The Otago Regional Council (ORC) science team presented a comprehensive State of the Environment (SOE) groundwater quality report for the entire Otago region to a meeting of the Data and Information Committee today.

The report provides baseline information on a region-wide scale about the state of groundwater in Otago. It combines data and analysis from 54 bores since the start of monitoring, dating back in some cases over thirty years. ORC monitors groundwater quarterly for a number of contaminants, including E. coli, arsenic, and nitrates.

Groundwater is located underground, below the water table. It accumulates in aquifers, which are layers of material that can transmit a significant amount of water. Groundwater is accessed via bores and wells.

General Manager Strategy, Policy and Science Gwyneth Elsum said the report found poor results in a number of areas across Otago.

“The results for groundwater quality vary widely across Otago, with degraded water quality particularly in parts of the Lower Clutha and North Otago areas, and better results for the Upper Clutha and Queenstown Lakes areas.

“The types of water quality issues also vary within the region, with E. coli accounting for the majority of poor results in the Lower Waitaki and Lower Taieri, nitrate concentrations being highest in North Otago and the Lower Clutha, and dissolved arsenic detected primarily in the Upper Clutha, Queenstown Lakes, and Central Otago areas – likely derived from schist in the underlying geology.”

Ms Elsum said E. coli results were the biggest concern in the overall findings.

“A majority of the monitoring bores – 75% – recorded elevated levels of E. coli above drinking water standards at some point in their monitoring history. While most of these recordings were not persistent, regular exceedances were found at bores in the Lower Taieri and Lower Waitaki areas.

“Not all of these bores are used for drinking water – with some used for monitoring, irrigation, and farm use. However, this consolidated overview of groundwater quality – the first of its kind for Otago – is a pertinent reminder that those on private drinking water supplies should test their bore water regularly and take steps to keep their bore head secure from potential contamination,” Ms Elsum said.

“When E. coli is detected at a monitoring site above national guidelines, ORC works with health authorities to notify anyone who may be using the bore for drinking water.”

The SOE groundwater data and analysis provide a good foundation for ORC to benchmark changes in future, and to direct the efforts necessary to address groundwater quality issues, Ms Elsum said.

“Having consolidated groundwater information on a regional scale means we can now make informed recommendations about how we address groundwater quality issues in Otago, and work with health authorities and local councils to provide public awareness of the responsibilities involved with private bores.”

ORC plans to increase its communications to remind and educate the community on the importance of maintaining a secure bore head to prevent contaminants entering groundwater.

“ORC has a number of workstreams underway to address issues raised by the report. In the short-term, these include improving consent conditions around bore security and ramping up education work alongside local councils and health authorities. In the medium-term, ORC will be replacing old SOE bores with new, dedicated monitoring bores at key sites throughout the region and looking at ways to strengthen controls on high-risk activities through the development of the Land and Water Regional Plan,” Ms Elsum said.

The report can be viewed in the Data and Information Committee agenda (p.432): https://www.orc.govt.nz/media/9640/agenda-daic-20210310.pdf

Advice for bore owners can be found in this ORC brochure: https://www.orc.govt.nz/media/5634/bore-brochure.pdf

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