Progress on improving Mill Stream
Sydney Water has been working hard to deliver on actions as part of our Authorisation conditions at Mill Stream for the past three years. However, unforeseen challenges including extreme wet weather and COVID restrictions have caused delays in completing some actions.
What have we done?
- We’ve removed about 3,800 tonnes of silt across 4.2 kilometres of the SWSOOS 1 sewer pipe.
- We’ve just completed a flow balancing trial which we have permanently implemented that will increase available capacity of the SWSOOS pipes.
- Since January 2022 we have removed 626 tonnes from the grit pits. We will build an improved worksite to support more frequent cleaning from an 8-week to a 6-week cycle.
- Following a community survey about odour in the area, our contractor completed repairs of SWSOOS 2 to ensure it was adequately sealed to ensure odours do not escape.
- We’ve been monitoring overflows 24/7, with gauges in place that send alerts so we can initiate clean-ups after every overflow. We’ve completed 35 clean ups which removed 586m3 of wastewater debris from April 2021 to September 2023.
What improvements have we seen?
- We’ve already reduced overflows from an average of 19 events per year and a volume of 3,094 ML per year to an average of 13 events/year and a volume of 1,237 ML/year.
What is planned?
Screening
We’ve finalised plans to install screening near our wastewater pumping station on General Holmes Drive. This will capture solid material and help prevent it from being released in the event of an overflow, reducing the debris entering Mill Stream.
The amount of debris captured will vary depending on the volume of rainfall – collecting 100% in regular events and around 40% in very large events. This may help to reduce bird numbers if the debris from overflows is attracting them to the area.
We’re expecting the screening to be completed and fully operational in 2025.
Silt removal
By the end of 2029 we would have removed about 7,300 tonnes of silt across 6.7 kilometres from the SWSOOS 2 sewer pipe.
Source control
Our current Source Control program will be completed by March 2024. Planning is underway for works continuing from 2025 to 2030 across five wastewater catchments. This will reduce the amount of stormwater entering our wastewater network and help prevent overloading and overflows.
Long term solutions
We continue to investigate and refine options for long-term solutions to provide for growth across the Malabar system, while we improve the environmental performance in the network. We will decide on the option to implement by early 2026.
