Formatted Title
Forensic Evaluation of Commingled PFAS Impacts in a Bedrock Aquifer from Two Different AFFF Discharges
Background/Objectives
A specialty chemical manufacturer in New Jersey had completed a remedial investigation of chlorinated volatile organics and specialty ethers, including 1,4-dioxane, that had impacted bedrock groundwater prior to the emergence of PFAS concerns. Because the site had experienced a chemical fire that was reportedly extinguished with a fire-fighting foam, a PFAS investigation was conducted late in the remedial investigation process. The initial samples from a limited groundwater investigation were only analyzed for perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS) and perfluorononanoic acid (PFNA), using Method 537.1, which were identified in groundwater in the former chemical fire area. As the investigation scope and PFAS analytical suite expanded, it became apparent that a second PFAS source was impacting bedrock groundwater. We will present a case study into our forensic assessment of PFAS plume sources as well as the fate and transport of the plumes.
Approach/Activities
Forensic assessment of PFAS impacts included identifying perfluoroalkyl acids (PFAAs), primarily PFOS and PFOA, and fluorotelomer precursors (4:2, 6:2, and 8:2 FTS) signatures of an off-site fire training center that used AFFF telomerization formulations. Another on-site source with PFAS of electrofluorination (ECF) origin (older than the off-site fire training center) was characterized using perfluoroalkane compounds perfluorooctane sulfonamide (FOSA) and n-methyl perfluorooctane-sulfonamidoacetic acid (NMeFOSAA). Pie charts and forensic bar graphs will be presented as well as plume maps in plan view and in cross-section. Site characterization was also complicated by two industrial water supply wells withdrawing impacted groundwater for the on-site manufacturing process, which then discharged the water to infiltration ponds.
Results/Lessons Learned
We will graphically present our characterization results and multiple lines of evidence, including site history, knowledge of sources, formulation databases, and collected analytical data. We will also present our fate and transport characterization in fractured bedrock, included mapping out more mobile short-chain degradation PFAA (C4 - C7). Although withdrawal of groundwater on site for manufacturing complicated the assessment, the distribution of PFAS was a better tracer than the ubiquitous chlorinated solvents from multiple on-site and off-site sources.