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Pyrethroid Pesticide Testing in Region 5, Central Valley

The Central Valley Regional Water Quality Control Board (Central Valley Water Board) adopted the Central Valley Pyrethroid Pesticides Total Maximum Daily Load and Basin Plan Amendment (BPA; Resolution R5-2017-0057) that established a Pyrethroids Control Program which includes concentration goals for six pyrethroids in wastewater effluent and surface water, a conditional prohibition, and monitoring requirements. The BPA was adopted by the Central Valley Water Board on 8 June 2017, approved by the State Water Resources Control Board (SWRCB) on 10 July 2018, by the Office of Administrative Law on 19 February 2019, and by the U.S. Environmental Protection Agency (EPA) on 22 April 2019. 

On 30 July 2019, Central Valley Water Board sent a letter to permitted entities under the National Pollution Discharge Elimination System (NPDES) and Municipal Separate Storm Sewer System (MS4) programs and Water Quality Coalitions in the Irrigated Lands Regulatory Program regarding baseline monitoring requirements of the Pyrethroids Control Program. However, there was an inconsistency in that 30 July letter regarding the temperatures for water column toxicity testing with Hyalella azteca. The purpose of this message and the attached letter is to resolve that inconsistency and clarify the Central Valley Water Boards expectations for the temperatures to be used in performing that toxicity test.

The Central Valley Water Board's 30 July 19 letter stated that EPA Method EPA-821-R-02-012 (EPA, 2002) should be used for water column toxicity testing with Hyalella azteca, and recommended that tests should follow the Measurement Quality Objectives provided in the Surface Water Ambient Monitoring Program Quality Assurance Program Plan (SWRCB, 2018) and the Southern California Coastal Water Research Project’s (SCCWRP) December 2016 guidance (Schiff and Greenstein, 2016) which both state that the tests should be performed at 23 degrees Celsius. EPA Method EPA-821-R-02-012 specifies that the temperature for water column toxicity test withHyalella azteca must be either 20 or 25 degrees Celsius.    

The EPA Method EPA-821-R-02-012 is used for accreditation of laboratories under the Environmental Lab Accreditation Program (ELAP) and is an established method under the Clean Water Act. For consistency with EPA Method EPA-821-R-02-012 and ELAP accreditation, the Central Valley Water Board is requiring that all Hyalella azteca water column toxicity testing for baseline and trend monitoring under the Pyrethroids Control Program must be performed at either 20 or 25 degrees Celsius. Additionally, the temperature chosen, either 20 or 25 degrees Celsius, should be consistent for all baseline and trend monitoring samples. Central Valley Water Board staff recommend selection of the temperature that is most consistent with the ambient temperature of the waters being tested.

Sediment toxicity testing under the Pyrethroids Control Program should continue to be performed at 23 degrees Celsius, as specified in EPA method EPA-600-R-99-064 (EPA, 2000).

If you have questions regarding ELAP-accredited methods for toxicity testing, please contact Steve Boggs, at the State Water Resource Control Board at (916) 449-5616 or .

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