Omakau wastewater treatment plant fix approved
The Central Otago District Council has authorised $165,000 of funding from the Emergency Event Reserve to pay for repairs to water and wastewater infrastructure at Omakau following the flooding of the Manuherekia River in July.
At the Council meeting yesterday (Wednesday 24 August 2022), councillors were briefed on the impact of the extreme rain event of 18-19 July. Record or near-record rainfall was documented at several weather stations in Central Otago.
Heavy rainfall resulted in widespread flooding, predominantly in the Māniatoto and Manuherekia areas. Water supplies in Naseby, Ranfurly, and in particular Omakau were affected, which resulted in a boil water notice for Omakau and Ophir for two weeks, which was lifted on 1 August.
The flooding also affected the oxidation ponds which were constructed in 1965, causing damage and resulting in a reduction in quality of effluent discharged to the Manuherekia River.
The two oxidation ponds, which were upgraded in 2018, were inundated with floodwater, and the security fencing that had been installed in the past 18 months was badly damaged
Assessment and repair began 20 July and the Council water team has been on site each day since then and in regular contact with the Otago Regional Council.
There was minimal damage to the pond liner with only minor patch welds required, and the plant is operational with monitoring results indicating a gradual return to normal operational service over the past three weeks,
“Given the severity of the event, we got away relatively lightly in terms of damage to the site, given the flood waters got to the top of the security fence. Once the flood waters receded and the debris was cleared there was not as much damage as we were expecting,” CODC Three Waters Director Julie Muir said.
She agreed with comments from councillors that the Council and community and the plant had “dodged a bullet”.
“However, everyone in the team was pretty upset because of the environmental implications (of the volume of untreated wastewater discharging into the river) but in an event of this size, there was not a lot we could do,” Ms Muir said.
It was agreed that there was no “quick fix”, and that the work underway to identify a new treatment site and options for discharge to land instead of to water would provide the best long-term outcome.
It was also agreed that while the communication to keep the community informed during the event had been appreciated, the Council needed to keep people updated with progress on the work being taken to develop future treatment plant location and discharge options.
Prior to this event, a workshop had been undertaken with stakeholders to identify the problems, and required outcomes of future investment for treatment of Omakau wastewater. The business case is currently being prepared which will provide detail regarding options, and a preferred way forward with associated cost estimates.
The options being considered include a combined treatment plant for Alexandra, Clyde and Omakau, as both the Alexandra and Omakau resource consents are due for renewal in the next five years. A solution, which provides treatment and discharge to meet current environmental requirements, is expected to be in the region of $30 million to $60 million.
Recent events have supported the need for this investment, and events such as this are expected to be more frequent as a consequence of climate change.
Repairs at Omakau will be completed during August. The ponds are expected to be back to normal operating conditions by the end of this month. The installation of an aerator, already programmed and funded before the flood event, will improve pond performance and discharge quality for the future.
A full report can be seen on the Council agenda by going to: http://centralotago.infocouncil.biz/
