Mass-Based, Field-Scale Demonstration of PFAS Retention within AFFF-Associated Source Areas

Area of Science:

• Environmental Science
• Environmental Chemistry
• Soil Science

Background:

• Aqueous film-forming foams (AFFF) used at training sites are a major source of poly- and perfluoroalkyl substances (PFAS) contamination.
• Understanding PFAS transport and fate in the environment is crucial for effective site remediation.
• PFAS mass retention processes in source zones can significantly impact plume development and contaminant discharge.

Purpose of the Study:

• To estimate the PFAS mass distribution in source and downgradient areas of an AFFF-impacted site.
• To identify the key PFAS compounds and their partitioning behavior.
• To evaluate the conversion rate of PFAS precursors to perfluoroalkyl acids (PFAAs) and assess mass discharge rates.

Main Methods:

• High-resolution sampling and analytical protocol to determine PFAS concentrations.
• Mass distribution analysis in source and downgradient zones.
• Estimation of precursor conversion rates and mass discharge rates.

Main Results:

• Total PFAS mass at the site was approximately 222 kg (106 kg PFAAs, 116 kg precursors).
• Zwitterionic and cationic PFAS precursors constituted 83% of the precursor mass, primarily in source areas.
• 82% of total PFAS mass was in lower-permeability soils, leading to a 99% decrease in mass discharge rate downgradient.

Conclusions:

• PFAS mass is significantly retained in source areas, particularly in low-permeability soils, due to hydrophobic partitioning, electrostatic interactions, and diffusion.
• The conversion rate of PFAS precursors to PFAAs is low (<2% annually).
• Retention processes in source zones are critical in limiting PFAS advection, transformation, and downgradient mass discharge at AFFF-impacted sites.