Arsenic has been found in some Marlborough groundwaters at levels above the human health limit specified in the New Zealand Drinking-water Standards.
These areas include Rarangi, Wairau Valley, Riverlands and parts of the Southern Valleys or Lower Wairau Plain.
Most of the arsenic detected to date has originated from natural sources such as the mineral arsenopyrite.
Risk factors for arsenic-rich groundwater include: geological faults, wetlands and deeply buried aquifers which are oxygen deficient. A small amount is also leached from residues in historic sheep dips and landfills.
In 2003/04 Marlborough District Council commissioned Plant and Food Research (formerly HortResearch) to investigate the extent of arsenic leaching from copper-chromium-arsenic (CCA) treated vineyard support posts to groundwater. They found that arsenic was lost to the soil immediately surrounding the post but remained localised, which meant it did not travel through the soil layer into the groundwater below.
For more information, see the Plant and Food Research website.
Arsenic is routinely tested for by Marlborough District Council, and surveys are planned in new areas to see if arsenic exists at harmful levels.
If you have concerns over the level of arsenic in your groundwater, you should have it tested.
To find commercial laboratories in Marlborough, see the Yellow Pages.
Diagram: origin of arsenic in Marlborough groundwater.
The presence of high levels of arsenic in Marlborough groundwater has only been discovered as recently as 2001.