Solving the PFAS puzzle

There are numerous research studies that could be conducted, but advances in a few key areas could move us forward significantly. The first would be the ability to properly and definitively identify the most important of the different compounds and their risk profiles. Second, would be to evaluate their fate and transport in the environment. Third is to decisively find practices to mitigate or contain their ability to spread over long periods of time in the environment. The fourth is to advance research on their treatment and destruction in various environmental media.

Globally, GHD’s Emerging Contaminants team has partnered with a number of clients, universities, industrial companies, associations, vendors, consultants, and laboratories to conduct leading edge research projects. These projects will advance our fundamental understanding and science and engineering around PFAS to develop more knowledge and better understanding of how to best manage PFAS in a practical and economic manner. Ryan Thomas, an Environmental Scientist and a leader of GHD’s North American Emerging Contaminants Group, tells us more about what is being done to create this fundamental base layer of knowledge and push the envelope to advance our understanding. 

PFAS are a large class (5,000+) of anthropogenic compounds used in a huge variety of consumer products due to their water and stain repellent, thermal resistance, and other properties. However, currently commercial analytical methods can accurately detect only around 30 of these compounds. USEPA has identified 75 priority compounds, with plans to group similar compounds in order to facilitate the faster development of risk assessments and improved management approaches (USEPA 2019).

The sheer volume of different PFAS and their use in a huge variety of products makes it daunting, if not practically possible, to identify all the potential forms, not to mention possible situations where they might be found. Because of the wide spread usage, background levels of PFAS are truly ubiquitous in the environment and in humans.

That being said, there are four major known sources of PFAS: fire training/fire response sites/airports, industrial sites, landfills, and wastewater treatment plants/biosolids. Other point and diffuse sources of PFAS exist, and may be significant locally, but generally are expected to be small by comparison to these main four sources. Knowing this, it makes sense to start with these sources to develop more precise forensic fingerprints for source materials, to facilitate future identification efforts. In partnership with a number of collaborators, our PFAS and Digital groups are developing machine learning projects that will enable us to accurately and precisely identify different types of PFAS at different sites.

“The technology is literally used to find multiple kinds of needles in many haystacks and the sources of the needles,” said Fred Taylor, a Senior GHD Principal and member of the research group. “We feed computer algorithms very large amounts of information and data from known sources to make it learn what PFAS is and what different PFAS compounds look like in the environment, creating forensic fingerprints that can be used to identify other multiple sources with a large degree of certainty. With so many complex and related PFAS compounds. and breakdown and transformation products, massive amounts of data and extensive, focused computing power are needed to clearly identify and fingerprint the many subtle differences in multiple sources once they have been in the environment for years.”

The source material comes from impacted environmental media such as groundwater, surface water, and soil from AFFF and non-AFFF contaminated sites in North America and Australia.

Understanding how contaminants move in the environment is a key step to be able to effectively map risk boundaries and identify remediation strategies. The resistance of most PFAS to biotic or abiotic degradation means that physical transport processes and commingled contaminants are critical for PFAS transport and potential for exposure.

To develop fate and transport models, our team chose representative sites that have PFAS and other contaminants, and then calibrated using years of multi-media PFAS data similar to current contaminant modelng practices. Preparing 3-D visualizations based on these models allow manipulations that help us to gain a good understanding of how PFAS and commingled contaminants migrate and preferentially accumulate in the environment. The knowledge gained from these models can be translated to other sites to identify significant receptors at risk and the effect over time of varying in situ and ex situ remedial techniques.

For contaminated solids (e.g., soil, sediment, biosolids, and building materials) there are two main ways that PFAS can be contained, if destruction is not practical or feasible. One is stabilization, and the other is containment. The challenge is that if the PFAS are not destroyed, it is critical to ensure that the PFAS cannot leach or spread beyond the containment system as required by site remedial goals. The advantage of these remediation or treatment options is that they are done in-situ, unlike more expensive remedial options such as excavation and off-site landfilling or incineration.

Currently, the lack of demonstrated remedial technologies hinders the ability to solve a wide range of site and contaminant conditions. GHD’s Innovative Technology Group (ITG) has partnered on several new research collaborations to develop and improve remedial technologies and innovative approaches for site remediation, with a goal of reducing overall site remediation effort, time, and costs.

PFAS found in soils are subject to leaching during precipitation weather events and/or irrigation events (ITRC 2018), so the ITG is evaluating the stabilization and solidification of PFAS-contaminated soil, sediment, and solid waste materials. Leaching is a function of structural properties and the specific media’s pH, redox conditions, partitioning with organic or clay rich soil or sediment, and other factors such as co-contaminants and environmental factors. Solid waste materials derived from contaminated infrastructure can also be a significant source of PFAS. Building materials such as metals, stones, glass fabrics, tiles, carpet, and concrete were typically coated with fluoropolymers to improve fire and weather resistance in various construction-related applications (OECD 2013). Particularly concrete can act as a PFAS sponge and slow release media to continue providing a source of PFAS release (GHD 2017). Construction and demolition (C&D) materials such as those previously mentioned generated from renovation and demolition projects typically are disposed of in non-hazardous unlined landfills. As a result, impacted solid waste generated from C&D activities need management to mitigate PFAS releases at unacceptable levels to groundwater, surface water, and drinking water sources.

PFAS found in soils are subject to leaching during precipitation weather events and/or irrigation events (ITRC 2018), so the ITG is evaluating the stabilization and solidification of PFAS-contaminated soil, sediment, and solid waste materials. Leaching is a function of structural properties and the specific media’s pH, redox conditions, partitioning with organic or clay rich soil or sediment, and other factors such as co-contaminants and environmental factors. Solid waste materials derived from contaminated infrastructure can also be a significant source of PFAS. Building materials such as metals, stones, glass fabrics, tiles, carpet, and concrete were typically coated with fluoropolymers to improve fire and weather resistance in various construction-related applications (OECD 2013). Particularly concrete can act as a PFAS sponge and slow release media to continue providing a source of PFAS release (GHD 2017). Construction and demolition (C&D) materials such as those previously mentioned generated from renovation and demolition projects typically are disposed of in non-hazardous unlined landfills. As a result, impacted solid waste generated from C&D activities need management to mitigate PFAS releases at unacceptable levels to groundwater, surface water, and drinking water sources.

To find out what optimal stabilization method will effectively stabilize PFAS and prevent leaching from solid materials, one research project will test various commercial and other stabilizing reagents. Typically, the amounts and types of stabilization agents required would then be confirmed by a treatability study where samples of the media at varying concentrations of contaminants are mixed with various amounts of stabilization agents. When the stabilization reactions are complete, a sample is taken and analyzed for various leaching procedures such as toxicity characteristic leaching procedure (TCLP) and/or synthetic precipitation leaching procedure (SPLP) to determine the reduction in leachability achieved.

There also is the need to develop alternatives to current commercially available products and methodologies that are more cost-effective and more sustainable, particularly for drinking water, groundwater, and leachate treatment.

One multi-million dollar project is aimed at developing a scalable modular technology that would treat PFAS from water sources including groundwater and surface waters. It would also employ a risk-based framework, to facilitate choosing sensible solutions that meet the expectations of all stakeholders, including owners and taxpayers. This project is being done in partnership with the University of Queensland Health, Queensland Urban Utilities, Airservices Australia and Australian Biorefining, supported by a grant from the Australian Research Council. Separate work in the area of risk assessment will help determine what acceptable or safe levels are, and is key to developing appropriate risk management strategies.

Various other treatability studies are also underway with a number of partners, including one that will directly compare select regenerable media technologies (surface-modified natural media) with synthetic resin and activated carbon. Testing using batch-equilibration reactors and column flushing apparatus experiments is being implemented to evaluate removal efficiency and longevity of each media when tested under identical conditions. Other studies areinvestigating the use of advanced oxidation treatment for water using chemical oxidants as photocatalysts, regeneration of absorbent media using solvent regeneration and advanced oxidation and electrochemical technologies to remove or destroy PFAs.

Advances in the treatment and destruction of PFAS in drinking water, groundwater, landfill leachate, soil, sediment, building materials, and biosolids are critical to help us better manage PFAS in our environment, and prevent it from continuing to spread at unacceptable risk levels.

Recognizing the importance of this research work has driven GHD to initiate research studies, provide in-kind services to support them, and partner with others to capture government funding to support studies. Our expertise in contaminant assessment and remediation, practical engineering, remedial economics, and in evaluating research concepts and results using evidence-based science will allow us to determine what approaches and technologies work in the real world. This experience will help the industry and the public sector improve decision-making for site-specific conditions of PFAS investigation, identification, assessment, and remedial technologies. GHD will share these results globally with our partners at seminars, conferences, and through publications so that our lessons learned can help guide others as the overall PFAS landscape continues to evolve.