Science Inventory

Reply to comment on “Long-term performance evaluation of zero-valent iron amended permeable reactive barriers for groundwater remediation–A mechanistic approach” by C. Noubactep, Geoscience Frontiers 14(2023), 101582

Citation:

Lawrinenko, M., S. Kurwadkar, AND R. Wilkin. Reply to comment on “Long-term performance evaluation of zero-valent iron amended permeable reactive barriers for groundwater remediation–A mechanistic approach” by C. Noubactep, Geoscience Frontiers 14(2023), 101582. Geoscience Frontiers. Elsevier B.V., Amsterdam, Netherlands, 14(4):101583, (2023). https://doi.org/10.1016/j.gsf.2023.101583

Impact/Purpose:

The selection of groundwater remediation technologies is best supported by a detailed understanding of groundwater geochemistry, hydrologic characteristics, and mechanistic behavior of the remediation technology. This paper describes the positive and negative aspects of site groundwater geochemistry and hydrology that play into the selection of the Permeable Reactive Barrier (PRB) technology for treating organic and inorganic contaminants in groundwater. The work reviews the factors that impact PRB longevity, including mineralization, gas generation, and microbial activity. The longevity issue for remedial technologies is a high priority of agency partners who frequently ask about remedial timeframes and effectiveness. Necessary site characterization activities are outlined that can be used develop system designs at contaminated sites. The work is of interest to the international environmental community, including EPA’s regional, program, and local partners.

Description:

Permeable reactive barriers (PRBs) are used for groundwater remediation at various sites worldwide. This technology has been efficient at appropriate sites for treating organic and inorganic contaminants using zero-valent iron (ZVI) as a reductant and as a reactive material. Continued development of the technology over the years suggests that a robust understanding of PRB performance and the mechanisms involved are still not fully understood. Conflicting information in the scientific literature downplays the critical role of ZVI corrosion in the remediation of various organic and inorganic pollutants. Additionally, there is a paucity of information on how different mechanisms act in tandem to affect ZVI-groundwater systems through time. In this review paper, we describe the underlying mechanisms of PRB performance and remove isolated misconceptions. We discuss the underlying mechanisms of ZVI transformation and aging in PRBs and the role of iron corrosion products. We review numerous sites to reinforce our understanding of the interactions between groundwater contaminants and ZVI and the authigenic minerals that form within PRBs. Our findings show that ZVI corrosion products and mineral precipitates play critical roles in the long-term performance of PRBs by influencing the reactivity of ZVI. Pore occlusion by mineral precipitates occurs at the influent side of PRBs and is enhanced by dissolved oxygen and groundwater rich in dissolved solids and high alkalinity, which negatively impacts hydraulic conductivity, allowing contaminants to potentially bypass the treatment zone. Further development of site characterization tools and models is needed to support effective PRB designs for groundwater remediation.