In June-July 2020 we asked for feedback about six potential discharging environments
- Discharging all of the city’s treated wastewater to the Manawatū River at the current Tōtara Road Wastewater Treatment Plant discharge point. The wastewater would be treated to a higher standard than that achieved through the current wastewater treatment plant.
- Discharging treated wastewater to the Manawatū River at the current Tōtara Road Wastewater Treatment Plant location when the river is in high flow, and at a new discharge point south of Opiki Bridge when river flows are lower. Some wastewater would be applied to land when flows in the Manawatū River are at their lowest.
- Applying treated wastewater to land, with discharges to the Manawatū River in exceptional circumstances.
- Applying treated wastewater to land, with discharges to the Manawatū River when the river flow rises above intermediate levels.
- Applying some of the city’s dry weather wastewater to land, with the remainder being discharged to groundwater via high rate infiltration (soakage) through the ground surface. Further assessment will consider whether some wastewater should be discharged to the Manawatū River when the level of groundwater is very high.
- Discharging most of the city’s treated wastewater to the ocean, and applying some to land. This option would require a pipeline and other infrastructure to move the treated wastewater to a coastal discharge point.
More than 1,100 people had their say on the options and environments, with both a full river and full land discharge being the joint most popular choice.
When considering people’s top two choices they also preferred a combination or hybrid of river and land discharges.
During that feedback period, the information provided was still at an early conceptual stage.
Subsequently we ruled out discharging to groundwater as an option, as it wasn’t well liked by our community – both the land areas and the treatment levels required were significant.
Previous discharge options
A number of technical assessments and evaluation processes are being carried out to inform the Council’s decision-making process to determine the BPO. This includes a multi-criteria assessment (MCA), cultural values assessment with iwi, RMA tests and this engagement process.
Out of the MCA process completed in 2020, two of the five options were identified as low preference. These options included "discharge to land 97 per cent of the time" and "dual river and land" options.
Discharge option: All to land
Majority of treated wastewater is discharged to land, either fluvial soils or coastal sands, occurring 97 per cent of the time.
This option is dramatically different to what we currently do, which is to discharge to the Manawatū River. To apply the treated wastewater at a safe and efficient rate, approximately 2,500ha to 3,500ha of land would be required. We would likely operate a ‘cut and carry’ operation over this land, which allows us to grow and supply cut grass as a form of income during operation of the site.
When the river is exceptionally high and the land area is saturated, during heavy rainfall periods, we would continue to discharge to the river during very high flows (approximately 3 per cent of the time). This river discharge would pass through a wetland or land passage, prior to discharging to the river.
Treatment and land requirements
The volume of treated wastewater, application rates and soil conditions and the level of treatment are core elements that help us determine the total land area we require for this option. Within the large land areas, we have estimated, we need to include a buffer area that helps avoid potential effects on neighbouring properties and the environment. Effects like spray drift, groundwater contamination or discharge from overland flow occurring on neighbouring properties need to be avoided.
The treatment proposed for this option is the lowest being considered across each of the options and is like what we currently do at the wastewater treatment plant. With this process, we would not be required to remove phosphorus, which is currently done prior to discharging to the river.
A significant investment in infrastructure is required to operate this land-based system. It requires centre pivot irrigators, on-site storage lagoons and rapid infiltration basins where possible. You will also see many bails while the cut and carry operation is underway. The operation of this treatment and discharge method is a highly complex operation at the scale proposed, as it requires adaption depending on climate conditions and wastewater flows out of the treatment plant.
Potential adverse effects
The types of soils we have identified in our region for the proposed discharge are highly productive soils, which provide the right environment for crops and agricultural activities. If we were to discharge our treated wastewater, it is highly likely that these activities could not continue where we operate. At almost 3,500ha, this is a significant area of land: "the size of Palmerston North's urban boundary".
Land required for this option is significant and cannot be accommodated entirely within the Palmerston North boundary, particularly the sands areas. At this large scale, our experts have identified the potential to impact on archaeological features and groundwater sources used for supply. The impact on individual landowners and communities is also significant.
This option is least likely to support a regionalised approach or adaptation in the future to allow for rapid growth. This is because the land areas are already significant and with growth, more land would be required to continue to operate this option without having adverse effects on the environment.
This option requires significant capital investment of approximately $400 million.
Discharge option: Dual river and land
This option continues to discharge to the river with some enhanced treatment upgrades and introduces a new discharge location and ta discharge to land. During the highest flows in the river, the discharge will continue at Tōtara Road, during medium flow a new discharge will occur at Opiki (into the river) and a land area (approximately 1,000ha), will be used for discharging wastewater.
Treatment and land requirements
Plant upgrades will be required for this option, including UV treatment, however the treatment upgrades proposed are less than we have identified for Option 1 and 2. This is because the timing and location of our discharge is occurring when the river is less sensitive to algae growth.
Infrastructure is required for this option, including pipelines, storage, pump stations and centre pivot irrigators. These assets require heavy capital investment.
Potential adverse effects
This option requires significantly less land than considered than other options, however, would still be the largest land-based discharge in the country if it was to proceed (almost twice the size). With a smaller land footprint compared to the other options, the potential impacts on archaeological features, groundwater and properties may be less depending on the location, however this is still a large land footprint and the effects still need to be considered with caution.
This option also introduces treated wastewater to three locations, with lesser treatment than proposed for Option 1. The potential for adverse effects may be managed with this option, however this is still an impact the Council has identified as being adverse, given it would now impact two new locations within the region.
We’ve done a lot since then
The information that informed the 2020 feedback period came from our work up to the end of 2019, so we could get your feedback in March. That feedback period was delayed to June-July due to the nationwide Covid-19 lockdown.
Council’s experts have now moved from a conceptual level to a more detailed understanding of each option. This work included investigations to explore proposed treatment levels and applying these to each of the options to determine preliminary effects of any discharge on water quality and land-use, at desktop level.
The nature of the wetland and/or land passage components has been developed, as well as a desktop analysis of the coastal environment and where best an ocean outfall pipe could be located. Land application elements were explored at desktop level to determine how we could meet One Plan targets for nitrogen application and leaching rates, leading to a refinement of the total land areas required. We have also been testing wastewater arriving at and leaving the current plant to understand specific contaminants (such as emerging organic contaminants) and how effectively they are removed.
To understand how we might meet future requirements, we have used advanced modelling tools to determine the potential effects of treatment levels and volumes of wastewater on periphyton (plant) growth in the river. The outcomes of the modelling confirm there are limited options we can consider that will meet these targets.
This new information means we’ve been able to come back to you with a reduced shortlist of three discharge options.
We’ve stepped up our iwi engagement
During the initial stages of this project when we were still considering all potential options for treating and discharging wastewater, our city mana whenua Rangitāne were involved. While we had some initial conversations with neighbouring iwi, following confirmation of a shortlist of options, and a better understanding of the receiving environments, we are now actively engaging with iwi with interests in the potentially affected receiving environments.
We’ve worked with stakeholders to get the reduced shortlist
As part of the option selection process, we have completed a Multi-Criteria Analysis (MCA). The MCA decision tool process is often used in large-scale and complex infrastructure projects in New Zealand to assess options from a range of criteria, and has been tested in the Environment Court. This process provides a systematic way of comparing options using a range of qualitative and quantitative measures. It enables key partners and stakeholders, who are provided with a range of assessments considering technical, social, cultural and affordability issues for each of the options.
The group were able to rank options across a wide range of criteria – and that’s how we’ve ended up with the shortlist that we’re consulting on.
These are the values we considered
We’ll be asking you to rank these values on the feedback form.
Degree of public exposure to health risks in treated wastewater (including through land application or re-use options.
Degree to which the option is resilient to natural hazards and climate change and offers operational resilience.
Māori cultural values
Potential adverse effects on the mauri of natural resources, on kai moana, and on the relationship of Māori, their cultures and traditions, with ancestral lands, water, sites, waahi tapu and other taonga.
Growth and economic development
Will the option support the population and economic growth the Council forecasts for Palmerston North?
Comparative capital, operational, whole of life costs of the option, assessment of this criterion includes consideration of land acquisition costs, capital gains and product net revenue.
Social and community considerations
Significance of potential social effects based on the gravity, distributive equity, the need for land acquisition and degree of permanence of land use change, and public support for the option.
Potential adverse environmental effects on the receiving environment (including Manawatū River), particularly in relation to water quality (including the matters listed in s107 (1)(c) to (g)), soils, aquatic ecology and terrestrial ecology.
Technology and infrastructure
Degree to which the option:
- uses reliable and proven technology
- can be staged
- is able to be constructed
- can be constructed within the appropriate timeframe
- allows resource recovery/ beneficial re-use.