A look at how PFAS should be considered during site investigations.
They say diamonds are forever — but unfortunately, PFAS (Per- and Polyfluoroalkyl Substances) are here to stay as well.
PFAS are a diverse group of synthetic chemicals that were used for over 50 years in industrial applications for stain resistance, non-stick materials and waterproofing. Beginning in the 1960s, PFAS became key components of aqueous film forming foams (AFFF) used for Class B firefighting. Because they don’t easily break down in the environment, PFAS today have been dubbed as “forever chemicals,” meaning they can travel thousands of kilometers through any environment before losing their potency.
The worldwide historic use of PFAS has resulted in public and regulatory concerns due to the release of these persistent chemicals into the environment. The very characteristics that made PFAS attractive in industrial applications — stability and resistance to chemical, thermal, or biological degradation — mean they are now a serious concern.
PFAS are believed to create human health risks at very low concentrations in drinking water. How PFAS impacts human health and the environment have made it the subject of ongoing research and media attention – you only need to watch the 2019 film Dark Waters to understand just how serious this problem is on a global scale. Potential adverse human health effects and risk factors from longer-chain PFAS exposure include increased serum cholesterol, thyroid disease, immune dysregulation, pregnancy-induced hypertension, and kidney and testicular cancers. Other studies have found positive correlations between long-chain PFAS exposure and low birth weight in humans, as well as suppressed immune system response and impaired kidney function.
Where are PFAS found?
Due to their prolific and largely undocumented use, PFAS can be found everywhere. From waterways and oceans to concrete infrastructure and soil, PFAS contamination has the potential to impact our food production processes and groundwater sources. Their usefulness in countless industries and subsequent undocumented release mean that PFAS are detected everywhere, even in the blood of polar bears in Antarctica!
So far, PFAS have been primarily found near sewage treatment plants, landfills, and places where fire-fighting foams have been used (e.g. mining operations, fuel refineries and storage facilities, airports, fire-training grounds and transport infrastructure).
For most people in PFAS affected areas, the highest risk of exposure is likely to be through the consumption of contaminated groundwater (i.e. bore water) and food grown using contaminated groundwater.
Identifying PFAS during site investigations
The potential presence of PFAS should be considered during any preliminary site investigation. A robust, site specific Conceptual Site Model (CSM) remains the basis for assessing potential PFAS risks. It is necessary to have a detailed understanding of the topography, geology, hydrology, and hydrogeology for all sites. In addition, knowledge of the types, properties and fate and transport of PFAS along with biotransformation of precursors are all crucial aspects in understanding PFAS sources, pathways and receptors.
Many PFAS sites consist of releases that happened decades before PFAS were regulated. As a result, contaminants have had years to develop, and in some cases, stabilize. Therefore, site characterization and investigations should not necessarily proceed the same way as for newer sites with more recent releases. It is extremely important to try and obtain information which is above and beyond a “standard” desk study to determine the likely use of PFAS. This might include interviews with former employees, chemical inventories and consulting local fire services. The absence of information on the use of PFAS should not be assumed to mean an absence of presence of PFAS.
The amount of information to be collected to complete an adequate assessment is a site-specific determination based on many factors such as the complexity of stratigraphic and lithologic variability, project objectives, and available budget. High resolution site characterization techniques can be used to obtain adequate subsurface information (for example, grain size, lithological interfaces, and high transmissivity zones) to complete stratigraphic assessments.
Geochemical parameters that may affect the movement of PFAS and subsequent remedies also require consideration during site investigations. The understanding of soil type (possibly including foc surface charge, exchange capacity, grain size, mineralogy, and water content) and groundwater chemistry at the site is needed to assess transformation, partitioning (including desorption), and migration in groundwater or soil. These and other geochemical data can be used to assess the viability of PFAS remedy options should remediation be necessary.
What’s being done about PFAS?
Global infrastructure consultancy AECOM has taken the approach to begin specializing in PFAS identification and eradication. In one example, AECOM completed 30 drillings and installed four groundwater monitoring wells to determine if the soil of a military site in Germany was impacted by PFAS. AECOM found that the concentrations in the soil did in fact exceed local regulatory threshold levels for PFAS, and that the groundwater was contaminated due to toxins transferring from the soil via seepage into the aquifer.
In Australia, the Department of Defence is currently running a PFAS Investigation process across all its military sites to determine the prevalence of any contaminants. The process is split into three steps:
• Preliminary Site Investigation (PSI)
This includes a desktop historical review, site inspections and may include limited sampling to determine the potential for PFAS contamination.
• Detailed site investigation (DSI)
Following a PSI, sampling, analysis and interpretation of soil, water, plants, animals and other environmental media is conducted. A DSI identifies the areas where legacy firefighting foam was previously used (source areas) and how far it has spread in the environment.
• Human Health and Ecological Risk Assessment
If the DSI identifies that contamination is present and sensitive ecological receptors such as marine life, plants or animals may be affected or that humans may have the potential to be exposed to the contamination, an assessment will be undertaken into the risk of PFAS contamination to human health and the environment.
The information collected in the above steps then forms the basis for site specific management plans that aim to address the risks identified.
In the United States, President Biden has released an interagency PFAS Pollution Plan to prevent PFAS from being released into the air, drinking systems, and food supply, and the actions to expand clean-up efforts.
The more we learn about PFAS contamination, the more we realize that the problem is more widespread than previously thought. It’s vital that Geotechnical Engineers, Environmental Consultants, Hydrogeologists, government agencies and private sector developers work together to advance our understanding of the physical, chemical, and biological processes that impact the movement of PFAS through an environment. By doing this, we’ll also be able to develop better remediation approaches and limit PFAS exposure to individuals around the world.