George (Bud) Ivey
President & Sr Remediation Specialist
Ivey International, Inc.
BC, CANADA
Date of Presentation: May 16, 2024
Subject Areas: New Technologies; Soil Remediation & Restoration; Groundwater Problems & Remediation
Overview:
Removal of PFAS from aquifers depends on groundwater pump and treat (P&T).
Groundwater is recovered and PFAS is removed, most often by filtration and granular activated carbon (GAC), with ion-exchange resins having increasing usage. P&T can take decades to complete as the efficacy of the process is limited by contaminant sorption (i.e. adsorption and absorption) to soils, hydraulic conductivity (K), and the relative low concentrations of PFAS in groundwater, even when the PFAS source zone is relatively close by.
Specialized surfactant enhanced recovery of PFAS contaminants, from source-zone areas has been demonstrated to be more cost-effective that using P&T alone. Operational time frames have potential to be significantly lowered, when used for PFAS source zones. This collaborative multi-year university column study work represents the first attempt to understand the potential of specialized surfactants, with additives, to increase the removal rates of PFAS, at a scale using reagent concentrations that are environmentally applicable.
Approach/Activities:
Large diameter column tests were designed to measure the effectiveness of a specifically developed surfactant formulation to potentially increase the concentration of PFOS and PFAS compounds in aqueous phase, in simulated enhanced recovery experiments. Solvent and surfactant extraction were compared. The experiments were run at the University of Greenwich, UK in collaboration, in collaboration with Ivey International Inc.
A series of column experiments were carried out using 75 cm high and 14 cm diameter columns. A mineral sand was used in the first instance, followed by the addition of 10% by mass activated carbon to show the impact of organic material. The columns filled with mineral sand and were saturated from the base and spiked with high concentrations of PFOA and PFOS to mimic a source zone. They were then drained and the effluent sampled.
They were filled again, one with solvents at 50% concentration, and the other with novel surfactant formulation at 4% concentration, drained and the effluent sampled. The columns were then deconstructed and a moisture profile was measured, with soil samples taken to measure the retained PFAS.
Further samples of the same soil were then mixed with activated carbon and the columns were set up again. The same procedures were followed, with an additional drainage carried out. A moisture profile was again taken during column deconstruction with soil samples taken to measure retained PFAS.
Results/Lessons Learned:
The experiments showed the effect of both solvent-enhanced extraction and surfactant enhanced extraction, as well as the mass of PFOA and PFOS retained following the drainage tests. Furthermore, the moisture profiles at the conclusion of the tests showed the positive effects of surfactant on the unsaturated soils. The addition of surfactant was demonstrated to lower the moisture content of soils, allowing more water to be drained and therefore greater mass removal of any liberated contaminant – including PFAS – in the drained layers. The surfactants reproducibly increased liberated the PFOA and PFOS by >200% to >700% compared to water flushing alone.