Enhanced attenuation (EA) to manage PFAS plumes in groundwater

Abstract

Remediation of per-and polyfluoroalkyl substances (PFAS) in groundwater is particularly challenging because of their unique chemical and fate and transport properties. Many conventional in-situ remediation technologies, commonly applied to address other groundwater contaminants, have proven ineffective for treatment of PFAS. Given their stability, destruction of PFAS in-situ has remained elusive as an in-situ treatment option. Consequently, new approaches to manage PFAS groundwater plumes are of great interest to environmental practitioners. We propose that enhancing PFAS retention can play an important role in reducing PFAS mass flux and providing long-term protection of downgradient groundwater receptors. Enhanced retention of PFAS fits directly into the enhanced attenuation (EA) framework, an established groundwater remediation strategy that was developed in the first decade of the 2000s for other groundwater contaminants. In this paper, we propose eight EA approaches for PFAS in groundwater, including technologies that are currently being implemented at PFAS sites (e.g., injection of particulate carbon amendments), applications of conventional remediation technologies to PFAS sites (e.g., capping to retain PFAS in the vadose zone), and novel, innovative approaches (e.g., intentional food grade LNAPL emplacement to retain PFAS) for enhanced PFAS retention. These EA approaches leverage the properties of PFAS to (i) facilitate sorption to conventional and novel sorbents, (ii) concentrate PFAS at air/water interface via gas sparging, and/or (iii) encourage retention via tidal pumping and PFAS salting out processes. For each of the proposed EA approaches, we describe the methodology or concept and discuss the key processes, potential applications, anticipated increases in PFAS retention compared to natural systems, potential challenges, alternate designs, and current likelihood of large-scale adoption.

Enhanced aggregation and interfacial adsorption of an aqueous film forming foam (AFFF) in high salinity matrices

“…Surface excess can be an indicator of PFAS retention on solids and is of particular importance for modeling PFAS transport in the vadose zone where there is high air–water interfacial area. 7,35–37 We found that surface excess ( Γ max ) did not vary substantially among the conditions tested (ultrapure, ABW, ASW). An equivalent minimum surface tension was observed in all three aqueous systems (Fig.…”

“…Environmental Science: Processes & Impacts interfacial area. 7,[35][36][37] We found that surface excess (G max ) did not vary substantially among the conditions tested (ultrapure, ABW, ASW). An equivalent minimum surface tension was observed in all three aqueous systems (Fig.…”

“…As evidenced by the growing body of literature on PFAS interfacial properties and partitioning behavior, 6,7,12,17,23,24,[35][36][37]42 there is heightened recognition within the research community of the ways that the surfactant behavior of PFAS affects the compounds' environmental fate. Interfacial accumulation has the potential to enhance the retention of these compounds, resulting in unexpected retention of PFAS within the source zone.…”

Medical Analogue Framework for Natural Remedies and Passive Risk‐Mitigation Measures in Environmental Remediation

“…MNA was established as a groundwater remedy in the mid‐1990s through early 2000s (U.S. EPA 1999; National Research Council [NRC] 2000; Suthersan 2001). Evidence for its applicability has been expanded over time for contaminant classes including: petroleum hydrocarbons (Newell and Connor 1998; ASTM 2016), wood preservatives (Stroo et al 1997), chlorinated solvents (U.S. EPA 1998; ITRC 1999); MTBE (U.S. EPA 2005a), metals and other inorganics (U.S. EPA 2007, 2009, 2015), radionuclides (U.S. EPA 2010), perchlorate (ESTCP 2010), and 1,4‐dioxane (Adamson et al 2015). The newest frontier for evaluating the applicability of MNA as an effective groundwater remedy is undoubtedly PFAS (e.g., Newell et al 2021a, 2021b).…”

Partitioning of Per‐ and Polyfluoroalkyl Substances to Weathered Light Non‐Aqueous Phase Liquid

“…Interactions between LNAPL (either mobile or residual) and PFAS have important implications for remedial strategies at contaminated sites. Recently, Newell et al (2022) explained how monitored natural attenuation (MNA) could be considered for PFAS sites in light of the fact that perfluoroalkyl acids such as PFOS and PFOA are unlikely to be degradable by naturally occurring microbes under relevant environmental conditions. A primary conclusion from these authors was that "retention" is a term and concept that should be considered for PFAS conceptual site models and the evaluation of PFAS natural attenuation.…”