Engineers Australia

Effective remediation of groundwater in acid sulphate soil terrain

Gyanendra Regmi, Buddhima Indraratna and Long Duc Nghiem

Abstract

Acidic groundwater, generated from acid sulphate soil (ASS), is a major geo-environmental problem in Australia. Manipulation of groundwater through the use of weirs and gates in the nearby creeks and drains of ASS, which is being practised right now for preventing pyrite oxidation, is not effective in low land floodplains due to the risk of flooding. The application of a permeable reactive barrier (PRB) can be an alternative for remediation of acidic groundwater in such floodplains. Laboratory column experiments were carried out prior to installation of the PRB for examining the efficiency of the material. Results of these experiments have shown that recycled concrete could effectively neutralise the acidic water for longer periods with complete removal of aluminium (Al) and iron (Fe). Despite the reduction of the efficiency of the recycled concrete due to armouring by accumulated precipitates of Al and Fe, excellent performance was observed for an extended period under controlled laboratory condition. Following these results, a pilot PRB was installed in the Broughton Creek flood plains in southeast NSW to observe its performance under varying natural conditions of the field. The PRB has been maintaining near neutral pH with complete removal of Al and Fe from the groundwater of ASS matching with the results of column test. The promising performance of the pilot PRB for the last three years shows that PRB can be used as one of the cost effective and environmental friendly alternative to other recently utilised techniques in ASS.