A phased program involving advanced site characterization approaches and tools is required to complete remedial investigations of complex PFAS sites.
In our presentation, we leverage information from investigation and characterization work at several Per-and polyfluoroalkyl substances (PFAS) impacted sites to highlight key components, approaches, and tools that should be considered during Remedial Investigations (RIs) for developing robust conceptual site models (CSMs). PFAS are a class of over 3,000 chemicals that have been measured in various environmental media and threaten human health (via consumption of contaminated drinking water and fish) and ecological receptors as PFAS are known to bioaccumulate in the food web.
In response to exposure risks from PFAS, several recent environmental regulations have been enacted or proposed. The United States Environmental Protection Agency (USEPA) has designated perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) as CERCLA hazardous substances and established Maximum Contaminant Levels (MCLs) for currently five PFAS along with MCLs based on Hazard Index of 1 for PFAS mixtures. Under the Clean Water Act, the USEPA has proposed ambient water quality criteria for PFOA and PFOS along with also proposing to regulate PFAS discharges to surface water under the National Pollutant Discharge Elimination System (NPDES). Additionally, some states have placed fish consumption advisories on severely affected aquatic environments and also established stringent surface water regulatory criteria. These current and impending regulations will necessitate remedial actions to mitigate PFAS impacts in environmental media (groundwater, soil, surface water and sediment).
PFAS can exhibit a wide range of behaviors depending on chemical properties, media composition, and geochemical factors. The understanding of the nature and extent as well as distribution and partitioning behavior of PFAS becomes an important element of remedial investigations and CSM development at Superfund sites. Because of their persistence and transport characteristics, PFAS in groundwater and surface water can travel great distances from release sources and ultimately impact drinking water sources. Several processes such as groundwater – surface water interaction (GSI), surface runoff, stormwater discharges, and groundwater infiltration into compromised storm sewer networks may be responsible for PFAS fate and transport at sites. Since PFAS migration can occur through multiple pathways, a comprehensive CSM that considers all potential fate and transport processes is critical to inform exposure risks and decision-making on remedial actions. A wholistic CSM evaluation from field investigations including assessments of PFAS fractionation in different environmental media and together with hydrogeology, geophysics, and flow measurements can help elucidate predominant transport pathways. We present observations and lessons learned on important PFAS migration mechanisms that should be investigated to develop accurate CSMs.
Poster presented at the 2025 Waste Management Symposia.