NCASI Review and Response

Review of Models for Evaluating Per-and Polyfluoroalkyl Substances in Land Applied Residuals and Biosolids

June 30, 2020 Attachment: Arcadis-PFAS-Residuals-Modeling-v1-1

Per- and polyfluoroalkyl substances (PFAS) are a complicated group of more than 3,000 man-made chemicals (ITRC 2017). In the past decade, awareness of the pervasiveness and unique characteristics of PFAS has grown rapidly into the realization that PFAS are ubiquitous in manufactured products, industrial processes, and (as a result) the environment. That realization has prompted an increase in our scientific understanding of PFAS characteristics, fate and transport processes, as well as efforts to mitigate the potential impacts of PFAS.

Our growing understanding includes determining if PFAS are present in wastewater treatment residuals from manufacturing sources (e.g., pulp and paper wastewater residuals) and biosolids from municipal wastewater utilities (collectively referred to as residuals herein) and assessing the potential for PFAS in soils amended with wastewater residuals to migrate into other environmental media such as groundwater, plants, or surface water. In response to the potential migration to other media, regulatory agencies have begun to evaluate the fate, transport, and effects of PFAS in land-applied residuals and, in some cases, develop guidelines to mitigate potential effects. Fate and transport models are critical to evaluating and establishing appropriate guidelines to developing screening levels. However, because of the unique properties of PFAS, it is unclear if current models are capable of adequately modeling PFAS fate and transport.

This report reviews available fate and transport models for the three primary migration pathways for PFAS in land-applied residuals: leaching to groundwater, surface water runoff, and plant uptake. Numerous models are available, but only a few are likely to be applicable to PFAS and able to account for their unique and diverse physicochemical characteristics. This review is intended to assist policymakers, regulators, and industry in their consideration of fate and transport models to apply when evaluating potential effects of PFAS in land-applied residuals and establishing appropriate screening values for PFAS in such residuals.

Models were identified by reviewing government compilations and conducting online searches for models used in North America. Models were then screened based on criteria of applicability, peer-review status, availability of updates and support, and accessibility of the model (Appendix A). Retained models were further evaluated for their ability to accurately simulate PFAS transport and account for processes and parameters that are likely to have substantial influence on the fate and transport of PFAS in land-applied residuals (Tables 2 through 4). The mechanisms and processes affecting PFAS transport through the three migration pathways listed below were examined as part of the screening process.

Version 1.1 of the report, released June 2020, contains updated model characteristics.

Contributors: Arcadis, NCASI, Water Environment Federation, American Forest & Paper Association, NACWA