Watercare has released an engagement report looking at the options for the future and asking for public feedback.
It has less than a decade to consult with communities, decide on an option, consent, build and have it fully operational.
The two most likely options are to bury the biosolids in another landfill or to build an incinerator to burn them.
Watercare says it could select one of those options, both options, or combine them with a “supplementary” solution.
The estimated cost is $600 million, although Watercare’s in-house biosolids expert Rob Tinholt says it’s still very early days.
“Given the scale and importance of managing Auckland’s biosolids for future generations, it is important that decisions are based on robust evidence and careful evaluation,” Tinholt told the Herald.
“Mana whenua, stakeholder and community engagement is helping inform the process by identifying the issues Aucklanders want considered as investigations continue.
“So far, we have invested around $350,000 to support engagement with mana whenua and raising awareness of the biosolids challenge across Auckland, ensuring Aucklanders have the opportunity to understand the issue and contribute to shaping long-term solutions.”
A new landfill would need a new location that would be capable of handling the quantity of biosolids produced at Māngere.
Incineration is commonly used in Europe and the United States, but not in Aotearoa. A new facility would also need to be built.
Other options that could be “supplementary” to a landfill or incinerator include emerging technologies, using for construction materials or various composting methods.
Watercare has acknowledged early consultation with communities is key.
Before releasing the latest proposal, it hosted community events, workshops, surveys and online information.
Feedback so far has stressed it must be affordable and not burden future generations with large bills.
Others said cost must not override environmental protections or long-term safety.
“The programme is currently assessing the long-term feasibility of the two core servicing approaches – landfill or incineration – along with a range of factors including technical performance, environmental impacts, operational requirements, consenting considerations, transport logistics, resilience and long-term value for Aucklanders,” Tinholt said.
“As part of that work, Watercare is undertaking detailed technical and financial assessments to understand the potential whole-of-life costs and benefits of different options over the long term.”
As for what happens to Pukeututu Island, Tinholt said once the quarried space is full, earth would be used to build up the contours of the island so it reflects the original volcanic cones.
Over the coming months, Watercare will look at global case studies for options and continue to work closely with mana whenua to ensure cultural perspectives are taken into account in decision-making.
Engagement with other communities will also continue.
Katie Bradford is a Senior Correspondent at the Herald. She has been a broadcast journalist for over 20 years and was based in the press gallery for 10 years. She specialises in politics, business and Auckland issues.