Poly-and perfluoroalkyl substances (PFAS) are contained in fire-fighting agents (e.g., aqueous film foaming foams (AFFF)), manufacturing of plastics, consumer goods used for grease repellents and waterproofing, among others. PFAS are widely used and long-lasting chemicals, which allows for the chemicals to bioaccumulate and persist in the environment.
Due to the strength of the chlorine – fluorine bond within the molecules, traditional in-situ remediation technologies such as chemical reduction, chemical oxidation, and bioremediation have shown limited success in the treatment of PFAS.
The D-FAS technology (U.S. Patent 10,752,521 held by Chris Nelson, PE of eMinus, LLC) is an in-situ remediation technology that utilizes the physiochemical properties of the PFAS to force it to accumulate at the air-water interface as gas bubbles. Within the PFAS-contaminated groundwater unit, air is injected into a groundwater well which causes the PFAS to foam and accumulate on the groundwater surface, where it is removed under vacuum. Once the foam is removed by vacuum, the foam collapses and condenses into a PFAS concentrate liquid. The pilot studies that have been conducted demonstrate that D-FAS is capable of not only removing high PFAS concentrations from source areas, but also from the less concentrated, downgradient areas in the plume.
BLDI and eMinus recently collaborated on a pilot test at a Naval Air Station on the east coast. The data from this pilot test area over a three-month operational period showed:
- 1,900 gallons of PFAS Concentrate recovered
- 95 grams of PFAS were removed
- Groundwater PFAS concentrations decreased over 90% in surrounding monitoring wells
Based on the results this pilot study and research conducted at 2 other sites, it has been demonstrated that each D-FAS treatment well can remove at least 0.19 kg/year of PFAS mass flux leaching from source soils. For one of the sites where extensive characterization was conducted, a remediation time frame of 23 years was projected to fully deplete all of the remaining source contaminant mass. For comparison, remediation times at the same site using a downgradient pump and treat system would require between 105 years and 2,188 years to achieve a similar outcome. In addition to the overall recovery efficacy of the D-FAS technology, a significant factor in the treatment timeframe reduction is due to increased bio-stimulation from oxygen introduced into the saturation zone via DFAS and the associated increase in PFAS precursor transformation/elution rates from soil due to the bio-stimulation.
While more work is needed to quantify the rate at which bio-stimulation increases precursor transformation and elution of PFAS mass from soil, the initial body of work supports use of D-FAS as the most time and cost-effective technology available for source zone treatment.
Source: D-FAS Technology White Paper: The Case for Source Area Treatment by eMinus, LLC, December 2021