Incubator Initiative - What is the best way to treat the iron-related clogging problem in the Limestone Coast?

Abstract

This study investigated the cause of iron related clogging of bores across the Limestone Coast region. A survey of 26 clogging-affected and unaffected bores found no apparent correlation between the presence of iron related bacteria (IRB) and the clogging status of the bore, with IRB detected in the majority of wells sampled. There was a clear correlation between affected bores and the redox potential of the groundwater, with strongly reducing waters associated with clogged bores. The most severely affected bores were also found to be severely oversaturated in respect to iron oxide minerals indicating a strong potential for iron precipitation. The highest Fe2+ concentrations were found in the deepest bores. This relationship needs to be further explored and will inform future mitigation strategies.

Summary

Iron clogging of bores, pumps and drippers is a persistent and growing problem for many irrigators in the Limestone Coast region, who rely on groundwater for irrigation. This study examined 26 bores used for viticulture irrigation in the region. Bores were either unaffected by clogging, affected to a minor/moderate degree or strongly affected by clogging. The results found no apparent correlation between the presence of iron related bacteria (IRB) and the clogging status of the well, with IRB detected in the majority of wells. The results suggest that IRB are widespread throughout the aquifer and it appears unlikely, that the perceived increase in iron clogging in the region is a result of the widespread introduction of IRB through drilling equipment. The survey of bores did find a clear correlation between affected bores and the redox potential of the groundwater, with strongly reducing waters associated with clogged bores. The most severely affected bores were also severely oversaturated in respect to iron oxide minerals, indicating a strong potential for iron precipitation. Under these conditions the ingress of oxygen, through well usage, would cause iron to precipitate rapidly. Interestingly, the higher concentrations of Fe2+ tended to be in the deeper bores, which were also often the most recently drilled. Further research is needed to explore this relationship in more detail. A sample of clogging material was also examined using the scanning electron microscope. This found evidence of both crystalline material and biological growth. This supports the findings that the clogging is most likely an inorganic problem which may be enhanced through the presence of bacteria and biofilm formation. Future research is needed to expand the dataset and to verify the conclusions drawn on the basis of the currently limited number of examined bores. Funding for this project was provided by Wine Australia through its Incubator Initiative. In-kind support was provided by Flinders University. This project could not have been completed without the input and support from Kerry De Garis (Limestone Coast Grape and Wine Council Inc.) and the irrigators who provided information and allowed us to sample a subset of bores on their properties.