Wellington City Council has agreed to borrow up to $16 million to fund repairs to the burst sewer pipes within the Mount Albert tunnel.
Both pipes failed in mid-January, and trucks have been transporting sludge from the Moa Point treatment facility to the landfill ever since.
A solution to the problem was found, with a German manufacturer designing a polyester liner which is then pulled through the pipeline.
Engineers from Germany were expected to arrive in April, but border controls as a result of Covid-19 delayed their arrival.
All five engineers arrived on Wednesday evening, and will be held in quarantine in Auckland for 14 days, before they are moved down to Wellington to assist with the insertion of the liner.
Updated figures from Wellington Water Limited show the cost of the repairs is forecasted to be between $4 million and $5 million.
On top of this, the cost of the existing solution - the transporting of the sludge via truck from the facility to the landfill - is expected to be between $8.7 million and $11.1 million.
That is provided the installation is completed by mid- to late-May, and if not, the cost of the transportation will be around $650,000 per week.
At an Emergency Council meeting on Thursday afternoon, via Zoom, councillors agreed to funding the repairs, which is to be raised through borrowing.
In the meeting agenda, it stated there was no room in the Council's current budget to fund the repairs. It pointed to previous water pipe problems earlier on that removed any flexibility.
"These costs are unbudgeted and cannot be funded through rates", the report said. "Any ability to reprioritise budgets was effectively subsumed by a separate sewer failure on the corner on the corner of Willis and Dixon Streets in December 2019."
The portfolio leader for 3 Waters infrastructure, Councillor Sean Rush, said he had spoken to Wellington Water to see what could be done in terms of using all the sludge in some positive way.
"Wellington Water will be coming back to us in September," he said, "to show us whatever options might be available, and any particular opportunities we can turn this sludge into resource, maybe make some electricity out of it, or fertiliser or others."