Most of Australia's precious groundwater is at risk of contamination in one way or another the key issue is how vulnerable is the groundwater which particular communities, industries or ecosystems rely on.
Protecting and managing the quality of groundwater has become a major challenge in the face of the growing range of threats which confront it, says Dr Claus Otto of CSIRO Land and Water, project leader of one of the nation's first integrated groundwater vulnerability assessment systems.
Cities like Perth and Newcastle depend on groundwater for drinking and domestic use, as do many rural communities. Fruit, vegetables, dairy products, meat and other farm produce grown on irrigation often rely on groundwater. Across huge areas of Australia cattle and sheep drink bore water. Natural ecosystems, rivers and wetlands also rely on groundwater when it comes to the surface.
But groundwater quality faces growing pressure from industrial chemicals and waste discharges, oil and solvent spills, detergents, fertilisers, sewage, polluted urban runoff and pesticides, says Dr Otto.
"We are finding coliform bacteria from sewage in groundwater, and that is a problem all across Australia, especially in smaller settlements where there is high reliance on septic disposal systems. It is a substantial human health issue.
"Many of our rivers are also under threat from agricultural and garden nutrients and pesticides which flow into them via groundwater," he adds, recalling one case where lawns irrigated with bore water died because it contained a herbicide which had leached in.
"All contaminants will eventually reach groundwater if they are in sufficient quantities. All groundwater should therefore be regarded as vulnerable."
Dr Otto's team has identified the key factors which determine how great is the risk to groundwater from seeping pollution and combined them in a vulnerability assessment which can be used by water managers to control the hazard.
"Ordinary hydrogeological maps will tell you about the depth and flow of the groundwater, but not its vulnerability to contamination," he explains.
To this must be added factors such as: how the surrounding land is used, how the groundwater is used, how rapidly it is recharged, the geology which surrounds it, the sort of soils which overlie it, the capacity of the soil to degrade various pollutants before they reach the water table, the rate at which various pollutants build up.
These factors can be combined in a digital map to give water managers, state agencies, local government, industries and communities a clearer understanding of the extent of the threat to their underground water and which areas are most at risk.
The map can also help them anticipate problems, and to identify areas where pollution monitoring and management should have a high priority.
Especially important, says Dr Otto, is the type of soil through which the contaminants must pass before they reach the water table. Clayey soils contain many bacteria which can break down, or bioremediate, pollutants before they reach the groundwater. Sandy soils, on the other hand, allow pollutants to pass through easily.
Groundwater vulnerability models are being developed to assess groundwater contamination by pesticides and nitrates in the Namoi Valley, New South Wales, and the Swan Coastal Plain, in Western Australia, respectively, and an integrated model is being developed for the Royal Australian Navy on Garden Island, in WA. The Navy can use this model to generate scenarios for various land use impacts on the island and marine waters. These, in turn, can be used to help prevent future groundwater problems.
More information:
Dr Claus Otto, CSIRO Land & Water 08 9333 6367
Margaret Bryant, CSIRO Land & Water 08 9387 0215
Email:claus.otto@per.clw.csiro.au