Wastewater spilled from manholes in the lower parts of the Escort Grove roadway, causing concern for residents. Council officers were dispatched to unblock the pipelines and clean up the area affected.
Water and waste service manager Rob Green says the overflow resulted from what is believed to have been a power surge.
"A series of back-up systems are in place to ensure that incidents such as this do not occur. Unfortunately," says Rob, "those systems did not work as effectively as they should and the resulting overflow occurred."
Rob Green says the Plant was back up and running between 4:30pm and 5pm yesterday and the damaged circuit board is being fixed.
"While this was a major outage there was only a small period of time, about five minutes, when untreated waste was discharged into the river. We immediately advised Horizon's Regional Council of the issue in accordance with Council's Resource Consent."
Rob Green says a review will determine the precise sequence of events in order to better understand which systems failed and those that did not, and the extent to which Council's response to the incident could have been better.
In the meantime, Council has written to residents to apologise for any inconvenience caused, to reassure them health and safety protocols were followed and to advise them that a review is being carried out to determine the course of events and to find out why systems failed, following which the issues will be rectified.