Participate Palmy

Discharge option 2

Hybrid discharge between land (55%) and the Manawatū River (45%).

All options for treating and discharging our wastewater are still under consideration. The three options we are presenting during this feedback period appear to score the highest across a range of criteria and values.

Wastewater from your homes and businesses would be treated to a slightly higher standard than currently and then discharged onto land 55% of the time and into the Manawatū River the remainder of the time.

The discharge to land would be over our warmer months when river levels are lower. We’d discharge to the river when the river levels are higher – typically over winter.

While there was strong support for a full land discharge during the 2020 engagement phase, the land area required was bigger than Palmy’s urban footprint – making this unaffordable and requiring large amounts of productive land.

This option would still need huge amounts of land – roughly 1740 hectares – making it by far the biggest land discharge in New Zealand. The land area includes large buffer areas so the wastewater wouldn’t run into streams or nearby water sources.

We’d be looking at alluvial land closer to Palmerston North for the land discharge. This is land near, but not next to, rivers. This type of land is silty and drains well. We’ve investigated land closer to the coast, but that’s not our preferred site because of the cost of this land and extra infrastructure required to treat and move wastewater from our plant to the coast.

Treatment

The wastewater would be treated to a higher standard than it currently is, but not as high as if we were discharging primarily to the river like in Option 1.

We’d enhance our removal of suspended solids and other contaminants, using biological treatment rather than chemical methods, as well as continuous clarification.

The discharge to the river would flow through a wetland or land passage before entering the waterway.

Some nutrients in wastewater that are applied to land are beneficial as they promote plant growth, which can earn an income. New innovative technology which uses less energy will be considered.

We’d be able to further improve treatment over time by investing in further treatment to improve wastewater quality.

Construction

We’d still use most of our existing treatment plant, but it would need upgrades to meet the new treatment levels, and to cope with a growing population.

We’d build a wetland and land passage for the treated water to flow through before entering the river.

We’d also need to build a pipe network to the land discharge site, invest in storage and irrigation equipment, and establish the site for crop growth.

Climate change

We need to factor in climate change for this option, as we are expecting there will be an increase in the intensity and occurrence of heavy rainfall events. This can impact the land based discharge due to the lands ability to absorb treated wastewater immediately after these events. This could mean we may need to discharge to the river more after these events. We’d attempt to mitigate this as much as possible during the design.

Costs

This option has high upfront costs because of the need to buy large amounts of land, and construct pipelines from our treatment plant to the irrigation area. We’d also need to invest in storage and irrigation equipment.

This option would also have high operational costs associated with the treatment for the river discharge, and staffing needed for maintenance of the land irrigation area and managing the land use.

This option would cost $260 million in capital costs and $5 million per annum for operation and maintenance.

Regional growth

We don’t think this option would accommodate other councils' wastewater in the future because of the constraints around acquiring even larger areas of land.

Trade-offs

  • This will require significant areas of land, and purchasing or leasing this would affect a significant number of people.
  • The kind of land needed for wastewater discharge is well draining soils, which means we’d be requiring land that is ideal for farming and food production.
  • There is no legislative guide to help us determine the long-term impacts of discharging onto land for up to 35 years (a potential maximum consent period).
  • We’d also still need to do more investigation into the cultural and archeological features of the land area – but we believe we can mitigate any potential effects.
  • We know many members of our community and our neighbours in Horowhenua do not want treated wastewater in the Manawatū River. People may refrain from recreational activities in the river as a result.
  • The discharge of even well treated wastewater during periods of high flow would negatively impact the mauri (life force) of the river and impact the mana of iwi, who are kaitiaki (guardians) of the river.
  • Given the very large land area required, it would be difficult to avoid discharging to land that does not hold significant cultural value for Māori.