Formatted Title
Ambient and Localized PFAS Background Concentrations Found in a Regional-Scale Investigation
Background/Objectives
As has become evident and acknowledged by many regulatory agencies, per- and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment and present in soils at ambient background concentrations due to long-range transport from air emissions point sources. Several states have published statewide background datasets of PFAS concentrations in soils or have initiated statewide background studies. However, PFAS may also be present in soils at localized background concentrations.
A regional-scale investigation specifically designed to evaluate the air emission and deposition pathway was initiated to support multiple site investigations. The investigation yielded a uniquely large dataset of more than 320 soil samples collected from remote, undisturbed, and mostly wooded sampling locations. Although not designed as a background study, PFAS concentrations in soil samples within the investigation dataset may represent ambient and/or localized background. To complete the regional investigation, the delineation of PFAS impacts from the sites under investigation needs to be distinguished from localized and/or ambient background concentrations.
Approach/Activities
Various evaluations of the regional investigation dataset of more than 320 soil samples were completed, including concentration trends by chain length, sample depth, distance and direction from potential sources, and spatial correlation/disparity among different PFAS analytes. Available statewide datasets of PFAS concentrations in soil from multiple states (e.g., Vermont, New Hampshire, Maine, Michigan, etc.) were compiled into an environmental database, and these background datasets were used for statistical comparison against the regional investigation data.
Results/Lessons Learned
Evaluations indicate the influence of multiple PFAS emissions within the region, a localized upwind PFAS emission source, and potentially ambient background concentrations. The applicability, usefulness, and limitations of statewide background datasets will be discussed. The discussions will focus on the connection between conceptual site models (CSMs), investigation design, and how to plan for the likelihood of localized and ambient PFAS background concentrations found during site investigations.