It has been said, "The only places we're not finding PFAS are places we're not looking" (Heidi Grether, Director, Michigan Department of Environmental Quality).
The widespread presence of per- and polyfluoroalkyl substances (PFAS) in the environment and its many possible sources make for complicated conceptual site models and difficulty in distinguishing sources of the impacts. The majority of PFAS constituents cannot be detected using commercially available analytical techniques. Progress is being made towards developing analytical techniques to improve the detection of these constituents, including recent research by the authors and academic and industry partners developing nuclear magnetic resonance (NMR)-based analytical techniques and total fluoride field screening, but it may be years before comprehensive site characterisation is achievable. However, the widespread detections of some PFAS in humans and wildlife and mounting evidence that PFAS bioaccumulate have raised concerns regarding human health and ecological risks and put pressure on the regulators to develop environmental criteria while the scientific understanding of the risks and behaviours of these compounds is still developing.
With the prevalence of PFAS detections, the current drinking water health advisory limits being set in Canada and abroad, and the anticipated future regulatory levels, there are many sites whose current remedial action plan or site closure plan will need to be re-evaluated to consider PFAS. Similar to the vapour intrusion (VI) pathway for volatile organic compounds (VOC) sites, which was often excluded from a site's investigation and remedial process, many sites which may have achieved closure will need to be/are being re-evaluated with respect to PFAS risks.
Thousands of closed sites in the United States have been or are being re-evaluated, and reopened if necessary, in terms of the VI pathway. Ranking criteria are applied to site re-evaluations which were chosen based on site conditions that are believed to play a significant role in the VI pathway. Similar re-evaluations are expected or ongoing for potential risks from PFAS at sites which have achieved closure or are well on their way through their site closure path. PFAS detections will result in major upheavals and potential reversals of approved in situ site remedies that may not be capable of treating PFAS. The US Department of the Navy for example, has issued site guidance for their remedial project managers which includes the recommendation to consider sampling for PFAS at closed sites if the conceptual site model strongly suggests PFAS have impacted media and supports current or potential future exposure. The behaviour of the PFAS constituents in the environment can vary widely depending on the composition of the PFAS mixture, the presence of co-contaminants, etc. It is essential that knowledgeable practitioners, who fundamentally understand the limitations and challenges associated with PFAS, direct investigation and remediation efforts to achieve successful mitigation of risk at PFAS sites.
This presentation will review case studies for sites where PFAS has significantly changed a site closure plan or reversed the closure designation, relate this to some of the guidance for site closure reversals based on the VI pathway and how it relates to Canadian federal contaminated sites.