Risk assessment is often a very useful tool to assess the potential risks of Per- and Polyfluoroalkyl Substances (collectively known as PFAS) in the environment based on the site-specific characteristics. This allows the development of risk management or remedial actions, if required, targeted to address the real issues.
Our team was called in to carry out a Detailed Quantitative Human Health and Ecological Risk Assessment (referred to as Site Specific Risk Assessment or SSRA) on a challenging site.
Complex hydrogeology and wildlife considerations
Our team found evidence of PFAS at former fire-fighting training grounds on the property itself, as well as nearby downstream areas, including surface watercourses. Complex hydrogeology, various impacted media (e.g. soil, sediment, groundwater, and surface water), and multiple exposure pathways and types of receptors at the site were also found.
Those receptors included a section of undisturbed woodland, considered to be a microenvironment supporting a high level of wildlife activity. Based on the results of a habitat and species at risk (SAR) assessment, receptors of concern considered by the SSRA included both terrestrial and aquatic ecological receptors, including birds of prey. For human receptors, exposure pathways including direct contact with soil, inhalation of dust and ingestion of fish from a river were considered.
Our assignment was to complete a detailed site characterization and risk assessment. The results were then used to develop a risk management strategy.
Food-chain modelling and site-specific tissue data
PFAS have a tendency, in animals and birds, to biomagnify – to increase in concentration in organisms as a result of their ingesting other plants or animals in which the contaminants are present. This meant it was important to develop a conceptual site model that included contaminant sources, release mechanisms, environmental transport and residency media, and exposure routes for each of the receptor groups.
The quantitative assessment included food-chain modelling for mammals and birds. The team completed a literature review to identify toxicological benchmarks, Toxicity Reference Values (TRVs), and transfer factors, and evaluate available toxicological data. A key objective of the sampling and analysis program was to collect site-specific tissue data to assess the potential for bioaccumulation and food chain transfer of PFAS. This meant that the team sampled and analyzed PFAS in grasses, berries, earthworms, and small mammals present on land as well as in aquatic plants, benthic invertebrates and small- and large-bodied fish. The fish tissue PFAS data was also used for the derivation of the fish tissue criteria for PFAS protective of human health based on the consumption of the fish.
Risk characterization was completed to determine the potential for adverse effects to receptors, and site-specific target levels (SSTLs) were developed for the protection of receptors for which risks were identified. A risk management and remediation plan was developed to address the specific risks that were identified in the assessment.
After successfully providing project deliverables within stated scope, quality, budget and schedule requirements, we were retained for all the subsequent phases of the work including biological surveys to assess receptors’ health, screening of remedial options, bench/pilot testing of the most promising options including innovative technologies, and remediation design for the fire-fighting training area.
* This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.