Seaview Wastewater Treatment Plant
The Seaview Wastewater Treatment Plant serves a population of about 160,000 in Upper Hutt, Lower Hutt and Wainuiomata. The wastewater is treated or cleaned through a series of screens, tanks, bioreactors, clarifiers and ultraviolet treatments before being discharged into the open sea near near Pencarrow Head / Te Raeakiaki where it is quickly diluted.
We will undertake planned maintenance on the thermal sludge dryer between Monday 20 April and Wednesday 29 April 2026 (eight days plus two days contingency).
For these works, the dryer will be shut down and the wet sludge that the dryer normally processes will be transported to the Silverstream Landfill. This increases the risk of odour in the community during maintenance period.
Wellington Water understands the importance of managing odour risks for the community. We are putting mitigations in place to reduce the impact of odour including using on-site odour neutralisers, wind protections when loading sludge, and airtight bins and wrapped trucks to transport the sludge. We will also closely monitor odour throughout these works.
Renewing components of the dryer is important for the ongoing reliability and functioning of the dryer and the plant. Thank you for your understanding and patience while this vital work is completed.
How is odour neutralised at the plant?
On-site odour neutraliser equipment sprays a safe chemical mix into the air to neutralise odours.
How does Seaview monitor odour?
On-site and community-located odour monitors measure hydrogen sulphide (H2S) levels. You can learn more and view the odour monitors.
What does the dryer do?
The dryer is a critical part of the biological wastewater treatment process at the Seaview plant. It dries out ‘sludge’, a by-product of the treatment process, so there is less volume to dispose of. Each day it reduces 50 tonnes of wet sludge to 12 tonnes of dry sludge which is transported to the Silverstream Landill.
When will the dryer be replaced?
Installed in 2001, the current dryer is reaching the end of its mechanical life. Replacing it is one of several major projects underway to upgrade and renew equipment at the Seaview plant. Construction to replace the dryer commenced in February 2026, and two new dryers are expected to be operational by December 2027. Find out more about this important project. In the meantime, we are working every day to keep the current dryer functioning reliably until the new dryers are ready to use.
Enquiries
Enquiries about this work can be made by emailing community@wellingtonwater.co.nz or call 04 912 4400.
Thermal sludge dryer maintenance updates
Update 1
As notified last week, planned maintenance at the Seaview Wastewater Treatment Plant is underway that may temporarily increase the level of odour in the community over the next 8–10 days.
Here’s the key information about the work underway:
- We are doing maintenance on the thermal sludge dryer – a critical part of the treatment process at Seaview.
- To complete this important maintenance, the dryer has been shut down, and we will transport the wet sludge the dryer normally processes to the Silverstream Landfill.
- This work is being done between Monday 20 April and Wednesday 29 April.
- There is an increased risk of odour, but we have a range of measures in place to manage this and reduce the impact on you.
Thank you for your understanding and patience.
If you have any questions or want to get in touch, please email customer.notifications@wellingtonwater.co.nz or call 04 912 4400.
Plan
We will undertake planned maintenance on the thermal sludge dryer at the Seaview Wastewater Treatment Plant between Monday 20 April and Wednesday 29 April 2026 (eight days plus two contingency days).
Renewing components of the dryer, which is a key part of the wastewater treatment process, is important for the ongoing reliability and functioning of the dryer and the plant.
This work will involve a shutdown of the dryer, and transportation of wet sludge to the Silverstream Landfill.
This will increase the risk of odour in the community, while the maintenance work is completed.
Mitigations to reduce the impact of odour on the community include on-site odour neutralisers, wind protections when loading sludge, and airtight bins and wrapped trucks to transport the sludge.
We will also undertake extensive odour monitoring.
For further information visit our website at www.wellingtonwater.co.nz/seaview-wastewater-treatment-plant.
If your questions aren’t answered there, please email community@wellingtonwater.co.nz or call 04 912 4400.
Thank you for your understanding and patience while this vital work is completed.
Odour level indicators
The level of odour experienced by the community is influenced by many internal and external factors.
With all these variables, odour can't be forecast with a high level of confidence.
What we can do is monitor the internal factors at the plant which can give an indication of possible odour, and communicate these clearly.
Odour monitors
We've installed odour monitors within the plant boundary and in the community, to capture levels of Hydrogen Sulphide (H2S). You can learn more and view them here.
The health and balance of the plant
Seaview Wastewater Treatment Plant uses a biological process to help treat wastewater, which we work to keep healthy and balanced. This process is complex, with a number of factors. Two of these are Mixed Liquor Suspended Solids and Dissolved Oxygen levels. We use these to help give an insight into how the biological process is managed. We'll update these every month in the graphs below, where green indicates the standard target range for these factors at Seaview Wastewater Treatment Plant. Please note that these ranges are not the same at every treatment plant.
When they are within or close to the target range, it is a good indication that we can expect odour to be at a minimum, unless there is an operational issue at the plant. However, some external factors (i.e. a weather event impacting the flow of wastewater into the plant) may require the team to make the levels higher or lower in order to keep the biological process balanced and healthy.
Plant maintenance and operations
Seaview is an aging plant, with routine operations and maintenance occurring every day, and unplanned urgent maintenance commonly needed to address issues as they crop up. Major project work is intermittent as we continue to address odour and work to upgrade the dryer.
All of these can affect the level of odour experienced by the community, so we work to keep people as up-to-date as possible with all the plant's maintenance and operations. We send notifications to our Interested Parties List, which you can sign up to by emailing customer.notifications@wellingtonwater.co.nz
We also update this page, and our Facebook page with the latest information.
Join the Seaview mailing list
Sign up if you want to receive notifications and updates about the plant - email customer.notifications@wellingtonwater.co.nz
Seaview Newsletter
Find more information about the Seaview Wastewater Treatment Plant activity and projects
Odour Project
Learn more about the ongoing works to reduce odour at Seaview Wastewater Treatment Plant
Odour monitors
Check out the Seaview odour monitors and learn more about odour here.
Making a complaint
If you have a complaint about Wellington Water directly, please call 04 912 4470 or email customer@wellingtonwater.co.nz to access our free complaints process.
After hours, please contact the Hutt City Council Call Centre on 04 570 6666 / 0800 488 824.
Greater Wellington Regional Council is the regulatory agency for reporting airborne discharges 0800 496 734.
Complaints to the Seaview Wastewater Treatment plant can be sent to the following contact details:
First point of contact: Veolia Duty Manager - Call 0800 928 371.
Veolia's Duty Manager contact number operates 24/7 as such complaints can be directly forwarded to them especially if the complaint is urgent and/or happened after office hours.
When a complaint is received, the following information will be recorded:
- Name
- Contact details of the customer
- Nature of the complaint
- Date and time
- Location
Complaints shall be actioned within 24 hours upon receipt and the records being written to the plant's operational incident log. Odour and/or wastewater discharge complaints will be forwarded to the regional council.
Plant performance
Current status: Non-compliant
Period: February 2026
Commentary:
Effluent quality was non‑compliant for faecal coliforms against both the 90‑day geomean and the 80th percentile parameters. Suspended solids are non-compliant on the 80th percentile. Biochemical oxygen demand is compliant with consent parameters.
Discharges:
There were two unauthorised discharges in February, the first on 14 February due to the UV system failure conveying to the coastal marine area (CMA). The 16 February discharge, to both the Waiwhetū Stream and CMA, was during a region-wide storm
event causing brief power outage to the UV system.
Odour Complaints
There was one odour complaint received in February. This was deemed offensive and objectionable by GWRC.
Items of significance:
Effluent non-compliance: There has been notable improvement to suspended solids during February with daily results now consistently within consent parameters. However, faecal coliform removal is proving more challenging with inconsistent daily
results affecting the parameter averages and delaying a trend towards compliance.
Please Explain letters: Five PX letters received from GWRC for prior events. We will respond by the notified due dates.
Odour Treatment Project
The new milliscreen odour treatment system was fully commissioned in December and main project works completed.
What’s coming up:
- Installation of the final community odour monitor.
- Independent assessment of the effectiveness of the Odour Control Project – Stages 1 and 2
Read all the Seaview wastewater treatment plant monthly performance reports
Resource consents
WGN050359 [39668] Discharge Treated Wastewater to Coastal Marine Area (Seaview WWTP)
WGN050359 [24539] Discharge Treated Wastewater to Coastal Marine Area (Seaview WWTP)
WGN120142 [31740] Construction to Coastal Marine Area Maintenance (Seaview WWTP)
WGN120142 [33406] Discharge of Treated WW to Fresh Water Wet Weather (Seaview WWTP)
WGN120142 [33407] Discharge of Treated WW to Coastal Marine Area Maintenance (Seaview WWTP)
WGN120142 [33408] Discharge Treated Wastewater to Stream (Seaview WWTP)
WGN930193 [1] Contaminants Discharge to Air Outfall Structure (Seaview WWTP)
WGN930193 [2] Contaminants Discharge to Air Venting Structure (Seaview WWTP)
WGN950162 [1] Contaminants Discharge to Air WWTP (Seaview WWTP)
WGN930194 Land Occupation by Outfall Pipeline and Structures (Seaview WWTP)
Compliance reports
Seaview Wastewater Treatment Plant - 2021 2022 Compliance Report
Seaview Wastewater Treatment Plant - Consent Compliance Report 2022 - 2023
Seaview Wastewater Treatment Plant - Consent Compliance Report 2023 - 2024
Resource consent reports
Annual Reports:
Seaview Wastewater Treatment Plant Annual Resource Consents Report 2024/25
Seaview Wastewater Treatment Plant Annual Resource Consents Report 2023-24
Seaview Wastewater Treatment Plant Annual Resource Consents Report 2022/ 23
Seaview Wastewater Treatment Plant Annual Resource Consents Report 2021/2022
Seaview Wastewater Treatment Plant Annual Resource Consents Report 2020/2021
Seaview Wastewater Treatment Plant and HCC/UHCC Trunk Main Annual Resource Consents Report 2019/2020
Quarterly Reports:
Seaview Wastewater Treatment Plant - July - September 2025 - Quarterly Resource Consents Report
Seaview Wastewater Treatment Plant - January - March 2025 - Quarterly Resource Consents Report
Seaview Wastewater Treatment Plant October - December 2024 - Quarterly Resource Consents Report
Seaview Wastewater Treatment Plant July - September 2024 - Quarterly Resource Consents Report
Seaview Wastewater Treatment Plant January - March 2023 - Quarterly Resource Consents Report
Appendices:
Appendix IV - Annual Resource Consents Report - Hutt Valley Tradewaste Report 2024/25
Appendix V - Annual Resource Consents Report - AEE Waiwhetu Stream Wet Weather Discharges 2024/25
Appendix VI - Annual Resource Consents Report - AEE Non-compliant Discharges 2024/25
Seaview Wastewater Treatment Plant Annual Consents Report 2023-24 - Appendix ||| Trade Waste
Public health statements on the use of the treatment plant odour neutraliser
Summary
Potential health concerns associated with exposure to quaternary ammonium compounds are most likely associated with direct contact with undiluted product i.e. the staff preparing the solution. Staff exposure risk is managed by following the correct health and safety procedures. Quaternary ammonium compounds are often part of household cleaning and disinfection products and so exposure to the public is relatively common. Given the level of dilution of the product used in the cannon, and the distance between the placement of the cannon and potential locations for public exposure (typically this type of cannon dispersal method has an estimated droplet range of 50-100 metres) that effectively dilutes the strength further, we would not expect this to represent a health risk for the general public.
Te Whatu Ora - Health NZ - April 2023
_________________________________
In May 2024, The plant operator, Veolia, switched to a new product Odour Neutraliser Plus (SCD1100) which is manufactured by biOx Environmental. This is a stabilised chlorine dioxide product that oxidises odour molecules such as Hydrogen Sulfide. The product is safe when used as directed and is utilised in wastewater treatment plants, landfills and transfer stations throughout New Zealand. While the previous product Hi Chem Disinfectant Reodorant presented no public health risks (see above) we decided to act on complaints from the community about the odour it generates and changed to Odour Neutraliser Plus (SCD1100). More information about this product
Independent assessment on the impact of the odour neutralisers
Regarding any impact of the odour neutralisers, an independent assessment has been undertaken and the report concluded that the potential health risks regarding the use of the odour deodorisers are low and acceptable in accordance with New Zealand Guidelines. A copy of the report can be found here.
Odour Investigation Reports
Seaview Wastewater Treatment Plant - Odour Deodoriser - Air Quality Assessment - October 2024
Seaview Wastewater Treatment Plant - Odour Investigation - June 2023
Seaview Wastewater Treatment Plant -Biofilter Flow Assessment -March 2024
Community Liaison Group
Consents
One of the nine resource consents permitting the operation of the plant, consent ‘WGN120142 [33408] Discharge Treated Wastewater to Stream ' expired in 2018.
Prior to the expiry of this consent, Hutt City Council applied to Greater Wellington Regional Council (GWRC) for a new consent to temporarily discharge treated wastewater to the Waiwhetū Stream.
While the reconsenting is underway, we continue to operate under the existing consent.
In general, the consents allow Hutt City Council to:
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discharge treated and partially treated effluent through an existing outfall,
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discharge mixed disinfected, treated and milli-screened wastewater during and/or immediately after heavy rainfall,
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discharge mixed disinfected, treated and milli-screened wastewater during maintenance,
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discharge of contaminants to the air, and
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to occupy the stream and coastal marine area with an outfall structure.