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Influence of Groundwater Constituents on Longevity of Iron-Based Permeable Barriers

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Recent work has demonstrated the utility of iron permeable reactive barriers PRBs for the in situ treatment of chlorinated hydrocarbons. In these systems, the surface of the granular iron acts as an electron donor with the reducible contaminant acting as an electron acceptor, thereby leading to corrosion of the material. Although the exact mechanisms involved have not been fully elucidated, field demonstration indicate that the reactions are rapid under environmentally relevant conditions. At the time of this writing, granular iron PRBs for the degradation of VOCs in groundwater have been installed at over 70 sites, including 53 sites located within the United States. Questions remain, however, concerning the longevity of effective contaminant removal at such installations. From a design standpoint, the long-term success of iron treatment walls is critically dependent on their ability to maintain a reactive surface and appropriate hydraulic residence times HRTs for treatment. Deteriorations in the performance of iron-based treatment processes may occur if either the chemical activity of the solid surface diminishes of if the mean hydraulic residence time of the porous medium is reduced. Moreover, changes in the hydraulic residence time distributions HRTDs of the porous medium may affect treatment efficiency in a manner that is strongly dependent on the nature of the reaction kinetics. At present, the relationships between the iron surface composition, reaction mechanisms, and reactivity are imperfectly understood. Although some studies have indicated little change over time in iron reactivity for chlorinated hydrocarbons, other investigations have demonstrated that specific groundwater constituents can act over the long term to either diminish or to enhance the reactivity of the irons interfacial region towards certain species.

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  • Water Pollution and Control

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