The objective of this project is to derive, demonstrate and validate a standardized environmentally relevant and scientifically defensible exposure design for laboratory toxicity testing (i.e., whole effluent toxicity [WET]) to assess impacts to receiving waters related to episodic discharges such as stormwater runoff. A modified WET test procedure also may be employed as an option to determine compliance where end-of-pipe numerical (chemical) concentration limits may be unattainable or potentially overprotective.



Technology Description

The project focuses on the demonstration, validation and assessment of a modification to WET testing protocols designed for continuous flow discharges for application to episodic and/or ephemeral discharges such as those associated with stormwater runoff. Standard WET protocols expose test organisms for substantially longer periods (48 hours to 7 days) than the time during which discharges are present at the end-of-pipe (generally less than 24 hours), potentially overestimating the toxic impact to organisms in the receiving environment, and triggering notices of violations and costly additional toxicity evaluations that might have little significance. Modification to the WET protocol entails reducing the exposure period to the toxicant/stormwater sample followed by transfer to clean laboratory seawater, or receiving water, for the remainder of the test. This exposure design ensures that all testing is conducted for the full duration of the standard WET test to account for potential latent effects related to the initial stormwater exposure. If applied properly, a modification to generate more realistic exposure conditions will still provide an appropriate level of protection, particularly given that the exposure at the end-of-pipe will be further reduced once it mixes in the receiving environment. Development of a modified test method, validated through the state of the art in situ monitoring and a rigorous interlaboratory calibration effort based on previous USEPA interlaboratory validation approaches, are key components of this project.


The DoD would benefit from scientifically defensible and sufficiently conservative modifications to the nature (i.e. duration) of the toxicity exposure required in National Pollutant Discharge Elimination System (NPDES) permits, increasing the likelihood for compliance, while ensuring continued protectiveness in compliance with the Clean Water Act. More representative test methods will also decrease the likelihood of spending significant resources on additional testing and treatment controls based on overly conservative or unrepresentative methodologies. Costs to develop systems to capture, divert and treat the first flush of stormwater at industrial facilities has been estimated to be on the order of hundreds of millions of dollars for the San Diego Bay Metro Navy alone, which will still not guarantee compliance. Application of the study should be applicable to DoD and other installations worldwide. (Anticipated Project Completion - 2023)


Colvin M., K. Kowal, N. Hayman, C. Stransky, J. VanVoorhis, S. Carlson, and G. Rosen. 2021. Pulsed Exposure Toxicity Testing: Baseline Evaluations and Considerations Using Copper and Zinc with Two Marine Species. Chemosphere, 277:130323. doi.org/10.1016/j.chemosphere.2021.130323.

Colvin M., G. Rosen, N. Hayman, B.C. Stransky, B. Phillips, T. Hoang, and K. Kowal. 2020. Standard Operating Procedures: Pulsed Exposure Methodology. NIWC Technical Document, 3397. DTIC: AD1092603.

Colvin M., G. Rosen, N.T. Hayman, and K. Kowal. 2020. Long-term Rainfall Analysis at Select DoD-relevant Sites for the Determination of Appropriate Toxicity Exposure Durations. NIWC Technical Document, 3392. DTIC: AD1091097

Rosen G., M. Colvin, C. Katz, J. Munson-Decker, and Hayman NT. 2019. Pulsed Exposure Toxicity Testing: Method Development and Initial Evaluation for Stormwater Compliance. NIWC Pacific Technical Document, 3393. DTIC: AD1082517

  • Stormwater,