The current wastewater treatment plant at Akaroa. Photo: Supplied/Christchurch City Council
A Banks Peninsula residents' group has renewed calls to scrap council plans for a wastewater plant in the Akaroa township, following a cost blowout of more than $70 million.
Under the Christchurch City Council proposal, the existing sewage plant would be relocated and treated wastewater discharged onto farmland and native plants at Hammond Point and Robinson's Bay, instead of into the harbour.
For more than 60 years, Akaroa's sewage has been treated and discharged into the sea at the bottom of the culturally significant Takapūneke Reserve.
The new scheme was initially budgeted at $94 million, but that figure has ballooned to $167.3 million.
The council was also exploring an alternative discharge option of sending treated wastewater directly into the ocean, instead of first irrigating it through land, but this would still cost $148.7 million.
Friends of Banks Peninsula deputy chair Suky Thompson said the council's plan was flawed and she was not surprised the cost had blown out.
"Our geotechnical engineer at the [resource consent] hearings recommended that much more geotechnical assessment was needed prior to putting this whole proposal up for a consent," she said.
"Twenty million dollars of that blowout is to carry out more geotechnical work on the site proposed for the treatment plant, but we think it will still blow out further because much of the steep land which the council proposes to irrigate to saturation hasn't had any geotechnical assessment."
Thompson said the proposal did not address Akaroa's leaky pipes.
"Our concern is that the amount of wastewater going through the system is largely determined by the poor quality of these sewer pipes in Akaroa, so it's infiltrated by an enormous amount of stormwater.
"That means that at times when it's the most wet, when the land is soggy, that's when there's also the most water running through the system so then it has to be stored in enormous storage tanks and the council is planning to irrigate right through winter keeping the land at saturated level which is not suitable for the steep, slip-prone slopes of Banks Peninsula.
"In our view it's time for the council to start being more realistic about what it can afford for such a small place as Akaroa -there's less than 1000 sewer connections going into the system."
Thompson said the money would be better used overhauling the town's sewerage network. She believed the alternative option of discharging treated wastewater into the ocean would be met with more approval in Akaroa.
"It would be much less intrusive to develop, it would be much more resilient going forward, so it's about the detail it's about the treatment standard that would be put in."
Photo: SUPPLIED
The council said the ocean discharging option would see a 15-16km wastewater pipeline running on the Akaroa Harbour floor, and wastewater discharged one to two kilometres beyond the harbour heads.
"The staff update showed operational costs of the ocean outfall would be approximately $380,000 per year, compared to $625,000 per year for land irrigation. Operational and construction risks were outlined, including challenges in identifying leaks and the limited options available for repairs. Staff also repeated their understanding that this option is repugnant to mana whenua.
Council head of three waters Gavin Hutchison said even though work was underway on investigating alternatives, no recommendations on a preferred future option would be made until the government's law changes around mandatory wastewater standards for discharge to water, land and overflows were implemented and the views of mana whenua sought.
"Having this information will help further inform potential future steps for the current application process. However, regardless of what the new standards permit, we still have a duty to consult under the Local Government Act and consider cultural and community impacts of any preferred option.
"Once we have an understanding of the impacts of the new wastewater standards, and have done further work, we expect to be able to brief the elected council on a preferred option for the future scheme in early 2026."
Te Rūnanga o Ngāi Tahu declined RNZ's interview request.
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