5.5 Groundwater quality
Groundwater salinity is highly variable – more information is needed on groundwater contamination
The natural and human-induced salinity of NSW ground water is highly variable and there are many areas where it is not suitable for consumption or irrigation. Contamination of ground water by nitrates, pesticides, pathogens, hydrocarbons and other substances is known to occur but only limited data is available to define the full extent of the problem.
In general, more knowledge is needed to ensure that the resource is managed appropriately.
NSW Indicator
Indicator |
Status of Indicator |
5.9 Exceedences of groundwater quality guidelines for salinity and contaminants |
Salinity in ground water varies across NSW and in some areas makes the water unsuitable for consumption or irrigation. Little is known about the extent and location of groundwater contamination in NSW. |
Importance of the issue
Many ecosystems require good quality ground water for their ongoing health and maintenance. These include surface water bodies, such as wetlands, rivers and lakes, which are connected to ground water, and terrestrial ecosystems. Changes in groundwater quality can significantly degrade these ecosystems causing a loss of terrestrial and aquatic species.
Ground water is a vital resource, supplying approximately 11% of the total water used in NSW. Uses include drinking, irrigation, watering stock, and domestic and industrial purposes. The availability of ground water for these uses depends on the quantity of the resource (see Water 5.4) and its quality.
The main impacts on groundwater quality in NSW are increased salinity and contamination by pollutants. Ground water of poor or unsuitable quality significantly limits its environmental value, increases the cost of water treatment, and may prevent some types of water use altogether. Once an aquifer is polluted, it is extremely difficult and expensive to restore and monitor.
For more information on ground water, see EPA 2000c.
Groundwater salinity
Natural salinity levels in ground water are predominantly determined by a combination of geology and the presence of airborne salts. Many areas of south-western NSW are underlain by sediments of marine origin which yield regionally saline ground waters. It is important to note that although groundwater quality may be influenced by the type of aquifer, good and poor quality water can be found in all aquifers, and the quality can be highly variable within a catchment. Natural salinity may be exacerbated by human activities, such as irrigation which causes accessions of saline irrigation water, inappropriate disposal of wastewaters, and the clearing of land. Excessive abstraction can cause saline water to enter a freshwater aquifer where coastal aquifers are hydraulically linked to the sea.
In some areas, the use of ground water is very limited because of its high salinity. In areas with low salinity and high yields there is more potential to use the resource. Table 5.6 shows the salinity levels and yields of aquifers and lists the common uses of ground water.
Table 5.6: Groundwater salinity, yield and common uses
|
High salinity (over 3000 milligrams/litre) |
Low salinity |
High yield |
Low yield |
Locations |
Most of the Darling catchment and south-western NSW
Large areas of the western Lachlan and lower Macquarie–Bogan (Bogan River area) catchments
Smaller areas of the Murrumbidgee, Namoi, Clarence, Richmond, Hunter and Sydney catchments |
Areas of inland groundwater systems, including the Murray, Murrumbidgee, Lachlan, Macquarie, Namoi, Gwydir and Hunter groundwater resources
Aquifers along the coastal plain, predominantly north of Newcastle |
Far north-eastern and south-eastern coastal sand bed aquifers
Smaller aquifers over much of the Sydney Basin, including the Blue Mountains
North-western NSW
Darling River corridor
Upper catchments of the Hunter and Namoi rivers
Castlereagh and Border Rivers catchments |
Use of ground water |
Limited |
Inland aquifers are used mainly for irrigation and stock watering, but potable water extraction is also an important use in these areas.
Coastal aquifers are used mainly for potable water supply and watering stock. |
Potable water extraction, town water supply, domestic and stock use, industrial purposes and small-scale irrigation only |
Source: DLWC data, as at 2002
Assessing how salinity levels in ground water might affect the ecosystems which depend on it is problematic. The effect of saline groundwater on river and wetland water quality is generally related to the level of dilution by surface flows. In times of low surface flow, even ground water in its natural state may significantly increase the salinity levels of aquatic ecosystems. However these ecosystems may also receive saline discharges from sources other than ground water (see Water 5.3), so any observed salinity increases may not be the result of ground water alone. In addition, little is known about the tolerances to changes in salinity levels of many flora and fauna species, including even those living within aquifers.
Groundwater contamination
Ground water may be contaminated by pollution from diffuse and point sources. Contaminants from diffuse sources include nitrates, pesticides and pathogens (see Water 5.3 and EPA 2000c). Agricultural practices, such as clearing of native vegetation (see Land 4.1 and Biodiversity 6.2), tillage of soils, the use of fertilisers, and excreta from grazing animals contribute to high levels of nitrates in ground water. Ground water can also be contaminated by agricultural pesticides where they are applied in excessive quantities.
Point-source contaminants are generally associated with urban development. These include underground storage tanks (hydrocarbons), landfills (various substances), septic tanks and human wastewater treatment (nitrates, bacteria, pathogens), intensive rural industries (nitrates), cattle and sheep dips (pesticides), manufacturing spills (pesticides, organochloride solvents), gasworks (coal, tars, ash, coke) and mining (heavy metals, acid, hydrocarbons, salinity).
Nitrates and pesticides are the most widespread known contaminants of ground water in Australia. In general, nitrate contamination is considered to be the most significant diffuse contaminant of ground water in Australia, because of its potential to adversely affect humans, animals and the environment. High nitrate levels in ground water are of concern where it is used for drinking, since an associated form (nitrite) may cause a debilitating condition called methaemoglobinaemia in some consumers.
Data for nitrate contamination of ground water is incomplete for NSW. However what is available suggests there are many localised areas with nitrate contamination. Areas where high nitrate levels have been recorded in ground water include parts of Sydney, aquifers adjacent to the Murray River west of Albury, some North Coast aquifers, aquifers in the Namoi catchment and many other localised contaminated sites.
Pesticide contamination has been detected in over 20% of samples in some agricultural areas in NSW (Ball et al. 2001).
There is little information on the contamination of ground water by other pollutants across the State, apart from known localised areas of contamination from petroleum products, agricultural chemicals and industrial sources, including gasworks. This is mainly because the cost of chemical sampling and analysis precludes the routine inclusion of various parameters in assessing groundwater quality. Chemical contamination of ground water from cattle and sheep dips, chemical manufacturing and pesticides have been recorded at a number of sites in NSW. Biological contaminants from livestock and septic tanks, including the bacterium Escherichia coli, hepatitis A and hepatitis E (see EPA 2000b) have also been detected in ground water. There are potentially many more areas of groundwater contamination than those recorded.
Response to the issue
Most of the responses to groundwater management address both quantity and quality issues and are covered in Water 5.4. The main response has been the recent development of statutory groundwater-sharing plans. Although the plans are principally focused on sharing water, they also address basic quality issues that affect how much suitable water is available.
A key part of the response to salinity has been to improve understanding and acceptance that ground water in many areas is naturally very saline and bringing it to the surface can cause problems.
The National Action Plan for Salinity and Water Quality and the Murray–Darling Basin Ministerial Council's Basin Salinity Management Strategy 2001–2015 are important responses that will help to manage groundwater quality. These are discussed in Land 4.3.
Effectiveness of responses
Although Government policies are in place to manage groundwater resources better, the limited information available on groundwater quality makes determining status and trends difficult. More monitoring of groundwater quality is needed to determine the effectiveness of management and whether the resource is suitable for consumption and other uses.
Groundwater-sharing plans will be subject to a mid-term review after five years, providing an opportunity to assess their effectiveness in protecting groundwater sources.
Future directions
Groundwater quality is affected by point- and diffuse-source pollution. Information on what can be done to prevent these types of pollution is covered in Water 5.3.
Better understanding of how groundwater quality affects the health of groundwater-dependent ecosystems is required. Knowledge is also scarce about the fauna and flora that live within aquifers and the quality of water they require.
Linked issues
2.1 Population and settlement patterns
4.1 Land-use changes
4.3 Induced soil salinity
4.6 Chemical contamination: land
5.1 Freshwater riverine ecosystem health
5.3 Surface water quality
5.4 Groundwater extraction
6.6 Aquatic ecosystems
6.7 Aquatic species diversity
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