On July 18 last year, the community was told not to drink the town’s tap water due to nitrate levels at the East Gore Water Treatment Plant reaching 11.4mg/L.
The maximum allowable for drinking is 11.3mg/L.
The ‘‘do not drink’’ notice was lifted on July 21, but since then Gore District Council has recorded many nitrate readings above 5mg/L, the maximum advised during pregnancy by the New Zealand College of Midwives.
The latest was in February this year, when it reached 6.76mg/L.
In a written briefing to the council, general manager for critical services Jason Domigan said dilution of water from the town’s Coopers Wells, by adding water piped from the Jacobstown Wells, had led to the water supply recording nitrate levels well below 11.3mg/L.
However, mixing water from the two sites was not enough to stop nitrate levels exceeding half the maximum at times, ‘‘which is not desirable for a community water supply,’’ he said.
In a separate dilution effort, the council has, since July 21, been pumping water from the Mataura River into the Coopers Wells using emergency powers allowed by Environment Southland.
Until December 11, the river water provided the only dilution while a pipe was being constructed to bring water from the Jacobstown Wells to the East Gore Water Treatment Plant.
The dilution using only the river water was not enough to drop nitrate levels below 5mg/L consistently.
Nitrate levels were largely above 5mg/L between mid-August and mid-November, reaching a high of 9.79mg/L on October 8.
Data provided by the council showed that, on average, 43% of water in the town’s supply now comes from Jacobstown Wells thanks to the new pipe, with the rest supplied from two Coopers Wells diluted by the river water.
However, the latest spike above 5mg/L in the drinking water supply happened after the Jacobstown pipe was hooked up.
It happened between February 12 and 26, with a peak spike of 6.76mg/L on February 25.
That month, the council had temporarily stopped pumping river water into its Coopers Wells to test undiluted nitrate levels in the wells, recording a high of 13.83mg/L in one of the wells, Mr Domigan said in his briefing.
Readings from the other Coopers Well shows a peak of 11.6mg/L on February 27.
Dilution of the Coopers Wells using the river water was then resumed — and ‘‘will continue to be used’’, Mr Domigan said.
The goal was to ‘‘keep nitrate levels as low as possible’’ and back to ‘‘well below 50%’’ of the maximum allowable.
The council was also investigating ‘‘longer-term options’’, Mr Domigan said.
On February 4, the council launched an online dashboard so people could view nitrate levels in the town’s supply and the latest reading was 4.09mg/L on May 12.
The council had not separately notified any health professionals when nitrate levels exceeded 5mg/L because the council does ‘‘not apply alternative thresholds set by external groups when determining public health messaging’’.
