Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7h. PFAS Fate and Transport

Formatted Title:

New England Regional Evaluation of Background PFAS Levels in Shallow Soils

Background/Objectives:

Identification of background concentrations of contaminants is an important part of environmental assessment that allows practitioners to distinguish regulated releases of contaminants to the environment from those related to natural and/or non-specific anthropogenic sources or release mechanisms. For per- and polyfluoroalkyl substances (PFAS), which have been in widespread use for approximately seven decades and for which some of the lowest regulatory limits have been set by regulatory agencies, it is important to understand the types and levels of PFAS in soil as a result of non-specific and/or unknown PFAS sources and migration pathways. However, to date there have been limited known state-wide studies conducted in the United States (currently just New Hampshire, Maine, Massachusetts and Vermont) and no large-scale regional studies that extend beyond individual state lines. This evaluation looks at each of the four New England state shallow soil studies, both comparatively and as a combined dataset. This combined dataset includes 329 primary shallow soil samples collected in the top 6 inches across central/northern New England (covering approximately 65,000 sq miles in area). This large dataset allows us to gain a regional perspective of PFAS disposition and concentration in shallow soils across New England. Given the ubiquitous nature of PFAS in the environment, our further objective was to establish “background” concentrations for PFAS that typically are observed in shallow soils absent any clear, distinct source(s). The concept of background is especially relevant to the assessment and remediation of PFAS at contaminated sites since some states have promulgated regulatory limits for PFAS in soil that appear to be at levels below typical regional background concentrations and, as such, could be potentially infeasible to achieve.

Approach/Activities:

Soil analytical results from the individual Maine, Vermont, New Hampshire, and Massachusetts datasets were combined. The USEPA statistical software program, ProUCL Version 5.2, was used to calculate summary statistics, conduct data distribution and outlier tests, and generate upper tolerance limits (UTLs). These statistical calculations were used for comparing the state studies’ PFAS frequencies and concentrations, as well as to calculate UTLs that could be considered representative of state or regional background concentrations of PFAS.

Results/Lessons Learned:

PFAS were detected in 95% of the shallow soil samples across central/northern New England, with PFOS being the most frequently detected compound across the regional dataset at 90.3% of samples, consistent with Mattias et al. (2022) study of PFAS across Sweden (89%). After PFOS, various perfluorocarboxylic acids (PFCAs) were also detected frequently, with PFOA being the most frequently detected PFCA. After PFOA, select differences among the states in the types of PFCAs commonly detected were observed. Collectively, the four datasets point to large-scale, regional PFAS impacts in shallow soil. Many of the data collected, as well as the calculated background UTLs, exceed regulatory limits (Massachusetts PFAS 6 Method 1 S1 standards) and proposed soil remediation standards (New Hampshire proposed leachability-based values for PFOA, PFNA and PFOS; September 2023). The presence of background levels of PFAS in shallow soil at concentrations exceeding regulatory limits is a technical dilemma that site owners/responsible parties, regulators, and practitioners will need to address.

This presentation will dive further into the results of the evaluation, by state and as a combined dataset, including the presentation of calculated UTLs to represent a regional background PFAS level.

Mattias, S., Kikuchi, J., Wiberg, K., Lutz, A. 2022. Spatial distribution and load of per- and polyfluoroalkyl substances (PFAS) in background soils in Sweden. Chemosphere. 295 (2022) 133944.

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Lisa McIntosh