The Mangauika Stream’s backwash pond showing the desludging process.
A discharge into the Mangauika Stream near Pirongia, which supplies treated drinking water to Te Awamutu and Pirongia, has copped Waipā District Council a formal warning from Waikato Regional Council.
The stream, which arises from Mount Pirongia and flows into the Waipā River, is downstream from the council’s Te Tahi Water Treatment Plant.
On May 18, the backwash discharge flow rate exceeded the regional council’s resource consent limit for more than three hours.
Water Services manager Martin Mould told the Service Committee this week the non-compliance was probably caused by the draining and desludging of the backwash pond the previous day.
When the alarm went off about midday on May 18, the duty operator stopped the flow, notified the regional council and prepared an incident report.
All discharge valves from the backwash pond had been shut down but flow rates continued. An inspection of the backwash pond chamber found an open valve in the scour drain.
The flow rates exceeded the consented limit of 8.7 litres per second and reached a peak flow rate of 12.96 litres per second during the incident.
Once that valve was turned off, the flow into the stream stopped.
Readings taken at the discharge spot and downstream showed no evidence of any sludge discharges.
The valve handle was removed on May 24 to prevent any other accidental opening, said Mould.
Councillor Susan O’Regan said she was concerned it took so long for elected representatives to find out. The first she knew about it was when the Service Committee agenda was published.
“With something as crucial as water supply, we need some really clear assurances,” she said, that there would not be other instances.
The Pirongia reservoir was opened on the Maungauika Stream in 1914.
The stream is a water quality and ecology site. It is hard-bottomed with the stream bed consisting of cobbles and bounders while the predominant vegetation upstream is indigenous forest. The stream passes through dense native forest with no stock access and good riparian cover.
