfied CEQA’s informational requirements.
Conflict with the Federal Clean Water Act
The appellate court ruled that the State Water Board’s mandate to use the TST in NPDES permits violated the Clean Water Act. Under 40 C.F.R. Part 136, only NOEC and IC25 endpoints are approved for WET testing in freshwater chronic toxicity. These methods are method-defined analytes, meaning the analyte (toxicity) is defined by the method used to measure it.
Because the TST applied a fundamentally different definition of toxicity and used an unapproved statistical endpoint (i.e., not NOEC or IC25), it amounted to a de facto redefinition of the analyte. This violated the federal rule that prohibits modifying EPA-approved methods for such analytes.
The court rejected arguments that the TST was merely an analytical method. It emphasized that statistical decisions, such as changing the null hypothesis or adjusting the toxicity threshold, directly altered the definition of “toxic.” Therefore, it was not a permissible modification but an unauthorized substitution that exceeded both federal and state authority in the context of NPDES permitting.
State Law Authority and the Role of CEQA
Despite federal preemption under the Clean Water Act for NPDES permits, the court affirmed the State Water Board’s authority under California law to adopt the Toxicity Provisions as a general state policy for water quality control. Under Water Code §§ 13140 and 13142, the State Water Board can formulate essential principles and guidelines to regulate activities affecting state water quality, even when those activities overlap with federal regulation.
Critically, the court upheld the State Water Board’s CEQA process, including its findings of no significant environmental impact from reasonably foreseeable compliance measures (primarily additional monitoring and data analysis). While more intrusive compliance strategies, such as structural upgrades, were discussed, the court agreed these were speculative and not mandatory outcomes of the new policy.
The CEQA claims were further weakened by the plaintiffs’ failure to develop several of their objections with specific citations or reasoned analysis. The court dismissed those under standard waiver principles.
Conclusion and Implications
This decision draws a clear jurisdictional line between federal and state regulatory powers when it comes to water quality enforcement. While California retains broad authority to regulate water quality under state law, even by enacting policies more stringent than federal baselines, it cannot mandate alternative methods in NPDES permits that deviate from federally approved procedures.
For CEQA practitioners and environmental regulators, the case reinforces that a well-documented Substitute Environmental Document can satisfy CEQA’s informational goals, even for statewide policies, so long as speculative impacts are identified and transparently discussed.
For NPDES permit holders, especially municipal wastewater agencies, the ruling offers a partial reprieve. While the Toxicity Provisions may still apply to state-only waters, they cannot currently enforce the TST in federal permits unless and until the EPA formally adopts it under 40 C.F.R. Part 136.
As federal and state agencies continue to evolve their scientific tools, this case highlights a recurring challenge in environmental law: balancing regulatory innovation with procedural and jurisdictional limits. The court’s opinion is available online at: https://www4.courts.ca.gov/opinions/documents/F087362.PDF
