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Groundwater quality

There are around 200 groundwater aquifers in New Zealand. The most extensive aquifers are shallow unconfined sand and gravel sediments. These aquifers contain relatively young, well-oxygenated and fast-flowing groundwater. The mineral content of groundwater in these aquifers is typically low but the shallow water table makes them vulnerable to pollutants such as nutrients and bacteria from land use.

About 1100 groundwater sites are monitored primarily by regional councils but also by the Institute of Geological and Nuclear Sciences. These wells or bores are typically sampled four times a year. The average well is about 20 metres deep, with a quarter of all monitoring wells less than 9 metres deep and another quarter deeper than 45 metres.

Sampling is generally undertaken in accordance with the national protocol for state of the environment groundwater sampling in New Zealand.

Environmental indicator

To report on groundwater quality, the following are measured:

While nitrate and bacteria (E. coli) concentrations are perhaps the most important indicators of the impact of land use on groundwater quality in New Zealand, many other additional measurements are made. These include pH, total dissolved solids, pesticides and some metals (eg, arsenic and iron).

Did you know?

  • The underground areas in which groundwater collects are known as aquifers.
  • In New Zealand, the largest aquifers are shallow porous gravels that occupy old river flood plains. Examples include the Heretaunga Plains in Hawke’s Bay and the Wairarapa, Manawatū, Canterbury and Southland Plains.
  • Other forms of aquifers include the fractured basalts of the Auckland region and the Coromandel Peninsula’s coastal sand aquifers.

 

Information on the limitations of the groundwater quality indicator.

 

This information has come from the latest state of the environment report, Environment New Zealand 2007.

 

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Last updated: December 2007