PFAS transport through quasi-saturated porous media: Air-water partitioning and mixture effects

September 12, 2023, 11:30 a.m. (CEST)

Time: September 12, 2023, 11:30 a.m. (CEST)
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September 12, 11:30 a.m. in seminar room 1, IWS building (PWR61)
PFAS transport through quasi-saturated porous media: Air-water partitioning and mixture effects
Lecture by Kevin Mumford (Queen's University, Kingston, Canada)

Understanding how per- and polyfluoroalkyl substances (PFAS) are transported is critical to site characterization, monitoring, risk assessment, and remediation planning.  This includes an understanding of PFAS retention and release at air-water interfaces.  These interfaces exist throughout the vadose zone, but can also exist as trapped air bubbles created by water table fluctuations, recharge, and biogenic gas production.  In addition to being directly applicable to transport through trapped gas zones at PFAS-impacted sites, laboratory experiments using emplaced trapped gas (quasi-saturated conditions) provide a controlled method to investigate PFAS behaviour, including the effects of different PFAS, concentrations, and mixtures. 

A series of laboratory experiments was conducted using one-dimensional sand-packed columns containing trapped air emplaced by sequential drainage and imbibition. Experiments were conducted using single-component solutions of PFOA, PFOS and 6:2 FTS, as well as mixtures of those PFAS and diluted aqueous film-forming foam (AFFF) solutions.  As expected, PFAS breakthrough was significantly delayed in the presence of trapped air bubbles, with greater delay for PFOS than for PFOA or 6:2 FTS.  This single-component behaviour will be discussed along with mixture effects, including separation during transport and concentration overshoot.  This behaviour extends to branched and linear PFOS isomers, and AFFF mixtures, whose transport was further complicated by the presence of hydrocarbon surfactants.  The experimental results will be presented along with early efforts to incorporate mixture effects into numerical simulations of PFAS transport.


Lecture of LS3 seminar series on tuesday 

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