Numerical Case Studies on Long-Term Effectiveness of Metallic Iron Based Permeable Reactive Barriers: Importance of Porosity Heterogeneity of the Barrier

This paper presents a three-dimensional (3-D) numerical groundwater flow and transport model of a metallic iron based permeable reactive barrier (Fe0-PRB) to assess how porosity heterogeneity of the barrier medium may affect groundwater flow over time and influence the long-term effectiveness of a Fe0-PRB. A 3-D high resolution aquifer outcrop analogue was utilized to implement aquifer heterogeneity. To evaluate the treatment perfor-mance of the PRB, the contaminant plume migration and groundwater residence time were investigated. The findings demonstrate that heterogeneity of porosity reduction of the barrier medium is an important factor in estimating the long-term performance of a continuous-wall Fe0-PRB. Ignoring the porosity heterogeneity of the barrier medium leads to an underestimation of the by-passing flow by 30%-41% in ten-years simulation, and of contaminant plume spread over time. Groundwater residence time simulations shows no evident residence time reduction during the operation of the Fe0-PRB. Installation of a pea gravel equalization zone can effectively reduce the heterogeneity of the barrier medium, and minimize the by-passing flow.