Council briefing on draft wastewater strategy highlights future pressures

7 Sept, 2022

A Mangawhai Wastewater Treatment Plant Advisory Group (MAG) is helping to guide a future strategy for the growing town’s wastewater disposal.

Kaipara District Council Elected Members were briefed on the draft Master Plan Strategy for the Mangawhai Community Wastewater Scheme at the September 7 Council Briefing. An early draft was first presented to Kaipara District Council (KDC) earlier this year, outlining possible options for wastewater disposal. Since then, Council has established a Mangawhai Wastewater Advisory Group (MAG), made up of community members including representatives from Mangawhai Matters, Mangawhai Business Association, and the Golf Club, Elected Members, wastewater engineers and staff from the KDC infrastructure team.

MAG has met monthly since April 2022 to understand and discuss the possible ways forward for Mangawhai’s wastewater management. This has included looking at growth projections for the area, network upgrades and a treatment plant upgrade, and various options for disposal. Funding streams including development contributions were also discussed. MAG does not have delegations to make decisions – any decision-making is brought to Council (and subject to community consultation if applicable).

Council staff have also continued to work with engineers and technical experts on additional reports that have highlighted the pressures on the scheme. Higher than previously projected development in Mangawhai is driving an increasing organic load; and more frequent and extreme wet weather events, exacerbated by climate change, are driving an increase in the hydraulic load (peak flows). The balance tank currently under construction will buffer the peak flows, but further upgrades are needed to cater to the increasing organic load.

Council had already prepared for other upgrades to the scheme. As part of the Long Term Plan 2021-2031 $1.5 million in funding was set aside in Year 1 to develop an irrigation system to dispose of treated wastewater via the Mangawhai golf course. A total of $36.2 million had been planned across twenty years as part of the Infrastructure Strategy to cover the various upgrades anticipated.

Sue Davidson, KDC General Manager for Sustainable Growth and Investment, says the further investigations completed this year shows that the budgeted future funding needs to be increased.

“Population growth and wet weather events had been considered as part of our initial planning. The investigations completed this year shows both of these infrastructure pressures are tracking higher than predicted and we believe that what we had initially planned for is now insufficient. There is a lot more work to do before decisions are made but the preliminary

scoping completed this year is estimating we could be looking at spending up to $90.5 million in the next twenty years.

“It is important that as part of this planning stage we fully understand any potential future costs – including increasing costs due to Covid-related pressures and the inflationary environment we are working in – so that these issues are considered by the community and the Council when making any future decision on the best way forward.”

Water is currently disposed to a farm on Brown Road and the Council is planning to supplement this with disposal to the Mangawhai Golf Course, as outlined in the Long Term Plan. This remains the Council’s preferred option and is supported by MAG. Additional disposal is also being considered via wetland at Brown Road. Future disposal to the golf course and wetland is also supported by Te Uri O Hau iwi.

At the Briefing, Council directed staff to continue with the investigations. This includes having the plans independently reviewed, revising the draft Wastewater Masterplan Strategy with the information gained from the recent reports, and starting on a concept design for the golf course irrigation system. Further detailed financial analysis will also be undertaken, including looking into future debt and development contributions. This will enable staff to refine the projected costs and development contributions for the next Annual Plan or Long Term Plan. Council will continue to work alongside iwi.

“Preliminary scoping completed this year is estimating we could be looking at spending up to $90.5 million in the next twenty years.

– Sue Davidson, KDC