Field Evaluation of the Performance and Heterogeneity of a Zero-valent Iron-based Permeable Reactive Barrier for Groundwater Remediation

Civil, Architectural and Environmental Engineering Department, The University of Austin at Texas Zero-valent iron (Fe0)-based permeable reactive barrier (PRB) is a state-of-the-art technology for groundwater remediation. Evaluation of the full-scale Fe0 PRB at Vapokon site, Denmark for over 3 years showed that chlorinated aliphatic hydrocarbons (CAHs) in groundwater was rapidly dechlorinated into less chlorinated or innocuous forms after flowing through the Fe0 PRB. About 73–87% of downgradient groundwater samples were treated to meet drinking water standards without noticeable deterioration of remediation effectiveness. Surprisingly, climatic variation of the remediation effectiveness was observed. Contrarily, continuous deterioration in the permeability and clogging of the Fe0 PRB probably caused by the mineral precipitates formed on the Fe0 surface was examined, which resulted in a preferential flow of contaminated groundwater through the Fe0 PRB. In addition, the reactive Fe0 material in the Fe0 PRB was more heterogeneous than that in laboratory columns which consequently shortened the residence time inside the Fe0 PRB for the CAH dechlorination. To alleviate the clogging problem and influence of the heterogeneity on the remediation effectiveness, a highly permeable ‘pre-barrier’ is recommended to be installed just upstream of the Fe0 PRB to first precipitate out most dissolved ions and a factor of safety of 3 should be applied to the thickness of the Fe0 PRB.