The report said it was "likely" intensive agriculture and winter forage crop grazing within the water capture zone of Gore District Council’s groundwater source for the town’s drinking water, known as the Coopers Wells, was a "contributor to high nitrogen concentrations".
The farming was a "plausible and avoidable source of nitrogen contributing to groundwater contamination."
Grazing of cows on winter crops had been a "repeated occurrence" and a "high-risk activity within the identified capture zone of the public supply wells".
The report, titled "Nitrogen Contamination in Southland Groundwater", includes an aerial photograph from 2023 of a field crammed with dairy cows immediately adjacent to the Coopers Wells.
The report calls for "targeted protection of the wellfield" through mapping of the water capture zone as a "drinking water protection zone" and implementation of "strengthened land-use rules or consent conditions" that should then be monitored by Gore council.
In July last year, nitrate concentrations exceeding the maximum advisory level — 11.3mg/L — were reported by Gore District Council, but no explanation given.
Prior to the report’s publication, Gore District Council had deferred to Environment Southland regarding questions about the cause of the nitrate spikes.
Environment Southland had said that the cause was undetermined and only latterly mentioned "intensive land use", but not cows.
In a response to the ODT last November, Environment Southland said its investigation into the Gore nitrate spikes was "complete and hasn’t identified a specific cause".
The statement said that the cause was "likely to be the result of intensive land use in the area" but added that "there are a lot of factors that can contribute to and mitigate nitrate reaching groundwater."
Private bore hole owners were encouraged in the statement to check and test for nitrate annually "preferably during spring or autumn when nitrate levels tend to be higher."
Responding to the Environment Southland report this week, Gore Mayor Ben Bell said the Gore District Council had taken "measures" since the nitrate spike last year to "reduce the likelihood of this occurring again".
He talked about 15-minute interval monitoring of nitrate concentration and regular updates of the results, provided on Gore’s website.
To dilute the nitrate concentration, the council had also finished building an under-river pipeline connecting its Jacobstown Well and the Coopers Well.
Mr Bell said the dilution solution was "significantly reducing the overall nitrate content".
