The Wellington City Council is facing a $185 million bill to deal with a looming wastewater sludge overload.
About 374,000 tonnes of sludge is processed at Moa Point treatment plant annually - a quantity which is expected to increase as the population grows.
But at the same time volumes of solid waste are projected to decrease as the council moves on waste minimisation.
This is a problem because sludge is disposed of by mixing it with solid waste at the landfill, which can be no less than a ratio of 4:1 solid waste to sludge.
The volume of sludge being produced is already close to or will soon exceed the consented ratio, so the council and Wellington Water have to come up with a new way to deal with it.
Sludge became a household name in Wellington after two high-pressure pipes running underneath Mt Albert failed in January, triggering a 24-hour trucking operation to get it to the landfill.
A team of technicians flew from Germany to fix the pipes as the first wave of the Covid-19 pandemic raged across the globe.
Wellington Water assessed 16 different options to deal with this new incoming sludge crisis, and landed on a preferred one with a price tag of $185m.
It's a two-stage solution, the first being something called a thermal hydrolysis and digestion plant.
This breaks down the sludge molecules by heat, reducing the total mass, which is easier to dry or dewater.
The second stage would be the installation of a thermal dryer.
This wouldn't eliminate the sludge but it would reduce the volume by up to 82 per cent and reduce carbon emissions by 63 per cent.
The end product would also be non-odorised and stable, which is acceptable to mana whenua and reduces risks associated with the transport of sludge for disposal.
The cost of the solution will come as somewhat of a headache for city councillors who are dealing with astronomical bills left, right and centre.
The hundreds of millions of dollars are mounting between Let's Get Wellington Moving, earthquake resilience problems, and the wider water network.
Wellington Water said in its report, to be tabled before councillors next week, that the cost included contingencies but didn't allow for inflation.
In 2018 a placeholder solution of sorts was put in the council's long term plan, which was the use of just the thermal dryer at a cost of $30m.
But between more detailed work completed since then, and updated forecasts predicting the sludge issues at the landfill are much more pressing, the solution has dramatically changed.
Wellington City councillors will consider the proposal at a strategy and policy committee meeting on Thursday.