NZ's highest treatment for city wastewater confirmed

Published on 16 September 2021

Palmerston North City Council has confirmed the 'best practicable option' for managing, treating and discharging the city's wastewater for the next 30 to 50 years.

The selected option will see treated wastewater discharged to both land and river.

Three quarters of the time the treated wastewater will be discharged to the Manawatū River. During the remainder of the time, the discharge of wastewater reduces to the river by 75% and this highly treated wastewater is then used to irrigate crops.

We will also look at diverting a higher proportion from the river over the lifespan of the consent.

The wastewater would also have the best treatment currently available in New Zealand, just one treatment stage down from being drinkable.

Currently the city's wastewater, which is all water that goes down a pipe inside your home or business, is discharged following treatment to the Manawatū River.

Our current consents end in June 2028, however following a consent review 8 years ago Council agreed to bring forward the date for applying for new consents to June 2022. Before that date we need to apply for new consents with our regulator, Horizons Regional Council.

Best practicable option specifics to be confirmed over the next year

Our proposed future management includes discharging to the river approximately three-quarters of the time (based on river flows).

During the remainder of the time, the discharge of wastewater reduces to the river by 75% and this highly treated wastewater is used to irrigate crops. The land discharge will occur all the time when the river flow is below half median, or a flow of 37 cumecs.

City Mayor Grant Smith says Council yesterday voted to cap the amount at 760 hectares of land to give communities some certainty over the amount of land needed. This gives farming, businesses and land owners some surety for their ongoing infrastructure investments.

"We estimate that we will need 760ha of land for irrigation, including buffer zones, within 30 years – when flows are expected to be 35% greater than today. We can plan for growth without changing all the land use on day one. While we will only be discharging to the land some of the time, the irrigation area, once developed, will be 250-plus hectares larger than any existing land treatment site currently in New Zealand, and with the highest treatment. Over the next 9 months we will be able to confirm we have the right amount of land required."

Although we hope the area and type of land needed can be located within the Palmerston North city boundaries and Rangitāne rohe, there is a chance we may need to look at land outside of Palmerston North. We have involved the Horowhenua and Manawatū communities in this project over the past 2 years due to the potential of any of the options affecting their region by river, ocean, or land.

Mayor Smith says Council's preferred approach to acquiring the land will be on a 'willing buyer, willing seller' basis.

"Throughout this process, we will work closely with potentially affected landowners."

The chosen option has indicative capital costs of $426 million dollars and annual operational costs of $7million dollars. We will have a better idea of the exact costs, and impact on ratepayers once the consent application and assessment of environmental effects have been completed and lodged with Horizons' Regional Council.

Read more detail about this option.

Best practicable option was one of the highest scorings in all assessments

Council reviewed more than 800 pages of reports to come to the decision, which is the best practicable option according to the criteria in our current consent. The reports included summaries of public feedback, cost assessments, Māori values, Resource Management Act planning assessments, an assessment of the options against Council's Eco City Strategy and the multi-criteria analysis. This was undertaken earlier in the project to compare options across a range of factors such as cost, public health, environmental impact, cultural values, social and recreation values, infrastructure complexity and resilience, and the ability to provide for growth.

From the technical experts' overall BPO assessment, this was the second recommended option as the BPO. The first recommended option was full discharge to the ocean, but this was not recommended as the BPO as it is completely unacceptable to the community, and also to iwi. These views were given weight as, in determining the BPO, the Council is required to have regard to both adverse effects on the environment, including on cultural values, and take into account Part 2 of the RMA, which includes consideration of the principles of the Treaty of Waitangi.

Extensive community engagement will continue during the next stages

Over the last 3 years community and stakeholder groups in Palmerston North, Horowhenua and the wider Manawatū region have been invited to provide feedback to Council. This has included three rounds of community engagement between 2019 and 2021.

Mayor Smith says Rangitāne o Manawatū, as mana whenua in Palmerston North and part of the project's steering group, have worked closely with Council officers and elected members at both governance and technical levels of the project.

"Engagement with iwi throughout the wider Horowhenua and Manawatū region has also occurred, and significant effort has been made by iwi to incorporate their values into the options assessment and selection process. We will continue to work closely with regional iwi over the coming year to refine and confirm the details of the option and to assess the likely environmental effects as part of developing the consent application."

Council voted to agree a project partnership or governance group to establish an adaptive management strategy to define the resource consent, which would include mana whenua Rangitāne and river iwi.

Role of Three Waters on Nature Calls

The government is proposing that water be managed by four regional entities across the country, with a final government decision pending in the next few months.

Council sought legal advice about whether we should proceed with selecting an option and preparing and lodging the consent applications, given the possibility that any new consents would become the responsibility of the new organisation to implement and manage. The advice recommended we proceed as planned given that the Three Waters proposal has yet to be confirmed, and even if implemented will not override our current legal obligations.

Updates will be provided at key points of the project

Over the coming year, we will continue to provide updates about this project at naturecalls.nz

Best practicable option background

Our BPO sees us removing more treated wastewater from the Manawatū River. We will also look at diverting a higher proportion from the river over the lifespan of the consent.

The option includes discharging to the river approximately three-quarters of the time (based on river flows).

During the remainder of the time, the discharge of wastewater reduces to the river by 75% and this highly treated wastewater is then used to irrigate crops.

While '˜cut and carry' pasture has been assumed in the option proposed, the detail of the crop or crop varieties that will be grown will be clarified during the consent phase over the coming year.

The land discharge will occur all the time when the river flow is below half median, or a flow of 37 cumecs. Irrigating land at this time when soils are drier and crops are growing vigorously will ensure most of the highly treated wastewater and nutrients are beneficially used by the crop, and not lost to groundwater or overland flow. It also means the river will be better able to disperse and dilute the water when we discharge into it.

Over the next year we will be confirming the river and irrigation modelling work and carry out further river monitoring and soil testing.

The option will require soil with good drainage qualities to prevent ponding of treated wastewater. We have not yet identified specific land areas, but these will be selected on a range of factors, including facilitating efficient irrigation operation and land management, limiting the impact on sensitive environments, and minimising the number of landowners affected.

A further agreement under adaptive management was voted on, to engage other reuse and diversion options, to further divert more wastewater from the river in the future. These options could include: repairing infiltration to the city's stormwater network, encouraging more primary treatment of trade waste, developing and recharging wetlands, considering the potential of irrigating on Council reserves, golf courses and race tracks, as well as reducing domestic water use.

The final consent application will identify some of these further diversion and reuse opportunities, and others will be added over the lifespan of the consent as new technologies become available and regulations change.

An adaptive management strategy will be developed and form part of our consent application. This means Council and key stakeholders will work together throughout the development of the consent to ensure the best results for our discharge environments, and will plan to take into account new technology and other reuse and diversion of wastewater options.