Hoisaeter, A., A. Pfaff, and G.D. Breedveld.
Journal of Contaminant Hydrology 222:112-122(2019)

Column studies were performed to measure the leaching and transport of PFOS in unsaturated soils at a Norwegian former firefighting training facility 15 years after aqueous film-forming foam (AFFF) use had ceased. PFOS accounted for 96% of the total PFAS concentration in site soil with concentrations ranging from <0.3 µg/kg to 6500 µg/kg. The column studies used similar soil and AFFFs to that at the site. Low (4.9 mm/day) and high (9.7 mm/day) water infiltration rates were applied for 14 (low) and 7 (high) weeks. The low infiltration rate represented 2 years of snow melting and the high infiltration rate represented extra water added in the areas with intensive firefighting training. In the low infiltration experiment, PFOS was not detected in the column leachate over 14 weeks. In the high-rate infiltration experiment, PFOS was detected after 14 days and concentrations increased from 20 ng/L to 2200 ng/L after 7 weeks. Soil extracted from the columns in 5 cm layers showed PFOS concentrations of ≤0.21-1700 µg/kg in the low-rate infiltration column with a clear max 30 cm and no PFOS detected below 60 cm. In the high-rate infiltration column, PFOS concentration ranged from 7.4-1000 µg/kg, with the highest concentrations found at 22-32 cm depth and a detection down to the deepest sample (~90 cm). Retardation factors for the average vertical transport of PFOS in the unsaturated zone were estimated to be 33-42 (low) and 16-21 (high), higher than estimated retardation factors (6.5 [low] and 5.8 [high]). The study suggests that PFOS is strongly attenuated in the unsaturated zone, mobility is dependent on infiltration rate, and attenuation rate increases with time.