Its latest forecast now has the plant due to be finished by the end of September.
The Northern Advocate also reported in the same article that Kerikeri households and businesses were expected to be able to connect to the scheme by July this year.
By December last year, FNDC said this would happen in September this year, but January next year is now the latest forecast.
The plant's project delivery performance was part of an update in FNDC chief executive Shaun Davidson's report to the council's meeting last Thursday.
This showed the plant red-carded on all five project plan performance target indicators. It failed to achieve across all targets, including project completion status, the scope for the project growing, its rates of progress and costs tracking.
Andy Finch, FNDC general manager infrastructure and asset management, said performance on those indicators was not unexpected for a project of the plant's size.
The indicators and their milestones had been set up at the start of the project. There had been a lot of changes since.
Indicators presented to the meeting showed a "fairly pessimistic" view of what would be a successful project.
"I don't think this metric does it any justice," Finch told councillors.
The report said the scope of the project had expanded due to design issues because the contract had been let without "issued for construction" drawings. These are detailed design drawings integral to assessing exactly what work is to be involved in a contract.
There were also significant impacts on the project's completion schedule, from addressing health and safety compliance issues identified through project risk assessment.
Johnston said delays had meant continued trucking of some of Kerikeri's sewage to Kaikohe for processing.
They had potentially impacted on the area's water quality as people held off upgrading septic tanks in expectation of being able to go onto a reticulated wastewater system.
Development was affected, sometimes illogically, Johnston said. Residential subdivisions in the new areas to be brought into the scheme could not go ahead while those in areas outside the scheme could.
FNDC said the new plant would triple the amount of wastewater treated by the town's existing Shepherd Rd plant. In December last year, it said this plant was due to be shut down in October.
The council said the new scheme would serve all properties already connected to Kerikeri's wastewater system plus 350 new properties on septic tanks.
It will also have the capacity to serve 400 further properties and is designed for expansion to provide for further growth.