Formatted Title
Historical Lessons Learned: What Might PFAS Site Closure Look Like?
Background/Objectives
Achieving site closure has been a challenge at many sites contaminated with fuels, solvents, or other pollutants. Now in the age of PFAS, we might think the prospects of ever achieving closure at a PFAS site may be impossible. However, historical lessons learned from fuels and solvents may provide clues on potential paths to PFAS site closure.
We believe early conceptualization of what PFAS site closure may look like is important to define, prior to the completion of characterization efforts, otherwise data gaps and increased costs may echo into the future.
Based on discussions during the Fall 2023 University Consortium, site closure means different things to different parts of the environmental industry. To some it means unrestricted land use and no additional costs required. To others it means the point where risks to receptors have been addressed and the site is “fit for use”, according to current land use. Given the unprecedented challenges associated with PFAS, we may need to redefine how we track and ultimately achieve site closure at PFAS sites, within this spectrum of definitions.
Approach/Activities
Lessons learned while achieving site closure at over 100 sites will be discussed. Site closure typically revolves around three themes:
- Simple Sites: Closed after investigation or limited remediation (simple dig and haul, etc.).
- Complicated Sites: Extensive remediation and/or closure is projected to the distant future.
- Alternative Frameworks: Low-threat closure or other metrics are used to document limited residual risk.
Site closure for PFAS may look very different from fuels and solvents sites, given the resistance to degradation under natural conditions for some PFAS (e.g., the perfluoroalkyl acids [PFAAs]) and potential for long-range transport under certain conditions. However, like enhanced attenuation (EA) or monitored natural attenuation (MNA) of other contaminants, PFAS enhanced retention (PER) and PFAS monitored retention (PMR) may end up being key components of PFAS remedies that ultimately achieve site closure. Future documentation efforts to justify stable or receding PFAS groundwater plumes may incorporate PER and PMR approaches into the broader theme of the “assimilative capacity” of an aquifer.
This presentation will lay out a general framework for calculating the assimilative capacity of an aquifer for PFAS.
Results/Lessons Learned
Examples of site closure for fuels and solvents will be presented for historical context, relative to PFAS. Then, concepts used to evaluate the assimilative capacity of an aquifer for PFAS at a real field site will be presented.