benson@engr.wisc.edu

Abstract This paper describes reactive transport simulations conducted to assess the impact of mineral fouling on the long-term performance of permeable reactive barriers employing granular zero valent iron (ZVI). Three minerals were assumed to form in the pore space (CaCO₃, FeCO₃, and Fe(OH)₂) and the inflowing groundwater was assumed to have the following composition: DO = 10^-8 M, Fe²⁺ = 10^-10 M, Ca²⁺ = 10^-3 M, OH^- = 10^-7 M, HCO₃^- = 10^-3 M, and CO₃^2- = 10^-7 M. Results of the simulations show that the porosity and hydraulic conductivity of the ZVI decrease over time and that flows are redistributed throughout the PRB in response to fouling of the pore space. Seepage velocities in the PRB increase, and residence times decrease, due to porosity reductions caused by accumulation of minerals in the pore space. Under the assumed conditions, only subtle changes occur within the first 10 years (i.e. the duration of the current field experience record with PRBs) and the most significant changes do not occur until the PRB has operated for at least 30 years. However, after 30–50 years, reductions in residence time of the order of 50% occurred. More rapid and extensive changes are likely to occur for conditions that result in greater precipitation rates (e.g. groundwater with higher ionic strength, higher velocity).