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.
This option would see all the wastewater from our homes and businesses being treated at our treatment plant and then piped to the coast before being discharged via a 2km ocean outfall off the Horowhenua/Manawatū Coast in the South Taranaki Bight.
Ocean discharge are the most common type of wastewater discharge in New Zealand, which means the impacts and consenting requirements are well understood.
An ocean outfall pipe takes the treated wastewater more than 2km off the coast, with the final section comprising a diffuser pipe with multiple outlet ports located around 20m deep to disperse the wastewater into the ocean.
We would carefully consider recreation values when selecting the location of the outfall pipe.
We’d ensure the treatment process for our wastewater meets guidelines for ocean water quality.
As we are at least 30km from the coast, this option would require significant investment in pipes and pump stations to move treated wastewater to the coast.
This option has high upfront costs with us needing to construct pump stations and a pipeline to take wastewater from our treatment plant to the ocean. The operational costs would be lower than the other options.
This option would cost $343 million in capital costs and $5 million per year in operation and maintenance costs (based on today's costs).
Climate change means we need to factor in sea level rise, warming temperatures and coastal erosion. We’d mitigate these measures as much as possible in the design.
This option best aligns with our project objectives in respect to growth as it could accommodate higher population and business growth than we’ve predicted.
We could also let other councils use the pipe to discharge as well, meaning this could become a regional solution.
- We know that many members of the Horowhenua and Manawatū communities do not want a treated wastewater discharge direct to the ocean. People may refrain from recreational activities in the ocean as a result.
- Some community members may also restrict their recreation and food gathering activity as a result of the discharge.
- The ocean is a significant taonga (treasure) for iwi and iwi and hapu in Manawatū and Horowhenua have indicated to us that this is not an acceptable option to them.
- The discharge of treated wastewater could negatively impact the mauri (life force) of the ocean, the ability to harvest kaimoana and impact on the mana of iwi, who are kaitiaki (guardians) of the ocean.
- We’d need to manage the construction carefully so it doesn’t impact sensitive environments, however it could also result in us being able to restore some dunes.
- We’d need to build a significant pipe network to get the treated wastewater from our treatment plant, to the sea. This would be expensive to construct due to the costs of the pump stations, pipeline and ocean outfall.