Development and Laboratory Validation of Mathematical Modeling Tools for Prediction of PFAS Transformation, Transport, and Retention in AFFF Source Areas

Linda Abriola | Tufts University

ER18-1149

Objective

The use of aqueous film forming foam (AFFF) in fire suppression over many decades has resulted in contamination of hundreds of Department of Defense (DoD) fire training areas with per- and polyfluoroalkyl substances (PFASs), often in the presence of chlorinated solvent and fuel hydrocarbon cocontaminants. Significant attention is now being focused on PFASs with the recent U.S. Environmental Protection Agency (EPA) issue of a drinking water health advisory for two ubiquitous PFASs, perfluorooctanoic acid and perfluorooctanesulfonic acid. Although PFAS groundwater contamination source areas typically exist as complex chemical mixtures, few studies have examined the mechanisms controlling partitioning or sorption/desorption processes and rates in such mixtures. Furthermore, despite a demonstrated potential for defluorination, the biotransformation of PFASs under conditions representative of natural groundwater systems remains largely unexplored. In addition, there is an absence of PFAS transport and transformation studies in flowing systems, which are necessary for the development and validation of predictive mathematical modeling tools. The primary objectives of this integrated experimental and modeling research are: (1) to improve the understanding of sequestration mechanisms (e.g., sorption, partitioning) and abiotic/biotic (aerobic/anaerobic) transformations that control the transport and persistence of selected PFASs (including representative perfluoroalkyl acids, as well as their precursors and transformation products) in natural aquifer materials; and (2) to develop and validate mathematical models and decision tools that describe the key processes governing transformation, transport, and retention of these selected PFASs in complex AFFF source areas.

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Technical Approach

This research is organized around four tasks, encompassing (1) transport and partitioning experiments; (2) coupled abiotic and biotic transformation experiments; (3) mathematical modeling and decision tool development; and (4) research translation and project reporting. A matrix of batch, column, and aquifer cell experiments of increasing scale and complexity will be undertaken with the selected PFASs individually and within mixtures, employing reference media and natural aquifer materials collected from PFAS-impacted sites. In selected experiments, sodium dodecyl sulfate and three representative nonaqueous phase liquids (NAPLs) (chlorinated solvents/fuel hydrocarbons) will be employed as representative of AFFF synthetic foaming agents and organic co-contaminants, respectively. Experiments will support the development and calibration/validation of mathematical modeling tools, designed to predict sorption, partitioning, and natural attenuation processes under flowing conditions in natural porous media. These modeling tools will also be used to explore potential PFAS transport and fate under representative field conditions, identified in collaboration with the Air Force Civil Engineering Center, and to develop screening level models and a decision matrix for use by site managers.

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Benefits

In addition to customary project outcomes (project reports, presentations and seminars, scientific publications in peer-reviewed journals, and the education of students trained with the knowledge and skills to address this important problem), this project will make several unique contributions that will aid the DoD in AFFF site management: (i) the elucidation of new scientific knowledge of PFAS retention and transformation behavior that will be integrated into a transport simulator, filling a significant gap by providing the data and insight necessary to make scientifically-informed decisions; (ii) the development of a screening model that will provide a useful tool for DoD decision-makers to make order-of-magnitude estimates of site characteristics, such as contaminant longevity and mobility; and (iii) the creation of a decision matrix that will serve as a quick-reference guide, linking site characteristics, and contaminant and co-contaminant properties with the likelihood of attenuation, so that the DoD can better target their programs to minimize risk. These unique contributions will facilitate the translation of rigorous academic results to field-applicable tools that may be readily used by consultants and field contractors, ultimately ensuring the best allocation of resources in a fiscally constrained environment. (Anticipated Project Completion - 2021)

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Points of Contact

Principal Investigator

Dr. Linda Abriola

Tufts University

Phone: 617-627-3237

Fax: 617-627-3819

Program Manager

Environmental Restoration

SERDP and ESTCP

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