Biofilter air distribution system renewal

Project update meeting

Thank you to members of the community, council staff and councillors, who attended a briefing on upcoming work to renew the odour control system at the plant on Tuesday 30 July.

We appreciated the interest and questions with useful discussion that followed. The presentation is available on our website and notes from the briefing will be published shortly.  See presentation and notes from briefing here

Primary sedimentation tanks works

These tanks are used to settle solids out of wastewater and have a mechanical system that scrapes solids out of the bottom of the tank. Some components of this system are worn out and need replacing. Work to replace this equipment is expected to take three weeks, finishing around mid to late August.

Preliminary works have started to gradually drain one of the tanks in preparation for cleaning on 1 August.

There is a risk of intermittent odour while we empty the tank because we will be moving solid matter around. We will use an odour neutraliser to mitigate the effects, but some odour may be noticeable while this early stage of work is underway.

Biofilter air distribution system renewal

Kia ora koutou

Welcome to the regular monthly update about Wellington Water’s operation of the Seaview Wastewater Treatment Plant and the programme of upgrade work.

You are receiving this email because you expressed an interest in the plant. Please feel free to share this with others who may be interested. You can join the mailing list by emailing customer.notifications@wellingtonwater.co.nz

In this issue

• Odour Treatment Renewal Project update

• Project update meeting -  Tuesday, 30 July

• Planned maintenance work

• Plant performance update

• Community tour of plant

• Get in touch

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Odour Treatment Renewal Project

An upgrade of the biofilter air distribution system is scheduled to begin in early August.

The biofilter is a key part of the system to manage odour. Odorous air is pumped to the biofilter, where it passes through a bed of media (mainly bark, gravel and limestone chip) containing microbes that break down the odour-causing compounds.

As a reminder, when the biofilter media was replaced in December 2023, a comprehensive mechanical and structural condition assessment was undertaken. It became evident that:

· The air distribution system (plenum) in all six biofilter cells needs replacing.

· The biofilter cell isolation system needs redesign and upgrading to isolate each of the six cells individually, this would avoid odour discharge to the environment during future routine maintenance events.

The design for the replacement air distribution system and cell isolation has been completed and is undergoing review in line with Wellington Water’s process.

We are close to having a contractor in place to undertake this work, and necessary equipment has been ordered.

This work is expected to take up to eight weeks, and it is possible that there may be some increase in odour while it is underway. We will reduce the risk as much as we can which may include using an odour neutraliser to reduce the impact.

We will keep the community well informed when the work is progressing and will also increase our odour scouting activities.

Further work packages in the Odour Treatment Renewal Project are aimed at ensuring odorous air gets to the biofilter for treatment rather than escaping into the wider environment.  Work is progressing well on designing new ventilation systems and replacing ducts.

Project update meeting

Come and join us for a briefing on the planned odour treatment renewal work. We will go through the design and work programme in detail and answer any questions. This briefing will be open to any interested members of the public.

When: Tuesday, July 30, from 6pm - 7pm

Where: Wellington Water (Level 4) 25, Victoria Street, Petone

RSVP - Community@wellingtonwater.co.nz (before July 23)

Planned Maintenance Work

From late July, we will be undertaking preliminary works on the primary sedimentation tanks (PST). These tanks have a mechanical system that scrapes the solids out of the bottom of the tank, but some components of this system are worn out and need replacing. We have to empty the tanks one at a time to replace this equipment.

There is a risk of odour while we empty the tanks and undertake this activity, because we will be moving the solid matter around. We will use an odour neutraliser to mitigate the effects, but some odour is unavoidable while this work is underway.

The mechanical work on the tanks is due to start after 9 August and should take 5-7 days. We will send notification emails to let you know when we anticipate an increase in odour from the plant.

Plant Performance update

The discharge from the plant is not compliant for faecal coliforms, one of three standards for the treated wastewater pumped out to Cook Strait. This means that treated effluent has exceeded the set limit for bacteria of 5000 cfu (colony forming units) per 100 ml, more than 18 times over 90 consecutive days.

The level of risk to public health is low, because this treated wastewater is pumped into the sea near Pencarrow Head/ Te Raeakiaki where it is quickly diluted.There were two consented discharges of fully treated effluent to the Waiwhetū Stream due to high rainfall within the catchment area, on 1 May and 22 May.

There were two odour complaints in May. The regulatory agency Greater Wellington Regional Council (GWRC) has been in contact with Wellington Water about plant performance and we have provided information to GWRC about how we are working to return to compliance.

You can find the May monthly performance dashboard on the Seaview webpage.

Plant investment

The Seaview Wastewater Treatment Plant is co-funded by Hutt City Council and Upper Hutt City Council, both signed off on their 2024-2034 Long Term Plans last week. These plans have increased capital expenditure, based on advice from Wellington Water for higher investment in critical water infrastructure. Based on the Hutt City Council’s LTP, $205 million has been allocated for works at the Seaview Wastewater Treatment Plant over the next 10 years. Upper Hutt City Council will contribute 30% of these costs (around $61 million) over the same period. Both councils are working closely with Wellington Water on the plant’s wider maintenance and improvements.  

Community Plant Tour

We had 20 people attend the recent public tour of the Seaview Wastewater Treatment Plant on Saturday, June 22.

Two groups were guided through the plant following a welcome and health and safety briefing. Wellington Water’s Chief Advisor Wastewater Steve Hutchison provided a history of the plant, its construction and networks connections.  

The plant operator Veolia, facilitated the walk around the plant explaining the different aspects of treatment and treatment processes. The tours ended with a Q & A session.

Thank you to those who attended for your interest and thoughtful questions about the plant and plant processes.

In the image below, one of the tour groups oversees the plant biofilter. This is where works in August to replace the air distribution system under the biofilter media (bark mixture) will be.

Kia ora koutou

Welcome to the regular monthly update about Wellington Water’s operation of the Seaview Wastewater Treatment Plant and the programme of upgrade work.

You are receiving this email because you expressed an interest in the plant. Please feel free to share this with others who may be interested. You can join the mailing list by emailing customer.notifications@wellingtonwater.co.nz

In this issue

·    Invitation to tour plant on Saturday, June 22

·    Odour Treatment Renewal Project update

·      Plant performance update

·      Odour neutraliser product

·      Public health signs

·      What’s next

·      Get in touch

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Invitation to tour plant

Wellington Water invites you to tour the Seaview Wastewater Treatment Plant to see first-hand how the plant works and where upgrade work will be taking place.

• Saturday, June 22

• 1.30pm to approx. 3.30 pm

• Seaview plant main entrance, Waterman Street, Seaview

• You must book in advance as numbers are limited

Please note the tour involves walking and climbing a number of stairs so if you have mobility issues it may not be suitable for you. The tour is also not suitable for children under the age of 12.

For health and safety reasons,

• People must wear long pants, long-sleeved tops and closed shoes. 

• We will provide safety equipment in the form of hard hats, hi-vis vests, safety glasses and disposable gloves, which must be worn.

Most of the tour route is outside, so jackets or rain gear may be required if it’s showery.

If the weather forecast is bad, the tour will be postponed to Saturday 6 July.

Numbers are limited so if there is a lot of interest we will add another date.
 

RSVP

Please book your place on the tour by emailing community@wellingtonwater.co.nz with your name, number of people attending, and your contact number in case of postponement. Please RSVP before Friday June 14.

Odour Treatment Renewal Project update

We are on track with design and planning for the next stage of work on the biofilter this winter.  Our consultant Beca developed the detailed design for improvements to the biofilter air distribution system (plenum) and biofilter cell isolation system. The design is now being peer-reviewed by Stantec.

Another work package is to repair leaks in the odour ducts running outside the buildings, which carry air to the biofilter for treatment. We expect to shortly receive a report summarising the external ducting condition assessment, which will inform the next steps. Design work is progressing for the milliscreening ducts and fans work package and the building odour treatment work package.

Plant Performance update

We are continuing efforts to improve the operation of the biological process and the ultra-violet (UV) disinfection system, but unfortunately the plant is still not compliant with one of three standards for treated wastewater discharged into Cook Strait.

You can find the April monthly performance dashboard here .

Since last September, effluent has exceeded the set level for bacteria, of 5000 cfu (colony forming units) per 100 millilitres at least 80% of the time. The level of risk to public health is low, because this treated wastewater is pumped into the sea near Pencarrow Head/ Te Raeakiaki where it is quickly diluted. Our goal is to return to compliance as soon as possible. 

There were two discharges in April. On 7 April, at the Pencarrow outfall, there was a release of undisinfected wastewater due to a power outage. On 12 April, there was a discharge of fully treated wastewater to the Waiwhetū Stream due to wet weather events. Overall, the plant received 35 odour complaints in April.  

Wellington Water is launching a review into the region’s metropolitan wastewater treatment plants. The purpose of this review is to assess why the plants are still having issues meeting resource consents and to identify any immediate improvements to current operating models.

We acknowledge there are challenges with treatment plant assets and their current condition. These ageing assets are a key contributor to the non-compliance with resource consents.

Most of the risks are currently being addressed through work to renew the assets. This will take time, as the work must be done while the plants are running and within the available council budget.

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Odour neutraliser product

 An odour neutraliser is sprayed at times within the Seaview plant boundary.

The plant operator, Veolia, recently 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.

An independent assessment (available here) shows that, while Odour Neutraliser Plus in its undiluted form is a hazardous substance, when it is diluted for use it falls below hazard classification thresholds; that is, the risk is low. At the Seaview plant, it is diluted at 500 parts water to 1 part chemical.

The previous product was called Hi Chem Disinfectant Reodorant. While we had advice from Public Health that this product was safe, we have listened to complaints from the community about the odour it generates and have stopped using it.

An action point from the March public meeting was to provide the amount of neutraliser odour spray used on a weekly basis.  Veolia uses an average of 12.5 litres per week of undiluted odour neutraliser product.

Public health signs

At the community meeting in March, there was discussion about the public health warning signs that are displayed when there is an overflow of treated wastewater into the Waiwhetū Stream, and whether there should be signage targeted at people fishing off the Waione Street Bridge.

There are currently two folding signs in locations specified in the resource consent at the Seaview Road Bridge (next to Urupa) and Port Road Bridge, (highlighted in orange). 

These signs are unfolded, or opened, to show a public health warning as soon as practical after an overflow. On the map, the treatment plant discharge point is shown (red arrow) and is downstream from the bridge.

For longer-term discharges during maintenance or repairs on the Main Outfall Pipeline, two folding signs at Seaview Marina and Marine Parade are also used (in red).

In addition, there are temporary signs near any location in Eastern Bays which are used to drain the section of the pipeline being worked on. 

We are aware of, and understand concerns regarding wastewater discharges, especially where there is a potential impact on mahinga kai, fishing or gathering shellfish. We are looking at how we can better manage these occasional discharges into the Waiwhetū Stream. In the meantime, however, we are assured the health risk to people fishing off the bridge is relatively low, for the following reasons; 

• The discharge point is downstream of the bridge with no affect on the full width of the river 

• Fish will avoid the discharge due to the presence of ammonia in the treated wastewater. 
  
  

We have now completed the action point from the March public meeting, of reviewing the signage. We can confirm the current signage meets the requirements set out in the current resource consent. We have discussed this with Greater Wellington Regional Council and Hutt City Council and are awaiting further feedback. 

Port Road Bridge sign

Next month

·     Peer review of the designs for the biofilter works will be completed  

·     Procurement of contractors and equipment for biofilter works to be confirmed

·     Notifications of odour issues and overflows

Get in touch

Book your place on plant tour: email community@wellingtonwater.co.nz

Join the mailing list for plant notifications and this monthly update, please email customer.notifications@wellingtonwater.co.nz

If you have any questions relating to this newsletter, email community@wellingtonwater.co.nz.

For complaints relating to specific incidents or properties should go to customer@wellingtonwater.co.nz

Thank you for taking the time to read this information.

Linda Fairbrother                                                      Blair Johnson

Project Lead, Major Projects                                         Head of Wastewater Contracts