Mineral precipitation and the associated reduction of hydraulic conductivity in a PRB

Permeable reactive barriers (PRB) have been used worldwide for the in-situ treatment of con-taminated ground water. One such contamination found in Australia is acidic groundwater enriched with high concentrations of dissolved aluminium and iron produced in acid sulfate soil (ASS) terrains. To treat this acidi-ty in groundwater, a PRB was installed in the Shoalhaven Floodplain and then monitored over a seven year pe-riod. This remediation process was satisfactory but there was a small decrease in efficiency due to a secondary mineral precipitation (aluminium and iron oxy/hydroxides) which reduced the hydraulic conductivity of the PRB. Numerical modelling carried out through MODFLOW and RT3D software showed that this reduction in hydraulic conductivity due to secondary mineral precipitation was 3% at the entrance of the PRB after seven years of installation. This result was satisfactory considering that the predicted longevity of the barrier was 19.5 years, assuming a mean groundwater velocity of 0.05 m/day.