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 periods.

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.

General Manager, Sue Davidson, says the beauty of the proposed system is that it is modular, which means the Council can keep adding to the intake. In future the tank could be repurposed as a treatment tank to maintain the treatment capacity as demand increases.

“As Mangawhai continues to grow, we would have the option of converting the balance tank to a processing tank,” says Sue.

The 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 $5.1 million.

Mayor Dr Jason Smith says the balance tank is a necessary part of the wastewater system.

“This balance tank has been planned for some time,” says Mayor Smith. We’ve been waiting until we needed the additional capacity before we built it. That time has now arrived.”

The Council has recently developed a model of the wastewater network so growth scenarios can be simulated and plan and prioritise interventions within the network. Council is also finalizing a long term strategy for the overall scheme (which includes the 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, the Council is also investigating the expansion of the disposal systems by using the treated effluent on the Mangawhai golf course. A high-level design and rough order of cost have been completed and are available on the Council website. The intention is to continue with further investigation in 2022.

Ultimately, the strategy will place the Council in a better position when the Three Waters initiative is introduced.

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

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