By Hayley Gastmeier
A block of Greytown land has been found to have soil arsenic levels four times that of the national health standard.
The section, on the corner of Mole St and Wood St, falls under an area of land earmarked for housing development.
An arsenic reading of 71mg/kg was uncovered at the site — the soil contaminant standard for health at rural residential and lifestyle blocks is 17mg/kg.
South Wairarapa District Council (SWDC) is in the process of forming a future development area (FDA) in Greytown as part of its combined district plan, with the potential to provide between 300 to 600 new residential lots.
The FDA encompasses land between Kuratawhiti St and Wood St, and Mole St and West St — about 35ha, which is in multiple ownership.
Soil testing was carried out at each of the blocks, as well as at the old Tate’s Orchard site at Kuratawhiti St, which the owners are hoping to subdivide.
Concentration levels exceed the national standards at both the Mole St and Wood St corner, and at the former Tate’s Orchard, where arsenic levels reached 27mg/kg.
At each site, a composite sample consisted of 20 subsamples, which were taken in a zig-zag pattern to a depth of 15cm.
EcoAgriLogic director Esther Dijkstra said the arsenic levels uncovered posed “no immediate risk to public health”.
But it was an issue that “couldn’t be ignored”.
With contamination levels breaching national environmental standards, the land was not able to be subdivided.
“Before housing can go on those particular blocks, remediation will need to be done.”
Mixing the soil was one possible way to reduce the toxin concentration.
Ms Dijkstra said at the site boasting 71mg/kg of arsenic, one option was to refrain from building houses on it and instead develop it into a public park.
Recreational areas, such as public areas with shrubs and seats, and dog parks, could be created on land with a maximum arsenic concentration of 80mg/kg.
The soil just had to be grassed.
More investigation was needed to determine whether mixing soil with 71mg/kg arsenic would provide adequate remediation to reduce the levels to standard.
Removing the top 15cm of soil and replacing it was another option.
“But the underlying layer would still be too high (at 22mg/kg) so you’d have to do some mixing as well.”
Ms Dijkstra said arsenic clung to soil particles, and eating unwashed vegetables grown in contaminated soil was harmful to humans.
As arsenic was not water soluble, however, it was generally safe to eat the vegetables, providing they were washed and peeled.
According to the Ministry of Health, arsenic is a substance found naturally in rock, often near gold deposits.
In the past, it has been used to kill insects that attack animals, timber, vegetables and fruit.
It said sites that may have been historically contaminated with arsenic include sheep dips, timber treatment yards, agricultural land or old orchards treated with arsenical pesticides and scrap yards.