239-8 Conventional and Novel Approaches to Understanding Geologic/Hydrogeologic Influences on PFAS Migration, Fate, and Transport

Session: Federal PFAS Remediation: Successes and Challenges

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Comprehensive data based on multiple lines of evidence and characterization technologies from initial Phase I Remedial Investigations (RIs) are used to develop PFAS conceptual site models at two active Department of Defense (DoD) installations in the western US. This presentation highlights technologies and lines of evidence used to evaluate the influence of (1) subsurface geology/hydrogeology and (2) historic and current remedial actions to address legacy contaminants on PFAS migration, fate, and transport at complex sites with multiple potential PFAS sources.

Investigations were conducted at potential AFFF release areas within two DoD installations to characterize PFAS impacts to environmental media. The following lines of evidence were used to evaluate PFAS sources and geologic and hydrogeologic controls on PFAS fate and transport: (1) presence and distribution of elevated index PFAS concentrations (greater than 100 times the project screening levels for one or more PFAS constituents) horizontally and vertically in GW and soil, (2) site history and available information on potential releases and previous remedial activities, (3) environmental sequence stratigraphy and geochemical and geotechnical sampling to assess site geology/hydrogeology and clarify the influence of complex subsurface geology on groundwater migration, and (4) evaluation of potential GW-surface water interactions on an installation-wide scale. In addition, innovative tools such as 2D/3D data evaluation, graphical methods, and insights from Battelle’s PFAS Signature^® Analysis (which utilizes non-target analyte analysis/evaluation and application of machine learning to support PFAS source identification) were also used to identify/distinguish potential PFAS sources.

Preliminary results indicate that while regional PFAS plumes with concentrations exceeding screening levels are diffuse, distribution of relatively elevated PFAS concentrations (100 times screening levels or greater) may be strongly hydrogeologically controlled. On a more localized scale, variations in subsurface lithology may also influence PFAS migration groundwater as well. In some locations, interactions between surface water and groundwater (also influenced by subsurface hydrogeology) have further complicated understanding of PFAS fate and transport.

 Although each evaluation tool used in these investigations provided valuable insights, no single tool was able to fully capture the nuances of PFAS source identification, fate, and transport. Rather, a combined approach (multiple lines of evidence) proved extremely insightful to understanding/developing PFAS CSMs and clarifying the strengths/weaknesses of each evaluation tool/analytical approach in various settings.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7911

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