"If the tank is full, the overflow goes into the line and goes to the UV channel for treatment."
The UV kills the bacteria before it is discharged into the Raumanga Stream.
Kandori said if the tank is not full, the water in the storage tank will flow down the lines to the district's main wastewater treatment plant.
The site will need to be regrassed once the weather improves and the ground dries out.
The boundary fences have become a regular sight for motorists travelling in and out of the city for the past nine months.
Downer, which has the contract for the council's wastewater project at Tarewa Park, has been contracted for the $17 million upgrade to the SH1 and Tarewa Rd intersection.
NZ Transport Agency senior manager project delivery Chris Hunt said the fencing will be repositioned to outline the construction site, machinery storage area and site office for the road upgrades.
"The team is working with WDC to open up as much of the park as possible while keeping the community safe."