Identifying the primary PFAS sources among many potential ones contributing to a groundwater plume can be extremely challenging, with the difficulty heightened by the large number of PFAS compounds and the ongoing questions surrounding their identification, breakdown, fate, and transport.
The environmental industry has historically relied on using a number of data evaluation and graphical visualization tools for source determination, from simple excel tables and pie charts to more complex statistical methods and advanced modeling and simulations. A significant body of knowledge has been developed to accurately identify the sources and timing, and to determine the appropriate response measures to address single and commingled petroleum, organic, and inorganic releases to the environment. However, continuing to advance our methodologies to determine our understanding of source markers of environmental impacts is critical to assessing the sources of impacts, completing comprehensive investigations, developing accurate conceptual site models, and determining appropriate remedial actions.
Using new digital tools, GHD’s Environmental and Digital Groups have been able to develop better methods to determine profiles for emerging contaminants such as per- and poly-fluoroalkyl substances (PFAS). PFAS are unique and very challenging to profile in comparison to conventional releases for multiple reasons: there are more than 5,000 PFAS compounds, with laboratory reference standards for only a few dozen, and PFAS are ubiquitous in the environment due to their wide use in industrial, institutional, commercial, and consumer product sources, and their persistency. These compounds can migrate very quickly over long distances, and their breakdown mechanisms/products and fate and transport are not yet fully understood. This makes it extremely challenging to identify primary PFAS sources contributing to the mass flux of PFAS to a groundwater plume
Developing a digital evaluation
To support source and remedial evaluations we set out to develop reasonably accurate digital fingerprints profiles for different sources of PFAS.
We selected PFAS groundwater data for 50 different sites from our databases, which were built over many decades of managing environmental data for thousands of sites in North America and Australia. Statistical programming was used to evaluate, refine, explore and visualize the data. An example graphic for one site is shown below:
Different colors were used for each PFAS compound. The y-axis represents the ratio of mass concentrations of the various PFAS compounds relative to each other, and discrete sampling rounds are shown along the x-axis. For this example, there were 29 sampling rounds over a number of years so the x-axis consists of 29 columns, each one representing one sampling round. This example facility exhibits a relatively consistent pattern of concentration ratios for each sampling round, with some minor variations. Thus this chart provides a visual profile or fingerpirnt of the various PFAS compounds present in groundwater at this site. The source of PFAS at this site is known to be from legacy PFOS AFFF and legacy fluorotelomer AFFF.
Another example graphic for a second site is shown below:
Similarly, the graphic provides an illustrated forensic fingerprint for PFAS compounds present at this site.
This evaluation demonstrates that reasonably diagnostic digital fingerprints can be determined for different sources of PFAS to support source and remedial evaluations. Further evaluations will include machine learning evaluations of fingerprints for sites with commingled PFAS from multiple sources to help identify and determine mass flux from individual sources. These tools will be used to improve site assessment efficiency and effectiveness, evaluate PFAS fate and transport, support conceptual site model development, provide easy to understand graphical data representations for clients and regulators, and assist in remedy evaluation, selection, and implementation.
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