The nature and distribution of per- and polyfluoroalkyl substances (PFASs) in aqueous film forming foam (AFFF)-impacted source areas remains poorly understood. This project addresses the Department of Defense (DoD) need for development and demonstration of rapid field screening methods for determining the extent of a plume over AFFF source areas and the use of rapid field assays to provide semi-quantitative screening values to reduce site investigation and remedial decision-making timeframes. The overarching objective of this project is to perform the bench-top experiments needed to evaluate the potential for using two existing borehole-deployable geophysical technologies, Nuclear Magnetic Resonance (NMR) and Complex Resistivity (CR), as rapid screening tools for evaluation of PFASs in soils/sediments. The tantalizing possibility that NMR and CR may be sensitive to PFASs in source zones results from the potential for PFAS sorption onto soil surfaces sufficiently modifying the geophysical responses.
Specific objectives of the project include: (1) acquire bench top NMR and CR measurements on three types of synthetic samples [sand/organic soils, sand/clays, sand/iron oxides] contaminated with PFAS and/or AFFF solutions at source zone concentrations, and (2) acquire bench top NMR and CR measurements on natural soils from AFFF source zone locations allowing a comparison of signal from contaminated versus uncontaminated soils.
This project will exclusively focus on bench-scale techniques to obtain a mechanistic assessment of the possibility of PFAS source zone assessment using NMR or CR. Measurements will be performed on both synthetic soils and natural soils acquired from AFFF-impacted sites. Synthetic soils provide controlled conditions where the composition of the sediments and the contaminants can be defined. They will be prepared as mixtures of Ottawa sand and constituents expected to enhance the sorption of PFASs onto soil surfaces. Natural soils will be acquired from AFFF-impacted sites. Real AFFF-impacted soils will likely contain a wide range of precursor compounds, including the cationic (highly sorbing) species. Furthermore, they provide an opportunity to more directly demonstrate site relevance. Soils will be spiked with groundwater containing a relatively wide range of PFASs. Soils will also be spiked with AFFF solution. NMR and CR measurements on synthetic soils will be performed daily over a period of 2 weeks (more if equilibration not reached) following initial spiking. NMR and CR measurements on natural soils will focus on a comparison of results between soils from contaminated locations versus soils from uncontaminated locations across the selected sites.
If successful, the primary benefit to the DoD would come from identification of currently available borehole-deployable candidate geophysical technologies for rapid screening to assess PFAS distribution, identify/delineate sources, and facilitate evaluation of remedial performance. Such a technology would promote management and treatment strategies based on field geophysical datasets by end users. However, a negative finding from this project would also be valuable information as it would dissuade DoD from investing funds into futile field-scale projects using these geophysical technologies to assist with PFAS characterization. There is a tendency for geophysical practitioners to oversell their tools/technologies to remedial project managers (RPMs) having limited understanding of the capabilities/limitations of the methods. This is particularly prevalent when a new class of contaminants is identified and in need of detection. A negative result from this project would deter unwanted expenditure on projects with a likelihood of being futile.