The objective of this Statement of Need (SON) was to develop an improved understanding of the self-assembly behavior of per- and polyfluoroalkyl substances (PFAS) in the subsurface at aqueous film-forming foam (AFFF)-impacted sites. Specific research areas of interest included:

• Characterization of the type and magnitude of supramolecular systems that potentially develop on or within environmentally-relevant media from legacy AFFF-relevant PFAS.
• Evaluation of the chemical and physical properties of these supramolecular systems as they pertain to their stability within the environment.
• Evaluation of relevant environmental factors that affect the formation and stability of supramolecular systems within source zones such as PFAS concentration, soil chemical/physical properties, etc.
• Assessment of the impact of supramolecular systems within source zones on the long-term mass discharge potential to groundwater as well as any remedial implications.

Proposals addressed one or more of the objectives listed above. Proposers were directed to review the document Summary Report: Strategic Workshop on Management of PFAS in the Environment for additional information on these research objectives. This document provides a summary of the March 2022 strategic workshop on PFAS in which research and demonstration needs were identified so as to improve the management and treatment of PFAS in the environment, ultimately reducing risk and site management costs.

Research and development activities at laboratory-, bench-, and field-scale were considered. Work did not necessarily have to culminate in a field-scale effort.

Quantifying the extent and long-term effect of supramolecular systems is critical to the long-term management of AFFF-impacted sites. Knowledge of the role supramolecular systems within source zones play in terms of regulating long-term groundwater impacts may dramatically improve risk assessment and site management decisions.

PFAS are present in AFFF used by the Department of Defense (DoD) and other organizations to extinguish hydrocarbon fires. Different AFFF formulations have been used, but all contain a complex mixture of PFAS, including those of greatest regulatory concern - the perfluoroalkyl acids (PFAAs) and potential PFAA precursors. The Environmental Protection Agency (EPA) has recommended a Health Advisory Level for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), and several states have promulgated standards for PFOA, PFOS, and some of the related PFAAs.

SERDP has been funding research on the environmental impact of AFFF for several years to improve PFAS analysis, to develop tools for assessing the fate of PFAS in the subsurface, and to evaluate the potential for in situ remediation. A recent SERDP and ESTCP-sponsored workshop identified a number of research needs, and proposers should view the Workshop Report to obtain additional detail concerning these discussions. PFOS is of particular concern to DoD, as it is the predominant PFAS at AFFF-impacted sites (Anderson et al., 2021). PFOS (and to a lesser extent PFHxS) was the primary PFAS in legacy electrochemical fluorination (ECF)-based AFFF formulations and may accumulate over time as a result of precursor transformation (Anderson et al., 2016; Zhang et al. 2017). Thus, both ECF- and telomer-based AFFF formulations are relevant to this SON.

It has been well established by the pharmaceutical industry that intermolecular interactions among amphiphilic PFAS result in the formation of various supramolecular systems such as bilayers and vesicles, which have been studied as model membranes for drug carrier and delivery systems for decades (Riess et al. 1996). To date, however, studies have largely evaluated this seemingly unique behavior of fluorinated amphiphiles in relatively simple aqueous systems (Berr and Jones 1989; Kunze et al. 1997; Srinivasan and Blankschtein 2005; Junior et al. 2006). More recent studies have begun to evaluate the effect of self-assembly as it pertains to the environmental fate of PFAS within engineered sorbent-based remedial systems (Uriakhil et al. 2021; Dong et al. 2021), but relatively little is known about the role these supramolecular systems play in regulating the transport of PFAS within source zone soils. Notably, recent field data from an AFFF-impacted site demonstrated greater sorption of specific PFAS to soils at higher concentrations contrary to concentration dependence resulting from the saturation of sorption sites implicating self-assembly as an operative process (Anderson et al. 2022). Clearly, additional research is needed to address this data gap. Ultimately, knowledge on the role of these supramolecular systems on the long-term groundwater mass discharge from source zones will greatly improve risk assessment and management decisions at AFFF-impacted sites.

The cost and time to meet the requirements of this SON were at the discretion of the proposer. Proposers submitting a Standard Proposal had to provide the rationale for this scale. The two options were as follows:

Standard Proposals: These proposals describe a complete research effort. The proposer should incorporate the appropriate time, schedule, and cost requirements to accomplish the scope of work proposed. SERDP projects normally run from two to five years in length and vary considerably in cost consistent with the scope of the effort. It is expected that most proposals will fall into this category.

Limited Scope Proposals: Proposers with innovative approaches to the SON that entail high technical risk or have minimal supporting data may submit a Limited Scope Proposal for funding up to $250,000 and approximately one year in duration. Such proposals may be eligible for follow-on funding if they result in a successful initial project. The objective of these proposals should be to acquire the data necessary to demonstrate proof-of-concept or reduction of risk that will lead to development of a future Standard Proposal. Proposers should submit Limited Scope Proposals in accordance with the SERDP Core Solicitation instructions and deadlines.