Monitored natural attenuation to manage PFAS impacts to groundwater: Potential guidelines

Abstract

Practical guidelines based on a three-tiered lines of evidence (LOEs) approach have been developed for evaluating monitored natural attenuation (MNA) at per-and polyfluoroalkyl substances (PFAS)-impacted groundwater sites using the scientific basis described in a companion paper (Newell et al., 2021). The three-tiered approach applies direct measurements and indirect measurements, calculations, and more complex field and modeling methods to assess PFAS retention in the subsurface. Data requirements to assess the LOEs for quantifying retention in both the vadose and saturated zones are identified, as are 10 key PFAS MNA questions and 10 tools that can be applied to address them. Finally, a list of potential methods to enhance PFAS MNA is provided for sites where MNA alone may not effectively manage the PFAS plumes. Overall, a practical framework for evaluating PFAS MNA that can result in more efficient, reliable management of some PFAS sites is provided.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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

“…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).…”

“…Lifecycle data collection, evaluation, and CSM refinement can offer a particularly high pay‐off when applied to characterization of the natural processes of: Mass flux/discharge including consideration of processes of matrix‐mediated contaminant retardation, including matrix diffusion and contaminant sorption (Horneman et al 2017; Horst et al 2021); Physical and chemical MNA processes that are potentially substantial but less well understood. For example: abiotic mineral‐mediated degradation of chlorinated volatile organic compounds (CVOCs; He et al 2015, Horst et al 2019) and chemical and physical attenuation mechanisms for new contaminant classes such as PFAS (Newell et al 2021a, 2021b); and Biological attenuation processes that are theoretically viable but for which the relevant microorganisms and pathways are unknown. …”

Enhanced attenuation (EA) to manage PFAS plumes in groundwater

“…For PFAS, the key retention processes that have the potential to impact fate and transport in the subsurface include air/water interfacial sorption, hydrophobic interactions, NAPL/water sorption, electrostatic interactions, “salting out,” and matrix diffusion (Costanza et al, 2019; Higgins & Luthy, 2006; Guelfo et al, 2021; Newell et al, 2021a; Sharifan et al, 2021; Van Glubt & Brusseau, 2021). These concepts were used to develop some potential guidelines on how retention based MNA could be applied at actual PFAS field sites (Newell et al, 2021b) and will be further developed as part of a Department of Defense‐sponsored (DoD) project on PFAS MNA (ESTCP, 2021a).…”

In situ gas sparging for concentration and removal of per‐ and polyfluoroalkyl substances (PFAS) from groundwater

“…This residence time would be a function of the mass flux from infiltration events and groundwater table fluctuations. Retention‐based monitored natural attenuation (MNA) would be a paradigm shift in thinking about how to manage PFAS, but work on this concept is now progressing (e.g., Environmental Security and Technology Certification Program [ESTCP], 2021a; Newell et al, 2021a, 2021b) . In situ retention is an emerging remedial strategy for many groundwater contaminants, including PFAS, via injection of sorbents such as activated carbon.…”