Formatted Title
Technologies to Support the Quality Control of PFAS Immobilization and Minimize Uncertainty
Background/Objectives
Per- and polyfluoroalkyl substances (PFAS) are contaminants of emerging concern due to their persistent nature and potential adverse health effects. PFAS contamination at airports is widespread and represented by two key modes, source zone contamination with high concentrations of PFAS related to firefighting activities, and more diffuse contamination broadly spread across airport sites. The larger proportion of PFAS mass is in the source zone soils, with the diffuse impacted soil represented by a significant volume of material capable of delivering a sustained PFAS mass flow to receptors. A sustainable approach is needed to manage high volumes of relatively low PFAS concentration soils where landfill disposal is considered both cost prohibitive and unsustainable and thermal destruction is not feasible. The presentation makes use of a case study where novel quality assurance tools were applied to support a large-scale PFAS immobilisation trial at an Australian International Airport.
Approach/Activities
A novel sorbent testing approach known as the Standardised Sorbent Qualities Measure (SSQM), which assesses the PFAS sorption/desorption capacity of sorbents under standard conditions, was used to evaluate a range of commercial sorbents for the treatment works based on SSQM scores and determine the appropriate mixing ratio. Soil treatment involved the addition of 1-2% of the preferred sorbent to stockpiled soil using three different blending methods to assess their ability to apply the sorbent evenly and efficiently: an excavator with sieve bucket, a pug mill, a portable Trommel screen. The Sorbent Application Uniformity Test (SAUT), a novel dye-based method, was used to assess the accuracy and precision of the mixing processes by assessing the mass of sorbent and its distribution throughout the material. In total, more than 500 soil samples were collected from 24 stockpiles including 50 quality control and quality assurance (QAQC) samples to enable high resolution assessment, equating to 1 sample per 32 tonnes of material before and after treatment. Samples were assessed for Total (methanol extractable PFAS) and leachable PFAS using the Australian Standard Leaching Procedure (ASLP) at both pH 5 and pH 7 (aqueous extraction).
Results/Lessons Learned
The validation of the soil blending quality for each tested soil blending technology was conducted using total and leachable PFAS assessment and demonstrated greater than 99% reduction in leachable fraction. PFAS leachability reduction was noted for shorter as well as long chain congeners. The application of the SSQM method, SAUT method and pre- and post- treatment ASLP analysis created a clear link between the treatment specification and validation requirements, allowing the capacity to assess immobilisation efficiency and sorbent blending quality (accuracy and precision). Overall, this increased certainty that immobilisation had been successfully achieved throughout the treated material and gave the client confidence that the immobilized material could be reused.