239-5 Where Geology Evolved into Remediation Geology: The Legacy of the AFCEC Hydrostratigraphic and Geologic Team (AFCEC-HGT)

Session: Federal PFAS Remediation: Successes and Challenges

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The United States Air Force, through the Air Force Civil Engineer Center (AFCEC), has played a pioneering role in applying geology to environmental restoration across its extensive portfolio of groundwater remediation sites. Leveraging access to research funding through Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP), and a network of subject matter experts (SMEs), AFCEC has led innovation in site characterization and remediation strategy.

In 2022, AFCEC conducted an enterprise-wide evaluation of over 80 installations to determine key drivers of remediation success. The study concluded that the quality and accuracy of the Conceptual Site Model (CSM) has the greatest impact on environmental restoration outcomes. AFCEC had anticipated this conclusion, having begun a significant shift more than a decade earlier.

In 2010, under hydrogeology SME John Gillespie, AFCEC introduced the Environmental Sequence Stratigraphy (ESS) methodology into its remedial investigations. ESS moves beyond conventional assumptions of homogeneous, isotropic aquifers by emphasizing geologic heterogeneity as the primary control on groundwater flow and contaminant transport. Borrowing from petroleum geology, ESS supports high-resolution, geology-based CSMs to better map fluid flow within the subsurface hydrostratigraphy.

Over the next 15 years, this approach matured into a coordinated program under the AFCEC Hydrostratigraphic and Geologic Team (AFCEC-HGT). The team brought together expert practitioners who collaborated to integrate geologic, hydrologic, and geophysical data into unified site models. This interdisciplinary approach institutionalized the use of ESS and advanced geologic modeling across Air Force restoration sites. The team also led training workshops, developed geologic cross sections and 3D models, and engaged stakeholders through field demonstrations using outcrop analogs to visualize subsurface conditions.

As per- and polyfluoroalkyl substances (PFAS) emerged as a primary contaminant of concern, the need for detailed, geology-driven CSMs became even more critical. The complex transport behavior of PFAS requires a precise understanding of flow paths, migration zones, and retention mechanisms—challenges ideally suited to ESS-based CSMs. During the Remedial Investigation (RI) phases, AFCEC-HGT’s work supported accurate plume delineation, optimized sampling strategies, and more effective remediation design.

This presentation introduces the ESS methodology, outlines its evolution and enterprise-wide implementation, and showcases case studies where robust geologic models and interdisciplinary collaboration improved restoration outcomes. The legacy of AFCEC-HGT illustrates the transformative impact of integrating classic geology into environmental remediation.

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

doi: 10.1130/abs/2025AM-7967

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