A legal stoush between the Whangarei District Council and an engineering company over the failed Marsden City development has been settled but the details are confidential.

In 2015, WDC filed a civil case in the High Court to try to recoup about $8 million from companies, including civil and structural engineers Cook Costello, it says were responsible for signing off the new development's faulty infrastructure.

Cook Costello designed and oversaw the construction of the development.

The story behind the once-hyped Marsden City development, which promised 2200 homes alongside new businesses and industry, soured in April 2014 when it was revealed that sections of the waste and stormwater systems vested to WDC had failed and would cost ratepayers millions to repair.

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The unforeseen effects of acid sulphate soils were to blame, WDC said, and it now had a new process for assessing the risk from this type of soil.

In a short statement last week, WDC confirmed the resolution of proceedings between the parties which it did not name.

The High Court registry could only say the matter was between the council, Cook Costello and "others".

"The terms of the resolution are confidential as between the parties and the Whangarei District Council believes the resolution will ensure the integrity of the assets that were the subject of the proceedings in the Marsden City development,'' the council statement said.

"Inspections and works have a commencement date of 1/2/18 with works to be completed by 31/5/19," it said.

WDC refused to make any other comment on the matter.

Early last year, WDC said an extra $40,000 was to be spent replacing the 25 manholes at the botched development south of Whangarei after contractors discovered more problems while repairing the subsiding systems.

A report into the contract, presented to the WDC infrastructure committee, said the contract value had already increased by $100,000, but this had been "insufficient to deal with the extent of the issues which have developed as the contract has progressed".

The major work contributing to the overspend included the installation of the PE (polyethylene) manholes and repairing damage discovered during manhole exposure.

Other work included the formation of concrete collars around all PE/concrete connections to ensure the connection was robust and sealed, which also required additional pumping of ground water.

Contractors also found holes which needed additional excavation, backfilling and sealing.

On top of that, stub flanges in the weirs of the PE manholes would be installed to allow the stormwater system to be emptied for future inspections, and grates were needed under manhole lids for health and safety reasons.