South East Queensland
19.5 Discharge from urban water system to surface water

Supporting information

a. Overview

The volumetric value for the line item at the end of the 2011–12 year was 62,517 ML.

This line item consists of urban water supply system (including potable and non-potable water), wastewater collection system and recycled water supply system discharges to surface water within the South East Queensland (SEQ) region.

Urban water supply system discharges

Discharges from the urban water supply system could not be quantified in a way that is complete, neutral and free from material error, but are expected to be minor compared to wastewater and recycled water discharges. Discharges may include supply system flushing, air valve releases and tank cleaning.

Wastewater collection system discharges

A number of wastewater treatment plants (WWTPs) discharge treated wastewater to rivers and creeks within the SEQ region. This line item includes discharges to freshwater rivers and creeks that form part of the surface water system. Discharges to estuarine rivers, creeks, inlets and the sea are reported in line item 19.7 Wastewater discharge outside of region. A number of WWTPs that discharge to the Brisbane River are included in line item 19.7 Wastewater discharge outside of region, as the Brisbane River is estuarine through much of the urban Brisbane area.

Recycled water supply system discharges

Reverse osmosis brine concentrate from the Bundamba advanced water treatment plant was discharged to the Bremer River as part of the Western Corridor Recycled Water Scheme treatment process.

Excess purified recycled water discharges occurred from the Gibson Island and Luggage Point advanced water treatment plants, but as the Brisbane River is estuarine at the discharge point, these discharges were reported in line item 19.7 Wastewater discharge outside of region. No excess purified recycled water discharges to surface water occurred from Bundamba advanced water treatment plant.

There is potential for recycled water discharges from the Western Corridor Recycled Water Scheme to Lake Wivenhoe in accordance with the current SEQ System Operating Plan when SEQ water grid storages fall below 40%. When the total volume of water stored by key water grid storages falls below 40% of the total water storage capacity of these storages, the supply of purified recycled water to Lake Wivenhoe from the Western Corridor Recycled Water Scheme is to be maximised, subject to appropriate approvals from Queensland Department of Natural Resources and Mines (DNRM). If and when purified recycled water is introduced into Lake Wivenhoe, this water will then be available for use throughout the entire SEQ region via the SEQ water grid.

 

Wastewater and recycled water discharges to surface water
Discharge description

Volume (ML)

Treated wastewater discharge

                       61,705

Excess recycled water discharge

0

Reverse osmosis concentrate discharge

                           812

Total SEQ region

                       62,517

 

b. Discharge to surface water from the urban water supply system

SEQ's urban water system comprises three sub-components: 

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

 There was no data available on water discharged to surface water during the 2011–12 year.

During the 2011–12 year, approximately 89% of the urban water supply system outflow (265,111 ML) was water supply to urban users (part of 19.4). Approximately 11% of the urban water was transferred back to groundwater storages (28,662 ML). There was no data available on discharge to surface water (part of 19.5) and operational losses.

The following figure shows all the inflows and outflows associated with the urban water supply system. For more detail on a particular flow associated with the urban water supply system, refer to the line item notes.


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



 

c. Discharge to surface water from the wastewater system

Approximately 25% of the wastewater collected (246,055 ML) was discharged to surface water during the 2011–12 year came from the wastewater system (62,517 ML). 

During the 2011–12 year, approximately 10% of wastewater collected was recycled; 82% discharged to the sea (19.7); and the rest discharged to surface water (19.5) and landscape (19.8) .  However, 1,005 ML was exported across the region boundary. The following figure shows all the inflows and outflows associated with the wastewater system. There was some unaccounted flow in the wastewater system that produced an error of  –19%. 

For more detail on a particular flow associated with the recycled water 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 during the 2011–12 year for SEQ's wastewater system; Line item numbers are provided in brackets.
Schematic diagram of water inflows and outflows during the 2011–12 year for SEQ's wastewater system; Line item numbers are provided in brackets.

 

 

Quantification approach

Data source

Queensland Department of Science, Information Technology, Innovation and Arts (DSITIA): licensed discharge data from the Point Source Database.

Seqwater: Western Corridor Recycled Water Scheme dataset.

 

Provided by

Bureau of Meteorology.

Method

Wastewater collection system discharges

Annual waste water treatment plant (WWTP) discharge volumes obtained from DSITIA's Point Source Database. Each WWTP discharge point was then identified and WWTP that discharge to surface water were selected and summed.

Recycled water supply system discharges

Annual advanced wastewater treatment plant discharge data for reverse osmosis concentrate was obtained from Seqwater datasets for Bundamba advanced wastewater treatment plant.

 

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

The uncertainty was not quantified.