Testing PFAS-Immobilization

About 800ha of predominantly agricultural fields have been contaminated with per- and polyfluorated alkylic substances (PFAS) about 10 years ago when waste from the paper industry was applied as compost. These substances affect various uses of the land (agriculture, open pit gravel quarries, and urban planning) and the underlying aquifer in the Rhine Valley as the main drinking water resource for surrounding cities and municipalities.

Remediation attempts have been limited to date, particularly due to the large areal extent of the contamination and the related high cost. One strategy that is currently being investigated is to immobilize the PFAS in the soil in-situ. A substance with a high sorption capacity would be applied on the ground surface and mixed with the soil. The then altered soil should still fulfill its original purpose (e.g., for agriculture). Another strategy could be to remove the contaminated soil and use it for construction (e.g., noise protection walls) after treatment with substances with a high sorption capacity.

The purpose of this research is to develop a test-strategy to evaluate the long-term leaching characteristics of soil treated with substances to increase its sorption capacity. Treated soil is being tested on three different scales (batch experiments, column experiments, lysimeters) and under different saturation conditions (saturated, variably saturated). The concentrations are being monitored over time and distinct PFAS substances as well as the organic fluorine after digestion will be measured. Mathematical models are being employed to evaluate the usefulness of various processes (e.g., equilibrium sorption) and the leaching behavior for time scales larger than possible in laboratory-experiments. A special challenge for both the analytical strategy and the numerical modeling poses the fact that PFAS consist of a more than 4700 compounds (according to OECD), from which currently only about 20 can be quantified. Some of the 20 can be formed from larger precursor compounds by microbial activity which makes the source term undefined.

The measured and modelled time-series of effluent concentrations serve as the basis for a simple and cost-effective method for the experimental testing of immobilization-measures for PFAS.