Influence of mineral precipitation on the performance and long-term stability of Fe 0 -permeable reactive barriers: A review on the basis of 19 Fe 0 -reactive barrier sites

Abstract

A comparative evaluation of the monitoring results from 19 Fe-0-permeable reactive barriers (PRBs) is presented which considers changes of groundwater composition within the Fe-0-PRBs, the type and distribution of mineral phases that precipitate, porosity reductions, extent of the load of inorganic groundwater constituents and the overall performance. The findings show that the changes in groundwater composition within the PRBs are extremely similar, independent of flow velocities, residence times, and concentrations of inorganic substances. In addition, the type and distribution of mineral precipitates do not show great variances with the largest mineral accumulations within the first 10 to 30 cm from the entrance face of the PRBs. From these comparisons it can be concluded that loads of dissolved inorganic species higher than 200 kg.a(-1).m(-2) limit the long-term performance of Fe-0-PRBs up to a few years due to porosity losses caused by mineral precipitation, independent of the type of construction. Moreover, detailed calculations of porosity and hydraulic conductivity decreases of the PRBs at the Rheine and Tubingen sites show that the influence of mineral fouling on the hydraulic permeability of a PRB can only be estimated by accounting for the interaction between reduction in porosity, permeability and flow rate. The findings suggest that it is possible to pre-estimate the porosity and permeability development for a potential PRB.