Poor groundwater has been found in areas across Otago, particularly around Lower Clutha and in North Otago.
Otago Regional Council scientists published the council’s first comprehensive state of the environment groundwater quality report for the entire region this week.
Historical data from 54 bores, dating back in some cases more than 30 years, showed poor water quality in some areas, council policy and science strategy general manager Gwyneth Elsum said.
Groundwater is located underground, below the water table, in aquifers accessed through bores and wells, and the report found its quality varied widely across the region.
E. coli results presented the biggest concern in the findings, Ms Elsum said.
Three-quarters (75%) of monitoring bores recorded levels of E. coli above drinking water standards at some point in their monitoring history.
Most of the recordings were not persistent, but levels were regular exceeded in the Lower Taieri and Lower Waitaki areas.
If E. coli was detected above national guidelines, the council worked with health authorities to notify anyone who could be using the bore for drinking water, she said.
Though not all the bores were used for drinking water, the results were a reminder for those on private supplies to test their water regularly and take steps to prevent contamination, she said.
E. coli accounted for the majority of poor results in the Lower Waitaki and Lower Taieri, she said.
Nitrate concentrations were highest in North Otago and the Lower Clutha.
And dissolved arsenic detected primarily in the Upper Clutha, Queenstown Lakes and Central Otago areas was likely due to the schist found in those areas.
In the short term, work under way included improving consent conditions around bores.
In the medium term, the council would replace old bores with new, dedicated monitoring bores throughout the region and investigate better controls on high-risk activities through council plans, Ms Elsum said.
