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Last updated:
08 July 2008
What is groundwater?
When rain falls on land, some water evaporates, some flows to streams and rivers and some seeps into the soil. Excess water in the soil seeps down until it reaches a level where the spaces within sediments or rocks are saturated with water. This is called the water table. Water in the saturated zone below the water table is called groundwater.
Most groundwater moves very slowly, compared to rivers and streams, because it has to flow through small openings. A rock or sediment layer that is capable of yielding useful supplies of groundwater is called an aquifer. Groundwater from aquifers can be brought to the surface by sinking bores or wells and installing a pump.
How does urbanisation increase the risk of pollution of groundwater?
Many human activities can contaminate groundwater in urban areas including;
• Chemical contamination from industry
• Leaking underground fuel storage tanks
• Leachate from rubbish tips or areas of fill
• Seepage from sewerage systems and agriculture
• Pollution from residential land uses for example the use of pesticides, fertilisers, chemicals, waste fuel and paints.
Some specific sites have been identified in urban areas where previous industrial use is known to have caused groundwater contamination. In Sydney, for example the Botany area has a long history of chemical industries and as a result parts of the groundwater in the North Botany Aquifer have been contaminated.
Some common contaminants identified in groundwater include;
• Chlorinated hydrocarbons
• Petroleum hydrocarbons
• Arsenic
• Chromium and other metals
• Nitrate
• Pathogens such as bacteria and viruses
Some of these can occur naturally in groundwater (e.g. arsenic and nitrate), but generally at much lower concentrations than those generated from human activity.
What happens to ground water once it is contaminated?
Groundwater contamination can move from the original source of contamination over a wide area or very deep underground. It is often difficult to know where the contamination has gone. Overlying soil or rock can hide the exact location of the contamination and present a substantial barrier to clean up efforts.
Contamination can persist for a long time as groundwater moves slowly and often lacks the natural biological, chemical, and physical processes that help cleanse surface water.
What are the health effects of contamination?
The risks to health will depend on the type and concentration of contaminants in the groundwater and also how often, for how long and in what ways people are exposed to the water (e.g. drinking, inhalation, or skin contact).
Often there is not enough information to assess the health risks from contaminated groundwater.
What is NSW Health's current advice?
Groundwater in urban areas should not be used for drinking or cooking where a reticulated water supply is available.
Residents in areas where contamination is likely (eg areas of previous industrial use) are also advised not to use groundwater for other domestic purposes, such as irrigation of fruit and vegetables, or use in spas and swimming pools. Should they wish to use it for these purposes the water should be regularly tested, and treated if necessary. However users should be aware that routine tests might not identify all potential contaminants.
Users should check for warnings issued by the Department of Environment and Conservation (DEC) or the Department of Natural Resources (DNR) identifying contamination of groundwater in their area. A list of contaminated sites that DEC regulates is available on a public register at
http://www.environment.nsw.gov.au/clm/searchregister.aspx
Information on groundwater quality is available on the DNR website at;
http://www.dnr.nsw.gov.au/water/water_quality.shtml
An alternative to using groundwater is to collect rainwater. A properly maintained rainwater tank can provide good quality water. In urban areas with a reticulated water supply NSW Health supports the use of rainwater for all non-drinking purposes such as garden watering and car washing. For more information on maintenance and safe use of rainwater tanks see NSW Health Rainwater Tanks brochure available at http://www.health.nsw.gov.au/pubs/r/pdf/rainwater020067.pdf.
Further information
For further health information and advice (including testing laboratories) contact the Environmental Health section of your local council or Public Health Unit.
For contact details for your Public Health Unit, look under 'NSW Department of Health' in the Telstra White Pages or http://www.health.nsw.gov.au/public-health/phus/phus.html
For further advice on bore licensing or installation and groundwater in your local area contact the Department of Natural Resources on (02) 9228 6333 or http://www.dnr.nsw.gov.au/
For further advice on groundwater contamination issues in your local area contact the Department of Environment and Conservation on 131 555.
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