Stabilization remediation of soils contaminated with per- and polyfluoroalkyl substances (PFASs)

Per- and polyfluoroalkyl substances (PFASs) are a major global concern in pollution of drinking water sources and aquatic environments. Due to the high persistence and mobility of these compounds, remediation methods for PFAS-contaminated soils are urgently needed to protect the surrounding environment and drinking water source areas. This is particularly important at firefighter training sites, due to the historical usage and release of PFAS-containing aqueous foams causing high levels of soil contamination, with high potential for leaching to groundwater and nearby environments. This thesis assessed the efficacy of stabilization remediation methodologies in mitigating PFAS leaching from contaminated soils. Screening of 44 PFAS sorbent materials showed that activated carbons (ACs) (granulated and pulverised, n = 5) were the best sorbent (mean removal efficiency >99.9%) for PFASs in aqueous solution. Based on these results, a commercially available injectable colloidal AC product (PlumeStop®) for soil stabilization was systematically assessed for PFAS retention efficiency. The best treatment efficiency for 10 different soils (fortified with 17 PFASs) treated with colloidal AC was observed for perfluorooctanoic acid (PFOA), 6:2 fluorotelomer sulfonate (6:2 FTSA) and perfluorohexane sulfonate (PFHxS), resulting in sorption increases of >80%. Assessment was also performed of a stabilization-solidification (S/S) technique that uses cementitious material to chemically stabilise PFASs and solidify the soil, decreasing hydraulic conductivity and thereby reducing PFAS leaching potential. The S/S technique was tested on PFAS-spiked soil using a cost-efficient cementitious material with a soil:binder ratio of 9:1 and seven different additives (including ACs) to 0.2% of dry weight (dw). In conservative leaching tests, treatment efficiency was highest for AC additive amended S/S remediation (e.g. >99.9% for longer-chain PFASs such as perfluorooctane sulfonate (PFOS)). To further assess the applicability and long-term stability of S/S treatment, a pilot-scale experiment was set up treating over six tons of field-contaminated soil using 15% cementitious binder and 0.2% dw mass-granulated AC. An artificial irrigation system was used to apply the equivalent of six years of precipitation. The treatment efficiency was >97% for four dominant PFASs homologues (perfluorohexanoic acid (PFHxA), PFOA, PFHxS and PFOS), but low (3%) for shortchain perfluoropentanoic acid (PFPeA). Ultimately, based on laboratory- and pilot-scale experiments, it can be concluded that stabilization remediation of PFAS-contaminated soils can be an efficient technique, in particular for longer-chain PFASs