Questions & Answers
- substantially reducing carbon emissions from the disposal of the city’s sludge
- substantially reducing odour emissions at the landfill associated with the disposal of sludge
- substantially reducing leachate to land and groundwater at the landfill from the disposal of sludge
- removing the risk of environmental degradation (particularly to streams) posed by failure of the existing sludge transfer pipelines between the Moa Point WWTP and Carey’s Gully
- substantially reducing the volume of material needing to be disposed of to landfill from the treatment of the city’s sludge; and
- treating odour currently periodically emitted from the existing Inlet Pump Station adjacent to Stewart Duff Drive.
What will the dried end-product be used for?
Internationally, treated biosolids are used in a range of ways, including as a soil conditioner or fertiliser, as fuel in industrial processes, and even as an additive to road paving. In order to consider these opportunities for treated biosolids from the Wellington SMF, we will be undertaking investigations and studies in partnership with iwi, technical specialists and community interest groups to identify options for biosolids reuse with consideration to environmental, cultural and public health outcomes.
The SMF has a capacity of 17,500 DS tonnes per week and could be at capacity by 2073. Do you think the per capita figure used in report is a little conservative given EU & US states use a higher value DS per capita than used in Connect Water (2021)?
Since the production of the Connect Water report in 2021, further analysis on sludge production has been undertaken to arrive at current and future sludge production estimates on which the plant has been sized. This work has been further reviewed by international experts.
What about noise pollution? How loud will it be during construction and also once the plant is up and running?
Most of the construction will occur during daytime and will be within limits set in New Zealand Standard 6803: 1999 Acoustics - Construction noise. There will be 5-10 times throughout the construction period where night works will be needed and standards may not be able to be met. A construction noise and vibration management plan will be prepared which will set out measure to minimise noise from these night-time works and will set out the process for advising local residents of upcoming noisy activities and how long these will occur for.
During operation, all noise will be with relevant district plan noise limits.
Does the facility need to mitigate hydrogen sulphide?
Yes – hydrogen sulphide is a by-product of the sludge treatment process, and specialist plant has been included in the design to treat this so that the biogas can be used as a renewable energy source.
Have serious investigations been made into through treatment and discharge to the deep waters of the Cook Strait, after consultations with iwi? At best 80% of the sludge will be dewatered and still 20% will still need to be landfilled.
All of the sludge will be treated to a high standard so that options to divert it from landfill can be explored and implemented. A wide range of options were considered for sludge management in Wellington, and the treatment and discharge to Cook Strait was not considered appropriate.
Are there alternative options to this sludge minimisation facility?
Over 25 different options were considered by a panel of national and technical experts, Wellington City Council and Wellington Water representatives, and iwi partners. Using a wide range of criteria, such as cost, environmental, social and cultural factors, a preferred option was selected. The preferred option was considered to be the best when compared to the alternative options to meet the objectives of this project.
If the sludge minimisation project goes ahead, does this mean the existing pipe to the landfill can be retired? If so, what is the expected saving per annum against the annual cost of running the sludge minimisation facility?
Once the Sludge Minimisation Facility is up and running at Moa point, those pipelines will no longer be needed. We are still developing the operating costs for the new plant but, the cost of pumping the sludge from Moa Point to Carey’s Gully and the maintenance costs of the pipeline will help offset the cost of running the Sludge Minimisation Facility.
Are the outdoor digester tanks similar to the Christchurch ones damaged by fire, still causing smell in the community?
No, the digesters are entirely different.
What water will be discharged from the new plant into the Cook Strait?
The water we remove from the sludge through the treatment process will be returned to the Moa Point Wastewater Treatment Plant so that it can be appropriately treated. No wastewater from this plant will be directly discharged to the environment. Further to this, only clean stormwater (from rooves and clean roads) will discharge to the local stormwater network.
You say 'no objectionable or offensive odour' at the neighbouring houses. Does this mean there will be odour closer to the plant?
The thermal hydrolysis, anaerobic digestion and thermal drying process is designed in a way that any odours are captured within the processing equipment and treated. As an extra measure, we are proposing to locate the processing plant within a building and capture the air from that building and treat it to a very high level.
The new sludge minimisation facility is quite different to a normal wastewater treatment plant because the sludge is kept within closed tanks and process plant. The plant is then placed inside a building, and the air from both the plant and the building is treated through a new odour treatment system. Our early consultation with the local community identified that one of the current issues is that odours are emitted from the inlet pump station when the doors are open for maintenance of the pumps. To address this, the inlet pump station will be enclosed in the new building as part of the sludge minimisation project.
Do you need to upgrade electrical reticulation, particularly the ring main unit?
We are working with Wellington Electricity to understand, as one of a number of commercial electricity consumers in the area, network upgrade requirements. One of the benefits of the Sludge Minimisation Facility is that the electricity produced from it may help defer the need to upgrade the local network for a while longer.
As to the dried waste, it cannot be used on food related commercial growing - for cultural & ethical reasons - it must be remembered the previous sludge was used in a failed project of using it as garden compost. It was toxic.
There are some restrictions on the use of biosolids for agriculture but this does not cover all agricultural activity. We will be undertaking investigations and studies in partnership with iwi, technical specialists and community interest groups to identify options for biosolids reuse with consideration to environmental, cultural and public health outcomes.
When is construction of the new facility expected to start and how long will it take?
We are working through detailed planning for construction of the plant at the moment, and expect construction to start in early 2023. We need to have the plant up and running by June 2026 in order to meet the requirements of the landfill resource consent.
What kind of geotechnical resilience has been allowed for in terms of the design (earthquake, landslide, etc)?
A natural hazards assessment has been undertaken as part of the design and consenting process to date, and specialist geotechnical and seismic engineers have undertaken analysis to confirm how best to protect the new facility from natural hazards. For example, the slopes behind the new SMF will be stabilised to prevent landslides.
Have you considered refurbishing or reusing the existing facility that will be decommissioned?
We are discussing with the Wellington City Council Landfill Operations Team whether there are any potential uses for the decommissioned facilities at Carey’s Gully.
You mentioned the end product could potentially be used as fertiliser. How does this fit with a Māori cultural perspective?
We will be undertaking investigations and studies in partnership with iwi, technical specialists and community interest groups to identify options for biosolids reuse with consideration to environmental, cultural and public health outcomes.
Can you confirm projected costs, and is this budgeted for by Wellington City Council?
Cost estimates are currently being updated for the plant and will be presented to Council in December 2022.
What's the lifespan of the new facility?
Different parts of the plant will have different 'design lives'. The overall design life of the plant is 50 years, but some parts (such as building and tank structures) are expected to have a life of 80+ years. Mechanical plant, which wears down, will have a shorter design life and will be replaced as part of a detailed asset management strategy for the new facility.
What ratio needs to be met for the dry weight sludge to be landfilled (Southern Landfill Class A)?
In general, landfills in New Zealand require sludge to be no less than 20% dry solids (80% water) so that it can be worked into the landfill by machines without them becoming stuck, or the sludge acting like a liquid I the landfill. The biosolids from the SMF will be 90% or more dry solids (10%or less moisture content) which has much greater benefits in terms of landfill operation and future potential reuse of the biosolids.
Will surplus electricity from the facility be put back into the grid?
We are considering a range of options of what to do with the electricity, including whether we put it into the grid, or use it for the Moa Point wastewater treatment plant.
Is there the possibility for the Moa Point SMF to produce ISSA (incinerated sewage sludge ash)?
No, the new SMF does not involve incineration so will not produce ISSA.
Can you tell us a bit more about the lizards and how that will be managed?
Two lizard species have been found on the site; the northern grass skink and the Ruakaka gecko. Both species are common throughout the lower North Island and are classified as ‘Not threatened’. Prior to construction, we will salvage as many lizards as practicable and relocate them to neighbouring council reserve land. We will shortly be submitting an application for a wildlife permit to the Department of Conservation to do this.
Are the Greater Wellington consents going to be notified?
Great Wellington has not yet made a decision on whether of notify the resource consent application that has been lodged for the SMF.
Were other locations considered?
Yes. An early study was undertaken to identify potential locations for the Sludge Minimisation Facility. It needs to be located in southern Wellington so that it is relatively close to the sources of the sludge – our wastewater treatment plants. There are limited site options in southern Wellington, and international experience tells us that sludge plants are best located right next to where the sludge comes from. As 95% of the sludge comes from Moa Point, it is most sensible to locate it here. The failure of the sludge transfer pipelines in 2020 has reinforced that this is the right decision – once the Sludge Minimisation Plant is up and running at Moa point, those pipelines will no longer be needed.
Wellington Airport is going to have a lot of construction going on at the same time. Has the cumulative effect of ALL construction going on in the area been considered, especially in terms of traffic?
Wellington City Council has been working closely with the airport to ensure construction SMF and airport construction activities are coordinated. The technical environmental assessments for the SMF have considered the cumulative effects during construction and operation. This has included for topics such as transport, noise and landscape and visual effects.
Will the operation of the plant affect the airport?
Wellington City Council has been working closely with the airport to ensure that the SMF will not adversely affect the operation of the airport. Specific issues include keeping with airport height restrictions and making sure the SMF buildings are finished in low reflective surfaces. In addition to the Resource Management Act process, the Civil Aviation Authority has strict standards which the SMF project will need to meet to ensure no adverse effects to the ongoing safe operation of the airport.
Will the trucks carrying dried sludge to the Southern Landfill give off odour?
One of the great benefits of the new SMF is that it produces a low odour product. We do not expect the product to produce any significant odour, but as an extra precaution we will use covered trucks to transport it from the SMF.
During the slope stabilisation process, artefacts and moa remains could possibly recovered as this area was previously used and occupied by Māori pre 1920s and therefore pre quarry, do you have any process for how this will be addressed?
An archaeological assessment has been undertaken by a professional archaeologist. The assessment concluded that, due to the highly modified nature of the site, the likelihood of archaeological artefacts being present was very low. Regardless, an accidental discovery protocol will be in place during construction setting our a process in the unlikely event that artefacts are discovered.
What happens to the sludge if the plant fails and can't process the sludge. Will it need to be trucked again?
The design includes lots of back-up systems to ensure that we can always produce a sludge product to a minimum standard that meets the landfill’s requirements.
Why are there currently no other plants like this in NZ? Does this pose a risk of lack of experienced operators?
The thermal hydrolysis plant will be the first of its kind in New Zealand, but the other aspects of the plant are already established in New Zealand. Thermal hydrolysis has been well established overseas for the last 10-15 years, mainly in Europe and North America. It is considered to be a world leading technology for treating sludge. By the time the Wellington plant is established, we expect there to be 3-4 other similar plants under construction across Australasia.
Will the new plant create jobs in the area?
Yes – Wellington City Council and our designer and constructor partners are committed to identifying and promoting employment and business opportunities in Wellington where this is possible. This is part of a broader outcomes (social procurement) plan for the project.
What impact will the Three Waters Reform have on the project?
We do not expect the reform to have a significant impact on the project, but we will be engaging with the Entity B team and the National Transition Unit to ensure this. The plant is also needed to enable solid waste minimisation reduction in Wellington, which falls outside of the scope of the three waters reform.
Who will be the operators of this SMF and what other projects do they operate in other regions or countries?
We will be selecting an operator through a procurement process so aren’t able to comment on this at this stage.
Are there penguins nesting at the site?
Ecological surveys have been undertaken and an ecological impact assessment has been completed. To date, no evidence of penguins nesting on site has been found. As a precaution though, a further survey will be undertaken prior to construction works starting on site. If nesting penguins are found, an exclusion zone will be established.
What are the main environmental benefits of the plant?
The SMF will have significant environmental benefits. These include: