South East Queensland
18.6 Infiltration to urban water system

Supporting information

This line item represents the infiltration of ground water into the urban water system, but the volume could not be quantified in a way that is complete, neutral, and free from material error due to the lack of both data and a suitable quantification approach. As urban water supply systems and recycled water supply systems are typically pressurised, it would be expected that little groundwater infiltration into these systems occurs.

Wastewater collection systems consist of gravity sewers and pumping mains. Groundwater infiltration into the gravity sewers occurs regularly where groundwater levels are higher than the sewer main. Tree roots, subsidence of pipe, or joint failure may result in groundwater intrusion.

Groundwater infiltration into wastewater collection systems could not be quantified in a way that is complete, neutral, and free from material error in the South East Queensland region as data were not available from the urban utilities. Line item 11.4 Wastewater collected was developed from wastewater treatment plant  inflow data and as such includes a component that would be due to groundwater infiltration. Groundwater infiltration has been included as an inflow to the urban water system through line item 11.4 'Wastewater collected'.

In the future, with advances in groundwater infiltration and stormwater ingress modelling, it may be possible to separate line item 11.4 'Wastewater collected' into groundwater infiltration, stormwater ingress, and wastewater collected.

The inclusion of groundwater infiltration in line item 11.4 'Wastewater collected' and omission of line item 11.8 'Infiltration from groundwater to urban water system' is not considered to be material to the water balance for the urban water system store. This flow is not a significant proportion of the groundwater store inflows and would not be considered material to the water balance for the groundwater store. Further information may be found in the Groundwater note.