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Impact of Aqueous Film Forming Foam (AFFF) source zones on vadose zone saturation and long-term ground water contamination
Citation:
Adegbule, A., J. Chen, J. Huang, AND M. Brooks. Impact of Aqueous Film Forming Foam (AFFF) source zones on vadose zone saturation and long-term ground water contamination. American Geophysical Union Fall Meeting, New Orleans, LA, December 13 - 17, 2021.
Impact/Purpose:
The intent of this presentation is to communicate research that is being conducted to broadly investigate the source zone characteristics of per- and polyfluoroalkyl substances (PFAS) in the subsurface. Specifically, this research focuses on practical screening-level characterization techniques for PFAS source zones, the retardation of PFAS in the vadose zone, PFAS induced drainage in the vadose zone, and the ability of the vadose zone to recover from PFAS-induced changes over time. Information on these topics is very important to the management of PFAS contaminated sites.
Description:
Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals which are used extensively in a variety of applications, including firefighting in the form of AFFF which is a very effective firefighting agent. However, releases of AFFF through training exercises or when fighting fires can be a major route by which PFAS are discharged into the subsurface environment. PFAS have surfactant properties which make them partition at air-water interfaces. In the vadose zone, soil is partially saturated and air-water interfaces abound. Partitioning at the air-water interface leads to retardation of these compounds in the subsurface. This retardation means the compounds can remain in the vadose zone for long periods of time and serve as a source for groundwater contamination. In addition, when concentrations of PFAS become large enough, they begin to lower the surface tension of the contaminated ground water, thus draining the vadose zone and changing fluid distribution. A proper understanding of the fate and transport of PFAS in the subsurface is a key step to containing its spread when contamination does occur. The focus of this work is: (1) to investigate practical screening-level characterization techniques for PFAS source zones, (2) to study the retardation of PFAS in the vadose zone, and (3) to study PFAS induced draining in the vadose zone as well as the ability of the vadose zone to recover from the changes over time. To investigate potential field screening tests, surface tension, specific conductance, refractive index, and light absorbance were measured using a commercially available AFFF product. For the remaining work, a two-dimensional (2D) physical model spiked with a potassium perfluorooctanesulfonate solution will be used to carry out the studies. Moreover, results from the physical experiments with the 2D model will be compared to a numerical model that is being developed using the EOS7R module of the TOUGH3 simulator. Preliminary results from the experiments will be presented.