Remediating ground water with zero-valent metals: Chemical considerations in barrier design

To gain perspective and insight into the performance of permeable reactive barriers containing granular iron metal, it is useful to compare the degradation kinetics of individual chlorinated solvents over a range of operating conditions. Pseudo first-order disappearance rate constants normalized to iron surface area concentration (k(SA)) recently have been reported for this purpose. This paper presents the results of further exploratory data analysis showing the extent to which variation in k(SA) is due to initial halocarbon concentration, iron type, and other factors. To aid in preliminary design calculations, representative values of k(SA) and a reactive transport model have been used to calculate the minimum barrier width needed for different ground water flow velocities and degrees of halocarbon conversion. Complete dechlorination of all degradation intermediates requires a wider treatment zone, but the effect is not simply additive because degradation occurs by sequential and parallel reaction pathways.