Update 6 September

The Porirua Wastewater Treatment Plant upgrades are considered critical work and have restarted in Alert Level 3.

All of the necessary safety precautions are being followed to keep our staff and their families safe. This includes social distancing, additional PPE and deep cleaning. Any tasks that do not meet distancing requirements will be delayed to lower alert levels.

The UV upgrade project is the first step in increasing the capacity of the plant by 2023 to stop overflows of partially treated wastewater from the plant to the sea during heavy rain (see What’s happening for further information).

This work is due to be completed towards the end of 2021. This is later than initially expected, due to:

  • the need to balance the operation of the plant with the work we’re doing;
  • the importance of protecting the health and safety of workers and contractors, including ensuring excavations were properly shored;
  • the shutdown of the site during Alert Level 4 and reduced productivity during Alert Level 3.

Here is a pre-lockdown photo showing works to date.

The next steps involve completing the floor of the channel and testing, backfilling, installing and testing the new UV equipment and pipes and connecting the new channel to the plant.

 

 

 

Alert Level 3

This project is critical and essential and will start up under Alert Level 3. All of the necessary safety precautions will be followed, including the use of PPE.

Update 1 April

As part of the planned improvements to the Porirua Wastewater Treatment Plant (WWTP), we are briefly shutting down the network pump stations on 7 April so we can survey and assess the treatment plant inlet. This shutdown will not result in any bypasses, overflows or unplanned discharges from the WWTP.

During this shutdown we will use information from an earlier shutdown in March which tells us how long it takes to isolate incoming flows. From here we will stop the pumps again and do a detailed survey of the milliscreen and undertake a concrete condition inspection. Two supervisors will be monitoring to make sure there is no risk to people and the environment. A Wellington Water shutdown plan, and authorisation will be in place before works proceed.

This is part of the Porirua Wastewater Programme to improve the wastewater system that serves Porirua and the northern suburbs of Wellington city. Read about it here

 

 

Update 12 March

Further testing of coastal water on Saturday March 6 shows the risk of illness from swimming remains low.

This is the final test following brief, planned, outages of the UV disinfection equipment on Thursday 25 February and Monday 1 March (see details below).

  

Sampling date

Location

Measurement (cfu/100 ml)

Indicator organism

 

Saturday 6 March

Te Korohiwa Rocks (south of outfall)

15

Enterococci

Green2

Saturday 6 March

200 metres South West of Outfall

13

Enterococci

Green2

Saturday 6 March

200 metres east of Treatment Plant outfall

13

Enterococci

Green2

Saturday 6 March

Titahi Bay South near stream mouth

13

Enterococci

Green2

Saturday 6 March

Titahi Bay Beach North 

13

Enterococci

Green2

Saturday 6 March

Mount Cooper (north of Titahi Bay)

7.3

Enterococci

Green2

Dry weather recreational testing standards:

  • Green: <140 cfu/100 ml
  • Amber alert: 140> (re-test)
  • Red alert: 280> (re-test, open signs and public warnings)

Update 8 March

Further testing of coastal water on Monday 1 March and Wednesday 3 March shows the risk of illness from swimming remains low. 

Testing has been undertaken following brief, planned, outages of the UV disinfection equipment on Thursday 25 February and Monday 1 March (see details below).

 

Sampling date

Location

Measurement (cfu/100 ml)

Indicator organism

 

Monday 1 March

Te Korohiwa Rocks (south of outfall)

22

Enterococci

Green2

Monday 1 March

200 metres South West of Outfall

18

Enterococci

Green2

Monday 1 March

200 metres east of Treatment Plant outfall

1.8

Enterococci

Green2

Monday 1 March

Titahi Bay South near stream mouth

90

Enterococci

Green2

Monday 1 March

Titahi Bay Beach North

9.1

Enterococci

Green2

Monday 1 March

Mount Cooper (north of Titahi Bay)

170

Enterococci

   

 

Sampling date

Location

Measurement (cfu/100 ml)

Indicator organism

 

Wednesday3 March

Te Korohiwa Rocks (south of outfall)

1.82

Enterococci

Green2

Wednesday 3 March

200 metres South West of Outfall

18

Enterococci

Green2

Wednesday 3 March

200 metres east of Treatment Plant outfall

<1.8

Enterococci

Green2

Wednesday 3 March

Titahi Bay South near stream mouth

<1.8

Enterococci

Green2

Wednesday 3 March

Titahi Bay Beach North 

9.1

Enterococci

Green2

Wednesday 3 March

Mount Cooper (north of Titahi Bay)

5.5

Enterococci

Green2

Dry weather recreational testing standards:

  • Green: <140 cfu/100 ml
  • Amber alert: 140> (re-test)
  • Red alert: 280> (re-test, open signs and public warnings)

 

Update 4 March

Following a brief, planned, outage of the UV disinfection equipment on Thursday 25 February, testing of coastal water shows the risk of illness from swimming remained low at the north end of Titahi Bay beach and four other sites along the coast.

However, near the outflow of the stream at the southern end of Titahi Bay beach there was a spike in bacteria numbers in the morning of Thursday 25 February. Wellington Water’s current analysis is that this was due to water quality effects from the stream, not the treatment plant, but we are investigating further.

We have had a number of indications of issues from stormwater outlets and the stream at the south end of Titahi Bay.  There is a permanent warning sign near the south beach access culvert for this reason. This is why the area that drains to the south end of Titahi Bay is a focus for Knowing your pipes investigations. As part of this project, we have started testing water quality in the stream at the southern end of the beach and the surrounding catchment.

The spike recorded on Thursday 25 February was not picked up in other testing, including our regular Baywatch testing slightly further along the beach on Friday 26 February.

Our current analysis is that the spike is not related to the treatment plant because monitoring sites closer to the treatment plant outfall show good water quality, and any effect from the treatment plant would have been expected to show up at all the monitoring sites along the coast, not just one. We will undertake further analysis as we get further water quality testing results from the stream through the Knowing your pipes project.

All other results from the resource consent shoreline monitoring show low bacteria counts that are consistent with our Baywatch beach testing.  As a reminder, there are three testing programmes detailed here

Monitoring following the brief UV disinfection outage, in line with the treatment plant resource consent, is continuing this week and further results will be shared as they come to hand.

Testing to monitor compliance with Treatment Plant Resource Consent 

Sampling date

Location

Measurement (cfu/100 ml)

Indicator organism

 

Thursday 25 February

Te Korohiwa Rocks (south of outfall)

7.3

Enterococci

Green2

Thursday 25 February

200 metres South West of Outfall

52

Enterococci

Green2

Thursday 25 February

200 metres east of Treatment Plant outfall

9.1

Enterococci

Green2

Thursday 25 February

Titahi Bay South near stream mouth

880

Enterococci

Red2

Thursday 25 February

Titahi Bay Beach North

1.8

Enterococci

Green2

Thursday 25 February

Mount Cooper (north of Titahi Bay)

13

Enterococci

Green2

 

 

Sampling date

Location

Measurement (cfu/100 ml)

Indicator organism

 

Saturday 27 February

Te Korohiwa Rocks (south of outfall)

3.6

Enterococci

Green2

Saturday 27 February

200 metres South West of Outfall

42

Enterococci

Green2

Saturday 27 February

200 metres east of Treatment Plant outfall

40

Enterococci

Green2

Saturday 27 February

Titahi Bay South near stream mouth

11

Enterococci

Green2

Saturday 27 February

Titahi Bay Beach North

11

Enterococci

Green2

Saturday 27 February

Mount Cooper (north of Titahi Bay)

16

Enterococci

Green2

Dry weather recreational testing standards:

  • Green: <140 cfu/100 ml
  • Amber alert: 140> (re-test)
  • Red alert: 280> (re-test, open signs and public warnings)

 

 

Update 1 March

The installation of a new power supply and switch board for the UV treatment equipment has been successfully completed.

This work required the UV treatment equipment to be offline for two short periods on Friday 25 February and Monday 1 March, in order to switchover to a temporary generator, and then from the generator to the new power supply. 

To minimise any risk to public health, this work was scheduled at a time when the tidal current would most effectively dilute the un-UV-disinfected wastewater.

In line with Resource Consent requirements, we are testing water quality this week. Results will be posted here as soon as they are available.

This project is part of the wider Porirua Wastewater Programme.

 

 

Update 23 February

Planned work at the Porirua Wastewater Treatment plant that will lead to a short outage of a small part of the treatment process will go ahead on Thursday 25 February.

There is a very low risk to recreational water users from this short outage.

This work involves upgrading the ultra-violet (UV) treatment equipment at the plant as part of a wider multi-million upgrade project - see 'What's happening' below.

To minimise any risk to public health on 25 February, the work is scheduled at a time when the tidal current will most effectively dilute the un-UV-treated wastewater. Independent consultants have conducted an assessment of any health risk from the short discharge of un-UV-treated wastewater. The modelling shows there would be no observable effect on the risk of illness from swimming at Titahi Bay beach, as a result of this work.

We will also be undertaking sampling at the beach 24 hours, three days and six days after the work, in line with the Resource Consent. We will post monitoring results on this page when they are available.

The contractors will do their best to bring the UV equipment back online as quickly as possible, but we want to notify the community that un-UV-treated wastewater may be discharged at Rukutane Point outfall on the following dates and times:

  • Between 7 am and 12 noon (at the latest) on Thursday 25 February
  • Between 9 am and 11 am (at the latest) on Monday 1 March 

This project is part of the Porirua Wastewater Programme.

 

What's happening?

We are upgrading the Porirua Wastewater Treatment Plant, with the installation of new ultra-violet (UV) disinfection equipment that will increase the volume of wastewater that can be disinfected. This project is part of the wider Porirua Wastewater Programme to support future growth and benefit the environment.

This is the first step in increasing the capacity of the plant by 2023, to stop overflows of partially treated wastewater from the plant to the sea during heavy rain.

Ultraviolet (UV) light disinfection is the final stage in treating wastewater. The treatment process removes solids and the vast majority of harmful bacteria before it gets to the UV stage. UV disinfection destroys remaining bacteria and viruses before the fully treated liquid is discharged to the sea.

Currently the Porirua wastewater treatment plant can treat a peak of 1,000 litres per second.  In heavy rain the amount of wastewater delivered by the network can reach up to 1,300 litres per second.  By 2023 the peak capacity of the plant will be 1,550 litres per second.

This will mean that the plant will be better able to treat all incoming wastewater, even after heavy rain. Combined with network upgrades the plant will also be able to handle a growing population over the coming decades. Find out more about the wastewater treatment process here.

wastewater plant illustration Oct 2024