NACWA, in partnership with the National Council for Air and Stream Improvement (NCASI) and the American Forest and Paper Association (AF&PA), is pleased to share with members a new report prepared by Stone Environmental detailing a more thorough “how-to” guide to understanding how the Pesticide Root Zone Model (PRZM) may be used to screen for PFAS potentially leaching into groundwater from land applied residuals and biosolids.

The PRZM approach uses the Pesticide Water Calculator developed by EPA to simulate pesticide applications to land surfaces and the subsequent transport to and fate of these chemicals to surface water and groundwater. This method is widely used by EPA and states for screening level assessments and refined risk assessments and may be the best model for estimating PFAS fate and transport.

As state and federal regulators continue to look to identify adequate management strategies for PFAS and consider models for screening purposes, it is imperative for users to understand key inputs, outputs, local site-specific conditions, and how sensitivities and assumptions play into such simulations.

This step-by-step guide to PRZM helps by demonstrating simulations and provides the necessary applications to ultimately yield the greatest confidence when using this modelling approach. Use of this PRZM screening-level modeling approach will allow regulators and other stakeholders to efficiently evaluate PFAS groundwater contamination potential and determine whether a more comprehensive and rigorous modeling and/or field investigation is warranted.

NACWA would like to thank Stone Environmental for their thorough guidance on this technical modelling approach as well as NCASI and AF&PA for including NACWA on this project. We encourage utilities share this guidance with state biosolids regulators.

If members have questions, please contact Emily Remmel, NACWA’s Regulatory Affairs Director.