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A groundwater risk assessment was carried out for 30 potable water supply systems under a framework of protecting drinking water quality across South Australia. A semi-quantitative Groundwater Risk Assessment Model (GRAM) was developed based on a "multi-barrier" approach using likelihood of release, contaminant pathway and consequence equation. Groundwater vulnerability and well integrity have been incorporated to the pathway component of the risk equation. The land use of the study basins varies from protected water reserves to heavily stocked grazing lands. Based on the risk assessment, 15 systems were considered as low risk, four as medium and 11 systems as at high risk. The GRAM risk levels were comparable with indicator bacteria-total coliform-detection. Most high risk systems were the result of poor well construction and casing corrosion rather than the land use. We carried out risk management actions, including changes to well designs and well operational practices, design to increase time of residence and setting the production zone below identified low permeable zones to provide additional barriers to contaminants. The highlight of the risk management element is the well integrity testing using down hole geophysical methods and camera views of the casing condition.

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Estimation of natural recharge and potential for seawater intrusion are critical considerations for management of coastal freshwater aquifers. We show hydrochemical signatures of groundwater to identify the influence of geological control on chemical processes in a coastal groundwater system. We used dominant hydrochemical facies, salinity and magnesium ions to determine two main groundwater flow paths with different origins and ages. Mixing of groundwater with different origins and ages results in unreliable recharge estimates using chlorofluorocarbon (CFC) and chloride mass balance (CMB) methods, thus limiting available methods for recharge assessment. Interpretation of hydrochemical data suggests that calcium carbonate dissolution, ion exchange processes and mixing with sea aerosol in coastal zones are the main influencing factors on groundwater chemistry. Restricted groundwater flows due to occurrence of a basement high at the southern side of the basin boundary influence the distance to the toe of the saline wedge. Thus, knowledge of geological control over groundwater systems forms an important part of characterising basins and contributes toward effective management of groundwater resources.