Formatted Title
Risk Assessment of PFAS Findings in Groundwater: An Approach Based on Data Trends from 1500 Small Industrial Sites
Background/Objectives
An assessment from the Danish Regions estimates that there are over 15,000 sites potentially contaminated with PFAS substances. In several ongoing or recently completed advanced investigations, PFAS has become a part of the investigation at a late stage, so there is only knowledge about the content of PFAS in water samples from deep monitoring boreholes. In these cases, there is little to none information about possible PFAS source areas, PFAS levels in the soil, or in the shallow groundwater. At some of these sites the site assessment has been administratively completed, so there is limited possibility for returning to the site for additional measurements.
Furthermore, the risk assessment of PFAS findings is complicated due to the fact that the transport rates of PFAS compounds are significantly different from cocontaminants (e.g. chlorinated solvents) especially for long-chain compounds like PFOS. Therefore, it’s uncertain how the composition and concentration levels will change over time and, consequently, the risk.
Additionally, there is uncertainty about the role of diffuse PFAS content in industrial areas that originate from numerous smaller sources.
The purpose of this presentation is to introduce a set of guidelines for the risk assessment of PFAS findings in groundwater at sites where a thorough PFAS focused investigation is not possible.
Approach/Activities
The project is based on data analysis from more than 1500 smaller industrial sites performed by the Danish regional authorities. Data analysis has been performed to examine trends in PFAS findings for different industries, at the individual PFAS substance level, and to correlate these findings with depth of detection. This data can be used to make forecasts regarding the expected source strength and vertical PFAS distribution for a site belonging to a specific industry, as long as it is a smaller industrial site or a dry cleaner.
Results/Lessons Learned
The data analysis confirms several previous hypotheses about which PFAS compounds have penetrated deeper aquifers while others are still bound higher in the soil.
Based on the dataset, various approaches to risk assessment are then presented, where data is used to calculate "backwards" using a vertical transport model (JAGG) and is "calibrated" according to the specific findings in the groundwater.
Uncertainty and the importance of different parameters such as infiltration, sorption coefficients, and source size are also discussed. Furthermore, the discussion includes how to deal with multiple unknown but likely sources within the same catchment area when assessing risks to groundwater.
The project's approach to risk assessment is a pragmatic tool to address the uncertainties that authorities and consultants face, especially at sites with limited data, when prioritizing investigation and remediation efforts.