A Mechanistic Understanding of PFASs in Source Zones: Characterization and Control
Jennifer Field | Oregon State University
The main objectives of this project are to:
- Characterize the transport of anionic, cationic, and zwitterionic per- and polyfluoroalkyl substances (PFASs) and their interactions with organic matter and mineral phases of pristine soils/sediments and with PFAS-coated soils/sediments,
- Characterize the number and type of thermodynamically-stable phases that form when aqueous film forming foams (AFFFs) are mixed with common non-aqueous phase liquids (NAPLs), such as JP4 and trichloroethene, and their impact on PFAS transport under saturated conditions, and
- Assess PFAS mobility under unsaturated conditions in the vadose zone to identify the key hydraulic parameters that control PFAS mobility and retention.
The technical approach consists of a three-year course of highly – controlled laboratory column experiments that will be conducted with soil and sediment under unsaturated (aerobic) and saturated (anoxic) conditions. Batch tests will be performed to characterize the number of thermodynamically-stable phases that form when AFFF and NAPL are mixed and to quantify PFASs sorption at the air-water interface. For each experimental system, the research team will quantify the transport characteristics of all 42 PFAS classes present in 3M AFFF (identified in the Statement of Need), including perfluorooctane sulfonate (PFOS) and perfluroooctanoate (PFOA). A total of 11 classes of PFASs are in 3M AFFF including four anionic, four cationic, and three zwitterionic classes.
The tasks are designed to meet the project objectives and to test the following hypotheses: 1] PFAS transport through soils/sediments depends on the level of organic matter decomposition (not just quantity) and mineralogy, 2] PFASs partition into PFAS-coated soils/sediment during repeated AFFF applications, 3] PFAS migration through soils is dependent upon whether the AFFF is released alone, or co-released in the presence of NAPL (fuels or solvents), and 4] PFAS sorption at air-water interfaces present in the vadose zone significantly impacts their phase partitioning and mobility under unsaturated conditions. Through SERDP projects ER-2126 (Higgins, PI) and ER-2128 (Field, PI), the team now possesses the capacity to quantify the individual PFASs, which is a technical skill necessary to unravel the complex nature of AFFF mixtures, their interactions with other surfactants, fuels, and solvents and their behavior in soils/sediments.
The experiments performed in this study will yield the data that are necessary to identify the key uncertainties in the fundamental mechanisms that control the nature and permanence of PFAS interactions with key components of source zones soils/sediments under unsaturated and saturated conditions, and in the presence of NAPL. Information gained from this project will allow for improved understanding of the mass associated with soils/sediments at field sites and practical approaches for enhancing or inhibiting PFAS release from source zones. (Anticipated Completion - January 2021)