Melbourne
11.4 Wastewater collected

Supporting Information

The volume presented in the water accounting statements (362,668 ML) represents the volume of wastewater collected within the Melbourne region from retail water authorities City West Water, South East Water, Yarra Valley Water and Western Water during the 2010–11 year.

The volume includes stormwater ingress and infiltration from groundwater, as they cannot be separated from the total volume collected.


Wastewater collected by retail water authorities

Authority

Volume (ML)

City West Water

86,777

South East Water

127,569

Yarra Valley Water

140,872

Western Water 7,450

Total

362,668



The majority of water was transferred to Melbourne Water's Eastern Treatment Plant and Western Treatment Plant. The breakdown of the volumes received by these treatment plants is presented in the following table.


Wastewater received by Melbourne Water

Wastewater received

Volume (ML)
Western Treatment Plant 180,745
Eastern Treatment Plant 144,563
Total 325,308

Quantification Approach

City West Water

Data Source

City West Water supervisory control and data acquisition (SCADA) database.

Provided by

City West Water.

Method

The volume was calculated from the following components:

·         wastewater collected from the City West Water service area, metered by Melbourne Water

·         wastewater collected at the Altona Treatment Plant, metered by City West Water

·         wastewater collected at the Sunshine Golf Club sewer mining plant, metered by City West Water.

Melbourne Water meters flows daily at bulk meters located on the wastewater collection network. The location of meters and details of the network are contained in a bulk supply agreements for each water authority.  

City West Water meters flows daily at the Altona Treatment Plant and Sunshine Golf Club.

Assumptions, Limitations, Caveats and Approximations

The volume of wastewater transferred from the City West Water service area to the wastewater treatment plant was based on formulae. Specific proportions of flows are allocated to City West Water, and remaining proportions to South East Water and Yarra Valley Water.

Uncertainty Information

Uncertainty is estimated to be +/– 10% based on meter specifications.

Melbourne Water

Data Source

Melbourne Water database.

Provided by

Melbourne Water.

Method

The volume of wastewater collected at Melbourne Water's Western Treatment Plant and Eastern Treatment Plant represents the total metered volume of wastewater received by Melbourne Water. Wastewater is metered at the influent pump stations of both the Eastern and Western treatment plants. These plants have primary inflow metering, as well as additional metering to record the inflows should the primary metering be offline.

Assumptions, Limitations, Caveats and Approximations

  • The total volume includes 57 ML/year of wastewater, which is an estimated volume based on historical averages from City West Water that enters the Western Treatment Plant downstream of the billing meter.
  • The Western Treatment Plant logs data daily and reports quarterly. The Eastern Treatment Plant logs data daily and reports monthly. Thus, metering periods align with the reporting period.

Uncertainty Information

At Eastern Treatment Plant, wastewater inflows are measured using magnetic flow meters with an associated uncertainty of +/– 5%.

At Western Treatment Plant, wastewater inflows are measured using magnetic flow meters with an associated uncertainty of +/– 15%.

South East Water

Data Source

South East Water database.

Provided by

South East Water and Melbourne Water.

Method

The volume was calculated from the following components:

  • Wastewater collected from the South East Water service area, metered by Melbourne Water
  • Wastewater collected at the South East Water's sewage treatment plants, metered by South East Water

Melbourne Water meters record flows daily at bulk meters located on the wastewater collection network. South East Water meters record flows daily at their sewage treatment plants.

Assumptions, Limitations, Caveats and Approximations

The volume of wastewater transferred from the South East Water service area to the wastewater treatment plant was based on formulas. Specific proportions of flows are allocated to South East Water, and remaining proportions to City West Water and Yarra Valley Water.

Uncertainty Information

+/– 5% in accordance with the WIRA 2011 independent annual audit report.

Western Water

Data Source

Western Water plant data.

Provided by

Western Water.

Method

The volume was calculated from the metered daily flows at the entrance of the Western Water Treatment Plant.

Assumptions, Limitations, Caveats and Approximations

The volume does not include wastewater collected from Woodend.

Uncertainty Information

+/– 5% in accordance with Summary Audit Report, October 2010 (Energy Services Commission 2010).

Yarra Valley Water

Data Source

Yarra Valley Water database.

Provided by

Yarra Valley Water.

Method

The volume was calculated from the following components:

·         Wastewater collected from the Yarra Valley Water service area, metered by Melbourne Water

·         Wastewater collected at the Yarra Valley Water's local treatment plants, metered by Yarra Valley Water.

Melbourne Water meters record flows daily at bulk meters located on the wastewater collection network.

Assumptions, Limitations, Caveats and Approximations

The volume of wastewater transferred from the Yarra Valley Water service area to Melbourne Water's Eastern Treatment Plant and Western Treatment Plant were based on formulae. Specific proportions of flows are allocated to Yarra Valley Water, and remaining proportions to City West Water and South East Water.

Uncertainty Information

Uncertainty is estimated to be +/– 10% based on meter specifications.

Comparative year

 The comparative year volume is 304,556 ML.