Wellington Scoop

Why sewage shouldn’t be buried in the landfill

by Ali Forrest and Angela Wilson
As residents of Ōwhiro Bay and of Wellington, we are looking for an integrated approach to waste. We would like to see joined-up thinking and a regional strategy for the whole waste cycle. A forward-looking capital city must lead the way. We should change our thinking and treat waste as a resource rather than a problem to dump.

Only the less developed cities of the world are still burying sewage in landfill. We should be leading – not following 30 years behind the EU.

Ōwhiro Bay’s immediate concern has been the southern landfill extension, but intimately linked with that is the problem of sewage sludge.

In April we were pushing for the Wellington city council to pause in its pursuit of resource consent for an extension to the landfill. We could see that until the issue of sewage sludge was addressed, the application shouldn’t be made – because no reduction in waste was possible while it was required for burying sewage sludge.

We wanted the council to wait for the sludge options paper from Wellington Water before deciding on the landfill extension. So we are very pleased that this has been done.


Our community wants this process to be transparent to the public. The options paper is very light on detail and it raises a huge number of questions.

We want to see

– all the background data – including the Concept Design Report cited in the document, evaluation criteria, cost benefit references to research papers, data

– the independent review by council officers, when it’s done, and anything that comes up during the course of council deliberations.

The community should be involved in this process, not just consulted in February on the chosen option. And this consultation should not be subsumed into the general LTP consultation – it needs to be done separately or it will get lost.

What we want

The proposed option (see below) is a great improvement on burying most of the biosolids, but is only part of the picture. It still relies on dumping sewage sludge as before.

We would like to see joined-up thinking and a regional strategy for the whole waste cycle; we don’t want resources dumped. Wellington Water, the Wellington city council and the regional council need to work together.

The sludge solution will be costly whichever one is chosen. The selected option may not be fully operational for possibly 15-20 years – we hope a lot less. We don’t want to find that it is obsolete before it even starts.

Sewage sludge in the landfill was promised as a temporary measure, but it looks to be remaining for fifty years.

Currently the sewage sludge is pumped 10 kilometres to the landfill. It is then centrifuged to remove some of the water, which flows the entire distance back in the sewers. There was no reason to pump the sewage across the city other than that Ōwhiro Bay was an easier target for the environmental impact than Moa Point at the time of the decision.

The original plan was to turn the sludge to compost. This scheme was stopped in 2009 ‘for a few months’ while new technologies were developed. The entire plant capability is now moth-balled on site.

We want the landfill to be limited, not expanded, and we want a end to burying sewage in the landfill. We want the South Coast to be celebrated and protected. The options paper perpetuates systems failures and does not address basic needs. The landfill remains as a cemetery for sewage sludge.

This is a hugely important decision for Wellington and one that we think will show whether Wellington is a truly forward-looking capital city that the rest of the country can use as a benchmark.

This is part of a presentation made yesterday to the Wellington City Council on behalf of the Owhiro Bay Residents Association.

Options from WCC
Wellington Water Limited identified and assessed 16 options. Eight of these were based at Carey’s Gully (the Southern Landfill) and eight at Moa Point. A review team with representatives from WWL, the Council, Mana Whenua, local, international and technical experts assessed these options against agreed selection criteria that reflected the Council’s aspirations.

The preferred option is a thermal hydrolysis and digestion plant with a thermal dryer located at Moa Point.

Officers propose to present this proposal and costs alongside other investment priorities for City Councillors to consider during the Long Term Plan process.

The preferred option does not eliminate sludge, however it does stabilise and greatly reduce the volume (by up to 80%). This reduction would enable residual sludge waste to be efficiently transported to disposal facilities other than the Southern landfill.

Sludge minimisation is essential if the City is to meet its waste minimisation and zero carbon aspirations. It is intrinsically linked to the future of the Southern Landfill, which must remain operational in order to dispose of sludge.

WWL’s advice delivers a two stage sludge management solution that:
•Reduces the volume of sludge disposed of at the landfill;
•Enables sludge disposal to be de-coupled from the landfill in the future;
•Significantly reduces the carbon emissions from sludge processing and disposal;
•Minimises odour generation; and
•Increases the resilience of the overall sludge management process.

The cost estimate is $185m plus operating costs. This is a higher level of investment for the Council, and in accordance with that level, officers propose to commission an independent review of the option selection process and estimates.

These are extracts from a paper presented yesterday to the Wellington City Council.


  1. Eugene Doyle, 23. October 2020, 21:14

    Very heartening to see such a positive response from Councillors to the Owhiro submission this week. Councillors Rush and Foon have been also very active in engaging with citizen groups across the city and that’s really appreciated. WCC and Wellington Water are both committed to sharing full documentation on the Sludge options … so great stuff, Wellington.

  2. Selwyn, 23. October 2020, 23:36

    Thanks Ali and Angela for your considered arguments. They must be a serious disruption to more of the same broken promises.