Efficiency assessment of PFAS immobilisation for large volumes of diffuse contaminated soil at airports.

Abstract

This study evaluated the feasibility of immobilising diffuse per- and poly-fluoroalkyl substance (PFAS) contaminated soil by developing and validating a novel field-scale methodology. The effectiveness of this approach was assessed via a field-scale trial conducted at an airport in Australia. Prior to full-scale treatment, laboratory trials were undertaken to determine optimal treatment reagents and application rates. The Standardised Sorbent Qualities Measure (SSQM) and Matrix Sorbent Qualities Measure (MSQM) were developed and applied to assess sorbent sorption/desorption capacity for PFAS under standardised conditions, facilitating sorbent selection. Three blending techniques were employed for field-scale trials: manual mixing with an excavator, large-scale rapid mixing using a pug mill, and a portable trommel screen. The efficacy of soil blending with a RemBind sorbent was validated using the sum of and leachable perfluorooctanesulfonic acid (PFOS) + perfluorohexanesulfonic acid (PFHxS) assessments. Results showed a substantial reduction in PFAS leachability, with mean PFOS + PFHxS concentrations generally decreasing to below the limit of reporting, resulting in over 98% reductions in leachable fractions. The Sorbent Application Uniformity Test (SAUT) effectively served as a quality assurance and quality control (QA/QC) measure alongside PFAS analysis, demonstrating consistent sorbent-soil blending across all methods evaluated. Overall, the large-scale trial at the airport confirmed that immobilisation using 1% to 2% RemBind 100 sorbent offered a viable, sustainable, and cost-effective solution, particularly for PFOS and PFHxS. Applying novel SSQM/MSQM and SAUT methods combined with pre-and post-treatment leachability analysis established a clear link between the sorbent application specification determined from laboratory-scale trials and field validation requirements. Thus, these methods are pertinent for assessing the immobilisation technique's efficacy and sorbent blending quality.