Mill Stream

We were granted a 3-year authorisation to operate the overflow points at Mill Stream, effective from 7 June 2024 to 31 March 2027 .

We remain firmly committed to improving environmental outcomes in the area surrounding Mill Stream. We continue to work on the immediate, near and long-term solutions to reduce the frequency and impact of wastewater overflows.

We have reapplied 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.

We are 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 long-term solutions is also being advanced. All activities are included in the 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.

We have been working hard to deliver on actions as part of our Authorisation conditions at Mill Stream for the past 3 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 wastewater pipe.
• We've completed a flow balancing trial, which we have permanently implemented. It 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 cleanups after every overflow. We've completed 35 cleanups, which removed 586 cubic metres 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 megalitres per year to an average of 13 events per year and a volume of 1,237 megalitres per 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 finished 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 wastewater pipe.

Source control

Our current source control program will be completed by March 2024. Planning is underway for work continuing from 2025 to 2030 across 5 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.

We've 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.

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