Evaluating the Effectiveness of Emerging Geophysical Methods to Characterize AFFF-Impacted Contaminant Source Areas

Highlights of SERDP- and ESTCP-Funded Projects
Oral Presentation

Prepared by , K. Keating

Contact Information: s.o.falzone@gmail.com; 973-353-5100


ABSTRACT

There currently exists a limited understanding of how to assess the threat from aqueous film forming foam (AFFF) -impacted source areas. Sorption is believed to play an important role in AFFF-impacted source areas, as some AFFF constituents (i.e. PFASs) tend to be cationic and zwitterionic, both of which associate with pore surfaces. The interaction of AFFF constituents and the pore surface is evidenced in recent studies that show a link between organic matter, ionic strength, and the concentration of AFFF constituents sorbed to the solid interface. Consequently, any site assessment must take into account sorption processes inherent within AFFF-impacted source areas. Geophysical methods have the ability to provide non-invasive 3D imaging of the subsurface. Two emerging methods, complex resistivity (CR) and nuclear magnetic resonance (NMR), are capable of assessing the mineral surface chemistry in porous media and offer the possibility of monitoring sorption processes.

We are evaluating the efficacy of using CR and NMR methods to characterize sorption in AFFF-impacted soils. CR quantifies electrical conduction and polarization in the porous network, whereas NMR leverages the magnetic coupling of H+ in water with the mineral surface, resulting in a measureable response that can be linked to surface processes. Preliminary data was collected in preparation for this study on different synthetic soils saturated with AFFF impacted groundwater. Soils saturated with 3M AFFF spiked artificial groundwater were compared to control samples saturated with clean artificial groundwater. The presence of AFFF resulted in a clear temporal response following AFFF contamination and a dependence on the presence of strongly sorbing soil constituents (i.e. clays, organic carbon), evident in the NMR and CR data. This response was absent in samples exposed to clean groundwater. This response manifests as a larger phase response in CR data, and longer transverse relaxation time in NMR data.