Influence of Precipitates on Hydraulic Performance of Permeable Reactive Barrier Filters

A study was conducted to elaborate a predictive model that deals with the hydraulic conductivity reduction of permeable reactive barriers (PRBs) used for the in situ treatment of contaminated groundwater. As PRBs are composed of reactive and permeable filters through which the contaminated groundwater flows, their longevity has to be studied from both hydraulic and chemical points of view. Therefore, one-dimensional (1D) column filtration experiments were performed at a pilot scale, and an integrated model based on the solution of the advection-reaction-dispersion (ARD) mass balance equation was developed to study the space and time evolution of the hydraulic conductivity. This model uses the well-known Kozeny-Carman relation, which considers that permeability depends on the porosity and specific surface of the porous media. The ARD equation is solved by using the PHREEQC software with numerous capacities on the chemical point of view. Thanks to specific assumptions on the geometry of the precipitations, by using the floating-spheres model and the introduction of the “balanced time principle,” the evolution of the profiles of conductivity are computed and compared with those deducted from differential pressure measurements in the laboratory. Results of numerical simulations conducted with the model show that the largest porosity reductions occur on a 10-cm-thick layer at the entrance of the PRB as a result of precipitation of calcite minerals (prefilter).