Melbourne
19.5 Discharge from urban water system to surface water

Supporting information

a. Discharge from urban water system

The volume presented (12,161 ML) represents the treated wastewater discharged to surface water from South East Water's sewage treatment plants (STPs), Western Water's recycled water plants (RWP) and Yarra Valley Water's local treatment plants (LTPs).

The breakdown of treated wastewater discharge to surface water in the Melbourne region during the 2011–12 year is presented in the following table.

Wastewater discharge
Authority Discharge location Volume (ML)
South East Water Pakenham STP to Deep Creek 380
Koo Wee Rup STP to Yallock Creek 102
Lang Lang STP to Adams Creek 33
Longwarry STP to King Parrot Creek 134
Subtotal for South East Water 6491
Western Water Bacchus Marsh RWP to Land lot/Lagoon 0
Gisborne RWP to Jacksons Creek 499
Melton RWP to Werribee River 775
Riddells Creek RWP to Riddells Creek 132
Romsey RWP to Deep Creek 261
Sunbury RWP to Jacksons Creek 1,601
Subtotal for Western Water 3,268
Yarra Valley Water Brushy Creek LTP to Brushy Creek 3,842
Craigieburn LTP to Merri Creek 858
Healesville LTP to Yarra River 396
Upper Yarra LTP to Yarra River 799
Lilydale LTP to Olinda Creek 2,114
Monbulk LTP to Sassafras Creek 20
Wallan LTP to Merri Creek 215
Subtotal for Yarra Valley Water 8,244
Total
12,161

1 Total volume reported by South East Water (650 ML) is greater than the volume derived from the rounded components (649 ML).


b. Wastewater system overview

The wastewater system is one of three sub-components of Melbourne's urban water system. The three sub-components are the:

  • Urban water supply system
  • Wastewater system
  • Recycled water system.

In the Melbourne region, wastewater is collected (11.4) from users by the four retail water authorities within the region:

  • City West Water
  • South East Water
  • Western Water
  • Yarra Valley Water.

Following collection, wastewater is either delivered to smaller, local wastewater treatment plants operated by the authorities, or, more commonly, delivered to one of Melbourne Water's major wastewater treatment plants: the Eastern Treatment Plant and Western Treatment Plant. During the 2011–12 year Melbourne Water received and treated almost 90% of the wastewater collected within the region. The breakdown of the volumes of wastewater received by Melbourne Water's treatment plants and the authority's smaller treatment plants is presented in the following table.

Wastewater inflow for treatment received by Melbourne Water and the retail water authority's treatment plants

Water authority treatment plants

Volume (ML)

Melbourne Water

Western Treatment Plant

180,840

Eastern Treatment Plant1

139,226

City West Water

5,474

South East Water

13,126

Western Water

7,966

Yarra Valley Water

10,560

Total

357,192

1 Includes 1,623 ML of treated wastewater received from Pakenham Sewage Treatment Plant.

During the 2011–12 year the majority (85%: 19.7) of treated wastewater was discharged to sea; approximately 11% was recycled and the remaining portion was discharged to surface water (3%: 19.5 ) and the landscape (<1%: 19.8).

The following figure shows all the inflows and outflows associated with the wastewater system. A small misbalance (> 1%) is shown. The misbalance can be attributed to metering inaccuracies, unaccounted losses and inaccuracies in the estimation of the recycled water on-site in process use.

For more detail on a particular flow associated with the wastewater system, refer to the line item notes. Note that volumes annotated with a * indicate flows between sub-components and are not reported in the account. As such, these flows do not have an associated line item number.

Schematic diagram of water inflows and outflows for Melbourne's wastewater system during the 2011–12 year. Line item numbers are provided in brackets.
Schematic diagram of water inflows and outflows for Melbourne's wastewater system during the 2011–12 year. Line item numbers are provided in brackets.

Quantification approach

South East Water

Data source

Internal database.

Provided by

South East Water.

Method

This item represents the daily metered volume of treated wastewater discharged to Deep Creek, Adams Creek, Parrot Creek and Yallock Creek. 

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

The uncertainty is estimated to be +/– 5% based on meter specifications.

Western Water

Data source

Recycled water plant (RWP) data.

Provided by

Western Water.

Method

Meters are located at the outlet of the treatment plants and are read daily by the treatment plant operators. 

Assumptions, limitations, caveats and approximations

Excludes discharge at Woodend RWP to Five Mile Creek, as this is not located within the Melbourne region.

Uncertainty information

The uncertainty is estimated to be +/– 5% based on meter specifications.

Yarra Valley Water

Data source

BI Reporting system, treatment plant and trade waste dashboard.

Provided by

Yarra Valley Water.

Method

Meters measuring the volume of treated wastewater discharged from local treatment plants to surface water are read daily.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

The uncertainty is estimated to be +/– 5% based on meter specifications.