Performance and economic comparison of PRB types in heterogeneous aquifers

Performance and cost are compared for horizontal permeable reactive barriers (HPRBs), funnel and gate permeable reactive barriers (FGPRBs) and caisson permeable reactive barriers (CPRBs) in heterogeneous aquifers that achieve the same goal (90% of effluent concentrations below 1% of the source concentration and complete plume capture). Variability in influent and effluent concentrations is compared for each permeable reactive barrier (PRB) with different levels of aquifer heterogeneity. HPRBs have the most variable influent and effluent concentrations because an HPRB does not induce upstream mixing. The PRB provides ‘short circuits’ that connect permeable lenses upstream and downstream, reducing residence time. CPRBs have the least variable influent and effluent concentrations for all levels of heterogeneity because of the flow convergence induced by the funnel and caisson homogenises flow rates and concentrations, resulting in less variability in residence time and effluent concentration. The FGPRB falls between the HPRB and the CPRB, and generally is the most cost effective PRB regardless of heterogeneity. The CPRB provides the most efficient use of reactive media but tends to be costlier than the FGPRB. FGPRBs use reactive media efficiently compared to HPRBs, as significant portions of HPRBs are not active in treatment, particularly in more heterogeneous aquifers.