Mill Stream

Sydney Water has re-applied for authorisation to periodically discharge diluted wastewater overflows during wet weather into Mill Stream at Sydney Airport. This authorisation is required because discharges can exceed accepted limits for water pollution as described in the Airports (Environment Protection) Regulations 1997. The authorisation is sought for the period to 31 March 2027.

Sydney Water is working to reduce the occurrence and impact of discharges, including clean ups after all overflows, desilting wastewater pipes, reducing stormwater inflow to the wastewater system, and solids screening. Planning for longer term solutions is also being advanced. All activities are included in Sydney Water’s Mill Stream Environmental Management Plan (EMP).

You may post your written submissions by 21 January 2024 to:

Sydney Airport Environment Officer

Airports Branch

Department of Infrastructure, Transport, Regional

Development, Communications and the Arts

GPO Box 594

Canberra ACT 2601

Alternatively, submissions may be emailed to AEO@infrastructure.gov.au.

For further information please contact Mr Iain Fairbairn, Sydney Water’s Head of Wastewater and Environment on 0414 459 291 or the Airport Environment Officer, Department of Infrastructure, Transport, Regional Development, Communications and the Arts Airport Environment Officer at AEO@infrastructure.gov.au.

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.

Sydney Water has finished desilting work on the South Western Sydney Ocean Outfall Sewer (SWSOOS) 1 trunk. This is part of our commitment to improving environmental outcomes at Mill Stream.

We have removed the construction shed at Grace Campbell Reserve and have returned the space back to the community.

Desilting is a critical process to minimise the risk of wastewater overflows and improve the reliability of our wastewater network.

This work involved removing particles and solids (silt) that accumulate at the bottom of the wastewater pipes. The build-up of silt over time can reduce the capacity of the pipe and can lead to overflows that impact our customers and the environment.

We thank the community for its ongoing patience as we work to improve outcomes for the community and the environment.