Investigation of Mineral-based Soil Amendments for Stabilization of Perfluoroalkyl Substances (PFAS) in Simulated Groundwater Environments
Amanda Barker | U.S. Army Engineer Research and Development Center-Cold Regions Research and Engineering Laboratory
Groundwater systems impacted by per- and polyfluoroalkyl substances (PFAS) represent a significant issue for the U.S. Department of Defense (DoD) and there still remains limited knowledge of basic chemical information concerning sorption to mineral amendments. This proof-of-concept effort will investigate a coupled treatment approach for PFAS in groundwater systems using two mineral-based treatment solutions (zerovalent iron coupled with liquid activated carbon) while also establishing key geochemical information that remain poorly understood (sorption isotherms andreaction kinetics). Specific objectives include the following:
- Determination of the overall efficiency of the relatively non-toxic mineral-based particulate amendments at reducing perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in simulated groundwater systems using fixed column systems filled with a silt loam porous material and mineral-based amendment.
- Assessment of how ionic strength plays a role in overall sorption isotherms of PFAS using batch reactors and spiked simulated groundwater.
- Investigation of the integrity of the amendments using advanced imagery techniques, particularly looking at aggregation over time, soil infiltration, and soil particle surface coverage.
The mobilization versus retention of PFAS via sorption onto two commercially-available mineral-based substrates (liquid activated carbon and zerovalent iron) will be investigated using batch adsorption reactors and column flow-through experiments. To determine sorption isotherm information, simulated groundwater spiked with PFOS and PFOA in varying ionic strength environments and varying mixtures of liquid activated carbon and zerovalent iron (Fe) will be mixed. To determine efficacy of removal of PFOS and PFOA in simulated groundwater by liquid activated carbon and zerovalent Fe, acrylic ‘flow cells’ (soil columns) will be loaded with a local silt loam porous medium and vary liquid activated carbon and zerovalent Fe additions while maintaining a pressure-driven hydraulic head. Aqueous samples from the batch reactors and columns will be analyzed for major ions using in-house instrumentation and PFOS and PFOA concentrations following EPA Method 537.1 modified for groundwater matrices. Once the column flow-through experiment is complete, the remaining soil/mineral-based amendment mixture will be sectioned and advanced imaging techniques (scanning electron microscopy and electron-probe micro-analysis) will be used to investigate amendment aggregation and spatial relationships with soil particles. The generated dataset will be used to construct sorption isotherms as a function of PFOS and PFOA concentrations and ionic strength information and PFOS and PFOA removal efficiency of commercially-available liquid activated carbon and zerovalent Fe.
This proof-of-concept effort seeks to take a step back from large field-scale efforts and instead use a detailed, incremental approach with a controlled laboratory experiment to understand sorption and immobilization of PFAS using mineral-based particulate amendments. The anticipated benefits from this effort will determine PFAS retention by particulate amendments and assess the structural integrity of two common and commercially-available amendments after reactions in simulated groundwater contaminated systems. Results from this effort will establish key sorption isotherm information on PFOS and PFOA, and mineral-based amendments, while gaining valuable insight into efficacy of liquid activated carbon and zerovalent Fe as potential injection amendments for contaminated groundwater systems.
Points of Contact
Dr. Amanda Barker
U.S. Army Engineer Research and Development Center-Cold Regions Research and Engineering Laboratory
SERDP and ESTCP