esm223_09_Other_Reading_PRB_zero-valent-Fe_EPA

esm223_09_Other_Reading_PRB_zero-valent-Fe_EPA - United...

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1 * U.S. EPA, Office of Research and Development, National Risk Management Research Laboratory, Subsurface Protection and Remediation Division, Ada, OK. Long-term Performance of Permeable Reactive Barriers Using Zero-valent Iron: An Evaluation at Two Sites United States Environmental Protection Agency ENVIRONMENTAL RESEARCH BRIEF Richard T. Wilkin*, Robert W. Puls*, and Guy W. Sewell* Background The permeable reactive barrier (PRB) technology is an in-situ approach for remediating groundwater contamination that combines subsurface fluid flow management with a passive chemical treatment zone. Removal of contaminants from a groundwater plume is achieved by altering chemical conditions in the plume as it moves through the reactive barrier. Because the reactive barrier approach is a passive treatment, a large plume can be treated in a cost-effective manner relative to traditional pump-and-treat systems. There have now been more than forty implementations of the technology in the past six years, which have proven that passive reactive barriers can be cost- effective and efficient approaches to remediate a variety of compounds of environmental concern. However, in all of the installations to date comparatively few data have been collected and reported on the long-term performance of these in-situ systems, especially with respect to the buildup of surface precipitates or biofouling (O’Hannesin and Gillham, 1998; McMahon et al., 1999; Puls et al., 1999; Vogan, 1999; Phillips et al., 2000; Liang et al., 2000). A detailed analysis of the rate of surface precipitate buildup in these types of passive, in-situ systems is critical to understanding how long these systems will remain effective and what methods may be employed to extend their lifetime or to improve their performance. Different types of minerals and surface coatings have been observed to form under different geochemical conditions that are dictated by aquifer chemistry and the composition of the permeable reaction zone (Powell et al., 1995; Mackenzie et al., 1999; Liang et al., 2000). Microbiological impacts are also important to understand in order to better predict how long these systems will remain effective in the subsurface (Scherer et al., 2000). The presence of a large reservoir of iron coupled with plentiful substrate availability supports the metabolic activity of iron-reducing, sulfate-reducing, and/or methanogenic bacteria. This enhanced microbial activity may beneficially influence zero-valent iron reductive dehalogenation reactions through favorable impacts to the iron surface or through direct microbial transformations of the target compounds. However, this enhancement may come at the expense of faster corrosion leading to faster precipitate buildup and potential biofouling of the permeable treatment zone.
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esm223_09_Other_Reading_PRB_zero-valent-Fe_EPA - United...

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