Formatted Title:

PFAS Distribution and Flux at a Groundwater/Surface Water Interface Using a Direct Drive High-Resolution Passive Sampler

Background/Objectives:

Per- and polyfluoroalkyl substances (PFAS) contamination of groundwaters and surface waters poses significant public and environmental health risks depending on the type and extent of contamination. Site characterization is crucial for assessing these risks and for prioritizing and guiding site remediation and sediment capping efforts. However, traditional sampling methods often face limitations, particularly in highly stratified aquifers or areas of low permeability.

Approach/Activities:

To address these challenges, high-resolution (<20 cm) passive profilers (HRPPs) were developed to provide site-specific data on geochemical conditions, porewater velocities, and contaminant profiles. In this study, 24 HRPPs were deployed using a vibracore and one additional HRPP onshore with a Geoprobe^TM. The samplers equilibrated for 26 to 28 days at water depths of 0.3 to 2.5 m in Ashumet Pond, a PFAS-contaminated site from previous use of aqueous film-forming foams (AFFF) at Joint Base Cape Cod (JBCC). These samplers reached sediment depths of 0.8 to 2.5 m, allowing for assessment of plume migration within sediments, surface water upwelling, and PFAS contamination flux to surface waters. Samples were also collected from existing wells and temporarily installed hydraulic profiling tools, or piezometers, and seepage velocities measured using flux meters, to compare monitoring methods.

Results/Lessons Learned:

Samples were analyzed for PFAS using high-performance liquid chromatography-mass spectrometry (HPLC-MS) per EPA Method 1633, with additional suspect screening and the total oxidizable precursor (TOP) assay to further identify and quantify potential unknown PFAS compounds and precursors, respectively. Major anions were measured via ion chromatography (IC) for geochemical indicators and conservative tracers to assess sediment porewater velocities. The HRPPs detected approximately 24 compounds, with concentrations ranging from 2 ppt to 39 ppb. Compared to seepage meters, HRPPs provided greater spatial and depth resolution of velocities rather than solely surface seepage at shallow depths. HRPPs also offer greater depth resolution of contaminant concentrations than temporarily installed piezometers, which missed small-scale variations in concentrations or hydrological conditions, and struggled to collect samples from lower permeability zones due to clogging of equipment. This case study demonstrates the effectiveness of HRPPs in providing high-resolution data and overcoming limitations of traditional sampling methods in complex hydrogeological conditions and areas of low permeability.

Todd Anderson

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PFAS Distribution and Flux at a Groundwater/Surface Water Interface Using a Direct Drive High-Resolution Passive Sampler