Reducing wastewater overflows
Across our region, councils, iwi and communities are working together to improve the mauri (health and wellbeing) of our streams, rivers and coastlines.
One of the things we can do is reduce the amount of wastewater that gets into the environment before it is treated.
Untreated wastewater overflows into the environment if there’s a blockage somewhere in the wastewater pipe network, or if there is more water than the pipes can carry, for example after heavy rain.
In most parts of the Hutt-Wainuiomata network, large overflows are infrequent.
However any overflow that results in human waste getting into our waterways is objectionable to Māori and many in the wider community. Overflows increase the risk of people getting sick and can affect the species living in and around waterways.
We want your views on the impact of overflows and what we can do about them.
Watch this video to find out more about the wastewater network, then have your say.
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Overview
Wellington Water is asking for public input as we plan future work to reduce overflows from the Hutt-Wainuiomata wastewater network.
Wellington Water manages the network on behalf of the Hutt and Upper Hutt Councils, and we are continually upgrading and repairing the network.
Dry weather blockages can occur anywhere across the network. Wellington Water moves quickly to clear the blockage and clean up any overflow.
There is always likely to be some overflows because of blockages or extreme weather events, but we can make improvements so they don’t happen so often.
We also inform residents about how to help avoid blockages or overloading the network .
To make sure we meet legal requirements under the Resource Management Act 1991, we are now building a picture across the whole network of where and when overflows are happening, both in dry weather because of blockages, and in heavy rain. This will help set future priorities.
About the wastewater network
Anything that goes down your kitchen sink, toilet or any other drains in your home or business is wastewater.
Wastewater contains 99% water and about 1% human and other waste. Because the waste component contains many bacteria and viruses that could be harmful to human health, it’s important it is kept separate from the drinking water network.
Māori culture also places high value on avoiding contamination of water with wastewater.
Wastewater from across Hutt and Wainuiomata is transported along a network of over 900 km of pipes, about 65 pumping stations and two storage tanks to the Seaview Wastewater Treatment plant.
At the plant, it’s cleaned and disinfected before being discharged out to the Cook Strait at an outfall past Pencarrow.
Find out how the treatment plant works here
The network is designed to be able to carry four to five times more water than the average daily flow, so that it can cope with extra water, for example when it rains.
Rain can get into the wastewater network through faulty plumbing or gully traps or holes in manhole covers (known as inflow). Groundwater can seep in through cracks or bad joints in pipes or manholes (known as infiltration).
Sometimes when it rains very heavily, there is more water than the pipe network can carry and untreated wastewater will overflow into the environment.
Sometimes, pipes get blocked, by material such as congealed fats and oils, wet wipes, tissues and menstrual products such as tampons, which create 'fatbergs' and 'rag monsters' in the system. Read all about them here! This can cause wastewater to overflow until the blockage can be cleared.
More information about the wastewater network is available at Wellington Water.
About wastewater overflows
Across the network there are over 60 relief points, or 'constructed overflows'. In emergencies or extreme weather events, wastewater is channelled through these into streams, rivers or out to sea.
These are deliberately designed to reduce the risk of untreated wastewater overflowing into buildings or roads, which would be a greater risk to public health.
You can see these points on the interactive map on this page.
Overflows can also happen at other points, for example through a manhole, when the buildup of wastewater
pushes up the manhole lid or overflows a gully trap. These are almost always caused by blockages. These happen relatively often but usually involve small amounts of wastewater.
Terms of engagement
Comments that you make here are made visible immediately. When making comments, or engaging in discussion, please:
1. Be respectful of others' comments and views;
2. Make sure your comment is relevant to the topic; and
3. Ddo not use any profanity, or offensive words or material.
We reserve the right to remove any comment which we deem to be using profanity or any other harmful or offensive words or material.
Have some questions?
What can be done to reduce wastewater overflows?
There are a number of things we can do, from increasing the capacity of the network so it can carry more wastewater, to reducing the volume of stormwater and groundwater getting in to the network,
to reducing blockages by being more careful about what we put down the drain.
There are a number of projects underway to renew our aging pipes and infrastructure, currently focussing on Wainuiomata and Naenae.
In recent years, we’ve succeeded in reducing overflows into the
Waiwhetū Stream by upgrading public pipes and working with over 2000 property owners to test private pipes and get them repaired where necessary.
Across the network, we continue to focus on identifying and fixing inflow (where rain gets into the wastewater network through faulty plumbing or gully traps or holes in manhole covers) and infiltration (where groundwater can seep in through inappropriate sub-soil drains or cracks or bad joints in pipes or manholes).
At work or at home, people can help by remembering the network is only designed for pee, poo and [toilet] paper and avoiding putting any other waste products down the drain.
Why are you consulting the public on overflows now?
Under New Zealand law (the Resource Management Act), special permission is required to discharge wastewater. This permission takes the form of a resource consent, issued by a regional council. The consent can include conditions that require steps to be taken to minimise the impact of the discharges and to reduce them over time.
Wellington Water will be making a formal application to Greater Wellington Regional Council for a consent to discharge wastewater across the catchment, including how it plans to minimise overflows. Your comments will contribute to the resource consent application.
Currently, a number of constructed overflows have individual resource consents, but we want a network-wide consent so that we can take a network-wide view of setting priorities for future work.
How much have you budgeted for to reducing wastewater overflows?
The cost depends on the work required. Councils are currently considering future investment in the water network (including wastewater) as part of their Long Term Plan discussions.
Why can’t we build a big enough system to carry all our wastewater without any overflows?
The cost would be prohibitive.
The majority of the Hutt Valley and Wainuiomata wastewater networks was designed to contain four to five times the normal dry weather flow to allow for entry of groundwater and stormwater into the system. But some areas of the Hutt Valley and Wainuiomata network have significantly more groundwater and stormwater inflows entering the system than the design allows for.
This is typical of other similar- aged towns and cities in New Zealand and internationally. It’s better for public health to have overflows channelled into a river or stream, where the concentration of bacteria is diluted, than having offensive overflows in houses, buildings or on streets.
How are you engaging with Mana Whenua about this?
We have met with representatives of Taranaki Whānui ki te Upoko o te Ika a Maui/Port Nicholson Block Settlement Trust and Ngati Toa, and they are considering and providing input into our approach.
Any iwi members living in the Hutt and Wainuiomata are welcome to comment directly to us, through this consultation, and we will be engaging with the iwi authorities throughout this process.
Why isn’t my stream on the map?
The map shows streams, rivers and beaches where there are constructed overflow points. If your stream’s not shown, it’s because there is no constructed overflow point, so no place for wastewater to be channelled into your stream. You can still place a comment in the general area.
What’s happening to stop overflows from the Seaview treatment plant?
Wellington Water is currently designing extra storage and changes to the treatment plant’s overflow system to reduce the impact of treated wastewater overflows into the Waiwhetū Stream.
What have you done to reduce overflows at the Rossiter Avenue overflow point in Waiwhetū?
An engineered overflow point at Rossiter Avenue in Waiwhetū has historically overflowed frequently (more than 30 times during the 2016/17 year). This was caused by an undersized pipe crossing over Waiwhetū Stream which acted as a choke point.
Wellington Water identified the problem and replaced the pipe with an inverted siphon underneath the streambed.
The new stream crossing was completed in June 2018 and since that time the overflow frequency has fallen to less than two events per year. The risk to public health and stream ecological health from overflow discharges at this location is now assessed as low.
Alongside this work, Wellington Water has also worked with over 2000 property owners around the Waiwhetū Stream to test private pipes and get them repaired where necessary.
Why are most of the frequent overflows, or red and orange dots on the map, in Wainuiomata?
Like the rest of the network, Wainuiomata has aging infrastructure designed for a smaller population. The bulk of the network was installed in the 1960’s, more than 50 years ago and the area has high groundwater levels.
A recent system performance assessment found that in Wainuiomata there are significant issues with inflow (where rain gets into the wastewater network through faulty plumbing or gully traps or holes in manhole covers or illegal connections of stormwater) and infiltration (where groundwater can seep in through inappropriate sub-soil drains or cracks or bad joints in pipes or manholes).
The assessment also identified the Wise Park pumping station in Rata Street as a constraint and the amount of wastewater the network can handle.
Wellington Water is actively monitoring flows through the network and water quality in Black Creek and Wainuiomata River, and has an ongoing pipe renewal programme underway.
Wellington Water is also considering further options for the area.
How does this project fit in with the work of the Whaitua te Whanganui-a-Tara Committee?
Whaitua te Whanganui-a-Tara Committee is a group of local people from Hutt Valley and Wellington assigned with developing a programme to improve the quality of our streams, rivers and harbour.
It is looking at the whole catchment, and all aspects of managing water quality and availability.
This project is focussed on reducing the overflow of wastewater into the environment; it’s just one part of the picture of improving water quality.
So this project contributes to the Whaitua’s planning, but is not the whole solution.
Whaitua is te reo Māori for catchment or space. The Wellington Region is divided into five whaitua, each of which has a Whaitua Committee assigned to develop a programme to improve water quality.
Find out more on the Greater Wellington Regional Council website.
