PFAS Monitored Retention (PMR) and PFAS Enhanced Retention (PER)

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Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) Monitored Retention (PMR) is an approach for managing PFAS-affected sites that relies on natural retention processes that can lessen the migration and maximum concentrations of many PFAS at impacted sites. Because PFAS have not yet been shown to degrade to harmless end products by natural abiotic or biological actions, these retention processes (e.g., sorption, matrix diffusion) are expected to be the primary factors that dictate how PFAS behave and move in the environment [1] [2][3][4][5][6][7], and they form the basis for PMR. The PMR concept has been incorporated into a framework (the “PMR Framework”) that can help users determine the suitability of PMR at a specific site or identify the highest priorities among a portfolio of PFAS-affected groundwater sites. The Framework provides guidance on collecting different types of data (lines of evidence) to support a PMR evaluation. It also describes enhanced retention strategies known as PFAS Enhanced Retention (PER) that may be applicable for management of sites where natural retention is insufficient on its own to protect downgradient receptors.

Related Article(s):


Contributor(s): Dr. David Adamson, P.E., Dr. Charles Newell, P.E. and Dr. Hans Stroo


Key Resource(s):

Introduction

Groundwater sites contaminated with PFAS are difficult to investigate and remediate due to strict cleanup goals, lack of natural degradation mechanisms for some PFAS, and the high mobility and persistence of several PFAS. Several factors contribute to the urgency of developing cost-effective strategies to manage PFAS sites:

  • The number of groundwater sites with PFAS that will require some type of management could be in the tens of thousands (Newell et al., 2020; 2022). Recent estimates suggest that there are 50,000 to 60,000 potential PFAS sites in the U.S. (EBJ, 2022; Salvatore et al., 2022).
  • No technologies currently exist that are capable of effectively and efficiently destroying PFAS in situ. Furthermore, the remediation industry is unlikely to be able to practically manage the large number of PFAS groundwater plumes using the only two technologies that are currently viable, groundwater pump and treat and in situ sorbents (Newell et al., 2022).
  • Despite a lack of natural processes that permanently sequester PFAS, there are natural processes can potentially retain PFAS in the subsurface for extended periods, limiting contaminant migration.
  • Consequently, retention could be an important factor in reducing the near-term risk associated with PFAS groundwater plumes at some sites and open up approaches for managing PFAS plumes based on retention (Newell et al., 2021a, b; 2022).
  • Even after active remediation, it is likely that low residual concentrations of PFAS will remain in soils and groundwater, and these may also be effectively controlled by retention.

As a result, understanding and potentially relying on processes that reduce PFAS migration rates and mass discharge rates is of considerable interest to site managers. This includes a variety of chemical and geochemical retention processes that have been incorporated into the PFAS Monitored Retention (PMR) approach that site owners, their consultants, and environmental regulators can use to prioritize and manage their portfolios of PFAS sites.

PMR versus MNA

PMR is a similar concept to monitored natural attenuation (MNA), and the term has recently been adopted in place of MNA to avoid potential confusion with destructive and/or permanent attenuation processes that are part of the MNA strategies for other constituents of concern (COCs).  However, many of the processes remain the same, and they are expected to reduce PFAS concentrations and mass discharge during transport from source areas.

The use of management based remedial approaches like MNA to control PFAS plumes poses several challenges, including that traditional MNA applications typically deal with petroleum hydrocarbons and chlorinated solvents, which can naturally break down to harmless end products at many sites. However, MNA as a remedy or site management strategy has been approved by regulators for some non-degrading metals, metalloids, and radionuclides (e.g., chromium, arsenic, and uranium) if the local geochemical conditions can sequester or immobilize these contaminants. This implies that even if some PFAS do not naturally degrade, passive management strategies may be feasible for PFAS plumes in groundwater because PFAS retention processes can help reduce their concentrations. Figure 1 shows how PMR fits into the development timeline for MNA-type approaches for different contaminant classes.


References

  1. ^ Interstate Technology and Regulatory Council (ITRC) PFAS Team, 2023. Technical/Regulatory Guidance: Per- and Polyfluoroalkyl Substances. ITRC PFAS Home Page Report pdf
  2. ^ 2.0 2.1 Newell, C.J., Adamson, D.T., Kulkarni, P.R., Nzeribe, B.N., Connor, J.A., Popovic, J., and Stroo, H.F., 2021a. Monitored Natural Attenuation to Manage PFAS Impacts to Groundwater: Scientific Basis. Groundwater Monitoring and Remediation, 41(4), pp.76–89. doi: 10.1111/gwmr.12486 Article pdf
  3. ^ 3.0 3.1 Newell, C.J., Adamson, D.T., Kulkarni, P.R., Nzeribe, B.N., Connor, J.A., Popovic, J., and Stroo, H.F., 2021b. Monitored Natural Attenuation to Manage PFAS Impacts to Groundwater: Potential Guidelines. Remediation Journal, 31(4), pp. 7–17. doi: 10.1002/rem.21697 Article pdf
  4. ^ Adamson, D.T., Kulkarni, P.R., Nickerson, A., Higgins, C.P., Field, J., Schwichtenberg, T., Newell, C., and Kornuc, J.J., 2022. Characterization of relevant site-specific PFAS fate and transport processes at multiple AFFF sites. Environmental Advances, 7, 100167. doi: 10.1016/j.envadv.2022.100167 Article pdf
  5. ^ Brusseau, M.L., 2018. Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Science of The Total Environment, 613–614, pp. 176–185. doi:10.1016/j.scitotenv.2017.09.065. Article pdf
  6. ^ Guelfo, J.L., Korzeniowski, S., Mills, M.A., Anderson, J., Anderson, R.H., Arblaster, J.A., Conder, J.M., Cousins, I.T., Dasu, K., Henry, B.J., Lee, L.S., Liu, J., McKenzie, E.R., and Willey, J., 2021. Environmental Sources, Chemistry, Fate, and Transport of Per- and Polyfluoroalkyl Substances: State of the Science, Key Knowledge Gaps, and Recommendations Presented at the August 2019 SETAC Focus Topic Meeting. Environmental Toxicology and Chemistry, 40(12), pp. 3234-3260. doi: 10.1002/etc.5182 Article pdf
  7. ^ Guo, B., Zeng, J., and Brusseau, M.L., 2020. A Mathematical Model for the Release, Transport, and Retention of Per‐ and Polyfluoroalkyl Substances (PFAS) in the Vadose Zone. Water Resources Research, 56(2), e2019WR026667. doi:10.1029/2019WR026667 Article pdf
  8. ^ Newell, C.J., Javed, H., Li, Y., Johnson, N.W., Richardson, S.D., Connor, J.A., and Adamson, D.T., 2022. Enhanced Attenuation (EA) to Manage PFAS Plumes in Groundwater. Remediation Journal 32(4), pp. 239–257. doi: 10.1002/rem.21731Article pdf
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