Sydney
11.4 Wastewater collected

The volume of 507,638 ML shown for this line item represents the metered wastewater volume collected within the Sydney region.  This volume can include wastewater discharged to the sewer after usage and any variation due to the ingress of stormwater; infiltration of groundwater; wastewater overflows to stormwater; and exfiltration of wastewater to groundwater. 

A breakdown of the wastewater collected by the urban system is provided in the following table.

A breakdown of the wastewater collected by Lithgow City Council, Sydney Water Corporation, Goulburn Mulwaree Council and Wingecarribee Shire Council is provided in the following tables. A breakdown for Shoalhaven City Council is not available as the volume is based on a calculation of all wastewater collected within the Shoalhaven City Council boundaries and the population of the within the Sydney region boundaries.

¹ Advanced water treatment plant

² Recycled water agreement: Veolia accesses Sydney Water Corporation's secondary treated wastewater and further treats for Sydney Water Corporation's customers

^3–5 A wet-weather wastewater treatment plant, which is only used during major storms

⁶ Volume of sewage supplied to other infrastructure operators

The wastewater system is one of three subcomponents of Sydney's urban water system. The three subcomponents are the:

• urban water supply system
• wastewater system
• recycled water system.

The Sydney region has several urban utilities responsible for managing wastewater in the region. Sydney Water Corporation, Shoalhaven City Council, Goulburn Mulwaree Council, Lithgow City Council, and Wingecarribee Shire Council all collect wastewater from users (11.4 Wastewater collected) and treat this wastewater at a number of wastewater treatment plants throughout the region.

During the 2012–13 year, a total of 507,638 ML was collected by the wastewater system. The majority of the outflow from the wastewater system (around 77%) was discharged to the sea (19.7 Wastewater discharge outside of region); around 10% was discharged to inland surface water (19.5 Urban water discharge to surface water) and a further 10% of that wastewater was recycled and the remainder was losses from the system (see 19.1 Evaporation from urban water system and 19.20 Other urban water decreases). The following figure shows all the inflows and outflows associated with the wastewater system.

For more detail on a particular flow associated with the wastewater system, refer to the line item notes. Note that volumes annotated with an asterisk (*) indicate flows between subcomponents 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 during the 2012–13 year for Sydney's wastewater system; line item numbers are provided in brackets

As separate data was not available, wastewater collected is assumed to be equal to the volume discharged to surface water reported in 19.5 Discharge from urban water system to surface water. These flows were measured by water channel and height sensors, and converting water level to a volume using a rating table.

• Wastewater collected is assumed to be equal to the volume discharged to surface water.
• Wastewater received at Lithgow and Wallerawang wastewater treatment plants
  includes inflow and infiltration resulting from stormwater, in addition to wastewater
  generated from potable water supplies made to the water distribution system.
  

This item represents the total metered volume of wastewater collected by Shoalhaven City Council's wastewater treatment plants.

The calculation includes:

• grease trap waste
• on-residential
• residential
• septic tank effluent
• septic tank sludge/pan
• tradewaste.

A breakdown is not available as total wastewater collected within the region can only be obtained through a calculation that combines inflows from various treatment plants within and outside the Sydney region boundaries and a population factor. 

The volumes shown are a calculation of the total wastewater volume collected in the Shoalhaven City Council boundaries and estimated factors are applied to extract data for wastewater collected only within the Sydney region boundaries. The estimated factors are based on the average wastewater collected per property and the number of connected properties within the reportable boundaries. The volume of wastewater collected/treated at sewerage treatment plants may also include any net ingress of stormwater or groundwater to the sewer system.

The volume is based on measured data. Estimated uncertainty based on meter accuracy is +/– 5%.

Volumes for both components have been derived from metered outflow data from the plants. The flow meter data are continually monitored and recorded using the Integrated Instrumentation Control Automation and Telemetry System (IICATS). The data are stored within an internal data management system. Adjustments are made to the data (if necessary) to correct any interruptions, errors and so on. From the data management system, data have been extracted for the reporting period.

Modelled wet weather overflows are determined by the hydraulic sewer system model. Wet weather overflow events are defined as sewage overflow that is not the result of an identified blockage in the Sydney Water Corporation's sewerage system or a system failure. It is a result of failure in the systems capacity. Wet weather overflow volume and events will be measured by the hydraulic system models as specified in the Environmental Protection Authority sewage treatment system licences.

• The volume does not include water losses in the treatment process including biosolid removal, de-watering and evaporation.
• Total wastewater treated can include net ingress from stormwater and groundwater.
• At wet-weather wastewater treatment plants, wastewater treated usually also includes a certain volume of stormwater.

The volume is based on measured data. Estimated uncertainty based on meter accuracy is +/– 2%.

This item represents the total volume of wastewater collected at wastewater treatment plants.  The volume is derived from data from inflow meters at wastewater treatment plant where applicable.

Total wastewater received can include net ingress from stormwater and groundwater. Inflows to plants have only been measured at Moss Vale, Berrima and Bundanoon wastewater treatment plants. In some cases,  treated volumes shown above are the same as discharge volumes shown under line item 19.5 Discharge from urban water system to surface water.

The volume is based on measured data. Estimated uncertainty based on meter accuracy and professional judgement is +/– 7%.