New wastewater balancing tank to expand Mangawhai's capacity

Kaipara District Council will spend $5m on a new balancing tank and inlet works at the Mangawhai wastewater treatment plant. Photo / Tania Whyte

A new balance tank and inlet works are to be installed at the Mangawhai wastewater treatment plant to expand the existing hydraulic capacity during the peak summer period.

The new module will expand the intake capacity of the plant, operating as an overflow tank during major peak flows events and general storm events. This added system is part of the planned expansion of the wastewater scheme in response to the growth of Mangawhai.

In future, the tank could be repurposed as a treatment tank to maintain the treatment capacity as demand increases.

Kaipara District Council had initially budgeted $3.1 million for the balance tank in the Long Term Plan, based on a high-level design.

Through the tendering process cost estimates were refined, and upon review of the high-level design there was also an increase to the original scope of works, to enable a fully functioning tank. The cost is now expected to be around $5.1m.

Mayor Jason Smith said the balance tank was a necessary part of the wastewater system.

"This balance tank has been planned for some time. We've been waiting until we needed the additional capacity before we built it. That time has now arrived."

KDC has recently developed a model of the wastewater network so growth scenarios can be simulated and plan and prioritise interventions within the network.

It is also finalising a long-term strategy for the overall scheme, including network, treatment plant and disposal area, outlining the sequence of steps needed to continue to increase the capacity of the scheme.

As part of this strategy, KDC is also investigating the expansion of the disposal systems by using the treated effluent on the Mangawhai golf course. A design and rough order of cost have been completed and details are available on the KDC website.

The balance tank will be funded by growth, through development contributions, and partly by current users, though loan and depreciation reserves.