Remediation of acidic groundwater by way of permeable reactive barrier

A permeable reactive barrier (PRB) was installed in the Shoalhaven Floodplain about 100 km south of Sydney (Australia), where acidic groundwater generation from pyritic soil poses a severe environmental and socioeconomic problem. Recycled concrete aggregates were a promising source of alkalinity-generating material and adopted as the reactive media for this PRB. The current study simulates the performance of the PRB through coupling geochemical reactions involved with recycled concrete and acidic groundwater with geohydraulics (transient groundwater flows). This is the first such attempt made for time-dependent modelling and performance verification of a PRB located in acid sulfate soil (ASS) terrain. The developed model describes the chemical clogging due to mineral precipitates and the associated reductions in porosity and hydraulic conductivity of the reactive medium. The governing equations of the model were incorporated into commercial software, MODFLOW and RT3D. The field results are in favourable agreement with the model predictions, confirming that the reduction in hydraulic conductivity due to mineral precipitation occurs predominantly at the entrance zone of the PRB and insignificantly in the middle and exit zones after 7 years of operation. Mineralogical analysis undertaken on sample specimens from the PRB also confirms that clogging is minimal at the entrance zone.