Participate Palmy

Option 4: Treated wastewater applied to land, with some discharge to the Manawatū River

The majority of treated wastewater would be applied to land. When the Manawatū River level is high, treated wastewater would be discharged from our current discharge point at Tōtara Road. Treated wastewater would be applied to land about 60-70% of the time and discharged to the river about 30-40% of the time.

Photo shows illustration of treated wastewater applied to land, combined with some discharge to the river.

The trigger for the shift from land application to river discharge will be the flow in the Manawatū River. River discharges would only occur when flow in the river is higher than normal and, as a result, the river is less sensitive to nutrients from the treated wastewater.

This option would require between 1,250 and 2,000 ha, depending on the land. This could affect a number of people given the area required and the relatively small landholdings on the Manawatū plains.

What we'd need to install or build

  • pipes to move the treated wastewater from the treatment plant to the land application site
  • storage basin and rapid infiltration basin to buffer flows to the land application area
  • irrigation infrastructure
  • a wetland / land passage facility for the river discharge
  • upgrades to the treatment plant at Tōtara Road

The plant upgrades could vary from minor capacity upgrades to a new treatment process, depending on the nature of the soils at the land application site. We’d need to purchase or lease this land. If a site with better quality soils is selected, then the treatment plant will require less upgrading. However, costs saved may be offset by higher land acquisition or lease costs.

We’d need to ensure we can acquire enough land with the right soils for absorbing treated wastewater, but we don’t believe this is a significant concern.

Cost

  • Lifetime cost: $312-621 million
  • Potential rate increase per year: $340-730
  • Total wastewater charge per rateable unit per year: $600-1,000