Casy Fath (cfath@barr.com), Brian Angerman (bangerman@barr.com) (Barr Engineering*,
Minneapolis, MN, USA), and Jonathan Dippert (J.Dippert@ctmale.com) (C.T. Male Associates,
Latham, NY, USA)

Background/Objectives. A regional-scale investigation was conducted to delineate PFAS in soils potentially attributable to emissions and deposition from a former industrial facility. Although not the primary objective of the investigation, the data provided several indications of additional sources within the investigation area based on the distribution of individual PFAS and forensic evaluation of PFAS results.

Approach/Activities. The investigation area was divided into a radial grid and ultimately extended to 10,000 feet beyond the facility. The sampling was designed to ensure sampling in all directions and at multiple distances. Each of the sampling locations was carefully vetted to ensure sample locations were undisturbed for last 70 years. Due to this vetting, sampling locations were collected from locations on private properties mostly in forested areas similar to statewide background studies.

Soil samples were collected from three depth intervals (0-2 inches below ground surface [bgs], 2-12 inch bgs, and 1-2 feet bgs) at each sampling location and analyzed for a list of 21 PFAS, Total Organic Carbon (TOC), and pH using standard laboratory methods. The dataset includes 321 soil samples collected from 107 individual sampling locations. Sampling locations were distributed throughout the investigation area to evaluate concentration trends with distance and spatial distributions of PFAS.

Results/Lessons Learned. Significant differences in concentrations and detection frequencies were observed between sampling depth intervals throughout the dataset. For example, some long-chain PFAS were detected frequently in the 0-2 inch samples, with almost no detections in deeper/wider sample intervals. The geographic pattern and “fingerprint” of these PFAS, keys lines of evidence indicating other sources within and near the investigation area, will be illustrated and discussed.

These forensic observations may only be possible with the relatively thin sampling interval and largely undisturbed sample locations. Since most concentrations were near the detection limits of the standards analytical methods, larger surface soil sample intervals (e.g., 0-6 inch or 0-12 inch bgs) commonly used in investigations and background studies, may “dilute” or wash out concentrations of certain PFAS below detectable limits. Similarly, sample locations with a history or evidence of disturbance (i.e. tilling, infilling, flooding, etc) may obscure these potentially observable PFAS concentrations.

Ultimately the discussion will focus on the practical implications and considerations for the sampling design of investigations and backgrounds studies using results from standard laboratory analytical methods.

* Barr employees performed work while seconded to BEC Engineering and Geology, PC.